On the Constancy of the Solar Diameter. II.

Kuhn, J. R.; Bush, R. I.; Emílio, M.; Scherrer, P. H.

doi:10.1086/423301

Cited by 97 publications

(112 citation statements)

References 23 publications

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“…The diameter appears to have changed either in phase with surface activity (Ulrich & Bertello 1995;Basu 1998;Emilio et al 2000;Noël 2004) or in antiphase with surface activity (Gilliland 1981;Sofia et al 1994;Laclare et al 1996;Li & Sofia 2001;Reis Neto et al 2003;Thuillier et al 2005;Egidi et al 2006). Some studies have detected no significant change at all (LaBonte & Howard 1981;Brown & Christensen-Dalsgaard 1998;Wittmann 2003;Kuhn et al 2004;Badache-Damiani & Rozelot 2006). …”

Section: ϫ3mentioning

confidence: 97%

A Virial Theorem Investigation of Magnetic Variations in the Sun

Stothers

2006

ApJ

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The magnetic virial theorem is applied here to a long-standing astrophysical problem, namely, the sign of the Sun's radius change during the solar activity cycle. The solar radius is theoretically found to decrease around the time of maximum magnetic field strength, in agreement with the best available observational evidence. This theoretical prediction, although simply based, instills some confidence by explicitly satisfying the conservation of total energy.

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Section: ϫ3mentioning

confidence: 97%

A Virial Theorem Investigation of Magnetic Variations in the Sun

Stothers

2006

ApJ

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“…Data from the Michelson Doppler Imager (MDI) instrument onboard the Solar and Heliospheric Observatory (SoHo) cover the whole solar cycle 23 and show no evidence of secular trends in the solar radius, or variations attributable to the 11 year cycle. Systematic changes in the solar radius with the sunspot cycle must be smaller than 23 milliarcsec (mas) peak-to-peak (Kuhn et al 2004;Bush et al 2010). Solar radius variations for different instruments are plotted in Fig.…”

Section: Solar Radius Variabilitymentioning

confidence: 99%

Ground-based measurements of the solar diameter during the rising phase of solar cycle 24

Meftah

Corbard

Irbah

et al. 2014

A&A

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Context. For the past thirty years, modern ground-based time-series of the solar radius have shown different apparent variations according to different instruments. The origins of these variations may result from the observer, the instrument, the atmosphere, or the Sun. Solar radius measurements have been made for a very long time and in different ways. Yet we see inconsistencies in the measurements. Numerous studies of solar radius variation appear in the literature, but with conflicting results. These measurement differences are certainly related to instrumental effects or atmospheric effects. Use of different methods (determination of the solar radius), instruments, and effects of Earth's atmosphere could explain the lack of consistency on the past measurements. A survey of the solar radius has been initiated in 1975 by Francis Laclare, at the Calern site of the Observatoire de la Côte d'Azur (OCA). Several efforts are currently made from space missions to obtain accurate solar astrometric measurements, for example, to probe the long-term variations of solar radius, their link with solar irradiance variations, and their influence on the Earth climate. Aims. The Picard program includes a ground-based observatory consisting of different instruments based at the Calern site (OCA, France). This set of instruments has been named "Picard Sol" and consists of a Ritchey-Chrétien telescope providing full-disk images of the Sun in five narrow-wavelength bandpasses (centered on 393.37, 535.7, 607.1, 782.2, and 1025.0 nm), a Sun-photometer that measures the properties of atmospheric aerosol, a pyranometer for estimating a global sky-quality index, a wide-field camera that detects the location of clouds, and a generalized daytime seeing monitor allowing us to measure the spatio-temporal parameters of the local turbulence. Picard Sol is meant to perpetuate valuable historical series of the solar radius and to initiate new time-series, in particular during solar cycle 24. Methods. We defined the solar radius by the inflection-point position of the solar-limb profiles taken at different angular positions of the image. Our results were corrected for the effects of refraction and turbulence by numerical methods. Results. From a dataset of more than 20 000 observations carried out between 2011 and 2013, we find a solar radius of 959.78 ± 0.19 arcsec (696 113 ± 138 km) at 535.7 nm after making all necessary corrections. For the other wavelengths in the solar continuum, we derive very similar results. The solar radius observed with the Solar Diameter Imager and Surface Mapper II during the period 2011-2013 shows variations shorter than 50 milli-arcsec that are out of phase with solar activity.

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“…This is perhaps somewhat unsurprising-in our direct experience of seeing stellar disks, there is only the sun, which is very nearly a perfect sphere: on an average radius of 959 .28 ± 0 .15 (Kuhn et al 2004) there is only a variation of only 9.0 ± 1.8 mas (Rozelot et al 2003) from equator to pole, indicating an oblateness (b/a − 1) of less than 10 −5 . However, for a surprisingly non-trivial number of stars, this degree of oblateness is in excess of 20% and, in certain cases, even 30%.…”

Section: Introductionmentioning

confidence: 99%

Interferometric observations of rapidly rotating stars

Belle

2012

Astron Astrophys Rev

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Optical interferometry provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Through direct observation of rotationally distorted photospheres at sub-milliarcsecond scales, we are now able to characterize latitude dependencies of stellar radius, temperature structure, and even energy transport. These detailed new views of stars are leading to revised thinking in a broad array of associated topics, such as spectroscopy, stellar evolution, and exoplanet detection. As newly advanced techniques and instrumentation mature, this topic in astronomy is poised to greatly expand in depth and influence.

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On the Constancy of the Solar Diameter. II.

Cited by 97 publications

References 23 publications

A Virial Theorem Investigation of Magnetic Variations in the Sun

A Virial Theorem Investigation of Magnetic Variations in the Sun

Ground-based measurements of the solar diameter during the rising phase of solar cycle 24

Interferometric observations of rapidly rotating stars

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