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From: TEICHMANN Elisabeth <Elisabeth.Teichmann@obs.unige.ch>

14 Herculis : A NEW EXTRASOLAR PLANET DISCOVERED AT THE HAUTE PROVENCE OBSERVATORY


In 1995 the discovery of a planet in orbit around the star 51 Pegasi, an almost perfect twin of our Sun, astonished astronomers. A very strange planet with a period as short as 4.23 days. This first discovery has subsequently been followed by a fascinating series of new discoveries: planets with quite diverse orbits, with periods ranging from 3.3 days to 1100 days, sometimes of circular shape, sometimes very elongated. These discoveries have revealed to astrophysicists the broad diversity of planetary systems around other stars. If our own planetary system has giant planets only in its most remote external regions, this is far from being the general rule.

Let us describe our recent discovery:

A GIANT PLANET WITH A LONG PERIOD

14 Herculis (Gliese 614) is a star somewhat less massive than our Sun (its mass is only 80% that of our Sun) and lies at a distance of 60 light-years as derived from the very precise HIPPARCOS astrometric satellite parallax. We have carefully measured 14 Herculis since 1994 at the Haute-Provence Observatory. These measurements have been done with the ELODIE spectrograph mounted on the 1.93 meter telescope. This summer, after more than four years of monitoring, the planet has completed its revolution around 14 Herculis. This planet has a slightly elongated orbit of 4.4 years. Its mass is about 3.3 times that of Jupiter and it is at a distance of 2.5 AU (1 AU is the Earth-Sun distance) from 14 Her.

This is the planetary orbit with the longest period among the presently discovered extrasolar planets. Nevertheless, this giant planet is still twice as close to 14 Her as Jupiter is to our Sun.

Take a look at a finding chart made with Starry Night showing the location of the star in the constellation Hercules.

Radial velocity curve for 14 Herculis obtained from observations made with the Elodie spectrograph.

This long-period planet, orbiting a nearby star, is a very promising candidate for direct imaging. The longer the period, the larger the separation between the planet and the parent star, therefore the easier it becomes to distinguish the feeble glow of the planet near the bright glare of the star. The predicted separation between the planet and 14 Her is 0.14 arcsec, sufficient to make us try its detection with the adaptive optics system of the CFHT 3.60m at the summit of Mauna Kea in Hawaii. Despite the high quality of the images obtained no companion could be detected: we are not dealing with a star or a brown dwarf orbiting in a plane almost perpendicular to the line-of-sight, but with a planet indeed. We will have to wait for the future availability of new instruments to obtain an image of the planet.

The content in heavy chemical elements of 14 Her is rather large compared to that of the Sun. This discovery reinforces the suggestion that giant planets are more frequently observed around metal-rich stars. Heavy chemical elements are needed to form dust or ice particles, and then by agglomeration, planetesimals and the cores of giant planets. If the quantity of dust is large enough, this is certainly a factor in favor of the formation of giant planets.


This planet has been discovered at the Haute-Provence Observatory (France) by a team of astronomers from Switzerland and France (Michel Mayor (1), Didier Queloz (1,2), Jean-Luc Beuzit (3), Jean-Marie Mariotti (4), Dominique Naef (1), Christian Perrier (5), Jean-Pierre Sivan (6)).

(1) Geneva Observatory, Switzerland
(2) JPL, Los Angeles, USA
(3) CFHT, Hawaii, USA
(4) ESO, Munich, Germany
(5) Grenoble Observatory, France
(6) Haute-Provence Observatory, France

L'annonce de la decouverte de cette nouvelle planete sera faite le 6 juillet 1998 lors de la conference "Protostars and Planets" qui aura lieu a Santa-Barbara, Californie du 6 au 10 juillet 1998.