DeepXMM-Newtonobservation of theη Chamaleontis cluster

Abstract

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-ofview. 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.

The unusual protoplanetary disk around the T Tauri star ET Chamaeleontis

“…To summarise, we find that (i) X-rays have very little effect (see Appendix D.2) and the neglecting of X-rays in our main model for ET Cha is fully justified. An X-ray luminosity of L X = 6 × 10 28 erg/s, as observed for ET Cha (López-Santiago et al 2010), turns out to be much less important for the disk heating and ionisation as compared to the strong FUV of ET Cha, L UV = 6.5 × 10 31 erg/s as measured between 912 and 2500 Å, based on our HST/COS and HST/STIS observations; (ii) the treatment of H 2 -formation on grain surfaces is one of the most important yet quite uncertain processes for astrochemical modelling. Appendix D.6 shows that different approaches to calculate the H 2 -formation rate lead to a systematic uncertainty in the model for the computation of the o-H 2 2.122 μm about a factor of 5.…”

“…We have run a comparison disk model with X-ray heating and chemistry included, as has recently been implemented by Aresu et al (2011), with X-ray luminosity L X = 6 × 10 28 erg/s (XMM observations by López-Santiago et al 2010). We assumed an X-ray emission temperature of T X = 10 7 K and a minimum energy of X-ray photons of 0.1 keV.…”

Star formation history of Canis Major OB1

“…characteristics of flare-like events in this work are similar to T Tauri stars of the Taurus Molecular Cloud (e.g., Stelzer et al 2007), or young stellar objects from the η Chamaleontis cluster (López-Santiago et al 2010). This similarity is shown in Fig.…”

“…In young stars, particularly T Tauri stars, the light curves of these events appear with different shapes (e.g., Favata et al 2005;Wolk et al 2005;Franciosini et al 2007;Stelzer et al 2007;López-Santiago et al 2010).…”

“…The , where Classical-and Weak-T Tauri are respectively represented by filled circles and squares. Filled triangles show young stellar objects associated with the η Chamaleontis cluster (López-Santiago et al 2010). …”