Solar radius determinations obtained with the CCD  astrolabe at TUBITAK National Observatory

Golbasi, O.; Chollet, F.; Kılıç, Hüseyin Selçuk; Sinceac, V.; Aslan, Z.; Sozen, E.

doi:10.1051/0004-6361:20010066

Cited by 19 publications

(24 citation statements)

References 13 publications

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“…Since no systematic observational error was found, a search was made for time variations of the solar radius. The value for the average semi-diameter agrees well with that obtained by the solar astrolabe at Tubitak (Golbasi et al 2001), namely 959. 03.…”

Section: Resultssupporting

confidence: 87%

CCD astrolabe solar diameter measurements in 1999–2000

Penna

Jilinski

Andrei

et al. 2002

A&A

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Abstract. Solar diameter observations are presented covering a period close to the maximum of the solar activity cycle 23, from July 1999 to December 2000, at the Observatório Nacional, Rio de Janeiro. The observations were made at λ = 5635Å, with a CCD Solar Astrolabe, thus timing the limb crossing through a fixed zenith distance. The formal precision of a single measurement is typically 0. 18. The results represent daily means from 4625 independent measurements. The series obtained has 225 homogeneously distributed points with a mean precision of 0. 12. The average value obtained for the solar semi-diameter within the analyzed period is 959. 01 ± 0. 02. The average of the observations, made under a wide range of different geometric, instrumental and environmental conditions, aims to provide results representing global variations of the solar radius. From this data, variations with amplitude equal to or larger than 0. 02 can be investigated. No statistically significant linear trend is obtained for the examined series. There is, however, some indication of an increasing trend for 1999 followed by a stabilization during 2000. Periodic variations are obtained with amplitudes between 0. 02 and 0. 07. Periods related to the solar rotation and the sunspot characteristic lifetime can be recognized.

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Section: Resultssupporting

confidence: 87%

CCD astrolabe solar diameter measurements in 1999–2000

Penna

Jilinski

Andrei

et al. 2002

A&A

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“…These solar astrolabes operate now in France (Laclare et al 1996), Chile (Noël 2002(Noël , 2003a, Brazil (Reis Neto et al 2003) and Turkey (Gölbaşi et al 2001). These measurements have been already analyzed and discussed, for instance by Ribes et al (1991), Laclare et al (1996), Noël (2002, Jilinski et al (1999), Wittmann (2001), Emilio et al (2000) and Pap et al (2001) 1 .…”

Section: Solar Radius Ground-based Observationsmentioning

confidence: 99%

Solar latitudinal distortions: From observations to theory

Lefebvre¹,

Rozelot²

2004

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Abstract. Solar diameters have been measured from different ground-based instruments on different sites all around the world.There are values dating back to three centuries ago, but the revival of interest began in the 1970s when it was claimed that a temporal periodic modulation had been found. The interest of such measurements, pinpointed from only two decades, may not lie in these temporal variations, but in the fact that a latitudinal heliographic dependence may exist. Such a solar shape distortion has been deduced from the analysis of solar astrolabe data sorted by heliographic latitudes, but observational evidence has also been obtained by means of a scanning heliometer (Pic du Midi Observatory). Latitudinal dependence implies sub-surfacic physical mechanisms and can be explained theoretically. Thus, in spite of the fact that ground-based observations are altered by seeing effects that may amplify or superimpose noise, it can be advanced that the solar shape is not a pure spheroid. We present here a new theory based upon the thermal-wind equation, which explains the observed distorted solar shape. Using the W parameter (called here asphericity-luminosity parameter), we show that large negative values (W ranging from around −0.075 up to −0.6) leading to a prolate Sun, are unlikely. The best range of W lies between around −0.075 and +0.6. Concerning observations, only space missions (or balloon flights) will be able to reach a clear conclusion. A space mission called PICARD is scheduled to be launched by 2008: one of its major aims is to measure these asphericities with astrometric precision.

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“…The monthly means are represented by the center of circles with diameters equal to their mean errors. For Rio de Janeiro they were computed from the homogeneous data set discussed above, and for Antalya from the individual daily measurements that are available at the home page of Tubitak Observatory (Golbasi et al 2001). On average, each monthly mean is based on 273 and 43 CCD observations for Rio de Janeiro and Antalya respectively, and on 38 visual observations for Santiago.…”

Section: Discusionmentioning

confidence: 99%

“…Astrolabe observations of the Sun give, among other solar parameters, an absolute measurement of the apparent solar radius (Laclare 1983). The work of Laclare was followed by programs of solar observations with modified Danjon astrolabes in São Paulo and Rio de Janeiro, Brazil (Leister & Benevides Soares 1990;Jilinski et al 1999), in San Fernando, Spain (Sánchez et al 1993), in Antalya, Turkey (Golbasi et al 2001) and in Santiago, Chile (Chollet & Noël 1993). All these astrolabes, except Santiago, are now equipped with CCD cameras.…”

Section: Introductionmentioning

confidence: 99%

On solar radius measurements with Danjon astrolabes

Noel

2002

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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.

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Solar radius determinations obtained with the CCD astrolabe at TUBITAK National Observatory

Cited by 19 publications

References 13 publications

CCD astrolabe solar diameter measurements in 1999–2000

CCD astrolabe solar diameter measurements in 1999–2000

Solar latitudinal distortions: From observations to theory

On solar radius measurements with Danjon astrolabes

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