UBV Paper Abstracts

Arribas S., Roger C.M. (1989 A&A 215, 305)


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)


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.

Last update: 7 Novembre 1995