The origin of subdwarf B stars – II

By Zhanwen Han, P. Podsiadlowski, P. Maxted, Thomas R. Marsh. 2003

473 citations recorded by the source corpus.

We have carried out a detailed binary population synthesis (BPS) study of the formation of subdwarf B (sdB) stars and related objects (sdO, sdOB stars) using the latest version of the BPS code developed by Han and co-workers. We systematically investigate the importance of the five main evolutionary channels in which the sdB stars form after one or two common-envelope (CE) phases, one or two phases of stable Roche lobe overflow (RLOF) or as the result of the merger of two helium white dwarfs (WDs). Our best BPS model can satisfactorily explain the main observational characteristics of sdB stars, in particular their distributions in the orbital period-minimum companion mass (log P-M-comp) diagram and in the effective temperature-surface gravity (T-eff- log g) diagram, their distributions of orbital period, log (gtheta(4))(theta = 5040 K / T-eff) and mass function, their binary fraction and the fraction of sdB binaries with WD companions, their birth rates and their space density. We obtain a Galactic formation rate for sdB stars of 0.014- 0.063 yr(-1) with a best estimate of similar to0.05 yr(-1) and a total number in the Galaxy of 2.4-9.5 x 10(6) with a best estimate of similar to6 x 10(6); half of these may be missing in observational surveys owing to selection effects. The intrinsic binary fraction is 76-89 per cent, although the observed frequency may be substantially lower owing to the selection effects. The first CE ejection channel, the first stable RLOF channel and the merger channel are intrinsically the most important channels, although observational selection effects tend to increase the relative importance of the second CE ejection and merger channels. We also predict a distribution of masses for sdB stars that is wider than is commonly assumed and that some sdB stars have companions of spectral type as early as B. The percentage of A-type stars with sdB companions can in principle be used to constrain some of the important parameters in the binary evolution model. We conclude that (i) the first RLOF phase needs to be more stable than is commonly assumed, either because the critical mass ratio q(crit) for dynamical mass transfer is higher or because of tidally enhanced stellar wind mass loss; (ii) mass transfer in the first stable RLOF phase is non-conservative, and the mass lost from the system takes away a specific angular momentum similar to that of the system; and (iii) common-envelope ejection is very efficient.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/77a326e1a55b4f7fe0be5b59b261dfdea18dd80c

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Michela Mapelli
2. D. Stello
3. E. Carretta
4. O. De Marco
5. A. Bragaglia
6. R. Gratton
7. N. Langer
8. W. Chaplin

In Instrumentation

1. E. Carretta
2. D. Stello
3. R. Gratton
4. F. D’Antona
5. A. Bragaglia
6. W. Chaplin
7. O. De Marco
8. B. Mosser

Citations in the corpus

• 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).”
• 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,…”
• A new route towards merging massive black holes (2016, background): “While the physics of this process is not yet well understood (Ivanova et al. 2013), some observational constraints exist for low-mass binaries (e.g. Han et al. 2003; Zorotovic et al. 2011).”
• PS1-10jh: THE DISRUPTION OF A MAIN-SEQUENCE STAR OF NEAR-SOLAR COMPOSITION (2013, background): “The known candidates are SdB/SdO stars (∼106 in the MW, Han et al. 2003), helium WDs (∼107 in the MW, Nelemans et al. 2001), and WR stars (∼104 in the MW, van der Hucht 2001).”
• 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.”
• 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).”
• Asteroseismology of old open clusters with Kepler: direct estimate of the integrated red giant branch mass-loss in NGC 6791 and 6819 (2011, background): “In this context, the extreme HB can be attributed to binary evolution following the same scenario as the production of extreme B and O subdwarfs in the Galactic field (e.g. Han et al. 2003).”
• US 708 – an unbound hyper-velocity subluminous O star (2005, background): “A recent population synthesis study (Han et al. 2003) identified three channels to form sdB stars: (i) one or two phases of common envelope evolution; (ii) stable Roche lobe overflow; and (iii) the merger of two helium-core white dwarfs.”
• THE sdB+M ECLIPSING SYSTEM HW VIRGINIS AND ITS CIRCUMBINARY PLANETS (2008, background): “After the massive component evolved through the redgiant phase, the binary star passed into its current configuration while losing very large amounts of mass (almost half of the original amount) during its common-envelope ejection episode (Han et al. 2002, 2003).”
• The second and third parameters of the horizontal branch in globular clusters (2010, background): “…successful cases, they might explain some groups of stars with anomalous colours on the HB (e.g., most field O-B subdwarfs are binaries, see e.g., Maxted et al. 2001; Napiwotzki et al. 2004; Han et al. 2003; however most of these in GCs seem to be single stars, see e.g., Moni Bidin et al. 2006).”
• Hot Subdwarf Stars (2009, unknown): “5 the resulting atmospheric parameters are compared to canonical models (Han et al., 2003) for EHB evolution.”
• Common envelope evolution: where we stand and how we can move forward (2012, background): “This combines the internal kinetic energy of the 1At least some population synthesis calculations (see, e.g., Han et al. 2003) have found better agreement with observations for particular classes of system by including the internal energy reservoir. particles and the energy stored in radiation.”
• 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).”