Latitude-Dependent Temperature Variations at the Solar Limb

Details Latitude-Dependent Temperature Variations at the Solar Limb Latitude-Dependent Temperature Variations at the Solar Limb

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh23b1549f&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SH23B-1549

Astronomy and Astrophysics

Astrophysics

[7507] Solar Physics, Astrophysics, And Astronomy / Chromosphere, [7524] Solar Physics, Astrophysics, And Astronomy / Magnetic Fields, [7529] Solar Physics, Astrophysics, And Astronomy / Photosphere, [7538] Solar Physics, Astrophysics, And Astronomy / Solar Irradiance

Scientific paper

We use observations from the solar aspect sensor of RHESSI to characterize the latitude dependence of the temperature of the photosphere at the solar limb. Previous observations have suggested the presence of a polar temperature excess as large as 1.5 K. The RHESSI observations, made with a rotating telescope in space, have great advantages in the rejection of systematic errors in the very precise photometry required for such an observation. This photometry is differential, i.e. relative to a mean limb-darkening function. The data base consists of about 1,000 images per day from linear CCDs with 1.73 arc sec square pixels, observing a narrow band (12nm FWHM) at 670 nm. Each image shows a chord crossing the disk at a different location as the spacecraft rotates and precesses around its average solar pointing. We fit an average limb-darkening function and reassemble the residuals into synoptic maps of differential intensity variations as function of position angle. We further mask these images against SOHO/EIT 284A images in order to eliminate magnetic regions. The analysis establishes a limit on the quadrupole dependence of temperature (brightness) on position angle of 0.04 +/- 0.02 K. This results in a possible correction of our precise measurement of the solar oblateness which is smaller than its rms error of 0.14 mas.

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