socas-navarro

explanation blue bibcodes open ADS page with paths to full text

Author name code: socas-navarro
ADS astronomy entries on 2022-09-14
author:"Socas Navarro, Hector"

---------------------------------------------------------
Title: Searching for technosignatures in exoplanetary systems with
current and future missions
Authors: Haqq-Misra, Jacob; Schwieterman, Edward W.; Socas-Navarro,
Hector; Kopparapu, Ravi; Angerhausen, Daniel; Beatty, Thomas G.;
Berdyugina, Svetlana; Felton, Ryan; Sharma, Siddhant; De la Torre,
Gabriel G.; Apai, Dániel; TechnoClimes 2020 workshop participants
2022AcAau.198..194H Altcode: 2022arXiv220600030H
Technosignatures refer to observational manifestations of technology
that could be detected through astronomical means. Most previous
searches for technosignatures have focused on searches for radio
signals, but many current and future observing facilities could also
constrain the prevalence of some non-radio technosignatures. This search
could thus benefit from broader participation by the astronomical
community, as contributions to technosignature science can also take
the form of negative results that provide statistically meaningful
quantitative upper limits on the presence of a signal. This paper
provides a synthesis of the recommendations of the 2020 TechnoClimes
workshop, which was an online event intended to develop a research
agenda to prioritize and guide future theoretical and observational
studies technosignatures. The paper provides a high-level overview
of the use of current and future missions to detect exoplanetary
technosignatures at ultraviolet, optical, or infrared wavelengths,
which specifically focuses on the detectability of atmospheric
technosignatures, artificial surface modifications, optical beacons,
space engineering and megastructures, and interstellar flight. This
overview does not derive any new quantitative detection limits but
is intended to provide additional science justification for the use
of current and planned observing facilities as well as to inspire
astronomers conducting such observations to consider the relevance of
their ongoing observations to technosignature science. This synthesis
also identifies possible technology gaps with the ability of current
and planned missions to search for technosignatures, which suggests
the need to consider technosignature science cases in the design of
future mission concepts.

---------------------------------------------------------
Title: The search for transit technosignatures
Authors: Socas-Navarro, Hector
2022cosp...44.2814S Altcode:
As a byproduct of the exoplanet revolution, we can now search for
technosignatures that would potentially leave an imprint on a planet's
transit light-curve data. This is an exciting new window that has
opened in recent years. We can now examine the space environment around
a planet in search for artificial megastructures or large collections
artifacts, such as satellite belts. This talk summarizes some possible
technosignatures that might be within the reach of current or upcoming
instrumentation, with emphasis on photometric observations. The axes of
merit or the ichnoscale diagram may be used to provide a quantitative
framework in which one can arrange technosignatures. A more detailed
discussion will be presented on the search for geosynchronous artifacts,
such as Clarke exobelts. These have the appealing peculiarity of being
"Occam-friendly", as well as a natural extrapolation of current human
technology and having typical lifetime scales of at least millions
of years.

---------------------------------------------------------
Title: Further support and a candidate location for Planet 9
Authors: Socas-Navarro, Hector
2022arXiv220507675S Altcode:
The existence of a hypothetical Planet 9 lurking in the outer
solar system has been invoked as a plausible explanation for the the
anomalous clustering in the orbits of some trans-Neptunian objects. Here
we propose to use meteors arriving at Earth as messengers with the
potential of revealing the presence of a hitherto undiscovered massive
object. The peculiar meteor CNEOS 2014-01-08, recently put forward as
the first interstellar meteor, might be one such messenger. Its origin
in the sky overlaps with the predicted band of possible Planet 9 orbits
and it is actually compatible with the highest probability region. The
odds of this coincidence being due to chance are of ~0.5\%. Furthermore,
some statistical anomalies about CNEOS 2014-01-08 are resolved under
the hypothesis that it was flung at Earth by Planet 9. Based on the
available data, we propose the region at coordinates RA:50.0{\pm}4°,
dec:11.8{\pm}1.8° in the constellation of Aries, as the first candidate
location for Planet 9.

---------------------------------------------------------
Title: Limitations of the Ca II 8542 Å Line for the Determination
of Magnetic Field Oscillations
Authors: Felipe, Tobias; Socas Navarro, Hector; Sangeetha, C. R.;
Milic, Ivan
2021ApJ...918...47F Altcode: 2021arXiv210702160F
Chromospheric umbral oscillations produce periodic brightenings
in the core of some spectral lines, known as umbral flashes. They
are also accompanied by fluctuations in velocity, temperature, and,
according to several recent works, magnetic field. In this study, we
aim to ascertain the accuracy of the magnetic field determined from
inversions of the Ca II 8542 Å line. We have developed numerical
simulations of wave propagation in a sunspot umbra. Synthetic Stokes
profiles emerging from the simulated atmosphere were computed and
then inverted using the NICOLE code. The atmospheres inferred from
the inversions have been compared with the original parameters from
the simulations. Our results show that the inferred chromospheric
fluctuations in velocity and temperature match the known oscillations
from the numerical simulation. In contrast, the vertical magnetic field
obtained from the inversions exhibits an oscillatory pattern with a ~300
G peak-to-peak amplitude, which is absent in the simulation. We have
assessed the error in the inferred parameters by performing numerous
inversions with slightly different configurations of the same Stokes
profiles. We find that when the atmosphere is approximately at rest,
the inversion tends to favor solutions that underestimate the vertical
magnetic field strength. On the contrary, during umbral flashes,
the values inferred from most of the inversions are concentrated at
stronger fields than those from the simulation. Our analysis provides
a quantification of the errors associated with the inversions of the
Ca II 8542 Å line and suggests caution with the interpretation of
the inferred magnetic field fluctuations.

---------------------------------------------------------
Title: Exploring the Sun's upper atmosphere with neural networks:
Reversed patterns and the hot wall effect
Authors: Socas-Navarro, H.; Asensio Ramos, A.
2021A&A...652A..78S Altcode:
We have developed an inversion procedure designed for high-resolution
solar spectro-polarimeters, such as those of Hinode and the
DKIST. The procedure is based on artificial neural networks trained
with profiles generated from random atmospheric stratifications
for a high generalization capability. When applied to Hinode data,
we find a hot fine-scale network structure whose morphology changes
with height. In the middle layers, this network resembles what is
observed in G-band filtergrams, but it is not identical. Surprisingly,
the temperature enhancements in the middle and upper photosphere have
a reversed pattern. Hot pixels in the middle photosphere, possibly
associated with small-scale magnetic elements, appear cool at the
log τ500 = −3 and −4 level, and vice versa. Finally,
we find hot arcs on the limb side of magnetic pores. We interpret them
as the first piece of direct observational evidence of the "hot wall"
effect, which is a prediction of theoretical models from the 1970's.

---------------------------------------------------------
Title: Concepts for future missions to search for technosignatures
Authors: Socas-Navarro, Hector; Haqq-Misra, Jacob; Wright, Jason
T.; Kopparapu, Ravi; Benford, James; Davis, Ross; TechnoClimes 2020
workshop participants
2021AcAau.182..446S Altcode: 2021arXiv210301536S
New and unique opportunities now exist to look for technosignatures (TS)
beyond traditional SETI radio searches, motivated by tremendous advances
in exoplanet science and observing capabilities in recent years. Space
agencies, both public and private, may be particularly interested in
learning about the community's views as to the optimal methods for
future TS searches with current or forthcoming technology. This report
is an effort in that direction. We put forward a set of possible mission
concepts designed to search for TS, although the data supplied by such
missions would also benefit other areas of astrophysics. We introduce
a novel framework to analyze a broad diversity of TS in a quantitative
manner. This framework is based on the concept of ichnoscale, which
is a new parameter related to the scale of a TS cosmic footprint,
together with the number of potential targets where such TS can be
searched for, and whether or not it is continuous in time.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: Long-term evolution of three light bridges developed on the
same sunspot
Authors: Griñón-Marín, A. B.; Pastor Yabar, A.; Centeno, R.;
Socas-Navarro, H.
2021A&A...647A.148G Altcode: 2021arXiv210204392B; 2021arXiv210204392G
One important feature of sunspots is the presence of light
bridges. These structures are elongated and bright (as compared
to the umbra) features that seem to be related to the formation
and evolution of sunspots. In this work, we studied the long-term
evolution and the stratification of different atmospheric parameters
of three light bridges formed in the same host sunspot by different
mechanisms. To accomplish this, we used data taken with the GREGOR
Infrared Spectrograph installed at the GREGOR telescope. These data
were inverted to infer the physical parameters of the atmosphere
where the observed spectral profiles were formed of the three light
bridges. We find that, in general, the behaviour of the three light
bridges is typical of this kind of structure with the magnetic
field strength, inclination, and temperature values between the
values at the umbra and the penumbra. We also find that they are of a
significantly non-magnetic character (particularly at the axis of the
light bridges) as it is deduced from the filling factor. In addition,
within the common behaviour of the physical properties of light bridges,
we observe that each one exhibits a particular behaviour. Another
interesting result is that the light bridge cools down, the magnetic
field decreases, and the magnetic field lines get more inclined higher
in the atmosphere. Finally, we studied the magnetic and non-magnetic
line-of-sight velocities of the light bridges. The former shows that
the magnetic component is at rest and, interestingly, its variation
with optical depth shows a bi-modal behaviour. For the line-of-sight
velocity of the non-magnetic component, we see that the core of the
light bridge is at rest or with shallow upflows and clear downflows
sinking through the edges.

---------------------------------------------------------
Title: Semi-empirical Models of Spicule from Inversion of Ca II 8542
Å Line
Authors: Kuridze, David; Socas-Navarro, Hector; Koza, Július;
Oliver, Ramon
2021ApJ...908..168K Altcode: 2020arXiv201203702K
We study a solar spicule observed off-limb using high-resolution imaging
spectroscopy in the Ca II 8542 Å line obtained with the CRisp Imaging
SpectroPolarimeter (CRISP) on the Swedish 1 m Solar Telescope. Using
a new version of the non-LTE code NICOLE specifically developed
for this problem we invert the spicule single- and double-peak line
profiles. This new version considers off-limb geometry and computes
atomic populations by solving the 1D radiative transfer assuming
a vertical stratification. The inversion proceeds by fitting the
observed spectral profiles at 14 different heights with synthetic
profiles computed in the model by solving the radiative transfer
problem along its length. Motivated by the appearance of double-peak
Ca II 8542 Å spicule profiles, which exhibit two distinct emission
features well separated in wavelength, we adopt a double-component
scenario. We start from the ansatz that the spicule parameters are
practically constant along the spicule axis for each component,
except for a density drop. Our results support this ansatz by
attaining very good fits to the entire set of 14 × 4 profiles (14
heights and 4 times). We show that the double-component model with
uniform temperature of 9560 K, exponential decrease of density with a
height scale of 1000-2000 km, and the counter-oriented line-of-sight
velocities of components reproduce the double-peak line profiles at
all spicule segments well. Analyses of the numerical response function
reveals the necessity of the inversions of spectra at multiple height
positions to obtain height-dependent, degeneracy-free reliable models
with a limited number of free parameters.

---------------------------------------------------------
Title: Mapping the Sun's upper photosphere with artificial neural
networks
Authors: Socas-Navarro, Hector; Asensio Ramos, Andres
2021arXiv210111445S Altcode:
We have developed an inversion procedure designed for high-resolution
solar spectro-polarimeters, such as Hinode/SP or DKIST/ViSP. The
procedure is based on artificial neural networks trained with
profiles generated from random atmospheric stratifications for a high
generalization capability. When applied to Hinode data we find a hot
fine-scale network structure whose morphology changes with height. In
the middle layers this network resembles what is observed in G-band
filtergrams but it is not identical. Surprisingly, the temperature
enhancements in the middle and upper photosphere have a reversed
pattern. Hot pixels in the middle photosphere, possibly associated to
small-scale magnetic elements, appear cool at the log(tau_500)=-3 and
-4 level, and viceversa. Finally, we find hot arcs on the limb side of
magnetic pores, which we interpret as the first direct observational
evidence of the "hot wall" effect in temperature.

---------------------------------------------------------
Title: Downflowing umbral flashes as evidence of standing waves in
sunspot umbrae
Authors: Felipe, T.; Henriques, V. M. J.; de la Cruz Rodríguez, J.;
Socas-Navarro, H.
2021A&A...645L..12F Altcode: 2021arXiv210104188F
Context. Umbral flashes are sudden brightenings commonly visible
in the core of some chromospheric lines. Theoretical and numerical
modeling suggests that they are produced by the propagation of shock
waves. According to these models and early observations, umbral flashes
are associated with upflows. However, recent studies have reported
umbral flashes in downflowing atmospheres. Aims: We aim to
understand the origin of downflowing umbral flashes. We explore how
the existence of standing waves in the umbral chromosphere impacts the
generation of flashed profiles. Methods: We performed numerical
simulations of wave propagation in a sunspot umbra with the code
MANCHA. The Stokes profiles of the Ca II 8542 Å line were synthesized
with the NICOLE code. Results: For freely propagating waves,
the chromospheric temperature enhancements of the oscillations are
in phase with velocity upflows. In this case, the intensity core of
the Ca II 8542 Å atmosphere is heated during the upflowing stage of
the oscillation. However, a different scenario with a resonant cavity
produced by the sharp temperature gradient of the transition region
leads to chromospheric standing oscillations. In this situation,
temperature fluctuations are shifted backward and temperature
enhancements partially coincide with the downflowing stage of the
oscillation. In umbral flash events produced by standing oscillations,
the reversal of the emission feature is produced when the oscillation
is downflowing. The chromospheric temperature keeps increasing while
the atmosphere is changing from a downflow to an upflow. During the
appearance of flashed Ca II 8542 Å cores, the atmosphere is upflowing
most of the time, and only 38% of the flashed profiles are associated
with downflows. Conclusions: We find a scenario that remarkably
explains the recent empirical findings of downflowing umbral flashes
as a natural consequence of the presence of standing oscillations
above sunspot umbrae.

---------------------------------------------------------
Title: Spatially resolved measurements of the solar photospheric
oxygen abundance
Authors: Cubas Armas, M.; Asensio Ramos, A.; Socas-Navarro, H.
2020A&A...643A.142C Altcode: 2020arXiv201002151C
 Aims: We report the results of a novel determination of
the solar oxygen abundance using spatially resolved observations
and inversions. We seek to derive the photospheric solar oxygen
abundance with a method that is robust against uncertainties in the
model atmosphere. Methods: We use observations with spatial
resolution obtained at the Vacuum Tower Telescope to derive the
oxygen abundance at 40 different spatial positions in granules and
intergranular lanes. We first obtain a model for each location by
inverting the Fe I lines with the NICOLE inversion code. These models
are then integrated into a hierarchical Bayesian model that is used
to infer the most probable value for the oxygen abundance that is
compatible with all the observations. The abundance is derived from the
[O I] forbidden line at 6300 Å taking into consideration all possible
nuisance parameters that can affect the abundance. Results: Our
results show good agreement in the inferred oxygen abundance for all the
pixels analyzed, demonstrating the robustness of the analysis against
possible systematic errors in the model. We find a slightly higher
oxygen abundance in granules than in intergranular lanes when treated
separately (log(ɛO) = 8.83 ± 0.02 vs. log(ɛO) =
8.76 ± 0.02), which is a difference of approximately 2-σ. This tension
suggests that some systematic errors in the model or the radiative
transfer still exist but are small. When taking all pixels together,
we obtain an oxygen abundance of log(ɛO) = 8.80 ± 0.03,
which is compatible with both granules and lanes within 1-σ. The
spread of results is due to both systematic and random errors.

---------------------------------------------------------
Title: The penumbral solar filaments from the photosphere to the
chromosphere
Authors: Murabito, M.; Ermolli, I.; Giorgi, F.; Stangalini, M.;
Guglielmino, S. L.; Jafarzadeh, S.; Socas-Navarro, H.; Romano, P.;
Zuccarello, F.
2020JPhCS1548a2017M Altcode:
The magnetic field structure of sunspots above the photosphere remain
poorly understood due to limitations in observations and the complexity
of these atmospheric layers. In this regard, we studied the large
isolated sunspot (70”× 80”) located in the active region NOAA
12546 with spectro-polarimetric measurements acquired along the Fe I
617.3 nm and Ca II 854.2 nm lines with the IBIS/DST instrument, under
excellent seeing conditions lasting more than three hours. Using the
Non Local Thermodynamic Equilibrium inversion code we inverted both
line measurements simultaneously to retrieve the three-dimensional
magnetic and thermal structure of the penumbral region from the
bottom of the photosphere to the middle chromosphere. The analysis
of data acquired at spectral ranges unexplored allow us to show clear
evidence of the spine and intra-spine structure of the magnetic field at
chromospheric heights. In particular, we found a peak-to-peak variations
of the magnetic field strength and inclination of about 200 G and 10°
chromospheric heights, respectively, and of about 300 G and 20° in the
photosphere. We also investigated the structure of the magnetic field
gradient in the penumbra along the vertical and azimuthal directions,
confirming previous results reported in the literature from data taken
at the spectral region of the He I 1083 nm triplet.

---------------------------------------------------------
Title: Discovery of long-period magnetic field oscillations and
motions in isolated sunspots
Authors: Griñón-Marín, A. B.; Pastor Yabar, A.; Socas-Navarro,
H.; Centeno, R.
2020A&A...635A..64G Altcode: 2020arXiv200106030G
We analyse the temporal evolution of the inclination component of
the magnetic field vector for the penumbral area of 25 isolated
sunspots. Compared to previous works, the use of data from the
HMI instrument aboard the SDO observatory facilitates the study
of a very long time series (≈1 week) with a good spatial and
temporal resolution. We used the wavelet technique and we found some
filamentary-shaped events with large wavelet power. Their distribution
of periods is broad, ranging from the lower limit for this study of 48
min up to 63 h. An interesting property of these events is that they
do not appear homogeneously all around the penumbra but they seem to
concentrate at particular locations. The cross-comparison of these
wavelet maps with AIA data shows that the regions where these events
appear are visually related to the coronal loops that connect the outer
penumbra to one or more neighbouring opposite polarity flux patches.

---------------------------------------------------------
Title: The 3D structure of the penumbra at high resolution from the
bottom of the photosphere to the middle chromosphere
Authors: Murabito, Mariarita; Ermolli, Ilaria; Giorgi, Fabrizio;
Stangalini, Marco; Guglielmino, Salvo L.; Jafarzadeh, Shahin;
Socas-Navarro, Hector; Romano, Paolo; Zuccarello, Francesca
2020IAUS..354..448M Altcode:
Sunspots are the most prominent feature of the solar magnetism in the
photosphere. Although they have been widely investigated in the past,
their structure remains poorly understood. Indeed, due to limitations
in observations and the complexity of the magnetic field estimation
at chromospheric heights, the magnetic field structure of sunspot
above the photosphere is still uncertain. Improving the present
knowledge of sunspot is important in solar and stellar physics,
since spot generation is seen not only on the Sun, but also on other
solar-type stars. In this regard, we studied a large, isolated sunspot
with spectro-polarimeteric measurements that were acquired at the Fe
I 6173 nm and Ca II 8542 nm lines by the spectropolarimeter IBIS/DST
under excellent seeing conditions lasting more than three hours. Using
the Non-LTE inversion code NICOLE, we inverted both line measurements
simultaneously, to retrieve the three-dimensional magnetic and thermal
structure of the penumbral region from the bottom of the photosphere
to the middle chromosphere. Our analysis of data acquired at spectral
ranges unexplored in previous studies shows clear spine and intra-spine
structure of the penumbral magnetic field at chromopheric heights. Our
investigation of the magnetic field gradient in the penumbra along
the vertical and azimuthal directions confirms results reported in
the literature from analysis of data taken at the spectral region of
the He I 1083 nm triplet.

---------------------------------------------------------
Title: High-resolution spectroscopy of Boyajian's star during optical
dimming events
Authors: Martínez González, M. J.; González-Fernández, C.; Asensio
Ramos, A.; Socas-Navarro, H.; Westendorp Plaza, C.; Boyajian, T. S.;
Wright, J. T.; Collier Cameron, A.; González Hernández, J. I.;
Holgado, G.; Kennedy, G. M.; Masseron, T.; Molinari, E.; Saario, J.;
Simón-Díaz, S.; Toledo-Padrón, B.
2019MNRAS.486..236M Altcode: 2019MNRAS.tmp..828M; 2018arXiv181206837M
Boyajian's star is an apparently normal main-sequence F-type star
with a very unusual light curve. The dipping activity of the star,
discovered during the Kepler mission, presents deep, asymmetric,
and aperiodic events. Here we present high-resolution spectroscopic
follow-up during some dimming events recorded post-Kepler observations,
from ground-based telescopes. We analyse data from the HERMES, HARPS-N,
and FIES spectrographs to characterize the stellar atmosphere and
to put some constraints on the hypotheses that have appeared in the
literature concerning the occulting elements. The star's magnetism,
if existing, is not extreme. The spots on the surface, if present,
would occupy 0.02 per cent of the area, at most. The chromosphere,
irrespective of the epoch of observation, is hotter than the values
expected from radiative equilibrium, meaning that the star has some
degree of activity. We find no clear evidence of the interstellar
medium or exocoments being responsible for the dimmings of the light
curve. However, we detect at 1-2σ level, a decrease of the radial
velocity of the star during the first dip recorded after the Kepler
observations. We claim the presence of an optically thick object with
likely inclined and high impact parameter orbits that produces the
observed Rossiter-McLaughlin effect.

---------------------------------------------------------
Title: Can a negative-mass cosmology explain dark matter and dark
energy?
Authors: Socas-Navarro, H.
2019A&A...626A...5S Altcode: 2019arXiv190208287S
A recent study by Farnes (2018, A&amp;A, 620, A92) proposed an
alternative cosmological model in which both dark matter and dark
energy are replaced with a single fluid of negative mass. This
paper presents a critical review of that model. A number of problems
and discrepancies with observations are identified. For instance,
the predicted shape and density of galactic dark matter halos
are incorrect. Also, halos would need to be less massive than the
baryonic component, otherwise they would become gravitationally
unstable. Perhaps the most challenging problem in this theory is
the presence of a large-scale version of the "runaway effect", which
would result in all galaxies moving in random directions at nearly
the speed of light. Other more general issues regarding negative
mass in general relativity are discussed, such as the possibility of
time-travel paradoxes. The simulation video is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201832760/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Height Dependence of the Penumbral Fine-scale Structure in
the Inner Solar Atmosphere
Authors: Murabito, Mariarita; Ermolli, I.; Giorgi, F.; Stangalini,
M.; Guglielmino, S. L.; Jafarzadeh, S.; Socas-Navarro, H.; Romano,
P.; Zuccarello, F.
2019ApJ...873..126M Altcode: 2018arXiv181209029M
We studied the physical parameters of the penumbra in a large and fully
developed sunspot, one of the largest over the last two solar cycles,
by using full-Stokes measurements taken at the photospheric Fe I 617.3
nm and chromospheric Ca II 854.2 nm lines with the Interferometric
Bidimensional Spectrometer. Inverting measurements with the Non-LTE
inversion COde (NICOLE) code, we obtained the three-dimensional
structure of the magnetic field in the penumbra from the bottom
of the photosphere up to the middle chromosphere. We analyzed the
azimuthal and vertical gradient of the magnetic field strength and
inclination. Our results provide new insights on the properties of the
penumbral magnetic fields in the chromosphere at atmospheric heights
unexplored in previous studies. We found signatures of the small-scale
spine and intraspine structure of both the magnetic field strength and
inclination at all investigated atmospheric heights. In particular,
we report typical peak-to-peak variations of the field strength and
inclination of ≈300 G and ≈20°, respectively, in the photosphere,
and of ≈200 G and ≈10° in the chromosphere. In addition, we
estimated the vertical gradient of the magnetic field strength in
the studied penumbra: we find a value of ≈0.3 G km-1
between the photosphere and the middle chromosphere. Interestingly,
the photospheric magnetic field gradient changes sign from negative
in the inner to positive in the outer penumbra.

---------------------------------------------------------
Title: Signatures of Magnetic Reconnection at the Footpoints of
Fan-shaped Jets on a Light Bridge Driven by Photospheric Convective
Motions
Authors: Bai, Xianyong; Socas-Navarro, Hector; Nóbrega-Siverio,
Daniel; Su, Jiangtao; Deng, Yuanyong; Li, Dong; Cao, Wenda; Ji, Kaifan
2019ApJ...870...90B Altcode: 2018arXiv181103723B
Dynamical jets are generally found on light bridges (LBs), which are
key to studying sunspot decay. So far, their formation mechanism
is not fully understood. In this paper, we used state-of-the-art
observations from the Goode Solar Telescope, the Interface Region
Imaging Spectrograph, the Spectro-polarimeter on board Hinode, and
the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory to analyze the fan-shaped jets on LBs in detail. A
continuous upward motion of the jets in the ascending phase is found
from the Hα velocity that lasts for 12 minutes and is associated
with the Hα line wing enhancements. Two mini jets appear on the
bright fronts of the fan-shaped jets visible in the AIA 171 and 193
Å channels, with a time interval as short as 1 minute. Two kinds of
small-scale convective motions are identified in the photospheric
images, along with the Hα line wing enhancements. One seems to be
associated with the formation of a new convection cell, and the other
manifests as the motion of a dark lane passing through the convection
cell. The finding of three-lobe Stokes V profiles and their inversion
with the NICOLE code indicate that there are magnetic field lines
with opposite polarities in LBs. From the Hα -0.8 Å images, we found
ribbon-like brightenings propagating along the LBs, possibly indicating
slipping reconnection. Our observation supports the idea that the
fan-shaped jets under study are caused by magnetic reconnection, and
photospheric convective motions play an important role in triggering
the magnetic reconnection.

---------------------------------------------------------
Title: On the Connection Between Planets, Dark Matter and Cancer
Authors: Socas-Navarro, Hector
2018arXiv181202482S Altcode:
In a recent paper, Zioutas and Valachovic (2018) claim that dark
matter is responsible for a significant fraction of the melanoma skin
cancer. This conclusion is drawn from their observation of a significant
correlation between skin melanoma incidence in the US and the inner
planets positions (especially those of Mercury and Earth). Here
I present a number of objections to their interpretation. Some
(but not all) of the counterarguments are based on the analysis
of a larger dataset from the same source, considering more cancer
types and separating by patient attributes, such as race. One of the
counterarguments is that, if the melanoma fluctuations with periods
similar to planetary orbits were produced by dark matter density
enhancements on Earth, then we would have to conclude that the black
population is somehow immune to dark matter, a conclusion that seems
incompatible with the current WIMP paradigm. Interestingly, some
periodicities are present in the data, including the ones reported
by Zioutas and Valachovic, but I argue that they must have a societal
rather than astronomical origin.

---------------------------------------------------------
Title: Inversions of synthetic umbral flashes: Effects of scanning
time on the inferred atmospheres
Authors: Felipe, T.; Socas-Navarro, H.; Przybylski, D.
2018A&A...614A..73F Altcode: 2018arXiv180205028F
Context. The use of instruments that record narrowband images at
selected wavelengths is a common approach in solar observations. They
allow scanning of a spectral line by sampling the Stokes profiles with
two-dimensional images at each line position, but require a compromise
between spectral resolution and temporal cadence. The interpretation
and inversion of spectropolarimetric data generally neglect changes in
the solar atmosphere during the scanning of line profiles. Aims:
We evaluate the impact of the time-dependent acquisition of various
wavelengths on the inversion of spectropolarimetric profiles from
chromospheric lines during umbral flashes. Methods: Numerical
simulations of nonlinear wave propagation in a sunspot model were
performed with the code MANCHA. Synthetic Stokes parameters in the Ca
II 8542 Å line in NLTE were computed for an umbral flash event using
the code NICOLE. Artificial profiles with the same wavelength coverage
and temporal cadence from reported observations were constructed and
inverted. The inferred atmospheric stratifications were compared with
the original simulated models. Results: The inferred atmospheres
provide a reasonable characterization of the thermodynamic properties
of the atmosphere during most of the phases of the umbral flash. The
Stokes profiles present apparent wavelength shifts and other spurious
deformations at the early stages of the flash, when the shock wave
reaches the formation height of the Ca II 8542 Å line. These features
are misinterpreted by the inversion code, which can return unrealistic
atmospheric models from a good fit of the Stokes profiles. The
misguided results include flashed atmospheres with strong downflows,
even though the simulation exhibits upflows during the umbral flash,
and large variations in the magnetic field strength. Conclusions:
Our analyses validate the inversion of Stokes profiles acquired by
sequentially scanning certain selected wavelengths of a line profile,
even in the case of rapidly changing chromospheric events such as
umbral flashes. However, the inversion results are unreliable during
a short period at the development phase of the flash.

---------------------------------------------------------
Title: Possible Photometric Signatures of Moderately Advanced
Civilizations: The Clarke Exobelt
Authors: Socas-Navarro, Hector
2018ApJ...855..110S Altcode: 2018arXiv180207723S
This paper puts forward a possible new indicator of the presence of
moderately advanced civilizations on transiting exoplanets. The idea
is to examine the region of space around a planet where potential
geostationary or geosynchronous satellites would orbit (hereafter,
the Clarke exobelt). Civilizations with a high density of devices
and/or space junk in that region, but otherwise similar to ours in
terms of space technology (our working definition of “moderately
advanced”), may leave a noticeable imprint on the light curve of
the parent star. The main contribution to such a signature comes from
the exobelt edge, where its opacity is maximum due to geometrical
projection. Numerical simulations have been conducted for a variety of
possible scenarios. In some cases, a Clarke exobelt with a fractional
face-on opacity of ∼10-4 would be easily observable with
existing instrumentation. Simulations of Clarke exobelts and natural
rings are used to quantify how they can be distinguished by their
light curves.

---------------------------------------------------------
Title: Alfvén wave dissipation in the solar chromosphere
Authors: Grant, Samuel D. T.; Jess, David B.; Zaqarashvili, Teimuraz
V.; Beck, Christian; Socas-Navarro, Hector; Aschwanden, Markus J.;
Keys, Peter H.; Christian, Damian J.; Houston, Scott J.; Hewitt,
Rebecca L.
2018NatPh..14..480G Altcode: 2018arXiv181007712G
Magnetohydrodynamic Alfvén waves1 have been a focus of
laboratory plasma physics2 and astrophysics3
for over half a century. Their unique nature makes them ideal energy
transporters, and while the solar atmosphere provides preferential
conditions for their existence4, direct detection has proved
difficult as a result of their evolving and dynamic observational
signatures. The viability of Alfvén waves as a heating mechanism relies
upon the efficient dissipation and thermalization of the wave energy,
with direct evidence remaining elusive until now. Here we provide the
first observational evidence of Alfvén waves heating chromospheric
plasma in a sunspot umbra through the formation of shock fronts. The
magnetic field configuration of the shock environment, alongside the
tangential velocity signatures, distinguish them from conventional
umbral flashes5. Observed local temperature enhancements
of 5% are consistent with the dissipation of mode-converted Alfvén
waves driven by upwardly propagating magneto-acoustic oscillations,
providing an unprecedented insight into the behaviour of Alfvén waves
in the solar atmosphere and beyond.

---------------------------------------------------------
Title: The First Post-Kepler Brightness Dips of KIC 8462852
Authors: Boyajian, Tabetha. S.; Alonso, Roi; Ammerman, Alex; Armstrong,
David; Asensio Ramos, A.; Barkaoui, K.; Beatty, Thomas G.; Benkhaldoun,
Z.; Benni, Paul; Bentley, Rory O.; Berdyugin, Andrei; Berdyugina,
Svetlana; Bergeron, Serge; Bieryla, Allyson; Blain, Michaela G.;
Capetillo Blanco, Alicia; Bodman, Eva H. L.; Boucher, Anne; Bradley,
Mark; Brincat, Stephen M.; Brink, Thomas G.; Briol, John; Brown,
David J. A.; Budaj, J.; Burdanov, A.; Cale, B.; Aznar Carbo, Miguel;
Castillo García, R.; Clark, Wendy J.; Clayton, Geoffrey C.; Clem,
James L.; Coker, Phillip H.; Cook, Evan M.; Copperwheat, Chris M.;
Curtis, J. L.; Cutri, R. M.; Cseh, B.; Cynamon, C. H.; Daniels, Alex
J.; Davenport, James R. A.; Deeg, Hans J.; De Lorenzo, Roberto; de
Jaeger, Thomas; Desrosiers, Jean-Bruno; Dolan, John; Dowhos, D. J.;
Dubois, Franky; Durkee, R.; Dvorak, Shawn; Easley, Lynn; Edwards, N.;
Ellis, Tyler G.; Erdelyi, Emery; Ertel, Steve; Farfán, Rafael. G.;
Farihi, J.; Filippenko, Alexei V.; Foxell, Emma; Gandolfi, Davide;
Garcia, Faustino; Giddens, F.; Gillon, M.; González-Carballo,
Juan-Luis; González-Fernández, C.; González Hernández, J. I.;
Graham, Keith A.; Greene, Kenton A.; Gregorio, J.; Hallakoun, Na'ama;
Hanyecz, Ottó; Harp, G. R.; Henry, Gregory W.; Herrero, E.; Hildbold,
Caleb F.; Hinzel, D.; Holgado, G.; Ignácz, Bernadett; Ilyin, Ilya;
Ivanov, Valentin D.; Jehin, E.; Jermak, Helen E.; Johnston, Steve;
Kafka, S.; Kalup, Csilla; Kardasis, Emmanuel; Kaspi, Shai; Kennedy,
Grant M.; Kiefer, F.; Kielty, C. L.; Kessler, Dennis; Kiiskinen,
H.; Killestein, T. L.; King, Ronald A.; Kollar, V.; Korhonen, H.;
Kotnik, C.; Könyves-Tóth, Réka; Kriskovics, Levente; Krumm, Nathan;
Krushinsky, Vadim; Kundra, E.; Lachapelle, Francois-Rene; LaCourse,
D.; Lake, P.; Lam, Kristine; Lamb, Gavin P.; Lane, Dave; Lau, Marie
Wingyee; Lewin, Pablo; Lintott, Chris; Lisse, Carey; Logie, Ludwig;
Longeard, Nicolas; Lopez Villanueva, M.; Whit Ludington, E.; Mainzer,
A.; Malo, Lison; Maloney, Chris; Mann, A.; Mantero, A.; Marengo,
Massimo; Marchant, Jon; Martínez González, M. J.; Masiero, Joseph R.;
Mauerhan, Jon C.; McCormac, James; McNeely, Aaron; Meng, Huan Y. A.;
Miller, Mike; Molnar, Lawrence A.; Morales, J. C.; Morris, Brett M.;
Muterspaugh, Matthew W.; Nespral, David; Nugent, C. R.; Nugent,
Katherine M.; Odasso, A.; O'Keeffe, Derek; Oksanen, A.; O'Meara,
John M.; Ordasi, András; Osborn, Hugh; Ott, John J.; Parks, J. R.;
Rodriguez Perez, Diego; Petriew, Vance; Pickard, R.; Pál, András;
Plavchan, P.; Pollacco, Don; Pozo Nuñez, F.; Pozuelos, F. J.; Rau,
Steve; Redfield, Seth; Relles, Howard; Ribas, Ignasi; Richards, Jon;
Saario, Joonas L. O.; Safron, Emily J.; Sallai, J. Martin; Sárneczky,
Krisztián; Schaefer, Bradley E.; Schumer, Clea F.; Schwartzendruber,
Madison; Siegel, Michael H.; Siemion, Andrew P. V.; Simmons, Brooke D.;
Simon, Joshua D.; Simón-Díaz, S.; Sitko, Michael L.; Socas-Navarro,
Hector; Sódor, Á.; Starkey, Donn; Steele, Iain A.; Stone, Geoff;
Strassmeier, Klaus G.; Street, R. A.; Sullivan, Tricia; Suomela, J.;
Swift, J. J.; Szabó, Gyula M.; Szabó, Róbert; Szakáts, Róbert;
Szalai, Tamás; Tanner, Angelle M.; Toledo-Padrón, B.; Tordai, Tamás;
Triaud, Amaury H. M. J.; Turner, Jake D.; Ulowetz, Joseph H.; Urbanik,
Marian; Vanaverbeke, Siegfried; Vanderburg, Andrew; Vida, Krisztián;
Vietje, Brad P.; Vinkó, József; von Braun, K.; Waagen, Elizabeth
O.; Walsh, Dan; Watson, Christopher A.; Weir, R. C.; Wenzel, Klaus;
Westendorp Plaza, C.; Williamson, Michael W.; Wright, Jason T.; Wyatt,
M. C.; Zheng, WeiKang; Zsidi, Gabriella
2018ApJ...853L...8B Altcode: 2018arXiv180100732B
We present a photometric detection of the first brightness dips of
the unique variable star KIC 8462852 since the end of the Kepler space
mission in 2013 May. Our regular photometric surveillance started in
2015 October, and a sequence of dipping began in 2017 May continuing
on through the end of 2017, when the star was no longer visible from
Earth. We distinguish four main 1%-2.5% dips, named “Elsie,”
“Celeste,” “Skara Brae,” and “Angkor,” which persist
on timescales from several days to weeks. Our main results so far
are as follows: (i) there are no apparent changes of the stellar
spectrum or polarization during the dips and (ii) the multiband
photometry of the dips shows differential reddening favoring non-gray
extinction. Therefore, our data are inconsistent with dip models that
invoke optically thick material, but rather they are in-line with
predictions for an occulter consisting primarily of ordinary dust,
where much of the material must be optically thin with a size scale
≪1 μm, and may also be consistent with models invoking variations
intrinsic to the stellar photosphere. Notably, our data do not place
constraints on the color of the longer-term “secular” dimming,
which may be caused by independent processes, or probe different
regimes of a single process.

---------------------------------------------------------
Title: Ca II 8542 Å brightenings induced by a solar microflare
Authors: Kuckein, C.; Diercke, A.; González Manrique, S. J.; Verma,
M.; Löhner-Böttcher, J.; Socas-Navarro, H.; Balthasar, H.; Sobotka,
M.; Denker, C.
2017A&A...608A.117K Altcode: 2017arXiv170906861K
 Aims: We study small-scale brightenings in Ca II 8542 Å
line-core images to determine their nature and effect on localized
heating and mass transfer in active regions. Methods:
High-resolution two-dimensional spectroscopic observations of a solar
active region in the near-infrared Ca II 8542 Å line were acquired
with the GREGOR Fabry-Pérot Interferometer attached to the 1.5-m GREGOR
telescope. Inversions of the spectra were carried out using the NICOLE
code to infer temperatures and line-of-sight (LOS) velocities. Response
functions of the Ca II line were computed for temperature and LOS
velocity variations. Filtergrams of the Atmospheric Imaging Assembly
(AIA) and magnetograms of the Helioseismic and Magnetic Imager (HMI)
were coaligned to match the ground-based observations and to follow the
Ca II brightenings along all available layers of the atmosphere. 
Results: We identified three brightenings of sizes up to 2” × 2”
that appeared in the Ca II 8542 Å line-core images. Their lifetimes
were at least 1.5 min. We found evidence that the brightenings belonged
to the footpoints of a microflare (MF). The properties of the observed
brightenings disqualified the scenarios of Ellerman bombs or Interface
Region Imaging Spectrograph (IRIS) bombs. However, this MF shared some
common properties with flaring active-region fibrils or flaring arch
filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric
and coronal layers according to the AIA channels; and (2) both show
flaring arches with lifetimes of about 3.0-3.5 min and lengths of
20” next to the brightenings. The inversions revealed heating by
600 K at the footpoint location in the ambient chromosphere during
the impulsive phase. Connecting the footpoints, a dark filamentary
structure appeared in the Ca II line-core images. Before the
start of the MF, the spectra of this structure already indicated
average blueshifts, meaning upward motions of the plasma along the
LOS. During the impulsive phase, these velocities increased up to -
2.2 km s-1. The structure did not disappear during the
observations. Downflows dominated at the footpoints. However, in
the upper photosphere, slight upflows occurred during the impulsive
phase. Hence, bidirectional flows are present in the footpoints
of the MF. Conclusions: We detected Ca II brightenings that
coincided with the footpoint location of an MF. The MF event led to
a rise of plasma in the upper photosphere, both before and during the
impulsive phase. Excess mass, previously raised to at most chromospheric
layers, slowly drained downward along arches toward the footpoints
of the MF. The movie associated to Fig. 2 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201731319/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Design of an adaptable Stokes polarimeter for exploring
chromospheric magnetism
Authors: Louis, Rohan E.; Bayanna, A. Raja; Socas Navarro, Héctor
2017AdSpR..60.1547L Altcode: 2017arXiv170607186L
The chromosphere is a highly complex and dynamic layer of the Sun,
that serves as a conduit for mass and energy supply between two, very
distinct regions of the solar atmosphere, namely, the photosphere and
corona. Inferring magnetic fields in the chromosphere, has thus become
an important topic, that can be addressed with large-aperture solar
telescopes to carry out highly sensitive polarimetric measurements. In
this article, we present a design of a polarimeter for investigating
the chromospheric magnetic field. The instrument consists of a number of
lenses, two ferro-electric liquid crystals, a Wollaston prism, and a CCD
camera. The optical design is similar to that of a commercial zoom lens
which allows a variable f# while maintaining focus and aberrations well
within the Airy disc. The optical design of the Adaptable ChRomOspheric
POLarimeter (ACROPOL) makes use of off-the-shelf components and is
described for the 70 cm Vacuum Tower Telescope and the 1.5 m GREGOR
telescope at Observatorio del Teide, Tenerife, Spain. Our design shows
that the optical train can be separated into two units where the first
unit, consisting of a single lens, has to be changed while going from
the VTT to the GREGOR configuration. We also discuss the tolerances
within which, diffraction limited performance can be achieved with
our design.

---------------------------------------------------------
Title: A Hot Downflowing Model Atmosphere for Umbral Flashes and
the Physical Properties of Their Dark Fibrils
Authors: Henriques, V. M. J.; Mathioudakis, M.; Socas-Navarro, H.;
de la Cruz Rodríguez, J.
2017ApJ...845..102H Altcode: 2017arXiv170605311H
We perform non-LTE inversions in a large set of umbral flashes,
including the dark fibrils visible within them, and in the quiescent
umbra by using the inversion code NICOLE on a set of full Stokes
high-resolution Ca II λ8542 observations of a sunspot at disk
center. We find that the dark structures have Stokes profiles that are
distinct from those of the quiescent and flashed regions. They are
best reproduced by atmospheres that are more similar to the flashed
atmosphere in terms of velocities, even if with reduced amplitudes. We
also find two sets of solutions that finely fit the flashed profiles:
a set that is upflowing, featuring a transition region that is deeper
than in the quiescent case and preceded by a slight dip in temperature,
and a second solution with a hotter atmosphere in the chromosphere but
featuring downflows close to the speed of sound at such heights. Such
downflows may be related, or even dependent, on the presence of coronal
loops, rooted in the umbra of sunspots, as is the case in the region
analyzed. Similar loops have been recently observed to have supersonic
downflows in the transition region and are consistent with the earlier
“sunspot plumes,” which were invariably found to display strong
downflows in sunspots. Finally, we find, on average, a magnetic field
reduction in the flashed areas, suggesting that the shock pressure is
moving field lines in the upper layers.

---------------------------------------------------------
Title: Search for torsional oscillations in isolated sunspots
Authors: Griñón-Marín, A. B.; Socas-Navarro, H.; Centeno, R.
2017A&A...604A..36G Altcode: 2017arXiv170601952G; 2017arXiv170601952B
In this work we seek evidence for global torsional oscillations in
alpha sunspots. We have used long time series of continuum intensity
and magnetic field vector maps from the Helioseismic and Magnetic
Imager (HMI) instrument on board the Solar Dynamics Observatory (SDO)
spacecraft. The time series analysed here span the total disk passage
of 25 isolated sunspots. We found no evidence of global long-term
periodic oscillations in the azimuthal angle of the sunspot magnetic
field within 1 degree. This study could help us to understand the
sunspot dynamics and its internal structure.

---------------------------------------------------------
Title: Uncertainties in the solar photospheric oxygen abundance
Authors: Cubas Armas, M.; Asensio Ramos, A.; Socas-Navarro, H.
2017A&A...600A..45C Altcode: 2017arXiv170106809C
 Aims: The purpose of this work is to better understand the
confidence limits of the photospheric solar oxygen abundance derived
from three-dimensional models using the forbidden [OI] line at 6300
Å, including correlations with other parameters involved. 
Methods: We worked with a three-dimensional empirical model and two
solar intensity atlases. Bayesian inference was employed as a tool
to determine the most probable value for the solar oxygen abundance
given the model chosen. We considered a number of error sources,
such as uncertainties in the continuum derivation, in the wavelength
calibration and in the abundance/strength of Ni. Results: Our
results show correlations between the effects of several parameters
employed in the derivation. The Bayesian analysis provides robust
confidence limits taking into account all of these factors in a rigorous
manner. We obtain that, given the empirical three-dimensional model and
the atlas observations employed here, the most probable value for the
solar oxygen abundance is log (ɛO) = 8.86 ± 0.04. However,
we note that this uncertainty does not consider possible sources of
systematic errors due to the model choice.

---------------------------------------------------------
Title: Inference of the chromospheric magnetic field orientation in
the Ca II 8542 Å line fibrils
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.; Martínez
González, M. J.; Socas-Navarro, H.
2017A&A...599A.133A Altcode: 2016arXiv161206088A
Context. Solar chromospheric fibrils, as observed in the core of
strong chromospheric spectral lines, extend from photospheric field
concentrations suggesting that they trace magnetic field lines. These
images have been historically used as proxies of magnetic fields
for many purposes. Aims: Use statistical analysis to test
whether the association between fibrils and magnetic field lines is
justified. Methods: We use a Bayesian hierarchical model to
analyze several tens of thousands of pixels in spectro-polarimetric
chromospheric images of penumbrae and chromospheric fibrils. We
compare the alignment between the field azimuth inferred from the
linear polarization signals through the transverse Zeeman effect and
the direction of the fibrils in the image. Results: We conclude
that, in the analyzed fields of view, fibrils are often well aligned
with the magnetic field azimuth. Despite this alignment, the analysis
also shows that there is a non-negligible dispersion. In penumbral
filaments, we find a dispersion with a standard deviation of 16°,
while this dispersion goes up to 34° in less magnetized regions.

---------------------------------------------------------
Title: First Detection of Sign-reversed Linear Polarization from
the Forbidden [O I] 630.03 nm Line
Authors: de Wijn, A. G.; Socas-Navarro, H.; Vitas, N.
2017ApJ...836...29D Altcode: 2017arXiv170108793D
We report on the detection of linear polarization of the forbidden
[O I] 630.03 nm spectral line. The observations were carried out
in the broader context of the determination of the solar oxygen
abundance, an important problem in astrophysics that still remains
unresolved. We obtained spectro-polarimetric data of the forbidden
[O I] line at 630.03 nm as well as other neighboring permitted lines
with the Solar Optical Telescope of the Hinode satellite. A novel
averaging technique was used, yielding very high signal-to-noise ratios
in excess of 105. We confirm that the linear polarization
is sign-reversed compared to permitted lines as a result of the line
being dominated by a magnetic dipole transition. Our observations
open a new window for solar oxygen abundance studies, offering an
alternative method to disentangle the Ni I blend from the [O I] line
at 630.03 nm that has the advantage of simple LTE formation physics.

---------------------------------------------------------
Title: Filamentary Oscillations in the Penumbra of Sunspots
Authors: Griñon, Ana Bélen; Pastor Yabar, A.; Socas-Navarro, H.;
Centeno, R.
2017psio.confE.111G Altcode: 2017psio.confE.111A
No abstract at ADS

---------------------------------------------------------
Title: Filamentary Oscillations in the Penumbra of Sunspots
Authors: Grión-Marín, A. B.; Socas-Navarro, H.; Centeno, R.
2016usc..confE..66G Altcode: 2016usc..confE..66B
The issue of long-term (on scales of several hours to days)
morphological changes in sunspots, and particularly the possible
existence of apparent rotational motions and oscillations, has drawn
attention since the early 20th century. This kind of study requires
data with high spatial resolution and good temporal sampling and
coverage. The HMI instrument on board the Solar Dynamics Observatory
routinely measures the full magnetic field vector in sunspots and allows
us to track them with consistent image quality and high cadence during
their entire disk passage. It is the ideal instrument to analyze the
evolution of sunspots, and in particular the azimuthal component of the
penumbral magnetic field. We carried out an analysis (Griñón-Marín et
al. 2016 -Submitted-) looking for torsional oscillations in the penumbra
of sunspots that led to no evidence of this kind of oscillation in the
25 sunspots analyzed. However, we detected filamentary-like oscillations
in some areas of the penumbra with periods of several hours. In this
contribution I will show their morphological analysis and discuss the
possible sources for such oscillations.

---------------------------------------------------------
Title: Small-scale magnetic flux emergence in a sunspot light bridge
Authors: Louis, Rohan E.; Bellot Rubio, Luis R.; de la Cruz Rodríguez,
Jaime; Socas-Navarro, Héctor; Ortiz, Ada
2015A&A...584A...1L Altcode: 2015arXiv150900741L
Context. Light bridges are convective intrusions in sunspots that
often show enhanced chromospheric activity. Aims: We seek
to determine the nature of flux emergence in a light bridge and the
processes related to its evolution in the solar atmosphere. 
Methods: We analyse a sequence of high-resolution spectropolarimetric
observations of a sunspot taken at the Swedish 1-m Solar Telescope. The
data consist of spectral scans of the photospheric Fe i line pair at
630 nm and the chromospheric Ca ii 854.2 nm line. Bisectors were used
to construct Dopplergrams from the Fe i 630.15 nm measurements. We
employed LTE and non-LTE inversions to derive maps of physical
parameters in the photosphere and chromosphere, respectively. 
Results: We observe the onset of blueshifts of about 2 km s-1
near the entrance of a granular light bridge on the limbward side of
the spot. The blueshifts lie immediately next to a strongly redshifted
patch that appeared six minutes earlier. Both patches can be seen for
25 min until the end of the sequence. The blueshifts coincide with
an elongated emerging granule, while the redshifts appear at the end
of the granule. In the photosphere, the development of the blueshifts
is accompanied by a simultaneous increase in field strength of about
400 G. The field inclination increases by some 25°, becoming nearly
horizontal. At the position of the redshifts, the magnetic field is
equally horizontal but of opposite polarity. An intense brightening
is seen in the Ca ii filtergrams over the blueshifts and redshifts,
about 17 min after their detection in the photosphere. The brightening
is due to emission in the blue wing of the Ca ii 854.2 nm line, close
to its knee. Non-LTE inversions reveal that this kind of asymmetric
emission is caused by a temperature enhancement of ~700 K between -5.0
≤ log τ ≤ -3.0 and a blueshift of 3 km s-1 at log τ
= -2.3 that decreases to zero at log τ = -6.0 Conclusions:
The photospheric blueshifts and redshifts observed in a granular
light bridge seem to be caused by the emergence of a small-scale,
flat Ω-loop with highly inclined footpoints of opposite polarity that
brings new magnetic field to the surface. The gas motions detected in
the two footpoints are reminiscent of a siphon flow. The rising loop
is probably confined to the lower atmosphere by the overlying sunspot
magnetic field and the interaction between the two flux systems may be
responsible for temperature enhancements in the upper photosphere/lower
chromosphere. This is the first time that magnetic flux is observed
to emerge in the strongly magnetised environment of sunspots, pushed
upwards by the convective flows of a granular light bridge. The
movie associated to Fig. 2 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201526854/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: NICOLE: NLTE Stokes Synthesis/Inversion Code
Authors: Socas-Navarro, H.
2015ascl.soft08002S Altcode:
NICOLE, written in Fortran 90, seeks the model atmosphere that provides
the best fit to the Stokes profiles (in a least-squares sense) of
an arbitrary number of simultaneously-observes spectral lines from
solar/stellar atmospheres. The inversion core used for the development
of NICOLE is the LORIEN engine (the Lovely Reusable Inversion ENgine),
which combines the SVD technique with the Levenberg-Marquardt
minimization method to solve the inverse problem.

---------------------------------------------------------
Title: An open-source, massively parallel code for non-LTE synthesis
and inversion of spectral lines and Zeeman-induced Stokes profiles
Authors: Socas-Navarro, H.; de la Cruz Rodríguez, J.; Asensio Ramos,
A.; Trujillo Bueno, J.; Ruiz Cobo, B.
2015A&A...577A...7S Altcode: 2014arXiv1408.6101S
With the advent of a new generation of solar telescopes and
instrumentation, interpreting chromospheric observations (in
particular, spectropolarimetry) requires new, suitable diagnostic
tools. This paper describes a new code, NICOLE, that has been
designed for Stokes non-LTE radiative transfer, for synthesis and
inversion of spectral lines and Zeeman-induced polarization profiles,
spanning a wide range of atmospheric heights from the photosphere
to the chromosphere. The code features a number of unique features
and capabilities and has been built from scratch with a powerful
parallelization scheme that makes it suitable for application on
massive datasets using large supercomputers. The source code is
written entirely in Fortran 90/2003 and complies strictly with the
ANSI standards to ensure maximum compatibility and portability. It
is being publicly released, with the idea of facilitating future
branching by other groups to augment its capabilities. The
source code is currently hosted at the following repository: <A
href="http://github.com/hsocasnavarro/NICOLE">https://github.com/hsocasnavarro/NICOLE</A>

---------------------------------------------------------
Title: The solar oxygen abundance from an empirical three-dimensional
model
Authors: Socas-Navarro, H.
2015A&A...577A..25S Altcode: 2014arXiv1409.6910S
The oxygen abundance in the solar photosphere, and consequently the
solar metallicity itself, is still a controversial question with
far-reaching implications in many areas of astrophysics. This paper
presents a new determination obtained by fitting the forbidden O i line
at 6300 Å with an observational 3D model. The approach presented
here is novel because previous determinations were based either
on 1D empirical stratifications or on 3D theoretical models. The
resulting best-fit abundances are log ɛ(O) = 8.90 and log ɛ(Ni) =
6.15. Nevertheless, by introducing minor tweaks in the model and the
procedure, it is possible to retrieve very different values, even
down to log ɛ(O) = 8.70. This extreme sensitivity of the abundance
to possible systematic effects is not specific to this particular
work, but probably reflects the real uncertainty inherent to all
abundance determinations based on a prescribed model atmosphere. As with the earlier version, the new 3D model is publicly
available and may be downloaded from the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/577/A25">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/577/A25</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: 3D model for fitting forbidden
OI 6300 line (Socas-Navarro, 2015)
Authors: Socas-Navarro, H.
2015yCat..35770025S Altcode: 2015yCat..35779025S
modelin.mod and modelout.mod contain three-dimensional
cubes each column represents the physical stratification of each
pixel, with the in and the out suffix referring to the two
atmospheric components coexisting with the filling factor. The code
manual has details on the file format and the variables stored. (3 data files).

---------------------------------------------------------
Title: Synthetic Observations of Wave Propagation in a Sunspot Umbra
Authors: Felipe, T.; Socas-Navarro, H.; Khomenko, E.
2014ApJ...795....9F Altcode: 2014arXiv1408.6565F
Spectropolarimetric temporal series from Fe I λ6301.5 Å and Ca II
infrared triplet lines are obtained by applying the Stokes synthesis
code NICOLE to a numerical simulation of wave propagation in a sunspot
umbra from MANCHA code. The analysis of the phase difference between
Doppler velocity and intensity core oscillations of the Fe I λ6301.5
Å line reveals that variations in the intensity are produced by
opacity fluctuations rather than intrinsic temperature oscillations,
except for frequencies between 5 and 6.5 mHz. On the other hand, the
photospheric magnetic field retrieved from the weak field approximation
provides the intrinsic magnetic field oscillations associated to wave
propagation. Our results suggest that this is due to the low magnetic
field gradient of our sunspot model. The Stokes parameters of the
chromospheric Ca II infrared triplet lines show striking variations as
shock waves travel through the formation height of the lines, including
emission self-reversals in the line core and highly abnormal Stokes V
profiles. Magnetic field oscillations inferred from the Ca II infrared
lines using the weak field approximation appear to be related with
the magnetic field strength variation between the photosphere and
the chromosphere.

---------------------------------------------------------
Title: Physical properties of a sunspot chromosphere with umbral
flashes
Authors: de la Cruz Rodríguez, J.; Rouppe van der Voort, L.;
Socas-Navarro, H.; van Noort, M.
2013A&A...556A.115D Altcode: 2013arXiv1304.0752D
We present new high-resolution spectro-polarimetric Ca IIλ8542
observations of umbral flashes in sunspots. At nearly 0.18 arcsec,
and spanning about one hour of continuous observation, this is the
most detailed dataset published thus far. Our study involves both LTE
and non-LTE inversions (but includes also a weak field analysis as a
sanity check) to quantify temperatures, mass flows and the full magnetic
field vector geometry. We confirm earlier reports that UFs have very
fine structure with hot and cool material intermixed at sub-arcsecond
scales. The shock front is roughly 1000 K hotter than the surrounding
material. We do not observe significant fluctuations of the field in the
umbra. In the penumbra, however, the passage of the running penumbral
waves alter the magnetic field strength by some 200 G (peak-to-peak
amplitude) but it does not change the field orientation (at least not
significantly within our sensitivity of a few degrees). From a fast
Fourier transform analysis, we find a trend of decreasing power at high
temporal frequencies at those locations with more horizontal magnetic
fields, for the line-of-sight velocity and magnetic field strength. In
the outer penumbra we find an absence of high frequency power while
there is increasingly more power at high frequencies towards the
umbra. Movie and Appendices A and B are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: The European Solar Telescope
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly,
B.; Pérez, A.; Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team
2013MmSAI..84..379C Altcode:
The European Solar Telescope (EST) is a project to design, build and
operate an European Solar 4-meter class telescope to be located in the
Canary Islands, with the participation of institutions from fifteen
European countries gathered around the consortium EAST (European
Association for Solar Telescopes). The project main objective up to the
present has been the development of the conceptual design study (DS)
of a large aperture Solar Telescope. The study has demonstrated the
scientific, technical and financial feasibility of EST. The DS has been
possible thanks to the co-financing allocated specifically by the EU
and the combined efforts of all the participant institutions. Different
existing alternatives have been analysed for all telescope systems and
subsystems, and decisions have been taken on the ones that are most
compatible with the scientific goals and the technical strategies. The
present status of some subsystems is reviewed in this paper.

---------------------------------------------------------
Title: Chromospheric Magnetic Fields: Observations, Simulations and
their Interpretation
Authors: de la Cruz Rodríguez, J.; Socas-Navarro, H.; Carlsson, M.;
Leenaarts, J.
2012ASPC..463...15D Altcode: 2012arXiv1203.4577D
The magnetic field of the quiet-Sun chromosphere remains a mystery
for solar physicists. The reduced number of chromospheric lines are
intrinsically hard to model and only a few of them are magnetically
sensitive. In this work, we use a 3D numerical simulation of the outer
layers of the solar atmosphere, to asses the reliability of non-LTE
inversions, in this case applied to the Ca II λ8542 Å line. We show
that NLTE inversions provide realistic estimates of physical quantities
from synthetic observations.

---------------------------------------------------------
Title: The European Solar Telescope
Authors: Socas-Navarro, H.
2012IAUSS...6E.212S Altcode:
In this presentation I will describe the current status of the European
Solar Telescope (EST) project. The EST design has a 4-m aperture
to achieve both a large photon collection and very high spatial
resolution. It includes a multi-conjugate adaptive system integrated
in the light path for diffraction-limited imaging. The optical train
is optimized to minimize instrumental polarization and to keep it
nearly constant as the telescope tracks the sky. A suite of visible
and infrared instruments are planned with a light distribution system
that accomodates full interoperability and simultaneous usage. The
science drivers emphasize combined observations at multiple heights
in the atmosphere to build a connected view of solar magnetism from
the photosphere to the corona.

---------------------------------------------------------
Title: 2nd ATST-EAST Workshop in Solar Physics: Magnetic Fields from
the Photosphere to the Corona
Authors: Rimmele, T. R.; Tritschler, A.; Wöger, F.; Collados Vera,
M.; Socas-Navarro, H.; Schlichenmaier, R.; Carlsson, M.; Berger, T.;
Cadavid, A.; Gilbert, P. R.; Goode, P. R.; Knölker, M.
2012ASPC..463.....R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Unusual Stokes V profiles during flaring activity of a
delta sunspot
Authors: Fischer, C. E.; Keller, C. U.; Snik, F.; Fletcher, L.;
Socas-Navarro, H.
2012A&A...547A..34F Altcode: 2012arXiv1209.0983F
 Aims: We analyze a set of full Stokes profile observations of
the flaring active region NOAA 10808. The region was recorded with
the Vector-Spectromagnetograph of the Synoptic Optical Long-term
Investigations of the Sun facility. The active region produced
several successive X-class flares between 19:00 UT and 24:00 UT on
September 13, 2005 and we aim to quantify transient and permanent
changes in the magnetic field and velocity field during one of the
flares, which has been fully captured. Methods: The Stokes
profiles were inverted using the height-dependent inversion code
LILIA to analyze magnetic field vector changes at the flaring site. We
report multilobed asymmetric Stokes V profiles found in the δ-sunspot
umbra. We fit the asymmetric Stokes V profiles assuming an atmosphere
consisting of two components (SIR inversions) to interpret the profile
shape. The results are put in context with Michelson Doppler Imager
(MDI) magnetograms and reconstructed X-ray images from the Reuven
Ramaty High Energy Solar Spectroscopic Imager. Results: We
obtain the magnetic field vector and find signs of restructuring
of the photospheric magnetic field during the flare close to the
polarity inversion line at the flaring site. At two locations in the
umbra we encounter strong fields (~3 kG), as inferred from the Stokes
I profiles, which, however, exhibit a low polarization signal. During
the flare we observe in addition asymmetric Stokes V profiles at one
of these sites. The asymmetric Stokes V profiles appear co-spatial
and co-temporal with a strong apparent polarity reversal observed
in MDI-magnetograms and a chromospheric hard X-ray source. The
two-component atmosphere fits of the asymmetric Stokes profiles
result in line-of-sight velocity differences in the range of ~12 km
s-1 to 14 km s-1 between the two components in
the photosphere. Another possibility is that local atmospheric heating
is causing the observed asymmetric Stokes V profile shape. In either
case our analysis shows that a very localized patch of ~5″ in the
photospheric umbra, co-spatial with a flare footpoint, exhibits a
subresolution fine structure.

---------------------------------------------------------
Title: LEMUR: Large European module for solar Ultraviolet
Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
Thomas; Winter, Berend; Young, Peter
2012ExA....34..273T Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
The solar outer atmosphere is an extremely dynamic environment
characterized by the continuous interplay between the plasma and the
magnetic field that generates and permeates it. Such interactions play a
fundamental role in hugely diverse astrophysical systems, but occur at
scales that cannot be studied outside the solar system. Understanding
this complex system requires concerted, simultaneous solar observations
from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
high spatial resolution (between 0.1” and 0.3”), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
from the chromosphere to the flaring corona), and the capability of
measuring magnetic fields through spectropolarimetry at visible and
near-infrared wavelengths. Simultaneous spectroscopic measurements
sampling the entire temperature range are particularly important. These
requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload
providing a significant improvement of imaging and spectropolarimetric
capabilities in the UV, visible, and near-infrared with respect to
what is available today and foreseen in the near future. The Large
European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload
of high-resolution imaging spectrographs and cameras. LEMUR consists
of two major components: a VUV solar telescope with a 30 cm diameter
mirror and a focal length of 3.6 m, and a focal-plane package composed
of VUV spectrometers covering six carefully chosen wavelength ranges
between 170 Å and 1270 Å. The LEMUR slit covers 280” on the Sun with
0.14” per pixel sampling. In addition, LEMUR is capable of measuring
mass flows velocities (line shifts) down to 2 km s - 1 or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.

---------------------------------------------------------
Title: Non-local thermodynamic equilibrium inversions from a 3D
magnetohydrodynamic chromospheric model
Authors: de la Cruz Rodríguez, J.; Socas-Navarro, H.; Carlsson, M.;
Leenaarts, J.
2012A&A...543A..34D Altcode: 2012arXiv1205.3171D
Context. The structure of the solar chromosphere is believed to
be governed by magnetic fields, even in quiet-Sun regions that
have a relatively weak photospheric field. During the past decade
inversion methods have emerged as powerful tools for analyzing the
chromosphere of active regions. The applicability of inversions to
infer the stratification of the physical conditions in a dynamic 3D
solar chromosphere has not yet been studied in detail. Aims:
This study aims to establish the diagnostic capabilities of non-local
thermodynamical equilibrium (NLTE) inversion techniques of Stokes
profiles induced by the Zeeman effect in the Ca ii λ8542 Å line. Methods: We computed the Ca ii atomic level populations in a snapshot
from a 3D radiation-MHD simulation of the quiet solar atmosphere in
non-LTE using the 3D radiative transfer code Multi3d. These populations
were used to compute synthetic full-Stokes profiles in the Ca ii
λ8542 Å line using 1.5D radiative transfer and the inversion code
Nicole. The profiles were then spectrally degraded to account for
finite filter width, and Gaussian noise was added to account for
finite photon flux. These profiles were inverted using Nicole and
the results were compared with the original model atmosphere. 
Results: Our NLTE inversions applied to quiet-Sun synthetic observations
provide reasonably good estimates of the chromospheric magnetic field,
line-of-sight velocities and somewhat less accurate, but still very
useful, estimates of the temperature. Three-dimensional scattering
of photons cause cool pockets in the chromosphere to be invisible in
the line profile and consequently they are also not recovered by the
inversions. To successfully detect Stokes linear polarization in this
quiet snapshot, a noise level below 10-3.5 is necessary.

---------------------------------------------------------
Title: Model Selection for Spectropolarimetric Inversions
Authors: Asensio Ramos, A.; Manso Sainz, R.; Martínez González,
M. J.; Viticchié, B.; Orozco Suárez, D.; Socas-Navarro, H.
2012ApJ...748...83A Altcode: 2012arXiv1201.5063A
Inferring magnetic and thermodynamic information from
spectropolarimetric observations relies on the assumption of
a parameterized model atmosphere whose parameters are tuned by
comparison with observations. Often, the choice of the underlying
atmospheric model is based on subjective reasons. In other cases,
complex models are chosen based on objective reasons (for instance,
the necessity to explain asymmetries in the Stokes profiles) but it
is not clear what degree of complexity is needed. The lack of an
objective way of comparing models has, sometimes, led to opposing
views of the solar magnetism because the inferred physical scenarios
are essentially different. We present the first quantitative model
comparison based on the computation of the Bayesian evidence ratios for
spectropolarimetric observations. Our results show that there is not
a single model appropriate for all profiles simultaneously. Data with
moderate signal-to-noise ratios (S/Ns) favor models without gradients
along the line of sight. If the observations show clear circular and
linear polarization signals above the noise level, models with gradients
along the line are preferred. As a general rule, observations with large
S/Ns favor more complex models. We demonstrate that the evidence ratios
correlate well with simple proxies. Therefore, we propose to calculate
these proxies when carrying out standard least-squares inversions to
allow for model comparison in the future.

---------------------------------------------------------
Title: NLTE inversions from a 3D MHD Chromospheric simulation
Authors: de la Cruz Rodriguez, J.; Socas-Navarro, H.; Carlsson, M.;
Leenaarts, J.
2012decs.confE..80D Altcode:
The structure of the solar chromosphere is believed to be governed
by magnetic fields, even in quiet Sun regions with a relatively weak
field. Measuring the magnetic field of the solar chromosphere is an
outstanding challenge for observers. Inversion codes allow for detailed
interpretation of full-Stokes data from spectral lines formed in the
chromosphere. However, the applicability of non-LTE inversions to infer
physical conditions in the dynamic 3D solar chromosphere, has not yet
been studied in detail. In this study, we use a snapshot from a 3D MHD
simulation of quiet-sun, extending from the photosphere to the corona,
to asses the reliability of non-LTE inversions to infer chromospheric
quantities, especially the magnetic field.

---------------------------------------------------------
Title: VFISV: Very Fast Inversion of the Stokes Vector for the
Helioseismic and Magnetic Imager
Authors: Borrero, J. M.; Tomczyk, S.; Kubo, M.; Socas-Navarro, H.;
Schou, J.; Couvidat, S.; Bogart, R.
2011SoPh..273..267B Altcode: 2009arXiv0901.2702B
In this paper we describe in detail the implementation and main
properties of a new inversion code for the polarized radiative transfer
equation (VFISV: Very Fast Inversion of the Stokes Vector). VFISV will
routinely analyze pipeline data from the Helioseismic and Magnetic
Imager (HMI) on-board of the Solar Dynamics Observatory (SDO). It
will provide full-disk maps (4096×4096 pixels) of the magnetic field
vector on the Solar Photosphere every ten minutes. For this reason
VFISV is optimized to achieve an inversion speed that will allow
it to invert sixteen million pixels every ten minutes with a modest
number (approx. 50) of CPUs. Here we focus on describing a number of
important details, simplifications and tweaks that have allowed us to
significantly speed up the inversion process. We also give details on
tests performed with data from the spectropolarimeter on-board of the
Hinode spacecraft.

---------------------------------------------------------
Title: Characterization of telescope polarization properties across
the visible and near-infrared spectrum. Case study: the Dunn Solar
Telescope
Authors: Socas-Navarro, H.; Elmore, D.; Asensio Ramos, A.; Harrington,
D. M.
2011A&A...531A...2S Altcode: 2010arXiv1009.2866S
Accurate astrophysical polarimetry requires a proper characterization
of the polarization properties of the telescope and instrumentation
employed to obtain the observations. Determining the telescope and
instrument Muller matrix is becoming increasingly difficult with
the increase in aperture size, precision requirements and instrument
complexity of new and upcoming projects. We have carried out a detailed
multi-wavelength characterization of the Dunn Solar Telescope (DST)
at the National Solar Observatory/Sacramento Peak as a case study and
explore various possibilites for the determination of its polarimetric
properties. We show that the telescope model proposed in this paper is
more suitable than that in previous work in that it describes better
the wavelength dependence of aluminum-coated mirrors. We explore the
adequacy of the degrees of freedom allowed by the model using a novel
mathematical formalism. Finally, we investigate the use of polarimeter
calibration data taken at different times of the day to characterize
the telescope and find that very valuable information on the telescope
properties can be obtained in this manner. The results are also
consistent with the entrance window polarizer measurements. This general
method opens interesting possibilities for the calibration of future
large-aperture telescopes and precision polarimetric instrumentation.

---------------------------------------------------------
Title: A high-resolution three-dimensional model of the solar
photosphere derived from Hinode observations
Authors: Socas-Navarro, H.
2011A&A...529A..37S Altcode: 2011arXiv1101.2100S
A new three-dimensional model of the solar photosphere is presented
in this paper and made publicly available to the community. This
model has the peculiarity of having been obtained by inverting
spectro-polarimetric observations, rather than by using numerical
radiation hydrodynamical simulations. The data used here are from
the spectro-polarimeter onboard the Hinode satellite, which routinely
delivers Stokes I, Q, U, and V profiles in the 6302 Å spectral region
with excellent quality, stability, and spatial resolution (approximately
0.3”). With this spatial resolution the major granular components
are resolved, which implies that the derived model needs no micro- or
macroturbulence to properly fit the widths of the observed spectral
lines. Not only does this model fit the observed data used for its
construction, but it can also fit previous solar atlas observations
satisfactorily.

---------------------------------------------------------
Title: The Polarization Optics for the European Solar Telescope
Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.;
Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.;
Snik, F.; Socas-Navarro, H.
2011ASPC..437..329B Altcode:
EST, the European Solar Telescope, is a 4-m class solar telescope,
which will be located at the Canary Islands. It is currently in the
conceptual design phase as a European funded project. In order to
fulfill the stringent requirements for polarimetric sensitivity
and accuracy, the polarimetry has been included in the design
work from the very beginning. The overall philosophy has been to
use a combination of techniques, which includes a telescope with
low (and stable) instrumental polarization, optimal full Stokes
polarimeters, differential measurement schemes, fast modulation
and demodulation, and accurate calibration, and at the same time not
giving up flexibility. The current baseline optical layout consists of a
14-mirror layout, which is polarimetrically compensated and non-varying
in time. In the polarization free F2 focus ample space is reserved for
calibration and modulators and a polarimetric switch. At instrument
level the s-, and p-planes of individual components are aligned,
resulting in a system in which eigenvectors can travel undisturbed
through the system.

---------------------------------------------------------
Title: Are solar chromospheric fibrils tracing the magnetic field?
Authors: de la Cruz Rodríguez, J.; Socas-Navarro, H.
2011A&A...527L...8D Altcode: 2011arXiv1101.3551D
Fibrils are thin elongated features visible in the solar chromosphere
in and around magnetized regions. Because of their visual appearance,
they have been traditionally considered a tracer of the magnetic field
lines. For the first time, we challenge that notion by comparing their
orientation to that of the magnetic field, obtained via high-resolution
spectropolarimetric observations of Ca ii lines. The short answer to
the question posed in the title is that mostly yes, but not always.

---------------------------------------------------------
Title: (1) The effect of magnetic fields on solar abundance
determinations (2) The solar photosphere in 3D. This time from
observations
Authors: Fabbian, D.; Socas-Navarro, H.
2010iac..talk..232F Altcode: 2010iac..talk..186F
No abstract at ADS

---------------------------------------------------------
Title: Are chromospheric fibrils tracing the magnetic field?
Authors: de la Cruz Rodríguez, J.; Socas-Navarro, H.
2010iac..talk..221D Altcode: 2010iac..talk..178D
No abstract at ADS

---------------------------------------------------------
Title: Utilization of redundant polarized solar spectra to infer
the polarization properties of the new generation of large aperture
solar telescopes
Authors: Elmore, David F.; Lin, Haosheng; Socas Navarro, Héctor;
Jaeggli, Sarah A.
2010SPIE.7735E..4EE Altcode: 2010SPIE.7735E.147E
Spectro-polarimetry plays an important role in the study of solar
magnetism and strongly influences the design of the new generation of
solar telescopes. Calibration of the polarization properties of the
telescope is a critical requirement needed to use these observations to
infer solar magnetic fields. However, the large apertures of these new
telescopes make direct calibration with polarization calibration optics
placed before all the telescope optical elements impractical. It is
therefore desirable to be able to infer the polarization properties
of the telescope optical elements utilizing solar observations
themselves. Taking advantage of the fact that the un-polarized,
linearly, and circularly polarized spectra originating from the Sun are
uncorrelated, we have developed techniques to utilize observations
of solar spectra with redundant combination of the polarization
states measured at several different telescope configurations to
infer the polarization properties of the telescope as a whole and of
its optical elements. We show results of these techniques applied to
spectro-plarimetric data obtained at the Dunn Solar Telescope.

---------------------------------------------------------
Title: European Solar Telescope: project status
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.;
Gelly, B.; Grivel-Gelly, C.; Pérez, A.; Socas-Navarro, H.; Soltau,
D.; Volkmer, R.
2010SPIE.7733E..0HC Altcode: 2010SPIE.7733E..15C
The European Solar Telescope is a project for a 4-meter class telescope
to be located in the Canary Islands. EST is promoted by the European
Association for Solar Telescopes (EAST). This is a consortium formed
by a number of research organizations from fifteen European countries
(Austria, Croatia, Czech Republic, France, Germany, Hungary, Italy,
the Netherlands, Norway, Poland, Slovak Republic, Spain, Sweden,
Switzerland, and United Kingdom). EST will specialize in high spatial
and temporal resolution using diverse instruments that can efficiently
produce two-dimensional spectropolarimetric information of the thermal,
dynamic and magnetic properties of the plasma over many scale heights
in the solar atmosphere. In this contribution, the status of the
development of the Design Study of EST is presented, emphasizing the
most important aspects of the optical design, mechanical structure, AO
and MCAO systems for wavefront correction, instruments and polarization
analysis.

---------------------------------------------------------
Title: The polarization optics for the European Solar Telescope (EST)
Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.;
Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.;
Snik, F.; Socas-Navarro, H.
2010SPIE.7735E..6IB Altcode: 2010SPIE.7735E.214B
EST (European Solar Telescope) is a 4-m class solar telescope, which
is currently in the conceptual design phase. EST will be located at
the Canary Islands and aims at observations with the best possible
spectral, spatial and temporal resolution and best polarimetric
performance, of the solar photosphere and chromosphere, using a
suite of instruments that can efficiently produce two-dimensional
spectropolarimetric information of the thermal, dynamic and magnetic
properties of the plasma over many scale heights, and ranging from
λ=350 until 2300 nm. In order to be able to fulfill the stringent
requirements for polarimetric sensitivity and accuracy, from the very
beginning the polarimetry has been included in the design work. The
overall philosophy has been to use a combination of techniques, which
includes a telescope with low (and stable) instrumental polarization,
optimal full Stokes polarimeters, differential measurement schemes,
fast modulation and demodulation, and accurate calibration. The
current baseline optical layout consists of a 14-mirror layout,
which is polarimetrically compensated and nonvarying in time. In the
polarization free F2 focus ample space is reserved for calibration and
modulators and a polarimetric switch. At instrument level the s-, and
p-planes of individual components are aligned, resulting in a system
in which eigenvectors can travel undisturbed through the system.

---------------------------------------------------------
Title: European Solar Telescope: Progress status
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly,
B.; Pérez, A.; Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team
2010AN....331..615C Altcode:
In this paper, the present status of the development of the design of
the European Solar Telescope is described. The telescope is devised to
have the best possible angular resolution and polarimetric performance,
maximizing the throughput of the whole system. To that aim, adaptive
optics and multi-conjugate adaptive optics are integrated in the
optical path. The system will have the possibility to correct for the
diurnal variation of the distance to the turbulence layers, by using
several deformable mirrors, conjugated at different heights. The
present optical design of the telescope distributes the optical
elements along the optical path in such a way that the instrumental
polarization induced by the telescope is minimized and independent
of the solar elevation and azimuth. This property represents a large
advantage for polarimetric measurements. The ensemble of instruments
that are planned is also presented.

---------------------------------------------------------
Title: Spectro-polarimetry in the era of large solar telescopes
Authors: Socas-Navarro, H.
2010AN....331..581S Altcode: 2010arXiv1005.4620S
This paper discusses some of the challenges of spectro-polarimetric
observations with a large aperture solar telescope such as the ATST or
the EST. The observer needs to reach a compromise between spatial and
spectral resolution, time cadence, and signal-to-noise ratio, as only
three of those four parameters can be pushed to the limit. Tunable
filters and grating spectrographs provide a natural compromise as
the former are more suitable for high-spatial resolution observations
while the latter are a better choice when one needs to work with many
wavelengths at full spectral resolution. Given the requirements for
the new science targeted by these facilities, it is important that 1)
tunable filters have some multi-wavelength capability; and 2) grating
spectrographs have some 2D field of view.

---------------------------------------------------------
Title: Observation and analysis of chromospheric magnetic fields .
Authors: de la Cruz Rodríguez, J.; Socas-Navarro, H.; van Noort,
M.; Rouppe van der Voort, L.
2010MmSAI..81..716D Altcode: 2010arXiv1004.0698D
The solar chromosphere is a vigorously dynamic region of the sun,
where waves and magnetic fields play an important role. To improve
chromospheric diagnostics, we present new observations in Ca II 8542
carried out with the SST/CRISP on La Palma, working in full-Stokes
mode. We measured Stokes line profiles in active regions. The line
profiles observed close to the solar limb show signals in all four
Stokes parameters, while profiles observed close to disk center only
show signals above the noise level in Stokes I and V. We used the NLTE
inversion code 'NICOLE' to derive atmospheric parameters in umbral
flashes present in a small round sunspot without penumbra.

---------------------------------------------------------
Title: Has Hinode Revealed the Missing Turbulent Flux of the
Quiet Sun?
Authors: Lites, B. W.; Kubo, M.; Socas-Navarro, H.; Berger, T.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A. M.; Ichimoto, K.; Katsukawa,
Y.; Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2009ASPC..405..173L Altcode:
The Hinode Spectro-Polarimeter has revealed the presence of surprisingly
strong horizontal magnetic fields nearly everywhere in the quiet
solar atmosphere. These horizontal fields, along with measures of the
vertical fields, may be the signature of the “hidden turbulent flux”
of the quiet Sun. The measured horizontal fields average at least to
55 Gauss: nearly 5 times that of the measured longitudinal apparent
flux density. The nature of these fields are reviewed, and discussed
in the light of recent magneto-convection numerical simulations of
the quiet Sun.

---------------------------------------------------------
Title: Direct Imaging of Fine Structure in the Chromosphere of a
Sunspot Umbra
Authors: Socas-Navarro, H.; McIntosh, S. W.; Centeno, R.; de Wijn,
A. G.; Lites, B. W.
2009ApJ...696.1683S Altcode: 2008arXiv0810.0597S
High-resolution imaging observations from the Hinode spacecraft in the
Ca II H line are employed to study the dynamics of the chromosphere
above a sunspot. We find that umbral flashes and other brightenings
produced by the oscillation are extremely rich in fine structure,
even beyond the resolving limit of our observations (0farcs22). The
umbra is tremendously dynamic to the point that our time cadence of
20 s does not suffice to resolve the fast lateral (probably apparent)
motion of the emission source. Some bright elements in our data set
move with horizontal propagation speeds of 30 km s-1. We have
detected filamentary structures inside the umbra (some of which have a
horizontal extension of ~1500 km) which, to our best knowledge, had not
been reported before. The power spectra of the intensity fluctuations
reveal a few distinct areas with different properties within the umbra
that seem to correspond with the umbral cores that form it. Inside
each one of these areas the dominant frequencies of the oscillation
are coherent, but they vary considerably from one core to another.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Models of solar magnetic structures
(Socas-Navarro, 2007)
Authors: Socas-Navarro, H.
2009yCat..21690439S Altcode:
The observations used in this work were acquired with the new
Spectro-Polarimeter for Infrared and Optical Regions (SPINOR;
Socas-Navarro et al., 2006SoPh..235...55S) on 2004 June 16. The data
set includes two chromospheric lines of the CaII infrared triplet at
849.8 and 854.2nm, recorded by two different cameras, as well as two
nearby FeI lines at 849.7 and 853.8nm. (7 data files).

---------------------------------------------------------
Title: Magnetic Fields of the Quiet Sun: A New Quantitative
Perspective From Hinode
Authors: Lites, B. W.; Kubo, M.; Socas-Navarro, H.; Berger, T.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Katsukawa, Y.;
Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2008ASPC..397...17L Altcode:
This article summarizes results of studies presented in two papers
already published: Lites et al. (2007a); Lites et al. (2007b). Please
see these for further details.

---------------------------------------------------------
Title: The participation of the Instituto de Astrofísica de Canarias
in the European Solar Telescope
Authors: Collados, M.; Calcines, A.; Diaz, J. J.; Gracia, F.;
Grivel-Gelly, C.; López, R.; Mangharam, H.; Páez, E.; Perez,
A.; Rasilla, J. L.; Rodríguez, L. F.; Sánchez-Capuchino, J.;
Socas-Navarro, H.
2008SPIE.7012E..32C Altcode: 2008SPIE.7012E.105C
This communication reviews the participation of the Instituto
de Astrofísica de Canarias (IAC) in the design of the European
Solar Telescope. Apart of being the coordinator institution of the
whole project, and, as such, responsible for the project managing,
the IAC leads several tasks like overall instrument definition or
characterization of the atmospheric turbulence profile with height or
the definition of adequate detectors. More in particular, the IAC will
design and build two long-base SHABAR (SHAdow BAnd Ranger), instruments
to measure medium-altitude seeing. The IAC is also responsible for the
design, together with other institutions, of the design of grating
spectropolarimeters suitable for multiwavelength high spatial and
spectral resolution.

---------------------------------------------------------
Title: A New Approach to the Solar Oxygen Abundance Problem
Authors: Centeno, R.; Socas-Navarro, H.
2008ApJ...682L..61C Altcode: 2008arXiv0803.0990S; 2008arXiv0803.0990C
In this work we present new data that sets strong constraints on
the solar oxygen abundance. Our approach, based on the analysis of
spectropolarimetric observations, is almost model-independent and
therefore extremely robust. The asymmetry of the Stokes V profile
of the 6300 Å [O I] and Ni I blend is used as an indicator of the
relative abundances of these two elements. The peculiar shape of the
profile requires a value of epsilonO = 730 ± 100 ppm
(parts per million), or log epsilonO = 8.86 ± 0.07 in
the logarithmic scale commonly used in astrophysics. The uncertainty
range includes the model dependence as well as uncertainties in the
oscillator strengths of the lines. We emphasize that the very low
degree of model dependence in our analysis makes it very reliable
compared to traditional determinations.

---------------------------------------------------------
Title: Multiline Spectropolarimetry of the Quiet Sun at 5250 and
6302 Å
Authors: Socas-Navarro, H.; Borrero, J. M.; Asensio Ramos, A.;
Collados, M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez
González, M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez
Almeida, J.
2008ApJ...674..596S Altcode:
The reliability of quiet-Sun magnetic field diagnostics based on the
Fe I lines at 6302 Å has been questioned by recent work. Here we
present the results of a thorough study of high-resolution multiline
observations taken with the new spectropolarimeter SPINOR, comprising
the 5250 and 6302 Å spectral domains. The observations were analyzed
using several inversion algorithms, including Milne-Eddington,
LTE with 1 and 2 components, and MISMA codes. We find that the
line-ratio technique applied to the 5250 Å lines is not sufficiently
reliable to provide a direct magnetic diagnostic in the presence
of thermal fluctuations and variable line broadening. In general,
one needs to resort to inversion algorithms, ideally with realistic
magnetohydrodynamic constrains. When this is done, the 5250 Å lines
do not seem to provide any significant advantage over those at 6302
Å. In fact, our results point toward a better performance with the
latter (in the presence of turbulent line broadening). In any case,
for very weak flux concentrations, neither spectral region alone
provides sufficient constraints to fully disentangle the intrinsic
field strengths. Instead, we advocate for a combined analysis of both
spectral ranges, which yields a better determination of the quiet-Sun
magnetic properties. Finally, we propose the use of two other Fe I
lines (at 4122 and 9000 Å) with identical line opacities that seem
to work much better than the others.

---------------------------------------------------------
Title: The Horizontal Magnetic Flux of the Quiet-Sun Internetwork
as Observed with the Hinode Spectro-Polarimeter
Authors: Lites, B. W.; Kubo, M.; Socas-Navarro, H.; Berger, T.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Katsukawa, Y.;
Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2008ApJ...672.1237L Altcode:
Observations of very quiet Sun using the Solar Optical
Telescope/Spectro-Polarimeter (SOT/SP) aboard the Hinode spacecraft
reveal that the quiet internetwork regions are pervaded by horizontal
magnetic flux. The spatial average horizontal apparent flux density
derived from wavelength-integrated measures of Zeeman-induced linear
polarization is BTapp = 55 Mx cm -2, as
compared to the corresponding average vertical apparent flux density of
| BLapp| = 11 Mx cm -2. Distributions
of apparent flux density are presented. Magnetic fields are organized on
mesogranular scales, with both horizontal and vertical fields showing
"voids" of reduced flux density of a few granules spatial extent. The
vertical fields are concentrated in the intergranular lanes, whereas the
stronger horizontal fields are somewhat separated spatially from the
vertical fields and occur most commonly at the edges of the bright
granules. High-S/N observations from disk center to the limb help
to constrain possible causes of the apparent imbalance between |
BLapp| and BTapp, with
unresolved structures of linear dimension on the surface smaller by at
least a factor of 2 relative to the SOT/SP angular resolution being one
likely cause of this discrepancy. Other scenarios for explaining this
imbalance are discussed. The horizontal fields are likely the source of
the "seething" fields of the quiet Sun discovered by Harvey et al. The
horizontal fields may also contribute to the "hidden" turbulent flux
suggested by studies involving Hanle effect depolarization of scattered
radiation.

---------------------------------------------------------
Title: Hinode Observations of Flux Emergence in Quiet and Active
Regions
Authors: Lites, B. W.; Centeno, R.; Kubo, M.; Socas-Navarro, H. Berger,
T.; Frank, Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.;
Katsukawa, Y.; Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2008ASPC..383...71L Altcode:
We review briefly the observational understanding of emergence of
flux in both the quiet Sun and active regions in the light of first
results from the joint Japan/US/UK Hinode mission. That spacecraft
is now providing us with our first continuous, high resolution
measurements of the photospheric vector magnetic field, along with
high resolution observations of the thermal and dynamic properties
of the chromosphere and corona. This review is intended to present a
few very early results and to highlight the potential for discovery
offered by this extraordinary new mission. The discovery of ubiquitous
horizontal magnetic flux in the quiet internetwork regions is presented.

---------------------------------------------------------
Title: Hinode Observations of Horizontal Quiet Sun Magnetic Flux
and the “Hidden Turbulent Magnetic Flux”
Authors: Lites, Bruce; Socas-Navarro, Hector; Kubo, Masahito; Berger,
Thomas; Frank, Zoe; Shine, Richard A.; Tarbell, Theodore D.; Title,
Alan M.; Ichimoto, Kiyoshi; Katsukawa, Yukio; Tsuneta, Saku; Suematsu,
Yoshinori; Shimizu, Toshifumi
2007PASJ...59S.571L Altcode:
We present observations of magnetic fields of the very quiet Sun
near disk center using the Spectro-Polarimeter of the Solar Optical
Telescope aboard the Hinode satellite. These observations reveal for
the first time the ubiquitous presence of horizontal magnetic fields in
the internetwork regions. The horizontal fields are spatially distinct
from the vertical fields, demonstrating that they are not arising mainly
from buffeting of vertical flux tubes by the granular convection. The
horizontal component has an average “apparent flux density” of
55Mxcm-2 (assuming the horizontal field structures are
spatially resolved), in contrast to the average apparent vertical flux
density of 11Mxcm-2. The vertical fields reside mainly in
the intergranular lanes, whereas the horizontal fields occur mainly
over the bright granules, with a preference to be near the outside
edge of the bright granules. The large apparent imbalance of vertical
and horizontal flux densities is discussed, and several scenarios are
presented to explain this imbalance.

---------------------------------------------------------
Title: Spectropolarimetric Inversions of the Ca II 8498 and 8542 Å
Lines in the Quiet Sun
Authors: Pietarila, A.; Socas-Navarro, H.; Bogdan, T.
2007ApJ...670..885P Altcode:
We study non-LTE inversions of the Ca II infrared triplet lines
as a tool for inferring physical properties of the quiet Sun. The
inversion code is successful in recovering the temperature, velocity,
and longitudinal magnetic flux density in the photosphere and
chromosphere, but the height range where the inversions are sensitive
is limited, especially in the chromosphere. We present results of
inverting spectropolarimetric observations of the lines in a quiet-Sun
region. We find three distinct ranges in chromospheric temperature: low
temperatures in the internetwork, high temperatures in the enhanced
magnetic network, and intermediate temperatures associated with
low magnetic flux regions in the network. The differences between
these regions become more pronounced with height as the plasma-β
decreases. These inversions support the picture of the chromosphere,
especially close to the magnetic network, being highly inhomogeneous
in both the vertical and horizontal directions.

---------------------------------------------------------
Title: Multi-Line Quiet Sun Spectro-Polarimetry at 5250 and 6302 Å
Authors: Socas-Navarro, H.; Borrero, J.; Asensio Ramos, A.; Collados,
M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez González,
M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez Almeida, J.
2007arXiv0710.1099S Altcode:
The reliability of quiet Sun magnetic field diagnostics based on the
\ion{Fe}{1} lines at 6302 Åhas been questioned by recent work. We
present here the results of a thorough study of high-resolution
multi-line observations taken with the new spectro-polarimeter SPINOR,
comprising the 5250 and 6302 Åspectral domains. The observations were
analyzed using several inversion algorithms, including Milne-Eddington,
LTE with 1 and 2 components, and MISMA codes. We find that the
line-ratio technique applied to the 5250 Ålines is not sufficiently
reliable to provide a direct magnetic diagnostic in the presence
of thermal fluctuations and variable line broadening. In general,
one needs to resort to inversion algorithms, ideally with realistic
magneto-hydrodynamical constrains. When this is done, the 5250 Ålines
do not seem to provide any significant advantage over those at 6302
Å. In fact, our results point towards a better performance with the
latter (in the presence of turbulent line broadening). In any case,
for very weak flux concentrations, neither spectral region alone
provides sufficient constraints to fully disentangle the intrinsic field
strengths. Instead, we advocate for a combined analysis of both spectral
ranges, which yields a better determination of the quiet Sun magnetic
properties. Finally, we propose the use of two other \ion{Fe}{1} lines
(at 4122 and 9000 Å) with identical line opacities that seem to work
much better than the others.

---------------------------------------------------------
Title: Emergence of Small-Scale Magnetic Loops in the Quiet-Sun
Internetwork
Authors: Centeno, R.; Socas-Navarro, H.; Lites, B.; Kubo, M.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Tsuneta, S.;
Katsukawa, Y.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2007ApJ...666L.137C Altcode: 2007arXiv0708.0844C
We study the emergence of magnetic flux at very small spatial
scales (less than 2") in the quiet-Sun internetwork. To this aim,
a time series of spectropolarimetric maps was taken at disk center
using the instrument SP/SOT on board Hinode. The LTE inversion of
the full Stokes vector measured in the Fe I 6301 and 6302 Å lines
allows us to retrieve the magnetic flux and topology in the region
of study. In the example presented here, the magnetic flux emerges
within a granular structure. The horizontal magnetic field appears
prior to any significant amount of vertical field. As time goes on,
the traces of the horizontal field disappear, while the vertical dipoles
drift-carried by the plasma motions-toward the surrounding intergranular
lanes. These events take place within typical granulation timescales.

---------------------------------------------------------
Title: Spectropolarimetric Observations of the Ca II λ8498 and
λ8542 in the Quiet Sun
Authors: Pietarila, A.; Socas-Navarro, H.; Bogdan, T.
2007ApJ...663.1386P Altcode: 2007arXiv0707.1310P
The Ca II infrared triplet is one of the few magnetically sensitive
chromospheric lines available for ground-based observations. We present
spectropolarimetric observations of the 8498 and 8542 Å lines in a
quiet Sun region near a decaying active region and compare the results
with a simulation of the lines in a high plasma-β regime. Cluster
analysis of Stokes V profile pairs shows that the two lines,
despite arguably being formed fairly close, often do not have similar
shapes. In the network, the local magnetic topology is more important in
determining the shapes of the Stokes V profiles than the phase of the
wave, contrary to what our simulations show. We also find that Stokes
V asymmetries are very common in the network, and the histograms of
the observed amplitude and area asymmetries differ significantly from
the simulation. Both the network and internetwork show oscillatory
behavior in the Ca II lines. It is stronger in the network, where
shocking waves, similar to those in the high-β simulation, are seen
and large self-reversals in the intensity profiles are common.

---------------------------------------------------------
Title: The Solar Oxygen Abundance Determined from Polarimetric
Observations
Authors: Norton, Aimee A.; Socas-Navarro, H.
2007AAS...210.2502N Altcode: 2007BAAS...39..131N
In this work we present support for recent claims that advocate a
downward revision of the solar oxygen abundance. Our analysis employs
spatially-resolved spectro-polarimetric observations including the Fe
I lines at 6302 Angstroms, and the O I infrared triplet around 7774
Angstroms, in the quiet Sun. We used the Fe I lines to reconstruct the
three-dimensional thermal and magnetic structure of the atmosphere. The
simultaneous O I observations were then employed to determine the
abundance of oxygen at each pixel, using both LTE and non-LTE (NLTE)
approaches to the radiative transfer. In this manner, we obtain
values of log eo=8.64 (NLTE) and 8.94 (LTE) dex. We find an unsettling
fluctuation of the oxygen abundance over the field of view. This is
likely an artifact indicating that, even with this relatively refined
strategy, important physical ingredients are still missing in the
picture. By examining the spatial distribution of the abundance,
we estimate realistic confidence limits of approximately 0.1 dex.

---------------------------------------------------------
Title: The Ca II Infrared Triplet Lines as Diagnostics of
Chromospheric Magnetism
Authors: Pietarila, A.; Socas-Navarro, H.; Bogdan, T.
2007ASPC..368..139P Altcode:
The Ca II infrared (IR) triplet lines are a promising candidate for
studying chromospheric magnetism and dynamics. To study how good
of a diagnostic the lines are for chromospheric magnetism in the
quiet Sun we have constructed a MHD simulation in the high plasma-β
regime, analyzed quiet Sun spectropolarimetric data of the lines and
used a non-local thermodynamic equilibrium (nLTE) inversion code on
the observations. In the simulation, where shocking acoustic waves
dominate the dynamics, the Ca lines show a time-varying pattern of
disappearing and reappearing Stokes V lobes. Waves are seen in the
observations as well, but the dynamics are more complex. Unlike in
the simulation, the observed Ca lines do not have similar shapes
and the Stokes V asymmetries are determined by the local magnetic
topology, not the phase of the wave. The fundamental differences
between the observations and the simulation lead one to conclude that
a 1D plane parallel atmosphere is not a valid approximation for the
chromosphere. Nor can the effects of magnetic fields on the dynamics
be neglected. This is further supported by the inversions failure to
reproduce line profile asymmetries caused by gradients in the velocity
and/or magnetic field. To explain the asymmetries, 3D structures and
strongly localized gradients need to be included. The work presented
here will be published in more detail elsewhere.

---------------------------------------------------------
Title: The Intrinsic Dimensionality of Spectropolarimetric Data
Authors: Asensio Ramos, A.; Socas-Navarro, H.; López Ariste, A.;
Martínez González, M. J.
2007ApJ...660.1690A Altcode: 2007astro.ph..1604A
The amount of information available in spectropolarimetric data is
estimated. To this end, the intrinsic dimensionality of the data is
inferred with the aid of a recently derived estimator based on nearest
neighbor considerations and obtained applying the principle of maximum
likelihood. We show in detail that the estimator correctly captures the
intrinsic dimension of artificial data sets with known dimension. The
effect of noise in the estimated dimension is analyzed thoroughly,
and we conclude that it introduces a positive bias that needs to be
accounted for. Real simultaneous spectropolarimetric observations
in the visible 630 nm and the near-infrared 1.5 μm spectral regions
are also investigated in detail, showing that the near-infrared data
set provides more information of the physical conditions in the solar
atmosphere than the visible data set. Finally, we demonstrate that the
amount of information present in an observed data set is a monotonically
increasing function of the number of available spectral lines.

---------------------------------------------------------
Title: Magnetic Flux Emergence In The Quiet Sun Photosphere
Authors: Centeno, Rebecca; Lites, B.; Socas-Navarro, H.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Tsuneta, S.;
Katsukawa, Y.; Suematsu, Y.; Kubo, M.; Shimizu, T.
2007AAS...210.9406C Altcode: 2007BAAS...39..218C
We study the emergence of magnetic flux at very small spacial scales
(less than 1 arcsec) in the quiet Sun internetwork. To this aim, several
time series of spectropolarimetric maps were taken at disk center using
the instrument SP/SOT on board Hinode. The LTE inversion of the full
Stokes vector measured in the Fe I 6301 and 6302 lines will allow us
to retrieve the magnetic flux and topology in the region of study. We
find that the magnetic flux emerges typically within the granular
structures. In many cases, the horizontal magnetic field appears
prior to any significant amount of vertical field. As time goes on,
the traces of the horizontal field dissapear while the the vertical
dipoles drift -carried by the plasma motions- towards the surrounding
intergranular lanes. Sometimes they stay trapped there for a while
but they eventually either disappear by disgregation/cancelation
or agregate to other magnetic field concentrations giving rise to
larger flux elements. The time scale of these events is of the order
of 10-20 minutes.

---------------------------------------------------------
Title: Ubiquitous Horizontal Magnetic Fields in the Quiet Solar
Photosphere as Revealed by HINODE Meaurements
Authors: Lites, Bruce W.; Socas Navarro, H.; Berger, T.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Katsukawa,
Y.; Tsuneta, S.; Suematsu, Y.; Kubo, M.; Shimizu, T.; Nagata, S.;
Hinode Team
2007AAS...210.6303L Altcode: 2007BAAS...39..171L
Measurements with the HINODE Spectro-Polarimeter (SP) of the quiet
Sun allow characterization of the weak, mixed-polarity magnetic
flux at the highest angular resolution to date (0.3"), and with good
polarimetric sensitivity(0.025% relative to the continuum). The image
stabilization of the HINODE spacecraft allows long integrations with
degradation of the image quality only by the evolution of the solar
granulation. From the Stokes V profile measurements we find an average
solar "Apparent Flux Density" of 14 Mx cm-2, with significant Stokes V
signals at every position on the disk at all times. However, there are
patches of meso-granular size (5-15") where the flux is very weak. At
this high sensitivity, transverse fields produce measurable Stokes
Q,U linear polarization signals over a majority of the area, with
apparent transverse flux densities in the internetwork significantly
larger than the corresponding longitudinal flux densities. When viewed
at the center of the solar disk, the Stokes V signals (longitudinal
fields) show a preference for occurrence in the intergranular lanes,
and the Q,U signals occur preferably over the granule interiors,
but neither association is exclusive. Hinode is an international
project supported by JAXA, NASA, PPARC and ESA. We are grateful to the
Hinode team for all their efforts in the design, build and operation
of the mission.

---------------------------------------------------------
Title: The Solar Oxygen Crisis: Probably Not the Last Word
Authors: Socas-Navarro, H.; Norton, A. A.
2007ApJ...660L.153S Altcode:
In this work we present support for recent claims that advocate a
downward revision of the solar oxygen abundance. Our analysis employs
spatially resolved spectropolarimetric observations including the Fe
I lines at 6302 Å and the O I infrared triplet around 7774 Å in the
quiet Sun. We used the Fe I lines to reconstruct the three-dimensional
thermal and magnetic structure of the atmosphere. The simultaneous
O I observations were then employed to determine the abundance of
oxygen at each pixel, using both LTE and non-LTE (NLTE) approaches
to the radiative transfer. In this manner, we obtain values of
logɛO=8.63 (NLTE) and 8.93 (LTE) dex. We find an unsettling
fluctuation of the oxygen abundance over the field of view. This is
likely an artifact indicating that, even with this relatively refined
strategy, important physical ingredients are still missing in the
picture. By examining the spatial distribution of the abundance,
we estimate realistic confidence limits of approximately 0.1 dex.

---------------------------------------------------------
Title: Spectropolarimetric observations of the Ca II 8498 A and 8542
A lines in the quiet Sun
Authors: Pietarila, A.; Socas-Navarro, H.; Bogdan, T.
2007arXiv0704.0617P Altcode:
The Ca II infrared triplet is one of the few magnetically sensitive
chromospheric lines available for ground-based observations. We present
spectropolarimetric observations of the 8498 A and 8542 A lines in a
quiet Sun region near a decaying active region and compare the results
with a simulation of the lines in a high plasma-beta regime. Cluster
analysis of Stokes V profile pairs shows that the two lines,
despite arguably being formed fairly close, often do not have similar
shapes. In the network, the local magnetic topology is more important in
determining the shapes of the Stokes V profiles than the phase of the
wave, contrary to what our simulations show. We also find that Stokes
V asymmetries are very common in the network, and the histograms of
the observed amplitude and area asymmetries differ significantly from
the simulation. Both the network and internetwork show oscillatory
behavior in the Ca II lines. It is stronger in the network, where
shocking waves, similar to those in the high-beta simulation, are seen
and large self-reversals in the intensity profiles are common.

---------------------------------------------------------
Title: Semiempirical Models of Solar Magnetic Structures
Authors: Socas-Navarro, H.
2007ApJS..169..439S Altcode:
This paper presents semiempirical models of various solar magnetic
structures, extending from the photosphere to the chromosphere. The
models have been derived from non-LTE inversions of high-resolution
spectropolarimetric observations of four Ca II and Fe I lines. The
observed targets are dark and bright components of a sunspot umbra;
dark and bright components of a sunspot penumbra; a canopy between two
sunspots; a facula; and a network element. These models may be employed,
e.g., to compute realistic synthetic Stokes spectra of photospheric
and chromospheric lines.

---------------------------------------------------------
Title: A synthetic stellar polarization atlas from 400 to 1000 nm
Authors: Socas-Navarro, H.; Asensio Ramos, A.; Manso Sainz, R.
2007A&A...465..339S Altcode: 2006astro.ph.12388S
Context: With the development of new polarimeters for large telescopes,
the spectro-polarimetric study of astrophysical bodies is becoming
feasible and, indeed, more frequent. In particular, this is permitting
the observational study of stellar magnetic fields. Aims: With
the aim to optimize and interpret this kind of observations, we have
produced a spectral atlas of circular polarization in a grid of stellar
atmospheric models with effective temperatures between 3500 and 10 000
K, surface gravities log(g)=3.5-5, metallicities between 10-2
and 1, and magnetic field strengths of 100, 1000 and 5000 G. Methods: We have computed the emergent Stokes I and V flux spectra
in LTE of more than 105 spectral lines. Results: The
atlas and several numerical tools are available in electronic format
and may be downloaded from http://download.hao.ucar.edu/pub/PSA/. In
this paper we review and discuss some of its most relevant features,
such as which spectral regions and individual lines harbor the
strongest signals, what are interesting lines to observe, how to
disentangle field strength from filling factor, etc. Full
line lists and spectra are only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/ qcat?J/A+A/465/339

---------------------------------------------------------
Title: VizieR Online Data Catalog: Synthetic stellar polarization
400-1000nm (Socas-Navarro+ 2007)
Authors: Socas-Navarro, H.; Asensio Ramos, A.; Manso Sainz, R.
2007yCat..34650339S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A suite of community tools for spectro-polarimetric analysis .
Authors: Lites, B.; Casini, R.; Garcia, J.; Socas-Navarro, H.
2007MmSAI..78..148L Altcode:
The National Center for Atmospheric Research (NCAR) has undertaken a
3-year initiative to develop the Community Spectro-polarimetric Analysis
Center (CSAC). The goal of this effort is to provide the community
with standardized tools for extracting the solar magnetic field
vector and related atmospheric parameters from spectro-polarimetric
observations. The emphasis will be to develop portable, efficient, and
well-documented procedures for analysis of data from the many new and
upcoming observational facilities, both ground- and space-based. The
initial focus of CSAC will be the development of robust methods
for inversion of Stokes spectral data, starting with a standard
Milne-Eddington inversion that has been the workhorse for analysis of
data from e.g. the Advanced Stokes Polarimeter. Upon completion of that
code, the program will move to more sophisticated methods that embrace
more realistic and detailed models of the solar atmosphere. Very
fast methods for inversion (neural networks or pattern recognition
techniques, for example) are also candidates. Finally, the CSAC is
intended to eventually provide standardized methods for resolution of
the 180-degree field azimuth ambiguity, and for visualization of the
resulting magnetic field vector maps. CSAC is formulated as a community
effort, and as such will receive guidance and input from the community.

---------------------------------------------------------
Title: On the Variation of the Peak Asymmetry of Low-l Solar p Modes
Authors: Jiménez-Reyes, S. J.; Chaplin, W. J.; Elsworth, Y.; García,
R. A.; Howe, R.; Socas-Navarro, H.; Toutain, T.
2007ApJ...654.1135J Altcode:
The resonant peaks of solar p modes show small amounts of asymmetry in
frequency. Here, we use five independent sets of contemporaneous data,
collected over a ~=8 yr period, to investigate whether peak asymmetry in
low angular degree p modes changes over the solar activity cycle. Three
of the data sets are from instruments on board the ESA/NASA SOHO
spacecraft (GOLF, MDI, and VIRGO/SPM); and two are from ground-based
networks (BiSON and GONG). Evidence for variation in asymmetry, well
correlated with the activity cycle, is uncovered in the GOLF and BiSON
Doppler velocity data. Suggestions of a similar trend are present in
the GONG Doppler velocity data. Apparent changes in the MDI Doppler
velocity data are somewhat less significant. Meanwhile, analysis of
the SPM intensity data failed to uncover any evidence for significant
change of the asymmetry parameter.

---------------------------------------------------------
Title: Spectral Line Selection for HMI
Authors: Norton, A. A.; Pietarila Graham, J. D.; Ulrich, R. K.;
Schou, J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; López Ariste, A.;
Bush, R. I.; Socas-Navarro, H.; Scherrer, P. H.
2006ASPC..358..193N Altcode:
We present information on two spectral lines, Fe I 6173 Å and Ni I 6768
Å, that were candidates for use in the Helioseismic and Magnetic Imager
(HMI) instrument. Both Fe I and Ni I profiles have clean continuum and
no blends that threaten performance. The higher Landé factor of Fe
I means its operational velocity range in regions of strong magnetic
field is smaller than for Ne I. Fe I performs better than Ni I for
vector magnetic field retrieval. Inversion results show that Fe I
consistently determines field strength and flux more accurately than
the Ni I line. Inversions show inclination and azimuthal errors are
recovered to ≈2° above 600 Mx/cm2 for Fe I and above
1000 Mx/cm2 for Ni I. The Fe I line was recommended, and
ultimately chosen, for use in HMI.

---------------------------------------------------------
Title: Spectral Line Selection for HMI: A Comparison of Fe I 6173
Å and Ni I 6768 Å
Authors: Norton, A. A.; Graham, J. Pietarila; Ulrich, R. K.; Schou,
J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; Ariste, A. López; Bush,
R. I.; Socas-Navarro, H.; Scherrer, P. H.
2006SoPh..239...69N Altcode: 2006SoPh..tmp...88N; 2006astro.ph..8124N
We present a study of two spectral lines, Fe I 6173 Å and Ni I 6768 Å,
that were candidates to be used in the Helioseismic and Magnetic Imager
(HMI) for observing Doppler velocity and the vector magnetic field. The
line profiles were studied using the Mt. Wilson Observatory, the
Advanced Stokes Polarimeter and the Kitt Peak-McMath Pierce telescope
and one-meter Fourier transform spectrometer atlas. Both Fe I and Ni
I profiles have clean continua and no blends that threaten instrument
performance. The Fe I line is 2% deeper, 15% narrower, and has a 6%
smaller equivalent width than the Ni I line. The potential of each
spectral line to recover pre-assigned solar conditions is tested
using a least-squares minimization technique to fit Milne-Eddington
models to tens of thousands of line profiles that have been sampled
at five spectral positions across the line. Overall, the Fe I line
has a better performance than the Ni I line for vector-magnetic-field
retrieval. Specifically, the Fe I line is able to determine field
strength, longitudinal and transverse flux four times more accurately
than the Ni I line in active regions. Inclination and azimuthal angles
can be recovered to ≈2° above 600 Mx cm−2
for Fe I and above 1000 Mx cm−2 for Ni I. Therefore, the
Fe I line better determines the magnetic-field orientation in plage,
whereas both lines provide good orientation determination in penumbrae
and umbrae. We selected the Fe I spectral line for use in HMI due to
its better performance for magnetic diagnostics while not sacrificing
velocity information. The one exception to the better performance of the
Fe I line arises when high field strengths combine with high velocities
to move the spectral line beyond the effective sampling range. The
higher geff of Fe I means that its useful range of velocity
values in regions of strong magnetic field is smaller than Ni I.

---------------------------------------------------------
Title: Erratum: “Polynomial Approximants for the Calculation
of Polarization Profiles in the He I 10830 Å Multiplet” (<A
href="bib_query?2005ApJS...160..312S">ApJS, 160, 312 [2005]</A>)
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Landi Degl'Innocenti,
E.
2006ApJS..166..441S Altcode:
In our published paper there is an error in the order of the rows in
Tables 1 through 6. We stated in the paper that the components are
sorted in the order of increasing wavelengths in the linear Zeeman
splitting (LZS) regime. However, in the published tables the values for
the σ+ and σ- components appear reversed. As
a result, researchers trying to implement our polynomial approximants
might apply the incomplete Paschen-Back splitting (IPBS) corrections
to the wrong components. To avoid any possible confusion, here we
reproduce the tables with the correct sorting (i.e., in the order of
increasing wavelengths in the LZS regime). For clarity, we have also
replaced the σ+/- notation with σred/blue. We thank Rebecca Centeno for bringing this error to our attention.

---------------------------------------------------------
Title: The Ca Ir Triplet As A Diagnostic For Chromospheric Magnetism
Authors: Pietarila, Anna M.; Socas-Navarro, H.; Bogdan, T. J.
2006SPD....37.1902P Altcode: 2006BAAS...38..247P
The Ca IR triplet lines are a good candidate for observing chromospheric
magnetic fields. Simulations of the lines in the high-beta regime,
spectropolarimetric observations and inversions of observations give
insight to their usability\suitability in observing QS magnetic fields
and dynamics. Propagating waves are clearly visible in the simulations,
both in Stokes V and I. Observed line profiles are found to be more
complicated, though they do indicate the presence of waves. We present
both simulated and observed profiles and analyze the ability of the
NLTE inversion algorithm to retrieve the underlying physics in the
solar atmosphere.

---------------------------------------------------------
Title: High Resolution Spectropolarimetry of Penumbral Formation
with IBIS
Authors: Reardon, Kevin; Casini, R.; Cavallini, F.; Tomczyk, S.;
Rouppe van der Voort, L.; Van Noort, M.; Woeger, F.; Socas Navarro,
H.; IBIS Team
2006SPD....37.3503R Altcode: 2006BAAS...38..260R
We present the results of first spectropolarimetric observations
made with the Interferometric Bidimensional Spectrometer (IBIS)
at the NSO/Dunn Solar Telescope. The use of narrowband imaging and
post-facto reconstruction techniques allows for observations close
to the diffraction limit of the vector magnetic field. We will show
observations of the the formation of an individual penumbral filament
around a small pore. We measure the magnetic field and velocity field
of the forming penumbral filament. The spectropolarimetric mode of
IBIS will be available to the community in the fall of 2006.

---------------------------------------------------------
Title: Site testing for the Advanced Technology Solar Telescope
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.;
Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn,
M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Streander, K.
2006SPIE.6267E..1TH Altcode: 2006SPIE.6267E..59H
The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope
being designed for high spatial, spectral and temporal resolution,
as well as IR and low-scattered light observations. The overall
limit of performance of the telescope is strongly influenced by the
qualities of the site at which it is located. Six sites were tested
with a seeing monitor and a sky brightness instrument for 1.5 to 2
years. The sites were Big Bear (California), Haleakala (Hawaii), La
Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak
(New Mexico), and San Pedro Martir (Baja California, Mexico). In this
paper we will describe the methods and results of the site survey,
which chose Haleakala as the location of the ATST.

---------------------------------------------------------
Title: Spectro-Polarimetric Observations and Non-Lte Modeling of
Ellerman Bombs
Authors: Socas-Navarro, Hector; Pillet, Valentín Martínez; Elmore,
David; Pietarila, Anna; Lites, Bruce W.; Sainz, Rafael Manso
2006SoPh..235...75S Altcode: 2005astro.ph..8667S
Ellerman bombs are bright emission features observed in the wings
of Hα, usually in the vicinity of magnetic concentrations. Here we
show that they can also be detected in the Ca II infrared triplet
lines, which are easier to interpret and therefore allow for more
detailed diagnostics. We present full Stokes observations of the
849.8 and 854.2 nm lines acquired with the new spectro-polarimeter
SPINOR. The data show no significant linear polarization at the level
of 3 × 10−4. The circular polarization profiles exhibit
measureable signals with a very intricate pattern of peaks. A non-LTE
analysis of the spectral profiles emerging from these features reveals
the presence of strong downflows (∼10 {km s−1}) in a
hot layer between the upper photosphere and the lower chromosphere.

---------------------------------------------------------
Title: Spinor: Visible and Infrared Spectro-Polarimetry at the
National Solar Observatory
Authors: Socas-Navarro, Hector; Elmore, David; Pietarila, Anna;
Darnell, Anthony; Lites, Bruce W.; Tomczyk, Steven; Hegwer, Steven
2006SoPh..235...55S Altcode: 2005astro.ph..8685S
The Spectro-Polarimeter for Infrared and Optical Regions (SPINOR)
is a new spectro-polarimeter that will serve as a facility instrument
for the Dunn Solar Telescope at the National Solar Observatory. This
instrument is capable of achromatic polarimetry over a very broad range
of wavelengths, from 430 to 1600 nm, allowing for the simultaneous
observation of several visible and infrared spectral regions with full
Stokes polarimetry. Another key feature of the design is its flexibility
to observe virtually any combination of spectral lines, limited only
by practical considerations (e.g., the number of detectors available,
space on the optical bench, etc.).

---------------------------------------------------------
Title: Simulation of Quiet-Sun Waves in the Ca II Infrared Triplet
Authors: Pietarila, A.; Socas-Navarro, H.; Bogdan, T.; Carlsson, M.;
Stein, R. F.
2006ApJ...640.1142P Altcode: 2005astro.ph.10744P
The Ca II infrared triplet lines around 8540 Å are good candidates
for observing chromospheric magnetism. Model spectra of these lines
are obtained by combining a radiation hydrodynamic simulation with a
Stokes synthesis code. The simulation shows interesting time-varying
behavior of the Stokes V profiles as waves propagate through the
formation region of the lines. Disappearing and reappearing lobes
in the Stokes V profiles as well as profile asymmetries are closely
related to the atmospheric velocity gradients.

---------------------------------------------------------
Title: On the fine structure of sunspot penumbrae. III. The vertical
extension of penumbral filaments
Authors: Borrero, J. M.; Solanki, S. K.; Lagg, A.; Socas-Navarro,
H.; Lites, B.
2006A&A...450..383B Altcode: 2005astro.ph.10586B
In this paper we study the fine structure of the penumbra as inferred
from the uncombed model (flux tube embedded in a magnetic surrounding)
when applied to penumbral spectropolarimetric data from the neutral
iron lines at 6300 Å. The inversion infers very similar radial
dependences in the physical quantities (LOS velocity, magnetic field
strength etc.) as those obtained from the inversion of the Fe I 1.56
μm lines. In addition, the large Stokes V area asymmetry exhibited
by the visible lines helps to constrain the size of the penumbral
flux tubes. As we demonstrate here, the uncombed model is able to
reproduce the area asymmetry with striking accuracy, returning flux
tubes as thick as 100-300 kilometers in the vertical direction, in
good agreement with previous investigations.

---------------------------------------------------------
Title: Influence of the Paschen-Back effect on the results of
polarimetric inversions of the He I 10830 Å triplet
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.; Socas-Navarro, H.
2006MSAIS...9..126S Altcode:
The He I triplet at 10830 Å has a great potential for determining the
magnetic field vector in the upper chromosphere. The triplet is Zeeman
sensitive (Landé factors 2.0, 1.75 and 1.25) and shows the signature of
the Hanle effect under appropriate conditions. Additionally, the Zeeman
sublevels are influenced by the Paschen-Back effect leading to changes
in strength and in position of the Zeeman components of the transitions
forming the triplet. In this work we calculate the influence of the
Paschen-Back effect on the Stokes profiles and investigate its relevance
to inversions on spectro-polarimetric data obtained with the Tenerife
Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope (VTT).

---------------------------------------------------------
Title: Evidence for Fine Structure in the Chromospheric Umbral
Oscillation
Authors: Centeno, R.; Socas-Navarro, H.; Collados, M.; Trujillo
Bueno, J.
2005ApJ...635..670C Altcode: 2005astro.ph.10740C
Novel spectropolarimetric observations of the He I multiplet are
used to explore the dynamics of the chromospheric oscillation above
sunspot umbrae. The results presented here provide strong evidence
in support of the two-component model proposed by Socas-Navarro
and coauthors. According to this model, the waves propagate only
inside channels of subarcsecond width (the “active” component),
whereas the rest of the umbra remains nearly at rest (the “quiet”
component). Although the observations support the fundamental elements
of that model, there is one particular aspect that is not compatible
with our data. We find that, contrary to the scenario as originally
proposed, the active component remains through the entire oscillation
cycle and harbors both the upflowing and the downflowing phase of
the oscillation.

---------------------------------------------------------
Title: Solar Site Survey for the Advanced Technology Solar
Telescope. I. Analysis of the Seeing Data
Authors: Socas-Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.;
Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer,
S.; Hill, F.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.;
Oncley, S.; Penn, M.; Rimmele, T.; Streander, K.
2005PASP..117.1296S Altcode: 2005astro.ph..8690S
The site survey for the Advanced Technology Solar Telescope concluded
recently after more than 2 years of data gathering and analysis. Six
locations, including lake, island, and continental sites, were
thoroughly probed for image quality and sky brightness. The present
paper describes the analysis methodology employed to determine the
height stratification of the atmospheric turbulence. This information
is crucial, because daytime seeing is often very different between the
actual telescope aperture (~30 m) and the ground. Two independent
inversion codes have been developed to simultaneously analyze
data from a scintillometer array and a solar differential image
monitor. We show here the results of applying them to a sample subset
of data from 2003 May that was used for testing. Both codes retrieve a
similar seeing stratification through the height range of interest. A
quantitative comparison between our analysis procedure and actual in
situ measurements confirms the validity of the inversions. The sample
data presented in this paper reveal a qualitatively different behavior
for the lake sites (dominated by high-altitude seeing) and the rest
(dominated by near-ground turbulence).

---------------------------------------------------------
Title: Are Electric Currents Heating the Magnetic Chromosphere?
Authors: Socas-Navarro, H.
2005ApJ...633L..57S Altcode: 2005astro.ph..8689S
This Letter presents an analysis of three-dimensional vector currents
and temperatures observed in a sunspot from the photosphere to the
chromosphere, spanning a range of heights of approximately 1500
km. With this unique data set, based on novel spectropolarimetric
observations of the 850 nm spectral region, it is possible to conduct
for the first time an empirical study of the relation between currents
and chromospheric heating. It is shown that while resistive current
dissipation contributes to heat the sunspot chromosphere, it is not
the dominant factor. The heating effect of current dissipation is more
important in the penumbra of the sunspot, but even there it is still
a relatively modest contribution.

---------------------------------------------------------
Title: The Three-dimensional Structure of a Sunspot Magnetic Field
Authors: Socas-Navarro, H.
2005ApJ...631L.167S Altcode: 2005astro.ph..8688S
We report on observations of the three-dimensional structure of
a sunspot magnetic field from the photosphere to the chromosphere,
obtained with the new visible/infrared spectropolarimeter SPINOR. The
observations, interpreted with a non-LTE modeling technique, reveal
a surprisingly complex topology with areas of opposite-sign torsion,
suggesting that flux ropes of opposite helicity may coexist together
in the same spot.

---------------------------------------------------------
Title: Polynomial Approximants for the Calculation of Polarization
Profiles in the He I 10830 Å Multiplet
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Landi Degl'Innocenti,
E.
2005ApJS..160..312S Altcode: 2005astro.ph..5321S
The He I multiplet at 10830 Å is formed in the incomplete
Paschen-Back regime for typical conditions found in solar and stellar
atmospheres. The positions and strengths of the various components
that form the Zeeman structure of this multiplet in the Paschen-Back
regime are approximated here by polynomials. The fitting errors
are smaller than ~10-2 mÅ in the component positions
and ~10-3 in the relative strengths. The approximant
polynomials allow for a very fast implementation of the incomplete
Paschen-Back regime in numerical codes for the synthesis and inversion
of polarization profiles in this important multiplet.

---------------------------------------------------------
Title: High precision polarimetry with the Advanced Technology
Solar Telescope
Authors: Socas-Navarro, Hector; Elmore, David F.; Keller, Christoph
U.; Seagraves, Paul H.; Streander, Kim V.; Card, Gregory L.; Warner,
Mark; Kuhn, Jeffrey R.; Mickey, Donald L.
2005SPIE.5901...52S Altcode:
This paper addresses the issue of calibrating the Advanced Technology
Solar Telescope for high-precision polarimetry, in particular of the
optical train above the Gregorian station (where suitable calibration
optics will be placed). Conventional techniques would not be adequate
for this telescope given its large aperture. Here we explore two
different methods that are currently being considered by the design
team. The first one is the "sub-aperture" method, which uses small
calibration optics above the primary mirror to calibrate a small
sub-aperture of the system. This calibration is then extended to the
full aperture by means of actual observations. The second method is
based on analyzing the polarization observed in a spectral line with
a peculiar Zeeman pattern, such as the FeII 614.9 nm line, which does
not produce any intrinsic linear polarization. Numerical simulations
are presented that show the robustness of both techniques and their
respective advantages and disadvantages are discussed.

---------------------------------------------------------
Title: The visible spectro-polarimeter for the advanced technology
solar telescope
Authors: Elmore, D. F.; Socas-Navarro, H.; Card, G. L.; Streander,
K. V.
2005SPIE.5901...60E Altcode:
The mission of the ATST visible spectro-polarimeter (ViSP) is to
provide precision measurements of the full state of polarization
(Stokes parameters) simultaneously at diverse wavelengths in the
visible spectrum and fully resolve (or nearly so) the profiles
of spectrum lines originating in the solar atmosphere. We present
the instrument science requirements, their flow down to instrument
specifications, and a preliminary ViSP design. The ViSP spectrograph
allows for reconfiguration while maintaining an immediately selectable
configuration. We describe how the ViSP will utilize the ATST
polarimetry facility.

---------------------------------------------------------
Title: An artificial neural network approach to the solution of
molecular chemical equilibrium
Authors: Asensio Ramos, A.; Socas-Navarro, H.
2005A&A...438.1021A Altcode: 2005astro.ph..5322A
A novel approach is presented for the solution of instantaneous
chemical equilibrium problems. The chemical equilibrium can be
considered, due to its intrinsically local character, as a mapping
of the three-dimensional parameter space spanned by the temperature,
hydrogen density and electron density into many one-dimensional
spaces representing the number density of each species. We take
advantage of the ability of artificial neural networks to approximate
non-linear functions and construct neural networks for the fast and
efficient solution of the chemical equilibrium problem in typical
stellar atmosphere physical conditions. The neural network approach
has the advantage of providing an analytic function, which can be
rapidly evaluated. The networks are trained with a learning set (that
covers the entire parameter space) until a relative error below 1%
is reached. It has been verified that the networks are not overtrained
by using an additional verification set. The networks are then applied
to a snapshot of realistic three-dimensional convection simulations
of the solar atmosphere showing good generalization properties.

---------------------------------------------------------
Title: The ATST Site Survey
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.;
Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.;
Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K.
2005AGUSMSP34A..04H Altcode:
The Advanced Technology Solar Telescope (ATST) will be the world's
largest aperture solar telescope, and is being designed for high
resolution, IR, and coronal research. It must be located at a site that
maximizes the scientific return of this substantial investment. We
present the instrumentation, analysis and results of the ATST site
survey. Two instrumentation sets were deployed at each of six sites to
measure seeing as a function of height, and sky brightness as a function
of wavelength and off-limb position. Analysis software was developed
to estimate the structure function Cn2 as a function of height near
the ground, and the results were verified by comparison with in-situ
measurements. Additional software was developed to estimate the sky
brightness. The statistics of the conditions at the sites were corrected
for observing habits and the annualized hours of specific observing
conditions were estimated. These results were used to identify three
excellent sites suitable to host the ATST: Haleakala, Big Bear and La
Palma. Among them, Haleakala is proposed as the optimal location of
the ATST, La Palma and Big Bear being viable alternative sites.

---------------------------------------------------------
Title: Polarimetric calibration of large-aperture
telescopes. II. Subaperture method
Authors: Socas-Navarro, Hector
2005JOSAA..22..907S Altcode: 2004astro.ph.10563S; 2005OSAJ...22..907S
A new method for absolute polarimetric calibration of large telescopes
is presented. The proposed method is highly accurate and is based on
the calibration of a small subaperture, which is then extended to
the full system by means of actual observations of an astronomical
source. The calibration procedure is described in detail along with
numerical simulations that explore its robustness and accuracy. The
advantages and disadvantages of this technique with respect to other
possible alternatives are discussed.

---------------------------------------------------------
Title: Strategies for Spectral Profile Inversion Using Artificial
Neural Networks
Authors: Socas-Navarro, H.
2005ApJ...621..545S Altcode: 2004astro.ph.10567S
This paper explores three different strategies for the inversion of
spectral lines (and their Stokes profiles) using artificial neural
networks. It is shown that a straightforward approach in which the
network is trained with synthetic spectra from a simplified model leads
to considerable errors in the inversion of real observations. This
problem can be overcome in at least two different ways that are
studied here in detail. The first method makes use of an additional
preprocessing autoassociative neural network to project the observed
profile into the theoretical model subspace. The second method
considers a suitable regularization of the neural network used for the
inversion. These new techniques are shown to be robust and reliable
when applied to the inversion of both synthetic and observed data.

---------------------------------------------------------
Title: Polarimetric calibration of large-aperture
telescopes. I. Beam-expansion method
Authors: Socas-Navarro, Hector
2005JOSAA..22..539S Altcode: 2005OSAJ...22..539S; 2004astro.ph.10564S
This paper describes a concept for the high-accuracy absolute
calibration of the instrumental polarization introduced by the
primary mirror of a large-aperture telescope. This procedure requires
a small aperture with polarization calibration optics (e.g., mounted
on the dome) followed by a lens that opens the beam to illuminate the
entire surface of the mirror. The Jones matrix corresponding to this
calibration setup (with a diverging incident beam) is related to that
of the normal observing setup (with a collimated incident beam) by an
approximate correction term. Numerical models of parabolic on-axis
and off-axis mirrors with surface imperfections are used to explore
its accuracy.

---------------------------------------------------------
Title: Physical Properties of Spicules from Simultaneous
Spectropolarimetric Observations of He I and Ca II Lines
Authors: Socas-Navarro, H.; Elmore, D.
2005ApJ...619L.195S Altcode: 2004astro.ph.10566S
We present full Stokes observations from SPINOR (Spectro-Polarimeter
for INfrared and Optical Regions, at the Dunn Solar Telescope) in the
Ca II infrared triplet and the He I multiplet at 1083 nm from which some
properties of spicules have been derived. There are important advantages
in multiline observations, particularly from different elements. We find
that the orientation of the plane of polarization is very different
for the Ca and He lines, which provides new model-independent direct
evidence of magnetic fields in spicules. Our data show that the Ca and
He lines have almost identical widths. Since the Ca atom is 10 times
heavier than He, we are able to conclude that most of the broadening
is nonthermal (~=16 km s-1) and to set an upper limit of
13 kK to the spicular temperatures. The bisectors of the lines span a
velocity range of over 15 km s-1 for the He line and 30 km
s-1 for the Ca ones. The vertical gradient of line-of-sight
velocities is also very different for both elements. We obtain 2.8 km
s-1 Mm-1 from He versus 6.4 km s-1
Mm-1 from Ca. These properties, and others from similar
observations, should be taken into account in future physical models
of spicules.

---------------------------------------------------------
Title: Feature Extraction Techniques for the Analysis of Spectral
Polarization Profiles
Authors: Socas-Navarro, H.
2005ApJ...620..517S Altcode: 2004astro.ph.10565S
This paper introduces a novel feature extraction technique for the
analysis of spectral line Stokes profiles. The procedure is based on the
use of an autoassociative artificial neural network containing nonlinear
hidden layers. The neural network extracts a small subset of parameters
from the profiles (features), from which it is then able to reconstruct
the original profile. This new approach is compared to two other
procedures that have been proposed in previous works, namely principal
component analysis and Hermitian function expansions. Depending on the
target application, each of these three techniques has some advantages
and disadvantages, which are discussed here.

---------------------------------------------------------
Title: Shocks in the Quiet Solar Photosphere: A Rather Common
Occurrence
Authors: Socas-Navarro, H.; Manso Sainz, R.
2005ApJ...620L..71S Altcode: 2004astro.ph.10568S
We present observations of the quiet solar photosphere in the Fe
I lines at 6302 Å where at least four different spatial locations
exhibit upward-directed supersonic flows. These upflows can only be
detected in the circular polarization profiles as a double-peaked
structure in the blue lobe of both Fe I lines. We have detected cases
of either magnetic polarity in the data. The polarization signals
associated with the upflows are very weak, which is probably why they
had not been seen before in this type of observation. We propose that
the observed flows are the signature of aborted convective collapse,
similar to the case reported by Bellot Rubio et al. Our data indicate
that this phenomenon occurs frequently in the quiet Sun, which means
that many magnetic elements (although the fraction is still unknown)
are destroyed even before they are formed completely. The spectral
signatures of supersonic upflows reported here are probably present
in most spectropolarimetric observations of sufficient signal-to-noise
ratio and spatial resolution.

---------------------------------------------------------
Title: Observational Evidence for Small-Scale Mixture of Weak and
Strong Fields in the Quiet Sun
Authors: Socas-Navarro, H.; Lites, B. W.
2004ApJ...616..587S Altcode: 2004astro.ph.10562S
Three different maps of the quiet Sun, observed with the Advanced Stokes
Polarimeter (ASP) and the Diffraction-Limited Stokes Polarimeter
(DLSP), show evidence of strong (~=1700 G) and weak (&lt;500 G)
fields coexisting within the resolution element at both network and
internetwork locations. The angular resolution of the observations
is of 1" (ASP) and 0.6" (DLSP). Even at the higher DLSP resolution,
a significant fraction of the network magnetic patches harbor a mixture
of strong and weak fields. Internetwork elements that exhibit kG fields
when analyzed with a single-component atmosphere are also shown to
harbor considerable amounts of weak fields. Only those patches for
which a single-component analysis yields weak fields do not show this
mixture of field strengths. Finally, there is a larger fractional area
of weak fields in the convective upflows than in the downflows.

---------------------------------------------------------
Title: A Simple Procedure for Optimizing the Height Resolution in
Spectral Line Inversions
Authors: Socas-Navarro, H.
2004ApJ...614..457S Altcode:
This paper presents a method to determine how much detail of the
height stratification of atmospheric parameters can be retrieved from
the inversion of spectral lines (and their polarization profiles,
when available) via χ2-minimization algorithms. An a
priori analysis of the response functions and their correlations
permits an evaluation of the optimal number of inversion nodes
and their locations. A number of problems of practical interest
are studied by applying this method to different photospheric and
chromospheric models of quiet Sun and sunspots. As a result of this
analysis I obtain the optimal discretization for retrieving the
temperature and magnetic field stratifications in such atmospheres. I
show that the Fe I lines at 6302 Å provide a height resolution for
temperature inversions close to Δτ500~=0.5 in the middle
photosphere. In comparison, the chromospheric Hα line allows for a
resolution of Δτ500~=1.5 through the chromosphere. This
kind of analysis may also be useful in other contexts in which
χ2-minimization algorithms are employed.

---------------------------------------------------------
Title: Motivation and Initial Results from SPINOR in the Near Infrared
Authors: Socas-Navarro, H.; Elmore, D.; Lites, W.
2004astro.ph.10576S Altcode:
SPINOR is a new spectro-polarimeter that will serve as a facility
instrument for the Dunn Solar Telescope at the National Solar
Observatory. This instrument is capable of achromatic operation over
a very broad range of wavelengths, from $\sim$400 up to 1600 nm,
allowing for the simultaneous observation of several visible and
infrared spectral regions with full Stokes polarimetry. Another key
feature of the design is its flexibility to observe virtually any
combination of spectral lines, limited only by practical considerations
(e.g., the number of detectors available, space on the optical bench,
etc). SPINOR is scheduled for commissioning by the end of 2005. In
this paper we report on the current status of the project and present
actual observations of active regions in the Ca II infrared triplet
and the He I multiplet at 1083 nm.

---------------------------------------------------------
Title: The Thermal and Magnetic Structure of Umbral Dots from the
Inversion of High-Resolution Full Stokes Observations
Authors: Socas-Navarro, H.; Martínez Pillet, V.; Sobotka, M.;
Vázquez, M.
2004ApJ...614..448S Altcode:
This paper presents the analysis of high-resolution Stokes observations
of eight different umbral dots in a sunspot. The spectra were recorded
with the La Palma Stokes Polarimeter, attached to the Swedish Vacuum
Solar Telescope. The observed line profiles have been inverted to
yield the height stratifications of temperature, magnetic field,
and line-of-sight velocity, as well as their respective Wilson
depressions. We report on systematic differences in the properties of
umbral dots with respect to the nearby umbra, including small upflows
(~100 m s-1), higher temperatures (~1 kK), and weaker fields
(~500 G) with more horizontal orientations (~10°). The field weakening
is strongly correlated with the Wilson depression, suggesting that
it may be due to an opacity effect (as one is looking at higher
layers). The inclination excess, on the other hand, is real and
cannot be ascribed to formation height issues. The results obtained
from our semiempirical modeling are discussed within the context
of the currently existing scenarios for the subsurface structure of
sunspots. The observational signatures revealed by our analysis fit
well within both the “spaghetti” and the monolithic models.

---------------------------------------------------------
Title: Solar site testing for the Advanced Technology Solar Telescope
Authors: Hill, Frank; Beckers, Jacques; Brandt, Peter; Briggs, John;
Brown, Timothy; Brown, W.; Collados, Manuel; Denker, Carsten; Fletcher,
Steven; Hegwer, Steven; Horst, T.; Komsa, Mark; Kuhn, Jeff; Lecinski,
Alice; Lin, Haosheng; Oncley, Steve; Penn, Matthew; Rimmele, Thomas
R.; Socas-Navarro, Hector; Streander, Kim
2004SPIE.5489..122H Altcode:
The location of the Advanced Technology Solar Telescope (ATST) is a
critical factor in the overall performance of the telescope. We have
developed a set of instrumentation to measure daytime seeing, sky
brightness, cloud cover, water vapor, dust levels, and weather. The
instruments have been located at six sites for periods of one to two
years. Here we describe the sites and instrumentation, discuss the
data reduction, and present some preliminary results. We demonstrate
that it is possible to estimate seeing as a function of height near the
ground with an array of scintillometers, and that there is a distinct
qualitative difference in daytime seeing between sites with or without
a nearby lake.

---------------------------------------------------------
Title: Multiline Stokes Analysis for the Study of Small-Scale Solar
Magnetic Fields
Authors: Socas-Navarro, H.
2004ApJ...613..610S Altcode:
Combining observations of spectral lines with different Zeeman
sensitivities, it is possible to infer some properties of the
small-scale solar magnetic fields. This paper presents a theoretical
analysis of the diagnostics potential of 14 different spectral
lines when used for this purpose. These lines span a broad range of
wavelengths from the visible to the near-infrared and have been employed
in recent studies of the quiet-Sun magnetism. It is shown here that the
visible lines analyzed provide only a rough picture of the unresolved
field distribution, but their results are more robust. Infrared
lines, on the other hand, have the potential of carrying much richer
information on the details of the distribution. However, this depends
critically on the sensitivity attained and the analysis performed. The
best results are obtained when a suitable combination of visible
and infrared lines is employed. The analysis of sample visible and
infrared quiet-Sun profiles confirms this assessment and suggests the
coexistence of weak and strong fields within the resolution element,
which would explain the observational discrepancy that surrounds this
issue. Finally, I present a table with optimum combinations of spectral
lines for three present or upcoming multiline solar spectropolarimeters
(THEMIS, SPINOR, and the TIP+POLIS combination).

---------------------------------------------------------
Title: Instrumentation for the Advanced Technology Solar Telescope
Authors: Rimmele, Thomas R.; Hubbard, Robert P.; Balasubramaniam,
K. S.; Berger, Tom; Elmore, David; Gary, G. Allen; Jennings, Don;
Keller, Christoph; Kuhn, Jeff; Lin, Haosheng; Mickey, Don; Moretto,
Gilberto; Socas-Navarro, Hector; Stenflo, Jan O.; Wang, Haimin
2004SPIE.5492..944R Altcode:
The 4-m aperture Advanced Technology Solar Telescope (ATST) is the
next generation ground based solar telescope. In this paper we provide
an overview of the ATST post-focus instrumentation. The majority of
ATST instrumentation is located in an instrument Coude lab facility,
where a rotating platform provides image de-rotation. A high order
adaptive optics system delivers a corrected beam to the Coude lab
facility. Alternatively, instruments can be mounted at Nasmyth or
a small Gregorian area. For example, instruments for observing the
faint corona preferably will be mounted at Nasmyth focus where maximum
throughput is achieved. In addition, the Nasmyth focus has minimum
telescope polarization and minimum stray light. We describe the set of
first generation instruments, which include a Visible-Light Broadband
Imager (VLBI), Visible and Near-Infrared (NIR) Spectropolarimeters,
Visible and NIR Tunable Filters, a Thermal-Infrared Polarimeter &amp;
Spectrometer and a UV-Polarimeter. We also discuss unique and efficient
approaches to the ATST instrumentation, which builds on the use of
common components such as detector systems, polarimetry packages and
various opto-mechanical components.

---------------------------------------------------------
Title: Signatures of Incomplete Paschen-Back Splitting in the
Polarization Profiles of the He I λ10830 Multiplet
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Landi Degl'Innocenti,
E.
2004ApJ...612.1175S Altcode: 2004astro.ph..9005S
We investigate the formation of polarization profiles induced by a
magnetic field in the He I multiplet at 10830 Å. Our analysis considers
the Zeeman splitting in the incomplete Paschen-Back regime. The effects
turn out to be important and produce measurable signatures on the
profiles, even for fields significantly weaker than the level-crossing
field (~400 G). When compared to profiles calculated with the usual
linear Zeeman effect, the incomplete Paschen-Back profiles exhibit
the following conspicuous differences: (1) a non-Doppler blueshift
of the Stokes V zero-crossing wavelength of the blue component;
(2) area and peak asymmetries, even in the absence of velocity and
magnetic gradients; and (3) a ~25% reduction in the amplitude of
the red component. These features do not vanish in the weak-field
limit. The spectral signatures that we analyze in this paper may be
found in previous observations published in the literature.

---------------------------------------------------------
Title: Characterization of Magnetic Flux in the Quiet Sun. II. The
Internetwork Fields at High Angular Resolution
Authors: Lites, B. W.; Socas-Navarro, H.
2004ApJ...613..600L Altcode:
This paper presents high-resolution (0.6") spectropolarimetric
observations of very quiet solar regions. We make determinations of the
magnetic flux density, intrinsic field strength, and magnetic filling
factor in these regions. Our results confirm other previous works in
that most of the internetwork flux is in the form of intrinsically
strong fields. However, in contrast to other recent observations, we
do not find a significant increase in the amount of unsigned magnetic
flux relative to that measured at an angular resolution of 1", nor do
we find that most internetwork lanes are populated by strong flux. We
discuss possible causes for this disparity. The lack of additional flux
with increased resolution may be used to set constrains on the typical
spatial scales at which mixed polarities occur (smaller than ~=0.6").

---------------------------------------------------------
Title: Magnetic Properties of the Solar Internetwork
Authors: Socas-Navarro, H.; Martínez Pillet, V.; Lites, B. W.
2004ApJ...611.1139S Altcode:
Advanced Stokes Polarimeter observations are used to study the
weakest polarization signals observed in the quiet photosphere with
flux densities in the range of 1.5-50 Mx cm-2, which
are found in internetwork regions. Our analysis allows us to reach
an unprecedented spectropolarimetric sensitivity at the cost of
sacrificing spatial resolution. We find evidence for intrinsically
different fields in granules and lanes and characterize the average
properties of the weakest observable flux concentrations. The magnetic
signals observed suggest a strong coupling between magnetic fields
and convective flows. Upflows bring up weak fields (equipartition or
weaker) to the surface, with stronger upflows carrying larger amounts
of flux. The circular polarization profiles observed in the granular
regions display a very strongly asymmetric shape, which contrasts with
the less asymmetric profiles observed in the downflowing regions. At
downflowing locations with speeds of 0.5 km s-1, both
weak and strong fields can be found. However, when the downflow speed
increases (up to about 1 km s-1) both the mean flux and the
intrinsic field strength show a tendency to increase. The asymmetry
of the circular polarization profiles also shows a clear trend as
a function of magnetic flux density. Low-flux regions display the
negative area asymmetry one naturally expects for field strengths
decreasing with height embedded in a downflowing environment. As we
move to stronger flux density locations, the well-known positive
area asymmetry develops and reaches even higher values than those
typically found in network regions. These results may have important
implications for our understanding of the coupling between magnetic
fields and convective processes that pervade the solar photosphere.

---------------------------------------------------------
Title: On the Diagnostic Potential of Hα for Chromospheric Magnetism
Authors: Socas-Navarro, H.; Uitenbroek, H.
2004ApJ...603L.129S Altcode:
We investigate the feasibility of measuring line-of-sight magnetic
field strength in the solar chromosphere through Stokes polarimetry in
the hydrogen Hα line. Because of the large intrinsic Doppler width
of the hydrogen line, the weak-field approximation applies even for
the strongest magnetic fields in the solar atmosphere. We calculate
the Hα response functions of Stokes I and V to perturbations in the
magnetic field and temperature in two different one-dimensional solar
models representing the average quiet Sun and a sunspot umbra. These
response functions show that the Hα line exhibits large photospheric
sensitivities in these solar models in addition to its chromospheric
sensitivity. One particularly striking example is the Stokes V response
in the quiet Sun, which is mostly photospheric when the field decreases
with height.

---------------------------------------------------------
Title: Magnetic Fields in the Quiet Sun: Observational Discrepancies
and Unresolved Structure
Authors: Socas-Navarro, H.; Sánchez Almeida, J.
2003ApJ...593..581S Altcode:
Observations of magnetically sensitive lines in the visible and the
infrared yield apparently contradictory values for the intrinsic
field strength in the internetwork quiet Sun. It is shown that this
discrepancy can be understood if one assumes that the magnetic field
is not homogeneous over the resolution element. The difference between
visible and infrared measurements may be used to set constrains on
the subpixel distribution of field strengths. We suggest a specific
probability density function that seems to satisfy the existing
observational constraints.

---------------------------------------------------------
Title: Measuring Solar Magnetic Fields with Artificial Neural Networks
Authors: Socas-Navarro, H.
2003NN.....16..355S Altcode:
The quantification of the solar magnetic field is a crucial step
in modern solar physics to understand the dynamics, activity and
variability of our star. Presently, a reliable inference of these
fields is only possible by means of a computer-intensive process that
has so far limited scientists to the analysis of observations from
small regions of the solar disk, and/or very crude spatial and temporal
resolution. This work presents a different approach to the problem, in
which a multilayer perceptron, trained with known synthetic profiles,
is able to recognize the profiles and return the magnetic field used to
synthesize them. The network is then confronted with real observations
of a sunspot which had been previously inverted using traditional
inversion techniques. A quantitative comparison between these two
procedures shows the reliability of the network when applied to points
having magnetic filling factors larger than approximately 70%. The
dramatic decrease in the re! quired computing time presents an
opportunity for the routine analysis of large-scale, high-resolution
solar observations.

---------------------------------------------------------
Title: Small-scale Magnetic Fields in the Quiet Sun
Authors: Socas-Navarro, H.
2003ASPC..307..330S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager (HMI) on SDO: Full Vector
Magnetography with a Filtergraph Polarimeter
Authors: Graham, J. D.; Norton, A.; López Ariste, A.; Lites, B.;
Socas-Navarro, H.; Tomczyk, S.
2003ASPC..307..131G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Fine Structure of Sunspot Umbrae (Invited review)
Authors: Socas-Navarro, H.
2003ASPC..286..267S Altcode: 2003ctmf.conf..267S
No abstract at ADS

---------------------------------------------------------
Title: Zeeman diagnostics of solar magnetic fields
Authors: Socas-Navarro, Hector
2002ESASP.505...45S Altcode: 2002solm.conf...45S; 2002IAUCo.188...45S
The next generation of space- and ground-based spectropolarimeters
demands new diagnostic tools capable of fast (ideally real-time)
and reliable interpretation of the Stokes data. This paper presents a
critical review of the various techniques that can be used for Solar
magnetometry, from traditional approaches, such as the magnetograph
formula, to very recent developments using artificial neural networks.

---------------------------------------------------------
Title: Inference of Solar Magnetic Field Parameters from Data with
Limited Wavelength Sampling
Authors: Graham, Jonathan D.; López Ariste, Arturo; Socas-Navarro,
Hector; Tomczyk, Steven
2002SoPh..208..211G Altcode:
We investigate the diagnostic potential of polarimetric measurements
with filtergraph instruments. Numerical simulations are used to explore
the possibility of inferring the magnetic field vector, its filling
factor, and the thermodynamics of model atmospheres when only a few
wavelength measurements are available. These simulations assume the
magnetic Sun to be represented by Milne-Eddington atmospheres. The
results indicate that two wavelength measurements are insufficient
to reliably determine the magnetic parameters, regardless of whether
magnetograph techniques or least-squares fitting inversions are
used. However, as few as four measurements analyzed with the inversion
technique provide enough information to retrieve the intrinsic magnetic
field with an accuracy better than 10% in most cases.

---------------------------------------------------------
Title: Converging Flows in the Penumbra of a δ Sunspot
Authors: Lites, B. W.; Socas-Navarro, H.; Skumanich, A.; Shimizu, T.
2002ApJ...575.1131L Altcode:
Doppler velocities in the penumbra of a δ-configuration sunspot
observed near the limb indicate flows that converge upon the
line separating locally positive and negative polarity magnetic
field (the polarity inversion line). These flows persist for many
hours. Observations of this region with the Advanced Stokes Polarimeter
(ASP) reveal a convex vector field geometry with magnetic lines of
force arching upward from positive polarity, then downward to negative
polarity. The straightforward interpretation of the combined Doppler
velocity and vector field information leads to an untenable physical
situation: were flows directed from both footpoints toward the tops
of arched magnetic lines of force, mass would rapidly load the tops of
the arches. However, there is no observational evidence of the dynamics
that such a loading would require. To better understand this apparent
contradiction, we perform two-component analyses of the observed Stokes
spectral profiles in the vicinity of the polarity inversion line, in
order to extract information about unresolved structure of the magnetic
field and its associated flows. Fits to the observed profiles, obtained
by use of two different inversion techniques, suggest strongly that, as
in penumbrae of simple sunspots, the field geometry in the convergence
zone is “fluted.” However, unlike in simple sunspots, which have only
an outward-directed Evershed flow in the more horizontal of the field
components, at each spatial point our analysis reveals flows in the two
components that are oppositely directed. We interpret these observations
as indicative of an interleaved system of field lines in the vicinity
of the polarity reversal, whereby the convergent streams are able to
slip past one another and return downward into the solar interior.

---------------------------------------------------------
Title: The Solar Internetowrk Magnetic Fields
Authors: Socas-Navarro, H.; Lites, B. W.
2002AAS...200.5516S Altcode: 2002BAAS...34R.950S
The properties of solar photospheric inter-network fields are studied
using observations from the Advanced Stokes Polarimeter. By averaging
over large areas of the observed map we are able to bring down the
noise level to approximately 10-5 and determine typical
magnetic properties of granules and intergranular lanes outside the
magnetic network.

---------------------------------------------------------
Title: Inference of Solar Vector Magnetic Fields with Filtergraph
Instruments
Authors: Graham, J. D.; Lites, B. W.; López Ariste, A.; Norton, A.;
Socas-Navarro, H.; Tomczyk, S.
2002AAS...200.5611G Altcode: 2002BAAS...34..736G
We investigate the diagnostic potential of polarimetric measurements
with filtergraph instruments. Numerical simulations are used to
explore the possibility of inferring the magnetic field vector, its
filling factor, and the thermodynamics of model atmospheres when
only a few wavelength measurements are available. The simulations
assume the magnetic sun to be represented by Milne-Eddington (ME)
atmospheres. The results indicate that two wavelength measurements
are insufficient to reliably determine the magnetic parameters,
regardless of whether magnetograph techniques or least-squares fitting
inversions are used. However, as few as four measurements analyzed
with the inversion technique provide enough information to retrieve the
intrinsic magnetic field with an accuracy better than 10 generated by
more general models and ASP data passed through a simulated filtergraph.

---------------------------------------------------------
Title: Magnetic Properties of Photospheric Regions with Very Low
Magnetic Flux
Authors: Socas-Navarro, H.; Sánchez Almeida, J.
2002ApJ...565.1323S Altcode: 2001astro.ph.10025S
The magnetic properties of the quiet Sun are investigated using a novel
inversion code, FATIMA, based on the Principal Component Analysis of
the observed Stokes profiles. The stability and relatively low noise
sensitivity of this inversion procedure allows for the systematic
inversion of large data sets with a very weak polarization signal. Its
application to quiet-Sun observations of network and internetwork
regions reveals that a significant fraction of the quiet-Sun contains
kilogauss fields (usually with very small filling factors) and confirms
that the pixels with weak polarization account for most of the magnetic
flux. Mixed polarities in the resolution element are also found to
occur more likely as the polarization weakens.

---------------------------------------------------------
Title: Pattern recognition techniques and the measurement of solar
magnetic fields
Authors: Lopez Ariste, Arturo; Rees, David E.; Socas-Navarro, Hector;
Lites, Bruce W.
2001SPIE.4477...96L Altcode:
Measuring vector magnetic fields in the solar atmosphere using the
profiles of the Stokes parameters of polarized spectral lines split
by the Zeeman effect is known as Stokes Inversion. This inverse
problem is usually solved by least-squares fitting of the Stokes
profiles. However least-squares inversion is too slow for the new
generation of solar instruments (THEMIS, SOLIS, Solar-B, ...) which will
produce an ever-growing flood of spectral data. The solar community
urgently requires a new approach capable of handling this information
explosion, preferably in real-time. We have successfully applied pattern
recognition and machine learning techniques to tackle this problem. For
example, we have developed PCA-inversion, a database search technique
based on Principal Component Analysis of the Stokes profiles. Search is
fast because it is carried out in low dimensional PCA feature space,
rather than the high dimensional space of the spectral signals. Such
a data compression approach has been widely used for search and
retrieval in many areas of data mining. PCA-inversion is the basis of
a new inversion code called FATIMA (Fast Analysis Technique for the
Inversion of Magnetic Atmospheres). Tests on data from HAO's Advanced
Stokes Polarimeter show that FATIMA isover two orders of magnitude
faster than least squares inversion. Initial tests on an alternative
code (DIANNE - Direct Inversion based on Artificial Neural NEtworks)
show great promise of achieving real-time performance. In this paper
we present the latest achievements of FATIMA and DIANNE, two powerful
examples of how pattern recognition techniques can revolutionize data
analysis in astronomy.

---------------------------------------------------------
Title: Fast Inversion of Spectral Lines Using Principal Components
Analysis. II. Inversion of Real Stokes Data
Authors: Socas-Navarro, H.; López Ariste, A.; Lites, B. W.
2001ApJ...553..949S Altcode:
The principal components analysis (PCA) technique is used to develop
an extremely fast and stable Stokes inversion code, suitable for
application to large data sets from instruments that operate under
standard conditions. This paper provides some tips on reducing the
dimensionality of the problem, which are then used to develop a
practical implementation of PCA for the automatic analysis of Stokes
profiles. The resulting code is tested using real spectropolarimetric
observations of the pair of Fe I lines at 6302 Å at a sunspot.

---------------------------------------------------------
Title: Observation of Linear Polarization in the Infrared Ca II
Triplet Lines during Umbral Flashes
Authors: López Ariste, A.; Socas-Navarro, H.; Molodij, G.
2001ApJ...552..871L Altcode:
We report on Télescope Héliographique pour l'Etude du Magnétisme et
des Instabilités Solaires (THEMIS)2 observations of linear polarization
events associated with umbral flashes observed in the Ca II infrared
(IR) triplet lines. The observed signals are usually delayed in time
and shifted in space when compared to the intensity and circular
polarization signals from the flash. The observations are compatible
with a scenario whereby flashes are produced by a perturbation
propagating along the magnetic field lines as they bend out toward
the penumbra. Only a fraction of the resolution element appears to
be emitting flashlike profiles, as if the waves were propagating only
within localized magnetic field lines. This localization, however, does
not impede the apparent propagation of the perturbation horizontally
within the umbra.

---------------------------------------------------------
Title: A Time-dependent Semiempirical Model of the Chromospheric
Umbral Oscillation
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
2001ApJ...550.1102S Altcode:
We present a time-dependent semiempirical model of the chromospheric
umbral oscillation in sunspots. This model has been obtained by
applying recently developed non-LTE inversion techniques to a time
series of spectropolarimetric observations. The model consists of
two optically thick unresolved atmospheric components: a “quiet”
component with downward velocities that covers most of the resolution
element and an “active” component with upward velocities as high as 10
km s-1 that covers a smaller filling factor and has a higher
temperature at the same chromospheric optical depth. This semiempirical
model accounts for all the observational signatures of the chromospheric
oscillation when the filling factor of the active component oscillates
between a few percent and 20% of the resolution element. We discuss
a plausible physical scenario in which upward-propagating waves in
a downflowing magnetized environment lead to periodic mass ejections
from the atmospheric layers where the waves become nonlinear. Based
on observations obtained with the Gregory Coudé Telescope, operated
on the island of Tenerife by the Observatory of Göttingen University
in the Spanish Observatorio del Teide of the Instituto de Astrofísica
de Canarias.

---------------------------------------------------------
Title: Converging Flows in the Penumbra of a δ-Sunspot
Authors: Lites, B. W.; Socas-Navarro, H.; Skumanich, A.; Shimizu, T.
2001ASPC..248..143L Altcode: 2001mfah.conf..143L
No abstract at ADS

---------------------------------------------------------
Title: Convergent Flows in the Penumbra of a δ-Sunspot
Authors: Lites, B. W.; Socas-Navarro, H.
2001ASPC..236..329L Altcode: 2001aspt.conf..329L
No abstract at ADS

---------------------------------------------------------
Title: Stokes Inversion Techniques: Recent Achievements and Future
Horizons
Authors: Socas-Navarro, H.
2001ASPC..236..487S Altcode: 2001aspt.conf..487S
No abstract at ADS

---------------------------------------------------------
Title: Non-LTE inversion of spectral lines and Stokes profiles
(Invited Review)
Authors: Socas-Navarro, H.
2001hsa..conf..233S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Anomalous Circular Polarization Profiles in Sunspot
Chromospheres
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
2000ApJ...544.1141S Altcode:
This paper presents a detailed description, analysis, and
interpretation of the spectropolarimetric observations recently
reported by Socas-Navarro, Trujillo Bueno, &amp; Ruiz Cobo. These
observations consist of time series of Stokes I and V profiles above a
sunspot umbra. The spectral lines observed simultaneously are the Ca II
chromospheric lines at 8498 and 8542 Å and the photospheric Fe I line
at 8497 Å. These spectropolarimetric observations unveil an intriguing
time-dependent behavior of the Stokes V profiles in the chromospheric
lines. This behavior should be considered as an observational reference
for future radiation magnetohydrodynamic simulations of sunspot
chromospheres. The analysis of the observed time series shows that a
“normal,” nearly antisymmetric V profile rapidly evolves toward an
“anomalous,” completely asymmetric profile, returning later to the
normal state. The occurrence of such anomalous circular polarization
profiles repeats itself with a periodicity of ~150 s. After giving
arguments to discard other scenarios, we are able to interpret the
anomalous V profiles as a consequence of the development of a second
unresolved atmospheric component. This unresolved component seems to be
the same that produces the umbral flashes observed in other sunspots,
where it is present with a larger filling factor. Based on observations
obtained with the Gregory Coudé Telescope, operated on the island of
Tenerife by the Observatory of Göttingen University, in the Spanish
Observatorio del Teide of the Instituto de Astrofísica de Canarias.

---------------------------------------------------------
Title: Untangling Sunspot Penumbrae: New Stokes Profile Analyses
Authors: Leka, K. D.; Socas-Navarro, H.
2000SPD....31.0119L Altcode: 2000BAAS...32..804L
We present preliminary analyses of Stokes [I, Q, U, V] spectra of a
sunspot penumbra using two different analysis/inversion procedures. It
has long been known that the Stokes spectra from sunspot penumbrae, even
at disk center, commonly show multiple lobes and asymmetries. Hence,
the magnetic/thermodynamic maps obtained from Stokes spectra using
Milne-Eddington approaches are good first approximations, but will not
uncover any further details of penumbral physics. Penumbrae are known to
be very structured, hence we first present the results of an inversion
using a recent augmentation to the HAO inversion routine: the ability to
model the observed spectra using two magnetic atmospheres in addition
to the non-magnetic atmosphere. Such a 'three-component' approach is
useful to interpret unresolved structures which contribute to signals
within the resolution elements. Second, we present the results of
an inversion using the new "LILIA" code, currently under development
at HAO. LILIA is the "community Stokes inversion code" component of
the Solar Magnetism Initiative (SMI), and is based on the strategy of
Ruiz Cobo and del Toro Iniesta (1992, ApJ, 398, 375). We describe the
strengths and limitations of the two approaches, with attention to
their application for the community at large to interpret data from
both current and future ground-based and space-based instruments.

---------------------------------------------------------
Title: Anomalous Polarization Profiles in Sunspots: Possible Origin
of Umbral Flashes
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
2000Sci...288.1396S Altcode: 2000Sci...288.1398S
We present time-series spectropolarimetric observations of sunspots
in the Ca II infrared triplet lines, which show a periodic occurrence
of anomalous, asymmetric, circular polarization profiles in the umbral
chromosphere. The profiles may be caused by the periodic development of
an unresolved atmospheric component in a downward flowing magnetized
environment. This active component with upward directed velocities
as high as 10 kilometers per second is connected to the umbral flash
(UF) phenomenon. We can explain the observations with a semiempirical
model of the chromospheric oscillation and of the sunspot magnetized
atmospheric plasma during a UF event.

---------------------------------------------------------
Title: Non-LTE Inversion of Stokes Profiles Induced by the Zeeman
Effect
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
2000ApJ...530..977S Altcode:
This paper presents a new diagnostic tool for the inference of the
thermal, dynamic, and magnetic properties of the solar chromosphere. It
consists of a non-LTE inversion code of Stokes profiles induced by
the Zeeman effect in magnetized stellar atmospheres. This code is the
generalization, to the non-LTE Stokes transfer case, of the inversion
code for unpolarized line profiles of Socas-Navarro, Ruiz Cobo, &amp;
Trujillo Bueno. It is based upon a full non-LTE multilevel treatment
of Zeeman line transfer in which the thermal, magnetic, and dynamic
properties of the atmospheric model are adjusted automatically by
means of nonlinear least-squares-fitting techniques until a best fit
to the observed Stokes profiles is obtained. Our non-LTE inversion
approach is based on the concept of response functions, which measure
the emergent Stokes profiles' first-order reaction to changes in the
atmospheric parameters. We generalize our fixed departure coefficients
(FDC) approximation in order to allow fast computation of such response
functions in the present non-LTE Zeeman line transfer context. We
present several numerical tests showing the reliability of our inversion
method for retrieving the information about the thermodynamics and
the magnetic field vector that is contained in the polarization
state of the chosen spectral lines. We also explore the limitations
of the inversion code by applying it to simulated observations where
the physical hypotheses on which it is based on are not met. Finally,
we apply our non-LTE Stokes inversion code to real spectropolarimetric
observations of a sunspot observed in the IR triplet lines of Ca II. As
a result, a new mean model of the sunspot chromosphere is provided.

---------------------------------------------------------
Title: Calculations of Self-Absorption Curves of Metallic Emission
Lines in Emission Line Stars
Authors: Socas-Navarro, H.; Israelian, G.; Friedjung, M.
2000ASPC..204..241S Altcode: 2000tiaf.conf..241S
No abstract at ADS

---------------------------------------------------------
Title: A new diagnostic tool for the solar chromosphere
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
1999ASSL..243..263S Altcode: 1999sopo.conf..263S
No abstract at ADS

---------------------------------------------------------
Title: NLTE Inversion of Spectral Lines and Stokes Profiles
Authors: Socas-Navarro, H.
1999PhDT.......278S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Non-LTE inversion of spectral lines and Stokes profiles
Authors: Socas Navarro, Héctor
1999PhDT.......540S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Non-LTE Inversion of Line Profiles
Authors: Socas-Navarro, H.; Ruiz Cobo, B.; Trujillo Bueno, J.
1998ApJ...507..470S Altcode:
In this paper we address the problem of the non-LTE (NLTE) inversion
of line profiles by means of a nonlinear least-squares minimization
procedure combined with very efficient multilevel transfer methods. Our
approach is based on the concept of response functions, which measure
the first-order response of the emergent profiles to changes in the
atmospheric conditions. We introduce the fixed departure coefficients
(FDC) approximation in order to compute these response functions in
a fast and straightforward manner. The accuracy of this approximation
is checked comparing FDC response functions with those obtained from
full NLTE computations. An NLTE inversion code based on these response
functions has been developed and extensively tested. Reference synthetic
profiles, similar to those expected from real observations, are given
as input to the inversion algorithm and the recovered models are shown
to be compatible with the reference models within the error bars. Our
NLTE inversion code thus provides a new tool for the investigation of
the chromospheres of the Sun and other stars.

---------------------------------------------------------
Title: Linearization versus Preconditioning: Which Approach Is Best
for Solving Multilevel Transfer Problems?
Authors: Socas-Navarro, H.; Trujillo Bueno, J.
1997ApJ...490..383S Altcode:
We present a critical analysis of linearization and preconditioning, the
two most used approaches proposed for achieving the required linearity
in the iterative solution of the multilevel transfer problem. By
distinguishing from the outset between the response of the radiation
field to the source function and opacity perturbations, we are able
to demonstrate that if the linearization strategy, on which the local
approximate Λ-operator option of the multilevel transfer code MULTI
is based, is applied neglecting the terms coming from the response of
the radiation field to the opacity perturbations, one then recovers the
same equations obtained using the preconditioning technique of Rybicki
&amp; Hummer. It is also shown that if this preconditioning technique
is applied taking into account the response of the radiation field
to both the source function and opacity variations, one then ends up
with the same equations found via the linearization method. Thus these
two approaches to the numerical solution of the multilevel transfer
problem turn out to be essentially the same, because similar equations
are obtained if the same information is taken into account. Finally,
it is pointed out that, if one wishes to guarantee positivity for
the atomic level populations, it is necessary to neglect the terms
associated with the response of the radiation field to the opacity
perturbations. Neglecting such terms does not deteriorate the
convergence rate of multilevel transfer methods that make use of a
local approximate operator.

---------------------------------------------------------
Title: Are NLTE effects important for the inversion of iron lines?
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.;
Shchukina, N. G.
1997joso.proc...86S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Star Formation in Normal and Barred Cluster Spirals
Authors: Moss, C.; Whittle, M.; Pesce, J. E.; Socas-Navarro, H.
1995ApL&C..31..215M Altcode: 1995astro.ph..3084M; 1995ApL....31..215M
An objective prism H alpha survey has shown that there is a population
of early type spiral galaxies in nearby clusters with strong central
bursts of star formation which could be due to galaxy--galaxy tidal
interactions. Such galaxies are rarely found in the field.