Hβ photometry of southern CP2 stars: is the uvbybeta luminosity calibration also valid for peculiar stars?

Abstract

We present Hβ photometry of 233 southern CP2 stars (covering the magnetic Ap stars according to the definition by Preston 1974) brighter than V < 8.5 mag from the list of Bidelman & MacConnell (1973). Absolute magnitudes derived from this photometry together with already existing uvby photometry is confronted with Hipparcos results available for a common subset of 152 stars. In order to compare peculiar with normal stars, we identified a sample of 1147 normal B to F-type stars using their published uvbybeta and Hipparcos data. For our analysis we divide both samples into three temperature as well as two Hipparcos parallax accuracy groups. The error distribution of both samples proved to be statistically comparable. As a result the absolute magnitudes for the B-type CP2 stars show up to be significantly too bright by an average of 0.5 mag using the actual photometric calibration. On the other hand, the photometric absolute magnitudes for cool A to F-type CP2 stars are up to three magnitudes fainter as compared to Hipparcos. Based on observations at ESO-La Silla and with the Hipparcos satellite