The M.A.S. Newsletter

Journal of the Mauritius Astronomical Society

May 2000 (Memo)

Dear Member,

After inquiring with the staff at the Mauritius Radio Telescope (MRT), we have to postpone the visit to the MRT. The visit is now scheduled for Thursday 10th of August. We shall meet in front of the gate of St Esprit College in Quatre Bornes at 19:00. In case you are coming for the visit, could you please inform us at one of the phone numbers listed below. We would also like to know if you have your own mean of transport. If yes, how many free places do you have?

CONTACT:

If there too few members interested, the visit will be cancelled.

Thanking you for your cooperation. The coming meeting will therefore be a general observation night.

Best regards. Some news...

European Astronomers Discover up to eight Extrasolar Planets:

A team of Swiss Astronomers that includes the duo who discovered the first planet around a Sun-like star announced earlier this month the discovery of up to eight more such worlds.

Michel Mayor and colleagues from the Geneva Observatory in Switzerland used a telescope in Chile to locate the worlds. Six of the eight appear to be gas giant planets, while the other two are more likely heavier brown dwarfs.

The astronomers found the planets with the widely-used radial velocity technique, where astronomers monitor changes in the wavelength of well-known spectral lines. Those changes are caused by a Doppler shift as the star wobbles under the gravitational influence of an orbiting planet: measuring the magnitude and period of those changes allows astronomers to determine the orbital period, distance, and minimum mass of the planet.

The discoveries bring to at least 40 the number of extrasolar planets around Sun-like stars discovered, a number that was zero until Mayor and Didier Queloz discovered a gas giant closely orbiting the star 51 Pegasi in the fall of 1995.

"The present discoveries complete and enlarge our still preliminary knowledge of extra-solar planetary systems, as well as the transition between planets and 'brown dwarfs'," said Mayor. The smallest of the new planets orbits the star HD 168746 140 light-years from Earth. It has a mass just 80% that of Saturn (24 percent the mass of Jupiter) and completes one orbit around the star every 6.4 days. Only two other extrasolar planets, discovered in March by veteran planet hunters Geoff Marcy and Paul Butler, have equal or smaller masses.

Two other planets are nearly as small. The planets orbiting HD 83443, 141 light-years away, is 1.17 times the mass of Saturn (0.35 times the mass of Jupiter) and completes an orbit in just under 3 days. The planet orbiting HD 108147 is similar, with a mass 1.15 times that of Saturn (O.34 that of Jupiter), but is in an eccentric orbit with a period of 10.88 days.

Three other new planets are somewhat more massive than Jupiter, and in more distant, eccentric orbits than the smaller worlds. HD 52265 hosts a planet 1.07 times the mass of Jupiter with a 119-day orbit. HD 82943 has a planet 2.2 times as massive as Jupiter in a 443-day orbit, and HD 169830 has a planet 2.96 times the mass of Juptter In a 230-day orbit.

Two other bodies discovered by Mayor and colleagues appear to be too massive to be planets, and lie in a poorly-understood transition region between planets and more massive brown dwarfs.

One with 13.7 times the mass of Jupiter, orbits HD 162020 in a 8.4-day orbit, while another, 14.7 times as massive as Jupiter, orbits HD 202206 in an eccentric 259-day orbit.

One of the two planets just slightly heavier than Saturn may prove to be the most interesting of the bunch. The data from HD 83443 shows evidence of a "drift" in the velocity data that may he evidence of a second planet orbiting the star, although additional observations will be needed to confirm this.

Mayor's group made the discovery using CORALIE, a high-precision spectrometer mounted on the 1.2-meter (47-inch) LeonhardEuler telescope at the European Southern Observatory's facility in La Silla, Chile. An even better spectrograph under developrnent, known as HARPS, will allow astronomers do detect planets as small as 10 times the mass of the Earth.

Serge Florens, Secretary

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