WorldWideScience

Sample records for stellar synthetic spectroscopy

  1. Science with Synthetic Stellar Surveys

    Science.gov (United States)

    Sanderson, Robyn Ellyn

    2018-04-01

    A new generation of observational projects is poised to revolutionize our understanding of the resolved stellar populations of Milky-Way-like galaxies at an unprecedented level of detail, ushering in an era of precision studies of galaxy formation. In the Milky Way itself, astrometric, spectroscopic and photometric surveys will measure three-dimensional positions and velocities and numerous chemical abundances for stars from the disk to the halo, as well as for many satellite dwarf galaxies. In the Local Group and beyond, HST, JWST and eventually WFIRST will deliver pristine views of resolved stars. The groundbreaking scale and dimensionality of this new view of resolved stellar populations in galaxies challenge us to develop new theoretical tools to robustly compare these surveys to simulated galaxies, in order to take full advantage of our new ability to make detailed predictions for stellar populations within a cosmological context. I will describe a framework for generating realistic synthetic star catalogs and mock surveys from state-of-the-art cosmological-hydrodynamical simulations, and present several early scientific results from, and predictions for, resolved stellar surveys of our Galaxy and its neighbors.

  2. FITspec: A New Algorithm for the Automated Fit of Synthetic Stellar Spectra for OB Stars

    Science.gov (United States)

    Fierro-Santillán, Celia R.; Zsargó, Janos; Klapp, Jaime; Díaz-Azuara, Santiago A.; Arrieta, Anabel; Arias, Lorena; Sigalotti, Leonardo Di G.

    2018-06-01

    In this paper we describe the FITspec code, a data mining tool for the automatic fitting of synthetic stellar spectra. The program uses a database of 27,000 CMFGEN models of stellar atmospheres arranged in a six-dimensional (6D) space, where each dimension corresponds to one model parameter. From these models a library of 2,835,000 synthetic spectra were generated covering the ultraviolet, optical, and infrared regions of the electromagnetic spectrum. Using FITspec we adjust the effective temperature and the surface gravity. From the 6D array we also get the luminosity, the metallicity, and three parameters for the stellar wind: the terminal velocity ({v}∞ ), the β exponent of the velocity law, and the clumping filling factor (F cl). Finally, the projected rotational velocity (v\\cdot \\sin i) can be obtained from the library of stellar spectra. Validation of the algorithm was performed by analyzing the spectra of a sample of eight O-type stars taken from the IACOB spectroscopic survey of Northern Galactic OB stars. The spectral lines used for the adjustment of the analyzed stars are reproduced with good accuracy. In particular, the effective temperatures calculated with the FITspec are in good agreement with those derived from spectral type and other calibrations for the same stars. The stellar luminosities and projected rotational velocities are also in good agreement with previous quantitative spectroscopic analyses in the literature. An important advantage of FITspec over traditional codes is that the time required for spectral analyses is reduced from months to a few hours.

  3. Atomic and Molecular Data for Optical Stellar Spectroscopy

    OpenAIRE

    Heiter, U.; Lind, K.; Asplund, M.; Barklem, P. S.; Bergemann, M.; Magrini, L.; Masseron, T.; Mikolaitis, Š.; Pickering, J. C.; Ruffoni, M. P.

    2015-01-01

    High-precision spectroscopy of large stellar samples plays a crucial role for several topical issues in astrophysics. Examples include studying the chemical structure and evolution of the Milky Way galaxy, tracing the origin of chemical elements, and characterizing planetary host stars. Data are accumulating from instruments that obtain high-quality spectra of stars in the ultraviolet, optical and infrared wavelength regions on a routine basis. These instruments are located at ground-based 2-...

  4. Synthetic H-R diagrams as an observational test of stellar evolution theory

    International Nuclear Information System (INIS)

    Mathews, G.J.; Becker, S.A.; Brunish, W.M.

    1983-07-01

    Synthetic H-R diagrams are constructed from a grid of stellar models. These are compared directly with observations of young clusters in the LMC and SMC as a test of the models and as a means to determine the age, age dispersion, and composition of the clusters. Significant discrepancies between the observed and model H-R diagrams indicate the possible influences of convective overshoot, large AGB mass-loss rates, and the best value for the mixing length parameter

  5. The STAGGER-grid: A grid of 3D stellar atmosphere models. V. Synthetic stellar spectra and broad-band photometry

    Science.gov (United States)

    Chiavassa, A.; Casagrande, L.; Collet, R.; Magic, Z.; Bigot, L.; Thévenin, F.; Asplund, M.

    2018-03-01

    Context. The surface structures and dynamics of cool stars are characterised by the presence of convective motions and turbulent flows which shape the emergent spectrum. Aims: We used realistic three-dimensional (3D) radiative hydrodynamical simulations from the STAGGER-grid to calculate synthetic spectra with the radiative transfer code OPTIM3D for stars with different stellar parameters to predict photometric colours and convective velocity shifts. Methods: We calculated spectra from 1000 to 200 000 Å with a constant resolving power of λ/Δλ = 20 000 and from 8470 and 8710 Å (Gaia Radial Velocity Spectrometer - RVS - spectral range) with a constant resolving power of λ/Δλ = 300 000. Results: We used synthetic spectra to compute theoretical colours in the Johnson-Cousins UBV (RI)C, SDSS, 2MASS, Gaia, SkyMapper, Strömgren systems, and HST-WFC3. Our synthetic magnitudes are compared with those obtained using 1D hydrostatic models. We showed that 1D versus 3D differences are limited to a small percent except for the narrow filters that span the optical and UV region of the spectrum. In addition, we derived the effect of the convective velocity fields on selected Fe I lines. We found the overall convective shift for 3D simulations with respect to the reference 1D hydrostatic models, revealing line shifts of between -0.235 and +0.361 km s-1. We showed a net correlation of the convective shifts with the effective temperature: lower effective temperatures denote redshifts and higher effective temperatures denote blueshifts. We conclude that the extraction of accurate radial velocities from RVS spectra need an appropriate wavelength correction from convection shifts. Conclusions: The use of realistic 3D hydrodynamical stellar atmosphere simulations has a small but significant impact on the predicted photometry compared with classical 1D hydrostatic models for late-type stars. We make all the spectra publicly available for the community through the POLLUX database

  6. Micro-Raman spectroscopy of natural and synthetic indigo samples.

    Science.gov (United States)

    Vandenabeele, Peter; Moens, Luc

    2003-02-01

    In this work indigo samples from three different sources are studied by using Raman spectroscopy: the synthetic pigment and pigments from the woad (Isatis tinctoria) and the indigo plant (Indigofera tinctoria). 21 samples were obtained from 8 suppliers; for each sample 5 Raman spectra were recorded and used for further chemometrical analysis. Principal components analysis (PCA) was performed as data reduction method before applying hierarchical cluster analysis. Linear discriminant analysis (LDA) was implemented as a non-hierarchical supervised pattern recognition method to build a classification model. In order to avoid broad-shaped interferences from the fluorescence background, the influence of 1st and 2nd derivatives on the classification was studied by using cross-validation. Although chemically identical, it is shown that Raman spectroscopy in combination with suitable chemometric methods has the potential to discriminate between synthetic and natural indigo samples.

  7. Raman spectroscopy of synthetic and natural iowaite.

    Science.gov (United States)

    Frost, Ray L; Adebajo, Moses O; Erickson, Kristy L

    2005-02-01

    The chemistry of a magnesium based hydrotalcite known as iowaite Mg6Fe2Cl2(OH)16.4H2O has been studied using Raman spectroscopy. Iowaite has chloride as the counter anion in the interlayer. The formula of synthetic iowaite was found to be Mg5.78Fe2.09(Cl,(CO3)0.5)(OH)16.4H2O. Oxidation of natural iowaite results in the formation of Mg4FeO(Cl,CO3) (OH)8.4H2O. X-ray diffraction (XRD) shows that the iowaite is a layered structure with a d(001) spacing of 8.0 angtsroms. For synthetic iowaite three Raman bands at 1376, 1194 and 1084 cm(-1) are attributed to CO3 stretching vibrations. These bands are not observed for the natural iowaite but are observed when the natural iowaite is exposed to air. The Raman spectrum of natural iowaite shows three bands at 708, 690 and 620 cm(-1) and upon exposure to air, two broad bands are found at 710 and 648 cm(-1). The Raman spectrum of synthetic iowaite has a very broad band at 712 cm(-1). The Raman spectrum of natural iowaite shows an intense band at 527 cm(-1). The air oxidized iowaite shows two bands at 547 and 484 cm(-1) attributed to the (CO3)(2-)nu2 bending mode. Raman spectroscopy has proven most useful for the study of the chemistry of iowaite and chemical changes induced in natural iowaite upon exposure to air.

  8. ACCELERATED FITTING OF STELLAR SPECTRA

    Energy Technology Data Exchange (ETDEWEB)

    Ting, Yuan-Sen; Conroy, Charlie [Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Rix, Hans-Walter [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)

    2016-07-20

    Stellar spectra are often modeled and fitted by interpolating within a rectilinear grid of synthetic spectra to derive the stars’ labels: stellar parameters and elemental abundances. However, the number of synthetic spectra needed for a rectilinear grid grows exponentially with the label space dimensions, precluding the simultaneous and self-consistent fitting of more than a few elemental abundances. Shortcuts such as fitting subsets of labels separately can introduce unknown systematics and do not produce correct error covariances in the derived labels. In this paper we present a new approach—Convex Hull Adaptive Tessellation (chat)—which includes several new ideas for inexpensively generating a sufficient stellar synthetic library, using linear algebra and the concept of an adaptive, data-driven grid. A convex hull approximates the region where the data lie in the label space. A variety of tests with mock data sets demonstrate that chat can reduce the number of required synthetic model calculations by three orders of magnitude in an eight-dimensional label space. The reduction will be even larger for higher dimensional label spaces. In chat the computational effort increases only linearly with the number of labels that are fit simultaneously. Around each of these grid points in the label space an approximate synthetic spectrum can be generated through linear expansion using a set of “gradient spectra” that represent flux derivatives at every wavelength point with respect to all labels. These techniques provide new opportunities to fit the full stellar spectra from large surveys with 15–30 labels simultaneously.

  9. Atomic and molecular data for optical stellar spectroscopy

    International Nuclear Information System (INIS)

    Heiter, U; Lind, K; Barklem, P S; Asplund, M; Bergemann, M; Magrini, L; Masseron, T; Mikolaitis, Š; Pickering, J C; Ruffoni, M P

    2015-01-01

    High-precision spectroscopy of large stellar samples plays a crucial role for several topical issues in astrophysics. Examples include studying the chemical structure and evolution of the Milky Way Galaxy, tracing the origin of chemical elements, and characterizing planetary host stars. Data are accumulating from instruments that obtain high-quality spectra of stars in the ultraviolet, optical and infrared wavelength regions on a routine basis. These instruments are located at ground-based 2–10 m class telescopes around the world, in addition to the spectrographs with unique capabilities available at the Hubble Space Telescope. The interpretation of these spectra requires high-quality transition data for numerous species, in particular neutral and singly ionized atoms, and di- or triatomic molecules. We rely heavily on the continuous efforts of laboratory astrophysics groups that produce and improve the relevant experimental and theoretical atomic and molecular data. The compilation of the best available data is facilitated by databases and electronic infrastructures such as the NIST Atomic Spectra Database, the VALD database, or the Virtual Atomic and Molecular Data Centre. We illustrate the current status of atomic data for optical stellar spectra with the example of the Gaia-ESO Public Spectroscopic Survey. Data sources for 35 chemical elements were reviewed in an effort to construct a line list for a homogeneous abundance analysis of up to 10 5 stars. (paper)

  10. Atomic and molecular data for optical stellar spectroscopy

    Science.gov (United States)

    Heiter, U.; Lind, K.; Asplund, M.; Barklem, P. S.; Bergemann, M.; Magrini, L.; Masseron, T.; Mikolaitis, Š.; Pickering, J. C.; Ruffoni, M. P.

    2015-05-01

    High-precision spectroscopy of large stellar samples plays a crucial role for several topical issues in astrophysics. Examples include studying the chemical structure and evolution of the Milky Way Galaxy, tracing the origin of chemical elements, and characterizing planetary host stars. Data are accumulating from instruments that obtain high-quality spectra of stars in the ultraviolet, optical and infrared wavelength regions on a routine basis. These instruments are located at ground-based 2-10 m class telescopes around the world, in addition to the spectrographs with unique capabilities available at the Hubble Space Telescope. The interpretation of these spectra requires high-quality transition data for numerous species, in particular neutral and singly ionized atoms, and di- or triatomic molecules. We rely heavily on the continuous efforts of laboratory astrophysics groups that produce and improve the relevant experimental and theoretical atomic and molecular data. The compilation of the best available data is facilitated by databases and electronic infrastructures such as the NIST Atomic Spectra Database, the VALD database, or the Virtual Atomic and Molecular Data Centre. We illustrate the current status of atomic data for optical stellar spectra with the example of the Gaia-ESO Public Spectroscopic Survey. Data sources for 35 chemical elements were reviewed in an effort to construct a line list for a homogeneous abundance analysis of up to 105 stars.

  11. Deriving stellar parameters with the SME software package

    Science.gov (United States)

    Piskunov, N.

    2017-09-01

    Photometry and spectroscopy are complementary tools for deriving accurate stellar parameters. Here I present one of the popular packages for stellar spectroscopy called SME with the emphasis on the latest developments and error assessment for the derived parameters.

  12. Photometric Separation of Stellar Properties Using SDSS Filters

    Science.gov (United States)

    Lenz, Dawn D.; Newberg, Jo; Rosner, Robert; Richards, Gordon T.; Stoughton, Chris

    1998-12-01

    Using synthetic photometry of Kurucz model spectra, we explore the colors of stars as a function of temperature, metallicity, and surface gravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. The synthetic colors show qualitative agreement with the few published observations in these filters. We find that the locus of synthetic stars is basically two-dimensional for 4500 advantageous to use more than two colors when determining stellar properties by color. Strategic observations in SDSS filters are required to resolve the source of a ~5% discrepancy between synthetic colors of Gunn-Stryker stars, Kurucz models, and external determinations of the metallicities and surface gravities. The synthetic star colors can be used to investigate the properties of any normal star and to construct analytic expressions for the photometric prediction of stellar properties in special cases.

  13. The stellar spectroscopy laboratory and curriculum counselling for secondary-school students

    International Nuclear Information System (INIS)

    Cenadelli, D.

    2011-01-01

    The stellar spectroscopy laboratory is the flagship of a wide-ranging work of curriculum counselling fostered by the Physics Department of the Milan University and the high school 'G. Parini' in Milan. In time, valuable results were gained in setting up a new way of collaboration between the high school and university worlds and in spurring secondary-school students to embark in a scientific, and more specifically physical, career. The present work briefly discusses the contents of the laboratory, its didactical value, its role of curriculum counselling and its effectiveness in directing students to take into consideration the physical sciences as a possible university choice.

  14. An application of deep learning in the analysis of stellar spectra

    Science.gov (United States)

    Fabbro, S.; Venn, K. A.; O'Briain, T.; Bialek, S.; Kielty, C. L.; Jahandar, F.; Monty, S.

    2018-04-01

    Spectroscopic surveys require fast and efficient analysis methods to maximize their scientific impact. Here, we apply a deep neural network architecture to analyse both SDSS-III APOGEE DR13 and synthetic stellar spectra. When our convolutional neural network model (StarNet) is trained on APOGEE spectra, we show that the stellar parameters (temperature, gravity, and metallicity) are determined with similar precision and accuracy as the APOGEE pipeline. StarNet can also predict stellar parameters when trained on synthetic data, with excellent precision and accuracy for both APOGEE data and synthetic data, over a wide range of signal-to-noise ratios. In addition, the statistical uncertainties in the stellar parameter determinations are comparable to the differences between the APOGEE pipeline results and those determined independently from optical spectra. We compare StarNet to other data-driven methods; for example, StarNet and the Cannon 2 show similar behaviour when trained with the same data sets; however, StarNet performs poorly on small training sets like those used by the original Cannon. The influence of the spectral features on the stellar parameters is examined via partial derivatives of the StarNet model results with respect to the input spectra. While StarNet was developed using the APOGEE observed spectra and corresponding ASSET synthetic data, we suggest that this technique is applicable to other wavelength ranges and other spectral surveys.

  15. Broad-band time-resolved near infrared spectroscopy in the TJ-II stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, M.C.; Pastor, I.; Cal, E. de la; McCarthy, K.J. [Laboratorio Nacional de Fusion, CIEMAT, Madrid (Spain); Diaz, D. [Universidad Autonoma de Madrid, Dept Quimica Fisica Aplicada, Madrid (Spain)

    2014-11-15

    First experimental results on broad-band, time-resolved Near Infrared (NIR;here loosely defined as covering from 750 to 1650 nm) passive spectroscopy using a high sensitivity InGaAs detector are reported for the TJ-II Stellarator. Experimental set-up is described together with its main characteristics, the most remarkable ones being its enhanced NIR response, broadband spectrum acquisition in a single shot, and time-resolved measurements with up to 1.8 kHz spectral rate. Prospects for future work and more extended physics studies in this newly open spectral region in TJ-II are discussed. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Optical spectroscopy and high pressure on emeralds: synthetic and natural

    Science.gov (United States)

    Sánchez-Alejo, M. A.; Hernández-Alcántara, J. M.; Flores Jiménez, C.; Calderón, T.; Murrieta S., H.; Camarillo García, E.

    2011-09-01

    Emerald, natural and synthetic, are the subject of study by means of optical spectroscopy techniques. Particularly, natural emeralds have been considered as a gemstone in jewelry not being so the synthetic ones. But, in general, the properties of these are very good for applications, for instance as a laser system, due to the impurities control. In this work a comparison between natural and synthetic emeralds is done. Chromium ions are the main responsible of the characteristic fascinating green color of these gemstones, entering in the crystals in octahedral sites. Absorption at room temperature show up two broad bands in the visible region and two narrow bands called the R-lines. That spectrum corresponds to trivalent chromium ions in an octahedral site, as it happens in ruby and alexandrite. On other hand, photoemission arises in the range 640-850 nm. at room temperature . It is shown that the luminescence spectra changes as the temperature is lowered. The effect on the main peak of luminescence when high pressure is applied on small samples of emerald shows as a linear function.

  17. Fourier transform Raman spectroscopy of synthetic and biological calcium phosphates.

    Science.gov (United States)

    Sauer, G R; Zunic, W B; Durig, J R; Wuthier, R E

    1994-05-01

    Fourier-transform (FT) Raman spectroscopy was used to characterize the organic and mineral components of biological and synthetic calcium phosphate minerals. Raman spectroscopy provides information on biological minerals that is complimentary to more widely used infrared methodologies as some infrared-inactive vibrational modes are Raman-active. The application of FT-Raman technology has, for the first time, enabled the problems of high sample fluorescence and low signal-to-noise that are inherent in calcified tissues to be overcome. Raman spectra of calcium phosphates are dominated by a very strong band near 960 cm-1 that arises from the symmetric stretching mode (v1) of the phosphate group. Other Raman-active phosphate vibrational bands are seen at approximately 1075 (v3), 590 (v4), and 435 cm-1 (v2). Minerals containing acidic phosphate groups show additional vibrational modes. The different calcium phosphate mineral phases can be distinguished from one another by the relative positions and shapes of these bands in the Raman spectra. FT-Raman spectra of nascent, nonmineralized matrix vesicles (MV) show a distinct absence of the phosphate v1 band even though these structures are rich in calcium and phosphate. Similar results were seen with milk casein and synthetic Ca-phosphatidyl-serine-PO4 complexes. Hence, the phosphate and/or acidic phosphate ions in these noncrystalline biological calcium phosphates is in a molecular environment that differs from that in synthetic amorphous calcium phosphate. In MV, the first distinct mineral phase to form contained acidic phosphate bands similar to those seen in octacalcium phosphate. The mineral phase present in fully mineralized MV was much more apatitic, resembling that found in bones and teeth.(ABSTRACT TRUNCATED AT 250 WORDS)

  18. StarNet: An application of deep learning in the analysis of stellar spectra

    Science.gov (United States)

    Kielty, Collin; Bialek, Spencer; Fabbro, Sebastien; Venn, Kim; O'Briain, Teaghan; Jahandar, Farbod; Monty, Stephanie

    2018-06-01

    In an era when spectroscopic surveys are capable of collecting spectra for hundreds of thousands of stars, fast and efficient analysis methods are required to maximize scientific impact. These surveys provide a homogeneous database of stellar spectra that are ideal for machine learning applications. In this poster, we present StarNet: a convolutional neural network model applied to the analysis of both SDSS-III APOGEE DR13 and synthetic stellar spectra. When trained on synthetic spectra alone, the calculated stellar parameters (temperature, surface gravity, and metallicity) are of excellent precision and accuracy for both APOGEE data and synthetic data, over a wide range of signal-to-noise ratios. While StarNet was developed using the APOGEE observed spectra and corresponding ASSeT synthetic grid, we suggest that this technique is applicable to other spectral resolutions, spectral surveys, and wavelength regimes. As a demonstration of this, we present a StarNet model trained on lower resolution, R=6000, IR synthetic spectra, describing the spectra delivered by Gemini/NIFS and the forthcoming Gemini/GIRMOS instrument (PI Sivanandam, UToronto). Preliminary results suggest that the stellar parameters determined from this low resolution StarNet model are comparable in precision to the high-resolution APOGEE results. The success of StarNet at lower resolution can be attributed to (1) a large training set of synthetic spectra (N ~200,000) with a priori stellar labels, and (2) the use of the entire spectrum in the solution rather than a few weighted windows, which are common methods in other spectral analysis tools (e.g. FERRE or The Cannon). Remaining challenges in our StarNet applications include rectification, continuum normalization, and wavelength coverage. Solutions to these problems could be used to guide decisions made in the development of future spectrographs, spectroscopic surveys, and data reduction pipelines, such as for the future MSE.

  19. THE LICK/SDSS LIBRARY. I. SYNTHETIC INDEX DEFINITION AND CALIBRATION

    International Nuclear Information System (INIS)

    Franchini, M.; Morossi, C.; Di Marcantonio, P.; Malagnini, M. L.; Chavez, M.

    2010-01-01

    A new synthetic library of spectral feature indices, Lick/Sloan Digital Sky Survey (SDSS), for stellar population studies is presented. Lick/SDSS is computed from synthetic spectra with resolving power R = 1800 to fully exploit the content of the spectroscopic SDSS-DR7 stellar database. The Lick/SDSS system is based on the Lick/IDS one complemented with a UV index in the wavelength region of Ca II H and K lines. The system is well suited to study α-element abundances in F, G, and K stars. The reliability of synthetic indices in reproducing the behaviors of observational ones with effective temperature, surface gravity, overall metallicity, and α-element abundances is tested by using empirical stellar libraries (ELODIE, INDO-U.S., and MILES) and the SDSS-DR7 spectroscopic database. The importance of using the same temperature scale in comparing theoretical and observational indices is discussed. The full consistency between Lick/SDSS and observational indices derived from the above mentioned stellar libraries is assessed. The comparison with indices computed from SDSS-DR7 spectra evidences good consistency for 'dwarf' stars and significant disagreement for 'giant' stars due to systematic overestimation of the stellar T eff by the SEGUE Stellar Parameter Pipeline.

  20. KINETyS II: Constraints on spatial variations of the stellar initial mass function from K-band spectroscopy

    Science.gov (United States)

    Alton, P. D.; Smith, R. J.; Lucey, J. R.

    2018-05-01

    We investigate the spatially resolved stellar populations of a sample of seven nearby massive Early-type galaxies (ETGs), using optical and near infrared data, including K-band spectroscopy. This data offers good prospects for mitigating the uncertainties inherent in stellar population modelling by making a wide variety of strong spectroscopic features available. We report new VLT-KMOS measurements of the average empirical radial gradients out to the effective radius in the strengths of the Ca I 1.98 μm and 2.26 μm features, the Na I 2.21 μm line, and the CO 2.30 μm bandhead. Following previous work, which has indicated an excess of dwarf stars in the cores of massive ETGs, we pay specific attention to radial variations in the stellar initial mass function (IMF) as well as modelling the chemical abundance patterns and stellar population ages in our sample. Using state-of-the-art stellar population models we infer an [Fe/H] gradient of -0.16±0.05 per dex in fractional radius and an average [Na/Fe] gradient of -0.35±0.09. We find a large but radially-constant enhancement to [Mg/Fe] of ˜ 0.4 and a much lower [Ca/Fe] enhancement of ˜ 0.1. Finally, we find no significant IMF radial gradient in our sample on average and find that most galaxies in our sample are consistent with having a Milky Way-like IMF, or at most a modestly bottom heavy IMF (e.g. less dwarf enriched than a single power law IMF with the Salpeter slope).

  1. AN EXPLORATION OF THE STATISTICAL SIGNATURES OF STELLAR FEEDBACK

    Energy Technology Data Exchange (ETDEWEB)

    Boyden, Ryan D.; Offner, Stella S. R. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Koch, Eric W.; Rosolowsky, Erik W., E-mail: soffner@astro.umass.edu [Department of Physics, University of Alberta, Edmonton, T6G 2E1 (Canada)

    2016-12-20

    All molecular clouds are observed to be turbulent, but the origin, means of sustenance, and evolution of the turbulence remain debated. One possibility is that stellar feedback injects enough energy into the cloud to drive observed motions on parsec scales. Recent numerical studies of molecular clouds have found that feedback from stars, such as protostellar outflows and winds, injects energy and impacts turbulence. We expand upon these studies by analyzing magnetohydrodynamic simulations of molecular clouds, including stellar winds, with a range of stellar mass-loss rates and magnetic field strengths. We generate synthetic {sup 12}CO(1–0) maps assuming that the simulations are at the distance of the nearby Perseus molecular cloud. By comparing the outputs from different initial conditions and evolutionary times, we identify differences in the synthetic observations and characterize these using common astrostatistics. We quantify the different statistical responses using a variety of metrics proposed in the literature. We find that multiple astrostatistics, including the principal component analysis, the spectral correlation function, and the velocity coordinate spectrum (VCS), are sensitive to changes in stellar mass-loss rates and/or time evolution. A few statistics, including the Cramer statistic and VCS, are sensitive to the magnetic field strength. These findings demonstrate that stellar feedback influences molecular cloud turbulence and can be identified and quantified observationally using such statistics.

  2. Good Abundances from Bad Spectra: II. Application and a New Stellar Color-Temperature Calibration

    Science.gov (United States)

    Jones, J. Bryn; Wyse, Rosemary F. G.; Gilmore, Gerard

    1995-07-01

    Stellar spectra derived from current multiple-object fiber-fed spectroscopic radial-velocity surveys, of the type feasible with, among other examples, AUTOFIB, 2dF, HYDRA, NESSIE, and the Sloan survey, differ significantly from those traditionally used for determination of stellar abundances. The spectra tend to be of moderate resolution (around 1 A) and signal-to-noise ratio (around 10-20 per resolution element), and cannot usually have reliable continuum shapes determined over wavelength ranges in excess of a few tens of Angstroms. Nonetheless, with care and a calibration of stellar effective temperature from photometry, independent of the spectroscopy, reliable iron abundances can be derived. We have developed techniques to extract true iron abundances and surface gravities from low signal-to-noise ratio, intermediate resolution spectra of G-type stars in the 4000-5000A wavelength region. The theoretical basis and calibration using synthetic spectra are described in detail in another paper (Jones, Gilmore and Wyse, 1995). The practical application of these techniques to observational data, which requires some modification from the ideal case of synthetic data, is given in the present paper. An externally-derived estimate of stellar effective temperature is required in order to constrain parameter space sufficiently; a new derivation of the V-I effective temperature relation is thus an integral part of the analysis presented here. We have derived this relationship from analysis of available relevant data for metal-poor G dwarfs, the first such calibration. We test and calibrate our techniques by analysis of spectra of the twilight sky, of member stars of the cluster M67, and of a set of field stars of known metallicity. We show that this method, combined with our new color-temperature calibration, can provide true iron abundances, with an uncertainty of less than 0.2 dex over the range of metallicty found in the Galactic thick and thin disks, from spectra

  3. Stellar Streams Discovered in the Dark Energy Survey

    Energy Technology Data Exchange (ETDEWEB)

    Shipp, N.; et al.

    2018-01-09

    We perform a search for stellar streams around the Milky Way using the first three years of multi-band optical imaging data from the Dark Energy Survey (DES). We use DES data covering $\\sim 5000$ sq. deg. to a depth of $g > 23.5$ with a relative photometric calibration uncertainty of $< 1 \\%$. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of $\\sim 50$ kpc. We search for stellar streams using a matched-filter in color-magnitude space derived from a synthetic isochrone of an old, metal-poor stellar population. Our detection technique recovers four previously known thin stellar streams: Phoenix, ATLAS, Tucana III, and a possible extension of Molonglo. In addition, we report the discovery of eleven new stellar streams. In general, the new streams detected by DES are fainter, more distant, and lower surface brightness than streams detected by similar techniques in previous photometric surveys. As a by-product of our stellar stream search, we find evidence for extra-tidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, as well as the large- and small-scale distribution of dark matter around the Milky Way.

  4. The Galactic stellar disc

    International Nuclear Information System (INIS)

    Feltzing, S; Bensby, T

    2008-01-01

    The study of the Milky Way stellar discs in the context of galaxy formation is discussed. In particular, we explore the properties of the Milky Way disc using a new sample of about 550 dwarf stars for which we have recently obtained elemental abundances and ages based on high-resolution spectroscopy. For all the stars we also have full kinematic information as well as information about their stellar orbits. We confirm results from previous studies that the thin and the thick discs have distinct abundance patterns. But we also explore a larger range of orbital parameters than what has been possible in our previous studies. Several new results are presented. We find that stars that reach high above the Galactic plane and have eccentric orbits show remarkably tight abundance trends. This implies that these stars formed out of well-mixed gas that had been homogenized over large volumes. We find some evidence that suggest that the event that most likely caused the heating of this stellar population happened a few billion years ago. Through a simple, kinematic exploration of stars with super-solar [Fe/H], we show that the solar neighbourhood contains metal-rich, high velocity stars that are very likely associated with the thick disc. Additionally, the HR1614 moving group and the Hercules and Arcturus stellar streams are discussed and it is concluded that, probably, a large fraction of the groups and streams so far identified in the disc are the result of evolution and interactions within the stellar disc rather than being dissolved stellar clusters or engulfed dwarf galaxies.

  5. Rapid identification of illegal synthetic adulterants in herbal anti-diabetic medicines using near infrared spectroscopy

    Science.gov (United States)

    Feng, Yanchun; Lei, Deqing; Hu, Changqin

    We created a rapid detection procedure for identifying herbal medicines illegally adulterated with synthetic drugs using near infrared spectroscopy. This procedure includes a reverse correlation coefficient method (RCCM) and comparison of characteristic peaks. Moreover, we made improvements to the RCCM based on new strategies for threshold settings. Any tested herbal medicine must meet two criteria to be identified with our procedure as adulterated. First, the correlation coefficient between the tested sample and the reference must be greater than the RCCM threshold. Next, the NIR spectrum of the tested sample must contain the same characteristic peaks as the reference. In this study, four pure synthetic anti-diabetic drugs (i.e., metformin, gliclazide, glibenclamide and glimepiride), 174 batches of laboratory samples and 127 batches of herbal anti-diabetic medicines were used to construct and validate the procedure. The accuracy of this procedure was greater than 80%. Our data suggest that this protocol is a rapid screening tool to identify synthetic drug adulterants in herbal medicines on the market.

  6. How elevated is the dynamical-to-stellar mass ratio of the ultra-compact dwarf S999?

    OpenAIRE

    Janz, Joachim; Forbes, Duncan A.; Norris, Mark A.; Strader, Jay; Penny, Samantha J.; Fagioli, Martina; Romanowsky, Aaron J.

    2015-01-01

    Here we present new Keck ESI high-resolution spectroscopy and deep archival HST/ACS imaging for S999, an ultra-compact dwarf in the vicinity of M87, which was claimed to have an extremely high dynamical-to-stellar mass ratio. Our data increase the total integration times by a factor of 5 and 60 for spectroscopy and imaging, respectively. This allows us to constrain the stellar population parameters for the first time (simple stellar population equivalent age $=7.6^{+2.0}_{-1.6}$ Gyr; $[Z/\\tex...

  7. Isotope ratio in stellar atmospheres and nucleosynthesis

    International Nuclear Information System (INIS)

    Barbuy, B.L.S.

    1987-01-01

    The determination of isotopic ratios in stellar atmospheres is studied. The isotopic shift of atomic and molecular lines of different species of a certain element is examined. CH and MgH lines are observed in order to obtain the 12 C: 13 C and 24 Mg: 25 Mg: 26 Mg isotpic ratios. The formation of lines in stellar atmospheres is computed and the resulting synthetic spectra are employed to determine the isotopic abundances. The results obtained for the isotopic ratios are compared to predictions of nucleosynthesis theories. Finally, the concept of primary and secondary element is discussed, and these definitions are applied to the observed variations in the abundance of elements as a function of metallicity. (author) [pt

  8. Comparison of stellar population model predictions using optical and infrared spectroscopy

    Science.gov (United States)

    Baldwin, C.; McDermid, R. M.; Kuntschner, H.; Maraston, C.; Conroy, C.

    2018-02-01

    We present Gemini/GNIRS cross-dispersed near-infrared spectra of 12 nearby early-type galaxies, with the aim of testing commonly used stellar population synthesis models. We select a subset of galaxies from the ATLAS3D sample which span a wide range of ages (single stellar population equivalent ages of 1-15 Gyr) at approximately solar metallicity. We derive star formation histories using four different stellar population synthesis models, namely those of Bruzual & Charlot, Conroy, Gunn & White, Maraston & Strömbäck and Vazdekis et al. We compare star formation histories derived from near-infrared spectra with those derived from optical spectra using the same models. We find that while all models agree in the optical, the derived star formation histories vary dramatically from model to model in the near-infrared. We find that this variation is largely driven by the choice of stellar spectral library, such that models including high-quality spectral libraries provide the best fits to the data, and are the most self-consistent when comparing optically derived properties with near-infrared ones. We also find the impact of age variation in the near-infrared to be subtle, and largely encoded in the shape of the continuum, meaning that the common approach of removing continuum information with a high-order polynomial greatly reduces our ability to constrain ages in the near-infrared.

  9. X-ray photoelectron spectroscopy of HUPA organic substances: natural and synthetic humic compounds

    International Nuclear Information System (INIS)

    Barre, N.; Mercier-Bion, F.; Reiller, P.

    2004-01-01

    X-ray photoelectron spectroscopy (XPS) results on the characterisation of the HUPA organic materials, i.e. natural humic substances ''GOHY 573'' (fulvic acid FA and humic acid HA) extracted from the Gorleben ground waters, and synthetic humic acids ''M1'' and ''M42'' obtained from a standard melanoidin preparation from FZ Rossendorf, are presented in this paper. XPS investigations were focused on the determination of the chemical environment of the major elements as carbon, nitrogen, oxygen and sulphur, and on the identification of trace metals trapped by these organic compounds. (orig.)

  10. BinMag: Widget for comparing stellar observed with theoretical spectra

    Science.gov (United States)

    Kochukhov, O.

    2018-05-01

    BinMag examines theoretical stellar spectra computed with Synth/SynthMag/Synmast/Synth3/SME spectrum synthesis codes and compare them to observations. An IDL widget program, BinMag applies radial velocity shift and broadening to the theoretical spectra to account for the effects of stellar rotation, radial-tangential macroturbulence, instrumental smearing. The code can also simulate spectra of spectroscopic binary stars by appropriate coaddition of two synthetic spectra. Additionally, BinMag can be used to measure equivalent width, fit line profile shapes with analytical functions, and to automatically determine radial velocity and broadening parameters. BinMag interfaces with the Synth3 (ascl:1212.010) and SME (ascl:1202.013) codes, allowing the user to determine chemical abundances and stellar atmospheric parameters from the observed spectra.

  11. Microlensing and the physics of stellar atmospheres

    NARCIS (Netherlands)

    Sackett, PD; Menzies, JW; Sackett, PD

    2001-01-01

    The simple physics of microlensing provides a well understood tool with which to probe the atmospheres of distant stars in the Galaxy and Local Group with high magnification and resolution. Recent results in measuring stellar surface structure through broad band photometry and spectroscopy of high

  12. Indicators of Mass in Spherical Stellar Atmospheres

    Science.gov (United States)

    Lester, John B.; Dinshaw, Rayomond; Neilson, Hilding R.

    2013-04-01

    Mass is the most important stellar parameter, but it is not directly observable for a single star. Spherical model stellar atmospheres are explicitly characterized by their luminosity ( L⋆), mass ( M⋆), and radius ( R⋆), and observations can now determine directly L⋆ and R⋆. We computed spherical model atmospheres for red giants and for red supergiants holding L⋆ and R⋆ constant at characteristic values for each type of star but varying M⋆, and we searched the predicted flux spectra and surface-brightness distributions for features that changed with mass. For both stellar classes we found similar signatures of the stars’ mass in both the surface-brightness distribution and the flux spectrum. The spectral features have been use previously to determine log 10(g), and now that the luminosity and radius of a non-binary red giant or red supergiant can be observed, spherical model stellar atmospheres can be used to determine a star’s mass from currently achievable spectroscopy. The surface-brightness variations of mass are slightly smaller than can be resolved by current stellar imaging, but they offer the advantage of being less sensitive to the detailed chemical composition of the atmosphere.

  13. Diagnostics Plan for the National Compact Stellarator Experiment

    International Nuclear Information System (INIS)

    D. Johnson; T. Brown; H. Neilson; G. Schilling; H. Takahashi; M. Zarnstorff; M. Cole; E. Lazarus; and M. Fenstermacher

    2002-01-01

    The National Compact Stellarator Experiment (NCSX) is a stellarator-tokamak hybrid seeking to combine the good confinement, high beta and moderate aspect ratio of the tokamak with the quasi-steady-state operation and good stability properties of the stellarator. A preliminary list of measurement requirements, intended to satisfy the needs of the phased research plan, provides the basis for a full complement of plasma diagnostics. It is important to consider this full set, even at this early stage, to assess the adequacy of the stellarator design for diagnostic port access. The 3-D nature of the plasma is a measurement challenge, as is the necessity for high spatial resolution to assess the quality of magnetic surfaces. Other diagnostic requirements include the need for re-entrant views that penetrate the cryostat, for a convenient e-beam probe for field line mapping, and for a diagnostic neutral beam for active spectroscopy

  14. X-shooter spectroscopy of young stellar objects in Lupus. Atmospheric parameters, membership, and activity diagnostics

    Science.gov (United States)

    Frasca, A.; Biazzo, K.; Alcalá, J. M.; Manara, C. F.; Stelzer, B.; Covino, E.; Antoniucci, S.

    2017-06-01

    Aims: A homogeneous determination of basic stellar parameters of young stellar object (YSO) candidates is needed to confirm their pre-main sequence evolutionary stage and membership to star forming regions (SFRs), and to get reliable values of the quantities related to chromospheric activity and accretion. Methods: We used the code ROTFIT and synthetic BT-Settl spectra for the determination of the atmospheric parameters (Teff and log g), veiling (r), radial (RV), and projected rotational velocity (vsini) from X-shooter spectra of 102 YSO candidates (95 of infrared Class II and seven Class III) in the Lupus SFR. The spectral subtraction of inactive templates, rotationally broadened to match the vsini of the targets, enabled us to measure the line fluxes for several diagnostics of both chromospheric activity and accretion, such as Hα, Hβ, Ca II, and Na I lines. Results: We have shown that 13 candidates can be rejected as Lupus members based on their discrepant RV with respect to Lupus and/or the very low log g values. At least 11 of them are background giants, two of which turned out to be lithium-rich giants. Regarding the members, we found that all Class III sources have Hα fluxes that are compatible with a pure chromospheric activity, while objects with disks lie mostly above the boundary between chromospheres and accretion. Young stellar objects with transitional disks display both high and low Hα fluxes. We found that the line fluxes per unit surface are tightly correlated with the accretion luminosity (Lacc) derived from the Balmer continuum excess. This rules out that the relationships between Lacc and line luminosities found in previous works are simply due to calibration effects. We also found that the Ca II-IRT flux ratio, FCaII8542/FCaII8498, is always small, indicating an optically thick emission source. The latter can be identified with the accretion shock near the stellar photosphere. The Balmer decrement reaches instead, for several accretors, high

  15. INTRIGOSS: A new Library of High Resolution Synthetic Spectra

    Science.gov (United States)

    Franchini, Mariagrazia; Morossi, Carlo; Di Marcancantonio, Paolo; Chavez, Miguel; GES-Builders

    2018-01-01

    INTRIGOSS (INaf Trieste Grid Of Synthetic Spectra) is a new High Resolution (HiRes) synthetic spectral library designed for studying F, G, and K stars. The library is based on atmosphere models computed with specified individual element abundances via ATLAS12 code. Normalized SPectra (NSP) and surface Flux SPectra (FSP), in the 4800-5400 Å wavelength range, were computed by means of the SPECTRUM code. The synthetic spectra are computed with an atomic and bi-atomic molecular line list including "bona fide" Predicted Lines (PLs) built by tuning loggf to reproduce very high SNR Solar spectrum and the UVES-U580 spectra of five cool giants extracted from the Gaia-ESO survey (GES). The astrophysical gf-values were then assessed by using more than 2000 stars with homogenous and accurate atmosphere parameters and detailed chemical composition from GES. The validity and greater accuracy of INTRIGOSS NSPs and FSPs with respect to other available spectral libraries is discussed. INTRIGOSS will be available on the web and will be a valuable tool for both stellar atmospheric parameters and stellar population studies.

  16. Modeling tracers of young stellar population age in star-forming galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Levesque, Emily M. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado 389-UCB, Boulder, CO 80309 (United States); Leitherer, Claus, E-mail: Emily.Levesque@colorado.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2013-12-20

    The young stellar population of a star-forming galaxy is the primary engine driving its radiative properties. As a result, the age of a galaxy's youngest generation of stars is critical for a detailed understanding of its star formation history, stellar content, and evolutionary state. Here we present predicted equivalent widths for the Hβ, Hα, and Brγ recombination lines as a function of stellar population age. The equivalent widths are produced by the latest generations of stellar evolutionary tracks and the Starburst99 stellar population synthesis code, and are the first to fully account for the combined effects of both nebular emission and continuum absorption produced by the synthetic stellar population. Our grid of model stellar populations spans six metallicities (0.001 < Z < 0.04), two treatments of star formation history (a 10{sup 6} M {sub ☉} instantaneous burst and a continuous star formation rate of 1 M {sub ☉} yr{sup –1}), and two different treatments of initial rotation rate (v {sub rot} = 0.0v {sub crit} and 0.4v {sub crit}). We also investigate the effects of varying the initial mass function. Given constraints on galaxy metallicity, our predicted equivalent widths can be applied to observations of star-forming galaxies to approximate the age of their young stellar populations.

  17. Spectroscopy Study of Synthetic Forsterite Obtained from Zeolite Precursors

    Directory of Open Access Journals (Sweden)

    Subotić, B.

    2008-02-01

    Full Text Available Important ceramics materials are prepared from aluminosilicate based precursors using novel methods, offering at the same time a better control over many important properties. Forsterite, due to its good refractoriness with melting point at 2163 K, excellent electrical insulation properties even at high temperatures, low dielectric permittivity, thermal expansion and chemical stability, is a material of interest to engineers and designers especially as an active medium for tuneable laser and is also a material of interest to SOFC (Solid oxide fuel cells manufacturers. The aim of this study is to investigate the synthesis of crystalline forsterite using different zeolite precursors previously activated by ball milling. Synthetic forsterite was synthesized from different zeolite precursors and MgO combining highenergy ball milling and thermal treatment of the mixture under determined conditions of time and temperature for each operation. In this research are studied the solid-state phase transformations taking place at temperatures below 1273 K. The obtained products were characterized using different spectroscopy techniques in comparison with surface analysis method and X-ray diffraction.

  18. The Space Stellar Photometry Mission COROT: Asteroseismology ...

    Indian Academy of Sciences (India)

    tribpo

    detect giant extra solar planets (detectable by spectroscopy from the ground) and determine their albedo. As COROT is devoted to stellar photometry, aiming at both a high precision and a long observation time, the search for exoplanets by the transit method can easily be integrated in the payload and in the mission profile.

  19. Neutron resonance spectroscopy

    International Nuclear Information System (INIS)

    Gunsing, F.

    2005-06-01

    The present document has been written in order to obtain the diploma 'Habilitation a Diriger des Recherches'. Since this diploma is indispensable to supervise thesis students, I had the intention to write a document that can be useful for someone starting in the field of neutron resonance spectroscopy. Although the here described topics are already described elsewhere, and often in more detail, it seemed useful to have most of the relevant information in a single document. A general introduction places the topic of neutron-nucleus interaction in a nuclear physics context. The large variations of several orders of magnitude in neutron-induced reaction cross sections are explained in terms of nuclear level excitations. The random character of the resonances make nuclear model calculation predictions impossible. Then several fields in physics where neutron-induced reactions are important and to which I have contributed in some way or another, are mentioned in a first synthetic chapter. They concern topics like parity nonconservation in certain neutron resonances, stellar nucleosynthesis by neutron capture, and data for nuclear energy applications. The latter item is especially important for the transmutation of nuclear waste and for alternative fuel cycles. Nuclear data libraries are also briefly mentioned. A second chapter details the R-matrix theory. This formalism is the foundation of the description of the neutron-nucleus interaction and is present in all fields of neutron resonance spectroscopy. (author)

  20. Spectroscopy the key to the stars

    CERN Document Server

    Robinson, Keith

    2007-01-01

    This is the first non-technical book on spectroscopy written specifically for practical amateur astronomers. It includes all the science necessary for a qualitative understanding of stellar spectra, but avoids a mathematical treatment which would alienate many of its intended readers. Any amateur astronomer who carries out observational spectroscopy and who wants a non-technical account of the physical processes which determine the intensity and profile morphology of lines in stellar spectra will find this is the only book written specially for them. It is an ideal companion to existing books

  1. SP_Ace: a new code to derive stellar parameters and elemental abundances

    Science.gov (United States)

    Boeche, C.; Grebel, E. K.

    2016-03-01

    Context. Ongoing and future massive spectroscopic surveys will collect large numbers (106-107) of stellar spectra that need to be analyzed. Highly automated software is needed to derive stellar parameters and chemical abundances from these spectra. Aims: We developed a new method of estimating the stellar parameters Teff, log g, [M/H], and elemental abundances. This method was implemented in a new code, SP_Ace (Stellar Parameters And Chemical abundances Estimator). This is a highly automated code suitable for analyzing the spectra of large spectroscopic surveys with low or medium spectral resolution (R = 2000-20 000). Methods: After the astrophysical calibration of the oscillator strengths of 4643 absorption lines covering the wavelength ranges 5212-6860 Å and 8400-8924 Å, we constructed a library that contains the equivalent widths (EW) of these lines for a grid of stellar parameters. The EWs of each line are fit by a polynomial function that describes the EW of the line as a function of the stellar parameters. The coefficients of these polynomial functions are stored in a library called the "GCOG library". SP_Ace, a code written in FORTRAN95, uses the GCOG library to compute the EWs of the lines, constructs models of spectra as a function of the stellar parameters and abundances, and searches for the model that minimizes the χ2 deviation when compared to the observed spectrum. The code has been tested on synthetic and real spectra for a wide range of signal-to-noise and spectral resolutions. Results: SP_Ace derives stellar parameters such as Teff, log g, [M/H], and chemical abundances of up to ten elements for low to medium resolution spectra of FGK-type stars with precision comparable to the one usually obtained with spectra of higher resolution. Systematic errors in stellar parameters and chemical abundances are presented and identified with tests on synthetic and real spectra. Stochastic errors are automatically estimated by the code for all the parameters

  2. Constraining stellar physics from red-giant stars in binaries – stellar rotation, mixing processes and stellar activity

    Directory of Open Access Journals (Sweden)

    Beck P. G.

    2017-01-01

    Full Text Available The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to an improved understanding of stellar structure and evolution - in particular for solar-like oscillators in this context. Binary stars are fascinating objects. Because they were formed together, binary systems provide a set of two stars with very well constrained parameters. Those can be used to study properties and physical processes, such as the stellar rotation, dynamics and rotational mixing of elements and allows us to learn from the differences we find between the two components. In this work, we discussed a detailed study of the binary system KIC 9163796, discovered through Kepler photometry. The ground-based follow-up spectroscopy showed that this system is a double-lined spectroscopic binary, with a mass ratio close to unity. However, the fundamental parameters of the components of this system as well as their lithium abundances differ substantially. Kepler photometry of this system allows to perform a detailed seismic analysis as well as to derive the orbital period and the surface rotation rate of the primary component of the system. Indications of the seismic signature of the secondary are found. The differing parameters are best explained with both components located in the early and the late phase of the first dredge up at the bottom of the red-giant branch. Observed lithium abundances in both components are in good agreement with prediction of stellar models including rotational mixing. By combining observations and theory, a comprehensive picture of the system can be drawn.

  3. Columbia University OSO-8 instrument for stellar and solar X-ray spectroscopy and polarimetry

    Energy Technology Data Exchange (ETDEWEB)

    Wolff, R S [Columbia Univ., New York (USA). Columbia Astrophysics Lab.

    1976-08-01

    A spectrometer and a polarimeter consisting of large-area panels of mosaic crystals have been constructed and prepared for use in the OSO-8 satellite. The instrumentation is planned for study of stellar and solar X-ray spectra between 1.8-8 keV and stellar X-ray polarization at 2.6 keV. Aspects of the design which enable the instrument to make measurements of the diverse range of stellar and solar phenomena are described. Some of the unique features, such as high sensitivity, high temporal resolution, and spectral range, are discussed. The applicability of the spectrometer and polarimeter to various current problems in X-ray astronomy is considered.

  4. Synthetic properties of models of globular clusters

    Energy Technology Data Exchange (ETDEWEB)

    Angeletti, L; Dolcetta, R; Giannone, P. (Rome Univ. (Italy). Osservatorio Astronomico)

    1980-05-01

    Synthetic and projected properties of models of globular clusters have been computed on the basis of stellar evolution and time changes of the dynamical cluster structure. Clusters with five and eight stellar groups (each group consisting of stars with the same mass) were studied. Mass loss from evolved stars was taken into account. Observational features were obtained at ages of 10-19 x 10/sup 9/ yr. The basic importance of the horizontal- and asymptotic-branch stars was pointed out. A comparison of the results with observed data of M3 is discussed with the purpose of obtaining general indications rather than a specific fit.

  5. Synthetic properties of models of globular clusters

    International Nuclear Information System (INIS)

    Angeletti, L.; Dolcetta, R.; Giannone, P.

    1980-01-01

    Synthetic and projected properties of models of globular clusters have been computed on the basis of stellar evolution and time changes of the dynamical cluster structure. Clusters with five and eight stellar groups (each group consisting of stars with the same mass) were studied. Mass loss from evolved stars was taken into account. Observational features were obtained at ages of 10-19 x 10 9 yr. The basic importance of the horizontal- and asymptotic-branch stars was pointed out. A comparison of the results with observed data of M3 is discussed with the purpose of obtaining general indications rather than a specific fit. (orig.)

  6. A synthetic-dynamic method for water solubility measurements in high pressure CO_2 using ATR–FTIR spectroscopy

    International Nuclear Information System (INIS)

    Comak, Gurbuz; Foltran, Stéphanie; Ke, Jie; Pérez, Eduardo; Sánchez-Vicente, Yolanda; George, Michael W.; Poliakoff, Martyn

    2016-01-01

    Highlights: • A synthetic method using ATR–FTIR spectroscopy has been developed to measure the solubility of water in CO_2_. • New data have been obtained for the dew point of the water at 4.05 MPa, 5.05 MPa and 6.03 MPa. • These data fill a gap in the literature and could be of significance for CO_2 transport in pipelines for CCS technology. - Abstract: A new synthetic method for studying phase behaviour is described using Attenuated Total Reflection (ATR) spectroscopy. The method has been developed to provide relevant information on the solubility of water in CO_2. The dew point of water has been determined at three different pressures, viz. (4.05, 5.05 and 6.03) MPa with mole fractions of water between 0.01 and 0.04. The data obtained fill the gap in the literature in these regions of pressures and temperatures and could be of high importance in the context of Carbon Capture and Storage (CCS) technology. Indeed, the presence of water in the captured CO_2 could damage the pipeline used for CO_2 transport. Hence, it is very important to have a fully understanding of the behaviour of the (CO_2 + H_2O) mixtures in wide range of temperature relevant for CCS.

  7. The Effect of Stellar Contamination on Transmission Spectra of Low-mass Exoplanets

    Science.gov (United States)

    Rackham, Benjamin V.; Apai, Daniel; Giampapa, Mark S.

    2017-10-01

    Transmission spectroscopy offers the exciting possibility of studying terrestrial exoplanet atmospheres in the near-term future. The Transiting Exoplanet Survey Satellite (TESS), scheduled for launch next year, is expected to discover thousands of transiting exoplanets around bright host stars, including an estimated twenty habitable zone super-Earths. The brightness of the TESS host stars, combined with refined observational strategies and near-future facilities, will enable searches for atmospheric signatures from smaller and cooler exoplanets. These observations, however, will be increasingly subject to noise introduced by heterogeneities in the host star photospheres, such as star spots and faculae. In short, the transmission spectroscopy method relies on the assumption that the spectrum of the transit chord does not differ from that of the integrated stellar disk or, if it does, the contribution of photospheric heterogeneities to the transmission spectrum can be constrained by variability monitoring. However, any axisymmetric populations of spots and faculae will strongly affect transmission spectra, and their presence cannot be deduced from monitoring efforts. A clear need exists for a more robust understanding of stellar contamination on transmission spectra. Here we summarize our work on the impact of heterogeneous stellar photospheres on transmission spectra and detail implications for atmospheric characterization efforts. By modeling spot and faculae distributions in stellar photospheres, we find that spot-covering fractions extrapolated from observed variability amplitudes are significantly underestimated. Likewise, corrections based on variability monitoring likely fall short of the actual stellar spectral contamination. We provide examples of contamination spectra for typical levels of stellar activity across a range of spectral types. For M dwarfs, molecular absorption features in spots and faculae can imprint apparent features in transmission spectra

  8. Stochastic 2-D galaxy disk evolution models. Resolved stellar populations in the galaxy M33

    Science.gov (United States)

    Mineikis, T.; Vansevičius, V.

    We improved the stochastic 2-D galaxy disk models (Mineikis & Vansevičius 2014a) by introducing enriched gas outflows from galaxies and synthetic color-magnitude diagrams of stellar populations. To test the models, we use the HST/ACS stellar photometry data in four fields located along the major axis of the galaxy M33 (Williams et al. 2009) and demonstrate the potential of the models to derive 2-D star formation histories in the resolved disk galaxies.

  9. Neutron resonance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Gunsing, F

    2005-06-15

    The present document has been written in order to obtain the diploma 'Habilitation a Diriger des Recherches'. Since this diploma is indispensable to supervise thesis students, I had the intention to write a document that can be useful for someone starting in the field of neutron resonance spectroscopy. Although the here described topics are already described elsewhere, and often in more detail, it seemed useful to have most of the relevant information in a single document. A general introduction places the topic of neutron-nucleus interaction in a nuclear physics context. The large variations of several orders of magnitude in neutron-induced reaction cross sections are explained in terms of nuclear level excitations. The random character of the resonances make nuclear model calculation predictions impossible. Then several fields in physics where neutron-induced reactions are important and to which I have contributed in some way or another, are mentioned in a first synthetic chapter. They concern topics like parity nonconservation in certain neutron resonances, stellar nucleosynthesis by neutron capture, and data for nuclear energy applications. The latter item is especially important for the transmutation of nuclear waste and for alternative fuel cycles. Nuclear data libraries are also briefly mentioned. A second chapter details the R-matrix theory. This formalism is the foundation of the description of the neutron-nucleus interaction and is present in all fields of neutron resonance spectroscopy. (author)

  10. Asteroseismology of Stellar Populations in the Milky Way

    CERN Document Server

    Eggenberger, Patrick; Girardi, Léo; Montalbán, Josefina

    2015-01-01

    The detection of radial and non-radial solar-like oscillations in thousands of G-K giants with CoRoT and Kepler is paving the road for detailed studies of stellar populations in the Galaxy. The available average seismic constraints allow largely model-independent determination of stellar radii and masses, and can be used to determine the position and age of thousands of stars in different regions of the Milky Way, and of giants belonging to open clusters. Such a close connection between stellar evolution, Galactic evolution, and asteroseismology opens a new very promising gate in our understanding of stars and galaxies.  This book represents a natural progression from the collection of review papers presented in the book 'Red Giants as Probes of the Structure and Evolution of the Milky Way', which appeared in the  Astrophysics and Space Science Proceedings series in 2012. This sequel volume contains review papers on spectroscopy, seismology of red giants, open questions in Galactic astrophysics, and discu...

  11. THE HUBBLE SPACE TELESCOPE UV LEGACY SURVEY OF GALACTIC GLOBULAR CLUSTERS. III. A QUINTUPLE STELLAR POPULATION IN NGC 2808

    International Nuclear Information System (INIS)

    Milone, A. P.; Marino, A. F.; Jerjen, H.; Piotto, G.; Renzini, A.; Bedin, L. R.; Anderson, J.; Bellini, A.; Cassisi, S.; Pietrinferni, A.; D’Antona, F.; Ventura, P.

    2015-01-01

    In this study we present the first results from multi-wavelength Hubble Space Telescope (HST) observations of the Galactic globular cluster (GC) NGC 2808 as an extension of the Hubble Space Telescope UV Legacy Survey of Galactic GCs (GO-13297 and previous proprietary and HST archive data). Our analysis allowed us to disclose a multiple-stellar-population phenomenon in NGC 2808 even more complex than previously thought. We have separated at least five different populations along the main sequence and the red giant branch (RGB), which we name A, B, C, D, and E (though an even finer subdivision may be suggested by the data). We identified the RGB bump in four out of the five RGBs. To explore the origin of this complex color–magnitude diagram, we have combined our multi-wavelength HST photometry with synthetic spectra, generated by assuming different chemical compositions. The comparison of observed colors with synthetic spectra suggests that the five stellar populations have different contents of light elements and helium. Specifically, if we assume that NGC 2808 is homogeneous in [Fe/H] (as suggested by spectroscopy for Populations B, C, D, E, but lacking for Population A) and that population A has a primordial helium abundance, we find that populations B, C, D, E are enhanced in helium by ΔY ∼ 0.03, 0.03, 0.08, 0.13, respectively. We obtain similar results by comparing the magnitude of the RGB bumps with models. Planned spectroscopic observations will test whether Population A also has the same metallicity, or whether its photometric differences with Population B can be ascribed to small [Fe/H] and [O/H] differences rather than to helium

  12. Solid-state 13C magic angle spinning NMR spectroscopy characterization of particle size structural variations in synthetic nanodiamonds

    International Nuclear Information System (INIS)

    Alam, Todd M.

    2004-01-01

    Solid-state 13 C magic angle spinning (MAS) NMR spectroscopy has been used to quantify the different carbon species observed in synthetically produced nanodiamonds. Two different diamond-like carbon species were observed using 13 C MAS NMR, which have been attributed to a highly ordered crystalline diamond phase and a disordered crystalline diamond phase. The relative ratio of these different diamond phases was found to vary with the particle size of the nanodiamond materials

  13. The SELGIFS data challenge: generating synthetic observations of CALIFA galaxies from hydrodynamical simulations

    Science.gov (United States)

    Guidi, G.; Casado, J.; Ascasibar, Y.; García-Benito, R.; Galbany, L.; Sánchez-Blázquez, P.; Sánchez, S. F.; Rosales-Ortega, F. F.; Scannapieco, C.

    2018-06-01

    In this work we present a set of synthetic observations that mimic the properties of the Integral Field Spectroscopy (IFS) survey CALIFA, generated using radiative transfer techniques applied to hydrodynamical simulations of galaxies in a cosmological context. The simulated spatially-resolved spectra include stellar and nebular emission, kinematic broadening of the lines, and dust extinction and scattering. The results of the radiative transfer simulations have been post-processed to reproduce the main properties of the CALIFA V500 and V1200 observational setups. The data has been further formatted to mimic the CALIFA survey in terms of field of view size, spectral range and sampling. We have included the effect of the spatial and spectral Point Spread Functions affecting CALIFA observations, and added detector noise after characterizing it on a sample of 367 galaxies. The simulated datacubes are suited to be analysed by the same algorithms used on real IFS data. In order to provide a benchmark to compare the results obtained applying IFS observational techniques to our synthetic datacubes, and test the calibration and accuracy of the analysis tools, we have computed the spatially-resolved properties of the simulations. Hence, we provide maps derived directly from the hydrodynamical snapshots or the noiseless spectra, in a way that is consistent with the values recovered by the observational analysis algorithms. Both the synthetic observations and the product datacubes are public and can be found in the collaboration website http://astro.ft.uam.es/selgifs/data_challenge/.

  14. STELLAR COLOR REGRESSION: A SPECTROSCOPY-BASED METHOD FOR COLOR CALIBRATION TO A FEW MILLIMAGNITUDE ACCURACY AND THE RECALIBRATION OF STRIPE 82

    International Nuclear Information System (INIS)

    Yuan, Haibo; Liu, Xiaowei; Xiang, Maosheng; Huang, Yang; Zhang, Huihua; Chen, Bingqiu

    2015-01-01

    In this paper we propose a spectroscopy-based stellar color regression (SCR) method to perform accurate color calibration for modern imaging surveys, taking advantage of millions of stellar spectra now available. The method is straightforward, insensitive to systematic errors in the spectroscopically determined stellar atmospheric parameters, applicable to regions that are effectively covered by spectroscopic surveys, and capable of delivering an accuracy of a few millimagnitudes for color calibration. As an illustration, we have applied the method to the Sloan Digital Sky Survey (SDSS) Stripe 82 data. With a total number of 23,759 spectroscopically targeted stars, we have mapped out the small but strongly correlated color zero-point errors present in the photometric catalog of Stripe 82, and we improve the color calibration by a factor of two to three. Our study also reveals some small but significant magnitude dependence errors in the z band for some charge-coupled devices (CCDs). Such errors are likely to be present in all the SDSS photometric data. Our results are compared with those from a completely independent test based on the intrinsic colors of red galaxies presented by Ivezić et al. The comparison, as well as other tests, shows that the SCR method has achieved a color calibration internally consistent at a level of about 5 mmag in u – g, 3 mmag in g – r, and 2 mmag in r – i and i – z. Given the power of the SCR method, we discuss briefly the potential benefits by applying the method to existing, ongoing, and upcoming imaging surveys

  15. A panchromatic study of the stellar populations in NGC 4303

    Science.gov (United States)

    Dametto, N. Z.; Riffel, R.; Colina, L. R.; Riffel, R. A.; Piqueras López, J.

    2017-07-01

    We present some preliminary results on a panchromatic study of the stellar populations (SPs) in NGC 4303, using HST/STIS long-slit spectroscopy for the ultra-violet (UV) and optical spectral range, while VLT/SINFONI IFU data were used for the near-infrared (NIR) part of the spectra.

  16. The stoichiometry of synthetic alunite as a function of hydrothermal aging investigated by solid-state NMR spectroscopy, powder X-ray diffraction and infrared spectroscopy

    DEFF Research Database (Denmark)

    Grube, Elisabeth; Nielsen, Ulla Gro

    2015-01-01

    The stoichiometry of a series of synthetic alunite (nominally KAl3(SO4)2(OH)6) samples prepared by hydrothermal methods as a function of reaction time (1 – 31 days) has been investigated by powder X-ray diffraction, Fourier transform infrared spectroscopy as well as solid-state 1H and 27Al magic...... of potassium defects present, from 17.261(1) to 17.324(5) Å. Solid-state 27Al MAS NMR revealed a decrease in the defect concentration as a function of time and showed the presence of 7-10 % impurities in the samples....

  17. MONTE CARLO SIMULATIONS OF GLOBULAR CLUSTER EVOLUTION. V. BINARY STELLAR EVOLUTION

    International Nuclear Information System (INIS)

    Chatterjee, Sourav; Umbreit, Stefan; Rasio, Frederic A.; Fregeau, John M.

    2010-01-01

    We study the dynamical evolution of globular clusters containing primordial binaries, including full single and binary stellar evolution using our Monte Carlo cluster evolution code updated with an adaptation of the single and binary stellar evolution codes SSE and BSE from Hurley et al. We describe the modifications that we have made to the code. We present several test calculations and comparisons with existing studies to illustrate the validity of the code. We show that our code finds very good agreement with direct N-body simulations including primordial binaries and stellar evolution. We find significant differences in the evolution of the global properties of the simulated clusters using stellar evolution compared with simulations without any stellar evolution. In particular, we find that the mass loss from the stellar evolution acts as a significant energy production channel simply by reducing the total gravitational binding energy and can significantly prolong the initial core contraction phase before reaching the binary-burning quasi-steady state of the cluster evolution. We simulate a large grid of models varying the initial cluster mass, binary fraction, and concentration parameter, and we compare properties of the simulated clusters with those of the observed Galactic globular clusters (GGCs). We find that simply including stellar evolution in our simulations and assuming the typical initial cluster half-mass radius is approximately a few pc independent of mass, our simulated cluster properties agree well with the observed GGC properties such as the core radius and the ratio of the core radius to the half-mass radius. We explore in some detail qualitatively different clusters in different phases of their evolution and construct synthetic Hertzsprung-Russell diagrams for these clusters.

  18. Stellar Pulsations, Impact of New Instrumentation and New Insights

    CERN Document Server

    Garrido, R; Balona, L; Christensen-Dalsgaard, J; 20th Stellar Pulsation Conference Series

    2013-01-01

    Analyses of photometric time series obtained from the MOST, CoRoT and Kepler space missions were presented at the 20th conference on Stellar Pulsations (Granada, September 2011). These results are leading to a re-appraisal of our views on stellar pulsation in some stars and posing some new and unexpected challenges. The very important and exciting role played by innovative ground-based observational techniques, such as interferometric measurements of giant pulsating stars and high-resolution spectroscopy in the near infrared, is also discussed. These Proceedings are distinguished by the format of the conference, which brings together a variety of related but different topics not found in other meetings of this nature.

  19. Evolutionary stellar population synthesis with MILES : I. The base models and a new line index system

    NARCIS (Netherlands)

    Vazdekis, A.; Sanchez-Blazquez, P.; Falcon-Barroso, J.; Cenarro, A. J.; Beasley, M. A.; Cardiel, N.; Gorgas, J.; Peletier, R. F.

    2010-01-01

    We present synthetic spectral energy distributions (SEDs) for single-age, single-metallicity stellar populations (SSPs) covering the full optical spectral range at moderately high resolution [full width at half-maximum (FWHM) = 2.3Å]. These SEDs constitute our base models, as they combine

  20. Near-infrared (JHK) spectroscopy of young stellar and substellar objects in orion

    International Nuclear Information System (INIS)

    Ingraham, P.; Albert, L.; Doyon, R.; Artigau, E.

    2014-01-01

    We performed low-resolution (R ∼ 40) near-infrared (0.9-2.4 μm) multi-object spectroscopy of 240 isolated point sources having apparent H-band magnitudes between 9 and 18 in the central 5' × 6' of the Orion Trapezium cluster. The observations were performed over four nights at the Canada-France-Hawaii Telescope using the visiting instrument SIMON, an infrared imager and multi-object spectrograph. We present the spectra of 104 objects with accurately derived spectral types including 7 new objects having masses below the hydrogen-burning limit, and 6 objects with masses below the deuterium-burning limit. The spectral classification is performed by fitting previously classified spectral templates of dwarf stars (K4-M3) and optically classified young stellar and substellar objects (M4-L0), to the entire 0.9-2.4 μm spectral energy distribution in order to assign a spectral type and visual extinction for each object. Of the 104 objects studied, 44 have been previously classified spectroscopically using various techniques. We perform a rigorous comparison between the previous classifications and our own and find them to be in good agreement. Using the dereddened H-band magnitudes, the classified objects are used to create an Hertzsprung-Russell diagram for the cluster. We find that the previous age estimates of ∼1 Myr to be consistent with our results. Consistent with previous studies, numerous objects are observed to have luminosities several magnitudes above the 1 Myr isochrone. Numerous objects exhibiting emission features in the J band are also reported

  1. Stellar Physics 2: Stellar Evolution and Stability

    CERN Document Server

    Bisnovatyi-Kogan, Gennady S

    2011-01-01

    "Stellar Physics" is a an outstanding book in the growing body of literature on star formation and evolution. Not only does the author, a leading expert in the field, very thoroughly present the current state of knowledge on stellar physics, but he handles with equal care the many problems that this field of research still faces. A bibliography with well over 1000 entries makes this book an unparalleled reference source. "Stellar Evolution and Stability" is the second of two volumes and can be read, as can the first volume "Fundamental Concepts and Stellar Equilibrium," as a largely independent work. It traces in great detail the evolution of protostars towards the main sequence and beyond this to the last stage of stellar evolution, with the corresponding vast range from white dwarfs to supernovae explosions, gamma-ray bursts and black hole formation. The book concludes with special chapters on the dynamical, thermal and pulsing stability of stars. This second edition is carefully updated in the areas of pre...

  2. The PyCASSO database: spatially resolved stellar population properties for CALIFA galaxies

    Science.gov (United States)

    de Amorim, A. L.; García-Benito, R.; Cid Fernandes, R.; Cortijo-Ferrero, C.; González Delgado, R. M.; Lacerda, E. A. D.; López Fernández, R.; Pérez, E.; Vale Asari, N.

    2017-11-01

    The Calar Alto Legacy Integral Field Area (CALIFA) survey, a pioneer in integral field spectroscopy legacy projects, has fostered many studies exploring the information encoded on the spatially resolved data on gaseous and stellar features in the optical range of galaxies. We describe a value-added catalogue of stellar population properties for CALIFA galaxies analysed with the spectral synthesis code starlight and processed with the pycasso platform. Our public database (http://pycasso.ufsc.br/, mirror at http://pycasso.iaa.es/) comprises 445 galaxies from the CALIFA Data Release 3 with COMBO data. The catalogue provides maps for the stellar mass surface density, mean stellar ages and metallicities, stellar dust attenuation, star formation rates, and kinematics. Example applications both for individual galaxies and for statistical studies are presented to illustrate the power of this data set. We revisit and update a few of our own results on mass density radial profiles and on the local mass-metallicity relation. We also show how to employ the catalogue for new investigations, and show a pseudo Schmidt-Kennicutt relation entirely made with information extracted from the stellar continuum. Combinations to other databases are also illustrated. Among other results, we find a very good agreement between star formation rate surface densities derived from the stellar continuum and the H α emission. This public catalogue joins the scientific community's effort towards transparency and reproducibility, and will be useful for researchers focusing on (or complementing their studies with) stellar properties of CALIFA galaxies.

  3. Degradation patterns of natural and synthetic textiles on a soil surface during summer and winter seasons studied using ATR-FTIR spectroscopy

    Science.gov (United States)

    Ueland, Maiken; Howes, Johanna M.; Forbes, Shari L.; Stuart, Barbara H.

    2017-10-01

    Textiles are a valuable source of forensic evidence and the nature and condition of textiles collected from a crime scene can assist investigators in determining the nature of the death and aid in the identification of the victim. Until now, much of the knowledge of textile degradation in forensic contexts has been based on the visual inspection of material collected from soil environments. The purpose of the current study was to investigate the potential of a more quantitative approach to the understanding of forensic textile degradation through the application of infrared spectroscopy. Degradation patterns of natural and synthetic textile materials as they were subjected to a natural outdoor environment in Australia were investigated. Cotton, polyester and polyester - cotton blend textiles were placed on a soil surface during the summer and winter seasons and were analysed over periods 1 and 1.5 years, respectively, and examined using attenuated total reflectance (ATR) spectroscopy. Statistical analysis of the spectral data obtained for the cotton material correlated with visual degradation and a difference in the onset of degradation between the summer and winter season was revealed. The synthetic material did not show any signs of degradation either visually or statistically throughout the experimental period and highlighted the importance of material type in terms of preservation. The cotton section from the polyester - cotton blend samples was found to behave in a similar manner to that of the 100% cotton samples, however principal component analysis (PCA) demonstrated that the degradation patterns were less distinct in both the summer and winter trial for the blend samples. These findings indicated that the presence of the synthetic material may have inhibited the degradation of the natural material. The use of statistics to analyse the spectral data obtained for textiles of forensic interest provides a better foundation for the interpretation of the data

  4. THE PROPAGATION OF UNCERTAINTIES IN STELLAR POPULATION SYNTHESIS MODELING. II. THE CHALLENGE OF COMPARING GALAXY EVOLUTION MODELS TO OBSERVATIONS

    International Nuclear Information System (INIS)

    Conroy, Charlie; Gunn, James E.; White, Martin

    2010-01-01

    Models for the formation and evolution of galaxies readily predict physical properties such as star formation rates, metal-enrichment histories, and, increasingly, gas and dust content of synthetic galaxies. Such predictions are frequently compared to the spectral energy distributions of observed galaxies via the stellar population synthesis (SPS) technique. Substantial uncertainties in SPS exist, and yet their relevance to the task of comparing galaxy evolution models to observations has received little attention. In the present work, we begin to address this issue by investigating the importance of uncertainties in stellar evolution, the initial stellar mass function (IMF), and dust and interstellar medium (ISM) properties on the translation from models to observations. We demonstrate that these uncertainties translate into substantial uncertainties in the ultraviolet, optical, and near-infrared colors of synthetic galaxies. Aspects that carry significant uncertainties include the logarithmic slope of the IMF above 1 M sun , dust attenuation law, molecular cloud disruption timescale, clumpiness of the ISM, fraction of unobscured starlight, and treatment of advanced stages of stellar evolution including blue stragglers, the horizontal branch, and the thermally pulsating asymptotic giant branch. The interpretation of the resulting uncertainties in the derived colors is highly non-trivial because many of the uncertainties are likely systematic, and possibly correlated with the physical properties of galaxies. We therefore urge caution when comparing models to observations.

  5. Stellar parametrization from Gaia RVS spectra

    Science.gov (United States)

    Recio-Blanco, A.; de Laverny, P.; Allende Prieto, C.; Fustes, D.; Manteiga, M.; Arcay, B.; Bijaoui, A.; Dafonte, C.; Ordenovic, C.; Ordoñez Blanco, D.

    2016-01-01

    Context. Among the myriad of data collected by the ESA Gaia satellite, about 150 million spectra will be delivered by the Radial Velocity Spectrometer (RVS) for stars as faint as GRVS~ 16. A specific stellar parametrization will be performed on most of these RVS spectra, I.e. those with enough high signal-to-noise ratio (S/N), which should correspond to single stars that have a magnitude in the RVS band brighter than ~14.5. Some individual chemical abundances will also be estimated for the brightest targets. Aims: We describe the different parametrization codes that have been specifically developed or adapted for RVS spectra within the GSP-Spec working group of the analysis consortium. The tested codes are based on optimisation (FERRE and GAUGUIN), projection (MATISSE), or pattern-recognition methods (Artificial Neural Networks). We present and discuss each of their expected performances in the recovered stellar atmospheric parameters (effective temperature, surface gravity, overall metallicity) for B- to K-type stars. The performances for determining of [α/Fe] ratios are also presented for cool stars. Methods: Each code has been homogeneously tested with a large grid of RVS simulated synthetic spectra of BAFGK-spectral types (dwarfs and giants), with metallicities varying from 10-2.5 to 10+ 0.5 the solar metallicity, and taking variations of ±0.4 dex in the composition of the α-elements into consideration. The tests were performed for S/N ranging from ten to 350. Results: For all the stellar types we considered, stars brighter than GRVS~ 12.5 are very efficiently parametrized by the GSP-Spec pipeline, including reliable estimations of [α/Fe]. Typical internal errors for FGK metal-rich and metal-intermediate stars are around 40 K in Teff, 0.10 dex in log(g), 0.04 dex in [M/H], and 0.03 dex in [α/Fe] at GRVS = 10.3. They degrade to 155 K in Teff, 0.15 dex in log(g), 0.10 dex in [M/H], and 0.1 dex in [α/Fe] at GRVS~ 12. Similar accuracies in Teff and [M/H] are

  6. The Virtual Observatory Service TheoSSA: Establishing a Database of Synthetic Stellar Flux Standards I. NLTE Spectral Analysis of the DA-Type White Dwarf G191-B2B *,**,***,****

    Science.gov (United States)

    Rauch, T.; Werner, K.; Bohlin, R.; Kruk, J. W.

    2013-01-01

    Hydrogen-rich, DA-type white dwarfs are particularly suited as primary standard stars for flux calibration. State-of-the-art NLTE models consider opacities of species up to trans-iron elements and provide reliable synthetic stellar-atmosphere spectra to compare with observations. Aims. We will establish a database of theoretical spectra of stellar flux standards that are easily accessible via a web interface. Methods. In the framework of the Virtual Observatory, the German Astrophysical Virtual Observatory developed the registered service TheoSSA. It provides easy access to stellar spectral energy distributions (SEDs) and is intended to ingest SEDs calculated by any model-atmosphere code. In case of the DA white dwarf G191-B2B, we demonstrate that the model reproduces not only its overall continuum shape but also the numerous metal lines exhibited in its ultraviolet spectrum. Results. TheoSSA is in operation and contains presently a variety of SEDs for DA-type white dwarfs. It will be extended in the near future and can host SEDs of all primary and secondary flux standards. The spectral analysis of G191-B2B has shown that our hydrostatic models reproduce the observations best at Teff =60 000 +/- 2000K and log g=7.60 +/- 0.05.We newly identified Fe vi, Ni vi, and Zn iv lines. For the first time, we determined the photospheric zinc abundance with a logarithmic mass fraction of -4.89 (7.5 × solar). The abundances of He (upper limit), C, N, O, Al, Si, O, P, S, Fe, Ni, Ge, and Sn were precisely determined. Upper abundance limits of about 10% solar were derived for Ti, Cr, Mn, and Co. Conclusions. The TheoSSA database of theoretical SEDs of stellar flux standards guarantees that the flux calibration of all astronomical data and cross-calibration between different instruments can be based on the same models and SEDs calculated with different model-atmosphere codes and are easy to compare.

  7. Application of Laser Induced Breakdown Spectroscopy to the identification of emeralds from different synthetic processes

    International Nuclear Information System (INIS)

    Agrosì, G.; Tempesta, G.; Scandale, E.; Legnaioli, S.; Lorenzetti, G.; Pagnotta, S.; Palleschi, V.; Mangone, A.; Lezzerini, M.

    2014-01-01

    Laser Induced Breakdown Spectroscopy can provide a useful contribution in mineralogical field in which the quantitative chemical analyses (including the evaluation of light elements) can play a key role in the studies on the origin of the emeralds. In particular, the chemical analyses permit to determine those trace elements, known as fingerprints, that can be useful to study their provenance. This technique, not requiring sample preparation results particularly suitable for gemstones, that obviously must be studied in a non-destructive way. In this paper, the LIBS technique was applied to distinguish synthetic emeralds grown by Biron hydrothermal method from those grown by Chatham flux method. The analyses performed by collinear double-pulse LIBS give a signal enhancement useful for the quantitative chemical analyses while guaranteeing a minimal sample damage. In this way it was obtained a considerable improvement on the detection limit of the trace elements, whose determination is essential for determining the origin of emerald gemstone. The trace elements V, Cr, and Fe and their relative amounts allowed the correct attribution of the manufacturer. Two different methods for quantitative analyses were used for this study: the standard Calibration-Free LIBS (CF-LIBS) method and its recent evolution, the One Point Calibration LIBS (OPC-LIBS). This is the first approach to the evaluation of the emerald origin by means of the LIBS technique. - Highlights: • A LIBS method for discrimination between synthetic emeralds is presented. • Only one standard of known composition is needed for the analysis. • A set of two kind of synthetic emeralds has been analyzed. • The cromophoric elements Cr, V and Fe amounts have been used to determine the origin of emerald gemstone

  8. Application of Laser Induced Breakdown Spectroscopy to the identification of emeralds from different synthetic processes

    Energy Technology Data Exchange (ETDEWEB)

    Agrosì, G. [Department of Scienze della Terra e Geoambientali, University of Bari, Bari (Italy); Tempesta, G., E-mail: gioacchino.tempesta@uniba.it [Department of Scienze della Terra e Geoambientali, University of Bari, Bari (Italy); Scandale, E. [Department of Scienze della Terra e Geoambientali, University of Bari, Bari (Italy); Legnaioli, S.; Lorenzetti, G.; Pagnotta, S.; Palleschi, V. [Institute of Chemistry of Organometallic Compounds, CNR, Pisa (Italy); Mangone, A. [Department of Chemistry, University of Bari, Bari (Italy); Lezzerini, M. [Department of Earth Sciences, University of Pisa, Pisa (Italy)

    2014-12-01

    Laser Induced Breakdown Spectroscopy can provide a useful contribution in mineralogical field in which the quantitative chemical analyses (including the evaluation of light elements) can play a key role in the studies on the origin of the emeralds. In particular, the chemical analyses permit to determine those trace elements, known as fingerprints, that can be useful to study their provenance. This technique, not requiring sample preparation results particularly suitable for gemstones, that obviously must be studied in a non-destructive way. In this paper, the LIBS technique was applied to distinguish synthetic emeralds grown by Biron hydrothermal method from those grown by Chatham flux method. The analyses performed by collinear double-pulse LIBS give a signal enhancement useful for the quantitative chemical analyses while guaranteeing a minimal sample damage. In this way it was obtained a considerable improvement on the detection limit of the trace elements, whose determination is essential for determining the origin of emerald gemstone. The trace elements V, Cr, and Fe and their relative amounts allowed the correct attribution of the manufacturer. Two different methods for quantitative analyses were used for this study: the standard Calibration-Free LIBS (CF-LIBS) method and its recent evolution, the One Point Calibration LIBS (OPC-LIBS). This is the first approach to the evaluation of the emerald origin by means of the LIBS technique. - Highlights: • A LIBS method for discrimination between synthetic emeralds is presented. • Only one standard of known composition is needed for the analysis. • A set of two kind of synthetic emeralds has been analyzed. • The cromophoric elements Cr, V and Fe amounts have been used to determine the origin of emerald gemstone.

  9. Gemini/GNIRS infrared spectroscopy of the Wolf-Rayet stellar wind in Cygnus X-3

    Science.gov (United States)

    Koljonen, K. I. I.; Maccarone, T. J.

    2017-12-01

    The microquasar Cygnus X-3 was observed several times with the Gemini North Infrared Spectrograph while the source was in the hard X-ray state. We describe the observed 1.0-2.4 μm spectra as arising from the stellar wind of the companion star and suggest its classification as a WN 4-6 Wolf-Rayet star. We attribute the orbital variations of the emission line profiles to the variations in the ionization structure of the stellar wind caused by the intense X-ray emission from the compact object. The strong variability observed in the line profiles will affect the mass function determination. We are unable to reproduce earlier results, from which the mass function for the Wolf-Rayet star was derived. Instead, we suggest that the system parameters are difficult to obtain from the infrared spectra. We find that the near-infrared continuum and the line spectra can be represented with non-LTE Wolf-Rayet atmosphere models if taking into account the effects arising from the peculiar ionization structure of the stellar wind in an approximative manner. From the representative models we infer the properties of the Wolf-Rayet star and discuss possible mass ranges for the binary components.

  10. Metal-rich, Metal-poor: Updated Stellar Population Models for Old Stellar Systems

    Science.gov (United States)

    Conroy, Charlie; Villaume, Alexa; van Dokkum, Pieter G.; Lind, Karin

    2018-02-01

    We present updated stellar population models appropriate for old ages (>1 Gyr) and covering a wide range in metallicities (‑1.5 ≲ [Fe/H] ≲ 0.3). These models predict the full spectral variation associated with individual element abundance variation as a function of metallicity and age. The models span the optical–NIR wavelength range (0.37–2.4 μm), include a range of initial mass functions, and contain the flexibility to vary 18 individual elements including C, N, O, Mg, Si, Ca, Ti, and Fe. To test the fidelity of the models, we fit them to integrated light optical spectra of 41 Galactic globular clusters (GCs). The value of testing models against GCs is that their ages, metallicities, and detailed abundance patterns have been derived from the Hertzsprung–Russell diagram in combination with high-resolution spectroscopy of individual stars. We determine stellar population parameters from fits to all wavelengths simultaneously (“full spectrum fitting”), and demonstrate explicitly with mock tests that this approach produces smaller uncertainties at fixed signal-to-noise ratio than fitting a standard set of 14 line indices. Comparison of our integrated-light results to literature values reveals good agreement in metallicity, [Fe/H]. When restricting to GCs without prominent blue horizontal branch populations, we also find good agreement with literature values for ages, [Mg/Fe], [Si/Fe], and [Ti/Fe].

  11. Multiple Stellar Populations in Star Clusters

    Science.gov (United States)

    Piotto, G.

    2013-09-01

    For half a century it had been astronomical dogma that a globular cluster (GC) consists of stars born at the same time out of the same material, and this doctrine has borne rich fruits. In recent years, high resolution spectroscopy and high precision photometry (from space and ground-based observations) have shattered this paradigm, and the study of GC populations has acquired a new life that is now moving it in new directions. Evidence of multiple stellar populations have been identified in the color-magnitude diagrams of several Galactic and Magellanic Cloud GCs where they had never been imagined before.

  12. Morphologies and stellar populations of galaxies in the core of Abell 2218

    NARCIS (Netherlands)

    Sánchez, S. F.; Cardiel, N.; Verheijen, M. A. W.; Pedraz, S.; Covone, G.

    2007-01-01

    We present a study of the stellar populations and morphologies of galaxies in the core of the galaxy cluster Abell 2218. Integral field spectroscopy (IFS) observations were performed using PMAS in the PPAK mode covering a field of view of similar to 74 x 64 arcsec(2) centred on the core of the

  13. Green-synthetized silver nanoparticles for Nanoparticle-Enhanced Laser Induced Breakdown Spectroscopy (NELIBS) using a mobile instrument

    Science.gov (United States)

    Poggialini, F.; Campanella, B.; Giannarelli, S.; Grifoni, E.; Legnaioli, S.; Lorenzetti, G.; Pagnotta, S.; Safi, A.; Palleschi, V.

    2018-03-01

    When compared to other analytical techniques, LIBS shows relatively low precision and, generally, high Limits of Detection (LODs). Until recently, the attempts in improving the LIBS performances have been based on the use of more stable/powerful lasers, high sensitivity detectors or controlled environmental parameters. This can hinder the competitiveness of LIBS by increasing the instrumental setup cost and the difficulty of operation. Sample treatment has proved to be a viable and simple way to increase the LIBS signal; in particular, the Nanoparticle-Enhanced Laser Induced Breakdown Spectroscopy (NELIBS) methodology uses a deposition of metal nanoparticles on the sample to greatly increase the emission of the LIBS plasma. In this work, we used a simple, fast, "green" and low-cost method to synthetize silver nanoparticles by using coffee extract as reducing agents for a silver nitrate solution. This allowed us to obtain nanoparticles of about 25 nm in diameter. We then explored the application of such nanoparticles to the NELIBS analysis of metallic samples with a mobile LIBS instrument. By adjusting the laser parameters and optimizing the sample preparation procedure, we obtained a NELIBS signal that is 4 times the LIBS one. This showed the potential of green-synthetized nanoparticle for NELIBS applications and suggests the possibility of an in-situ application of the technique.

  14. Stellarator-Spheromak

    International Nuclear Information System (INIS)

    Moroz, P.E.

    1997-03-01

    A novel concept for magnetic plasma confinement, Stellarator-Spheromak (SSP), is proposed. Numerical analysis with the classical-stellarator-type outboard stellarator windings demonstrates a number of potential advantages of SSP for controlled nuclear fusion. Among the main ones are: simple and compact magnet coil configuration, absence of material structures (e.g. magnet coils or conducting walls) in the center of the torus, high rotational transform, and a possibility of MHD equilibria with very high β (pressure/magnetic pressure) of the confined plasma

  15. Growth and optical spectroscopy of synthetic diamonds

    International Nuclear Information System (INIS)

    Mudryj, A.V.; Larionova, T.P.; Shakin, I.A.; Gysakov, G.A.; Dubrov, G.A.; Tikhonov, V.V.

    2003-01-01

    It is studied the growth and optical properties of synthetic diamonds, which may be used for detection of ionizing radiation, optical windows, heat removal, ultraviolet and thermo sensors, optoelectronic devices. Optical properties of diamonds (grown in different technological conditions) were studied in temperature range 78 - 300 K by means of measuring transmission in spectral band 0.2 - 25 μm, photoluminescence and registration of luminescence excitation spectra in spectral band 0.2 - 2 μm

  16. PREFACE: A Stellar Journey A Stellar Journey

    Science.gov (United States)

    Asplund, M.

    2008-10-01

    astronomical talk, student lecture, musical concert or theatre play. Another attribute of Bengt is his boundless optimism, which not the least has helped many of his students overcome the unavoidable moments of despair (this is only true as long as one is aware of the well-known BG factor: multiply any of Bengt's estimates for the time required to complete a task by at least a factor of three). His personal traits make working with Bengt always very enjoyable as well as highly educating. Bengt's work also extends well beyond the domain of astronomy, including music, literature, theatre, religion, research ethics, science policy and science popularization. Bengt is an excellent role model for a successful scientist with a rich and rewarding life outside of academia. The symposium A Stellar Journey was divided into five sessions covering basically the main research areas Bengt has worked on: Stellar atmospheres, Solar/stellar spectroscopy, Stellar parameters, Stellar evolution and nucleosynthesis and Stellar populations. In addition, one afternoon was devoted to a session entitled Anything but astronomy (see the symposium program), which tried to showcase Bengt's diverse interests outside of astronomy with talks ranging from religion and history of science over science popularization and future studies to literature and music. My task, as chair of the Scientific Organizing Committee, to put together an exciting scientific program of invited reviews and talks was made considerably easier thanks to the excellent suggestions by the other SOC members: Ann Boesgaard, Sofia Feltzing, John Lattanzio, Andre Maeder, Bertrand Plez and Monique Spite. I believe in the end we were successful in achieving our charge, an impression corroborated by the many encouraging comments from various participants during and after the conference. I am particularly grateful to Nils Bergvall, Bengt Edvardsson and Bertrand Plez for their time-consuming efforts in arranging the extraordinary and greatly

  17. MASSCLEANage-STELLAR CLUSTER AGES FROM INTEGRATED COLORS

    International Nuclear Information System (INIS)

    Popescu, Bogdan; Hanson, M. M.

    2010-01-01

    We present the recently updated and expanded MASSCLEANcolors, a database of 70 million Monte Carlo models selected to match the properties (metallicity, ages, and masses) of stellar clusters found in the Large Magellanic Cloud (LMC). This database shows the rather extreme and non-Gaussian distribution of integrated colors and magnitudes expected with different cluster age and mass and the enormous age degeneracy of integrated colors when mass is unknown. This degeneracy could lead to catastrophic failures in estimating age with standard simple stellar population models, particularly if most of the clusters are of intermediate or low mass, like in the LMC. Utilizing the MASSCLEANcolors database, we have developed MASSCLEANage, a statistical inference package which assigns the most likely age and mass (solved simultaneously) to a cluster based only on its integrated broadband photometric properties. Finally, we use MASSCLEANage to derive the age and mass of LMC clusters based on integrated photometry alone. First, we compare our cluster ages against those obtained for the same seven clusters using more accurate integrated spectroscopy. We find improved agreement with the integrated spectroscopy ages over the original photometric ages. A close examination of our results demonstrates the necessity of solving simultaneously for mass and age to reduce degeneracies in the cluster ages derived via integrated colors. We then selected an additional subset of 30 photometric clusters with previously well-constrained ages and independently derive their age using the MASSCLEANage with the same photometry with very good agreement. The MASSCLEANage program is freely available under GNU General Public License.

  18. IR spectroscopy of synthetic glasses with Mercury surface composition: Analogs for remote sensing

    Science.gov (United States)

    Morlok, Andreas; Klemme, Stephan; Weber, Iris; Stojic, Aleksandra; Sohn, Martin; Hiesinger, Harald

    2017-11-01

    In a study to provide ground-truth data for mid-infrared observations of the surface of Mercury with the MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument onboard the ESA/JAXA BepiColombo mission, we have studied 17 synthetic glasses. These samples have the chemical compositions of characteristic Hermean surface areas based on MESSENGER data. The samples have been characterized using optical microscopy, EMPA and Raman spectroscopy. Mid-infrared spectra have been obtained from polished thin sections using Micro-FTIR, and of powdered size fractions of bulk material (0-25, 25-63, 93-125 and 125-250 μm) in the 2.5-18 μm range. The synthetic glasses display mostly spectra typical for amorphous materials with a dominating, single Reststrahlen Band (RB) at 9.5-10.7 μm. RB Features of crystalline forsterite are found in some cases at 9.5-10.2 μm, 10.4-11.2 μm, and at 11.9 μm. Dendritic crystallization starts at a MgO content higher than 23 wt.% MgO. The Reststrahlen Bands, Christiansen Features (CF), and Transparency Features (TF) shift depending on the SiO2 and MgO contents. Also a shift of the Christiansen Feature of the glasses compared with the SCFM (SiO2/(SiO2+CaO+FeO+MgO)) index is observed. This shift could potentially help distinguish crystalline and amorphous material in remote sensing data. A comparison between the degree of polymerization of the glass and the width of the characteristic strong silicate feature shows a weak positive correlation. A comparison with a high-quality mid-IR spectrum of Mercury shows some moderate similarity to the results of this study, but does not explain all features.

  19. STELLAR ATMOSPHERES, ATMOSPHERIC EXTENSION, AND FUNDAMENTAL PARAMETERS: WEIGHING STARS USING THE STELLAR MASS INDEX

    Energy Technology Data Exchange (ETDEWEB)

    Neilson, Hilding R.; Lester, John B. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, M5S 3H4 (Canada); Baron, Fabien; Norris, Ryan; Kloppenborg, Brian, E-mail: neilson@astro.utoronto.ca [Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, Georgia State University, P.O. Box 5060, Atlanta, GA 30302-5060 (United States)

    2016-10-20

    One of the great challenges of understanding stars is measuring their masses. The best methods for measuring stellar masses include binary interaction, asteroseismology, and stellar evolution models, but these methods are not ideal for red giant and supergiant stars. In this work, we propose a novel method for inferring stellar masses of evolved red giant and supergiant stars using interferometric and spectrophotometric observations combined with spherical model stellar atmospheres to measure what we call the stellar mass index, defined as the ratio between the stellar radius and mass. The method is based on the correlation between different measurements of angular diameter, used as a proxy for atmospheric extension, and fundamental stellar parameters. For a given star, spectrophotometry measures the Rosseland angular diameter while interferometric observations generally probe a larger limb-darkened angular diameter. The ratio of these two angular diameters is proportional to the relative extension of the stellar atmosphere, which is strongly correlated to the star’s effective temperature, radius, and mass. We show that these correlations are strong and can lead to precise measurements of stellar masses.

  20. The fundamentals of stellar astrophysics

    International Nuclear Information System (INIS)

    Collins, G.W. II.

    1989-01-01

    A broad overview of theoretical stellar astrophysics is presented in a textbook intended for graduate students. Chapters are devoted to fundamental principles, assumptions, theorems, and polytropes; energy sources and sinks; the flow of energy through the star and the construction of stellar models; the theory of stellar evolution; relativistic stellar structure; the structure of distorted stars; stellar pulsation and oscillation. Also discussed are the flow of radiation through the stellar atmosphere, the solution of the radiative-transfer equation, the environment of the radiation field, the construction of a stellar model atmosphere, the formation and shape of spectral lines, LTE breakdown, illuminated and extended stellar atmospheres, and the transfer of polarized radiation. Diagrams, graphs, and sample problems are provided. 164 refs

  1. Uncertainties and Systematic Effects on the estimate of stellar masses in high z galaxies

    Science.gov (United States)

    Salimbeni, S.; Fontana, A.; Giallongo, E.; Grazian, A.; Menci, N.; Pentericci, L.; Santini, P.

    2009-05-01

    We discuss the uncertainties and the systematic effects that exist in the estimates of the stellar masses of high redshift galaxies, using broad band photometry, and how they affect the deduced galaxy stellar mass function. We use at this purpose the latest version of the GOODS-MUSIC catalog. In particular, we discuss the impact of different synthetic models, of the assumed initial mass function and of the selection band. Using Chariot & Bruzual 2007 and Maraston 2005 models we find masses lower than those obtained from Bruzual & Chariot 2003 models. In addition, we find a slight trend as a function of the mass itself comparing these two mass determinations with that from Bruzual & Chariot 2003 models. As consequence, the derived galaxy stellar mass functions show diverse shapes, and their slope depends on the assumed models. Despite these differences, the overall results and scenario is observed in all these cases. The masses obtained with the assumption of the Chabrier initial mass function are in average 0.24 dex lower than those from the Salpeter assumption, at all redshifts, causing a shift of galaxy stellar mass function of the same amount. Finally, using a 4.5 μm-selected sample instead of a Ks-selected one, we add a new population of highly absorbed, dusty galaxies at z~=2-3 of relatively low masses, yielding stronger constraints on the slope of the galaxy stellar mass function at lower masses.

  2. Limb Darkening and Planetary Transits: Testing Center-to-limb Intensity Variations and Limb-darkening Directly from Model Stellar Atmospheres

    Energy Technology Data Exchange (ETDEWEB)

    Neilson, Hilding R.; Lester, John B. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); McNeil, Joseph T.; Ignace, Richard, E-mail: neilson@astro.utoronto.ca [Department of Physics and Astronomy, East Tennessee State University, Box 70652, Johnson City, TN 37614 (United States)

    2017-08-10

    The transit method, employed by Microvariability and Oscillation of Stars ( MOST ), Kepler , and various ground-based surveys has enabled the characterization of extrasolar planets to unprecedented precision. These results are precise enough to begin to measure planet atmosphere composition, planetary oblateness, starspots, and other phenomena at the level of a few hundred parts per million. However, these results depend on our understanding of stellar limb darkening, that is, the intensity distribution across the stellar disk that is sequentially blocked as the planet transits. Typically, stellar limb darkening is assumed to be a simple parameterization with two coefficients that are derived from stellar atmosphere models or fit directly. In this work, we revisit this assumption and compute synthetic planetary-transit light curves directly from model stellar atmosphere center-to-limb intensity variations (CLIVs) using the plane-parallel Atlas and spherically symmetric SAtlas codes. We compare these light curves to those constructed using best-fit limb-darkening parameterizations. We find that adopting parametric stellar limb-darkening laws leads to systematic differences from the more geometrically realistic model stellar atmosphere CLIV of about 50–100 ppm at the transit center and up to 300 ppm at ingress/egress. While these errors are small, they are systematic, and they appear to limit the precision necessary to measure secondary effects. Our results may also have a significant impact on transit spectra.

  3. Massive star populations in I Zw 18: A probe of stellar evolution in the early universe

    OpenAIRE

    Schaerer, Daniel; de Mello, Duilia; Leitherer, Claus; Heldmann, Jennifer

    1998-01-01

    We present a study of the gaseous and stellar emission in I Zw18, the most metal-poor star-forming galaxy known. Archival HST WFPC2 and FOS data have been used to analyze the spatial distribution of [OIII], Halpha, and HeII 4686. The latter is used to identify Wolf-Rayet stars found by ground-based spectroscopy and to locate nebular HeII emission. Most of the HeII emission is associated with the NW stellar cluster, displaced from the surrounding shell-like [OIII] and Halpha emission. We found...

  4. Fluorine Abundances of AGB Stars in Stellar Clusters

    Science.gov (United States)

    Hren, A.; Lebzelter, T.; Aringer, B.; Hinkle, K. H.; Nowotny, W.

    2015-08-01

    We have measured the abundance of fluorine, [F/Fe], in a number of AGB stars in stellar clusters have correlated the results with their C/O ratios. This allows us to investigate the change in the fluorine abundance along the evolution on the giant branch. The target list includes primarily O-rich stars in three LMC globular clusters - NGC 1806, NGC 1846 and NGC 1978 - as well as Rup 106 and 47 Tuc in our Galaxy. The observational data were obtained with the PHOENIX spectrograph, and the COMA code was used for modelling the synthetic spectra. Within individual clusters, we find consistent [F/Fe] values at similar C/O for most of our target stars.

  5. Resolving stellar populations with crowded field 3D spectroscopy

    Science.gov (United States)

    Kamann, S.; Wisotzki, L.; Roth, M. M.

    2013-01-01

    We describe a new method of extracting the spectra of stars from observations of crowded stellar fields with integral field spectroscopy (IFS). Our approach extends the well-established concept of crowded field photometry in images into the domain of 3-dimensional spectroscopic datacubes. The main features of our algorithm follow. (1) We assume that a high-fidelity input source catalogue already exists, e.g. from HST data, and that it is not needed to perform sophisticated source detection in the IFS data. (2) Source positions and properties of the point spread function (PSF) vary smoothly between spectral layers of the datacube, and these variations can be described by simple fitting functions. (3) The shape of the PSF can be adequately described by an analytical function. Even without isolated PSF calibrator stars we can therefore estimate the PSF by a model fit to the full ensemble of stars visible within the field of view. (4) By using sparse matrices to describe the sources, the problem of extracting the spectra of many stars simultaneously becomes computationally tractable. We present extensive performance and validation tests of our algorithm using realistic simulated datacubes that closely reproduce actual IFS observations of the central regions of Galactic globular clusters. We investigate the quality of the extracted spectra under the effects of crowding with respect to the resulting signal-to-noise ratios (S/N) and any possible changes in the continuum level, as well as with respect to absorption line spectral parameters, radial velocities, and equivalent widths. The main effect of blending between two nearby stars is a decrease in the S/N in their spectra. The effect increases with the crowding in the field in a way that the maximum number of stars with useful spectra is always ~0.2 per spatial resolution element. This balance breaks down when exceeding a total source density of one significantly detected star per resolution element. We also explore the

  6. Stellar and wind parameters of massive stars from spectral analysis

    Science.gov (United States)

    Araya, Ignacio; Curé, Michel

    2017-11-01

    The only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line-force parameters α, k and δ (from the line-driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line-force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line-force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind-Momentum Luminosity Relationship (WLR).

  7. Compact stellarators as reactors

    International Nuclear Information System (INIS)

    Lyon, J.F.; Valanju, P.; Zarnstorff, M.C.; Hirshman, S.; Spong, D.A.; Strickler, D.; Williamson, D.E.; Ware, A.

    2001-01-01

    Two types of compact stellarators are examined as reactors: two- and three-field-period (M=2 and 3) quasi-axisymmetric devices with volume-average =4-5% and M=2 and 3 quasi-poloidal devices with =10-15%. These low-aspect-ratio stellarator-tokamak hybrids differ from conventional stellarators in their use of the plasma-generated bootstrap current to supplement the poloidal field from external coils. Using the ARIES-AT model with B max =12T on the coils gives Compact Stellarator reactors with R=7.3-8.2m, a factor of 2-3 smaller R than other stellarator reactors for the same assumptions, and neutron wall loadings up to 3.7MWm -2 . (author)

  8. FRIENDS OF HOT JUPITERS. III. AN INFRARED SPECTROSCOPIC SEARCH FOR LOW-MASS STELLAR COMPANIONS

    Energy Technology Data Exchange (ETDEWEB)

    Piskorz, Danielle; Knutson, Heather A.; Ngo, Henry; Batygin, Konstantin [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA (United States); Muirhead, Philip S. [Institute for Astrophysical Research, Boston University, Boston, MA (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, South Bend, IN (United States); Hinkley, Sasha [Department of Physics and Astronomy, University of Exeter, Exeter (United Kingdom); Morton, Timothy D., E-mail: dpiskorz@gps.caltech.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States)

    2015-12-01

    Surveys of nearby field stars indicate that stellar binaries are common, yet little is known about the effects that these companions may have on planet formation and evolution. The Friends of Hot Jupiters project uses three complementary techniques to search for stellar companions to known planet-hosting stars: radial velocity monitoring, adaptive optics imaging, and near-infrared spectroscopy. In this paper, we examine high-resolution K band infrared spectra of fifty stars hosting gas giant planets on short-period orbits. We use spectral fitting to search for blended lines due to the presence of cool stellar companions in the spectra of our target stars, where we are sensitive to companions with temperatures between 3500 and 5000 K and projected separations less than 100 AU in most systems. We identify eight systems with candidate low-mass companions, including one companion that was independently detected in our AO imaging survey. For systems with radial velocity accelerations, a spectroscopic non-detection rules out scenarios involving a stellar companion in a high inclination orbit. We use these data to place an upper limit on the stellar binary fraction at small projected separations, and show that the observed population of candidate companions is consistent with that of field stars and also with the population of wide-separation companions detected in our previous AO survey. We find no evidence that spectroscopic stellar companions are preferentially located in systems with short-period gas giant planets on eccentric and/or misaligned orbits.

  9. FRIENDS OF HOT JUPITERS. III. AN INFRARED SPECTROSCOPIC SEARCH FOR LOW-MASS STELLAR COMPANIONS

    International Nuclear Information System (INIS)

    Piskorz, Danielle; Knutson, Heather A.; Ngo, Henry; Batygin, Konstantin; Muirhead, Philip S.; Crepp, Justin R.; Hinkley, Sasha; Morton, Timothy D.

    2015-01-01

    Surveys of nearby field stars indicate that stellar binaries are common, yet little is known about the effects that these companions may have on planet formation and evolution. The Friends of Hot Jupiters project uses three complementary techniques to search for stellar companions to known planet-hosting stars: radial velocity monitoring, adaptive optics imaging, and near-infrared spectroscopy. In this paper, we examine high-resolution K band infrared spectra of fifty stars hosting gas giant planets on short-period orbits. We use spectral fitting to search for blended lines due to the presence of cool stellar companions in the spectra of our target stars, where we are sensitive to companions with temperatures between 3500 and 5000 K and projected separations less than 100 AU in most systems. We identify eight systems with candidate low-mass companions, including one companion that was independently detected in our AO imaging survey. For systems with radial velocity accelerations, a spectroscopic non-detection rules out scenarios involving a stellar companion in a high inclination orbit. We use these data to place an upper limit on the stellar binary fraction at small projected separations, and show that the observed population of candidate companions is consistent with that of field stars and also with the population of wide-separation companions detected in our previous AO survey. We find no evidence that spectroscopic stellar companions are preferentially located in systems with short-period gas giant planets on eccentric and/or misaligned orbits

  10. 21 CFR 175.250 - Paraffin (synthetic).

    Science.gov (United States)

    2010-04-01

    ... hydrocarbons. Lower molecular-weight fractions are removed by distillation. The residue is hydrogenated and may... its components by a solvent separation method, using synthetic isoparaffinic petroleum hydrocarbons... method E131-81a, “Standard Definitions of Terms and Symbols Relating to Molecular-Spectroscopy,” which is...

  11. Stellar magnetic activity

    International Nuclear Information System (INIS)

    Schrijver, C.J.

    1986-01-01

    The stellar emission in the chromospheric Ca II H+K lines is compared with the coronal soft X-ray emission, measuring the effects of non-radiative heating in the outer atmosphere at temperatures differing two orders of magnitude. The comparison of stellar flux densities in Ca II H+K and X-rays is extended to fluxes from the transition-region and the high-temperature chromosphere. The stellar magnetic field is probably generated in the differentially rotating convective envelope. The relation between rotation rate and the stellar level of activity measured in chromospheric, transition-region, and coronal radiative diagnostics is discovered. X-ray observations of the binary λ Andromedae are discussed. The departure of M-type dwarfs from the main relations, and the implications for the structure of the chromospheres of these stars are discussed. Variations of the average surface flux densities of the Sun during the 11-year activity cycle agree with flux-flux relations derived for other cool stars, suggesting that the interpretation of the stellar relations may be furthered by studying the solar analogue in more detail. (Auth.)

  12. Thermal Infrared Emission Spectroscopy of Synthetic Allophane and its Potential Formation on Mars

    Science.gov (United States)

    Rampe, E. B.; Kraft, M. D.; Sharp, T. G.; Golden, D. C.; Ming, Douglas W.

    2010-01-01

    Allophane is a poorly-crystalline, hydrous aluminosilicate with variable Si/Al ratios approx.0.5-1 and a metastable precursor of clay minerals. On Earth, it forms rapidly by aqueous alteration of volcanic glass under neutral to slightly acidic conditions [1]. Based on in situ chemical measurements and the identification of alteration phases [2-4], the Martian surface is interpreted to have been chemically weathered on local to regional scales. Chemical models of altered surfaces detected by the Mars Exploration Rover Spirit in Gusev crater suggest the presence of an allophane-like alteration product [3]. Thermal infrared (TIR) spectroscopy and spectral deconvolution models are primary tools for determining the mineralogy of the Martian surface [5]. Spectral models of data from the Thermal Emission Spectrometer (TES) indicate a global compositional dichotomy, where high latitudes tend to be enriched in a high-silica material [6,7], interpreted as high-silica, K-rich volcanic glass [6,8]. However, later interpretations proposed that the high-silica material may be an alteration product (such as amorphous silica, clay minerals, or allophane) and that high latitude surfaces are chemically weathered [9-11]. A TIR spectral library of pure minerals is available for the public [12], but it does not contain allophane spectra. The identification of allophane on the Martian surface would indicate high water activity at the time of its formation and would help constrain the aqueous alteration environment [13,14]. The addition of allophane to the spectral library is necessary to address the global compositional dichotomy. In this study, we characterize a synthetic allophane by IR spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM) to create an IR emission spectrum of pure allophane for the Mars science community to use in Martian spectral models.

  13. sunstardb: A Database for the Study of Stellar Magnetism and the Solar-stellar Connection

    Science.gov (United States)

    Egeland, Ricky

    2018-05-01

    The “solar-stellar connection” began as a relatively small field of research focused on understanding the processes that generate magnetic fields in stars and sometimes lead to a cyclic pattern of long-term variability in activity, as demonstrated by our Sun. This area of study has recently become more broadly pertinent to questions of exoplanet habitability and exo-space weather, as well as stellar evolution. In contrast to other areas of stellar research, individual stars in the solar-stellar connection often have a distinct identity and character in the literature, due primarily to the rarity of the decades-long time-series that are necessary for studying stellar activity cycles. Furthermore, the underlying stellar dynamo is not well understood theoretically, and is thought to be sensitive to several stellar properties, e.g., luminosity, differential rotation, and the depth of the convection zone, which in turn are often parameterized by other more readily available properties. Relevant observations are scattered throughout the literature and existing stellar databases, and consolidating information for new studies is a tedious and laborious exercise. To accelerate research in this area I developed sunstardb, a relational database of stellar properties and magnetic activity proxy time-series keyed by individual named stars. The organization of the data eliminates the need for the problematic catalog cross-matching operations inherent when building an analysis data set from heterogeneous sources. In this article I describe the principles behind sunstardb, the data structures and programming interfaces, as well as use cases from solar-stellar connection research.

  14. Atmospheric stellar parameters for large surveys using FASMA, a new spectral synthesis package

    Science.gov (United States)

    Tsantaki, M.; Andreasen, D. T.; Teixeira, G. D. C.; Sousa, S. G.; Santos, N. C.; Delgado-Mena, E.; Bruzual, G.

    2018-02-01

    In the era of vast spectroscopic surveys focusing on Galactic stellar populations, astronomers want to exploit the large quantity and good quality of data to derive their atmospheric parameters without losing precision from automatic procedures. In this work, we developed a new spectral package, FASMA, to estimate the stellar atmospheric parameters (namely effective temperature, surface gravity and metallicity) in a fast and robust way. This method is suitable for spectra of FGK-type stars in medium and high resolution. The spectroscopic analysis is based on the spectral synthesis technique using the radiative transfer code, MOOG. The line list is comprised of mainly iron lines in the optical spectrum. The atomic data are calibrated after the Sun and Arcturus. We use two comparison samples to test our method, (i) a sample of 451 FGK-type dwarfs from the high-resolution HARPS spectrograph; and (ii) the Gaia-ESO benchmark stars using both high and medium resolution spectra. We explore biases in our method from the analysis of synthetic spectra covering the parameter space of our interest. We show that our spectral package is able to provide reliable results for a wide range of stellar parameters, different rotational velocities, different instrumental resolutions and for different spectral regions of the VLT-GIRAFFE spectrographs, used amongst others for the Gaia-ESO survey. FASMA estimates stellar parameters in less than 15 m for high-resolution and 3 m for medium-resolution spectra. The complete package is publicly available to the community.

  15. Orbital Evolution and Orbital Phase Resolved Spectroscopy of the ...

    Indian Academy of Sciences (India)

    binary. We have carried out orbital phase resolved spectroscopy to mea- ... agreement with a simple model of a spherically symmetric stellar wind from the .... has a set of Narrow Field Instruments (NFI) comprising one Low Energy Concen-.

  16. Star Classification for the Kepler Input Catalog: From Images to Stellar Parameters

    Science.gov (United States)

    Brown, T. M.; Everett, M.; Latham, D. W.; Monet, D. G.

    2005-12-01

    The Stellar Classification Project is a ground-based effort to screen stars within the Kepler field of view, to allow removal of stars with large radii (and small potential transit signals) from the target list. Important components of this process are: (1) An automated photometry pipeline estimates observed magnitudes both for target stars and for stars in several calibration fields. (2) Data from calibration fields yield extinction-corrected AB magnitudes (with g, r, i, z magnitudes transformed to the SDSS system). We merge these with 2MASS J, H, K magnitudes. (3) The Basel grid of stellar atmosphere models yields synthetic colors, which are transformed to our photometric system by calibration against observations of stars in M67. (4) We combine the r magnitude and stellar galactic latitude with a simple model of interstellar extinction to derive a relation connecting {Teff, luminosity} to distance and reddening. For models satisfying this relation, we compute a chi-squared statistic describing the match between each model and the observed colors. (5) We create a merit function based on the chi-squared statistic, and on a Bayesian prior probability distribution which gives probability as a function of Teff, luminosity, log(Z), and height above the galactic plane. The stellar parameters ascribed to a star are those of the model that maximizes this merit function. (6) Parameter estimates are merged with positional and other information from extant catalogs to yield the Kepler Input Catalog, from which targets will be chosen. Testing and validation of this procedure are underway, with encouraging initial results.

  17. Neutron flux measurements at the Wendelstein VII-A stellarator

    International Nuclear Information System (INIS)

    Weller, A.; Maassberg, H.

    1985-10-01

    In addition to charge exchange analysis (CX) and charge exchange recombination spectroscopy (CXRS), the time evolution of the central ion temperature during neutral beam heated plasma discharges in the Wendelstein VII-A stellarator is derived from the neutron flux from thermal D-D reactions. In general, good quantitative agreement between the different methods is obtained. Neutron flux measurements also permit to investigate the slowing down of fast D + -ions from neutral beam injection (NBI). The results agree well with the predictions based on the assumption of a collisional slowing down mechanism. (orig.)

  18. Neoclassical transport in stellarators - a comparison of conventional stellarator/torsatrons with the advanced stellarator, Wendelstein 7X

    Energy Technology Data Exchange (ETDEWEB)

    Beidler, C D [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany)

    1991-01-01

    A general expression for the magnitude of a stellarator's magnetic field, in terms of a Fourier decomposition, is too complicated to lend itself easily to analytic transport calculations. The great majority of stellarator-type devices, however, may be accurately described if one retains only those harmonics with m=0 and m=1. In the long-mean-free-path regime an analytical approximation to the particle's bounce-averaged kinetic equation can then be found. Using a numerical solution of this equation, it is possible to calculate the particle and heat fluxes due to helical-ripple transport in stellarators throughout the entire long-mean-free-path regime. 3 figs.

  19. Do stellar and nebular abundances in the Cocoon nebula agree?

    Science.gov (United States)

    García-Rojas, J.; Simón-Díaz, S.; Esteban, C.

    2015-05-01

    The Cocoon nebula is an apparently spherical Galactic HII region ionized by a single star (BD+46 3474). This nebula seems to be appropriate to investigate the chemical behavior of oxygen and other heavy elements from two different points of view: a detailed analysis of the chemical content of the ionized gas through nebular spectrophotometry and a detailed spectroscopic analysis of the spectrum of the ionizing star using the state-of-the-art stellar atmosphere modelling. In this poster we present the results from a set of high-quality observations, from 2m-4m class telescopes, including the optical spectrum of the ionizing star BD+46 3474, along with long-slit spatially resolved spectroscopy of the nebula. We have used state-of-the-art stellar atmosphere codes to determine stellar parameters and the chemical content of several heavy elements. Traditional nebular techniques along with updated atomic data have been used to compute gaseous abundances of O, N and S in the Cocoon nebula. Thanks to the low ionization degree of the nebula, we could determine total abundances directly from observable ions (no ionization correction factors were needed) for three of the analyzed elements (O, S, and N). The derived stellar and nebular abundances are compared and the influence of the possible presence of the so-called temperature fluctuations on the nebula is discussed. The results of this study are presented in more detail in García-Rojas, Simón-Díaz & Esteban 2014, A&A, 571, A93.

  20. The Belgian repository of fundamental atomic data and stellar spectra (BRASS). I. Cross-matching atomic databases of astrophysical interest

    Science.gov (United States)

    Laverick, M.; Lobel, A.; Merle, T.; Royer, P.; Martayan, C.; David, M.; Hensberge, H.; Thienpont, E.

    2018-04-01

    Context. Fundamental atomic parameters, such as oscillator strengths, play a key role in modelling and understanding the chemical composition of stars in the Universe. Despite the significant work underway to produce these parameters for many astrophysically important ions, uncertainties in these parameters remain large and can propagate throughout the entire field of astronomy. Aims: The Belgian repository of fundamental atomic data and stellar spectra (BRASS) aims to provide the largest systematic and homogeneous quality assessment of atomic data to date in terms of wavelength, atomic and stellar parameter coverage. To prepare for it, we first compiled multiple literature occurrences of many individual atomic transitions, from several atomic databases of astrophysical interest, and assessed their agreement. In a second step synthetic spectra will be compared against extremely high-quality observed spectra, for a large number of BAFGK spectral type stars, in order to critically evaluate the atomic data of a large number of important stellar lines. Methods: Several atomic repositories were searched and their data retrieved and formatted in a consistent manner. Data entries from all repositories were cross-matched against our initial BRASS atomic line list to find multiple occurrences of the same transition. Where possible we used a new non-parametric cross-match depending only on electronic configurations and total angular momentum values. We also checked for duplicate entries of the same physical transition, within each retrieved repository, using the non-parametric cross-match. Results: We report on the number of cross-matched transitions for each repository and compare their fundamental atomic parameters. We find differences in log(gf) values of up to 2 dex or more. We also find and report that 2% of our line list and Vienna atomic line database retrievals are composed of duplicate transitions. Finally we provide a number of examples of atomic spectral lines

  1. THE DiskMass SURVEY. III. STELLAR KINEMATICS VIA CROSS-CORRELATION

    International Nuclear Information System (INIS)

    Westfall, Kyle B.; Bershady, Matthew A.; Verheijen, Marc A. W.

    2011-01-01

    We describe a new cross-correlation (CC) approach used by our survey to derive stellar kinematics from galaxy-continuum spectroscopy. This approach adopts the formal error analysis derived by Statler, but properly handles spectral masks. Thus, we address the primary concerns regarding application of the CC method to censored data, while maintaining its primary advantage by consolidating kinematic and template-mismatch information toward different regions of the CC function. We identify a systematic error in the nominal CC method of approximately 10% in velocity dispersion incurred by a mistreatment of detector-censored data, which is eliminated by our new method. We derive our approach from first principles, and we use Monte Carlo simulations to demonstrate its efficacy. An identical set of Monte Carlo simulations performed using the well-established penalized-pixel-fitting code of Cappellari and Emsellem compares favorably with the results from our newly implemented software. Finally, we provide a practical demonstration of this software by extracting stellar kinematics from SparsePak spectra of UGC 6918.

  2. Surface modification of polyester synthetic leather with tetramethylsilane by atmospheric pressure plasma

    Science.gov (United States)

    Kan, C. W.; Kwong, C. H.; Ng, S. P.

    2015-08-01

    Much works have been done on synthetic materials but scarcely on synthetic leather owing to its surface structures in terms of porosity and roughness. This paper examines the use of atmospheric pressure plasma (APP) treatment for improving the surface performance of polyester synthetic leather by use of a precursor, tetramethylsilane (TMS). Plasma deposition is regarded as an effective, simple and single-step method with low pollution. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) confirm the deposition of organosilanes on the sample's surface. The results showed that under a particular combination of treatment parameters, a hydrophobic surface was achieved on the APP treated sample with sessile drop static contact angle of 138°. The hydrophobic surface is stable without hydrophilic recovery 30 days after plasma treatment.

  3. Models for stellar flares

    International Nuclear Information System (INIS)

    Cram, L.E.; Woods, D.T.

    1982-01-01

    We study the response of certain spectral signatures of stellar flares (such as Balmer line profiles and the broad-band continuum) to changes in atmospheric structure which might result from physical processes akin to those thought to occur in solar flares. While each physical process does not have a unique signature, we can show that some of the observed properties of stellar flares can be explained by a model which involves increased pressures and temperatures in the flaring stellar chromosphere. We suggest that changes in stellar flare area, both with time and with depth in the atmosphere, may play an important role in producing the observed flare spectrum

  4. An Advanced N -body Model for Interacting Multiple Stellar Systems

    Energy Technology Data Exchange (ETDEWEB)

    Brož, Miroslav [Astronomical Institute of the Charles University, Faculty of Mathematics and Physics, V Holešovičkách 2, CZ-18000 Praha 8 (Czech Republic)

    2017-06-01

    We construct an advanced model for interacting multiple stellar systems in which we compute all trajectories with a numerical N -body integrator, namely the Bulirsch–Stoer from the SWIFT package. We can then derive various observables: astrometric positions, radial velocities, minima timings (TTVs), eclipse durations, interferometric visibilities, closure phases, synthetic spectra, spectral energy distribution, and even complete light curves. We use a modified version of the Wilson–Devinney code for the latter, in which the instantaneous true phase and inclination of the eclipsing binary are governed by the N -body integration. If all of these types of observations are at one’s disposal, a joint χ {sup 2} metric and an optimization algorithm (a simplex or simulated annealing) allow one to search for a global minimum and construct very robust models of stellar systems. At the same time, our N -body model is free from artifacts that may arise if mutual gravitational interactions among all components are not self-consistently accounted for. Finally, we present a number of examples showing dynamical effects that can be studied with our code and we discuss how systematic errors may affect the results (and how to prevent this from happening).

  5. Structural Elucidation of Metabolites of Synthetic Cannabinoid UR-144 by Cunninghamella elegans Using Nuclear Magnetic Resonance (NMR) Spectroscopy.

    Science.gov (United States)

    Watanabe, Shimpei; Kuzhiumparambil, Unnikrishnan; Fu, Shanlin

    2018-03-08

    The number of new psychoactive substances keeps on rising despite the controlling efforts by law enforcement. Although metabolism of the newly emerging drugs is continuously studied to keep up with the new additions, the exact structures of the metabolites are often not identified due to the insufficient sample quantities for techniques such as nuclear magnetic resonance (NMR) spectroscopy. The aim of the study was to characterise several metabolites of the synthetic cannabinoid (1-pentyl-1H-indol-3-yl) (2,2,3,3-tetramethylcyclopropyl) methanone (UR-144) by NMR spectroscopy after the incubation with the fungus Cunninghamella elegans. UR-144 was incubated with C. elegans for 72 h, and the resulting metabolites were chromatographically separated. Six fractions were collected and analysed by NMR spectroscopy. UR-144 was also incubated with human liver microsomes (HLM), and the liquid chromatography-high resolution mass spectrometry analysis was performed on the HLM metabolites with the characterised fungal metabolites as reference standards. Ten metabolites were characterised by NMR analysis including dihydroxy metabolites, carboxy and hydroxy metabolites, a hydroxy and ketone metabolite, and a carboxy and ketone metabolite. Of these metabolites, dihydroxy metabolite, carboxy and hydroxy metabolites, and a hydroxy and ketone metabolite were identified in HLM incubation. The results indicate that the fungus is capable of producing human-relevant metabolites including the exact isomers. The capacity of the fungus C. elegans to allow for NMR structural characterisation by enabling production of large amounts of metabolites makes it an ideal model to complement metabolism studies.

  6. Measuring the Evolution of Stellar Populations And Gas Metallicity in Galaxies with Far-Infrared Space Spectroscopy

    Science.gov (United States)

    Stacey, Gordon

    We propose a study of the evolution of stellar populations and gas metallicities in about 80 nearby star forming galaxies based on mining the NASA data archives for observations of the [NIII] 57 µm, [OIII] 52 µm and/or 88 µm, [NII] 122 and [CII] 158 µm far-infrared (FIR) fine- structure lines and other archives for thermal radio continuum. These lines are powerful probes of both stellar populations and gas properties and our primary science derives from these tracers. For sources that show both signs of active galactic nuclei (AGN) and star formation, we will take advantage of the readily available NASA Spitzer IRS data base that includes mid-IR [NeII] 12.8 µm, [NeIII] 15.6 µm and [NeV] 14.3 µm, [OIV] 25.9 µm and PAH observations. These complementary data reveal the relative fractions of the FIR line emission that might arise from star formation and the narrow line regions (NLR) associated with an AGN, thereby providing a robust set of observations to compare with star formation models. Subsets of the FIR lines have been detected from hundreds of nearby galaxies. From both theoretical studies and the results of these pioneering observations we know that these lines can be powerful probes of stellar populations and star formation in galaxies. Here we plan to use various combinations of the lines to constrain (1) the age of the stellar populations (through lines that trace the hardness of the stellar radiation fields, hence stellar spectral type), (2) the degree of processing of the interstellar medium (through lines that trace growth of secondary to primary element abundances for example, the N/O ratio), (3) the efficiency of star formation (through growth in absolute abundances of N and O, the N/H and O/H ratios), and (4) the current day mass function of upper main sequence stars. Surprisingly, there has been no systematic study of the large sample of these line detections made with PACS on Herschel in order to truly assess and calibrate their diagnostic

  7. Shock compression of synthetic opal

    International Nuclear Information System (INIS)

    Inoue, A; Okuno, M; Okudera, H; Mashimo, T; Omurzak, E; Katayama, S; Koyano, M

    2010-01-01

    Structural change of synthetic opal by shock-wave compression up to 38.1 GPa has been investigated by using SEM, X-ray diffraction method (XRD), Infrared (IR) and Raman spectroscopies. Obtained information may indicate that the dehydration and polymerization of surface silanole due to high shock and residual temperature are very important factors in the structural evolution of synthetic opal by shock compression. Synthetic opal loses opalescence by 10.9 and 18.4 GPa of shock pressures. At 18.4 GPa, dehydration and polymerization of surface silanole and transformation of network structure may occur simultaneously. The 4-membered ring of TO 4 tetrahedrons in as synthetic opal may be relaxed to larger ring such as 6-membered ring by high residual temperature. Therefore, the residual temperature may be significantly high at even 18.4 GPa of shock compression. At 23.9 GPa, opal sample recovered the opalescence. Origin of this opalescence may be its layer structure by shock compression. Finally, sample fuse by very high residual temperature at 38.1 GPa and the structure closes to that of fused SiO 2 glass. However, internal silanole groups still remain even at 38.1 GPa.

  8. Shock compression of synthetic opal

    Science.gov (United States)

    Inoue, A.; Okuno, M.; Okudera, H.; Mashimo, T.; Omurzak, E.; Katayama, S.; Koyano, M.

    2010-03-01

    Structural change of synthetic opal by shock-wave compression up to 38.1 GPa has been investigated by using SEM, X-ray diffraction method (XRD), Infrared (IR) and Raman spectroscopies. Obtained information may indicate that the dehydration and polymerization of surface silanole due to high shock and residual temperature are very important factors in the structural evolution of synthetic opal by shock compression. Synthetic opal loses opalescence by 10.9 and 18.4 GPa of shock pressures. At 18.4 GPa, dehydration and polymerization of surface silanole and transformation of network structure may occur simultaneously. The 4-membered ring of TO4 tetrahedrons in as synthetic opal may be relaxed to larger ring such as 6-membered ring by high residual temperature. Therefore, the residual temperature may be significantly high at even 18.4 GPa of shock compression. At 23.9 GPa, opal sample recovered the opalescence. Origin of this opalescence may be its layer structure by shock compression. Finally, sample fuse by very high residual temperature at 38.1 GPa and the structure closes to that of fused SiO2 glass. However, internal silanole groups still remain even at 38.1 GPa.

  9. Shock compression of synthetic opal

    Energy Technology Data Exchange (ETDEWEB)

    Inoue, A; Okuno, M; Okudera, H [Department of Earth Sciences, Kanazawa University Kanazawa, Ishikawa, 920-1192 (Japan); Mashimo, T; Omurzak, E [Shock Wave and Condensed Matter Research Center, Kumamoto University, Kumamoto, 860-8555 (Japan); Katayama, S; Koyano, M, E-mail: okuno@kenroku.kanazawa-u.ac.j [JAIST, Nomi, Ishikawa, 923-1297 (Japan)

    2010-03-01

    Structural change of synthetic opal by shock-wave compression up to 38.1 GPa has been investigated by using SEM, X-ray diffraction method (XRD), Infrared (IR) and Raman spectroscopies. Obtained information may indicate that the dehydration and polymerization of surface silanole due to high shock and residual temperature are very important factors in the structural evolution of synthetic opal by shock compression. Synthetic opal loses opalescence by 10.9 and 18.4 GPa of shock pressures. At 18.4 GPa, dehydration and polymerization of surface silanole and transformation of network structure may occur simultaneously. The 4-membered ring of TO{sub 4} tetrahedrons in as synthetic opal may be relaxed to larger ring such as 6-membered ring by high residual temperature. Therefore, the residual temperature may be significantly high at even 18.4 GPa of shock compression. At 23.9 GPa, opal sample recovered the opalescence. Origin of this opalescence may be its layer structure by shock compression. Finally, sample fuse by very high residual temperature at 38.1 GPa and the structure closes to that of fused SiO{sub 2} glass. However, internal silanole groups still remain even at 38.1 GPa.

  10. Stellar structure and evolution

    International Nuclear Information System (INIS)

    Kippernhahn, R.; Weigert, A.

    1990-01-01

    This book introduces the theory of the internal structure of stars and their evolution in time. It presents the basic physics of stellar interiors, methods for solving the underlying equations, and the most important results necessary for understanding the wide variety of stellar types and phenomena. The evolution of stars is discussed from their birth through normal evolution to possibly spectacular final stages. Chapters on stellar oscillations and rotation are included

  11. Near-Field Cosmology with Resolved Stellar Populations Around Local Volume LMC Stellar-Mass Galaxies

    Science.gov (United States)

    Carlin, Jeffrey L.; Sand, David J.; Willman, Beth; Brodie, Jean P.; Crnojevic, Denija; Forbes, Duncan; Hargis, Jonathan R.; Peter, Annika; Pucha, Ragadeepika; Romanowsky, Aaron J.; Spekkens, Kristine; Strader, Jay

    2018-06-01

    We discuss our ongoing observational program to comprehensively map the entire virial volumes of roughly LMC stellar mass galaxies at distances of ~2-4 Mpc. The MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos) survey will deliver the first census of the dwarf satellite populations and stellar halo properties within LMC-like environments in the Local Volume. Our results will inform our understanding of the recent DES discoveries of dwarf satellites tentatively affiliated with the LMC/SMC system. This program has already yielded the discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep Subaru+HyperSuprimeCam imaging reaching ~2 magnitudes below its TRGB, and at least two additional candidate satellites. We will summarize the survey results and status to date, highlighting some challenges encountered and lessons learned as we process the data for this program through a prototype LSST pipeline. Our program will examine whether LMC stellar mass dwarfs have extended stellar halos, allowing us to assess the relative contributions of in-situ stars vs. merger debris to their stellar populations and halo density profiles. We outline the constraints on galaxy formation models that will be provided by our observations of low-mass galaxy halos and their satellites.

  12. A Simple LIBS (Laser-Induced Breakdown Spectroscopy) Laboratory Experiment to Introduce Undergraduates to Calibration Functions and Atomic Spectroscopy

    Science.gov (United States)

    Chinni, Rosemarie C.

    2012-01-01

    This laboratory experiment introduces students to a different type of atomic spectroscopy: laser-induced breakdown spectroscopy (LIBS). LIBS uses a laser-generated spark to excite the sample; once excited, the elemental emission is spectrally resolved and detected. The students use LIBS to analyze a series of standard synthetic silicate samples…

  13. Double-helix stellarator

    International Nuclear Information System (INIS)

    Moroz, P.E.

    1997-09-01

    A new stellarator configuration, the Double-Helix Stellarator (DHS), is introduced. This novel configuration features a double-helix center post as the only helical element of the stellarator coil system. The DHS configuration has many unique characteristics. One of them is the extreme low plasma aspect ratio, A ∼ 1--1.2. Other advantages include a high enclosed volume, appreciable rotational transform, and a possibility of extreme-high-β MHD equilibria. Moreover, the DHS features improved transport characteristics caused by the absence of the magnetic field ripple on the outboard of the torus. Compactness, simplicity and modularity of the coil system add to the DHS advantages for fusion applications

  14. A DETECTION OF GAS ASSOCIATED WITH THE M31 STELLAR STREAM

    Energy Technology Data Exchange (ETDEWEB)

    Koch, Andreas [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Danforth, Charles W.; Keeney, Brian A. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389-UCB, Boulder, CO 80309 (United States); Rich, R. Michael [Physics and Astronomy Building, 430 Portola Plaza, Box 951547, Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Ibata, Rodrigo [Observatoire de Strasbourg, 11, rue de l’Université, F-67000, Strasbourg (France)

    2015-07-10

    Detailed studies of stellar populations in the halos of the Milky Way and the Andromeda (M31) galaxies have shown increasing numbers of tidal streams and dwarf galaxies, attesting to a complicated and on-going process of hierarchical structure formation. The most prominent feature in the halo of M31 is the Giant Stellar Stream, a structure ∼4.°5 in extent along the sky, which is close to, but not coincident with the galaxy's minor axis. The stars that make up this stream are kinematically and chemically distinct from the other stars in the halo. Here, we present Hubble Space Telescope/Cosmic Origins Spectrograph high-resolution ultraviolet absorption spectra of three active galactic nuclei sight lines which probe the M31 halo, including one that samples gas in the main southwestern portion of the Giant Stream. We see two clear absorption components in many metal species at velocities typical of the M31 halo and a third, blueshifted component which arises in the stream. Photoionization modeling of the column density ratios in the different components shows gas in an ionization state typical of that seen in other galaxy halo environments and suggests solar to slightly super-solar metallicity, consistent with previous findings from stellar spectroscopy.

  15. Stellar Initial Mass Function: Trends With Galaxy Mass And Radius

    Science.gov (United States)

    Parikh, Taniya

    2017-06-01

    There is currently no consensus about the exact shape and, in particular, the universality of the stellar initial mass function (IMF). For massive galaxies, it has been found that near-infrared (NIR) absorption features, which are sensitive to the ratio of dwarf to giant stars, deviate from a Milky Way-like IMF; their modelling seems to require a larger fraction of low mass stars. There are now increasing results looking at whether the IMF varies not only with galaxy mass, but also radially within galaxies. The SDSS-IV/MaNGA integral-field survey will provide spatially resolved spectroscopy for 10,000 galaxies at R 2000 from 360-1000nm. Spectra of early-type galaxies were stacked to achieve high S/N which is particularly important for features in the NIR. Trends with galaxy radius and mass were compared to stellar population models for a range of absorption features in order to separate degeneracies due to changes in stellar population parameters, such as age, metallicity and element abundances, with potential changes in the IMF. Results for 611 galaxies show that we do not require an IMF steeper than Kroupa as a function of galaxy mass or radius based on the NaI index. The Wing-Ford band hints towards a steeper IMF at large radii however we do not have reliable measurements for the most massive galaxies.

  16. The Magellanic Analog Dwarf Companions and Stellar Halos (MADCASH) Survey: Near-Field Cosmology with Resolved Stellar Populations Around Local Volume LMC Stellar-Mass Galaxies

    Science.gov (United States)

    Carlin, Jeffrey L.; Sand, David J.; Willman, Beth; Brodie, Jean P.; Crnojevic, Denija; Peter, Annika; Price, Paul A.; Romanowsky, Aaron J.; Spekkens, Kristine; Strader, Jay

    2017-01-01

    We discuss the first results of our observational program to comprehensively map nearly the entire virial volumes of roughly LMC stellar mass galaxies at distances of ~2-4 Mpc. The MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos) survey will deliver the first census of the dwarf satellite populations and stellar halo properties within LMC-like environments in the Local Volume. These will inform our understanding of the recent DES discoveries of dwarf satellites tentatively affiliated with the LMC/SMC system. We will detail our discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep Subaru+HyperSuprimeCam imaging reaching ~2 magnitudes below its TRGB. We will summarize the survey results and status to date, highlighting some challenges encountered and lessons learned as we process the data for this program through a prototype LSST pipeline. Our program will examine whether LMC stellar mass dwarfs have extended stellar halos, allowing us to assess the relative contributions of in-situ stars vs. merger debris to their stellar populations and halo density profiles. We outline the constraints on galaxy formation models that will be provided by our observations of low-mass galaxy halos and their satellites.

  17. Surface modification of polyester synthetic leather with tetramethylsilane by atmospheric pressure plasma

    Energy Technology Data Exchange (ETDEWEB)

    Kan, C.W., E-mail: tccwk@polyu.edu.hk [Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon (Hong Kong); Kwong, C.H. [Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon (Hong Kong); Ng, S.P. [Hong Kong Community College, The Hong Kong Polytechnic University (Hong Kong)

    2015-08-15

    Highlights: • Atmospheric pressure plasma treatment improved surface performance of polyester synthetic leather with tetramethylsilane. • XPS and FTIR confirmed the deposition of organosilanes on the sample's surface. • Contact angle increases to 138° after plasma treatment. - Abstract: Much works have been done on synthetic materials but scarcely on synthetic leather owing to its surface structures in terms of porosity and roughness. This paper examines the use of atmospheric pressure plasma (APP) treatment for improving the surface performance of polyester synthetic leather by use of a precursor, tetramethylsilane (TMS). Plasma deposition is regarded as an effective, simple and single-step method with low pollution. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) confirm the deposition of organosilanes on the sample's surface. The results showed that under a particular combination of treatment parameters, a hydrophobic surface was achieved on the APP treated sample with sessile drop static contact angle of 138°. The hydrophobic surface is stable without hydrophilic recovery 30 days after plasma treatment.

  18. Surface modification of polyester synthetic leather with tetramethylsilane by atmospheric pressure plasma

    International Nuclear Information System (INIS)

    Kan, C.W.; Kwong, C.H.; Ng, S.P.

    2015-01-01

    Highlights: • Atmospheric pressure plasma treatment improved surface performance of polyester synthetic leather with tetramethylsilane. • XPS and FTIR confirmed the deposition of organosilanes on the sample's surface. • Contact angle increases to 138° after plasma treatment. - Abstract: Much works have been done on synthetic materials but scarcely on synthetic leather owing to its surface structures in terms of porosity and roughness. This paper examines the use of atmospheric pressure plasma (APP) treatment for improving the surface performance of polyester synthetic leather by use of a precursor, tetramethylsilane (TMS). Plasma deposition is regarded as an effective, simple and single-step method with low pollution. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) confirm the deposition of organosilanes on the sample's surface. The results showed that under a particular combination of treatment parameters, a hydrophobic surface was achieved on the APP treated sample with sessile drop static contact angle of 138°. The hydrophobic surface is stable without hydrophilic recovery 30 days after plasma treatment

  19. The effect of stellar evolution uncertainties on the rest-frame ultraviolet stellar lines of C IV and He II in high-redshift Lyman-break galaxies

    Science.gov (United States)

    Eldridge, John J.; Stanway, Elizabeth R.

    2012-01-01

    Young, massive stars dominate the rest-frame ultraviolet (UV) spectra of star-forming galaxies. At high redshifts (z > 2), these rest-frame UV features are shifted into the observed-frame optical and a combination of gravitational lensing, deep spectroscopy and spectral stacking analysis allows the stellar population characteristics of these sources to be investigated. We use our stellar population synthesis code Binary Population and Spectral Synthesis (BPASS) to fit two strong rest-frame UV spectral features in published Lyman-break galaxy spectra, taking into account the effects of binary evolution on the stellar spectrum. In particular, we consider the effects of quasi-homogeneous evolution (arising from the rotational mixing of rapidly rotating stars), metallicity and the relative abundance of carbon and oxygen on the observed strengths of He IIλ1640 Å and C IVλ1548, 1551 Å spectral lines. We find that Lyman-break galaxy spectra at z ˜ 2-3 are best fitted with moderately sub-solar metallicities, and with a depleted carbon-to-oxygen ratio. We also find that the spectra of the lowest metallicity sources are best fitted with model spectra in which the He II emission line is boosted by the inclusion of the effect of massive stars being spun-up during binary mass transfer so these rapidly rotating stars experience quasi-homogeneous evolution.

  20. COMPARISON OF ALPHA-ELEMENT-ENHANCED SIMPLE STELLAR POPULATION MODELS WITH MILKY WAY GLOBULAR CLUSTERS

    International Nuclear Information System (INIS)

    Lee, Hyun-chul; Worthey, Guy; Dotter, Aaron

    2009-01-01

    We present simple stellar population (SSP) models with scaled-solar and α-element-enhanced abundances. The SSP models are based on the Dartmouth Stellar Evolution Database, our library of synthetic stellar spectra, and a detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity. In order to test the relative importance of a variety of SSP model ingredients, we compare our SSP models with integrated spectra of 41 Milky Way globular clusters (MWGCs) from Schiavon et al. Using the Mg b and Ca4227 indices, we confirm that Mg and Ca are enhanced by about +0.4 and +0.2 dex, respectively, in agreement with results from high-resolution spectra of individual stars in MWGCs. Balmer lines, particularly Hγ and Hδ, of MWGCs are reproduced by our α-enhanced SSP models not only because of the combination of isochrone and spectral effects but also because of our reasonable HB treatment. Moreover, it is shown that the Mg abundance significantly influences Balmer and iron line indices. Finally, the investigation of power-law initial mass function (IMF) variations suggests that an IMF much shallower than Salpeter is unrealistic because the Balmer lines are too strong on the metal-poor side to be compatible with observations.

  1. The BRAVE Program. I. Improved Bulge Stellar Velocity Dispersion Estimates for a Sample of Active Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Batiste, Merida; Bentz, Misty C.; Manne-Nicholas, Emily R. [Department of Physics and Astronomy, Georgia State University, 25 Park Place, Atlanta, GA 30303 (United States); Onken, Christopher A. [Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611 (Australia); Bershady, Matthew A., E-mail: batiste@astro.gsu.edu [Department of Astronomy, University of Wisconsin, 475 N. Charter Street, Madison, WI 53706 (United States)

    2017-02-01

    We present new bulge stellar velocity dispersion measurements for 10 active galaxies with secure M {sub BH} determinations from reverberation mapping. These new velocity dispersion measurements are based on spatially resolved kinematics from integral-field (IFU) spectroscopy. In all but one case, the field of view of the IFU extends beyond the effective radius of the galaxy, and in the case of Mrk 79 it extends to almost one half the effective radius. This combination of spatial resolution and field of view allows for secure determinations of stellar velocity dispersion within the effective radius for all 10 target galaxies. Spatially resolved maps of the first ( V ) and second ( σ {sub ⋆}) moments of the line of sight velocity distribution indicate the presence of kinematic substructure in most cases. In future projects we plan to explore methods of correcting for the effects of kinematic substructure in the derived bulge stellar velocity dispersion measurements.

  2. Ripple transport in helical-axis advanced stellarators - a comparison with classical stellarator/torsatrons

    International Nuclear Information System (INIS)

    Beidler, C.D.; Hitchon, W.N.G.

    1993-08-01

    Calculations of the neoclassical transport rates due to particles trapped in the helical ripples of a stellarator's magnetic field are carried out, based on solutions of the bounce-averaged kinetic equation. These calculations employ a model for the magnetic field strength, B, which is an accurate approximation to the actual B for a wide variety of stellarator-type devices, among which are Helical-Axis Advanced Stellarators (Helias) as well as conventional stellarators and torsatrons. Comparisons are carried out in which it is shown that the Helias concept leads to significant reductions in neoclassical transport rates throughout the entire long-mean-free-path regime, with the reduction being particularly dramatic in the ν -1 regime. These findings are confirmed by numerical simulations. Further, it is shown that the behavior of deeply trapped particles in Helias can be fundamentally different from that in classical stellarator/torsatrons; as a consequence, the beneficial effects of a radial electric field on the transport make themselves felt at lower collision frequency than is usual. (orig.)

  3. Convection and stellar oscillations

    DEFF Research Database (Denmark)

    Aarslev, Magnus Johan

    2017-01-01

    for asteroseismology, because of the challenges inherent in modelling turbulent convection in 1D stellar models. As a result of oversimplifying the physics near the surface, theoretical calculations systematically overestimate the oscillation frequencies. This has become known as the asteroseismic surface effect. Due...... to lacking better options, this frequency difference is typically corrected for with ad-hoc formulae. The topic of this thesis is the improvement of 1D stellar convection models and the effects this has on asteroseismic properties. The source of improvements is 3D simulations of radiation...... atmospheres to replace the outer layers of stellar models. The additional turbulent pressure and asymmetrical opacity effects in the atmosphere model, compared to convection in stellar evolution models, serve to expand the atmosphere. The enlarged acoustic cavity lowers the pulsation frequencies bringing them...

  4. Stellarator Research Opportunities: A report of the National Stellarator Coordinating Committee

    Energy Technology Data Exchange (ETDEWEB)

    Gates, David A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Anderson, David [University of Wisconsin-Madison

    2017-06-01

    This document is the product of a stellarator community workshop, organized by the National Stellarator Coordinating Committee and referred to as Stellcon, that was held in Cambridge, Massachusetts in February 2016, hosted by MIT. The workshop was widely advertised, and was attended by 40 scientists from 12 different institutions including national labs, universities and private industry, as well as a representative from the Department of Energy. The final section of this document describes areas of community wide consensus that were developed as a result of the discussions held at that workshop. Areas where further study would be helpful to generate a consensus path forward for the US stellarator program are also discussed. The program outlined in this document is directly responsive to many of the strategic priorities of FES as articulated in “Fusion Energy Sciences: A Ten-Year Perspective (2015-2025)” [2]. The natural disruption immunity of the stellarator directly addresses “Elimination of transient events that can be deleterious to toroidal fusion plasma confinement devices” an area of critical importance for the U.S. fusion energy sciences enterprise over the next decade. Another critical area of research “Strengthening our partnerships with international research facilities,” is being significantly advanced on the W7-X stellarator in Germany and serves as a test-bed for development of successful international collaboration on ITER. This report also outlines how materials science as it relates to plasma and fusion sciences, another critical research area, can be carried out effectively in a stellarator. Additionally, significant advances along two of the Research Directions outlined in the report; “Burning Plasma Science: Foundations - Next-generation research capabilities”, and “Burning Plasma Science: Long pulse - Sustainment of Long-Pulse Plasma Equilibria” are proposed.

  5. Stellarator Research Opportunities: A Report of the National Stellarator Coordinating Committee

    Science.gov (United States)

    Gates, D. A.; Anderson, D.; Anderson, S.; Zarnstorff, M.; Spong, D. A.; Weitzner, H.; Neilson, G. H.; Ruzic, D.; Andruczyk, D.; Harris, J. H.; Mynick, H.; Hegna, C. C.; Schmitz, O.; Talmadge, J. N.; Curreli, D.; Maurer, D.; Boozer, A. H.; Knowlton, S.; Allain, J. P.; Ennis, D.; Wurden, G.; Reiman, A.; Lore, J. D.; Landreman, M.; Freidberg, J. P.; Hudson, S. R.; Porkolab, M.; Demers, D.; Terry, J.; Edlund, E.; Lazerson, S. A.; Pablant, N.; Fonck, R.; Volpe, F.; Canik, J.; Granetz, R.; Ware, A.; Hanson, J. D.; Kumar, S.; Deng, C.; Likin, K.; Cerfon, A.; Ram, A.; Hassam, A.; Prager, S.; Paz-Soldan, C.; Pueschel, M. J.; Joseph, I.; Glasser, A. H.

    2018-02-01

    This document is the product of a stellarator community workshop, organized by the National Stellarator Coordinating Committee and referred to as Stellcon, that was held in Cambridge, Massachusetts in February 2016, hosted by MIT. The workshop was widely advertised, and was attended by 40 scientists from 12 different institutions including national labs, universities and private industry, as well as a representative from the Department of Energy. The final section of this document describes areas of community wide consensus that were developed as a result of the discussions held at that workshop. Areas where further study would be helpful to generate a consensus path forward for the US stellarator program are also discussed. The program outlined in this document is directly responsive to many of the strategic priorities of FES as articulated in "Fusion Energy Sciences: A Ten-Year Perspective (2015-2025)" [1]. The natural disruption immunity of the stellarator directly addresses "Elimination of transient events that can be deleterious to toroidal fusion plasma confinement devices" an area of critical importance for the US fusion energy sciences enterprise over the next decade. Another critical area of research "Strengthening our partnerships with international research facilities," is being significantly advanced on the W7-X stellarator in Germany and serves as a test-bed for development of successful international collaboration on ITER. This report also outlines how materials science as it relates to plasma and fusion sciences, another critical research area, can be carried out effectively in a stellarator. Additionally, significant advances along two of the Research Directions outlined in the report; "Burning Plasma Science: Foundations - Next-generation research capabilities", and "Burning Plasma Science: Long pulse - Sustainment of Long-Pulse Plasma Equilibria" are proposed.

  6. Habitability in different Milky Way stellar environments: a stellar interaction dynamical approach.

    Science.gov (United States)

    Jiménez-Torres, Juan J; Pichardo, Bárbara; Lake, George; Segura, Antígona

    2013-05-01

    Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the solar neighborhood, however, is rather poor; thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of stars in more crowded stellar environments, such as stellar clusters. We found that in open clusters habitable zones are not readily disrupted; this is true if they evaporate in less than 10(8) yr. For older clusters the results may not be the same. We specifically studied the case of Messier 67, one of the oldest open clusters known, and show the effect of this environment on debris disks. We also considered the conditions in globular clusters, the Galactic nucleus, and the Galactic bulge-bar. We calculated the probability of whether Oort clouds exist in these Galactic environments.

  7. The “Building Blocks” of Stellar Halos

    Directory of Open Access Journals (Sweden)

    Kyle A. Oman

    2017-08-01

    Full Text Available The stellar halos of galaxies encode their accretion histories. In particular, the median metallicity of a halo is determined primarily by the mass of the most massive accreted object. We use hydrodynamical cosmological simulations from the apostle project to study the connection between the stellar mass, the metallicity distribution, and the stellar age distribution of a halo and the identity of its most massive progenitor. We find that the stellar populations in an accreted halo typically resemble the old stellar populations in a present-day dwarf galaxy with a stellar mass ∼0.2–0.5 dex greater than that of the stellar halo. This suggests that had they not been accreted, the primary progenitors of stellar halos would have evolved to resemble typical nearby dwarf irregulars.

  8. Constraining the Stellar Mass Function in the Galactic Center via Mass Loss from Stellar Collisions

    Directory of Open Access Journals (Sweden)

    Douglas Rubin

    2011-01-01

    Full Text Available The dense concentration of stars and high-velocity dispersions in the Galactic center imply that stellar collisions frequently occur. Stellar collisions could therefore result in significant mass loss rates. We calculate the amount of stellar mass lost due to indirect and direct stellar collisions and find its dependence on the present-day mass function of stars. We find that the total mass loss rate in the Galactic center due to stellar collisions is sensitive to the present-day mass function adopted. We use the observed diffuse X-ray luminosity in the Galactic center to preclude any present-day mass functions that result in mass loss rates >10-5M⨀yr−1 in the vicinity of ~1″. For present-day mass functions of the form, dN/dM∝M-α, we constrain the present-day mass function to have a minimum stellar mass ≲7M⨀ and a power-law slope ≳1.25. We also use this result to constrain the initial mass function in the Galactic center by considering different star formation scenarios.

  9. Principles of Stellar Interferometry

    CERN Document Server

    Glindemann, Andreas

    2011-01-01

    Over the last decade, stellar interferometry has developed from a specialist tool to a mainstream observing technique, attracting scientists whose research benefits from milliarcsecond angular resolution. Stellar interferometry has become part of the astronomer’s toolbox, complementing single-telescope observations by providing unique capabilities that will advance astronomical research. This carefully written book is intended to provide a solid understanding of the principles of stellar interferometry to students starting an astronomical research project in this field or to develop instruments and to astronomers using interferometry but who are not interferometrists per se. Illustrated by excellent drawings and calculated graphs the imaging process in stellar interferometers is explained starting from first principles on light propagation and diffraction wave propagation through turbulence is described in detail using Kolmogorov statistics the impact of turbulence on the imaging process is discussed both f...

  10. Advanced stellarator power plants

    International Nuclear Information System (INIS)

    Miller, R.L.

    1994-01-01

    The stellarator is a class of helical/toroidal magnetic fusion devices. Recent international progress in stellarator power plant conceptual design is reviewed and comparisons in the areas of physics, engineering, and economics are made with recent tokamak design studies

  11. Compact stellarator coils

    International Nuclear Information System (INIS)

    Pomphrey, N.; Berry, L.A.; Boozer, A.H.

    2001-01-01

    Experimental devices to study the physics of high-beta (β>∼4%), low aspect ratio (A<∼4.5) stellarator plasmas require coils that will produce plasmas satisfying a set of physics goals, provide experimental flexibility, and be practical to construct. In the course of designing a flexible coil set for the National Compact Stellarator Experiment, we have made several innovations that may be useful in future stellarator design efforts. These include: the use of Singular Value Decomposition methods for obtaining families of smooth current potentials on distant coil winding surfaces from which low current density solutions may be identified; the use of a Control Matrix Method for identifying which few of the many detailed elements of the stellarator boundary must be targeted if a coil set is to provide fields to control the essential physics of the plasma; the use of Genetic Algorithms for choosing an optimal set of discrete coils from a continuum of potential contours; the evaluation of alternate coil topologies for balancing the tradeoff between physics objective and engineering constraints; the development of a new coil optimization code for designing modular coils, and the identification of a 'natural' basis for describing current sheet distributions. (author)

  12. Spectral Resolution-linked Bias in Transit Spectroscopy of Extrasolar Planets

    Science.gov (United States)

    Deming, Drake; Sheppard, Kyle

    2017-05-01

    We re-visit the principles of transmission spectroscopy for transiting extrasolar planets, focusing on the overlap between the planetary spectrum and the illuminating stellar spectrum. Virtually all current models of exoplanetary transmission spectra utilize an approximation that is inaccurate when the spectrum of the illuminating star has a complex line structure, such as molecular bands in M-dwarf spectra. In those cases, it is desirable to model the observations using a coupled stellar-planetary radiative transfer model calculated at high spectral resolving power, followed by convolution to the observed resolution. Not consistently accounting for overlap of stellar M-dwarf and planetary lines at high spectral resolution can bias the modeled amplitude of the exoplanetary transmission spectrum, producing modeled absorption that is too strong. We illustrate this bias using the exoplanet TRAPPIST-1b, as observed using Hubble Space Telescope/WFC3. The bias in this case is about 250 ppm, 12% of the modeled transit absorption. Transit spectroscopy using JWST will have access to longer wavelengths where the water bands are intrinsically stronger, and the observed signal-to-noise ratios will be higher than currently possible. We therefore expect that this resolution-linked bias will be especially important for future JWST observations of TESS-discovered super-Earths and mini-Neptunes transiting M-dwarfs.

  13. Use of the stellarator expansion to investigate plasma equilibrium in modular stellarators

    International Nuclear Information System (INIS)

    Anania, G.; Johnson, J.L.; Weimer, K.E.

    1982-11-01

    A numerical code utilizing a large-aspect ratio, small-helical-distortion expansion is developed and used to investigate the effect of plasma currents on stellarator equilibrium. Application to modular stellarator configurations shows that a large rotational transform, and hence large coil deformation, is needed to achieve high-beta equilibria

  14. Stellar CME candidates: towards a stellar CME-flare relation

    Science.gov (United States)

    Paraskevi Moschou, Sofia; Drake, Jeremy J.; Cohen, Ofer; Alvarado-Gomez, Julian D.; Garraffo, Cecilia

    2018-06-01

    For decades the Sun has been the only star that allowed for direct CME observations. Recently, with the discovery of multiple extrasolar systems, it has become imperative that the role of stellar CMEs be assessed in the context of exoplanetary habitability. Solar CMEs and flares show a higher association with increasing flaring energy, with strong flares corresponding to large and fast CMEs. As argued in earlier studies, extrasolar environments around active stars are potentially dominated by CMEs, as a result of their extreme flaring activity. This has strong implications for the energy budget of the system and the atmospheric erosion of orbiting planets.Nevertheless, with current instrumentation we are unable to directly observe CMEs in even the closest stars, and thus we have to look for indirect techniques and observational evidence and signatures for the eruption of stellar CMEs. There are three major observational techniques for tracing CME signatures in other stellar systems, namely measuring Type II radio bursts, Doppler shifts in UV/optical lines or transient absorption in the X-ray spectrum. We present observations of the most probable stellar CME candidates captured so far and examine the different observational techniques used together with their levels of uncertainty. Assuming that they were CMEs, we try to asses their kinematic and energetic characteristics and place them in an extension of the well-established solar CME-flare energy scaling law. We finish by discussing future observations for direct measurements.

  15. Stellar wind theory

    International Nuclear Information System (INIS)

    Summers, D.

    1980-01-01

    The theory of stellar winds as given by the equations of classical fluid dynamics is considered. The equations of momentum and energy describing a steady, spherically symmetric, heat-conducting, viscous stellar wind are cast in a dimensionless form which involves a thermal conduction parameter E and a viscosity parameter γ. An asymptotic analysis is carried out, for fixed γ, in the cases E→O and E→infinity (corresponding to small and large thermal conductivity, respectively), and it is found that it is possible to construct critical solutions for the wind velocity and temperature over the entire flow. The E→O solution represents a wind which emanates from the star at low, subsonic speeds, accelerates through a sonic point, and then approaches a constant asymptotic speed, with its temperature varying as r/sup -4/3/ at large distances r from the star; the E→infinity solution represents a wind which, after reaching an approximately constant speed, with temperature varying as r/sup -2/7/, decelerates through a diffuse shock and approaches a finite pressure at infinity. A categorization is made of all critical stellar wind solutions for given values of γ and E, and actual numerical examples are given. Numerical solutions are obtained by integrating upstream 'from infinity' from initial values of the flow parameters given by appropriate asymptotic expansions. The role of viscosity in stellar wind theory is discussed, viscous and inviscid stellar wind solutions are compared, and it is suggested that with certain limitations, the theory presented may be useful in analyzing winds from solar-type stars

  16. Stellarator fusion neutronics research in Australia

    International Nuclear Information System (INIS)

    Zimin, S.; Cross, R.C.

    1997-01-01

    The new status of the H-INF Heliac Stellaralor as a National Facility and the signed international Implementing Agreement on 'Collaboration in the Development of the Stellarator Concept' represents a significant encouragement for further fusion research in Australia. In this report the future of fusion research in Australia is discussed with special attention being paid to the importance of Stellarator power plant studies and in particular stellarator fusion neutronics. The main differences between tokamak and stellarator neutronics analyses are identified, namely the neutron wall loading, geometrical modelling and total heating in in-vessel reactor components including toroidal field (TF) coils. Due to the more complicated nature of stellarator neutronics analyses, simplified approaches to fusion neutronics already developed for tokamaks are expected to be even more important and widely used for designing a Conceptual Stellarator Power Plant

  17. Effect of stellar activity on the high precision transit light curve

    Directory of Open Access Journals (Sweden)

    Oshagh, M.

    2015-01-01

    Full Text Available Stellar activity features such as spots and plages can create difficulties in determining planetary parameters through spectroscopic and photometric observations. The overlap of a transiting planet and a stellar spot, for instance, can produce anomalies in the transit light curve that may lead to inaccurate estimation of the transit duration, depth, and timing. Such inaccuracies can affect the precise derivation of the planet’s radius. In this talk we will present the results of a quantitative study on the effects of stellar spots on high precision transit light curves. We show that spot anomalies can lead to the estimate of a planet radius that is 4% smaller than the real value. The effects on the transit duration can also be of the order of 4%, longer or shorter. Depending on the size and distribution of spots, anomalies can also produce transit timing variations with significant amplitudes. For instance, TTVs with signal amplitudes of 200 seconds can be produced by spots as large as the largest sunspot. Finally, we examine the impact of active regions on the transit depth measurements in different wavelengths, in order to probe the impact of this effect on transmission spectroscopy measurements. We show that significant (up to 10% underestimation/overestimation of the planet-to-star radius ratio can be measured, especially in the short wavelength regime.

  18. The SLUGGS survey: wide-field stellar kinematics of early-type galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Arnold, Jacob A. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Romanowsky, Aaron J.; Brodie, Jean P.; Woodley, Kristin A. [University of California Observatories, 1156 High Street, Santa Cruz, CA 95064 (United States); Forbes, Duncan A.; Blom, Christina; Kartha, Sreeja S.; Pastorello, Nicola; Pota, Vincenzo; Usher, Christopher [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia); Strader, Jay [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Spitler, Lee R. [Department of Physics and Astronomy, Faculty of Sciences, Macquarie University, Sydney, NSW 2109 (Australia); Foster, Caroline, E-mail: romanow@ucolick.org [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW (Australia)

    2014-08-20

    We present stellar kinematics of 22 nearby early-type galaxies (ETGs), based on two-dimensional (2D) absorption line stellar spectroscopy out to ∼2-4 R {sub e} (effective radii), as part of the ongoing SLUGGS Survey. The galaxies span a factor of 20 in intrinsic luminosity, as well as a full range of environment and ETG morphology. Our data consist of good velocity resolution (σ{sub inst} ∼ 25 km s{sup –1}) integrated stellar-light spectra extracted from the individual slitlets of custom made Keck/DEIMOS slitmasks. We extract stellar kinematics measurements (V, σ, h {sub 3}, and h {sub 4}) for each galaxy. Combining with literature values from smaller radii, we present 2D spatially resolved maps of the large-scale kinematic structure in each galaxy. We find that the kinematic homogeneity found inside 1 R {sub e} often breaks down at larger radii, where a variety of kinematic behaviors are observed. While central slow rotators remain slowly rotating in their halos, central fast rotators show more diversity, ranging from rapidly increasing to rapidly declining specific angular momentum profiles in the outer regions. There are indications that the outer trends depend on morphological type, raising questions about the proposed unification of the elliptical and lenticular (S0) galaxy families in the ATLAS{sup 3D} survey. Several galaxies in our sample show multiple lines of evidence for distinct disk components embedded in more slowly rotating spheroids, and we suggest a joint photometric-kinematic approach for robust bulge-disk decomposition. Our observational results appear generally consistent with a picture of two-phase (in-situ plus accretion) galaxy formation.

  19. High-cadence spectroscopy of M-dwarfs - II. Searching for stellar pulsations with HARPS

    Science.gov (United States)

    Berdiñas, Z. M.; Rodríguez-López, C.; Amado, P. J.; Anglada-Escudé, G.; Barnes, J. R.; MacDonald, J.; Zechmeister, M.; Sarmiento, L. F.

    2017-08-01

    Stellar oscillations appear all across the Hertzsprung-Russell diagram. Recent theoretical studies support their existence also in the atmosphere of M dwarfs. These studies predict for them short periodicities ranging from 20 min to 3 h. Our Cool Tiny Beats (CTB) programme aims at finding these oscillations for the very first time. With this goal, CTB explores the short time domain of M dwarfs using radial velocity data from the High Accuracy Radial velocity Planet Searcher (HARPS)-European Southern Observatory and HARPS-N high-precision spectrographs. Here we present the results for the two most long-term stable targets observed to date with CTB, GJ 588 and GJ 699 (I.e. Barnard's star). In the first part of this work we detail the correction of several instrumental effects. These corrections are especially relevant when searching for subnight signals. Results show no significant signals in the range where M dwarfs pulsations were predicted. However, we estimate that stellar pulsations with amplitudes larger than ˜0.5 m s-1 can be detected with a 90 per cent completeness with our observations. This result, along with the excess of power regions detected in the periodograms, opens the possibility of non-resolved very low amplitude pulsation signals. Next generation more precise instrumentation would be required to detect such oscillations. However, the possibility of detecting pulsating M-dwarf stars with larger amplitudes is feasible due to the short size of the analysed sample. This motivates the need for completeness of the CTB survey.

  20. Moessbauer Study of Discoloration of Synthetic Resin Covered Electric Switches

    International Nuclear Information System (INIS)

    Kuzmann, E.; Muzsay, I.; Homonnay, Z.; Vertes, A.

    2002-01-01

    57 Fe Moessbauer spectroscopy and X-ray diffractometry were used to investigate brown discoloration and sediments formed on the surface of synthetic resin product covered electronic switches. The Moessbauer measurement revealed that alloyed steels and iron-containing corrosion products are associated with the discolored layers. Iron, and iron corrosion products were shown by both MS and XRD in the sediments formed eventually during the finishing of the synthetic resin products after machining and washing with water solution.

  1. Starlight An Introduction to Stellar Physics for Amateurs

    CERN Document Server

    Robinson, Keith

    2009-01-01

    When you look up at the sky at night and see the stars, do you understand what you’re looking at? What is starlight made up of, and how does it travel to us? How are stars born, and how do they die? How do we figure out how far away are the stars and how massive they are? Can we know which stars will go supernova and which will end up as white dwarfs or black holes? How long will our Sun continue to shine down on us, and how do we know its age? There are so many questions, and in this engaging and informative book by Keith Robinson, which serves as a companion to his very popular earlier book called Spectroscopy – the Key to the Stars, you will learn the basics of stellar physics and the answers to many of these questions, as well as how to figure out some of those answers for yourself. We have come so far in our understanding of stellar light and heat. By reading this book, you, too, can understand many of the secrets of the fiery Sun that rules our Solar System and the gemlike points of light in the nig...

  2. Atmospheric stellar parameters from cross-correlation functions

    Science.gov (United States)

    Malavolta, L.; Lovis, C.; Pepe, F.; Sneden, C.; Udry, S.

    2017-08-01

    The increasing number of spectra gathered by spectroscopic sky surveys and transiting exoplanet follow-up has pushed the community to develop automated tools for atmospheric stellar parameters determination. Here we present a novel approach that allows the measurement of temperature (Teff), metallicity ([Fe/H]) and gravity (log g) within a few seconds and in a completely automated fashion. Rather than performing comparisons with spectral libraries, our technique is based on the determination of several cross-correlation functions (CCFs) obtained by including spectral features with different sensitivity to the photospheric parameters. We use literature stellar parameters of high signal-to-noise (SNR), high-resolution HARPS spectra of FGK main-sequence stars to calibrate Teff, [Fe/H] and log g as a function of CCF parameters. Our technique is validated using low-SNR spectra obtained with the same instrument. For FGK stars we achieve a precision of σ _{{T_eff}} = 50 K, σlog g = 0.09 dex and σ _{{{[Fe/H]}}} =0.035 dex at SNR = 50, while the precision for observation with SNR ≳ 100 and the overall accuracy are constrained by the literature values used to calibrate the CCFs. Our approach can easily be extended to other instruments with similar spectral range and resolution or to other spectral range and stars other than FGK dwarfs if a large sample of reference stars is available for the calibration. Additionally, we provide the mathematical formulation to convert synthetic equivalent widths to CCF parameters as an alternative to direct calibration. We have made our tool publicly available.

  3. First Toroidal Rotation Measurements of Protons and Impurities in the TJ-II Stellarator; Primeras Medidas de Rotacion Toroidal de Protones e Impurezas en el Stellarator TJ-II

    Energy Technology Data Exchange (ETDEWEB)

    Rapisarda, D.; Zurro, B.; Baciero, A.

    2006-07-01

    First absolute toroidal rotation measurements in the TJ-II stellarator, by using passive emission spectroscopy, are presented. The wavelength calibration is performed by using a spectral system which combines the spectra coming from the plasma and from a lamp in real time. Measurements have been made both for protons and some impurity ions (C4+, He+), in discharges created by electron cyclotron resonance heating, and in discharges with neutral beam injection heating. In addition, a description of the systems as well as the calibration procedures an data analysis is addressed. (Author) 10 refs.

  4. The virtual observatory service TheoSSA: Establishing a database of synthetic stellar flux standards. I. NLTE spectral analysis of the DA-type white dwarf G191-B2B

    Science.gov (United States)

    Rauch, T.; Werner, K.; Bohlin, R.; Kruk, J. W.

    2013-12-01

    Context. Hydrogen-rich, DA-type white dwarfs are particularly suited as primary standard stars for flux calibration. State-of-the-art NLTE models consider opacities of species up to trans-iron elements and provide reliable synthetic stellar-atmosphere spectra to compare with observations. Aims: We will establish a database of theoretical spectra of stellar flux standards that are easily accessible via a web interface. Methods: In the framework of the Virtual Observatory, the German Astrophysical Virtual Observatory developed the registered service TheoSSA. It provides easy access to stellar spectral energy distributions (SEDs) and is intended to ingest SEDs calculated by any model-atmosphere code. In case of the DA white dwarf G191-B2B, we demonstrate that the model reproduces not only its overall continuum shape but also the numerous metal lines exhibited in its ultraviolet spectrum. Results: TheoSSA is in operation and contains presently a variety of SEDs for DA-type white dwarfs. It will be extended in the near future and can host SEDs of all primary and secondary flux standards. The spectral analysis of G191-B2B has shown that our hydrostatic models reproduce the observations best at and log g = 7.60 ± 0.05. We newly identified Fe vi, Ni vi, and Zn iv lines. For the first time, we determined the photospheric zinc abundance with a logarithmic mass fraction of -4.89 (7.5 × solar). The abundances of He (upper limit), C, N, O, Al, Si, O, P, S, Fe, Ni, Ge, and Sn were precisely determined. Upper abundance limits of about 10% solar were derived for Ti, Cr, Mn, and Co. Conclusions: The TheoSSA database of theoretical SEDs of stellar flux standards guarantees that the flux calibration of all astronomical data and cross-calibration between different instruments can be based on the same models and SEDs calculated with different model-atmosphere codes and are easy to compare. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope

  5. Quasisymmetry equations for conventional stellarators

    International Nuclear Information System (INIS)

    Pustovitov, V.D.

    1994-11-01

    General quasisymmetry condition, which demands the independence of B 2 on one of the angular Boozer coordinates, is reduced to two equations containing only geometrical characteristics and helical field of a stellarator. The analysis is performed for conventional stellarators with a planar circular axis using standard stellarator expansion. As a basis, the invariant quasisymmetry condition is used. The quasisymmetry equations for stellarators are obtained from this condition also in an invariant form. Simplified analogs of these equations are given for the case when averaged magnetic surfaces are circular shifted torii. It is shown that quasisymmetry condition can be satisfied, in principle, in a conventional stellarator by a proper choice of two satellite harmonics of the helical field in addition to the main harmonic. Besides, there appears a restriction on the shift of magnetic surfaces. Thus, in general, the problem is closely related with that of self-consistent description of a configuration. (author)

  6. Stellar formation

    CERN Document Server

    Reddish, V C

    1978-01-01

    Stellar Formation brings together knowledge about the formation of stars. In seeking to determine the conditions necessary for star formation, this book examines questions such as how, where, and why stars form, and at what rate and with what properties. This text also considers whether the formation of a star is an accident or an integral part of the physical properties of matter. This book consists of 13 chapters divided into two sections and begins with an overview of theories that explain star formation as well as the state of knowledge of star formation in comparison to stellar structure

  7. Optimizing Stellarators for Turbulent Transport

    International Nuclear Information System (INIS)

    Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.

    2010-01-01

    Up to now, the term 'transport-optimized' stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.

  8. Stellar Structure and Evolution

    CERN Document Server

    Kippenhahn, Rudolf; Weiss, Achim

    2013-01-01

    This long-awaited second edition of the classical textbook on Stellar Structure and Evolution by Kippenhahn and Weigert is a thoroughly revised version of the original text. Taking into account modern observational constraints as well as additional physical effects such as mass loss and diffusion, Achim Weiss and Rudolf Kippenhahn have succeeded in bringing the book up to the state-of-the-art with respect to both the presentation of stellar physics and the presentation and interpretation of current sophisticated stellar models. The well-received and proven pedagogical approach of the first edition has been retained. The book provides a comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The models developed to explain the stability, dynamics and evolution of the stars are presented and great care is taken to detail the various stages in a star’s life. Just as the first edition, which remained a standard work for more than 20 years after its...

  9. Results of Compact Stellarator Engineering Trade Studies

    International Nuclear Information System (INIS)

    Brown, Tom; Bromberg, L.; Cole, M.

    2009-01-01

    A number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study

  10. Results of Compact Stellarator Engineering Trade Studies

    International Nuclear Information System (INIS)

    Brown, T.; Bromberg, L.; Cole, M.

    2009-01-01

    A number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study.

  11. Traceability of synthetic drugs by position-specific deuterium isotope ratio analysis

    Energy Technology Data Exchange (ETDEWEB)

    Brenna, Elisabetta [Dipartimento di Chimica, Materiali e di Ingegneria Chimica del Politecnico di Milano and Istituto CNR per la Chimica del Riconoscimento Molecolare, Via Mancinelli 7, Milan I-20131 (Italy)], E-mail: elisabetta.brenna@polimi.it; Fronza, Giovanni [Dipartimento di Chimica, Materiali e di Ingegneria Chimica del Politecnico di Milano (Italy) and Instituto CNR per la Chimica del Riconoscimento Molecolare, Via Mancinelli 7, Milan I-20131 (Italy)], E-mail: giovanni.fronza@polimi.it; Fuganti, Claudio [Dipartimento di Chimica, Materiali e di Ingegneria Chimica del Politecnico di Milano (Italy) and Istituto CNR per la Chimica del Riconoscimento Molecolare, Via Mancinelli 7, Milan I-20131 (Italy)

    2007-10-10

    Samples of fluoxetine of different origin were submitted to natural abundance {sup 2}H NMR spectroscopy. The deuterium content at the various sites of the molecule was found to depend on its synthetic history. Hints on the synthetic procedure can be obtained by comparison with standard compounds, whose synthesis is known. These preliminary results give an idea of the potential of site-specific isotope ratio analysis in the fight against patent infringement and drug counterfeiting.

  12. Traceability of synthetic drugs by position-specific deuterium isotope ratio analysis

    International Nuclear Information System (INIS)

    Brenna, Elisabetta; Fronza, Giovanni; Fuganti, Claudio

    2007-01-01

    Samples of fluoxetine of different origin were submitted to natural abundance 2 H NMR spectroscopy. The deuterium content at the various sites of the molecule was found to depend on its synthetic history. Hints on the synthetic procedure can be obtained by comparison with standard compounds, whose synthesis is known. These preliminary results give an idea of the potential of site-specific isotope ratio analysis in the fight against patent infringement and drug counterfeiting

  13. Spectroscopy of a Synthetic Trapped Ion Qubit

    Science.gov (United States)

    Hucul, David; Christensen, Justin E.; Hudson, Eric R.; Campbell, Wesley C.

    2017-09-01

    133Ba+ has been identified as an attractive ion for quantum information processing due to the unique combination of its spin-1 /2 nucleus and visible wavelength electronic transitions. Using a microgram source of radioactive material, we trap and laser cool the synthetic A =133 radioisotope of barium II in a radio-frequency ion trap. Using the same, single trapped atom, we measure the isotope shifts and hyperfine structure of the 62P1 /2↔62S1 /2 and 62P1 /2↔52D3 /2 electronic transitions that are needed for laser cooling, state preparation, and state detection of the clock-state hyperfine and optical qubits. We also report the 62P1 /2↔52D3 /2 electronic transition isotope shift for the rare A =130 and 132 barium nuclides, completing the spectroscopic characterization necessary for laser cooling all long-lived barium II isotopes.

  14. Characterization of alkali silica reaction gels using Raman spectroscopy

    International Nuclear Information System (INIS)

    Balachandran, C.; Muñoz, J.F.; Arnold, T.

    2017-01-01

    The ability of Raman spectroscopy to characterize amorphous materials makes this technique ideal to study alkali silica reaction (ASR) gels. The structure of several synthetic ASR gels was thoroughly characterized using Raman Spectroscopy. The results were validated with additional techniques such as Fourier transmission infrared spectroscopy, X-ray powder diffraction and thermogravimetric analysis. The Raman spectra were found to have two broad bands in the 800 to 1200 cm −1 range and the 400 to 700 cm −1 range indicating the amorphous nature of the gel. Important information regarding the silicate polymerization was deduced from both of these spectral regions. An increase in alkali content of the gels caused a depolymerization in the silicate framework which manifested in the Raman spectra as a gradual shift of predominant peaks in both regions. The trends in silicate depolymerization were in agreement with results from a NMR spectroscopy study on similar synthetic ASR gels.

  15. Targeted Optimization of Quasi-Symmetric Stellarators

    International Nuclear Information System (INIS)

    Hegna, Chris C.; Talmadge, J. N.

    2016-01-01

    The proposed research focuses on targeted areas of plasma physics dedicated to improving the stellarator concept. Research was pursued in the technical areas of edge/divertor physics in 3D configurations, magnetic island physics in stellarators, the role of 3D shaping on microinstabilities and turbulent transport and energetic ion confinement in stellarators.

  16. Targeted Optimization of Quasi-Symmetric Stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Hegna, Chris C. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics; Anderson, D. T. [Univ. of Wisconsin, Madison, WI (United States); Talmadge, J. N. [Univ. of Wisconsin, Madison, WI (United States)

    2016-10-06

    The proposed research focuses on targeted areas of plasma physics dedicated to improving the stellarator concept. Research was pursued in the technical areas of edge/divertor physics in 3D configurations, magnetic island physics in stellarators, the role of 3D shaping on microinstabilities and turbulent transport and energetic ion confinement in stellarators.

  17. Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

    Energy Technology Data Exchange (ETDEWEB)

    Jabran Zahid, H. [Smithsonian Astrophysical Observatory, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kudritzki, Rolf-Peter; Ho, I-Ting [University of Hawaii at Manoa, Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Conroy, Charlie [Department of Astronomy, Harvard University, Cambridge, MA, 02138 (United States); Andrews, Brett, E-mail: zahid@cfa.harvard.edu [PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260 (United States)

    2017-09-20

    We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.

  18. Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

    International Nuclear Information System (INIS)

    Jabran Zahid, H.; Kudritzki, Rolf-Peter; Ho, I-Ting; Conroy, Charlie; Andrews, Brett

    2017-01-01

    We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.

  19. Application of Raman spectroscopy and surface-enhanced Raman scattering to the analysis of synthetic dyes found in ballpoint pen inks.

    Science.gov (United States)

    Geiman, Irina; Leona, Marco; Lombardi, John R

    2009-07-01

    The applicability of Raman spectroscopy and surface-enhanced Raman scattering (SERS) to the analysis of synthetic dyes commonly found in ballpoint inks was investigated in a comparative study. Spectra of 10 dyes were obtained using a dispersive system (633 nm, 785 nm lasers) and a Fourier transform system (1064 nm laser) under different analytical conditions (e.g., powdered pigments, solutions, thin layer chromatography [TLC] spots). While high fluorescence background and poor spectral quality often characterized the normal Raman spectra of the dyes studied, SERS was found to be generally helpful. Additionally, dye standards and a single ballpoint ink were developed on a TLC plate following a typical ink analysis procedure. SERS spectra were successfully collected directly from the TLC plate, thus demonstrating a possible forensic application for the technique.

  20. Recovering star formation histories: Integrated-light analyses vs. stellar colour-magnitude diagrams

    Science.gov (United States)

    Ruiz-Lara, T.; Pérez, I.; Gallart, C.; Alloin, D.; Monelli, M.; Koleva, M.; Pompei, E.; Beasley, M.; Sánchez-Blázquez, P.; Florido, E.; Aparicio, A.; Fleurence, E.; Hardy, E.; Hidalgo, S.; Raimann, D.

    2015-11-01

    Context. Accurate star formation histories (SFHs) of galaxies are fundamental for understanding the build-up of their stellar content. However, the most accurate SFHs - those obtained from colour-magnitude diagrams (CMDs) of resolved stars reaching the oldest main-sequence turnoffs (oMSTO) - are presently limited to a few systems in the Local Group. It is therefore crucial to determine the reliability and range of applicability of SFHs derived from integrated light spectroscopy, as this affects our understanding of unresolved galaxies from low to high redshift. Aims: We evaluate the reliability of current full spectral fitting techniques in deriving SFHs from integrated light spectroscopy by comparing SFHs from integrated spectra to those obtained from deep CMDs of resolved stars. Methods: We have obtained a high signal-to-noise (S/N ~ 36.3 per Å) integrated spectrum of a field in the bar of the Large Magellanic Cloud (LMC) using EFOSC2 at the 3.6-metre telescope at La Silla Observatory. For this same field, resolved stellar data reaching the oMSTO are available. We have compared the star formation rate (SFR) as a function of time and the age-metallicity relation (AMR) obtained from the integrated spectrum using STECKMAP, and the CMD using the IAC-star/MinnIAC/IAC-pop set of routines. For the sake of completeness we also use and discuss other synthesis codes (STARLIGHT and ULySS) to derive the SFR and AMR from the integrated LMC spectrum. Results: We find very good agreement (average differences ~4.1%) between the SFR (t) and the AMR obtained using STECKMAP on the integrated light spectrum, and the CMD analysis. STECKMAP minimizes the impact of the age-metallicity degeneracy and has the advantage of preferring smooth solutions to recover complex SFHs by means of a penalized χ2. We find that the use of single stellar populations (SSPs) to recover the stellar content, using for instance STARLIGHT or ULySS codes, hampers the reconstruction of the SFR (t) and AMR

  1. HST-WFC3 Near-Infrared Spectroscopy of Quenched Galaxies at zeta approx 1.5 from the WISP Survey: Stellar Populations Properties

    Science.gov (United States)

    Bedregal, A. G.; Scarlata, C.; Henry, A. L.; Atek, H.; Rafelski, M.; Teplitz, H. I.; Dominguez, A.; Siana, B.; Colbert, J. W.; Malkan, M.; hide

    2013-01-01

    We combine Hubble Space Telescope (HST) G102 and G141 near-IR (NIR) grism spectroscopy with HST/WFC3- UVIS, HST/WFC3-IR, and Spitzer/IRAC [3.6 microns] photometry to assemble a sample of massive (log(Mstar/M solar mass) at approx 11.0) and quenched (specific star formation rate spectroscopy for quenched sources at these redshifts. In contrast to the local universe, zeta approx 1.5 quenched galaxies in the high-mass range have a wide range of stellar population properties. We find that their spectral energy distributions (SEDs) are well fitted with exponentially decreasing star formation histories and short star formation timescales (tau less than or equal to 100 M/yr). Quenched galaxies also show a wide distribution in ages, between 1 and 4 G/yr. In the (u - r)0-versus-mass space quenched galaxies have a large spread in rest-frame color at a given mass. Most quenched galaxies populate the zeta appro. 1.5 red sequence (RS), but an important fraction of them (32%) have substantially bluer colors. Although with a large spread, we find that the quenched galaxies on the RS have older median ages (3.1 G/yr) than the quenched galaxies off the RS (1.5 G/yr). We also show that a rejuvenated SED cannot reproduce the observed stacked spectra of (the bluer) quenched galaxies off the RS. We derive the upper limit on the fraction of massive galaxies on the RS at zeta approx 1.5 to be 2 and the zeta approx 1.5 RS. According to their estimated ages, the time required for quenched galaxies off the RS to join their counterparts on the z approx. 1.5 RS is of the order of approx. 1G/yr.

  2. Comparisons between observational color-magnitude diagrams and synthetic cluster diagrams for young star clusters in the Magellanic Clouds

    International Nuclear Information System (INIS)

    Recker, S.A.; Brunish, W.M.; Mathews, G.J.

    1984-01-01

    Young star clusters ( 8 yr) in the Magellanic Clouds (MC) can be used to test the current status of the theory of stellar evolution as applied to intermediate and massive stars. The color-magnitude diagram of many young clusters in the MC shows large numbers of stars in both the main sequence and post main sequence evolutionary phases. Using a grid of stellar evolution models, synthetic cluster H-R diagrams are constructed and compared to observed color-magnitude diagrams to determine the age, age spread, and composition for any given cluster. In addition, for those cases where the data is of high quality, detailed comparisons between theory and observation can provide a diagnostic of the accuracy of the stellar evolution models. Initial indications of these comparisons suggest that the theoretical models should be altered to include: a larger value for the mixing length parameter, a larger rate of mass loss during the asymptotic giant branch phase, and possibly convective overshoot during the core burning phases. (Auth.)

  3. Correcting Estimates of the Occurrence Rate of Earth-like Exoplanets for Stellar Multiplicity

    Science.gov (United States)

    Cantor, Elliot; Dressing, Courtney D.; Ciardi, David R.; Christiansen, Jessie

    2018-06-01

    One of the most prominent questions in the exoplanet field has been determining the true occurrence rate of potentially habitable Earth-like planets. NASA’s Kepler mission has been instrumental in answering this question by searching for transiting exoplanets, but follow-up observations of Kepler target stars are needed to determine whether or not the surveyed Kepler targets are in multi-star systems. While many researchers have searched for companions to Kepler planet host stars, few studies have investigated the larger target sample. Regardless of physical association, the presence of nearby stellar companions biases our measurements of a system’s planetary parameters and reduces our sensitivity to small planets. Assuming that all Kepler target stars are single (as is done in many occurrence rate calculations) would overestimate our search completeness and result in an underestimate of the frequency of potentially habitable Earth-like planets. We aim to correct for this bias by characterizing the set of targets for which Kepler could have detected Earth-like planets. We are using adaptive optics (AO) imaging to reveal potential stellar companions and near-infrared spectroscopy to refine stellar parameters for a subset of the Kepler targets that are most amenable to the detection of Earth-like planets. We will then derive correction factors to correct for the biases in the larger set of target stars and determine the true frequency of systems with Earth-like planets. Due to the prevalence of stellar multiples, we expect to calculate an occurrence rate for Earth-like exoplanets that is higher than current figures.

  4. Stellar photometry and polarimetry

    International Nuclear Information System (INIS)

    Golay, M.; Serkowski, K.

    1976-01-01

    A critical review of progress made in stellar photometry and polarimetry over the period 1973-1975 is presented. Reports of photometric measurements from various observatories throughout the world are summarized. The summary of work on stellar polarimetry lists the review papers, the catalogues and lists of standard stars, and descriptions of new observing techniques. (B.R.H.)

  5. Does the stellar distribution flare? A comparison of stellar scale heights with LAB H I data

    Energy Technology Data Exchange (ETDEWEB)

    Kalberla, P. M. W.; Kerp, J.; Dedes, L. [Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn (Germany); Haud, U., E-mail: pkalberla@astro.uni-bonn.de [Tartu Observatory, 61602 Tõravere (Estonia)

    2014-10-10

    The question of whether the stellar populations in the Milky Way take part in the flaring of scale heights as observed for the H I gas is a matter of debate. Standard mass models for the Milky Way assume a constant scale height for each of the different stellar distributions. However, there is mounting evidence that at least some of the stellar distributions reach, at large galactocentric distances, high altitudes, which are incompatible with a constant scale height. We discuss recent observational evidence for stellar flaring and compare it with H I data from the Leiden/Argentine/Bonn survey. Within the systemic and statistical uncertainties we find a good agreement between both.

  6. Cannibalization and rebirth in the NGC 5387 system. I. The stellar stream and star-forming region

    Energy Technology Data Exchange (ETDEWEB)

    Beaton, Rachael L.; Majewski, Steven R.; Johnson, Kelsey E.; Verbiscer, Anne [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Martínez-Delgado, David [Max Planck Institut fur Astronomie, D-69117 Heidelberg (Germany); D' Onghia, Elena [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States); Zibetti, Stefano [INAF-Osservatorio Astrofisico di Arcetri, I-50125 Firenze (Italy); Gabany, R. Jay [Black Bird II Observatory, Alder Springs, CA 93602 (United States); Blanton, Michael, E-mail: rbeaton@virginia.edu [Department of Physics, New York University, New York, NY 10003 (United States)

    2014-08-01

    We have identified a low surface brightness stellar stream from visual inspection of Sloan Digital Sky Survey (SDSS) imaging for the edge-on, spiral galaxy NGC 5387. An optically blue overdensity coincident with the stream intersection with the NGC 5387 disk was also identified in SDSS and in the Galaxy Evolution Explorer Deep Imaging Survey contributing 38% of the total far-UV integrated flux from NGC 5387. Deeper optical imaging was acquired with the Vatican Advanced Technology Telescope that confirmed the presence of both features. The stellar stream is red in color, (B – V) = 0.7, has a stellar mass of 6 × 10{sup 8} M{sub ☉}, which implies a 1:50 merger ratio, has a circular radius, R{sub circ} ∼ 11.7 kpc, formed in ∼240 Myr, and the progenitor had a total mass of ∼4 × 10{sup 10} M{sub ☉}. Spectroscopy from LBT+MODS1 was used to determine that the blue overdensity is at the same redshift as NGC 5387, consists of young stellar populations (∼10 Myr), is metal-poor (12 + log (O/H) = 8.03), and is forming stars at an enhanced rate (∼1-3 M{sub ☉} yr{sup –1}). The most likely interpretations are that the blue overdensity is (1) a region of enhanced star formation in the outer disk of NGC 5387 induced by the minor accretion event or (2) the progenitor of the stellar stream experiencing enhanced star formation. Additional exploration of these scenarios is presented in a companion paper.

  7. Cannibalization and rebirth in the NGC 5387 system. I. The stellar stream and star-forming region

    International Nuclear Information System (INIS)

    Beaton, Rachael L.; Majewski, Steven R.; Johnson, Kelsey E.; Verbiscer, Anne; Martínez-Delgado, David; D'Onghia, Elena; Zibetti, Stefano; Gabany, R. Jay; Blanton, Michael

    2014-01-01

    We have identified a low surface brightness stellar stream from visual inspection of Sloan Digital Sky Survey (SDSS) imaging for the edge-on, spiral galaxy NGC 5387. An optically blue overdensity coincident with the stream intersection with the NGC 5387 disk was also identified in SDSS and in the Galaxy Evolution Explorer Deep Imaging Survey contributing 38% of the total far-UV integrated flux from NGC 5387. Deeper optical imaging was acquired with the Vatican Advanced Technology Telescope that confirmed the presence of both features. The stellar stream is red in color, (B – V) = 0.7, has a stellar mass of 6 × 10 8 M ☉ , which implies a 1:50 merger ratio, has a circular radius, R circ ∼ 11.7 kpc, formed in ∼240 Myr, and the progenitor had a total mass of ∼4 × 10 10 M ☉ . Spectroscopy from LBT+MODS1 was used to determine that the blue overdensity is at the same redshift as NGC 5387, consists of young stellar populations (∼10 Myr), is metal-poor (12 + log (O/H) = 8.03), and is forming stars at an enhanced rate (∼1-3 M ☉ yr –1 ). The most likely interpretations are that the blue overdensity is (1) a region of enhanced star formation in the outer disk of NGC 5387 induced by the minor accretion event or (2) the progenitor of the stellar stream experiencing enhanced star formation. Additional exploration of these scenarios is presented in a companion paper.

  8. Wisconsin torsatron/stellarator program, FY 1989

    International Nuclear Information System (INIS)

    Shohet, J.L.; Anderson, D.T.; Anderson, F.S.B.; Talmadge, J.N.

    1988-07-01

    This proposal documents recent activities within the University of Wisconsin-Madison Torsatron/Stellarator Laboratory and presents plans for future research activities for a three year period. Research efforts have focused on fundamental stellarator physics issues through experimental investigations on the Interchangeable Module Stellarator (IMS) and the Proto-Cleo Stellarator. Theoretical activities and studies of new configurations are being undertaken to support and broaden the experimental program. Experimental research at the Torsatron Stellarator Laboratory has been primarily concerned with effects induced through electron-cyclotron resonant frequency plasma production and heating in the IMS device. Plasma electric fields have been shown to play a major role in particle transport and confinement in IMS. ECRF heating at 6 kG has produced electron tail populations in agreement with Monte-Carlo models. Electric and magnetic fields have been shown to alter the particle flows to the IMS modular divertors. 48 refs

  9. Introduction to stellar astrophysics. V. 1

    International Nuclear Information System (INIS)

    Boehm-Vitense, E.

    1989-01-01

    This textbook introduces basic elements of fundamental astronomy and astrophysics which serve as a foundation for understanding the structure, evolution, and observed properties of stars. The first half of the book explains how stellar motions, distances, luminosities, colours, radii, masses and temperatures are measured or derived. The author then shows how data of these sorts can be arranged to classify stars through their spectra. Stellar rotation and stellar magnetic fields are introduced. Stars with peculiar spectra and pulsating stars also merit special attention. The endpoints of stellar evolutions are briefly described. There is a separate chapter on the Sun and a final one on interstellar absorption. (author)

  10. The influence of galaxy environment on the stellar initial mass function of early-type galaxies

    Science.gov (United States)

    Rosani, Giulio; Pasquali, Anna; La Barbera, Francesco; Ferreras, Ignacio; Vazdekis, Alexandre

    2018-06-01

    In this paper, we investigate whether the stellar initial mass function (IMF) of early-type galaxies depends on their host environment. To this purpose, we have selected a sample of early-type galaxies from the SPIDER catalogue, characterized their environment through the group catalogue of Wang et al., and used their optical Sloan Digital Sky Survey (SDSS) spectra to constrain the IMF slope, through the analysis of IMF-sensitive spectral indices. To reach a high enough signal-to-noise ratio, we have stacked spectra in velocity dispersion (σ0) bins, on top of separating the sample by galaxy hierarchy and host halo mass, as proxies for galaxy environment. In order to constrain the IMF, we have compared observed line strengths and predictions of MIUSCAT/EMILES synthetic stellar population models, with varying age, metallicity, and `bimodal' (low-mass tapered) IMF slope (Γ _b). Consistent with previous studies, we find that Γ _b increases with σ0, becoming bottom-heavy (i.e. an excess of low-mass stars with respect to the Milky Way like IMF) at high σ0. We find that this result is robust against the set of isochrones used in the stellar population models, as well as the way the effect of elemental abundance ratios is taken into account. We thus conclude that it is possible to use currently state-of-the-art stellar population models and intermediate resolution spectra to consistently probe IMF variations. For the first time, we show that there is no dependence of Γb on environment or galaxy hierarchy, as measured within the 3 arcsec SDSS fibre, thus leaving the IMF as an intrinsic galaxy property, possibly set already at high redshift.

  11. Progress Toward Attractive Stellarators

    International Nuclear Information System (INIS)

    Neilson, G.H.; Bromberg, L.; Brown, T.G.; Gates, D.A.; Ku, L.P.; Zarnstorff, M.C.; Boozer, A.H.; Harris, J.H.; Meneghini, O.; Mynick, H.E.; Pomphrey, N.; Reiman, A.H.; Xanthopoulos, P.

    2011-01-01

    The quasi-axisymmetric stellarator (QAS) concept offers a promising path to a more compact stellarator reactor, closer in linear dimensions to tokamak reactors than previous stellarator designs. Concept improvements are needed, however, to make it more maintainable and more compatible with high plant availability. Using the ARIES-CS design as a starting point, compact stellarator designs with improved maintenance characteristics have been developed. While the ARIES-CS features a through-the-port maintenance scheme, we have investigated configuration changes to enable a sector-maintenance approach, as envisioned for example in ARIES AT. Three approaches are reported. The first is to make tradeoffs within the QAS design space, giving greater emphasis to maintainability criteria. The second approach is to improve the optimization tools to more accurately and efficiently target the physics properties of importance. The third is to employ a hybrid coil topology, so that the plasma shaping functions of the main coils are shared more optimally, either with passive conductors made of high-temperature superconductor or with local compensation coils, allowing the main coils to become simpler. Optimization tools are being improved to test these approaches.

  12. Stellar magnetic activity and exoplanets

    Directory of Open Access Journals (Sweden)

    Vidotto A.A.

    2017-01-01

    Full Text Available It has been proposed that magnetic activity could be enhanced due to interactions between close-in massive planets and their host stars. In this article, I present a brief overview of the connection between stellar magnetic activity and exoplanets. Stellar activity can be probed in chromospheric lines, coronal emission, surface spot coverage, etc. Since these are manifestations of stellar magnetism, these measurements are often used as proxies for the magnetic field of stars. Here, instead of focusing on the magnetic proxies, I overview some recent results of magnetic field measurements using spectropolarimetric observations. Firstly, I discuss the general trends found between large-scale magnetism, stellar rotation, and coronal emission and show that magnetism seems to be correlated to the internal structure of the star. Secondly, I overview some works that show evidence that exoplanets could (or not act as to enhance the activity of their host stars.

  13. Transport in stellarators

    International Nuclear Information System (INIS)

    Maassberg, H.; Brakel, R.; Burhenn, R.; Gasparino, U.; Grigull, P.; Kick, M.; Kuehner, G.; Ringler, H.; Sardei, F.; Stroth, U.; Weller, A.

    1993-01-01

    The local electron and ion heat transport as well as the particle and impurity transport properties in stellarators are reviewed. In this context, neoclassical theory is used as a guideline for the comparison of the experimental results of the quite different confinement concepts. At sufficiently high temperatures depending on the specific magnetic configuration, neoclassical predictions are confirmed by experimental findings. The confinement properties in the LMFP collisionality regime are discussed with respect to the next stellarator generation, for which at higher temperatures the neoclassical transport is expected to become more important. (orig.)

  14. Stellar oscillations in planet-hosting giant stars

    Energy Technology Data Exchange (ETDEWEB)

    Hatzes, Artie P; Zechmeister, Mathias [Thueringer Landessternwarte, Sternwarte 5, D-07778 (Germany)], E-mail: artie@tls-tautenburg.de

    2008-10-15

    Recently a number of giant extrasolar planets have been discovered around giant stars. These discoveries are important because many of these giant stars have intermediate masses in the range 1.2-3 Msun. Early-type main sequence stars of this mass range have been avoided by radial velocity planet search surveys due the difficulty of getting the requisite radial velocity precision needed for planet discoveries. Thus, giant stars can tell us about planet formation for stars more massive than the sun. However, the determination of stellar masses for giant stars is difficult due to the fact that evolutionary tracks for stars covering a wide range of masses converge to the same region of the H-R diagram. We report here on stellar oscillations in three planet-hosting giant stars: HD 13189, {beta} Gem, and {iota} Dra. Precise stellar radial velocity measurements for these stars show variations whose periods and amplitudes are consistent with solar-like p-mode oscillations. The implied stellar masses for these objects based on the characteristics of the stellar oscillations are consistent with the predictions of stellar isochrones. An investigation of stellar oscillations in planet hosting giant stars offers us the possibility of getting an independent determination of the stellar mass for these objects which is of crucial importance for extrasolar planet studies.

  15. Astrospheres and Solar-like Stellar Winds

    Directory of Open Access Journals (Sweden)

    Wood Brian E.

    2004-07-01

    Full Text Available Stellar analogs for the solar wind have proven to be frustratingly difficult to detect directly. However, these stellar winds can be studied indirectly by observing the interaction regions carved out by the collisions between these winds and the interstellar medium (ISM. These interaction regions are called "astrospheres", analogous to the "heliosphere" surrounding the Sun. The heliosphere and astrospheres contain a population of hydrogen heated by charge exchange processes that can produce enough H I Ly alpha absorption to be detectable in UV spectra of nearby stars from the Hubble Space Telescope (HST. The amount of astrospheric absorption is a diagnostic for the strength of the stellar wind, so these observations have provided the first measurements of solar-like stellar winds. Results from these stellar wind studies and their implications for our understanding of the solar wind are reviewed here. Of particular interest are results concerning the past history of the solar wind and its impact on planetary atmospheres.

  16. Enhanced-confinement class of stellarators

    International Nuclear Information System (INIS)

    Mynick, H.E.; Chu, T.K.; Boozer, A.H.

    1981-08-01

    A class of stellarators has been found in which the transport is reduced by an order of magnitude from transport in conventional stellarators, by localizing the helical ripple to the inside of the torus. The reduction is observed in numerical experiments and explained theoretically

  17. Introduction to stellar structure

    CERN Document Server

    Maciel, Walter J

    2016-01-01

    In the first part of this book, the author presents the basic properties of the stellar interior and describes them thoroughly, along with deriving the main stellar structure equations of temperature, density, pressure and luminosity, among others. The process and application of solving these equations is explained, as well as linking these results with actual observations.  The second part of the text describes what happens to a star over time, and how to determine this by solving the same equations at different points during a star’s lifetime. The fate of various stars is quite different depending on their masses, and this is described in the final parts of the book. This text can be used for an upper level undergraduate course or an introductory graduate course on stellar physics.

  18. Near-term directions in the World Stellarator Program

    International Nuclear Information System (INIS)

    Lyon, J.F.

    1990-01-01

    Interest in stellarators has increased because of the progress being made in the development of this concept and the inherent advantages of stellarators as candidates for an attractive, steady-state fusion reactor. Three new stellarator experiments started operation in 1988, and three more are scheduled to start in the next few years. In addition, design studies have started on large next-generation stellarator experiments for the mid-1990s. These devices are designed to test four basic approaches to stellarator configuration optimization. Ways in which these devices complement each other in exploring the potential of the stellarator concept and the main issues that they will address during the next decade are described

  19. The Resolved Stellar Populations Early Release Science Program

    Science.gov (United States)

    Gilbert, Karoline; Weisz, Daniel; Resolved Stellar Populations ERS Program Team

    2018-06-01

    The Resolved Stellar Populations Early Release Science Program (PI D. Weisz) will observe Local Group targets covering a range of stellar density and star formation histories, including a globular cluster, and ultra-faint dwarf galaxy, and a star-forming dwarf galaxy. Using observations of these diverse targets we will explore a broad science program: we will measure star formation histories, the sub-solar stellar initial mass function, and proper motions, perform studies of evolved stars, and map extinction in the target fields. Our observations will be of high archival value for other science such as calibrating stellar evolution models, studying variable stars, and searching for metal-poor stars. We will determine optimal observational setups and develop data reduction techniques that will be common to JWST studies of resolved stellar populations. We will also design, test, and release point spread function (PSF) fitting software specific to NIRCam and NIRISS, required for the crowded stellar regime. Prior to the Cycle 2 Call for Proposals, we will release PSF fitting software, matched HST and JWST catalogs, and clear documentation and step-by-step tutorials (such as Jupyter notebooks) for reducing crowded stellar field data and producing resolved stellar photometry catalogs, as well as for specific resolved stellar photometry science applications.

  20. First Toroidal Rotation Measurements of Protons and Impurities in the TJ-II Stellarator

    International Nuclear Information System (INIS)

    Rapisarda, D.; Zurro, B.; Baciero, A.

    2006-01-01

    First absolute toroidal rotation measurements in the TJ-II stellarator, by using passive emission spectroscopy, are presented. The wavelength calibration is performed by using a spectral system which combines the spectra coming from the plasma and from a lamp in real time. Measurements have been made both for protons and some impurity ions (C4+, He+), in discharges created by electron cyclotron resonance heating, and in discharges with neutral beam injection heating. In addition, a description of the systems as well as the calibration procedures an data analysis is addressed. (Author) 10 refs

  1. Turbulence optimisation in stellarator experiments

    Energy Technology Data Exchange (ETDEWEB)

    Proll, Josefine H.E. [Max-Planck/Princeton Center for Plasma Physics (Germany); Max-Planck-Institut fuer Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald (Germany); Faber, Benjamin J. [HSX Plasma Laboratory, University of Wisconsin-Madison, Madison, WI 53706 (United States); Helander, Per; Xanthopoulos, Pavlos [Max-Planck/Princeton Center for Plasma Physics (Germany); Lazerson, Samuel A.; Mynick, Harry E. [Plasma Physics Laboratory, Princeton University, P.O. Box 451 Princeton, New Jersey 08543-0451 (United States)

    2015-05-01

    Stellarators, the twisted siblings of the axisymmetric fusion experiments called tokamaks, have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of stellarators in which the laminar transport is reduced to levels below that of tokamaks by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. Recent analytical theory suggests that the large configuration space of stellarators allows for an additional optimisation of the magnetic field to also reduce the turbulent transport. In this talk, the idea behind the turbulence optimisation is explained. We also present how an optimised equilibrium is obtained and how it might differ from the equilibrium field of an already existing device, and we compare experimental turbulence measurements in different configurations of the HSX stellarator in order to test the optimisation procedure.

  2. SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

    International Nuclear Information System (INIS)

    Daemgen, Sebastian; Bonavita, Mariangela; Jayawardhana, Ray; Lafrenière, David; Janson, Markus

    2015-01-01

    We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at ∼3 M ☉ and low-mass stars at ∼0.2 M ☉ . We detected 74 companion candidates, 34 of these reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as ∼2 M Jup . The inferred multiplicity frequency within our sensitivity limits between ∼10-1500 AU is 26.3 −4.9 +6.6 %. Applying a completeness correction, 62% ± 14% of all Taurus stars between 0.7 and 1.4 M ☉ appear to be multiple. Higher order multiples were found in 1.8 −1.5 +4.2 % of the cases, in agreement with previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5%-8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low-mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of ∼2 Myr and ∼20 Myr, respectively

  3. SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

    Energy Technology Data Exchange (ETDEWEB)

    Daemgen, Sebastian [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5H 3H4 (Canada); Bonavita, Mariangela [The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Jayawardhana, Ray [Physics and Astronomy, York University, Toronto, Ontario L3T 3R1 (Canada); Lafrenière, David [Department of Physics, University of Montréal, Montréal, QC (Canada); Janson, Markus, E-mail: daemgen@astro.utoronto.ca [Department of Astronomy, Stockholm University, Stockholm (Sweden)

    2015-02-01

    We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at ∼3 M {sub ☉} and low-mass stars at ∼0.2 M {sub ☉}. We detected 74 companion candidates, 34 of these reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as ∼2 M {sub Jup}. The inferred multiplicity frequency within our sensitivity limits between ∼10-1500 AU is 26.3{sub −4.9}{sup +6.6}%. Applying a completeness correction, 62% ± 14% of all Taurus stars between 0.7 and 1.4 M {sub ☉} appear to be multiple. Higher order multiples were found in 1.8{sub −1.5}{sup +4.2}% of the cases, in agreement with previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5%-8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low-mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of ∼2 Myr and ∼20 Myr, respectively.

  4. The Stellar Initial Mass Function in Early-type Galaxies from Absorption Line Spectroscopy. I. Data and Empirical Trends

    Science.gov (United States)

    van Dokkum, Pieter G.; Conroy, Charlie

    2012-11-01

    The strength of gravity-sensitive absorption lines in the integrated light of old stellar populations is one of the few direct probes of the stellar initial mass function (IMF) outside of the Milky Way. Owing to the advent of fully depleted CCDs with little or no fringing it has recently become possible to obtain accurate measurements of these features. Here, we present spectra covering the wavelength ranges 0.35-0.55 μm and 0.72-1.03 μm for the bulge of M31 and 34 early-type galaxies from the SAURON sample, obtained with the Low Resolution Imaging Spectrometer on Keck. The signal-to-noise ratio is >~ 200 Å-1 out to 1 μm, which is sufficient to measure gravity-sensitive features for individual galaxies and to determine how they depend on other properties of the galaxies. Combining the new data with previously obtained spectra for globular clusters in M31 and the most massive elliptical galaxies in the Virgo cluster, we find that the dwarf-sensitive Na I λ8183, 8195 doublet and the FeH λ9916 Wing-Ford band increase systematically with velocity dispersion, while the giant-sensitive Ca II λ8498, 8542, 8662 triplet decreases with dispersion. These trends are consistent with a varying IMF, such that galaxies with deeper potential wells have more dwarf-enriched mass functions. In a companion paper, we use a comprehensive stellar population synthesis model to demonstrate that IMF effects can be separated from age and abundance variations and quantify the IMF variation among early-type galaxies.

  5. THE STELLAR INITIAL MASS FUNCTION IN EARLY-TYPE GALAXIES FROM ABSORPTION LINE SPECTROSCOPY. I. DATA AND EMPIRICAL TRENDS

    International Nuclear Information System (INIS)

    Van Dokkum, Pieter G.; Conroy, Charlie

    2012-01-01

    The strength of gravity-sensitive absorption lines in the integrated light of old stellar populations is one of the few direct probes of the stellar initial mass function (IMF) outside of the Milky Way. Owing to the advent of fully depleted CCDs with little or no fringing it has recently become possible to obtain accurate measurements of these features. Here, we present spectra covering the wavelength ranges 0.35-0.55 μm and 0.72-1.03 μm for the bulge of M31 and 34 early-type galaxies from the SAURON sample, obtained with the Low Resolution Imaging Spectrometer on Keck. The signal-to-noise ratio is ∼> 200 Å –1 out to 1 μm, which is sufficient to measure gravity-sensitive features for individual galaxies and to determine how they depend on other properties of the galaxies. Combining the new data with previously obtained spectra for globular clusters in M31 and the most massive elliptical galaxies in the Virgo cluster, we find that the dwarf-sensitive Na I λ8183, 8195 doublet and the FeH λ9916 Wing-Ford band increase systematically with velocity dispersion, while the giant-sensitive Ca II λ8498, 8542, 8662 triplet decreases with dispersion. These trends are consistent with a varying IMF, such that galaxies with deeper potential wells have more dwarf-enriched mass functions. In a companion paper, we use a comprehensive stellar population synthesis model to demonstrate that IMF effects can be separated from age and abundance variations and quantify the IMF variation among early-type galaxies.

  6. A catalog of stellar spectrophotometry

    Science.gov (United States)

    Adelman, S. J.; Pyper, D. M.; Shore, S. N.; White, R. E.; Warren, W. H., Jr.

    1989-01-01

    A machine-readable catalog of stellar spectrophotometric measurements made with rotating grating scanner is introduced. Consideration is given to the processes by which the stellar data were collected and calibrated with the fluxes of Vega (Hayes and Latham, 1975). A sample page from the spectrophotometric catalog is presented.

  7. The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys

    Science.gov (United States)

    Sarbadhicary, Sumit; Badenes, Carles; Chomiuk, Laura; Maldonado, Jessica; Caprioli, Damiano; Heger, Mairead; Huizenga, Daniel

    2018-01-01

    Our understanding of the progenitors of many stellar species, such as supernovae, massive and low-mass He-burning stars, is limited because of many poorly constrained aspects of stellar evolution theory. For my dissertation, I have focused on using Local Group galaxy surveys to constrain stellar evolution scenarios by measuring delay-time distributions (DTD). The DTD is the hypothetical occurrence rate of a stellar object per elapsed time after a brief burst of star formation. It is the measured distribution of timescales on which stars evolve, and therefore serves as a powerful observational constraint on theoretical progenitor models. The DTD can be measured from a survey of stellar objects and a set of star-formation histories of the host galaxy, and is particularly effective in the Local Group, where high-quality star-formation histories are available from resolved stellar populations. I am currently calculating a SN DTD with supernova remnants (SNRs) in order to provide the strongest constraints on the progenitors of thermonuclear and core-collapse supernovae. However, most SNRs do not have reliable age measurements and their evolution depends on the ambient environment. For this reason, I wrote a radio light curve model of an SNR population to extract the visibility times and rates of supernovae - crucial ingredients for the DTD - from an SNR survey. The model uses observational constraints on the local environments from multi-wavelength surveys, accounts for missing SNRs and employs the latest models of shock-driven particle acceleration. The final calculation of the SN DTD in the Local Group is awaiting completion of a systematic SNR catalog from deep radio-continuum images, now in preparation by a group led by Dr. Laura Chomiuk. I have also calculated DTDs for the LMC population of RR Lyrae and Cepheid variables, which serve as important distance calibrators and stellar population tracers. We find that Cepheids can have delay-times between 10 Myrs - 1 Gyr

  8. Recent advances in non-LTE stellar atmosphere models

    Science.gov (United States)

    Sander, Andreas A. C.

    2017-11-01

    In the last decades, stellar atmosphere models have become a key tool in understanding massive stars. Applied for spectroscopic analysis, these models provide quantitative information on stellar wind properties as well as fundamental stellar parameters. The intricate non-LTE conditions in stellar winds dictate the development of adequate sophisticated model atmosphere codes. The increase in both, the computational power and our understanding of physical processes in stellar atmospheres, led to an increasing complexity in the models. As a result, codes emerged that can tackle a wide range of stellar and wind parameters. After a brief address of the fundamentals of stellar atmosphere modeling, the current stage of clumped and line-blanketed model atmospheres will be discussed. Finally, the path for the next generation of stellar atmosphere models will be outlined. Apart from discussing multi-dimensional approaches, I will emphasize on the coupling of hydrodynamics with a sophisticated treatment of the radiative transfer. This next generation of models will be able to predict wind parameters from first principles, which could open new doors for our understanding of the various facets of massive star physics, evolution, and death.

  9. No Evidence for Multiple Stellar Populations in the Low-mass Galactic Globular Cluster E 3

    Science.gov (United States)

    Salinas, Ricardo; Strader, Jay

    2015-08-01

    Multiple stellar populations are a widespread phenomenon among Galactic globular clusters. Even though the origin of the enriched material from which new generations of stars are produced remains unclear, it is likely that self-enrichment will be feasible only in clusters massive enough to retain this enriched material. We searched for multiple populations in the low mass (M˜ 1.4× {10}4 {M}⊙ ) globular cluster E3, analyzing SOAR/Goodman multi-object spectroscopy centered on the blue cyanogen (CN) absorption features of 23 red giant branch stars. We find that the CN abundance does not present the typical bimodal behavior seen in clusters hosting multistellar populations, but rather a unimodal distribution that indicates the presence of a genuine single stellar population, or a level of enrichment much lower than in clusters that show evidence for two populations from high-resolution spectroscopy. E3 would be the first bona fide Galactic old globular cluster where no sign of self-enrichment is found. Based on observations obtained at the Southern Astrophysical Research (SOAR) Telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the US National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  10. TWO-DIMENSIONAL MAPPING OF YOUNG STARS IN THE INNER 180 pc OF NGC 1068: CORRELATION WITH MOLECULAR GAS RING AND STELLAR KINEMATICS

    Energy Technology Data Exchange (ETDEWEB)

    Storchi-Bergmann, Thaisa; Riffel, Rogerio; Vale, Tiberio Borges [Departamento de Astronomia, Universidade Federal do Rio Grande do Sul, IF, CP 15051, 91501-970 Porto Alegre, RS (Brazil); Riffel, Rogemar A.; Diniz, Marlon R. [Departamento de Fisica, Centro de Ciencias Naturais e Exatas, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS (Brazil); McGregor, Peter J., E-mail: thaisa@ufrgs.br [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia)

    2012-08-20

    We report the first two-dimensional mapping of the stellar population and non-stellar continua within the inner 180 pc (radius) of NGC 1068 at a spatial resolution of 8 pc, using integral field spectroscopy in the near-infrared. We have applied the technique of spectral synthesis to data obtained with the instrument NIFS and the adaptive optics module ALTAIR at the Gemini North Telescope. Two episodes of recent star formation are found to dominate the stellar population contribution: the first occurred 300 Myr ago, extending over most of the nuclear region; the second occurred just 30 Myr ago, in a ring-like structure at Almost-Equal-To 100 pc from the nucleus, where it is coincident with an expanding ring of H{sub 2} emission. Inside the ring, where a decrease in the stellar velocity dispersion is observed, the stellar population is dominated by the 300 Myr age component. In the inner 35 pc, the oldest age component (age {>=} 2 Gyr) dominates the mass, while the flux is dominated by blackbody components with temperatures in the range 700 K {<=} T {<=} 800 K which we attribute to the dusty torus. We also find some contribution from blackbody and power-law components beyond the nucleus which we attribute to dust emission and scattered light.

  11. Engineering aspects of compact stellarators

    International Nuclear Information System (INIS)

    Nelson, B.E.; Benson, R.D.; Brooks, A.

    2003-01-01

    Compact stellarators could combine the good confinement and high beta of a tokamak with the inherently steady state, disruption-free characteristics of a stellarator. Two U.S. compact stellarator facilities are now in the conceptual design phase: the National Compact Stellarator Experiment (NCSX) and the Quasi- Poloidal Stellarator (QPS). NCSX has a major radius of 1.4 m and a toroidal field up to 2 T. The primary feature of both NCSX and QPS is the set of modular coils that provide the basic magnetic configuration. These coils represent a major engineering challenge due to the complex shape, precise geometric accuracy, and high current density of the windings. The winding geometry is too complex for conventional hollow copper conductor construction. Instead, the modular coils will be wound with flexible, multi strand cable conductor that has been compacted to a 75% copper packing fraction. Inside the NCSX coil set and surrounding the plasma is a highly contoured vacuum vessel. The vessel consists of three identical, 120 deg. segments that are bolted together at double sealed joints. The QPS device has a major radius of 0.9 m, a toroidal field of 1 T, and an aspect ratio of only 2.7. Instead of an internal vacuum vessel, the QPS modular coils will operate in an external vacuum tank. (author)

  12. The Stellar Imager (SI) Project: Resolving Stellar Surfaces, Interiors, and Magnetic Activity

    Science.gov (United States)

    Carpenter, Kenneth G.; Schrijver, K.; Karovska, M.

    2007-01-01

    The Stellar Imager (SI) is a UV/Optical. Space-Based Interferometer designed to enable 0.1 milli-arcsec (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. The science of SI focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. Its prime goal is to enable long-term forecasting of solar activity and the space weather that it drives. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we discuss the science goals, technology needs, and baseline design of the SI mission.

  13. ChromaStarPy: A Stellar Atmosphere and Spectrum Modeling and Visualization Lab in Python

    Science.gov (United States)

    Short, C. Ian; Bayer, Jason H. T.; Burns, Lindsey M.

    2018-02-01

    We announce ChromaStarPy, an integrated general stellar atmospheric modeling and spectrum synthesis code written entirely in python V. 3. ChromaStarPy is a direct port of the ChromaStarServer (CSServ) Java modeling code described in earlier papers in this series, and many of the associated JavaScript (JS) post-processing procedures have been ported and incorporated into CSPy so that students have access to ready-made data products. A python integrated development environment (IDE) allows a student in a more advanced course to experiment with the code and to graphically visualize intermediate and final results, ad hoc, as they are running it. CSPy allows students and researchers to compare modeled to observed spectra in the same IDE in which they are processing observational data, while having complete control over the stellar parameters affecting the synthetic spectra. We also take the opportunity to describe improvements that have been made to the related codes, ChromaStar (CS), CSServ, and ChromaStarDB (CSDB), that, where relevant, have also been incorporated into CSPy. The application may be found at the home page of the OpenStars project: http://www.ap.smu.ca/OpenStars/.

  14. AN ORBIT FIT FOR THE GRILLMAIR DIONATOS COLD STELLAR STREAM

    International Nuclear Information System (INIS)

    Willett, Benjamin A.; Newberg, Heidi Jo; Zhang Haotong; Yanny, Brian; Beers, Timothy C.

    2009-01-01

    We use velocity and metallicity information from Sloan Digital Sky Survey and Sloan Extension for Galactic Understanding and Exploration stellar spectroscopy to fit an orbit to the narrow 63 deg. stellar stream of Grillmair and Dionatos. The stars in the stream have a retrograde orbit with eccentricity e = 0.33 (perigalacticon of 14.4 kpc and apogalacticon of 28.7 kpc) and inclination approximately i ∼ 35 deg. In the region of the orbit which is detected, it has a distance of about 7-11 kpc from the Sun. Assuming a standard disk plus bulge and logarithmic halo potential for the Milky Way stars plus dark matter, the stream stars are moving with a large space velocity of approximately 276 km s -1 at perigalacticon. Using this stream alone, we are unable to determine if the dark matter halo is oblate or prolate. The metallicity of the stream is [Fe/H] = -2.1 ± 0.1. Observed proper motions for individual stream members above the main sequence turnoff are consistent with the derived orbit. None of the known globular clusters in the Milky Way have positions, radial velocities, and metallicities that are consistent with being the progenitor of the GD-1 stream.

  15. An Orbit Fit for the Grillmair Dionatos Cold Stellar Stream

    Energy Technology Data Exchange (ETDEWEB)

    Willett, Benjamin A.; Newberg, Heidi Jo; Zhang, Haotong; Yanny, Brian; Beers, Timothy C.

    2009-01-01

    We use velocity and metallicity information from Sloan Digital Sky Survey and Sloan Extension for Galactic Understanding and Exploration stellar spectroscopy to fit an orbit to the narrow 63{sup o} stellar stream of Grillmair and Dionatos. The stars in the stream have a retrograde orbit with eccentricity e = 0.33 (perigalacticon of 14.4 kpc and apogalacticon of 28.7 kpc) and inclination approximately i {approx} 35{sup o}. In the region of the orbit which is detected, it has a distance of about 7-11 kpc from the Sun. Assuming a standard disk plus bulge and logarithmic halo potential for the Milky Way stars plus dark matter, the stream stars are moving with a large space velocity of approximately 276 km s{sup -1} at perigalacticon. Using this stream alone, we are unable to determine if the dark matter halo is oblate or prolate. The metallicity of the stream is [Fe/H] = -2.1 {+-} 0.1. Observed proper motions for individual stream members above the main sequence turnoff are consistent with the derived orbit. None of the known globular clusters in the Milky Way have positions, radial velocities, and metallicities that are consistent with being the progenitor of the GD-1 stream.

  16. The dwarfs beyond: The stellar-to-halo mass relation for a new sample of intermediate redshift low-mass galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Miller, Sarah H.; Ellis, Richard S.; Newman, Andrew B. [California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125 (United States); Benson, Andrew, E-mail: smiller@astro.caltech.edu [Carnegie Observatories, 813 Santa Barbara St, Pasadena, CA 91101 (United States)

    2014-02-20

    A number of recent challenges to the standard ΛCDM paradigm relate to discrepancies that arise in comparing the abundance and kinematics of local dwarf galaxies with the predictions of numerical simulations. Such arguments rely heavily on the assumption that the Local Volume's dwarf and satellite galaxies form a representative distribution in terms of their stellar-to-halo mass ratios. To address this question, we present new, deep spectroscopy using DEIMOS on Keck for 82 low-mass (10{sup 7}-10{sup 9} M {sub ☉}), star-forming galaxies at intermediate redshift (0.2 < z < 1). For 50% of these we are able to determine resolved rotation curves using nebular emission lines and thereby construct the stellar mass Tully-Fisher relation to masses as low as 10{sup 7} M {sub ☉}. Using scaling relations determined from weak lensing data, we convert this to a stellar-to-halo mass relation for comparison with abundance matching predictions. We find a discrepancy between our observations and the predictions from abundance matching in the sense that we observe 3-12 times more stellar mass at a given halo mass. We suggest possible reasons for this discrepancy, as well as improved tests for the future.

  17. Evaluation of synthetic linear motor-molecule actuation energetics

    OpenAIRE

    Brough, Branden; Northrop, Brian H.; Schmidt, Jacob J.; Tseng, Hsian-Rong; Houk, Kendall N.; Stoddart, J. Fraser; Ho, Chih-Ming

    2006-01-01

    By applying atomic force microscope (AFM)-based force spectroscopy together with computational modeling in the form of molecular force-field simulations, we have determined quantitatively the actuation energetics of a synthetic motor-molecule. This multidisciplinary approach was performed on specifically designed, bistable, redox-controllable [2]rotaxanes to probe the steric and electrostatic interactions that dictate their mechanical switching at the single-molecule level. The fusion of expe...

  18. Synthetic Stromgren photometry for F dwarf stars

    Science.gov (United States)

    Bell, R. A.

    1988-01-01

    Recent synthetic spectrum and color calculations for cool dwarf star models are tested by comparison with observation. The accuracy of the computed dependence of the thermal colors B-V and b-y on effective temperature is examined, and H-beta indices are presented and compared with observed values. The accuracy of the predictions of the Stromgren uvby system metal-abundance indicator m1 and luminosity indicator c1 are tested. A new calibration of the c1, b-y diagram in terms of absolute magnitudes is given, making use of recent calculations of stellar isochrones. Observations of very metal-poor subdwarfs are used to study the accuracy of the isochrones. The c1, b-y diagram of the subdwarfs is compared with that of the turnoff-region stars in the very metal-poor globular cluster NGC 6397.

  19. Estimating precise metallicity and stellar mass evolution of galaxies

    Science.gov (United States)

    Mosby, Gregory

    2018-01-01

    The evolution of galaxies can be conveniently broken down into the evolution of their contents. The changing dust, gas, and stellar content in addition to the changing dark matter potential and periodic feedback from a super-massive blackhole are some of the key ingredients. We focus on the stellar content that can be observed, as the stars reflect information about the galaxy when they were formed. We approximate the stellar content and star formation histories of unresolved galaxies using stellar population modeling. Though simplistic, this approach allows us to reconstruct the star formation histories of galaxies that can be used to test models of galaxy formation and evolution. These models, however, suffer from degeneracies at large lookback times (t > 1 Gyr) as red, low luminosity stars begin to dominate a galaxy’s spectrum. Additionally, degeneracies between stellar populations at different ages and metallicities often make stellar population modeling less precise. The machine learning technique diffusion k-means has been shown to increase the precision in stellar population modeling using a mono-metallicity basis set. However, as galaxies evolve, we expect the metallicity of stellar populations to vary. We use diffusion k-means to generate a multi-metallicity basis set to estimate the stellar mass and chemical evolution of unresolved galaxies. Two basis sets are formed from the Bruzual & Charlot 2003 and MILES stellar population models. We then compare the accuracy and precision of these models in recovering complete (stellar mass and metallicity) histories of mock data. Similarities in the groupings of stellar population spectra in the diffusion maps for each metallicity hint at fundamental age transitions common to both basis sets that can be used to identify stellar populations in a given age range.

  20. Kepler Stellar Properties Catalog Update for Q1-Q17 DR25 Transit Search

    Science.gov (United States)

    Mathur, Savita; Huber, Daniel

    2016-01-01

    Huber et al. (2014) presented revised stellar properties for 196,468 Kepler targets, which were used for the Q1-Q16 TPSDV planet search (Tenenbaum et al. 2014). The catalog was based on atmospheric properties (i.e., temperature (Teff), surface gravity (log(g)), and metallicity ([FeH])) published in the literature using a variety of methods (e.g., asteroseismology, spectroscopy, exoplanet transits, photometry), which were then homogeneously fitted to a grid of Dartmouth (DSEP) isochrones (Dotter et al. 2008). The catalog was updated in early 2015 for the Q1-Q17 Data Release (DR) 24 transit search (Seader et al. 2015) based on the latest classifications of Kepler targets in the literature at that time. The methodology followed Huber et al. (2014). Here we provide updated stellar properties of 197,096 Kepler targets. Like the previous catalog, this update is based on atmospheric properties that were either published in the literature or provided by the Kepler community follow-up program (CFOP). The input values again come from different methods: asteroseismology, spectroscopy, flicker, and photometry. This catalog update was developed to support the SOC 9.3 TPSDV planet search (Twicken et al. 2016), which is expected to be the final search and data release by the Kepler project.In this document, we describe the method and the inputs that were used to build the catalog. The methodology follows Huber et al. (2014) with a few improvements as described in Section 2.

  1. Stellar winds

    International Nuclear Information System (INIS)

    Weymann, R.J.

    1978-01-01

    It is known that a steady outflow of material at comparable rates of mass loss but vastly different speeds is now known to be ubiquitous phenomenon among both the luminous hot stars and the luminous but cool red giants. The flows are probably massive enough in both cases to give rise to significant effects on stellar evolution and the mass balance between stars and the interstellar medium. The possible mechanisms for these phenomena as well as the methods of observation used are described. In particular, the mass-loss processes in stars other than the sun that also involve a steady flow of matter are considered. The evidence for their existence is described, and then the question of whether the process thought to produce the solar wind is also responsible for producing these stellar winds is explored

  2. Two-fluid limits on stellarator performance: Explanation of three stellarator puzzles and comparison to axisymmetric plasmas

    International Nuclear Information System (INIS)

    Sugiyama, L.E.; Strauss, H.R.; Park, W.; Fu, G.Y.; Breslau, J.A.; Chen, J.

    2005-01-01

    The basic two-fluid processes, those related to the nonlinearly self-consistent diamagnetic drifts of the electrons and ions, are shown to have fundamentally different effects on the steady state and beta limits of stellarator configurations, compared to MHD predictions. Nonlinear numerical simulation shows that the ideal MHD ballooning modes and the resistive MHD ballooning and interchange modes at relatively high mode numbers, that set the most severe theoretical limits on beta in stellarators with fixed boundary, are easily stabilized by two-fluid effects at realistic parameters, including finite Larmor radius effects related to the ion diamagnetic drift. Magnetic reconnection at low-order rational magnetic surfaces, on the other hand, is enhanced through the parallel component of the two-fluid electron pressure gradient in Ohm's law. The accelerated reconnection rates may impose the true intrinsic limit on beta in stellarators, as a 'soft' or confinement mediated limit in β e , due to steady confinement degradation in the presence of large magnetic islands. Study of the corresponding axisymmetric configurations shows that the helical component of the stellarator configuration provides an important amplifying factor for these effects. The two-fluid results may explain several previously puzzling experimental observations on stellarator behavior. (author)

  3. NGC 3628-UCD1:A possible $ω$ Cen Analog Embedded in a Stellar Stream

    OpenAIRE

    Jennings, Zachary G.; Romanowsky, Aaron J.; Brodie, Jean P.; Janz, Joachim; Norris, Mark A.; Forbes, Duncan A.; Martinez-Delgado, David; Fagioli, Martina; Penny, Samantha J.

    2015-01-01

    Using Subaru/Suprime-Cam wide-field imaging and both Keck/ESI and LBT/MODS spectroscopy, we identify and characterize a compact star cluster, which we term NGC 3628-UCD1, embedded in a stellar stream around the spiral galaxy NGC 3628. The size and luminosity of UCD1 are similar to $\\omega$ Cen, the most luminous Milky Way globular cluster, which has long been suspected to be the stripped remnant of an accreted dwarf galaxy. The object has a magnitude of $i=19.3$ mag (${\\rm L}_{\\rm i}=1.4\\time...

  4. The Spectroscopy and H-band Imaging of Virgo Cluster Galaxies (SHIVir) Survey: Scaling Relations and the Stellar-to-total Mass Relation

    Energy Technology Data Exchange (ETDEWEB)

    Ouellette, Nathalie N.-Q.; Courteau, Stéphane [Department of Physics, Engineering Physics and Astronomy, Queen’s University, Kingston, ON K7L 3N6 (Canada); Holtzman, Jon A. [Department of Physics and Astronomy, New Mexico State University, Las Cruces, NM, 88003-8001 (United States); Dutton, Aaron A. [Department of Physics, New York University Abu Dhabi, Abu Dhabi (United Arab Emirates); Cappellari, Michele [Sub-department of Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH (United Kingdom); Dalcanton, Julianne J. [Department of Astronomy, University of Washington, Seattle, WA, 98195 (United States); McDonald, Michael [MIT Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA, 02139 (United States); Roediger, Joel C.; Côté, Patrick; Ferrarese, Laura [Herzberg Institute of Astrophysics, National Research Council, Victoria, BC, V9E 2E7 (Canada); Taylor, James E. [Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, N2L 3G1 (Canada); Tully, R. Brent [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822-1839 (United States); Peng, Eric W. [Department of Astronomy, Peking University, Beijing 100871 (China)

    2017-07-01

    We present parameter distributions and fundamental scaling relations for 190 Virgo cluster galaxies in the SHIVir survey. The distribution of galaxy velocities is bimodal about V {sub circ} ∼ 125 km s{sup −1}, hinting at the existence of dynamically unstable modes in the inner regions of galaxies. An analysis of the Tully-Fisher relation (TFR) of late-type galaxies (LTGs) and the fundamental plane (FP) of early-type galaxies (ETGs) is presented, yielding a compendium of galaxy scaling relations. The slope and zero-point of the Virgo TFR match those of field galaxies, while scatter differences likely reflect distinct evolutionary histories. The velocities minimizing scatter for the TFR and FP are measured at large apertures where the baryonic fraction becomes subdominant. While TFR residuals remain independent of any galaxy parameters, FP residuals (i.e., the FP “tilt”) correlate strongly with the dynamical-to-stellar mass ratio, yielding stringent galaxy formation constraints. We construct a stellar-to-total mass relation (STMR) for ETGs and LTGs and find linear but distinct trends over the range M {sub *} = 10{sup 8–11} M {sub ⊙}. Stellar-to-halo mass relations (SHMRs), which probe the extended dark matter halo, can be scaled down to masses estimated within the optical radius, showing a tight match with the Virgo STMR at low masses; possibly inadequate halo abundance matching prescriptions and broad radial scalings complicate this comparison at all masses. While ETGs appear to be more compact than LTGs of the same stellar mass in projected space, their mass-size relations in physical space are identical. The trends reported here may soon be validated through well-resolved numerical simulations.

  5. Thermal and structural characterization of synthetic and natural nanocrystalline hydroxyapatite.

    Science.gov (United States)

    Sofronia, Ancuta M; Baies, Radu; Anghel, Elena M; Marinescu, Cornelia A; Tanasescu, Speranta

    2014-10-01

    The aim of this work was to study the thermal stability on heating and to obtain the processing parameters of synthetic and bone-derived hydroxyapatite over temperatures between room temperature and 1400°C by thermal analysis (thermogravimetry (TG)/differential scanning calorimetry (DSC) and thermo-mechanical analysis-TMA). Structural and surface modifications related to samples origin and calcination temperature were investigated by Fourier transformed infrared (FTIR) and Raman spectroscopy, X-ray diffraction (XRD) and BET method. FTIR spectra indicated that the organic constituents and carbonate are no longer present in the natural sample calcined at 800°C. Raman spectra highlighted the decomposition products of the hydroxyapatite. The calcination treatment modifies the processes kinetics of the synthetic samples, being able to isolate lattice water desorption processes of decarbonization and the dehydroxylation processes. Shrinkage of calcined synthetic sample increases by 10% compared to uncalcined synthetic powder. From the TMA correlated with TG analysis and heat capacity data it can be concluded that sintering temperature of the synthetic samples should be chosen in the temperature range of the onset of dehydroxylation and the temperature at which oxyapatite decomposition begins. Copyright © 2014 Elsevier B.V. All rights reserved.

  6. Oscillations in stellar atmospheres

    International Nuclear Information System (INIS)

    Costa, A.; Ringuelet, A.E.; Fontenla, J.M.

    1989-01-01

    Atmospheric excitation and propagation of oscillations are analyzed for typical pulsating stars. The linear, plane-parallel approach for the pulsating atmosphere gives a local description of the phenomenon. From the local analysis of oscillations, the minimum frequencies are obtained for radially propagating waves. The comparison of the minimum frequencies obtained for a variety of stellar types is in good agreement with the observed periods of the oscillations. The role of the atmosphere in the globar stellar pulsations is thus emphasized. 7 refs

  7. A MACHINE-LEARNING METHOD TO INFER FUNDAMENTAL STELLAR PARAMETERS FROM PHOTOMETRIC LIGHT CURVES

    International Nuclear Information System (INIS)

    Miller, A. A.; Bloom, J. S.; Richards, J. W.; Starr, D. L.; Lee, Y. S.; Butler, N. R.; Tokarz, S.; Smith, N.; Eisner, J. A.

    2015-01-01

    A fundamental challenge for wide-field imaging surveys is obtaining follow-up spectroscopic observations: there are >10 9 photometrically cataloged sources, yet modern spectroscopic surveys are limited to ∼few× 10 6 targets. As we approach the Large Synoptic Survey Telescope era, new algorithmic solutions are required to cope with the data deluge. Here we report the development of a machine-learning framework capable of inferring fundamental stellar parameters (T eff , log g, and [Fe/H]) using photometric-brightness variations and color alone. A training set is constructed from a systematic spectroscopic survey of variables with Hectospec/Multi-Mirror Telescope. In sum, the training set includes ∼9000 spectra, for which stellar parameters are measured using the SEGUE Stellar Parameters Pipeline (SSPP). We employed the random forest algorithm to perform a non-parametric regression that predicts T eff , log g, and [Fe/H] from photometric time-domain observations. Our final optimized model produces a cross-validated rms error (RMSE) of 165 K, 0.39 dex, and 0.33 dex for T eff , log g, and [Fe/H], respectively. Examining the subset of sources for which the SSPP measurements are most reliable, the RMSE reduces to 125 K, 0.37 dex, and 0.27 dex, respectively, comparable to what is achievable via low-resolution spectroscopy. For variable stars this represents a ≈12%-20% improvement in RMSE relative to models trained with single-epoch photometric colors. As an application of our method, we estimate stellar parameters for ∼54,000 known variables. We argue that this method may convert photometric time-domain surveys into pseudo-spectrographic engines, enabling the construction of extremely detailed maps of the Milky Way, its structure, and history

  8. The Effects of Stellar Dynamics on the Evolution of Young, Dense Stellar Systems

    Science.gov (United States)

    Belkus, H.; van Bever, J.; Vanbeveren, D.

    In this paper, we report on first results of a project in Brussels in which we study the effects of stellar dynamics on the evolution of young dense stellar systems using 3 decades of expertise in massive-star evolution and our population (number and spectral) synthesis code. We highlight an unconventionally formed object scenario (UFO-scenario) for Wolf Rayet binaries and study the effects of a luminous blue variable-type instability wind mass-loss formalism on the formation of intermediate-mass black holes.

  9. Stellar remnants

    CERN Document Server

    Kawaler, S D; Srinivasan, G

    1997-01-01

    This volume examines the internal structure, origin and evolution of white dwarfs, neutron stars and black holes, all objects at the final stage of stellar evolution. It covers topics such as: pulsation of white dwarfs; millisecond pulsars; and the dynamics around black holes.

  10. The relation between stellar evolution and cosmology

    International Nuclear Information System (INIS)

    Tayler, R.J.

    1984-01-01

    Observations of star clusters combined with the theory of stellar evolution enable us to estimate the ages of stars while cosmological observations and theories give us a value for the age of the Universe. This is the most important interaction between cosmology and stellar evolution because it is clearly necessary that stars are younger than the Universe. Stellar evolution also plays an important role in relating the present chemical composition of the Universe to its original composition. The author restricts the review to a discussion of the relation between stellar evolution and the big bang cosmological theory because there is such a good qualitative agreement between the hot big bang theory and observations. (Auth.)

  11. TEM turbulence optimisation in stellarators

    Science.gov (United States)

    Proll, J. H. E.; Mynick, H. E.; Xanthopoulos, P.; Lazerson, S. A.; Faber, B. J.

    2016-01-01

    With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has been achieved via shaping of the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence is addressed in the present paper. Recent analytical and numerical findings suggest TEMs are stabilised when a large fraction of trapped particles experiences favourable bounce-averaged curvature. This is the case for example in Wendelstein 7-X (Beidler et al 1990 Fusion Technol. 17 148) and other Helias-type stellarators. Using this knowledge, a proxy function was designed to estimate the TEM dynamics, allowing optimal configurations for TEM stability to be determined with the STELLOPT (Spong et al 2001 Nucl. Fusion 41 711) code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stellarator experiment HSX (Anderson et al 1995 Fusion Technol. 27 273) is presented for which a reduction of the linear growth rates is achieved over a broad range of the operational parameter space. As an important consequence of this property, the turbulent heat flux levels are reduced compared with the initial configuration.

  12. The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

    International Nuclear Information System (INIS)

    Christensen-Dalsgaard, Joergen; Carpenter, Kenneth G; Schrijver, Carolus J; Karovska, Margarita

    2011-01-01

    The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is a 'Landmark/Discovery Mission' in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ('NASA Space Science Vision Missions' (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

  13. The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

    Science.gov (United States)

    Christensen-Dalsgaard, Jørgen; Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita; Si Team

    2011-01-01

    The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is a "Landmark/Discovery Mission" in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

  14. The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

    Science.gov (United States)

    Christensen-Dalsgaard, Jorgen; Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

    2012-01-01

    The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled processes in the Universe. SI is a "LandmarklDiscovery Mission" in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission

  15. The Quasi-Toroidal Stellarator: An Innovative Confinement Experiment

    International Nuclear Information System (INIS)

    Knowlton, S. F.

    2001-01-01

    To develop a new class of stellarators that exhibit improved confinement compared to conventional stellarators. This approach generally makes use of a designed symmetry of the magnetic field strength along a particular coordinate axis in the toroidal geometry of the stellarator, and is referred to as quasi-symmetry

  16. When the Jeans Do Not Fit: How Stellar Feedback Drives Stellar Kinematics and Complicates Dynamical Modeling in Low-mass Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    El-Badry, Kareem; Quataert, Eliot [Department of Astronomy, University of California, Berkeley, CA (United States); Wetzel, Andrew R.; Hopkins, Philip F. [TAPIR, California Institute of Technology, Pasadena, CA (United States); Geha, Marla [Department of Astronomy, Yale University, New Haven, CT (United States); Kereš, Dusan; Chan, T. K. [Department of Physics, Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla (United States); Faucher-Giguère, Claude-André, E-mail: kelbadry@berkeley.edu [Department of Physics and Astronomy and CIERA, Northwestern University, Evanston, IL (United States)

    2017-02-01

    In low-mass galaxies, stellar feedback can drive gas outflows that generate non-equilibrium fluctuations in the gravitational potential. Using cosmological zoom-in baryonic simulations from the Feedback in Realistic Environments project, we investigate how these fluctuations affect stellar kinematics and the reliability of Jeans dynamical modeling in low-mass galaxies. We find that stellar velocity dispersion and anisotropy profiles fluctuate significantly over the course of galaxies’ starburst cycles. We therefore predict an observable correlation between star formation rate and stellar kinematics: dwarf galaxies with higher recent star formation rates should have systemically higher stellar velocity dispersions. This prediction provides an observational test of the role of stellar feedback in regulating both stellar and dark-matter densities in dwarf galaxies. We find that Jeans modeling, which treats galaxies as virialized systems in dynamical equilibrium, overestimates a galaxy’s dynamical mass during periods of post-starburst gas outflow and underestimates it during periods of net inflow. Short-timescale potential fluctuations lead to typical errors of ∼20% in dynamical mass estimates, even if full three-dimensional stellar kinematics—including the orbital anisotropy—are known exactly. When orbital anisotropy is not known a priori, typical mass errors arising from non-equilibrium fluctuations in the potential are larger than those arising from the mass-anisotropy degeneracy. However, Jeans modeling alone cannot reliably constrain the orbital anisotropy, and problematically, it often favors anisotropy models that do not reflect the true profile. If galaxies completely lose their gas and cease forming stars, fluctuations in the potential subside, and Jeans modeling becomes much more reliable.

  17. When the Jeans Do Not Fit: How Stellar Feedback Drives Stellar Kinematics and Complicates Dynamical Modeling in Low-mass Galaxies

    International Nuclear Information System (INIS)

    El-Badry, Kareem; Quataert, Eliot; Wetzel, Andrew R.; Hopkins, Philip F.; Geha, Marla; Kereš, Dusan; Chan, T. K.; Faucher-Giguère, Claude-André

    2017-01-01

    In low-mass galaxies, stellar feedback can drive gas outflows that generate non-equilibrium fluctuations in the gravitational potential. Using cosmological zoom-in baryonic simulations from the Feedback in Realistic Environments project, we investigate how these fluctuations affect stellar kinematics and the reliability of Jeans dynamical modeling in low-mass galaxies. We find that stellar velocity dispersion and anisotropy profiles fluctuate significantly over the course of galaxies’ starburst cycles. We therefore predict an observable correlation between star formation rate and stellar kinematics: dwarf galaxies with higher recent star formation rates should have systemically higher stellar velocity dispersions. This prediction provides an observational test of the role of stellar feedback in regulating both stellar and dark-matter densities in dwarf galaxies. We find that Jeans modeling, which treats galaxies as virialized systems in dynamical equilibrium, overestimates a galaxy’s dynamical mass during periods of post-starburst gas outflow and underestimates it during periods of net inflow. Short-timescale potential fluctuations lead to typical errors of ∼20% in dynamical mass estimates, even if full three-dimensional stellar kinematics—including the orbital anisotropy—are known exactly. When orbital anisotropy is not known a priori, typical mass errors arising from non-equilibrium fluctuations in the potential are larger than those arising from the mass-anisotropy degeneracy. However, Jeans modeling alone cannot reliably constrain the orbital anisotropy, and problematically, it often favors anisotropy models that do not reflect the true profile. If galaxies completely lose their gas and cease forming stars, fluctuations in the potential subside, and Jeans modeling becomes much more reliable.

  18. On plasma radiative properties in stellar conditions

    International Nuclear Information System (INIS)

    Turck-Chieze, S.; Delahaye, F.; Gilles, D.; Loisel, G.; Piau, L.; Loisel, G.

    2009-01-01

    The knowledge of stellar evolution is evolving quickly thanks to an increased number of opportunities to scrutinize the stellar internal plasma properties by stellar seismology and by 1D and 3D simulations. These new tools help us to introduce the internal dynamical phenomena in stellar modeling. A proper inclusion of these processes supposes a real confidence in the microscopic physics used, partly checked by solar or stellar acoustic modes. In the present paper we first recall which fundamental physics has been recently verified by helioseismology. Then we recall that opacity is an important ingredient of the secular evolution of stars and we point out why it is necessary to measure absorption coefficients and degrees of ionization in the laboratory for some well identified astrophysical conditions. We examine two specific experimental conditions which are accessible to large laser facilities and are suitable to solve some interesting questions of the stellar community: are the solar internal radiative interactions properly estimated and what is the proper role of the opacity in the excitation of the non-radial modes in the envelop of the β Cepheids and the Be stars? At the end of the paper we point out the difficulties of the experimental approach that we need to overcome. (authors)

  19. Hydrodynamics and stellar winds an introduction

    CERN Document Server

    Maciel, Walter J

    2014-01-01

    Stellar winds are a common phenomenon in the life of stars, from the dwarfs like the Sun to the red giants and hot supergiants, constituting one of the basic aspects of modern astrophysics. Stellar winds are a hydrodynamic phenomenon in which circumstellar gases expand towards the interstellar medium. This book presents an elementary introduction to the fundamentals of hydrodynamics with an application to the study of stellar winds. The principles of hydrodynamics have many other applications, so that the book can be used as an introduction to hydrodynamics for students of physics, astrophysics and other related areas.

  20. Stellarator Coil Design and Plasma Sensitivity

    International Nuclear Information System (INIS)

    Ku, Long-Poe; Boozer, Allen H.

    2010-01-01

    The rich information contained in the plasma response to external magnetic perturbations can be used to help design stellarator coils more effectively. We demonstrate the feasibility by first devel oping a simple, direct method to study perturbations in stellarators that do not break stellarator symmetry and periodicity. The method applies a small perturbation to the plasma boundary and evaluates the resulting perturbed free-boundary equilibrium to build up a sensitivity matrix for the important physics attributes of the underlying configuration. Using this sensitivity information, design methods for better stellarator coils are then developed. The procedure and a proof-of-principle application are given that (1) determine the spatial distributions of external normal magnetic field at the location of the unperturbed plasma boundary to which the plasma properties are most sen- sitive, (2) determine the distributions of external normal magnetic field that can be produced most efficiently by distant coils, (3) choose the ratios of the magnitudes of the the efficiently produced magnetic distributions so the sensitive plasma properties can be controlled. Using these methods, sets of modular coils are found for the National Compact Stellarator Experiment (NCSX) that are either smoother or can be located much farther from the plasma boundary than those of the present design.

  1. Review of stellarator research world wide

    International Nuclear Information System (INIS)

    Shonet, J.L.

    1987-01-01

    The world-wide effort in stellarators has evolved considerably during the past few years. Stellarator facilities are located in the Australia, Federal Republic of Germany, Japan, the Soviet Union, Spain, the United Kingdom and the United States. Dimensions of stellarators range from less than 20 centimeters in major radius to more than 2 meters, and magnetic field values between 0.2 Tesla to more than 3.0 Tesla. Stellarators are made in a variety of magnetic configurations with wide ranges of toroidal aspect ratios and methods of generating the stellarator magnetic surfaces. In particular, continuous helical coils, twisted modular coils, or twisted vacuum chambers all provide different means to generate nested toroidal magnetic surfaces without the need for currents flowing in the plasma. The goal of present day experiments is to accumulate a physics data base. This is being done by increasing electron and ion temperatures with non-ohmic heating, by transport and scaling studies considering neoclassical scaling, global scaling, effects of electric fields, the bootstrap current and magnetic islands. Higher betas are being attempted by designing suitable magnetic configurations, pellet injection and/or minimizing transport losses. Plasma-wall interactions and particle control are being examined by divertor, pumped-limiter and carbonization experiments

  2. Synthetic biology, inspired by synthetic chemistry.

    Science.gov (United States)

    Malinova, V; Nallani, M; Meier, W P; Sinner, E K

    2012-07-16

    The topic synthetic biology appears still as an 'empty basket to be filled'. However, there is already plenty of claims and visions, as well as convincing research strategies about the theme of synthetic biology. First of all, synthetic biology seems to be about the engineering of biology - about bottom-up and top-down approaches, compromising complexity versus stability of artificial architectures, relevant in biology. Synthetic biology accounts for heterogeneous approaches towards minimal and even artificial life, the engineering of biochemical pathways on the organismic level, the modelling of molecular processes and finally, the combination of synthetic with nature-derived materials and architectural concepts, such as a cellular membrane. Still, synthetic biology is a discipline, which embraces interdisciplinary attempts in order to have a profound, scientific base to enable the re-design of nature and to compose architectures and processes with man-made matter. We like to give an overview about the developments in the field of synthetic biology, regarding polymer-based analogs of cellular membranes and what questions can be answered by applying synthetic polymer science towards the smallest unit in life, namely a cell. Copyright © 2012 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  3. Edge biasing in the WEGA stellarator

    International Nuclear Information System (INIS)

    Lischtschenko, Oliver

    2009-01-01

    The WEGA stellarator is used to confine low temperature, overdense (densities exceeding the cut-off density of the heating wave) plasmas by magnetic fields in the range of B=50-500 mT. Microwave heating systems are used to ignite gas discharges using hydrogen, helium, neon or argon as working gases. The produced plasmas have been analyzed using Langmuir and emissive probes, a single-channel interferometer and ultra-high resolution Doppler spectroscopy. For a typical argon discharge in the low field operation, B=56 mT, the maximum electron density is n e ∝10 18 m -3 with temperatures in the range of T=4-12 eV. The plasma parameters are determined by using Langmuir probes and are cross-checked with interferometry. It is demonstrated within this work that the joint use of emissive probes and ultra-high resolution Doppler spectroscopy allows a precise measurement of the radial electric field. The focus of this work is on demonstrating the ability to modify the existing radial electric field in a plasma by using the biasing probe. This work commences with a basic approach and first establishes the diagnostic tools in a well-known discharge. Then the perturbation caused by the biasing probe is assessed. Following the characterization of the unperturbed plasmas, plasma states altered by the operation of the energized biasing probe are characterized. During biasing the plasma two different stable plasma states have been found. The two observed plasma states differ in plasma parameter profiles, such as density, temperature, electric field and confined energy. (orig.)

  4. Exploring stellar evolution with gravitational-wave observations

    Science.gov (United States)

    Dvorkin, Irina; Uzan, Jean-Philippe; Vangioni, Elisabeth; Silk, Joseph

    2018-05-01

    Recent detections of gravitational waves from merging binary black holes opened new possibilities to study the evolution of massive stars and black hole formation. In particular, stellar evolution models may be constrained on the basis of the differences in the predicted distribution of black hole masses and redshifts. In this work we propose a framework that combines galaxy and stellar evolution models and use it to predict the detection rates of merging binary black holes for various stellar evolution models. We discuss the prospects of constraining the shape of the time delay distribution of merging binaries using just the observed distribution of chirp masses. Finally, we consider a generic model of primordial black hole formation and discuss the possibility of distinguishing it from stellar-origin black holes.

  5. Dwarf galaxy dark matter density profiles inferred from stellar and gas kinematics

    International Nuclear Information System (INIS)

    Adams, Joshua J.; Simon, Joshua D.; Fabricius, Maximilian H.; Bender, Ralf; Thomas, Jens; Van den Bosch, Remco C. E.; Van de Ven, Glenn; Barentine, John C.; Gebhardt, Karl; Hill, Gary J.; Murphy, Jeremy D.; Swaters, R. A.

    2014-01-01

    We present new constraints on the density profiles of dark matter (DM) halos in seven nearby dwarf galaxies from measurements of their integrated stellar light and gas kinematics. The gas kinematics of low-mass galaxies frequently suggest that they contain constant density DM cores, while N-body simulations instead predict a cuspy profile. We present a data set of high-resolution integral-field spectroscopy on seven galaxies and measure the stellar and gas kinematics simultaneously. Using Jeans modeling on our full sample, we examine whether gas kinematics in general produce shallower density profiles than are derived from the stars. Although two of the seven galaxies show some localized differences in their rotation curves between the two tracers, estimates of the central logarithmic slope of the DM density profile, γ, are generally robust. The mean and standard deviation of the logarithmic slope for the population are γ = 0.67 ± 0.10 when measured in the stars and γ = 0.58 ± 0.24 when measured in the gas. We also find that the halos are not under-concentrated at the radii of half their maximum velocities. Finally, we search for correlations of the DM density profile with stellar velocity anisotropy and other baryonic properties. Two popular mechanisms to explain cored DM halos are an exotic DM component or feedback models that strongly couple the energy of supernovae into repeatedly driving out gas and dynamically heating the DM halos. While such models do not yet have falsifiable predictions that we can measure, we investigate correlations that may eventually be used to test models. We do not find a secondary parameter that strongly correlates with the central DM density slope, but we do find some weak correlations. The central DM density slope weakly correlates with the abundance of α elements in the stellar population, anti-correlates with H I fraction, and anti-correlates with vertical orbital anisotropy. We expect, if anything, the opposite of these

  6. Reliability of stellar inclination estimated from asteroseismology: analytical criteria, mock simulations and Kepler data analysis

    Science.gov (United States)

    Kamiaka, Shoya; Benomar, Othman; Suto, Yasushi

    2018-05-01

    Advances in asteroseismology of solar-like stars, now provide a unique method to estimate the stellar inclination i⋆. This enables to evaluate the spin-orbit angle of transiting planetary systems, in a complementary fashion to the Rossiter-McLaughlineffect, a well-established method to estimate the projected spin-orbit angle λ. Although the asteroseismic method has been broadly applied to the Kepler data, its reliability has yet to be assessed intensively. In this work, we evaluate the accuracy of i⋆ from asteroseismology of solar-like stars using 3000 simulated power spectra. We find that the low signal-to-noise ratio of the power spectra induces a systematic under-estimate (over-estimate) bias for stars with high (low) inclinations. We derive analytical criteria for the reliable asteroseismic estimate, which indicates that reliable measurements are possible in the range of 20° ≲ i⋆ ≲ 80° only for stars with high signal-to-noise ratio. We also analyse and measure the stellar inclination of 94 Kepler main-sequence solar-like stars, among which 33 are planetary hosts. According to our reliability criteria, a third of them (9 with planets, 22 without) have accurate stellar inclination. Comparison of our asteroseismic estimate of vsin i⋆ against spectroscopic measurements indicates that the latter suffers from a large uncertainty possibly due to the modeling of macro-turbulence, especially for stars with projected rotation speed vsin i⋆ ≲ 5km/s. This reinforces earlier claims, and the stellar inclination estimated from the combination of measurements from spectroscopy and photometric variation for slowly rotating stars needs to be interpreted with caution.

  7. Comparative studies of stellarator and tokamak transport

    Energy Technology Data Exchange (ETDEWEB)

    Stroth, U; Burhenn, R; Geiger, J; Giannone, L.; Hartfuss, H J; Kuehner, G; Ledl, L; Simmet, E E; Walter, H [Max-Planck-Inst. fuer Plasmaphysik, IPP-Euratom Association, Garching (Germany); ECRH Team; W7-AS Team

    1997-09-01

    Transport properties in the W7-AS stellarator and in tokamaks are compared. The parameter dependences and the absolute values of the energy confinement time are similar. Indications are found that the density dependence, which is usually observed in stellarator confinement, can vanish above a critical density. The density dependence in stellarators seems to be similar to that in the linear ohmic confinement regime, which, in small tokamaks, extends to high density values, too. Because of the similarity in the gross confinement properties, transport in stellarators and tokamaks should not be dominated by the parameters which are very different in the two concepts, i.e. magnetic shear, major rational values of the rotational transform and plasma current. A difference in confinement is that there exists evidence for pinches in the particle and, possibly, energy transport channels in tokamaks whereas in stellarators no pinches have been observed, so far. In order to study the effect of plasma current and toroidal electric fields, stellarator discharges were carried out with an increasing amount of plasma current. From these experiments, no clear evidence of a connection of pinches with these parameters is found. The transient response in W7-AS plasmas can be described in terms of a non-local model. As in tokamaks, also cold pulse experiments in W7-AS indicate the importance of non-local transport. (author). 8 refs, 5 figs.

  8. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. IV. A CANDIDATE BROWN DWARF OR LOW-MASS STELLAR COMPANION TO HIP 67526

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Peng; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Ma Bo; Wang, Ji [Astronomy Department, University of Florida, 211 Bryant Space Science Center, P.O. Box 112055, Gainesville, FL 32611 (United States); Cargile, Phillip; Hebb, Leslie; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Porto de Mello, Gustavo F.; Ferreira, Leticia D. [Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira do Pedro Antonio, 43, CEP: 20080-090, Rio de Janeiro, RJ (Brazil); Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I. [Instituto de Astrofisica de Canarias, C/Via Lactea S/N, E-38200 La Laguna (Spain); Gaudi, B. Scott [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghezzi, Luan [Laboratorio Interinstitucional de e-Astronomia (LIneA), Rio de Janeiro, RJ 20921-400 (Brazil); Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Agol, Eric, E-mail: jpaty@mail.ustc.edu.cn [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); and others

    2013-09-15

    We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Keplerian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695{sup +0.0188}{sub -0.0187} days, an eccentricity of 0.4375 {+-} 0.0040, and a semi-amplitude of 2948.14{sup +16.65}{sub -16.55} m s{sup -1}. Using additional high-resolution spectroscopy, we find the host star has an effective temperature T{sub eff} = 6004 {+-} 34 K, a surface gravity log g (cgs) =4.55 {+-} 0.17, and a metallicity [Fe/H] =+0.04 {+-} 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 {+-} 0.09 M{sub Sun} and 0.92 {+-} 0.19 R{sub Sun }. The minimum mass of MARVELS-5b is 65.0 {+-} 2.9M{sub Jup}, indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 {+-} 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M{sub Sun} at a separation larger than 40 AU.

  9. Direct Imaging of Stellar Surfaces: Results from the Stellar Imager (SI) Vision Mission Study

    Science.gov (United States)

    Carpenter, Kenneth; Schrijver, Carolus; Karovska, Margarita

    2006-01-01

    The Stellar Imager (SI) is a UV-Optical, Space-Based Interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and stellar interiors (via asteroseismology) and of the Universe in general. SI is identified as a "Flagship and Landmark Discovery Mission'' in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory'' in the Exploration of the Universe Division (EUD) Roadmap (May, 2005). The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes: The 0.1 mas resolution of this deep-space telescope will transform point sources into extended sources, and snapshots into evolving views. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we will discuss the results of the SI Vision Mission Study, elaborating on the science goals of the SI Mission and a mission architecture that could meet those goals.

  10. The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

    Energy Technology Data Exchange (ETDEWEB)

    Christensen-Dalsgaard, Joergen [Department of Physics and Astronomy, Aarhus University (Denmark); Carpenter, Kenneth G [Code 667 NASA-GSFC, Greenbelt, MD 20771 (United States); Schrijver, Carolus J [LMATC 3251 Hanover St., Bldg. 252, Palo Alto, CA 94304 (United States); Karovska, Margarita, E-mail: jcd@phys.au.d, E-mail: Kenneth.G.Carpenter@nasa.gov, E-mail: schryver@lmsal.com, E-mail: karovska@head.cfa.harvard.edu [60 Garden St., Cambridge, MA 02138 (United States)

    2011-01-01

    The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is a 'Landmark/Discovery Mission' in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ('NASA Space Science Vision Missions' (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

  11. Geometric phase modulation for stellar interferometry

    International Nuclear Information System (INIS)

    Roy, M.; Boschung, B.; Tango, W.J.; Davis, J.

    2002-01-01

    Full text: In a long baseline optical interferometer, the fringe visibility is normally measured by modulation of the optical path difference between the two arms of the instruments. To obtain accurate measurements, the spectral bandwidth must be narrow, limiting the sensitivity of the technique. The application of geometric phase modulation technique to stellar interferometry has been proposed by Tango and Davis. Modulation of the geometric phase has the potential for improving the sensitivity of optical interferometers, and specially the Sydney University Stellar Interferometer (SUSI), by allowing broad band modulation of the light signals. This is because a modulator that changes the geometric phase of the signal is, in principle, achromatic. Another advantage of using such a phase modulator is that it can be placed in the common path traversed by the two orthogonally polarized beams emerging from the beam combiner in a stellar interferometer. Thus the optical components of the modulator do not have to be interferometric quality and could be relatively easily introduced into SUSI. We have investigated the proposed application in a laboratory-based experiment using a Mach-Zehnder interferometer with white-light source. This can be seen as a small model of an amplitude stellar interferometer where the light source takes the place of the distant star and two corner mirrors replaces the entrance pupils of the stellar interferometer

  12. The Stellar Imager (SI)"Vision Mission"

    Science.gov (United States)

    Carpenter, Ken; Danchi, W.; Leitner, J.; Liu, A.; Lyon, R.; Mazzuca, L.; Moe, R.; Chenette, D.; Karovska, M.; Allen, R.

    2004-01-01

    The Stellar Imager (SI) is a "Vision" mission in the Sun-Earth Connection (SEC) Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar magnetic activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, at ultraviolet wavelengths, on the order of 100 micro-arcsec and thus baselines on the order of 0.5 km. These requirements call for a large, multi-spacecraft (less than 20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. SI's resolution will make it an invaluable resource for many other areas of astrophysics, including studies of AGN s, supernovae, cataclysmic variables, young stellar objects, QSO's, and stellar black holes. ongoing mission concept and technology development studies for SI. These studies are designed to refine the mission requirements for the science goals, define a Design Reference Mission, perform trade studies of selected major technical and architectural issues, improve the existing technology roadmap, and explore the details of deployment and operations, as well as the possible roles of astronauts and/or robots in construction and servicing of the facility.

  13. Radiative otacity tables for 40 stellar mixtures

    International Nuclear Information System (INIS)

    Cox, A.N.; Tabor, J.E.

    1976-01-01

    Using improved methods, radiative opacities for 40 mixtures of elements are given for use in calculations of stellar structure, stellar evolution, and stellar pulsation. The major improvements over previous Los Alamos data are increased iron abundance in the composition, better allowance for the continuum depression for bound electrons, and corrections in some bound-electron energy levels. These opacities have already been widely used, and represent a relatively homogeneous set of data for stellar structures. Further improvements to include more bound-bound (line) transitions by a smearing technique and to include molecular absorptions are becoming available, and in a few years these tables, as well as all previous tables, will be outdated. At high densities the conduction of energy will dominate radiation flow, and this effect must be added separately

  14. On origin of stellar clusters

    International Nuclear Information System (INIS)

    Tovmasyan, G.M.

    1977-01-01

    The ratios of the gas component of the mass of young stellar clusters to their stellar mass are considered. They change by more than four orders from one cluster to another. The results are in direct contradiction with the hypothesis of formation of cluster stars from a preliminarily existing gas cloud by its condensation, and they favour the Ambartsumian hypothesis of the joint origin of stars and gas clouds from superdense protostellar matter

  15. Ultra-low dispersion spectroscopy of stars and galaxies

    International Nuclear Information System (INIS)

    Bappu, M.K.V.; Parthasarathy, M.

    1977-01-01

    Application of ultra-low dispersion spectroscopy 10,000 A mm - 1 , is described to study the nuclei of elliptical galaxies, the quasi-stellar objects and for the discovery of faint OB stars, reddened stars and red stars. The instrument used is an f/2 slitless spectrograph with a three degree quartz prism at the Cassegrain focus of the 102-cm Ritchey-Chratien reflector at Kavalur. The spectra cover a field of 40 minutes of arc and the dispersion is 10,000 A mm - 1 . Ultra-low dispersion spectra (microspectra) were obtained for fifteen elliptical and three SO galaxies from the list of Ekers and Ekers (1973) who classified them as compact and extended sources from the observations of radio emission at 6 cms. From an analysis of micro-spectra and from direct photographs with graded exposure times, it is found that all compact radio galaxies in the Ekers list also have optically compact nuclei. Some of these elliptical galaxies with compact nuclei show enhancement of intensity in the blue violet region. From an examination of microspectra of forty-three of the known quasi-stellar objects of different redshifts it is found that the most striking characteristic of the spectra is their flat appearance. This characteristic flatness is also noticed in the microspectrum of the large redshift quasi-stellar objects like OH 471 and OQ 172 which do not have UV excess. Because of this characteristic difference in the appearance of the microspectra of the quasi-stellar objects and stellar objects, it is possible to detect new OSO's with this technique. An application of this technique to detect red stars in our galaxy and in the Large Magellanic cloud is discussed. (author)

  16. The Masses and Stellar Content of Nuclei in Early-Type Galaxies from Multi-Band Photometry and Spectroscopy

    Science.gov (United States)

    Spengler, Chelsea; Côté, Patrick; Roediger, Joel; Ferrarese, Laura; Sánchez-Janssen, Rubén; Toloba, Elisa; Liu, Yiqing; Guhathakurta, Puragra; Cuillandre, Jean-Charles; Gwyn, Stephen; Zirm, Andrew; Muñoz, Roberto; Puzia, Thomas; Lançon, Ariane; Peng, Eric; Mei, Simona; Powalka, Mathieu

    2018-01-01

    It is now established that most, if not all, massive galaxies host central supermassive black holes (SMBHs), and that these SMBHs are linked to the growth their host galaxies as shown by several scaling relations. Within the last couple of decades, it has become apparent that most lower-mass galaxies without obvious SMBHs nevertheless contain some sort of central massive object in the form of compact stellar nuclei that also follow identical (or similar) scaling relations. These nuclei are challenging to study given their small sizes and relatively faint magnitudes, but understanding their origins and relationship to their hosts is critical to gaining a more complete picture of galaxy evolution. To that end, we highlight selected results from an analysis of 39 nuclei and their early-type hosts in the Virgo Cluster using ten broadband filters: F300W, F475W, F850LP, F160W, u*griz, and Ks. We estimate masses, metallicities and ages using simple stellar population (SSP) models. For 19 nuclei, we compare to SSP parameters derived from Keck and Gemini spectra and find reasonable agreement between the photometric and spectroscopic metallicity: the RMS scatter is 0.3 dex. We reproduce the nucleus-galaxy mass fraction of 0.33 ± 0.08% for galaxy stellar masses 108.4-1010.3 M⊙ with a typical precision of ~35% for the nuclei masses. Based on available model predictions, there is no single preferred formation scenario for nuclei, suggesting that nuclei are formed stochastically through a mix of processes. Nuclei metallicities are statistically identical to those of their hosts, appearing 0.07 ± 0.3 dex more metal-rich on average — although, omitting galaxies with unusual origins (i.e., compact ellipticals), nuclei are 0.20 ± 0.28 dex more metal-rich. We find no clear age difference between nuclei and their galaxies, with nuclei displaying a broad range of ages. Interestingly, we find that the most massive nuclei may be flatter and more closely aligned with the semi

  17. Theories for convection in stellar atmospheres

    International Nuclear Information System (INIS)

    Nordlund, Aa.

    1976-02-01

    A discussion of the fundamental differences between laboratory convection in a stellar atmosphere is presented. The shortcomings of laterally homogeneous model atmospheres are analysed, and the extent to which these shortcoming are avoided in the two-component representation is discussed. Finally a qualitative discussion on the scaling properties of stellar granulation is presented. (Auth.)

  18. The Prospect for Detecting Stellar Coronal Mass Ejections

    Science.gov (United States)

    Osten, Rachel A.; Crosley, Michael Kevin

    2018-06-01

    The astrophysical study of mass loss, both steady-state and transient, on the cool half of the HR diagram has implications bothfor the star itself and the conditions created around the star that can be hospitable or inimical to supporting life. Recent results from exoplanet studies show that planets around M dwarfs are exceedingly common, which together with the commonality of M dwarfs in our galaxy make this the dominant mode of star and planet configurations. The closeness of the exoplanets to the parent M star motivate a comprehensive understanding of habitability for these systems. Radio observations provide the most clear signature of accelerated particles and shocks in stars arising as the result of MHD processes in the stellar outer atmosphere. Stellar coronal mass ejections have not been conclusively detected, despite the ubiquity with which their radiative counterparts in an eruptive event (stellar flares) have. I will review some of the different observational methods which have been used and possibly could be used in the future in the stellar case, emphasizing some of the difficulties inherent in such attempts. I will provide a framework for interpreting potential transient stellar mass loss in light of the properties of flares known to occur on magnetically active stars. This uses a physically motivated way to connect the properties of flares and coronal mass ejections and provides a testable hypothesis for observing or constraining transient stellar mass loss. I will describe recent results using radio observations to detect stellar coronal mass ejections, and what those results imply about transient stellar mass loss. I will provide some motivation for what could be learned in this topic from space-based low frequency radio experiments.

  19. Collisionless microinstabilities in stellarators. II. Numerical simulations

    International Nuclear Information System (INIS)

    Proll, J. H. E.; Xanthopoulos, P.; Helander, P.

    2013-01-01

    Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-J geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here, the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes, and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-J configurations

  20. Evolution of rotating stellar clusters at the stage of inelastic collisions

    International Nuclear Information System (INIS)

    Romanova, M.M.

    1985-01-01

    The dynamics of a gas-stellar disk in a dense stellar cluster of small ellipticity (epsilon or approximately 0.2-0.3. Possible existence of a thin stellar disk in a dense stellar cluster is analysed. With epsilon in the above range, collisions between cluster and disk stars are shown to have no effect on the evolution of the disk up to the instability time, provided that the ratio of disk stellar mass to the cluster stellar mass > or approximately 0.04

  1. Superbanana orbits in stellarator geometries

    International Nuclear Information System (INIS)

    Derr, J.A.; Shohet, J.L.

    1979-04-01

    The presence of superbanana orbit types localized to either the interior or the exterior of stellarators and torsatrons is numerically investigated for 3.5 MeV alpha particles. The absence of the interior superbanana in both geometries is found to be due to non-conservation of the action. Exterior superbananas are found in the stellarator only, as a consequence of the existence of closed helical magnetic wells. No superbananas of either type are found in the torsatron

  2. Stellar Parameters for Trappist-1

    Science.gov (United States)

    Van Grootel, Valérie; Fernandes, Catarina S.; Gillon, Michael; Jehin, Emmanuel; Manfroid, Jean; Scuflaire, Richard; Burgasser, Adam J.; Barkaoui, Khalid; Benkhaldoun, Zouhair; Burdanov, Artem; Delrez, Laetitia; Demory, Brice-Olivier; de Wit, Julien; Queloz, Didier; Triaud, Amaury H. M. J.

    2018-01-01

    TRAPPIST-1 is an ultracool dwarf star transited by seven Earth-sized planets, for which thorough characterization of atmospheric properties, surface conditions encompassing habitability, and internal compositions is possible with current and next-generation telescopes. Accurate modeling of the star is essential to achieve this goal. We aim to obtain updated stellar parameters for TRAPPIST-1 based on new measurements and evolutionary models, compared to those used in discovery studies. We present a new measurement for the parallax of TRAPPIST-1, 82.4 ± 0.8 mas, based on 188 epochs of observations with the TRAPPIST and Liverpool Telescopes from 2013 to 2016. This revised parallax yields an updated luminosity of {L}* =(5.22+/- 0.19)× {10}-4 {L}ȯ , which is very close to the previous estimate but almost two times more precise. We next present an updated estimate for TRAPPIST-1 stellar mass, based on two approaches: mass from stellar evolution modeling, and empirical mass derived from dynamical masses of equivalently classified ultracool dwarfs in astrometric binaries. We combine them using a Monte-Carlo approach to derive a semi-empirical estimate for the mass of TRAPPIST-1. We also derive estimate for the radius by combining this mass with stellar density inferred from transits, as well as an estimate for the effective temperature from our revised luminosity and radius. Our final results are {M}* =0.089+/- 0.006 {M}ȯ , {R}* =0.121+/- 0.003 {R}ȯ , and {T}{eff} = 2516 ± 41 K. Considering the degree to which the TRAPPIST-1 system will be scrutinized in coming years, these revised and more precise stellar parameters should be considered when assessing the properties of TRAPPIST-1 planets.

  3. ESTIMATION OF DISTANCES TO STARS WITH STELLAR PARAMETERS FROM LAMOST

    Energy Technology Data Exchange (ETDEWEB)

    Carlin, Jeffrey L.; Newberg, Heidi Jo [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Liu, Chao; Deng, Licai; Li, Guangwei; Luo, A-Li; Wu, Yue; Yang, Ming; Zhang, Haotong [Key Lab of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Beers, Timothy C. [Department of Physics and JINA: Joint Institute for Nuclear Astrophysics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Chen, Li; Hou, Jinliang; Smith, Martin C. [Shanghai Astronomical Observatory, 80 Nandan Road, Shanghai 200030 (China); Guhathakurta, Puragra [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Hou, Yonghui [Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042 (China); Lépine, Sébastien [Department of Physics and Astronomy, Georgia State University, 25 Park Place, Suite 605, Atlanta, GA 30303 (United States); Yanny, Brian [Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States); Zheng, Zheng, E-mail: jeffreylcarlin@gmail.com [Department of Physics and Astronomy, University of Utah, UT 84112 (United States)

    2015-07-15

    We present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star’s absolute magnitude. This technique is tailored specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ∼5° diameter “plate” that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and target selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ∼20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ∼40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.

  4. Plea for stellarator funding raps tokamaks

    International Nuclear Information System (INIS)

    Blake, M.

    1992-01-01

    The funding crunch in magnetic confinement fusion development has moved the editor of a largely technical publication to speak out on a policy issue. James A. Rome, who edits Stellarator News from the Fusion Energy Division at Oak Ridge National Laboratory, wrote an editorial that appeared on the front page of the May 1992 issue. It was titled open-quotes The US Stellarator Program: A Time for Renewal,close quotes and while it focused chiefly on that subject (and lamented the lack of funding for the operation of the existing ATF stellarator at Oak Ridge), it also cited some of the problems inherent in the mainline MCF approach--the tokamak--and stated that if the money can be found for further tokamak design upgrades, it should also be found for stellarators. Rome wrote, open-quotes There is growing recognition in the US, and elsewhere, that the conventional tokamak does not extrapolate to a commercially competitive energy source except with very high field coils ( 1000 MWe).close quotes He pointed up open-quotes the difficulty of simultaneously satisfying conflicting tokamak requirements for efficient current drive, high bootstrap-current fraction, complete avoidance of disruptions, adequate beta limits, and edge-plasma properties compatible with improved (H-mode) confinement and acceptable erosion of divertor plates.close quotes He then called for support for the stellarator as open-quotes the only concept that has performance comparable to that achieved in tokamaks without the plasma-current-related limitations listed above.close quotes

  5. ON THE ORIGIN OF STELLAR MASSES

    International Nuclear Information System (INIS)

    Krumholz, Mark R.

    2011-01-01

    It has been a longstanding problem to determine, as far as possible, the characteristic masses of stars in terms of fundamental constants; the almost complete invariance of this mass as a function of the star-forming environment suggests that this should be possible. Here I provide such a calculation. The typical stellar mass is set by the characteristic fragment mass in a star-forming cloud, which depends on the cloud's density and temperature structure. Except in the very early universe, the latter is determined mainly by the radiation released as matter falls onto seed protostars. The energy yield from this process is ultimately set by the properties of deuterium burning in protostellar cores, which determines the stars' radii. I show that it is possible to combine these considerations to compute a characteristic stellar mass almost entirely in terms of fundamental constants, with an extremely weak residual dependence on the interstellar pressure and metallicity. This result not only explains the invariance of stellar masses, it resolves a second mystery: why fragmentation of a cold, low-density interstellar cloud, a process with no obvious dependence on the properties of nuclear reactions, happens to select a stellar mass scale such that stellar cores can ignite hydrogen. Finally, the weak residual dependence on the interstellar pressure and metallicity may explain recent observational hints of a smaller characteristic mass in the high-pressure, high-metallicity cores of giant elliptical galaxies.

  6. New Low-mass Stars in the 25 Orionis Stellar Group and Orion OB1a Sub-association from SDSS-III/BOSS Spectroscopy

    Science.gov (United States)

    Suárez, Genaro; Downes, Juan José; Román-Zúñiga, Carlos; Covey, Kevin R.; Tapia, Mauricio; Hernández, Jesús; Petr-Gotzens, Monika G.; Stassun, Keivan G.; Briceño, César

    2017-07-01

    The Orion OB1a sub-association is a rich low-mass star (LMS) region. Previous spectroscopic studies have confirmed 160 LMSs in the 25 Orionis stellar group (25 Ori), which is the most prominent overdensity of Orion OB1a. Nonetheless, the current census of the 25 Ori members is estimated to be lower than 50% complete, leaving a large number of members to be still confirmed. We retrieved 172 low-resolution stellar spectra in Orion OB1a observed as ancillary science in the SDSS-III/BOSS survey, for which we classified their spectral types and determined physical parameters. To determine memberships, we analyzed the {{{H}}}α emission, Li I λ6708 absorption, and Na I λλ8183, 8195 absorption as youth indicators in stars classified as M type. We report 50 new LMSs spread across the 25 Orionis, ASCC 18, and ASCC 20 stellar groups with spectral types from M0 to M6, corresponding to a mass range of 0.10≤slant m/{M}⊙ ≤slant 0.58. This represents an increase of 50% in the number of known LMSs in the area and a net increase of 20% in the number of 25 Ori members in this mass range. Using parallax values from the Gaia DR1 catalog, we estimated the distances to these three stellar groups and found that they are all co-distant, at 338 ± 66 pc. We analyzed the spectral energy distributions of these LMSs and classified their disks into evolutionary classes. Using H-R diagrams, we found a suggestion that 25 Ori could be slightly older than the other two observed groups in Orion OB1a.

  7. Status of stellarator research

    International Nuclear Information System (INIS)

    Wobig, H.

    1985-01-01

    In recent years main activities in stellarator research were focussed on production and investigation of currentless plasmas. Several heating methods have been applied: electron cyclotron heating, ion cyclotron heating and neutral beam injection. The parameters achieved in HELIOTRON E and W VII-A are: antin 20 m 3 , Tsub(i) <= 1 keV. The confinement is improved as compared with ohmically heated discharges. By ECRH (P = 200 kW) it is possible to heat electrons up to 1.4 keV, confinement in this regime is dominated already by trapped particle effects. Toroidal currents up to 2 kA - either bootstrap currents or externally driven currents - were observed. High β-values (antiβ = 2%) have been obtained in HELIOTRON E, in this regime already pressure driven MHD-modes were observed. Future experiments (ATF-1 and W VII-AS) will extend the parameter regime to temperatures of several keV. These experiments will give important information about critical problems of the stellarator line (β-limit, neoclassical confinement impurity transport). A few reactor studies of stellarators exist, attention is mainly concentrated on technical problems of the modular coil system

  8. Solar and stellar oscillations

    International Nuclear Information System (INIS)

    Fossat, E.

    1981-01-01

    We try to explain in simple words what a stellar oscillation is, what kind of restoring forces and excitation mechanisms can be responsible for its occurence, what kind of questions the theoretician asks to the observer and what kind of tools the latter is using to look for the answers. A selected review of the most striking results obtained in the last few years in solar seismology and the present status of their consequences on solar models is presented. A brief discussion on the expected extension towards stellar seismology will end the paper. A selected bibliography on theory as well as observations and recent papers is also included. (orig.)

  9. NEAR-INFRARED SPECTRA OF GALACTIC STELLAR CLUSTERS DETECTED ON SPITZER/GLIMPSE IMAGES

    International Nuclear Information System (INIS)

    Messineo, Maria; Davies, Ben; Figer, Donald F.; Ivanov, Valentin D.; Schuller, Frederic; Menten, Karl M.; Habing, Harm J.; Petr-Gotzens, Monika G.

    2009-01-01

    We present near-infrared spectroscopic observations of massive stars in three stellar clusters located in the direction of the inner Galaxy. One of them, the Quartet, is a new discovery while the other two were previously reported as candidate clusters identified on mid-infrared Spitzer images (GLIMPSE20 and GLIMPSE13). Using medium-resolution (R = 900-1320) H and K spectroscopy, we firmly establish the nature of the brightest stars in these clusters, yielding new identifications of an early WC and two Ofpe/WN9 stars in the Quartet and an early WC star in GLIMPSE20. We combine this information with the available photometric measurements from Two Micron All Sky Survey, to estimate cluster masses, ages, and distances. The presence of several massive stars places the Quartet and GLIMPSE20 among the small sample of known Galactic stellar clusters with masses of a few 10 3 M sun , and ages from 3 to 8 Myr. We estimate a distance of about 3.5 kpc for GLIMPSE20 and 6.0 kpc for Quartet. The large number of giant stars identified in GLIMPSE13 indicates that it is another massive (∼6500 M sun ) cluster, but older, with an age between 30 and 100 Myr, at a distance of about 3 kpc.

  10. Spectral Resolution-linked Bias in Transit Spectroscopy of Extrasolar Planets

    Energy Technology Data Exchange (ETDEWEB)

    Deming, Drake; Sheppard, Kyle [Department of Astronomy, University of Maryland at College Park, College Park, MD 20742 (United States)

    2017-05-20

    We re-visit the principles of transmission spectroscopy for transiting extrasolar planets, focusing on the overlap between the planetary spectrum and the illuminating stellar spectrum. Virtually all current models of exoplanetary transmission spectra utilize an approximation that is inaccurate when the spectrum of the illuminating star has a complex line structure, such as molecular bands in M-dwarf spectra. In those cases, it is desirable to model the observations using a coupled stellar–planetary radiative transfer model calculated at high spectral resolving power, followed by convolution to the observed resolution. Not consistently accounting for overlap of stellar M-dwarf and planetary lines at high spectral resolution can bias the modeled amplitude of the exoplanetary transmission spectrum, producing modeled absorption that is too strong. We illustrate this bias using the exoplanet TRAPPIST-1b, as observed using Hubble Space Telescope /WFC3. The bias in this case is about 250 ppm, 12% of the modeled transit absorption. Transit spectroscopy using JWST will have access to longer wavelengths where the water bands are intrinsically stronger, and the observed signal-to-noise ratios will be higher than currently possible. We therefore expect that this resolution-linked bias will be especially important for future JWST observations of TESS-discovered super-Earths and mini-Neptunes transiting M-dwarfs.

  11. Spectral Resolution-linked Bias in Transit Spectroscopy of Extrasolar Planets

    International Nuclear Information System (INIS)

    Deming, Drake; Sheppard, Kyle

    2017-01-01

    We re-visit the principles of transmission spectroscopy for transiting extrasolar planets, focusing on the overlap between the planetary spectrum and the illuminating stellar spectrum. Virtually all current models of exoplanetary transmission spectra utilize an approximation that is inaccurate when the spectrum of the illuminating star has a complex line structure, such as molecular bands in M-dwarf spectra. In those cases, it is desirable to model the observations using a coupled stellar–planetary radiative transfer model calculated at high spectral resolving power, followed by convolution to the observed resolution. Not consistently accounting for overlap of stellar M-dwarf and planetary lines at high spectral resolution can bias the modeled amplitude of the exoplanetary transmission spectrum, producing modeled absorption that is too strong. We illustrate this bias using the exoplanet TRAPPIST-1b, as observed using Hubble Space Telescope /WFC3. The bias in this case is about 250 ppm, 12% of the modeled transit absorption. Transit spectroscopy using JWST will have access to longer wavelengths where the water bands are intrinsically stronger, and the observed signal-to-noise ratios will be higher than currently possible. We therefore expect that this resolution-linked bias will be especially important for future JWST observations of TESS-discovered super-Earths and mini-Neptunes transiting M-dwarfs.

  12. Stellar CCD Photometry: New Approach, Principles and Application

    Science.gov (United States)

    El-Bassuny Alawy, A.

    A new approach is proposed and developed to handle pre-processed CCD frames in order to identify stellar images and derive their relevant parameters. It relies on: 1) Identifying stellar images and assigning approximate positions of their centres using an artificial intelligence technique, (Knowledge Based System), 2) Accurate determination of the centre co-ordinates applying an elementary statistical concept and 3) Estimating the image peak intensity as a stellar magnitude measure employing simple numerical analysis approach. The method has been coded for personal computer users. A CCD frame of the star cluster M67 was adopted as a test case. The results obtained are discussed in comparison with the DAOPHOTII ones and the corresponding published data. Exact coincidence has been found between both results except in very few cases. These exceptions have been discussed in the light of the basis of both methods and the cluster plates. It has been realised that the method suggested represents a very simple, extremely fast, high precision method of stellar CCD photometry. Moreover, it is more capable than DAOPHOTII of handling blended and distorted stellar images. These characteristics show the usefulness of the present method in some astronomical applications, such as auto-focusing and auto-guiding, beside the main purpose, viz. stellar photometry.

  13. Planets, stars and stellar systems

    CERN Document Server

    Bond, Howard; McLean, Ian; Barstow, Martin; Gilmore, Gerard; Keel, William; French, Linda

    2013-01-01

    This is volume 3 of Planets, Stars and Stellar Systems, a six-volume compendium of modern astronomical research covering subjects of key interest to the main fields of contemporary astronomy. This volume on “Solar and Stellar Planetary Systems” edited by Linda French and Paul Kalas presents accessible review chapters From Disks to Planets, Dynamical Evolution of Planetary Systems, The Terrestrial Planets, Gas and Ice Giant Interiors, Atmospheres of Jovian Planets, Planetary Magnetospheres, Planetary Rings, An Overview of the Asteroids and Meteorites, Dusty Planetary Systems and Exoplanet Detection Methods. All chapters of the handbook were written by practicing professionals. They include sufficient background material and references to the current literature to allow readers to learn enough about a specialty within astronomy, astrophysics and cosmology to get started on their own practical research projects. In the spirit of the series Stars and Stellar Systems published by Chicago University Press in...

  14. The Stellar IMF from Isothermal MHD Turbulence

    Science.gov (United States)

    Haugbølle, Troels; Padoan, Paolo; Nordlund, Åke

    2018-02-01

    We address the turbulent fragmentation scenario for the origin of the stellar initial mass function (IMF), using a large set of numerical simulations of randomly driven supersonic MHD turbulence. The turbulent fragmentation model successfully predicts the main features of the observed stellar IMF assuming an isothermal equation of state without any stellar feedback. As a test of the model, we focus on the case of a magnetized isothermal gas, neglecting stellar feedback, while pursuing a large dynamic range in both space and timescales covering the full spectrum of stellar masses from brown dwarfs to massive stars. Our simulations represent a generic 4 pc region within a typical Galactic molecular cloud, with a mass of 3000 M ⊙ and an rms velocity 10 times the isothermal sound speed and 5 times the average Alfvén velocity, in agreement with observations. We achieve a maximum resolution of 50 au and a maximum duration of star formation of 4.0 Myr, forming up to a thousand sink particles whose mass distribution closely matches the observed stellar IMF. A large set of medium-size simulations is used to test the sink particle algorithm, while larger simulations are used to test the numerical convergence of the IMF and the dependence of the IMF turnover on physical parameters predicted by the turbulent fragmentation model. We find a clear trend toward numerical convergence and strong support for the model predictions, including the initial time evolution of the IMF. We conclude that the physics of isothermal MHD turbulence is sufficient to explain the origin of the IMF.

  15. Direct UV/Optical Imaging of Stellar Surfaces: The Stellar Imager (SI) Vision Mission

    Science.gov (United States)

    Carpenter, Kenneth G.; Lyon, Richard G.; Schrijver, Carolus; Karovska, Margarita; Mozurkewich, David

    2007-01-01

    The Stellar Imager (SI) is a UV/optical, space-based interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives, in support of the Living with a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in thc Universe. SI is a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap. We discuss herein the science goals of the SI Mission, a mission architecture that could meet those goals, and the technologies needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

  16. Medium-resolution near-infrared spectroscopy of massive young stellar objects

    Science.gov (United States)

    Pomohaci, R.; Oudmaijer, R. D.; Lumsden, S. L.; Hoare, M. G.; Mendigutía, I.

    2017-12-01

    We present medium-resolution (R ∼ 7000) near-infrared echelle spectroscopic data for 36 massive young stellar objects (MYSOs) drawn from the Red MSX Source survey. This is the largest sample observed at this resolution at these wavelengths of MYSOs to date. The spectra are characterized mostly by emission from hydrogen recombination lines and accretion diagnostic lines. One MYSO shows photospheric H I absorption, a comparison with spectral standards indicates that the star is an A-type star with a low surface gravity, implying that the MYSOs are probably swollen, as also suggested by evolutionary calculations. An investigation of the Brγ line profiles shows that most are in pure emission, while 13 ± 5 per cent display P Cygni profiles, indicative of outflow, while less than 8 ± 4 per cent have inverse P Cygni profiles, indicative of infall. These values are comparable with investigations into the optically bright Herbig Be stars, but not with those of Herbig Ae and T Tauri stars, consistent with the notion that the more massive stars undergo accretion in a different fashion than lower mass objects that are undergoing magnetospheric accretion. Accretion luminosities and rates as derived from the Br γ line luminosities agree with results for lower mass sources, providing tentative evidence for massive star formation theories based on scaling of low-mass scenarios. We present Br γ/Br12 line profile ratios exploiting the fact that optical depth effects can be traced as a function of Doppler shift across the lines. These show that the winds of MYSOs in this sample are nearly equally split between constant, accelerating and decelerating velocity structures. There are no trends between the types of features we see and bolometric luminosities or near-infrared colours.

  17. Stellar Spectral Classification with Locality Preserving Projections ...

    Indian Academy of Sciences (India)

    With the help of computer tools and algorithms, automatic stellar spectral classification has become an area of current interest. The process of stellar spectral classification mainly includes two steps: dimension reduction and classification. As a popular dimensionality reduction technique, Principal Component Analysis (PCA) ...

  18. Inferring probabilistic stellar rotation periods using Gaussian processes

    Science.gov (United States)

    Angus, Ruth; Morton, Timothy; Aigrain, Suzanne; Foreman-Mackey, Daniel; Rajpaul, Vinesh

    2018-02-01

    Variability in the light curves of spotted, rotating stars is often non-sinusoidal and quasi-periodic - spots move on the stellar surface and have finite lifetimes, causing stellar flux variations to slowly shift in phase. A strictly periodic sinusoid therefore cannot accurately model a rotationally modulated stellar light curve. Physical models of stellar surfaces have many drawbacks preventing effective inference, such as highly degenerate or high-dimensional parameter spaces. In this work, we test an appropriate effective model: a Gaussian Process with a quasi-periodic covariance kernel function. This highly flexible model allows sampling of the posterior probability density function of the periodic parameter, marginalizing over the other kernel hyperparameters using a Markov Chain Monte Carlo approach. To test the effectiveness of this method, we infer rotation periods from 333 simulated stellar light curves, demonstrating that the Gaussian process method produces periods that are more accurate than both a sine-fitting periodogram and an autocorrelation function method. We also demonstrate that it works well on real data, by inferring rotation periods for 275 Kepler stars with previously measured periods. We provide a table of rotation periods for these and many more, altogether 1102 Kepler objects of interest, and their posterior probability density function samples. Because this method delivers posterior probability density functions, it will enable hierarchical studies involving stellar rotation, particularly those involving population modelling, such as inferring stellar ages, obliquities in exoplanet systems, or characterizing star-planet interactions. The code used to implement this method is available online.

  19. Ultraviolet photometry of stellar populations in galaxies

    International Nuclear Information System (INIS)

    Deharveng, J.M.

    1981-01-01

    The UV flux of stellar populations, which is essentially emitted by young stars, conveys information on the process of star formation and its recent history. However, the evaluation of the flux arising from the young stellar component may be difficult. In the case of late type galaxies it is hampered by the extinction and the effect of scattered stellar radiation. In the case of early type galaxies, the star formation, if any, has to be disentangled from the contribution of hot evolved stars and of a possible 'active' phenomenon. A review of observations and results relevant two cases is presented [fr

  20. Equilibrium 𝛽-limits in classical stellarators

    Science.gov (United States)

    Loizu, J.; Hudson, S. R.; Nührenberg, C.; Geiger, J.; Helander, P.

    2017-12-01

    A numerical investigation is carried out to understand the equilibrium -limit in a classical stellarator. The stepped-pressure equilibrium code (Hudson et al., Phys. Plasmas, vol. 19 (11), 2012) is used in order to assess whether or not magnetic islands and stochastic field-lines can emerge at high . Two modes of operation are considered: a zero-net-current stellarator and a fixed-iota stellarator. Despite the fact that relaxation is allowed (Taylor, Rev. Mod. Phys., vol. 58 (3), 1986, pp. 741-763), the former is shown to maintain good flux surfaces up to the equilibrium -limit predicted by ideal-magnetohydrodynamics (MHD), above which a separatrix forms. The latter, which has no ideal equilibrium -limit, is shown to develop regions of magnetic islands and chaos at sufficiently high , thereby providing a `non-ideal -limit'. Perhaps surprisingly, however, the value of at which the Shafranov shift of the axis reaches a fraction of the minor radius follows in all cases the scaling laws predicted by ideal-MHD. We compare our results to the High-Beta-Stellarator theory of Freidberg (Ideal MHD, 2014, Cambridge University Press) and derive a new prediction for the non-ideal equilibrium -limit above which chaos emerges.

  1. The Stellar Imager (SI) Mission Concept

    Science.gov (United States)

    Carpenter, Kenneth G.; Schrijver, Carolus J.; Lyon, Richard G.; Mundy, Lee G.; Allen, Ronald J.; Armstrong, Thomas; Danchi, William C.; Karovska, Margarita; Marzouk, Joe; Mazzuca, Lisa M.; hide

    2002-01-01

    The Stellar Imager (SI) is envisioned as a space-based, UV-optical interferometer composed of 10 or more one-meter class elements distributed with a maximum baseline of 0.5 km. It is designed to image stars and binaries with sufficient resolution to enable long-term studies of stellar magnetic activity patterns, for comparison with those on the sun. It will also support asteroseismology (acoustic imaging) to probe stellar internal structure, differential rotation, and large-scale circulations. SI will enable us to understand the various effects of the magnetic fields of stars, the dynamos that generate these fields, and the internal structure and dynamics of the stars. The ultimate goal of the mission is to achieve the best-possible forecasting of solar activity as a driver of climate and space weather on time scales ranging from months up to decades, and an understanding of the impact of stellar magnetic activity on life in the Universe. In this paper we describe the scientific goals of the mission, the performance requirements needed to address these goals, the "enabling technology" development efforts being pursued, and the design concepts now under study for the full mission and a possible pathfinder mission.

  2. Improving 1D Stellar Models with 3D Atmospheres

    Science.gov (United States)

    Rørsted Mosumgaard, Jakob; Silva Aguirre, Víctor; Weiss, Achim; Christensen-Dalsgaard, Jørgen; Trampedach, Regner

    2017-10-01

    Stellar evolution codes play a major role in present-day astrophysics, yet they share common issues. In this work we seek to remedy some of those by the use of results from realistic and highly detailed 3D hydrodynamical simulations of stellar atmospheres. We have implemented a new temperature stratification extracted directly from the 3D simulations into the Garching Stellar Evolution Code to replace the simplified atmosphere normally used. Secondly, we have implemented the use of a variable mixing-length parameter, which changes as a function of the stellar surface gravity and temperature - also derived from the 3D simulations. Furthermore, to make our models consistent, we have calculated new opacity tables to match the atmospheric simulations. Here, we present the modified code and initial results on stellar evolution using it.

  3. Confinement and heating in modular and continuous coil stellarators

    International Nuclear Information System (INIS)

    Anderson, D.T.; Anderson, F.S.B.; Bonomo, R.L.

    1983-01-01

    Major efforts on the Proto-Cleo stellarator have focused on ICRH of a net current-free plasma, measurements of plasma secondary currents, RF heating by externally induced magnetic reconnection through the formation and destruction of an internal separatrix, and RF current drive experiments. Efforts on the Proto-Cleo torsatron have focused on electron heat conduction. A modular stellarator has been designed and is under fabrication at the University of Wisconsin. The Interchangeable Module Stellarator (IMS) is designed to approximate closely the magnetic properties of the existing Proto-Cleo stellarator as much as possible. Monte-Carlo transport calculations have been made in flux coordinates using model fields patterned after magnetic fields in Proto-Cleo and IMS. Plasma simulation techniques using a 2.5-dimensional particle-in-cell method have been utilized in a numerical search for the bootstrap current. A current is found which is proportional to temperature and density gradients but is independent of poloidal field. The behaviour of charged particles moving in a stellarator under the influence of a steady magnetic field is analysed in terms of the Hamiltonian of the moving particle and the technique of repeated canonical transformations to identify possible adiabatic invariants and drift motions. An improved theory of collisionless particle motion in stellarators has been developed for a family of stellarator configurations. The broad range of configurations encompassed by this family permits an understanding of the differences in numerically observed transport coefficients. Two procedures have been developed to calculate the bootstrap current in non-axisymmetric stellarators. In fully toroidal stellarators the flows and consequent bootstrap current are reduced from their axisymmetric values by a factor of order l slash-l/m in the Pfirsch-Schlueter regime. (author)

  4. Characterizing Exoplanet Habitability with Emission Spectroscopy

    Science.gov (United States)

    Robinson, Tyler

    2018-01-01

    Results from NASA’s Kepler mission and other recent exoplanet surveys have demonstrated that potentially habitable exoplanets are relatively common, especially in the case of low-mass stellar hosts. The next key question that must be addressed for such planets is whether or not these worlds are actually habitable, implying they could sustain surface liquid water. Only through investigations of the potential habitability of exoplanets and through searches for biosignatures from these planets will we be able to understand if the emergence of life is a common phenomenon in our galaxy. Emission spectroscopy for transiting exoplanets (sometimes called secondary eclipse spectroscopy) is a powerful technique that future missions will use to study the atmospheres and surfaces of worlds orbiting in the habitable zones of nearby, low-mass stars. Emission observations that span the mid-infrared wavelength range for potentially habitable exoplanets provide opportunities to detect key habitability and life signatures, and also allow observers to probe atmospheric and surface temperatures. This presentation will outline the case for using emission spectroscopy to understand if an exoplanet can sustain surface liquid water, which is believed to be a critical precursor to the origin of life.

  5. The Stellar-Dynamical Oeuvre James Binney

    Indian Academy of Sciences (India)

    tribpo

    of the eigenvalues of M. The variation of the stellar density from point to point .... of Σ,(ΔΕ)2 , where ∆ Ε is the change in energy that a star suffers during a binary ... could use these results to calculate the relaxation time in a stellar system if he .... the region of enhanced density that tails behind it like a wake behind a ship. By.

  6. Two novel compact toroidal concepts with Stellarator features

    International Nuclear Information System (INIS)

    Moroz, P.E.

    1997-07-01

    Two novel compact toroidal concepts are presented. One is the Stellarator-Spheromak (SSP) and another is the Extreme-Low-Aspect-Ratio Stellarator (ELARS). An SSP device represents a hybrid between a spherical stellarator (SS) and a spheromak. This configuration retains the main advantages of spheromaks ans has a potential for improving the spheromak concept regarding its main problems. The MHD equilibrium in an SSP with very high β of the confined plasma is demonstrated. Another concept, ELARS, represents an extreme limit of the SS approach, and considers devices with stellarator features and aspect ratios A ∼ 1. We have succeeded in finding ELARS configurations with extremely compact, modular, and simple design compatible with significant rotational transform, large plasma volume, and good particle transport characteristics

  7. Evaluating Stellarator Divertor Designs with EMC3

    Science.gov (United States)

    Bader, Aaron; Anderson, D. T.; Feng, Y.; Hegna, C. C.; Talmadge, J. N.

    2013-10-01

    In this paper various improvements of stellarator divertor design are explored. Next step stellarator devices require innovative divertor solutions to handle heat flux loads and impurity control. One avenue is to enhance magnetic flux expansion near strike points, somewhat akin to the X-Divertor concept in Tokamaks. The effect of judiciously placed external coils on flux deposition is calculated for configurations based on the HSX stellarator. In addition, we attempt to optimize divertor plate location to facilitate the external coil placement. Alternate areas of focus involve altering edge island size to elucidate the driving physics in the edge. The 3-D nature of stellarators complicates design and necessitates analysis of new divertor structures with appropriate simulation tools. We evaluate the various configurations with the coupled codes EMC3-EIRENE, allowing us to benchmark configurations based on target heat flux, impurity behavior, radiated power, and transitions to high recycling and detached regimes. Work supported by DOE-SC0006103.

  8. Robust Modeling of Stellar Triples in PHOEBE

    Science.gov (United States)

    Conroy, Kyle E.; Prsa, Andrej; Horvat, Martin; Stassun, Keivan G.

    2017-01-01

    The number of known mutually-eclipsing stellar triple and multiple systems has increased greatly during the Kepler era. These systems provide significant opportunities to both determine fundamental stellar parameters of benchmark systems to unprecedented precision as well as to study the dynamical interaction and formation mechanisms of stellar and planetary systems. Modeling these systems to their full potential, however, has not been feasible until recently. Most existing available codes are restricted to the two-body binary case and those that do provide N-body support for more components make sacrifices in precision by assuming no stellar surface distortion. We have completely redesigned and rewritten the PHOEBE binary modeling code to incorporate support for triple and higher-order systems while also robustly modeling data with Kepler precision. Here we present our approach, demonstrate several test cases based on real data, and discuss the current status of PHOEBE's support for modeling these types of systems. PHOEBE is funded in part by NSF grant #1517474.

  9. Stellar signatures of AGN-jet-triggered star formation

    International Nuclear Information System (INIS)

    Dugan, Zachary; Silk, Joseph; Bryan, Sarah; Gaibler, Volker; Haas, Marcel

    2014-01-01

    To investigate feedback between relativistic jets emanating from active galactic nuclei and the stellar population of the host galaxy, we analyze the long-term evolution of the orbits of the stars formed in the galaxy-scale simulations by Gaibler et al. of jets in massive, gas-rich galaxies at z ∼ 2-3. We find strong, jet-induced differences in the resulting stellar populations of galaxies that host relativistic jets and galaxies that do not, including correlations in stellar locations, velocities, and ages. Jets are found to generate distributions of increased radial and vertical velocities that persist long enough to effectively augment the stellar structure of the host. The jets cause the formation of bow shocks that move out through the disk, generating rings of star formation within the disk. The bow shock often accelerates pockets of gas in which stars form, yielding populations of stars with significant radial and vertical velocities, some of which have large enough velocities to escape the galaxy. These stellar population signatures can serve to identify past jet activity as well as jet-induced star formation.

  10. Color-size Relations of Disc Galaxies with Similar Stellar Masses

    Science.gov (United States)

    Fu, W.; Chang, R. X.; Shen, S. Y.; Zhang, B.

    2011-01-01

    To investigate the correlations between colors and sizes of disc galaxies with similar stellar masses, a sample of 7959 local face-on disc galaxies is collected from the main galaxy sample of the Seventh Data Release of Sloan Digital Sky Survey (SDSS DR7). Our results show that, under the condition that the stellar masses of disc galaxies are similar, the relation between u-r and size is weak, while g-r, r-i and r-z colors decrease with disk size. This means that the color-size relations of disc galaxies with similar stellar masses do exist, i.e., the more extended disc galaxies with similar stellar masses tend to have bluer colors. An artificial sample is constructed to confirm that this correlation is not driven by the color-stellar mass relations and size-stellar mass relation of disc galaxies. Our results suggest that the mass distribution of disk galaxies may have an important influence on their stellar formation history, i.e., the galaxies with more extended mass distribution evolve more slowly.

  11. Environmental effects on stellar populations of star clusters and dwarf galaxies

    Science.gov (United States)

    Pasetto, Stefano; Cropper, Mark; Fujita, Yutaka; Chiosi, Cesare; Grebel, Eva K.

    2017-03-01

    We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation of gravitationally bound systems in an external environment. Ram pressure, Kelvin-Helmholtz and Rayleigh-Taylor instabilities, and tidal forces are accounted for separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment. We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system thus investigating the detectability limits of these different effects for future observational projects and their relevance. The developed theoretical framework has direct applications to the cases of massive star clusters, dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy.

  12. Environmental effects on stellar populations of dwarf galaxies and star clusters

    Science.gov (United States)

    Pasetto, Stefano; Cropper, Mark; fujita, Yutaka; Chiosi, Cesare; Grebel, Eva K.

    2015-08-01

    We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation history of gravitationally bound system in an external environment. Ram pressure, Kelvin-Helmholtz instability, Rayleigh-Taylor, and tidal forces are accounted separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment useful in observational applications as well as theoretical interpretations of numerical results.We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system thus investigating the detectability limits of these different effects for future observational projects and their relevance.The theoretical framework developed has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy.

  13. The effect of ISM absorption on stellar activity measurements and its relevance for exoplanet studies

    Science.gov (United States)

    Fossati, L.; Marcelja, S. E.; Staab, D.; Cubillos, P. E.; France, K.; Haswell, C. A.; Ingrassia, S.; Jenkins, J. S.; Koskinen, T.; Lanza, A. F.; Redfield, S.; Youngblood, A.; Pelzmann, G.

    2017-05-01

    Past ultraviolet and optical observations of stars hosting close-in Jupiter-mass planets have shown that some of these stars present an anomalously low chromospheric activity, significantly below the basal level. For the hot Jupiter planet host WASP-13, observations have shown that the apparent lack of activity is possibly caused by absorption from the intervening interstellar medium (ISM). Inspired by this result, we study the effect of ISM absorption on activity measurements (S and log R 'HK indices) for main-sequence late-type stars. To this end, we employ synthetic stellar photospheric spectra combined with varying amounts of chromospheric emission and ISM absorption. We present the effect of ISM absorption on activity measurements by varying several instrumental (spectral resolution), stellar (projected rotational velocity, effective temperature, and chromospheric emission flux), and ISM parameters (relative velocity between stellar and ISM Ca II lines, broadening b-parameter, and Ca II column density). We find that for relative velocities between the stellar and ISM lines smaller than 30-40 km s-1 and for ISM Ca II column densities log NCaII ⪆ 12, the ISM absorption has a significant influence on activity measurements. Direct measurements and three dimensional maps of the Galactic ISM absorption indicate that an ISM Ca II column density of log NCaII = 12 is typically reached by a distance of about 100 pc along most sight lines. In particular, for a Sun-like star lying at a distance greater than 100 pc, we expect a depression (bias) in the log R'HK value larger than 0.05-0.1 dex, about the same size as the typical measurement and calibration uncertainties on this parameter. This work shows that the bias introduced by ISM absorption must always be considered when measuring activity for stars lying beyond 100 pc. We also consider the effect of multiple ISM absorption components. We discuss the relevance of this result for exoplanet studies and revise the

  14. Helical post stellarator. Part 1: Vacuum configuration

    International Nuclear Information System (INIS)

    Moroz, P.E.

    1997-08-01

    Results on a novel type of stellarator configuration, the Helical Post Stellarator (HPS), are presented. This configuration is different significantly from all previously known stellarators due to its unique geometrical characteristics and unique physical properties. Among those are: the magnetic field has only one toroidal period (M = 1), the plasma has an extremely low aspect ratio, A ∼ 1, and the variation of the magnetic field, B, along field lines features a helical ripple on the inside of the torus. Among the main advantages of a HPS for a fusion program are extremely compact, modular, and simple design compatible with significant rotational transform, large plasma volume, and improved particle transport characteristics

  15. The WEGA Stellarator: Results and Prospects

    International Nuclear Information System (INIS)

    Otte, M.; Andruczyk, D.; Koenig, R.; Laqua, H. P.; Lischtschenko, O.; Marsen, S.; Schacht, J.; Podoba, Y. Y.; Wagner, F.; Warr, G. B.; Holzhauer, E.; Howard, J.; Krupnik, L.; Zhezhera, A.; Urban, J.; Preinhalter, J.

    2008-01-01

    In this article an overview is given on results from magnetic flux surface measurements, applied ECR heating scenarios for 2.45 GHz and 28 GHz, fluctuation and transport studies and plasma edge biasing experiments performed in the WEGA stellarator. Examples for the development of new diagnostics and the machine control system are given that will be used at Wendelstein 7-X stellarator, which is currently under construction in Greifswald

  16. INTEGRAL FIELD SPECTROSCOPY OF SUPERNOVA EXPLOSION SITES: CONSTRAINING THE MASS AND METALLICITY OF THE PROGENITORS. I. TYPE Ib AND Ic SUPERNOVAE

    Energy Technology Data Exchange (ETDEWEB)

    Kuncarayakti, Hanindyo; Maeda, Keiichi [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan); Doi, Mamoru; Morokuma, Tomoki; Hashiba, Yasuhito [Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Aldering, Greg [Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Arimoto, Nobuo [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Pereira, Rui [CNRS/IN2P3, Institut de Physique Nucleaire de Lyon, 4 Rue Enrico Fermi, F-69622 Villeurbanne Cedex (France); Usuda, Tomonori, E-mail: hanindyo.kuncarayakti@ipmu.jp [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A' ohoku Place, Hilo, HI 96720 (United States)

    2013-08-01

    Integral field spectroscopy of 11 Type Ib/Ic supernova (SN Ib/Ic) explosion sites in nearby galaxies has been obtained using UH88/SNIFS and Gemini-N/GMOS. The use of integral field spectroscopy enables us to obtain both spatial and spectral information about the explosion site, enabling the identification of the parent stellar population of the SN progenitor star. The spectrum of the parent population provides metallicity determination via strong-line method and age estimation obtained via comparison with simple stellar population models. We adopt this information as the metallicity and age of the SN progenitor, under the assumption that it was coeval with the parent stellar population. The age of the star corresponds to its lifetime, which in turn gives the estimate of its initial mass. With this method we were able to determine both the metallicity and initial (zero-age main sequence) mass of the progenitor stars of SNe Ib and Ic. We found that on average SN Ic explosion sites are more metal-rich and younger than SN Ib sites. The initial mass of the progenitors derived from parent stellar population age suggests that SN Ic has more massive progenitors than SN Ib. In addition, we also found indication that some of our SN progenitors are less massive than {approx}25 M{sub Sun }, indicating that they may have been stars in a close binary system that have lost their outer envelope via binary interactions to produce SNe Ib/Ic, instead of single Wolf-Rayet stars. These findings support the current suggestions that both binary and single progenitor channels are in effect in producing SNe Ib/Ic. This work also demonstrates the power of integral field spectroscopy in investigating SN environments and active star-forming regions.

  17. Progress in modular-stellarator fusion-power-reactor conceptual designs

    International Nuclear Information System (INIS)

    Sviatoslavsky, I.N.; Van Sciver, S.W.; Kulcinski, G.L.

    1982-01-01

    Recent encouraging experimental results on stellarators/torsatrons/heliotrons (S/T/H) have revived interest in these concepts as possible fusion power reactors. The use of modular coils to generate the stellarator topology has added impetus to this renewed interest. Studies of the modular coil approach to stellarators by UW-Madison and Los Alamos National Laboratory are summarized in this paper

  18. The galaxy population of Abell 1367: the stellar mass-metallicity relation

    Science.gov (United States)

    Mouhcine, M.; Kriwattanawong, W.; James, P. A.

    2011-04-01

    Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galaxies traces a sequence of varying metallicity at a narrow range of luminosity-weighted stellar ages. Lenticular galaxies in the red sequence, however, exhibit a substantial spread of luminosity-weighted stellar metallicities and ages. For red-sequence lenticular galaxies and blue cloud galaxies, low-mass galaxies tend to be on average dominated by stellar populations of younger luminosity-weighted ages. Sample galaxies exhibit a strong correlation between integrated stellar mass and luminosity-weighted stellar metallicity. Galaxies with signs of morphological disturbance and ongoing star formation activity, tend to be underabundant with respect to passive galaxies in the red sequence of comparable stellar masses. We argue that this could be due to tidally driven gas flows towards the star-forming regions, carrying less enriched gas and diluting the pre-existing gas to produce younger stellar populations with lower metallicities than would be obtained prior to the interaction. Finally, we find no statistically significant evidence for changes in the luminosity-weighted ages and metallicities for either red-sequence or blue-cloud galaxies, at fixed stellar mass, with location within the cluster. We dedicate this work to the memory of our friend and colleague C. Moss who died suddenly recently.

  19. Thermal and structural characterization of synthetic and natural nanocrystalline hydroxyapatite

    International Nuclear Information System (INIS)

    Sofronia, Ancuta M.; Baies, Radu; Anghel, Elena M.; Marinescu, Cornelia A.; Tanasescu, Speranta

    2014-01-01

    The aim of this work was to study the thermal stability on heating and to obtain the processing parameters of synthetic and bone-derived hydroxyapatite over temperatures between room temperature and 1400 °C by thermal analysis (thermogravimetry (TG)/differential scanning calorimetry (DSC) and thermo-mechanical analysis—TMA). Structural and surface modifications related to samples origin and calcination temperature were investigated by Fourier transformed infrared (FTIR) and Raman spectroscopy, X-ray diffraction (XRD) and BET method. FTIR spectra indicated that the organic constituents and carbonate are no longer present in the natural sample calcined at 800 °C. Raman spectra highlighted the decomposition products of the hydroxyapatite. The calcination treatment modifies the processes kinetics of the synthetic samples, being able to isolate lattice water desorption processes of decarbonization and the dehydroxylation processes. Shrinkage of calcined synthetic sample increases by 10% compared to uncalcined synthetic powder. From the TMA correlated with TG analysis and heat capacity data it can be concluded that sintering temperature of the synthetic samples should be chosen in the temperature range of the onset of dehydroxylation and the temperature at which oxyapatite decomposition begins. - Highlights: • Specific surface area of HA powder was reduced from 19.2 to 9.5 m 2 /g by calcination. • Raman spectra indicate the presence of B-type CO 3 group in HA synthetic samples. • The onset temperature of HA densification and dehydroxylation processes correspond. • Calcination of HA influences reactions kinetics with consequences on densification. • Shrinkage of calcined HA sample increases by 10% with respect to uncalcined sample

  20. Thermal and structural characterization of synthetic and natural nanocrystalline hydroxyapatite

    Energy Technology Data Exchange (ETDEWEB)

    Sofronia, Ancuta M. [Ilie Murgulescu Institute of Physical Chemistry of the Romanian Academy, 060021 Bucharest (Romania); Baies, Radu [National Research Institute for Electrochemistry and Condensed Matter, 300224 Timisoara (Romania); Anghel, Elena M. [Ilie Murgulescu Institute of Physical Chemistry of the Romanian Academy, 060021 Bucharest (Romania); Marinescu, Cornelia A., E-mail: alcorina@chimfiz.icf.ro [Ilie Murgulescu Institute of Physical Chemistry of the Romanian Academy, 060021 Bucharest (Romania); Tanasescu, Speranta [Ilie Murgulescu Institute of Physical Chemistry of the Romanian Academy, 060021 Bucharest (Romania)

    2014-10-01

    The aim of this work was to study the thermal stability on heating and to obtain the processing parameters of synthetic and bone-derived hydroxyapatite over temperatures between room temperature and 1400 °C by thermal analysis (thermogravimetry (TG)/differential scanning calorimetry (DSC) and thermo-mechanical analysis—TMA). Structural and surface modifications related to samples origin and calcination temperature were investigated by Fourier transformed infrared (FTIR) and Raman spectroscopy, X-ray diffraction (XRD) and BET method. FTIR spectra indicated that the organic constituents and carbonate are no longer present in the natural sample calcined at 800 °C. Raman spectra highlighted the decomposition products of the hydroxyapatite. The calcination treatment modifies the processes kinetics of the synthetic samples, being able to isolate lattice water desorption processes of decarbonization and the dehydroxylation processes. Shrinkage of calcined synthetic sample increases by 10% compared to uncalcined synthetic powder. From the TMA correlated with TG analysis and heat capacity data it can be concluded that sintering temperature of the synthetic samples should be chosen in the temperature range of the onset of dehydroxylation and the temperature at which oxyapatite decomposition begins. - Highlights: • Specific surface area of HA powder was reduced from 19.2 to 9.5 m{sup 2}/g by calcination. • Raman spectra indicate the presence of B-type CO{sub 3} group in HA synthetic samples. • The onset temperature of HA densification and dehydroxylation processes correspond. • Calcination of HA influences reactions kinetics with consequences on densification. • Shrinkage of calcined HA sample increases by 10% with respect to uncalcined sample.

  1. Natural - synthetic - artificial!

    DEFF Research Database (Denmark)

    Nielsen, Peter E

    2010-01-01

    The terms "natural," "synthetic" and "artificial" are discussed in relation to synthetic and artificial chromosomes and genomes, synthetic and artificial cells and artificial life.......The terms "natural," "synthetic" and "artificial" are discussed in relation to synthetic and artificial chromosomes and genomes, synthetic and artificial cells and artificial life....

  2. A COMPARISON OF STELLAR ELEMENTAL ABUNDANCE TECHNIQUES AND MEASUREMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Hinkel, Natalie R.; Young, Patrick A.; Pagano, Michael D.; Desch, Steven J.; Anbar, Ariel D. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Adibekyan, Vardan; Mena, Elisa Delgado; Sousa, Sergio G.; Santos, Nuno C. [Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto (Portugal); Blanco-Cuaresma, Sergi [Observatoire de Genève, Université de Genève, CH-1290 Versoix (Switzerland); Carlberg, Joleen K. [NASA Goddard Space Flight Center, Code 667, Greenbelt MD 20771 (United States); Liu, Fan [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia); Nordlander, Thomas; Korn, Andreas; Gruyters, Pieter; Heiter, Ulrike [Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala (Sweden); Jofré, Paula [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Soubiran, Caroline, E-mail: natalie.hinkel@gmail.com [CNRS/Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac (France)

    2016-09-01

    Stellar elemental abundances are important for understanding the fundamental properties of a star or stellar group, such as age and evolutionary history, as well as the composition of an orbiting planet. However, as abundance measurement techniques have progressed, there has been little standardization between individual methods and their comparisons. As a result, different stellar abundance procedures determine measurements that vary beyond the quoted error for the same elements within the same stars. The purpose of this paper is to better understand the systematic variations between methods and offer recommendations for producing more accurate results in the future. We invited a number of participants from around the world (Australia, Portugal, Sweden, Switzerland, and the United States) to calculate 10 element abundances (C, O, Na, Mg, Al, Si, Fe, Ni, Ba, and Eu) using the same stellar spectra for four stars (HD 361, HD 10700, HD 121504, and HD 202206). Each group produced measurements for each star using (1) their own autonomous techniques, (2) standardized stellar parameters, (3) a standardized line list, and (4) both standardized parameters and a line list. We present the resulting stellar parameters, absolute abundances, and a metric of data similarity that quantifies the homogeneity of the data. We conclude that standardization of some kind, particularly stellar parameters, improves the consistency between methods. However, because results did not converge as more free parameters were standardized, it is clear there are inherent issues within the techniques that need to be reconciled. Therefore, we encourage more conversation and transparency within the community such that stellar abundance determinations can be reproducible as well as accurate and precise.

  3. The stellar metallicity gradients in galaxy discs in a cosmological scenario

    Science.gov (United States)

    Tissera, Patricia B.; Machado, Rubens E. G.; Sanchez-Blazquez, Patricia; Pedrosa, Susana E.; Sánchez, Sebastián F.; Snaith, Owain; Vilchez, Jose

    2016-08-01

    Context. The stellar metallicity gradients of disc galaxies provide information on disc assembly, star formation processes, and chemical evolution. They also might store information on dynamical processes that could affect the distribution of chemical elements in the gas phase and the stellar components. Understanding their joint effects within a hierarchical clustering scenario is of paramount importance. Aims: We studied the stellar metallicity gradients of simulated discs in a cosmological simulation. We explored the dependence of the stellar metallicity gradients on stellar age and on the size and mass of the stellar discs. Methods: We used a catalogue of galaxies with disc components selected from a cosmological hydrodynamical simulation performed including a physically motivated supernova feedback and chemical evolution. Disc components were defined based on angular momentum and binding energy criteria. The metallicity profiles were estimated for stars with different ages. We confront our numerical findings with results from the Calar Alto Legacy Integral Field Area (CALIFA) Survey. Results: The simulated stellar discs are found to have metallicity profiles with slopes in global agreement with observations. Low stellar mass galaxies tend to have a larger variety of metallicity slopes. When normalized by the half-mass radius, the stellar metallicity gradients do not show any dependence and the dispersion increases significantly, regardless of the galaxy mass. Galaxies with stellar masses o f around 1010M⊙ show steeper negative metallicity gradients. The stellar metallicity gradients correlate with the half-mass radius. However, the correlation signal is not present when they are normalized by the half-mass radius. Stellar discs with positive age gradients are detected to have negative and positive metallicity gradients, depending on the relative importance of recent star formation activity in the central regions. Conclusions: Our results suggest that inside

  4. Models of hot stellar systems

    International Nuclear Information System (INIS)

    Van Albada, T.S.

    1986-01-01

    Elliptical galaxies consist almost entirely of stars. Sites of recent star formation are rare, and most stars are believed to be several billion years old, perhaps as old as the Universe itself (--10/sup 10/ yrs). Stellar motions in ellipticals show a modest amount of circulation about the center of the system, but most support against the force of gravity is provided by random motions; for this reason ellipticals are called 'hot' stellar systems. Spiral galaxies usually also contain an appreciable amount of gas (--10%, mainly atomic hydrogen) and new stars are continually being formed out of this gas, especially in the spiral arms. In contrast to ellipticals, support against gravity in spiral galaxies comes almost entirely from rotation; random motions of the stars with respect to rotation are small. Consequently, spiral galaxies are called 'cold' stellar systems. Other than in hot systems, in cold systems the collective response of stars to variations in the force field is an essential part of the dynamics. The present overview is limited to mathematical models of hot systems. Computational methods are also discussed

  5. CCFpams: Atmospheric stellar parameters from cross-correlation functions

    Science.gov (United States)

    Malavolta, Luca; Lovis, Christophe; Pepe, Francesco; Sneden, Christopher; Udry, Stephane

    2017-07-01

    CCFpams allows the measurement of stellar temperature, metallicity and gravity within a few seconds and in a completely automated fashion. Rather than performing comparisons with spectral libraries, the technique is based on the determination of several cross-correlation functions (CCFs) obtained by including spectral features with different sensitivity to the photospheric parameters. Literature stellar parameters of high signal-to-noise (SNR) and high-resolution HARPS spectra of FGK Main Sequence stars are used to calibrate the stellar parameters as a function of CCF areas.

  6. The Properties of Post-Starburst Quasars Based on Optical Spectroscopy

    OpenAIRE

    Cales, Sabrina L.; Brotherton, Michael S.; Shang, Zhaohui; Runnoe, Jessie C.; DiPompeo, Michael A.; Bennert, Vardha Nicola; Canalizo, Gabriela; Hiner, Kyle D.; Stoll, R.; Ganguly, Rajib; Diamond-Stanic, Aleksandar

    2012-01-01

    We present optical spectroscopy of a sample of 38 post-starburst quasars (PSQs) at z ~ 0.3, 29 of which have morphological classifications based on Hubble Space Telescope imaging. These broad-lined active galactic nuclei (AGNs) possess the spectral signatures of massive intermediate-aged stellar populations making them potentially useful for studying connections between nuclear activity and host galaxy evolution. We model the spectra in order to determine the ages and masses of the host stell...

  7. Assessment of global stellarator confinement: Status of the international stellarator confinement scaling data base

    International Nuclear Information System (INIS)

    Dinklage, A.; Beidler, C.D.; Dose, V.; Geiger, J.; Kus, A.; Preuss, R.; Ascasibar, E.; Tribaldos, V.; Harris, J.H.; Murakami, S.; Sano, F.; Okamura, S.; Suzuki, Y.; Watanabe, K.Y.; Yamada, H.; Yokoyama, M.; Stroth, U.; Talmadge, J.

    2005-01-01

    Different stellarator/heliotron devices along with their respective flexibility cover a large magnetic configuration space. Since the ultimate goal of stellarator research aims at an alternative fusion reactor concept, the exploration of the most promising configurations requires a comparative assessment of the plasma performance and how different aspects of a 3D configuration influence it. Therefore, the International Stellarator Confinement Database (ISCDB) has been re- initiated in 2004 and the ISS95 database has been extended to roughly 3000 discharges from eight different devices. Further data-sets are continuously added. A revision of a data set restricted to comparable scenarios lead to the ISS04 scaling law which confirmed ISS95 but also revealed clearly the necessity to incorporate configuration descriptive parameters. In other words, an extension beyond the set of regression parameters used for ISS95/ISS04 appears to be necessary and candidates, such as the elongation are investigated. Since grouping of data is a key-issue for deriving ISS04, basic assumptions are revised, e.g. the dependence on the heating scheme. Moreover, an assessment of statistical approaches is investigated with respect to their impact on the scaling. A crucial issue is the weighting of data groups which is discussed in terms of error-in-variable techniques and Bayesian model comparison. The latter is employed for testing scaling ansatzes depending on scaling invariance principles hence allowing the assessment of applicability of theory-based scaling laws on stellarator confinement. 1. ISCDB resources are jointly hosted by NIFS and IPP, see http://iscdb.nifs.ac.jp and http://www.ipp.mpg.de/ISS. (author)

  8. Stellarator physics

    International Nuclear Information System (INIS)

    1990-07-01

    This document consists of the proceedings of the Seventh International Workshop on Stellarators, held in Oak Ridge, Tennessee, USA, 10-14 April, 1989. The document consists of a summary of presentations, an overview of experimental results, and papers presented at the workshop on transport, impurities and divertors, diagnostics, ECH confinement experiments, equilibrium and stability studies, RF heating, confinement, magnetic configurations, and new experiments. Refs, figs and tabs

  9. THE FORMATION OF SECONDARY STELLAR GENERATIONS IN MASSIVE YOUNG STAR CLUSTERS FROM RAPIDLY COOLING SHOCKED STELLAR WINDS

    Energy Technology Data Exchange (ETDEWEB)

    Wünsch, R.; Palouš, J.; Ehlerová, S. [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague (Czech Republic); Tenorio-Tagle, G. [Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla, México (Mexico)

    2017-01-20

    We study a model of rapidly cooling shocked stellar winds in young massive clusters and estimate the circumstances under which secondary star formation, out of the reinserted winds from a first stellar generation (1G), is possible. We have used two implementations of the model: a highly idealized, computationally inexpensive, spherically symmetric semi-analytic model, and a complex, three-dimensional radiation-hydrodynamic, simulation; they are in a good mutual agreement. The results confirm our previous findings that, in a cluster with 1G mass 10{sup 7} M {sub ⊙} and half-mass–radius 2.38 pc, the shocked stellar winds become thermally unstable, collapse into dense gaseous structures that partially accumulate inside the cluster, self-shield against ionizing stellar radiation, and form the second generation (2G) of stars. We have used the semi-analytic model to explore a subset of the parameter space covering a wide range of the observationally poorly constrained parameters: the heating efficiency, η {sub he}, and the mass loading, η {sub ml}. The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if η {sub he} ≲ 10%, which is suggested by the observations. Furthermore, for low η {sub he}, the model provides a self-consistent mechanism predicting 2G stars forming only in the central zones of the cluster. Finally, we have calculated the accumulated warm gas emission in the H30 α recombination line, analyzed its velocity profile, and estimated its intensity for super star clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas should be detectable with ALMA.

  10. Stellar-to-halo mass relation of cluster galaxies

    International Nuclear Information System (INIS)

    Niemiec, Anna; Jullo, Eric; Limousin, Marceau; Giocoli, Carlo

    2017-01-01

    In the formation of galaxy groups and clusters, the dark matter haloes containing satellite galaxies are expected to be tidally stripped in gravitational interactions with the host. We use galaxy-galaxy weak lensing to measure the average mass of dark matter haloes of satellite galaxies as a function of projected distance to the centre of the host, since stripping is expected to be greater for satellites closer to the centre of the cluster. We further classify the satellites according to their stellar mass: assuming that the stellar component of the galaxy is less disrupted by tidal stripping, stellar mass can be used as a proxy of the infall mass. We study the stellar to halo mass relation of satellites as a function of the cluster-centric distance to measure tidal stripping. We use the shear catalogues of the DES science veri cation archive, the CFHTLenS and the CFHT Stripe 82 surveys, and we select satellites from the redMaPPer catalogue of clusters. For galaxies located in the outskirts of clusters, we nd a stellar to halo mass relation in good agreement with the theoretical expectations from Moster, Naab & White (2013) for central galaxies. In the centre of the cluster, we nd that this relation is shifted to smaller halo mass for a given stellar mass. We interpret this nding as further evidence for tidal stripping of dark matter haloes in high density environments.

  11. Teaching stellar interferometry with polymer optical fibers

    Science.gov (United States)

    Illarramendi, M. A.; Arregui, L.; Zubia, J.; Hueso, R.; Sanchez-Lavega, A.

    2017-08-01

    In this manuscript we show the design of a simple experiment that reproduces the operation of the Michelson stellar interferometer by using step-index polymer optical fibers. The emission of stellar sources, single or binary stars, has been simulated by the laser light emerging from the output surface of the 2 meter-long polymer optical fiber. This light has an emission pattern that is similar to the emission pattern of stellar sources - circular, uniform, spatially incoherent, and quasi-monochromatic. Light coming from the fiber end faces passes through two identical pinholes located on a lid covering the objective of a small telescope, thus producing interference. Interference fringes have been acquired using a camera that is coupled to a telescope. The experiments have been carried out both outdoors in the daytime and indoors. By measuring the fringe visibilities, we have determined the size of our artificial stellar sources and the distance between them, when placing them at distances of 54 m from the telescope in the indoor measurements and of 75 m in the outdoor ones.

  12. Stellar axion models

    Energy Technology Data Exchange (ETDEWEB)

    Nowakowski, Daniel; Kuster, Markus; Meister, Claudia V.; Fuelbert, Florian; Hoffmann, Dieter H.H. [TU Darmstadt (Germany). Institut fuer Kernphysik; Weiss, Achim [Max-Planck-Institut fuer Astrophysik, Garching (Germany)

    2010-07-01

    An axion helioscope is typically operated to observe the sun as an axion source. Additional pointings at celestial sources, e.g. stars in other galaxies, result in possible detections of axions from distant galactic objects. For the observation of supplementary axion sources we therefore calculate the thereotical axion flux from distant stars by extending axionic flux models for the axion Primakoff effect in the sun to other main sequence stars. The main sequence star models used for our calculations are based on full stellar structure calculations. To deduce the effective axion flux of stellar objects incident on the Earth the All-Sky catalogue was used to obtain the spectral class and distance of the stars treated. Our calculations of the axion flux in the galactic plane show that for a zero age main sequence star an maximum axion flux of {phi}{sub a}=303.43 cm{sup -2}s{sup -1} could be expected. Furthermore we present estimates of axion fluxes from time-evolved stars.

  13. The fluctuation theory of the stellar mass loss

    International Nuclear Information System (INIS)

    Andriesse, C.D.

    1981-01-01

    The idea that fluctuations in the mass flow are as significant as the very existence of the flow has led to the development of a fluctuation theory of the stellar mass loss. A general theory for fluctuations in non-equilibrium systems - and such are stellar atmospheres - was developed long ago. In developing the general theory to a specific stellar theory, however, the arguments have not come up in their logical order. The present sketch of this theory improves on that order and is offered as a framework for further study. (Auth.)

  14. Infrared spectroscopy and density functional theory investigation of calcite, chalk, and coccoliths-do we observe the mineral surface?

    DEFF Research Database (Denmark)

    Andersson, Martin Peter; Hem, Caroline Piper; Schultz, Logan Nicholas

    2014-01-01

    broadening from macroscopic dielectric effects. We detect water adsorbed on the high surface area synthetic calcite, which permits observation of the chemistry of thin liquid films on calcite using transmission infrared spectroscopy. The combination of infrared spectroscopy and density functional theory also...... asymmetric for the coccoliths and the synthetic calcite prepared using the carbonation method. It can be very well fitted by two peaks: a narrow Lorenzian at lower frequency and a broader Gaussian at higher frequency. These two samples both have a high specific surface area. Density functional theory...

  15. Stellar Relics from the Early Galaxy T. Sivarani

    Indian Academy of Sciences (India)

    metal-poor stars is used to study the chemical history of the galaxy. Apart from this,. 5 .... They fit a color-magnitude diagram in order to trace different stellar population and derived a ... distinctly different stellar population with a different origin.

  16. Development of code PRETOR for stellarator simulation

    International Nuclear Information System (INIS)

    Dies, J.; Fontanet, J.; Fontdecaba, J.M.; Castejon, F.; Alejandre, C.

    1998-01-01

    The Department de Fisica i Enginyeria Nuclear (DFEN) of the UPC has some experience in the development of the transport code PRETOR. This code has been validated with shots of DIII-D, JET and TFTR, it has also been used in the simulation of operational scenarios of ITER fast burnt termination. Recently, the association EURATOM-CIEMAT has started the operation of the TJ-II stellarator. Due to the need of validating the results given by others transport codes applied to stellarators and because all of them made some approximations, as a averaging magnitudes in each magnetic surface, it was thought suitable to adapt the PRETOR code to devices without axial symmetry, like stellarators, which is very suitable for the specific needs of the study of TJ-II. Several modifications are required in PRETOR; the main concerns to the models of: magnetic equilibrium, geometry and transport of energy and particles. In order to solve the complex magnetic equilibrium geometry the powerful numerical code VMEC has been used. This code gives the magnetic surface shape as a Fourier series in terms of the harmonics (m,n). Most of the geometric magnitudes are also obtained from the VMEC results file. The energy and particle transport models will be replaced by other phenomenological models that are better adapted to stellarator simulation. Using the proposed models, it is pretended to reproduce experimental data available from present stellarators, given especial attention to the TJ-II of the association EURATOM-CIEMAT. (Author)

  17. Reviews in modern astronomy, deciphering the universe through spectroscopy

    CERN Document Server

    von Berlepsch, Regina

    2011-01-01

    This 22nd volume in the series contains 15 invited reviews and highlight contributions from outstanding speakers presented during the 2009 annual meeting of the Astronomical Society on the subject of ""Deciphering the Universe through Spectroscopy"", held in Potsdam, Germany. Topics range from the measurements of magnetic fields on the surface of the sun via detailed measurements of abundances in stellar atmospheres to the kinematics of the universe at its largest scales. The result is a systematic overview of the latest astronomical and cosmological research.

  18. Stellar Wakes from Dark Matter Subhalos.

    Science.gov (United States)

    Buschmann, Malte; Kopp, Joachim; Safdi, Benjamin R; Wu, Chih-Liang

    2018-05-25

    We propose a novel method utilizing stellar kinematic data to detect low-mass substructure in the Milky Way's dark matter halo. By probing characteristic wakes that a passing dark matter subhalo leaves in the phase-space distribution of ambient halo stars, we estimate sensitivities down to subhalo masses of ∼10^{7}  M_{⊙} or below. The detection of such subhalos would have implications for dark matter and cosmological models that predict modifications to the halo-mass function at low halo masses. We develop an analytic formalism for describing the perturbed stellar phase-space distributions, and we demonstrate through idealized simulations the ability to detect subhalos using the phase-space model and a likelihood framework. Our method complements existing methods for low-mass subhalo searches, such as searches for gaps in stellar streams, in that we can localize the positions and velocities of the subhalos today.

  19. Stellar Wakes from Dark Matter Subhalos

    Science.gov (United States)

    Buschmann, Malte; Kopp, Joachim; Safdi, Benjamin R.; Wu, Chih-Liang

    2018-05-01

    We propose a novel method utilizing stellar kinematic data to detect low-mass substructure in the Milky Way's dark matter halo. By probing characteristic wakes that a passing dark matter subhalo leaves in the phase-space distribution of ambient halo stars, we estimate sensitivities down to subhalo masses of ˜107 M⊙ or below. The detection of such subhalos would have implications for dark matter and cosmological models that predict modifications to the halo-mass function at low halo masses. We develop an analytic formalism for describing the perturbed stellar phase-space distributions, and we demonstrate through idealized simulations the ability to detect subhalos using the phase-space model and a likelihood framework. Our method complements existing methods for low-mass subhalo searches, such as searches for gaps in stellar streams, in that we can localize the positions and velocities of the subhalos today.

  20. STELLAR TRANSITS IN ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Béky, Bence; Kocsis, Bence

    2013-01-01

    Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit light curves using the Novikov-Thorne thin accretion disk model, including general relativistic effects. Based on the expected properties of stellar cusps, we find that around 10 6 solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low-mass AGNs to 1% photometric accuracy in optical, or ∼10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination, and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit light curves could be used to image accretion disks with unprecedented resolution, allowing us to resolve the SMBH silhouette in distant AGNs.

  1. Is the Mercier criterion relevant to stellarator stability?

    International Nuclear Information System (INIS)

    Carreras, B.A.; Lynch, V.E.; Ichiguchi, K.; Wakatani, M.; Tatsuno, T.

    2001-01-01

    Local flattening of the pressure profile at the resonant surfaces may significantly change the stellarator stability properties. This flattening may be an intrinsic consequence of the three-dimensional nature of the equilibrium and may invalidate the local stability criteria often used in stellarator design. (author)

  2. Close stellar encounters in globular clusters

    International Nuclear Information System (INIS)

    Bailyn, C.D.

    1989-01-01

    Stellar encounters are expected to produce a variety of interesting objects in the cores of globular clusters, either through the formation of binaries by tidal capture, or direct collisions. Here, I describe several attempts to observe the products of stellar encounters. In particular, the use of color maps has demonstrated the existence of a color gradient in the core of M15, which seems to be caused by a population of faint blue objects concentrated towards the cluster center. (author)

  3. Compact Starburst Galaxies with Fast Outflows: Spatially Resolved Stellar Mass Profiles

    Science.gov (United States)

    Gottlieb, Sophia; Diamond-Stanic, Aleksandar; Lipscomb, Charles; Ohene, Senyo; Rines, Josh; Moustakas, John; Sell, Paul; Tremonti, Christy; Coil, Alison; Rudnick, Gregory; Hickox, Ryan C.; Geach, James; Kepley, Amanda

    2018-01-01

    Powerful galactic winds driven by stellar feedback and black hole accretion are thought to play an important role in regulating star formation in galaxies. In particular, strong stellar feedback from supernovae, stellar winds, radiation pressure, and cosmic rays is required by simulations of star-forming galaxies to prevent the vast majority of baryons from cooling and collapsing to form stars. However, it remains unclear whether these stellar processes play a significant role in expelling gas and shutting down star formation in massive progenitors of quiescent galaxies. What are the limits of stellar feedback? We present multi-band photometry with HST/WFC3 (F475W, F814W, F160W) for a dozen compact starburst galaxies at z~0.6 with half-light radii that suggest incredibly large central escape velocities. These massive galaxies are driving fast (>1000 km/s) outflows that have been previously attributed to stellar feedback associated with the compact (r~100 pc) starburst. But how compact is the stellar mass? In the context of the stellar feedback hypothesis, it is unclear whether these fast outflows are being driven at velocities comparable to the escape velocity of an incredibly dense stellar system (as predicted by some models of radiation-pressure winds) or at velocities that exceed the central escape velocity by large factor. Our spatially resolved measurements with HST show that the stellar mass is more extended than the light, and this requires that the physical mechanism responsible for driving the winds must be able to launch gas at velocities that are factors of 5-10 beyond the central escape velocity.

  4. Photoacoustic spectroscopy of β-hematin

    International Nuclear Information System (INIS)

    Samson, Edward B; Goldschmidt, Benjamin S; Whiteside, Paul J D; Sudduth, Amanda S M; Custer, John R; Viator, John A; Beerntsen, Brenda

    2012-01-01

    Malaria affects over 200 million individuals annually, resulting in 800 000 fatalities. Current tests use blood smears and can only detect the disease when 0.1–1% of blood cells are infected. We are investigating the use of photoacoustic flowmetry to sense as few as one infected cell among 10 million or more normal blood cells, thus diagnosing infection before patients become symptomatic. Photoacoustic flowmetry is similar to conventional flow cytometry, except that rare cells are targeted by nanosecond laser pulses to induce ultrasonic responses. This system has been used to detect single melanoma cells in 10 ml of blood. Our objective is to apply photoacoustic flowmetry to detection of the malaria pigment hemozoin, which is a byproduct of parasite-digested hemoglobin in the blood. However, hemozoin is difficult to purify in quantities greater than a milligram, so a synthetic analog, known as β-hematin was derived from porcine hemin. The specific purpose of this study is to establish the efficacy of using β-hematin, rather than hemozoin, for photoacoustic measurements. We characterized β-hematin using UV–vis spectroscopy, TEM, and FTIR, then tested the effects of laser irradiation on the synthetic product. We finally determined its absorption spectrum using photoacoustic excitation. UV–vis spectroscopy verified that β-hematin was distinctly different from its precursor. TEM analysis confirmed its previously established nanorod shape, and comparison of the FTIR results with published spectroscopy data showed that our product had the distinctive absorbance peaks at 1661 and 1206 cm −1 . Also, our research indicated that prolonged irradiation dramatically alters the physical and optical properties of the β-hematin, resulting in increased absorption at shorter wavelengths. Nevertheless, the photoacoustic absorption spectrum mimicked that generated by UV–vis spectroscopy, which confirms the accuracy of the photoacoustic method and strongly suggests

  5. Early detection of emerging street drugs by near infrared spectroscopy and chemometrics.

    Science.gov (United States)

    Risoluti, R; Materazzi, S; Gregori, A; Ripani, L

    2016-06-01

    Near-infrared spectroscopy (NIRs) is spreading as the tool of choice for fast and non-destructive analysis and detection of different compounds in complex matrices. This paper investigated the feasibility of using near infrared (NIR) spectroscopy coupled to chemometrics calibration to detect new psychoactive substances in street samples. The capabilities of this approach in forensic chemistry were assessed in the determination of new molecules appeared in the illicit market and often claimed to contain "non-illegal" compounds, although exhibiting important psychoactive effects. The study focused on synthetic molecules belonging to the classes of synthetic cannabinoids and phenethylamines. The approach was validated comparing results with officials methods and has been successfully applied for "in site" determination of illicit drugs in confiscated real samples, in cooperation with the Scientific Investigation Department (Carabinieri-RIS) of Rome. The achieved results allow to consider NIR spectroscopy analysis followed by chemometrics as a fast, cost-effective and useful tool for the preliminary determination of new psychoactive substances in forensic science. Copyright © 2016 Elsevier B.V. All rights reserved.

  6. TRACING THE EVOLUTION OF HIGH-REDSHIFT GALAXIES USING STELLAR ABUNDANCES

    Energy Technology Data Exchange (ETDEWEB)

    Crosby, Brian D.; O’Shea, Brian W. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Beers, Timothy C. [Department of Physics and JINA—Center for the Evolution of the Elements, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Tumlinson, Jason, E-mail: crosby.bd@gmail.com [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2016-03-20

    This paper presents the first results from a model for chemical evolution that can be applied to N-body cosmological simulations and quantitatively compared to measured stellar abundances from large astronomical surveys. This model convolves the chemical yield sets from a range of stellar nucleosynthesis calculations (including asymptotic giant branch stars, Type Ia and II supernovae, and stellar wind models) with a user-specified stellar initial mass function (IMF) and metallicity to calculate the time-dependent chemical evolution model for a “simple stellar population” (SSP) of uniform metallicity and formation time. These SSP models are combined with a semianalytic model for galaxy formation and evolution that uses merger trees from N-body cosmological simulations to track several α- and iron-peak elements for the stellar and multiphase interstellar medium components of several thousand galaxies in the early (z ≥ 6) universe. The simulated galaxy population is then quantitatively compared to two complementary data sets of abundances in the Milky Way stellar halo and is capable of reproducing many of the observed abundance trends. The observed abundance ratio distributions are best reproduced with a Chabrier IMF, a chemically enriched star formation efficiency of 0.2, and a redshift of reionization of 7. Many abundances are qualitatively well matched by our model, but our model consistently overpredicts the carbon-enhanced fraction of stars at low metallicities, likely owing to incomplete coverage of Population III stellar yields and supernova models and the lack of dust as a component of our model.

  7. Plant synthetic biology.

    Science.gov (United States)

    Liu, Wusheng; Stewart, C Neal

    2015-05-01

    Plant synthetic biology is an emerging field that combines engineering principles with plant biology toward the design and production of new devices. This emerging field should play an important role in future agriculture for traditional crop improvement, but also in enabling novel bioproduction in plants. In this review we discuss the design cycles of synthetic biology as well as key engineering principles, genetic parts, and computational tools that can be utilized in plant synthetic biology. Some pioneering examples are offered as a demonstration of how synthetic biology can be used to modify plants for specific purposes. These include synthetic sensors, synthetic metabolic pathways, and synthetic genomes. We also speculate about the future of synthetic biology of plants. Copyright © 2015 Elsevier Ltd. All rights reserved.

  8. The low-luminosity stellar mass function

    International Nuclear Information System (INIS)

    Kroupa, Pavel; Tout, C.A.; Gilmore, Gerard

    1990-01-01

    The stellar mass function for low-mass stars is constrained using the stellar luminosity function and the slope of the mass-luminosity relation. We investigate the range of mass functions for stars with absolute visual magnitude fainter than M V ≅ +5 which are consistent with both the local luminosity function and the rather poorly determined mass-absolute visual magnitude relation. Points of inflexion in the mass-luminosity relation exist because of the effects of H - , H 2 and of other molecules on the opacity and equation of state. The first two of these correspond to absolute magnitudes M V ≅ +7 and M V ≅ +12, respectively, at which structure is evident in the stellar luminosity function (a flattening and a maximum, respectively). Combining the mass-luminosity relation which shows these inflexion points with a peaked luminosity function, we test smooth mass functions in the mass range 0.9-0.1 the solar mass. (author)

  9. TEM-turbulence in stellarators and its optimization

    Science.gov (United States)

    Proll, Josefine H. E.; Helander, Per; Lazerson, Samuel; Mynick, Harry; Xanthopoulos, Pavlos

    2014-10-01

    Quasi-isodynamic stellarators, which are especially optimized for neoclassical transport, have been shown to be resilient towards trapped-electrons modes (TEMs) in large regions of parameter space. In these configurations, all particles have average ``good curvature.'' It was shown analytically that, thanks to this property, particles that bounce faster than the mode in question draw energy from it near marginal stability, so that the ordinary density-gradient-driven TEM has to be stable in the electrostatic and collisionless limit.This has been confirmed in linear flux-tube simulations that were performed with the GENE code. Several magnetic field configurations were compared and it was found that the growth rates of the TEMs drop with increasing degree of quasi-isodynamicity. These findings can be used to optimize stellarators with respect to TEM turbulence by reducing the fraction of trapped particles with bounce averaged ``bad curvature.'' An appropriate proxy function has therefore been designed to be implemented in STELLOPT, a stellarator optimization tool that can now be used to further explore the configuration space of neoclassically optimized stellarators with the aim to extract designs with improved turbulent transport. This work was facilitated by the Max-Planck/Princeton Center for Plasma Physics.

  10. The study of synthetic food dyes by positron annihilation lifetime spectroscopy.

    Science.gov (United States)

    Pivtsaev, A. A.; Razov, V. I.

    2015-06-01

    By method of positron annihilation lifetime spectroscopy (PALS), substances are food dyes were studied: E-102 (Tartrazine), E-124 (Ponso 4R), E 132 (Indigo carmine), E-133 (Brilliant Blue), E-151 (Black Shiny). They are examined for the presence of carcinogenic properties. The difference between dyes having explicit carcinogenic properties and mutagenic properties (non-explicit carcinogens) is established.

  11. Wimps and stellar structure

    International Nuclear Information System (INIS)

    Bouquet, A.; Salati, P.

    1988-01-01

    We present the results of an analytic approximation to compute the effects of WIMPs on stellar structures in a self-consistent way. We examine in particular the case of the Sun and of horizontal branch stars

  12. Interaction effects on galaxy pairs with Gemini/GMOS- III: stellar population synthesis

    Science.gov (United States)

    Krabbe, A. C.; Rosa, D. A.; Pastoriza, M. G.; Hägele, G. F.; Cardaci, M. V.; Dors, O. L., Jr.; Winge, C.

    2017-05-01

    We present an observational study of the impacts of interactions on the stellar population in a sample of galaxy pairs. Long-slit spectra in the wavelength range 3440-7300 Å obtained with the Gemini Multi-Object Spectrograph (GMOS) at Gemini South for 15 galaxies in nine close pairs were used. The spatial distributions of the stellar population contributions were obtained using the stellar population synthesis code starlight. Taking into account the different contributions to the emitted light, we found that most of the galaxies in our sample are dominated by young/intermediate stellar populations. This result differs from the one derived for isolated galaxies, where the old stellar population dominates the disc surface brightness. We interpreted such different behaviour as being due to the effect of gas inflows along the discs of interacting galaxies on the star formation over a time-scale of the order of about 2 Gyr. We also found that, in general, the secondary galaxy of a pair has a higher contribution from the young stellar population than the primary one. We compared the estimated values of stellar and nebular extinction derived from the synthesis method and the Hα/Hβ emission-line ratio, finding that nebular extinctions are systematically higher than stellar ones by about a factor of 2. We did not find any correlation between nebular and stellar metallicities. Neither did we find a correlation between stellar metallicities and ages, while a positive correlation between nebular metallicities and stellar ages was obtained, with older regions being the most metal-rich.

  13. 8. stellarator workshop

    International Nuclear Information System (INIS)

    1991-07-01

    The technical reports in this collection of papers were presented at the 8th International Workshop on Stellarators, and International Atomic Energy Agency Technical Committee Meeting. They include presentations on transport, magnetic configurations, fluctuations, equilibrium, stability, edge plasma and wall aspects, heating, diagnostics, new concepts and reactor studies. Refs, figs and tabs

  14. New schemes for confinement of fusion products in stellarators

    International Nuclear Information System (INIS)

    Cooper, W.A.; Isaev, M.Yu.; Heyn, M.F.

    2003-01-01

    Improved energetic-particle confinement is found in new stellarator and toroidal mirror field configurations. The possibility of fulfilling the condition of poloidal closure of the contours of the second adiabatic invariant for all reflected particles is studied for stellarators with poloidally closed contours of the magnetic field B on the magnetic surfaces through computational stellarator optimization. It is shown that by adjusting the geometry this is possible in a major fraction of the plasma volume. The most salient characteristic (as compared to previous quasi-iso dynamic configurations) is a magnetic axis whose curvature vanishes in all cross-sections with an extremum of B on the magnetic axis and renders possible a 3D structure of B with unprecedently high collisionless α-particle confinement. Sectionally isometric vacuum magnetic field toroidal mirror traps are analytically constructed with the help of the paraxial (or 'thin tube') approximation. Application of standard computational stellarator tools to this type of ι = 0 stellarator shows excellent alignment of second adiabatic invariant contours and equilibrium surfaces as well as directly calculated collisionless confinement of energetic particles. (author)

  15. Stellar Companions of Exoplanet Host Stars in K2

    Science.gov (United States)

    Matson, Rachel; Howell, Steve; Horch, Elliott; Everett, Mark

    2018-01-01

    Stellar multiplicity has significant implications for the detection and characterization of exoplanets. A stellar companion can mimic the signal of a transiting planet or distort the true planetary radii, leading to improper density estimates and over-predicting the occurrence rates of Earth-sized planets. Determining the fraction of exoplanet host stars that are also binaries allows us to better determine planetary characteristics as well as establish the relationship between binarity and planet formation. Using high-resolution speckle imaging to obtain diffraction limited images of K2 planet candidate host stars we detect stellar companions within one arcsec and up to six magnitudes fainter than the host star. By comparing our observed companion fraction to TRILEGAL star count simulations, and using the known detection limits of speckle imaging, we find the binary fraction of K2 planet host stars to be similar to that of Kepler host stars and solar-type field stars. Accounting for stellar companions in exoplanet studies is therefore essential for deriving true stellar and planetary properties as well as maximizing the returns for TESS and future exoplanet missions.

  16. USING STELLAR DENSITIES TO EVALUATE TRANSITING EXOPLANETARY CANDIDATES

    International Nuclear Information System (INIS)

    Tingley, B.; Deeg, H. J.; Bonomo, A. S.

    2011-01-01

    One of the persistent complications in searches for transiting exoplanets is the low percentage of the detected candidates that ultimately prove to be planets, which significantly increases the load on the telescopes used for the follow-up observations to confirm or reject candidates. Several attempts have been made at creating techniques that can pare down candidate lists without the need of additional observations. Some of these techniques involve a detailed analysis of light curve characteristics; others estimate the stellar density or some proxy thereof. In this paper, we extend upon this second approach, exploring the use of independently calculated stellar densities to identify the most promising transiting exoplanet candidates. We use a set of CoRoT candidates and the set of known transiting exoplanets to examine the potential of this approach. In particular, we note the possibilities inherent in the high-precision photometry from space missions, which can detect stellar asteroseismic pulsations from which accurate stellar densities can be extracted without additional observations.

  17. Disentangling stellar activity from exoplanetary signals with interferometry

    Directory of Open Access Journals (Sweden)

    Ligi Roxanne

    2015-01-01

    Full Text Available Stellar activity can express as many forms at stellar surfaces: dark spots, convective cells, bright plages. Particularly, dark spots and bright plages add noise on photometric data or radial velocity measurements used to detect exoplanets, and thus lead to false detection or disrupt their derived parameters. Since interferometry provides a very high angular resolution, it may constitute an interesting solution to distinguish the signal of a transiting exoplanet and that of stellar activity. It has also been shown that granulation adds bias in visibility and closure phase measurements, affecting in turn the derived stellar parameters. We analyze the noises generated by dark spots on interferometric observables and compare them to exoplanet signals. We investigate the current interferometric instruments able to measure and disentangle these signals, and show that there is a lack in spatial resolution. We thus give a prospective of the improvements to be brought on future interferometers, which would also significantly extend the number of available targets.

  18. A Study of E+A Galaxies Through SDSS-MaNGA Integral Field Spectroscopy

    Science.gov (United States)

    Wally, Muhammad; Weaver, Olivia A.; Anderson, Miguel Ricardo; Liu, Allen; Falcone, Julia; Wallack, Nicole Lisa; James, Olivia; Liu, Charles

    2017-01-01

    We outline the selection process and analysis of sixteen E+A galaxies observed by the Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey as a part of the fourth generation of the Sloan Digital Sky Survey (SDSS-IV). We present their Integral field spectroscopy and analyze their spatial distribution of stellar ages, metallicities and other stellar population properties. We can potentially study the variation in these properties as a function of redshift. This work was supported by the Alfred P. Sloan Foundation via the SDSS-IV Faculty and Student Team (FAST) initiative, ARC Agreement #SSP483 to the CUNY College of Staten Island. This work was also supported by grants to The American Museum of Natural History, and the CUNY College of Staten Island through The National Science Foundation.

  19. Nuclear challenges and progress in designing stellarator fusion power plants

    International Nuclear Information System (INIS)

    El-Guebaly, L.A.; Wilson, P.; Henderson, D.; Sawan, M.; Sviatoslavsky, G.; Tautges, T.; Slaybaugh, R.; Kiedrowski, B.; Ibrahim, A.

    2008-01-01

    Over the past 5-6 decades, stellarator power plants have been studied in the US, Europe, and Japan as an alternate to the mainline magnetic fusion tokamaks, offering steady-state operation and eliminating the risk of plasma disruptions. The earlier 1980s studies suggested large-scale stellarator power plants with an average major radius exceeding 20 m. The most recent development of the compact stellarator concept delivered ARIES-CS - a compact stellarator with 7.75 m average major radius, approaching that of tokamaks. For stellarators, the most important engineering parameter that determines the machine size and cost is the minimum distance between the plasma boundary and mid-coil. Accommodating the breeding blanket and necessary shield within this distance to protect the ARIES-CS superconducting magnet represents a challenging task. Selecting the ARIES-CS nuclear and engineering parameters to produce an economic optimum, modeling the complex geometry for 3D nuclear analysis to confirm the key parameters, and minimizing the radwaste stream received considerable attention during the design process. These engineering design elements combined with advanced physics helped enable the compact stellarator to be a viable concept. This paper provides a brief historical overview of the progress in designing stellarator power plants and a perspective on the successful integration of the nuclear activity into the final ARIES-CS configuration

  20. The rise and fall of stellar across the peak of cosmic star formation history: effects of mergers versus diffuse stellar mass acquisition

    Science.gov (United States)

    Welker, C.; Dubois, Y.; Devriendt, J.; Pichon, C.; Kaviraj, S.; Peirani, S.

    2017-02-01

    Building galaxy merger trees from a state-of-the-art cosmological hydrodynamical simulation, Horizon-AGN, we perform a statistical study of how mergers and diffuse stellar mass acquisition processes drive galaxy morphologic properties above z > 1. By diffuse mass acquisition here, we mean both accretion of stars by unresolved mergers (relative stellar mass growth smaller than 4.5 per cent) as well as in situ star formation when no resolved mergers are detected along the main progenitor branch of a galaxy. We investigate how stellar densities, galaxy sizes and galaxy morphologies (defined via shape parameters derived from the inertia tensor of the stellar density) depend on mergers of different mass ratios. We investigate how stellar densities, effective radii and shape parameters derived from the inertia tensor depend on mergers of different mass ratios. We find strong evidence that diffuse stellar accretion and in situ formation tend to flatten small galaxies over cosmic time, leading to the formation of discs. On the other hand, mergers, and not only the major ones, exhibit a propensity to puff up and destroy stellar discs, confirming the origin of elliptical galaxies. We confirm that mergers grow galaxy sizes more efficiently than diffuse processes (r_{0.5}∝ M_s^{0.85} and r_{0.5}∝ M_s^{0.1} on average, respectively) and we also find that elliptical galaxies are more susceptible to grow in size through mergers than disc galaxies with a size-mass evolution r_{0.5}∝ M_s^{1.2} instead of r_{0.5}∝ M_s^{-0.5}-M^{0.5} for discs depending on the merger mass ratio. The gas content drives the size-mass evolution due to merger with a faster size growth for gas-poor galaxies r_{0.5}∝ M_s2 than for gas-rich galaxies r0.5 ∝ Ms.

  1. Star-disc interaction in galactic nuclei: formation of a central stellar disc

    Science.gov (United States)

    Panamarev, Taras; Shukirgaliyev, Bekdaulet; Meiron, Yohai; Berczik, Peter; Just, Andreas; Spurzem, Rainer; Omarov, Chingis; Vilkoviskij, Emmanuil

    2018-05-01

    We perform high-resolution direct N-body simulations to study the effect of an accretion disc on stellar dynamics in an active galactic nucleus (AGN). We show that the interaction of the nuclear stellar cluster (NSC) with the gaseous accretion disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc on to the super-massive black hole is balanced by the capture of stars from the NSC into the stellar disc, yielding a stationary density profile. We derive the migration time through the AD to be 3 per cent of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7 per cent of the mass and 5 per cent of the influence radius of the super-massive black hole. An AD lifetime shorter than the migration time would result in a less massive nuclear stellar disc. The detection of such a stellar disc could point to past activity of the hosting galactic nucleus.

  2. The Contribution of Stellar Winds to Cosmic Ray Production

    Science.gov (United States)

    Seo, Jeongbhin; Kang, Hyesung; Ryu, Dongsu

    2018-04-01

    Massive stars blow powerful stellar winds throughout their evolutionary stages from the main sequence to Wolf-Rayet phases. The wind mechanical energy of a massive star deposited to the interstellar medium can be comparable to the explosion energy of a core-collapse supernova that detonates at the end of its life In this study, we estimate the kinetic energy deposition by massive stars in our Galaxy by considering the integrated Galactic initial mass function and modeling the stellar wind luminosity. The mass loss rate and terminal velocity of stellar winds during the main sequence, red supergiant, and Wolf-Rayet stages are estimated by adopting theoretical calculations and observational data published in the literature. We find that the total stellar wind luminosity by all massive stars in the Galaxy is about Lw ≈ 1.1×1041 ergs, which is about 1/4 of the power of supernova explosions, LSN ≈ 4.8×1041 ergs. If we assume that ˜1-1% of the wind luminosity could be converted to Galactic cosmic rays (GCRs) through collisonless shocks such as termination shocks in stellar bubbles and superbubbles, colliding-wind shocks in binaries, and bow-shocks of massive runaway stars, stellar winds are expected to make a significant contribution to GCR production, though lower than that of supernova remnants.

  3. The Advanced Stellar Compass onboard the Oersted satellite

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Eisenman, Allan R.; Liebe, Carl Christian

    1997-01-01

    In 1997 the first Danish satellite will be launched. The primarily scientific objective of the satellite is to map the magnetic field of the Earth. The attitude of the satellite is determined by an advanced stellar compass (star tracker). An advanced stellar compass consists of a CCD camera...

  4. The Resolved Stellar Populations Early Release Science Program

    Science.gov (United States)

    Weisz, Daniel; Anderson, J.; Boyer, M.; Cole, A.; Dolphin, A.; Geha, M.; Kalirai, J.; Kallivayalil, N.; McQuinn, K.; Sandstrom, K.; Williams, B.

    2017-11-01

    We propose to obtain deep multi-band NIRCam and NIRISS imaging of three resolved stellar systems within 1 Mpc (NOI 104). We will use this broad science program to optimize observational setups and to develop data reduction techniques that will be common to JWST studies of resolved stellar populations. We will combine our expertise in HST resolved star studies with these observations to design, test, and release point spread function (PSF) fitting software specific to JWST. PSF photometry is at the heart of resolved stellar populations studies, but is not part of the standard JWST reduction pipeline. Our program will establish JWST-optimized methodologies in six scientific areas: star formation histories, measurement of the sub-Solar mass stellar IMF, extinction maps, evolved stars, proper motions, and globular clusters, all of which will be common pursuits for JWST in the local Universe. Our observations of globular cluster M92, ultra-faint dwarf Draco II, and star-forming dwarf WLM, will be of high archival value for other science such as calibrating stellar evolution models, measuring properties of variable stars, and searching for metal-poor stars. We will release the results of our program, including PSF fitting software, matched HST and JWST catalogs, clear documentation, and step-by-step tutorials (e.g., Jupyter notebooks) for data reduction and science application, to the community prior to the Cycle 2 Call for Proposals. We will host a workshop to help community members plan their Cycle 2 observations of resolved stars. Our program will provide blueprints for the community to efficiently reduce and analyze JWST observations of resolved stellar populations.

  5. Recent advances in modeling stellar interiors (u)

    Energy Technology Data Exchange (ETDEWEB)

    Guzik, Joyce Ann [Los Alamos National Laboratory

    2010-01-01

    Advances in stellar interior modeling are being driven by new data from large-scale surveys and high-precision photometric and spectroscopic observations. Here we focus on single stars in normal evolutionary phases; we will not discuss the many advances in modeling star formation, interacting binaries, supernovae, or neutron stars. We review briefly: (1) updates to input physics of stellar models; (2) progress in two and three-dimensional evolution and hydrodynamic models; (3) insights from oscillation data used to infer stellar interior structure and validate model predictions (asteroseismology). We close by highlighting a few outstanding problems, e.g., the driving mechanisms for hybrid {gamma} Dor/{delta} Sct star pulsations, the cause of giant eruptions seen in luminous blue variables such as {eta} Car and P Cyg, and the solar abundance problem.

  6. Effect of finite β on stellarator transport

    International Nuclear Information System (INIS)

    Mynick, H.E.

    1984-04-01

    A theory of the modification of stellarator transport due to the presence of finite plasma pressure is developed, and applied to a range of stellarator configurations. For many configurations of interest, plasma transport can change by more than an order of magnitude in the progression from zero pressure to the equilibrium β limit of the device. Thus, a stellarator with transport-optimized vacuum fields can have poor confinement at the desired operating β. Without an external compensating field, increasing β tends to degrade confinement, unless the initial field structure is very carefully chosen. The theory permits one to correctly determine this vacuum structure, in terms of the desired structure of the field at a prescribed operating β. With a compensating external field, the deleterious effect of finite β on transport can be partially eliminated

  7. Stellar magnetic activity – Star-Planet Interactions

    Directory of Open Access Journals (Sweden)

    Poppenhaeger, K.

    2015-01-01

    Full Text Available Stellar magnetic activity is an important factor in the formation and evolution of exoplanets. Magnetic phenomena like stellar flares, coronal mass ejections, and high-energy emission affect the exoplanetary atmosphere and its mass loss over time. One major question is whether the magnetic evolution of exoplanet host stars is the same as for stars without planets; tidal and magnetic interactions of a star and its close-in planets may play a role in this. Stellar magnetic activity also shapes our ability to detect exoplanets with different methods in the first place, and therefore we need to understand it properly to derive an accurate estimate of the existing exoplanet population. I will review recent theoretical and observational results, as well as outline some avenues for future progress.

  8. Space Weather: Linking Stellar Explosions to the Human Endeavor

    Science.gov (United States)

    Knipp, Delores

    2017-06-01

    Arguably humans have flourished as a result of stellar explosions; we are, after all, stardust. Nonetheless, rapid technology advances of the last 200 years sometimes put society and individuals on a collision course with the natural variability of stellar and solar atmospheres. Human space exploration, routine satellite navigation system applications, aviation safety, and electric power grids are examples of such vulnerable endeavors. In this presentation I will outline how global society relies on ‘normal’ solar and stellar emissions, yet becomes susceptible to extremes of these emissions. The imprints of these astronomical-terrestrial interactions abound. In particular, I will highlight ways in which stellar/solar bursts link with our space-atmosphere-interaction region, producing multi-year patterns in cosmic ray detection, gorgeous aurora, and deep concern for good order and function of global community.

  9. The study of synthetic food dyes by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Pivtsaev, A A; Razov, V I

    2015-01-01

    By method of positron annihilation lifetime spectroscopy (PALS), substances are food dyes were studied: E-102 (Tartrazine), E-124 (Ponso 4R), E 132 (Indigo carmine), E-133 (Brilliant Blue), E-151 (Black Shiny). They are examined for the presence of carcinogenic properties. The difference between dyes having explicit carcinogenic properties and mutagenic properties (non-explicit carcinogens) is established. (paper)

  10. Design, construction and validation of the UST-1 modular stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Queral, V., E-mail: vicentemanuel.queral@ciemat.es

    2016-11-15

    Highlights: • A small and simple low cost two period modular stellarator is reviewed. • It is defined as a monolithic circular surface torus with carved grooves. • The grooves are accurately mechanised by a new toroidal milling machine. • A very simple e-beam field mapping system has been built and utilized. - Abstract: Stellarator advancement is hindered, among others, by the requirement of geometric complexity at high accuracy and the still scarce universities and research centres following the stellarator line. In this framework, the objectives of the small UST-1 stellarator development were to: (i) explore and test the performance of one possible accurate construction method for stellarators (ii) encourage universities and small fusion research centres to build simple and economical stellarators (iii) educative purpose. Therefore, UST-1 was properly designed to be easily built by a milling machine working on toroidal coordinates, being the winding surface circular poloidally and toroidally. The coil frame is a sole monolithic toroidal thick surface equipped with grooves mechanised by the toroidal milling machine. Only one double pancake is wound in each groove so as to compress the conductor on the laterals of the groove in order to speed up and simplify the winding process. The physics design, the conceptual engineering design and the construction process of UST-1 is presented. The toroidal milling machine is described. The e-beam field line mapping experiments carried out to validate the resulting magnetic configuration are reported. The developed construction method has been proved for the small UST-1 stellarator. Small stellarators are valuable for quick tests of diagnostics, educative purposes, assessment of new confinement concepts, turbulence studies and other applications.

  11. Design, construction and validation of the UST-1 modular stellarator

    International Nuclear Information System (INIS)

    Queral, V.

    2016-01-01

    Highlights: • A small and simple low cost two period modular stellarator is reviewed. • It is defined as a monolithic circular surface torus with carved grooves. • The grooves are accurately mechanised by a new toroidal milling machine. • A very simple e-beam field mapping system has been built and utilized. - Abstract: Stellarator advancement is hindered, among others, by the requirement of geometric complexity at high accuracy and the still scarce universities and research centres following the stellarator line. In this framework, the objectives of the small UST-1 stellarator development were to: (i) explore and test the performance of one possible accurate construction method for stellarators (ii) encourage universities and small fusion research centres to build simple and economical stellarators (iii) educative purpose. Therefore, UST-1 was properly designed to be easily built by a milling machine working on toroidal coordinates, being the winding surface circular poloidally and toroidally. The coil frame is a sole monolithic toroidal thick surface equipped with grooves mechanised by the toroidal milling machine. Only one double pancake is wound in each groove so as to compress the conductor on the laterals of the groove in order to speed up and simplify the winding process. The physics design, the conceptual engineering design and the construction process of UST-1 is presented. The toroidal milling machine is described. The e-beam field line mapping experiments carried out to validate the resulting magnetic configuration are reported. The developed construction method has been proved for the small UST-1 stellarator. Small stellarators are valuable for quick tests of diagnostics, educative purposes, assessment of new confinement concepts, turbulence studies and other applications.

  12. Electrochemical impedance spectroscopy of supercapacitors: A novel analysis approach using evolutionary programming

    Science.gov (United States)

    Oz, Alon; Hershkovitz, Shany; Tsur, Yoed

    2014-11-01

    In this contribution we present a novel approach to analyze impedance spectroscopy measurements of supercapacitors. Transforming the impedance data into frequency-dependent capacitance allows us to use Impedance Spectroscopy Genetic Programming (ISGP) in order to find the distribution function of relaxation times (DFRT) of the processes taking place in the tested device. Synthetic data was generated in order to demonstrate this technique and a model for supercapacitor ageing process has been obtained.

  13. Synthetic Cannabinoids

    Directory of Open Access Journals (Sweden)

    Aslihan Okan Ibiloglu

    2017-09-01

    Full Text Available Synthetic cannabinoids which is a subgroup of cannabinoids are commonly used for recreational drug use throughout the whole world. Although both marijuana and synthetic cannabinoids stimulate the same receptors, cannabinoid receptor 1 (CB1 and cannabinoid receptor 2 (CB2, studies have shown that synthetic cannabinoids are much more potent than marijuana. The longer use of synthetic cannabinoids can cause severe physical and psychological symptoms that might even result in death, similar to many known illicit drugs. Main treatment options mostly involve symptom management and supportive care. The aim of this article is to discuss clinical and pharmacological properties of the increasingly used synthetic cannabinoids. [Psikiyatride Guncel Yaklasimlar - Current Approaches in Psychiatry 2017; 9(3.000: 317-328

  14. Optimisation of stellarator systems: Possible ways

    International Nuclear Information System (INIS)

    Cooper, W.A.; Isaev, M.; Leneva, A.E.; Mikhailov, M.; Shafranov, V.D.; Subbotin, A.A.

    2001-01-01

    The results of our search for advanced helical (stellarator) systems with a small number of field periods over the last five years are presented. The comparison of stellarator systems with toroidal (helical or axial) and poloidal directions of the contours with B = constant on the magnetic surface as well as systems with Helias and Heliac-like orientation of the magnetic surfaces cross-sections with respect to the principal normal to the magnetic axis is undertaken. Particular attention is paid to some attractive features of the systems with constant B-lines in the poloidal direction. (author)

  15. Optimisation of stellarator systems: Possible ways

    International Nuclear Information System (INIS)

    Cooper, W.A.; Isaev, M.Yu.; Leneva, A.E.; Mikhailov, M.I.; Sharfranov, V.D.; Subbotin, A.A.

    1999-01-01

    The results of our search for advanced helical (stellarator) systems with a small number of field periods over the last five years are presented. The comparison of stellarator systems with toroidal (helical or axial) and poloidal directions of the contours with B = constant on the magnetic surface as well as systems with Helias and Heliac-like orientation of the magnetic surfaces cross-sections with respect to the principal normal to the magnetic axis is undertaken. Particular attention is paid to some attractive features of the systems with constant B-lines in the poloidal direction. (author)

  16. Relativistic stellar dynamics

    International Nuclear Information System (INIS)

    Contopoulos, G.

    1983-01-01

    In this paper, three main areas of relativistic stellar dynamics are reviewed: (a) The dynamics of clusters, or nuclei of galaxies, of very high density; (b) The dynamics of systems containing a massive black hole; and (c) The dynamics of particles (and photons) in an expanding Universe. The emphasis is on the use of orbit perturbations. (Auth.)

  17. BOOK REVIEW: Stellarator and Heliotron Devices

    Science.gov (United States)

    Johnson, John L.

    1999-02-01

    Stellarators and tokamaks are the most advanced devices that have been developed for magnetic fusion applications. The two approaches have much in common; tokamaks have received the most attention because their axisymmetry justifies the use of simpler models and provides a more forgiving geometry. However, recent advances in treating more complicated three dimensional systems have made it possible to design stellarators that are not susceptible to disruptions and do not need plasma current control. This has excited interest recently. The two largest new magnetic experiments in the world are the LHD device, which commenced operation in Toki, Japan, in 1998 and W7-X, which should become operational in Greifswald, Germany, in 2004. Other recently commissioned stellarators, including H-1 in Canberra, Australia, TJ-II in Madrid, Spain, and IMS in Madison, Wisconsin, have joined these in rejuvenating the stellarator programme. Thus, it is most appropriate that the author has made the lecture material that he presents to his students in the Graduate School of Energy Science at Kyoto University available to everyone. Stellarator and Heliotron Devices provides an excellent treatment of stellarator theory. It is aimed at graduate students who have a good understanding of classical mechanics and mathematical techniques. It contains good descriptions and derivations of essentially every aspect of fusion theory. The author provides an excellent qualitative introduction to each subject, pointing out the strengths and weaknesses of the models that are being used and describing our present understanding. He judiciously uses simple models which illustrate the similarities and differences between stellarators and tokamaks. To some extent the treatment is uneven, rigorous derivations starting with basic principles being given in some cases and relations and equations taken from the original papers being used as a starting point in others. This technique provides an excellent training

  18. Medium Resolution Spectroscopy and Chemical Composition of Galactic Globular Clusters

    Directory of Open Access Journals (Sweden)

    Khamidullina D. A.

    2014-12-01

    Full Text Available We used integrated-light medium-resolution spectra of six Galactic globular clusters and model stellar atmospheres to carry out population synthesis and to derive chemical composition and age of the clusters. We used medium-resolution spectra of globular clusters published by Schiavon et al. (2005, as well as our long-slit observations with the 1.93 m telescope of the Haute Provence Observatory. The observed spectra were fitted to the theoretical ones interactively. As an initial approach, we used masses, radii and log g of stars in the clusters corresponding to the best fitting isochrones in the observed color-magnitude diagrams. The computed synthetic blanketed spectra of stars were summed according to the Chabrier mass function. To improve the determination of age and helium content, the shape and depth of the Balmer absorption lines was analysed. The abundances of Mg, Ca, C and several other elements were derived. A reasonable agreement with the literature data both in chemical composition and in age of the clusters is found. Our method might be useful for the development of stellar population models and for a better understanding of extragalactic star clusters.

  19. Medium resolution spectroscopy and chemical composition of Galactic globular clusters

    Science.gov (United States)

    Khamidullina, D. A.; Sharina, M. E.; Shimansky, V. V.; Davoust, E.

    We used integrated-light medium-resolution spectra of six Galactic globular clusters and model stellar atmospheres to carry out population synthesis and to derive chemical composition and age of the clusters. We used medium-resolution spectra of globular clusters published by Schiavon et al. (2005), as well as our long-slit observations with the 1.93 m telescope of the Haute Provence Observatory. The observed spectra were fitted to the theoretical ones interactively. As an initial approach, we used masses, radii and log g of stars in the clusters corresponding to the best fitting isochrones in the observed color-magnitude diagrams. The computed synthetic blanketed spectra of stars were summed according to the Chabrier mass function. To improve the determination of age and helium content, the shape and depth of the Balmer absorption lines was analysed. The abundances of Mg, Ca, C and several other elements were derived. A reasonable agreement with the literature data both in chemical composition and in age of the clusters is found. Our method might be useful for the development of stellar population models and for a better understanding of extragalactic star clusters.

  20. Electron Capture Cross Sections for Stellar Nucleosynthesis

    Directory of Open Access Journals (Sweden)

    P. G. Giannaka

    2015-01-01

    Full Text Available In the first stage of this work, we perform detailed calculations for the cross sections of the electron capture on nuclei under laboratory conditions. Towards this aim we exploit the advantages of a refined version of the proton-neutron quasiparticle random-phase approximation (pn-QRPA and carry out state-by-state evaluations of the rates of exclusive processes that lead to any of the accessible transitions within the chosen model space. In the second stage of our present study, we translate the abovementioned e--capture cross sections to the stellar environment ones by inserting the temperature dependence through a Maxwell-Boltzmann distribution describing the stellar electron gas. As a concrete nuclear target we use the 66Zn isotope, which belongs to the iron group nuclei and plays prominent role in stellar nucleosynthesis at core collapse supernovae environment.

  1. Equilibrium reconstruction in stellarators: V3FIT

    Energy Technology Data Exchange (ETDEWEB)

    Hanson, J.D.; Knowlton, S.F. [Physics Department, Auburn University, Auburn, AL (United States); Hirshman, S.P.; Lazarus, E.A. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Lao, L.L. [General Atomics, San Diego, CA (United States)

    2003-07-01

    The first section describes a general response function formalism for computing stellarator magnetic diagnostic signals, which is the first step in developing a reconstruction capability. The approach parallels that used in the EFIT two-dimensional (2-D) equilibrium reconstruction code. The second section describes the two codes we have written, V3RFUN and V3POST. V3RFUN computes the response functions for a specified magnetic diagnostic coil, and V3POST uses the response functions calculated by V3RFUN, along with the plasma current information supplied by the equilibrium code VMEC, to compute the expected magnetic diagnostic signals. These two codes are currently being used to design magnetic diagnostic for the NCSX stellarator (at PPPL) and the CTH toroidal hybrid stellarator (at Auburn University). The last section of the paper describes plans for the V3FIT code. (orig.)

  2. Optical studies of high quality synthetic diamond

    International Nuclear Information System (INIS)

    Sharp, S.J.

    1999-01-01

    This thesis is concerned with the study of fundamental and defect induced optical properties of synthetic diamond grown using high pressure, high temperature (HPHT) synthesis or chemical vapour deposition (CVD). The primary technique used for investigation is cathodoluminescence (including imaging and decay-time measurements) in addition to other forms of optical spectroscopy. This thesis is timely in that the crystallinity and purity of synthetic diamond has increased ten fold over the last few years. The diamond exciton emission, which is easily quenched by the presence of defects, is studied in high quality samples in detail. In addition the ability now exists to engineer the isotopic content of synthetic diamond to a high degree of accuracy. The experimental chapters are divided as follows: Chapter 2: High resolution, low temperature spectra reveal a splitting of the free-exciton phonon recombination emission peaks and the bound-exciton zero phonon line. Included are measurements of the variation in intensity and decay-time as a function of temperature. Chapter 3: The shift in energy of the phonon-assisted free-exciton phonon replicas with isotopic content has been measured. The shift is in agreement with the results of interatomic force model for phonon scattering due to isotope disorder. Chapter 4: A study of the shift in energy with isotopic content of the diamond of the GR1 band due to the neutral vacancy has allowed a verification of the theoretical predictions due to the Jahn Teller effect. Chapter 5: The spatial distribution of the free-exciton luminescence is studied in HPHT synthetic and CVD diamond. A variation in intensity with distance from the surface is interpreted as a significant non-radiative loss of excitons to the surface. Chapter 6: The decay-times of all known self-interstitial related centres have been measured in order to calculate the concentration of these centres present in electron irradiated diamond. (author)

  3. Stellar streams and the galaxies they reside in

    Science.gov (United States)

    Pearson, Sarah

    2018-01-01

    As galaxies collide, as smaller galaxies are disrupted by larger galaxies, or as clusters of stars orbit a galaxy, a gravitational tidal interaction unfolds and the systems tear apart into distinct morphological and kinematic structures. In my thesis, I have exploited these structures to understand various components of galaxies, such as the baryon cycle in dwarf galaxy interactions (Pearson et al. 2016, Pearson et al. 2017b). In this talk, I will focus on my thesis work related to the stellar stream emerging from the old, globular cluster, Palomar 5 (Pal 5), orbiting our own Milky Way. As the stellar stream members were once closely tied together in energy and angular momentum space, we can use their distribution in phase space to trace back where they were once located and what affected them along their paths. In particular, I will show that the mere existence of Pal 5’s thin stream can rule out a moderately triaxial potential model of our Galaxy (Pearson et al. 2015) and that the debris of Pal 5-like streams will spread much further in space in a triaxial potential (a mechanism which I dubbed “stream fanning”) . Additionally, I will show that the Milky Way's Galactic bar, can punch holes in stellar streams and explain the recently discovered length asymmetry between Pal 5’s leading and trailing arm (Pearson et al. 2017a). These holes grow and have locations along stellar streams dependent on the Galactic bar orientation, mass and rotational speed, which provides an intriguing methodology for studying our own Milky Way’s Galactic bar in more detail. The fact that the bar can create under densities in stellar streams, further demonstrates that we should be careful when interpreting gaps in stellar streams as indirect evidence of the existence of dark matter subhalos in our Galaxy.

  4. THE STELLAR MASS DENSITY AND SPECIFIC STAR FORMATION RATE OF THE UNIVERSE AT z ∼ 7

    International Nuclear Information System (INIS)

    Gonzalez, Valentino; Bouwens, Rychard J.; Illingworth, Garth; Labbe, Ivo; Franx, Marijn; Kriek, Mariska; Brammer, Gabriel B.

    2010-01-01

    We use a robust sample of 11 z ∼ 7 galaxies (z 850 dropouts) to estimate the stellar mass density (SMD) of the universe when it was only ∼750 Myr old. We combine the very deep optical to near-infrared photometry from the Hubble Space Telescope Advanced Camera for Surveys and NICMOS cameras with mid-infrared Spitzer Infrared Array Camera (IRAC) imaging available through the GOODS program. After carefully removing the flux from contaminating foreground sources, we have obtained reliable photometry in the 3.6 μm and 4.5 μm IRAC channels. The spectral shapes of these sources, including their rest-frame optical colors, strongly support their being at z ∼ 7 with a mean photometric redshift of (z) = 7.2 ± 0.5. We use Bruzual and Charlot synthetic stellar population models to constrain their stellar masses and star formation histories. We find stellar masses that range over (0.1-12) x 10 9 M sun and average ages from 20 Myr to 425 Myr with a mean of ∼300 Myr, suggesting that in some of these galaxies most of the stars were formed at z > 8 (and probably at z ∼> 10). The best fits to the observed SEDs are consistent with little or no dust extinction, in agreement with recent results at z ∼ 4-8. The star formation rates (SFRs) are in the range from 5 to 20 M sun yr -1 . From this sample, we measure an SMD of 6.6 +5.4 -3.3 x 10 5 M sun Mpc -3 to a limit of M UV,AB z=3 ). Combined with a fiducial lower limit for their ages (80 Myr), this implies a maximum SFR density of 0.008 M sun yr -1 Mpc -3 . This is well below the critical level needed to reionize the universe at z ∼ 8 using standard assumptions. However, this result is based on luminous sources (>L*) and does not include the dominant contribution of the fainter galaxies. Strikingly, we find that the specific SFR is constant from z ∼ 7 to z ∼ 2 but drops substantially at more recent times.

  5. Cosmic abundances: The impact of stellar duplicity

    OpenAIRE

    Jorissen, A.; Van Eck, S.

    2004-01-01

    The mass-transfer scenario links chemical peculiarities with stellar duplicity for an increasing number of stellar classes (classical and dwarf barium stars, subgiant and giant CH stars, S stars without technetium, yellow symbiotic stars, WIRRING stars, Abell-35-like nuclei of planetary nebulae...). Despite these successes, the mass-transfer scenario still faces several problems: What is the mass-transfer mode? Why orbital elements of dwarf barium stars do not fully match those of the classic...

  6. New Classes of Quasi-helically Symmetric Stellarators

    International Nuclear Information System (INIS)

    Ku, L.P.; Boozer, A.H.

    2010-01-01

    New classes of quasi-helically symmetric stellarators with aspect ratios (le) 10 have been found which are stable to the perturbation of magnetohydrodynamic modes at plasma pressures of practical interest. These configurations have large rotational transform and good quality of flux surfaces. Characteristics of some selected examples are discussed in detail. The feasibility of using modular coils for these stellarators has been investigated. It is shown that practical designs for modular coils can be achieved.

  7. [From synthetic biology to synthetic humankind].

    Science.gov (United States)

    Nouvel, Pascal

    2015-01-01

    In this paper, we propose an historical survey of the expression "synthetic biology" in order to identify its main philosophical components. The result of the analysis is then used to investigate the meaning of the notion of "synthetic man". It is shown that both notions share a common philosophical background that can be summed up by the short but meaningful assertion: "biology is technology". The analysis allows us to distinguish two notions that are often confused in transhumanist literature: the notion of synthetic man and the notion of renewed man. The consequences of this crucial distinction are discussed. Copyright © 2015 Académie des sciences. Published by Elsevier SAS. All rights reserved.

  8. Plasma equilibrium and stability in stellarators

    International Nuclear Information System (INIS)

    Pustovitov, V.D.; Shafranov, V.D.

    1987-01-01

    A review of theoretical methods of investigating plasma equilibrium and stability in stellarators is given. Principles forming the basis of toroidal plasma equilibrium and its stabilization, and the main results of analytical theory and numerical calculations are presented. Configurations with spiral symmetry and usual stellarators with plane axis and spiral fields are considered in detail. Derivation of scalar two-dimensional equations, describing equilibrium in these systems is given. These equations were used to obtain one-dimensional equations for displacement and ellipticity of magnetic surfaces. The model of weak-elliptic displaced surfaces was used to consider the evolution of plasma equilibrium in stellarators after elevation of its pressure: change of profile of rotational transformation after change of plasma pressure, current generation during its fast heating and its successive damping due to finite plasma conductivity were described. The derivation of equations of small oscillations in the form, suitable for local disturbance investigation is presented. These equations were used to obtain Mercier criteria and ballon model equations. General sufficient conditions of plasma stability in systems with magnetic confinement were derived

  9. The structure of the nuclear stellar cluster of the Milky Way

    International Nuclear Information System (INIS)

    Schoedel, Rainer; Eckart, Andreas

    2006-01-01

    The structure of the nuclear stellar cluster of the Milky Way is of particular interest because it is the densest stellar cluster in our Galaxy, where the theoretical prediction of the formation of a stellar cusp around the central supermassive black hole, Sagittarius A* (Sgr A*) can be examined. We present high-resolution adaptive optics observations with multiple intermediate band liters of the inner ∼20'' around Sgr A*. From the images, stellar number counts and a detailed map of the interstellar extinction toward the central 0.5 pc of the Milky Way were determined. The extinction map is consistent with a putative southwest-northeast aligned outfbw from the central arcseconds. An azimuthally averaged, crowding and extinction corrected stellar density profle presents clear evidence for the existence of a stellar cusp around Sgr A*. We show that the profle of the surface brightness density is dominated by the brightest stars in the central arcseconds and is different from the shape of the stellar cluster as inferred from the number counts. Several density peaks found in the cluster may indicate clumping, possibly related to the last epoch of star formation in the Galactic Center. There is evidence for a common proper motion of the stars in one of these clumps

  10. Nuclear challenges and progress in designing stellarator power plants

    International Nuclear Information System (INIS)

    El-Guebaly, L.

    2007-01-01

    As an alternate to the mainline magnetic fusion tokamaks, the stellarator concept offers a steady state operation without external driven current, eliminating the risk of plasma irruptions. Over the past 2-3 decades, stellarator power plants have been studied in the U.S., Japan, and Europe to enhance the physics and engineering aspects and optimize the design parameters that are subject to numerous constraints. The earlier 1980's studies delivered large stellarators with an average major radius exceeding 20 m. The most recent development of the compact stellarator concept has led to the construction of the National Compact Stellarator Experiment (NCSX) in the U.S. and the 3 years power plant study of ARIES-CS, a compact stellarator with 7.75 m average major radius, approaching that of tokamaks. The ARIES-CS first wall configuration deviates from the standard practice of uniform toroidal shape in order to achieve compactness. Modeling such a complex geometry for 3-D nuclear analysis was a challenging engineering task. A novel approach based on coupling the CAD model with the MCNP Monte Carlo code was developed to model, for the first time ever, the complex stellarator geometry for nuclear assessments. The most important parameter that determines the stellarator size and cost is the minimum distance between the plasma boundary and mid-coil. Accommodating the breeding blanket and necessary shield to protect the superconducting magnet represented another challenging task. An innovative approach utilizing a non-uniform blanket combined with a highly efficient WC shield for this highly constrained area reduced the radial standoff (and machine size and cost) by 25- 30%, which is significant. As stellarators generate more radwaste than tokamaks, managing ARIES-CS active materials during operation and after plant decommissioning was essential for the environmental attractiveness of the machine. The geological disposal option could be replaced with more attractive scenarios

  11. The Stagger-grid: A grid of 3D stellar atmosphere models. I. Methods and general properties

    Science.gov (United States)

    Magic, Z.; Collet, R.; Asplund, M.; Trampedach, R.; Hayek, W.; Chiavassa, A.; Stein, R. F.; Nordlund, Å.

    2013-09-01

    Aims: We present the Stagger-grid, a comprehensive grid of time-dependent, three-dimensional (3D), hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. This grid of 3D models is intended for various applications besides studies of stellar convection and atmospheres per se, including stellar parameter determination, stellar spectroscopy and abundance analysis, asteroseismology, calibration of stellar evolution models, interferometry, and extrasolar planet search. In this introductory paper, we describe the methods we applied for the computation of the grid and discuss the general properties of the 3D models as well as of their temporal and spatial averages (here denoted ⟨3D⟩ models). Methods: All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~ 220 grid models range in effective temperature, Teff, from 4000 to 7000 K in steps of 500 K, in surface gravity, log g, from 1.5 to 5.0 in steps of 0.5 dex, and metallicity, [Fe/H], from - 4.0 to + 0.5 in steps of 0.5 and 1.0 dex. Results: We find a tight scaling relation between the vertical velocity and the surface entropy jump, which itself correlates with the constant entropy value of the adiabatic convection zone. The range in intensity contrast is enhanced at lower metallicity. The granule size correlates closely with the pressure scale height sampled at the depth of maximum velocity. We compare the ⟨3D⟩ models with currently widely applied one-dimensional (1D) atmosphere models, as well as with theoretical 1D hydrostatic models generated with the same EOS and opacity tables as the 3D models, in order to isolate the effects of using self-consistent and hydrodynamic modeling of convection, rather than the classical mixing length theory approach. For the first time, we are able to quantify systematically over a broad

  12. THE STELLAR MASS COMPONENTS OF GALAXIES: COMPARING SEMI-ANALYTICAL MODELS WITH OBSERVATION

    International Nuclear Information System (INIS)

    Liu Lei; Yang Xiaohu; Mo, H. J.; Van den Bosch, Frank C.; Springel, Volker

    2010-01-01

    We compare the stellar masses of central and satellite galaxies predicted by three independent semi-analytical models (SAMs) with observational results obtained from a large galaxy group catalog constructed from the Sloan Digital Sky Survey. In particular, we compare the stellar mass functions of centrals and satellites, the relation between total stellar mass and halo mass, and the conditional stellar mass functions, Φ(M * |M h ), which specify the average number of galaxies of stellar mass M * that reside in a halo of mass M h . The SAMs only predict the correct stellar masses of central galaxies within a limited mass range and all models fail to reproduce the sharp decline of stellar mass with decreasing halo mass observed at the low mass end. In addition, all models over-predict the number of satellite galaxies by roughly a factor of 2. The predicted stellar mass in satellite galaxies can be made to match the data by assuming that a significant fraction of satellite galaxies are tidally stripped and disrupted, giving rise to a population of intra-cluster stars (ICS) in their host halos. However, the amount of ICS thus predicted is too large compared to observation. This suggests that current galaxy formation models still have serious problems in modeling star formation in low-mass halos.

  13. The conducting shell stellarator: A simple means for producing complicated fields

    International Nuclear Information System (INIS)

    Sheffield, G.V.

    1997-01-01

    One of the main characteristics of stellarators, both helical and modular, is that their coil sets must take difficult shapes in order to produce the complicated stellarator magnetic fields. The complex coil shapes make fabrication difficult and costly compared to say the toroidal field, TF, coil set of a tokamak. The conducting shell stellarator, CSS, configuration described in this report shows that complicated stellarator fields can be produced by inducing eddy currents in a conducting shell from a simple TF coil set (a field that varies like 1/R). This technique is applicable not only to a pulsed system at room or cryogenic temperatures, but can be implemented for a superconducting TF with a superconducting shell in a stellarator reactor. The CSS has the added benefit that within this device the metallic shell which can be made up of discrete plates can be changed out and replaced with new plates to create a different stellarator configuration within the same TF coil set. The work of creating the complicated magnetics is done by the passive conductor reshaping the simple TF field

  14. Detecting stellar-wind bubbles through infrared arcs in H II regions

    Science.gov (United States)

    Mackey, Jonathan; Haworth, Thomas J.; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert; Harries, Tim J.

    2016-02-01

    Mid-infrared arcs of dust emission are often seen near ionizing stars within H II regions. A possible explanations for these arcs is that they could show the outer edges of asymmetric stellar wind bubbles. We use two-dimensional, radiation-hydrodynamics simulations of wind bubbles within H II regions around individual stars to predict the infrared emission properties of the dust within the H II region. We assume that dust and gas are dynamically well-coupled and that dust properties (composition, size distribution) are the same in the H II region as outside it, and that the wind bubble contains no dust. We post-process the simulations to make synthetic intensity maps at infrared wavebands using the torus code. We find that the outer edge of a wind bubble emits brightly at 24 μm through starlight absorbed by dust grains and re-radiated thermally in the infrared. This produces a bright arc of emission for slowly moving stars that have asymmetric wind bubbles, even for cases where there is no bow shock or any corresponding feature in tracers of gas emission. The 24 μm intensity decreases exponentially from the arc with increasing distance from the star because the dust temperature decreases with distance. The size distribution and composition of the dust grains has quantitative but not qualitative effects on our results. Despite the simplifications of our model, we find good qualitative agreement with observations of the H II region RCW 120, and can provide physical explanations for any quantitative differences. Our model produces an infrared arc with the same shape and size as the arc around CD -38°11636 in RCW 120, and with comparable brightness. This suggests that infrared arcs around O stars in H II regions may be revealing the extent of stellar wind bubbles, although we have not excluded other explanations.

  15. Recent Progress in MHD Stability Calculations of Compact Stellarators

    International Nuclear Information System (INIS)

    Fu, G.Y.; Ku, L.P.; Redi, M.H.; Kessel, C.; Monticello, D.A.; Reiman, A.; Cooper, W.A.; Nuehrenberg, C.; Sanchez, R.; Ware, A.; Hirshman, S.P.; Spong, D.A.

    2000-01-01

    A key issue for compact stellarators is the stability of beta-limiting MHD modes, such as external kink modes driven by bootstrap current and pressure gradient. We report here recent progress in MHD stability studies for low-aspect-ratio Quasi-Axisymmetric Stellarators (QAS) and Quasi-Omnigeneous Stellarators (QOS). We find that the N = 0 periodicity-preserving vertical mode is significantly more stable in stellarators than in tokamaks because of the externally generated rotational transform. It is shown that both low-n external kink modes and high-n ballooning modes can be stabilized at high beta by appropriate 3D shaping without a conducting wall. The stabilization mechanism for external kink modes in QAS appears to be an enhancement of local magnetic shear due to 3D shaping. The stabilization of ballooning mode in QOS is related to a shortening of the normal curvature connection length

  16. KINEMATICS OF CLASSICAL CEPHEIDS IN THE NUCLEAR STELLAR DISK

    International Nuclear Information System (INIS)

    Matsunaga, Noriyuki; Fukue, Kei; Yamamoto, Ryo; Kobayashi, Naoto; Hamano, Satoshi; Inno, Laura; Genovali, Katia; Bono, Giuseppe; Baba, Junichi; Fujii, Michiko S.; Aoki, Wako; Tsujimoto, Takuji; Kondo, Sohei; Ikeda, Yuji; Nishiyama, Shogo; Nagata, Tetsuya

    2015-01-01

    Classical Cepheids are useful tracers of the Galactic young stellar population because their distances and ages can be determined from their period-luminosity and period-age relations. In addition, the radial velocities and chemical abundance of the Cepheids can be derived from spectroscopic observations, providing further insights into the structure and evolution of the Galaxy. Here, we report the radial velocities of classical Cepheids near the Galactic center, three of which were reported in 2011 and a fourth being reported for the first time. The velocities of these Cepheids suggest that the stars orbit within the nuclear stellar disk, a group of stars and interstellar matter occupying a region of ∼200 pc around the center, although the three-dimensional velocities cannot be determined until the proper motions are known. According to our simulation, these four Cepheids formed within the nuclear stellar disk like younger stars and stellar clusters therein

  17. Stellar compass for the Clementine Mission

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, B. [Lawrence Livermore National Lab., CA (United States)

    1994-11-15

    A CCD sensor with 42 x 28 degrees FOV and 576 x 384 pixels was built by the Advanced Technology Program (ATP) in the Physics Department at LLNL. That sensor, called the StarTracker camera, is used on the Clementine Lunar Mapping mission between January and May, 1994. Together with the Stellar Compass software, the StarTracker camera provided a way of identifying its orientation to within about 150 microradians in camera body pitch and yaw. This presentation will be an overview of basically how the Stellar Compass software works, along with showing some of its performance results.

  18. Weakly interacting massive particles and stellar structure

    International Nuclear Information System (INIS)

    Bouquet, A.

    1988-01-01

    The existence of weakly interacting massive particles (WIMPs) may solve both the dark matter problem and the solar neutrino problem. Such particles affect the energy transport in the stellar cores and change the stellar structure. We present the results of an analytic approximation to compute these effects in a self-consistent way. These results can be applied to many different stars, but we focus on the decrease of the 8 B neutrino flux in the case of the Sun

  19. AXISYMMETRIC SIMULATIONS OF HOT JUPITER–STELLAR WIND HYDRODYNAMIC INTERACTION

    International Nuclear Information System (INIS)

    Christie, Duncan; Arras, Phil; Li, Zhi-Yun

    2016-01-01

    Gas giant exoplanets orbiting at close distances to the parent star are subjected to large radiation and stellar wind fluxes. In this paper, hydrodynamic simulations of the planetary upper atmosphere and its interaction with the stellar wind are carried out to understand the possible flow regimes and how they affect the Lyα transmission spectrum. Following Tremblin and Chiang, charge exchange reactions are included to explore the role of energetic atoms as compared to thermal particles. In order to understand the role of the tail as compared to the leading edge of the planetary gas, the simulations were carried out under axisymmetry, and photoionization and stellar wind electron impact ionization reactions were included to limit the extent of the neutrals away from the planet. By varying the planetary gas temperature, two regimes are found. At high temperature, a supersonic planetary wind is found, which is turned around by the stellar wind and forms a tail behind the planet. At lower temperatures, the planetary wind is shut off when the stellar wind penetrates inside where the sonic point would have been. In this regime mass is lost by viscous interaction at the boundary between planetary and stellar wind gases. Absorption by cold hydrogen atoms is large near the planetary surface, and decreases away from the planet as expected. The hot hydrogen absorption is in an annulus and typically dominated by the tail, at large impact parameter, rather than by the thin leading edge of the mixing layer near the substellar point

  20. AXISYMMETRIC SIMULATIONS OF HOT JUPITER–STELLAR WIND HYDRODYNAMIC INTERACTION

    Energy Technology Data Exchange (ETDEWEB)

    Christie, Duncan; Arras, Phil; Li, Zhi-Yun [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States)

    2016-03-20

    Gas giant exoplanets orbiting at close distances to the parent star are subjected to large radiation and stellar wind fluxes. In this paper, hydrodynamic simulations of the planetary upper atmosphere and its interaction with the stellar wind are carried out to understand the possible flow regimes and how they affect the Lyα transmission spectrum. Following Tremblin and Chiang, charge exchange reactions are included to explore the role of energetic atoms as compared to thermal particles. In order to understand the role of the tail as compared to the leading edge of the planetary gas, the simulations were carried out under axisymmetry, and photoionization and stellar wind electron impact ionization reactions were included to limit the extent of the neutrals away from the planet. By varying the planetary gas temperature, two regimes are found. At high temperature, a supersonic planetary wind is found, which is turned around by the stellar wind and forms a tail behind the planet. At lower temperatures, the planetary wind is shut off when the stellar wind penetrates inside where the sonic point would have been. In this regime mass is lost by viscous interaction at the boundary between planetary and stellar wind gases. Absorption by cold hydrogen atoms is large near the planetary surface, and decreases away from the planet as expected. The hot hydrogen absorption is in an annulus and typically dominated by the tail, at large impact parameter, rather than by the thin leading edge of the mixing layer near the substellar point.

  1. Stellar Velocity Dispersion: Linking Quiescent Galaxies to Their Dark Matter Halos

    Science.gov (United States)

    Zahid, H. Jabran; Sohn, Jubee; Geller, Margaret J.

    2018-06-01

    We analyze the Illustris-1 hydrodynamical cosmological simulation to explore the stellar velocity dispersion of quiescent galaxies as an observational probe of dark matter halo velocity dispersion and mass. Stellar velocity dispersion is proportional to dark matter halo velocity dispersion for both central and satellite galaxies. The dark matter halos of central galaxies are in virial equilibrium and thus the stellar velocity dispersion is also proportional to dark matter halo mass. This proportionality holds even when a line-of-sight aperture dispersion is calculated in analogy to observations. In contrast, at a given stellar velocity dispersion, the dark matter halo mass of satellite galaxies is smaller than virial equilibrium expectations. This deviation from virial equilibrium probably results from tidal stripping of the outer dark matter halo. Stellar velocity dispersion appears insensitive to tidal effects and thus reflects the correlation between stellar velocity dispersion and dark matter halo mass prior to infall. There is a tight relation (≲0.2 dex scatter) between line-of-sight aperture stellar velocity dispersion and dark matter halo mass suggesting that the dark matter halo mass may be estimated from the measured stellar velocity dispersion for both central and satellite galaxies. We evaluate the impact of treating all objects as central galaxies if the relation we derive is applied to a statistical ensemble. A large fraction (≳2/3) of massive quiescent galaxies are central galaxies and systematic uncertainty in the inferred dark matter halo mass is ≲0.1 dex thus simplifying application of the simulation results to currently available observations.

  2. The Influence of Atomic Diffusion on Stellar Ages and Chemical Tagging

    Energy Technology Data Exchange (ETDEWEB)

    Dotter, Aaron; Conroy, Charlie; Cargile, Phillip [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Asplund, Martin, E-mail: aaron.dotter@gmail.com [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT (Australia)

    2017-05-10

    In the era of large stellar spectroscopic surveys, there is an emphasis on deriving not only stellar abundances but also the ages for millions of stars. In the context of Galactic archeology, stellar ages provide a direct probe of the formation history of the Galaxy. We use the stellar evolution code MESA to compute models with atomic diffusion—with and without radiative acceleration—and extra mixing in the surface layers. The extra mixing consists of both density-dependent turbulent mixing and envelope overshoot mixing. Based on these models we argue that it is important to distinguish between initial, bulk abundances (parameters) and current, surface abundances (variables) in the analysis of individual stellar ages. In stars that maintain radiative regions on evolutionary timescales, atomic diffusion modifies the surface abundances. We show that when initial, bulk metallicity is equated with current, surface metallicity in isochrone age analysis, the resulting stellar ages can be systematically overestimated by up to 20%. The change of surface abundances with evolutionary phase also complicates chemical tagging, which is the concept that dispersed star clusters can be identified through unique, high-dimensional chemical signatures. Stars from the same cluster, but in different evolutionary phases, will show different surface abundances. We speculate that calibration of stellar models may allow us to estimate not only stellar ages but also initial abundances for individual stars. In the meantime, analyzing the chemical properties of stars in similar evolutionary phases is essential to minimize the effects of atomic diffusion in the context of chemical tagging.

  3. Age gradients in the stellar populations of massive star forming regions based on a new stellar chronometer

    Energy Technology Data Exchange (ETDEWEB)

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.; Broos, Patrick S.; Townsley, Leisa K.; Luhman, Kevin L. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Naylor, Tim [School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Povich, Matthew S. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States); Garmire, Gordon P. [Huntingdon Institute for X-ray Astronomy, LLC, 10677 Franks Road, Huntingdon, PA 16652 (United States)

    2014-06-01

    A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, Age {sub JX} . Stellar masses are derived from X-ray luminosities using the L{sub X} -M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. Age {sub JX} is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The Age {sub JX} method has been applied to 5525 out of 31,784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The Age {sub JX} ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J – H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters.

  4. The impact of Spitzer infrared data on stellar mass estimates - and a revised galaxy stellar mass function at 0 < z < 5

    Science.gov (United States)

    Elsner, F.; Feulner, G.; Hopp, U.

    2008-01-01

    Aims:We estimate stellar masses of galaxies in the high redshift universe with the intention of determining the influence of newly available Spitzer/IRAC infrared data on the analysis. Based on the results, we probe the mass assembly history of the universe. Methods: We use the GOODS-MUSIC catalog, which provides multiband photometry from the U-filter to the 8 μm Spitzer band for almost 15 000 galaxies with either spectroscopic (for ≈7% of the sample) or photometric redshifts, and apply a standard model fitting technique to estimate stellar masses. We than repeat our calculations with fixed photometric redshifts excluding Spitzer photometry and directly compare the outcomes to look for systematic deviations. Finally we use our results to compute stellar mass functions and mass densities up to redshift z = 5. Results: We find that stellar masses tend to be overestimated on average if further constraining Spitzer data are not included into the analysis. Whilst this trend is small up to intermediate redshifts z ⪉ 2.5 and falls within the typical error in mass, the deviation increases strongly for higher redshifts and reaches a maximum of a factor of three at redshift z ≈ 3.5. Thus, up to intermediate redshifts, results for stellar mass density are in good agreement with values taken from literature calculated without additional Spitzer photometry. At higher redshifts, however, we find a systematic trend towards lower mass densities if Spitzer/IRAC data are included.

  5. THE RAVE CATALOG OF STELLAR ELEMENTAL ABUNDANCES: FIRST DATA RELEASE

    Energy Technology Data Exchange (ETDEWEB)

    Boeche, C.; Williams, M.; De Jong, R. S.; Steinmetz, M. [Leibniz-Institut fuer Astrophysik Potsdam (AIP), D-14482 Potsdam (Germany); Siebert, A.; Bienayme, O. [Observatoire Astronomique de Strasbourg, Universite de Strasbourg, CNRS, UMR 7550, F-67000 Strasbourg (France); Fulbright, J. P.; Ruchti, G. R. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Bland-Hawthorn, J. [Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006 (Australia); Campbell, R. [Department of Physics and Astronomy, Western Kentucky University, Bowling Green, KY (United States); Freeman, K. C. [Research School of Astronomy and Astrophysics, Australia National University, Weston Creek, Canberra ACT 2611 (Australia); Gibson, B. K. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Gilmore, G. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Grebel, E. K. [Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg, D-69120 Heidelberg (Germany); Helmi, A. [Kapteyn Astronomical Institute, University of Groningen, 9700 AV Groningen (Netherlands); Munari, U. [INAF Osservatorio Astronomico di Padova, Asiago I-36012 (Italy); Navarro, J. F. [Department of Physics and Astronomy, University of Victoria, Victoria BC V8W 3P6 (Canada); Parker, Q. A.; Reid, W. [Department of Physics and Astronomy, Faculty of Sciences, Macquarie University, Sydney, NSW 2109 (Australia); Seabroke, G. M. [Mullard Space Science Laboratory, University College London, Holmbury, St. Mary RH5 6NT (United Kingdom); and others

    2011-12-15

    We present chemical elemental abundances for 36,561 stars observed by the RAdial Velocity Experiment (RAVE), an ambitious spectroscopic survey of our Galaxy at Galactic latitudes |b| > 25 Degree-Sign and with magnitudes in the range 9 stellar parameters, and it contains chemical abundances for the elements Mg, Al, Si, Ca, Ti, Fe, and Ni, with a mean error of {approx}0.2 dex, as judged from accuracy tests performed on synthetic and real spectra. Abundances are estimated through a dedicated processing pipeline in which the curve of growth of individual lines is obtained from a library of absorption line equivalent widths to construct a model spectrum that is then matched to the observed spectrum via a {chi}{sup 2} minimization technique. We plan to extend this pipeline to include estimates for other elements, such as oxygen and sulfur, in future data releases.

  6. Young Stellar Objects from Soft to Hard X-rays

    Science.gov (United States)

    Güdel, Manuel

    2009-05-01

    Magnetically active stars are the sites of efficient particle acceleration and plasma heating, processes that have been studied in detail in the solar corona. Investigation of such processes in young stellar objects is much more challenging due to various absorption processes. There is, however, evidence for violent magnetic energy release in very young stellar objects. The impact on young stellar environments (e.g., circumstellar disk heating and ionization, operation of chemical networks, photoevaporation) may be substantial. Hard X-ray devices like those carried on Simbol-X will establish a basis for detailed studies of these processes.

  7. STELLAR, GAS, AND DARK MATTER CONTENT OF BARRED GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Cervantes Sodi, Bernardo, E-mail: b.cervantes@crya.unam.mx [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Campus Morelia, A.P. 3-72, C.P. 58089 Michoacán, México (Mexico)

    2017-01-20

    We select a sample of galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) where galaxies are classified, through visual inspection, as hosting strong bars, weak bars, or as unbarred galaxies, and make use of H i mass and kinematic information from the Arecibo Legacy Fast ALFA survey catalog, to study the stellar, atomic gas, and dark matter content of barred disk galaxies. We find, in agreement with previous studies, that the bar fraction increases with increasing stellar mass. A similar trend is found with total baryonic mass, although the dependence is not as strong as with stellar mass, due to the contribution of gas. The bar fraction shows a decrease with increasing gas mass fraction. This anticorrelation between the likelihood of a galaxy hosting a bar with the gas richness of the galaxy results from the inhibiting effect the gas has in the formation of bars. We also find that for massive galaxies with stellar masses larger than 10{sup 10} M {sub ⊙}, at fixed stellar mass, the bar fraction decreases with increasing global halo mass (i.e., halo mass measured up to a radius of the order of the H i disk extent).

  8. THE ESTIMATION OF STAR FORMATION RATES AND STELLAR POPULATION AGES OF HIGH-REDSHIFT GALAXIES FROM BROADBAND PHOTOMETRY

    International Nuclear Information System (INIS)

    Lee, Seong-Kook; Ferguson, Henry C.; Somerville, Rachel S.; Wiklind, Tommy; Giavalisco, Mauro

    2010-01-01

    We explore methods to improve the estimates of star formation rates and mean stellar population ages from broadband photometry of high-redshift star-forming galaxies. We use synthetic spectral templates with a variety of simple parametric star formation histories to fit broadband spectral energy distributions. These parametric models are used to infer ages, star formation rates, and stellar masses for a mock data set drawn from a hierarchical semi-analytic model of galaxy evolution. Traditional parametric models generally assume an exponentially declining rate of star formation after an initial instantaneous rise. Our results show that star formation histories with a much more gradual rise in the star formation rate are likely to be better templates, and are likely to give better overall estimates of the age distribution and star formation rate distribution of Lyman break galaxies (LBGs). For B- and V-dropouts, we find the best simple parametric model to be one where the star formation rate increases linearly with time. The exponentially declining model overpredicts the age by 100% and 120% for B- and V-dropouts, on average, while for a linearly increasing model, the age is overpredicted by 9% and 16%, respectively. Similarly, the exponential model underpredicts star formation rates by 56% and 60%, while the linearly increasing model underpredicts by 15% and 22%, respectively. For U-dropouts, the models where the star formation rate has a peak (near z ∼ 3) provide the best match for age-overprediction is reduced from 110% to 26%-and star formation rate-underprediction is reduced from 58% to 22%. We classify different types of star formation histories in the semi-analytic models and show how the biases behave for the different classes. We also provide two-band calibration formulae for stellar mass and star formation rate estimations.

  9. Proceedings of the 13th International Stellarator Workshop

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2002-07-01

    These proceedings include submitted abstracts and papers summarising the work as presented by participants in either oral or poster sessions and the highlights of the Workshop presented by Professor Jeffrey Harris. He stressed that while notable progress has been made in stellarator research overall, the world stellarator program faces important challenges in the coming years. Lead times for the construction of the next generation of devices are approximately 5 years, which makes maintaining continuity in research programs more difficult. The development of a compelling reactor vision based on the stellarator is an important task, especially in the context of renewed activity on the ITER tokamak project. The sharing of ideas, techniques, and results via international collaboration is more important than ever. Individual presentations have been separately indexed.

  10. Scientific visualization of 3-dimensional optimized stellarator configurations

    International Nuclear Information System (INIS)

    Spong, D.A.

    1998-01-01

    The design techniques and physics analysis of modern stellarator configurations for magnetic fusion research rely heavily on high performance computing and simulation. Stellarators, which are fundamentally 3-dimensional in nature, offer significantly more design flexibility than more symmetric devices such as the tokamak. By varying the outer boundary shape of the plasma, a variety of physics features, such as transport, stability, and heating efficiency can be optimized. Scientific visualization techniques are an important adjunct to this effort as they provide a necessary ergonomic link between the numerical results and the intuition of the human researcher. The authors have developed a variety of visualization techniques for stellarators which both facilitate the design optimization process and allow the physics simulations to be more readily understood

  11. Comprehensive Chiroptical Spectroscopy, Applications in Stereochemical Analysis of Synthetic Compounds, Natural Products, and Biomolecules

    CERN Document Server

    Berova, Nina; Nakanishi, Koji; Woody, Robert W

    2012-01-01

    This book provides an introduction to the important methods of chiroptical spectroscopy in general, and circular dichroism (CD) in particular, which are increasingly important in all areas of chemistry, biochemistry, and structural biology. The book can be used as a text for undergraduate and graduate students and as a reference for researchers in academia and industry. Experimental methods and instrumentation are described with topics ranging from the most widely used methods (electronic and vibrational CD) to frontier areas such as nonlinear spectroscopy and photoelectron CD,

  12. Applications of Raman spectroscopy to gemology.

    Science.gov (United States)

    Bersani, Danilo; Lottici, Pier Paolo

    2010-08-01

    Being nondestructive and requiring short measurement times, a low amount of material, and no sample preparation, Raman spectroscopy is used for routine investigation in the study of gemstone inclusions and treatments and for the characterization of mounted gems. In this work, a review of the use of laboratory Raman and micro-Raman spectrometers and of portable Raman systems in the gemology field is given, focusing on gem identification and on the evaluation of the composition, provenance, and genesis of gems. Many examples are shown of the use of Raman spectroscopy as a tool for the identification of imitations, synthetic gems, and enhancement treatments in natural gemstones. Some recent developments are described, with particular attention being given to the semiprecious stone jade and to two important organic materials used in jewelry, i.e., pearls and corals.

  13. Optical spectroscopy of the blue supergiant Sk-69° 279 and its circumstellar shell with SALT

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Maryeva, O. V.; Berdnikov, L. N.

    2018-02-01

    We report the results of optical spectroscopy of the blue supergiant Sk-69° 279 and its circular shell in the Large Magellanic Cloud (LMC) with the Southern African Large Telescope (SALT). We classify Sk-69° 279 as an O9.2 Iaf star and analyse its spectrum by using the stellar atmosphere code CMFGEN, obtaining a stellar temperature of ≈30 kK, a luminosity of log (L*/ L⊙) = 5.54, a mass-loss rate of log (\\dot{M}/ M_{⊙} yr^{-1}) = -5.26, and a wind velocity of 800km s-1. We found also that Sk-69° 279 possesses an extended atmosphere with an effective temperature of ≈24 kK and that its surface helium and nitrogen abundances are enhanced, respectively, by factors of ≈2 and 20-30. This suggests that either Sk-69° 279 was initially a (single) fast-rotating ( ≳ 400 km s- 1) star, which only recently evolved off the main sequence, or that it is a product of close binary evolution. The long-slit spectroscopy of the shell around Sk-69° 279 revealed that its nitrogen abundance is enhanced by the same factor as the stellar atmosphere, which implies that the shell is composed mostly of the CNO processed material lost by the star. Our findings support previous propositions that some massive stars can produce compact circumstellar shells and, presumably, appear as luminous blue variables while they are still on the main sequence or have only recently left it.

  14. Magnetohydrodynamic theory of plasma equilibrium and stability in stellarators: Survey of results

    International Nuclear Information System (INIS)

    Shafranov, V.D.

    1983-01-01

    The main advantage of a stellarator is its capability of steady-state operation. It can be exploited as a reactor if stable plasma confinement can be achieved with #betta#approx.10%. Therefore, this limiting pressure value is a key factor in stellarator development. This paper contains a survey of current ideas on the magnetohydrodynamic equilibrium and stability properties of stellarators with sufficiently high pressure. Here, any system of nested toroidal magnetic surfaces generated by external currents is considered a stellarator. Systems produced by helical or equivalent windings, including torsatrons and heliotrons, will be called ordinary stellarators, in contrast to those with spatial axes. It is shown that adequate confinement can be achieved

  15. Stellar population synthesis

    International Nuclear Information System (INIS)

    Pickles, A.J.

    1989-01-01

    The techniques used to derive astrophysically useful information from observations of the integrated light of composite stellar systems are briefly reviewed. A synthesis technique, designed to separate and describe on a standard system the competing effects of age and metallicity variations is introduced, and illustrated by its application to the study of the history of star formation in bright elliptical galaxies in clusters. (author)

  16. Overdense Plasma Operation in the WEGA Stellarator

    Czech Academy of Sciences Publication Activity Database

    Otte, M.; Laqua, H.P.; Marsen, S.; Podoba, Y.; Preinhaelter, Josef; Stange, T.; Urban, Jakub; Wagner, F.; Zhang, D.

    2010-01-01

    Roč. 50, č. 8 (2010), s. 785-789 ISSN 0863-1042. [International Stellarator/Heliotron Workshop/17th./. Princeton, 12.10.2009-16.10.2009] R&D Projects: GA ČR GA202/08/0419; GA MŠk 7G09042 Institutional research plan: CEZ:AV0Z20430508 Keywords : Stellarator * Bernstein waves * overdense plasma * supra -thermal electrons Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.006, year: 2010 http://dx.doi.org/10.1002/ctpp.200900053

  17. Recent advances in stellarator optimization

    Science.gov (United States)

    Gates, D. A.; Boozer, A. H.; Brown, T.; Breslau, J.; Curreli, D.; Landreman, M.; Lazerson, S. A.; Lore, J.; Mynick, H.; Neilson, G. H.; Pomphrey, N.; Xanthopoulos, P.; Zolfaghari, A.

    2017-12-01

    Computational optimization has revolutionized the field of stellarator design. To date, optimizations have focused primarily on optimization of neoclassical confinement and ideal MHD stability, although limited optimization of other parameters has also been performed. The purpose of this paper is to outline a select set of new concepts for stellarator optimization that, when taken as a group, present a significant step forward in the stellarator concept. One of the criticisms that has been leveled at existing methods of design is the complexity of the resultant field coils. Recently, a new coil optimization code—COILOPT++, which uses a spline instead of a Fourier representation of the coils,—was written and included in the STELLOPT suite of codes. The advantage of this method is that it allows the addition of real space constraints on the locations of the coils. The code has been tested by generating coil designs for optimized quasi-axisymmetric stellarator plasma configurations of different aspect ratios. As an initial exercise, a constraint that the windings be vertical was placed on large major radius half of the non-planar coils. Further constraints were also imposed that guaranteed that sector blanket modules could be removed from between the coils, enabling a sector maintenance scheme. Results of this exercise will be presented. New ideas on methods for the optimization of turbulent transport have garnered much attention since these methods have led to design concepts that are calculated to have reduced turbulent heat loss. We have explored possibilities for generating an experimental database to test whether the reduction in transport that is predicted is consistent with experimental observations. To this end, a series of equilibria that can be made in the now latent QUASAR experiment have been identified that will test the predicted transport scalings. Fast particle confinement studies aimed at developing a generalized optimization algorithm are also

  18. Stellar Atmospheric Modelling for the ACCESS Program

    Science.gov (United States)

    Morris, Matthew; Kaiser, Mary Elizabeth; Bohlin, Ralph; Kurucz, Robert; ACCESS Team

    2018-01-01

    A goal of the ACCESS program (Absolute Color Calibration Experiment for Standard Stars) is to enable greater discrimination between theoretical astrophysical models and observations, where the comparison is limited by systematic errors associated with the relative flux calibration of the targets. To achieve these goals, ACCESS has been designed as a sub-orbital rocket borne payload and ground calibration program, to establish absolute flux calibration of stellar targets at flight candidates, as well as a selection of A and G stars from the CALSPEC database. Stellar atmosphere models were generated using Atlas 9 and Atlas 12 Kurucz stellar atmosphere software. The effective temperature, log(g), metallicity, and redenning were varied and the chi-squared statistic was minimized to obtain a best-fit model. A comparison of these models and the results from interpolation between grids of existing models will be presented. The impact of the flexibility of the Atlas 12 input parameters (e.g. solar metallicity fraction, abundances, microturbulent velocity) is being explored.

  19. Clustering in the stellar abundance space

    Science.gov (United States)

    Boesso, R.; Rocha-Pinto, H. J.

    2018-03-01

    We have studied the chemical enrichment history of the interstellar medium through an analysis of the n-dimensional stellar abundance space. This work is a non-parametric analysis of the stellar chemical abundance space. The main goal is to study the stars from their organization within this abundance space. Within this space, we seek to find clusters (in a statistical sense), that is, stars likely to share similar chemo-evolutionary history, using two methods: the hierarchical clustering and the principal component analysis. We analysed some selected abundance surveys available in the literature. For each sample, we labelled the group of stars according to its average abundance curve. In all samples, we identify the existence of a main enrichment pattern of the stars, which we call chemical enrichment flow. This flow is set by the structured and well-defined mean rate at which the abundances of the interstellar medium increase, resulting from the mixture of the material ejected from the stars and stellar mass-loss and interstellar medium gas. One of the main results of our analysis is the identification of subgroups of stars with peculiar chemistry. These stars are situated in regions outside of the enrichment flow in the abundance space. These peculiar stars show a mismatch in the enrichment rate of a few elements, such as Mg, Si, Sc and V, when compared to the mean enrichment rate of the other elements of the same stars. We believe that the existence of these groups of stars with peculiar chemistry may be related to the accretion of planetary material on to stellar surfaces or may be due to production of the same chemical element by different nucleosynthetic sites.

  20. The Resilience of Kepler Systems to Stellar Obliquity

    Science.gov (United States)

    Spalding, Christopher; Marx, Noah W.; Batygin, Konstantin

    2018-04-01

    The Kepler mission and its successor K2 have brought forth a cascade of transiting planets. Many of these planetary systems exhibit multiple members, but a large fraction possess only a single transiting example. This overabundance of singles has led to the suggestion that up to half of Kepler systems might possess significant mutual inclinations between orbits, reducing the transiting number (the so-called “Kepler Dichotomy”). In a recent paper, Spalding & Batygin demonstrated that the quadrupole moment arising from a young, oblate star is capable of misaligning the constituent orbits of a close-in planetary system enough to reduce their transit number, provided that the stellar spin axis is sufficiently misaligned with respect to the planetary orbital plane. Moreover, tightly packed planetary systems were shown to be susceptible to becoming destabilized during this process. Here, we investigate the ubiquity of the stellar obliquity-driven instability within systems with a range of multiplicities. We find that most planetary systems analyzed, including those possessing only two planets, underwent instability for stellar spin periods below ∼3 days and stellar tilts of order 30°. Moreover, we are able to place upper limits on the stellar obliquity in systems such as K2-38 (obliquity ≲20°), where other methods of measuring the spin–orbit misalignment are not currently available. Given the known parameters of T-Tauri stars, we predict that up to one-half of super-Earth-mass systems may encounter the instability, in general agreement with the fraction typically proposed to explain the observed abundance of single-transiting systems.

  1. Nonlinear MHD and energetic particle modes in stellarators

    International Nuclear Information System (INIS)

    Strauss, H.R.; Fu, G.Y.; Park, W.; Breslau, J.; Sugiyama, L.E.

    2003-01-01

    The M3D (Multi-level 3D) project carries out simulation studies of plasmas using multiple levels of physics, geometry and grid models. The M3D code has been applied to ideal, resistive, two fluid, and hybrid simulations of compact quasi axisymmetric stellarators. When β exceeds a threshold, moderate toroidal mode number (n ∼ 10) modes grow exponentially, clearly distinguishable from the equilibrium evolution. The β limits are significantly higher than the infinite mode number ballooning limits. In the presence of resistivity, these modes occur well below the ideal limit. Their growth rate scaling with resistivity is similar to tearing modes. At low resistivity, the modes couple to resistive interchanges, which are unstable in most stellarators. Two fluid simulations with M3D show that resistive modes can be stabilized by diamagnetic drift. The two fluid computations are done with a realistic value of the Hall parameter, the ratio of ion skin depth to major radius. Hybrid gyrokinetic simulations with energetic particles indicate that global shear Alfven TAE - like modes can be destabilized in stellarators. Computations in a two-period compact stellarator obtained a predominantly n=1 toroidal mode with the expected TAE frequency. It is found that TAE modes are more stable in the two-period compact stellarator that in a tokamak with the same q and pressure profiles. M3D combines a two dimensional unstructured mesh with finite element discretization in poloidal planes, and fourth order finite differencing in the toroidal direction. (author)

  2. Proton Testing of Advanced Stellar Compass Digital Processing Unit

    DEFF Research Database (Denmark)

    Thuesen, Gøsta; Denver, Troelz; Jørgensen, Finn E

    1999-01-01

    The Advanced Stellar Compass Digital Processing Unit was radiation tested with 300 MeV protons at Proton Irradiation Facility (PIF), Paul Scherrer Institute, Switzerland.......The Advanced Stellar Compass Digital Processing Unit was radiation tested with 300 MeV protons at Proton Irradiation Facility (PIF), Paul Scherrer Institute, Switzerland....

  3. Proceedings of US-Japan heliotron-stellarator workshop: Volume 4

    International Nuclear Information System (INIS)

    1987-01-01

    This paper is the fourth of four volumes on the US-Japan Heliotron-Stellarator workshop. It contains talks on the following: Compact torsatron studies; Low aspect ratio torsatron design; Optimized small stellarator designs; Currents in ATF; Computations of 3-D equilibria with islands; and Magnetic surface mapping studies

  4. Specific features of plasma equilibrium in closed mixed-type stellarators

    International Nuclear Information System (INIS)

    Shafranov, V.D.; Mikhajlov, M.I.

    1992-01-01

    High values of rotational transformation (i/2π>1) are studied in terms of their usefulness for plasma equilibrium using stellarators with spatial magnetic axis and circular cross section of averaged magnetic surfaces. It is shown that, in contrast to a conventional stellarator with circular magnetic axis, where ultimate equilibrium pressure grows proportionally (i/2π) 2 equilibrium in lost in more complex stellarators consisting of heterogeneous sections as rotational transformation approaches, over period of the system, whole-number values. At the same time, in case when the transformation approaches a whole-number value of i/2π, short-circuit of secondary currents occurs within one of the periods of the system and ultimate equilibrium pressure value can exceed that in a conventional stellarator having the same length of the system and rotational transformation value

  5. STELLAR: fast and exact local alignments

    Directory of Open Access Journals (Sweden)

    Weese David

    2011-10-01

    Full Text Available Abstract Background Large-scale comparison of genomic sequences requires reliable tools for the search of local alignments. Practical local aligners are in general fast, but heuristic, and hence sometimes miss significant matches. Results We present here the local pairwise aligner STELLAR that has full sensitivity for ε-alignments, i.e. guarantees to report all local alignments of a given minimal length and maximal error rate. The aligner is composed of two steps, filtering and verification. We apply the SWIFT algorithm for lossless filtering, and have developed a new verification strategy that we prove to be exact. Our results on simulated and real genomic data confirm and quantify the conjecture that heuristic tools like BLAST or BLAT miss a large percentage of significant local alignments. Conclusions STELLAR is very practical and fast on very long sequences which makes it a suitable new tool for finding local alignments between genomic sequences under the edit distance model. Binaries are freely available for Linux, Windows, and Mac OS X at http://www.seqan.de/projects/stellar. The source code is freely distributed with the SeqAn C++ library version 1.3 and later at http://www.seqan.de.

  6. Probing the low-stellar-mass domain with Kepler and APOGEE observations of eclipsing binaries

    Science.gov (United States)

    Prsa, Andrej; Hambleton, Kelly

    2018-01-01

    Observations of low-mass stars (M models, where observed radii can be inflated by as much as 5-15% as compared to model predictions. One of the proposed explanations for this discrepancy that is gaining traction are stellar magnetic fields impeding the onset of convection and the subsequent bloating of the star. Here we present modeling analysis results of two benchmark eclipsing binaries, KIC 3003991 and KIC 2445134, with low mass companions (M ~ 0.2 MSun and M ~ 0.5 MSun, respectively). The models are based on Kepler photometry and APOGEE spectroscopy. APOGEE is a part of the Sloan spectroscopic survey that observes in the near-infrared, providing greater sensitivity towards fainter, red companions. We combine the binary modeling software PHOEBE with emcee, an affine invariant Markov chain Monte Carlo sampler; celerite, a Gaussian process library; and our own codes to create a modeling suite capable of modeling correlated noise, shot noise, nuisance astrophysical signals (such as spots) and the full set of eclipsing binary parameters. The results are obtained within a probabilistic framework, with robust mass and radius uncertainties ~1-4%. We overplot the derived masses, radii and temperatures over evolutionary models and note stellar size bloating w.r.t. model predictions for both systems. This work has been funded by the NSF grant #1517460.

  7. Distinguishing the albedo of exoplanets from stellar activity

    Science.gov (United States)

    Serrano, L. M.; Barros, S. C. C.; Oshagh, M.; Santos, N. C.; Faria, J. P.; Demangeon, O.; Sousa, S. G.; Lendl, M.

    2018-03-01

    Context. Light curves show the flux variation from the target star and its orbiting planets as a function of time. In addition to the transit features created by the planets, the flux also includes the reflected light component of each planet, which depends on the planetary albedo. This signal is typically referred to as phase curve and could be easily identified if there were no additional noise. As well as instrumental noise, stellar activity, such as spots, can create a modulation in the data, which may be very difficult to distinguish from the planetary signal. Aims: We analyze the limitations imposed by the stellar activity on the detection of the planetary albedo, considering the limitations imposed by the predicted level of instrumental noise and the short duration of the obervations planned in the context of the CHEOPS mission. Methods: As initial condition, we have assumed that each star is characterized by just one orbiting planet. We built mock light curves that included a realistic stellar activity pattern, the reflected light component of the planet and an instrumental noise level, which we have chosen to be at the same level as predicted for CHEOPS. We then fit these light curves to try to recover the reflected light component, assuming the activity patterns can be modeled with a Gaussian process. Results: We estimate that at least one full stellar rotation is necessary to obtain a reliable detection of the planetary albedo. This result is independent of the level of noise, but it depends on the limitation of the Gaussian process to describe the stellar activity when the light curve time-span is shorter than the stellar rotation. As an additional result, we found that with a 6.5 magnitude star and the noise level of CHEOPS, it is possible to detect the planetary albedo up to a lower limit of Rp = 0.03 R*. Finally, in presence of typical CHEOPS gaps in the simulations, we confirm that it is still possible to obtain a reliable albedo.

  8. A relation between the characteristic stellar ages of galaxies and their intrinsic shapes

    Science.gov (United States)

    van de Sande, Jesse; Scott, Nicholas; Bland-Hawthorn, Joss; Brough, Sarah; Bryant, Julia J.; Colless, Matthew; Cortese, Luca; Croom, Scott M.; d'Eugenio, Francesco; Foster, Caroline; Goodwin, Michael; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; McDermid, Richard M.; Medling, Anne M.; Owers, Matt S.; Richards, Samuel N.; Sharp, Rob

    2018-04-01

    Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum1-3. A galaxy's mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy's mass was assembled. Resolved stellar dynamics4 trace the change in angular momentum due to mergers, but major mergers tend to obscure the effect of earlier interactions5. With the rise of large multi-object integral field spectroscopic surveys, such as SAMI6 and MaNGA7, and single-object integral field spectroscopic surveys (for example, ATLAS3D (ref. 8), CALIFA9, MASSIVE10), it is now feasible to connect a galaxy's star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, morphology and environment4,11,12. Using the SAMI Galaxy Survey, here we present a combined study of spatially resolved stellar kinematics and global stellar populations. We find a strong correlation of stellar population age with location in the (V/σ, ɛe) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well.

  9. A relation between the characteristic stellar ages of galaxies and their intrinsic shapes

    Science.gov (United States)

    van de Sande, Jesse; Scott, Nicholas; Bland-Hawthorn, Joss; Brough, Sarah; Bryant, Julia J.; Colless, Matthew; Cortese, Luca; Croom, Scott M.; d'Eugenio, Francesco; Foster, Caroline; Goodwin, Michael; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; McDermid, Richard M.; Medling, Anne M.; Owers, Matt S.; Richards, Samuel N.; Sharp, Rob

    2018-06-01

    Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum1-3. A galaxy's mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy's mass was assembled. Resolved stellar dynamics4 trace the change in angular momentum due to mergers, but major mergers tend to obscure the effect of earlier interactions5. With the rise of large multi-object integral field spectroscopic surveys, such as SAMI6 and MaNGA7, and single-object integral field spectroscopic surveys (for example, ATLAS3D (ref. 8), CALIFA9, MASSIVE10), it is now feasible to connect a galaxy's star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, morphology and environment4,11,12. Using the SAMI Galaxy Survey, here we present a combined study of spatially resolved stellar kinematics and global stellar populations. We find a strong correlation of stellar population age with location in the (V/σ, ɛe) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well.

  10. On the universal stellar law

    Science.gov (United States)

    Krot, Alexander

    In this work, we consider a statistical theory of gravitating spheroidal bodies to derive and develop the universal stellar law for extrasolar systems. Previously, the statistical theory for a cosmogonic body forming (so-called spheroidal body)has been proposed [1-3]. This theory starts from the conception for forming a spheroidal body inside a gas-dust protoplanetary nebula; it permits us to derive the form of distribution functions, mass density, gravitational potentials and strengths both for immovable and rotating spheroidal bodies as well as to find the distribution function of specific angular momentum[1-3]. If we start from the conception for forming a spheroidal body as a protostar (in particular, proto-Sun) inside a prestellar (presolar) nebula then the derived distribution functions of particle (as well as the mass density of an immovable spheroidal body) characterizes the first stage of evolution: from a prestellar molecular cloud (the presolar nebula) to the forming core of protostar (the proto-Sun) together with its shell as a stellar nebula (the solar nebula). This work derives the equation of state of an ideal stellar substance based on conception of gravitating spheroidal body. Using this equation, we obtain the universal stellar law (USL) for the planetary systems connecting temperature, size and mass of each of stars. This work also considers the Solar corona in the connection with USL. Then it is accounting under calculation of the ratio of temperature of the Solar corona to effective temperature of the Sun’ surfaceand modification of USL. To test justice of the modified USLfor different types of stars, the temperature of stellar corona is estimated. The prediction of parameters of stars is carrying out by means of the modified USL,as well as the Hertzsprung-Russell’s dependence [5-7]is derivedby means of USL directly. This paper also shows that knowledge of some characteristics for multi-planet extrasolar systems refines own parameters of

  11. Stellar evolution

    CERN Document Server

    Meadows, A J

    2013-01-01

    Stellar Evolution, Second Edition covers the significant advances in the understanding of birth, life, and death of stars.This book is divided into nine chapters and begins with a description of the characteristics of stars according to their brightness, distance, size, mass, age, and chemical composition. The next chapters deal with the families, structure, and birth of stars. These topics are followed by discussions of the chemical composition and the evolution of main-sequence stars. A chapter focuses on the unique features of the sun as a star, including its evolution, magnetic fields, act

  12. The Dark Energy Survey: Prospects for resolved stellar populations

    Energy Technology Data Exchange (ETDEWEB)

    Rossetto, Bruno M. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Santiago, Basílio X. [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); Girardi, Léo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Osservatorio Astronomica di Padova-INAF, Padova (Italy); Camargo, Julio I. B. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Balbinot, Eduardo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); da Costa, Luiz N. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Yanny, Brian [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Maia, Marcio A. G. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Makler, Martin [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro (Brazil); Ogando, Ricardo L. C. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Pellegrini, Paulo S. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Ramos, Beatriz [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); de Simoni, Fernando [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Armstrong, R. [Univ. of Illinois, Urbana, IL (United States); Bertin, E. [Univ. Pierre et Marie Curie, Paris (France); Desai, S. [Univ. of Illinois, Urbana, IL (United States); Kuropatkin, N. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lin, H. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Mohr, J. J. [Max-Planck-Institut fur extraterrestrische Physik, Garching (Germany); Tucker, D. L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

    2011-05-06

    Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 x 108 stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy.

  13. Variation of galactic cold gas reservoirs with stellar mass

    NARCIS (Netherlands)

    Maddox, Natasha; Hess, Kelley M.; Obreschkow, Danail; Blyth, S.-L.; Jarvis, Matt J.

    The stellar and neutral hydrogen (H I) mass functions at z ˜ 0 are fundamental benchmarks for current models of galaxy evolution. A natural extension of these benchmarks is the two-dimensional distribution of galaxies in the plane spanned by stellar and H I mass, which provides a more stringent test

  14. Stellar Wind Retention and Expulsion in Massive Star Clusters

    Science.gov (United States)

    Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

    2018-05-01

    Mass and energy injection throughout the lifetime of a star cluster contributes to the gas reservoir available for subsequent episodes of star formation and the feedback energy budget responsible for ejecting material from the cluster. In addition, mass processed in stellar interiors and ejected as winds has the potential to augment the abundance ratios of currently forming stars, or stars which form at a later time from a retained gas reservoir. Here we present hydrodynamical simulations that explore a wide range of cluster masses, compactnesses, metallicities and stellar population age combinations in order to determine the range of parameter space conducive to stellar wind retention or wind powered gas expulsion in star clusters. We discuss the effects of the stellar wind prescription on retention and expulsion effectiveness, using MESA stellar evolutionary models as a test bed for exploring how the amounts of wind retention/expulsion depend upon the amount of mixing between the winds from stars of different masses and ages. We conclude by summarizing some implications for gas retention and expulsion in a variety of compact (σv ≳ 20 kms-1) star clusters including young massive star clusters (105 ≲ M/M⊙ ≲ 107, age ≲ 500 Myrs), intermediate age clusters (105 ≲ M/M⊙ ≲ 107, age ≈ 1 - 4 Gyrs), and globular clusters (105 ≲ M/M⊙ ≲ 107, age ≳ 10 Gyrs).

  15. Trapped-particle instabilities in quasi-isodynamic stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Proll, Josefine Henriette Elise

    2014-01-28

    The confinement of energy has always been a challenge in magnetic confinement fusion devices. Due to their toroidal shape there exist regions of high and low magnetic field, so that the particles are divided into two classes - trapped ones that are periodically reflected in regions of high magnetic field with a characteristic frequency, and passing particles, whose parallel velocity is high enough that they largely follow a magnetic field line around the torus without being reflected. The radial drift that a particle experiences due to the field inhomogeneity depends strongly on its position, and the net drift therefore depends on the path taken by the particle. While the radial drift is close to zero for passing particles, trapped particles experience a finite radial net drift and are therefore lost in classical stellarators. These losses are described by the so-called neoclassical transport theory. Recent optimised stellarator geometries, however, in which the trapped particles precess around the torus poloidally and do not experience any net drift, promise to reduce the neoclassical transport down to the level of tokamaks. In these optimised stellarators, the neoclassical transport becomes small enough so that turbulent transport may limit the confinement instead. The turbulence is driven by small-scale-instabilities, which tap the free energy of density or temperature gradients in the plasma. Some of these instabilities are driven by the trapped particles and therefore depend strongly on the magnetic geometry, so the question arises how the optimisation affects the stability. In this thesis, collisionless electrostatic microinstabilities are studied both analytically and numerically. Magnetic configurations where the action integral of trapped-particle bounce motion, J, only depends on the radial position in the plasma and where its maximum is in the plasma centre, so-called maximum-J configurations, are of special interest. This condition can be achieved

  16. Trapped-particle instabilities in quasi-isodynamic stellarators

    International Nuclear Information System (INIS)

    Proll, Josefine Henriette Elise

    2014-01-01

    The confinement of energy has always been a challenge in magnetic confinement fusion devices. Due to their toroidal shape there exist regions of high and low magnetic field, so that the particles are divided into two classes - trapped ones that are periodically reflected in regions of high magnetic field with a characteristic frequency, and passing particles, whose parallel velocity is high enough that they largely follow a magnetic field line around the torus without being reflected. The radial drift that a particle experiences due to the field inhomogeneity depends strongly on its position, and the net drift therefore depends on the path taken by the particle. While the radial drift is close to zero for passing particles, trapped particles experience a finite radial net drift and are therefore lost in classical stellarators. These losses are described by the so-called neoclassical transport theory. Recent optimised stellarator geometries, however, in which the trapped particles precess around the torus poloidally and do not experience any net drift, promise to reduce the neoclassical transport down to the level of tokamaks. In these optimised stellarators, the neoclassical transport becomes small enough so that turbulent transport may limit the confinement instead. The turbulence is driven by small-scale-instabilities, which tap the free energy of density or temperature gradients in the plasma. Some of these instabilities are driven by the trapped particles and therefore depend strongly on the magnetic geometry, so the question arises how the optimisation affects the stability. In this thesis, collisionless electrostatic microinstabilities are studied both analytically and numerically. Magnetic configurations where the action integral of trapped-particle bounce motion, J, only depends on the radial position in the plasma and where its maximum is in the plasma centre, so-called maximum-J configurations, are of special interest. This condition can be achieved

  17. Optical observations of close binaries with the Mark III Stellar Interferometer

    International Nuclear Information System (INIS)

    Pan, X.P.; Shao, M.; Colavita, M.M.; Armstrong, T.; Mozurkewich, D.

    1990-01-01

    For the first time, four spectroscopic binaries have been directly resolved with the Mark III Stellar Interferometer. Observations in 1988 and 1989 were analyzed, and visual orbits for four binaries have been determined. The semimajor axes for Beta Tri, Alpha Equ, Alpha And and Beta Ari are approximately 0.008 arcsec, 0.012 arcsec, 0.024 arcsec and 0.037 arcsec, respectively. The magnitude differences between two components are 0.5, 0.7, 1.8 and 2.6 mag, respectively. All of the orbital elements for Alpha And and Beta Ari were determined from interferometric data only, and agree well with spectroscopic observations. Predictions of relative position between the two components for these binaries are consistent with the measurements to less than 0.001 arcsec. Combined with data from spectroscopy, masses and distance for the double-lined spectroscopic binary Beta Ari are derived, and the results indicate that both components of Beta Ari agree well with the empirical mass-luminosity relation. 12 refs

  18. Electrochemical treatment of trypan blue synthetic wastewater and its degradation pathway

    Directory of Open Access Journals (Sweden)

    ANANTHA N. SUBBA RAO

    2013-11-01

    Full Text Available The trypan blue (TB dye synthetic wastewater was treated in presence of chloride ions by electrochemical method. The effect of current density, pH, initial concentration of dye and supporting electrolyte on color and COD removal were investigated. The UV-Vis ab­sorption intensity, chemical oxygen demand (COD, cyclic voltammetry (CV, Fourier transform- infrared spectroscopy (FT-IR, gas chromatography – mass spectrometry (GC-MS analysis were conducted to investigate the kinetics and degradation pathway of TB dye.

  19. Infrared Extinction and Stellar Populations in the Milky Way Midplane

    Science.gov (United States)

    Zasowski, Gail; Majewski, S. R.; Benjamin, R. A.; Nidever, D. L.; Skrutskie, M. F.; Indebetouw, R.; Patterson, R. J.; Meade, M. R.; Whitney, B. A.; Babler, B.; Churchwell, E.; Watson, C.

    2012-01-01

    The primary laboratory for developing and testing models of galaxy formation, structure, and evolution is our own Milky Way, the closest large galaxy and the only one in which we can resolve large numbers of individual stars. The recent availability of extensive stellar surveys, particularly infrared ones, has enabled precise, contiguous measurement of large-scale Galactic properties, a major improvement over inferences based on selected, but scattered, sightlines. However, our ability to fully exploit the Milky Way as a galactic laboratory is severely hampered by the fact that its midplane and central bulge -- where most of the Galactic stellar mass lies -- is heavily obscured by interstellar dust. Therefore, proper consideration of the interstellar extinction is crucial. This thesis describes a new extinction-correction method (the RJCE method) that measures the foreground extinction towards each star and, in many cases, enables recovery of its intrinsic stellar type. We have demonstrated the RJCE Method's validity and used it to produce new, reliable extinction maps of the heavily-reddened Galactic midplane. Taking advantage of the recovered stellar type information, we have generated maps probing the extinction at different heliocentric distances, thus yielding information on the elusive three-dimensional distribution of the interstellar dust. We also performed a study of the interstellar extinction law itself which revealed variations previously undetected in the diffuse ISM and established constraints on models of ISM grain formation and evolution. Furthermore, we undertook a study of large-scale stellar structure in the inner Galaxy -- the bar(s), bulge(s), and inner spiral arms. We used observed and extinction-corrected infrared photometry to map the coherent stellar features in these heavily-obscured parts of the Galaxy, placing constraints on models of the central stellar mass distribution.

  20. Free-boundary Full-pressure Island Healing in a Stellarator: Coil-healing

    International Nuclear Information System (INIS)

    Hudson, S.R.; Reiman, A.; Strickler, D.; Brooks, A.; Monticello, D.A.; Hirshman, S.P.

    2002-01-01

    The lack of axisymmetry in stellarators guarantees that in general magnetic islands and chaotic magnetic field lines will exist. As particle transport is strongly tied to the magnetic field lines, magnetic islands and chaotic field lines result in poor plasma confinement. For stellarators to be feasible candidates for fusion power stations it is essential that, to a good approximation, the magnetic field lines lie on nested flux-surfaces, and the suppression of magnetic islands is a critical issue for stellarator coil design, particularly for small aspect ratio devices. A procedure for modifying stellarator coil designs to eliminate magnetic islands in free-boundary full-pressure magnetohydrodynamic equilibria is presented. Islands may be removed from coil-plasma free-boundary equilibria by making small changes to the coil geometry and also by variation of trim coil currents. A plasma and coil design relevant to the National Compact Stellarator Experiment is used to illustrate the technique

  1. Operations of a non-stellar object tracker in space

    DEFF Research Database (Denmark)

    Riis, Troels; Jørgensen, John Leif; Betto, Maurizio

    1999-01-01

    The ability to detect and track non-stellar objects by utilizing a star tracker may seem rather straight forward, as any bright object, not recognized as a star by the system is a non stellar object. However, several pitfalls and errors exist, if a reliable and robust detection is required. To te...

  2. Nitric oxide reduction over a synthetic coal char

    Energy Technology Data Exchange (ETDEWEB)

    C. Pevida; A. Arenillas; F. Rubiera; J.J. Pis [Instituto Nacional del Carbon, CSIC, Oviedo (Spain)

    2003-07-01

    In the present work, the mechanisms involved in the NO heterogeneous reduction have been investigated. A synthetic coal char was used as the carbon source. This synthetic coal was made from a mixture of model compounds and provides well-known functionalities, including nitrogenated ones, similar to those found in a high volatile bituminous coal. The char was obtained by pyrolysis of the synthetic coal, up to 1123 K, under helium atmosphere in a fixed bed reactor. Char texture and structure were characterised by N{sub 2} and CO{sub 2} adsorption isotherms at 77 and 273 K, respectively, X-ray diffraction, immersion calorimetry in C{sub 6}H{sub 6} and scanning electron microscopy (SEM). Temperature programmed reactions (TPR) were carried out in a thermogravimetric analyser using 400 ppm NO diluted in Ar as the reactant gas. The char was heated at 15 K min{sup -1} from room temperature to 1273 K. Gaseous products were simultaneously analysed by mass spectrometry (MS) and Fourier transform infrared spectroscopy (FTIR). The influence of nitrogen in the solid phase on the reduction mechanism was evaluated by comparing the results for chars with and without nitrogen in their composition. The results of this preliminary study showed that the presence of nitrogen in the chars composition did not favour the heterogeneous NO reduction. In addition, low temperature NO chemisorption on the carbon surface creates complexes that take an active part in the subsequent reactions with NO. 5 refs., 4 figs., 3 tabs.

  3. Neutral beam heating in stellarators: a numerical approach

    International Nuclear Information System (INIS)

    Hokin, S.A.; Rome, J.A.; Hender, T.C.; Fowler, R.H.

    1983-03-01

    Calculation of neutral beam deposition and heating in stellarators is complicated by the twisty stellarator geometry and by the usual beam focusing, divergence, and cross-sectional shape considerations. A new deposition code has been written that takes all of this geometry into account. A unique feature of this code is that it gives particle deposition in field-line coordinates, enabling the thermalization problem to be solved more efficiently

  4. Old stellar populations how to study the fossil record of galaxy formation

    CERN Document Server

    Cassisi, Santi

    2013-01-01

    The book discusses the theoretical path to decoding the information gathered from observations of old stellar systems. It focuses on old stellar systems because these are the fossil record of galaxy formation and provide invaluable information ont he evolution of cosmic structures and the universe as a whole. The aim is to present results obtained in the past few years for theoretical developments in low mass star research and in advances in our knowledge of the evolution of old stellar systems. A particularly representative case is the recent discovery of multiple stellar populations in galac

  5. Benchmarking the Multidimensional Stellar Implicit Code MUSIC

    Science.gov (United States)

    Goffrey, T.; Pratt, J.; Viallet, M.; Baraffe, I.; Popov, M. V.; Walder, R.; Folini, D.; Geroux, C.; Constantino, T.

    2017-04-01

    We present the results of a numerical benchmark study for the MUltidimensional Stellar Implicit Code (MUSIC) based on widely applicable two- and three-dimensional compressible hydrodynamics problems relevant to stellar interiors. MUSIC is an implicit large eddy simulation code that uses implicit time integration, implemented as a Jacobian-free Newton Krylov method. A physics based preconditioning technique which can be adjusted to target varying physics is used to improve the performance of the solver. The problems used for this benchmark study include the Rayleigh-Taylor and Kelvin-Helmholtz instabilities, and the decay of the Taylor-Green vortex. Additionally we show a test of hydrostatic equilibrium, in a stellar environment which is dominated by radiative effects. In this setting the flexibility of the preconditioning technique is demonstrated. This work aims to bridge the gap between the hydrodynamic test problems typically used during development of numerical methods and the complex flows of stellar interiors. A series of multidimensional tests were performed and analysed. Each of these test cases was analysed with a simple, scalar diagnostic, with the aim of enabling direct code comparisons. As the tests performed do not have analytic solutions, we verify MUSIC by comparing it to established codes including ATHENA and the PENCIL code. MUSIC is able to both reproduce behaviour from established and widely-used codes as well as results expected from theoretical predictions. This benchmarking study concludes a series of papers describing the development of the MUSIC code and provides confidence in future applications.

  6. THE OBSERVED RELATION BETWEEN STELLAR MASS, DUST EXTINCTION, AND STAR FORMATION RATE IN LOCAL GALAXIES

    International Nuclear Information System (INIS)

    Zahid, H. J.; Kewley, L. J.; Kudritzki, R. P.; Yates, R. M.

    2013-01-01

    In this study, we investigate the relation between stellar mass, dust extinction, and star formation rate (SFR) using ∼150,000 star-forming galaxies from SDSS DR7. We show that the relation between dust extinction and SFR changes with stellar mass. For galaxies at the same stellar mass, dust extinction is anti-correlated with the SFR at stellar masses 10 M ☉ . There is a sharp transition in the relation at a stellar mass of 10 10 M ☉ . At larger stellar masses, dust extinction is positively correlated with the SFR for galaxies at the same stellar mass. The observed relation between stellar mass, dust extinction, and SFR presented in this study helps to confirm similar trends observed in the relation between stellar mass, metallicity, and SFR. The relation reported in this study provides important new constraints on the physical processes governing the chemical evolution of galaxies. The correlation between SFR and dust extinction for galaxies with stellar masses >10 10 M ☉ is shown to extend to the population of quiescent galaxies suggesting that the physical processes responsible for the observed relation between stellar mass, dust extinction, and SFR may be related to the processes leading to the shutdown of star formation in galaxies.

  7. THE OBSERVED RELATION BETWEEN STELLAR MASS, DUST EXTINCTION, AND STAR FORMATION RATE IN LOCAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Zahid, H. J.; Kewley, L. J.; Kudritzki, R. P. [Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Dr., Honolulu, HI 96822 (United States); Yates, R. M. [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany)

    2013-02-15

    In this study, we investigate the relation between stellar mass, dust extinction, and star formation rate (SFR) using {approx}150,000 star-forming galaxies from SDSS DR7. We show that the relation between dust extinction and SFR changes with stellar mass. For galaxies at the same stellar mass, dust extinction is anti-correlated with the SFR at stellar masses <10{sup 10} M {sub Sun }. There is a sharp transition in the relation at a stellar mass of 10{sup 10} M {sub Sun }. At larger stellar masses, dust extinction is positively correlated with the SFR for galaxies at the same stellar mass. The observed relation between stellar mass, dust extinction, and SFR presented in this study helps to confirm similar trends observed in the relation between stellar mass, metallicity, and SFR. The relation reported in this study provides important new constraints on the physical processes governing the chemical evolution of galaxies. The correlation between SFR and dust extinction for galaxies with stellar masses >10{sup 10} M {sub Sun} is shown to extend to the population of quiescent galaxies suggesting that the physical processes responsible for the observed relation between stellar mass, dust extinction, and SFR may be related to the processes leading to the shutdown of star formation in galaxies.

  8. Astronomical Spectroscopy for Amateurs

    CERN Document Server

    Harrison, Ken M

    2011-01-01

    Astronomical Spectroscopy for Amateurs is a complete guide for amateur astronomers who are looking for a new challenge beyond astrophotography. The book provides a brief overview of the history and development of the spectroscope, then a short introduction to the theory of stellar spectra, including details on the necessary reference spectra required for instrument testing and spectral comparison. The various types of spectroscopes available to the amateur are then described. Later sections cover all aspects of setting up and using various types of commercially available and home-built spectroscopes, starting with basic transmission gratings and going through more complex models, all the way to the sophisticated Littrow design. The final part of the text is about practical spectroscope design and construction. This book uniquely brings together a collection of observing, analyzing, and processing hints and tips that will allow the amateur to build skills in preparing scientifically acceptable spectra data. It...

  9. 176Lu: Cosmic clock or stellar thermometer

    International Nuclear Information System (INIS)

    Ward, R.A.; Beer, H.; Kaeppeler, F.; Wisshak, K.

    1980-12-01

    We quantitatively examine the various experimental and theoretical aspects of the stellar synthesis of the long-lived ground state of 176 Lu (3.6 x 10 10 y). We discuss the various regimes of stellar temperature and free-neutron density in which either: (i) the internal electromagnetic couplings between 176 Lusup(o) and 176 Lusup(m) (3.68 hours) are sufficiently slow that they may be treated as separate nuclei, or (ii) the internal couplings are rapidly able to establish thermal equilibrium between 176 Lusup(o) and 176 Lusup(m). (orig.)

  10. METALLICITY AND AGE OF THE STELLAR STREAM AROUND THE DISK GALAXY NGC 5907

    Energy Technology Data Exchange (ETDEWEB)

    Laine, Seppo; Grillmair, Carl J.; Capak, Peter [Spitzer Science Center-Caltech, MS 314-6, Pasadena, CA 91125 (United States); Arendt, Richard G. [CRESST/UMBC/NASA GSFC, Code 665, Greenbelt, MD 20771 (United States); Romanowsky, Aaron J. [Department of Physics and Astronomy, San José State University, One Washington Square, San Jose, CA 95192 (United States); Martínez-Delgado, David [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Ashby, Matthew L. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Davies, James E. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Majewski, Stephen R. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Brodie, Jean P.; Arnold, Jacob A. [University of California Observatories and Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); GaBany, R. Jay, E-mail: seppo@ipac.caltech.edu [Black Bird Observatory, 5660 Brionne Drive, San Jose, CA 95118 (United States)

    2016-09-01

    Stellar streams have become central to studies of the interaction histories of nearby galaxies. To characterize the most prominent parts of the stellar stream around the well-known nearby ( d  = 17 Mpc) edge-on disk galaxy NGC 5907, we have obtained and analyzed new, deep gri Subaru/Suprime-Cam and 3.6 μ m Spitzer /Infrared Array Camera observations. Combining the near-infrared 3.6 μ m data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along an ∼60 kpc long segment of the stream. We have fitted the stellar spectral energy distribution with a single-burst stellar population synthesis model and we use it to distinguish between the proposed satellite accretion and minor/major merger formation models of the stellar stream around this galaxy. We conclude that a massive minor merger (stellar mass ratio of at least 1:8) can best account for the metallicity of −0.3 inferred along the brightest parts of the stream.

  11. Physics of Compact Advanced Stellarators

    International Nuclear Information System (INIS)

    Zarnstorff, M.C.; Berry, L.A.; Brooks, A.; Fredrickson, E.; Fu, G.-Y.; Hirshman, S.; Hudson, S.; Ku, L.-P.; Lazarus, E.; Mikkelsen, D.; Monticello, D.; Neilson, G.H.; Pomphrey, N.; Reiman, A.; Spong, D.; Strickler, D.; Boozer, A.; Cooper, W.A.; Goldston, R.; Hatcher, R.; Isaev, M.; Kessel, C.; Lewandowski, J.; Lyon, J.; Merkel, P.; Mynick, H.; Nelson, B.E.; Nuehrenberg, C.; Redi, M.; Reiersen, W.; Rutherford, P.; Sanchez, R.; Schmidt, J.; White, R.B.

    2001-01-01

    Compact optimized stellarators offer novel solutions for confining high-beta plasmas and developing magnetic confinement fusion. The 3-D plasma shape can be designed to enhance the MHD stability without feedback or nearby conducting structures and provide drift-orbit confinement similar to tokamaks. These configurations offer the possibility of combining the steady-state low-recirculating power, external control, and disruption resilience of previous stellarators with the low-aspect ratio, high beta-limit, and good confinement of advanced tokamaks. Quasi-axisymmetric equilibria have been developed for the proposed National Compact Stellarator Experiment (NCSX) with average aspect ratio 4-4.4 and average elongation of approximately 1.8. Even with bootstrap-current consistent profiles, they are passively stable to the ballooning, kink, vertical, Mercier, and neoclassical-tearing modes for beta > 4%, without the need for external feedback or conducting walls. The bootstrap current generates only 1/4 of the magnetic rotational transform at beta = 4% (the rest is from the coils), thus the equilibrium is much less nonlinear and is more controllable than similar advanced tokamaks. The enhanced stability is a result of ''reversed'' global shear, the spatial distribution of local shear, and the large fraction of externally generated transform. Transport simulations show adequate fast-ion confinement and thermal neoclassical transport similar to equivalent tokamaks. Modular coils have been designed which reproduce the physics properties, provide good flux surfaces, and allow flexible variation of the plasma shape to control the predicted MHD stability and transport properties

  12. Exploration of Stellarator Configuration Space with Global Search Methods

    International Nuclear Information System (INIS)

    Mynick, H.E.; Pomphrey, N.; Ethier, S.

    2001-01-01

    An exploration of stellarator configuration space z for quasi-axisymmetric stellarator (QAS) designs is discussed, using methods which provide a more global view of that space. To this end, we have implemented a ''differential evolution'' (DE) search algorithm in an existing stellarator optimizer, which is much less prone to become trapped in local, suboptimal minima of the cost function chi than the local search methods used previously. This search algorithm is complemented by mapping studies of chi over z aimed at gaining insight into the results of the automated searches. We find that a wide range of the attractive QAS configurations previously found fall into a small number of classes, with each class corresponding to a basin of chi(z). We develop maps on which these earlier stellarators can be placed, the relations among them seen, and understanding gained into the physics differences between them. It is also found that, while still large, the region of z space containing practically realizable QAS configurations is much smaller than earlier supposed

  13. A STELLAR MASS THRESHOLD FOR QUENCHING OF FIELD GALAXIES

    International Nuclear Information System (INIS)

    Geha, M.; Blanton, M. R.; Yan, R.; Tinker, J. L.

    2012-01-01

    We demonstrate that dwarf galaxies (10 7 stellar 9 M ☉ , –12 > M r > –18) with no active star formation are extremely rare ( Hα stellar 9 M ☉ below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1σ upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0 × 10 9 M ☉ , ending star formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.

  14. STELLAR NUCLEI AND INNER POLAR DISKS IN LENTICULAR GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Sil’chenko, Olga K., E-mail: olga@sai.msu.su [Sternberg Astronomical Institute, M.V. Lomonosov Moscow State University, Moscow, 119992 (Russian Federation); Isaac Newton Institute, Chile, Moscow Branch (Chile)

    2016-09-01

    I analyze statistics of the stellar population properties for stellar nuclei and bulges of nearby lenticular galaxies in different environments by using panoramic spectral data of the integral-field spectrograph SAURON retrieved from the open archive of the Isaac Newton Group. I also estimate the fraction of nearby lenticular galaxies having inner polar gaseous disks by exploring the volume-limited sample of early-type galaxies of the ATLAS-3D survey. By inspecting the two-dimensional velocity fields of the stellar and gaseous components with the running tilted-ring technique, I have found seven new cases of inner polar disks. Together with those, the frequency of inner polar disks in nearby S0 galaxies reaches 10%, which is much higher than the frequency of large-scale polar rings. Interestingly, the properties of the nuclear stellar populations in the inner polar ring hosts are statistically the same as those in the whole S0 sample, implying similar histories of multiple gas-accretion events from various directions.

  15. STELLAR NUCLEI AND INNER POLAR DISKS IN LENTICULAR GALAXIES

    International Nuclear Information System (INIS)

    Sil’chenko, Olga K.

    2016-01-01

    I analyze statistics of the stellar population properties for stellar nuclei and bulges of nearby lenticular galaxies in different environments by using panoramic spectral data of the integral-field spectrograph SAURON retrieved from the open archive of the Isaac Newton Group. I also estimate the fraction of nearby lenticular galaxies having inner polar gaseous disks by exploring the volume-limited sample of early-type galaxies of the ATLAS-3D survey. By inspecting the two-dimensional velocity fields of the stellar and gaseous components with the running tilted-ring technique, I have found seven new cases of inner polar disks. Together with those, the frequency of inner polar disks in nearby S0 galaxies reaches 10%, which is much higher than the frequency of large-scale polar rings. Interestingly, the properties of the nuclear stellar populations in the inner polar ring hosts are statistically the same as those in the whole S0 sample, implying similar histories of multiple gas-accretion events from various directions.

  16. FT-Raman and FT-IR spectroscopy of synthetic Mg/Zn/Al-hydrotalcites

    International Nuclear Information System (INIS)

    Leishman, N.; Kloprogge, J.T.; Fry, R.; Frost, R.L.

    1998-01-01

    Full text: Hydrotalcites, also known as layered double hydroxides, are less well known and more diffuse in nature than cationic clays. They can be visualised as positively charged hydroxide layers comparable to brucite in which a part of the Mg 2+ is substituted by a trivalent metal like Al 3+ or Fe 3+ separated by charge compensating mostly hydrated interlayer anions. In synthetic hydrotalcites a broad range of compositions are possible of the type [M 2+ 1-x M 3+ x (OH) 2 ][A n- ] x/n -yH 2 O, where M 2+ and M 3+ are the di- and trivalent cations in the octahedral positions within the hydroxide layers with x between 0.17 and 0.33. A n- is an exchangeable interlayer anion. The hydrotalcites with Mg/Zn/Al atomic ratios of 6/0/2, 4/2/2, 2/4/2 and 0/6/2 were synthesised by the slow simultaneous addition of a mixed aluminum-magnesium-zinc nitrate solution and a NaOH solution under vigorous stirring buffering the pH at ± 10. The products were washed to eliminate excess salt and dried at 60 deg C. The nature of the resulting material was checked by XRD and TEM. Both proved the materials to exist of only crystalline hydrotalcite except for the Zn 6 Al 2 (OH) 16 CO 3 .nH 2 O, which contained some unidentified products. The infrared and Raman spectra of synthetic hydrotalcites with different Mg/Zn ratios reveal complicated spectra. Based on the differences in the spectra between the various hydrotalcites and comparison to the comparable hydroxides and hydroxycarbonates a much more detailed band assignment can be made than has been published before

  17. Modular Stellarator Fusion Reactor concept

    International Nuclear Information System (INIS)

    Miller, R.L.; Krakowski, R.A.

    1981-08-01

    A preliminary conceptual study is made of the Modular Stellarator Reactor (MSR). A steady-state ignited, DT-fueled, magnetic fusion reactor is proposed for use as a central electric-power station. The MSR concept combines the physics of the classic stellarator confinement topology with an innovative, modular-coil design. Parametric tradeoff calculations are described, leading to the selection of an interim design point for a 4-GWt plant based on Alcator transport scaling and an average beta value of 0.04 in an l = 2 system with a plasma aspect ratio of 11. The physics basis of the design point is described together with supporting magnetics, coil-force, and stress computations. The approach and results presented herein will be modified in the course of ongoing work to form a firmer basis for a detailed conceptual design of the MSR

  18. Stabilization of magnetohydrodynamic instabilities in a current-carrying stellarator

    International Nuclear Information System (INIS)

    Matsuoka, K.; Miyamoto, K.

    1979-02-01

    Stable profiles against MHD instabilities are given in a cylindrical current-carrying stellarator. The comparison theorem, i.e., guiding principle for stabilization, is obtained in the same way as in a tokamak. As the external rotational transform due to an l = 2 helical field increases, MHD properties in a stellarator are improved than in a tokamak and the minimum value of q(a) which provides simultaneous stabilization of MHD modes can be lowered less than 2 even without a conducting shell. In an l = 3 stellarator, however, as shown from the Euler equation, the configuration becomes more unstable than in a tokamak and strong tailoring of the current profile is necessary in order to stabilize MHD modes. (author)

  19. Stellar Velocity Dispersion: Linking Quiescent Galaxies to their Dark Matter Halos

    OpenAIRE

    Zahid, H. Jabran; Sohn, Jubee; Geller, Margaret J.

    2018-01-01

    We analyze the Illustris-1 hydrodynamical cosmological simulation to explore the stellar velocity dispersion of quiescent galaxies as an observational probe of dark matter halo velocity dispersion and mass. Stellar velocity dispersion is proportional to dark matter halo velocity dispersion for both central and satellite galaxies. The dark matter halos of central galaxies are in virial equilibrium and thus the stellar velocity dispersion is also proportional to dark matter halo mass. This prop...

  20. Stellar clusters in the Gaia era

    Science.gov (United States)

    Bragaglia, Angela

    2018-04-01

    Stellar clusters are important for astrophysics in many ways, for instance as optimal tracers of the Galactic populations to which they belong or as one of the best test bench for stellar evolutionary models. Gaia DR1, with TGAS, is just skimming the wealth of exquisite information we are expecting from the more advanced catalogues, but already offers good opportunities and indicates the vast potentialities. Gaia results can be efficiently complemented by ground-based data, in particular by large spectroscopic and photometric surveys. Examples of some scientific results of the Gaia-ESO survey are presented, as a teaser for what will be possible once advanced Gaia releases and ground-based data will be combined.

  1. Predictions of stellar occultations by TNOs/Centaurs using Gaia

    Science.gov (United States)

    Desmars, Josselin; Camargo, Julio; Berard, Diane; Sicardy, Bruno; Leiva, Rodrigo; Vieira-Martins, Roberto; Braga-Ribas, Felipe; Assafin, Marcelo; Rossi, Gustavo; Chariklo occultations Team, Rio Group, Lucky Star Occultation Team, Granada Occultation Team

    2017-10-01

    Stellar occultations are the unique technique from the ground to access physical parameters of the distant solar system objects, such as the measure of the size and the shape at kilometric level, the detection of tenuous atmospheres (few nanobars), and the investigation of close vicinity (satellites, rings, jets).Predictions of stellar occultations require accurate positions of the star and the object.The Gaia DR1 catalog now allows to get stellar position to the milliarcsecond (mas) level. The main uncertainty in the prediction remains in the position of the object (tens to hundreds of mas).Now, we take advantage of the NIMA method for the orbit determination that uses the most recent observations reduced by the Gaia DR1 catalog and the astrometric positions derived from previous positive occultations.Up to now, we have detected nearly 50 positive occultations for about 20 objects that provide astrometric positions of the object at the time of the occultation. The uncertainty of these positions only depends on the uncertainty on the position of the occulted stars, which is a few mas with the Gaia DR1 catalog. The main limitation is now on the proper motion of the star which is only given for bright stars in the Tycho-Gaia Astrometric Solution. This limitation will be solved with the publicationof the Gaia DR2 expected on April 2018 giving proper motions and parallaxes for the Gaia stars. Until this date, we use hybrid stellar catalogs (UCAC5, HSOY) that provide proper motions derived from Gaia DR1 and another stellar catalog.Recently, the Gaia team presented a release of three preliminary Gaia DR2 stellar positions involved in the occultations by Chariklo (22 June and 23 July 2017) and by Triton (5 October 2017).Taking the case of Chariklo as an illustration, we will present a comparison between the proper motions of DR2 and the other catalogs and we will show how the Gaia DR2 will lead to a mas level precision in the orbit and in the prediction of stellar

  2. The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies

    OpenAIRE

    Kirby, Evan N.; Cohen, Judith G.; Guhathakurta, Puragra; Cheng, Lucy; Bullock, James S.; Gallazzi, Anna

    2013-01-01

    We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same massmetallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z * σ M * 0.30±0. 02 . The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar massstellar metallicity relation for galaxies as massive asM*...

  3. ORIENTATIONAL MICRO-RAMAN SPECTROSCOPY ON HYDROXYAPATITE SINGLE-CRYSTALS AND HUMAN ENAMEL CRYSTALLITES

    NARCIS (Netherlands)

    TSUDA, H; ARENDS, J

    Single crystals of synthetic hydroxyapatite have been examined by orientational micro-Raman spectroscopy. The observed Raman bands include the PO43-/OH- internal and external. modes over the spectral range from 180 to 3600 cm(-1). The Raman-active symmetry tensors (A, E(1), and E(2)) of

  4. Magnetic studies on synthetic phosphoferrite Fe2+3(H2O)3(PO4)2

    International Nuclear Information System (INIS)

    Moreira, L.F.; Diehl, L.M.A.; Torres-Tapia, E.C.; Domingues, P.H.; Mattievich, E.

    1994-01-01

    Synthetic crystals of phosphoferrite were studied by Moessbauer spectroscopy for temperatures ranging from 4.2 to 17.5 K. The analysis of the behaviour of the hyperfine fields for the two unequivalent sites near the Neel temperature (17.4 K) allowed the determination of the critical exponent β for each site as β 1 = 0.171 and β 2 = 0.314. (orig.)

  5. Intrinsic Turbulence Stabilization in a Stellarator

    Directory of Open Access Journals (Sweden)

    P. Xanthopoulos

    2016-06-01

    Full Text Available The magnetic surfaces of modern stellarators are characterized by complex, carefully optimized shaping and exhibit locally compressed regions of strong turbulence drive. Massively parallel computer simulations of plasma turbulence reveal, however, that stellarators also possess two intrinsic mechanisms to mitigate the effect of this drive. In the regime where the length scale of the turbulence is very small compared to the equilibrium scale set by the variation of the magnetic field, the strongest fluctuations form narrow bandlike structures on the magnetic surfaces. Thanks to this localization, the average transport through the surface is significantly smaller than that predicted at locations of peak turbulence. This feature results in a numerically observed upshift of the onset of turbulence on the surface towards higher ion temperature gradients as compared with the prediction from the most unstable regions. In a second regime lacking scale separation, the localization is lost and the fluctuations spread out on the magnetic surface. Nonetheless, stabilization persists through the suppression of the large eddies (relative to the equilibrium scale, leading to a reduced stiffness for the heat flux dependence on the ion temperature gradient. These fundamental differences with tokamak turbulence are exemplified for the QUASAR stellarator [G. H. Neilson et al., IEEE Trans. Plasma Sci. 42, 489 (2014].

  6. Integrated Circuit Stellar Magnitude Simulator

    Science.gov (United States)

    Blackburn, James A.

    1978-01-01

    Describes an electronic circuit which can be used to demonstrate the stellar magnitude scale. Six rectangular light-emitting diodes with independently adjustable duty cycles represent stars of magnitudes 1 through 6. Experimentally verifies the logarithmic response of the eye. (Author/GA)

  7. THE MAGELLANIC INTER-CLOUD PROJECT (MAGIC). I. EVIDENCE FOR INTERMEDIATE-AGE STELLAR POPULATIONS IN BETWEEN THE MAGELLANIC CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Noeel, N. E. D.; Read, J. I. [ETH Zuerich, Institute for Astronomy, Wolfgang-Pauli-Strasse 27, CH-8093 Zuerich (Switzerland); Conn, B. C.; Rix, H.-W. [Max Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany); Carrera, R. [Instituto de Astrofisica de Canarias, C/Via Lactea s/n, E-38200, La Laguna, Tenerife (Spain); Dolphin, A., E-mail: noelia@phys.ethz.ch [Raytheon Company, P.O. Box 11337, Tucson, AZ 85734-1337 (United States)

    2013-05-10

    The origin of the gas in between the Magellanic Clouds (MCs)-known as the ''Magellanic Bridge'' (MB)-is puzzling. Numerical simulations suggest that the MB formed from tidally stripped gas and stars in a recent interaction between the MCs. However, the apparent lack of stripped intermediate- or old-age stars associated with the MB is at odds with this picture. In this paper, we present the first results from the MAGellanic Inter-Cloud program (MAGIC) aimed at probing the stellar populations in the inter-Cloud region. We present observations of the stellar populations in two large fields located in between the Large and Small Magellanic Clouds (LMC/SMC), secured using the WFI camera on the 2.2 m telescope in La Silla. Using a synthetic color-magnitude diagram technique, we present the first quantitative evidence for the presence of intermediate-age and old stars in the inter-Cloud region. The intermediate-age stars-which make up {approx}28% of all stars in the region-are not present in fields at a similar distance from the SMC in a direction pointing away from the LMC. This provides potential evidence that these intermediate-age stars could have been tidally stripped from the SMC. However, spectroscopic studies will be needed to confirm or rule out the tidal origin for the inter-Cloud gas and stars.

  8. Designing synthetic biology.

    Science.gov (United States)

    Agapakis, Christina M

    2014-03-21

    Synthetic biology is frequently defined as the application of engineering design principles to biology. Such principles are intended to streamline the practice of biological engineering, to shorten the time required to design, build, and test synthetic gene networks. This streamlining of iterative design cycles can facilitate the future construction of biological systems for a range of applications in the production of fuels, foods, materials, and medicines. The promise of these potential applications as well as the emphasis on design has prompted critical reflection on synthetic biology from design theorists and practicing designers from many fields, who can bring valuable perspectives to the discipline. While interdisciplinary connections between biologists and engineers have built synthetic biology via the science and the technology of biology, interdisciplinary collaboration with artists, designers, and social theorists can provide insight on the connections between technology and society. Such collaborations can open up new avenues and new principles for research and design, as well as shed new light on the challenging context-dependence-both biological and social-that face living technologies at many scales. This review is inspired by the session titled "Design and Synthetic Biology: Connecting People and Technology" at Synthetic Biology 6.0 and covers a range of literature on design practice in synthetic biology and beyond. Critical engagement with how design is used to shape the discipline opens up new possibilities for how we might design the future of synthetic biology.

  9. XRD and FTIR crystallinity indices in sound human tooth enamel and synthetic hydroxyapatite

    International Nuclear Information System (INIS)

    Reyes-Gasga, José; Martínez-Piñeiro, Esmeralda L.; Rodríguez-Álvarez, Galois; Tiznado-Orozco, Gaby E.; García-García, Ramiro

    2013-01-01

    The crystallinity index (CI) is a measure of the percentage of crystalline material in a given sample and it is also correlated to the degree of order within the crystals. In the literature two ways are reported to measure the CI: X-ray diffraction and infrared spectroscopy. Although the CI determined by these techniques has been adopted in the field of archeology as a structural order measure in the bone with the idea that it can help e.g. in the sequencing of the bones in chronological and/or stratigraphic order, some debate remains about the reliability of the CI values. To investigate similarities and differences between the two techniques, the CI of sound human tooth enamel and synthetic hydroxyapatite (HAP) was measured in this work by X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR), at room temperature and after heat treatment. Although the (CI) XRD index is related to the crystal structure of the samples and the (CI) FTIR index is related to the vibration modes of the molecular bonds, both indices showed similar qualitative behavior for heat-treated samples. At room temperature, the (CI) XRD value indicated that enamel is more crystalline than synthetic HAP, while (CI) FTIR indicated the opposite. Scanning (SEM) and transmission (TEM) images were also used to corroborate the measured CI values. - Highlights: • XRD and FTIR crystallinity indices for tooth enamel and synthetic HAP were obtained. • SEM and TEM images were more correlated with (CI) XRD than with (CI) FTIR . • Regardless of the temperature, (CI) XRD and (CI) FTIR showed similar behavior. • XRD and FTIR crystallinity indices resulted in a fast and qualitative measurement

  10. Solar-stellar Coffee: A Model For Informal Interdisciplinary Professional Development

    Science.gov (United States)

    Metcalfe, Travis S.

    2007-12-01

    Initiated at NCAR more than two years ago, solar-stellar coffee is a weekly informal discussion of recent papers that are relevant to solar and stellar physics. The purpose is to generate awareness of new papers, to discuss their connections to past and current work, and to encourage a broader and more interdisciplinary view of solar physics. The discussion is local, but traffic to the website (http://coffee.solar-stellar.org/) is global -- suggesting that solar and stellar astronomers around the world find value in this intelligent pre-filter for astro-ph and other sources (papers are selected by local participants). In addition to enhancing the preprint posting and reading habits of solar physicists (with the associated boost in citation rates), the weekly discussion also provides an interdisciplinary professional development opportunity for graduate students, postdocs, and early career scientists. The web page is driven by a simple set of scripts (available on request), so this interaction model can easily be replicated at other institutions for topics of local interest. The concept of solar-stellar coffee began with support from an NSF Astronomy & Astrophysics Postdoctoral Fellowship under award AST-0401441. The National Center for Atmospheric Research is a federally funded research and development center sponsored by the National Science Foundation.

  11. Not-so-simple stellar populations in nearby, resolved massive star clusters

    Science.gov (United States)

    de Grijs, Richard; Li, Chengyuan

    2018-02-01

    Around the turn of the last century, star clusters of all kinds were considered ‘simple’ stellar populations. Over the past decade, this situation has changed dramatically. At the same time, star clusters are among the brightest stellar population components and, as such, they are visible out to much greater distances than individual stars, even the brightest, so that understanding the intricacies of star cluster composition and their evolution is imperative for understanding stellar populations and the evolution of galaxies as a whole. In this review of where the field has moved to in recent years, we place particular emphasis on the properties and importance of binary systems, the effects of rapid stellar rotation, and the presence of multiple populations in Magellanic Cloud star clusters across the full age range. Our most recent results imply a reverse paradigm shift, back to the old simple stellar population picture for at least some intermediate-age (˜1-3 Gyr old) star clusters, opening up exciting avenues for future research efforts.

  12. USING CLOSE WHITE DWARF + M DWARF STELLAR PAIRS TO CONSTRAIN THE FLARE RATES IN CLOSE STELLAR BINARIES

    Energy Technology Data Exchange (ETDEWEB)

    Morgan, Dylan P.; West, Andrew A. [Astronomy Department, Boston University, 725 Commonwealth Ave, Boston, MA 02215 (United States); Becker, Andrew C., E-mail: dpmorg@bu.edu [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    2016-05-01

    We present a study of the statistical flare rates of M dwarfs (dMs) with close white dwarf (WD) companions (WD+dM; typical separations <1 au). Our previous analysis demonstrated that dMs with close WD companions are more magnetically active than their field counterparts. One likely implication of having a close binary companion is increased stellar rotation through disk-disruption, tidal effects, and/or angular momentum exchange; increased stellar rotation has long been associated with an increase in stellar activity. Previous studies show a strong correlation between dMs that are magnetically active (showing H α in emission) and the frequency of stellar flare rates. We examine the difference between the flare rates observed in close WD+dM binary systems and field dMs. Our sample consists of a subset of 181 close WD+dM pairs from Morgan et al. observed in the Sloan Digital Sky Survey Stripe 82, where we obtain multi-epoch observations in the Sloan ugriz -bands. We find an increase in the overall flaring fraction in the close WD+dM pairs (0.09 ± 0.03%) compared to the field dMs (0.0108 ± 0.0007%) and a lower flaring fraction for active WD+dMs (0.05 ± 0.03%) compared to active dMs (0.28 ± 0.05%). We discuss how our results constrain both the single and binary dM flare rates. Our results also constrain dM multiplicity, our knowledge of the Galactic transient background, and may be important for the habitability of attending planets around dMs with close companions.

  13. First results from stellar occultations in the "GAIA era"

    Science.gov (United States)

    Benedetti-Rossi, G.; Vieira-Martins, R.; Sicardy, B.

    2017-09-01

    Stellar occultation is a powerful technique to study distant solar system bodies. It allows high angular resolution of the occulting body from the analysis of a light curve acquired with high temporal resolution with uncertainties comparable as probes. In the "GAIA era", stellar occultations is now able to obtain even more impressive results such as the presence of atmosphere, rings and topographic features.

  14. Stellar configurations in f(R) theories of gravity

    International Nuclear Information System (INIS)

    Henttunen, K.; Multamaeki, T.; Vilja, I.

    2008-01-01

    We study stellar configurations and the space-time around them in metric f(R) theories of gravity. In particular, we focus on the polytropic model of the Sun in two specific cases: the f(R)=R-μ 4 /R model and a model with a stabilizing higher order term f(R)=R-μ 4 /R+βR 3 /(3μ 4 ). We show how the stellar configuration in the f(R) theory can, by appropriate initial conditions, be selected to be equal to that described by the Lane-Emden equation and how a simple scaling relation exists between the solutions. We also derive the correct solution analytically near the center of the star in f(R) theory. Previous analytical and numerical results are confirmed, indicating that the space-time around the Sun is incompatible with solar system constraints in the f(R)=R-μ 4 /R model. Numerical work shows that stellar configurations, with a regular metric at the center, lead to γ PPN ≅1/2 outside the star for both models, i.e., the Schwarzschild-de Sitter space-time is not the correct vacuum solution for such configurations. This shows that even when one fine-tunes the initial conditions inside a star such that the mass of the effective scalar in the equivalent scalar-tensor theory is large, γ PPN is still 1/2 outside the star. Conversely, by selecting the Schwarzschild-de Sitter metric as the outside solution, or equivalently setting the mass of the effective scalar to be large outside the star, we find that the stellar configuration is unchanged but the metric is irregular at the center. The possibility of constructing a f(R) theory compatible with the solar system experiments and possible new constraints arising from the radius-mass relation of stellar objects is discussed

  15. Rotational stellar structures based on the Lagrangian variational principle

    International Nuclear Information System (INIS)

    Yasutake, Nobutoshi; Fujisawa, Kotaro; Yamada, Shoichi

    2017-01-01

    A new method for multi-dimensional stellar structures is proposed in this study. As for stellar evolution calculations, the Heney method is the defacto standard now, but basically assumed to be spherical symmetric. It is one of the difficulties for deformed stellar-evolution calculations to trace the potentially complex movements of each fluid element. On the other hand, our new method is very suitable to follow such movements, since it is based on the Lagrange coordinate. This scheme is also based on the variational principle, which is adopted to the studies for the pasta structures inside of neutron stars. Our scheme could be a major break through for evolution calculations of any types of deformed stars: proto-planets, proto-stars, and proto-neutron stars, etc. (paper)

  16. Rotational stellar structures based on the Lagrangian variational principle

    Science.gov (United States)

    Yasutake, Nobutoshi; Fujisawa, Kotaro; Yamada, Shoichi

    2017-06-01

    A new method for multi-dimensional stellar structures is proposed in this study. As for stellar evolution calculations, the Heney method is the defacto standard now, but basically assumed to be spherical symmetric. It is one of the difficulties for deformed stellar-evolution calculations to trace the potentially complex movements of each fluid element. On the other hand, our new method is very suitable to follow such movements, since it is based on the Lagrange coordinate. This scheme is also based on the variational principle, which is adopted to the studies for the pasta structures inside of neutron stars. Our scheme could be a major break through for evolution calculations of any types of deformed stars: proto-planets, proto-stars, and proto-neutron stars, etc.

  17. STELLAR MASSES FROM THE CANDELS SURVEY: THE GOODS-SOUTH AND UDS FIELDS

    Energy Technology Data Exchange (ETDEWEB)

    Santini, P.; Fontana, A.; Castellano, M.; Grazian, A.; Amorin, R. [INAF-Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monte Porzio Catone, Roma (Italy); Ferguson, H. C. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Mobasher, B. [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Barro, G. [UCO/Lick Observatory and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Finkelstein, S. L. [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States); Hsu, L. T.; Salvato, M.; Wuyts, S.; Galametz, A. [Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312, D-85741 Garching (Germany); Lee, B. [Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States); Lee, S.-K. [Center for the Exploration of the Origin of the Universe, Department of Physics and Astronomy, Seoul National University, Seoul (Korea, Republic of); Pforr, J. [National Optical Astronomy Observatories, 950 N Cherry Avenue, Tucson, AZ 85719 (United States); Wiklind, T. [Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile); Almaini, O. [University of Nottingham, School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Cooper, M. C. [Center for Galaxy Evolution, Department of Physics and Astronomy, University of California, Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); Weiner, B., E-mail: paola.santini@oa-roma.inaf.it [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); and others

    2015-03-10

    We present the public release of the stellar mass catalogs for the GOODS-S and UDS fields obtained using some of the deepest near-IR images available, achieved as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey project. We combine the effort from 10 different teams, who computed the stellar masses using the same photometry and the same redshifts. Each team adopted their preferred fitting code, assumptions, priors, and parameter grid. The combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. Thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. The choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). On the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. The inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ∼80% of the sample). Nevertheless, the stellar mass for the subsample of young galaxies (age <100 Myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for <20 Myr sources) if nebular contribution is ignored.

  18. STELLAR MASSES FROM THE CANDELS SURVEY: THE GOODS-SOUTH AND UDS FIELDS

    International Nuclear Information System (INIS)

    Santini, P.; Fontana, A.; Castellano, M.; Grazian, A.; Amorin, R.; Ferguson, H. C.; Mobasher, B.; Barro, G.; Finkelstein, S. L.; Hsu, L. T.; Salvato, M.; Wuyts, S.; Galametz, A.; Lee, B.; Lee, S.-K.; Pforr, J.; Wiklind, T.; Almaini, O.; Cooper, M. C.; Weiner, B.

    2015-01-01

    We present the public release of the stellar mass catalogs for the GOODS-S and UDS fields obtained using some of the deepest near-IR images available, achieved as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey project. We combine the effort from 10 different teams, who computed the stellar masses using the same photometry and the same redshifts. Each team adopted their preferred fitting code, assumptions, priors, and parameter grid. The combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. Thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. The choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). On the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. The inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ∼80% of the sample). Nevertheless, the stellar mass for the subsample of young galaxies (age <100 Myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for <20 Myr sources) if nebular contribution is ignored

  19. GALAXY FORMATION WITH COLD GAS ACCRETION AND EVOLVING STELLAR INITIAL MASS FUNCTION

    International Nuclear Information System (INIS)

    Kang Xi; Lin, W. P.; Skibba, Ramin; Chen, D. N.

    2010-01-01

    The evolution of the galaxy stellar mass function is especially useful to test the current model of galaxy formation. Observational data have revealed a few inconsistencies with predictions from the ΛCDM model. For example, most massive galaxies have already been observed at very high redshifts, and they have experienced only mild evolution since then. In conflict with this, semi-analytical models (SAMs) of galaxy formation predict an insufficient number of massive galaxies at high redshift and a rapid evolution between redshift 1 and 0. In addition, there is a strong correlation between star formation rate (SFR) and stellar mass for star-forming galaxies, which can be roughly reproduced with the model, but with a normalization that is too low at high redshift. Furthermore, the stellar mass density obtained from the integral of the cosmic star formation history is higher than the measured one by a factor of 2. In this paper, we study these issues using an SAM that includes (1) cold gas accretion in massive halos at high redshift; (2) tidal stripping of stellar mass from satellite galaxies; and (3) an evolving stellar initial mass function (IMF; bottom-light) with a higher gas recycle fraction. Our results show that the combined effects from (1) and (2) can predict sufficiently massive galaxies at high redshifts and reproduce their mild evolution at low redshift, while the combined effects of (1) and (3) can reproduce the correlation between SFR and stellar mass for star-forming galaxies across a wide range of redshifts. A bottom-light/top-heavy stellar IMF could partly resolve the conflict between the stellar mass density and cosmic star formation history.

  20. 3D radiative transfer in stellar atmospheres

    International Nuclear Information System (INIS)

    Carlsson, M

    2008-01-01

    Three-dimensional (3D) radiative transfer in stellar atmospheres is reviewed with special emphasis on the atmospheres of cool stars and applications. A short review of methods in 3D radiative transfer shows that mature methods exist, both for taking into account radiation as an energy transport mechanism in 3D (magneto-) hydrodynamical simulations of stellar atmospheres and for the diagnostic problem of calculating the emergent spectrum in more detail from such models, both assuming local thermodynamic equilibrium (LTE) and in non-LTE. Such methods have been implemented in several codes, and examples of applications are given.

  1. Comparative Modelling of the Spectra of Cool Giants

    Science.gov (United States)

    Lebzelter, T.; Heiter, U.; Abia, C.; Eriksson, K.; Ireland, M.; Neilson, H.; Nowotny, W; Maldonado, J; Merle, T.; Peterson, R.; hide

    2012-01-01

    Our ability to extract information from the spectra of stars depends on reliable models of stellar atmospheres and appropriate techniques for spectral synthesis. Various model codes and strategies for the analysis of stellar spectra are available today. Aims. We aim to compare the results of deriving stellar parameters using different atmosphere models and different analysis strategies. The focus is set on high-resolution spectroscopy of cool giant stars. Methods. Spectra representing four cool giant stars were made available to various groups and individuals working in the area of spectral synthesis, asking them to derive stellar parameters from the data provided. The results were discussed at a workshop in Vienna in 2010. Most of the major codes currently used in the astronomical community for analyses of stellar spectra were included in this experiment. Results. We present the results from the different groups, as well as an additional experiment comparing the synthetic spectra produced by various codes for a given set of stellar parameters. Similarities and differences of the results are discussed. Conclusions. Several valid approaches to analyze a given spectrum of a star result in quite a wide range of solutions. The main causes for the differences in parameters derived by different groups seem to lie in the physical input data and in the details of the analysis method. This clearly shows how far from a definitive abundance analysis we still are.

  2. Hydromagnetic instability in a stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Kruskal, M D; Gottlieb, M B; Johnson, J L; Goldman, L M [Project Matterhorn, Princeton University, Princeton, NJ (United States)

    1958-07-01

    It was noted that when there is a uniform externally imposed longitudinal field much larger than the field of the discharge current, one should expect instabilities in the form of a lateral displacement of the plasma column into a helix of large pitch. At the wavelength of fastest growth the e-folding time approximates the time it takes a sound wave in the plasma to traverse the radius of the plasma column. This problem has been re-examines under the conditions which might be expected to occur in the stellarator during ohmic heating, including the presence of external conductors. The theory is applied to the stellarator; and it is shown that the external conductors are in fact unimportant. The important effects due to the finite length of the Machine are discussed and the effects of more general current distributions are considered. The results from the experiments are given.

  3. Cosmic-ray-modified stellar winds. III. A numerical iterative approach

    International Nuclear Information System (INIS)

    Ko, C.M.; Jokipii, J.R.; Webb, G.M.

    1988-01-01

    A numerical iterative method is used to determine the modification of a stellar wind flow with a termination shock by the galactic cosmic rays. A two-fluid model consisting of cosmic rays and thermal stellar wind gas is used in which the cosmic rays are coupled to the background flow via scattering with magnetohydrodynamic waves or irregularities. A polytropic model is used to describe the thermal stellar wind gas, and the cosmic-rays are modeled as a hot, low-density gas with negligible mass flux. The positive galactic cosmic-ray pressure gradient serves to brake the outflowing stellar wind gas, and the cosmic rays modify the location of the critical point of the wind, the location of the shock, the wind fluid velocity profile, and the thermal gas entropy constants on both sides of the shock. The transfer of energy to the cosmic rays results in an outward radial flux of cosmic-ray energy. 21 references

  4. Nano-FTIR Spectroscopy to Investigate the Silicate Mineralogy of Mercury Analogues: Supporting MERTIS Onboard BepiColombo Mission

    Science.gov (United States)

    Varatharajan, I.; Maturilli, A.; Helbert, J.; Ulrich, G.; Born, K.; Namur, O.; Kästner, B.; Hecht, L.; Charlier, B.; Hiesinger, H.

    2018-05-01

    Nano-FTIR Spectroscopy is used to investigate the silicate mineralogy of synthetic Mercury analogues produced under reduced conditions representing different Mercury terrains. The study will support MERTIS payload onboard BepiColombo mission.

  5. Insights from Synthetic Star-forming Regions. III. Calibration of Measurement and Techniques of Star Formation Rates

    Energy Technology Data Exchange (ETDEWEB)

    Koepferl, Christine M.; Robitaille, Thomas P. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Dale, James E., E-mail: koepferl@usm.lmu.de [University Observatory Munich, Scheinerstr. 1, D-81679 Munich (Germany)

    2017-11-01

    Through an extensive set of realistic synthetic observations (produced in Paper I), we assess in this part of the paper series (Paper III) how the choice of observational techniques affects the measurement of star formation rates (SFRs) in star-forming regions. We test the accuracy of commonly used techniques and construct new methods to extract the SFR, so that these findings can be applied to measure the SFR in real regions throughout the Milky Way. We investigate diffuse infrared SFR tracers such as those using 24 μ m, 70 μ m and total infrared emission, which have been previously calibrated for global galaxy scales. We set up a toy model of a galaxy and show that the infrared emission is consistent with the intrinsic SFR using extra-galactic calibrated laws (although the consistency does not prove their reliability). For local scales, we show that these techniques produce completely unreliable results for single star-forming regions, which are governed by different characteristic timescales. We show how calibration of these techniques can be improved for single star-forming regions by adjusting the characteristic timescale and the scaling factor and give suggestions of new calibrations of the diffuse star formation tracers. We show that star-forming regions that are dominated by high-mass stellar feedback experience a rapid drop in infrared emission once high-mass stellar feedback is turned on, which implies different characteristic timescales. Moreover, we explore the measured SFRs calculated directly from the observed young stellar population. We find that the measured point sources follow the evolutionary pace of star formation more directly than diffuse star formation tracers.

  6. Monitoring emulsion homopolymerization reactions using FT-Raman spectroscopy

    Directory of Open Access Journals (Sweden)

    M. M. Reis

    2005-03-01

    Full Text Available The present work describes a methodology for estimation of monomer concentration during homopolymerization reactions by Raman spectroscopy. The estimation is done using linear models based on two different approaches: a univariate approach and a multivariate approach (with principal component regression, PCR, or partial least squares regression, PLS. The linear models are fitted with data from spectra collected from synthetic samples, i.e., samples prepared by dispersing a known concentration of monomer in polymer emulsions. Homopolymerizations of butyl acrylate and of vinyl acetate were monitored by collecting samples from the reactor, and results show that the methodology is efficient for the model fitting and that Raman spectroscopy is a promising technique for on-line monitoring of the emulsion polymerization process.

  7. Determination and identification of synthetic cannabinoids and their metabolites in different matrices by modern analytical techniques – a review

    International Nuclear Information System (INIS)

    Znaleziona, Joanna; Ginterová, Pavlína; Petr, Jan; Ondra, Peter; Válka, Ivo; Ševčík, Juraj; Chrastina, Jan; Maier, Vítězslav

    2015-01-01

    Highlights: • Synthetic cannabinoids from analytical point of view. • Determination and identification methods of synthetic cannabinoids in different matrices. • Analytical techniques used from thin layer chromatography to high resolution mass spectrometry. • Detailed survey of gas and liquid chromatography methods for synthetic cannabinoids analysis. - Abstract: Synthetic cannabinoids have gained popularity due to their easy accessibility and psychoactive effects. Furthermore, they cannot be detected in urine by routine drug monitoring. The wide range of active ingredients in analyzed matrices hinders the development of a standard analytical method for their determination. Moreover, their possible side effects are not well known which increases the danger. This review is focused on the sample preparation and the determination of synthetic cannabinoids in different matrices (serum, urine, herbal blends, oral fluid, hair) published since 2004. The review includes separation and identification techniques, such as thin layer chromatography, gas and liquid chromatography and capillary electrophoresis, mostly coupled with mass spectrometry. The review also includes results by spectral methods like infrared spectroscopy, nuclear magnetic resonance or direct-injection mass spectrometry

  8. Determination and identification of synthetic cannabinoids and their metabolites in different matrices by modern analytical techniques – a review

    Energy Technology Data Exchange (ETDEWEB)

    Znaleziona, Joanna; Ginterová, Pavlína; Petr, Jan [Regional Centre of Advanced Technologies and Materials, Department of Analytical Chemistry, Faculty of Science, Palacký University, 17. Listopadu 12, Olomouc CZ-77146 (Czech Republic); Ondra, Peter; Válka, Ivo [Department of Forensic Medicine and Medical Law Faculty Hospital, Hněvotínská 3, Olomouc CZ-77146 (Czech Republic); Ševčík, Juraj [Regional Centre of Advanced Technologies and Materials, Department of Analytical Chemistry, Faculty of Science, Palacký University, 17. Listopadu 12, Olomouc CZ-77146 (Czech Republic); Chrastina, Jan [Institute of Special Education Studies, Faculty of Education, Palacký University, Žižkovo náměsti 5, Olomouc CZ-77146 (Czech Republic); Maier, Vítězslav, E-mail: vitezslav.maier@upol.cz [Regional Centre of Advanced Technologies and Materials, Department of Analytical Chemistry, Faculty of Science, Palacký University, 17. Listopadu 12, Olomouc CZ-77146 (Czech Republic)

    2015-05-18

    Highlights: • Synthetic cannabinoids from analytical point of view. • Determination and identification methods of synthetic cannabinoids in different matrices. • Analytical techniques used from thin layer chromatography to high resolution mass spectrometry. • Detailed survey of gas and liquid chromatography methods for synthetic cannabinoids analysis. - Abstract: Synthetic cannabinoids have gained popularity due to their easy accessibility and psychoactive effects. Furthermore, they cannot be detected in urine by routine drug monitoring. The wide range of active ingredients in analyzed matrices hinders the development of a standard analytical method for their determination. Moreover, their possible side effects are not well known which increases the danger. This review is focused on the sample preparation and the determination of synthetic cannabinoids in different matrices (serum, urine, herbal blends, oral fluid, hair) published since 2004. The review includes separation and identification techniques, such as thin layer chromatography, gas and liquid chromatography and capillary electrophoresis, mostly coupled with mass spectrometry. The review also includes results by spectral methods like infrared spectroscopy, nuclear magnetic resonance or direct-injection mass spectrometry.

  9. Rate of formation of neutron stars in the galaxy estimated from stellar statistics

    International Nuclear Information System (INIS)

    Endal, A.S.

    1979-01-01

    Stellar statistics and stellar evolution models can be used to estimate the rate of formation of neutron stars in the Galaxy. A recent analysis by Hills suggests that the mean interval between neutron-star births is greater than 27 years. This is incompatible with estimates based on pulsar statistics. However, a closer examination of the stellar data shows that Hill's result is incorrect. A mean interval between neutron-star births as short as 4 years is consistent with (though certainly not required by) stellar evolution theory

  10. The SAMI Galaxy Survey: Gravitational Potential and Surface Density Drive Stellar Populations. I. Early-type Galaxies

    Science.gov (United States)

    Barone, Tania M.; D’Eugenio, Francesco; Colless, Matthew; Scott, Nicholas; van de Sande, Jesse; Bland-Hawthorn, Joss; Brough, Sarah; Bryant, Julia J.; Cortese, Luca; Croom, Scott M.; Foster, Caroline; Goodwin, Michael; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; Lorente, Nuria P. F.; Medling, Anne M.; Owers, Matt S.; Richards, Samuel N.

    2018-03-01

    The well-established correlations between the mass of a galaxy and the properties of its stars are considered to be evidence for mass driving the evolution of the stellar population (SP). However, for early-type galaxies (ETGs), we find that g ‑ i color and stellar metallicity [Z/H] correlate more strongly with gravitational potential Φ than with mass M, whereas SP age correlates best with surface density Σ. Specifically, for our sample of 625 ETGs with integral-field spectroscopy from the Sydney-AAO Multi-object Integral-field Galaxy Survey, compared to correlations with mass, the color–Φ, [Z/H]–Φ, and age–Σ relations show both a smaller scatter and a lower residual trend with galaxy size. For the star formation duration proxy [α/Fe], we find comparable results for trends with Φ and Σ, with both being significantly stronger than the [α/Fe]–M relation. In determining the strength of a trend, we analyze both the overall scatter, and the observational uncertainty on the parameters, in order to compare the intrinsic scatter in each correlation. These results lead us to the following inferences and interpretations: (1) the color–Φ diagram is a more precise tool for determining the developmental stage of the SP than the conventional color–mass diagram; and (2) gravitational potential is the primary regulator of global stellar metallicity, via its relation to the gas escape velocity. Furthermore, we propose the following two mechanisms for the age and [α/Fe] relations with Σ: (a) the age–Σ and [α/Fe]–Σ correlations arise as results of compactness-driven quenching mechanisms; and/or (b) as fossil records of the {{{Σ }}}SFR}\\propto {{{Σ }}}gas} relation in their disk-dominated progenitors.

  11. Evaluation of poly(vinylpyrrolidone) and collagen by Low Field Nuclear Magnetic Resonance Spectroscopy

    International Nuclear Information System (INIS)

    Costa, Paula de M.; Tavares, Maria I.B.

    2005-01-01

    Blends of natural and synthetic polymers represent a new class of materials with better mechanical properties and biocompatibility than those of the single components. Collagen and poly(vinylpyrrolidone) are well known for their important biological properties. The blending of collagen with poly(vinylpyrrolidone) makes it possible to obtain new materials in which strong interactions between the synthetic and biological components occur. Do to the excellent biocompatibility of these polymers, this blend has been much studied intending biomedical applications. And a one technique that can provide important information on molecular mobility, compatibility and even evaluate the interactions that can occur with these polymers is the Low Field Nuclear Magnetic Resonance Spectroscopy. Thus, the purpose of this work is to evaluate collagen and poly(vinylpyrrolidone) by Low Field Nuclear Magnetic Resonance Spectroscopy. From the values of relaxation times obtained, we can conclude that these materials have different interactions, and different mobility domains, confirming the heterogeneity and complexity of these materials. (author)

  12. A Compact Quasi-axisymmetric Stellarator Reactor

    International Nuclear Information System (INIS)

    Ku, L.P.

    2003-01-01

    We report the progress made in assessing the potential of compact, quasi-axisymmetric stellarators as power-producing reactors. Using an aspect ratio A=4.5 configuration derived from NCSX and optimized with respect to the quasi-axisymmetry and MHD stability in the linear regime as an example, we show that a reactor of 1 GW(e) maybe realizable with a major radius *8 m. This is significantly smaller than the designs of stellarator reactors attempted before. We further show the design of modular coils and discuss the optimization of coil aspect ratios in order to accommodate the blanket for tritium breeding and radiation shielding for coil protection. In addition, we discuss the effects of coil aspect ratio on the peak magnetic field in the coils

  13. Modular Stellarator Fusion Reactor (MSR) concept

    International Nuclear Information System (INIS)

    Miller, R.L.; Krakowski, R.A.

    1981-01-01

    A preliminary conceptual study has been made of the Modulator Stellarator Reactor (MSR) as a stedy-state, ignited, DT-fueled, magnetic fusion reactor. The MSR concept combines the physics of classic stellarator confinement with an innovative, modular-coil design. Parametric tradeoff calculations are described, leading to the selection of an interim design point for a 4.8-GWt plant based on Alcator transport scaling and an average beta value of 0.04 in an l = 2 system with a plasma aspect ratio of 11. Neither an economic analysis nor a detailed conceptual engineering design is presented here, as the primary intent of this scoping study is the elucidation of key physics tradeoffs, constraints, and uncertainties for the ultimate power-reactor embodiment

  14. 50 CFR 226.202 - Critical habitat for Stellar sea lions.

    Science.gov (United States)

    2010-10-01

    ... 50 Wildlife and Fisheries 7 2010-10-01 2010-10-01 false Critical habitat for Stellar sea lions... Critical habitat for Stellar sea lions. Steller Sea Lion (Eumetopias jubatus) (a) Alaska rookeries, haulouts, and associated areas. In Alaska, all major Steller sea lion rookeries identified in Table 1 and...

  15. Stellar dynamics and black holes

    Indian Academy of Sciences (India)

    Chandrasekhar's most important contribution to stellar dynamics was the concept of dynamical friction. I briefly review that work, then discuss some implications of Chandrasekhar's theory of gravitational encounters for motion in galactic nuclei. Author Affiliations. David Merritt1. Department of Physics, Rochester Institute ...

  16. Using stellar spectra to illustrate thermal radiation laws

    Science.gov (United States)

    Kaltcheva, N. T.; Pritzl, B. J.

    2018-05-01

    Stars are point-source emitters that are the closest to the definition of a blackbody in comparison to all other similar sources of radiation found in nature. Existing libraries on stellar spectra are thus a valuable resource that can be used to introduce the laws of thermal radiation in a classroom setting. In this article we briefly describe some of the opportunities that available databases on stellar spectra provide for students to gain a deeper understanding on thermal radiation and spectral line characteristics.

  17. Coronal seismology waves and oscillations in stellar coronae

    CERN Document Server

    Stepanov, Alexander; Nakariakov, Valery M

    2012-01-01

    This concise and systematic account of the current state of this new branch of astrophysics presents the theoretical foundations of plasma astrophysics, magneto-hydrodynamics and coronal magnetic structures, taking into account the full range of available observation techniques -- from radio to gamma. The book discusses stellar loops during flare energy releases, MHD waves and oscillations, plasma instabilities and heating and charged particle acceleration. Current trends and developments in MHD seismology of solar and stellar coronal plasma systems are also covered, while recent p

  18. CLASH-VLT: The stellar mass function and stellar mass density profile of the z=0.44 cluster of galaxies MACS J1206.2-0847

    CERN Document Server

    Annunziatella, M; Mercurio, A.; Nonino, M.; Rosati, P.; Balestra, I.; Presotto, V.; Girardi, M.; Gobat, R.; Grillo, C.; Medezinski, E.; Kelson, D.; Postman, M.; Scodeggio, M.; Brescia, M.; Sartoris, B.; Demarco, R.; Fritz, A.; Koekemoer, A.; Lemze, D.; Lombardi, M.; Bradley, L.; Coe, D.; Donahue, M.; Regös, E.; Umetsu, K.; Vanzella, E.; Infante, L.; Kuchner, U.; Maier, C.; Verdugo, M.; Ziegler, B.

    2014-01-01

    Context. The study of the galaxy stellar mass function (SMF) in relation to the galaxy environment and the stellar mass density profile, rho(r), is a powerful tool to constrain models of galaxy evolution. Aims. We determine the SMF of the z=0.44 cluster of galaxies MACS J1206.2-0847 separately for passive and star-forming (SF) galaxies, in different regions of the cluster, from the center out to approximately 2 virial radii. We also determine rho(r) to compare it to the number density and total mass density profiles. Methods. We use the dataset from the CLASH-VLT survey. Stellar masses are obtained by SED fitting on 5-band photometric data obtained at the Subaru telescope. We identify 1363 cluster members down to a stellar mass of 10^9.5 Msolar. Results. The whole cluster SMF is well fitted by a double Schechter function. The SMFs of cluster SF and passive galaxies are statistically different. The SMF of the SF cluster galaxies does not depend on the environment. The SMF of the passive population has a signif...

  19. MHD stability calculations of high-β quasi-axisymmetric stellarators

    International Nuclear Information System (INIS)

    Fu, G.Y.; Ku, L.P.; Pomphrey, N.; Redi, M.; Kessel, C.; Monticello, D.; Reiman, A.; Hughes, M.; Cooper, W.A.; Nuehrenberg, C.

    2001-01-01

    The MHD stability of quasi-axisymmetric compact stellarators is investigated. It is shown that bootstrap current driven external kink modes can be stabilized by a combination of edge magnetic shear and appropriate 3D plasma boundary shaping while maintaining good quasi-axisymmetry. The results demonstrate that there exists a new class of stellarators with quasi-axisymmetry, large bootstrap current, high MHD beta limit, and compact size. (author)

  20. MHD stability calculations of high-β quasi-axisymmetric stellarators

    International Nuclear Information System (INIS)

    Fu, G.Y.; Ku, L.P.; Pomphrey, N.; Redi, M.H.; Kessel, C.; Monticello, D.A.; Reiman, A.; Hughes, M.; Cooper, W.A.; Nuehrenberg, C.

    1999-01-01

    The MHD stability of quasi-axisymmetric compact stellarators is investigated. It is shown that bootstrap current driven external kink modes can be stabilized by a combination of edge magnetic shear and appropriate 3D plasma boundary shaping while maintaining good quasi-axisymmetry. The results demonstrate that there exists a new class of stellarators with quasi-axisymmetry, large bootstrap current, high MHD beta limit, and compact size. (author)

  1. MHD Stability Calculations of High-Beta Quasi-Axisymmetric Stellarators

    International Nuclear Information System (INIS)

    Kessel, C.; Fu, G.Y.; Ku, L.P.; Redi, M.H.; Pomphrey, N.

    1999-01-01

    The MHD stability of quasi-axisymmetric compact stellarators is investigated. It is shown that bootstrap current driven external kink modes can be stabilized by a combination of edge magnetic shear and appropriate 3D plasma boundary shaping while maintaining good quasi-axisymmetry. The results demonstrate that there exists a new class of stellarators with quasi-axisymmetry, large bootstrap current, high MHD beta limit, and compact size

  2. Design studies of low-aspect ratio quasi-omnigenous stellarators

    International Nuclear Information System (INIS)

    Spong, D.A.; Hirshman, S.; Whitson, J.C.

    2001-01-01

    Significant progress has been made in the development of new modest-size compact stellarator devices that could test optimization principles for the design of a more attractive reactor. These are 3 and 4 field period low-aspect-ratio quasi-omnigenous (QO) stellarators based on an optimization method that targets improved confinement, stability, ease of coil design, low-aspect-ratio, and low bootstrap current. (author)

  3. A library of IUE white dwarf spectra for stellar population analyses.

    Science.gov (United States)

    Bica, E.; Bonatto, C.; Giovannini, O.

    1996-10-01

    We present high Signal to Noise ratio IUE spectra of different classes of white dwarfs, to be used as templates for stellar population analyses in the ultraviolet region. We present average stellar parameters associated to each group. The library contains 6 groups for DA's, 2 for DO's and 5 for DB's. We also present equivalent widths of spectral features, and continuum measurements. We call attention to the spectral characteristics which are promising indicators of the presence of white dwarfs in the spectra of composite stellar populations.

  4. RUPRECHT 147: THE OLDEST NEARBY OPEN CLUSTER AS A NEW BENCHMARK FOR STELLAR ASTROPHYSICS

    Energy Technology Data Exchange (ETDEWEB)

    Curtis, Jason L.; Wright, Jason T. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Wolfgang, Angie [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Brewer, John M. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Johnson, John Asher, E-mail: jcurtis@psu.edu [Department of Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)

    2013-05-15

    Ruprecht 147 is a hitherto unappreciated open cluster that holds great promise as a standard in fundamental stellar astrophysics. We have conducted a radial velocity survey of astrometric candidates with Lick, Palomar, and MMT observatories and have identified over 100 members, including 5 blue stragglers, 11 red giants, and 5 double-lined spectroscopic binaries (SB2s). We estimate the cluster metallicity from spectroscopic analysis, using Spectroscopy Made Easy (SME), and find it to be [M/H] = +0.07 {+-} 0.03. We have obtained deep CFHT/MegaCam g'r'i'z' photometry and fit Padova isochrones to the (g' - i') and Two Micron All Sky Survey (J - K{sub S} ) color-magnitude diagrams, using the {tau}{sup 2} maximum-likelihood procedure of Naylor, and an alternative method using two-dimensional cross-correlations developed in this work. We find best fits for Padova isochrones at age t = 2.5 {+-} 0.25 Gyr, m - M = 7.35 {+-} 0.1, and A{sub V} = 0.25 {+-} 0.05, with additional uncertainty from the unresolved binary population and possibility of differential extinction across this large cluster. The inferred age is heavily dependent on our choice of stellar evolution model: fitting Dartmouth and PARSEC models yield age parameters of 3 Gyr and 3.25 Gyr, respectively. At {approx}300 pc and {approx}3 Gyr, Ruprecht 147 is by far the oldest nearby star cluster.

  5. RUPRECHT 147: THE OLDEST NEARBY OPEN CLUSTER AS A NEW BENCHMARK FOR STELLAR ASTROPHYSICS

    International Nuclear Information System (INIS)

    Curtis, Jason L.; Wright, Jason T.; Wolfgang, Angie; Brewer, John M.; Johnson, John Asher

    2013-01-01

    Ruprecht 147 is a hitherto unappreciated open cluster that holds great promise as a standard in fundamental stellar astrophysics. We have conducted a radial velocity survey of astrometric candidates with Lick, Palomar, and MMT observatories and have identified over 100 members, including 5 blue stragglers, 11 red giants, and 5 double-lined spectroscopic binaries (SB2s). We estimate the cluster metallicity from spectroscopic analysis, using Spectroscopy Made Easy (SME), and find it to be [M/H] = +0.07 ± 0.03. We have obtained deep CFHT/MegaCam g'r'i'z' photometry and fit Padova isochrones to the (g' – i') and Two Micron All Sky Survey (J – K S ) color-magnitude diagrams, using the τ 2 maximum-likelihood procedure of Naylor, and an alternative method using two-dimensional cross-correlations developed in this work. We find best fits for Padova isochrones at age t = 2.5 ± 0.25 Gyr, m – M = 7.35 ± 0.1, and A V = 0.25 ± 0.05, with additional uncertainty from the unresolved binary population and possibility of differential extinction across this large cluster. The inferred age is heavily dependent on our choice of stellar evolution model: fitting Dartmouth and PARSEC models yield age parameters of 3 Gyr and 3.25 Gyr, respectively. At ∼300 pc and ∼3 Gyr, Ruprecht 147 is by far the oldest nearby star cluster.

  6. Recon Spectroscopy with TRES

    Science.gov (United States)

    Latham, David W.; TRES Team

    2018-01-01

    The Tillinghast Reflector Echelle Spectrograph (TRES) on the 1.5-m Tillinghast Reflector at the Fred L. Whipple Observatory on Mount Hopkins has been a workhorse for reconnaissance spectroscopy of transiting-planet candidates identified by a variety of ground- and space-based photometric surveys, including Vulcan, TrES, HATNet, KELT, QES, Kepler, and K2. In support of NASA missions, quick-look classifications of effective temperature, surface gravity, metallicity, line broadening due to rotation, and absolute radial velocity have been uploaded to ExoFOP at NExScI on a timely schedule. More careful results derived using the Stellar Parameter Classification (SPC) tool can be provided in support of publications. For example, SPC results for effective temperature and metallicity have been used extensively to help constrain asteroseismic analyses of Kepler and K2 targets. TRES has also been used effectively for orbital solutions, Rossiter-McLaughlin observations, and Doppler tomography of large planets orbiting brighter. We look forward to continuing this work on TESS Objects of Interest.

  7. The Incomplete Conditional Stellar Mass Function: Unveiling the Stellar Mass Functions of Galaxies at 0.1 < Z < 0.8 from BOSS Observations

    Science.gov (United States)

    Guo, Hong; Yang, Xiaohu; Lu, Yi

    2018-05-01

    We propose a novel method to constrain the missing fraction of galaxies using galaxy clustering measurements in the galaxy conditional stellar mass function (CSMF) framework, which is applicable to surveys that suffer significantly from sample selection effects. The clustering measurements, which are not sensitive to the random sampling (missing fraction) of galaxies, are widely used to constrain the stellar–halo mass relation (SHMR). By incorporating a missing fraction (incompleteness) component into the CSMF model (ICSMF), we use the incomplete stellar mass function and galaxy clustering to simultaneously constrain the missing fractions and the SHMRs. Tests based on mock galaxy catalogs with a few typical missing fraction models show that this method can accurately recover the missing fraction and the galaxy SHMR, hence providing us with reliable measurements of the galaxy stellar mass functions. We then apply it to the Baryon Oscillation Spectroscopic Survey (BOSS) over the redshift range of 0.1 1011 M ⊙. We find that the sample completeness for BOSS is over 80% at z account, we provide accurate measurements of the stellar mass functions for galaxies with {10}11 {M}ȯ < {M}* < {10}12 {M}ȯ , as well as the SHMRs, over the redshift range 0.1 < z < 0.8 in this largest galaxy redshift survey.

  8. A STELLAR-MASS-DEPENDENT DROP IN PLANET OCCURRENCE RATES

    International Nuclear Information System (INIS)

    Mulders, Gijs D.; Pascucci, Ilaria; Apai, Dániel

    2015-01-01

    The Kepler spacecraft has discovered a large number of planets with up to one-year periods and down to terrestrial sizes. While the majority of the target stars are main-sequence dwarfs of spectral type F, G, and K, Kepler covers stars with effective temperatures as low as 2500 K, which corresponds to M stars. These cooler stars allow characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around FGK stars. In this paper, we calculate the occurrence of planets around stars of different spectral types as a function of planet radius and distance from the star and show that they are significantly different from each other. We further identify two trends. First, the occurrence of Earth- to Neptune-sized planets (1-4 R ⊕ ) is successively higher toward later spectral types at all orbital periods probed by Kepler; planets around M stars occur twice as frequently as around G stars, and thrice as frequently as around F stars. Second, a drop in planet occurrence is evident at all spectral types inward of a ∼10 day orbital period, with a plateau further out. By assigning to each spectral type a median stellar mass, we show that the distance from the star where this drop occurs is stellar mass dependent, and scales with semi-major axis as the cube root of stellar mass. By comparing different mechanisms of planet formation, trapping, and destruction, we find that this scaling best matches the location of the pre-main-sequence co-rotation radius, indicating efficient trapping of migrating planets or planetary building blocks close to the star. These results demonstrate the stellar-mass dependence of the planet population, both in terms of occurrence rate and of orbital distribution. The prominent stellar-mass dependence of the inner boundary of the planet population shows that the formation or migration of planets is sensitive to the stellar parameters

  9. Physics Design of the National Compact Stellarator Experiment

    International Nuclear Information System (INIS)

    Neilson, G.H.; Zarnstorff, M.C.; Lyon, J.F.

    2002-01-01

    Compact quasi-axisymmetric stellarators offer the possibility of combining the steady-state low-recirculating power, external control, and disruption resilience of previous stellarators with the low-aspect ratio, high beta-limit, and good confinement of advanced tokamaks. Quasi-axisymmetric equilibria have been developed for the proposed National Compact Stellarator Experiment (NCSX) with average aspect ratio approximately 4.4 and average elongation approximately 1.8. Even with bootstrap-current consistent profiles, they are passively stable to the ballooning, kink, vertical, Mercier, and neoclassical-tearing modes for b > 4%, without the need for external feedback or conducting walls. The bootstrap current generates only 1/4 of the magnetic rotational transform at b = 4% (the rest is from the coils). Transport simulations show adequate fast-ion confinement and thermal neoclassical transport similar to equivalent tokamaks. Modular coils have been designed which reproduce the physics properties, provide good flux surfaces, and allow flexible variation of the plasma shape to control the predicted MHD stability and transport properties

  10. Plasma flow healing of magnetic islands in stellarators

    International Nuclear Information System (INIS)

    Hegna, C. C.

    2012-01-01

    Recent experiments from the large helical device (LHD) demonstrate a correlation between the “healing” of vacuum magnetic islands in stellarators and changes in the plasma flow. A model explaining this phenomenon is developed based on self-consistent torque balance and island evolution equations. In conventional stellarators, neoclassical flow damping physics plays an important role in establishing the flow profiles. The balance of neoclassical damping and cross-field viscosity produces a radial boundary layer for the plasma rotation profile outside the separatrix of a locked magnetic island. The width of this boundary layer decreases as the plasma becomes less collisional. Associated with these flow effects are plasma currents flowing in the island region that attempt to suppress island formation. These currents are enhanced as the collisionality drops making magnetic island healing occur more readily in high temperature conventional stellarators. The analytic theory produces a critical β for healing that scales monotonically with collisionality and is in qualitative agreement with LHD observations.

  11. Reduction of Islands in Full-pressure Stellarator Equilibria

    International Nuclear Information System (INIS)

    Hudson, S.R.; Monticello, D.A.; Reiman, A.H.

    2001-01-01

    The control of magnetic islands is a crucial issue in designing Stellarators. Islands are associated with resonant radial magnetic fields at rational rotational-transform surfaces and can lead to chaos and poor plasma confinement. In this article, we show that variations in the resonant fields of a full-pressure stellarator equilibrium can be related to variations in the boundary via a coupling matrix, and inversion of this matrix determines a boundary modification for which the island content is significantly reduced. The numerical procedure is described and the results of island optimization are presented. Equilibria with islands are computed using the Princeton Iterative Equilibrium Solver, and resonant radial fields are calculated via construction of quadratic-flux-minimizing surfaces. A design candidate for the National Compact Stellarator Experiment [Phys. Plasmas 8, 2001], which has a large island, is used to illustrate the technique. Small variations in the boundary shape are used to reduce island size and to reverse the phase of a major island chain

  12. Astrobiological Effects of Stellar Radiation in Circumstellar Environments

    Science.gov (United States)

    Cuntz, Manfred; Gurdemir, Levent; Guinan, Edward F.; Kurucz, Robert L.

    2006-10-01

    The centerpiece of all life on Earth is carbon-based biochemistry. Previous scientific research has suggested that biochemistry based on carbon may also play a decisive role in extraterrestrial life forms, i.e., alien life outside of Earth, if existent. In the following, we explore if carbon-based macromolecules (such as DNA) in the environments of stars other than the Sun are able to survive the effects of energetic stellar radiation, such as UV-C in the wavelength band between 200 and 290 nm. We focus on main-sequence stars akin to the Sun, but of hotter (F-type stars) and cooler (K- and M-type stars) surface temperature. Emphasis is placed on investigating the radiative environment in stellar habitable zones (HZs). Stellar habitable zones have an important relevance in astrobiology because they constitute circumstellar regions in which a planet of suitable size can have surface temperatures for water to exist in liquid form.

  13. Control-matrix approach to stellarator design and control

    International Nuclear Information System (INIS)

    Mynick, H. E.; Pomphrey, N.

    2000-01-01

    The full space Z(equivalent to){Z j=1,...,Nz } of independent variables defining a stellarator configuration is large. To find attractive design points in this space, or to understand operational flexibility about a given design point, one needs insight into the topography in Z-space of the physics figures of merit P i which characterize the machine performance, and means of determining those directions in Z-space which give one independent control over the P i , as well as those which affect none of them, and so are available for design flexibility. The control matrix (CM) approach described here provides a mathematical means of obtaining these. In this work, the CM approach is described and used in studying some candidate Quasi-Axisymmetric (QA) stellarator configurations the National Compact Stellarator Experiment design group has been considering. In the process of the analysis, a first exploration of the topography of the configuration space in the vicinity of these candidate systems has been performed, whose character is discussed

  14. Nonlinear MHD and energetic particle modes in stellarators

    International Nuclear Information System (INIS)

    Strauss, H.R.

    2002-01-01

    The M3D code has been applied to ideal, resistive, two fluid, and hybrid simulations of compact quasi axisymmetric stellarators. When beta exceeds a threshold, low poloidal mode number (m=6∼18) modes grow exponentially, clearly distinguishable from the equilibrium evolution. Simulations of NCSX have beta limits are significantly higher than the infinite mode number ballooning limits. In the presence of resistivity, these modes occur well below the ideal limit. Their growth rate scaling with resistivity is similar to tearing modes. With sufficient viscosity, the growth rate becomes slow enough to allow calculations of magnetic island evolution. Hybrid gyrokinetic simulations with energetic particles indicate that global shear Alfven TAE - like modes can be destabilized in stellarators. Computations in a two - period compact stellarator obtained a predominantly n=1 toroidal mode with about the expected TAE frequency. Work is in progress to study fast ion-driven Alfven modes in NCSX. (author)

  15. UV Stellar Distribution Model for the Derivation of Payload

    Directory of Open Access Journals (Sweden)

    Young-Jun Choi

    1999-12-01

    Full Text Available We present the results of a model calculation of the stellar distribution in a UV and centered at 2175Å corresponding to the well-known bump in the interstellar extinction curve. The stellar distribution model used here is based on the Bahcall-Soneira galaxy model (1980. The source code for model calculation was designed by Brosch (1991 and modified to investigate various designing factors for UV satellite payload. The model predicts UV stellar densities in different sky directions, and its results are compared with the TD-1 star counts for a number of sky regions. From this study, we can determine the field of view, size of optics, angular resolution, and number of stars in one orbit. There will provide the basic constrains in designing a satellite payload for UV observations.

  16. Non-local thermodynamic equilibrium stellar spectroscopy with 1D and 3D models - II. Chemical properties of the Galactic metal-poor disk and the halo

    DEFF Research Database (Denmark)

    Bergemann, Maria; Collet, Remo; Schönrich, Ralph

    2016-01-01

    We have analysed high-resolution spectra of 328 stars and derived Mg abundances using non-local thermodynamic equilibrium (NLTE) spectral line formation calculations and plane-parallel model stellar atmospheres derived from the mean stratification of 3D hydrodynamical surface convection simulations...

  17. Solar and Stellar X-ray Cycles

    Science.gov (United States)

    Martens, P. C. H.; SADE Team

    2004-05-01

    Stern et al. have shown that Yohkoh-SXT full disk X-ray irradiance shows an 11 year cycle with an max/min amplitude ratio of a factor 30. Similar cyclic X-ray variation in Sun-like stars observed by ROSAT and its predecessors is observed in only a few cases and limited to a factor two or three. We will show, by means of detailed bandpass comparisons, that this discrepancy cannot be ascribed to the differences in energy response between SXT and the stellar soft X-ray detectors. Is the Sun exceptional? After centuries of geocentric and heliocentric worldviews we find this a difficult proposition to entertain. But perhaps the Sun is a member of a small class of late-type stars with large amplitudes in their X-ray cycles. The stellar X-ray observations listed in the HEASARC catalog are too sparse to verify this hypothesis. To resolve these and related questions we have proposed a small low-cost stellar X-ray spectroscopic imager originally called SADE to obtain regular time series from late and early-type stars and accretion disks. This instrument is complimentary to the much more advanced Chandra and XMM-Newton observatories, and allows them to focus on those sources that require their full spatial and spectral resolution. We will describe the basic design and spectroscopic capability of SADE and show it meets the mission requirements.

  18. TIDAL STELLAR DISRUPTIONS BY MASSIVE BLACK HOLE PAIRS. II. DECAYING BINARIES

    International Nuclear Information System (INIS)

    Chen Xian; Liu, F. K.; Sesana, Alberto; Madau, Piero

    2011-01-01

    Tidal stellar disruptions have traditionally been discussed as a probe of the single, massive black holes (MBHs) that are dormant in the nuclei of galaxies. We have previously used numerical scattering experiments to show that three-body interactions between bound stars in a stellar cusp and a non-evolving 'hard' MBH binary will also produce a burst of tidal disruptions, caused by a combination of the secular 'Kozai effect' and by close resonant encounters with the secondary hole. Here, we derive basic analytical scalings of the stellar disruption rates with the system parameters, assess the relative importance of the Kozai and resonant encounter mechanisms as a function of time, discuss the impact of general relativistic (GR) and extended stellar cusp effects, and develop a hybrid model to self-consistently follow the shrinking of an MBH binary in a stellar background, including slingshot ejections and tidal disruptions. In the case of a fiducial binary with primary hole mass M 1 = 10 7 M sun and mass ratio q = M 2 /M 1 = 1/81, embedded in an isothermal cusp, we derive a stellar disruption rate N-dot * ∼ 0.2 yr -1 lasting ∼3 x 10 5 yr. This rate is three orders of magnitude larger than the corresponding value for a single MBH fed by two-body relaxation, confirming our previous findings. For q 10% of the tidal-disruption events may originate in MBH binaries.

  19. Compact stellar object: the formation and structure

    Energy Technology Data Exchange (ETDEWEB)

    Duarte, S.B. [Centro Brasileiro de Pesquisas Fisicas (CBPF/MCT), Rio de Janeiro, RJ (Brazil)

    2012-07-01

    Full text: The formation of compact objects is viewed at the final stages of stellar evolution. The supernova explosion events are then focalized to explain the formation of pulsars, hybrid neutron star and the limit case of the latter, the quark stars. We discuss the stability and structure of these objects in connection with the properties of the hadron and quark-gluon plasma equation of state. The hadron-quark phase transition in deep interior of these objects is discussed taking into account the implications on the density distribution of matter along the radial direction. The role of neutrinos confinement in the ultradense stellar medium in the early stages of pulsar formation is another interesting aspect to be mentioned in this presentation. Recent results for maximum mass of compact stellar objects for different forms of equations of state will be shown, presenting some theoretical predictions for maximum mass of neutron stars allowed by different equations of state assigned to dense stellar medium. Although a density greater than few times the nuclear equilibrium density appears in deep interior of the core, at the crust the density decreases by several orders of magnitude where a variety of hadronic states appears, the 'pasta'-states of hadrons. More externally, a lattice of nuclei can be formed permeated not only by electrons but also by a large amount of free neutrons and protons. These are possible structure of neutron star crust to have the density and pressures with null values at the neutron star surface. The ultimate goal of this talk is to give a short view of the compact star area for students and those who are introducing in this subject. (author)

  20. The kinematic footprints of five stellar streams in Andromeda's halo

    Science.gov (United States)

    Chapman, S. C.; Ibata, R.; Irwin, M.; Koch, A.; Letarte, B.; Martin, N.; Collins, M.; Lewis, G. F.; McConnachie, A.; Peñarrubia, J.; Rich, R. M.; Trethewey, D.; Ferguson, A.; Huxor, A.; Tanvir, N.

    2008-11-01

    We present a spectroscopic analysis of five stellar streams (`A', `B', `Cr', `Cp' and `D') as well as the extended star cluster, EC4, which lies within Stream`C', all discovered in the halo of M31 from our Canada-France-Hawaii Telescope/MegaCam survey. These spectroscopic results were initially serendipitous, making use of our existing observations from the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, and thereby emphasizing the ubiquity of tidal streams that account for ~70 per cent of the M31 halo stars in the targeted fields. Subsequent spectroscopy was then procured in Stream`C' and Stream`D' to trace the velocity gradient along the streams. Nine metal-rich ([Fe/H] ~ -0.7) stars at vhel = -349.5kms-1,σv,corr ~ 5.1 +/- 2.5km s-1 are proposed as a serendipitous detection of Stream`Cr', with follow-up kinematic identification at a further point along the stream. Seven metal-poor ([Fe/H] ~-1.3) stars confined to a narrow, 15 km s-1 velocity bin centred at vhel = -285.6, σv,corr = 4.3+1.7-1.4 km s-1 represent a kinematic detection of Stream`Cp', again with follow-up kinematic identification further along the stream. For the cluster EC4, candidate member stars with average [Fe/H] ~-1.4, are found at vhel = -282 suggesting it could be related to Stream`Cp'. No similarly obvious cold kinematic candidate is found for Stream`D', although candidates are proposed in both of two spectroscopic pointings along the stream (both at ~ -400km s-1). Spectroscopy near the edge of Stream`B' suggests a likely kinematic detection at vhel ~ -330, σv,corr ~ 6.9km s-1, while a candidate kinematic detection of Stream`A' is found (plausibly associated to M33 rather than M31) with vhel ~ -170, σv,corr = 12.5km s-1. The low dispersion of the streams in kinematics, physical thickness and metallicity makes it hard to reconcile with a scenario whereby these stream structures as an ensemble are related to the giant southern stream. We conclude that the M31 stellar

  1. Beryllium abundances along the evolutionary sequence of the open cluster IC 4651 - A new test for hydrodynamical stellar models

    Science.gov (United States)

    Smiljanic, R.; Pasquini, L.; Charbonnel, C.; Lagarde, N.

    2010-02-01

    Context. Previous analyses of lithium abundances in main sequence and red giant stars have revealed the action of mixing mechanisms other than convection in stellar interiors. Beryllium abundances in stars with Li abundance determinations can offer valuable complementary information on the nature of these mechanisms. Aims: Our aim is to derive Be abundances along the whole evolutionary sequence of an open cluster. We focus on the well-studied open cluster IC 4651. These Be abundances are used with previously determined Li abundances, in the same sample stars, to investigate the mixing mechanisms in a range of stellar masses and evolutionary stages. Methods: Atmospheric parameters were adopted from a previous abundance analysis by the same authors. New Be abundances have been determined from high-resolution, high signal-to-noise UVES spectra using spectrum synthesis and model atmospheres. The careful synthetic modeling of the Be lines region is used to calculate reliable abundances in rapidly rotating stars. The observed behavior of Be and Li is compared to theoretical predictions from stellar models including rotation-induced mixing, internal gravity waves, atomic diffusion, and thermohaline mixing. Results: Beryllium is detected in all the main sequence and turn-off sample stars, both slow- and fast-rotating stars, including the Li-dip stars, but is not detected in the red giants. Confirming previous results, we find that the Li dip is also a Be dip, although the depletion of Be is more modest than for Li in the corresponding effective temperature range. For post-main-sequence stars, the Be dilution starts earlier within the Hertzsprung gap than expected from classical predictions, as does the Li dilution. A clear dispersion in the Be abundances is also observed. Theoretical stellar models including the hydrodynamical transport processes mentioned above are able to reproduce all the observed features well. These results show a good theoretical understanding of the

  2. NH3 (10-00) in the pre-stellar core L1544

    DEFF Research Database (Denmark)

    Caselli, P.; Bizzocchi, L.; Keto, E.

    2017-01-01

    GHz and study the abundance profile of ammonia across the pre-stellar core L1544 to test current theories of its physical and chemical structure. Recently calculated collisional coefficients have been included in our non-LTE radiative transfer code to reproduce Herschel observations. A gas......Pre-stellar cores represent the initial conditions in the process of star and planet formation, therefore it is important to study their physical and chemical structure. Because of their volatility, nitrogen-bearing molecules are key to study the dense and cold gas present in pre-stellar cores....... The NH3 rotational transition detected with Herschel-HIFI provides a unique combination of sensitivity and spectral resolution to further investigate physical and chemical processes in pre-stellar cores. Here we present the velocity-resolved Herschel-HIFI observations of the ortho-NH3(10-00) line at 572...

  3. Development of the stellarator/heliotron research

    International Nuclear Information System (INIS)

    Iiyoshi, A.

    1991-05-01

    The author reviewed the history of the development of the stellarator/heliotron system, and pointed out the important role of the radial electric field in plasma transport in helical devices. (J.P.N.)

  4. Freedom and Responsibility in Synthetic Genomics: The Synthetic Yeast Project

    OpenAIRE

    Sliva, Anna; Yang, Huanming; Boeke, Jef D.; Mathews, Debra J. H.

    2015-01-01

    First introduced in 2011, the Synthetic Yeast Genome (Sc2.0) Project is a large international synthetic genomics project that will culminate in the first eukaryotic cell (Saccharomyces cerevisiae) with a fully synthetic genome. With collaborators from across the globe and from a range of institutions spanning from do-it-yourself biology (DIYbio) to commercial enterprises, it is important that all scientists working on this project are cognizant of the ethical and policy issues associated with...

  5. Magnetohydrodynamic instabilities in a stellarator

    International Nuclear Information System (INIS)

    Matsuoka, K.; Miyamoto, K.; Ohasa, K.; Wakatani, M.

    1977-05-01

    Numerical studies of stability on kink and resistive tearing modes in a linear stellarator are presented for various current profiles and helical fields. In the case of an l = 2 helical field, a magnetic shear vanishes and the stability diagram is given by the straight lines with iota sup(σ) + iota sup(delta) = const., where iota sup(σ) is a rotational transform due to the plasma current and iota sup(delta) is due to the helical field. In the l = 2 stellarator with chi sup(delta) > 0.5, the m.h.d. stability against kink and tearing modes is improved compared with that in tokamaks. While an l = 3 helical component exists, the magnetic shear plays an important role in the stability properties. The stability diagrams become fairly complex; however, they can be explained by properties of the Euler equation. It should be noted that the internal kink modes become more unstable than in tokamaks by the l = 3 helical field. (auth.)

  6. Characterizing stellar and exoplanetary environments

    CERN Document Server

    Khodachenko, Maxim

    2015-01-01

    In this book an international group of specialists discusses studies of exoplanets subjected to extreme stellar radiation and plasma conditions. It is shown that such studies will help us to understand how terrestrial planets and their atmospheres, including the early Venus, Earth and Mars, evolved during the host star’s active early phase. The book presents an analysis of findings from Hubble Space Telescope observations of transiting exoplanets, as well as applications of advanced numerical models for characterizing the upper atmosphere structure and stellar environments of exoplanets. The authors also address detections of atoms and molecules in the atmosphere of “hot Jupiters” by NASA’s Spitzer telescope. The observational and theoretical investigations and discoveries presented are both timely and important in the context of the next generation of space telescopes. 
 The book is divided into four main parts, grouping chapters on exoplanet host star radiation and plasma environments, exoplanet u...

  7. Construction concepts and validation of the 3D printed UST_2 modular stellarator

    Science.gov (United States)

    Queral, V.

    2015-03-01

    High accuracy, geometric complexity and thus high cost of stellarators tend to hinder the advance of stellarator research. Nowadays, new manufacturing methods might be developed for the production of small and middle-size stellarators. The methods should demonstrate advantages with respect common fabrication methods, like casting, cutting, forging and welding, for the construction of advanced highly convoluted modular stellarators. UST2 is a small modular three period quasi-isodynamic stellarator of major radius 0.26 m and plasma volume 10 litres being currently built to validate additive manufacturing (3D printing) for stellarator construction. The modular coils are wound in grooves defined on six 3D printed half period frames designed as light truss structures filled by a strong filler. A geometrically simple assembling configuration has been concocted for UST2 so as to try to lower the cost of the device while keeping the positioning accuracy of the different elements. The paper summarizes the construction and assembling concepts developed, the devised positioning methodology, the design of the coil frames and positioning elements and, an initial validation of the assembling of the components.

  8. Future prospects for stellar intensity interferometry

    International Nuclear Information System (INIS)

    Lake, R.J.W.

    2002-01-01

    Full text: The technique of Stellar Intensity lnterferometry (SII) was first successfully demonstrated by Hanbury-Brown in 1956 at Jodrell Bank. SII uses the correlation in intensity fluctuations of starlight as a function of observational baseline to determine angular diameters and other gross features of main sequence stars. In 1962 an observatory was established by Hanbury-Brown in Narrabri NSW. Between 1965 and 1972 the angular diameters of 32 stars covering the spectral range O to F were measured. Orbital parameters of several unresolved binary stars were also determined and attempts were made by the author to directly measure the limb darkening of Sirius and the rotational distortion of Altair. Following the success of the Narrabri SII the Australian Federal Government provided a grant to Sydney University to develop a Very Large SII capable of making observational measurements on about a thousand stars. The development of this VLSII was however shelved in preference to the development of a potentially more sensitive long baseline Michelson Stellar Interferometer. This latter instrument known as SUSI (Sydney University Stellar Interferometer) has been in operation at Narrabri since 1995. Encouraged by the early results of SUSI and their own efforts in the use of active optics to reduce the effects of atmospheric scintillation a number of international observatories are now active in the development of long baseline or large aperture Michelson Stellar Interferometers. However SII while sacrificing sensitivity has a number of technical advantages over MSI as SII is far less sensitive to atmospheric effects and can be readily developed to work over very long baselines. This paper through technical review and theoretical modeling examines how a modern VLSII could be constructed and operated and addresses the limitations to its sensitivity. In particular it examines how existing Australian industry could contribute to the development of a VLSII with sufficient

  9. The history and development of nonlinear stellar pulsation codes

    International Nuclear Information System (INIS)

    Davis, C.G.

    1987-01-01

    This review is limited to the history and development of nonlinear stellar pulsation codes and methods. The narrative includes examples of practical interest in the application of these numerical methods to problems in stellar pulsation such as Cepheid mass discrepancy, the delineation of the RR Lyrae instability strip, and the question of the development of double-mode pulsation as observed in Cepheids, RR Lyrae and other variable stars. 15 refs

  10. Final phases of stellar evolution and the supernova phenomenon

    Energy Technology Data Exchange (ETDEWEB)

    Gallino, R [Torino, Universita, Turin, Italy; Masani, A [CNR, Laboratorio di Cosmo-geofisica, Turin, Italy

    1977-12-01

    Various theoretical aspects of the final stages of stellar evolution are reviewed in the framework of gravitational collapse and thermonuclear reactions (C-12 and O-16) in degenerate electron conditions. Attention is given to the evolution of supermassive stars, massive stars, and low-mass stars and to such topics as neutrino emission in intermediate-mass stars, white-dwarf supernovae, rotational instability, and stellar collisions and eclipsing binary systems.

  11. Review of recent stellarator results in the USA, the USSR, and Japan

    International Nuclear Information System (INIS)

    Lyon, J.F.

    1990-12-01

    Stellarators with significant magnetic shear in the United States, the Soviet Union, and Japan are described, and recent results are discussed in terms of their contributions to the physics understanding relevant for stellarator optimization and to toroidal confinement understanding in general. The areas discussed are the properties of stellarators with significant shear, magnetic surfaces, trapped-particle losses, magnetohydrodynamic (MHD) stability, global confinement scaling, local transport, fluctuations, and particle and impurity control. 58 refs., 23 figs

  12. LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

    Science.gov (United States)

    Lin, Ming-Yi; Davies, R. I.; Hicks, E. K. S.; Burtscher, L.; Contursi, A.; Genzel, R.; Koss, M.; Lutz, D.; Maciejewski, W.; Müller-Sánchez, F.; Orban de Xivry, G.; Ricci, C.; Riffel, R.; Riffel, R. A.; Rosario, D.; Schartmann, M.; Schnorr-Müller, A.; Shimizu, T.; Sternberg, A.; Sturm, E.; Storchi-Bergmann, T.; Tacconi, L.; Veilleux, S.

    2018-02-01

    In a complete sample of local 14-195 keV selected active galactic nuclei (AGNs) and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, eight AGNs and five inactive galaxies. The stellar velocity fields show a disc-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN, but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disc structure, which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies.

  13. Characterization of Thermal Stability of Synthetic and Semi-Synthetic Engine Oils

    Directory of Open Access Journals (Sweden)

    Anand Kumar Tripathi

    2015-03-01

    Full Text Available Engine oils undergo oxidative degradation and wears out during service. Hence it is important to characterize ageing of engine oils at different simulated conditions to evaluate the performance of existing oils and also design new formulations. This work focuses on characterizing the thermo-oxidative degradation of synthetic and semi-synthetic engine oils aged at 120, 149 and 200 °C. Apparent activation energy of decomposition of aged oils evaluated using the isoconversional Kissinger-Akahira-Sunose technique was used as a thermal stability marker. The temporal variation of stability at different ageing temperatures was corroborated with kinematic viscosity, oxidation, sulfation and nitration indices, total base number, antiwear additive content and molecular structure of the organic species present in the oils. At the lowest temperature employed, synthetic oil underwent higher rate of oxidation, while semi-synthetic oil was stable for longer time periods. At higher temperatures, the initial rate of change of average apparent activation energy of synthetic oil correlated well with a similar variation in oxidation number. A mixture of long chain linear, branched, and cyclic hydrocarbons were observed when semi-synthetic oil was degraded at higher temperatures.

  14. Intracluster age gradients in numerous young stellar clusters

    Science.gov (United States)

    Getman, K. V.; Feigelson, E. D.; Kuhn, M. A.; Bate, M. R.; Broos, P. S.; Garmire, G. P.

    2018-05-01

    The pace and pattern of star formation leading to rich young stellar clusters is quite uncertain. In this context, we analyse the spatial distribution of ages within 19 young (median t ≲ 3 Myr on the Siess et al. time-scale), morphologically simple, isolated, and relatively rich stellar clusters. Our analysis is based on young stellar object (YSO) samples from the Massive Young Star-Forming Complex Study in Infrared and X-ray and Star Formation in Nearby Clouds surveys, and a new estimator of pre-main sequence (PMS) stellar ages, AgeJX, derived from X-ray and near-infrared photometric data. Median cluster ages are computed within four annular subregions of the clusters. We confirm and extend the earlier result of Getman et al. (2014): 80 per cent of the clusters show age trends where stars in cluster cores are younger than in outer regions. Our cluster stacking analyses establish the existence of an age gradient to high statistical significance in several ways. Time-scales vary with the choice of PMS evolutionary model; the inferred median age gradient across the studied clusters ranges from 0.75 to 1.5 Myr pc-1. The empirical finding reported in the present study - late or continuing formation of stars in the cores of star clusters with older stars dispersed in the outer regions - has a strong foundation with other observational studies and with the astrophysical models like the global hierarchical collapse model of Vázquez-Semadeni et al.

  15. Effects of the radial electric field in a quasisymmetric stellarator

    International Nuclear Information System (INIS)

    Landreman, Matt; Catto, Peter J

    2011-01-01

    Recent calculations have shown that a radial electric field can significantly alter the neoclassical ion heat flux, ion flow, bootstrap current and residual zonal flow in a tokamak, even when the E x B drift is much smaller than the ion thermal speed. Here we show the novel analytical methods used in these calculations can be adapted to a quasisymmetric stellarator. The methods are based on using the conserved helical momentum ψ * instead of the poloidal or toroidal flux as a radial coordinate in the kinetic equation. The banana-regime calculations also employ a model collision operator that keeps only the velocity-space derivatives normal to the trapped-passing boundary, even as this boundary is shifted and deformed by the E x B drift. We prove the isomorphism between quasisymmetric stellarators and tokamaks extends to the finite-E x B generalizations of both banana-regime and plateau-regime neoclassical theory and the residual zonal flow. The plateau-regime results may be relevant to the HSX stellarator, and both the plateau- and banana-regime results can be used to validate stellarator transport codes.

  16. A 'Rosetta Stone' to Interpret the UV-HST Photometry of Multiple Stellar Populations in Globular Clusters

    Science.gov (United States)

    Renzini, Alvio

    2011-10-01

    In this proposal we intend to firmly identify the chemical species responsible for the UV and UV-optical color differences exhibited by the multiple stellar populations harboured by two Galactic globular clusters: omega Centauri and 47 Tucanae, one with highly helium enriched sub-populations {omega Centauri}, the other not.We plan to collect ultraviolet STIS spectra for stars in the crowded cores of the clusters, where HST photometry is already available for thousands of stars in more than 10 filters, from F225W to F850LP. This WFC3+ACS photometric database has allowed us to show that UV colors are remarkably effective in separating the different cluster sub-populations, and with the proposed STIS spectroscopy we can quantify the chemical abundance differences among such sub-populations, most notably in Nitrogen and Oxygen. The resulting calibration of the UV colors in terms of CNO abundances will provide a new effective tool for the chemical characterization of large numbers of globular cluster stars belonging to the various sub-populations in each cluster, and to better isolate the specific role of the helium abundance.The plan is to observe at least one star for each of the main principal stellar sub-populations in each of the two clusters. These objects are selected on the basis of their accurate photometry and astrometry already in hand, based on existing UV-HST images.

  17. Operando formation of an ultra-low friction boundary film from synthetic magnesium silicon hydroxide additive

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Qiuying; Rudenko, Pavlo; Miller, Dean J.; Wen, Jianguo; Berman, Diana; Zhang, Yuepeng; Arey, Bruce; Zhu, Zihua; Erdemir, Ali

    2017-06-01

    The paper reports the operando and self-healing formation of DLC films at sliding contact surfaces by the addition of synthetic magnesium silicon hydroxide (MSH) nanoparticles to base oil. The formation of such films leads to a reduction of the coefficient of friction by nearly an order of magnitude and substantially reduces wear losses. The ultralow friction layer characterized by transmission electron microscope (TEM), electron energy loss spectroscopy (EELS), and Raman spectroscopy consists of amorphous DLC containing SiOx that forms in a continuous and self-repairing manner during operation. This environmentally benign and simple approach offers promise for significant advances in lubrication and reduced energy losses in engines and other mechanical systems.

  18. Radio continuum emission from young stellar objects in L1641

    International Nuclear Information System (INIS)

    Morgan, J.A.; Snell, R.L.; Strom, K.M.

    1990-01-01

    The results of a 6 and 20 cm radio continuum survey of young stellar objects in the L1641 region located south of the Orion Nebula are presented. Four are identified as low-luminosity young stellar objects in L1641 and three more as Herbig-Haro or Herbig-Haro-like objects. These objects have bolometric luminosities between 80 and 300 solar, and their 6-20 cm spectral index suggests optically thick, free-free emission. They are characterized by a rising spectrum between 2.2 and 25 microns, have no optical counterparts, and are associated with stellar wind activity. Thus, detectable radio continuum emission may be produced only by the youngest and most luminous objects in L1641. 34 refs

  19. Helical ripple transport in stellarators at low collision frequency

    International Nuclear Information System (INIS)

    Beidler, C.D.

    1987-12-01

    Numerical and analytical techniques have been developed to investigate the plasma transport which is due to particles trapping/detrapping in the local helical ripple wells of a stellarator's magnetic field. This process is of considerable importance as it provides the dominant transport mechanism in a stellarator plasma at ''low'' collision frequency: that is, when the frequency with which a particle is collisionally detrapped from a local ripple well is less than the bounce frequency of the particle in that well. A form of the longitudinal adiabatic invariant, J, is constructed and shown to describe accurately the orbits of ripple trapped particles. Unlike previous expressions for J, the form derived here correctly accounts for the local toroidal variation of the magnetic field. The expression for J is incorporated into a rapid ''hybrid'' Monte Carlo simulation of ripple transport in stellarators. The simulation is a hybrid in the sense that particle orbits in the narrow region of phase space on either side of the ripple trapping/detrapping boundary are followed using guiding center equations of motion while orbits in the remainder of phase space are described using adiabatic invariants. An analytical expression for the distribution function of ripple trapped particles in a stellarator - valid at all low collision frequencies - has been obtained by series solution of the bounce - averaged kinetic equation. This solution has been applied to both 'standard' and a class of 'transport optimized' stellarator magnetic fields. Analytical estimates of the diffusion coefficient obtained from the series solution show excellent agreement with the numerical results of the hybrid Monte Carlo code in all cases studied. 55 refs., 30 figs

  20. Optical and near-infrared survey of the stellar contents associated with the star-forming complex Sh2-252

    Science.gov (United States)

    Jose, Jessy; Pandey, A. K.; Ogura, K.; Samal, M. R.; Ojha, D. K.; Bhatt, B. C.; Chauhan, N.; Eswaraiah, C.; Mito, H.; Kobayashi, N.; Yadav, R. K.

    2012-08-01

    We present the analyses of the stellar contents associated with the extended H II region Sh2-252 using deep optical UBVRI photometry, slit and slitless spectroscopy along with the near-infrared (NIR) data from Two-Micron All-Sky Survey (2MASS) for an area ˜ 1 × 1 deg2. We have studied the sub-regions of Sh2-252, which includes four compact-H II (CH II ) regions, namely A, B, C and E, and two clusters, NGC 2175s and Teutsch 136 (Teu 136). Of the 15 spectroscopically observed bright stars, eight have been identified as massive members of spectral class earlier than B3. From the spectrophotometric analyses, we derived the average distance of the region as 2.4 ± 0.2 kpc, and the reddening E(B - V) of the massive members is found to vary between 0.35 and 2.1 mag. We found that NGC 2175s and Teu 136, located towards the eastern edge of the complex, are the sub-clusters of Sh2-252. The stellar surface density distribution in K band shows clustering associated with the regions A, C, E, NGC 2175s and Teu 136. We have also identified the candidate ionizing sources of the CH II regions. 61 Hα emission sources are identified using slitless spectroscopy. The distribution of the Hα emission sources and candidate young stellar objects (YSOs) with IR excess on the V/(V - I) colour-magnitude diagram (CMD) shows that a majority of them have approximate ages between 0.1 and 5 Myr and masses in the range of 0.3-2.5 M⊙. The optical CMDs of the candidate pre-main-sequence (PMS) sources in the individual regions also show an age spread of 0.1-5 Myr for each of them. We calculated the K-band luminosity functions (KLFs) for the sub-regions A, C, E, NGC 2175s and Teu 136. Within errors, the KLFs for all the sub-regions are found to be similar and comparable to that of young clusters of age <5 Myr. We also estimated the mass function of the PMS sample of the individual regions in the mass range of 0.3-2.5 M⊙. In general, the slopes of the MFs of all the sub-regions are found