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.
Figure 2.
NICI observation of HD
100546 in the Ks band,
processed to reveal
multiple southern spiral
arms (left), which are
modeled (colored lines
overlaid, right).
monitoring with Kepler shows a regular
brightness variation at the 1 percent level
with a period of 8.9 hours. The team models this variability as the presence of a single
“spot” of lower-than-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
Figure 3.
Zooming in to the
star’s central 3
arcseconds shows a
candidate planet to
the south, which may
be responsible for
producing the spiral
arms. (The spot marked
to the north of the
star is an artifact of
processing).
28
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.
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
GeminiFocus 2013 Year in Review
January2014