66 research outputs found
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
Mid-J CO emission from the Orion BN/KL explosive outflow
High spatial resolution low-J 12CO observations have shown that the
wide-angle outflow seen in the Orion BN/KL region correlates with the famous H2
fingers. Recently, high-resolution large-scale mappings of mid- and higher-J CO
emissions have been reported toward the Orion molecular cloud 1 core region
using the APEX telescope. Therefore, it is of interest to investigate this
outflow in the higher-J 12CO emission, which is likely excited by shocks. The
observations were carried out using the dual-color heterodyne array CHAMP+ on
the APEX telescope. The images of the Orion BN/KL region were obtained in the
12CO J=6-5 and J=7-6 transitions with angular resolutions of 8.6 and 7.4
arcsec, respectively. The results show a good agreement between our higher-J
12CO emission and SMA low-J 12CO data, which indicates that this wide-angle
outflow in Orion BN/KL is likely the result of an explosive event that is
related to the runaway objects from a dynamically decayed multiple system. From
our observations, we estimate that the kinetic energy of this explosive outflow
is about 1-2x10^47 erg. In addition, a scenario has been proposed where part of
the outflow is decelerated and absorbed in the cloud to explain the lack of CO
bullets in the southern part of BN/KL, which in turn induces the methanol
masers seen in this region.Comment: 5 pages, 4 figure
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
The APEX-CHAMP+ view of the Orion Molecular Cloud 1 core - Constraining the excitation with submillimeter CO multi-line observations
A high density portion of the Orion Molecular Cloud 1 (OMC-1) contains the
prominent, warm Kleinmann-Low (KL) nebula that is internally powered by an
energetic event plus a farther region in which intermediate to high mass stars
are forming. Its outside is affected by ultraviolet radiation from the
neighboring Orion Nebula Cluster and forms the archetypical photon-dominated
region (PDR) with the prominent bar feature. Its nearness makes the OMC-1 core
region a touchstone for research on the dense molecular interstellar medium and
PDRs. Using the Atacama Pathfinder Experiment telescope (APEX), we have imaged
the line emission from the multiple transitions of several carbon monoxide (CO)
isotopologues over the OMC-1 core region. Our observations employed the 2x7
pixel submillimeter CHAMP+ array to produce maps (~ 300 arcsec x 350 arcsec) of
12CO, 13CO, and C18O from mid-J transitions (J=6-5 to 8-7). We also obtained
the 13CO and C18O J=3-2 images toward this region. The 12CO line emission shows
a well-defined structure which is shaped and excited by a variety of phenomena,
including the energetic photons from hot, massive stars in the nearby Orion
Nebula's central Trapezium cluster, active high- and intermediate-mass star
formation, and a past energetic event that excites the KL nebula. Radiative
transfer modeling of the various isotopologic CO lines implies typical H2
densities in the OMC-1 core region of ~10^4-10^6 cm^-3 and generally elevated
temperatures (~ 50-250 K). We estimate a warm gas mass in the OMC-1 core region
of 86-285 solar masses.Comment: 11 pages, 9 figures, accepted by A&
Muon capture by 3He nuclei followed by proton and deuteron production
The paper describes an experiment aimed at studying muon capture by
nuclei in pure and mixtures at various densities. Energy distributions of
protons and deuterons produced via and are measured for the
energy intervals MeV and MeV, respectively. Muon capture
rates, and are obtained using two different analysis methods. The
least--squares methods gives , . The Bayes theorem
gives ,
. The experimental
differential capture rates, and , are compared with theoretical
calculations performed using the plane--wave impulse approximation (PWIA) with
the realistic NN interaction Bonn B potential. Extrapolation to the full energy
range yields total proton and deuteron capture rates in good agreement with
former results.Comment: 17 pages, 13 figures, accepted for publication in PR
Comparison of 13CO Line and Far-Infrared Continuum Emission as a Diagnostic of Dust and Molecular Gas Physical Conditions: III. Systematic Effects and Scientific Implications
Far-infrared continuum data from the {\it COBE}/{\it DIRBE} instrument were
combined with Nagoya 4-m \cOone spectral line data to infer the
multiparsec-scale physical conditions in the OrionA and B molecular clouds,
using 140\um/240\um dust color temperatures and the 240\um/\cOone
intensity ratios. In theory, the ratio of far-IR, submillimeter, or millimeter
continuum to that of a \cO (or \Co) rotational line can place reliable
upper limits on the temperature of the dust and molecular gas on multi-parsec
scales; on such scales, both the line and continuum emission are optically
thin, resulting in a continuum-to-line ratio that suffers no loss of
temperature sensitivity in the high-temperature limit as occurs for ratios of
CO rotational lines or ratios of continuum emission in different wavelength
bands. Two-component models fit the Orion data best, where one has a
fixed-temperature and the other has a spatially varying temperature. The former
represents gas and dust towards the surface of the clouds that are heated
primarily by a very large-scale (i.e. kpc) interstellar radiation
field. The latter represents gas and dust at greater depths into the clouds and
are shielded from this interstellar radiation field and heated by local stars.
The inferred physical conditions are consistent with those determined from
previously observed maps of \COone and \Jtwo that cover the entire OrionA and B molecular clouds. The models require that the dust-gas temperature
difference is 0K. If this surprising result applies to much of the
Galactic ISM, except in unusual regions such as the Galactic Center, then there
are a number implications.Comment: The work of Schnee et al. 2006 is relevant here. This is now
mentioned in the Discussion and in the Conclusions. In the third version,
I've corrected a few typos and slightly changed the emphasis on the cold
gas/dust. In the version of March 2007, I've fixed a few typos and updated a
few reference
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
Search for NN-decoupled dibaryons using the process below the pion production threshold
The energy spectrum for high energy -rays ( MeV)
from the process emitted at in the laboratory
frame has been measured at an energy below the pion production threshold,
namely, at 216 MeV. The resulting photon energy spectrum extracted from
coincidence events consists of a narrow peak at a photon energy
of about 24 MeV and a relatively broad peak in the energy range of (50 - 70)
MeV. The statistical significances for the narrow and broad peaks are
5.3 and 3.5, respectively. This behavior of the photon energy
spectrum is interpreted as a signature of the exotic dibaryon resonance
with a mass of about 1956 MeV which is assumed to be formed in the
radiative process followed by its electromagnetic
decay via the mode. The experimental spectrum is
compared with those obtained by means of Monte Carlo simulations.Comment: 14 pages, LaTex, 6 eps-figures, accepted for publication in
Phys.Rev.
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