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Observations of the J = 1-0 transition of CS at 49 GHz in southern molecular clouds
Abstract
The J = 1–0 transition of CS at 49 GHz has been detected at Parkes in 37 out of a total of 57 molecular concentrations, most of
which are associated with H II regions. The telescope beamwidth was 1.5 arcmin and the sensitivity limit in ‘corrected antenna temperature’ was about 1
K. Typical peak temperature and half-intensity width were 2.0 K and 4.7 km/s respectively; the corresponding CS column density
exceeds 1014 cm−2. It was found that the CS, CO, H2CO and H II velocities agreed within about 2km/s on average and any systematic variation in velocity through the cloud concentrations
is small.
The CS distribution was partly mapped over the nearby H II regions Ori A, NGC6334 and M17. The results for the Orion cloud do not support the suggestion that the whole cloud rotates.
Aims. We aim to identify bipolar Galactic H II regions and to understand their parental cloud structures, morphologies, evolution, and impact on the formation of new generations of stars.
Methods. We use the Spitzer -GLIMPSE, Spitzer -MIPSGAL, and Herschel -Hi-GAL surveys to identify bipolar H II regions and to examine their morphologies. We search for their exciting star(s) using NIR data from the 2MASS, UKIDSS, and VISTA surveys. Massive molecular clumps are detected near these bipolar nebulae, and we estimate their temperatures, column densities, masses, and densities. We locate Class 0/I young stellar objects (YSOs) in their vicinities using the Spitzer and Herschel -PACS emission.
Results. Numerical simulations suggest bipolar H II regions form and evolve in a two-dimensional flat- or sheet-like molecular cloud. We identified 16 bipolar nebulae in a zone of the Galactic plane between ℓ ± 60° and | b | < 1°. This small number, when compared with the 1377 bubble H II regions in the same area, suggests that most H II regions form and evolve in a three-dimensional medium. We present the catalogue of the 16 bipolar nebulae and a detailed investigation for six of these. Our results suggest that these regions formed in dense and flat structures that contain filaments. We find that bipolar H II regions have massive clumps in their surroundings. The most compact and massive clumps are always located at the waist of the bipolar nebula, adjacent to the ionised gas. These massive clumps are dense, with a mean density in the range of 10 ⁵ cm ⁻³ to several 10 ⁶ cm ⁻³ in their centres. Luminous Class 0/I sources of several thousand solar luminosities, many of which have associated maser emission, are embedded inside these clumps. We suggest that most, if not all, massive 0/I YSO formation has probably been triggered by the expansion of the central bipolar nebula, but the processes involved are still unknown. Modelling of such nebula is needed to understand the star formation processes at play.
We probe the structure and kinematics of two neighbouring H ii regions identified as cometary and bipolar, using radio recombination lines (RRL). The H172α RRLs from these H ii regions: G351.69–1.15 and G351.63–1.25, are mapped using GMRT, India. We also detect carbon RRLs C172α towards both these regions. The hydrogen RRLs display the effects of pressure and dynamical broadening in the line profiles, with the dynamical broadening (∼15 km/s) playing a major role in the observed profile of G351.69–1.15. We investigate the kinematics of molecular gas species towards this H ii region from the MALT90 pilot survey. The molecular gas is mostly distributed towards the north and north-west of the cometary head. The molecular line profiles indicate signatures of turbulence and outflow in this region. The ionized gas at the cometary tail is blue shifted by ∼8 km/s with respect to the ambient molecular cloud, consistent with the earlier proposed champagne flow scenario. The relative velocity of ∼5 km/s between the northern and southern lobes of the bipolar H ii region G351.63–1.25 is consistent with the premise that the bipolar morphology is a result of the expanding ionized lobes within a flat molecular cloud.
Observations are made of 16 points in molecular clouds associated with galactic HII regions. The ESO 1.4-m CoudeAuxiliary Telescope at La Silla (Chile) is used. Three of the sources, namely RCW 36, 38 and 74C, are considered especially interesting because they show signs of self-absorption. The most likely candidate in this matter is thought to be RCW 38, where the velocities of the higher excitation molecules cluster around the velocity of the dip. In the case of RCW 36, the molecules have velocities close to that of the higher-velocity peak, indicating that there may be two separate clouds. With RCW 74C, only a very shallow dip is seen. At Las Campanas (Chile), a 14 x 14 arcmin area around the radio continuum source G327.3-0.5 is mapped. It is noted that this radio source is very close to the optical HII region RCW 97. Various features from these observations are discussed.
Line surveys of the Southern Milky Way carried out with the Parkes 64-m and Epping 4-m radio telescopes are listed and discussed, with particular attention given to CO surveys toward H II regions. A comparison is made between CO and other molecules observed toward the H II regions, including H2CO, CS, HCN, and HCO(+). It is shown that (1) CO velocities are generally about 0.5 km/s lower than the average velocities of the other molecules; (2) CO profile widths are considerably larger than those of the other molecules; and (3) the profile areas of CO and CS are well correlated.
N-band (10.5 μm) and/or Q-band (20.0 μm) images taken with MANIAC on the ESO/MPI 2.2-m telescope are presented for 31 methanol maser sites and 19 ultracompact (UC) H ii regions. Most of the maser sites and UC H ii regions are coincident with mid-infrared (MIR) sources to within the positional uncertainties of ∼ 3 arcsec, consistent with the maser emission being powered by the MIR source. The IRAS source positions, however, do not always coincide with the MIR sources.
Based on an average infrared spectral energy distribution, we deduce that the MIR objects are luminous enough that they should also produce a strong ionizing radiation. Some sources are consistent with stars of later spectral type, but not all can be. A number of maser sites show no detectable radio continuum emission associated with MIR emission, despite a powering source luminous enough potentially to produce an UC H ii region. Since no signs of an UC H ii region are detected here, these maser sites might be produced during a very early stage of stellar evolution.
We present objects that show evidence of outflow activity stemming from a maser site, exhibiting CO and/or CS line profiles indicative of outflows coincident with the MIR source. These cases are promising examples of maser sites signposting the earliest stages of high-mass star formation.
We have conducted a survey of SiO emission towards galactic H_2O and OH masers and ultracompact HII regions using the 15-m SEST and the 20-m Onsala telescope. With the SEST the transitions (v=0,J=2-1) and (v=0,J=3-2) of SiO at 3 and 2 mm were measured simultaneously. With Onsala only the (v=0,J=2-1) line was accessible. Altogether 369 objects were observed and SiO was detected towards 137 of them. The detection rate is highest towards the most intense H_2O masers, which probably require powerful shocks to be excited. The SiO detection rate correlates also with the integrated far-infrared flux density and the FIR luminosity of the associated IRAS point source, indicating that the occurrence of shocks is related to the amount of radiation from the central stellar source(s). For flux and luminosity limited samples the SiO detection rate is higher in the inner 7 kpc from the galactic centre than elsewhere. This suggests that dense cores belonging to the so called ``molecular ring" provide particularly favourable conditions for the production of gaseous SiO. The full widths above 2sigma of the SiO(J=2-1) lines, which are likely to be related to the associated shock velocities, range from 2 to 60 km s(-1) except for the line in Ori KL which has a full width of about 100 km s(-1) . The median of our sample is 19 km s(-1) . The SiO lines are single-peaked and the peak velocities are always close to the ambient cloud velocity as determined from published CS observations. These line characteristics are compared with the predictions of kinematical bow-shock models. The SiO line shapes correspond with the model of \cite[Raga & Cabrit (1993)]{R93} where the emission arises from turbulent wakes behind bow-shocks. However, the number of symmetric, relatively narrow profiles indicates that at least in some of the observed sources SiO emission arises also from the quiescent gas component. We suggest that this is due to evaporation of silicon compounds from grain mantles and their reprocessing to SiO in dense quiescent gas according to the model of \cite[McKay (1995, 1996).]{M95} These reactions may be initiated and sustained by ionizing radiation from shocks, in the same way as the enhancement of HCO(+) near Herbig-Haro objects has been explained in the model of \cite[Wolfire & Koenigl (1993).]{W93} The excitation temperatures of SiO(J=2-1) and (J=3-2) transitions were determined towards three strong sources using measurements in isotopically substituted SiO. In all three sources the transitions are clearly subthermally excited, implying moderate densities (< 3 10(6) cm(-3) ) in the SiO emission regions. The entire Tables~B.1 and B.2 and the spectra of all the detected SiO sources are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
A series of maps are presented which show the distribution of HCO(+) in
the direction of NGC 6334 as a function of radial velocity. The
observations were carried out in May and June 1979 as part of a larger
program of HCO(+) observations at the Epping 4-m millimeter-wave radio
telescope. The radial velocities described in the maps are separated by
about 1.2 km/s. A comparison of the HCO(+) contours in the maps with
contours of 69-micron and 6-cm continuum emission indicates a close
relationship between molecules, dust and ionized gas in the overall
diffuse components and in more compact regions of NGC 6334.
Observations of the J = 2→1 line of CO have been made towards 17
positions in the southern galactic plane where H2O masers
have been detected. apparent self-absorption is found for RCW 38. In the
vicinity of the Carina H2O maser the CO linewidth is broader
than at neighbouring positions, which may be related to outflow. The J =
5→4 line of CS has been observed towards the H II region G
322.2+0.6. From a comparison with the J = 1→0 line observed
previously, an H2 density of 8×105
cm-3 is derived.
The interstellar H2CO/H2CS abundance ratio was investigated by means of
observations of the 3-GHz absorption of H2CS in dense H2CO clouds, most
of which were in association with continuum sources. The H2CS
2(11)-2(12) transition was detected towards a total of 11 continuum
sources at a rest frequency of 3139.391 + or - 0.002 MHz.
Formaldehyde/thioformaldehyde optical depth ratios from 100-340 are
calculated from the H2CS spectra, and used to estimate H2CO/H2CS
abundance ratios between 7 and 22, with a median of 9.0. These values
are significantly lower than the usually accepted O/S cosmic abundance
ratio of 40, suggesting the presence of preferential selection effects
in molecular formation.
CO observations of the molecular cloud complex in the vicinity of IC
5146 reveal three regions of enhanced emission, all lying around the
periphery of the Sharpless region S125. The most intense region has a
peak CO line temperature of 41 K. The continued existence of this hot
spot can be accounted for by an embedded protostar of luminosity class
between B0.5 and Bi. A comparison with H I observations of about the
same spatial and velocity resolution shows that the surrounding H I
cloud emission is generally strong where the CO emission is weak.
The velocity of the H II region, S125, is blueshifted with respect to
the gas behind it by 5.6 km s-1. This has yielded an estimate
for the expansion age of the H II region of about 105 yr, a
factor of 30 smaller than the age given for the stellar cluster.
The whole complex along the elongated dust lane, to a distance of 16.1
pc from the center of S125, shows a velocity gradient of 0.26 km
s-1 pc-1. Rotation is considered as a possible
cause for the extended geometry of the region.
An unusual circular region of very filamentary nebulosity, 3.5 pc
diameter, exists on the southern edge of the interstellar complex of NGC
6334. This surrounds an O6.6 star. Narrow band, Schmidt photographs
centered on the H-alpha and N II and S II forbidden band lines, a
Fabry-Perot interferogram of the N II forbidden band line, three
intermediate dispersion (10 A/mm) AAT spectra, and VLA measurements,
have now been obtained of this object. Many components over a range in
radial velocity of 150 km/sec are found over the face of the nebula. As
this nebula is a thermal radio source and the line ratios imply
radiative ionization, energetic stellar winds and radiation pressure
from Lyman photons are a possible source of these motions.
An attempt was made to extend previous southern CO observations and to
search for objects exhibiting rotation, wide linewidths, or
self-absorption; the presence of these effects in molecular spectra is
very useful for modeling the thermal and dynamical structures of these
star formation regions. The present survey was biased toward objects
exhibiting recent star formation activity, indicated by the presence of
interstellar water-vapor maser sources. Observations were made with the
2.5-m du Pont telescope of the Las Campanas Observatory. Particular
attention is given to RCW 38 and the Carina Nebula.
Twenty-five H II regions of relatively high emission measure have been observed with a telescope beam of half-power width 2.3 arcmin near
14.7 GHz (76α) for their radio recombination lines of hydrogen, helium, carbon and other elements. Spectra are presented together with
observational and derived parameters. Electron temperatures and the helium abundance ratios $[N(\text{He}^+)/N(\text H^+)]$ and their distribution with galactic radius are discussed. No correlation was found between the He+ abundance and galactic radius. Carbon recombination lines were detected in 20 sources; their radial velocities and those
of the hydrogen lines are compared with the velocities of several molecular species observed in the directions of the same
sources. Lines of another element, assumed to be sulphur, were detected in four sources.
Observations from a sample of six regions of star formation in the 244 GHz, J = 5 → 4 rotational transition of CS at 244 GHz. In combination with published results at lower frequencies, we show the J = 5 → 4 line temperatures for OMC-1, M17 SW, W3(OH) and Ori B to be consistent with constant density large velocity gradient
(LVG) models, indicating typical abundances $X/(dV/dr) \sim 4 \times 10^{-10}\enspace\text{km}^{-1}$ s pc, and densities $n_{\text H_2} \sim 10^5 \enspace\text {cm}^{-3}$. For two clouds, W51 and DR21(OH), however, the results may indicate the need for substantial levels of CS thermalization,
suggesting in turn high source densities and beam dilution.
We have observed the 158 μm2P3/2←2P1/2 fine-structure line of C II, the J = 9 → 8, 12 → 11, and 17 → 16 lines of 12CO, and the J = 9 → 8 rotational transition of 13CO in the molecular cloud and photodissociation region (PDR) associated with NGC 3576. The line profiles were fully resolved using a heterodyne spectrometer with better than 1 km s-1 resolution. The high-J CO emission arises from a spatially compact region near the infrared peak that is characterized by a kinetic temperature near 150 K and a density nH2 5 × 105 cm-3. The 12CO J = 9 → 8 line is found to be optically thick and arises from a more extended, cooler region with Tkin ~ 60 K. The increase in excitation temperature with the rotational level of CO suggests that the ionizing source is located behind much of the molecular cloud. Less than 1% of the molecular cloud material is found in the warm PDR and cloud interface region. The C II fine-structure line emission is intense over more than 4' × 4' and shows a central "self-absorption" feature at many locations. This absorption may represent a cooler or less dense component of ionized gas associated with the foreground molecular cloud.
We examine the 13 most luminous sources in the WMAP free-free map using the Spitzer GLIMPSE and Midcourse Space Experiment surveys to identify massive star formation complexes, emitting one-third of the Galactic free-free luminosity. We identify star-forming complexes (SFCs) by a combination of bubble morphology in 8 μm emission and radio recombination line radial velocities. We find 40 SFCs associated with our WMAP sources and determine unique distances up to 31. We interpret the bubbles as evidence for radial expansion. The radial velocity distribution for each source allows us to measure the intrinsic speed of a complex's expansion. This speed is consistent with the size and age of the bubbles. The high free-free luminosities, combined with negligible synchrotron emission, demonstrate that the bubbles are not driven by supernovae. The kinetic energy of the largest bubbles is a substantial fraction of that measured in the older superbubbles found by Heiles. We find that the energy injected into the interstellar medium by our bubbles is similar to that required to maintain turbulent motion in the gas disk inside 8 kpc. We report a number of new SFCs powered by massive (M
* > 104M
☉) star clusters. We measure the scale height of the Galactic O stars to be h
* = 35 ± 5 pc. We determine an empirical relationship between the 8 μm and free-free emission of the form F
8 μm ∝ F
2ff. Finally, we find that the bubble geometry is more consistent with a spherical shell rather than a flattened disk.
We present near-IR (NIR) J, H, and Ks images and K-band spectroscopy of two newly discovered stellar clusters at different stages of evolution. Our spectra suggest the presence of massive young stellar objects in the heavily embedded cluster in the star-forming region near radio source G353.4-0.4 and an O5–O6 V star in the cluster near radio source G305+00.2. We determine a K-band luminosity function (KLF) for both clusters and an initial mass function (IMF) for the cluster near G305+00.2. The derived IMF slope is Γ = -1.5 if the KLF is used to derive the IMF and is Γ = -0.98 if the color-magnitude diagram (CMD) and spectra are used. The more reliable CMD-based slope is flatter than the Salpeter value usually found for stellar clusters. We find that using the KLF alone to derive an IMF is likely to produce an overly steep slope in stellar clusters subject to variable extinction.
We present searches for molecular gas (CO, OH, CS, and NH3) in six gigahertz-peaked spectrum (GPS) radio sources. We do not detect gas in any source and place upper limits on the mass of molecular gas that are generally in the range from ~109 to a few times 1010 M. These limits are consistent with the following interpretations: (1) GPS sources do not require very dense gas in their hosts, and (2) the GPS sources are unlikely to be confined by dense gas and will evolve to become larger radio sources.
High-resolution far-infrared observations of a large area of the star-forming complex RCW 106 obtained using the TIFR 1-m
balloon-borne telescope are presented. Intensity maps have been obtained simultaneously in two bands centred around 150 and
210 μm. Intensity maps have also been obtained in the four IRAS bands using HIRES-processed IRAS data. From the 150- and 210-μm maps, reliable maps of dust temperature and optical depth have been generated. The star formation
in this complex has occurred in five linear sub-clumps. Using the map at 210 μm, which has a spatial resolution superior to
that of IRAS at 100 μm, 23 sources have been identified. The spectral energy distribution (SED) and luminosity of these sources have been
determined using the associations with the IRAS maps. The luminosity distribution of these sources has been obtained. Assuming these embedded sources to be zero-age main-sequence
stars and using the mass—luminosity relation for these, the power-law slope of the initial mass function is found to be −1.73±0.5.
This index for this very young complex is about the same as that for more evolved complexes and clusters. Radiation transfer
calculations in spherically symmetric geometry have been undertaken to fit the SEDs of 13 sources with fluxes in both the
TIFR and the IRAS bands. From this, the r−2 density distribution in the envelopes is ruled out. Finally, a correlation is seen between the luminosity of embedded sources
and the computed dust masses of the envelopes.
The ammonia emission associated with southern galacticHii regions have been studied. Some physical parameters, computed for each individual sources, were derived and a brief discussion follows.
Aims. We analyse the distribution of the molecular gas towards the region containing the open cluster Havlen-Moffat 1 (HM 1) the Wolf-Rayet stars WR 87, WR 89, and WR 91, and the star forming regions RCW 121 and RCW 122, with the aim of looking for a possible physical relationship among these objects.Methods. We used the carbon monoxide observations carried out at $\lambda$ ~ 2.6 mm with the 4 m NANTEN radiotelescope; new flux density determinations derived from already existing radio continuum surveys at 2.417, 5, 8.35, and 14.35 GHz; continuum flux density determinations available in the literature; and the Midcourse Space Experiment (MSX) and the Improved Reprocessing of the IRAS Survey (IRIS) databases.Results. Adopting a distance of 5 kpc for RCW 121 and RCW 122, we found a giant molecular cloud (GMC) with a linear extent of ~100 $\times$ 20 pc to be associated with galactic star-forming regions. The total mass of this GMC is of the order of 1.2 $\times$ 10$^6$ solar masses and its mean radial velocity is about -15 km s$^{-1}$. Within the GMC there are individual molecular gas concentrations, having total molecular masses in the range from 4.6 $\times$ 10$^4$ $M_\odot$ (RCW 122 C) to 2.2 $\times$ 10$^5$ $M_\odot$ (RCW 122). The CO profiles observed toward the peak of the molecular concentrations are broad, with typical full-width half-maximum around 6 to 7 km s$^{-1}$, and show line asymmetries and/or double-peaked shape that change with the observed position within a given CO concentration. An analysis of the MSX and IRAS databases show that each CO concentration has a strong IR counterpart. The dust temperature of these concentrations range from 46 K (RCW 121) to 76 K (RCW 122 C). Their infrared luminosity are a few times 10$^5$ $L_{\odot}$. The new radio continuum flux density determinations are in good agreement with previous determinations at other frequencies, and confirm the thermal nature of RCW 121 and RCW 122. Based on the newly-determined 5 GHz flux density, we found that to power these Hii regions, each of them must harbour a sizable number of O type stars. Under the assumption that all the ionizing stars have a O7 V spectral type, at least ~8 and ~4 of these stars would be needed to ionize RCW 122 and RCW 121, respectively.
The 64-m spacecraft communication antenna of the NASA-JPL Deep Space Network has been equipped for spectral line observations at K band (18-25 GHz). To demonstrate the potential of this system, preliminary observations of the (1, 1) transition of ammonia are reported for a selection of eight southern molecular clouds. Estimates of gas density and ammonia column density are reported for six sources.
The Parkes 64-m antenna has been used to map ammonia emission in the (J,K = 1,1) and (J,K = 2,2) transitions toward molecular cloud complex NGC 6334. This complex contains a number of OH and H 2 O masers, HII regions and IR sources, and is a rich source of molecular line emission.
Distributions of observed and derived quantities are presented with a linear resolution of ∼ 1 pc. Velocity anomalies are present near the two OH masers NGC 6334A and B, and the source of ammonia emission located near the northernmost H 2 O maser is one of the most intense sources of NH 3 emission in the Galaxy.
NGC 6334 has been mapped with a 40-250 micron photometer with 1 arcmin resolution. Six sources of far-infrared radiation have been detected. The second-strongest source was not detected in an earlier (2.7 years) 40-350 micron survey of the same region. This source is interpreted as a variable far-infrared source. The new source, located at the position of OH and H2O maser sources, is extended (0.7 arcmin FWHM) and has a bolometric luminosity of 190,000 solar luminosities and may represent a hitherto unobserved transient stage of protostellar collapse.
We have mapped the dust continuum emission from the molecular cloud covering a region of 28pcx94pc associated with the well-known HII region RCW 106 at 1.2 mm using SIMBA on SEST. The observations, having an HPBW of 24" (0.4 pc), reveal 95 clumps. Owing to the higher sensitivity to colder dust and higher angular resolution the present observations identify new emission features and also show that most of the IRAS sources in this region consist of multiple dust emission peaks. The detected millimeter sources (MMS) include on one end the exotic MMS5 (associated with IRAS 16183-4958, one of the brightest infrared sources in our Galaxy) and the bright (and presumably cold) source MMS54, with no IRAS or MSX associations on the other end. Around 10% of the sources are associated with signposts of high mass star formation activity. Assuming a uniform dust temperature of 20 K we estimate the total mass of the GMC associated with RCW 106 to be ~10^5\msun. The constituent millimeter clumps cover a range of masses and radii between 40 to 10^4 \msun and 0.3 to 1.9 pc. Densities of the clumps range between (0.5-6) 10^4 cm^{-3}. We have decomposed the continuum emission into gaussian and arbitrary shaped clumps using the two independent structure analysis tools gaussclumps and clumpfind respectively. The clump mass spectrum was found to have an index of 1.6+-0.3, independent of the decomposition algorithm used. The index of the mass spectrum for the mass and length scales covered here are consistent with results derived from large scale CO observations. Comment: 12 Pages, 6 Figs. A&A Journal Format
We have observed molecular-line transitions between 84 and 147 GHz in 24 dense southern molecular clouds with declinations south of -30 degrees using the Mopra and SEST radio telescopes. The results of observations of 2-mm and 3-mm transitions of the molecules CO, CS, C2H, CH3OH, HCN, HNC, HCO+, HC3N, OCS, HNCO and SO and several of their isotopomers are discussed in this paper, including ratios of the emission from the 12C, 13C and 18O isotopomers of CO, CS, HCO+, HCN and HNC. This paper lists the calibrated observational data for each molecular cloud and discusses some general properties of this sample. The calibration process for the Mopra antenna of the ATCA is described in an appendix.
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We have measured intensities of the J = 3-2, 2-1, and 1-0 transitions of
carbon monosulfide in five molecular clouds associated with galactic H
II regions. The two higher-lying lines were mapped in each source, and
the lowest line, J = 1-0, was observed at the map centers. The observed
intensity ratios are shown to be dominated by effects of instrumental
resolution. The observations are corrected for these effects and
discussed in terms of recently published calculations for radiative
transfer in collapsing clouds.
The reported observations were made with an 11-m radio telescope. The CO map considered has a peak near the position of the infrared continuum source. There is little correlation between the CO contours and any optical structure. The CO contours show a pronounced north-south orientation. CS was observed as a representative example of a stable molecule with a higher dipole moment than CO. Questions regarding the structure of Orion A are discussed, giving attention to various models.
A new surface covering the inner 16.7-m diameter section of the Parkes radio telescope has allowed observations to be made
at millimetre wavelengths. A survey of 83 late-type stars for v = 1, J = 1–0 and v = 2, J = 1–0 emission from SiO at 43 GHz has yielded 10 new sources. There is a strong correlation between stars detected with SiO
emission and those known to emit H2 O radiation. Observations of the new SiO sources and of some of the previously known sources have confirmed previous conclusions
that source spectra vary with time, some sources having timescales of a few days.
Results are reported for a survey of eight galactic dark clouds and dust
globules conducted in the two rotational transitions of (C-12)(S-32) at
48,991 MHz and 97,981.01 MHz and the rotational transition of
(C-12)(S-34) at 96,412.95 MHz. The surveyed sources included IC 1848-1,
the Taurus dark cloud, Orion A, ORI-I-2, B227, L134, L121, B335, and
B163. Carbon monosulfide emission was detected in all the clouds except
B163, indicating that CS is widespread in dust clouds. Excitation
temperatures of between 2.9 and 7.0 K are derived together with optical
depths greater than unity, and molecular hydrogen densities greater than
10,000 per cu cm are deduced along with CS/H2 abundances of between 10
to the -8th power and 10 to the -9th power. The results are shown to be
consistent with models in which line-of-sight flow velocities account
for the observed line widths, the molecular transitions are optically
thick, and radiation trapping becomes important.
A new complex of infrared sources about one minute across has been discovered in Orion. Associated with this cluster is an extended molecular cloud producing intense CO emission. Its measured infrared luminosity is less than 500 times the luminosity of the sun. The complex is hypothesized to be composed of pre-main-sequence sources. Several arguments suggest that these stars heat dust in the larger molecular cloud and thus cause the strong CO emission. The complex is not associated with a known visible or radio continuum feature, and searches over a 0.7 x 0.7-deg field show no other comparable unknown 2.2-micron sources.