Limitations of Stellar Abundance Determinations

The information content of (photospheric) stellar spectra and the accuracy of abundance determinations are discussed. Besides the physical properties of the line spectra, the spectral resolution, the signal-to-noise ratio, but also the incompleteness of the knowledge of the contributing blends limit the abundance information. For a perfect model atmosphere the main factors determining the accuracy of the abundances are S/N, the line saturation, and the location of the continuum (or, in a synthetic spectrum, the background of numerous lines). In addition systematic errors introduced by missing atomic data and an imperfect model atmosphere (non-LTE, line blanketing, hydrodynamics) are important. The typical accuracy of abundance determinations is discussed for main sequence stars for which the most reliable data are available, and for a few selected other stellar types.

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Needs for Atomic Data for Quantitative Analysis of Stellar Spectra

Highlights of Astronomy ◽

10.1017/s153929960000602x ◽

1983 ◽

Vol 6 ◽

pp. 781-787 ◽

Cited By ~ 4

Author(s):

B. Baschek

Keyword(s):

Quantitative Analysis ◽

Model Atmosphere ◽

High Spectral Resolution ◽

Iteration Step ◽

Atomic Data ◽

Synthetic Spectrum ◽

Theoretical Spectrum ◽

Stellar Spectrum ◽

Stellar Spectra ◽

Element Abundances

The goal of a quantitative analysis of a stellar spectrum is to derive the physical and chemical state of the stellar atmosphere, i.e. by definition the region emitting the spectrum. Of particular interest are the element abundances, they have to be determined together with the temperatures and densities (pressures) in the atmosphere. A detailed analysis usually is an iterative procedure: a model atmosphere is constructed from reasonable starting values of the parameters (effective temperature, surface gravity, element abundances,...) and used to calculate a theoretical, “synthetic” spectrum. By comparing the observed with the theoretical spectrum, improved stellar parameters are gained for the next iteration step.Ideally, all atomic data entering the analysis should be known with sufficient accuracy, i.e. errors in the analysis should be due to uncertainties in the assumptions of the models, in the treatment of the velocity fields etc., and not due to insufficient atomic data. In the last decade, the ultraviolet portion of the spectrum below λ ≲ 3200 Å has become accessible by satellites such as Copernicus and the International Ultraviolet Explorer (IUE) with high spectral resolution. Studies of stellar spectra in this new range have revealed the needs for a large amount of atomic data required for the analyses.

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The Belgian Repository of fundamental Atomic data and Stellar Spectra (BRASS)

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320000046 ◽

2019 ◽

Vol 15 (S350) ◽

pp. 386-387

Author(s):

M. Laverick ◽

A. Lobel ◽

P. Royer ◽

T. Merle ◽

C. Martayan ◽

...

Keyword(s):

Quality Assessment ◽

State Of The Art ◽

Oscillator Strengths ◽

Atomic Data ◽

Synthetic Spectrum ◽

High Quality ◽

Data Repositories ◽

Stellar Spectra ◽

Atomic Transitions ◽

Stellar Spectroscopy

AbstractThe Belgian Repository of fundamental Atomic data and Stellar Spectra (BRASS) aims to provide one of the largest systematic and homogeneous quality assessment to date of literature atomic data required for stellar spectroscopy. By comparing state-of-the-art synthetic spectrum calculations with extremely high-quality observed benchmark spectra, we have critically evaluated fundamental atomic data, such as line wavelengths and oscillator strengths, for thousands of astrophysically-relevant transitions found in the literature and across several major atomic data repositories. These proceedings provide a short overview of the BRASS project to date, highlighting our recent efforts to investigate and quality-assess the atomic literature data pertaining to over a thousand atomic transitions present in FGK-type stellar spectra. BRASS provides all quality assessed data, theoretical spectra, and observed spectra in a new interactive database under development at brass.sdf.org.

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The methods for searching hypervelocity star candidates from the SDSS

Proceedings of the International Astronomical Union ◽

10.1017/s174392131300687x ◽

2013 ◽

Vol 9 (S298) ◽

pp. 421-421

Author(s):

Yinbi Li ◽

Ali Luo ◽

Gang Zhao ◽

Youjun Lu

Keyword(s):

Black Hole ◽

Velocity Distribution ◽

Radial Velocity ◽

Binary Stars ◽

High Velocity ◽

Main Sequence ◽

Galactic Center ◽

Main Sequence Stars ◽

Massive Black Hole ◽

Stellar Spectra

AbstractHyper-velocity stars are believed to be ejected out from the Galactic center through dynamical interactions of (binary) stars with the central massive black hole(s). In this paper, we firstly select F and G type main sequence stars from about 370,000 stellar spectra of DR7. Then, we select 369 high velocity stars from main sequence samples using the radial velocity distribution. Finally, we find 13 possible unbound hyper-velocity star candidates from the 369 high velocity stars.

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NLTE Model Atmospheres for Extremely Hot Compact Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900163387 ◽

2000 ◽

Vol 195 ◽

pp. 423-424

Author(s):

T. Rauch ◽

J. L. Deetjen ◽

S. Dreizler ◽

K. Werner

Keyword(s):

Signal To Noise Ratio ◽

Far Infrared ◽

Model Atmosphere ◽

Stellar Model ◽

Compact Stars ◽

Local Thermal Equilibrium ◽

High Signal ◽

X Rays ◽

Metal Line ◽

Stellar Spectra

Present observational techniques provide stellar spectra with high resolution at a high signal-to-noise ratio over the complete wavelength range—from the far infrared to X-rays.The effects of Non-“Local Thermal Equilibrium” (NLTE) are particularly important for hot stars, hence the use of reliable NLTE stellar model atmosphere fluxes is required for an adequate spectral analysis.State-of-the-art NLTE model atmospheres include metal-line blanketing of millions of lines of all elements from hydrogen up to the iron-group elements, and thus permit precise analyses of extremely hot compact stars, e.g., central stars of planetary nebulae, PG 1159 stars, white dwarfs, and neutron stars. Their careful spectroscopic study is of great interest in several branches of modern astrophysics, e.g., stellar and galactic evolution, and interstellar matter.

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Gravitational waves from bodies orbiting the Galactic center black hole and their detectability by LISA

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935406 ◽

2019 ◽

Vol 627 ◽

pp. A92 ◽

Cited By ~ 7

Author(s):

E. Gourgoulhon ◽

A. Le Tiec ◽

F. H. Vincent ◽

N. Warburton

Keyword(s):

Black Holes ◽

Black Hole ◽

Main Sequence ◽

Signal To Noise Ratio ◽

Brown Dwarfs ◽

Compact Objects ◽

Main Sequence Stars ◽

Signal To Noise ◽

Noise Ratio ◽

Sgr A

Aims. We present the first fully relativistic study of gravitational radiation from bodies in circular equatorial orbits around the massive black hole at the Galactic center, Sgr A* and we assess the detectability of various kinds of objects by the gravitational wave detector LISA. Methods. Our computations are based on the theory of perturbations of the Kerr spacetime and take into account the Roche limit induced by tidal forces in the Kerr metric. The signal-to-noise ratio in the LISA detector, as well as the time spent in LISA band, are evaluated. We have implemented all the computational tools in an open-source SageMath package, within the Black Hole Perturbation Toolkit framework. Results. We find that white dwarfs, neutrons stars, stellar black holes, primordial black holes of mass larger than 10−4 M⊙, main-sequence stars of mass lower than ∼2.5 M⊙, and brown dwarfs orbiting Sgr A* are all detectable in one year of LISA data with a signal-to-noise ratio above 10 for at least 105 years in the slow inspiral towards either the innermost stable circular orbit (compact objects) or the Roche limit (main-sequence stars and brown dwarfs). The longest times in-band, of the order of 106 years, are achieved for primordial black holes of mass ∼10−3 M⊙ down to 10−5 M⊙, depending on the spin of Sgr A*, as well as for brown dwarfs, just followed by white dwarfs and low mass main-sequence stars. The long time in-band of these objects makes Sgr A* a valuable target for LISA. We also consider bodies on close circular orbits around the massive black hole in the nucleus of the nearby galaxy M 32 and find that, among them, compact objects and brown dwarfs stay for 103–104 years in LISA band with a one-year signal-to-noise ratio above ten.

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29. Stellar Spectra

Transactions of the International Astronomical Union ◽

10.1017/s0251107x00006416 ◽

1985 ◽

Vol 19 (1) ◽

pp. 353-374

Author(s):

J. Jugaku ◽

G. Cayrel de Strobel ◽

Y. Andrillat ◽

W. K. Bonsack ◽

P. S. Conti ◽

...

Keyword(s):

Magnetic Fields ◽

Main Sequence ◽

Circumstellar Matter ◽

Magellanic Clouds ◽

Be Stars ◽

Main Sequence Stars ◽

Stellar Spectra ◽

Stellar Magnetic Fields

During the triennium under review, Commission 29 has sponsored or cosponsored the following IAU meetings: Symposium 102, “Solar and Stellar Magnetic Fields,” Zurich, Switzerland, August 1982; Symposium 108, “Structure and Evolution of the Magellanic Clouds,” Tübingen, FRG, September 1983; Symposium 111, “Calibration of Fundamental Stellar Quantities,” Como, Italy, May 1984; and Colloquium 82, “Cepheids: Observation and Theory,” Toronto, Canada, May-June 1984. Commission 29 has also supported or sponsored several IAU meetings proposed for 1985 and 1986. They include “Luminous Stars and Associations in Galaxies,” Porto Heli, Greece, May 1985; “Upper Main Sequence Stars with Anomalous Abundances,” Crimea, USSR, May 1985; “Astrochemistry,” Goa, India, December 1985; “Hydrogen Deficient Stars and Related Objects,” Bangalore, India, December 1985; “Circumstellar Matter,” Heidelberg, FRG, June 1986; and “Be Stars,” Boulder, USA, August 1986.

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The Belgian repository of fundamental atomic data and stellar spectra

Canadian Journal of Physics ◽

10.1139/cjp-2016-0750 ◽

2017 ◽

Vol 95 (9) ◽

pp. 833-839 ◽

Cited By ~ 5

Author(s):

A. Lobel ◽

P. Royer ◽

C. Martayan ◽

M. Laverick ◽

T. Merle ◽

...

Keyword(s):

Atomic Line ◽

Atomic Data ◽

High Signal ◽

Atmospheric Parameter ◽

Synthetic Spectrum ◽

Signal To Noise ◽

Stellar Spectra ◽

Novel Approach ◽

Spectrum Synthesis ◽

Quality Assessments

BRASS is an international networking project of the Federal Government of Belgium for the development of a new public database providing accurate fundamental atomic data of vital importance for stellar spectroscopic research. The BRASS database will offer atomic line data that is thoroughly tested by comparing theoretical and observed stellar spectra. We are in the course of performing extensive quality assessments of selected atomic input data with advanced radiative transfer spectrum synthesis calculations that we compare in detail to high-resolution Mercator-HERMES and ESO-VLT-UVES spectra of very high signal-to-noise ratios for about 30 hot and cool bright stars of B, A, F, G, and K spectral types. The new database will provide the tested and validated values of absorption lines we retrieve from various existing atomic repositories, such as NIST and VAMDC. The validated atomic datasets, combined with the observed and theoretical spectra, will be interactively offered online at brass.sdf.org. The combination of these datasets is a novel approach for its development, which will provide a universal reference for advanced stellar spectroscopic research. We present the atmospheric parameter results of a subset of five benchmark stars observed with signal-to-noise ratios of 800–1200. The observed and theoretical spectra of the Sun and 51 Peg between 4000 and 6800 Å are offered online in the BRASS Data Interface. It also incorporates a new list of ∼900 metal lines for which we compute blending below 5% of the equivalent width useful for detailed line profile modeling and synthetic spectrum fit quality assessments of atomic line data.

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Chromospheric activity as a function of age in main-sequence stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900053146 ◽

1966 ◽

Vol 24 ◽

pp. 40-43

Author(s):

O. C. Wilson ◽

A. Skumanich

Keyword(s):

Main Sequence ◽

The Sun ◽

Main Sequence Stars ◽

Tentative Conclusion ◽

Chromospheric Activity ◽

General Field ◽

Large Clusters

Evidence previously presented by one of the authors (1) suggests strongly that chromospheric activity decreases with age in main sequence stars. This tentative conclusion rests principally upon a comparison of the members of large clusters (Hyades, Praesepe, Pleiades) with non-cluster objects in the general field, including the Sun. It is at least conceivable, however, that cluster and non-cluster stars might differ in some fundamental fashion which could influence the degree of chromospheric activity, and that the observed differences in chromospheric activity would then be attributable to the circumstances of stellar origin rather than to age.

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On The Radii of Ap Stars

International Astronomical Union Colloquium ◽

10.1017/s025292110008043x ◽

1976 ◽

Vol 32 ◽

pp. 49-55 ◽

Cited By ~ 1

Author(s):

F.A. Catalano ◽

G. Strazzulla

Keyword(s):

Observational Data ◽

Line Width ◽

Main Sequence ◽

Main Sequence Stars ◽

Ap Stars

SummaryFrom the analysis of the observational data of about 100 Ap stars, the radii have been computed under the assumption that Ap are main sequence stars. Radii range from 1.4 to 4.9 solar units. These values are all compatible with the Deutsch's period versus line-width relation.

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