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Title: FULLY RESOLVED QUIET-SUN MAGNETIC FLUX TUBE OBSERVED WITH THE SUNRISE/IMAX INSTRUMENT

Abstract

Until today, the small size of magnetic elements in quiet-Sun areas has required the application of indirect methods, such as the line-ratio technique or multi-component inversions, to infer their physical properties. A consistent match to the observed Stokes profiles could only be obtained by introducing a magnetic filling factor that specifies the fraction of the observed pixel filled with magnetic field. Here, we investigate the properties of a small magnetic patch in the quiet Sun observed with the IMaX magnetograph on board the balloon-borne telescope SUNRISE with unprecedented spatial resolution and low instrumental stray light. We apply an inversion technique based on the numerical solution of the radiative transfer equation to retrieve the temperature stratification and the field strength in the magnetic patch. The observations can be well reproduced with a one-component, fully magnetized atmosphere with a field strength exceeding 1 kG and a significantly enhanced temperature in the mid to upper photosphere with respect to its surroundings, consistent with semi-empirical flux tube models for plage regions. We therefore conclude that, within the framework of a simple atmospheric model, the IMaX measurements resolve the observed quiet-Sun flux tube.

Authors:
; ; ; ; ; ; ; ;  [1]; ;  [2]; ;  [3];  [4];  [5];  [6];  [7]
  1. Max-Planck-Institut fuer Sonnensystemforschung, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau (Germany)
  2. Instituto de Astrofisica de Canarias, C/Via Lactea s/n, 38200 La Laguna, Tenerife (Spain)
  3. Kiepenheuer-Institut fuer Sonnenphysik, Schoeneckstrasse 6, 79104 Freiburg (Germany)
  4. Instituto de Astrofisica de AndalucIa (CSIC), Apartado de Correos 3004, 18080 Granada (Spain)
  5. Grupo de AstronomIa y Ciencias del Espacio, Universidad de Valencia, 46980 Paterna, Valencia (Spain)
  6. High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000 (United States)
  7. Lockheed Martin Solar and Astrophysics Laboratory, Bldg. 252, 3251 Hanover Street, Palo Alto, CA 94304 (United States)
Publication Date:
OSTI Identifier:
21452697
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 723; Journal Issue: 2; Other Information: DOI: 10.1088/2041-8205/723/2/L164
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; MAGNETIC FIELDS; MAGNETIC FLUX; NUMERICAL SOLUTION; PHOTOSPHERE; SPATIAL RESOLUTION; SUN; TELESCOPES; ATMOSPHERES; MAIN SEQUENCE STARS; MATHEMATICAL SOLUTIONS; RESOLUTION; SOLAR ATMOSPHERE; STARS; STELLAR ATMOSPHERES

Citation Formats

Lagg, A., Solanki, S. K., Riethmueller, T. L., Schuessler, M., Hirzberger, J., Feller, A., Borrero, J. M., Barthol, P., Gandorfer, A., MartInez Pillet, V., Bonet, J. A., Schmidt, W., Berkefeld, T., Del Toro Iniesta, J. C., Domingo, V., Knoelker, M., and Title, A. M., E-mail: lagg@mps.mpg.d. FULLY RESOLVED QUIET-SUN MAGNETIC FLUX TUBE OBSERVED WITH THE SUNRISE/IMAX INSTRUMENT. United States: N. p., 2010. Web. doi:10.1088/2041-8205/723/2/L164.
Lagg, A., Solanki, S. K., Riethmueller, T. L., Schuessler, M., Hirzberger, J., Feller, A., Borrero, J. M., Barthol, P., Gandorfer, A., MartInez Pillet, V., Bonet, J. A., Schmidt, W., Berkefeld, T., Del Toro Iniesta, J. C., Domingo, V., Knoelker, M., & Title, A. M., E-mail: lagg@mps.mpg.d. FULLY RESOLVED QUIET-SUN MAGNETIC FLUX TUBE OBSERVED WITH THE SUNRISE/IMAX INSTRUMENT. United States. doi:10.1088/2041-8205/723/2/L164.
Lagg, A., Solanki, S. K., Riethmueller, T. L., Schuessler, M., Hirzberger, J., Feller, A., Borrero, J. M., Barthol, P., Gandorfer, A., MartInez Pillet, V., Bonet, J. A., Schmidt, W., Berkefeld, T., Del Toro Iniesta, J. C., Domingo, V., Knoelker, M., and Title, A. M., E-mail: lagg@mps.mpg.d. Wed . "FULLY RESOLVED QUIET-SUN MAGNETIC FLUX TUBE OBSERVED WITH THE SUNRISE/IMAX INSTRUMENT". United States. doi:10.1088/2041-8205/723/2/L164.
@article{osti_21452697,
title = {FULLY RESOLVED QUIET-SUN MAGNETIC FLUX TUBE OBSERVED WITH THE SUNRISE/IMAX INSTRUMENT},
author = {Lagg, A. and Solanki, S. K. and Riethmueller, T. L. and Schuessler, M. and Hirzberger, J. and Feller, A. and Borrero, J. M. and Barthol, P. and Gandorfer, A. and MartInez Pillet, V. and Bonet, J. A. and Schmidt, W. and Berkefeld, T. and Del Toro Iniesta, J. C. and Domingo, V. and Knoelker, M. and Title, A. M., E-mail: lagg@mps.mpg.d},
abstractNote = {Until today, the small size of magnetic elements in quiet-Sun areas has required the application of indirect methods, such as the line-ratio technique or multi-component inversions, to infer their physical properties. A consistent match to the observed Stokes profiles could only be obtained by introducing a magnetic filling factor that specifies the fraction of the observed pixel filled with magnetic field. Here, we investigate the properties of a small magnetic patch in the quiet Sun observed with the IMaX magnetograph on board the balloon-borne telescope SUNRISE with unprecedented spatial resolution and low instrumental stray light. We apply an inversion technique based on the numerical solution of the radiative transfer equation to retrieve the temperature stratification and the field strength in the magnetic patch. The observations can be well reproduced with a one-component, fully magnetized atmosphere with a field strength exceeding 1 kG and a significantly enhanced temperature in the mid to upper photosphere with respect to its surroundings, consistent with semi-empirical flux tube models for plage regions. We therefore conclude that, within the framework of a simple atmospheric model, the IMaX measurements resolve the observed quiet-Sun flux tube.},
doi = {10.1088/2041-8205/723/2/L164},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 723,
place = {United States},
year = {Wed Nov 10 00:00:00 EST 2010},
month = {Wed Nov 10 00:00:00 EST 2010}
}
  • We present observational evidence for oscillations of magnetic flux density in the quiet areas of the Sun. The majority of magnetic fields on the solar surface have strengths of the order of or lower than the equipartition field (300-500 G). This results in a myriad of magnetic fields whose evolution is largely determined by the turbulent plasma motions. When granules evolve they squash the magnetic field lines together or pull them apart. Here, we report on the periodic deformation of the shapes of features in circular polarization observed at high resolution with SUNRISE. In particular, we note that the areamore » of patches with a constant magnetic flux oscillates with time, which implies that the apparent magnetic field intensity oscillates in antiphase. The periods associated with this oscillatory pattern are compatible with the granular lifetime and change abruptly, which suggests that these oscillations might not correspond to characteristic oscillatory modes of magnetic structures, but to the forcing by granular motions. In one particular case, we find three patches around the same granule oscillating in phase, which means that the spatial coherence of these oscillations can reach 1600 km. Interestingly, the same kind of oscillatory phenomenon is also found in the upper photosphere.« less
  • Isolated flux tubes are considered to be fundamental magnetic building blocks of the solar photosphere. Their formation is usually attributed to the concentration of magnetic field to kG strengths by the convective collapse mechanism. However, the small size of the magnetic elements in quiet-Sun areas has prevented this scenario from being studied in fully resolved structures. Here, we report on the formation and subsequent evolution of one such photospheric magnetic flux tube, observed in the quiet Sun with unprecedented spatial resolution (0.''15-0.''18) and high temporal cadence (33 s). The observations were acquired by the Imaging Magnetograph eXperiment on board themore » SUNRISE balloon-borne solar observatory. The equipartition field strength magnetic element is the result of the merging of several same polarity magnetic flux patches, including a footpoint of a previously emerged loop. The magnetic structure is then further intensified to kG field strengths by convective collapse. The fine structure found within the flux concentration reveals that the scenario is more complex than can be described by a thin flux tube model with bright points and downflow plumes being established near the edges of the kG magnetic feature. We also observe a daisy-like alignment of surrounding granules and a long-lived inflow toward the magnetic feature. After a subsequent weakening process, the field is again intensified to kG strengths. The area of the magnetic feature is seen to change in anti-phase with the field strength, while the brightness of the bright points and the speed of the downflows varies in phase. We also find a relation between the brightness of the bright point and the presence of upflows within it.« less
  • Using the IMaX instrument on board the SUNRISE stratospheric balloon telescope, we have detected extremely shifted polarization signals around the Fe I 5250.217 A spectral line within granules in the solar photosphere. We interpret the velocities associated with these events as corresponding to supersonic and magnetic upflows. In addition, they are also related to the appearance of opposite polarities and highly inclined magnetic fields. This suggests that they are produced by the reconnection of emerging magnetic loops through granular upflows. The events occupy an average area of 0.046 arcsec{sup 2} and last for about 80 s, with larger events havingmore » longer lifetimes. These supersonic events occur at a rate of 1.3 x 10{sup -5} occurrences per second per arcsec{sup 2}.« less
  • The evolution of the physical parameters of magnetic bright points (MBPs) located in the quiet Sun (mainly in the interwork) during their lifetime is studied. First, we concentrate on the detailed description of the magnetic field evolution of three MBPs. This reveals that individual features follow different, generally complex, and rather dynamic scenarios of evolution. Next, we apply statistical methods on roughly 200 observed MBP evolutionary tracks. MBPs are found to be formed by the strengthening of an equipartition field patch, which initially exhibits a moderate downflow. During the evolution, strong downdrafts with an average velocity of 2.4 km s{supmore » –1} set in. These flows, taken together with the concurrent strengthening of the field, suggest that we are witnessing the occurrence of convective collapses in these features, although only 30% of them reach kG field strengths. This fraction might turn out to be larger when the new 4 m class solar telescopes are operational as observations of MBPs with current state of the art instrumentation could still be suffering from resolution limitations. Finally, when the bright point disappears (although the magnetic field often continues to exist) the magnetic field strength has dropped to the equipartition level and is generally somewhat weaker than at the beginning of the MBP's evolution. Also, only relatively weak downflows are found on average at this stage of the evolution. Only 16% of the features display upflows at the time that the field weakens, or the MBP disappears. This speaks either for a very fast evolving dynamic process at the end of the lifetime, which could not be temporally resolved, or against strong upflows as the cause of the weakening of the field of these magnetic elements, as has been proposed based on simulation results. It is noteworthy that in about 10% of the cases, we observe in the vicinity of the downflows small-scale strong (exceeding 2 km s{sup –1}) intergranular upflows related spatially and temporally to these downflows. The paper is complemented by a detailed discussion of aspects regarding the applied methods, the complementary literature, and in depth analysis of parameters like magnetic field strength and velocity distributions. An important difference to magnetic elements and associated bright structures in active region plage is that most of the quiet Sun bright points display significant downflows over a large fraction of their lifetime (i.e., in more than 46% of time instances/measurements they show downflows exceeding 1 km s{sup –1}).« less
  • Bright points (BPs) are manifestations of small magnetic elements in the solar photosphere. Their brightness contrast not only gives insight into the thermal state of the photosphere (and chromosphere) in magnetic elements, but also plays an important role in modulating the solar total and spectral irradiance. Here, we report on simultaneous high-resolution imaging and spectropolarimetric observations of BPs using SUNRISE balloon-borne observatory data of the quiet Sun at the disk center. BP contrasts have been measured between 214 nm and 525 nm, including the first measurements at wavelengths below 388 nm. The histograms of the BP peak brightness show amore » clear trend toward broader contrast distributions and higher mean contrasts at shorter wavelengths. At 214 nm, we observe a peak brightness of up to five times the mean quiet-Sun value, the highest BP contrast so far observed. All BPs are associated with a magnetic signal, although in a number of cases it is surprisingly weak. Most of the BPs show only weak downflows, the mean value being 240 m s{sup -1}, but some display strong down- or upflows reaching a few km s{sup -1}.« less