Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998larm.confe..12p&link_type=abstract
"IX Latin American Regional IAU Meeting, "Focal Points in Latin American Astronomy", held in Tonantzintla, Mexico, Nov 9-13, 199
Astronomy and Astrophysics
Astronomy
Scientific paper
The Astrolabe observations at the Observatorio Nacional, Rio de Janeiro, Brazil, (phi = -22deg 53' 43", lambda = -0h 27m 42s), started in 1976. The first solar observations were made visually in 1978. In 1993 a project was begun to automatize the Danjon Astrolabe towards the obtaining of high quality, digital solar images. This project entails a co-operation with the Observatories of Cote d'Azur and of Paris, for the exchanging of methods and results. The site quality enables to get about 50% of days of observation per year. Presently, the observations are made twice daily (on the morning and afternoon), with a variable angle objective prism, which allows to cover the zenith distances from 25deg to 55deg. These observations aim to the measure of variations of the observed solar diameter. On fine weather, up to 50 independent measures are obtained per day. A number of filters was tried to maximize the s/n rate and improve on the images quality, being the effective observational wavelength close to 6400AA. At the end of the first year of regular observations, 2706 observations were done. For this partial result, the average precision of a single measurement is at 0".6, while for the session (either A.M. or P.M.) is at 0".2. The average value of the observed solar semi-diameter for the period is 959.31+/- 0.03 arcsec. The characteristics of the station and of the program are presented. The full series is analyzed for robustness, through self-correlation estimation and Monte Carlo simulations. Daily asymmetries, monthly and seasonal trends are discussed, in order to appraisal the existence of periods inherent to the data series.
Andrei Alexander H.
Jilinski E. G.
Penna Jucira Lousada
Puliaev S. P.
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