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摘要
Aims. We identify and characterize low-mass stars in the similar to 3Myr old Trumpler16 region by means of a deep Chandra X-ray observation, and study their optical and near-IR properties. We compare the X-ray activity of Trumpler 16 stars with the known characteristics of Orion and Cygnus OB2 stars.
Methods. We analyzed a 88.4 ks Chandra ACIS-I observation pointed at the center of Trumpler 16. Because of diffuse X- ray emission, source detection was performed using the PWDetect code for two different energy ranges: 0.5-8.0 keV and 0.9-8.0 keV. Results were merged into a single final list. We positionally correlated X- ray sources with optical and 2MASS catalogs. Source events were extracted with the IDL-based routine ACIS-Extract. X- ray variability was characterized using the Kolmogorov-Smirnov test and spectra were fitted by using XSPEC. The X- ray spectra of early-type, massive stars were analyzed individually.
Results. Our list of X- ray sources consists of 1035 entries, 660 of which have near-IR counterparts and are probably associated with Trumpler 16 members. From near-IR, color-color, and color-magnitude diagrams we compute individual masses of stars and their Av values. The cluster median extinction is A(v) = 3.6 mag, while OB- type stars appear less absorbed, having A(v) = 2.0 mag. About 15% of the near-IR counterparts show disk-induced excesses. X- ray variability is found in 77 sources, and typical X- ray spectral parameters are N-H similar to 5.37 x 10(21) cm(-2) and kT similar to 1.95 keV. The OB stars appear, softer with a median kT similar to 0.65 keV. The median X-ray luminosity is 6.3 x 10(30) erg s(-1), while variable sources show a larger median L-x value of 13 x 10(30) erg s(-1). OB-stars have an even higher median L-x of 80 x 10(30) erg s(-1), about 10 times that of the low-mass stars.
Conclusions. The Trumpler 16 region has a very rich population of low- mass X- ray emitting stars. A large fraction of its circumstellar disks have survived the intense radiation field of its massive stars. Stars with masses 1.5-2.5 M-circle dot display X- ray activity similar to the CygOB2 stars, but much less intense than observed for Orion nebula cluster members.
- 出版日期2008-11
