The Dwarf that Carries a World (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 1 Dec 2005 12:27:10 -0500 (EST)
ESO Education and Public Relations Dept.
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Text with all links and the photos are available on the ESO
Website at URL:
http://www.eso.org/outreach/press-rel/pr-2005/pr-30-05.html
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Contacts
Xavier Delfosse
LAOG, France
Phone: +33 (0) 476 63 55 10
Stéphane Udry
Geneva Observatory, Switzerland
Phone: +41 22 755 26 11
For immediate release: 30 November 2005
ESO Press Release 30/05
The Dwarf that Carries a World
HARPS Instrument Finds Neptune-Mass Exoplanet Around Small Star
A team of French and Swiss astronomers [1] have discovered
one of the lightest exoplanets ever found using the HARPS
instrument [2] on ESO's 3.6-m telescope at La Silla (Chile).
The new planet orbits a star belonging to the class of red
dwarfs. As these stars are very common, this discovery proves
crucial in the census of other planetary systems.
"Our finding possibly means that planets are rather frequent
around the smallest stars," says Xavier Delfosse, from the
Laboratoire d'Astrophysique de Grenoble (France) and co-author
of the paper relating the work. "It certainly tells us that
red dwarfs are ideal targets for the search for exoplanets."
The host star, Gl 581 [3], is located 20.5 light-years away
in the Libra constellation (The Scales), and has a mass of
only one third the mass of the Sun. Such red dwarfs are at
least 50 times fainter than the Sun and are the most common
stars in our Galaxy: among the 100 closest stars to the Sun,
80 belong to this class.
Being so numerous in our vicinity, it is thus fundamental to
know if such stars also harbour planets. Previous surveys
were rather unsuccessful: observations of about 200 red
dwarfs revealed only 2 with planets.
"But previous surveys may have missed many planets due to
their insufficient precision," says Stéphane Udry, from the
Geneva Observatory and co-author of the work. "This is why
we decided to make use of the ultra-precise, second
generation, HARPS spectrograph. Our new result indicates
this was the right strategy."
ESO PR Photo 37/05
Radial Velocity Curve of Gliese 581 (HARPS/3.6m)
Caption: ESO PR Photo 37/05 shows the radial velocities of
the red dwarf Gl 581 as a function of the orbital phase.
The amplitude of the detected variation is 13.2 m/s and
the curve is consistent with a circular orbit. The orbital
period is 5.366 days.
The newly found planet is about 17 times the Earth's mass,
or about the mass of Neptune. It is therefore one of the
smallest ever found [4]. It is rather close to its host
star and completes a full circle in only 5.4 days: the mean
distance is about 6 million kilometres. By comparison,
Mercury, the closest planet to the Sun, is at a distance of
58 million kilometres and completes an orbit in 88 days.
Being so close, this alien world must be very hot, about
150 degrees.
The planet was revealed by the wobble it induces on the
host star. With the HARPS very precise measurements, the
astronomers found the star to move back and forth with a
maximum velocity of 13 metres/second, or a little bit less
than 50 km/h.
The astronomers have published their results in a Letter to
the Editor of Astronomy and Astrophysics ("The HARPS search
for southern extra-solar planets. VI. A Neptune-mass planet
around the nearby M dwarf Gl 518", by X. Bonfils et al.,
A&A 443, L15, 2005).
Notes
[1]: The team is composed of Xavier Bonfils (Laboratoire
d'Astrophysique de Grenoble (LAOG), France, and Geneva
Observatory, Switzerland), Thierry Forveille (CFHT Corporation,
Hawaii, USA and LAOG), Xavier Delfosse and Christian Perrier
(LAOG), Stéphane Udry, Michel Mayor, Francesco Pepe, and
Didier Queloz (Geneva Observatory), François Bouchy
(Laboratoire d'Astrophysique de Marseille, France), and
Jean-Louis Bertaux (Service d'Aéronomie du CNRS, France).
[2]: HARPS (High Accuracy Radial Velocity for Planetary
Searches) is the most precise spectrograph to date, measuring
radial velocities with a precision better than 1 m/s, or 3.6
km/h.
[3]: Gl 581, or Gliese 581, is the 581th entry in the Gliese
Catalogue, which lists all known stars within 25 parsecs
(81.5 light years) of the Sun. It was originally compiled by
Gliese and published in 1969, and later updated by Gliese
and Jahreiss in 1991.
[4]: Of the 170 exoplanets known today, 5 are possibly less
massive than the one orbiting Gl 581: Gliese 876d (7.3 Earth's
masses, or 7.3 ME), HD 160691 d (14 ME), 55 Cnc e (14.4 ME),
HD 212301 b (14.4 ME) and HD 4308 b (15 ME). The masses
indicated are in fact minimum masses, as the inclination of
the system is unknown. One Jupiter mass is 18.6 Neptune
masses or 319 Earth masses.
The INSU-CNRS has also issued a press release in French.
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Terhi Loukiainen, +358 9 7748 8385
Denmark: Dr. Michael Linden-Vørnle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Prof. Massimo Capaccioli, +39-081-55 75 511
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
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