Wavelength-dependent Crosstalk in Trench-Assisted Multi-Core Fibers

DEFF Research Database (Denmark)

Ye, Feihong; Tu, Jiajing; Saitoh, Kunimasa

2014-01-01

Analytical expressions for wavelength-dependent crosstalk in homogeneous trench-assisted multi-core fibers are derived. The calculated results from the expressions agree well with the numerical simulation results based on finite element method.......Analytical expressions for wavelength-dependent crosstalk in homogeneous trench-assisted multi-core fibers are derived. The calculated results from the expressions agree well with the numerical simulation results based on finite element method....

Multi-Wavelength Interferometric Observations of YSO Disks

Science.gov (United States)

Ragland, Sam; Akeson, R.; Armandroff, T.; Colavita, M.; Cotton, W.; Danchi, W.; Hillenbrand, L.; Millan-Gabet, R.; Ridgway, S. T.; Traub, W.; Wizinowich, P.

2010-01-01

We initiated a multi-color interferometric study of YSO disks in the K, L and N bands using the Keck Interferometer. The initial results on two Herbig Ae/Be stars will be presented. Our observations are sensitive to the radial distribution of temperature in the inner region of the YSO disks. The geometric models show that the apparent size increases linearly with wavelength, suggesting that the disk is extended with a temperature gradient. We will discuss our results in conjunction with the previous measurements of these targets.

Stellar Populations in Compact Galaxy Groups: a Multi-wavelength Study of HCGs 16, 22, and 42, Their Star Clusters, and Dwarf Galaxies

Science.gov (United States)

Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Fedotov, K.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Desjardins, T. D.; Gallagher, S. C.; Walker, L. M.;

Imaging of Stellar Surfacess Using Radio Facilities Including ALMA

Science.gov (United States)

O'Gorman, Eamon

2018-04-01

Until very recently, studies focusing on imaging stars at continuum radio wavelengths (here defined as submillimeter, millimeter, and centimeter wavelengths) has been scarce. These studies have mainly been carried out with the Very Large Array on a handful of evolved stars (i.e., Asymptotic Giant Branch and Red Supergiant stars) whereby their stellar disks have just about been spatially resolved. Some of these results however, have challenged our historical views on the nature of evolved star atmospheres. Now, the very long baselines of the Atacama Large Millimeter/submillimeter Array and the newly upgraded Karl G. Jansky Very Large Array provide a new opportunity to image these atmospheres at unprecedented spatial resolution and sensitivity across a much wider portion of the radio spectrum. In this talk I will first provide a history of stellar radio imaging and then discuss some recent exciting ALMA results. Finally I will present some brand new multi-wavelength ALMA and VLA results for the famous red supergiant Antares.

Broadband multi-wavelength Brillouin lasers with an operating wavelength range of 1500–1600 nm generated by four-wave mixing in a dual wavelength Brillouin fiber laser cavity

Science.gov (United States)

Li, Q.; Jia, Z. X.; Weng, H. Z.; Li, Z. R.; Yang, Y. D.; Xiao, J. L.; Chen, S. W.; Huang, Y. Z.; Qin, W. P.; Qin, G. S.

2018-05-01

We demonstrate broadband multi-wavelength Brillouin lasers with an operating wavelength range of 1500–1600 nm and a frequency separation of ~9.28 GHz generated by four-wave mixing in a dual wavelength Brillouin fiber laser cavity. By using one continuous-wave laser as the pump source, multi-wavelength Brillouin lasers with an operating wavelength range of 1554–1574 nm were generated via cascaded Brillouin scattering and four-wave mixing. Interestingly, when pumped by two continuous-wave lasers with an appropriate frequency separation, the operating wavelength range of the multi-wavelength Brillouin lasers was increased to 1500–1600 nm due to cavity-enhanced cascaded four-wave mixing among the frequency components generated by two pump lasers in the dual wavelength Brillouin laser cavity.

Multi-wavelength Ocean Profiling and Atmospheric Lidar

Data.gov (United States)

National Aeronautics and Space Administration — We propose to build and demonstrate the world's first multi-wavelength ocean-profiling high spectral resolution lidar (HSRL). The lidar will provide profiles of...

A 12 GHz wavelength spacing multi-wavelength laser source for wireless communication systems

Science.gov (United States)

Peng, P. C.; Shiu, R. K.; Bitew, M. A.; Chang, T. L.; Lai, C. H.; Junior, J. I.

2017-08-01

This paper presents a multi-wavelength laser source with 12 GHz wavelength spacing based on a single distributed feedback laser. A light wave generated from the distributed feedback laser is fed into a frequency shifter loop consisting of 50:50 coupler, dual-parallel Mach-Zehnder modulator, optical amplifier, optical filter, and polarization controller. The frequency of the input wavelength is shifted and then re-injected into the frequency shifter loop. By re-injecting the shifted wavelengths multiple times, we have generated 84 optical carriers with 12 GHz wavelength spacing and stable output power. For each channel, two wavelengths are modulated by a wireless data using the phase modulator and transmitted through a 25 km single mode fiber. In contrast to previously developed schemes, the proposed laser source does not incur DC bias drift problem. Moreover, it is a good candidate for radio-over-fiber systems to support multiple users using a single distributed feedback laser.

The Resilience of Kepler Multi-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 transiting members. However, a large fraction possesses only a single transiting planet. This high abundance of singles, dubbed the "Kepler Dichotomy," has been hypothesized to arise from significant mutual inclinations between orbits in multi-planet systems. Alternatively, the single-transiting population truly possesses no other planets in the system, but the true origin of the overabundance of single systems remains unresolved. In this work, we propose that planetary systems typically form with a coplanar, multiple-planetary architecture, but that quadrupolar gravitational perturbations from their rapidly-rotating host star subsequently disrupt this primordial coplanarity. We demonstrate that, given sufficient stellar obliquity, even systems beginning with 2 planetary constituents are susceptible to dynamical instability soon after planet formation, as a result of the stellar quadrupole moment. This mechanism stands as a widespread, yet poorly explored pathway toward planetary system instability. Moreover, by requiring that observed multi-systems remain coplanar on Gyr timescales, we are able to place upper limits on the stellar obliquity in systems such as K2-38 (obliquity < 20 degrees), where other methods of measuring spin-orbit misalignment are not currently available.

Frequency domain phase retrieval of simultaneous multi-wavelength phase-shifting interferometry

International Nuclear Information System (INIS)

Yin, Zhenxing; Zhong, Liyun; Xu, Xiaofei; Zhang, Wangping; Lu, Xiaoxu; Tian, Jindong

2016-01-01

In simultaneous multi-wavelength phase-shifting interferometry, we propose a novel frequency domain phase retrieval (FDPR) algorithm. First, using only a one-time phase-shifting operation, a sequence of simultaneous multi-wavelength phase-shifting interferograms (SPSMWIs) are captured by a monochrome charge-coupled device. Second, by performing a Fourier transform for each pixel of SPSMWIs, the wrapped phases of each wavelength can be retrieved from the complex amplitude located in the spectral peak of each wavelength. Finally, the phase of the synthetic wavelength can be obtained by the subtraction between the wrapped phases of a single wavelength. In this study, the principle and the application condition of the proposed approach are discussed. Both the simulation and the experimental result demonstrate the simple and convenient performance of the proposed FDPR approach. (paper)

A HIGH-RESOLUTION, MULTI-EPOCH SPECTRAL ATLAS OF PECULIAR STARS INCLUDING RAVE, GAIA , AND HERMES WAVELENGTH RANGES

International Nuclear Information System (INIS)

Tomasella, Lina; Munari, Ulisse; Zwitter, Tomaz

2010-01-01

We present an Echelle+CCD, high signal-to-noise ratio, high-resolution (R = 20,000) spectroscopic atlas of 108 well-known objects representative of the most common types of peculiar and variable stars. The wavelength interval extends from 4600 to 9400 A and includes the RAVE, Gaia, and HERMES wavelength ranges. Multi-epoch spectra are provided for the majority of the observed stars. A total of 425 spectra of peculiar stars, which were collected during 56 observing nights between 1998 November and 2002 August, are presented. The spectra are given in FITS format and heliocentric wavelengths, with accurate subtraction of both the sky background and the scattered light. Auxiliary material useful for custom applications (telluric dividers, spectrophotometric stars, flat-field tracings) is also provided. The atlas aims to provide a homogeneous database of the spectral appearance of stellar peculiarities, a tool useful both for classification purposes and inter-comparison studies. It could also serve in the planning and development of automated classification algorithms designed for RAVE, Gaia, HERMES, and other large-scale spectral surveys. The spectrum of XX Oph is discussed in some detail as an example of the content of the present atlas.

2μm all fiber multi-wavelength Tm/Ho co-doped fiber laser

Science.gov (United States)

Zhang, Junhong; Jiang, Qiuxia; Wang, Xiaofa

2017-10-01

A 2 μm all fiber multi-wavelength Tm/Ho co-doped fiber laser based on a simple ring cavity is experimentally demonstrated. Compared with other 2 μm multi-wavelength Tm/Ho co-doped fiber lasers, the multi-wavelength fiber laser is obtained by the gain saturation effect and inhomogeneous broadening effect without any frequency selector component, filter component or polarization-dependent component. When the pump power is about 304 mW, the fiber laser enters into single-wavelength working state around 1967.76 nm. Further increasing the pump power to 455 mW, a stable dual-wavelength laser is obtained at room temperature. The bimodal power difference between λ1 and λ2 is 5.528 dB. The fluctuations of wavelength and power are less than 0.03 nm and 0.264 dB in an hour, which demonstrates that the multi-wavelength fiber laser works at a stable state. Furthermore, a research about the relationship between the pump power and the output spectra has been made.

A MODEL FOR (QUASI-)PERIODIC MULTIWAVELENGTH PHOTOMETRIC VARIABILITY IN YOUNG STELLAR OBJECTS

Energy Technology Data Exchange (ETDEWEB)

Kesseli, Aurora Y. [Boston University, 725 Commonwealth Ave, Boston, MA 02215 (United States); Petkova, Maya A.; Wood, Kenneth; Gregory, Scott G. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9AD (United Kingdom); Whitney, Barbara A. [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St, Madison, WI 53706 (United States); Hillenbrand, L. A. [Astronomy Department, California Institute of Technology, Pasadena, CA 91125 (United States); Stauffer, J. R.; Morales-Calderon, M.; Rebull, L. [Spitzer Science Center, California Institute of Technology, CA 91125 (United States); Alencar, S. H. P., E-mail: aurorak@bu.com [Departamento de Física—ICEx—UFMG, Av. Antônio Carlos, 6627, 30270-901, Belo Horizonte, MG (Brazil)

2016-09-01

We present radiation transfer models of rotating young stellar objects (YSOs) with hot spots in their atmospheres, inner disk warps, and other three-dimensional effects in the nearby circumstellar environment. Our models are based on the geometry expected from magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hot spots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project to determine if these processes can explain the variability observed at optical and mid-infrared wavelengths in young stars. We focus on those variables exhibiting “dipper” behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hot-spot size and temperature affects the optical and near-infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR light curve variations. Clumpy disk distributions with non-uniform fractal density structure produce more stochastic light curves. We conclude that magneto-accretion theory is consistent with certain aspects of the multiwavelength photometric variability exhibited by low-mass YSOs. More detailed modeling of individual sources can be used to better determine the stellar hot-spot and inner disk geometries of particular sources.

STELLAR POPULATIONS IN COMPACT GALAXY GROUPS: A MULTI-WAVELENGTH STUDY OF HCGs 16, 22, AND 42, THEIR STAR CLUSTERS, AND DWARF GALAXIES

International Nuclear Information System (INIS)

Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Gronwall, C.; Fedotov, K.; Desjardins, T. D.; Gallagher, S. C.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Walker, L. M.; Johnson, K. E.; Tzanavaris, P.

2013-01-01

We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 ''associates'' (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

Mr-Moose: An advanced SED-fitting tool for heterogeneous multi-wavelength datasets

Science.gov (United States)

Drouart, G.; Falkendal, T.

2018-04-01

We present the public release of Mr-Moose, a fitting procedure that is able to perform multi-wavelength and multi-object spectral energy distribution (SED) fitting in a Bayesian framework. This procedure is able to handle a large variety of cases, from an isolated source to blended multi-component sources from an heterogeneous dataset (i.e. a range of observation sensitivities and spectral/spatial resolutions). Furthermore, Mr-Moose handles upper-limits during the fitting process in a continuous way allowing models to be gradually less probable as upper limits are approached. The aim is to propose a simple-to-use, yet highly-versatile fitting tool fro handling increasing source complexity when combining multi-wavelength datasets with fully customisable filter/model databases. The complete control of the user is one advantage, which avoids the traditional problems related to the "black box" effect, where parameter or model tunings are impossible and can lead to overfitting and/or over-interpretation of the results. Also, while a basic knowledge of Python and statistics is required, the code aims to be sufficiently user-friendly for non-experts. We demonstrate the procedure on three cases: two artificially-generated datasets and a previous result from the literature. In particular, the most complex case (inspired by a real source, combining Herschel, ALMA and VLA data) in the context of extragalactic SED fitting, makes Mr-Moose a particularly-attractive SED fitting tool when dealing with partially blended sources, without the need for data deconvolution.

A multi-wavelength analysis of the diffuse H II region G25.8700+0.1350

Science.gov (United States)

Cichowolski, S.; Duronea, N. U.; Suad, L. A.; Reynoso, E. M.; Dorda, R.

2018-02-01

We present a multi-wavelength investigation of the H II region G25.8700+0.1350, located in the inner part of the Galaxy. In radio continuum emission, the region is seen as a bright arc-shaped structure. An analysis of the H I line suggests that G25.8700+0.1350 lies at a distance of 6.5 kpc. The ionized gas is bordered by a photodissociation region, which is encircled by a molecular structure where four molecular clumps are detected. At infrared wavelengths, the region is also very conspicuous. Given the high level of visual absorption in the region, the exciting stars should be searched for in the infrared band. In this context, we found in the literature one Wolf-Rayet and one red supergiant, which, together with 37 2MASS sources that are candidate O-type stars, could be related to the origin of G25.8700+0.1350. Finally, as expanding H II regions are hypothesized to trigger star formation, we used different infrared point source catalogues to search for young stellar object candidates (cYSOs). A total of 45 cYSOs were identified projected on to the molecular clouds.

Swift Multi-wavelength Observing Campaigns: Strategies and Outcomes

Science.gov (United States)

Krimm, Hans A.

2007-01-01

The Swift gamma-ray burst explorer has been operating since December 2004 as both a gamma-ray burst (GRB) monitor and telescope and a multi-wavelength observatory, covering the energy range from V band and near UV to hard X rays above 150 keV. It is designed to rapidly repoint to observe newly discovered GRBs, and this maneuverability, combined with an easily changed observing program, allows Swift to also be an effective multiwavelength observatory for non-GRB targets, both as targets of opportunity and pre-planned multi-wavelength observing campaigns. Blazars are particularly attractive targets for coordinated campaigns with TeV experiments since many blazars are bright in both the hard X-ray and TeV energy ranges. Successful coordinated campaigns have included observations of 3C454.3 during its 2005 outburst. The latest Swift funding cycles allow for non- GRB related observations to be proposed. The Burst Alert Telescope on Swift also serves as a hard X-ray monitor with a public web page that includes light curves for over 400 X-ray sources and is used to alert the astronomical community about increased activity from both known and newly discovered sources. This presentation mill include Swift capabilities, strategies and policies for coordinated multi-wavelength observations as well as discussion of the potential outcomes of such campaigns.

All-optical multi-wavelength conversion with negative power penalty by a commercial SOA-MZI for WDM wavelength multicast

NARCIS (Netherlands)

Yan, N.; Jung, H.D.; Tafur Monroy, I.; Waardt, de H.; Koonen, A.M.J.

2007-01-01

WDM wavelength multicast is demonstrated by all-optical multi-wavelength conversion at 10 Gb/s using a commercial SOA-MZI. We report for the first time simultaneous one-to-four conversion with negative power penalty of 1.84 dB.

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

The metastable dynamo model of stellar rotational evolution

International Nuclear Information System (INIS)

Brown, Timothy M.

2014-01-01

This paper introduces a new empirical model for the rotational evolution of Sun-like stars—those with surface convection zones and non-convective interior regions. Previous models do not match the morphology of observed (rotation period)-color diagrams, notably the existence of a relatively long-lived 'C-sequence' of fast rotators first identified by Barnes. This failure motivates the Metastable Dynamo Model (MDM) described here. The MDM posits that stars are born with their magnetic dynamos operating in a mode that couples very weakly to the stellar wind, so their (initially very short) rotation periods at first change little with time. At some point, this mode spontaneously and randomly changes to a strongly coupled mode, the transition occurring with a mass-dependent lifetime that is of the order of 100 Myr. I show that with this assumption, one can obtain good fits to observations of young clusters, particularly for ages of 150-200 Myr. Previous models and the MDM both give qualitative agreement with the morphology of the slower-rotating 'I-sequence' stars, but none of them have been shown to accurately reproduce the stellar-mass-dependent evolution of the I-sequence stars, especially for clusters older than a few hundred million years. I discuss observational experiments that can test aspects of the MDM, and speculate that the physics underlying the MDM may be related to other situations described in the literature, in which stellar dynamos may have a multi-modal character.

The next generation of galaxy evolution models: A symbiosis of stellar populations and chemical abundances

Science.gov (United States)

Kotulla, Ralf

2012-10-01

Over its lifespan Hubble has invested significant effort into detailed observations of galaxies both in the local and distant universe. To extract the physical information from the observed {spectro-}photometry requires detailed and accurate models. Stellar population synthesis models are frequently used to obtain stellar masses, star formation rate, galaxy ages and star formation histories. Chemical evolution models offer another valuable and complementary approach to gain insight into many of the same aspects, yet these two methods have rarely been used in combination.Our proposed next generation of galaxy evolution models will help us improve our understanding of how galaxies form and evolve. Building on GALEV evolutionary synthesis models we incorporate state-of-the-art input physics for stellar evolution of binaries and rotating stars as well as new spectral libraries well matched to the modern observational capabilities. Our improved chemical evolution model allows us to self-consistently trace abundances of individual elements, fully accounting for the increasing initial abundances of successive stellar generations. GALEV will support variable Initial Mass Functions {IMF}, enabling us to test recent observational findings of a non-universal IMF by predicting chemical properties and integrated spectra in an integrated and consistent manner.HST is the perfect instrument for testing this approach. Its wide wavelength coverage from UV to NIR enables precise SED fitting, and with its spatial resolution we can compare the inferred chemical evolution to studies of star clusters and resolved stellar populations in nearby galaxies.

Wavelength-Dependence of Inter-Core Crosstalk in Homogeneous Multi-Core Fibers

DEFF Research Database (Denmark)

Ye, Feihong; Saitoh, Kunimasa; Takenaga, Katsuhiro

2016-01-01

The wavelength dependence of inter-core crosstalk in homogeneous multi-core fibers (MCFs) is investigated, and the corresponding analytical expressions are derived. The derived analytical expressions can be used to determine the crosstalk at any wavelength necessary for designing future MCF...

A multi-institutional Stellarator Configuration Study

Science.gov (United States)

Gates, David

2017-10-01

A multi-institutional study aimed at mapping the space of quasi-axisymmetric stellarators has begun. The goal is to gain improved understanding of the dependence of important physics and engineering parameters (e.g. bootstrap current, stability, coil complexity, etc.) on plasma shape (average elongation, aspect ratio, number of periods). In addition, the stellarator optimization code STELLOPT will be upgraded with new capabilities such as improved coil design algorithms such as COILOPT + + and REGCOIL, divertor optimization options, equilibria with islands using the SPEC code, and improved bootstrap current calculations with the SFINCS code. An effort is underway to develop metrics for divertor optimization. STELLOPT has also had numerous improvements to numerical algorithms and parallelization capabilities. Simultaneously, we also are pursuing the optimization of turbulent transport according to the method of proxy functions. Progress made to date includes an elongation scan on quasi-axisymmetric equilibria and an initial comparison between the SFINCS code and the BOOTSJ calculation of bootstrap current currently available in STELLOPT. Further progress on shape scans and subsequent physics analysis will be reported. The status of the STELLOPT upgrades will be described. The eventual goal of this exercise is to identify attractive configurations for future US experimental facilities.. This work is supported by US DoE Contract Number DE-AC02-09CH11466.

System and Method for Multi-Wavelength Optical Signal Detection

Science.gov (United States)

McGlone, Thomas D. (Inventor)

2017-01-01

The system and method for multi-wavelength optical signal detection enables the detection of optical signal levels significantly below those processed at the discrete circuit level by the use of mixed-signal processing methods implemented with integrated circuit technologies. The present invention is configured to detect and process small signals, which enables the reduction of the optical power required to stimulate detection networks, and lowers the required laser power to make specific measurements. The present invention provides an adaptation of active pixel networks combined with mixed-signal processing methods to provide an integer representation of the received signal as an output. The present invention also provides multi-wavelength laser detection circuits for use in various systems, such as a differential absorption light detection and ranging system.

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.

Measurement and correction of transverse chromatic offsets for multi-wavelength retinal microscopy in the living eye.

Science.gov (United States)

Harmening, Wolf M; Tiruveedhula, Pavan; Roorda, Austin; Sincich, Lawrence C

2012-09-01

A special challenge arises when pursuing multi-wavelength imaging of retinal tissue in vivo, because the eye's optics must be used as the main focusing elements, and they introduce significant chromatic dispersion. Here we present an image-based method to measure and correct for the eye's transverse chromatic aberrations rapidly, non-invasively, and with high precision. We validate the technique against hyperacute psychophysical performance and the standard chromatic human eye model. In vivo correction of chromatic dispersion will enable confocal multi-wavelength images of the living retina to be aligned, and allow targeted chromatic stimulation of the photoreceptor mosaic to be performed accurately with sub-cellular resolution.

Multi-Wavelength Variability in PKS 2155-304 Y. G. Zheng1,2, L ...

Indian Academy of Sciences (India)

2009), we attempt to model the multi-wavelength variability in PKS 2155-304. We assume that the acceleration process is a stochastic process and we describe it as the diffusion of the particle momentum. Throughout the paper, we assume the. Hubble constant H0 = 70 km s−1. Mpc. −1. , the matter energy density M = 0.27,.

Multi-Wavelength Monitoring of GRS 1915+105

Science.gov (United States)

Bandyopadhyay, R.; Martini, P.; Gerard, E.; Charles, P. A.; Wagner, R. M.; Shrader, C.; Shahbaz, T.; Mirabel, I. F.

1997-01-01

Since its discovery in 1992, the superluminal X-ray transient GRS 1915+105 has been extensively observed in an attempt to understand its behaviour. We present here first results from a multi-wavelength campaign undertaken from July to September 1996. This study includes X-ray data from the RXTE All Sky Monitor and BATSE, two-frequency data from the Nancay radio telescope, and infrared photometry from the 1.8 m Perkins telescope at Lowell Observatory. The first long-term well-sampled IR light curve of GRS 1915+105 is presented herein and is consistent with the interpretation of this source as a long-period binary. We compare the various light curves, searching for correlations in the behaviour of the source at differing wavelengths and for possible periodicities.

Simultaneous identification of optical constants and PSD of spherical particles by multi-wavelength scattering-transmittance measurement

Science.gov (United States)

Zhang, Jun-You; Qi, Hong; Ren, Ya-Tao; Ruan, Li-Ming

2018-04-01

An accurate and stable identification technique is developed to retrieve the optical constants and particle size distributions (PSDs) of particle system simultaneously from the multi-wavelength scattering-transmittance signals by using the improved quantum particle swarm optimization algorithm. The Mie theory are selected to calculate the directional laser intensity scattered by particles and the spectral collimated transmittance. The sensitivity and objective function distribution analysis were conducted to evaluate the mathematical properties (i.e. ill-posedness and multimodality) of the inverse problems under three different optical signals combinations (i.e. the single-wavelength multi-angle light scattering signal, the single-wavelength multi-angle light scattering and spectral transmittance signal, and the multi-angle light scattering and spectral transmittance signal). It was found the best global convergence performance can be obtained by using the multi-wavelength scattering-transmittance signals. Meanwhile, the present technique have been tested under different Gaussian measurement noise to prove its feasibility in a large solution space. All the results show that the inverse technique by using multi-wavelength scattering-transmittance signals is effective and suitable for retrieving the optical complex refractive indices and PSD of particle system simultaneously.

MoS2-wrapped microfiber-based multi-wavelength soliton fiber laser

Science.gov (United States)

Lu, Feifei

2017-11-01

The single-, dual- and triple-wavelength passively mode-locked erbium-doped fiber lasers are demonstrated with MoS2 and polarization-dependent isolator (PD-ISO). The saturable absorber is fabricated by wrapping an MoS2 around a microfiber. The intracavity PD-ISO acts as a wavelength-tunable filter with a polarization controller (PC) by adjusting the linear birefringence. Single-wavelength mode-locked fiber laser can self-start with suitable pump power. With appropriate PC state, dual- and triple-wavelength operations can be observed when gains at different wavelengths reach a balance. It is noteworthy that dual-wavelength pulses exhibiting peak and dip sidebands, respectively, are demonstrated in the experiment. The proposed simple and multi-wavelength all-fiber conventional soliton lasers could possess potential applications in numerous fields, such as sensors, THz generations and optical communications.

Chemometric analysis of in-line multi-wavelength fluorescence measurements obtained during cultivations with a lipase producing Aspergillus oryzae strain

DEFF Research Database (Denmark)

Haack, Martin Brian; Eliasson Lantz, Anna; Mortensen, P.P.

2007-01-01

The filamentous fungus, Aspergillus oryzae, was cultivated in batch and fed-batch cultivations in order to investigate the use of multi-wavelength fluorescence for monitoring course of events during filamentous fungi cultivations. The A. oryzae strain applied expressed a fungal lipase from...... Thermomyces lanuginosus. Spectra of multi-wavelength fluorescence were collected every 5 min with the BioView system (DELTA, Denmark) and both explorative and predictive models, correlating the fluorescence data with cell mass and lipase activity, were built. During the cultivations, A. oryzae displayed...

Stellar-Mass Black Holes in the Solar Neighborhood

CERN Document Server

Chisholm, J S R; Kolb, Edward W; Chisholm, James R.; Dodelson, Scott; Kolb, Edward W.

2003-01-01

We search for nearby, isolated, accreting, ``stellar-mass'' (3 to $100M_\\odot$) black holes. Models suggest a synchrotron spectrum in visible wavelengths and some emission in X-ray wavelengths. Of 3.7 million objects in the Sloan Digital Sky Survey Early Data Release, about 150,000 have colors and properties consistent with such a spectrum, and 47 of these objects are X-ray sources from the ROSAT All Sky Survey. Optical spectra exclude seven of these. We give the positions and colors of these 40 black-hole candidates, as well as a measure of their distances from the stellar loci in color--color space. We discuss uncertainties the expected number of sources, and the contribution of black holes to local dark matter.

Advanced Fabrication of Single-Mode and Multi-Wavelength MIR-QCLs

Directory of Open Access Journals (Sweden)

Martin J. Süess

2016-05-01

Full Text Available In this article we present our latest work on the optimization of mid-infrared quantum cascade laser fabrication techniques. Our efforts are focused on low dissipation devices, broad-area high-power photonic crystal lasers, as well as multi-wavelength devices realized either as arrays or multi-section distributed feedback (DFB devices. We summarize our latest achievements and update them with our most recent results.

Design of multi-wavelength tunable filter based on Lithium Niobate

Science.gov (United States)

Zhang, Ailing; Yao, Yuan; Zhang, Yue; Song, Hongyun

2018-05-01

A multi-wavelength tunable filter is designed. It consists of multiple waveguides among multiple waveguide gratings. A pair of electrodes were placed on both sides of each waveguide. The tunable filter uses the electro-optic effect of Lithium Niobate to tune the phase caused by each waveguide. Consequently, the wavelength and wavelength spacing of the filter are tuned by changing external voltages added on the electrode pairs. The tunable property of the filter is analyzed by phase matching condition and transfer-matrix method. Numerical results show that not only multiple wavelengths with narrow bandwidth are tuned with nearly equal spacing by synchronously changing the voltages added on all electrode pairs, but also the number of wavelengths is determined by the number of phase shifts caused by electrode pairs. Furthermore, due to the electro-optic effect of Lithium Niobate, the tuning speed of the filter can reach the order of ns.

(LBA-and-WRM)-based DBA scheme for multi-wavelength upstream transmission supporting 10 Gbps and 1 Gbps in MAN

Science.gov (United States)

Zhang, Yuchao; Gan, Chaoqin; Gou, Kaiyu; Xu, Anni; Ma, Jiamin

2018-01-01

DBA scheme based on Load balance algorithm (LBA) and wavelength recycle mechanism (WRM) for multi-wavelength upstream transmission is proposed in this paper. According to 1 Gbps and 10 Gbps line rates, ONUs are grouped into different VPONs. To facilitate wavelength management, resource pool is proposed to record wavelength state. To realize quantitative analysis, a mathematical model describing metro-access network (MAN) environment is presented. To 10G-EPON upstream, load balance algorithm is designed to ensure load distribution fairness for 10G-OLTs. To 1G-EPON upstream, wavelength recycle mechanism is designed to share remained wavelengths. Finally, the effectiveness of the proposed scheme is demonstrated by simulation and analysis.

Multi-wavelength imaging of solar plasma. High-beta disruption model of solar flares

International Nuclear Information System (INIS)

Shibasaki, Kiyoto

2007-01-01

Solar atmosphere is filled with plasma and magnetic field. Activities in the atmosphere are due to plasma instabilities in the magnetic field. To understand the physical mechanisms of activities / instabilities, it is necessary to know the physical conditions of magnetized plasma, such as temperature, density, magnetic field, and their spatial structures and temporal developments. Multi-wavelength imaging is essential for this purpose. Imaging observations of the Sun at microwave, X-ray, EUV and optical ranges are routinely going on. Due to free exchange of original data among solar physics and related field communities, we can easily combine images covering wide range of spectrum. Even under such circumstances, we still do not understand the cause of activities in the solar atmosphere well. The current standard model of solar activities is based on magnetic reconnection: release of stored magnetic energy by reconnection is the cause of solar activities on the Sun such as solar flares. However, recent X-ray, EUV and microwave observations with high spatial and temporal resolution show that dense plasma is involved in activities from the beginning. Based on these observations, I propose a high-beta model of solar activities, which is very similar to high-beta disruptions in magnetically confined fusion experiments. (author)

Multi-Wavelength Polarimetry of Isolated Neutron Stars

Directory of Open Access Journals (Sweden)

Roberto P. Mignani

2018-03-01

Full Text Available Isolated neutron stars are known to be endowed with extreme magnetic fields, whose maximum intensity ranges from 10 12 – 10 15 G, which permeates their magnetospheres. Their surrounding environment is also strongly magnetized, especially in the compact nebulae powered by the relativistic wind from young neutron stars. The radiation from isolated neutron stars and their surrounding nebulae is, thus, supposed to bring a strong polarization signature. Measuring the neutron star polarization brings important information about the properties of their magnetosphere and of their highly magnetized environment. Being the most numerous class of isolated neutron stars, polarization measurements have been traditionally carried out for radio pulsars, hence in the radio band. In this review, I summarize multi-wavelength linear polarization measurements obtained at wavelengths other than radio both for pulsars and other types of isolated neutron stars and outline future perspectives with the upcoming observing facilities.

A Multi-Wavelength Thermal Infrared and Reflectance Scene Simulation Model

Science.gov (United States)

Ballard, J. R., Jr.; Smith, J. A.; Smith, David E. (Technical Monitor)

2002-01-01

Several theoretical calculations are presented and our approach discussed for simulating overall composite scene thermal infrared exitance and canopy bidirectional reflectance of a forest canopy. Calculations are performed for selected wavelength bands of the DOE Multispectral Thermal Imagery and comparisons with atmospherically corrected MTI imagery are underway. NASA EO-1 Hyperion observations also are available and the favorable comparison of our reflective model results with these data are reported elsewhere.

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.

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.

Understanding the formation and evolution of early-type galaxies based on newly developed single-burst stellar population synthesis models in the infrared

Science.gov (United States)

Roeck, Benjamin

2015-12-01

The detailed study of the different stellar populations which can be observed in galaxies is one of the most promising methods to shed light on the evolutionary histories of galaxies. So far, stellar population analysis has been carried out mainly in the optical wavelength range. The infrared spectral range, on the other hand, has been poorly studied so far, although it provides very important insights, particularly into the cooler stellar populations which are present in galaxies. However, in the last years, space telescopes like the Spitzer Space Telescope or the Wide-field Infrared Survey Explorer and instruments like the spectrograph X-Shooter on the Very Large Telescope have collected more and more photometric and spectroscopic data in this wavelength range. In order to analyze these observations, it is necessary to dispose of reliable and accurate stellar population models in the infrared. Only a small number of stellar population models in the infrared exist in the literature. They are mostly based on theoretical stellar libraries and very often cover only the near-infrared wavelength range at a rather low resolution. Hence, we developed new single-burst stellar population models between 8150 and 50000Å which are exclusively based on 180 spectra from the empirical Infrared Telescope Facility stellar library. We computed our single stellar population models for two different sets of isochrones and various types of initial mass functions of different slopes. Since the stars of the Infrared Telescope Facility library present only a limited coverage of the stellar atmospheric parameter space, our models are of sufficient quality only for ages larger than 1 Gyr and metallicities between [Fe/H] = 0.40 and 0.26. By combining our single stellar population models in the infrared with the extended medium-resolution Isaac Newton Telescope library of empirical spectra in the optical spectral range, we created the first single stellar population models covering the

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.

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.

Transient Mass-loss Analysis of Solar Observations Using Stellar Methods

Energy Technology Data Exchange (ETDEWEB)

Crosley, M. K.; Norman, C. [Johns Hopkins University, Department of Physics and Astronomy, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Osten, R. A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2017-08-10

Low-frequency dynamic spectra of radio bursts from nearby stars offer the best chance to directly detect the stellar signature of transient mass loss on low-mass stars. Crosley et al. (2016) proposes a multi-wavelength methodology to determine coronal mass ejection (CME) parameters, such as speed, mass, and kinetic energy. We test the validity and accuracy of the results derived from the methodology by using Geostationary Operational Environmental Satellite X-ray observations and Bruny Island Radio Spectrometer radio observations. These are analogous observations to those that would be found in the stellar studies. Derived results from these observations are compared to direct white light measurements of the Large Angle and Spectrometric Coronagraph. We find that, when a pre-event temperature can be determined, the accuracy of CME speeds are within a few hundred km s{sup −1}, and are reliable when specific criteria has been met. CME mass and kinetic energies are only useful in determining the approximate order of magnitude measurements when considering the large errors associated to them. These results will be directly applicable to the interpretation of any detected stellar events and the derivation of stellar CME properties.

On-line monitoring of fermentation processes using multi-wavelength fluorescence

DEFF Research Database (Denmark)

Odman, Peter; Petersen, Nanna; Johansen, Claus Lindvald

2007-01-01

. The model system considered in this work is the antibiotic production by Streptomyces coelicolor, a filamentous bacterium. In addition to predicting concentrations of biomass in the fermentation broth, the data allowed detection of different physiological states, i.e. growth phase and phosphate limitation......Fermentation processes often suffer from a lack of real-time methods for on-line determination of variables like the concentrations of nutrients and products. This work aims at investigating the possibilities of implementing an on-line fermentation monitoring system based on multi......-wavelength fluorescence (MWF). This type of sensor has previously showed promising accuracy and selectivity for in situ monitoring of cell mass and certain metabolites in bioreactors (Lantz et al., 2006). The sensor generates multivariate data outputs, which necessitate chemometric modeling for signal interpretation...

Multi-wavelength Observations of Solar Acoustic Waves Near Active Regions

Science.gov (United States)

Monsue, Teresa; Pesnell, Dean; Hill, Frank

2018-01-01

Active region areas on the Sun are abundant with a variety of waves that are both acoustically helioseismic and magnetohydrodynamic in nature. The occurrence of a solar flare can disrupt these waves, through MHD mode-mixing or scattering by the excitation of these waves. We take a multi-wavelength observational approach to understand the source of theses waves by studying active regions where flaring activity occurs. Our approach is to search for signals within a time series of images using a Fast Fourier Transform (FFT) algorithm, by producing multi-frequency power map movies. We study active regions both spatially and temporally and correlate this method over multiple wavelengths using data from NASA’s Solar Dynamics Observatory. By surveying the active regions on multiple wavelengths we are able to observe the behavior of these waves within the Solar atmosphere, from the photosphere up through the corona. We are able to detect enhancements of power around active regions, which could be acoustic power halos and of an MHD-wave propagating outward by the flaring event. We are in the initial stages of this study understanding the behaviors of these waves and could one day contribute to understanding the mechanism responsible for their formation; that has not yet been explained.

Feasibility Study of Multi-Wavelength Differential Absorption LIDAR for CO2 Monitoring

Directory of Open Access Journals (Sweden)

Chengzhi Xiang

2016-06-01

Full Text Available To obtain a better understanding of carbon cycle and accurate climate prediction models, highly accurate and temporal resolution observation of atmospheric CO2 is necessary. Differential absorption LIDAR (DIAL remote sensing is a promising technology to detect atmospheric CO2. However, the traditional DIAL system is the dual-wavelength DIAL (DW-DIAL, which has strict requirements for wavelength accuracy and stability. Moreover, for on-line and off-line wavelengths, the system’s optical efficiency and the change of atmospheric parameters are assumed to be the same in the DW-DIAL system. This assumption inevitably produces measurement errors, especially under rapid aerosol changes. In this study, a multi-wavelength DIAL (MW-DIAL is proposed to map atmospheric CO2 concentration. The MW-DIAL conducts inversion with one on-line and multiple off-line wavelengths. Multiple concentrations of CO2 are then obtained through difference processing between the single on-line and each of the off-line wavelengths. In addition, the least square method is adopted to optimize inversion results. Consequently, the inversion concentration of CO2 in the MW-DIAL system is found to be the weighted average of the multiple concentrations. Simulation analysis and laboratory experiments were conducted to evaluate the inversion precision of MW-DIAL. For comparison, traditional DW-DIAL simulations were also conducted. Simulation analysis demonstrated that, given the drifting wavelengths of the laser, the detection accuracy of CO2 when using MW-DIAL is higher than that when using DW-DIAL, especially when the drift is large. A laboratory experiment was also performed to verify the simulation analysis.

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.

Unveiling the First Black Holes With JWST:Multi-wavelength Spectral Predictions

Science.gov (United States)

Natarajan, Priyamvada; Pacucci, Fabio; Ferrara, Andrea; Agarwal, Bhaskar; Ricarte, Angelo; Zackrisson, Erik; Cappelluti, Nico

2017-04-01

Growing supermassive black holes (˜ {10}9 {M}⊙ ) that power luminous z> 6 quasars from light seeds—the remnants of the first stars—within a Gyr of the Big Bang poses a timing challenge. The formation of massive black hole seeds via direct collapse with initial masses ˜ {10}4{--}{10}5 {M}⊙ alleviates this problem. Viable direct-collapse black hole formation sites, the satellite halos of star-forming galaxies, merge and acquire stars to produce a new, transient class of high-redshift objects, obese black hole galaxies (OBGs). The accretion luminosity outshines that of the stars in OBGs. We predict the multi-wavelength energy output of OBGs and growing Pop III remnants at z = 9 for standard and slim disk accretion, as well as high and low metallicities of the associated stellar population. We derive robust selection criteria for OBGs—a pre-selection to eliminate blue sources, followed by color-color cuts ([{F}090W-{F}220W]> 0;-0.3sift out OBGs from other bright, high- and low-redshift contaminants in the infrared. OBGs with predicted {M}{AB}< 25 are unambiguously detectable by the Mid-Infrared Instrument (MIRI), on the upcoming James Webb Space Telescope (JWST). For parameters explored here, growing Pop III remnants with predicted {M}{AB}< 30 will likely be undetectable by JWST. We demonstrate that JWST has the power to discriminate between initial seeding mechanisms.

Multi-wavelength HPLC fingerprints from complex substances: An exploratory chemometrics study of the Cassia seed example

Energy Technology Data Exchange (ETDEWEB)

Ni Yongnian, E-mail: ynni@ncu.edu.cn [Stake Laboratory of Food Science and Technology, Nanchang University, Nanchang, Jiangxi 330047 (China); Department of Chemistry, Nanchang University, Nanchang, Jiangxi 330047 (China); Lai Yanhua [Department of Chemistry, Nanchang University, Nanchang, Jiangxi 330047 (China); Brandes, Sarina; Kokot, Serge [Applied Chemistry Cluster, School of Physical and Chemical Sciences, Queensland University of Technology, Brisbane, Queensland 4001 (Australia)

2009-08-11

Multi-wavelength fingerprints of Cassia seed, a traditional Chinese medicine (TCM), were collected by high-performance liquid chromatography (HPLC) at two wavelengths with the use of diode array detection. The two data sets of chromatograms were combined by the data fusion-based method. This data set of fingerprints was compared separately with the two data sets collected at each of the two wavelengths. It was demonstrated with the use of principal component analysis (PCA), that multi-wavelength fingerprints provided a much improved representation of the differences in the samples. Thereafter, the multi-wavelength fingerprint data set was submitted for classification to a suite of chemometrics methods viz. fuzzy clustering (FC), SIMCA and the rank ordering MCDM PROMETHEE and GAIA. Each method highlighted different properties of the data matrix according to the fingerprints from different types of Cassia seeds. In general, the PROMETHEE and GAIA MCDM methods provided the most comprehensive information for matching and discrimination of the fingerprints, and appeared to be best suited for quality assurance purposes for these and similar types of sample.

Multi-wavelength HPLC fingerprints from complex substances: An exploratory chemometrics study of the Cassia seed example

International Nuclear Information System (INIS)

Ni Yongnian; Lai Yanhua; Brandes, Sarina; Kokot, Serge

2009-01-01

Multi-wavelength fingerprints of Cassia seed, a traditional Chinese medicine (TCM), were collected by high-performance liquid chromatography (HPLC) at two wavelengths with the use of diode array detection. The two data sets of chromatograms were combined by the data fusion-based method. This data set of fingerprints was compared separately with the two data sets collected at each of the two wavelengths. It was demonstrated with the use of principal component analysis (PCA), that multi-wavelength fingerprints provided a much improved representation of the differences in the samples. Thereafter, the multi-wavelength fingerprint data set was submitted for classification to a suite of chemometrics methods viz. fuzzy clustering (FC), SIMCA and the rank ordering MCDM PROMETHEE and GAIA. Each method highlighted different properties of the data matrix according to the fingerprints from different types of Cassia seeds. In general, the PROMETHEE and GAIA MCDM methods provided the most comprehensive information for matching and discrimination of the fingerprints, and appeared to be best suited for quality assurance purposes for these and similar types of sample.

Multi-wavelength HPLC fingerprints from complex substances: An exploratory chemometrics study of the Cassia seed example.

Science.gov (United States)

Ni, Yongnian; Lai, Yanhua; Brandes, Sarina; Kokot, Serge

2009-08-11

Multi-wavelength fingerprints of Cassia seed, a traditional Chinese medicine (TCM), were collected by high-performance liquid chromatography (HPLC) at two wavelengths with the use of diode array detection. The two data sets of chromatograms were combined by the data fusion-based method. This data set of fingerprints was compared separately with the two data sets collected at each of the two wavelengths. It was demonstrated with the use of principal component analysis (PCA), that multi-wavelength fingerprints provided a much improved representation of the differences in the samples. Thereafter, the multi-wavelength fingerprint data set was submitted for classification to a suite of chemometrics methods viz. fuzzy clustering (FC), SIMCA and the rank ordering MCDM PROMETHEE and GAIA. Each method highlighted different properties of the data matrix according to the fingerprints from different types of Cassia seeds. In general, the PROMETHEE and GAIA MCDM methods provided the most comprehensive information for matching and discrimination of the fingerprints, and appeared to be best suited for quality assurance purposes for these and similar types of sample.

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.

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.

Making Sense of Atmospheric Models and Fundamental Stellar Properties at the Bottom of the Main Sequence

Science.gov (United States)

Dieterich, Sergio; Henry, Todd; Jao, W.-C.; Washington, Robert; Silverstein, Michele; Winters, J.; RECONS

2018-01-01

We present a detailed comparison of atmospheric model predictions and photometric observations for late M and L dwarfs. We discuss which wavelength regions are best for determining the fundamental properties of these cool stellar and substellar atmospheres and use this analysis to refine the HR diagram for the hydrogen burning limit first presented in 2014. We also add several new objects to the HR diagram and find little qualitative difference in the HR diagram's overall morphology when compared to our 2014 results. The L2 dwarf 2MASS 0523-1403 remains the smallest hydrogen burning star for which we calculated a radius, thus likely indicating the end of the stellar main sequence. This work is supported by the NSF Astronomy and Astrophysics Postdoctoral Fellowship program through grant AST-1400680.

A new stellar library in the region of the CO index at 2.3 mu m - New index definition and empirical fitting functions

NARCIS (Netherlands)

Marmol-Queralto, E.; Cardiel, N.; Cenarro, A. J.; Vazdekis, A.; Gorgas, J.; Pedraz, S.; Peletier, R. F.; Sanchez-Blazquez, P.

2008-01-01

Context. The analysis of unresolved stellar populations demands evolutionary synthesis models with realistic physical ingredients and extended wavelength coverage. Aims. We quantitatively describe the first CO bandhead at 2.3 mu m to allow stellar population models to provide improved predictions in

Soliton-based ultrafast multi-wavelength nonlinear switching in dual-core photonic crystal fibre

International Nuclear Information System (INIS)

Stajanca, P; Pysz, D; Michalka, M; Bugar, I; Andriukaitis, G; Balciunas, T; Fan, G; Baltuska, A

2014-01-01

Systematic experimental study of ultrafast multi-wavelength all-optical switching performance in a dual-core photonic crystal fibre is presented. The focus is on nonlinearly induced switching between the two output ports at non-excitation wavelengths, which are generated during nonlinear propagation of femtosecond pulses in the anomalous dispersion region of a dual-core photonic crystal fibre made of multicomponent glass. Spatial and spectral characteristics of the fibre output radiation were measured separately for both fibre cores under various polarization and intensity conditions upon selective, individual excitation of each fibre core. Polarization-controlled nonlinear switching performance at multiple non-excitation wavelengths was demonstrated in the long-wavelength optical communication bands and beyond. Depending on the input pulse polarization, narrowband switching operation at 1560 nm and 1730 nm takes place with double core extinction ratio contrasts of 9 dB and 14.5 dB, respectively. Moreover, our approach allows switching with simultaneous wavelength shift from 1650 to 1775 nm with extinction ratio contrast larger than 18 dB. In addition, non-reciprocal behaviour of the soliton fission process under different fibre core excitations was observed and its effect on the multi-wavelength nonlinear switching performance was explained, taking into account the slight dual-core structure asymmetry. The obtained results represent ultrafast all-optical switching with an extended dimension of wavelength shift, controllable with both the input radiation intensity and the polarization by simple propagation along a 14 mm long fibre. (paper)

STELLAR MASSES AND STAR FORMATION RATES OF LENSED, DUSTY, STAR-FORMING GALAXIES FROM THE SPT SURVEY

Energy Technology Data Exchange (ETDEWEB)

Ma, Jingzhe; Gonzalez, Anthony H. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Spilker, J. S.; Marrone, D. P. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Strandet, M. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69 D-53121 Bonn (Germany); Ashby, M. L. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aravena, M. [Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago (Chile); Béthermin, M.; Breuck, C. de; Gullberg, B. [European Southern Observatory, Karl Schwarzschild Straße 2, D-85748 Garching (Germany); Bothwell, M. S. [Cavendish Laboratory, University of Cambridge, JJ Thompson Avenue, Cambridge CB3 0HA (United Kingdom); Brodwin, M. [Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Chapman, S. C. [Dalhousie University, Halifax, Nova Scotia (Canada); Fassnacht, C. D. [Department of Physics, University of California, One Shields Avenue, Davis, CA 95616 (United States); Greve, T. R. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Hezaveh, Y. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305 (United States); Malkan, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States); Saliwanchik, B. R., E-mail: jingzhema@ufl.edu [Department of Physics, Case Western Reserve University, Cleveland, OH 44106 (United States); and others

2015-10-10

To understand cosmic mass assembly in the universe at early epochs, we primarily rely on measurements of the stellar masses and star formation rates (SFRs) of distant galaxies. In this paper, we present stellar masses and SFRs of six high-redshift (2.8 ≤ z ≤ 5.7) dusty, star-forming galaxies (DSFGs) that are strongly gravitationally lensed by foreground galaxies. These sources were first discovered by the South Pole Telescope (SPT) at millimeter wavelengths and all have spectroscopic redshifts and robust lens models derived from Atacama Large Millimeter/submillimeter Array observations. We have conducted follow-up observations to obtain multi-wavelength imaging data using the Hubble Space Telescope (HST), Spitzer, Herschel, and the Atacama Pathfinder EXperiment. We use the high-resolution HST/Wide Field Camera 3 images to disentangle the background source from the foreground lens in Spitzer/IRAC data. The detections and upper limits provide important constraints on the spectral energy distributions (SEDs) for these DSFGs, yielding stellar masses, IR luminosities, and SFRs. The SED fits of six SPT sources show that the intrinsic stellar masses span a range more than one order of magnitude with a median value ∼5 ×10{sup 10} M{sub ⊙}. The intrinsic IR luminosities range from 4 × 10{sup 12} L{sub ⊙} to 4 × 10{sup 13} L{sub ⊙}. They all have prodigious intrinsic SFRs of 510–4800 M{sub ⊙} yr{sup −1}. Compared to the star-forming main sequence (MS), these six DSFGs have specific SFRs that all lie above the MS, including two galaxies that are a factor of 10 higher than the MS. Our results suggest that we are witnessing ongoing strong starburst events that may be driven by major mergers.

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.

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.

Applications of the k – ω Model in Stellar Evolutionary Models

Energy Technology Data Exchange (ETDEWEB)

Li, Yan, E-mail: ly@ynao.ac.cn [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216 (China)

2017-05-20

The k – ω model for turbulence was first proposed by Kolmogorov. A new k – ω model for stellar convection was developed by Li, which could reasonably describe turbulent convection not only in the convectively unstable zone, but also in the overshooting regions. We revised the k – ω model by improving several model assumptions (including the macro-length of turbulence, convective heat flux, and turbulent mixing diffusivity, etc.), making it applicable not only for convective envelopes, but also for convective cores. Eight parameters are introduced in the revised k – ω model. It should be noted that the Reynolds stress (turbulent pressure) is neglected in the equation of hydrostatic support. We applied it into solar models and 5 M {sub ⊙} stellar models to calibrate the eight model parameters, as well as to investigate the effects of the convective overshooting on the Sun and intermediate mass stellar models.

Experimental verification of a very low crosstalk wavelength router construction using arrayed-waveguide grating multi/demultiplexers

DEFF Research Database (Denmark)

Liu, Fenghai; Pedersen, Rune Johan Skullerud; Peucheret, Christophe

1999-01-01

A very low crosstalk N×N wavelength router construction based on 1×N AWG multi/demultiplexers has been proposed. The peak crosstalk level of -53 dB is measured in such an 8×8 wavelength router and the power penalty from the router is negligible. Rather large wavelength routing networks can be built...

Computational models of stellar collapse and core-collapse supernovae

International Nuclear Information System (INIS)

Ott, Christian D; O'Connor, Evan; Schnetter, Erik; Loeffler, Frank; Burrows, Adam; Livne, Eli

2009-01-01

Core-collapse supernovae are among Nature's most energetic events. They mark the end of massive star evolution and pollute the interstellar medium with the life-enabling ashes of thermonuclear burning. Despite their importance for the evolution of galaxies and life in the universe, the details of the core-collapse supernova explosion mechanism remain in the dark and pose a daunting computational challenge. We outline the multi-dimensional, multi-scale, and multi-physics nature of the core-collapse supernova problem and discuss computational strategies and requirements for its solution. Specifically, we highlight the axisymmetric (2D) radiation-MHD code VULCAN/2D and present results obtained from the first full-2D angle-dependent neutrino radiation-hydrodynamics simulations of the post-core-bounce supernova evolution. We then go on to discuss the new code Zelmani which is based on the open-source HPC Cactus framework and provides a scalable AMR approach for 3D fully general-relativistic modeling of stellar collapse, core-collapse supernovae and black hole formation on current and future massively-parallel HPC systems. We show Zelmani's scaling properties to more than 16,000 compute cores and discuss first 3D general-relativistic core-collapse results.

Multi-wavelength mid-IR light source for gas sensing

Science.gov (United States)

Karioja, Pentti; Alajoki, Teemu; Cherchi, Matteo; Ollila, Jyrki; Harjanne, Mikko; Heinilehto, Noora; Suomalainen, Soile; Viheriälä, Jukka; Zia, Nouman; Guina, Mircea; Buczyński, Ryszard; Kasztelanic, Rafał; Kujawa, Ireneusz; Salo, Tomi; Virtanen, Sami; Kluczyński, Paweł; Sagberg, Hâkon; Ratajczyk, Marcin; Kalinowski, Przemyslaw

2017-02-01

Cost effective multi-wavelength light sources are key enablers for wide-scale penetration of gas sensors at Mid-IR wavelength range. Utilizing novel Mid-IR Si-based photonic integrated circuits (PICs) filter and wide-band Mid-IR Super Luminescent Light Emitting Diodes (SLEDs), we show the concept of a light source that covers 2.5…3.5 μm wavelength range with a resolution of price can be lowered in high volumes by utilizing tailored molded IR lens technology and automated packaging and assembling technologies. The status of the development of the key components of the light source are reported. The PIC is based on the use of micron-scale SOI technology, SLED is based on AlGaInAsSb materials and the lenses are tailored heavy metal oxide glasses fabricated by the use of hot-embossing. The packaging concept utilizing automated assembly tools is depicted. In safety and security applications, the Mid-IR wavelength range covered by the novel light source allows for detecting several harmful gas components with a single sensor. At the moment, affordable sources are not available. The market impact is expected to be disruptive, since the devices currently in the market are either complicated, expensive and heavy instruments, or the applied measurement principles are inadequate in terms of stability and selectivity.

Multi-wavelength study of PPDs using an OPO tunable pulse laser microscope system

International Nuclear Information System (INIS)

Yoshimura, Koji; Nakamura, Isamu

2012-01-01

We have developed a new pulsed laser microscope system whose wavelength is continuously tunable from 410 nm to 2200 nm by using an optical parametric oscillator (OPO) laser system. The laser spot can be focused to ∼2μm diameter, small enough to measure pixel-by-pixel performance of PPDs (pixelated photon detectors). Using multi-wavelength laser light, we plan to probe PPDs at various depths, thanks to their different penetration lengths in the silicon layer. In this paper, details of the commissioning of the laser microscope system and pilot measurements on a PPD at several wavelengths will be presented.

Multi-wavelength study of PPDs using an OPO tunable pulse laser microscope system

Energy Technology Data Exchange (ETDEWEB)

Yoshimura, Koji, E-mail: koji.yoshimura@kek.jp [High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Nakamura, Isamu [High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)

2012-12-11

We have developed a new pulsed laser microscope system whose wavelength is continuously tunable from 410 nm to 2200 nm by using an optical parametric oscillator (OPO) laser system. The laser spot can be focused to {approx}2{mu}m diameter, small enough to measure pixel-by-pixel performance of PPDs (pixelated photon detectors). Using multi-wavelength laser light, we plan to probe PPDs at various depths, thanks to their different penetration lengths in the silicon layer. In this paper, details of the commissioning of the laser microscope system and pilot measurements on a PPD at several wavelengths will be presented.

Estimate of rain evaporation rates from dual-wavelength lidar measurements: comparison against a model analytical solution

Science.gov (United States)

Lolli, Simone; Di Girolamo, Paolo; Demoz, Belay; Li, Xiaowen; Welton, Ellsworth J.

2018-04-01

Rain evaporation significantly contributes to moisture and heat cloud budgets. In this paper, we illustrate an approach to estimate the median volume raindrop diameter and the rain evaporation rate profiles from dual-wavelength lidar measurements. These observational results are compared with those provided by a model analytical solution. We made use of measurements from the multi-wavelength Raman lidar BASIL.

Multi-wavelength investigations on feedback of massive star formation

Science.gov (United States)

Yuan, Jinghua

2014-05-01

In the course of massive star formation, outflows, ionizing radiation and intense stellar winds could heavily affect their adjacent environs and natal clouds. There are several outstanding open questions related to these processes: i) whether they can drive turbulence in molecular clouds; ii) whether they are able to trigger star formation; iii) whether they can destroy natal clouds to terminate star formation at low efficiencies. This thesis investigates feedback in different stages of massive star formation. Influence of such feedback to the ambient medium has been revealed. A new type of millimeter methanol maser is detected for the first time. An uncommon bipolar outflow prominent in the mid-infrared is discovered. And features of triggered star formation are found on the border of an infrared bubble and in the surroundings of a Herbig Be star. Extended green objects (EGOs) are massive outflow candidates showing prominent shocked features in the mid-infrared. We have carried out a high resolution study of the EGO G22.04+0.22 (hereafter, G22) based on archived SMA data. Continuum and molecular lines at 1.3 mm reveal that G22 is still at a hot molecular core stage. A very young multi-polar outflow system is detected, which is interacting with the adjacent dense gas. Anomalous emission features from CH3OH (8,-1,8 - 7,0,7) and CH3OH (4,2,2 - 3,1,2) are proven to be millimeter masers. It is the first time that maser emission of CH3OH (8,-1,8 - 7,0,7) at 218.440 GHz is detected in a massive star-forming region. Bipolar outflows have been revealed and investigated almost always in the microwave or radio domain. It's sort of rare that hourglass-shaped morphology be discovered in the mid-infrared. Based on GLIMPSE data, we have discovered a bipolar object resembling an hourglass at 8.0 um. It is found to be associated with IRAS 18114-1825. Analysis based on fitted SED, optical spectroscopy, and infrared color indices suggests IRAS 18114-1825 is an uncommon bipolar

Artificial neural network model for photosynthetic pigments identification using multi wavelength chromatographic data

Science.gov (United States)

Prilianti, K. R.; Hariyanto, S.; Natali, F. D. D.; Indriatmoko, Adhiwibawa, M. A. S.; Limantara, L.; Brotosudarmo, T. H. P.

2016-04-01

The development of rapid and automatic pigment characterization method become an important issue due to the fact that there are only less than 1% of plant pigments in the earth have been explored. In this research, a mathematical model based on artificial intelligence approach was developed to simplify and accelerate pigment characterization process from HPLC (high-performance liquid chromatography) procedure. HPLC is a widely used technique to separate and identify pigments in a mixture. Input of the model is chromatographic data from HPLC device and output of the model is a list of pigments which is the spectrum pattern is discovered in it. This model provides two dimensional (retention time and wavelength) fingerprints for pigment characterization which is proven to be more accurate than one dimensional fingerprint (fixed wavelength). Moreover, by mimicking interconnection of the neuron in the nervous systems of the human brain, the model have learning ability that could be replacing expert judgement on evaluating spectrum pattern. In the preprocessing step, principal component analysis (PCA) was used to reduce the huge dimension of the chromatographic data. The aim of this step is to simplify the model and accelerate the identification process. Six photosynthetic pigments i.e. zeaxantin, pheophytin a, α-carotene, β-carotene, lycopene and lutein could be well identified by the model with accuracy up to 85.33% and processing time less than 1 second.

Multi-wavelength Characterization of Brown and Black Carbon from Filter Samples

Science.gov (United States)

Johnson, M. M.; Yatavelli, R. L. N.; Chen, L. W. A. A.; Gyawali, M. S.; Arnott, W. P.; Wang, X.; Chakrabarty, R. K.; Moosmüller, H.; Watson, J. G.; Chow, J. C.

2014-12-01

Particulate matter (PM) scatters and absorbs solar radiation and thereby affects visibility, the Earth's radiation balance, and properties and lifetimes of clouds. Understanding the radiative forcing (RF) of PM is essential to reducing the uncertainty in total anthropogenic and natural RF. Many instruments that measure light absorption coefficients (βabs [λ], Mm-1) of PM have used light at near-infrared (NIR; e.g., 880 nm) or red (e.g., 633 nm) wavelengths. Measuring βabs over a wider wavelength range, especially including the ultraviolet (UV) and visible, allows for contributions from black carbon (BC), brown carbon (BrC), and mineral dust (MD) to be differentiated. This will help to determine PM RF and its emission sources. In this study, source and ambient samples collected on Teflon-membrane and quartz-fiber filters are used to characterize and develop a multi-wavelength (250 - 1000 nm) filter-based measurement method of PM light absorption. A commercially available UV-visible spectrometer coupled with an integrating sphere is used for quantifying diffuse reflectance and transmittance of filter samples, from which βabs and absorption Ǻngström exponents (AAE) of the PM deposits are determined. The filter-based light absorption measurements of laboratory generated soot and biomass burning aerosol are compared to 3-wavelength photoacoustic absorption measurements to evaluate filter media and loading effects. Calibration factors are developed to account for differences between filter types (Teflon-membrane vs. quartz-fiber), and between filters and in situ photoacoustic absorption values. Application of multi-spectral absorption measurements to existing archived filters, including specific source samples (e.g. diesel and gasoline engines, biomass burning, dust), will also be discussed.

Waveguide-integrated single- and multi-photon detection at telecom wavelengths using superconducting nanowires

International Nuclear Information System (INIS)

Ferrari, Simone; Kahl, Oliver; Kovalyuk, Vadim; Goltsman, Gregory N.; Korneev, Alexander; Pernice, Wolfram H. P.

2015-01-01

We investigate single- and multi-photon detection regimes of superconducting nanowire detectors embedded in silicon nitride nanophotonic circuits. At near-infrared wavelengths, simultaneous detection of up to three photons is observed for 120 nm wide nanowires biased far from the critical current, while narrow nanowires below 100 nm provide efficient single photon detection. A theoretical model is proposed to determine the different detection regimes and to calculate the corresponding internal quantum efficiency. The predicted saturation of the internal quantum efficiency in the single photon regime agrees well with plateau behavior observed at high bias currents

Waveguide-integrated single- and multi-photon detection at telecom wavelengths using superconducting nanowires

Energy Technology Data Exchange (ETDEWEB)

Ferrari, Simone; Kahl, Oliver [Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe 76132 (Germany); Kovalyuk, Vadim [Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe 76132 (Germany); Department of Physics, Moscow State Pedagogical University, Moscow 119992 (Russian Federation); Goltsman, Gregory N. [Department of Physics, Moscow State Pedagogical University, Moscow 119992 (Russian Federation); National Research University Higher School of Economics, 20 Myasnitskaya Ulitsa, Moscow 101000 (Russian Federation); Korneev, Alexander [Department of Physics, Moscow State Pedagogical University, Moscow 119992 (Russian Federation); Moscow Institute of Physics and Technology (State University), Moscow 141700 (Russian Federation); Pernice, Wolfram H. P., E-mail: wolfram.pernice@kit.edu [Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe 76132 (Germany); Department of Physics, University of Münster, 48149 Münster (Germany)

2015-04-13

We investigate single- and multi-photon detection regimes of superconducting nanowire detectors embedded in silicon nitride nanophotonic circuits. At near-infrared wavelengths, simultaneous detection of up to three photons is observed for 120 nm wide nanowires biased far from the critical current, while narrow nanowires below 100 nm provide efficient single photon detection. A theoretical model is proposed to determine the different detection regimes and to calculate the corresponding internal quantum efficiency. The predicted saturation of the internal quantum efficiency in the single photon regime agrees well with plateau behavior observed at high bias currents.

Reduction of short wavelength reflectance of multi-wall carbon nanotubes through ultraviolet laser irradiation

Science.gov (United States)

Stephens, Michelle S.; Simonds, Brian J.; Yung, Christopher S.; Conklin, Davis; Livigni, David J.; Oliva, Alberto Remesal; Lehman, John H.

2018-05-01

Multi-wall carbon nanotube coatings are used as broadband, low-reflectance absorbers for bolometric applications and for stray light control. They are also used as high emittance blackbody radiators. Irradiation of single wall carbon nanotubes with ultraviolet (UV) laser light has been shown to remove amorphous carbon debris, but there have been few investigations of the interaction of UV light with the more complex physics of multi-wall carbon nanotubes. We present measurements of reflectance and surface morphology before and after exposure of multi-wall carbon nanotube coatings to 248 nm UV laser light. We show that UV exposure reduces the reflectivity at wavelengths below 600 nm and present modeling of the thermal cycling the UV exposure causes at the surface of the carbon nanotubes. This effect can be used to flatten the spectral shape of the reflectivity curve of carbon nanotube absorber coatings used for broadband applications. Finally, we find that the effect of UV exposure depends on the nanotube growth process.

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.

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.

Prospects for Measuring Abundances of >20 Elements with Low-resolution Stellar Spectra

Energy Technology Data Exchange (ETDEWEB)

Ting Yuan-Sen; Conroy, Charlie; Cargile, Phillip [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)

2017-07-01

Understanding the evolution of the Milky Way calls for the precise abundance determination of many elements in many stars. A common perception is that deriving more than a few elemental abundances ([Fe/H], [ α /Fe], perhaps [C/H], [N/H]) requires medium-to-high spectral resolution, R ≳ 10,000, mostly to overcome the effects of line blending. In a recent work, we presented an efficient and practical way to model the full stellar spectrum, even when fitting a large number of stellar labels simultaneously. In this paper, we quantify to what precision the abundances of many different elements can be recovered, as a function of spectroscopic resolution and wavelength range. In the limit of perfect spectral models and spectral normalization, we show that the precision of elemental abundances is nearly independent of resolution, for a fixed exposure time and number of detector pixels; low-resolution spectra simply afford much higher S/N per pixel and generally larger wavelength range in a single setting. We also show that estimates of most stellar labels are not strongly correlated with one another once R ≳ 1000. Modest errors in the line-spread function, as well as small radial velocity errors, do not affect these conclusions, and data-driven models indicate that spectral (continuum) normalization can be achieved well enough in practice. These results, to be confirmed with an analysis of observed low-resolution data, open up new possibilities for the design of large spectroscopic stellar surveys and for the reanalysis of archival low-resolution data sets.

Employing Machine-Learning Methods to Study Young Stellar Objects

Science.gov (United States)

Moore, Nicholas

2018-01-01

Vast amounts of data exist in the astronomical data archives, and yet a large number of sources remain unclassified. We developed a multi-wavelength pipeline to classify infrared sources. The pipeline uses supervised machine learning methods to classify objects into the appropriate categories. The program is fed data that is already classified to train it, and is then applied to unknown catalogues. The primary use for such a pipeline is the rapid classification and cataloging of data that would take a much longer time to classify otherwise. While our primary goal is to study young stellar objects (YSOs), the applications extend beyond the scope of this project. We present preliminary results from our analysis and discuss future applications.

Objective identification of informative wavelength regions in galaxy spectra

Energy Technology Data Exchange (ETDEWEB)

Yip, Ching-Wa; Szalay, Alexander S.; Budavári, Tamás; Wyse, Rosemary F. G. [Department of Physics and Astronomy, The Johns Hopkins University, 3701 San Martin Drive, Baltimore, MD 21218 (United States); Mahoney, Michael W. [Department of Mathematics, Stanford University, Stanford, CA 94305 (United States); Csabai, István; Dobos, Laszlo, E-mail: cwyip@pha.jhu.edu, E-mail: szalay@jhu.edu, E-mail: mmahoney@cs.stanford.edu [Department of Physics of Complex Systems, Eötvös Loránd University, H-1117 Budapest (Hungary)

2014-05-01

Understanding the diversity in spectra is the key to determining the physical parameters of galaxies. The optical spectra of galaxies are highly convoluted with continuum and lines that are potentially sensitive to different physical parameters. Defining the wavelength regions of interest is therefore an important question. In this work, we identify informative wavelength regions in a single-burst stellar population model using the CUR Matrix Decomposition. Simulating the Lick/IDS spectrograph configuration, we recover the widely used D {sub n}(4000), Hβ, and Hδ {sub A} to be most informative. Simulating the Sloan Digital Sky Survey spectrograph configuration with a wavelength range 3450-8350 Å and a model-limited spectral resolution of 3 Å, the most informative regions are: first region—the 4000 Å break and the Hδ line; second region—the Fe-like indices; third region—the Hβ line; and fourth region—the G band and the Hγ line. A principal component analysis on the first region shows that the first eigenspectrum tells primarily the stellar age, the second eigenspectrum is related to the age-metallicity degeneracy, and the third eigenspectrum shows an anti-correlation between the strengths of the Balmer and the Ca K and H absorptions. The regions can be used to determine the stellar age and metallicity in early-type galaxies that have solar abundance ratios, no dust, and a single-burst star formation history. The region identification method can be applied to any set of spectra of the user's interest, so that we eliminate the need for a common, fixed-resolution index system. We discuss future directions in extending the current analysis to late-type galaxies. ASCII formatted tables of the regional eigenspectra are available.

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.

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.

Computational models of stellar collapse and core-collapse supernovae

Energy Technology Data Exchange (ETDEWEB)

Ott, Christian D; O' Connor, Evan [TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA (United States); Schnetter, Erik; Loeffler, Frank [Center for Computation and Technology, Louisiana State University, Baton Rouge, LA (United States); Burrows, Adam [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States); Livne, Eli, E-mail: cott@tapir.caltech.ed [Racah Institute of Physics, Hebrew University, Jerusalem (Israel)

2009-07-01

Core-collapse supernovae are among Nature's most energetic events. They mark the end of massive star evolution and pollute the interstellar medium with the life-enabling ashes of thermonuclear burning. Despite their importance for the evolution of galaxies and life in the universe, the details of the core-collapse supernova explosion mechanism remain in the dark and pose a daunting computational challenge. We outline the multi-dimensional, multi-scale, and multi-physics nature of the core-collapse supernova problem and discuss computational strategies and requirements for its solution. Specifically, we highlight the axisymmetric (2D) radiation-MHD code VULCAN/2D and present results obtained from the first full-2D angle-dependent neutrino radiation-hydrodynamics simulations of the post-core-bounce supernova evolution. We then go on to discuss the new code Zelmani which is based on the open-source HPC Cactus framework and provides a scalable AMR approach for 3D fully general-relativistic modeling of stellar collapse, core-collapse supernovae and black hole formation on current and future massively-parallel HPC systems. We show Zelmani's scaling properties to more than 16,000 compute cores and discuss first 3D general-relativistic core-collapse results.

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.

Stellar populations in medium redshift clusters

International Nuclear Information System (INIS)

Pickles, A.J.; van der Kruit, P.C.; Pickles, A.J.

1990-01-01

We present a set of model isochrone spectra formed by combining stellar spectra in the proportions appropriate to the isochrone tabulations of VandenBerg, together with a Miller-Scalo mass function. The model spectra cover the wave-length range 3000-10000 A and have been constructed for metallicities in the range - 1.0 ≤ [Fe/H] ≤ 0.5, and for isochrone ages of 2 to 15 billion years. The model spectra follow the isochrone tabulations by including contributions from stars along the main sequence and subgiant branch to the base of the giant branch, fully constraining the main sequence turnoff and early post main sequence evolutionary phases. They are useful for deconvolving the competing effects of age and metallicity dispersion in composite systems. Other important components such as Horizontal branch, red giant and asymptotic branch stars are not included explicitly because they are not yet tabulated by VandenBerg, and because their fractional contributions to a composite population are less certain. These components should be added as extra parameters from a stellar library when fitting real composite spectra

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

Topological insulator: Bi{sub 2}Se{sub 3}/polyvinyl alcohol film-assisted multi-wavelength ultrafast erbium-doped fiber laser

Energy Technology Data Exchange (ETDEWEB)

Guo, Bo; Yao, Yong, E-mail: yaoyong@hit.edu.cn; Yang, Yan-Fu; Yuan, Yi-Jun; Wang, Rui-Lai [Department of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055 (China); Wang, Shu-Guang; Ren, Zhong-Hua [Department of Materials Science and Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055 (China); Yan, Bo [College of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450052 (China)

2015-02-14

We experimentally demonstrate a multi-wavelength ultrafast erbium-doped fiber laser incorporating a μm-scale topological insulator: Bi{sub 2}Se{sub 3}/Polyvinyl Alcohol film as both an excellent saturable absorber for mode-locking and a high-nonlinear medium to induce a giant third order optical nonlinear effect for mitigating the mode competition of erbium-doped fiber laser and stabilizing the multi-wavelength oscillation. By properly adjusting the pump power and the polarization state, the single-, dual-, triple-, four-wavelength mode-locking pulse could be stably initiated. For the four-wavelength operation, we obtain its pulse width of ∼22 ps and a fundamental repetition rate of 8.83 MHz. The fiber laser exhibits the maximum output power of 9.7 mW with the pulse energy of 1.1 nJ and peak power of 50 W at the pump power of 155 mW. Our study shows that the simple, stable, low-cost multi-wavelength ultrafast fiber laser could be applied in various potential fields, such as optical communication, biomedical research, and radar system.

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.

Multi-client quantum key distribution using wavelength division multiplexing

International Nuclear Information System (INIS)

Grice, Warren P.; Bennink, Ryan S.; Earl, Dennis Duncan; Evans, Philip G.; Humble, Travis S.; Pooser, Raphael C.; Schaake, Jason; Williams, Brian P.

2011-01-01

Quantum Key Distribution (QKD) exploits the rules of quantum mechanics to generate and securely distribute a random sequence of bits to two spatially separated clients. Typically a QKD system can support only a single pair of clients at a time, and so a separate quantum link is required for every pair of users. We overcome this limitation with the design and characterization of a multi-client entangled-photon QKD system with the capacity for up to 100 clients simultaneously. The time-bin entangled QKD system includes a broadband down-conversion source with two unique features that enable the multi-user capability. First, the photons are emitted across a very large portion of the telecom spectrum. Second, and more importantly, the photons are strongly correlated in their energy degree of freedom. Using standard wavelength division multiplexing (WDM) hardware, the photons can be routed to different parties on a quantum communication network, while the strong spectral correlations ensure that each client is linked only to the client receiving the conjugate wavelength. In this way, a single down-conversion source can support dozens of channels simultaneously--and to the extent that the WDM hardware can send different spectral channels to different clients, the system can support multiple client pairings. We will describe the design and characterization of the down-conversion source, as well as the client stations, which must be tunable across the emission spectrum.

Application of quantum-dot multi-wavelength lasers and silicon photonic ring resonators to data-center optical interconnects

Science.gov (United States)

Beckett, Douglas J. S.; Hickey, Ryan; Logan, Dylan F.; Knights, Andrew P.; Chen, Rong; Cao, Bin; Wheeldon, Jeffery F.

2018-02-01

Quantum dot comb sources integrated with silicon photonic ring-resonator filters and modulators enable the realization of optical sub-components and modules for both inter- and intra-data-center applications. Low-noise, multi-wavelength, single-chip, laser sources, PAM4 modulation and direct detection allow a practical, scalable, architecture for applications beyond 400 Gb/s. Multi-wavelength, single-chip light sources are essential for reducing power dissipation, space and cost, while silicon photonic ring resonators offer high-performance with space and power efficiency.

Notes on the apparent discordance of pulse oximetry and multi-wavelength haemoglobin photometry

NARCIS (Netherlands)

Nijland, R.; Jongsma, H.W.; Nijhuis, J.G.; Oeseburg, Berend; Zijlstra, Willem

1995-01-01

Multi-wavelength photometers, blood gas analysers and pulse oximeters are widely used to measure various oxygen-related quantities. The definitions of these quantities are not always correct. This paper gives insight in the various definitions for oxygen quantities. Furthermore, the possible

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

Switchable multi-wavelength erbium-doped fiber ring laser based on a tapered in-line Mach–Zehnder interferometer

Science.gov (United States)

Zhou, Yuxin; Wang, Xin; Tang, Zijuan; Lou, Shuqin

2018-05-01

In this paper, a switchable multi-wavelength erbium-doped fiber ring laser based on a tapered in-line Mach–Zehnder interferometer is proposed. The in-line Mach–Zehnder interferometer is fabricated by splicing a large-core fiber between two segments of single mode fibers, in which the first splicing point is tapered and the second splicing point is connected directly. By carefully rotating the polarization controller, switchable single-, dual-, triple- and quad-wavelength lasing outputs can be obtained with a side mode suppression ratio higher than 50 dB. The maximal peak power difference of multi-wavelength lasing is 3.67 dB, demonstrating a good power equalization performance. Furthermore, the proposed laser is proven to be very stable at room temperature. The wavelength shifts and peak power fluctuations are less than 0.02 nm and 1.3 dB over half an hour. In addition, stable quintuple-wavelength lasing with a side mode suppression ratio higher than 50 dB can also be realized when the filter length is changed.

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.

Stellar Content of the Young Supershell GSH 305+01-24

Science.gov (United States)

Kaltcheva, N.; Golev, V.

2013-06-01

We combine several multi-wavelength surveys (Wisconsin Halpha Mapper Northern Sky Survey, MSX Mid-IR Galactic Plane Survey, WISE All-Sky Data Release, CO survey of the Milky Way, and the Southern Galactic Plane HI Survey) with intermediate-band uvby photometry to investigate the correlation between the young stars and various interstellar components related to the GSH 305+01-24 supershell seen toward Centaurus. The region shows striking similarities between the stellar distribution and Hα and HI emission morphologies. We identity 161 O-B9 stars at an average distance modulus 11.09 ± 0.71 (s.d.) mag located within the supershell and study their interaction with the surrounding interstellar material.

Multiple optical code-label processing using multi-wavelength frequency comb generator and multi-port optical spectrum synthesizer.

Science.gov (United States)

Moritsuka, Fumi; Wada, Naoya; Sakamoto, Takahide; Kawanishi, Tetsuya; Komai, Yuki; Anzai, Shimako; Izutsu, Masayuki; Kodate, Kashiko

2007-06-11

In optical packet switching (OPS) and optical code division multiple access (OCDMA) systems, label generation and processing are key technologies. Recently, several label processors have been proposed and demonstrated. However, in order to recognize N different labels, N separate devices are required. Here, we propose and experimentally demonstrate a large-scale, multiple optical code (OC)-label generation and processing technology based on multi-port, a fully tunable optical spectrum synthesizer (OSS) and a multi-wavelength electro-optic frequency comb generator. The OSS can generate 80 different OC-labels simultaneously and can perform 80-parallel matched filtering. We also demonstrated its application to OCDMA.

The faint radio source population at 15.7 GHz - II. Multi-wavelength properties

Science.gov (United States)

Whittam, I. H.; Riley, J. M.; Green, D. A.; Jarvis, M. J.; Vaccari, M.

2015-11-01

A complete, flux density limited sample of 96 faint (>0.5 mJy) radio sources is selected from the 10C survey at 15.7 GHz in the Lockman Hole. We have matched this sample to a range of multi-wavelength catalogues, including Spitzer Extragalactic Representative Volume Survey, Spitzer Wide-area Infrared Extragalactic survey, United Kingdom Infrared Telescope Infrared Deep Sky Survey and optical data; multi-wavelength counterparts are found for 80 of the 96 sources and spectroscopic redshifts are available for 24 sources. Photometric redshifts are estimated for the sources with multi-wavelength data available; the median redshift of the sample is 0.91 with an interquartile range of 0.84. Radio-to-optical ratios show that at least 94 per cent of the sample are radio loud, indicating that the 10C sample is dominated by radio galaxies. This is in contrast to samples selected at lower frequencies, where radio-quiet AGN and star-forming galaxies are present in significant numbers at these flux density levels. All six radio-quiet sources have rising radio spectra, suggesting that they are dominated by AGN emission. These results confirm the conclusions of Paper I that the faint, flat-spectrum sources which are found to dominate the 10C sample below ˜1 mJy are the cores of radio galaxies. The properties of the 10C sample are compared to the Square Kilometre Array Design Studies Simulated Skies; a population of low-redshift star-forming galaxies predicted by the simulation is not found in the observed sample.

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.

[Investigation of multi-wavelength effect during the measurement of UV-enhanced film's emission spectrum].

Science.gov (United States)

Liu, Meng; Ni, Zheng-ji; Zhang, Da-wei; Huang, Yuan-shen; Zhuang, Song-lin

2009-09-01

The UV-responsive detector is a dual-use device for civilian and military after the laser and IR-responsive sensors. Typical image sensor coated with a layer of down-convert frequency thin film on it's photosurface to enhance UV response is the key technology of enhancing UV-response. The UV-enhanced thin film was made in the experimental laboratory using the Zn2SiO4:Mn phosphor by spin coating method. Two peaks at 520 and 560 nm respectively in the emission spectrum of the UV-enhanced film were found by SP1702 spectrograph when the excitation wavelength was 260 and 280 nm. The peaks were found in the process of experiment of measuring and counting the quantum efficiency of UV-enhanced thin film. But the light peaks at 520 and 560 nm are not the emission light peaks by the exciting light of 260 and 280 nm. The reason why the light at 520 and 560 nm is not the emission light was analyzed based on the measurement principle of grating spectrograph. The reasons for the multi-wavelength of light overlaps during the measurement of emission spectrum were also discussed. And the equipment used to separate the overlapped different wavelengths was designed, which will be used to resolve the problem of the overlap of multi-wavelength.

Molecular transport network security using multi-wavelength optical spins.

Science.gov (United States)

Tunsiri, Surachai; Thammawongsa, Nopparat; Mitatha, Somsak; Yupapin, Preecha P

2016-01-01

Multi-wavelength generation system using an optical spin within the modified add-drop optical filter known as a PANDA ring resonator for molecular transport network security is proposed. By using the dark-bright soliton pair control, the optical capsules can be constructed and applied to securely transport the trapped molecules within the network. The advantage is that the dark and bright soliton pair (components) can securely propagate for long distance without electromagnetic interference. In operation, the optical intensity from PANDA ring resonator is fed into gold nano-antenna, where the surface plasmon oscillation between soliton pair and metallic waveguide is established.

Probabilistic classification method on multi wavelength chromatographic data for photosynthetic pigments identification

Science.gov (United States)

Prilianti, K. R.; Setiawan, Y.; Indriatmoko, Adhiwibawa, M. A. S.; Limantara, L.; Brotosudarmo, T. H. P.

2014-02-01

Environmental and health problem caused by artificial colorant encourages the increasing usage of natural colorant nowadays. Natural colorant refers to the colorant that is derivate from living organism or minerals. Extensive research topic has been done to exploit these colorant, but recent data shows that only 0.5% of the wide range of plant pigments in the earth has been exhaustively used. Hence development of the pigment characterization technique is an important consideration. High-performance liquid chromatography (HPLC) is a widely used technique to separate pigments in a mixture and identify it. In former HPLC fingerprinting, pigment characterization was based on a single chromatogram from a fixed wavelength (one dimensional) and discard the information contained at other wavelength. Therefore, two dimensional fingerprints have been proposed to use more chromatographic information. Unfortunately this method leads to the data processing problem due to the size of its data matrix. The other common problem in the chromatogram analysis is the subjectivity of the researcher in recognizing the chromatogram pattern. In this research an automated analysis method of the multi wavelength chromatographic data was proposed. Principal component analysis (PCA) was used to compress the data matrix and Maximum Likelihood (ML) classification was applied to identify the chromatogram pattern of the existing pigments in a mixture. Three photosynthetic pigments were selected to show the proposed method. Those pigments are β-carotene, fucoxanthin and zeaxanthin. The result suggests that the method could well inform the existence of the pigments in a particular mixture. A simple computer application was also developed to facilitate real time analysis. Input of the application is multi wavelength chromatographic data matrix and the output is information about the existence of the three pigments.

Backscattering of gyrotron radiation and short-wavelength turbulence during electron cyclotron resonance plasma heating in the L-2M stellarator

Energy Technology Data Exchange (ETDEWEB)

Batanov, G. M.; Borzosekov, V. D., E-mail: tinborz@gmail.com; Kovrizhnykh, L. M.; Kolik, L. V.; Konchekov, E. M.; Malakhov, D. V.; Petrov, A. E.; Sarksyan, K. A.; Skvortsova, N. N.; Stepakhin, V. D.; Kharchev, N. K. [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)

2013-06-15

Backscattering of gyrotron radiation ({theta} = {pi}) by short-wavelength density fluctuations (k{sub Up-Tack} = 30 cm{sup -1}) in the plasma of the L-2M stellarator was studied under conditions of electron cyclotron resonance (ECR) plasma heating at the second harmonic of the electron gyrofrequency (75 GHz). The scattering of the O-wave emerging due to the splitting of the linearly polarized gyrotron radiation into the X- and O-waves was analyzed. The signal obtained after homodyne detection of scattered radiation is a result of interference of the reference signal, the quasi-steady component, and the fast oscillating component. The coefficients of reflection of the quasi-steady component, R{sub =}{sup 2}(Y), and fast oscillating component, R{sub {approx}}{sup 2}(Y), of scattered radiation are estimated. The growth of the R{sub {approx}}{sup 2}(Y) coefficient from 3.7 Multiplication-Sign 10{sup -4} to 5.2 Multiplication-Sign 10{sup -4} with increasing ECR heating power from 190 to 430 kW is found to correlate with the decrease in the energy lifetime from 1.9 to 1.46 ms. The relative density of short-wavelength fluctuations is estimated to be Left-Pointing-Angle-Bracket n{sub {approx}}{sup 2} Right-Pointing-Angle-Bracket / Left-Pointing-Angle-Bracket n{sub e}{sup 2} Right-Pointing-Angle-Bracket = 3 Multiplication-Sign 10{sup -7}. It is shown that the frequencies of short-wavelength fluctuations are in the range 10-150 kHz. The recorded short-wavelength fluctuations can be interpreted as structural turbulence, the energy of which comprises {approx}10% of the total fluctuations energy. Simulations of transport processes show that neoclassical heat fluxes are much smaller than anomalous ones. It is suggested that short-wavelength turbulence plays a decisive role in the anomalous heat transport.

MODEL-INDEPENDENT STELLAR AND PLANETARY MASSES FROM MULTI-TRANSITING EXOPLANETARY SYSTEMS

International Nuclear Information System (INIS)

Montet, Benjamin T.; Johnson, John Asher

2013-01-01

Precise exoplanet characterization requires precise classification of exoplanet host stars. The masses of host stars are commonly estimated by comparing their spectra to those predicted by stellar evolution models. However, spectroscopically determined properties are difficult to measure accurately for stars that are substantially different from the Sun, such as M-dwarfs and evolved stars. Here, we propose a new method to dynamically measure the masses of transiting planets near mean-motion resonances and their host stars by combining observations of transit timing variations with radial velocity (RV) measurements. We derive expressions to analytically determine the mass of each member of the system and demonstrate the technique on the Kepler-18 system. We compare these analytic results to numerical simulations and find that the two are consistent. We identify eight systems for which our technique could be applied if follow-up RV measurements are collected. We conclude that this analysis would be optimal for systems discovered by next-generation missions similar to TESS or PLATO, which will target bright stars that are amenable to efficient RV follow-up.

Effects of cuff inflation and deflation on pulse transit time measured from ECG and multi-wavelength PPG.

Science.gov (United States)

Liu, Jing; Li, Yao; Ding, Xiao-Rong; Dai, Wen-Xuan; Zhang, Yuan-Ting

2015-01-01

Pulse transit time (PTT), which refers to the time it takes a pulse wave to travel between two arterial sites is a promising index for cuff-less blood pressure (BP) estimation, as well as non-invasive assessment of arterial functions. However, it has not been investigated whether PTTs measured from ECG and different wavelength PPG are equally affected by the arterial status. Furthermore, comparison between the changes of different PTTs can provide enlightenment on the hardware implementation of the PTT-based BP estimation method. This work mainly studied the changes of PTTs calculated from electrocardiogram (ECG) and multi-wavelength photoplethysmogram (PPG) after exerting cuff pressure on the upper arm. A four-channel PPG acquisition system was developed to collect the multi-wavelength PPG signals of red, yellow, green and blue light at the fingertip simultaneously. Ten subjects participated in the experiment and their PTTs measured from different PPG and ECG signals before and after exerting cuff pressure were compared. This study found that within one minute after the four-minute cuff inflation and deflation process, the PTT measured from ECG and yellow PPG experienced a significant increase (p0.9) compared with that before exerting cuff pressure. This indicates that PTTs calculated from different wavelength PPG have different recoverability from smooth muscle relaxation. Another interesting finding is that the PTT calculated from ECG and yellow PPG had a strong correlation (|r|>0.7) with the time difference between yellow PPG and other PPG signals, which implies the potential of the time difference between yellow PPG and other PPGs as a complementary to PTT-based model for blood pressure estimation.

Design, fabrication, and testing of stellar coronagraphs for exoplanet imaging

Science.gov (United States)

Knight, Justin M.; Brewer, John; Hamilton, Ryan; Ward, Karen; Milster, Tom D.; Guyon, Olivier

2017-09-01

Complex-mask coronagraphs destructively interfere unwanted starlight with itself to enable direct imaging of exoplanets. This is accomplished using a focal plane mask (FPM); a FPM can be a simple occulter mask, or in the case of a complex-mask, is a multi-zoned device designed to phase-shift starlight over multiple wavelengths to create a deep achromatic null in the stellar point spread function. Creating these masks requires microfabrication techniques, yet many such methods remain largely unexplored in this context. We explore methods of fabrication of complex FPMs for a Phased-Induced Amplitude Apodization Complex-Mask Coronagraph (PIAACMC). Previous FPM fabrication efforts for PIAACMC have concentrated on mask manufacturability while modeling science yield, as well as assessing broadband wavelength operation. Moreover current fabrication efforts are concentrated on assessing coronagraph performance given a single approach. We present FPMs fabricated using several process paths, including deep reactive ion etching and focused ion beam etching using a silicon substrate. The characteristic size of the mask features is 5μm with depths ranging over 1μm. The masks are characterized for manufacturing quality using an optical interferometer and a scanning electron microscope. Initial testing is performed at the Subaru Extreme Adaptive Optics testbed, providing a baseline for future experiments to determine and improve coronagraph performance within fabrication tolerances.

Carbon Abundances In The Light Of 3D Model Stellar Atmospheres

DEFF Research Database (Denmark)

Collet, Remo

Classical spectroscopic analyses of late-type stars generally rely on the interpretation of observations with the use of stationary, one-dimensional (1D), hydrostatic model stellar atmospheres. In recent years, however, there has been significant development in the field of three-dimensional (3D......) hydrodynamic modelling of stellar atmospheres and stellar spectra. In this contribution, I describe quantitatively the impact of realistic, time-dependent, 3D hydrodynamic model atmospheres on the spectroscopic determination of carbon abundances from CH molecular lines for stars with a wide range of stellar...... parameters and compositions. I show that the differences with respect to classical analyses based on 1D models can be significant in very metal-poor stars and of the order of -0.5 to -1 dex in terms of logarithmic abundances of these important elements. I also examine the dependence of differential 3D-1D...

Nebular Continuum and Line Emission in Stellar Population Synthesis Models

Energy Technology Data Exchange (ETDEWEB)

Byler, Nell; Dalcanton, Julianne J. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Conroy, Charlie; Johnson, Benjamin D., E-mail: ebyler@astro.washington.edu [Department of Astronomy, Harvard University, Cambridge, MA 02138 (United States)

2017-05-01

Accounting for nebular emission when modeling galaxy spectral energy distributions (SEDs) is important, as both line and continuum emissions can contribute significantly to the total observed flux. In this work, we present a new nebular emission model integrated within the Flexible Stellar Population Synthesis code that computes the line and continuum emission for complex stellar populations using the photoionization code Cloudy. The self-consistent coupling of the nebular emission to the matched ionizing spectrum produces emission line intensities that correctly scale with the stellar population as a function of age and metallicity. This more complete model of galaxy SEDs will improve estimates of global gas properties derived with diagnostic diagrams, star formation rates based on H α , and physical properties derived from broadband photometry. Our models agree well with results from other photoionization models and are able to reproduce observed emission from H ii regions and star-forming galaxies. Our models show improved agreement with the observed H ii regions in the Ne iii/O ii plane and show satisfactory agreement with He ii emission from z = 2 galaxies, when including rotating stellar models. Models including post-asymptotic giant branch stars are able to reproduce line ratios consistent with low-ionization emission regions. The models are integrated into current versions of FSPS and include self-consistent nebular emission predictions for MIST and Padova+Geneva evolutionary tracks.

Stable C-band fiber laser with switchable multi-wavelength output using coupled microfiber Mach-Zehnder interferometer

Science.gov (United States)

Ahmad, H.; Jasim, A. A.

2017-07-01

A compact coupled microfiber Mach-Zehnder interferometer (CM-MZI) is proposed and experimentally demonstrated for C-band region multi-wavelength tuning and switching in a fiber laser. The CM-MZI is fabricated using a 9 μm single tapered silica optical microfiber fabricated by flame-drawing technique and exploits multi-mode interference to produce spatial mode beating and suppress mode competition of the homogeneous gain medium. The output wavelength spacing is immune to changes in the external environment, but can be changed from 1.5 nm to 1.4 nm by slightly modifying the path-length difference of the CM-MZI. The proposed laser is capable of generating single, dual, triple, quintuple, and sextuple stabilize wavelengths outputs over a range of more than 32 nm using polarization rotation (PR) and macro-bending. The lasers having a 3 dB line-width of less than ∼30 pm and peak-to-floor of about 55 dB at a pump power of 38 mW.

Real-Time and Meter-Scale Absolute Distance Measurement by Frequency-Comb-Referenced Multi-Wavelength Interferometry.

Science.gov (United States)

Wang, Guochao; Tan, Lilong; Yan, Shuhua

2018-02-07

We report on a frequency-comb-referenced absolute interferometer which instantly measures long distance by integrating multi-wavelength interferometry with direct synthetic wavelength interferometry. The reported interferometer utilizes four different wavelengths, simultaneously calibrated to the frequency comb of a femtosecond laser, to implement subwavelength distance measurement, while direct synthetic wavelength interferometry is elaborately introduced by launching a fifth wavelength to extend a non-ambiguous range for meter-scale measurement. A linearity test performed comparatively with a He-Ne laser interferometer shows a residual error of less than 70.8 nm in peak-to-valley over a 3 m distance, and a 10 h distance comparison is demonstrated to gain fractional deviations of ~3 × 10 -8 versus 3 m distance. Test results reveal that the presented absolute interferometer enables precise, stable, and long-term distance measurements and facilitates absolute positioning applications such as large-scale manufacturing and space missions.

Comparison of different Aethalometer correction schemes and a reference multi-wavelength absorption technique for ambient aerosol data

Science.gov (United States)

Saturno, Jorge; Pöhlker, Christopher; Massabò, Dario; Brito, Joel; Carbone, Samara; Cheng, Yafang; Chi, Xuguang; Ditas, Florian; Hrabě de Angelis, Isabella; Morán-Zuloaga, Daniel; Pöhlker, Mira L.; Rizzo, Luciana V.; Walter, David; Wang, Qiaoqiao; Artaxo, Paulo; Prati, Paolo; Andreae, Meinrat O.

2017-08-01

Deriving absorption coefficients from Aethalometer attenuation data requires different corrections to compensate for artifacts related to filter-loading effects, scattering by filter fibers, and scattering by aerosol particles. In this study, two different correction schemes were applied to seven-wavelength Aethalometer data, using multi-angle absorption photometer (MAAP) data as a reference absorption measurement at 637 nm. The compensation algorithms were compared to five-wavelength offline absorption measurements obtained with a multi-wavelength absorbance analyzer (MWAA), which serves as a multiple-wavelength reference measurement. The online measurements took place in the Amazon rainforest, from the wet-to-dry transition season to the dry season (June-September 2014). The mean absorption coefficient (at 637 nm) during this period was 1.8 ± 2.1 Mm-1, with a maximum of 15.9 Mm-1. Under these conditions, the filter-loading compensation was negligible. One of the correction schemes was found to artificially increase the short-wavelength absorption coefficients. It was found that accounting for the aerosol optical properties in the scattering compensation significantly affects the absorption Ångström exponent (åABS) retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct åABS, which is commonly implemented in brown carbon contribution calculations. Additionally, we found that the wavelength dependence of uncompensated Aethalometer attenuation data significantly correlates with the åABS retrieved from offline MWAA measurements.

Tunable multi-wavelength polymer laser based on a triangular-lattice photonic crystal structure

International Nuclear Information System (INIS)

Huang, Wenbin; Pu, Donglin; Qiao, Wen; Wan, Wenqiang; Liu, Yanhua; Ye, Yan; Wu, Shaolong; Chen, Linsen

2016-01-01

A continuously tunable multi-wavelength polymer laser based on a triangular-lattice photonic crystal cavity is demonstrated. The triangular-lattice resonator was initially fabricated through multiple interference exposure and was then replicated into a low refractive index polymer via UV-nanoimprinting. The blend of a blue-emitting conjugated polymer and a red-emitting one was used as the gain medium. Three periods in the scalene triangular-lattice structure yield stable tri-wavelength laser emission (625.5 nm, 617.4 nm and 614.3 nm) in six different directions. A uniformly aligned liquid crystal (LC) layer was incorporated into the cavity as the top cladding layer. Upon heating, the orientation of LC molecules and thus the effective refractive index of the lasing mode changes which continuously shifts the lasing wavelength. A maximum tuning range of 12.2 nm was observed for the lasing mode at 625.5 nm. This tunable tri-wavelength polymer laser is simple constructed and cost-effective. It may find application in the fields of biosensors and photonic integrated circuits. (paper)

Massive stellar content of some Galactic supershells

Science.gov (United States)

Kaltcheva, Nadejda; Golev, Valeri

2015-08-01

The giant Galactic H II regions provide a unique opportunity to study the OB-star influence on the surrounding interstellar matter. In this contribution, several multi-wavelength surveys (Wisconsin H-α Mapper Northern Sky Survey, Southern H-α Sky Survey Atlas, MSX Mid-IR Galactic Plane Survey, WISE All-Sky Data Release, CO survey of the Milky Way, and the Southern Galactic Plane HI Survey) are combined with available intermediate-band uvbyβ photometry to attempt a precise spatial correlation between the OB-stars and the neutral and ionized material. Our study is focused on the H I supershell GSH 305+01-24 in Centaurus, the Car OB2 supershell, the Cygnus star-forming complex and the GSH 224-01+24 shell toward the GMN 39/Seagull nebula region. We refine the massive stellar content of these star-forming fields and study the energetics of its interaction with the shells’ material.

Real-Time and Meter-Scale Absolute Distance Measurement by Frequency-Comb-Referenced Multi-Wavelength Interferometry

Directory of Open Access Journals (Sweden)

Guochao Wang

2018-02-01

Full Text Available We report on a frequency-comb-referenced absolute interferometer which instantly measures long distance by integrating multi-wavelength interferometry with direct synthetic wavelength interferometry. The reported interferometer utilizes four different wavelengths, simultaneously calibrated to the frequency comb of a femtosecond laser, to implement subwavelength distance measurement, while direct synthetic wavelength interferometry is elaborately introduced by launching a fifth wavelength to extend a non-ambiguous range for meter-scale measurement. A linearity test performed comparatively with a He–Ne laser interferometer shows a residual error of less than 70.8 nm in peak-to-valley over a 3 m distance, and a 10 h distance comparison is demonstrated to gain fractional deviations of ~3 × 10−8 versus 3 m distance. Test results reveal that the presented absolute interferometer enables precise, stable, and long-term distance measurements and facilitates absolute positioning applications such as large-scale manufacturing and space missions.

Discrete multi-wavelength tuning of a continuous wave diode-pumped Nd:GdVO4 laser

Science.gov (United States)

Nadimi, Mohammad; Waritanant, Tanant; Major, Arkady

2018-05-01

Discrete multi-wavelength operation of a diode-pumped Nd:GdVO4 laser at four different wavelengths was demonstrated using a single birefringent filter plate. The laser achieved maximum output powers of 5.92 W, 5.66 W, 5.56 W and 3.98 W at 1063.2 nm, 1070.8 nm, 1082.5 nm and 1086.2 nm wavelengths, respectively. To the best of our knowledge, apart from achieving the maximum output powers at ~1071 nm and ~1086 nm and best efficiencies at ~1071 nm, ~1083 nm and ~1086 nm wavelengths for a Nd:GdVO4 laser, this is also the largest number of wavelengths from the 4F3/2  →  4I11/2 transition that was ever obtained in a controlled manner from a single laser setup based on any of the Nd-doped laser crystals.

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.

Multi-wavelength copper vapour lasers for novel materials processing application

International Nuclear Information System (INIS)

Knowles, M.; Foster-Turner, R.; Kearsley, A.; Evans, J.

1995-01-01

The copper vapour laser (CVL) is a high average power, short pulse laser with a multi-kilohertz pulse repetition rate. The CVL laser lines (511 nm and 578 nm) combined with the good beam quality and high peak power available from these lasers allow it to operate in a unique parameter space. Consequently, it has demonstrated many unique and advantageous machining characteristics. We have also demonstrated efficient conversion of CVL radiation to other wavelengths using non-linear frequency conversion, dye lasers and Ti:AL 2 O 3 . Output powers of up to 4 W at 255 nm have been achieved by frequency doubling. The frequency doubled CVL is inherently narrow linewidth and frequency locked making it a suitable source for UV photolithography. Slope efficiencies in excess of 25 % have been achieved with CVL pumped Ti:Al 2 O 3 and dye lasers. These laser extend the wavelengths options into the red and infrared regions of the spectrum. The near diffraction limited beams from these tunable lasers can be efficiently frequency doubled into the blue and near UV. The wide range of wavelength options from the CVL enable a wide variety of materials processing and material interactions to be explored. A European consortium for Copper Laser Applications in Manufacture and Production (CLAMP) has been set up under the EUREKA scheme to coordinate the commercial and technical expertise currently available in Europe. (author)

Multi-Wavelength Studies on H2O Maser Host Galaxies J. S. Zhang ...

Indian Academy of Sciences (India)

on two projects: X-ray data analysis of individual maser source using. X-ray penetrability to explore maser host obscured AGN; multi- wavelength ... Figure 1. Adaptively smoothed three-color image in 0.3–8.0keV and spectra with fitting ... It provides a perspective to improve the accuracy of the Hubble constant H0 and to.

Comparison of different Aethalometer correction schemes and a reference multi-wavelength absorption technique for ambient aerosol data

Directory of Open Access Journals (Sweden)

J. Saturno

2017-08-01

Full Text Available Deriving absorption coefficients from Aethalometer attenuation data requires different corrections to compensate for artifacts related to filter-loading effects, scattering by filter fibers, and scattering by aerosol particles. In this study, two different correction schemes were applied to seven-wavelength Aethalometer data, using multi-angle absorption photometer (MAAP data as a reference absorption measurement at 637 nm. The compensation algorithms were compared to five-wavelength offline absorption measurements obtained with a multi-wavelength absorbance analyzer (MWAA, which serves as a multiple-wavelength reference measurement. The online measurements took place in the Amazon rainforest, from the wet-to-dry transition season to the dry season (June–September 2014. The mean absorption coefficient (at 637 nm during this period was 1.8 ± 2.1 Mm−1, with a maximum of 15.9 Mm−1. Under these conditions, the filter-loading compensation was negligible. One of the correction schemes was found to artificially increase the short-wavelength absorption coefficients. It was found that accounting for the aerosol optical properties in the scattering compensation significantly affects the absorption Ångström exponent (åABS retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct åABS, which is commonly implemented in brown carbon contribution calculations. Additionally, we found that the wavelength dependence of uncompensated Aethalometer attenuation data significantly correlates with the åABS retrieved from offline MWAA measurements.

Crystal structure of core streptavidin determined from multi-wavelength anomalous diffraction of synchrotron radiation

International Nuclear Information System (INIS)

Hendrickson, W.A.; Paehler, A.; Smith, J.L.; Satow, Y.; Merritt, E.A.; Phizackerley, R.P.

1989-01-01

A three-dimensional crystal structure of the biotin-binding core of streptavidin has been determined at 3.1-angstrom resolution. The structure was analyzed from diffraction data measured at three wavelengths from a single crystal of the selenobiotinyl complex with streptavidin. Streptavidin is a tetramer with subunits arrayed in D 2 symmetry. Each protomer is an 8-stranded β-barrel with simple up-down topology. Biotin molecules are bound at one end of each barrel. This study demonstrates the effectiveness of multi-wavelength anomalous diffraction (MAD) procedures for macromolecular crystallography and provides a basis for detailed study of biotin-avidin interactions

Mesa Isochrones and Stellar Tracks (MIST). I. Solar-scaled Models

Science.gov (United States)

Choi, Jieun; Dotter, Aaron; Conroy, Charlie; Cantiello, Matteo; Paxton, Bill; Johnson, Benjamin D.

2016-06-01

This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages (5≤slant {log}({Age}) [{year}]≤slant 10.3), masses (0.1≤slant M/{M}⊙ ≤slant 300), and metallicities (-2.0≤slant [{{Z}}/{{H}}]≤slant 0.5). The models are self-consistently and continuously evolved from the pre-main sequence (PMS) to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the PMS to the end of core helium burning for -4.0≤slant [{{Z}}/{{H}}]\\lt -2.0. We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at http://waps.cfa.harvard.edu/MIST/.

Dual-wavelength DFB quantum cascade lasers: sources for multi-species trace gas spectroscopy

Science.gov (United States)

Kapsalidis, Filippos; Shahmohammadi, Mehran; Süess, Martin J.; Wolf, Johanna M.; Gini, Emilio; Beck, Mattias; Hundt, Morten; Tuzson, Béla; Emmenegger, Lukas; Faist, Jérôme

2018-06-01

We report on the design, fabrication, and performance of dual-wavelength distributed-feedback (DFB) quantum cascade lasers (QCLs) emitting at several wavelengths in the mid-infrared (mid-IR) spectrum. In this work, two new designs are presented: for the first one, called "Neighbour" DFB, two single-mode DFB QCLs are fabricated next to each other, with minimal lateral distance, to allow efficient beam-coupling into multi-pass gas cells. In addition, the minimal distance allows either laser to be used as an integrated heater for the other, allowing to extend the tuning range of its neighbour without any electrical cross-talk. For the second design, the Vernier effect was used to realize a switchable DFB laser, with two target wavelengths which are distant by about 300 cm^{-1}. These devices are promising laser sources for Tunable Diode Laser Absorption Spectroscopy applications targeting simultaneous detection of multiple gasses, with distant spectral features, in compact and mobile setups.

Multi-wavelength study of infrared galaxies

International Nuclear Information System (INIS)

Marcillac, Delphine

2005-01-01

This thesis deals with a panchromatic study of luminous infrared galaxies (LIRGs) detected at 15 microns by ISOCAM (camera aboard ISO) and at 24 microns by MIPS (camera aboard the recently launched Spitzer satellite). These galaxies are today considered to be the Rosetta Stone of galaxy evolution since they are found to be far more numerous at high redshift and it is thought that a large part of stars seen in the local universe are born in such phases. The first part of this thesis presents a new study dedicated to dust emission of distant LIRGs in the mid-infrared range. Their dust emission has been compared to those of a local sample of LIRGs in addition to the prediction of several spectral energy distributions (SEDs) built on data available in the local universe. It has been shown that distant and local LIRGs present similar mid infrared spectral energy distribution: similar PAH bumps are detected in both local and distant LIRGs, however distant LIRGs show evidence of a stronger silicate absorption at 10 microns associated silicate grains. It also shows that distant LIRG mid infrared emission can be used together with local SEDs in order to estimate the total infrared luminosity. The second part of this thesis is dedicated to the burst of star formation and to the recent star formation history of these galaxies, which is responsible for the dust emission. This study was done thanks to a combination of high resolution spectra (R=2000 in the rest frame) obtained at VLT/FORS2 and the stellar population synthesis models called GALAXEV (Bruzual and Charlot, 2003). It has been shown that the burst of star formation has a duration of about 0.1 Gyear. About 10 % of the stellar content is formed during this burst of star formation. (author) [fr

The environment and star formation of H II region Sh2-163: a multi-wavelength study

Science.gov (United States)

Yu, Naiping; Wang, Jun-Jie; Li, Nan

2014-12-01

To investigate the environment of H II region Sh2-163 and search for evidence of triggered star formation in this region, we performed a multi-wavelength study of this H II region. Most of our data were taken from large-scale surveys: 2MASS, CGPS, MSX and SCUBA. We also made CO molecular line observations, using the 13.7-m telescope. The ionized region of Sh2-163 is detected by both the optical and radio continuum observations. Sh2-163 is partially bordered by an arc-like photodissociation region (PDR), which is coincident with the strongest optical and radio emissions, indicating interactions between the H II region and the surrounding interstellar medium. Two molecular clouds were discovered on the border of the PDR. The morphology of these two clouds suggests they are compressed by the expansion of Sh2-163. In cloud A, we found two molecular clumps. And it seems star formation in clump A2 is much more active than in clump A1. In cloud B, we found new outflow activities and massive star(s) are forming inside. Using 2MASS photometry, we tried to search for embedded young stellar object (YSO) candidates in this region. The very good agreement between CO emission, infrared shell and YSOs suggest that it is probably a star formation region triggered by the expansion of Sh2-163. We also found the most likely massive protostar related to IRAS 23314+6033.

Atomic Data for Stellar Astrophysics: from the UV to the IR

Science.gov (United States)

Wahlgren, Glenn M.

2011-01-01

The study of stars and stellar evolution relies heavily on the analysis of stellar spectra. The need for atomic line data from the ultraviolet (UV) to the infrared (lR) regions is greater now than ever. In the past twenty years, the time since the launch of the Hubble Space Telescope, great progress has been made in acquiring atomic data for UV transitions. The optical wavelength region, now expanded by progress in detector technology, continues to provide motivation for new atomic data. In addition, investments in new instrumentation for ground-based and space observatories has lead to the availability of high-quality spectra at IR wavelengths, where the need for atomic data is most critical. In this review, examples are provided of the progress made in generating atomic data for stellar studies, with a look to the future for addressing the accuracy and completeness of atomic data for anticipated needs.

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.

Helical axis stellarator equilibrium model

International Nuclear Information System (INIS)

Koniges, A.E.; Johnson, J.L.

1985-02-01

An asymptotic model is developed to study MHD equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two-dimensional generalized partial differential equation of the Grad-Shafranov type. A stellarator-expansion free-boundary equilibrium code is modified to solve the helical-axis equations. The expansion model is used to predict the equilibrium properties of Asperators NP-3 and NP-4. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift

Many faces of compact objects: distance, optical extinction and multi-wavelength behaviour

International Nuclear Information System (INIS)

Corbel, Stephane

1999-01-01

This thesis is devoted to a multi-wavelength study of accretion-ejection phenomena around compact stars (black holes and neutron stars). The first part of this manuscript describes problems related to the determination of the distance and the optical extinction to compact objects - fundamental parameters for the evaluation of the energy budget of these systems. To this end, the structure and the dynamics of the Galaxy are studied by observations of the atomic and molecular gas along the line of sight to compact stars. This method leads to the first evaluation of the distance to two Soft Gamma Repeaters: SGR 1806-20 and SGR 1627-41. We then draw some conclusions on the nature of these sources of recurrent gamma-ray bursts. The above method is then applied to two X-ray binaries: Cir X-1 and GX 339-4. In the second part of this thesis, we present a multi-wavelength study of the Galactic black hole candidate GX 339-4. We first discuss the characteristics of the radio emission from GX 339-4. In 1998, GX 339-4 underwent a transition to a soft-high X-ray state and observations in three wavelength regimes (radio, soft and hard X-rays) revealed new patterns of behaviour. This allowed us to constrain the region of origin of the radio emission (a compact jet) in GX 339-4 and allowed a better understanding of the physical coupling between accretion and ejection in GX 339-4. An analogy with the black hole candidate Cyg X-1 is then presented. Finally, these results are discussed in the context of micro-quasars and active galactic nuclei in order to gain a deeper insight into the accretion-ejection coupling around compact objects. (author) [fr

Characterizing Extragalactic Star Formation with GALEX Legacy Photometric Analysis of UV-Bright Stellar Complexes

Science.gov (United States)

Thilker, David

At the close of nearly a decade of observing, GALEX has accumulated an unprecedented archive of ultraviolet (UV) images revealing both the scope and intricacy of star formation (SF) in many thousands of galaxies inhabiting the local universe. If the observed hierarchical SF morphology can be quantified systematically, and physically interpreted with multi-wavelength ancillary data and modeling, then the low redshift GALEX legacy will approach completion. However, the GALEX GR6 pipeline database contains a highly incomplete census of young stellar complexes even for very well-studied galaxies. We propose to apply a dedicated photometry algorithm that has been optimized for measuring the properties of irregularly shaped sources in crowded galaxy images containing spatially variant, diffuse intra-clump emission. Structures will be selected in the UV, but we will compile UV-visible-MIR SEDs for each detection utilizing Pan-STARRS1+SDSS and WISE data. These SEDs will then be fit using population-synthesis models to derive estimated stellar mass, age, and extinction. Processing will be completed for the entire diameter-limited GALEX Large Galaxy Atlas (GLGA) sample of 20,000+ galaxies, at a variety of standardized spatial resolutions. Although the precise categorization of the cataloged substructures will depend on galaxy distance, the outcome of our analysis will be a catalog similar to the stellar association surveys of past decades for very nearby galaxies based on resolved stars (e.g. van den Bergh 1964, Hodge 1986, Efremov et al. 1987), except that our investigation will probe a galaxy sample of dramatically larger size using the integrated UV light from such groupings of young stars. Our algorithm is multi-scale in nature and will thus preserve the hierarchical properties of the stellar distribution, by linking sub-clumps to their larger-scale parent feature(s). The resulting database will be a fundamental resource for follow-up multi-wavelength studies probing SF

A Multi-Wavelength Opto-Electronic Patch Sensor to Effectively Detect Physiological Changes against Human Skin Types.

Science.gov (United States)

Yan, Liangwen; Hu, Sijung; Alzahrani, Abdullah; Alharbi, Samah; Blanos, Panagiotis

2017-06-21

Different skin pigments among various ethnic group people have an impact on spectrometric illumination on skin surface. To effectively capture photoplethysmographic (PPG) signals, a multi-wavelength opto-electronic patch sensor (OEPS) together with a schematic architecture of electronics were developed to overcome the drawback of present PPG sensor. To perform a better in vivo physiological measurement against skin pigments, optimal illuminations in OEPS, whose wavelength is compatible with a specific skin type, were optimized to capture a reliable physiological sign of heart rate (HR). A protocol was designed to investigate an impact of five skin types in compliance with Von Luschan's chromatic scale. Thirty-three healthy male subjects between the ages of 18 and 41 were involved in the protocol implemented by means of the OEPS system. The results show that there is no significant difference ( p: 0.09, F = 3.0) in five group tests with the skin types across various activities throughout a series of consistent measurements. The outcome of the present study demonstrates that the OEPS, with its multi-wavelength illumination characteristics, could open a path in multiple applications of different ethnic groups with cost-effective health monitoring.

A Multi-Wavelength Opto-Electronic Patch Sensor to Effectively Detect Physiological Changes against Human Skin Types

Directory of Open Access Journals (Sweden)

Liangwen Yan

2017-06-01

Full Text Available Different skin pigments among various ethnic group people have an impact on spectrometric illumination on skin surface. To effectively capture photoplethysmographic (PPG signals, a multi-wavelength opto-electronic patch sensor (OEPS together with a schematic architecture of electronics were developed to overcome the drawback of present PPG sensor. To perform a better in vivo physiological measurement against skin pigments, optimal illuminations in OEPS, whose wavelength is compatible with a specific skin type, were optimized to capture a reliable physiological sign of heart rate (HR. A protocol was designed to investigate an impact of five skin types in compliance with Von Luschan’s chromatic scale. Thirty-three healthy male subjects between the ages of 18 and 41 were involved in the protocol implemented by means of the OEPS system. The results show that there is no significant difference (p: 0.09, F = 3.0 in five group tests with the skin types across various activities throughout a series of consistent measurements. The outcome of the present study demonstrates that the OEPS, with its multi-wavelength illumination characteristics, could open a path in multiple applications of different ethnic groups with cost-effective health monitoring.

A multi-wavelength (u.v. to visible) laser system for early detection of oral cancer

Science.gov (United States)

Najda, S. P.; Perlin, P.; Leszczyński, M.; Slight, T. J.; Meredith, W.; Schemmann, M.; Moseley, H.; Woods, J. A.; Valentine, R.; Kalra, S.; Mossey, P.; Theaker, E.; Macluskey, M.; Mimnagh, G.; Mimnagh, W.

2015-03-01

A multi-wavelength (360nm - 440nm), real-time Photonic Cancer Detector (PCD) optical system based on GaN semiconductor laser technology is outlined. A proof of concept using blue laser technology for early detection of cancer has already been tested and proven for esophageal cancer. This concept is expanded to consider a wider range of wavelengths and the PCD will initially be used for early diagnosis of oral cancers. The PCD creates an image of the oral cavity (broad field white light detection) and maps within the oral cavity any suspicious lesions with high sensitivity using a narrow field tunable detector.

Multi-band high resolution spectroscopy rules out the hot Jupiter BD+20 1790b. First data from the GIARPS Commissioning

Science.gov (United States)

Carleo, I.; Benatti, S.; Lanza, A. F.; Gratton, R.; Claudi, R.; Desidera, S.; Mace, G. N.; Messina, S.; Sanna, N.; Sissa, E.; Ghedina, A.; Ghinassi, F.; Guerra, J.; Harutyunyan, A.; Micela, G.; Molinari, E.; Oliva, E.; Tozzi, A.; Baffa, C.; Baruffolo, A.; Bignamini, A.; Buchschacher, N.; Cecconi, M.; Cosentino, R.; Endl, M.; Falcini, G.; Fantinel, D.; Fini, L.; Fugazza, D.; Galli, A.; Giani, E.; González, C.; González-Álvarez, E.; González, M.; Hernandez, N.; Hernandez Diaz, M.; Iuzzolino, M.; Kaplan, K. F.; Kidder, B. T.; Lodi, M.; Malavolta, L.; Maldonado, J.; Origlia, L.; Ventura, H. Perez; Puglisi, A.; Rainer, M.; Riverol, L.; Riverol, C.; San Juan, J.; Scuderi, S.; Seemann, U.; Sokal, K. R.; Sozzetti, A.; Sozzi, M.

2018-05-01

Context. Stellar activity is currently challenging the detection of young planets via the radial velocity (RV) technique. Aims: We attempt to definitively discriminate the nature of the RV variations for the young active K5 star BD+20 1790, for which visible (VIS) RV measurements show divergent results on the existence of a substellar companion. Methods: We compare VIS data with high precision RVs in the near-infrared (NIR) range by using the GIANO-B and IGRINS spectrographs. In addition, we present for the first time simultaneous VIS-NIR observations obtained with GIARPS (GIANO-B and HARPS-N) at Telescopio Nazionale Galileo (TNG). Orbital RVs are achromatic, so the RV amplitude does not change at different wavelengths, while stellar activity induces wavelength-dependent RV variations, which are significantly reduced in the NIR range with respect to the VIS. Results: The NIR radial velocity measurements from GIANO-B and IGRINS show an average amplitude of about one quarter with respect to previously published VIS data, as expected when the RV jitter is due to stellar activity. Coeval multi-band photometry surprisingly shows larger amplitudes in the NIR range, explainable with a mixture of cool and hot spots in the same active region. Conclusions: In this work, the claimed massive planet around BD+20 1790 is ruled out by our data. We exploited the crucial role of multi-wavelength spectroscopy when observing young active stars: thanks to facilities like GIARPS that provide simultaneous observations, this method can reach its maximum potential.

Adaptation of an aerosol retrieval algorithm using multi-wavelength and multi-pixel information of satellites (MWPM) to GOSAT/TANSO-CAI

Science.gov (United States)

Hashimoto, M.; Takenaka, H.; Higurashi, A.; Nakajima, T.

2017-12-01

Aerosol in the atmosphere is an important constituent for determining the earth's radiation budget, so the accurate aerosol retrievals from satellite is useful. We have developed a satellite remote sensing algorithm to retrieve the aerosol optical properties using multi-wavelength and multi-pixel information of satellite imagers (MWPM). The method simultaneously derives aerosol optical properties, such as aerosol optical thickness (AOT), single scattering albedo (SSA) and aerosol size information, by using spatial difference of wavelegths (multi-wavelength) and surface reflectances (multi-pixel). The method is useful for aerosol retrieval over spatially heterogeneous surface like an urban region. In this algorithm, the inversion method is a combination of an optimal method and smoothing constraint for the state vector. Furthermore, this method has been combined with the direct radiation transfer calculation (RTM) numerically solved by each iteration step of the non-linear inverse problem, without using look up table (LUT) with several constraints. However, it takes too much computation time. To accelerate the calculation time, we replaced the RTM with an accelerated RTM solver learned by neural network-based method, EXAM (Takenaka et al., 2011), using Rster code. And then, the calculation time was shorternd to about one thouthandth. We applyed MWPM combined with EXAM to GOSAT/TANSO-CAI (Cloud and Aerosol Imager). CAI is a supplement sensor of TANSO-FTS, dedicated to measure cloud and aerosol properties. CAI has four bands, 380, 674, 870 and 1600 nm, and observes in 500 meters resolution for band1, band2 and band3, and 1.5 km for band4. Retrieved parameters are aerosol optical properties, such as aerosol optical thickness (AOT) of fine and coarse mode particles at a wavelenth of 500nm, a volume soot fraction in fine mode particles, and ground surface albedo of each observed wavelength by combining a minimum reflectance method and Fukuda et al. (2013). We will show

Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

Energy Technology Data Exchange (ETDEWEB)

Andrews, Brett H. [PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Weinberg, David H.; Schönrich, Ralph; Johnson, Jennifer A., E-mail: andrewsb@pitt.edu [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)

2017-02-01

Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]–[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]–[Fe/H] unlike the observed bimodality (separate high- α and low- α sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]–[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of α -elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.

Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

International Nuclear Information System (INIS)

Andrews, Brett H.; Weinberg, David H.; Schönrich, Ralph; Johnson, Jennifer A.

2017-01-01

Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]–[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]–[Fe/H] unlike the observed bimodality (separate high- α and low- α sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]–[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of α -elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.

Multi-wavelength spectrophotometric analysis for detection of xanthochromia in cerebrospinal fluid and accuracy for the diagnosis of subarachnoid hemorrhage.

Science.gov (United States)

Smith, Andrew; Wu, Alan H B; Lynch, Kara L; Ko, Nerissa; Grenache, David G

2013-09-23

Cerebrospinal fluid (CSF) was examined for bilirubin, an important indicator for diagnosis of subarachnoid hemorrhage (SAH). A multi-wavelength (340, 415, and 460 nm) spectrophotometric assay was developed for the quantitative measurement of bilirubin in CSF, enabling the mathematical correction for absorbance of hemoglobin and proteins. Bilirubin and hemoglobin results were correlated to HPLC and a standard colorimetric assay, respectively. A subset of samples was sent for an absorbance reading at 450 nm following baseline correction. The multi-wavelength bilirubin assay was validated on 70 patients with confirmed SAH and 70 patients with neurologic symptoms who ruled out for SAH. The multi-wavelength spectrophometric assay demonstrated no interferences due to proteins (albumin) up to 30 g/l or oxyhemoglobin up to 260 mg/l. The assay limit of detection was 0.2 mg/l, linear to 20 mg/l, and CVs ranged from 1 to 6% at bilirubin concentrations of 0.84 and 2.1mg/l. The spectrophotometric assay correlated to HPLC and the colorimetric assay for bilirubin and hemoglobin, respectively. Results also correlated to the absorbance method (with removal of samples with high hemoglobin and proteins). The area under the ROC curve for diagnosis of SAH was 0.971 and 0.954 for the HPLC and spectrophotometric assay, respectively. At a cutoff of 0.2mg/l, the clinical specificity was 100% for both assays, and the clinical sensitivity was 94.3% and 88.6% for SAH for the HPLC and spectrophotometric asays, respectively. The multi-wavelength spectrophotometric assay is an objective alternative to visual inspection, HPLC, and absorbance for CSF bilirubin. Copyright © 2013 Elsevier B.V. All rights reserved.

High-angular-resolution stellar imaging with occultations from the Cassini spacecraft - III. Mira

Science.gov (United States)

Stewart, Paul N.; Tuthill, Peter G.; Nicholson, Philip D.; Hedman, Matthew M.

2016-04-01

We present an analysis of spectral and spatial data of Mira obtained by the Cassini spacecraft, which not only observed the star's spectra over a broad range of near-infrared wavelengths, but was also able to obtain high-resolution spatial information by watching the star pass behind Saturn's rings. The observed spectral range of 1-5 microns reveals the stellar atmosphere in the crucial water-bands which are unavailable to terrestrial observers, and the simultaneous spatial sampling allows the origin of spectral features to be located in the stellar environment. Models are fitted to the data, revealing the spectral and spatial structure of molecular layers surrounding the star. High-resolution imagery is recovered revealing the layered and asymmetric nature of the stellar atmosphere. The observational data set is also used to confront the state-of-the-art cool opacity-sampling dynamic extended atmosphere models of Mira variables through a detailed spectral and spatial comparison, revealing in general a good agreement with some specific departures corresponding to particular spectral features.

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

Multi-photon ionization of atoms in intense short-wavelength radiation fields

Science.gov (United States)

Meyer, Michael

2015-05-01

The unprecedented characteristics of XUV and X-ray Free Electron Lasers (FELs) have stimulated numerous investigations focusing on the detailed understanding of fundamental photon-matter interactions in atoms and molecules. In particular, the high intensities (up to 106 W/cm2) giving rise to non-linear phenomena in the short wavelength regime. The basic phenomenology involves the production of highly charged ions via electron emission to which both sequential and direct multi-photon absorption processes contribute. The detailed investigation of the role and relative weight of these processes under different conditions (wavelength, pulse duration, intensity) is the key element for a comprehensive understanding of the ionization dynamics. Here the results of recent investigations are presented, performed at the FELs in Hamburg (FLASH) and Trieste (FERMI) on atomic systems with electronic structures of increasing complexity (Ar, Ne and Xe). Mainly, electron spectroscopy is used to obtain quantitative information about the relevance of various multi-photon ionization processes. For the case of Ar, a variety of processes including above threshold ionization (ATI) from 3p and 3s valence shells, direct 2p two-photon ionization and resonant 2p-4p two-photon excitations were observed and their role was quantitatively determined comparing the experimental ionization yields to ab-initio calculations of the cross sections for the multi-photon processes. Using Ar as a benchmark to prove the reliability of the combined experimental and theoretical approach, the more complex and intriguing case of Xe was studied. Especially, the analysis of the two-photon ATI from the Xe 4d shell reveals new insight into the character of the 4d giant resonance, which was unresolved in the linear one-photon regime. Finally, the influence of intense XUV radiation to the relaxation dynamics of the Ne 2s-3p resonance was investigated by angle-resolved electron spectroscopy, especially be observing

Systematic problems with using dark matter simulations to model stellar halos

International Nuclear Information System (INIS)

Bailin, Jeremy; Bell, Eric F.; Valluri, Monica; Stinson, Greg S.; Debattista, Victor P.; Couchman, H. M. P.; Wadsley, James

2014-01-01

The limits of available computing power have forced models for the structure of stellar halos to adopt one or both of the following simplifying assumptions: (1) stellar mass can be 'painted' onto dark matter (DM) particles in progenitor satellites; (2) pure DM simulations that do not form a luminous galaxy can be used. We estimate the magnitude of the systematic errors introduced by these assumptions using a controlled set of stellar halo models where we independently vary whether we look at star particles or painted DM particles, and whether we use a simulation in which a baryonic disk galaxy forms or a matching pure DM simulation that does not form a baryonic disk. We find that the 'painting' simplification reduces the halo concentration and internal structure, predominantly because painted DM particles have different kinematics from star particles even when both are buried deep in the potential well of the satellite. The simplification of using pure DM simulations reduces the concentration further, but increases the internal structure, and results in a more prolate stellar halo. These differences can be a factor of 1.5-7 in concentration (as measured by the half-mass radius) and 2-7 in internal density structure. Given this level of systematic uncertainty, one should be wary of overinterpreting differences between observations and the current generation of stellar halo models based on DM-only simulations when such differences are less than an order of magnitude.

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

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.

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...

Multiplicity in Early Stellar Evolution

Science.gov (United States)

Reipurth, B.; Clarke, C. J.; Boss, A. P.; Goodwin, S. P.; Rodríguez, L. F.; Stassun, K. G.; Tokovinin, A.; Zinnecker, H.

Observations from optical to centimeter wavelengths have demonstrated that multiple systems of two or more bodies is the norm at all stellar evolutionary stages. Multiple systems are widely agreed to result from the collapse and fragmentation of cloud cores, despite the inhibiting influence of magnetic fields. Surveys of class 0 protostars with millimeter interferometers have revealed a very high multiplicity frequency of about 2/3, even though there are observational difficulties in resolving close protobinaries, thus supporting the possibility that all stars could be born in multiple systems. Near-infrared adaptive optics observations of class I protostars show a lower binary frequency relative to the class 0 phase, a declining trend that continues through the class II/III stages to the field population. This loss of companions is a natural consequence of dynamical interplay in small multiple systems, leading to ejection of members. We discuss observational consequences of this dynamical evolution, and its influence on circumstellar disks, and we review the evolution of circumbinary disks and their role in defining binary mass ratios. Special attention is paid to eclipsing PMS binaries, which allow for observational tests of evolutionary models of early stellar evolution. Many stars are born in clusters and small groups, and we discuss how interactions in dense stellar environments can significantly alter the distribution of binary separations through dissolution of wider binaries. The binaries and multiples we find in the field are the survivors of these internal and external destructive processes, and we provide a detailed overview of the multiplicity statistics of the field, which form a boundary condition for all models of binary evolution. Finally, we discuss various formation mechanisms for massive binaries, and the properties of massive trapezia.

Old star clusters: Bench tests of low mass stellar models

Directory of Open Access Journals (Sweden)

Salaris M.

2013-03-01

Full Text Available Old star clusters in the Milky Way and external galaxies have been (and still are traditionally used to constrain the age of the universe and the timescales of galaxy formation. A parallel avenue of old star cluster research considers these objects as bench tests of low-mass stellar models. This short review will highlight some recent tests of stellar evolution models that make use of photometric and spectroscopic observations of resolved old star clusters. In some cases these tests have pointed to additional physical processes efficient in low-mass stars, that are not routinely included in model computations. Moreover, recent results from the Kepler mission about the old open cluster NGC6791 are adding new tight constraints to the models.

Multi-wavelength observations of novae in outburst

International Nuclear Information System (INIS)

Starrfield, S.; Arizona State Univ., Tempe, AZ

1989-01-01

This review serves as the introduction to the observational studies of novae and I will mention a number of results that will be emphasized by other reviewers. Therefore, I will try to provide the physical framework for multi-wavelength observations as applied to studies of novae. I divide the outburst into phases based on the physical effects that are occurring at that time. The first phase is the rise to bolometric maximum and occurs on a convective time scale. The second phase is the rise to visual maximum and occurs on the time scale for the envelope to expand to ∼10 12 cm. The third phase is the time when the nova is emitting at constant bolometric luminosity, but declining optical magnitude, and it lasts until most of the accreted material has been either exhausted or eroded from the surface of the white dwarf. The fourth and final phase is the return is the return to quiescence (turn-off phase) and it occurs at the time that nuclear burning is ending. I will discuss each of these phases in turn and end with a discussion. 36 refs

Multi-wavelength lasers using AWGs

NARCIS (Netherlands)

Besten, den J.H.

2003-01-01

Multiwavelength lasers using AWGs can be used as digitally tunable lasers with simple channel selection, and for generating multiple wavelengths simultanously. In this paper a number of different configurations is reviewed.

Observation of Asian dust properties by using multi-wavelength LIDAR system at anmyeon island, Korea

International Nuclear Information System (INIS)

Choi, Sung Chul; Ko, Do Kyeoung; Lee, Jong Min; Kim, Young Joon; Noh, Young Min

2004-01-01

The Asian dust affect climate both directly and indirectly because they act as effective ice nuclei and forms ice cloud. However, little is known about spatial distribution and trajectory because few measurement data are available in the free troposphere over East Asia, where a large amount of Asian dust are transported form desert regions in Asian continent. LIDAR system is an effective tool for remotely measuring the vertical distribution of aerosol optical properties. For measurement of Asian dust optical properties, a multi-wavelength LIDAR system developed by the Advanced Environment Monitoring Research Center (ADEMRC), Gwangju Institute Science and Technology (GIST), Korea. This paper presents the results of ground-based multi-wavelength LIDAR measurements of the Asian dust aerosol over Anmyeon Island (36.40N, 126.10E) during the spring of 2004. To discriminate between Asian dust and cloud, depolarization ratio is useful for the detection of these particles and the LIDAR ratio. Also, we discuss the relationship between LIDAR ratio and other optical properties from LIDAR measurement, i.e., the depolarization ratio, aerosol extinction coefficient and LIDAR ratio

The EDGE-CALIFA survey: validating stellar dynamical mass models with CO kinematics

Science.gov (United States)

Leung, Gigi Y. C.; Leaman, Ryan; van de Ven, Glenn; Lyubenova, Mariya; Zhu, Ling; Bolatto, Alberto D.; Falcón-Barroso, Jesus; Blitz, Leo; Dannerbauer, Helmut; Fisher, David B.; Levy, Rebecca C.; Sanchez, Sebastian F.; Utomo, Dyas; Vogel, Stuart; Wong, Tony; Ziegler, Bodo

2018-06-01

Deriving circular velocities of galaxies from stellar kinematics can provide an estimate of their total dynamical mass, provided a contribution from the velocity dispersion of the stars is taken into account. Molecular gas (e.g. CO), on the other hand, is a dynamically cold tracer and hence acts as an independent circular velocity estimate without needing such a correction. In this paper, we test the underlying assumptions of three commonly used dynamical models, deriving circular velocities from stellar kinematics of 54 galaxies (S0-Sd) that have observations of both stellar kinematics from the Calar Alto Legacy Integral Field Area (CALIFA) survey, and CO kinematics from the Extragalactic Database for Galaxy Evolution (EDGE) survey. We test the asymmetric drift correction (ADC) method, as well as Jeans, and Schwarzschild models. The three methods each reproduce the CO circular velocity at 1Re to within 10 per cent. All three methods show larger scatter (up to 20 per cent) in the inner regions (R < 0.4Re) that may be due to an increasingly spherical mass distribution (which is not captured by the thin disc assumption in ADC), or non-constant stellar M/L ratios (for both the JAM and Schwarzschild models). This homogeneous analysis of stellar and gaseous kinematics validates that all three models can recover Mdyn at 1Re to better than 20 per cent, but users should be mindful of scatter in the inner regions where some assumptions may break down.

Multi-wavelength Brillouin Raman erbium-doped fiber laser generation in a linear cavity

International Nuclear Information System (INIS)

Shirazi, M R; Harun, S W; Ahmad, H

2014-01-01

A multi-wavelength Brillouin Raman erbium-doped fiber laser is proposed and demonstrated. The setup uses a 7.7 km dispersion compensating fiber simultaneously as the Brillouin and Raman nonlinear gain media and operates in conjunction with a 3 m erbium-doped fiber as the linear gain medium. At a Brillouin pump (BP) wavelength of 1530 nm, where Raman and erbium gains overlap each other, 34 Brillouin Stokes lines having line spacing of 0.075 nm are created by using a Raman pump power of only 24.1 dBm, an erbium pump power of about 22.1 dBm, and a BP power of 6.5 dBm in the proposed linear cavity. The system is highly efficient and is able to generate many comparable peak-power lines at a low pump power. (paper)

Quantitative structural modeling on the wavelength interval (Δλ) in synchronous fluorescence spectroscopy

Science.gov (United States)

Samari, Fayezeh; Yousefinejad, Saeed

2017-11-01

Emission fluorescence spectroscopy has an extremely restricted scope of application to analyze of complex mixtures since its selectivity is reduced by the extensive spectral overlap. Synchronous fluorescence spectroscopy (SFS) is a technique enables us to analyze complex mixtures with overlapped emission and/or excitation spectra. The difference of excitation and emission wavelength of compounds (interval wavelength or Δλ) is an important characteristic in SFS. Thus a multi-parameter model was constructed to predict Δλ in 63 fluorescent compounds and the regression coefficient in training set, cross validation and test set were 0.88, 0.85 and 0.91 respectively. Furthermore, the applicability and validity of model were evaluated using different statistical methods such as y-scrambling and applicability domain. It was concluded that increasing average valence connectivity, number of Al2-NH functional group and Geary autocorrelation (lag 4) with electronegative weights can lead to increasing Δλ in the fluorescent compounds. The current study obtained an insight into the structural properties of compounds effective on their Δλ as an important parameter in SFS.

Improved methods for the measurement and analysis of stellar magnetic fields

Science.gov (United States)

Saar, Steven H.

1988-01-01

The paper presents several improved methods for the measurement of magnetic fields on cool stars which take into account simple radiative transfer effects and the exact Zeeman patterns. Using these methods, high-resolution, low-noise data can be fitted with theoretical line profiles to determine the mean magnetic field strength in stellar active regions and a model-dependent fraction of the stellar surface (filling factor) covered by these regions. Random errors in the derived field strength and filling factor are parameterized in terms of signal-to-noise ratio, wavelength, spectral resolution, stellar rotation rate, and the magnetic parameters themselves. Weak line blends, if left uncorrected, can have significant systematic effects on the derived magnetic parameters, and thus several methods are developed to compensate partially for them. The magnetic parameters determined by previous methods likely have systematic errors because of such line blends and because of line saturation effects. Other sources of systematic error are explored in detail. These sources of error currently make it difficult to determine the magnetic parameters of individual stars to better than about + or - 20 percent.

The Young Massive Stellar Cluster Sandage-96 after the Explosion of SN 2004DJ in NGC 2403

Science.gov (United States)

Vinko, J.; Sarneczky, K.; Balog, Z.; Immler, S.; Sugerman, B.; Brown, P. J.; Misselt, K.; Szabo, Gy. M.; Klagyivik, P.; Kun, M.;

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.

Study of ocean red tide multi-parameter monitoring technology based on double-wavelength airborne lidar system

Science.gov (United States)

Lin, Hong; Wang, Xinming; Liang, Kun

2010-10-01

For monitoring and forecasting of the ocean red tide in real time, a marine environment monitoring technology based on the double-wavelength airborne lidar system is proposed. An airborne lidar is father more efficient than the traditional measure technology by the boat. At the same time, this technology can detect multi-parameter about the ocean red tide by using the double-wavelength lidar.It not only can use the infrared laser to detect the scattering signal under the water and gain the information about the red tise's density and size, but also can use the blue-green laser to detect the Brillouin scattering signal and deduce the temperature and salinity of the seawater.The red tide's density detecting model is firstly established by introducing the concept about the red tide scattering coefficient based on the Mie scattering theory. From the Brillouin scattering theory, the relationship about the blue-green laser's Brillouin scattering frequency shift value and power value with the seawater temperature and salinity is found. Then, the detecting mode1 of the saewater temperature and salinity can be established. The value of the red tide infrared scattering signal is evaluated by the simulation, and therefore the red tide particles' density can be known. At the same time, the blue-green laser's Brillouin scattering frequency shift value and power value are evaluated by simulating, and the temperature and salinity of the seawater can be known. Baed on the multi-parameters, the ocean red tide's growth can be monitored and forecasted.

SED Modeling of 20 Massive Young Stellar Objects

Science.gov (United States)

Tanti, Kamal Kumar

In this paper, we present the spectral energy distributions (SEDs) modeling of twenty massive young stellar objects (MYSOs) and subsequently estimated different physical and structural/geometrical parameters for each of the twenty central YSO outflow candidates, along with their associated circumstellar disks and infalling envelopes. The SEDs for each of the MYSOs been reconstructed by using 2MASS, MSX, IRAS, IRAC & MIPS, SCUBA, WISE, SPIRE and IRAM data, with the help of a SED Fitting Tool, that uses a grid of 2D radiative transfer models. Using the detailed analysis of SEDs and subsequent estimation of physical and geometrical parameters for the central YSO sources along with its circumstellar disks and envelopes, the cumulative distribution of the stellar, disk and envelope parameters can be analyzed. This leads to a better understanding of massive star formation processes in their respective star forming regions in different molecular clouds.

A LARGE, MASSIVE, ROTATING DISK AROUND AN ISOLATED YOUNG STELLAR OBJECT

International Nuclear Information System (INIS)

Quanz, Sascha P.; Beuther, Henrik; Steinacker, Juergen; Linz, Hendrik; Krause, Oliver; Henning, Thomas; Birkmann, Stephan M.; Zhang Qizhou

2010-01-01

We present multi-wavelength observations and a radiative transfer model of a newly discovered massive circumstellar disk of gas and dust which is one of the largest disks known today. Seen almost edge-on, the disk is resolved in high-resolution near-infrared (NIR) images and appears as a dark lane of high opacity intersecting a bipolar reflection nebula. Based on molecular line observations, we estimate the distance to the object to be 3.5 kpc. This leads to a size for the dark lane of ∼10,500 AU but due to shadowing effects the true disk size could be smaller. In Spitzer/IRAC 3.6 μm images, the elongated shape of the bipolar reflection nebula is still preserved and the bulk of the flux seems to come from disk regions that can be detected due to the slight inclination of the disk. At longer IRAC wavelengths, the flux is mainly coming from the central regions penetrating directly through the dust lane. Interferometric observations of the dust continuum emission at millimeter wavelengths with the Submillimeter Array confirm this finding as the peak of the unresolved millimeter-emission coincides perfectly with the peak of the Spitzer/IRAC 5.8 μm flux and the center of the dark lane seen in the NIR images. Simultaneously acquired CO data reveal a molecular outflow along the northern part of the reflection nebula which seems to be the outflow cavity. An elongated gaseous disk component is also detected and shows signs of rotation. The emission is perpendicular to the molecular outflow and thus parallel to but even more extended than the dark lane in the NIR images. Based on the dust continuum and the CO observations, we estimate a disk mass of up to a few solar masses depending on the underlying assumptions. Whether the disk-like structure is an actual accretion disk or rather a larger-scale flattened envelope or pseudodisk is difficult to discriminate with the current data set. The existence of HCO + /H 13 CO + emission proves the presence of dense gas in the disk

MULTI-WAVELENGTH CHARACTERIZATION OF STELLAR FLARES ON LOW-MASS STARS USING SDSS AND 2MASS TIME-DOMAIN SURVEYS

Energy Technology Data Exchange (ETDEWEB)

Davenport, James R. A.; Becker, Andrew C.; Kowalski, Adam F.; Hawley, Suzanne L.; Schmidt, Sarah J.; Hilton, Eric J. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Sesar, Branimir [Division of Physics, Mathematics and Astronomy, Caltech, Pasadena, CA 91125 (United States); Cutri, Roc, E-mail: jrad@astro.washington.edu [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States)

2012-03-20

We present the first rates of flares from M dwarf stars in both red optical and near-infrared (NIR) filters. We have studied {approx}50,000 M dwarfs from the Sloan Digital Sky Survey (SDSS) Stripe 82 area and 1321 M dwarfs from the Two Micron All Sky Survey (2MASS) Calibration Scan Point Source Working Database that overlap SDSS imaging fields. We assign photometric spectral types from M0 to M6 using (r - i) and (i - z) colors for every star in our sample. Stripe 82 stars each have 50-100 epochs of data, while 2MASS Calibration stars have {approx}1900 epochs. From these data we estimate the observed rates and theoretical detection thresholds for flares in eight photometric bands as a function of spectral type. Optical flare rates are found to be in agreement with previous studies, while the frequency per hour of NIR flare detections is found to be more than two orders of magnitude lower. An excess of small-amplitude flux increases in all bands exhibits a power-law distribution, which we interpret as the result of flares below our detection thresholds. In order to investigate the recovery efficiency for flares in each filter, we extend a two-component flare model into the NIR. Quiescent M0-M6 spectral templates were used with the model to predict the photometric response of flares from u to K{sub s} . We determine that red optical filters are sensitive to flares with u-band amplitudes {approx}>2 mag, and NIR filters to flares with {Delta}u {approx}> 4.5 mag. Our model predicts that M0 stars have the best color contrast for J-band detections, but M4-M6 stars should yield the highest rate of NIR flares with amplitudes of {Delta}J {>=} 0.01 mag. Characterizing flare rates and photometric variations at longer wavelengths is important for predicting the signatures of M dwarf variability in next-generation surveys, and we discuss their impact on surveys such as the Large Synoptic Survey Telescope.

MULTI-WAVELENGTH CHARACTERIZATION OF STELLAR FLARES ON LOW-MASS STARS USING SDSS AND 2MASS TIME-DOMAIN SURVEYS

International Nuclear Information System (INIS)

Davenport, James R. A.; Becker, Andrew C.; Kowalski, Adam F.; Hawley, Suzanne L.; Schmidt, Sarah J.; Hilton, Eric J.; Sesar, Branimir; Cutri, Roc

2012-01-01

We present the first rates of flares from M dwarf stars in both red optical and near-infrared (NIR) filters. We have studied ∼50,000 M dwarfs from the Sloan Digital Sky Survey (SDSS) Stripe 82 area and 1321 M dwarfs from the Two Micron All Sky Survey (2MASS) Calibration Scan Point Source Working Database that overlap SDSS imaging fields. We assign photometric spectral types from M0 to M6 using (r – i) and (i – z) colors for every star in our sample. Stripe 82 stars each have 50-100 epochs of data, while 2MASS Calibration stars have ∼1900 epochs. From these data we estimate the observed rates and theoretical detection thresholds for flares in eight photometric bands as a function of spectral type. Optical flare rates are found to be in agreement with previous studies, while the frequency per hour of NIR flare detections is found to be more than two orders of magnitude lower. An excess of small-amplitude flux increases in all bands exhibits a power-law distribution, which we interpret as the result of flares below our detection thresholds. In order to investigate the recovery efficiency for flares in each filter, we extend a two-component flare model into the NIR. Quiescent M0-M6 spectral templates were used with the model to predict the photometric response of flares from u to K s . We determine that red optical filters are sensitive to flares with u-band amplitudes ∼>2 mag, and NIR filters to flares with Δu ∼> 4.5 mag. Our model predicts that M0 stars have the best color contrast for J-band detections, but M4-M6 stars should yield the highest rate of NIR flares with amplitudes of ΔJ ≥ 0.01 mag. Characterizing flare rates and photometric variations at longer wavelengths is important for predicting the signatures of M dwarf variability in next-generation surveys, and we discuss their impact on surveys such as the Large Synoptic Survey Telescope.

Host Galaxy Properties and Black Hole Mass of Swift J164449.3+573451 from Multi-wavelength Long-term Monitoring and HST Data

Science.gov (United States)

Yoon, Yongmin; Im, Myungshin; Jeon, Yiseul; Lee, Seong-Kook; Choi, Philip; Gehrels, Neil; Pak, Soojong; Sakamoto, Takanori; Urata, Yuji

2015-07-01

We study the host galaxy properties of the tidal disruption object Swift J164449.3+573451 using long-term optical to near-infrared (NIR) data. First, we decompose the galaxy surface brightness distribution and analyze the morphology of the host galaxy using high-resolution Hubble Space Telescope WFC3 images. We conclude that the host galaxy is bulge-dominant and well described by a single Sérsic model with Sérsic index n=3.43+/- 0.05. Adding a disk component, the bulge to total host galaxy flux ratio (B/ T) is 0.83 ± 0.03, which still indicates a bulge-dominant galaxy. Second, we estimate multi-band fluxes of the host galaxy through long-term light curves. Our long-term NIR light curves reveal the pure host galaxy fluxes ˜500 days after the burst. We fit spectral energy distribution models to the multi-band fluxes from the optical to NIR of the host galaxy and determine its properties. The stellar mass, the star formation rate, and the age of the stellar population are {log}({M}\\star /{M}⊙ )={9.14}-0.10+0.13, {0.03}-0.03+0.28 {M}⊙ yr-1, and {0.63}-0.43+0.95 Gyr. Finally, we estimate the mass of the central super massive black hole which is responsible for the tidal disruption event. The black hole mass is estimated to be {10}6.7+/- 0.4 {M}⊙ from {M}{BH}-{M}\\star ,{bul} and {M}{BH}-{L}{bul} relations for the K band, although a smaller value of ˜ {10}5 {M}⊙ cannot be excluded convincingly if the host galaxy harbors a pseudobulge.

Wavelength stabilized multi-kW diode laser systems

Science.gov (United States)

Köhler, Bernd; Unger, Andreas; Kindervater, Tobias; Drovs, Simon; Wolf, Paul; Hubrich, Ralf; Beczkowiak, Anna; Auch, Stefan; Müntz, Holger; Biesenbach, Jens

2015-03-01

We report on wavelength stabilized high-power diode laser systems with enhanced spectral brightness by means of Volume Holographic Gratings. High-power diode laser modules typically have a relatively broad spectral width of about 3 to 6 nm. In addition the center wavelength shifts by changing the temperature and the driving current, which is obstructive for pumping applications with small absorption bandwidths. Wavelength stabilization of high-power diode laser systems is an important method to increase the efficiency of diode pumped solid-state lasers. It also enables power scaling by dense wavelength multiplexing. To ensure a wide locking range and efficient wavelength stabilization the parameters of the Volume Holographic Grating and the parameters of the diode laser bar have to be adapted carefully. Important parameters are the reflectivity of the Volume Holographic Grating, the reflectivity of the diode laser bar as well as its angular and spectral emission characteristics. In this paper we present detailed data on wavelength stabilized diode laser systems with and without fiber coupling in the spectral range from 634 nm up to 1533 nm. The maximum output power of 2.7 kW was measured for a fiber coupled system (1000 μm, NA 0.22), which was stabilized at a wavelength of 969 nm with a spectral width of only 0.6 nm (90% value). Another example is a narrow line-width diode laser stack, which was stabilized at a wavelength of 1533 nm with a spectral bandwidth below 1 nm and an output power of 835 W.

Stellar Radial Velocities with IGRINS at McDonald Observatory

Science.gov (United States)

Mace, Gregory; Jaffe, Daniel; Park, Chan; Lee, Jae-Joon

2016-06-01

Exoplanet searches with dedicated instrumentation have made 1 m/s radial velocity (RV) precision routine.Yet, RVs for large samples of stars generally remain at the 1km/s level.TheImmersion Grating Infrared Spectrometer (IGRINS) is a revolutionary instrument that exploits broad spectral coverage at high-resolution in the near-infrared.IGRINS on the 2.7 meter Harlan J. Smith Telescope at McDonald Observatory is nearly as sensitive as CRIRES at the 8 meter Very Large Telescope. However, IGRINS at R=45,000 has more than 30 times the spectral grasp of CRIRES.The use of a silicon immersion grating facilitates a compact cryostat while providing simultaneous wavelength coverage from 1.45 - 2.45 microns. Wehave developed a pipeline to cross-correlate the more than 20,000 resolution elements in two IGRINS exposures and provide relative RVs with uncertainties of 50m/s (product for multi-epoch studies of low-mass, stellar and substellar multiplicity.

Deriving Stellar Masses for the ALFALFA α.100 Sample

Science.gov (United States)

Hess, Logan; Cornell 2017 Summer REU

2018-01-01

For this project, we explore different methods of deriving the stellar masses of galaxies in the ALFALFA (Arecibo Legacy Fast ALFA) α.100 survey. In particular, we measure the effectiveness of SED (Spectral Energy Distribution) on the sample. SED fitting was preformed by MAGPHYS (Multi-wavelength Analysis of Galaxy Physical Properties), utilizing a wide range of photometry in the UV, optical, and IR bands. Photometry was taken from GALAX GR6/7 (UV), SDSS DR13 (optical), WISE All-Sky (near-IR), and Herschel PACS/SPIRE (far-IR). The efficiency of SED fitting increases with a broader range of photometry, however detection rates varied significantly across the different bands. Using a more “comprehensive” sample of galaxies, the GSWLC-A (GALAX, SDSS, WISE Legacy Catalog All-Sky Survey), we aimed to measure which combination of bands provided the largest sample return with the lowest amount of uncertainty, which could then be used to estimate the masses of the galaxies in the α.100 sample.

IRAS 20050+2720: ANATOMY OF A YOUNG STELLAR CLUSTER

International Nuclear Information System (INIS)

Günther, H. M.; Wolk, S. J.; Spitzbart, B.; Forbrich, J.; Wright, N. J.; Bourke, T. L.; Gutermuth, R. A.; Allen, L.; Megeath, S. T.; Pipher, J. L.

2012-01-01

IRAS 20050+2720 is young star-forming region at a distance of 700 pc without apparent high-mass stars. We present results of our multi-wavelength study of IRAS 20050+2720 which includes observations by Chandra and Spitzer, and Two Micron All Sky Survey and UBVRI photometry. In total, about 300 young stellar objects (YSOs) in different evolutionary stages are found. We characterize the distribution of YSOs in this region using a minimum spanning tree analysis. We newly identify a second cluster core, which consists mostly of class II objects, about 10' from the center of the cloud. YSOs of earlier evolutionary stages are more clustered than more evolved objects. The X-ray luminosity function (XLF) of IRAS 20050+2720 is roughly lognormal, but steeper than the XLF of the more massive Orion Nebula complex. IRAS 20050+2720 shows a lower N H /A K ratio compared with the diffuse interstellar medium.

IRAS 20050+2720: ANATOMY OF A YOUNG STELLAR CLUSTER

Energy Technology Data Exchange (ETDEWEB)

Guenther, H. M.; Wolk, S. J.; Spitzbart, B.; Forbrich, J.; Wright, N. J.; Bourke, T. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Allen, L. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Megeath, S. T. [Department of Physics and Astronomy, MS-113, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606 (United States); Pipher, J. L., E-mail: hguenther@cfa.harvard.edu [Department of Physics and Astronomy, University of Rochester, 500 Wilson Boulevard, Rochester, NY 14627 (United States)

2012-10-01

IRAS 20050+2720 is young star-forming region at a distance of 700 pc without apparent high-mass stars. We present results of our multi-wavelength study of IRAS 20050+2720 which includes observations by Chandra and Spitzer, and Two Micron All Sky Survey and UBVRI photometry. In total, about 300 young stellar objects (YSOs) in different evolutionary stages are found. We characterize the distribution of YSOs in this region using a minimum spanning tree analysis. We newly identify a second cluster core, which consists mostly of class II objects, about 10' from the center of the cloud. YSOs of earlier evolutionary stages are more clustered than more evolved objects. The X-ray luminosity function (XLF) of IRAS 20050+2720 is roughly lognormal, but steeper than the XLF of the more massive Orion Nebula complex. IRAS 20050+2720 shows a lower N{sub H}/A{sub K} ratio compared with the diffuse interstellar medium.

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.

A new stellar spectrum interpolation algorithm and its application to Yunnan-III evolutionary population synthesis models

Science.gov (United States)

Cheng, Liantao; Zhang, Fenghui; Kang, Xiaoyu; Wang, Lang

2018-05-01

In evolutionary population synthesis (EPS) models, we need to convert stellar evolutionary parameters into spectra via interpolation in a stellar spectral library. For theoretical stellar spectral libraries, the spectrum grid is homogeneous on the effective-temperature and gravity plane for a given metallicity. It is relatively easy to derive stellar spectra. For empirical stellar spectral libraries, stellar parameters are irregularly distributed and the interpolation algorithm is relatively complicated. In those EPS models that use empirical stellar spectral libraries, different algorithms are used and the codes are often not released. Moreover, these algorithms are often complicated. In this work, based on a radial basis function (RBF) network, we present a new spectrum interpolation algorithm and its code. Compared with the other interpolation algorithms that are used in EPS models, it can be easily understood and is highly efficient in terms of computation. The code is written in MATLAB scripts and can be used on any computer system. Using it, we can obtain the interpolated spectra from a library or a combination of libraries. We apply this algorithm to several stellar spectral libraries (such as MILES, ELODIE-3.1 and STELIB-3.2) and give the integrated spectral energy distributions (ISEDs) of stellar populations (with ages from 1 Myr to 14 Gyr) by combining them with Yunnan-III isochrones. Our results show that the differences caused by the adoption of different EPS model components are less than 0.2 dex. All data about the stellar population ISEDs in this work and the RBF spectrum interpolation code can be obtained by request from the first author or downloaded from http://www1.ynao.ac.cn/˜zhangfh.

Terahertz detectors for long wavelength multi-spectral imaging.

Energy Technology Data Exchange (ETDEWEB)

Lyo, Sungkwun Kenneth; Wanke, Michael Clement; Reno, John Louis; Shaner, Eric Arthur; Grine, Albert D.

2007-10-01

The purpose of this work was to develop a wavelength tunable detector for Terahertz spectroscopy and imaging. Our approach was to utilize plasmons in the channel of a specially designed field-effect transistor called the grating-gate detector. Grating-gate detectors exhibit narrow-linewidth, broad spectral tunability through application of a gate bias, and no angular dependence in their photoresponse. As such, if suitable sensitivity can be attained, they are viable candidates for Terahertz multi-spectral focal plane arrays. When this work began, grating-gate gate detectors, while having many promising characteristics, had a noise-equivalent power (NEP) of only 10{sup -5} W/{radical}Hz. Over the duration of this project, we have obtained a true NEP of 10{sup -8} W/{radical}Hz and a scaled NEP of 10{sup -9}W/{radical}Hz. The ultimate goal for these detectors is to reach a NEP in the 10{sup -9{yields}-10}W/{radical}Hz range; we have not yet seen a roadblock to continued improvement.

Characterization of female breast lesions from multi-wavelength time-resolved optical mammography

International Nuclear Information System (INIS)

Spinelli, Lorenzo; Torricelli, Alessandro; Pifferi, Antonio; Taroni, Paola; Danesini, Gianmaria; Cubeddu, Rinaldo

2005-01-01

Characterization of both malignant and benign lesions in the female breast is presented as the result of a clinical study that involved more than 190 subjects in the framework of the OPTIMAMM European project. All the subjects underwent optical mammography, by means of a multi-wavelength time-resolved mammograph, in the range 637-985 nm. Optical images were processed by applying a perturbation model, relying on a nonlinear approximation of time-resolved transmittance curves in the presence of an inclusion, with the aim of estimating the major tissue constituents (i.e. oxy- and deoxy-haemoglobin, lipid and water) and structural parameters (linked to dimension and density of the scatterer centres) for both the lesion area and the surrounding tissue. The critical factors for the application of the perturbation model on in vivo data are also discussed. Forty-six malignant and 68 benign lesions were analysed. A subset of 32 cancers, 40 cysts and 14 fibroadenomas were found reliable for the perturbation analysis. For cancers, we show a higher blood content with respect to the surrounding tissue, while cysts are characterized by a lower concentration of scattering centres with respect to the surrounding tissue. For fibroadenomas, the low number of cases does not allow any definite conclusions

Multi-metal, Multi-wavelength Surface-Enhanced Raman Spectroscopy Detection of Neurotransmitters.

Science.gov (United States)

Moody, Amber S; Sharma, Bhavya

2018-04-05

The development of a sensor for the rapid and sensitive detection of neurotransmitters could provide a pathway for the diagnosis of neurological diseases, leading to the discovery of more effective treatment methods. We investigate the use of surface enhanced Raman spectroscopy (SERS) based sensors for the rapid detection of melatonin, serotonin, glutamate, dopamine, GABA, norepinephrine, and epinephrine. Previous studies have demonstrated SERS detection of neurotransmitters; however, there has been no comprehensive study on the effect of the metal used as the SERS substrate or the excitation wavelength used for detection. Here, we present the detection of 7 neurotransmitters using both silver and gold nanoparticles at excitation wavelengths of 532, 633, and 785 nm. Over the range of wavelengths investigated, the SERS enhancement on the silver and gold nanoparticles varies, with an average enhancement factor of 10 5 -10 6 . The maximum SERS enhancement occurs at an excitation wavelength of 785 nm for the gold nanoparticles and at 633 nm for the silver nanoparticles.

Robust and economical multi-sample, multi-wavelength UV/vis absorption and fluorescence detector for biological and chemical contamination

Science.gov (United States)

Lu, Peter J.; Hoehl, Melanie M.; Macarthur, James B.; Sims, Peter A.; Ma, Hongshen; Slocum, Alexander H.

2012-09-01

We present a portable multi-channel, multi-sample UV/vis absorption and fluorescence detection device, which has no moving parts, can operate wirelessly and on batteries, interfaces with smart mobile phones or tablets, and has the sensitivity of commercial instruments costing an order of magnitude more. We use UV absorption to measure the concentration of ethylene glycol in water solutions at all levels above those deemed unsafe by the United States Food and Drug Administration; in addition we use fluorescence to measure the concentration of d-glucose. Both wavelengths can be used concurrently to increase measurement robustness and increase detection sensitivity. Our small robust economical device can be deployed in the absence of laboratory infrastructure, and therefore may find applications immediately following natural disasters, and in more general deployment for much broader-based testing of food, agricultural and household products to prevent outbreaks of poisoning and disease.

A Multi-Wavelength IR Laser for Space Applications

Science.gov (United States)

Li, Steven X.; Yu, Anthony W.; Sun, Xiaoli; Fahey, Molly E.; Numata, Kenji; Krainak, Michael A.

2017-01-01

We present a laser technology development with space flight heritage to generate laser wavelengths in the near- to mid-infrared (NIR to MIR) for space lidar applications. Integrating an optical parametric crystal to the LOLA (Lunar Orbiter Laser Altimeter) laser transmitter design affords selective laser wavelengths from NIR to MIR that are not easily obtainable from traditional diode pumped solid-state lasers. By replacing the output coupler of the LOLA laser with a properly designed parametric crystal, we successfully demonstrated a monolithic intra-cavity optical parametric oscillator (iOPO) laser based on all high technology readiness level (TRL) subsystems and components. Several desired wavelengths have been generated including 2.1 microns, 2.7 microns and 3.4 microns. This laser can also be used in trace-gas remote sensing, as many molecules possess their unique vibrational transitions in NIR to MIR wavelength region, as well as in time-of-flight mass spectrometer where desorption of samples using MIR laser wavelengths have been successfully demonstrated.

SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES

International Nuclear Information System (INIS)

Wuyts, Stijn; Förster Schreiber, Natascha M.; Genzel, Reinhard; Lutz, Dieter; Guo Yicheng; Giavalisco, Mauro; Barro, Guillermo; Faber, Sandra M.; Kocevski, Dale D.; Koo, David C.; McGrath, Elizabeth; Bell, Eric F.; Dekel, Avishai; Ferguson, Henry C.; Grogin, Norman A.; Koekemoer, Anton M.; Lotz, Jennifer; Hathi, Nimish P.; Huang, Kuang-Han; Newman, Jeffrey A.

2012-01-01

We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies (SFGs) at 0.5 10 M ☉ and have specific star formation rates (SFRs) above 1/t H . We model the seven-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible in the inferred stellar mass distributions. Off-center clumps contribute up to ∼20% to the integrated SFR, but only 7% or less to the integrated mass of all massive SFGs at z ∼ 1 and z ∼ 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100-200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.

Enhanced Deformation of Azobenzene-Modified Liquid Crystal Polymers under Dual Wavelength Exposure: A Photophysical Model

Science.gov (United States)

Liu, Ling; Onck, Patrick R.

2017-08-01

Azobenzene-embedded liquid crystal polymers can undergo mechanical deformation in response to ultraviolet (UV) light. The natural rodlike trans state azobenzene absorbs UV light and isomerizes to a bentlike cis state, which disturbs the order of the polymer network, leading to an anisotropic deformation. The current consensus is that the magnitude of the photoinduced deformation is related to the statistical building up of molecules in the cis state. However, a recent experimental study [Liu and Broer, Nat. Commun. 6 8334 (2015)., 10.1038/ncomms9334] shows that a drastic (fourfold) increase of the photoinduced deformation can be generated by exposing the samples simultaneously to 365 nm (UV) and 455 nm (visible) light. To elucidate the physical mechanism that drives this increase, we develop a two-light attenuation model and an optomechanical constitutive relation that not only accounts for the statistical accumulation of cis azobenzenes, but also for the dynamic trans-cis-trans oscillatory isomerization process. Our experimentally calibrated model predicts that the optimal single-wavelength exposure is 395 nm light, a pronounced shift towards the visible spectrum. In addition, we identify a range of optimal combinations of two-wavelength lights that generate a favorable response for a given amount of injected energy. Our model provides mechanistic insight into the different (multi)wavelength exposures used in experiments and, at the same time, opens new avenues towards enhanced, multiwavelength optomechanical behavior.

A SEMI-ANALYTICAL MODEL OF VISIBLE-WAVELENGTH PHASE CURVES OF EXOPLANETS AND APPLICATIONS TO KEPLER- 7 B AND KEPLER- 10 B

Energy Technology Data Exchange (ETDEWEB)

Hu, Renyu [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Demory, Brice-Olivier [Astrophysics Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Seager, Sara; Lewis, Nikole [Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Showman, Adam P., E-mail: renyu.hu@jpl.nasa.gov [Department of Planetary Sciences, University of Arizona, Tucson, AZ 85721 (United States)

2015-03-20

Kepler has detected numerous exoplanet transits by measuring stellar light in a single visible-wavelength band. In addition to detection, the precise photometry provides phase curves of exoplanets, which can be used to study the dynamic processes on these planets. However, the interpretation of these observations can be complicated by the fact that visible-wavelength phase curves can represent both thermal emission and scattering from the planets. Here we present a semi-analytical model framework that can be applied to study Kepler and future visible-wavelength phase curve observations of exoplanets. The model efficiently computes reflection and thermal emission components for both rocky and gaseous planets, considering both homogeneous and inhomogeneous surfaces or atmospheres. We analyze the phase curves of the gaseous planet Kepler- 7 b and the rocky planet Kepler- 10 b using the model. In general, we find that a hot exoplanet’s visible-wavelength phase curve having a significant phase offset can usually be explained by two classes of solutions: one class requires a thermal hot spot shifted to one side of the substellar point, and the other class requires reflective clouds concentrated on the same side of the substellar point. Particularly for Kepler- 7 b, reflective clouds located on the west side of the substellar point can best explain its phase curve. The reflectivity of the clear part of the atmosphere should be less than 7% and that of the cloudy part should be greater than 80%, and the cloud boundary should be located at 11° ± 3° to the west of the substellar point. We suggest single-band photometry surveys could yield valuable information on exoplanet atmospheres and surfaces.

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.

α Centauri A as a potential stellar model calibrator: establishing the nature of its core

Science.gov (United States)

Nsamba, B.; Monteiro, M. J. P. F. G.; Campante, T. L.; Cunha, M. S.; Sousa, S. G.

2018-05-01

Understanding the physical process responsible for the transport of energy in the core of α Centauri A is of the utmost importance if this star is to be used in the calibration of stellar model physics. Adoption of different parallax measurements available in the literature results in differences in the interferometric radius constraints used in stellar modelling. Further, this is at the origin of the different dynamical mass measurements reported for this star. With the goal of reproducing the revised dynamical mass derived by Pourbaix & Boffin, we modelled the star using two stellar grids varying in the adopted nuclear reaction rates. Asteroseismic and spectroscopic observables were complemented with different interferometric radius constraints during the optimisation procedure. Our findings show that best-fit models reproducing the revised dynamical mass favour the existence of a convective core (≳ 70% of best-fit models), a result that is robust against changes to the model physics. If this mass is accurate, then α Centauri A may be used to calibrate stellar model parameters in the presence of a convective core.

Multi-species trace gas sensing with dual-wavelength QCLs

Science.gov (United States)

Hundt, P. Morten; Tuzson, Béla; Aseev, Oleg; Liu, Chang; Scheidegger, Philipp; Looser, Herbert; Kapsalidis, Filippos; Shahmohammadi, Mehran; Faist, Jérôme; Emmenegger, Lukas

2018-06-01

Instrumentation for environmental monitoring of gaseous pollutants and greenhouse gases tends to be complex, expensive, and energy demanding, because every compound measured relies on a specific analytical technique. This work demonstrates an alternative approach based on mid-infrared laser absorption spectroscopy with dual-wavelength quantum cascade lasers (QCLs). The combination of two dual- and one single-DFB QCL yields high-precision measurements of CO (0.08 ppb), CO2 (100 ppb), NH3 (0.02 ppb), NO (0.4 ppb), NO2 (0.1 ppb), N2O (0.045 ppb), and O3 (0.11 ppb) simultaneously in a compact setup (45 × 45 cm2). The lasers are driven time-multiplexed in intermittent continuous wave mode with a repetition rate of 1 kHz. The individual spectra are real-time averaged (1 s) by an FPGA-based data acquisition system. The instrument was assessed for environmental monitoring and benchmarked with reference instrumentation to demonstrate its potential for compact multi-species trace gas sensing.

Multi-wavelength studies of TeV γ-ray emitting BL Lac objects

International Nuclear Information System (INIS)

Kaufmann, Sarah Sabine

2012-01-01

The discovery of TeV γ-ray emission of BL Lac objects gave new insights in the particle acceleration and the emission processes of the highly relativistic jets. To shed light on the conditions in the high energetic jets of the TeV γ-ray emitting BL Lac objects, I have studied in great detail the spectral energy distribution (SED) of sources with different characteristics. BL Lac objects with exceptional very high energy spectra (soft and hard spectra) and with large differences in the emission peak frequencies, to cover the different classes of BL Lac objects, have been chosen. The basic aim of this thesis was, to study with new, simultaneous multi- avelength (MWL) observations, if the emission processes of these extreme cases of TeV BL Lac objects can be explained by the synchrotron Self-Compton (SSC) model which is well established for the class of BL Lac objects at lower energies. We proposed MWL observations in the optical, UV and X-ray regime, to be conducted simultaneous to very high energy observations with the H.E.S.S. experiment, to study the emission processes. Simultaneous observations are crucial, since BL Lac objects are variable at all wavebands. I have analysed the MWL observations and conducted detailed variability and spectral studies in each wavelength range. The different kind of absorption at each wavelength as well as the influence of the host galaxy of the AGN has been considered to obtain the intrinsic jet spectrum. I have then applied the commonly used theoretical jet model, the SSC model, to the SED. I conducted a MWL campaign on a BL Lac object with the softest TeV spectrum, PKS 2005-489, during which it was observed in a very bright X-ray state. The good spectral coverage of the emission peaks allowed a detailed study of the SSC model. The extreme BL Lac object 1ES 0229+200 exhibits a hard intrinsic TeV spectrum. With my MWL campaign I found a clear cut-off in the optical range and therefore a high minimum Lorentz factor is needed to

Multi-wavelength studies of TeV γ-ray emitting BL Lac objects

Energy Technology Data Exchange (ETDEWEB)

Kaufmann, Sarah Sabine

2012-12-21

The discovery of TeV γ-ray emission of BL Lac objects gave new insights in the particle acceleration and the emission processes of the highly relativistic jets. To shed light on the conditions in the high energetic jets of the TeV γ-ray emitting BL Lac objects, I have studied in great detail the spectral energy distribution (SED) of sources with different characteristics. BL Lac objects with exceptional very high energy spectra (soft and hard spectra) and with large differences in the emission peak frequencies, to cover the different classes of BL Lac objects, have been chosen. The basic aim of this thesis was, to study with new, simultaneous multi- avelength (MWL) observations, if the emission processes of these extreme cases of TeV BL Lac objects can be explained by the synchrotron Self-Compton (SSC) model which is well established for the class of BL Lac objects at lower energies. We proposed MWL observations in the optical, UV and X-ray regime, to be conducted simultaneous to very high energy observations with the H.E.S.S. experiment, to study the emission processes. Simultaneous observations are crucial, since BL Lac objects are variable at all wavebands. I have analysed the MWL observations and conducted detailed variability and spectral studies in each wavelength range. The different kind of absorption at each wavelength as well as the influence of the host galaxy of the AGN has been considered to obtain the intrinsic jet spectrum. I have then applied the commonly used theoretical jet model, the SSC model, to the SED. I conducted a MWL campaign on a BL Lac object with the softest TeV spectrum, PKS 2005-489, during which it was observed in a very bright X-ray state. The good spectral coverage of the emission peaks allowed a detailed study of the SSC model. The extreme BL Lac object 1ES 0229+200 exhibits a hard intrinsic TeV spectrum. With my MWL campaign I found a clear cut-off in the optical range and therefore a high minimum Lorentz factor is needed to

Seeing red in M32: Constraints on the stellar content from near- and mid-infrared observations and applications for studies of more distant galaxies {sup ,} {sup ,}

Energy Technology Data Exchange (ETDEWEB)

Davidge, T. J. [Dominion Astrophysical Observatory, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)

2014-08-10

The properties of asymptotic giant branch (AGB) stars in the Local Group galaxy M32 are investigated using ground- and space-based observations that span the 1-8 μm wavelength interval, with the goal of demonstrating the utility of infrared observations as probes of stellar content. Comparisons with isochrones indicate that the brightest resolved stars in M32 have ages of a few gigayears and are younger on average than AGB stars with the same intrinsic brightness in the outer disk of M31. Accounting for stellar variability is shown to be essential for modeling AGB luminosity functions (LFs). Model LFs that assume the star-forming history measured by Monachesi et al. and the variability properties of Galactic AGB stars match both the K and [5.8] LFs of M32. Models also suggest that the slope of the [5.8] LF between M{sub [5.8]} = –8.5 and –10.0 is sensitive to the mix of stellar ages, and a sizeable fraction of the stars in M32 must have an age older than 7 Gyr in order to match the [5.8] LF. The structural properties of M32 in the infrared are also investigated. The effective radii that are computed from near-infrared and mid-infrared isophotes are similar to those measured at visible wavelengths, suggesting that the stellar content of M32 is well mixed. However, isophotes at radii >16'' (>60 pc) in the near- and mid-infrared are flatter than those at visible wavelengths. The coefficient of the fourth-order cosine term in the Fourier expansion of isophotes changes from 'boxy' values at r < 16'' to 'disky' values at r > 48''in [3.6] and [4.5]. The mid-infrared colors near the center of M32 do not vary systematically with radius, providing evidence of a well mixed stellar content in this part of the galaxy.

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.

Use of a reflective semiconductor optical amplifier and dual-ring architecture design to produce a stable multi-wavelength fiber laser

International Nuclear Information System (INIS)

Yeh, Chien-Hung; Chow, Chi-Wai; Lu, Shao-Sheng

2014-01-01

In this work, we propose and demonstrate a multi-wavelength laser source produced by utilizing a C-band reflective semiconductor optical amplifier (RSOA) with a dual-ring fiber cavity. Here, the laser cavity consists of an RSOA, a 1 × 2 optical coupler, a 2 × 2 optical coupler and a polarization controller. As a result, thirteen to eighteen wavelengths around the L band could be generated simultaneously when the bias current of the C-band RSOA was driven at 30–70 mA. In addition, the output stabilities of the power and wavelength are also discussed. (paper)

Use of a reflective semiconductor optical amplifier and dual-ring architecture design to produce a stable multi-wavelength fiber laser

Science.gov (United States)

Yeh, Chien-Hung; Chow, Chi-Wai; Lu, Shao-Sheng

2014-05-01

In this work, we propose and demonstrate a multi-wavelength laser source produced by utilizing a C-band reflective semiconductor optical amplifier (RSOA) with a dual-ring fiber cavity. Here, the laser cavity consists of an RSOA, a 1 × 2 optical coupler, a 2 × 2 optical coupler and a polarization controller. As a result, thirteen to eighteen wavelengths around the L band could be generated simultaneously when the bias current of the C-band RSOA was driven at 30-70 mA. In addition, the output stabilities of the power and wavelength are also discussed.

Free-boundary stability of straight stellarators

International Nuclear Information System (INIS)

Barnes, D.C.; Cary, J.R.

1984-02-01

The sharp-boundary model is used to investigate the stability of straight stellarators to free-boundary, long-wavelength modes. To correctly analyze the heliac configuration, previous theory is generalized to the case of arbitrary helical aspect ratio (ratio of plasma radius to periodicity lengths). A simple low-β criterion involving the vacuum field and the normalized axial current is derived and used to investigate a large variety of configurations. The predictions of this low-β theory are verified by numerical minimization of deltaW at arbitrary β. The heliac configuration is found to be remarkably stable, with a critical β of over 15% determined by the lack of equilibrium rather than the onset of instability. In addition, other previously studied systems are found to be stabilized by net axial plasma current

Model-independent Exoplanet Transit Spectroscopy

Science.gov (United States)

Aronson, Erik; Piskunov, Nikolai

2018-05-01

We propose a new data analysis method for obtaining transmission spectra of exoplanet atmospheres and brightness variation across the stellar disk from transit observations. The new method is capable of recovering exoplanet atmosphere absorption spectra and stellar specific intensities without relying on theoretical models of stars and planets. We simultaneously fit both stellar specific intensity and planetary radius directly to transit light curves. This allows stellar models to be removed from the data analysis. Furthermore, we use a data quality weighted filtering technique to achieve an optimal trade-off between spectral resolution and reconstruction fidelity homogenizing the signal-to-noise ratio across the wavelength range. Such an approach is more efficient than conventional data binning onto a low-resolution wavelength grid. We demonstrate that our analysis is capable of reproducing results achieved by using an explicit quadratic limb-darkening equation and that the filtering technique helps eliminate spurious spectral features in regions with strong telluric absorption. The method is applied to the VLT FORS2 observations of the exoplanets GJ 1214 b and WASP-49 b, and our results are in agreement with previous studies. Comparisons between obtained stellar specific intensity and numerical models indicates that the method is capable of accurately reconstructing the specific intensity. The proposed method enables more robust characterization of exoplanetary atmospheres by separating derivation of planetary transmission and stellar specific intensity spectra (that is model-independent) from chemical and physical interpretation.

Study of the strongly ionized medium in active galactic n ('Warm Absorber'): multi-wavelength modelling and plasma diagnostics in the X-ray spectral range

International Nuclear Information System (INIS)

Porquet, Delphine

1999-01-01

The so-called 'Warm Absorber' medium is observed in the central region of Active Galactic Nuclei and particularly in Seyfert l galaxies. lt is mainly characterized by O(VII) and O(VIII) absorption edges detected in the soft X-rays. Its study (modelization and observation) is an important key tool to understand Active Galactic Nuclei. The work presented here consists in modelling the Warm Absorber, and in developing X-ray spectroscopy diagnostics to constrain the physical parameters of any hot medium such as the Warm Absorber. The physical parameters of the Warm Absorber (density, temperature, ionization processes..) are difficult to determine only on the basis of present X-ray data. In particular, the value of the density cannot be derived only from the modelling of the resonance lines and of the soft X-ray absorption edges since there are almost insensitive to the density in the range of values expected for the Warm Absorber. lt is why we have developed diagnostic methods based on a multi-wavelength approach. The modelling is made with two complementary computational codes: PEGAS, and IRIS which takes into account the most accurate atomic data. With these two codes, we have modelled several types of plasma ionisation processes (photoionized plasmas and/or collisional). Results for the Warm Absorber were compared to multi-wavelength observations (mainly the optical iron coronal lines [Fe X] 6375 Angstroms, [Fe XI] 7892 Angstroms, and [Fe XIV] 5303 Angstroms). The proposed method has allowed to show that the Warm Absorber could be responsible of the emission of these lines totally or partially. All models of the Warm Absorber producing coronal line equivalent widths larger than observed were ruled out. This strongly constrains the physical parameters of the Warm Absorber, and particularly its density (n H ≥10 10 cm -3 ). The new generation of X-ray satellites (Chandra/AXAF, XMM...) will produce spectra at high spectral resolution and high sensitivity

Synthesis of multi-wavelength temporal phase-shifting algorithms optimized for high signal-to-noise ratio and high detuning robustness using the frequency transfer function

OpenAIRE

Servin, Manuel; Padilla, Moises; Garnica, Guillermo

2016-01-01

Synthesis of single-wavelength temporal phase-shifting algorithms (PSA) for interferometry is well-known and firmly based on the frequency transfer function (FTF) paradigm. Here we extend the single-wavelength FTF-theory to dual and multi-wavelength PSA-synthesis when several simultaneous laser-colors are present. The FTF-based synthesis for dual-wavelength PSA (DW-PSA) is optimized for high signal-to-noise ratio and minimum number of temporal phase-shifted interferograms. The DW-PSA synthesi...

Stable numerical method in computation of stellar evolution

International Nuclear Information System (INIS)

Sugimoto, Daiichiro; Eriguchi, Yoshiharu; Nomoto, Ken-ichi.

1982-01-01

To compute the stellar structure and evolution in different stages, such as (1) red-giant stars in which the density and density gradient change over quite wide ranges, (2) rapid evolution with neutrino loss or unstable nuclear flashes, (3) hydrodynamical stages of star formation or supernova explosion, (4) transition phases from quasi-static to dynamical evolutions, (5) mass-accreting or losing stars in binary-star systems, and (6) evolution of stellar core whose mass is increasing by shell burning or decreasing by penetration of convective envelope into the core, we face ''multi-timescale problems'' which can neither be treated by simple-minded explicit scheme nor implicit one. This problem has been resolved by three prescriptions; one by introducing the hybrid scheme suitable for the multi-timescale problems of quasi-static evolution with heat transport, another by introducing also the hybrid scheme suitable for the multi-timescale problems of hydrodynamic evolution, and the other by introducing the Eulerian or, in other words, the mass fraction coordinate for evolution with changing mass. When all of them are combined in a single computer code, we can compute numerically stably any phase of stellar evolution including transition phases, as far as the star is spherically symmetric. (author)

MULTI-WAVELENGTH POLARIMETRY AND SPECTRAL STUDY OF THE M87 JET DURING 2002–2008

Energy Technology Data Exchange (ETDEWEB)

Avachat, Sayali S.; Perlman, Eric S. [Department of Physics and Space Sciences, 150 W. University Boulevard, Florida Institute of Technology, Melbourne, FL 32901 (United States); Adams, Steven C. [Department of Physics and Astronomy, University of Georgia, Athens, GA, 30605 (United States); Cara, Mihai; Sparks, William B. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Owen, Frazer [National Radio Astronomy Observatory, Array Operations Center, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801-0387 (United States); Georganopoulos, Markos [Department of Physics, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 (United States)

2016-11-20

We present a multi-wavelength polarimetric and spectral study of the M87 jet obtained at sub-arcsecond resolution between 2002 and 2008. The observations include multi-band archival VLA polarimetry data sets along with Hubble Space Telescope ( HST ) imaging polarimetry. These observations have better angular resolution than previous work by factors of 2–3 and in addition, allow us to explore the time domain. These observations envelop the huge flare in HST-1 located 0.″86 from the nucleus. The increased resolution enables us to view more structure in each knot, showing several resolved sub-components. We also see apparent helical structure in the polarization vectors in several knots, with polarization vectors turning either clockwise or counterclockwise near the flux maxima in various places as well as showing filamentary undulations. Some of these characteristics are correlated with flux and polarization maxima while others are not. We also examine the total flux and fractional polarization and look for changes in both radio and optical since the observations of Perlman et al. (1999) and test them against various models based on shocks and instabilities in the jet. Our results are broadly consistent with previous spine-sheath models and recollimation shock models; however, they require additional combinations of features to explain the observed complexity, e.g., shearing of magnetic field lines near the jet surface and compression of the toroidal component near shocks. In particular, in many regions we find apparently helical features both in total flux and polarization. We discuss the physical interpretation of these features.

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.

A two-column formalism for time-dependent modelling of stellar convection. I. Description of the method

Science.gov (United States)

Stökl, A.

2008-11-01

Context: In spite of all the advances in multi-dimensional hydrodynamics, investigations of stellar evolution and stellar pulsations still depend on one-dimensional computations. This paper devises an alternative to the mixing-length theory or turbulence models usually adopted in modelling convective transport in such studies. Aims: The present work attempts to develop a time-dependent description of convection, which reflects the essential physics of convection and that is only moderately dependent on numerical parameters and far less time consuming than existing multi-dimensional hydrodynamics computations. Methods: Assuming that the most extensive convective patterns generate the majority of convective transport, the convective velocity field is described using two parallel, radial columns to represent up- and downstream flows. Horizontal exchange, in the form of fluid flow and radiation, over their connecting interface couples the two columns and allows a simple circulating motion. The main parameters of this convective description have straightforward geometrical meanings, namely the diameter of the columns (corresponding to the size of the convective cells) and the ratio of the cross-section between up- and downdrafts. For this geometrical setup, the time-dependent solution of the equations of radiation hydrodynamics is computed from an implicit scheme that has the advantage of being unaffected by the Courant-Friedrichs-Lewy time-step limit. This implementation is part of the TAPIR-Code (short for The adaptive, implicit RHD-Code). Results: To demonstrate the approach, results for convection zones in Cepheids are presented. The convective energy transport and convective velocities agree with expectations for Cepheids and the scheme reproduces both the kinetic energy flux and convective overshoot. A study of the parameter influence shows that the type of solution derived for these stars is in fact fairly robust with respect to the constitutive numerical

THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S4G): MULTI-COMPONENT DECOMPOSITION STRATEGIES AND DATA RELEASE

International Nuclear Information System (INIS)

Salo, Heikki; Laurikainen, Eija; Laine, Jarkko; Comerón, Sebastien; Gadotti, Dimitri A.; Kim, Taehyun; Buta, Ron; Sheth, Kartik; Muñoz-Mateos, Juan Carlos; Zaritsky, Dennis; Hinz, Joannah L.; Ho, Luis; Knapen, Johan; Cisternas, Mauricio; Athanassoula, E.; Bosma, Albert; Laine, Seppo; Regan, Michael; De Paz, Armando Gil; Menendez-Delmestre, Karin

2015-01-01

The Spitzer Survey of Stellar Structure in Galaxies (S 4 G) is a deep 3.6 and 4.5 μm imaging survey of 2352 nearby (<40 Mpc) galaxies. We describe the S 4 G data analysis pipeline 4, which is dedicated to two-dimensional structural surface brightness decompositions of 3.6 μm images, using GALFIT3.0. Besides automatic 1-component Sérsic fits, and 2-component Sérsic bulge + exponential disk fits, we present human-supervised multi-component decompositions, which include, when judged appropriate, a central point source, bulge, disk, and bar components. Comparison of the fitted parameters indicates that multi-component models are needed to obtain reliable estimates for the bulge Sérsic index and bulge-to-total light ratio (B/T), confirming earlier results. Here, we describe the preparations of input data done for decompositions, give examples of our decomposition strategy, and describe the data products released via IRSA and via our web page (www.oulu.fi/astronomy/S4G-PIPELINE4/MAIN). These products include all the input data and decomposition files in electronic form, making it easy to extend the decompositions to suit specific science purposes. We also provide our IDL-based visualization tools (GALFIDL) developed for displaying/running GALFIT-decompositions, as well as our mask editing procedure (MASK-EDIT) used in data preparation. A detailed analysis of the bulge, disk, and bar parameters derived from multi-component decompositions will be published separately

Multi-wavelength metal-dielectric nonpolarizing beam splitters in the near-infrared range

Science.gov (United States)

Hui Shi, Jin; Ping Wang, Zheng; Ying Guan, Chun; Yang, Jun; Shu Fu, Tian

2011-04-01

A 21-layer multi-wavelength metal-dielectric nonpolarizing cube beam splitter was designed by use of an optimization method and theoretically investigated in the near-infrared range. The angular dependence of the reflectance and differential phases induced by reflection and transmission were presented. The simulation results revealed that the non-polarizing effect could be achieved for both the amplitude and phase characteristics at 1310 and 1550 nm. The differences between the simulated and the target reflectance of 50% are less than 2% and differential phases are less than 5°in the range 1300-1320 nm and 1540-1550 nm for both p- and s-components.

SOLAR STELLAR AND SUBSTELLAR ENVIRONMENT. I. LOCATION IN THE GALAXY AND CATALOGUES

OpenAIRE

Захожай, В. А.; Харьковский национальный университет им. В.Н.Каразина; Бабенко, М. А.; Херсонский государственный университет

2016-01-01

Structure of the solar neighborhoods (ten parsecs space, Local stellar system andthe Gould Belt), their place in the Galaxy and the distance from its center are analyzed. For the region within 10 pcfrom the Sun, except the stellar component, the contents of extrasolar planets and protoplanetary disks are presented.The catalogues of closest to Sun stars and substars that are compiled based on the results of ground-based and cosmic(HIPPARCOS) missions in the optical and infrared wavelengths ran...

Multi-wavelength laser based on an arrayed waveguide grating and Sagnac loop reflectors monolithically integrated on InP

NARCIS (Netherlands)

Muñoz, P.; García-Olcina, R.; Doménech, J.D.; Rius, M.; Capmany, J.; Chen, L.R.; Habib, C.; Leijtens, X.J.M.; Vries, de T.; Heck, M.J.R.; Augustin, L.M.; Nötzel, R.; Robbins, D.J.

2010-01-01

In this paper, a multi-wavelength laser monolithically integrated on InP is presented. A linear laser cavity is built between two integrated Sagnac loop reflectors, with an Arrayed Waveguide Grating (AWG) as frequency selective device, and Semiconductor Optical Amplifiers (SOA) as gain sections. The

MULTI-WAVELENGTH OBSERVATIONS OF COMET C/2011 L4 (PAN-STARRS)

Energy Technology Data Exchange (ETDEWEB)

Yang, Bin; Keane, Jacqueline; Meech, Karen [NASA Astrobiology Institute, University of Hawaii, Honolulu, HI 96822 (United States); Owen, Tobias; Wainscoat, Richard, E-mail: yangbin@ifa.hawaii.edu [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)

2014-04-01

The dynamically new comet C/2011 L4 (Pan-STARRS) is one of the brightest comets observed since the great comet C/1995 O1 (Hale-Bopp). Here, we present our multi-wavelength observations of C/2011 L4 during its in-bound passage to the inner solar system. A strong absorption band of water ice at 2.0 μm was detected in the near-infrared spectra, obtained with the 8 m Gemini-North and 3 m Infrared Telescope Facility Telescopes. The companion 1.5 μm band of water ice, however, was not observed. Spectral modeling shows that the absence of the 1.5 μm feature can be explained by the presence of sub-micron-sized fine ice grains. No gas lines (i.e., CN, HCN, or CO) were observed pre-perihelion in either the optical or the submillimeter. We derived 3σ upper limits for the CN and CO production rates. The comet exhibited a very strong continuum in the optical and its slope seemed to become redder as the comet approached the Sun. Our observations suggest that C/2011 L4 is an unusually dust-rich comet with a dust-to-gas mass ratio >4.

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.

Stellar physics with the ALHAMBRA photometric system

International Nuclear Information System (INIS)

Villegas, T Aparicio; Alfaro, E J; Moles, M; Benítez, N; Perea, J; Olmo, A del; Cristóbal-Hornillos, D; Cervio, M; Delgado, R M González; Márquez, I; Masegosa, J; Prada, F; Cabrera-Caño, J; Fernández-Soto, A; Aguerri, J A L; Cepa, J; Broadhurst, T; Castander, F J; Infante, L; Martínez, V J

2011-01-01

The ALHAMBRA photometric system was specifically designed to perform a tomography of the Universe in some selected areas. Although mainly designed for extragalactic purposes, its 20 contiguous, equal-width, medium-band photometric system in the optical wavelength range, shows a great capacity for stellar classification. In this contribution we propose a methodology for stellar classification and physical parameter estimation (T eff , log g, [Fe/H], and color excess E(B – V)) based on 18 independent reddening-free Q-values from the ALHAMBRA photometry. Based on the theoretical Spectral library BaSeL 2.2, and applied to 288 stars from the Next Generation spectral Library (NGSL), we discuss the reliability of the method and its dependence on the extinction law used.

Color correction for chromatic distortion in a multi-wavelength digital holographic system

International Nuclear Information System (INIS)

Lin, Li-Chien; Huang, Yi-Lun; Tu, Han-Yen; Lai, Xin-Ji; Cheng, Chau-Jern

2011-01-01

A multi-wavelength digital holographic (MWDH) system has been developed to record and reconstruct color images. In comparison to working with digital cameras, however, high-quality color reproduction is difficult to achieve, because of the imperfections from the light sources, optical components, optical recording devices and recording processes. Thus, we face the problem of correcting the colors altered during the digital holographic process. We therefore propose a color correction scheme to correct the chromatic distortion caused by the MWDH system. The scheme consists of two steps: (1) creating a color correction profile and (2) applying it to the correction of the distorted colors. To create the color correction profile, we generate two algorithms: the sequential algorithm and the integrated algorithm. The ColorChecker is used to generate the distorted colors and their desired corrected colors. The relationship between these two color patches is fixed into a specific mathematical model, the parameters of which are estimated, creating the profile. Next, the profile is used to correct the color distortion of images, capturing and preserving the original vibrancy of the reproduced colors for different reconstructed images

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)

Influence of stellar multiplicity on planet formation. I. Evidence of suppressed planet formation due to stellar companions within 20 au and validation of four planets from the Kepler multiple planet candidates

International Nuclear Information System (INIS)

Wang, Ji; Fischer, Debra A.; Xie, Ji-Wei; Barclay, Thomas

2014-01-01

The planet occurrence rate for multiple stars is important in two aspects. First, almost half of stellar systems in the solar neighborhood are multiple systems. Second, the comparison of the planet occurrence rate for multiple stars to that for single stars sheds light on the influence of stellar multiplicity on planet formation and evolution. We developed a method of distinguishing planet occurrence rates for single and multiple stars. From a sample of 138 bright (K P < 13.5) Kepler multi-planet candidate systems, we compared the stellar multiplicity rate of these planet host stars to that of field stars. Using dynamical stability analyses and archival Doppler measurements, we find that the stellar multiplicity rate of planet host stars is significantly lower than field stars for semimajor axes less than 20 AU, suggesting that planet formation and evolution are suppressed by the presence of a close-in companion star at these separations. The influence of stellar multiplicity at larger separations is uncertain because of search incompleteness due to a limited Doppler observation time baseline and a lack of high-resolution imaging observation. We calculated the planet confidence for the sample of multi-planet candidates and find that the planet confidences for KOI 82.01, KOI 115.01, KOI 282.01, and KOI 1781.02 are higher than 99.7% and thus validate the planetary nature of these four planet candidates. This sample of bright Kepler multi-planet candidates with refined stellar and orbital parameters, planet confidence estimation, and nearby stellar companion identification offers a well-characterized sample for future theoretical and observational study.

SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES

Energy Technology Data Exchange (ETDEWEB)

Wuyts, Stijn; Foerster Schreiber, Natascha M.; Genzel, Reinhard; Lutz, Dieter [Max-Planck-Institut fuer extraterrestrische Physik, Postfach 1312, Giessenbachstr., D-85741 Garching (Germany); Guo Yicheng; Giavalisco, Mauro [Astronomy Department, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States); Barro, Guillermo; Faber, Sandra M.; Kocevski, Dale D.; Koo, David C.; McGrath, Elizabeth [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Dekel, Avishai [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Ferguson, Henry C.; Grogin, Norman A.; Koekemoer, Anton M.; Lotz, Jennifer [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Hathi, Nimish P. [Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States); Huang, Kuang-Han [Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Newman, Jeffrey A. [Department of Physics and Astronomy, University of Pittsburgh, 3941 O' Hara Street, Pittsburgh, PA 15260 (United States); and others

2012-07-10

We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies (SFGs) at 0.5 < z < 1.5 and 326 SFGs at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of GOODS-South. Galaxies were selected to be more massive than 10{sup 10} M{sub Sun} and have specific star formation rates (SFRs) above 1/t{sub H} . We model the seven-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible in the inferred stellar mass distributions. Off-center clumps contribute up to {approx}20% to the integrated SFR, but only 7% or less to the integrated mass of all massive SFGs at z {approx} 1 and z {approx} 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100-200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.

RADIAL DISTRIBUTION OF STARS, GAS, AND DUST IN SINGS GALAXIES. III. MODELING THE EVOLUTION OF THE STELLAR COMPONENT IN GALAXY DISKS

International Nuclear Information System (INIS)

Munoz-Mateos, J. C.; Boissier, S.; Gil de Paz, A.; Zamorano, J.; Gallego, J.; Kennicutt, R. C. Jr; Moustakas, J.; Prantzos, N.

2011-01-01

We analyze the evolution of 42 spiral galaxies in the Spitzer Infrared Nearby Galaxies Survey. We make use of ultraviolet (UV), optical, and near-infrared radial profiles, corrected for internal extinction using the total-infrared to UV ratio, to probe the emission of stellar populations of different ages as a function of galactocentric distance. We fit these radial profiles with models that describe the chemical and spectro-photometric evolution of spiral disks within a self-consistent framework. These backward evolutionary models successfully reproduce the multi-wavelength profiles of our galaxies, except for the UV profiles of some early-type disks for which the models seem to retain too much gas. From the model fitting we infer the maximum circular velocity of the rotation curve V C and the dimensionless spin parameter λ. The values of V C are in good agreement with the velocities measured in H I rotation curves. Even though our sample is not volume limited, the resulting distribution of λ is close to the lognormal function obtained in cosmological N-body simulations, peaking at λ ∼ 0.03 regardless of the total halo mass. We do not find any evident trend between λ and Hubble type, besides an increase in the scatter for the latest types. According to the model, galaxies evolve along a roughly constant mass-size relation, increasing their scale lengths as they become more massive. The radial scale length of most disks in our sample seems to have increased at a rate of 0.05-0.06 kpc Gyr -1 , although the same cannot be said of a volume-limited sample. In relative terms, the scale length has grown by 20%-25% since z = 1 and, unlike the former figure, we argue that this relative growth rate can be indeed representative of a complete galaxy sample.

Radial Distribution of Stars, Gas, and Dust in SINGS Galaxies. III. Modeling the Evolution of the Stellar Component in Galaxy Disks

Science.gov (United States)

Muñoz-Mateos, J. C.; Boissier, S.; Gil de Paz, A.; Zamorano, J.; Kennicutt, R. C., Jr.; Moustakas, J.; Prantzos, N.; Gallego, J.

2011-04-01

We analyze the evolution of 42 spiral galaxies in the Spitzer Infrared Nearby Galaxies Survey. We make use of ultraviolet (UV), optical, and near-infrared radial profiles, corrected for internal extinction using the total-infrared to UV ratio, to probe the emission of stellar populations of different ages as a function of galactocentric distance. We fit these radial profiles with models that describe the chemical and spectro-photometric evolution of spiral disks within a self-consistent framework. These backward evolutionary models successfully reproduce the multi-wavelength profiles of our galaxies, except for the UV profiles of some early-type disks for which the models seem to retain too much gas. From the model fitting we infer the maximum circular velocity of the rotation curve V C and the dimensionless spin parameter λ. The values of V C are in good agreement with the velocities measured in H I rotation curves. Even though our sample is not volume limited, the resulting distribution of λ is close to the lognormal function obtained in cosmological N-body simulations, peaking at λ ~ 0.03 regardless of the total halo mass. We do not find any evident trend between λ and Hubble type, besides an increase in the scatter for the latest types. According to the model, galaxies evolve along a roughly constant mass-size relation, increasing their scale lengths as they become more massive. The radial scale length of most disks in our sample seems to have increased at a rate of 0.05-0.06 kpc Gyr-1, although the same cannot be said of a volume-limited sample. In relative terms, the scale length has grown by 20%-25% since z = 1 and, unlike the former figure, we argue that this relative growth rate can be indeed representative of a complete galaxy sample.

PyTranSpot: A tool for multiband light curve modeling of planetary transits and stellar spots

Science.gov (United States)

Juvan, Ines G.; Lendl, M.; Cubillos, P. E.; Fossati, L.; Tregloan-Reed, J.; Lammer, H.; Guenther, E. W.; Hanslmeier, A.

2018-02-01

Several studies have shown that stellar activity features, such as occulted and non-occulted starspots, can affect the measurement of transit parameters biasing studies of transit timing variations and transmission spectra. We present PyTranSpot, which we designed to model multiband transit light curves showing starspot anomalies, inferring both transit and spot parameters. The code follows a pixellation approach to model the star with its corresponding limb darkening, spots, and transiting planet on a two dimensional Cartesian coordinate grid. We combine PyTranSpot with a Markov chain Monte Carlo framework to study and derive exoplanet transmission spectra, which provides statistically robust values for the physical properties and uncertainties of a transiting star-planet system. We validate PyTranSpot's performance by analyzing eleven synthetic light curves of four different star-planet systems and 20 transit light curves of the well-studied WASP-41b system. We also investigate the impact of starspots on transit parameters and derive wavelength dependent transit depth values for WASP-41b covering a range of 6200-9200 Å, indicating a flat transmission spectrum.

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)

Measuring the opacity of stellar interior matter in terrestrial laboratories

Science.gov (United States)

Bailey, James

2015-11-01

How does energy propagate from the core to the surface of the Sun, where it emerges to warm the Earth? Nearly a century ago Eddington recognized that the attenuation of radiation by stellar matter controls the internal structure of stars like the sun. Opacities for high energy density (HED) matter are challenging to calculate because accurate and complete descriptions of the energy levels, populations, and plasma effects such as continuum lowering and line broadening are needed for partially ionized atoms. This requires approximations, in part because billions of bound-bound and bound-free electronic transitions can contribute to the opacity. Opacity calculations, however, have never been benchmarked against laboratory measurements at stellar interior conditions. Laboratory opacity measurements were limited in the past by the challenges of creating and diagnosing sufficiently large and uniform samples at the extreme conditions found inside stars. In research conducted over more than 10 years, we developed an experimental platform on the Z facility and measured wavelength-resolved iron opacity at electron temperatures Te = 156-195 eV and densities ne = 0.7-4.0 x 1022 cm-3 - conditions very similar to the radiation/convection boundary zone within the Sun. The wavelength-dependent opacity in the 975-1775 eV photon energy range is 30-400% higher than models predict. This raises questions about how well we understand the behavior of atoms in HED plasma. These measurements may also help resolve decade-old discrepancies between solar model predictions and helioseismic observations. This talk will provide an overview of the measurements, investigations of possible errors, and ongoing experiments aimed at testing hypotheses to resolve the model-data discrepancy. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.

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)

First tests of a multi-wavelength mini-DIAL system for the automatic detection of greenhouse gases

Science.gov (United States)

Parracino, S.; Gelfusa, M.; Lungaroni, M.; Murari, A.; Peluso, E.; Ciparisse, J. F.; Malizia, A.; Rossi, R.; Ventura, P.; Gaudio, P.

2017-10-01

Considering the increase of atmospheric pollution levels in our cities, due to emissions from vehicles and domestic heating, and the growing threat of terrorism, it is necessary to develop instrumentation and gather know-how for the automatic detection and measurement of dangerous substances as quickly and far away as possible. The Multi- Wavelength DIAL, an extension of the conventional DIAL technique, is one of the most powerful remote sensing methods for the identification of multiple substances and seems to be a promising solution compared to existing alternatives. In this paper, first in-field tests of a smart and fully automated Multi-Wavelength mini-DIAL will be presented and discussed in details. The recently developed system, based on a long-wavelength infrared (IR-C) CO2 laser source, has the potential of giving an early warning, whenever something strange is found in the atmosphere, followed by identification and simultaneous concentration measurements of many chemical species, ranging from the most important Greenhouse Gases (GHG) to other harmful Volatile Organic Compounds (VOCs). Preliminary studies, regarding the fingerprint of the investigated substances, have been carried out by cross-referencing database of infrared (IR) spectra, obtained using in-cell measurements, and typical Mixing Ratios in the examined region, extrapolated from the literature. First experiments in atmosphere have been performed into a suburban and moderately-busy area of Rome. Moreover, to optimize the automatic identification of the harmful species to be recognized on the basis of in cell measurements of the absorption coefficient spectra, an advanced multivariate statistical method for classification has been developed and tested.

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.

Experimental evidence of the generation of multi-hundred megabar pressures in 0.26 μm wavelength laser experiments

International Nuclear Information System (INIS)

Fabro, R.; Faral, B.; Virmont, J.; Pepin, H.; Cottet, F.; Romain, J.P.

1986-01-01

A 9 μm thick aluminium foil is accelerated to a velocity of about 160 km/s by a laser of 0.26 μm wavelength and intensity of 10 15 W/cm 2 and collides with an aluminium impact foil. The measurement of the velocity of the induced shock wave in the impact foil, using a step method at the rear of the impact foil, gives pressures in the multi-hundred megabar range. The dynamics and constraints of this shock wave are presented and the effect of X-ray preheating, which can be important at this laser wavelength, is discussed. (author)

Experimental evidence of the generation of multi-hundred megabar pressures in 0. 26. mu. m wavelength laser experiments

Energy Technology Data Exchange (ETDEWEB)

Fabro, R.; Faral, B.; Virmont, J.; Pepin, H.; Cottet, F.; Romain, J.P.

A 9 ..mu..m thick aluminium foil is accelerated to a velocity of about 160 km/s by a laser of 0.26 ..mu..m wavelength and intensity of 10/sup 15/ W/cm/sup 2/ and collides with an aluminium impact foil. The measurement of the velocity of the induced shock wave in the impact foil, using a step method at the rear of the impact foil, gives pressures in the multi-hundred megabar range. The dynamics and constraints of this shock wave are presented and the effect of X-ray preheating, which can be important at this laser wavelength, is discussed.

The first multi-wavelength campaign of AXP 4U 0142+61 from radio to hard X-rays

NARCIS (Netherlands)

den Hartog, P.R.; Kuiper, L.; Hermsen, W.; Rea, N.; Durant, M.; Stappers, B.; Kaspi, V.M.; Dib, R.

2007-01-01

For the first time a quasi-simultaneous multi-wavelength campaign has been performed on an Anomalous X-ray Pulsar from the radio to the hard X-ray band. 4U 0142+61 was an INTEGRAL target for 1 Ms in July 2005. During these observations it was also observed in the X-ray band with Swift and RXTE, in

Tutorial: Asteroseismic Stellar Modelling with AIMS

Science.gov (United States)

Lund, Mikkel N.; Reese, Daniel R.

The goal of aims (Asteroseismic Inference on a Massive Scale) is to estimate stellar parameters and credible intervals/error bars in a Bayesian manner from a set of asteroseismic frequency data and so-called classical constraints. To achieve reliable parameter estimates and computational efficiency, it searches through a grid of pre-computed models using an MCMC algorithm—interpolation within the grid of models is performed by first tessellating the grid using a Delaunay triangulation and then doing a linear barycentric interpolation on matching simplexes. Inputs for the modelling consist of individual frequencies from peak-bagging, which can be complemented with classical spectroscopic constraints. aims is mostly written in Python with a modular structure to facilitate contributions from the community. Only a few computationally intensive parts have been rewritten in Fortran in order to speed up calculations.

THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G): MULTI-COMPONENT DECOMPOSITION STRATEGIES AND DATA RELEASE

Energy Technology Data Exchange (ETDEWEB)

Salo, Heikki; Laurikainen, Eija; Laine, Jarkko; Comerón, Sebastien [Astronomy and Space Physics, University of Oulu, FI-90014 (Finland); Gadotti, Dimitri A.; Kim, Taehyun [European Southern Observatory, Casilla 19001, Santiago 19 (Chile); Buta, Ron [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 (United States); Sheth, Kartik; Muñoz-Mateos, Juan Carlos [National Radio Astronomy Observatory/NAASC, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Zaritsky, Dennis; Hinz, Joannah L. [University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721 (United States); Ho, Luis [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Knapen, Johan; Cisternas, Mauricio [Instituto de Astrofísica de Canarias, E-38205 La Laguna (Spain); Athanassoula, E.; Bosma, Albert [Aix Marseille Universite, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France); Laine, Seppo [Spitzer Science Center—Caltech, MS 314-6, Pasadena, CA 91125 (United States); Regan, Michael [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); De Paz, Armando Gil [Departamento de Astrofísica, Universidad Complutense de Madrid, Madrid E-28040 (Spain); Menendez-Delmestre, Karin [Observatorio do Valongo, Universidade Federal de Rio de Janeiro, Ladeira Pedro Antonio, 43, Saude CEP 20080-090, Rio de Janeiro—RJ (Brazil); and others

2015-07-20

The Spitzer Survey of Stellar Structure in Galaxies (S{sup 4}G) is a deep 3.6 and 4.5 μm imaging survey of 2352 nearby (<40 Mpc) galaxies. We describe the S{sup 4}G data analysis pipeline 4, which is dedicated to two-dimensional structural surface brightness decompositions of 3.6 μm images, using GALFIT3.0. Besides automatic 1-component Sérsic fits, and 2-component Sérsic bulge + exponential disk fits, we present human-supervised multi-component decompositions, which include, when judged appropriate, a central point source, bulge, disk, and bar components. Comparison of the fitted parameters indicates that multi-component models are needed to obtain reliable estimates for the bulge Sérsic index and bulge-to-total light ratio (B/T), confirming earlier results. Here, we describe the preparations of input data done for decompositions, give examples of our decomposition strategy, and describe the data products released via IRSA and via our web page (www.oulu.fi/astronomy/S4G-PIPELINE4/MAIN). These products include all the input data and decomposition files in electronic form, making it easy to extend the decompositions to suit specific science purposes. We also provide our IDL-based visualization tools (GALFIDL) developed for displaying/running GALFIT-decompositions, as well as our mask editing procedure (MASK-EDIT) used in data preparation. A detailed analysis of the bulge, disk, and bar parameters derived from multi-component decompositions will be published separately.

Intra-Day Variability of Sagittarius A* at Multi-Wavelengths Z. Q. ...

Indian Academy of Sciences (India)

detect the weak counterpart of Sgr A* at NIR/IR wavelength. Genzel et al. ... of QPO activity is still hotly debated mainly because of the low signal-noise ratio ... 7 mm light curves could be fitted simultaneously with the expanding plasmon model.

Alien wavelength modeling tool and field trial

DEFF Research Database (Denmark)

Sambo, N.; Sgambelluri, A.; Secondini, M.

2015-01-01

A modeling tool is presented for pre-FEC BER estimation of PM-QPSK alien wavelength signals. A field trial is demonstrated and used as validation of the tool's correctness. A very close correspondence between the performance of the field trial and the one predicted by the modeling tool has been...

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

The effects of LMWOAs on biodegradation of multi-component PAHs in aqueous solution using dual-wavelength fluorimetry

International Nuclear Information System (INIS)

Wei Xingyuan; Sang Lingzi; Chen Jianing; Zhu Yaxian; Zhang Yong

2009-01-01

Biodegradation of dissolved fluorene (Flu), phenanthrene (Ph) and pyrene (Py), three polycyclic aromatic hydrocarbons (PAHs), singly or as a mixture of the three, by two bacterial strains, MEBIC 5140 (Mycobacterium flavescens) and MEBIC 5141 (Mycobacterium scrofulaceum), as well as the effects of low molecular weight organic acids (LMWOAs), e.g. malic acid, citric acid and butyric acid on biodegradation of the three PAHs in mineral salts medium aqueous solution were investigated using a newly established dual-wavelength fluorimetric method. The results showed that biodegradation processes can be monitored simultaneously, quickly and simply by dual-wavelength fluorimetry. Both co-metabolism and inhibitory effects were found during the biodegradation of the three PAHs by MEBIC 5140 and MEBIC 5141. Positive effects of butyric acid and negative effects of citric acid on biodegradation of the three PAHs in a mixture were observed. - Biodegradation processes of dissolved multi-component PAHs in a mixture and effects of LMWOAs were investigated using a dual-wavelength fluorimetry.

The Updated BaSTI Stellar Evolution Models and Isochrones. I. Solar-scaled Calculations

DEFF Research Database (Denmark)

Hidalgo, Sebastian L.; Pietrinferni, Adriano; Cassisi, Santi

2018-01-01

We present an updated release of the BaSTI (a Bag of Stellar Tracks and Isochrones) stellar model and isochrone library for a solar-scaled heavy element distribution. The main input physics that have been changed from the previous BaSTI release include the solar metal mixture, electron conduction...... to metal enrichment ratio dY/dZ = 1.31. The isochrones cover an age range between 20 Myr and 14.5 Gyr, consistently take into account the pre-main-sequence phase, and have been translated to a large number of popular photometric systems. Asteroseismic properties of the theoretical models have also been...... calculated. We compare our isochrones with results from independent databases and with several sets of observations to test the accuracy of the calculations. All stellar evolution tracks, asteroseismic properties, and isochrones are made available through a dedicated web site....

A NEW GENERATION OF PARSEC-COLIBRI STELLAR ISOCHRONES INCLUDING THE TP-AGB PHASE

International Nuclear Information System (INIS)

Marigo, Paola; Aringer, Bernhard; Chen, Yang; Dussin, Marco; Nanni, Ambra; Pastorelli, Giada; Rodrigues, Thaíse S.; Trabucchi, Michele; Bladh, Sara; Montalbán, Josefina; Girardi, Léo; Bressan, Alessandro; Rosenfield, Philip; Dalcanton, Julianne; Groenewegen, Martin A. T.; Wood, Peter R.

2017-01-01

We introduce a new generation of PARSEC–COLIBRI stellar isochrones that includes a detailed treatment of the thermally pulsing asymptotic giant branch (TP-AGB) phase, covering a wide range of initial metallicities (0.0001 < Z i < 0.06). Compared to previous releases, the main novelties and improvements are use of new TP-AGB tracks and related atmosphere models and spectra for M and C-type stars; inclusion of the surface H+He+CNO abundances in the isochrone tables, accounting for the effects of diffusion, dredge-up episodes and hot-bottom burning; inclusion of complete thermal pulse cycles, with a complete description of the in-cycle changes in the stellar parameters; new pulsation models to describe the long-period variability in the fundamental and first-overtone modes; and new dust models that follow the growth of the grains during the AGB evolution, in combination with radiative transfer calculations for the reprocessing of the photospheric emission. Overall, these improvements are expected to lead to a more consistent and detailed description of properties of TP-AGB stars expected in resolved stellar populations, especially in regard to their mean photometric properties from optical to mid-infrared wavelengths. We illustrate the expected numbers of TP-AGB stars of different types in stellar populations covering a wide range of ages and initial metallicities, providing further details on the “C-star island” that appears at intermediate values of age and metallicity, and about the AGB-boosting effect that occurs at ages close to 1.6-Gyr for populations of all metallicities. The isochrones are available through a new dedicated web server.

A NEW GENERATION OF PARSEC-COLIBRI STELLAR ISOCHRONES INCLUDING THE TP-AGB PHASE

Energy Technology Data Exchange (ETDEWEB)

Marigo, Paola; Aringer, Bernhard; Chen, Yang; Dussin, Marco; Nanni, Ambra; Pastorelli, Giada; Rodrigues, Thaíse S.; Trabucchi, Michele; Bladh, Sara; Montalbán, Josefina [Dipartimento di Fisica e Astronomia Galileo Galilei, Università di Padova, Vicolo dell’Osservatorio 3, I-35122 Padova (Italy); Girardi, Léo [Osservatorio Astronomico di Padova—INAF, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy); Bressan, Alessandro [SISSA, via Bonomea 365, I-34136 Trieste (Italy); Rosenfield, Philip [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Dalcanton, Julianne [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Groenewegen, Martin A. T. [Koninklijke Sterrenwacht van België, Ringlaan 3, B-1180 Brussels (Belgium); Wood, Peter R. [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia)

2017-01-20

We introduce a new generation of PARSEC–COLIBRI stellar isochrones that includes a detailed treatment of the thermally pulsing asymptotic giant branch (TP-AGB) phase, covering a wide range of initial metallicities (0.0001 < Z {sub i} < 0.06). Compared to previous releases, the main novelties and improvements are use of new TP-AGB tracks and related atmosphere models and spectra for M and C-type stars; inclusion of the surface H+He+CNO abundances in the isochrone tables, accounting for the effects of diffusion, dredge-up episodes and hot-bottom burning; inclusion of complete thermal pulse cycles, with a complete description of the in-cycle changes in the stellar parameters; new pulsation models to describe the long-period variability in the fundamental and first-overtone modes; and new dust models that follow the growth of the grains during the AGB evolution, in combination with radiative transfer calculations for the reprocessing of the photospheric emission. Overall, these improvements are expected to lead to a more consistent and detailed description of properties of TP-AGB stars expected in resolved stellar populations, especially in regard to their mean photometric properties from optical to mid-infrared wavelengths. We illustrate the expected numbers of TP-AGB stars of different types in stellar populations covering a wide range of ages and initial metallicities, providing further details on the “C-star island” that appears at intermediate values of age and metallicity, and about the AGB-boosting effect that occurs at ages close to 1.6-Gyr for populations of all metallicities. The isochrones are available through a new dedicated web server.

EARLY-TYPE GALAXIES AT z ∼ 1.3. II. MASSES AND AGES OF EARLY-TYPE GALAXIES IN DIFFERENT ENVIRONMENTS AND THEIR DEPENDENCE ON STELLAR POPULATION MODEL ASSUMPTIONS

International Nuclear Information System (INIS)

Raichoor, A.; Mei, S.; Huertas-Company, M.; Nakata, F.; Kodama, T.; Stanford, S. A.; Rettura, A.; Jee, M. J.; Holden, B. P.; Illingworth, G.; Postman, M.; White, R. L.; Rosati, P.; Blakeslee, J. P.; Demarco, R.; Eisenhardt, P.; Tanaka, M.

2011-01-01

We have derived masses and ages for 79 early-type galaxies (ETGs) in different environments at z ∼ 1.3 in the Lynx supercluster and in the GOODS/CDF-S field using multi-wavelength (0.6-4.5 μm; KPNO, Palomar, Keck, Hubble Space Telescope, Spitzer) data sets. At this redshift the contribution of the thermally pulsing asymptotic giant branch (TP-AGB) phase is important for ETGs, and the mass and age estimates depend on the choice of the stellar population model used in the spectral energy distribution fits. We describe in detail the differences among model predictions for a large range of galaxy ages, showing the dependence of these differences on age. Current models still yield large uncertainties. While recent models from Maraston and Charlot and Bruzual offer better modeling of the TP-AGB phase with respect to less recent Bruzual and Charlot models, their predictions do not often match. The modeling of this TP-AGB phase has a significant impact on the derived parameters for galaxies observed at high redshift. Some of our results do not depend on the choice of the model: for all models, the most massive galaxies are the oldest ones, independent of the environment. When using the Maraston and Charlot and Bruzual models, the mass distribution is similar in the clusters and in the groups, whereas in our field sample there is a deficit of massive (M ∼> 10 11 M sun ) ETGs. According to those last models, ETGs belonging to the cluster environment host on average older stars with respect to group and field populations. This difference is less significant than the age difference in galaxies of different masses.

Wavelength-Dependent PSFs and their Impact on Weak Lensing Measurements

Science.gov (United States)

Carlsten, S. G.; Strauss, Michael A.; Lupton, Robert H.; Meyers, Joshua E.; Miyazaki, Satoshi

2018-06-01

We measure and model the wavelength dependence of the point spread function (PSF) in the Hyper Suprime-Cam Subaru Strategic Program survey. We find that PSF chromaticity is present in that redder stars appear smaller than bluer stars in the g, r, and i-bands at the 1-2 per cent level and in the z and y-bands at the 0.1-0.2 per cent level. From the color dependence of the PSF, we fit a model between the monochromatic PSF size based on weighted second moments, R, and wavelength of the form R(λ)∝λ-b. We find values of b between 0.2 and 0.5, depending on the epoch and filter. This is consistent with the expectations of a turbulent atmosphere with an outer scale length of ˜10 - 100 m, indicating that the atmosphere is dominating the chromaticity. In the best seeing data, we find that the optical system and detector also contribute some wavelength dependence. Meyers & Burchat (2015b) showed that b must be measured to an accuracy of ˜0.02 not to dominate the systematic error budget of the Large Synoptic Survey Telescope (LSST) weak lensing (WL) survey. Using simple image simulations, we find that b can be inferred with this accuracy in the r and i-bands for all positions in the LSST focal plane, assuming a stellar density of 1 star arcmin-2 and that the optical component of the PSF can be accurately modeled. Therefore, it is possible to correct for most, if not all, of the bias that the wavelength-dependent PSF will introduce into an LSST-like WL survey.

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.

A tunable narrow-line-width multi-wavelength Er-doped fiber laser based on a high birefringence fiber ring mirror and an auto-tracking filter

Science.gov (United States)

Jia, Xiu-jie; Liu, Yan-ge; Si, Li-bin; Guo, Zhan-cheng; Fu, Sheng-gui; Kai, Gui-yun; Dong, Xiao-yi

2008-01-01

A novel multi-wavelength erbium-doped fiber laser operating in C-band is proposed and successfully demonstrated. The wavelength interval between the wavelengths is about 0.22 nm. The 3 dB bandwidth of the laser is about 0.012 nm, and the output power reaches 4.8 mW. By using a high birefringence fiber ring mirror (HiBi-FLM) and a tunable FBG, the laser realizes switchable and tunable characteristic. The mode hopping can be effectively prevented. Moreover, this laser can improve wavelength stability significantly by taking advantage of an un-pumped Er3+-doped fiber at the standing-wave section. The laser can operate in stable narrow-line-width with single-, dual-wavelength, and unstable triple-wavelength output at room temperature.

Multi-Wavelength Spectroscopy of Tidal Disruption Flares: A Legacy Sample for the LSST Era

Science.gov (United States)

Cenko, Stephen

2017-08-01

When a star passes within the sphere of disruption of a massive black hole, tidal forces will overcome self-gravity and unbind the star. While approximately half of the stellar debris is ejected at high velocities, the remaining material stays bound to the black hole and accretes, resulting in a luminous, long-lived transient known as a tidal disruption flare (TDF). In addition to serving as unique laboratories for accretion physics, TDFs offer the hope of measuring black hole masses in galaxies much too distant for resolved kinematic studies.In order to realize this potential, we must better understand the detailed processes by which the bound debris circularizes and forms an accretion disk. Spectroscopy is critical to this effort, as emission and absorption line diagnostics provide insight into the location and physical state (velocity, density, composition) of the emitting gas (in analogy with quasars). UV spectra are particularly critical, as most strong atomic features fall in this bandpass, and high-redshift TDF discoveries from LSST will sample rest-frame UV wavelengths.Here we propose to obtain a sequence of UV (HST) and optical (Gemini/GMOS) spectra for a sample of 5 TDFs discovered by the Zwicky Transient Facility, doubling the number of TDFs with UV spectra. Our observations will directly test models for the generation of the UV/optical emission (circularization vs reprocessing) by searching for outflows and measuring densities, temperatures, and composition as a function of time. This effort is critical to developing the framework by which we can infer black hole properties (e.g., mass) from LSST TDF discoveries.

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.

HUBBLE SPACE TELESCOPE/NEAR-INFRARED CAMERA AND MULTI-OBJECT SPECTROMETER OBSERVATIONS OF THE GLIMPSE9 STELLAR CLUSTER

International Nuclear Information System (INIS)

Messineo, Maria; Figer, Donald F.; Davies, Ben; Trombley, Christine; Kudritzki, R. P.; Rich, R. Michael; MacKenty, John

2010-01-01

We present Hubble Space Telescope/Near-Infrared Camera and Multi-Object Spectrometer photometry, and low-resolution K-band spectra of the GLIMPSE9 stellar cluster. The newly obtained color-magnitude diagram shows a cluster sequence with H - K S = ∼1 mag, indicating an interstellar extinction A K s = 1.6 ± 0.2 mag. The spectra of the three brightest stars show deep CO band heads, which indicate red supergiants with spectral type M1-M2. Two 09-B2 supergiants are also identified, which yield a spectrophotometric distance of 4.2 ± 0.4 kpc. Presuming that the population is coeval, we derive an age between 15 and 27 Myr, and a total cluster mass of 1600 ± 400 M sun , integrated down to 1 M sun . In the vicinity of GLIMPSE9 are several H II regions and supernova remnants, all of which (including GLIMPSE9) are probably associated with a giant molecular cloud (GMC) in the inner galaxy. GLIMPSE9 probably represents one episode of massive star formation in this GMC. We have identified several other candidate stellar clusters of the same complex.

On the universal stellar law

Science.gov (United States)

Krot, Alexander

stars. In this connection, comparison with estimations of temperatures using of the regression dependences for multi-planet extrasolar systems [8] testifies the obtained results entirely. References 1. Krot, A.M.:2009, A statistical approach to investigate the formation of the solar system. Chaos, Solitons and Fractals41(3), 1481-1500. 2. Krot, A.M.:2012, A models of forming planets and distribution of planetary distances and orbits in the solar system based on the statistical theory of spheroidal bodies. In:Solar System: Structure, Formation and Exploration, ch.9 (Ed. by Matteo de Rossi). New York, Nova Science Publishers, pp. 201-264. - ISBN: 978-1-62100-057-0. 3. Krot, A. M.:2012, A statistical theory of formation of gravitating cosmogonicbodies. Minsk,Bel. Navuka, 4. 448 p. - ISBN 978-985-08-1442-5 [monograph in Russian]. 5. Eddington, A.S.: 1916,On the radiative equilibrium of the stars.Mon. Not. Roy. Astron. Soc.84 (7), 525-528. 6. Jeans, J.: 1929, Astronomy and cosmogony. Cambridge, University Press. 7. Chandrasekhar, S.:1939, An introduction to the study of stellar structure.Cambridge, University Press. 8. Pintr, P., Peřinová, V., Lukš, A., Pathak, A.:2013, Statistical and regression analyses of detected extrasolar systems. Planetary and Space Science, 75(1), 37-45.

Multi-wavelength study of the Seyfert 1 galaxy NGC 3783 with XMM-Newton

CERN Document Server

Blustin, A J; Behar, E; Kaastra, J S; Kahn, S M; Page, M J; Sako, M; Steenbrugge, K C

2002-01-01

We present the analysis of multi-wavelength XMM-Newton data from the Seyfert galaxy NGC 3783, including UV imaging, X-ray and UV lightcurves, the 0.2-10 keV X-ray continuum, the iron K-alpha emission line, and high-resolution spectroscopy and modelling of the soft X-ray warm absorber. The 0.2-10 keV spectral continuum can be well reproduced by a power-law at higher energies; we detect a prominent Fe K-alpha emission line, with both broad and narrow components, and a weaker emission line at 6.9 keV which is probably a combination of Fe K-beta and Fe XXVI. We interpret the significant deficit of counts in the soft X-ray region as being due to absorption by ionised gas in the line of sight. This is demonstrated by the large number of narrow absorption lines in the RGS spectrum from iron, oxygen, nitrogen, carbon, neon, argon, magnesium, silicon and sulphur. The wide range of iron states present in the spectrum enables us to deduce the ionisation structure of the absorbing medium. We find that our spectrum contai...

Multi-wavelength fiber laser in the S-band region using a Sagnac loop mirror as a comb generator in an SOA gain medium

International Nuclear Information System (INIS)

Zulkifli, M Z; Hassan, N A; Awang, N A; Ahmad, H; Ghani, Z A; Harun, S W

2010-01-01

A simple design of multi-wavelength generation in the S-band region of the optical network transmission is proposed. The design consists of broad-band fiber Bragg grating (BB-FBG), which acts as a filter to enhance operation in the S-band region. A Sagnac loop mirror (SLM) is used to generate multiple wavelength oscillations in the ring cavity. The output consists of 60 lasing wavelengths oscillating simultaneously between 1464 nm and 1521 nm with a spacing of 0.92 nm and an output linewidth of 0.66 nm

Implications of Stellar Feedback for Dynamical Modeling of the Milky Way and Dwarf Galaxies

Science.gov (United States)

Wetzel, Andrew

2018-04-01

I will present recent results on dynamical modeling of stellar populations from the FIRE cosmological zoom-in baryonic simulations of Milky Way-like and dwarf galaxies. First, I will discuss the dynamical formation of the Milky Way, including the origin of thin+thick stellar disk morphology. I also will discuss the curious origin of metal-rich stars on halo-like orbits near the Sun, as recently measured by Gaia, with new insights from FIRE simulations on stellar radial migration/heating. Next, I will discuss role of stellar feedback in generating non-equilibrium fluctuations of the gravitational potential in low-mass 'dwarf' galaxies, which can explain the origin of cores in their dark-matter density profiles. In particular, we predict significant observable effects on stellar dynamics, including radial migration, size fluctuations, and population gradients, which can provide observational tests of feedback-driven core formation. Finally, this scenario can explain the formation of newly discovered 'ultra-diffuse' galaxies.

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...

Modelling Quasi-Periodic Pulsations in Solar and Stellar Flares

Science.gov (United States)

McLaughlin, J. A.; Nakariakov, V. M.; Dominique, M.; Jelínek, P.; Takasao, S.

2018-02-01

Solar flare emission is detected in all EM bands and variations in flux density of solar energetic particles. Often the EM radiation generated in solar and stellar flares shows a pronounced oscillatory pattern, with characteristic periods ranging from a fraction of a second to several minutes. These oscillations are referred to as quasi-periodic pulsations (QPPs), to emphasise that they often contain apparent amplitude and period modulation. We review the current understanding of quasi-periodic pulsations in solar and stellar flares. In particular, we focus on the possible physical mechanisms, with an emphasis on the underlying physics that generates the resultant range of periodicities. These physical mechanisms include MHD oscillations, self-oscillatory mechanisms, oscillatory reconnection/reconnection reversal, wave-driven reconnection, two loop coalescence, MHD flow over-stability, the equivalent LCR-contour mechanism, and thermal-dynamical cycles. We also provide a histogram of all QPP events published in the literature at this time. The occurrence of QPPs puts additional constraints on the interpretation and understanding of the fundamental processes operating in flares, e.g. magnetic energy liberation and particle acceleration. Therefore, a full understanding of QPPs is essential in order to work towards an integrated model of solar and stellar flares.

A New Method for Deriving the Stellar Birth Function of Resolved Stellar Populations.

Science.gov (United States)

Gennaro, M.; Tchernyshyov, K.; Brown, T. M.; Gordon, K. D.

2015-07-01

We present a new method for deriving the stellar birth function (SBF) of resolved stellar populations. The SBF (stars born per unit mass, time, and metallicity) is the combination of the initial mass function (IMF), the star formation history (SFH), and the metallicity distribution function (MDF). The framework of our analysis is that of Poisson Point Processes (PPPs), a class of statistical models suitable when dealing with points (stars) in a multidimensional space (the measurement space of multiple photometric bands). The theory of PPPs easily accommodates the modeling of measurement errors as well as that of incompleteness. Our method avoids binning stars in the color-magnitude diagram and uses the whole likelihood function for each data point; combining the individual likelihoods allows the computation of the posterior probability for the population's SBF. Within the proposed framework it is possible to include nuisance parameters, such as distance and extinction, by specifying their prior distributions and marginalizing over them. The aim of this paper is to assess the validity of this new approach under a range of assumptions, using only simulated data. Forthcoming work will show applications to real data. Although it has a broad scope of possible applications, we have developed this method to study multi-band Hubble Space Telescope observations of the Milky Way Bulge. Therefore we will focus on simulations with characteristics similar to those of the Galactic Bulge. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

HFF-DeepSpace Photometric Catalogs of the 12 Hubble Frontier Fields, Clusters, and Parallels: Photometry, Photometric Redshifts, and Stellar Masses

Science.gov (United States)

Shipley, Heath V.; Lange-Vagle, Daniel; Marchesini, Danilo; Brammer, Gabriel B.; Ferrarese, Laura; Stefanon, Mauro; Kado-Fong, Erin; Whitaker, Katherine E.; Oesch, Pascal A.; Feinstein, Adina D.; Labbé, Ivo; Lundgren, Britt; Martis, Nicholas; Muzzin, Adam; Nedkova, Kalina; Skelton, Rosalind; van der Wel, Arjen

2018-03-01

We present Hubble multi-wavelength photometric catalogs, including (up to) 17 filters with the Advanced Camera for Surveys and Wide Field Camera 3 from the ultra-violet to near-infrared for the Hubble Frontier Fields and associated parallels. We have constructed homogeneous photometric catalogs for all six clusters and their parallels. To further expand these data catalogs, we have added ultra-deep K S -band imaging at 2.2 μm from the Very Large Telescope HAWK-I and Keck-I MOSFIRE instruments. We also add post-cryogenic Spitzer imaging at 3.6 and 4.5 μm with the Infrared Array Camera (IRAC), as well as archival IRAC 5.8 and 8.0 μm imaging when available. We introduce the public release of the multi-wavelength (0.2–8 μm) photometric catalogs, and we describe the unique steps applied for the construction of these catalogs. Particular emphasis is given to the source detection band, the contamination of light from the bright cluster galaxies (bCGs), and intra-cluster light (ICL). In addition to the photometric catalogs, we provide catalogs of photometric redshifts and stellar population properties. Furthermore, this includes all the images used in the construction of the catalogs, including the combined models of bCGs and ICL, the residual images, segmentation maps, and more. These catalogs are a robust data set of the Hubble Frontier Fields and will be an important aid in designing future surveys, as well as planning follow-up programs with current and future observatories to answer key questions remaining about first light, reionization, the assembly of galaxies, and many more topics, most notably by identifying high-redshift sources to target.

Spatial distribution of turbulence in the Wendelstein 7-AS stellarator (invited paper)

DEFF Research Database (Denmark)

Basse, N.P.; Michelsen, Poul; Zoletnik, S.

2002-01-01

In this paper measurements of short wavelength electron density fluctuations using collective scattering of infrared light are presented. The Wendelstein 7-AS (W7-AS) stellarator (Renner H et al 1989 Plasma Phys. Control. Fusion 31 1579) and the diagnostic are briefly described. A series of plasm...

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.

THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ≤ z ≤ 6.5 IN CANDELS

International Nuclear Information System (INIS)

Salmon, Brett; Papovich, Casey; Tilvi, Vithal; Finkelstein, Steven L.; Finlator, Kristian; Behroozi, Peter; Lu, Yu; Wechsler, Risa H.; Dahlen, Tomas; Ferguson, Henry C.; Davé, Romeel; Dekel, Avishai; Dickinson, Mark; Giavalisco, Mauro; Long, James; Mobasher, Bahram; Reddy, Naveen; Somerville, Rachel S.

2015-01-01

Distant star-forming galaxies show a correlation between their star formation rates (SFRs) and stellar masses, and this has deep implications for galaxy formation. Here, we present a study on the evolution of the slope and scatter of the SFR-stellar mass relation for galaxies at 3.5 ≤ z ≤ 6.5 using multi-wavelength photometry in GOODS-S from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and Spitzer Extended Deep Survey. We describe an updated, Bayesian spectral-energy distribution fitting method that incorporates effects of nebular line emission, star formation histories that are constant or rising with time, and different dust-attenuation prescriptions (starburst and Small Magellanic Cloud). From z = 6.5 to z = 3.5 star-forming galaxies in CANDELS follow a nearly unevolving correlation between stellar mass and SFR that follows SFR ∼ M ⋆ a with a =0.54 ± 0.16 at z ∼ 6 and 0.70 ± 0.21 at z ∼ 4. This evolution requires a star formation history that increases with decreasing redshift (on average, the SFRs of individual galaxies rise with time). The observed scatter in the SFR-stellar mass relation is tight, σ(log SFR/M ☉ yr –1 ) < 0.3-0.4 dex, for galaxies with log M * /M ☉ > 9 dex. Assuming that the SFR is tied to the net gas inflow rate (SFR ∼ M-dot gas ), then the scatter in the gas inflow rate is also smaller than 0.3–0.4 dex for star-forming galaxies in these stellar mass and redshift ranges, at least when averaged over the timescale of star formation. We further show that the implied star formation history of objects selected on the basis of their co-moving number densities is consistent with the evolution in the SFR-stellar mass relation

Laser warning receiver to identify the wavelength and angle of arrival of incident laser light

Science.gov (United States)

Sinclair; Michael B.; Sweatt, William C.

2010-03-23

A laser warning receiver is disclosed which has up to hundreds of individual optical channels each optically oriented to receive laser light from a different angle of arrival. Each optical channel has an optical wedge to define the angle of arrival, and a lens to focus the laser light onto a multi-wavelength photodetector for that channel. Each multi-wavelength photodetector has a number of semiconductor layers which are located in a multi-dielectric stack that concentrates the laser light into one of the semiconductor layers according to wavelength. An electrical signal from the multi-wavelength photodetector can be processed to determine both the angle of arrival and the wavelength of the laser light.

Optical cross-connect circuit using hitless wavelength selective switch.

Science.gov (United States)

Goebuchi, Yuta; Hisada, Masahiko; Kato, Tomoyuki; Kokubun, Yasuo

2008-01-21

We have proposed and demonstrated the basic elements of a full matrix optical switching circuit (cross-connect circuit) using a hitless wavelength selective switch (WSS). The cross-connect circuits are made of a multi-wavelength channel selective switch consisting of cascaded hitless WSSs, and a multi-port switch. These switching elements are realized through the individual Thermo-Optic (TO) tuning of a series-coupled microring resonator, and can switch arbitrary wavelength channels without blocking other wavelength channels during tuning. We demonstrate a four wavelength selective switch using a parallel topology of double series coupled microring resonators and a three wavelength selective switch using a parallel topology of quadruple series coupled microring resonators. Since the spectrum shape of quadruple series coupled microring is much more box-like than the double series, a high extinction ratio of 39.0-46.6 dB and low switching cross talk of 19.3-24.5 dB were achieved.

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.

The new MQ/AAO/Strasbourg multi-wavelength and spectroscopic PNe database: MASPN

Science.gov (United States)

Parker, Quentin Andrew; Bojicic, Ivan; Frew, David; Acker, Agnes; Ochsenbein, Francois; MASPN Database Team

2015-01-01

We are in a new golden age of PN discovery. This is thanks in particular to high sensitivity, wide-field, narrow-band surveys of the Galactic plane undertaken on the UKST in Australia and the Isaac Newton telescope on La Palma. Together these telescopes and their H-alpha surveys have provided very significant Planetary Nebulae (PNe) discoveries that have more than doubled the totals accrued by all telescopes over the previous 250 years. However, these PNe are not simply more of the same found in previous catalogues. Most new PNe are more obscured, evolved and of lower surface brightness than previous compilations while others are faint but compact and more distant. This has required an extensive and time-consuming programme of spectroscopic confirmation on a variety of 2m and 4m telescopes that is now largely complete. The scope of any future large-scale PNe studies, particularly those of a statistical nature or undertaken to understand true PNe diversity and evolution should now reflect this fresh PN population landscape of the combined sample of ~3500 Galactic PNe now available. Such studies should be coloured and nuanced by these recent major discoveries and the massive, high sensitivity, high resolution, multi-wavelength imaging surveys now available across much of the electromagnetic spectrum.Following this motivation we provide, for the first time, an accessible, reliable, on-line "one-stop" SQL database for essential, up-to date information for all known Galactic PN. We have attempted to: i) Reliably remove the many PN mimics/false ID's that have biased previous compilations and subsequent studies; ii) Provide accurate, updated positions, sizes, morphologies, radial velocities, fluxes, multi-wavelength imagery and spectroscopy; iii) Link to CDS/Vizier and hence provide archival history for each object; iv) Provide an interface to sift, select, browse, collate, investigate, download and visualise the complete currently known Galactic PNe diaspora and v

Development of SAC-OCDMA in FSO with multi-wavelength laser source

Science.gov (United States)

Moghaddasi, Majid; Mamdoohi, Ghazaleh; Muhammad Noor, Ahmad Shukri; Mahdi, Mohd Adzir; Ahmad Anas, Siti Barirah

2015-12-01

We propose and demonstrate a free space optical network, based on spectral amplitude coding optical code division multiple access (SAC-OCDMA) with a multi-wavelength laser source. A detailed theoretical analysis that represents the characteristics of SAC-OCDMA system was developed. In addition to the impact of turbulence, influences of several system noises such as optical beat interference (OBI), relative intensity noise, and receiver noises, have been studied. From the numerical results, it was found that the influence of OBI is more dominant, especially at higher received power. Two different codes, namely, modified quadratic congruence and modified double weight, are then compared with the latter which provides better performance. A transmission distance of 2.6 km with 10 users and an 8 cm aperture diameter is advisable whenever the turbulence is moderate. These results can be improved when a beam divergence smaller than 1 mrad is utilized.

Surveying the agents of galaxy evolution in the tidally stripped, low metallicity small Magellanic Cloud (SAGE-SMC). III. Young stellar objects

International Nuclear Information System (INIS)

Sewiło, M.; Carlson, L. R.; Seale, J. P.; Meixner, M.; Gordon, K.; Shiao, B.

2013-01-01

The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK s ) and optical (UBVI) data, we identified a population of ∼1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.

Surveying the agents of galaxy evolution in the tidally stripped, low metallicity small Magellanic Cloud (SAGE-SMC). III. Young stellar objects

Energy Technology Data Exchange (ETDEWEB)

Sewiło, M. [The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Carlson, L. R. [Sterrewacht Leiden, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Seale, J. P.; Meixner, M.; Gordon, K.; Shiao, B., E-mail: mmsewilo@pha.jhu.edu, E-mail: carlson@strw.leidenuniv.nl, E-mail: seale@stsci.edu, E-mail: meixner@stsci.edu, E-mail: kgordon@stsci.edu, E-mail: shiao@stsci.edu [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); and others

2013-11-20

The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK {sub s}) and optical (UBVI) data, we identified a population of ∼1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.

A Toolbox for Imaging Stellar Surfaces

Science.gov (United States)

Young, John

2018-04-01

In this talk I will review the available algorithms for synthesis imaging at visible and infrared wavelengths, including both gray and polychromatic methods. I will explain state-of-the-art approaches to constraining the ill-posed image reconstruction problem, and selecting an appropriate regularisation function and strength of regularisation. The reconstruction biases that can follow from non-optimal choices will be discussed, including their potential impact on the physical interpretation of the results. This discussion will be illustrated with example stellar surface imaging results from real VLTI and COAST datasets.

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.

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-...

Comparison of Mesa and Device Diameter Variation in Double Wafer-Fused Multi Quantum-Well, Long-Wavelength, Vertical Cavity Surface Emitting Lasers

International Nuclear Information System (INIS)

Menon, P.S.; Kandiah, K.; Burhanuddin Yeop Majlis; Shaari, S.

2011-01-01

Long-wavelength vertical-cavity surface-emitting lasers (LW-VCSELs) have profound advantages compared to traditional edge-emitting lasers offering improved properties with respect to mode selectivity, fibre coupling, threshold currents and integration into 2D arrays or with other electronic devices. Its commercialization is gaining momentum as the local and access network in optical communication system expand. Numerical modeling of LW-VCSEL utilizing wafer-fused InP-based multi-quantum wells (MQW) and GaAs-based distributed Bragg reflectors (DBRs) is presented in this paper. Emphasis is on the device and mesa/pillar diameter design parameter comparison and its effect on the device characteristics. (author)

Limb darkening laws for two exoplanet host stars derived from 3D stellar model atmospheres. Comparison with 1D models and HST light curve observations

Science.gov (United States)

Hayek, W.; Sing, D.; Pont, F.; Asplund, M.

2012-03-01

We compare limb darkening laws derived from 3D hydrodynamical model atmospheres and 1D hydrostatic MARCS models for the host stars of two well-studied transiting exoplanet systems, the late-type dwarfs HD 209458 and HD 189733. The surface brightness distribution of the stellar disks is calculated for a wide spectral range using 3D LTE spectrum formation and opacity sampling⋆. We test our theoretical predictions using least-squares fits of model light curves to wavelength-integrated primary eclipses that were observed with the Hubble Space Telescope (HST). The limb darkening law derived from the 3D model of HD 209458 in the spectral region between 2900 Å and 5700 Å produces significantly better fits to the HST data, removing systematic residuals that were previously observed for model light curves based on 1D limb darkening predictions. This difference arises mainly from the shallower mean temperature structure of the 3D model, which is a consequence of the explicit simulation of stellar surface granulation where 1D models need to rely on simplified recipes. In the case of HD 189733, the model atmospheres produce practically equivalent limb darkening curves between 2900 Å and 5700 Å, partly due to obstruction by spectral lines, and the data are not sufficient to distinguish between the light curves. We also analyze HST observations between 5350 Å and 10 500 Å for this star; the 3D model leads to a better fit compared to 1D limb darkening predictions. The significant improvement of fit quality for the HD 209458 system demonstrates the higher degree of realism of 3D hydrodynamical models and the importance of surface granulation for the formation of the atmospheric radiation field of late-type stars. This result agrees well with recent investigations of limb darkening in the solar continuum and other observational tests of the 3D models. The case of HD 189733 is no contradiction as the model light curves are less sensitive to the temperature stratification of

The Updated BaSTI Stellar Evolution Models and Isochrones. I. Solar-scaled Calculations

Science.gov (United States)

Hidalgo, Sebastian L.; Pietrinferni, Adriano; Cassisi, Santi; Salaris, Maurizio; Mucciarelli, Alessio; Savino, Alessandro; Aparicio, Antonio; Silva Aguirre, Victor; Verma, Kuldeep

2018-04-01

We present an updated release of the BaSTI (a Bag of Stellar Tracks and Isochrones) stellar model and isochrone library for a solar-scaled heavy element distribution. The main input physics that have been changed from the previous BaSTI release include the solar metal mixture, electron conduction opacities, a few nuclear reaction rates, bolometric corrections, and the treatment of the overshooting efficiency for shrinking convective cores. The new model calculations cover a mass range between 0.1 and 15 M ⊙, 22 initial chemical compositions between [Fe/H] = ‑3.20 and +0.45, with helium to metal enrichment ratio dY/dZ = 1.31. The isochrones cover an age range between 20 Myr and 14.5 Gyr, consistently take into account the pre-main-sequence phase, and have been translated to a large number of popular photometric systems. Asteroseismic properties of the theoretical models have also been calculated. We compare our isochrones with results from independent databases and with several sets of observations to test the accuracy of the calculations. All stellar evolution tracks, asteroseismic properties, and isochrones are made available through a dedicated web site.

Evolution and nucleosynthesis of asymptotic giant branch stellar models of low metallicity

Energy Technology Data Exchange (ETDEWEB)

Fishlock, Cherie K.; Karakas, Amanda I.; Yong, David [Research School of Astronomy and Astrophysics, Australian National University, Canberra ACT 2611 (Australia); Lugaro, Maria, E-mail: cherie.fishlock@anu.edu.au, E-mail: amanda.karakas@anu.edu.au, E-mail: david.yong@anu.edu.au, E-mail: maria.lugaro@monash.edu [Monash Centre for Astrophysics, Monash University, Clayton VIC 3800 (Australia)

2014-12-10

We present stellar evolutionary tracks and nucleosynthetic predictions for a grid of stellar models of low- and intermediate-mass asymptotic giant branch (AGB) stars at Z = 0.001 ([Fe/H] =–1.2). The models cover an initial mass range from 1 M {sub ☉} to 7 M {sub ☉}. Final surface abundances and stellar yields are calculated for all elements from hydrogen to bismuth as well as isotopes up to the iron group. We present the first study of neutron-capture nucleosynthesis in intermediate-mass AGB models, including a super-AGB model, of [Fe/H] = –1.2. We examine in detail a low-mass AGB model of 2 M {sub ☉} where the {sup 13}C(α,n){sup 16}O reaction is the main source of neutrons. We also examine an intermediate-mass AGB model of 5 M {sub ☉} where intershell temperatures are high enough to activate the {sup 22}Ne neutron source, which produces high neutron densities up to ∼10{sup 14} n cm{sup –3}. Hot bottom burning is activated in models with M ≥ 3 M {sub ☉}. With the 3 M {sub ☉} model, we investigate the effect of varying the extent in mass of the region where protons are mixed from the envelope into the intershell at the deepest extent of each third dredge-up. We compare the results of the low-mass models to three post-AGB stars with a metallicity of [Fe/H] ≅ – 1.2. The composition is a good match to the predicted neutron-capture abundances except for Pb and we confirm that the observed Pb abundances are lower than what is calculated by AGB models.

Spectra of late type dwarf stars of known abundance for stellar population models

Science.gov (United States)

Oconnell, R. W.

1990-01-01

The project consisted of two parts. The first was to obtain new low-dispersion, long-wavelength, high S/N IUE spectra of F-G-K dwarf stars with previously determined abundances, temperatures, and gravities. To insure high quality, the spectra are either trailed, or multiple exposures are taken within the large aperture. Second, the spectra are assembled into a library which combines the new data with existing IUE Archive data to yield mean spectral energy distributions for each important type of star. My principal responsibility is the construction and maintenance of this UV spectral library. It covers the spectral range 1200-3200A and is maintained in two parts: a version including complete wavelength coverage at the full spectral resolution of the Low Resolution cameras; and a selected bandpass version, consisting of the mean flux in pre-selected 20A bands. These bands are centered on spectral features or continuum regions of special utility - e.g. the C IV lambda 1550 or Mg II lambda 2800 feature. In the middle-UV region, special emphasis is given to those features (including continuum 'breaks') which are most useful in the study of F-G-K star spectra in the integrated light of old stellar populations.

Gravitational Waves from Stellar Black Hole Binaries and the Impact on Nearby Sun-like Stars

Energy Technology Data Exchange (ETDEWEB)

Lopes, Ilídio [Centro Multidisciplinar de Astrofísica, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Silk, Joseph, E-mail: ilidio.lopes@tecnico.ulisboa.pt, E-mail: silk@astro.ox.ac.uk [Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98 bis Boulevard Arago, Paris F-75014 (France)

2017-07-20

We investigate the impact of resonant gravitational waves on quadrupole acoustic modes of Sun-like stars located nearby stellar black hole binary systems (such as GW150914 and GW151226). We find that the stimulation of the low-overtone modes by gravitational radiation can lead to sizeable photometric amplitude variations, much larger than the predictions for amplitudes driven by turbulent convection, which in turn are consistent with the photometric amplitudes observed in most Sun-like stars. For accurate stellar evolution models, using up-to-date stellar physics, we predict photometric amplitude variations of 1–10{sup 3} ppm for a solar mass star located at a distance between 1 au and 10 au from the black hole binary and belonging to the same multi-star system. The observation of such a phenomenon will be within the reach of the Plato mission because the telescope will observe several portions of the Milky Way, many of which are regions of high stellar density with a substantial mixed population of Sun-like stars and black hole binaries.

Multi-wavelength emission from 3C 66A: clues to its redshift and gamma-ray emission location

International Nuclear Information System (INIS)

Yan Da-Hai; Fan Zhong-Hui; Zhou Yao; Dai Ben-Zhong

2013-01-01

The quasi-simultaneous multi-wavelength emission of TeV blazar 3C 66A is studied by using a one-zone multi-component leptonic jet model. It is found that the quasi-simultaneous spectral energy distribution of 3C 66A can be well reproduced; in particular, the first three months of its average Fermi-LAT spectrum can be well reproduced by the synchrotron self-Compton component plus external Compton component of the broad line region (BLR). Clues to its redshift and gamma-ray emission location are obtained. The results indicate the following. (i) On the redshift: The theoretical intrinsic TeV spectra can be predicted by extrapolating the reproduced GeV spectra. Through comparing these extrapolated TeV spectra with the corrected observed TeV spectra from extragalactic background light, it is suggested that the redshift of 3C 66A could be between 0.1 and 0.3, with the most likely value being ∼ 0.2. (ii) On the gamma-ray emission location: To well reproduce the GeV emission of 3C 66A under different assumptions on the BLR, the gamma-ray emission region is always required to be beyond the inner zone of the BLR. The BLR absorption effect on gamma-ray emission confirms this point.

Stellar activity for every TESS star in the Southern sky

Science.gov (United States)

Howard, Ward S.; Law, Nicholas; Fors, Octavi; Corbett, Henry T.; Ratzloff, Jeff; del Ser, Daniel

2018-01-01

Although TESS will search for Earths around more than 200,000 nearby stars, the life-impacting superflare occurrence of these stars remains poorly characterized. We monitor long-term stellar flare occurrence for every TESS star in the accessible sky at 2-minute cadence with the CTIO-based Evryscope, a combination of twenty-four telescopes, together giving instantaneous sky coverage of 8000 square degrees. In collaboration with Owens Valley Long Wavelength Array (LWA) all-sky monitoring, Evryscope also provides optical counterparts to radio flare, CME, and exoplanet-magnetosphere stellar activity searches. A Northern Evryscope will be installed at Mount Laguna Observatory, CA in collaboration with SDSU later this year, enabling stellar activity characterization for the full TESS target list and both continuous viewing zones, as well as providing 100% overlap with LWA radio activity. Targets of interest (e.g. Proxima Cen, TRAPPIST-1) are given special focus. We are currently sensitive to stellar activity down to 1% precision at g' ~ 10 and about 0.2 of a magnitude at g' ~ 15. With 2-minute cadence and a projected 5-year timeline, with 2+ years already recorded, we present preliminary results from an activity characterization of every Southern TESS target.

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).

Tunable and switchable multi-wavelength erbium-doped fiber laser with highly nonlinear photonic crystal fiber and polarization controllers

International Nuclear Information System (INIS)

Liu, X M; Lin, A; Zhao, W; Lu, K Q; Wang, Y S; Zhang, T Y; Chung, Y

2008-01-01

We have proposed a novel multi-wavelength erbium-doped fiber laser by using two polarization controllers and a sampled chirped fiber Bragg grating(SC-FBG). On the assistance of SC-FBG, the proposed fiber lasers with excellent stability and uniformity are tunable and switchable by adjusting the polarization controllers. Our laser can stably lase two waves and up to eight waves simultaneously at room temperature

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)

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.

Being WISE. I. Validating stellar population models and M */L ratios at 3.4 and 4.6 μm

International Nuclear Information System (INIS)

Norris, Mark A.; Meidt, Sharon; Van de Ven, Glenn; Schinnerer, Eva; Groves, Brent; Querejeta, Miguel

2014-01-01

Using data from the Wide-field Infrared Survey Explorer mission, we have measured near infra-red (NIR) photometry of a diverse sample of dust-free stellar systems (globular clusters, dwarf and giant early-type galaxies) which have metallicities that span the range -2.2 < [Fe/H] (dex) < 0.3. This dramatically increases the sample size and broadens the metallicity regime over which the 3.4 (W1) and 4.6 μm (W2) photometry of stellar populations have been examined. We find that the W1 – W2 colors of intermediate and old (>2 Gyr) stellar populations are insensitive to the age of the stellar population, but that the W1 – W2 colors become bluer with increasing metallicity, a trend not well reproduced by most stellar population synthesis (SPS) models. In common with previous studies, we attribute this behavior to the increasing strength of the CO absorption feature located in the 4.6 μm bandpass with metallicity. Having used our sample to validate the efficacy of some of the SPS models, we use these models to derive stellar mass-to-light ratios in the W1 and W2 bands. Utilizing observational data from the SAURON and ATLAS3D surveys, we demonstrate that these bands provide extremely simple, yet robust stellar mass tracers for dust free older stellar populations that are freed from many of the uncertainties common among optical estimators.

A Multi-instrument and Multi-wavelength High Angular Resolution Study of MWC 614: Quantum Heated Particles Inside the Disk Cavity

Science.gov (United States)

Kluska, Jacques; Kraus, Stefan; Davies, Claire L.; Harries, Tim; Willson, Matthew; Monnier, John D.; Aarnio, Alicia; Baron, Fabien; Millan-Gabet, Rafael; Ten Brummelaar, Theo; Che, Xiao; Hinkley, Sasha; Preibisch, Thomas; Sturmann, Judit; Sturmann, Laszlo; Touhami, Yamina

2018-03-01

High angular resolution observations of young stellar objects are required to study the inner astronomical units of protoplanetary disks in which the majority of planets form. As they evolve, gaps open up in the inner disk regions and the disks are fully dispersed within ∼10 Myr. MWC 614 is a pretransitional object with a ∼10 au radius gap. We present a set of high angular resolution observations of this object including SPHERE/ZIMPOL polarimetric and coronagraphic images in the visible, Keck/NIRC2 near-infrared (NIR) aperture masking observations, and Very Large Telescope Interferometer (AMBER, MIDI, and PIONIER) and Center for High Angular Resolution Astronomy (CLASSIC and CLIMB) long-baseline interferometry at infrared wavelengths. We find that all the observations are compatible with an inclined disk (i ∼ 55° at a position angle of ∼20°–30°). The mid-infrared data set confirms that the disk inner rim is at 12.3 ± 0.4 au from the central star. We determined an upper mass limit of 0.34 M ⊙ for a companion inside the cavity. Within the cavity, the NIR emission, usually associated with the dust sublimation region, is unusually extended (∼10 au, 30 times larger than the theoretical sublimation radius) and indicates a high dust temperature (T ∼ 1800 K). As a possible result of companion-induced dust segregation, quantum heated dust grains could explain the extended NIR emission with this high temperature. Our observations confirm the peculiar state of this object where the inner disk has already been accreted onto the star, exposing small particles inside the cavity to direct stellar radiation. Based on observations made with the Keck observatory (NASA program ID N104N2) and with ESO telescopes at the Paranal Observatory (ESO program IDs 073.C-0720, 077.C-0226, 077.C-0521, 083.C-0984, 087.C-0498(A), 190.C-0963, 095.C-0883) and with the Center for High Angular Resolution Astronomy observatory.

Multi-wavelength approach towards on-product overlay accuracy and robustness

Science.gov (United States)

Bhattacharyya, Kaustuve; Noot, Marc; Chang, Hammer; Liao, Sax; Chang, Ken; Gosali, Benny; Su, Eason; Wang, Cathy; den Boef, Arie; Fouquet, Christophe; Huang, Guo-Tsai; Chen, Kai-Hsiung; Cheng, Kevin; Lin, John

2018-03-01

Success of diffraction-based overlay (DBO) technique1,4,5 in the industry is not just for its good precision and low toolinduced shift, but also for the measurement accuracy2 and robustness that DBO can provide. Significant efforts are put in to capitalize on the potential that DBO has to address measurement accuracy and robustness. Introduction of many measurement wavelength choices (continuous wavelength) in DBO is one of the key new capabilities in this area. Along with the continuous choice of wavelengths, the algorithms (fueled by swing-curve physics) on how to use these wavelengths are of high importance for a robust recipe setup that can avoid the impact from process stack variations (symmetric as well as asymmetric). All these are discussed. Moreover, another aspect of boosting measurement accuracy and robustness is discussed that deploys the capability to combine overlay measurement data from multiple wavelength measurements. The goal is to provide a method to make overlay measurements immune from process stack variations and also to report health KPIs for every measurement. By combining measurements from multiple wavelengths, a final overlay measurement is generated. The results show a significant benefit in accuracy and robustness against process stack variation. These results are supported by both measurement data as well as simulation from many product stacks.

INFRARED SPECTROGRAPH SPECTROSCOPY AND MULTI-WAVELENGTH STUDY OF LUMINOUS STAR-FORMING GALAXIES AT z ≅ 1.9

International Nuclear Information System (INIS)

Huang, J.-S.; Lai, K.; Younger, J. D.; Fazio, G. G.; Faber, S. M.; Koo, D.; Daddi, E.; Laird, E. S.; Omont, A.; Wu, Y.; Bundy, K.; Cattaneo, A.; Chapman, S. C.; Conselice, C. J.; Dickinson, M.; Egami, E.; Im, M.; Le Floc'h, E.; Papovich, C.; Rigopoulou, D.

2009-01-01

We analyze a sample of galaxies chosen to have F 24μm > 0.5 mJy and satisfy a certain IRAC color criterion. Infrared Spectrograph (IRS) spectra yield redshifts, spectral types, and polycyclic aromatic hydrocarbons (PAH) luminosities, to which we add broadband photometry from optical through IRAC wavelengths, MIPS from 24-160 μm, 1.1 mm, and radio at 1.4 GHz. Stellar population modeling and IRS spectra together demonstrate that the double criteria used to select this sample have efficiently isolated massive star-forming galaxies at z ∼ 1.9. This is the first starburst (SB)-dominated ultraluminous infrared galaxies (ULIRG) sample at high redshift with total infrared luminosity measured directly from FIR and millimeter photometry, and as such gives us the first accurate view of broadband spectral energy distributions for SB galaxies at extremely high luminosity and at all wavelengths. Similar broadband data are assembled for three other galaxy samples-local SB galaxies, local active galactic nucleus (AGN)/ULIRGs, and a second 24 μm-luminous z ∼ 2 sample dominated by AGN. L PAH /L IR for the new z ∼ 2 SB sample is the highest ever seen, some three times higher than in local SBs, whereas in AGNs this ratio is depressed below the SB trend, often severely. Several pieces of evidence imply that AGNs exist in this SB-dominated sample, except two of which even host very strong AGN, while they still have very strong PAH emission. The Advanced Camera for Surveys images show that most objects have very extended morphologies in the rest-frame ultraviolet band, thus extended distribution of PAH molecules. Such an extended distribution prevents further destruction PAH molecules by central AGNs. We conclude that objects in this sample are ULIRGs powered mainly by SB; and the total infrared luminosity density contributed by this type of objects is 0.9-2.6 x 10 7 L sun Mpc -3 .

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.

A New High-Precision Correction Method of Temperature Distribution in Model Stellar Atmospheres

Directory of Open Access Journals (Sweden)

Sapar A.

2013-06-01

Full Text Available The main features of the temperature correction methods, suggested and used in modeling of plane-parallel stellar atmospheres, are discussed. The main features of the new method are described. Derivation of the formulae for a version of the Unsöld-Lucy method, used by us in the SMART (Stellar Model Atmospheres and Radiative Transport software for modeling stellar atmospheres, is presented. The method is based on a correction of the model temperature distribution based on minimizing differences of flux from its accepted constant value and on the requirement of the lack of its gradient, meaning that local source and sink terms of radiation must be equal. The final relative flux constancy obtainable by the method with the SMART code turned out to have the precision of the order of 0.5 %. Some of the rapidly converging iteration steps can be useful before starting the high-precision model correction. The corrections of both the flux value and of its gradient, like in Unsöld-Lucy method, are unavoidably needed to obtain high-precision flux constancy. A new temperature correction method to obtain high-precision flux constancy for plane-parallel LTE model stellar atmospheres is proposed and studied. The non-linear optimization is carried out by the least squares, in which the Levenberg-Marquardt correction method and thereafter additional correction by the Broyden iteration loop were applied. Small finite differences of temperature (δT/T = 10−3 are used in the computations. A single Jacobian step appears to be mostly sufficient to get flux constancy of the order 10−2 %. The dual numbers and their generalization – the dual complex numbers (the duplex numbers – enable automatically to get the derivatives in the nilpotent part of the dual numbers. A version of the SMART software is in the stage of refactorization to dual and duplex numbers, what enables to get rid of the finite differences, as an additional source of lowering precision of the

The Stellar Initial Mass Function in Early-type Galaxies from Absorption Line Spectroscopy. IV. A Super-Salpeter IMF in the Center of NGC 1407 from Non-parametric Models

Energy Technology Data Exchange (ETDEWEB)

Conroy, Charlie [Department of Astronomy, Harvard University, Cambridge, MA, 02138 (United States); Van Dokkum, Pieter G. [Department of Astronomy, Yale University, New Haven, CT, 06511 (United States); Villaume, Alexa [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

2017-03-10

It is now well-established that the stellar initial mass function (IMF) can be determined from the absorption line spectra of old stellar systems, and this has been used to measure the IMF and its variation across the early-type galaxy population. Previous work focused on measuring the slope of the IMF over one or more stellar mass intervals, implicitly assuming that this is a good description of the IMF and that the IMF has a universal low-mass cutoff. In this work we consider more flexible IMFs, including two-component power laws with a variable low-mass cutoff and a general non-parametric model. We demonstrate with mock spectra that the detailed shape of the IMF can be accurately recovered as long as the data quality is high (S/N ≳ 300 Å{sup −1}) and cover a wide wavelength range (0.4–1.0 μ m). We apply these flexible IMF models to a high S/N spectrum of the center of the massive elliptical galaxy NGC 1407. Fitting the spectrum with non-parametric IMFs, we find that the IMF in the center shows a continuous rise extending toward the hydrogen-burning limit, with a behavior that is well-approximated by a power law with an index of −2.7. These results provide strong evidence for the existence of extreme (super-Salpeter) IMFs in the cores of massive galaxies.

First results of the multi-purpose real-time processing video camera system on the Wendelstein 7-X stellarator and implications for future devices

Science.gov (United States)

Zoletnik, S.; Biedermann, C.; Cseh, G.; Kocsis, G.; König, R.; Szabolics, T.; Szepesi, T.; Wendelstein 7-X Team

2018-01-01

A special video camera has been developed for the 10-camera overview video system of the Wendelstein 7-X (W7-X) stellarator considering multiple application needs and limitations resulting from this complex long-pulse superconducting stellarator experiment. The event detection intelligent camera (EDICAM) uses a special 1.3 Mpixel CMOS sensor with non-destructive read capability which enables fast monitoring of smaller Regions of Interest (ROIs) even during long exposures. The camera can perform simple data evaluation algorithms (minimum/maximum, mean comparison to levels) on the ROI data which can dynamically change the readout process and generate output signals. Multiple EDICAM cameras were operated in the first campaign of W7-X and capabilities were explored in the real environment. Data prove that the camera can be used for taking long exposure (10-100 ms) overview images of the plasma while sub-ms monitoring and even multi-camera correlated edge plasma turbulence measurements of smaller areas can be done in parallel. These latter revealed that filamentary turbulence structures extend between neighboring modules of the stellarator. Considerations emerging for future upgrades of this system and similar setups on future long-pulse fusion experiments such as ITER are discussed.

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.

VERIFYING ASTEROSEISMICALLY DETERMINED PARAMETERS OF KEPLER STARS USING HIPPARCOS PARALLAXES: SELF-CONSISTENT STELLAR PROPERTIES AND DISTANCES

Energy Technology Data Exchange (ETDEWEB)

Silva Aguirre, V.; Chaplin, W. J.; Bedding, T. R.; Christensen-Dalsgaard, J.; Kjeldsen, H. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Casagrande, L. [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, ACT 2611 (Australia); Basu, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Campante, T. L.; Monteiro, M. J. P. F. G. [Centro de Astrofisica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Huber, D. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Miglio, A.; Elsworth, Y.; Hekker, S. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Serenelli, A. M.; Garcia, R. A.; Mathur, S. [Kavli Institute for Theoretical Physics, Santa Barbara, CA 93106 (United States); Ballot, J. [CNRS, Institut de Recherche en Astrophysique et Planetologie, 14 avenue Edouard Belin, F-31400 Toulouse (France); Creevey, O. L. [Laboratoire Lagrange, UMR 7293, Universite de Nice Sophia-Antipolis, CNRS, Observatoire de la Cote dAzur, F-06304 Nice Cedex 4 (France); Gilliland, R. L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA (United States); Metcalfe, T. S. [Space Science Institute, Boulder, CO 80301 (United States); and others

2012-09-20

Accurately determining the properties of stars is of prime importance for characterizing stellar populations in our Galaxy. The field of asteroseismology has been thought to be particularly successful in such an endeavor for stars in different evolutionary stages. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is mandatory. With this purpose, we present a new technique to obtain stellar properties by coupling asteroseismic analysis with the InfraRed Flux Method. By using two global seismic observables and multi-band photometry, the technique allows us to obtain masses, radii, effective temperatures, bolometric fluxes, and hence distances for field stars in a self-consistent manner. We apply our method to 22 solar-like oscillators in the Kepler short-cadence sample, that have accurate Hipparcos parallaxes. Our distance determinations agree to better than 5%, while measurements of spectroscopic effective temperatures and interferometric radii also validate our results. We briefly discuss the potential of our technique for stellar population analysis and models of Galactic Chemical Evolution.

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

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.

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

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.)

EFFECT OF A STELLAR COMPANION ON THE MODELING OF HD 142527 INFRARED SED

OpenAIRE

Erick Nagel

2014-01-01

The discovery of a companion of the Herbig Ae/Be star HD 142527 motivates the study of the effect that it produces on the SED. The main change on the system configuration is the formation of a gap in the disk. Due to this change, a wall (outer edge of the gap), which is frontally illuminated by stellar radiation is formed. We present a model for the SED, considering all the components: a disk with two gaps (one produced by the stellar companion and the other by potential planets), three walls...

The ATLAS3D project - XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

NARCIS (Netherlands)

Scott, Nicholas; Cappellari, Michele; Davies, Roger L.; Kleijn, Gijs Verdoes; Bois, Maxime; Alatalo, Katherine; Blitz, Leo; Bournaud, Frédéric; Bureau, Martin; Crocker, Alison; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

We explore the connection between the local escape velocity, Vesc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of

The ATLAS(3D) project : XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

NARCIS (Netherlands)

Scott, Nicholas; Cappellari, Michele; Davies, Roger L.; Kleijn, Gijs Verdoes; Bois, Maxime; Alatalo, Katherine; Blitz, Leo; Bournaud, Frederic; Bureau, Martin; Crocker, Alison; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnovic, Davor; Kuntschner, Harald; McDermid, Richard M.; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

2013-01-01

We explore the connection between the local escape velocity, V-esc, and the stellar population properties in the ATLAS(3D) survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses

Longitudinal variability in Jupiter's zonal winds derived from multi-wavelength HST observations

Science.gov (United States)

Johnson, Perianne E.; Morales-Juberías, Raúl; Simon, Amy; Gaulme, Patrick; Wong, Michael H.; Cosentino, Richard G.

2018-06-01

Multi-wavelength Hubble Space Telescope (HST) images of Jupiter from the Outer Planets Atmospheres Legacy (OPAL) and Wide Field Coverage for Juno (WFCJ) programs in 2015, 2016, and 2017 are used to derive wind profiles as a function of latitude and longitude. Wind profiles are typically zonally averaged to reduce measurement uncertainties. However, doing this destroys any variations of the zonal-component of winds in the longitudinal direction. Here, we present the results derived from using a "sliding-window" correlation method. This method adds longitudinal specificity, and allows for the detection of spatial variations in the zonal winds. Spatial variations are identified in two jets: 1 at 17 ° N, the location of a prominent westward jet, and the other at 7 ° S, the location of the chevrons. Temporal and spatial variations at the 24°N jet and the 5-μm hot spots are also examined.

Noctilucent cloud particle size determination based on multi-wavelength all-sky analysis

Science.gov (United States)

Ugolnikov, Oleg S.; Galkin, Alexey A.; Pilgaev, Sergey V.; Roldugin, Alexey V.

2017-10-01

The article deals with the analysis of color distribution in noctilucent clouds (NLC) in the sky based on multi-wavelength (RGB) CCD-photometry provided with the all-sky camera in Lovozero in the north of Russia (68.0°N, 35.1°E) during the bright expanded NLC performance in the night of August 12, 2016. Small changes in the NLC color across the sky are interpreted as the atmospheric absorption and extinction effects combined with the difference in the Mie scattering functions of NLC particles for the three color channels of the camera. The method described in this paper is used to find the effective monodisperse radius of particles about 55 nm. The result of these simple and cost-effective measurements is in good agreement with previous estimations of comparable accuracy. Non-spherical particles, Gaussian and lognormal distribution of the particle size are also considered.

SEMI-EMPIRICAL WHITE DWARF INITIAL-FINAL MASS RELATIONSHIPS: A THOROUGH ANALYSIS OF SYSTEMATIC UNCERTAINTIES DUE TO STELLAR EVOLUTION MODELS

International Nuclear Information System (INIS)

Salaris, Maurizio; Serenelli, Aldo; Weiss, Achim; Miller Bertolami, Marcelo

2009-01-01

Using the most recent results about white dwarfs (WDs) in ten open clusters, we revisit semiempirical estimates of the initial-final mass relation (IFMR) in star clusters, with emphasis on the use of stellar evolution models. We discuss the influence of these models on each step of the derivation. One intention of our work is to use consistent sets of calculations both for the isochrones and the WD cooling tracks. The second one is to derive the range of systematic errors arising from stellar evolution theory. This is achieved by using different sources for the stellar models and by varying physical assumptions and input data. We find that systematic errors, including the determination of the cluster age, are dominating the initial mass values, while observational uncertainties influence the final mass primarily. After having determined the systematic errors, the initial-final mass relation allows us finally to draw conclusions about the physics of the stellar models, in particular about convective overshooting.

The LAMOST stellar parameter pipeline at Peking University - LSP3

Science.gov (United States)

Xiang, M. S.; Liu, X. W.; Yuan, H. B.; Huang, Y.; Huo, Z. Y.; Zhang, H. W.; Chen, B. Q.; Zhang, H. H.; Sun, N. C.; Wang, C.; Zhao, Y. H.; Shi, J. R.; Luo, A. L.; Li, G. P.; Wu, Y.; Bai, Z. R.; Zhang, Y.; Hou, Y. H.; Yuan, H. L.; Li, G. W.; Wei, Z.

2015-03-01

We introduce the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) stellar parameter pipeline at Peking University - LSP3, developed and implemented for the determinations of radial velocity Vr and stellar atmospheric parameters (effective temperature Teff, surface gravity log g, metallicity [Fe/H]) for the LAMOST Spectroscopic Survey of the Galactic Anticentre (LSS-GAC). We describe the algorithms of LSP3 and examine the accuracy of parameters yielded by it. The precision and accuracy of parameters yielded are investigated by comparing results of multi-epoch observations and of candidate members of open and globular clusters, with photometric calibration, as well as with independent determinations available from a number of external data bases, including the PASTEL archive, the APOGEE, SDSS and RAVE surveys, as well as those released in the LAMOST DR1. The uncertainties of LSP3 parameters are characterized and quantified as a function of the spectral signal-to-noise ratio (SNR) and stellar atmospheric parameters. We conclude that the current implementation of LSP3 has achieved an accuracy of 5.0 km s-1, 150 K, 0.25 dex, 0.15 dex for the radial velocity, effective temperature, surface gravity and metallicity, respectively, for LSS-GAC spectra of FGK stars of SNRs per pixel higher than 10. The LSP3 has been applied to over a million LSS-GAC spectra collected hitherto. Stellar parameters yielded by the LSP3 will be released to the general public following the data policy of LAMOST, together with estimates of the interstellar extinction E(B - V) and stellar distances, deduced by combining spectroscopic and multiband photometric measurements using a variety of techniques.

Being WISE. I. Validating stellar population models and M {sub *}/L ratios at 3.4 and 4.6 μm

Energy Technology Data Exchange (ETDEWEB)

Norris, Mark A.; Meidt, Sharon; Van de Ven, Glenn; Schinnerer, Eva; Groves, Brent; Querejeta, Miguel, E-mail: norris@mpia.de [Max Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany)

2014-12-10

Using data from the Wide-field Infrared Survey Explorer mission, we have measured near infra-red (NIR) photometry of a diverse sample of dust-free stellar systems (globular clusters, dwarf and giant early-type galaxies) which have metallicities that span the range -2.2 < [Fe/H] (dex) < 0.3. This dramatically increases the sample size and broadens the metallicity regime over which the 3.4 (W1) and 4.6 μm (W2) photometry of stellar populations have been examined. We find that the W1 – W2 colors of intermediate and old (>2 Gyr) stellar populations are insensitive to the age of the stellar population, but that the W1 – W2 colors become bluer with increasing metallicity, a trend not well reproduced by most stellar population synthesis (SPS) models. In common with previous studies, we attribute this behavior to the increasing strength of the CO absorption feature located in the 4.6 μm bandpass with metallicity. Having used our sample to validate the efficacy of some of the SPS models, we use these models to derive stellar mass-to-light ratios in the W1 and W2 bands. Utilizing observational data from the SAURON and ATLAS3D surveys, we demonstrate that these bands provide extremely simple, yet robust stellar mass tracers for dust free older stellar populations that are freed from many of the uncertainties common among optical estimators.

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.

MULTI-WAVELENGTH AFTERGLOWS OF FAST RADIO BURSTS

International Nuclear Information System (INIS)

Yi, Shuang-Xi; Gao, He; Zhang, Bing

2014-01-01

The physical origin of fast radio bursts (FRBs) is unknown. Detecting electromagnetic counterparts to FRBs in other wavelengths is essential to measure their distances and to determine their physical origin. Assuming that at least some of them are of cosmological origin, we calculate their afterglow light curves in multiple wavelengths (X-rays, optical, and radio) by assuming a range of total kinetic energies and redshifts. We focus on forward shock emission, but also consider the possibility that some of the FRBs might have bright reverse shock emission. In general, FRB afterglows are too faint to be detected by current detectors. Only if an FRB has a very low radiative efficiency in radio (hence, a very large kinetic energy), and when it is close enough to observe can its afterglow be detected in the optical and radio bands. We discuss observational strategies for detecting these faint afterglows using future telescopes such as Large Synoptic Survey Telescope and Expanded Very Large Array

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.

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.

A new mechanical stellar wind feedback model for the Rosette Nebula

Science.gov (United States)

Wareing, C. J.; Pittard, J. M.; Wright, N. J.; Falle, S. A. E. G.

2018-04-01

The famous Rosette Nebula has an evacuated central cavity formed from the stellar winds ejected from the 2-6 Myr old codistant and comoving central star cluster NGC 2244. However, with upper age estimates of less than 110 000 yr, the central cavity is too young compared to NGC 2244 and existing models do not reproduce its properties. A new proper motion study herein using Gaia data reveals the ejection of the most massive star in the Rosette, HD 46223, from NGC 2244 occurred 1.73 (+0.34, -0.25) Myr (1σ uncertainty) in the past. Assuming this ejection was at the birth of the most massive stars in NGC 2244, including the dominant centrally positioned HD 46150, the age is set for the famous ionized region at more than 10 times that derived for the cavity. Here, we are able to reproduce the structure of the Rosette Nebula, through simulation of mechanical stellar feedback from a 40 M⊙ star in a thin sheet-like molecular cloud. We form the 135 000 M⊙ cloud from thermally unstable diffuse interstellar medium (ISM) under the influence of a realistic background magnetic field with thermal/magnetic pressure equilibrium. Properties derived from a snapshot of the simulation at 1.5 Myr, including cavity size, stellar age, magnetic field, and resulting inclination to the line of sight, match those derived from observations. An elegant explanation is thus provided for the stark contrast in age estimates based on realistic diffuse ISM properties, molecular cloud formation and stellar wind feedback.

Constraining the Stellar Populations and Star Formation Histories of Blue Compact Dwarf Galaxies with SED Fits

Energy Technology Data Exchange (ETDEWEB)

Janowiecki, Steven [International Center for Radio Astronomy Research, M468, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009 (Australia); Salzer, John J.; Zee, Liese van [Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405 (United States); Rosenberg, Jessica L. [Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030 (United States); Skillman, Evan, E-mail: steven.janowiecki@uwa.edu.au [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street, SE Minneapolis, MN, 55455 (United States)

2017-02-10

We discuss and test possible evolutionary connections between blue compact dwarf galaxies (BCDs) and other types of dwarf galaxies. BCDs provide ideal laboratories to study intense star formation episodes in low-mass dwarf galaxies, and have sometimes been considered a short-lived evolutionary stage between types of dwarf galaxies. To test these connections, we consider a sample of BCDs as well as a comparison sample of nearby galaxies from the Local Volume Legacy (LVL) survey for context. We fit the multi-wavelength spectral energy distributions (SED, far-ultra-violet to far-infrared) of each galaxy with a grid of theoretical models to determine their stellar masses and star formation properties. We compare our results for BCDs with the LVL galaxies to put BCDs in the context of normal galaxy evolution. The SED fits demonstrate that the star formation events currently underway in BCDs are at the extreme of the continuum of normal dwarf galaxies, both in terms of the relative mass involved and in the relative increase over previous star formation rates. Today’s BCDs are distinctive objects in a state of extreme star formation that is rapidly transforming them. This study also suggests ways to identify former BCDs whose star formation episodes have since faded.

THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ≤ z ≤ 6.5 IN CANDELS

Energy Technology Data Exchange (ETDEWEB)

Salmon, Brett; Papovich, Casey; Tilvi, Vithal [George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy Texas A and M University, College Station, TX 77843 (United States); Finkelstein, Steven L. [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States); Finlator, Kristian [DARK fellow, Dark Cosmology Centre, Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, DK-2100 Copenhagen O (Denmark); Behroozi, Peter; Lu, Yu; Wechsler, Risa H. [Physics Department, Stanford University, Particle Astrophysics, SLAC National Accelerator Laboratory, Kavli Institute for Particle Astrophysics and Cosmology Stanford, CA 94305 (United States); Dahlen, Tomas; Ferguson, Henry C. [Space Telescope Science Institute, Baltimore, MD (United States); Davé, Romeel [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Dekel, Avishai [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Dickinson, Mark [National Optical Astronomy Observatories, Tucson, AZ (United States); Giavalisco, Mauro [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Long, James [Department of Statistics, Texas A and M University, College Station, TX 77843-3143 (United States); Mobasher, Bahram; Reddy, Naveen [Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521 (United States); Somerville, Rachel S., E-mail: bsalmon@physics.tamu.edu [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States)

2015-02-01

Distant star-forming galaxies show a correlation between their star formation rates (SFRs) and stellar masses, and this has deep implications for galaxy formation. Here, we present a study on the evolution of the slope and scatter of the SFR-stellar mass relation for galaxies at 3.5 ≤ z ≤ 6.5 using multi-wavelength photometry in GOODS-S from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and Spitzer Extended Deep Survey. We describe an updated, Bayesian spectral-energy distribution fitting method that incorporates effects of nebular line emission, star formation histories that are constant or rising with time, and different dust-attenuation prescriptions (starburst and Small Magellanic Cloud). From z = 6.5 to z = 3.5 star-forming galaxies in CANDELS follow a nearly unevolving correlation between stellar mass and SFR that follows SFR ∼ M{sub ⋆}{sup a} with a =0.54 ± 0.16 at z ∼ 6 and 0.70 ± 0.21 at z ∼ 4. This evolution requires a star formation history that increases with decreasing redshift (on average, the SFRs of individual galaxies rise with time). The observed scatter in the SFR-stellar mass relation is tight, σ(log SFR/M {sub ☉} yr{sup –1}) < 0.3-0.4 dex, for galaxies with log M {sub *}/M {sub ☉} > 9 dex. Assuming that the SFR is tied to the net gas inflow rate (SFR ∼ M-dot {sub gas}), then the scatter in the gas inflow rate is also smaller than 0.3–0.4 dex for star-forming galaxies in these stellar mass and redshift ranges, at least when averaged over the timescale of star formation. We further show that the implied star formation history of objects selected on the basis of their co-moving number densities is consistent with the evolution in the SFR-stellar mass relation.

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.

Radiometric Calibration of a Dual-Wavelength, Full-Waveform Terrestrial Lidar.

Science.gov (United States)

Li, Zhan; Jupp, David L B; Strahler, Alan H; Schaaf, Crystal B; Howe, Glenn; Hewawasam, Kuravi; Douglas, Ewan S; Chakrabarti, Supriya; Cook, Timothy A; Paynter, Ian; Saenz, Edward J; Schaefer, Michael

2016-03-02

Radiometric calibration of the Dual-Wavelength Echidna(®) Lidar (DWEL), a full-waveform terrestrial laser scanner with two simultaneously-pulsing infrared lasers at 1064 nm and 1548 nm, provides accurate dual-wavelength apparent reflectance (ρ(app)), a physically-defined value that is related to the radiative and structural characteristics of scanned targets and independent of range and instrument optics and electronics. The errors of ρ(app) are 8.1% for 1064 nm and 6.4% for 1548 nm. A sensitivity analysis shows that ρ(app) error is dominated by range errors at near ranges, but by lidar intensity errors at far ranges. Our semi-empirical model for radiometric calibration combines a generalized logistic function to explicitly model telescopic effects due to defocusing of return signals at near range with a negative exponential function to model the fall-off of return intensity with range. Accurate values of ρ(app) from the radiometric calibration improve the quantification of vegetation structure, facilitate the comparison and coupling of lidar datasets from different instruments, campaigns or wavelengths and advance the utilization of bi- and multi-spectral information added to 3D scans by novel spectral lidars.

Optimizing wavelength choice for quantitative optoacoustic imaging using the Cramer-Rao lower bound

International Nuclear Information System (INIS)

Modgil, Dimple; La Riviere, Patrick J

2010-01-01

Several papers have recently addressed the issue of estimating chromophore concentration in optoacoustic imaging (OAI) using multiple wavelengths. The choice of wavelengths obviously affects the accuracy and precision of the estimates. One might assume that the wavelengths that maximize the extinction coefficients of the chromophores would be the most suitable. However, this may not always be the case since the distribution of light intensity in the medium is also wavelength dependent. In this paper, we explore a method for optimizing the choice of wavelengths based on the Cramer-Rao lower bound (CRLB) on the variance of the chromophore concentration. This lower bound on variance can be evaluated numerically for different wavelengths using the variation of the extinction coefficients and scattering coefficients with wavelength. The wavelengths that give the smallest variance will be considered optimal for multi-wavelength OAI to estimate the chromophore concentrations. The expression for the CRLB has been derived analytically for estimating the concentration of multiple chromophores for several simple phantom models for the case when the optoacoustic signal is proportional to the product of the optical absorption and the illumination function. This approach could be easily extended to other geometries.

Optimizing wavelength choice for quantitative optoacoustic imaging using the Cramer-Rao lower bound.

Science.gov (United States)

Modgil, Dimple; La Riviére, Patrick J

2010-12-07

Several papers have recently addressed the issue of estimating chromophore concentration in optoacoustic imaging (OAI) using multiple wavelengths. The choice of wavelengths obviously affects the accuracy and precision of the estimates. One might assume that the wavelengths that maximize the extinction coefficients of the chromophores would be the most suitable. However, this may not always be the case since the distribution of light intensity in the medium is also wavelength dependent. In this paper, we explore a method for optimizing the choice of wavelengths based on the Cramer-Rao lower bound (CRLB) on the variance of the chromophore concentration. This lower bound on variance can be evaluated numerically for different wavelengths using the variation of the extinction coefficients and scattering coefficients with wavelength. The wavelengths that give the smallest variance will be considered optimal for multi-wavelength OAI to estimate the chromophore concentrations. The expression for the CRLB has been derived analytically for estimating the concentration of multiple chromophores for several simple phantom models for the case when the optoacoustic signal is proportional to the product of the optical absorption and the illumination function. This approach could be easily extended to other geometries.

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.

A High-resolution Multi-wavelength Simultaneous Imaging System with Solar Adaptive Optics

Energy Technology Data Exchange (ETDEWEB)

Rao, Changhui; Zhu, Lei; Gu, Naiting; Rao, Xuejun; Zhang, Lanqiang; Bao, Hua; Kong, Lin; Guo, Youming; Zhong, Libo; Ma, Xue’an; Li, Mei; Wang, Cheng; Zhang, Xiaojun; Fan, Xinlong; Chen, Donghong; Feng, Zhongyi; Wang, Xiaoyun; Wang, Zhiyong, E-mail: gunaiting@ioe.ac.cn [The Key Laboratory on Adaptive Optics, Chinese Academy of Sciences, P.O. Box 350, Shuangliu, Chengdu 610209, Sichuan (China)

2017-10-01

A high-resolution multi-wavelength simultaneous imaging system from visible to near-infrared bands with a solar adaptive optics system, in which seven imaging channels, including the G band (430.5 nm), the Na i line (589 nm), the H α line (656.3 nm), the TiO band (705.7 nm), the Ca ii IR line (854.2 nm), the He i line (1083 nm), and the Fe i line (1565.3 nm), are chosen, is developed to image the solar atmosphere from the photosphere layer to the chromosphere layer. To our knowledge, this is the solar high-resolution imaging system with the widest spectral coverage. This system was demonstrated at the 1 m New Vaccum Solar Telescope and the on-sky high-resolution observational results were acquired. In this paper, we will illustrate the design and performance of the imaging system. The calibration and the data reduction of the system are also presented.

The Peculiar Binary System AE Aquarii from its Characteristic Multi-wavelength Emission

Directory of Open Access Journals (Sweden)

Oruru B.

2014-01-01

Full Text Available The multi-wavelength properties of the novalike variable system AE Aquarii are discussed in terms of the interaction between the accretion inflow from a late-type main sequence star and the magnetosphere of a fast rotating white dwarf. This results in an efficient magnetospheric propeller process and particle acceleration. The spin-down of the white dwarf at a period rate of 5.64×10−14 s s−1 results in a huge spin-down luminosity of Ls−d ≃ 6 10×33 erg s−1. Hence, the observed non-thermal hard X-ray emission and VHE and TeV gamma-ray emission may suggest that AE Aquarii can be placed in the category of spin-powered pulsars. Besides, observed hard X-ray luminosity of LX,hard ≤ 5 × 1030 erg s−1 constitutes 0.1 % of the total spin-down luminosity of the white dwarf. This paper will discuss some recent theoretical studies and data analysis of the system.

Multi-band, multi-epoch observations of the transiting warm Jupiter WASP-80b

Energy Technology Data Exchange (ETDEWEB)

Fukui, Akihiko; Kuroda, Daisuke [Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Asakuchi, Okayama 719-0232 (Japan); Kawashima, Yui; Ikoma, Masahiro; Kurosaki, Kenji [Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Bunkyo-ku, Tokyo 113-0033 (Japan); Narita, Norio; Nishiyama, Shogo; Takahashi, Yasuhiro H.; Nagayama, Shogo [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Onitsuka, Masahiro; Baba, Haruka; Ryu, Tsuguru [The Graduate University for Advanced Studies, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Ita, Yoshifusa; Onozato, Hiroki [Astronomical Institute, Graduate School of Science, Tohoku University, 6-3 Aramaki Aoba, Aoba-ku, Sendai, Miyagi 980-8578 (Japan); Hirano, Teruyuki; Kawauchi, Kiyoe [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan); Hori, Yasunori [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Nagayama, Takahiro [Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Tamura, Motohide [Department of Astronomy, Graduate School of Science, The University of Tokyo, and National Astronomical Observatory of Japan (Japan); Kawai, Nobuyuki, E-mail: afukui@oao.nao.ac.jp [Department of Physics, Tokyo Institute of Technology, 2-12-1, Oookayama, Meguro, Tokyo 152-8551 (Japan); and others

2014-08-01

WASP-80b is a warm Jupiter transiting a bright late-K/early-M dwarf, providing a good opportunity to extend the atmospheric study of hot Jupiters toward the lower temperature regime. We report multi-band, multi-epoch transit observations of WASP-80b by using three ground-based telescopes covering from optical (g', R{sub c}, and I{sub c} bands) to near-infrared (NIR; J, H, and K{sub s} bands) wavelengths. We observe 5 primary transits, each in 3 or 4 different bands simultaneously, obtaining 17 independent transit light curves. Combining them with results from previous works, we find that the observed transmission spectrum is largely consistent with both a solar abundance and thick cloud atmospheric models at a 1.7σ discrepancy level. On the other hand, we find a marginal spectral rise in the optical region compared to the NIR region at the 2.9σ level, which possibly indicates the existence of haze in the atmosphere. We simulate theoretical transmission spectra for a solar abundance but hazy atmosphere, finding that a model with equilibrium temperature of 600 K can explain the observed data well, having a discrepancy level of 1.0σ. We also search for transit timing variations, but find no timing excess larger than 50 s from a linear ephemeris. In addition, we conduct 43 day long photometric monitoring of the host star in the optical bands, finding no significant variation in the stellar brightness. Combined with the fact that no spot-crossing event is observed in the five transits, our results confirm previous findings that the host star appears quiet for spot activities, despite the indications of strong chromospheric activities.

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.

FRIENDS OF HOT JUPITERS. II. NO CORRESPONDENCE BETWEEN HOT-JUPITER SPIN-ORBIT MISALIGNMENT AND THE INCIDENCE OF DIRECTLY IMAGED STELLAR COMPANIONS

Energy Technology Data Exchange (ETDEWEB)

Ngo, Henry; Knutson, Heather A.; Hinkley, Sasha; Batygin, Konstantin [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA (United States); Crepp, Justin R.; Bechter, Eric B. [Department of Physics, University of Notre Dame, Notre Dame, IN (United States); Howard, Andrew W. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI (United States); Johnson, John A. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Morton, Timothy D. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA (United States); Muirhead, Philip S., E-mail: hngo@caltech.edu [Department of Astronomy, Boston University, Boston, MA (United States)

2015-02-20

Multi-star systems are common, yet little is known about a stellar companion's influence on the formation and evolution of planetary systems. For instance, stellar companions may have facilitated the inward migration of hot Jupiters toward to their present day positions. Many observed short-period gas giant planets also have orbits that are misaligned with respect to their star's spin axis, which has also been attributed to the presence of a massive outer companion on a non-coplanar orbit. We present the results of a multi-band direct imaging survey using Keck NIRC2 to measure the fraction of short-period gas giant planets found in multi-star systems. Over three years, we completed a survey of 50 targets ('Friends of Hot Jupiters') with 27 targets showing some signature of multi-body interaction (misaligned or eccentric orbits) and 23 targets in a control sample (well-aligned and circular orbits). We report the masses, projected separations, and confirmed common proper motion for the 19 stellar companions found around 17 stars. Correcting for survey incompleteness, we report companion fractions of 48% ± 9%, 47% ± 12%, and 51% ± 13% in our total, misaligned/eccentric, and control samples, respectively. This total stellar companion fraction is 2.8σ larger than the fraction of field stars with companions approximately 50-2000 AU. We observe no correlation between misaligned/eccentric hot Jupiter systems and the incidence of stellar companions. Combining this result with our previous radial velocity survey, we determine that 72% ± 16% of hot Jupiters are part of multi-planet and/or multi-star systems.

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.

The M33 Synoptic Stellar Survey. II. Mira Variables

Energy Technology Data Exchange (ETDEWEB)

Yuan, Wenlong; Macri, Lucas M. [George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); He, Shiyuan; Long, James; Huang, Jianhua Z., E-mail: lmacri@tamu.edu [Department of Statistics, Texas A and M University, College Station, TX 77843 (United States)

2017-04-01

We present the discovery of 1847 Mira candidates in the Local Group galaxy M33 using a novel semi-parametric periodogram technique coupled with a random forest classifier. The algorithms were applied to ∼2.4 × 10{sup 5} I -band light curves previously obtained by the M33 Synoptic Stellar Survey. We derive preliminary period–luminosity relations at optical, near-infrared, and mid-infrared wavelengths and compare them to the corresponding relations in the Large Magellanic Cloud.

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...

Exploiting physical constraints for multi-spectral exo-planet detection

Science.gov (United States)

Thiébaut, Éric; Devaney, Nicholas; Langlois, Maud; Hanley, Kenneth

2016-07-01

We derive a physical model of the on-axis PSF for a high contrast imaging system such as GPI or SPHERE. This model is based on a multi-spectral Taylor series expansion of the diffraction pattern and predicts that the speckles should be a combination of spatial modes with deterministic chromatic magnification and weighting. We propose to remove most of the residuals by fitting this model on a set of images at multiple wavelengths and times. On simulated data, we demonstrate that our approach achieves very good speckle suppression without additional heuristic parameters. The residual speckles1, 2 set the most serious limitation in the detection of exo-planets in high contrast coronographic images provided by instruments such as SPHERE3 at the VLT, GPI4, 5 at Gemini, or SCExAO6 at Subaru. A number of post-processing methods have been proposed to remove as much as possible of the residual speckles while preserving the signal from the planets. These methods exploit the fact that the speckles and the planetary signal have different temporal and spectral behaviors. Some methods like LOCI7 are based on angular differential imaging8 (ADI), spectral differential imaging9, 10 (SDI), or on a combination of ADI and SDI.11 Instead of working on image differences, we propose to tackle the exo-planet detection as an inverse problem where a model of the residual speckles is fit on the set of multi-spectral images and, possibly, multiple exposures. In order to reduce the number of degrees of freedom, we impose specific constraints on the spatio-spectral distribution of stellar speckles. These constraints are deduced from a multi-spectral Taylor series expansion of the diffraction pattern for an on-axis source which implies that the speckles are a combination of spatial modes with deterministic chromatic magnification and weighting. Using simulated data, the efficiency of speckle removal by fitting the proposed multi-spectral model is compared to the result of using an approximation

Simultaneous, multi-wavelength flare observations of nearby low-mass stars

Science.gov (United States)

Thackeray, Beverly; Barclay, Thomas; Quintana, Elisa; Villadsen, Jacqueline; Wofford, Alia; Schlieder, Joshua; Boyd, Patricia

2018-01-01

Low-mass stars are the most common stars in the Galaxy and have been targeted in the tens-of-thousands by K2, the re-purposed Kepler mission, as they are prime targets to search for and characterize small, Earth-like planets. Understanding how these fully convective stars drive magnetic activity that manifests as stochastic, short-term brightenings, or flares, provides insight into the prospects of planetary habitability. High energy radiation and energetic particle emission associated with these stars can erode atmospheres, and impact habitability. An innovative campaign to study low mass stars through simultaneous multi-wavelength observations is currently underway with observations ongoing in the X-ray, UV, optical, and radio. I will present early results of our pilot study of the nearby M-Dwarf star Wolf 359 (CN Leo) using K2, SWIFT, and ground based radio observatories, forming a comprehensive picture of flare activity from an M-Dwarf, and discuss the potential impact of these results on exoplanets. "This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE1322106. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation."

High quality 3D shape reconstruction via digital refocusing and pupil apodization in multi-wavelength holographic interferometry

Science.gov (United States)

Xu, Li

Multi-wavelength holographic interferometry (MWHI) has good potential for evolving into a high quality 3D shape reconstruction technique. There are several remaining challenges, including I) depth-of-field limitation, leading to axial dimension inaccuracy of out-of-focus objects; and 2) smearing from shiny smooth objects to their dark dull neighbors, generating fake measurements within the dark area. This research is motivated by the goal of developing an advanced optical metrology system that provides accurate 3D profiles for target object or objects of axial dimension larger than the depth-of-field, and for objects with dramatically different surface conditions. The idea of employing digital refocusing in MWHI has been proposed as a solution to the depth-of-field limitation. One the one hand, traditional single wavelength refocusing formula is revised to reduce sensitivity to wavelength error. Investigation over real example demonstrates promising accuracy and repeatability of reconstructed 3D profiles. On the other hand, a phase contrast based focus detection criterion is developed especially for MWHI, which overcomes the problem of phase unwrapping. The combination for these two innovations gives birth to a systematic strategy of acquiring high quality 3D profiles. Following the first phase contrast based focus detection step, interferometric distance measurement by MWHI is implemented as a next step to conduct relative focus detection with high accuracy. This strategy results in +/-100mm 3D profile with micron level axial accuracy, which is not available in traditional extended focus image (EFI) solutions. Pupil apodization has been implemented to address the second challenge of smearing. The process of reflective rough surface inspection has been mathematically modeled, which explains the origin of stray light and the necessity of replacing hard-edged pupil with one of gradually attenuating transmission (apodization). Metrics to optimize pupil types and

Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library

Science.gov (United States)

Yee, Samuel W.; Petigura, Erik A.; von Braun, Kaspar

2017-02-01

Classification of stars, by comparing their optical spectra to a few dozen spectral standards, has been a workhorse of observational astronomy for more than a century. Here, we extend this technique by compiling a library of optical spectra of 404 touchstone stars observed with Keck/HIRES by the California Planet Search. The spectra have high resolution (R ≈ 60,000), high signal-to-noise ratio (S/N ≈ 150/pixel), and are registered onto a common wavelength scale. The library stars have properties derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry. To address a lack of well-characterized late-K dwarfs in the literature, we measure stellar radii and temperatures for 23 nearby K dwarfs, using modeling of the spectral energy distribution and Gaia parallaxes. This library represents a uniform data set spanning the spectral types ˜M5-F1 (T eff ≈ 3000-7000 K, R ⋆ ≈ 0.1-16 R ⊙). We also present “Empirical SpecMatch” (SpecMatch-Emp), a tool for parameterizing unknown spectra by comparing them against our spectral library. For FGKM stars, SpecMatch-Emp achieves accuracies of 100 K in effective temperature (T eff), 15% in stellar radius (R ⋆), and 0.09 dex in metallicity ([Fe/H]). Because the code relies on empirical spectra it performs particularly well for stars ˜K4 and later, which are challenging to model with existing spectral synthesizers, reaching accuracies of 70 K in T eff, 10% in R ⋆, and 0.12 dex in [Fe/H]. We also validate the performance of SpecMatch-Emp, finding it to be robust at lower spectral resolution and S/N, enabling the characterization of faint late-type stars. Both the library and stellar characterization code are publicly available.

Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library

Energy Technology Data Exchange (ETDEWEB)

Yee, Samuel W.; Petigura, Erik A. [California Institute of Technology (United States); Von Braun, Kaspar, E-mail: syee@caltech.edu [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States)

2017-02-10

Classification of stars, by comparing their optical spectra to a few dozen spectral standards, has been a workhorse of observational astronomy for more than a century. Here, we extend this technique by compiling a library of optical spectra of 404 touchstone stars observed with Keck/HIRES by the California Planet Search. The spectra have high resolution ( R ≈ 60,000), high signal-to-noise ratio (S/N ≈ 150/pixel), and are registered onto a common wavelength scale. The library stars have properties derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry. To address a lack of well-characterized late-K dwarfs in the literature, we measure stellar radii and temperatures for 23 nearby K dwarfs, using modeling of the spectral energy distribution and Gaia parallaxes. This library represents a uniform data set spanning the spectral types ∼M5–F1 ( T {sub eff} ≈ 3000–7000 K, R {sub ⋆} ≈ 0.1–16 R {sub ⊙}). We also present “Empirical SpecMatch” (SpecMatch-Emp), a tool for parameterizing unknown spectra by comparing them against our spectral library. For FGKM stars, SpecMatch-Emp achieves accuracies of 100 K in effective temperature ( T {sub eff}), 15% in stellar radius ( R {sub ⋆}), and 0.09 dex in metallicity ([Fe/H]). Because the code relies on empirical spectra it performs particularly well for stars ∼K4 and later, which are challenging to model with existing spectral synthesizers, reaching accuracies of 70 K in T {sub eff}, 10% in R {sub ⋆}, and 0.12 dex in [Fe/H]. We also validate the performance of SpecMatch-Emp, finding it to be robust at lower spectral resolution and S/N, enabling the characterization of faint late-type stars. Both the library and stellar characterization code are publicly available.

Optical Monitoring of Young Stellar Objects

Science.gov (United States)

Kar, Aman; Jang-Condell, Hannah; Kasper, David; Findlay, Joseph; Kobulnicky, Henry A.

2018-06-01

Observing Young Stellar Objects (YSOs) for variability in different wavelengths enables us to understand the evolution and structure of the protoplanetary disks around stars. The stars observed in this project are known YSOs that show variability in the Infrared. Targets were selected from the Spitzer Space Telescope Young Stellar Object Variability (YSOVAR) Program, which monitored star-forming regions in the mid-infrared. The goal of our project is to investigate any correlation between the variability in the infrared versus the optical. Infrared variability of YSOs is associated with the heating of the protoplanetary disk while accretion signatures are observed in the H-alpha region. We used the University of Wyoming’s Red Buttes Observatory to monitor these stars for signs of accretion using an H-alpha narrowband filter and the Johnson-Cousins filter set, over the Summer of 2017. We perform relative photometry and inspect for an image-to-image variation by observing these targets for a period of four months every two to three nights. The study helps us better understand the link between accretion and H-alpha activity and establish a disk-star connection.

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.

Sub-wavelength metamaterial cylinders with multiple dipole resonances

DEFF Research Database (Denmark)

Arslanagic, Samel; Breinbjerg, Olav

2009-01-01

It has been shown that the sub-wavelength resonances of the individual MTM cylinders also occur for electrically small configurations combining 2 or 4 cylinders. For the 2-and 4-cylinder configurations the overall size is 1/20 and 1/12.5 of the smallest wavelength, respectively. These MTM...... configuration thus offer the possibility for multi-resonant electrically small configurations....

Wavelength selection for portable noninvasive blood component measurement system based on spectral difference coefficient and dynamic spectrum

Science.gov (United States)

Feng, Ximeng; Li, Gang; Yu, Haixia; Wang, Shaohui; Yi, Xiaoqing; Lin, Ling

2018-03-01

Noninvasive blood component analysis by spectroscopy has been a hotspot in biomedical engineering in recent years. Dynamic spectrum provides an excellent idea for noninvasive blood component measurement, but studies have been limited to the application of broadband light sources and high-resolution spectroscopy instruments. In order to remove redundant information, a more effective wavelength selection method has been presented in this paper. In contrast to many common wavelength selection methods, this method is based on sensing mechanism which has a clear mechanism and can effectively avoid the noise from acquisition system. The spectral difference coefficient was theoretically proved to have a guiding significance for wavelength selection. After theoretical analysis, the multi-band spectral difference coefficient-wavelength selection method combining with the dynamic spectrum was proposed. An experimental analysis based on clinical trial data from 200 volunteers has been conducted to illustrate the effectiveness of this method. The extreme learning machine was used to develop the calibration models between the dynamic spectrum data and hemoglobin concentration. The experiment result shows that the prediction precision of hemoglobin concentration using multi-band spectral difference coefficient-wavelength selection method is higher compared with other methods.

A new class of relativistic stellar models

Science.gov (United States)

Haggag, Salah

1995-03-01

Einstein field equations for a static and spherically symmetric perfect fluid are considered. A formulation given by Patino and Rago is used to obtain a class of nine solutions, two of them are Tolman solutions I, IV and the remaining seven are new. The solutions are the correct ones corresponding to expressions derived by Patino and Rago which have been shown by Knutsen to be incorrect. Similar to Tolan solution IV each of the new solutions satisfies energy conditions inside a sphere in some range of two independent parameters. Besides, each solution could be matched to the exterior Schwarzschild solution at a boundary where the pressure vanishes and thus the solutions constitute a class of new physically reasonable stellar models.

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

Two-mode PLC-based mode multi/demultiplexer for mode and wavelength division multiplexed transmission.

Science.gov (United States)

Hanzawa, Nobutomo; Saitoh, Kuimasa; Sakamoto, Taiji; Matsui, Takashi; Tsujikawa, Kyozo; Koshiba, Masanori; Yamamoto, Fumihiko

2013-11-04

We proposed a PLC-based mode multi/demultiplexer (MUX/DEMUX) with an asymmetric parallel waveguide for mode division multiplexed (MDM) transmission. The mode MUX/DEMUX including a mode conversion function with an asymmetric parallel waveguide can be realized by matching the effective indices of the LP(01) and LP(11) modes of two waveguides. We report the design of a mode MUX/DEMUX that can support C-band WDM-MDM transmission. The fabricated mode MUX/DEMUX realized a low insertion loss of less than 1.3 dB and high a mode extinction ratio that exceeded 15 dB. We used the fabricated mode MUX/DEMUX to achieve a successful 2 mode x 4 wavelength x 10 Gbps transmission over a 9 km two-mode fiber with a penalty of less than 1 dB.

Transit time magnetic pumping experiments in the proto-cleo stellarator

International Nuclear Information System (INIS)

Millar, W.

1975-04-01

Experiments are described in which magnetic field perturbations at frequencies approximately 100 kHz, of the type required for Transit Time Magnetic Pumping, are applied to the PROTO-CLEO stellarator. The chief effect is an increase in the plasma loss rate, which is investigated in some detail. The importance of electrostatic fields is discussed, and attention is drawn to the possibility of operating in a region not explored here, with long wavelength and low frequency. (author)

From theoretical stellar spectra to realistic models of the Milky Way : a never ending Odyssey

OpenAIRE

Ammon, Karin

2007-01-01

The last chapter is dedicated to the compilation of the results and the discussion about the success of - but also about the problems that have arisen during - and in part also survived - this work. The main goal of this thesis was, firstly, to convert the stellar parameters given by galaxy models into observables, and then to compare these theoretical stellar distributions in different viewing directions with real observational data to check, if it is possible to find a best-fitt...

Luminosity excesses in low-mass young stellar objects - a statistical study

International Nuclear Information System (INIS)

Strom, K.M.; Strom, S.E.; Kenyon, S.J.; Hartmann, L.

1988-01-01

This paper presents a statistical study in which the observed total luminosity is compared quantitatively with an estimate of the stellar luminosity for a sample of 59 low-mass young stellar objects (YSOs) in the Taurus-Auriga complex. In 13 of the analyzed YSOs, luminosity excesses greater than 0.20 are observed together with greater than 0.6 IR excesses, which typically contribute the bulk of the observed excess luminosity and are characterized by spectral energy distributions which are flat or rise toward long wavelengths. The analysis suggests that YSOs showing the largest luminosity excesses typically power optical jets and/or molecular outflows or have strong winds, as evidenced by the presence of O I emission, indicating a possible correlation between accretion and mass-outflow properties. 38 references

A multi-wavelength, high-contrast contact radiography system for the study of low-density aerogel foams

Energy Technology Data Exchange (ETDEWEB)

Opachich, Y. P., E-mail: opachiyp@nv.doe.gov; Koch, J. A.; Haugh, M. J.; Romano, E.; Lee, J. J.; Huffman, E.; Weber, F. A. [National Security Technologies, LLC, Livermore, California 94550 (United States); Bowers, J. W. [National Security Technologies, LLC, Livermore, California 94550 (United States); University of California at Berkeley, Berkeley, California 94720 (United States); Benedetti, L. R.; Wilson, M.; Prisbrey, S. T.; Wehrenberg, C. E.; Baumann, T. F.; Lenhardt, J. M.; Cook, A.; Arsenlis, A.; Park, H.-S.; Remington, B. A. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

2016-07-15

A multi-wavelength, high contrast contact radiography system has been developed to characterize density variations in ultra-low density aerogel foams. These foams are used to generate a ramped pressure drive in materials strength experiments at the National Ignition Facility and require precision characterization in order to reduce errors in measurements. The system was used to characterize density variations in carbon and silicon based aerogels to ∼10.3% accuracy with ∼30 μm spatial resolution. The system description, performance, and measurement results collected using a 17.8 mg/cc carbon based JX–6 (C{sub 20}H{sub 30}) aerogel are discussed in this manuscript.

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.

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.

Solar Prominence Modelling and Plasma Diagnostics at ALMA Wavelengths

Science.gov (United States)

Rodger, Andrew; Labrosse, Nicolas

2017-09-01

Our aim is to test potential solar prominence plasma diagnostics as obtained with the new solar capability of the Atacama Large Millimeter/submillimeter Array (ALMA). We investigate the thermal and plasma diagnostic potential of ALMA for solar prominences through the computation of brightness temperatures at ALMA wavelengths. The brightness temperature, for a chosen line of sight, is calculated using the densities of electrons, hydrogen, and helium obtained from a radiative transfer code under non-local thermodynamic equilibrium (non-LTE) conditions, as well as the input internal parameters of the prominence model in consideration. Two distinct sets of prominence models were used: isothermal-isobaric fine-structure threads, and large-scale structures with radially increasing temperature distributions representing the prominence-to-corona transition region. We compute brightness temperatures over the range of wavelengths in which ALMA is capable of observing (0.32 - 9.6 mm), however, we particularly focus on the bands available to solar observers in ALMA cycles 4 and 5, namely 2.6 - 3.6 mm (Band 3) and 1.1 - 1.4 mm (Band 6). We show how the computed brightness temperatures and optical thicknesses in our models vary with the plasma parameters (temperature and pressure) and the wavelength of observation. We then study how ALMA observables such as the ratio of brightness temperatures at two frequencies can be used to estimate the optical thickness and the emission measure for isothermal and non-isothermal prominences. From this study we conclude that for both sets of models, ALMA presents a strong thermal diagnostic capability, provided that the interpretation of observations is supported by the use of non-LTE simulation results.

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.)

Study of African Dust with Multi-Wavelength Raman Lidar During "Shadow" Campaign in Senegal

Science.gov (United States)

Veselovskii, Igor; Goloub, Philippe; Podvin, Thierry; Bovchaliuk, Valentyn; Tanre, Didier; Derimian, Yevgeny; Korenskiy, Mikhail; Dubovik, Oleg

2016-06-01

West Africa and the adjacent oceanic regions are very important locations for studying dust properties and their influence on weather and climate. The SHADOW (Study of SaHAran Dust Over West Africa) campaign is performing a multi-scale and multi-laboratory study of aerosol properties and dynamics using a set of in situ and remote sensing instruments at an observation site located at IRD (Institute for Research and Development) Center, Mbour, Senegal (14°N, 17°W). In this paper, we present the results of lidar measurements performed during the first phase of SHADOW which occurred in March-April, 2015. The multiwavelength Mie-Raman lidar acquired 3β+2α+1δ measurements during this period. This set of measurements has permitted particle intensive properties such as extinction and backscattering Ångström exponents (BAE) for 355/532 nm wavelengths corresponding lidar ratios and depolarization ratio at 532 nm to be determined. The backscattering Ångström exponent during the dust episodes decreased to ~-0.7, while the extinction Ångström exponent though being negative, was greater than -0.2. Low values of BAE can likely be explained by an increase in the imaginary part of the dust refractive index at 355 nm compared to 532 nm.

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)

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.

The more the merrier: grid based modelling of Kepler dwarfs with 5-dimensional stellar grids

Directory of Open Access Journals (Sweden)

Serenelli Aldo

2017-01-01

Full Text Available We present preliminary results of our grid based modelling (GBM of the dwarf/subgiant sample of stars observed with Kepler including global asteroseismic parameters. GBM analysis in this work is based on a large grid of stellar models that is characterized by five independent parameters: model mass and age, initial metallicity (Zini, initial helium (Yini, and mixing length parameter (αMLT. Using this grid relaxes assumptions used in all previous GBM work where the initial composition is determined by a single parameter and that αMLT is fixed to a solar-calibrated value. The new grid allows us to study, for example, the impact of different galactic chemical enrichment models on the determination of stellar parameters such as mass radius and age. Also, it allows to include new results from stellar atmosphere models on αMLT in the GBM analysis in a simple manner. Alternatively, it can be tested if global asteroseismology is a useful tool to constraint our ignorance on quantities such as Yini and αMLT. Initial findings show that mass determination is robust with respect to freedom in the latter quantities, with a 4.4% maximum deviation for extreme assumptions regarding prior information on Yini – Zini relations and aMLT. On the other hand, tests carried out so far seem to indicate that global seismology does not have much power to constrain Yini – Zni relations of αMLT values without resourcing to additional information.

Effect of binary stars on the dynamical evolution of stellar clusters. II. Analytic evolutionary models

International Nuclear Information System (INIS)

Hills, J.G.

1975-01-01

We use analytic models to compute the evolution of the core of a stellar system due simultaneously to stellar evaporation which causes the system (core) to contract and to its binaries which cause it to expand by progressively decreasing its binding energy. The evolution of the system is determined by two parameters: the initial number of stars in the system N 0 , and the fraction f/subb/ of its stars which are binaries. For a fixed f/subb/, stellar evaporation initially dominates the dynamical evolution if N 0 is sufficiently large due to the fact that the rate of evaporation is determined chiefly by long-range encounters which increase in importance as the number of stars in the system increases. If stellar evaporation initially dominates, the system first contracts, but as N/subc/, the number of remaining stars in the system, decreases by evaporation, the system reaches a minimum radius and a maximum density and then it expands monotonically as N/subc/ decreases further. Open clusters expand monotonically from the beginning if they have anything approaching average Population I binary frequencies. Globular clusters are highly deficient in binaries in order to have formed and retained the high-density stellar cores observed in most of them. We estimate that for these system f/subb/ < or = 0.15

Modeling Multi-Level Systems

CERN Document Server

Iordache, Octavian

2011-01-01

This book is devoted to modeling of multi-level complex systems, a challenging domain for engineers, researchers and entrepreneurs, confronted with the transition from learning and adaptability to evolvability and autonomy for technologies, devices and problem solving methods. Chapter 1 introduces the multi-scale and multi-level systems and highlights their presence in different domains of science and technology. Methodologies as, random systems, non-Archimedean analysis, category theory and specific techniques as model categorification and integrative closure, are presented in chapter 2. Chapters 3 and 4 describe polystochastic models, PSM, and their developments. Categorical formulation of integrative closure offers the general PSM framework which serves as a flexible guideline for a large variety of multi-level modeling problems. Focusing on chemical engineering, pharmaceutical and environmental case studies, the chapters 5 to 8 analyze mixing, turbulent dispersion and entropy production for multi-scale sy...

Current driven drift instability in the W VII-A stellarator

International Nuclear Information System (INIS)

Deutsch, R.; Wobig, H.

1978-12-01

The instability region and growth rates of current driven drift modes in the W VII-A stellarator are calculated. Several theoretical results are evaluated for specific temperature and density profiles. It is found that in the outer region of the plasma-column (r > 6 cm) collisional drift waves with wavelengths (k 2 x + K 2 y)sup(-1/2) = 0.13 - 0.3 cm exist. In this region also the electron thermal conductivity determined experimentally appears to be large. (orig./GG) [de

Synchronous optical packet switch architecture with tunable single and multi-channels wavelength converters

Science.gov (United States)

Hamza, Haitham S.; Adel, Reham

2017-07-01

In this paper, we propose a bufferless synchronous optical packet switch (OPS) architecture named the Limited-range wavelength conversion with Dynamic Pump-wavelength Selection (LDPS) architecture. LDPS is equipped with a dedicated limited-range wavelength converters (LRWCs, and a shared pool of parametric wavelength converters (PWCs) with dynamic pump-wavelength selection (DPS). The adoption of hybrid conversion types in the proposed architecture aims at improving the packet loss rate (PLR) compared to conventional architecture with single conversion types, while reducing (or at least maintaining) the conversion distance (d) of used wavelength converters. Packet contention in the proposed architecture is resolved using the first available algorithm (FAA) and the dynamic pump-wavelength selection algorithm (DPSA). The performance of the proposed architecture is compared to two well-known conventional architectures; namely, the LRWC architecture that uses dedicated LRWCS for each input wavelength, and the DPS architecture that uses a shared pool of dynamic pump-wavelength converters (PWCs). Simulation results show that, for the same value of d, the new architecture reduces the PLR compared to the LRWC architecture by up to 40 % and 99.7 % for traffic loads, 0.5 and 1; respectively. In addition, for d = 1 , the new architecture reduces the PLR compared to the DPS architecture by up to 10 % and 99.3 % for traffic loads, 0.5 and 1; respectively.

The SOLA Team: A Star Formation Project To Study the Soul of Lupus with ALMA

Science.gov (United States)

De Gregorio-Monsalvo, Itziar; Saito, M.; Rodon, J.; Takahashi, S.

2017-06-01

The SOLA team is a multi-national and multi-wavelength collaboration composed by scientists with technical expertise in ALMA and in infrared and optical techniques. The aim of the team is to establish a low-mass star formation scenario based on the Lupus molecular clouds. In this talk I will present our unique catalog of pre-stellar and proto-stellar cores toward Lupus molecular clouds, the results on our latest studies in protoplanetary disks, as well as our ALMA Cycle 3 data aiming at testing the formation mechanism of sub-stellar objects in Lupus molecular clouds.

TESTING GALAXY FORMATION MODELS WITH THE GHOSTS SURVEY: THE COLOR PROFILE OF M81's STELLAR HALO

International Nuclear Information System (INIS)

Monachesi, Antonela; Bell, Eric F.; Bailin, Jeremy; Radburn-Smith, David J.; Dalcanton, Julianne J.; Vlajić, Marija; De Jong, Roelof S.; Streich, David; Holwerda, Benne W.

2013-01-01

We study the properties of the stellar populations in M81's outermost part, which hereafter we will call the stellar halo, using Hubble Space Telescope (HST) Advanced Camera for Surveys observations of 19 fields from the GHOSTS survey. The observed fields probe the stellar halo out to a projected distance of ∼50 kpc from the galactic center. Each field was observed in both F606W and F814W filters. The 50% completeness levels of the color-magnitude diagrams (CMDs) are typically at 2 mag below the tip of the red giant branch (TRGB). Fields at distances closer than 15 kpc show evidence of disk-dominated populations whereas fields at larger distances are mostly populated by halo stars. The red giant branch (RGB) of the M81's halo CMDs is well matched with isochrones of ∼10 Gyr and metallicities [Fe/H] ∼ – 1.2 dex, suggesting that the dominant stellar population of M81's halo has a similar age and metallicity. The halo of M81 is characterized by a color distribution of width ∼0.4 mag and an approximately constant median value of (F606W – F814W) ∼1 mag measured using stars within the magnitude range 23.7 ∼ 15 kpc, we detect no color gradient in the stellar halo of M81. We place a limit of 0.03 ± 0.11 mag difference between the median color of RGB M81 halo stars at ∼15 and at 50 kpc, corresponding to a metallicity difference of 0.08 ± 0.35 dex over that radial range for an assumed constant age of 10 Gyr. We compare these results with model predictions for the colors of stellar halos formed purely via accretion of satellite galaxies. When we analyze the cosmologically motivated models in the same way as the HST data, we find that they predict no color gradient for the stellar halos, in good agreement with the observations.

How Does the Shape of the Stellar Spectrum Affect the Raman Scattering Features in the Albedo of Exoplanets?

Energy Technology Data Exchange (ETDEWEB)

Oklopčić, Antonija [California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Hirata, Christopher M. [Center for Cosmology and Astroparticle Physics, Ohio State University, 191 West Woodruff Avenue, Columbus, OH 43210 (United States); Heng, Kevin, E-mail: oklopcic@astro.caltech.edu [Center for Space and Habitability, University of Bern, Sidlerstrasse 5, CH-3012, Bern (Switzerland)

2017-09-10

The diagnostic potential of the spectral signatures of Raman scattering, imprinted in planetary albedo spectra at short optical wavelengths, has been demonstrated in research on planets in the solar system, and has recently been proposed as a probe of exoplanet atmospheres, complementary to albedo studies at longer wavelengths. Spectral features caused by Raman scattering offer insight into the properties of planetary atmospheres, such as the atmospheric depth, composition, and temperature, as well as the possibility of detecting and spectroscopically identifying spectrally inactive species, such as H{sub 2} and N{sub 2}, in the visible wavelength range. Raman albedo features, however, depend on both the properties of the atmosphere and the shape of the incident stellar spectrum. Identical planetary atmospheres can produce very different albedo spectra depending on the spectral properties of the host star. Here we present a set of geometric albedo spectra calculated for atmospheres with H{sub 2}/He, N{sub 2}, and CO{sub 2} composition, irradiated by different stellar types ranging from late A to late K stars. Prominent albedo features caused by Raman scattering appear at different wavelengths for different types of host stars. We investigate how absorption due to the alkali elements sodium and potassium may affect the intensity of Raman features, and we discuss the preferred strategies for detecting Raman features in future observations.

Synthesis of multi-wavelength temporal phase-shifting algorithms optimized for high signal-to-noise ratio and high detuning robustness using the frequency transfer function.

Science.gov (United States)

Servin, Manuel; Padilla, Moises; Garnica, Guillermo

2016-05-02

Synthesis of single-wavelength temporal phase-shifting algorithms (PSA) for interferometry is well-known and firmly based on the frequency transfer function (FTF) paradigm. Here we extend the single-wavelength FTF-theory to dual and multi-wavelength PSA-synthesis when several simultaneous laser-colors are present. The FTF-based synthesis for dual-wavelength (DW) PSA is optimized for high signal-to-noise ratio and minimum number of temporal phase-shifted interferograms. The DW-PSA synthesis herein presented may be used for interferometric contouring of discontinuous industrial objects. Also DW-PSA may be useful for DW shop-testing of deep free-form aspheres. As shown here, using the FTF-based synthesis one may easily find explicit DW-PSA formulae optimized for high signal-to-noise and high detuning robustness. To this date, no general synthesis and analysis for temporal DW-PSAs has been given; only ad hoc DW-PSAs formulas have been reported. Consequently, no explicit formulae for their spectra, their signal-to-noise, their detuning and harmonic robustness has been given. Here for the first time a fully general procedure for designing DW-PSAs (or triple-wavelengths PSAs) with desire spectrum, signal-to-noise ratio and detuning robustness is given. We finally generalize DW-PSA to higher number of wavelength temporal PSAs.

Aerosol observation using multi-wavelength Mie-Raman lidars of the Ad-Net and aerosol component analysis

Directory of Open Access Journals (Sweden)

Nishizawa Tomoaki

2018-01-01

Full Text Available We deployed multi-wavelength Mie-Raman lidars (MMRL at three sites of the AD-Net and have conducted continuous measurements using them since 2013. To analyze the MMRL data and better understand the externally mixing state of main aerosol components (e.g., dust, sea-salt, and black carbon in the atmosphere, we developed an integrated package of aerosol component retrieval algorithms, which have already been developed or are being developed, to estimate vertical profiles of the aerosol components. This package applies to the other ground-based lidar network data (e.g., EARLINET and satellite-borne lidar data (e.g., CALIOP/CALIPSO and ATLID/EarthCARE as well as the other lidar data of the AD-Net.

Aerosol observation using multi-wavelength Mie-Raman lidars of the Ad-Net and aerosol component analysis

Science.gov (United States)

Nishizawa, Tomoaki; Sugimoto, Nobuo; Shimizu, Atsushi; Uno, Itsushi; Hara, Yukari; Kudo, Rei

2018-04-01

We deployed multi-wavelength Mie-Raman lidars (MMRL) at three sites of the AD-Net and have conducted continuous measurements using them since 2013. To analyze the MMRL data and better understand the externally mixing state of main aerosol components (e.g., dust, sea-salt, and black carbon) in the atmosphere, we developed an integrated package of aerosol component retrieval algorithms, which have already been developed or are being developed, to estimate vertical profiles of the aerosol components. This package applies to the other ground-based lidar network data (e.g., EARLINET) and satellite-borne lidar data (e.g., CALIOP/CALIPSO and ATLID/EarthCARE) as well as the other lidar data of the AD-Net.

Span Restoration in Optical Networks with Limited Wavelength Conversion

DEFF Research Database (Denmark)

Ruepp, Sarah Renée; Buron, Jakob Due; Andriolli, N

2007-01-01

Next generation optical networks provide functionalities to dynamically provision and recover connections, while emerging technologies allow for the conversion between wavelengths. These devices are however expensive and hence it is likely that only few are deployed throughout the network...... converter-saving wavelength assignment in GMPLS networks. The converter saving property of the Suggested Vector is particularly desirable in span restoration, where the pre-failure path stubs have to be merged to the restoration path at the failure-adjacent nodes. In order to avoid wavelength conversion....... Furthermore, we describe different scenarios to extend the suggested vector wavelength assignment scheme to multi-domain networks with focus on span restoration....

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

Nonlinear Simulations of Trapped Electron Mode Turbulence in Low Magnetic Shear Stellarators

Science.gov (United States)

Faber, B. J.; Pueschel, M. J.; Terry, P. W.; Hegna, C. C.

2017-10-01

Optimized stellarators, like the Helically Symmetric eXperiment (HSX), often operate with small global magnetic shear to avoid low-order rational surfaces and magnetic islands. Nonlinear, flux-tube gyrokinetic simulations of density-gradient-driven Trapped Electron Mode (TEM) turbulence in HSX shows two distinct spectral fluctuation regions: long-wavelength slab-like TEMs localized by global magnetic shear that extend along field lines and short-wavelength TEMs localized by local magnetic shear to a single helical bad curvature region. The slab-like TEMs require computational domains significantly larger than one poloidal turn and are computationally expensive, making turbulent optimization studies challenging. A computationally more efficient, zero-average-magnetic-shear approximation is shown to sufficiently describe the relevant nonlinear physics and replicate finite-shear computations, and can be exploited in quasilinear models based on linear gyrokinetics as a feasible optimization tool. TEM quasilinear heat fluxes are computed with the zero-shear approximation and compared to experimentally-relevant nonlinear gyrokinetic TEM heat fluxes for HSX. Research supported by U.S. DoE Grants DE-FG02-99ER54546, DE-FG02-93ER54222 and DE-FG02-89ER53291.

Modeling the DBR laser used as wavelength conversion device

DEFF Research Database (Denmark)

Braagaard, Carsten; Mikkelsen, Benny; Durhuus, Terji

1994-01-01

In this paper, a novel and efficient way to model the dynamic field in optical DBR-type semiconductor devices is presented. The model accounts for the longitudinal carrier, photon, and refractive index distribution. Furthermore, the model handles both active and passive sections that may include...... gratings. Thus, simulations of components containing, e.g., gain sections, absorptive sections, phase sections, and gratings, placed arbitrarily along the longitudinal direction of the cavity, are possible. Here, the model has been used for studying the DBR laser as a wavelength converter. Particularly...

Multi-waveband Behavior of Blazars

Directory of Open Access Journals (Sweden)

Marscher Alan P.

2013-12-01

Full Text Available The author reviews recent progress toward understanding blazars that multi-waveband monitoring observations have advanced. The primary techniques include the compilation of multi-waveband light curves, multi-epoch VLBI images at radio wavelengths, plots of linear polarization vs. time at radio through optical wavelengths, and spectral energy distributions (SEDs. Correlations and the coincidence or lag of events across wavebands and in the images indicate where the events take place relative to the “core” that lies ≳ 0.5 pc from the central engine. Rotations of the polarization electric vector suggest a helical geometry of the magnetic field upstream of the millimeter-wave core, while rapid fluctuations in degree and position angle of polarization imply that the jet plasma is turbulent in and downstream of the core. The author is developing a numerical model that simulates the emission from such turbulence as it interacts with a conical standing shock in the core region.

Modeling Nearly Spherical Pure-bulge Galaxies with a Stellar Mass-to-light Ratio Gradient under the ΛCDM and MOND Paradigms. I. Methodology, Dynamical Stellar Mass, and Fundamental Mass Plane

Science.gov (United States)

Chae, Kyu-Hyun; Bernardi, Mariangela; Sheth, Ravi K.

2018-06-01

We carry out spherical Jeans modeling of nearly round pure-bulge galaxies selected from the ATLAS3D sample. Our modeling allows for gradients in the stellar mass-to-light ratio (M ⋆/L) through analytic prescriptions parameterized with a “gradient strength” K introduced to accommodate any viable gradient. We use a generalized Osipkov–Merritt model for the velocity dispersion (VD) anisotropy. We produce Monte Carlo sets of models based on the stellar VD profiles under both the ΛCDM and MOND paradigms. Here, we describe the galaxy data, the empirical inputs, and the modeling procedures of obtaining the Monte Carlo sets. We then present the projected dynamical stellar mass, {M}\\star {{e}}, within the effective radius R e, and the fundamental mass plane (FMP) as a function of K. We find the scaling of the K-dependent mass with respect to the ATLAS3D reported mass as: {log}}10[{M}\\star {{e}}(K)/{M}\\star {{e}}{{A}3{{D}}}]=a\\prime +b\\prime K with a‧ = ‑0.019 ± 0.012 and b‧ = ‑0.18 ± 0.02 (ΛCDM), or a‧ = ‑0.023 ± 0.014 and b‧ = ‑0.23 ± 0.03 (MOND), for 0 ≤ K expectation and only the zero-point scales with K. The median value of K for the ATLAS3D galaxies is ={0.53}-0.04+0.05. We perform a similar analysis of the much larger SDSS DR7 spectroscopic sample. In this case, only the VD within a single aperture is available, so we impose the additional requirement that the VD slope be similar to that in the ATLAS3D galaxies. Our analysis of the SDSS galaxies suggests a positive correlation of K with stellar mass.

Empirical tests of pre-main-sequence stellar evolution models with eclipsing binaries

Science.gov (United States)

Stassun, Keivan G.; Feiden, Gregory A.; Torres, Guillermo

2014-06-01

We examine the performance of standard pre-main-sequence (PMS) stellar evolution models against the accurately measured properties of a benchmark sample of 26 PMS stars in 13 eclipsing binary (EB) systems having masses 0.04-4.0 M⊙ and nominal ages ≈1-20 Myr. We provide a definitive compilation of all fundamental properties for the EBs, with a careful and consistent reassessment of observational uncertainties. We also provide a definitive compilation of the various PMS model sets, including physical ingredients and limits of applicability. No set of model isochrones is able to successfully reproduce all of the measured properties of all of the EBs. In the H-R diagram, the masses inferred for the individual stars by the models are accurate to better than 10% at ≳1 M⊙, but below 1 M⊙ they are discrepant by 50-100%. Adjusting the observed radii and temperatures using empirical relations for the effects of magnetic activity helps to resolve the discrepancies in a few cases, but fails as a general solution. We find evidence that the failure of the models to match the data is linked to the triples in the EB sample; at least half of the EBs possess tertiary companions. Excluding the triples, the models reproduce the stellar masses to better than ∼10% in the H-R diagram, down to 0.5 M⊙, below which the current sample is fully contaminated by tertiaries. We consider several mechanisms by which a tertiary might cause changes in the EB properties and thus corrupt the agreement with stellar model predictions. We show that the energies of the tertiary orbits are comparable to that needed to potentially explain the scatter in the EB properties through injection of heat, perhaps involving tidal interaction. It seems from the evidence at hand that this mechanism, however it operates in detail, has more influence on the surface properties of the stars than on their internal structure, as the lithium abundances are broadly in good agreement with model predictions. The

TESTING STELLAR POPULATION SYNTHESIS MODELS WITH SLOAN DIGITAL SKY SURVEY COLORS OF M31's GLOBULAR CLUSTERS

International Nuclear Information System (INIS)

Peacock, Mark B.; Zepf, Stephen E.; Maccarone, Thomas J.; Kundu, Arunav

2011-01-01

Accurate stellar population synthesis models are vital in understanding the properties and formation histories of galaxies. In order to calibrate and test the reliability of these models, they are often compared with observations of star clusters. However, relatively little work has compared these models in the ugriz filters, despite the recent widespread use of this filter set. In this paper, we compare the integrated colors of globular clusters in the Sloan Digital Sky Survey (SDSS) with those predicted from commonly used simple stellar population (SSP) models. The colors are based on SDSS observations of M31's clusters and provide the largest population of star clusters with accurate photometry available from the survey. As such, it is a unique sample with which to compare SSP models with SDSS observations. From this work, we identify a significant offset between the SSP models and the clusters' g - r colors, with the models predicting colors which are too red by g - r ∼ 0.1. This finding is consistent with previous observations of luminous red galaxies in the SDSS, which show a similar discrepancy. The identification of this offset in globular clusters suggests that it is very unlikely to be due to a minority population of young stars. The recently updated SSP model of Maraston and Stroembaeck better represents the observed g - r colors. This model is based on the empirical MILES stellar library, rather than theoretical libraries, suggesting an explanation for the g - r discrepancy.

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.

Simulation-optimization framework for multi-site multi-season hybrid stochastic streamflow modeling

Science.gov (United States)

Srivastav, Roshan; Srinivasan, K.; Sudheer, K. P.

2016-11-01

A simulation-optimization (S-O) framework is developed for the hybrid stochastic modeling of multi-site multi-season streamflows. The multi-objective optimization model formulated is the driver and the multi-site, multi-season hybrid matched block bootstrap model (MHMABB) is the simulation engine within this framework. The multi-site multi-season simulation model is the extension of the existing single-site multi-season simulation model. A robust and efficient evolutionary search based technique, namely, non-dominated sorting based genetic algorithm (NSGA - II) is employed as the solution technique for the multi-objective optimization within the S-O framework. The objective functions employed are related to the preservation of the multi-site critical deficit run sum and the constraints introduced are concerned with the hybrid model parameter space, and the preservation of certain statistics (such as inter-annual dependence and/or skewness of aggregated annual flows). The efficacy of the proposed S-O framework is brought out through a case example from the Colorado River basin. The proposed multi-site multi-season model AMHMABB (whose parameters are obtained from the proposed S-O framework) preserves the temporal as well as the spatial statistics of the historical flows. Also, the other multi-site deficit run characteristics namely, the number of runs, the maximum run length, the mean run sum and the mean run length are well preserved by the AMHMABB model. Overall, the proposed AMHMABB model is able to show better streamflow modeling performance when compared with the simulation based SMHMABB model, plausibly due to the significant role played by: (i) the objective functions related to the preservation of multi-site critical deficit run sum; (ii) the huge hybrid model parameter space available for the evolutionary search and (iii) the constraint on the preservation of the inter-annual dependence. Split-sample validation results indicate that the AMHMABB model is

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.

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.

PHAT STELLAR CLUSTER SURVEY. I. YEAR 1 CATALOG AND INTEGRATED PHOTOMETRY

International Nuclear Information System (INIS)

Johnson, L. Clifton; Dalcanton, Julianne J.; Fouesneau, Morgan; Hodge, Paul W.; Weisz, Daniel R.; Williams, Benjamin F.; Beerman, Lori C.; Seth, Anil C.; Caldwell, Nelson; Gouliermis, Dimitrios A.; Larsen, Søren S.; Olsen, Knut A. G.; San Roman, Izaskun; Sarajedini, Ata; Bianchi, Luciana; Dolphin, Andrew E.; Girardi, Léo; Guhathakurta, Puragra; Kalirai, Jason; Lang, Dustin

2012-01-01

The Panchromatic Hubble Andromeda Treasury (PHAT) survey is an ongoing Hubble Space Telescope (HST) multi-cycle program to obtain high spatial resolution imaging of one-third of the M31 disk at ultraviolet through near-infrared wavelengths. In this paper, we present the first installment of the PHAT stellar cluster catalog. When completed, the PHAT cluster catalog will be among the largest and most comprehensive surveys of resolved star clusters in any galaxy. The exquisite spatial resolution achieved with HST has allowed us to identify hundreds of new clusters that were previously inaccessible with existing ground-based surveys. We identify 601 clusters in the Year 1 sample, representing more than a factor of four increase over previous catalogs within the current survey area (390 arcmin 2 ). This work presents results derived from the first ∼25% of the survey data; we estimate that the final sample will include ∼2500 clusters. For the Year 1 objects, we present a catalog with positions, radii, and six-band integrated photometry. Along with a general characterization of the cluster luminosities and colors, we discuss the cluster luminosity function, the cluster size distributions, and highlight a number of individually interesting clusters found in the Year 1 search.

PHAT STELLAR CLUSTER SURVEY. I. YEAR 1 CATALOG AND INTEGRATED PHOTOMETRY

Energy Technology Data Exchange (ETDEWEB)

Johnson, L. Clifton; Dalcanton, Julianne J.; Fouesneau, Morgan; Hodge, Paul W.; Weisz, Daniel R.; Williams, Benjamin F.; Beerman, Lori C. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Seth, Anil C. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Caldwell, Nelson [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gouliermis, Dimitrios A. [Institut fuer Theoretische Astrophysik, Zentrum fuer Astronomie der Universitaet Heidelberg, Albert-Ueberle-Strasse 2, D-69120 Heidelberg (Germany); Larsen, Soren S. [Department of Astrophysics, IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen (Netherlands); Olsen, Knut A. G. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); San Roman, Izaskun; Sarajedini, Ata [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055 (United States); Bianchi, Luciana [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Girardi, Leo [Osservatorio Astronomico di Padova-INAF, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Guhathakurta, Puragra [Department of Astronomy and Astrophysics, University of California Observatories/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Kalirai, Jason [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Lang, Dustin, E-mail: lcjohnso@astro.washington.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); and others

2012-06-20

The Panchromatic Hubble Andromeda Treasury (PHAT) survey is an ongoing Hubble Space Telescope (HST) multi-cycle program to obtain high spatial resolution imaging of one-third of the M31 disk at ultraviolet through near-infrared wavelengths. In this paper, we present the first installment of the PHAT stellar cluster catalog. When completed, the PHAT cluster catalog will be among the largest and most comprehensive surveys of resolved star clusters in any galaxy. The exquisite spatial resolution achieved with HST has allowed us to identify hundreds of new clusters that were previously inaccessible with existing ground-based surveys. We identify 601 clusters in the Year 1 sample, representing more than a factor of four increase over previous catalogs within the current survey area (390 arcmin{sup 2}). This work presents results derived from the first {approx}25% of the survey data; we estimate that the final sample will include {approx}2500 clusters. For the Year 1 objects, we present a catalog with positions, radii, and six-band integrated photometry. Along with a general characterization of the cluster luminosities and colors, we discuss the cluster luminosity function, the cluster size distributions, and highlight a number of individually interesting clusters found in the Year 1 search.

Cool WISPs for stellar cooling excesses

Energy Technology Data Exchange (ETDEWEB)

Giannotti, Maurizio [Physical Sciences, Barry University, 11300 NE 2nd Avenue, Miami Shores, FL 33161 (United States); Irastorza, Igor; Redondo, Javier [Departamento de Física Teórica, Universidad de Zaragoza, Pedro Cerbuna 12, E-50009, Zaragoza, España (Spain); Ringwald, Andreas, E-mail: mgiannotti@barry.edu, E-mail: igor.irastorza@cern.ch, E-mail: jredondo@unizar.es, E-mail: andreas.ringwald@desy.de [Theory group, Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg (Germany)

2016-05-01

Several stellar systems (white dwarfs, red giants, horizontal branch stars and possibly the neutron star in the supernova remnant Cassiopeia A) show a mild preference for a non-standard cooling mechanism when compared with theoretical models. This exotic cooling could be provided by Weakly Interacting Slim Particles (WISPs), produced in the hot cores and abandoning the star unimpeded, contributing directly to the energy loss. Taken individually, these excesses do not show a strong statistical weight. However, if one mechanism could consistently explain several of them, the hint could be significant. We analyze the hints in terms of neutrino anomalous magnetic moments, minicharged particles, hidden photons and axion-like particles (ALPs). Among them, the ALP or a massless HP represent the best solution. Interestingly, the hinted ALP parameter space is accessible to the next generation proposed ALP searches, such as ALPS II and IAXO and the massless HP requires a multi TeV energy scale of new physics that might be accessible at the LHC.

Cool WISPs for stellar cooling excesses

International Nuclear Information System (INIS)

Giannotti, Maurizio; Irastorza, Igor; Redondo, Javier; Ringwald, Andreas

2016-01-01

Several stellar systems (white dwarfs, red giants, horizontal branch stars and possibly the neutron star in the supernova remnant Cassiopeia A) show a mild preference for a non-standard cooling mechanism when compared with theoretical models. This exotic cooling could be provided by Weakly Interacting Slim Particles (WISPs), produced in the hot cores and abandoning the star unimpeded, contributing directly to the energy loss. Taken individually, these excesses do not show a strong statistical weight. However, if one mechanism could consistently explain several of them, the hint could be significant. We analyze the hints in terms of neutrino anomalous magnetic moments, minicharged particles, hidden photons and axion-like particles (ALPs). Among them, the ALP or a massless HP represent the best solution. Interestingly, the hinted ALP parameter space is accessible to the next generation proposed ALP searches, such as ALPS II and IAXO and the massless HP requires a multi TeV energy scale of new physics that might be accessible at the LHC.

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

Size and Shape of Chariklo from Multi-epoch Stellar Occultations

Science.gov (United States)

Leiva, R.; Sicardy, B.; Camargo, J. I. B.; Ortiz, J.-L.; Desmars, J.; Bérard, D.; Lellouch, E.; Meza, E.; Kervella, P.; Snodgrass, C.; Duffard, R.; Morales, N.; Gomes-Júnior, A. R.; Benedetti-Rossi, G.; Vieira-Martins, R.; Braga-Ribas, F.; Assafin, M.; Morgado, B. E.; Colas, F.; De Witt, C.; Sickafoose, A. A.; Breytenbach, H.; Dauvergne, J.-L.; Schoenau, P.; Maquet, L.; Bath, K.-L.; Bode, H.-J.; Cool, A.; Lade, B.; Kerr, S.; Herald, D.

2017-10-01

We use data from five stellar occultations observed between 2013 and 2016 to constrain Chariklo’s size and shape, and the ring reflectivity. We consider four possible models for Chariklo (sphere, Maclaurin spheroid, triaxial ellipsoid, and Jacobi ellipsoid), and we use a Bayesian approach to estimate the corresponding parameters. The spherical model has a radius R = 129 ± 3 km. The Maclaurin model has equatorial and polar radii a=b={143}-6+3 {km} and c={96}-4+14 {km}, respectively, with density {970}-180+300 {kg} {{{m}}}-3. The ellipsoidal model has semiaxes a={148}-4+6 {km}, b={132}-5+6 {km}, and c={102}-8+10 {km}. Finally, the Jacobi model has semiaxes a = 157 ± 4 km, b = 139 ± 4 km, and c = 86 ± 1 km, and density {796}-4+2 {kg} {{{m}}}-3. Depending on the model, we obtain topographic features of 6-11 km, typical of Saturn icy satellites with similar size and density. We constrain Chariklo’s geometric albedo between 3.1% (sphere) and 4.9% (ellipsoid), while the ring I/F reflectivity is less constrained between 0.6% (Jacobi) and 8.9% (sphere). The ellipsoid model explains both the optical light curve and the long-term photometry variation of the system, giving a plausible value for the geometric albedo of the ring particles of 10%-15%. The derived mass of Chariklo of 6-8 × 1018 kg places the rings close to 3:1 resonance between the ring mean motion and Chariklo’s rotation period. 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 U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

IN-SYNC I: Homogeneous stellar parameters from high-resolution apogee spectra for thousands of pre-main sequence stars

International Nuclear Information System (INIS)

Cottaar, Michiel; Meyer, Michael R.; Covey, Kevin R.; Nidever, David L.; Stassun, Keivan G.; Foster, Jonathan B.; Tan, Jonathan C.; Da Rio, Nicola; Chojnowski, S. Drew; Skrutskie, Michael; Majewski, Steven R.; Wilson, John C.; Zasowski, Gail; Flaherty, Kevin M.; Frinchaboy, Peter M.

2014-01-01

Over two years, 8859 high-resolution H-band spectra of 3493 young (1-10 Myr) stars were gathered by the multi-object spectrograph of the APOGEE project as part of the IN-SYNC ancillary program of the SDSS-III survey. Here we present the forward modeling approach used to derive effective temperatures, surface gravities, radial velocities, rotational velocities, and H-band veiling from these near-infrared spectra. We discuss in detail the statistical and systematic uncertainties in these stellar parameters. In addition, we present accurate extinctions by measuring the E(J – H) of these young stars with respect to the single-star photometric locus in the Pleiades. Finally, we identify an intrinsic stellar radius spread of about 25% for late-type stars in IC 348 using three (nearly) independent measures of stellar radius, namely, the extinction-corrected J-band magnitude, the surface gravity, and the Rsin i from the rotational velocities and literature rotation periods. We exclude that this spread is caused by uncertainties in the stellar parameters by showing that the three estimators of stellar radius are correlated, so that brighter stars tend to have lower surface gravities and larger Rsin i than fainter stars at the same effective temperature. Tables providing the spectral and photometric parameters for the Pleiades and IC 348 have been provided online.

Use of multi-frequency, multi-polarization, multi-angle airborne radars for class discrimination in a southern temperature forest

Science.gov (United States)

Mehta, N. C.

1984-01-01

The utility of radar scatterometers for discrimination and characterization of natural vegetation was investigated. Backscatter measurements were acquired with airborne multi-frequency, multi-polarization, multi-angle radar scatterometers over a test site in a southern temperate forest. Separability between ground cover classes was studied using a two-class separability measure. Very good separability is achieved between most classes. Longer wavelength is useful in separating trees from non-tree classes, while shorter wavelength and cross polarization are helpful for discrimination among tree classes. Using the maximum likelihood classifier, 50% overall classification accuracy is achieved using a single, short-wavelength scatterometer channel. Addition of multiple incidence angles and another radar band improves classification accuracy by 20% and 50%, respectively, over the single channel accuracy. Incorporation of a third radar band seems redundant for vegetation classification. Vertical transmit polarization is critically important for all classes.

Stress measurements by multi-reflection grazing-incidence X-ray diffraction method (MGIXD) using different radiation wavelengths and different incident angles

International Nuclear Information System (INIS)

Marciszko, Marianna; Baczmański, Andrzej; Braham, Chedly; Wróbel, Mirosław; Wroński, Sebastian; Cios, Grzegorz

2017-01-01

The presented study introduces the development of the multi-reflection grazing-incidence X-ray diffraction method (MGIXD) for residual stress determination. The proposed new methodology is aimed at obtaining more reliable experimental data and increasing the depth of non-destructive stress determination below the sample surface. To verify proposed method measurements were performed on a classical X-ray diffractometer (Cu Kα radiation) and using synchrotron radiation (three different wavelengths: λ = 1.2527 Å, λ = 1.5419 Å and λ = 1.7512 Å). The Al2017 alloy subjected to three different surface treatments was investigated in this study. The obtained results showed that the proposed development of MGIXD method, in which not only different incident angles but also different wavelengths of X-ray are used, can be successfully applied for residual stress determination, especially when stress gradients are present in the sample.

Studies of spherical tori, stellarators and anisotropic pressure with M3D

International Nuclear Information System (INIS)

Sugiyama, L.E.; Park, W.; Hudson, S.; Tang, X.-Z.; Strauss, H.R.; Stutman, D.

2001-01-01

The M3D (Multi-level 3D) project simulates plasmas using multiple levels of physics, geometry, and grid models in one code package. The M3D code has been extended to fundamentally nonaxisymmetric and small aspect ratio, R/a>or∼1, configurations. Applications include the nonlinear stability of the NSTX spherical torus and the spherical pinch, and the relaxation of stellarator equilibria. The fluid-level physics model has been extended to evolve the anisotropic pressures p jparallel and p jperpendicular for the ion and electron species. Results show that when the density evolves, other terms in addition to the neoclassical collisional parallel viscous force, such as B· ∇p e in the Ohm's law, can be strongly destabilizing for nonlinear magnetic islands. (author)

Photoionization modeling of the LWS fine-structure lines in IR bright galaxies

Science.gov (United States)

Satyapal, S.; Luhman, M. L.; Fischer, J.; Greenhouse, M. A.; Wolfire, M. G.

1997-01-01

The long wavelength spectrometer (LWS) fine structure line spectra from infrared luminous galaxies were modeled using stellar evolutionary synthesis models combined with photoionization and photodissociation region models. The calculations were carried out by using the computational code CLOUDY. Starburst and active galactic nuclei models are presented. The effects of dust in the ionized region are examined.

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

A new multi-wavelength optical-plethysmograph for quantitative determination of pulpal hemoglobin content and oxygen level using green and near-infrared LEDs

Science.gov (United States)

Kakino, S.; Miwa, Z.; Kirimoto, A.; Ohuchi, K.; Takatani, S.; Takagi, Y.

2007-02-01

A new multi-wavelength optical-plethysmograph has been designed to study the relation between the transmitted optical density (OD) of the tooth vs. hemoglobin (Hb) content and oxygen saturation (SO II) of the pulpal blood using the 467, 506, 522 and 810 nm light emitting diodes (LEDs). The experimental model utilized the extracted human upper incisor where the pulp cavity was filled with the blood having various values of Hb and SO II. A resin cap was made to fit the tooth crown and optical fibers for transmission measurement. The LEDs were pulsed sequentially at 520 Hz with the pulse duration of 240 μs. The OD as a function of Hb for the isosbestic wavelengths of 506 and 522 nm increased almost linearly from 8.0 to 11.0 for Hb changing from 0.0 (saline control) to 2.5 g/dL, but beyond 2.5 g/dL no change was observed. At 810 nm, the OD increased linearly till Hb of 13.4 g/dL, but its change was much smaller with 1.0 OD per 13.4 g/dL. As for SO II, the OD at 467 nm with Hb of 1.0 g/dL that simulated the mean pulpal Hb content in vivo varied by about 1.0 for SO II changing from 100 to 40%. The OD change with respect to Hb change at 506 and 522 nm showed better sensitivity than that at 810 nm. The combination of 467 and 506 or 522 nm wavelengths can provide a noninvasive measurement of both pulpal Hb content and SO II to diagnose pulp vitality of teeth in vivo.

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.)

Models of large-scale magnetic fields in stellar interiors. Application to solar and ap stars

International Nuclear Information System (INIS)

Duez, Vincent

2009-01-01

Stellar astrophysics needs today new models of large-scale magnetic fields, which are observed through spectropolarimetry at the surface of Ap/Bp stars, and thought to be an explanation for the uniform rotation of the solar radiation zone, deduced from helio seismic inversions. During my PhD, I focused on describing the possible magnetic equilibria in stellar interiors. The found configurations are mixed poloidal-toroidal, and minimize the energy for a given helicity, in analogy with Taylor states encountered in spheromaks. Taking into account the self-gravity leads us to the 'non force-free' equilibria family, that will thus influence the stellar structure. I derived all the physical quantities associated with the magnetic field; then I evaluated the perturbations they induce on gravity, thermodynamic quantities as well as energetic ones, for a solar model and an Ap star. 3D MHD simulations allowed me to show that these equilibria form a first stable states family, the generalization of such states remaining an open question. It has been shown that a large-scale magnetic field confined in the solar radiation zone can induce an oblateness comparable to a high core rotation law. I also studied the secular interaction between the magnetic field, the differential rotation and the meridional circulation in the aim of implementing their effects in a next generation stellar evolution code. The influence of the magnetism on convection has also been studied. Finally, hydrodynamic processes responsible for the mixing have been compared with diffusion and a change of convection's efficiency in the case of a CoRoT star target. (author) [fr

Performance analysis of incoherent multi-wavelength OCDMA systems under the impact of four-wave mixing.

Science.gov (United States)

Dang, Ngoc T; Pham, Anh T

2010-05-10

In this paper, we comprehensively analyze the impact of four wave mixing (FWM) on the performance of incoherent multi-wavelength optical code-division multiple-access (MW-OCDMA) systems. We also consider many other interferences and noises, including multiple access interference, optical beating interference, and receiver noise, in the analysis. From the numerical results, we can find the power ranges of different MW-OCDMA systems, in which the impact of FWM is dominant and consequently results in an increase in the bit-error rate of the systems. We also find that the impact of FWM becomes more severe when the frequency spacing is small and/or dispersion-shifted fiber is used. In addition, we quantitatively discuss the impact of FWM on the number of supportable users and power penalty in the MW-OCDMA systems. (c) 2010 Optical Society of America.

The lick-index calibration of the Gemini multi-object spectrographs

International Nuclear Information System (INIS)

Puzia, Thomas H.; Miller, Bryan W.; Trancho, Gelys; Basarab, Brett; Mirocha, Jordan T.; Butler, Karen

2013-01-01

We present the calibration of the spectroscopic Lick/IDS standard line-index system for measurements obtained with the Gemini Multi-Object Spectrographs known as GMOS-North and GMOS-South. We provide linear correction functions for each of the 25 standard Lick line indices for the B600 grism and two instrumental setups, one with 0.''5 slit width and 1 × 1 CCD pixel binning (corresponding to ∼2.5 Å spectral resolution) and the other with 0.''75 slit width and 2 × 2 binning (∼4 Å). We find small and well-defined correction terms for the set of Balmer indices Hβ, Hγ A , and Hδ A along with the metallicity sensitive indices Fe5015, Fe5270, Fe5335, Fe5406, Mg 2 , and Mgb that are widely used for stellar population diagnostics of distant stellar systems. We find other indices that sample molecular absorption bands, such as TiO 1 and TiO 2 , with very wide wavelength coverage or indices that sample very weak molecular and atomic absorption features, such as Mg 1 , as well as indices with particularly narrow passband definitions, such as Fe4384, Ca4455, Fe4531, Ca4227, and Fe5782, which are less robustly calibrated. These indices should be used with caution.

PRIMUS: CONSTRAINTS ON STAR FORMATION QUENCHING AND GALAXY MERGING, AND THE EVOLUTION OF THE STELLAR MASS FUNCTION FROM z = 0-1

Energy Technology Data Exchange (ETDEWEB)

Moustakas, John [Department of Physics and Astronomy, Siena College, 515 Loudon Road, Loudonville, NY 12211 (United States); Coil, Alison L.; Mendez, Alexander J. [Center for Astrophysics and Space Sciences, Department of Physics, University of California, 9500 Gilman Dr., La Jolla, CA 92093 (United States); Aird, James [Department of Physics, Durham University, Durham DH1 3LE (United Kingdom); Blanton, Michael R. [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Cool, Richard J. [MMT Observatory, University of Arizona, 1540 E Second Street, Tucson, AZ 85721 (United States); Eisenstein, Daniel J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Wong, Kenneth C. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Zhu, Guangtun [Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Arnouts, Stephane, E-mail: jmoustakas@siena.edu [Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743 (United States)

2013-04-10

We measure the evolution of the stellar mass function (SMF) from z = 0-1 using multi-wavelength imaging and spectroscopic redshifts from the PRism MUlti-object Survey (PRIMUS) and the Sloan Digital Sky Survey (SDSS). From PRIMUS we construct an i < 23 flux-limited sample of {approx}40, 000 galaxies at z = 0.2-1.0 over five fields totaling Almost-Equal-To 5.5 deg{sup 2}, and from the SDSS we select {approx}170, 000 galaxies at z = 0.01-0.2 that we analyze consistently with respect to PRIMUS to minimize systematic errors in our evolutionary measurements. We find that the SMF of all galaxies evolves relatively little since z = 1, although we do find evidence for mass assembly downsizing; we measure a Almost-Equal-To 30% increase in the number density of {approx}10{sup 10} M{sub sun} galaxies since z Almost-Equal-To 0.6, and a {approx}< 10% change in the number density of all {approx}> 10{sup 11} M{sub sun} galaxies since z Almost-Equal-To 1. Dividing the sample into star-forming and quiescent using an evolving cut in specific star formation rate, we find that the number density of {approx}10{sup 10} M{sub sun} star-forming galaxies stays relatively constant since z Almost-Equal-To 0.6, whereas the space density of {approx}> 10{sup 11} M{sub sun} star-forming galaxies decreases by Almost-Equal-To 50% between z Almost-Equal-To 1 and z Almost-Equal-To 0. Meanwhile, the number density of {approx}10{sup 10} M{sub sun} quiescent galaxies increases steeply toward low redshift, by a factor of {approx}2-3 since z Almost-Equal-To 0.6, while the number of massive quiescent galaxies remains approximately constant since z Almost-Equal-To 1. These results suggest that the rate at which star-forming galaxies are quenched increases with decreasing stellar mass, but that the bulk of the stellar mass buildup within the quiescent population occurs around {approx}10{sup 10.8} M{sub sun}. In addition, we conclude that mergers do not appear to be a dominant channel for the stellar mass

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.

Simple approach to three-color two-photon microscopy by a fiber-optic wavelength convertor.

Science.gov (United States)

Li, Kuen-Che; Huang, Lynn L H; Liang, Jhih-Hao; Chan, Ming-Che

2016-11-01

A simple approach to multi-color two-photon microscopy of the red, green, and blue fluorescent indicators was reported based on an ultra-compact 1.03-μm femtosecond laser and a nonlinear fiber. Inside the nonlinear fiber, the 1.03-μm laser pulses were simultaneously blue-shifted to 0.6~0.8 μm and red-shifted to 1.2~1.4 μm region by the Cherenkov radiation and fiber Raman gain effects. The wavelength-shifted 0.6~0.8 μm and 1.2~1.4 μm radiations were co-propagated with the residual non-converted 1.03-μm pulses inside the same nonlinear fiber to form a fiber-output three-color femtosecond source. The application of the multi-wavelength sources on multi-color two-photon fluorescence microscopy were also demonstrated. Overall, due to simple system configuration, convenient wavelength conversion, easy wavelength tunability within the entire 0.7~1.35 μm bio-penetration window and less requirement for high power and bulky light sources, the simple approach to multi-color two-photon microscopy could be widely applicable as an easily implemented and excellent research tool for future biomedical and possibly even clinical applications.

YOUNG STELLAR CLUSTERS CONTAINING MASSIVE YOUNG STELLAR OBJECTS IN THE VVV SURVEY

Energy Technology Data Exchange (ETDEWEB)

Borissova, J.; Alegría, S. Ramírez; Kurtev, R.; Medina, N.; Navarro, C.; Kuhn, M.; Gromadzki, M.; Retamales, G.; Fernandez, M. A.; Agurto-Gangas, C.; Amigo, P. [Instituto de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Casilla 5030 (Chile); Alonso, J.; Decany, I. [Millennium Institute of Astrophysics (MAS), Santiago (Chile); Lucas, P. W.; Pena, C. Contreras; Thompson, M. A. [Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom); Chené, A.-N. [Gemini Observatory, Northern Operations Center, 670 N. A’ohoku Place, Hilo, HI 96720 (United States); Minniti, D. [Departamento de Ciencias Físicas, Universidad Andres Bello, Republica 220, Santiago (Chile); Catelan, M. [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22 (Chile); Morales, E. F. E., E-mail: jura.borissova@uv.cl [Max-Planck-Institute for Astronomy (Germany)

2016-09-01

The purpose of this research is to study the connections of the global properties of eight young stellar clusters projected in the Vista Variables in the Via Lactea (VVV) ESO Large Public Survey disk area and their young stellar object (YSO) populations. The analysis is based on the combination of spectroscopic parallax-based reddening and distance determinations with main-sequence and pre-main-sequence ishochrone fitting to determine the basic parameters (reddening, age, distance) of the sample clusters. The lower mass limit estimations show that all clusters are low or intermediate mass (between 110 and 1800  M {sub ⊙}), the slope Γ of the obtained present-day mass functions of the clusters is close to the Kroupa initial mass function. The YSOs in the cluster’s surrounding fields are classified using low resolution spectra, spectral energy distribution fits with theoretical predictions, and variability, taking advantage of multi-epoch VVV observations. All spectroscopically confirmed YSOs (except one) are found to be massive (more than 8 M {sub ⊙}). Using VVV and GLIMPSE color–color cuts we have selected a large number of new YSO candidates, which are checked for variability and 57% are found to show at least low-amplitude variations. In few cases it was possible to distinguish between YSO and AGB classifications on the basis of light curves.

Variability of Massive Young Stellar Objects in Cygnus-X

Science.gov (United States)

Thomas, Nancy H.; Hora, J. L.; Smith, H. A.

2013-01-01

Young stellar objects (YSOs) are stars in the process of formation. Several recent investigations have shown a high rate of photometric variability in YSOs at near- and mid-infrared wavelengths. Theoretical models for the formation of massive stars (1-10 solar masses) remain highly idealized, and little is known about the mechanisms that produce the variability. An ongoing Spitzer Space Telescope program is studying massive star formation in the Cygnus-X region. In conjunction with the Spitzer observations, we have conducted a ground-based near-infrared observing program of the Cygnus-X DR21 field using PAIRITEL, the automated infrared telescope at Whipple Observatory. Using the Stetson index for variability, we identified variable objects and a number of variable YSOs in our time-series PAIRITEL data of DR21. We have searched for periodicity among our variable objects using the Lomb-Scargle algorithm, and identified periodic variable objects with an average period of 8.07 days. Characterization of these variable and periodic objects will help constrain models of star formation present. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

Young Stellar Variability of GM Cephei by Circumstellar Dust Clumps

Science.gov (United States)

Huang, Po-Chieh; Chen, Wen-Ping; Hu, Chia-Ling; Burkhonov, Otabek; Ehgamberdiev, Shuhrat; Liu, Jinzhong; Naito, Hiroyuki; Pakstiene, Erika; Qvam, Jan Kare Trandem; Rätz, Stefanie; Semkov, Evgeni

2018-04-01

UX Orionis stars are a sub-type of Herbig Ae/be or T Tauri stars exhibiting sporadic extinction of stellar light due to circumstellar dust obscuration. GM Cep is such an UX Orionis star in the young (∼ 4 Myr) open cluster Trumpler 37 at ∼ 900 pc, showing a prominent infrared access, H-alpha emission, and flare activity. Our multi-color photometric monitoring from 2009 to 2016 showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) cyclic, but not strictly periodical, occultation events, each lasting for a couple months, with a probable recurrence time of about two years, (iii) normal dust reddening as the star became redder when dimmer, (iv) the unusual "blueing" phenomena near the brightness minima, during which the star appeared bluer when dimmer, and (v) a noticeable polarization, from 3 to 9 percent in g', r', and i' -bands. The occultation events may be caused by dust clumps, signifying the density inhomogeneity in a young stellar disk from grain coagulation to planetesimal formation. The level of polarization was anti-correlated with the brightness in the bright state, when the dust clump backscattered stellar light. We discussed two potential hypotheses: orbiting dust clumps versus dust clumps along a spiral arm structure.

Stochastic multi-period multi-product multi-objective Aggregate Production Planning model in multi-echelon supply chain

Directory of Open Access Journals (Sweden)

Kaveh Khalili-Damghani

2017-07-01

Full Text Available In this paper a multi-period multi-product multi-objective aggregate production planning (APP model is proposed for an uncertain multi-echelon supply chain considering financial risk, customer satisfaction, and human resource training. Three conflictive objective functions and several sets of real constraints are considered concurrently in the proposed APP model. Some parameters of the proposed model are assumed to be uncertain and handled through a two-stage stochastic programming (TSSP approach. The proposed TSSP is solved using three multi-objective solution procedures, i.e., the goal attainment technique, the modified ε-constraint method, and STEM method. The whole procedure is applied in an automotive resin and oil supply chain as a real case study wherein the efficacy and applicability of the proposed approaches are illustrated in comparison with existing experimental production planning method.

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/.

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/.

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

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

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)

An ultra-wideband tunable multi-wavelength Brillouin fibre laser based on a semiconductor optical amplifier and dispersion compensating fibre in a linear cavity configuration

International Nuclear Information System (INIS)

Zulkifli, M Z; Ahmad, H; Hassan, N A; Jemangin, M H; Harun, S W

2011-01-01

A multi-wavelength Brillouin fibre laser (MBFL) with an ultra-wideband tuning range from 1420 nm to 1620 nm is demonstrated. The MBFL uses an ultra-wideband semiconductor optical amplifier (SOA) and a dispersion compensating fibre (DCF) as the linear gain medium and nonlinear gain medium, respectively. The proposed MBFL has a wide tuning range covering the short (S-), conventional (C-) and long (L-) bands with a wavelength spacing of 0.08 nm, making it highly suitable for DWDM system applications. The output power of the observed Brillouin Stokes ranges approximately from -5.94 dBm to -0.41 dBm for the S-band, from -4.34 dBm to 0.02 dBm for the C-band and from -2.19 dBm to 0.39 dBm for the L-band. The spacing between each adjacent wavelengths of all the three bands is about 0.08 nm, which is approximately 10.7 GHz for the frequency domain. (lasers)

An automated wavelength selection for flame spectroscopy

International Nuclear Information System (INIS)

Hurteau, M.; Mislan, J.P.; Ashley, R.W.

1976-01-01

A simple electro-mechanical programming system is described for use with a flame spectrophotometer. Its application for automated sequential multi-element analysis is illustrated. Reproducibility of wavelength settings are within +-0.5 A. Precision and sensitivities are at least as good as those obtained for single element determinations. (author)

A local leaky-box model for the local stellar surface density-gas surface density-gas phase metallicity relation

Science.gov (United States)

Zhu, Guangtun Ben; Barrera-Ballesteros, Jorge K.; Heckman, Timothy M.; Zakamska, Nadia L.; Sánchez, Sebastian F.; Yan, Renbin; Brinkmann, Jonathan

2017-07-01

We revisit the relation between the stellar surface density, the gas surface density and the gas-phase metallicity of typical disc galaxies in the local Universe with the SDSS-IV/MaNGA survey, using the star formation rate surface density as an indicator for the gas surface density. We show that these three local parameters form a tight relationship, confirming previous works (e.g. by the PINGS and CALIFA surveys), but with a larger sample. We present a new local leaky-box model, assuming star-formation history and chemical evolution is localized except for outflowing materials. We derive closed-form solutions for the evolution of stellar surface density, gas surface density and gas-phase metallicity, and show that these parameters form a tight relation independent of initial gas density and time. We show that, with canonical values of model parameters, this predicted relation match the observed one well. In addition, we briefly describe a pathway to improving the current semi-analytic models of galaxy formation by incorporating the local leaky-box model in the cosmological context, which can potentially explain simultaneously multiple properties of Milky Way-type disc galaxies, such as the size growth and the global stellar mass-gas metallicity relation.

Multi-objective optimization for generating a weighted multi-model ensemble

Science.gov (United States)

Lee, H.

2017-12-01

Many studies have demonstrated that multi-model ensembles generally show better skill than each ensemble member. When generating weighted multi-model ensembles, the first step is measuring the performance of individual model simulations using observations. There is a consensus on the assignment of weighting factors based on a single evaluation metric. When considering only one evaluation metric, the weighting factor for each model is proportional to a performance score or inversely proportional to an error for the model. While this conventional approach can provide appropriate combinations of multiple models, the approach confronts a big challenge when there are multiple metrics under consideration. When considering multiple evaluation metrics, it is obvious that a simple averaging of multiple performance scores or model ranks does not address the trade-off problem between conflicting metrics. So far, there seems to be no best method to generate weighted multi-model ensembles based on multiple performance metrics. The current study applies the multi-objective optimization, a mathematical process that provides a set of optimal trade-off solutions based on a range of evaluation metrics, to combining multiple performance metrics for the global climate models and their dynamically downscaled regional climate simulations over North America and generating a weighted multi-model ensemble. NASA satellite data and the Regional Climate Model Evaluation System (RCMES) software toolkit are used for assessment of the climate simulations. Overall, the performance of each model differs markedly with strong seasonal dependence. Because of the considerable variability across the climate simulations, it is important to evaluate models systematically and make future projections by assigning optimized weighting factors to the models with relatively good performance. Our results indicate that the optimally weighted multi-model ensemble always shows better performance than an arithmetic

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

Generalized modeling of multi-component vaporization/condensation phenomena for multi-phase-flow analysis

International Nuclear Information System (INIS)

Morita, K.; Fukuda, K.; Tobita, Y.; Kondo, Sa.; Suzuki, T.; Maschek, W.

2003-01-01

A new multi-component vaporization/condensation (V/C) model was developed to provide a generalized model for safety analysis codes of liquid metal cooled reactors (LMRs). These codes simulate thermal-hydraulic phenomena of multi-phase, multi-component flows, which is essential to investigate core disruptive accidents of LMRs such as fast breeder reactors and accelerator driven systems. The developed model characterizes the V/C processes associated with phase transition by employing heat transfer and mass-diffusion limited models for analyses of relatively short-time-scale multi-phase, multi-component hydraulic problems, among which vaporization and condensation, or simultaneous heat and mass transfer, play an important role. The heat transfer limited model describes the non-equilibrium phase transition processes occurring at interfaces, while the mass-diffusion limited model is employed to represent effects of non-condensable gases and multi-component mixture on V/C processes. Verification of the model and method employed in the multi-component V/C model of a multi-phase flow code was performed successfully by analyzing a series of multi-bubble condensation experiments. The applicability of the model to the accident analysis of LMRs is also discussed by comparison between steam and metallic vapor systems. (orig.)

Spectral Quantitative Analysis Model with Combining Wavelength Selection and Topology Structure Optimization

Directory of Open Access Journals (Sweden)

Qian Wang

2016-01-01

Full Text Available Spectroscopy is an efficient and widely used quantitative analysis method. In this paper, a spectral quantitative analysis model with combining wavelength selection and topology structure optimization is proposed. For the proposed method, backpropagation neural network is adopted for building the component prediction model, and the simultaneousness optimization of the wavelength selection and the topology structure of neural network is realized by nonlinear adaptive evolutionary programming (NAEP. The hybrid chromosome in binary scheme of NAEP has three parts. The first part represents the topology structure of neural network, the second part represents the selection of wavelengths in the spectral data, and the third part represents the parameters of mutation of NAEP. Two real flue gas datasets are used in the experiments. In order to present the effectiveness of the methods, the partial least squares with full spectrum, the partial least squares combined with genetic algorithm, the uninformative variable elimination method, the backpropagation neural network with full spectrum, the backpropagation neural network combined with genetic algorithm, and the proposed method are performed for building the component prediction model. Experimental results verify that the proposed method has the ability to predict more accurately and robustly as a practical spectral analysis tool.

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.

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/.

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

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.

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

A novel multi-wavelength procedure for blood pressure estimation using opto-physiological sensor at peripheral arteries and capillaries

Science.gov (United States)

Scardulla, Francesco; Hu, Sijung; D'Acquisto, Leonardo; Pasta, Salvatore; Barrett, Laura; Blanos, Panagiotis; Yan, Liangwen

2018-02-01

In this study, the Carelight multi-wavelength opto-electronic patch sensor (OEPS) was adopted to assess the effectiveness of a new approach for estimating the systolic blood pressure (SBP) through the changes in the morphology of the OEPS signal. Specifically, the SBP was estimated by changing the pressure exerted on an inflatable cuff placed around the left upper arm. Pressure acquisitions were performed both with gold standard (i.e. electronic sphygmomanometer), and Carelight sensor (experimental procedure), on subjects from a multiethnic cohort (aged 28 +/- 7). The OEPS sensor was applied together with a manual inflatable cuff, going slightly above the level of the SBP with increases of +10mmHg and subsequently deflated by 10mmHg until reaching full deflation. The OEPS signals were captured using four wavelength illumination sources (i.e., green 525 nm, orange 595 nm, red 650 nm and IR 870 nm) on three different measuring sites, namely forefinger, radial artery and wrist. The implemented algorithm provides information on the instant when the SBP was reached and the signal is lost since the vessel is completely blocked. Similarly, it detected the signal resumption when the external pressure dropped below the SBP. The findings demonstrated a good correlation between the variation of the pressure and the corresponding OEPS signal with the most accurate result achieved in the fingertip among all wavelengths, with a temporal identification error of 8.07 %. Further studies will improve the clinical relevance on a cohort of patients diagnosed with hyper- or hypotension, in order to develop a wearable blood-pressure device.

OMEGA: a short-wavelength laser for fusion experiments

International Nuclear Information System (INIS)

Soures, J.M.; Hutchison, R.J.; Jacobs, S.D.; Lund, L.D.; McCrory, R.L.; Richardson, M.C.

1983-01-01

The OMEGA, Nd:glass laser facility was constructed for the purpose of investigating the feasibility of direct-drive laser fusion. With 24 beams producing a total energy of 4 kJ or a peak power of 12 TW, OMEGA is capable of nearly uniform illumination of spherical targets. Six of the OMEGA beams have recently been converted to short-wavelength operation (351 nm). In this paper, we discuss details of the system design and performance, with particular emphasis on the frequency-conversion system and multi-wavelength diagnostic system

A comparison of LBGs, DRGs, and BzK galaxies: their contribution to the stellar mass density in the GOODS-MUSIC sample

Science.gov (United States)

Grazian, A.; Salimbeni, S.; Pentericci, L.; Fontana, A.; Nonino, M.; Vanzella, E.; Cristiani, S.; de Santis, C.; Gallozzi, S.; Giallongo, E.; Santini, P.

2007-04-01

Context: The classification scheme for high redshift galaxies is complex at the present time, with simple colour-selection criteria (i.e. EROs, IEROs, LBGs, DRGs, BzKs), resulting in ill-defined properties for the stellar mass and star formation rate of these distant galaxies. Aims: The goal of this work is to investigate the properties of different classes of high-z galaxies, focusing in particular on the stellar masses of LBGs, DRGs, and BzKs, in order to derive their contribution to the total mass budget of the distant Universe. Methods: We used the GOODS-MUSIC catalog, containing ~3000 Ks-selected (~10 000 z-selected) galaxies with multi-wavelength coverage extending from the U band to the Spitzer 8~μm band, with spectroscopic or accurate photometric redshifts. We selected samples of BM/BX/LBGs, DRGs, and BzK galaxies to discuss the overlap and the limitations of these criteria, which can be overridden by a selection criterion based on physical parameters. We then measured the stellar masses of these galaxies and computed the stellar mass density (SMD) for the different samples up to redshift ≃4. Results: We show that the BzK-PE criterion is not optimal for selecting early type galaxies at the faint end. On the other hand, BzK-SF is highly contaminated by passively evolving galaxies at red z-Ks colours. We find that LBGs and DRGs contribute almost equally to the global SMD at z≥ 2 and, in general, that star-forming galaxies form a substantial fraction of the universal SMD. Passively evolving galaxies show a strong negative density evolution from redshift 2 to 3, indicating that we are witnessing the epoch of mass assembly of such objects. Finally we have indications that by pushing the selection to deeper magnitudes, the contribution of less massive DRGs could overtake that of LBGs. Deeper surveys, like the HUDF, are required to confirm this suggestion.

MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): PLANETS, OSCILLATIONS, ROTATION, AND MASSIVE STARS

International Nuclear Information System (INIS)

Paxton, Bill; Cantiello, Matteo; Bildsten, Lars; Arras, Phil; Brown, Edward F.; Dotter, Aaron; Mankovich, Christopher; Montgomery, M. H.; Stello, Dennis; Timmes, F. X.; Townsend, Richard

2013-01-01

We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA star. Improvements in MESA star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 M ☉ stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA star solves the fully coupled stellar structure and composition equations, and we show how this has improved the scaling of MESA's calculational speed on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit that packages all the required components needed to form a unified, maintained, and well-validated build environment for MESA. We also highlight a few tools developed by the community for rapid visualization of MESA star results

AGES OF 70 DWARFS OF THREE POPULATIONS IN THE SOLAR NEIGHBORHOOD: CONSIDERING O AND C ABUNDANCES IN STELLAR MODELS

Energy Technology Data Exchange (ETDEWEB)

Ge, Z. S.; Bi, S. L.; Liu, K.; Wu, Y. Q. [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Chen, Y. Q.; Zhao, J. K. [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Li, T. D. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Ferguson, J. W. [Department of Physics, Wichita State University, Wichita, KS 67260-0032 (United States)

2016-12-20

Oxygen and carbon are important elements in stellar populations. Their behavior refers to the formation history of the stellar populations. C and O abundances would also obviously influence stellar opacities and the overall metal abundance Z . With observed high-quality spectroscopic properties, we construct stellar models with C and O elements to give more accurate ages for 70 metal-poor dwarfs, which have been determined to be high- α halo, low- α halo, and thick-disk stars. Our results show that high- α halo stars are somewhat older than low- α halo stars by around 2.0 Gyr. The thick-disk population has an age range in between the two halo populations. The age distribution profiles indicate that high- α halo and low- α halo stars match the in situ accretion simulation by Zolotov et al., and the thick-disk stars might be formed in a relatively quiescent and long-lasting process. We also note that stellar ages are very sensitive to O abundance, since the ages clearly increase with increasing [O/Fe] values. Additionally, we obtain several stars with peculiar ages, including 2 young thick-disk stars and 12 stars older than the universe age.

Improving the Ni I atomic model for solar and stellar atmospheric models

International Nuclear Information System (INIS)

Vieytes, M. C.; Fontenla, J. M.

2013-01-01

Neutral nickel (Ni I) is abundant in the solar atmosphere and is one of the important elements that contribute to the emission and absorption of radiation in the spectral range between 1900 and 3900 Å. Previously, the Solar Radiation Physical Modeling (SRPM) models of the solar atmosphere only considered a few levels of this species. Here, we improve the Ni I atomic model by taking into account 61 levels and 490 spectral lines. We compute the populations of these levels in full NLTE using the SRPM code and compare the resulting emerging spectrum with observations. The present atomic model significantly improves the calculation of the solar spectral irradiance at near-UV wavelengths, which is important for Earth atmospheric studies, and particularly for ozone chemistry.

Improving the Ni I atomic model for solar and stellar atmospheric models

Energy Technology Data Exchange (ETDEWEB)

Vieytes, M. C. [Instituto de de Astronomía y Física del Espacio, CONICET and UNTREF, Buenos Aires (Argentina); Fontenla, J. M., E-mail: mariela@iafe.uba.ar, E-mail: johnf@digidyna.com [North West Research Associates, 3380 Mitchell Lane, Boulder, CO 80301 (United States)

2013-06-01

Neutral nickel (Ni I) is abundant in the solar atmosphere and is one of the important elements that contribute to the emission and absorption of radiation in the spectral range between 1900 and 3900 Å. Previously, the Solar Radiation Physical Modeling (SRPM) models of the solar atmosphere only considered a few levels of this species. Here, we improve the Ni I atomic model by taking into account 61 levels and 490 spectral lines. We compute the populations of these levels in full NLTE using the SRPM code and compare the resulting emerging spectrum with observations. The present atomic model significantly improves the calculation of the solar spectral irradiance at near-UV wavelengths, which is important for Earth atmospheric studies, and particularly for ozone chemistry.

Survivable integrated grooming in multi-granularity optical networks

Science.gov (United States)

Wu, Jingjing; Guo, Lei; Wei, Xuetao; Liu, Yejun

2012-05-01

Survivability is an important issue to ensure the service continuity in optical network. At the same time, with the granularity of traffic demands ranging from sub-wavelength-level to wavelength-level, traffic demands need to be aggregated and carried over the network in order to utilize resources effectively. Therefore, multi-granularity grooming is proposed to save the cost and reduce the number of switching ports in Optical-Cross Connects (OXCs). However, current works mostly addressed the survivable wavelength or waveband grooming. Therefore, in this paper, we propose three heuristic algorithms called Multi-granularity Dedicated Protection Grooming (MDPG), Multi-granularity Shared Protection Grooming (MSPG) and Multi-granularity Mixed Protection Grooming (MMPG), respectively. All of them are performed based on the Survivable Multi-granularity Integrated Auxiliary Graph (SMIAG) that includes one Wavelength Integrated Auxiliary Graph (WIAG) for wavelength protection and one waveBand Integrated Auxiliary Graph (BIAG) for waveband protection. Numerical results show that MMPG has the lowest average port-cost, the best resource utilization ratio and the lowest blocking probability among these three algorithms. Compared with MDPG, MSPG has lower average port-cost, better resource utilization ratio and lower blocking probability.

High color rendering index of remote-type white LEDs with multi-layered quantum dot-phosphor films and short-wavelength pass dichroic filters

Science.gov (United States)

Yoon, Hee Chang; Oh, Ji Hye; Do, Young Rag

2014-09-01

This paper introduces high color rendering index (CRI) white light-emitting diodes (W-LEDs) coated with red emitting (Sr,Ca)AlSiN3:Eu phosphors and yellowish-green emitting AgIn5S8/ZnS (AIS/ZS) quantum dots (QDs) on glass or a short-wavelength pass dichroic filter (SPDF), which transmit blue wavelength regions and reflect yellow wavelength regions. The red emitting (Sr,Ca)AlSiN3:Eu phosphor film is coated on glass and a SPDF using a screen printing method, and then the yellowish-green emitting AIS/ZS QDs are coated on the red phosphor (Sr,Ca)AlSiN3:Eu film-coated glass and SPDF using the electrospray (e-spray) method.To fabricate the red phosphor film, the optimum amount of phosphor is dispersed in a silicon binder to form a red phosphor paste. The AIS/ZS QDs are mixed with dimethylformamide (DMF), toluene, and poly(methyl methacrylate) (PMMA) for the e-spray coating. The substrates are spin-coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to fabricate a conductive surface. The CRI of the white LEDs is improved through inserting the red phosphor film between the QD layer and the glass substrate. Furthermore, the light intensities of the multi-layered phosphor films are enhanced through changing the glass substrate to the SPDF. The correlated color temperatures (CCTs) vary as a function of the phosphor concentration in the phosphor paste. The optical properties of the yellowish-green AIS/ZS QDs and red (Sr,Ca)AlSiN3:Eu phosphors are characterized using photoluminescence (PL), and the multi-layered QD-phosphor films are measured using electroluminescence (EL) with an InGaN blue LED (λmax = 450 nm) at 60 mA.

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.

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.

Rapid multi-wavelength optical assessment of circulating blood volume without a priori data

Science.gov (United States)

Loginova, Ekaterina V.; Zhidkova, Tatyana V.; Proskurnin, Mikhail A.; Zharov, Vladimir P.

2016-03-01

The measurement of circulating blood volume (CBV) is crucial in various medical conditions including surgery, iatrogenic problems, rapid fluid administration, transfusion of red blood cells, or trauma with extensive blood loss including battlefield injuries and other emergencies. Currently, available commercial techniques are invasive and time-consuming for trauma situations. Recently, we have proposed high-speed multi-wavelength photoacoustic/photothermal (PA/PT) flow cytometry for in vivo CBV assessment with multiple dyes as PA contrast agents (labels). As the first step, we have characterized the capability of this technique to monitor the clearance of three dyes (indocyanine green, methylene blue, and trypan blue) in an animal model. However, there are strong demands on improvements in PA/PT flow cytometry. As additional verification of our proof-of-concept of this technique, we performed optical photometric CBV measurements in vitro. Three label dyes—methylene blue, crystal violet and, partially, brilliant green—were selected for simultaneous photometric determination of the components of their two-dye mixtures in the circulating blood in vitro without any extra data (like hemoglobin absorption) known a priori. The tests of single dyes and their mixtures in a flow system simulating a blood transfusion system showed a negligible difference between the sensitivities of the determination of these dyes under batch and flow conditions. For individual dyes, the limits of detection of 3×10-6 M‒3×10-6 M in blood were achieved, which provided their continuous determination at a level of 10-5 M for the CBV assessment without a priori data on the matrix. The CBV assessment with errors no higher than 4% were obtained, and the possibility to apply the developed procedure for optical photometric (flow cytometry) with laser sources was shown.

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/.

A Comparison between Physics-based and Polytropic MHD Models for Stellar Coronae and Stellar Winds of Solar Analogs

Energy Technology Data Exchange (ETDEWEB)

Cohen, O. [Lowell Center for Space Science and Technology, University of Massachusetts, Lowell, MA 01854 (United States)

2017-02-01

The development of the Zeeman–Doppler Imaging (ZDI) technique has provided synoptic observations of surface magnetic fields of low-mass stars. This led the stellar astrophysics community to adopt modeling techniques that have been used in solar physics using solar magnetograms. However, many of these techniques have been neglected by the solar community due to their failure to reproduce solar observations. Nevertheless, some of these techniques are still used to simulate the coronae and winds of solar analogs. Here we present a comparative study between two MHD models for the solar corona and solar wind. The first type of model is a polytropic wind model, and the second is the physics-based AWSOM model. We show that while the AWSOM model consistently reproduces many solar observations, the polytropic model fails to reproduce many of them, and in the cases where it does, its solutions are unphysical. Our recommendation is that polytropic models, which are used to estimate mass-loss rates and other parameters of solar analogs, must first be calibrated with solar observations. Alternatively, these models can be calibrated with models that capture more detailed physics of the solar corona (such as the AWSOM model) and that can reproduce solar observations in a consistent manner. Without such a calibration, the results of the polytropic models cannot be validated, but they can be wrongly used by others.

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

Numerical modeling of macrodispersion in heterogeneous media: a comparison of multi-Gaussian and non-multi-Gaussian models

Science.gov (United States)

Wen, Xian-Huan; Gómez-Hernández, J. Jaime

1998-03-01

The macrodispersion of an inert solute in a 2-D heterogeneous porous media is estimated numerically in a series of fields of varying heterogeneity. Four different random function (RF) models are used to model log-transmissivity (ln T) spatial variability, and for each of these models, ln T variance is varied from 0.1 to 2.0. The four RF models share the same univariate Gaussian histogram and the same isotropic covariance, but differ from one another in terms of the spatial connectivity patterns at extreme transmissivity values. More specifically, model A is a multivariate Gaussian model for which, by definition, extreme values (both high and low) are spatially uncorrelated. The other three models are non-multi-Gaussian: model B with high connectivity of high extreme values, model C with high connectivity of low extreme values, and model D with high connectivities of both high and low extreme values. Residence time distributions (RTDs) and macrodispersivities (longitudinal and transverse) are computed on ln T fields corresponding to the different RF models, for two different flow directions and at several scales. They are compared with each other, as well as with predicted values based on first-order analytical results. Numerically derived RTDs and macrodispersivities for the multi-Gaussian model are in good agreement with analytically derived values using first-order theories for log-transmissivity variance up to 2.0. The results from the non-multi-Gaussian models differ from each other and deviate largely from the multi-Gaussian results even when ln T variance is small. RTDs in non-multi-Gaussian realizations with high connectivity at high extreme values display earlier breakthrough than in multi-Gaussian realizations, whereas later breakthrough and longer tails are observed for RTDs from non-multi-Gaussian realizations with high connectivity at low extreme values. Longitudinal macrodispersivities in the non-multi-Gaussian realizations are, in general, larger than

Optimization of dual-wavelength intravascular photoacoustic imaging of atherosclerotic plaques using Monte Carlo optical modeling

Science.gov (United States)

Dana, Nicholas; Sowers, Timothy; Karpiouk, Andrei; Vanderlaan, Donald; Emelianov, Stanislav

2017-10-01

Coronary heart disease (the presence of coronary atherosclerotic plaques) is a significant health problem in the industrialized world. A clinical method to accurately visualize and characterize atherosclerotic plaques is needed. Intravascular photoacoustic (IVPA) imaging is being developed to fill this role, but questions remain regarding optimal imaging wavelengths. We utilized a Monte Carlo optical model to simulate IVPA excitation in coronary tissues, identifying optimal wavelengths for plaque characterization. Near-infrared wavelengths (≤1800 nm) were simulated, and single- and dual-wavelength data were analyzed for accuracy of plaque characterization. Results indicate light penetration is best in the range of 1050 to 1370 nm, where 5% residual fluence can be achieved at clinically relevant depths of ≥2 mm in arteries. Across the arterial wall, fluence may vary by over 10-fold, confounding plaque characterization. For single-wavelength results, plaque segmentation accuracy peaked at 1210 and 1720 nm, though correlation was poor (blood, a primary and secondary wavelength near 1210 and 1350 nm, respectively, may offer the best implementation of dual-wavelength IVPA imaging. These findings could guide the development of a cost-effective clinical system by highlighting optimal wavelengths and improving plaque characterization.

A PHYSICAL MODEL FOR THE 0 {approx}< z {approx}< 8 REDSHIFT EVOLUTION OF THE GALAXY ULTRAVIOLET LUMINOSITY AND STELLAR MASS FUNCTIONS

Energy Technology Data Exchange (ETDEWEB)

Tacchella, Sandro; Carollo, C. Marcella [Department of Physics, Institute for Astronomy, ETH Zurich, CH-8093 Zurich (Switzerland); Trenti, Michele, E-mail: tasandro@phys.ethz.ch [Kavli Institute for Cosmology and Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom)

2013-05-10

We present a model to understand the redshift evolution of the UV luminosity and stellar mass functions of Lyman break galaxies. Our approach is based on the assumption that the luminosity and stellar mass of a galaxy is related to its dark-matter (DM) halo assembly and gas infall rate. Specifically, galaxies experience a burst of star formation at the halo assembly time, followed by a constant star formation rate, representing a secular star formation activity sustained by steady gas accretion. Star formation from steady gas accretion is the dominant contribution to the galaxy UV luminosity at all redshifts. The model is calibrated by constructing a galaxy luminosity versus halo mass relation at z = 4 via abundance matching. After this luminosity calibration, the model naturally fits the z = 4 stellar mass function, and correctly predicts the evolution of both luminosity and stellar mass functions from z = 0 to z = 8. While the details of star formation efficiency and feedback are hidden within our calibrated luminosity versus halo mass relation, our study highlights that the primary driver of galaxy evolution across cosmic time is the buildup of DM halos, without the need to invoke a redshift-dependent efficiency in converting gas into stars.

Simultaneous multi-wavelength ultraviolet excited single-phase white light emitting phosphor Ba1-x(Zr,Ti)Si3O9:xEu

Science.gov (United States)

Zhou, Zhenzhen; Liu, Guanghui; Ni, Jia; Liu, Wanlu; Liu, Qian

2018-05-01

A kind of novel compound Ba1-x(Zr,Ti)Si3O9:xEu simultaneously activated by different-valence Eu2+ and Eu3+ ions has been successfully synthesized. The existence of Ti4+-O2- charge transfer (CT) transitions in Ba1-xZrSi3O9:xEu is proved by the photoluminescence spectra and first principle calculations, and the Ti4+ ions come from the impurities in commercial ZrO2 raw materials. Under the excitation of multi-wavelength ultraviolet radiation (λEX = 392, 260, 180 nm), Ba1-xZrSi3O9:xEu (x = 0.15) can directly emit nearly white light. The coexistence of multiple luminescent centers and the energy transfer among Zr4+-O2- CT state, Ti4+-O2- CT state, Eu2+ and Eu3+ ions play important roles in the white light emission. Ba1-xZrSi3O9:xEu (x = 0.15) has good thermal stability, in particular, the intensity of emission spectrum (λEX = 392 nm) at 150 °C is ∼96% of that at room temperature. In general, the multi-wavelength ultraviolet-excited single-phase white light emitting phosphor Ba1-x(Zr,Ti)Si3O9:xEu possesses a promise for applications in white light emitting diodes (WLEDs), agriculture, medicine and other photonic fields.

THE RELATION BETWEEN DYNAMICAL MASS-TO-LIGHT RATIO AND COLOR FOR MASSIVE QUIESCENT GALAXIES OUT TO z ∼ 2 AND COMPARISON WITH STELLAR POPULATION SYNTHESIS MODELS

International Nuclear Information System (INIS)

Van de Sande, Jesse; Franx, Marijn; Kriek, Mariska; Bezanson, Rachel; Van Dokkum, Pieter G.

2015-01-01

We explore the relation between the dynamical mass-to-light ratio (M/L) and rest-frame color of massive quiescent galaxies out to z ∼ 2. We use a galaxy sample with measured stellar velocity dispersions in combination with Hubble Space Telescope and ground-based multi-band photometry. Our sample spans a large range in log M dyn /L g (of 1.6 dex) and log M dyn /L K (of 1.3 dex). There is a strong, approximately linear correlation between the M/L for different wavebands and rest-frame color. The root-mean-square scatter in log M dyn /L residuals implies that it is possible to estimate the M/L with an accuracy of ∼0.25 dex from a single rest-frame optical color. Stellar population synthesis (SPS) models with a Salpeter stellar initial mass function (IMF) cannot simultaneously match M dyn /L g versus (g – z) rest-frame and M dyn /L K versus (g – K) rest-frame . By changing the slope of the IMF we are still unable to explain the M/L of the bluest and reddest galaxies. We find that an IMF with a slope between α = 2.35 and α = 1.35 provides the best match. We also explore a broken IMF with a Salpeter slope at M < 1 M ☉ and M > 4 M ☉ and a slope α in the intermediate region. The data favor a slope of α = 1.35 over α = 2.35. Nonetheless, our results show that variations between different SPS models are comparable to the IMF variations. In our analysis we assume that the variation in M/L and color is driven by differences in age, and that other contributions (e.g., metallicity evolution, dark matter) are small. These assumptions may be an important source of uncertainty as galaxies evolve in more complex ways

The LAMOST stellar spectroscopic survey and the Galactic halo

International Nuclear Information System (INIS)

Liu Chao; Deng Licai

2015-01-01

The formation and evolution of galaxies is an extremely important and fundamental question in modern astrophysics. Among the galaxies, the Milky Way is a very special sample not only because we live in it, but also because it is the only one in which we can carefully and individually observe its member stars. It has been confirmed that the Galactic halo, including both the stellar spheroid and the dark matter halo, contains fairly complicated structures, from which the overall shape, formation, and evolutionary history of our Galaxy can be unveiled. Moreover, some very rare and special stars in the Milky Way can be used as tracers to indirectly detect the core region of the Galaxy around the central super-massive black hole, which is also a hot topic of astrophysics. The LAMOST survey of the Milky Way will collect millions of stellar spectra at low wavelength resolution, making it the largest of such projects throughout the world. Its data base is very suitable for the study of the structure and evolution of the Milky Way. In this article, we report our on-going studies on the Galactic halo with LAMOST data, and present some early scientific results. (authors)

An applicable approach for extracting human heart rate and oxygen saturation during physical movements using a multi-wavelength illumination optoelectronic sensor system

Science.gov (United States)

Alharbi, Samah; Hu, Sijung; Mulvaney, David; Blanos, Panagiotis

2018-02-01

The ability to gather physiological parameters such as heart rate (HR) and oxygen saturation (SpO2%) during physical movement allows to continuously monitor personal health status without disrupt their normal daily activities. Photoplethysmography (PPG) based pulse oximetry and similar principle devices are unable to extract the HR and SpO2% reliably during physical movement due to interference in the signals that arise from motion artefacts (MAs). In this research, a flexible reflectance multi-wavelength optoelectronic patch sensor (OEPS) has been developed to overcome the susceptibility of conventional pulse oximetry readings to MAs. The OEPS incorporates light embittered diodes as illumination sources with four different wavelengths, e.g. green, orange, red, and infrared unlike the conventional pulse oximetry devices that normally measure the skin absorption of only two wavelengths (red and infrared). The additional green and orange wavelengths were found to be distinguish to the absorption of deoxyhemoglobin (RHb) and oxyhemoglobin (HbO2). The reliability of extracting physiological parameters from the green and orange wavelengths is due to absorbed near to the surface of the skin, thereby shortening the optical path and so effectively reducing the influence of physical movements. To compensate of MAs, a three-axis accelerometer was used as a reference with help of adaptive filter to reduce MAs. The experiments were performed using 15 healthy subjects aged 20 to 30. The primary results show that there are no significant difference of heart rate and oxygen saturation measurements between commercial devices and OEPS Green (r=0.992), Orange(r=0.984), Red(r=0.952) and IR(r=0.97) and SpO2% (r = 0.982, p = 0.894).

VizieR Online Data Catalog: STAGGER-grid of 3D stellar models. V. (Chiavassa+, 2018)

Science.gov (United States)

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

2018-01-01

Table B0: RHD simulations' stellar parameters, bolometric magnitude, and bolometric correction for Johnson-Cousins, 2MASS, SDSS (columns 13 to 17), and Gaia systems Table 4: RHD simulations' stellar parameters, bolometric magnitude, and bolometric correction for SkyMapper photometric system, and Stroemgren index b-y, m1=(v-b)-(b-y), and c1=(u-v)-(v-b) Table 5: RHD simulations' stellar parameters, bolometric magnitude, and bolometric correction for the HST-WFC3 in VEGA system Table 6: RHD simulations' stellar parameters, bolometric magnitude, and bolometric correction for the HST-WFC3 in ST system Table 7: RHD simulations' stellar parameters, bolometric magnitude, and bolometric correction for the HST-WFC3 in AB system (5 data files).

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

The origin of stellar winds: Subatmospheric nonthermal storage modes versus radiation pressure

International Nuclear Information System (INIS)

Cannon, C.J.; Thomas, R.N.

1977-01-01

Most current models of matter-flux in hot stars place its origin in radiation pressure, and then model the flow explicitly to produce no chromosphere-corona. Our model of the stellar atmosphere as a transition zone between stellar interior and interstellar medium places the origin of matter-flux, chromosphere-corona, and spectral ''emission classes'' in subatmospheric nonthermal kinetic energy storage, equally for all stars, hot or cold. Current observations of both hot and cold stars suggest chromospheres to be a universal phenomenon, correlated with matter-fluxes, and enhanced in ''emission-class'' stars. To clarify the difference between the two kinds of models above, we reformulate the wind-tunnel analogy to stellar winds, suggesting that stars satisfy and ''imperfect,'' such model;i.e., transsonic shocks occur before the throat, corresponding to an imposed outward velocity in the storage section, or subatmosphere. We then investigate the stability of an arbitrary stellar atmosphere, hot or cold, to suggest a cause for such an outward subatmospheric velocity

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.)

Multi-population genomic prediction using a multi-task Bayesian learning model.