1,016 research outputs found
The Corporate Bond Market in Canada
The Canadian corporate bond market has experienced a renaissance, in recent years, against a background of low inflation, reduced public borrowing, and the lowest levels of long-term interest rates in a generation. The authors examine the influences shaping the market and also compare the Canadian market with those of other countries. The increased level of activity in the market has been accompanied by the development of new products and by greater investor interest in instruments with higher returns and higher credit risk. A more dynamic Canadian corporate bond market is a welcome development since it offers borrowers an alternative source of funds, especially companies that have typically relied on the banking system and on the U.S. corporate bond market for financings involving higher levels of credit risk.
Physical properties of a very diffuse HI structure at high Galactic latitude
The main goal of this analysis is to present a new method to estimate the
physical properties of diffuse cloud of atomic hydrogen observed at high
Galactic latitude. This method, based on a comparison of the observations with
fractional Brownian motion simulations, uses the statistical properties of the
integrated emission, centroid velocity and line width to constrain the physical
properties of the 3D density and velocity fields, as well as the average
temperature of HI. We applied this method to interpret 21 cm observations
obtained with the Green Bank Telescope of a very diffuse HI cloud at high
Galactic latitude located in Firback North 1. We first show that the
observations cannot be reproduced solely by highly-turbulent CNM type gas and
that there is a significant contribution of thermal broadening to the line
width observed. To reproduce the profiles one needs to invoke two components
with different average temperature and filling factor. We established that, in
this very diffuse part of the ISM, 2/3 of the column density is made of WNM and
1/3 of thermally unstable gas (T ~2600 K). The WNM gas is mildly supersonic
(~1) and the unstable phase is definitely sub-sonic (~0.3). The density
contrast (i.e., the standard deviation relative to the mean of density
distribution) of both components is close to 0.8. The filling factor of the WNM
is 10 times higher that of the unstable gas, which has a density structure
closer to what would be expected for CNM gas. This field contains a signature
of CNM type gas at a very low level (N_H ~ 3 x 10^19) which could have been
formed by a convergent flow of WNM gas.Comment: 13 pages, 12 figures, accepted for publication in A&
Dust models post-Planck: constraining the far-infrared opacity of dust in the diffuse interstellar medium
We compare the performance of several dust models in reproducing the dust
spectral energy distribution (SED) per unit extinction in the diffuse
interstellar medium (ISM). We use our results to constrain the variability of
the optical properties of big grains in the diffuse ISM, as published by the
Planck collaboration.
We use two different techniques to compare the predictions of dust models to
data from the Planck HFI, IRAS and SDSS surveys. First, we fit the far-infrared
emission spectrum to recover the dust extinction and the intensity of the
interstellar radiation field (ISRF). Second, we infer the ISRF intensity from
the total power emitted by dust per unit extinction, and then predict the
emission spectrum. In both cases, we test the ability of the models to
reproduce dust emission and extinction at the same time.
We identify two issues. Not all models can reproduce the average dust
emission per unit extinction: there are differences of up to a factor
between models, and the best accord between model and observation is obtained
with the more emissive grains derived from recent laboratory data on silicates
and amorphous carbons. All models fail to reproduce the variations in the
emission per unit extinction if the only variable parameter is the ISRF
intensity: this confirms that the optical properties of dust are indeed
variable in the diffuse ISM.
Diffuse ISM observations are consistent with a scenario where both ISRF
intensity and dust optical properties vary. The ratio of the far-infrared
opacity to the band extinction cross-section presents variations of the
order of ( in extreme cases), while ISRF intensity varies
by ( in extreme cases). This must be accounted for in
future modelling.Comment: A&A, in pres
Optimizing ISOCAM data processing using spatial redundancy
We present new data processing techniques that allow to correct the main
instrumental effects that degrade the images obtained by ISOCAM, the camera on
board the Infrared Space Observatory (ISO). Our techniques take advantage of
the fact that a position on the sky has been observed by several pixels at
different times. We use this information (1) to correct the long term variation
of the detector response, (2) to correct memory effects after glitches and
point sources, and (3) to refine the deglitching process. Our new method allows
the detection of faint extended emission with contrast smaller than 1% of the
zodiacal background. The data reduction corrects instrumental effects to the
point where the noise in the final map is dominated by the readout and the
photon noises. All raster ISOCAM observations can benefit from the data
processing described here. These techniques could also be applied to other
raster type observations (e.g. ISOPHOT or IRAC on SIRTF).Comment: 13 pages, 10 figures, to be published in Astronomy and Astrophysics
Supplement Serie
Power Spectrum Analysis of Far-IR Background Fluctuations in 160 Micron Maps From the Multiband Imaging Photometer for Spitzer
We describe data reduction and analysis of fluctuations in the cosmic far-IR
background (CFIB) in observations with the Multiband Imaging Photometer for
Spitzer (MIPS) instrument 160 micron detectors. We analyzed observations of an
8.5 square degree region in the Lockman Hole, part of the largest low-cirrus
mapping observation with this instrument. We measured the power spectrum of the
CFIB in these observations by fitting a power law to the IR cirrus component,
the dominant foreground contaminant, and subtracting this cirrus signal. The
CFIB power spectrum in the range 0.2 arc min^{-1} <k< 0.5 arc min^{-1} is
consistent with previous measurements of a relatively flat component. However,
we find a large power excess at low k, which falls steeply to the flat
component in the range 0.03 arc min^{-1} <k< 0.1 arc min^{-1}. This low-k power
spectrum excess is consistent with predictions of a source clustering
"signature". This is the first report of such a detection in the far-IR.Comment: This is the version of the paper accepted by A&A, which includes
various changes and new material. The superior-quality PDF with integrated
figures may be downloaded at
http://www-astro.lbl.gov/~bruce/spitzerpaper1/cfibaa_pub.pdf 15 pages,
figures integrated with text. This paper supersedes astro-ph/050416
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