Network of Small Telescopes Discovers Distant Planet Orbiting Another Star

http://www.lowell.edu/press_room/rel...rES-1_rls.html

For Immediate Release

Lowell Observatory
August 24, 2004

This is a joint announcement from the Astrophysical Institute of the
Canaries (IAC), National Center for Atmospheric Research (NCAR),
Harvard-Smithsonian Center for Astrophysics (CfA), Lowell Observatory,
and California Institute of Technology.

Note to Editors: High-resolution artwork and animation of the newly
discovered planet TrES-1 is posted online at
http://www.lowell.edu/press_room/TrES-1_images.html

Network of Small Telescopes Discovers Distant Planet

Flagstaff, AZ - Fifteen years ago, the largest telescopes in the world had
yet to locate a planet orbiting another star. Today telescopes no larger
than those available in department stores are proving capable of
spotting previously unknown worlds. A newfound planet detected by a
small, 4-inch-diameter telescope demonstrates that we are at the cusp of
a new age of planet discovery. Soon, new worlds may be located at an
accelerating pace, bringing the detection of the first Earth-sized world
one step closer.

"This discovery demonstrates that even humble telescopes can make huge
contributions to planet searches," says Guillermo Torres of the
Harvard-Smithsonian Center for Astrophysics (CfA), a co-author on the
study.

This is the first extrasolar planet discovery made by a dedicated survey
of many thousands of relatively bright stars in large regions of the
sky. It was made using the Trans-Atlantic Exoplanet Survey (TrES), a
network of small, relatively inexpensive telescopes designed to look
specifically for planets orbiting bright stars. A team of scientists
co-led by Edward Dunham of Lowell Observatory, Timothy Brown of NCAR,
and David Charbonneau (CfA), developed the TrES network. The network's
telescopes are located in Palomar Observatory (California, USA), Lowell
Observatory (Arizona, USA), and the Canary Islands (Spain).

"The advantage of working as a network is that we can 'stretch the
night' and monitor our fields for a longer time, increasing our chance
of discovering a planet," says Georgi Mandushev (Lowell Observatory), a
co-author of the paper.

This research study will be posted online at
http://arxiv.org/abs/astro-ph/0408421 and will appear in an upcoming
issue of The Astrophysical Journal Letters.

"It took several Ph.D. scientists working full-time to develop the data
analysis methods for this search program, but the equipment itself uses
simple, off-the-shelf components," says co-author David Charbonneau
(CfA/Caltech).

Although the small telescopes of the TrES network made the initial
discovery, follow-up observations at other facilities were required.
Observations at the W. M. Keck Observatory which operates the world's
two largest telescopes in Hawaii for the University of California,
Caltech, and NASA, were particularly crucial in confirming the planet's
existence.

Planet Shadows

The newfound planet is a Jupiter-sized gas giant orbiting a star located
about 500 light years from the Earth in the constellation Lyra. This
world circles its star every 3.03 days at a distance of only 4 million
miles (6 million kilometers), much closer and faster than the planet
Mercury in our solar system.

Although such planets are relatively common, astronomers used an
uncommon technique to discover it. This world was found by the "transit
method," which looks for a dip in a star's brightness when a planet
crosses directly in front of the star and casts a shadow. A
Jupiter-sized planet blocks only about 1/100th of the light from a
Sun-like star, but that is enough to make it detectable.

"This Jupiter-sized planet was observed doing the same thing that
happened in June when Venus moved across (or transited) the face of our
Sun," says Mandushev. "The difference is that this planet is outside our
solar system, roughly 500 light years away."

To be successful, transit searches must examine many stars because we
only see a transit if a planetary system is located nearly edge-on to
our line of sight. A number of different transit searches currently are
underway. Most examine limited areas of the sky and focus on fainter
stars because they are more common, thereby increasing the chances of
finding a transiting system. However the TrES network concentrates on
searching brighter stars in larger swaths of the sky because planets
orbiting bright stars are easier to study directly.

"All that we have to work with is the light that comes from the star,"
says Tim Brown (NCAR), a study co-author. "It's much harder to learn
anything when the stars are faint."

Most known extrasolar planets were found using the "Doppler method,"
which detects a planet's gravitational effect on its star by looking for
shifts in the star's spectrum, or rainbow of colors. However, the
information that can be gleaned about a planet using the Doppler method
is limited. For example, only a lower limit to the mass can be
determined because the angle at which we view the system is unknown. A
high-mass brown dwarf whose orbit is highly inclined to our line of
sight produces the same signal as a low-mass planet that is nearly edge-on.

"When astronomers find a transiting planet, we know that its orbit is
essentially edge-on, so we can calculate its exact mass. From the amount
of light it blocks, we learn its physical size. In one instance, we've
even been able to detect and study a giant planet's atmosphere," says
Charbonneau.

Sorting Suspects

The TrES survey examined approximately 12,000 stars in 36 square degrees
of the sky (about half of the size of the bowl of the Big Dipper) in the
constellation of Lyra. Roi Alonso (IAC), a graduate student of Brown's,
identified 16 possible candidates for planet transits. "The TrES survey
gave us our initial line-up of suspects. Then, we had to make a lot of
follow-up observations to eliminate the imposters," says co-author
Alessandro Sozzetti (University of Pittsburgh/CfA).

After compiling the list of candidates in late April, the researchers
used telescopes at CfA's Whipple Observatory in Arizona, Oak Ridge
Observatory in Massachusetts, and Lowell Observatory in Arizona to
obtain additional photometric (brightness) observations, as well as
spectroscopic observations that eliminated eclipsing binary stars.

In a matter of two month's time, the team had zeroed in on the most
promising candidate. High-resolution spectroscopic observations by
Torres and Sozzetti using time provided by NASA on the 10-meter-diameter
Keck I telescope in Hawaii clinched the case.

"Without this follow-up work the photometric surveys can't tell which of
their candidates are actually planets. The proof of the pudding is a
spectroscopic orbit for the parent star. That's why the Keck
observations of this star were so important in proving that we had found
a true planetary system," says co-author David Latham (CfA).

Remarkably Normal

The planet, called TrES-1, is much like Jupiter in mass and size. It is
likely to be a gas giant composed primarily of hydrogen and helium, the
most common elements in the Universe. But unlike Jupiter, it orbits very
close to its star, giving it a temperature of around 1500 degrees F.

Astronomers are particularly interested in TrES-1 because its structure
agrees so well with theory, in contrast to the first discovered
transiting planet, HD 209458b. The latter world contains about the same
mass as TrES-1, yet is around 30% larger in size. Even its proximity to
its star and the accompanying heat don't explain such a large size.

"Finding TrES-1 and seeing how normal it is makes us suspect that HD
209458b is an 'oddball' planet," says Charbonneau.

TrES-1 orbits its star every 72 hours, placing it among a group of
similar planets known as "hot Jupiters." Such worlds likely formed much
further away from their stars and then migrated inward, sweeping away
any other planets in the process. The many planetary systems found to
contain hot Jupiters indicate that our solar system may be unusual for
its relatively quiet history.

Both the close orbit of TrES-1 and its migration history make it
unlikely to possess any moons or rings. Nevertheless, astronomers will
continue to examine this system closely because precise photometric
observations may detect moons or rings if they exist. In addition,
detailed spectroscopic observations may give clues to the presence and
composition of the planet's atmosphere.

The paper, "TrES-1: The Transiting Planet of a Bright K0V Star,"
descibing these results is authored by: Roi Alonso (IAC); Timothy M.
Brown (NCAR); Guillermo Torres and David W. Latham (CfA); Alessandro
Sozzetti (University of Pittsburgh/CfA); Georgi Mandushev (Lowell
Observatory), Juan A. Belmonte (IAC); David Charbonneau (CfA/Caltech);
Hans J. Deeg (IAC); Edward W. Dunham (Lowell Observatory); Francis T.
O'Donovan (Caltech); and Robert Stefanik (CfA).

The W.M. Keck Observatory is operated by the California Association for
Research in Astronomy, a scientific partnership of the California
Institute of Technology, the University of California, and the National
Aeronautics and Space Administration (NASA).

Funding for the research that led to this planet's discovery was
provided by NASA's Origins of Solar Systems Program.

Founded in 1894, Lowell Observatory pursues the study of astronomy,
conducts pure research in astronomical phenomena, and maintains quality
public education and outreach programs.

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contact: Steele Wotkyns
Public Relations Manager
(928) 233-3232

www.lowell.edu

For additional information:
This research study, "TrES-1: The Transiting Planet of a Bright K0V
Star," will be posted online at http://arxiv.org/abs/astro-ph/0408421
and will appear in an
upcoming issue of The Astrophysical Journal Letters.
High-resolution artwork and animation of the newly discovered planet
TrES-1 is online at
http://www.lowell.edu/press_room/TrES-1_images.html

Harvard-Smithsonian Center for Astrophysics press release
http://cfa-www.harvard.edu/ep/pressrel.html

National Center for Atmospheric Research press release
http://www.ucar.edu/news/releases/

Astrophysical Institute of the Canaries press release
http://www.iac.es/gabinete/noticias/noticias.htm