cludes a black hole and stars results in an upper limit on black hole mass of 150 MSun. Thus,
although M71 presents the opportunity for
high-resolution measurements, it does not
appear to hold an intermediate-mass black
hole in its core.
Figure 4 .
Visibility amplitude
as a function
of baseline for
observations at 8.74
microns. The thick
solid line shows the
model prediction, for
the basic model (A,
top) and including
the additional
hot, optically
thick component
attributed to a
companion (B,
bottom). The thin
solid line represents
the contribution of
the central star, the
dotted line shows
the optically thin
disk, and the dashed
line represents
the optically thick
disk emission. The
insets show the
Gemini data and
corresponding
model.
Physically, the team interprets this component
as a self-luminous companion. Modeled as a
single object, it would be located 3.5 AU from
the star. Given the age of the system of about
10 million years, the companion’s modeled luminosity implies a mass of 8-10 MJupiter. A single
object would mean an asymmetric emission
distribution. Further analysis shows that the
observations are consistent with asymmetry,
with the largest expected at 8.74 mm, but the
asymmetry is not a significant requirement.
A Self-Luminous Companion
to TW Hydrae
Variable star TW Hydrae exhibits an important and nearby example of a transitional disk,
the state between a pre-main sequence star,
which is embedded in its natal cocoon, and an
evolved planetary system. Now, Timothy Arnold (Steward Observatory, University of Arizona) and colleagues have used novel mid-infrared observations with the Thermal Region
Camera and Spectrograph (T-ReCS) on Gemini
South to find tentative evidence for a planetary companion within the disk of TW Hya.
This result builds on previous analyses, which
had already suggested that the disk has a gap
23
(based on the spectral energy distribution;
SED), and which measure the extent of the
disk at millimeter wavelengths to approximately 100 astronomical units (AU). The model presented here begins with an optically thin
disk and optically thick emission located at
3.9 AU (which could be the illuminated face
of a flared optically thick disk) in addition to
the central star. While these components sufficiently account for the current SED, which
includes new observations at 8.74, 11.7, and
18.3 microns (mm), they cannot account for
the very well-resolved emission in the shortest
bandpass (Figure 4). The required addition is
an optically thick component inside the thick
disk that is hotter than equilibrium temperature at that distance from the star.
GeminiFocus
These conclusions are based on the novel approach of speckle imaging with T-ReCS. The
exposure times of individual recorded frames
are extremely very short (around 170 milliseconds) to achieve diffraction-limited images,
avoiding the atmospheric blurring that arises
on longer timescales. With this approach, Fourier techniques are employed to analyze the
data fully (T. Arnold et al., The Astrophysical
Journal, 750: 119, 2012).
This work offers significant possible evidence
for the presence of a planet in a transitional
disk system. Planet formation may generally
contribute to the ev