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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 & k lines, the Mg II 2798.75 Å &
2798.82 Å triplet blend, the C II 1334 Å & 1335 Å lines, and the
Si IV 1394 Å & 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.