DETECTION OF REMNANT DUST CLOUD ASSOCIATED WITH THE 2007 OUTBURST OF 17P/HOLMES

Abstract

ABSTRACT This article reports a new optical observation of 17P/Holmes one orbital period after the historical outburst event in 2007. We detected not only a common dust tail near the nucleus but also a long narrow structure that extended along the position angle 274.°6 ± 0.°1 beyond the field of view (FOV) of the Kiso Wide Field Camera, i.e., >0.°2 eastward and >2.°0 westward from the nuclear position. The width of the structure decreased westward with increasing distance from the nucleus. We obtained the total cross section of the long extended structure in the FOV, C FOV = (2.3 ± 0.5) × 1010 m2. From the position angle, morphology, and mass, we concluded that the long narrow structure consists of materials ejected during the 2007 outburst. On the basis of the dynamical behavior of dust grains in the solar radiation field, we estimated that the long narrow structure would be composed of 1 mm–1 cm grains having an ejection velocity of >50 m s−1. The velocity was more than one order of magnitude faster than that of millimeter–centimeter grains from typical comets around a heliocentric distance r h of 2.5 AU. We considered that sudden sublimation of a large amount of water-ice (≈1030 mol s−1) would be responsible for the high ejection velocity. We finally estimated a total mass of M TOT = (4–8) × 1011 kg and a total kinetic energy of E TOT = (1–6) × 1015 J for the 2007 outburst ejecta, which are consistent with those of previous studies that were conducted soon after the outburst.