scholarly journals Differential Abundances of B-type Supergiants in M33

1999 ◽  
Vol 192 ◽  
pp. 272-276
Author(s):  
M. I. Monteverde ◽  
A. Herrero
Keyword(s):  
H Ii Regions ◽  
Line Formation ◽  
Atmospheric Parameters ◽  
Oxygen Abundance ◽  
Abundance Gradient ◽  
Preliminary Results ◽  
Metal Abundances ◽  
Effective Temperatures ◽  
Abundance Determination

In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants. In the following study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. Determination of atmospheric parameters is based on analyses of silicon ionisation balance.Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral standards in our Galaxy.We compare our results with the abundances expected from studies of H II regions.

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 Temperature Scale and Iron Abundances of Very Hot Central Stars of Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 169-176 ◽  
Author(s):  
Klaus Werner ◽  
Jochen L. Deetjen ◽  
Stefan Dreizler ◽  
Thomas Rauch ◽  
Jeff W. Kruk
Keyword(s):  
Temperature Scale ◽  
Model Atmosphere ◽  
Uv Spectra ◽  
Stellar Surface ◽  
Line Profiles ◽  
Considerable Uncertainty ◽  
Metal Abundances ◽  
Effective Temperatures ◽  
Central Stars

The determination of effective temperatures of very hot central stars (Teff > 70 000 K) by model atmosphere analyses of optical H and He line profiles is afflicted with considerable uncertainty, primarily due to the lack of neutral helium lines. Ionization balances of metals, accessible only with UV lines, allow more precise temperature estimates. The potential of iron lines is pointed out. At the same time iron and other metal abundances, hardly investigated until today, may be derived from UV spectra. We describe recent HST spectroscopy performed for this purpose.A search for iron lines in FUV spectra of the hottest H-deficient central stars (PG1159-type, Teff >100000 K) taken with FUSE was unsuccessful. The derived deficiency is interpreted in terms of iron depletion due to n-capture nucleosynthesis in intershell matter, which is now exposed at the stellar surface as a consequence of a late He shell flash.

scholarly journals 18. Model Atmospheres for Hydrogen-Deficient White Dwarfs

1971 ◽  
Vol 42 ◽  
pp. 125-129
Author(s):  
I. Bues
Keyword(s):  
Effective Temperature ◽  
White Dwarfs ◽  
Atmospheric Parameters ◽  
Metal Abundances ◽  
Different Parts

The determination of atmospheric parameters for non-DA white dwarfs is investigated with the computed helium-rich model atmospheres by Bues (1970). Only poor predictions are possible from UBV colors alone for DB and DC stars. From uvby colors a determination of effective temperature is possible within 1000 K. Profiles of lines in different parts of the spectrum are necessary for better results.A deficiency of metal abundances for the cooler non-DA stars is obtained.

scholarly journals The Chemical Composition of Vega

1988 ◽  
Vol 132 ◽  
pp. 395-399
Author(s):  
Detlef Gigas
Keyword(s):  
Chemical Composition ◽  
Numerical Simulations ◽  
Preliminary Results ◽  
Abundance Determination

A non-LTE abundance determination of magnesium, iron, and barium was carried out for the atmosphere of Vega. The results indicate marked underabundances of these elements relative to the solar values. First preliminary results of numerical simulations of convective and oscillatory phenomena in the atmosphere of Vega are briefly described.

scholarly journals The oxygen abundance gradient in M81 and the robustness of abundance determinations in H ii regions

2015 ◽  
Vol 455 (3) ◽  
pp. 2627-2643 ◽  
Author(s):  
K. Z. Arellano-Córdova ◽  
M. Rodríguez ◽  
Y. D. Mayya ◽  
D. Rosa-González
Keyword(s):  
H Ii Regions ◽  
Oxygen Abundance ◽  
Abundance Gradient

scholarly journals A Generalization of the Cors Method to Determine Cepheid Radii: Theory and Application

1985 ◽  
Vol 82 ◽  
pp. 43-47
Author(s):  
B. Caccin ◽  
B. Buonaura ◽  
A. Onnembo ◽  
G. Russo ◽  
A. M. Sambuco ◽  
...  
Keyword(s):  
Photometric System ◽  
Atmospheric Parameters ◽  
Preliminary Results ◽  
Empirical Determination ◽  
Direct Use ◽  
Good Agreement

AbstractThe CORS method for the empirical determination of the radii of pulsating variables (Caccin et al., 1981; Sollazzo et al., 1981) is discussed in the framework of the quasistatlc approximation to the variations of the atmospheric parameters (Unno, 1965) and reformulated in a way that does not make direct use of theoretical calibrations of the photometric system in terms of model atmospheres. The radii calculated with this approach are in good agreement with those previously obtained by means of Pel's calibrations of the VBLUW system (Sollazzo et al.,1981) which lead to a period-radius relation coinciding, within the errors, with the theoretical one (Cogan, 1978) and, consequently, mass determinations consistent with pulsational masses (Cox, 1979). The method can be immediately applied to any other multicolour system, and very promising preliminary results are obtained by using recent UBV data by Gieren (1982).

scholarly journals Distribution of refractory and volatile elements in CoRoT planet host stars

2009 ◽  
Vol 5 (S265) ◽  
pp. 424-425
Author(s):  
C. Chavero ◽  
R. de la Reza ◽  
R. C. Domingos ◽  
N. A. Drake ◽  
C. B. Pereira ◽  
...  
Keyword(s):  
Internal Migration ◽  
Spectroscopic Determination ◽  
Atmospheric Parameters ◽  
Chemical Abundances ◽  
Volatile Elements ◽  
Preliminary Results ◽  
Transiting Planets ◽  
Host Stars ◽  
Flat Distribution

AbstractWe report on preliminary results of spectroscopic determination of the atmospheric parameters and chemical abundances of the parent stars of the recently discovered transiting planets CoRoT-2b and CoRoT-4b. We found a flat distribution of the relative abundances as a function of their condensation temperatures. Also, we introduce a new methodology to investigate a relation between the abundances of these stars and the internal migration of their planets.

scholarly journals Metal abundances in hot white dwarfs with signatures of a superionized wind

2018 ◽  
Vol 609 ◽  
pp. A107 ◽  
Author(s):  
K. Werner ◽  
T. Rauch ◽  
J. W. Kruk
Keyword(s):  
Spectral Type ◽  
White Dwarfs ◽  
Light Metals ◽  
Line Formation ◽  
Iron Group ◽  
Gravitational Settling ◽  
Abundance Patterns ◽  
Metal Abundances ◽  
Effective Temperatures ◽  
Absorption Features

About a dozen hot white dwarfs with effective temperatures Teff = 65 000−120 000 K exhibit unusual absorption features in their optical spectra. These objects were tentatively identified as Rydberg lines of ultra-high excited metals in ionization stages v–x, indicating line formation in a dense environment with temperatures near 106 K. Since some features show blueward extensions, it was argued that they stem from a superionized wind. A unique assignment of the lines to particular elements is not possible, although they probably stem from C, N, O, and Ne. To further investigate this phenomenon, we analyzed the ultraviolet spectra available from only three stars of this group; that is, two helium-rich white dwarfs, HE 0504–2408 and HS 0713+3958 with spectral type DO, and a hydrogen-rich white dwarf, HS 2115+1148 with spectral type DAO. We identified light metals (C, N, O, Si, P, and S) with generally subsolar abundances and heavy elements from the iron group (Cr, Mn, Fe, Co, Ni) with solar or oversolar abundance. The abundance patterns are not unusual for hot WDs and can be interpreted as the result of gravitational settling and radiative levitation of elements. As to the origin of the ultra-high ionized metals lines, we discuss the possible presence of a multicomponent radiatively driven wind that is frictionally heated.

scholarly journals Stellar Parameters for a Sample of Stars with Planets

2009 ◽  
Vol 5 (S265) ◽  
pp. 432-433
Author(s):  
Luan Ghezzi ◽  
Katia Cunha ◽  
Francisco X. de Araújo ◽  
Verne V. Smith ◽  
Ramiro de la Reza ◽  
...  
Keyword(s):  
Control Sample ◽  
Giant Planets ◽  
Atmospheric Parameters ◽  
Important Ingredient ◽  
Chemical Abundances ◽  
Large Sample ◽  
Formation And Evolution ◽  
Effective Temperatures ◽  
Metallicity Distribution

AbstractThe study of chemical abundances in stars with planets is an important ingredient for the models of formation and evolution of planetary systems. In order to determine accurate abundances, it is crucial to have a reliable set of atmospheric parameters. In this work, we describe the homogeneous determination of effective temperatures, surface gravities and iron abundances for a large sample of stars with planets as well as a control sample of stars without giant planets. Our results indicate that the metallicity distribution of the stars with planets is more metal rich by ~0.13 dex than the control sample stars.

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