J/A+A/702/A11 Radial velocities of 329 BHB stars (Guo+, 2025)
The binary fraction of blue horizontal-branch (BHB) stars.
Guo Y., Chen K., Li Z., Ju J., Liu C., Xue X., Dorsch M., Han Z., Chen X.
<Astron. Astrophys. 702, A11 (2025)>
=2025A&A...702A..11G 2025A&A...702A..11G (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, spectroscopic ; Stars, horizontal branch ;
Radial velocities ; Optical
Keywords: methods: data analysis - statistical - catalogs -
surveys - binaries: spectroscopic - stars: horizontal-branch
Abstract:
Blue horizontal branch (BHB) stars are old, low-mass, metal-poor stars
that serve as important tracers of the Galactic halo structure,
kinematics, and evolution. Understanding their binary properties
provides key insights into their formation channels and the role of
binary interactions in the evolution of horizontal branch stars.
We investigated the intrinsic binary fraction fbin of BHB stars and
its dependences on metallicity, kinematics, and effective temperature.
We collected 299 BHB stars from LAMOST with multiple radial velocity
(RV) measurements and classified the sample into halo-like and
disk-like BHBs based on their kinematics and metallicity, and into
bluer and redder BHBs based on their effective temperature. We then
investigated the observed binary fraction for each group based on the
radial velocity variations and applied a set of Monte Carlo
simulations, assuming distributions of f(P)∝Ppi and
f(q)∝qkappa, to correct the observed binary fraction for
observational biases and to derive the intrinsic binary fraction.
The observed binary fraction of BHB stars is 18%±2% for cases with
n≥2 and 21%±3% for cases with n≥3, where n represents the number
of observation times. After correcting for observational biases, the
intrinsic binary fraction increases to 31%±3% for n≥2 and 32%±3%
for n≥3. A clear contrast is observed between halo-like and disk-like
BHB stars, with halo-like BHBs exhibiting a lower intrinsic binary
fraction (28%±3% for n≥2 and 29%±3% for n≥3) compared to
disk-like BHBs (46%±11% and 51%±11%, respectively), indicating
different formation pathways. In particular, halo-like BHB stars are
more likely to have formed via a single-star evolution channel,
whereas disk-like BHB stars may predominantly result from binary
evolution processes. Additionally, we find that bluer BHB stars
exhibit a significantly higher binary fraction (42%±6% for n≥2 and
45%±6% for n≥3) than redder BHB stars (24%±5% and 23%±5%,
respectively), which suggests a possible link between binarity and the
effective temperature, although more samples are required to confirm
this. No correlation is found between π (κ) and metallicity
or kinematics, nor between π (κ) and the effective
temperature of BHB stars.
Description:
Radial velocity catalog.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 84 2045 The radial velocity catalog
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension (J2000)
11- 19 F9.5 deg DEdeg Declination (J2000)
21- 36 F16.10 d MJD Modified Julian Date of the observation
38- 43 F6.2 --- snr Signal-to-noise ratio of the spectrum
45- 54 F10.4 K Teff Effective temperature
56- 62 F7.5 [cm/s2] logg Surface gravity
64- 71 F8.5 [-] [Fe/H] Metallicity [Fe/H]
73- 79 F7.2 km/s RV Radial velocity
81- 84 F4.2 km/s e_RV Uncertainty in radial velocity
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Acknowledgements:
Yanjun Guo, guoyanjun(at)ynao.ac.cn
(End) Patricia Vannier [CDS] 04-Aug-2025