The ROSAT galactic plane survey: Analysis of a low latitude sample area in Cygnus

被引:0
|
作者
Motch, C
Guillout, P
Haberl, F
Pakull, M
Pietsch, W
Reinsch, K
机构
[1] MAX PLANCK INST EXTRATERR PHYS, D-85748 GARCHING, GERMANY
[2] STERNWARTE, D-37083 GOTTINGEN, GERMANY
关键词
X-ray general; X-ray stars; stars:activity; stars:neutron; stars:statistics;
D O I
暂无
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We present the analysis of the point source content of a low galactic latitude region selected from the ROSAT all-sky survey. The test field is centered at l = 90 degrees, b = 0 degrees and has an area of 64.5 deg(2). A total of 128 soft X-ray sources are detected above a maximum likelihood of 8. Catalogue searches and optical follow-up observations show that in this direction of the galactic plane, 85% of the sources brighter than 0.03 PSPC cts s(-1) are identified with active coronae. F-K type stars represent 67% (+/- 13%) of the stellar identifications and M type stars account for 19% (+/- 6%). A small but significant number of X-ray sources are associated with A type stars on the basis of positional coincidence. These results together with those of similar optical campaigns demonstrate that the soft X-ray population of the Milky Way is largely dominated by active stars. We show that the density and distribution in flux and spectral type of the active coronae detected in X-rays are consistent with the picture drawn from current stellar population models and age dependent X-ray luminosity functions. The modelling of this population suggests that most of the stars detected by ROSAT in this direction are younger than 1 Gyr. This opens the possibility to extract in a novel way large samples of young stars from the ROSAT all-sky survey. The small number of unidentified sources at low X-ray flux put rather strong constraints on the hypothetical X-ray emission from old neutron stars accreting from the interstellar medium. Our observations clearly rule out models which assume no dynamical heating for this population and a total number of N-ns = 10(9) neutron stars in the Galaxy. If accretion on polar caps is the dominant mode then our upper limit may imply N-ns approximate to 10(8). Among the non coronal identifications are three white dwarfs, a Seyfert 1 active nucleus, two early type stars and one cataclysmic variable. We also report the discovery of a Me + WD close binary system with P-orb approximate to 12 h.(1).
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页码:111 / 133
页数:23
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