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We first review the current knowledge of Hipparcos systematic and random errors, in particular small-scale correlations. Then, assuming Gaussian parallax errors and using examples from the recent Hipparcos literature, we show how random errors may be misinterpreted as systematic errors, or transformed into systematic errors. Finally we summarise how to get unbiased estimates of absolute magnitudes and distances, using either Bayesian or non-parametrical methods. These methods may be applied to get either mean quantities or individual estimates. In particular, we underline the notion of astrometry-based luminosity, which avoids the truncation biases and allows a full use of Hipparcos samples.
Y dwarfs provide a unique opportunity to study free-floating objects with masses $<$30 M$_{Jup}$ and atmospheric temperatures approaching those of known Jupiter-like exoplanets. Obtaining distances to these objects is an essential step towards charac
Emission from the 6.7 GHz methanol maser transition is very strong, is relatively stable, has small internal motions, and is observed toward numerous massive star-forming regions in the Galaxy. Our goal is to perform high-precision astrometry using t
The theoretical prediction that trigonometric parallaxes suffer from a statistical effect, has become topical again now that the results of the Hipparcos satellite have become available. This statistical effect, the so-called Lutz-Kelker bias, causes
We investigate the properties of K0V stars with Hipparcos parallaxes and spectral types taken from the Michigan Spectral Survey. The sample of 200 objects allows the empirical investigation of the magnitude selection (Malmquist) bias, which appears c
We report data for $I$ band Surface Brightness Fluctuation (SBF) magnitudes, V-I colors, and distance moduli for 300 galaxies. The Survey contains E, S0 and early-type spiral galaxies in the proportions of 49:42:9, and is essentially complete for E g