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

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 mJykm s ^-1, corresponding to OH production rate 2.8 × 10 ²⁸ molecules s ^-1 (Despois et al. inversion model, or 1.0 × 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 3σ limit of 0.06 K km s ^-1 for HCN on July 4 after the impact gives the limit to the HCN production rate of < 1.8 × 10 ²⁵ s ^-1. We did not detect the HCN 1-0 line, 6.7 GHz CH ₃OH 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 3σ limit on HCN emission of 2.5 K km s ^-1 from the ATCA around impact corresponds to limit < 4 × 10 ²⁹ HCN molecules released by the impact.