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The HIPPARCOS Mission: a New Era for Variable Star Astronomy

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M. Grenon

Observatoire de Genève, 1290 Sauverny, Switzerland

L. Eyer

Observatoire de Genève, 1290 Sauverny, Switzerland; current affiliation: Princeton University, Princeton, NJ

Abstract
Initially planned as a pure astrometric mission, HipparcoS was optimized to produce the highest achievable photometric accuracy in the Hp broad- band and in the Tycho B T and VT bands. A complex calibration process allowed for coping with the rapid change of the optics and for fixing the magnitude scale to better than 0.001 magnitude throughout the mission.

The time series accumulated allowed the classification of all 118,204 program stars as constant, suspect or variable. 2,712 stars were found as periodic, with well defined periods and amplitudes, and 5,544 as non-periodic with a wild range of behaviors. 3,300 variables are new discoveries. The rest of the stars could be demonstrated as constant or microvariable. For the very first time, the distribution of the variability across the Hr diagram may be described quantitatively.

The contribution of the AAVSO to the success of the space mission is recalled and the results of the joint HIPPARCOS-AAVSO observations are presented.

Some of the old and new variables require additional observations from the ground, either visual, with photometers, or with CCDs. After Hipparcos, revisions of current observing programs on variable stars seem necessary. Suggestions for a follow-up of HIPPARCOS mission by amateur and professional astronomers are made.

Link to article on ADS [5]