Phase Angle Effects on Sungrazing Comets Observed by SOHO (original) (raw)

2008

Knight, Michael F. A’Hearn, Doug A. Biesecker, Guillaume Faury, Doug P. Hamilton, Philippe Lamy, and Antoine Llebaria, University of Maryland, College Park, MD, USA, NOAA, Boulder, CO, USA, Laboratoire d’Astronomie Spatiale, Marseille, France Unlike most comets seen at larger heliocentric distances, sungrazing comets seen near perihelion are often observed over a wide range of phase angles in a short time. The phase angle of the Marsden group comet C/1999 U2 changed by nearly 120◦ over ∼37 hours. Furthermore, many are seen at high phase angles where forward scattering is very important. The few comets that have been seen at large phase angles, including C/1976 V1 West, 96P/Machholz 1, and C/2006 P1 McNaught, have shown dramatic brightening. Studies by Kolokolova et al. [1] and Marcus [2] have quantified the phase dependence of brightness due to scattering off dust in the coma, showing a gentle increase due to backscattering (phase angle 100◦), and a relatively flat curve in between....