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An extensive modelling of CO line emission from the circumstellar envelopes around a number of carbon stars is performed. By combining radio observations and infrared observations obtained by ISO the circumstellar envelope characteristics are probed over a large radial range. The combined data set gives better determined envelope parameters, and puts constraints on the mass loss history of these carbon stars. Moreover, analysis of the dust emission puts further constraints on the mass-loss rate history. The stars presented here are not likely to have experienced any drastic long-term, mass-loss rate modulations, at least less than a factor of about 5, over the past thousands of years

This poster presents polarimetry and direct images in the atomic Na D (λ1= 5890 A, λ2= 5896 A) and K I (λ= 7699 A) resonance lines, showing shells around the nearby bright carbon stars R Scl and U Ant. They confirm results obtained in CO radio line observations. A simple analytical model shows that the observed intensities are consistent with resonance line scattering of stellar light provided that about 1% of the K and Na has remained in neutral form.

We report on and discuss the detection of an emission feature at 14.98 µm from the oxygen-rich, semi-regularly pulsating Asymptotic Giant Branch star R Crateris, a feature which we suggest to be due to the 21 0 Q-branch of circumstellar CO2. We also suggest a reasonable excitation mechanism, which could explain the height, the width and the asymmetry of the feature.

Using the IRAM interferometer we have observed four carbon stars (U Cam, CIT6, Y CVn, IRC+40540) in the HCN(J =1 → 0) and CN(N =1 → 0) lines. Here we present some results for CIT6 and U Cam.

O-rich SRa and SRb variables have been observed in the 12CO(1–0) and (2–1) lines. A total of 40 stars were observed and 19 detections can be reported. The majority of the objects are weak in CO and have envelopes with small expansion velocities between 1.9 to 15.6 km/s. No correlation is found between period and expansion velocity for the short period objects whereas a trend may be present for the long period ones.

Lake Hecklan, in central Sweden, was fertilized with phosphorus and nitrogen during thermal stratification (late May-early Oct) 1984–1987. The nutrient additions were relatively small and raised the total phosphorus concentrations from 6 to 10 µg l−1. The working hypothesis was that this moderate increase in the phosphorus concentration could increase the phytoplankton biomass without adverse changes in the planktonic community structure. The fertilization increased the phytoplankton biomass from 0.1 to a maximum of 2 mm3 l−1. Chrysophyceae and Cryptophyceae dominated throughout the experimental period. Thus, the phytoplankton composition remained typical for a Swedish forest lake and provided a potential for increased zooplankton growth. An increased growth of zooplankton was indicated by increased biomass of Cladocera and Copepoda in 1984 and 1985, and by increased fecundity of herbivorous zooplankton.

We present observations, which are part of an ongoing investigation, of the CO (J=1-0) emission in the spiral galaxy M51. The spectra were obtained in a beamswitched on-on mode with the Onsala 20 m antenna (beam size ∿33″), equipped with a cooled mixer and a 512·1 MHz multichannel receiver, and are shown in Figure 1. The inset diagram shows the observed positions superposed on the optical outline of the galaxy. With the present signal-to-noise ratio there is no evidence for an arm-interarm intensity contrast. This is even more apparent in integrated intensity. This result agrees with the lower resolution findings of Rickard et al. (1981). We have observed 13CO in one position (22″ south of the center). The 13CO to 12CO ratio, ∿0.1, agrees with Bell results from observations with a 1!7 beam (Encrenaz et al. {dy1979}).