Radio observations of comet 9P/Tempel 1 with the Australia Telescope facilities during the Deep Impact encounter

Abstract

We present radio observations of comet 9P/Tempel 1 associated with the Deep Impact spacecraft collision of 2005 July 4. Weak 18-cm OH emission was detected with the Parkes 64-m telescope, in data averaged over July 4-6, at a level of 12 +/- 3 mJy km s(-1), corresponding to OH production rate 2.8 x 10(28) molecules s(-1) ( Despois et al. inversion model, or 1.0 x 10(28) s(-1) for the Schleicher & A`Hearn model). We did not detect the HCN 1-0 line with the Mopra 22-m telescope over the period July 2-6. The 3 sigma limit of 0.06K kms(-1) for HCN on July 4 after the impact gives the limit to the HCN production rate of < 1.8 x 10(25) s(-1). We did not detect the HCN 1-0 line, 6.7 GHz CH3OH line or 3.4-mm continuum with the Australia Telescope Compact Array (ATCA) on July 4, giving further limits on any small-scale structure due to an outburst. The 3 sigma limit on HCN emission of 2.5Kkms(-1) from the ATCA around impact corresponds to limit < 4 x 10(29) HCN molecules released by the impact.