Detection of a warm molecular wind in DG Tauri^*

¹ Department of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield, Herts AL10 9AB, UK
² School of Cosmic Physics, Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
³ Joint Astronomy Centre, 660 North A'ohoku Place, University Park, Hilo, Hawaii 96720, USA
⁴ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁵ Anglo-Australian Observatory, PO Box 296, Epping, NSW 1710, Australia
⁶ National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan
⁷ Subaru Telescope, 650 North A'ohoku Place, Hilo, Hawaii 96720, USA

Corresponding author: M. Takami, takami@star.herts.ac.uk

Received: 17 October 2003
Accepted: 24 November 2003

Abstract

We detect near-infrared H₂ emission in DG Tau using the Infrared Camera and Spectrograph (IRCS) on the 8.2-m SUBARU telescope. The spectra obtained along the jet axis show that the centroidal position of the 1–0 S(1) emission is offset by 0.2'' from the star towards the jet, while those obtained perpendicular to the jet axis show a marginal extension, indicating that the emission line region has a typical width of ~0.6''. Their line profiles show a peak velocity of ~15 km s^-1 blueshifted from the systemic velocity. These results indicate that the emission originates from a warm molecular wind with a flow length and width of ~40 and ~80 AU, respectively. The line flux ratios ( and an upper limit for ) suggest that the flow is thermalized at a temperature of ~2000 K, and is likely heated by shocks or ambipolar diffusion. The observed velocity and spatial extension suggest that the H₂ and forbidden line emission originate from different components of the same flow, i.e., a fast and partially ionised component near the axis and a slow molecular component surrounding it. Such a flow geometry agrees with model predictions of magneto-centrifugal driven winds.