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Author name code: cabrera-solana
ADS astronomy entries on 2022-09-14
author:"Cabrera Solana, Daniel"
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Title: Temporal evolution of the Evershed flow in
sunspots. II. Physical properties and nature of Evershed clouds
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Borrero, J. M.;
Del Toro Iniesta, J. C.
2008A&A...477..273C Altcode: 2007arXiv0709.1601C
Context: Evershed clouds (ECs) represent the most conspicuous
variation of the Evershed flow in sunspot penumbrae. <BR />Aims:
We determine the physical properties of ECs from high spatial and
temporal resolution spectropolarimetric measurements. This information
is used to investigate the nature of the EC phenomenon. <BR />Methods:
The Stokes profiles of four visible and three infrared spectral lines
are subject to inversions based on simple one-component models as well
as more sophisticated realizations of penumbral flux tubes embedded
in a static ambient field (uncombed models). <BR />Results: According
to the one-component inversions, the EC phenomenon can be understood
as a perturbation of the magnetic and dynamic configuration of the
penumbral filaments along which the ECs move. The uncombed inversions,
on the other hand, suggest that ECs are the result of enhancements
in the visibility of penumbral flux tubes. We conjecture that
these enhancements are caused by a perturbation of the thermodynamic
properties of the tubes, rather than by changes in the vector magnetic
field. This mechanism is investigated performing numerical experiments
of thick penumbral tubes in mechanical equilibrium with a background
field. <BR />Conclusions: While the one-component inversions confirm
many of the properties indicated by a simple line parameter analysis
(Paper I of this series), we give more credit to the results of the
uncombed inversions because they take into account, at least in an
approximate manner, the fine structure of the penumbra. <P />Appendix
A is only available in electronic form at http://www.aanda.org
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Title: Temporal evolution of the Evershed flow in
sunspots. I. Observational characterization of Evershed clouds
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; Del Toro
Iniesta, J. C.
2007A&A...475.1067C Altcode: 2007arXiv0707.2629C
Context: The magnetic and kinematic properties of the photospheric
Evershed flow are relatively well known, but not completely
understood. The evolution of the flow with time, which is mainly due
to the appearance of velocity packets called Evershed clouds (ECs),
may provide information to further constrain its origin. <BR />Aims:
We undertake a detailed analysis of the evolution of the Evershed flow
by studying the properties of ECs. In this first paper we determine
the sizes, proper motions, location in the penumbra, and frequency
of appearance of ECs, as well as their typical Doppler velocities,
linear and circular polarization signals, Stokes V area asymmetries,
and continuum intensities. <BR />Methods: High-cadence, high-resolution,
full vector spectropolarimetric measurements in visible and infrared
lines are used to characterize the EC phenomenon through a simple
line-parameter analysis. <BR />Results: ECs appear in the mid penumbra
and propagate outward along filaments having large linear polarization
signals and enhanced Evershed flows. The frequency of appearance of
ECs varies between 15 and 40 min in different filaments. ECs exhibit
the largest Doppler velocities and linear-to-circular polarization
ratios of the whole penumbra. In addition, lines formed deeper in the
atmosphere show larger Doppler velocities, much in the same way as
the “quiescent” Evershed flow. According to our observations, ECs
can be classified in two groups: type I ECs, which vanish in the outer
penumbra, and type II ECs, which cross the outer penumbral boundary and
enter the sunspot moat. Most of the observed ECs belong to type I. On
average, type II ECs can be detected as velocity structures outside
of the spot for only about 14 min. Their proper motions in the moat
are significantly reduced with respect to the ones they had in the
penumbra. <P />Appendices A and B are only available in electronic
form at http://www.aanda.org
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Title: Temporal evolution of the Evershed flow and its magnetic
properties
Authors: Cabrera Solana, Daniel
2007PhDT........27C Altcode:
No abstract at ADS
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Title: Inversion of Visible and IR Stokes Profiles in Sunspots
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; Del Toro
Iniesta, J. C.
2006ASPC..358...25C Altcode:
We present an analysis of simultaneous observations of a sunspot
in two different spectral ranges (630 nm and 1565 nm). The dataset
was acquired with the POlarimetric LIttrow Spectrograph (POLIS) and
the Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower
Telescope (VTT) of Observatorio del Teide. Inversions of both sets
of lines are carried out to retrieve physical quantities such as
temperature and magnetic fields. We find that: a) the differences
between the atmospheric parameters inferred from the two ranges
are small, demonstrating that inversion techniques provide unique
results; b) there is a cross-talk between temperature and stray light
for visible lines; c) a more realistic treatment of the stray light
contamination is required. Making use of both visible and infrared
lines we obtain < dB/dz >=-2.3±0.6 G km<SUP>-1</SUP> and <
dγ/dz >=-0.019±0.015 deg km<SUP>-1</SUP> in the umbra. Finally,
we show how simultaneous spectro-polarimetric observations of the Sun
in visible and infrared wavelengths improve the diagnostic capabilities
of a single spectral range alone.
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Title: Evershed Clouds as Precursors of Moving Magnetic Features
around Sunspots
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; del Toro
Iniesta, J. C.
2006ApJ...649L..41C Altcode: 2006astro.ph..9108C
The relation between the Evershed flow and moving magnetic features
(MMFs) is studied using high-cadence, simultaneous spectropolarimetric
measurements of a sunspot in visible (630.2 nm) and near-infrared
(1565 nm) lines. Doppler velocities, magnetograms, and total linear
polarization maps are calculated from the observed Stokes profiles. We
follow the temporal evolution of two Evershed clouds that move radially
outward along the same penumbral filament. Eventually, the clouds
cross the visible border of the spot and enter the moat region, where
they become MMFs. The flux patch farther from the sunspot has the same
polarity of the spot, while the MMF closer to it has opposite polarity
and exhibits abnormal circular polarization profiles. Our results
provide strong evidence that at least some MMFs are the continuation
of the penumbral Evershed flow into the moat. This, in turn, suggests
that MMFs are magnetically connected to sunspots.
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Title: Sensitivity of spectral lines to temperature, velocity,
and magnetic field
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; del Toro Iniesta,
J. C.
2005A&A...439..687C Altcode:
We present an analytical and numerical study of the sensitivity of
weak solar photospheric lines to temperature, velocity, and magnetic
fields. Our investigation is based on the concept of response functions
(Landi degl'Innocenti & Landi degl'Innocenti 1977; Ruiz Cobo &
del Toro Iniesta 1994). Lines commonly used in solar spectropolarimetry,
like Fe I 630.25 nm in the visible and Fe I 1564.85 nm in the infrared,
are examined in detail as emerging from reference quiet Sun and sunspot
models. We develop a simple phenomenological model capable of describing
the response of any given line to these atmospheric parameters. We
find that: (a) the sensitivity of the lines to velocity and magnetic
fields increases with the sharpness of the intensity and circular
polarization profiles; (b) the sensitivity to temperature is determined
mainly by the variation of the source function with temperature,
which is smaller at longer wavelengths; and (c) lines quoted to be
insensitive to temperature, like Fe I 1564.85 nm and Fe I 557.61 nm,
exhibit larger changes in equivalent width than lines presumed to
have higher sensitivities to T, such as Fe I 630.25 nm. The relations
provided by our model are universal and can be used to decide which
line is better suited to measuring a given atmospheric parameter. The
results of this study are of practical interest for the design of new
instruments and for better exploitation of existing ones.
