4,295 research outputs found
Herschel Measurements of Molecular Oxygen in Orion
We report observations of three rotational transitions of molecular oxygen (O_2) in emission from the H_2 Peak 1 position of vibrationally excited molecular hydrogen in Orion. We observed the 487 GHz, 774 GHz, and 1121 GHz lines using the Heterodyne Instrument for the Far Infrared on the Herschel Space Observatory, having velocities of 11 km s^(â1) to 12 km s^(â1) and widths of 3 km s^(â1). The beam-averaged column density is N(O_2) = 6.5 Ă 10^(16) cm^(â2), and assuming that the source has an equal beam-filling factor for all transitions (beam widths 44, 28, and 19"), the relative line intensities imply a kinetic temperature between 65 K and 120 K. The fractional abundance of O_2 relative to H_2 is (0.3-7.3) Ă 10^(â6). The unusual velocity suggests an association with a ~5" diameter source, denoted Peak A, the Western Clump, or MF4. The mass of this source is ~10 M_â and the dust temperature is â„150 K. Our preferred explanation of the enhanced O_2 abundance is that dust grains in this region are sufficiently warm (T â„ 100 K) to desorb water ice and thus keep a significant fraction of elemental oxygen in the gas phase, with a significant fraction as O_2. For this small source, the line ratios require a temperature â„180 K. The inferred O_2 column density â5 Ă 10^(18) cm^(â2) can be produced in Peak A, having N(H_2) â4 Ă 10^(24) cm^(â2). An alternative mechanism is a low-velocity (10-15 km s^(â1)) C-shock, which can produce N(O_2) up to 10^(17) cm^(â2)
Dust emission in the Sagittarius B2 molecular cloud core
A model is presented for the dust emission from the Sagittarius B2 molecular cloud core which reproduces the observed spectrum between 30 and 1300 micron, as well as the distribution of the emission at 1300 micron. The model is based on the assumption that Sgr B2(N) continuum source is located behind the dust cloud associated with Sgr B2(M) continuum source. The fact that Sgr B2(N) is stronger at 1300 micron can be attributed to a local column density maximum at the position of this source. Absence of a 53 micron emission peak at the position of Sgr B2(N) suggests that the luminosity of the north source is lower than that of the middle source
Chemical Treatment of Molten Non-Ferrous Metals
The use of different fluxes for the removal of undesirable impurities from various non-ferrous metals and alloys has been stated. Oxidizing conditions for the removal of hydrogen and deoxidation of some alloys by phosphorus, copper, magnesium mag nesium-boron, etc., have been described.The fluxes for elimination of lead oxide and the
effect of nickel on lead bronzes have been mentioned.
Elimination of A1203 by different fluxing techniques
is described. The use of MgCla flux for Al-Mg
alloy sand degassing by chlorine through the introduction
of hexachloroethane have been outlined.Grain refinement by boron and titanium has been described
A Direct Measurement of the Total Gas Column Density in Orion KL
The large number of high-J lines of C^(18)O available via the Herschel Space Observatory provide an unprecedented ability to model the total CO column density in hot cores. Using the emission from all the observed lines (up to J = 15-14), we sum the column densities in each individual level to obtain the total column after correcting for the population in the unobserved states. With additional knowledge of source size, V_(LSR), and line width, and both local thermodynamic equilibrium (LTE) and non-LTE modeling, we have determined the total C^(18)O column densities in the Extended Ridge, Outflow/Plateau, Compact Ridge, and Hot Core components of Orion KL to be 1.4 Ă 10^(16) cm^(â2), 3.5 Ă 10^(16) cm^(â2), 2.2 Ă 10^(16) cm^(â2), and 6.2 Ă 10^(16) cm^(â2), respectively. We also find that the C^(18)O/C^(17)O abundance ratio varies from 1.7 in the Outflow/Plateau, 2.3 in the Extended Ridge, 3.0 in the Hot Core, and to 4.1 in the Compact Ridge. This is in agreement with models in which regions with higher ultraviolet radiation fields selectively dissociate C^(17)O, although care must be taken when interpreting these numbers due to the size of the uncertainties in the C^(18)O/C^(17)O abundance ratio
Detection of a dense clump in a filament interacting with W51e2
In the framework of the Herschel/PRISMAS Guaranteed Time Key Program, the
line of sight to the distant ultracompact HII region W51e2 has been observed
using several selected molecular species. Most of the detected absorption
features are not associated with the background high-mass star-forming region
and probe the diffuse matter along the line of sight. We present here the
detection of an additional narrow absorption feature at ~70 km/s in the
observed spectra of HDO, NH3 and C3. The 70 km/s feature is not uniquely
identifiable with the dynamic components (the main cloud and the large-scale
foreground filament) so-far identified toward this region. The narrow
absorption feature is similar to the one found toward low-mass protostars,
which is characteristic of the presence of a cold external envelope. The
far-infrared spectroscopic data were combined with existing ground-based
observations of 12CO, 13CO, CCH, CN, and C3H2 to characterize the 70 km/s
component. Using a non-LTE analysis of multiple transitions of NH3 and CN, we
estimated the density (n(H2) (1-5)x10^5 cm^-3) and temperature (10-30 K) for
this narrow feature. We used a gas-grain warm-up based chemical model with
physical parameters derived from the NH3 data to explain the observed
abundances of the different chemical species. We propose that the 70 km/s
narrow feature arises in a dense and cold clump that probably is undergoing
collapse to form a low-mass protostar, formed on the trailing side of the
high-velocity filament, which is thought to be interacting with the W51 main
cloud. While the fortuitous coincidence of the dense clump along the line of
sight with the continuum-bright W51e2 compact HII region has contributed to its
non-detection in the continuum images, this same attribute makes it an
appropriate source for absorption studies and in particular for ice studies of
star-forming regions.Comment: Accepted for publication in A&
A FIR-Survey of TNOs and Related Bodies
The small solar-system bodies that reside between 30 and 50 AU are often
referred to as the Trans Neptunian Objects, or TNOs. A far-infrared (FIR)
mission with survey capabilities, like the prospective Cryogenic Aperture Large
Infrared Space Telescope Observatory (CALISTO; Goldsmith et al. 2008), offers
the potential for the first time of really probing the population of TNOs, and
related populations, down to moderates sizes, and out to distances exceeding
100 AU from the Sun.Comment: 3 pages, 1 figure, a short whitepaper submitted in response to the
Cosmic Origins Program Analysis Group Call for White Papers, in anticipation
of the Far IR Surveyor Workshop, June 3rd - 5th 2015 at Caltech's Beckman
Institute, Pasadena, Californi
Massive Quiescent Cores in Orion. -- II. Core Mass Function
We have surveyed submillimeter continuum emission from relatively quiescent
regions in the Orion molecular cloud to determine how the core mass function in
a high mass star forming region compares to the stellar initial mass function.
Such studies are important for understanding the evolution of cores to stars,
and for comparison to formation processes in high and low mass star forming
regions. We used the SHARC II camera on the Caltech Submillimeter Observatory
telescope to obtain 350 \micron data having angular resolution of about 9
arcsec, which corresponds to 0.02 pc at the distance of Orion. Our analysis
combining dust continuum and spectral line data defines a sample of 51 Orion
molecular cores with masses ranging from 0.1 \Ms to 46 \Ms and a mean mass of
9.8 \Ms, which is one order of magnitude higher than the value found in typical
low mass star forming regions, such as Taurus. The majority of these cores
cannot be supported by thermal pressure or turbulence, and are probably
supercritical.They are thus likely precursors of protostars. The core mass
function for the Orion quiescent cores can be fitted by a power law with an
index equal to -0.850.21. This is significantly flatter than the Salpeter
initial mass function and is also flatter than the core mass function found in
low and intermediate star forming regions. Thus, it is likely that
environmental processes play a role in shaping the stellar IMF later in the
evolution of dense cores and the formation of stars in such regions.Comment: 30 pages, 10 figures, accepted by Ap
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