Astronomers Confirm the First Image of a Planet Outside of Our SolarSystem (Forwarded)

ESO Education and Public Relations Dept.

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Gael Chauvin
ESO-Santiago
Chile
Phone: +56-2-463-3063
Email:

Ben Zuckerman
UCLA
Los Angeles, USA
Phone: +1-310-8259338
Email:

Anne-Marie Lagrange
LAOG
Grenoble, France
Phone: +33-1-44964377
Email:

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For immediate release: 30 April 2005

ESO Press Release 12/05

Yes, it is the Image of an Exoplanet

Astronomers Confirm the First Image of a Planet Outside of Our Solar
System [1]

Among the most essential quests of modern astronomers, taking direct
images of planets outside of our solar system is certainly up there
among chart-toppers. Obtaining such images of a so-called exoplanet
would enable scientists to study in detail the physical nature of
the object and, in particular, to analyse the composition of its
atmosphere. The astronomers' ultimate goal is of course to perform
such analysis for earth-sized planets, in the hope of detecting a
telltale signature of extraterrestrial life.

Such an ultimate objective is still at least decades in the
future, as earth-size and even Jupiter-size planets around
stars as old as the Sun are too faint to be detected by
present-day technology.

Nevertheless, great progress can be achieved by taking images of
giant planets orbiting much younger objects. Because giant planets a
few tens of millions of years old are much hotter and brighter than
their older brethren, they can be much more easily detected.
Moreover, as the first tens of millions of years are considered to
have been a critical period in the formation of Earth and of our own
solar system, the study of nearby young planetary systems provides
astronomers with invaluable insight on our own origins, something
that is difficult if not impossible to decipher from investigation
of old, mature planetary systems.

ESO PR Photo 14a/05
The Brown Dwarf 2M1207 and its Planetary Companion (VLT/NACO)

Caption: ESO PR Photo 14a/05 The first planet outside of our solar
system to be imaged orbits a brown dwarf (centre-right) at a
distance that is nearly twice as far as Neptune is from the sun.
The photo is based on three near-infrared exposures (in the H, K
and L' wavebands) with the NACO adaptive-optics facility at the
8.2-m VLT Yepun telescope at the ESO Paranal Observatory.

Several surveys are therefore currently in progress that
particularly aim at finding and taking direct images of sub-stellar
companions -- brown dwarfs and exoplanets -- close to very young
objects. Last year, an international team of astronomers [2]
reported the first image of a Giant Planet Companion to 2M1207
(see ESO PR 23/04). On NACO/VLT images obtained in April 2004, they
detected a faint reddish speck of light in the close vicinity of
this young brown dwarf member of the 8 million year old TW Hydrae
Association. The feeble companion, now called 2M1207b, is more than
100 times fainter than the brown dwarf, 2M1207A. The spectrum of
the companion presents the strong signature of water molecules.
Based on the infrared colours and the spectral data, evolutionary
model calculations lead to the conclusion that 2M1207b is a 5
Jupiter-masses planet [3]. Its mass can be estimated also by use
of a different method of analysis which focuses on the strength
of its gravitational field; this technique suggests that the mass
might be even less than 5 Jupiter mass.

In April 2004, the spectroscopic and photometric analysis strongly
indicated a planetary mass object close to the star. An alternative
explanation, that the faint detected object was a background source
unrelated to the young brown dwarf (such as an extragalactic object
or a peculiar cool star with unusual infrared colours), appeared
very unlikely. Observations with the Hubble Space Telescope,
obtained in August 2004 (i.e. only 4 months later), corroborated the
VLT/NACO observations, even though they were obtained too soon after
the NACO ones to provide a definite answer. Additional observations
at a later epoch were required to prove beyond any doubt that the
two objects, 2M1207A and 2M1207b, indeed move together in the sky
and are therefore gravitationally bound to each other.

ESO PR Photo 14b/05
Positions of 2M1207A and of its Companion (VLT/NACO)

Caption: ESO PR Photo 14b/05 shows the relative position of
2M1207b with respect to 2M1207a at three different epochs (April
2004, February and March 2005). The top panel shows the
separation between the two objects in milli-arcseconds, while the
lower one represents the relative angle. The blue line shows the
predicted change in position if the feeble speck of light would
have been a background object. It is clear however that the data
indicate that the two objects move together in the sky, hence are
bound (red line).

Such additional observations have now just been performed by the
same team of European and American astronomers. They used again NACO
on Yepun, the fourth 8.2-m Unit Telescope of ESO's Very Large
Telescope [4]. The team took new images in February and March 2005
and measured the apparent motion on the sky of the young brown
dwarf. For the three different epochs (April 2004, February and
March 2005), they then accurately determined the relative position
of the Giant Planet Companion with respect to the brown dwarf.

These observations show, with high accuracy, that there is no change
in relative position between the two objects. This is exactly what
one expects over a time scale of one year if 2M1207b is
gravitationally bound to its host 2M1207A [5]. Over much longer time
spans, we should see the two objects orbiting around each other.

For Gael Chauvin, astronomer at ESO and leader of the team of
astronomers who conducted the study, "this new set of NACO
measurements unambiguously confirms that 2M1207b is a planetary mass
companion to the young brown dwarf 2M1207A. The image released last
year is thus truly the first image ever taken of a planet outside of
our solar system."

ESO PR Photo 14c/05 ESO PR Video 02/05
Artist's rendering of the The First Image of a Exoplanet
2M1207 System Confirmed

Caption: ESO PR Photo 14c/05 shows an artist's rendering of the
first planet outside of our solar system to be imaged orbiting a
brown dwarf (right). The giant planet is approximately five times
the mass of Jupiter. Both objects are believed to be very young,
less than 10 million years old. The brown dwarf is still
surrounded by a circumstellar disc.

ESO PR Video Clip 02/05 is a small montage providing excerpts of
an interview with Dr. Gael Chauvin (ESO), leader of the team of
astronomers who took the image of the 2M1207 system, as well as a
computer animation of what the system might look like.

"The two objects -- the giant planet and the young brown dwarf --
are moving together; we have observed them for a year, and the new
images essentially confirm our 2004 finding", says Benjamin
Zuckerman, UCLA professor of physics and astronomy, member of NASA's
Astrobiology Institute, and a member of the team. "I'm more than 99
percent confident. This would also be the first time that a planet
outside of our solar system has been detected far from a star or
brown dwarf -- nearly twice as far as the distance between Neptune
and the sun."

"Given the rather unusual properties of the 2M1207 system, the giant
planet most probably did not form like the planets in our solar
system," says Gael Chauvin. "Instead it must have formed the same
way our Sun formed, by a one-step gravitational collapse of a cloud
of gas and dust.

ESO PR Photo 14d/05
The Star AB Pictoris and its Companion (VLT/NACO)

Caption: ESO PR Photo 14d/05 is a coronagraphic image of AB
Pictoris showing its tiny companion (bottom left). The data was
obtained on 16 March 2003 with NACO on the VLT, using a 1.4 arcsec
occulting mask on top of AB Pictoris.

In the course of the same survey, the astronomers also discovered
an interesting companion to the young star AB Pictoris of the 30
million years old Tucana-Horlogium Association located about 150
light years from Earth. This companion, imaged for the first time
in March 2003, has a near-infrared luminosity and spectrum which
points to a light and cool object.

Using the same strategy as for 2M1207b, the astronomers observed the
AB Pic system at different epochs over a time span of a year and a
half and confirmed that the companion is not a background object.
Evolutionary model calculations point to a 13 to 14 Jupiter masses
object with a temperature of ~1700 Kelvin. As the presently accepted
separation between a high mass planet and a low mass brown dwarf is
at 13.6 Jupiter masses [6], the newly discovered companion thus may
lie at the exact boundary between these two classes of sub-stellar
objects. It might therefore play the role of a unique "Rosetta
stone" in the future. Remarkably, this companion is located very
far from its host star -- about 9 times further from AB Pictoris
than Neptune is from the Sun. Nothing like this situation has ever
been seen before in a planetary system.

Recently, a group of German astronomers presented evidence, based on
VLT/NACO data, for a sub-stellar companion to the 1 million year old
star GQ Lup (see ESO PR 09/05). However, the precise nature of this
sub-stellar companion is still unknown as the very young age of the
system makes comparison with theoretical models quite complicated.
It was therefore only possible to assess with certainty that the
close companion to GQ Lup has most probably a mass between 1 and
42 Jupiter-masses, and therefore could be either an exoplanet or a
brown dwarf.

The discovery of 2M1207b, AB Pic b and GQ Lup b/B, all within a
short period of time, bring evidence that new, carefully designed
surveys, using state-of-art instruments on the most advanced
facilities, can provide astronomers with images of planetary
companions.

The first image of an exoplanet may now have been taken and
confirmed and there can be little doubt that others will follow
soon. The detailed study of a growing number of exoplanets with
different masses and orbital properties will provide insight on
theoretical formation models and afford a unique opportunity to
learn more about how the solar system formed, hence about our own
origins.

Anne-Marie Lagrange, another member of the team from the Grenoble
Observatory (France), looks towards the futu "Our discovery
represents a first step towards one of the most important goals
of modern astrophysics: to characterize the physical structure and
chemical composition of giant and, eventually, terrestrial-like
planets."

More information

Read the associated press release at
http://www.eso.org/outreach/press-re.../pr-12-05.html

The result about 2M1207 presented in this ESO Press Release is
described in a Letter to the Editor accepted for publication in
Astronomy and Astrophysics ("Confirmation of a Giant Planet
Companion to the brown dwarf 2MASSWJ1207334-393254" by G. Chauvin
et al.). The work on AB Pictoris will also be published by Astronomy
and Astrophysics ("A light substellar companion to the star HIP
30034" by G. Chauvin et al.)

Notes

[1]: This is a coordinated ESO/UCLA/CNRS Press Release

[2]: The team consists of Gael Chauvin and Christophe Dumas (ESO-
Chile), Anne-Marie Lagrange and Jean-Luc Beuzit (LAOG, Grenoble,
France), Benjamin Zuckerman and Inseok Song (UCLA, Los Angeles,
USA), David Mouillet (LAOMP, Tarbes, France) and Patrick Lowrance
(IPAC, Pasadena, USA).

[3]: 2M1207A and its companion belong to the TW Hydrae association
and are therefore most probably 8 million year old. Evolutionary
model predictions are still uncertain at such young ages and need
to be calibrated, which could modify the nominal mass of the
planet. However, even an implausibly large error of a factor ten
on the predicted flux would still place 2M1207b within the
planetary mass regime.

[4]: NACO is an adaptive optics instrument, which can compensate
for the blurring effect of the atmosphere.

[5]: Due to the estimated period of ~2500 years for 2M1207B, the
orbital motion of the companion around 2M1207A is not expected to
be detected with NACO over only one year. Several decades will be
indeed necessary with NACO. Moreover, due to the accuracy of the
VLT/NACO measurements and the looseness of the young association,
the fact that the two objects are so close and move together on
the sky can only mean they are gravitationally bound.

[6]: The International Astronomical Union has recently adopted a
definition to differentiate giant planets and brown dwarf
companions. The latter are objects with masses above the minimum
mass for deuterium burning (13.6 MJup). Based on this criterion,
2M1207B can be consider as a giant planet companion orbiting a
young brown dwarf.

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