OGLE-2007-BLG-349
Astronomers using NASA's Hubble Space Telescope, and a trick of
nature, have confirmed the existence of a planet orbiting two stars in
the system OGLE-2007-BLG-349, located 8,000 light-years away towards the
center of our galaxy.
The planet orbits roughly 300 million miles from the stellar duo,
about the distance from the asteroid belt to our sun. It completes an
orbit around both stars roughly every seven years. The two red dwarf
stars are a mere 7 million miles apart, or 14 times the diameter of the
moon's orbit around Earth.
The Hubble observations represent the first time such a three-body
system has been confirmed using the gravitational microlensing
technique. Gravitational microlensing occurs when the gravity of a
foreground star bends and amplifies the light of a background star that
momentarily aligns with it. The particular character of the light
magnification can reveal clues to the nature of the foreground star and
any associated planets.
The three objects were discovered in 2007 by an international
collaboration of five different groups: Microlensing Observations in
Astrophysics (MOA), the Optical Gravitational Lensing Experiment
(OGLE), the Microlensing Follow-up Network (MicroFUN), the Probing
Lensing Anomalies Network (PLANET), and the Robonet Collaboration.
These ground-based observations uncovered a star and a planet, but a
detailed analysis also revealed a third body that astronomers could not
definitively identify.
"The ground-based observations suggested two possible scenarios for
the three-body system: a Saturn-mass planet orbiting a close binary
star pair or a Saturn-mass and an Earth-mass planet orbiting a single
star," explained David Bennett of the NASA Goddard Space Flight Center
in Greenbelt, Maryland, the paper's first author.
The sharpness of the Hubble images allowed the research team to
separate the background source star and the lensing star from their
neighbors in the very crowded star field. The Hubble observations
revealed that the starlight from the foreground lens system was too
faint to be a single star, but it had the brightness expected for two
closely orbiting red dwarf stars, which are fainter and less massive
than our sun. "So, the model with two stars and one planet is the only
one consistent with the Hubble data," Bennett said.
Bennett's team conducted the follow-up observations with Hubble's
Wide Field Planetary Camera 2. "We were helped in the analysis by the
almost perfect alignment of the foreground binary stars with the
background star, which greatly magnified the light and allowed us to
see the signal of the two stars," Bennett explained.
Kepler has discovered 10 other planets orbiting tight binary stars,
but these are all much closer to their stars than the one studied by
Hubble.
Now that the team has shown that microlensing can successfully detect
planets orbiting double-star systems, Hubble could provide an
essential role in this new realm in the continued search for
exoplanets.
The team's results have been accepted for publication in The Astronomical Journal.
Contact:
Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
David Bennett
NASA Goddard Space Flight Center in Greenbelt, Maryland
301-286-5473 (office) / 574-315-6621 (cell)
david.p.bennett@nasa.gov
Source : HubbleSite
