Photometric determination of facular contrasts near the solar disk center

Lawrence, J. K.; Chapman, G. A.; Herzog, A. D.

doi:10.1086/165973

Cited by 26 publications

(13 citation statements)

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“…We find that the average contrast of facular regions is essentially positive at the disk center in the PSPT blue and red bands. This result agrees with those previously obtained by authors who do not use identification methods based on magneticfield flux thresholding (Lawrence 1988;Lawrence Chapman & Herzog 1988;Ahern & Chapman 2000;Walton et al 2003). In contrast, results obtained with these last methods (Foukal et al 1990;Topka et al 1992;Ortiz et al 2002Ortiz et al , 2006 show that facular regions at photospheric levels have negative contrasts at the disk center with respect to the neighboring quiet regions.…”

Section: Contrast CLVsupporting

confidence: 93%

“…Moreover, the distance between the measured curve and the one obtained with the approximation increases from the limb toward the disk center. These results confirm earlier findings by Chapman & Mc Guire (1977) and Lawrence et al (1988) from observations of smaller samples of facular features. Thus, significant errors may be introduced when monochromatic measurements of facular contrasts are used to estimate bolometric luminosity (Foukal et al 2004) or irradiance excess.…”

Section: Wavelength Size and Time Dependencessupporting

confidence: 92%

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Photometric properties of facular features over the activity cycle

Ermolli¹,

Criscuoli

Centrone³

et al. 2007

A&A

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Aims. We have analyzed the contrast of facular features identified in a large dataset of PSPT full-disk photometric images and SoHO/MDI magnetograms, obtained from 1998 to 2005. The aim of this work is to contribute to the improvement of semi-empirical atmospheric models and of irradiance studies and to understand the reasons for the controversial results of facular contrast already presented in the literature. Methods. We used different identification methods to analyze their effects upon the results obtained. We also analyzed the effects of the limited information content in the analyzed images. Results. We show that selection effects associated with the identification method may produce significant differences in the results. The facular contrast is not only a function of both selection methods and the heliocentric angle, but also of feature size, activity level, and content of the analyzed images. Comparisons of the results obtained with computations of the most recent semi-empirical atmospheric models of facular features show that these models reproduce limb-angle corrected contrast measurements with an offset up to ≈1% from the disk center to µ = 0.3.

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Section: Contrast CLVsupporting

confidence: 93%

Section: Wavelength Size and Time Dependencessupporting

confidence: 92%

Photometric properties of facular features over the activity cycle

Ermolli¹,

Criscuoli

Centrone³

et al. 2007

A&A

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“…Our most interesting finding is the remarkable agreement between the SBI curve and a bolometric contrast curve shown in Figure 4, calculated (J. K. Lawrence 2004, private communication) using a simple blackbody correction to the monochromatic facular contrasts measured at a similar angular resolution by Lawrence et al (1988). In this correction, the monochromatic contrast in a green (524.5 nm) or red (626.4 nm) passband of width 0.15 nm was used to calculate the blackbody temperature from the Planck function.…”

Section: Discussionsupporting

confidence: 53%

Broadband Measurements of Facular Photometric Contrast Using the Solar Bolometric Imager

Foukal

Bernasconi

Eaton

et al. 2004

ApJ

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We present the first photometric measurements of solar faculae in broadband light. Our measurements were made during the recent flight of the Solar Bolometric Imager (SBI), a 30 cm balloon-borne telescope that imaged the Sun with a spectrally constant response between about 0.31 and 2.6 mm. Our curve of facular contrast versus limb distance agrees well with values obtained by the blackbody correction of monochromatic measurements. This decreases uncertainty in the facular irradiance contribution, which limits searches for other possible mechanisms of solar luminosity variation, besides changes of photospheric magnetism.

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“…Various studies examining the photometric contrast of faculae, as identified in calcium line images, reported positive values near disc centre (Lawrence et al 1988;Walton et al 2003;Foukal et al 2004). The apparent divergence between the findings of these works, and the largely negative contrast near disc centre reported here (Fig.…”

Section: Facular Contribution To Variation In Solar Irradiancecontrasting

confidence: 52%

Intensity contrast of solar network and faculae

Yeo

Solanki

Krivova

2013

A&A

105

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Aims. This study aims at setting observational constraints on the continuum and line core intensity contrast of network and faculae, specifically, their relationship with magnetic field and disc position. Methods. Full-disc magnetograms and intensity images by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) were employed. Bright magnetic features, representing network and faculae, were identified and the relationship between their intensity contrast at continuum and line core with magnetogram signal and heliocentric angle examined. Care was taken to minimize the inclusion of the magnetic canopy and straylight from sunspots and pores as network and faculae.Results. In line with earlier studies, network features, on a per unit magnetic flux basis, appeared brighter than facular features. Intensity contrasts in the continuum and line core differ considerably, most notably, they exhibit opposite centre-to-limb variations. We found this difference in behaviour to likely be due to the different mechanisms of the formation of the two spectral components. From a simple model based on bivariate polynomial fits to the measured contrasts we confirmed spectral line changes to be a significant driver of facular contribution to variation in solar irradiance. The discrepancy between the continuum contrast reported here and in the literature was shown to arise mainly from differences in spatial resolution and treatment of magnetic signals adjacent to sunspots and pores. Conclusions. HMI is a source of accurate contrasts and low-noise magnetograms covering the full solar disc. For irradiance studies it is important to consider not just the contribution from the continuum but also from the spectral lines. In order not to underestimate long-term variations in solar irradiance, irradiance models should take the greater contrast per unit magnetic flux associated with magnetic features with low magnetic flux into account.

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Photometric determination of facular contrasts near the solar disk center

Cited by 26 publications

References 0 publications

Photometric properties of facular features over the activity cycle

Photometric properties of facular features over the activity cycle

Broadband Measurements of Facular Photometric Contrast Using the Solar Bolometric Imager

Intensity contrast of solar network and faculae

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