2008A&A...483..171N


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.14CEST00:21:32

2008A&A...483..171N - Astronomy and Astrophysics, volume 483, 171-182 (2008/5-3)

Chandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund 2.

NAZE Y., RAUW G. and MANFROID J.

Abstract (from CDS):

Westerlund2 is a young and massive, obscured stellar cluster of our Galaxy. It harbors the most massive star with well-determined parameters, WR20a (82+83M), a dozen very early O-type stars (O3-7), and a wealth of PMS stars. Although of clear significance, this star cluster has not been well-studied. The high-energy properties of this cluster, especially those of its early-type stars are examined in detail. The variability of the X-ray sources is investigated. A monitoring of the field was performed using three Chandra observations. This dataset probes daily as well as monthly to yearly timescales and provides the deepest X-ray view of the cluster to date. The two Wolf-Rayet stars WR20a (WN6ha+WN6ha) and WR20b (WN6ha) were analyzed in detail. They are both luminous and display hard spectra, but WR20b does not appear to vary. In contrast, WR20a, a known eclipsing, colliding-wind binary, brightens in the X-ray domain during eclipses, i.e. when the collision is seen face-on. This can be explained by the properties of the wind-wind collision zone, whose high density leads to a large absorbing column (2x1024cm2). All twelve O-type stars previously classified spectroscopically, two eclipsing binaries previously identified and nine newly-identified, O-type star candidates are detected in the high-energy domain; ten of those could be analyzed spectroscopically. Four are overluminous, but the others have typical LX/LBOL ratios, suggesting that several O-type objects are actually binaries. Variability at the ∼2σ level is detected for a majority of the sources, of unknown origin for single objects. Faint, soft, diffuse emission pervades the entire field-of-view but no clear structure can be identified, even at the position of a blister proposed to correspond to the TeV source HESS J1023-575. The X-ray properties of PMS objects, in particular the brightest flaring ones, are also investigated. They provided an additional argument in favor of a large distance (∼8kpc) for the cluster.

Abstract Copyright:

Journal keyword(s): Galaxy: open clusters and associations: individual: Westerlund 2 - X-rays: stars - stars: individual: WR20a - stars: individual: WR20b

Nomenclature: Tables 2, 3: Cl* Westerlund 2 NRM N (Nos 1-4). Table 5: [NRM2008] A (Nos A-H).

CDS comments: Tables 2, 3: Src N = Cl* Westerlund 2 NRM N.

Simbad objects: 41

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Number of rows : 41

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NAME Orion Nebula Cluster OpC 05 35.0 -05 29           ~ 1977 1
2 HD 50896 WR* 06 54 13.0440847499 -23 55 42.020318514 5.74 6.63 6.91 7.74   WN4b 736 0
3 NAME Car Arm PoG 10 00 -60.0           ~ 378 1
4 HESS J1023-575 gam 10 23 -57.5           ~ 53 0
5 2MASS J10233426-5748092 pr? 10 23 34.2628748206 -57 48 09.333429596           ~ 2 0
6 HD 90273 * 10 23 44.4544231274 -57 38 31.535286472 8.35 9.25 9.05 9.58   ON7V((f)) 71 0
7 Cl* Westerlund 2 MSP 165 * 10 23 55.1750402864 -57 45 26.927837541 17.271 17.386 15.610 14.98 13.153 O4V 9 0
8 Cl* Westerlund 2 MSP 182 * 10 23 56.1788715852 -57 45 30.029039017 15.681 15.965 14.514 13.87 12.411 O4III 14 0
9 2MASS J10235719-5742595 Y*? 10 23 57.197 -57 42 59.55           ~ 2 0
10 V* V712 Car bL* 10 23 58.0120989646 -57 45 48.938103165 15.466 15.473 13.5 12.6   O3If*/WN6+O3If*/WN6 147 1
11 Cl Westerlund 2 OpC 10 23 58.1 -57 45 49   11.59 10.5     ~ 278 0
12 Cl* Westerlund 2 MSP 120 * 10 23 58.4356845541 -57 45 12.999412039 17.864 17.964 16.204 15.7 13.871 ~ 6 0
13 Cl* Westerlund 2 MSP 223 * 10 23 59.192 -57 45 40.27 17.493 17.681 16.015   13.634 O7-8 9 0
14 [NRM2008] C Y*? 10 23 59.97 -57 44 21.5         19.800 ~ 3 0
15 Cl* Westerlund 2 MSP 44 * 10 24 00.4967154977 -57 44 44.503326361 16.761 16.945 15.587 15.11 13.826 B1V+PMS 13 0
16 UCAC3 65-98348 PM* 10 24 00.51 -57 45 23.9 15.792 16.031 14.546 13.83 12.414 O4V 11 0
17 2MASS J10240073-5745253 Y*? 10 24 00.736 -57 45 25.39   15.50 14.14     O6.5V 12 0
18 [NRM2008] D pr? 10 24 00.86 -57 45 56.8           ~ 1 0
19 Cl* Westerlund 2 MSP 188 * 10 24 01.258 -57 45 30.86   14.60 13.32     O3V+O5.5 11 0
20 Cl* Westerlund 2 MSP 175 * 10 24 01.3850123850 -57 45 29.612766482 15.188 15.495 14.084   12.045 O4V 13 0
21 Cl* Westerlund 2 MSP 263 * 10 24 01.517 -57 45 56.98 16.791 16.863 15.053 14.31 12.582 O6V 11 0
22 [NRM2008] E pr? 10 24 01.58 -57 45 22.7           ~ 1 0
23 Cl* Westerlund 2 MSP 167 * 10 24 02.012 -57 45 27.98   15.48 14.19     O8V 13 0
24 [NRM2008] F pr? 10 24 02.05 -57 44 33.0           ~ 2 0
25 Cl* Westerlund 2 NRM 4 * 10 24 02.302 -57 45 35.14   14.66 13.22     O6III 10 0
26 Cl* Westerlund 2 MSP 183 * 10 24 02.3604641221 -57 45 30.605449290 15.423 15.496 13.878     O3V(f) 12 0
27 Cl Westerlund 2 5 * 10 24 02.4402256870 -57 44 36.149582896 14.149 14.514 13.155 12.2   O5/5.5V/III(f) 24 0
28 Cl* Westerlund 2 MSP 199 * 10 24 02.6481591579 -57 45 34.353113883 15.870 16.082 14.554   12.398 O3V 13 0
29 [NRM2008] G pr? 10 24 03.21 -57 45 34.5           ~ 1 0
30 Cl* Westerlund 2 MSP 171 * 10 24 04.8971990368 -57 45 28.396379266 15.975 16.134 14.528 13.91 12.307 O5V 14 0
31 Cl* Westerlund 2 NRM 3 * 10 24 06.6414801654 -57 47 15.885374971   18.117 16.473 15.88 13.90 O9.5V 4 0
32 [NRM2008] H pr? 10 24 10.15 -57 46 35.9           ~ 1 0
33 GUM 29 HII 10 24 14.6 -57 46 58           ~ 192 0
34 Cl* Westerlund 2 NRM 2 * 10 24 16.2512757176 -57 43 43.768717807   16.511 14.914 14.1   O8.5III 4 0
35 WR 20b WR* 10 24 18.3972653285 -57 48 29.778301585     13.7 12.0   WN6ha 46 0
36 Cl* Westerlund 2 NRM 1 * 10 24 21.280 -57 47 27.55   16.083 14.671 14.0   O6V 2 0
37 [GCB88] 8 MoC 10 26 -57.8           ~ 4 0
38 Ass Car OB 1 As* 10 38 -59.0           ~ 141 0
39 HD 96548 WR* 11 06 17.2033098417 -65 30 35.237611013 7.10 7.80 7.70 8.49   WN8h 388 0
40 NGC 6231 OpC 16 54 08.51 -41 49 36.0   2.83 2.6     ~ 485 0
41 HD 165688 WR* 18 07 56.9612003141 -19 23 56.866361615 10.46 10.31 9.87 9.85   WN5-6b 144 0

    Equat.    Gal    SGal    Ecl

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2020.07.14-00:21:32

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