SIMBAD references

We have mapped the dense quiescent core L 1498 in C¹⁸O(1-0), C¹⁸O(2-1), CS(2-1), and CS(3-2) with angular resolutions between 12 and 25 arcseconds. We have also obtained spectra of C³⁴S(2-1) and (3-2) as well as of CS(5-4) at one position. Our C¹⁸O maps show a ring-shaped structure in good agreement with a recent study by Zhou et al. (1994). From our C¹⁸O map, we find a mass of 0.9 solar masses for the core. Comparison with a recent millimeter continuum observation suggests that CO may be underabundant by a factor of 3 relative to average molecular cloud material but the uncertainties in this number are large. We find several small scale structures in our maps with a diameter of approximately 0.02 parsec and a mass of approximately 0.01 solar masses. These are not gravitationally bound whereas the larger scale core seems to be. An intriguing feature of our results is that the CS profiles are double-peaked with the blue peak generally stronger than the red. If one decomposes the double-peaked profiles, one finds that the individual CS velocity component linewidths are extremely narrow (0.11-0.18km/s) and only marginally wider than the width expected for pure thermal broadening (0.10km/s). We conclude that we are observing a structure which is to a good approximation static. The double-peaked nature of the CS profiles could either be due to absorption by a foreground low density cloud or because we are observing two layers of gas adjacent to one another and with slightly different line-of-sight velocities.