The absolute magnitude of K0V stars from Hipparcos data using an analytical treatment of the Malmquist bias

Abstract

We calculate the average absolute magnitude for Hipparcos single K0V stars, using a theoretical curve for the distance-dependent Malmquist bias in the data. This method is shown to be well applicable to stellar data with good parallaxes and gives results in agreement with a previous study that used another treatment of the bias developed in extragalactic astronomy (finding the "unbiased plateau"). In particular, we point out that such a fit, which uses stars in the biased part of the sample, may be less vulnerable to the fluctuations in the unbiased plateau whose definition is also somewhat subjective. We found for K0V stars M_0=5.8, with the spread of the luminosity function being 0.3 mag. It is shown that inclusion of Hipparcos non-single stars may underestimate M₀ by about 0.05-0.1 mag. During the study it was found that about 20% of the sample may be mis-classified K0IV stars.