## 5. ConclusionsAmong the two methods presented in this paper to represent the pdf of the distance determined from the parallax has two disavantages. -
The distribution is strongly asymmetrical and can be used only numerically in later computations. -
In deriving the rms from the variances, the unprobable large values of *x*play a major role, increasing the rms in a way that can be considered as unrealistic.
The Gaussian representation of
has the advantage of being usable as such in
further evaluations of uncertainties of quantities depending among
others on the observed parallaxes. One may remark from Table 2
that the quality of fit worsens rather quickly when Finally, the tables presented show that the solutions degrade for large values of . It is not reasonnable to use any pdf for . Then, the determination of the distance from parallaxes looses its physical significance, and photometric determinations are definitely better. In any case, cutting a sample at some value of may introduce a bias, so that users are invited to ascertain that the sample satisfies the conditions of applicability of the method. © European Southern Observatory (ESO) 1998 Online publication: November 9, 1998 |