1,730 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 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
Photoprotection capacity differs among microphytobenthic diatoms inhabiting intertidal mudflats: Possible consequences on their spatial distribution related to the light environment
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&
Low temperature transition to a superconducting phase in boron-doped silicon films grown on (001)-oriented silicon wafers
We report on a detailed analysis of the superconducting properties of
boron-doped silicon films grown along the 001 direction by Gas Immersion Laser
Doping. The doping concentration cB has been varied up to approx. 10 at.% by
increasing the number of laser shots to 500. No superconductivity could be
observed down to 40mK for doping level below 2.5 at.%. The critical temperature
Tc then increased steeply to reach 0.6K for cB = 8 at%. No hysteresis was found
for the transitions in magnetic field, which is characteristic of a type II
superconductor. The corresponding upper critical field Hc2(0) was on the order
of 1000 G, much smaller than the value previously reported by Bustarret et al.
in Nature (London) 444, 465 (2006).Comment: 4 pages including 4 figures, submitted to PRB-Rapid Communicatio
Ecological niche predicts photoprotection capacity of microphytobenthic diatoms inhabiting intertidal mudflats
A focus on L dwarfs with trigonometric parallaxes
This is an author-created, un-copyedited version of an article published in Publications of the Astronomical Society of the Pacific. Under embargo until 14 May 2019. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1538-3873/aaacc5.We report new parallax measurements for ten L and early T type dwarfs, five of which have no previous published values, using observations over 3 years at the robotic Liverpool Telescope. The resulting parallaxes and proper motions have median errors of 2\,mas and 1.5\,mas/year respectively. Their space motions indicate they are all Galactic disk members. We combined this sample with other objects with astrometry from the Liverpool Telescope and with published literature astrometry to construct a sample of 260 L and early T type dwarfs with measured parallaxes, designated the Astrometry Sample. We study the kinematics of the Astrometry Sample, and derived a solar motion of \,\kms~ with respect to the local standard of rest, in agreement with recent literature. We derive a kinematic age of 1.5-1.7\,Gyr for the Astrometry Sample assuming the age increases monotonically with the total velocity for a given disk sample. This kinematic age is less than half literature values for other low mass dwarf samples. We believe this difference arises for two reasons (1) the sample is mainly composed of mid to late L dwarfs which are expected to be relatively young and (2) the requirement that objects have a measured parallax biases the sample to the brighter examples which tend to be younger.Peer reviewedFinal Accepted Versio
Phenotypic and genotypic characterization of Bradyrhizobia nodulating the leguminous tree Acacia albida
A
Mechanism and Uses of a Membrane Peptide that Targets Tumors and Other Acidic Tissues \u3cem\u3eIn Vivo\u3c/em\u3e
The pH-selective insertion and folding of a membrane peptide, pHLIP [pH (low) insertion peptide], can be used to target acidic tissue in vivo, including acidic foci in tumors, kidneys, and inflammatory sites. In a mouse breast adenocarcinoma model, fluorescently labeled pHLIP finds solid acidic tumors with high accuracy and accumulates in them even at a very early stage of tumor development. The fluorescence signal is stable for \u3e4 days and is approximately five times higher in tumors than in healthy counterpart tissue. In a rat antigen-induced arthritis model, pHLIP preferentially accumulates in inflammatory foci. pHLIP also maps the renal cortical interstitium; however, kidney accumulation can be reduced significantly by providing mice with bicarbonate-containing drinking water. The peptide has three states: soluble in water, bound to the surface of a membrane, and inserted across the membrane as an α-helix. At physiological pH, the equilibrium is toward water, which explains its low affinity for cells in healthy tissue; at acidic pH, titration of Asp residues shifts the equilibrium toward membrane insertion and tissue accumulation. The replacement of two key Asp residues located in the transmembrane part of pHLIP by Lys or Asn led to the loss of pH-sensitive insertion into membranes of liposomes, red blood cells, and cancer cells in vivo, as well as to the loss of specific accumulation in tumors. pHLIP nanotechnology introduces a new method of detecting, targeting, and possibly treating acidic diseased tissue by using the selective insertion and folding of membrane peptides
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