An X-ray survey of low-mass stars in Trumpler 16 with Chandra

Abstract

Aims. We identify and characterize low-mass stars in the ∼3 Myr old Trumpler 16 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 A v 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 ∼ 5.37 × 10 21 cm −2 and kT ∼ 1.95 keV. The OB stars appear, softer with a median kT ∼ 0.65 keV. The median X-ray luminosity is 6.3 × 10 30 erg s −1 , while variable sources show a larger median L x value of 13 × 10 30 erg s −1 . OB-stars have an even higher median L x of 80 × 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 display X-ray activity similar to the Cyg OB2 stars, but much less intense than observed for Orion nebula cluster members.

The Search for Low-Mass Companions of B Stars in the Carina Nebula Cluster Trumpler 16

“…Combining this reddening with a temperature of log T (K) 7.5 using a PIMMS Raymond-Smith model, we obtained a factor of 1.6 to deredden the observed flux. This is a typical temperature found by Albacete-Colombo et al (2008) for low-mass stars in Tr 16. The luminosity is computed from the dereddened fluxes and a distance of 2.3 kpc (Column 6 in Table 3; Smith 2006).…”

X-Ray Star Clusters in the Carina Complex

“…The curved southern boundary of the cluster may, in part, be caused by absorption in the V-shaped dust lane that crosses the middle of the Carina field. See Figure 1 of Albacete-Colombo et al (2008) for the spatial relationship between the dust lane and the X-ray population. Evans et al (2003) and Albacete-Colombo et al (2008) give detailed Chandra studies of the X-ray properties of Trumpler 16 stars.…”

HRC-I/ChandraX-ray observations towardsσ Orionis

“…An exposure map, needed by the source detection algorithm and to renormalise source count rates, was calculated with the CIAO tool mkexpmap assuming a monochromatic spectrum (k B T = 1.0 keV). See further details in Albacete-Colombo et al (2008), where a similar reduction process was performed.…”