High-resolution imaging spectroscopy of two micro-pores and an arch filament system in a small emerging-flux region

Abstract

Context. Emerging flux regions mark the first stage in the accumulation of magnetic flux eventually leading to pores, sunspots, and (complex) active regions. These flux regions are highly dynamic, show a variety of fine structure, and in many cases live only for a short time (less than a day) before dissolving quickly into the ubiquitous quiet-Sun magnetic field. Aims. The purpose of this investigation is to characterize the temporal evolution of a minute emerging flux region, the associated photospheric and chromospheric flow fields, and the properties of the accompanying arch filament system. We aim to explore flux emergence and decay processes and investigate if they scale with structure size and magnetic flux contents. Methods. This study is based on imaging spectroscopy with the Göttingen Fabry-Pérot Interferometer at the Vacuum Tower Telescope, Observatorio del Teide, Tenerife, Spain on 2008 August 7. Photospheric horizontal proper motions were measured with Local Correlation Tracking using broadband images restored with multi-object multi-frame blind deconvolution. Cloud model (CM) inversions of line scans in the strong chromospheric absorption Hα λ656.28 nm line yielded CM parameters (Doppler velocity, Doppler width, optical thickness, and source function), which describe the cool plasma contained in the arch filament system. Results. The high-resolution observations cover the decay and convergence of two micro-pores with diameters of less than one arcsecond and provide decay rates for intensity and area. The photospheric horizontal flow speed is suppressed near the two micro-pores indicating that the magnetic field is already sufficiently strong to affect the convective energy transport. The micro-pores are accompanied by a small arch filament system as seen in Hα, where small-scale loops connect two regions with Hα line-core brightenings containing an emerging flux region with opposite polarities. The Doppler width, optical thickness, and source function reach the largest values near the Hα line-core brightenings. The chromospheric velocity of the cloud material is predominantly directed downwards near the footpoints of the loops with velocities of up to 12 km s −1 , whereas loop tops show upward motions of about 3 km s −1 . Some of the loops exhibit signs of twisting motions along the loop axis. Conclusions. Micro-pores are the smallest magnetic field concentrations leaving a photometric signature in the photosphere. In the observed case, they are accompanied by a miniature arch filament system indicative of newly emerging flux in the form of Ω-loops. Flux emergence and decay take place on a time-scale of about two days, whereas the photometric decay of the micro-pores is much more rapid (a few hours), which is consistent with the incipient submergence of Ω-loops. Considering lifetime and evolution timescales, impact on the surrounding photospheric proper motions, and flow speed of the chromospheric plasma at the loop tops and footpoints, the results are representative for the smallest emergin...

Cloud model inversions of strong chromospheric absorption lines using principal component analysis

“…Compared to González Manrique et al (), the current implementation of the CM inversions includes a refinement step that links spectral line to CM parameters. Furthermore, the CM database is organized according to the absolute contrast so that only a subset of the CM contrast profiles has to be compared to the observed ones.…”

“…These equations are contrived in terms of the observed intensity I ( λ ) of the dynamic cloud‐like feature and the undisturbed quiet‐Sun background reference frame I qS ( λ ). A simple CM inversion approach is nonlinear least‐squares fitting, for example, with the MPFIT software package (Markwardt ), where the quiet‐Sun background profile is handed to the fitting routine in a structure as private data (González Manrique et al ). However, the iterative nature of the algorithm and the tendency to get lost in local extrema render this procedure inefficient.…”

“…CM inversions of H α contrast profiles were presented by González Manrique et al () who used least‐squares minimization (Markwardt ) to infer the CM parameters. Their study focused on a small‐scale arch filament system in an emerging flux region.…”

Dynamics and connectivity of an extended arch filament system

“…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.…”

The Dynamics of AR 12700 in Its Early Emerging Phase. II. Fan-shaped Activities Relevant to Arch Filament Systems

“…Employing observations of the Vacuum Tower Telescope (VTT; von der Lühe 1998), Xu et al (2010) performed the first investigation on the vector magnetic field and Doppler velocity in the lower solar atmospheric layers of a young emerging-flux region. González Manrique et al (2017) analyzed VTT observations of an AFS and presented the decay and convergence of two micro-pores with diameters of less than one arc-second in a small emerging-flux region. Goode Solar Telescope (Goode & Cao 2012) observed the emergence of small-scale flux ropes in the photosphere (Vargas Domínguez et al 2014) and the chromosphere (Yan et al 2017).…”