Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsp51a..04f&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #SP51A-04
Astronomy and Astrophysics
Astrophysics
7500 Solar Physics, Astrophysics, And Astronomy, 7509 Corona, 7513 Coronal Mass Ejections (2101), 7524 Magnetic Fields, 7531 Prominence Eruptions
Scientific paper
Prominence cavities in coronal helmet streamers are readily detectable in white light coronagraph images, yet their interpretation may be complicated by projection effects. In order to determine a cavity's density structure, it is essential to quantify the contribution of non-cavity features along the line of sight. We model the coronal cavity as an axisymmetric torus that encircles the Sun at constant latitude, and fit it to observations of a white light cavity observed by the Mauna Loa Solar Observatory (MLSO) MK4 coronagraph from January 25-30, 2006. We demonstrate that spurious non-cavity contributions (including departures from axisymmetry) are minimal enough to be incorporated in a density analysis as conservatively estimated uncertainties in the data. We calculate a radial density profile for cavity material and for the surrounding helmet streamer (which we refer to as the "cavity rim"), and find that the cavity density is depleted by a maximum of 40 percent compared to the surrounding helmet streamer at low altitudes (1.18 solar radii), but is consistently higher (double or more) than in coronal holes. We also find that the relative density depletion between cavity and surrounding helmet decreases as a function of height. We show that both increased temperature in the cavity relative to the surrounding helmet streamer and a magnetic flux rope configuration might lead to such a flattened density profile. Finally, our model provides general observational guidelines that can be used to determine when a cavity is sufficiently unobstructed to be a good candidate for plasma diagnostics.
Detoma G.
Fan Ying
Füller Johann
Gibson Sarah Elizabeth
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