Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope

Balthasar, H.; Gömöry, P.; Manrique, S. J. González; Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.; Berkefeld, T.; Collados, M.; Denker, C.; Feller, A.; Hofmann, Axel; Lagg, A.; Nicklas, H.; Suárez, D. Orozco; Yabar, A. Pastor; Rezaei, Reza; Schlichenmaier, R.; Schmidt, Dirk; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Lühe, O. von der; Waldmann, T.

doi:10.1002/asna.201612432

Cited by 10 publications

(13 citation statements)

References 29 publications

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“…Unfortunately, the observations were too short to cover the entire decreasing phase. Other studies examining He i 10830 Å also identify supersonic velocities at the footpoints of up to 40 km s −1 (Lagg et al 2007;Balthasar et al 2016).…”

Section: Discussionmentioning

confidence: 85%

“…The AFSs are very dynamic, and LOS velocity maps show strong downflows in the chromosphere at the footpoints of the AFS and upflows at the loop tops. Average velocities are in the range 20-50 km s −1 (Bruzek 1967;González Manrique et al 2018), and the upflows are in the range 1.5-20 km s −1 at the loop tops (González Manrique et al 2017aBalthasar et al 2016). Typical AFSs contain bundles of 5 to 15 individual small filamentary structures with a width of Article number, page 1 of 14 arXiv:1908.01510v1 [astro-ph.SR] 5 Aug 2019 A&A proofs: manuscript no.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics and connectivity of an extended arch filament system

Diercke

Kuckein

Denker

2019

A&A

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Aims. In this study, we analyzed a filament system, which expanded between moving magnetic features (MMFs) of a decaying sunspot and opposite flux outside of the active region from the nearby quiet-Sun network. This configuration deviated from a classical arch filament system (AFS), which typically connects two pores in an emerging flux region. Thus, we called this system an extended AFS. We contrasted classical and extended AFSs with an emphasis on the complex magnetic structure of the latter. Furthermore, we examined the physical properties of the extended AFS and described its dynamics and connectivity. Methods. The extended AFS was observed with two instruments at the Dunn Solar Telescope (DST). The Rapid Oscillations in the Solar Atmosphere (ROSA) imager provided images in three different wavelength regions, which covered the dynamics of the extended AFS at different atmospheric heights. The Interferometric Bidimensional Spectropolarimeter (IBIS) provided spectroscopic Hα data and spectropolarimetric data that was obtained in the near-infrared (NIR) Ca ii λ8542 Å line. We derived the corresponding line-of-sight (LOS) velocities and used He ii λ304 Å extreme ultraviolet (EUV) images of the Atmospheric Imaging Assembly (AIA) and LOS magnetograms of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) as context data.Results. The NIR Ca ii Stokes-V maps are not suitable to definitively define a clear polarity inversion line and to classify this chromospheric structure. Nevertheless, this unusual AFS connects the MMFs of a decaying sunspot with the network field. At the southern footpoint, we measured that the flux decreases over time. We find strong downflow velocities at the footpoints of the extended AFS, which increase in a time period of 30 minutes. The velocities are asymmetric at both footpoints with higher velocities at the southern footpoint. An EUV brigthening appears in one of the arch filaments, which migrates from the northern footpoint toward the southern one. This activation likely influences the increasing redshift at the southern footpoint. Conclusions. The extended AFS exhibits a similar morphology as classical AFSs, for example, threaded filaments of comparable length and width. Major differences concern the connection from MMFs around the sunspot with the flux of the neighboring quiet-Sun network, converging footpoint motions, and longer lifetimes of individual arch filaments of about one hour, while the extended AFS is still very dynamic.

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Section: Discussionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Dynamics and connectivity of an extended arch filament system

Diercke

Kuckein

Denker

2019

A&A

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“…The spectral range comprised the photospheric Ca i 10838.97 Å and Si i 10827.09 Å lines. Both lines are Zeeman triplets with an effective Landé factor of g eff = 1.5 (Balthasar et al 2016). Moreover, the spectral range included the chromospheric He i 10830 Å triplet.…”

Section: Spectropolarimetric Rasters Scans In the Near Infraredmentioning

confidence: 99%

Height variation of magnetic field and plasma flows in isolated bright points

Kuckein

2019

A&A

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Aims. The expansion with height of the solar photospheric magnetic field and the plasma flows is investigated for three isolated bright points (BPs). Methods. The BPs were observed simultaneously with three different instruments attached to the 1.5-meter GREGOR telescope: (1) filtergrams of Ca ii H and blue continuum (4505 Å) with the HiFI, (2) imaging spectroscopy of the Na i D 2 line at 5890 Å with the GFPI, and (3) slit spectropolarimetry in the 1 µm spectral range with the GRIS. Spectral-line inversions were carried out for the Si i 10827 Å Stokes profiles.Results. Bright points are identified in the Ca ii H and blue continuum filtergrams. Moreover, they are also detected in the blue wing of the Na i D 2 and Si i 10827 Å lines, as well as in the Ca i 10839 Å line-core images. We carried out two studies to validate the expansion of the magnetic field with height. On the one hand, we compare the photospheric Stokes V signals of two different spectral lines that are sensitive to different optical depths (Ca i vs. Si i). The area at which the Stokes V signal is significantly large is almost three times larger for the Si i line -sensitive to higher layers -than for the Ca i one. On the other hand, the inferred line-of-sight (LOS) magnetic fields at two optical depths (log τ = −1.0 vs. −2.5) from the Si i line reveal spatially broader fields in the higher layer, up to 51% more extensive in one of the BPs. The dynamics of BPs are tracked along the Na i D 2 and Si i lines. The inferred flows from Na i D 2 Doppler shifts are rather slow in BPs ( 1 km s −1 ). However, the Si i line shows intriguing Stokes profiles with important asymmetries. The analysis of these profiles unveils the presence of two components, a fast and a slow one, within the same resolution element. The faster one, with a smaller filling factor of ∼0.3, exhibits LOS velocities of about 6 km s −1 . The slower component is slightly blueshifted. Conclusions. The present work provides observational evidence for the expansion of the magnetic field with height. Moreover, fast flows are likely present in BPs but are sometimes hidden because of observational limitations.

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“…A group of pores connected via an arch filament system with a spot of opposite polarity was investigated by Balthasar et al (2016) and Balthasar et al (2018). The observations were performed with the GREGOR Infrared spectrograph (GRIS, Collados et al, 2012 at the GREGOR telescope.…”

Section: Muglachmentioning

confidence: 99%

The Problem of the Height Dependence of Magnetic Fields in Sunspots

Balthasar

2018

Sol Phys

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To understand the physics of sunspots, it is important to know the properties of their magnetic field, and especially its height stratification plays a substantial rôle. There are mainly two methods to assess this stratification, but they yield different magnetic gradients in the photospheric layers. Determinations based on the different origin of several spectral lines and the slope of their profiles result in gradients of −2 to −3 G km −1 , or even steeper. This is similar for the total magnetic field strength and for the vertical component of the magnetic field. The other option is to determine the horizontal partial derivatives of the magnetic field, and with the condition divB = 0, also the vertical derivative is known. With this method, gradients of −0.5 G km −1 and shallower are obtained. Obviously, these results do not agree. If chromospheric spectral lines are included, only shallow gradients around −0.5 G km −1 are encountered. Shallow gradients are also found from gyro-resonance measurements in the radio wave range 300 -2000 GHz. Some indirect methods are also considered, but they cannot clarify the total picture. An analysis of a numerical simulation of a sunspot indicates a shallow gradient over a wide height range, but with slightly steeper gradients in deep layers. Several ideas to explain the discrepancy are also discussed. With no doubts cast on Maxwell's equations, the first one is to look at the uncertainties of the formation heights of spectral lines, but a wider range of these heights would require an extension of the solar photosphere that is incompatible with observations and the theory of stellar atmospheres. Submerging and rising magnetic flux might play a rôle in the outer penumbra, if the resolution is too low to separate them, but it is not likely that this effect acts also in the umbra. A quick investigation assuming a spatial small scale structure of sunspots together with twist and writhe of individual flux tubes shows a reduction of the measured magnetic field strength for spectral lines sensitive to a larger height range. However, sophisticated investigations are required to prove that the explanation for the discrepancy lies here, and the problem of the height gradient of the magnetic field in sunspots is still not solved.

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Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope

Cited by 10 publications

References 29 publications

Dynamics and connectivity of an extended arch filament system

Dynamics and connectivity of an extended arch filament system

Height variation of magnetic field and plasma flows in isolated bright points

The Problem of the Height Dependence of Magnetic Fields in Sunspots

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