Limits to the Radiative Asymmetry of the Quiet Solar Disk

Details Limits to the Radiative Asymmetry of the Quiet Solar Disk Limits to the Radiative Asymmetry of the Quiet Solar Disk

Jan 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008apj...672.1228l&link_type=abstract

The Astrophysical Journal, Volume 672, Issue 2, pp. 1228-1236.

Astronomy and Astrophysics

Astronomy

3

Line: Formation, Stars: Planetary Systems, Sun: Chromosphere, Sun: Faculae, Plages, Sun: Granulation, Sun: Photosphere

Scientific paper

Precise data on the uniformity of photospheric radiation over the solar disk seems not to exist. Such information is necessary to separate the radiative behavior of the quiet basal atmosphere from the active (magnetic) atmosphere. Is the latter the sole source of known irradiance variation? How uniform can a solar-like stellar disk be? To obtain this information we have made monochromatic scans along the central meridian of the quiet Sun using single element detectors which do not require flat fielding. The scans were in continua and in selected Fraunhofer lines ranging from 3134 to 46880 Å the observational epoch was near solar minimum: 2006 October to 2007 February. The meridian was chosen to avoid rotational Doppler shifts. We extract the asymmetry between the north and south hemispheres and present it as our main product. In the near-infrared and visible continuum, averaging over granulation and avoiding sunspots, we found that such asymmetry was as low as 0.05% (at 34168 Å on 2007 February 8). In the violet and ultraviolet this asymmetry typically increases to 1%. Asymmetry is larger in the cores of the medium strong photospheric and chromospheric lines, which refer to higher levels in the atmosphere, and may reach 15%. The contrast of faculae increases in the blue (and with improved spatial resolution or seeing), and is the probable source for the measured asymmetries. We also find that line core scans are in general flatter than continuum scans.

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