341 research outputs found
Near-Infrared, Adaptive Optics Observations of the T Tauri Multiple-Star System
With high-angular-resolution, near-infrared observations of the young stellar
object T Tauri at the end of 2002, we show that, contrary to previous reports,
none of the three infrared components of T Tau coincide with the compact radio
source that has apparently been ejected recently from the system (Loinard,
Rodriguez, and Rodriguez 2003). The compact radio source and one of the three
infrared objects, T Tau Sb, have distinct paths that depart from orbital or
uniform motion between 1997 and 2000, perhaps indicating that their interaction
led to the ejection of the radio source. The path that T Tau Sb took between
1997 and 2003 may indicate that this star is still bound to the presumably more
massive southern component, T Tau Sa. The radio source is absent from our
near-infrared images and must therefore be fainter than K = 10.2 (if located
within 100 mas of T Tau Sb, as the radio data would imply), still consistent
with an identity as a low-mass star or substellar object.Comment: 11 pages, 3 figures, submitted to ApJ
Improved Si:As BIBIB (Back-Illuminated Blocked-Impurity-Band) hybrid arrays
Results of a program to increase the short wavelength (less than 10 microns) detective quantum efficiency, eta/beta, of Si:As Impurity Band Conduction arrays are presented. The arrays are epitaxially grown Back-Illuminated Blocked (BIB) Impurity-Band (BIBIB) 10x50 detectors bonded to switched-FET multiplexers. It is shown that the 4.7 microns detective quantum efficiency increases proportionately with the thickness of the infrared active layer. A BIB array with a thick active layer, designed for low dark current, exhibits eta/beta = 7 to 9 percent at 4.7 microns for applied bias voltages between 3 and 5 V. The product of quantum efficiency and photoelectric gain, etaG, increases from 0.3 to 2.5 as the voltage increases from 3 to 5 V. Over this voltage range, the dark current increases from 8 to 120 e(-)s(-1) at a device temperature of 4.2 K and is under 70 e(-)s(-1) for all voltages at 2 K. Because of device gain, the effective dark current (equivalent photon rate) is less than 3 e(-)s(-1) under all operating conditions. The effective read noise (equivalent photon noise) is found to be less than 12 electrons under all operating conditions and for integration times between 0.05 and 100 seconds
Joint Astrophysics Nascent Universe Satellite:. utilizing GRBs as high redshift probes
The Joint Astrophysics Nascent Universe Satellite (JANUS) is a multiwavelength cosmology mission designed to address fundamental questions about the cosmic dawn. It has three primary science objectives: (1) measure the massive star formation rate over 5 †z †12 by discovering and observing high-z gamma-ray bursts (GRBs) and their afterglows, (2) enable detailed studies of the history of reionization and metal enrichment in the early Universe, and (3) map the growth of the first supermassive black holes by discovering and observing the brightest quasars at z â„ 6. A rapidly slewing spacecraft and three science instruments â the X-ray Coded Aperture Telescope (XCAT), the Near InfraRed Telescope (NIRT), and the GAmma-ray Transient Experiment for Students (GATES) â make-up the JANUS observatory and are responsible for realizing the three primary science objectives. The XCAT (0.5â20 keV) is a wide field of view instrument responsible for detecting and localizing âŒ60 z â„ 5 GRBs, including âŒ8 z â„ 8 GRBs, during a 2-year mission. The NIRT (0.7â1.7 ”m) refines the GRB positions and provides rapid (†30 min) redshift information to the astronomical community. Concurrently, the NIRT performs a 20, 000 deg2 survey of the extragalactic sky discovering and localizing âŒ300 z â„ 6 quasars, including âŒ50 at z â„ 7, over a two-year period. The GATES provides high-energy (15 keV â1.0 MeV) spectroscopy as well as 60â500 keV polarimetry of bright GRBs. Here we outline the JANUS instrumentation and the mission science motivations
Moderate Resolution Spectroscopy For The Space Infrared Telescope Facility (SIRTF)
A conceptual design for an infrared spectrometer capable of both low resolution (λ/Î-λ = 50; 2.5-200 microns) and moderate resolution (1000; 4-200 microns) and moderate resolution (1000; 4-200 microns) has been developed. This facility instrument will permit the spectroscopic study in the infrared of objects ranging from within the solar system to distant galaxies. The spectroscopic capability provided by this instrument for SIRTF will give astronomers orders of magnitude greater sensitivity for the study of faint objects than had been previously available. The low resolution mode will enable detailed studies of the continuum radiation. The moderate resolution mode of the instrument will permit studies of a wide range of problems, from the infrared spectral signatures of small outer solar system bodies such as Pluto and the satellites of the giant planets, to investigations of more luminous active galaxies and QS0s at substantially greater distances. A simple design concept has been developed for the spectrometer which supports the science investigation with practical cryogenic engineering. Operational flexibility is preserved with a minimum number of mechanisms. The five modules share a common aperture, and all gratings share a single scan mechanism. High reliability is achieved through use of flight-proven hardware concepts and redundancy. The design controls the heat load into the SIRTF cryogen, with all heat sources other than the detectors operating at 7K and isolated from the 4K cold station. Two-dimensional area detector arrays are used in the 2.5-120ÎŒm bands to simultaneously monitor adjacent regions in extended objects and to measure the background near point sources
Spitzer-IRS Spectroscopy of the Prototypical Starburst Galaxy NGC7714
We present observations of the starburst galaxy NGC 7714 with the Infrared
Spectrograph IRS on board the Spitzer Space Telescope. The spectra yield a
wealth of ionic and molecular features that allow a detailed characterization
of its properties. NGC 7714 has an HII region-like spectrum with strong PAH
emission features. We find no evidence for an obscured active galactic nucleus,
and with [NeIII]/[NeII]~0.73, NGC7714 lies near the upper end of
normal-metallicity starburst galaxies. With very little slicate absorption and
a temperature of the hottest dust component of 340K, NGC 7714 is the perfect
template for a young, unobscured starburstComment: To appear in the special ApJSS issue on early results from Spitze
The Extraordinary Mid-infrared Spectrum of the Blue Compact Dwarf Galaxy SBS0335-052
SBS0335-052 is a blue compact dwarf galaxy (BCD) with one of the lowest known
metallicities, ZZ_{\sun}/41, making it a local example of how
primordial starburst galaxies and their precursors might appear. A spectrum
obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope
clearly shows silicate absorption features, emission lines of [SIV] and
[NeIII], and puts strong upper limits on the PAH emission features. The
observed low resolution spectrum (R~90) extends from 5.3 to 35microns and peaks
at ~28microns. The spectrum is compared to IRS observations of the prototypical
starburst nucleus NGC7714. SBS0335-052 is quite unlike normal starburst
galaxies, which show strong PAH bands, low ionization emission lines, and a
continuum peak near 80microns. The continuum difference for m
implies a substantial reduction in the mass of cold dust. If the spectrum of
this very low metallicity galaxy is representative of star forming galaxies at
higher redshifts, it may be difficult to distinguish them from AGNs which also
show relatively featureless flat spectra in the mid-IR.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 2 figure
M/L, H-alpha Rotation Curves, and HI Measurements for 329 Nearby Cluster and Field Spirals: II. Evidence for Galaxy Infall
We have conducted a study of optical and HI properties of spiral galaxies
(size, luminosity, H-alpha flux distribution, circular velocity, HI gas mass)
to explore the role of gas stripping as a driver of morphological evolution in
clusters. We find a strong correlation between the spiral and S0 fractions
within clusters, and the spiral fraction scales tightly with cluster X-ray gas
luminosity. We explore young star formation and identify spirals that are (1)
asymmetric, with truncated H-alpha emission and HI gas reservoirs on the
leading edge of the disk, on a first pass through the dense intracluster medium
in the cores of rich clusters; (2) strongly HI deficient and stripped, with
star formation confined to the inner 5 kpc/h and 3 disk scale lengths; (3)
reddened, extremely HI deficient and quenched, where star formation has been
halted across the entire disk. We propose that these spirals are in successive
stages of morphological transformation, between infalling field spirals and
cluster S0s, and that the process which acts to remove the HI gas reservoir
suppresses new star formation on a similarly fast timescale. These data suggest
that gas stripping plays a significant role in morphological transformation and
rapid truncation of star formation across the disk.Comment: 24 pages, 12 figures; accepted for publication in AJ;
higher-resolution figures available at http://astronomy.nmsu.edu/nicol
The Mid-IR Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy
We present 5-38um mid-infrared spectra at a spectral resolution of R~65-130
of a large sample of 22 starburst nuclei taken with the Infrared Spectrograph
IRS on board the Spitzer Space Telescope. The spectra show a vast range in
starburst SEDs. The silicate absorption ranges from essentially no absorption
to heavily obscured systems with an optical depth of tau(9.8um)~5. The spectral
slopes can be used to discriminate between starburst and AGN powered sources.
The monochromatic continuum fluxes at 15um and 30um enable a remarkably
accurate estimate of the total infrared luminosity of the starburst. We find
that the PAH equivalent width is independent of the total starburst luminosity
L_IR as both continuum and PAH feature scale proportionally. However, the
luminosity of the 6.2um feature scales with L_IR and can be used to approximate
the total infrared luminosity of the starburst. Although our starburst sample
covers about a factor of ten difference in the [NeIII]/[NeII] ratio, we found
no systematic correlation between the radiation field hardness and the PAH
equivalent width or the 7.7um/11.3um PAH ratio. These results are based on
spatially integrated diagnostics over an entire starburst region, and local
variations may be ``averaged out''. It is presumably due to this effect that
unresolved starburst nuclei with significantly different global properties
appear spectrally as rather similar members of one class of objects.Comment: 22 pages, accepted for publication in ApJ, a high-resolution version
is available from http://www.strw.leidenuniv.nl/~brandl/IRS_starbursts.pd
Observations of Ultraluminous Infrared Galaxies with the Infrared Spectrograph on the Spitzer Space Telescope: Early Results on Mrk 1014, Mrk 463, and UGC 5101
We present spectra taken with the Infrared Spectrograph on Spitzer covering
the 5-38micron region of three Ultraluminous Infrared Galaxies (ULIRGs): Mrk
1014 (z=0.163), and Mrk 463 (z=0.051), and UGC 5101 (z=0.039). The continua of
UGC 5101 and Mrk 463 show strong silicate absorption suggesting significant
optical depths to the nuclei at 10microns. UGC 5101 also shows the clear
presence of water ice in absorption. PAH emission features are seen in both Mrk
1014 and UGC 5101, including the 16.4micron line in UGC 5101. The fine
structure lines are consistent with dominant AGN power sources in both Mrk 1014
and Mrk 463. In UGC 5101 we detect the [NeV] 14.3micron emission line providing
the first direct evidence for a buried AGN in the mid-infrared. The detection
of the 9.66micron and 17.03micron H emission lines in both UGC 5101 and
Mrk 463 suggest that the warm molecular gas accounts for 22% and 48% of the
total molecular gas masses in these galaxies.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 3 figure
Esophageal intramural pseudodiverticulosis characterized by barium esophagography: a case report
<p>Abstract</p> <p>Introduction</p> <p>Esophageal intramural pseudodiverticulosis is a rare condition characterized by the dilatation of the submucosal glands.</p> <p>Case presentation</p> <p>We present a case of esophageal intramural pseudodiverticulosis in a 72-year-old Caucasian man who presented with dysphagia and with a background history of alcohol abuse. An upper gastrointestinal endoscopy of our patient showed an esophageal stricture with abnormal mucosal appearances, but no malignant cells were seen at biopsy. Appearances on a barium esophagram were pathognomonic for esophageal intramural pseudodiverticulosis.</p> <p>Conclusion</p> <p>We demonstrate the enduring usefulness of barium esophagography in the characterization of abnormal mucosal appearances at endoscopy.</p
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