RHESSI observations of the X-ray limb of the Sun
Motivation
Observations of X-ray sources occulted by the solar limb provides a unique
opportunity to study its structure.
The authoritative results for the limb location (ie, the solar radius)
at visible wavelengths come from drift scans repeated for many years
and finally reported by
Brown & Christiansen-Dalsgaard in 1998.
The number they reported, 695.508 +- 0.026 Mm (equatorial radius
of the photosphere, ie the height of τ5000=1),
differs by almost 0.5 Mm from the previously accepted value
of 695.99 Mm (Allen).
We expect to learn several things via careful analysis of the X-ray limb
structure, although we may not be able to compete with this precision!
There really is no data base comparable to RHESSI's, since all other
observations of the limb involve longer wavelengths with complicated
radiation properties.
The X-ray absorption limb mainly just depends on the mean mass
distribution of the quiet solar atmosphere.
X-rays only have the photoeffect and Compton scattering as absorbing
agents and are generally quite different in nature from the optical
observations.
We are proposing to have a short organizational session on this topic
at the RHESSI
Annapolis meeting as a part of Working
Group 1.
There will be only one presentation, and mostly discussion.
Disclaimer
This session is not about flares directly, but only as sources of
background illumination for the limb.
Cosmic X-ray sources would be even better but they are probably not
bright enough.
X-ray absorption
|
X-ray absorption cross-section of the
solar atmosphere, following the abundances
in Asplund et al. (2009):
Note the factor of [hν/(1 keV)]3 applied to keep
things viewable (courtesy Natasha Jeffrey).
|
|
Materials
Last circular
Gordon Hurford's Genoa presentation
Brown & Christiansen-Dalsgaard
(1998)
Krucker & Lin (2008); also some
analysis (courtesy Glesener & Hurford)
Kontar & Jeffrey (2010)
Organizing committee
The session organizers are Hurford, Krucker, and Hudson.
Please send feedback to Hugh
Hudson.