Figure 1. GPI imaging of the planetary system HR 8799 in K band, showing
3 of the 4 planets. (Planet b is outside the field of view shown here,
off to the left.) These data were obtained on November 17, 2013 during
the first week of operation of GPI and in relatively challenging weather
conditions, but with GPI’s advanced adaptive optics system and
coronagraph the planets can still be clearly seen and their spectra
measured (see Figure 2). Image credit: Christian Marois (NRC Canada), Patrick Ingraham (Stanford University) and the GPI Team. Full-resolution image
Figure 2. GPI spectroscopy of planets c and d in the HR 8799 system.
While earlier work showed that the planets have similar overall
brightness and colors, these newly-measured spectra show surprisingly
large differences. The spectrum of planet d increases smoothly from
1.9-2.2 microns while planet c’s spectrum shows a sharper kink upwards
just beyond 2 microns. These new GPI results indicate that these
similar-mass and equal-age planets nonetheless have significant
differences in atmospheric properties, for in-stance more open spaces
between patchy cloud cover on planet c versus uniform cloud cover on
planet d, or perhaps differences in atmospheric chemistry. These data
are helping refine and improve a new generation of atmospheric models to
explain these effects. Image credit: Patrick Ingraham (Stanford
University), Mark Marley (NASA Ames), Didier Saumon (Los Alamos National
Laboratory) and the GPI Team. Full-resolution image
Figure 3. GPI imaging polarimetry of the circumstellar disk around HR
4796A, a ring of dust and planetesimals similar in some ways to a scaled
up version of the solar system’s Kuiper Belt. These GPI observations
reveal a complex pattern of variations in brightness and polarization
around the HR 4796A disk. The western side (tilted closer to the Earth)
appears brighter in polarized light, while in total intensity the
eastern side appears slightly brighter, particularly just to the east of
the widest apparent separation points of the disk. Reconciling this
complex and apparently-contradictory pattern of brighter and darker
regions required a major overhaul of our understanding of this
circumstellar disk. Image credit: Marshall Perrin (Space Telescope
Science Institute), Gaspard Duchene (UC Berkeley), Max Millar-Blanchaer
(University of Toronto), and the GPI Team. Full-resolution image
Figure 4. Diagram depicting the GPI team's revised model for the
orientation and composition of the HR 4796A ring. To explain the
observed polarization levels, the disk must consist of relatively large
(> 5 µm) silicate dust particles, which scatter light most strongly
and polarize it more for forward scattering. To explain the relative
faintness of the east side in total intensity, the disk must be dense
enough to be slightly opaque, comparable to Saturn’s optically thick
rings, such that on the near side of the disk our view of its brightly
illuminated inner portion is partially obscured. This revised model
requires the disk to be much narrower and flatter than expected, and
poses a new challenge for theories of disk dynamics to explain. GPI’s
high contrast imaging and polarimetry capabilities together were
essential for this new synthesis. Image credit: Marshall Perrin (Space Telescope Science Institute). Full-resolution image
Stunning exoplanet images and spectra from the first year of science
operations with the Gemini Planet Imager (GPI) were featured today in a
press conference at the 225th meeting of the American Astronomical
Society (AAS) in Seattle, Washington. The Gemini Planet Imager GPI is an
advanced instrument designed to observe the environments close to
bright stars to detect and study Jupiter-like exoplanets (planets around
other stars) and see protostellar material (disk, rings) that might be
lurking next to the star.
Marshall Perrin (Space Telescope Science Institute), one of the
instrument’s team leaders, presented a pair of recent and promising
results at the press conference. He revealed some of the most detailed
images and spectra ever of the multiple planet system HR 8799. His
presentation also included never-seen details in the dusty ring of the
young star HR 4796A. “GPI’s advanced imaging capabilities have delivered
exquisite images and data,” said Perrin. “These improved views are
helping us piece together what’s going on around these stars, yet also
posing many new questions.”
The GPI spectra obtained for two of the planetary members of the HR 8799
system presents a challenge for astronomers. GPI team member Patrick
Ingraham (Stanford University), lead the paper on HR 8799. Ingraham
reports that the shape of the spectra for the two planets differ more
profoundly than expected based on their similar colors, indicating
significant differences between the companions. “Current atmospheric
models of exoplanets cannot fully explain the subtle differences in
color that GPI has revealed. We infer that it may be differences in the
coverage of the clouds or their composition.” Ingraham adds, "The fact
that GPI was able to extract new knowledge from these planets on the
first commissioning run in such a short amount of time, and in
conditions that it was not even designed to work, is a real testament to
how revolutionary GPI will be to the field of exoplanets."
Perrin, who is working to understand the dusty ring around the young
star HR 4796A, said that the new GPI data present an unprecedented level
of detail in studies of the ring’s polarized light. “GPI not only sees
the disk more clearly than previous instruments, it can also measure how
polarized its light appears, which has proven crucial in under-standing
its physical properties.” Specifically, the GPI measurements of the
ring show it must be partially opaque, implying it is far denser and
more tightly compressed than similar dust found in the outskirts of our
own Solar System, which is more diffuse. The ring circling HR 4796A is
about twice the diameter of the planetary orbits in our Solar System and
its star about twice our Sun’s mass. “These data taken during GPI
commissioning show how exquisitely well its polarization mode works for
studying disks. Such observations are critical in advancing our
understanding of all types and sizes of planetary systems – and
ultimately how unique our own solar system might be,” said Perrin.
During the commissioning phase, the GPI team observed a variety of
targets, ranging from asteroids in our solar system, to an old star near
its death. Other teams of scientists have been using GPI as well and
already astronomers around the world have published eight papers in
peer-reviewed journals using GPI data. “This might be the most
productive new instrument Gemini has ever had,” said Professor James
Graham of the University of California, who leads the GPI science team
and who will describe the GPI exoplanet survey (see below) in a talk
scheduled at the AAS meeting on Thursday, January 8th.
The Gemini Observatory staff integrated the complex instrument into the
telescope’s software and helped to characterize GPI’s performance. “Even
though it’s so complicated, GPI now operates almost automatically,”
said Gemini’s instrument scientist for GPI Fredrik Rantakyro. “This
allows us to start routine science operations.” The instrument is now
available to astronomers and their proposals are scheduled to start
ob-serving in early 2015. In addition, “shared risk” observations are
already underway, starting in November 2014.
The one thing GPI hasn’t done yet is discovered a new planet. “For the
early tests, we concentrated on known planets or disks” said GPI PI
Bruce Macintosh. Now that GPI is fully operational, the search for new
planets has begun. In addition to observations by astronomers
world-wide, the Gemini Planet Imager Exoplanet Survey (GPIES) will look
at 600 carefully selected stars over the next few years. GPI ‘sees’
planets through the infrared light they emit when they’re young, so the
GPIES team has assembled a list of the youngest and closest stars. So
far the team has observed 50 stars, and analysis of the data is ongoing.
Discovering a planet requires confirmation observations to distinguish a
true planet orbiting the target star from a distant star that happens
to sneak into GPI’s field of view - a process that could take years with
previous instruments. The GPIES team found one such object in their
first survey run, but GPI observations were sensitive enough to almost
immediately rule it out. Macintosh said, “With GPI, we can tell almost
instantly that something isn’t a planet – rather than months of
uncertainty, we can get over our disappointment almost immediately. Now
it’s time to find some real planets!”
About GPI/GPIES
The Gemini Planet Imager (GPI) instrument was constructed by an
international collaboration led by Lawrence Livermore National
Laboratory under Gemini’s supervision. The GPI Exoplanet Survey (GPIES)
is the core science program to be carried out with it. GPIES is led by
Bruce Macintosh, now a professor at Stanford University and James
Graham, professor at the University of California at Berkeley and is
designed to find young, Jupiter-like exoplanets. They survey will
observe 600 young nearby stars in 890 hours over three years. Targets
have been carefully selected by team members at Arizona State
University, the University of Georgia, and UCLA. The core of the data
processing architecture is led by Marshall Perrin of the Space Telescope
Science Institute, with the core software originally written by
University of Montreal, data management infrastructure from UC Berkeley
and Cornell University, and contributions from all the other team
institutions. The SETI institute located in California manages GPIES’s
communications and public out-reach. Several teams located at the Dunlap
Institute, the University of Western Ontario, the University of
Chicago, the Lowell Observatory, NASA Ames, the American Museum of
Natural History, University of Arizona and the University of California
at San Diego and at Santa Cruz also contribute to the survey. The GPI
Exoplanet Survey is supported by the NASA Origins Program NNX14AG80, the
NSF AAG pro-gram, and grants from other institutions including the
University of California Office of the President. Dropbox Inc. has
generously provided storage space for the entire survey's archive.
Media Contacts:
-
Peter Michaud
Public Information and Outreach Manager
Gemini Observatory, Hilo, HI
Email: pmichaud@gemini.edu
Cell: (808) 936-6643
Desk: (808) 974-2510
Science Contacts:
- Marshall Perrin
STScI
Email: mperrin@stsci.edu
Phone: (410) 507-5483
- James R. Graham
University of California Berkeley
Email: jrg@berkeley.edu
Cell: (510) 926-9820
Source: Gemini Observatory
