Warm and hot circumstellar gas in V1647 Ori during the 2008-2009 outburst

Abstract

The pre-main sequence star V1647 Ori started a new outburst in August 2008. From October 2008 to February 2009 we monitored V1647 Ori, obtaining quasi-simultaneous VLT-CRIRES near-IR spectroscopy, VLT-VISIR mid-IR spectroscopy and VLT-FORS2 optical spectroscopy. We studied the evolution of H₂ and CO emission from hot and warm gas and Hα and forbidden line-emission during the initial outburst phase of V1647 Ori. Hα is observed in emission displaying P-Cygni profiles with blue-shifted absorption up to –700 km/s, suggesting the presence of a high velocity wind (Fig. 1a). [OI] emission at 6300 Å is observed displaying a blue-shifted emission shoulder, indicating the presence of material moving away from the star (Fig. 1b). We detect H₂ 1-0 S(1) and CO (P4 to P14 and P30-P38) ro-vibrational lines centered at the velocity of the star at all epochs (Fig. 1c & d). This strongly suggests that the H₂ and CO emission originates from a disk and not from a warm outflow. The H₂ 1–0 S(0) and 2-1 S(1) ro-vibrational lines at 2.22 and 2.24 μm and the pure-rotational H₂ 0–0 S(1) and 0–0 S(2) lines at 17 and 12 μm were not detected in our spectra. Changes in the Hα and [OI] profiles and the H₂ and CO emission observed do not correlate. We modeled the H₂ and CO line profiles assuming emission from a flat disk in keplerian rotation with line intensity decreasing with radius (I ~ I₀(R/R_min)^−α). We found that the disk of V1647 Ori is observed nearly face-on and that the line emission is produced within a fraction of an AU of the star (Fig. 1d).