966 research outputs found
Expanded Very Large Array Observations of the Nebula Around G79.29+0.46
We have observed the radio nebula surrounding the Galactic luminous blue variable candidate G79.29+0.46 with the Expanded Very Large Array (EVLA) at 6 cm. These new radio observations allow a morphological comparison between the radio emission, which traces the ionized gas component, and the mid-IR emission, a tracer of the dust component. The InfraRed Array Camera (8 Ī¼m) and the Multiband Imaging Photometer for Spitzer (24 Ī¼m and 70 Ī¼m) images have been reprocessed and compared with the EVLA map. We confirm the presence of a second shell at 24 Ī¼m and also provide evidence for its detection at 70 Ī¼m. The differences between the spatial morphology of the radio and mid-IR maps indicate the existence of two dust populations, the cooler one emitting mostly at longer wavelengths. Analysis of the two dusty, nested shells have provided us with an estimate of the characteristic timescales for shell ejection, providing important constraints for stellar evolutionary models. Finer details of the ionized gas distribution can be appreciated thanks to the improved quality of the new 6 cm image, most notably the highly structured texture of the nebula. Evidence of interaction between the nebula and the surrounding interstellar medium can be seen in the radio map, including brighter features that delineate regions where the shell structure is locally modified. In particular, the brighter filaments in the southwest region appear to frame the shocked southwestern clump reported from CO observations
Infrared Observations of the Helix Planetary Nebula
We have mapped the Helix (NGC 7293) planetary nebula (PN) with the IRAC instrument on the Spitzer Space Telescope. The Helix is one of the closest bright PNs and therefore provides an opportunity to resolve the small-scale structure in the nebula. The emission from this PN in the 5.8 and 8 Ī¼m IRAC bands is dominated by the pure rotational lines of molecular hydrogen, with a smaller contribution from forbidden line emission such as [Ar III] in the ionized region. The IRAC images resolve the "cometary knots," which have been previously studied in this PN. The "tails" of the knots and the radial rays extending into the outer regions of the PN are seen in emission in the IRAC bands. IRS spectra on the main ring and the emission in the IRAC bands are consistent with shock-excited H_2 models, with a small (~10%) component from photodissociation regions. In the northeast arc, the H_2 emission is located in a shell outside the HĪ± emission
Cascaded acceleration of proton beams in ultrashort laser-irradiated microtubes
A cascaded ion acceleration scheme is proposed by use of ultrashort
laser-irradiated microtubes. When the electrons of a microtube are blown away
by intense laser pulses, strong charge-separation electric fields are formed in
the microtube both along the axial and along the radial directions. By
controlling the time delay between the laser pulses and a pre-accelerated
proton beam injected along the microtube axis, we demonstrate that this proton
beam can be further accelerated by the transient axial electric field in the
laser-irradiated microtube. Moreover, the collimation of the injected proton
beam can be enhanced by the inward radial electric field. Numerical simulations
show that this cascaded ion acceleration scheme works efficiently even at
non-relativistic laser intensities, and it can be applied to injected proton
beams in the energy range from 1 to 100 MeV. Therefore, it is particularly
suitable for cascading acceleration of protons to higher energy.Comment: 13 pages, 4 figure
The Mass Distributions of Starless and Protostellar Cores in Gould Belt Clouds
Using data from the SCUBA Legacy Catalogue (850 um) and Spitzer Space
Telescope (3.6 - 70 um), we explore dense cores in the Ophiuchus, Taurus,
Perseus, Serpens, and Orion molecular clouds. We develop a new method to
discriminate submillimeter cores found by SCUBA as starless or protostellar,
using point source photometry from Spitzer wide field surveys. First, we
identify infrared sources with red colors associated with embedded young
stellar objects (YSOs). Second, we compare the positions of these
YSO-candidates to our submillimeter cores. With these identifications, we
construct new, self-consistent starless and protostellar core mass functions
(CMFs) for the five clouds. We find best fit slopes to the high-mass end of the
CMFs of -1.26 +/- 0.20, -1.22 +/- 0.06, -0.95 +/- 0.20, and -1.67 +/- 0.72 for
Ophiuchus, Taurus, Perseus, and Orion, respectively. Broadly, these slopes are
each consistent with the -1.35 power-law slope of the Salpeter IMF at higher
masses, but suggest some differences. We examine a variety of trends between
these CMF shapes and their parent cloud properties, potentially finding a
correlation between the high-mass slope and core temperature. We also find a
trend between core mass and effective size, but we are very limited by
sensitivity. We make similar comparisons between core mass and size with visual
extinction (for A_V >= 3) and find no obvious trends. We also predict the
numbers and mass distributions of cores that future surveys with SCUBA-2 may
detect in each of these clouds.Comment: 56 pages, 18 figures, fixed typo in Eq 1, results in paper remain
unchange
Evaluation of effective resistances in pseudo-distance-regular resistor networks
In Refs.[1] and [2], calculation of effective resistances on distance-regular
networks was investigated, where in the first paper, the calculation was based
on the stratification of the network and Stieltjes function associated with the
network, whereas in the latter one a recursive formula for effective
resistances was given based on the Christoffel-Darboux identity. In this paper,
evaluation of effective resistances on more general networks called
pseudo-distance-regular networks [21] or QD type networks \cite{obata} is
investigated, where we use the stratification of these networks and show that
the effective resistances between a given node such as and all of the
nodes belonging to the same stratum with respect to
(, belonging to the -th stratum with respect
to the ) are the same. Then, based on the spectral techniques, an
analytical formula for effective resistances such that
(those nodes , of
the network such that the network is symmetric with respect to them) is given
in terms of the first and second orthogonal polynomials associated with the
network, where is the pseudo-inverse of the Laplacian of the network.
From the fact that in distance-regular networks,
is satisfied for all nodes
of the network, the effective resistances
for ( is diameter of the network which
is the same as the number of strata) are calculated directly, by using the
given formula.Comment: 30 pages, 7 figure
AbundĆ¢ncia e distribuiĆ§Ć£o de lianas sobre as copas de espĆ©cies arbĆ³reas em uma floresta estacional semidecidual.
S-CANDELS: The Spitzer-Cosmic Assembly Near-Infrared Deep Extragalactic Survey. Survey Design, Photometry, and Deep IRAC Source Counts
The Spitzer-Cosmic Assembly Deep Near-Infrared Extragalactic Legacy Survey
(S-CANDELS; PI G. Fazio) is a Cycle 8 Exploration Program designed to detect
galaxies at very high redshifts (z > 5). To mitigate the effects of cosmic
variance and also to take advantage of deep coextensive coverage in multiple
bands by the Hubble Space Telescope Multi-Cycle Treasury Program CANDELS,
S-CANDELS was carried out within five widely separated extragalactic fields:
the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, COSMOS,
the HST Deep Field North, and the Extended Groth Strip. S-CANDELS builds upon
the existing coverage of these fields from the Spitzer Extended Deep Survey
(SEDS) by increasing the integration time from 12 hours to a total of 50 hours
but within a smaller area, 0.16 square degrees. The additional depth
significantly increases the survey completeness at faint magnitudes. This paper
describes the S-CANDELS survey design, processing, and publicly-available data
products. We present IRAC dual-band 3.6+4.5 micron catalogs reaching to a depth
of 26.5 AB mag. Deep IRAC counts for the roughly 135,000 galaxies detected by
S-CANDELS are consistent with models based on known galaxy populations. The
increase in depth beyond earlier Spitzer/IRAC surveys does not reveal a
significant additional contribution from discrete sources to the diffuse Cosmic
Infrared Background (CIB). Thus it remains true that only roughly half of the
estimated CIB flux from COBE/DIRBE is resolved.Comment: 23 pages, 19 figures, accepted by ApJ
Radio continuum properties of young planetary nebulae
We have selected a small sample of post-AGB stars in transition towards the
planetary nebula and present new Very Large Array multi-frequency high-angular
resolution radio observations of them. The multi-frequency data are used to
create and model the targets' radio continuum spectra, proving that these stars
started their evolution as very young planetary nebulae. In the optically thin
range, the slopes are compatible with the expected spectral index (-0.1). Two
targets (IRAS 18062+2410 and 17423-1755) seem to be optically thick even at
high frequency, as observed in a handful of other post-AGB stars in the
literature, while a third one (IRAS 20462+3416) shows a possible contribution
from cold dust. In IRAS 18062+2410, where we have three observations spanning a
period of four years, we detect an increase in its flux density, similar to
that observed in CRL 618.
High-angular resolution imaging shows bipolar structures that may be due to
circumstellar tori, although a different hypothesis (i.e., jets) could also
explain the observations. Further observations and monitoring of these sources
will enable us to test the current evolutionary models of planetary nebulae.Comment: 8 pages, 3 figures, accepted for publication in MNRA
Chirped pulse Raman amplification in plasma
Raman amplification in plasma has been proposed to be a promising method of amplifying short radiation pulses. Here, we investigate chirped pulse Raman amplification (CPRA) where the pump pulse is chirped and leads to spatiotemporal distributed gain, which exhibits superradiant scaling in the linear regime, usually associated with the nonlinear pump depletion and Compton amplification regimes. CPRA has the potential to serve as a high-efficiency high-fidelity amplifier/compressor stage
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