Nancy A. Levenson
Science Highlights
The following summaries highlight several recent papers based on
Gemini data. Included is the detection of a possible (proto)planet
around a nearby star, a new limit on the binary nature of cool Y dwarfs,
the downsizing of a once extreme black hole, and the detection of an
ultraviolet wind expelled by a quasar at nearly 20% the speed of light.
Traces of Planet Formation in a Stellar Disk
Planets form in the disks around young stars, and the relatively nearby TW Hydrae is an excellent candidate in which to observe this process. In polarimetric observations with the
Gemini Planet Imager (GPI) on the Gemini South telescope, Valerie Rapson (Rochester Institute of Technology, New York) and collaborators probe the disk of TW Hya — from about 80
astronomical units (AU) to within 10 AU of the central star — at a resolution of about 1.5 AU
and detect structure. The observations show a gap located around 23 AU that is about 5 AU
wide, suggesting the presence of a forming planet (Figure 1).
The researchers deduce the properties
of the possible (proto)planet comparing with simulations. They find good
agreement with a planet of mass 0.16
MJupiter located at 21 AU from the star,
about the distance of Uranus from the
Sun. Details of the differences between
the model and observations suggest
that more complex distributions of
dust in the disk (radially and vertically)
may be relevant. The authors acknowledge other processes that can create
gaps and rings, such as grain fragmentation and ice condensation fronts. A
definitive test would be to observe the
April 2016
GeminiFocus
Figure 1.
Radially scaled
polarized intensity
in the J-band shows
the variation of dust
density distribution in
the disk of TW Hydrae.
The coronagraph blocks
light in the central
region. Comparison
with simulations
suggests that the gap
around 23 AU could be
cleared by a planet of
mass about 0.2 MJupiter.
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