Andrew Yee[_1_]
July 11th 07, 05:18 PM
ESO Education and Public Relations Dept.
----------------------------------------------------------------------------
Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/public/outreach/press-rel/pr-2007/pr-29-07.html
----------------------------------------------------------------------------
Contacts:
Luca Pasquini
ESO Garching, Germany
Phone: +49 89 3200 6792
Artie Hatzes
Thuringer Landessternwarte Tautenburg, Germany
Phone: +49-36427-863-51
For Immediate Release: 6 July 2007
ESO Science Release 29/07
Star Surface Polluted by Planetary Debris
Looking at the chemical composition of stars that host planets, astronomers
have found that while dwarf stars often show iron enrichment on their
surface, giant stars do not. The astronomers think that the planetary debris
falling onto the outer layer of the star produces a detectable effect in a
dwarf star, but this pollution is diluted by the giant star and mixed into
its interior.
"It is a little bit like a Tiramisu or a Capuccino," says Luca Pasquini from
ESO, lead-author of the paper reporting the results. "There is cocoa powder
only on the top!"
Just a few years after the discovery of the first exoplanet it became
evident that planets are preferentially found around stars that are enriched
in iron. Planet-hosting stars are on average almost twice as rich in metals
than their counterparts with no planetary system.
The immediate question is whether this richness in metals enhances planet
formation, or whether it is caused by the presence of planets. The classic
chicken and egg problem. In the first case, the stars would be metal-rich
down to their centre. In the second case, debris from the planetary system
would have polluted the star and only the external layers would be affected
by this pollution.
When observing stars and taking spectra, astronomers indeed only see the
outer layers and can't make sure the whole star has the same composition.
When planetary debris fall onto a star, the material will stay in the outer
parts, polluting it and leaving traces in the spectra taken.
A team of astronomers has decided to tackle this question by looking at a
different kind of stars: red giants. These are stars that, as will the Sun
in several billion years, have exhausted the hydrogen in their core. As a
result, they have puffed up, becoming much larger and cooler.
Looking at the distribution of metals in fourteen planet-hosting giants, the
astronomers found that their distribution was rather different from normal
planet-hosting stars.
"We find that evolved stars are not enriched in metals, even when hosting
planets," says Pasquini. "Thus, the anomalies found in planet-hosting stars
seem to disappear when they get older and puff up!"
Looking at the various options, the astronomers conclude that the most
likely explanation lies in the difference in the structure between red
giants and solar-like stars: the size of the convective zone, the region
where all the gas is completely mixed. In the Sun, this convective zone
comprises only 2% of the star's mass. But in red giants, the convective zone
is huge, encompassing 35 times more mass. The polluting material would thus
be 35 times more diluted in a red giant than in a solar-like star.
"Although the interpretation of the data is not straightforward, the
simplest explanation is that solar-like stars appear metal-rich because of
the pollution of their atmospheres," says co-author Artie Hatzes, Director
of the Thuringer Landessternwarte Tautenburg (Germany) where some of the data
were obtained.
When the star was still surrounded by a proto-planetary disc, material
enriched in more heavy elements would fall onto the star, thereby polluting
its surface. The metal excess produced by this pollution, while visible in
the thin atmospheres of solar-like stars, is completely diluted in the
extended, massive atmospheres of the giants.
More Information
"Evolved stars hint to an external origin of enhanced metallicity in
planet-hosting stars", by L. Pasquini et al. To appear in Astronomy and
Astrophysics. The paper is available on astro-ph at
http://arxiv.org/abs/0707.0788
The team is composed of L. Pasquini and M.P. Dlinger (ESO), A. Weiss
(Max-Planck-Institut fur Astrophysik, Garching, Germany), L. Girardi
(INAF-Osservatorio Astronomico di Padova, Italy), C. Chavero (Instituto de
Astrofisica de Canarias, Tenerife, Spain, and Observatorio Nacional/MCT, Rio
de Janeiro, Brasil), A. P. Hatzes (Thinger Landessternwarte Tautenburg,
Germany), L. da Silva (Observatorio Nacional/MCT, Rio de Janeiro, Brasil),
and J. Setiawan (Max Planck Institute f Astronomie, Heidelberg, Germany).
The data have been partially collected at ESO, and partially at the 2-m
telescope of the Thuringer Landessternwarte Tautenburg (TLS).
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Czech Republic: Pavel Suchan, +420 267 103 040
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vornle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Spain: Dr. Miguel Mas-Hesse, +34918131196
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
----------------------------------------------------------------------------
ESO Press Information is available on Receive email notification
the WWW at about important news from
http://www.eso.org/outreach/press-rel/ ESO - subscribe to the
ESO-NEWS Mailing List.
----------------------------------------------------------------------------
Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
----------------------------------------------------------------------------
----------------------------------------------------------------------------
Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/public/outreach/press-rel/pr-2007/pr-29-07.html
----------------------------------------------------------------------------
Contacts:
Luca Pasquini
ESO Garching, Germany
Phone: +49 89 3200 6792
Artie Hatzes
Thuringer Landessternwarte Tautenburg, Germany
Phone: +49-36427-863-51
For Immediate Release: 6 July 2007
ESO Science Release 29/07
Star Surface Polluted by Planetary Debris
Looking at the chemical composition of stars that host planets, astronomers
have found that while dwarf stars often show iron enrichment on their
surface, giant stars do not. The astronomers think that the planetary debris
falling onto the outer layer of the star produces a detectable effect in a
dwarf star, but this pollution is diluted by the giant star and mixed into
its interior.
"It is a little bit like a Tiramisu or a Capuccino," says Luca Pasquini from
ESO, lead-author of the paper reporting the results. "There is cocoa powder
only on the top!"
Just a few years after the discovery of the first exoplanet it became
evident that planets are preferentially found around stars that are enriched
in iron. Planet-hosting stars are on average almost twice as rich in metals
than their counterparts with no planetary system.
The immediate question is whether this richness in metals enhances planet
formation, or whether it is caused by the presence of planets. The classic
chicken and egg problem. In the first case, the stars would be metal-rich
down to their centre. In the second case, debris from the planetary system
would have polluted the star and only the external layers would be affected
by this pollution.
When observing stars and taking spectra, astronomers indeed only see the
outer layers and can't make sure the whole star has the same composition.
When planetary debris fall onto a star, the material will stay in the outer
parts, polluting it and leaving traces in the spectra taken.
A team of astronomers has decided to tackle this question by looking at a
different kind of stars: red giants. These are stars that, as will the Sun
in several billion years, have exhausted the hydrogen in their core. As a
result, they have puffed up, becoming much larger and cooler.
Looking at the distribution of metals in fourteen planet-hosting giants, the
astronomers found that their distribution was rather different from normal
planet-hosting stars.
"We find that evolved stars are not enriched in metals, even when hosting
planets," says Pasquini. "Thus, the anomalies found in planet-hosting stars
seem to disappear when they get older and puff up!"
Looking at the various options, the astronomers conclude that the most
likely explanation lies in the difference in the structure between red
giants and solar-like stars: the size of the convective zone, the region
where all the gas is completely mixed. In the Sun, this convective zone
comprises only 2% of the star's mass. But in red giants, the convective zone
is huge, encompassing 35 times more mass. The polluting material would thus
be 35 times more diluted in a red giant than in a solar-like star.
"Although the interpretation of the data is not straightforward, the
simplest explanation is that solar-like stars appear metal-rich because of
the pollution of their atmospheres," says co-author Artie Hatzes, Director
of the Thuringer Landessternwarte Tautenburg (Germany) where some of the data
were obtained.
When the star was still surrounded by a proto-planetary disc, material
enriched in more heavy elements would fall onto the star, thereby polluting
its surface. The metal excess produced by this pollution, while visible in
the thin atmospheres of solar-like stars, is completely diluted in the
extended, massive atmospheres of the giants.
More Information
"Evolved stars hint to an external origin of enhanced metallicity in
planet-hosting stars", by L. Pasquini et al. To appear in Astronomy and
Astrophysics. The paper is available on astro-ph at
http://arxiv.org/abs/0707.0788
The team is composed of L. Pasquini and M.P. Dlinger (ESO), A. Weiss
(Max-Planck-Institut fur Astrophysik, Garching, Germany), L. Girardi
(INAF-Osservatorio Astronomico di Padova, Italy), C. Chavero (Instituto de
Astrofisica de Canarias, Tenerife, Spain, and Observatorio Nacional/MCT, Rio
de Janeiro, Brasil), A. P. Hatzes (Thinger Landessternwarte Tautenburg,
Germany), L. da Silva (Observatorio Nacional/MCT, Rio de Janeiro, Brasil),
and J. Setiawan (Max Planck Institute f Astronomie, Heidelberg, Germany).
The data have been partially collected at ESO, and partially at the 2-m
telescope of the Thuringer Landessternwarte Tautenburg (TLS).
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Czech Republic: Pavel Suchan, +420 267 103 040
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vornle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Spain: Dr. Miguel Mas-Hesse, +34918131196
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
----------------------------------------------------------------------------
ESO Press Information is available on Receive email notification
the WWW at about important news from
http://www.eso.org/outreach/press-rel/ ESO - subscribe to the
ESO-NEWS Mailing List.
----------------------------------------------------------------------------
Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
----------------------------------------------------------------------------