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Author name code: drews
ADS astronomy entries on 2022-09-14
author:"Drews, Ainar" 

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Title: High-resolution observations of the solar photosphere,
    chromosphere, and transition region. A database of coordinated IRIS
    and SST observations
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson,
   M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.;
   Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques,
   V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.;
   Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.;
   Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.;
   Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski,
   M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P.
2020A&A...641A.146R    Altcode: 2020arXiv200514175R
  NASA's Interface Region Imaging Spectrograph (IRIS) provides
  high-resolution observations of the solar atmosphere through ultraviolet
  spectroscopy and imaging. Since the launch of IRIS in June 2013, we
  have conducted systematic observation campaigns in coordination with
  the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides
  complementary high-resolution observations of the photosphere and
  chromosphere. The SST observations include spectropolarimetric imaging
  in photospheric Fe I lines and spectrally resolved imaging in the
  chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present
  a database of co-aligned IRIS and SST datasets that is open for
  analysis to the scientific community. The database covers a variety
  of targets including active regions, sunspots, plages, the quiet Sun,
  and coronal holes.

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Title: A multi-diagnostic spectral analysis of penumbral microjets
Authors: Drews, Ainar; Rouppe van der Voort, Luc
2020A&A...638A..63D    Altcode: 2020arXiv200502608D
  Context. Penumbral microjets (PMJs) are short-lived, jet-like objects
  found in the penumbra of sunspots. They were first discovered in
  chromospheric lines and have later also been shown to exhibit signals
  in transition region (TR) lines. Their origin and manner of evolution
  is not yet settled. <BR /> Aims: We perform a comprehensive analysis of
  PMJs through the use of spectral diagnostics that span from photospheric
  to TR temperatures to constrain PMJ properties. Methods We employed
  high-spatial-resolution Swedish 1-m Solar Telescope observations in the
  Ca II 8542 Å and H α lines, IRIS slit-jaw images, and IRIS spectral
  observations in the Mg II h &amp; k lines, the Mg II 2798.75 Å &amp;
  2798.82 Å triplet blend, the C II 1334 Å &amp; 1335 Å lines, and the
  Si IV 1394 Å &amp; 1403 Å lines. We derived a wide range of spectral
  diagnostics from these and investigated other secondary phenomena
  associated with PMJs. <BR /> Results: We find that PMJs exhibit varying
  degrees of signal in all of our studied spectral lines. We find low
  or negligible Doppler velocities and velocity gradients throughout
  our diagnostics and all layers of the solar atmosphere associated
  with these. Dark features in the inner wings of H α and Ca II 8542
  Å imply that PMJs form along pre-existing fibril structures. We find
  evidence for upper photospheric heating in a subset of PMJs through
  emission in the wings of the Mg II triplet lines. There is little
  evidence for ubiquitous twisting motion in PMJs. There is no marked
  difference in onset-times for PMJ brightenings in different spectral
  lines. <BR /> Conclusions: PMJs most likely exhibit only very modest
  mass-motions, contrary to earlier suggestions. We posit that PMJs form
  at upper photospheric or chromospheric heights at pre-existing fibril
  structures. <P />Movies associated to Appendix B are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202037911/olm">https://www.aanda.org</A>

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Title: Penumbral microjets at high spatial and temporal resolution
Authors: Rouppe van der Voort, Luc H. M.; Drews, Ainar
2019A&A...626A..62R    Altcode: 2019arXiv190502981R
  Context. Sunspot observations in chromospheric spectral lines have
  revealed short-lived linear bright transients that are commonly
  referred to as penumbral microjets (PMJs). Details on the origin and
  physical nature of PMJs are to a large extend still unknown. <BR />
  Aims: We aim to characterize the dynamical nature of PMJs to provide
  guidance for future modeling efforts. <BR /> Methods: We analyzed
  high spatial (0.̋1) and temporal resolution (1 s) Ca II H filtergram
  (0.1 nm bandwidth) observations of a sunspot that were obtained on two
  consecutive days with the Swedish 1 m Solar Telescope. <BR /> Results:
  We find that PMJs appear to be the rapid brightening of an already
  existing (faint) fibril. The rapid brightening is the fast increase
  (typically less than 10 s) in intensity over significant length (several
  hundreds of kilometers) of the existing fibril. For most PMJs, no clear
  root or source from where the brightening appears to originate can be
  identified. After the fast onset, about half of the PMJs have tops that
  move with an apparent velocity of between 5 and 14 km s<SUP>-1</SUP>,
  most of them upward. No significant motion of the top is observed in
  the other PMJs. About one-third of the PMJs split into two parallel
  and coevolving linear features during the later phases of their
  lifetimes. <BR /> Conclusions: We conclude that mass flows can play only
  a limited role in the onset phase of PMJs. It is more likely that we
  see the effect of a fast heating front. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201935343/olm">https://www.aanda.org</A>

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Title: Observationally Based Models of Penumbral Microjets
Authors: Esteban Pozuelo, S.; de la Cruz Rodríguez, J.; Drews, A.;
   Rouppe van der Voort, L.; Scharmer, G. B.; Carlsson, M.
2019ApJ...870...88E    Altcode: 2018arXiv181107881E
  We study the polarization signals and physical parameters of penumbral
  microjets (PMJs) by using high spatial resolution data taken in the
  Fe I 630 nm pair, Ca II 854.2 nm, and Ca II K lines with the CRISP
  and CHROMIS instruments at the Swedish 1 m Solar Telescope. We
  infer their physical parameters, such as physical observables in
  the photosphere and chromospheric velocity diagnostics, by different
  methods, including inversions of the observed Stokes profiles with
  the STiC code. PMJs harbor overall brighter Ca II K line profiles
  and conspicuous polarization signals in Ca II 854.2 nm, specifically
  in circular polarization that often shows multiple lobes mainly due
  to the shape of Stokes I. They usually overlap photospheric regions
  with a sheared magnetic field configuration, suggesting that magnetic
  reconnections could play an important role in the origin of PMJs. The
  discrepancy between their low LOS velocities and the high apparent
  speeds reported on earlier, as well as the existence of different
  vertical velocity gradients in the chromosphere, indicate that PMJs
  might not be entirely related to mass motions. Instead, PMJs could
  be due to perturbation fronts induced by magnetic reconnections
  occurring in the deep photosphere that propagate through the
  chromosphere. This reconnection may be associated with current heating
  that produces temperature enhancements from the temperature minimum
  region. Furthermore, enhanced collisions with electrons could also
  increase the coupling to the local conditions at higher layers during
  the PMJ phase, giving a possible explanation for the enhanced emission
  in the overall Ca II K profiles emerging from these transients.

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Title: Microjets in the penumbra of a sunspot
Authors: Drews, Ainar; Rouppe van der Voort, Luc
2017A&A...602A..80D    Altcode: 2017arXiv170206078D
  Context. Penumbral microjets (PMJs) are short-lived jets found in
  the penumbra of sunspots, first observed in wide-band Ca II H line
  observations as localized brightenings, and are thought to be caused
  by magnetic reconnection. Earlier work on PMJs has focused on smaller
  samples of by-eye selected events and case studies. <BR /> Aims: It
  is our goal to present an automated study of a large sample of PMJs
  to place the basic statistics of PMJs on a sure footing and to study
  the PMJ Ca II 8542 Å spectral profile in detail. <BR /> Methods: High
  spatial resolution and spectrally well-sampled observations in the Ca II
  8542 Å line obtained from the Swedish 1-m Solar Telescope (SST) were
  reduced by a principle component analysis and subsequently used in the
  automated detection of PMJs using the simple machine learning algorithm
  k-nearest neighbour. PMJ detections were verified with co-temporal
  Ca II H line observations. <BR /> Results: We find a total of 453
  tracked PMJ events, 4253 PMJs detections tallied over all timeframes,
  and a detection rate of 21 events per timestep. From these, an average
  length, width and lifetime of 640 km, 210 km and 90 s are obtained. The
  average PMJ Ca II 8542 Å line profile is characterized by enhanced
  inner wings, often in the form of one or two distinct peaks, and a
  brighter line core as compared to the quiet-Sun average. Average blue
  and red peak positions are determined at - 10.4 km s<SUP>-1</SUP> and +
  10.2 km s<SUP>-1</SUP> offsets from the Ca II 8542 Å line core. We find
  several clusters of PMJ hot-spots within the sunspot penumbra, in which
  PMJ events occur in the same general area repeatedly over time. <BR />
  Conclusions: Our results indicate smaller average PMJs sizes and longer
  lifetimes compared to previously published values, but with statistics
  still in the same orders of magnitude. The investigation and analysis
  of the PMJ line profiles strengthens the proposed heating of PMJs to
  transition region temperatures. The presented statistics on PMJs form
  a solid basis for future investigations and numerical modelling of PMJs.