302 research outputs found
Superconducting resonator circuits at frequencies above the gap frequency
The frequency response of three superconductive niobium resonating circuits, formed by a Nb microstrip and a Nb tunnel junction, is measured and analyzed at frequencies above the superconducting gap frequency. The circuits are placed in a waveguide system and the frequency response is determined with a Fourier transform spectrometer. The calculated and measured resonance frequencies and bandwidths are in good agreement with the extreme anomalous limit of the MattisâBardeen theory on the anomalous skin effect in superconductors [D.C. Mattis and J. Bardeen, Phys. Rev. 111, 412 (1958)]. The observed loss is higher than predicted by this theory, in agreement with previous observations on Nb films. The use of other materials for striplines as tuning circuits for heterodyne superconducting tunnel junction mixers is analyzed
Neon and Sulfur Abundances of Planetary Nebulae in the Magellanic Clouds
The chemical abundances of neon and sulfur for 25 planetary nebulae (PNe) in
the Magellanic Clouds are presented. These abundances have been derived using
mainly infrared data from the Spitzer Space Telescope. The implications for the
chemical evolution of these elements are discussed. A comparison with similarly
obtained abundances of Galactic PNe and HII regions and Magellanic Clouds HII
regions is also given. The average neon abundances are 6.0x10(-5) and
2.7x10(-5) for the PNe in the Large and Small Magellanic Clouds respectively.
These are ~1/3 and 1/6 of the average abundances of Galactic planetary nebulae
to which we compare. The average sulfur abundances for the LMC and SMC are
respectively 2.7x10(-6) and 1.0x10(-6). The Ne/S ratio (23.5) is on average
higher than the ratio found in Galactic PNe (16) but the range of values in
both data sets is similar for most of the objects. The neon abundances found in
PNe and HII regions agree with each other. It is possible that a few (3-4) of
the PNe in the sample have experienced some neon enrichment, but for two of
these objects the high Ne/S ratio can be explained by their very low sulfur
abundances. The neon and sulfur abundances derived in this paper are also
compared to previously published abundances using optical data and
photo-ionization models.Comment: 13 pages, 4 tables, 5 figures. Accepted for publication in Ap
Identification of SH ro-vibrational lines in R And
We report the identification of SH ro-vibrational lines in the
published high-resolution infrared spectrum of the S-type star, R And. This is
the first astronomical detection of this molecule. The lines show inverse
P-Cygni profiles, indicating infall motion of the molecular layer due to
stellar pulsation. A simple spherical shell model with a constant infall
velocity is adopted to determine the condition of the layer. It is found that a
single excitation temperature of 2200 K reproduces the observed line
intensities satisfactory. SH is located in a layer from 1.0 to ~1.1 stellar
radii, which is moving inward with a velocity of 9 km s-1. These results are
consistent with the previous measurements of CO transitions. The
estimated molecular abundance SH/H is 1x10^-7, consistent with a thermal
equilibrium calculation.Comment: 10 pages, 2 figures. Accepted for publication in ApJ Letter
Infrared Spectroscopy of Molecular Supernova Remnants
We present Infrared Space Observatory spectroscopy of sites in the supernova
remnants W28, W44, and 3C391, where blast waves are impacting molecular clouds.
Atomic fine-structure lines were detected from C, N, O, Si, P, and Fe. The S(3)
and S(9) lines of H2 were detected for all three remnants. The observations
require both shocks into gas with moderate (~ 100 /cm3) and high (~10,000 /cm3)
pre-shock densities, with the moderate density shocks producing the ionic lines
and the high density shock producing the molecular lines. No single shock model
can account for all of the observed lines, even at the order of magnitude
level. We find that the principal coolants of radiative supernova shocks in
moderate-density gas are the far-infrared continuum from dust grains surviving
the shock, followed by collisionally-excited [O I] 63.2 and [Si II] 34.8 micron
lines. The principal coolant of the high-density shocks is
collisionally-excited H2 rotational and ro-vibrational line emission. We
systematically examine the ground-state fine structure of all cosmically
abundant elements, to explain the presence or lack of all atomic fine lines in
our spectra in terms of the atomic structure, interstellar abundances, and a
moderate-density, partially-ionized plasma. The [P II] line at 60.6 microns is
the first known astronomical detection. There is one bright unidentified line
in our spectra, at 74.26 microns. The presence of bright [Si II] and [Fe II]
lines requires partial destruction of the dust. The required gas-phase
abundance of Fe suggests 15-30% of the Fe-bearing grains were destroyed. The
infrared continuum brightness requires ~1 Msun of dust survives the shock,
suggesting about 1/3 of the dust mass was destroyed, in agreement with the
depletion estimate and with theoretical models for dust destruction.Comment: 40 pages; 10 figures; accepted by ApJ July 11, 200
The acâJosephson effect above the gap frequency
The rfâpower dependence of the acâJosephson steps is measured at 720 GHz, using small area Nb tunnel junctions. This frequency is well above the gap frequency of Nb. The junction is placed in a waveguide, and connected to a superconducting stripline, which effectively tunes out the junction capacitance and facilitates the coupling of the radiation to the junction. We observe three Josephson steps, and the first step crosses the zero current axis over a considerable range of rfâpower. This indicates the possible application of THz Josephson steps in voltage standards. The data are compared to the theory and we find clear evidence for the predicted intrinsic rollâoff of the Josephson current amplitude above the gap frequency
The infrared spectrum of the Be star gamma Cassiopeiae
We present the 2.4-45 micrometer ISO-SWS spectrum of the Be star gamma Cas
(B0.5 IVe). The spectrum is characterised by a thermal continuum which can be
well fit by a power-law S_nu ~ nu^0.99 over the entire SWS wavelength range.
For an isothermal disc of ionized gas with constant opening angle, this
correponds to a density gradient rho(r) ~ r^(-2.8). We report the detection of
the Humphreys bound-free jump in emission at 3.4 micrometer. The size of the
jump is sensitive to the electron temperature of the gas in the disc, and we
find T~9000 K, i.e. much lower than the stellar effective temperature
(25000-30000 K). The spectrum is dominated by numerous emission lines, mostly
from HI, but also some HeI lines are detected. Several spectral features cannot
be identified. The line strengths of the HI{\sc i} emission lines do not follow
case B recombination line theory. The line strengths and widths suggest that
many lines are optically thick and come from an inner, high density region with
radius 3-5 R_star and temperature above that of the bulk of the disc material.
Only the alpha, beta and gamma transitions of the series lines contain a
contribution from the outer regions. The level populations deviate
significantly from LTE and are highly influenced by the optically thick, local
(disc) continuum radiation field. The inner disk may be rotating more rapidly
than the stellar photosphere.Comment: 8 pages, 5 figure, accepted by A&
ISO observations of far-infrared rotational emission lines of water vapor toward the supergiant star VY Canis Majoris
We report the detection of numerous far-infrared emission lines of water
vapor toward the supergiant star VY Canis Majoris. A 29.5 - 45 micron grating
scan of VY CMa, obtained using the Short Wavelength Spectrometer (SWS) of the
Infrared Space Observatory (ISO) at a spectral resolving power of approximately
2000, reveals at least 41 spectral features due to water vapor that together
radiate a total luminosity ~ 25 solar luminosities. In addition to pure
rotational transitions within the ground vibrational state, these features
include rotational transitions within the (010) excited vibrational state. The
spectrum also shows the doublet Pi 1/2 (J=5/2) <-- doublet Pi 3/2 (J=3/2) OH
feature near 34.6 micron in absorption. Additional SWS observations of VY CMa
were carried out in the instrument's Fabry-Perot mode for three water
transitions: the 7(25)-6(16) line at 29.8367 micron, the 4(41)-3(12) line
31.7721 micron, and the 4(32)-3(03) line at 40.6909 micron. The higher spectral
resolving power of approximately 30,000 thereby obtained permits the line
profiles to be resolved spectrally for the first time and reveals the "P Cygni"
profiles that are characteristic of emission from an outflowing envelope.Comment: 11 pages (inc. 2 figures), LaTeX, uses aaspp4.sty, accepted for
publication in ApJ Letter
ISO-SWS spectroscopy of NGC 1068
We present ISO-SWS spectroscopy of NGC 1068 for the wavelength range 2.4 to
45um, detecting a total of 36 emission lines. Most of the observed transitions
are fine structure and recombination lines originating in the narrow line
region. We compare the line profiles of optical lines and reddening-insensitive
infrared lines to constrain the dynamical structure and extinction properties
of the NLR. The considerable differences found are most likely explained by two
effects. (1) The spatial structure of the NLR is a combination of a highly
ionized outflow cone and lower excitation extended emission. (2) Parts of the
NLR, mainly in the receding part at velocities above systemic, are subject to
extinction that is significantly suppressing optical emission. Line asymmetries
and net blueshifts remain, however, even for infrared fine structure lines
suffering very little obscuration. This may be either due to an intrinsic
asymmetry of the NLR, or due to a very high column density obscuring component
which is hiding part of the NLR even from infrared view. Mid-infrared emission
of molecular hydrogen in NGC 1068 arises in a dense molecular medium at
temperatures of a few hundred Kelvin that is most likely closely related to the
warm and dense components seen in the near-infrared H2 transitions, and in
millimeter wave tracers of molecular gas. Any emission of the putative pc-scale
molecular torus is likely overwhelmed by this larger scale emission.Comment: aastex (V4), 9 eps figures. Accepted by Ap
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