7,353 research outputs found
PILOT: design and capabilities
The proposed design for PILOT is a general-purpose, wide-field 1 degree 2.4m,
f/10 Ritchey-Chretien telescope, with fast tip-tilt guiding, for use 0.5-25
microns. The design allows both wide-field and diffraction-limited use at these
wavelengths. The expected overall image quality, including median seeing, is
0.28-0.3" FWHM from 0.8-2.4 microns. Point source sensitivities are estimated.Comment: 4 pages, Proceedings of 2nd ARENA conference 'The Astrophysical
Science Cases at Dome C', Potsdam, 17-21 September 200
The brightness distribution of IRC +10216 at 11 microns
The brightness distribution of IRC +10216 at a wavelength of 11 microns was measured in detail using a spatial interferometer. This brightness distribution appears to have azimuthal symmetry; an upper limit of 1.1 may be set to the ellipticity at 11 microns if the object has a major axis oriented either along or perpendicular to the major axis of the optical image. The radial distribution shows both compact and extended emission. The extended component, which is due to thermal emission from circumstellar dust, contributes 91% of the total flux and has a 1/e diameter of 0.90 minutes. The tapered shape of this component is consistent with a l/r squared dust density dependence. The compact component is unresolved (less than 0.2 minutes in diameter) and represents emission from the central star seen through the circumstellar envelope
Pulse Profiles, Accretion Column Dips and a Flare in GX 1+4 During a Faint State
The Rossi X-ray Timing Explorer (RXTE) spacecraft observed the X-ray pulsar
GX 1+4 for a period of 34 hours on July 19/20 1996. The source faded from an
intensity of ~20 mCrab to a minimum of <~0.7 mCrab and then partially recovered
towards the end of the observation. This extended minimum lasted ~40,000
seconds. Phase folded light curves at a barycentric rotation period of
124.36568 +/- 0.00020 seconds show that near the center of the extended minimum
the source stopped pulsing in the traditional sense but retained a weak dip
feature at the rotation period. Away from the extended minimum the dips are
progressively narrower at higher energies and may be interpreted as
obscurations or eclipses of the hot spot by the accretion column. The pulse
profile changed from leading-edge bright before the extended minimum to
trailing-edge bright after it. Data from the Burst and Transient Source
Experiment (BATSE) show that a torque reversal occurred <10 days after our
observation. Our data indicate that the observed rotation departs from a
constant period with a Pdot/P value of ~-1.5% per year at a 4.5 sigma
significance. We infer that we may have serendipitously obtained data, with
high sensitivity and temporal resolution about the time of an accretion disk
spin reversal. We also observed a rapid flare which had some precursor
activity, close to the center of the extended minimum.Comment: 19 pages, 6 figures, accepted for publication in Astrophysical
Journal (tentatively scheduled for vol. 529 #1, 20 Jan 2000
Spatial heterodyne interferometry of VY Canis Major's, alpha Orionis, alpha Scorpii, and R leonis at 11 microns
Using the technique of heterodyne interferometry, measurements were made of the spatial distribution of 11 micron radiation from four late type stars. The circumstellar shells surrounding VY Canis Majoris, alpha Orionis, and alpha Scorpii were resolved, whereas that of R Leonis was only partially resolved at a fringe spacing of 0.4 sec
A new application of emulsions to measure the gravitational force on antihydrogen
We propose to build and operate a detector based on the emulsion film
technology for the measurement of the gravitational acceleration on antimatter,
to be performed by the AEgIS experiment (AD6) at CERN. The goal of AEgIS is to
test the weak equivalence principle with a precision of 1% on the gravitational
acceleration g by measuring the vertical position of the anni- hilation vertex
of antihydrogen atoms after their free fall in a horizontal vacuum pipe. With
the emulsion technology developed at the University of Bern we propose to
improve the performance of AEgIS by exploiting the superior position resolution
of emulsion films over other particle de- tectors. The idea is to use a new
type of emulsion films, especially developed for applications in vacuum, to
yield a spatial resolution of the order of one micron in the measurement of the
sag of the antihydrogen atoms in the gravitational field. This is an order of
magnitude better than what was planned in the original AEgIS proposal.Comment: 17 pages, 14 figure
Radiative recombination data for modeling dynamic finite-density plasmas
We have calculated partial final-state resolved radiative recombination (RR) rate coefficients from the initial ground and metastable levels of all elements up to and including Zn, plus Kr, Mo, and Xe, for all isoelectronic sequences up to Na-like forming Mg-like. The data are archived according to the Atomic Data and Analysis Structure (ADAS) data class adf48, which spans a temperature range of z2(101-107) K, where z is the initial ion charge. Fits to total rate coefficients have been determined, for both the ground and metastable levels, and those for the ground are presented here. Comparison is made both with previous RR rate coefficients and with (background) R-matrix photoionization cross sections. This RR database complements a dielectronic recombination (DR) database already produced, and both are being used to produce updated ionization balances for both (electron) collisionally ionized and photoionized plasmas
Luminosity indicators in dusty photoionized environments
The luminosity of the central source in ionizing radiation is an essential
parameter in a photoionized environment, and one of the most fundamental
physical quantities one can measure. We outline a method of determining
luminosity for any emission-line region using only infrared data. In dusty
environments, grains compete with hydrogen in absorbing continuum radiation.
Grains produce infrared emission, and hydrogen produces recombination lines. We
have computed a very large variety of photoionization models, using ranges of
abundances, grain mixtures, ionizing continua, densities, and ionization
parameters. The conditions were appropriate for such diverse objects as H II
regions, planetary nebulae, starburst galaxies, and the narrow and broad line
regions of active nuclei. The ratio of the total thermal grain emission
relative to H (IR/H) is the primary indicator of whether the
cloud behaves as a classical Str\"{o}mgren sphere (a hydrogen-bounded nebula)
or whether grains absorb most of the incident continuum (a dust-bounded
nebula). We find two global limits: when infrared recombination
lines determine the source luminosity in ionizing photons; when
the grains act as a bolometer to measure the luminosity.Comment: 12 pages 3 figures. Accepted ASP Sept.9
Laminar flow of two miscible fluids in a simple network
When a fluid comprised of multiple phases or constituents flows through a
network, non-linear phenomena such as multiple stable equilibrium states and
spontaneous oscillations can occur. Such behavior has been observed or
predicted in a number of networks including the flow of blood through the
microcirculation, the flow of picoliter droplets through microfluidic devices,
the flow of magma through lava tubes, and two-phase flow in refrigeration
systems. While the existence of non-linear phenomena in a network with many
inter-connections containing fluids with complex rheology may seem
unsurprising, this paper demonstrates that even simple networks containing
Newtonian fluids in laminar flow can demonstrate multiple equilibria.
The paper describes a theoretical and experimental investigation of the
laminar flow of two miscible Newtonian fluids of different density and
viscosity through a simple network. The fluids stratify due to gravity and
remain as nearly distinct phases with some mixing occurring only by diffusion.
This fluid system has the advantage that it is easily controlled and modeled,
yet contains the key ingredients for network non-linearities. Experiments and
3D simulations are first used to explore how phases distribute at a single
T-junction. Once the phase separation at a single junction is known, a network
model is developed which predicts multiple equilibria in the simplest of
networks. The existence of multiple stable equilibria is confirmed
experimentally and a criteria for their existence is developed. The network
results are generic and could be applied to or found in different physical
systems
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