The disk-bearing young star IM Lupi

Abstract

Classical T Tauri stars (CTTS) differ in their X-ray signatures from older pre-main sequence stars, e.g. weak-lined TTS (WTTS). CTTS show a soft excess and deviations from the low-density coronal limit in the He-like triplets. We test whether these features correlate with accretion or the presence of a disk by observing IM Lup, a disk-bearing object apparently in transition between CTTS and WTTS without obvious accretion. We analyse a Chandra grating spectrum and additional XMM-Newton data of IM Lup and accompanying optical spectra, some of them taken simultaneously to the X-ray observations. We fit the X-ray emission lines and decompose the Ha emission line in different components. In X-rays IM Lup has a bright and hot active corona, where elements of low first-ionisation potential are depleted. The He-like Ne IX triplet is in the low-density state, but due to the small number of counts a high-density scenario cannot be excluded on the 90% confidence level. In all X-ray properties IM Lup resembles a main-sequence star, but it is also compatible with CTTS signatures on the 90% confidence level, thus we cannot decide if the soft excess and deviations from the low-density coronal limit in the He-like triplets in CTTS require accretion or only the presence of a disk. IM Lup is chromospherically active, which explains most of the emission in Ha. Despite its low equivalent width, the complexity of the Ha line profile is reminiscent of CTTS. We present an estimate for the mass accretion rate of 10e-11 Msun/yr.