Results from the Mt. Wilson Solar Photographic Archive Digitization Project

Details Results from the Mt. Wilson Solar Photographic Archive Digitization Project Results from the Mt. Wilson Solar Photographic Archive Digitization Project

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009spd....40.1516b&link_type=abstract

American Astronomical Society, SPD meeting #40, #15.16; Bulletin of the American Astronomical Society, Vol. 41, p.838

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Scientific paper

We have digitized almost 40,000 ionized CaK line spectroheliograms that were obtained at the 60-foot solar tower, between 1915 and 1985, as a part of the monitoring program of the Mount Wilson Observatory. From the analysis of these photographic solar images we have derived a Ca II K index, defined as the average fractional area of the visible solar disk occupied by plages and active network. Our time series agrees very well with a different reduction of the same data base and other Ca K spectroheliograms long-term synoptic programs, such as those at Kodaikanal Observatory (India), and at the National Solar Observatory at Sacramento Peak (USA). We show that using appropriate proxies it is possible to extend this time series up to date, making this data set one of the longest Ca II K index series currently available. The rate of solar rotation over the whole solar surface can also be determined as a function of time using the day-to day motions of features visible on these CaK images. We present here preliminary results about the rotation rate pattern determined by cross-correlating observations taken on successive days for separate latitude zones spanning the solar disk.

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