We performed a photometric survey of the star Pictoris and a few
Pictoris-like candidates during a total of about eighteen months from 1995 to 1998,
using the automatic 50 cm Danish telescope atop La Silla Observatory and
its Strömgren uvby photometer.
No star observed during this campaign except HD 38392 and
Pictoris showed any significant
variations. This negative result reveals the quality of the observations
and enforces the reality of the two variations observed.
This also seems to indicate that short and long-term variations for these
Pictoris-like stars
must be exceptional.
In the case of HD 38392, a periodic variation was clearly detected with a period
of 21.4 days, probably related to
the stellar rotation period. Having some activity at its surface, this induces some
weak photometric variations in all
indexes followed in our survey.
Concerning
Pictoris, a new long-term variation has been seen with an increase of the star
brightness starting from January 1996.
These long-term light variations, which could be due to inhomogeneous
distribution of the dust within the disks, are very weak and need several
years of observation to be detected.
It is interesting to recall that the photometric event in November
1981 was observed after such a slow increase of the star brightness
in the preceding years (Lecavelier et al. 1995a).
It thus appears important to continue the photometric survey of this star with
a time coverage as dense as possible.
Acknowledgements
We are grateful to the Copenhagen University Observatory SAT group, led by Jens Viggo Clausen, which supplied preliminary reductions on the daily raw data. We are also very grateful to the observers who spent a lot of time at La Silla Observatory to ensure the successful execution of the SAT program, i.e. J.-P. Beaulieu, Jens Viggo Clausen, Rosa Clément, Frédéric Derue, Bodil E. Helt, Helge Jonch-Sorensen, Bjarne R. Jorgensen, Nadia T. Kaltcheva, Kirsten Kraiberg Knudsen, Soeren Schack Larsen, Cédric Ledoux, Raslan Leguet, Cécile Loup, Jean Mouette, David Mouillet, Anton Norup Soerensen and Lambertus Leonardus Vos.
On the other hand, we would like to thank Bernard Nicolet, Noël Cramer and Gilbert Burki, from Geneva Observatory, who provided us with many photometric data on the Geneva system.
Last, but not least, we are also grateful to Paula Sartoretti who gave us very useful help during the 1996-1997 campaign, and J. Bouvier for his very fruitful comments on the paper.
Copyright The European Southern Observatory (ESO)