The isotopic abundance ratio 12C/13C in some carbon-bearing molecules is discussed in the context of chemical fractionation via ion-molecule and exchange reactions in dense interstellar clouds. These processes can lead to enhancement of 12C in molecules not related to carbon monoxide. The effect is transient and takes place preferentially outside the cores of the interstellar clouds. However, some enhancement of 12C should remain in gases frozen onto dust grains and may be reflected in larger objects such as cometary nuclei.

The abundances of elements in the interstellar medium (ISM) result from a complex sequence of nucleosynthetic processes which started some ten billion years ago in the Big Bang and are still going on. Their study and in particular their comparison with the stellar and the solar system abundances may give clues to: i) the properties of the early Universe, ii) the evolution of galaxies (rate of star formation, Initial Mass Function of stars, stellar nucleosynthesis and rate of ejection of matter by stars), and iii) the flux of low-energy cosmic rays. (See e.g. Reeves 1974, Audouze and Tinsley 1976).

Deuterated formaldehyde has been detected for the first time in interstellar clouds; the observed ratio HDCO/H2CO implies formation by gas phase chemistry.

Interstellar shock waves have a significant influence on the structure and dynamics of interstellar matter and probably trigger star formation in suitably dense regions. In this paper the overall structure of regions near shock waves is reviewed. In addition we discuss the main observational effects of shocks on interstellar molecules, including: (i) acceleration to velocities 1 km s-1 < vs < 100 km s-1 relative to the ambient gas, (ii) excitation of infrared lines in the heated postshock gas, and (iii) production of high abundances of certain molecular species such as H, OH, H2O, CH+, OCS, and SiO through high temperature chemical reactions in the T ≳ 1000 K postshock gas. The molecular region around the BN infrared source in Orion and the high velocity molecules in IC443 are discussed as possible examples of shocked molecular gas.

Some techniques for observing shock waves in interstellar clouds are discussed. It is concluded that recent measurements of molecular hydrogen emission provide the best currently available technique for studying shocks. The results of measurements toward the Orion nebula are discussed, and a discussion and summary of the currently known H2 sources is given.

The 12.28μm pure rotational line of molecular hydrogen has been detected in emission from the region of vibration-rotation line emission in Orion. The line shapes, widths, and velocities are similar to those observed in the V=1 → 0 transition at 2.12μm. Constraints imposed by these new results on models of the emitting region are discussed.

New spectra of the 2.12μm line of H2 in Orion have been obtained during 1979 February at the Mount Wilson 2.5m and Palomar 5m telescopes. These data provide wider spatial coverage and higher spatial resolution than the observations reported earlier by Nadeau and Geballe (1979). The complete data, displayed here in two maps, are consistent with the earlier interpretation, which is summarized below.

We have constructed models of relatively high-density radiation-bounded filaments near the nucleus of a Seyfert 2 galaxy. The amount of molecular hydrogen predicted by the models for reasonable values of the physical parameters is consistent with observations of the infrared continuum and the quadrupole rotation-vibration lines of H2 in NGC 1068.

A survey of 14 SNR's in the 4.8 GHz absorption line of H2CO shows that two of them, W28 and W44, possibly interact with molecular clouds. The interaction leads to acceleration of a part of the molecular cloud to a velocity of ∼5 km s-1 without a significant increase in the kinetic temperature or turbulence.

We will discuss molecular envelopes around post main sequence stars. Topics that will be covered include chemical composition, physical properties, mass loss and evolution. In view of the following papers by Drs. Snyder and Goldreich we will have little to say about circumstellar masers here.

Observations have been made of J=2-1 CO in eleven circumstellar clouds including seven carbon stars and four oxygen-rich stars. Observations in four sources, including IRC+10216 have already been published (Wannier et al. 1979, henceforth Paper I) and the remaining observations are being prepared for publication (Knapp et al. 1980, henceforth Paper II). Several results are discussed below with special emphasis on the implications for two sources, namely IRC+10216 and Mira (o Ceti). The observations of IRC+10216 show CO emission over a diameter of 6 arcmin (∼ 0.5pc), a result suggesting a very large mass-loss rate. Mira is unique among the objects studied in displaying a small CO opacity and a high CO excitation temperature. It is suggested that this heating results from the orbital velocity of Mira due to its close binary companion.

IRC+10216 (CW Leo) is a carbon star surrounded by an expanding circumstellar envelope which is rich in molecules. Recently, Betz et al.1 reported the detection of rotation-vibration transitions of NH3 (ν2 band) in absorption against the infrared continuum of circumstellar dust. We now report the detection of the (1,1) and possibly the (2,2) inversion transitions of (para) NH3, the first radio detection of ammonia in a star. This information can be used to determine the thermal structure of the envelope of IRC+10216.

The observed molecular column-densities in IRC +10216 can be matched by chemical-equilibrium calculations for T∼1250°K, P∼100 dyn cm-2 and no graphite grain formation. Condensation of silicon carbide into grains may explain the low observed abundances of SiO and SiS.

Ammonia has been detected in the circumstellar envelopes of IRC+10216, VY CMa, VX Sgr, and IRC+10420. A number of absorption lines of 14NH3 in the ν2 vibration-rotation band around 28 THz (950 cm-1) have been observed at a velocity resolution of 0.2 km/s. Typical linewidths are 1 to 4 km/s, and the details of the line profiles provide additional insights on the process of mass loss in these stars.

Spectroscopy of circumstellar molecular species in the 2-14μm range provides evidence for a range of shell optical depths in the +10216 class of stars. In some cases a photospheric spectrum is present. The spectrum of +10216 shows absorption over a range of velocities including two distinct velocities of different excitation temperature. The occurrence of multiple velocities may be common in similar objects.

High resolution spectra of red giants and long period variables exhibit lines of infrared CO vibration-rotation bands arising in circumstellar material. In the few such stars so far observed at very high resolution (≲ 1 km/s) the circumstellar material appears localized in 3 distinct regimes with temperatures of 800K, 200K and 75K and expansion velocities of 0, 10 and 16 km/s rather than being uniformly distributed.

OH, H2O and SiO are the 3 known molecular masers associated with stars. The known transitions, their line profiles, radial velocities, temporal intensity variations and polarization properties are discussed. Current work on determination of circumstellar shell sizes is reviewed. Possible future research topics are outlined.

Our previous observations established the small angular size and high brightness temperature of emission from the v=1, J=1-0 transition of SiO from the circumstellar envelopes of the supergiant VX Sgr and the Mira variable R Cas. We performed a second VLBI experiment on the SiO masers in several late type stars on 31 Oct.-2 Nov. 1978 to compare the physical characteristics of the SiO masers in the v=1 and v=2 states. With an energy separation of 1258 cm-1 (an equivalent temperature of 1753 K) between the two vibrational states, differences in excitation and pumping of the maser states may lead to different maser properties.

Published data on a select group of SiO maser sources have been analyzed for velocity variations as a function of phase. No apparent correlation was found to a level of about 2 km/s. This places constraints on the location of the maser molecules. Such a correlation should be present at some level. The implications for future high resolution infrared measurements are discussed.

We report a series of observations of the v=1, J=2-1 transition of SiO (86243.28 MHz) toward four Mira variables (o Cet, R Leo, W Hya, and R Cas) and Orion A over the period September 1976 - February 1978. Observations were made with the 6-m mm-wave telescope of the Tokyo Astronomical Observatory. Most of the spectra were taken with an acousto-optical spectrometer with an effective resolution of about 57 kHz.