The ESO microvariability Key Program and the detection of extrasolar planets and brown dwarfs

Abstract

A few months ago the European Southern Observatory, La Silla, Chile, approved a proposal for a “Key Program” called “Microvariability of Bright Stars.” This project pretends to monitor several thousands of bright stars (V≤6^m) by means of photoelectric photometery with a fully-automatic 50-cm telescope using one broadband filter (Johnson V). One thousand stars per night will be observed with an accuracy of ±0^m003; each star will be measured each night at least once. The main aim is to search in a large, unbiased sample of stars of all spectral types and luminosities for variations with amplitudes ≥0^m01 and time scales of ≥ one day.

As a by-product, this project includes the possibility to detect large planets and brown dwarfs by means of eclipses. Constraints on size and number of detected planets are given, taking into account the relative radii of planets and stars, the separation, inclination and periods of planetary orbits, as well as the expected eclipse durations and amplitudes. The photometric accuracy implies that the planetary radii must be of the order of 10% of the stellar radius; i.e., we refer to Jupiter-sized and larger bodies. Only planets around main-sequence stars will be detectable, not those of giants and supergiants. If a total of about 2000 main sequence stars are monitored each night during one year (or every n^th night during n years), we expect statistically one eclipse event if all stars would have planets at an orbital distance of about 400 stellar radii (a ≈ 2.0 AU); 10 eclipse events if all stars would have planets at a distance of 130 R. (a ≈ 0.6 AU); and 100 eclipse events if all stars would have planets at a distance of 40 R. (a ≈ 0.2 AU). Statistically relevant information can only be obtained for those types of planetary systems for which a considerable number of events is expected if they are frequent. Therefore, the rate of occurrence of systems with giant planets and brown dwarfs (or upper limits for this rate) will be determined for orbital distances smaller than 100 stellar radii (about 0.5 AU) in a statisically complete manner.