Astron. Astrophys. 332, 875-876 (1998)

1. Introduction

In a recent paper, Fernley et al. (1997) have studied the absolute magnitude of RR Lyrae stars by using a statistical-parallax algorithm developed by Hawley et al. (1986). This method has been introduced as an improvement over earlier algorithms such as:

• the maximum-likelihood algorithm developed by Clube and Jones and applied to RR Lyrae stars in several studies (Clube & Jones 1971, 1974; Clube & Dawe 1980); this method will be called herafter the CJD algorithm;
• another maximum-likelihood method introduced by Rigal (1958), subsequently improved by Jung (1968, 1970) and generalized by Heck (1975a); this method, called hereafter the RJH algorithm, has been applied to numerous categories of stars (see, for instance, the URL: http://vizier.u-strasbg.fr/~heck/p-md.htm) including RR Lyrae stars (Heck 1972, 1973, 1975b; Heck & Jung 1975; Heck & Lakaye 1978).

The CJD and RJH algorithms have already been confronted on synthetic data (Jones et al. 1980) and, notwithstanding their different formulations, both gave the correct solution.

The publication of an exhaustive sample of data (including Hipparcos proper motions) for RR Lyrae stars by Fernley et al. (1997) made it interesting to test on it the RJH algorithm and to compare the results with those obtained with the algorithm by Hawley et al. (1986).

© European Southern Observatory (ESO) 1998

Online publication: March 30, 1998
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