69 research outputs found
Thalidomide: History, withdrawal, renaissance and safety concerns
Peer reviewedPostprin
SDSS J141624.08+134826.7: A Nearby Blue L Dwarf From the Sloan Digital Sky Survey
We present the discovery of a bright (J = 13.1 mag) nearby L6 dwarf found in
a search for L-type ultracool subdwarfs in the Sloan Digital Sky Survey (SDSS)
Data Release 7. SDSS J141624.08+134826.7 exhibits blue near-infrared colors
compared to other optically-typed L6 objects, but its optical and near-infrared
spectra do not show metal-poor features characteristic of known L-type
ultracool subdwarfs. Instead, SDSS J141624.08+134826.7 is probably a nearby
example of the class of L dwarfs with low condensate opacities which exhibit
unusually blue near-infrared colors for a given spectral type. Its deep 1.4 and
1.9 um H2O absorption bands, weak 2.3 um CO feature, strong 0.99 um FeH band,
and shallow optical TiO and CaH bands resemble the spectra of other blue L
dwarfs which are believed to have unusually thin or large-grained cloud
structure. The luminosity of SDSS J141624.08+134826.7 implies that it is either
a high-mass brown dwarf or a low mass star, depending on its age, and its UVW
space motion suggests a thin-disk membership. With a spectrophotometric
distance of 8.4 +/- 1.9 pc, SDSS J141624.08+134826.7 is one of the nearest L
dwarfs to the Sun and is therefore an excellent target for high resolution
imaging, spectroscopic, and astrometric follow-up observations.Comment: Accepted by ApJ; 9 pages, 3 figure
Discovery of two L & T binaries with wide separations and peculiar photometric properties
We present spatially resolved photometric and spectroscopic observations of
two wide brown dwarf binaries uncovered by the SIMP near-infrared proper motion
survey. The first pair (SIMP J1619275+031350AB) has a separation of 0.691"
(15.2 AU) and components T2.5+T4.0, at the cooler end of the ill-understood
J-band brightening. The system is unusual in that the earlier-type primary is
bluer in J-Ks than the later-type secondary, whereas the reverse is expected
for binaries in the late-L to T dwarf range. This remarkable color reversal can
possibly be explained by very different cloud properties between the two
components. The second pair (SIMP J1501530-013506AB) consists of an L4.5+L5.5
(separation 0.96", 30-47 AU) with a surprisingly large flux ratio (Delta J
=1.79 mag) considering the similar spectral types of its components. The large
flux ratio could be explained if the primary is itself an equal-luminosity
binary, which would make it one of the first known triple brown dwarf systems.
Adaptive optics observations could not confirm this hypothesis, but it remains
a likely one, which may be verified by high-resolution near-infrared
spectroscopy. These two systems add to the handful of known brown dwarf
binaries amenable to resolved spectroscopy without the aid of adaptive optics
and constitute prime targets to test brown dwarf atmosphere models.Comment: accepted for publication in 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
The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
We present the first results from our high-precision infrared (IR) astrometry
program at the Canada-France-Hawaii Telescope. We measure parallaxes for 83
ultracool dwarfs (spectral types M6--T9) in 49 systems, with a median
uncertainty of 1.1 mas (2.3%) and as good as 0.7 mas (0.8%). We provide the
first parallaxes for 48 objects in 29 systems, and for another 27 objects in 17
systems, we significantly improve upon published results, with a median (best)
improvement of 1.7x (5x). Three systems show astrometric perturbations
indicative of orbital motion; two are known binaries (2MASSJ0518-2828AB and
2MASSJ1404-3159AB) and one is spectrally peculiar (SDSSJ0805+4812). In
addition, we present here a large set of Keck adaptive optics imaging that more
than triples the number of binaries with L6--T5 components that have both
multi-band photometry and distances. Our data enable an unprecedented look at
the photometric properties of brown dwarfs as they cool through the L/T
transition. Going from \approxL8 to \approxT4.5, flux in the Y and J bands
increases by \approx0.7 mag and \approx0.5 mag, respectively (the Y- and J-band
"bumps"), while flux in the H, K, and L' bands declines monotonically. This
wavelength dependence is consistent with cloud clearing over a narrow range of
temperature, since condensate opacity is expected to dominate at 1.0--1.3
micron. Interestingly, despite more than doubling the near-IR census of L/T
transition objects, we find a conspicuous paucity of objects on the
color--magnitude diagram just blueward of the late-L/early-T sequence. This
"L/T gap" occurs at MKO(J-H) = 0.1--0.3 mag, MKO(J-K) = 0.0--0.4 mag, and
implies that the last phases of cloud evolution occur rapidly. Finally, we
provide a comprehensive update to the absolute magnitudes of ultracool dwarfs
as a function of spectral type using a combined sample of 314 objects.Comment: Accepted to ApJ. New arXiv posting includes 4 new parallaxes and an
overall improvement in precision of 1.3x thanks to additional CFHT astrometry
for many targets. All data compiled in this paper (and more) are available
online: http://www.cfa.harvard.edu/~tdupuy/pl
NEW EVIDENCE FOR A SUBSTELLAR LUMINOSITY PROBLEM: DYNAMICAL MASS FOR THE BROWN DWARF BINARY Gl 417BC
We present new evidence for a problem with cooling rates predicted by
substellar evolutionary models that implies model-derived masses in the
literature for brown dwarfs and directly imaged planets may be too high. Based
on our dynamical mass for Gl 417BC (L4.5+L6) and a gyrochronology system age
from its young, solar-type host star, commonly used models predict luminosities
0.20.4 dex lower than we observe. This corroborates a similar
luminosityage discrepancy identified in our previous work on the L4+L4
binary HD 130948BC, which coincidentally has nearly identical component masses
(5055 ) and age (800 Myr) as Gl 417BC. Such a
luminosity offset would cause systematic errors of 15%25% in model-derived
masses at this age. After comparing different models, including cloudless
models that should not be appropriate for mid-L dwarfs like Gl 417BC and HD
130948BC but actually match their luminosities better, we speculate the
observed over-luminosity could be caused by opacity holes (i.e., patchy clouds)
in these objects. Moreover, from hybrid substellar evolutionary models that
account for cloud disappearance we infer the corresponding phase of
over-luminosity may extend from a few hundred Myr up to a few Gyr and cause
masses to to be over-estimated by up to 25%, even well after clouds disappear
from view entirely. Thus, the range of of ages and spectral types affected by
this potential systematic shift in luminosity evolution would encompass most
known directly imaged gas-giants and field brown dwarfs.Comment: accepted to Ap
Evolutionary genetic dissection of human interferons
As revealed by population genetic analyses, different human interferon genes evolved under distinct selective constraints and signatures of positive selection vary according to geographic region, suggesting that some sequence changes may have conferred an advantage by increasing resistance to viral infection
The Mass-Luminosity Relation in the L/T Transition:Individual Dynamical Masses for the New J-Band Flux Reversal Binary SDSSJ105213.51+442255.7AB
We have discovered that SDSSJ105213.51+442255.7 (T0.51.0) is a binary in
Keck laser guide star adaptive optics imaging, displaying a large J-to-K-band
flux reversal (J = -0.450.09 mag, K = 0.520.05 mag).
We determine a total dynamical mass from Keck orbital monitoring (885
) and a mass ratio by measuring the photocenter orbit from
CFHT/WIRCam absolute astrometry ( = 0.780.07). Combining these
provides the first individual dynamical masses for any field L or T dwarfs,
493 for the L6.51.5 primary and 393
for the T1.51.0 secondary. Such a low mass ratio for a nearly equal
luminosity binary implies a shallow massluminosity relation over the L/T
transition (log/log). This
provides the first observational support that cloud dispersal plays a
significant role in the luminosity evolution of substellar objects. Fully
cloudy models fail our coevality test for this binary, giving ages for the two
components that disagree by 0.2 dex (2.0). In contrast, our observed
masses and luminosities can be reproduced at a single age by "hybrid"
evolutionary tracks where a smooth change from a cloudy to cloudless
photosphere around 1300 K causes slowing of luminosity evolution. Remarkably,
such models also match our observed JHK flux ratios and colors well. Overall,
it seems that the distinguishing features SDSSJ1052+4422AB, like a J-band flux
reversal and high-amplitude variability, are normal for a field L/T binary
caught during the process of cloud dispersal, given that the age
(1.11 Gyr) and surface gravity (log = 5.05.2) of
SDSSJ1052+4422AB are typical for field ultracool dwarfs.Comment: Accepted to ApJ; 33 pages, 8 figures, 5 table
Genome-Wide Analyses Reveal a Role for Peptide Hormones in Planarian Germline Development
Genomic/peptidomic analyses of the planarian Schmidtea mediterranea identifies >200 neuropeptides and uncovers a conserved neuropeptide required for proper maturation and maintenance of the reproductive system
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