The disk-bearing young star IM Lupi: X-ray properties and limits on accretion

The disk-bearing young star IM Lupi: X-ray properties and limits on accretion

Context. Classical T Tauri stars (CTTS) differ in their X-ray signatures from older pre-main sequence stars, e.g. weaklined TTS (WTTS). CTTS show a soft excess and deviations from the low-density coronal limit in the He-like triplets.
Aims. We test whether these features correlate with accretion or the presence of a disk by observing IM Lup, a diskbearing object apparently in transition between CTTS and WTTS without obvious accretion.
Methods. 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 H emission line in different components.
Results. 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 H. Despite its low
equivalent width, the complexity of the H line profile is reminiscent of CTTS. We present an estimate for the mass
accretion rate of 10−11M yr−1.

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