UBV Paper Abstracts
Arribas S., Roger C.M. (1989 A&A 215, 305)
Abstract
From a new set of infrared photometry we have derived the effective
temperatures with a 3% error for a sample of low main sequence stars with
spectroscopic determinations of their metal content. This has been used
to extend the previous (B-V), Teff, [Fe/H] empirical calibrations for
population I up to 4000K as well as to analyse the influence of some
limitations of previous works. The agreement with the empirical calibration
of Arribas and Martinez Roger (1988) is very good for almost the complete
tenperature and metallicity range. Only for Teff lower than 5000 K and the
lowest metallicities, that calibration does not reproduce the observed
behaviour. Comparison with theoretical models shows that for solar abundance
they are predicting exceedingly blue colours. Particularly in the new range
analyzed (4000K < Teff < 5000K) the differences with the VandenBerg and
Bell (1985) calibration can be as large as 0.09 mag. The new Buser and Kurucz
(1988) models show better agreement. In both models the effect of metallicity
in colours is underestimated. The possible influence of metallicity on the
(V-K): Teff relation has also been investigated and was found to be about
30 K/dex for this spectral range.
These results support the suggestion of Magain (1987) that opacity at the
ultraviolet is larger than that considered by the current atmosphere models
for late type stars.
Carney B.W. (1977, ApJ 233, 211)
Abstract
The relation between stellar ultraviolet excesses and abundances is reexamined
with the aid of new data and an investigation is made of the accuracy of
previous analyses. A high-resolution echellogram of the subdwarf HD 201891 is
analysed to illustrate some of the problems. Generally, the earliest and latest
analytical techniques yield consistent results for dwarfs. New UBV
data yield normalized ultraviolet excesses, d(U-B)0.6, which are compared
to abundances to produce a graphical relation that may be used to estimate
[FE/H] to 0.2 dex. given UBV colors accuracte to 0.01 mag. The
relation suggests a possible discontinuity between the halo and old-disk
stars.
epaunzen@physics.muni.cz
Last update: 7 Novembre 1995