1932

Abstract

Eight extrasolar planet candidates have now been identified, all revealed by Keplerian Doppler shifts in their host stars. The masses ( sin ) lie between 0.5 and 7 M, and the semimajor axes are less than 2.1 astronomical units (AU). Doppler detectability favors high masses and small orbits, and improvements will render Saturn masses detectable within a few years. The substellar mass function (d/d) for companions is roughly flat from 70 down to 10 M, but it exhibits a sharp increase for masses below 5 M. For three of these companions (47 UMa, ρ Crb, and 55 Cnc), their circular orbits must be primordial (not tidally induced), indicating formation in a disk, as presumed for Solar System planets. Eccentric orbits may be explained by gravitational perturbations, either by companion stars, other planets, or disk resonances. The detections imply that ∼6% of solar-type stars have giant planets within 2 AU. The small orbits ( < 2 AU) imply that the planets formed either in situ, without the benefit of ice grains, or suffered inward migration. Orbital decay within 1 Myr in disks appears inevitable and may shape the planet mass distribution. The observed stability of spectral line shapes suggests that nonradial stellar oscillations do not affect the planet detections.

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/content/journals/10.1146/annurev.astro.36.1.57
1998-09-01
2024-03-28
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  • Article Type: Review Article
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