1997A&A...326..608B


Query : 1997A&A...326..608B

1997A&A...326..608B - Astronomy and Astrophysics, volume 326, 608-613 (1997/10-2)

Soft X-ray emission from intermediate-age open clusters: NGC 6940.

BELLONI T. and TAGLIAFERRI G.

Abstract (from CDS):

We present the results of soft X-ray observations of the intermediate-age open cluster NGC 6940 performed with the ROSAT PSPC. We detected 18 sources, four of which are identified with member stars of the cluster and five with active field stars. Another source is identified with an active giant star that could belong to the cluster, although it is not classified as a cluster member. The remaining eight, most likely of extragalactic nature, need to be identified through optical follow-up. As in the case of old clusters such as M 67 and NGC 752, a high fraction of the detected members are binaries: in NGC 6940 three out of four of the identified members are among the only six binaries known in the cluster. All four sources have X-ray luminosities typical of RS CVn binaries. However, only two of the three detected binaries have system characteristics typical of active X-ray binaries. The high X-ray luminosity of the other two sources needs to be explained. All four identified members are red giants, in agreement with the presence of a saturation level. The four field stars identified as counterparts of X-ray sources are all very active, with X-ray luminosities in the range 1029-1030erg/s, and deserve further optical investigation. We confirm the results found in other old open clusters, i.e. that binaries are still very active coronal sources at an age greater than 1Gyr, and that good spatial resolution images in the X-ray band are a powerful tool to investigate their evolution in clusters of different ages.

Abstract Copyright:

Journal keyword(s): stars: activity - open clusters and associations: individual: NGC 6940 - X-rays: stars

Nomenclature: Table 1: [BT97] NN (Nos 1-18)

Simbad objects: 22

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Number of rows : 22
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 NGC 752 OpC 01 56 54 +37 47.6           ~ 584 0
2 NGC 2682 OpC 08 51 23 +11 48.8           ~ 2173 0
3 IC 4651 OpC 17 24 51 -49 55.0           ~ 329 0
4 [BT97] 5 X 20 33 43.3 +28 22 53           ~ 1 0
5 HD 334742 * 20 33 57.1242028656 +28 31 03.354030660   10.59 10.09     F5 5 0
6 [BT97] 10 X 20 34 02.8 +28 18 30           ~ 1 0
7 NGC 6940 84 SB* 20 34 13.5741204984 +28 14 28.146005376   11.3 10.6     F4III 14 0
8 HD 334747 SB* 20 34 22.9214393424 +28 21 41.372151840   10.92 10.24     F8 21 0
9 NGC 6940 108 * 20 34 25.6781992248 +28 13 41.614047948   12.23 11.19     F0V 17 0
10 NGC 6940 111 SB* 20 34 26.9613874632 +28 22 41.946097152   12.61 11.53     G5 12 0
11 [BT97] 8 X 20 34 28.2 +28 20 39           ~ 1 0
12 NGC 6940 114 * 20 34 28.5330441744 +28 28 43.894280712   12.31 11.17     G8III 5 0
13 NGC 6940 OpC 20 34 30 +28 16.7           ~ 170 0
14 [BT97] 14 X 20 34 30.5 +28 09 55           ~ 1 0
15 [BT97] 16 X 20 34 31.9 +28 32 17           ~ 1 0
16 Cl* NGC 6940 LL 137 * 20 34 46.3 +28 20 31   15.06 13.82     ~ 1 0
17 [BT97] 1 X 20 35 04.3 +28 19 10           ~ 1 0
18 [BT97] 15 X 20 35 07.3 +28 09 26           ~ 1 0
19 HD 196244 PM* 20 35 08.4813543720 +28 24 12.034022328   8.63 8.29     A2 7 0
20 [BT97] 11 X 20 35 17.9 +28 18 31           ~ 1 0
21 [BT97] 2 X 20 35 20.4 +28 33 11           ~ 1 0
22 HD 340540 PM* 20 35 56.5723060728 +27 42 40.186989072   10.09 9.08     K0 9 0

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2022.05.22-22:23:10

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