Probing the rotation curve of the outer accretion disk in FU Orionis objects with long-wavelength spectroscopy

¹ Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA, Cambridge, UK
² Università degli Studi di Milano, Dipartimento di Fisica, via Celoria 16, 20133 Milano, Italy

Corresponding author: G. Lodato, lodato@sns.it

Received: 6 March 2003
Accepted: 4 July 2003

Abstract

Studies of the Spectral Energy Distribution of Young Stellar Objects suggest that the outer disk of FU Orionis objects might be self-gravitating. In this paper we propose a method to test directly whether, in these objects, significant deviations from Keplerian rotation occur. In a first approach, we have used a simplified model of the disk vertical structure that allows us to quickly bring out effects related to the disk self-gravity. We find that the often studied optical and near-infrared line profiles are produced too close to the central object to provide significant evidence for non-Keplerian rotation. Based on parameters relevant for the case of FU Ori, we show that high-resolution long-wavelength spectroscopy, of the far-infrared H₂ pure rotational lines (sometimes observed in “passive” protostellar disks) and sub-mm CO lines, should be well suited to probe the rotation curve in the outer disk, thus measuring to what extent it is affected by the disk self-gravity. The results of the present exploratory paper should be extended soon to a more realistic treatment of the disk vertical structure.