J/A+A/660/A122 O stars companion mass function (Reggiani+, 2022)
Probing the low-mass end of the O stars companion mass function.
Reggiani M., Rainot A., Sana H., Almeida L.A., Caballero-Nieves S.,
Kratter K., Lacour S., Le Bouquin J.-B., Zinnecker H.
<Astron. Astrophys. 660, A122 (2022)>
=2022A&A...660A.122R 2022A&A...660A.122R (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Photometry, infrared
Keywords: binaries: general - star: massive - star: imaging - star: formation
Abstract:
Past observations of O-type stars in the Galaxy have shown that almost
all massive stars are part of a binary or higher-order multiple
system. Given the wide range of separations at which these companions
are found, several observational techniques have been adopted to
characterize them. Despite the recent advancements in interferometric
and adaptive optics observations, contrasts greater than 4 in the H
band have never been reached between 100 and 1000mas.
Using new adaptive optics (AO) assisted coronagraphic observations, we
aim to study the multiplicity properties of a sample of 18 dwarf (or
sub-giant) O stars in the galactic field and in OB associations to
probe the existence of stellar companions in the angular separation
range from 0.15" to 6" down to very low mass ratios.
We used VLT/SPHERE to observe simultaneously with the IRDIS and IFS
sub-systems 18 O-type stars within 6kpc and ages between 1 and 5Myr.
The IFS YJH band observations have allowed us to probe the presence of
sub-solar companions in a 1.7"x1.7" field-of-view down to magnitude
limits of ΔH=10 at 0.4". In the wider 12"x12" IRDIS
field-of-view, we reached contrasts of ΔK=12 at 1", enabling us
to look for even fainter companions at larger angular separations and
to probe the source density of the surrounding portion of the sky.
This paper presents five newly discovered intermediate (<1")
separation companions, three of which are smaller than 0.2 M-☉_.
If confirmed by future analyses of proper motions, these new
detections represent the lowest-mass companions ever found around
O-type stars. Additionally, 29 other sources are found in the IRDIS
field-of-view with spurious association probabilities smaller than 5%.
Assuming that all sources detected within 1" are physically bound
companions, the observed (uncorrected for bias) fraction of companions
for O-type stars between 150 and 900mas is 0.39±0.15, whereas it
increases to 1.6±0.3 in the separation range from 0.9" to 6".
These findings clearly support the notion that massive stars form
almost exclusively in multiple systems, serving as proof of concept
that supports the application of larger AO-assisted coronagraphic
surveys as a crucial step in placing constraints on the multiplicity
properties of massive star companions in regions of the parameter
space that have previously gone unexplored. These results also
demonstrate that the companion mass function is populated down to the
lowest stellar masses.
Description:
Database used for the studied sample.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 75 430 Catalog
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Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Target ID of the central star
12- 13 I2 --- StarID [1/64] ID number of the detected sources
around the central star
15- 19 F5.3 arcsec Sep Radial separation in arcseconds of the
StarID source from the central star
21- 25 F5.3 arcsec e_Sep Error on the radial separation
27- 33 F7.3 deg PA Position angle of the StarID source wrt the
central star (from N to E)
35- 41 F7.3 deg e_PA Error on position angle of the StarID source
wrt the central star
43- 48 F6.3 mag dmagK1 ? Magnitude difference in the K1 band of the
StarID source wrt the central star
49 A1 --- n_dmagK1 [i] i for infinity
50- 54 F5.3 mag e_dmagK1 ? Error on the magnitude difference in the
K1 band of the StarID source wrt the
central star
56- 61 F6.3 mag dmagK2 ? Magnitude difference in the K2 band of the
StarID source wrt the central star
62 A1 --- n_dmagK2 [i] i for infinity
63- 69 F7.3 mag e_dmagK2 ? Error on the magnitude difference in the
K2 band of the StarID source wrt the
central star
71- 75 F5.3 --- ProbK1 [0/0.955] Spurious association probability
of the StarID source
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Acknowledgements:
Maddalena Reggiani, maddalena.reggiani(at)kuleuven.be
(End) Patricia Vannier [CDS] 09-Dec-2021