. Determination of Teff from Walraven colour indices
The effective temperatures and corresponding spectral types of variables were
determined from the Walraven dereddened [B − U ] and [B − L] colour indices
in quadratures derived from our observations (van Houten et al., 2003) using
the calibration of Brand & Wouterloot (1988). They are listed in Table 1. All
quantities are in the usual notation of the Walraven colour system: use of logI
instead of magnitudes. The V − B colour determines the reddening, B − U
measures the Balmer jump, so it is a good temperature indicator for O and B
stars, B−L mainly depends on gravity. The last two parameters were dereddened
using the formulae published by Brand & Wouterloot (1988).