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A&A 396, 667-672 (2002)
DOI: 10.1051/0004-6361:20021447
On solar radius measurements with Danjon astrolabes
F. NoëlDepartamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
(Received 31 July 2002 / Accepted 5 September 2002 )
Abstract
During the last 25 years the Danjon astrolabe has been used extensively for
measuring the apparent solar diameter. Here we discuss some aspects of the
results obtained with the CCD astrolabes of Antalya (Turkey) and Rio de
Janeiro (Brazil), and with the visual astrolabes of CERGA (France) and
Santiago (Chile). The most extended databases obtained with these astrolabes
are those of CERGA and probably Santiago. However, concerning observed
variations in time of the solar radius, the results of both stations are
discrepant. While the CERGA results show a marginal radius variation in
opposing phase with solar magnetic activity, those of Santiago give a
significant variation in time, but in phase with solar activity. According
to Chollet & Sinceac (1999) the apparent solar radius variation is identical
for all astrolabe measures (except Santiago) and anticorrelated with the
magnetic cycle of the Sun. However, we show here that according to published
results, the astrolabes of Antalya and Santiago give similar radius variation.
With respect to the results of Rio de Janeiro, they show strong internal
inconsitencies due probably to instrumental modifications made during its
observational campaign. After removing these inconsistencies, the results of
Rio de Janeiro become almost identical to those of Santiago. The results of
these astrolabes, Antalya, Rio de Janeiro and Santiago, are in agreement with
recent results obtained with different observational techniques, which show
also that the apparent solar radius would vary in phase with solar magnetic
activity.
Key words: astrometry -- Sun: fundamental parameters -- Sun: actvity
© ESO 2002
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