bello-gonzalez

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Author name code: bello-gonzalez
ADS astronomy entries on 2022-09-14
author:"Bello Gonzalez, Nazaret"

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Title: Evolution of the flow field in decaying active
regions. II. Converging flows at the periphery of naked spots
Authors: Strecker, H.; Bello González, N.
2022A&A...664A.195S Altcode: 2022arXiv220814272S
Context. In a previous work, we investigated the evolution of the flow
field around sunspots during sunspot decay and compared it with the
flow field of supergranular cells. The decay of a sunspot proceeds as
it interacts with its surroundings. This is manifested by the changes
observed in the flow field surrounding the decaying spot. 
Aims: We now investigate in detail the evolution of the flow field in
the direct periphery of the sunspots of the same sample and aim to
provide a complete picture of the role of large-scale flows present
in sunspot cells. Methods: We analyse the horizontal velocity
profiles of sunspots obtained from observations by the Helioseismic
and Magnetic Imager (HMI) on board the Solar Dynamics Observatory
(SDO). We follow their evolution across the solar disc from their stable
phase to their decay and their final disappearance. Results:
We find two different scenarios for the evolution of the flow region
surrounding a spot in the final stage of its decay: (i) either the
flow cell implodes and disappears under the action of the surrounding
supergranules or (ii) it outlives the spot. In the later case, an
inwards flow towards the remaining naked spot develops in the vicinity
closest to the spot followed by an outflow further out. These findings
provide observational evidence to theoretical predictions by realistic
magnetohydrodynamic (MHD) sunspot and moat region simulations. 
Conclusions: The Evershed flow and the moat flow, both connected to
the presence of fully fledged sunspots in a spot cell, vanish when
penumbrae decay. Moat flows decline into supergranular flows. The final
fate of a spot cell depends on its interaction with the surrounding
supergranular cells. In the case of non-imploding spot cells, the
remaining naked spot develops a converging inflow driven by radiative
cooling and a geometrical alignment of granules in its periphery which
is similar to that observed in pores. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142564/olm">https://www.aanda.org</A>
This paper is mainly based on Part II of
the Ph.D. thesis "On the decay of sunspots", <A
href="https://freidok.uni-freiburg.de/data/165760">https://freidok.uni-freiburg.de/data/165760</A>.

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Title: Characterization of magneto-convection in sunspots. The
Gough-Tayler stability criterion in MURaM sunspot simulations
Authors: Schmassmann, M.; Rempel, M.; Bello González, N.;
Schlichenmaier, R.; Jurčák, J.
2021A&A...656A..92S Altcode:
Context. Observations have shown that in stable sunspots, the umbral
boundary is outlined by a critical value of the vertical magnetic
field component. However, the nature of the distinct magnetoconvection
regimes in the umbra and penumbra is still unclear. Aims: We
analyse a sunspot simulation in an effort to understand the origin
of the convective instabilities giving rise to the penumbral and
umbral distinct regimes. Methods: We applied the criterion
from Gough &amp; Tayler (1966, MNRAS, 133, 85), accounting for the
stabilising effect of the vertical magnetic field, to investigate
the convective instabilities in a MURaM sunspot simulation. 
Results: We find: (1) a highly unstable shallow layer right beneath the
surface extending all over the simulation box in which convection is
triggered by radiative cooling in the photosphere; (2) a deep umbral
core (beneath −5 Mm) stabilised against overturning convection
that underlies a region with stable background values permeated
by slender instabilities coupled to umbral dots; (3) filamentary
instabilities below the penumbra nearly parallel to the surface and
undulating instabilities coupled to the penumbra which originate
in the deep layers. These deep-rooted instabilities result in the
vigorous magneto-convection regime characteristic of the penumbra; (4)
convective downdrafts in the granulation, penumbra, and umbra develop
at about 2 km s−1, 1 km s−1, and 0.1 km
s−1, respectively, indicating that the granular regime of
convection is more vigorous than the penumbra convection regime, which,
in turn, is more vigorous than the close-to-steady umbra; (5) the GT
criterion outlines both the sunspot magnetopause and peripatopause,
highlighting the tripartite nature of the sub-photospheric layers
of magnetohydrodynamic (MHD) sunspot models; and, finally, (6)
the Jurčák criterion is the photospheric counterpart of the GT
criterion in deep layers. Conclusions: The GT criterion as a
diagnostic tool reveals the tripartite nature of sunspot structure
with distinct regimes of magneto-convection in the umbra, penumbra,
and granulation operating in realistic MHD simulations. Movies associated with Figs. 2 and 3 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141607/olm">https://www.aanda.org</A>

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Title: Magnetic properties on the boundary of an evolving pore
Authors: García-Rivas, M.; Jurčák, J.; Bello González, N.
2021A&A...649A.129G Altcode: 2021arXiv210208459G
Context. Analyses of the magnetic properties on umbrae boundaries
have led to the Jurčák criterion, which states that umbra-penumbra
boundaries in stable sunspots are equally defined by a constant value
of the vertical magnetic field, Bvercrit, and by
a 50% continuum intensity of the quiet Sun, IQS. Umbrae with
vertical magnetic fields stronger than Bvercrit
are stable, whereas umbrae with vertical magnetic fields weaker than
Bvercrit are unstable and prone to vanishing. Aims: We aim to investigate the existence of a critical value of
the vertical magnetic field on a pore boundary and its role in the
evolution of the magnetic structure. Methods: We analysed
SDO/HMI vector field maps corrected for scattered light and with a
temporal cadence of 12 min during a 26.5-hour period. A continuum
intensity threshold (Ic = 0.55 IQS) is used to
define the pore boundary and we study the temporal evolution of the
magnetic properties there. Results: We observe well-defined
stages in the pore evolution: (1) during the initial formation
phase, total magnetic field strength (B) and vertical magnetic field
(Bver) increase to their maximum values of ∼1920 G and
∼1730 G, respectively; (2) then the pore reaches a stable phase;
(3) in a second formation phase, the pore undergoes a rapid growth
in terms of size, along with a decrease in B and Bver on
its boundary. In the newly formed area of the pore, Bver
remains mostly below 1731 G and B remains everywhere below 1921 G;
(4) ultimately, pore decay starts. We find overall that pore areas with
Bver &lt; 1731 G, or equivalently B &lt; 1921 G, disintegrate
faster than regions that fulfil this criteria. Conclusions:
We find that the most stable regions of the pore, similarly to the
case of umbral boundaries, are defined by a critical value of the
vertical component of the magnetic field that is comparable to that
found in stable sunspots. In addition, in this case study, the same
pore areas can be similarly well-defined by a critical value of the
total magnetic field strength.

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Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.

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Title: Solar pores - A magnetic evolution laboratory
Authors: García-Rivas, M.; Jurčák, J.; Bello González, N.
2020sea..confE.198G Altcode:
Analyses of the vector magnetic field on solar magnetic structures led
to the Jurčák criterion, an empirical law that connects a critical
value of the vertical component of the magnetic field to the umbral
magnetoconvective mode in stable sunspots. We study the evolution of the
vertical component of the magnetic field (Bver) on evolving
pores and the existence of an equivalent critical vertical magnetic
value to provide steadiness. Indeed, we find that areas with weak
Bver are unstable and granulation takes over them. However,
areas with strong Bver show longer lifetimes.

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Title: Characterization of the umbra-penumbra boundary by the vertical
component of the magnetic field. Analysis of ground-based data from
the GREGOR Infrared Spectrograph
Authors: Lindner, P.; Schlichenmaier, R.; Bello González, N.
2020A&A...638A..25L Altcode: 2020arXiv200409956L
Context. The vertical component of the magnetic field was found to
reach a constant value at the boundary between penumbra and umbra of
stable sunspots in a recent statistical study of Hinode/SP data. This
finding has profound implications as it can serve as a criterion to
distinguish between fundamentally different magneto-convective modes
operating in the sun. Aims: The objective of this work is to
verify the existence of a constant value for the vertical component of
the magnetic field (B⊥) at the boundary between umbra and
penumbra from ground-based data in the near-infrared wavelengths and to
determine its value for the GREGOR Infrared Spectrograph (GRIS@GREGOR)
data. This is the first statistical study on the Jurčák criterion with
ground-based data, and we compare it with the results from space-based
data (Hinode/SP and SDO/HMI). Methods: Eleven spectropolarimetric
data sets from the GRIS@GREGOR slit-spectograph containing fully-fledged
stable sunspots were selected from the GRIS archive. SIR inversions
including a polarimetric straylight correction are used to produce
maps of the magnetic field vector using the Fe I 15648 Å and 15662 Å
lines. Averages of B⊥ along the contours between penumbra
and umbra are analyzed for the 11 data sets. In addition, contours at
the resulting B⊥const are drawn onto maps and
compared to intensity contours. The geometric difference between these
contours, ΔP, is calculated for each data set. Results: Averaged
over the 11 sunspots, we find a value of B⊥const
= (1787 ± 100) gauss. The difference from the values previously derived
from Hinode/SP and SDO/HMI data is explained by instrumental differences
and by the formation characteristics of the respective lines that were
used. Contours at B⊥ = B⊥const and
contours calculated in intensity maps match from a visual inspection
and the geometric distance ΔP was found to be on the order of 2
pixels. Furthermore, the standard deviation between different data sets
of averages along umbra-penumbra contours is smaller for B⊥
than for B∥ by a factor of 2.4. Conclusions: Our
results provide further support to the Jurčák criterion with the
existence of an invariable value B⊥const at the
umbra-penumbra boundary. This fundamental property of sunspots can act
as a constraining parameter in the calibration of analysis techniques
that calculate magnetic fields. It also serves as a requirement for
numerical simulations to be realistic. Furthermore, it is found
that the geometric difference, ΔP, between intensity contours
and contours at B⊥ = B⊥const
acts as an index of stability for sunspots. The data from
the GRIS instrument is publicly available in the archive at <A
href="http://sdc.leibniz-kis.de">http://sdc.leibniz-kis.de</A>.

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Title: A distinct magnetic property of the inner penumbral
boundary. III. Analysis of simulated sunspots
Authors: Jurčák, Jan; Schmassmann, Markus; Rempel, Matthias; Bello
González, Nazaret; Schlichenmaier, Rolf
2020A&A...638A..28J Altcode: 2020arXiv200403940J
Context. Analyses of sunspot observations revealed a fundamental
magnetic property of the umbral boundary: the invariance of the
vertical component of the magnetic field. Aims: We analyse
the magnetic properties of the umbra-penumbra boundary in simulated
sunspots and thus assess their similarity to observed sunspots. We
also aim to investigate the role of the plasma β and the ratio of
kinetic to magnetic energy in simulated sunspots in the convective
motions because these quantities cannot be reliably determined from
observations. Methods: We used a set of non-gray simulation
runs of sunspots with the MURaM code. The setups differed in terms
of subsurface magnetic field structure and magnetic field boundary
imposed at the top of the simulation domain. These data were used to
synthesize the Stokes profiles, which were then degraded to the Hinode
spectropolarimeter-like observations. Then, the data were treated
like real Hinode observations of a sunspot, and magnetic properties
at the umbral boundaries were determined. Results: Simulations
with potential field extrapolation produce a realistic magnetic field
configuration on the umbral boundaries of the sunspots. Two simulations
with a potential field upper boundary, but different subsurface
magnetic field structures, differ significantly in the extent of their
penumbrae. Increasing the penumbra width by forcing more horizontal
magnetic fields at the upper boundary results in magnetic properties
that are not consistent with observations. This implies that the size of
the penumbra is given by the subsurface structure of the magnetic field,
that is, by the depth and inclination of the magnetopause, which is
shaped by the expansion of the sunspot flux rope with height. None of
the sunspot simulations is consistent with the observed properties of
the magnetic field and the direction of the Evershed flow at the same
time. Strong outward-directed Evershed flows are only found in setups
with an artificially enhanced horizontal component of the magnetic
field at the top boundary that are not consistent with the observed
magnetic field properties at the umbra-penumbra boundary. We stress
that the photospheric boundary of simulated sunspots is defined by a
magnetic field strength of equipartition field value.

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Title: Analysis Methods of the Flow Field around Decaying Sunspots
Authors: Strecker, H.; Bello González, N.
2019ASPC..526..311S Altcode: 2018arXiv181101621S
The moat flow, a radial outflow surrounding fully-fledged sunspots,
is a well characterised phenomenon. Nevertheless, its origin and
especially its relation to the penumbra is still a controversial
topic. We investigate the evolution of the horizontal velocity of the
flow around sunspots over several days during sunspot decay. SDO/HMI
Doppler maps which allow for the continuous observation of an active
region are used. We describe the analysis method used to retrieve
the horizontal velocity of the flow field for different positions
on the solar disc. For that purpose, several large and small scale
flow patterns, like, e.g., differential rotation, the centre-to-limb
variation in the convective blueshift, and a residual pattern caused
by instrumental effects, have to be taken into account in order to
properly measure the horizontal velocity of the flow field surrounding
the sunspots. We find that the flow field around sunspots with fully
developed penumbra has a decreasing velocity profile with increasing
distances to the sunspot, as already found by other authors. Most
important, the velocity amplitude decreases and the profile changes as
the penumbra dissolves and the sunspots decay. Our findings confirm the
related disappearance of the moat flow with penumbra. Yet, we observe
a remnant outflow after the penumbra disappears, which hints towards
the possible overtaking of the moat flow by a supergranular flow in
decaying sunspots.

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Title: Photospheric Magnetic Fields of the Trailing Sunspots in
Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V Altcode: 2018arXiv180507752V
The solar magnetic field is responsible for all aspects of solar
activity. Sunspots are the main manifestation of the ensuing solar
activity. Combining high-resolution and synoptic observations has
the ambition to provide a comprehensive description of the sunspot
growth and decay processes. Active region NOAA 12396 emerged on 2015
August 3 and was observed three days later with the 1.5-meter GREGOR
solar telescope on 2015 August 6. High-resolution spectropolarimetric
data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
with the chromospheric He I λ1083.0 nm triplet. These near-infrared
spectropolarimetric observations were complemented by synoptic
line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO).

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Title: New Insights on Penumbra Magneto-Convection
Authors: Bello González, N.; Jurčák, J.; Schlichenmaier, R.;
Rezaei, R.
2019ASPC..526..261B Altcode:
Fully-fledged penumbrae are a well characterised phenomenon from
an observational point of view. Also, MHD simulations reproduce the
observed characteristics and provide us with insights on the physical
mechanisms possibly running behind the observed processes. Yet, how this
penumbral magneto-convection sets in is still an open question. Due to
the fact that penumbra formation is a relatively fast process (of the
order of hours), it has eluded its observation with sufficient spatial
resolution by both space- and ground-based solar observatories. Only
recently, some researchers have witnessed the onset of both orphan
and sunspot penumbrae in detail. We are one of those. In July 2009, we
observed the early stages of the NOAA 11024 AR leading sunspot while
developing its penumbra. The spectro-polarimetric dataset lead us to
new observational findings. In this contribution, we put into context
our and other authors' results to draw the overall picture of sunspot
formation. Most important, the comparison on the properties of different
types of penumbrae lead us to the conclusion that the formation of
penumbrae is not just one mechanism. While the sole cause necessary
for penumbral magneto-convection is a stably inclined magnetic field,
observations show that inclined fields can be caused by flux emergence,
to form orphan penumbrae, or by field lines transported down from
upper photospheric layers, to form sunspot penumbra. This conclusion,
together with the recent findings by Jur\čák and collaborators on
a canonical value of the vertical component of the magnetic field
blocking the action of penumbral magneto-convection in umbral areas,
is a crucial step forward towards the understanding of the coupling
of solar plasmas and magnetic fields in penumbral atmospheres.

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Title: Observations of solar small-scale magnetic flux-sheet emergence
Authors: Fischer, C. E.; Borrero, J. M.; Bello González, N.;
Kaithakkal, A. J.
2019A&A...622L..12F Altcode: 2019arXiv190105870F
 Aims: Two types of flux emergence were recently discovered
in numerical simulations: magnetic loops and magnetic sheet
emergence. While magnetic loop emergence has been documented well in
recent years using high-resolution full Stokes data from ground-based
telescopes as well as satellites, magnetic sheet emergence is
still an understudied process. We report here on the first clear
observational evidence of a magnetic sheet emergence and characterise
its development. Methods: Full Stokes spectra from the Hinode
spectropolarimeter were inverted with the Stokes Inversion based on
Response functions (SIR) code to obtain solar atmospheric parameters
such as temperature, line-of-sight velocities, and full magnetic
field vector information. Results: We analyse a magnetic
flux emergence event observed in the quiet-Sun internetwork. After a
large-scale appearance of linear polarisation, a magnetic sheet with
horizontal magnetic flux density of up to 194 Mx cm-2
hovers in the low photosphere spanning a region of 2-3 arcsec. The
magnetic field azimuth obtained through Stokes inversions clearly
shows an organised structure of transversal magnetic flux density
emerging. The granule below the magnetic flux sheet tears the
structure apart leaving the emerged flux to form several magnetic
loops at the edges of the granule. Conclusions: A large amount
of flux with strong horizontal magnetic fields surfaces through
the interplay of buried magnetic flux and convective motions. The
magnetic flux emerges within 10 minutes and we find a longitudinal
magnetic flux at the foot points of the order of ∼1018
Mx. This is one to two orders of magnitude larger than what has been
reported for small-scale magnetic loops. The convective flows feed
the newly emerged flux into the pre-existing magnetic population on
a granular scale. Movie attached to Fig. 5 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201834628/olm">https://www.aanda.org</A>

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Title: Evolution of the flow field in decaying active
regions. Transition from a moat flow to a supergranular flow
Authors: Strecker, H.; Bello González, N.
2018A&A...620A.122S Altcode: 2018arXiv181101607S
Context. Fully fledged sunspots are known to be surrounded by a radial
outflow called the moat flow. Aims: We investigate the evolution
of the horizontal flow field around sunspots during their decay, that
is, from fully fledged to naked spots, after they loose the penumbra,
to the remnant region after the spot has fully dissolved. 
Methods: We analysed the extension and horizontal velocity of the
flow field around eight sunspots using SDO/HMI Doppler maps. By
assuming a radially symmetrical flow field, the applied analysis
method determines the radial dependence of the azimuthally averaged
flow field. For comparison, we studied the flow in supergranules
using the same technique. Results: All investigated, fully
fledged sunspots are surrounded by a flow field whose horizontal
velocity profile decreases continuously from 881 m s-1
at 1.1 Mm off the spot boundary, down to 199 m s-1 at a
mean distance of 11.9 Mm to that boundary, in agreement with other
studies. Once the penumbra is fully dissolved, however, the velocity
profile of the flow changes: The horizontal velocity increases with
increasing distance to the spot boundary until a maximum value of
about 398 m s-1 is reached. Then, the horizontal velocity
decreases for farther distances to the spot boundary. In supergranules,
the horizontal velocity increases with increasing distance to their
centre up to a mean maximum velocity of 355 m s-1. For larger
distances, the horizontal velocity decreases. We thus find that the
velocity profile of naked sunspots resembles that of supergranular
flows. The evolution of the flow field around individual sunspots
is influenced by the way the sunspot decays and by the interplay
with the surrounding flow areas. Conclusions: Observations
of the flow around eight decaying sunspots suggest that as long as
penumbrae are present, sunspots with their moat cell are embedded in
network cells. The disappearance of the penumbra (and consequently
the moat flow) and the competing surrounding supergranular cells, both
have a significant role in the evolution of the flow field: The moat
cell transforms into a supergranule, which hosts the remaining naked
spot. The movies associated to Figs A.1-A.8 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201732164/olm">https://www.aanda.org</A>

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Title: Magnetic properties of a long-lived sunspot. Vertical magnetic
field at the umbral boundary
Authors: Schmassmann, M.; Schlichenmaier, R.; Bello González, N.
2018A&A...620A.104S Altcode: 2018arXiv181009358S
Context. In a recent statistical study of sunspots in 79 active regions,
the vertical magnetic field component Bver averaged along the
umbral boundary is found to be independent of sunspot size. The authors
of that study conclude that the absolute value of Bver at the
umbral boundary is the same for all spots. Aims: We investigate
the temporal evolution of Bver averaged along the umbral
boundary of one long-lived sunspot during its stable phase. 
Methods: We analysed data from the HMI instrument on-board SDO. Contours
of continuum intensity at Ic = 0.5Iqs, whereby
Iqs refers to the average over the quiet sun areas, are used
to extract the magnetic field along the umbral boundary. Projection
effects due to different formation heights of the Fe I 617.3 nm line
and continuum are taken into account. To avoid limb artefacts, the
spot is only analysed for heliocentric angles smaller than 60°. 
Results: During the first disc passage, NOAA AR 11591, Bver
remains constant at 1693 G with a root-mean-square deviation of 15 G,
whereas the magnetic field strength varies substantially (mean 2171 G,
rms of 48 G) and shows a long term variation. Compensating for formation
height has little influence on the mean value along each contour, but
reduces the variations along the contour when away from disc centre,
yielding a better match between the contours of Bver =
1693 G and Ic = 0.5Iqs. Conclusions:
During the disc passage of a stable sunspot, its umbral boundary can
equivalently be defined by using the continuum intensity Ic
or the vertical magnetic field component Bver. Contours of
fixed magnetic field strength fail to outline the umbral boundary. Movies associated with Figs. 3 and 5 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833441/olm">https://www.aanda.org</A>

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Title: Flows along arch filaments observed in the GRIS `very fast
spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2017IAUS..327...28G Altcode: 2017arXiv170102206G
A new generation of solar instruments provides improved spectral,
spatial, and temporal resolution, thus facilitating a better
understanding of dynamic processes on the Sun. High-resolution
observations often reveal multiple-component spectral line profiles,
e.g., in the near-infrared He i 10830 Å triplet, which provides
information about the chromospheric velocity and magnetic fine
structure. We observed an emerging flux region, including two small
pores and an arch filament system, on 2015 April 17 with the `very
fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
situated at the 1.5-meter GREGOR solar telescope at Observatorio del
Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
per minute) spectral scans of the solar surface and its potential to
follow dynamic processes on the Sun. We demonstrate the performance
of the `very fast spectroscopic mode' by tracking chromospheric
high-velocity features in the arch filament system.

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Title: Chromospheric impact of an exploding solar granule
Authors: Fischer, C. E.; Bello González, N.; Rezaei, R.
2017A&A...602L..12F Altcode: 2017arXiv170600770F
Context. Observations of multi-wavelength and therefore height-dependent
information following events throughout the solar atmosphere and
unambiguously assigning a relation between these rapidly evolving
layers are rare and difficult to obtain. Yet, they are crucial for our
understanding of the physical processes that couple the different
regimes in the solar atmosphere. Aims: We characterize
the exploding granule event with simultaneous observations of
Hinode spectroplarimetric data in the solar photosphere and Hinode
broadband Ca II H images combined with Interface Region Imaging
Spectrograph (IRIS) slit spectra. We follow the evolution of an
exploding granule and its connectivity throughout the atmosphere and
analyze the dynamics of a magnetic element that has been affected
by the abnormal granule. Methods: In addition to magnetic
flux maps we use a local correlation tracking method to infer the
horizontal velocity flows in the photosphere and apply a wavelet
analysis on several IRIS chromospheric emission features such as
Mg II k2v and Mg II k3 to detect oscillatory phenomena indicating
wave propagation. Results: During the vigorous expansion of
the abnormal granule we detect radially outward horizontal flows,
causing, together with the horizontal flows from the surrounding
granules, the magnetic elements in the bordering intergranular lanes
to be squeezed and elongated. In reaction to the squeezing, we detect
a chromospheric intensity and velocity oscillation pulse which we
identify as an upward traveling hot shock front propagating clearly
through the IRIS spectral line diagnostics of Mg II h&amp;k. 
Conclusions: Exploding granules can trigger upward-propagating shock
fronts that dissipate in the chromosphere. Movies associated
to Figs. A.1 and A.2 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201731120/olm">http://www.aanda.org</A>

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Title: High-resolution imaging spectroscopy of two micro-pores and
an arch filament system in a small emerging-flux region
Authors: González Manrique, S. J.; Bello González, N.; Denker, C.
2017A&A...600A..38G Altcode: 2017arXiv170310140G
Context. Emerging flux regions mark the first stage in the accumulation
of magnetic flux eventually leading to pores, sunspots, and (complex)
active regions. These flux regions are highly dynamic, show a variety
of fine structure, and in many cases live only for a short time (less
than a day) before dissolving quickly into the ubiquitous quiet-Sun
magnetic field. Aims: The purpose of this investigation is to
characterize the temporal evolution of a minute emerging flux region,
the associated photospheric and chromospheric flow fields, and the
properties of the accompanying arch filament system. We aim to explore
flux emergence and decay processes and investigate if they scale with
structure size and magnetic flux contents. Methods: This study
is based on imaging spectroscopy with the Göttingen Fabry-Pérot
Interferometer at the Vacuum Tower Telescope, Observatorio del Teide,
Tenerife, Spain on 2008 August 7. Photospheric horizontal proper motions
were measured with Local correlation tracking using broadband images
restored with multi-object multi-frame blind deconvolution. Cloud model
(CM) inversions of line scans in the strong chromospheric absorption
Hαλ656.28 nm line yielded CM parameters (Doppler velocity, Doppler
width, optical thickness, and source function), which describe the
cool plasma contained in the arch filament system. Results:
The high-resolution observations cover the decay and convergence of two
micro-pores with diameters of less than one arcsecond and provide decay
rates for intensity and area. The photospheric horizontal flow speed
is suppressed near the two micro-pores indicating that the magnetic
field is already sufficiently strong to affect the convective energy
transport. The micro-pores are accompanied by a small arch filament
system as seen in Hα, where small-scale loops connect two regions
with Hα line-core brightenings containing an emerging flux region
with opposite polarities. The Doppler width, optical thickness,
and source function reach the largest values near the Hα line-core
brightenings. The chromospheric velocity of the cloud material is
predominantly directed downwards near the footpoints of the loops
with velocities of up to 12 km s-1, whereas loop tops show
upward motions of about 3 km s-1. Some of the loops exhibit
signs of twisting motions along the loop axis. Conclusions:
Micro-pores are the smallest magnetic field concentrations leaving a
photometric signature in the photosphere. In the observed case, they
are accompanied by a miniature arch filament system indicative of newly
emerging flux in the form of Ω-loops. Flux emergence and decay take
place on a time-scale of about two days, whereas the photometric decay
of the micro-pores is much more rapid (a few hours), which is consistent
with the incipient submergence of Ω-loops. Considering lifetime and
evolution timescales, impact on the surrounding photospheric proper
motions, and flow speed of the chromospheric plasma at the loop tops
and footpoints, the results are representative for the smallest emerging
flux regions still recognizable as such.

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Title: A distinct magnetic property of the inner penumbral
boundary. II. Formation of a penumbra at the expense of a pore
Authors: Jurčák, J.; Bello González, N.; Schlichenmaier, R.;
Rezaei, R.
2017A&A...597A..60J Altcode: 2016arXiv161201745J; 2016A&A...597A..60J
Context. We recently presented evidence that stable
umbra-penumbra boundaries are characterised by a distinct
canonical value of the vertical component of the magnetic
field, Bstablever. In order to trigger
the formation of a penumbra, large inclinations in the magnetic
field are necessary. In sunspots, the penumbra develops and
establishes by colonising both umbral areas and granulation, that
is, penumbral magneto-convection takes over in umbral regions with
Bver&lt;Bstablever, as well as
in granular convective areas. Eventually, a stable umbra-penumbra
boundary settles at Bstablever. Aims:
Here, we aim to study the development of a penumbra initiated at
the boundary of a pore, where the penumbra colonises the entire pore
ultimately. Methods: We have used Hinode/SOT G-band images to
study the evolution of the penumbra. Hinode/SOT spectropolarimetric
data were used to infer the magnetic field properties in the studied
region. Results: The penumbra forms at the boundary of a pore
located close to the polarity inversion line of NOAA 10960. As the
penumbral bright grains protrude into the pore, the magnetic flux in
the forming penumbra increases at the expense of the pore magnetic
flux. Consequently, the pore disappears completely giving rise to an
orphan penumbra. At all times, the vertical component of the magnetic
field in the pore is smaller than Bstablever
≈ 1.8 kG. Conclusions: Our findings are in an agreement
with the need of Bstablever for establishing
a stable umbra-penumbra boundary: while Bver in
the pore is smaller than Bstablever, the
protrusion of penumbral grains into the pore area is not blocked,
a stable pore-penumbra boundary does not establish, and the pore
is fully overtaken by the penumbral magneto-convective mode. This
scenario could also be one of the mechanisms giving rise to orphan
penumbrae. The movie associated to Fig. 1 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201628547/olm">http://www.aanda.org</A>

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Title: Canonical Bver value on umbra/penumbra boundaries
Authors: Jurcak, Jan; Bello González, Nazaret; Schlichenmaier, Rolf;
Rezaei, Reza
2017psio.confE.112J Altcode:
No abstract at ADS

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Title: Magnetic field reconstruction based on sunspot oscillations
Authors: Löhner-Böttcher, J.; Bello González, N.; Schmidt, W.
2016AN....337.1040L Altcode: 2016arXiv160105925L
The magnetic field of a sunspot guides magnetohydrodynamic waves
toward higher atmospheric layers. In the upper photosphere and lower
chromosphere, wave modes with periods longer than the acoustic
cut-off period become evanescent. The cut-off period essentially
changes due to the atmospheric properties, e.g., increases for
larger zenith inclinations of the magnetic field. In this work, we
aim at introducing a novel technique of reconstructing the magnetic
field inclination on the basis of the dominating wave periods in
the sunspot chromosphere and upper photosphere. On 2013 August 21,
we observed an isolated, circular sunspot (NOAA11823) for 58 min in
a purely spectroscopic multi-wavelength mode with the Interferometric
Bidimensional Spectro-polarimeter (IBIS) at the Dunn Solar Telescope. By
means of a wavelet power analysis, we retrieved the dominating wave
periods and reconstructed the zenith inclinations in the chromosphere
and upper photosphere. The results are in good agreement with the
lower photospheric HMI magnetograms. The sunspot's magnetic field
in the chromosphere inclines from almost vertical (0°)
in the umbra to around 60° in the outer penumbra. With
increasing altitude in the sunspot atmosphere, the magnetic field of
the penumbra becomes less inclined. We conclude that the reconstruction
of the magnetic field topology on the basis of sunspot oscillations
yields consistent and conclusive results. The technique opens up a
new possibility to infer the magnetic field inclination in the solar
chromosphere.

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Title: Horizontal flow fields in and around a small active region. The
transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016A&A...596A...3V Altcode: 2016arXiv160507462V
Context. The solar magnetic field is responsible for all aspects
of solar activity. Thus, emergence of magnetic flux at the surface
is the first manifestation of the ensuing solar activity. 
Aims: Combining high-resolution and synoptic observations aims to
provide a comprehensive description of flux emergence at photospheric
level and of the growth process that eventually leads to a mature
active region. Methods: The small active region NOAA 12118
emerged on 2014 July 17 and was observed one day later with the 1.5-m
GREGOR solar telescope on 2014 July 18. High-resolution time-series
of blue continuum and G-band images acquired in the blue imaging
channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
complemented by synoptic line-of-sight magnetograms and continuum
images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO). Horizontal proper motions and
horizontal plasma velocities were computed with local correlation
tracking (LCT) and the differential affine velocity estimator (DAVE),
respectively. Morphological image processing was employed to measure
the photometric and magnetic area, magnetic flux, and the separation
profile of the emerging flux region during its evolution. 
Results: The computed growth rates for photometric area, magnetic
area, and magnetic flux are about twice as high as the respective
decay rates. The space-time diagram using HMI magnetograms of five days
provides a comprehensive view of growth and decay. It traces a leaf-like
structure, which is determined by the initial separation of the two
polarities, a rapid expansion phase, a time when the spread stalls,
and a period when the region slowly shrinks again. The separation
rate of 0.26 km s-1 is highest in the initial stage, and
it decreases when the separation comes to a halt. Horizontal plasma
velocities computed at four evolutionary stages indicate a changing
pattern of inflows. In LCT maps we find persistent flow patterns such
as outward motions in the outer part of the two major pores, a diverging
feature near the trailing pore marking the site of upwelling plasma and
flux emergence, and low velocities in the interior of dark pores. We
detected many elongated rapidly expanding granules between the two
major polarities, with dimensions twice as large as the normal granules.

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Title: Fitting peculiar spectral profiles in He I 10830Å absorption
features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s-1 for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.

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Title: Flow and magnetic field properties in the trailing sunspots
of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1090V Altcode:
Improved measurements of the photospheric and chromospheric
three-dimensional magnetic and flow fields are crucial for a precise
determination of the origin and evolution of active regions. We present
an illustrative sample of multi-instrument data acquired during a
two-week coordinated observing campaign in August 2015 involving,
among others, the GREGOR solar telescope (imaging and near-infrared
spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
and Interface Region Imaging Spectrograph (IRIS). The observations
focused on the trailing part of active region NOAA 12396 with complex
polarity inversion lines and strong intrusions of opposite polarity
flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
spectral profiles in the photospheric Si I λ1082.7 nm line, the
chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
provided maps of Doppler velocity and magnetic field at different
atmospheric heights. We compare quick-look maps with those obtained
with the “Stokes Inversions based on Response functions” (SIR)
code, which furnishes deeper insight into the magnetic properties
of the region. We find supporting evidence that newly emerging flux
and intruding opposite polarity flux are hampering the formation
of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
expected after cessation of flux emergence in proximity to the sunspots.

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Title: Quiet Sun Magnetic Field Evolution Observed with Hinode SOT
and IRIS
Authors: Fischer, C. E.; Bello González, N.; Rezaei, R.
2016ASPC..504...19F Altcode:
We study two physical processes that can be commonly observed in
the quiet sun and involve temporal evolution of the magnetic field:
convective collapse and flux cancellation. The aim is to investigate
the response of the chromosphere to the magnetic events in the
photosphere below. We have calibrated and aligned a co-spatial and
co-temporal 3 hour quiet sun time series observed with the Hinode
SOT (Solar Optical Telescope) and the IRIS (Interface Region Imaging
Spectrograph) satellites. Convective collapse events are identified in
the photosphere by inverting spectropolarimetric data and searching for
magnetic field intensification, preceded by a downflow and accompanied
by the development of a bright point in Ca II H images. We find a
corresponding downflow in the low chromosphere as deduced from IRIS
Mg II k and h spectra and an ensuing oscillatory velocity pattern. We
use magnetograms in the high photosphere to study pairs of magnetic
elements involved in flux cancellation and find an increase in the
entire quasi-continuum of the IRIS Mg II k and h spectrum following
the flux cancellation process and indicating a substantial energy
deposit into the lower atmosphere.

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Title: Flows in and around Active Region NOAA12118 Observed with
the GREGOR Solar Telescope and SDO/HMI
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016ASPC..504...29V Altcode: 2016arXiv160301109V
Accurate measurements of magnetic and velocity fields in and around
solar active regions are key to unlocking the mysteries of the
formation and the decay of sunspots. High spatial resolution images
and spectral sequences with a high cadence obtained with the GREGOR
solar telescope give us an opportunity to scrutinize 3-D flow fields
with local correlation tracking and imaging spectroscopy. We present
GREGOR early science data acquired in 2014 July - August with the GREGOR
Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series
of blue continuum (λ 450.6 nm) images of the small active region
NOAA 12118 were restored with the speckle masking technique to derive
horizontal proper motions and to track the evolution of morphological
changes. In addition, high-resolution observations are discussed in
the context of synoptic data from the Solar Dynamics Observatory.

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Title: Signatures of running penumbral waves in sunspot photospheres
Authors: Löhner-Böttcher, J.; Bello González, N.
2015A&A...580A..53L Altcode: 2015arXiv150309106L
Context. The highly dynamic atmosphere above sunspots exhibits a wealth
of magnetohydrodynamic waves. Recent studies suggest a coupled nature of
the most prominent phenomena: umbral flashes and running penumbral waves
(RPWs). Aims: From an observational point of view, we perform a
height-dependent study of RPWs, compare their wave characteristics, and
aim to track down these so far only chromospherically observed phenomena
to photospheric layers to prove the upward propagating field-guided
nature of RPWs. Methods: We analyze a time series (58 min) of
multiwavelength observations of an isolated circular sunspot (NOAA11823)
taken at high spatial and temporal resolution in spectroscopic mode with
the Interferometric BIdimensional Spectro-polarimeter (IBIS/DST). By
means of a multilayer intensity sampling, velocity comparisons,
wavelet power analysis, and sectorial studies of time slices,
we retrieve the power distribution, characteristic periodicities,
and propagation characteristics of sunspot waves at photospheric and
chromospheric levels. Results: Signatures of RPWs are found at
photospheric layers. Those continuous oscillations occur preferably at
periods between 4-6 min starting at the inner penumbral boundary. The
photospheric oscillations all have a slightly delayed, more defined
chromospheric counterpart with larger relative velocities, which
are linked to preceding umbral flash events. In all of the layers,
the power of RPWs follows a filamentary fine-structure and shows a
typical ring-shaped power distribution increasing in radius for larger
wave periods. The analysis of time slices reveals apparent horizontal
velocities for RPWs at photospheric layers of ≈51 km s-1,
which decrease to ≈37 km s-1 at chromospheric heights. Conclusions: The observations strongly support the scenario of RPWs
being upward propagating slow-mode waves guided by the magnetic field
lines. Clear evidence for RPWs at photospheric layers is given. The
inverse proportionality of the peak period and cut-off period on
the field inclination is supported by the observations. The larger
apparent horizontal velocities at photospheric heights hint at the
more horizontal penumbral field inclination.

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Title: A distinct magnetic property of the inner penumbral
boundary. Formation of a stable umbra-penumbra boundary in a sunspot
Authors: Jurčák, J.; Bello González, N.; Schlichenmaier, R.;
Rezaei, R.
2015A&A...580L...1J Altcode:
Context. A sunspot emanates from a growing pore or protospot. In order
to trigger the formation of a penumbra, large inclinations at the
outskirts of the protospot are necessary. The penumbra develops and
establishes by colonising both umbral areas and granulation. Evidence
for a unique stable boundary value for the vertical component of the
magnetic field strength, Bstablever, was found
along the umbra-penumbra boundary of developed sunspots. Aims: We
study the changing value of Bver as the penumbra forms and as
it reaches a stable state. We compare this with the corresponding value
in fully developed penumbrae. Methods: We use broadband G-band
images and spectropolarimetric GFPI/VTT data to study the evolution
of and the vertical component of the magnetic field on a forming
umbra-penumbra boundary. For comparison with stable sunspots, we also
analyse the two maps observed by Hinode/SP on the same spot after the
penumbra formed. Results: The vertical component of the magnetic
field, Bver, at the umbra-penumbra boundary increases during
penumbra formation owing to the incursion of the penumbra into umbral
areas. After 2.5 h, the penumbra reaches a stable state as shown
by the GFPI data. At this stable stage, the simultaneous Hinode/SP
observations show a Bver value comparable to that of
umbra-penumbra boundaries of fully fledged sunspots. Conclusions:
We confirm that the umbra-penumbra boundary, traditionally defined by
an intensity threshold, is also characterised by a distinct canonical
magnetic property, namely by Bverstable. During
the penumbra formation process, the inner penumbra extends
into regions where the umbra previously prevailed. Hence, in
areas where Bver&lt;Bstablever,
the magneto-convection mode operating in the umbra turns into a
penumbral mode. Eventually, the inner penumbra boundary settles at
Bverstable, which hints toward the role of
Bverstable as inhibitor of the penumbral mode
of magneto-convection.

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Title: A distinct magnetic property of the inner penumbral boundary
Authors: Jurčák, Jan; Bello Gonzalez, Nazaret; Schlichenmaier,
Rolf; Rezaei, Reza
2015arXiv150608574J Altcode:
A sunspot emanates from a growing pore or protospot. In order to
trigger the formation of a penumbra, large inclinations at the
outskirts of the protospot are necessary. The penumbra develops and
establishes by colonising both umbral areas and granulation. Evidence
for a unique stable boundary value for the vertical component of the
magnetic field strength, $B^{\rm stable}_{\rm ver}$, was found along
the umbra-penumbra boundary of developed sunspots. We use broadband
G-band images and spectropolarimetric GFPI/VTT data to study the
evolution of and the vertical component of the magnetic field on a
forming umbra-penumbra boundary. For comparison with stable sunspots,
we also analyse the two maps observed by Hinode/SP on the same spot
after the penumbra formed. The vertical component of the magnetic
field, $B_{\rm ver}$, at the umbra-penumbra boundary increases
during penumbra formation owing to the incursion of the penumbra into
umbral areas. After 2.5 hours, the penumbra reaches a stable state
as shown by the GFPI data. At this stable stage, the simultaneous
Hinode/SP observations show a $B_{\rm ver}$ value comparable to that of
umbra-penumbra boundaries of fully fledged sunspots. We confirm that
the umbra-penumbra boundary, traditionally defined by an intensity
threshold, is also characterised by a distinct canonical magnetic
property, namely by $B^{\rm stable}_{\rm ver}$. During the penumbra
formation process, the inner penumbra extends into regions where the
umbra previously prevailed. Hence, in areas where $B_{\rm ver} &lt;
B^{\rm stable}_{\rm ver}$, the magneto-convection mode operating in
the umbra turns into a penumbral mode. Eventually, the inner penumbra
boundary settles at $B^{\rm stable}_{\rm ver}$, which hints toward the
role of $B_{\rm ver}^{\rm stable}$ as inhibitor of the penumbral mode
of magneto-convection.

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Title: Evolution of magnetic field inclination in a forming penumbra
Authors: Jurčák, Jan; Bello González, Nazaret; Schlichenmaier,
Rolf; Rezaei, Reza
2014PASJ...66S...3J Altcode: 2014PASJ..tmp...93J
As a sunspot penumbra forms, the magnetic field vector at the outer
boundary of the protospot undergoes a transformation. We study the
changes of the magnetic field vector at this boundary as a penumbral
segment forms. We analyze a set of spectropolarimetric maps covering
2 hr during the formation of a sunspot in NOAA 11024. The data were
recorded with the GFPI instrument attached to the German VTT. We
observe a stationary umbra/quiet Sun boundary, where the magnetic
field becomes more horizontal with time. The magnetic field inclination
increases by 5°, reaching a maximum value of about 59°. The maximum
inclination coincides with the onset of filament formation. In time,
the penumbra filaments become longer and the penumbral bright grains
protrude into the umbra, where the magnetic field is stronger and
more vertical. Consequently, we observe a decrease in the magnetic
field inclination at the boundary as the penumbra grows. In summary,
in order to initiate the formation of the penumbra, the magnetic
field at the umbral (protospot) boundary becomes more inclined. As
the penumbra grows, the umbra/penumbra boundary migrates inwards,
and at this boundary the magnetic field turns more vertical again,
while it remains inclined in the outer penumbra.

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Title: First successful deployment of the ZIMPOL-3 system at the
GREGOR telescope
Authors: Ramelli, Renzo; Gisler, Daniel; Bianda, Michele; Bello
González, Nazaret; Berdyugina, Svetlana; Soltau, Dirk
2014SPIE.9147E..3GR Altcode:
Since several years the Zurich Imaging polarimeter (ZIMPOL)
system is successfully used as a high sensitivity polarimeter. The
polarimeter system, which is mainly based on a fast modulator and a
special demodulating camera with a masked CCD, has been continuously
improved. The third version of the system (ZIMPOL-3) is routinely used
at IRSOL, Locarno. The fast modulation allows to "freeze" intensity
variations due to seeing, and to achieve a polarimetric sensitivity
below 10-5 if the photon statistics is large enough. In
October 2013 the ZIMPOL system has been brought and installed for the
first time at the GREGOR telescope in Tenerife for a spectropolarimetric
observing campaign. There, the system configuration took advantage
from the calibration unit installed at the primary focus of the GREGOR
telescope, while the analyzer was inserted in the optical path just
before the spectrograph slit after several folding mirrors. This
setup has been tested successfully by the authors for the first time
in this occasion.

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Title: On the structure and dynamics of Ellerman bombs. Detailed
study of three events and modelling of Hα
Authors: Bello González, N.; Danilovic, S.; Kneer, F.
2013A&A...557A.102B Altcode:
 Aims: We study the structure and dynamics of three Ellerman
bombs (EBs) observed in an evolving active region. Methods: The
active region NOAA 11271 was observed with the Vacuum Tower Telescope
at Observatorio del Teide/Tenerife on August 18, 2011. We used the
two-dimensional Triple Etalon SOlar Spectrometer (TESOS) to obtain time
sequences of the active region and of EBs in Hα at a cadence of 15
s. Simultaneously, we obtained full Stokes profiles with the Tenerife
Infrared Polarimeter (TIP II) in the two magnetically sensitive Fe i
infrared lines (IR) at 1.56 μ, scanning spatial sections of the area
with cadences of 28-46 s. The Hα data were reconstructed with speckle
methods to study the evolution of the atmospheric stratification. Two
methods were used to extract magnetic field information from the IR
Stokes profiles: 1) fitting of the (Q,U,V) profiles by Gaussians; and
2) applying the Milne-Eddington approximation, assuming two separate
magnetic structures in the resolution element and fitting by trial and
error some profiles from the EB areas. Data from SDO-HMI and -AIA were
also used. We performed two-dimensional (2D) non-LTE radiative transfer
calculations of Hα in parameterised models of EBs. Results:
The three EBs studied in detail occurred in a complex active region near
sunspots. They were very bright with a factor of 1.5-2.8 brighter than
the nearby area. They lived for 1/2 h and longer. They were related to
broadband faculae, but the latter were not the brightest features in the
field of view. The EBs occurred in magnetic field configurations with
opposite polarity close together. One EB was located at the outskirts
of a penumbra of a complex sunspot and showed repeated "flaring" in
SDO-AIA data. Another was close to a strong field patch and moved into
this during the end of its lifetime. The third EB showed clear changes
of field structure during the time it was observed. We obtained from
the 2D modelling that heating and increase in Hα opacity are likely
to occur at heights of 300-800 km. Line shifts and asymmetries can
well be reproduced by velocities at these heights and also at much
larger heights. Conclusions: The three EBs occurred at sites
with magnetic fields of opposite polarity, which were likely the cause
of the Hα brightening upon reconnection.

---------------------------------------------------------
Title: The project of installing a ZIMPOL_3 polarimeter at GREGOR
in Tenerife
Authors: Bianda, M.; Ramelli, R.; Stenflo, J.; Berdyugina, S.; Gisler,
D.; Defilippis, I.; Bello González, N.
2013MmSAI..84..413B Altcode:
A project of collaboration between Kiepenheuer Institut für
Sonnenphysik, KIS, and Istituto Ricerche Solari Locarno, IRSOL,
includes the installation of a ZIMPOL_3 high resolution polarimeter at
the 1.5 meter aperture solar telescope GREGOR in Tenerife. Important
scientific topics are expected to be investigated, in particular in the
case of events showing faint amplitude polarization signatures like
scattering polarization effects, and the Hanle effect. This project
has also a technical importance, this combination can be used as test
bench for future polarimeters to be installed on the new generation
solar telescopes.

---------------------------------------------------------
Title: The GREGOR Solar Telescope on Tenerife
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.;
Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.;
Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.
2012ASPC..463..365S Altcode: 2012arXiv1202.4289S
2011 was a successful year for the GREGOR project. The telescope was
finally completed in May with the installation of the 1.5-meter primary
mirror. The installation of the first-light focal plane instruments was
completed by the end of the year. At the same time, the preparations
for the installation of the high-order adaptive optics were finished,
its integration to the telescope is scheduled for early 2012. This
paper describes the telescope and its instrumentation in their present
first-light configuration, and provides a brief overview of the science
goals of GREGOR.

---------------------------------------------------------
Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
2012IAUSS...6E.203D Altcode:
The 1.5-meter GREGOR solar telescope is a new facility for
high-resolution observations of the Sun. The telescope is located at the
Spanish Observatorio del Teide on Tenerife. The telescope incorporates
advanced designs for a foldable-tent dome, an open steel-truss telescope
structure, and active and passive means to minimize telescope and mirror
seeing. Solar fine structure can be observed with a dedicated suite
of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
Interferometer", and the "Grating Infrared Spectrograph". All post-focus
instruments benefit from a high-order (multi-conjugate) adaptive optics
system, which enables observations close to the diffraction limit of
the telescope. The inclusion of a spectrograph for stellar activity
studies and the search for solar twins expands the scientific usage
of the GREGOR to the nighttime domain. We report on the successful
commissioning of the telescope until the end of 2011 and the first
steps towards science verification in 2012.

---------------------------------------------------------
Title: Comparing Simultaneous Measurements of two High-Resolution
Imaging Spectropolarimeters: The `Göttingen' FPI@VTT and CRISP@SST
Authors: Bello González, N.; Bellot Rubio, L. R.; Ortiz, A.; Rezaei,
R.; Rouppe van der Voort, L.; Schlichenmaier, R.
2012ASPC..463..251B Altcode: 2012arXiv1204.1023B
In July 2009, the leading spot of the active region NOAA11024 was
observed simultaneously and independently with the ‘Göttingen’
FPI at VTT and CRISP at SST, i.e., at two different sites,
telescopes, instruments and using different spectral lines. The data
processing and data analysis have been carried out independently
with different techniques. Maps of physical parameters retrieved
from 2D spectro-polarimetric data observed with ‘Göttingen’
FPI and CRISP show an impressive agreement. In addition, the
‘Göttingen’ FPI maps also exhibit a notable resemblance with
simultaneous TIP (spectrographic) observations. The consistency in the
results demonstrates the excellent capabilities of these observing
facilities. Besides, it confirms the solar origin of the detected
signals and the reliability of FPI-based spectro-polarimeters.

---------------------------------------------------------
Title: A retrospective of the GREGOR solar telescope in scientific
literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
2012AN....333..810D Altcode: 2012arXiv1210.3167D
In this review, we look back upon the literature, which had the
GREGOR solar telescope project as its subject including science cases,
telescope subsystems, and post-focus instruments. The articles date
back to the year 2000, when the initial concepts for a new solar
telescope on Tenerife were first presented at scientific meetings. This
comprehensive bibliography contains literature until the year 2012,
i.e., the final stages of commissioning and science verification. Taking
stock of the various publications in peer-reviewed journals and
conference proceedings also provides the “historical” context
for the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.

---------------------------------------------------------
Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
Strassmeier, K. G.; Waldmann , T. A.
2012AN....333..796S Altcode:
The 1.5 m telescope GREGOR opens a new window to the understanding
of solar small-scale magnetism. The first light instrumentation
includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
spectro-polarimeter for the visible wavelength range, the GRating
Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
excellent performance of the first two instruments has already been
demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
solar telescope and number 3 in the world. Its all-reflective Gregory
design provides a large wavelength coverage from the near UV up to at
least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
is equipped with a high-order adaptive optics system, with a subaperture
size of 10 cm, and a deformable mirror with 256 actuators. The science
goals are focused on, but not limited to, solar magnetism. GREGOR
allows us to measure the emergence and disappearance of magnetic flux
at the solar surface at spatial scales well below 100 km. Thanks to its
spectro-polarimetric capabilities, GREGOR will measure the interaction
between the plasma flows, different kinds of waves, and the magnetic
field. This will foster our understanding of the processes that heat the
chromosphere and the outer layers of the solar atmosphere. Observations
of the surface magnetic field at very small spatial scales will shed
light on the variability of the solar brightness.

---------------------------------------------------------
Title: The GREGOR Fabry-Pérot Interferometer
Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.;
Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados,
M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.;
Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer,
R.; Wittmann, A. D.; Woche, M.
2012AN....333..880P Altcode: 2012arXiv1210.2921P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two
tunable etalons in collimated mounting. Thanks to its large-format,
high-cadence CCD detectors with sophisticated computer hard- and
software it is capable of scanning spectral lines with a cadence
that is sufficient to capture the dynamic evolution of the solar
atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well
suited for quiet Sun and sunspot observations. However, in the vector
spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The
spectral coverage in the spectroscopic mode extends from 530-860 nm
with a theoretical spectral resolution of R ≈ 250,000, whereas in
the vector spectropolarimetric mode the wavelength range is at present
limited to 580-660 nm. The combination of fast narrow-band imaging and
post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales
down to ∼50 km on the solar surface.

---------------------------------------------------------
Title: Shear and vortex motions in a forming sunspot . Twist
relaxation in magnetic flux ropes
Authors: Bello González, N.; Kneer, F.; Schlichenmaier, R.
2012A&A...538A..62B Altcode:
 Aims: We measure proper motions of fine structures in a forming
sunspot to infer information about the dynamics of flux emergence at
the sub-photospheric level. Methods: The active region NOAA
11024 was observed with the Vacuum Tower Telescope at Observatorio del
Teide/Tenerife over several days in July 2009. Here, we concentrate
on a two-hour sequence taken on July 4, when the leading spot was
at an early stage of its evolution. Speckle reconstructions from Ca
ii K images and polarimetric data in Fe i λ6173 allow us to study
proper motions of umbral fine structures. Results: We detect
three prominent features: (1) A light bridge, divided by a dark lane
along its axis, shows proper motions in opposing directions on its
sides, with velocities of ~100-500 m s-1. The flows are
seen in both the Ca ii K and the broadband time sequences. (2) Umbral
dots in one umbral region outline a vortex with speeds of up to 550
m s-1. The direction of the motion of the umbral dots is
different from that in the light bridge. (3) At one rim of the umbra,
the fine structure of the magnetic field moves horizontally with typical
velocities of 250-300 m s-1, prior to the formation of the
penumbra. Conclusions: We report on shear and vortex motions in
a forming sunspot and interpret them as tracers of twist relaxation
in magnetic flux ropes. We suggest that the forming sunspot contains
detached magnetic flux ropes that emerge at the surface with different
amounts of twist. As they merge to form a sunspot, they untwist giving
rise to the observed shear and vortex motions.

---------------------------------------------------------
Title: The formation of sunspot penumbra. Magnetic field properties
Authors: Rezaei, R.; Bello González, N.; Schlichenmaier, R.
2012A&A...537A..19R Altcode: 2011arXiv1111.3189R
 Aims: We study the magnetic flux emergence and formation of
a sunspot penumbra in the active region NOAA 11024. Methods:
We simultaneously observed the Stokes parameters of the photospheric
iron lines at 1089.6 nm with the TIP and 617.3 nm with the GFPI
spectropolarimeters along with broad-band images using G-band and
Ca ii K filters at the German VTT. The photospheric magnetic field
vector was reconstructed from an inversion of the measured Stokes
profiles. Using the AZAM code, we converted the inclination from
line-of-sight (LOS) to the local reference frame (LRF). Results:
Individual filaments are resolved in maps of magnetic parameters. The
formation of the penumbra is intimately related to the inclined
magnetic field. No penumbra forms in areas with strong magnetic field
strength and small inclination. Within 4.5 h observing time, the LRF
magnetic flux of the penumbra increases from 9.7 × 1020
to 18.2 × 1020 Mx, while the magnetic flux of the umbra
remains constant at ~3.8 × 1020 Mx. Magnetic flux in the
immediate surroundings is incorporated into the spot, and new flux is
supplied via small flux patches (SFPs), which on average have a flux
of 2-3 × 1018 Mx. The spot's flux increase rate of 4.2 ×
1016 Mx s-1 corresponds to the merging of one
SFP per minute. We also find that, during the formation of the spot
penumbra, a) the maximum magnetic field strength of the umbra does not
change; b) the magnetic neutral line keeps the same position relative
to the umbra; c) the new flux arrives on the emergence side of the
spot while the penumbra forms on the opposite side; d) the average
LRF inclination of the light bridges decreases from 50° to 37°;
and e) as the penumbra develops, the mean magnetic field strength
at the spot border decreases from 1.0 to 0.8 kG. Conclusions:
The SFPs associated with elongated granules are the building blocks of
structure formation in active regions. During the sunspot formation,
their contribution is comparable to the coalescence of pores. Besides a
set of critical parameters for the magnetic field, a quiet environment
in the surroundings is important for penumbral formation. As remnants
of trapped granulation between merging pores, the light bridges are
found to play a crucial role in the formation process. They seem to
channel the magnetic flux through the spot during its formation. Light
bridges are also the locations where the first penumbral filaments form.

---------------------------------------------------------
Title: On acoustic and gravity waves in the solar photosphere and
their energy transport
Authors: Kneer, F.; Bello González, N.
2011A&A...532A.111K Altcode:
 Aims: We study acoustic and atmospheric gravity waves in the
quiet Sun to estimate their energy transport to the chromosphere. Methods: A two-dimensional time sequence from quiet Sun disc centre
was analysed with simultaneous spectroscopic observations in Fe i 5576
Å and Fe i 5434 Å (both with Landé factor g = 0). We calculated
response functions of the velocities for the line minimum shifts
and atmospheric transmissions of waves for the two lines. For this,
NLTE line formation in granular and intergranular model atmospheres
from numerical simulations were performed. For the interpretation
of the observed waves and for the estimates of energy fluxes, we
assumed adiabatic propagation of plane waves in an isothermal model
atmosphere. Fourier analyses of intensity and velocity fluctuations
were carried out. They yield power, phase, and coherence as functions of
frequency ν (from temporal Fourier transforms) and in the kh
- ν plane (from three-dimensional transforms). The power spectra,
together with the mass densities at velocity formation heights, give
then the energy fluxes. Results: The rms velocities found here
in the acoustic and gravity wave domains are lower by a factor ~1.5
as in earlier work. We therefore admit a factor of 2 for an upward
correction of the estimated fluxes. For acoustic waves we find: 1)
upward propagating waves are present on the Sun with frequencies up to
14-15 mHz (periods U ≈ 70 s); 2) the approximation of plane adiabatic
waves in an isothermal atmosphere appears adequate for estimating the
energy fluxes; 3) the acoustic energy fluxes are in the same range
as found in our earlier work from ground-based, two-dimensional
spectroscopy, 1500-3100 W m-2 at an atmospheric height
of ~380 km and 1300-2700 W m-2 at 570 km. The energy flux
carried by gravity waves is difficult to determine. We find: 1) phase
and coherence spectra between continuum and velocity fluctuations
show that convective overshoot and gravity waves are superimposed. We
account for the convective flows using these coherence spectra. 2) At
low frequencies, the vertical wavelength Λz can be short
(≪300 km), yielding large corrections for atmospheric transmissions
(factors &gt; 100). We thus exclude from the flux estimates waves
with |kz| &gt; 20 Mm-1 and with vertical group
velocities υgr,z &lt; 0.3 km s-1. They are
likely to be strongly reduced in amplitude by radiative damping. 3)
With these caveats, the energy fluxes carried by gravity waves are found
in the range of 4000 - 8200 W m-2 at 380 km and 700-1400
W m-2 at 570 km. Gravity waves thus also contribute to the
energy transport into the chromosphere.

---------------------------------------------------------
Title: Polarimetry with GREGOR
Authors: Balthasar, H.; Bello González, N.; Collados, M.; Denker,
C.; Feller, A.; Hofmann, A.; Lagg, A.; Nagaruju, L.; Puschmann, K. G.;
Soltau, D.; Volkmer, R.
2011ASPC..437..351B Altcode:
A brief description of the new 1.5-meter solar telescope GREGOR located
at the Observatorio del Teide in Tenerife will be given. GREGOR will
provide a spatial resolution of about 75 km on the Sun, and with its
light collecting capability we will be able to study the development
of small magnetic features with high cadence. From the beginning,
it will be equipped with the GREGOR Fabry-Pérot Interferometer
(GFPI) for the visible spectral range and with a GRating Infrared
Spectrograph (GRIS). Both postfocus instruments can be combined
with a polarimeter, and in both cases the light is modulated by two
ferro-electric liquid crystals. A calibration unit can be inserted to
determine the instrumental polarization. Because of the altazimuthal
mount, time-dependent rotation of the polarimetric reference plane
is introduced, and we have to develop a polarization model of the
telescope. Measurements to verify this model are in preparation.

---------------------------------------------------------
Title: SUNRISE: Instrument, Mission, Data, and First Results
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
Gandorfer, A.; Hirzberger, J.; Riethmüller, T. L.; Schüssler, M.;
Bonet, J. A.; Martínez Pillet, V.; del Toro Iniesta, J. C.; Domingo,
V.; Palacios, J.; Knölker, M.; Bello González, N.; Berkefeld, T.;
Franz, M.; Schmidt, W.; Title, A. M.
2010ApJ...723L.127S Altcode: 2010arXiv1008.3460S
The SUNRISE balloon-borne solar observatory consists of a 1 m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system, and further infrastructure. The first
science flight of SUNRISE yielded high-quality data that revealed the
structure, dynamics, and evolution of solar convection, oscillations,
and magnetic fields at a resolution of around 100 km in the quiet
Sun. After a brief description of instruments and data, the first
qualitative results are presented. In contrast to earlier observations,
we clearly see granulation at 214 nm. Images in Ca II H display narrow,
short-lived dark intergranular lanes between the bright edges of
granules. The very small-scale, mixed-polarity internetwork fields
are found to be highly dynamic. A significant increase in detectable
magnetic flux is found after phase-diversity-related reconstruction
of polarization maps, indicating that the polarities are mixed right
down to the spatial resolution limit and probably beyond.

---------------------------------------------------------
Title: Detection of Vortex Tubes in Solar Granulation from
Observations with SUNRISE
Authors: Steiner, O.; Franz, M.; Bello González, N.; Nutto, Ch.;
Rezaei, R.; Martínez Pillet, V.; Bonet Navarro, J. A.; del Toro
Iniesta, J. C.; Domingo, V.; Solanki, S. K.; Knölker, M.; Schmidt,
W.; Barthol, P.; Gandorfer, A.
2010ApJ...723L.180S Altcode: 2010arXiv1009.4723S
We have investigated a time series of continuum intensity maps and
corresponding Dopplergrams of granulation in a very quiet solar region
at the disk center, recorded with the Imaging Magnetograph eXperiment
(IMaX) on board the balloon-borne solar observatory SUNRISE. We
find that granules frequently show substructure in the form of lanes
composed of a leading bright rim and a trailing dark edge, which move
together from the boundary of a granule into the granule itself. We
find strikingly similar events in synthesized intensity maps from an
ab initio numerical simulation of solar surface convection. From cross
sections through the computational domain of the simulation, we conclude
that these granular lanes are the visible signature of (horizontally
oriented) vortex tubes. The characteristic optical appearance of vortex
tubes at the solar surface is explained. We propose that the observed
vortex tubes may represent only the large-scale end of a hierarchy of
vortex tubes existing near the solar surface.

---------------------------------------------------------
Title: Bright Points in the Quiet Sun as Observed in the Visible
and Near-UV by the Balloon-borne Observatory SUNRISE
Authors: Riethmüller, T. L.; Solanki, S. K.; Martínez Pillet, V.;
Hirzberger, J.; Feller, A.; Bonet, J. A.; Bello González, N.; Franz,
M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; del Toro Iniesta,
J. C.; Domingo, V.; Gandorfer, A.; Knölker, M.; Schmidt, W.
2010ApJ...723L.169R Altcode: 2010arXiv1009.1693R
Bright points (BPs) are manifestations of small magnetic elements
in the solar photosphere. Their brightness contrast not only gives
insight into the thermal state of the photosphere (and chromosphere) in
magnetic elements, but also plays an important role in modulating the
solar total and spectral irradiance. Here, we report on simultaneous
high-resolution imaging and spectropolarimetric observations of
BPs using SUNRISE balloon-borne observatory data of the quiet Sun
at the disk center. BP contrasts have been measured between 214 nm
and 525 nm, including the first measurements at wavelengths below
388 nm. The histograms of the BP peak brightness show a clear trend
toward broader contrast distributions and higher mean contrasts at
shorter wavelengths. At 214 nm, we observe a peak brightness of up to
five times the mean quiet-Sun value, the highest BP contrast so far
observed. All BPs are associated with a magnetic signal, although in
a number of cases it is surprisingly weak. Most of the BPs show only
weak downflows, the mean value being 240 m s-1, but some
display strong down- or upflows reaching a few km s-1.

---------------------------------------------------------
Title: Detection of Large Acoustic Energy Flux in the Solar Atmosphere
Authors: Bello González, N.; Franz, M.; Martínez Pillet, V.; Bonet,
J. A.; Solanki, S. K.; del Toro Iniesta, J. C.; Schmidt, W.; Gandorfer,
A.; Domingo, V.; Barthol, P.; Berkefeld, T.; Knölker, M.
2010ApJ...723L.134B Altcode: 2010arXiv1009.4795B
We study the energy flux carried by acoustic waves excited by convective
motions at sub-photospheric levels. The analysis of high-resolution
spectropolarimetric data taken with IMaX/SUNRISE provides a total
energy flux of ~6400-7700 W m-2 at a height of ~250 km
in the 5.2-10 mHz range, i.e., at least twice the largest energy
flux found in previous works. Our estimate lies within a factor of
two of the energy flux needed to balance radiative losses from the
chromosphere according to the estimates of Anderson &amp; Athay and
revives interest in acoustic waves for transporting energy to the
chromosphere. The acoustic flux is mainly found in the intergranular
lanes but also in small rapidly evolving granules and at the bright
borders, forming dark dots and lanes of splitting granules.

---------------------------------------------------------
Title: Acoustic waves in the solar atmosphere at high spatial
resolution. II. Measurement in the Fe I 5434 Å line
Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev,
O.; Shchukina, N.
2010A&A...522A..31B Altcode:
 Aims: We investigate the energy supply of the solar chromosphere
by acoustic waves. Methods: A time sequence with high spatial
and temporal resolution from the quiet Sun disc centre in Fe i
5434 Å (Landé factor g = 0) is analysed. We used models from a
numerical simulation of granular convection and apply NLTE spectral
line transfer to determine the height of formation. For estimates of
acoustic energy flux, we adopted wave propagation with inclinations
of the wave vector with respect to the vertical of 0°, 30°, and
45°. For a granular and an intergranular model, the transmissions of
the atmosphere to high-frequency waves were determined for the three
inclination angles. Wavelet and Fourier analyses were performed
and the resulting power spectra were corrected for atmospheric
transmission. Results: We find waves with periods down to ~40
s. They occur intermittently in space and time. The velocity signal
is formed at a height of 500 km in the granular model and at 620 km
in the intergranule. At periods shorter than the acoustic cutoff
(~190 s), ~40% of the waves occur above granules and ~60% above
intergranules. By adopting vertical propagation, we estimate total
fluxes above granules of 2750-3360 W m-2, and of 910-1 000
W m-2 above intergranules. The weighted average is 1730-2
060 W m-2. The estimates of the total fluxes increase by 15%
when inclined wave propagation of 45° is assumed.

---------------------------------------------------------
Title: Surface Waves in Solar Granulation Observed with SUNRISE
Authors: Roth, M.; Franz, M.; Bello González, N.; Martínez Pillet,
V.; Bonet, J. A.; Gandorfer, A.; Barthol, P.; Solanki, S. K.;
Berkefeld, T.; Schmidt, W.; del Toro Iniesta, J. C.; Domingo, V.;
Knölker, M.
2010ApJ...723L.175R Altcode: 2010arXiv1009.4790R
Solar oscillations are expected to be excited by turbulent flows in
the intergranular lanes near the solar surface. Time series recorded
by the IMaX instrument on board the SUNRISE observatory reveal solar
oscillations at high spatial resolution, which allow the study of
the properties of oscillations with short wavelengths. We analyze
two time series with synchronous recordings of Doppler velocity and
continuum intensity images with durations of 32 minutes and 23 minutes,
respectively, recorded close to the disk center of the Sun to study
the propagation and excitation of solar acoustic oscillations. In
the Doppler velocity data, both the standing acoustic waves and the
short-lived, high-degree running waves are visible. The standing
waves are visible as temporary enhancements of the amplitudes of the
large-scale velocity field due to the stochastic superposition of
the acoustic waves. We focus on the high-degree small-scale waves by
suitable filtering in the Fourier domain. Investigating the propagation
and excitation of f- and p 1-modes with wavenumbers k&gt;1.4
Mm-1, we also find that exploding granules contribute to
the excitation of solar p-modes in addition to the contribution of
intergranular lanes.

---------------------------------------------------------
Title: The GREGOR Fabry-Perot interferometer: a new instrument for
high-resolution solar observations
Authors: Denker, Carsten; Balthasar, Horst; Hofmann, Axel; Bello
González, Nazaret; Volkmer, Reiner
2010SPIE.7735E..6MD Altcode: 2010SPIE.7735E.217D
The GREGOR Fabry-Ṕerot Interferometer (GFPI) is one of the first-light
instruments of the 1.5-meter GREGOR solar telescope currently being
commissioned at Observatorio del Teide (OT), Tenerife, Spain. A
spectral resolution of R ~ 250, 000 over the wavelength range from
530-860 nm can be achieved using a tunable dual etalon system. A high
spectral resolving power is needed to extract physical parameters
(e.g., temperature, plasma velocity and the magnetic field vector) from
inversions of photospheric and chromospheric spectral lines. The GFPI
is outfitted with a polarimeter, which accurately measures the full
Stokes vector. Precision polarimetry is facilitated by a calibration
unit in the immediate vicinity of GREGOR's secondary focus. The GFPI
operates close to the diffraction limit of GREGOR, thus providing
access to fine structures as small as 60 km on the solar surface. The
field-of-view (FOV) of 52" × 40" is sufficiently large to cover
significant portions of active regions. Large-format, high-cadence
CCD detectors are an integral part of the instrument to ensure that
scans of spectral lines can be obtained in time spans corresponding
to the evolution time scale of solar phenomena such as granulation,
evolving magnetic fields or dynamic chromospheric features. Besides
describing the technical features of the GFPI and providing a status
report on commissioning the instrument, we will use two-dimensional
spectropolarimetric data obtained with the Vacuum Tower Telescope
(VTT) at OT to illustrate GFPI's science capabilities.

---------------------------------------------------------
Title: The role of emerging bipoles in the formation of a sunspot
penumbra
Authors: Schlichenmaier, R.; Bello González, N.; Rezaei, R.; Waldmann,
T. A.
2010AN....331..563S Altcode: 2010arXiv1003.1313S
The generation of magnetic flux in the solar interior and its transport
from the convection zone into the photosphere, the chromosphere,
and the corona will be in the focus of solar physics research for
the next decades. With 4 m class telescopes, one plans to measure
essential processes of radiative magneto-hydrodynamics that are needed
to understand the nature of solar magnetic fields. One key-ingredient
to understand the behavior of solar magnetic field is the process
of flux emergence into the solar photosphere, and how the magnetic
flux reorganizes to form the magnetic phenomena of active regions
like sunspots and pores. Here, we present a spectropolarimetric and
imaging data set from a region of emerging magnetic flux, in which a
proto-spot without penumbra forms a penumbra. During the formation of
the penumbra the area and the magnetic flux of the spot increases. First
results of our data analysis demonstrate that the additional magnetic
flux, which contributes to the increasing area of the penumbra, is
supplied by the region of emerging magnetic flux. We observe emerging
bipoles that are aligned such that the spot polarity is closer to the
spot. As an emerging bipole separates, the pole of the spot polarity
migrates towards the spot, and finally merges with it. We speculate
that this is a fundamental process, which makes the sunspot accumulate
magnetic flux. As more and more flux is accumulated a penumbra forms
and transforms the proto-spot into a full-fledged sunspot.

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Title: The formation of a sunspot penumbra
Authors: Schlichenmaier, R.; Rezaei, R.; Bello González, N.; Waldmann,
T. A.
2010A&A...512L...1S Altcode:
Context. The formation of a penumbra is crucial for our understanding
of solar magnetism, but it has not been observed in detail. 
Aims: We aim to enhance our knowledge of how a sunspot penumbra forms
and how sunspots grow in size. Methods: We present a data
set of the active region NOAA 11024 acquired at the German VTT with
speckle-reconstructed images in the G-band and Ca ii K. The data set
includes spectropolarimetric profiles from GFPI in Fe i 617.3 nm and
TIP in Fe i 1089.6 nm. Results: On 2009 July 4, at 08:30 UT,
a leading spot without penumbra and pores of opposite polarity were
present in the active region. For the next 4:40 h, we observed the
formation of a penumbra in the leading spot at a cadence of 5 images per
second. We produced speckle reconstructed images of 0.3 arcsec spatial
resolution or better, interrupted by one large gap of 35 min and a
few more small gaps of about 10 min. The leading spot initially has a
size of 230 arcsec2 with only a few penumbral filaments and
then grows to a size of 360 arcsec2. The penumbra forms in
segments, and it takes about 4 h until it encircles half of the umbra,
on the side opposite the following polarity. On the side towards the
following polarity, elongated granules mark a region of magnetic flux
emergence. Conclusions: This ongoing emergence appears to prevent
a steady penumbra from forming on this side. While the penumbra forms,
the umbral area is constant; i.e., the increase in the total spot
area is caused exclusively by the growth of the penumbra. From this
we conclude that the umbra has reached an upper size limit and that
any new magnetic flux that joins the spot is linked to the process of
penumbral formation. Movies are only available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: On the energy flux in acoustic waves in the solar atmosphere .
Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev, O.
2010MmSAI..81..757B Altcode:
The energy supply for the radiative losses of the quiet solar
chromosphere is studied. Time sequences from quiet Sun disc centre
were obtained with the “Göttingen” Fabry-Pérot spectrometer at
the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, in the
non-magnetic Fe I 5576 Å line. The data were reconstructed with speckle
methods. The velocities as measured at the line minimum were subjected
to Fourier and wavelet analysis. The energy fluxes were corrected for
the transmission of the solar atmosphere. We find an energy flux of
∼ 3 000 W m-2 at a height of h=250 km. Approximately 2/3
of it is carried by waves in the 5-10 mHz range, and 1/3 in the 10-20
mHz band. The waves occur predominantly above inter-granular areas. We
speculate that the acoustic flux in waves with periods shorter than the
acoustic cutoff period (U≈190 s) can contribute to the basal heating
of the solar chromosphere, in addition to atmospheric gravity waves.

---------------------------------------------------------
Title: Acoustic waves in the solar atmosphere at high spatial
resolution
Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev, O.
2009A&A...508..941B Altcode:
Aims. The energy supply for the radiative losses of the quiet solar
chromosphere is studied. On the basis of high spatial resolution data,
we investigate the amount of energy flux carried by acoustic waves in
the solar photosphere. Methods: Time sequences from quiet Sun disc
centre were obtained with the “Göttingen” Fabry-Perot spectrometer
at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, in
the non-magnetic Fe i 5576 Å line. The data were reconstructed with
speckle methods. The velocity and intensity fluctuations at line minimum
were subjected to Fourier and wavelet analyses. The energy fluxes at
frequencies higher than the acoustic cutoff frequency (period U ≈
190 s) were corrected for the transmission of the solar atmosphere,
which reduces the signal from short-period waves. Results:
Both Fourier and wavelet analysis give an amount of energy flux of
~3000 W m-2 at a height h = 250 km. Approximately 2/3 of
it is carried by waves in the 5-10 mHz range, and 1/3 in the 10-20
mHz band. Extrapolation of the flux spectra gives an energy flux
of 230-400 W m-2 at frequencies ν &gt; 20 mHz. We find
that the waves occur predominantly above inter-granular areas. 
Conclusions: We conclude that the acoustic flux in waves with periods
shorter than the acoustic cutoff period can contribute to the basal
heating of the solar chromosphere, in addition to the atmospheric
gravity waves found recently.

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Title: Full-Stokes Polarimetry with Speckle Techniques
Authors: Bello González, N.; Kneer, F.; Okunev, O.
2009ASPC..405..407B Altcode:
The new full-Stokes polarimeter implemented in the 2D `Göttingen'
Fabry-Perot spectrometer, based on ferroelectric liquid crystals,
yields magnetograms with minimised seeing induced crosstalk. A
spatial resolution of 0."30--0."35 is achieved after applying speckle
methods. The detection limit for the magnetic field strength is 16 G
(≡ 3σ), yielding a polarimetric sensitivity of 7--8×1015
Mx. Examples of intensity maps, Dopplergrams and magnetograms from
quiet Sun are discussed.

---------------------------------------------------------
Title: A full-Stokes polarimeter for the GREGOR Fabry-Perot
interferometer
Authors: Balthasar, Horst; Bello González, N.; Collados, M.; Denker,
C.; Hofmann, A.; Kneer, F.; Puschmann, K. G.
2009IAUS..259..665B Altcode:
One of the first post-focus instruments of the new solar telescope
GREGOR will be a Fabry-Perot spectrometer, which is an upgrade of the
Göttingen Fabry-Perot interferometer at the Vacuum Tower Telescope
(VTT) on Tenerife. This spectrometer is equipped with a full-Stokes
polarimeter. The modulation is performed with two ferroelectric liquid
crystals, one acting nominally as quarter-wave plate, and the other as
half-wave plate. A modified Savart plate serves as polarimetric beam
splitter. With the present liquid crystals, the optimum wavelength range
of this polarimeter is between 580 and 660 nm. The spectro-polarimeter
will benefit from the capabilities of the new telescope GREGOR which
will provide a spatial resolution of about 0″.1 (75 km on the solar
surface). Thus we will be able to investigate small magnetic features,
and we will study their development with high cadence.

---------------------------------------------------------
Title: Dynamics of small-scale magnetic fields on the Sun:
observations and numerical simulations
Authors: Bello González, N.; Yelles Chaouche, L.; Okunev, O.;
Kneer, F.
2009A&A...494.1091B Altcode:
Context: Small-scale magnetic fields play an important role in the
structure and the dynamics of the solar atmosphere. Aims: This
study aims at revealing the evolution of magnetic fields, together
with granular convection in the quiet Sun by means of observations
with high spatial, spectral, and temporal resolution and of numerical
MHD simulations. Methods: Time sequences from quiet Sun disc
centre were obtained with the upgraded “Göttingen” Fabry-Perot
spectropolarimeter at the Vacuum Tower Telescope, Observatorio del
Teide/Tenerife, in the Fe I 6173 Å line. The data were reconstructed
with speckle methods. For comparison with the observations, numerical
simulations of granular magnetoconvection were carried out with the
MURaM code. The intensities and Stokes vectors emerging from the
simulation box were degraded in wavelength, spatial co-ordinates, and
noise to the quality of the observations. Results: The noise in
the observed magnetograms from the centre-of-gravity method is σ_B≈2
G, yielding a polarimetric sensitivity of 3 × 1015 Mx, at a
cadence of 23 s with 0.33 arcsec spatial resolution in a field of view
of ∼33 arcsec× 25 arcsec. Many of the observed V profiles in network
and internetwork (IN) areas exhibit strong asymmetries that indicate
strong magnetoconvection. The temporal evolutions of IN structures and
of a bright point (BP), as seen in broadband and line-minimum images,
in Dopplergrams, and in magnetograms, are presented. The magnetic
field structure in the numerical MHD simulations is even more complex
than seen in the observations. Correspondingly, the emergent Stokes
profiles are often very abnormal. The degradation yields a reduction
of the intrinsic field strength to the “observed” one by a factor
4-5. The spectral resolution of the spectrometer is adequate, yet
the limitation in spatial resolution and by noise filtering swamps
the details seen in the non-degraded simulations. A BP was not found
in the simulations, presumably because BP's are not so common and
the simulated box is quiet small: only 6 Mm wide in both horizontal
directions. Conclusions: The combination of high-resolution
observations with numerical simulation is a highly valuable means
for studying small-scale magnetic fields on the Sun. Two-dimensional,
low-noise data with spectral resolution as good as achieved here and
with spatial resolution of 0.1 arcsec and better are needed to better
understand this important part of the solar magnetism. A movie
is only available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Small-scale magnetic field dynamics on the Sun at high spatial
and temporal resolution
Authors: Bello González, N.; Okunev, O.; Kneer, F.
2008A&A...490L..23B Altcode:
Aims: We present examples of the time evolution of phenomena
occurring in the quiet Sun photosphere as seen from observations of
high spatial and spectral resolution and with a time cadence of 23
s. Methods: A time sequence of about 5 min has been taken with the
Göttingen Fabry-Perot spectropolarimeter at the VTT in the Fe I 6173 Å
line. The data were reconstructed with speckle methods. Results:
With a polarimetric sensitivity of 2 × 10-3~Ic
(σ_B=2 G), the formation of a bright point as seen from broadband and
line-minimum intensities, as well as in magnetograms and Dopplergrams
can be traced in detail. Other events, like a stable mixed-polarity
configuration in the intergranules and the appearance of magnetic
signature above granules in both dark and bright areas are presented.

---------------------------------------------------------
Title: Evolution of Small-scale Magnetodynamics on the Sun with High
Spatial and Temporal Resolution
Authors: Bello González, N.; Kneer, F.
2008ESPM...12..2.6B Altcode:
For the detection and study of small-scale magnetic fields on
the Sun, observations with both high spatial resolution and high
polarimetric sensitivity are required. The combination formed by
the upgraded Göttingen FPI spectrometer (spectral resolution of
25mÅ, at 617.3nm), full Stokes polarimeter, Adaptive Optics (KAOS)
and speckle reconstruction techniques, provide broadband images of
0.25 arcsec spatial resolution and magnetograms of 0.33 arcsec, with
minimised seeing induced signals yielding a polarimetric sensitivity
of ~0.002 Ic. A description of the optical system as well as results
from the analysis of intensity maps, Dopplergrams and magnetograms from
quiet and active regions on the Sun will be presented. The data were
taken in the FeI 6173Å. We select few examples from the huge variety
of magnetodynamic processes seen in the observations, e.g. the fast
evolution of a bright point in broadband and line minimum intensity,
in magnetograms, and in Dopplergrams is shown. Further examples
indicate convective collapse, magnetic field advection, and magnetic
field diffusion.

---------------------------------------------------------
Title: High-resolution Spectropolarimetry with the Vacuum Tower
Telescope at the Observatorio del Teide/Tenerife: History and Success
of the Göttingen Programme
Authors: Kneer, F.; Bello Gonzalez, N.
2008ESPM...12.2.30K Altcode:
The efforts of the Göttingen solar physics group on high spatial
resolution and 2D spectroscopy started in 1986. First results were
obtained with speckle broadband imaging (de Boer 1992) and with 2D
spectroscopy by means of one Fabry-Perot etalon (FPI) and a Universal
Birefringent Filter (UBF). 2D Stokes V polarimetry followed soon. The
UBF was replaced by a 2nd FPI which allowed short exposures also in
the narrow-band channel of the spectrometer. Thus 2D spectropolari-
metry could be combined with speckle reconstruction. The “Göttingen
FPI” has been upgraded in 2005 for high efficiency and in 2007 for
full Stokes polarimetry and good spectral resolution. It has become
a fast and versatile instrument that has been, and will be, operated
sucessfully for many scientific programmes on the atmospheric dynamics
of the Sun.

---------------------------------------------------------
Title: First-Light Science Cases for the GREGOR Fabry-Perot
Interferometer
Authors: Denker, C.; Balthasar, H.; Bello González, N.; Collados,
M.; Kneer, H. F. Nicklas; Puschmann, K. G.
2008ESPM...12..6.8D Altcode:
The light-gathering capacity and resolving power of the 1.5-meter
aperture GREGOR telescope will provide solar observations of
the full Stokes vector with high temporal, spectral and spatial
resolution. As one of the first-light instruments, the GREGOR
Fabry-Perot Interferometer (GFPI) is well suited for observations
with adaptive optics (AO) correction. Post-facto image correction
(speckle masking imaging and deconvolution) will further enhance
the data quality to approach the diffraction-limited resolution of
the telescope. We will describe the GFPI optical design and its basic
operating procedures. Instruments characteristics such as field-of-view,
cadence, spectral resolution, and spectroscopic/polarimetric observing
modes will result in boundary conditions, which have to be carefully
considered in optimizing the scientific outcome of the first-light
observations. We will present two science cases for quiet Sun and
active region studies to illustrate the capabilities of this imaging
spectro-polarimeter.

---------------------------------------------------------
Title: Fast events and waves in an active region of the Sun observed
in Hα with high spatial resolution
Authors: Sánchez-Andrade Nuño, B.; Bello González, N.; Blanco
Rodríguez, J.; Kneer, F.; Puschmann, K. G.
2008A&A...486..577S Altcode:
Context: We study the chromosphere of an active region of the Sun in
the Hα line. Aims: The development of new instrumentation and new
methods of data analysis allows to scrutinize the dynamics of the solar
chromosphere with high spatial, spectral, and temporal resolution. The
observations we present shed light on some magneto-dynamic processes
occurring above an active region in the chromosphere. Methods:
We took a time series of 55 min in Hα from AR 10875 at θ≈36°. We
used the “Göttingen” Fabry-Perot spectrometer at the Vacuum Tower
Telescope, Observatorio del Teide/Tenerife, to obtain two-dimensional
spectrograms in Hα. Adaptive optics and image reconstruction yielded
a spatial resolution better than 0.5 arcsec throughout the time
sequence. From the wealth of structures, we selected areas of interest
to study further, in detail, some ongoing processes. Results:
A small straight surge developed aside of a pore with upward phase
speed of 100 km s-1 and line-of-sight (LOS) velocity of 15
km s-1. The surge retreated rapidly with LOS velocity of
45 km s-1 at its mouth. It underwent a rebound and fell
back again. Two sympathetic mini-flares were observed that lasted
only approximately 40 s, but showed strong Hα emission. We found
magnetoacoustic waves in long fibrils as mainly short wave trains,
short packets or pulses, i.e., solitary waves consisting of small
(1´´-2´´) blobs. They start at either end of the fibrils and travel
with phase speeds of 12-14 km s-1, i.e., close to the tube
speed and approximately the sound velocity for sufficiently large
magnetic field strengths. Some waves speed up to reach velocities of
the order of 30 km s-1. This is much lower than the expected
Alfvén velocity of ≥200 km s-1 for reasonable magnetic
field strengths and mass densities. We suggest that slow waves are not
purely longitudinal, but possess gas velocities perpendicular to the
direction of propagation of few km s-1. Also, fast waves
travel along sinuous lines suggesting entangled magnetic fields. They
spread out along the direction of propagation in the course of their
evolution and often vanish. We discuss the implications.

---------------------------------------------------------
Title: Narrow-band full Stokes polarimetry of small structures on
the Sun with speckle methods
Authors: Bello González, N.; Kneer, F.
2008A&A...480..265B Altcode:
Aims:For the detection and the study of small-scale magnetic fields
on the Sun, it is important to obtain observations with both high
spatial resolution and high polarimetric sensitivity. Methods:
A second narrow-band etalon and a full Stokes polarimeter, based on
ferroelectric liquid crystals, were implemented in the two-dimensional
“Göttingen” Fabry-Perot spectrometer/polarimeter at the Vacuum
Tower Telescope, Observatorio del Teide/Tenerife. First observations
with the Fe I 6173 Å line and their data analysis with speckle
methods are described. Results: The new polarimeter yields
magnetograms of a field of view of 31 arcsec×52 arcsec with minimised
seeing induced signals and without spurious signals as from the use of
beam-splitting calcites. The achieved spatial and temporal resolution
are 0.30-0.35 arcsec and 36 s, respectively. With a detection limit
for the field strength of 16 G (\cor3σ), a polarimetric sensitivity
of 7-8×1015 Mx is obtained. Examples of intensity maps,
Dopplergrams, and magnetograms from quiet and active regions on the
Sun are discussed. Some of the results on solar magnetism are on 1)
a pore with small-scale structure where we find a region with very
low temperature gradient, 2) polar faculae with strong magnetic field
signals and weaker signals in other areas surrounding them, and 3)
small-scale inter-network magnetic fields with area fillings in the
resolution elements of the order of 0.15.

---------------------------------------------------------
Title: Temporal evolution of intensity, velocity and magnetic field
of sunspots at high spatial resolution
Authors: Bello González, N.; Kneer, F.; Puschmann, K. G.
2007msfa.conf..217B Altcode:
We present results of sunspot observations obtained in April 2006
with the new "Göttingen" Fabry-Perot spectrometer. Thanks to the
large field of view (77"x58") of the new optical setup it has been
possible to perform 2D-spectropolarimetric observations of a small
sunspot and ist surroundings at a heliocentric angle [Theta] ~ 40Å. A
long time series of about one hour has been taken scanning along the
magnetic Fe I 6173 Å and the non-magnetic Fe I 5576 Å spectral lines
quasi-simultaneously. Hence, with the help of image reconstruction
techniques, the temporal evolution of the sunspot fine-structure in
intensity as well as in velocity and magnetic field is analysed at
high spatial resolution.

---------------------------------------------------------
Title: Spectropolarimetry of sunspot penumbrae
Authors: Bello Gonzalez, Nazaret
2006PhDT.......345B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Synthesis of Stokes Profiles from a Two Component Penumbral
Model
Authors: Bello González, N.; Okunev, O.; Kneer, F.
2005ESASP.600E..56B Altcode: 2005ESPM...11...56B; 2005dysu.confE..56B
No abstract at ADS

---------------------------------------------------------
Title: Analysis of Polarimetric Sunspot Data from Tesos/vtt/tenerife
Authors: Valdivielso Casas, L.; Bello González, N.; Puschmann, K. G.;
Sánchez-Andrade Nuño, B.; Kneer, F.
2005ESASP.596E..67V Altcode: 2005ccmf.confE..67V
No abstract at ADS

---------------------------------------------------------
Title: Study of Asymmetries of Stokes Profiles from High Spatial
Resolution Spectropolarimetry
Authors: Bello González, N.; Okunev, O.; Kneer, F.
2005ESASP.596E..50B Altcode: 2005ccmf.confE..50B
No abstract at ADS

---------------------------------------------------------
Title: Polarimetry of sunspot penumbrae with high spatial resolution
Authors: Bello González, N.; Okunev, O. V.; Domínguez Cerdeña,
I.; Kneer, F.; Puschmann, K. G.
2005A&A...434..317B Altcode:
We present two-dimensional high-spatial-resolution spectropolarimetric
observations of sunspot penumbrae. They were obtained in April 2002 and
May 2003 with the "Göttingen" Fabry-Pérot spectrometer at the Vacuum
Tower Telescope at the Observatorio del Teide (Tenerife). Speckle
methods were applied for image reconstruction which resulted
in a spatial resolution of 0.5 arcsec in the magnetograms of the
penumbrae. We analysed Stokes I and V profiles of the Fe II 6149 Å
line, which exhibits no instrumental Stokes Q/U→ V crosstalk, and of
the Fe I line pair at 6302 Å. The main results are the following: 1)
on scales larger than 0.5 arcsec, the intensity pattern of penumbrae
stays the same in the continuum and core images of the 6301.5 Å line,
which stem from 0 km and 300 km (above τ_5=1), respectively. Yet
at scales of 0.5 arcsec and smaller the pattern in the two spectral
features is clearly different. 2) On the limb side of sunspots the
Evershed flow is carried by dark filaments and on the centre side by
bright features and their somewhat weakened tails. We explain this with
a picture in which the velocity of hot rising gas is best seen on the
centre side, while on the limb side the horizontal outward and possibly
downward flows are seen when the gas has cooled down. 3) The un-combed
structure of the magnetic field is confirmed. On the limb side, the more
horizontal fields coincide with dark fibrils or with diffuse intensity
structures. Generally, the more horizontal fields are located at the
positions of strong outflows. 4) Strong line-of-sight components of
the magnetic fields are not found in bright filaments but in dark
structures, somewhat displaced from the darkest parts. Their positions
do not coincide with those of the strongest velocity fields. In general,
our results are compatible with the picture of low lying flow channels
coincident with the horizontal magnetic field, or possibly emerging and
diving down into sub-photospheric layers, like a "sea serpent". Some
further dynamic phenomena are discussed, which demonstrate the richness
of processes in penumbrae, and reveal unexpected properties.

---------------------------------------------------------
Title: Spectropolarimetry in a sunspot penumbra at high spatial
resolution
Authors: Bello González, N.; Okunev, O.; Kneer, F.
2005ASSL..320..183B Altcode: 2005smp..conf..183B
We present results from polarimetric data on sunspot penumbrae obtained
with the Vacuum Tower Telescope at the Observatorio del Teide, Tenerife,
using the `Göttingen' Fabry-Pérot Interferometer. Speckle image
reconstruction has been performed giving us a spatial resolution of
0.6”. The observations were taken in the Fe II 6149.2 Å line which,
given its particular Zeeman splitting, has no instrumental (Q,U) to V
crosstalk and provides us measurements of I and V Stokes profiles to
analyse velocities and magnetic fields in penumbrae.

---------------------------------------------------------
Title: Polarimetry in sunspot penumbrae at high spatial resolution.
Authors: Bello Gonzalez, N.; Okunev, O.; Dominguez Cerdena, I.;
Kneer, F.
2004ANS...325...79B Altcode: 2004ANS...325..P03B; 2004ANS...325a..79B
No abstract at ADS

---------------------------------------------------------
Title: Velocity and Magnetic Fields in Sunspot Penumbrae at Hight
Spatial and Spectral Resolution
Authors: Bello González, Nazaret; Kneer, Franz
2003ANS...324...28B Altcode: 2003ANS...324..D03B
No abstract at ADS