2,274 research outputs found
Two Extraordinary Substellar Binaries at the T/Y Transition and the Y-Band Fluxes of the Coolest Brown Dwarfs
Using Keck laser guide star adaptive optics imaging, we have found that the
T9 dwarf WISE J1217+1626 and T8 dwarf WISE J1711+3500 are exceptional binaries,
with unusually wide separations (~0.8 arcsec, 8-15 AU), large near-IR flux
ratios (~2-3 mags), and small mass ratios (~0.5) compared to previously known
field ultracool binaries. Keck/NIRSPEC H-band spectra give a spectral type of
Y0 for WISE J1217+1626B, and photometric estimates suggest T9.5 for WISE
J1711+3500B. The WISE J1217+1626AB system is very similar to the T9+Y0 binary
CFBDSIR J1458+1013AB; these two systems are the coldest known substellar
multiples, having secondary components of ~400 K and being planetary-mass
binaries if their ages are <~1 Gyr. Both WISE J1217+1626B and CFBDSIR
J1458+1013B have strikingly blue Y-J colors compared to previously known T
dwarfs, including their T9 primaries. Combining all available data, we find
that Y-J color drops precipitously between the very latest T dwarfs and the Y
dwarfs. The fact that this is seen in (coeval, mono-metallicity) binaries
demonstrates that the color drop arises from a change in temperature, not
surface gravity or metallicity variations among the field population. Thus, the
T/Y transition established by near-IR spectra coincides with a significant
change in the ~1 micron fluxes of ultracool photospheres. One explanation is
the depletion of potassium, whose broad absorption wings dominate the far-red
optical spectra of T dwarfs. This large color change suggests that far-red data
may be valuable for classifying objects of <~500 K.Comment: ApJ, in press (accepted Aug 1, 2012). Small cosmetic changes in
version 2 to match final publicatio
A Model-Independent Mass and Moderate Eccentricity for ÎČ Pic b
We use a cross-calibration of Hipparcos and Gaia DR2 astrometry for
Pic to measure the mass of the giant planet Pic b in a comprehensive joint orbit analysis that includes published relative
astrometry and radial velocities. Our mass uncertainty is somewhat higher than
previous work because our astrometry from the Hipparcos-Gaia Catalog of
Accelerations accounts for the error inflation and systematic terms that are
required to bring the two data sets onto a common astrometric reference frame,
and because we fit freely for the host-star mass .
This first model-independent mass for a directly imaged planet is inconsistent
with cold-start models given the age of the Pic moving group
Myr) but consistent with hot- and warm-start models, concordant with past work.
We find a higher eccentricity for Pic b compared to
previous orbital fits. If confirmed by future observations, this eccentricity
may help explain inner edge, scale height, and brightness asymmetry of
Pic's disk. It could also potentially signal that Pic b has migrated
inward to its current location, acquiring its eccentricity from interaction
with the 3:1 outer Lindblad resonance in the disk.Comment: ApJ Letters, accepte
Room temperature low-threshold InAs/InP quantum dot single mode photonic crystal microlasers at 1.5 ÎŒm using cavity-confined slow light
We have designed, fabricated, and characterized an InP photonic crystal slab structure that supports a cavity-confined slow-light mode, i.e. a bandgap-confined valence band-edge mode. Three dimensional finite difference in time domain calculations predict that this type of structure can support electromagnetic modes with large quality factors and small mode volumes. Moreover these modes are robust with respect to fabrication imperfections. In this paper, we demonstrate room-temperature laser operation at 1,5 Όm of a cavity-confined slow-light mode under pulsed excitation. The gain medium is a single layer of InAs/lnP quantum dots. An effective peak pump power threshold of 80 ΌW is reported. © 2009 Optical Society of America
ADAPTIVE OPTICS IMAGING OF VHS 1256-1257: A LOW MASS COMPANION TO A BROWN DWARF BINARY SYSTEM
Recently, Gauza et al. (2015) reported the discovery of a companion to the
late M-dwarf, VHS J125601.92-125723.9 (VHS 1256-1257). The companion's absolute
photometry suggests its mass and atmosphere are similar to the HR 8799 planets.
However, as a wide companion to a late-type star, it is more accessible to
spectroscopic characterization. We discovered that the primary of this system
is an equal-magnitude binary. For an age Myr the A and B components
each have a mass of , and the b component
has a mass of , making VHS 1256-1257 only the third brown
dwarf triple system. There exists some tension between the spectrophotometric
distance of pc and the parallax distance of pc. At
12.7 pc VHS1256-1257 A and B would be the faintest known M7.5 objects, and are
even faint outliers among M8 types. If the larger spectrophotmetric distance is
more accurate than the parallax, then the mass of each component increases. In
particular, the mass of the b component increases well above the deuterium
burning limit to and the mass of each binary
component increases to . At 17.1 pc, the UVW
kinematics of the system are consistent with membership in the AB~Dor moving
group. The architecture of the system resembles a hierarchical stellar multiple
suggesting it formed via an extension of the star-formation process to low
masses. Continued astrometric monitoring will resolve this distance uncertainty
and will provide dynamical masses for a new benchmark system.Comment: Accepted to ApJ
Gravity in the Local Universe : density and velocity fields using CosmicFlows-4
This article publicly releases three-dimensional reconstructions of the local
Universe gravitational field below z=0.8 that were computed using the
CosmicFlows-4 catalog of 56,000 galaxy distances and its sub-sample of 1,008
type Ia supernovae distances. The article also provides measurements of the
growth rate of structure using the pairwise correlation of radial peculiar
velocities f sigma8 = 0.38(+/-0.04) (ungrouped CF4), f sigma8 = 0.36(+/-0.05)
(grouped CF4), f sigma8 = 0.30(+/-0.06) (SNIa) and of the bulk flow in the 3D
reconstructed Local Universe of 230 +/- 136 km s-1 at 300 Mpc of distance from
the observer. The exploration of 10,000 reconstructions gives that the
distances delivered by the Cosmicflows-4 catalog are compatible with a Hubble
constant of H0 = 74.5 +/- 0.1 (grouped CF4), H0 = 75.0 +/- 0.35 (ungrouped CF4)
and H0 = 75.5 +/- 0.95 (CF4 SNIa subsample).Comment: Submitted A&A Oct 31st, 2022 / (AA/2022/45331) / Accepted January
2023 All Figures and values updated after the december 2022 major correction
in CF4 catalo
Mapping the Shores of the Brown Dwarf Desert III: Young Moving Groups
We present the results of an aperture masking interferometry survey for
substellar companions around 67 members of the young (~8-200Myr) nearby
(~5-86pc) AB Doradus, Beta Pictoris, Hercules-Lyra, TW Hya, and
Tucana-Horologium stellar associations. Observations were made at near infrared
wavelengths between 1.2-3.8 microns using the adaptive optics facilities of the
Keck II, VLT UT4, and Palomar Hale Telescopes. Typical contrast ratios of
~100-200 were achieved at angular separations between ~40-320mas, with our
survey being 100% complete for companions with masses below 0.25\msolar across
this range. We report the discovery of a \msolar companion to
HIP14807, as well as the detections and orbits of previously known stellar
companions to HD16760, HD113449, and HD160934. We show that the companion to
HD16760 is in a face-on orbit, resulting in an upward revision of its mass from
\mjupiter to \msolar. No substellar
companions were detected around any of our sample members, despite our ability
to detect companions with masses below 80\mjupiter for 50 of our targets: of
these, our sensitivity extended down to 40\mjupiter around 30 targets, with a
subset of 22 subject to the still more stringent limit of 20\mjupiter. A
statistical analysis of our non-detection of substellar companions allows us to
place constraints on their frequency around ~0.2-1.5\msolar stars. In
particular, considering companion mass distributions that have been proposed in
the literature, we obtain an upper limit estimate of ~9-11% for the frequency
of 20-80\mjupiter companions between 3-30AU at 95% confidence, assuming that
their semimajor axes are distributed according to in this range.Comment: Accepted by Ap
Deep search for companions to probable young brown dwarfs
We have obtained high contrast images of four nearby, faint, and very low
mass objects 2MASSJ04351455-1414468, SDSSJ044337.61+000205.1,
2MASSJ06085283-2753583 and 2MASSJ06524851-5741376 (here after 2MASS0435-14,
SDSS0443+00, 2MASS0608-27 and 2MASS0652-57), identified in the field as
probable isolated young brown dwarfs. Our goal was to search for binary
companions down to the planetary mass regime. We used the NAOS-CONICA adaptive
optics instrument (NACO) and its unique capability to sense the wavefront in
the near-infrared to acquire sharp images of the four systems in Ks, with a
field of view of 28"*28". Additional J and L' imaging and follow-up
observations at a second epoch were obtained for 2MASS0652-57. With a typical
contrast DKs= 4.0-7.0 mag, our observations are sensitive down to the planetary
mass regime considering a minimum age of 10 to 120 Myr for these systems. No
additional point sources are detected in the environment of 2MASS0435-14,
SDSS0443+00 and 2MASS0608-27 between 0.1-12" (i.e about 2 to 250 AU at 20 pc).
2MASS0652-57 is resolved as a \sim230 mas binary. Follow-up observations reject
a background contaminate, resolve the orbital motion of the pair, and confirm
with high confidence that the system is physically bound. The J, Ks and L'
photometry suggest a q\sim0.7-0.8 mass ratio binary with a probable semi-major
axis of 5-6 AU. Among the four systems, 2MASS0652-57 is probably the less
constrained in terms of age determination. Further analysis would be necessary
to confirm its youth. It would then be interesting to determine its orbital and
physical properties to derive the system's dynamical mass and to test
evolutionary model predictions.Comment: Research note, 5 pages, 2 tables and 3 figures, accepted to A&
Human rights and ethical reasoning : capabilities, conventions and spheres of public action
This interdisciplinary article argues that human rights must be understood in terms of opportunities for social participation and that social and economic rights are integral to any discussion of the subject. We offer both a social constructionist and a normative framework for a sociology of human rights which reaches beyond liberal individualism, combining insights from the work of Amartya Sen and from French convention theory. Following Sen, we argue that human rights are founded on the promotion of human capabilities as ethical demands shaped by public reasoning. Using French convention theory, we show how the terms of such deliberation are shaped by different constructions of collectively held values and the compromises reached between them. We conclude by demonstrating how our approach offers a new perspective on spheres of public action and the role these should play in promoting social cohesion, individual capabilities and human rights
Risk-based inspection as a cost-effective strategy to reduce human exposure to cysticerci of Taenia saginata in low-prevalence settings
Taenia saginata cysticercus is the larval stage of the zoonotic parasite Taenia saginata, with a life-cycle involving both cattle and humans. The public health impact is considered low. The current surveillance system, based on post-mortem inspection of carcasses has low sensitivity and leads to considerable economic burden. Therefore, in the interests of public health and food production efficiency, this study aims to explore the potential of risk-based and cost-effective meat inspection activities for the detection and control of T. saginata cysticercus in low prevalence settings
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