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Development and first year of results from the Heliometer of Observatório Nacional

Published online by Cambridge University Press:  18 July 2013

Alexandre H. Andrei
Affiliation:
(1) Observatório Nacional/MCTI-Brasil; (2) Osservatorio Astrofisico di Torino/INAF-Italia; (3) SYRTE/Observatoire de Paris-France; (4) Observatório do Valongo/UFRJ-Brasil email: oat1@on.br
Victor A. D'Ávila
Affiliation:
Universidade Estadual do Rio de Janeiro, Brasil Observatório Nacional/MCTI, Brasil
Eugânio Reis Neto
Affiliation:
Museu de Astronomia e Ciâncias Afins/MCTI, Brasil
Jucira L. Penna
Affiliation:
Universidade Estadual do Rio de Janeiro, Brasil
Sérgio C. Boscardin
Affiliation:
Universidade Estadual do Rio de Janeiro, Brasil
Alissandro Coletti
Affiliation:
Azeheb/FACC, Brasil
Luiz C. Oliveira
Affiliation:
NGC51, Brasil
Costantino Sigismondi
Affiliation:
Sapienza Università di Roma, Italia
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Abstract

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Recent research on global climate changes points to three distinct sources of climate disturbance: anthropogenic; natural changes in the oceans and atmosphere; and irregularities in the solar cycles. One of the most direct ways to survey an exogenous component of the climatic variability is through the measurement of variations in the diameter and shape of the solar disk. At Observatório Nacional/MCTI, Rio de Janeiro, after several years of diameter observation using a CCD Solar Astrolabe, these measurements are now performed by a state-of-the-art Solar Heliometer. The heliometric method is one of the most successful techniques to measure small variations of angles. Its principle has been used for the latest space borne astrometric missions, aiming to milli-arcsecond precision. The success of this method relies in the fact that it minimizes the dependence of angular measurements to the thermal and mechanical stability of the instrument. However in the classic heliometer the objective is split into two halves to which is applied a linear displacement along the cut, thus still leaving room for a residual dependence with the focus, due to non-concentricity of the beams of the two images. The focus variation, as well as the effects brought by the large temperature variations during solar observations, was tackled in the Solar Heliometer by having all optical elements and their niches made on CCZ, and the telescope tube on carbon fiber, both materials of negligible thermal coefficient. Additionally, the measures are made perpendicular to the separation direction and the plate scale can be known at every time from the solar motion itself. We present the results from the first year of measurements, in special exploring the upheaval of solar activity on late 2011.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2013 

References

Penna, J. L., Andrei, A. H., Boscardin, S. C., Reis Neto, E., & D'Ávila, V. A. 2010, IAU S264, 49Google Scholar