1,159 research outputs found
DISCOVERY OF A LOW-LUMINOSITY, TIGHT SUBSTELLAR BINARY AT THE T/Y TRANSITION
We have discovered that the brown dwarf WISEJ014656.66+423410.0 is a close
binary (0.08750.0021 arcsec, 0.93 AU) from Keck laser
guide star adaptive optics imaging. Our photometry for this system reveals that
both components are less luminous than those in any known substellar binary.
Combining a new integrated-light spectrum (T9p) and resolved YJH-band
photometry from Keck allows us to perform spectral decomposition and assign
component types of T9 and Y0. Many of the unusual features in the spectrum
might be explained by high surface gravity: Y-band peak broadened to the blue;
J-band peak broadened to the red; H-band peak shifted slightly to the red; and
red Y-J colors. Interestingly, the very low component luminosities imply that
the T9 primary is unexpectedly cold ( = 34545 K assuming an
age of 10 Gyr), making it 100 K cooler than any other late-T dwarf and
comparable to Y dwarfs. One intriguing explanation for this apparent
discrepancy is that the J- and H-band spectral features that trigger the
transition from T to Y spectral types are highly gravity-dependent. This can be
tested directly in the very near future by orbit monitoring. We constrain the
orbital period to be 10 yr by combining evolutionary model-based mass
estimates for the components (1221 , 1 at 10
Gyr) with a statistical constraint on the semimajor axis (1.3 AU).
Such a period is shorter than any other known T/Y transition binary, meaning
that WISEJ0146+4234AB will likely yield a dynamical mass within the next few
years.Comment: Accepted to ApJ (2015 Feb 14); 24 pages, 4 figures, 5 table
THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS
(Abridged) We present a large, uniform analysis of young (~10-150 Myr)
ultracool dwarfs, based on new high-precision IR parallaxes for 68 objects. We
find that low-gravity (VL-G) late-M and L dwarfs form a continuous sequence in
IR color-magnitude diagrams, separate from field objects and current
theoretical models. VL-G objects also appear distinct from young substellar
(brown dwarf and exoplanet) companions, suggesting the two populations have a
different range of physical properties. In contrast, at the L/T transition,
young, old, and peculiar objects all span a narrow range in near-IR absolute
magnitudes. At a given spectral type, the IR absolute magnitudes of young
objects can be offset from ordinary field dwarfs, with the largest offsets
occurring in the Y and J bands for late-M dwarfs (brighter than the field) and
mid/late-L dwarfs (fainter than the field). Overall, low-gravity (VL-G) objects
have the most uniform photometric behavior while intermediate-gravity (INT-G)
objects are more diverse, suggesting a third governing parameter beyond
spectral type and gravity class. We examine the moving group memberships for
all young ultracool dwarfs with parallaxes, changing/refuting the status of 23
objects and fortifying the status of another 28 objects. We use our resulting
age-calibrated sample to establish empirical young isochrones and find a
declining frequency of VL-G objects relative to INT-G objects with increasing
age. Notable objects in our sample include high-velocity INT-G objects; very
red, late-L dwarfs with high surface gravities; candidate disk-bearing members
of the MBM20 cloud and beta Pic moving group; and very young distant
interlopers. Finally, we provide a comprehensive summary of the absolute
magnitudes and spectral classifications of 102 young ultracool dwarfs, found in
the field and as substellar companions to young stars.Comment: ApJ, in press, 138 pages including 33 figures and 15 tables.
Compilation of young ultracool dwarfs and young substellar (brown dwarf and
exoplanet) companions available at the Database of Ultracool Parallaxes (see
http://www.as.utexas.edu/~tdupuy/plx
The Young L Dwarf 2MASS J11193254-1137466 Is a Planetary-mass Binary
We have discovered that the extremely red, low-gravity L7 dwarf 2MASS
J11193254-1137466 is a 0.14" (3.6 AU) binary using Keck laser guide star
adaptive optics imaging. 2MASS J11193254-1137466 has previously been identified
as a likely member of the TW Hydrae Association (TWA). Using our updated
photometric distance and proper motion, a kinematic analysis based on the
BANYAN II model gives an 82% probability of TWA membership. At TWA's 103
Myr age and using hot-start evolutionary models, 2MASS J11193254-1137466AB is a
pair of brown dwarfs, making it the
lowest-mass binary discovered to date. We estimate an orbital period of
years. One component is marginally brighter in band but
fainter in band, making this a probable flux-reversal binary, the first
discovered with such a young age. We also imaged the spectrally similar TWA L7
dwarf WISEA J114724.10-204021.3 with Keck and found no sign of binarity. Our
evolutionary model-derived estimate for WISEA J114724.10-204021.3
is 230 K higher than for 2MASS J11193254-1137466AB, at odds with their
spectral similarity. This discrepancy suggests that WISEA J114724.10-204021.3
may actually be a tight binary with masses and temperatures very similar to
2MASS J11193254-1137466AB, or further supporting the idea that near-infrared
spectra of young ultracool dwarfs are shaped by factors other than temperature
and gravity. 2MASS J11193254-1137466AB will be an essential benchmark for
testing evolutionary and atmospheric models in the young planetary-mass regime.Comment: Accepted to ApJ Letters. 8 pages, 3 figures, 2 table
The extracellular A-loop of dual oxidases affects the specificity of reactive oxygen species release
NADPH oxidase (Nox) family proteins produce superoxide (O2.-) directly by transferring an electron to molecular oxygen. Dual oxidases (Duoxes) also produce an O2.- intermediate, although the final species secreted by mature Duoxes is H2O2, suggesting that intramolecular O2.- dismutation or other mechanisms contribute to H2O2 release. We explored the structural determinants affecting reactive oxygen species formation by Duox enzymes. Duox2 showed O2.- leakage when mismatched with Duox activator 1 (DuoxA1). Duox2 released O2.- even in correctly matched combinations, including Duox2 + DuoxA2 and Duox2 + N-terminally tagged DuoxA2 regardless of the type or number of tags. Conversely, Duox1 did not release O2.- in any combination. Chimeric Duox2 possessing the A-loop of Duox1 showed no O2.- leakage; chimeric Duox1 possessing the A-loop of Duox2 released O2.-. Moreover, Duox2 proteins possessing the A-loops of Nox1 or Nox5 co-expressed with DuoxA2 showed enhanced O2.- release, and Duox1 proteins possessing the A-loops of Nox1 or Nox5 co-expressed with DuoxA1 acquired O2.- leakage. Although we identified Duox1 A-loop residues (His1071, His1072, and Gly1074) important for reducing O2.- release, mutations of these residues to those of Duox2 failed to convert Duox1 to an O2.- releasing enzyme. Using immunoprecipitation and endoglycosidase H sensitivity assays, we found that the A-loop of Duoxes binds to DuoxA N termini, creating more stable, mature Duox-DuoxA complexes. In conclusion, the A-loops of both Duoxes support H2O2 production through interaction with corresponding activators, but complex formation between the Duox1 A-loop and DuoxA1 results in tighter control of H2O2 release by the enzyme complex. © 2015, American Society for Biochemistry and Molecular Biology Inc
Comparison of SMILES ClO profiles with satellite, balloon-borne and ground-based measurements
We evaluate the quality of ClO profiles derived from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station (ISS). Version 2.1.5 of the level-2 product generated by the National Institute of Information and Communications Technology (NICT) is the subject of this study. Based on sensitivity studies, the systematic error was estimated as 5–10 pptv at the pressure range of 80–20 hPa, 35 pptv at the ClO peak altitude (~ 4 hPa), and 5–10 pptv at pressures ≤ 0.5 hPa for daytime mid-latitude conditions. For nighttime measurements, a systematic error of 8 pptv was estimated for the ClO peak altitude (~ 2 hPa). The SMILES NICT v2.1.5 ClO profiles agree with those derived from another level-2 processor developed by the Japan Aerospace Exploration Agency (JAXA) within the bias uncertainties, except for the nighttime measurements in the low and middle latitude regions where the SMILES NICT v2.1.5 profiles have a negative bias of ~ 30 pptv in the lower stratosphere. This bias is considered to be due to the use of a limited spectral bandwidth in the retrieval process of SMILES NICT v2.1.5, which makes it difficult to distinguish between the weak ClO signal and wing contributions of spectral features outside the bandwidth. In the middle and upper stratosphere outside the polar regions, no significant systematic bias was found for the SMILES NICT ClO profile with respect to data sets from other instruments such as the Aura Microwave Limb Sounder (MLS), the Odin Sub-Millimetre Radiometer (SMR), the Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), and the ground-based radiometer at Mauna Kea, which demonstrates the scientific usability of the SMILES ClO data including the diurnal variations. Inside the chlorine-activated polar vortex, the SMILES NICT v2.1.5 ClO profiles show larger volume mixing ratios by 0.4 ppbv (30%) at 50 hPa compared to those of the JAXA processed profiles. This discrepancy is also considered to be an effect of the limited spectral bandwidth in the retrieval processing. We also compared the SMILES NICT ClO profiles of chlorine-activated polar vortex conditions with those measured by the balloon-borne instruments: Terahertz and submillimeter Limb Sounder (TELIS) and the MIPAS-balloon instrument (MIPAS-B). In conclusion, the SMILES NICT v2.1.5 ClO data can be used at pressures ≤ ~30 hPa for scientific analysis
ASS1 Overexpression: A Hallmark of Sonic Hedgehog Hepatocellular Adenomas; Recommendations for Clinical Practice.
Until recently, 10% of hepatocellular adenomas (HCAs) remained unclassified (UHCA). Among the UHCAs, the sonic hedgehog HCA (shHCA) was defined by focal deletions that fuse the promoter of Inhibin beta E chain with GLI1. Prostaglandin D2 synthase was proposed as immunomarker. In parallel, our previous work using proteomic analysis showed that most UHCAs constitute a homogeneous subtype associated with overexpression of argininosuccinate synthase (ASS1). To clarify the use of ASS1 in the HCA classification and avoid misinterpretations of the immunohistochemical staining, the aims of this work were to study (1) the link between shHCA and ASS1 overexpression and (2) the clinical relevance of ASS1 overexpression for diagnosis. Molecular, proteomic, and immunohistochemical analyses were performed in UHCA cases of the Bordeaux series. The clinico-pathological features, including ASS1 immunohistochemical labeling, were analyzed on a large international series of 67 cases. ASS1 overexpression and the shHCA subgroup were superimposed in 15 cases studied by molecular analysis, establishing ASS1 overexpression as a hallmark of shHCA. Moreover, the ASS1 immunomarker was better than prostaglandin D2 synthase and only found positive in 7 of 22 shHCAs. Of the 67 UHCA cases, 58 (85.3%) overexpressed ASS1, four cases were ASS1 negative, and in five cases ASS1 was noncontributory. Proteomic analysis performed in the case of doubtful interpretation of ASS1 overexpression, especially on biopsies, can be a support to interpret such cases. ASS1 overexpression is a specific hallmark of shHCA known to be at high risk of bleeding. Therefore, ASS1 is an additional tool for HCA classification and clinical diagnosis
Individual Dynamical Masses of Ultracool Dwarfs
We present the full results of our decade-long astrometric monitoring
programs targeting 31 ultracool binaries with component spectral types M7-T5.
Joint analysis of resolved imaging from Keck Observatory and Hubble Space
Telescope and unresolved astrometry from CFHT/WIRCam yields parallactic
distances for all systems, robust orbit determinations for 23 systems, and
photocenter orbits for 19 systems. As a result, we measure 38 precise
individual masses spanning 30-115 . We determine a
model-independent substellar boundary that is 70 in mass
(L4 in spectral type), and we validate Baraffe et al. (2015)
evolutionary model predictions for the lithium-depletion boundary (60 at field ages). Assuming each binary is coeval, we test models of the
substellar mass-luminosity relation and find that in the L/T transition, only
the Saumon & Marley (2008) "hybrid" models accounting for cloud clearing match
our data. We derive a precise, mass-calibrated spectral type-effective
temperature relation covering 1100-2800 K. Our masses enable a novel direct
determination of the age distribution of field brown dwarfs spanning L4-T5 and
30-70 . We determine a median age of 1.3 Gyr, and our population
synthesis modeling indicates our sample is consistent with a constant star
formation history modulated by dynamical heating in the Galactic disk. We
discover two triple-brown-dwarf systems, the first with directly measured
masses and eccentricities. We examine the eccentricity distribution, carefully
considering biases and completeness, and find that low-eccentricity orbits are
significantly more common among ultracool binaries than solar-type binaries,
possibly indicating the early influence of long-lived dissipative gas disks.
Overall, this work represents a major advance in the empirical view of very
low-mass stars and brown dwarfs.Comment: ApJS, in press. This arxiv posting contains all figures (111 pages)
and tables (107 pages). Updated version contains additional acknowledgments
and references and corrects typo
On The Unusual Variability of 2MASS J06195260-2903592: A Long-Lived Disk around a Young Ultracool Dwarf
We present the characterization of the low-gravity M6 dwarf 2MASS J0619-2903
previously identified as an unusual field object based on its strong IR excess
and variable near-IR spectrum. Multiple epochs of low-resolution (R~150)
near-IR spectra show large-amplitude (~0.1-0.5 mag) continuum variations on
timescales of days to 12 years, unlike the small-amplitude variability typical
for field ultracool dwarfs. The variations between epochs are well-modeled as
changes in the relative extinction ( mag). Likewise,
Pan-STARRS optical photometry varies on timescales as long as 11 years (and
possibly as short as an hour) and implies similar amplitude changes.
NEOWISE mid-IR light curves also suggest changes on 6-month timescales, with
amplitudes consistent with the optical/near-IR extinction variations. However,
near-IR spectra, near-IR photometry, and optical photometry obtained in the
past year indicate the source can also be stable on hourly and monthly
timescales. From comparison to objects of similar spectral type, the total
extinction of 2MASS J0619-2903 seems to be mag, with perhaps
epochs of lower extinction. Gaia EDR3 finds that 2MASS J0619-2903 has a
wide-separation (1.2' = 10450 AU) stellar companion, with an isochronal age of
Myr and a mass of Msun. Adopting this
companion's age and EDR3 distance (145.20.6 pc), we estimate a mass of
0.11-0.17 Msun for 2MASS J0619-2903. Altogether, 2MASS J0619-2903 appears to
possess an unusually long-lived primordial circumstellar disk, perhaps making
it a more obscured analog to the "Peter Pan" disks found around a few M dwarfs
in nearby young moving groups.Comment: AJ, in pres
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