scholarly journals NLTE abundances of C, O, Ca, Ti, and Fe in the reference BAF-type stars

2017 ◽  
Vol 13 (S334) ◽  
pp. 360-361
Author(s):  
Tatyana Sitnova ◽  
Tatyana Ryabchikova ◽  
Sofya Alexeeva ◽  
Lyudmila Mashonkina
Keyword(s):  
Local Thermodynamic Equilibrium ◽  
Signal To Noise Ratio ◽  
Model Atmosphere ◽  
High Signal ◽  
Complete Model ◽  
Near Ir ◽  
Hydrostatic Model ◽  
Non Local ◽  
Model Atom ◽  
Abundance Determination

AbstractWe present accurate methods of abundance determination based on the non-local thermodynamic equilibrium (NLTE) line formation for carbon, oxygen, calcium, titanium, and iron in the atmospheres of BAF-type stars. For C I-II, O I, Ca I-II, and Ti I-II, their comprehensive model atoms were described in our previous papers. A fairly complete model atom of Fe I-II is first applied in this study. We determine the NLTE abundances of the nine BAF-type stars with well-determined atmospheric parameters, using high-resolution and high signal-to-noise ratio spectral observations in the broad wavelength range, from the UV to the IR. For C, Ca, Ti, and Fe, NLTE leads to consistent abundances from the lines of the two ionisation stages. The C I, Ca II, and Fe II emission lines were detected in the near IR spectrum of the late B-type subgiant star HD 160762. They are well reproduced in the classical hydrostatic model atmosphere, when applying our NLTE methods.

scholarly journals Recent Results on Abundance Determinations

1993 ◽  
Vol 138 ◽  
pp. 27-41
Author(s):  
Saul J. Adelman
Keyword(s):  
Signal To Noise Ratio ◽  
Model Atmosphere ◽  
Bulletin Board ◽  
High Signal ◽  
Rotating Stars ◽  
Signal To Noise ◽  
Peculiar Stars ◽  
Noise Data ◽  
Noise Ratio ◽  
Moving Groups

AbstractI review abundance determinations of normal B5-F4 and peculiar stars published since 1984. Several analyses performed with photographic spectrograms indicate interesting stars which should be analyzed with high signal-to-noise data. Studies of stars of known ages which belong to clusters, associations, and moving groups should led to the most direct confrontations with theory. The increase in signal-to-noise ratio provided by electronic detectors with respect to photographic plates should allow accurate analyses of moderating rotating stars. High resolution, high signal-to-noise ratio studies have revealed crucial information about the line profiles of Sirius, Vega, and other A stars. It would aid comparison of analyses if we could agree on a standard set of gf-values and line damping constants. A computer bulletin board would be a useful means to provide and maintain such data as well as model atmosphere codes.

scholarly journals Non-local thermodynamic equilibrium line formation for Si i–ii–iii in A–B stars and the origin of Si ii emission lines in ι Her

2020 ◽  
Vol 493 (4) ◽  
pp. 6095-6108 ◽  
Author(s):  
Lyudmila Mashonkina
Keyword(s):  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Emission Lines ◽  
Atomic Data ◽  
Line Formation ◽  
Atmospheric Parameters ◽  
B Stars ◽  
Non Local ◽  
Effective Temperatures ◽  
Model Atom

ABSTRACT A comprehensive model atom was developed for Si i–ii–iii using the most up-to-date atomic data available so far. Based on non-local thermodynamic equilibrium (NLTE) line formation for Si i, Si ii and Si iii and high-resolution observed spectra, we determined the NLTE abundances for a sample of nine unevolved A9–B3 type stars with well-determined atmospheric parameters. For each star, NLTE reduces the line-to-line scatter for Si ii substantially compared with the LTE case and leads to consistent mean abundances from lines of different ionization stages. In the hottest star of our sample, ι Her, Si ii is subject to overionization that drives emission in the lines arising from the high-excitation doublet levels. Our NLTE calculations reproduced 10 emission lines of Si ii observed in ι Her. The same overionization effect leads to greatly weakened Si ii lines, which are observed in absorption in ι Her. Large positive NLTE abundance corrections (up to 0.98 dex for 5055 Å) were useful for achieving consistent mean abundances from lines of the two ionization stages, Si ii and Si iii. It was found that NLTE effects are overestimated for the Si ii 6347, 6371 Å doublet in ι Her, while the new model atom works well for cooler stars. At this stage, we failed to understand this problem. We computed a grid of the NLTE abundance corrections for lines of Si i, Si ii and Si iii in model atmospheres with effective temperatures and surface gravities characteristic of unevolved A–B type stars.

scholarly journals GALEX absolute calibration and extinction coefficients based on white dwarfs

2019 ◽  
Vol 489 (4) ◽  
pp. 5046-5052 ◽  
Author(s):  
Renae E Wall ◽  
Mukremin Kilic ◽  
P Bergeron ◽  
B Rolland ◽  
C Genest-Beaulieu ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
White Dwarfs ◽  
Signal To Noise Ratio ◽  
Model Atmosphere ◽  
Absolute Calibration ◽  
High Signal ◽  
Extinction Coefficients ◽  
Near Ultraviolet ◽  
The Galaxy ◽  
Far Ultraviolet

ABSTRACT We use 1837 DA white dwarfs with high signal-to-noise ratio spectra and Gaia parallaxes to verify the absolute calibration and extinction coefficients for the Galaxy Evolution Explorer (GALEX). We use white dwarfs within 100 pc to verify the linearity correction to the GALEX data. We find that the linearity correction is valid for magnitudes brighter than 15.95 and 16.95 for the far-ultraviolet (FUV) and near-ultraviolet (NUV) bands, respectively. We also use DA white dwarfs beyond 250 pc to calculate extinction coefficients in the FUV and NUV bands: RFUV = 8.01 ± 0.07 and RNUV = 6.72 ± 0.04. These are consistent with the predicted extinction coefficients for Milky Way-type dust in the FUV, but smaller than predictions in the NUV. With well understood optical spectra and state-of-the-art model atmosphere analysis, these white dwarfs currently provide the best constraints on the extinction coefficients for the GALEX data.

scholarly journals Model atmosphere analysis of two new early–type O4 dwarfs stars

2017 ◽  
Vol 2 (2) ◽  
pp. 559-564 ◽  
Author(s):  
D.A. Fouda ◽  
M. Hamdy ◽  
M. Nouh ◽  
M. Beheary ◽  
Abdelaziz Bakrey ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Rotational Velocity ◽  
Model Atmosphere ◽  
Surface Gravity ◽  
High Signal ◽  
Early Type ◽  
Atmospheric Models ◽  
Signal To Noise ◽  
Dwarf Stars ◽  
Synthetic Spectra

AbstractWe present a synthetic spectra study of two new galactic early-type O4 dwarf stars(ALS 19618 and BD+50886) with high signal-to-noise ratio, typically S/N ∼ 300, medium-rosalution R ∼ 2500 optical spectra of O4 dwarfs stars from Galactic O-Stars Spectroscopic Survey (GOSSS), The main stellar parameters (Teff, surface gravity, rotational velocity) have been established using non-LTE, line-blanketed, atmospheric models calculated by TLUSTY204 and SYNSPEC49.

scholarly journals NLTE spectral analysis of the intermediate helium-rich subdwarf B star CPD−20°1123

2020 ◽  
Vol 497 (1) ◽  
pp. 67-80 ◽  
Author(s):  
L Löbling
Keyword(s):  
Optical Spectrum ◽  
Local Thermodynamic Equilibrium ◽  
Model Atmosphere ◽  
Stellar Atmosphere ◽  
Light Metals ◽  
Helium Burning ◽  
Number Ratio ◽  
Metal Abundances ◽  
Non Local ◽  
Intermediate Surface

ABSTRACT Subdwarf B (sdB) stars are core helium-burning stars with stratified atmospheres. Their atmospheres are dominated by hydrogen (H) while the helium (He) and metal abundances are shaped by an interplay of gravitational settling and radiative levitation. However, a small fraction of these show spectra dominated by He i absorption lines. In between these groups of He-deficient and extreme He-rich sdBs, some are found to have intermediate surface He abundances. These objects are proposed to be young ‘normal’ (He-deficient) sdBs for which the dynamical stratification of the atmosphere is still ongoing. We present an analysis of the optical spectrum of such an intermediate He-rich sdB, namely CPD−20°1123, by means of non-local thermodynamic equilibrium (NLTE) stellar atmosphere models. It has a He-to-H number ratio of He/H = 0.13 ± 0.05 and its effective temperature of $\mbox{$T_\mathrm{eff}$} = 25\, 500 \pm 1000 \, \mathrm{K}$ together with a surface gravity of $\log \, (g$ / cm s−2) = 5.3 ± 0.3 places the star close to the high-temperature edge until which it may be justified to use LTE model atmospheres. This work states a test of the Tübingen NLTE Model Atmosphere Package for this temperature regime. We present the first application of revised, elaborated model atoms of low ionization stages of light metals usable with this atmosphere code.

scholarly journals Fe I/Fe II ionization equilibrium in cool stars: NLTE versus LTE

2009 ◽  
Vol 5 (S265) ◽  
pp. 197-200 ◽  
Author(s):  
Lyudmila Mashonkina ◽  
Thomas Gehren ◽  
Jianrong Shi ◽  
Andreas Korn ◽  
Frank Grupp
Keyword(s):  
Local Thermodynamic Equilibrium ◽  
The Sun ◽  
Line Formation ◽  
Formation Model ◽  
Hydrogen Atoms ◽  
Cool Stars ◽  
Solar Metallicity ◽  
Non Local ◽  
The Difference ◽  
Model Atom

AbstractNon-local thermodynamic equilibrium (NLTE) line formation for neutral and singly-ionized iron is considered through a range of stellar parameters characteristic of cool stars. A comprehensive model atom for Fe I and Fe II is presented. Our NLTE calculations support the earlier conclusions that the statistical equilibrium (SE) of Fe I shows an underpopulation of Fe I terms. However, the inclusion of the predicted high-excitation levels of Fe I in our model atom leads to a substantial decrease in the departures from LTE. As a test and first application of the Fe I/II model atom, iron abundances are determined for the Sun and four selected stars with well determined stellar parameters and high-quality observed spectra. Within the error bars, lines of Fe I and Fe II give consistent abundances for the Sun and two metal-poor stars when inelastic collisions with hydrogen atoms are taken into account in the SE calculations. For the close-to-solar metallicity stars Procyon and β Vir, the difference (Fe II - Fe I) is about 0.1 dex independent of the line formation model, either NLTE or LTE. We evaluate the influence of departures from LTE on Fe abundance and surface gravity determination for cool stars.

scholarly journals Stellar laboratories

2020 ◽  
Vol 637 ◽  
pp. A4
Author(s):  
T. Rauch ◽  
S. Gamrath ◽  
P. Quinet ◽  
M. Demleitner ◽  
M. Knörzer ◽  
...  
Keyword(s):  
Mass Fraction ◽  
Local Thermodynamic Equilibrium ◽  
Model Atmosphere ◽  
Spectral Lines ◽  
Oscillator Strengths ◽  
Atomic Data ◽  
Uv Spectrum ◽  
Hot Stars ◽  
Non Local ◽  
First Time

Context. Accurate atomic data is an essential ingredient for the calculation of reliable non-local thermodynamic equilibrium (NLTE) model atmospheres that are mandatory for the spectral analysis of hot stars. Aims. We aim to search for and identify for the first time spectral lines of copper (atomic number Z = 29) and indium (Z = 49) in hot white dwarf (WD) stars and to subsequently determine their photospheric abundances. Methods. Oscillator strengths of Cu IV–VII were calculated to include radiative and collisional bound-bound transitions of Cu in our NLTE model-atmosphere calculations. Oscillator strengths of In IV - VI were compiled from the literature. Results. We newly identified 1 Cu IV, 51 Cu V, 2 Cu VI, and 5 In V lines in the ultraviolet (UV) spectrum of DO-type WD RE 0503−289. We determined the photospheric abundances of 9.3 × 10−5 (mass fraction, 132 times solar) and 3.0 × 10−5 (56 600 times solar), respectively; we also found Cu overabundances in the DA-type WD G191−B2B (6.3 × 10−6, 9 times solar). Conclusions. All identified Cu IV-VI lines in the UV spectrum of RE 0503−289 were simultaneously well reproduced with our newly calculated oscillator strengths. With the detection of Cu and In in RE 0503−289, the total number of trans-iron elements (Z > 28) in this extraordinary WD reaches an unprecedented number of 18.

scholarly journals NLTE Model Atmospheres for Extremely Hot Compact Stars

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.

Near-IR Multiplex Bandpass Spectrometer Utilizing Liquid Molecular Filters

1995 ◽  
Vol 49 (4) ◽  
pp. 493-498 ◽  
Author(s):  
Andrew Fong ◽  
Gary M. Hieftje
Keyword(s):  
Propylene Glycol ◽  
High Throughput ◽  
Near Infrared ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Ir Radiation ◽  
Near Ir ◽  
Infrared Spectrometer ◽  
Near Infrared Spectrometer

A simple near-infrared spectrometer is described which uses common liquids as near-IR spectral filters. Each filter substance passes multiple bands of near-IR radiation. This new type of spectrometer offers simplicity, cost advantages, and enhanced throughput. The high throughput is useful for ensuring the high signal-to-noise ratio typically needed for chemometrics. The high throughput also allows the use of longer sample pathlengths. The performance of the spectrometer is demonstrated in the determination of methanol through a 1-cm pathlength of water and in the determination of trace amounts of water in organic solvents such as propylene glycol and dimethyl sulfoxide (DMSO). Best-case detection limits were 0.02% (w/w) methanol in water, 0.0006% water in DMSO, and 0.004% water in propylene glycol.

scholarly journals Helium Abundance in the Most Metal-Deficient Dwarf Galaxies

1999 ◽  
Vol 171 ◽  
pp. 390-392
Author(s):  
Y.I. Izotov
Keyword(s):  
Mass Fraction ◽  
Dwarf Galaxies ◽  
Signal To Noise Ratio ◽  
Emission Lines ◽  
High Signal ◽  
Weighted Mean ◽  
Ratio Spectrum ◽  
Abundance Determination ◽  
Better Than ◽  
The Continuum

AbstractThe high-quality long-exposure spectroscopic observations of the two most-metal deficient blue compact galaxies I Zw 18 and SBS 0335–052 are discussed. We confirm previous findings that underlying stellar absorption strongly influences the observed intensities of He I emission lines in the brightest NW component of I Zw 18, and hence this component should not be used for primordial He abundance determination. The effect of underlying stellar absorption, though present, is much smaller in the SE component. The extremely high signal-to-noise ratio spectrum (≥ 100 in the continuum) of the BCG SBS 0335–052 allows us to measure the helium mass fraction with precision better than 2% in nine different regions along the slit. The weighted mean of helium mass fraction in two most metal-deficient BCGs I Zw 18 and SBS 0335–052, Y=0.2462±0.0009, after correction for the He production in massive stars results in primordial He mass fraction Yp = 0.2452±0.0009.

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