UVCS Observation of Sungrazer C/2001 C2: Possible Comet Fragmentation and Plasma-Dust Interactions

In this paper we analyze SOHO Ultraviolet Coronagraph Spectrometer (UVCS) observations of the sungrazing comet C/2001 C2, a member of the Kreutz family, observed on 2001 February 7 at heliocentric distances of 4.98 and 3.60 R. This comet apparently went through sequential fragmentation events along its path: further indication of fragmentation processes is provided by UVCS observations, which show the presence of two separate tails in the 4.98 R data set, which we interpret as two fragments unresolved by LASCO images, one of which sublimates before reaching 3.60 R. The cometary hydrogen Ly signal, decaying exponentially with time, has been interpreted in terms of the H2O outgassing rate and the interactions of coronal protons with atoms created by the photodissociation of water. However, one of the fragments shows an additional Ly contribution, constant with time, which adds to the temporally decaying signal. This contribution has been ascribed to the sublimation of pyroxene dust grains, whose end products neutralize coronal protons via charge exchange processes. Hence, the two fragments have different composition; differences throughout the comet body may have been the primary cause for the comet fragmentation.