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