Third generation stellar models for asteroseismology of hot B subdwarf stars

Abstract

Context. Asteroseismic determinations of structural parameters of hot B subdwarfs (sdB) have been carried out for more than a decade now. These analyses rely on stellar models whose reliability for the required task needs to be evaluated critically. Aims. We present new models of the so-called third generation (3G) dedicated to the asteroseismology of sdB stars, in particular to long-period pulsators observed from space. These parameterized models are complete static structures suitable for analyzing both p-and g-mode pulsators, contrary to the former second generation (2G) models that were limited to p-modes. While the reliability of the 2G models has been successfully verified in the past, this important test still has to be conducted on the 3G structures. Methods. The close eclipsing binary PG 1336−018 provides a unique opportunity to test the reliability of hot B subdwarf models. We compared the structural parameters of the sdB component in PG 1336−018 obtained from asteroseismology based on the 3G models, with those derived independently from the modeling of the reflection/irradiation effect and the eclipses observed in the light curve. Results. The stellar parameters inferred from asteroseismology using the 3G models are found to be remarkably consistent with both the preferred orbital solution obtained from the binary light curve modeling and the updated spectroscopic estimates for the surface gravity of the star. The seismology gives M * = 0.471 ± 0.006 M , R * = 0.1474 ± 0.0009 R , and log g = 5.775 ± 0.007, while orbital modeling leads to M * = 0.466 ± 0.006 M , R * = 0.15 ± 0.01 R , log g = 5.77 ± 0.06, and spectroscopy yields log g = 5.771 ± 0.015. In comparison, seismology from a former analysis based on the 2G models gave very similar results with M * = 0.459 ± 0.005 M , R * = 0.151 ± 0.001 R , and log g = 5.739 ± 0.002. We also show that the uncertainties on the input physics included in stellar models have, at the current level of accuracy, no noticeable impact on the structural parameters derived by asteroseismology. Conclusions. The stellar models (both of second and third generation) presently used to carry out quantitative seismic analyses of sdB stars are reliable for the task. The stellar parameters inferred by this technique, at least for those that could be tested (M * , R, and log g), appear to be both very precise and accurate, as no significant systematic effect has been found.

Binaries discovered by the MUCHFUSS project

“…Due to the early spectral type of the primary star, the gravity darkening (Van Grootel et al 2013a;Drechsel et al 2001;Geier et al 2011d;Maxted et al 2002;Klepp & Rauch 2011;Østensen et al 2008Wood & Saffer 1999;Almeida et al 2012;Barlow et al 2013). The open dots represent other sdB binaries from the literature.…”

The enigmatic He-sdB pulsator LS IV-14°116: new insights from the VLT

“…It is then quite fitting that stars located at the intersection between the p-and g-mode instability regions appear to be hybrids and show both rapid and slow luminosity variations (Schuh et al 2006). The two types of sdB pulsator have now been very successfully analysed using asteroseismology A&A 576, A65 (2015) (e.g., Van Grootel et al 2013;Charpinet et al 2011), where the internal parameters of the star are derived from the observed pulsation spectrum to a high accuracy and can be used to start constraining the proposed evolutionary scenarios.…”

Pulsations in hot subdwarf stars: recent advances and prospects for testing stellar physics

“…The technique was then vastly improved over the years with the development of sophisticated optimization tools and a new generation of stellar models. The typical outcomes from the asteroseismic studies of p-mode pulsators have been the determination of fundamental parameters -such as the mass, surface gravity, and hydrogen dominated envelope mass of the star -to unprecedented levels of precision (e.g., Charpinet et al 2005;Van Grootel et al 2013) and in some cases the determination of the internal rotation (e.g., Charpinet et al 2008). These (still ongoing) efforts led to the seismic analysis of 15 sdB pulsators so far, with interesting applications such as, for instance, inferring their mass distribution (Fontaine et al 2012), a key information to understand the still unclear processes leading to the formation of sdB stars (see, Charpinet et al 2011a;Geier 2015 and references therein).…”

“…An example of such tests is illustrated in Figure 2 (see also Van Grootel et al 2013). The idea here was to evaluate the impact of changing the iron abundance profile in the envelope of a sdB star from a nonuniform distribution derived by assuming diffusive equilibrium between radiative levitation and gravitational settling (the "standard" models) to profiles that either reduce the amount of levitating iron by a factor of 2 (test case 1) or 4 (test Figure 2.…”