Walraven Paper Abstracts

Lub J., Pel J.W. (1977, A&A 54, 137)


In this paper we discuss the properties of the Walraven VBLUW photometric system, in use at the Leiden Southern Station. A careful analysis of the standard star observations of different observing seasons shows that colour changes as small as 0.01 on a timescale of a few years are detectable. The variation of the early standard stars is largest in (B-U), the Balmer jump index. Special attention is paid to the stability of the photometric passbands, and a new determination of the filter profiles is given. The stable and accurate definition of the passbands is an important feature of the VBLUW photometer, which is particularly valuable for the comparison of observed stars with theoretical colours. The properties of the VBLUW system with respect to atmospheric extinction and interstellar reddening are discussed, and it is shown that the colour-terms in the extinction and reddening corrections are sufficiently small to be neglected. For the colour excesses we adopt: E(B-V)/E(V-B)=0.64; E(U-W)/E(V-B)=0.45; E(B-L)/E(V-B)=0.43. Theoretical colours are derived from a grid of model atmosphere fluxes computed by Kurucz (1975), and the application of the VBLUW photometry to the classification of stars of spectral type A to G is discussed. A three-dimensional classification in terms of temperature, effective gravity and heavy element abundance appears to be possible in this spectral range. We find that below Te=8000 K the VBLUW photometry is more than twice as sensitive to differences in heavy element abundance as is the Stromgren uvby system. The tables at the end of this paper give numerical data for the computed theoretical colours. We also give VBLUW photometry for 148 bright stars of known M.K. spectral type, and for 54 Hyades stars. The photometric properties and theoretical colours discussed in this paper will be the strating point for the interpretation of a large body of VBLUW data on Cepheids and RR Lyrae variables.

Last update: 7 Novembre 1995