Ammonia Column Density Research Articles

Ammonia observations of Planck cold cores

Single-pointing observations of NH$_ $\,(1,1) and (2,2) were conducted toward 672 Planck Early Cold Cores (ECCs) using the Nanshan 26-m radio telescope. Out of these sources, a detection rate of 37<!PCT!> (249 cores) was achieved, with a $\,(1,1) hyperfine structure detected in 187 cores and $\,(2,2) emission lines detected in 76 of them. The detection rate of $ is positively correlated with the continuum emission fluxes at a frequency of 857\,GHz. Among the observed 672 cores, sim 22<!PCT!> have associated stellar and infrared objects within the beam size (sim 2arcmin ). This suggests that most of the cores in our sample may be starless. The kinetic temperatures of the cores range from 8.9 to 20.7\,K, with an average of 12.3\,K, indicating a coupling between gas and dust temperatures. The ammonia column densities range from 3.6\,times \,1014 to 6.07\,times $, with a median value of 2.04\,times $. The fractional abundances of ammonia range from 0.3 to 9.7\,times $, with an average of 2.7\,times $, which is one order of magnitude larger than that of massive star-forming (MSF) regions and infrared dark clouds (IRDCs). The correlation between thermal and nonthermal velocity dispersion of the NH$_ $\,(1,1) inversion transition indicates the dominance of supersonic nonthermal motions in the dense gas traced by $, and the relationship between these two parameters in Planck cold cores is weaker, with lower values observed for both parameters relative to other samples under our examination. The cumulative distribution shapes of line widths in the Planck cold cores closely resemble those of the dense cores found in regions of Cepheus, in addition to Orion L1630 and L1641, with higher values compared to Ophiuchus.

The Effelsberg survey of FU Orionis and EX Lupi objects

Context. FU Orionis (FUor) and EX Lupi (EXor) type objects represent two small but rather spectacular groups of low-mass, young, eruptive stars. In both cases, outbursts of several magnitudes are observed, which are attributed to enhanced mass accretion from the circumstellar disc onto the central protostar. Although these objects are well studied at optical and near-infrared wavelengths, their host molecular environments are poorly explored because of the scarcity of systematic molecular line observations. Aims. We aim to carry out the first dedicated survey of the molecular environments of a large sample of FUors and EXors, observing a total of 51 sources, including some Gaia alerts, to study the ammonia (NH3) emission in their host environments. Methods. We observed the ammonia (J, K) = (1,1), (2,2), and (3,3) inversion transitions at ~23.7 GHz in position-switching mode using the Effelsberg 100-m radio telescope. For 19 of the 51 sources in our sample, we derived H2 column densities and dust temperatures using archival Herschel/SPIRE data at 250 µm, 300 µm, and 500 µm. Results. We detected the NH3 (1,1) transition toward 28 sources and the (2,2) transition toward 12 sources, while the (3,3) transition was detected towards only two sources in our sample. We find kinetic temperatures between ~12 K and 21 K, ammonia column densities from 5.2 × 1013 cm−2 to 3.2 × 1015 cm−2, and fractional ammonia abundances with respect to H2 from 4.7 × 10−9 to 1.5 × 10−7. These results are comparable to those found in infrared dark clouds (IRDCs). Our kinematic analysis suggests that most of the eruptive stars in our sample reside in rather quiescent (sonic or transonic) host environments. Conclusions. Our NH3 observations and analysis of the SPIRE dust-based H2 column density maps confirm the presence of dense material towards seven sources in our sample; additional sources might also harbour dense gas based on their NH2 (2,2) detections, potentially indicating an earlier phase than originally classified. Based on our results, we suggest that observations targeting additional molecular lines would help to refine the evolutionary classification of eruptive stars.

Star formation time-scale in the molecular filament WB 673

ABSTRACT We present the observations of ammonia emission lines toward the interstellar filament WB 673 hosting the dense clumps WB 673, WB 668, S233-IR, and G173.57+2.43. LTE analysis of the lines allows us to estimate gas kinetic temperature (≲30K in all the clumps), number density (7–17 × 103 cm−3), and ammonia column density (≈1–1.5 × 1015 cm−2) in the dense clumps. We find signatures of collapse in WB 673 and presence of compact spatially unresolved dense clumps in S233-IR. We reconstruct 1D density and temperature distributions in the clumps and estimate their ages using astrochemical modelling. Considering CO, CS, NH3, and N2H+ molecules (plus HCN and HNC for WB 673), we find a chemical age of tchem = 1–3 × 105 yrs, providing the best agreement between the simulated and observed column densities in all the clumps. Therefore, we consider tchem as the chemical age of the entire filament. A long preceding low-density stage of gas accumulation in the astrochemical model would break the agreement between the simulated and observed column densities. We suggest that rapid star formation over a ∼105 yrs time-scale take place in the filament.

KFPA Examinations of Young STellar Object Natal Environments (KEYSTONE): Hierarchical Ammonia Structures in Galactic Giant Molecular Clouds

Abstract We present initial results from the K-band Focal Plane Array Examinations of Young STellar Object Natal Environments survey, a large project on the 100 m Green Bank Telescope mapping ammonia emission across 11 giant molecular clouds at distances of 0.9–3.0 kpc (Cygnus X North, Cygnus X South, M16, M17, Mon R1, Mon R2, NGC 2264, NGC 7538, Rosette, W3, and W48). This data release includes the NH3 (1,1) and (2,2) maps for each cloud, which are modeled to produce maps of kinetic temperature, centroid velocity, velocity dispersion, and ammonia column density. Median cloud kinetic temperatures range from 11.4 ± 2.2 K in the coldest cloud (Mon R1) to 23.0 ± 6.5 K in the warmest cloud (M17). Using dendrograms on the NH3 (1,1) integrated intensity maps, we identify 856 dense gas clumps across the 11 clouds. Depending on the cloud observed, 40%–100% of the clumps are aligned spatially with filaments identified in H2 column density maps derived from spectral energy distribution fitting of dust continuum emission. A virial analysis reveals that 523 of the 835 clumps (∼63%) with mass estimates are bound by gravity alone. We find no significant difference between the virial parameter distributions for clumps aligned with the dust-continuum filaments and those unaligned with filaments. In some clouds, however, hubs or ridges of dense gas with unusually high mass and low virial parameters are located within a single filament or at the intersection of multiple filaments. These hubs and ridges tend to host water maser emission, multiple 70 μm detected protostars, and have masses and radii above an empirical threshold for forming massive stars.

Spatiotemporal Evolution of Atmospheric Ammonia Columns over the Indo-Gangetic Plain by Exploiting Satellite Observations

This study was aimed at presenting a continuous and spatially coherent picture of ammonia (NH3) distribution over the Indo-Gangetic Plain (IGP) by exploiting satellite observations. Atmospheric columns of ammonia were mapped over South Asia by using TES observations on board NASA’s Aura satellite. Monthly mean data were used to identify emission sources of atmospheric ammonia across the South Asian region. Data were analysed to explore temporal trends, seasonal cycles, and hot spots of atmospheric ammonia within the study area. The results show that the IGP region has the most ammonia concentrations in terms of column densities, and hence this region has been identified as an ammonia hot spot. This is attributed majorly to extensive agricultural activity. Time series showed a slight increase in ammonia column densities over the study area from 2004 to 2011. Different seasonal cycles were identified across the IGP region with maximum NH3 columns observed during the month of July in most of the subregions. Seasonality in an ammonia column is driven by different cropping patterns and meteorological conditions in the IGP subregions. Global emission inventories of atmospheric ammonia were largely overestimating as compared to satellite observations.

Hot ammonia around young O-type stars

To constrain theoretical models of high-mass star formation, observational signatures of mass accretion in O-type forming stars are desirable. Using the JVLA, we have mapped the hot and dense molecular gas in the hot core NGC7538 IRS1, with 0.2'' angular resolution, in seven metastable (J=K) inversion transitions of ammonia: (J,K)=(6,6), (7,7), (9,9), (10,10), (12,12), (13,13), and (14,14). These lines arise from energy levels between ~400 K and ~1950 K above the ground state, and are observed in absorption against the HC-HII region associated with NGC7538 IRS1. With a 500 AU linear resolution, we resolve the elongated North-South ammonia structure into two compact components: the main core and a southernmost component. Previous observations of the radio continuum with a 0.08'' (or 200 AU) resolution, resolved in turn the compact core in two (northern and southern) components. These features correspond to a triple system of high-mass YSOs IRS1a, IRS1b, and IRS1c identified with VLBI measurements of methanol masers. The velocity maps of the compact core show a clear velocity gradient in all lines, which is indicative of rotation in a (circumbinary) envelope, containing ~40 solar masses (dynamical mass). In addition, we derived physical conditions of the molecular gas: rotational temperatures ~280 K, ammonia column densities ~1.4-2.5 x 10^19 cm-2, H_2 volume densities ~3.5-6.2 x 10^10 cm-3, and a total gas mass in the range of 19-34 solar masses, for the main core. We conclude that NGC7538 IRS1 is the densest hot molecular core known, containing a rotating envelope which hosts a multiple system of high-mass YSOs, possibly surrounded by accretion disks. Future JVLA observations in the A-configuration are needed to resolve the binary system in the core and may allow to study the gas kinematics in the accretion disks associated with individual binary members.

ATCA SURVEY OF AMMONIA IN THE GALACTIC CENTER: THE TEMPERATURES OF DENSE GAS CLUMPS BETWEEN Sgr A* AND Sgr B2

We present a large-scale, interferometric survey of ammonia (1,1) and (2,2) toward the Galactic Center observed with the Australia Telescope Compact Array (ATCA). The survey covers Delta l ~1degree (~150pc) at an assumed distance of 8.5 kpc) and Delta b ~0.2degree (~30pc) which spans the region between the supermassive black hole SgrA* and the massive star forming region SgrB2. The resolution is ~20'' (~0.8pc) and emission at scales >~2' (>~3.2pc) is filtered out due to missing interferometric short spacings. Consequently, the data represent the denser, compact clouds and disregards the large scale, diffuse gas. Many of the clumps align with the 100 pc dust ring and mostly anti-correlate with 1.2cm continuum emission. We present a kinetic temperature map of the dense gas. The temperature distribution peaks at ~38K with a width at half maximum between 18K and 61K (measurements sensitive within Tkin~10-80K). Larger clumps are on average warmer than smaller clumps which suggests internal heating sources. Our observations indicate that the circumnuclear disk ~1.5 pc around SgrA* is supplied with gas by the 20km/s molecular cloud. This gas is substantially cooler than gas ~3-15pc away from SgrA*. We find a strong temperature gradient across SgrB2. Ammonia column densities correlate well with SCUBA 850um fluxes, but the relation is shifted from the origin, which may indicate a requirement for a minimum amount of dust to form and shield ammonia. Around the Arches and Quintuplet clusters we find shell morphologies with UV-influenced gas in their centers, followed by ammonia and radio continuum layers.

DETECTION OF WIDESPREAD HOT AMMONIA IN THE GALACTIC CENTER

We present the detection of metastable inversion lines of ammonia from energy levels high above the ground state. We detect these lines in both emission and absorption toward fifteen of seventeen positions in the central 300 parsecs of the Galaxy. In total, we observe seven metastable transitions of ammonia: (8,8), (9,9), (10,10), (11,11), (12,12), (13,13) and (15,15), with energies (in Kelvins) ranging from 680 to 2200 K. We also map emission from ammonia (8,8) and (9,9) in two clouds in the Sgr A complex (M-0.02-0.07 and M-0.13-0.08), and we find that the line emission is concentrated toward the the dense centers of these molecular clouds. The rotational temperatures derived from the metastable lines toward M-0.02-0.07 and M-0.13-0.08 and an additional cloud (M0.25+0.01) range from 350 to 450 K. Similarly highly-excited lines of ammonia have previously been observed toward Sgr B2, where gas with kinetic temperatures of ~600 K has been inferred. Our observations show that the existence of a hot molecular gas component is not unique to Sgr B2, but rather appears common to many Galactic center molecular clouds. In M-0.02-0.07, we find that the hot ammonia, contributes ~10% of the cloud's total ammonia column density, and further, that the hot ammonia in this cloud arises in gas which is extended or uniformly distributed on ~10 arcsecond scales. We discuss the implications of these constraints upon the nature of this hot gas component. In addition to the detection of hot metastable ammonia line emission, we also detect for the first time emission from nonmetastable inversion transitions of ammonia in both M-0.02-0.07 and M-0.13-0.08.

Properties of dense cores in clustered massive star-forming regions at high angular resolution

We aim at characterising dense cores in the clustered environments associated with massive star-forming regions. For this, we present an uniform analysis of VLA NH3(1,1) and (2,2) observations towards a sample of 15 massive star-forming regions, where we identify a total of 73 cores, classify them as protostellar, quiescent starless, or perturbed starless, and derive some physical properties. The average sizes and ammonia column densities are 0.06 pc and 10^15 cm^-2, respectively, with no significant differences between the starless and protostellar cores, while the linewidth and rotational temperature of quiescent starless cores are smaller, 1.0 km/s and 16 K, than those of protostellar (1.8 km/s, 21 K), and perturbed starless (1.4 km/s, 19 K) cores. Such linewidths and temperatures for these quiescent starless cores in the surroundings of massive stars are still significantly larger than the typical values measured in starless cores of low-mass star-forming regions, implying an important non-thermal component. We confirm at high angular resolutions the correlations previously found with single-dish telescopes between the linewidth, the temperature of the cores, and the bolometric luminosity. In addition, we find a correlation between the temperature of each core and the incident flux from the most massive star in the cluster, suggesting that the large temperatures measured in the starless cores of our sample could be due to heating from the nearby massive star. A simple virial equilibrium analysis seems to suggest a scenario of a self-similar, self-graviting, turbulent, virialised hierarchy of structures from clumps (0.1-10 pc) to cores (0.05 pc). A closer inspection of the dynamical state taking into account external pressure effects, reveal that relatively strong magnetic field support may be needed to stabilise the cores, or that they are unstable and thus on the verge of collapse.

FIRST DETECTION OF AMMONIA IN THE LARGE MAGELLANIC CLOUD: THE KINETIC TEMPERATURE OF DENSE MOLECULAR CORES IN N 159 W

The first detection of ammonia (NH3) is reported from the Magellanic Clouds. Using the Australia Telescope Compact Array, we present a targeted search for the (J,K) = (1,1) and (2,2) inversion lines towards seven prominent star-forming regions in the Large Magellanic Cloud (LMC). Both lines are detected in the massive star-forming region N159W, which is located in the peculiar molecular ridge south of 30 Doradus, a site of extreme star formation strongly influenced by an interaction with the Milky Way halo. Using the ammonia lines, we derive a kinetic temperature of ~16K, which is 2-3 times below the previously derived dust temperature. The ammonia column density, averaged over ~17" is ~6x10^{12} cm^{-2} <1.5x10^{13} cm^{-2} over 9" in the other six sources) and we derive an ammonia abundance of ~4x10^{-10} with respect to molecular hydrogen. This fractional abundance is 1.5-5 orders of magnitude below those observed in Galactic star-forming regions. The nitrogen abundance in the LMC (~10% solar) and the high UV flux, which can photo-dissociate the particularly fragile NH3 molecule, must both contribute to the low fractional NH3 abundance, and we likely only see the molecule in an ensemble of the densest, best shielded cores of the LMC.

Ammonia in infrared dark clouds

Infrared Dark Clouds appear to be the long sought population of cold and dense aggregations with the potential of harbouring the earliest stages of massive star formation. Up to now there has been no systematic study on the temperature distribution, velocity fields, chemical and physical state toward this new cloud population. Knowing these properties is crucial for understanding the presence, absence and the very potential of star formation. The present paper aims at addressing these questions. We analyse temperature structures and velocity fields and gain information on their chemical evolution. The gas emission is remarkably coextensive with the extinction seen at infrared wavelengths and with the submillimeter dust emission. Our results show that IRDCs are on average cold (T 100 M_sun), highly turbulent (1 -- 3 km/s) and exhibit significant velocity structure (variations around 1 -- 2 km/s over the cloud). We find an increasing trend in temperature from IRDCs with high ammonia column density to high mass protostellar objects and hot core/Ultracompact Hii regions stages of early warm high-mass star formation while linewidths of IRDCs are smaller. On the basis of this sample, we infer that while active star formation is not yet pervasive in most IRDCs, local condensations might collapse in the future or have already begun forming stars.

The Temperature Distribution of Dense Molecular Gas in the Center of NGC 253

[abridged] We present interferometric maps of ammonia (NH3) of the nearby starburst galaxy NGC 253 [star formation rate: ~2.8 Mo yr^(-1)]. The observations have been taken with the Australia Telescope Compact Array and include the para-NH3 (1,1), (2,2), and the ortho-NH3 (3,3) and (6,6) inversion lines. Six major complexes of dense ammonia are identified, three of them on either side of the starburst center, out to projected galactocentric radii of \~250 pc. [...] The application of radiative transfer large velocity gradient models reveals that the bulk of the ammonia molecules is embedded in a one-temperature gas phase. Kinetic temperatures of this gas are ~200 and 140 K toward the south-west and north-east [of the nucleus of NGC 253], respectively. The temperatures under which ammonia was formed in the past are with >~30 K also warmer toward the south-west than toward the north-east (~15-20 K). This is indicated by the ortho-to-para ammonia ratio which is ~1 and 1.5-2.5 toward the south-west and north-east, respectively. Ammonia column densities in the brightest complexes are in the range of 6-11x10^(14) cm^(-2), which adds up to a total ammonia mass of ~20 Mo, about evenly distributed toward both sides of the nucleus. [...] Toward the center of NGC 253, NH3 (1,1), (2,2), and (6,6) is detected in absorption against an unresolved continuum source. At the same location, however, ammonia (3,3) is found in emission which indicates maser activity. This would be the first detected extragalactic NH3 maser. Evidence for an expanding shell in the south-western complex is provided. [...] The shell and X-ray properties can be reproduced by the energy input of a highly obscured young stellar cluster with a mass of ~10^5 Mo which also heats the dense gas.

ISO ammonia line absorption reveals a layer of hot gas veiling Sgr B2

We report the rst results of the unbiased spectral high resolution survey obtained towards Sgr B2 with the Long Wavelength Spectrometer on board ISO. The survey detected more than one hundreds lines from several molecules. Ammonia is the molecule with the largest number (21) of detected lines in the survey. We detected NH3 transitions from levels with energies from 45 to 500 cm 1 . The detected transitions are from both para and ortho ammonia and metastable and non-metastable levels. All the ammonia lines are in absortion against the FIR continuum of Sgr B2. With such a large number of detected lines in such a large range of energy levels, we could very eciently constrain the main parameters of the absorbing gas layer. The gas is at (700 100) K and has a density lower than 10 4 cm 3 . The total NH3 column density in the layer is (3 1) 10 16 cm 2 , equally shared between ortho and para ammonia. Given the derived relatively high gas temperature and ammonia column density, our observations support the hypothesis previously proposed of a layer of shocked gas between us and Sgr B2. We also discuss previous observations of far infrared line absorption from other molecules, like H2 Oa nd HF, in the light of this hot absorbing layer. If the absorption is done by the hot absorbing layer rather than by the warm envelope surrounding Sgr B2, as was previously supposed in order to interpret the mentioned observations, the derived H2O and HF abundances are one order of magitude larger than previously estimated. Yet, the present H2O and HF observations do not allow one to disentangle the absorption from the hot layer against the warm envelope. Our conclusions are hence that care should be applied when interpreting the absorption observations in Sgr B2, as the hot layer clearly seen in the ammonia transitions may substantially contribute to the absorption.

Hyperfine anomalies in the ammonia (1,1) inversion transition: Can they be a tracer of systematic motion?

The hyperfine lines of an ammonia (1,1) inversion transition often exhibit anomalous intensity ratios towards star-forming cores. It has been known that the anomaly is only partially attributable to a non-LTE effect on the hyperfine transitions. In an attempt to investigate how systematic motion like expansion and contraction affect the line anomaly, whose existence is quite likely in star-forming cores, we have carried out radiative transfer calculations fully taking into account the hyperfine splitting of energy levels and the line overlap effect caused by the systematic motion. It is demonstrated that in a bundle of transitions from the (2,2) to (1,1) levels, photons emitted from one transition can be absorbed by another transition due to the systematic motion and the small frequency differences among the hyperfine transitions, resulting in drastic changes in the level populations of (1,1) sub-states. Expansion (contraction) is found to strengthen the inner as well as outer satellite lines on the red (blue) side, while suppressing those on the other side. The line anomaly becomes prominent as the ammonia column density increases. It is concluded that the hyperfine line intensity ratios could be a good probe for tracing the systematic motion inside the dense cores without relying on detailed analysis of line shapes.

Dense Cores Mapped in Ammonia: A Database

We present a database of 264 cores mapped in the (J,K) = (1,1) and (2,2) lines of NH3. We list the core gas properties?peak positions, total ammonia column densities, intrinsic line widths, kinetic temperatures, volume densities, core sizes, aspect ratios, and velocity gradients, as well as the properties of associated young stellar objects (YSOs)?associated IRAS sources along with their luminosities and core-YSO distances, outflow velocities, and SIMBAD and cluster associations. We also present the results of our statistical analysis and enumerate important pairwise correlations among the various gas and YSO properties. The results indicate that the association of stellar clusters with star-forming cores has a greater impact on their properties than does the presence of associated YSOs within these cores, although the latter influence is also statistically significant. In other words, the difference in core properties (nonthermal line widths, kinetic temperatures, and core sizes) between cores with and without associated YSOs is less significant when compared with the difference in these properties between cores with and without cluster associations. Furthermore, core gas and YSO properties show a significant dependence on the star-forming region in which the core is located. For instance, cores in Orion have larger line widths, higher kinetic temperatures, and larger sizes compared with cores in Taurus. Similarly, YSOs in Orion are more luminous than those in Taurus. These cluster and regional dependencies seem important enough that they ought to be accounted for in any self-consistent theory of star formation. Finally, the ratio of starless to stellar cores is too small (8:12 in Taurus, 2:41 in Orion A) to be consistent with ambipolar diffusion timescales that predict ratios as high as 3-30. This result is true even for regions that are known to be well surveyed and not to suffer from significant sample biases.

A study of the physics and chemistry of TMC-1.

We present a comprehensive study of the physical and chemical conditions along the TMC-1 ridge. Temperatures were estimated from observations of CH3CCH, NH3, and CO. Densities were obtained from a multitransition study of HC3N. The values of the density and temperature allow column densities for 13 molecular species to be estimated from statistical equilibrium calculations, using observations of rarer isotopomers where possible, to minimize opacity effects. The most striking abundance variations relative to HCO+ along the ridge were seen for HC3N, CH3CCH, and SO, while smaller variations were seen in CS, C2H, and HCN. On the other hand, the NH3, HNC, and N2H+ abundances relative to HCO+ were determined to be constant, indicating that the so-called NH3 peak in TMC-1 is probably a peak in the ammonia column density rather than a relative abundance peak. In contrast, the well-studied cyanopolyyne peak is most likely due to an enhancement in the abundance of long-chain carbon species. Comparisons of the derived abundances to the results of time-dependent chemical models show good overall agreement for chemical timescales around 10(5) yr. We find that the observed abundance gradients can be explained either by a small variation in the chemical timescale from 1.2 x 10(5) to 1.8 x 10(5) yr or by a factor of 2 change in the density along the ridge. Alternatively, a variation in the C/O ratio from 0.4 to 0.5 along the ridge produces an abundance gradient similar to that observed.

Ammonia clumps in the Orion and Cepheus clouds

We present statistics of clump properties in the Orion and Cepheus cloud complexes based on ammonia mapping observations. Surroundings of about 50 IRAS sources earlier found to have associated molecular line emission (Wouterloot, Walmsley and Henkel, 1988) were mapped in NH3(1,1) and (2,2) with the Effelsberg 100-m telescope. Our main interest has been in determining the clump sizes and masses on the basis of the ammonia column density distribution, which together with the observed velocity dispersion lead to a rough estimate of the dynamical state. We also have studied the star-clump separations which should give us estimates of the source ages. Special attention has been paid to comparison of our Orion data with the Benson and Myers (1989, hereafter BM89) results in Taurus because the linear resolutions in the two studies are similar.

Ammonia clumps in the Orion and Cepheus clouds

We present statistics of clump properties in the Orion and Cepheus cloud complexes based on ammonia mapping observations. Surroundings of about 50 IRAS sources earlier found to have associated molecular line emission (Wouterloot, Walmsley and Henkel, 1988) were mapped in NH3(1,1) and (2,2) with the Effelsberg 100-m telescope. Our main interest has been in determining the clump sizes and masses on the basis of the ammonia column density distribution, which together with the observed velocity dispersion lead to a rough estimate of the dynamical state. We also have studied the star-clump separations which should give us estimates of the source ages. Special attention has been paid to comparison of our Orion data with the Benson and Myers (1989, hereafter BM89) results in Taurus because the linear resolutions in the two studies are similar.

Sensitive ammonia observations in the southern hemisphere

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.

Detection of New Ammonia Sources

Ammonia is a favoured molecule for the study of molecular clouds since several important parameters of the cloud can be deduced from simple observations of the J,K=1,1 and 2,2 inversion doublet transitions and the hyperfine structure in the (1,1) line. With the additional knowledge of the kinetic temperature Tk from observations of CO, for example, it is possible to compute the excitation temperature of the (1,1) line (T11), the rotational temperature between the (1,1) and (2,2) levels (T21), the molecular hydrogen density n(H2) and ammonia column density N(NH3) (see, for example, Martin and Barrett, 1978).