and pollution,” he says. “The brown dwarf
was effectively hidden by the dust until we
looked with the right instrument. But when
we observed SDSS 1557 in detail, we recog-
nized the brown dwarf’s subtle gravitation-
al pull on the white dwarf.”
From the Gemini data the team estimated
that the white dwarf has a surface tempera-
ture of 21,800 Kelvin (about 3.5 times hot-
ter than the Sun) and a mass of ~0.4 solar
masses; the brown dwarf companion has a
mass of ~0.063 solar masses.
The research is published in the February
27th online issue of Nature Astronomy.
See the University College London press re-
lease here.
β Pictoris b: an Exoplanet with
the Atmosphere of a Brown
Dwarf
Figure 3.
Using advanced
imaging techniques and
the special capabilities
of the Gemini Planet
Imager (GPI), the light
from β Pictoris has been
suppressed in these
images using GPI’s Y,
J, H, K1, and K2 filters.
The arrow indicates
the location of the
exoplanet β Pictoris b in
in all but the left image.
14
A team of astronomers led by Jeffrey Chil-
cote (University of Toronto) uses the Gemi-
ni Planet Imager (GPI) at the Gemini South
telescope in Chile to refine our understand-
ing of the β Pictoris system. The system
contains the ~ 13 Jupiter mass companion
β Pictoris b, which is at the mass boundary
sometimes used to distinguish between an
exoplanet and a brown dwarf. Brown dwarfs
are objects that are not massive enough
for sustained nuclear reactions; and brown
dwarfs less massive than 13 Jupiters cannot
even start a nuclear reaction.
GeminiFocus
Based on the GPI data, combined with
planetary evolution and atmospheric mod-
els, Chilcote suggests a “hot-start” planet
formation scenario for β Pictoris b, which
has a surface temperature of about 1,724
K. He adds, “This is consistent with the disk
instability formation mechanism for wide-
orbit giant exoplanets.” However, the char-
acteristics for the atmosphere of β Pictoris
b found in this work best matches that of
a low-surface-gravity (L2±1) brown dwarf,
not a planet.
The team studied β Pictoris b during the ver-
ification and commissioning of the Gemini
Planet Imager, and as part of an astrometric
(position) monitoring program designed to
constrain the orbit of the exoplanet (Figure
3). This work is also part of a Gemini Large
and Long program.
“With GPI, the Gemini Observatory is at the
forefront of exoplanet exploration,” says
Chilcote. He adds, “Direct imaging allows
for the discovery of planets on solar-sys-
tems-scale orbits, provides new insight into
the formation and characteristics of extra-
solar systems, and enables direct spectro-
scopic observations of their atmospheres.”
The full results are accepted for publication
in The Astrophysical Journal Letters. A pre-
print is available here.
Peter Michaud is the Public Information Out-
reach Manager of Gemini Observatory. He can
be reached at: [email protected]
April 2017