2014A&A...566A...4L


Query : 2014A&A...566A...4L

2014A&A...566A...4L - Astronomy and Astrophysics, volume 566A, 4-4 (2014/6-1)

Three new X-ray emitting O-type subdwarf stars discovered with Chandra.

LA PALOMBARA N., ESPOSITO P., MEREGHETTI S. and TIENGO A.

Abstract (from CDS):

X-ray observations of sdO stars are a useful tool to investigate their properties, but so far only two sdO stars were detected at X-rays. We aimed to perform the first systematic search for X-ray emission from sdO stars to characterize the X-ray emission from single and binary sdO stars.We observed a complete flux-limited sample of 19 sdO stars with the Chandra HRC-I camera to measure the count rate of the detected sources or to set a tight upper limit on it for the undetected sources. We obtained a robust detection of BD+37°1977 and Feige 34 and a marginal detection of BD+28° 4211. The estimated luminosity of BD+37°1977 is above 1031 erg/s, which is high enough to suggest the possible presence of an accreting compact companion. This possibility is unlikely for all the other targets (both detected and undetected), since in their case LX≲1030erg/s. On the other hand, for all 19 targets the estimated value of LX (or its upper limit) implies an X-ray/bolometric flux ratio that agrees with log(LX/Lbol)=-6.7±0.5, which is the range of values typical of main-sequence and giant O stars. The observing campaign performed by Chandra has discovered three new X-ray emitting sdO stars; for one of them the observed X-ray flux might be emitted by an accreting compact companion, while for the other two stars it is most probably due to intrinsic emission. The same is possibile for the 16 undetected stars.

Abstract Copyright:

Journal keyword(s): subdwarfs - X-rays: stars - X-rays: binaries - stars: individual: BD+37 1977 - stars: individual: Feige 34 - stars: individual: BD+28 4211

Simbad objects: 21

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Number of rows : 21
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 BD+37 442 HS* 01 58 33.4346638392 +38 34 23.842803324   9.69 9.92     sdOHe 67 0
2 LS I +63 198 HS* 03 29 05.6683420320 +64 04 42.157890228 11.71 13.18 13.20 12.96 13.2 sdOB 19 0
3 LS V +22 38 * 06 16 13.3274391960 +22 45 48.779291448 11.69 11.775 10.726 10.450   B0.2III: 27 1
4 HD 49798 HXB 06 48 04.7001531360 -44 18 58.436036028 6.758 8.017 8.287 8.391 8.543 sdO6 326 0
5 CD-31 4800 HS* 07 36 30.1950207312 -32 12 43.685045964 9 10.26 10.48 10.81   sdO8p 70 0
6 BD-03 2179 HS* 08 02 14.8870205088 -03 58 16.343922324 8.8 10.044 10.29 10.64 10.60 sdO 50 0
7 BD+75 325 HS* 08 10 49.4903003712 +74 57 57.931973676 8.002 9.23 9.50 9.698 9.884 sdO5 253 0
8 CD-45 5058 HS* 09 20 10.1317907208 -45 31 54.942917700 9.81 11.03 11.33 11.62   sdO 58 0
9 BD+37 1977 HS* 09 24 26.3929652664 +36 42 53.295009624   9.86 10.15     sdO 48 0
10 BD+48 1777 HS* 09 30 46.7817886272 +48 16 23.756157840   10.41 10.70     sdO9: 37 0
11 Feige 34 HS* 10 39 36.7358839104 +43 06 09.212615280 9.613 10.91 11.14 11.319 11.464 sdOp 675 0
12 BD+18 2647 HS* 12 41 51.7899961800 +17 31 19.750566756 10.261 11.70 11.63 11.969 12.159 sdOpec 181 1
13 CD-46 8926 HS* 13 53 08.2139106408 -46 43 42.314548008   11.04 11.30     sdO 45 0
14 HD 127493 HS* 14 32 21.4926471192 -22 39 25.646693688 8.64 9.74 10.08     sdOHe 100 0
15 LS IV -12 1 HS* 16 23 43.9896591936 -12 12 33.642833328 10.06 11.14 11.17     sdO 36 0
16 BD+39 3226 HS* 17 46 31.9115217336 +39 19 09.070120164   9.89 10.18     sdOHe 42 0
17 CD-51 11879 HS* 19 02 11.7428660328 -51 30 09.561616380   11.44 11.55     sdO 40 0
18 CD-23 15853 HS* 19 55 38.2263208824 -23 13 42.229548120   11.39 11.64     sdO 24 0
19 LS IV +10 9 HS* 20 43 02.4781026312 +10 34 21.001039644 10.51 11.71 12.06     sdO 36 0
20 BD+28 4211 HS* 21 51 11.0221915656 +28 51 50.367627468 8.922 10.25 10.58 10.656 10.831 sdO2VIIIHe5 797 0
21 BD+25 4655 HS* 21 59 41.9748629928 +26 25 57.403455672 8.27 9.39 9.68     sdO6 118 0

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