Solar luminosity fluctuations during the disk transit of an active region

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

doi:10.1086/163160

Cited by 26 publications

(12 citation statements)

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“…The color dependence of facular contrasts is important when one wishes to convert irradiance or luminosity measurements made in a narrow wavelength band to estimated bolometric values. Leaving aside the facular excess emission in the ultraviolet (Lean, 1984), which may amount to some 5~o of overall facular energy output (Chapman, Herzog, and Lawrence, 1986), the simplest approach is to assume that the quiet Sun photosphere and the facular patches radiate as black-bodies with the faculae at a slightly elevated temperature. Differentiation of the Planck function in the Wien approximation gives (see Chapman and McGuire, 1977) AI/I = AB/B = hcAT/kT 2 .…”

Section: Discussionmentioning

confidence: 99%

Multi-color photometric observations of facular contrasts

Lawrence

1988

Sol Phys

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We have analyzed high-resolution, digital, photometric images of solar active regions made at various center-limb positions on 21-24 July, 1983. The images were made at three continuum wavelengths: 5245 ~ in the green (bandpass 1.5 A), 6264 A in the red (ban@ass 1.5 A), 10 000 ]~ in the infrared (bandpass 3 A.), and also at 8662 A in the Car1 infrared line (bandpass 3/i 0. In all continuum colors, the contrasts of facular patches, as opposed to individual facular elements, appear to behave as linear functions of 1/cos 0, where 0 is the heliocentric angle (# = 0 at the limb, 1 at disk center). The relative contrasts in the different continuum colors are roughly proportional to (wavelength)-1, as expected from a Planck distributioin in the Wien approximation. The observed variation of the relative contrasts with center-limb position is compared to two simple theoretical models.

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Section: Discussionmentioning

confidence: 99%

Multi-color photometric observations of facular contrasts

Lawrence

1988

Sol Phys

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“…Brahde 1972;Hansen 1973;Albregtsen & Maltby 1981;Lawrence et al 1985;Barducci et al 1972;Martínez Pillet 1992). Toner & Jefferies (1993) and Toner et al (1997) proposed a technique based on the estimate of the zero crossing of the Hankel transform for observed images.…”

Section: Introductionmentioning

confidence: 99%

Stray-light restoration of full-disk CaII K solar observations: a case study

Criscuoli¹,

Ermolli²

2008

A&A

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Aims. We investigate whether restoration techniques, such as those developed for application to current observations, can be used to remove stray-light degradation effects on archive CaII K full-disk observations. We analyze to what extent these techniques can recover homogeneous time series of data. Methods. We develop a restoration algorithm based on a method presented by Walton & Preminger (1999, ApJ, 514, 959). We apply this algorithm to data for both present-day and archive CaII K full-disk observations, which were acquired using the PSPT mounted at the Rome Observatory, or obtained by digitization of Mt Wilson photographic-archive spectroheliograms. Results. We show that the restoring algorithm improves both spatial resolution and photometric contrast of the analyzed solar observations. We find that the improvement in spatial resolution is similar for analyzed recent and archive data. On the other hand, the improvement of photometric contrast is quite poor for the archive data, with respect to the one obtained for the present-day images. We show that the quality of restored archive data depends on the photographic calibration applied to the original observations. In particular, photometry can be recovered with a restoring algorithm if the photographic-calibration preserves the intensity information stored in the original data, principally outside the solar-disk observations.

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“…We need to know the true centre-to-limb variation for each wavelength region of interest. Following other recent works (see, e.g., Lawrence et al, 1985) we use the 5th degree polynomial fit given by Pierce and Slaughter (1977), who accounted for the stray-light correction. This polynomial representation of the centre-tolimb variation very well fits our observations (in regions far from the limb) even before we apply any correction to the data.…”

Section: Evaluation Of the Functions ~G(r B) And (Ijl(r B)mentioning

confidence: 99%

“…This procedure has been used mainly in three different research fields in solar physics. The most common has been the correction of sunspot intensities (Kneer and Mattig, 1968;Wittmann and SchrOter, 1969;Mattig, 1971;Maltby and Staveland, 1971;Brahde, 1972Brahde, , 1974Mullan, 1973;Mykland, 1973 ;Albregtsen and Maltby, 1981 ;Sobotka, 1983 ;Lawrence et al, 1985;Jefferies and Duvall, 1991); secondly, to correct centre-to-limb observations (Pierce and Slaughter, 1977;Petro et al, 1984) and finally for Doppler measurements (Albregtsen and Andersen, 1985 ;Andersen, 1985Andersen, , 1986. In spite of all the work cited, we still lack a procedure of stray-light correction applicable to a digitized sunspot image.…”

Section: Introductionmentioning

confidence: 99%

Stray-light effects on the solar intensity distribution

Pillet

1992

Sol Phys

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A description of the stray-light problem based on a radiative transfer approach is presented. The two-dimensional convolution that describes the effect of the stray-light is recovered in this formalism. On the other hand, the normalization condition used for the spread function in our procedure is different from the one used in the old approach. The controversy raised by the old normalization condition is satisfactorily eliminated within our description. We have applied our formalism to aureole observations and derived the spread function parameters. These parameters are similar to the ones used in the standard approach but now a new quantity appears. It is derived consistently within our formalism and it allows a description of different atmospheric quality conditions without changing the actual shape of the spread function. This possibility is also a new characteristic of our formalism that has no analogy to the old one. Finally, the information derived from limb profiles is used to correct sunspot images. The correction does not need to make any assumption about the shape of the spot but it uses the information contained on the image itself. It is shown how, for large spots, the contamination of stray-light can be considered as an added constant level of light throughout the umbra.

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Solar luminosity fluctuations during the disk transit of an active region

Cited by 26 publications

References 0 publications

Multi-color photometric observations of facular contrasts

Multi-color photometric observations of facular contrasts

Stray-light restoration of full-disk CaII K solar observations: a case study

Stray-light effects on the solar intensity distribution

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