Correlations Between Full Disk Magnetograms and Solar Contrast

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Session 44 -- Solar Observations and Theory
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[44.10] Correlations Between Full Disk Magnetograms and Solar Contrast

S.R. Walton, G.A. Chapman (SFO/CSUN), Y. Jayasinha (Van Nuys HS)

We have embarked on a pilot project to investigate the photometric properties of sunspots as a function of cycle phase and the relation between those properties and the magnetic field. The present study uses full-disk solar contrast maps from the San Fernando Observatory (SFO) Cartesian Full Disk Telescope 2 (CFDT2) and full-disk magnetograms from the National Solar Observatory Spectromagnetograph during the period 11 August to 23 August 1992; active region NOAA 7260 transited the disk during this period. The CFDT2 instrument is scanned by the earth's rotation, so its astrometric quality is very high. We fit an accurate limb to the CFDT2 intensity map, and used this limb plus the time difference between the CFDT2 and NSO images to re-interpolate the CFDT2 image onto the same image scale, orientation, and time of observation as the NSO images. A contrast map is then produced from the CFDT2 image. This procedure is entirely automatic and quite accurate, and is thus potentially suitable for the unattended processing of much larger amounts of data. From these co-aligned images, we produce two-dimensional histograms, using CFDT2 images taken in both red continuum and the core of the K line. These histograms contain quite a bit of scatter around zero field and zero contrast, which seems to be real. We do see a difference between small and large spots, in the sense that smaller sunspots show a slower growth of negative contrast with increasing flux than large sunspots. In other words, if one chooses a pixel inside a small and a large sunspot with the same magnetic flux, the corresponding contrast will be larger in the large spot. There is a ''cutoff'' flux of about 1500G above which the sunspot stays at the same contrast, roughly 20\%, as the field strength increases.

This research was supported in part by grants NSF ATM-9115111 and NASA NAGW-3017, and by the NSF Young Scholars Program. We are grateful to J. Harvey and H. Jones of NSO for providing the magnetograms.

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