Probing the Solar Wind Acceleration Region with the Sun--Grazing Comet C/2002 S2

TL;DR

This study uses UV observations of sungrazing comet C/2002 S2 to probe the solar corona and solar wind, revealing complex plasma interactions and estimating the comet's nucleus size through novel spectral analysis and simulations.

Contribution

It introduces a new method combining UV spectral analysis and Monte Carlo simulations to study comet-solar wind interactions and coronal properties.

Findings

Detected blue- and red-shifted emissions indicating solar wind and magnetic field interactions.

Estimated the comet nucleus diameter to be about 9 meters.

Observed the outgassing rate increase as the comet approached the Sun, despite decreasing optical brightness.

Abstract

Comet C/2002 S2, a member of the Kreutz family of Sungrazing comets, was discovered in white light images of the SOHO/LASCO coronagraph on 2002 September 18 and observed in \hi\, \lya\, emission by the SOHO/UVCS instrument at four different heights as it approached the Sun. The \hi\, \lya\, line profiles detected by UVCS are analyzed to determine the spectral parameters: line intensity, width and Doppler shift with respect to the coronal background. Two dimensional comet images of these parameters are reconstructed at the different heights. A novel aspect of the observations of this sungrazing comet data is that, whereas the emission from the most of the tail is blue--shifted, that along one edge of the tail is red--shifted. We attribute these shifts to a combination of solar wind speed and interaction with the magnetic field. In order to use the comet to probe the density, temperature and speed of the corona and solar wind through which it passes, as well as to determine the outgassing rate of the comet, we develop a Monte Carlo simulation of the \hi\, \lya\, emission of a comet moving through a coronal plasma. From the outgassing rate, we estimate a nucleus diameter of about 9 meters. This rate steadily increases as the comet approaches the Sun while the optical brightness decreases by more than a factor of ten and suddenly recovers. This indicates that the optical brightness is determined by the lifetimes of the grains, sodium atoms and molecules produced by the comet.