J/A+A/652/A70 NGC 330 seen by MUSE. II. (Bodensteiner+, 2021)
The young massive SMC cluster NGC 330 seen by MUSE.
II. Multiplicity properties of the massive-star population.
Bodensteiner J., Sana H., Wang C., Langer N., Mahy L., Banyard G.,
de Koter A., de Mink S.E., Evans C.J., Goetberg Y., Patrick L.R.,
Schneider F.R.N., Tramper F.
<Astron. Astrophys. 652, A70 (2021)>
=2021A&A...652A..70B 2021A&A...652A..70B (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Clusters, open ; Populations, stellar;
Radial velocities
Keywords: stars: massive - stars: emission-line, Be - binaries: spectroscopic -
blue stragglers -
open clusters and associations: individual: NGC 330 -
Magellanic Clouds
Abstract:
Observations of massive stars in open clusters younger than 8 Myr have
shown that a majority of them are in binary systems, most of which
will interact during their life. While these can be used as a proxy of
the initial multiplicity properties, studying populations of massive
stars older than ∼20Myr allows us to probe the outcome of such
interactions after a significant number of systems have experienced
mass and angular momentum transfer and possibly even merged.
Using multi-epoch integral-field spectroscopy, we aim to investigate
the multiplicity properties of the massive-star population in the
dense core of the ∼40Myr-old cluster NGC 330 in the Small Magellanic
Cloud in order to search for possible imprints of stellar evolution on
the multiplicity properties.
We obtained six epochs of VLT/MUSE observations operated in wide-field
mode with the extended wavelength setup and supported by adaptive
optics.We extract spectra and measure radial velocities for stars
brighter than mF814W=19. We identify single-lined spectroscopic
binaries through significant RV variability with a peak-to-peak
amplitude larger than 20km/s. We also identify double-lined
spectroscopic binaries, and quantify the observational biases for
binary detection. In particular, we take into account that binary
systems with similar line strength are difficult to detect in our data
set.
The observed spectroscopic binary fraction among the stars brighter
than mF814W=19 (∼5.5M☉ on the main sequence) is
fobsSB=13.2±2:0%. Considering period and mass ratio ranges from
log(P)=0.15-3.5 (about 1.4 to 3160d), and q=0.1-1.0, and a
representative set of orbital parameter distributions, we find a
bias-corrected close binary fraction of fcl=34+8-7%. This
fraction seems to decline for the fainter stars, which indicates
either that the close binary fraction drops in the B-type domain, or
that the period distribution becomes more heavily weighted towards
longer orbital periods.We further find that both fractions vary
strongly in different regions of the color-magnitude diagram that
corresponds to different evolutionary stages. This probably reveals
the imprint of the binary history of different groups of stars. In
particular, we find that the observed spectroscopic binary fraction of
Be stars (fobsSB=2±2%) is significantly lower than the one of
B-type stars (fobsSB=9±2%).
In this work we provide the first homogeneous RV study of a large
sample of B-type stars at a low metallicity ([Fe/H]≲-1.0). The
overall bias-corrected close binary fraction (log(P)<3.5d) of the
B-star population in NGC 330 is lower than the one reported for
younger Galactic and LMC clusters in previous works. More data are,
however, needed to establish whether the observed differences result
from an age or a metallicity effect.
Description:
Six epochs of observations of NGC 330 were obtained with MUSE between
August 2017 and December 2018.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 149 340 Compilation of all parameters derived for
the sample stars
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See also:
J/A+A/634/A51 : NGC 330 seen by MUSE (Bodensteiner+, 2020)
Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [10/732] Identification number
5- 13 F9.6 deg RAdeg Right ascension (J2000)
15- 24 F10.6 deg DEdeg Declination (J2000)
26- 29 F4.1 mag F814W F814W magnitude from Milone et al.,
(2018MNRAS.477.2640M 2018MNRAS.477.2640M)
31- 44 A14 --- SpType Spectral type
46- 51 A6 --- lines Line used (1)
53- 57 F5.1 km/s RV1 ?=- Radial velocity for epoch 1 (2017-08-15)
59- 62 F4.1 km/s e_RV1 ?=- rms uncertainty on RV1
64- 68 F5.1 km/s RV2 ?=- Radial velocity for epoch 2 (2017-09-18)
70- 73 F4.1 km/s e_RV2 ?=- rms uncertainty on RV2
75- 79 F5.1 km/s RV3 ?=- Radial velocity for epoch 3 (2018-11-06)
81- 85 F5.1 km/s e_RV3 ?=- rms uncertainty on RV3
87- 91 F5.1 km/s RV4 ?=- Radial velocity for epoch 4 (2018-11-19)
93- 96 F4.1 km/s e_RV4 ?=- rms uncertainty on RV4
98-102 F5.1 km/s RV5 ?=- Radial velocity for epoch 5 (2018-11-22)
104-107 F4.1 km/s e_RV5 ?=- rms uncertainty on RV5
109-113 F5.1 km/s RV6 ?=- Radial velocity for epoch 6 (2018-12-18)
115-118 F4.1 km/s e_RV6 ?=- rms uncertainty on RV6
120-122 A3 --- Flag Flag (2)
124-150 A27 --- Com Comments
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Note (1): indicates which spectral lines among HeI λλ 4713.15,
4921.93, 5015.68, 5047.74, 6678.15, 7065.19Å were used to measure RVs
(an 'x' indicates that the line was used, while '-' indicates that it was
not used).
Note (2): Flag as follows:
sin = no significant RV shifts were detected
SB1 = flagged as binary based on RV variability
SB2 = composite SB2 spectrum
- = no RV measurements were possible
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Acknowledgements:
Julia Bodensteiner, julia.bodensteiner(at)kuleuven.be
References:
Bodensteiner et al., Paper I 2020A&A...634A..51B 2020A&A...634A..51B, Cat. J/A+A/634/A51
(End) Patricia Vannier [CDS] 08-Jun-2021