899 research outputs found
Massive molecular outflows at high spatial resolution
We present high-spatial resolution Plateau de Bure Interferometer CO(2-1) and
SiO(2-1) observations of one intermediate-mass and one high-mass star-forming
region. The intermediate-mass region IRAS20293+3952 exhibits four molecular
outflows, one being as collimated as the highly collimated jet-like outflows
observed in low-mass star formation sources. Furthermore, comparing the data
with additional infrared H2 and cm observations we see indications that the
nearby ultracompact HII region triggers a shock wave interacting with the
outflow. The high-mass region IRAS19217+1651 exhibits a bipolar outflow as well
and the region is dominated by the central driving source. Adding two more
sources from the literature, we compare position-velocity diagrams of the
intermediate- to high-mass sources with previous studies in the low-mass
regime. We find similar kinematic signatures, some sources can be explained by
jet-driven outflows whereas other are better constrained by wind-driven models.
The data also allow to estimate accretion rates varying from a few times
10^{-5}Msun/yr for the intermediate-mass sources to a few times 10^{-4}Msun/yr
for the high-mass source, consistent with models explaining star formation of
all masses via accretion processes.Comment: 14 pages text, 4 tables, 8 figures, accepted for Ap
Laboratory Measurement of the Pure Rotational Transitions of the HCNH+ and its Isotopic Species
The pure rotational transitions of the protonated hydrogen cyanide ion,
HCNH+, and its isotopic species, HCND+ and DCND+, were measured in the 107 -
482 GHz region with a source modulated microwave spectrometer. The ions were
generated in the cell with a magnetically confined dc-glow discharge of HCN
and/or DCN. The rotational constant B0 and the centrifugal distortion constant
D0 for each ion were precisely determined by a least-squares fitting to the
observed spectral lines. The observed rotational transition frequencies by
laboratory spectroscopy and the predicted ones are accurate in about 30 to 40
kHz and are useful as rest frequencies for astronomical searches of HCNH+ and
HCND+.Comment: 14 pages in TeX, 1 figures in JPE
Dissipative structures of diffuse molecular gas: I - Broad HCO(1-0) emission
Results: We report the detection of broad HCO+(1-0) lines (10 mK < T < 0.5
K). The interpretation of 10 of the HCO+ velocity components is conducted in
conjunction with that of the associated optically thin 13CO emission. The
derived HCO+ column densities span a broad range, , and the inferred HCO+ abundances, , are more than one order of magnitude above
those produced by steady-state chemistry in gas weakly shielded from UV
photons, even at large densities. We compare our results with the predictions
of non-equilibrium chemistry, swiftly triggered in bursts of turbulence
dissipation and followed by a slow thermal and chemical relaxation phase,
assumed isobaric. The set of values derived from the observations, i.e. large
HCO+ abundances, temperatures in the range of 100--200 K and densities in the
range 100--1000 cm3, unambiguously belongs to the relaxation phase. The
kinematic properties of the gas suggest in turn that the observed HCO+ line
emission results from a space-time average in the beam of the whole cycle
followed by the gas and that the chemical enrichment is made at the expense of
the non-thermal energy. Last, we show that the "warm chemistry" signature (i.e
large abundances of HCO+, CH+, H20 and OH) acquired by the gas within a few
hundred years, the duration of the impulsive chemical enrichment, is kept over
more than thousand years. During the relaxation phase, the \wat/OH abundance
ratio stays close to the value measured in diffuse gas by the SWAS satellite,
while the OH/HCO+ ratio increases by more than one order of magnitude.Comment: 14 page
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
Massive Infrared-Quiet Dense Cores: Unveiling the Initial Conditions of High-Mass Star Formation
As Pr. Th. Henning said at the conference, cold precursors of high-mass stars
are now "hot topics". We here propose some observational criteria to identify
massive infrared-quiet dense cores which can host the high-mass analogs of
Class 0 protostars and pre-stellar condensations. We also show how far-infrared
to millimeter imaging surveys of entire complexes forming OB stars are starting
to unveil the initial conditions of high-mass star formation
Circumbinary Molecular Rings Around Young Stars in Orion
We present high angular resolution 1.3 mm continuum, methyl cyanide molecular
line, and 7 mm continuum observations made with the Submillimeter Array and the
Very Large Array, toward the most highly obscured and southern part of the
massive star forming region OMC1S located behind the Orion Nebula. We find two
flattened and rotating molecular structures with sizes of a few hundred
astronomical units suggestive of circumbinary molecular rings produced by the
presence of two stars with very compact circumstellar disks with sizes and
separations of about 50 AU, associated with the young stellar objects 139-409
and 134-411. Furthermore, these two circumbinary rotating rings are related to
two compact and bright {\it hot molecular cores}. The dynamic mass of the
binary systems obtained from our data are 4 M for 139-409 and
0.5 M for 134-411. This result supports the idea that
intermediate-mass stars will form through {\it circumstellar disks} and
jets/outflows, as the low mass stars do. Furthermore, when intermediate-mass
stars are in multiple systems they seem to form a circumbinary ring similar to
those seen in young, multiple low-mass systems (e.g., GG Tau and UY Aur).Comment: Accepted by Astronomy and Astrophysic
A Line Survey of Orion KL from 325 to 360 GHz
We present a high-sensitivity spectral line survey of the high-mass star-forming region Orion KL in the 325-360 GHz frequency band. The survey was conducted at the Caltech Submillimeter Observatory on Mauna Kea, Hawaii. The sensitivity achieved is typically 0.1-0.5 K and is limited mostly by the sideband separation method utilized. We find 717 resolvable features consisting of 1004 lines, among which 60 are unidentified. The identified lines are due to 34 species and various isotopomers. Most of the unidentified lines are weak, and many of them most likely due to isotopomers or vibrationally or torsionally excited states of known species with unknown line frequencies, but a few reach the 2-5 K level. No new species have been identified, but we were able to strengthen evidence for the identification of ethanol in Orion and found the first nitrogen sulfide line in this source. The molecule dominating the integrated line emission is SO_2, which emits twice the intensity of CO, followed by SO, which is only slightly stronger than CO. In contrast, the largest number of lines is emitted from heavy organic rotors like HCOOCH_3, CH_3CH_2CN, and CH_3OCH_3, but their contribution to the total flux is unimportant. CH_3OH is also very prominent, both in the number of lines and in integrated flux. An interesting detail of this survey is the first detection of vibrationally excited HCN in the v_2 = 2 state, 2000 K above ground. Clearly this is a glimpse into the very inner part of the Orion hot core
Submillimeter spectroscopy of southern hot cores: NGC6334(I) and G327.3-0.6
High-mass star-forming regions are known to have a rich molecular spectrum
from many species. Some of the very highly excited lines are emitted from very
hot and dense gas close to the central object(s). The physics and chemistry of
the inner cores of two high mass star forming regions, NGC6334(I) and
G327.3-0.6, shall be characterized. Submillimeter line surveys with the APEX
telescope provide spectra which sample many molecular lines at high excitation
stages. Partial spectral surveys were obtained, the lines were identified,
physical parameters were determined through fitting of the spectra. Both
sources show similar spectra that are comparable to that of the only other high
mass star forming region ever surveyed in this frequency range}, Orion-KL, but
with an even higher line density. Evidence for very compact, very hot sources
is found.Comment: APEX A&A special issue, accepte
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
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