Joint H and X-Ray Observations of Massive X-Ray Binaries.
III. The Be X-ray Binaries HDE 245770 = A 0535+26 and X Persei
E. D. Grundstrom,1
T. S. Boyajian,1,2
C. Finch,1
D. R. Gies,1,2
W. Huang,2,3
M. V. McSwain,2,4,5
D. P. O'Brien,1
R. L. Riddle,2,6
M. L. Trippe,1
S. J. Williams,1,2
D. W. Wingert,1,2 and
R. A. Zaballa1
1
Center for High Angular Resolution Astronomy and
Department of Physics and Astronomy,
Georgia State University, PO Box 4106, Atlanta GA 30302-4106
2
Visiting Astronomer, Kitt Peak National Observatory,
National Optical Astronomy Observatory, operated by the Association
of Universities for Research in Astronomy, Inc., under contract with
the National Science Foundation
3
Department of Astronomy, California Institute of Technology, MC
105-24, Pasadena, CA 91125
4
Astronomy Department, Yale University, New Haven, CT 06520-8101
5
NSF Astronomy and Astrophysics Postdoctoral Fellow
6
Thirty Meter Telescope, 2632 E. Washington Blvd., Pasadena, CA
91107
We present results from an H monitoring
campaign of the Be X-ray binary systems HDE 245770 =
A 0535+26 and X Per. We use the H
equivalent widths together with adopted values of the Be star
effective temperature, disk inclination, and disk outer boundary to
determine the half-maximum emission radius of the disk as a function
of time. The observations of HDE 245770 document the rapid spectral
variability that apparently accompanied the regeneration of a new
circumstellar disk. This disk grew rapidly during the years 1998 --
2000, but then slowed in growth in subsequent years. The outer disk
radius is probably truncated by resonances between the disk gas and
neutron star orbital periods. Two recent X-ray outbursts appear to
coincide with the largest disk half-maximum emission radius attained
over the last decade. Our observations of X Per indicate that its
circumstellar disk has recently grown to near record proportions, and
concurrently the system has dramatically increased in X-ray flux,
presumably the result of enhanced mass accretion from the disk. We
find that the H half-maximum emission radius
of the disk surrounding X Per reached a size about six times larger
than the stellar radius, a value, however, that is well below the
minimum separation between the Be star and neutron star. We suggest
that spiral arms excited by tidal interaction at periastron may help
lift disk gas out to radii where accretion by the neutron star
companion becomes more effective.
Accepted by ApJ
Preprints from
erika@chara.gsu.edu
or on the web at
http://arxiv.org/abs/astro-ph/0702283
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