X-raying massive star forming regions

ALBACETE-COLOMBO J.F

Malargue, Mendoza, Argentina.

Congreso; L Reunion Anual de la Asociacion Argentina de Astronomia; 2007

Asociacion Argentina de Astronomia

Because X-rays get deep inside the gas and dust structures in whichstars born, X-ray observations with high spatial resolution becomes acrucial tool to identify members and understand high energy processesoccurring in young stars. With the aim to address some aspects ofthese problems, we have used two Chandra X-ray observations of twoGalactic massive star forming regions:  - Cygnus OB2: Is anextremely massive Star Forming Region (SFR), that has an age~2 Myrs and is located at a distance of ~1450 pc. We use a97.7 ksec ACIS-I Chandra observation, in which we detect 1003 X-raysources (25 of them known OB-type stars). 766 X-ray sources have a2MASS near-IR counterpart, however incomplete limit of the 2MASSphotometry makes that fainter stars (masses less than 0.9 Moremain hidden. We performed X-ray spectral analysis of 423 sources(those with more than 20 ph.), which are normally distributed with amedian log(NH~22.3 cm^-2, equivalent to Av~7 mag. This results is coincident with the typical Av obtained from the IR analysis. The relation between Lx and masses of the CygnusOB2 and "Chandra Ultra-deep Project}" (COUP) stars, accounting for masses >1.0 Mo, are in good agreement. This supports that physical mechanism that produce X-rays in low-mass stars is well correlated with the age (Albacete Colombo et al. 2007a). We use the Maximum Likelihood Block (MLB) algorithm to define and search for flaring stars. We found 144 X-ray sources show X-ray variability. The flare frequency of stars in the Cygnus OB2 region is ~1/660 1/ksec. We also compare variability results with that the ONC region. In order to avoid statistical biasintroduced by different exposure length and distance effects, were-analyzed the Chandra Orion Ultra-deep Project (COUP) data usingsame constrains in the MLB algorithm that used previously for theanalysis of the Cygnus OB2. We found that flare frequency of starswith masses above 1Mo, in both cluster, is roughly the same,i.e. 1 flare per star every 1000 ksec (Albacete Colombo et al. 2007b). - Trumpler 16: This region is one of most massive SFRof the Galaxy, comprising the extremely luminous LBV starEta-Carina. This region is a 2250 pc distance and their massivestellar content has been studied previously with XMM-Newton data byAlbacete Colombo et al. (2003). However the X-ray properties of theyoung low-mass stars of the region still remain unknown until now. Weuse 89.0 ksec Chandra observation. We study the effect of the diffuseX-ray emission that mask the faint stellar X-ray population of theregion. After to reduce background by considering a multi Xray-bandsource detection process, we finally report a total of 1035 X-raysources. They appear inhomogeneous distributed along the ACIS-I fieldof view. 650 of the sources have a 2MASS near-IR counterpart. Thesharp cut in detected X-ray source spatial distribution follow thesame distribution of the V-shape gas and dust structure of the region.Differential absorption of the region (Av~3-7 mag)delineates the spatial distribution of observed X-ray sources. Wefound more than 100 X-ray sources compatible with a population ofT-Tauri stars. Spectral X-ray analysis was performed on 563 sources,with a median log(NH~21.8 cm^-2, equivalent to Av~3.5 mag. Masses of identified IR counterpart corresponds to stars with more than 1Mo (Albacete Colombo et al. 2007c).