Stellar parameters of Be stars observed with X-shooter

TL;DR

This study analyzes a large archive of telluric star spectra to identify and characterize Be stars, especially late types, revealing their fundamental parameters, rotational velocities, and disk properties, with many new detections and implications for their distribution.

Contribution

It introduces an adapted BCD method for late B stars and provides a comprehensive analysis of Be stars in the X-shooter archive, including many newly identified objects.

Findings

78 Be stars identified, 48 previously unreported

Late type Be stars tend to have more tenuous disks and less variability

The Be/B star ratio may not depend strongly on spectral subtype

Abstract

Aims. The X-shooter archive of several thousand telluric 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, utilizing 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 due to uncertainties in determining the photospheric contribution are useful only in a subsample of Be stars for determining the pure emission contribution. Results. A total of 78 Be stars, mostly late type ones, were identified in the X-shooter telluric standard star archive, out of which 48 had not been reported before. The general trend of late type Be stars having more tenuous disks and being less variable than early type ones is confirmed. 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.