Artist's conception of the Kepler-13AB binary star system as revealed
by observations including the new Gemini Observatory data. The two
stars (A and B) are large, massive bluish stars (center) with the
transiting "hot Jupiter" (Kepler-13b) in the foreground (left corner).
Star B and its low mass red dwarf companion star are seen in the
background to the right. Credit: Gemini Observatory/NSF/AURA/Artwork by Joy Pollard. Download JPG 4.4MB | TIFF 9.3MB
In an unprecedented feat, an American research team discovered hidden
secrets of an elusive exoplanet using a powerful new instrument at the
8-meter Gemini North telescope on Maunakea in Hawai‘i. The findings not
only classify a Jupiter-sized exoplanet in a close binary star system,
but also conclusively demonstrate, for the first time, which star the
planet orbits.
The breakthrough occurred when Steve B. Howell of the NASA Ames
Research Center and his team used a high-resolution imaging instrument
of their design — named ‘Alopeke (a contemporary Hawaiian word for Fox).
The team observed exoplanet Kepler-13b as it passed in front of
(transited) one of the stars in the Kepler-13AB binary star system some
2,000 light years distant. Prior to this attempt, the true nature of the
exoplanet was a mystery.
“There was confusion over Kepler-13b: was it a low-mass star or a hot
Jupiter-like world? So we devised an experiment using the sly
instrument ‘Alopeke,” Howell said. The research was recently published
in the Astronomical Journal.
"We monitored both stars, Kepler A and Kepler B, simultaneously while
looking for any changes in brightness during the planet’s transit,”
Howell explained. “To our pleasure, we not only solved the mystery, but
also opened a window into a new era of exoplanet research.”
“This dual win has elevated the importance of instruments like
‘Alopeke in exoplanet research,” said Chris Davis of the National
Science Foundation, one of Gemini’s sponsoring agencies. “The exquisite
seeing and telescope abilities of Gemini Observatory, as well as the
innovative ‘Alopeke instrument made this discovery possible in merely
four hours of observations."
‘Alopeke performs “speckle imaging,” collecting a thousand
60-millisecond exposures every minute. After processing this large
amount of data, the final images are free of the adverse effects of
atmospheric turbulence — which can bloat, blur, and distort star images.
“About one half of all exoplanets orbit a star residing in a binary
system, yet, until now, we were at a loss to robustly determine which
star hosts the planet,” said Howell.
The team’s analysis revealed a clear drop in the light from Kepler A,
proving that the planet orbits the brighter of the two stars. Moreover,
‘Alopeke simultaneously provides data at both red and blue wavelengths,
an unusual capability for speckle imagers. Comparing the red and blue
data, the researchers were surprised to discover that the dip in the
star’s blue light was about twice as deep as the dip seen in red light.
This can be explained by a hot exoplanet with a very extended
atmosphere, which more effectively blocks the light at blue wavelengths.
Thus, these multi-color speckle observations give a tantalizing glimpse
into the appearance of this distant world.
Early observations once pointed to the transiting object being either
a low-mass star or a brown dwarf (an object somewhere between the
heaviest planets and the lightest stars). But Howell and his team’s
research almost certainly shows the object to be a Jupiter-like
gas-giant exoplanet with a “puffed up” atmosphere due to exposure to the
tremendous radiation from its host star.
'Alopeke has an identical twin at the Gemini South telescope in
Chile, named Zorro, which is the word for fox in Spanish. Like 'Alopeke,
Zorro is capable of speckle imaging in both blue and red wavelengths.
The presence of these instruments in both hemispheres allows Gemini
Observatory to resolve the thousands of exoplanets known to be in
multiple star systems.
"Speckle imaging is experiencing a renaissance with technology like
fast, low noise detectors becoming more easily available," said team
member and ‘Alopeke instrument scientist Andrew Stephens at the Gemini
North telescope. "Combined with Gemini's large primary mirror, ‘Alopeke
has real potential to make even more significant exoplanet discoveries
by adding another dimension to the search."
First proposed by French astronomer Antoine Labeyrie in 1970, speckle
imaging is based on the idea that atmospheric turbulence can be
“frozen” when obtaining very short exposures. In these short exposures,
stars look like collections of little spots, or speckles, where each of
these speckles has the size of the telescope’s optimal limit of
resolution. When taking many exposures, and using a clever mathematical
approach, these speckles can be reconstructed to form the true image of
the source, removing the effect of atmospheric turbulence. The result is
the highest-quality image that a telescope can produce, effectively
obtaining space-based resolution from the ground — making these
instruments superb probes of extrasolar environments that may harbor
planets.
The discovery of planets orbiting other stars has changed the view of our place in the Universe. Space missions like NASA’s Kepler/K2 Space Telescope and the Transiting Exoplanet Survey Satellite (TESS)
have revealed that there are twice as many planets orbiting stars in
the sky than there are stars visible to the unaided eyes; to date the
total discovery count hovers around 4,000. While these telescopes detect
exoplanets by looking for tiny dips in the brightness of a star when a
planet crosses in front of it, they have their limits.
“These missions observe large fields of view containing hundreds of
thousands of stars, so they don’t have the fine spatial resolution
necessary to probe deeper,” Howell said. “One of the major discoveries
of exoplanet research is that about one-half of all exoplanets orbit
stars that reside in binary systems. Making sense of these complex
systems requires technologies that can conduct time sensitive
observations and investigate the finer details with exceptional
clarity.”
“Our work with Kepler-13b stands as a model for future research of
exoplanets in multiple star systems,” Howell continued. “The
observations highlight the ability of high-resolution imaging with
powerful telescopes like Gemini to not only assess which stars with
planets are in binaries, but also robustly determine which of the stars
the exoplanet orbits.”
Source: Gemini Observatory
Media Contacts:
Peter Michaud
Public Information and Outreach Manager
Gemini Observatory, Hilo, HI
email: pmichaud@gemini.edu
Desk: (808) 974-2510
Cell: (808) 936-6643
Alyssa Grace
Public Information and Outreach Assistant
Gemini Observatory, Hilo, HI
email: agrace@gemini.edu
Desk: (808) 974-2531
Science Contacts:
Steve B. Howell
Space Science and Astrobiology Division
NASA Ames Research Center, Moffett Field, CA
email: steve.b.howell@nasa.gov
Desk: (650) 604-4238
Cell: (520) 461-6925
Andrew Stephens
Instrument Scientist
Gemini Observatory, Hilo, HI
email: astephens@gemini.edu
Desk: (808) 974-2611
Peter Michaud
Public Information and Outreach Manager
Gemini Observatory, Hilo, HI
email: pmichaud@gemini.edu
Desk: (808) 974-2510
Cell: (808) 936-6643
Alyssa Grace
Public Information and Outreach Assistant
Gemini Observatory, Hilo, HI
email: agrace@gemini.edu
Desk: (808) 974-2531
Science Contacts:
Steve B. Howell
Space Science and Astrobiology Division
NASA Ames Research Center, Moffett Field, CA
email: steve.b.howell@nasa.gov
Desk: (650) 604-4238
Cell: (520) 461-6925
Andrew Stephens
Instrument Scientist
Gemini Observatory, Hilo, HI
email: astephens@gemini.edu
Desk: (808) 974-2611