ASCA Observation of Cygnus OB2 Association

Details ASCA Observation of Cygnus OB2 Association ASCA Observation of Cygnus OB2 Association

Dec 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996pasj...48..813k&link_type=abstract

Publications of the Astronomical Society of Japan, v.48, p.813-818.

Astronomy and Astrophysics

Astronomy

27

Stars: Individual (Cygnus Ob2), Stars: X-Rays, X-Rays: Spectra

Scientific paper

ASCA observed Cygnus OB2 association on 1993 April 29. Four OB stars (5, 8a, 9, and 12; the designation from Schulte 1958, Astron. Jahresber. 58.12376) were clearly detected. In the X-ray spectra of three stars (5, 8a, and 12), at least two emission lines from SiXIII and SXV were identified. The spectra of three stars (5, 9, and 12) can be simulated using the single thin thermal spectra with temperatures of 1.26 +/- 0.12 keV [(1.46 +/- 0.14) times 10(7) K], 2.46 +/- 0.68 keV [(2.85 +/- 0.79) times 10(7) K], and 0.90 +/- 0.05 keV [(1.04 +/- 0.06) times 10(7) K], respectively. However, the spectrum of 8a, which is statistically the best one, requires two-component thin thermal spectra with temperatures of 0.62 +/- 0.04 keV [(0.72 +/- 0.05) times 10(7) K] and 1.47 +/- 0.10 keV [(1.71 +/- 0.12) times 10(7) K]. The emission measures of the four observed stars are ~ 10(56-57) cm(-3) , and their photoelectric absorption column densities are (1--2)times 10(22) H cm(-2) . The apparent low metal abundances are suggested in all four stars, if the X-ray emission region is really optically thin. This might be explained by an enrichment of light elements, such as He and N. Another possibility is that the emission region is not really optically thin, and that the line strength is suppressed.

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