251 research outputs found
High Spatial Resolution Thermal-Infrared Spectroscopy with ALES: Resolved Spectra of the Benchmark Brown Dwarf Binary HD 130948BC
We present 2.9-4.1 micron integral field spectroscopy of the L4+L4 brown
dwarf binary HD 130948BC, obtained with the Arizona Lenslets for Exoplanet
Spectroscopy (ALES) mode of the Large Binocular Telescope Interferometer
(LBTI). The HD 130948 system is a hierarchical triple system, in which the G2V
primary is joined by two co-orbiting brown dwarfs. By combining the age of the
system with the dynamical masses and luminosities of the substellar companions,
we can test evolutionary models of cool brown dwarfs and extra-solar giant
planets. Previous near-infrared studies suggest a disagreement between HD
130948BC luminosities and those derived from evolutionary models. We obtained
spatially-resolved, low-resolution (R~20) L-band spectra of HD 130948B and C to
extend the wavelength coverage into the thermal infrared. Jointly using JHK
photometry and ALES L-band spectra for HD 130948BC, we derive atmospheric
parameters that are consistent with parameters derived from evolutionary
models. We leverage the consistency of these atmospheric quantities to favor a
younger age (0.50 \pm 0.07 Gyr) of the system compared to the older age (0.79
\pm 0.22 Gyr) determined with gyrochronology in order to address the luminosity
discrepancy.Comment: 17 pages, 9 figures, Accepted to Ap
Quiescent H2 Emission From Pre-Main Sequence Stars in Chamaeleon I
We report the discovery of quiescent emission from molecular hydrogen gas
located in the circumstellar disks of six pre-main sequence stars, including
two weak-line T Tauri stars (TTS), and one Herbig AeBe star, in the Chamaeleon
I star forming region. For two of these stars, we also place upper limits on
the 2->1 S(1)/1->0 S(1) line ratios of 0.4 and 0.5. Of the 11 pre-main sequence
sources now known to be sources of quiescent near-infrared hydrogen emission,
four possess transitional disks, which suggests that detectable levels of H
emission and the presence of inner disk holes are correlated. These H
detections demonstrate that these inner holes are not completely devoid of gas,
in agreement with the presence of observable accretion signatures for all four
of these stars and the recent detections of [Ne II] emission from three of
them. The overlap in [Ne II] and H detections hints at a possible
correlation between these two features and suggests a shared excitation
mechanism of high energy photons. Our models, combined with the kinematic
information from the H lines, locate the bulk of the emitting gas at a few
tens of AU from the stars. We also find a correlation between H detections
and those targets which possess the largest H equivalent widths,
suggesting a link between accretion activity and quiescent H emission. We
conclude that quiescent H emission from relatively hot gas within the disks
of TTS is most likely related to on-going accretion activity, the production of
UV photons and/or X-rays, and the evolutionary status of the dust grain
populations in the inner disks.Comment: 12 pages, emulateapj, Accepted by Ap
The Michigan Infrared Test Thermal ELT N-band (MITTEN) Cryostat
We introduce the Michigan Infrared Test Thermal ELT N-band (MITTEN) Cryostat,
a new facility for testing infrared detectors with a focus on mid-infrared
(MIR) wavelengths (8-13 microns). New generations of large format, deep well,
fast readout MIR detectors are now becoming available to the astronomical
community. As one example, Teledyne Imaging Sensors (TIS) has introduced a
long-wave Mercury-Cadmium-Telluride (MCT) array, GeoSnap, with high quantum
efficiency (> 65 %) and improved noise properties compared to previous
generation Si:As blocked impurity band (BIB) detectors. GeoSnap promises
improved sensitivities, and efficiencies, for future background-limited MIR
instruments, in particular with future extremely large telescopes (ELTs). We
describe our new test facility suitable for measuring characteristics of these
detectors, such as read noise, dark current, linearity, gain, pixel
operability, quantum efficiency, and point source imaging performance relative
to a background scene, as well as multiple point sources of differing contrast.
MITTEN has an internal light source, and soon an accompanying filter wheel and
aperture plate, reimaged onto the detector using an Offner relay. The baseline
temperature of the cryostat interior is maintained < 40 K and the optical bench
maintains a temperature of 16 K using a two-stage pulse-tube cryocooler package
from Cryomech. No measurable background radiation from the cryostat interior
has yet been detected.Comment: 10 pages, 6 figures, To appear in the SPIE Proceedings 'Astronomical
Telescopes and Instrumentation' (2020
Outcome of Respiratory Syncytial Virus Lower Respiratory Tract Disease in Hematopoietic Cell Transplant Recipients Receiving Aerosolized Ribavirin: Significance of Stem Cell Source and Oxygen Requirement
AbstractRespiratory syncytial virus (RSV) infection is an important complication after hematopoietic cell transplantation (HCT), and RSV lower respiratory tract disease (LRD) results in substantial early mortality and late airflow obstruction among survivors. Factors associated with poor outcome are unknown. We evaluated the effect of transplant and treatment factors on overall survival, mortality from respiratory failure, and pulmonary function among 82 HCT recipients who had RSV LRD between 1990 and 2011. All patients received aerosolized ribavirin. In multivariable analyses, only the use of marrow or cord blood as graft source (adjusted hazard ratio [aHR], 4.1; 95% confidence interval [CI], 1.8 to 9.0; P < .001) and oxygen requirement (aHR, 3.3; 95% CI, 1.5 to 6.7; P = .003) remained independently associated with overall mortality and death due to respiratory failure (aHR, 4.7; 95% CI, 1.8 to 13; P = .002 and aHR, 5.4; 95% CI, 1.8 to 16; P = .002, respectively). Antibody-based treatments, including intravenous immunoglobulin and palivizumab, were not independently associated with improved outcome and did not alter the associations of the graft source and oxygen requirements in statistical models. In conclusion, use of peripheral blood stem cells as graft source and lack of oxygen requirement at diagnosis appear to be important factors associated with improved survival of HCT recipients with RSV LRD. These results may explain differences in outcomes reported from RSV infection over time and may guide the design of future interventional trials
The Epsilon Calculus and Herbrand Complexity
Hilbert's epsilon-calculus is based on an extension of the language of
predicate logic by a term-forming operator . Two fundamental
results about the epsilon-calculus, the first and second epsilon theorem, play
a role similar to that which the cut-elimination theorem plays in sequent
calculus. In particular, Herbrand's Theorem is a consequence of the epsilon
theorems. The paper investigates the epsilon theorems and the complexity of the
elimination procedure underlying their proof, as well as the length of Herbrand
disjunctions of existential theorems obtained by this elimination procedure.Comment: 23 p
Co-phasing the Large Binocular Telescope: status and performance of LBTI/PHASECam
The Large Binocular Telescope Interferometer is a NASA-funded nulling and
imaging instrument designed to coherently combine the two 8.4-m primary mirrors
of the LBT for high-sensitivity, high-contrast, and high-resolution infrared
imaging (1.5-13 um). PHASECam is LBTI's near-infrared camera used to measure
tip-tilt and phase variations between the two AO-corrected apertures and
provide high-angular resolution observations. We report on the status of the
system and describe its on-sky performance measured during the first semester
of 2014. With a spatial resolution equivalent to that of a 22.8-meter telescope
and the light-gathering power of single 11.8-meter mirror, the co-phased LBT
can be considered to be a forerunner of the next-generation extremely large
telescopes (ELT).Comment: 8 pages, 5 figures, SPIE Conference proceeding
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