Broadband Measurements of Facular Photometric Contrast Using the Solar Bolometric Imager

Foukal, P.; Bernasconi, P. N.; Eaton, H.; Rust, David M.

doi:10.1086/423787

Cited by 27 publications

(24 citation statements)

References 18 publications

(22 reference statements)

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“…In particular, the simultaneous use of five different identification methods applied to the same sample of data allows us to explain some of the differences existing among previously reported results. Figure 11 shows the comparison of the results we obtained with those recently presented from similar studies Ortiz et al 2002;Walton et al 2003;Foukal et al 2004). We find that the average contrast of facular regions is essentially positive at the disk center in the PSPT blue and red bands.…”

Section: Contrast CLVsupporting

confidence: 71%

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: 71%

Photometric properties of facular features over the activity cycle

Ermolli¹,

Criscuoli

Centrone³

et al. 2007

A&A

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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: 49%

“…(3) and (4), scaled by B l μ /15 −1.85 and integrated over B l /μ = 15 G to 800 G, at 0.1 day intervals taking μ from the trajectory of NOAA 7986 estimated earlier. The resulting time series were then scaled by μ (to correct for the CLV of projected area on the solar disc) and the limb darkening function from Foukal et al (2004). Given the approximate manner of this derivation, the results are non-quantitative.…”

Section: Facular Contribution To Variation In Solar Irradiancementioning

confidence: 99%

“…9) and in the similar studies listed in Table 2, where network and faculae were characterized by the magnetogram signal, arises from the different selection methods (Ermolli et al 2007). Significantly, the results of Foukal et al (2004) were based on near total light broadband measurements. From the statistical analysis of an extensive catalogue of fulldisc photometric observations obtained with the SFO/CFDT1, Walton et al (2003) found contrast, in a continuum passband (i.e., negligible spectral line contribution) in the visible red, averaged over each facular region (as identified in the Ca II K) to be positive (∼0.005) near disc centre.…”

Section: Facular Contribution To Variation In Solar Irradiancementioning

confidence: 99%

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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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“…However, almost every facular contrast measurement found in the literature is monochromatic. Foukal et al (2004) have recently shown that this problem can be circumvented by applying a blackbody correction to monochromatic facular contrasts, thus converting such measurements a posteriori into bolometric contrasts.…”

Section: Comparison With Previous Observationsmentioning

confidence: 99%

The intensity contrast of solar photospheric faculae and network elements

Ortiz¹,

Domingo²

2006

A&A

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We studied the radiative properties of small magnetic elements (active region faculae and the network) during the rising phase of solar cycle 23 from 1996 to 2001, determining their contrasts as a function of heliocentric angle, magnetogram signal, and the solar cycle phase. We combined near-simultaneous full disk images of the line-of-sight magnetic field and photospheric continuum intensity provided by the MDI instrument on board the SOHO spacecraft. Sorting the magnetogram signal into different ranges allowed us to distinguish between the contrast of different magnetic structures. We find that the contrast center-to-limb variation (CLV) of these small magnetic elements is independent of time with a 10% precision, when measured during the rising phase of solar cycle 23. A 2-dimensional empirical expression for the contrast of photospheric features as a function of both the position on the disk and the averaged magnetic field strength was determined, showing its validity through the studied time period. A study of the relationship between magnetogram signal and the peak contrasts shows that the intrinsic contrast (maximum contrast per unit of magnetic flux) of network flux tubes is higher than that of active region faculae during the solar cycle.

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Broadband Measurements of Facular Photometric Contrast Using the Solar Bolometric Imager

Cited by 27 publications

References 18 publications

Photometric properties of facular features over the activity cycle

Photometric properties of facular features over the activity cycle

Intensity contrast of solar network and faculae

The intensity contrast of solar photospheric faculae and network elements

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