Why are there no radial velocities listed in the Hipparcos Catalogue? Isn't it obvious that these are rather closely connected with the other five astrometric parameters, and anyone studying stellar kinematics would like to have them in a convenient form? What can amateur astronomers contribute to follow-up observations now that the Hipparcos and Tycho Catalogues are available? Is this an error in one of the parallaxes, or is one of the components itself an astrometric binary whose erratic motion has yielded an incorrect parallax? But one is labelled "51 ly" and the other "44 ly". At the bottom right there is a binary with a common proper motion. There seems to be an error in the Millennium Star Atlas, chart 736. Why does the Millennium Star Atlas show distances in light-years, when the rest of the Hipparcos Catalogue works in milliarcsec and its related reciprocal, the parsec? How do I get more details of objects shown in the Millennium Star Atlas? For example, how do I get the period and other details of the variable objects shown in the Atlas? How about the existence of comparable quality astrometric data in conflict with the Hipparcos results? So what evidence is there that the astrometric data for individual objects are reliable? suggests that the Hipparcos parallaxes might have a systematic error of 1 mas in some areas of the sky, particularly for the Pleiades, which would explain some main sequence fitting discrepancies. Oudmaijer et al.) are revisiting the results using a "proper Lutz-Kelker correction". The distance scale determined from the Hipparcos Cepheid measurements by Feast & Catchpole (1997, MNRAS, 286, L1) gives a distance modulus of the LMC of 18.70+/-0.10. Oudmaijer et al, they state in the Abstract "This statistical effect, the so-called Lutz-Kelker bias, causes measured parallaxes to be too large." And later "We find that there is indeed a large bias affecting parallaxes, with an average and scatter comparable to predictions." Does this mean that all the Hipparcos parallaxes are biased? In a paper published in MNRAS "The Lutz-Kelker bias in trigonometric parallaxes" by R.D. What does the project have to say about that? Are all the Hipparcos parallaxes suspect? Szabados has reported (Hipparcos Venice '97, ESA SP-402, page 657) that undetected orbital motion in Cepheid binaries "falsifies the trigonometric parallax determined from the Hipparcos measurements". Concerning binaries and the effect on parallaxes, L. If I know only a HIP number, how can I find its corresponding TYC entry? Why don't you provide a cross reference that way round? If I know a TYC identifier, I can find its corresponding HIP number (if such a correspondence exists) through Field T31. I've found a couple of cases where the cross-reference given for a HIP star is different to that given for the corresponding TYC star. Why doesn't the Hipparcos website allow interrogation according to various important cross-identifiers: BD, or CD for example? Please explain the catalogues in the context of some other recent catalogues that I've heard about which make use of the Hipparcos and Tycho data, in particular the ACT and the TRC. Who are the Hipparcos and Tycho catalogues named after? (compiled and interpreted by the Project Scientist, unless otherwise indicated)
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