J/MNRAS/484/1838 Spatial substructure of Cygnus OB2 (Berlanas+, 2019)
Disentangling the spatial substructure of Cygnus OB2 from Gaia DR2.
Berlanas S.R., Wright N.J., Herrero A., Drew J.E., Lennon D.J.
<Mon. Not. R. Astron. Soc., 484, 1838-1842 (2019)>
=2019MNRAS.484.1838B 2019MNRAS.484.1838B (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Parallaxes, trigonometric
Keywords: astrometry - parallaxes - stars: distances - stars: early-type -
stars: massive -
open clusters and associations: individual: Cygnus OB2
Abstract:
For the first time, we have explored the spatial substructure of the
Cygnus OB2 association using parallaxes from the recent second Gaia
data release. We find significant line-of-sight substructure within
the association, which we quantify using a parametrized model that
reproduces the observed parallax distribution. This inference approach
is necessary due to the non-linearity of the parallax distance
transformation and the asymmetry of the resulting probability
distribution. Using a Markov Chain Monte Carlo ensemble sampler and an
unbinned maximum likelihood test, we identify two different stellar
groups superposed on the association. We find the main Cygnus OB2
group at ∼1760pc, further away than recent estimates have envisaged,
and a foreground group at ∼1350pc. We also calculate individual
membership probabilities and identify outliers as possible non-members
of the association.
Description:
The sample of stars used for this study is comprised of known OB
members of Cygnus OB2 within a radius of 1° of the coordinates
l=79.8 and b=+0.8. This produced a sample of 229 members of Cygnus
OB2, 167 of which are located in the core of the region. We adopted
RUWE≤1.4 as the selection criterion for good astrometric solutions.
This cut caused us to discard 29 stars, resulting in a sample of 200
targets with reliable Gaia astrometry. To infer the distance to the
Cygnus OB2 association, we use a parametrized model of the distance to
the association to reproduce the observed parallax distribution.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 67 29 List of stars that have not passed the
selection criteria
tablea2.dat 74 200 List of Cygnus OB2 sources used in this work
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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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2- 18 A17 --- Name Common name of the star
23- 41 I19 --- GaiaDR2 Gaia DR2 source identification
45- 50 F6.3 mas Plx Parallax given by Gaia DR2 (1)
54- 58 F5.3 mas e_Plx Parallax error given by Gaia DR2
63- 67 F5.2 mag Gmag G magnitude given by Gaia DR2
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Note (1): systematic uncertainties are not included in parallax values.
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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3- 19 A17 --- Name Common name of the star
24- 42 I19 --- GaiaDR2 Gaia DR2 source identification
47- 51 F5.3 mas Plx Parallax given by Gaia DR2 (1)
55- 59 F5.3 mas e_Plx Parallax error given by Gaia DR2
64- 68 F5.2 mag Gmag G magnitude given by Gaia DR2
74 I1 --- Group [0/3] Membership group (2)
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Note (1): systematic uncertainties are not included in parallax values.
Note (2): Groups as follows:
1 = foreground group (at ∼1350pc)
2 = main group (at ∼1760pc)
3 = foreground or background contaminants
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Acknowledgements:
Sara Berlanas, sara.rb(at)ua.es
(End) Sara R. Berlanas [UA, Spain], Patricia Vannier [CDS] 03-Sep-2020