J/A+A/664/A146 Westerlund 1 under light of Gaia EDR3 (Negueruela+, 2022)
Westerlund 1 under the light of Gaia EDR3:
Distance, isolation, extent, and a hidden population.
Negueruela I., Alfaro E.J., Dorda R., Marco A., Maiz Apellaniz J.,
Gonzalez-Fernandez C.
<Astron. Astrophys. 664, A146 (2022)>
=2022A&A...664A.146N 2022A&A...664A.146N (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Parallaxes, trigonometric ; Proper motions ;
Radial velocities
Keywords: open clusters and associations: individual: Westerlund 1 -
stars: evolution - stars: early-type - supergiants -
stars: fundamental parameters
Abstract:
The young massive cluster Westerlund 1 offers the promise of a grand
laboratory for the study of high-mass star evolution, but its basic
parameters are still poorly known.
In this paper, we aim at a better characterisation of the cluster by
determining some basic kinematic properties and analysing the area
surrounding the cluster and the population in its foreground.
We have used Gaia early data release 3 (EDR3) data, together with
spectra of a large sample of luminous stars in the field surrounding
Westerlund 1, to explore the extent of the cluster. We carried out a
non-parametric analysis of proper motions and membership
determination. We investigated the reddening and proper motions of
several dozen OB stars and red supergiants less than one degree away
from Westerlund 1.
We identify a population of kinematic members of Westerlund 1 that
largely includes the known spectroscopic members. From their EDR3
parallaxes, we derive a distance to the cluster of
4.23+0.23-0.21kpc. We analyse the extinction in this direction,
finding that it increases by a large amount around 2.8kpc, which in
all likelihood is due to dark clouds associated with the Scutum-Crux
arm. As a consequence, we hardly see any stars at distances comparable
(or higher) than that of the cluster. The proper motions of
Westerlund 1, however, are very similar to those of stars in the field
surrounding it which are - almost without exception - less distant,
but distinct. We find a second, astrometrically well-defined
population in the foreground (d∼2kpc), centred ∼8arcmin away, which
is likely connected to the possible open cluster BH 197. Westerlund 1
is very elongated, an effect that seems real and not driven by the
very heavy extinction to the east and south. We find a low-density
halo extending to distances up to 10 arcmin from the cluster centre,
mainly in the north-west quadrant. A few OB stars at larger distances
from the cluster, most notably the luminous blue variable (LBV) MN48,
share its proper motions, suggesting that Westerlund 1 has little or
no peculiar motion with respect to the field population of the Norma
arm. Despite this, we are unable to find any red supergiant that could
belong to an extended population related to the cluster, although we
observe several dozen such objects in the foreground, demonstrating
the richness of the field population along this sightline. We find a
substantial population of luminous OB members obscured by several more
magnitudes of extinction than most known members. These objects,
mostly located in the central region of the cluster, increase the
population of OB supergiants by about 25%.
Description:
Gaia DR3 parameters for stars discussed in the text, together with
other relevant astrophysical information.
Table B1: Gaia EDR3 data for previously catalogued members of
Westerlund 1 (and one new member). Names are as in Clark et al.
(2020A&A...635A.187C 2020A&A...635A.187C, Cat J/A+A/635/A187, [CRN2020] W1NNN in Simbad).
Parallaxes are not corrected for zero point bias. The KM column
indicates whether the star is considered a bona fide kinematic member
by our Bayesian analysis (+) or not (-). The AAOmega column indicates
if that star was observed by this instrument.
Table C1: "Blue" targets observed with AAOmega. The IDs are used to
identify targets in the text.
Table C2: "Red" targets observed with AAOmega. The IDs are used to
identify targets in the text.
Parallaxes are not corrected for zero point bias. The vhel column
lists our measurements. Infrared magnitudes are from 2MASS and
distance estimates, from Bailer-Jones et al. (2021AJ....161..147B 2021AJ....161..147B,
Cat. I/352) The radial velocities can be considered accurate to 3km/s
(the dispersion of their difference with respect to Gaia DR2 values.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tableb1.dat 142 166 Gaia DR3 parameters for stars discussed
in the text
tablec1.dat 118 34 "Blue" targets observed with AAOmega
tablec2.dat 143 321 "Red" targets observed with AAOmega
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See also:
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
I/352 : Distances to 1.47 billion stars in Gaia EDR3
(Bailer-Jones+, 2021)
J/A+A/635/A187 : Massive binaries in Westerlund 1. VII. (Clark+, 2020)
Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- ID Catalogue ID, NNNN or WNNNa (1)
7- 8 I2 h RAh Right ascension (J2000)
10- 11 I2 min RAm Right ascension (J2000)
13- 16 F4.1 s RAs Right ascension (J2000)
18 A1 --- DE- Declination sign (J2000)
19- 20 I2 deg DEd Declination (J2000)
22- 23 I2 arcmin DEm Declination (J2000)
25- 28 F4.1 arcsec DEs Declination (J2000)
30- 48 I19 --- GaiaEDR3 ID Gaia EDR3
50- 54 F5.2 mas plx ? Parallax
57- 60 F4.2 mas e_plx ? Error of the parallax
62- 67 F6.2 mas/yr pmRA ? Proper motion in RA
70- 73 F4.2 mas/yr e_pmRA ? Error of the proper motion in RA
75- 80 F6.2 mas/yr pmDE ? Proper motion in DE
83- 86 F4.2 mas/yr e_pmDE ? Error of the proper motion in DE
89- 94 F6.3 mag Gmag ? G magnitude from Gaia EDR3
97-101 F5.3 mag e_Gmag ? Error of G magnitude from Gaia EDR3
104-109 F6.3 mag BPmag ? BP magnitude from Gaia EDR3
112-116 F5.3 mag e_BPmag ? Error of BP magnitude from Gaia EDR3
119-124 F6.3 mag RPmag ? RP magnitude from Gaia EDR3
127-131 F5.3 mag e_RPmag ? Error of RP magnitude from Gaia EDR3
134-138 F5.3 mag BP-RP ? Colour BP-RP
140 A1 --- InAAOmega [±] If present in the AAOmega survey
142 A1 --- KinMember [±] If tagged as Kinematic Member
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Note (1): Names WNNNa and WAA from Clark et al. (2020A&A...635A.187C 2020A&A...635A.187C,
Cat J/A+A/635/A187).
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Byte-by-byte Description of file: tablec1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- ID Internal name, NNN or BNN
5- 23 I19 --- GaiaEDR3 ID Gaia EDR3
25- 26 I2 h RAh Right ascension (J2000)
28- 29 I2 min RAm Right ascension (J2000)
31- 34 F4.1 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)
48- 52 F5.2 mas plx Parallax
54- 57 F4.2 mas e_plx Parallax error
59- 63 F5.2 mas/yr pmRA Proper motion in RA
65- 68 F4.2 mas/yr e_pmRA Error of the proper motion in RA
70- 74 F5.2 mas/yr pmDE Proper motion in DEC
76- 79 F4.2 mas/yr e_pmDE Error of the proper motion in DEC
81- 84 F4.1 mag Gmag G magnitude from Gaia EDR3
86- 89 I4 pc d Distance from Bailer-Jones+2021
91- 94 I4 pc e_d Estimation of lower error in distance
96- 99 I4 pc E_d Estimation of upper error in distance
101-108 A8 --- SpType Estimated spectral type
111-114 F4.1 mag Kmag Ks magnitude in 2MASS
116-118 F3.1 mag J-K J-K colour in 2MASS
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Byte-by-byte Description of file: tablec2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID Internal name
5- 23 I19 --- GaiaEDR3 ID Gaia EDR3
25- 26 I2 h RAh Right ascension (J2000)
28- 29 I2 min RAm Right ascension (J2000)
31- 35 F5.2 s RAs Right ascension (J2000)
37 A1 --- DE- Declination sign (J2000)
38- 39 I2 deg DEd Declination (J2000)
41- 42 I2 arcmin DEm Declination (J2000)
44- 48 F5.2 arcsec DEs Declination (J2000)
50- 54 F5.2 mas plx Parallax
56- 59 F4.2 mas e_plx Parallax error
61- 66 F6.2 mas/yr pmRA Proper motion in RA
68- 71 F4.2 mas/yr e_pmRA Error of the proper motion in RA
73- 78 F6.2 mas/yr pmDE Proper motion in DE
80- 83 F4.2 mas/yr e_pmDE Error of the proper motion in DE
86- 89 F4.1 mag Gmag ? G magnitude from Gaia EDR3
91- 94 I4 pc d Distance from Bailer-Jones et al.
(2021AJ....161..147B 2021AJ....161..147B, Cat. I/352)
97-100 I4 pc e_d Estimation of lower error in distance
102-105 I4 pc E_d Estimation of upper error in distance
107-116 A10 --- SpType Estimated spectral type
118-123 F6.1 km/s RV ? Radial velocity from AAOmega data
125-130 F6.1 km/s RVGDR2 ?=- Radial velocity from Gaia DR2
132-134 F3.1 km/s e_RVGDR2 ?=- Error in Gaia radial velocity
136-138 F3.1 mag Kmag Ks magnitude in 2MASS
141-143 F3.1 mag J-K ? J-K colour in 2MASS
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Acknowledgements:
Ignacio Negueruela, ignacio.negueruela(at)ua.es
(End) Patricia Vannier [CDS] 21-Jul-2022