Evidence for T Tauri-like emission in the EXor V1118 Ori from near-IR and X-ray data

Abstract

Aims. We present a near-IR study of the EXor variable V1118 Ori, performed by following a slightly declining phase after a recent outburst. In particular, the near-IR (0.8-2.3 μm) spectrum, obtained for the first time, shows a wide variety of emission features of the H I (Paschen and Brackett series), He I recombination, and CO overtone. Methods. By comparing the observed spectrum with a wind model, a mass loss rate of 4 × 10-8 M⊙ yr -1 can be derived along with other parameters whose values are typical of an accreting T Tauri star. In addition, we have used X-ray data from the XMM archive, taken in two different epochs during the declining phase monitored in IR. The X-ray emission (in the range 0.5-10 keV) permits us to derive several parameters (as plasma temperatures and LX luminosity) that confirm the T Tauri nature of the source. Results. In the near-IR, the object maintains a low extinction (Av ≤ 2) during all the activity phases, confirming that variable extinction does not contribute to brightness variations. The lack of both a significant amount of circumstellar material and any evidence of IR cooling from collimated jet/outflow driven by the source indicates that at least this member of the EXor class is in a late stage of the pre-main sequence evolution. When going from inactive to active phases, the luminosity increases considerably (from 1.4 L⊙ to more than 25 L⊙) and the observed spectral energy distribution assumes different shapes, all typical of a T Tauri star. In the X-ray regime, an evident fading is present, detected in the post-outburst phase, which cannot be reconciled with the presence of any absorbing material. This circumstance, combined with the persistence (in the pre- and post-outburst phases) of a temperature component at about 10 MK, suggests that accretion has some influence in regulating the coronal activity. © ESO 2006.