The red clump absolute magnitude based on revised Hipparcos parallaxes

TL;DR

This paper recalibrates the absolute magnitude of red clump stars using revised Hipparcos parallaxes, revealing a fainter K-band magnitude than previous estimates due to selection biases, and refines their use as distance indicators.

Contribution

It provides updated absolute magnitudes for red clump stars in I and K bands based on a new model accounting for selection biases and population effects.

Findings

$M_I = -0.22 \\pm 0.03$ mag in I-band

$M_K = -1.54 \\pm 0.04$ mag in K-band

Fainter K-band magnitude supports previous population correction results.

Abstract

Over the past decade the use of the red clump (RC) as distance indicator has increased in importance as this evolutionary phase is well populated and a good local calibration exists. The absolute calibration of the RC in the $I$ and $K$ band is investigated again based on the recently published revised Hipparcos parallaxes. A numerical model is developed that takes the various selection criteria and the properties of the Hipparcos catalogue into account. The biases involved in applying certain selections are estimated with this model. The absolute magnitudes that are found are $M_{\rm I} = -0.22 \pm 0.03$ and $M_{\rm K} = -1.54 \pm 0.04$ (on the 2MASS system). The $I$-band value is in good agreement with previous determinations, the $K$-band value is fainter than previously quoted, and this seems to be related to a selection bias whereby accurate $K$-magnitudes are only available for relatively few bright stars. Applying population corrections to the absolute $K$ magnitude of RC stars in clusters supports the fainter magnitude scale.