8,676 research outputs found
SPIRAL Phase A: A Prototype Integral Field Spectrograph for the AAT
We present details of a prototype fiber feed for use on the Anglo-Australian
Telescope (AAT) that uses a dedicated fiber-fed medium/high resolution (R >
10000) visible-band spectrograph to give integral field spectroscopy (IFS) of
an extended object. A focal reducer couples light from the telescope to the
close-packed lenslet array and fiber feed, allowing the spectrograph be used on
other telescopes with the change of a single lens. By considering the
properties of the fibers in the design of the spectrograph, an efficient design
can be realised, and we present the first scientific results of a prototype
spectrograph using a fiber feed with 37 spatial elements, namely the detection
of Lithium confirming a brown dwarf candidate and IFS of the supernova remnant
SN1987A.Comment: 41 pages, 15 figures, 3 tables; accepted by PAS
SwSt 1: an O-rich planetary nebula around a C-rich central star
The hydrogen-deficient carbon-rich [WCL] type central star HD167362 and its
oxygen-rich planetary nebula (PN) SwSt~1 are investigated. The nebular
chemistry might indicate a recent origin for the carbon-rich stellar spectrum.
Its stellar and nebular properties might therefore provide further
understanding of the origin of the [WCL] central star class. The UV-IR stellar
spectra are modelled with state of the codes and show ~40kK central star with a
wind and a C/O~3, indicative of efficient third dredge-up. The synthetic
stellar flux distribution is used to model the high density, compact PN, which
has a solar C/O ratio, is still enshrouded by 1200K and 230K dust shells and,
reported here for the first time, in molecular hydrogen. Although it appears
that the change in C/O ratio has been recent, the published spectroscopy since
1895 has been re-examined and no clear spectral change is seen. If an event
occurred that has turned it into a hydrogen-deficient central star, it did not
happen in the last 100 years.Comment: 31 pages, 19 figures (some are gif files), MNRAS in pres
Integral throat entrance development, qualification and production for the Antares 3 nozzle
Although design analyses of a G-90 graphite integral throat entrance for the Antares 3 solid rocket motor nozzle indicated acceptable margins of safety, the nozzle throat insert suffered a thermostructural failure during the first development firing. Subsequent re-analysis using properties measured on material from the same billet as the nozzle throat insert showed negative margins. Carbon-carbon was investigated and found to result in large positive margins of safety. The G-90 graphite was replaced by SAI fast processed 4-D material which uses Hercules HM 10000 fiber as the reinforcement. Its construction allows powder filling of the interstices after preform fabrication which accelerates the densification process. Allied 15V coal tar pitch is then used to complete densification. The properties were extensively characterized on this material and six nozzles were subjected to demonstration, development and qualification firings
Variable-Speed-of-Light Cosmology and Second Law of Thermodynamics
We examine whether the cosmologies with varying speed of light (VSL) are
compatible with the second law of thermodynamics. We find that the VSL
cosmology with varying fundamental constant is severely constrained by the
second law of thermodynamics, whereas the bimetric cosmological models are less
constrained.Comment: 15 pages, LaTeX, Revised version with minor corrections to appear in
Phys. Rev.
Lateral dopant profiling in MOS structures on a 100 nm scale using scanning capacitance microscopy
Journal ArticleScanning capacitance microscopy and atomic force microscopy have been used to image the extent of lateral dopant diffusion in MOS structures. The data are capacitance vs. voltage measurements made on a submicron scale. The technique is non-destructive when imaging uncleaved samples. New experimental data are presented here on actual, cleaved device structures which clearly indicate the two-dimensional dopant profile in terms of a spatially varying modulated capacitance signal. First-order deconvolution indicates the technique has much promise for the quantitative characterization of dopant profiles. The potential of the technique to illuminate important device-related phenomena on a local scale is also discussed
A dense disk of dust around the born-again Sakurai's object
In 1996, Sakurai's object (V4334 Sgr) suddenly brightened in the centre of a
faint Planetary Nebula (PN). This very rare event was interpreted as the
reignition of a hot white dwarf that caused a rapid evolution back to the cool
giant phase. From 1998 on, a copious amount of dust has formed continuously,
screening out the star which has remained embedded in this expanding high
optical depth envelope. The new observations, reported here, are used to study
the morphology of the circumstellar dust in order to investigate the hypothesis
that Sakurai's Object is surrounded by a thick spherical envelope of dust. We
have obtained unprecedented, high-angular resolution spectro-interferometric
observations, taken with the mid-IR interferometer MIDI/VLTI, which resolve the
dust envelope of Sakurai's object. We report the discovery of a unexpectedly
compact (30 x 40 milliarcsec, 105 x 140 AU assuming a distance of 3.5 kpc),
highly inclined, dust disk. We used Monte Carlo radiative-transfer simulations
of a stratified disk to constrain its geometric and physical parameters,
although such a model is only a rough approximation of the rapidly evolving
dust structure. Even though the fits are not fully satisfactory, some useful
and robust constraints can be inferred. The disk inclination is estimated to be
75+/-3 degree with a large scale height of 47+/-7 AU. The dust mass of the disk
is estimated to be 6 10^{-5} solar mass. The major axis of the disk (132+/-3
degree) is aligned with an asymmetry seen in the old PN that was
re-investigated as part of this study. This implies that the mechanism
responsible for shaping the dust envelope surrounding Sakurai's object was
already at work when the old PN formed.Comment: A&A Letter, accepte
The Flux Ratio Method for Determining the Dust Attenuation of Starburst Galaxies
The presence of dust in starburst galaxies complicates the study of their
stellar populations as the dust's effects are similar to those associated with
changes in the galaxies' stellar age and metallicity. This degeneracy can be
overcome for starburst galaxies if UV/optical/near-infrared observations are
combined with far-infrared observations. We present the calibration of the flux
ratio method for calculating the dust attenuation at a particular wavelength,
Att(\lambda), based on the measurement of F(IR)/F(\lambda) flux ratio. Our
calibration is based on spectral energy distributions (SEDs) from the PEGASE
stellar evolutionary synthesis model and the effects of dust (absorption and
scattering) as calculated from our Monte Carlo radiative transfer model. We
tested the attenuations predicted from this method for the Balmer emission
lines of a sample starburst galaxies against those calculated using radio
observations and found good agreement. The UV attenuation curves for a handful
of starburst galaxies were calculated using the flux ratio method, and they
compare favorably with past work. The relationship between Att(\lambda) and
F(IR)/F(\lambda) is almost completely independent of the assumed dust
properties (grain type, distribution, and clumpiness). For the UV, the
relationship is also independent of the assumed stellar properties (age,
metallicity, etc) accept for the case of very old burst populations. However at
longer wavelengths, the relationship is dependent on the assumed stellar
properties.Comment: accepted by the ApJ, 18 pages, color figures, b/w version at
http://mips.as.arizona.edu/~kgordon/papers/fr_method.htm
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