TY - JOUR A1 - Cheng, Xin A1 - Kliem, Bernhard A1 - Ding, Mingde T1 - Unambiguous evidence of filament splitting-induced partial eruptions JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - Coronal mass ejections are often considered to result from the full eruption of a magnetic flux rope (MFR). However, it is recognized that, in some events, the MFR may release only part of its flux, with the details of the implied splitting not completely established due to limitations in observations. Here, we investigate two partial eruption events including a confined and a successful one. Both partial eruptions are a consequence of the vertical splitting of a filament-hosting MFR involving internal reconnection. A loss of equilibrium in the rising part of the magnetic flux is suggested by the impulsive onset of both events and by the delayed onset of reconnection in the confined event. The remaining part of the flux might be line-tied to the photosphere in a bald patch (BP) separatrix surface, and we confirm the existence of extended BP sections for the successful eruption. The internal reconnection is signified by brightenings in the body of one filament and between the rising and remaining parts of both filaments. It evolves quickly into the standard current sheet reconnection in the wake of the eruption. As a result, regardless of being confined or successful, both eruptions produce hard X-ray sources and flare loops below the erupting but above the surviving flux, as well as a pair of flare ribbons enclosing the latter. KW - Sun: magnetic fields KW - Sun: corona KW - Sun: coronal mass ejections (CMEs) KW - Sun: flares Y1 - 2018 U6 - https://doi.org/10.3847/1538-4357/aab08d SN - 0004-637X SN - 1538-4357 VL - 856 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Lee, Jeongwoo A1 - White, Stephen M. A1 - Liu, Chang A1 - Kliem, Bernhard A1 - Masuda, Satoshi T1 - Magnetic Structure of a Composite Solar Microwave Burst JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - A composite flare consisting of an impulsive flare SOL2015-06-21T01:42 (GOES class M2.0) and a more gradual, long-duration flare SOL2015-06-21T02:36 (M2.6) from NOAA Active Region 12371, is studied using observations with the Nobeyama Radioheliograph (NoRH) and the Solar Dynamics Observatory (SDO). While composite flares are defined by their characteristic time profiles, in this paper we present imaging observations that demonstrate the spatial relationship of the two flares and allow us to address the nature of the evolution of a composite event. The NoRH maps show that the first flare is confined not only in time, but also in space, as evidenced by the stagnation of ribbon separation and the stationarity of the microwave source. The NoRH also detected another microwave source during the second flare, emerging from a different location where thermal plasma is so depleted that accelerated electrons could survive longer against Coulomb collisional loss. The AIA 131 angstrom images show that a sigmoidal EUV hot channel developed after the first flare and erupted before the second flare. We suggest that this eruption removed the high-lying flux to let the separatrix dome underneath reconnect with neighboring flux and the second microwave burst follow. This scenario explains how the first microwave burst is related to the much-delayed second microwave burst in this composite event. KW - Sun: activity KW - Sun: coronal mass ejections (CMEs) KW - Sun: flares KW - Sun: magnetic fields KW - Sun: radio radiation KW - Sun: UV radiation Y1 - 2018 U6 - https://doi.org/10.3847/1538-4357/aaadbc SN - 0004-637X SN - 1538-4357 VL - 856 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Verma, Meetu A1 - Denker, Carsten A1 - Balthasar, H. A1 - Kuckein, Christoph A1 - Rezaei, R. A1 - Sobotka, Michal A1 - Deng, N. A1 - Wang, Haimin A1 - Tritschler, A. A1 - Collados, M. A1 - Diercke, Andrea A1 - González Manrique, Sergio Javier T1 - High-resolution imaging and near-infrared spectroscopy of penumbral decay JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. Combining high-resolution spectropolarimetric and imaging data is key to understanding the decay process of sunspots as it allows us to scrutinize the velocity and magnetic fields of sunspots and their surroundings. Methods. Active region NOAA 12597 was observed on 2016 September 24 with the 1.5-meter GREGOR solar telescope using high-spatial-resolution imaging as well as imaging spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal proper motions were estimated with local correlation tracking, whereas line-of-sight (LOS) velocities were computed with spectral line fitting methods. The magnetic field properties were inferred with the "Stokes Inversions based on Response functions" (SIR) code for the Si I and Ca I NIR lines. Results. At the time of the GREGOR observations, the leading sunspot had two light bridges indicating the onset of its decay. One of the light bridges disappeared, and an elongated, dark umbral core at its edge appeared in a decaying penumbral sector facing the newly emerging flux. The flow and magnetic field properties of this penumbral sector exhibited weak Evershed flow, moat flow, and horizontal magnetic field. The penumbral gap adjacent to the elongated umbral core and the penumbra in that penumbral sector displayed LOS velocities similar to granulation. The separating polarities of a new flux system interacted with the leading and central part of the already established active region. As a consequence, the leading spot rotated 55 degrees clockwise over 12 h. Conclusions. In the high-resolution observations of a decaying sunspot, the penumbral filaments facing the flux emergence site contained a darkened area resembling an umbral core filled with umbral dots. This umbral core had velocity and magnetic field properties similar to the sunspot umbra. This implies that the horizontal magnetic fields in the decaying penumbra became vertical as observed in flare-induced rapid penumbral decay, but on a very different time-scale. KW - Sun: photosphere KW - sunspots KW - Sun: magnetic fields KW - Sun: infrared KW - techniques: imaging spectroscopy KW - techniques: spectroscopic Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201731801 SN - 1432-0746 VL - 614 PB - EDP Sciences CY - Les Ulis ER -