Figure 2.
Magnitude differences
for real and simulated
detections of stellar
companions plotted as
a function of separation
in AU. The cyan points
are the 21 K2 exoplanet
hosts at known distances
that have stellar
companions discovered
by DSSI on Gemini. Open
black circles represent
a random sampling of
simulated stellar systems
with bound components
that would be detectable
by Gemini/DSSI, while
filled gray circles
represent detectable
line-of-sight companions
from the same
simulations. The dashed
gray line at 50 AU marks
the semi-major axis
within which a previous
study had concluded
that stellar companions
are suppressed among
Kepler exoplanet hosts.
(Figure adapted from
Matsen et al., 2018.)
12
mission has observed a series of fields along
the ecliptic plane, each one for 80 days, and
has detected more than 500 exoplanet can-
didates. The different observing strategy
results in differences in the distributions of
mass and orbital properties as compared to
the original Kepler sample.
The team observed 206 unique K2 planet
hosts with DSSI and detected a total of 29
stellar companions, including 23 compan-
ions to the 102 stars observed at Gemini. In
order to assess the intrinsic binarity, the team
compared their detections to expectations
from simulations of both the Gemini and
WIYN DSSI samples. Figure 2 compares the
distributions in magnitude difference and
separation of the simulated and actual Gem-
ini observations. Assuming the field binarity
fraction of 40-50%, the simulations predict
26 ± 6% of the exoplanet hosts should have
companions detectable by DSSI on Gemini,
consistent with the observations. Thus, the
fraction of binary stars among K2 exoplanet
hosts is consistent with that found among
the general population of nearby stars of
similar mass.
GeminiFocus
“While we have known that about 50% of all
stars are binary, to confirm a similar ratio in
exoplanet host stars helps set some impor-
tant constraints on the formation of poten-
tial exoplanets seen by Kepler,” said Rachel
Matson of NASA’s Ames Research Center,
the study’s lead author. “In our sample we
did not find evidence that the proximity of a
companion star suppresses the formation of
exoplanets, even at distances as small as 50
astronomical units.” The paper is accepted
for publication in The Astrophysical Journal,
and a preprint is available online.
AO Constraints on Psyche’s
Shape, Density, and Polar Axis
The Main Belt asteroid 16 Psyche is one of
the defining members of the metallic M-
class asteroids. The classification is based
on its high radar albedo, which suggests
that Psyche’s surface is about 90% nickel-
iron metal. This could indicate that Psyche
is the remnant core of a larger differenti-
ated body. Although its mean diameter of
about 225 km places it 35th among Main
Belt asteroids, it ranks 11th in terms of mass.
July 2018