Subaru exchange time, along with the SuperNova Integral Field Spectrograph at the
University of Hawai‘i 88-inch telescope, also
on Mauna Kea. They targeted nearby galaxies, where 1 arcsecond typically corresponds
to 230 light-years (70 parsecs), to distinguish
the progenitor star clusters. The data show
that other nearby clusters display a somewhat different history and metallicity from
the supernova site (Figure 8). These results
are published in The Astronomical Journal,
and in a separate paper. The team applies
identical techniques to the host environments of Type II supernovae.
Resolving a Stellar Disk at
Earth-Sun Distance Scales
Planets in the disks around young stars may
carve gaps or dynamically affect their environment. These so-called transitional and
pre-transitional disks are therefore interesting as important stages in the development
of planets. An international team led by
Stefan Kraus (Harvard-Smithsonian Center
for Astrophysics) used multiple telescopes,
including Gemini South, to resolve the disk
around V1247 Orionis on physical scales of
astronomical units (AU; the average EarthSun distance), finding asymmetries and unambiguous evidence for a gap in the disk.
The observations included an uncommon
use of Gemini’s Thermal Region Camera
Spectrograph (T-ReCS) for mid-infrared (MIR)
imaging, using short exposures and interferometric analysis techniques to determine
the disk orientation and geometry. Considering longer-baseline MIR interferometry in
addition, a compact disk is evident, extending over 0.2 AU. The inferred structure (Figure 9), based on the full set of observations,
shows a hot inner disk, a cool outer disk, and
optically thin carbon-rich dust in the gap between them. The emission in the gap region
appears to be asymmetric, and the dependence on observed wavelength implies that
this is due to density inhomogeneities, rather than the
presence of a single
body like a planet.
The persistence of
the hot inner disk,
with material located at the dust sublimation radius (corresponding to the
hottest temperature
where it can survive), rules out some
proposed methods
of clearing gaps in similar planetary disks, including photoevaporation, instabilities, and
grain growth. Instead, the authors conclude
that dynamical clearing of the gap, due to
developing planetary or other companions,
is the most likely origin. Other well-studied
transitional and pre-transitional disks do not
show evidence for such optically thin material close to the star, which suggests that
V1247 Orionis may show us an earlier stage
of development. The complete results are
published in The Astrophysical Journal.
Figure 9.
Model of the
environment of V1247
Orionis includes a hot
optically thick inner
disk, a cool optically
thick outer disk, and
optically thin dust in the
gap between them.
Gemini NICI Planet-finding
Campaign
Astronomers have evidence for hundreds
of planets around stars beyond the Sun, but
only a handful are observed in direct imaging. The planets are intrinsically faint, and
detecting them near their bright host stars
adds to the challenges. The Near-Infrared Coronagraphic Imager (NICI) at Gemini South is
capable of imaging faint extrasolar planets,
reaching greater sensitivity than previous
ground- or space-based instruments. (NICI
can detect an object one million times fainter than its bright host at a projected separation of 1 arcsecond; about one two thousandth of the Moon’s apparent diameter.)
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