875 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 simple approach to the correlation of rotovibrational states in four-atomic molecules
The problem of correlation between quantum states of four-atomic molecules in
different geometrical configurations is reviewed in detail. A general, still
simple rule is obtained which allows one to correlate states of a linear
four-atomic molecule with those of any kind of non-linear four-atomic molecule.Comment: 16 pages (+8 figures), Postscript (ready to print!
A 492 GHz cooled Schottky receiver for radio-astronomy
We developed a 492 GHz cooled GaAs Schottky receiver driven by a solid state local oscillator with a DSB noise temperature of 550 K measured at the telescope. The receiver-bandwidth is approx. equal to 1.0 GHz. Quasi-optical mirrors focus the sky and local oscillator radiation into the mixer. Stability analysis via the Allan variance method shows that the total system including a 1 GHz bandwidth acousto-optical spectrometer built in Cologne allows integration times up to 100 sec per half switching cycle. We successfully used the receiver at the KOSMA 3 m telescope on Gornergrat (3150m) located in the central Swiss Alps near Zermatt during January-February 1992 for observations of the 492 GHz, (CI) (3)P1 to (3)P0 fine structure line in several galactic sources. These observations confirm that Gornergrat is an excellent winter submillimeter site in accordance with previous predictions based on the atmospheric opacity from KOSMA 345 GHz measurements
Experimental Confirmation of Quantum Monodromy: The Millimeter Wave Spectrum of Cyanogen Isothiocyanate NCNCS
We have made energy-momentum maps for the experimental end-over-end rotational energy and the two-dimensional bending vibrational energy, both of which confirm the dominating effects of nontrivial quantum monodromy in cyanogen isothiocyanate. Accidental resonances in the rotational spectra yield accurate intervals between bending states
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Notations and conventions in molecular spectroscopy: part 1. General spectroscopic notation
The field of Molecular Spectroscopy was surveyed in order to determine a set of
conventions and symbols which are in common use in the spectroscopic literature. This
document, which is Part I in a series, establishes the notations and conventions used for
general spectroscopic notations and deals with quantum mechanics, quantum numbers
(vibrational states, angular momentum and energy levels), spectroscopic transitions, and
miscellaneous notations (e.g. spectroscopic terms). Further parts will follow, dealing inter
alia with symmetry notation, permutation and permutation-inversion symmetry notation,
vibration-rotation spectroscopy and electronic spectroscopy
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Notations and conventions in molecular spectroscopy: part 2. Symmetry notation
The field of Molecular Spectroscopy was surveyed in order to determine a set of
conventions and symbols which are in common use in the spectroscopic literature. This
document, which is Part 2 in a series, establishes the notations and conventions used for the
description of symmetry in rigid molecules, using the Schoenflies notation. It deals firstly
with the symmetry operators of the molecular point groups (also drawing attention to the
difference between symmetry operators and elements). The conventions and notations of the
molecular point groups are then established, followed by those of the representations of these
groups as used in molecular spectroscopy. Further parts will follow, dealing inter alia with
permutation and permutation-inversion symmetry notation, vibration-rotation spectroscopy
and electronic spectroscopy
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
Star formation associated with the infrared dust bubble N68
We investigated the environment of the infrared dust bubble N68 and searched
for evidence of triggered star formation in its surroundings. We performed a
multiwavelength study of the nebula with data taken from several large-scale
surveys: GLIMPSE, MIPSGAL, IRAS, NVSS, GRS, and JCMT. We analyzed the spectral
profile and the distribution of the molecular gas (^{13}CO J = 1 - 0 and J = 3
- 2), and the dust in the environment of the N68. The position-velocity diagram
clearly shows that the N68 may be expanding outward. We used two three-color
images of the mid-infrared emission to explore the physical environment, and
one color-color diagram to investigate the distribution of young stellar
objects (YSOs). We found that the 24 \mu m emission is surrounded by the 8.0
\mu m emission. Morphologically, the 1.4 GHz continuum correlates strongly with
the 24 \mu m emission, and the ^{13}CO J = 1 - 0 and J = 3 - 2 emissions
correlate well with the 8.0 \mu m emission. We investigated two compact cores
located at the shell of the N68. The spectral intensity ratios of ^{13}CO J = 3
- 2 to J = 1 - 0 range from 5 to 0.3. In addition, young star objects, masers,
IRAS, and UC HII regions distribute at the shell of bubble. The active region
may be triggered by the expanding of the bubble N68.Comment: 10 pages, 11 figures, submited to RA
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