Comparison of the Hα circumstellar disks in Be/X-ray binaries and Be stars

¹ Institute of Astronomy, Bulgarian Academy of Sciences and Isaac Newton Institute of Chile, Bulgarian Branch, National Astronomical Observatory Rozhen, PO Box 136, 4700 Smolyan, Bulgaria
² Foundation for Research and Technology-Hellas, 71110 Heraklion, Crete, Greece
³ Physics Department, University of Crete, 71003 Heraklion, Crete, Greece
⁴ Departamento de Física, EPS, Universidad de Jaén, C/ Virgen de la Cabeza, 2, 23071 Jaén, Spain
⁵ Physics and Astronomy Department, Southampton University, Southampton, S017 1BJ, UK
⁶ Departamento de Astronomía, Universidad de Valencia, 46100 Burjassot, Valencia, Spain
⁷ National Astronomical Observatory Rozhen, PO Box 136, 4700 Smolyan, Bulgaria

Corresponding author: R. K. Zamanov, rozhen@mbox.digsys.bg

Received: 2 June 2000
Accepted: 14 December 2000

Abstract

We present a comparative study of the circumstellar disks in Be/X-ray binaries and isolated Be stars based upon the Hα emission line. From this comparison it follows that the overall structure of the disks in the Be/X-ray binaries is similar to the disks of other Be stars, i.e. they are axisymmetric and rotationally supported. The factors for the line broadening (rotation and temperature) in the disks of the Be stars and the Be/X-ray binaries seem to be identical. However, we do detect some intriguing differences between the envelopes. On average, the circumstellar disks of the Be/X-ray binaries are twice as dense as the disks of the isolated Be stars. The different distribution of the Be/X-ray binaries and the Be stars seen in the full width half maximum versus peak separation diagram indicates that the disks in Be/X-ray binaries have on average a smaller size, probably truncated by the compact object.