93 research outputs found
Numerical Modeling of Dependent Credit Rating Transitions with Asynchronously Moving Industries
Two models of dependent credit rating migrations governed by industry-specific Markovian matrices, are considered. Caused by macroeconomic factors, positive and negative unobserved tendencies, encoded as values "1" or "0" of the corresponding variables, modify the transition probabilities and render the evolutions dependent. They are neither synchronized across industry sectors, nor over credit classes: an upswing in some of them can coexist with a decline of the rest. The models are tested on Standard and Poor's data. MATLAB optimization software and maximum likelihood estimators are used. Obtained distributions of the hidden variables demonstrate that the considered industries migrate asynchronously trough credit classes. Since downgrading probabilities are less affected by the unobserved tendencies, estimated by Monte-Carlo simulations distributions of defaults, exhibit lighter, than for the known coupling models, tails for schemes with asynchronously moving industries. Moreover, the lightest tails were obtained in the case of industry-specific transition matrices
A Sample of [CII] Clouds Tracing Dense Clouds in Weak FUV Fields observed by Herschel
The [CII] fine--structure line at 158um is an excellent tracer of the warm
diffuse gas in the ISM and the interfaces between molecular clouds and their
surrounding atomic and ionized envelopes. Here we present the initial results
from Galactic Observations of Terahertz C+ (GOTC+), a Herschel Key Project
devoted to study the [CII] fine structure emission in the galactic plane using
the HIFI instrument. We use the [CII] emission together with observations of CO
as a probe to understand the effects of newly--formed stars on their
interstellar environment and characterize the physical and chemical state of
the star-forming gas. We collected data along 16 lines--of--sight passing near
star forming regions in the inner Galaxy near longitudes 330 degrees and 20
degrees. We identify fifty-eight [CII] components that are associated with
high--column density molecular clouds as traced by 13CO emission. We combine
[CII], 12CO, and 13CO observations to derive the physical conditions of the
[CII]--emitting regions in our sample of high--column density clouds based on
comparison with results from a grid of Photon Dominated Region (PDR) models.
From this unbiased sample, our results suggest that most of [CII] emission
originates from clouds with H2 volume densities between 10e3.5 and 10e5.5 cm^-3
and weak FUV strength (CHI_0=1-10). We find two regions where our analysis
suggests high densities >10e5 cm^-3 and strong FUV fields (CHI=10e4-10e6),
likely associated with massive star formation. We suggest that [CII] emission
in conjunction with CO isotopes is a good tool to differentiate between regions
of massive star formation (high densities/strong FUV fields) and regions that
are distant from massive stars (lower densities/weaker FUV fields) along the
line--of--sightComment: To be published in A&A HIFI Special Editio
C detection of warm dark gas in diffuse clouds
We present the first results of the Herschel open time key program, Galactic
Observations of Terahertz C (GOT C+) survey of the [CII] fine-structure
line at 1.9 THz (158 microns) using the HIFI instrument on Herschel. We
detected 146 interstellar clouds along sixteen lines-of-sight towards the inner
Galaxy. We also acquired HI and CO isotopologue data along each line-of-sight
for analysis of the physical conditions in these clouds. Here we analyze 29
diffuse clouds (A < 1.3 mag.) in this sample characterized by having
[CII] and HI emission, but no detectable CO. We find that [CII] emission is
generally stronger than expected for diffuse atomic clouds, and in a number of
sources is much stronger than anticipated based on their HI column density. We
show that excess [CII] emission in these clouds is best explained by the
presence of a significant diffuse warm H, dark gas, component. This first
[CII] 158 micron detection of warm dark gas demonstrates the value of this
tracer for mapping this gas throughout the Milky Way and in galaxies.Comment: To be published in A&A HIFI Special Editio
Interstellar CN and CH+ in Diffuse Molecular Clouds: 12C/13C Ratios and CN Excitation
We present very high signal-to-noise ratio absorption-line observations of CN
and CH+ along 13 lines of sight through diffuse molecular clouds. The data are
examined to extract precise isotopologic ratios of 12CN/13CN and 12CH+/13CH+ in
order to assess predictions of diffuse cloud chemistry. Our results on
12CH+/13CH+ confirm that this ratio does not deviate from the ambient 12C/13C
ratio in local interstellar clouds, as expected if the formation of CH+
involves nonthermal processes. We find that 12CN/13CN, however, can be
significantly fractionated away from the ambient value. The dispersion in our
sample of 12CN/13CN ratios is similar to that found in recent surveys of
12CO/13CO. For sight lines where both ratios have been determined, the
12CN/13CN ratios are generally fractionated in the opposite sense compared to
12CO/13CO. Chemical fractionation in CO results from competition between
selective photodissociation and isotopic charge exchange. An inverse
relationship between 12CN/13CN and 12CO/13CO follows from the coexistence of CN
and CO in diffuse cloud cores. However, an isotopic charge exchange reaction
with CN may mitigate the enhancements in 12CN/13CN for lines of sight with low
12CO/13CO ratios. For two sight lines with high values of 12CO/13CO, our
results indicate that about 50 percent of the carbon is locked up in CO, which
is consistent with the notion that these sight lines probe molecular cloud
envelopes where the transition from C+ to CO is expected to occur. An analysis
of CN rotational excitation yields a weighted mean value for T_01(12CN) of
2.754 +/- 0.002 K, which implies an excess over the temperature of the cosmic
microwave background of only 29 +/- 3 mK. This modest excess eliminates the
need for a local excitation mechanism beyond electron and neutral collisions.
The rotational excitation temperatures in 13CN show no excess over the
temperature of the CMB.Comment: 27 pages, 21 figures, emulateapj style, accepted for publication in
Ap
First observations with CONDOR, a 1.5 THz heterodyne receiver
The THz atmospheric windows centered at roughly 1.3 and 1.5~THz, contain
numerous spectral lines of astronomical importance, including three high-J CO
lines, the N+ line at 205 microns, and the ground transition of para-H2D+. The
CO lines are tracers of hot (several 100K), dense gas; N+ is a cooling line of
diffuse, ionized gas; the H2D+ line is a non-depleting tracer of cold (~20K),
dense gas. As the THz lines benefit the study of diverse phenomena (from
high-mass star-forming regions to the WIM to cold prestellar cores), we have
built the CO N+ Deuterium Observations Receiver (CONDOR) to further explore the
THz windows by ground-based observations. CONDOR was designed to be used at the
Atacama Pathfinder EXperiment (APEX) and Stratospheric Observatory For Infrared
Astronomy (SOFIA). CONDOR was installed at the APEX telescope and test
observations were made to characterize the instrument. The combination of
CONDOR on APEX successfully detected THz radiation from astronomical sources.
CONDOR operated with typical Trec=1600K and spectral Allan variance times of
30s. CONDOR's first light observations of CO 13-12 emission from the hot core
Orion FIR4 (= OMC1 South) revealed a narrow line with T(MB) = 210K and
delta(V)=5.4km/s. A search for N+ emission from the ionization front of the
Orion Bar resulted in a non-detection. The successful deployment of CONDOR at
APEX demonstrates the potential for making observations at THz frequencies from
ground-based facilities.Comment: 4 pages + list of objects, 3 figures, to be published in A&A special
APEX issu
Performance of the Scintillator System Prototype of the NUCLEON Space Experiment
Abstract The NUCLEON space experiment has been proposed to perform direct measurements of CR energy spectrum and composition up to E ∼ 10 15 eV. The NUCLEON detector consists of layers of different detectors: scintillator detectors with WLS fibers and silicon pad and microstrip ones. The results of beam and space qualification tests of the scintillator detectors are presented
The origin of the [C II] emission in the S140 PDRs - new insights from HIFI
Using Herschel's HIFI instrument we have observed [C II] along a cut through
S140 and high-J transitions of CO and HCO+ at two positions on the cut,
corresponding to the externally irradiated ionization front and the embedded
massive star forming core IRS1. The HIFI data were combined with available
ground-based observations and modeled using the KOSMA-tau model for photon
dominated regions. Here we derive the physical conditions in S140 and in
particular the origin of [C II] emission around IRS1. We identify three
distinct regions of [C II] emission from the cut, one close to the embedded
source IRS1, one associated with the ionization front and one further into the
cloud. The line emission can be understood in terms of a clumpy model of
photon-dominated regions. At the position of IRS1, we identify at least two
distinct components contributing to the [C II] emission, one of them a small,
hot component, which can possibly be identified with the irradiated outflow
walls. This is consistent with the fact that the [C II] peak at IRS1 coincides
with shocked H2 emission at the edges of the outflow cavity. We note that
previously available observations of IRS1 can be well reproduced by a
single-component KOSMA-tau model. Thus it is HIFI's unprecedented spatial and
spectral resolution, as well as its sensitivity which has allowed us to uncover
an additional hot gas component in the S140 region.Comment: accepted for publication in Astronomy and Astrophysics (HIFI special
issue
CO, CI and CII observations of NGC 7023
We present new data on the photodissociation regions associated with the
reflection nebula NGC7023. 13CO(3-2) emission, delineates a molecular cloud
containing a cavity largely devoid of molecular gas around this star. Neutral
carbon is closely associated with the 13CO emission while ionized carbon is
found inside and at the edges of the cavity. The ionized carbon appears to be,
at least in part, associated with HI. We have mapped the northern and southern
rims in 12CO(6-5) emission and found a good association with the H2
rovibrational emission, though the warm CO gas permeates a larger fraction of
the molecular cloud than the vibrationally excited H2. The results are compared
with PDR models. We suggest that a second PDR has been created at the surface
of the molecular cloud by the scattered radiation from HD 200775. This second
PDR produces a layer of atomic carbon at the surface of the sheet, which
increases the predicted [C]/[CO] abundance ratio to 10%, close to the observed
value.Comment: 34 pages, 8 figure
[CII] at 158 mic as a star formation tracer in late-type galaxies
We present a calibration of the massive star formation rate vs. [CII]
luminosity relation based on a sample of nearby, late-type galaxies observed
with ISO-LWS and imaged in the Halpha+[NII] line. The relation holds for far-IR
luminosities 10^8 < L_{FIR} < 10^{10.5} L (solar units). The derived star
formation rates have an uncertainty of about a factor of 10. Part of this
uncertainty is due to the different mix of contributions to the [CII] emission
from the different components of the interstellar medium in individual
galaxies, as discussed in an appendix.Comment: Accepted for publication on Astronomy & Astrophysic
Modeling dependent credit rating transitions: a comparison of coupling schemes and empirical evidence
- …