2012A&A...539A...5C


Query : 2012A&A...539A...5C

2012A&A...539A...5C - Astronomy and Astrophysics, volume 539A, 5-5 (2012/3-1)

Is the massive young cluster Westerlund I bound ?

COTTAAR M., MEYER M.R., ANDERSEN M. and ESPINOZA P.

Abstract (from CDS):

Westerlund I is the richest young cluster currently known in our Galaxy, making it one of the most massive clusters for which we can resolve the individual stars even in the crowded centre. This makes it an ideal target to assess whether massive clusters formed currently will remain bound or will disperse and contribute significantly to the stellar field population. We measure the radial velocity dispersion of Westerlund I to explore whether the cluster is either currently in virial equilibrium, in the process of collapse, or expanding and dispersing into the field. We obtained MIKE/Magellan high resolution optical spectra of 22 post main-sequence stars in Westerlund I for 2 or 3 epochs with a maximum baseline of about one year. Radial velocities variations between these spectra are measured by means of cross-correlation. We calculate the velocity dispersion from the cross-correlation of five yellow hypergiants and one luminous blue variable, that show little radial velocity variations between epochs and have many spectral features in common. After taking into account the effect of small number statistics and undetected binaries, we estimate the velocity dispersion for the massive stars in Westerlund I to be 2.1+3.3–2.1km/s. For several different assumptions concerning possible mass segregation and the elongation of the cluster, we find that Westerlund I is subvirial at the 90% confidence level. We can rule out that the cluster is significantly supervirial at the 97% confidence level, indicating that Westerlund I is currently bound. This implies that Westerlund I has survived past the point where any gas expulsion has taken place and is expected to survive for billions of years.

Abstract Copyright:

Journal keyword(s): open clusters and associations: individual: Westerlund I - stars: kinematics and dynamics - supergiants

Simbad objects: 24

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Number of rows : 24
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 Cl* Westerlund 1 W 56 * 16 46 58.9489660320 -45 51 48.908566764   21.7 17.46     O9.5B0.5Ia 8 0
2 Cl* Westerlund 1 W 2 * 16 46 59.7175806088 -45 50 51.190946043   20.4 16.978 14.287 11.771 O9.5B0.5Ia 16 0
3 Cl* Westerlund 1 W 57a * 16 47 01.3600091808 -45 51 45.804003408   20.7 16.877 13.83 11.13 B4Ia 14 0
4 Cl* Westerlund 1 BKS H * 16 47 01.4269856784 -45 50 37.248841536   18.781 14.47     F3Ia+ 26 0
5 Cl* Westerlund 1 W 12 sg* 16 47 02.2214295629 -45 50 58.987616665   22.0 17.575 13.611   A5Ia+ 23 0
6 Cl* Westerlund 1 W 11 * 16 47 02.2390158456 -45 50 47.186514564   21.2 17.508 14.599 11.898 O9.5B0.5Ia 15 0
7 Cl* Westerlund 1 W 23a s*b 16 47 02.5776330614 -45 51 08.902293204   22.1 18.316 14.986 12.081 B2Ia+B:I? 16 0
8 Cl* Westerlund 1 W 237 s*r 16 47 03.1097130192 -45 52 18.960733164   22.8 19.008 13.634   M3I 25 0
9 Hen 3-1250 Em* 16 47 03.6281794392 -45 50 14.365482036   20.0 15.972     B5Ia+ 25 0
10 Cl* Westerlund 1 BKS F s*y 16 47 03.6850109472 -45 50 43.536110712     15.05     F5Ia+ 20 0
11 Cl Westerlund 1 OpC 16 47 04.00 -45 51 04.9           ~ 511 0
12 Cl* Westerlund 1 W 33 * 16 47 04.1256274968 -45 50 48.488202564   20.090 15.61 12.803   B5Ia+ 20 0
13 Cl* Westerlund 1 W 9 WR* 16 47 04.1419806984 -45 50 31.311670632   21.8 17.47 14.47 11.74 Be 49 0
14 Cl* Westerlund 1 W 238 * 16 47 04.4263582176 -45 52 27.788277972   21.4 17.820 14.98 12.45 O9.5B0.5Ia 14 0
15 Cl* Westerlund 1 W 28 s*b 16 47 04.6646286552 -45 50 38.503394520   20.9 17.146 14.303   B2Ia 12 0
16 Cl* Westerlund 1 W 8 * 16 47 04.7959778348 -45 50 25.013789709   19.9 15.913     F8Ia+ 18 0
17 2MASS J16470540-4550367 LP? 16 47 05.4076906176 -45 50 36.617071668   22.1 16.79     M5-6Ia 32 0
18 Cl* Westerlund 1 W 265 * 16 47 06.2785465416 -45 49 23.774098692   22.0 17.739   10.54 F1-5Ia+ 22 0
19 Cl* Westerlund 1 W 13 s*b 16 47 06.4540771320 -45 50 26.072579796   21.1 17.19 14.63 12.06 B0.5Ia++OB 31 0
20 Cl* Westerlund 1 W 16 * 16 47 06.6158603112 -45 50 42.186706944   20.5 16.248     A5Ia+ 25 0
21 Cl* Westerlund 1 W 243 s*b 16 47 07.5040736160 -45 52 29.123491188   19.873 15.730     LBV 56 0
22 Cl* Westerlund 1 W 71 * 16 47 08.4584673360 -45 50 49.338181284   21.5 17.531 14.158 11.16 B2.5Ia 20 0
23 Cl* Westerlund 1 W 70 * 16 47 09.3836656992 -45 50 49.668960804   21.2 16.88   11.352 B3Ia 16 0
24 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 13083 0

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2022.08.09-03:53:39

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