A search for evidence of irradiation in Centaurus X-4 during quiescence

¹ INAF – Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate (Lc), Italy e-mail: paolo.davanzo@brera.inaf.it
² Università degli Studi dell'Insubria, Dipartimento di Fisica e Matematica, via Valleggio 11, 22100 Como, Italy
³ Instituto de Astrofìsica de Canarias, 38200 La Laguna, Tenerife, Spain

Received: 11 July 2006
Accepted: 5 September 2006

Abstract

Aims.We present a study of the neutron star X-Ray Transient Cen X-4. Our aim is to look for any evidence of irradiation of the companion with a detailed analysis of its radial velocity curve, relative contribution of the donor star and Doppler tomography of the main emission lines.

Methods.To improve our study all our data are compared with a set of simulations that consider different physical parameters of the system, like the disc aperture angle and the mass ratio.

Results.We conclude that neither the radial velocity curve nor the orbital variation of the relative donor's contribution to the total flux are affected by irradiation. On the other hand, we do see emission from the donor star at Hα and HeI λ5876 which we tentatively attribute to irradiation effects. In particular, the Hα emission from the companion is clearly asymmetric and we suggest is produced by irradiation from the hot-spot. Finally, from the velocity of the HeI λ5876 spot we constrain the disc opening angle to .