Deep XMM-Newton observation of the η?Chamaleontis cluster

摘要

Context. The members of the η Chamaleontis cluster are in an evolutionary stage in which disks are rapidly evolving. It also exhibits some peculiarities, such as the large fraction of binaries and accretion disks, probably related to the cluster formation process. Its proximity makes this stellar group an ideal target for studying the relation between X-ray emission and those stellar parameters. Aims. Our main objective is to determine the general X-ray properties of the cluster members in terms of coronal temperature, column density, emission measure, X-ray luminosity, and variability. We also aim to establish the relation between the X-ray luminosity of these stars and other stellar parameters, such as effective temperature, binarity, and the presence of accretion disks. Finally, a study of flare energies in each flare event detected during the observations and their relation with some stellar parameters is also performed. Methods. We used proprietary data from a deep XMM-Newton EPIC observation targeting the core of the η Chamaleontis cluster. Specific software for the reduction of XMM-Newton data was used to analyze our observation. To detect sources in the composed EPIC pn+mos image, we used the wavelet-based code PWDetect. General coronal properties were derived from plasma model fitting. X-ray light curves in the 0.3?8.0?keV energy range were generated for each star. Results. We determine both the coronal properties and variability of the η Chamaleontis members in the XMM-Newton EPIC field-of-view. A total of six flare-like events are clearly detected in five different stars. For them, we derived coronal properties during the flare events and pseudo-quiescent state separately. In our observations, stars that experienced a flare event have higher X-ray luminosities in the pseudo-quiescent state than cluster members of similar spectral type that exhibit no evidence of flaring independently of whether they have an accretion disk or not. Observed flare energies are typical of both pre-main- and main-sequence M stars. We detected no difference between flare energies of stars with and without an accretion disk.