# Walraven Paper Abstracts

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

## Abstract

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.

mermio@scsun.unige.ch

Last update: 7 Novembre 1995