Other
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsp53b..01b&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #SP53B-01
Other
7507 Chromosphere, 7524 Magnetic Fields, 7536 Solar Activity Cycle (2162)
Scientific paper
The Mount Wilson solar photographic archive digitization project makes available to the scientific community in digital form a selection of the solar images in the archives of the Carnegie Observatories. This archive contains over 150,000 images of the Sun which were acquired over a time span in excess of 100 years. The images include broad-band images called White Light Directs, ionized CaK line spectroheliograms and Hydrogen Balmer alpha spectroheliograms. This project will digitize essentially all of the CaK and broad-band direct images out of the archive with 12 bits of significant precision and up to 3000 by 3000 spatial pixels. The analysis of this data set will permit a variety of retrospective analyzes of the state of the solar magnetism and provide a temporal baseline of about 100 years for many solar properties. We have already completed the digitization of the CaK series and we are currently working on the broad-band direct images. Solar images have been extracted and identified with original logbook parameters of observation time and scan format, and they are available from the project web site at www.astro.ucla.edu/~ulrich/MW_SPADP. We present preliminary results on a CaK plage index time series derived from the analysis of 70 years of CaK observations, from 1915 to 1985. One of the main problem we encountered during the calibration process of these images is the presence of a vignetting function. This function is linked to the relative position between the pupil and the grating. As a result of this effect the intensity and its gradient are highly variable from one image to another. We currently remove this effect by using a running median filter to determine the background of the image and divide the image by this background to obtain a flat image. A plage index value is then computed from the intensity distribution of this flat image. We show that the temporal variability of our CaK plage index agrees very well with the behavior of the international sunspot number series.
Bertello Luca
Boyden John E.
Javaraiah J.
Ulrich Richard K.
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