A global jet/circulation model for young stars

¹ Dublin Institute for Advanced Studies, 5 Merrion Square Dublin 2, Ireland
² GRAAL, CC 72, Université de Montpellier II, 34095 Montpellier Cedex 05, France
³ Department of Physics, Queen's University, Kingston, ON K7L 3N6, Canada
⁴ McLennan Labs, Univ. of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada
⁵ Department of Physics and Astronomy, Univ. of Rochester, Rochester, NY 14627-0171, USA
⁶ Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, 50125 Firenze, Italy

Corresponding author: T. Lery, Thibaut.Lery@graal.univ-montp2.fr

Received: 6 March 2001
Accepted: 4 March 2002

Abstract

Powerful, highly collimated jets, surrounded by bipolar molecular outflows, are commonly observed near Young Stellar Objects (YSOs). In the usual theoretical picture of star formation, a jet is ejected from a magnetized accretion disk, with a molecular outflow being driven either by the jet or by a wider wind coming from the disk. Here, we propose an alternative global model for the flows surrounding YSOs. In addition to a central accretion-ejection engine driving the jet, the molecular outflow is powered by the infalling matter and follows a circulation pattern around the central object without necessarily being entrained by a jet. It is shown that the model produces a heated pressure-driven outflow with magneto-centrifugal acceleration and collimation. We report solutions for the three different parts of this self-similar model, i.e. the jet, the infalling envelope and the circulating matter that eventually forms the molecular outflow. This new picture of the accretion/outflow phase provides a possible explanation for several observed properties of YSO outflows. The most relevant ones are the presence of high mass molecular outflows around massive protostars, and a realistic fraction (typically 0.1) of the accretion flow that goes into the jet.