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A solar cycle lengthwise series of solar diameter measurements

Published online by Cambridge University Press:  26 February 2010

J. L. Penna ,
A. H. Andrei ,
S. C. Boscardin ,
E. Reis Neto  and
V. A. d'Ávila
J. L. Penna
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil email: oat1@on.br
A. H. Andrei
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil email: oat1@on.br Obs. do Valongo/UFRJ-BR, Rio de Janeiro, Brazil
S. C. Boscardin
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil email: oat1@on.br
E. Reis Neto
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil email: oat1@on.br
V. A. d'Ávila
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil email: oat1@on.br UERJ-BR, Rio de Janeiro, Brazil
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Abstract

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The measurements of the solar photospheric diameter rank among the most difficult astronomic observations. Reasons for this are the fuzzy definition of the limb, the SNR excess, and the adverse daytime seeing condition. As a consequence there are very few lengthy and consistent time series of such measurements. Using modern techniques, just the series from the IAG/USP and from Calern/OCA span more than one solar cycle. The Rio de Janeiro Group observations started in 1997, and therefore in 2008 one complete solar cycle time span can be analyzed. The series shares common principles of observation and analysis with the ones afore mentioned, and it is complementary on time to them. The distinctive features are the larger number of individual points and the improved precision. The series contains about 25,000 single observations, evenly distributed on a day-by-day basis. The typical error of a single observation is half an arc-second, enabling us to investigate variations at the expected level of tens of arc-second on a weekly basis. These features prompted to develop a new methodology for the investigation of the heliophysical scenarios leading to the observed variations, both on time and on heliolatitude. The algorithms rely on running averages and time shifts to derive the correlation and statistical incertitude for the comparison of the long term and major episodes variations of the solar diameter against activity markers. The results bring support to the correlation between the diameter variation and the solar activity, but evidentiating two different regimens for the long term trend and the major solar events.

Keywords

Sun: photospherefundamental parametersactivityinstrumentation: photometersmethods: statistical
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 5 , Symposium S264: Solar and Stellar Variability: Impact on Earth and Planets , August 2009 , pp. 49 - 54
Copyright
Copyright © International Astronomical Union 2010

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