Stellar parameters of Be stars observed with X-shooter^⋆,⋆⋆

¹ ESO – European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago, Chile
e-mail: ahmedsh2911@gmail.com
² Astronomy Department, National Research Institute of Astronomy and Geophysics (NRIAG), 11421 Helwan, Cairo, Egypt
³ Kottamia Center of Scientific Excellence in Astronomy and Space Science (KCScE, STDF, ASRT), Cairo, Egypt
⁴ ESO – European Organisation for Astronomical Research in the Southern Hemisphere, Karl-Schwarzschild-Str. 2, Garchingnwt, Germany
⁵ Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706, USA
⁶ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo (USP), Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, Brazil
⁷ Astronomy and Meteorology Department, Faculty of Science, Al-Azhar University, Cairo, Egypt

Received: 9 July 2017
Accepted: 26 October 2017

Abstract

Aims. The X-shooter archive of several thousand telluric standard star spectra was skimmed for Be and Be shell stars to derive the stellar fundamental parameters and statistical properties, in particular for the less investigated late-type Be stars and the extension of the Be phenomenon into early A stars.

Methods. An adapted version of the BCD method is used, using the Balmer discontinuity parameters to determine effective temperature and surface gravity. This method is optimally suited for late B stars. The projected rotational velocity was obtained by profile fitting to the Mg ii lines of the targets, and the spectra were inspected visually for the presence of peculiar features such as the infrared Ca ii triplet or the presence of a double Balmer discontinuity. The Balmer line equivalent widths were measured, but they are only useful for determining the pure emission contribution in a subsample of Be stars owing to uncertainties in determining the photospheric contribution.

Results. A total of 78, mostly late-type, Be stars, were identified in the X-shooter telluric standard star archive, out of which 48 had not been reported before. We confirm the general trend that late-type Be stars have more tenuous disks and are less variable than early-type Be stars. The relatively large number (48) of relatively bright (V> 8.5) additional Be stars casts some doubt on the statistics of late-type Be stars; they are more common than currently thought. The Be/B star fraction may not strongly depend on spectral subtype.