Photometric properties of facular features over the activity cycle

Ermolli, I.; Criscuoli, S.; Centrone, Mauro; Giorgi, F.; Penza, V.

doi:10.1051/0004-6361:20065995

Cited by 58 publications

(60 citation statements)

References 42 publications

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“…The apparent divergence between the findings of these works, and the largely negative contrast near disc centre reported here (Fig. 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.…”

Section: Facular Contribution To Variation In Solar Irradiancecontrasting

confidence: 73%

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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Section: Facular Contribution To Variation In Solar Irradiancecontrasting

confidence: 73%

Intensity contrast of solar network and faculae

Yeo

Solanki

Krivova

2013

A&A

105

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“…In order to identify the Ca II K features corresponding to facular regions we applied the Ktr decomposition method described by Ermolli et al (2007a) to contrast images. This method is based on a combination of pixel contrast and connectivity.…”

Section: Preliminary Resultsmentioning

confidence: 99%

The digitized archive of the Arcetri spectroheliograms. Preliminary results from the analysis of Ca II K images

Ermolli

Marchei

Centrone

et al. 2009

A&A

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Context. The increasing interest in the recovery of historic data and the availability of new hardware resources is leading to projects to digitize photographic archives of astronomical observations. In addition to preservation, solar archives are digitized because the observations stored in such archives have the potential of providing unique information about solar magnetism, which can improve knowledge about long-term solar changes. Aims. The solar tower of the Arcetri Astrophysical Observatory produced synoptic observations of the solar atmosphere from 1926 to 1974. The photographic archive contains about 13 000 plates of full-disk Ca II K and H α spectroheliograms acquired during about 5000 observing days. The program for the digitization and distribution of the images of this archive was carried out at the Rome Astronomical Observatory and is now complete. Methods. Nearly 13 000 plates were scanned with a commercial device and stored on DVD, as well as in a database accessible online. Image processing was developed for the reduction of the data and their photographic calibration. Results. The obtained digital archive provides the astronomical community with the Arcetri historical solar observations and with measurements of solar features identified in such observations. As an example, we show some preliminary results concerning the temporal variability of facular regions identified in the time-series of Ca II K observations. Conclusions. Existing programs studying solar activity and variability, as well as new scientific projects, will benefit from the Arcetri digital archive, since it extends the temporal baseline of digital full-disk solar observations, and it provides data for the inter-calibration of results obtained from measurements performed in similar observations.

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“…The identification method applied was Ktr, which was described by Ermolli et al (2007a). We found that the number of features identified in restored images was remarkably larger than those found in the original data, the increase being approximately 500%, 300%, and 35% for the SD-PSPT, PSPT, and MW data sets, respectively.…”

Section: Contrast Of Solar Featuresmentioning

confidence: 93%

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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Photometric properties of facular features over the activity cycle

Cited by 58 publications

References 42 publications

Intensity contrast of solar network and faculae

Intensity contrast of solar network and faculae

The digitized archive of the Arcetri spectroheliograms. Preliminary results from the analysis of Ca II K images

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

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