J/A+A/657/A4 RVs of 18 Galactic luminous blue variable stars (Mahy+, 2022)
Multiplicity of Galactic luminous blue variable stars.
Mahy L., Lanthermann C., Hutsemekers D., Kluska J., Lobel A., Manick R.,
Miszalski B., Reggiani M., Sana H., Gosset E.
<Astron. Astrophys. 657, A4 (2022)>
=2022A&A...657A...4M 2022A&A...657A...4M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Stars, blue ; Stars, luminous ;
Spectroscopy ; Radial velocities ; Optical
Keywords: stars: variables: S Doradus - stars: evolution - binaries: general -
stars: massive
Abstract:
Luminous blue variables (LBVs) are characterised by strong photometric
and spectroscopic variability. They are thought to be in a transitory
phase between O-type stars on the main sequence and the Wolf-Rayet
stage. Recent studies also evoked the possibility that they might be
formed through binary interaction. Only a few are known in binary
systems so far, but their multiplicity fraction is still uncertain.
We derive the binary fraction of the Galactic LBV population. We
combine multi-epoch spectroscopy and long-baseline interferometry to
probe separations from 0.1 to 120mas around confirmed and candidate
LBVs.
We used a cross-correlation technique to measure the radial velocities
of these objects. We identified spectroscopic binaries through
significant radial velocity variability with an amplitude larger than
35km/s. We also investigated the observational biases to take them
into account when we established the intrinsic binary fraction. We
used candid to detect interferometric companions, derive their flux
fractions, and their positions on the sky.
From the multi-epoch spectroscopy, we derive an observed spectroscopic
binary fraction of 26-10+16%. Considering period and mass ratio ranges
from log(Porb)=0-3 (i.e. from 1 to 1000days), q=0.1-1.0, and a
representative set of orbital parameter distributions, we find a
bias-corrected binary fraction of 62-24+38%. Based on data of the
interferometric campaign, we detect a binary fraction of 70±9% at
projected separations between 1 and 120mas. Based on the derived
primary diameters and considering the distances of these objects, we
measure for the first time the exact radii of Galactic LBVs to be
between 100 and 650R☉. This means that it is unlikely that
short-period systems are included among LBV-like stars.
This analysis shows for the first time that the binary fraction in the
Galactic LBV population is large. If they form through single-star
evolution, their orbit must be large initially. If they form through a
binary channel, the implication is that either massive stars in short
binary systems must undergo a phase of fully non-conservative mass
transfer to be able to sufficiently widen the orbit to form an LBV, or
that LBVs form through merging in initially binary or triple systems.
Interferometric follow-up would provide the distributions of orbital
parameters at more advanced stages and would serve to quantitatively
test the binary evolution in massive stars.
Description:
Spectroscopic and interferometric analysis of Galactic Luminous Blue
Variable stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 46 18 Sample stars
tablea1.dat 255 419 Compilation of RVs derived for the sample stars
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 22 A22 --- Star Star name
24- 25 I2 h RAh Right ascension (J2000)
27- 28 I2 min RAm Right ascension (J2000)
30- 34 F5.2 s RAS Right ascension (J2000)
36 A1 --- DE- Declination sign (J2000)
37- 38 I2 deg DEd Declination (J2000)
40- 41 I2 arcmin DEm Declination (J2000)
43- 46 F4.1 arcsec DEs Declination (J2000)
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 22 A22 --- Star Star name
24- 32 F9.4 d HJD Heliocentric Julian date
34- 38 F5.1 km/s SiII4128-4130 ?=- SiII radial velocity
40- 42 F3.1 km/s e_SiII4128-4130 ?=- Error on SiII RV
44- 48 F5.1 km/s SIII4253 ?=- SIII radial velocity
50- 52 F3.1 km/s e_SIII4253 ?=- Error on SiIII RV
54- 58 F5.1 km/s HeI4471 ?=- HeI radial velocity
60- 62 F3.1 km/s e_HeI4471 ?=- Error on HeI RV
64- 68 F5.1 km/s MgII4481 ?=- MgII radial velocity
70- 72 F3.1 km/s e_MgII4481 ?=- Error on MgII RV
74- 78 F5.1 km/s HeI4471+MgII4481 ?=- HeI and MgII
radial velocity
80- 82 F3.1 km/s e_HeI4471+MgII4481 ?=- Error on HeI+MgII RV
84- 88 F5.1 km/s FeII4526-34-36 ?=- FeII radial velocity
90- 92 F3.1 km/s e_FeII4526-34-36 ?=- Error on FeII RV
94- 98 F5.1 km/s SiIII4552 ?=- SiIII radial velocity
100-102 F3.1 km/s e_SiIII4552 ?=- Error on SiIII RV
104-108 F5.1 km/s NII4630 ?=- NII radial velocity
110-112 F3.1 km/s e_NII4630 ?=- Error on NII RV
114-118 F5.1 km/s SiIII4813-19-28 ?=- SiIII radial velocity
120-122 F3.1 km/s e_SiIII4813-19-28 ?=- Error on SiIII RV
124-127 F4.1 km/s FeIII5156 ?=- FeIII radial velocity
129-131 F3.1 km/s e_FeIII5156 ?=- Error on FeIII RV
133-137 F5.1 km/s SII5454-74 ?=- SII radial velocity
139-141 F3.1 km/s e_SII5454-74 ?=- Error on SII RV
143-148 F6.1 km/s NII5666-76-79-86+AlIII5723 ?=- NII and AlIII
radial velocity
150-152 F3.1 km/s e_NII5666-76-79-86+AlIII5723 ?=- Error on NII+AlIII RV
154-158 F5.1 km/s HeI5876 ?=- HeI radial velocity
160-162 F3.1 km/s e_HeI5876 ?=- Error on HeI RV
164-168 F5.1 km/s SiII5979 ?=- SiII radial velocity
170-172 F3.1 km/s e_SiII5979 ?=- Error on SiII RV
174-178 F5.1 km/s FeII6179 ?=- FeII radial velocity
180-182 F3.1 km/s e_FeII6179 ?=- Error on FeII RV
184-188 F5.1 km/s SiII6347 ?=- SiII radial velocity
190-192 F3.1 km/s e_SiII6347 ?=- Error on SiII RV
194-198 F5.1 km/s SiII6371 ?=- SiII radial velocity
200-202 F3.1 km/s e_SiII6371 ?=- Error on SiII RV
204 I1 km/s SiII6347-71 ?=- SiII radial velocity
206 I1 km/s e_SiII6347-71 ?=- Error on SiII RV
208-212 F5.1 km/s NeI6402 ?=- NeI radial velocity
214-216 F3.1 km/s e_NeI6402 ?=- Error on NeI RV
218-222 F5.1 km/s SII6449 ?=- SII radial velocity
224-226 F3.1 km/s e_SII6449 ?=- Error on SII RV
228-231 F4.1 km/s CII6578-83 ?=- CII radial velocity
233-235 F3.1 km/s e_CII6578-83 ?=- Error on CII RV
237-240 F4.1 km/s MgII21347-21438 ?=- MgII radial velocity
242-244 F3.1 km/s e_MgII21347-21438 ?=- Error on MgII RV
246-251 F6.1 --- Mean ?=- Mean radial velocity
253-255 F3.1 --- e_Mean ?=- Error on mean RV
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Acknowledgements:
Laurent Mahy, laurent.mahy(at)oma.be
(End) Patricia Vannier [CDS] 12-Dec-2021