1,957 research outputs found
Preparation of microscopic cross sections of U235 for reactor calculations
Preparation of microscopic cross section of uranium 235 for high temperature reactor calculation
ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
(abbreviated) We aim to study the inner wind of the well-known AGB star CW
Leo. Different diagnostics probing different geometrical scales have pointed
toward a non-homogeneous mass-loss process: dust clumps are observed at
milli-arcsec scale, a bipolar structure is seen at arcsecond-scale and
multi-concentric shells are detected beyond 1". We present the first ALMA Cycle
0 band 9 data around 650 GHz. The full-resolution data have a spatial
resolution of 0".42x0".24, allowing us to study the morpho-kinematical
structure within ~6". Results: We have detected 25 molecular lines. The
emission of all but one line is spatially resolved. The dust and molecular
lines are centered around the continuum peak position. The dust emission has an
asymmetric distribution with a central peak flux density of ~2 Jy. The
molecular emission lines trace different regions in the wind acceleration
region and suggest that the wind velocity increases rapidly from about 5 R*
almost reaching the terminal velocity at ~11 R*. The channel maps for the
brighter lines show a complex structure; specifically for the 13CO J=6-5 line
different arcs are detected within the first few arcseconds. The curved
structure present in the PV map of the 13CO J=6-5 line can be explained by a
spiral structure in the inner wind, probably induced by a binary companion.
From modeling the ALMA data, we deduce that the potential orbital axis for the
binary system lies at a position angle of ~10-20 deg to the North-East and that
the spiral structure is seen almost edge-on. We infer an orbital period of 55
yr and a binary separation of 25 au (or ~8.2 R*). We tentatively estimate that
the companion is an unevolved low-mass main-sequence star. The ALMA data hence
provide us for the first time with the crucial kinematical link between the
dust clumps seen at milli-arcsecond scale and the almost concentric arcs seen
at arcsecond scale.Comment: 22 pages, 18 Figures, Astronomy & Astrophysic
The Molecular Interstellar Medium in Ultraluminous Infrared Galaxies
We present CO observations of a large sample of ultraluminous IR galaxies out
to z = 0.3. Most of the galaxies are interacting, but not completed mergers.
All but one have high CO(1-0) luminosities, log(Lco [K-km/s-pc^2]) = 9.92 +/-
0.12. The dispersion in Lco is only 30%, less than that in the FIR luminosity.
The integrated CO intensity correlates Strongly with the 100 micron flux
density, as expected for a black body model in which the mid and far IR
radiation are optically thick. We use this model to derive sizes of the FIR and
CO emitting regions and the enclosed dynamical masses. Both the IR and CO
emission originate in regions a few hundred parsecs in radius. The median value
of Lfir/Lco = 160 Lsun/(K-km/s-pc^2), within a factor of two of the black body
limit for the observed FIR temperatures. The entire ISM is a scaled up version
of a normal galactic disk with densities a factor of 100 higher, making even
the intercloud medium a molecular region. Using three different techniques of
H2 mass estimation, we conclude that the ratio of gas mass to Lco is about a
factor of four lower than for Galactic molecular clouds, but that the gas mass
is a large fraction of the dynamical mass. Our analysis of CO emission reduces
the H2 mass from previous estimates of 2-5e10 Msun to 0.4-1.5e10 Msun, which is
in the range found for molecular gas rich spiral galaxies. A collision
involving a molecular gas rich spiral could lead to an ultraluminous galaxy
powered by central starbursts triggered by the compression of infalling
preexisting GMC's.Comment: 34 pages LaTeX with aasms.sty, 14 Postscript figures, submitted to
ApJ Higher quality versions of Figs 2a-f and 7a-c available by anonymous FTP
from ftp://sbast1.ess.sunysb.edu/solomon/
High resolution 10 mu spectrometry at different planetary latitudes. A practical Hadamard transform spectrometer for astronomical application
Infrared observations at different latitudes were studied in order to obtain spectra in the 10 micrometers region to understand differences in chemical composition or physical structure of the optical features. In order to receive such spectra of a rotating planet, simultaneous observations at different latitudes were made. A Hadamard transform spectrometer with 15 entrance slits was used to obtain 15 simultaneous spectra, at a resolution of 0.01 micrometers. The spectral band covered contained 255 spectral elements
Calculation of an optimized telescope apodizer for Terrestrial Planet Finder coronagraphic telescope
One of two approaches to implementing NASA's Terrestrial Planet Finder is to
build a space telescope that utilizes the techniques of coronagraphy and
apodization to suppress diffraction and image exo-planets. We present a method
for calculation of a telescope's apodizer which suppresses the side lobes of
the image of a star so as to optimally detect an Earth-like planet. Given the
shape of a telescope's aperture and given a search region for a detector, we
solve an integral equation to determine an amplitude modulation (an apodizer)
which suppresses the star's energy in the focal plane search region. The method
is quite general and yields as special cases the product apodizer reported by
Nisenson and Papaliolios (2001) and the Prolate spheroidal apodizer of Kasdin
et al (2002), and Aime et al (2002). We show computer simulations of the
apodizers and the corresponding point spread functions for various
aperture-detector configurations.Comment: 16 Pages, 9 figures, Accepted for publication in June issue of PAS
Radiative Transfer Effects in He I Emission Lines
We consider the effect of optical depth of the 2 ^{3}S level on the nebular
recombination spectrum of He I for a spherically symmetric nebula with no
systematic velocity gradients. These calculations, using many improvements in
atomic data, can be used in place of the earlier calculations of Robbins. We
give representative Case B line fluxes for UV, optical, and IR emission lines
over a range of physical conditions: T=5000-20000 K, n_{e}=1-10^{8} cm^{-3},
and tau_{3889}=0-100. A FORTRAN program for calculating emissivities for all
lines arising from quantum levels with n < 11 is also available from the
authors.
We present a special set of fitting formulae for the physical conditions
relevant to low metallicity extragalactic H II regions: T=12,000-20,000 K,
n_{e}=1-300 cm^{-3}, and tau_{3889} < 2.0. For this range of physical
conditions, the Case B line fluxes of the bright optical lines 4471 A, 5876 A,
and 6678 A, are changed less than 1%, in agreement with previous studies.
However, the 7065 A corrections are much smaller than those calculated by
Izotov & Thuan based on the earlier calculations by Robbins. This means that
the 7065 A line is a better density diagnostic than previously thought. Two
corrections to the fitting functions calculated in our previous work are also
given.Comment: To be published in 10 April 2002 ApJ; relevant code available at
ftp://wisp.physics.wisc.edu/pub/benjamin/Heliu
Herschel/HIFI Spectral Mapping of C, CH, and CH in Orion BN/KL: The Prevailing Role of Ultraviolet Irradiation in CH Formation
The CH ion is a key species in the initial steps of interstellar carbon
chemistry. Its formation in diverse environments where it is observed is not
well understood, however, because the main production pathway is so endothermic
(4280 K) that it is unlikely to proceed at the typical temperatures of
molecular clouds. We investigation CH formation with the first
velocity-resolved spectral mapping of the CH rotational
transitions, three sets of CH -doubled triplet lines, C and
C, and CHOH 835~GHz E-symmetry Q branch transitions, obtained
with Herschel/HIFI over 12 arcmin centered on the Orion BN/KL
source. We present the spatial morphologies and kinematics, cloud boundary
conditions, excitation temperatures, column densities, and C optical
depths. Emission from C, CH, and CH is indicated to arise in the
diluted gas, outside of the explosive, dense BN/KL outflow. Our models show
that UV-irradiation provides favorable conditions for steady-state production
of CH in this environment. Surprisingly, no spatial or kinematic
correspondences of these species are found with H S(1) emission tracing
shocked gas in the outflow. We propose that C is being consumed by rapid
production of CO to explain the lack of C and CH in the outflow, and
that fluorescence provides the reservoir of H excited to higher
ro-vibrational and rotational levels. Hence, in star-forming environments
containing sources of shocks and strong UV radiation, a description of CH
formation and excitation conditions is incomplete without including the
important --- possibly dominant --- role of UV irradiation.Comment: Accepted for publication in The Astrophysical Journa
Optical Imaging of Very Luminous Infrared Galaxy Systems: Photometric Properties and Late Evolution
A sample of 19 low redshift (0.03z0.07) very luminous infrared galaxy
(VLIRG: L[8-1000 m] ) systems (30
galaxies) has been imaged in , , and . These objects cover a
luminosity range that is key to linking the most luminous infrared galaxies
with the population of galaxies at large. We have obtained photometry for all
of these VLIRG systems, the individual galaxies (when detached), and their
nuclei, and the relative behavior of these classes has been studied in optical
color-magnitude diagrams. The photometric properties of the sample are also
compared with previously studied samples of ULIRGs. The mean observed
photometric properties of VLIRG and ULIRG samples, considered as a whole, are
indistinguishable at optical wavelengths. This suggests that not only ULIRG,
but also the more numerous population of VLIRGs, have similar rest-frame
optical photometric properties as the submillimeter galaxies (SMG), reinforcing
the connection between low-{\it z} LIRGs -- high-{\it z} SMGs. When the nuclei
of the {\it young} and {\it old} interacting systems are considered separately,
some differences between the VLIRG and the ULIRG samples are found. In
particular, the old VLIRGs are less luminous and redder than old ULIRG systems.
If confirmed with larger samples, this behavior suggests that the late-stage
evolution is different for VLIRGs and ULIRGs. Specifically, as suggested from
spectroscopic data, the present photometric observations support the idea that
the activity during the late phases of VLIRG evolution is dominated by
starbursts, while a higher proportion of ULIRGs could evolve into a QSO type of
object.Comment: 27 pages, 5 figures (degraded to reduce space). Figures 1 and 2 are
multiple page figures (i.e. Fig 1a,b and Fig2a-g
GGD 37: An Extreme Protostellar Outflow
We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne v]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne v] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s(-1). The presence of an extended photoionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.Jet Propulsion Laboratory, under NASA 1407NASA 1257184Jet Propulsion Laboratory (JPL) 960803University of Rochester 31419-5714Astronom
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