High resolution observations of the molecular cloud around NGC 7538 IRS 1 in the J=1-0 transition of 13CO show that the lower bound for density in that region is about 2 × 103 cm−3. The study of various molecular transitions and the continuum measurements of the H II region indicate that the conditions required by the Boland and de Jong model for the excitation of the H2CO maser are not very stringent or unique.

Since the discovery of the 616-523 rotational transition of interstellar water in maser emission, several hundred sources have been discovered. Their profiles are very variable, presenting correlated variability (Gammon, 1976) or anticorrelated variability (Cesaroni, 1990). Several models have been proposed to explain this variability. Strong Galactic masers, such as W49 and W51 (Kylafis et al. 1991), and also an extremely strong outburst detected by Abraham et al. (1981) in Orion, could not be fully explained based on current models. We have monitored from October 1989 to July 1991 a very strong water vapour eruption in the +28 km s−1 feature, originated from W49N. Here we present the results and discuss the possible correlated variability of this feature with the one that appeared at +62 km s−1.

Interferometric observations of the 21-cm line of atomic hydrogen resolve out the emission from extended, line-of-sight clouds and allow the detailed study of compact H I structures in the surroundings of some stars. These atomic hydrogen components most probably are the result of photodissociation of gas that originally was in molecular form. They have been observed in H II regions, reflection nebulae, and planetary nebulae. The study of this atomic hydrogen component is important to determine the mass and physical conditions of gas in the environment of luminous stars and to test our theoretical knowledge of photodissociation regions.

High spectral resolution observations of dense cores in lines of NH3 have provided no clear evidence for infall, even when the cores possess embedded low mass protostars or young stellar objects (Menten et al., 1984; Menten and Walmsley, 1985; Myers and Benson, 1983). Infall is expected to continue until protostellar winds begin to affect the dynamics of the cores.

We present C/He ratios in the wind of a sample of 5 central stars of planetary nebulae having WC spectrum. The resulting values are comparable to those observed in population I WR stars.

We report the results of our analysis of a well observed sample of southern planetary nebulae. The average S/O and Ar/O ratios are comparable to the solar value and to those observed in galactic H II regions. The He abundance correlates with the N/O ratio, confirming the trend found by previous studies, indicating the surface contamination of the progenitors by dredge-up episodes.

We have investigated gas-phase chemistry in a remnant red giant wind, during transition to a planetary nebula, using the interacting stellar winds model. Rapid destruction by UV of most existing molecules is predicted, within ~ 100 yrs of the core star heating up, suggesting that the large molecules in CRL 618 may be destroyed within decades. However, significant abundances of some hydrogenated molecules and ions (eg. CH+, CH2+, CH3+, CH, CH2, NH) may form behind the shock predicted by the interacting stellar winds model. Also, survival and/or formation of observable amounts of some molecules (eg. HCN, CN, HC3N) may occur in dense clumps which survive transition, and may explain the existence eg. of HCN in NGC 7027.

Molecular observations and models of the chemical processes in the ejecta of novae and supernovae are reviewed. Although only a few molecular species have been identified, the information that they give has provided great insight into the physical and chemical conditions. We now have quite a detailed understanding of the processes at work in both novae and supernovae.

The 8.1 μm Δv = 1 emission band of silicon monoxide detected in SN 1987A is modelled. Near day 500 the SiO mass is 4 ± 2 10−6M⊙ and the excitation temperature is ~1500 K. The mass of SiO is about 10 percent of the mass of dust inferred from the mid infrared emission near day 600, while the temperature is close to the condensation temperature of silicate grains. The SiO molecules may have been precursors to dust grain formation.

Recent ultraviolet, infrared, millimeter and centimeter-wavelength observations have revealed that HH objects are also sources of molecular line emission. Infrared observations have shown that H2 line emission in HH objects presents a wide and complex variety of morphologies, being in most of the cases similar to that observed at optical wavelengths. New high-angular resolution radio observations of molecular lines have revealed that small high-density condensations are frequently found in association with HH objects. Below, a brief review of molecular emission in HH objects is presented.

High mass-loss molecular winds are characterstic of two important phases of stellar evolution, very young protostars and stars on the asymptotic branch. Novel chemical processes in these winds suggest a variety of new astronomical observations.

Chemical models of protostellar and other outflows have been reassessed in the light of new chemical data. In particular, reactions involving excited hydrogen (2s,p) are shown to be important in hot, dense outflows. The H(n=2) + H → H2 + hv reaction is much less of a contributor to the H2 formation rate than the recently measured H(n=2) + H → H2+ + e- reaction, providing conditions allow the 0.75eV endothermicity of this reaction to be overcome.

With physical conditions very similar to those of molecular clouds, circumstellar envelopes (CSEs) are the sites for a rich chemistry. Hovever their simpler geometries, the variations in elemental composition, and the short time scales of the outflows, make them objects of particular interest to the astrochemist. For a recent and general review of circumstellar chemistry the reader may refer to Omont (1990). Here we give only a very short overview (Section 2), then we report on some of the very recent observational advances in this field (Section 3).

We determined temperatures and Lithium 6707 A resonance line equivalent width of a sample of 62 T Tauri stars. Lithium abundances were then estimated by using a grid of curves of growth. The lithium abundance is shown to decrease with the distance of the stars to the nearest dense core of a molecular cloud. This effect is interpreted as being due to the ages of the stars, the youngest ones being closer to still active star formation regions.

We have used the James Clerk Maxwell Telescope to observe 11 lines of SiCC with excitation energies up to 330 K above the ground state in IRC 10216. An excitation analysis indicates Trot = 43 ± 5 K within a given Ka ladder and Texc = 160 ± 50 K between Ka ladders. The column density of SiCC is estimated to be 3 × 1015 cm−2, more than an order of magnitude higher than previous estimates.

IRAS 15194-5115 was discovered by IRAS and identified as a carbon star by Meadows et al. (1987). It is the third brightest carbon star at 12 μm, the brighter ones are IRC+10216 and CIT6. Its infrared properties are similar to those of IRC+10216. Le Bertre and Epchtein (1990) have monitored the star in the near-infrared and derived a period of 578 days. The distance to IRAS 15194-5115 is estimated to about 1 kpc from infrared observations, and also by comparing its bolometric luminosity with that of IRC+10216.

We observed two carbon stars with silicate emission, C1003 and BM GEM, and we calculated the abundances ratios. The results are compared with them of R0 stars (Dominy, 1984).

The H2O maser source in G305.8 - 0.2 was first detected by Haynes et al. (1984). Inspection of the Southern Hemisphere radio surveys did not show any strong compact HII region or water maser placed nearby this source. The IRAS point source catalog (2.0) shows a strong source in the direction of the maser. We analysed the temporal variation and line profile of the H2O maser emission and discussed the nature of its associated IRAS source. These source characteristics seem compatible with the hypothesis that the maser is associated with a protostellar disk around an early-type star of spectral type 07 to 09 surrounded by a spherical shell of gas and dust.

There is strong evidence for magnetic fields in molecular clouds to be oriented parallel to the direction of bipolar outflows. We have evidence for Alfvén waves in molecular clouds from the facts that: (i) the velocity width of CO lines, ΔV, is approximately twice the gravitational energy, and (ii) polarization maps indicate well-defined magnetic fields. These facts indicate that ΔV is wave-like and not eddy-like. We study the Alfvén wave protostellar model of Jatenco-Pereira and Opher (1989) to explain the observed bipolar outflows and turbulence in molecular clouds. We assume that the Alfvén waves are primarily dissipated by non-linear damping and examine the physical parameters necessary to produce the observed massive low-velocity bipolar outflows (u∞ ∿ 10 − 50 km s−1 and Ṁ ∿ 10−3 M⊙ yr−1) and turbulence in molecular clouds.

We analyzed the optical spectra of cool component of symbiotic star SY Mus by means of spectral synthesis technique in order to derive the atomic abundances using the Minneart formulae for computing the atmospheric opacities. We obtained a satisfactory agreement between the observed and computed spectra and the resulting abundances were consistent to the solar abundances.