Shell lines in disks around Be stars. 1: Simple approximations for Keplerian disks

Details Shell lines in disks around Be stars. 1: Simple approximations for Keplerian disks Shell lines in disks around Be stars. 1: Simple approximations for Keplerian disks

Mar 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...295..423h&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 295, no. 2, p. 423-434

Other

35

Absorption Spectra, Accretion Disks, Astronomical Models, B Stars, Beryllium, Emission Spectra, Line Spectra, Stellar Envelopes, Hydrodynamic Equations, Iron, Isothermal Processes, Kepler Laws, Mathematical Models, Turbulence

Scientific paper

This paper investigates so-called shell absorption lines occurring in Be star disks seen edge-on. These lines are counterparts of absorption troughs in P Cyg-type profiles for different geometry and kinematics and offer a probe of a small portion of the circumstellar disk. Contrary to other studies, this investigation concentrates on Fe lines as prototype examples for metallic shell lines, which have an extremely small thermal width (2 km/s at 104 K). However, it is also demonstrated that incorporation of turbulence provides a powerful tool to generalize the results towards lines from arbitrary ions. As a simple, though not unphysical model, a purely Keplerian, isothermal disk in hydrodynamic equilibrium is adopted. It is shown that resulting Fe shell profiles consist of a broad kinematic part and a narrow thermal core, the narrowness of which depends on the intrinsic Doppler width of the line. The outer disk radius Rd may cause, under certain circumstances, cusps at radial velocities +/- Vd = Rd-3/2. These cusps can become the deepest points in the line profile, thus causing a central peak. Finally it is demonstrated that if the disk becomes turbulent, the central peak disappears, and the Fe shell profiles are identical to hydrogenic lines from non-turbulent disks.

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