is common. The inner ring of DoAr 44
may be replenished by material from the
outer disk, accounting for the large water
content it maintains compared with similar objects. Alternatively, planets may affect the chemistry in this region where
terrestrial planets develop.
The warm (450 K) water arises in the inner ring, appearing in emission at mid-infrared wavelengths (Figure 7). The data were
obtained at a spectral resolution R ~ 80,000
using the Texas Echelon Cross Echelle Spectrograph (TEXES), a visitor instrument on the
Gemini North telescope. Colette Salyk (National Optical Astronomy Observatory and
Vassar College) and collaborators used the
kinematic characteristics of the spectrally
resolved emission to determine the location
of its origin, at 0.3 AU. Avoiding destruction
of water molecules in this region close to
the stellar source requires material in the region — either gas or dust — as protection
against the star’s strong radiation. The paper
appears in The Astrophysical Journal Letters,
volume 810, page L24.
The eccentric structure of the emitting disk
is consistent with the system being shaped
by planets like those in our Solar System,
at similar distances from the parent star.
Many previously discovered systems have
required unusual planets — super-sized
Jupiters far from the disk’s center — to create the observed structures. GPI’s excellent
resolution and contrast allow probing more
distant Sun-like systems than previously
possible. GPI provides spectra along with
the images, and the results are consistent
with a significant water ice component. The
complete work has been published in The
Astrophysical Journal Letters, volume 807,
page L7.
July 2015
Continuum-subtracted
TEXES spectrum (black)
and dominant “hot”
model fit (blue), which
yields the temperature
(450 K) and location
(0.3 AU) of the
emitting water vapor.
A “warm” component
(red) is required to
account for additional
measurements at longer
wavelengths. The sum
of the models is plotted
in gray.
Figure 8.
This GPI image of
HD 115600 in the H
band (around 1.6
μm) clearly shows the
disk that resembles
the Kuiper belt of our
own Solar System. The
coronagraph blocks the
light of the central star
(at the position of the
cross). The diamond
marks the disk’s center.
A Solar System Analogue, in
Formation
Observations using the Gemini Planet Imager (GPI) reveal an analogue of our own Solar
System at an early stage of evolution. The debris disk, which resembles the Sun’s “Kuiper
belt,” belongs to the young star HD 115600
— a star in the right environment (a massive
OB association) to represent the site of the
Sun’s formation, with similar mass (1.4 to 1.5
MSun). Thayne Currie (National Astronomical Observatory of Japan) and collaborators
have discovered this extrasolar debris disk in
direct imaging (Figure 8), and they use the
images and spectral information from GPI
to determine its properties and possible unseen planets.
January 2016
Figure 7.
Finding the Outer Edge
of Young Stars Near the
Galactic Center
The very center of the Milky Way Galaxy
contains a number of massive stars — despite either the inhospitable environment
2015 Year in Review
GeminiFocus
25