SSP seminar

EUV and X-Ray Observations of Comet Lovejoy (C/2011 W3) in the Lower Corona

Patrick McCauley, CfA

Monday 22 April 2013, Noon
Pratt Conference Room, 60 Garden Street

On December 16, 2011, Comet Lovejoy (C/2011 W3) came within just 0.2 R_sun of the photosphere and emerged from behind the solar disk to the surprise of many. Observations were recorded by a number of solar observatories, and we present analyses of those taken by the X-Ray Telescope (XRT) aboard Hinode and the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. We explore a single set of contemporaneous images in detail and characterize the emission in each of the 8 wavelength bands. As material sublimates from the nucleus and is immersed in coronal plasma, it rapidly ionizes through charge states seldom seen in the lower corona. O III through O VII are observed, along with C IV, and we derive outgassing rates where applicable. We estimate peak rates of 10^32.5 Oxygen atoms per second and a total mass loss of ~10^13 g during the egress (assuming that all neutral oxygen comes from sublimated water molecules). From this, we expect that the nucleus was on the order of 600 m in diameter on approach to perihelion. Our data show that material was ejected from the nucleus in distinct outbursts, which may result from the explosion of interior pockets of water ice, as proposed by Sekanina & Chodas (2012). This suggests a tensile strength that is greater than what the canonical "rubble pile" model would imply and may be significant to our general understanding of cometary compositions. Additional and supporting analyses include a differential emission measure to characterize the coronal environment and a positional comparison with the expected trajectory.


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