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Vigorous convection in a sunspot granular light bridge
Lagg, Andreas,Solanki, Sami K.,van Noort, Michiel,Danilovic, Sanja Springer-Verlag 2014 Astronomy and astrophysics Vol.568 No.1
<P>Context. Light bridges are the most prominent manifestation of convection in sunspots. The brightest representatives are granular light bridges composed of features that appear to be similar to granules. Aims. An in-depth study of the convective motions, temperature stratification, and magnetic field vector in and around light bridge granules is presented with the aim of identifying similarities and differences to typical quiet-Sun granules. Methods. Spectropolarimetric data from the Hinode Solar Optical Telescope were analyzed using a spatially coupled inversion technique to retrieve the stratified atmospheric parameters of light bridge and quiet-Sun granules. Results. Central hot upflows surrounded by cooler fast downflows reaching 10 km s <SUP>− 1</SUP> clearly establish the convective nature of the light bridge granules. The inner part of these granules in the near surface layers is field free and is covered by a cusp-like magnetic field configuration. We observe hints of field reversals at the location of the fast downflows. The quiet-Sun granules in the vicinity of the sunspot are covered by a low-lying canopy field extending radially outward from the spot. Conclusions. The similarities between quiet-Sun and light bridge granules point to the deep anchoring of granular light bridges in the underlying convection zone. The fast, supersonic downflows are most likely a result of a combination of invigorated convection in the light bridge granule due to radiative cooling into the neighboring umbra and the fact that we sample deeper layers, since the downflows are immediately adjacent to the slanted walls of the Wilson depression.</P>
FULLY RESOLVED QUIET-SUN MAGNETIC FLUX TUBE OBSERVED WITH THE SUNRISE/IMAX INSTRUMENT
Lagg, A.,Solanki, S. K.,Riethmü,ller, T. L.,Martí,nez Pillet, V.,Schü,ssler, M.,Hirzberger, J.,Feller, A.,Borrero, J. M.,Schmidt, W.,del Toro Iniesta, J. C.,Bonet, J. A.,Barthol, P.,Berk IOP Publishing 2010 ASTROPHYSICAL JOURNAL LETTERS - Vol.723 No.2
Probing deep photospheric layers of the quiet Sun with high magnetic sensitivity
Lagg, A.,Solanki, S. K.,Doerr, H.-P.,Martí,nez Gonzá,lez, M. J.,Riethmü,ller, T.,Collados Vera, M.,Schlichenmaier, R.,Orozco Suá,rez, D.,Franz, M.,Feller, A.,Kuckein, C.,Schmidt, EDP Sciences 2016 Astronomy and astrophysics Vol.596 No.-
Properties of solar plage from a spatially coupled inversion of Hinode SP data
Buehler, D.,Lagg, A.,Solanki, S. K.,van Noort, M. EDP Sciences 2015 Astronomy and astrophysics Vol.576 No.-
<P>Aims. The properties of magnetic fields forming an extended plage region in AR10953 were investigated. Methods. Stokes spectra of the Fe I line pair at 6302Å recorded by the spectropolarimeter aboard the Hinode satellite were inverted using the SPINOR code. The code performed a 2D spatially coupled inversion on the Stokes spectra, allowing the retrieval of gradients in optical depth within the atmosphere of each pixel, whilst accounting for the effects of the instrument’s PSF. Consequently, no magnetic filling factor was needed. Results. The inversion results reveal that plage is composed of magnetic flux concentrations (MFCs) with typical field strengths of 1520G at log?(τ) = −0.9 and inclinations of 10°15°. The MFCs expand by forming magnetic canopies composed of weaker and more inclined magnetic fields. The expansion and average temperature stratification of isolated MFCs can be approximated well with an empirical plage thin flux tube model. The highest temperatures of MFCs are located at their edges in all log(τ) layers. Whilst the plasma inside MFCs is nearly at rest, each is surrounded by a ring of downflows of on average 2.4 km s<SUP>−1</SUP> at log(τ) = 0 and peak velocities of up to 10 km s<SUP>−1</SUP>, which are supersonic. The downflow ring of an MFC weakens and shifts outwards with height, tracing the MFC’s expansion. Such downflow rings often harbour magnetic patches of opposite polarity to that of the main MFC with typical field strengths below 300 G at log?(τ) = 0. These opposite polarity patches are situated beneath the canopy of their main MFC. We found evidence of a strong broadening of the Stokes profiles in MFCs and particularly in the downflow rings surrounding MFCs (expressed by a microturbulence in the inversion). This indicates the presence of strong unresolved velocities. Larger magnetic structures such as sunspots cause the field of nearby MFCs to be more inclined.</P>
Xu, Z.,Lagg, A.,Solanki, S.,Liu, Y. IOP Publishing 2012 The Astrophysical journal Vol.749 No.2
<P>Vector magnetic fields of an active region filament in the photosphere and upper chromosphere are obtained from spectro-polarimetric observations recorded with the Tenerife Infrared Polarimeter (TIP II) at the German Vacuum Tower Telescope. We apply Milne-Eddington inversions on full Stokes vectors of the photospheric Si I 1082.7 nm and the upper chromospheric He I triplet at 1083.0 nm to obtain the magnetic field vector and velocity maps in two atmosphere layers. We find that (1) a complete filament was already present in H alpha at the beginning of the TIP II data acquisition. Only a partially formed one, composed of multiple small threads, was present in He I. (2) The AR filament comprises two sections. One shows strong magnetic field intensities, about 600-800 G in the upper chromosphere and 800-1000 G in the photosphere. The other exhibits only comparatively weak magnetic field strengths in both layers. (3) The Stokes V signal is indicative of a dip in the magnetic field strength close to the chromospheric PIL. (4) In the chromosphere, consistent upflows are found along the PIL flanked by downflows. (5) The transversal magnetic field is nearly parallel to the PIL in the photosphere and inclined by 20 degrees-30 degrees in the chromosphere. (6) The chromospheric magnetic field around the filament is found to be in normal configuration, while the photospheric field presents a concave magnetic topology. The observations are consistent with the emergence of a flux rope with a subsequent formation of a filament.</P>
Multicomponent He I 10 830 A profiles in an active filament
Sasso, C.,Lagg, A.,Solanki, S.K. EDP Sciences 2011 Astronomy and astrophysics Vol.526 No.1
<P>Aims. We present new spectropolarimetric observations of the chromospheric He I 10 830 angstrom multiplet observed in a filament during its phase of activity. Methods. The data were recorded with the new Tenerife Infrared Polarimeter (TIP-II) at the German Vacuum Tower Telescope (VTT) on 2005 May 18. We inverted the He Stokes profiles using multiple atmospheric components. Results. The observed He Stokes profiles display a remarkably wide variety of shapes. Most of the profiles show very broad Stokes I absorptions and complex and spatially variable Stokes V signatures. The inversion of the profiles shows evidence of different atmospheric blue-and redshifted components of the He I lines within the resolution element (similar to 1 arcsec), with supersonic velocities of up to similar to 100 km s(-1). Up to five different atmospheric components are found in the same profile. We show that even these complex profiles can be reliably inverted.</P>
Morphological Properties of Slender Ca ${\rm{II}}$ H Fibrils Observed by Sunrise II
Gafeira, R.,Lagg, A.,Solanki, S. K.,Jafarzadeh, S.,Noort, M. van,Barthol, P.,Rodrí,guez, J. Blanco,Iniesta, J. C. del Toro,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Knö,lker, M.,Suá,rez, American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1
<P>We use seeing-free high spatial resolution Ca II H data obtained by the SUNRISE observatory to determine properties of slender fibrils in the lower solar chromosphere. In this work we use intensity images taken with the SUFI instrument in the Ca II H line during the second scientific flight of the SUNRISE observatory to identify and track elongated bright structures. After identification, we analyze theses structures to extract their morphological properties. We identify 598 slender Ca II H fibrils (SCFs) with an average width of around 180 km, length between 500 and 4000 km, average lifetime of approximate to 400 s, and average curvature of 0.002 arcsec(-1). The maximum lifetime of the SCFs within our time series of 57 minutes is approximate to 2000 s. We discuss similarities and differences of the SCFs with other small-scale, chromospheric structures such as spicules of type I and II, or Ca II K fibrils.</P>