New memberships, mean parallaxes and proper motions of all 9 open clusters closer than 300 pc (except the Hyades) and 9 rich clusters between 300 and 500 pc have been computed using Hipparcos data. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to 0.5 mas/yr for proper motions, are of great interest for calibrating photometric parallaxes as well as for kinematical studies. Caref...

The concept of absolute trigonometric parallax measurements is formulated in strict mathematical terms, in connection with the widely discussed plans for a future astrometric space mission. The parallaxes determined for a large number of stars spread all over the sky are absolute if the expected error (accidental or systematic) of the zero–point, as well as other large–scale distortions are ord...

Aims. We investigate and parameterize high proper motion red stars in the Torino Observatory Parallax Program. Methods. Observations of 27 objects were made over the period 1994–2001 on the 1.05 m Torino telescope. The trigonometric parallaxes and proper motions were determined using standard techniques. Results. We determine parallaxes and proper motions, and by comparison to models we infer m...

TheHIPPARCOSsatellite hasmeasured trigonometric parallaxes for 20 white dwarfs. With the exception of one each of the spectral types DZ, DC, DB, DQ, the majority are of spectral type DA. We compare the parallaxes with the most recent ground-based determinations. Froma spectroscopic analysis of new optical observations we determine atmospheric parameters Teff and log g. From the angular diameter...

We show that the errors in the Hipparcos parallaxes towards the Pleiades and the Hyades open clusters are spatially correlated over angular scales of 2 to 3 degrees, with an amplitude of up to 2 mas. We suggest that this correlation on small angular scales is a generic feature of the Hipparcos parallaxes all over the sky. We predict the parallaxes of individual cluster members, πpm, from their ...

Reconsidering calibration of statistical distance scales for planetary nebulæ leads naturally to examining precision and especially the systematic errors of other methods. Here we present a different calibration strategy based on the precise trigonometric parallaxes for sixteen central stars published by Harris et al. (2007) of USNO, with four improved by Benedict et al. using the Hubble Space ...

High precision trigonometric parallaxes from the Hipparcos satellite and accurate metal abundances ((Fe/H], O/Fe], and /Fe]) from high resolution spectroscopy for about 30 local subdwarfs have been used to derive distances and ages for a carefully selected sample of nine globular clusters. We nd that Hipparcos parallaxes are smaller than the corresponding ground-based measurements leading, to a...

Context. Ages, chemical compositions, velocity vectors, and Galactic orbits for stars in the solar neighbourhood are fundamental test data for models of Galactic evolution. The Geneva-Copenhagen Survey of the Solar neighbourhood (Nordström et al. 2004; GCS), a magnitude-complete, kinematically unbiased sample of 16,682 nearby F and G dwarfs, is the largest available sample with complete data fo...

Hipparcos parallaxes will play a major role in the astrophysical applications of the Hipparcos results and in this respect their accuracy is more important than their precision, at least for all the investigations of statistical character. In this Chapter, the systematic errors of the Hipparcos astrometric parameters, including the parallaxes, are evaluated by examining the possible sources of ...