228 research outputs found
The Directly Imaged Planet around the Young Solar Analog 1RXS J160929.1-210524: Confirmation of Common Proper Motion, Temperature and Mass
Giant planets are usually thought to form within a few tens of AU of their
host stars, and hence it came as a surprise when we found what appeared to be a
planetary mass (~0.008 Msun) companion around the 5 Myr-old solar mass star
1RXS J160929.1-210524 in the Upper Scorpius association. At the time, we took
the object's membership in Upper Scorpius -- established from near-infrared, H-
and K-band spectroscopy -- and its proximity (2.2", or 330 AU) to the primary
as strong evidence for companionship, but could not verify their common proper
motion. Here, we present follow-up astrometric measurements that confirm that
the companion is indeed co-moving with the primary star, which we interpret as
evidence that it is a truly bound planetary mass companion. We also present new
J-band spectroscopy and 3.0-3.8 microns photometry of the companion. Based on a
comparison with model spectra, these new measurements are consistent with the
previous estimate of the companion effective temperature of 1800+/-200 K. We
present a new estimate of the companion mass based on evolution models and the
calculated bolometric luminosity of the companion; we obtain a value of 0.008
(-0.002/+0.003) Msun, again consistent with our previous result. Finally, we
present angular differential imaging observations of the system allowing us to
rule out additional planets in the system more massive than 1, 2 and 8 Mjup at
projected separations larger than 3" (~440 AU), 0.7" (~100 AU) and 0.35" (~50
AU), respectively. This companion is the least massive known to date at such a
large orbital distance; it shows that objects in the planetary mass range exist
at orbital separations of several hundred AU, posing a serious challenge for
current formation models.Comment: Published in ApJ, 8 pages in emulateapj forma
HST/NICMOS detection of HR 8799 b in 1998
Three planets have been directly imaged around the young star HR 8799. The
planets are 5-13 Mjup and orbit the star at projected separations of 24-68 AU.
While the initial detection occurred in 2007, two of the planets were recovered
in a re-analysis of data obtained in 2004. Here we present a detection of the
furthest planet of that system, HR 8799 b, in archival HST/NICMOS data from
1998. The detection was made using the locally-optimized combination of images
algorithm to construct, from a large set of HST/NICMOS images of different
stars taken from the archive, an optimized reference point-spread function
image used to subtract the light of the primary star from the images of HR
8799. This new approach improves the sensitivity to planets at small
separations by a factor of ~10 compared to traditional roll deconvolution. The
new detection provides an astrometry point 10 years before the most recent
observations, and is consistent with a Keplerian circular orbit with a~70 AU
and low orbital inclination. The new photometry point, in the F160W filter, is
in good agreement with an atmosphere model with intermediate clouds and
vertical stratification, and thus suggests the presence of significant water
absorption in the planet's atmosphere. The success of the new approach used
here highlights a path for the search and characterization of exoplanets with
future space telescopes, such as the James Webb Space Telescope or a
Terrestrial Planet Finder.Comment: ApJL, in pres
BANYAN. II. Very Low Mass and Substellar Candidate Members to Nearby, Young Kinematic Groups With Previously Known Signs of Youth
We present Bayesian Analysis for Nearby Young AssociatioNs II (BANYAN II), a
modified Bayesian analysis for assessing the membership of later-than-M5
objects to any of several Nearby Young Associations (NYAs). In addition to
using kinematic information (from sky position and proper motion), this
analysis exploits 2MASS-WISE color-magnitude diagrams in which old and young
objects follow distinct sequences. As an improvement over our earlier work, the
spatial and kinematic distributions for each association are now modelled as
ellipsoids whose axes need not be aligned with the Galactic coordinate axes,
and we use prior probabilities matching the expected populations of the NYAs
considered versus field stars. We present an extensive contamination analysis
to characterize the performance of our new method. We find that Bayesian
probabilities are generally representative of contamination rates, except when
a parallax measurement is considered. In this case contamination rates become
significantly smaller and hence Bayesian probabilities for NYA memberships are
pessimistic. We apply this new algorithm to a sample of 158 objects from the
literature that are either known to display spectroscopic signs of youth or
have unusually red near-infrared colors for their spectral type. Based on our
analysis, we identify 25 objects as new highly probable candidates to NYAs,
including a new M7.5 bona fide member to Tucana-Horologium, making it the
latest-type member. In addition, we reveal that a known L2{\gamma} dwarf is
co-moving with a bright M5 dwarf, and we show for the first time that two of
the currently known ultra red L dwarfs are strong candidates to the AB Doradus
moving group. Several objects identified here as highly probable members to
NYAs could be free-floating planetary-mass objects if their membership is
confirmed.Comment: 35 pages, 10 figures; accepted for publication in The Astrophysical
Journal (in press); Several typographic correction
Near Infrared Observations of GQ Lup b Using the Gemini Integral Field Spectrograph NIFS
We present new JHK spectroscopy (R ~ 5000) of GQ Lup b, acquired with the
near-infrared integral field spectrograph NIFS and the adaptive optics system
ALTAIR at the Gemini North telescope. Angular differential imaging was used in
the J and H bands to suppress the speckle noise from GQ Lup A; we show that
this approach can provide improvements in signal-to-noise ratio (S/N) by a
factor of 2 - 6 for companions located at subarcsecond separations. Based on
high quality observations and GAIA synthetic spectra, we estimate the companion
effective temperature to Teff = 2400 +/- 100 K, its gravity to log g = 4.0 +/-
0.5, and its luminosity to log(L/L_s) = -2.47 +/- 0.28. Comparisons with the
predictions of the DUSTY evolutionary tracks allow us to constrain the mass of
GQ Lup b to 8 - 60 MJup, most likely in the brown dwarf regime. Compared with
the spectra published by Seifahrt and collaborators, our spectra of GQ Lup b
are significantly redder (by 15 - 50%) and do not show important Pa\beta
emission. Our spectra are in excellent agreement with the lower S/N spectra
previously published by McElwain and collaborators.Comment: 34 pages, 10 figures, accepted for publication in Ap
Discovery of a ~23 Mjup Brown Dwarf Orbiting ~700 AU from the Massive Star HIP 78530 in Upper Scorpius
We present the discovery of a substellar companion on a wide orbit around the
~2.5 Msun star HIP 78530, which is a member of the 5 Myr-old Upper Scorpius
association. We have obtained follow-up imaging over two years and show that
the companion and primary share common proper motion. We have also obtained JHK
spectroscopy of the companion and confirm its low surface gravity, in
accordance with the young age of the system. A comparison with Drift-Phoenix
synthetic spectra indicates an effective temperature of 2800+/-200 K and a
comparison with template spectra of young and old dwarfs indicates a spectral
type of M8+/-1. The mass of the companion is estimated to be 19-26 Mjup based
on its bolometric luminosity and the predictions of evolutionary models. The
angular separation of the companion is 4.5", which at the distance of the
primary star, 156.7 pc, corresponds to a projected separation of ~710 AU. This
companion features one of the lowest mass ratios (~0.009) of any known
companion at separations greater than 100 AU.Comment: To appear in ApJ, 9 pages, 9 figure
How do Most Planets Form? -- Constraints on Disk Instability from Direct Imaging
Core accretion and disk instability have traditionally been regarded as the
two competing possible paths of planet formation. In recent years, evidence
have accumulated in favor of core accretion as the dominant mode, at least for
close-in planets. However, it might be hypothesized that a significant
population of wide planets formed by disk instabilities could exist at large
separations, forming an invisible majority. In previous work, we addressed this
issue through a direct imaging survey of B2--A0-type stars, and concluded that
<30% of such stars form and retain planets and brown dwarfs through disk
instability, leaving core accretion as the likely dominant mechanism. In this
paper, we extend this analysis to FGKM-type stars by applying a similar
analysis to the Gemini Deep Planet Survey (GDPS) sample. The results strengthen
the conclusion that substellar companions formed and retained around their
parent stars by disk instabilities are rare. Specifically, we find that the
frequency of such companions is <8% for FGKM-type stars under our most
conservative assumptions, for an outer disk radius of 300 AU, at 99%
confidence. Furthermore, we find that the frequency is always <10% at 99%
confidence independently of outer disk radius, for any radius from 5 to 500 AU.
We also simulate migration at a wide range of rates, and find that the
conclusions hold even if the companions move substantially after formation.
Hence, core accretion remains the likely dominant formation mechanism for the
total planet population, for every type of star from M-type through B-type.Comment: 10 pages, 4 figures, accepted for publication in Ap
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