Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sp21a04w&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SP21A-04
Physics
7536 Solar Activity Cycle (2162), 7537 Solar And Stellar Variability, 7594 Instruments And Techniques
Scientific paper
We present results from a study of facular regions on images taken at the San Fernando Observatory (SFO) CFDT1 telescope; the images are 512 square full disk photometric images taken through two filters: 672.3~nm center, 10~nm bandpass (``red'') and 393.4~nm center, 1~nm bandpass (``Ca~II~K''). Faculae were identified using an algorithm which requires three adjacent pixels above a contrast trigger, allowing reliable identification of very faint features (contrasts of order a few tenths of a percent). Over 147,000 red faculae were identified, and about 800,000 Ca~II~K faculae. In addition, we computed the contrasts of pixels on the red images cospatial with Ca~II~K faculae. Our observations were interpreted with reference to flux tube models of solar faculae. There are continuous but systematic differences among facular regions. We find that the contrast of Ca~II~K faculae is relatively insensitive to heliocentric angle, but is a strong function of facular size, in the sense that larger Ca~II~K faculae are always brighter. The contrast of red faculae is a function of both heliocentric angle and size. We conclude that larger regions contain larger flux tubes, contain deeper flux tubes, and have larger filling factors than small facular regions. Comparisons of cospatial pixels on red and Ca~II~K images show a tight correlation between the average contrast of a region in the continuum and its size and heliocentric angle in the Ca~II~K images. This relation might allow deduction of the average continuum facular contrast for time periods when only areas and locations of Ca~II~K faculae are available, and is thus important for proxies of the solar irradiance. The largest Ca~II~K faculae are found in the activity belts, but the smaller regions are more uniformly distributed, so our smaller Ca~II~K regions are actually bright network. Graphs of dN/dA, the differential size distribution, of Ca~II~K faculae, show that network is equally prevalant at all phases of the solar cycle, and thus cannot account for changes in solar irradiance from maximum to minimum. This work was supported by NSF grant ATM-9912132 and NASA grant NAG5-7191.
Chapman Gary A.
Preminger Dora G.
Walton Stephen R.
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