Bennett, Philip D.

Contact Email: pbennett@casa.colorado.edu
Institute: Center for Astrophysics and Space Astronomy
University of Colorado
First Coauthor: Alexander Brown
Institute: CASA, University of Colorado
Second Coauthor: Wendy H. Bauer
Institute: Wellesley College
Research URL:http://origins.colorado.edu/~pbennett/index.html
Subject Area: Stellar Atmospheres, Circumstellar Material
Waveband: Ultraviolet
Technique: Spectroscopy
Presentation: Poster Display
Title: A Preliminary Model Chromosphere for the VV Cephei Supergiant Primary (M2 Iab)
Abstract: We recently observed the UV spectrum during total eclipse and egress phases of the long-period (20.3 yrs) binary VV Cephei (M2 Iab + B0) with the HST/STIS echelle spectrograph. The M2 primary does not contribute significantly to the UV spectrum, which arises, directly and indirectly, from photons emitted by the hot companion. An emission line spectrum is seen during totality, formed by hot star photons scattered into the line of sight by the massive wind of the cool supergiant. As egress progresses, the direct line of sight to the secondary is restored, and the continuum (of the companion) reappears. Superimposed upon this early-type continuum is a very rich absorption spectrum formed in the M supergiant's chromosphere. Also seen is additional absorption from an extended circumstellar envelope and rapidly-varying accretion emission, presumably formed near the hot star. We focus on the chromospheric absorption spectrum, and analyze a region of spectrum near 3000 A, where the density of lines is low enough so that them continuum is clearly visible. Using the tau-v method, we derive chromospheric hydrogen column density distributions for each observed line of sight. >From these, we construct an empirical model of the supergiant's chromosphere. We present some preliminary results of this analysis at this meeting.