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Pietro Bernasconi   Submitted: 2008-01-24 12:56

Variations in total solar irradiance (TSI) correlate well with changes in projected area of photospheric magnetic flux tubes associated with dark sunspots and bright faculae in active regions and network. This correlation does not, however, rule out possible TSI contributions from photospheric brightness inhomogeneities located outside flux tubes, and spatially correlated with them. Previous reconstructions of TSI report agreement with radiometry that seems to rule out significant ?extra-flux tube? contributions. We show that these reconstructions are more sensitive to the facular contrasts used than has been generally recognized. Measurements with the Solar Bolometric Imager (SBI) provide the first reliable support for the relatively high, wide-band, disc-center contrasts required to produce 10 % rms agreement. Longer-term bolometric imaging will be required to determine whether the small but systematic TSI residuals we see here are caused by remaining errors in spot and facular areas and contrasts, or by extra-flux tube brightness structures such as bright rings around sunspots, or ?convective stirring? around active regions.

Authors: P. Foukal; P. N. Bernasconi
Projects: None

Publication Status: Solar Physics, in press
Last Modified: 2008-01-25 08:22
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Advanced Automated Solar Filament Detection and Characterization Code: Description, Performance, and Results  

Pietro Bernasconi   Submitted: 2005-02-23 06:21

We present a code for automated detection, classification, and tracking of solar filaments in full-disk H-apha images that can contribute to Living With a Star science investigations and space weather forecasting. The program can reliably identify filaments; determine their chirality and other relevant parameters like filament area, length, and average orientation with respect to the equator. It is also capable of tracking the day-by-day evolution of filaments while they travel across the visible disk. The code was tested by analyzing daily Hα images taken at the Big Bear Solar Observatory from mid 2000 until beginning of 2005. It identified and established the chirality of thousands of filaments without human intervention. We compared the results with a list of filament proprieties manually compiled by Pevtsov et al. (2003) over the same period of time. The computer list matches Pevtsov’s list with a 72% accuracy. The code results confirm the hemispheric chirality rule stating that dextral filaments predominate in the north and sinistral ones predominate in the south. The main difference between the two lists is that the code finds significantly more filaments without an identifiable chirality. This may be due to a tendency of human operators to be biased, thereby assigning a chirality in less clear cases, while the code is totally unbiased. We also have found evidence that filaments obeying the chirality rule tend to be larger and last longer than the ones that do not follow the hemispherical rule. Filaments adhering to the hemispheric rule also tend to be more tilted toward the equator between latitudes 10° and 30°, than the ones that do not.

Authors: Bernasconi, P.N, Rust, D.M., Hakim, D.
Projects: None

Publication Status: accepted for publication in Solar Physics
Last Modified: 2005-02-23 06:21
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Broadband Measurements of Facular Photometric Contrast with the Solar Bolometric Imager  

Pietro Bernasconi   Submitted: 2004-06-30 08:52

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 which imaged the Sun with spectrally constant response between about 0.31 and 2.6 microns. Our curve of facular contrast versus limb distance agrees well with values obtained by black-body correction of monochromatic measurements. This decreases uncertainty in the facular irradiance contribution, which limits searches for other possible mechanisms of solar luminosity variation, besides changing photospheric magnetism.

Authors: Foukal, P., Bernasconi, P. N., Eaton, H. A. C., and Rust, D. M.
Projects: None

Publication Status: Published in ApJ 611, L57 (2004)
Last Modified: 2004-07-22 15:04
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The Solar Bolometric Imager  

Pietro Bernasconi   Submitted: 2004-04-06 11:39

The balloon-borne Solar Bolometric Imager (SBI) will provide the first bolometric (integrated light) maps of the solar photosphere. It will evaluate the photometric contribution of magnetic structures more accurately than has been possible with spectrally selective imaging over restricted wavebands. More accurate removal of the magnetic feature contribution will enable us to determine if solar irradiance variation mechanisms exist other than the effects of photospheric magnetism. The SBI detector is an array of 320x240 ferro-electric thermal IR elements whose spectral absorptance has been extended and flattened by a deposited layer of gold-black. The telescope itself is a 30-cm Dall-Kirkham design with uncoated primary and secondary pyrex mirrors. The combination of telescope and bolometric array provides an image of the Sun with a flat spectral response between 0.28 μm and 2.6 μm, over a field of view of 917x687 arcsec, and a pixel size of 2.8 arcsec. After a successful set of ground-based tests, the instrument is being readied for a one-day stratospheric balloon flight that will take place in September 2003. The observing platform will be the gondola previously used for the Flare Genesis Experiment (FGE), retrofitted to house and control the SBI telescope and detector. The balloon flight will enable SBI to image over essentially the full spectral range accepted by non-imaging space-borne radiometers such as ACRIM, making the data sets complementary. The SBI flight will also provide important engineering data to validate the space worthiness of the novel gold-blackened thermal array detectors, and verify the thermal performance of the SBI's uncoated optics in a vacuum environment.

Authors: Bernasconi, P. N., Eaton, H. A. C., Foukal, P., Rust, D. M.
Projects:

Publication Status: Published in Advances in Space Research 33, 1746 (2004)
Last Modified: 2004-05-26 08:41
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Advanced Automated Solar Filament Detection and Characterization Code: Description, Performance, and Results
Broadband Measurements of Facular Photometric Contrast with the Solar Bolometric Imager
The Solar Bolometric Imager

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