Design and DSP implementation of star image acquisition and star point fast acquiring and tracking

Science.gov (United States)

Zhou, Guohui; Wang, Xiaodong; Hao, Zhihang

2006-02-01

Star sensor is a special high accuracy photoelectric sensor. Attitude acquisition time is an important function index of star sensor. In this paper, the design target is to acquire 10 samples per second dynamic performance. On the basis of analyzing CCD signals timing and star image processing, a new design and a special parallel architecture for improving star image processing are presented in this paper. In the design, the operation moving the data in expanded windows including the star to the on-chip memory of DSP is arranged in the invalid period of CCD frame signal. During the CCD saving the star image to memory, DSP processes the data in the on-chip memory. This parallelism greatly improves the efficiency of processing. The scheme proposed here results in enormous savings of memory normally required. In the scheme, DSP HOLD mode and CPLD technology are used to make a shared memory between CCD and DSP. The efficiency of processing is discussed in numerical tests. Only in 3.5ms is acquired the five lightest stars in the star acquisition stage. In 43us, the data in five expanded windows including stars are moved into the internal memory of DSP, and in 1.6ms, five star coordinates are achieved in the star tracking stage.

Rates of star formation

International Nuclear Information System (INIS)

Larson, R.B.

1977-01-01

It is illustrated that a theoretical understanding of the formation and evolution of galaxies depends on an understanding of star formation, and especially of the factors influencing the rate of star formation. Some of the theoretical problems of star formation in galaxies, some approaches that have been considered in models of galaxy evolution, and some possible observational tests that may help to clarify which processes or models are most relevant are reviewed. The material is presented under the following headings: power-law models for star formation, star formation processes (conditions required, ways of achieving these conditions), observational indications and tests, and measures of star formation rates in galaxies. 49 references

First results from the LIFE project: discovery of two magnetic hot evolved stars

Science.gov (United States)

Martin, A. J.; Neiner, C.; Oksala, M. E.; Wade, G. A.; Keszthelyi, Z.; Fossati, L.; Marcolino, W.; Mathis, S.; Georgy, C.

2018-04-01

We present the initial results of the Large Impact of magnetic Fields on the Evolution of hot stars (LIFE) project. The focus of this project is the search for magnetic fields in evolved OBA giants and supergiants with visual magnitudes between 4 and 8, with the aim to investigate how the magnetic fields observed in upper main-sequence (MS) stars evolve from the MS until the late post-MS stages. In this paper, we present spectropolarimetric observations of 15 stars observed using the ESPaDOnS instrument of the Canada-France-Hawaii Telescope. For each star, we have determined the fundamental parameters and have used stellar evolution models to calculate their mass, age, and radius. Using the least-squared deconvolution technique, we have produced averaged line profiles for each star. From these profiles, we have measured the longitudinal magnetic field strength and have calculated the detection probability. We report the detection of magnetic fields in two stars of our sample: a weak field of Bl = 1.0 ± 0.2 G is detected in the post-MS A5 star 19 Aur and a stronger field of Bl = -230 ± 10 G is detected in the MS/post-MS B8/9 star HR 3042.

Rejuvenation of the Innocent Bystander: Results from a Pilot X-ray Study of Dwarf Carbon Stars

Science.gov (United States)

Mazzoni, Fernando; Montez, Rodolfo; Green, Paul

2018-01-01

We present the results of a pilot study by the Chandra X-ray Observatory of X-ray emission from dwarf Carbon (dC) stars. Carbon stars were thought to be exclusively AGB stars but main sequence dwarfs showing carbon molecular bands appear to be the dominant variety. The existence of dC stars is surprising since dwarf stars cannot intrinsically produce carbon as an AGB star can. It is hypothesized that dC stars are polluted by an evolved companion star. Evidence of past pollution can appear in X-ray emission where increased coronal activity (“spin-up”) or mass accretion via a disk can be detected. Using the Chandra X-ray Observatory we detected X-ray photons in the vicinity of all the dC stars in our a pilot sample. For each detection we characterized the X-ray emission and compared to the emission expected from potential emission scenarios. Although the process that produces the X-ray emission from dC stars is presently unclear and our pilot sample is small, our results suggest that X-ray emission might be a universal characteristic of dC stars. Further examination of the X-ray emission plus future X-ray and multiwavelength observations will help us better understand the nature of these intriguing stars.

A Survey for hot Central Stars of Planetary Nebulae I. Methods and First Results

OpenAIRE

Kanarek, Graham C.; Shara, Michael M.; Faherty, Jacqueline K.; Zurek, David; Moffat, Anthony F. J.

2015-01-01

We present the results of initial spectrographic followup with the Very Large Telescope (UT3, Melipal) for $K_s \\ge 14$ Galactic plane CIV emission-line candidates in the near-infrared (NIR). These 7 faint stars all display prominent HeI and CIV emission lines characteristic of a carbon-rich Wolf-Rayet star. They have NIR colours which are much too blue to be those of distant, classical WR stars. The magnitudes and colours are compatible with those expected for central stars of planetary nebu...

Design and application of star map simulation system for star sensors

Science.gov (United States)

Wu, Feng; Shen, Weimin; Zhu, Xifang; Chen, Yuheng; Xu, Qinquan

2013-12-01

Modern star sensors are powerful to measure attitude automatically which assure a perfect performance of spacecrafts. They achieve very accurate attitudes by applying algorithms to process star maps obtained by the star camera mounted on them. Therefore, star maps play an important role in designing star cameras and developing procession algorithms. Furthermore, star maps supply significant supports to exam the performance of star sensors completely before their launch. However, it is not always convenient to supply abundant star maps by taking pictures of the sky. Thus, star map simulation with the aid of computer attracts a lot of interests by virtue of its low price and good convenience. A method to simulate star maps by programming and extending the function of the optical design program ZEMAX is proposed. The star map simulation system is established. Firstly, based on analyzing the working procedures of star sensors to measure attitudes and the basic method to design optical system by ZEMAX, the principle of simulating star sensor imaging is given out in detail. The theory about adding false stars and noises, and outputting maps is discussed and the corresponding approaches are proposed. Then, by external programming, the star map simulation program is designed and produced. Its user interference and operation are introduced. Applications of star map simulation method in evaluating optical system, star image extraction algorithm and star identification algorithm, and calibrating system errors are presented completely. It was proved that the proposed simulation method provides magnificent supports to the study on star sensors, and improves the performance of star sensors efficiently.

IMAGE ANALYSIS FOR COSMOLOGY: RESULTS FROM THE GREAT10 STAR CHALLENGE

International Nuclear Information System (INIS)

Kitching, T. D.; Heymans, C.; Rowe, B.; Witherick, D.; Gill, M.; Massey, R.; Courbin, F.; Gentile, M.; Meylan, G.; Georgatzis, K.; Gruen, D.; Kilbinger, M.; Li, G. L.; Mariglis, A. P.; Storkey, A.; Xin, B.

2013-01-01

We present the results from the first public blind point-spread function (PSF) reconstruction challenge, the GRavitational lEnsing Accuracy Testing 2010 (GREAT10) Star Challenge. Reconstruction of a spatially varying PSF, sparsely sampled by stars, at non-star positions is a critical part in the image analysis for weak lensing where inaccuracies in the modeled ellipticity e and size R 2 can impact the ability to measure the shapes of galaxies. This is of importance because weak lensing is a particularly sensitive probe of dark energy and can be used to map the mass distribution of large scale structure. Participants in the challenge were presented with 27,500 stars over 1300 images subdivided into 26 sets, where in each set a category change was made in the type or spatial variation of the PSF. Thirty submissions were made by nine teams. The best methods reconstructed the PSF with an accuracy of σ(e) ≈ 2.5 × 10 –4 and σ(R 2 )/R 2 ≈ 7.4 × 10 –4 . For a fixed pixel scale, narrower PSFs were found to be more difficult to model than larger PSFs, and the PSF reconstruction was severely degraded with the inclusion of an atmospheric turbulence model (although this result is likely to be a strong function of the amplitude of the turbulence power spectrum).

Star-forming galaxy models: Blending star formation into TREESPH

Science.gov (United States)

Mihos, J. Christopher; Hernquist, Lars

1994-01-01

We have incorporated star-formation algorithms into a hybrid N-body/smoothed particle hydrodynamics code (TREESPH) in order to describe the star forming properties of disk galaxies over timescales of a few billion years. The models employ a Schmidt law of index n approximately 1.5 to calculate star-formation rates, and explicitly include the energy and metallicity feedback into the Interstellar Medium (ISM). Modeling the newly formed stellar population is achieved through the use of hybrid SPH/young star particles which gradually convert from gaseous to collisionless particles, avoiding the computational difficulties involved in creating new particles. The models are shown to reproduce well the star-forming properties of disk galaxies, such as the morphology, rate of star formation, and evolution of the global star-formation rate and disk gas content. As an example of the technique, we model an encounter between a disk galaxy and a small companion which gives rise to a ring galaxy reminiscent of the Cartwheel (AM 0035-35). The primary galaxy in this encounter experiences two phases of star forming activity: an initial period during the expansion of the ring, and a delayed phase as shocked material in the ring falls back into the central regions.

STABLE CONIC-HELICAL ORBITS OF PLANETS AROUND BINARY STARS: ANALYTICAL RESULTS

Energy Technology Data Exchange (ETDEWEB)

Oks, E. [Physics Department, 206 Allison Lab., Auburn University, Auburn, AL 36849 (United States)

2015-05-10

Studies of planets in binary star systems are especially important because it was estimated that about half of binary stars are capable of supporting habitable terrestrial planets within stable orbital ranges. One-planet binary star systems (OBSS) have a limited analogy to objects studied in atomic/molecular physics: one-electron Rydberg quasimolecules (ORQ). Specifically, ORQ, consisting of two fully stripped ions of the nuclear charges Z and Z′ plus one highly excited electron, are encountered in various plasmas containing more than one kind of ion. Classical analytical studies of ORQ resulted in the discovery of classical stable electronic orbits with the shape of a helix on the surface of a cone. In the present paper we show that despite several important distinctions between OBSS and ORQ, it is possible for OBSS to have stable planetary orbits in the shape of a helix on a conical surface, whose axis of symmetry coincides with the interstellar axis; the stability is not affected by the rotation of the stars. Further, we demonstrate that the eccentricity of the stars’ orbits does not affect the stability of the helical planetary motion if the center of symmetry of the helix is relatively close to the star of the larger mass. We also show that if the center of symmetry of the conic-helical planetary orbit is relatively close to the star of the smaller mass, a sufficiently large eccentricity of stars’ orbits can switch the planetary motion to the unstable mode and the planet would escape the system. We demonstrate that such planets are transitable for the overwhelming majority of inclinations of plane of the stars’ orbits (i.e., the projections of the planet and the adjacent start on the plane of the sky coincide once in a while). This means that conic-helical planetary orbits at binary stars can be detected photometrically. We consider, as an example, Kepler-16 binary stars to provide illustrative numerical data on the possible parameters and the

Optimized star sensors laboratory calibration method using a regularization neural network.

Science.gov (United States)

Zhang, Chengfen; Niu, Yanxiong; Zhang, Hao; Lu, Jiazhen

2018-02-10

High-precision ground calibration is essential to ensure the performance of star sensors. However, the complex distortion and multi-error coupling have brought great difficulties to traditional calibration methods, especially for large field of view (FOV) star sensors. Although increasing the complexity of models is an effective way to improve the calibration accuracy, it significantly increases the demand for calibration data. In order to achieve high-precision calibration of star sensors with large FOV, a novel laboratory calibration method based on a regularization neural network is proposed. A multi-layer structure neural network is designed to represent the mapping of the star vector and the corresponding star point coordinate directly. To ensure the generalization performance of the network, regularization strategies are incorporated into the net structure and the training algorithm. Simulation and experiment results demonstrate that the proposed method can achieve high precision with less calibration data and without any other priori information. Compared with traditional methods, the calibration error of the star sensor decreased by about 30%. The proposed method can satisfy the precision requirement for large FOV star sensors.

First results from NuSTAR observations of Mkn 421

DEFF Research Database (Denmark)

Baloković, M.; Ajello, M.; Blandford, R. D.

2013-01-01

2013. Here we present some initial results based on NuSTAR data from January through March 2013, as well as calibration observations conducted in 2012. Although the observations cover some of the faintest hard X-ray flux states ever observed forMkn 421, the sensitivity is high enough to resolve intra-day...

IMAGE ANALYSIS FOR COSMOLOGY: RESULTS FROM THE GREAT10 STAR CHALLENGE

Energy Technology Data Exchange (ETDEWEB)

Kitching, T. D.; Heymans, C. [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom); Rowe, B.; Witherick, D. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Gill, M. [Center for Cosmology and AstroParticle Physics, Physics Department, The Ohio State University, Columbus, OH (United States); Massey, R. [Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE (United Kingdom); Courbin, F.; Gentile, M.; Meylan, G. [Laboratoire d' Astrophysique, Ecole Polytechnique Federale de Lausanne (EPFL) (Switzerland); Georgatzis, K. [Department of Information and Computer Science, Aalto University, P.O. Box 15400, FI-00076 Aalto (Finland); Gruen, D. [Department of Physics and Astronomy, 209 South 33rd Street, University of Pennsylvania, Philadelphia, PA 19104 (United States); Kilbinger, M. [Excellence Cluster Universe, Boltzmannstr. 2, D-85748 Garching (Germany); Li, G. L. [Purple Mountain Observatory, 2 West Beijing Road, Nanjing 210008 (China); Mariglis, A. P.; Storkey, A. [School of Informatics, University of Edinburgh, 10 Crichton Street, Edinburgh EH8 9AB (United Kingdom); Xin, B., E-mail: t.kitching@ucl.ac.uk [Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907 (United States)

2013-04-01

We present the results from the first public blind point-spread function (PSF) reconstruction challenge, the GRavitational lEnsing Accuracy Testing 2010 (GREAT10) Star Challenge. Reconstruction of a spatially varying PSF, sparsely sampled by stars, at non-star positions is a critical part in the image analysis for weak lensing where inaccuracies in the modeled ellipticity e and size R {sup 2} can impact the ability to measure the shapes of galaxies. This is of importance because weak lensing is a particularly sensitive probe of dark energy and can be used to map the mass distribution of large scale structure. Participants in the challenge were presented with 27,500 stars over 1300 images subdivided into 26 sets, where in each set a category change was made in the type or spatial variation of the PSF. Thirty submissions were made by nine teams. The best methods reconstructed the PSF with an accuracy of {sigma}(e) Almost-Equal-To 2.5 Multiplication-Sign 10{sup -4} and {sigma}(R {sup 2})/R {sup 2} Almost-Equal-To 7.4 Multiplication-Sign 10{sup -4}. For a fixed pixel scale, narrower PSFs were found to be more difficult to model than larger PSFs, and the PSF reconstruction was severely degraded with the inclusion of an atmospheric turbulence model (although this result is likely to be a strong function of the amplitude of the turbulence power spectrum).

ISO-SWS spectrophotometry of galactic Wolf-Rayet stars: preliminary results.

NARCIS (Netherlands)

van der Hucht, K. A.; Morris, P. W.; Williams, P. M.; Setia Gunawan, D. Y. A.; Beintema, D. A.; Boxhoorn, D. R.; de Graauw, T.; Heras, A.; Kester, D. J. M.; Lahuis, F.; Leech, K. J.; Roelfsema, P. R.; Salama, A.; Valentijn, E. A.; Vandenbussche, B.

1996-01-01

ISO-SWS spectra of seven late-type galactic Wolf-Rayet stars are discussed. A high resolution spectrum (2.3-29.6μm, λ/{DELTA}λ=~820-1700) of the WC8 star WR11 (γ^2^ Vel) is shown and its Ne abundance is discussed. Medium resolution spectra (λ/{DELTA}λ=~250-600) of the WC8-9 stars WR48a, WR98a,

Neutron star/red giant encounters in globular clusters

International Nuclear Information System (INIS)

Bailyn, C.D.

1988-01-01

The author presents a simple expression for the amount by which xsub(crit) is diminished as a star evolves xsub(crit) Rsub(crit)/R*, where Rsub(crit) is the maximum distance of closest approach between two stars for which the tidal energy is sufficient to bind the system, and R* is the radius of the star on which tides are being raised. Also it is concluded that tidal capture of giants by neutron stars resulting in binary systems is unlikely in globular clusters. However, collisions between neutron stars and red giants, or an alternative process involving tidal capture of a main-sequence star into an initially detached binary system, may result either in rapidly rotating neutron stars or in white dwarf/neutron star binaries. (author)

Star Tracker Performance Estimate with IMU

Science.gov (United States)

Aretskin-Hariton, Eliot D.; Swank, Aaron J.

2015-01-01

A software tool for estimating cross-boresight error of a star tracker combined with an inertial measurement unit (IMU) was developed to support trade studies for the Integrated Radio and Optical Communication project (iROC) at the National Aeronautics and Space Administration Glenn Research Center. Typical laser communication systems, such as the Lunar Laser Communication Demonstration (LLCD) and the Laser Communication Relay Demonstration (LCRD), use a beacon to locate ground stations. iROC is investigating the use of beaconless precision laser pointing to enable laser communication at Mars orbits and beyond. Precision attitude knowledge is essential to the iROC mission to enable high-speed steering of the optical link. The preliminary concept to achieve this precision attitude knowledge is to use star trackers combined with an IMU. The Star Tracker Accuracy (STAcc) software was developed to rapidly assess the capabilities of star tracker and IMU configurations. STAcc determines the overall cross-boresight error of a star tracker with an IMU given the characteristic parameters: quantum efficiency, aperture, apparent star magnitude, exposure time, field of view, photon spread, detector pixels, spacecraft slew rate, maximum stars used for quaternion estimation, and IMU angular random walk. This paper discusses the supporting theory used to construct STAcc, verification of the program and sample results.

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

Energy Technology Data Exchange (ETDEWEB)

Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)

2015-03-01

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

International Nuclear Information System (INIS)

Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph

2015-01-01

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear

Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

Energy Technology Data Exchange (ETDEWEB)

Theodorakis, P E [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Avgeropoulos, A [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Freire, J J [Departamento de Ciencias y Tecnicas FisicoquImicas, Universidad Nacional de Educacion a Distancia, Facultad de Ciencias, Senda del Rey 9, 28040 Madrid (Spain); Kosmas, M [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece); Vlahos, C [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece)

2007-11-21

The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.

Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

Science.gov (United States)

Theodorakis, P. E.; Avgeropoulos, A.; Freire, J. J.; Kosmas, M.; Vlahos, C.

2007-11-01

The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.

Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

International Nuclear Information System (INIS)

Theodorakis, P E; Avgeropoulos, A; Freire, J J; Kosmas, M; Vlahos, C

2007-01-01

The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results

Neutron Stars and NuSTAR

Science.gov (United States)

Bhalerao, Varun

2012-05-01

My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses

NuSTAR Results and Future Plans for Magnetar and Rotation-Powered Pulsar Observations

Science.gov (United States)

An, H.; Kaspi, V. M.; Archibald, R.; Bachetti, M.; Bhalerao, V.; Bellm, E. C.; Beloborodov, A. M.; Boggs, S. E.; Chakrabarty, D.; Christensen, F. E.;

A Star-Wheel Stair-Climbing Wheelchair

Institute of Scientific and Technical Information of China (English)

ZHANG Li; WU Bo; JIN Ai-min; JIANG Shi-hong; ZHENG Yu-fei; ZHANG Shuai

2014-01-01

In order to achieve a wheelchair climb stairs function, this paper designs a star-wheel stair-climbing mechanism. Through the effect of the lock coupling, the star-wheel stair-climbing mechanism is formed to be fixed axis gear train or planetary gear train achieving flat-walking and stair-climbing functions. Crossing obstacle analysis obtains the maximum height and minimum width of obstacle which the wheelchair can cross. Stress-strain analysis in Solidworks simulation is performed to verify material strength.

Calendar Year 2007 Program Benefits for U.S. EPA Energy Star Labeled Products: Expanded Methodology

Energy Technology Data Exchange (ETDEWEB)

Sanchez, Marla; Homan, Gregory; Lai, Judy; Brown, Richard

2009-09-24

This report provides a top-level summary of national savings achieved by the Energy Star voluntary product labeling program. To best quantify and analyze savings for all products, we developed a bottom-up product-based model. Each Energy Star product type is characterized by product-specific inputs that result in a product savings estimate. Our results show that through 2007, U.S. EPA Energy Star labeled products saved 5.5 Quads of primary energy and avoided 100 MtC of emissions. Although Energy Star-labeled products encompass over forty product types, only five of those product types accounted for 65percent of all Energy Star carbon reductions achieved to date, including (listed in order of savings magnitude)monitors, printers, residential light fixtures, televisions, and furnaces. The forecast shows that U.S. EPA?s program is expected to save 12.2 Quads of primary energy and avoid 215 MtC of emissions over the period of 2008?2015.

Results from the STAR TPC system test

International Nuclear Information System (INIS)

Betts, W.

1996-01-01

A system test of various components of the Solenoidal Tracker at RHIC (STAR) detector, operating in concern, has recently come on-line. Communication between a major sub-detector, a sector of the Time Projection Chamber (TPC), and the trigger, data acquisition and slow controls systems has been established, enabling data from cosmic ray muons to be collected. First results from an analysis of the TPC data are presented. These include measurements of system noise, electronic parameters such as amplifier gains and pedestal values, and tracking resolution for cosmic ray muons and laser induced ionization tracks. A discussion on the experience gained in integrating the different components for the system test is also given

High-contrast imaging in multi-star systems: progress in technology development and lab results

Science.gov (United States)

Belikov, Ruslan; Pluzhnik, Eugene; Bendek, Eduardo; Sirbu, Dan

2017-09-01

We present the continued progress and laboratory results advancing the technology readiness of Multi-Star Wavefront Control (MSWC), a method to directly image planets and disks in multi-star systems such as Alpha Centauri. This method works with almost any coronagraph (or external occulter with a DM) and requires little or no change to existing and mature hardware. In particular, it works with single-star coronagraphs and does not require the off-axis star(s) to be coronagraphically suppressed. Because of the ubiquity of multistar systems, this method increases the science yield of many missions and concepts such as WFIRST, Exo-C/S, HabEx, LUVOIR, and potentially enables the detection of Earthlike planets (if they exist) around our nearest neighbor star, Alpha Centauri, with a small and low-cost space telescope such as ACESat. Our lab demonstrations were conducted at the Ames Coronagraph Experiment (ACE) laboratory and show both the feasibility as well as the trade-offs involved in using MSWC. We show several simulations and laboratory tests at roughly TRL-3 corresponding to representative targets and missions, including Alpha Centauri with WFIRST. In particular, we demonstrate MSWC in Super-Nyquist mode, where the distance between the desired dark zone and the off-axis star is larger than the conventional (sub-Nyquist) control range of the DM. Our laboratory tests did not yet include a coronagraph, but did demonstrate significant speckle suppression from two independent light sources at sub- as well as super-Nyquist separations.

Low-mass stars with mass loss and low-luminosity carbon star formation

International Nuclear Information System (INIS)

Boothroyd, A.I.

1987-01-01

The effects of large carbon enrichments in static stellar envelopes were investigated, using new Los Alamos opacities (including low-temperature carbon and molecular opacities) and including carbon ionizations. To search for the production of low-mass,low-luminosity carbon stars, detailed stellar evolutionary computations were carried out for a grid of low-mass stars of two different metallicities. The stars were evolved from the main sequence through all intermediate stages and through helium-shell flashes on the asymptotic giant branch. The effects of the latest nuclear reaction rates, the new Los Alamos opacities, Reimers-type wind mass loss, and detailed treatment of convection and semi-convection were investigated. Two low-luminosity carbon stars were achieved, in excellent agreement with observations. Conditions favoring dredge-up (and thus carbon-star production) include a reasonably large convective mixing length, low metallicity, relatively large envelope mass, and high flash strength. Mass loss was of major importance, tending to oppose dredge-up; the total mass-loss amounts inferred from observations suffice to prevent formation of high-mass, high-luminosity carbon stars

The STAR experiment at RHIC

International Nuclear Information System (INIS)

Marx, J.N.

1994-01-01

STAR (Solenoidal Tracker at RHIC) will be one of two large, sophisticated experiments ready to take data when the Relativistic Heavy Ion Collider (RHIC) comes on-line in 1999. The design of STAR, its construction and commissioning and the physics program using the detector are the responsibility of a collaboration of over 250 members from 30 institutions, world-wide. The overall approach of the STAR Collaboration to the physics challenge of studying collisions of highly relativistic nuclei is to focus on measurements of the properties of the many hadrons produced in the collisions. The STAR detector is optimized to detect and identify hadrons over a large solid angle so that individual events can be characterized, in detail, based on their hadronic content. The broad capabilities of the STAR detector will permit an examination of a wide variety of proposed signatures for the Quark Gluon Plasma (QGP), using the sample of events which, on an event-by-event basis, appear to come from collisions resulting in a large energy density over a nuclear volume. In order to achieve this goal, the STAR experiment is based on a solenoid geometry with tracking detectors using the time projection chamber approach and covering a large range of pseudo-rapidity so that individual tracks can be seen within the very high track density expected in central collisions at RHIC. STAR also uses particle identification by the dE/dx technique and by time-of-flight. Electromagnetic energy is detected in a large, solid-angle calorimeter. The construction of STAR, which will be located in the Wide Angle Hall at the 6 o'clock position at RHIC, formally began in early 1993

Deep coupling of star tracker and MEMS-gyro data under highly dynamic and long exposure conditions

Science.gov (United States)

Sun, Ting; Xing, Fei; You, Zheng; Wang, Xiaochu; Li, Bin

2014-08-01

Star trackers and gyroscopes are the two most widely used attitude measurement devices in spacecrafts. The star tracker is supposed to have the highest accuracy in stable conditions among different types of attitude measurement devices. In general, to detect faint stars and reduce the size of the star tracker, a method with long exposure time method is usually used. Thus, under dynamic conditions, smearing of the star image may appear and result in decreased accuracy or even failed extraction of the star spot. This may cause inaccuracies in attitude measurement. Gyros have relatively good dynamic performance and are usually used in combination with star trackers. However, current combination methods focus mainly on the data fusion of the output attitude data levels, which are inadequate for utilizing and processing internal blurred star image information. A method for tracking deep coupling stars and MEMS-gyro data is proposed in this work. The method achieves deep fusion at the star image level. First, dynamic star image processing is performed based on the angular velocity information of the MEMS-gyro. Signal-to-noise ratio (SNR) of the star spot could be improved, and extraction is achieved more effectively. Then, a prediction model for optimal estimation of the star spot position is obtained through the MEMS-gyro, and an extended Kalman filter is introduced. Meanwhile, the MEMS-gyro drift can be estimated and compensated though the proposed method. These enable the star tracker to achieve high star centroid determination accuracy under dynamic conditions. The MEMS-gyro drift can be corrected even when attitude data of the star tracker are unable to be solved and only one navigation star is captured in the field of view. Laboratory experiments were performed to verify the effectiveness of the proposed method and the whole system.

The risky business of hiring stars.

Science.gov (United States)

Groysberg, Boris; Nanda, Ashish; Nohria, Nitin

2004-05-01

With the battle for the best and brightest people heating up again, you're most likely out there looking for first-rate talent in the ranks of your competitors. Chances are, you're sold on the idea of recruiting from outside your organization, since developing people within the firm takes time and money. But the authors, who have tracked the careers of high-flying CEOs, researchers, software developers, and leading professionals, argue that top performers quickly fade after leaving one company for another. To study this phenomenon in greater detail, the authors analyzed the ups and downs of more than 1,000 star stock analysts, a well-defined group for which there are abundant data. The results were striking. After a star moves, not only does her performance plunge, but so does the effectiveness of the group she joins--and the market value of her new company. Moreover, transplanted stars don't stay with their new organizations for long, despite the astronomical salaries firms pay to lure them from rivals. Most companies that hire stars overlook the fact that an executive's performance is not entirely transferable because his personal competencies inevitably include company-specific skills. When the star leaves the old company for the new, he cannot take with him many of the resources that contributed to his achievements. As a result, he is unable to repeat his performance in another company--at least not until he learns to work the new system, which could take years. The authors conclude that companies cannot gain a competitive advantage or successfully grow by hiring stars from outside. Instead, they should focus on cultivating talent from within and do everything possible to retain the stars they create. Firms shouldn't fight the star wars, because winning could be the worst thing that happens to them.

Initial results from NuSTAR observations of the Norma arm

DEFF Research Database (Denmark)

Bodaghee, Arash; Tomsick, John A.; Krivonos, Roman

2014-01-01

Results are presented for an initial survey of the Norma Arm gathered with the focusing hard X-ray telescope NuSTAR. The survey covers 0.2 deg2 of sky area in the 3-79 keV range with a minimum and maximum raw depth of 15 ks and 135 ks, respectively. Besides a bright black-hole X-ray binary...

Physics of Neutron Star Crusts

Directory of Open Access Journals (Sweden)

Chamel Nicolas

2008-12-01

Full Text Available The physics of neutron star crusts is vast, involving many different research fields, from nuclear and condensed matter physics to general relativity. This review summarizes the progress, which has been achieved over the last few years, in modeling neutron star crusts, both at the microscopic and macroscopic levels. The confrontation of these theoretical models with observations is also briefly discussed.

Reversal of diuretic-associated impaired glucose tolerance and new-onset diabetes: results of the STAR-LET study.

Science.gov (United States)

Bakris, George; Molitch, Mark; Zhou, Qian; Sarafidis, Pantelis; Champion, Annette; Bacher, Peter; Sowers, James R

2008-01-01

Reversal of new-onset diabetes secondary to thiazide diuretic use remains questionable. STAR-LET was a 6-month extension of the Study of Trandolapril/Verapamil SR and Insulin Resistance (STAR), which assessed the effects of a fixed-dose renin-angiotensin system inhibitor (RASI)/hydrochlorothiazide (HCTZ) combination on changes in 2-hour oral glucose tolerance test (OGTT) results. STAR-LET explored whether the glycemic impact of HCTZ could be reversed by conversion to a RASI/verapamil combination. The primary outcome was change in 2-hour OGTT results. Fifty-one percent of the STAR patients were enrolled in STAR-LET. The 2-hour OGTT value (mmol/L) was unchanged from STAR baseline in the RASI/verapamil group (7.7+/-2.4 vs 8.1+/-3.3; P=.18) and improved in those who were switched from RASI/HCTZ to RASI/verapamil (8.5+/-3.0 vs 7.2+/-2.3; P<.001). This exploratory study suggests that the impairment in glycemic control seen with use of a thiazide diuretic combined with a RASI can be reversed by switching to a regimen that does not include a diuretic.

Deep coupling of star tracker and MEMS-gyro data under highly dynamic and long exposure conditions

International Nuclear Information System (INIS)

Sun, Ting; Xing, Fei; You, Zheng; Wang, Xiaochu; Li, Bin

2014-01-01

Star trackers and gyroscopes are the two most widely used attitude measurement devices in spacecrafts. The star tracker is supposed to have the highest accuracy in stable conditions among different types of attitude measurement devices. In general, to detect faint stars and reduce the size of the star tracker, a method with long exposure time method is usually used. Thus, under dynamic conditions, smearing of the star image may appear and result in decreased accuracy or even failed extraction of the star spot. This may cause inaccuracies in attitude measurement. Gyros have relatively good dynamic performance and are usually used in combination with star trackers. However, current combination methods focus mainly on the data fusion of the output attitude data levels, which are inadequate for utilizing and processing internal blurred star image information. A method for tracking deep coupling stars and MEMS-gyro data is proposed in this work. The method achieves deep fusion at the star image level. First, dynamic star image processing is performed based on the angular velocity information of the MEMS-gyro. Signal-to-noise ratio (SNR) of the star spot could be improved, and extraction is achieved more effectively. Then, a prediction model for optimal estimation of the star spot position is obtained through the MEMS-gyro, and an extended Kalman filter is introduced. Meanwhile, the MEMS-gyro drift can be estimated and compensated though the proposed method. These enable the star tracker to achieve high star centroid determination accuracy under dynamic conditions. The MEMS-gyro drift can be corrected even when attitude data of the star tracker are unable to be solved and only one navigation star is captured in the field of view. Laboratory experiments were performed to verify the effectiveness of the proposed method and the whole system. (paper)

A near-infrared survey for pre-main sequence stars in Taurus

Science.gov (United States)

Gomez, Mercedes; Kenyon, Scott J.; Hartmann, Lee

1994-01-01

We present a near-infrared survey of approximately 2 sq deg covering parts of L1537, L1538, and Heiles cloud 2 in the Taurus-Auriga molecular cloud. Although this study is more sensitive than previous attempts to identify pre-main sequence stars in Taurus-Auriga, our survey regions contain only one new optically visible, young star. We did find several candidate embedded protostars; additional 10 micrometer photometry is necessary to verify the pre-main sequence nature of these sources. Our results--combined with those of previous surveys--show that the L1537/L1538 clouds contain no pre-main sequence stars. These two clouds are less dense than the active star formation sites in Taurus-Auriga, which suggests a cloud must achieve a threshold density to form stars.

A Brightness-Referenced Star Identification Algorithm for APS Star Trackers

Science.gov (United States)

Zhang, Peng; Zhao, Qile; Liu, Jingnan; Liu, Ning

2014-01-01

Star trackers are currently the most accurate spacecraft attitude sensors. As a result, they are widely used in remote sensing satellites. Since traditional charge-coupled device (CCD)-based star trackers have a limited sensitivity range and dynamic range, the matching process for a star tracker is typically not very sensitive to star brightness. For active pixel sensor (APS) star trackers, the intensity of an imaged star is valuable information that can be used in star identification process. In this paper an improved brightness referenced star identification algorithm is presented. This algorithm utilizes the k-vector search theory and adds imaged stars' intensities to narrow the search scope and therefore increase the efficiency of the matching process. Based on different imaging conditions (slew, bright bodies, etc.) the developed matching algorithm operates in one of two identification modes: a three-star mode, and a four-star mode. If the reference bright stars (the stars brighter than three magnitude) show up, the algorithm runs the three-star mode and efficiency is further improved. The proposed method was compared with other two distinctive methods the pyramid and geometric voting methods. All three methods were tested with simulation data and actual in orbit data from the APS star tracker of ZY-3. Using a catalog composed of 1500 stars, the results show that without false stars the efficiency of this new method is 4∼5 times that of the pyramid method and 35∼37 times that of the geometric method. PMID:25299950

A modern search for Wolf-Rayet stars in the Magellanic Clouds: First results

Energy Technology Data Exchange (ETDEWEB)

Massey, Philip; Neugent, Kathryn F. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Morrell, Nidia [Las Campanas Observatory, Carnegie Observatories, Casilla 601 La Serena (Chile); Hillier, D. John, E-mail: phil.massey@lowell.edu, E-mail: kneugent@lowell.edu, E-mail: nmorrell@lco.cl, E-mail: hillier@pitt.edu [Department of Physics and Astronomy and Pittsburgh Particle Physics, Astrophysics, and Cosmology Center (PITT PACC), University of Pittsburgh, Pittsburgh, PA 15260 (United States)

2014-06-10

Over the years, directed surveys and incidental spectroscopy have identified 12 Wolf-Rayet (WR) stars in the Small Magellanic Cloud (SMC) and 139 in the Large Magellanic Cloud (LMC), numbers which are often described as 'essentially complete'. Yet, new WRs are discovered in the LMC almost yearly. We have therefore initiated a new survey of both Magellanic Clouds using the same interference-filter imaging technique previously applied to M31 and M33. We report on our first observing season, in which we have successfully surveyed ∼15% of our intended area of the SMC and LMC. Spectroscopy has confirmed nine newly found WRs in the LMC (a 6% increase), including one of WO-type, only the third known in that galaxy and the second to be discovered recently. The other eight are WN3 stars that include an absorption component. In two, the absorption is likely from an O-type companion, but the other six are quite unusual. Five would be classified naively as 'WN3+O3 V', but such a pairing is unlikely given the rarity of O3 stars, the short duration of this phase (which is incommensurate with the evolution of a companion to a WN star), and because these stars are considerably fainter than O3 V stars. The sixth star may also fall into this category. CMFGEN modeling suggests these stars are hot, bolometrically luminous, and N-rich like other WN3 stars, but lack the strong winds that characterize WNs. Finally, we discuss two rare Of?p stars and four Of supergiants we found, and propose that the B[e] star HD 38489 may have a WN companion.

HD 101065, the Most Peculiar Star: First Results from Precise Radial ...

Indian Academy of Sciences (India)

Abstract. In this paper we discuss the prospects for asteroseismology with spatial resolution and motivate studies of the most chemically peculiar. roAp star HD 101065. We present the first results from a high-precision radial velocity (RV) study of HD 101065 based on data spanning four nights that were acquired using the ...

CLOSE COMPANIONS TO YOUNG STARS. I. A LARGE SPECTROSCOPIC SURVEY IN CHAMAELEON I AND TAURUS-AURIGA

International Nuclear Information System (INIS)

Nguyen, Duy Cuong; Brandeker, Alexis; Van Kerkwijk, Marten H.; Jayawardhana, Ray

2012-01-01

We present the results of a multiplicity survey of 212 T Tauri stars in the Chamaeleon I and Taurus-Auriga star-forming regions, based on high-resolution spectra from the Magellan Clay 6.5 m telescope. From these data, we achieved a typical radial velocity (RV) precision of ∼80 m s –1 with slower rotators yielding better precision, in general. For 174 of these stars, we obtained multi-epoch data with sufficient time baselines to identify binaries based on RV variations. We identified eight close binaries and four close triples, of which three and two, respectively, are new discoveries. The spectroscopic multiplicity fractions we find for Chamaeleon I (7%) and Taurus-Auriga (6%) are similar to each other, and to the results of field star surveys in the same mass and period regime. However, unlike the results from imaging surveys, the frequency of systems with close companions in our sample is not seen to depend on primary mass. Additionally, we do not find a strong correlation between accretion and close multiplicity. This implies that close companions are not likely the main source of the accretion shut down observed in weak-lined T Tauri stars. Our results also suggest that sufficient RV precision can be achieved for at least a subset of slowly rotating young stars to search for hot Jupiter planets.

Unsupervised classification of variable stars

Science.gov (United States)

Valenzuela, Lucas; Pichara, Karim

2018-03-01

During the past 10 years, a considerable amount of effort has been made to develop algorithms for automatic classification of variable stars. That has been primarily achieved by applying machine learning methods to photometric data sets where objects are represented as light curves. Classifiers require training sets to learn the underlying patterns that allow the separation among classes. Unfortunately, building training sets is an expensive process that demands a lot of human efforts. Every time data come from new surveys; the only available training instances are the ones that have a cross-match with previously labelled objects, consequently generating insufficient training sets compared with the large amounts of unlabelled sources. In this work, we present an algorithm that performs unsupervised classification of variable stars, relying only on the similarity among light curves. We tackle the unsupervised classification problem by proposing an untraditional approach. Instead of trying to match classes of stars with clusters found by a clustering algorithm, we propose a query-based method where astronomers can find groups of variable stars ranked by similarity. We also develop a fast similarity function specific for light curves, based on a novel data structure that allows scaling the search over the entire data set of unlabelled objects. Experiments show that our unsupervised model achieves high accuracy in the classification of different types of variable stars and that the proposed algorithm scales up to massive amounts of light curves.

Quantitative characterization of the reliability of simplex buses and stars to compare their benefits in fieldbuses

International Nuclear Information System (INIS)

Barranco, Manuel; Proenza, Julián; Almeida, Luís

2015-01-01

Fieldbuses targeted to highly dependable distributed embedded systems are shifting from bus to star topologies. Surprisingly, despite the efforts into this direction, engineers lack of analyses that quantitatively characterize the system reliability achievable by buses and stars. Thus, to guide engineers in developing adequate bus and star fieldbuses, this work models, quantifies and compares the system reliability provided by simplex buses and stars for the case of the Controller Area Network (CAN). It clarifies how relevant dependability-related aspects affect reliability, refuting some intuitive ideas, and revealing some previously unknown bus and star benefits. - Highlights: • SANs models that quantify the reliability of simplex buses/stars in fieldbuses. • Models cover system relevant dependability-related features abstracted in the literature. • Results refute intuitive ideas about buses and stars and show some unexpected effects. • Models and results can guide the design of reliable simplex bus/stars fieldbuses

A NEAR-INFRARED SURVEY OF THE INNER GALACTIC PLANE FOR WOLF-RAYET STARS. I. METHODS AND FIRST RESULTS: 41 NEW WR STARS

International Nuclear Information System (INIS)

Shara, Michael M.; Gerke, Jill; Zurek, David; Moffat, Anthony F. J.; Doyon, Rene; Villar-Sbaffi, Alfredo; Stanonik, Kathryn; Artigau, Etienne; Drissen, Laurent

2009-01-01

The discovery of new Wolf-Rayet (WR) stars in our Galaxy via large-scale narrowband optical surveys has been severely limited by dust extinction. Recent improvements in infrared technology have made narrowband-broadband imaging surveys viable again. We report a new J, K, and narrowband imaging survey of 300 deg 2 of the plane of the Galaxy, spanning 150 degrees in Galactic longitude and reaching 1 degree above and below the Galactic plane. The survey has a useful limiting magnitude of K = 15 over most of the observed Galactic plane, and K = 14 within a few degrees of the Galactic center. Thousands of emission line candidates have been detected. In spectrographic follow-ups of 173 WR star candidates we have discovered 41 new WR stars, 15 of type WN and 26 of type WC. Star subtype assignments have been confirmed with K-band spectra, and distances approximated using the method of spectroscopic parallax. A few of the new WR stars are among the most distant known in our Galaxy. The distribution of these new WR stars is seen to follow that of previously known WR stars along the spiral arms of the Galaxy. Tentative radial velocities were also measured for most of the new WR stars.

Optical System Error Analysis and Calibration Method of High-Accuracy Star Trackers

Directory of Open Access Journals (Sweden)

Zheng You

2013-04-01

Full Text Available The star tracker is a high-accuracy attitude measurement device widely used in spacecraft. Its performance depends largely on the precision of the optical system parameters. Therefore, the analysis of the optical system parameter errors and a precise calibration model are crucial to the accuracy of the star tracker. Research in this field is relatively lacking a systematic and universal analysis up to now. This paper proposes in detail an approach for the synthetic error analysis of the star tracker, without the complicated theoretical derivation. This approach can determine the error propagation relationship of the star tracker, and can build intuitively and systematically an error model. The analysis results can be used as a foundation and a guide for the optical design, calibration, and compensation of the star tracker. A calibration experiment is designed and conducted. Excellent calibration results are achieved based on the calibration model. To summarize, the error analysis approach and the calibration method are proved to be adequate and precise, and could provide an important guarantee for the design, manufacture, and measurement of high-accuracy star trackers.

Optical system error analysis and calibration method of high-accuracy star trackers.

Science.gov (United States)

Sun, Ting; Xing, Fei; You, Zheng

2013-04-08

The star tracker is a high-accuracy attitude measurement device widely used in spacecraft. Its performance depends largely on the precision of the optical system parameters. Therefore, the analysis of the optical system parameter errors and a precise calibration model are crucial to the accuracy of the star tracker. Research in this field is relatively lacking a systematic and universal analysis up to now. This paper proposes in detail an approach for the synthetic error analysis of the star tracker, without the complicated theoretical derivation. This approach can determine the error propagation relationship of the star tracker, and can build intuitively and systematically an error model. The analysis results can be used as a foundation and a guide for the optical design, calibration, and compensation of the star tracker. A calibration experiment is designed and conducted. Excellent calibration results are achieved based on the calibration model. To summarize, the error analysis approach and the calibration method are proved to be adequate and precise, and could provide an important guarantee for the design, manufacture, and measurement of high-accuracy star trackers.

In Orbit Performance of a Fully Autonomous Star Tracker

DEFF Research Database (Denmark)

Jørgensen, John Leif

1999-01-01

The Department of Automation at DTU has developed the Advanced Stellar Compass (ASC), a fully autonomous star tracker, for use as high precision attitude reference onboard spacecrafts. The ASC is composed of a CCD-based camera and a powerful microprocessor containing star catalogue, image......-analysis software and a search engine. The unit autonomously performs all tasks necessary to calculate the inertial attitude from a star image. To allow for flexible attitude manoeuvres, the ASC can, simultaneously, drive from one to four cameras, efficiently removing dropouts from, e.g., sun blinding of one camera......, it is difficult to test and verify the true robustness and accuracy of a star tracker on ground. This is caused by the fact that only real-sky tests offer high fidelity stimulation of the sensor, while the atmosphere instabilities result in a dominant noise source intrinsically limiting the achievable accuracy...

EMACSS: Evolve Me A Cluster of StarS

Science.gov (United States)

Alexander, Poul E. R.; Gieles, Mark

2012-03-01

The star cluster evolution code Evolve Me A Cluster of StarS (EMACSS) is a simple yet physically motivated computational model that describes the evolution of some fundamental properties of star clusters in static tidal fields. The prescription is based upon the flow of energy within the cluster, which is a constant fraction of the total energy per half-mass relaxation time. According to Henon's predictions, this flow is independent of the precise mechanisms for energy production within the core, and therefore does not require a complete description of the many-body interactions therein. Dynamical theory and analytic descriptions of escape mechanisms is used to construct a series of coupled differential equations expressing the time evolution of cluster mass and radius for a cluster of equal-mass stars. These equations are numerically solved using a fourth-order Runge-Kutta integration kernel; the results were benchmarked against a data base of direct N-body simulations. EMACSS is publicly available and reproduces the N-body results to within 10 per cent accuracy for the entire post-collapse evolution of star clusters.

A hybrid method for accurate star tracking using star sensor and gyros.

Science.gov (United States)

Lu, Jiazhen; Yang, Lie; Zhang, Hao

2017-10-01

Star tracking is the primary operating mode of star sensors. To improve tracking accuracy and efficiency, a hybrid method using a star sensor and gyroscopes is proposed in this study. In this method, the dynamic conditions of an aircraft are determined first by the estimated angular acceleration. Under low dynamic conditions, the star sensor is used to measure the star vector and the vector difference method is adopted to estimate the current angular velocity. Under high dynamic conditions, the angular velocity is obtained by the calibrated gyros. The star position is predicted based on the estimated angular velocity and calibrated gyros using the star vector measurements. The results of the semi-physical experiment show that this hybrid method is accurate and feasible. In contrast with the star vector difference and gyro-assisted methods, the star position prediction result of the hybrid method is verified to be more accurate in two different cases under the given random noise of the star centroid.

Small star trackers for modern space vehicles

Science.gov (United States)

Kouzmin, Vladimir; Jushkov, Vladimir; Zaikin, Vladimir

2017-11-01

Based on experience of many years creation of spacecrafts' star trackers with diversified detectors (from the first star trackers of 60's to tens versions of star trackers in the following years), using technological achievements in the field of optics and electronics the NPP "Geofizika-Cosmos" has provided celestial orientation for all the space vehicles created in Russia and now has developed a series of new star trackers with CCD matrix and special processors, which are able to meet needs in celestial orientation of the modern spacecrafts for the nearest 10-15 years. In the given article the main characteristics and description of some star trackers' versions are presented. The star trackers have various levels of technical characteristics and use both combined (Russian and foreign) procurement parts, and only national (Russian) procurement parts for the main units.

Impact of star formation inhomogeneities on merger rates and interpretation of LIGO results

International Nuclear Information System (INIS)

O'Shaughnessy, R; Kopparapu, R K; Belczynski, K

2012-01-01

Within the next decade, ground based gravitational-wave detectors are in principle capable of determining the compact object merger rate per unit volume of the local universe to better than 20% with more than 30 detections. These measurements will constrain our models of stellar, binary and star cluster evolution in the nearby present-day and ancient universe. We argue that the stellar models are sensitive to heterogeneities (in age and metallicity at least) in such a way that the predicted merger rates are subject to an additional 30-50% systematic errors unless these heterogeneities are taken into account. Without adding new electromagnetic constraints on massive binary evolution or relying on more information from each merger (e.g., binary masses and spins), as few as the 5 merger detections could exhaust the information available in a naive comparison to merger rate predictions. As a concrete example immediately relevant to analysis of initial and enhanced LIGO results, we use a nearby-universe catalog to demonstrate that no one tracer of stellar content can be consistently used to constrain merger rates without introducing a systematic error of order O(30%) at 90% confidence (depending on the type of binary involved). For example, though binary black holes typically take many Gyr to merge, binary neutron stars often merge rapidly; different tracers of stellar content are required for these two types. More generally, we argue that theoretical binary evolution can depend sufficiently sensitively on star-forming conditions-even assuming no uncertainty in binary evolution model-that the distribution of star-forming conditions must be incorporated to reduce the systematic error in merger rate predictions below roughly 40%. We emphasize that the degree of sensitivity to star-forming conditions depends on the binary evolution model and on the amount of relevant variation in star-forming conditions. For example, if after further comparison with electromagnetic and

Transitional Disks Associated with Intermediate-Mass Stars: Results of the SEEDS YSO Survey

Science.gov (United States)

Grady, C.; Fukagawa, M.; Maruta, Y.; Ohta, Y.; Wisniewski, J.; Hashimoto, J.; Okamoto, Y.; Momose, M.; Currie, T.; McElwain, M.;

The NuSTAR Extragalactic Surveys: Initial Results and Catalog from the Extended Chandra Deep Field South

DEFF Research Database (Denmark)

Mullaney, J. R.; Del-Moro, A.; Aird, J.

2015-01-01

We present the initial results and the source catalog from the Nuclear Spectroscopic Telescope Array (NuSTAR) survey of the Extended Chandra Deep Field South (hereafter, ECDFS)—currently the deepest contiguous component of the NuSTAR extragalactic survey program. The survey covers the full ≈30......V fluxes) span the range L10 40 keV (0.7 300) 10 erg s» - ´ 43 1 -- ,sampling below the “knee” of the X-ray luminosity function out to z ~ 0.8-1. Finally, we identify oneNuSTAR source that has neither a Chandra nor an XMM-Newton counterpart, but that shows evidence of nuclearactivity at infrared...

Results of a search for γ Dor and δ SCT stars with the Kepler spacecraft

Energy Technology Data Exchange (ETDEWEB)

Bradley, P. A.; Miles, L. F. [XCP-6, MS F-699 Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Guzik, J. A. [XTD-NTA, MS T-086 Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Uytterhoeven, K. [Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain and Departamento de Astrofisica, Universidad de La Laguna, E-38200 La Laguna, Tenerife (Spain); Jackiewicz, J. [New Mexico State University, Las Cruces, NM 88003 (United States); Kinemuchi, K., E-mail: pbradley@lanl.gov [Apache Point Observatory, Sunspot, NM 88349 (United States)

2015-02-01

The light curves of 2768 stars with effective temperatures and surface gravities placing them near the gamma Doradus (γ Dor)/delta Scuti (δ Sct) instability region were observed as part of the Kepler Guest Observer program from Cycles 1 through 5. The light curves were analyzed in a uniform manner to search for γ Dor, δ Sct, and hybrid star pulsations. The γ Dor, δ Sct, and hybrid star pulsations extend asteroseismology to stars slightly more massive (1.4–2.5 M{sub ⊙}) than our Sun. We find 207 γ Dor, 84 δ Sct, and 32 hybrid candidate stars. Many of these stars are cooler than the red edge of the γ Dor instability strip as determined from ground-based observations made before Kepler. A few of our γ Dor candidate stars lie on the hot side of the ground-based γ Dor instability strip. The hybrid candidate stars cover the entire region between 6200 K and the blue edge of the ground-based δ Sct instability strip. None of our candidate stars are hotter than the hot edge of the ground-based δ Sct instability strip. Our discoveries, coupled with the work of others, show that Kepler has discovered over 2000 γ Dor, δ Sct, and hybrid star candidates in the 116 square degree Kepler field of view. We found relatively few variable stars fainter than magnitude 15, which may be because they are far enough away to lie between spiral arms in our Galaxy, where there would be fewer stars.

Results of a search for γ Dor and δ SCT stars with the Kepler spacecraft

International Nuclear Information System (INIS)

Bradley, P. A.; Miles, L. F.; Guzik, J. A.; Uytterhoeven, K.; Jackiewicz, J.; Kinemuchi, K.

2015-01-01

The light curves of 2768 stars with effective temperatures and surface gravities placing them near the gamma Doradus (γ Dor)/delta Scuti (δ Sct) instability region were observed as part of the Kepler Guest Observer program from Cycles 1 through 5. The light curves were analyzed in a uniform manner to search for γ Dor, δ Sct, and hybrid star pulsations. The γ Dor, δ Sct, and hybrid star pulsations extend asteroseismology to stars slightly more massive (1.4–2.5 M ⊙ ) than our Sun. We find 207 γ Dor, 84 δ Sct, and 32 hybrid candidate stars. Many of these stars are cooler than the red edge of the γ Dor instability strip as determined from ground-based observations made before Kepler. A few of our γ Dor candidate stars lie on the hot side of the ground-based γ Dor instability strip. The hybrid candidate stars cover the entire region between 6200 K and the blue edge of the ground-based δ Sct instability strip. None of our candidate stars are hotter than the hot edge of the ground-based δ Sct instability strip. Our discoveries, coupled with the work of others, show that Kepler has discovered over 2000 γ Dor, δ Sct, and hybrid star candidates in the 116 square degree Kepler field of view. We found relatively few variable stars fainter than magnitude 15, which may be because they are far enough away to lie between spiral arms in our Galaxy, where there would be fewer stars.

THE Be STAR SPECTRA (BeSS) DATABASE

International Nuclear Information System (INIS)

Neiner, C.; De Batz, B.; Cochard, F.; Floquet, M.; Mekkas, A.; Desnoux, V.

2011-01-01

Be stars vary on many timescales, from hours to decades. A long time base of observations to analyze certain phenomena in these stars is therefore necessary. Collecting all existing and future Be star spectra into one database has thus emerged as an important tool for the Be star community. Moreover, for statistical studies, it is useful to have centralized information on all known Be stars via an up-to-date catalog. These two goals are what the Be Star Spectra (BeSS, http://basebe.obspm.fr) database proposes to achieve. The database contains an as-complete-as-possible catalog of known Be stars with stellar parameters, as well as spectra of Be stars from all origins (any wavelength, any epoch, any resolution, etc.). It currently contains over 54,000 spectra of more than 600 different Be stars among the ∼2000 Be stars in the catalog. A user can access and query this database to retrieve information on Be stars or spectra. Registered members can also upload spectra to enrich the database. Spectra obtained by professional as well as amateur astronomers are individually validated in terms of format and science before being included in BeSS. In this paper, we present the database itself as well as examples of the use of BeSS data in terms of statistics and the study of individual stars.

Recent results of the STAR high-energy polarized proton-proton program at RHIC at BNL

International Nuclear Information System (INIS)

Surrow, Bernd

2007-01-01

The STAR experiment at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is carrying out a spin physics program colliding transverse or longitudinal polarized proton beams at √(s) 200 - 500GeV to gain a deeper insight into the spin structure and dynamics of the proton. These studies provide fundamental tests of Quantum Chromodynamics (QCD).One of the main objectives of the STAR spin physics program is the determination of the polarized gluon distribution function through a measurement of the longitudinal double-spin asymmetry, ALL, for various processes. Recent results will be shown on the measurement of ALL for inclusive jet production, neutral pion production and charged pion production at √(s) = 200GeV. In addition to these measurements involving longitudinal polarized proton beams, the STAR collaboration has performed several important measurements employing transverse polarized proton beams. New results on the measurement of the transverse single-spin asymmetry, AN, for forward neutral pion production and the first measurement of AN for mid-rapidity di-jet production will be discussed

Extreme neutron stars from Extended Theories of Gravity

Energy Technology Data Exchange (ETDEWEB)

Astashenok, Artyom V. [I. Kant Baltic Federal University, Institute of Physics and Technology, Nevskogo st. 14, Kaliningrad, 236041 (Russian Federation); Capozziello, Salvatore [Dipartimento di Fisica, Università di Napoli ' ' Federico II' ' , Via Cinthia, 9, Napoli, I-80126 Italy (Italy); Odintsov, Sergei D., E-mail: artyom.art@gmail.com, E-mail: capozziello@na.infn.it, E-mail: odintsov@ieec.uab.es [Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona (Spain)

2015-01-01

We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from f(R) and f(G) extensions of General Relativity where functions of the Ricci curvature invariant R and the Gauss-Bonnet invariant G are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in f(R) gravity. In principle, massive stars with M > 4M{sub ☉} can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities ρ{sub c} ∼ 1.5–2.0 GeV/fm{sup 3}) are possible considering quadratic corrections of f(G) gravity. The magnetic field strength in the star center is of order 6–8 × 10{sup 18} G. In general, we can say that other branches of massive neutron stars are possible considering the extra pressure contributions coming from gravity extensions. Such a feature can constitute both a probe for alternative theories and a way out to address anomalous self-gravitating compact systems.

Further stable neutron star models from f(R) gravity

Energy Technology Data Exchange (ETDEWEB)

Astashenok, Artyom V. [I. Kant Baltic Federal University, Institute of Physics and Technology, Nevskogo st. 14, Kaliningrad, 236041 (Russian Federation); Capozziello, Salvatore [Dipartimento di Fisica, Università di Napoli ' ' Federico II' ' , Via Cinthia, 9, Napoli, I–80126 (Italy); Odintsov, Sergei D., E-mail: artyom.art@gmail.com, E-mail: capozziello@na.infn.it, E-mail: odintsov@ieec.uab.es [Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona (Spain)

2013-12-01

Neutron star models in perturbative f(R) gravity are considered with realistic equations of state. In particular, we consider the FPS, SLy and other equations of state and a case of piecewise equation of state for stars with quark cores. The mass-radius relations for f(R) = R+R(e{sup −R/R{sub 0}}−1) model and for R{sup 2} models with logarithmic and cubic corrections are obtained. In the case of R{sup 2} gravity with cubic corrections, we obtain that at high central densities (ρ > 10ρ{sub ns}, where ρ{sub ns} = 2.7 × 10{sup 14} g/cm{sup 3} is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass ∼ 1.9M{sub ⊙} (SLy equation). A similar situation takes place for AP4 and BSK20 EoS. Such an effect can give rise to more compact stars than in General Relativity. If observationally identified, such objects could constitute a formidable signature for modified gravity at astrophysical level. Another interesting result can be achieved in modified gravity with only a cubic correction. For some EoS, the upper limit of neutron star mass increases and therefore these EoS can describe realistic star configurations (although, in General Relativity, these EoS are excluded by observational constraints)

Further stable neutron star models from f(R) gravity

International Nuclear Information System (INIS)

Astashenok, Artyom V.; Capozziello, Salvatore; Odintsov, Sergei D.

2013-01-01

Neutron star models in perturbative f(R) gravity are considered with realistic equations of state. In particular, we consider the FPS, SLy and other equations of state and a case of piecewise equation of state for stars with quark cores. The mass-radius relations for f(R) = R+R(e −R/R 0 −1) model and for R 2 models with logarithmic and cubic corrections are obtained. In the case of R 2 gravity with cubic corrections, we obtain that at high central densities (ρ > 10ρ ns , where ρ ns = 2.7 × 10 14 g/cm 3 is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass ∼ 1.9M ⊙ (SLy equation). A similar situation takes place for AP4 and BSK20 EoS. Such an effect can give rise to more compact stars than in General Relativity. If observationally identified, such objects could constitute a formidable signature for modified gravity at astrophysical level. Another interesting result can be achieved in modified gravity with only a cubic correction. For some EoS, the upper limit of neutron star mass increases and therefore these EoS can describe realistic star configurations (although, in General Relativity, these EoS are excluded by observational constraints)

Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

Energy Technology Data Exchange (ETDEWEB)

Hopkins, Philip F. [TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125 (United States); Conroy, Charlie, E-mail: phopkins@caltech.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2017-02-01

Large dust grains can fluctuate dramatically in their local density, relative to the gas, in neutral turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains (>100 Å) under these conditions. This can have important consequences for star formation and stellar metal abundances in extremely metal-poor stars. Low-mass stars can form in dust-enhanced regions almost immediately after some dust forms even if the galaxy-average metallicity is too low for fragmentation to occur. We argue that the metal abundances of these “promoted” stars may contain interesting signatures as the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced and/or fluctuate almost independently. Remarkably, the otherwise puzzling abundance patterns of some metal-poor stars can be well fit by standard IMF-averaged core-collapse SNe yields if we allow for fluctuating local dust-to-gas ratios. We also show that the observed log-normal distribution of enhancements in pure SNe yields, shows very large enhancements and variations up to factors of ≳100 as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. Together, this suggests that (1) dust exists in second-generation star formation, (2) local dust-to-gas ratio fluctuations occur in protogalaxies and can be important for star formation, and (3) the light element abundances of these stars may be affected by the local chemistry of dust where they formed, rather than directly tracing nucleosynthesis from earlier populations.

Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

International Nuclear Information System (INIS)

Hopkins, Philip F.; Conroy, Charlie

2017-01-01

Large dust grains can fluctuate dramatically in their local density, relative to the gas, in neutral turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains (>100 Å) under these conditions. This can have important consequences for star formation and stellar metal abundances in extremely metal-poor stars. Low-mass stars can form in dust-enhanced regions almost immediately after some dust forms even if the galaxy-average metallicity is too low for fragmentation to occur. We argue that the metal abundances of these “promoted” stars may contain interesting signatures as the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced and/or fluctuate almost independently. Remarkably, the otherwise puzzling abundance patterns of some metal-poor stars can be well fit by standard IMF-averaged core-collapse SNe yields if we allow for fluctuating local dust-to-gas ratios. We also show that the observed log-normal distribution of enhancements in pure SNe yields, shows very large enhancements and variations up to factors of ≳100 as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. Together, this suggests that (1) dust exists in second-generation star formation, (2) local dust-to-gas ratio fluctuations occur in protogalaxies and can be important for star formation, and (3) the light element abundances of these stars may be affected by the local chemistry of dust where they formed, rather than directly tracing nucleosynthesis from earlier populations.

Calendar Year 2008 Program Benefits for ENERGY STAR Labeled Products

Energy Technology Data Exchange (ETDEWEB)

Homan, GregoryK; Sanchez, Marla; Brown, RichardE; Lai, Judy

2010-08-24

This paper presents current and projected savings for ENERGY STAR labeled products, and details the status of the model as implemented in the September 2009 spreadsheets. ENERGY STAR is a voluntary energy efficiency labeling program operated jointly by the Environmental Protection Agency (US EPA) and the U.S. Department of Energy (US DOE), designed to identify and promote energy-efficient products, buildings and practices. Since the program inception in 1992, ENERGY STAR has become a leading international brand for energy efficient products, and currently labels more than thirty products, spanning office equipment, heating, cooling and ventilation equipment, commercial and residential lighting, home electronics, and major appliances. ENERGY STAR's central role in the development of regional, national and international energy programs necessitates an open process whereby its program achievements to date as well as projected future savings are shared with stakeholders. This report presents savings estimates for ENERGY STAR labeled products. We present estimates of energy, dollar, and carbon savings achieved by the program in the year 2008, annual forecasts for 2009 and 2010, and cumulative savings estimates for the period 1993 through 2008 and cumulative forecasts for the period 2009 through 2015. Through 2008 the program saved 8.8 Quads of primary energy and avoided the equivalent of 158 metric tones carbon (MtC). The forecast for the period 2009-2015 is 18.1 Quads or primary energy saved and 316 MtC emissions avoided. The sensitivity analysis bounds the best estimate of carbon avoided between 104 MtC and 213 MtC (1993 to 2008) and between 206 MtC and 444 MtC (2009 to 2015). In this report we address the following questions for ENERGY STAR labeled products: (1) How are ENERGY STAR impacts quantified; (2) What are the ENERGY STAR achievements; and (3) What are the limitations to our method?

VARIABLE STARS IN THE LARGE MAGELLANIC CLOUD GLOBULAR CLUSTER NGC 2257. I. RESULTS BASED ON 2007-2008 B, V PHOTOMETRY

International Nuclear Information System (INIS)

Nemec, James M.; Walker, Alistair; Jeon, Young-Beom

2009-01-01

The variable stars in the Large Magellanic Cloud star cluster NGC 2257 are reinvestigated using photometry (to ∼20th mag) of over 400 new B, V CCD images taken with the CTIO 0.9 m telescope on 14 nights in 2007 December and 2008 January. New period searches have been made using two independent algorithms (CLEAN, Period04); the resultant periods of most of the stars are consistent with the pulsation periods derived previously, and where there are discrepancies these have been resolved. For the B and V light curves, accurate Fourier coefficients and parameters are given. Six new variable stars have been discovered (V45-50), including a bright candidate long-period variable star showing secondary oscillations (V45) and two anomalously bright RRc stars (V48 and V50), which are shown to be brightened and reddened by nearby red giant stars. Also discovered among the previously known variable stars are three double-mode RR Lyrae stars (V8, V16, and V34) and several Blazhko variables. Archival Hubble Space Telescope images and the photometry by Johnson et al. have been used to define better the properties of the most crowded variable stars. The total number of cluster variable stars now stands at forty-seven: 23 RRab stars, four of which show Blazhko amplitude variations; 20 RRc stars, one showing clear Blazhko variations and another showing possible Blazhko variations; the three RRd stars, all having the dominant period ∼0.36 day and period ratios P 1 /P 0 ∼0.7450; and an LPV star located near the tip of the red giant branch. A comparison of the RRd stars with those in other environments shows them to be most similar to those in IC4499.

Star Formation in Taurus: Preliminary Results from 2MASS

Science.gov (United States)

Beichman, C. A.; Jarrett, T.

1993-01-01

Data with the 2MASS prototype camera were obtained in a 2.3 sq. deg region in Taurus containing Heiles Cloud 2, a region known from IRAS observations to contain a number of very young solar type stars.

GMC Collisions as Triggers of Star Formation. III. Density and Magnetically Regulated Star Formation

Energy Technology Data Exchange (ETDEWEB)

Wu, Benjamin [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Tan, Jonathan C. [Department of Physics, University of Florida, Gainesville, FL 32611 (United States); Christie, Duncan [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Nakamura, Fumitaka [National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Van Loo, Sven [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Collins, David, E-mail: ben.wu@nao.ac.jp [Department of Physics, Florida State University, Tallahassee, FL 32306-4350 (United States)

2017-06-01

We study giant molecular cloud (GMC) collisions and their ability to trigger star cluster formation. We further develop our three-dimensional magnetized, turbulent, colliding GMC simulations by implementing star formation subgrid models. Two such models are explored: (1) “Density-Regulated,” i.e., fixed efficiency per free-fall time above a set density threshold and (2) “Magnetically Regulated,” i.e., fixed efficiency per free-fall time in regions that are magnetically supercritical. Variations of parameters associated with these models are also explored. In the non-colliding simulations, the overall level of star formation is sensitive to model parameter choices that relate to effective density thresholds. In the GMC collision simulations, the final star formation rates and efficiencies are relatively independent of these parameters. Between the non-colliding and colliding cases, we compare the morphologies of the resulting star clusters, properties of star-forming gas, time evolution of the star formation rate (SFR), spatial clustering of the stars, and resulting kinematics of the stars in comparison to the natal gas. We find that typical collisions, by creating larger amounts of dense gas, trigger earlier and enhanced star formation, resulting in 10 times higher SFRs and efficiencies. The star clusters formed from GMC collisions show greater spatial substructure and more disturbed kinematics.

Chemical abundances of fast-rotating massive stars. I. Description of the methods and individual results

Science.gov (United States)

Cazorla, Constantin; Morel, Thierry; Nazé, Yaël; Rauw, Gregor; Semaan, Thierry; Daflon, Simone; Oey, M. S.

2017-07-01

Aims: Recent observations have challenged our understanding of rotational mixing in massive stars by revealing a population of fast-rotating objects with apparently normal surface nitrogen abundances. However, several questions have arisen because of a number of issues, which have rendered a reinvestigation necessary; these issues include the presence of numerous upper limits for the nitrogen abundance, unknown multiplicity status, and a mix of stars with different physical properties, such as their mass and evolutionary state, which are known to control the amount of rotational mixing. Methods: We have carefully selected a large sample of bright, fast-rotating early-type stars of our Galaxy (40 objects with spectral types between B0.5 and O4). Their high-quality, high-resolution optical spectra were then analysed with the stellar atmosphere modelling codes DETAIL/SURFACE or CMFGEN, depending on the temperature of the target. Several internal and external checks were performed to validate our methods; notably, we compared our results with literature data for some well-known objects, studied the effect of gravity darkening, or confronted the results provided by the two codes for stars amenable to both analyses. Furthermore, we studied the radial velocities of the stars to assess their binarity. Results: This first part of our study presents our methods and provides the derived stellar parameters, He, CNO abundances, and the multiplicity status of every star of the sample. It is the first time that He and CNO abundances of such a large number of Galactic massive fast rotators are determined in a homogeneous way. Based on observations obtained with the Heidelberg Extended Range Optical Spectrograph (HEROS) at the Telescopio Internacional de Guanajuato (TIGRE) with the SOPHIE échelle spectrograph at the Haute-Provence Observatory (OHP; Institut Pytheas; CNRS, France), and with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph at the Magellan II Clay telescope

Overview Michelin Star Reputation Restaurant in Hospitality Industry

Directory of Open Access Journals (Sweden)

Agung Gita Subakti

2013-05-01

Full Text Available For most chefs and Restaurateur, having his restaurant being awarded one or more stars in the famous Michelin Guide Rouge represents a major achievement, recognition of their work, and also important publicity generating increased notoriety. In this specific industry, experts play a decisive role, and reputation of restaurants and chefs are basically established according to their opinions. The aim of this paper is to overview some of the Restaurants achieving the Michelin Star Reputation and able to sustain it for years. Moreover, how these reputations are made and to understand better the development of gaining such a high reputation.

Star Masses and Star-Planet Distances for Earth-like Habitability.

Science.gov (United States)

Waltham, David

2017-01-01

This paper presents statistical estimates for the location and duration of habitable zones (HZs) around stars of different mass. The approach is based upon the assumption that Earth's location, and the Sun's mass, should not be highly atypical of inhabited planets. The results support climate-model-based estimates for the location of the Sun's HZ except models giving a present-day outer-edge beyond 1.64 AU. The statistical approach also demonstrates that there is a habitability issue for stars smaller than 0.65 solar masses since, otherwise, Earth would be an extremely atypical inhabited world. It is difficult to remove this anomaly using the assumption that poor habitability of planets orbiting low-mass stars results from unfavorable radiation regimes either before, or after, their stars enter the main sequence. However, the anomaly is well explained if poor habitability results from tidal locking of planets in the HZs of small stars. The expected host-star mass for planets with intelligent life then has a 95% confidence range of 0.78 M ⊙ planets with at least simple life is 0.57 M ⊙  < M < 1.64 M ⊙ . Key Words: Habitability-Habitable zone-Anthropic-Red dwarfs-Initial mass function. Astrobiology 17, 61-77.

Spectral differential imaging detection of planets about nearby stars

International Nuclear Information System (INIS)

Smith, W.H.

1987-01-01

Direct ground-based optical imaging of planets in orbit about nearby stars may be accomplished by spectral differential imaging using multiple passband acoustooptic filters with a CCD. This technique provides two essential results. First, it provides a means to modulate the stellar flux reflected from a planet while leaving the flux from the star and other sources in the same field of view unmodulated. Second, spectral differential imaging enables the CCD detector to achieve a sufficiently high dynamic range to locate planets near a star in spite of an integrated brightness differential of 5 x 10 8 . Spectral differential imaging at nearby diffraction limited imaging conditions with telescope apodization can reduce the time to conduct a sensitive planetary search to a few hours in some cases. The feasibility of this idea is discussed here and shown to provide, in principle, the discrimination and sensitivity to detect a Jovian-class planet about stars at distances of about 10 parsecs. The detection of brown dwarfs is shown to be feasible as well. 31 references

B- AND A-TYPE STARS IN THE TAURUS-AURIGA STAR-FORMING REGION

International Nuclear Information System (INIS)

Mooley, Kunal; Hillenbrand, Lynne; Rebull, Luisa; Padgett, Deborah; Knapp, Gillian

2013-01-01

We describe the results of a search for early-type stars associated with the Taurus-Auriga molecular cloud complex, a diffuse nearby star-forming region noted as lacking young stars of intermediate and high mass. We investigate several sets of possible O, B, and early A spectral class members. The first is a group of stars for which mid-infrared images show bright nebulae, all of which can be associated with stars of spectral-type B. The second group consists of early-type stars compiled from (1) literature listings in SIMBAD, (2) B stars with infrared excesses selected from the Spitzer Space Telescope survey of the Taurus cloud, (3) magnitude- and color-selected point sources from the Two Micron All Sky Survey, and (4) spectroscopically identified early-type stars from the Sloan Digital Sky Survey coverage of the Taurus region. We evaluated stars for membership in the Taurus-Auriga star formation region based on criteria involving: spectroscopic and parallactic distances, proper motions and radial velocities, and infrared excesses or line emission indicative of stellar youth. For selected objects, we also model the scattered and emitted radiation from reflection nebulosity and compare the results with the observed spectral energy distributions to further test the plausibility of physical association of the B stars with the Taurus cloud. This investigation newly identifies as probable Taurus members three B-type stars: HR 1445 (HD 28929), τ Tau (HD 29763), 72 Tau (HD 28149), and two A-type stars: HD 31305 and HD 26212, thus doubling the number of stars A5 or earlier associated with the Taurus clouds. Several additional early-type sources including HD 29659 and HD 283815 meet some, but not all, of the membership criteria and therefore are plausible, though not secure, members.

A search for β Cephei variable stars in the Magellanic Clouds: motivation and first results for the LMC

International Nuclear Information System (INIS)

Sterken, C.; Jerzykiewicz, M.

1988-01-01

Motivation for starting a programme of detecting and investigating β Cephei variables in the Magellanic Clouds is given. Differential photoelectric observations are then reported of six LMC stars which fall in the instability strip defined by the galactic β Cephei variables. Three programme stars are found to exhibit short-term brightness variations. One of them, showing a sinusoidal light-curve with an amplitude (half-range) equal to 0.0070 ± 0.0011 mag and a period equal to about 5 hr, is a promising β Cephei candidate. In the case of the other two variable programme stars, the interpretation of the results is less straightforward. The remaining three programme stars are shown to be constant on a short time-scale, two to within ± 0.010 mag, and one to within ± 0.005 magn. (author)

Cartography of the sun and the stars

CERN Document Server

Neiner, Coralie

2016-01-01

The mapping of the surface of stars requires diverse skills, analysis techniques and advanced modeling, i.e. the collaboration of scientists in various specialties. This volume gives insights into new techniques allowing for the first time to obtain resolved images of stars. It takes stock of what has been achieved so far in Chile, on the ESO VLTI instrument or, in the States, on the CHARA instrument. In recent times interferometry, combined with adaptive optics has allowed to reconstruct images of stars. Besides the Sun (of course) by now five stars have been resolved in detail. In addition to interferometry, this book highlights techniques used for mapping the surfaces of stars using photometry made by space observatories; Zeeman- and Doppler Imaging; mapping the surface element abundances via spectroscopy. This book will also take stock of the best images of the  solar surface, made by connecting the differential rotation to the underlying physical parameters derived from helioseismology. Recent measureme...

Poor Results for High Achievers

Science.gov (United States)

Bui, Sa; Imberman, Scott; Craig, Steven

2012-01-01

Three million students in the United States are classified as gifted, yet little is known about the effectiveness of traditional gifted and talented (G&T) programs. In theory, G&T programs might help high-achieving students because they group them with other high achievers and typically offer specially trained teachers and a more advanced…

How star women build portable skills.

Science.gov (United States)

Groysberg, Boris

2008-02-01

In May 2004, with the war for talent in high gear, Groysberg and colleagues from Harvard Business School wrote in these pages about the risks of hiring star performers away from competitors. After studying the fortunes of more than 1,000 star stock analysts, they found that when a star switched companies, not only did his performance plunge, so did the effectiveness of the group he joined and the market value of his new company. But further analysis of the data reveals that it's not that simple. In fact, one group of analysts reliably maintained star rankings even after changing employers: women. Unlike their male counterparts, female stars who switched firms performed just as well, in the aggregate, as those who stayed put. The 189 star women in the sample (18% of the star analysts studied) achieved a higher rank after switching firms than the men did. Why the discrepancy? First, says the author, the best female analysts appear to have built their franchises on portable, external relationships with clients and the companies they covered, rather than on relationships rooted within their firms. By contrast, male analysts built up greater firm- and team-specific human capital by investing more in the internal networks and unique capabilities and resources of their own companies. Second, women took greater care when assessing a prospective new employer. In this article, Groysberg explores the reasons behind the star women's portable performance.

Descendants of the first stars: the distinct chemical signature of second generation stars

Science.gov (United States)

Hartwig, Tilman; Yoshida, Naoki; Magg, Mattis; Frebel, Anna; Glover, Simon C. O.; Gómez, Facundo A.; Griffen, Brendan; Ishigaki, Miho N.; Ji, Alexander P.; Klessen, Ralf S.; O'Shea, Brian W.; Tominaga, Nozomu

2018-05-01

Extremely metal-poor (EMP) stars in the Milky Way (MW) allow us to infer the properties of their progenitors by comparing their chemical composition to the metal yields of the first supernovae. This method is most powerful when applied to mono-enriched stars, i.e. stars that formed from gas that was enriched by only one previous supernova. We present a novel diagnostic to identify this subclass of EMP stars. We model the first generations of star formation semi-analytically, based on dark matter halo merger trees that yield MW-like halos at the present day. Radiative and chemical feedback are included self-consistently and we trace all elements up to zinc. Mono-enriched stars account for only ˜1% of second generation stars in our fiducial model and we provide an analytical formula for this probability. We also present a novel analytical diagnostic to identify mono-enriched stars, based on the metal yields of the first supernovae. This new diagnostic allows us to derive our main results independently from the specific assumptions made regarding Pop III star formation, and we apply it to a set of observed EMP stars to demonstrate its strengths and limitations. Our results may provide selection criteria for current and future surveys and therefore contribute to a deeper understanding of EMP stars and their progenitors.

Predictive modeling of treatment resistant depression using data from STAR*D and an independent clinical study.

Science.gov (United States)

Nie, Zhi; Vairavan, Srinivasan; Narayan, Vaibhav A; Ye, Jieping; Li, Qingqin S

2018-01-01

Identification of risk factors of treatment resistance may be useful to guide treatment selection, avoid inefficient trial-and-error, and improve major depressive disorder (MDD) care. We extended the work in predictive modeling of treatment resistant depression (TRD) via partition of the data from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) cohort into a training and a testing dataset. We also included data from a small yet completely independent cohort RIS-INT-93 as an external test dataset. We used features from enrollment and level 1 treatment (up to week 2 response only) of STAR*D to explore the feature space comprehensively and applied machine learning methods to model TRD outcome at level 2. For TRD defined using QIDS-C16 remission criteria, multiple machine learning models were internally cross-validated in the STAR*D training dataset and externally validated in both the STAR*D testing dataset and RIS-INT-93 independent dataset with an area under the receiver operating characteristic curve (AUC) of 0.70-0.78 and 0.72-0.77, respectively. The upper bound for the AUC achievable with the full set of features could be as high as 0.78 in the STAR*D testing dataset. Model developed using top 30 features identified using feature selection technique (k-means clustering followed by χ2 test) achieved an AUC of 0.77 in the STAR*D testing dataset. In addition, the model developed using overlapping features between STAR*D and RIS-INT-93, achieved an AUC of > 0.70 in both the STAR*D testing and RIS-INT-93 datasets. Among all the features explored in STAR*D and RIS-INT-93 datasets, the most important feature was early or initial treatment response or symptom severity at week 2. These results indicate that prediction of TRD prior to undergoing a second round of antidepressant treatment could be feasible even in the absence of biomarker data.

Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region

Science.gov (United States)

Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

2011-11-01

Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young ( ≲ several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young (~1-2 Myr) star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known OB stars, HD 319881 and [N78] 34. Follow-up spectroscopy of three other bow-shock-producing stars showed that they are massive (O-type) stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution (long before the second mechanism for production of runaway stars, based on a supernova explosion in a massive tight binary system, begins to operate) and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular

IR photometry results and dust envelope model for symbiotic Mira star candidate V 335 Vul

Science.gov (United States)

Bogdanov, M. B.; Taranova, O. G.; Shenavrin, V. I.

2017-10-01

We present the results of JHKLM-photometry for the symbiotic Mira star candidate V 335 Vul. Based on the average flux data, supplemented by IRAS, MSX, AKARI, and WISE mid-IR observations, we calculated a model of a spherically symmetric dust envelope of the star, made up of amorphous carbon and silicon carbide particles. The optical depth of the envelope in the visible range with a dust temperature at the inner boundary of T 1 = 1300 K is τ V = 0.58. For an envelope expansion velocity of 26.5 km s-1, the estimated mass loss rate is equal to 5.7 × 10-7 M ⊙ yr-1.

Improved autonomous star identification algorithm

International Nuclear Information System (INIS)

Luo Li-Yan; Xu Lu-Ping; Zhang Hua; Sun Jing-Rong

2015-01-01

The log–polar transform (LPT) is introduced into the star identification because of its rotation invariance. An improved autonomous star identification algorithm is proposed in this paper to avoid the circular shift of the feature vector and to reduce the time consumed in the star identification algorithm using LPT. In the proposed algorithm, the star pattern of the same navigation star remains unchanged when the stellar image is rotated, which makes it able to reduce the star identification time. The logarithmic values of the plane distances between the navigation and its neighbor stars are adopted to structure the feature vector of the navigation star, which enhances the robustness of star identification. In addition, some efforts are made to make it able to find the identification result with fewer comparisons, instead of searching the whole feature database. The simulation results demonstrate that the proposed algorithm can effectively accelerate the star identification. Moreover, the recognition rate and robustness by the proposed algorithm are better than those by the LPT algorithm and the modified grid algorithm. (paper)

A Panoramic View of Star Formation in Milky Way: Recent Results from Galactic Plane FIR/Sub-mm Surveys

Science.gov (United States)

Elia, Davide

2017-11-01

The star formation process involves a continuous gas flow from galactic (kpc) down to stellar (AU) scales. While targeted observations of single star forming sources are needed to understand the steps of this process with increasing detail, large unbiased Galactic plane surveys permit to reconstruct the map of star forming sites across the Milky Way, considered as an unique star formation engine. On the one hand, such surveys provide the community with a huge number of candidate targets for future follow-up observations with state-of-the-art telescope facilities, on the other hand they can provide reliable estimates of global parameters, such as Galactic star formation efficiency and rate, through which it is possible to establish comparisons with other galaxies. In this talk I will review the main results of recent FIR/sub-mm continuum emission Galactic surveys, with special attention to the Hi-GAL Herschel project, having the advantage (but also the complication) of being a multi-wavelength survey covering the spectral range in which the cold interstellar dust is expected to emit. The subsequent VIALACTEA project represents an articulate effort to combine Hi-GAL with other continuum and line surveys to refine the census of star forming clumps in the Galactic plane, and to use it to describe the Milky Way as a whole. Interpretation limitations imposed by the loss of detail with increasing distance are also discussed.

NuSTAR results and future plans for magnetar and rotation‐powered pulsar observations

DEFF Research Database (Denmark)

An, H.; Kaspi, V.M.; Archibald, R.

2014-01-01

The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing hard X‐ray mission in orbit and operates in the 3–79 keV range. NuSTAR's sensitivity is roughly two orders of magnitude better than previous missions in this energy band thanks to its superb angular resolution. Since its lau...

GW170817: a neutron star merger in a mass-transferring triple system

Science.gov (United States)

Chang, Philip; Murray, Norman

2018-02-01

The light curve of GW170817 is surprisingly blue and bright. Assuming that the event is a binary neutron star merger, we argue that blueness and brightness of the light curve is the result of ejecta that contains an substantial amount of thermal energy. To achieve this, the ejecta must be reheated at a substantial distance (1-2000 solar radii) from the merger to avoid losing the energy to adiabatic cooling. We show that this reheating can occur if the merger occurs in a hierarchical triple system where the outer star has evolved and filled its Roche lobe. The outer star feeds mass to the inner binary, forming a circumbinary disc, driving the inner binary to merge. Because the outer star fills its Roche lobe, a substantial fraction of the dynamical ejecta collides with the evolved star, reheating the ejecta in the process. We suggest that the process of mass transfer in hierarchical triples tends to form coplanar triple systems such as PSR J0337+1715, and may provide electromagnetic counterparts to binary black hole mergers.

PHOTOMETRY OF VARIABLE STARS FROM DOME A, ANTARCTICA: RESULTS FROM THE 2010 OBSERVING SEASON

Energy Technology Data Exchange (ETDEWEB)

Wang, Lingzhi; Zhu, Zonghong [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Macri, Lucas M.; Wang, Lifan [Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); Ashley, Michael C. B.; Lawrence, Jon S.; Luong-Van, Daniel; Storey, John W. V. [School of Physics, University of New South Wales, NSW 2052 (Australia); Cui, Xiangqun; Feng, Long-Long; Gong, Xuefei; Liu, Qiang; Shang, Zhaohui; Yang, Huigen; Yang, Ji; Yuan, Xiangyan; Zhou, Xu; Zhu, Zhenxi [Chinese Center for Antarctic Astronomy, Nanjing 210008 (China); Pennypacker, Carl R. [Center for Astrophysics, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); York, Donald G., E-mail: wanglingzhi@bao.ac.cn [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637 (United States)

2013-12-01

We present results from a season of observations with the Chinese Small Telescope ARray, obtained over 183 days of the 2010 Antarctic winter. We carried out high-cadence time-series aperture photometry of 9125 stars with i ∼< 15.3 mag located in a 23 deg{sup 2} region centered on the south celestial pole. We identified 188 variable stars, including 67 new objects relative to our 2008 observations, thanks to broader synoptic coverage, a deeper magnitude limit, and a larger field of view. We used the photometric data set to derive site statistics from Dome A. Based on two years of observations, we find that extinction due to clouds at this site is less than 0.1 and 0.4 mag during 45% and 75% of the dark time, respectively.

Star Cluster Structure from Hierarchical Star Formation

Science.gov (United States)

Grudic, Michael; Hopkins, Philip; Murray, Norman; Lamberts, Astrid; Guszejnov, David; Schmitz, Denise; Boylan-Kolchin, Michael

2018-01-01

Young massive star clusters (YMCs) spanning 104-108 M⊙ in mass generally have similar radial surface density profiles, with an outer power-law index typically between -2 and -3. This similarity suggests that they are shaped by scale-free physics at formation. Recent multi-physics MHD simulations of YMC formation have also produced populations of YMCs with this type of surface density profile, allowing us to narrow down the physics necessary to form a YMC with properties as observed. We show that the shallow density profiles of YMCs are a natural result of phase-space mixing that occurs as they assemble from the clumpy, hierarchically-clustered configuration imprinted by the star formation process. We develop physical intuition for this process via analytic arguments and collisionless N-body experiments, elucidating the connection between star formation physics and star cluster structure. This has implications for the early-time structure and evolution of proto-globular clusters, and prospects for simulating their formation in the FIRE cosmological zoom-in simulations.

New ultra metal-poor stars from SDSS: follow-up GTC medium-resolution spectroscopy

Science.gov (United States)

Aguado, D. S.; Allende Prieto, C.; González Hernández, J. I.; Rebolo, R.; Caffau, E.

2017-07-01

Context. The first generation of stars formed in the Galaxy left behind the chemical signatures of their nucleosynthesis in the interstellar medium, visible today in the atmospheres of low-mass stars that formed afterwards. Sampling the chemistry of those low-mass provides insight into the first stars. Aims: We aim to increase the samples of stars with extremely low metal abundances, identifying ultra metal-poor stars from spectra with modest spectral resolution and signal-to-noise ratio (S/N). Achieving this goal involves deriving reliable metallicities and carbon abundances from such spectra. Methods: We carry out follow-up observations of faint, V > 19, metal-poor candidates selected from SDSS spectroscopy and observed with the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at GTC. The SDSS and follow-up OSIRIS spectra were analyzed using the FERRE code to derive effective temperatures, surface gravities, metallicities and carbon abundances. In addition, a well-known extremely metal-poor star has been included in our sample to calibrate the analysis methodology. Results: We observed and analyzed five metal-poor candidates from modest-quality SDSS spectra. All stars in our sample have been confirmed as extremely metal-poor stars, in the [Fe/H] Palma. Programme ID GTC2E-16A and ID GTC65-16B.

The Vixen Star Book user guide how to use the star book ten and the original star book

CERN Document Server

Chen, James

2016-01-01

This book is for anyone who owns, or is thinking of owning, a Vixen Star Book Ten telescope mount or its predecessor. A revolution in amateur astronomy has occurred in the past decade with the wide availability of high tech, computer-driven, Go-To telescopes. Vixen Optics is leading the way by offering the Star Book Ten system, with its unique star map graphics software. The Star Book Ten is the latest version of computer telescope control using star map graphics as a user interface, first introduced in the original Star Book first offered in 2003. The increasingly complicated nature of this software means that learning to optimize this program is not straightforward, and yet the resulting views when all features are correctly deployed can be phenomenal. After a short history of computerized Go-To telescopes for the consumer amateur astronomer market, Chen offers a treasury of technical information. His advice, tips, and solutions aid the user in getting the most out of the Star Book Ten system in observing s...

By Draconis Stars

Science.gov (United States)

Bopp, Bernard W.

An optical spectroscopic survey of dK-M stars has resulted in the discovery of several new H-alpha emission objects. Available optical data suggest these stars have a level of chromospheric activity midway between active BY Dra stars and quiet dM's. These "marginal" BY Dra stars are single objects that have rotation velocities slightly higher than that of quiet field stars but below that of active flare/BY Dra objects. The marginal BY Dra stars provide us with a class of objects rotating very near a "trigger velocity" (believed to be 5 km/s) which appears to divide active flare/BY Dra stars from quiet dM's. UV data on Mg II emission fluxes and strength of transition region features such as C IV will serve to fix activity levels in the marginal objects and determine chromosphere and transition-region heating rates. Simultaneous optical magnetic field measures will be used to explore the connection between fieldstrength/filling-factor and atmospheric heating. Comparison of these data with published information on active and quiet dM stars will yield information on the character of the stellar dynamo as it makes a transition from "low" to "high" activity.

Neutron stars

International Nuclear Information System (INIS)

Irvine, J.M.

1978-01-01

The subject is covered in chapters entitled: introduction (resume of stellar evolution, gross characteristics of neutron stars); pulsars (pulsar characteristics, pulsars as neutron stars); neutron star temperatures (neutron star cooling, superfluidity and superconductivity in neutron stars); the exterior of neutron stars (the magnetosphere, the neutron star 'atmosphere', pulses); neutron star structure; neutron star equations of state. (U.K.)

Star formation

International Nuclear Information System (INIS)

Woodward, P.R.

1978-01-01

Theoretical models of star formation are discussed beginning with the earliest stages and ending in the formation of rotating, self-gravitating disks or rings. First a model of the implosion of very diffuse gas clouds is presented which relies upon a shock at the edge of a galactic spiral arm to drive the implosion. Second, models are presented for the formation of a second generation of massive stars in such a cloud once a first generation has formed. These models rely on the ionizing radiation from massive stars or on the supernova shocks produced when these stars explode. Finally, calculations of the gravitational collapse of rotating clouds are discussed with special focus on the question of whether rotating disks or rings are the result of such a collapse. 65 references

Fundamental problems and basic tests of stellar evolution theory - the case of carbon stars

International Nuclear Information System (INIS)

Iben, I. Jr.

1984-01-01

Carbon stars are thought to be in the asymptotic giant branch (AGB) phase of evolution, alternately burning hydrogen and helim in shells above an electron-degenerate carbon-oxygen (CO) core. In model stars of large CO core mass, the source of neutrons for producing the neutron-rich isotopes is the 22 Ne(α,n) 25 Mg reaction and the isotopes are produced in the solar system s-process distribution. In models of small core mass, the 13 C(α,n) 16 O reaction is thought to be responsible for the release of neutrons, and the resultant distribution of neutron-rich isotopes is expected to vary considerably from one star to the next, with the distribution in isolated instances possibly resembling the solar system distribution of r-process isotopes. There is qualitative accord between the properties of carbon stars in the Magellanic Clouds and properties of model stars, but considerably more theoretical work is required before a quantitative match is achieved. (Auth.)

Mechanism of mRNA-STAR domain interaction: Molecular dynamics simulations of Mammalian Quaking STAR protein.

Science.gov (United States)

Sharma, Monika; Anirudh, C R

2017-10-03

STAR proteins are evolutionary conserved mRNA-binding proteins that post-transcriptionally regulate gene expression at all stages of RNA metabolism. These proteins possess conserved STAR domain that recognizes identical RNA regulatory elements as YUAAY. Recently reported crystal structures show that STAR domain is composed of N-terminal QUA1, K-homology domain (KH) and C-terminal QUA2, and mRNA binding is mediated by KH-QUA2 domain. Here, we present simulation studies done to investigate binding of mRNA to STAR protein, mammalian Quaking protein (QKI). We carried out conventional MD simulations of STAR domain in presence and absence of mRNA, and studied the impact of mRNA on the stability, dynamics and underlying allosteric mechanism of STAR domain. Our unbiased simulations results show that presence of mRNA stabilizes the overall STAR domain by reducing the structural deviations, correlating the 'within-domain' motions, and maintaining the native contacts information. Absence of mRNA not only influenced the essential modes of motion of STAR domain, but also affected the connectivity of networks within STAR domain. We further explored the dissociation of mRNA from STAR domain using umbrella sampling simulations, and the results suggest that mRNA binding to STAR domain occurs in multi-step: first conformational selection of mRNA backbone conformations, followed by induced fit mechanism as nucleobases interact with STAR domain.

Massive stars in galaxies

International Nuclear Information System (INIS)

Humphreys, R.M.

1987-01-01

The relationship between the morphologic type of a galaxy and the evolution of its massive stars is explored, reviewing observational results for nearby galaxies. The data are presented in diagrams, and it is found that the massive-star populations of most Sc spiral galaxies and irregular galaxies are similar, while those of Sb spirals such as M 31 and M 81 may be affected by morphology (via differences in the initial mass function or star-formation rate). Consideration is also given to the stability-related upper luminosity limit in the H-R diagram of hypergiant stars (attributed to radiation pressure in hot stars and turbulence in cool stars) and the goals of future observation campaigns. 88 references

Motion-blurred star acquisition method of the star tracker under high dynamic conditions.

Science.gov (United States)

Sun, Ting; Xing, Fei; You, Zheng; Wei, Minsong

2013-08-26

The star tracker is one of the most promising attitude measurement devices used in spacecraft due to its extremely high accuracy. However, high dynamic performance is still one of its constraints. Smearing appears, making it more difficult to distinguish the energy dispersive star point from the noise. An effective star acquisition approach for motion-blurred star image is proposed in this work. The correlation filter and mathematical morphology algorithm is combined to enhance the signal energy and evaluate slowly varying background noise. The star point can be separated from most types of noise in this manner, making extraction and recognition easier. Partial image differentiation is then utilized to obtain the motion parameters from only one image of the star tracker based on the above process. Considering the motion model, the reference window is adopted to perform centroid determination. Star acquisition results of real on-orbit star images and laboratory validation experiments demonstrate that the method described in this work is effective and the dynamic performance of the star tracker could be improved along with more identified stars and guaranteed position accuracy of the star point.

Search for OB stars running away from young star clusters. I. NGC 6611

Science.gov (United States)

Gvaramadze, V. V.; Bomans, D. J.

2008-11-01

N-body simulations have shown that the dynamical decay of the young (~1 Myr) Orion Nebula cluster could be responsible for the loss of at least half of its initial content of OB stars. This result suggests that other young stellar systems could also lose a significant fraction of their massive stars at the very beginning of their evolution. To confirm this expectation, we used the Mid-Infrared Galactic Plane Survey (completed by the Midcourse Space Experiment satellite) to search for bow shocks around a number of young (⪉several Myr) clusters and OB associations. We discovered dozens of bow shocks generated by OB stars running away from these stellar systems, supporting the idea of significant dynamical loss of OB stars. In this paper, we report the discovery of three bow shocks produced by O-type stars ejected from the open cluster NGC 6611 (M16). One of the bow shocks is associated with the O9.5Iab star HD165319, which was suggested to be one of “the best examples for isolated Galactic high-mass star formation” (de Wit et al. 2005, A&A, 437, 247). Possible implications of our results for the origin of field OB stars are discussed.

Stability of boson stars

International Nuclear Information System (INIS)

Gleiser, M.

1988-01-01

Boson stars are gravitationally bound, spherically symmetric equilibrium configurations of cold, free, or interacting complex scalar fields phi. As these equilibrium configurations naturally present local anisotropy, it is sensible to expect departures from the well-known stability criteria for fluid stars. With this in mind, I investigate the dynamical instability of boson stars against charge-conserving, small radial perturbations. Following the method developed by Chandrasekhar, a variational base for determining the eigenfrequencies of the perturbations is found. This approach allows one to find numerically an upper bound for the central density where dynamical instability occurs. As applications of the formalism, I study the stability of equilibrium configurations obtained both for the free and for the self-interacting [with V(phi) = (λ/4)chemical bondphichemical bond 4 ] massive scalar field phi. Instabilities are found to occur not for the critical central density as in fluid stars but for central densities considerably higher. The departure from the results for fluid stars is sensitive to the coupling λ; the higher the value of λ, the more the stability properties of boson stars approach those of a fluid star. These results are linked to the fractional anisotropy at the radius of the configuration

Matter and Radiation in Strong Magnetic Fields of Neutron Stars

International Nuclear Information System (INIS)

Lai, D

2006-01-01

Neutron stars are found to possess magnetic fields ranging from 10 8 G to 10 15 G, much larger than achievable in terrestrial laboratories. Understanding the properties of matter and radiative transfer in strong magnetic fields is essential for the proper interpretation of various observations of magnetic neutron stars, including radio pulsars and magnetars. This paper reviews the atomic/molecular physics and condensed matter physics in strong magnetic fields, as well as recent works on modeling radiation from magnetized neutron star atmospheres/surface layers

First Kepler results on compact pulsators - V. Slowly pulsating subdwarf B stars in short-period binaries

DEFF Research Database (Denmark)

Kawaler, Stephen D.; Reed, Michael D.; Østensen, Roy H.

2010-01-01

of sdB stars with a close M-dwarf companion with orbital periods of less than half a day. Because the orbital period is so short, the stars should be in synchronous rotation, and if so, the rotation period should imprint itself on the multiplet structure of the pulsations. However, we do not find clear......The survey phase of the Kepler Mission includes a number of hot subdwarf B (sdB) stars to search for non-radial pulsations. We present our analysis of two sdB stars that are found to be g-mode pulsators of the V1093 Her class. These two stars also display the distinct irradiation effect typical...... evidence for such rotational splitting. Though the stars do show some frequency spacings that are consistent with synchronous rotation, they also display multiplets with splittings that are much smaller. Longer-duration time series photometry will be needed to determine if those small splittings...

Dark stars: a new study of the first stars in the Universe

International Nuclear Information System (INIS)

Freese, Katherine; Bodenheimer, Peter; Gondolo, Paolo; Spolyar, Douglas

2009-01-01

We have proposed that the first phase of stellar evolution in the history of the Universe may be dark stars (DSs), powered by dark matter (DM) heating rather than by nuclear fusion. Weakly interacting massive particles, which may be their own antipartners, collect inside the first stars and annihilate to produce a heat source that can power the stars. A new stellar phase results, a DS, powered by DM annihilation as long as there is DM fuel, with lifetimes from millions to billions of years. We find that the first stars are very bright (∼10 6 L o-dot ) and cool (T surf surf > 50 000 K); hence DS should be observationally distinct from standard Pop III stars. Once the DM fuel is exhausted, the DS becomes a heavy main sequence star; these stars eventually collapse to form massive black holes that may provide seeds for supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate black holes.

Achieving OSHA VPP ``STAR'' status and its benefits

Energy Technology Data Exchange (ETDEWEB)

Lehr, J; Sammons, J; Bayer, R

1998-07-01

The Occupational Safety and Health Administration (OSHA) created the Voluntary Protection Program (hereafter referred to as VPP) to recognize industrial institutions that demonstrate exemplary safety and health programs, which exceed the minimum requirements, set forth by the Code of Federal Regulations. The Montenay International Corporation, parent company of Montenay Energy Resources of Montgomery County, Inc. (hereafter referred to as MERMCI) committed resources, manpower and funding to prepare the site for OSHA VPP acceptance. MERMCI first scrutinized all aspects of their safety and health program; comparing existing practices to OSHA guidelines for total safety compliance. Having met preliminary guidelines, dedicated personnel prepared the application, which took about one (1) year. The application was submitted to OSHA in Washington, D.C. and Philadelphia region III office for preliminary approval. The regional VPP administrator visited the site to verify qualifications governing the basis for program admittance. Injury and illness rates, industry average comparisons and initial record keeping practices were examined. A tentative date was set to perform an in-depth inspection of the facility, interview the majority of the employees and make a determination for program approval. The OSHA inspectors thoroughly inspected the facility and made a recommendation for MERMCI to participate in the Voluntary Protection Program at the STAR level.

Covering tree with stars

DEFF Research Database (Denmark)

Baumbach, Jan; Guo, Jian-Ying; Ibragimov, Rashid

2013-01-01

We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting ...

The Destructive Birth of Massive Stars and Massive Star Clusters

Science.gov (United States)

Rosen, Anna; Krumholz, Mark; McKee, Christopher F.; Klein, Richard I.; Ramirez-Ruiz, Enrico

2017-01-01

amplified. Our results suggest that the combined effect of turbulence, magnetic pressure, and radiative feedback from massive stars is responsible for the low star formation efficiencies observed in molecular clouds.

Identifying the Academic Rising Stars via Pairwise Citation Increment Ranking

KAUST Repository

Zhang, Chuxu

2017-08-02

Predicting the fast-rising young researchers (the Academic Rising Stars) in the future provides useful guidance to the research community, e.g., offering competitive candidates to university for young faculty hiring as they are expected to have success academic careers. In this work, given a set of young researchers who have published the first first-author paper recently, we solve the problem of how to effectively predict the top k% researchers who achieve the highest citation increment in Δt years. We explore a series of factors that can drive an author to be fast-rising and design a novel pairwise citation increment ranking (PCIR) method that leverages those factors to predict the academic rising stars. Experimental results on the large ArnetMiner dataset with over 1.7 million authors demonstrate the effectiveness of PCIR. Specifically, it outperforms all given benchmark methods, with over 8% average improvement. Further analysis demonstrates that temporal features are the best indicators for rising stars prediction, while venue features are less relevant.

Neutron star natal kicks and the long-term survival of star clusters

Science.gov (United States)

Contenta, Filippo; Varri, Anna Lisa; Heggie, Douglas C.

2015-04-01

We investigate the dynamical evolution of a star cluster in an external tidal field by using N-body simulations, with focus on the effects of the presence or absence of neutron star natal velocity kicks. We show that, even if neutron stars typically represent less than 2 per cent of the total bound mass of a star cluster, their primordial kinematic properties may affect the lifetime of the system by up to almost a factor of 4. We interpret this result in the light of two known modes of star cluster dissolution, dominated by either early stellar evolution mass-loss or two-body relaxation. The competition between these effects shapes the mass-loss profile of star clusters, which may either dissolve abruptly (`jumping'), in the pre-core-collapse phase, or gradually (`skiing'), after having reached core collapse.

Stars Just Got Bigger - A 300 Solar Mass Star Uncovered

Science.gov (United States)

2010-07-01

they age," says Paul Crowther. "Being a little over a million years old, the most extreme star R136a1 is already 'middle-aged' and has undergone an intense weight loss programme, shedding a fifth of its initial mass over that time, or more than fifty solar masses." If R136a1 replaced the Sun in our Solar System, it would outshine the Sun by as much as the Sun currently outshines the full Moon. "Its high mass would reduce the length of the Earth's year to three weeks, and it would bathe the Earth in incredibly intense ultraviolet radiation, rendering life on our planet impossible," says Raphael Hirschi from Keele University, who belongs to the team. These super heavyweight stars are extremely rare, forming solely within the densest star clusters. Distinguishing the individual stars - which has now been achieved for the first time - requires the exquisite resolving power of the VLT's infrared instruments [2]. The team also estimated the maximum possible mass for the stars within these clusters and the relative number of the most massive ones. "The smallest stars are limited to more than about eighty times more than Jupiter, below which they are 'failed stars' or brown dwarfs," says team member Olivier Schnurr from the Astrophysikalisches Institut Potsdam. "Our new finding supports the previous view that there is also an upper limit to how big stars can get, although it raises the limit by a factor of two, to about 300 solar masses." Within R136, only four stars weighed more than 150 solar masses at birth, yet they account for nearly half of the wind and radiation power of the entire cluster, comprising approximately 100 000 stars in total. R136a1 alone energises its surroundings by more than a factor of fifty compared to the Orion Nebula cluster, the closest region of massive star formation to Earth. Understanding how high mass stars form is puzzling enough, due to their very short lives and powerful winds, so that the identification of such extreme cases as R136a1

Neutron Star Science with the NuSTAR

Energy Technology Data Exchange (ETDEWEB)

Vogel, J. K. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2015-10-16

The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, helped scientists obtain for the first time a sensitive high-­energy X-­ray map of the sky with extraordinary resolution. This pioneering telescope has aided in the understanding of how stars explode and neutron stars are born. LLNL is a founding member of the NuSTAR project, with key personnel on its optics and science team. We used NuSTAR to observe and analyze the observations of different neutron star classes identified in the last decade that are still poorly understood. These studies not only help to comprehend newly discovered astrophysical phenomena and emission processes for members of the neutron star family, but also expand the utility of such observations for addressing broader questions in astrophysics and other physics disciplines. For example, neutron stars provide an excellent laboratory to study exotic and extreme phenomena, such as the equation of state of the densest matter known, the behavior of matter in extreme magnetic fields, and the effects of general relativity. At the same time, knowing their accurate populations has profound implications for understanding the life cycle of massive stars, star collapse, and overall galactic evolution.

Numerical study of rotating relativistic stars

International Nuclear Information System (INIS)

Wilson, J.R.

1975-01-01

The equations of structure for rotating stars in general relativity are presented and put in a form suitable for computer calculations. The results of equilibrium calculations for supermassive stars, neutron stars, and magnetically supported stars are reported, as are calculations of collapsing, rotating, and magnetized stars in the slowly changing gravitational field approximation. (auth)

CMOS Active Pixel Sensor Star Tracker with Regional Electronic Shutter

Science.gov (United States)

Yadid-Pecht, Orly; Pain, Bedabrata; Staller, Craig; Clark, Christopher; Fossum, Eric

1996-01-01

The guidance system in a spacecraft determines spacecraft attitude by matching an observed star field to a star catalog....An APS(active pixel sensor)-based system can reduce mass and power consumption and radiation effects compared to a CCD(charge-coupled device)-based system...This paper reports an APS (active pixel sensor) with locally variable times, achieved through individual pixel reset (IPR).

Does early career achievement lead to earlier death? Assessment of the precocity-longevity effect in professional basketball players

Directory of Open Access Journals (Sweden)

Nick Wattie

2016-11-01

Full Text Available Objectives: To examine the precocity-longevity (P-L effect in North American professional basketball players who debuted between 1946 and 1979, and to determine whether playing position and decade of play influenced the relationship between age of career achievements and lifespan. Methods: 1852 players were evaluated from a recognized sports archive (i.e., sports-reference.com, which provided information on date of birth, death, and career debut, playing position, and indicators of achievement (i.e., All-Star team and/or All-League team selection. Athletes were categorized as above or below the median age of professional debut, and median age of selection to first All-Star team and/or All-League team. Analyses of deceased players (n = 598 were comprised of bivariate correlations between age of achievement (age of debut, age of first All-Star game and age of first All-League team selection and age of death, and t-tests to compared the average age of death of early and late achievers (p < .05. Survival analyses, using the entire sample (living and deceased players, compared the lifespans between those who debuted above and below the median age of achievement for each indicator of achievement. Results: Only the correlation between age of professional debut and age of death (r = .33, p < .001 and age of first all-star game and age of death (r = .29, p < .05 and the t-test comparing the average death age of early (66.4 y and later (69.3 y debut age groups (p =.01, reached statistical significance. However, survival analyses demonstrated a trend for lower risk of death for early achievers, with one exception (i.e., age of debut this trend was not statistically significant. Conclusions: Results did not support the P-L hypothesis, suggesting that sample characteristics (i.e., physical fitness of high performance athletes, and measurement methodologies, may influence support for the proposed hypothesis in sport. However, future research would benefit

Methods to Directly Image Exoplanets around Alpha Centauri and Other Multi-Star Systems

Science.gov (United States)

Belikov, R.; Sirbu, D.; Bendek, E.; Pluzhnik, E.

2017-12-01

The majority of FGK stars exist as multi-star star systems, and thus form a potentially rich target sample for direct imaging of exoplanets. A large fraction of these stars have starlight leakage from their companion that is brighter than rocky planets. This is in particular true of Alpha Centauri, which is 2.4x closer and about an order of magnitude brighter than any other FGK star, and thus may be the best target for any direct imaging mission, if the light of both stars can be suppressed. Thus, the ability to suppress starlight from two stars improves both the quantity and quality of Sun-like targets for missions such as WFIRST, LUVOIR, and HabEx. We present an analysis of starlight leak challenges in multi-star systems and techniques to solve those challenges, with an emphasis on imaging Alpha Centauri with WFIRST. For the case of internal coronagraphs, the fundamental problem appears to be independent wavefront control of multiple stars (at least if the companion is close enough or bright enough that it cannot simply be removed by longer exposure times or post-processing). We present a technique called Multi-Star Wavefront Control (MSWC) as a solution to this challenge and describe the results of our technology development program that advanced MSWC to TRL 3. Our program consisted of lab demonstrations of dark zones in two-star systems, validated simulations, as well as simulated predictions demonstrating that with this technology, contrasts needed for Earth-like planets are in principle achievable. We also demonstrate MSWC in Super-Nyquist mode, which allows suppression of multiple stars at separations greater than the spatial Nyquist limit of the deformable mirror.

O stars and Wolf-Rayet stars

International Nuclear Information System (INIS)

Conti, P.S.; Underhill, A.B.; Jordan, S.; Thomas, R.

1988-01-01

Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented

O stars and Wolf-Rayet stars

Science.gov (United States)

Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (Editor); Thomas, Richard (Editor)

1988-01-01

Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

Results of a Long-Term Spectral and Photometric Monitoring of the Herbig Ae Star HD 179218

Science.gov (United States)

Kozlova, O. V.; Alekseev, I. Yu.

2017-06-01

We present the results of the long-term spectroscopic and photometric monitoring of the Herbig Ae star HD 179218. The high-resolution spectra (R = 20000) were made on the 2.6-m telescope at the Crimean Astrophysical Observatory (CrAO) in the regions of Hα emission line. The photometric observations were obtained on 1.25-m telescope AZT-11 (CrAO) equipped with the UBVRI electrophotometer-polarimeter. Our results showed that Hα emission parameters demonstrate the long- term variability on the time scale about 4000 days. The same variability is observed in the change of the stellar brightness in V-band. The unusual behavior the V-I color index depending on the stellar brightness in the V-band can be concluded that around the star there is an additional source of IR-radiation. We believe that the obtained results can be explained by the presence in the vicinity of HD 179218 a low-mass component.

Star-Branched Polymers (Star Polymers)

KAUST Repository

Hirao, Akira

2015-09-01

The synthesis of well-defined regular and asymmetric mixed arm (hereinafter miktoarm) star-branched polymers by the living anionic polymerization is reviewed in this chapter. In particular, much attention is being devoted to the synthetic development of miktoarm star polymers since 2000. At the present time, the almost all types of multiarmed and multicomponent miktoarm star polymers have become feasible by using recently developed iterative strategy. For example, the following well-defined stars have been successfully synthesized: 3-arm ABC, 4-arm ABCD, 5-arm ABCDE, 6-arm ABCDEF, 7-arm ABCDEFG, 6-arm ABC, 9-arm ABC, 12-arm ABC, 13-arm ABCD, 9-arm AB, 17-arm AB, 33-arm AB, 7-arm ABC, 15-arm ABCD, and 31-arm ABCDE miktoarm star polymers, most of which are quite new and difficult to synthesize by the end of the 1990s. Several new specialty functional star polymers composed of vinyl polymer segments and rigid rodlike poly(acetylene) arms, helical polypeptide, or helical poly(hexyl isocyanate) arms are introduced.

Formation of stars and star clusters in colliding galaxies

International Nuclear Information System (INIS)

Belles, Pierre-Emmanuel

2012-01-01

Mergers are known to be essential in the formation of large-scale structures and to have a significant role in the history of galaxy formation and evolution. Besides a morphological transformation, mergers induce important bursts of star formation. These starburst are characterised by high Star Formation Efficiencies (SFEs) and Specific Star Formation Rates, i.e., high Star Formation Rates (SFR) per unit of gas mass and high SFR per unit of stellar mass, respectively, compared to spiral galaxies. At all redshifts, starburst galaxies are outliers of the sequence of star-forming galaxies defined by spiral galaxies. We have investigated the origin of the starburst-mode of star formation, in three local interacting systems: Arp 245, Arp 105 and NGC 7252. We combined high-resolution JVLA observations of the 21-cm line, tracing the HI diffuse gas, with UV GALEX observations, tracing the young star-forming regions. We probe the local physical conditions of the Inter-Stellar Medium (ISM) for independent star-forming regions and explore the atomic-to-dense gas transformation in different environments. The SFR/HI ratio is found to be much higher in central regions, compared to outer regions, showing a higher dense gas fraction (or lower HI gas fraction) in these regions. In the outer regions of the systems, i.e., the tidal tails, where the gas phase is mostly atomic, we find SFR/HI ratios higher than in standard HI-dominated environments, i.e., outer discs of spiral galaxies and dwarf galaxies. Thus, our analysis reveals that the outer regions of mergers are characterised by high SFEs, compared to the standard mode of star formation. The observation of high dense gas fractions in interacting systems is consistent with the predictions of numerical simulations; it results from the increase of the gas turbulence during a merger. The merger is likely to affect the star-forming properties of the system at all spatial scales, from large scales, with a globally enhanced turbulence

Spectrophotometry of Symbiotic Stars (Abstract)

Science.gov (United States)

Boyd, D.

2017-12-01

(Abstract only) Symbiotic stars are fascinating objects - complex binary systems comprising a cool red giant star and a small hot object, often a white dwarf, both embedded in a nebula formed by a wind from the giant star. UV radiation from the hot star ionizes the nebula, producing a range of emission lines. These objects have composite spectra with contributions from both stars plus the nebula and these spectra can change on many timescales. Being moderately bright, they lend themselves well to amateur spectroscopy. This paper describes the symbiotic star phenomenon, shows how spectrophotometry can be used to extract astrophysically useful information about the nature of these systems, and gives results for three symbiotic stars based on the author's observations.

Statistical investigation of flare stars. III. Flare stars in the general galactic star field

International Nuclear Information System (INIS)

Mirzoyan, L.V.; Ambaryan, V.V.; Garibdzhanyan, A.T.; Mirzoyan, A.L.

1989-01-01

Some questions relating to the existence of a large number of flare stars in the general star field of the Galaxy are discussed. It is shown that only a small proportion of them can be found by photographic observations, and the fraction of field flare stars among such stars found in the regions of star clusters and associations does not exceed 10%. The ratio of the numbers of flare stars of the foreground and the background for a particular system depends on its distance, reaching zero at a distance of about 500 pc. The spatial density of flare stars in the Pleiades is at least two orders of magnitude greater than in the general galactic field. A lower limit for the number of flare stars in the Galaxy is estimated at 4.2 ·10 9 , and the number of nonflare red dwarfs at 2.1·10 10 . There are grounds for believing that they were all formed in star clusters and associations

Symbiotic stars

International Nuclear Information System (INIS)

Boyarchuk, A.A.

1975-01-01

There are some arguments that the symbiotic stars are binary, where one component is a red giant and the other component is a small hot star which is exciting a nebula. The symbiotic stars belong to the old disc population. Probably, symbiotic stars are just such an evolutionary stage for double stars as planetary nebulae for single stars. (Auth.)

Quark core stars, quark stars and strange stars

International Nuclear Information System (INIS)

Grassi, F.

1988-01-01

A recent one flavor quark matter equation of state is generalized to several flavors. It is shown that quarks undergo a first order phase transition. In addition, this equation of state depends on just one parameter in the two flavor case, two parameters in the three flavor case, and these parameters are constrained by phenomenology. This equation of state is then applied to the hadron-quark transition in neutron stars and the determination of quark star stability, the investigation of strange matter stability and possible strange star existence. 43 refs., 6 figs

Kinematic and spatial distributions of barium stars - are the barium stars and Am stars related?

International Nuclear Information System (INIS)

Hakkila, J.

1989-01-01

The possibility of an evolutionary link between Am stars and barium stars is considered, and an examination of previous data suggests that barium star precursors are main-sequence stars of intermediate mass, are most likely A and/or F dwarfs, and are intermediate-mass binaries with close to intermediate orbital separations. The possible role of mass transfer in the later development of Am systems is explored. Mass transfer and loss from systems with a range of masses and orbital separations may explain such statistical peculiarities of barium stars as the large dispersion in absolute magnitude, the large range of elemental abundances from star to star, and the small number of stars with large peculiar velocities. 93 refs

Mass and age of red giant branch stars observed with LAMOST and Kepler

Science.gov (United States)

Wu, Yaqian; Xiang, Maosheng; Bi, Shaolan; Liu, Xiaowei; Yu, Jie; Hon, Marc; Sharma, Sanjib; Li, Tanda; Huang, Yang; Liu, Kang; Zhang, Xianfei; Li, Yaguang; Ge, Zhishuai; Tian, Zhijia; Zhang, Jinghua; Zhang, Jianwei

2018-04-01

Obtaining accurate and precise masses and ages for large numbers of giant stars is of great importance for unraveling the assemblage history of the Galaxy. In this paper, we estimate masses and ages of 6940 red giant branch (RGB) stars with asteroseismic parameters deduced from Kepler photometry and stellar atmospheric parameters derived from LAMOST spectra. The typical uncertainties of mass is a few per cent, and that of age is ˜20 per cent. The sample stars reveal two separate sequences in the age-[α/Fe] relation - a high-α sequence with stars older than ˜8 Gyr and a low-α sequence composed of stars with ages ranging from younger than 1 Gyr to older than 11 Gyr. We further investigate the feasibility of deducing ages and masses directly from LAMOST spectra with a machine learning method based on kernel based principal component analysis, taking a sub-sample of these RGB stars as a training data set. We demonstrate that ages thus derived achieve an accuracy of ˜24 per cent. We also explored the feasibility of estimating ages and masses based on the spectroscopically measured carbon and nitrogen abundances. The results are quite satisfactory and significantly improved compared to the previous studies.

Spectrophotometry of carbon stars

Energy Technology Data Exchange (ETDEWEB)

Oganesyan, R.K.; Karapetyan, M.S.; Nersisyan, S.E.

1986-01-01

The results are given of the spectrophotometric investigation of 56 carbon stars in the spectral range from 4000 to 6800 A with resolution 3 A. The observed energy distributions of these stars are determined relative to the flux at the wavelength /sub 0/ = 5556; they are presented in the form of graphs. The energy distributions have been obtained for the first time for 35 stars. Variation in the line Ba II 4554 A has been found in the spectra of St Cam, UU Aur, and RV Mon. Large changes have taken place in the spectra of RT UMa and SS Vir. It is noted that the spectra of carbon stars have a depression, this being situated in different spectral regions for individual groups of stars.

3-D reconstructions of active stars

DEFF Research Database (Denmark)

Korhonen, Heidi Helena

2012-01-01

Stars are usually faint point sources and investigating their surfaces and interiors observationally is very demanding. Here I give a review on the state-of-the-art observing techniques and recent results on studying interiors and surface features of active stars.......Stars are usually faint point sources and investigating their surfaces and interiors observationally is very demanding. Here I give a review on the state-of-the-art observing techniques and recent results on studying interiors and surface features of active stars....

DECISION TREE CLASSIFIERS FOR STAR/GALAXY SEPARATION

International Nuclear Information System (INIS)

Vasconcellos, E. C.; Ruiz, R. S. R.; De Carvalho, R. R.; Capelato, H. V.; Gal, R. R.; LaBarbera, F. L.; Frago Campos Velho, H.; Trevisan, M.

2011-01-01

We study the star/galaxy classification efficiency of 13 different decision tree algorithms applied to photometric objects in the Sloan Digital Sky Survey Data Release Seven (SDSS-DR7). Each algorithm is defined by a set of parameters which, when varied, produce different final classification trees. We extensively explore the parameter space of each algorithm, using the set of 884,126 SDSS objects with spectroscopic data as the training set. The efficiency of star-galaxy separation is measured using the completeness function. We find that the Functional Tree algorithm (FT) yields the best results as measured by the mean completeness in two magnitude intervals: 14 ≤ r ≤ 21 (85.2%) and r ≥ 19 (82.1%). We compare the performance of the tree generated with the optimal FT configuration to the classifications provided by the SDSS parametric classifier, 2DPHOT, and Ball et al. We find that our FT classifier is comparable to or better in completeness over the full magnitude range 15 ≤ r ≤ 21, with much lower contamination than all but the Ball et al. classifier. At the faintest magnitudes (r > 19), our classifier is the only one that maintains high completeness (>80%) while simultaneously achieving low contamination (∼2.5%). We also examine the SDSS parametric classifier (psfMag - modelMag) to see if the dividing line between stars and galaxies can be adjusted to improve the classifier. We find that currently stars in close pairs are often misclassified as galaxies, and suggest a new cut to improve the classifier. Finally, we apply our FT classifier to separate stars from galaxies in the full set of 69,545,326 SDSS photometric objects in the magnitude range 14 ≤ r ≤ 21.

Evolution of massive close binary stars

International Nuclear Information System (INIS)

Masevich, A.G.; Tutukov, A.V.

1982-01-01

Some problems of the evolution of massive close binary stars are discussed. Most of them are nonevolutionized stars with close masses of components. After filling the Roche cavity and exchange of matter between the components the Wolf-Rayet star is formed. As a result of the supernovae explosion a neutron star or a black hole is formed in the system. The system does not disintegrate but obtains high space velocity owing to the loss of the supernovae envelope. The satellite of the neutron star or black hole - the star of the O or B spectral class loses about 10 -6 of the solar mass for a year. Around the neighbouring component a disc of this matter is formed the incidence of which on a compact star leads to X radiation appearance. The neutron star cannot absorb the whole matter of the widening component and the binary system submerges into the common envelope. As a result of the evolution of massive close binary systems single neutron stars can appear which after the lapse of some time become radiopulsars. Radiopulsars with such high space velocities have been found in our Galaxy [ru

Recent Results from the SAFIR Project

Directory of Open Access Journals (Sweden)

M. Sánchez-Portal

2014-12-01

Full Text Available The "Seyfert and star formation Activity in the Far-Infrared" (SAFIR project is aimed at studying the physical nature of the nuclear IR emission and star formation properties of a small sample of nearby Seyfert galaxies observed with the PACS and SPIRE instruments on board the Herschel space observatory. In this paper, we review the achieved results, that reveal the importance of the far-IR range to improve the quality and reliability of the estimates of basic AGN torus parameters, and describe some preliminary outcome from the on-going work on the dust properties of resolved AGN host galaxies.

MAGNETIC FLUX EXPULSION IN STAR FORMATION

International Nuclear Information System (INIS)

Zhao Bo; Li Zhiyun; Nakamura, Fumitaka; Krasnopolsky, Ruben; Shang, Hsien

2011-01-01

Stars form in dense cores of magnetized molecular clouds. If the magnetic flux threading the cores is dragged into the stars, the stellar field would be orders of magnitude stronger than observed. This well-known 'magnetic flux problem' demands that most of the core magnetic flux be decoupled from the matter that enters the star. We carry out the first exploration of what happens to the decoupled magnetic flux in three dimensions, using a magnetohydrodynamic (MHD) version of the ENZO adaptive mesh refinement code. The field-matter decoupling is achieved through a sink particle treatment, which is needed to follow the protostellar accretion phase of star formation. We find that the accumulation of the decoupled flux near the accreting protostar leads to a magnetic pressure buildup. The high pressure is released anisotropically along the path of least resistance. It drives a low-density expanding region in which the decoupled magnetic flux is expelled. This decoupling-enabled magnetic structure has never been seen before in three-dimensional MHD simulations of star formation. It generates a strong asymmetry in the protostellar accretion flow, potentially giving a kick to the star. In the presence of an initial core rotation, the structure presents an obstacle to the formation of a rotationally supported disk, in addition to magnetic braking, by acting as a rigid magnetic wall that prevents the rotating gas from completing a full orbit around the central object. We conclude that the decoupled magnetic flux from the stellar matter can strongly affect the protostellar collapse dynamics.

Discriminating strange star mergers from neutron star mergers by gravitational-wave measurements

International Nuclear Information System (INIS)

Bauswein, A.; Oechslin, R.; Janka, H.-T.

2010-01-01

We perform three-dimensional relativistic hydrodynamical simulations of the coalescence of strange stars and explore the possibility to decide on the strange matter hypothesis by means of gravitational-wave measurements. Self-binding of strange quark matter and the generally more compact stars yield features that clearly distinguish strange star from neutron star mergers, e.g. hampering tidal disruption during the plunge of quark stars. Furthermore, instead of forming dilute halo structures around the remnant as in the case of neutron star mergers, the coalescence of strange stars results in a differentially rotating hypermassive object with a sharp surface layer surrounded by a geometrically thin, clumpy high-density strange quark matter disk. We also investigate the importance of including nonzero temperature equations of state in neutron star and strange star merger simulations. In both cases we find a crucial sensitivity of the dynamics and outcome of the coalescence to thermal effects, e.g. the outer remnant structure and the delay time of the dense remnant core to black hole collapse depend on the inclusion of nonzero temperature effects. For comparing and classifying the gravitational-wave signals, we use a number of characteristic quantities like the maximum frequency during inspiral or the dominant frequency of oscillations of the postmerger remnant. In general, these frequencies are higher for strange star mergers. Only for particular choices of the equation of state the frequencies of neutron star and strange star mergers are similar. In such cases additional features of the gravitational-wave luminosity spectrum like the ratio of energy emitted during the inspiral phase to the energy radiated away in the postmerger stage may help to discriminate coalescence events of the different types. If such characteristic quantities could be extracted from gravitational-wave signals, for instance with the upcoming gravitational-wave detectors, a decision on the

The Drifting Star

Science.gov (United States)

2008-04-01

temperature is 6150 K, its mass is 1.25 times that of the Sun, and its age is 625 million years. Moreover, the star is found to be more metal-rich than the Sun by about 50%. ESO PR Photo 09b/08 ESO PR Photo 09b/08 Constellations "These results show the power of asteroseismology when using a very precise instrument such as HARPS," says Vauclair. "It also shows that Iota Horologii has the same metal abundance and age as the Hyades cluster and this cannot be a coincidence." The Hyades is an ensemble of stars that is seen with the unaided eye in the Northern constellation Taurus ("The Bull"). This open cluster, located 151 light-years away, contains stars that were formed together 625 million years ago. The star Iota Horologii must have thus formed together with the stars of the Hyades cluster but must have slowly drifted away, being presently more than 130 light-years away from its original birthplace. This is an important result to understand how stars move on the galactic highways of the Milky Way. This also means that the amount of metals present in the star is due to the original cloud from which it formed and not because it engulfed planetary material. "The chicken and egg question of whether the star got planets because it is metal-rich, or whether it is metal-rich because it made planets that were swallowed up is at least answered in one case," says Vauclair. More information The astronomers' study is being published as a Letter to the Editor in Astronomy and Astrophysics ("The exoplanet-host star iota Horologii: an evaporated member of the primordial Hyades cluster", by S. Vauclair et al.). The team is composed of Sylvie Vauclair, Marion Laymand, Gérard Vauclair, Alain Hui Bon Hoa, and Stéphane Charpinet (LATT, Toulouse, France), François Bouchy (IAP, Paris, France), and Michaël Bazot (University of Porto, Portugal).

PG 0308 + 096 and PG 1026 + 002 - Two new short period binary stars resulting from common-envelope evolution

Science.gov (United States)

Saffer, Rex A.; Wade, Richard A.; Liebert, James; Green, Richard F.; Sion, Edward M.; Bechtold, J.; Foss, Diana; Kidder, K.

1993-01-01

Ultraviolet spectroscopy, optical spectroscopy, and spectrophotometry have been used to study the excess UV stars PG 0308 + 096 and PG 1026 + 002. Both objects are short-period binary systems, each containing a DA white dwarf star and a dM star. Orbital periods of approximately 0.284 day for PG 0308 + 096, and aproximately 0.597 day for PG 1026, have been found by spectroscopic analysis of the H-alpha emission line. Ly-alpha and Balmer line profile fitting were used to estimate the mass of white dwarf stars; mass estimates for the dM stars are based on their spectral types. The orbital inclinations are derived from these masses, the periods, and amplitudes of the H-alpha radial velocity curves. The equivalent width of the H-alpha emission line, in each binary system, varies with the orbital phase in such a manner as to imply that it arises, in large part at least, from the hemisphere of the M star that faces the white dwarf star.

The twinkling of stars

International Nuclear Information System (INIS)

Jakeman, E.; Parry, G.; Pike, E.R.; Pusey, P.N.

1978-01-01

This article collects together some of the main ideas and experimental results on the twinkling of stars. Statistical methods are used to characterise the features of the scintillation and to investigate the ways in which these depend on the zenith angle of the star, the bandwidth of the light and various other parameters. Some new results are included which demonstrate the advantages of using photon counting methods in experiments on stellar scintillation. Since the twinkling of stars is a consequence of the turbulence in the Earth's magnetic atmosphere then measurements can be used to deduce some features of the structure of the turbulence. Some of the experiments designed to do this are discussed and the results reported. (author)

Sky coverage modeling for the whole sky for laser guide star multiconjugate adaptive optics.

Science.gov (United States)

Wang, Lianqi; Andersen, David; Ellerbroek, Brent

2012-06-01

The scientific productivity of laser guide star adaptive optics systems strongly depends on the sky coverage, which describes the probability of finding natural guide stars for the tip/tilt wavefront sensor(s) to achieve a certain performance. Knowledge of the sky coverage is also important for astronomers planning their observations. In this paper, we present an efficient method to compute the sky coverage for the laser guide star multiconjugate adaptive optics system, the Narrow Field Infrared Adaptive Optics System (NFIRAOS), being designed for the Thirty Meter Telescope project. We show that NFIRAOS can achieve more than 70% sky coverage over most of the accessible sky with the requirement of 191 nm total rms wavefront.

The SOFIA Massive (SOMA) Star Formation Survey. I. Overview and First Results

Energy Technology Data Exchange (ETDEWEB)

De Buizer, James M.; Shuping, Ralph [SOFIA-USRA, NASA Ames Research Center, MS 232-12, Moffett Field, CA 94035 (United States); Liu, Mengyao; Tan, Jonathan C.; Staff, Jan E.; Tanaka, Kei E. I. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Zhang, Yichen [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Beltrán, Maria T. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Whitney, Barbara [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St, Madison, WI 53706 (United States)

2017-07-01

We present an overview and first results of the Stratospheric Observatory For Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the FORCAST instrument to image massive protostars from ∼10 to 40 μ m. These wavelengths trace thermal emission from warm dust, which in Core Accretion models mainly emerges from the inner regions of protostellar outflow cavities. Dust in dense core envelopes also imprints characteristic extinction patterns at these wavelengths, causing intensity peaks to shift along the outflow axis and profiles to become more symmetric at longer wavelengths. We present observational results for the first eight protostars in the survey, i.e., multiwavelength images, including some ancillary ground-based mid-infrared (MIR) observations and archival Spitzer and Herschel data. These images generally show extended MIR/FIR emission along directions consistent with those of known outflows and with shorter wavelength peak flux positions displaced from the protostar along the blueshifted, near-facing sides, thus confirming qualitative predictions of Core Accretion models. We then compile spectral energy distributions and use these to derive protostellar properties by fitting theoretical radiative transfer models. Zhang and Tan models, based on the Turbulent Core Model of McKee and Tan, imply the sources have protostellar masses m {sub *} ∼ 10–50 M {sub ⊙} accreting at ∼10{sup −4}–10{sup −3} M {sub ⊙} yr{sup −1} inside cores of initial masses M {sub c} ∼ 30–500 M {sub ⊙} embedded in clumps with mass surface densities Σ{sub cl} ∼ 0.1–3 g cm{sup −2}. Fitting the Robitaille et al. models typically leads to slightly higher protostellar masses, but with disk accretion rates ∼100× smaller. We discuss reasons for these differences and overall implications of these first survey results for massive star formation theories.

Observing Double Stars

Science.gov (United States)

Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca

2012-05-01

Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.

Comparing the asteroseismic properties of pulsating extremely low-mass pre-white dwarf stars and δ Scuti stars

Directory of Open Access Journals (Sweden)

Arias J.P.Sánchez

2017-01-01

Full Text Available We present the first results of a detailed comparison between the pulsation properties of pulsating Extremely Low-Mass pre-white dwarf stars (the pre-ELMV variable stars and δ Scuti stars. The instability domains of these very different kinds of stars nearly overlap in the log Teff vs. log g diagram, leading to a degeneracy in the classification of the stars. Our aim is to provide asteroseismic tools for their correct classification.

The nuclear spectroscopic telescope array (NuSTAR) high-energy X-ray mission

DEFF Research Database (Denmark)

Harrison, Fiona A.; Craig, William W.; Christensen, Finn Erland

2013-01-01

The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 2012 June 13, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the ~10 keV high-energy cutoff achieved by all previous X...

Satellite Angular Velocity Estimation Based on Star Images and Optical Flow Techniques

Directory of Open Access Journals (Sweden)

Giancarmine Fasano

2013-09-01

Full Text Available An optical flow-based technique is proposed to estimate spacecraft angular velocity based on sequences of star-field images. It does not require star identification and can be thus used to also deliver angular rate information when attitude determination is not possible, as during platform de tumbling or slewing. Region-based optical flow calculation is carried out on successive star images preprocessed to remove background. Sensor calibration parameters, Poisson equation, and a least-squares method are then used to estimate the angular velocity vector components in the sensor rotating frame. A theoretical error budget is developed to estimate the expected angular rate accuracy as a function of camera parameters and star distribution in the field of view. The effectiveness of the proposed technique is tested by using star field scenes generated by a hardware-in-the-loop testing facility and acquired by a commercial-off-the shelf camera sensor. Simulated cases comprise rotations at different rates. Experimental results are presented which are consistent with theoretical estimates. In particular, very accurate angular velocity estimates are generated at lower slew rates, while in all cases the achievable accuracy in the estimation of the angular velocity component along boresight is about one order of magnitude worse than the other two components.

NUCLEOSYNTHESIS AND EVOLUTION OF MASSIVE METAL-FREE STARS

International Nuclear Information System (INIS)

Heger, Alexander; Woosley, S. E.

2010-01-01

The evolution and explosion of metal-free stars with masses 10-100 M sun are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. Such stars would have been the first to form after the big bang and may have left a distinctive imprint on the composition of the early universe. When the supernova yields are integrated over a Salpeter initial mass function (IMF), the resulting elemental abundance pattern is qualitatively solar, but with marked deficiencies of odd-Z elements with 7 ≤ Z ≤ 13. Neglecting the contribution of the neutrino wind from the neutron stars that they form, no appreciable abundances are made for elements heavier than germanium. The computed pattern compares favorably with what has been observed in metal-deficient stars with [Z] ∼ sun ; where 1 B = 1 Bethe = 10 51 erg) for a Salpeter IMF, and may have played a role in reionizing the universe. Neglecting rotation, most of the stars end their lives as blue supergiants and form supernovae with distinctive light curves resembling SN 1987A, but some produce primary nitrogen due to dredge-up and become red supergiants. These make brighter supernovae like typical Type IIp's. For the lower mass supernovae considered, the distribution of remnant masses clusters around typical modern neutron star masses, but above 20-30 M sun , with the value depending on explosion energy, black holes are copiously formed by fallback, with a maximum hole mass of ∼40 M sun . A novel automated fitting algorithm is developed for determining optimal combinations of explosion energy, mixing, and IMF in the large model database to agree with specified data sets. The model is applied to the low-metallicity sample of Cayrel et al. and the two ultra-iron-poor stars HE0107-5240 and HE1327-2326. Best agreement with these very low metallicity stars is achieved with very little mixing, and none of the metal-deficient data sets considered show the need for a high-energy explosion component. In

Carbon stars in lmc clusters revisited

OpenAIRE

Marigo, Paola; Girardi, Leo Alberto; Chiosi, Cesare

1996-01-01

Examining the available data for AGB stars in the Large Magellanic Cloud (LMC) clusters, we address the question about the mass interval of low- and intermediate-mass stars which eventually evolve into carbon stars (C stars) during the TP-AGB phase. We combine the data compiled by Frogel, Mould & Blanco (1990) - near infrared photometry and spectral classification for luminous AGB stars in clusters - with the ages for individual clusters derived from independent methods. The resulting distrib...

Spectroscopic survey of Kepler stars - II. FIES/NOT observations of A- and F-type stars

Science.gov (United States)

Niemczura, E.; Polińska, M.; Murphy, S. J.; Smalley, B.; Kołaczkowski, Z.; Jessen-Hansen, J.; Uytterhoeven, K.; Lykke, J. M.; Triviño Hage, A.; Michalska, G.

2017-09-01

We have analysed high-resolution spectra of 28 A and 22 F stars in the Kepler field, observed using the Fibre-Fed Échelle Spectrograph at the Nordic Optical Telescope. We provide spectral types, atmospheric parameters and chemical abundances for 50 stars. Balmer, Fe I and Fe II lines were used to derive effective temperatures, surface gravities and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. Effective temperatures calculated by spectral energy distribution fitting are in good agreement with those determined from the spectral line analysis. The stars analysed include chemically peculiar stars of the Am and λ Boo types, as well as stars with approximately solar chemical abundances. The wide distribution of projected rotational velocity, vsin I, is typical for A and F stars. The microturbulence velocities obtained are typical for stars in the observed temperature and surface gravity ranges. Moreover, we affirm the results of Niemczura et al. that Am stars do not have systematically higher microturbulent velocities than normal stars of the same temperature.

Which of Kepler's Stars Flare?

Science.gov (United States)

Kohler, Susanna

2017-12-01

The habitability of distant exoplanets is dependent upon many factors one of which is the activity of their host stars. To learn about which stars are most likely to flare, a recent study examines tens of thousands of stellar flares observed by Kepler.Need for a Broader SampleArtists rendering of a flaring dwarf star. [NASAs Goddard Space Flight Center/S. Wiessinger]Most of our understanding of what causes a star to flare is based on observations of the only star near enough to examine in detail the Sun. But in learning from a sample size of one, a challenge arises: we must determine which conclusions are unique to the Sun (or Sun-like stars), and which apply to other stellar types as well.Based on observations and modeling, astronomers think that stellar flares result from the reconnection of magnetic field lines in a stars outer atmosphere, the corona. The magnetic activity is thought to be driven by a dynamo caused by motions in the stars convective zone.HR diagram of the Kepler stars, with flaring main-sequence (yellow), giant (red) and A-star (green) stars in the authors sample indicated. [Van Doorsselaere et al. 2017]To test whether these ideas are true generally, we need to understand what types of stars exhibit flares, and what stellar properties correlate with flaring activity. A team of scientists led by Tom Van Doorsselaere (KU Leuven, Belgium) has now used an enormous sample of flares observed by Kepler to explore these statistics.Intriguing TrendsVan Doorsselaere and collaborators used a new automated flare detection and characterization algorithm to search through the raw light curves from Quarter 15 of the Kepler mission, building a sample of 16,850 flares on 6,662 stars. They then used these to study the dependence of the flare occurrence rate, duration, energy, and amplitude on the stellar spectral type and rotation period.This large statistical study led the authors to several interesting conclusions, including:Flare star incidence rate as a a

The structure and evolution of galacto-detonation waves - Some analytic results in sequential star formation models of spiral galaxies

Science.gov (United States)

Cowie, L. L.; Rybicki, G. B.

1982-01-01

Waves of star formation in a uniform, differentially rotating disk galaxy are treated analytically as a propagating detonation wave front. It is shown, that if single solitary waves could be excited, they would evolve asymptotically to one of two stable spiral forms, each of which rotates with a fixed pattern speed. Simple numerical solutions confirm these results. However, the pattern of waves that develop naturally from an initially localized disturbance is more complex and dies out within a few rotation periods. These results suggest a conclusive observational test for deciding whether sequential star formation is an important determinant of spiral structure in some class of galaxies.

School Counselors: Closing Achievement Gaps and Writing Results Reports

Science.gov (United States)

Hartline, Julie; Cobia, Debra

2012-01-01

Charged with closing the achievement gap for marginalized students, school counselors need to be able to identify gaps, develop interventions, evaluate effectiveness, and share results. This study examined 100 summary results reports submitted by school counselors after having received four days of training on the ASCA National Model. Findings…

Covering tree with stars

DEFF Research Database (Denmark)

Baumbach, Jan; Guo, Jiong; Ibragimov, Rashid

2015-01-01

We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting...... tree is isomorphic to T? We prove that in the general setting, CST is NP-complete, which implies that the tree edit distance considered here is also NP-hard, even when both input trees having diameters bounded by 10. We also show that, when the number of distinct stars is bounded by a constant k, CTS...

Evolution of star systems supplied by external stars: a model for Galaxy nuclei

International Nuclear Information System (INIS)

Dokuchaev, V.I.; Ozernoj, L.M.; AN SSSR, Moscow. Inst. Yadernykh Issledovanij)

1985-01-01

Extended rarefied environments around the core of a non-isothermic galaxy nucleus can supply the core by both energies and masses of external stars due to relaxation mechanisms. These factors can influence considerably the secular evolution of the core when competing with usual star evaporation from it. Conditions are found under which external environments influence the core evolution much more than star evaporation. This results in expansion of the core instead of its collapse

PROGRESSIVE STAR FORMATION IN THE YOUNG GALACTIC SUPER STAR CLUSTER NGC 3603

International Nuclear Information System (INIS)

Beccari, Giacomo; Spezzi, Loredana; De Marchi, Guido; Andersen, Morten; Paresce, Francesco; Young, Erick; Panagia, Nino; Bond, Howard; Balick, Bruce; Calzetti, Daniela; Carollo, C. Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Saha, Abhijit

2010-01-01

Early Release Science observations of the cluster NGC 3603 with the WFC3 on the refurbished Hubble Space Telescope allow us to study its recent star formation history. Our analysis focuses on stars with Hα excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with Hα excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.

Connecting the Cosmic Star Formation Rate with the Local Star Formation

Science.gov (United States)

Gribel, Carolina; Miranda, Oswaldo D.; Williams Vilas-Boas, José

2017-11-01

We present a model that unifies the cosmic star formation rate (CSFR), obtained through the hierarchical structure formation scenario, with the (Galactic) local star formation rate (SFR). It is possible to use the SFR to generate a CSFR mapping through the density probability distribution functions commonly used to study the role of turbulence in the star-forming regions of the Galaxy. We obtain a consistent mapping from redshift z˜ 20 up to the present (z = 0). Our results show that the turbulence exhibits a dual character, providing high values for the star formation efficiency ( ˜ 0.32) in the redshift interval z˜ 3.5{--}20 and reducing its value to =0.021 at z = 0. The value of the Mach number ({{ M }}{crit}), from which rapidly decreases, is dependent on both the polytropic index (Γ) and the minimum density contrast of the gas. We also derive Larson’s first law associated with the velocity dispersion ( ) in the local star formation regions. Our model shows good agreement with Larson’s law in the ˜ 10{--}50 {pc} range, providing typical temperatures {T}0˜ 10{--}80 {{K}} for the gas associated with star formation. As a consequence, dark matter halos of great mass could contain a number of halos of much smaller mass, and be able to form structures similar to globular clusters. Thus, Larson’s law emerges as a result of the very formation of large-scale structures, which in turn would allow the formation of galactic systems, including our Galaxy.

THE GALACTIC O-STAR SPECTROSCOPIC SURVEY (GOSSS). II. BRIGHT SOUTHERN STARS

International Nuclear Information System (INIS)

Sota, A.; Apellániz, J. Maíz; Alfaro, E. J.; Morrell, N. I.; Barbá, R. H.; Arias, J. I.; Walborn, N. R.; Gamen, R. C.

2014-01-01

We present the second installment of GOSSS, a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ∼ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog (GOSC). In this paper we include bright stars and other objects drawn mostly from the first version of GOSC, all of them south of δ = –20°, for a total number of 258 O stars. We also revise the northern sample of Paper I to provide the full list of spectroscopically classified Galactic O stars complete to B = 8, bringing the total number of published GOSSS stars to 448. Extensive sequences of exceptional objects are given, including the early Of/WN, O Iafpe, Ofc, ON/OC, Onfp, Of?p, and Oe types, as well as double/triple-lined spectroscopic binaries. The new spectral subtype O9.2 is also discussed. The magnitude and spatial distributions of the observed sample are analyzed. We also present new results from OWN, a multi-epoch high-resolution spectroscopic survey coordinated with GOSSS that is assembling the largest sample of Galactic spectroscopic massive binaries ever attained. The OWN data combined with additional information on spectroscopic and visual binaries from the literature indicate that only a very small fraction (if any) of the stars with masses above 15-20 M ☉ are born as single systems. In the future we will publish the rest of the GOSSS survey, which is expected to include over 1000 Galactic O stars

Load Sharing Behavior of Star Gearing Reducer for Geared Turbofan Engine

Science.gov (United States)

Mo, Shuai; Zhang, Yidu; Wu, Qiong; Wang, Feiming; Matsumura, Shigeki; Houjoh, Haruo

2017-07-01

Load sharing behavior is very important for power-split gearing system, star gearing reducer as a new type and special transmission system can be used in many industry fields. However, there is few literature regarding the key multiple-split load sharing issue in main gearbox used in new type geared turbofan engine. Further mechanism analysis are made on load sharing behavior among star gears of star gearing reducer for geared turbofan engine. Comprehensive meshing error analysis are conducted on eccentricity error, gear thickness error, base pitch error, assembly error, and bearing error of star gearing reducer respectively. Floating meshing error resulting from meshing clearance variation caused by the simultaneous floating of sun gear and annular gear are taken into account. A refined mathematical model for load sharing coefficient calculation is established in consideration of different meshing stiffness and supporting stiffness for components. The regular curves of load sharing coefficient under the influence of interactions, single action and single variation of various component errors are obtained. The accurate sensitivity of load sharing coefficient toward different errors is mastered. The load sharing coefficient of star gearing reducer is 1.033 and the maximum meshing force in gear tooth is about 3010 N. This paper provides scientific theory evidences for optimal parameter design and proper tolerance distribution in advanced development and manufacturing process, so as to achieve optimal effects in economy and technology.

Doubly differential star-16-QAM for fast wavelength switching coherent optical packet transceiver.

Science.gov (United States)

Liu, Fan; Lin, Yi; Walsh, Anthony J; Yu, Yonglin; Barry, Liam P

2018-04-02

A coherent optical packet transceiver based on doubly differential star 16-ary quadrature amplitude modulation (DD-star-16-QAM) is presented for spectrally and energy efficient reconfigurable networks. The coding and decoding processes for this new modulation format are presented, simulations and experiments are then performed to investigate the performance of the DD-star-16-QAM in static and dynamic scenarios. The static results show that the influence of frequency offset (FO) can be cancelled out by doubly differential (DD) coding and the correction range is only limited by the electronic bandwidth of the receivers. In the dynamic scenario with a time-varying FO and linewidth, the DD-star-16-QAM can overcome the time-varying FO, and the switching time of around 70 ns is determined by the time it takes the dynamic linewidth to reach the requisite level. This format can thus achieve a shorter waiting time after switching tunable lasers than the commonly used square-16-QAM, in which the transmission performance is limited by the frequency transients after the wavelength switch.

The first stars: CEMP-no stars and signatures of spinstars

Science.gov (United States)

Maeder, André; Meynet, Georges; Chiappini, Cristina

2015-04-01

Aims: The CEMP-no stars are "carbon-enhanced-metal-poor" stars that in principle show no evidence of s- and r-elements from neutron captures. We try to understand the origin and nucleosynthetic site of their peculiar CNO, Ne-Na, and Mg-Al abundances. Methods: We compare the observed abundances to the nucleosynthetic predictions of AGB models and of models of rotating massive stars with internal mixing and mass loss. We also analyze the different behaviors of α- and CNO-elements, as well the abundances of elements involved in the Ne-Na and Mg-Al cycles. Results: We show that CEMP-no stars exhibit products of He-burning that have gone through partial mixing and processing by the CNO cycle, producing low 12C/13C and a broad variety of [C/N] and [O/N] ratios. From a 12C/13C vs. [C/N] diagram, we conclude that neither the yields of AGB stars (in binaries or not) nor the yields of classic supernovae can fully account for the observed CNO abundances in CEMP-no stars. Better agreement is obtained once the chemical contribution by stellar winds of fast-rotating massive stars is taken into account, where partial mixing takes place, leading to various amounts of CNO being ejected. The [(C+N+O)/H] ratios of CEMP-no stars vary linearly with [Fe/H] above [Fe/H] = -4.0 indicating primary behavior by (C+N+O). Below [Fe/H] = -4.0, [(C+N+O)/H] is almost constant as a function of [Fe/H], implying very high [(C+N+O)/Fe] ratios up to 4 dex. In view of the timescales, such abundance ratios reflect more individual nucleosynthetic properties, rather than an average chemical evolution. The high [(C+N+O)/Fe] ratios (as well as the high [(C+N+O)/α-elements]) imply that stellar winds from partially mixed stars were the main source of these excesses of heavy elements now observed in CEMP-no stars. The ranges covered by the variations of [Na/Fe], [Mg/Fe], and [Al/Fe] are much broader than for the α-elements (with an atomic mass number above 24) and are comparable to the wide ranges covered

Energy Star Concepts for Highway Vehicles

Energy Technology Data Exchange (ETDEWEB)

Greene, D.L.

2003-06-24

The authors of this report, under the sponsorship of the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) Weatherization and Intergovernmental Program, have investigated the possible application of Energy Star ratings to passenger cars and light trucks. This study establishes a framework for formulating and evaluating Energy Star rating methods that is comprised of energy- and environmental-based metrics, potential vehicle classification systems, vehicle technology factors, and vehicle selection criteria. The study tests several concepts and Energy Star rating methods using model-year 2000 vehicle data--a spreadsheet model has been developed to facilitate these analyses. This study tests two primary types of rating systems: (1) an outcome-based system that rates vehicles based on fuel economy, GHG emissions, and oil use and (2) a technology-based system that rates vehicles based on the energy-saving technologies they use. Rating methods were evaluated based on their ability to select vehicles with high fuel economy, low GHG emissions, and low oil use while preserving a full range of service (size and acceleration) and body style choice. This study concludes that an Energy Star rating for passenger cars and light trucks is feasible and that several methods could be used to achieve reasonable tradeoffs between low energy use and emissions and diversity in size, performance, and body type. It also shows that methods that consider only fuel economy, GHG emissions, or oil use will not select a diverse mix of vehicles. Finally, analyses suggest that methods that encourage the use of technology only, may result in increases in acceleration power and weight rather than reductions in oil use and GHG emissions and improvements in fuel economy.

Entanglement distribution in star network based on spin chain in diamond

Science.gov (United States)

Zhu, Yuan-Ming; Ma, Lei

2018-06-01

After star network of spins was proposed, generating entanglement directly through spin interactions between distant parties became possible. We propose an architecture which involves coupled spin chains based on nitrogen-vacancy centers and nitrogen defect spins to expand star network. The numerical analysis shows that the maximally achievable entanglement Em exponentially decays with the length of spin chains M and spin noise. The entanglement capability of this configuration under the effect of disorder and spin loss is also studied. Moreover, it is shown that with this kind of architecture, star network of spins is feasible in measurement of magnetic-field gradient.

Planck 2013 results. XXX. Cosmic infrared background measurements and implications for star formation

Science.gov (United States)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bethermin, M.; Bielewicz, P.; Blagrave, K.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chen, X.; Chiang, H. C.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Ghosh, T.; Giard, M.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Hanson, D.; Harrison, D.; Helou, G.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Kalberla, P.; Keihänen, E.; Kerp, J.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lacasa, F.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Langer, M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leonardi, R.; León-Tavares, J.; Lesgourgues, J.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savini, G.; Scott, D.; Seiffert, M. D.; Serra, P.; Shellard, E. P. S.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Türler, M.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Welikala, N.; White, M.; White, S. D. M.; Winkel, B.; Yvon, D.; Zacchei, A.; Zonca, A.

2014-11-01

We present new measurements of cosmic infrared background (CIB) anisotropies using Planck. Combining HFI data with IRAS, the angular auto- and cross-frequency power spectrum is measured from 143 to 3000 GHz, and the auto-bispectrum from 217 to 545 GHz. The total areas used to compute the CIB power spectrum and bispectrum are about 2240 and 4400 deg2, respectively. After careful removal of the contaminants (cosmic microwave background anisotropies, Galactic dust, and Sunyaev-Zeldovich emission), and a complete study of systematics, the CIB power spectrum is measured with unprecedented signal to noise ratio from angular multipoles ℓ ~ 150 to 2500. The bispectrum due to the clustering of dusty, star-forming galaxies is measured from ℓ ~ 130 to 1100, with a total signal to noise ratio of around 6, 19, and 29 at 217, 353, and 545 GHz, respectively. Two approaches are developed for modelling CIB power spectrum anisotropies. The first approach takes advantage of the unique measurements by Planck at large angular scales, and models only the linear part of the power spectrum, with a mean bias of dark matter haloes hosting dusty galaxies at a given redshift weighted by their contribution to the emissivities. The second approach is based on a model that associates star-forming galaxies with dark matter haloes and their subhaloes, using a parametrized relation between the dust-processed infrared luminosity and (sub-)halo mass. The two approaches simultaneously fit all auto- and cross-power spectra very well. We find that the star formation history is well constrained up to redshifts around 2, and agrees with recent estimates of the obscured star-formation density using Spitzer and Herschel. However, at higher redshift, the accuracy of the star formation history measurement is strongly degraded by the uncertainty in the spectral energy distribution of CIB galaxies. We also find that the mean halo mass which is most efficient at hosting star formation is log (Meff/M⊙) = 12

Evolution of magnetized, differentially rotating neutron stars: Simulations in full general relativity

International Nuclear Information System (INIS)

Duez, Matthew D.; Liu, Yuk Tung; Shapiro, Stuart L.; Stephens, Branson C.; Shibata, Masaru

2006-01-01

We study the effects of magnetic fields on the evolution of differentially rotating neutron stars, which can be formed in stellar core collapse or binary neutron star coalescence. Magnetic braking and the magnetorotational instability (MRI) both act on differentially rotating stars to redistribute angular momentum. Simulations of these stars are carried out in axisymmetry using our recently developed codes which integrate the coupled Einstein-Maxwell-MHD equations. We consider stars with two different equations of state (EOS), a gamma-law EOS with Γ=2, and a more realistic hybrid EOS, and we evolve them adiabatically. Our simulations show that the fate of the star depends on its mass and spin. For initial data, we consider three categories of differentially rotating, equilibrium configurations, which we label normal, hypermassive and ultraspinning. Normal configurations have rest masses below the maximum achievable with uniform rotation, and angular momentum below the maximum for uniform rotation at the same rest mass. Hypermassive stars have rest masses exceeding the mass limit for uniform rotation. Ultraspinning stars are not hypermassive, but have angular momentum exceeding the maximum for uniform rotation at the same rest mass. We show that a normal star will evolve to a uniformly rotating equilibrium configuration. An ultraspinning star evolves to an equilibrium state consisting of a nearly uniformly rotating central core, surrounded by a differentially rotating torus with constant angular velocity along magnetic field lines, so that differential rotation ceases to wind the magnetic field. In addition, the final state is stable against the MRI, although it has differential rotation. For a hypermassive neutron star, the MHD-driven angular momentum transport leads to catastrophic collapse of the core. The resulting rotating black hole is surrounded by a hot, massive, magnetized torus undergoing quasistationary accretion, and a magnetic field collimated along

Model stars with degenerate dwarf cores and helium-burning shells - A stationary-burning approximation

Energy Technology Data Exchange (ETDEWEB)

Iben, I. Jr.; Tutukov, A.V. (Illinois Univ., Urbana (USA); Astronomicheskii Sovet, Moscow (USSR))

1989-07-01

The characteristics of model stars consisting of a degenerate dwarf core and an envelope which is burning a nuclear fuel or fuels in its interior are explored. The models are relevant to stars which are accreting matter from a companion, to single stars in late stages of evolution, to stripped noninteracting remnants of binary star evolution, and to merging and merged degenerate dwarfs. For any given mass and choice of nuclear fuels, a sequence of models is constructed which differ with respect to the mass of the degenerate core and the envelope characteristics. Each sequence has at least three distinct branches: a degenerate dwarf branch along which envelope mass increases with decreasing luminosity, a plateau branch characterized by a very small envelope mass and by a nearly constant luminosity which reaches the maximum achievable value for the sequence, and an asymptotic giant branch which is at the lowest temperatures achievable and along which envelope mass decreases with increasing luminosity. 78 refs.

Model stars with degenerate dwarf cores and helium-burning shells - A stationary-burning approximation

International Nuclear Information System (INIS)

Iben, I. Jr.; Tutukov, A.V.

1989-01-01

The characteristics of model stars consisting of a degenerate dwarf core and an envelope which is burning a nuclear fuel or fuels in its interior are explored. The models are relevant to stars which are accreting matter from a companion, to single stars in late stages of evolution, to stripped noninteracting remnants of binary star evolution, and to merging and merged degenerate dwarfs. For any given mass and choice of nuclear fuels, a sequence of models is constructed which differ with respect to the mass of the degenerate core and the envelope characteristics. Each sequence has at least three distinct branches: a degenerate dwarf branch along which envelope mass increases with decreasing luminosity, a plateau branch characterized by a very small envelope mass and by a nearly constant luminosity which reaches the maximum achievable value for the sequence, and an asymptotic giant branch which is at the lowest temperatures achievable and along which envelope mass decreases with increasing luminosity. 78 refs

Regular Generalized Star Star closed sets in Bitopological Spaces

OpenAIRE

K. Kannan; D. Narasimhan; K. Chandrasekhara Rao; R. Ravikumar

2011-01-01

The aim of this paper is to introduce the concepts of τ1τ2-regular generalized star star closed sets , τ1τ2-regular generalized star star open sets and study their basic properties in bitopological spaces.

The Maximum Flux of Star-Forming Galaxies

Science.gov (United States)

Crocker, Roland M.; Krumholz, Mark R.; Thompson, Todd A.; Clutterbuck, Julie

2018-04-01

The importance of radiation pressure feedback in galaxy formation has been extensively debated over the last decade. The regime of greatest uncertainty is in the most actively star-forming galaxies, where large dust columns can potentially produce a dust-reprocessed infrared radiation field with enough pressure to drive turbulence or eject material. Here we derive the conditions under which a self-gravitating, mixed gas-star disc can remain hydrostatic despite trapped radiation pressure. Consistently taking into account the self-gravity of the medium, the star- and dust-to-gas ratios, and the effects of turbulent motions not driven by radiation, we show that galaxies can achieve a maximum Eddington-limited star formation rate per unit area \\dot{Σ }_*,crit ˜ 10^3 M_{⊙} pc-2 Myr-1, corresponding to a critical flux of F*, crit ˜ 1013L⊙ kpc-2 similar to previous estimates; higher fluxes eject mass in bulk, halting further star formation. Conversely, we show that in galaxies below this limit, our one-dimensional models imply simple vertical hydrostatic equilibrium and that radiation pressure is ineffective at driving turbulence or ejecting matter. Because the vast majority of star-forming galaxies lie below the maximum limit for typical dust-to-gas ratios, we conclude that infrared radiation pressure is likely unimportant for all but the most extreme systems on galaxy-wide scales. Thus, while radiation pressure does not explain the Kennicutt-Schmidt relation, it does impose an upper truncation on it. Our predicted truncation is in good agreement with the highest observed gas and star formation rate surface densities found both locally and at high redshift.

Mass loss from Wolf-Rayet stars

International Nuclear Information System (INIS)

Willis, A.J.

1982-01-01

Recent results relating to the stellar winds and mass loss rates of the WR stars are reviewed, emphasising new data and their interpretation acquired at UV, IR and Radio wavelengths. The subject is discussed under the headings: physical and chemical properties of WR stars (effective temperatures and radiative luminosities; masses; chemical abundances); velocity, ionisation and excitation structure of WR winds; mass loss rates of WR stars; mass loss properties of WR stars in the LMC; comparisons with theoretical models of mass loss; ring nebulae around WR stars; conclusions. (author)

Cataclysmic Variable Stars

Science.gov (United States)

Hellier, Coel

2001-01-01

Cataclysmic variable stars are the most variable stars in the night sky, fluctuating in brightness continually on timescales from seconds to hours to weeks to years. The changes can be recorded using amateur telescopes, yet are also the subject of intensive study by professional astronomers. That study has led to an understanding of cataclysmic variables as binary stars, orbiting so closely that material transfers from one star to the other. The resulting process of accretion is one of the most important in astrophysics. This book presents the first account of cataclysmic variables at an introductory level. Assuming no previous knowledge of the field, it explains the basic principles underlying the variability, while providing an extensive compilation of cataclysmic variable light curves. Aimed at amateur astronomers, undergraduates, and researchers, the main text is accessible to those with no mathematical background, while supplementary boxes present technical details and equations.

Nanotechnology applications and implications research supported by the US Environmental Protection Agency STAR grants program.

Science.gov (United States)

Savage, Nora; Thomas, Treye A; Duncan, Jeremiah S

2007-10-01

Since 2002, the US Environmental Protection Agency (EPA) has been funding research on the environmental aspects of nanotechnology through its Science to Achieve Results (STAR) grants program. In total, more than $25 million has been awarded for 86 research projects on the environmental applications and implications of nanotechnology. In the applications area, grantees have produced promising results in green manufacturing, remediation, sensors, and treatment using nanotechnology and nanomaterials. Although there are many potential benefits of nanotechnology, there has also been increasing concern about the environmental and health effects of nanomaterials, and there are significant gaps in the data needed to address these concerns. Research performed by STAR grantees is beginning to address these needs.

A computer-based measure of resultant achievement motivation.

Science.gov (United States)

Blankenship, V

1987-08-01

Three experiments were conducted to develop a computer-based measure of individual differences in resultant achievement motivation (RAM) on the basis of level-of-aspiration, achievement motivation, and dynamics-of-action theories. In Experiment 1, the number of atypical shifts and greater responsiveness to incentives on 21 trials with choices among easy, intermediate, and difficult levels of an achievement-oriented game were positively correlated and were found to differentiate the 62 subjects (31 men, 31 women) on the amount of time they spent at a nonachievement task (watching a color design) 1 week later. In Experiment 2, test-retest reliability was established with the use of 67 subjects (15 men, 52 women). Point and no-point trials were offered in blocks, with point trials first for half the subjects and no-point trials first for the other half. Reliability was higher for the atypical-shift measure than for the incentive-responsiveness measure and was higher when points were offered first. In Experiment 3, computer anxiety was manipulated by creating a simulated computer breakdown in the experimental condition. Fifty-nine subjects (13 men, 46 women) were randomly assigned to the experimental condition or to one of two control conditions (an interruption condition and a no-interruption condition). Subjects with low RAM, as demonstrated by a low number of typical shifts, took longer to choose the achievement-oriented task, as predicted by the dynamics-of-action theory. The difference was evident in all conditions and most striking in the computer-breakdown condition. A change of focus from atypical to typical shifts is discussed.

A survey for variable young stars with small telescopes: First results from HOYS-CAPS

Science.gov (United States)

Froebrich, D.; Campbell-White, J.; Scholz, A.; Eislöffel, J.; Zegmott, T.; Billington, S. J.; Donohoe, J.; Makin, S. V.; Hibbert, R.; Newport, R. J.; Pickard, R.; Quinn, N.; Rodda, T.; Piehler, G.; Shelley, M.; Parkinson, S.; Wiersema, K.; Walton, I.

2018-05-01

Variability in Young Stellar Objects (YSOs) is one of their primary characteristics. Long-term, multi-filter, high-cadence monitoring of large YSO samples is the key to understand the partly unusual light-curves that many of these objects show. Here we introduce and present the first results of the HOYS-CAPScitizen science project which aims to perform such monitoring for nearby (d < 1 kpc) and young (age < 10 Myr) clusters and star forming regions, visible from the northern hemisphere, with small telescopes. We have identified and characterised 466 variable (413 confirmed young) stars in 8 young, nearby clusters. All sources vary by at least 0.2 mag in V, have been observed at least 15 times in V, R and I in the same night over a period of about 2 yrs and have a Stetson index of larger than 1. This is one of the largest samples of variable YSOs observed over such a time-span and cadence in multiple filters. About two thirds of our sample are classical T-Tauri stars, while the rest are objects with depleted or transition disks. Objects characterised as bursters show by far the highest variability. Dippers and objects whose variability is dominated by occultations from normal interstellar dust or dust with larger grains (or opaque material) have smaller amplitudes. We have established a hierarchical clustering algorithm based on the light-curve properties which allows the identification of the YSOs with the most unusual behaviour, and to group sources with similar properties. We discuss in detail the light-curves of the unusual objects V2492 Cyg, V350 Cep and 2MASS J21383981+5708470.

W UMa stars and angular momentum loss

International Nuclear Information System (INIS)

Vilhu, O.; Rahunen, T.

1980-01-01

The structure and evolution of W UMa stars is still unsolved although considerable progress has been achieved in recent years. The authors aim is to find out whether it is possible to obtain more extreme mass ratios, what is the angular momentum needed and what is the time scale. (Auth.)

The Search for New Luminous Blue Variable Stars: Near-Infrared Spectroscopy of Stars With 24 micron Shells

Science.gov (United States)

Stringfellow, Guy; Gvaramadze, Vasilii

2010-02-01

Luminous Blue Variable (LBV) stars represent an extremely rare class of very luminous and massive stars. Only about a dozen confirmed Galactic LBV stars are known to date, which precludes us from determining a solid evolutionary connection between LBV and other intermediate (e.g. Ofpe/WN9, WNL) phases in the life of very massive stars. The known LBV stars each have their own unique properties, so new discoveries add insight into the properties and evolutionary status of LBVs and massive stars; even one new discovery of objects of this type could provide break-through results in the understanding of the intermediate stages of massive star evolution. We have culled a prime sample of possible LBV candidates from the Spitzer 24 (micron) archival data. All have circumstellar nebulae, rings, and shells (typical of LBVs and related stars) surrounding reddened central stars. Spectroscopic followup of about two dozen optically visible central stars associated with the shells from this sample showed that they are either candidate LBVs, late WN-type Wolf-Rayet stars or blue supergiants. We propose infrared spectroscopic observations of the central stars for a large fraction (23 stars) of our northern sample to determine their nature and discover additional LBV candidates. These stars have no plausible optical counterparts, so infrared spectra are needed. This program requires two nights of Hale time using TripleSpec.

Fabrication of hexagonal star-shaped and ring-shaped patterns arrays by Mie resonance sphere-lens-lithography

Science.gov (United States)

Liu, Xianchao; Wang, Jun; Li, Ling; Gou, Jun; Zheng, Jie; Huang, Zehua; Pan, Rui

2018-05-01

Mie resonance sphere-lens-lithography has proved to be a good candidate for fabrication of large-area tunable surface nanopattern arrays. Different patterns on photoresist surface are obtained theoretically by adjusting optical coupling among neighboring spheres with different gap sizes. The effect of light reflection from the substrate on the pattern produced on the photoresist with a thin thickness is also discussed. Sub-micron hexagonal star-shaped and ring-shaped patterns arrays are achieved with close-packed spheres arrays and spheres arrays with big gaps, respectively. Changing of star-shaped vertices is induced by different polarization of illumination. Experimental results agree well with the simulation. By using smaller resonance spheres, sub-400 nm star-shaped and ring-shaped patterns can be realized. These tunable patterns are different from results of previous reports and have enriched pattern morphology fabricated by sphere-lens-lithography, which can find application in biosensor and optic devices.

I-Love relations for incompressible stars and realistic stars

Science.gov (United States)

Chan, T. K.; Chan, AtMa P. O.; Leung, P. T.

2015-02-01

In spite of the diversity in the equations of state of nuclear matter, the recently discovered I-Love-Q relations [Yagi and Yunes, Science 341, 365 (2013), 10.1126/science.1236462], which relate the moment of inertia, tidal Love number (deformability), and the spin-induced quadrupole moment of compact stars, hold for various kinds of realistic neutron stars and quark stars. While the physical origin of such universality is still a current issue, the observation that the I-Love-Q relations of incompressible stars can well approximate those of realistic compact stars hints at a new direction to approach the problem. In this paper, by establishing recursive post-Minkowskian expansion for the moment of inertia and the tidal deformability of incompressible stars, we analytically derive the I-Love relation for incompressible stars and show that the so-obtained formula can be used to accurately predict the behavior of realistic compact stars from the Newtonian limit to the maximum mass limit.

Dynamic photonic lightpaths in the StarPlane network

NARCIS (Netherlands)

Grosso, P.; Marchal, D.; Maassen, J.; Bernier, E.; Xu, L.; de Laat, C.

2009-01-01

The StarPlane project enables users to dynamically control network photonic paths. Applications running on the Distributed ASCI Supercomputer (DAS-3) can manipulate wavelengths in the Dutch research and education network SURFnet6. The goal is to achieve fast switching times so that when the

Photometry of Southern Hemisphere red dwarf stars

Science.gov (United States)

Weistrop, D.

1980-01-01

Results are presented for a photometric investigation of a spectroscopically selected sample of red dwarf stars in the Southern Hemisphere. Absolute magnitudes and distances for the stars are estimated from broadband red colors. Three stars which may be subluminous are identified, as are several stars which may be within 25 pc. The tangential velocity and velocity dispersion of the sample are similar to values found in other studies of nearby late-type stars.

The Wolf-Rayet stars

International Nuclear Information System (INIS)

Cherepashchuk, A.M.; Khaliullin, K.F.

1983-01-01

One may say that the observational evidence now available for Wolf-Rayet stars, particularly the results gained by analyzing eclipsing binary systems prove that at least some of these objects are helium stars. At the same time, the low electron temperatures in the emission-line zones, the indisputable evidence of a highly extended atmosphere and the steady loss of material by these stars all strongly support the fluorescence model proposed by a previous study, whereby Wolf-Rayet envelopes would owe their luminosity to conversion of the short-wavelength radiation emitted by the hot stellar core

Entropy Production of Stars

Directory of Open Access Journals (Sweden)

Leonid M. Martyushev

2015-06-01

Full Text Available The entropy production (inside the volume bounded by a photosphere of main-sequence stars, subgiants, giants, and supergiants is calculated based on B–V photometry data. A non-linear inverse relationship of thermodynamic fluxes and forces as well as an almost constant specific (per volume entropy production of main-sequence stars (for 95% of stars, this quantity lies within 0.5 to 2.2 of the corresponding solar magnitude is found. The obtained results are discussed from the perspective of known extreme principles related to entropy production.

The Power of Stars Across Industries

DEFF Research Database (Denmark)

Hofmann, Julian; Clement, Michel; Hennig-Thurau, Thorsten

Stars as ‘human brands’ help consumers to assess the uncertain quality of experiential products and provide an important risk-reducing function. Nevertheless, managers of (fully integrated) media companies should be aware of potentially differences in the impact of stars across industries when...... making budget allocation decisions or deciding on the appropriate remuneration of stars. Based on a unique dataset the authors compare, for the first time, the impact of stars on product success across movies, books, and musical recordings. The results indicate significantly positive effects of star...... power in all three media industries but reveal substantial differences regarding the effect sizes....

Do All O Stars Form in Star Clusters?

Science.gov (United States)

Weidner, C.; Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

The question whether or not massive stars can form in isolation or only in star clusters is of great importance for the theory of (massive) star formation as well as for the stellar initial mass function of whole galaxies (IGIMF-theory). While a seemingly easy question it is rather difficult to answer. Several physical processes (e.g. star-loss due to stellar dynamics or gas expulsion) and observational limitations (e.g. dust obscuration of young clusters, resolution) pose severe challenges to answer this question. In this contribution we will present the current arguments in favour and against the idea that all O stars form in clusters.

MMT HYPERVELOCITY STAR SURVEY. II. FIVE NEW UNBOUND STARS

Energy Technology Data Exchange (ETDEWEB)

Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J., E-mail: wbrown@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)

2012-05-20

We present the discovery of five new unbound hypervelocity stars (HVSs) in the outer Milky Way halo. Using a conservative estimate of Galactic escape velocity, our targeted spectroscopic survey has now identified 16 unbound HVSs as well as a comparable number of HVSs ejected on bound trajectories. A Galactic center origin for the HVSs is supported by their unbound velocities, the observed number of unbound stars, their stellar nature, their ejection time distribution, and their Galactic latitude and longitude distribution. Other proposed origins for the unbound HVSs, such as runaway ejections from the disk or dwarf galaxy tidal debris, cannot be reconciled with the observations. An intriguing result is the spatial anisotropy of HVSs on the sky, which possibly reflects an anisotropic potential in the central 10-100 pc region of the Galaxy. Further progress requires measurement of the spatial distribution of HVSs over the southern sky. Our survey also identifies seven B supergiants associated with known star-forming galaxies; the absence of B supergiants elsewhere in the survey implies there are no new star-forming galaxies in our survey footprint to a depth of 1-2 Mpc.

Discovery of a New Nearby Star

Science.gov (United States)

Teegarden, B. J.; Pravdo, S. H.; Covey, K.; Frazier, O.; Hawley, S. L.; Hicks, M.; Lawrence, K.; McGlynn, T.; Reid, I. N.; Shaklan, S. B.

2003-01-01

We report the discovery of a nearby star with a very large proper motion of 5.06 +/- 0.03 arcsec/yr. The star is called SO025300.5+165258 and referred to herein as HPMS (high proper motion star). The discovery came as a result of a search of the SkyMorph database, a sensitive and persistent survey that is well suited for finding stars with high proper motions. There are currently only 7 known stars with proper motions greater than 5 arcsec/yr. We have determined a preliminary value for the parallax of pi = 0.43 +/- 0.13 arcsec. If this value holds our new star ranks behind only the Alpha Centauri system (including Proxima Centauri) and Barnard's star in the list of our nearest stellar neighbours. The spectrum and measured tangential velocity indicate that HPMS is a main-sequence star with spectral type M6.5. However, if our distance measurement is correct, the HPMS is underluminous by 1.2 +/- 0.7 mag.

Wolf-Rayet stars and galactic structure

International Nuclear Information System (INIS)

Stenholm, B.

1975-01-01

A 15 0 wide strip along the galactic equator between longitudes 250 0 and 360 0 has been searched for Wolf-Rayet stars. Six new WR stars and four new planetary nebulae have been found. Seven stars earlier listed as WR stars have been rejected as such. The new WR stars in the 'Luminous Stars in the Southern Milky Way' are discussed. A sample of 154 WR stars has been treated statistically. For the distribution in longitude, comparisons are made with OB stars and classical cepheids. The differences in distribution are thought to be an age effect. An effort to explain the empty interval towards the anticentre is made. The distribution in latitude is compared with young clusters and long-period cepheids. The physical plane formed by these objects is tilted about one degree to the galactic plane and the tilt is upwards in the Cygnus direction. This result is also received by a least squares solution of the objects when given in rectangular coordinates. The WR star sample is regarded as fairly complete up to a distance of 5 kpc. (orig.) [de

Magnetic fields in beta Cep, SPB, and Be stars

OpenAIRE

Schoeller, M.; Hubrig, S.; Briquet, M.; Ilyin, I.

2013-01-01

Recent observational and theoretical results emphasize the potential significance of magnetic fields for structure, evolution, and environment of massive stars. Depending on their spectral and photometric behavior, the upper main-sequence B-type stars are assigned to different groups, such as beta Cep stars and slowly pulsating B (SPB) stars, He-rich and He-deficient Bp stars, Be stars, BpSi stars, HgMn stars, or normal B-type stars. All these groups are characterized by different magnetic fi...

Giant CP stars

International Nuclear Information System (INIS)

Loden, L.O.; Sundman, A.

1989-01-01

This study is part of an investigation of the possibility of using chemically peculiar (CP) stars to map local galactic structure. Correct luminosities of these stars are therefore crucial. CP stars are generally regarded as main-sequence or near-main-sequence objects. However, some CP stars have been classified as giants. A selection of stars, classified in literature as CP giants, are compared to normal stars in the same effective temperature interval and to ordinary 'non giant' CP stars. There is no clear confirmation of a higher luminosity for 'CP giants', than for CP stars in general. In addition, CP characteristics seem to be individual properties not repeated in a component star or other cluster members. (author). 50 refs., 5 tabs., 3 figs

Bursting star formation and the overabundance of Wolf-Rayet stars

International Nuclear Information System (INIS)

Bodigfee, G.; Deloore, C.

1985-01-01

The ratio of the number of WR-stars to their OB progenitors appears to be significantly higher in some extragalactic systems than in our Galaxy. This overabundance of Wolf-Rayet-stars can be explained as a consequence of a recent burst of star formation. It is suggested that this burst is the manifestation of a long period nonlinear oscillation in the star formation process, produced by positive feedback effects between young stars and the interstellar medium. Star burst galaxies with large numbers of WR-stars must generate gamma fluxes but due to the distance, all of them are beyond the reach of present-day detectors, except probably 30 Dor

Instability and star evolution

International Nuclear Information System (INIS)

Mirzoyan, L.V.

1981-01-01

The observational data are discussed which testify that the phenomena of dynamical instability of stars and stellar systems are definite manifestations of their evolution. The study of these phenomena has shown that the instability is a regular phase of stellar evolution. It has resulted in the recognition of the most important regularities of the process of star formation concerning its nature. This became possible due to the discovery in 1947 of stellar associations in our Galaxy. The results of the study of the dynamical instability of stellar associations contradict the predictions of classical hypothesis of stellar condensation. These data supplied a basis for a new hypothesis on the formation of stars and nebulae by the decay of superdense protostars [ru

TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

Energy Technology Data Exchange (ETDEWEB)

Liu Tie; Wu Yuefang; Zhang Huawei [Department of Astronomy, Peking University, 100871 Beijing (China); Qin Shengli, E-mail: liutiepku@gmail.com [I. Physikalisches Institut, Universitaet zu Koeln, Zuelpicher Str. 77, 50937 Koeln (Germany)

2012-05-20

The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10{sup 3} cm{sup -3} and kinematic temperature {approx}20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

International Nuclear Information System (INIS)

Liu Tie; Wu Yuefang; Zhang Huawei; Qin Shengli

2012-01-01

The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10 3 cm –3 and kinematic temperature ∼20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

Mass-Radius diagram for compact stars

International Nuclear Information System (INIS)

Carvalho, G A; Jr, R M Marinho; Malheiro, M

2015-01-01

The compact stars represent the final stage in the evolution of ordinary stars, they are formed when a star ceases its nuclear fuel, in this point the process that sustain its stability will stop. After this, the internal pressure can no longer stand the gravitational force and the star colapses [2]. In this work we investigate the structure of these stars which are described by the equations of Tolman-Openheimer-Volkof (TOV) [1]. These equations show us how the pressure varies with the mass and radius of the star. We consider the TOV equations for both relativistic and non-relativistic cases. In the case of compact stars (white dwarfs and neutron stars) the internal pressure that balances the gravitational pressure is essentialy the pressure coming from the degeneracy of fermions. To have solved the TOV equations we need a equation of state that shows how this internal pressure is related to the energy density or mass density. Instead of using politropic equations of state we have solved the equations numericaly using the exact relativistic energy equation for the model of fermion gas at zero temperature. We obtain results for the mass-radius relation for white dwarfs and we compared with the results obtained using the politropic equations of state. In addition we discussed a good fit for the mass-radius relation. (paper)

IDENTIFYING BLUE HORIZONTAL BRANCH STARS USING THE z FILTER

International Nuclear Information System (INIS)

Vickers, John J.; Grebel, Eva K.; Huxor, Avon P.

2012-01-01

In this paper we present a new method for selecting blue horizontal branch (BHB) candidates based on color-color photometry. We make use of the Sloan Digital Sky Survey z band as a surface gravity indicator and show its value for selecting BHB stars from quasars, white dwarfs, and main-sequence A-type stars. Using the g, r, i, and z bands, we demonstrate that extraction accuracies on a par with more traditional u, g, and r photometric selection methods may be achieved. We also show that the completeness necessary to probe major Galactic structure may be maintained. Our new method allows us to efficiently select BHB stars from photometric sky surveys that do not include a u-band filter such as the Panoramic Survey Telescope and Rapid Response System.

What Have Researchers Learned from Project STAR?

Science.gov (United States)

Schanzenbach, Diane Whitmore

2007-01-01

Project STAR (Student/Teacher Achievement Ratio) was a large-scale randomized trial of reduced class sizes in kindergarten through the third grade. Because of the scope of the experiment, it has been used in many policy discussions. For example, the California statewide class-size-reduction policy was justified, in part, by the successes of…

Star Polymers.

Science.gov (United States)

Ren, Jing M; McKenzie, Thomas G; Fu, Qiang; Wong, Edgar H H; Xu, Jiangtao; An, Zesheng; Shanmugam, Sivaprakash; Davis, Thomas P; Boyer, Cyrille; Qiao, Greg G

2016-06-22

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

Relativistic model for anisotropic strange stars

Science.gov (United States)

Deb, Debabrata; Chowdhury, Sourav Roy; Ray, Saibal; Rahaman, Farook; Guha, B. K.

2017-12-01

In this article, we attempt to find a singularity free solution of Einstein's field equations for compact stellar objects, precisely strange (quark) stars, considering Schwarzschild metric as the exterior spacetime. To this end, we consider that the stellar object is spherically symmetric, static and anisotropic in nature and follows the density profile given by Mak and Harko (2002) , which satisfies all the physical conditions. To investigate different properties of the ultra-dense strange stars we have employed the MIT bag model for the quark matter. Our investigation displays an interesting feature that the anisotropy of compact stars increases with the radial coordinate and attains its maximum value at the surface which seems an inherent property for the singularity free anisotropic compact stellar objects. In this connection we also perform several tests for physical features of the proposed model and show that these are reasonably acceptable within certain range. Further, we find that the model is consistent with the energy conditions and the compact stellar structure is stable with the validity of the TOV equation and Herrera cracking concept. For the masses below the maximum mass point in mass vs radius curve the typical behavior achieved within the framework of general relativity. We have calculated the maximum mass and radius of the strange stars for the three finite values of bag constant Bg.

Wolf-Rayet stars

Energy Technology Data Exchange (ETDEWEB)

Sahade, J

1981-12-01

Aspects of the problems of the Wolf-Rayet stars related to their chemical composition, their evolutionary status, and their apparent dichotomy in two spectral sequences are discussed. Dogmas concerning WR stars are critically discussed, including the belief that WR stars lack hydrogen, that they are helium stars evolved from massive close binaries, and the existence of a second WR stage in which the star is a short-period single-lined binary. The relationship of WR stars with planetary nebulae is addressed, as is the membership of these stars in clusters and associations. The division of WR stars into WN and WC sequences is considered, questioning the reasonability of accounting for WR line formation in terms of abundance differences.

Global and photospheric physical parameters of active dwarf stars

International Nuclear Information System (INIS)

Pettersen, B.R.

1983-01-01

Physical parameters (temperature, luminosity, radius, mass and chemical abundance) of the photospheres of red dwarf flare stars and spotted stars are determined for quiescent conditions. The interrelations between these quantities are compared to the results of theoretical investigation for low mass stars. The evolutionary state of flare stars is discussed. Observational results from spectroscopic and photometric methods to determine the rotation of active dwarfs are reviewed. The possibilities of global oscillations in dwarf stars are considered and preliminary results of a photometric search for oscillation in red dwarf luminosities are presented. (orig.)

Empirical Bolometric Fluxes and Angular Diameters of 1.6 Million Tycho-2 Stars and Radii of 350,000 Stars with Gaia DR1 Parallaxes

Science.gov (United States)

Stevens, Daniel J.; Stassun, Keivan G.; Gaudi, B. Scott

2017-12-01

We present bolometric fluxes and angular diameters for over 1.6 million stars in the Tycho-2 catalog, determined using previously determined empirical color-temperature and color-flux relations. We vet these relations via full fits to the full broadband spectral energy distributions for a subset of benchmark stars and perform quality checks against the large set of stars for which spectroscopically determined parameters are available from LAMOST, RAVE, and/or APOGEE. We then estimate radii for the 355,502 Tycho-2 stars in our sample whose Gaia DR1 parallaxes are precise to ≲ 10 % . For these stars, we achieve effective temperature, bolometric flux, and angular diameter uncertainties of the order of 1%-2% and radius uncertainties of order 8%, and we explore the effect that imposing spectroscopic effective temperature priors has on these uncertainties. These stellar parameters are shown to be reliable for stars with {T}{eff} ≲ 7000 K. The over half a million bolometric fluxes and angular diameters presented here will serve as an immediate trove of empirical stellar radii with the Gaia second data release, at which point effective temperature uncertainties will dominate the radius uncertainties. Already, dwarf, subgiant, and giant populations are readily identifiable in our purely empirical luminosity-effective temperature (theoretical) Hertzsprung-Russell diagrams.

StarDOM: From STAR format to XML

International Nuclear Information System (INIS)

Linge, Jens P.; Nilges, Michael; Ehrlich, Lutz

1999-01-01

StarDOM is a software package for the representation of STAR files as document object models and the conversion of STAR files into XML. This allows interactive navigation by using the Document Object Model representation of the data as well as easy access by XML query languages. As an example application, the entire BioMagResBank has been transformed into XML format. Using an XML query language, statistical queries on the collected NMR data sets can be constructed with very little effort. The BioMagResBank/XML data and the software can be obtained at http://www.nmr.embl-heidelberg.de/nmr/StarDOM/

Stacked Star Formation Rate Profiles of Bursty Galaxies Exhibit “Coherent” Star Formation

Science.gov (United States)

Orr, Matthew E.; Hayward, Christopher C.; Nelson, Erica J.; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Kereš, Dušan; Chan, T. K.; Schmitz, Denise M.; Miller, Tim B.

2017-11-01

In a recent work based on 3200 stacked Hα maps of galaxies at z˜ 1, Nelson et al. find evidence for “coherent star formation”: the stacked star formation rate (SFR) profiles of galaxies above (below) the “star formation main sequence” (MS) are above (below) that of galaxies on the MS at all radii. One might interpret this result as inconsistent with highly bursty star formation and evidence that galaxies evolve smoothly along the MS rather than crossing it many times. We analyze six simulated galaxies at z˜ 1 from the Feedback in Realistic Environments (FIRE) project in a manner analogous to the observations to test whether the above interpretations are correct. The trends in stacked SFR profiles are qualitatively consistent with those observed. However, SFR profiles of individual galaxies are much more complex than the stacked profiles: the former can be flat or even peak at large radii because of the highly clustered nature of star formation in the simulations. Moreover, the SFR profiles of individual galaxies above (below) the MS are not systematically above (below) those of MS galaxies at all radii. We conclude that the time-averaged coherent star formation evident stacks of observed galaxies is consistent with highly bursty, clumpy star formation of individual galaxies and is not evidence that galaxies evolve smoothly along the MS.

STARS no star on Kauai

International Nuclear Information System (INIS)

Jones, M.

1993-01-01

The island of Kuai, home to the Pacific Missile Range Facility, is preparing for the first of a series of Star Wars rocket launches expected to begin early this year. The Strategic Defense Initiative plans 40 launches of the Stategic Target System (STARS) over a 10-year period. The focus of the tests appears to be weapons and sensors designed to combat multiple-warhead ICBMs, which will be banned under the START II Treaty that was signed in January. The focus of this article is to express the dubious value of testing the STARS at a time when their application will not be an anticipated problem

Ground vibration test results of a JetStar airplane using impulsive sine excitation

Science.gov (United States)

Kehoe, Michael W.; Voracek, David F.

1989-01-01

Structural excitation is important for both ground vibration and flight flutter testing. The structural responses caused by this excitation are analyzed to determine frequency, damping, and mode shape information. Many excitation waveforms have been used throughout the years. The use of impulsive sine (sin omega t)/omega t as an excitation waveform for ground vibration testing and the advantages of using this waveform for flight flutter testing are discussed. The ground vibration test results of a modified JetStar airplane using impulsive sine as an excitation waveform are compared with the test results of the same airplane using multiple-input random excitation. The results indicated that the structure was sufficiently excited using the impulsive sine waveform. Comparisons of input force spectrums, mode shape plots, and frequency and damping values for the two methods of excitation are presented.

OBSERVATIONAL CONSTRAINTS ON FIRST-STAR NUCLEOSYNTHESIS. I. EVIDENCE FOR MULTIPLE PROGENITORS OF CEMP-NO STARS

Energy Technology Data Exchange (ETDEWEB)

Yoon, Jinmi; Beers, Timothy C.; Placco, Vinicius M.; Rasmussen, Kaitlin C.; Carollo, Daniela [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); He, Siyu [Department of Physics, Xi’an Jiaotong University, Shaanxi, 710049 (China); Hansen, Terese T. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Roederer, Ian U. [Joint Institute for Nuclear Astrophysics-Center for the Evolution of the Elements (JINA-CEE) (United States); Zeanah, Jeff, E-mail: jinmi.yoon@nd.edu [Z Solutions, Inc., 9430 Huntcliff Trace, Atlanta, GA 30350 (United States)

2016-12-10

We investigate anew the distribution of absolute carbon abundance, A (C) = log ϵ (C), for carbon-enhanced metal-poor (CEMP) stars in the halo of the Milky Way, based on high-resolution spectroscopic data for a total sample of 305 CEMP stars. The sample includes 147 CEMP- s (and CEMP- r / s ) stars, 127 CEMP-no stars, and 31 CEMP stars that are unclassified, based on the currently employed [Ba/Fe] criterion. We confirm previous claims that the distribution of A (C) for CEMP stars is (at least) bimodal, with newly determined peaks centered on A (C) = 7.96 (the high-C region) and A (C) = 6.28 (the low-C region). A very high fraction of CEMP- s (and CEMP- r / s ) stars belongs to the high-C region, while the great majority of CEMP-no stars resides in the low-C region. However, there exists complexity in the morphology of the A (C)-[Fe/H] space for the CEMP-no stars, a first indication that more than one class of first-generation stellar progenitors may be required to account for their observed abundances. The two groups of CEMP-no stars we identify exhibit clearly different locations in the A (Na)- A (C) and A (Mg)- A (C) spaces, also suggesting multiple progenitors. The clear distinction in A (C) between the CEMP- s (and CEMP- r / s ) stars and the CEMP-no stars appears to be as successful, and likely more astrophysically fundamental, for the separation of these sub-classes as the previously recommended criterion based on [Ba/Fe] (and [Ba/Eu]) abundance ratios. This result opens the window for its application to present and future large-scale low- and medium-resolution spectroscopic surveys.

Moments of inertia of neutron stars

Energy Technology Data Exchange (ETDEWEB)

Greif, Svenja Kim; Hebeler, Kai; Schwenk, Achim [Institut fuer Kernphysik, Technische Universitaet Darmstadt (Germany); ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum fuer Schwerionenforschung GmbH (Germany)

2016-07-01

Neutron stars are unique laboratories for matter at extreme conditions. While nuclear forces provide systematic constraints on properties of neutron-rich matter up to around nuclear saturation density, the composition of matter at high densities is still unknown. Recent precise observations of 2 M {sub CircleDot} neutron stars made it possible to derive systematic constraints on the equation of state at high densities and also neutron star radii. Further improvements of these constraints require the observation of even heavier neutron stars or a simultaneous measurement of mass and radius of a single neutron star. Since the precise measurement of neutron star radii is an inherently difficult problem, the observation of moment of inertia of neutron stars provides a promising alternative, since they can be measured by pulsar timing experiments. We present a theoretical framework that allows to calculate moments of inertia microscopically, we show results based on state of the art equations of state and illustrate how future measurements of moments of inertia allow to constrain the equation of state and other properties of neutron stars.

Water in Star-forming Regions with Herschel (WISH): recent results and trends

Science.gov (United States)

van Dishoeck, E. F.

2012-03-01

Water is a key molecule in the physics and chemistry of star- and planet-forming regions. In the `Water in Star-forming Regions with Herschel' (WISH) Key Program, we have obtained a comprehensive set of water data toward a large sample of well-characterized protostars, covering a wide range of masses and luminosities --from the lowest to the highest mass protostars--, as well as evolutionary stages --from pre-stellar cores to disks. Lines of both ortho- and para-H_2O and their isotopologues, as well as chemically related hydrides, are observed with the HIFI and PACS instruments. The data elucidate the physical processes responsible for the warm gas, probe dynamical processes associated with forming stars and planets (outflow, infall, expansion), test basic chemical processes and reveal the chemical evolution of water and the oxygen-reservoir into planet-forming disks. In this brief talk a few recent WISH highlights will be presented, including determinations of the water abundance in each of the different physical components (inner and outer envelope, outflow) and constraints on the ortho/para ratio. Special attention will be given to trends found across the sample, especially the similarity in profiles from low to high-mass protostars and the evolution of the gas-phase water abundance from prestellar cores to disks. More details can be found at http://www.strw.leidenuniv.nl/WISH, whereas overviews are given in van Dishoeck et al. (2011, PASP 123, 138), Kristensen & van Dishoeck (2011, Astronomische Nachrichten 332, 475) and Bergin & van Dishoeck (2012, Phil. Trans. Royal Soc. A).

Dark stars in Starobinsky's model

Science.gov (United States)

Panotopoulos, Grigoris; Lopes, Ilídio

2018-01-01

In the present work we study non-rotating dark stars in f (R ) modified theory of gravity. In particular, we have considered bosonic self-interacting dark matter modeled inside the star as a Bose-Einstein condensate, while as far as the modified theory of gravity is concerned we have assumed Starobinsky's model R +a R2. We solve the generalized structure equations numerically, and we obtain the mass-to-ratio relation for several different values of the parameter a , and for two different dark matter equation-of-states. Our results show that the dark matter stars become more compact in the R-squared gravity compared to general relativity, while at the same time the highest star mass is slightly increased in the modified gravitational theory. The numerical value of the highest star mass for each case has been reported.

Delta isobars in neutron stars

Directory of Open Access Journals (Sweden)

Pagliara Giuseppe

2015-01-01

Full Text Available The appearance of delta isobars in beta-stable matter is regulated by the behavior of the symmetry energy at densities larger than saturation density. We show that by taking into account recent constraints on the density derivative of the symmetry energy and the theoretical and experimental results on the excitations of delta isobars in nuclei, delta isobars are necessary ingredients for the equations of state used for studying neutron stars. We analyze the effect of the appearance of deltas on the structure of neutron stars: as in the case of hyperons, matter containing delta is too soft for allowing the existence of 2M⊙ neutron stars. Quark stars on the other hand, could reach very massive configurations and they could form from a process of conversion of hadronic stars in which an initial seed of strangeness appears through hyperons.

Numerical evidence for 'multiscalar stars'

International Nuclear Information System (INIS)

Hawley, Scott H.; Choptuik, Matthew W.

2003-01-01

We present a class of general relativistic solitonlike solutions composed of multiple minimally coupled, massive, real scalar fields which interact only through the gravitational field. We describe a two-parameter family of solutions we call ''phase-shifted boson stars'' (parametrized by central density ρ 0 and phase δ), which are obtained by solving the ordinary differential equations associated with boson stars and then altering the phase between the real and imaginary parts of the field. These solutions are similar to boson stars as well as the oscillating soliton stars found by Seidel and Suen [E. Seidel and W. M. Suen, Phys. Rev. Lett. 66, 1659 (1991)]; in particular, long-time numerical evolutions suggest that phase-shifted boson stars are stable. Our results indicate that scalar solitonlike solutions are perhaps more generic than has been previously thought

RADIAL VELOCITY MONITORING OF KEPLER HEARTBEAT STARS

Energy Technology Data Exchange (ETDEWEB)

Shporer, Avi [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Fuller, Jim [TAPIR, Walter Burke Institute for Theoretical Physics, Mailcode 350-17, Caltech, Pasadena, CA 91125 (United States); Isaacson, Howard [Department of Astronomy, University of California, Berkeley CA 94720 (United States); Hambleton, Kelly; Prša, Andrej [Department of Astrophysics and Planetary Science, Villanova University, 800 East Lancaster Avenue, Villanova, PA 19085 (United States); Thompson, Susan E. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Kurtz, Donald W. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE (United Kingdom); Howard, Andrew W. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); O’Leary, Ryan M. [JILA, University of Colorado and NIST, 440 UCB, Boulder, 80309-0440 (United States)

2016-09-20

Heartbeat stars (HB stars) are a class of eccentric binary stars with close periastron passages. The characteristic photometric HB signal evident in their light curves is produced by a combination of tidal distortion, heating, and Doppler boosting near orbital periastron. Many HB stars continue to oscillate after periastron and along the entire orbit, indicative of the tidal excitation of oscillation modes within one or both stars. These systems are among the most eccentric binaries known, and they constitute astrophysical laboratories for the study of tidal effects. We have undertaken a radial velocity (RV) monitoring campaign of Kepler HB stars in order to measure their orbits. We present our first results here, including a sample of 22 Kepler HB systems, where for 19 of them we obtained the Keplerian orbit and for 3 other systems we did not detect a statistically significant RV variability. Results presented here are based on 218 spectra obtained with the Keck/HIRES spectrograph during the 2015 Kepler observing season, and they have allowed us to obtain the largest sample of HB stars with orbits measured using a single instrument, which roughly doubles the number of HB stars with an RV measured orbit. The 19 systems measured here have orbital periods from 7 to 90 days and eccentricities from 0.2 to 0.9. We show that HB stars draw the upper envelope of the eccentricity–period distribution. Therefore, HB stars likely represent a population of stars currently undergoing high eccentricity migration via tidal orbital circularization, and they will allow for new tests of high eccentricity migration theories.

RADIAL VELOCITY MONITORING OF KEPLER HEARTBEAT STARS

International Nuclear Information System (INIS)

Shporer, Avi; Fuller, Jim; Isaacson, Howard; Hambleton, Kelly; Prša, Andrej; Thompson, Susan E.; Kurtz, Donald W.; Howard, Andrew W.; O’Leary, Ryan M.

2016-01-01

Heartbeat stars (HB stars) are a class of eccentric binary stars with close periastron passages. The characteristic photometric HB signal evident in their light curves is produced by a combination of tidal distortion, heating, and Doppler boosting near orbital periastron. Many HB stars continue to oscillate after periastron and along the entire orbit, indicative of the tidal excitation of oscillation modes within one or both stars. These systems are among the most eccentric binaries known, and they constitute astrophysical laboratories for the study of tidal effects. We have undertaken a radial velocity (RV) monitoring campaign of Kepler HB stars in order to measure their orbits. We present our first results here, including a sample of 22 Kepler HB systems, where for 19 of them we obtained the Keplerian orbit and for 3 other systems we did not detect a statistically significant RV variability. Results presented here are based on 218 spectra obtained with the Keck/HIRES spectrograph during the 2015 Kepler observing season, and they have allowed us to obtain the largest sample of HB stars with orbits measured using a single instrument, which roughly doubles the number of HB stars with an RV measured orbit. The 19 systems measured here have orbital periods from 7 to 90 days and eccentricities from 0.2 to 0.9. We show that HB stars draw the upper envelope of the eccentricity–period distribution. Therefore, HB stars likely represent a population of stars currently undergoing high eccentricity migration via tidal orbital circularization, and they will allow for new tests of high eccentricity migration theories.

THE CLASSIFICATION OF KEPLER B-STAR VARIABLES

International Nuclear Information System (INIS)

McNamara, Bernard J.; Jackiewicz, Jason; McKeever, Jean

2012-01-01

The light curves of 252 B-star candidates in the Kepler database are analyzed in a similar fashion to that done by Balona et al. to further characterize B-star variability, increase the sample of variable B stars for future study, and to identify stars whose power spectra include particularly interesting features such as frequency groupings. Stars are classified as either constant light emitters, β Cep stars, slowly pulsating B stars (SPBs), hybrid pulsators, binaries or stars whose light curves are dominated by rotation (Bin/Rot), hot subdwarfs, or white dwarfs. One-hundred stars in our sample were found to be either light constants or to be variable at a level of less than 0.02 mmag. We increase the number of candidate B-star variables found in the Kepler database by Balona et al. in the following fashion: β Cep stars from 0 to 10, SPBs from eight to 54, hybrid pulsators from seven to 21, and Bin/Rot stars from 23 to 82. For comparison purposes, approximately 51 SPBs and six hybrids had been known prior to 2007. The number of β Cep stars known prior to 2004 was 93. A secondary result of this study is the identification of an additional 11 pulsating white dwarf candidates, four of which possess frequency groupings.

Preliminary results of variable star search using KMTNet data

Directory of Open Access Journals (Sweden)

Jeon Young-Beom

2017-01-01

Full Text Available The KMTNet (Korea Microlensing Telescope Network was completed on October 2nd in 2015. There are three 1.6 m telescopes in Chile (CTIO, Australia (SSO and South Africa (SAAO. The field of view of the CCD camera is 2 degree × 2 degree. We are monitoring and observing the bulge region for 24-hour continuous observations using the KMTNet telescopes. I present the characteristics of CCD camera and telescope, and the status of observation programs. We are still developing CCD cameras to accurate photometry. From the KMTNet data, we can obtain accurate 24-hour continuous time-series data for many variable stars.

Assessment of antimycotoxigenic and antioxidant activity of star anise (Illicium verum in vitro

Directory of Open Access Journals (Sweden)

Soher E. Aly

2016-01-01

Full Text Available In recent years scientists have focused on the identification and the application of natural products for inactivation of mycotoxins. Essential oils with antimicrobial properties are probably the most promising method for the prevention of potentially toxigenic fungi. Thus the aim of this work is to characterise star anise (Illicium verum and to assess its antioxidant and antifungal and antimycotoxigenic properties using different methods. Results revealed that the major components of star anise essential oil identified by GC/MS were trans-anethole (82.7%, carryophyllene (4.8% and limonene (2.3%. Total phenolics of ethanol and methanol extracts recorded 112.4 and 96.3 mg GAE/g DW respectively, whereas higher total flavonoid content was recorded for the ethanol extract than the methanol extract. Star anise essential oil showed lower antioxidant activity (55.6 mg/mL than the extracts using DPPH-scavenging and β-carotene/linoleic acid assays. Results revealed growth reduction of Aspergillus flavus, Aspergillus parasiticus and Fusarium verticillioides by 83.2%, 72.8% and 65.11%, respectively when using 100 ppm of the star anise essential oil, where a complete inhibition was achieved at 200 ppm for A. flavus and A. parasiticus respectively. Aflatoxin B1 and Fumonisin B1 production were inhibited completely at 100 and 200 ppm respectively. It could be concluded that star anise extracts could be considered an important substance that should be explored for the discovery and development of newer and safer food supplements as well as drug products.

Spectroscopic survey of Kepler stars - II. FIES/NOT observations of A- and F-type stars

DEFF Research Database (Denmark)

Niemczura, E.; Polinska, M.; Murphy, S. J.

2017-01-01

to derive effective temperatures, surface gravities and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. Effective temperatures calculated by spectral energy distribution fitting are in good agreement with those determined...... obtained are typical for stars in the observed temperature and surface gravity ranges. Moreover, we affirm the results of Niemczura et al. that Am stars do not have systematically higher microturbulent velocities than normal stars of the same temperature....

StarLogo TNG

Science.gov (United States)

Klopfer, Eric; Scheintaub, Hal; Huang, Wendy; Wendel, Daniel

Computational approaches to science are radically altering the nature of scientific investigatiogn. Yet these computer programs and simulations are sparsely used in science education, and when they are used, they are typically “canned” simulations which are black boxes to students. StarLogo The Next Generation (TNG) was developed to make programming of simulations more accessible for students and teachers. StarLogo TNG builds on the StarLogo tradition of agent-based modeling for students and teachers, with the added features of a graphical programming environment and a three-dimensional (3D) world. The graphical programming environment reduces the learning curve of programming, especially syntax. The 3D graphics make for a more immersive and engaging experience for students, including making it easy to design and program their own video games. Another change to StarLogo TNG is a fundamental restructuring of the virtual machine to make it more transparent. As a result of these changes, classroom use of TNG is expanding to new areas. This chapter is concluded with a description of field tests conducted in middle and high school science classes.

Artificial guide stars for adaptive optics using unmanned aerial vehicles

Science.gov (United States)

Basden, A. G.; Brown, Anthony M.; Chadwick, P. M.; Clark, P.; Massey, R.

2018-06-01

Astronomical adaptive optics (AO) systems are used to increase effective telescope resolution. However, they cannot be used to observe the whole sky since one or more natural guide stars of sufficient brightness must be found within the telescope field of view for the AO system to work. Even when laser guide stars are used, natural guide stars are still required to provide a constant position reference. Here, we introduce a technique to overcome this problem by using rotary unmanned aerial vehicles (UAVs) as a platform from which to produce artificial guide stars. We describe the concept that relies on the UAV being able to measure its precise relative position. We investigate the AO performance improvements that can be achieved, which in the cases presented here can improve the Strehl ratio by a factor of at least 2 for a 8 m class telescope. We also discuss improvements to this technique, which is relevant to both astronomical and solar AO systems.

StarClose Vascular Closure Device: Prospective Study on 222 Deployments in an Interventional Radiology Practice

International Nuclear Information System (INIS)

Imam, Atique; Carter, Ranjana M. S.; Phillips-Hughes, Jane; Boardman, Philip; Uberoi, Raman

2007-01-01

The StarClose device (Abbott Vascular Devices; Abbott Laboratories, Redwood City, CA) utilizes an externally placed Nitinol clip to achieve arterial closure following femoral artery puncture. The objectives of this study were to assess the efficacy and complications of the StarClose device in patients undergoing interventional radiological procedures. Preprocedural clotting status, pulse and blood pressure, severity of vessel calcification, sheath size, and time to deployment were recorded. Postdeployment complications immediately postprocedure, at 1 h, at 2 h, and at 1 week were recorded. A duplex scan was performed in the first 10 patients to assess any immediate vascular complications. Deployments were successful in 96% achieving immediate hemostasis. Mean deployment time was 48 s. There were no major complications. The StarClose device was found to have a high technical and clinical efficacy

A design of calibration single star simulator with adjustable magnitude and optical spectrum output system

Science.gov (United States)

Hu, Guansheng; Zhang, Tao; Zhang, Xuan; Shi, Gentai; Bai, Haojie

2018-03-01

In order to achieve multi-color temperature and multi-magnitude output, magnitude and temperature can real-time adjust, a new type of calibration single star simulator was designed with adjustable magnitude and optical spectrum output in this article. xenon lamp and halogen tungsten lamp were used as light source. The control of spectrum band and temperature of star was realized with different multi-beam narrow band spectrum with light of varying intensity. When light source with different spectral characteristics and color temperature go into the magnitude regulator, the light energy attenuation were under control by adjusting the light luminosity. This method can completely satisfy the requirements of calibration single star simulator with adjustable magnitude and optical spectrum output in order to achieve the adjustable purpose of magnitude and spectrum.

Tidal Love Numbers of Neutron Stars

International Nuclear Information System (INIS)

Hinderer, Tanja

2008-01-01

For a variety of fully relativistic polytropic neutron star models we calculate the star's tidal Love number k 2 . Most realistic equations of state for neutron stars can be approximated as a polytrope with an effective index n ∼ 0.5-1.0. The equilibrium stellar model is obtained by numerical integration of the Tolman-Oppenheimer-Volkhov equations. We calculate the linear l = 2 static perturbations to the Schwarzschild spacetime following the method of Thorne and Campolattaro. Combining the perturbed Einstein equations into a single second-order differential equation for the perturbation to the metric coefficient g tt and matching the exterior solution to the asymptotic expansion of the metric in the star's local asymptotic rest frame gives the Love number. Our results agree well with the Newtonian results in the weak field limit. The fully relativistic values differ from the Newtonian values by up to ∼24%. The Love number is potentially measurable in gravitational wave signals from inspiralling binary neutron stars.

Achieving High Reliability with People, Processes, and Technology.

Science.gov (United States)

Saunders, Candice L; Brennan, John A

2017-01-01

High reliability as a corporate value in healthcare can be achieved by meeting the "Quadruple Aim" of improving population health, reducing per capita costs, enhancing the patient experience, and improving provider wellness. This drive starts with the board of trustees, CEO, and other senior leaders who ingrain high reliability throughout the organization. At WellStar Health System, the board developed an ambitious goal to become a top-decile health system in safety and quality metrics. To achieve this goal, WellStar has embarked on a journey toward high reliability and has committed to Lean management practices consistent with the Institute for Healthcare Improvement's definition of a high-reliability organization (HRO): one that is committed to the prevention of failure, early identification and mitigation of failure, and redesign of processes based on identifiable failures. In the end, a successful HRO can provide safe, effective, patient- and family-centered, timely, efficient, and equitable care through a convergence of people, processes, and technology.

Rotating Quark Stars in General Relativity

Directory of Open Access Journals (Sweden)

Enping Zhou

2018-03-01

Full Text Available We have built quasi-equilibrium models for uniformly rotating quark stars in general relativity. The conformal flatness approximation is employed and the Compact Object CALculator (cocal code is extended to treat rotating stars with surface density discontinuity. In addition to the widely used MIT bag model, we have considered a strangeon star equation of state (EoS, suggested by Lai and Xu, that is based on quark clustering and results in a stiff EoS. We have investigated the maximum mass of uniformly rotating axisymmetric quark stars. We have also built triaxially deformed solutions for extremely fast rotating quark stars and studied the possible gravitational wave emission from such configurations.

Gravitational waves from remnant massive neutron stars of binary neutron star merger: Viscous hydrodynamics effects

Science.gov (United States)

Shibata, Masaru; Kiuchi, Kenta

2017-06-01

Employing a simplified version of the Israel-Stewart formalism of general-relativistic shear-viscous hydrodynamics, we explore the evolution of a remnant massive neutron star of binary neutron star merger and pay special attention to the resulting gravitational waveforms. We find that for the plausible values of the so-called viscous alpha parameter of the order 10-2 the degree of the differential rotation in the remnant massive neutron star is significantly reduced in the viscous time scale, ≲5 ms . Associated with this, the degree of nonaxisymmetric deformation is also reduced quickly, and as a consequence, the amplitude of quasiperiodic gravitational waves emitted also decays in the viscous time scale. Our results indicate that for modeling the evolution of the merger remnants of binary neutron stars we would have to take into account magnetohydrodynamics effects, which in nature could provide the viscous effects.

Calendar Year 2009 Program Benefits for ENERGY STAR Labeled Products

Energy Technology Data Exchange (ETDEWEB)

Homan, Gregory K; Sanchez, Marla C.; Brown, Richard E.

2010-11-15

ENERGY STAR is a voluntary energy efficiency labeling program operated jointly by the Environmental Protection Agency (US EPA) and the U.S. Department of Energy (US DOE), designed to identify and promote energy-efficient products, buildings and practices. Since the program inception in 1992, ENERGY STAR has become a leading international brand for energy efficient products, and currently labels more than thirty products, spanning office equipment, heating, cooling and ventilation equipment, commercial and residential lighting, home electronics, and major appliances. ENERGY STAR's central role in the development of regional, national and international energy programs necessitates an open process whereby its program achievements to date as well as projected future savings are shared with stakeholders. This report presents savings estimates from the use ENERGY STAR labeled products. We present estimates of energy, dollar, and carbon savings achieved by the program in the year 2009, annual forecasts for 2010 and 2011, and cumulative savings estimates for the period 1993 through 2009 and cumulative forecasts for the period 2010 through 2015. Through 2009 the program saved 9.5 Quads of primary energy and avoided the equivalent of 170 million metric tons carbon (MMTC). The forecast for the period 2009-2015 is 11.5 Quads or primary energy saved and 202 MMTC emissions avoided. The sensitivity analysis bounds the best estimate of carbon avoided between 110 MMTC and 231 MMTC (1993 to 2009) and between 130 MMTC and 285 MMTC (2010 to 2015).

Flare stars in Pleiades. 5

International Nuclear Information System (INIS)

Mirzoyan, L.V.; Chavushyan, O.S.; Erastova, L.K.; Oganyan, G.B.; Melikyan, N.D.; Natsvlishvili, R.Sh.; Tsvetkov, M.K.

1977-01-01

The results of photographic observations of stellar flares in the Pleiades region made in the Byurakan and Abastumany astrophysical observatories in 1973-1974 are presented. The observations and revisions of the pictures taken earlier helped to detect 20 new flare stars and 62 repeated flares of flare stars known before. Two-colour photographic and UV observation of 21 flares were carried out. The observation data point to considerable differences in the mean frequency of flares of various flare stars in the Pleiades

Monitoring pulsating giant stars in M33: star formation history and chemical enrichment

Science.gov (United States)

Javadi, A.; van Loon, J. Th

2017-06-01

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). A new method has been developed by us to use pulsating giant stars to reconstruct the star formation history of galaxies over cosmological time as well as using them to map the dust production across their host galaxies. In first Instance the central square kiloparsec of M33 was monitored and long period variable stars (LPVs) were identified. We give evidence of two epochs of a star formation rate enhanced by a factor of a few. These stars are also important dust factories, we measure their dust production rates from a combination of our data with Spitzer Space Telescope mid-IR photometry. Then the monitoring survey was expanded to cover a much larger part of M33 including spiral arms. Here we present our methodology and describe results for the central square kiloparsec of M33 [1-4] and disc of M33 [5-8].

Monitoring pulsating giant stars in M33: star formation history and chemical enrichment

International Nuclear Information System (INIS)

Javadi, A; Van Loon, J Th

2017-01-01

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). A new method has been developed by us to use pulsating giant stars to reconstruct the star formation history of galaxies over cosmological time as well as using them to map the dust production across their host galaxies. In first Instance the central square kiloparsec of M33 was monitored and long period variable stars (LPVs) were identified. We give evidence of two epochs of a star formation rate enhanced by a factor of a few. These stars are also important dust factories, we measure their dust production rates from a combination of our data with Spitzer Space Telescope mid-IR photometry. Then the monitoring survey was expanded to cover a much larger part of M33 including spiral arms. Here we present our methodology and describe results for the central square kiloparsec of M33 [1–4] and disc of M33 [5–8]. (paper)

BPS Skyrmions as neutron stars

Energy Technology Data Exchange (ETDEWEB)

Adam, C., E-mail: adam@fpaxp1.usc.es [Departamento de Física de Partículas, Universidad de Santiago de Compostela and Instituto Galego de Física de Altas Enerxias (IGFAE), E-15782 Santiago de Compostela (Spain); Naya, C.; Sanchez-Guillen, J.; Vazquez, R. [Departamento de Física de Partículas, Universidad de Santiago de Compostela and Instituto Galego de Física de Altas Enerxias (IGFAE), E-15782 Santiago de Compostela (Spain); Wereszczynski, A. [Institute of Physics, Jagiellonian University, Reymonta 4, Kraków (Poland)

2015-03-06

The BPS Skyrme model has been demonstrated already to provide a physically intriguing and quantitatively reliable description of nuclear matter. Indeed, the model has both the symmetries and the energy–momentum tensor of a perfect fluid, and thus represents a field theoretic realization of the “liquid droplet” model of nuclear matter. In addition, the classical soliton solutions together with some obvious corrections (spin–isospin quantization, Coulomb energy, proton-neutron mass difference) provide an accurate modeling of nuclear binding energies for heavier nuclei. These results lead to the rather natural proposal to try to describe also neutron stars by the BPS Skyrme model coupled to gravity. We find that the resulting self-gravitating BPS Skyrmions provide excellent results as well as some new perspectives for the description of bulk properties of neutron stars when the parameter values of the model are extracted from nuclear physics. Specifically, the maximum possible mass of a neutron star before black-hole formation sets in is a few solar masses, the precise value of which depends on the precise values of the model parameters, and the resulting neutron star radius is of the order of 10 km.

Imaging Variable Stars with HST

Science.gov (United States)

Karovska, M.

2012-06-01

(Abstract only) The Hubble Space Telescope (HST) observations of astronomical sources, ranging from objects in our solar system to objects in the early Universe, have revolutionized our knowledge of the Universe its origins and contents. I highlight results from HST observations of variable stars obtained during the past twenty or so years. Multiwavelength observations of numerous variable stars and stellar systems were obtained using the superb HST imaging capabilities and its unprecedented angular resolution, especially in the UV and optical. The HST provided the first detailed images probing the structure of variable stars including their atmospheres and circumstellar environments. AAVSO observations and light curves have been critical for scheduling of many of these observations and provided important information and context for understanding of the imaging results of many variable sources. I describe the scientific results from the imaging observations of variable stars including AGBs, Miras, Cepheids, semiregular variables (including supergiants and giants), YSOs and interacting stellar systems with a variable stellar components. These results have led to an unprecedented understanding of the spatial and temporal characteristics of these objects and their place in the stellar evolutionary chains, and in the larger context of the dynamic evolving Universe.

VARIABILITY AND STAR FORMATION IN LEO T, THE LOWEST LUMINOSITY STAR-FORMING GALAXY KNOWN TODAY

Energy Technology Data Exchange (ETDEWEB)

Clementini, Gisella; Cignoni, Michele; Ramos, Rodrigo Contreras; Federici, Luciana; Tosi, Monica [INAF, Osservatorio Astronomico di Bologna, I-40127 Bologna (Italy); Ripepi, Vincenzo; Marconi, Marcella; Musella, Ilaria, E-mail: gisella.clementini@oabo.inaf.it, E-mail: rodrigo.contreras@oabo.inaf.it, E-mail: luciana.federici@oabo.inaf.it, E-mail: monica.tosi@oabo.inaf.it, E-mail: michele.cignoni@unibo.it, E-mail: ripepi@na.astro.it, E-mail: marcella@na.astro.it, E-mail: ilaria@na.astro.it [INAF, Osservatorio Astronomico di Capodimonte, I-80131 Napoli (Italy)

2012-09-10

We present results from the first combined study of variable stars and star formation history (SFH) of the Milky Way 'ultra-faint' dwarf (UFD) galaxy Leo T, based on F606W and F814W multi-epoch archive observations obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We have detected 14 variable stars in the galaxy. They include one fundamental-mode RR Lyrae star and 11 Anomalous Cepheids with periods shorter than 1 day, thus suggesting the occurrence of multiple star formation episodes in this UFD, of which one about 10 Gyr ago produced the RR Lyrae star. A new estimate of the distance to Leo T of 409{sup +29}{sub -27} kpc (distance modulus of 23.06 {+-} 0.15 mag) was derived from the galaxy's RR Lyrae star. Our V, V - I color-magnitude diagram (CMD) of Leo T reaches V {approx} 29 mag and shows features typical of a galaxy in transition between dwarf irregular and dwarf spheroidal types. A quantitative analysis of the SFH, based on the comparison of the observed V, V - I CMD with the expected distribution of stars for different evolutionary scenarios, confirms that Leo T has a complex SFH dominated by two enhanced periods about 1.5 and 9 Gyr ago, respectively. The distribution of stars and gas shows that the galaxy has a fairly asymmetric structure.

DARK STARS: A NEW LOOK AT THE FIRST STARS IN THE UNIVERSE

International Nuclear Information System (INIS)

Spolyar, Douglas; Bodenheimer, Peter; Freese, Katherine; Gondolo, Paolo

2009-01-01

We have proposed that the first phase of stellar evolution in the history of the universe may be dark (matter powered) stars (DSs), luminous objects powered by dark matter (DM) heating rather than by nuclear fusion, and in this paper we examine the history of these DSs. The power source is annihilation of weakly interacting massive particles (WIMPs) which are their own antiparticles. These WIMPs are the best motivated DM candidates and may be discovered by ongoing direct or indirect detection searches (e.g., Fermi/GLAST) or at the Large Hadron Collider at CERN. A new stellar phase results, powered by DM annihilation as long as there is a DM fuel, from millions to billions of years. We build up the DSs from the time DM heating becomes the dominant power source, accreting more and more matter onto them. We have included many new effects in the current study, including a variety of particle masses and accretion rates, nuclear burning, feedback mechanisms, and possible repopulation of DM density due to capture. Remarkably, we find that in all these cases, we obtain the same result: the first stars are very large, 500-1000 times as massive as the Sun; as well as puffy (radii 1-10 AU), bright (10 6 -10 7 L sun ), and cool (T surf sun and the temperatures are much hotter (T surf > 50,000 K). Hence DSs should be observationally distinct from standard Pop III stars. In addition, DSs avoid the (unobserved) element enrichment produced by the standard first stars. Once the DM fuel is exhausted, the DS becomes a heavy main-sequence star; these stars eventually collapse to form massive black holes that may provide seeds for the supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate-mass black holes.

Capabilities of a Laser Guide Star for a Large Segmented Space Telescope

Science.gov (United States)

Clark, James R.; Carlton, Ashley; Douglas, Ewan S.; Males, Jared R.; Lumbres, Jennifer; Feinberg, Lee; Guyon, Olivier; Marlow, Weston; Cahoy, Kerri L.

2018-01-01

Large segmented mirror telescopes are planned for future space telescope missions such as LUVOIR (Large UV Optical Infrared Surveyor) to enable the improvement in resolution and contrast necessary to directly image Earth-like exoplanets, in addition to making contributions to general astrophysics. The precision surface control of these complex, large optical systems, which may have over a hundred meter-sized segments, is a challenge. Our initial simulations show that imaging a star of 2nd magnitude or brighter with a Zernike wavefront sensor should relax the segment stability requirements by factors between 10 and 50 depending on the wavefront control strategy. Fewer than fifty stars brighter than magnitude 2 can be found in the sky. A laser guide star (LGS) on a companion spacecraft will allow the telescope to target a dimmer science star and achieve wavefront control to the required stability without requiring slew or repointing maneuvers.We present initial results for one possible mission architecture, with a LGS flying at 100,000 km range from the large telescope in an L2 halo orbit, using a laser transmit power of 8 days) for an expenditure of system, it can be accommodated in a 6U CubeSat bus, but may require an extended period of time to transition between targets and match velocities with the telescope (e.g. 6 days to transit 10 degrees). If the LGS uses monopropellant propulsion, it must use at least a 27U bus to achieve the the same delta-V capability, but can transition between targets much more rapidly (flight are being refined. A low-cost prototype mission (e.g. between a small satellite in LEO and an LGS in GEO) to validate the feasibility is in development.

Flare stars in Pleiades. 6

International Nuclear Information System (INIS)

Mirzoyan, L.V.; Chavushyan, O.S.; Oganyan, G.B.; Ambaryan, V.V.; Garibdzhanyan, A.T.; Melikyan, N.D.; Natsvlishvili, R.Sh.; AN Gruzinskoj SSR, Abastumani. Abastumanskaya Astrofizicheskaya Observatoriya)

1981-01-01

The results of photographic observations of stellar flares in the Pleiades region carried out at the Byurakan and Abastumani astrophysical observatories during 1976-1979 are given. On the basis of these observations 17 new flare stars have been found. Total number of all known flare stars in the Pleiades region on 1 June 1980 reached 524, and the number of all flares-1244. The observational data on distribution of flare stars according to the observed flares is satisfactorily represented by the average frequency function introduced by V.A.Ambartsumian. The total number of the flare stars in the Pleiades is of the order of 1100. Using three telescopes, synchronous photographic observations of stellar flares in Pleiades in U, B, V, system are carried out. The colour indices U-B and B-V of stellar flares in periods including the maximum of the flare slightly differ from that of photoelectrically defined for flares of UV Ceti type stars, which testifies the physical relationship of flare stars in Pleiades and in the vicinity of the Sun [ru

Neutron-Star Radius from a Population of Binary Neutron Star Mergers.

Science.gov (United States)

Bose, Sukanta; Chakravarti, Kabir; Rezzolla, Luciano; Sathyaprakash, B S; Takami, Kentaro

2018-01-19

We show how gravitational-wave observations with advanced detectors of tens to several tens of neutron-star binaries can measure the neutron-star radius with an accuracy of several to a few percent, for mass and spatial distributions that are realistic, and with none of the sources located within 100 Mpc. We achieve such an accuracy by combining measurements of the total mass from the inspiral phase with those of the compactness from the postmerger oscillation frequencies. For estimating the measurement errors of these frequencies, we utilize analytical fits to postmerger numerical relativity waveforms in the time domain, obtained here for the first time, for four nuclear-physics equations of state and a couple of values for the mass. We further exploit quasiuniversal relations to derive errors in compactness from those frequencies. Measuring the average radius to well within 10% is possible for a sample of 100 binaries distributed uniformly in volume between 100 and 300 Mpc, so long as the equation of state is not too soft or the binaries are not too heavy. We also give error estimates for the Einstein Telescope.

First results of Chinese particle instruments in the Double Star Program

Directory of Open Access Journals (Sweden)

J. B. Cao

2005-11-01

Full Text Available Double Star Program (DSP aims to investigate the trigger mechanism and physical models of geomagnetic storms and substorms. The DSP involves two satellites: the equatorial satellite of DSP (TC-1 in China and the polar satellite of DSP (TC-2 in China. On board the two satellites of TC-1 and TC-2, there are four kinds of particle instruments developed by the Center for Space Science and Applied Research (CSSAR, namely: the High Energy Electron Detector (HEED, TC-1, 2, the High Energy Proton Detector (HEPD, TC-1, 2, the High Energy Heavy Ion Detector (HID, TC-1, 2 and the Low Energy Ion Detector (LEID, TC-2. HEED, HEPD and HID were developed and calibrated in China. The LEID was developed in China and calibrated in France. This paper introduces the scientific objectives and characteristics of each instrument, their status and some preliminary results.

2004 status report: Savings estimates for the Energy Star(R)voluntarylabeling program

Energy Technology Data Exchange (ETDEWEB)

Webber, Carrie A.; Brown, Richard E.; McWhinney, Marla

2004-03-09

ENERGY STAR(R) is a voluntary labeling program designed toidentify and promote energy-efficient products, buildings and practices.Operated jointly by the Environmental Protection Agency (EPA) and theU.S. Department of Energy (DOE), ENERGY STAR labels exist for more thanthirty products, spanning office equipment, residential heating andcooling equipment, commercial and residential lighting, home electronics,and major appliances. This report presents savings estimates for a subsetof ENERGY STAR labeled products. We present estimates of the energy,dollar and carbon savings achieved by the program in the year 2003, whatwe expect in 2004, and provide savings forecasts for two marketpenetration scenarios for the periods 2004 to 2010 and 2004 to 2020. Thetarget market penetration forecast represents our best estimate of futureENERGY STAR savings. It is based on realistic market penetration goalsfor each of the products. We also provide a forecast under the assumptionof 100 percent market penetration; that is, we assume that all purchasersbuy ENERGY STAR-compliant products instead of standard efficiencyproducts throughout the analysis period.

Spacecraft angular velocity estimation algorithm for star tracker based on optical flow techniques

Science.gov (United States)

Tang, Yujie; Li, Jian; Wang, Gangyi

2018-02-01

An integrated navigation system often uses the traditional gyro and star tracker for high precision navigation with the shortcomings of large volume, heavy weight and high-cost. With the development of autonomous navigation for deep space and small spacecraft, star tracker has been gradually used for attitude calculation and angular velocity measurement directly. At the same time, with the dynamic imaging requirements of remote sensing satellites and other imaging satellites, how to measure the angular velocity in the dynamic situation to improve the accuracy of the star tracker is the hotspot of future research. We propose the approach to measure angular rate with a nongyro and improve the dynamic performance of the star tracker. First, the star extraction algorithm based on morphology is used to extract the star region, and the stars in the two images are matched according to the method of angular distance voting. The calculation of the displacement of the star image is measured by the improved optical flow method. Finally, the triaxial angular velocity of the star tracker is calculated by the star vector using the least squares method. The method has the advantages of fast matching speed, strong antinoise ability, and good dynamic performance. The triaxial angular velocity of star tracker can be obtained accurately with these methods. So, the star tracker can achieve better tracking performance and dynamic attitude positioning accuracy to lay a good foundation for the wide application of various satellites and complex space missions.

Barium and Tc-poor S stars: Binary masqueraders among carbon stars

OpenAIRE

Jorissen, A.; Van Eck, S.

1997-01-01

The current understanding of the origin of barium and S stars is reviewed, based on new orbital elements and binary frequencies. The following questions are addressed: (i) Is binarity a necessary condition to produce a barium star? (ii) What is the mass transfer mode (wind accretion or RLOF?) responsible for their formation? (iii) Do barium stars form as dwarfs or as giants? (iv) Do barium stars evolve into Tc-poor S stars? (v) What is the relative frequency of Tc-rich and Tc-poor S stars?

Radio stars

International Nuclear Information System (INIS)

Hjellming, R.M.

1976-01-01

Any discussion of the radio emission from stars should begin by emphasizing certain unique problems. First of all, one must clarify a semantic confusion introduced into radio astronomy in the late 1950's when most new radio sources were described as radio stars. All of these early 'radio stars' were eventually identified with other galactic and extra-galactic objects. The study of true radio stars, where the radio emission is produced in the atmosphere of a star, began only in the 1960's. Most of the work on the subject has, in fact, been carried out in only the last few years. Because the real information about radio stars is quite new, it is not surprising that major aspects of the subject are not at all understood. For this reason this paper is organized mainly around three questions: what is the available observational information; what physical processes seem to be involved; and what working hypotheses look potentially fruitful. (Auth.)

Neutron star structure from QCD

CERN Document Server

Fraga, Eduardo S; Vuorinen, Aleksi

2016-01-01

In this review article, we argue that our current understanding of the thermodynamic properties of cold QCD matter, originating from first principles calculations at high and low densities, can be used to efficiently constrain the macroscopic properties of neutron stars. In particular, we demonstrate that combining state-of-the-art results from Chiral Effective Theory and perturbative QCD with the current bounds on neutron star masses, the Equation of State of neutron star matter can be obtained to an accuracy better than 30% at all densities.

NEAR-INFRARED SPECTROSCOPY OF POST-AGB STARS

NARCIS (Netherlands)

OUDMAIJER, RD; WATERS, LBFM; VANDERVEEN, WECJ; GEBALLE, TR

The results of a medium resolution near-infrared spectral survey of 18 post-AGB candidate stars are presented. Most of the stars have near-infrared hydrogen lines in absorption, which is normal for their spectral types. Three stars, HD 101584, HD 179821 and HD 170756 have the CO first overtone bands

Radio stars

International Nuclear Information System (INIS)

Hjellming, R.M.; Gibson, D.M.

1985-01-01

Studies of stellar radio emission became an important field of research in the 1970's and have now expanded to become a major area of radio astronomy with the advent of new instruments such as the Very Large Array in New Mexico and transcontinental telescope arrays. This volume contains papers from the workshop on stellar continuum radio astronomy held in Boulder, Colorado, and is the first book on the rapidly expanding field of radio emission from stars and stellar systems. Subjects covered include the observational and theoretical aspects of stellar winds from both hot and cool stars, radio flares from active double star systems and red dwarf stars, bipolar flows from star-forming regions, and the radio emission from X-ray binaries. (orig.)

Stars Form Surprisingly Close to Milky Way's Black Hole

Science.gov (United States)

2005-10-01

The supermassive black hole at the center of the Milky Way has surprisingly helped spawn a new generation of stars, according to observations from NASA's Chandra X-ray Observatory. This novel mode of star formation may solve several mysteries about the supermassive black holes that reside at the centers of nearly all galaxies. "Massive black holes are usually known for violence and destruction," said Sergei Nayakshin of the University of Leicester, United Kingdom, and coauthor of a paper on this research in an upcoming issue of the Monthly Notices of the Royal Astronomical Society. "So it's remarkable that this black hole helped create new stars, not just destroy them." Black holes have earned their fearsome reputation because any material -- including stars -- that falls within the so-called event horizon is never seen again. However, these new results indicate that the immense disks of gas known to orbit many black holes at a "safe" distance from the event horizon can help nurture the formation of new stars. Animation of Stars Forming Around Black Hole Animation of Stars Forming Around Black Hole This conclusion came from new clues that could only be revealed in X-rays. Until the latest Chandra results, astronomers have disagreed about the origin of a mysterious group of massive stars discovered by infrared astronomers to be orbiting less than a light year from the Milky Way's central black hole, a.k.a. Sagittarius A*, or Sgr A*. At such close distances to Sgr A*, the standard model for star formation predicts that gas clouds from which stars form should have been ripped apart by tidal forces from the black hole. Two models to explain this puzzle have been proposed. In the disk model, the gravity of a dense disk of gas around Sgr A* offsets the tidal forces and allows stars to form; in the migration model, the stars formed in a star cluster far away from the black hole and migrated in to form the ring of massive stars. The migration scenario predicts about a

The ACS LCID project. X. the star formation history of IC 1613: Revisiting the over-cooling problem

Energy Technology Data Exchange (ETDEWEB)

Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455 (United States); Hidalgo, Sebastian L.; Monelli, Matteo; Gallart, Carme; Aparicio, Antonio, E-mail: skillman@astro.umn.edu, E-mail: shidalgo@iac.es, E-mail: monelli@iac.es, E-mail: carme@iac.es, E-mail: aparicio@iac.es [Instituto de Astrofísica de Canarias, Vía Láctea s/n, E-38200 La Laguna, Tenerife, Canary Islands (Spain); and others

2014-05-01

We present an analysis of the star formation history (SFH) of a field near the half-light radius in the Local Group dwarf irregular galaxy IC 1613 based on deep Hubble Space Telescope Advanced Camera for Surveys imaging. Our observations reach the oldest main sequence turn-off, allowing a time resolution at the oldest ages of ∼1 Gyr. Our analysis shows that the SFH of the observed field in IC 1613 is consistent with being constant over the entire lifetime of the galaxy. These observations rule out an early dominant episode of star formation in IC 1613. We compare the SFH of IC 1613 with expectations from cosmological models. Since most of the mass is in place at early times for low-mass halos, a naive expectation is that most of the star formation should have taken place at early times. Models in which star formation follows mass accretion result in too many stars formed early and gas mass fractions that are too low today (the 'over-cooling problem'). The depth of the present photometry of IC 1613 shows that, at a resolution of ∼1 Gyr, the star formation rate is consistent with being constant, at even the earliest times, which is difficult to achieve in models where star formation follows mass assembly.

Environmental effects on star formation in dwarf galaxies and star clusters

Science.gov (United States)

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

2015-08-01

We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation history of gravitationally bound system in an external environment.Ram pressure, Kelvin-Helmholtz instability, Rayleigh-Taylor, and tidal forces are accounted separately in an analytical framework and compared in their role in influencing the star forming regions. The two-fluids instability at the interface between a stellar system and its surrounding hotter and less dense environment is related to the star formation processes through a set of differential equations. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment useful in theoretical interpretations of numerical results as well as observational applications. We show how spherical coordinates naturally enlighten the interpretation of the two-fluids instability in a geometry that directly applies to astrophysical case. Finally, we consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams of the orbiting system thus investigating the detectability limits of these different effects for future observational projects and their relevance.The theoretical framework developed has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy.

Hyperon-mixed neutron stars

International Nuclear Information System (INIS)

Takatsuka, Tatsuyuki

2004-01-01

Hyperon mixing in neutron star matter is investigated by the G-matrix-based effective interaction approach under the attention to use the YN and the YY potentials compatible with hypernuclear data and is shown to occur at densities relevant to neutron star cores, together with discussions to clarify the mechanism of hyperon contamination. It is remarked that developed Y-mixed phase causes a dramatic softening of the neutron star equation of state and leads to the serious problem that the resulting maximum mass M max for neutron star model contradicts the observed neutron star mass (M max obs = 1.44 M Θ ), suggesting the necessity of some extra repulsion'' in hypernuclear system. It is shown that the introduction of three-body repulsion similar to that in nuclear system can resolve the serious situation and under the consistency with observation (M max > M obs ) the threshold densities for Λ and Σ - are pushed to higher density side, from 2ρ 0 to ∼ 4ρ 0 (ρ 0 being the nuclear density). On the basis of a realistic Y-mixed neutron star model, occurrence of Y-superfluidity essential for ''hyperon cooling'' scenario is studied and both of Λ- and Σ - -superfluids are shown to be realized with their critical temperatures 10 8-9 K, meaning that the hyperon cooling'' is a promising candidate for a fast non-standard cooling demanded for some neutron stars with low surface temperature. A comment is given as to the consequence of less attractive ΛΛ interaction suggested by the ''NAGARA event'' ΛΛ 6 He. (author)

Hydromagnetic rotational braking of magnetic stars

International Nuclear Information System (INIS)

Fleck, R.C. Jr.

1980-01-01

It is suggested that the magnetic Ap stars can be rotationally decelerated to long periods by the braking action of the associated magnetic field on time scales of order 10 7 --10 10 years depending on whether the star's dipole field is aligned perpendicular or parallel to the rotation axis. Rotation includes a toroidal magnetic field in the plasma surrounding a star, and the accompanying magnetic stresses produce a net torque acting to despin the star. These results indicate that it is not necessary to postulate mass loss or mass accretion for this purely hydromagnetic braking effect

Software and mathematical support of Kazakhstani star tracker

Science.gov (United States)

Akhmedov, D.; Yelubayev, S.; Ten, V.; Bopeyev, T.; Alipbayev, K.; Sukhenko, A.

2016-10-01

Currently the specialists of Kazakhstan have been developing the star tracker that is further planned to use on Kazakhstani satellites of various purposes. At the first stage it has been developed the experimental model of star tracker that has following characteristics: field of view 20°, update frequency 2 Hz, exclusion angle 40°, accuracy of attitude determination of optical axis/around optical axis 15/50 arcsec. Software and mathematical support are the most high technology parts of star tracker. The results of software and mathematical support development of experimental model of Kazakhstani star tracker are represented in this article. In particular, there are described the main mathematical models and algorithms that have been used as a basis for program units of preliminary image processing of starry sky, stars identification and star tracker attitude determination. The results of software and mathematical support testing with the help of program simulation complex using various configurations of defects including image sensor noises, point spread function modeling, optical system distortion up to 2% are presented. Analysis of testing results has shown that accuracy of attitude determination of star tracker is within the permissible range

Star Products and Applications

OpenAIRE

Iida, Mari; Yoshioka, Akira

2010-01-01

Star products parametrized by complex matrices are defined. Especially commutative associative star products are treated, and star exponentials with respect to these star products are considered. Jacobi's theta functions are given as infinite sums of star exponentials. As application, several concrete identities are obtained by properties of the star exponentials.

Limiting rotational period of neutron stars

Science.gov (United States)

Glendenning, Norman K.

1992-11-01

We seek an absolute limit on the rotational period for a neutron star as a function of its mass, based on the minimal constraints imposed by Einstein's theory of relativity, Le Chatelier's principle, causality, and a low-density equation of state, uncertainties in which can be evaluated as to their effect on the result. This establishes a limiting curve in the mass-period plane below which no pulsar that is a neutron star can lie. For example, the minimum possible Kepler period, which is an absolute limit on rotation below which mass shedding would occur, is 0.33 ms for a M=1.442Msolar neutron star (the mass of PSR1913+16). A still lower curve, based only on the structure of Einstein's equations, limits any star whatsoever to lie in the plane above it. Hypothetical stars such as strange stars, if the matter of which they are made is self-bound in bulk at a sufficiently large equilibrium energy density, can lie in the region above the general-relativistic forbidden region, and in the region forbidden to neutron stars.

Limiting rotational period of neutron stars

International Nuclear Information System (INIS)

Glendenning, N.K.

1992-01-01

We seek an absolute limit on the rotational period for a neutron star as a function of its mass, based on the minimal constraints imposed by Einstein's theory of relativity, Le Chatelier's principle, causality, and a low-density equation of state, uncertainties in which can be evaluated as to their effect on the result. This establishes a limiting curve in the mass-period plane below which no pulsar that is a neutron star can lie. For example, the minimum possible Kepler period, which is an absolute limit on rotation below which mass shedding would occur, is 0.33 ms for a M=1.442M circle-dot neutron star (the mass of PSR1913+16). A still lower curve, based only on the structure of Einstein's equations, limits any star whatsoever to lie in the plane above it. Hypothetical stars such as strange stars, if the matter of which they are made is self-bound in bulk at a sufficiently large equilibrium energy density, can lie in the region above the general-relativistic forbidden region, and in the region forbidden to neutron stars

Power optimization in the STAR-LM modular natural convection reactor system. Topic 2.1 advanced reactor power plants

International Nuclear Information System (INIS)

Spencer, B.W.; Sienicki, J.J.; Farmer, M.T.

2001-01-01

The secure, transportable, autonomous reactor (STAR) project addresses the needs of developing countries and independent power producers for a small (300 MWt), multi-purpose energy system. The STAR-LM variant described here is a liquid metal cooled, fast spectrum reactor system. Previous development of a reference STAR-LM design resulted in a 300 MWt modular, pool- type reactor based on criteria for factory fabrication of modules, full transportability of modules (barge, rail, overland), fast construction and startup, and semi-autonomous operation. Earlier work on the reference 300 MWt concept focused first on addressing whether 100% natural circulation heat transport was achievable under the module size constraints for full transportability and under the coolant and cladding peak temperature limitations imposed by the existing Russian database for ferritic-martensitic core material with oxide-layer corrosion protection. Secondly, owing to uncertainties and limitations in the available Russian materials compatibility database, the objective of the reference design was to address how low the coolant and cladding peak temperatures could be commensurate with achieving 300 MWt power level with 100% natural circulation in a fully transportable module size. In the present work we have refocused the approach to attempt to maximize the power achievable in the reactor module based on preserving the criteria for full module transportability and remaining within the materials compatibility database limits. (author)

CU-STARs: Promoting STEM Diversity by Addressing First-year Attrition of Underrepresented Minorities

Science.gov (United States)

Battersby, Cara; Silvia, Devin W.; Ellingson, Erica; Sturner, Andrew P.; Peck, Courtney

2015-01-01

Upon first entering university, the fraction of students interested in pursuing a STEM major are distributed according to societal demographics (with 25% being underrepresented minorities), but by graduation, the fraction of students receiving STEM degrees is unbalanced, with underrepresented minorities receiving only 15% of STEM bachelor's degrees. The CU-STARs (CU Science, Technology, and Astronomy Recruits) program at the University of Colorado, Boulder is targeted to address the main triggers of early career attrition for underrepresented minorities in STEM disciplines. A select group of students are given financial support through work-study at the Fiske planetarium on campus, while resources to address other triggers of attrition are available to the entire cohort of interested students (typically ~5-10 per year). These resources are designed to promote social engagement and mentorship, while also providing a support network and resources to combat inadequate high school preparation for STEM courses. We achieve these goals through activities that include social events, mentor meetings, free tutoring, and special events to meet and talk with scientists. The culmination of the program for the recruits are a series of high school outreach events in underserved areas (inner city and rural alike), in which they become the expert. The STARs are paid for their time and take the lead in planning, teaching, and facilitating programs for the high school students, including classroom presentations, interactive lab activities, solar observing, and star parties. The high school outreach events provide role models and STEM exposure for the underserved high school community while simultaneously cementing the personal achievements and successes for the STARs. CU-STARs is now in its 4th year and is still growing. We are beginning the process of formal assessments of the program's success. We present details of the program implementation, a discussion of potential obstacles

NEW X-RAY DETECTIONS OF WNL STARS

International Nuclear Information System (INIS)

Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner; Sokal, Kimberly R.

2012-01-01

Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star X-ray detections so far have been of earlier WN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNL stars) have proved more difficult to detect, an important exception being WR 79a (WN9ha). We present here new X-ray detections of the WNL stars WR 16 (WN8h) and WR 78 (WN7h). These new results, when combined with previous detections, demonstrate that X-ray emission is present in WN stars across the full range of spectral types, including later WNL stars. The two WN8 stars observed to date (WR 16 and WR 40) show unusually low X-ray luminosities (L x ) compared to other WN stars, and it is noteworthy that they also have the lowest terminal wind speeds (v ∞ ). Existing X-ray detections of about a dozen WN stars reveal a trend of increasing L x with wind luminosity L wind = (1/2)M-dot v 2 ∞ , suggesting that wind kinetic energy may play a key role in establishing X-ray luminosity levels in WN stars.

NEW X-RAY DETECTIONS OF WNL STARS

Energy Technology Data Exchange (ETDEWEB)

Skinner, Stephen L. [Center for Astrophysics and Space Astronomy (CASA), University of Colorado, Boulder, CO 80309-0389 (United States); Zhekov, Svetozar A. [Space and Solar-Terrestrial Research Institute, Moskovska str. 6, Sofia-1000 (Bulgaria); Guedel, Manuel [Department of Astronomy, University of Vienna, Tuerkenschanzstr. 17, A-1180 Vienna (Austria); Schmutz, Werner [Physikalisch-Meteorologisches Observatorium Davos (PMOD), Dorfstrasse 33, CH-7260 Davos Dorf (Switzerland); Sokal, Kimberly R., E-mail: Stephen.Skinner@colorado.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)

2012-05-15

Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star X-ray detections so far have been of earlier WN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNL stars) have proved more difficult to detect, an important exception being WR 79a (WN9ha). We present here new X-ray detections of the WNL stars WR 16 (WN8h) and WR 78 (WN7h). These new results, when combined with previous detections, demonstrate that X-ray emission is present in WN stars across the full range of spectral types, including later WNL stars. The two WN8 stars observed to date (WR 16 and WR 40) show unusually low X-ray luminosities (L{sub x} ) compared to other WN stars, and it is noteworthy that they also have the lowest terminal wind speeds (v{sub {infinity}}). Existing X-ray detections of about a dozen WN stars reveal a trend of increasing L{sub x} with wind luminosity L{sub wind} = (1/2)M-dot v{sup 2}{sub {infinity}}, suggesting that wind kinetic energy may play a key role in establishing X-ray luminosity levels in WN stars.

Asteroseismology of solar-type stars: particular physical effects

Energy Technology Data Exchange (ETDEWEB)

Carrier, F [Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium); Eggenberger, P; Leyder, J-C [Institut d' Astrophysique et de Geophysique de l' Universite de Liege, 17 Allee du 6 aout, 4000 Liege (Belgium)], E-mail: fabien@ster.kuleuven.be

2008-10-15

Since the success of helioseismology, numerous efforts have been made to detect solar-like oscillations on other stars. The measurement of the frequencies of p-mode oscillations provides an insight into the internal structure and is nowadays the most powerful constraint on the theory of stellar evolution. The existing asteroseismic observations were mainly motivated by the need to explore the seismological properties of stars with various global parameters, i.e. various locations in the HR diagram. With the aim of testing different physical effects on solar-like oscillations, we report here detection of acoustic modes on solar-like targets achieved with the spectrograph HARPS installed on the 3.6-m telescope at ESO La Silla Observatory.

Effect of catalogues coordinate errors of a star onto determination of the physical libration of the Moon from the observations of stars

Science.gov (United States)

Petrova, Natalia; Kocoulin, Valerii; Nefediev, Yurii

2016-07-01

In the Kazan University computer simulation is carried out for observation of lunar physical libration in projects planned installation of measuring equipment on the lunar surface. One such project is the project of ILOM (Japan), in which on the lunar pole an optical telescope with CCD will be equipped. As a result, the determining the selenographic coordinates (x and y) of a star with an accuracy of 1 ms of arc will be achieved. On the basis of the analytical theory of physical libration we developed a technique for solving the inverse problem of the libration. And we have already shown, for example, that the error in determining selenographic coordinates about ɛ seconds does not lead to errors in the determination of the libration angles ρ and Iσ larger than the 1.414ɛ. Libration in longitude is not determined from observations of the polar star (Petrova et al., 2012). The accuracy of the libration in the inverse problem depends on accuracy of the coordinates of the stars - α and δ - taken from the star catalogs. Checking this influence is the task of the present study. To do simulation we have developed that allows to choose the stars, falling in the field of view of the lunar telescope on observation period. Equatorial coordinates of stars were chosen by us from several fundamental catalogs: UCAC2-BSS, Hipparcos, Tycho, FK6 (part I, III) and the Astronomical Almanac. An analysis of these catalogues from the point of view accuracy of coordinates of stars represented in them was performed by Nefediev et al., 2013. The largest error, 20-70 ms, found in the catalogues UCAC2 and Tycho, the others have an error about a millisecond of arc. We simulated the observations with mentioned errors and got the following results. 1. The error in the declination Δδ of the star causes the same order error in libration parameters ρ and Iσ , while the sensitivity of libration to errors in Δα is ten time smaller. Fortunately, due to statistics (30 to 70, depending on

Heavy Metal Stars

Science.gov (United States)

2001-08-01

La Silla Telescope Detects Lots of Lead in Three Distant Binaries Summary Very high abundances of the heavy element Lead have been discovered in three distant stars in the Milky Way Galaxy . This finding strongly supports the long-held view that roughly half of the stable elements heavier than Iron are produced in common stars during a phase towards the end of their life when they burn their Helium - the other half results from supernova explosions. All the Lead contained in each of the three stars weighs about as much as our Moon. The observations show that these "Lead stars" - all members of binary stellar systems - have been more enriched with Lead than with any other chemical element heavier than Iron. This new result is in excellent agreement with predictions by current stellar models about the build-up of heavy elements in stellar interiors. The new observations are reported by a team of Belgian and French astronomers [1] who used the Coude Echelle Spectrometer on the ESO 3.6-m telescope at the La Silla Observatory (Chile). PR Photo 26a/01 : A photo of HD 196944 , one of the "Lead stars". PR Photo 26b/01 : A CES spectrum of HD 196944 . The build-up of heavy elements Astronomers and physicists denote the build-up of heavier elements from lighter ones as " nucleosynthesis ". Only the very lightest elements (Hydrogen, Helium and Lithium [2]) were created at the time of the Big Bang and therefore present in the early universe. All the other heavier elements we now see around us were produced at a later time by nucleosynthesis inside stars. In those "element factories", nuclei of the lighter elements are smashed together whereby they become the nuclei of heavier ones - this process is known as nuclear fusion . In our Sun and similar stars, Hydrogen is being fused into Helium. At some stage, Helium is fused into Carbon, then Oxygen, etc. The fusion process requires positively charged nuclei to move very close to each other before they can unite. But with increasing

Interaction between bosonic dark matter and stars

Science.gov (United States)

Brito, Richard; Cardoso, Vitor; Macedo, Caio F. B.; Okawa, Hirotada; Palenzuela, Carlos

2016-02-01

We provide a detailed analysis of how bosonic dark matter "condensates" interact with compact stars, extending significantly the results of a recent Letter [1]. We focus on bosonic fields with mass mB , such as axions, axion-like candidates and hidden photons. Self-gravitating bosonic fields generically form "breathing" configurations, where both the spacetime geometry and the field oscillate, and can interact and cluster at the center of stars. We construct stellar configurations formed by a perfect fluid and a bosonic condensate, and which may describe the late stages of dark matter accretion onto stars, in dark-matter-rich environments. These composite stars oscillate at a frequency which is a multiple of f =2.5 ×1014(mBc2/eV ) Hz . Using perturbative analysis and numerical relativity techniques, we show that these stars are generically stable, and we provide criteria for instability. Our results also indicate that the growth of the dark matter core is halted close to the Chandrasekhar limit. We thus dispel a myth concerning dark matter accretion by stars: dark matter accretion does not necessarily lead to the destruction of the star, nor to collapse to a black hole. Finally, we argue that stars with long-lived bosonic cores may also develop in other theories with effective mass couplings, such as (massless) scalar-tensor theories.

An Investigation on the Use of Different Centroiding Algorithms and Star Catalogs in Astro-Geodetic Observations

Science.gov (United States)

Basoglu, Burak; Halicioglu, Kerem; Albayrak, Muge; Ulug, Rasit; Tevfik Ozludemir, M.; Deniz, Rasim

2017-04-01

In the last decade, the importance of high-precise geoid determination at local or national level has been pointed out by Turkish National Geodesy Commission. The Commission has also put objective of modernization of national height system of Turkey to the agenda. Meanwhile several projects have been realized in recent years. In Istanbul city, a GNSS/Levelling geoid was defined in 2005 for the metropolitan area of the city with an accuracy of ±3.5cm. In order to achieve a better accuracy in this area, "Local Geoid Determination with Integration of GNSS/Levelling and Astro-Geodetic Data" project has been conducted in Istanbul Technical University and Bogazici University KOERI since January 2016. The project is funded by The Scientific and Technological Research Council of Turkey. With the scope of the project, modernization studies of Digital Zenith Camera System are being carried on in terms of hardware components and software development. Accentuated subjects are the star catalogues, and centroiding algorithm used to identify the stars on the zenithal star field. During the test observations of Digital Zenith Camera System performed between 2013-2016, final results were calculated using the PSF method for star centroiding, and the second USNO CCD Astrograph Catalogue (UCAC2) for the reference star positions. This study aims to investigate the position accuracy of the star images by comparing different centroiding algorithms and available star catalogs used in astro-geodetic observations conducted with the digital zenith camera system.

Origin and evolutionary stage of symbiotic stars

Energy Technology Data Exchange (ETDEWEB)

Tutukov, A V; Yungel' son, L R [AN SSSR, Moscow. Astronomicheskij Sovet

1976-08-01

Symbiotic stars are considered which best of all are described by the binary star model. An analysis of properties of symbiotic stars shows that their hot components should be either carbon-oxygen dwarfs with thin hydrogen-helium envelopes or helium stars with thin mantles. Cold components are red giants losing matter at the rate of 10/sup -5/-10/sup -6/ M/yr over the period of 10/sup 5/-10/sup 6/ years (M is the Sun mass). Such systems can be formed of wide pairs as a result of loss of envelope of an initially more massive star of the system by way of continuous outflow of matter or expulsion due to dynamic instability at the red giant stage,, and also of closer pairs as a result of exchange of matter between the components. It has been shown that hot components of symbiotic stars can accrete 10/sup -6/-10/sup -9/ M/yr, and some consequencies of accretion on a C-O dwarf have been considered.

First stars X. The nature of three unevolved carbon-enhanced metal-poor stars

DEFF Research Database (Denmark)

Sivarani, T.; Beers, T.C.; Bonifacio, P.

2006-01-01

Stars: abundances, stars: population II, Galaxy: abundances, stars: AGB and post-AGB Udgivelsesdato: Nov.......Stars: abundances, stars: population II, Galaxy: abundances, stars: AGB and post-AGB Udgivelsesdato: Nov....

The Space-Time Asymmetry Research (STAR) program

Science.gov (United States)

Buchman, Sasha

Stanford University, NASA Ames, and international partners propose the Space-Time Asymme-try Research (STAR) program, a series of three Science and Technology Development Missions, which will probe the fundamental relationships between space, time and gravity. What is the nature of space-time? Is space truly isotropic? Is the speed of light truly isotropic? If not, what is its direction and location dependency? What are the answers beyond Einstein? How will gravity and the standard model ultimately be combined? The first mission, STAR-1, will measure the absolute anisotropy of the velocity of light to one part in 1017 , derive the Kennedy-Thorndike (KT) coefficient to 7x10-10 (150-fold improvement over modern ground measurements), derive the Michelson-Morley (MM) coefficient to 10-11 (confirming the ground measurements), and derive the coefficients of Lorentz violation in the Standard Model Exten-sion (SME), in the range 7x10-17 to 10-13 (an order of magnitude improvement over ground measurements). The follow-on missions will achieve a factor of 100 higher sensitivities. The core instruments are high stability optical cavities and high accuracy gas spectroscopy frequency standards using the "NICE-OHMS technique. STAR-1 is accomplished with a fully redundant instrument flown on a standard bus, spin-stabilized spacecraft with a mission lifetime of two years. Spacecraft and instrument have a total mass of less than 180 kg and consume less than 200 W of power. STAR-1 would launch in 2015 as a secondary payload in a 650 km, sun-synchronous orbit. We describe the STAR-1 mission in detail and the STAR series in general, with a focus on how each mission will build on the development and success of the previous missions, methodically enhancing both the capabilities of the STAR instrument suite and our understanding of this important field. By coupling state-of-the-art scientific instrumentation with proven and cost-effective small satellite technology in an environment

EXTENDED STAR FORMATION IN THE INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 2209

International Nuclear Information System (INIS)

Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

2012-01-01

We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters.

A study of flare stars in the taurus region

International Nuclear Information System (INIS)

Khodzhaev, A.S.

1986-01-01

The results are given of a search for flare stars in the region of the dark clouds in Taurus together with the results of photometric, H /sub alpha/ -spectroscopic, and statistical investigations of them. Photographic observations during 1980-1984 revealed 92 new flare stars, 13 of which were found to be known Orion variables with 16 repeated flares of 13 previously known flare stars. Their apparent distribution is considered. The question of whether the flare stars belong to a dark cloud is discussed. A comparative analysis of the flare stars in the Taurus region and other aggregates is made. The Hertzsprung-Russell (V, B - V) and two-color (U - B, B - V) diagrams for the flare stars are similar to the corresponding diagrams constructed for star clusters and associations (Pleiades, Orion, etc.). The total number of flare stars in the region of the dark clouds in Taurus is estimated at ≥ 500

RR Lyrae Stars in M4

Science.gov (United States)

Kuehn, Charles A.; Moskalik, Pawel; Drury, Jason A.

2017-10-01

Observations by Kepler/K2 have revolutionized the study of RR Lyrae stars by allowing the detection of new phenomna, such as low amplitude additional modes and period doubling, which had not previously been seen from the ground. During campaign 2, K2 observed the globular cluster M4, providiing the first opportunity to study a sizeable group of RR Lyrae stars that belong to a single population; the other RR Lyrae stars that have been observed from space are field stars in the galactic halo and thus belong to an assortment of populations. In this poster we present the results of our study of the RR Lyrae variables in M4 from K2 photometry. We have identified additional, low amplitude pulsation modes in both observed RRc stars. In 3 RRab stars we have found the Blazhko effect with periods of 16.6d, 22.4d, and 44.5d.

RR Lyrae Stars in M4

Directory of Open Access Journals (Sweden)

Kuehn Charles A

2017-01-01

Full Text Available Observations by Kepler/K2 have revolutionized the study of RR Lyrae stars by allowing the detection of new phenomna, such as low amplitude additional modes and period doubling, which had not previously been seen from the ground. During campaign 2, K2 observed the globular cluster M4, providiing the first opportunity to study a sizeable group of RR Lyrae stars that belong to a single population; the other RR Lyrae stars that have been observed from space are field stars in the galactic halo and thus belong to an assortment of populations. In this poster we present the results of our study of the RR Lyrae variables in M4 from K2 photometry. We have identified additional, low amplitude pulsation modes in both observed RRc stars. In 3 RRab stars we have found the Blazhko effect with periods of 16.6d, 22.4d, and 44.5d.

Attention and Intelligence: The Validity of the Star Counting Test.

NARCIS (Netherlands)

Jong, de P.F.; Das-Smaal, E.A.

1995-01-01

The mechanisms underlying performance on the Star Counting Test (SCT) and its nomothetic span were investigated along with the relationships between working memory capacity, fluid intelligence (Gf), speed, and school achievement. The SCT is an attention test for children that requires the

Applicability of Broad-Band Photometry for Determining the Properties of Stars and Interstellar Extinction

Science.gov (United States)

Sichevskij, S. G.

2018-01-01

The feasibility of the determination of the physical conditions in star's atmosphere and the parameters of interstellar extinction from broad-band photometric observations in the 300-3000 nm wavelength interval is studied using SDSS and 2MASS data. The photometric accuracy of these surveys is shown to be insufficient for achieving in practice the theoretical possibility of estimating the atmospheric parameters of stars based on ugriz and JHK s photometry exclusively because such determinations result in correlations between the temperature and extinction estimates. The uncertainty of interstellar extinction estimates can be reduced if prior data about the temperature are available. The surveys considered can nevertheless be potentially valuable sources of information about both stellar atmospheric parameters and the interstellar medium.

THE CHANDRA VARIABLE GUIDE STAR CATALOG

International Nuclear Information System (INIS)

Nichols, Joy S.; Lauer, Jennifer L.; Morgan, Douglas L.; Sundheim, Beth A.; Henden, Arne A.; Huenemoerder, David P.; Martin, Eric

2010-01-01

Variable stars have been identified among the optical-wavelength light curves of guide stars used for pointing control of the Chandra X-ray Observatory. We present a catalog of these variable stars along with their light curves and ancillary data. Variability was detected to a lower limit of 0.02 mag amplitude in the 4000-10000 A range using the photometrically stable Aspect Camera on board the Chandra spacecraft. The Chandra Variable Guide Star Catalog (VGUIDE) contains 827 stars, of which 586 are classified as definitely variable and 241 are identified as possibly variable. Of the 586 definite variable stars, we believe 319 are new variable star identifications. Types of variables in the catalog include eclipsing binaries, pulsating stars, and rotating stars. The variability was detected during the course of normal verification of each Chandra pointing and results from analysis of over 75,000 guide star light curves from the Chandra mission. The VGUIDE catalog represents data from only about 9 years of the Chandra mission. Future releases of VGUIDE will include newly identified variable guide stars as the mission proceeds. An important advantage of the use of space data to identify and analyze variable stars is the relatively long observations that are available. The Chandra orbit allows for observations up to 2 days in length. Also, guide stars were often used multiple times for Chandra observations, so many of the stars in the VGUIDE catalog have multiple light curves available from various times in the mission. The catalog is presented as both online data associated with this paper and as a public Web interface. Light curves with data at the instrumental time resolution of about 2 s, overplotted with the data binned at 1 ks, can be viewed on the public Web interface and downloaded for further analysis. VGUIDE is a unique project using data collected during the mission that would otherwise be ignored. The stars available for use as Chandra guide stars are

White Dwarf Stars

OpenAIRE

Kepler, S. O.; Romero, Alejandra Daniela; Pelisoli, Ingrid; Ourique, Gustavo

2017-01-01

White dwarf stars are the final stage of most stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white dwarf stars from 5000 to 39000. This number includes only white dwarf stars with log g >= 6.5 stars, i.e., excluding the Extremely Low Mass white dw...

Modeling jet and outflow feedback during star cluster formation

Energy Technology Data Exchange (ETDEWEB)

Federrath, Christoph [Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, VIC 3800 (Australia); Schrön, Martin [Department of Computational Hydrosystems, Helmholtz Centre for Environmental Research-UFZ, Permoserstr. 15, D-04318 Leipzig (Germany); Banerjee, Robi [Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg (Germany); Klessen, Ralf S., E-mail: christoph.federrath@monash.edu [Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Strasse 2, D-69120 Heidelberg (Germany)

2014-08-01

Powerful jets and outflows are launched from the protostellar disks around newborn stars. These outflows carry enough mass and momentum to transform the structure of their parent molecular cloud and to potentially control star formation itself. Despite their importance, we have not been able to fully quantify the impact of jets and outflows during the formation of a star cluster. The main problem lies in limited computing power. We would have to resolve the magnetic jet-launching mechanism close to the protostar and at the same time follow the evolution of a parsec-size cloud for a million years. Current computer power and codes fall orders of magnitude short of achieving this. In order to overcome this problem, we implement a subgrid-scale (SGS) model for launching jets and outflows, which demonstrably converges and reproduces the mass, linear and angular momentum transfer, and the speed of real jets, with ∼1000 times lower resolution than would be required without the SGS model. We apply the new SGS model to turbulent, magnetized star cluster formation and show that jets and outflows (1) eject about one-fourth of their parent molecular clump in high-speed jets, quickly reaching distances of more than a parsec, (2) reduce the star formation rate by about a factor of two, and (3) lead to the formation of ∼1.5 times as many stars compared to the no-outflow case. Most importantly, we find that jets and outflows reduce the average star mass by a factor of ∼ three and may thus be essential for understanding the characteristic mass of the stellar initial mass function.

THE PREVALENCE AND IMPACT OF WOLF–RAYET STARS IN EMERGING MASSIVE STAR CLUSTERS

Energy Technology Data Exchange (ETDEWEB)

Sokal, Kimberly R.; Johnson, Kelsey E.; Indebetouw, Rémy [Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903 (United States); Massey, Philip, E-mail: krs9tb@virginia.edu [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States)

2016-08-01

We investigate Wolf–Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point in the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4 m Mayall Telescope at Kitt Peak National Observatory and the 6.5 m MMT.{sup 4} We identify 21 sources with significantly detected WR signatures, which we term “emerging WR clusters.” WR features are detected in ∼50% of the radio-selected sample, and thus we find that WR stars are commonly present in currently emerging massive star clusters. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process.

The vast population of Wolf-Rayet and red supergiant stars in M101. I. Motivation and first results

Energy Technology Data Exchange (ETDEWEB)

Shara, Michael M.; Bibby, Joanne L.; Zurek, David [Department of Astrophysics, American Museum of Natural History, Central Park West and 79th Street, New York, NY 10024-5192 (United States); Crowther, Paul A. [Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH (United Kingdom); Moffat, Anthony F. J. [Département de Physique, Université de Montréal, CP 6128 Succ. C-V, Montréal, QC H3C 3J7 (Canada); Drissen, Laurent [Département de Physique, Université Laval, Pavillon Vachon, Quebec City, QC G1K 7P4 (Canada)

2013-12-01

Assembling a catalog of at least 10,000 Wolf-Rayet (W-R) stars is an essential step in proving (or disproving) that these stars are the progenitors of Type Ib and Type Ic supernovae. To this end, we have used the Hubble Space Telescope (HST) to carry out a deep, He II optical narrowband imaging survey of the ScI spiral galaxy M101. Almost the entire galaxy was imaged with the unprecedented depth and resolution that only the HST affords. Differenced with archival broadband images, the narrowband images allow us to detect much of the W-R star population of M101. We describe the extent of the survey and our images, as well as our data reduction procedures. A detailed broadband-narrowband imaging study of a field east of the center of M101, containing the giant star-forming region NGC 5462, demonstrates our completeness limits, how we find W-R candidates, their properties and spatial distribution, and how we rule out most contaminants. We use the broadband images to locate luminous red supergiant (RSG) candidates. The spatial distributions of the W-R and RSG stars near NGC 5462 are strikingly different. W-R stars dominate the complex core, while RSGs dominate the complex halo. Future papers in this series will describe and catalog more than a thousand W-R and RSG candidates that are detectable in our images, as well as spectra of many of those candidates.

Egyptian "Star Clocks"

Science.gov (United States)

Symons, Sarah

Diagonal, transit, and Ramesside star clocks are tables of astronomical information occasionally found in ancient Egyptian temples, tombs, and papyri. The tables represent the motions of selected stars (decans and hour stars) throughout the Egyptian civil year. Analysis of star clocks leads to greater understanding of ancient Egyptian constellations, ritual astronomical activities, observational practices, and pharaonic chronology.

Asteroseismology of white dwarf stars. I - Adiabatic results

Energy Technology Data Exchange (ETDEWEB)

Bradley, P.A.; Winget, D.E. (Texas, University (USA) McDonald Observatory, Austin (USA))

1991-02-01

A preliminary investigation of the asteroseismological properties of chemically stratified evolutionary DA and DB white dwarf models is reported. The period and kinetic energy distributions for nonradial g-modes of spherical harmonic indices l = 1-3 are computed in the adiabatic approximation, and the effects of varying the total stellar masss and the surface layer masses on the pulsation properties are studied using an extensive grid of models. Significant resonant mode trapping due to chemical stratification is found. Modes trapped in the outer layers have much lower kinetic energies; these minima also show up as minima in the period spacing between modes of consecutive radial overtone k. Mode trapping occurs at the same or nearly the same value of k for different l-values. Thus, l-values of trapped modes may be identified on the basis of their period ratios. It is shown that observational identification of these period ratios can be used to constrain the mass of the star and its surface layer. 68 refs.

Missing mass from low-luminosity stars

International Nuclear Information System (INIS)

Hawkins, M.R.S.

1986-01-01

Results from a deep photometric survey for low-luminosity stars show a turnup to the luminosity function at faint magnitudes, and reopen the possibility that the missing mass in the solar neighbourhood is made up of stars after all. (author)

NuSTAR Hard X-ray Optics

DEFF Research Database (Denmark)

Koglin, Jason E.; Christensen, Finn Erland; Craig, William W.

2005-01-01

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a small explorer (SMEX) mission currently under an extended Phase A study by NASA. NuSTAR will be the first satellite mission to employ focusing optics in the hard X-ray band (8- 80 keV). Its design eliminates high detector backgrounds, allows...... and production process. We also describe the progress of several components of our independent optics development program that are beginning to reach maturity and could possibly be incorporated into the NuSTAR production scheme. We then present environmental test results that are being conducted in preparation...... of full space qualification of the NuSTAR optics....

The Fermi Gamma-Ray Space Telescope, Exploding Stars, Neutron Stars, and Black Holes

Science.gov (United States)

Thompson, David J.

2010-01-01

Since August, 2008, the Fermi Gamma-ray Space Telescope has been scanning the sky, producing a full-sky image every three hours. These cosmic gamma-rays come from extreme astrophysical phenomena, many related to exploding stars (supernovae) or what these explosions leave behind: supernova remnants, neutron stars, and black holes. This talk uses sample Fermi results, plus simple demonstrations, to illustrate the exotic properties of these endpoints of stellar evolution.

Symbiotic stars

International Nuclear Information System (INIS)

Kafatos, M.; Michalitsianos, A.G.

1984-01-01

Among the several hundred million binary systems estimated to lie within 3000 light years of the solar system, a tiny fraction, no more than a few hundred, belong to a curious subclass whose radiation has a wavelength distribution so peculiar that it long defied explanation. Such systems radiate strongly in the visible region of the spectrum, but some of them do so even more strongly at both shorter and longer wavelengths: in the ultraviolet region and in the infrared and radio regions. This odd distribution of radiation is best explained by the pairing of a cool red giant star and an intensely hot small star that is virtually in contact with its larger companion. Such objects have become known as symbiotic stars. On photographic plate only the giant star can be discerned, but evidence for the existence of the hot companion has been supplied by satellite-born instruments capable of detecting ultraviolet radiation. The spectra of symbiotic stars indicate that the cool red giant is surrounded by a very hot ionized gas. Symbiotic stars also flared up in outbursts indicating the ejection of material in the form of a shell or a ring. Symbiotic stars may therefore represent a transitory phase in the evolution of certain types of binary systems in which there is substantial transfer of matter from the larger partner to the smaller

2005 Status Report Savings Estimates for the ENERGY STAR(R)Voluntary Labeling Program

Energy Technology Data Exchange (ETDEWEB)

Webber, Carrie A.; Brown, Richard E.; Sanchez, Marla

2006-03-07

ENERGY STAR(R) is a voluntary labeling program designed toidentify and promote energy-efficient products, buildings and practices.Operated jointly by the Environmental Protection Agency (EPA) and theU.S. Department of Energy (DOE), Energy Star labels exist for more thanforty products, spanning office equipment, residential heating andcooling equipment, commercial and residential lighting, home electronics,and major appliances. This report presents savings estimates for a subsetof ENERGY STAR labeled products. We present estimates of the energy,dollar and carbon savings achieved by the program in the year 2004, whatwe expect in 2005, and provide savings forecasts for two marketpenetration scenarios for the periods 2005 to 2010 and 2005 to 2020. Thetarget market penetration forecast represents our best estimate of futureENERGY STAR savings. It is based on realistic market penetration goalsfor each of the products. We also provide a forecast under the assumptionof 100 percent market penetration; that is, we assume that all purchasersbuy ENERGY STAR-compliant products instead of standard efficiencyproducts throughout the analysis period.

2007 Status Report: Savings Estimates for the ENERGY STAR(R)VoluntaryLabeling Program

Energy Technology Data Exchange (ETDEWEB)

Sanchez, Marla; Webber, Carrie A.; Brown, Richard E.; Homan,Gregory K.

2007-03-23

ENERGY STAR(R) is a voluntary labeling program designed toidentify and promote energy-efficient products, buildings and practices.Operated jointly by the Environmental Protection Agency (EPA) and theU.S. Department of Energy (DOE), ENERGY STAR labels exist for more thanthirty products, spanning office equipment, residential heating andcooling equipment, commercial and residential lighting, home electronics,and major appliances. This report presents savings estimates for a subsetof ENERGY STAR labeled products. We present estimates of the energy,dollar and carbon savings achieved by the program in the year 2006, whatwe expect in 2007, and provide savings forecasts for two marketpenetration scenarios for the periods 2007 to 2015 and 2007 to 2025. Thetarget market penetration forecast represents our best estimate of futureENERGY STAR savings. It is based on realistic market penetration goalsfor each of the products. We also provide a forecast under the assumptionof 100 percent market penetration; that is, we assume that all purchasersbuy ENERGY STAR-compliant products instead of standard efficiencyproducts throughout the analysis period.

Star formation is boosted (and quenched) from the inside-out: radial star formation profiles from MaNGA

Science.gov (United States)

Ellison, Sara L.; Sánchez, Sebastian F.; Ibarra-Medel, Hector; Antonio, Braulio; Mendel, J. Trevor; Barrera-Ballesteros, Jorge

2018-02-01

The tight correlation between total galaxy stellar mass and star formation rate (SFR) has become known as the star-forming main sequence. Using ˜487 000 spaxels from galaxies observed as part of the Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we confirm previous results that a correlation also exists between the surface densities of star formation (ΣSFR) and stellar mass (Σ⋆) on kpc scales, representing a `resolved' main sequence. Using a new metric (ΔΣSFR), which measures the relative enhancement or deficit of star formation on a spaxel-by-spaxel basis relative to the resolved main sequence, we investigate the SFR profiles of 864 galaxies as a function of their position relative to the global star-forming main sequence (ΔSFR). For galaxies above the global main sequence (positive ΔSFR) ΔΣSFR is elevated throughout the galaxy, but the greatest enhancement in star formation occurs at small radii (<3 kpc, or 0.5Re). Moreover, galaxies that are at least a factor of 3 above the main sequence show diluted gas phase metallicities out to 2Re, indicative of metal-poor gas inflows accompanying the starbursts. For quiescent/passive galaxies that lie at least a factor of 10 below the star-forming main sequence, there is an analogous deficit of star formation throughout the galaxy with the lowest values of ΔΣSFR in the central 3 kpc. Our results are in qualitative agreement with the `compaction' scenario in which a central starburst leads to mass growth in the bulge and may ultimately precede galactic quenching from the inside-out.

Unveiling hidden properties of young star clusters: differential reddening, star-formation spread, and binary fraction

Science.gov (United States)

Bonatto, C.; Lima, E. F.; Bica, E.

2012-04-01

Context. Usually, important parameters of young, low-mass star clusters are very difficult to obtain by means of photometry, especially when differential reddening and/or binaries occur in large amounts. Aims: We present a semi-analytical approach (ASAmin) that, when applied to the Hess diagram of a young star cluster, is able to retrieve the values of mass, age, star-formation spread, distance modulus, foreground and differential reddening, and binary fraction. Methods: The global optimisation method known as adaptive simulated annealing (ASA) is used to minimise the residuals between the observed and simulated Hess diagrams of a star cluster. The simulations are realistic and take the most relevant parameters of young clusters into account. Important features of the simulations are a normal (Gaussian) differential reddening distribution, a time-decreasing star-formation rate, the unresolved binaries, and the smearing effect produced by photometric uncertainties on Hess diagrams. Free parameters are cluster mass, age, distance modulus, star-formation spread, foreground and differential reddening, and binary fraction. Results: Tests with model clusters built with parameters spanning a broad range of values show that ASAmin retrieves the input values with a high precision for cluster mass, distance modulus, and foreground reddening, but they are somewhat lower for the remaining parameters. Given the statistical nature of the simulations, several runs should be performed to obtain significant convergence patterns. Specifically, we find that the retrieved (absolute minimum) parameters converge to mean values with a low dispersion as the Hess residuals decrease. When applied to actual young clusters, the retrieved parameters follow convergence patterns similar to the models. We show how the stochasticity associated with the early phases may affect the results, especially in low-mass clusters. This effect can be minimised by averaging out several twin clusters in the

Star tracking method based on multiexposure imaging for intensified star trackers.

Science.gov (United States)

Yu, Wenbo; Jiang, Jie; Zhang, Guangjun

2017-07-20

The requirements for the dynamic performance of star trackers are rapidly increasing with the development of space exploration technologies. However, insufficient knowledge of the angular acceleration has largely decreased the performance of the existing star tracking methods, and star trackers may even fail to track under highly dynamic conditions. This study proposes a star tracking method based on multiexposure imaging for intensified star trackers. The accurate estimation model of the complete motion parameters, including the angular velocity and angular acceleration, is established according to the working characteristic of multiexposure imaging. The estimation of the complete motion parameters is utilized to generate the predictive star image accurately. Therefore, the correct matching and tracking between stars in the real and predictive star images can be reliably accomplished under highly dynamic conditions. Simulations with specific dynamic conditions are conducted to verify the feasibility and effectiveness of the proposed method. Experiments with real starry night sky observation are also conducted for further verification. Simulations and experiments demonstrate that the proposed method is effective and shows excellent performance under highly dynamic conditions.

Abundance analyses of thirty cool carbon stars

International Nuclear Information System (INIS)

Utsumi, Kazuhiko

1985-01-01

The results were previously obtained by use of the absolute gf-values and the cosmic abundance as a standard. These gf-values were found to contain large systematic errors, and as a result, the solar photospheric abundances were revised. Our previous results, therefore, must be revised by using new gf-values, and abundance analyses are extended for as many carbon stars as possible. In conclusion, in normal cool carbon stars heavy metals are overabundant by factors of 10 - 100 and rare-earth elements are overabundant by a factor of about 10, and in J-type cool carbon stars, C 12 /C 13 ratio is smaller, C 2 and CN bands and Li 6708 are stronger than in normal cool carbon stars, and the abundances of s-process elements with respect to Fe are nearly normal. (Mori, K.)

Life of a star

International Nuclear Information System (INIS)

Henbest, Nigel.

1988-01-01

The paper concerns the theory of stellar evolution. A description is given of:- how a star is born, main sequence stars, red giants, white dwarfs, supernovae, neutron stars and black holes. A brief explanation is given of how the death of a star as a supernova can trigger off the birth of a new generation of stars. Classification of stars and the fate of our sun, are also described. (U.K.)

Neutrino Processes in Neutron Stars

Directory of Open Access Journals (Sweden)

Kolomeitsev E.E.

2010-10-01

Full Text Available The aim of these lectures is to introduce basic processes responsible for cooling of neutron stars and to show how to calculate the neutrino production rate in dense strongly interacting nuclear medium. The formalism is presented that treats on equal footing one-nucleon and multiple-nucleon processes and reactions with virtual bosonic modes and condensates. We demonstrate that neutrino emission from dense hadronic component in neutron stars is subject of strong modifications due to collective effects in the nuclear matter. With the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved. With these findings the so-called “standard” and “non-standard” cooling scenarios are replaced by one general “nuclear medium cooling scenario” which relates slow and rapid neutron star coolings to the star masses (interior densities. The lectures are split in four parts. Part I: After short introduction to the neutron star cooling problem we show how to calculate neutrino reaction rates of the most efficient one-nucleon and two-nucleon processes. No medium effects are taken into account in this instance. The effects of a possible nucleon pairing are discussed. We demonstrate that the data on neutron star cooling cannot be described without inclusion of medium effects. It motivates an assumption that masses of the neutron stars are different and that neutrino reaction rates should be strongly density dependent. Part II: We introduce the Green’s function diagram technique for systems in and out of equilibrium and the optical theorem formalism. The latter allows to perform calculations of production rates with full Green’s functions including all off-mass-shell effects. We demonstrate how this formalism works within the quasiparticle approximation. Part III: The basic concepts of the nuclear Fermi liquid approach are introduced. We show how strong

Understand B-type stars

Science.gov (United States)

1982-01-01

When observations of B stars made from space are added to observations made from the ground and the total body of observational information is confronted with theoretical expectations about B stars, it is clear that nonthermal phenomena occur in the atmospheres of B stars. The nature of these phenomena and what they imply about the physical state of a B star and how a B star evolves are examined using knowledge of the spectrum of a B star as a key to obtaining an understanding of what a B star is like. Three approaches to modeling stellar structure (atmospheres) are considered, the characteristic properties of a mantle, and B stars and evolution are discussed.

The STAR cluster-finder ASIC

Energy Technology Data Exchange (ETDEWEB)

Botlo, M.; LeVine, M.J.; Scheetz, R.A.; Schulz, M.W. [Brookhaven National Lab., Upton, NY (United States); Short, P.; Woods, J. [InnovASIC, Inc., Albuquerque, NM (United States); Crosetto, D. [Rice Univ., Houston, TX (United States). Bonner Nuclear Lab.

1997-12-01

STAR is a large TPC-based experiment at RHIC, the relativistic heavy ion collider at Brookhaven National Laboratory. The STAR experiment reads out a TPC and an SVT (silicon vertex tracker), both of which require in-line pedestal subtraction, compression of ADC values from 10-bit to 8-bit, and location of time sequences representing responses to charged-particle tracks. The STAR cluster finder ASIC responds to all of these needs. Pedestal subtraction and compression are performed using lookup tables in attached RAM. The authors describe its design and implementation, as well as testing methodology and results of tests performed on foundry prototypes.

Flare stars

International Nuclear Information System (INIS)

Nicastro, A.J.

1981-01-01

The least massive, but possibly most numerous, stars in a galaxy are the dwarf M stars. It has been observed that some of these dwarfs are characterized by a short increase in brightness. These stars are called flare stars. These flare stars release a lot of energy in a short amount of time. The process producing the eruption must be energetic. The increase in light intensity can be explained by a small area rising to a much higher temperature. Solar flares are looked at to help understand the phenomenon of stellar flares. Dwarfs that flare are observed to have strong magnetic fields. Those dwarf without the strong magnetic field do not seem to flare. It is believed that these regions of strong magnetic fields are associated with star spots. Theories on the energy that power the flares are given. Astrophysicists theorize that the driving force of a stellar flare is the detachment and collapse of a loop of magnetic flux. The mass loss due to stellar flares is discussed. It is believed that stellar flares are a significant contributor to the mass of interstellar medium in the Milky Way

A new deterministic model of strange stars

Energy Technology Data Exchange (ETDEWEB)

Rahaman, Farook; Shit, G.C. [Jadavpur University, Department of Mathematics, Kolkata, West Bengal (India); Chakraborty, Koushik [Government Training College, Department of Physics, Hooghly, West Bengal (India); Kuhfittig, P.K.F. [Milwaukee School of Engineering, Department of Mathematics, Milwaukee, WI (United States); Rahman, Mosiur [Meghnad Saha Institute of Technology, Department of Mathematics, Kolkata (India)

2014-10-15

The observed evidence for the existence of strange stars and the concomitant observed masses and radii are used to derive an interpolation formula for the mass as a function of the radial coordinate. The resulting general mass function becomes an effective model for a strange star. The analysis is based on the MIT bag model and yields the energy density, as well as the radial and transverse pressures. Using the interpolation function for the mass, it is shown that a mass-radius relation due to Buchdahl is satisfied in our model. We find the surface redshift (Z) corresponding to the compactness of the stars. Finally, from our results, we predict some characteristics of a strange star of radius 9.9 km. (orig.)

NEAR-INFRARED PERIODIC AND OTHER VARIABLE FIELD STARS IN THE FIELD OF THE CYGNUS OB7 STAR-FORMING REGION

Energy Technology Data Exchange (ETDEWEB)

Wolk, Scott J.; Rice, Thomas S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aspin, Colin A. [Institute for Astronomy, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720 (United States)

2013-04-15

We present a subset of the results of a three-season, 124 night, near-infrared monitoring campaign of the dark clouds Lynds 1003 and Lynds 1004 in the Cygnus OB7 star-forming region. In this paper, we focus on the field star population. Using three seasons of UKIRT J, H, and K-band observations spanning 1.5 years, we obtained high-quality photometry on 9200 stars down to J = 17 mag, with photometric uncertainty better than 0.04 mag. After excluding known disk-bearing stars we identify 149 variables-1.6% of the sample. Of these, about 60 are strictly periodic, with periods predominantly <2 days. We conclude this group is dominated by eclipsing binaries. A few stars have long period signals of between 20 and 60 days. About 25 stars have weak modulated signals, but it was not clear if these were periodic. Some of the stars in this group may be diskless young stellar objects with relatively large variability due to cool starspots. The remaining {approx}60 stars showed variations which appear to be purely stochastic.

On origin and evolutionary stage of symbiotic stars

International Nuclear Information System (INIS)

Tutukov, A.V.; Yungel'son, L.R.

1976-01-01

Symbiotic stars are considered which best of all are described by the binary star model. An analysis of properties of symbiotic stars shows that their hot components should be either carbon-oxygen dwarfs with thin hydrogen-helium envelopes or helium stars with thin mantles. Cold components are red giants losing matter with the rate of 10 -5 -10 -6 M/yr over the period of 10 5 -10 6 years (M is the Sun mass). Such systems can be formed of wide pairs as a result of loss of envelope of an initially more massive star of the system by way of continuous outflow of matter or expulsion due to dynamic instability at the stage of red giant, and also of more close pairs as a result of exchange of matter between the components. It has been shown that hot components of symbiotic stars can accrete 10 -6 -10 -9 M/yr and some consequencies of accretion on a C-O dwarf have been considered

GRACE star camera noise

Science.gov (United States)

Harvey, Nate

2016-08-01

Extending results from previous work by Bandikova et al. (2012) and Inacio et al. (2015), this paper analyzes Gravity Recovery and Climate Experiment (GRACE) star camera attitude measurement noise by processing inter-camera quaternions from 2003 to 2015. We describe a correction to star camera data, which will eliminate a several-arcsec twice-per-rev error with daily modulation, currently visible in the auto-covariance function of the inter-camera quaternion, from future GRACE Level-1B product releases. We also present evidence supporting the argument that thermal conditions/settings affect long-term inter-camera attitude biases by at least tens-of-arcsecs, and that several-to-tens-of-arcsecs per-rev star camera errors depend largely on field-of-view.

Synthesis of cationic star polymers by simplified electrochemically mediated ATRP

Directory of Open Access Journals (Sweden)

P. Chmielarz

2016-10-01

Full Text Available Cyclodextrin-based cationic star polymers were synthesized using β-cyclodextrin (β-CD core, and 2-(dimethylamino ethyl methacrylate (DMAEMA as hydrophilic arms. Star-shaped polymers were prepared via a simplified electrochemically mediated ATRP (seATRP under potentiostatic and galvanostatic conditions. The polymerization results showed molecular weight (MW evolution close to theoretical values, and maintained narrow molecular weight distribution (MWD of obtained stars. The rate of the polymerizations was controlled by applying more positive potential values thereby suppressing star-star coupling reactions. Successful chain extension of the ω-functional arms with a hydrophobic n-butyl acrylate (BA formed star block copolymers and confirmed the living nature of the β-CD-PDMAEMA star polymers prepared by seATRP. Novelty of this work is that the β-CD-PDMAEMA-b-PBA cationic star block copolymers were synthesized for the first time via seATRP procedure, utilizing only 40 ppm of catalyst complex. The results from 1H NMR spectral studies support the formation of cationic star (copolymers.

Shooting stars

International Nuclear Information System (INIS)

Maurette, M.; Hammer, C.

1985-01-01

A shooting star passage -even a star shower- can be sometimes easily seen during moonless black night. They represent the partial volatilization in earth atmosphere of meteorites or micrometeorites reduced in cosmic dusts. Everywhere on earth, these star dusts are searched to be gathered. This research made one year ago on the Greenland ice-cap is this article object; orbit gathering projects are also presented [fr

STAR-TO-STAR IRON ABUNDANCE VARIATIONS IN RED GIANT BRANCH STARS IN THE GALACTIC GLOBULAR CLUSTER NGC 3201

International Nuclear Information System (INIS)

Simmerer, Jennifer; Ivans, Inese I.; Filler, Dan; Francois, Patrick; Charbonnel, Corinne; Monier, Richard; James, Gaël

2013-01-01

We present the metallicity as traced by the abundance of iron in the retrograde globular cluster NGC 3201, measured from high-resolution, high signal-to-noise spectra of 24 red giant branch stars. A spectroscopic analysis reveals a spread in [Fe/H] in the cluster stars at least as large as 0.4 dex. Star-to-star metallicity variations are supported both through photometry and through a detailed examination of spectra. We find no correlation between iron abundance and distance from the cluster core, as might be inferred from recent photometric studies. NGC 3201 is the lowest mass halo cluster to date to contain stars with significantly different [Fe/H] values.

Star-to-star Iron Abundance Variations in Red Giant Branch Stars in the Galactic Globular Cluster NGC 3201

Science.gov (United States)

Simmerer, Jennifer; Ivans, Inese I.; Filler, Dan; Francois, Patrick; Charbonnel, Corinne; Monier, Richard; James, Gaël

2013-02-01

We present the metallicity as traced by the abundance of iron in the retrograde globular cluster NGC 3201, measured from high-resolution, high signal-to-noise spectra of 24 red giant branch stars. A spectroscopic analysis reveals a spread in [Fe/H] in the cluster stars at least as large as 0.4 dex. Star-to-star metallicity variations are supported both through photometry and through a detailed examination of spectra. We find no correlation between iron abundance and distance from the cluster core, as might be inferred from recent photometric studies. NGC 3201 is the lowest mass halo cluster to date to contain stars with significantly different [Fe/H] values.

Web-Based STAR E-Learning Course Increases Empathy and Understanding in Dementia Caregivers: Results from a Randomized Controlled Trial in the Netherlands and the United Kingdom

Science.gov (United States)

Meiland, Franka; van der Roest, Henriëtte; Kevern, Peter; Abiuso, Francesca; Bengtsson, Johan; Giuliano, Angele; Duca, Annalise; Sanders, Jennifer; Basnett, Fern; Nugent, Chris; Kingston, Paul; Dröes, Rose-Marie

2015-01-01

Background The doubling of the number of people with dementia in the coming decades coupled with the rapid decline in the working population in our graying society is expected to result in a large decrease in the number of professionals available to provide care to people with dementia. As a result, care will be supplied increasingly by untrained informal caregivers and volunteers. To promote effective care and avoid overburdening of untrained and trained caregivers, they must become properly skilled. To this end, the European Skills Training and Reskilling (STAR) project, which comprised experts from the domains of education, technology, and dementia care from 6 countries (the Netherlands, Sweden, Italy, Malta, Romania, and the United Kingdom), worked together to create and evaluate a multilingual e-learning tool. The STAR training portal provides dementia care training both for informal and formal caregivers. Objective The objective of the current study was to evaluate the user friendliness, usefulness, and impact of STAR with informal caregivers, volunteers, and professional caregivers. Methods For 2 to 4 months, the experimental group had access to the STAR training portal, a Web-based portal consisting of 8 modules, 2 of which had a basic level and 6 additional modules at intermediate and advanced levels. The experimental group also had access to online peer and expert communities for support and information exchange. The control group received free access to STAR after the research had ended. The STAR training portal was evaluated in a randomized controlled trial among informal caregivers and volunteers in addition to professional caregivers (N=142) in the Netherlands and the United Kingdom. Assessments were performed with self-assessed, online, standardized questionnaires at baseline and after 2 to 4 months. Primary outcome measures were user friendliness, usefulness, and impact of STAR on knowledge, attitudes, and approaches of caregivers regarding dementia

Ages of evolved low mass stars: Central stars of planetary nebulae and white dwarfs

Directory of Open Access Journals (Sweden)

Costa R.D.D.

2013-03-01

Full Text Available We have developed several methods to estimate the ages of central stars of planetary nebulae (CSPN, which are based either on observed nebular properties or on data from the stars themselves. Our goal is to derive the age distribution of these stars and compare the results with empirical distributions for CSPN and white dwarfs. We have initially developed three methods based on nebular abundances, using (i an age-metallicity relation which is also a function of the galactocentric distance; (ii an age-metallicity relation obtained for the galactic disk, and (iii the central star masses derived from the observed nitrogen abundances. In this work we present two new, more accurate methods, which are based on kinematic properties: (I in this method, the expected rotation velocities of the nebulae around the galactic centre at their galactocentric distances are compared with the predicted values for the galactic rotation curve, and the differences are attributed to the different ages of the evolved stars; (II we determine directly the U, V, W, velocity components of the stars, as well as the velocity dispersions, and use the dispersion-age relation by the Geneva-Copenhagen survey. These methods were applied to two large samples of galactic CSPN. We conclude that most CSPN in the galactic disk have ages under 5 Gyr, and that the age distribution is peaked around 1 to 3 Gyr.

Sounds of a Star

Science.gov (United States)

2001-06-01

in Alpha Cen A with the CORALIE spectrograph on the 1.2-m Swiss telescope at the ESO La Silla observatory. Several "eigenmodes" appear as high peaks in the frequency interval between 1.7 and 3 mHz; they correspond to oscillation periods in the range from 5 to 10 min. A very similar pattern is observed in the Sun. The data from five nights of observations were then searched to detect any changes of velocity and hence, oscillations. Astronomers use sophisticated mathematical methods for this kind of analysis, and normally present their results in terms of a "power spectrum" ( PR Photo 23b/01 ). It displays the "intensity" of oscillations at different frequencies, that is, of different periods; particularly high "peaks" indicate a "real" oscillation of that frequency. The comb of peaks visible between 2-3 mHz is the unambiguous and typical signature of solar-like oscillations . This frequency corresponds to a period of about 7 minutes, close to the well-known 5-minute oscillations of our Sun. This is in full agreement with expectations from theoretical models of the two stars. Continued detailed modeling of these new results will further improve the associated determination of the mass, radius, age, chemical composition and other properties of Alpha Cen A . This result is another proof of the excellent performance of the CORALIE spectrograph, providing extremely accurate measurements without the present investigation would have been impossible. Models of stellar interiors Our current understanding of stellar interiors is severely limited by lack of detailed and accurate observations of stars other than the Sun. In technical terms, for a complete description of the conditions inside a star, we need detailed knowledge of at least five stellar parameters (mass, age, initial content of helium and heavier elements, and a parameter describing the convection). However, in most cases, only two stellar properties can be measured directly (the temperature and the luminosity), so

Chromospheres in metal deficient field stars

International Nuclear Information System (INIS)

Dupree, A.K.; Hartmann, L.; Smith, G.

1984-01-01

The chromospheric structure of red giant stars with metal deficient atmospheres presents a fundamental observational and theoretical problem for atmospheric theory. Moreover, the occurrence and rate of mass loss from these stars have consequences for the theory of stellar evolution of low mass stars in globular clusters. This paper reports some results from a systematic program to assess the presence and character of chromospheric line profiles and their variations, and to obtain quantitative measurements of radiative losses from chromospheres. Such data are needed to constrain semi-empirical models of these atmospheres. Three metal deficient field stars have been observed both in the ultraviolet and optical spectral regions: HD 165195, HD 110281, and HD 232078. High dispersion spectra near the Hα transition were obtained with the echelle spectrograph and reticon detector at the F.L. Whipple Observatory of SAO. These stars were observed twice in 1983, separated by a two month interval. IUE spectra were also obtained using the long wavelength cameras in low dispersion mode. Observations of the three stars are discussed

Destruction of a Magnetized Star

Science.gov (United States)

Kohler, Susanna

2017-01-01

completely.Amplifying EncountersFor stars that survive their encounter with the black hole, Guillochon and McCourt find that the process of partial disruption and re-accretion can amplify the magnetic field of the star by up to a factor of 20. Repeated encounters of the star with the black hole could amplify the field even more.The authors suggest an interesting implication of this idea: a population of highly magnetized stars may have formed in our own galactic center, resulting from their encounters with the supermassive black hole Sgr A*.A turbulent magnetic field forms after a partial stellar disruption and re-accretion of the tidal tails. [Adapted from Guillochon McCourt 2017]Effects in DestructionFor stars that are completely shredded and form a tidal stream after their encounter with the black hole, the authors find that the magnetic field geometry straightens within the stream of debris. There, the pressure of the magnetic field eventually dominates over the gas pressure and self-gravity.Guillochon and McCourt find that the fields new configuration isnt ideal for powering jets from the black hole but it is strong enough to influence how the stream interacts with itself and its surrounding environment, likely affecting what we can expect to see from these short-lived events.These simulations have clearly demonstrated the need to further explore the role of magnetic fields in the disruptions of stars by black holes.BonusCheck out the full (brief) video from one of the simulations by Guillochon and McCourt (be sure to watch it in high-res!). It reveals the evolution of a stars magnetic field configuration as the star is partially disrupted by the forces of a supermassive black hole and then re-accretes.CitationJames Guillochon and Michael McCourt 2017 ApJL 834 L19. doi:10.3847/2041-8213/834/2/L19

THE INFRARED SPECTRAL PROPERTIES OF MAGELLANIC CARBON STARS

Energy Technology Data Exchange (ETDEWEB)

Sloan, G. C. [Cornell Center for Astrophysics and Planetary Science, Cornell Univ., Ithaca, NY 14853-6801 (United States); Kraemer, K. E. [Institute for Scientific Research, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA 02467 (United States); McDonald, I.; Zijlstra, A. A. [Jodrell Bank Centre for Astrophysics, Univ. of Manchester, Manchester M13 9PL (United Kingdom); Groenewegen, M. A. T. [Koninklijke Sterrenwacht van België, Ringlaan 3, B-1180 Brussels (Belgium); Wood, P. R. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia); Lagadec, E. [Observatoire de la Côte d’Azur, F-06300, Nice (France); Boyer, M. L. [CRESST and Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD, 20771 (United States); Kemper, F.; Srinivasan, S. [Academia Sinica, Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, NTU/AS, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan, R.O.C. (China); Matsuura, M. [School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff, CF24 3AA (United Kingdom); Sahai, R. [Jet Propulsion Laboratory, California Institute of Technology, MS 183-900, Pasadena, CA 91109 (United States); Sargent, B. A. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Van Loon, J. Th. [Lennard Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom); Volk, K., E-mail: sloan@isc.astro.cornell.edu [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States)

2016-07-20

The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C{sub 2}H{sub 2} at 7.5 μ m. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the asymptotic giant branch and/or they may have non-spherical dust geometries.

THE INFRARED SPECTRAL PROPERTIES OF MAGELLANIC CARBON STARS

International Nuclear Information System (INIS)

Sloan, G. C.; Kraemer, K. E.; McDonald, I.; Zijlstra, A. A.; Groenewegen, M. A. T.; Wood, P. R.; Lagadec, E.; Boyer, M. L.; Kemper, F.; Srinivasan, S.; Matsuura, M.; Sahai, R.; Sargent, B. A.; Van Loon, J. Th.; Volk, K.

2016-01-01

The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C 2 H 2 at 7.5 μ m. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the asymptotic giant branch and/or they may have non-spherical dust geometries.

Young and Waltzing Binary Stars

Science.gov (United States)

2001-10-01

ADONIS Observes Low-mass Eclipsing System in Orion Summary A series of very detailed images of a binary system of two young stars have been combined into a movie . In merely 3 days, the stars swing around each other. As seen from the earth, they pass in front of each other twice during a full revolution, producing eclipses during which their combined brightness diminishes . A careful analysis of the orbital motions has now made it possible to deduce the masses of the two dancing stars . Both turn out to be about as heavy as our Sun. But while the Sun is about 4500 million years old, these two stars are still in their infancy. They are located some 1500 light-years away in the Orion star-forming region and they probably formed just 10 million years ago . This is the first time such an accurate determination of the stellar masses could be achieved for a young binary system of low-mass stars . The new result provides an important piece of information for our current understanding of how young stars evolve. The observations were obtained by a team of astronomers from Italy and ESO [1] using the ADaptive Optics Near Infrared System (ADONIS) on the 3.6-m telescope at the ESO La Silla Observatory. PR Photo 29a/01 : The RXJ 0529.4+0041 system before primary eclipse PR Photo 29b/01 : The RXJ 0529.4+0041 system at mid-primary eclipse PR Photo 29c/01 : The RXJ 0529.4+0041 system after primary eclipse PR Photo 29d/01 : The RXJ 0529.4+0041 system before secondary eclipse PR Photo 29e/01 : The RXJ 0529.4+0041 system at mid-secondary eclipse PR Photo 29f/01 : The RXJ 0529.4+0041 system after secondary eclipse PR Video Clip 06/01 : Video of the RXJ 0529.4+0041 system Binary stars and stellar masses Since some time, astronomers have noted that most stars seem to form in binary or multiple systems. This is quite fortunate, as the study of binary stars is the only way in which it is possible to measure directly one of the most fundamental quantities of a star, its mass. The mass of a

THE CHEMICAL ABUNDANCES OF STARS IN THE HALO (CASH) PROJECT. II. A SAMPLE OF 14 EXTREMELY METAL-POOR STARS ,

International Nuclear Information System (INIS)

Hollek, Julie K.; Sneden, Christopher; Shetrone, Matthew; Frebel, Anna; Roederer, Ian U.; Beers, Timothy C.; Kang, Sung-ju; Thom, Christopher

2011-01-01

We present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R ∼15, 000) and corresponding high-resolution (R ∼35, 000) Magellan Inamori Kyocera Echelle spectra. The stars span a metallicity range from [Fe/H] from –2.9 to –3.9, including four new stars with [Fe/H] < –3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]< – 3. We also find four neutron-capture-enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H] ∼< –3.0) of the brightest stars included in CASH and are used to calibrate a newly developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire ∼500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manual analysis from a high-resolution spectrum.

Deriving temperature, mass, and age of evolved stars from high-resolution spectra. Application to field stars and the open cluster IC 4651

Science.gov (United States)

Biazzo, K.; Pasquini, L.; Girardi, L.; Frasca, A.; da Silva, L.; Setiawan, J.; Marilli, E.; Hatzes, A. P.; Catalano, S.

2007-12-01

Aims:We test our capability of deriving stellar physical parameters of giant stars by analysing a sample of field stars and the well studied open cluster IC 4651 with different spectroscopic methods. Methods: The use of a technique based on line-depth ratios (LDRs) allows us to determine with high precision the effective temperature of the stars and to compare the results with those obtained with a classical LTE abundance analysis. Results: (i) For the field stars we find that the temperatures derived by means of the LDR method are in excellent agreement with those found by the spectral synthesis. This result is extremely encouraging because it shows that spectra can be used to firmly derive population characteristics (e.g., mass and age) of the observed stars. (ii) For the IC 4651 stars we use the determined effective temperature to derive the following results. a) The reddening E(B-V) of the cluster is 0.12±0.02, largely independent of the color-temperature calibration used. b) The age of the cluster is 1.2±0.2 Gyr. c) The typical mass of the analysed giant stars is 2.0±0.2~M⊙. Moreover, we find a systematic difference of about 0.2 dex in log g between spectroscopic and evolutionary values. Conclusions: We conclude that, in spite of known limitations, a classical spectroscopic analysis of giant stars may indeed result in very reliable stellar parameters. We caution that the quality of the agreement, on the other hand, depends on the details of the adopted spectroscopic analysis. Based on observations collected at the ESO telescopes at the Paranal and La Silla Observatories, Chile.

Olivier Chesneau's Work on Low Mass Stars

Science.gov (United States)

Lagadec, E.

2015-12-01

During his too short career, Olivier Chesneau pioneered the study of the circumstellar environments of low mass evolved stars using very high angular resolution techniques. He applied state of the art high angular resolution techniques, such as optical interferometry and adaptive optics imaging, to the the study of a variety of objects, from AGB stars to Planetary Nebulae, via e.g. Born Again stars, RCB stars and Novae. I present here an overview of this work and most important results by focusing on the paths he followed and key encounters he made to reach these results. Olivier liked to work in teams and was very strong at linking people with complementary expertises to whom he would communicate his enthusiasm and sharp ideas. His legacy will live on through the many people he inspired.

Star polymer-based unimolecular micelles and their application in bio-imaging and diagnosis.

Science.gov (United States)

Jin, Xin; Sun, Pei; Tong, Gangsheng; Zhu, Xinyuan

2018-02-03

As a novel kind of polymer with covalently linked core-shell structure, star polymers behave in nanostructure in aqueous medium at all concentration range, as unimolecular micelles at high dilution condition and multi-micelle aggregates in other situations. The unique morphologies endow star polymers with excellent stability and functions, making them a promising platform for bio-application. A variety of functions including imaging and therapeutics can be achieved through rational structure design of star polymers, and the existence of plentiful end-groups on shell offers the opportunity for further modification. In the last decades, star polymers have become an attracting platform on fabrication of novel nano-systems for bio-imaging and diagnosis. Focusing on the specific topology and physicochemical properties of star polymers, we have reviewed recent development of star polymer-based unimolecular micelles and their bio-application in imaging and diagnosis. The main content of this review summarizes the synthesis of integrated architecture of star polymers and their self-assembly behavior in aqueous medium, focusing especially on the recent advances on their bio-imaging application and diagnosis use. Finally, we conclude with remarks and give some outlooks for further exploration in this field. Copyright © 2018 Elsevier Ltd. All rights reserved.

On the Spatially Resolved Star Formation History in M51. I. Hybrid UV+IR Star Formation Laws and IR Emission from Dust Heated by Old Stars

Science.gov (United States)

Eufrasio, R. T.; Lehmer, B. D.; Zezas, A.; Dwek, E.; Arendt, R. G.; Basu-Zych, A.; Wiklind, T.; Yukita, M.; Fragos, T.; Hornschemeier, A. E.; Markwardt, L.; Ptak, A.; Tzanavaris, P.

2017-12-01

We present LIGHTNING, a new spectral energy distribution fitting procedure, capable of quickly and reliably recovering star formation history (SFH) and extinction parameters. The SFH is modeled as discrete steps in time. In this work, we assumed lookback times of 0-10 Myr, 10-100 Myr, 0.1-1 Gyr, 1-5 Gyr, and 5-13.6 Gyr. LIGHTNING consists of a fully vectorized inversion algorithm to determine SFH step intensities and combines this with a grid-based approach to determine three extinction parameters. We apply our procedure to the extensive far-UV-to-far-IR photometric data of M51, convolved to a common spatial resolution and pixel scale, and make the resulting maps publicly available. We recover, for M51a, a peak star formation rate (SFR) between 0.1 and 5 Gyr ago, with much lower star formation activity over the past 100 Myr. For M51b, we find a declining SFR toward the present day. In the outskirt regions of M51a, which includes regions between M51a and M51b, we recover an SFR peak between 0.1 and 1 Gyr ago, which corresponds to the effects of the interaction between M51a and M51b. We utilize our results to (1) illustrate how UV+IR hybrid SFR laws vary across M51 and (2) provide first-order estimates for how the IR luminosity per unit stellar mass varies as a function of the stellar age. From the latter result, we find that IR emission from dust heated by stars is not always associated with young stars and that the IR emission from M51b is primarily powered by stars older than 5 Gyr.

Highlights from STAR

International Nuclear Information System (INIS)

Schweda, Kai

2004-01-01

Selected results from the STAR collaboration are presented. We focus on recent results on jet-like correlations, nuclear modification factors of identified hadrons, elliptic flow of multi-strange baryons Ξ and Ω, and resonance yields. First measurements of open charm production at RHIC are presented

Wolf-Rayet stars in open clusters and associations

International Nuclear Information System (INIS)

Lundstroem, I.; Stenholm, B.

1982-01-01

The authors have made a search for line-of-sight coincidences between WR stars and open clusters using the new catalogue of galactic WR stars (van der Hucht et al., 1981, called the HCLS catalogue) and the catalogue of open cluster data (Lyngaa and Lundstroem, 1980). As a measure of the separation they used the angular distance between the WR star and the cluster centre expressed with the cluster angular radius, r', as unit. By comparing the results found from the real angular distributions of WR stars and open clusters with those found if the WR stars were redistributed by changing signs in their latitudes, it is concluded that the majority of WR stars with separations less than 3r' are true cluster members. For larger separations only a few stars can be expected to be members. The authors have therefore limited their investigation to those WR stars that were found within 5r' from an open cluster. (Auth.)

Hyperon-mixed neutron star matter and neutron stars

International Nuclear Information System (INIS)

Nishizaki, Shigeru; Takatsuka, Tatsuyuki; Yamamoto, Yasuo

2002-01-01

Effective Σ - n and Σ - Σ - interactions are derived from the G-matrix calculations for {n+Σ - } matter and employed in the investigation of hyperon mixing in neutron star matter. The threshold densities ρ t (Y) at which hyperons start to appear are between 2ρ 0 and 3ρ 0 (where ρ 0 is the normal nuclear density) for both Λ and Σ - , and their fractions increase rapidly with baryon density, reaching 10% already for ρ≅ρ t + ρ 0 . The mechanism of hyperon mixing and single-particle properties, such as the effective mass and the potential depth, are analyzed taking into account the roles of YN and NN interactions. The resulting equation of state is found to be too soft to sustain the observed neutron star mass M obs =1.44(solar mass). We discuss the reason for this and stress the necessity of the ''extra repulsion'' for YN and YY interactions to resolve this crucial problem. It is remarked that ρ t (Y) would be as large as 4ρ 0 for neutron stars compatible with M obs . A comment is given regarding the effects on the Y-mixing problem from a less attractive ΛΛ interaction, newly suggested by the NAGARA event. (author)

STAR-TYPE LOCAL AREA NETWORK ACCESS CONTROL

Institute of Scientific and Technical Information of China (English)

逯昭义; 齐藤忠夫

1990-01-01

The multiple access fashion is a new resolution for the star-type local area network (LAN) access control and star-type optical fibre LAN. Arguments about this network are discussed, and the results are introduced.

Nonradial pulsations of hot evolved stars

International Nuclear Information System (INIS)

Starrfield, S.G.

1987-01-01

There are three classes of faint blue variable stars: the ZZ Ceti variables (DAV degenerate dwarfs), the DBV variables (DB degenerate dwarfs), and the GW Vir variables (DOV degenerate dwarfs). None of these classes of variable stars were known at the time of the last blue star meeting. Observational and theoretical studies of the ZZ Ceti variables, the DBV variables, and the GW Vir variables have shown them to be pulsating in nonradial g-modes. The cause of the pulsation has been determined for each class of variable star and, in all cases, also involves predictions of the stars envelope composition. The predictions are that the ZZ Ceti variables must have pure hydrogen surface layers, the DBV stars must have pure helium surface layers, and the GW Vir stars must have carbon and oxygen rich surface layers with less than 30% (by mass) of helium. Given these compositions, it is found that pulsation driving occurs as a result of the kappa and gamma effects operating in the partial ionization zones of either hydrogen or helium. In addition, a new driving mechanism, called convection blocking, also occurs in these variables. For the GW Vir variables, it is the kappa and gamma effects in the partial ionization regions of carbon and oxygen. 45 refs

Central stars of planetary nebulae. II. New OB-type and emission-line stars

Science.gov (United States)

Weidmann, W. A.; Gamen, R.

2011-07-01

Context. There are more than 3000 confirmed and probably known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims: We have undertaken a spectroscopic survey of the central stars in PNe to identify their spectral types. Methods: We performed spectroscopic observations at low resolution with the 2-m telescope at CASLEO, Argentina. Results: We present the spectra of 46 central stars of PNe, most of them are OB-type and emission-line stars. Based on data collected at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina y Universidades Nacionales de La Plata, Córdoba y San Juan, Argentina.The reduced spectra (FITS files) are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A172

Accretion Processes in Star Formation

DEFF Research Database (Denmark)

Küffmeier, Michael

for short-lived radionuclides that enrich the cloud as a result of supernova explosions of the massive stars allows us to analyze the distribution of the short-lived radionuclides around young forming stars. In contradiction to results from highly-idealized models, we find that the discrepancy in 26 Al...... that the accretion process of stars is heterogeneous in space, time and among different protostars. In some cases, disks form a few thousand years after stellar birth, whereas in other cases disk formation is suppressed due to efficient removal of angular momentum. Angular momentum is mainly transported outward...... with potentially observable fluctuations in the luminosity profile that are induced by variations in the accretion rate. Considering that gas inside protoplanetary disks is not fully ionized, I implemented a solver that accounts for nonideal MHD effects into a newly developed code framework called dispatch...

Energy production in stars

International Nuclear Information System (INIS)

Bethe, Hans.

1977-01-01

Energy in stars is released partly by gravitation, partly by nuclear reactions. For ordinary stars like our sun, nuclear reactions predominate. However, at the end of the life of a star very large amounts of energy are released by gravitational collapse; this can amount to as much as 10 times the total energy released nuclear reactions. The rotational energy of pulsars is a small remnant of the energy of gravitation. The end stage of small stars is generally a white dwarf, of heavy stars a neutron star of possibly a black hole

Star clusters in the Whirlpool Galaxy

NARCIS (Netherlands)

Scheepmaker, R.A.

2009-01-01

This thesis presents the results of observational studies of the star cluster population in the interacting spiral galaxy M51, also known as the Whirlpool galaxy. Observations taken by the Hubble Space Telescope in the optical and the near-UV are used to determine fundamental properties of the star

Final binary star results from the ESO VLT Lunar occultations program

Energy Technology Data Exchange (ETDEWEB)

Richichi, A. [National Astronomical Research Institute of Thailand, 191 Siriphanich Bldg., Huay Kaew Road, Suthep, Muang, Chiang Mai 50200 (Thailand); Fors, O. [Departament Astronomia i Meteorologia and Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (UB/IEEC), Martí i Franqués 1, E-08028 Barcelona (Spain); Cusano, F. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Ivanov, V. D., E-mail: andrea4work@gmail.com [European Southern Observatory, Ave. Alonso de Cordova 3107, Casilla 19001, Santiago 19 (Chile)

2014-03-01

We report on 13 subarcsecond binaries, detected by means of lunar occultations in the near-infrared at the ESO Very Large Telescope (VLT). They are all first-time detections except for the visual binary HD 158122, which we resolved for the first time in the near-infrared. The primaries have magnitudes in the range K = 4.5-10.0, and companions in the range K = 6.8-11.1. The magnitude differences have a median value of 2.4, with the largest being 4.6. The projected separations are in the range of 4-168 mas, with a median of 13 mas. We discuss and compare our results with the available literature. With this paper, we conclude the mining for binary star detections in the 1226 occultations recorded at the VLT with the ISAAC instrument. We expect that the majority of these binaries may be unresolvable by adaptive optics on current telescopes, and they might be challenging for long-baseline interferometry. However, they constitute an interesting sample for future larger telescopes and for astrometric missions such as GAIA.

IRAS far-infrared colours of normal stars

Science.gov (United States)

Waters, L. B. F. M.; Cote, J.; Aumann, H. H.

1987-01-01

The analysis of IRAS observations at 12, 25, 60 and 100 microns of bright stars of spectral type O to M is presented. The objective is to identify the 'normal' stellar population and to characterize it in terms of the relationships between (B-V) and (V-/12/), between (R-I) and (V-/12/), and as a function of spectral type and luminosity class. A well-defined relation is found between the color of normal stars in the visual (B-V), (R-I) and in the IR, which does not depend on luminosity class. Using the (B-V), (V-/12/) relation for normal stars, it is found that B and M type stars show a large fraction of deviating stars, mostly with IR excess that is probably caused by circumstellar material. A comparison of IRAS colors with the Johnson colors as a function of spectral type shows good agreement except for the K0 to M5 type stars. The results will be useful in identifying the deviating stars detected with IRAS.

Stars and Flowers, Flowers and Stars

Science.gov (United States)

Minti, Hari

2012-12-01

The author, a graduated from the Bucharest University (1964), actually living and working in Israel, concerns his book to variable stars and flowers, two domains of his interest. The analogies includes double stars, eclipsing double stars, eclipses, Big Bang. The book contains 34 chapters, each of which concerns various relations between astronomy and other sciences and pseudosciences such as Psychology, Religion, Geology, Computers and Astrology (to which the author is not an adherent). A special part of the book is dedicated to archeoastronomy and ethnoastronomy, as well as to history of astronomy. Between the main points of interest of these parts: ancient sanctuaries in Sarmizegetusa (Dacia), Stone Henge(UK) and other. The last chapter of the book is dedicated to flowers. The book is richly illustrated. It is designed for a wide circle of readers.

The STAR Vertex Position Detector

Energy Technology Data Exchange (ETDEWEB)

Llope, W.J., E-mail: llope@rice.edu [Rice University, Houston, TX 77005 (United States); Zhou, J.; Nussbaum, T. [Rice University, Houston, TX 77005 (United States); Hoffmann, G.W. [University of Texas, Austin, TX 78712 (United States); Asselta, K. [Brookhaven National Laboratory, Upton, NY 11973 (United States); Brandenburg, J.D.; Butterworth, J. [Rice University, Houston, TX 77005 (United States); Camarda, T.; Christie, W. [Brookhaven National Laboratory, Upton, NY 11973 (United States); Crawford, H.J. [University of California, Berkeley, CA 94720 (United States); Dong, X. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Engelage, J. [University of California, Berkeley, CA 94720 (United States); Eppley, G.; Geurts, F. [Rice University, Houston, TX 77005 (United States); Hammond, J. [Brookhaven National Laboratory, Upton, NY 11973 (United States); Judd, E. [University of California, Berkeley, CA 94720 (United States); McDonald, D.L. [Rice University, Houston, TX 77005 (United States); Perkins, C. [University of California, Berkeley, CA 94720 (United States); Ruan, L.; Scheblein, J. [Brookhaven National Laboratory, Upton, NY 11973 (United States); and others

2014-09-21

The 2×3 channel pseudo Vertex Position Detector (pVPD) in the STAR experiment at RHIC has been upgraded to a 2×19 channel detector in the same acceptance, called the Vertex Position Detector (VPD). This detector is fully integrated into the STAR trigger system and provides the primary input to the minimum-bias trigger in Au+Au collisions. The information from the detector is used both in the STAR Level-0 trigger and offline to measure the location of the primary collision vertex along the beam pipe and the event “start time” needed by other fast-timing detectors in STAR. The offline timing resolution of single detector channels in full-energy Au+Au collisions is ∼100 ps, resulting in a start time resolution of a few tens of picoseconds and a resolution on the primary vertex location of ∼1 cm.

First results from the ground calibration of the NuSTAR flight optics

DEFF Research Database (Denmark)

Koglin, Jason E.; An, HongJun; Barriere, Nicolas

2011-01-01

NuSTAR is a hard X-ray satellite experiment to be launched in 2012. Two optics with 10.15 m focal length focus Xrays with energies between 5 and 80 keV onto CdZnTe detectors located at the end of a deployable mast. The FM1 and FM2 flight optics were built at the same time based on the same design...

Cold DUst around NEarby Stars (DUNES). First results. A resolved exo-Kuiper belt around the solar-like star ζ2 Ret

NARCIS (Netherlands)

Eiroa, C.; Fedele, D.; Maldonado, J.; Gonzalez-Garcia, B. M.; Rodmann, J.; Heras, A. M.; Pilbratt, G. L.; Augereau, J. -Ch.; Mora, A.; Montesinos, B.; Ardila, D.; Bryden, G.; Liseau, R.; Stapelfeldt, K.; Launhardt, R.; Solano, E.; Bayo, A.; Absil, O.; Arevalo, M.; Barrado, D.; Beichmann, C.; Danchi, W.; del Burgo, C.; Ertel, S.; Fridlund, M.; Fukagawa, M.; Gutierrez, R.; Gruen, E.; Kamp, I.; Krivov, A.; Lebreton, J.; Loehne, T.; Lorente, R.; Marshall, J.; Martinez-Arnaiz, R.; Meeus, G.; Montes, D.; Morbidelli, A.; Mueller, S.; Mutschke, H.; Nakagawa, T.; Olofsson, G.; Ribas, I.; Roberge, A.; Sanz-Forcada, J.; Thebault, P.; White, G. J.; Wolf, S.; Walker, H.

We present the first far-IR observations of the solar-type stars δ Pav, HR 8501, 51 Peg and ζ2 Ret, taken within the context of the DUNES Herschel open time key programme (OTKP). This project uses the PACS and SPIRE instruments with the objective of studying infrared excesses due to exo-Kuiper belts

High-precision atmospheric parameter and abundance determination of massive stars, and consequences for stellar and Galactic evolution

International Nuclear Information System (INIS)

Nieva, Maria-Fernanda; Przybilla, Norbert; Irrgang, Andreas

2011-01-01

The derivation of high precision/accuracy parameters and chemical abundances of massive stars is of utmost importance to the fields of stellar evolution and Galactic chemical evolution. We concentrate on the study of OB-type stars near the main sequence and their evolved progeny, the BA-type supergiants, covering masses of ∼6 to 25 solar masses and a range in effective temperature from ∼8000 to 35 000 K. The minimization of the main sources of systematic errors in the atmospheric model computation, the observed spectra and the quantitative spectral analysis play a critical role in the final results. Our self-consistent spectrum analysis technique employing a robust non-LTE line formation allows precise atmospheric parameters of massive stars to be derived, achieving 1σ-uncertainties as low as 1% in effective temperature and ∼0.05–0.10 dex in surface gravity. Consequences on the behaviour of the chemical elements carbon, nitrogen and oxygen are discussed here in the context of massive star evolution and Galactic chemical evolution, showing tight relations covered in previous work by too large statistical and systematic uncertainties. The spectral analysis of larger star samples, like from the upcoming Gaia-ESO survey, may benefit from these findings.

Burst switching without guard interval in all-optical software-define star intra-data center network

Science.gov (United States)

Ji, Philip N.; Wang, Ting

2014-02-01

Optical switching has been introduced in intra-data center networks (DCNs) to increase capacity and to reduce power consumption. Recently we proposed a star MIMO OFDM-based all-optical DCN with burst switching and software-defined networking. Here, we introduce the control procedure for the star DCN in detail for the first time. The timing, signaling, and operation are described for each step to achieve efficient bandwidth resource utilization. Furthermore, the guidelines for the burst assembling period selection that allows burst switching without guard interval are discussed. The star all-optical DCN offers flexible and efficient control for next-generation data center application.

Radiation pressure in super star cluster formation

Science.gov (United States)

Tsang, Benny T.-H.; Milosavljević, Miloš

2018-05-01

The physics of star formation at its extreme, in the nuclei of the densest and the most massive star clusters in the universe—potential massive black hole nurseries—has for decades eluded scrutiny. Spectroscopy of these systems has been scarce, whereas theoretical arguments suggest that radiation pressure on dust grains somehow inhibits star formation. Here, we harness an accelerated Monte Carlo radiation transport scheme to report a radiation hydrodynamical simulation of super star cluster formation in turbulent clouds. We find that radiation pressure reduces the global star formation efficiency by 30-35%, and the star formation rate by 15-50%, both relative to a radiation-free control run. Overall, radiation pressure does not terminate the gas supply for star formation and the final stellar mass of the most massive cluster is ˜1.3 × 106 M⊙. The limited impact as compared to in idealized theoretical models is attributed to a radiation-matter anti-correlation in the supersonically turbulent, gravitationally collapsing medium. In isolated regions outside massive clusters, where the gas distribution is less disturbed, radiation pressure is more effective in limiting star formation. The resulting stellar density at the cluster core is ≥108 M⊙ pc-3, with stellar velocity dispersion ≳ 70 km s-1. We conclude that the super star cluster nucleus is propitious to the formation of very massive stars via dynamical core collapse and stellar merging. We speculate that the very massive star may avoid the claimed catastrophic mass loss by continuing to accrete dense gas condensing from a gravitationally-confined ionized phase.

IUE observations of new A star candidate proto-planetary systems

Science.gov (United States)

Grady, Carol A.

1994-01-01

As a result of the detection of accreting gas in the A5e PMS Herbig Ae star, HR 5999, most of the observations for this IUE program were devoted to Herbig Ae stars rather than to main sequence A stars. Mid-UV emission at optical minimum light was detected for UX Ori (A1e), BF Ori (A5e), and CQ Tau (F2e). The presence of accreting gas in HD 45677 and HD 50138 prompted reclassification of these stars as Herbig Be stars rather than as protoplanetary nebulae. Detailed results are discussed.

How bright planets became dim stars: planetary speculations in John Herschel's double star astronomy.

Science.gov (United States)

Case, Stephen

2014-03-01

Previous research on the origins of double star astronomy in the early nineteenth century emphasized the role mathematical methods and instrumentation played in motivating early observations of these objects. The work of the British astronomer John Herschel, however, shows that questions regarding the physical nature of double stars were also important. In particular, an analysis of John Herschel's early work on double stars illustrates the way in which speculations regarding these objects were shaped by assumptions of the properties of stars themselves. For Herschel, a major consideration in double star astronomy was distinguishing between types of double stars. Optical doubles were useful in determining parallax while binary doubles were not. In practice, classification of a specific double star pair into one of these categories was based on the assumption that stars were of approximately the same luminosity and thus differences in relative brightness between stars were caused by difference in distances. Such assumptions, though ultimately abandoned, would lead Herschel in the 1830s to advance the possibility that the dim companion stars in certain double star pairs were not stars at all but in fact planets. Copyright © 2014 Elsevier Ltd. All rights reserved.

Spectrophotometry of peculiar B and A stars. II. Eleven mercury-manganese stars

International Nuclear Information System (INIS)

Adelman, S.J.; Pyper, D.M.

1979-01-01

Spectrophotometry of eleven HgMn stars is presented for the optical region. As found in Paper I, the HgMn stars have systematically larger Δiota* and Δa values than the normal main sequence stars due to differences with respect to the mean continuum particularly of the lambda4464 values and the lambda5200 region, respectively. The HgMn stars exhibit a continuous range in the behavior of both the lambda4200 and lambda5200 regions between those stars that have index values larger than the appropriate criterion of presence and present definite evidence for the features to those stars with only a slight possibility of such features. The strengths of the lambda4200 and lambda5200 features appear not to be correlated. In the HgMn stars, both features may be due to differential line blocking. In the energy distribution of all eleven stars, the Balmer jump regions best fit the predictions of slightly hotter solar composition, log g=4.0, fully line blanketed model atmospheres than do the corresponding Paschen continua

Stars, their evolution and their stability

International Nuclear Information System (INIS)

Chandrasekhar, S.

1984-01-01

The most important fact concerning a star is its mass. It is measured in units of the mass of the sun, which is 2 x 10 33 g: stars with masses very much less than, or very much more than the mass of the sun are relatively infrequent. The current theories of stellar structure and evolution derive their successes largely from the fact that the following combination of the dimensions of a mass provides a correct measure of stellar masses: natural constant = (hc/G) 3 2 1/H 2 approx. = 29.2 times the mass of sun where G is the constant of gravitation and H is the mass of hydrogen atom. There is an upper limit, M sub limit, to the mass of stars which can become degenerate configurations, as the last stage in their evolution; and stars with M > M sub limit must have end states which cannot be predicted from the considerations presented in this paper. For stars with mass less than 0.43 x the mass of the sun, the end stage of evolution can only be that of the white dwarfs. The inability of massive stars to become white dwarfs must result in the development of much more extreme conditions in their interiors and eventually in the onset of gravitational collapse attended by the supernova phenomena. Neutron stars or black holes form as the natural end products of stellar evolution of massive stars. 24 references, 7 figures, 2 tables

X-ray sources in regions of star formation. I. The naked T Tauri stars

International Nuclear Information System (INIS)

Walter, F.M.

1986-01-01

Einstein X-ray observations of regions of active star formation in Taurus, Ophiuchus, and Corona Australis show a greatly enhanced surface density of stellar X-ray sources over that seen in other parts of the sky. Many of the X-ray sources are identified with low-mass, pre-main-sequence stars which are not classical T Tauri stars. The X-ray, photometric, and spectroscopic data for these stars are discussed. Seven early K stars in Oph and CrA are likely to be 1-solar-mass post-T Tauri stars with ages of 10-million yr. The late K stars in Taurus are not post-T Tauri, but naked T Tauri stars, which are coeval with the T Tauri stars, differing mainly in the lack of a circumstellar envelope. 72 references

Wave Star

DEFF Research Database (Denmark)

Kramer, Morten; Brorsen, Michael; Frigaard, Peter

Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star.......Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star....

Axisymmetric general relativistic hydrodynamics: Long-term evolution of neutron stars and stellar collapse to neutron stars and black holes

International Nuclear Information System (INIS)

Shibata, Masaru

2003-01-01

We report a new implementation for axisymmetric simulation in full general relativity. In this implementation, the Einstein equations are solved using the Nakamura-Shibata formulation with the so-called cartoon method to impose an axisymmetric boundary condition, and the general relativistic hydrodynamic equations are solved using a high-resolution shock-capturing scheme based on an approximate Riemann solver. As tests, we performed the following simulations: (i) long-term evolution of nonrotating and rapidly rotating neutron stars, (ii) long-term evolution of neutron stars of a high-amplitude damping oscillation accompanied with shock formation, (iii) collapse of unstable neutron stars to black holes, and (iv) stellar collapses to neutron stars. Tests (i)-(iii) were carried out with the Γ-law equation of state, and test (iv) with a more realistic parametric equation of state for high-density matter. We found that this new implementation works very well: It is possible to perform the simulations for stable neutron stars for more than 10 dynamical time scales, to capture strong shocks formed at stellar core collapses, and to accurately compute the mass of black holes formed after the collapse and subsequent accretion. In conclusion, this implementation is robust enough to apply to astrophysical problems such as stellar core collapse of massive stars to a neutron star, and black hole, phase transition of a neutron star to a high-density star, and accretion-induced collapse of a neutron star to a black hole. The result for the first simulation of stellar core collapse to a neutron star started from a realistic initial condition is also presented

Pulsar glitches in a strangeon star model

Science.gov (United States)

Lai, X. Y.; Yun, C. A.; Lu, J. G.; Lü, G. L.; Wang, Z. J.; Xu, R. X.

2018-05-01

Pulsar-like compact stars provide us a unique laboratory to explore properties of dense matter at supra-nuclear densities. One of the models for pulsar-like stars is that they are totally composed of "strangeons", and in this paper, we studied the pulsar glitches in a strangeon star model. Strangeon stars would be solidified during cooling, and the solid stars would be natural to have glitches as the result of starquakes. Based on the starquake model established before, we proposed that when the starquake occurs, the inner motion of the star which changes the moment of inertia and has impact on the glitch sizes, is divided into plastic flow and elastic motion. The plastic flow which is induced in the fractured part of the outer layer, would move tangentially to redistribute the matter of the star and would be hard to recover. The elastic motion, on the other hand, changes its shape and would recover significantly. Under this scenario, we could understand the behaviors of glitches without significant energy releasing, including the Crab and the Vela pulsars, in an uniform model. We derive the recovery coefficient as a function of glitch size, as well as the time interval between two successive glitches as the function of the released stress. Our results show consistency with observational data under reasonable ranges of parameters. The implications on the oblateness of the Crab and the Vela pulsars are discussed.

STAR*D: helping to close the gap between science and practice.

Science.gov (United States)

Shern, David L; Moran, Hazel

2009-11-01

Practical clinical trials, such as STAR*D (Sequenced Treatment Alternatives to Relieve Depression), extend the traditional randomized controlled trial to real-world settings. Consumers and clinicians should be encouraged by STAR*D's 70% remission rate and should realize that for many participants remission required medication switching and augmentation. Policy makers should recognize the importance of easy access to a full range of treatments. Researchers should be sobered by the high attrition rate and the 30% of participants who did not achieve remission. Although more such practical trials are needed, future work must more meaningfully involve consumers in design, analysis, and interpretation.

Neutron star formation in theoretical supernovae. Low mass stars and white dwarfs

International Nuclear Information System (INIS)

Nomoto, K.

1986-01-01

The presupernova evolution of stars that form semi-degenerate or strongly degenerate O + Ne + Mg cores is discussed. For the 10 to 13 Msub solar stars, behavior of off-center neon flashes is crucial. The 8 to 10 m/sub solar stars do not ignite neon and eventually collapse due to electron captures. Properties of supernova explosions and neutron stars expected from these low mass progenitors are compared with the Crab nebula. The conditions for which neutron stars form from accretion-induced collapse of white dwarfs in clsoe binary systems is also examined

2003 status report savings estimates for the energy star(R)voluntary labeling program

Energy Technology Data Exchange (ETDEWEB)

Webber, Carrie A.; Brown, Richard E.; McWhinney, Marla

2004-11-09

ENERGY STAR(R) is a voluntary labeling program designed to identify and promote energy-efficient products, buildings and practices. Operated jointly by the Environmental Protection Agency (EPA) and the U.S. Department of Energy (DOE), ENERGY STAR labels exist for more than thirty products, spanning office equipment, residential heating and cooling equipment, commercial and residential lighting, home electronics, and major appliances. This report presents savings estimates for a subset of ENERGY STAR program activities, focused primarily on labeled products. We present estimates of the energy, dollar and carbon savings achieved by the program in the year 2002, what we expect in 2003, and provide savings forecasts for two market penetration scenarios for the period 2003 to 2020. The target market penetration forecast represents our best estimate of future ENERGY STAR savings. It is based on realistic market penetration goals for each of the products. We also provide a forecast under the assumption of 100 percent market penetration; that is, we assume that all purchasers buy ENERGY STAR-compliant products instead of standard efficiency products throughout the analysis period.

2002 status report: Savings estimates for the ENERGY STAR(R) voluntary labeling program

Energy Technology Data Exchange (ETDEWEB)

Webber, Carrie A.; Brown, Richard E.; McWhinney, Marla; Koomey, Jonathan

2003-03-03

ENERGY STAR [registered trademark] is a voluntary labeling program designed to identify and promote energy-efficient products, buildings and practices. Operated jointly by the Environmental Protection Agency (EPA) and the U.S. Department of Energy (DOE), ENERGY STAR labels exist for more than thirty products, spanning office equipment, residential heating and cooling equipment, commercial and residential lighting, home electronics, and major appliances. This report presents savings estimates for a subset of ENERGY STAR program activities, focused primarily on labeled products. We present estimates of the energy, dollar and carbon savings achieved by the program in the year 2001, what we expect in 2002, and provide savings forecasts for two market penetration scenarios for the period 2002 to 2020. The target market penetration forecast represents our best estimate of future ENERGY STAR savings. It is based on realistic market penetration goals for each of the products. We also provide a forecast under the assumption of 100 percent market penetration; that is, we assume that all purchasers buy ENERGY STAR-compliant products instead of standard efficiency products throughout the analysis period.

Beryllium abundances in Hg-Mn stars

International Nuclear Information System (INIS)

Boesgaard, A.M.; Heacox, W.D.; Wolff, S.C.; Borsenberger, J.; Praderie, F.

1982-01-01

The Hg-Mn stars show anomalous line strengths of many chemical elements including Be. We have observed the Be ii resonance doublet at lambdalambda 3130, 3131 at 6.7 A mm -1 in 43 Hg-Mn stars and 10 normal stars in the same temperature range with the coude spectrograph of the 2.24 m University of Hawaii telescope at Mauna Kea. Measured equivalent widths of the two lines and/or the blend of the doublet have been compared with predictions from (1) LTE model atmospheres and (2) non-LTE line formation on non-LTE model atmospheres. (For strong Be ii lines, the LTE calculations result in more Be by factors of 2 to 4 than do the non-LTE calculations.) Overabundances of factors of 20--2 x 10 4 relative to solar have been found for 75% of the Hg-Mn stars. The 25% with little or no Be are typically among the cooler Hg-Mn stars, but for the stars with Be excesses, there is only marginal evidence for a correlationi of the size of the overabundance and temperature. It is suggested that diffusion driven by radiation pressure is responsible for the observed Be abundance anomalies

TIME-VARYING DYNAMICAL STAR FORMATION RATE

Energy Technology Data Exchange (ETDEWEB)

Lee, Eve J.; Chang, Philip; Murray, Norman, E-mail: evelee@berkeley.edu [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, University of Toronto, Toronto, ON M5S 3H8 (Canada)

2015-02-10

We present numerical evidence of dynamic star formation in which the accreted stellar mass grows superlinearly with time, roughly as t {sup 2}. We perform simulations of star formation in self-gravitating hydrodynamic and magnetohydrodynamic turbulence that is continuously driven. By turning the self-gravity of the gas in the simulations on or off, we demonstrate that self-gravity is the dominant physical effect setting the mass accretion rate at early times before feedback effects take over, contrary to theories of turbulence-regulated star formation. We find that gravitational collapse steepens the density profile around stars, generating the power-law tail on what is otherwise a lognormal density probability distribution function. Furthermore, we find turbulent velocity profiles to flatten inside collapsing regions, altering the size-line width relation. This local flattening reflects enhancements of turbulent velocity on small scales, as verified by changes to the velocity power spectra. Our results indicate that gas self-gravity dynamically alters both density and velocity structures in clouds, giving rise to a time-varying star formation rate. We find that a substantial fraction of the gas that forms stars arrives via low-density flows, as opposed to accreting through high-density filaments.

Gemini Spectroscopic Survey of Young Intermediate-Mass Star-Forming Regions

Science.gov (United States)

Lundquist, Michael; Kobulnicky, Henry

2018-01-01

The majority of stars form in embedded clusters. Current research into star formation has focused on either high-mass star-forming regions or low-mass star-forming regions. We present the results from a Gemini spectroscopic survey of young intermediate-mass star-forming regions. These are star forming regions selected to produce stars up to but not exceeding 8 solar masses. We obtained spectra of these regions with GNIRS on Gemini North and Flamingos-2 on Gemini South. We also combine this with near-infrared imaging from 2MASS, UKIDSS, and VVV to study the stellar content.

Minnesota STAR Project: Meeting the Needs of Struggling Adult Readers

Science.gov (United States)

Johnson, Kimberly A.; Frank, Margaret M.

2012-01-01

This paper reports on findings and implications from a two-year evaluation of the Minnesota STudent Achievement in Reading (STAR) Project. This long-term, job-embedded, professional development activity is provided for Minnesota Adult Basic Education (ABE) practitioners serving intermediate-level adult students reading between 4.0 to 8.9 grade…

THE STAR FORMATION HISTORY OF THE LARGE MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Harris, Jason; Zaritsky, Dennis

2009-01-01

We present the first ever global, spatially resolved reconstruction of the star formation history (SFH) of the Large Magellanic Cloud (LMC), based on the application of our StarFISH analysis software to the multiband photometry of 20 million of its stars from the Magellanic Clouds Photometric Survey. The general outlines of our results are consistent with previously published results: following an initial burst of star formation, there was a quiescent epoch from approximately 12 to 5 Gyr ago. Star formation then resumed and has proceeded until the current time at an average rate of roughly 0.2 M sun yr -1 , with temporal variations at the factor of 2 level. The re-ignition of star formation about 5 Gyr ago, in both the LMC and Small Magellanic Cloud (SMC), is suggestive of a dramatic event at that time in the Magellanic system. Among the global variations in the recent star formation rate are peaks at roughly 2 Gyr, 500 Myr, 100 Myr, and 12 Myr. The peaks at 500 Myr and 2 Gyr are nearly coincident with similar peaks in the SFH of the SMC, suggesting a joint history for these galaxies extending back at least several Gyr. The chemical enrichment history recovered from our StarFISH analysis is in broad agreement with that inferred from the LMC's star cluster population, although our constraints on the ancient chemical enrichment history are weak. We conclude from the concordance between the star formation and chemical enrichment histories of the field and cluster populations that the field and cluster star formation modes are tightly coupled.

The HOSTS Survey—Exozodiacal Dust Measurements for 30 Stars

Science.gov (United States)

Ertel, S.; Defrère, D.; Hinz, P.; Mennesson, B.; Kennedy, G. M.; Danchi, W. C.; Gelino, C.; Hill, J. M.; Hoffmann, W. F.; Rieke, G.; Shannon, A.; Spalding, E.; Stone, J. M.; Vaz, A.; Weinberger, A. J.; Willems, P.; Absil, O.; Arbo, P.; Bailey, V. P.; Beichman, C.; Bryden, G.; Downey, E. C.; Durney, O.; Esposito, S.; Gaspar, A.; Grenz, P.; Haniff, C. A.; Leisenring, J. M.; Marion, L.; McMahon, T. J.; Millan-Gabet, R.; Montoya, M.; Morzinski, K. M.; Pinna, E.; Power, J.; Puglisi, A.; Roberge, A.; Serabyn, E.; Skemer, A. J.; Stapelfeldt, K.; Su, K. Y. L.; Vaitheeswaran, V.; Wyatt, M. C.

2018-05-01

The Hunt for Observable Signatures of Terrestrial Systems survey searches for dust near the habitable zones (HZs) around nearby, bright main-sequence stars. We use nulling interferometry in the N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early-type and Sun-like stars, but decrease from {60}-21+16% for stars with previously detected cold dust to {8}-3+10% for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focusing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable Large Binocular Telescope Interferometer (LBTI) excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are limited so far, and extending the survey is critical to informing the design of future exo-Earth imaging surveys.

HUBBLE TARANTULA TREASURY PROJECT. III. PHOTOMETRIC CATALOG AND RESULTING CONSTRAINTS ON THE PROGRESSION OF STAR FORMATION IN THE 30 DORADUS REGION

Energy Technology Data Exchange (ETDEWEB)

Sabbi, E.; Anderson, J.; Cignoni, M.; Marel, R. P. van der; Panagia, N.; Sana, H.; Aloisi, A.; Arab, H.; Gordon, K. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States); Lennon, D. J. [ESA—European Space Astronomy Center, Apdo. de Correo 78, E-28691 Associate Villanueva de la Cañada, Madrid (Spain); Zaritsky, D. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Marchi, G. De [Space Science Department, European Space Agency, Keplerlaan 1, 2200 AG Noordwijk (Netherlands); Gouliermis, D. A. [Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Grebel, E. K. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); III, J. S. Gallagher [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States); Smith, L. J. [ESA/STScI, 3700 San Martin Drive, Baltimore, MD, 21218 (United States); Tosi, M. [Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Evans, C. J. [UK Astronomy Technology Center, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Boyer, M. [Observational Cosmology Lab, Code 665, NASA, Goddard Space Flight Center, Greenbelt, MD, 20771 (United States); Mink, S. E. de, E-mail: sabbi@stsci.edu [Astronomical Institute “Anton Pannekoek,”University of Amsterdam, P.O. Box 94249, NL-1090 GE Amsterdam (Netherlands); and others

2016-01-15

We present and describe the astro-photometric catalog of more than 800,000 sources found in the Hubble Tarantula Treasury Project (HTTP). HTTP is a Hubble Space Telescope Treasury program designed to image the entire 30 Doradus region down to the sub-solar (∼0.5 M{sub ⊙}) mass regime using the Wide Field Camera 3 and the Advanced Camera for Surveys. We observed 30 Doradus in the near-ultraviolet (F275W, F336W), optical (F555W, F658N, F775W), and near-infrared (F110W, F160W) wavelengths. The stellar photometry was measured using point-spread function fitting across all bands simultaneously. The relative astrometric accuracy of the catalog is 0.4 mas. The astro-photometric catalog, results from artificial star experiments, and the mosaics for all the filters are available for download. Color–magnitude diagrams are presented showing the spatial distributions and ages of stars within 30 Dor as well as in the surrounding fields. HTTP provides the first rich and statistically significant sample of intermediate- and low-mass pre-main sequence candidates and allows us to trace how star formation has been developing through the region. The depth and high spatial resolution of our analysis highlight the dual role of stellar feedback in quenching and triggering star formation on the giant H ii region scale. Our results are consistent with stellar sub-clustering in a partially filled gaseous nebula that is offset toward our side of the Large Magellanic Cloud.

General Relativity and Compact Stars

International Nuclear Information System (INIS)

Glendenning, Norman K.

2005-01-01

Compact stars--broadly grouped as neutron stars and white dwarfs--are the ashes of luminous stars. One or the other is the fate that awaits the cores of most stars after a lifetime of tens to thousands of millions of years. Whichever of these objects is formed at the end of the life of a particular luminous star, the compact object will live in many respects unchanged from the state in which it was formed. Neutron stars themselves can take several forms--hyperon, hybrid, or strange quark star. Likewise white dwarfs take different forms though only in the dominant nuclear species. A black hole is probably the fate of the most massive stars, an inaccessible region of spacetime into which the entire star, ashes and all, falls at the end of the luminous phase. Neutron stars are the smallest, densest stars known. Like all stars, neutron stars rotate--some as many as a few hundred times a second. A star rotating at such a rate will experience an enormous centrifugal force that must be balanced by gravity or else it will be ripped apart. The balance of the two forces informs us of the lower limit on the stellar density. Neutron stars are 10 14 times denser than Earth. Some neutron stars are in binary orbit with a companion. Application of orbital mechanics allows an assessment of masses in some cases. The mass of a neutron star is typically 1.5 solar masses. They can therefore infer their radii: about ten kilometers. Into such a small object, the entire mass of our sun and more, is compressed

STATISTICAL PROPERTIES OF GALACTIC δ SCUTI STARS: REVISITED

International Nuclear Information System (INIS)

Chang, S.-W.; Kim, D.-W.; Byun, Y.-I.; Protopapas, P.

2013-01-01

We present statistical characteristics of 1578 δ Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodríguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates, color, rotational velocity, spectral type, period, amplitude, and binarity. The majority of our sample is well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag), and spectral types (A-F type). Given this list of δ Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types, and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in Rodríguez's work. All the δ Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their uniqueness in showing δ Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the Web interface http://stardb.yonsei.ac.kr/DeltaScuti.

Introduction to neutron stars

Energy Technology Data Exchange (ETDEWEB)

Lattimer, James M. [Dept. of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States)

2015-02-24

Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

Polarization of Be stars

International Nuclear Information System (INIS)

Johns, M.W.

1975-01-01

Linear polarization of starlight may be produced by electron scattering in the extended atmospheres of early type stars. Techniques are investigated for the measurement and interpretation of this polarization. Polarimetric observations were made of twelve visual double star systems in which at least one member was a B type star as a means of separating the intrinsic stellar polarization from the polarization produced in the interstellar medium. Four of the double stars contained a Be star. Evidence for intrinsic polarization was found in five systems including two of the Be systems, one double star with a short period eclipsing binary, and two systems containing only normal early type stars for which emission lines have not been previously reported. The interpretation of these observations in terms of individual stellar polarizations and their wavelength dependence is discussed. The theoretical basis for the intrinsic polarization of early type stars is explored with a model for the disk-like extended atmospheres of Be stars. Details of a polarimeter for the measurement of the linear polarization of astronomical point sources are also presented with narrow band (Δ lambda = 100A) measurements of the polarization of γ Cas from lambda 4000 to lambda 5800

Star pattern recognition algorithm aided by inertial information

Science.gov (United States)

Liu, Bao; Wang, Ke-dong; Zhang, Chao

2011-08-01

Star pattern recognition is one of the key problems of the celestial navigation. The traditional star pattern recognition approaches, such as the triangle algorithm and the star angular distance algorithm, are a kind of all-sky matching method whose recognition speed is slow and recognition success rate is not high. Therefore, the real time and reliability of CNS (Celestial Navigation System) is reduced to some extent, especially for the maneuvering spacecraft. However, if the direction of the camera optical axis can be estimated by other navigation systems such as INS (Inertial Navigation System), the star pattern recognition can be fulfilled in the vicinity of the estimated direction of the optical axis. The benefits of the INS-aided star pattern recognition algorithm include at least the improved matching speed and the improved success rate. In this paper, the direction of the camera optical axis, the local matching sky, and the projection of stars on the image plane are estimated by the aiding of INS firstly. Then, the local star catalog for the star pattern recognition is established in real time dynamically. The star images extracted in the camera plane are matched in the local sky. Compared to the traditional all-sky star pattern recognition algorithms, the memory of storing the star catalog is reduced significantly. Finally, the INS-aided star pattern recognition algorithm is validated by simulations. The results of simulations show that the algorithm's computation time is reduced sharply and its matching success rate is improved greatly.

The WFCAM multiwavelength Variable Star Catalog

Science.gov (United States)

Ferreira Lopes, C. E.; Dékány, I.; Catelan, M.; Cross, N. J. G.; Angeloni, R.; Leão, I. C.; De Medeiros, J. R.

2015-01-01

Context. Stellar variability in the near-infrared (NIR) remains largely unexplored. The exploitation of public science archives with data-mining methods offers a perspective for a time-domain exploration of the NIR sky. Aims: We perform a comprehensive search for stellar variability using the optical-NIR multiband photometric data in the public Calibration Database of the WFCAM Science Archive (WSA), with the aim of contributing to the general census of variable stars and of extending the current scarce inventory of accurate NIR light curves for a number of variable star classes. Methods: Standard data-mining methods were applied to extract and fine-tune time-series data from the WSA. We introduced new variability indices designed for multiband data with correlated sampling, and applied them for preselecting variable star candidates, i.e., light curves that are dominated by correlated variations, from noise-dominated ones. Preselection criteria were established by robust numerical tests for evaluating the response of variability indices to the colored noise characteristic of the data. We performed a period search using the string-length minimization method on an initial catalog of 6551 variable star candidates preselected by variability indices. Further frequency analysis was performed on positive candidates using three additional methods in combination, in order to cope with aliasing. Results: We find 275 periodic variable stars and an additional 44 objects with suspected variability with uncertain periods or apparently aperiodic variation. Only 44 of these objects had been previously known, including 11 RR Lyrae stars on the outskirts of the globular cluster M 3 (NGC 5272). We provide a preliminary classification of the new variable stars that have well-measured light curves, but the variability types of a large number of objects remain ambiguous. We classify most of the new variables as contact binary stars, but we also find several pulsating stars, among which

INFRARED TWO-COLOR DIAGRAMS FOR AGB STARS, POST-AGB STARS, AND PLANETARY NEBULAE

Energy Technology Data Exchange (ETDEWEB)

Suh, Kyung-Won, E-mail: kwsuh@chungbuk.ac.kr [Department of Astronomy and Space Science, Chungbuk National University, Cheongju-City, 362-763 (Korea, Republic of)

2015-08-01

We present various infrared two-color diagrams (2CDs) for asymptotic giant branch (AGB) stars, post-AGB stars, and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use catalogs from the available literature for the sample of 4903 AGB stars (3373 O-rich; 1168 C-rich; 362 S-type), 660 post-AGB stars (326 post-AGB; 334 pre-PN), and 1510 PNe in our Galaxy. For each object in the catalog, we cross-identify the IRAS, AKARI, Midcourse Space Experiment, and 2MASS counterparts. The IR 2CDs can provide useful information about the structure and evolution of the dust envelopes as well as the central stars. To find possible evolutionary tracks from AGB stars to PNe on the 2CDs, we investigate spectral evolution of post-AGB stars by making simple but reasonable assumptions on the evolution of the central star and dust shell. We perform radiative transfer model calculations for the detached dust shells around evolving central stars in the post-AGB phase. We find that the theoretical dust shell model tracks using dust opacity functions of amorphous silicate and amorphous carbon roughly coincide with the densely populated observed points of AGB stars, post-AGB stars, and PNe on various IR 2CDs. Even though some discrepancies are inevitable, the end points of the theoretical post-AGB model tracks generally converge in the region of the observed points of PNe on most 2CDs.

NO CLEAR SUBMILLIMETER SIGNATURE OF SUPPRESSED STAR FORMATION AMONG X-RAY LUMINOUS ACTIVE GALACTIC NUCLEI

Energy Technology Data Exchange (ETDEWEB)

Harrison, C. M.; Alexander, D. M.; Mullaney, J. R.; Del Moro, A.; Rovilos, E. [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Altieri, B.; Coia, D. [Herschel Science Centre, European Space Astronomy Centre, Villanueva de la Canada, E-28691 Madrid (Spain); Charmandaris, V. [Department of Physics and Institute of Theoretical and Computation Physics, University of Crete, 71003 Heraklion (Greece); Daddi, E.; Le Floc' h, E.; Leiton, R. [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, Irfu/Service d Astrophysique, CEA-Saclay, Orme des Merisiers, F-91191 Gif-sur-Yvette Cedex (France); Dannerbauer, H. [Insitut fuer Astrophysik, Universitaet Wien, Tuerkenschanzstrasse 17, A-1180 Wien (Austria); Dasyra, K. [Observatoire de Paris, LERMA (CNRS:UMR8112), 61 Av. de l' Observatoire, F-75014 Paris (France); Dickinson, M.; Kartaltepe, J. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Hickox, R. C. [Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755 (United States); Ivison, R. J. [UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Magnelli, B.; Popesso, P.; Rosario, D. [Max-Planck-Institut fuer Extraterrestrische Physik (MPE), Postfach 1312, D-85741 Garching (Germany); and others

2012-11-20

Many theoretical models require powerful active galactic nuclei (AGNs) to suppress star formation in distant galaxies and reproduce the observed properties of today's massive galaxies. A recent study based on Herschel-SPIRE submillimeter observations claimed to provide direct support for this picture, reporting a significant decrease in the mean star formation rates (SFRs) of the most luminous AGNs (L{sub X} >10{sup 44} erg s{sup -1}) at z Almost-Equal-To 1-3 in the Chandra Deep Field-North (CDF-N). In this Letter, we extend these results using Herschel-SPIRE 250 {mu}m data in the COSMOS and Chandra Deep Field-South fields to achieve an order-of-magnitude improvement in the number of sources at L{sub X} >10{sup 44} erg s{sup -1}. On the basis of our analysis, we find no strong evidence for suppressed star formation in L{sub X} >10{sup 44} erg s{sup -1} AGNs at z Almost-Equal-To 1-3. The mean SFRs of the AGNs are constant over the broad X-ray luminosity range of L{sub X} Almost-Equal-To 10{sup 43}-10{sup 45} erg s{sup -1} (with mean SFRs consistent with typical star-forming galaxies at z Almost-Equal-To 2; (SFRs) Almost-Equal-To 100-200 M{sub Sun} yr{sup -1}). We suggest that the previous CDF-N results were likely due to low number statistics. We discuss our results in the context of current theoretical models.

Interacting binary stars

CERN Document Server

Sahade, Jorge; Ter Haar, D

1978-01-01

Interacting Binary Stars deals with the development, ideas, and problems in the study of interacting binary stars. The book consolidates the information that is scattered over many publications and papers and gives an account of important discoveries with relevant historical background. Chapters are devoted to the presentation and discussion of the different facets of the field, such as historical account of the development in the field of study of binary stars; the Roche equipotential surfaces; methods and techniques in space astronomy; and enumeration of binary star systems that are studied

Wolf-Rayet stars and O-star runaways with HIPPARCOS - I. Kinematics

NARCIS (Netherlands)

Moffat, AFJ; Marchenko, SV; Seggewiss, W; van der Hucht, KA; Schrijver, H; Stenholm, B; Lundstrom, [No Value; Gunawan, DYAS; Sutantyo, W; van den Heuvel, EPJ; De Cuyper, JP; Gomez, AE

Reliable systemic radial velocities are almost impossible to secure for Wolf-Rayet stars, difficult for O stars. Therefore, to study the motions - both systematic in the Galaxy and peculiar - of these two related types of hot, luminous star, we have examined the Hipparcos proper motions of some 70

Massive stars and the energy balance of the ISM: I. The imapct of an isolated 60 M star

Science.gov (United States)

Yorke, H. W.; Freyer, T.; Hensler, G.

2002-01-01

We present results of numerical simulations carried out with a 2D radiation hydrodynamics code in order to study the impact of massive stars on their surrounding interstellar medium. This first paper deals with the evolution of the circumstellar gas around an isolated 60 M star.

Evolution of variable stars

International Nuclear Information System (INIS)

Becker, S.A.

1986-08-01

Throughout the domain of the H R diagram lie groupings of stars whose luminosity varies with time. These variable stars can be classified based on their observed properties into distinct types such as β Cephei stars, δ Cephei stars, and Miras, as well as many other categories. The underlying mechanism for the variability is generally felt to be due to four different causes: geometric effects, rotation, eruptive processes, and pulsation. In this review the focus will be on pulsation variables and how the theory of stellar evolution can be used to explain how the various regions of variability on the H R diagram are populated. To this end a generalized discussion of the evolutionary behavior of a massive star, an intermediate mass star, and a low mass star will be presented. 19 refs., 1 fig., 1 tab

Calendar Year 2007 Program Benefits for ENERGY STAR Labeled Products

Energy Technology Data Exchange (ETDEWEB)

Sanchez, Marla Christine; Homan, Gregory; Brown, Richard

2008-10-31

ENERGY STAR is a voluntary energy efficiency-labeling program operated jointly by the United States Department of Energy and the United States Environmental Protection Agency (US EPA). Since the program inception in 1992, ENERGY STAR has become a leading international brand for energy efficient products. ENERGY STAR's central role in the development of regional, national, and international energy programs necessitates an open process whereby its program achievements to date as well as projected future savings are shared with committed stakeholders. Through 2007, the program saved 7.1 Quads of primary energy and avoided 128 MtC equivalent. The forecast shows that the program is expected to save 21.2 Quads of primary energy and avoid 375 MtC equivalent over the period 2008-2015. The sensitivity analysis bounds the best estimate of carbon avoided between 84 MtC and 172 MtC (1993 to 2007) and between 243 MtC and 519 MtC (2008 to 2015).

Models of symbiotic stars

Science.gov (United States)

Friedjung, Michael

1993-01-01

One of the most important features of symbiotic stars is the coexistence of a cool spectral component that is apparently very similar to the spectrum of a cool giant, with at least one hot continuum, and emission lines from very different stages of ionization. The cool component dominates the infrared spectrum of S-type symbiotics; it tends to be veiled in this wavelength range by what appears to be excess emission in D-type symbiotics, this excess usually being attributed to circumstellar dust. The hot continuum (or continua) dominates the ultraviolet. X-rays have sometimes also been observed. Another important feature of symbiotic stars that needs to be explained is the variability. Different forms occur, some variability being periodic. This type of variability can, in a few cases, strongly suggest the presence of eclipses of a binary system. One of the most characteristic forms of variability is that characterizing the active phases. This basic form of variation is traditionally associated in the optical with the veiling of the cool spectrum and the disappearance of high-ionization emission lines, the latter progressively appearing (in classical cases, reappearing) later. Such spectral changes recall those of novae, but spectroscopic signatures of the high-ejection velocities observed for novae are not usually detected in symbiotic stars. However, the light curves of the 'symbiotic nova' subclass recall those of novae. We may also mention in this connection that radio observations (or, in a few cases, optical observations) of nebulae indicate ejection from symbiotic stars, with deviations from spherical symmetry. We shall give a historical overview of the proposed models for symbiotic stars and make a critical analysis in the light of the observations of symbiotic stars. We describe the empirical approach to models and use the observational data to diagnose the physical conditions in the symbiotics stars. Finally, we compare the results of this empirical

The stars: an absolute radiometric reference for the on-orbit calibration of PLEIADES-HR satellites

Science.gov (United States)

Meygret, Aimé; Blanchet, Gwendoline; Mounier, Flore; Buil, Christian

2017-09-01

The accurate on-orbit radiometric calibration of optical sensors has become a challenge for space agencies who gather their effort through international working groups such as CEOS/WGCV or GSICS with the objective to insure the consistency of space measurements and to reach an absolute accuracy compatible with more and more demanding scientific needs. Different targets are traditionally used for calibration depending on the sensor or spacecraft specificities: from on-board calibration systems to ground targets, they all take advantage of our capacity to characterize and model them. But achieving the in-flight stability of a diffuser panel is always a challenge while the calibration over ground targets is often limited by their BDRF characterization and the atmosphere variability. Thanks to their agility, some satellites have the capability to view extra-terrestrial targets such as the moon or stars. The moon is widely used for calibration and its albedo is known through ROLO (RObotic Lunar Observatory) USGS model but with a poor absolute accuracy limiting its use to sensor drift monitoring or cross-calibration. Although the spectral irradiance of some stars is known with a very high accuracy, it was not really shown that they could provide an absolute reference for remote sensors calibration. This paper shows that high resolution optical sensors can be calibrated with a high absolute accuracy using stars. The agile-body PLEIADES 1A satellite is used for this demonstration. The star based calibration principle is described and the results are provided for different stars, each one being acquired several times. These results are compared to the official calibration provided by ground targets and the main error contributors are discussed.

Insights from Synthetic Star-forming Regions. III. Calibration of Measurement and Techniques of Star Formation Rates

Energy Technology Data Exchange (ETDEWEB)

Koepferl, Christine M.; Robitaille, Thomas P. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Dale, James E., E-mail: koepferl@usm.lmu.de [University Observatory Munich, Scheinerstr. 1, D-81679 Munich (Germany)

2017-11-01

Through an extensive set of realistic synthetic observations (produced in Paper I), we assess in this part of the paper series (Paper III) how the choice of observational techniques affects the measurement of star formation rates (SFRs) in star-forming regions. We test the accuracy of commonly used techniques and construct new methods to extract the SFR, so that these findings can be applied to measure the SFR in real regions throughout the Milky Way. We investigate diffuse infrared SFR tracers such as those using 24 μ m, 70 μ m and total infrared emission, which have been previously calibrated for global galaxy scales. We set up a toy model of a galaxy and show that the infrared emission is consistent with the intrinsic SFR using extra-galactic calibrated laws (although the consistency does not prove their reliability). For local scales, we show that these techniques produce completely unreliable results for single star-forming regions, which are governed by different characteristic timescales. We show how calibration of these techniques can be improved for single star-forming regions by adjusting the characteristic timescale and the scaling factor and give suggestions of new calibrations of the diffuse star formation tracers. We show that star-forming regions that are dominated by high-mass stellar feedback experience a rapid drop in infrared emission once high-mass stellar feedback is turned on, which implies different characteristic timescales. Moreover, we explore the measured SFRs calculated directly from the observed young stellar population. We find that the measured point sources follow the evolutionary pace of star formation more directly than diffuse star formation tracers.

Are star formation rates of galaxies bimodal?

Science.gov (United States)

Feldmann, Robert

2017-09-01

Star formation rate (SFR) distributions of galaxies are often assumed to be bimodal with modes corresponding to star-forming and quiescent galaxies, respectively. Both classes of galaxies are typically studied separately, and SFR distributions of star-forming galaxies are commonly modelled as lognormals. Using both observational data and results from numerical simulations, I argue that this division into star-forming and quiescent galaxies is unnecessary from a theoretical point of view and that the SFR distributions of the whole population can be well fitted by zero-inflated negative binomial distributions. This family of distributions has three parameters that determine the average SFR of the galaxies in the sample, the scatter relative to the star-forming sequence and the fraction of galaxies with zero SFRs, respectively. The proposed distributions naturally account for (I) the discrete nature of star formation, (II) the presence of 'dead' galaxies with zero SFRs and (III) asymmetric scatter. Excluding 'dead' galaxies, the distribution of log SFR is unimodal with a peak at the star-forming sequence and an extended tail towards low SFRs. However, uncertainties and biases in the SFR measurements can create the appearance of a bimodal distribution.

RADIATION-DRIVEN IMPLOSION AND TRIGGERED STAR FORMATION

International Nuclear Information System (INIS)

Bisbas, Thomas G.; Wuensch, Richard; Whitworth, Anthony P.; Walch, Stefanie; Hubber, David A.

2011-01-01

We present simulations of initially stable isothermal clouds exposed to ionizing radiation from a discrete external source, and identify the conditions that lead to radiatively driven implosion and star formation. We use the smoothed particle hydrodynamics code SEREN and a HEALPix-based photoionization algorithm to simulate the propagation of the ionizing radiation and the resulting dynamical evolution of the cloud. We find that the incident ionizing flux, Φ LyC , is the critical parameter determining the cloud evolution. At moderate fluxes, a large fraction of the cloud mass is converted into stars. As the flux is increased, the fraction of the cloud mass that is converted into stars and the mean masses of the individual stars both decrease. Very high fluxes simply disperse the cloud. Newly formed stars tend to be concentrated along the central axis of the cloud (i.e., the axis pointing in the direction of the incident flux). For given cloud parameters, the time, t * , at which star formation starts is proportional to Φ -1/3 LyC . The pattern of star formation found in the simulations is similar to that observed in bright-rimmed clouds.

A new method for determining which stars are near a star sensor field-of-view

Science.gov (United States)

Yates, Russell E., Jr.; Vedder, John D.

1991-01-01

A new method is described for determining which stars in a navigation star catalog are near a star sensor field of view (FOV). This method assumes that an estimate of spacecraft inertial attitude is known. Vector component ranges for the star sensor FOV are computed, so that stars whose vector components lie within these ranges are near the star sensor FOV. This method requires no presorting of the navigation star catalog, and is more efficient than tradition methods.

Star identification methods, techniques and algorithms

CERN Document Server

Zhang, Guangjun

2017-01-01

This book summarizes the research advances in star identification that the author’s team has made over the past 10 years, systematically introducing the principles of star identification, general methods, key techniques and practicable algorithms. It also offers examples of hardware implementation and performance evaluation for the star identification algorithms. Star identification is the key step for celestial navigation and greatly improves the performance of star sensors, and as such the book include the fundamentals of star sensors and celestial navigation, the processing of the star catalog and star images, star identification using modified triangle algorithms, star identification using star patterns and using neural networks, rapid star tracking using star matching between adjacent frames, as well as implementation hardware and using performance tests for star identification. It is not only valuable as a reference book for star sensor designers and researchers working in pattern recognition and othe...

Cyclotron Lines in Accreting Neutron Star Spectra

Science.gov (United States)

Wilms, Jörn; Schönherr, Gabriele; Schmid, Julia; Dauser, Thomas; Kreykenbohm, Ingo

2009-05-01

Cyclotron lines are formed through transitions of electrons between discrete Landau levels in the accretion columns of accreting neutron stars with strong (1012 G) magnetic fields. We summarize recent results on the formation of the spectral continuum of such systems, describe recent advances in the modeling of the lines based on a modification of the commonly used Monte Carlo approach, and discuss new results on the dependence of the measured cyclotron line energy from the luminosity of transient neutron star systems. Finally, we show that Simbol-X will be ideally suited to build and improve the observational database of accreting and strongly magnetized neutron stars.

On the evolution of stars

International Nuclear Information System (INIS)

Kippenhahn, R.

1989-01-01

A popular survey is given of the present knowledge on evolution and ageing of stars. Main sequence stars, white dwarf stars, and red giant stars are classified in the Hertzsprung-Russell (HR)-diagram by measurable quantities: surface temperature and luminosity. From the HR-diagram it can be concluded to star mass and age. Star-forming processes in interstellar clouds as well as stellar burning processes are illustrated. The changes occurring in a star due to the depletion of the nuclear energy reserve are described. In this frame the phenomena of planetary nebulae, supernovae, pulsars, neutron stars as well as of black holes are explained

MAGNETIC FIELDS OF STARS

OpenAIRE

Bychkov, V. D.; Bychkova, L. V.; Madej, J.

2008-01-01

Now it is known about 1212 stars of the main sequence and giants (from them 610 stars - it is chemically peculiarity (CP) stars) for which direct measurements of magnetic fields were spent (Bychkov et al.,2008). Let's consider, what representations were generated about magnetic fields (MT) of stars on the basis of available observations data.

Filament and core formation in nearby molecular clouds: results from the CARMA Large Area Star Formation Survey

Science.gov (United States)

Storm, Shaye; Mundy, Lee G.; Fernández-López, Manuel; Lee, Katherine I.; Ostriker, Eve C.; Looney, Leslie; Chen, Che-Yu; Classy Collaboration

2015-01-01

Stars rarely form in isolation, so it is critical to understand how the parsec-scale molecular cloud environment shapes the formation of individual dense cores at the sub-0.1 pc scale. To address the pathway to core formation in a clustered environment, I co-developed the CARMA Large Area Star Formation Survey, which spectrally imaged dense gas tracer lines across 800 square arcminutes of the Perseus and Serpens Molecular clouds with 7'' angular resolution. There are four key results from initial papers. First, I created a new non-binary dendrogram code that shows correlation between the hierarchical complexity of dense, N2H+ (J=1-0) structures and the amount of star formation activity in a cluster. This may imply that feedback from young protostars changes the structure of dense gas within a cluster and increases the amount of high column density material. Second, we discovered strong radial velocity gradients within filaments that are an order of magnitude larger than detected axial gradients. We see similar radial gradients in filaments formed in numerical simulations of converging, turbulent flows; this suggests that the observed filaments are accreting material from an environment that is flattened at larger scales, and that they are more likely to fragment locally into cores than to support the flow of gas along the filament length. Third, we constructed two size-linewidth relations using the dendrogram-identified gas structures and our high resolution maps of the gas centroid velocity and line-of-sight velocity dispersion. The two relations show distinct behavior, and we developed a theoretical framework based on isotropic turbulence to show that they support the clustered regions being flattened (sheet-like) at parsec scales, with depths on the order 0.1-0.2 pc into the sky. Finally, we found that many filaments seen with Herschel show substructure in our high resolution maps, which implies that measuring the widths of filaments may be more complex than

Symbiotic stars

Science.gov (United States)

Kafatos, M.; Michalitsianos, A. G.

1984-01-01

The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

Study on the flare stars in the Taurus region

International Nuclear Information System (INIS)

Khodzhaev, A.S.

1986-01-01

The results of the search of flare stars and their photometric, Hsub(α)-spectroscopic and statistical study in the Taurus are presented. By means of photographic observations carried out during 1980-1984, 92 new flare stars were discovered, 13 of which are known Orion Population variables, and 16 repeated flare-ups among 13 known flare stars. Spatial distribution of these stars was considered and the problem of their membership was discussed. Comparative analysis of the data of flare stars in the Taurus with that of other systems has been carried out. The Herzsprung-Russel and two-colour (U-B, B-V) diagrams for the Taurus flare stars are similar to the diagrams of stellar clusters and associations (Pleiades, Orion etc.). The estimated total number of flare stars in this region is larger than 500

Non-LTE analysis of extremely helium-rich stars. The hot sdO stars LSE 153, 259 and 263

Science.gov (United States)

Husfeld, D.; Butler, K.; Heber, U.; Drilling, J. S.

1989-01-01

Results of a non-LTE fine analysis based mainly on high-resolution CASPEC spectra for three extremely helium-rich sdO stars are discussed in order to explain hydrogen deficiency in single stars. High temperature (Teff = 70,000 to 75,000 K) and a position in the log Teff - log g diagram were found close to the Eddington limit. Various abundance estimates are derived for hydrogen (upper limits only), carbon, nitrogen, and magnesium. Hydrogen is reduced to less than 10 percent by number in LSE 153 and LSE 263, and to less than 5 percent in LSE 259. The hydrogen deficiency is accompanied by nitrogen- and carbon-enrichment in LSE 153 and LSE 259 only. In LSE 263, carbon is depleted by about 1 dex. Stellar masses obtained by assuming that a core mass-luminosity relation holds for these stars, were found to be in the range 0.6-0.9 solar mass, yielding luminosities log L/L:solar = 3.7-4.5. Two of the program stars (LSE 153 and 259) appear to be possible successors of the R CrB and helium B stars, whereas the third star (LSE 263) displays a much lower carbon content in its photosphere making it an exceptional case among the known hydrogen deficient stars.

Subluminous Wolf-Rayet stars: Observations

International Nuclear Information System (INIS)

Heap, S.R.

1982-01-01

The author has used the fact that some central stars are WR stars and others are say, O stars, as a focal point for his presentation. In attempting to answer this question he has considered how the properties of WR-type central stars differ from those of O-type stars. The study begins with the classification and calibration of WR spectra, then goes on to the physical properties of WR-type central stars, and at the end returns to the question of what distinguishes a Wolf-Rayet star. The observational data for central stars are neither complete nor precise. Nevertheless, they suggest that what distinguishes a WR central star is not so much its present physical properties (e.g. temperature, gravity), but rather, its fundamental properties (initial and evolutionary history). (Auth.)

Survival of the Scandinavian total ankle replacement (STAR): results of ten to nineteen years follow-up.

Science.gov (United States)

Frigg, Arno; Germann, Ursula; Huber, Martin; Horisberger, Monika

2017-10-01

The purpose of this study was to evaluate survival and clinical outcome of the Scandinavian total ankle replacement (STAR) prosthesis after a minimum of ten years up to a maximum of 19 years. Fifty STAR prostheses in 46 patients with end stage ankle osteoarthritis operated between 1996 and 2006 by the same surgeon (MH) were included. Minimal follow-up was ten years (median 14.6 years, 95% confidence interval [CI] 12.9-16.4). Clinical (Kofoed score) and radiological assessments were taken before the operation and at one, ten (+2), and 16 (±3) years after implantation. The primary endpoint was defined as exchange of the whole prosthesis or conversion to arthrodesis (def. 1), exchange of at least one metallic component (def. 2), or exchange of any component including the inlay (due to breakage or wear) (def. 3). Survival was estimated according to Kaplan-Meier. Further reoperations related to STAR were also recorded. The ten year survival rate was (def. 1) 94% (CI 82-98%), (def. 2) 90% (CI, 77-96%), and (def. 3) 78% (CI 64-87%). The 19-year survival rate was (def. 1) 91% (CI 78-97%), (def. 2) 75% (CI 53-88%), and (def. 3) 55% (CI 34-71%). Considering any re-operations related to STAR, 52% (26/50) of prostheses were affected by re-operations. Mean pre-operative Kofoed score was 49, which improved to 84 after one year (n = 50), to 90 after ten years (n = 46), and to 89 after 16 years (n = 28). The survival rate for def. 1 and 2 was high. However, re-operations occurred in 52% of all STAR prosthesis. Retrospective cohort study, evidence Level 4.

SALT Spectroscopy of Evolved Massive Stars

Science.gov (United States)

Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

2017-06-01

Long-slit spectroscopy with the Southern African Large Telescope (SALT) of central stars of mid-infrared nebulae detected with the Spitzer Space Telescope and Wide-Field Infrared Survey Explorer (WISE) led to the discovery of numerous candidate luminous blue variables (cLBVs) and other rare evolved massive stars. With the recent advent of the SALT fiber-fed high-resolution echelle spectrograph (HRS), a new perspective for the study of these interesting objects is appeared. Using the HRS we obtained spectra of a dozen newly identified massive stars. Some results on the recently identified cLBV Hen 3-729 are presented.

Web-Based STAR E-Learning Course Increases Empathy and Understanding in Dementia Caregivers: Results from a Randomized Controlled Trial in the Netherlands and the United Kingdom.

Science.gov (United States)

Hattink, Bart; Meiland, Franka; van der Roest, Henriëtte; Kevern, Peter; Abiuso, Francesca; Bengtsson, Johan; Giuliano, Angele; Duca, Annalise; Sanders, Jennifer; Basnett, Fern; Nugent, Chris; Kingston, Paul; Dröes, Rose-Marie

2015-10-30

The doubling of the number of people with dementia in the coming decades coupled with the rapid decline in the working population in our graying society is expected to result in a large decrease in the number of professionals available to provide care to people with dementia. As a result, care will be supplied increasingly by untrained informal caregivers and volunteers. To promote effective care and avoid overburdening of untrained and trained caregivers, they must become properly skilled. To this end, the European Skills Training and Reskilling (STAR) project, which comprised experts from the domains of education, technology, and dementia care from 6 countries (the Netherlands, Sweden, Italy, Malta, Romania, and the United Kingdom), worked together to create and evaluate a multilingual e-learning tool. The STAR training portal provides dementia care training both for informal and formal caregivers. The objective of the current study was to evaluate the user friendliness, usefulness, and impact of STAR with informal caregivers, volunteers, and professional caregivers. For 2 to 4 months, the experimental group had access to the STAR training portal, a Web-based portal consisting of 8 modules, 2 of which had a basic level and 6 additional modules at intermediate and advanced levels. The experimental group also had access to online peer and expert communities for support and information exchange. The control group received free access to STAR after the research had ended. The STAR training portal was evaluated in a randomized controlled trial among informal caregivers and volunteers in addition to professional caregivers (N=142) in the Netherlands and the United Kingdom. Assessments were performed with self-assessed, online, standardized questionnaires at baseline and after 2 to 4 months. Primary outcome measures were user friendliness, usefulness, and impact of STAR on knowledge, attitudes, and approaches of caregivers regarding dementia. Secondary outcome measures

A Hard X-Ray Study of the Normal Star-Forming Galaxy M83 with NuSTAR

DEFF Research Database (Denmark)

Yukita, M.; Hornschemeier, A. E.; Lehmer, B. D.

2016-01-01

We present the results from sensitive, multi-epoch NuSTAR observations of the late-type star-forming galaxy M83 (d = 4.6 Mpc). This is the first investigation to spatially resolve the hard (E > 10 keV) X-ray emission of this galaxy. The nuclear region and similar to 20 off-nuclear point sources......, including a previously discovered ultraluminous X-ray source, are detected in our NuSTAR observations. The X-ray hardnesses and luminosities of the majority of the point sources are consistent with hard X-ray sources resolved in the starburst galaxy NGC 253. We infer that the hard X-ray emission is most...

Revealing evolved massive stars with Spitzer

Science.gov (United States)

Gvaramadze, V. V.; Kniazev, A. Y.; Fabrika, S.

2010-06-01

Massive evolved stars lose a large fraction of their mass via copious stellar wind or instant outbursts. During certain evolutionary phases, they can be identified by the presence of their circumstellar nebulae. In this paper, we present the results of a search for compact nebulae (reminiscent of circumstellar nebulae around evolved massive stars) using archival 24-μm data obtained with the Multiband Imaging Photometer for Spitzer. We have discovered 115 nebulae, most of which bear a striking resemblance to the circumstellar nebulae associated with luminous blue variables (LBVs) and late WN-type (WNL) Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). We interpret this similarity as an indication that the central stars of detected nebulae are either LBVs or related evolved massive stars. Our interpretation is supported by follow-up spectroscopy of two dozen of these central stars, most of which turn out to be either candidate LBVs (cLBVs), blue supergiants or WNL stars. We expect that the forthcoming spectroscopy of the remaining objects from our list, accompanied by the spectrophotometric monitoring of the already discovered cLBVs, will further increase the known population of Galactic LBVs. This, in turn, will have profound consequences for better understanding the LBV phenomenon and its role in the transition between hydrogen-burning O stars and helium-burning WR stars. We also report on the detection of an arc-like structure attached to the cLBV HD 326823 and an arc associated with the LBV R99 (HD 269445) in the LMC. Partially based on observations collected at the German-Spanish Astronomical Centre, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK); fabrika@sao.ru (SF)

America's Star Libraries

Science.gov (United States)

Lyons, Ray; Lance, Keith Curry

2009-01-01

"Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

Star marketer’s impact on the market strategy choice

Directory of Open Access Journals (Sweden)

Vlašić Goran

2017-01-01

Full Text Available We focus on understanding the role of star marketers in pursuing a market-driven vs. a market-driving strategy. Results indicate that market-driving and market-driven strategies are two approaches that can be pursued by market-oriented firms. A star marketer has a robust positive influence on market-driving strategy. In contrast, a star marketer has no meaningful influence on market-driven strategy. In short, while star marketers are very important for market-driving strategy and long term success, they represent an unnecessary cost and provide no added value to companies focusing on market-driven strategies and short term results.

The Snapshot A Star SurveY (SASSY)

Science.gov (United States)

Garani, Jasmine I.; Nielsen, Eric; Marchis, Franck; Liu, Michael C.; Macintosh, Bruce; Rajan, Abhijith; De Rosa, Robert J.; Jinfei Wang, Jason; Esposito, Thomas M.; Best, William M. J.; Bowler, Brendan; Dupuy, Trent; Ruffio, Jean-Baptiste

2018-01-01

The Snapshot A Star Survey (SASSY) is an adaptive optics survey conducted using NIRC2 on the Keck II telescope to search for young, self-luminous planets and brown dwarfs (M > 5MJup) around high mass stars (M > 1.5 M⊙). We present the results of a custom data reduction pipeline developed for the coronagraphic observations of our 200 target stars. Our data analysis method includes basic near infrared data processing (flat-field correction, bad pixel removal, distortion correction) as well as performing PSF subtraction through a Reference Differential Imaging algorithm based on a library of PSFs derived from the observations using the pyKLIP routine. We present the results from the pipeline of a few stars from the survey with analysis of candidate companions. SASSY is sensitive to companions 600,000 times fainter than the host star withint the inner few arcseconds, allowing us to detect companions with masses ~8MJup at age 110 Myr. This work was supported by the Leadership Alliance's Summer Research Early Identification Program at Stanford University, the NSF REU program at the SETI Institute and NASA grant NNX14AJ80G.

Hyperfast pulsars as the remnants of massive stars ejected from young star clusters

Science.gov (United States)

Gvaramadze, Vasilii V.; Gualandris, Alessia; Portegies Zwart, Simon

2008-04-01

Recent proper motion and parallax measurements for the pulsar PSR B1508+55 indicate a transverse velocity of ~1100kms-1, which exceeds earlier measurements for any neutron star. The spin-down characteristics of PSR B1508+55 are typical for a non-recycled pulsar, which implies that the velocity of the pulsar cannot have originated from the second supernova disruption of a massive binary system. The high velocity of PSR B1508+55 can be accounted for by assuming that it received a kick at birth or that the neutron star was accelerated after its formation in the supernova explosion. We propose an explanation for the origin of hyperfast neutron stars based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star which attained its peculiar velocity (similar to that of the pulsar) in the course of a strong dynamical three- or four-body encounter in the core of dense young star cluster. To check this hypothesis, we investigated three dynamical processes involving close encounters between: (i) two hard massive binaries, (ii) a hard binary and an intermediate-mass black hole (IMBH) and (iii) a single stars and a hard binary IMBH. We find that main-sequence O-type stars cannot be ejected from young massive star clusters with peculiar velocities high enough to explain the origin of hyperfast neutron stars, but lower mass main-sequence stars or the stripped helium cores of massive stars could be accelerated to hypervelocities. Our explanation for the origin of hyperfast pulsars requires a very dense stellar environment of the order of 106- 107starspc-3. Although such high densities may exist during the core collapse of young massive star clusters, we caution that they have never been observed.

RED CLUMP STARS IN THE SAGITTARIUS TIDAL STREAMS

International Nuclear Information System (INIS)

Carrell, Kenneth; Chen Yuqin; Wilhelm, Ronald

2012-01-01

We have probed a section (l ∼ 150, b ∼ –60) of the trailing tidal arm of the Sagittarius dwarf spheroidal galaxy by identifying a sample of Red Clump (RC) stream stars. RC stars are not generally found in the halo field, but are found in significant numbers in both the Sagittarius galaxy and its tidal streams, making them excellent probes of stream characteristics. Our target sample was selected using photometric data from the Sloan Digital Sky Survey, Data Release 6, which was constrained in color to match the Sagittarius RC stars. Spectroscopic observations of the target stars were conducted at Kitt Peak National Observatory using the WIYN telescope. The resulting spectroscopic sample is magnitude limited and contains both main-sequence disk stars and evolved RC stars. We have developed a method to systematically separate these two stellar classes using kinematic information and a Bayesian approach for surface gravity determination. The resulting RC sample allows us to determine an absolute stellar density of ρ = 2.7 ± 0.5 RC stars kpc –3 at this location in the stream. Future measurements of stellar densities for a variety of populations and at various locations along the streams will lead to a much improved understanding of the original nature of the Sagittarius galaxy and the physical processes controlling its disruption and subsequent stream generation.

Lots of Small Stars Born in Starburst Region

Science.gov (United States)

1999-10-01

at 2.166 µm. Images of the NGC 3603 region were obtained in three near-IR filter bands (J s , H and K s ) with the ISAAC instrument at the ANTU telescope. The observations were made in "service" mode on April 4 - 6 and 9, 1999, during selected periods when the (optical) seeing was equal to or better than 0.4 arcsec. This was a most essential requirement in order to achieve sufficient angular resolution (image sharpness) that would allow to do accurate photometric measurements of individual stars in this crowded cluster . This particular observing mode, during which ESO observers at ANTU kept careful track of the actual atmospheric conditions, contributed greatly to securing the very high quality images needed for this programme. In view of the many comparatively bright stars in the field, the observing strategy was to use the shortest possible exposure time (1.77 sec) to keep the number of over-exposed (saturated) stellar images to a minimum. As the minimum time required to stabilize the telescope's active optics control system and guarantee the optimum optical quality was about 1 min, thirty-four short exposures were made at each sky position and then co-added to an effective one-minute exposure. After each such series, the telescope pointing was offset in a random pattern up to 20 arcsec from the center; this enlarged the imaged sky area somewhat and facilitated the subtraction of the infrared emission from the sky background. The individual 1-min exposures were then very carefully co-aligned to obtain the highest possible spatial resolution and co-added. The resulting images cover a sky field of 3.4 x 3.4 arcmin 2 with a pixel size of 0.074 arcsec. The effective exposure times of the final broad-band images in the central 2.5 x 2.5 arcmin 2 area are 37, 45, and 48 min in the J s , H and K s filters, respectively. The final step involved the computer-aided detection of the individual stars in the frames, the measurement of their brightness as seen in the different

Parameters and abundances in luminous stars

International Nuclear Information System (INIS)

Earle Luck, R.

2014-01-01

Parameters and abundances for 451 stars of spectral types F, G, and K of luminosity classes I and II have been derived. Absolute magnitudes and E(B – V) have been derived for the warmer stars in order to investigate the galactic abundance gradient. The value found here: d[Fe/H]/dR ∼ –0.06 dex kpc –1 , agrees well with previous determinations. Stellar evolution indicators have also been investigated with the derived C/O ratios indicating that standard CN processing has been operating. Perhaps the most surprising result found in these supposedly relatively young intermediate-mass stars is that both [O/Fe] and [C/Fe] show a correlation with [Fe/H] much the same as found in older populations. While the stars were selected based on luminosity class, there does exist a significant [Fe/H] range in the sample. The likely explanation of this is that there is a significant range in age in the sample; that is, some of the sample are low-mass red-giant stars with types that place them within the selection criteria.

Ultracompact X-ray binary stars

NARCIS (Netherlands)

Haaften, L.M. van

2013-01-01

Ultracompact X-ray binary stars usually consist of a neutron star and a white dwarf, two stars bound together by their strong gravity and orbiting each other very rapidly, completing one orbit in less than one hour. Neutron stars are extremely compact remnants of the collapsed cores of massive stars

On the core-mass-shell-luminosity relation for shell-burning stars

International Nuclear Information System (INIS)

Jeffery, C.S.; Saint Andrews Univ.

1988-01-01

Core-mass-shell-luminosity relations for several types of shell-burning star have been calculated using simultaneous differential equations derived from simple homology approximations. The principal objective of obtaining a mass-luminosity relation for helium giants was achieved. This relation gives substantially higher luminosities than the equivalent relation for H-shell stars with core masses greater than 1 solar mass. The algorithm for calculating mass-luminosity relations in this fashion was investigated in detail. Most of the assumptions regarding the physics in the shell do not play a critical role in determining the core-mass-shell-luminosity relation. The behaviour of the core-mass-core-radius relation for a growing degenerate core as a single unique function of mass and growth rate needs to be defined before a single core-mass-shell-luminosity relation for all H-shell stars can be obtained directly from the homology approximations. (author)

Asteroid 'Bites the Dust' Around Dead Star

Science.gov (United States)

2009-01-01

NASA's Spitzer Space Telescope set its infrared eyes upon the dusty remains of shredded asteroids around several dead stars. This artist's concept illustrates one such dead star, or 'white dwarf,' surrounded by the bits and pieces of a disintegrating asteroid. These observations help astronomers better understand what rocky planets are made of around other stars. Asteroids are leftover scraps of planetary material. They form early on in a star's history when planets are forming out of collisions between rocky bodies. When a star like our sun dies, shrinking down to a skeleton of its former self called a white dwarf, its asteroids get jostled about. If one of these asteroids gets too close to the white dwarf, the white dwarf's gravity will chew the asteroid up, leaving a cloud of dust. Spitzer's infrared detectors can see these dusty clouds and their various constituents. So far, the telescope has identified silicate minerals in the clouds polluting eight white dwarfs. Because silicates are common in our Earth's crust, the results suggest that planets similar to ours might be common around other stars.