ar X iv : a st ro - p h / 04 01 07 3 v 1 7 J an 2 00 4 Combined BIMA and OVRO observations of comet C / 1999 S 4 ( LINEAR )

We present results from an observing campaign of the molecular content of the coma of comet C/1999 S4 (LINEAR) carried out jointly with the millimeter-arrays of the Berkeley-Illinois-Maryland Association (BIMA) and the Owens Valley Radio Observatory (OVRO). Using the BIMA array in autocorrelation (‘single-dish’) mode, we detected weak HCN J=1–0 emission from comet C/1999 S4 (LINEAR) at 14 ± 4 mK kms averaged over the 143 beam. The three days over which emission was detected, 2000 July 21.9–24.2, immediately precede the reported full breakup of the nucleus of this comet. During this same period, we find an upper limit for HCN 1–0 of 144 mJy beam km s (203 mK kms) in the 9 × 12 synthesized beam of combined observations of BIMA and OVRO in cross-correlation (‘imaging’) mode. Together with reported values of HCN 1–0 emission in the 28 IRAM 30-meter beam, our data probe the spatial distribution of the HCN emission from radii of 1300 to 19,000 km. Using literature results of HCN excitation in cometary comae, we find that the relative line Astronomy Department, University of California, 601 Cambell Hall # 3411, Berkeley, CA 94720-3411, USA Steward Observatory, The University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA Current address: Sterrewacht Leiden, P.O. Box 9513, 2300 RA, Leiden, The Netherlands Hat Creek Radio Observatory, 42231 Bidwell Rd, Hat Creek, CA 96040, USA Department of Astronomy, University of Illinois, 1002 W. Green Street, Urbana, IL 61801, USA Lowell Observatory, 1400 Mars Hill Rd, Flagstaff, AZ 86001, USA Astronomy Department, University of Maryland, College Park, MD 20742, USA Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA Department of Earth Sciences, National Taiwan Normal University Academia Sinica, Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan, ROC Division of Geological and Planetary Sciences, California Institute of Technology 150-21, Pasadena, CA 91125, USA Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA