483 research outputs found
Discovery of a Visual T-Dwarf Triple System and Binarity at the L/T Transition
We present new high contrast imaging of 8 L/T transition brown dwarfs using
the NIRC2 camera on the Keck II telescope. One of our targets, the T3.5 dwarf
2MASS J08381155 + 1511155, was resolved into a hierarchal triple with projected
separations of 2.5+/-0.5 AU and 27+/-5 AU for the BC and A(BC) components
respectively. Resolved OSIRIS spectroscopy of the A(BC) components confirm that
all system members are T dwarfs. The system therefore constitutes the first
triple T-dwarf system ever reported. Using resolved photometry to model the
integrated-light spectrum, we infer spectral types of T3, T3, and T4.5 for the
A, B, and C components respectively. The uniformly brighter primary has a bluer
J-Ks color than the next faintest component, which may reflect a sensitive
dependence of the L/T transition temperature on gravity, or alternatively
divergent cloud properties amongst components. Relying on empirical trends and
evolutionary models we infer a total system mass of 0.034-0.104 Msun for the BC
components at ages of 0.3-3 Gyr, which would imply a period of 12-21 yr
assuming the system semi-major axis to be similar to its projection. We also
infer differences in effective temperatures and surface gravities between
components of no more than ~150 K and ~0.1 dex. Given the similar physical
properties of the components, the 2M0838+15 system provides a controlled sample
for constraining the relative roles of effective temperature, surface gravity,
and dust clouds in the poorly understood L/T transition regime. Combining our
imaging survey results with previous work we find an observed binary fraction
of 4/18 or 22_{-8}^{+10}% for unresolved spectral types of L9-T4 at separations
>~0.1 arcsec. This translates into a volume-corrected frequency of
13^{-6}_{+7}%, which is similar to values of ~9-12% reported outside the
transition. (ABRIDGED)Comment: Accepted for publication in the Astrophysical Journal. 23 pages, 12
figure
Two Wide Planetary-Mass Companions to Solar-Type Stars in Upper Scorpius
At wide separations, planetary-mass and brown dwarf companions to solar type
stars occupy a curious region of parameters space not obviously linked to
binary star formation or solar-system scale planet formation. These companions
provide insight into the extreme case of companion formation (either binary or
planetary), and due to their relative ease of observation when compared to
close companions, they offer a useful template for our expectations of more
typical planets. We present the results from an adaptive optics imaging survey
for wide (50-500 AU) companions to solar type stars in Upper Scorpius. We
report one new discovery of a ~14 M_J companion around GSC 06214-00210, and
confirm that the candidate planetary mass companion 1RXS J160929.1-210524
detected by Lafreniere et al (2008) is in fact co-moving with its primary star.
In our survey, these two detections correspond to ~4% of solar type stars
having companions in the 6-20 M_J mass and 200-500 AU separation range. This
figure is higher than would be expected if brown dwarfs and planetary mass
companions were drawn from an extrapolation of the binary mass function.
Finally, we discuss implications for the formation of these objects.Comment: 11 Pages, 7 Figures, Accepted for Ap
Near-Infrared Spectroscopy of the Extrasolar Planet HR 8799 b
[Abridged] We present 2.12-2.23 um high contrast integral field spectroscopy
of the extrasolar planet HR 8799 b. Our observations were obtained with OSIRIS
on the Keck II telescope and sample the 2.2 um CH4 feature, which is useful for
spectral classification and as a temperature diagnostic for ultracool objects.
The spectrum of HR 8799 b is relatively featureless, with little or no methane
absorption, and does not exhibit the strong CH4 seen in T dwarfs of similar
absolute magnitudes. Overall, we find that HR 8799 b has a spectral type
consistent with L5-T2, although its SED is atypical compared to most field
objects. We fit the 2.2 um spectrum and the infrared SED using the Hubeny &
Burrows, Burrows et al., and Ames-Dusty model atmosphere grids, which
incorporate nonequilibrium chemistry, non-solar metallicities, and clear and
cloudy variants. No models agree with all of the data, but those with
intermediate clouds produce significantly better fits. The largest discrepancy
occurs in the J-band, which is highly suppressed in HR 8799 b. The best-fitting
effective temperatures range from 1300-1700 K with radii between ~0.3-0.5 RJup.
These values are inconsistent with evolutionary model-derived values of 800-900
K and 1.1-1.3 RJup based on the luminosity of HR 8799 b and the age of HR 8799,
a discrepancy that probably results from imperfect atmospheric models or the
limited range of physical parameters covered by the models. The low temperature
inferred from evolutionary models indicates that HR 8799 b is ~400 K cooler
than field L/T transition objects, providing further evidence that the L/T
transition is gravity-dependent. With an unusually dusty photosphere, an
exceptionally low luminosity for its spectral type, and hints of extreme
secondary physical parameters, HR 8799 b appears to be unlike any class of
field brown dwarf currently known.Comment: 21 pages, 23 figures; accepted by Ap
L'évolution et la fonction de la tromperie
L'évolution et la fonction de la tromperieDans cet article nous nous penchons sur l'évolution et la fonction de la tromperie à l'intérieur d'un cadre sociobiologique intégrant des données récentes de la primatologie et de la psychologie cognitive. Quatre niveaux phylogénétiques de tromperie sont définis : la morphologie trompeuse (mimétisme), les schemes fixes de comportement, le comportement appris, et la tromperie tactique. Cette dernière fait appel à des processus cognitifs avancés et a été documentée chez le chimpanzé en captivité. Nous en décrivons les étapes ontogénétiques chez l'être humain et faisons ressortir ses caractéristiques originales. En dernier lieu, nous présentons des taxonomies fonctionnelles, basées sur les conséquences immédiates de la tromperie, et nous abordons le rôle de ce comportement dans l'évolution de l'intelligence.Evolution and Function of DeceptionA sociobiological framework for understanding the evolution and function of deception is presented integrating recent work in primatology and cognitive psychology. Four phylogenetic levels of deception are defined and illustrated including deception based upon: 1) misleading morphology, 2) fixed actions patterns, 3) learned behavior, and 4) tactical deliberations. The fourth level of deception, implying advanced cognition, is documented in semi-naturalistic and experimental studies of chimpanzees, and analyzed in terms of discrete progressions in order to understand the prerequisites of such behavior and its rarity in the animal world. Finally, functional taxonomies of deception are reviewed from the standpoint of immediate consequences, as well as its role in the evolution of human intelligence
Discovery of the brightest T dwarf in the northern hemisphere
We report the discovery of a bright (H=12.77) brown dwarf designated SIMP
J013656.5+093347. The discovery was made as part of a near-infrared proper
motion survey, SIMP (Sondage Infrarouge de Mouvement Propre), which uses proper
motion and near-infrared/optical photometry to identify brown dwarf candidates.
A low resolution (lambda/dlambda~40) spectrum of this brown dwarf covering the
0.88-2.35 microns wavelength interval is presented. Analysis of the spectrum
indicates a spectral type of T2.5+/-0.5. A photometric distance of 6.4+/-0.3 pc
is estimated assuming it is a single object. Current observations rule out a
binary of mass ratio ~1 and separation >5 AU. SIMP 0136 is the brightest T
dwarf in the northern hemisphere and is surpassed only by Eps Indi Bab over the
whole sky. It is thus an excellent candidate for detailed studies and should
become a benchmark object for the early-T spectral class.Comment: 4 pages, 3 figures, To be published in November 1, 2006 issue of
ApJL. Following IAU recommendation, the survey acronym (IBIS) was changed to
SIM
Mineralogy and genesis of saproitte and strongly weathered soils in the Appalachian region of Canada
Spitzer 3.6 micron and 4.5 micron full-orbit lightcurves of WASP-18
We present new lightcurves of the massive hot Jupiter system WASP-18 obtained
with the Spitzer spacecraft covering the entire orbit at 3.6 micron and 4.5
micron. These lightcurves are used to measure the amplitude, shape and phase of
the thermal phase effect for WASP-18b. We find that our results for the thermal
phase effect are limited to an accuracy of about 0.01% by systematic noise
sources of unknown origin. At this level of accuracy we find that the thermal
phase effect has a peak-to-peak amplitude approximately equal to the secondary
eclipse depth, has a sinusoidal shape and that the maximum brightness occurs at
the same phase as mid-occultation to within about 5 degrees at 3.6 micron and
to within about 10 degrees at 4.5 micron. The shape and amplitude of the
thermal phase curve imply very low levels of heat redistribution within the
atmosphere of the planet. We also perform a separate analysis to determine the
system geometry by fitting a lightcurve model to the data covering the
occultation and the transit. The secondary eclipse depths we measure at 3.6
micron and 4.5 micron are in good agreement with previous measurements and
imply a very low albedo for WASP-18b. The parameters of the system (masses,
radii, etc.) derived from our analysis are in also good agreement with those
from previous studies, but with improved precision. We use new high-resolution
imaging and published limits on the rate of change of the mean radial velocity
to check for the presence of any faint companion stars that may affect our
results. We find that there is unlikely to be any significant contribution to
the flux at Spitzer wavelengths from a stellar companion to WASP-18. We find
that there is no evidence for variations in the times of eclipse from a linear
ephemeris greater than about 100 seconds over 3 years.Comment: 17 pages, 10 figures. Accpeted for publication in MNRA
The Vector Vortex Coronagraph: Laboratory Results and First Light at Palomar Observatory
High-contrast coronagraphy will be needed to image and characterize faint
extra-solar planetary systems. Coronagraphy is a rapidly evolving field, and
many enhanced alternatives to the classical Lyot coronagraph have been proposed
in the past ten years. Here, we discuss the operation of the vector vortex
coronagraph, which is one of the most efficient possible coronagraphs. We first
present recent laboratory results, and then first light observations at the
Palomar observatory. Our near-infrared H-band (centered at ~ 1.65 microns) and
K-band (centered at ~ 2.2 microns) vector vortex devices demonstrated excellent
contrast results in the lab, down to ~ 1e-6 at an angular separation of 3 lb/d.
On sky, we detected a brown dwarf companion 3000 times fainter than its host
star (HR 7672) in the Ks band (centered at ~2.15 microns), at an angular
separation of ~ 2.5 lb/d. Current and next-generation high-contrast instruments
can directly benefit from the demonstrated capabilities of such a vector
vortex: simplicity, small inner working angle, high optical throughput (>90%),
and maximal off-axis discovery space
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