The last two years have witnessed the first detections of extra-solar planets. Following the discovery of a planet near 51 Peg by Mayor & Queloz (1995) and similar results for 47 UMa, 70 Vir and HD 114762, the discovery of 3 new cases was announced by Butler et al. (1997). Among these stars is Cnc (HR 3522, HD 75732). Cnc is a solar-type star with spectral class G8V, slightly metal-rich, at a distance of 12.5 pc. Its age inferred from CaII H and K fluxes is 5 Gyr (Baliunas et al. 1997). According to Butler et al. (1997), the planet near Cnc has a period of 14.65 days implying a semi major axis of 0.11 AU. The inferred mass is . This is one of the 51 Pegasi-like "hot Jupiter" planets. The Doppler velocity of the primary also exhibits a long term trend consistent with a second, as yet unconfirmed companion ( yr, ). Cnc is also a resolved double star with an M5 dwarf companion (HD 75732B, ) at a distance of approximately 1150 AU from the primary.
In 1983 IRAS detected infrared excess from several main-sequence stars, e.g. Vega, Pic, Formalhaut. This excess was attributed to a disk of dust around the star, which was later confirmed dramatically in the case of Pic by the observation of scattered light from the disk. Subsequent analysis of the IRAS data base showed that this phenomenon was widely spread among main-sequence stars (Aumann et al. 1984 , Aumann 1985). The detection of planets around other main sequence stars raised the question whether planets and Vega-like disks can exist together. Unfortunately, the star Cnc was not on any target list for ISO. We therefore applied for discretionary time which was subsequently granted. ISOPHOT measurements were obtained only a few days before the star disappeared from ISO's visibility zone.
© European Southern Observatory (ESO) 1998
Online publication: December 16, 1997