The main goal of this proposal is to plan coordinated observations between HINODE instruments and the SST and DOT telescopes on La Palma (Canary Islands). These observations will produce a comprehensive data set of high precision, high resolution spectro-polarimetric and imaging measurements for the study of
the magnetic fine structure of the solar atmosphere and its effects on solar irradiance variations.
In particular, we propose to investigate the photometric and physical properties of small-size magnetic elements observed on quiet Sun and facular regions. Analysis of the radiative emission measured on the observed regions, together with results derived from spectro-polarimetric inversions, and outcomes of multi-dimensional MHD simulations, will allow us to depict the thermal stratification in regions with different flux element aggregations and improve our understanding of the mechanisms that drive irradiance variations.
Recent results of solar irradiance measurements, both spectral and total emission, have called current knowledge on the matter into question (Domingo et al. 2009; Froehlich 2009; Harder et al. 2009; Steinhilber 2010; Ball et al. 2011; Krivova, Solanki, Schmutz 2011). This is mainly due to lack of detailed knowledge of the temperature stratification in magnetic regions and contribution of quiet Sun regions to total irradiance variations. Indeed, variations of spectral irradiance have been proposed to reflect temporal variations of the stratification of magnetic features. This hypothesis is supported by results from observations of small-size magnetic features (Ishikawa et al. 2007) and flux tube models recently developed (Criscuoli & Rast 2009), which show that physical properties of magnetic elements depend also on their environment and their degree of aggregation. Nevertheless, attempts to reproduce irradiance with constraints derived from these kind of measurements and flux tube models are still lacking. On the other hand, quiet Sun regions have been also proposed to affect total irradiance variations, but evaluation of their contribution, mostly due to effects of unresolved magnetic fields, is particularly controversial.
To contribute to this topic of research we plan to analyze observations acquired with CRISP at FeI 557.6 and FeI 630.2 nm, and with SOT/SP at FeI 630.2 nm on both quiet and facular regions. The analysis of the variation of the shape of the first line, which is insensitive to magnetic field but very sensitive to temperature gradients, on quiet and magnetic regions, and inversions of spectro-polarimetric data acquired in the second line, from both SST and HINODE, will allow us to investigate the physical parameters of the photosphere in the various regions.
In particular, comparison of results from spectro-polarimetric observations in the FeI 630.2 nm in various regions will allow us to investigate the variation of the properties of magnetic regions with their degree of aggregation. Comparison of results from this analysis with detailed spectral synthesis from multidimensional MHD simulations of the solar photosphere will improve our knowledge of the physical mechanisms that drive irradiance variations. The analysis of data contemporaneously acquired with DOT, imaging (approximately) the same FOV, will allow us to investigate the effects of small-size magnetic elements and of their aggregation on measurements of photometric properties of the quiet Sun and magnetic features at various atmospheric heights.
Joint observations with HINODEfs EIS and XRT for corona are also required, to provide us with complementary information to achieve our objectives.
Ball, W. T., Unruh, Y. C., Krivova, N. A., Solanki, S., Harder, J. W. 2011, A&A, 530, A71
Criscuoli, S. & Rast, M. 2009 A&A, 495, 621
Domingo, V.; Ermolli, I.; Fox, P.; Fröhlich, C.; Haberreiter, M. et al. 2009 SSRV 145, 337
Froehlich , C. 2009, A&A 501, L27
Harder, J. W., Fontenla, J. M., Pilewskie, P., Richard, E. C., Woods,. N. 2009, GeoRL 3607801
Krivova, N. A., Solanki, S. K., Schmutz, W. 2011, A&A, 529, A81
Ishikawa, R., Tsuneta, S., Kitakoshi, Y., Katsukawa, Y., Bonet, J.A.et al.2007 A&A 472, 911
Steinhilber, F. 2010, A&A 523, A39