A seismic approach to testing different formation channels of subdwarf B stars

Abstract

There are many unknowns in the formation of subdwarf B stars. Different formation channels are considered to be possible and to lead to a variety of helium-burning subdwarfs. All seismic models to date, however, assume that a subdwarf B star is a post-helium-flash-core surrounded by a thin inert layer of hydrogen. We examine an alternative formation channel, in which the subdwarf B star originates from a massive (>~2 Msun) red giant with a non-degenerate helium-core. Although these subdwarfs may evolve through the same region of the log g-Teff diagram as the canonical post-flash subdwarfs, their interior structure is rather different. We examine how this difference affects their pulsation modes and whether it can be observed. Using detailed stellar evolution calculations we construct subdwarf B models from both formation channels. The iron accumulation in the driving region due to diffusion, which causes the excitation of the modes, is approximated by a Gaussian function. The pulsation modes and frequencies are calculated with a non-adiabatic pulsation code. A detailed comparison of two subdwarf B models from different channels, but with the same log g and Teff, shows that their mode excitation is different. The excited frequencies are lower for the post-flash than for the post-non-degenerate subdwarf B star. This is mainly due to the differing chemical composition of the stellar envelope. A more general comparison between two grids of models shows that the excited frequencies of most post-non-degenerate subdwarfs cannot be well-matched with the frequencies of post-flash subdwarfs. In the rare event that an acceptable seismic match is found, additional information, such as mode identification and log g and Teff determinations, allows us to distinguish between the two formation channels.

arXiv comment10 pages, 8 figures, 2 tables, accepted for publication in A&A

References in corpus (21)

• The Origin of Subdwarf B Star (I): the Formation Channels
• The origin of sdB stars (II)
• Approximate input physics for stellar modelling
• The binary fraction of extreme horizontal branch stars
• The Origin of Extreme Horizontal Branch Stars
• The Potential of Asteroseismology for Hot, Subdwarf B Stars: A New Class of Pulsating Stars?
• Flash Mixing on the White Dwarf Cooling Curve: Understanding Hot Horizontal Branch Anomalies in NGC 2808
• Spectral analysis of sdB stars from the Hamburg Quasar Survey
• A comparison of Rosseland-mean opacities from OP and OPAL
• Models of Metal Poor Stars with Gravitational Settling and Radiative Accelerations: I. Evolution and Abundance Anomalies
• First full evolutionary computation of the He-flash induced mixing in Population II stars
• The binary properties of the pulsating subdwarf B eclipsing binary PG 1336-018 (NY Vir)
• Gravity-mode pulsations in subdwarf B stars: a critical test of stellar opacity
• A more detailed look at the Opacities for Enriched Carbon and Oxygen Mixtures
• Hot Horizontal Branch Stars: Predictions for Mass Loss
• On the helium flash in low-mass Population III Red Giant stars
• On the importance of inner-shell transitions for opacity calculations
• On constructing horizontal branch models
• An evolutionary study of the pulsating subdwarf B eclipsing binary PG1336-018 (NY Vir)
• Spectroscopic analysis of sdB stars from the ESO Supernova Ia Progenitor Survey
• Instability strips of main sequence B stars: a parametric study of iron enhancement

Cited by in corpus (18)

• Hot subluminous stars
• A selection of hot subluminous stars in the GALEX survey II. Subdwarf atmospheric parameters
• Pulsating red giant stars in eccentric binary systems discovered from Kepler space-based photometry
• Beyond Mixing-length Theory: a step toward 321D
• Slowing down atomic diffusion in subdwarf B stars: mass loss or turbulence?
• A survey for pulsating subdwarf B stars with the Nordic Optical Telescope
• Discovery of post-mass-transfer helium-burning red giants using asteroseismology
• TESS first look at evolved compact pulsators : Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494-7018
• Impact of helium diffusion and helium-flash-induced carbon production on gravity-mode pulsations in subdwarf B stars
• First Kepler results on compact pulsators II: KIC 010139564, a new pulsating subdwarf B (V361 Hya) star with an additional low-frequency mode
• Gravitational settling in pulsating subdwarf B stars and their progenitors
• The blue-edge problem of the V1093 Her instability strip revisited using evolutionary models with atomic diffusion
• MAIA, a three-channel imager for asteroseismology: instrument design
• Structure and evolution of pulsating hot subdwarfs
• Space observations of AA Doradus provide consistent mass determinations. New HW-Vir systems observed with TESS
• A 500 pc volume-limited sample of hot subluminous stars II. Atmospheric parameters, mass distribution, and kinematics
• Angular momentum transfer between oscillations and rotation in subdwarf B hybrid pulsators
• Discerning internal conditions of pulsating hot subdwarf B stars. Modelling multiple trapped modes in KIC 10001893