scholarly journals Recipes for bolometric corrections and Gaia luminosities of B-type stars: application to an asteroseismic sample

2020 ◽  
Vol 495 (3) ◽  
pp. 2738-2753 ◽  
Author(s):  
May G Pedersen ◽  
Ana Escorza ◽  
Péter I Pápics ◽  
Conny Aerts
Keyword(s):  
Statistical Model ◽  
Thermodynamic Equilibrium ◽  
Statistical Models ◽  
Local Thermodynamic Equilibrium ◽  
Space Mission ◽  
Instability Strip ◽  
Spectroscopic Parameters ◽  
Non Local ◽  
Effective Temperatures ◽  
Eddington Limit

ABSTRACT We provide three statistical model prescriptions for the bolometric corrections appropriate for B-type stars as a function of (i) Teff, (ii) Teff and log g, and (iii)Teff, log g and [M/H]. These statistical models have been calculated for 27 different filters, including those of the Gaia space mission, and were derived based on two different grids of bolometric corrections assuming LTE and LTE+NLTE, respectively. Previous such work has mainly been limited to a single photometric passband without taking into account non-local thermodynamic equilibrium (NLTE) effects on the bolometric corrections. Using these statistical models, we calculate the luminosities of 34 slowly pulsating B-type (SPB) stars with available spectroscopic parameters, to place them in the Hertzsprung–Russell diagram and to compare their position to the theoretical SPB instability strip. We find that excluding NLTE effects has no significant effect on the derived luminosities for the temperature range 11 500–21 000 K. We conclude that spectroscopic parameters are needed in order to achieve meaningful luminosities of B-type stars. The three prescriptions for the bolometric corrections are valid for any galactic B-type star with effective temperatures and surface gravities in the ranges 10 000–30 000 K and 2.5–4.5 dex, respectively, covering regimes below the Eddington limit.

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.

Diagnosing Fe Plasma In Non-Local Thermodynamic Equilibrium

2013 ◽  
Vol 82 (2) ◽  
pp. 024501
Author(s):  
Xiao-Ying Han ◽  
Fei-Lu Wang ◽  
Ze-Qing Wu ◽  
Jun Yan ◽  
Gang Zhao
Keyword(s):  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Non Local

scholarly journals Discovery of a second pulsating intermediate helium-enriched sdOB star

2019 ◽  
Vol 623 ◽  
pp. L12 ◽  
Author(s):  
M. Latour ◽  
E. M. Green ◽  
G. Fontaine
Keyword(s):  
Galactic Halo ◽  
Local Thermodynamic Equilibrium ◽  
Variable Stars ◽  
Light Curves ◽  
Atmospheric Parameters ◽  
Instability Strip ◽  
Long Period ◽  
Non Local ◽  
Halo Population ◽  
Low Amplitude

We present the discovery of long-period, low-amplitude, g-mode pulsations in the intermediate He-rich hot subdwarf (sdOB) star Feige 46. So far, only one other He-enriched sdOB star (LS IV−14 ° 116) was known to exhibit such pulsations. From our ground-based light curves of Feige 46, we extracted five independent periodicities ranging from 2294 s to 3400 s. We fit our optical spectrum of the star with our grid of non-local thermodynamic equilibrium (NLTE) model atmospheres and derived the following atmospheric parameters: Teff = 36120 ± 230 K, log g = 5.93 ± 0.04, and log N(He)/N(H) = −0.32 ± 0.03 (formal fitting errors only). These parameters are very similar to those of LS IV−14 ° 116 and place Feige 46 well outside of the instability strip where the hydrogen-rich g-mode sdB pulsators are found. We used the Gaia parallax and proper motion of Feige 46 to perform a kinematic analysis of this star and found that it likely belongs to the Galactic halo population. This is most certainly an intriguing and interesting result given that LS IV−14 ° 116 is also a halo object. The mechanism responsible for the pulsations in these two peculiar objects remains unclear, but a possible scenario involves the ϵ-mechanism. Although they are the only two members in their class of variable stars, these pulsators appear to have more in common than just their pulsation properties.

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