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Astron. Astrophys. 340, L35-L38 (1998)

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Letter to the Editor

On the uncertainty of distances derived from parallax measurements

J. Kovalevsky

CERGA, Observatoire de la Côte d'Azur, Av. Copernic, F-06130 Grasse, France

Received 1 September 1998 / Accepted 18 October 1998


The problem of determining the distances and their uncertainties from the measurements of parallaxes has no straight forward solution. In contrast to Bayesian-like approaches, a direct approach is possible assuming that the probability density function (pdf) in relative distance is cut for negative distances. This gives an asymmetrical pdf which is difficult to use and overestimates variances. It is proposed to fit it by a Gaussian pdf which minimizes the deviation from the actual pdf for the central interval, and the weighted deviation from most of the pdf. The characteristics of this Gaussian is given as functions of the parallax and its rms.

Key words: distances – parallaxes – stars – statistics

© European Southern Observatory (ESO) 1998

Online publication: November 9, 1998