X-ray survey of the Chameleon I star forming region

ALBACETE COLOMBO, J. F; LÓPEZ-SANTIAGO, J.

Dublin

Conferencia; The X-ray Universe; 2014

European Space Agency (ESA)

The Chamaleon I dark molecular cloud, hereafter Cha I, is an active site of recent star formation located at high galactic latitude (b ~ -15deg). It belongs to the Chamaleon complex which is one of the nearest SFR (d ~ 160 pc). These two characteristics result in low foreground extinction and poor contamination with background objects, which makes it of special interest for the unbiased determination of the true population of young stars. Cha I has been the target of a large number of studies, including spectroscopy in Halpha (Comeron et al. 1999, 2000), monitoring of photometric variability (Carpenter et al. 2002), and IR photometry (Luhman et al. 2000; Luhman 2004; Manoj et al. 2011), who carried out a thorough spectroscopic study to obtain precise spectral types and membership census of Cha I stars. The substellar limit in Cha I, based on the members of median age (Stelzer & Micela 2007), corresponds to the spectral type M6-M6.5 (Baraffe et al. 1998). Finally, X-ray studies using Einstein Observatory (Feigelson & Kriss 1989), ROSAT (Feigelson et al. 1993; Alcala et al. 1995, 1997), Chandra (Feigelson & Lawson 2004; Stelzer & Micela 2007) and XMM-Newton observations (Stelzer et al. 2004; Robrade & Schmitt 2007) have partially revealed the Cha I X-ray stellar population, but leaving a large part of it unexplored in the X-rays.! We present preliminary study of the Cha I X-ray stellar content and describe the nature of 484 X-rays sources detected in the analysis of 8 XMM-Newton X-ray observations. We correlate them with optical, mid- and near- infrared Spitzer and 2MASS counterparts. One third of the X-ray sources shows 2MASS counterparts and 14 X-ray sources out of 54 Spitzer sources, exhibit mid-IR colors, indicative of stars with circumstellar discs. The range of Av absorption is between 0.1 to 0.5 mag. We performed X-ray spectral analysis of X-ray sources with more than 30 X-ray photons in the spectra. The extinction is highly variable over the entire stellar field. We estimate X-ray plasma temperatures, abundances and fluxes of stars. Typical X-ray spectral parameters are log(NH) ~21.45 (cm-2) with 1 sigma dispersion of 0.4 dex, and a not normal temperature kT~0.71 keV, with a hard tail temperature distribution towards 1.5 keV. We test the X-ray Luminosity Function (XLF) approaches as it was computed from spectral fits or via conversion factor (CF). It is biased by the effect of the NH absorption correction to the X-ray luminosity. The XLF of known SFRs could be biased if the Lx of stars were obtained via CF rather than the spectral fits.