The origin of subdwarf B stars – I. The formation channels

By Zhanwen Han, P. Podsiadlowski, P. Maxted, Thomas R. Marsh, N. Ivanova. 2002

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Subdwarf B (sdB) stars (and related sdO/sdOB stars) are believed to be helium-core-burning objects with very thin hydrogen-rich envelopes. In recent years it has become increasingly clear from observational surveys that a large fraction of these objects are members of binary systems. To understand their formation better, we present the results of a detailed investigation of the three main binary evolution channels that can lead to the formation of sdB stars: the common-envelope (CE) ejection channel, the stable Roche lobe overflow (RLOF) channel, and the double helium white dwarfs (WDs) merger channel. The CE ejection channel leads to the formation of sdB stars in short-period binaries with typical orbital periods between 0.1 and 10 d, very thin hydrogen-rich envelopes and a mass distribution sharply peaked around similar to0.46 M-.. On the other hand, under the assumption that all mass transferred is soon lost, the stable RLOF channel produces sdB stars with similar masses but long orbital periods (400-1500 d) and with rather thick hydrogen-rich envelopes. The merger channel gives rise to single sdB stars whose hydrogen-rich envelopes are extremely thin but which have a fairly wide distribution of masses (0.4-0.65 M-.). We obtained the conditions for the formation of sdB stars from each of these channels using detailed stellar and binary evolution calculations where we modelled the detailed evolution of sdB stars and carried out simplified binary population synthesis simulations. The observed period distribution of sdB stars in compact binaries strongly constrains the CE ejection parameters. The best fits to the observations are obtained for very efficient CE ejection where the envelope ionization energy is included, consistent with previous results. We also present the distribution of sdB stars in the T (eff) -log g diagram, the Hertzsprung-Russell diagram and the distribution of mass functions.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9cd681182d92fb7be716cb67a6087c171eabaf3f

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Citations in the corpus

Galactic distribution of merging neutron stars and black holes – prospects for short gamma-ray burst progenitors and LIGO/VIRGO (2003, background): “This tiny envelope seems to have important effects on the subsequent radial evolution of the helium star (e.g. Han et al. 2002).”
Post-common-envelope binaries from SDSS. IX: Constraining the common-envelope efficiency (2010, background): “However, as most EHB stars appear to be members of close binary systems, the binary-formation channel proposed by Han et al. (2002, 2003) has become a popular alternative.”
On the α formalism for the common envelope interaction (2010, background): “…such as cataclysmic variables (CV; King 1988; Warner 1995), close binary central stars of planetary nebula (PN; De Marco 2009), subdwarf B binaries (Han et al. 2002, 2003; MoralesRueda et al. 2003), low-mass X-ray binaries (Charles & Coe 2006), the progenitors of Type Ia supernovae (Belczynski,…”
THE sdB+M ECLIPSING SYSTEM HW VIRGINIS AND ITS CIRCUMBINARY PLANETS (2008, background): “The time to achieve Roche-lobe contact and hence to initiate mass transfer is about 1.4 Gyr, which is longer than the timescale (∼108 yr) that the sdB primary star needs to evolve into a white dwarf (Wood et al. 1993; Hu et al. 2007).”
Reconstructing the evolution of white dwarf binaries: further evidence for an alternative algorithm for the outcome of the common-envelope phase in close binaries (2004, methodology): “For the sdB stars with no independent determinationof the mass we use the results of Han et al. (2002) and consider all c 2004 RAS, MNRAS000, 1–11 core masses that are just about to ignite helium plus all helium core masses that are non-degenerate as possible progenitors of the sdB stars.”
Modeling the Panchromatic Spectral Energy Distributions of Galaxies (2013, background): “In fact, binary star evolution may also create blue straggler stars and extreme HB stars, which would suggest that binary evolution can affect older stellar populations as well (Han et al. 2002, 2003, Zhang et al. 2005).”
Supernova Type Ia progenitors from merging double white dwarfs - Using a new population synthesis model (2012, background): “As shown by Han et al. (2002), degenerate stars do not ignite helium at a fixed core mass, but instead the core mass at helium ignition is a decreasing function of the ZAMS mass of the star.”
The origin of subdwarf B stars – II (2003, background): “To understand the formation of sdB stars, Han et al. (2002) (hereafter Paper I) have performed a systematic study of the various binary evolution channels that can produce sdB stars.”
On the formation and evolution of black hole binaries (2002, methodology): “…process which have suggested that the CE ejection process must be very efficient; see e.g. the recent study of sdB stars in compact binaries by Han et al. (2002, 2003) (these are short-period binaries that have formed through a very well defined CE channel and are hence particularly…”
A circumbinary disc in the final stages of common envelope and the core-degenerate scenario for Type Ia supernovae (2011, background): “The ionization energy might become an important source in extended AGB stars that have low binding energy per unit mass (e.g., Han et al. 2002; see Soker & Harpaz 2003 for a different view).”
Common envelope evolution: where we stand and how we can move forward (2012, methodology): “IV: Termination of the self-regulating phase The self-regulated spiral-in ends with the ejection of the envelope (e.g., via delayed dynamical ejection, Ivanova 2002; Han et al. 2002), or when either of the secondary or core of the primary overfills its Roche lobe.”
Dawes Review 6: The Impact of Companions on Stellar Evolution (2016, methodology): “The code used by, e.g., Han et al. (2002), also interpolates on a grid of pre-calculated detailed models (Han et al., 1995).”
The helium star donor channel for the progenitors of Type Ia supernovae (2009, background): “…simulation requires as input the initial mass function (IMF) of the primary, the mass-ratio distribution, the distribution of initial orbital separations, the eccentricity distribution of binary orbit, and the star formation rate (SFR) (e.g., Han et al. 1995a, 2002, 2003; Wang & Han 2009, 2010c).”
A Binary Model for the UV-upturn of Elliptical Galaxies (2006, methodology): “The BPS code of Han et al. was originally developed in 1994 and has been updated regularly ever since (Han, Podsiadlowski & Eggleton 1994; Han 1995; Han, Podsiadlowski & Eggleton 1995a; Han et al. 1995b; Han 1998; Han et al. 2002, 2003; Han & Podsiadlowski 2004).”