Pseudomagnitude Distances: Application to the Pleiades cluster

TL;DR

This paper introduces the use of pseudomagnitudes, a reddening-free observational tool, to estimate stellar distances, and applies it to determine the Pleiades cluster distance, confirming a known measurement anomaly.

Contribution

It demonstrates how absolute pseudomagnitudes can be used to measure stellar distances and applies this method to the Pleiades cluster using Hipparcos data.

Findings

Pseudomagnitudes are effective reddening-free distance indicators.

The Pleiades cluster distance is estimated at approximately 139 parsecs.

Hipparcos measurements of some Pleiades stars show a known distance anomaly.

Abstract

The concept of pseudomagnitude was recently introduced by Chelli et al. (2016), to estimate apparent stellar diameters using a strictly observational methodology. Pseudomagnitudes are distance indicators, which have the remarkable property of being reddening free. In this study, we use Hipparcos parallax measurements to compute the mean absolute pseudomagnitudes of solar neighbourhood dwarf stars as a function of their spectral type. To illustrate the use of absolute pseudomagnitudes, we derive the distance moduli of $360$ Pleiades stars and find that the centroid of their distribution is $5.715\pm0.018$, corresponding to a distance of $139.0\pm1.2$\,pc. We locate the subset of $\sim 50$ Pleiades stars observed by Hipparcos at a mean distance of $135.5\pm3.7$\,pc, thus confirming the frequently reported anomaly in the Hipparcos measurements of these stars.