Observations of the 18-cm OH lines of Comet 103P/Hartley 2 at Nançay in support to the EPOXI and Herschel missions

The 18-cm radio lines of the OH radical were observed in Comet 103P/Hartley 2 with the Nançay radio telescope in support to its flyby by the EPOXI mission and to observations with the Herschel Space Observatory. The OH lines were detected from 24 September to 15 December 2010. These observations are used to estimate the gas expansion velocity within the coma to 0.83 ± 0.08 km s−1 in October 2010. The water production increased steeply but progressively before perihelion, and reached 1.9 ± 0.3 × 1028 s−1 just before the EPOXI flyby.

► The 18-cm lines of OH were monitored in 103P/Hartley 2 at Nançay radio telescope. ► From line shapes, the expansion velocity of the gas coma was 0.83 ± 0.08 km s−1. ► The water production rate was 1.9 ± 0.3 × 1028 s−1 just before the EPOXI flyby. ► The water production increased steeply, but progressively, before perihelion.