Volume 475, Number 2, November IV 2007
|Page(s)||651 - 657|
|Published online||18 June 2007|
HeI doubled emission lines from A0535+26 ≡ HDE 245770
A possible interpretation
INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica – Roma, Area di Ricerca CNR di Roma-2, via del Fosso del Cavaliere 100, 00133 Roma, Italy e-mail: email@example.com
2 INFN – Sezione di Roma-2, via della Ricerca Scientifica 1, 00133 Roma, Italy
3 INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
4 Departamento de Astrofísica, Universidad de La Laguna, Avda Astrofísico F. Sànchez s/n, 30071 La Laguna, Spain
5 Università di Roma “La Sapienza”, Piazzale A. Moro 5, 00185 Roma, Italy
6 Departamento de Ciencias del Espacio y Tecnologías Electrónicas INTA Carretera de Ajalvir Km 4, 28850 Torrejón de Ardóz, Spain
Accepted: 17 April 2007
We report results of the spectroscopy for V725 Tau (HDE 245770, BD +26°883), commonly known as Flavia's star, which is the optical counterpart of the X-ray pulsar A0535+26, carried out at the 1.5 m Loiano telescope during one run of observations of this star spread over a period of years. The HeI emission lines clearly show doubling, which is good evidence for the presence of a disc. In this paper we critically discuss the possibility that this disc is a temporary accretion disc around the neutron star, a view that contrasts to the usual interpretation, which considers that this sort of doubling in the HeI emission lines is due to a disc formed by gas expelled from the Be star. In the former case the outer radius of the accretion disc could range from 5.9 1010 cm to 2.1 1011 cm, taking the most probable range into account for the orbital inclination of the binary system, from 35° to 39°. The presence of such a temporary accretion disc around the neutron star was predicted by Giovannelli & Ziółkowski (1990).
Key words: X-rays: binaries / accretion, accretion disks / stars: emission line, Be / stars: binaries: close
© ESO, 2007
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