Photometry and imaging of Comet 103P/Hartley in the 2010–2011 apparition

Abstract The results of a CARA (Cometary Archive for Afρ ) campaign on Comet 103P/Hartley 2 are presented. The main goal was to monitor extensively the comet during the apparition with CCD R and I imaging and photometry, as a support of EPOXI mission. The Afρ quantity showed a progressively rising ascending branch, followed by an apparent flat maximum that lasted for 2 months, from about −10 to +50 days from perihelion. In this period, Afρ peaked at around 100 cm in R band with strong short term fluctuations between 70 and 140 cm. Early signs of activity were detectable well before perihelion (about 80–90 days before) and a random variability is also present in the descending branch after perihelion. Three post perihelion data points (between +55 and +61 days) from the 1997–1998 apparition show a bit higher Afρ value of our observation and a similar fast variation. The average Afρ behavior, corrected for the solar phase effect, is strongly asymmetric and shows a more steeper ascending branch, approaching to perihelion. Morphology and coma asymmetry, as well as the sunward and tailward profiles are examined. An average gradient indicatively between ∼ ρ −0.7 and ρ −1 is observed in the inner coma ( ρ