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Description
We present molecular observations carried out with the IRAM 30m telescope at wavelengths around 1.15mm towards the Oort cloud comets C/2012 S1 (ISON) and C/2013 R1 (Lovejoy) when they were at 0.6 and 1AU, respectively, from the Sun. We detect HCN, HNC, and CH3OH in both comets, together with the ion HCO+ in comet ISON and a few weak unidentified lines in comet Lovejoy, one of which could be tentatively assigned to methylamine (CH3NH2). The monitoring of the HCN J=3-2 line showed a tenfold enhancement in comet ISON on November 14.4 UT due to an outburst of activity whose exact origin is unknown, although it could be related to some break up of the nucleus. The set of CH_3_OH lines observed was used to derive the kinetic temperature in the coma, 90K in comet ISON and 60K in comet Lovejoy. The HNC/HCN ratios derived, 0.18 in ISON and 0.05 in Lovejoy, are comparable to those found in most previous comets and are consistent with an enhancement of HNC as the comet approaches the Sun. Phosphine (PH3) was also searched for unsuccessfully in both comets through its fundamental 1_0_-0_0_ transition, and 3 sigma upper limits corresponding to PH_3_/H_2_O ratios 4-10 times above the solar P/O elemental ratio could be derived.
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