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

¹ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio, Italy e-mail: [dloren;giannini;calzol;puccetti;antoniucci;dipaola;nisini]@mporzio.astro.it
² Università degli Studi di Cagliari – Dipartimento di Fisica, S.P. Monserrato-Sestu Km 0.700, 09042 Monserrato-CA, Italy
³ Università degli Studi di Roma “Tor Vergata” – Dipartimento di Fisica, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁴ Central Astronomical Observatory of Pulkovo, Pulkovskoe shosse 65, 196140 St. Petersburg, Russia e-mail: arkharov@mail.ru
⁵ Astronomical Institute of St. Petersburg University, Russia e-mail: vml@VL1104.spb.edu

Received: 21 November 2005
Accepted: 28 February 2006

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 (Paschen and Brackett series),  recombination, and CO overtone.

Methods.By comparing the observed spectrum with a wind model, a mass loss rate of 4  10 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 L_X luminosity) that confirm the T Tauri nature of the source.

Results.In the near-IR, the object maintains a low extinction (A_V  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  to more than 25 ) 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.