Using advanced imaging techniques and the special capabilities of the
Gemini Planet Imager (GPI) the light from β Pictoris has been suppressed
in these images using GPI’s Y, J, H, K1 and K2 filters. The arrow
indicates the location of the exoplanet β Pictoris b in all but the left
image.
Using the Gemini Planet Imager (GPI), a team of astronomers led by J.
Chilcote (University of Toronto) found that the low mass stellar
companion β Pictoris b is about 13 times more massive than Jupiter with a
surface temperature of about 1720 K. While these parameters are in good
agreement with earlier observations, they allow better comparisons with
planetary evolution models. The Gemini data indicate that β Pictoris b
best matches an exoplanet with an atmosphere like that of a low-surface
gravity (L21) brown dwarf.
Observations at the Gemini South telescope in Chile, using the Gemini
Planet Imager (GPI), are refining our understanding of the β Pictoris
system. The system contains the ~ 13 Jupiter mass companion β Pictoris b
which is at the mass boundary sometimes used to distinguish between an
exoplanet and a brown dwarf. Brown dwarfs are objects that are not
massive enough for sustained nuclear reactions. Brown dwarfs less
massive than 13 Jupiters cannot even start a nuclear reaction.
Based on the GPI data, combined with planetary evolution and atmospheric models, Chilcote suggests a “hot-start” planet formation scenario for β Pictoris b. He adds, “This is consistent with the disk instability formation mechanism for wide-orbit giant exoplanets.” However, the characteristics for the atmosphere of β Pictoris b found in this work best match those of low-surface gravity brown dwarfs, not planets.
The team studied β Pictoris b during the verification and commissioning
of the Gemini Planet Imager and as part of an astrometric (position)
monitoring program designed to constrain the orbit of the exoplanet.
This work is also part of a Gemini Large and Long Program.
“With GPI the Gemini Observatory is at the forefront of exoplanet
exploration,” said Chilcote. He adds, “Direct imaging allows for the
discovery of planets on solar systems-scale orbits, provides new insight
into the formation and characteristics of extrasolar systems, and
enable direct spectroscopic observations of their atmospheres.”
Since the first detection of an exoplanet in 1995 (51 Pegasi b) the
discovery and characterization of extrasolar planets has changed the
understanding of planetary systems and their formation. Over the past
two decades, more than 3400 of planetary systems with stars of various
masses and at different stages of evolution have been detected. Some of
these planetary systems present features very similar to our solar
system. The current challenge for astronomers is to better characterize
these planets, especially the exoplanet atmospheres which can give us
information about the history of formation of the planets.
The full results are accepted for publication in The Astrophysical Journal Letters. A preprint is available here.
Abstract:
Using the Gemini Planet Imager (GPI) located at Gemini South, we
measured the near-infrared (1.0– 2.4 µm) spectrum of the planetary
companion to the nearby, young star β Pictoris. We compare the spectrum
obtained with currently published model grids and with known substellar
objects and present the best matching models as well as the best
matching observed objects. Comparing the empirical measurement of the
bolometric luminosity to evolutionary models, we find a mass of 12.9 ±
0.2MJup, an effective temperature of 1724 ± 15 K, a radius of 1.46 ± 0.01 RJup,
and a surface gravity of log g = 4.18 ± 0.01 [dex] (cgs). The stated
uncertainties are statistical errors only, and do not incorporate any
uncertainty on the evolutionary models. Using atmospheric models, we
find an effective temperature of 1700 − 1800 K and a surface gravity of
log g = 3.5–4.0 [dex] depending upon model. These values agree well with
other publications and with “hot-start” predictions from planetary
evolution models. Further, we find that the spectrum of β Pic b best
matches a low-surface gravity L2 ± 1 brown dwarf. Finally comparing the
spectrum to field brown dwarfs we find the the spectrum best matches
2MASS J04062677–381210 and 2MASS J03552337+1133437.
Source: Gemini Observatory