1. Sizes of masing regions in W3(OH) The BIMA interferometer was used to observe 24 methanol lines toward W3(OH) with spectral resolution better than 1.2 km/s. This source is a prototypical class II methanol maser source. We detected emission in new maser transitions toward it [3]. Analysis of these observations has brought considerable improvement to the model of the masing region in front of W3(OH) and has predicted strong absorption in 6 methanol lines with frequencies 84.52121, 85.56807, 94.54181, 95.16952, 105.06376, and 109.15321 GHz. The profiles of these lines can be well fitted with a superposition of 2 gaussians corresponding to common emitting and absorbing regions. Detailed analysis is currently underway, but it is clear that the depths of the absorptions are in accord with the model predictions. Most importantly, the maps in these lines at the maser velocities are spatially anticorrelated with the maser emission. That means that the size of the masing region is about the total spread of the 6.7 GHz class II

We used the BIMA array to observe the hot molecular core W3(E2O). Our continuum maps at wavelengths of 1.4mm and 2.8mm both achieve sub-aresecond angular resolutions and show a double-peaked morphology. The angular separation of the two sources is 1."19 corresponding to 2.43 x 10(3) AU at the source distance of 2.04 kpc. The flux densities of the two sources at lambda lambda 1.4nnn and 2.8mm have a spectral index of 3, translating to an opacity law of kappa(v) alpha v. The small spectral indices suggest that grain growth has begun in the hot core. We have also observed 5 of the K-components of the methyl cyanide (CH3CN) J = 12-11 transition. A radial velocity difference of 2.81 km s(-1) is found for the gas in the two continuum peaks. Interpreting these two sources as binary components in orbit about one another, we find a minimum mass of 22 M-circle dot for the system. Power-law density distributions close to the free-fall value, r(-1.5), are found for both components, suggesting continuing accretion. The derived luminosities suggest the two sources have equivalent zero-age main sequence (ZAMS) spectral type 130.5 - B0. A velocity gradient previously detected. may be explained by unresolved binary rotation with a small velocity difference.

This paper reports the results of a small imaging survey of eight evolved stars including two AGB stars (IRC + 10216 and Mira), five proto-planetary nebula (PPN) candidates (AFGL 2688, IRAS 22272+5435, HD 161796, 89 Her, and HD 179821), and a planetary nebula (PN, NGC 7027). We present high-resolution (CO)-C-12 J = 1 -> 0 maps of their full molecular envelopes made by combining BIMA Millimeter Array and NRAO 12 m telescope observations. For the PPNe and PN, the neutral molecular envelopes are compared with images taken at optical, near-IR, and mid-IR wavelengths. Drawing from the literature, we augmented our BIMA survey sample to 38 well-studied sources with CO emission maps. We classified this sample of sources based on the kinematics and morphologies of the CO emission into three types: spherical/elliptical/shell sources, disk sources, and structured outflow sources. Confirming previous studies, we find strong evidence for the photodissociation of the molecular envelope as an object evolves from the AGB to PN stages. While the spherical AGB stars follow theoretical expectations for mass-loss rate versus envelope size, the post-AGB structured outflow sources have significantly higher mass-loss rates than expected probably because of their recent superwinds. We find evidence that the structured outflows are clearly younger than the AGB wind. The disk sources have little correlation between mass-loss rate and envelope size because their properties are determined more by the properties of the central stars and disk evolution than by the mass-loss rate history that shapes the spherical and structured-outflow sources.

Author Institution: Dept. of Astronomy, University of Illinois at Urbana-Champaign,; Illinois 61801

We introduce a method for analyzing radio interferometry data that produces maps that are optimal in the Bayesian sense of maximum posterior probability density, given certain prior assumptions. It is similar to maximum-entropy techniques, but with an exact accounting of the multiplicity instead of the usual approximation involving Stirling's formula. It also incorporates an Occam factor, automatically limiting the effective amount of detail in the map to that justified by the data. We use Gibbs sampling to determine, to any desired degree of accuracy, the multidimensional posterior density distribution. From this we can construct a mean posterior map and other measures of the posterior density, including confidence limits on any well-defined function of the posterior map.

Molecular cloud cores are often found to contain regions with high abundances of organic molecules such as formaldehyde, methanol, ethanol, dimethyl ether, and methyl formate. First we will review the status of observations of these molecules in a number of sources and discuss some of the limitations of present techniques. Then we will discuss systematic factors involved in the conversion of column densities into fractional abundances and introduce an independent method of calibrating that conversion. Finally we will present recent results from high spatial resolution observations of W3(OH).

We present the results of an interferometric study of 38 millimeter-wave lines of CH3OH in the vicinity of the massive star forming region W3(OH/H2O). These lines cover a wide range of excitation energies and line strengths, allowing for a detailed study of excitation mechanisms and opacities. In this paper we concentrate on the region around the water maser source W3(H2O) and a region extending about 30 arcsec to the south and west of the hydroxyl maser source W3(OH). The methanol emitting region around W3(H2O) has an extent of 2.0 x 1.2 arcsec (4400 x 2600 AU). The density is of order 10 cm, sufficient to thermalize most of the methanol lines. The kinetic temperature is approximately 140 K and the methanol fractional abundance greater than 10, indicative of a high degree of grain mantle evaporation. The W3(H2O) source contains sub-structure, with peaks corresponding to the TW source and Wyrowski’s B/C, separated by 2500 AU in projection. The kinematics are consistent with these being distinct protostellar cores in a wide binary orbit and a dynamical mass for the region of a few tens of M⊙. The extended methanol emission to the southwest of W3(OH) is seen strongly only from the lowest excitation lines and from lines known elsewhere to be class I methanol masers, namely the 84.5 GHz 5−1–40 E and 95.2 GHz 80–71 A + lines. This suggests that this region, like class I maser sources, is dominated by collisional excitation. Within this region there are two compact clumps, which we denote as swA and swB, each about 15 arcsec (0.16 pc projected distance) away from W3(OH). Excitation analysis of these clumps indicates the presence of lines with inverted populations but only weak amplification. The sources swA and swB appear to have kinetic temperatures of order 50–100 K and densities of order 10–10 cm. The methanol fractional abundance for the warmer clump is of order 10, suggestive of partial grain mantle evaporation. The clumping occurs on mass scales of order 1 M⊙. Subject headings: ISM:clouds—ISM:individual (W3)—ISM:molecules—masers—radio lines:ISM University of Illinois, 1002 W. Green St., Urbana, IL 61801; sutton@astro.uiuc.edu Astronomical Observatory, Ural State University, Lenin Street 51, Ekaterinburg 620083, Russia; andrej.sobolev@usu.ru; svetlana.salii@usu.ru; malyshev@ampural.ru; osan@mail.ur.ru Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod 603950, Russia; zin@appl.scinnov.ru

We have detected strong methyl cyanide (CH3CN) emission lines from the hot core regions W51e1 and W51e2, using the BIMA Array. This is the first survey of CH3CN toward W51 to utilize both 3 mm (J=5-4 and 6-5) and 1 mm (J=12-11, 13-12, and 14-13) transitions as probes of the physical and chemical conditions present in these regions. The emission reveals molecular clumps centered on the ultracompact H II regions found by Zhang and colleagues. The CH3CN lines show large optical depths in the lower K transitions toward both regions in W51. To determine the true kinetic temperatures, densities, and column densities of the emitting regions W51e1 and e2, statistical equilibrium models were used to calculate the relative populations of each energy level. The best fit to the observed spectra toward W51e1 is given by a temperature of 123(11) K, a hydrogen density of 5(1)x10(5) cm(-3), and a total methyl cyanide column density of 1.4(1)x10(16) cm(-2). The uncertainties describe a nominal 90% confidence interval for the last digit given. The best fit to the observed spectra toward W51e2 is given by a temperature of 153(21) K, a hydrogen density of 5(2)x10(5) cm(-3), and a total methyl cyanide column density of 3.8(7)x10(16) cm(-2). Our observations indicate that CH3CN can be used as a good probe of the physical conditions present in hot molecular cores and as a tracer of hard-to-detect large molecular species. Despite the differences in molecular structure and chemical formation mechanisms, methyl cyanide (CH3CN), ethyl cyanide (CH3CH2CN), and acetic acid (CH3COOH) are found to have similar abundances toward the W51e1 and e2 regions. In contrast, for a column density of CH3CN more than 15 times smaller than the column density of HCOOCH3 the integrated line flux is more than 7 times larger. Thus, because CH3CN lines are easy to detect, it appears to be a much better tracer of CH3CH2CN and CH3COOH than HCOOCH3.

We present the results of an interferometric study of 38 millimeter-wave lines of CH3OH in the region around the water maser source W3(H2O) and a region extending about 30" to the south and west of the hydroxyl maser source W3(OH). The methanol emitting region around W3(H2O) has an extent of 2.0" x 1.2" (4400 x 2600 AU). The density is of order 1.e7 cm-3, sufficient to thermalize most of the methanol lines. The kinetic temperature is approximately 140 K and the methanol fractional abundance greater than 1.e-6, indicative of a high degree of grain mantle evaporation. The W3(H2O) source contains sub-structure, with peaks corresponding to the TW source and Wyrowski's B/C, separated by 2500 AU in projection. The kinematics are consistent with these being distinct protostellar cores in a wide binary orbit and a dynamical mass for the region of a few tens of Mo. The extended methanol emission to the southwest of W3(OH) is seen strongly only from the lowest excitation lines and from lines known elsewhere to be class I methanol masers, namely the 84.5 GHz 5(-1)-4(0)E and 95.2 GHz 8(0)-7(1)A+ lines. Within this region there are two compact clumps, which we denote as swA and swB, each about 15" (0.16 pc projected distance) away from W3(OH). Excitation analysis of these clumps indicates the presence of lines with inverted populations but only weak amplification. The sources swA and swB appear to have kinetic temperatures of order 50-100 K and densities of order 1.e5 - 1.e6 cm-3. The methanol fractional abundance for the warmer clump is of order 1.e-7, suggestive of partial grain mantle evaporation. The clumping occurs on mass scales of order 1 Mo.

We report molecular line observations of the G34.26+0.15/34.24+0.13 complex, which contains a bright molecular core and a proto-B-star. ATCA observations show that both objects are closely associated with 6.7 v GHz class II methanol masers. Methanol line series at 96, 157 and 241 v GHz towards the protostar position were observed at SEST. Modelling of the methanol data shows that the molecular core embedding protostar is not greatly influenced by the outflow from the young stellar object. Molecular line mapping at Onsala reveals the presence of a cavity and two compact clumps to the southeast of the bright molecular core. The protostar is situated at the edge of one compact clump. It is very likely that the material outflowing from the protostar freely escapes towards the cavity. Comparison of the line profiles of different molecules shows substantial chemical inhomogeneity within the region.

We present 12CO J=1-0 observations of a small sample of evolved stars to investigate the evolution of the molecular envelope from the AGB phase to the formation of the PN.

The relative role of the stellar radiation field, the stellar outflows and the interstellar radiation field (ISRF) in transforming the molecular ejecta into atomic gas was the subject of our ISO LWS and SWS spectroscopy study of 24 evolved stars which span the range from AGB stars to proto-planetary nebulae (PPNs) and PNs. The far-infrared (FIR) atomic fine-structure lines are powerful probes of the warm atomic gas in photodissociation regions (PDRs) and shocks. This paper summarizes and compares the ISO spectroscopy studies of carbon-rich (C-rich) and oxygen-rich (O-rich) evolved stars, published by Fong et al. (2001) and Castro-Carrizo et al. (2001), respectively. We find that photodissociation, not shocks, is responsible for the chemical change from molecular to atomic gas.

Current models of class II methanol masers are able to describe the brightnesses of the strongest masers and provide a basis for explaining observed line ratios. Determination of the physical parameters in the source requires observational data in many maser transitions. In order to provide observational constraints for models we searched for and detected 7 new methanol masers. This allowed us to constrain the physical parameters of the 3 sources with the greatest number of detected methanol maser lines: W3(OH), NGC6334F, and G345.01+1.79. The models accurately account for the fluxes of the bulk of the detected maser lines. Remaining discrepancies most probably reflect the fact that the most prominent components of the different maser lines are formed under different conditions. This is supported by comparison of the line profiles. We outline directions for future studies in the field.

We report interferometric observations of nine class II methanol maser candidate lines toward W3(OH). Narrow maser emission spikes at vLSR = -43.1 km s-1 are present in three of the lines: 31-40 A+, 72-63 A+, and 72-63 A-. For all three lines the maser position is near the northern edge of the W3(OH) ultracompact H II region (maser emission is also seen near the southern edge in the 31-40 A+ line). For the remaining six lines there is no obvious counterpart to the narrow maser spike at -43.1 km s-1. Additional spatially extended emission is present in all nine lines over the range from -41 to -48 km s-1. By comparing our observed flux densities with an extensive set of model calculations, we infer physical characteristics of the maser region. In these calculations the methanol is excited by infrared radiation from warm dust, and this excited gas amplifies the free-free background emission from the ultracompact H II region. The gas forming the narrow maser spikes appears to have both high kinetic temperature, Tkin ≥ 110 K, and high density, n ≈ 107 cm-3. Low-temperature solutions are ruled out by the observed line ratios and low-density solutions by the unphysically large path length that would be required. The gas is rich in methanol (2NM = NA + NE ≳ 10-6N), and the methanol column density in the tangential direction for each symmetry species (divided by line width) is NM/ΔV ≈ 1012 cm-3 s. Somewhat lower values of n and NM/ΔV are also acceptable. The size of the region emitting the maser spike is of order 100 × 1000 AU. In most of the lines the broad emission from -41 to -48 km s-1 can also be attributed to weak maser action, produced in gas with similar physical conditions (high density and temperature). It differs from the narrow spike emission mainly through a beaming factor that can be interpreted as an elongation factor for clumps of maser gas. The combination of narrow and broad emission can arise naturally from an ensemble of clumps of different elongations and orientations. In this unified picture the best fit to the data is provided by n ≈ 2 × 106 cm-3 and NM/ΔV ≈ 4 × 1011 cm-3 s, somewhat lower than the values obtained for just the spike component. The methanol maser clumps may be present in an expanding shell surrounding the H II region, similar to the material producing OH maser emission in this source.

We present preliminary results from a (CO)-C-12 J=1-0 imaging survey of evolved stars which includes the PPNe: IRAS 22272+5435, HD 161796 and AFGL 2343. This survey complements the low excitation atomic gas study presented here by Fong et al. and Castro-Carrizo et al. The CO emission images of these three PPNe reveal round and detached ring structures that are expanding. These simple structures contrast with the bipolar outflows embedded in the larger envelopes of the two best studied PPNe, AFGL 618 and AFGL 2688.

We present ISO LWS and SWS observations of far-infrared atomic fine structure lines in 12 carbon-rich evolved stars from the AGB phase to the formation of the PN. Our analysis shows that photodissociation and not shocks dominates the evolution of the circumstellar envelope by transforming the initially molecular AGB envelopes into the atomic gas found in PPNe and PNe. Atomic mass estimates are also derived.