100 research outputs found
On the frequency of N2H+ and N2D+
Context : Dynamical studies of prestellar cores search for small velocity
differences between different tracers. The highest radiation frequency
precision is therefore required for each of these species. Aims : We want to
adjust the frequency of the first three rotational transitions of N2H+ and N2D+
and extrapolate to the next three transitions. Methods : N2H+ and N2D+ are
compared to NH3 the frequency of which is more accurately known and which has
the advantage to be spatially coexistent with N2H+ and N2D+ in dark cloud
cores. With lines among the narrowests, and N2H+ and NH3 emitting region among
the largests, L183 is a good candidate to compare these species. Results : A
correction of ~10 kHz for the N2H+ (J:1-0) transition has been found (~0.03
km/s) and similar corrections, from a few m/s up to ~0.05 km/s are reported for
the other transitions (N2H+ J:3-2 and N2D+ J:1-0, J:2-1, and J:3-2) compared to
previous astronomical determinations. Einstein spontaneous decay coefficients
(Aul) are included
Molecular Beams
Contains research objectives and reports on two research projects.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E)Sloan Fund for Basic Research (M. I. T. Grant 99
Molecular Beams
Contains reports on four research projects.Lincoln Laboratory, Purchase Order DDL BB-107U. S. Air Force under Contract AF 19(628)-50
Herschel/HIFI deepens the circumstellar NH3 enigma
Circumstellar envelopes (CSEs) of a variety of evolved stars have been found
to contain ammonia (NH3) in amounts that exceed predictions from conventional
chemical models by many orders of magnitude. The observations reported here
were performed in order to better constrain the NH3 abundance in the CSEs of
four, quite diverse, oxygen-rich stars using the NH3 ortho J_K = 1_0 - 0_0
ground-state line. We used the Heterodyne Instrument for the Far Infrared
aboard Herschel to observe the NH3 J_K = 1_0 - 0_0 transition near 572.5 GHz,
simultaneously with the ortho-H2O J_Ka,Kc = 1_1,0 -1_0,1 transition, toward VY
CMa, OH 26.5+0.6, IRC+10420, and IK Tau. We conducted non-LTE radiative
transfer modeling with the goal to derive the NH3 abundance in these objects'
CSEs. For the latter two stars, Very Large Array imaging of NH3
radio-wavelength inversion lines were used to provide further constraints,
particularly on the spatial extent of the NH3-emitting regions. Results. We
find remarkably strong NH3 emission in all of our objects with the NH3 line
intensities rivaling those obtained for the ground state H2O line. The NH3
abundances relative to H2 are very high and range from 2 x 10-7 to 3 x 10-6 for
the objects we have studied. Our observations confirm and even deepen the
circumstellar NH3 enigma. While our radiative transfer modeling does not yield
satisfactory fits to the observed line profiles, it leads to abundance
estimates that confirm the very high values found in earlier studies. New ways
to tackle this mystery will include further Herschel observations of more NH3
lines and imaging with the Expanded Very Large Array.Comment: 4+2 page
Herschel Observations of a Potential Core Forming Clump: Perseus B1-E
We present continuum observations of the Perseus B1-E region from the
Herschel Gould Belt Survey. These Herschel data reveal a loose grouping of
substructures at 160 - 500 micron not seen in previous submillimetre
observations. We measure temperature and column density from these data and
select the nine densest and coolest substructures for follow-up spectral line
observations with the Green Bank Telescope. We find that the B1-E clump has a
mass of ~ 100 solar masses and appears to be gravitationally bound.
Furthermore, of the nine substructures examined here, one substructure (B1-E2)
appears to be itself bound. The substructures are typically less than a Jeans
length from their nearest neighbour and thus, may interact on a timescale of ~
1 Myr. We propose that B1-E may be forming a first generation of dense cores,
which could provide important constraints on the initial conditions of
prestellar core formation. Our results suggest that B1-E may be influenced by a
strong, localized magnetic field, but further observations are still required.Comment: 14 pages, 8 figures, published in A&A: Minor calibration correctio
Molecular Beams
Contains research objectives and reports on two research projects.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 36-039-AMC-03200(E
The kinetic temperature of a molecular cloud at redshift 0.7: Ammonia in the gravitational lens B0218+357
Using the Effelsberg 100-m telescope, absorption in the (J,K) = (1,1), (2,2)
and (3,3) inversion lines of ammonia (NH_3) was detected at a redshift of z =
0.6847 toward the gravitational lens system B0218+357. The lambda ~ 2cm
absorption peaks at 0.5-1.0 % of the continuum level and appears to cover a
smaller fraction of the radio continuum background than lines at millimeter
wavelengths. Measured intensities are consistent with a rotation temperature of
~35K, corresponding to a kinetic temperature of ~55K. The column density toward
the core of image A then becomes N(NH_3) ~ 1 * 10^(14)cm^(-2) and fractional
abundance and gas density are of order X(NH_3)~10^(-8) and n(H_2)~5 *
10^(3)cm^(-3), respectively. Upper limits are reported for the (2,1) and (4,4)
lines of NH_3 and for transitions of the SO, DCN, OCS, SiO, C_3N, H_2CO, SiC_2,
HC_3N, HC_5N, and CH_3OH molecules. These limits and the kinetic temperature
indicate that the absorption lines are not arising from a cold dark cloud but
from a warm, diffuse, predominantly molecular medium. The physical parameters
of the absorbing molecular complex, seen at a projected distance of ~2 kpc to
the center of the lensing galaxy, are quite peculiar when compared with the
properties of clouds in the Galaxy or in nearby extragalactic systems.Comment: 7 pages, 2 figures accepted by A&
Intracavity Raman Scattering from Molecular Beams: Direct Determination of Local Properties in an Expanding Jet Beam
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