J/A+A/698/A41 BLOeM. Early B dwarfs and giants at Z=0.2 (Villasenor+, 2025)
Binarity at LOw Metallicity (BLOeM):
Enhanced multiplicity of early B-type dwarfs and giants at Z=0.2 Z☉.
Villasenor J.I., Sana H., Mahy L., Shenar T., Bodensteiner J.,
Britavskiy N., Lennon D.J., Moe M., Patrick L.R., Pawlak M., Bowman D.M.,
Crowther P.A., de Mink S.E., Deshmukh K., Evans C.J., Fabry M.,
Fouesneau M., Holgado G., Langer N., Maiz Apellaniz J., Mandel I.,
Oskinova L.M., Pauli D., Ramachandran V., Renzo M., Rix H.-W., Rocha D.F.,
Sander A.A.C.S., Schneider F.R.N., Sen K., Simon-Diaz S., van Loon J.T.,
Toonen S., Vink J.S.
<Astron. Astrophys. 698, A41 (2025)>
=2025A&A...698A..41V 2025A&A...698A..41V (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, spectroscopic ; Stars, B-type ; Radial velocities
Keywords: binaries: close - binaries: spectroscopic - stars: early-type -
stars: massive - Magellanic Clouds
Abstract:
Early B-type stars with initial masses between 8 and 15 solM are
frequently found in multiple systems, as evidenced by multi-epoch
spectroscopic campaigns in the Milky Way and the Large Magellanic
Cloud (LMC). Previous studies have shown no strong metallicity
dependence in the close-binary (a<10au) fraction or orbital-period
distributions between the Milky Way's solar metallicity (Z☉) and
that of the LMC (Z=0.5Z☉). However, similar analyses for a large
sample of massive stars in more metal-poor environments are still
scarce. We focus on 309 early B-type stars (luminosity classes
III-V) from the Binarity at LOw Metallicity (BLOeM) campaign, which
targeted nearly 1000 massive stars in the Small Magellanic Cloud (SMC,
Z=0.2Z☉) using VLT/FLAMES multi-epoch spectroscopy. By applying
binary detection criteria consistent with previous works on Galactic
and LMC samples, we identify 153 stars (91 SB1, 59 SB2, 3 SB3)
exhibiting significant radial-velocity (RV) variations, resulting in
an observed multiplicity fraction of fobs=50±3. Using Monte
Carlo simulations to account for observational biases, we infer an
intrinsic close-binary fraction of fbin=80±8. This fraction
reduces to ∼55% when increasing our RV threshold from 20 to 80km/s,
however, an independent Markov chain Monte Carlo analysis of the
peak-to-peak RV distribution (ΔRVmax) confirms a high
multiplicity fraction of fbin=79+5. These findings suggest a
possible anti-correlation between metallicity and the fraction of
close B-type binaries, with the SMC multiplicity fraction
significantly exceeding previous measurements in the LMC and the
Galaxy. The enhanced fraction of close binaries at SMC's low
metallicity may have broad implications for massive-star evolution in
the early Universe. More frequent mass transfer and envelope stripping
could boost the production of exotic transients, stripped supernovae,
gravitational-wave progenitors, and sustained UV ionising flux,
potentially affecting cosmic reionisation. Theoretical predictions of
binary evolution under metal-poor conditions will provide a key test
of our results.
Description:
We present our radial velocity analysis for the sample of B-type dwarf
and giant stars observed by the BLOeM campaign in the SMC. The
analysis includes radial velocity determination from nine epochs of
VLT/FLAMES spectroscopy and spectroscopic binary classifications.
Orbital periods and their significance are also provided.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tabled1.dat 151 309 Results of RV analysis
tabled2.dat 59 41 Eclipsing binaries from OGLE
--------------------------------------------------------------------------------
See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AcA/66/421 : Eclipsing binaries in the Magellanic System (Pawlak+, 2016)
J/A+A/690/A289 : Binarity at LOw Metallicity (BLOeM). I. (Shenar+, 2024)
J/A+A/698/A38 : BLOeM. Oe and Be stars (Bodensteiner+, 2025)
J/A+A/698/A39 : BLOeM. BAF-type supergiants (Patrick+, 2025)
J/A+A/698/A40 : BLOeM. SMC early B supergiants multiplicity (Britavskiy+ 2025)
Byte-by-byte Description of file: tabled1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- BLOeM Field-ID number (N-NNN)
7- 25 I19 --- GaiaDR3 GAIA DR3 ID
27- 37 F11.8 deg RAdeg Right ascension (J2000)
39- 50 F12.8 deg DEdeg Declination (J2000)
52- 56 F5.2 mag Gmag Gaia G magnitude
58- 71 A14 --- SpType Spectral type and luminosity class
73 I1 --- n [3/9] Number of epochs available or
used in RV determination
75- 81 F7.2 km/s dRV Maximum radial velocity difference
83- 87 F5.2 --- dRVsigni Detection significance
89- 93 A5 --- Bin Binary classification
95-100 F6.2 d Per Orbital period
102-103 A2 --- Persigni [S P NS] Orbital period significance (1)
105-114 F10.7 d POGLE ? Orbital period from OGLE
116-151 A36 --- Comments Comments
--------------------------------------------------------------------------------
Note (1): Orbital period significance as follows:
S = significant
P = tentative
NS = not significant
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tabled2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- BLOeM BLOeM field-ID number (BLOeM N-NNN)
13- 29 A17 --- OGLE OGLE identifier
31- 41 A11 --- SpType Spectral type (1)
43- 47 F5.2 mag Imag OGLE I-band magnitude (2)
49- 55 F7.4 d Per OGLE orbital period (2)
57- 59 A3 --- Type OGLE classification (2) (3)
--------------------------------------------------------------------------------
Note (1): Spectral types are from Shenar et al.
(2024A&A...690A.289S 2024A&A...690A.289S, Cat. J/A+A/690/A289).
Note (2): OGLE orbital periods, I-band magnitudes and Types are from
Pawlak et al. (2016AcA....66..421P 2016AcA....66..421P, Cat. J/AcA/66/421)
Note (3): Types as follows:
NC = detached or semi-detached
C = contact
ELL = ellipsoidal
--------------------------------------------------------------------------------
Acknowledgements:
Jaime Villasenor, villasenor(at)mpia.de
References:
Shenar et al., 2024A&A...690A.289S 2024A&A...690A.289S Cat. J/A+A/690/A289
(End) Patricia Vannier [CDS] 03-Apr-2025