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

TL;DR

This paper analyzes EUV and X-ray observations of Comet Lovejoy during its close approach to the Sun, revealing rapid ionization processes, high outgassing rates, and detailed plasma emission characteristics in the solar corona.

Contribution

It provides the first detailed analysis of simultaneous EUV and X-ray data of a sungrazing comet, characterizing ionization stages and estimating mass-loss rates during perihelion.

Findings

Detected multiple ionization stages of oxygen in the comet's tail.

Estimated high outgassing rates of about 10^32.5 oxygen atoms per second.

Measured a total mass loss of approximately 10^13 grams during the event.

Abstract

We present an analysis of EUV and soft X-ray emission detected toward Comet Lovejoy (C/2011 W3) during its post-perihelion traverse of the solar corona on December 16, 2011. Observations were recorded by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory and the X-Ray Telescope (XRT) aboard Hinode. A single set of contemporaneous images is explored in detail, along with prefatory consideration for time evolution using only the 171 A data. For each of the eight passbands, we characterize the emission and derive outgassing rates where applicable. As material sublimates from the nucleus and is immersed in coronal plasma, it rapidly ionizes through charge states seldom seen in this environment. The AIA data show four stages of oxygen ionization (O III - O VI) along with C IV, while XRT likely captured emission from O VII, a line typical of the corona. With a nucleus of at least several hundred meters upon approach to a perihelion that brought the comet to within 0.2 solar radii of the photosphere, Lovejoy was the most significant sungrazer in recent history. Correspondingly high outgassing rates on the order of 10^32.5 oxygen atoms per second are estimated. Assuming that the neutral oxygen comes from water, this translates to a mass-loss rate of about 9.5E9 g/s, and based only on the 171 A observations, we find a total mass loss of approximately 10^13 g over the AIA egress. Additional and supporting analyses include a differential emission measure to characterize the coronal environment, consideration for the opening angle, and a comparison of the emission's leading edge with the expected position of the nucleus.