This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1\22 ESO - Distant World in Peril Discovered from La Silla- ALMA- AVO
Part 2 of 3

A planet around HD 47536
------------------------
ESO PR Photo 05b/03              ESO PR Photo 05c/03
Preview - JPEG: 400 x 462 pix    Preview - JPEG: 400 x 433 pix
- 68k                            - 112k
Normal - JPEG: 800 x 924 pix -   Normal - JPEG: 800 x 866 pix
- 360k                           - 256k

ESO PR Photo 05d/03           Captions: PR Photo 05b/03 shows a
                              sky area of 10 x 10 arcmin2 around
                              the 6th-magnitude giant star HD
                              47536 which a new exoplanet has been
Preview - JPEG: 477 x 400 pix found (reproduced from the Digital
- 96k                         Sky Survey [STScI Digitized Sky
Normal - JPEG: 953 x 800 pix  Survey, (C) 1993, 1994, AURA, Inc.
-272k                         all rights reserved - cf.
                              http://archive.eso.org/dss/dss]).
                              The pattern is caused by internal
                              reflections in the telescope from
                              this relatively bright object. PR
                              Photo 05c/03 displays the "velocity
                              curve" of HD 47536, caused by the
                              pull of the orbiting planet during
                              the 712-day period (abscissa: Julian
                              Date - 2,400,000; ordinate: velocity
                              in kilometres per second along the
                              line-of-sight). Error bars indicate
                              the accuracy of the measurements.
                              The fully-drawn curve is the
                              computed velocity curve,
                              corresponding to the best-fitting
                              planetary orbit. The lower part of
                              the diagram displays the deviation of
                              the measurements from this curve - in
                              the mean about 0.025 km/sec, or 25
                              m/sec. In PR Photo 05d/03, the
                              distribution of the distances of the
                              100+ known exoplanets is shown, with
                              the planet around HD 47536 at the
                              extreme end.

The extensive observations began three years ago, with the main aim to 
pin down the cause(s) for any possible long-term variations. For this 
programme to succeed, it was also necessary to monitor other 
properties of these stars, in particular more rapid changes in the 
upper atmosphere ("stellar activity").

The first results indicate that about 70% of these stars display
velocity variations. Among them, the 6th-magnitude star HD 47536 in 
the southern constellation of Canis Major (The Great Dog) soon caught 
the eye of the observers, as the measured velocity variations strongly 
indicated the presence of a planetary companion. The same FEROS 
spectra also show that other possible explanations, including stellar 
activity, are very unlikely to be responsible for those variations.

At a distance of 396 light-years, the new exoplanet is the second-most
remote one found to date. It moves around HD 47536 in a slightly 
elongated orbit and one revolution lasts almost exactly two Earth 
years (712 days).  Depending on the mass of the star (which is not 
well known yet), the distance of the planet from the star is somewhere 
between 240 and 337 million km (the mean distance of planet Mars to 
the Sun is 228 million km) and the new planet has between 4.9 and 9.7 
times the mass of planet Jupiter (for assumed stellar mass 1.1 and 3.0 
times that of the Sun, respectively).  The indicated planetary mass is 
in any case too small for this object to be a "failed star", it is a 
bona-fide planet.

Implications
------------
"We are very excited about this discovery", says Luca Pasquini of ESO,
"because it now widens the search for exoplanets towards more massive 
stars.  The observational problem is that most massive stars rotate 
very rapidly during the first phase of the lives. This makes accurate 
measurements of minute velocity variations caused by the gravitaional 
pull of accompanying planets virtually impossible. However, in the 
later phase of their lives when they become giants, they slow down 
considerably and we then have a much better chance of detecting 
possible exoplanets in orbit around them."

The giant planet in orbit around HD 47536 is now most probably 
witnessing some of those dramatic events that will happen to the Earth 
some billions of years from now. Its central star is slowly but 
steadily expanding and occupies a progressively larger fraction of the 
sky above the planet. The insolation is becoming more and more 
intense, with the resulting atmospheric effects - rising temperature 
and violent winds. Some tens of millions of years from now, the 
unlucky planet is doomed to lose its gaseous layers entirely and the 
surface will become burning hot.

The discovery has other interesting implications. For years, the 
present team of astronomers has been studying certain giant stars that 
are found to contain much lithium. However, this light element is 
rapidly consumed in such stars and it should really not be there, see 
also ESO PR 10/01.

"No problem now", says team member Licio da Silva from the 
Observatorio Nacional in Rio de Janeiro (Brazil), "one obvious 
possibility is that those stars have obtained their lithium by 
recently swallowing a nearby planet.  But until recently, this 
hypothesis was considered rather exotic, because of the lack of 
evidence of planets in danger". Indeed, with this discovery of a giant 
planet near a giant star, that explanation is looking quite plausible.

Perspectives
------------
With over 70 other giant stars still under close scrutiny, the 
perspectives for the present programme appear very promising. The 
present discovery comes at a moment when the team is working hard to 
sift through the many observational data - it is quite possible that 
they will find other giant stars with planet-induced velocity 
variations.

At the same time, the observational means for this kind of research 
are getting ever more powerful. Soon, the HARPS very high-precision 
spectrometer will be installed at the ESO 3.6-m telescope on La Silla. 
It has been built by the Geneva Observatory in collaboration with ESO 
and will be dedicated to the search for exoplanets.

More information
----------------
The information presented in this Press Release is based on a research
article ("Evidence of a Sub-Stellar Companion around HD 47536" by
Johny Setiawan et al.) that will soon appear as a Letter to the Editor
in the European research journal "Astronomy & Astrophysics" (Vol. 398
No. 2, p. L19 - February 2003).

Notes

[1]: The only known exoplanet that is farther away is that just found 
around the dwarf star OGLE-TR-56b. Until now, four exoplanets are 
known in orbits around giant stars, the present one around HD 47536 
and others around HD 27442, iota Draconis and gamma Cephei. With a 
diameter of about 33 million km (i.e., 23.5 times that of the Sun), HD 
47536 is by far the largest of these stars (the three others have 
diameters smaller than 20 million km).

[2]: The team consists of Johny Setiawan and Oskar von der Luehe
(Kiepenheuer-Institut fuer Sonnenphysik, Freiburg (Breisgau), 
Germany), Artie Hatzes (Thueringer Landessternwarte, Tautenburg, 
Germany), Luca Pasquini (ESO, Garching, Germany), Dominique Naef, 
Didier Queloz and Stephane Udry (Observatoire de Geneve, Switzerland), 
Licio da Silva (Observatorio Nacional, Rio de Janeiro, Brazil) and Leo 
Girardi (Osservatorio Astronomico di Trieste, Italy).

(continued)

---