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Thermal Structure of Magnetic Funnel Flows

Published online by Cambridge University Press:  25 May 2016

Steven C. Martin
Steven C. Martin*
Affiliation:
Department of Astronomy & Astrophysics, The University of Chicago, 5640 South Ellis Ave., Chicago, Illinois 60637, USA

Abstract

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The thermodynamic structure of gas that is channeled by stellar magnetic fields onto a young (pre–main-sequence) star is presented. In this model, the star possesses a dipole magnetic field which disrupts the inner regions of a geometrically thin accretion disk and channels the inflowing gas onto the stellar surface, thereby forming an accretion funnel. The temperature and ionization degree of the inflowing gas is calculated by solving the heat equation coupled to statistical rate equations for hydrogen. It is found that for typical accretion rates of ∼ 10–7M⊘yr–1, temperatures of ∼ 7000 K and hydrogen ionization fractions (nH+/nH) of ∼ 10–2 can be attained in the funnel flow. The principal heat source is found to be adiabatic compression, and coolants include bremsstrahlung radiation as well as line emission from the Ca II and Mg II ions. The relatively hot and ionized funnel flow lead to observational signatures such as inverse P Cygni line profiles seen in upper Balmer and near-infrared lines. In addition, carbon monoxide bandhead emission may be an important tracer of the outer portions of the funnel flow.

Type
IV. Disks, Winds, and Magnetic Fields
Information
Symposium - International Astronomical Union , Volume 182: Herbig-Haro Flows and the Birth of Low Mass Stars , 1997 , pp. 455 - 463
Copyright
Copyright © Kluwer 1997 

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