369 research outputs found
Physical conditions in the Protoplanetary Nebula CRL 618 derived from observations of vibrationally excited HCCCN
We used the Effelsberg 100m and IRAM 30m telescopes to observe vibrationally
excited cyanoacetylene (HCCCN) in several rotational transitions toward the
proto-planetary nebula CRL618. Lines from 9 different vibrationally excited
states with energies ranging up to 1600 K above ground were detected. The lines
show P Cygni profiles indicating that the HCCCN emission originates from an
expanding and accelerating molecular envelope. The HCCCN rotational temperature
varies with velocity, peaks at 520 K, 3 km/s blue-shifted from the systemic
velocity and decreases with higher blueshift of the gas. The column density of
the absorbing HCCCN is 3-6 x 1E17 cm^2. We modeled spectra based on spherical
models of the expanding envelope which provide an excellent fit to the
observations, and discuss the implications of the models. Additionally, lines
from 13C substituted cyanoacetylene were observed. They can be used to
constrain the 12C/13C ratio in this source to 10+-2.Comment: 27 pages, 9 figures, to appear in Ap
A Pre-Protostellar Core in L1551
Large field surveys of NH3, C2S, 13CO and C18O in the L1551 dark cloud have
revealed a prolate, pre-protostellar molecular core (L1551-MC) in a relatively
quiescent region to the northwest of the well-known IRS 5 source. The kinetic
temperature is measured to be 9K, the total mass is ~2Msun, and the average
particle density is 10^4-10^5 cm^(-3). L1551-MC is 2.25' x 1.11' in projection
oriented at a position angle of 133deg. The turbulent motions are on the order
of the sound speed in the medium and contain 4% of the gravitational energy,
E_{grav}, of the core. The angular momentum vector is projected along the major
axis of L1551-MC corresponding to a rotational energy of 2.5E-3(sin
i)^(-2)|E_{grav}|. The thermal energy constitutes about a third of |E_{grav}|
and the virial mass is approximately equal to the total mass. L1551-MC is
gravitationally bound and in the absence of strong, ~160 microgauss, magnetic
fields will likely contract on a ~0.3 Myr time scale. The line profiles of many
molecular species suggest that the cold quiescent interior is surrounded by a
dynamic, perhaps infalling envelope which is embedded within the ambient
molecular gas of L1551.Comment: 27 pages, 7 figures, ApJ accepte
Rotational cooling of molecules using lamps
We investigate theoretically the application of tailored incoherent
far-infrared fields in combination with laser excitation of a single
rovibrational transition for rotational cooling of translationally cold polar
diatomic molecules. The cooling schemes are effective on a timescale shorter
than typical unperturbed trapping times in ion traps and comparable to
obtainable confinement times of neutral molecules.Comment: 5 pages, 2 figure
Detection of FeO towards SgrB2
We have observed the J=5-4 ground state transition of FeO at a frequency of
153 GHz towards a selection of galactic sources.
Towards the galactic center source SgrB2, we see weak absorption at
approximately the velocity of other features towards this source (62 km
s LSR).
Towards other sources, the results were negative as they were also for
MgOH(3-2) and FeC(6-5). We tentatively conclude that the absorption seen toward
SgrB2 is due to FeO in the hot ( 500 K) relatively low density absorbing
gas known to be present in this line of sight.
This is the first (albeit tentative) detection of FeO or any iron--containing
molecule in the interstellar gas. Assuming the observed absorption to be due to
FeO, we estimate [FeO]/[SiO] to be of order or less than 0.002 and
[FeO]/[H] of order . This is compatible with our negative
results in other sources.
Our results suggest that the iron liberated from grains in the shocks
associated with SgrB2 remains atomic and is not processed into molecular form.Comment: 1 postscrit figure,10 page
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
Study of Photon Dominated Regions in Cepheus B
Aim: The aim of the paper is to understand the emission from the photon
dominated regions in Cepheus B, estimate the column densities of neutral carbon
in bulk of the gas in Cepheus B and to derive constraints on the factors which
determine the abundance of neutral carbon relative to CO. Methods: This paper
presents 15'x15' fully sampled maps of CI at 492 GHz and 12CO 4-3 observed with
KOSMA at 1' resolution. The new observations have been combined with the FCRAO
12CO 1-0, IRAM-30m 13CO 2-1 and C18O 1-0 data, and far-infrared continuum data
from HIRES/IRAS. The KOSMA-tau spherical PDR model has been used to understand
the CI and CO emission from the PDRs in Cepheus B and to explain the observed
variation of the relative abundances of both C^0 and CO. Results: The emission
from the PDR associated with Cepheus B is primarily at V_LSR between -14 and
-11 km s^-1. We estimate about 23% of the observed CII emission from the
molecular hotspot is due to the ionized gas in the HII region. Over bulk of the
material the C^0 column density does not change significantly, (2.0+-1.4)x10^17
cm^-2, although the CO column density changes by an order of magnitude. The
observed \cbyco abundance ratio varies between 0.06 and 4 in Cepheus B. We find
an anti-correlation of the observed C/CO abundance ratio with the observed
hydrogen column density, which holds even when all previous observations
providing C/CO ratios are included. Here we show that this observed variation
of C/CO abundance with total column density can be explained only by clumpy
PDRs consisting of an ensemble of clumps. At high H2 column densities high mass
clumps, which exhibit low C/CO abundance, dominate, while at low column
densities, low mass clumps with high C/CO abundance dominate.Comment: 12 pages, 10 figures, Accepted for publication in A&
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
A Spectral Line Survey of Selected 3 mm Bands Toward Sagittarius B2(N-LMH) Using the NRAO 12 Meter Radio Telescope and the BIMA Array I. The Observational Data
We have initiated a spectral line survey, at a wavelength of 3 millimeters,
toward the hot molecular core Sagittarius B2(N-LMH). This is the first spectral
line survey of the Sgr B2(N) region utilizing data from both an interferometer
(BIMA Array) and a single-element radio telescope (NRAO 12 meter). In this
survey, covering 3.6 GHz in bandwidth, we detected 218 lines (97 identified
molecular transitions, 1 recombination line, and 120 unidentified transitions).
This yields a spectral line density (lines per 100 MHz) of 6.06, which is much
larger than any previous 3 mm line survey. We also present maps from the BIMA
Array that indicate that most highly saturated species (3 or more H atoms) are
products of grain chemistry or warm gas phase chemistry. Due to the nature of
this survey we are able to probe each spectral line on multiple spatial scales,
yielding information that could not be obtained by either instrument alone.Comment: 35 pages, 15 figures, to be published in The Astrophysical Journa
Accurate laboratory rest frequencies of vibrationally excited CO up to and up to 2 THz
Astronomical observations of (sub)millimeter wavelength pure rotational
emission lines of the second most abundant molecule in the Universe, CO, hold
the promise of probing regions of high temperature and density in the innermost
parts of circumstellar envelopes. The rotational spectrum of vibrationally
excited CO up to \varv = 3 has been measured in the laboratory between 220
and 1940 GHz with relative accuracies up to , corresponding
to kHz near 1 THz. The rotational constant and the quartic
distortion parameter have been determined with high accuracy and even the
sextic distortion term was determined quite well for \varv = 1 while
reasonable estimates of were obtained for \varv = 2 and 3. The present
data set allows for the prediction of accurate rest frequencies of
vibrationally excited CO well beyond 2 THz.Comment: Astron. Astrophys, accepted; 5 pages, 2 Figures, 2 Table
The Photon Dominated Region in the IC 348 molecular cloud
In this paper we discuss the physical conditions of clumpy nature in the IC
348 molecular cloud.
We combine new observations of fully sampled maps in [C I] at 492 GHz and
12CO 4--3, taken with the KOSMA 3 m telescope at about 1' resolution, with
FCRAO data of 12CO 1--0, 13CO 1--0 and far-infrared continuum data observed by
HIRES/IRAS. To derive the physical parameters of the region we analyze the
three different line ratios. A first rough estimate of abundance is obtained
from an LTE analysis. To understand the [C I] and CO emission from the PDRs in
IC 348, we use a clumpy PDR model. With an ensemble of identical clumps, we
constrain the total mass from the observed absolute intensities. Then we apply
a more realistic clump distribution model with a power law index of 1.8 for
clump-mass spectrum and a power law index of 2.3 for mass-size relation.
We provide detailed fits to observations at seven representative positions in
the cloud, revealing clump densities between 4 10 cm and 4
10 cm and C/CO column density ratios between 0.02 and 0.26. The
derived FUV flux from the model fit is consistent with the field calculated
from FIR continuum data, varying between 2 and 100 Draine units across the
cloud. We find that both an ensemble of identical clumps and an ensemble with a
power law clump mass distribution produce line intensities which are in good
agreement (within a factor ~ 2) with the observed intensities. The models
confirm the anti-correlation between the C/CO abundance ratio and the hydrogen
column density found in many regions.Comment: 11 pages, 8 figures, accepted by A&
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