117 research outputs found
Polarisation Observations of HO 620.701 GHz Maser Emission with Herschel/HIFI in Orion KL
Context. The high intensities and narrow bandwidths exhibited by some
astronomical masers make them ideal tools for studying star-forming giant
molecular clouds. The water maser transition at
620.701 GHz can only be observed from above Earth's strongly absorbing
atmosphere; its emission has recently been detected from space. Aims. We sought
to further characterize the star-forming environment of Orion KL by
investigating the linear polarisation of a source emitting a narrow 620.701 GHz
maser feature with the heterodyne spectrometer HIFI on board the Herschel Space
Observatory. Methods. High-resolution spectral datasets were collected over a
thirteen month period beginning in 2011 March, to establish not only the linear
polarisation but also the temporal variability of the source. Results. Within a
uncertainty, no polarisation was detected to an upper limit of
approximately 2%. These results are compared with coeval linear polarisation
measurements of the 22.235 GHz maser line from
the Effelsberg 100-m radio telescope, typically a much stronger maser
transition. Although strongly polarised emission is observed for one component
of the 22.235 GHz maser at 7.2 km s, a weaker component at the same
velocity as the 620.701 GHz maser at 11.7 km s is much less polarised.Comment: Accepted for publication in A&
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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Distribution ofWater Vapor in Molecular Clouds
We report the results of a large-area study of water vapor along the Orion Molecular Cloud ridge, the purpose of which was to determine the depth-dependent distribution of gas-phase water in dense molecular clouds. We find that the water vapor measured toward 77 spatial positions along the face-on Orion ridge, excluding positions surrounding the outflow associated with BN/KL and IRc2, display integrated intensities that correlate strongly with known cloud surface tracers such as CN, C2H, 13CO J = 5-4, and HCN, and less well with the volume tracer N2H+. Moreover, at total column densities corresponding to A V\u3c 15 mag, the ratio of H2O to C18O integrated intensities shows a clear rise approaching the cloud surface. We show that this behavior cannot be accounted for by either optical depth or excitation effects, but suggests that gas-phase water abundances fall at large A V. These results are important as they affect measures of the true water-vapor abundance in molecular clouds by highlighting the limitations of comparing measured water-vapor column densities with such traditional cloud tracers as 13CO or C18O. These results also support cloud models that incorporate freeze out of molecules as a critical component in determining the depth-dependent abundance of water vapor
Submillimeter Wave Astronomy Satellite observations of comet 9P/Tempel 1 and Deep Impact
On 4 July 2005 at 5:52 UT the Deep Impact mission successfully completed its
goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on
the nucleus and ejecting material into the coma of the comet. NASA's
Submillimeter Wave Astronomy Satellite (SWAS) observed the 1(10)-1(01)
ortho-water ground-state rotational transition in comet 9P/Tempel 1 before,
during, and after the impact. No excess emission from the impact was detected
by SWAS and we derive an upper limit of 1.8e7 kg on the water ice evaporated by
the impact. However, the water production rate of the comet showed large
natural variations of more than a factor of three during the weeks before and
after the impact. Episodes of increased activity with Q(H2O)~1e28 molecule/s
alternated with periods with low outgassing (Q(H2O)<~5e27 molecule/s). We
estimate that 9P/Tempel 1 vaporized a total of N~4.5e34 water molecules (~1.3e9
kg) during June-September 2005. Our observations indicate that only a small
fraction of the nucleus of Tempel 1 appears to be covered with active areas.
Water vapor is expected to emanate predominantly from topographic features
periodically facing the Sun as the comet rotates. We calculate that appreciable
asymmetries of these features could lead to a spin-down or spin-up of the
nucleus at observable rates.Comment: 38 pages, 2 tables, 7 figures; Icarus, in pres
Water Abundance in Molecular Cloud Cores
We present Submillimeter Wave Astronomy Satellite (SWAS) observations of the
1_{10}-1_{01} transition of ortho-water at 557 GHz toward 12 molecular cloud
cores. The water emission was detected in NGC 7538, Rho Oph A, NGC 2024, CRL
2591, W3, W3(OH), Mon R2, and W33, and was not detected in TMC-1, L134N, and
B335. We also present a small map of the water emission in S140. Observations
of the H_2^{18}O line were obtained toward S140 and NGC 7538, but no emission
was detected. The abundance of ortho-water relative to H_2 in the giant
molecular cloud cores was found to vary between 6x10^{-10} and 1x10^{-8}. Five
of the cloud cores in our sample have previous water detections; however, in
all cases the emission is thought to arise from hot cores with small angular
extents. The water abundance estimated for the hot core gas is at least 100
times larger than in the gas probed by SWAS. The most stringent upper limit on
the ortho-water abundance in dark clouds is provided in TMC-1, where the
3-sigma upper limit on the ortho-water fractional abundance is 7x10^{-8}.Comment: 5 pages, 3 Postscript figures, uses aastex.cls, emulateapj5.sty
(included), and apjfonts.sty (included
The Distribution of Water Emission in M17SW
We present a 17-point map of the M17SW cloud core in the 1_{10}-1_{01}
transition of ortho-water at 557 GHz obtained with the Submillimeter Wave
Astronomy Satellite. Water emission was detected in 11 of the 17 observed
positions. The line widths of the water emission vary between 4 and 9 km
s^{-1}, and are similar to other emission lines that arise in the M17SW core. A
direct comparison is made between the spatial extent of the water emission and
the ^{13}CO J = 5\to4 emission; the good agreement suggests that the water
emission arises in the same warm, dense gas as the ^{13}CO emission. A spectrum
of the H_2^{18}O line was also obtained at the center position of the cloud
core, but no emission was detected. We estimate that the average abundance of
ortho-water relative to H_2 within the M17 dense core is approximately
1x10^{-9}, 30 times smaller than the average for the Orion core. Toward the H
II region/molecular cloud interface in M17SW the ortho-water abundance may be
about 5 times larger than in the dense core.Comment: 4 pages, 3 Postscript figures, uses aastex.cls, emulateapj5.sty
(included), and apjfonts.sty (included
A Brief Update on the CMZoom Survey
The inner few hundred parsecs of the Milky Way, the Central Molecular Zone (CMZ), is our closest laboratory for understanding star formation in the extreme environments (hot, dense, turbulent gas) that once dominated the universe. We present an update on the first large-area survey to expose the sites of star formation across the CMZ at high-resolution in submillimeter wavelengths: the CMZoom survey with the Submillimeter Array (SMA). We identify the locations of dense cores and search for signatures of embedded star formation. CMZoom is a three-year survey in its final year and is mapping out the highest column density regions of the CMZ in dust continuum and a variety of spectral lines around 1.3 mm. CMZoom combines SMA compact and subcompact configurations with single-dish data from BGPS and the APEX telescope, achieving an angular resolution of about 4" (0.2 pc) and good image fidelity up to large spatial scales
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Extended [C I] and (CO)-C-13 (5 -\u3e 4) emission in M17SW
We mapped a 13 × 22 pc region in emission from 492 GHz [C I] and, for the first time, 551 GHz 13CO (5 → 4) in the giant molecular cloud M17SW. The morphologies of the [C I] and 13CO emission are strikingly similar. The extent and intensity of the [C I] and 13CO (5 → 4) emission is explained as arising from photodissociation regions on the surfaces of embedded molecular clumps. Modeling of the 13CO (5 → 4) emission in comparison to 13CO (1 → 0) indicates a temperature gradient across the cloud, peaking to at least 63 K near the M17 ionization front and decreasing to at least 20 K at the western edge of the cloud. We see no correlation between gas density and column density. The beam-averaged column density of C I in the core is 1 × 1018 cm-2, and the mean column density ratio N(C I)/N(CO) is about 0.4. The variations of N(C I)/N(CO) with position in M17SW indicate a similar clump size distribution throughout the cloud
Polarisation observations of H_2O J_(K-1) K_1 = 5_(32) – 4_(41) 620.701 GHz maser emission with Herschel/HIFI in Orion KL
Context. The high intensities and narrow bandwidths exhibited by some astronomical masers make them ideal tools for studying star-forming giant molecular clouds. The water maser transition J_(K-1K1) = 5_(32)−4_(41) at 620.701 GHz can only be observed from above Earth’s strongly absorbing atmosphere; its emission has recently been detected from space.
Aims. We sought to further characterize the star-forming environment of Orion KL by investigating the linear polarisation of a source emitting a narrow 620.701 GHz maser feature with the heterodyne spectrometer HIFI on board the Herschel Space Observatory.
Methods. High-resolution spectral datasets were collected over a thirteen month period beginning in 2011 March, to establish not only the linear polarisation but also the temporal variability of the source.
Results. Within a 3σ uncertainty, no polarisation was detected to an upper limit of approximately 2%. These results are compared with coeval linear polarisation measurements of the 22.235 GHz J_(K-1K1) = 6_(16) – 5_(23) maser line from the Effelsberg 100-m radio telescope, typically a much stronger maser transition. Although strongly polarised emission is observed for one component of the 22.235 GHz maser at 7.2 km s^(-1), a weaker component at the same velocity as the 620.701 GHz maser at 11.7 km s^(-1) is much less polarised
The Galactic Centre in the Far Infrared
We analyse the far infrared dust emission from the Galactic Centre region,
including the Circumnuclear Disk (CND) and other structures, using Herschel
PACS and SPIRE photometric observations. These Herschel data are complemented
by unpublished observations by the Infrared Space Observatory Long Wavelength
Spectrometer (ISO LWS), which used parallel mode scans to obtain photometric
images of the region with a larger beam than Herschel but with a complementary
wavelength coverage and more frequent sampling with ten detectors observing at
ten different wavelengths in the range from 46 to 180 \mum, where the emission
peaks. We also include data from the MSX at 21.3 \mum for completeness. We
model the combined ISO LWS continuum plus Herschel PACS and SPIRE photometric
data toward the central 2 pc in Sgr A*, a region that includes the CND. We find
that the FIR spectral energy distribution is best represented by a continuum
that is the sum of three greybody curves from dust at temperatures of 90, 44.5,
and 23 K. We obtain temperature and molecular hydrogen column density maps of
the region. We estimate the mass of the inner part of the CND to be ~5.0x10e+4
Msum, with luminosities: Lcavity ~2.2x10e+6 Lsun and Lcnd ~1.5x10e+6 Lsun in
the central 2 pc radius around SgrA* . We find from the Herschel and ISO data
that the cold component of the dust dominates the total dust mass, with a
contribution of ~3.2x10E+4 Msun; this important cold material had escaped the
notice of earlier studies that relied on shorter wavelength observations. The
hotter component disagrees with some earlier estimates, but is consistent with
measured gas temperatures and with models that imply shock heating or turbulent
effects are at work. We find that the dust grain sizes apparently change widely
across the region, perhaps in response to the temperature variations, and we
map that distribution.Comment: 14 pages, 8 figure
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