Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/science/preprints/prep1204/prep1204.bib
Дата изменения: Wed Oct 7 22:27:01 1998
Дата индексирования: Sat Dec 22 14:58:49 2007
Кодировка:
Поисковые слова: south pole
BIB-VERSION:: AST-PP-v1.0
ID:: epreps.stsci//prep1204
ENTRY:: March 9, 1998
TITLE:: HST/FOS Eclipse Observations of the Nova-Like Cataclysmic Variable UX Ursae Majoris
SUBTITLE::
AUTHOR:: Knigge, Christian (1)
AUTHOR:: Long, Knox S. (1)
AUTHOR:: Wade, Richard A. (2)
AUTHOR:: Baptista, Raymundo (3)
AUTHOR:: Horne, Keith (4)
AUTHOR:: Hubeny, Ivan (5)
AUTHOR:: Rutten, René G.M. (6)
AFFIL:: (1) Space Telescope Science Institute 3700 San Martin Drive Baltimore, MD 21218 USA
AFFIL:: (2) The Pennsylvania State University Department of Astronomy and Astrophysics, 525 Davey Laboratory University Park, PA 16802
AFFIL:: (3) Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Universitario, Trindade, 88040 Florianopolis, Brasil
AFFIL:: (4) Department of Physics and Astronomy, The University of St. Andrews, North Haugh, St. Andrews, Fife, KY16 9SS, UK
AFFIL:: (5) NASA Goddard Space Flight Center, Greenbelt, MD 20771
AFFIL:: (6) Isaac Newton Group, Apartado de correos 321, E-38780 Santa Cruz de La Palma, Spain
DATE:: December 1997
JOURNAL:: To appear in: The Astrophysical Journal
SUBMITTED:: 6 August 1997
ACCEPTED:: 25 November 1997
OTHER_ACCESS::
COPYRIGHT:: Copyright 1997 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved.
LANGUAGE:: English
ABSTRACT::

We present and analyze Hubble Space Telescope Faint observations
of the eclipsing nova-like cataclysmic variable UX UMa
obtained with the Faint Object Spectrograph. Two eclipses each
were observed with the G160L grating (covering the ultraviolet
waveband) in August of 1994 and with the PRISM (covering the
near-ultraviolet to near-infrared) in November of the same year. The
system was ~50% brighter in November than in August,
which, if due to a change in the accretion rate, indicates a fairly
substantial increase in M· SIZE=-1>acc by 50%.



The eclipse light curves are qualitatively consistent with the
gradual occultation of an accretion disk with a radially decreasing
temperature distribution. The light curves also exhibit asymmetries
about mid-eclipse that are likely due to a bright spot at the disk
edge. Bright spot spectra have been constructed by differencing the
mean spectra observed at pre- and post-eclipse orbital phases. These
difference spectra contain ultraviolet absorption lines and show the
Balmer jump in emission. This suggests that part of the bright spot
may be optically thin in the continuum and vertically extended enough
to veil the inner disk and/or the outflow from UX UMa in some
spectral lines.



Model disk spectra constructed as ensembles of stellar atmospheres
provide poor descriptions of the observed post-eclipse spectra,
despite the fact that UX UMa's light should be dominated by
the disk at this time. Suitably scaled single temperature model
stellar atmospheres with Teff ~
12,500-14,500 K actually provide a better match to both the
ultraviolet and optical post-eclipse spectra. Evidently, great care
must be taken in attempts to derive accretion rates from comparisons
of disk models to observations.



One way to reconcile disk models with the observed post-eclipse
spectra is to postulate the presence of a significant amount of
optically thin material in the system. Such an optically thin
component might be associated with the transition region
("chromosphere") between the disk photosphere and the fast wind from
the system, whose presence has been suggested by
Knigge & Drew (1997). In any event, the
wind/chromosphere is likely to be the region in which many, if not
most, of the UV lines are formed. This is clear from the plethora of
emission lines that appear in the mid-eclipse spectra, some of which
appear as absorption features in spectra taken at out-of-eclipse
orbital phases.





END:: epreps.stsci//prep1204