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Astron. Astrophys. 328, 544-550 (1997)

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Microvariability survey with the Hubble Space Telescope Fine Guidance Sensors

Exploring the instrumental properties * **

small.htm R. Kuschnig 1, W.W. Weiss 1, R. Gruber 1, P.Y. Bely 2 and H. Jenkner *** 2

1 Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17 A-1180 Vienna, Austria (last_name@galileo.ast.univie.ac.at)
2 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA (last_name@stsci.edu)

Received 21 October 1996 / Accepted 7 March 1997

Abstract

The suitability of the Hubble Space Telescope (HST) Fine Guidance Sensors (FGS) for a magnitude limited survey of microvariability among guide stars is investigated. The linearity, relative sensitivity, and dead-time constants of the three FGSs are determined, and the photon noise limitation of the FGS photometry is confirmed. The noise spectrum is found to be "white" and a procedure is described which provides an estimate of the mean noise amplitude for any guide star observation. We derive a criterion, given a specific probability, to predict an upper limit for peaks in the amplitude spectrum of time series.

We give examples for constant, known variable, and new variable guide stars, and illustrate that our FGS noise model will permit the automatic detection of microvariability within our survey of HST data. Presently, the lowest noise level found in FGS data obtained between November 1992 and December 1993 is 200 ppm, but better data by an order of magnitude are expected to be obtainable during the life-time of HST.

Key words: instruments: Hubble Space Telescope – HST Fine Guidance Sensors – stars: activity – oscillations – variables

* Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
** Also based on observations obtained with the 1.5 m Danish Telescope at ESO, La Silla.
*** On assignment from the Astrophysics Division, Space Science Department, European Space Agency.

Send offprint requests to: Rainer Kuschnig

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998

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