@article{KontogiannisDinevaDierckeetal.2020,
  author    = {Kontogiannis, Ioannis and Dineva, Ekaterina Ivanova and Diercke, Andrea and Verma, Meetu and Kuckein, Christoph and Balthasar, Horst and Denker, Carsten},
  title     = {High-resolution spectroscopy of an erupting minifilament and its impact on the nearby chromosphere},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  volume    = {898},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  number    = {2},
  publisher = {Institute of Physics Publ.},
  address   = {London},
  issn      = {0004-637X},
  doi       = {10.3847/1538-4357/aba117},
  pages     = {12},
  year      = {2020},
  abstract  = {We study the evolution of a minifilament eruption in a quiet region at the center of the solar disk and its impact on the ambient atmosphere. We used high spectral resolution imaging spectroscopy in H alpha acquired by the echelle spectrograph of the Vacuum Tower Telescope, Tenerife, Spain; photospheric magnetic field observations from the Helioseismic Magnetic Imager; and UV/EUV imaging from the Atmospheric Imaging Assembly of the Solar Dynamics Observatory. The H alpha line profiles were noise-stripped using principal component analysis and then inverted to produce physical and cloud model parameter maps. The minifilament formed between small-scale, opposite-polarity magnetic features through a series of small reconnection events, and it erupted within an hour after its appearance in H alpha. Its development and eruption exhibited similarities to large-scale erupting filaments, indicating the action of common mechanisms. Its eruption took place in two phases, namely, a slow rise and a fast expansion, and it produced a coronal dimming, before the minifilament disappeared. During its eruption, we detected a complicated velocity pattern, indicative of a twisted, thread-like structure. Part of its material returned to the chromosphere, producing observable effects on nearby low-lying magnetic structures. Cloud model analysis showed that the minifilament was initially similar to other chromospheric fine structures, in terms of optical depth, source function, and Doppler width, but it resembled a large-scale filament on its course to eruption. High spectral resolution observations of the chromosphere can provide a wealth of information regarding the dynamics and properties of minifilaments and their interactions with the surrounding atmosphere.},
  language  = {en}
}
@article{VermaMatijevičDenkeretal.2021,
  author    = {Verma, Meetu and Matijevič, Gal and Denker, Carsten and Diercke, Andrea and Dineva, Ekaterina Ivanova and Balthasar, Horst and Kamlah, Robert and Kontogiannis, Ioannis and Kuckein, Christoph and Pal, Partha S.},
  title     = {Classification of high-resolution Solar H alpha spectra using t-distributed stochastic neighbor embedding},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  volume    = {907},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  number    = {1},
  publisher = {Institute of Physics Publ.},
  address   = {London},
  issn      = {1538-4357},
  doi       = {10.3847/1538-4357/abcd95},
  pages     = {14},
  year      = {2021},
  abstract  = {The H alpha spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in H alpha include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mottles and rosettes, among others. This study is based on high-spectral resolution H alpha spectra obtained with the Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic neighbor embedding (t-SNE) is a machine-learning algorithm, which is used for nonlinear dimensionality reduction. In this application, it projects H alpha spectra onto a two-dimensional map, where it becomes possible to classify the spectra according to results of cloud model (CM) inversions. The CM parameters optical depth, Doppler width, line-of-sight velocity, and source function describe properties of the cloud material. Initial results of t-SNE indicate its strong discriminatory power to separate quiet-Sun and plage profiles from those that are suitable for CM inversions. In addition, a detailed study of various t-SNE parameters is conducted, the impact of seeing conditions on the classification is assessed, results for various types of input data are compared, and the identified clusters are linked to chromospheric features. Although t-SNE proves to be efficient in clustering high-dimensional data, human inference is required at each step to interpret the results. This exploratory study provides a framework and ideas on how to tailor a classification scheme toward specific spectral data and science questions.},
  language  = {en}
}