average luminosity that
moves in and out of view
as the dwarf rotates. They
suggest that a magnetic
starspot could provide
such cooler material, although they also consider
the possibility of clouds in
the atmosphere (similar to
Jupiter’s Great Red Spot),
which could also produce
the same effect.
Given their spectral characteristics, which include
broadening of emission lines and a bluer
or hotter continuum, the strong flares observed with Gemini (Figure 1) also have a
magnetic origin. In contrast to the quiescent
characteristic temperature of 2300 K, the
flare corresponds to a temperature of 8000
K. These results show a continuity of flare
properties from the higher-mass M dwarfs
to the L class. They also confirm W1906+40
as a magnetically active brown dwarf, despite the attribution of variability observed
in some L dwarfs due to atmospheric variations, such as changing cloud distributions.
Complete results are in press in The Astrophysical Journal; a preprint is available at
arXiv 1310.5940.
Spiral Patterns in
a Protoplanetary Disk
Spiral patterns measured in a protoplanetary disk offer an exemplary study aimed
at accounting for the full process of planet
formation. Planets are expected to form in
the remains surrounding the formation of
a star, called a protoplanetary disk. The star
HD 100546 is an excellent candidate for such
a detailed investigation, being young (age
5-10 million years), and showing excess infrared emission, which is characteristic of a
dusty — potentially planet-forming — disk.
January2014
The disk, which extends from the central star
to distances of 80 times that between the
Earth and Sun, has previously been resolved
and some of its spiral patterns identified. In
new work using archival observations obtained with the Near-Infrared Coronographic Imager on the Gemini South telescope,
Anthony Boccaletti (Observatoire de Paris,
France) and collaborators show additional
detail of the spiral patterns in HD 100546
and uncover hints of a planet that may be
responsible for producing them.
Special data processing techniques of angular differential imaging reveal the subtle details of the spirals in the near-infrared, resolving the southern feature into multiple arms,
and provide contrast
at the level of 10-5 to
10-6 at distances of
1 and 2 arcseconds
from the star, respectively (Figure 2). The
team models these
arms and concludes
that
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