The radius of the Sun at centimeter waves and the brightness distribution across the disk

Fürst, E.; Hirth, W.; Lantos, P.

doi:10.1007/bf00174532

Cited by 17 publications

(9 citation statements)

References 8 publications

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“…Moreover, the correlation of radius with sunspot number is seen to decrease significantly until it becomes anti-correlated. The mean radius values in Table 1 are smaller than those expected from previous measurements at other radio wavelengths (Bachurin 1983;Costa et al 1985Costa et al , 1999Furst et al 1979) where the radius was calculated at the point where the brightness temperature was half the value of the quiet Sun brightness temperature. Previous observations, however, were performed by single dish telescopes that have beams many times wider than the 10 synthesized beam of the NoRH interferometer.…”

Section: Discussioncontrasting

confidence: 60%

Radius variations over a solar cycle

Selhorst

Silva

Costa

2004

A&A

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Abstract.We report the analysis of solar radius determination for more than 3800 maps at 17 GHz from the Nobeyama Radioheliograph (NoRH) over a solar cycle (1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003). The aim of this work is to determine the radius dependence on solar activity at 17 GHz. This study was divided into two parts: (i) the mean solar radius calculated using the coordinates around the solar limb, and (ii) the mean polar radius using only the coordinates within ±30• of the poles. While a good correlation between the mean solar radius and the sunspot number was found, the polar radius variations were found to be anti-correlated with sunspot number during this period. Nevertheless, the results showed the polar radius to have the same temporal evolution as the polar limb brightening at 17 GHz throughout the solar cycle, indicating a close relationship between them. A variation of 3 was found for the mean radius from minimum to solar maximum, while the polar radius presented a variation of 1 during the same period. Moreover, the distribution of center-to-limb distances showed a large increase in the equatorial regions with a double peaked profile during periods of maximum activity. From this work, we have concluded that the measurements of the solar radius at radio frequencies are influenced by various solar features, which make the definition of the solar radius a difficult task. Despite this, the study of solar radius is able to provide a good indication of the changes in the solar atmosphere.

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Section: Discussioncontrasting

confidence: 60%

Radius variations over a solar cycle

Selhorst

Silva

Costa

2004

A&A

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“…Selhorst, Silva e Costa (2004) 17 12.3 ± 1.1 976.6 ± 1.5 Costa, Homor e Kaufmann (1986) 22 16.0 ± 0.6 981.7 ± 0.8 Fürst, Hirth e Lantos (1979) 25 14 ± 3 979 ± 4 Wrixon (1970) 30 14 ± 3 979 ± 4 Pelyushenko e Chernyshev (1983) 35 14 ± 2 979 ± 3 Costa, Homor e Kaufmann (1986) 44 12.5 ± 1.0 978.1 ± 1.3 Costa et al (1999) 48 17.4 ± 1.4 983.6 ± 1.9 Pelyushenko e Chernyshev (1983) 48 9.7 ± 2.1 973.1 ± 2.9 Coates (1958) 70 7 ± 3 969 ± 5 Kisliakov et al (1975) 74 5 ± 3 967 ± 4 Swanson (1973) Based on temporal observational series throughout many years, the optical solar radius is not constant and shows slight variations between 0.01 ′′ and 0.50 ′′ approximately. Such variations are correlated with the 11-year solar activity cycle.…”

Section: Authorsmentioning

confidence: 99%

“…Frequency Altitude Radius (GHz) (10 6 m) (arcsec) Fürst, Hirth e Lantos (1979) 3 80 ± 12 1070 ± 17 Fürst, Hirth e Lantos (1979) 5 44 ± 6 1020 ± 9 Bachurin (1983) 9 22 ± 1 989 ± 2 Fürst, Hirth e Lantos (1979) 11 23 ± 4 991 ± 5 Bachurin (1983) 13 30 ± 1 989 ± 2 Wrixon (1970) 16 22 ± 3 990 ± 4…”

Section: Authorsmentioning

confidence: 99%

Solar Radius at Subterahertz Frequencies and Its Relation to Solar Activity

Menezes

Válio

2017

Sol Phys

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The Sun emits radiation at several wavelengths of the electromagnetic spectrum. In the optical band, the solar radius is 695,700 km and this is what defines the photosphere, the visible surface of the Sun. However, as the altitude increases, the electromagnetic radiation is produced at other frequencies, causing the solar radius to change as function of wavelength. These measurements enable a better understanding of the solar atmosphere and the radius dependence on the solar cycle is a good indicator of the changes that occur in the atmospheric structure. We measure the solar radius at the subterahertz frequencies of 0.212 and 0.405 THz -i.e., the altitude where these emissions are primarily generated -and also analyse the radius variation over the 11-year solar activity cycle. For this, we used radio maps of the solar disk for the period between 1999 and 2017, reconstructed from daily scans made by the Solar Submillimeterwave Telescope (SST), installed at El Leoncito Astronomical Complex (CASLEO) in the Argentinean Andes. Our measurements yield radii of 966.5 ′′ ± 2.8 ′′ for 0.2 THz and 966.5 ′′ ± 2.7 ′′ for 0.4 THz. This implies a height of (5.0 ± 2.0 × 10 6 ) m above the photosphere. Furthermore, we also observed strong anti-correlation between the radius variation and the solar activity at both frequencies.

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“…Nevertheless, many authors have also reported the absence of such brightening, for example at 25 GHz (Furst et al 1979), 35 GHz (Kawabata et al 1980), 88 GHz (Simon & Zirin 1969;Joensen et al 1974), 98 GHz (Kosugi et al 1986), 100 GHz (Belkora et al 1992), and 114 GHz (Wannier et al 1983). Usually, the presence of jets, called spicules, has been blamed Send offprint requests to: C. L. Selhorst, e-mail: caius@craam.mackenzie.br for the lack of brightening detection (Simon & Zirin 1969;Wannier et al 1983).…”

Section: Introductionmentioning

confidence: 99%

Temporal and angular variation of the solar limb brightening at 17 GHz

Selhorst

Silva

Costa

et al. 2003

A&A

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Abstract. In order to better understand the atmosphere structure of the Sun, we have analyzed over 3000 daily maps of the Sun taken at 17 GHz from the Nobeyama Radioheliograph (NoRH) from 1992 through 2001, focusing on the excess brightness temperature observed near the limb. The purpose of this work is to characterize the limb brightness in two ways: (i) study the temporal variation of the intensity and radial width of polar brightening; and (ii) measure the brightness distribution along the limb as a function of position angle and compare it with data at other wavelengths throughout the solar cycle. The mean intensity of the polar regions were found to be approximately 13% and 14% above quiet Sun levels at the North and South poles, respectively. Moreover, the polar brightenings are strongly anti-correlated with solar activity (as measured by sunspot number). The radial width of the excess brightness is slightly over 1 arcmin for both polar regions. Only a small variation with the solar cycle was observed during the decline of last maximum, that is, the Southern polar brightening was found to be both wider and brighter than the Northern one for the 23rd cycle. As for the angular variation of the limb brightening, for a month during a period of minimum activity, it reaches 25% above quiet Sun levels at the poles, ∼15% near the equator, and 10% at intermediate regions. Hα images also show brightening enhancements at the polar regions for the same period. We also found a strong anti-correlation between the radio polar brightenings and the coronal holes seen in soft X-ray images from 1992 to 2001. There seems to be a strong association of the radio limb brightening at 17 GHz with faculae. The implications of these correlations are discussed.

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The radius of the Sun at centimeter waves and the brightness distribution across the disk

Cited by 17 publications

References 8 publications

Radius variations over a solar cycle

Radius variations over a solar cycle

Solar Radius at Subterahertz Frequencies and Its Relation to Solar Activity

Temporal and angular variation of the solar limb brightening at 17 GHz

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