Author name code: martinez-pillet
ADS astronomy entries on 2022-09-14
author:"Martinez Pillet, Valentin"
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Title: A Compact Full-disk Solar Magnetograph based on miniaturization
of GONG instrument
Authors: Gosain, Sanjay; Harvey, Jack; Martinez-Pillet, Valentin;
Woods, Tom; Hill, Frank
Bibcode: 2022arXiv220707728G
Altcode:
Designing compact instruments is the key for the scientific exploration
by smaller spacecrafts such as cubesats or by deep space missions. Such
missions require compact instrument designs to have minimal instrument
mass. Here we present a proof of concept for miniaturization of the
Global Oscillation Network Group GONG instrument. GONG instrument
routinely obtains solar full disk Doppler and magnetic field maps of
the solar photosphere using Ni 676 nm absorption line. A key concept
for miniaturization of GONG optical design is to replace the bulky
Lyot filter with a narrow-band interference filter and reduce the
length of feed telescope. We present validation of the concept via
numerical modeling as well as by proof of concept observations.
Title: Observational Approach to Computing the Poynting Flux in the
Quiet Sun Photosphere
Authors: Tilipman, Dennis; Martínez Pillet, Valentin; Tremblay,
Benoit; Kazachenko, Maria; Milic, Ivan; Yadav, Rahul
Bibcode: 2022cosp...44.2516T
Altcode:
Understanding magnetically-driven processes in the quiet Sun is
crucial for understanding chromospheric and coronal heating. The main
goal of our study is to quantify the energy output of the quiet Sun
photosphere. The amount of magnetic energy being transported upwards
from the photosphere can be expressed in terms of the vertical component
of Poynting flux, which is a cross-product of magnetic and electric
fields. While magnetic fields and energy fluxes within active regions
and plage have been evaluated before, quiet Sun magnetograms have only
recently become available with the launch of missions such as Hinode
and Sunrise and the Daniel K. Inouye Solar Telescope (DKIST) coming
online early this year. In this presentation, we present estimates
of Poynting flux using IMaX data. As the electric field E is one
of the two principal quantities required to compute Poynting flux,
we use two distinct approaches to infer E. In the first approach, we
derive the electric field using ideal plasma assumption with horizontal
velocities obtained from the convolutional neural network (DeepVel,
Asensio Ramos et al. 2017). In the second approach, we derive E using
the PDFI-SS approach uncurling Faraday's law (Fisher et al. 2020). We
discuss the distribution of Poynting flux and whether it is sufficient
to explain chromospheric and coronal heating.
Title: Searching for a Solar Source of Magnetic-Field Switchbacks
in Parker Solar Probe's First Encounter
Authors: de Pablos, D.; Samanta, T.; Badman, S. T.; Schwanitz, C.;
Bahauddin, S. M.; Harra, L. K.; Petrie, G.; Mac Cormack, C.; Mandrini,
C. H.; Raouafi, N. E.; Martinez Pillet, V.; Velli, M.
Bibcode: 2022SoPh..297...90D
Altcode:
Parker Solar Probe observations show ubiquitous magnetic-field reversals
closer to the Sun, often referred to as "switchbacks". The switchbacks
have been observed before in the solar wind near 1 AU and beyond, but
their occurrence was historically rare. PSP measurements below ∼ 0.2
AU show that switchbacks are, however, the most prominent structures
in the "young" solar wind. In this work, we analyze remote-sensing
observations of a small equatorial coronal hole to which PSP was
connected during the perihelion of Encounter 1. We investigate whether
some of the switchbacks captured during the encounter were of coronal
origin by correlating common switchback in situ signatures with remote
observations of their expected coronal footpoint. We find strong
evidence that timescales present in the corona are relevant to the
outflowing, switchback-filled solar wind, as illustrated by strong
linear correlation. We also determine that spatial analysis of the
observed region is optimal, as the implied average solar-wind speed
more closely matches that observed by PSP at the time. We observe that
hemispherical structures are strongly correlated with the radial proton
velocity and the mass flux in the solar wind. The above findings suggest
that a subpopulation of the switchbacks are seeded at the corona and
travel into interplanetary space.
Title: The early spectropolarimetric inversions
Authors: Martinez Pillet, V.
Bibcode: 2022fysr.confE..51M
Altcode:
In the late 80's A. Skumanich played a leading role in advancing our
understanding of radiative transfer processes in stellar atmospheres
in the presence of a magnetic field. Of his multiple contributions,
developing robust inferences of the vector magnetic field estimates
on the sun from spectropolarimetric observations were particularly
important. It demonstrated how consistent and reliable vector magnetic
field estimates could be obtained limited only by noise in the
data. Andy's links with the international community that develop the
theory of polarized radiative transfer were vital. In the early 90's,
the Advanced Stokes Polarimeter (ASP) demonstrated from a practical
standpoint the relevance of the theoretical developments in which Andy
participated. The ASP convinced the solar community that reliable
vector magnetic field measurements are possible. This significant
achievement paved the way for proposing a facility equipped with four
spectro-polarimeters —the Daniel K Inouye Solar Telescope— to
the community.
Title: Velocities of an Erupting Filament
Authors: Wang, Shuo; Jenkins, Jack M.; Muglach, Karin; Martinez Pillet,
Valentin; Beck, Christian; Long, David M.; Choudhary, Debi Prasad;
McAteer, James
Bibcode: 2022ApJ...926...18W
Altcode: 2021arXiv211107830W
Solar filaments exist as stable structures for extended periods of
time before many of them form the core of a coronal mass ejection
(CME). We examine the properties of an erupting filament on 2017 May
29-30 with high-resolution He I 10830 Å and Hα spectra from the
Dunn Solar Telescope, full-disk Dopplergrams of He I 10830 Å from
the Chromospheric Telescope, and EUV and coronograph data from SDO
and STEREO. Pre-eruption line-of-sight velocities from an inversion
of He I with the HAZEL code exhibit coherent patches of 5 Mm extent
that indicate counter-streaming and/or buoyant behavior. During the
eruption, individual, aligned threads appear in the He I velocity
maps. The distribution of velocities evolves from Gaussian to strongly
asymmetric. The maximal optical depth of He I 10830 Å decreased from
τ = 1.75 to 0.25, the temperature increased by 13 kK, and the average
speed and width of the filament increased from 0 to 25 km s-1
and 10 to 20 Mm, respectively. All data sources agree that the filament
rose with an exponential acceleration reaching 7.4 m s-2
that increased to a final velocity of 430 km s-1 at 22:24
UT; a CME was associated with this filament eruption. The properties
during the eruption favor a kink/torus instability, which requires
the existence of a flux rope. We conclude that full-disk chromospheric
Dopplergrams can be used to trace the initial phase of on-disk filament
eruptions in real time, which might potentially be useful for modeling
the source of any subsequent CMEs.
Title: An Alternative Approach to Measuring Solar Velocities on the
Solar Dynamics Observatory (SDO) Using the Helioseismic and Magnetic
Imager (HMI)
Authors: Cavin, Brittany; Martinez-Pillet, Valentin
Bibcode: 2021AGUFMSH55D1864C
Altcode:
Aboard the Solar Dynamics Observatory (SDO), the Helioseismic and
Magnetic Imager (HMI) measures the velocity of the Sun's magnetic
fields. However, there is a calibration issue causing an artificial
24h periodicity. The SDO spacecraft's velocity leaks into the solar
velocities data. The spacecraft's velocity is much greater than the
solar velocities and causes inaccurate data. I compared the current
HMI Method results with a Gaussian Fit Method, that could help bypass
the calibration error and avoid the leak of spacecraft velocity
on the solar data. By plotting the Sun's spectra at six different
wavelengths, I could use a Gaussian fit to calculate the center at
each pixel. After noticing trends in the two methods, we show that
the Gaussian Method does not display a 24h leakage. However, it can be
sensitive at identifying the velocities at Sunspot locations, varying
only slightly from the original HMI data. We demonstrate that the main
difference between the gaussian and the HMI methods is the use of the
calibration provided by the sensitivity curves.
Title: Quantifying Magnetic Energy Flux in the Quiet Sun Photosphere
using Sunrise/IMaX Observations
Authors: Tilipman, Dennis; Kazachenko, Maria; Tremblay, Benoit;
Martinez-Pillet, Valentin; Milic, Ivan
Bibcode: 2021AGUFMSH42B..04T
Altcode:
Understanding magnetically-driven processes in the quiet Sun is
crucial for understanding chromospheric and coronal heating. The main
goal of our study is to quantify the energy output of the quiet Sun
photosphere. The amount of magnetic energy can be expressed in terms of
the Poynting flux, which is a cross-product of magnetic and electric
fields. Poynting flux has been computed for active regions and plage,
but the weakness of polarimetric signal in the quiet Sun presents
a bigger challenge. Quiet Sun magnetic fields have only recently
become observable with the launch of missions such as Hinode and
Sunrise. The Daniel K. Inouye Solar Telescope (DKIST) is expected to
further improve the quality of these observations -- both spatial and
temporal resolutions, as well as polarimetric signal, are expected to
improve significantly, allowing us to perform reliable inversions of
magnetic, electric, and velocity fields, all of which are required
to compute the Poynting flux. We test different inversion methods
on Sunrise/IMaX data in order to streamline this process once DKIST
becomes operational and to understand the limitations of these inversion
techniques. In this work, we present our results obtained from velocity
and electric field inversions of photospheric images, magnetograms and
Doppler velocities from Sunrise/IMaX, the challenges associated with
these inversions, and implications for future DKIST observations. We
also discuss approaches to extend this analysis from photosphere to
overlying layers of the atmosphere, which would allow us to study how
these layers respond to magnetic energy injections from below.
Title: Diagnostic capabilities of spectropolarimetric observations for
understanding solar phenomena. I. Zeeman-sensitive photospheric lines
Authors: Quintero Noda, C.; Barklem, P. S.; Gafeira, R.; Ruiz Cobo,
B.; Collados, M.; Carlsson, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Uitenbroek, H.; Katsukawa, Y.
Bibcode: 2021A&A...652A.161Q
Altcode: 2021arXiv210605084Q
Future ground-based telescopes will expand our capabilities for
simultaneous multi-line polarimetric observations in a wide range of
wavelengths, from the near-ultraviolet to the near-infrared. This
creates a strong demand to compare candidate spectral lines to
establish a guideline of the lines that are most appropriate for each
observation target. We focused in this first work on Zeeman-sensitive
photospheric lines in the visible and infrared. We first examined their
polarisation signals and response functions using a 1D semi-empirical
atmosphere. Then we studied the spatial distribution of the line core
intensity and linear and circular polarisation signals using a realistic
3D numerical simulation. We ran inversions of synthetic profiles, and
we compared the heights at which we obtain a high correlation between
the input and the inferred atmosphere. We also used this opportunity
to revisit the atomic information we have on these lines and computed
the broadening cross-sections due to collisions with neutral hydrogen
atoms for all the studied spectral lines. The results reveal that
four spectral lines stand out from the rest for quiet-Sun and network
conditions: Fe I 5250.2, 6302, 8468, and 15 648 Å. The first three
form higher in the atmosphere, and the last line is mainly sensitive to
the atmospheric parameters at the bottom of the photosphere. However,
as they reach different heights, we strongly recommend using at least
one of the first three candidates together with the Fe I 15 648 Å line
to optimise our capabilities for inferring the thermal and magnetic
properties of the lower atmosphere.
Title: A journey of exploration to the polar regions of a star:
probing the solar poles and the heliosphere from high helio-latitude
Authors: Harra, Louise; Andretta, Vincenzo; Appourchaux, Thierry;
Baudin, Frédéric; Bellot-Rubio, Luis; Birch, Aaron C.; Boumier,
Patrick; Cameron, Robert H.; Carlsson, Matts; Corbard, Thierry;
Davies, Jackie; Fazakerley, Andrew; Fineschi, Silvano; Finsterle,
Wolfgang; Gizon, Laurent; Harrison, Richard; Hassler, Donald M.;
Leibacher, John; Liewer, Paulett; Macdonald, Malcolm; Maksimovic,
Milan; Murphy, Neil; Naletto, Giampiero; Nigro, Giuseppina; Owen,
Christopher; Martínez-Pillet, Valentín; Rochus, Pierre; Romoli,
Marco; Sekii, Takashi; Spadaro, Daniele; Veronig, Astrid; Schmutz, W.
Bibcode: 2021ExA...tmp...93H
Altcode: 2021arXiv210410876H
A mission to view the solar poles from high helio-latitudes (above 60°)
will build on the experience of Solar Orbiter as well as a long heritage
of successful solar missions and instrumentation (e.g. SOHO Domingo et
al. (Solar Phys. 162(1-2), 1-37 1995), STEREO Howard et al. (Space
Sci. Rev. 136(1-4), 67-115 2008), Hinode Kosugi et al. (Solar
Phys. 243(1), 3-17 2007), Pesnell et al. Solar Phys. 275(1-2),
3-15 2012), but will focus for the first time on the solar poles,
enabling scientific investigations that cannot be done by any other
mission. One of the major mysteries of the Sun is the solar cycle. The
activity cycle of the Sun drives the structure and behaviour of the
heliosphere and of course, the driver of space weather. In addition,
solar activity and variability provides fluctuating input into the
Earth climate models, and these same physical processes are applicable
to stellar systems hosting exoplanets. One of the main obstructions
to understanding the solar cycle, and hence all solar activity,
is our current lack of understanding of the polar regions. In this
White Paper, submitted to the European Space Agency in response to the
Voyage 2050 call, we describe a mission concept that aims to address
this fundamental issue. In parallel, we recognise that viewing the Sun
from above the polar regions enables further scientific advantages,
beyond those related to the solar cycle, such as unique and powerful
studies of coronal mass ejection processes, from a global perspective,
and studies of coronal structure and activity in polar regions. Not
only will these provide important scientific advances for fundamental
stellar physics research, they will feed into our understanding of
impacts on the Earth and other planets' space environment.
Title: Preparing for DKIST: Using SUNRISE/IMaX Magnetic Field and
Doppler Data to Estimate Velocity, Electric Fields and Energy Fluxes
in the Quiet Sun
Authors: Tilipman, D.; Kazachenko, M.; Tremblay, B.; Martinez
Pillet, V.
Bibcode: 2021AAS...23821306T
Altcode:
Understanding processes in the quiet Sun is crucial for understanding
the Sun in general. The overarching goal of our study is to quantify
the energy output of the quiet Sun, which can be expressed in terms
of the Poynting flux. To know this quantity, one needs to know the
vector magnetic and the electric fields. The latter can be obtained
using Maxwell's equations and the observed magnetic fields and
Doppler velocities. Quiet Sun magnetic fields have only recently
become observable with the launch of missions such as Hinode and
SUNRISE. The Daniel K. Inouye Solar Telescope (DKIST) is expected
to improve the quality of these observations even further. While
the SUNRISE/IMaX images have a resolution of 0.15 arcsec/pixel,
the DKIST ViSP instrument available in the first cycle will provide
magnetograms with a resolution of 0.05 arcsec/pixel. The cadence of
images provided by the VBI is 7 seconds compared to 12 seconds by
IMaX. The signal-to-noise ratio of Stokes vectors measurements is
likewise expected to improve. In this presentation, we present
our preliminary results obtained from velocity and electric field
inversions of photospheric images, magnetograms and Doppler velocities
from SUNRISE/IMaX, the challenges associated with these inversions,
and implications for DKIST observations. Specifically, we use Fourier
Local Correlation Tracking (FLCT) and machine-learning-based algorithm,
DeepVel, to obtain, respectively, optical flows and velocity fields,
and compare these with quantities derived using the PDFI electric-field
inversion method.
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
Bibcode: 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: A Journey of Exploration to the Polar Regions of a Star:
Probing the Solar Poles and the Heliosphere from High Helio-Latitude
Authors: Finsterle, W.; Harra, L.; Andretta, V.; Appourchaux, T.;
Baudin, F.; Bellot Rubio, L.; Birch, A.; Boumier, P.; Cameron, R. H.;
Carlsson, M.; Corbard, T.; Davies, J. A.; Fazakerley, A. N.; Fineschi,
S.; Gizon, L. C.; Harrison, R. A.; Hassler, D.; Leibacher, J. W.;
Liewer, P. C.; Macdonald, M.; Maksimovic, M.; Murphy, N.; Naletto, G.;
Nigro, G.; Owen, C. J.; Martinez-Pillet, V.; Rochus, P. L.; Romoli,
M.; Sekii, T.; Spadaro, D.; Veronig, A.
Bibcode: 2020AGUFMSH0110005F
Altcode:
A mission to view the solar poles from high helio-latitudes (above
60°) will build on the experience of Solar Orbiter as well as a long
heritage of successful solar missions and instrumentation (e.g. SOHO,
STEREO, Hinode, SDO), but will focus for the first time on the solar
poles, enabling scientific investigations that cannot be done by
any other mission. One of the major mysteries of the Sun is the solar
cycle. The activity cycle of the Sun drives the structure and behaviour
of the heliosphere and is, of course, the driver of space weather. In
addition, solar activity and variability provides fluctuating input
into the Earth climate models, and these same physical processes
are applicable to stellar systems hosting exoplanets. One of the
main obstructions to understanding the solar cycle, and hence all
solar activity, is our current lack of understanding of the polar
regions. We describe a mission concept that aims to address this
fundamental issue. In parallel, we recognise that viewing the Sun
from above the polar regions enables further scientific advantages,
beyond those related to the solar cycle, such as unique and powerful
studies of coronal mass ejection processes, from a global perspective,
and studies of coronal structure and activity in polar regions. Not
only will these provide important scientific advances for fundamental
stellar physics research, they will feed into our understanding of
impacts on the Earth and other planets' space environment.
Title: Power spectrum of turbulent convection in the solar photosphere
Authors: Yelles Chaouche, L.; Cameron, R. H.; Solanki, S. K.;
Riethmüller, T. L.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.;
Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort,
M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2020A&A...644A..44Y
Altcode: 2020arXiv201009037Y
The solar photosphere provides us with a laboratory for understanding
turbulence in a layer where the fundamental processes of transport
vary rapidly and a strongly superadiabatic region lies very closely
to a subadiabatic layer. Our tools for probing the turbulence are
high-resolution spectropolarimetric observations such as have recently
been obtained with the two balloon-borne SUNRISE missions, and numerical
simulations. Our aim is to study photospheric turbulence with the
help of Fourier power spectra that we compute from observations
and simulations. We also attempt to explain some properties of the
photospheric overshooting flow with the help of its governing equations
and simulations. We find that quiet-Sun observations and smeared
simulations are consistent with each other and exhibit a power-law
behavior in the subgranular range of their Doppler velocity power
spectra with a power-law index of ≈ - 2. The unsmeared simulations
exhibit a power law that extends over the full range between the
integral and Taylor scales with a power-law index of ≈ - 2.25. The
smearing, reminiscent of observational conditions, considerably reduces
the extent of the power-law-like portion of the power spectra. This
suggests that the limited spatial resolution in some observations
might eventually result in larger uncertainties in the estimation of
the power-law indices. The simulated vertical velocity power spectra
as a function of height show a rapid change in the power-law index
(at the subgranular range) from roughly the optical depth unity layer,
that is, the solar surface, to 300 km above it. We propose that the
cause of the steepening of the power-law index is the transition from
a super- to a subadiabatic region, in which the dominant source of
motions is overshooting convection. A scale-dependent transport of
the vertical momentum occurs. At smaller scales, the vertical momentum
is more efficiently transported sideways than at larger scales. This
results in less vertical velocity power transported upward at small
scales than at larger scales and produces a progressively steeper
vertical velocity power law below 180 km. Above this height, the
gravity work progressively gains importance at all relevant scales,
making the atmosphere progressively more hydrostatic and resulting
in a gradually less steep power law. Radiative heating and cooling of
the plasma is shown to play a dominant role in the plasma energetics
in this region, which is important in terms of nonadiabatic damping
of the convective motions.
Title: Challenges and Advances in Modeling of the Solar Atmosphere:
A White Paper of Findings and Recommendations
Authors: Criscuoli, Serena; Kazachenko, Maria; Kitashvili, Irina;
Kosovichev, Alexander; Martínez Pillet, Valentín; Nita, Gelu;
Sadykov, Viacheslav; Wray, Alan
Bibcode: 2021arXiv210100011C
Altcode:
The next decade will be an exciting period for solar astrophysics, as
new ground- and space-based instrumentation will provide unprecedented
observations of the solar atmosphere and heliosphere. The synergy
between modeling effort and comprehensive analysis of observations
is crucial for the understanding of the physical processes behind
the observed phenomena. However, the unprecedented wealth of data on
one hand, and the complexity of the physical phenomena on the other,
require the development of new approaches in both data analysis and
numerical modeling. In this white paper, we summarize recent numerical
achievements to reproduce structure, dynamics, and observed phenomena
from the photosphere to the low corona and outline challenges we expect
to face for the interpretation of future observations.
Title: Coordination within the remote sensing payload on the Solar
Orbiter mission
Authors: Auchère, F.; Andretta, V.; Antonucci, E.; Bach, N.;
Battaglia, M.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Caminade,
S.; Carlsson, M.; Carlyle, J.; Cerullo, J. J.; Chamberlin, P. C.;
Colaninno, R. C.; Davila, J. M.; De Groof, A.; Etesi, L.; Fahmy,
S.; Fineschi, S.; Fludra, A.; Gilbert, H. R.; Giunta, A.; Grundy,
T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.;
Howard, R. A.; Hurford, G.; Kleint, L.; Kolleck, M.; Krucker, S.;
Lagg, A.; Landini, F.; Long, D. M.; Lefort, J.; Lodiot, S.; Mampaey,
B.; Maloney, S.; Marliani, F.; Martinez-Pillet, V.; McMullin, D. R.;
Müller, D.; Nicolini, G.; Orozco Suarez, D.; Pacros, A.; Pancrazzi,
M.; Parenti, S.; Peter, H.; Philippon, A.; Plunkett, S.; Rich, N.;
Rochus, P.; Rouillard, A.; Romoli, M.; Sanchez, L.; Schühle, U.;
Sidher, S.; Solanki, S. K.; Spadaro, D.; St Cyr, O. C.; Straus, T.;
Tanco, I.; Teriaca, L.; Thompson, W. T.; del Toro Iniesta, J. C.;
Verbeeck, C.; Vourlidas, A.; Watson, C.; Wiegelmann, T.; Williams,
D.; Woch, J.; Zhukov, A. N.; Zouganelis, I.
Bibcode: 2020A&A...642A...6A
Altcode:
Context. To meet the scientific objectives of the mission, the Solar
Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing
(RS) instruments designed for joint operations with inter-instrument
communication capabilities. Indeed, previous missions have shown that
the Sun (imaged by the RS instruments) and the heliosphere (mainly
sampled by the IS instruments) should be considered as an integrated
system rather than separate entities. Many of the advances expected
from Solar Orbiter rely on this synergistic approach between IS and
RS measurements.
Aims: Many aspects of hardware development,
integration, testing, and operations are common to two or more
RS instruments. In this paper, we describe the coordination effort
initiated from the early mission phases by the Remote Sensing Working
Group. We review the scientific goals and challenges, and give an
overview of the technical solutions devised to successfully operate
these instruments together.
Methods: A major constraint for the
RS instruments is the limited telemetry (TM) bandwidth of the Solar
Orbiter deep-space mission compared to missions in Earth orbit. Hence,
many of the strategies developed to maximise the scientific return from
these instruments revolve around the optimisation of TM usage, relying
for example on onboard autonomy for data processing, compression,
and selection for downlink. The planning process itself has been
optimised to alleviate the dynamic nature of the targets, and an
inter-instrument communication scheme has been implemented which can
be used to autonomously alter the observing modes. We also outline the
plans for in-flight cross-calibration, which will be essential to the
joint data reduction and analysis.
Results: The RS instrument
package on Solar Orbiter will carry out comprehensive measurements
from the solar interior to the inner heliosphere. Thanks to the close
coordination between the instrument teams and the European Space
Agency, several challenges specific to the RS suite were identified
and addressed in a timely manner.
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
Bibcode: 2020A&A...642A...3Z
Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.
Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Solanki, S. K.; del Toro Iniesta, J. C.; Woch, J.; Gandorfer,
A.; Hirzberger, J.; Alvarez-Herrero, A.; Appourchaux, T.; Martínez
Pillet, V.; Pérez-Grande, I.; Sanchis Kilders, E.; Schmidt, W.;
Gómez Cama, J. M.; Michalik, H.; Deutsch, W.; Fernandez-Rico, G.;
Grauf, B.; Gizon, L.; Heerlein, K.; Kolleck, M.; Lagg, A.; Meller, R.;
Müller, R.; Schühle, U.; Staub, J.; Albert, K.; Alvarez Copano, M.;
Beckmann, U.; Bischoff, J.; Busse, D.; Enge, R.; Frahm, S.; Germerott,
D.; Guerrero, L.; Löptien, B.; Meierdierks, T.; Oberdorfer, D.;
Papagiannaki, I.; Ramanath, S.; Schou, J.; Werner, S.; Yang, D.;
Zerr, A.; Bergmann, M.; Bochmann, J.; Heinrichs, J.; Meyer, S.;
Monecke, M.; Müller, M. -F.; Sperling, M.; Álvarez García, D.;
Aparicio, B.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Cobos
Carracosa, J. P.; Girela, F.; Hernández Expósito, D.; Herranz, M.;
Labrousse, P.; López Jiménez, A.; Orozco Suárez, D.; Ramos, J. L.;
Barandiarán, J.; Bastide, L.; Campuzano, C.; Cebollero, M.; Dávila,
B.; Fernández-Medina, A.; García Parejo, P.; Garranzo-García, D.;
Laguna, H.; Martín, J. A.; Navarro, R.; Núñez Peral, A.; Royo, M.;
Sánchez, A.; Silva-López, M.; Vera, I.; Villanueva, J.; Fourmond,
J. -J.; de Galarreta, C. Ruiz; Bouzit, M.; Hervier, V.; Le Clec'h,
J. C.; Szwec, N.; Chaigneau, M.; Buttice, V.; Dominguez-Tagle, C.;
Philippon, A.; Boumier, P.; Le Cocguen, R.; Baranjuk, G.; Bell,
A.; Berkefeld, Th.; Baumgartner, J.; Heidecke, F.; Maue, T.; Nakai,
E.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Blanco
Rodríguez, J.; Domingo, V.; Ferreres Sabater, A.; Gasent Blesa,
J. L.; Rodríguez Martínez, P.; Osorno Caudel, D.; Bosch, J.; Casas,
A.; Carmona, M.; Herms, A.; Roma, D.; Alonso, G.; Gómez-Sanjuan, A.;
Piqueras, J.; Torralbo, I.; Fiethe, B.; Guan, Y.; Lange, T.; Michel,
H.; Bonet, J. A.; Fahmy, S.; Müller, D.; Zouganelis, I.
Bibcode: 2020A&A...642A..11S
Altcode: 2019arXiv190311061S
Aims: This paper describes the Polarimetric and Helioseismic
Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and
helioseismology instrument to observe the Sun from outside the Sun-Earth
line. It is the key instrument meant to address the top-level science
question: How does the solar dynamo work and drive connections between
the Sun and the heliosphere? SO/PHI will also play an important role
in answering the other top-level science questions of Solar Orbiter,
while hosting the potential of a rich return in further science.
Methods: SO/PHI measures the Zeeman effect and the Doppler shift
in the Fe I 617.3 nm spectral line. To this end, the instrument
carries out narrow-band imaging spectro-polarimetry using a tunable
LiNbO3 Fabry-Perot etalon, while the polarisation modulation
is done with liquid crystal variable retarders. The line and the nearby
continuum are sampled at six wavelength points and the data are recorded
by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data
are reduced on board, including being inverted under the assumption of
a Milne-Eddington atmosphere, although simpler reduction methods are
also available on board. SO/PHI is composed of two telescopes; one,
the Full Disc Telescope, covers the full solar disc at all phases of
the orbit, while the other, the High Resolution Telescope, can resolve
structures as small as 200 km on the Sun at closest perihelion. The high
heat load generated through proximity to the Sun is greatly reduced by
the multilayer-coated entrance windows to the two telescopes that allow
less than 4% of the total sunlight to enter the instrument, most of
it in a narrow wavelength band around the chosen spectral line.
Results: SO/PHI was designed and built by a consortium having partners
in Germany, Spain, and France. The flight model was delivered to
Airbus Defence and Space, Stevenage, and successfully integrated into
the Solar Orbiter spacecraft. A number of innovations were introduced
compared with earlier space-based spectropolarimeters, thus allowing
SO/PHI to fit into the tight mass, volume, power and telemetry budgets
provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal)
challenges posed by the mission's highly elliptical orbit.
Title: Understanding the origins of the heliosphere: integrating
observations and measurements from Parker Solar Probe, Solar Orbiter,
and other space- and ground-based observatories
Authors: Velli, M.; Harra, L. K.; Vourlidas, A.; Schwadron,
N.; Panasenco, O.; Liewer, P. C.; Müller, D.; Zouganelis, I.;
St Cyr, O. C.; Gilbert, H.; Nieves-Chinchilla, T.; Auchère, F.;
Berghmans, D.; Fludra, A.; Horbury, T. S.; Howard, R. A.; Krucker,
S.; Maksimovic, M.; Owen, C. J.; Rodríguez-Pacheco, J.; Romoli,
M.; Solanki, S. K.; Wimmer-Schweingruber, R. F.; Bale, S.; Kasper,
J.; McComas, D. J.; Raouafi, N.; Martinez-Pillet, V.; Walsh, A. P.;
De Groof, A.; Williams, D.
Bibcode: 2020A&A...642A...4V
Altcode:
Context. The launch of Parker Solar Probe (PSP) in 2018, followed
by Solar Orbiter (SO) in February 2020, has opened a new window in
the exploration of solar magnetic activity and the origin of the
heliosphere. These missions, together with other space observatories
dedicated to solar observations, such as the Solar Dynamics Observatory,
Hinode, IRIS, STEREO, and SOHO, with complementary in situ observations
from WIND and ACE, and ground based multi-wavelength observations
including the DKIST observatory that has just seen first light,
promise to revolutionize our understanding of the solar atmosphere
and of solar activity, from the generation and emergence of the Sun's
magnetic field to the creation of the solar wind and the acceleration of
solar energetic particles.
Aims: Here we describe the scientific
objectives of the PSP and SO missions, and highlight the potential for
discovery arising from synergistic observations. Here we put particular
emphasis on how the combined remote sensing and in situ observations of
SO, that bracket the outer coronal and inner heliospheric observations
by PSP, may provide a reconstruction of the solar wind and magnetic
field expansion from the Sun out to beyond the orbit of Mercury in the
first phases of the mission. In the later, out-of-ecliptic portions of
the SO mission, the solar surface magnetic field measurements from SO
and the multi-point white-light observations from both PSP and SO will
shed light on the dynamic, intermittent solar wind escaping from helmet
streamers, pseudo-streamers, and the confined coronal plasma, and on
solar energetic particle transport.
Methods: Joint measurements
during PSP-SO alignments, and magnetic connections along the same
flux tube complemented by alignments with Earth, dual PSP-Earth,
and SO-Earth, as well as with STEREO-A, SOHO, and BepiColumbo will
allow a better understanding of the in situ evolution of solar-wind
plasma flows and the full three-dimensional distribution of the
solar wind from a purely observational point of view. Spectroscopic
observations of the corona, and optical and radio observations,
combined with direct in situ observations of the accelerating solar
wind will provide a new foundation for understanding the fundamental
physical processes leading to the energy transformations from solar
photospheric flows and magnetic fields into the hot coronal plasma
and magnetic fields and finally into the bulk kinetic energy of the
solar wind and solar energetic particles.
Results: We discuss
the initial PSP observations, which already provide a compelling
rationale for new measurement campaigns by SO, along with ground-
and space-based assets within the synergistic context described above.
Title: On the Magnetic Nature of an Exploding Granule as Revealed
by Sunrise/IMaX
Authors: Guglielmino, Salvo L.; Martínez Pillet, Valentín; Ruiz
Cobo, Basilio; Bellot Rubio, Luis R.; del Toro Iniesta, José Carlos;
Solanki, Sami K.; Riethmüller, Tino L.; Zuccarello, Francesca
Bibcode: 2020ApJ...896...62G
Altcode: 2020arXiv200503371G
We study the photospheric evolution of an exploding granule
observed in the quiet Sun at high spatial (∼0"3) and temporal
(31.5 s) resolution by the imaging magnetograph Sunrise/IMaX in 2009
June. These observations show that the exploding granule is cospatial
to a magnetic flux emergence event occurring at mesogranular scale
(up to ∼12 Mm2 area). Using a modified version of the
SIR code for inverting the IMaX spectropolarimetric measurements, we
obtain information about the magnetic configuration of this photospheric
feature. In particular, we find evidence of highly inclined emerging
fields in the structure, carrying a magnetic flux content up to ∼4
× 1018 Mx. The balance between gas and magnetic pressure
in the region of flux emergence, compared with a very quiet region of
the Sun, indicates that the additional pressure carried by the emerging
flux increases the total pressure by about 5% and appears to allow the
granulation to be modified, as predicted by numerical simulations. The
overall characteristics suggest that a multipolar structure emerges
into the photosphere, resembling an almost horizontal flux sheet. This
seems to be associated with exploding granules. Finally, we discuss
the origin of such flux emergence events.
Title: Solar Disk Center Shows Scattering Polarization in the Sr I
4607 Å Line
Authors: Zeuner, Franziska; Manso Sainz, Rafael; Feller, Alex; van
Noort, Michiel; Solanki, Sami K.; Iglesias, Francisco A.; Reardon,
Kevin; Martínez Pillet, Valentín
Bibcode: 2020ApJ...893L..44Z
Altcode: 2020arXiv200403679Z
Magnetic fields in turbulent, convective high-β plasma naturally
develop highly tangled and complex topologies - the solar photosphere
being the paradigmatic example. These fields are mostly undetectable by
standard diagnostic techniques with finite spatio-temporal resolution
due to cancellations of Zeeman polarization signals. Observations of
resonance scattering polarization have been considered to overcome
these problems. But up to now, observations of scattering polarization
lack the necessary combination of high sensitivity and high spatial
resolution in order to directly infer the turbulent magnetic structure
at the resolution limit of solar telescopes. Here, we report the
detection of clear spatial structuring of scattering polarization
in a magnetically quiet solar region at disk center in the Sr I
4607 Å spectral line on granular scales, confirming theoretical
expectations. We find that the linear polarization presents a
strong spatial correlation with the local quadrupole of the radiation
field. The result indicates that polarization survives the dynamic and
turbulent magnetic environment of the middle photosphere and is thereby
usable for spatially resolved Hanle observations. This is an important
step toward the long-sought goal of directly observing turbulent
solar magnetic fields at the resolution limit and investigating their
spatial structure.
Title: Magnetic Structure of an Erupting Filament
Authors: Wang, Shuo; Jenkins, Jack M.; Martinez Pillet, Valentin;
Beck, Christian; Long, David M.; Prasad Choudhary, Debi; Muglach,
Karin; McAteer, James
Bibcode: 2020ApJ...892...75W
Altcode: 2020arXiv200202104W
The full 3D vector magnetic field of a solar filament prior to
eruption is presented. The filament was observed with the Facility
Infrared Spectropolarimeter at the Dunn Solar Telescope in the
chromospheric He I line at 10830 Å on 2017 May 29 and 30. We inverted
the spectropolarimetric observations with the Hanle and Zeeman Light
code to obtain the chromospheric magnetic field. A bimodal distribution
of field strength was found in or near the filament. The average field
strength was 24 Gauss, but prior to the eruption we find the 90th
percentile of field strength was 435 Gauss for the observations on May
29. The field inclination was about 67° from the solar vertical. The
field azimuth made an angle of about 47°-65° to the spine axis. The
results suggest an inverse configuration indicative of a flux rope
topology. He I intensity threads were found to be coaligned with the
magnetic field direction. The filament had a sinistral configuration
as expected for the southern hemisphere. The filament was stable on
2017 May 29 and started to rise during two observations on May 30,
before erupting and causing a minor coronal mass ejection. There
was no obvious change of the magnetic topology during the eruption
process. Such information on the magnetic topology of erupting filaments
could improve the prediction of the geoeffectiveness of solar storms.
Title: Solar physics in the 2020s: DKIST, parker solar probe, and
solar orbiter as a multi-messenger constellation
Authors: Martinez Pillet, V.; Tritschler, A.; Harra, L.; Andretta, V.;
Vourlidas, A.; Raouafi, N.; Alterman, B. L.; Bellot Rubio, L.; Cauzzi,
G.; Cranmer, S. R.; Gibson, S.; Habbal, S.; Ko, Y. K.; Lepri, S. T.;
Linker, J.; Malaspina, D. M.; Matthews, S.; Parenti, S.; Petrie, G.;
Spadaro, D.; Ugarte-Urra, I.; Warren, H.; Winslow, R.
Bibcode: 2020arXiv200408632M
Altcode:
The National Science Foundation (NSF) Daniel K. Inouye Solar Telescope
(DKIST) is about to start operations at the summit of Haleakala
(Hawaii). DKIST will join the early science phases of the NASA
and ESA Parker Solar Probe and Solar Orbiter encounter missions. By
combining in-situ measurements of the near-sun plasma environment and
detail remote observations of multiple layers of the Sun, the three
observatories form an unprecedented multi-messenger constellation to
study the magnetic connectivity inside the solar system. This white
paper outlines the synergistic science that this multi-messenger
suite enables.
Title: ngGONG: The Next Generation GONG - A New Solar Synoptic
Observational Network
Authors: Hill, Frank; Hammel, Heidi; Martinez-Pillet, Valentin; de
Wijn, A.; Gosain, S.; Burkepile, J.; Henney, C. J.; McAteer, J.; Bain,
H. M.; Manchester, W.; Lin, H.; Roth, M.; Ichimoto, K.; Suematsu, Y.
Bibcode: 2019BAAS...51g..74H
Altcode: 2019astro2020U..74H
The white paper describes a next-generation GONG, a ground-based
geographically distributed network of instrumentation to continually
observe the Sun. This would provide data for solar magnetic field
research and space weather forecasting, and would extend the time
coverage of helioseismology.
Title: On the Magnetic Nature of Solar Exploding Granules
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo,
B.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.; Solanki, S. K.;
Zuccarello, F.
Bibcode: 2019ASPC..526..299G
Altcode:
We report on spectropolarimetric observations acquired by the imaging
magnetograph SUNRISE/IMaX at high spatial 0.''3 and temporal (31.5 s)
resolution during the first science flight of this balloon-borne solar
observatory. We describe the photospheric evolution of an exploding
granule observed in the quiet Sun. This granule is cospatial with
a magnetic flux emergence event occurring at mesogranular scales
(up to ∼12 Mm2 area). Using a modified version of the
SIR code, we show that we can estimate the longitudinal field also
in the presence of a residual cross-talk in these IMaX longitudinal
measurements. We determine the magnetic flux content of the structure
(∼3 ×1018 Mx), which appears to have a multipolar
configuration, and discuss the origin of such flux emergence events.
Title: Synoptic Studies of the Sun as a Key to Understanding Stellar
Astrospheres
Authors: Martinez Pillet, Valentin; Hill, Frank; Hammel, Heidi B.;
de Wijn, Alfred G.; Gosain, Sanjay; Burkepile, Joan; Henney, Carl;
McAteer, R. T. James; Bain, Hazel; Manchester, Ward; Lin, Haosheng;
Roth, Markus; Ichimoto, Kiyoshi; Suematsu, Yoshinori
Bibcode: 2019BAAS...51c.110M
Altcode: 2019astro2020T.110M; 2019arXiv190306944M
Ground-based solar observations provide key contextual data (i.e., the
"big picture") to produce a complete description of the only astrosphere
we can study in situ: our Sun's heliosphere. This white paper outlines
the current paradigm for ground-based solar synoptic observations,
and indicates those areas that will benefit from focused attention.
Title: Doppler Events in the Solar Photosphere: The Coincident
Superposition of Fast Granular Flows and p-Mode Coherence Patches
Authors: McClure, R. Lee; Rast, Mark P.; Martínez Pillet, Valentin
Bibcode: 2019SoPh..294...18M
Altcode: 2018arXiv181108944M
Observations of the solar photosphere show spatially compact
large-amplitude Doppler velocity events with short lifetimes. In data
from the Imaging Magnetograph eXperiment (IMaX) on the first flight of
the SUNRISE balloon in 2009, events with velocities in excess of 4σ
from the mean can be identified in both intergranular downflow lanes
and granular upflows. We show that the statistics of such events are
consistent with the random superposition of strong convective flows
and p-mode coherence patches. Such coincident superposition complicates
the identification of acoustic wave sources in the solar photosphere,
and may be important in the interpretation of spectral line profiles
formed in solar photosphere.
Title: The Critical Science Plan for DKIST
Authors: Rast, M.; Cauzzi, G.; Martinez Pillet, V.
Bibcode: 2019NCimC..42....7R
Altcode:
The 4-meter Daniel K. Inouye Solar Telescope is nearing completion on
Haleakala, Maui, with first light expected in 2020. In preparation
for early science, the National Solar Observatory is reaching out
to the solar community in order to define the critical science goals
for the first two years of DKIST operations. The overall aim of this
"Critical Science Plan" is to be ready, by start of operations, to
execute a set of observations that take full advantage of the DKIST
capabilities to address critical compelling science.
Title: SOPHISM: Software Instrument Simulator
Authors: Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Orozco
Suárez, D.; Martínez Pillet, V.; Bonet, J. A.; Feller, A.;
Hirzberger, J.; Lagg, A.; Piqueras, J.; Gasent Blesa, J. L.
Bibcode: 2018ascl.soft10017B
Altcode:
SOPHISM models astronomical instrumentation from the entrance
of the telescope to data acquisition at the detector, along with
software blocks dealing with, for example, demodulation, inversion,
and compression. The code performs most analyses done with light
in astronomy, such as differential photometry, spectroscopy, and
polarimetry. The simulator offers flexibility and implementation of new
effects and subsystems, making it user-adaptable for a wide variety
of instruments. SOPHISM can be used for all stages of instrument
definition, design, operation, and lifetime tracking evaluation.
Title: SOPHISM: An End-to-end Software Instrument Simulator
Authors: Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Orozco
Suárez, D.; Martínez Pillet, V.; Bonet, J. A.; Feller, A.;
Hirzberger, J.; Lagg, A.; Piqueras, J.; Gasent Blesa, J. L.
Bibcode: 2018ApJS..237...35B
Altcode:
We present a software simulator for the modeling of astronomical
instrumentation, which includes platform effects and software
processing. It is an end-to-end simulator, from the entrance of
the telescope to the data acquisition at the detector, along with
software blocks dealing, e.g., with demodulation, inversion, and
compression. Developed following the Solar Orbiter/Polarimetric
and Helioseismic Imager (SO/PHI) instrument, it comprises elements
such as a filtergraph, polarimetric modulator, detector, vibrations,
and accumulations. Through these, the simulator performs most of the
analyses that can be done with light in astronomy, such as differential
photometry, spectroscopy, and polarimetry. The simulator is coded
with high flexibility and ease of implementation of new effects and
subsystems. Thus, it allows for the user to adapt it to a wide variety
of instruments, even not exclusively solar ones, as illustrated with
an example of application to a night-time observation. The simulator
can provide support in the phase of instrument design and help assess
tolerances and test solutions to underperformances arising during the
instrument operations. All this makes SOPHISM a very valuable tool
for all the stages of astronomical instrument definition, design,
operation, and lifetime tracking evaluation.
Title: Construction update of the Daniel K. Inouye Solar Telescope
project
Authors: Warner, Mark; Rimmele, Thomas R.; Martinez Pillet, Valentin;
Casini, Roberto; Berukoff, Steve; Craig, Simon C.; Ferayorni, Andrew;
Goodrich, Bret D.; Hubbard, Robert P.; Harrington, David; Jeffers,
Paul; Johansson, Erik M.; Kneale, Ruth; Kuhn, Jeff; Liang, Chen; Lin,
Haosheng; Marshall, Heather; Mathioudakis, Mihalis; McBride, William
R.; McMullin, Joseph; McVeigh, William; Sekulic, Predrag; Schmidt,
Wolfgang; Shimko, Steve; Sueoka, Stacey; Summers, Rich; Tritschler,
Alexandra; Williams, Timothy R.; Wöger, Friedrich
Bibcode: 2018SPIE10700E..0VW
Altcode:
Construction of the Daniel K. Inouye Solar Telescope (DKIST) is
well underway on the Haleakalā summit on the Hawaiian island of
Maui. Featuring a 4-m aperture and an off-axis Gregorian configuration,
the DKIST will be the world's largest solar telescope. It is designed
to make high-precision measurements of fundamental astrophysical
processes and produce large amounts of spectropolarimetric and
imaging data. These data will support research on solar magnetism
and its influence on solar wind, flares, coronal mass ejections,
and solar irradiance variability. Because of its large aperture, the
DKIST will be able to sense the corona's magnetic field—a goal that
has previously eluded scientists—enabling observations that will
provide answers about the heating of stellar coronae and the origins
of space weather and exo-weather. The telescope will cover a broad
wavelength range (0.35 to 28 microns) and operate as a coronagraph
at infrared (IR) wavelengths. Achieving the diffraction limit of
the 4-m aperture, even at visible wavelengths, is paramount to these
science goals. The DKIST's state-of-the-art adaptive optics systems
will provide diffraction-limited imaging, resolving features that are
approximately 20 km in size on the Sun. At the start of operations,
five instruments will be deployed: a visible broadband imager (VTF),
a visible spectropolarimeter (ViSP), a visible tunable filter (VTF),
a diffraction-limited near-IR spectropolarimeter (DLNIRSP), and a
cryogenic near-IR spectropolarimeter (cryo-NIRSP). At the end of
2017, the project finished its fifth year of construction and eighth
year overall. Major milestones included delivery of the commissioning
blank, the completed primary mirror (M1), and its cell. Commissioning
and testing of the coudé rotator is complete and the installation
of the coudé cleanroom is underway; likewise, commissioning of the
telescope mount assembly (TMA) has also begun. Various other systems and
equipment are also being installed and tested. Finally, the observatory
integration, testing, and commissioning (IT&C) activities have
begun, including the first coating of the M1 commissioning blank and
its integration within its cell assembly. Science mirror coating and
initial on-sky activities are both anticipated in 2018.
Title: Inferring telescope polarization properties through spectral
lines without linear polarization
Authors: Derks, A.; Beck, C.; Martínez Pillet, V.
Bibcode: 2018A&A...615A..22D
Altcode: 2018arXiv180401153D
Context. Polarimetric observations taken with ground- or space-based
telescopes usually need to be corrected for changes of the polarization
state in the optical path.
Aims: We present a technique
to determine the polarization properties of a telescope through
observations of spectral lines that have no or negligible intrinsic
linear polarization signals. For such spectral lines, any observed
linear polarization must be induced by the telescope optics. We apply
the technique to observations taken with the Spectropolarimeter for
Infrared and Optical Regions (SPINOR) at the Dunn Solar Telescope
(DST) and demonstrate that we can retrieve the characteristic
polarization properties of the DST at three wavelengths of 459,
526, and 615 nm.
Methods: We determine the amount of crosstalk
between the intensity Stokes I and the linear and circular polarization
states Stokes Q, U, and V, and between Stokes V and Stokes Q and U in
spectropolarimetric observations of active regions. We fit a set of
parameters that describe the polarization properties of the DST to
the observed crosstalk values. We compare our results to parameters
that were derived using a conventional telescope calibration unit
(TCU).
Results: The values for the ratio of reflectivities X =
rs/rp and the retardance τ of the DST turret
mirrors from the analysis of the crosstalk match those derived with
the TCU within the error bars. We find a negligible contribution of
retardance from the entrance and exit windows of the evacuated part
of the DST. Residual crosstalk after applying a correction for the
telescope polarization stays at a level of 3-10% regardless of which
parameter set is used, but with an rms fluctuation in the input data
of already a few percent. The accuracy in the determination of the
telescope properties is thus more limited by the quality of the input
data than the method itself.
Conclusions: It is possible to
derive the parameters that describe the polarization properties of a
telescope from observations of spectral lines without intrinsic linear
polarization signal. Such spectral lines have a dense coverage (about
50 nm separation) in the visible part of the spectrum (400-615 nm),
but none were found at longer wavelengths. Using spectral lines without
intrinsic linear polarization is a promising tool for the polarimetric
calibration of current or future solar telescopes such as the Daniel
K. Inouye Solar Telescope (DKIST).
Title: Getting Ready for the Third Science Flight of SUNRISE
Authors: Barthol, Peter; Katsukawa, Yukio; Lagg, Andreas; Solanki,
Sami K.; Kubo, Masahito; Riethmueller, Tino; Martínez Pillet,
Valentin; Gandorfer, Achim; Feller, Alex; Berkefeld, . Thomas; Orozco
Suárez, David; Del Toro Iniesta, Jose Carlos; Bernasconi, Pietro;
Álvarez-Herrero, Alberto; Quintero Noda, Carlos
Bibcode: 2018cosp...42E.215B
Altcode:
SUNRISE is a balloon-borne, stratospheric solar observatory dedicated
to the investigation of the structure and dynamics of the Sun's
magnetic field and its interaction with convective plasma flows and
waves. The previous science flights of SUNRISE in 2009 and 2013 have
led to many new scientific results, so far described in around 90
refereed publications. This success has shown the huge potential of the
SUNRISE concept and the recovery of the largely intact payload offers
the opportunity for a third flight.The scientific instrumentation of
SUNRISE 3 will have extended capabilities in particular to measure
magnetic fields, plasma velocities and temperatures with increased
sensitivity and over a larger height range in the solar atmosphere, from
the convectively dominated photosphere up to the still poorly understood
chromosphere. The latter is the key interaction region between magnetic
field, waves and radiation and plays a central role in transporting
energy to the outer layers of the solar atmosphere including the
corona.SUNRISE 3 will carry 2 new grating-based spectro-polarimeters
with slit-scanning and context imaging with slitjaw cameras. The
SUNRISE UV Spectro-polarimeter and Imager (SUSI) will explore the rich
near-UV range between 300 nm and 430 nm which is poorly accessible
from the ground. The SUNRISE Chromospheric Infrared spectro-Polarimeter
(SCIP) will sample 2 spectral windows in the near-infrared, containing
many spectral lines highly sensitive to magnetic fields at different
formation heights. In addition to the two new instruments the Imaging
Magnetograph eXperiment (IMaX), an etalon-based tunable filtergraph and
spectro-polarimeter flown on both previous missions, will be upgraded
to IMaX+, enhancing its cadence and giving access to 2 spectral lines
in the visible spectral range. All three instruments will allow
investigating both the photosphere and the chromosphere and will
ideally complement each other in terms of sensitivity, height coverage
and resolution.A new gondola with a sophisticated attitude control
system including roll damping will provide improved pointing/tracking
performance. Upgraded image stabilization with higher bandwidth will
further reduce residual jitter, maximizing the quality of the science
data.SUNRISE 3 is a joint project of the German Max-Planck-Institut für
Sonnensystemforschung together with the Spanish SUNRISE consortium, the
Johns Hopkins University Applied Physics Laboratory, USA, the German
Kiepenheuer Institut für Sonnenphysik, the National Astronomical
Observatory of Japan and the Japan Aerospace eXploraion Agency (JAXA).
Title: Design of a next generation synoptic solar observing network:
solar physics research integrated network group (SPRING)
Authors: Gosain, Sanjay; Roth, Markus; Hill, Frank; Pevtsov, Alexei;
Martinez Pillet, Valentin; Thompson, Michael J.
Bibcode: 2018SPIE10702E..4HG
Altcode:
Long-term synoptic observations of the Sun in different wavelength
regions are essential to understand its secular behavior. Such
observations have proven very important for discovery of 11 year
solar activity cycle, 22 year magnetic cycle, polar field reversals,
Hale's polarity law, Joy's law, that helped Babcock and Leighton
to propose famous solar dynamo model. In more recent decades, the
societal impact of the secular changes in Sun's output has been felt in
terms of solar inputs to terrestrial climate-change and space-weather
hazards. Further, it has been realized that to better understand the
activity phenomena such as flares and coronal mass ejections (CMEs)
one needs synoptic observations in multiple spectral lines to enable
tomographic inference of physical parameters. Currently, there are
both space and ground based synoptic observatories. However, given
the requirements for the long-term stability and reliability of such
synoptic datasets, ground-based facilities are more preferable. Also,
the ground based observatories are easy to maintain or upgrade while
detailed and frequent calibrations are easily possible. The only
ground-based facility that currently provides full-disk velocity and
magnetic field maps of the Sun around the clock and at good cadence,
is the Global Oscillations Network Group (GONG) network of National
Solar Observatory (NSO) which is operational since the mid 90s. Due
to its aging instrumentation, operating for nearly three decades, and
new requirements to obtain multiwavelength observations, a need is felt
in the solar community to build a next generation synoptic observatory
network. A group of international observatories have come together under
the auspices of SOLARNET program, funded by European Union (EU), to
carryout a preliminary design study of such a synoptic solar observing
facility called "SPRING", which stands for Solar Physics Research
Integrated Network Group. In this article we will present concept of
SPRING and the optical design concept of its major instruments.ts.
Title: Status of the Daniel K. Inouye Solar Telescope: unraveling
the mysteries the Sun.
Authors: Rimmele, Thomas R.; Martinez Pillet, Valentin; Goode, Philip
R.; Knoelker, Michael; Kuhn, Jeffrey Richard; Rosner, Robert; Casini,
Roberto; Lin, Haosheng; von der Luehe, Oskar; Woeger, Friedrich;
Tritschler, Alexandra; Fehlmann, Andre; Jaeggli, Sarah A.; Schmidt,
Wolfgang; De Wijn, Alfred; Rast, Mark; Harrington, David M.; Sueoka,
Stacey R.; Beck, Christian; Schad, Thomas A.; Warner, Mark; McMullin,
Joseph P.; Berukoff, Steven J.; Mathioudakis, Mihalis; DKIST Team
Bibcode: 2018AAS...23231601R
Altcode:
The 4m Daniel K. Inouye Solar Telescope (DKIST) currently under
construction on Haleakala, Maui will be the world’s largest solar
telescope. Designed to meet the needs of critical high resolution and
high sensitivity spectral and polarimetric observations of the sun,
this facility will perform key observations of our nearest star that
matters most to humankind. DKIST’s superb resolution and sensitivity
will enable astronomers to address many of the fundamental problems
in solar and stellar astrophysics, including the origin of stellar
magnetism, the mechanisms of coronal heating and drivers of the
solar wind, flares, coronal mass ejections and variability in solar
and stellar output. DKIST will also address basic research aspects of
Space Weather and help improve predictive capabilities. In combination
with synoptic observations and theoretical modeling DKIST will unravel
the many remaining mysteries of the Sun.The construction of DKIST is
progressing on schedule with 80% of the facility complete. Operations
are scheduled to begin early 2020. DKIST will replace the NSO
facilities on Kitt Peak and Sac Peak with a national facility with
worldwide unique capabilities. The design allows DKIST to operate as
a coronagraph. Taking advantage of its large aperture and infrared
polarimeters DKIST will be capable to routinely measure the currently
illusive coronal magnetic fields. The state-of-the-art adaptive optics
system provides diffraction limited imaging and the ability to resolve
features approximately 20 km on the Sun. Achieving this resolution
is critical for the ability to observe magnetic structures at their
intrinsic, fundamental scales. Five instruments will be available at
the start of operations, four of which will provide highly sensitive
measurements of solar magnetic fields throughout the solar atmosphere
- from the photosphere to the corona. The data from these instruments
will be distributed to the world wide community via the NSO/DKIST data
center located in Boulder. We present examples of science objectives
and provide an overview of the facility and project status, including
the ongoing efforts of the community to develop the critical science
plan for the first 2-3 years of operations.
Title: Inferring Telescope Polarization Properties Through Spectral
Lines Without Linear Polarization
Authors: Derks, Alysa; Beck, Christian; Martinez Pillet, Valentin
Bibcode: 2018tess.conf21060D
Altcode:
We present a technique to determine the polarization properties
of a telescope through observations of spectral lines that have
no or negligible intrinsic linear polarization signals. For such
spectral lines, any observed linear polarization must be induced by
the telescope optics. We apply the technique to observations taken
with SPINOR at the Dunn Solar Telescope (DST) and demonstrate that we
can retrieve the characteristic polarization properties of the DST at
three wavelengths of 459, 526, and 615 nm. The values for the ratio
of reflectivities X = rs/rp and the retardance τ of the DST turret
mirrors from the analysis of the crosstalk match those derived with
the TCU within the error bars. We conclude that it is possible
to derive the parameters that describe the polarization properties
of a telescope from observations of spectral lines without intrinsic
linear polarization signal. Such spectral lines have a dense coverage
(about 50 nm separation) in the visible part of the spectrum (400-615
nm), but none were found at longer wavelengths. Using spectral lines
without intrinsic linear polarization is a promising tool for the
polarimetric calibration of current or future solar telescopes such
as the Daniel K. Inouye Solar Telescope (DKIST).
Title: The Life Cycle of Active Region Magnetic Fields
Authors: Cheung, M. C. M.; van Driel-Gesztelyi, L.; Martínez Pillet,
V.; Thompson, M. J.
Bibcode: 2018smf..book..317C
Altcode:
No abstract at ADS
Title: The Maximum Entropy Limit of Small-scale Magnetic Field
Fluctuations in the Quiet Sun
Authors: Gorobets, A. Y.; Berdyugina, S. V.; Riethmüller, T. L.;
Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
Gizon, L.; Hirzberger, J.; van Noort, M.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..233....5G
Altcode: 2017arXiv171008361G
The observed magnetic field on the solar surface is characterized by a
very complex spatial and temporal behavior. Although feature-tracking
algorithms have allowed us to deepen our understanding of this behavior,
subjectivity plays an important role in the identification and tracking
of such features. In this paper, we continue studies of the temporal
stochasticity of the magnetic field on the solar surface without relying
either on the concept of magnetic features or on subjective assumptions
about their identification and interaction. We propose a data analysis
method to quantify fluctuations of the line-of-sight magnetic field by
means of reducing the temporal field’s evolution to the regular Markov
process. We build a representative model of fluctuations converging to
the unique stationary (equilibrium) distribution in the long time limit
with maximum entropy. We obtained different rates of convergence to the
equilibrium at fixed noise cutoff for two sets of data. This indicates
a strong influence of the data spatial resolution and mixing-polarity
fluctuations on the relaxation process. The analysis is applied to
observations of magnetic fields of the relatively quiet areas around an
active region carried out during the second flight of the Sunrise/IMaX
and quiet Sun areas at the disk center from the Helioseismic and
Magnetic Imager on board the Solar Dynamics Observatory satellite.
Title: The Life Cycle of Active Region Magnetic Fields
Authors: Cheung, M. C. M.; van Driel-Gesztelyi, L.; Martínez Pillet,
V.; Thompson, M. J.
Bibcode: 2017SSRv..210..317C
Altcode: 2016SSRv..tmp...46C
We present a contemporary view of how solar active region
magnetic fields are understood to be generated, transported and
dispersed. Empirical trends of active region properties that guide model
development are discussed. Physical principles considered important
for active region evolution are introduced and advances in modeling
are reviewed.
Title: Slender Ca II H Fibrils Mapping Magnetic Fields in the Low
Solar Chromosphere
Authors: Jafarzadeh, S.; Rutten, R. J.; Solanki, S. K.; Wiegelmann, T.;
Riethmüller, T. L.; van Noort, M.; Szydlarski, M.; Blanco Rodríguez,
J.; Barthol, P.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.;
Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Schmidt, W.
Bibcode: 2017ApJS..229...11J
Altcode: 2016arXiv161003104J
A dense forest of slender bright fibrils near a small solar active
region is seen in high-quality narrowband Ca II H images from the SuFI
instrument onboard the Sunrise balloon-borne solar observatory. The
orientation of these slender Ca II H fibrils (SCF) overlaps with the
magnetic field configuration in the low solar chromosphere derived
by magnetostatic extrapolation of the photospheric field observed
with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are
qualitatively aligned with small-scale loops computed from a novel
inversion approach based on best-fit numerical MHD simulation. Such
loops are organized in canopy-like arches over quiet areas that differ
in height depending on the field strength near their roots.
Title: Magneto-static Modeling from Sunrise/IMaX: Application to an
Active Region Observed with Sunrise II
Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki, S. K.;
Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller,
T. L.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...18W
Altcode: 2017arXiv170101458N; 2017arXiv170101458W
Magneto-static models may overcome some of the issues facing force-free
magnetic field extrapolations. So far they have seen limited use
and have faced problems when applied to quiet-Sun data. Here we
present a first application to an active region. We use solar vector
magnetic field measurements gathered by the IMaX polarimeter during
the flight of the Sunrise balloon-borne solar observatory in 2013
June as boundary conditions for a magneto-static model of the higher
solar atmosphere above an active region. The IMaX data are embedded
in active region vector magnetograms observed with SDO/HMI. This work
continues our magneto-static extrapolation approach, which was applied
earlier to a quiet-Sun region observed with Sunrise I. In an active
region the signal-to-noise-ratio in the measured Stokes parameters
is considerably higher than in the quiet-Sun and consequently the
IMaX measurements of the horizontal photospheric magnetic field allow
us to specify the free parameters of the model in a special class of
linear magneto-static equilibria. The high spatial resolution of IMaX
(110-130 km, pixel size 40 km) enables us to model the non-force-free
layer between the photosphere and the mid-chromosphere vertically
by about 50 grid points. In our approach we can incorporate some
aspects of the mixed beta layer of photosphere and chromosphere, e.g.,
taking a finite Lorentz force into account, which was not possible with
lower-resolution photospheric measurements in the past. The linear model
does not, however, permit us to model intrinsic nonlinear structures
like strongly localized electric currents.
Title: The Second Flight of the Sunrise Balloon-borne Solar
Observatory: Overview of Instrument Updates, the Flight, the Data,
and First Results
Authors: Solanki, S. K.; Riethmüller, T. L.; Barthol, P.; Danilovic,
S.; Deutsch, W.; Doerr, H. -P.; Feller, A.; Gandorfer, A.; Germerott,
D.; Gizon, L.; Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.;
Lagg, A.; Meller, R.; Tomasch, G.; van Noort, M.; Blanco Rodríguez,
J.; Gasent Blesa, J. L.; Balaguer Jiménez, M.; Del Toro Iniesta,
J. C.; López Jiménez, A. C.; Orozco Suarez, D.; Berkefeld, T.;
Halbgewachs, C.; Schmidt, W.; Álvarez-Herrero, A.; Sabau-Graziati,
L.; Pérez Grande, I.; Martínez Pillet, V.; Card, G.; Centeno, R.;
Knölker, M.; Lecinski, A.
Bibcode: 2017ApJS..229....2S
Altcode: 2017arXiv170101555S
The Sunrise balloon-borne solar observatory, consisting of a 1 m
aperture telescope that provides a stabilized image to a UV filter
imager and an imaging vector polarimeter, carried out its second science
flight in 2013 June. It provided observations of parts of active regions
at high spatial resolution, including the first high-resolution images
in the Mg II k line. The obtained data are of very high quality, with
the best UV images reaching the diffraction limit of the telescope
at 3000 Å after Multi-Frame Blind Deconvolution reconstruction
accounting for phase-diversity information. Here a brief update is
given of the instruments and the data reduction techniques, which
includes an inversion of the polarimetric data. Mainly those aspects
that evolved compared with the first flight are described. A tabular
overview of the observations is given. In addition, an example time
series of a part of the emerging active region NOAA AR 11768 observed
relatively close to disk center is described and discussed in some
detail. The observations cover the pores in the trailing polarity of
the active region, as well as the polarity inversion line where flux
emergence was ongoing and a small flare-like brightening occurred in
the course of the time series. The pores are found to contain magnetic
field strengths ranging up to 2500 G, and while large pores are clearly
darker and cooler than the quiet Sun in all layers of the photosphere,
the temperature and brightness of small pores approach or even exceed
those of the quiet Sun in the upper photosphere.
Title: A Tale of Two Emergences: Sunrise II Observations of Emergence
Sites in a Solar Active Region
Authors: Centeno, R.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger,
J.; Riethmüller, T. L.; van Noort, M.; Orozco Suárez, D.; Berkefeld,
T.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....3C
Altcode: 2016arXiv161003531C
In 2013 June, the two scientific instruments on board the second Sunrise
mission witnessed, in detail, a small-scale magnetic flux emergence
event as part of the birth of an active region. The Imaging Magnetograph
Experiment (IMaX) recorded two small (∼ 5\prime\prime )
emerging flux patches in the polarized filtergrams of a photospheric Fe
I spectral line. Meanwhile, the Sunrise Filter Imager (SuFI) captured
the highly dynamic chromospheric response to the magnetic fields pushing
their way through the lower solar atmosphere. The serendipitous capture
of this event offers a closer look at the inner workings of active
region emergence sites. In particular, it reveals in meticulous detail
how the rising magnetic fields interact with the granulation as they
push through the Sun’s surface, dragging photospheric plasma in
their upward travel. The plasma that is burdening the rising field
slides along the field lines, creating fast downflowing channels at
the footpoints. The weight of this material anchors this field to the
surface at semi-regular spatial intervals, shaping it in an undulatory
fashion. Finally, magnetic reconnection enables the field to release
itself from its photospheric anchors, allowing it to continue its
voyage up to higher layers. This process releases energy that lights
up the arch-filament systems and heats the surrounding chromosphere.
Title: Photospheric Response to an Ellerman Bomb-like Event—An
Analogy of Sunrise/IMaX Observations and MHD Simulations
Authors: Danilovic, S.; Solanki, S. K.; Barthol, P.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.;
Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.;
Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....5D
Altcode: 2016arXiv160903817D
Ellerman Bombs are signatures of magnetic reconnection, which is an
important physical process in the solar atmosphere. How and where they
occur is a subject of debate. In this paper, we analyze Sunrise/IMaX
data, along with 3D MHD simulations that aim to reproduce the exact
scenario proposed for the formation of these features. Although
the observed event seems to be more dynamic and violent than the
simulated one, simulations clearly confirm the basic scenario for the
production of EBs. The simulations also reveal the full complexity of
the underlying process. The simulated observations show that the Fe I
525.02 nm line gives no information on the height where reconnection
takes place. It can only give clues about the heating in the aftermath
of the reconnection. However, the information on the magnetic field
vector and velocity at this spatial resolution is extremely valuable
because it shows what numerical models miss and how they can be
improved.
Title: Kinematics of Magnetic Bright Features in the Solar Photosphere
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.;
Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon,
L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M.
Bibcode: 2017ApJS..229....8J
Altcode: 2016arXiv161007634J
Convective flows are known as the prime means of transporting magnetic
fields on the solar surface. Thus, small magnetic structures are good
tracers of turbulent flows. We study the migration and dispersal
of magnetic bright features (MBFs) in intergranular areas observed
at high spatial resolution with Sunrise/IMaX. We describe the flux
dispersal of individual MBFs as a diffusion process whose parameters are
computed for various areas in the quiet-Sun and the vicinity of active
regions from seeing-free data. We find that magnetic concentrations
are best described as random walkers close to network areas (diffusion
index, γ =1.0), travelers with constant speeds over a supergranule
(γ =1.9{--}2.0), and decelerating movers in the vicinity of flux
emergence and/or within active regions (γ =1.4{--}1.5). The three
types of regions host MBFs with mean diffusion coefficients of 130
km2 s-1, 80-90 km2 s-1,
and 25-70 km2 s-1, respectively. The MBFs in
these three types of regions are found to display a distinct kinematic
behavior at a confidence level in excess of 95%.
Title: Spectropolarimetric Evidence for a Siphon Flow along an
Emerging Magnetic Flux Tube
Authors: Requerey, Iker S.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol,
P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.;
van Noort, M.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...15R
Altcode: 2016arXiv161106732R
We study the dynamics and topology of an emerging magnetic flux
concentration using high spatial resolution spectropolarimetric data
acquired with the Imaging Magnetograph eXperiment on board the sunrise
balloon-borne solar observatory. We obtain the full vector magnetic
field and the line of sight (LOS) velocity through inversions of
the Fe I line at 525.02 nm with the SPINOR code. The derived vector
magnetic field is used to trace magnetic field lines. Two magnetic flux
concentrations with different polarities and LOS velocities are found
to be connected by a group of arch-shaped magnetic field lines. The
positive polarity footpoint is weaker (1100 G) and displays an upflow,
while the negative polarity footpoint is stronger (2200 G) and shows
a downflow. This configuration is naturally interpreted as a siphon
flow along an arched magnetic flux tube.
Title: A New MHD-assisted Stokes Inversion Technique
Authors: Riethmüller, T. L.; Solanki, S. K.; Barthol, P.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Blanco Rodríguez, J.;
Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez
Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...16R
Altcode: 2016arXiv161105175R
We present a new method of Stokes inversion of spectropolarimetric
data and evaluate it by taking the example of a Sunrise/IMaX
observation. An archive of synthetic Stokes profiles is obtained
by the spectral synthesis of state-of-the-art magnetohydrodynamics
(MHD) simulations and a realistic degradation to the level of the
observed data. The definition of a merit function allows the archive
to be searched for the synthetic Stokes profiles that best match the
observed profiles. In contrast to traditional Stokes inversion codes,
which solve the Unno-Rachkovsky equations for the polarized radiative
transfer numerically and fit the Stokes profiles iteratively, the new
technique provides the full set of atmospheric parameters. This gives
us the ability to start an MHD simulation that takes the inversion
result as an initial condition. After a relaxation process of half an
hour solar time we obtain physically consistent MHD data sets with
a target similar to the observation. The new MHD simulation is used
to repeat the method in a second iteration, which further improves
the match between observation and simulation, resulting in a factor
of 2.2 lower mean {χ }2 value. One advantage of the new
technique is that it provides the physical parameters on a geometrical
height scale. It constitutes a first step toward inversions that give
results consistent with the MHD equations.
Title: Solar Coronal Loops Associated with Small-scale Mixed Polarity
Surface Magnetic Fields
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.;
Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van
Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco
Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....4C
Altcode: 2016arXiv161007484C
How and where are coronal loops rooted in the solar lower
atmosphere? The details of the magnetic environment and its evolution
at the footpoints of coronal loops are crucial to understanding the
processes of mass and energy supply to the solar corona. To address
the above question, we use high-resolution line-of-sight magnetic
field data from the Imaging Magnetograph eXperiment instrument on the
Sunrise balloon-borne observatory and coronal observations from the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory
of an emerging active region. We find that the coronal loops are
often rooted at the locations with minor small-scale but persistent
opposite-polarity magnetic elements very close to the larger dominant
polarity. These opposite-polarity small-scale elements continually
interact with the dominant polarity underlying the coronal loop through
flux cancellation. At these locations we detect small inverse Y-shaped
jets in chromospheric Ca II H images obtained from the Sunrise Filter
Imager during the flux cancellation. Our results indicate that magnetic
flux cancellation and reconnection at the base of coronal loops due
to mixed polarity fields might be a crucial feature for the supply of
mass and energy into the corona.
Title: Moving Magnetic Features around a Pore
Authors: Kaithakkal, A. J.; Riethmüller, T. L.; Solanki, S. K.; Lagg,
A.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; vanNoort,
M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...13K
Altcode: 2016arXiv160905664K
Spectropolarimetric observations from Sunrise/IMaX, obtained in 2013
June, are used for a statistical analysis to determine the physical
properties of moving magnetic features (MMFs) observed near a pore. MMFs
of the same and opposite polarity, with respect to the pore, are found
to stream from its border at an average speed of 1.3 km s-1
and 1.2 km s-1, respectively, with mainly same-polarity MMFs
found further away from the pore. MMFs of both polarities are found to
harbor rather weak, inclined magnetic fields. Opposite-polarity MMFs
are blueshifted, whereas same-polarity MMFs do not show any preference
for up- or downflows. Most of the MMFs are found to be of sub-arcsecond
size and carry a mean flux of ∼1.2 × 1017 Mx.
Title: Convectively Driven Sinks and Magnetic Fields in the Quiet-Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
Schmidt, Wolfgang
Bibcode: 2017ApJS..229...14R
Altcode: 2016arXiv161007622R
We study the relation between mesogranular flows, convectively
driven sinks and magnetic fields using high spatial resolution
spectropolarimetric data acquired with the Imaging Magnetograph
eXperiment on board Sunrise. We obtain the horizontal velocity
flow fields of two quiet-Sun regions (31.2 × 31.2 Mm2)
via local correlation tracking. Mesogranular lanes and the central
position of sinks are identified using Lagrange tracers. We find
6.7× {10}-2 sinks per Mm2 in the two observed
regions. The sinks are located at the mesogranular vertices and turn
out to be associated with (1) horizontal velocity flows converging to a
central point and (2) long-lived downdrafts. The spatial distribution
of magnetic fields in the quiet-Sun is also examined. The strongest
magnetic fields are preferentially located at sinks. We find that 40% of
the pixels with longitudinal components of the magnetic field stronger
than 500 G are located in the close neighborhood of sinks. In contrast,
the small-scale magnetic loops detected by Martínez González et al. in
the same two observed areas do not show any preferential distribution
at mesogranular scales. The study of individual examples reveals
that sinks can play an important role in the evolution of quiet-Sun
magnetic features.
Title: A science driven update to the Daniel K Inouye Solar Telescope
Authors: Martínez Pillet, Valentín
Bibcode: 2017psio.confE..79M
Altcode:
No abstract at ADS
Title: Blending of Ground- and Space-Based Magnetograms: Application
to L1-L5 Solar Wind and Coronal Hole Predictions
Authors: Berger, T. E.; Pevtsov, A. A.; Martinez-Pillet, V.; Bertello,
L.; Petrie, G. J. D.; Arge, C. N.; Henney, C. J.; Biesecker, D. A.
Bibcode: 2016AGUFMSH11C2241B
Altcode:
We examine the effect of blending ground-based Global Oscillations
Network Group (GONG) line-of-sight solar magnetic flux maps
("magnetograms") with space-based magnetograms from the Solar Dynamics
Observatory (SDO) Helioseismic and Magnetic Imager (HMI) instrument on
solar wind and coronal hole model-based forecasts. The longitudinally
blended maps are used to "reforecast" solar wind conditions using the
Wang-Sheeley-Arge (WSA) solar wind model during historical periods
of coronal hole High Speed Streams (HSS) and Corotating Interaction
Regions (CIRs) and compared to Advanced Composition Explorer (ACE)
data at the L1 Lagrangian point. The same WSA runs are repeated using
GONG and HMI data alone to determine the effect of data blending. The
blended maps are also used to create Potential Field Source Surface
(PFSS) maps of open coronal field lines and compared with historical
coronal hole data from SDO Atmospheric Imaging Assembly (AIA)
images. The study addresses the feasibility of combining ground- and
space-based data from instruments with widely disparate and varying
spatiotemporal resolution and flux sensitivity levels for use as inputs
to solar wind and coronal hole forecasting models. The results are
relevant to mission studies considering blended data inputs from,
e.g., L5 Lagrangian point satellite instruments with ground-based
measurements on the Sun-Earth line, as well as to expected magnetogram
data from the Solar Orbiter Polarimetric and Helioseismic Imager (PHI)
instrument. This study complements others that examine the utility
of having multiple viewpoint (e.g. L1 and L5) magnetogram inputs to
solar wind models by exploring data blending from disparate instruments.
Title: Construction status of the Daniel K. Inouye solar telescope
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Warner, Mark;
Martinez Pillet, Valentin; Casini, Roberto; Berukoff, Steve; Craig,
Simon C.; Elmore, David; Ferayorni, Andrew; Goodrich, Bret D.;
Hubbard, Robert P.; Harrington, David; Hegwer, Steve; Jeffers, Paul;
Johansson, Erik M.; Kuhn, Jeff; Lin, Haosheng; Marshall, Heather;
Mathioudakis, Mihalis; McBride, William R.; McVeigh, William; Phelps,
LeEllen; Schmidt, Wolfgang; Shimko, Steve; Sueoka, Stacey; Tritschler,
Alexandra; Williams, Timothy R.; Wöger, Friedrich
Bibcode: 2016SPIE.9906E..1BM
Altcode:
We provide an update on the construction status of the Daniel
K. Inouye Solar Telescope. This 4-m diameter facility is designed to
enable detection and spatial/temporal resolution of the predicted,
fundamental astrophysical processes driving solar magnetism at
their intrinsic scales throughout the solar atmosphere. These data
will drive key research on solar magnetism and its influence on
solar winds, flares, coronal mass ejections and solar irradiance
variability. The facility is developed to support a broad wavelength
range (0.35 to 28 microns) and will employ state-of-the-art adaptive
optics systems to provide diffraction limited imaging, resolving
features approximately 20 km on the Sun. At the start of operations,
there will be five instruments initially deployed: Visible Broadband
Imager (VBI; National Solar Observatory), Visible SpectroPolarimeter
(ViSP; NCAR High Altitude Observatory), Visible Tunable Filter (VTF
(a Fabry-Perot tunable spectropolarimeter); Kiepenheuer Institute for
Solarphysics), Diffraction Limited NIR Spectropolarimeter (DL-NIRSP;
University of Hawaii, Institute for Astronomy) and the Cryogenic NIR
Spectropolarimeter (Cryo-NIRSP; University of Hawaii, Institute for
Astronomy). As of mid-2016, the project construction is in its 4th
year of site construction and 7th year overall. Major milestones in
the off-site development include the conclusion of the polishing of
the M1 mirror by University of Arizona, College of Optical Sciences,
the delivery of the Top End Optical Assembly (L3), the acceptance of
the Deformable Mirror System (Xinetics); all optical systems have been
contracted and are either accepted or in fabrication. The Enclosure
and Telescope Mount Assembly passed through their factory acceptance
in 2014 and 2015, respectively. The enclosure site construction
is currently concluding while the Telescope Mount Assembly site
erection is underway. The facility buildings (Utility and Support
and Operations) have been completed with ongoing work on the thermal
systems to support the challenging imaging requirements needed for the
solar research. Finally, we present the construction phase performance
(schedule, budget) with projections for the start of early operations.
Title: Construction Status and Early Science with the Daniel K. Inouye
Solar Telescope
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Warner, Mark;
Martinez Pillet, Valentin; Craig, Simon; Woeger, Friedrich; Tritschler,
Alexandra; Berukoff, Steven J.; Casini, Roberto; Goode, Philip R.;
Knoelker, Michael; Kuhn, Jeffrey Richard; Lin, Haosheng; Mathioudakis,
Mihalis; Reardon, Kevin P.; Rosner, Robert; Schmidt, Wolfgang
Bibcode: 2016SPD....4720101M
Altcode:
The 4-m Daniel K. Inouye Solar Telescope (DKIST) is in its seventh
year of overall development and its fourth year of site construction
on the summit of Haleakala, Maui. The Site Facilities (Utility
Building and Support & Operations Building) are in place with
ongoing construction of the Telescope Mount Assembly within. Off-site
the fabrication of the component systems is completing with early
integration testing and verification starting.Once complete this
facility will provide the highest sensitivity and resolution for study
of solar magnetism and the drivers of key processes impacting Earth
(solar wind, flares, coronal mass ejections, and variability in solar
output). The DKIST will be equipped initially with a battery of first
light instruments which cover a spectral range from the UV (380 nm)
to the near IR (5000 nm), and capable of providing both imaging and
spectro-polarimetric measurements throughout the solar atmosphere
(photosphere, chromosphere, and corona); these instruments are being
developed by the National Solar Observatory (Visible Broadband Imager),
High Altitude Observatory (Visible Spectro-Polarimeter), Kiepenheuer
Institute (Visible Tunable Filter) and the University of Hawaii
(Cryogenic Near-Infrared Spectro-Polarimeter and the Diffraction-Limited
Near-Infrared Spectro-Polarimeter). Further, a United Kingdom consortium
led by Queen's University Belfast is driving the development of high
speed cameras essential for capturing the highly dynamic processes
measured by these instruments. Finally, a state-of-the-art adaptive
optics system will support diffraction limited imaging capable of
resolving features approximately 20 km in scale on the Sun.We present
the overall status of the construction phase along with the current
challenges as well as a review of the planned science testing and the
transition into early science operations.
Title: Ca II 854.2 nm Spectromagnetograms: A Powerful Chromospheric
Diagnostic
Authors: Harvey, J. W.; Bertello, Luca; Branston, D.; Britanik, J.;
Bulau, S.; Cole, L.; Gosain, Sanjay; Harker, Brian; Jones, Harrison P.;
Marble, A.; Martinez Pillet, V.; Pevtsov, A.; Schramm, K.; Streander,
Kim; Villegas, H.
Bibcode: 2016SPD....4710106H
Altcode:
The transition from physical dominance by plasma flows in the
photosphere to magnetic pressure in the solar chromosphere motivates
as many diagnostic observations as possible across this important
region. Among the few ground-accessible spectral lines formed within
the chromosphere, the Ca II 854.2 nm line has the desirable properties
of presence everywhere on the solar disk, Zeeman sensitivity, and
narrow line width. Mapped observations of circular polarization within
this line (spectromagnetograms) have been made at NSO infrequently
since 1974, with regular daily full-disk observations starting in
August 1996. Full-disk spectral observations of the complete Stokes
polarization vector are now being made regularly since November
2015. It is not easy to estimate chromospheric magnetic field
properties from the 854.2 nm line profile polarization. To provide
rough quick-look vector field maps we found that the weak-field
approximation provides a fair first estimate of the line-of-sight
component but appears to be too simple to interpret the transverse
magnetic field from frequently asymmetric, linearly-polarized line
profiles. More realistic estimates of the chromospheric vector field,
short of extremely lengthy, full 3D, non-local radiative transfer
inversions, are being investigated. We briefly introduce recent
instrumental modifications and observational characteristics, sample
observations, and results concerning the expansion of the chromospheric
field with increasing height, the presence of large areas of weak,
nearly horizontal fields, and field estimates in plages, sunspots,
flares, filaments, and filament channels. The Stokes spectra will be
freely available to the community.This work utilizes SOLIS data obtained
by the NSO Integrated Synoptic Program (NISP), managed by the National
Solar Observatory, which is operated by the Association of Universities
for Research in Astronomy (AURA), Inc. under a cooperative agreement
with the National Science Foundation.
Title: Resolving the source of the solar acoustic oscillations:
What will be possible with DKIST?
Authors: Rast, Mark; Martinez Pillet, Valentin
Bibcode: 2016SPD....4720105R
Altcode:
The solar p-modes are likely excited by small-scale convective dynamics
in the solar photosphere, but the detailed source properties are not
known. Theoretical models differ and observations are yet unable to
differentiate between them. Resolving the underlying source events
is more than a curiosity. It is important to the veracity of global
helioseismic measurements (including local spectral methods such
as ring diagram analysis) because global p-mode line shapes and thus
accurate frequency determinations depend critically on the relationship
between intensity and velocity during the excitation events. It is
also fundamental to improving the accuracy of the local time-distance
measurements because in these kernel calculations depend on knowledge
of the source profile and the properties of the excitation noise. The
Daniel K. Inouye Solar Telescope (DKIST) will have the spatial
resolution and spectral range needed to resolve the solar acoustic
excitation events in both time and space (horizontally and with
height) using multi-wavelength observations. Inversions to determine
the dynamic and thermodynamic evolution of the discrete small-scale
convective events that serve as acoustic sources may also be possible,
though determination of the pressure fluctuations associated with the
sources is a challenge. We describe the DKIST capabilities anticipated
and the preliminary work needed to prepare for them.
Title: Magnetic flux submergence in the photosphere: A target
for DKIST
Authors: Martinez Pillet, Valentin
Bibcode: 2016SPD....47.0404M
Altcode:
While magnetic flux emergence is ubiquitous on the Sun and relatively
well observed, the opposite process, flux submergence, is elusive. In
the absence of large-scale submergence processes, it has always been
assumed that submergence occurs at granular or smaller scales. Models
that explain flux rope and filament formation near neutral lines,
specifically need small-scale submergence. The same is true for dynamo
models that propose the repair of the large-scale toroidal tubes after
they have emerged to the surface. However, the detection of field
lines being pulled back down into the solar photosphere has escaped
clear detection. In this work, I demonstrate that DKIST capabilities
are uniquely tailored to observe and characterize small-scale
flux submergence, if it indeed happens on the Sun. By searching for
transverse fields at small scales and studying their Doppler shifts, an
understanding of the nature of flux submergence can be achieved. Such
studies are particularly relevant near magnetic neutral lines where
filaments are formed though poorly understood processes.
Title: Magneto-static Modeling of the Mixed Plasma Beta Solar
Atmosphere Based on Sunrise/IMaX Data
Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki,
S. K.; Martínez Pillet, V.; Borrero, J. M.
Bibcode: 2015ApJ...815...10W
Altcode: 2015arXiv151105568W
Our aim is to model the three-dimensional magnetic field structure
of the upper solar atmosphere, including regions of non-negligible
plasma beta. We use high-resolution photospheric magnetic field
measurements from SUNRISE/IMaX as the boundary condition for a
magneto-static magnetic field model. The high resolution of IMaX
allows us to resolve the interface region between the photosphere
and corona, but modeling this region is challenging for the following
reasons. While the coronal magnetic field is thought to be force-free
(the Lorentz force vanishes), this is not the case in the mixed plasma
β environment in the photosphere and lower chromosphere. In our model,
pressure gradients and gravity forces are self-consistently taken into
account and compensate for the non-vanishing Lorentz force. Above a
certain height (about 2 Mm) the non-magnetic forces become very weak
and consequently the magnetic field becomes almost force-free. Here,
we apply a linear approach where the electric current density consists
of a superposition of a field-line parallel current and a current
perpendicular to the Sun's gravity field. We illustrate the prospects
and limitations of this approach and give an outlook for an extension
toward a nonlinear model.
Title: ADAHELI: exploring the fast, dynamic Sun in the x-ray, optical,
and near-infrared
Authors: Berrilli, Francesco; Soffitta, Paolo; Velli, Marco; Sabatini,
Paolo; Bigazzi, Alberto; Bellazzini, Ronaldo; Bellot Rubio, Luis
Ramon; Brez, Alessandro; Carbone, Vincenzo; Cauzzi, Gianna; Cavallini,
Fabio; Consolini, Giuseppe; Curti, Fabio; Del Moro, Dario; Di Giorgio,
Anna Maria; Ermolli, Ilaria; Fabiani, Sergio; Faurobert, Marianne;
Feller, Alex; Galsgaard, Klaus; Gburek, Szymon; Giannattasio, Fabio;
Giovannelli, Luca; Hirzberger, Johann; Jefferies, Stuart M.; Madjarska,
Maria S.; Manni, Fabio; Mazzoni, Alessandro; Muleri, Fabio; Penza,
Valentina; Peres, Giovanni; Piazzesi, Roberto; Pieralli, Francesca;
Pietropaolo, Ermanno; Martinez Pillet, Valentin; Pinchera, Michele;
Reale, Fabio; Romano, Paolo; Romoli, Andrea; Romoli, Marco; Rubini,
Alda; Rudawy, Pawel; Sandri, Paolo; Scardigli, Stefano; Spandre,
Gloria; Solanki, Sami K.; Stangalini, Marco; Vecchio, Antonio;
Zuccarello, Francesca
Bibcode: 2015JATIS...1d4006B
Altcode:
Advanced Astronomy for Heliophysics Plus (ADAHELI) is a project concept
for a small solar and space weather mission with a budget compatible
with an European Space Agency (ESA) S-class mission, including launch,
and a fast development cycle. ADAHELI was submitted to the European
Space Agency by a European-wide consortium of solar physics research
institutes in response to the "Call for a small mission opportunity
for a launch in 2017," of March 9, 2012. The ADAHELI project builds
on the heritage of the former ADAHELI mission, which had successfully
completed its phase-A study under the Italian Space Agency 2007 Small
Mission Programme, thus proving the soundness and feasibility of
its innovative low-budget design. ADAHELI is a solar space mission
with two main instruments: ISODY: an imager, based on Fabry-Pérot
interferometers, whose design is optimized to the acquisition of
highest cadence, long-duration, multiline spectropolarimetric images
in the visible/near-infrared region of the solar spectrum. XSPO: an
x-ray polarimeter for solar flares in x-rays with energies in the 15
to 35 keV range. ADAHELI is capable of performing observations that
cannot be addressed by other currently planned solar space missions,
due to their limited telemetry, or by ground-based facilities, due to
the problematic effect of the terrestrial atmosphere.
Title: Dynamics of Multi-cored Magnetic Structures in the Quiet Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
Schmidt, Wolfgang
Bibcode: 2015ApJ...810...79R
Altcode: 2015arXiv150806998R
We report on the dynamical interaction of quiet-Sun magnetic fields and
granular convection in the solar photosphere as seen by Sunrise. We
use high spatial resolution (0.″15-0.″18) and temporal cadence
(33 s) spectropolarimetric Imaging Magnetograph eXperiment data,
together with simultaneous CN and Ca ii H filtergrams from Sunrise
Filter Imager. We apply the SIR inversion code to the polarimetric
data in order to infer the line of sight velocity and vector magnetic
field in the photosphere. The analysis reveals bundles of individual
flux tubes evolving as a single entity during the entire 23 minute data
set. The group shares a common canopy in the upper photospheric layers,
while the individual tubes continually intensify, fragment and merge in
the same way that chains of bright points in photometric observations
have been reported to do. The evolution of the tube cores are driven
by the local granular convection flows. They intensify when they
are “compressed” by surrounding granules and split when they are
“squeezed” between two moving granules. The resulting fragments
are usually later regrouped in intergranular lanes by the granular
flows. The continual intensification, fragmentation and coalescence of
flux results in magnetic field oscillations of the global entity. From
the observations we conclude that the magnetic field oscillations first
reported by Martínez González et al. correspond to the forcing by
granular motions and not to characteristic oscillatory modes of thin
flux tubes.
Title: Division II: Commission 12: Solar Radiation and Structure
Authors: Kosovichev, Alexander; Cauzzi, Gianna; Martinez Pillet,
Valentin; Asplund, Martin; Brandenburg, Axel; Chou, Dean-Yi;
Christensen-Dalsgaard, Jorgen; Gan, Weiqun; Kuznetsov, Vladimir D.;
Rovira, Marta G.; Shchukina, Nataliya; Venkatakrishnan, P.
Bibcode: 2015IAUTB..28..109K
Altcode:
The President of C12, Alexander Kosovichev, presented the status of
the Commission and its working Group(s). Primary activities included
organization of international meetings (IAU Symposia, Special Sessions
and Joint Discussion); review and support of proposals for IAU sponsored
meetings; organization of working groups on the Commission topics
to promote the international cooperation; preparation of triennial
report on the organizational and science activities of Commission
members. Commission 12 broadly encompasses topics of solar research
which include studies of the Sun's internal structure, composition,
dynamics and magnetism (through helioseismology and other techniques),
studies of the quiet photosphere, chromosphere and corona, and also
research of the mechanisms of solar radiation, and its variability on
various time scales. Some overlap with topics covered by Commission
10 Solar Activity is unavoidable, and many activities are sponsored
jointly by these two commissions. The Commission website can be found
at http://sun.stanford.edu/IAU-Com12/, with information about related
IAU Symposiums and activities, and links to appropriate web sites.
Title: Centre-to-limb properties of small, photospheric quiet-Sun jets
Authors: Rubio da Costa, F.; Solanki, S. K.; Danilovic, S.; Hizberger,
J.; Martínez-Pillet, V.
Bibcode: 2015A&A...574A..95R
Altcode: 2014arXiv1412.1620R
Context. Strongly Doppler-shifted Stokes V profiles have been detected
in the quiet Sun with the IMaX instrument on-board the SUNRISE
stratospheric balloon-borne telescope. High velocities are required
to produce such signals, hence these events have been interpreted as
jets, although other sources are also possible.
Aims: We aim
to characterize the variation of the main properties of these events
(occurrence rate, lifetime, size, and velocities) with their position on
the solar disk between disk centre and the solar limb.
Methods:
These events were identified in SUNRISE/IMaX data according to the same
objective criteria at all available positions on the solar disk. Their
properties were determined using standard techniques.
Results:
Our study yielded a number of new insights into this phenomenon. Most
importantly, the number density of these events is independent of
the heliocentric angle, meaning that the investigated supersonic
flows are nearly isotropically distributed. Size and lifetime are
also nearly independent of the heliocentric angle, while their
intensity contrast increases towards the solar limb. The Stokes V
jets are associated with upflow velocities deduced from Stokes I,
which are stronger towards the limb. Their intensity decreases with
time, while their line-of-sight velocity does not display a clear
temporal evolution. Their association with linear polarization signals
decreases towards the limb.
Conclusions: The density of events
appears to be independent of heliocentric angle, establishing that they
are directed nearly randomly. If these events are jets triggered by
magnetic reconnection between emerging magnetic flux and the ambient
field, then our results suggest that there is no preferred geometry
for the reconnection process.
Title: The Formation and Disintegration of Magnetic Bright Points
Observed by Sunrise/IMaX
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.;
Jurčák, J.; Martínez Pillet, V.; Solanki, S. K.; Schmidt, W.
Bibcode: 2014ApJ...796...79U
Altcode: 2014arXiv1411.3240U
The evolution of the physical parameters of magnetic bright points
(MBPs) located in the quiet Sun (mainly in the interwork) during
their lifetime is studied. First, we concentrate on the detailed
description of the magnetic field evolution of three MBPs. This
reveals that individual features follow different, generally complex,
and rather dynamic scenarios of evolution. Next, we apply statistical
methods on roughly 200 observed MBP evolutionary tracks. MBPs are found
to be formed by the strengthening of an equipartition field patch,
which initially exhibits a moderate downflow. During the evolution,
strong downdrafts with an average velocity of 2.4 km s-1
set in. These flows, taken together with the concurrent strengthening of
the field, suggest that we are witnessing the occurrence of convective
collapses in these features, although only 30% of them reach kG field
strengths. This fraction might turn out to be larger when the new 4
m class solar telescopes are operational as observations of MBPs with
current state of the art instrumentation could still be suffering from
resolution limitations. Finally, when the bright point disappears
(although the magnetic field often continues to exist) the magnetic
field strength has dropped to the equipartition level and is generally
somewhat weaker than at the beginning of the MBP's evolution. Also,
only relatively weak downflows are found on average at this stage of
the evolution. Only 16% of the features display upflows at the time
that the field weakens, or the MBP disappears. This speaks either for
a very fast evolving dynamic process at the end of the lifetime, which
could not be temporally resolved, or against strong upflows as the cause
of the weakening of the field of these magnetic elements, as has been
proposed based on simulation results. It is noteworthy that in about 10%
of the cases, we observe in the vicinity of the downflows small-scale
strong (exceeding 2 km s-1) intergranular upflows related
spatially and temporally to these downflows. The paper is complemented
by a detailed discussion of aspects regarding the applied methods,
the complementary literature, and in depth analysis of parameters
like magnetic field strength and velocity distributions. An important
difference to magnetic elements and associated bright structures in
active region plage is that most of the quiet Sun bright points display
significant downflows over a large fraction of their lifetime (i.e.,
in more than 46% of time instances/measurements they show downflows
exceeding 1 km s-1).
Title: Comparison of solar photospheric bright points between Sunrise
observations and MHD simulations
Authors: Riethmüller, T. L.; Solanki, S. K.; Berdyugina, S. V.;
Schüssler, M.; Martínez Pillet, V.; Feller, A.; Gandorfer, A.;
Hirzberger, J.
Bibcode: 2014A&A...568A..13R
Altcode: 2014arXiv1406.1387R
Bright points (BPs) in the solar photosphere are thought to be the
radiative signatures (small-scale brightness enhancements) of magnetic
elements described by slender flux tubes or sheets located in the darker
intergranular lanes in the solar photosphere. They contribute to the
ultraviolet (UV) flux variations over the solar cycle and hence may
play a role in influencing the Earth's climate. Here we aim to obtain
a better insight into their properties by combining high-resolution
UV and spectro-polarimetric observations of BPs by the Sunrise
Observatory with 3D compressible radiation magnetohydrodynamical
(MHD) simulations. To this end, full spectral line syntheses are
performed with the MHD data and a careful degradation is applied
to take into account all relevant instrumental effects of the
observations. In a first step it is demonstrated that the selected
MHD simulations reproduce the measured distributions of intensity at
multiple wavelengths, line-of-sight velocity, spectral line width,
and polarization degree rather well. The simulated line width also
displays the correct mean, but a scatter that is too small. In
the second step, the properties of observed BPs are compared with
synthetic ones. Again, these are found to match relatively well,
except that the observations display a tail of large BPs with strong
polarization signals (most likely network elements) not found in the
simulations, possibly due to the small size of the simulation box. The
higher spatial resolution of the simulations has a significant effect,
leading to smaller and more numerous BPs. The observation that most BPs
are weakly polarized is explained mainly by the spatial degradation,
the stray light contamination, and the temperature sensitivity of the Fe
i line at 5250.2 Å. Finally, given that the MHD simulations are highly
consistent with the observations, we used the simulations to explore
the properties of BPs further. The Stokes V asymmetries increase with
the distance to the center of the mean BP in both observations and
simulations, consistent with the classical picture of a production
of the asymmetry in the canopy. This is the first time that this has
been found also in the internetwork. More or less vertical kilogauss
magnetic fields are found for 98% of the synthetic BPs underlining
that basically every BP is associated with kilogauss fields. At the
continuum formation height, the simulated BPs are on average 190 K
hotter than the mean quiet Sun, the mean BP field strength is found to
be 1750 G, and the mean inclination is 17°, supporting the physical
flux-tube paradigm to describe BPs. On average, the synthetic BPs
harbor downflows increasing with depth. The origin of these downflows
is not yet understood very well and needs further investigation.
Title: Construction status of the Daniel K. Inouye Solar Telescope
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Martínez Pillet,
Valentin; Berger, Thomas E.; Casini, Roberto; Craig, Simon C.; Elmore,
David F.; Goodrich, Bret D.; Hegwer, Steve L.; Hubbard, Robert P.;
Johansson, Erik M.; Kuhn, Jeffrey R.; Lin, Haosheng; McVeigh, William;
Schmidt, Wolfgang; Shimko, Steve; Tritschler, Alexandra; Warner,
Mark; Wöger, Friedrich
Bibcode: 2014SPIE.9145E..25M
Altcode:
The Daniel K. Inouye Solar Telescope (DKIST, renamed in December 2013
from the Advanced Technology Solar Telescope) will be the largest
solar facility built when it begins operations in 2019. Designed
and developed to meet the needs of critical high resolution and high
sensitivity spectral and polarimetric observations of the Sun, the
observatory will enable key research for the study of solar magnetism
and its influence on the solar wind, flares, coronal mass ejections
and solar irradiance variations. The 4-meter class facility will
operate over a broad wavelength range (0.38 to 28 microns, initially
0.38 to 5 microns), using a state-of-the-art adaptive optics system to
provide diffraction-limited imaging and the ability to resolve features
approximately 25 km on the Sun. Five first-light instruments will be
available at the start of operations: Visible Broadband Imager (VBI;
National Solar Observatory), Visible SpectroPolarimeter (ViSP; NCAR High
Altitude Observatory), Visible Tunable Filter (VTF; Kiepenheuer Institut
für Sonnenphysik), Diffraction Limited Near InfraRed SpectroPolarimeter
(DL-NIRSP; University of Hawai'i, Institute for Astronomy) and the
Cryogenic Near InfraRed SpectroPolarimeter (Cryo-NIRSP; University of
Hawai'i, Institute for Astronomy). As of mid-2014, the key subsystems
have been designed and fabrication is well underway, including the
site construction, which began in December 2012. We provide an update
on the development of the facilities both on site at the Haleakalā
Observatories on Maui and the development of components around the
world. We present the overall construction and integration schedule
leading to the handover to operations in mid 2019. In addition, we
outline the evolving challenges being met by the project, spanning the
full spectrum of issues covering technical, fiscal, and geographical,
that are specific to this project, though with clear counterparts to
other large astronomical construction projects.
Title: The History of a Quiet-Sun Magnetic Element Revealed by
IMaX/SUNRISE
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Bonet, José A.; Martínez Pillet, Valentín; Solanki,
Sami K.; Schmidt, Wolfgang
Bibcode: 2014ApJ...789....6R
Altcode: 2014arXiv1405.2837R
Isolated flux tubes are considered to be fundamental magnetic building
blocks of the solar photosphere. Their formation is usually attributed
to the concentration of magnetic field to kG strengths by the convective
collapse mechanism. However, the small size of the magnetic elements in
quiet-Sun areas has prevented this scenario from being studied in fully
resolved structures. Here, we report on the formation and subsequent
evolution of one such photospheric magnetic flux tube, observed in
the quiet Sun with unprecedented spatial resolution (0.''15-0.''18)
and high temporal cadence (33 s). The observations were acquired by
the Imaging Magnetograph eXperiment on board the SUNRISE balloon-borne
solar observatory. The equipartition field strength magnetic element
is the result of the merging of several same polarity magnetic flux
patches, including a footpoint of a previously emerged loop. The
magnetic structure is then further intensified to kG field strengths
by convective collapse. The fine structure found within the flux
concentration reveals that the scenario is more complex than can be
described by a thin flux tube model with bright points and downflow
plumes being established near the edges of the kG magnetic feature. We
also observe a daisy-like alignment of surrounding granules and a
long-lived inflow toward the magnetic feature. After a subsequent
weakening process, the field is again intensified to kG strengths. The
area of the magnetic feature is seen to change in anti-phase with the
field strength, while the brightness of the bright points and the speed
of the downflows varies in phase. We also find a relation between the
brightness of the bright point and the presence of upflows within it.
Title: A Spectro-polarimetric Analysis of Sunspot Umbrae
Authors: Watson, Fraser; Tritschler, Alexandra; Penn, Matthew J.;
Beck, Christian; Livingston, William; Martinez Pillet, Valentin
Bibcode: 2014AAS...22411202W
Altcode:
The recent quiet solar cycle has invited new questions as to
the nature of the solar magnetic field and how it changes over
time. To investigate this, we use the National Solar Observatory’s
McMath-Pierce Solar Telescope Facility (McMP) and Dunn Solar Telescope
(DST) to compare measurements of sunspots from five active regions
observed in 2013. Both BABO at the McMP and FIRS at the DST were
used to provide spectra of the Fe 1564.8nm line, which is affected
by the presence of magnetic fields. The magnetic field is derived
from Zeeman splitting in Stokes-I by BABO, and by inversion of the
Stokes parameters from FIRS data allowing for comparisons of sunspot
properties between the two instruments.. We present the first results
from this study including the magnetic fields in sunspot umbrae from
five active regions measured simultaneously by BABO and FIRS.
Title: Solar Surface and Atmospheric Dynamics
Authors: Martínez Pillet, V.
Bibcode: 2014mpcp.book...65M
Altcode: 2014mcp..book...65M
Various aspects of the magnetism of the quiet sun are reviewed. The
suggestion that a small scale dynamo acting at granular scales generates
what we call the quiet sun fields is studied in some detail. Although
dynamo action has been proved numerically, it is argued that current
simulations are still far from achieving the complexity that might
be present on the Sun. We based this statement not so much on the
low magnetic Reynolds numbers used in the simulations but, above all,
in the smallness of the kinetic Reynolds numbers employed by them. It
is argued that the low magnetic Prandtl number at the solar surface
may pose unexpected problems for the identification of the observed
internetwork fields with dynamo action at granular scales. Some form
of turbulent dynamo at bigger (and deeper) scales is favored. The
comparison between the internetwork fields observed by Hinode and the
magnetism inferred from Hanle measurements are converging towards a
similar description. They are both described as randomly oriented,
largely transverse fields in the several hecto-Gauss range. These
similarities are ever making more natural to assume that they are
the same. However, and because of the large voids of magnetic flux
observed in the spatial distribution of the internetwork fields,
it is argued that they are not likely to be generated by dynamo
action in the intergranular lanes. It is concluded that if a dynamo
is acting at granular scales, the end product might have not been
observed yet at current spatial resolutions and sensitivities with
the Zeeman effect. Thus an effort to increase these resolutions and
polarimetric sensitivities must be made. New ground- and space-based
telescopes are needed. The opportunity offered by the Solar Orbiter
mission to observe the Quiet Sun dynamics at the poles is seen as one
of the most important tests for confirming the existence, or otherwise,
of a granularly driven surface dynamo.
Title: Solar Surface and Atmospheric Dynamics. The Photosphere
Authors: Martínez Pillet, V.
Bibcode: 2013SSRv..178..141M
Altcode: 2013SSRv..tmp...21M; 2013arXiv1301.6933M; 2013SSRv..tmp...14M
Various aspects of the magnetism of the quiet sun are reviewed. The
suggestion that a small scale dynamo acting at granular scales generates
what we call the quiet sun fields is studied in some detail. Although
dynamo action has been proved numerically, it is argued that current
simulations are still far from achieving the complexity that might
be present on the Sun. We based this statement not so much on the
low magnetic Reynolds numbers used in the simulations but, above all,
in the smallness of the kinetic Reynolds numbers employed by them. It
is argued that the low magnetic Prandtl number at the solar surface
may pose unexpected problems for the identification of the observed
internetwork fields with dynamo action at granular scales. Some form
of turbulent dynamo at bigger (and deeper) scales is favored. The
comparison between the internetwork fields observed by Hinode and the
magnetism inferred from Hanle measurements are converging towards a
similar description. They are both described as randomly oriented,
largely transverse fields in the several hecto-Gauss range. These
similarities are ever making more natural to assume that they are
the same. However, and because of the large voids of magnetic flux
observed in the spatial distribution of the internetwork fields,
it is argued that they are not likely to be generated by dynamo
action in the intergranular lanes. It is concluded that if a dynamo
is acting at granular scales, the end product might have not been
observed yet at current spatial resolutions and sensitivities with
the Zeeman effect. Thus an effort to increase these resolutions and
polarimetric sensitivities must be made. New ground- and space-based
telescopes are needed. The opportunity offered by the Solar Orbiter
mission to observe the Quiet Sun dynamics at the poles is seen as one
of the most important tests for confirming the existence, or otherwise,
of a granularly driven surface dynamo.
Title: Temporal relation between quiet-Sun transverse fields and
the strong flows detected by IMaX/SUNRISE
Authors: Quintero Noda, C.; Martínez Pillet, V.; Borrero, J. M.;
Solanki, S. K.
Bibcode: 2013A&A...558A..30Q
Altcode: 2013arXiv1309.0627Q
Context. Localized strongly Doppler-shifted Stokes V signals were
detected by IMaX/SUNRISE. These signals are related to newly emerged
magnetic loops that are observed as linear polarization features.
Aims: We aim to set constraints on the physical nature and causes
of these highly Doppler-shifted signals. In particular, the temporal
relation between the appearance of transverse fields and the strong
Doppler shifts is analyzed in some detail.
Methods: We calculated
the time difference between the appearance of the strong flows and the
linear polarization. We also obtained the distances from the center
of various features to the nearest neutral lines and whether they
overlap or not. These distances were compared with those obtained from
randomly distributed points on observed magnetograms. Various cases of
strong flows are described in some detail.
Results: The linear
polarization signals precede the appearance of the strong flows by on
average 84 ± 11 s. The strongly Doppler-shifted signals are closer
(0.″19) to magnetic neutral lines than randomly distributed points
(0.″5). Eighty percent of the strongly Doppler-shifted signals are
close to a neutral line that is located between the emerging field and
pre-existing fields. That the remaining 20% do not show a close-by
pre-existing field could be explained by a lack of sensitivity or
an unfavorable geometry of the pre-existing field, for instance, a
canopy-like structure.
Conclusions: Transverse fields occurred
before the observation of the strong Doppler shifts. The process is
most naturally explained as the emergence of a granular-scale loop
that first gives rise to the linear polarization signals, interacts
with pre-existing fields (generating new neutral line configurations),
and produces the observed strong flows. This explanation is indicative
of frequent small-scale reconnection events in the quiet Sun.
Title: First evidence of interaction between longitudinal and
transverse waves in solar magnetic elements
Authors: Stangalini, M.; Solanki, S. K.; Cameron, R.; Martínez
Pillet, V.
Bibcode: 2013A&A...554A.115S
Altcode: 2013arXiv1304.7088S
Small-scale magnetic fields are thought to play an important role in
the heating of the outer solar atmosphere. By taking advantage of
the unprecedented high-spatial and temporal cadence of the Imaging
Magnetograph eXperiment (IMaX), the filter vector polarimeter on board
the Sunrise balloon-borne observatory, we study the transversal and
longitudinal velocity oscillations in small magnetic elements. The
results of this analysis are then compared to magnetohydrodynamic (MHD)
simulations, showing excellent agreement. We found buffeting-induced
transverse oscillations with velocity amplitudes of the order of 1-2
km s-1 to be common along with longitudinal oscillations
with amplitudes ~0.4 km s-1. Moreover, we also found an
interaction between transverse oscillations and longitudinal velocity
oscillations, showing a ± 90° phase lag at the frequency at which
they exhibit the maximum coherence in the power spectrum. Our results
are consistent with the theoretical picture in which MHD longitudinal
waves are excited inside small magnetic elements as a response of the
flux tube to the forcing action of the granular flows.
Title: Is Magnetic Reconnection the Cause of Supersonic Upflows in
Granular Cells?
Authors: Borrero, J. M.; Martínez Pillet, V.; Schmidt, W.; Quintero
Noda, C.; Bonet, J. A.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.
Bibcode: 2013ApJ...768...69B
Altcode: 2013arXiv1303.2557B
In a previous work, we reported on the discovery of supersonic magnetic
upflows on granular cells in data from the SUNRISE/IMaX instrument. In
the present work, we investigate the physical origin of these events
employing data from the same instrument but with higher spectral
sampling. By means of the inversion of Stokes profiles we are able
to recover the physical parameters (temperature, magnetic field,
line-of-sight velocity, etc.) present in the solar photosphere at the
time of these events. The inversion is performed in a Monte-Carlo-like
fashion, that is, repeating it many times with different initializations
and retaining only the best result. We find that many of the events are
characterized by a reversal in the polarity of the magnetic field along
the vertical direction in the photosphere, accompanied by an enhancement
in the temperature and by supersonic line-of-sight velocities. In
about half of the studied events, large blueshifted and redshifted
line-of-sight velocities coexist above/below each other. These features
can be explained in terms of magnetic reconnection, where the energy
stored in the magnetic field is released in the form of kinetic
and thermal energy when magnetic field lines of opposite polarities
coalesce. However, the agreement with magnetic reconnection is not
perfect and, therefore, other possible physical mechanisms might also
play a role.
Title: Evolution of the Fine Structure of Magnetic Fields in the
Quiet Sun: Observations from Sunrise/IMaX and Extrapolations
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Peter,
H.; Barthol, P.; Gandorfer, A.; Martínez Pillet, V.; Schmidt, W.;
Knölker, M.
Bibcode: 2013SoPh..283..253W
Altcode:
Observations with the balloon-borne Sunrise/Imaging Magnetograph
eXperiment (IMaX) provide high spatial resolution (roughly 100 km at
disk center) measurements of the magnetic field in the photosphere of
the quiet Sun. To investigate the magnetic structure of the chromosphere
and corona, we extrapolate these photospheric measurements into
the upper solar atmosphere and analyze a 22-minute long time series
with a cadence of 33 seconds. Using the extrapolated magnetic-field
lines as tracer, we investigate temporal evolution of the magnetic
connectivity in the quiet Sun's atmosphere. The majority of magnetic
loops are asymmetric in the sense that the photospheric field strength
at the loop foot points is very different. We find that the magnetic
connectivity of the loops changes rapidly with a typical connection
recycling time of about 3±1 minutes in the upper solar atmosphere and
12±4 minutes in the photosphere. This is considerably shorter than
previously found. Nonetheless, our estimate of the energy released by
the associated magnetic-reconnection processes is not likely to be the
sole source for heating the chromosphere and corona in the quiet Sun.
Title: Structure and dynamics of isolated internetwork Ca II H bright
points observed by SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Feller, A.; Lagg, A.;
Pietarila, A.; Danilovic, S.; Riethmüller, T. L.; Martínez Pillet, V.
Bibcode: 2013A&A...549A.116J
Altcode: 2012arXiv1211.4836J
Aims: We aim to improve our picture of the low chromosphere in
the quiet-Sun internetwork by investigating the intensity, horizontal
velocity, size and lifetime variations of small bright points (BPs;
diameter smaller than 0.3 arcsec) observed in the Ca II H 3968 Å
passband along with their magnetic field parameters, derived from
photospheric magnetograms.
Methods: Several high-quality
time series of disc-centre, quiet-Sun observations from the Sunrise
balloon-borne solar telescope, with spatial resolution of around 100
km on the solar surface, have been analysed to study the dynamics
of BPs observed in the Ca II H passband and their dependence on the
photospheric vector magnetogram signal.
Results: Parameters such
as horizontal velocity, diameter, intensity and lifetime histograms of
the isolated internetwork and magnetic Ca II H BPs were determined. Mean
values were found to be 2.2 km s-1, 0.2 arcsec (≈150 km),
1.48 ⟨ ICa ⟩ and 673 s, respectively. Interestingly, the
brightness and the horizontal velocity of BPs are anti-correlated. Large
excursions (pulses) in horizontal velocity, up to 15 km s-1,
are present in the trajectories of most BPs. These could excite kink
waves travelling into the chromosphere and possibly the corona, which we
estimate to carry an energy flux of 310 W m-2, sufficient to
heat the upper layers, although only marginally.
Conclusions:
The stable observing conditions of Sunrise and our technique for
identifying and tracking BPs have allowed us to determine reliable
parameters of these features in the internetwork. Thus we find, e.g.,
that they are considerably longer lived than previously thought. The
large velocities are also reliable, and may excite kink waves. Although
these wave are (marginally) energetic enough to heat the quiet corona,
we expect a large additional contribution from larger magnetic elements
populating the network and partly also the internetwork.
Title: Inversions of L12-2 IMaX data of an emerging flux mantle
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo,
B.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.; Solanki, S. K.;
Sunrise/IMaX Team
Bibcode: 2013MmSAI..84..355G
Altcode:
We present the analysis of a flux emergence event observed with
the IMaX magnetograph flown aboard the SUNRISE balloon. IMaX took a
15' sequence with cadence of 31 s along the Fe I line at 525.0 nm,
acquiring only Stokes I and V at 12 line positions (L12-2 mode). This
sequence shows the emergence of a flux mantle at mesogranular scale,
cospatial with a large exploding granule. An undesired cross-talk
between Stokes U and V was found in such L12-2 data. We show that the
use of a modified version of the SIR inversion code is able to remove
such effect in inferring the physical quantities of interest.
Title: Towards the next frontier in high precision solar polarimetry:
10^-4
Authors: Martinez Pillet, V.
Bibcode: 2012IAUSS...6E.304M
Altcode:
In the last two decades, solar physics has greatly explored the
10^-3 polarimetric sensitivity level (referred to the continuum
intensity). This has provided us with a quantitatively accurate picture
of the photospheric magnetism for mean longitudinal fields in the range
of about 5 Gauss. However, the same 10^-3 detection levels translate
into a sensitivity to transverse fields of the order of 100 Gauss,
which shows that our picture of the magnetic field is fundamentally
biased. The Zeeman effect is perverse enough to tell us that a 5 G
sensitivity in the transverse fields will only be achieved when we
reach the 10^-5 sensitivity level. While the Hanle effect is already
helping us to detect hidden transverse fields at the photosphere, it is
also clear that it biases our results in other ways. Thus, we are left
with the imperious need to progress towards increasing our polarimetric
sensitivities one order of magnitude or even better. In this talk, I
will present the science cases that expect us in the 10^-4 sensitivity
world and the technical challenges that we must face for that.
Title: The GREGOR Fabry-Pérot Interferometer
Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.;
Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados,
M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.;
Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer,
R.; Wittmann, A. D.; Woche, M.
Bibcode: 2012AN....333..880P
Altcode: 2012arXiv1210.2921P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two
tunable etalons in collimated mounting. Thanks to its large-format,
high-cadence CCD detectors with sophisticated computer hard- and
software it is capable of scanning spectral lines with a cadence
that is sufficient to capture the dynamic evolution of the solar
atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well
suited for quiet Sun and sunspot observations. However, in the vector
spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The
spectral coverage in the spectroscopic mode extends from 530-860 nm
with a theoretical spectral resolution of R ≈ 250,000, whereas in
the vector spectropolarimetric mode the wavelength range is at present
limited to 580-660 nm. The combination of fast narrow-band imaging and
post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales
down to ∼50 km on the solar surface.
Title: 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
Bibcode: 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: Resolving the Internal Magnetic Structure of the Solar Network
Authors: Martínez González, M. J.; Bellot Rubio, L. R.; Solanki,
S. K.; Martínez Pillet, V.; Del Toro Iniesta, J. C.; Barthol, P.;
Schmidt, W.
Bibcode: 2012ApJ...758L..40M
Altcode: 2012arXiv1209.2584M
We analyze the spectral asymmetry of Stokes V (circularly polarized)
profiles of an individual network patch in the quiet Sun observed
by Sunrise/IMaX. At a spatial resolution of 0farcs15-0farcs18, the
network elements contain substructure which is revealed by the spatial
distribution of Stokes V asymmetries. The area asymmetry between the
red and blue lobes of Stokes V increases from nearly zero at the core
of the structure to values close to unity at its edges (single-lobed
profiles). Such a distribution of the area asymmetry is consistent
with magnetic fields expanding with height, i.e., an expanding
magnetic canopy (which is required to fulfill pressure balance and
flux conservation in the solar atmosphere). Inversion of the Stokes
I and V profiles of the patch confirms this picture, revealing a
decreasing field strength and increasing height of the canopy base
from the core to the periphery of the network patch. However, the
non-roundish shape of the structure and the presence of negative area
and amplitude asymmetries reveal that the scenario is more complex than
a canonical flux tube expanding with height surrounded by downflows.
Title: Assessing the Behavior of Modern Solar Magnetographs and
Spectropolarimeters
Authors: Del Toro Iniesta, J. C.; Martínez Pillet, V.
Bibcode: 2012ApJS..201...22D
Altcode: 2012arXiv1205.4845D
The design and later use of modern spectropolarimeters and magnetographs
require a number of tolerance specifications that allow the developers
to build the instrument and then the scientists to interpret the data
accuracy. Such specifications depend both on device-specific features
and on the physical assumptions underlying the particular measurement
technique. Here we discuss general properties of every magnetograph,
such as the detectability thresholds for the vector magnetic field and
the line-of-sight velocity, as well as specific properties of a given
type of instrument, namely, that based on a pair of nematic liquid
crystal variable retarders and a Fabry-Pérot etalon (or several) for
carrying out the light polarization modulation and spectral analysis,
respectively. We derive formulae that give the detection thresholds
in terms of the signal-to-noise ratio of the observations and the
polarimetric efficiencies of the instrument. Relationships are also
established between inaccuracies in the solar physical quantities and
instabilities in the instrument parameters. Such relationships allow,
for example, one to translate scientific requirements for the velocity
or the magnetic field into requirements for temperature or voltage
stability. We also demonstrate that this type of magnetograph can
theoretically reach the optimum polarimetric efficiencies of an ideal
polarimeter, regardless of the optics in between the modulator and the
analyzer. Such optics induce changes in the instrument parameters that
are calculated.
Title: An active region filament studied simultaneously in the
chromosphere and photosphere. II. Doppler velocities
Authors: Kuckein, C.; Martínez Pillet, V.; Centeno, R.
Bibcode: 2012A&A...542A.112K
Altcode: 2012arXiv1204.5090K
Context. Paper I presents the magnetic structure, inferred for the
photosphere and the chromosphere, of a filament that developed in active
region (AR) NOAA 10781, observed on 2005 July 3 and July 5.
Aims: In this paper we complement those results with the velocities
retrieved from Doppler shifts measured at the chromosphere and the
photosphere in the AR filament area.
Methods: The velocities
and magnetic field parameters were inferred from full Stokes inversions
of the photospheric Si I 10 827 Å line and the chromospheric He i 10
830 Å triplet. Various inversion methods with different numbers of
atmospheric components and different weighting schemes of the Stokes
profiles were used. The velocities were calibrated on an absolute
scale.
Results: A ubiquitous chromospheric downflow is found
in the faculae surrounding the filament, with an average velocity of
1.6 km s-1. The filament region, however, displays upflows
in the photosphere on both days, when the linear polarization (which
samples the transverse component of the fields) is given more weight
in the inversions. The upflow speeds of the transverse fields in the
filament region average -0.15 km s-1. In the chromosphere,
the situation is different for the two days of observation. On July 3,
the chromospheric portion of the filament is moving upward as a whole
with a mean speed of -0.24 km s-1. However, on July 5 only
the section above an orphan penumbra shows localized upflow patches,
while the rest of the filament is dominated by the same downflows
observed elsewhere in the facular region. Photospheric supersonic
downflows that last for tens of minutes are detected below the filament,
close to the PIL.
Conclusions: The observed velocity pattern
in this AR filament strongly suggests a scenario where the transverse
fields are mostly dominated by upflows. The filament flux rope is seen
to be emerging at all places and both heights, with a few exceptions
in the chromosphere. This happens within a surrounding facular
region that displays a generalized downflow in the chromosphere and
localized downflows of supersonic character at the photosphere. No
large scale downflow of transverse field lines is observed at the
photosphere. Appendices A and B are available in electronic form
at http://www.aanda.org
Title: The ESA/NASA mission Solar Orbiter
Authors: Martínez Pillet, V.
Bibcode: 2012iac..talk..388M
Altcode: 2012iac..talk..305M
No abstract at ADS
Title: Division II: Sun and Heliosphere
Authors: Martínez Pillet, Valentín; Klimchuk, James A.; Melrose,
Donald B.; Cauzzi, Gianna; van Driel-Gesztelyi, Lidia; Gopalswamy,
Natchimuthuk; Kosovichev, Alexander; Mann, Ingrid; Schrijver,
Carolus J.
Bibcode: 2012IAUTA..28...61M
Altcode: 2012IAUTA..28...61P
The solar activity cycle entered a prolonged quiet phase that started
in 2008 and ended in 2010. This minimum lasted for a year longer
than expected and all activity proxies, as measured from Earth and
from Space, reached minimum values never observed before (de Toma,
2012). The number of spotless days from 2006 to 2009 totals 800, the
largest ever recorded in modern times. Solar irradiance was at historic
minimums. The interplanetary magnetic field was measured at values as
low as 2.9 nT and the cosmic rays were observed at records-high. While
rumors spread that the Sun could be entering a grand minimum quiet
phase (such as the Maunder minimum of the XVII century), activity
took over in 2010 and we are now well into Solar Cycle 24 (albeit,
probably, a low intensity cycle), approaching towards a maximum due
by mid 2013. In addition to bringing us the possibility to observe
a quiet state of the Sun and of the Heliosphere that was previously
not recorded with modern instruments, the Sun has also shown us how
little we know about the dynamo mechanism that drives its activity as
all solar cycle predictions failed to see this extended minimum coming.
Title: Solar magnetism eXplorer (SolmeX). Exploring the magnetic
field in the upper atmosphere of our closest star
Authors: Peter, Hardi; Abbo, L.; Andretta, V.; Auchère, F.; Bemporad,
A.; Berrilli, F.; Bommier, V.; Braukhane, A.; Casini, R.; Curdt,
W.; Davila, J.; Dittus, H.; Fineschi, S.; Fludra, A.; Gandorfer, A.;
Griffin, D.; Inhester, B.; Lagg, A.; Landi Degl'Innocenti, E.; Maiwald,
V.; Sainz, R. Manso; Martínez Pillet, V; Matthews, S.; Moses, D.;
Parenti, S.; Pietarila, A.; Quantius, D.; Raouafi, N. -E.; Raymond, J.;
Rochus, P.; Romberg, O.; Schlotterer, M.; Schühle, U.; Solanki, S.;
Spadaro, D.; Teriaca, L.; Tomczyk, S.; Trujillo Bueno, J.; Vial, J. -C.
Bibcode: 2012ExA....33..271P
Altcode: 2011arXiv1108.5304P; 2011ExA...tmp..134P
The magnetic field plays a pivotal role in many fields of
Astrophysics. This is especially true for the physics of the solar
atmosphere. Measuring the magnetic field in the upper solar atmosphere
is crucial to understand the nature of the underlying physical
processes that drive the violent dynamics of the solar corona—that
can also affect life on Earth. SolmeX, a fully equipped solar space
observatory for remote-sensing observations, will provide the first
comprehensive measurements of the strength and direction of the
magnetic field in the upper solar atmosphere. The mission consists
of two spacecraft, one carrying the instruments, and another one in
formation flight at a distance of about 200 m carrying the occulter to
provide an artificial total solar eclipse. This will ensure high-quality
coronagraphic observations above the solar limb. SolmeX integrates two
spectro-polarimetric coronagraphs for off-limb observations, one in
the EUV and one in the IR, and three instruments for observations on
the disk. The latter comprises one imaging polarimeter in the EUV for
coronal studies, a spectro-polarimeter in the EUV to investigate the low
corona, and an imaging spectro-polarimeter in the UV for chromospheric
studies. SOHO and other existing missions have investigated the emission
of the upper atmosphere in detail (not considering polarization),
and as this will be the case also for missions planned for the near
future. Therefore it is timely that SolmeX provides the final piece of
the observational quest by measuring the magnetic field in the upper
atmosphere through polarimetric observations.
Title: Solar Particle Acceleration Radiation and Kinetics (SPARK). A
mission to understand the nature of particle acceleration
Authors: Matthews, Sarah A.; Williams, David R.; Klein, Karl-Ludwig;
Kontar, Eduard P.; Smith, David M.; Lagg, Andreas; Krucker, Sam;
Hurford, Gordon J.; Vilmer, Nicole; MacKinnon, Alexander L.; Zharkova,
Valentina V.; Fletcher, Lyndsay; Hannah, Iain G.; Browning, Philippa
K.; Innes, Davina E.; Trottet, Gerard; Foullon, Clare; Nakariakov,
Valery M.; Green, Lucie M.; Lamoureux, Herve; Forsyth, Colin; Walton,
David M.; Mathioudakis, Mihalis; Gandorfer, Achim; Martinez-Pillet,
Valentin; Limousin, Olivier; Verwichte, Erwin; Dalla, Silvia; Mann,
Gottfried; Aurass, Henri; Neukirch, Thomas
Bibcode: 2012ExA....33..237M
Altcode: 2011ExA...tmp..124M
Energetic particles are critical components of plasma populations
found throughout the universe. In many cases particles are accelerated
to relativistic energies and represent a substantial fraction of
the total energy of the system, thus requiring extremely efficient
acceleration processes. The production of accelerated particles
also appears coupled to magnetic field evolution in astrophysical
plasmas through the turbulent magnetic fields produced by diffusive
shock acceleration. Particle acceleration is thus a key component
in helping to understand the origin and evolution of magnetic
structures in, e.g. galaxies. The proximity of the Sun and the range
of high-resolution diagnostics available within the solar atmosphere
offers unique opportunities to study the processes involved in particle
acceleration through the use of a combination of remote sensing
observations of the radiative signatures of accelerated particles, and
of their plasma and magnetic environment. The SPARK concept targets the
broad range of energy, spatial and temporal scales over which particle
acceleration occurs in the solar atmosphere, in order to determine how
and where energetic particles are accelerated. SPARK combines highly
complementary imaging and spectroscopic observations of radiation from
energetic electrons, protons and ions set in their plasma and magnetic
context. The payload comprises focusing-optics X-ray imaging covering
the range from 1 to 60 keV; indirect HXR imaging and spectroscopy
from 5 to 200 keV, γ-ray spectroscopic imaging with high-resolution
LaBr3 scintillators, and photometry and source localisation
at far-infrared wavelengths. The plasma environment of the regions
of acceleration and interaction will be probed using soft X-ray
imaging of the corona and vector magnetography of the photosphere
and chromosphere. SPARK is designed for solar research. However,
in addition it will be able to provide exciting new insights into the
origin of particle acceleration in other regimes, including terrestrial
gamma-ray flashes (TGF), the origin of γ-ray bursts, and the possible
existence of axions.
Title: Influence of phase-diversity image reconstruction techniques
on circular polarization asymmetries
Authors: Asensio Ramos, A.; Martínez González, M. J.; Khomenko,
E.; Martínez Pillet, V.
Bibcode: 2012A&A...539A..42A
Altcode: 2011arXiv1111.2496A
Context. Full Stokes filter-polarimeters are key instruments for
investigating the rapid evolution of magnetic structures on the solar
surface. To this end, the image quality is routinely improved using
a-posteriori image reconstruction methods.
Aims: We analyze
the robustness of circular polarization asymmetries to phase-diversity
image reconstruction techniques.
Methods: We used snapshots of
magneto-hydrodynamical simulations carried out with different initial
conditions to synthesize spectra of the magnetically sensitive Fe
i line at 5250.2 Å. We degraded the synthetic profiles spatially
and spectrally to simulate observations with the IMaX full Stokes
filter-polarimeter. We also simulated the focused/defocused pairs of
images used by the phase-diversity algorithm for reconstruction and the
polarimetric modulation scheme. We assume that standard optimization
methods are able to infer the projection of the wavefront on the Zernike
polynomials with 10% precision. We also consider the less favorable case
of 25% precision. We obtain reconstructed monochromatic modulated images
that are later demodulated and compared with the original maps.
Results: Although asymmetries are often difficult to define in the
quiet Sun due to the complexity of the Stokes V profiles, we show
how asymmetries are degraded with spatial and spectral smearing. The
results indicate that, although image reconstruction techniques reduce
the spatial smearing, they can modify the asymmetries of the profiles,
which are mainly caused by the appearance of spatially-correlated noise.
Title: Diffusivity of Isolated Internetwork Ca II H Bright Points
Observed by SuFI/SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Feller, A.;
Pietarila, A.; Lagg, A.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knoelker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A.
Bibcode: 2012decs.confE..99J
Altcode:
We analyze trajectories of the proper motion of intrinsically magnetic,
isolated internetwork Ca II H BPs (with mean lifetime of 461 sec) to
obtain their diffusivity behaviors. We use high spatial and temporal
resolution image sequences of quiet-Sun, disc-centre observations
obtained in the Ca II H 397 nm passband of the Sunrise Filter Imager
(SuFI) on board the SUNRISE balloon-borne solar observatory. In
order to avoid misidentification, the BPs are semi-manually selected
and then automatically tracked. The trajectory of each BP is then
calculated and its diffusion index is described by a power law
exponent, using which we classify the BPs' trajectories into sub-,
normal and super- diffusive. In addition, the corresponding diffusion
coefficients (D) based on the observed displacements are consequently
computed. We find a strong super-diffusivity at a height sampled by the
SuFI/SUNRISE Ca II H passband (i.e. a height corresponding roughly to
the temperature minimum). We find that 74% of the identified tiny BPs
are super-diffusive, 18% move randomly (i.e. their motion corresponds
to normal diffusion) and only 8% belong to the sub-diffusion regime. In
addition, we find that 53% of the super-diffusion regime (i.e. 39% of
all BPs) have the diffusivity index of 2 which are termed as "Ballistic
BPs". Finally, we explore the distribution of diffusion index with the
help of a simple simulation. The results suggest that the BPs are random
walkers superposed by a systematic (background) velocity in which the
magnitude of each component (and hence their ratio) depends on the time
and spatial scales. We further discuss a simple sketch to explain the
diffusivity of observed BPs while they migrate within a supergranule
(i.e. internetwork areas) or close to the network regions.
Title: Doppler velocities studied simultaneously in the chromosphere
and photosphere of an active region filament
Authors: Kuckein, C.; Martinez Pillet, V.; Centeno, R.
Bibcode: 2012decs.confE..42K
Altcode:
We present line-of-sight velocities retrieved simultaneously at
two different heights (chromosphere and photosphere) on two days
in an active region (AR) filament. The velocities, as well as the
magnetic field parameters, were inferred from full Stokes inversions
of the photospheric Si I 10827A line and the chromospheric He I 10830A
triplet. Various inversion methods with different number of components
and different weights of the Stokes parameters were used. Moreover,
the velocities were calibrated on an absolute scale. We found a
ubiquitous chromospheric downflow in the faculae surrounding the
AR filament with an average velocity of 1.6 km/s. However, in the
filament region, upflows in the photosphere were detected, when the
Stokes signals from the transverse fields are given more weight in the
inversions. In the chromosphere, the filament is also moving upward
as a whole with a mean speed of -0.24 km/s as deduced from the He I
inversions. However, on the second day the chromospheric portion above
an orphan penumbra shows localized upflow patches while the rest of the
filament is dominated by the same downflows observed elsewhere in the
plage region. Photospheric supersonic downflows are detected below the
filament, close to the PIL, that last for tens of minutes. The observed
velocities in this AR filament strongly suggest a scenario where the
transverse fields are mostly dominated by upflows. The filament flux
rope is seen to be emerging at all heights with a few exceptions in
the chromosphere. No large scale downflow of transverse field lines
is observed in the photosphere.
Title: An active region filament studied simultaneously in the
chromosphere and photosphere. I. Magnetic structure
Authors: Kuckein, C.; Martínez Pillet, V.; Centeno, R.
Bibcode: 2012A&A...539A.131K
Altcode: 2011arXiv1112.1672K
Aims: A thorough multiwavelength, multiheight study of the
vector magnetic field in a compact active region filament (NOAA 10781)
on 2005 July 3 and 5 is presented. We suggest an evolutionary scenario
for this filament.
Methods: Two different inversion codes were
used to analyze the full Stokes vectors acquired with the Tenerife
Infrared Polarimeter (TIP-II) in a spectral range that comprises the
chromospheric He i 10 830 Å multiplet and the photospheric Si i 10
827 Å line. In addition, we used SOHO/MDI magnetograms, as well as
BBSO and TRACE images, to study the evolution of the filament and its
active region (AR). High-resolution images of the Dutch Open Telescope
were also used.
Results: An active region filament (formed
before our observing run) was detected in the chromospheric helium
absorption images on July 3. The chromospheric vector magnetic field
in this portion of the filament was strongly sheared (parallel to the
filament axis), whereas the photospheric field lines underneath had
an inverse polarity configuration. From July 3 to July 5, an opening
and closing of the polarities on either side of the polarity inversion
line (PIL) was recorded, resembling the recently discovered process
of the sliding door effect seen by Hinode. This is confirmed with both
TIP-II and SOHO/MDI data. During this time, a newly created region that
contained pores and orphan penumbrae at the PIL was observed. On July
5, a normal polarity configuration was inferred from the chromospheric
spectra, while strongly sheared field lines aligned with the PIL were
found in the photosphere. In this same data set, the spine of the
filament is also observed in a different portion of the field of view
and is clearly mapped by the silicon line core.
Conclusions:
The inferred vector magnetic fields of the filament suggest a flux rope
topology. Furthermore, the observations indicate that the filament is
divided in two parts, one which lies in the chromosphere and another
one that stays trapped in the photosphere. Therefore, only the top
of the helical structure is seen by the helium lines. The pores and
orphan penumbrae at the PIL appear to be the photospheric counterpart
of the extremely low-lying filament. We suggest that orphan penumbrae
are formed in very narrow PILs of compact ARs and are the photospheric
manifestation of flux ropes in the photosphere.
Title: The Three-dimensional Structure of an Active Region Filament
as Extrapolated from Photospheric and Chromospheric Observations
Authors: Yelles Chaouche, L.; Kuckein, C.; Martínez Pillet, V.;
Moreno-Insertis, F.
Bibcode: 2012ApJ...748...23Y
Altcode: 2012arXiv1201.2456Y
The three-dimensional structure of an active region filament is studied
using nonlinear force-free field extrapolations based on simultaneous
observations at a photospheric and a chromospheric height. To that end,
we used the Si I 10827 Å line and the He I 10830 Å triplet obtained
with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope
(Tenerife). The two extrapolations have been carried out independently
from each other and their respective spatial domains overlap in
a considerable height range. This opens up new possibilities for
diagnostics in addition to the usual ones obtained through a single
extrapolation from, typically, a photospheric layer. Among those
possibilities, this method allows the determination of an average
formation height of the He I 10830 Å signal of ≈2 Mm above the
surface of the Sun. It allows, as well, a cross-check of the obtained
three-dimensional magnetic structures to verify a possible deviation
from the force-free condition, especially at the photosphere. The
extrapolations yield a filament formed by a twisted flux rope whose
axis is located at about 1.4 Mm above the solar surface. The twisted
field lines make slightly more than one turn along the filament within
our field of view, which results in 0.055 turns Mm-1. The
convex part of the field lines (as seen from the solar surface)
constitutes dips where the plasma can naturally be supported. The
obtained three-dimensional magnetic structure of the filament depends
on the choice of the observed horizontal magnetic field as determined
from the 180° solution of the azimuth. We derive a method to check
for the correctness of the selected 180° ambiguity solution.
Title: The Frontier between Small-scale Bipoles and Ephemeral Regions
in the Solar Photosphere: Emergence and Decay of an Intermediate-scale
Bipole Observed with SUNRISE/IMaX
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Bonet, J. A.;
del Toro Iniesta, J. Carlos; Bellot Rubio, L. R.; Solanki, S. K.;
Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M.
Bibcode: 2012ApJ...745..160G
Altcode: 2011arXiv1110.1405G
We report on the photospheric evolution of an intermediate-scale (≈4
Mm footpoint separation) magnetic bipole, from emergence to decay,
observed in the quiet Sun at high spatial (0farcs3) and temporal (33 s)
resolution. The observations were acquired by the Imaging Magnetograph
Experiment imaging magnetograph during the first science flight of the
SUNRISE balloon-borne solar observatory. The bipole flux content is 6 ×
1017 Mx, representing a structure bridging the gap between
granular scale bipoles and the smaller ephemeral regions. Footpoints
separate at a speed of 3.5 km s-1 and reach a maximum
distance of 4.5 Mm before the field dissolves. The evolution of the
bipole is revealed to be very dynamic: we found a proper motion of
the bipole axis and detected a change of the azimuth angle of 90° in
300 s, which may indicate the presence of some writhe in the emerging
structure. The overall morphology and behavior are in agreement with
previous analyses of bipolar structures emerging at the granular scale,
but we also found several similarities with emerging flux structures
at larger scales. The flux growth rate is 2.6 × 1015 Mx
s-1, while the mean decay rate is one order of magnitude
smaller. We describe in some detail the decay phase of the bipole
footpoints that includes break up into smaller structures, and
interaction with preexisting fields leading to cancellation, but it
appears to be dominated by an as-yet unidentified diffusive process
that removes most of the flux with an exponential flux decay curve. The
diffusion constant (8 × 102 km2 s-1)
associated with this decay is similar to the values used to describe
the large-scale diffusion in flux transport models.
Title: Magnetic field emergence in mesogranular-sized exploding
granules observed with sunrise/IMaX data
Authors: Palacios, J.; Blanco Rodríguez, J.; Vargas Domínguez, S.;
Domingo, V.; Martínez Pillet, V.; Bonet, J. A.; Bellot Rubio, L. R.;
Del Toro Iniesta, J. C.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
Berkefeld, T.; Schmidt, W.; Knölker, M.
Bibcode: 2012A&A...537A..21P
Altcode: 2011arXiv1110.4555P
We report on magnetic field emergences covering significant
areas of exploding granules. The balloon-borne mission Sunrise
provided high spatial and temporal resolution images of the solar
photosphere. Continuum images, longitudinal and transverse magnetic
field maps and Dopplergrams obtained by IMaX onboard Sunrise are
analyzed by local correlation traking (LCT), divergence calculation
and time slices, Stokes inversions and numerical simulations are also
employed. We characterize two mesogranular-scale exploding granules
where ~1018 Mx of magnetic flux emerges. The emergence
of weak unipolar longitudinal fields (~100 G) start with a single
visible magnetic polarity, occupying their respective granules' top
and following the granular splitting. After a while, mixed polarities
start appearing, concentrated in downflow lanes. The events last around
20 min. LCT analyses confirm mesogranular scale expansion, displaying
a similar pattern for all the physical properties, and divergence
centers match between all of them. We found a similar behaviour
with the emergence events in a numerical MHD simulation. Granule
expansion velocities are around 1 kms-1 while magnetic
patches expand at 0.65 kms-1. One of the analyzed events
evidences the emergence of a loop-like structure. Advection of
the emerging magnetic flux features is dominated by convective
motion resulting from the exploding granule due to the magnetic
field frozen in the granular plasma. Intensification of the
magnetic field occurs in the intergranular lanes, probably
because of being directed by the downflowing plasma. Movies
associated to Figs. 2-4 are available in electronic form at http://www.aanda.org
Title: Evolution of the fine structure of magnetic fields in the
quiet Sun: Combining Sunrise observations and modelling
Authors: Wiegelmann, T.; Solanki, S.; Borrero, J.; Martinez Pillet,
V.; Sunrise Team
Bibcode: 2011AGUFMSH41B..06W
Altcode:
Observations with the balloon borne SUNRISE/IMAX instrument provide
us with unprecedented high spatial resolution (pixel size 40 km)
measurements of the magnetic field in the photosphere of the quiet
Sun. To investigate the magnetic structure of the chromosphere and
corona we extrapolate these photospheric measurements into the upper
solar atmosphere and analyse a timeseries with a cadence of 33s. We find
that the majority of closed loops which reach into the chromosphere
or corona have one foot point in strong photospheric magnetic field
regions (B>300 G). Most loops are asymmetric and the weaker foot
point is often located in the internetwork. We find that the magnetic
connectivity of the loops changes rapidly with a typical recycling
time of about 2 min in the upper solar atmosphere and 14 min in the
photosphere. We discuss, to which extend the observed topological
changes can be interpreted as evidence for magnetic reconnection and
the relevance of these processes for coronal heating.
Title: Continuous upflow of material in an active region filament
from thephotosphere to the corona
Authors: Kuckein, C.; Centeno, R.; Martinez Pillet, V.
Bibcode: 2011hsa6.conf..636K
Altcode:
Using spectropolarimetric data of an Active Region (AR) filament
we have carried out inversions in order to infer vector magnetic
fields in the photosphere (Si I line) and in the chromosphere
(He I line). Our filament lies above the polarity inversion line
(PIL) situated close to disk center and presents strong Zeeman-like
signatures in both photospheric and chromospheric lines. Pore-like
formations with both polarities are identified in the continuum under
the PIL. The azimuth ambiguity is solved at both heights using the
AZAM code. A comparison between the photospheric and chromospheric
vector magnetic fields revealed that they are well aligned in some
areas of the filament. However, especially at chromospheric heights,
the magnetic field is mostly aligned with the dark threads of the
filament. Velocity signatures indicating upflows of field lines are
found at both heights. The combination of all these findings strongly
suggests an emerging flux rope scenario.
Title: Space-qualified liquid-crystal variable retarders for
wide-field-of-view coronagraphs
Authors: Uribe-Patarroyo, N.; Alvarez-Herrero, A.; García Parejo,
P.; Vargas, J.; Heredero, R. L.; Restrepo, R.; Martínez Pillet, V.;
del Toro Iniesta, J. C.; López, A.; Fineschi, S.; Capobianco, G.;
Georges, M.; López, M.; Boer, G.; Manolis, I.
Bibcode: 2011SPIE.8148E..10U
Altcode: 2011SPIE.8148E..31U
Liquid-crystal variable retarders (LCVRs) are an emergent technology
for space-based polarimeters, following its success as polarization
modulators in ground-based polarimeters and ellipsometers. Wide-field
double nematic LCVRs address the high angular sensitivity of nematic
LCVRs at some voltage regimes. We present a work in which wide-field
LCVRs were designed and built, which are suitable for wide-field-of-view
instruments such as polarimetric coronagraphs. A detailed model of
their angular acceptance was made, and we validated this technology
for space environmental conditions, including a campaign studying the
effects of gamma, proton irradiation, vibration and shock, thermo-vacuum
and ultraviolet radiation.
Title: Sunspots and Active Region Filaments: What do they have
in common?
Authors: Martinez Pillet, V.
Bibcode: 2011sdmi.confE...7M
Altcode:
Sunspots are preceded by a well documented and spectacular phase of
magnetic flux emergence, easy to idnetify in almost any spectral
range. This phase is followed by a more subtle process of flux
disappearance that includes diffusion and magnetic cancellation. The
decay phase coincides with the development of an active region filament
at the Neutral Line that slowly evolves and often gets spelled in
CME events. These Active Region filaments harbor field strengths
of several hundredths of Gauss which represent the strongest field
concentrations second only to the sunspots themselves. However, no
link between the sunspots and the Active Region filaments are known
to exists. The conditions under which these two ingredients of Active
Regions can indeed be related to each other will be reviewed in the
light of recent observations made in the He 10830 A spectral region.
Title: Ubiquitous quiet-Sun jets
Authors: Martínez Pillet, V.; Del Toro Iniesta, J. C.; Quintero
Noda, C.
Bibcode: 2011A&A...530A.111M
Altcode: 2011arXiv1104.5564M
Context. IMaX/Sunrise has recently reported the temporal evolution
of highly dynamic and strongly Doppler shifted Stokes V signals in
the quiet Sun.
Aims: We attempt to identify the same quiet-Sun
jets in the Hinode spectropolarimeter (SP) data set.
Methods:
We generate combinations of linear polarization magnetograms with blue-
and redshifted far-wing circular polarization magnetograms to allow an
easy identification of the quiet-Sun jets.
Results: The jets are
identified in the Hinode data where both red- and blueshifted cases
are often found in pairs. They appear next to regions of transverse
fields that exhibit quiet-Sun neutral lines. They also have a clear
tendency to occur in the outer boundary of the granules. These regions
always display highly displaced and anomalous Stokes V profiles.
Conclusions: The quiet Sun is pervaded with jets formed when new field
regions emerge at granular scales loaded with horizontal field lines
that interact with their surroundings. This interaction is suggestive
of some form of reconnection of the involved field lines that generates
the observed high speed flows.
Title: Continuous Upflow of Material in an Active Region Filament
from the Photosphere to the Corona
Authors: Kuckein, C.; Centeno, R.; Martínez Pillet, V.
Bibcode: 2011ASPC..437..275K
Altcode: 2010arXiv1010.4260K
Using spectropolarimetric data of an Active Region (AR) filament
we have carried out inversions in order to infer vector magnetic
fields in the photosphere (Si I line) and in the chromosphere
(He I line). Our filament lies above the polarity inversion line
(PIL) situated close to disk center and presents strong Zeeman-like
signatures in both photospheric and chromospheric lines. Pore-like
formations with both polarities are identified in the continuum under
the PIL. The azimuth ambiguity is solved at both heights using the
AZAM code. A comparison between the photospheric and chromospheric
vector magnetic fields revealed that they are well aligned in some
areas of the filament. However, especially at chromospheric heights,
the magnetic field is mostly aligned with the dark threads of the
filament. Velocity signatures indicating upflows of field lines are
found at both heights. The combination of all these findings strongly
suggests an emerging flux rope scenario.
Title: Unnoticed Magnetic Field Oscillations in the Very Quiet Sun
Revealed by SUNRISE/IMaX
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
R.; Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; López Ariste,
A.; Schmidt, W.; Barthol, P.; Gandorfer, A.
Bibcode: 2011ApJ...730L..37M
Altcode: 2011arXiv1103.0145M
We present observational evidence for oscillations of magnetic flux
density in the quiet areas of the Sun. The majority of magnetic
fields on the solar surface have strengths of the order of or lower
than the equipartition field (300-500 G). This results in a myriad of
magnetic fields whose evolution is largely determined by the turbulent
plasma motions. When granules evolve they squash the magnetic field
lines together or pull them apart. Here, we report on the periodic
deformation of the shapes of features in circular polarization observed
at high resolution with SUNRISE. In particular, we note that the
area of patches with a constant magnetic flux oscillates with time,
which implies that the apparent magnetic field intensity oscillates
in antiphase. The periods associated with this oscillatory pattern
are compatible with the granular lifetime and change abruptly, which
suggests that these oscillations might not correspond to characteristic
oscillatory modes of magnetic structures, but to the forcing by granular
motions. In one particular case, we find three patches around the same
granule oscillating in phase, which means that the spatial coherence
of these oscillations can reach 1600 km. Interestingly, the same kind
of oscillatory phenomenon is also found in the upper photosphere.
Title: Mesogranulation and the Solar Surface Magnetic Field
Distribution
Authors: Yelles Chaouche, L.; Moreno-Insertis, F.; Martínez Pillet,
V.; Wiegelmann, T.; Bonet, J. A.; Knölker, M.; Bellot Rubio, L. R.;
del Toro Iniesta, J. C.; Barthol, P.; Gandorfer, A.; Schmidt, W.;
Solanki, S. K.
Bibcode: 2011ApJ...727L..30Y
Altcode: 2010arXiv1012.4481Y
The relation of the solar surface magnetic field with mesogranular
cells is studied using high spatial (≈100 km) and temporal (≈30
s) resolution data obtained with the IMaX instrument on board
SUNRISE. First, mesogranular cells are identified using Lagrange
tracers (corks) based on horizontal velocity fields obtained through
local correlation tracking. After ≈20 minutes of integration, the
tracers delineate a sharp mesogranular network with lanes of width
below about 280 km. The preferential location of magnetic elements in
mesogranular cells is tested quantitatively. Roughly 85% of pixels with
magnetic field higher than 100 G are located in the near neighborhood
of mesogranular lanes. Magnetic flux is therefore concentrated in
mesogranular lanes rather than intergranular ones. Second, magnetic
field extrapolations are performed to obtain field lines anchored in
the observed flux elements. This analysis, therefore, is independent
of the horizontal flows determined in the first part. A probability
density function (PDF) is calculated for the distribution of distances
between the footpoints of individual magnetic field lines. The PDF has
an exponential shape at scales between 1 and 10 Mm, with a constant
characteristic decay distance, indicating the absence of preferred
convection scales in the mesogranular range. Our results support
the view that mesogranulation is not an intrinsic convective scale
(in the sense that it is not a primary energy-injection scale of solar
convection), but also give quantitative confirmation that, nevertheless,
the magnetic elements are preferentially found along mesogranular lanes.
Title: The Solar Orbiter Mission and its Polarimetric and Helioseismic
Imager (SO/PHI)
Authors: Gandorfer, Achim; Solanki, Sami K.; Woch, Joachim; Martínez
Pillet, Valentin; Álvarez Herrero, Alberto; Appourchaux, Thierry
Bibcode: 2011JPhCS.271a2086G
Altcode:
We briefly outline the scientific and instrumental aspects of ESA's
Solar Orbiter mission. Special emphasis is given to the Polarimetric
and Helioseismic Imager, the instrument with the highest relevance for
helioseismology applications, which will observe gas motions and the
vector magnetic field in the photosphere at high spatial and temporal
resolution.
Title: The Imaging Magnetograph eXperiment (IMaX) for the Sunrise
Balloon-Borne Solar Observatory
Authors: Martínez Pillet, V.; del Toro Iniesta, J. C.;
Álvarez-Herrero, A.; Domingo, V.; Bonet, J. A.; González Fernández,
L.; López Jiménez, A.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.;
Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer,
T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados, M.; Deutsch, W.;
Feller, A.; Girela, F.; Grauf, B.; Heredero, R. L.; Herranz, M.;
Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.;
Orozco Suárez, D.; Ramos, G.; Reina, M.; Ramos, J. L.; Rodríguez,
P.; Sánchez, A.; Uribe-Patarroyo, N.; Barthol, P.; Gandorfer, A.;
Knoelker, M.; Schmidt, W.; Solanki, S. K.; Vargas Domínguez, S.
Bibcode: 2011SoPh..268...57M
Altcode: 2010SoPh..tmp..181M; 2010arXiv1009.1095M
The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter
built by four institutions in Spain that flew on board the Sunrise
balloon-borne solar observatory in June 2009 for almost six days over
the Arctic Circle. As a polarimeter, IMaX uses fast polarization
modulation (based on the use of two liquid crystal retarders),
real-time image accumulation, and dual-beam polarimetry to reach
polarization sensitivities of 0.1%. As a spectrograph, the instrument
uses a LiNbO3 etalon in double pass and a narrow band
pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the
high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four
Stokes parameters at various points inside the spectral line. This
allows vector magnetograms, Dopplergrams, and intensity frames to be
produced that, after reconstruction, reach spatial resolutions in the
0.15 - 0.18 arcsec range over a 50×50 arcsec field of view. Time
cadences vary between 10 and 33 s, although the shortest one only
includes longitudinal polarimetry. The spectral line is sampled in
various ways depending on the applied observing mode, from just two
points inside the line to 11 of them. All observing modes include
one extra wavelength point in the nearby continuum. Gauss equivalent
sensitivities are 4 G for longitudinal fields and 80 G for transverse
fields per wavelength sample. The line-of-sight velocities are estimated
with statistical errors of the order of 5 - 40 m s−1. The
design, calibration, and integration phases of the instrument,
together with the implemented data reduction scheme, are described in
some detail.
Title: The Wave-Front Correction System for the Sunrise Balloon-Borne
Solar Observatory
Authors: Berkefeld, T.; Schmidt, W.; Soltau, D.; Bell, A.;
Doerr, H. P.; Feger, B.; Friedlein, R.; Gerber, K.; Heidecke, F.;
Kentischer, T.; v. d. Lühe, O.; Sigwarth, M.; Wälde, E.; Barthol,
P.; Deutsch, W.; Gandorfer, A.; Germerott, D.; Grauf, B.; Meller, R.;
Álvarez-Herrero, A.; Knölker, M.; Martínez Pillet, V.; Solanki,
S. K.; Title, A. M.
Bibcode: 2011SoPh..268..103B
Altcode: 2010SoPh..tmp..236B; 2010arXiv1009.3196B
This paper describes the wave-front correction system developed for
the Sunrise balloon telescope, and it provides information about its
in-flight performance. For the correction of low-order aberrations,
a Correlating Wave-Front Sensor (CWS) was used. It consisted of a
six-element Shack - Hartmann wave-front sensor (WFS), a fast tip-tilt
mirror for the compensation of image motion, and an active telescope
secondary mirror for focus correction. The CWS delivered a stabilized
image with a precision of 0.04 arcsec (rms), whenever the coarse
pointing was better than ± 45 arcsec peak-to-peak. The automatic
focus adjustment maintained a focus stability of 0.01 waves in the
focal plane of the CWS. During the 5.5 day flight, good image quality
and stability were achieved during 33 hours, containing 45 sequences,
which lasted between 10 and 45 min.
Title: The Sunrise Mission
Authors: Barthol, P.; Gandorfer, A.; Solanki, S. K.; Schüssler,
M.; Chares, B.; Curdt, W.; Deutsch, W.; Feller, A.; Germerott, D.;
Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.; Meller, R.;
Müller, R.; Riethmüller, T. L.; Tomasch, G.; Knölker, M.; Lites,
B. W.; Card, G.; Elmore, D.; Fox, J.; Lecinski, A.; Nelson, P.;
Summers, R.; Watt, A.; Martínez Pillet, V.; Bonet, J. A.; Schmidt,
W.; Berkefeld, T.; Title, A. M.; Domingo, V.; Gasent Blesa, J. L.;
del Toro Iniesta, J. C.; López Jiménez, A.; Álvarez-Herrero, A.;
Sabau-Graziati, L.; Widani, C.; Haberler, P.; Härtel, K.; Kampf,
D.; Levin, T.; Pérez Grande, I.; Sanz-Andrés, A.; Schmidt, E.
Bibcode: 2011SoPh..268....1B
Altcode: 2010arXiv1009.2689B; 2010SoPh..tmp..224B
The first science flight of the balloon-borne Sunrise telescope took
place in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset
Island in northern Canada. We describe the scientific aims and
mission concept of the project and give an overview and a description
of the various hardware components: the 1-m main telescope with its
postfocus science instruments (the UV filter imager SuFI and the imaging
vector magnetograph IMaX) and support instruments (image stabilizing
and light distribution system ISLiD and correlating wavefront sensor
CWS), the optomechanical support structure and the instrument mounting
concept, the gondola structure and the power, pointing, and telemetry
systems, and the general electronics architecture. We also explain
the optimization of the structural and thermal design of the complete
payload. The preparations for the science flight are described,
including AIV and ground calibration of the instruments. The course
of events during the science flight is outlined, up to the recovery
activities. Finally, the in-flight performance of the instrumentation
is discussed.
Title: The Filter Imager SuFI and the Image Stabilization and Light
Distribution System ISLiD of the Sunrise Balloon-Borne Observatory:
Instrument Description
Authors: Gandorfer, A.; Grauf, B.; Barthol, P.; Riethmüller, T. L.;
Solanki, S. K.; Chares, B.; Deutsch, W.; Ebert, S.; Feller, A.;
Germerott, D.; Heerlein, K.; Heinrichs, J.; Hirche, D.; Hirzberger,
J.; Kolleck, M.; Meller, R.; Müller, R.; Schäfer, R.; Tomasch,
G.; Knölker, M.; Martínez Pillet, V.; Bonet, J. A.; Schmidt, W.;
Berkefeld, T.; Feger, B.; Heidecke, F.; Soltau, D.; Tischenberg, A.;
Fischer, A.; Title, A.; Anwand, H.; Schmidt, E.
Bibcode: 2011SoPh..268...35G
Altcode: 2010SoPh..tmp..176G; 2010arXiv1009.1037G
We describe the design of the Sunrise Filter Imager (SuFI) and the
Image Stabilization and Light Distribution (ISLiD) unit onboard the
Sunrise balloon borne solar observatory. This contribution provides the
necessary information which is relevant to understand the instruments'
working principles, the relevant technical data, and the necessary
information about calibration issues directly related to the science
data.
Title: SUNRISE: Instrument, Mission, Data, and First Results
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
Gandorfer, A.; Hirzberger, J.; Riethmüller, T. L.; Schüssler, M.;
Bonet, J. A.; Martínez Pillet, V.; del Toro Iniesta, J. C.; Domingo,
V.; Palacios, J.; Knölker, M.; Bello González, N.; Berkefeld, T.;
Franz, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.127S
Altcode: 2010arXiv1008.3460S
The SUNRISE balloon-borne solar observatory consists of a 1 m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system, and further infrastructure. The first
science flight of SUNRISE yielded high-quality data that revealed the
structure, dynamics, and evolution of solar convection, oscillations,
and magnetic fields at a resolution of around 100 km in the quiet
Sun. After a brief description of instruments and data, the first
qualitative results are presented. In contrast to earlier observations,
we clearly see granulation at 214 nm. Images in Ca II H display narrow,
short-lived dark intergranular lanes between the bright edges of
granules. The very small-scale, mixed-polarity internetwork fields
are found to be highly dynamic. A significant increase in detectable
magnetic flux is found after phase-diversity-related reconstruction
of polarization maps, indicating that the polarities are mixed right
down to the spatial resolution limit and probably beyond.
Title: Supersonic Magnetic Upflows in Granular Cells Observed with
SUNRISE/IMAX
Authors: Borrero, J. M.; Martínez-Pillet, V.; Schlichenmaier, R.;
Solanki, S. K.; Bonet, J. A.; del Toro Iniesta, J. C.; Schmidt, W.;
Barthol, P.; Gandorfer, A.; Domingo, V.; Knölker, M.
Bibcode: 2010ApJ...723L.144B
Altcode: 2010arXiv1009.1227B
Using the IMaX instrument on board the SUNRISE stratospheric balloon
telescope, we have detected extremely shifted polarization signals
around the Fe I 5250.217 Å spectral line within granules in the solar
photosphere. We interpret the velocities associated with these events
as corresponding to supersonic and magnetic upflows. In addition, they
are also related to the appearance of opposite polarities and highly
inclined magnetic fields. This suggests that they are produced by the
reconnection of emerging magnetic loops through granular upflows. The
events occupy an average area of 0.046 arcsec2 and last for
about 80 s, with larger events having longer lifetimes. These supersonic
events occur at a rate of 1.3 × 10-5 occurrences per second
per arcsec2.
Title: Detection of Vortex Tubes in Solar Granulation from
Observations with SUNRISE
Authors: Steiner, O.; Franz, M.; Bello González, N.; Nutto, Ch.;
Rezaei, R.; Martínez Pillet, V.; Bonet Navarro, J. A.; del Toro
Iniesta, J. C.; Domingo, V.; Solanki, S. K.; Knölker, M.; Schmidt,
W.; Barthol, P.; Gandorfer, A.
Bibcode: 2010ApJ...723L.180S
Altcode: 2010arXiv1009.4723S
We have investigated a time series of continuum intensity maps and
corresponding Dopplergrams of granulation in a very quiet solar region
at the disk center, recorded with the Imaging Magnetograph eXperiment
(IMaX) on board the balloon-borne solar observatory SUNRISE. We
find that granules frequently show substructure in the form of lanes
composed of a leading bright rim and a trailing dark edge, which move
together from the boundary of a granule into the granule itself. We
find strikingly similar events in synthesized intensity maps from an
ab initio numerical simulation of solar surface convection. From cross
sections through the computational domain of the simulation, we conclude
that these granular lanes are the visible signature of (horizontally
oriented) vortex tubes. The characteristic optical appearance of vortex
tubes at the solar surface is explained. We propose that the observed
vortex tubes may represent only the large-scale end of a hierarchy of
vortex tubes existing near the solar surface.
Title: Where the Granular Flows Bend
Authors: Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; del Toro
Iniesta, J. C.; Gandorfer, A.; Bonet, J. A.; Domingo, V.; Schmidt,
W.; Barthol, P.; Knölker, M.
Bibcode: 2010ApJ...723L.159K
Altcode: 2010arXiv1008.0517K
Based on IMaX/SUNRISE data, we report on a previously undetected
phenomenon in solar granulation. We show that in a very narrow region
separating granules and intergranular lanes, the spectral line width
of the Fe I 5250.2 Å line becomes extremely small. We offer an
explanation of this observation with the help of magneto-convection
simulations. These regions with extremely small line widths correspond
to the places where the granular flows bend from upflow in granules
to downflow in intergranular lanes. We show that the resolution and
image stability achieved by IMaX/SUNRISE are important requisites to
detect this interesting phenomenon.
Title: Bright Points in the Quiet Sun as Observed in the Visible
and Near-UV by the Balloon-borne Observatory SUNRISE
Authors: Riethmüller, T. L.; Solanki, S. K.; Martínez Pillet, V.;
Hirzberger, J.; Feller, A.; Bonet, J. A.; Bello González, N.; Franz,
M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; del Toro Iniesta,
J. C.; Domingo, V.; Gandorfer, A.; Knölker, M.; Schmidt, W.
Bibcode: 2010ApJ...723L.169R
Altcode: 2010arXiv1009.1693R
Bright points (BPs) are manifestations of small magnetic elements
in the solar photosphere. Their brightness contrast not only gives
insight into the thermal state of the photosphere (and chromosphere) in
magnetic elements, but also plays an important role in modulating the
solar total and spectral irradiance. Here, we report on simultaneous
high-resolution imaging and spectropolarimetric observations of
BPs using SUNRISE balloon-borne observatory data of the quiet Sun
at the disk center. BP contrasts have been measured between 214 nm
and 525 nm, including the first measurements at wavelengths below
388 nm. The histograms of the BP peak brightness show a clear trend
toward broader contrast distributions and higher mean contrasts at
shorter wavelengths. At 214 nm, we observe a peak brightness of up to
five times the mean quiet-Sun value, the highest BP contrast so far
observed. All BPs are associated with a magnetic signal, although in
a number of cases it is surprisingly weak. Most of the BPs show only
weak downflows, the mean value being 240 m s-1, but some
display strong down- or upflows reaching a few km s-1.
Title: Transverse Component of the Magnetic Field in the Solar
Photosphere Observed by SUNRISE
Authors: Danilovic, S.; Beeck, B.; Pietarila, A.; Schüssler, M.;
Solanki, S. K.; Martínez Pillet, V.; Bonet, J. A.; del Toro Iniesta,
J. C.; Domingo, V.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.149D
Altcode: 2010arXiv1008.1535D
We present the first observations of the transverse component of
a photospheric magnetic field acquired by the imaging magnetograph
SUNRISE/IMaX. Using an automated detection method, we obtain statistical
properties of 4536 features with significant linear polarization
signal. We obtain a rate of occurrence of 7 × 10-4
s-1 arcsec-2, which is 1-2 orders of magnitude
larger than the values reported by previous studies. We show that
these features have no characteristic size or lifetime. They appear
preferentially at granule boundaries with most of them being caught
in downflow lanes at some point. Only a small percentage are entirely
and constantly embedded in upflows (16%) or downflows (8%).
Title: Detection of Large Acoustic Energy Flux in the Solar Atmosphere
Authors: Bello González, N.; Franz, M.; Martínez Pillet, V.; Bonet,
J. A.; Solanki, S. K.; del Toro Iniesta, J. C.; Schmidt, W.; Gandorfer,
A.; Domingo, V.; Barthol, P.; Berkefeld, T.; Knölker, M.
Bibcode: 2010ApJ...723L.134B
Altcode: 2010arXiv1009.4795B
We study the energy flux carried by acoustic waves excited by convective
motions at sub-photospheric levels. The analysis of high-resolution
spectropolarimetric data taken with IMaX/SUNRISE provides a total
energy flux of ~6400-7700 W m-2 at a height of ~250 km
in the 5.2-10 mHz range, i.e., at least twice the largest energy
flux found in previous works. Our estimate lies within a factor of
two of the energy flux needed to balance radiative losses from the
chromosphere according to the estimates of Anderson & Athay and
revives interest in acoustic waves for transporting energy to the
chromosphere. The acoustic flux is mainly found in the intergranular
lanes but also in small rapidly evolving granules and at the bright
borders, forming dark dots and lanes of splitting granules.
Title: Magnetic Loops in the Quiet Sun
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Martínez
Pillet, V.; del Toro Iniesta, J. C.; Domingo, V.; Bonet, J. A.;
Barthol, P.; Gandorfer, A.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.185W
Altcode: 2010arXiv1009.4715W
We investigate the fine structure of magnetic fields in the atmosphere
of the quiet Sun. We use photospheric magnetic field measurements from
SUNRISE/IMaX with unprecedented spatial resolution to extrapolate
the photospheric magnetic field into higher layers of the solar
atmosphere with the help of potential and force-free extrapolation
techniques. We find that most magnetic loops that reach into the
chromosphere or higher have one footpoint in relatively strong magnetic
field regions in the photosphere. Ninety-one percent of the magnetic
energy in the mid-chromosphere (at a height of 1 Mm) is in field
lines, whose stronger footpoint has a strength of more than 300 G,
i.e., above the equipartition field strength with convection. The
loops reaching into the chromosphere and corona are also found to be
asymmetric in the sense that the weaker footpoint has a strength B <
300 G and is located in the internetwork (IN). Such loops are expected
to be strongly dynamic and have short lifetimes, as dictated by the
properties of the IN fields.
Title: SUNRISE/IMaX Observations of Convectively Driven Vortex Flows
in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Palacios,
J.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.;
Domingo, V.; Berkefeld, T.; Schmidt, W.; Gandorfer, A.; Barthol, P.;
Knölker, M.
Bibcode: 2010ApJ...723L.139B
Altcode: 2010arXiv1009.1992B
We characterize the observational properties of the convectively driven
vortex flows recently discovered on the quiet Sun, using magnetograms,
Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE
telescope. By visual inspection of time series, we find some 3.1
× 10-3 vortices Mm-2 minute-1,
which is a factor of ~1.7 larger than previous estimates. The mean
duration of the individual events turns out to be 7.9 minutes, with
a standard deviation of 3.2 minutes. In addition, we find several
events appearing at the same locations along the duration of the time
series (31.6 minutes). Such recurrent vortices show up in the proper
motion flow field map averaged over the time series. The typical
vertical vorticities are lsim6 × 10-3 s-1,
which corresponds to a period of rotation of some 35 minutes. The
vortices show a preferred counterclockwise sense of rotation, which
we conjecture may have to do with the preferred vorticity impinged by
the solar differential rotation.
Title: Retrieval of solar magnetic fields from high-spatial resolution
filtergraph data: the Imaging Magnetograph eXperiment (IMaX)
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Martínez Pillet,
V.; Bonet, J. A.; Vargas Domínguez, S.; Del Toro Iniesta, J. C.
Bibcode: 2010A&A...522A.101O
Altcode: 2010arXiv1006.5510O
Context. The design of modern instruments does not only imply thorough
studies of instrumental effects but also a good understanding of the
scientific analysis planned for the data.
Aims: We investigate
the reliability of Milne-Eddington (ME) inversions of high-resolution
magnetograph measurements such as those to be obtained with the Imaging
Magnetograph eXperiment (IMaX) aboard the Sunrise balloon. We also
provide arguments to choose either Fe I 525.02 or 525.06 nm as the
most suitable line for IMaX.
Methods: We reproduce an IMaX
observation using magnetoconvection simulations of the quiet Sun
and synthesizing the four Stokes profiles emerging from them. The
profiles are degraded by spatial and spectral resolution, noise,
and limited wavelength sampling, just as real IMaX measurements. We
invert these data and estimate the uncertainties in the retrieved
physical parameters caused by the ME approximation and the spectral
sampling.
Results: It is possible to infer the magnetic field
strength, inclination, azimuth, and line-of-sight velocity from
standard IMaX measurements (4 Stokes parameters, 5 wavelength points,
and a signal-to-noise ratio of 1000) applying ME inversions to any
of the Fe I lines at 525 nm. We also find that telescope diffraction
has important effects on the spectra coming from very high resolution
observations of inhomogeneous atmospheres. Diffration reduces the
amplitude of the polarization signals and changes the asymmetry of
the Stokes profiles.
Conclusions: The two Fe I lines at 525 nm
meet the scientific requirements of IMaX, but Fe I 525.02 nm is to be
preferred because it leads to smaller uncertainties in the retrieved
parameters and offers a better detectability of the weakest (linear)
polarization signals prevailing in the quiet Sun.
Title: Surface Waves in Solar Granulation Observed with SUNRISE
Authors: Roth, M.; Franz, M.; Bello González, N.; Martínez Pillet,
V.; Bonet, J. A.; Gandorfer, A.; Barthol, P.; Solanki, S. K.;
Berkefeld, T.; Schmidt, W.; del Toro Iniesta, J. C.; Domingo, V.;
Knölker, M.
Bibcode: 2010ApJ...723L.175R
Altcode: 2010arXiv1009.4790R
Solar oscillations are expected to be excited by turbulent flows in
the intergranular lanes near the solar surface. Time series recorded
by the IMaX instrument on board the SUNRISE observatory reveal solar
oscillations at high spatial resolution, which allow the study of
the properties of oscillations with short wavelengths. We analyze
two time series with synchronous recordings of Doppler velocity and
continuum intensity images with durations of 32 minutes and 23 minutes,
respectively, recorded close to the disk center of the Sun to study
the propagation and excitation of solar acoustic oscillations. In
the Doppler velocity data, both the standing acoustic waves and the
short-lived, high-degree running waves are visible. The standing
waves are visible as temporary enhancements of the amplitudes of the
large-scale velocity field due to the stochastic superposition of
the acoustic waves. We focus on the high-degree small-scale waves by
suitable filtering in the Fourier domain. Investigating the propagation
and excitation of f- and p 1-modes with wavenumbers k>1.4
Mm-1, we also find that exploding granules contribute to
the excitation of solar p-modes in addition to the contribution of
intergranular lanes.
Title: Fully Resolved Quiet-Sun Magnetic flux Tube Observed with
the SUNRISE/IMAX Instrument
Authors: Lagg, A.; Solanki, S. K.; Riethmüller, T. L.; Martínez
Pillet, V.; Schüssler, M.; Hirzberger, J.; Feller, A.; Borrero,
J. M.; Schmidt, W.; del Toro Iniesta, J. C.; Bonet, J. A.; Barthol, P.;
Berkefeld, T.; Domingo, V.; Gandorfer, A.; Knölker, M.; Title, A. M.
Bibcode: 2010ApJ...723L.164L
Altcode: 2010arXiv1009.0996L
Until today, the small size of magnetic elements in quiet-Sun areas has
required the application of indirect methods, such as the line-ratio
technique or multi-component inversions, to infer their physical
properties. A consistent match to the observed Stokes profiles could
only be obtained by introducing a magnetic filling factor that specifies
the fraction of the observed pixel filled with magnetic field. Here,
we investigate the properties of a small magnetic patch in the quiet
Sun observed with the IMaX magnetograph on board the balloon-borne
telescope SUNRISE with unprecedented spatial resolution and low
instrumental stray light. We apply an inversion technique based on
the numerical solution of the radiative transfer equation to retrieve
the temperature stratification and the field strength in the magnetic
patch. The observations can be well reproduced with a one-component,
fully magnetized atmosphere with a field strength exceeding 1 kG and
a significantly enhanced temperature in the mid to upper photosphere
with respect to its surroundings, consistent with semi-empirical flux
tube models for plage regions. We therefore conclude that, within the
framework of a simple atmospheric model, the IMaX measurements resolve
the observed quiet-Sun flux tube.
Title: Quiet-sun Intensity Contrasts in the Near-ultraviolet as
Measured from SUNRISE
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Schüssler,
M.; Borrero, J. M.; Afram, N.; Unruh, Y. C.; Berdyugina, S. V.;
Gandorfer, A.; Solanki, S. K.; Barthol, P.; Bonet, J. A.; Martínez
Pillet, V.; Berkefeld, T.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.154H
Altcode:
We present high-resolution images of the Sun in the near-ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1 m SUNRISE balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range are
among the highest values ever obtained for quiet-Sun solar surface
structures—up to 32.8% at a wavelength of 214 nm. We compare the
rms contrasts obtained from the observational data with theoretical
intensity contrasts obtained from numerical magnetohydrodynamic
simulations. For 388 nm and 312 nm the observations agree well with
the numerical simulations whereas at shorter wavelengths discrepancies
between observed and simulated contrasts remain.
Title: The Electrical Current Density Vector in the Inner Penumbra
of a Sunspot
Authors: Puschmann, K. G.; Ruiz Cobo, B.; Martínez Pillet, V.
Bibcode: 2010ApJ...721L..58P
Altcode: 2010arXiv1008.2131P
We determine the entire electrical current density vector in a
geometrical three-dimensional volume of the inner penumbra of a
sunspot from an inversion of spectropolarimetric data obtained with
Hinode/SP. Significant currents are seen to wrap around the hotter,
more elevated regions with lower and more horizontal magnetic fields
that harbor strong upflows and radial outflows (the intraspines). The
horizontal component of the current density vector is 3-4 times larger
than the vertical; nearly all previous studies only obtain the vertical
component Jz , thus strongly underestimating the current
density. The current density \vec{J} and the magnetic field \vec{B}
form an angle of about 20°. The plasma β at the 0 km level is larger
than 1 in the intraspines and is one order of magnitude lower in the
background component of the penumbra (spines). At the 200 km level,
the plasma β is below 0.3, nearly everywhere. The plasma β surface
as well as the surface optical depth unity is very corrugated. At the
borders of intraspines and inside, \vec{B} is not force-free at deeper
layers and nearly force-free at the top layers. The magnetic field of
the spines is close to being potential everywhere. The dissipated ohmic
energy is five orders of magnitudes smaller than the solar energy flux
and thus negligible for the energy balance of the penumbra.
Title: A Geometrical Height Scale for Sunspot Penumbrae
Authors: Puschmann, K. G.; Ruiz Cobo, B.; Martínez Pillet, V.
Bibcode: 2010ApJ...720.1417P
Altcode: 2010arXiv1007.2779P
Inversions of spectropolarimetric observations of penumbral filaments
deliver the stratification of different physical quantities in an
optical depth scale. However, without establishing a geometrical
height scale, their three-dimensional geometrical structure cannot
be derived. This is crucial in understanding the correct spatial
variation of physical properties in the penumbral atmosphere and to
provide insights into the mechanism capable of explaining the observed
penumbral brightness. The aim of this work is to determine a global
geometrical height scale in the penumbra by minimizing the divergence of
the magnetic field vector and the deviations from static equilibrium as
imposed by a force balance equation that includes pressure gradients,
gravity, and the Lorentz force. Optical depth models are derived from
the inversion of spectropolarimetric data of an active region observed
with the Solar Optical Telescope on board the Hinode satellite. We
use a genetic algorithm to determine the boundary condition for the
inference of geometrical heights. The retrieved geometrical height
scale permits the evaluation of the Wilson depression at each pixel and
the correlation of physical quantities at each height. Our results fit
into the uncombed penumbral scenario, i.e., a penumbra composed of flux
tubes with channeled mass flow and with a weaker and more horizontal
magnetic field as compared with the background field. The ascending
material is hotter and denser than their surroundings. We do not find
evidence of overturning convection or field-free regions in the inner
penumbral area analyzed. The penumbral brightness can be explained by
the energy transfer of the ascending mass carried by the Evershed flow,
if the physical quantities below z = -75 km are extrapolated from the
results of the inversion.
Title: Quiet-Sun intensity contrasts in the near ultraviolet
Authors: Hirzberger, Johann; Feller, Alex; Riethmüller, Tino L.;
Schüssler, Manfred; Borrero, Juan M.; Afram, Nadine; Unruh, Yvonne C.;
Berdyugina, Svetlana V.; Gandorfer, Achim; Solanki, Sami K.; Barthol,
Peter; Bonet, Jose A.; Martínez Pillet, Valentin; Berkefeld, Thomas;
Knölker, Michael; Schmidt, Wolfgang; Title, Alan M.
Bibcode: 2010arXiv1009.1050H
Altcode:
We present high-resolution images of the Sun in the near ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1-m Sunrise balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range
are among the highest values ever obtained for quiet-Sun solar
surface structures - up to 32.8% at a wavelength of 214 nm. We
compare with theoretical intensity contrasts obtained from numerical
magneto-hydrodynamic simulations. For 388 nm and 312 nm the observations
agree well with the numerical simulations whereas at shorter wavelengths
discrepancies between observed and simulated contrasts remain.
Title: Flight control software for the wave-front sensor of SUNRISE
1m balloon telescope
Authors: Bell, Alexander; Barthol, Peter; Berkefeld, Thomas; Feger,
Bernhard; Gandorfer, Achim M.; Heidecke, Frank; Knoelker, Michael;
Martinez Pillet, Valentin; Schmidt, Wolfgang; Sigwarth, Michael;
Solanki, Sami K.; Soltau, Dirk; Title, Alan M.
Bibcode: 2010SPIE.7740E..03B
Altcode: 2010SPIE.7740E...2B
This paper describes the flight control software of the wave-front
correction system that flew on the 2009 science flight of the Sunrise
balloon telescope. The software discussed here allowed fully automated
operations of the wave-front sensor, communications with the adaptive
optics sub-system, the pointing system, the instrument control unit
and the main telescope controller. The software was developed using
modern object oriented analysis and design techniques, and consists
of roughly 13.000 lines of C++ code not counting code written for the
on-board communication layer. The software operated error free during
the 5.5 day flight.
Title: SUNRISE Impressions from a successful science flight
Authors: Schmidt, W.; Solanki, S. K.; Barthol, P.; Berkefeld, T.;
Gandorfer, A.; Knölker, M.; Martínez Pillet, V.; Schüssler, M.;
Title, A.
Bibcode: 2010AN....331..601S
Altcode:
SUNRISE is a balloon-borne telescope with an aperture of one meter. It
is equipped with a filter imager for the UV wavelength range between
214 nm and 400 nm (SUFI), and with a spectro-polarimeter that measures
the magnetic field of the photosphere using the Fe I line at 525.02
nm that has a Landé factor of 3. SUNRISE performed its first science
flight from 8 to 14 June 2009. It was launched at the Swedish ESRANGE
Space Center and cruised at an altitude of about 36 km and geographic
latitudes between 70 and 74 degrees to Somerset Island in northern
Canada. There, all data, the telescope and the gondola were successfully
recovered. During its flight, Sunrise achieved high pointing stability
during 33 hours, and recorded about 1.8 TB of science data. Already at
this early stage of data processing it is clear that SUNRISE recorded
UV images of the solar photosphere, and spectropolarimetric measurements
of the quiet Sun's magnetic field of unprecedented quality.
Title: Characterization of horizontal flows around solar pores from
high-resolution time series of images
Authors: Vargas Domínguez, S.; de Vicente, A.; Bonet, J. A.; Martínez
Pillet, V.
Bibcode: 2010A&A...516A..91V
Altcode: 2010arXiv1003.2134V
Context. Though there is increasing evidence linking the moat flow and
the Evershed flow along the penumbral filaments, there is not a clear
consensus regarding the existence of a moat flow around umbral cores
and pores, and the debate is still open. Solar pores appear to be a
suitable scenario to test the moat-penumbra relation as they correspond
to a direct interaction between the umbra and the convective plasma
in the surrounding photosphere without any intermediate structure in
between.
Aims: We study solar pores based on high-resolution
ground-based and satellite observations.
Methods: Local
correlation tracking techniques were applied to different-duration
time series to analyze the horizontal flows around several solar
pores.
Results: Our results establish that the flows calculated
from different solar pore observations are coherent among each other
and show the determining and overall influence of exploding events in
the granulation around the pores. We do not find any sign of moat-like
flows surrounding solar pores, but a clearly defined region of inflows
surrounding them.
Conclusions: The connection between moat
flows and flows associated to penumbral filaments is hereby reinforced.
Title: The IMaX polarimeter for the solar telescope SUNRISE of the
NASA long duration balloon program
Authors: Alvarez-Herrero, A.; Martínez-Pillet, V.; Del Toro Iniesta,
J. C.; Domingo, V.
Bibcode: 2010EPJWC...505002A
Altcode:
On June 8th 2009 the SUNRISE mission was successfully launched. This
mission consisted of a 1m aperture solar telescope on board of a
stratospheric balloon within the Long Duration Balloon NASA program. The
flight followed the foreseen circumpolar trajectory over the Artic
and the duration was 5 days and 17 hours. One of the two postfocal
instruments onboard was IMaX, the Imaging Magnetograph eXperiment. This
instrument is a solar magnetograph which is a diffraction limited imager
capable to resolve 100 km on the solar surface, and simultaneously
a high sensitivity polarimeter (<10-3) and a high
resolution spectrograph (bandwidth <70mÅ). The magnetic vectorial
map can be extracted thanks to the well-know Zeeman effect, which takes
place in the solar atoms, allowing to relate polarization and spectral
measurements to magnetic fields. The technological challenge of the IMaX
development has a special relevance due to the utilization of innovative
technologies in the Aeroespacial field and it is an important precedent
for future space missions such as Solar Orbiter from ESA. Among these
novel technologies the utilization of Liquid Crystal Variable Retarders
(LCVRs) as polarization modulators and a LiNbO3 etalon as
tunable spectral filter are remarkable. Currently the data obtained
is being analyzed and the preliminary results show unprecedented
information about the solar dynamics.
Title: Division II: Sun and Heliosphere
Authors: Melrose, Donald B.; Martinez Pillet, Valentin; Webb, David
F.; Bougeret, Jean-Louis; Klimchuk, James A.; Kosovichev, Alexander;
van Driel-Gesztelyi, Lidia; von Steiger, Rudolf
Bibcode: 2010IAUTB..27..146M
Altcode:
This report is on activities of the Division at the General Assembly
in Rio de Janeiro. Summaries of scientific activities over the past
triennium have been published in Transactions A, see Melrose et
al. (2008), Klimchuk et al. (2008), Martinez Pillet et al. (2008) and
Bougeret et al. (2008). The business meeting of the three Commissions
were incorporated into the business meeting of the Division. This
report is based in part on minutes of the business meeting, provided
by the Secretary of the Division, Lidia van Driel-Gesztelyi, and it
also includes reports provided by the Presidents of the Commissions
(C10, C12, C49) and of the Working Groups (WGs) in the Division.
Title: Spectropolarimetric inversions of the He I 10830 Å multiplet
in an active region filament.
Authors: Kuckein, C.; Centeno, R.; Martínez Pillet, V.
Bibcode: 2010MmSAI..81..668K
Altcode: 2010arXiv1001.2434K
Full-Stokes spectropolarimetric data (in the 10830 Å region)
of an active region filament were obtained in July 2005 using
the Tenerife Infrared Polarimeter instrument. The polarization
profiles in the filament show Zeeman-like signatures. Milne-Eddington
inversions were performed to infer the chromospheric magnetic field,
inclination, azimuth, velocity and Doppler width from the He I 10830
Å multiplet. Field strengths of the order of 600-800 G were found in
the filament. Strong transverse fields at chromospheric levels were
detected near the polarity inversion line. To our knowledge, these are
the highest field strengths reliably measured in these structures. Our
findings suggest the possible presence of a flux rope.
Title: High resolution imaging and polarimetry with SUNRISE, a
balloon-borne stratospheric solar observatory
Authors: Barthol, Peter; Chares, Bernd; Deutsch, Werner; Feller, Alex;
Gandorfer, Achim; Grauf, Bianca; Hirzberger, Johann; Meller, Reinhard;
Riethmueller, Tino; Schuessler, Manfred; Solanki, Sami K.; Knoelker,
Michael; Martinez Pillet, Valentin; Schmidt, Wolfgang; Title, Alan
Bibcode: 2010cosp...38.4063B
Altcode: 2010cosp.meet.4063B
SUNRISE is an international collaboration for the development
and operation of a meter-class balloon-borne stratospheric solar
observatory. Prime science goal is the study of structure and dynamics
of the magnetic field in the solar atmosphere and the interaction of
the magnetic field with convective plasma flows. These processes are
studied by high resolution imaging in the UV and polarimetry at visible
wavelengths. The instrument has been successfully launched on June 8,
2009 from ESRANGE, Kiruna, Northern Sweden. During the more than 5
days flight about 1.5 TByte of scientific data were collected. The
paper gives an overview of the instrument and mission, examples of
the scientific output will also be presented. SUNRISE is a joint
project of the Max-Planck-Institut fuer Sonnensystemforschung (MPS),
Katlenburg-Lindau, with the Kiepenheuer-Institut fuer Sonnenphysik
(KIS), Freiburg, the High-Altitude Observatory (HAO), Boulder, the
Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, and
the Spanish IMaX consortium.
Title: The Ultraviolet Filter Imager (SuFI) onboard the Sunrise
balloon-borne solar observatory: Instrument description and first
results
Authors: Gandorfer, Achim; Barthol, Peter; Feller, Alex; Grauf,
Bianca; Hirzberger, Johann; Riethmueller, Tino; Solanki, Sami K.;
Berkefeld, Thomas; Knoelker, Michael; Martinez Pillet, Valentin;
Schmidt, Wolfgang; Title, Alan
Bibcode: 2010cosp...38.4064G
Altcode: 2010cosp.meet.4064G
We describe the design of the near UV filter imager SuFi onboard
Sunrise, which was successfully flown in the stratosphere in June
2009. During its five days flight SuFI captured the highest contrast
images of solar granulation ever. SuFI is a diffraction limited filter
imager with an effective focal length of 121m, working in 5 distinct
wavelength bands between 210nm and 397nm. It is based on a two mirror
modified Schwarzschild microscope, which is integral part of the central
Image stabilization and light Distribution unit (ISLiD) of Sunrise,
which acts as the reimaging optics between the 1m telescope and the
science instruments. The key technical features of the instrument are
presented under the view of the specific demands of balloon-borne
optical systems. First results obtained with the instrument are
presented to demonstrate the capabilities of the instrument.
Title: UV intensity distributions of the quiet Sun observed with
Sunrise
Authors: Hirzberger, Johann; Feller, A.; Riethmueller, T.; Borrero,
J. M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knoelker, M.; Martínez Pillet, V.; Schmidt, W.; Solanki, S.; Title, A.
Bibcode: 2010cosp...38.1735H
Altcode: 2010cosp.meet.1735H
High resolution solar images in the near UV have been obtained with
the Solar UV Filtergraph (SUFI) onboard the Sunrise balloon borne
observatory, amongst others in wavelength regions not accessible
from the ground. We present intensity distributions of the quiet
Sun at different heliocentric angles, from disk center to the solar
limb. These results, obtained in spectral windows at 214 nm, 313 nm
(OH band), 388 nm (CN band) and 396.7 nm (CaIIH), represent an important
validation of numerical models of the solar photosphere and are, thus,
fundamental ingredients for our understanding of the thermal processes
in the solar surface region.
Title: Relation between the Sunrise photospheric magnetic field and
the Ca II H bright features
Authors: Jafarzadeh, Shahin; Hirzberger, J.; Feller, A.; Lagg, A.;
Solanki, S. K.; Pietarila, A.; Danilovic, S.; Riethmueller, T.;
Barthol, P.; Berkefeld, T.; Gandorfer, A.; Knülker, M.; Martínez
Pillet, V.; Schmidt, W.; Schüssler, M.; Title, A.
Bibcode: 2010cosp...38.2856J
Altcode: 2010cosp.meet.2856J
Recent observations from the Sunrise balloon-borne solar telescope
have enabled us to reach an unprecedented high spatial resolution
on the solar surface with the near-ultraviolet photo-spheric and
chromospheric images as well as the magnetograms. We use these high
resolution observations to investigate the structure of the solar
upper photosphere and lower chromosphere as well as their temporal
evolutions. We study the relation between the inter-granular Ca II
397 nm bright structures in images obtained by the Sunrise Filter
Imager (SuFI) and their corresponding photospheric vector magnetic
field computed from the Imaging Magnetogram eXperiment (IMaX)
observations. The targets under study are in a quiet Sun region and
close to disc-centre.
Title: Supersonic Continuation of the Evershed Flow Outside a Sunspot
as Observed with Hinode
Authors: Martínez Pillet, V.; Katsukawa, Y.; Puschmann, K. G.;
Ruiz Cobo, B.
Bibcode: 2009ApJ...701L..79M
Altcode: 2009arXiv0907.3835M
We report on the discovery of mostly horizontal field channels just
outside sunspot penumbrae (in the so-called "moat" region) that are
seen to sustain supersonic flows (line-of-sight component of 6 km
s-1). The spectral signature of these supersonic flows
corresponds to circular polarization profiles with an additional,
satellite, third lobe of the same sign as the parent sunspot' Stokes
V blue lobe, for both downflows and upflows. This is consistent with
an outward directed flow that we interpret as the continuation of the
magnetized Evershed flow outside sunspots at supersonic speeds. In
Stokes Q and U, a clear signature of a transverse field connecting
the two flow streams is observed. Such an easily detectable spectral
signature should allow for a clear identification of these horizontal
field channels in other spectropolarimetric sunspot data. For the spot
analyzed in this paper, a total of five channels with this spectral
signature have been unambiguously found.
Title: Magnetic field strength of active region filaments
Authors: Kuckein, C.; Centeno, R.; Martínez Pillet, V.; Casini, R.;
Manso Sainz, R.; Shimizu, T.
Bibcode: 2009A&A...501.1113K
Altcode: 2009arXiv0904.4876K
Aims: We study the vector magnetic field of a filament observed over a
compact active region neutral line.
Methods: Spectropolarimetric
data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830
Å spectral region provide full Stokes vectors that were analyzed
using three different methods: magnetograph analysis, Milne-Eddington
inversions, and PCA-based atomic polarization inversions.
Results:
The inferred magnetic field strengths in the filament are around 600-700
G by all these three methods. Longitudinal fields are found in the
range of 100-200 G whereas the transverse components become dominant,
with fields as high as 500-600 G. We find strong transverse fields
near the neutral line also at photospheric levels.
Conclusions:
Our analysis indicates that strong (higher than 500 G, but below kG)
transverse magnetic fields are present in active region filaments. This
corresponds to the highest field strengths reliably measured in these
structures. The profiles of the helium 10 830 Å lines observed in
this active region filament are dominated by the Zeeman effect.
Title: POLAR investigation of the Sun—POLARIS
Authors: Appourchaux, T.; Liewer, P.; Watt, M.; Alexander, D.;
Andretta, V.; Auchère, F.; D'Arrigo, P.; Ayon, J.; Corbard, T.;
Fineschi, S.; Finsterle, W.; Floyd, L.; Garbe, G.; Gizon, L.; Hassler,
D.; Harra, L.; Kosovichev, A.; Leibacher, J.; Leipold, M.; Murphy,
N.; Maksimovic, M.; Martinez-Pillet, V.; Matthews, B. S. A.; Mewaldt,
R.; Moses, D.; Newmark, J.; Régnier, S.; Schmutz, W.; Socker, D.;
Spadaro, D.; Stuttard, M.; Trosseille, C.; Ulrich, R.; Velli, M.;
Vourlidas, A.; Wimmer-Schweingruber, C. R.; Zurbuchen, T.
Bibcode: 2009ExA....23.1079A
Altcode: 2008ExA...tmp...40A; 2008arXiv0805.4389A
The POLAR Investigation of the Sun (POLARIS) mission uses a combination
of a gravity assist and solar sail propulsion to place a spacecraft
in a 0.48 AU circular orbit around the Sun with an inclination of 75°
with respect to solar equator. This challenging orbit is made possible
by the challenging development of solar sail propulsion. This first
extended view of the high-latitude regions of the Sun will enable
crucial observations not possible from the ecliptic viewpoint or from
Solar Orbiter. While Solar Orbiter would give the first glimpse of
the high latitude magnetic field and flows to probe the solar dynamo,
it does not have sufficient viewing of the polar regions to achieve
POLARIS’s primary objective: determining the relation between the
magnetism and dynamics of the Sun’s polar regions and the solar cycle.
Title: Entrega de IMaX al globo polar SUNRISE
Authors: Martínez Pillet, V.
Bibcode: 2009iac..talk...44M
Altcode: 2009iac..talk...49M
No abstract at ADS
Title: Division II: Sun and Heliosphere
Authors: Melrose, Donald B.; Martínez Pillet, Valentin; Webb, David
F.; van Driel-Gesztelyi, Lidia; Bougeret, Jean-Louis; Klimchuk,
James A.; Kosovichev, Alexander; von Steiger, Rudolf
Bibcode: 2009IAUTA..27...73M
Altcode:
Division II of the IAU provides a forum for astronomers and
astrophysicists studying a wide range of phenomena related to the
structure, radiation and activity of the Sun, and its interaction with
the Earth and the rest of the solar system. Division II encompasses
three Commissions, 10, 12 and 49, and four Working Groups.
Title: Commission 12: Solar Radiation and Structure
Authors: Martínez Pillet, Valentin; Kosovichev, Alexander;
Mariska, John T.; Bogdan, Thomas J.; Asplund, Martin; Cauzzi, Gianna;
Christensen-Dalsgaard, Jørgen; Cram, Lawrence E.; Gan, Weiqun; Gizon,
Laurent; Heinzl, Petr; Rovira, Marta G.; Venkatakrishnan, P.
Bibcode: 2009IAUTA..27..104M
Altcode:
Commission 12 encompasses investigations on the internal structure
and dynamics of the Sun, mostly accessible through the techniques of
local and global helioseismology, the quiet solar atmosphere, solar
radiation and its variability, and the nature of relatively stable
magnetic structures like sunspots, faculae and the magnetic network. A
revision of the progress made in these fields is presented. For some
specific topics, the review has counted with the help of experts
outside the Commission Organizing Committee that are leading and/or
have recently presented relevant works in the respective fields. In
this cases the contributor's name is given in parenthesis.
Title: SUNRISE: High resolution UV/VIS observations of the sun from
the stratosphere
Authors: Sunrise Team; Barthol, P.; Gandorfer, A. M.; Solanki,
S. K.; Knölker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.;
SUNRISE Team
Bibcode: 2008AdSpR..42...70S
Altcode:
SUNRISE is an international project for the development, construction
and operation of a balloon-borne solar telescope with an aperture
of 1 m, working in the UV/VIS spectral domain. The main scientific
goal of SUNRISE is to understand the structure and dynamics of the
magnetic field in the atmosphere of the Sun. SUNRISE will provide
near diffraction-limited images of the photosphere and chromosphere
with an unprecedented resolution down to 35 km on the solar surface
at wavelengths around 220 nm. Active in-flight alignment and image
stabilization techniques are used. The focal-plane instrumentation
consists of a polarization sensitive spectrograph, a Fabry Perot
filter magnetograph and a phase-diverse filter imager working in
the near UV. The first stratospheric long-duration balloon flight
of SUNRISE is planned in summer 2009 from the Swedish ESRANGE
station. SUNRISE is a joint project of the German Max-Planck-Institut
für Sonnensystemforschung (MPS), Katlenburg-Lindau, with the
Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, Germany, the
High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin
Solar and Astrophysics Laboratory (LMSAL), Palo Alto, USA, and the
Spanish IMaX consortium. This paper will give an overview about the
mission and a description of its scientific and technological aspects.
Title: Moat Flow in the Vicinity of Sunspots for Various Penumbral
Configurations
Authors: Vargas Domínguez, S.; Rouppe van der Voort, L.; Bonet,
J. A.; Martínez Pillet, V.; Van Noort, M.; Katsukawa, Y.
Bibcode: 2008ApJ...679..900V
Altcode: 2008arXiv0802.1457V
High-resolution time series of sunspots have been obtained with
the Swedish 1 m Solar Telescope between 2003 and 2006 at different
locations on the solar disk. Proper motions in seven different active
regions have been studied. The analysis was performed by applying local
correlation tracking to every series of sunspots, each of them more than
40 minutes long. The sunspots' shapes include a different variety of
penumbral configurations. We report on the systematic behavior of the
large-scale outflows surrounding the sunspots, commonly known as moat
flows, that are essentially present only when preceded by a penumbra
not tangential but perpendicular to the sunspot border. We present
one case for which this rule appears not to be confirmed. We speculate
that the magnetic neutral line, which is located in the vicinity of the
anomalous region, might be responsible for blocking the outflow. These
new results confirm the systematic and strong relation between the
moat flows and the existence of penumbrae. A comparative statistical
study between moats and standard granulation is also performed.
Title: Spectropolarimetry of a Decaying Sunspot Penumbra
Authors: Bellot Rubio, L. R.; Tritschler, A.; Martínez Pillet, V.
Bibcode: 2008ApJ...676..698B
Altcode: 2007arXiv0712.2937B
We report on high angular resolution, high-precision spectropolarimetric
measurements of a decaying sunspot. The spot gradually lost
its penumbra during the course of 3 days. In the late stages of
evolution, where the only remnant of the spot is a naked umbra, we
find small-scale inhomogeneities in the magnetic canopy surrounding
it. The inhomogeneities are observed as finger-like structures
of weak and nearly horizontal magnetic fields extending 1''-2''
from the border of the umbra. These fields are not associated with
filamentary structures in continuum intensity or with conspicuous
Evershed flows. The Stokes profiles emerging from the fingers exhibit
blueshifts, which we interpret as upward motions. This previously
unknown fine structure may be related to penumbral field lines that
no longer carry strong Evershed flows and rise to the chromosphere,
producing the disappearance of the penumbra at photospheric levels.
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.
Bibcode: 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: In-situ Flux Losses in Active Regions
Authors: Dalda, A. S.; Martinez Pillet, V. M.
Bibcode: 2008ASPC..383..115D
Altcode:
We have investigated the total magnetic flux losses of three active
regions, and the contribution of the cancellations that occur in
the decay phase. Magnetic flux losses represent about 50%--70% of
the magnetic flux in the active region. We have also found a clear
correlation between cancellations and outward directed events in the
chromosphere and the corona.
Title: Division II: Sun and Heliosphere
Authors: Webb, David F.; Melrose, Donald B.; Benz, Arnold O.; Bogdan,
Thomas J.; Bougeret, Jean-Louis; Klimchuk, James A.; Martinez-Pillet,
Valentin
Bibcode: 2007IAUTB..26..101W
Altcode:
Division II provides a forum for astronomers studying a wide range of
problems related to the structure, radiation and activity of the Sun,
and its interaction with the Earth and the rest of the solar system.
Title: Supersonic Downflows in the Photosphere Discovered in Sunspot
Moat Regions
Authors: Shimizu, T.; Martinez-Pillet, V.; Collados, M.; Ruiz-Cobo,
B.; Centeno, R.; Beck, C.; Katsukawa, Y.
Bibcode: 2007ASPC..369..113S
Altcode:
This paper reports on our new findings from the International
Time Program observations at the Canaries islands, Spain, in July
2005. We have found small-scale photospheric events with extremely
red-shifted Stokes V signals in sunspot moat regions. A preliminary
estimate of the physical conditions for an observed Stokes V profile
indicates the presence of a downward motion with a supersonic speed
in the order of 10 km/s. With the currently evaluated observational
information, we interprete the supersonic flows as downward motion from
magnetic reconnection occurring at the upper chromosphere or lower
photosphere. With coordinated observations of the Solar-B onboard
telescopes, Stokes measurements by the SOT spectro-polarimeter would
give new information for further understanding the nature of these
events with strongly red-shifted Stokes V, and for discussing the
physical conditions involving in possible magnetic reconnections in
the lower solar atmosphere.
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.
Bibcode: 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: The Use of Spectro-Polarimetric Measurements to determine
the Plasma Heating
Authors: Jurčák, J.; Martinez Pillet, V.; Sobotka, M.
Bibcode: 2007ASPC..369..171J
Altcode:
We present the possible use of spectro-polarimetric measurements on
a set of data recorded with La Palma Stokes Polarimeter attached to
the Swedish Vacuum Solar Telescope. The stratification over the solar
atmosphere of different physical parameters is retrieved from these data
using the Stokes Inversion based on Response functions (SIR). We derive
the vertical component of electric current density coming out from the
stratification of the magnetic field strength and orientation of the
magnetic field vector. We also found spatial and height correlation
between the temperature enhancement and increase of electric current
density, this could be caused by the energy dissipation stored in the
magnetic field configuration.
Title: On the Moat-Penumbra Relation
Authors: Vargas Domínguez, S.; Bonet, J. A.; Martínez Pillet, V.;
Katsukawa, Y.; Kitakoshi, Y.; Rouppe van der Voort, L.
Bibcode: 2007ApJ...660L.165V
Altcode: 2007astro.ph..2713V
Proper motions in a sunspot group with a δ-configuration and close to
the solar disk center have been studied by employing local correlation
tracking techniques. The analysis is based on a more than 1 hr time
series of G-band images. Radial outflows with a mean speed of 0.67
km s-1 have been detected around the spots, the well-known
sunspots moats. However, these outflows are not found in those umbral
core sides without penumbra. Moreover, moat flows are only found
in those sides of penumbrae located in the direction marked by the
penumbral filaments. Penumbral sides perpendicular to them show no
moat flow. These results strongly suggest a relation between the
moat flow and the well-known, filament-aligned Evershed flow. The
standard picture of a moat flow originating from a blocking of the
upward propagation of heat is discussed in some detail.
Title: Properties of sunspots in cycle 23. I. Dependence of brightness
on sunspot size and cycle phase
Authors: Mathew, S. K.; Martínez Pillet, V.; Solanki, S. K.; Krivova,
N. A.
Bibcode: 2007A&A...465..291M
Altcode: 2007astro.ph..1401M
Aims:In this paper we investigate the dependence of umbral core
brightness, as well as the mean umbral and penumbral brightness on the
phase of the solar cycle and on the size of the sunspot.
Methods:
Albregtsen & Maltby (1978, Nature, 274, 41) reported an increase
in umbral core brightness from the early to the late phase of solar
cycle from the analysis of 13 sunspots which cover solar cycles 20
and 21. Here we revisit this topic by analysing continuum images
of more than 160 sunspots observed by the MDI instrument on board
the SOHO spacecraft for the period between 1998 March to 2004 March,
i.e. a sizable part of solar cycle 23. The advantage of this data set
is its homogeneity, with no seeing fluctuations. A careful stray light
correction, which is validated using the Mercury transit of 7th May,
2003, is carried out before the umbral and penumbral intensities are
determined. The influence of the Zeeman splitting of the nearby Ni I
spectral line on the measured "continuum" intensity is also taken into
account.
Results: We did not observe any significant variation
in umbral core, mean umbral and mean penumbral intensities with solar
cycle, which is in contrast to earlier findings for the umbral core
intensity. We do find a strong and clear dependence of the umbral
brightness on sunspot size, however. The penumbral brightness also
displays a weak dependence. The brightness-radius relationship has
numerous implications, some of which, such as those for the energy
transport in umbrae, are pointed out.
Title: Commission 12: Solar Radiation & Structure
Authors: Bogdan, Thomas. J.; Martínez Pillet, Valentin; Asplund,
M.; Christensen-Dalsgaard, J.; Cauzzi, G.; Cram, L. E.; Dravins, D.;
Gan, W.; Henzl, P.; Kosovichev, A.; Mariska, J. T.; Rovira, M. G.;
Venkatakrishnan, P.
Bibcode: 2007IAUTA..26...89B
Altcode:
Commission 12 covers research on the internal structure and dynamics
of the Sun, the "quiet" solar atmosphere, solar radiation and its
variability, and the nature of relatively stable magnetic structures
like sunspots, faculae and the magnetic network. There is considerable
productive overlap with the other Commissions of Division II as
investigations move progressively toward the fertile intellectual
boundaries between traditional research disciplines. In large part,
the solar magnetic field provides the linkage that connects these
diverse themes. The same magnetic field that produces the more subtle
variations of solar structure and radiative output over the 11 yr
activity cycle is also implicated in rapid and often violent phenomena
such as flares, coronal mass ejections, prominence eruptions, and
episodes of sporadic magnetic reconnection.The last three years have
again brought significant progress in nearly all the research endeavors
touched upon by the interests of Commission 12. The underlying causes
for this success remain the same: sustained advances in computing
capabilities coupled with diverse observations with increasing levels
of spatial, temporal and spectral resolution. It is all but impossible
to deal with these many advances here in anything except a cursory and
selective fashion. Thankfully, the Living Reviews in Solar Physics; has
published several extensive reviews over the last two years that deal
explicitly with issues relevant to the purview of Commission 12. The
reader who is eager for a deeper and more complete understanding of
some of these advances is directed to http://www.livingreviews.org
for access to these articles.
Title: Division II: Sun and Heliosphere
Authors: Webb, David F.; Melrose, Donald B.; Benz, Arnold O.; Bogdan,
Thomas J.; Bougeret, Jean-Louis; Klimchuk, James A.; Martinez Pillet,
Valentin
Bibcode: 2007IAUTA..26...69W
Altcode:
Division II of the IAU provides a forum for astronomers studying a wide
range of phenomena related to the structure, radiation and activity
of the Sun, and its interaction with the Earth and the rest of the
solar system. Division II encompasses three Commissions, 10, 12 and
49, and four working groups. During the last triennia the activities
of the division involved some reorganization of the division and its
working groups, developing new procedures for election of division and
commission officers, promoting annual meetings from within the division
and evaluating all the proposed meetings, evaluating the division's
representatives for the IAU to international scientific organizations,
and participating in general IAU business.
Title: L iquid Crystal Variable Retarders For Aerospace Applications
Authors: Álavarez-Herrero, A.; Heredero, R. L.; Uribe-Patarroyo, N.;
Sánchez, A.; Reina, M.; Ramos, G.; Belenguer, T.; del Toro, J. C.;
Jochum, L.; Martínez-Pillet, V.
Bibcode: 2007ESASP.641E..54A
Altcode:
Polarization modulators based on Liquid Crystal Variable Retarders
(LCVRs) are envisaged as a powerful and versatile solution whose
main advantage is the lack of mechanisms (i.e. rotating plates). An
extensive test campaign has been carried out in order to demonstrate
the feasibility of the LCVRs for the IMaX/SUNRISE magnetograph in
environmental conditions similar to space conditions. Analysis of the
influence of vacuum, temperature, vibration, gamma and ultraviolet
radiation was performed by measuring the effects of these tests on
the optical retardance, the response time, the wavefront distortion
and the transmittance, including "in-situ" measurements. Outgassing
rates of the different parts of the LCVRs were also studied. From the
results obtained it can be concluded that these optical devices are
suitable for SUNRISE and seem to be excellent candidates for aerospace
missions as Solar Orbiter.
Title: Evidence Of An Association Between The Presence Of Penumbrae
And Strong Radial Outflows In Sunspots
Authors: Santiago, Vargas Domínguez; Bonet, J. A.; Martinez Pillet,
V.; Katsukawa, Y.
Bibcode: 2007ESASP.641E..87S
Altcode:
Time series of high-resolution images of the complex ac-tive region NOAA
10786 are studied. The observations were performed in G-band (430.5 nm)
and in the nearby continuum (463.3 nm), on July 9, 2005 at the Swedish
1-meter Solar Telecope (SST) in La Palma. Granular proper motions in the
surroundings of the sunspots have been quantified. A large-scale radial
outflow in the velocity range 0.3 - 1 km s-1 has been measured around
the sunspots by using local correlation tracking techniques. However,
this outflow is not found in those regions around the sunspots with
no penumbral structure. This result evidences an association between
penumbrae and the existence of strong horizontal outflows (the moat)
in sunspots.
Title: SUNRISE: High resolution UV/VIS observations of the Sun from
the stratosphere
Authors: Gandorfer, A. M.; Solanki, S. K.; Barthol, P.; Martínez
Pillet, V.; Schmidt, W.; Title, A. M.; Knölker, M.
Bibcode: 2007msfa.conf...69G
Altcode:
SUNRISE is an international project for the development, construction,
and operation of a balloon-borne solar telescope with an aperture
of 1 m, working in the UV/VIS spectral domain. The main scientific
goal of SUNRISE is to understand the structure and dynamics of the
magnetic field in the atmosphere of the Sun. SUNRISE will provide
near diffraction-limited images of the photosphere and chromosphere
with an unpredecented resolution down to 35 km on the solar surface at
wavelengths around 220 nm. The focal-plane instrumentation consists of a
polarization sensitive spectrograph, a Fabry-Perot filter magnetograph,
and a phase-diverse filter imager working in the near UV. The first
stratospheric long-duration balloon flight of SUNRISE is planned in
summer 2009 from the Swedish ESRANGE station. SUNRISE is a joint project
of the German Max-Planck-Institut für Sonnensystemforschung (MPS),
Katlenburg-Lindau, with the Kiepenheuer-Institut für Sonnenphysik
(KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder,
USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo
Alto, USA, and the Spanish IMaX consortium. In this paper we will
present a brief description of the scientific and technological aspects
of SUNRISE.
Title: Instrumental Approaches to Magnetic and Velocity Measurements
in and out of the Ecliptic Plane
Authors: Martinez Pillet, V.
Bibcode: 2007ESASP.651E..27M
Altcode:
Velocity and magnetic fields are derived from subtracting intensity
measurements made at different times and, normally, under different
conditions. This differential imaging property puts important
requirements on image stabilization. Examples of the implications for
the Solar Orbiter mission are discussed. Similarly, we review how
spectral and polarization measurements can be done and analyzed in
the context of the Solar Orbiter mission.
Title: Design Of A Fabry Perot Interferometer For The VIM Instrument
Aboard Solar Orbiter
Authors: Trosseille, C.; Appourchaux, T.; Martinez Pillet, V.
Bibcode: 2007ESASP.641E..85T
Altcode:
The spectral analyser of the Visible light Imager and Magnetograph
(VIM) is a critical device whose concept is dependent on scientific
requirements and technical trade-offs, which are directly driven by
the nature of the mission. Here, we report on the choices that were
made to fulfill the scientific needs, while constantly keeping an eye
on feasibility. We also list the critical points and remaining issues
that should be investigated and addressed properly in further work.
Title: T hermal Feasibility Study Of The Solar Orbiter Visible Light
Imager And Magnetograph (VIM)
Authors: Pérez-Grande, I.; Martínez-Pillet, V.; Woch, J.; Hartwig, H.
Bibcode: 2007ESASP.641E..76P
Altcode:
In order to determine the feasibility of the Solar Orbiter instrument
Visible Light Imager and Magnetograph (VIM), a thermal analysis focused
on the critical elements of the instrument has been carried out. The
thermal solution has been sought for the hot case and the performance
in the cold operational and survival modes has been analysed.
Title: S pace Qualification Of A Thin Wafer Lithium Niobate Etalon
For The Visible Light Imager And Magnetograph (Vim)
Authors: Schühle, U.; Mathew, S. K.; Wedemeier, M.; Hartwig, H.;
Ballesteros, E.; Martinez Pillet, V.; Solanki, S. K.
Bibcode: 2007ESASP.641E..82S
Altcode:
For the Visible Light Imager and Magnetograph (VIM) a high-resolution
filtergraph is under design. The system takes advantage of a lithium
niobate (LiNbO3) crystal which can be used as a scanning filter using
high voltage for tuning. We have undertaken first studies to qualify
a lithium niobate wafer of 70 mm aperture size for deployment and use
in space. We show the results of the mechanical mounting and vibration
and thermal cycling tests as well as stability tests under fast voltage
tuning in vacuum. Although these tests have all been very successful,
further environmental testing is necessary to fully space-qualify the
filter for the Solar Orbiter mission.
Title: Instrumental Approaches To Magnetic And Velocity Measurements
In And Out Of The Ecliptic Plane
Authors: Martínez Pillet, V.
Bibcode: 2007ESASP.641E..27M
Altcode: 2006ESASP.641E..27M
Velocity and magnetic fields are derived from subtracting intensity
measurements made at different times and, normally, under different
conditions. This differential imaging property puts important
requirements on image stabilization. Examples of the implications for
the Solar Orbiter mission are discussed. Similarly, we review how
spectral and polarization measurements can be done and analyzed in
the context of the Solar Orbiter mission.
Title: Evidence of an association between the presence of penumbrae
and strong radial outflows in sunspots
Authors: Vargas Domínguez, S.; Bonet, J. A.; Martinez Pillet, V.;
Katsukawa, Y.
Bibcode: 2006astro.ph.11500V
Altcode:
Time series of high-resolution images of the complex active region NOAA
10786 are studied. The observations were performed in G-band (430.5 nm)
and in the nearby continuum (463.3 nm), on July 9, 2005 at the Swedish
1-meter Solar Telecope (SST) in La Palma. Granular proper motions in the
surroundings of the sunspots have been quantified. A large-scale radial
outflow in the velocity range 0.3 - 1 km s^[-1] has been measured around
the sunspots by using local correlation tracking techniques. However,
this outflow is not found in those regions around the sunspots with
no penumbral structure. This result evidences an association between
penumbrae and the existence of strong horizontal outflows (the moat)
in sunspots.
Title: The magnetic canopy above light bridges
Authors: Jurčák, J.; Martínez Pillet, V.; Sobotka, M.
Bibcode: 2006A&A...453.1079J
Altcode:
An analysis of high-resolution Stokes observations of two light
bridges in active region NOAA 8990 is presented. The observations were
recorded with the La Palma Stokes Polarimeter attached to the Swedish
Vacuum Solar Telescope. The stratification over the solar atmosphere
of different physical parameters is retrieved from these data using
the Stokes inversion based on response functions (SIR). Our results
confirm previous observations of features such as the decrease in
magnetic field strength and the increase in inclination in the light
bridges. We also confirm a temperature increase in these structures
with respect to the surrounding umbrae. The maps of the magnetic field
strength and of the orientation of the magnetic field vector indicate
the presence of a canopy structure above the light bridges. We derive
the vertical component of electric current density (J_z) from the
configuration of the magnetic field. The increased temperature found
in the upper layers is studied in the context of the proposed canopy
topology and could also explain the recently observed chromospheric
heating processes found above light bridges.
Title: SUNRISE: high resolution UV/VIS observations of the Sun from
the stratosphere
Authors: Gandorfer, A. M.; Solanki, S. K.; Barthol, P.; Lites, B. W.;
Martínez Pillet, V.; Schmidt, W.; Soltau, D.; Title, A. M.
Bibcode: 2006SPIE.6267E..0SG
Altcode: 2006SPIE.6267E..25G
SUNRISE is an international project for the development, construction,
and operation of a balloon-borne solar telescope with an aperture
of 1 m, working in the UV/VIS spectral domain. The main scientific
goal of SUNRISE is to understand the structure and dynamics of the
magnetic field in the atmosphere of the Sun. SUNRISE will provide
near diffraction-limited images of the photosphere and chromosphere
with an unpredecented resolution down to 35 km on the solar surface at
wavelengths around 220 nm. The focal-plane instrumentation consists of a
polarization sensitive spectrograph, a Fabry-Perot filter magnetograph,
and a phase-diverse filter imager working in the near UV. The first
stratospheric long-duration balloon flight of SUNRISE is planned
in Summer 2009 from the swedish ESRANGE station. SUNRISE is a joint
project of the german Max-Planck-Institut fur Sonnensystemforschung
(MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut fur Sonnenphysik
(KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder,
USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto,
USA, and the spanish IMaX consortium. In this paper we will present
an actual update on the mission and give a brief description of its
scientific and technological aspects.
Title: Detailed design of the imaging magnetograph experiment (IMaX):
a visible imager magnetograph for the Sunrise mission
Authors: Álvarez-Herrero, A.; Belenguer, T.; Pastor, C.; González,
L.; Heredero, R. L.; Ramos, G.; Reina, M.; Sánchez, A.; Villanueva,
J.; Sabau, L.; Martínez Pillet, V.; Bonet, J. A.; Collados, M.;
Jochum, L.; Ballesteros, E.; Medina Trujillo, J. L.; Ruiz, Cobo B.;
González, J. C.; del Toro Iniesta, J. C.; López Jiménez, A. C.;
Castillo Lorenzo, J.; Herranz, M.; Jerónimo, J. M.; Mellado, P.;
Morales, R.; Rodríguez, J.; Domingo, V.; Gasent, J. L.; Rodríquez, P.
Bibcode: 2006SPIE.6265E..4CA
Altcode: 2006SPIE.6265E.132A
In this work, it is described the Imaging Magnetograph eXperiment,
IMaX, one of the three postfocal instruments of the Sunrise mission. The
Sunrise project consists on a stratospheric balloon with a 1 m aperture
telescope, which will fly from the Antarctica within the NASA Long
Duration Balloon Program. IMaX will provide vector magnetograms
of the solar surface with a spatial resolution of 70 m. This data
is relevant for understanding how the magnetic fields emerge in
the solar surface, how they couple the photospheric base with the
million degrees of temperature of the solar corona and which are the
processes that are responsible of the generation of such an immense
temperatures. To meet this goal IMaX should work as a high sensitivity
polarimeter, high resolution spectrometer and a near diffraction
limited imager. Liquid Crystal Variable Retarders will be used as
polarization modulators taking advantage of the optical retardation
induced by application of low electric fields and avoiding mechanical
mechanisms. Therefore, the interest of these devices for aerospace
applications is envisaged. The spectral resolution required will be
achieved by using a LiNbO 3 Fabry-Perot etalon in double
pass configuration as spectral filter before the two CCDs detectors. As
well phase-diversity techniques will be implemented in order to improve
the image quality. Nowadays, IMaX project is in the detailed design
phase before fabrication, integration, assembly and verification. This
paper briefly describes the current status of the instrument and the
technical solutions developed to fulfil the scientific requirements.
Title: Lithium niobate Fabry-Perot etalons in double-pass
configuration for spectral filtering in the visible imager
magnetograph IMaX for the SUNRISE mission
Authors: Álvarez-Herrero, A.; Belenguer, T.; Pastor, C.; Heredero,
R. L.; Ramos, G.; Martínez Pillet, V.; Bonet Navarro, J. A.
Bibcode: 2006SPIE.6265E..2GA
Altcode: 2006SPIE.6265E..74A
The Imaging MAgnetograph eXperiment, IMaX, is one of the three postfocal
instruments of the Sunrise mission. The Sunrise project consists of
a stratospheric balloon with a 1 m aperture telescope, which will fly
from the Antarctica within the NASA Long Duration Balloon Program. IMaX
should work as a diffraction limited imager and it should be capable to
carry out polarization measurements and spectroscopic analysis with high
resolution (50.000-100.000 range). The spectral resolution required will
be achieved by using a LiNbO 3 (z-cut) Fabry-Perot etalon
in double pass configuration as spectral filter. Up to our knowledge,
few works in the literature describe the associated problems of using
these devices in an imager instrument (roughness, off-normal incidence,
polarization sensitivity...). Because of that, an extensive and detailed
analysis of etalon has been carried out. Special attention has been
taken in order to determine the wavefront transmission error produced
by the imperfections of a real etalon in double pass configuration
working in collimated beam. Different theoretical models, numeric
simulations and experimental data are analysed and compared obtaining
a complete description of the etalon response.
Title: A Detailed Analysis of an Ephemeral Region .
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo, B.;
Zuccarello, F.; Lites, B. W.
Bibcode: 2006MSAIS...9..103G
Altcode:
In order to improve the understanding of the process of emergence of
magnetic flux on the solar surface, we studied the temporal evolution of
an ephemeral region using \emph{Advanced Stokes Polarimeter} data. We
adopted two different approaches: first, we used a Milne-Eddington
inversion to obtain mean parameters of the emerging bipole magnetic
configuration. Then, we considered the full radiative transfer
equation, and we studied the trend of all the previous parameters as
a function of the optical depth tau . We pointed out peculiar flows,
such as an initial upflow of 1.5 ;textrm {km s}-1 where the
zenith angle is essentially horizontal, and downflows decreasing in
time in footpoints, characterized by a vertical field. These results
seem to confirm the emerging bipole topology, due to magnetic flux
tube emergence. The results obtained with this inversion confirm the
structure found with Milne-Eddington code. However we found regions
in which the presence of two distinct magnetic components is highly
significant. It also seems very interesting the trend of the temperature
with optical depth: the plasma temperature appears to grow up in the
high photosphere above the emerging bipole.
Title: SUNRISE: high-resolution UV/VIS observations of the Sun from
the stratosphere
Authors: Solanki, S. K.; Barthol, P.; Gandorfer, A.; Schüssler, M.;
Lites, B. W.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.
Bibcode: 2006cosp...36.2416S
Altcode: 2006cosp.meet.2416S
SUNRISE is a balloon-borne solar telescope with an aperture of 1m
working in the UV VIS optical domain The main scientific goal of
SUNRISE is to study the structure and dynamics of the magnetic field
in the atmosphere of the Sun at high spatial resolution SUNRISE will
provide diffraction-limited images of the photosphere and chromosphere
with an unprecedented resolution down to 35km at wavelengths around
220nm Focal-plane instruments are a UV filter imager a Fabry-Perot
filter magnetograph and a spectrograph polarimeter Stratospheric
long-duration balloon flights of SUNRISE over the North Atlantic
and or Antarctica are planned SUNRISE is a joint project of the
Max-Planck-Institut fuer Sonnensystemforschung MPS Katlenburg-Lindau
with the Kiepenheuer-Institut fuer Sonnenphysik KIS Freiburg the
High-Altitude Observatory HAO Boulder the Lockheed-Martin Solar and
Astrophysics Lab LMSAL Palo Alto and the spanish IMaX consortium The
presentation will give an overview about the mission and a description
of the instrumentation now at the beginning of the hardware construction
phase
Title: The Canopy Structure above Light Bridges
Authors: Jurčák, J.; Sobotka, M.; Martínez Pillet, V.
Bibcode: 2006CEAB...30...55J
Altcode:
An analysis of high-resolution Stokes observations of two light bridges
in the active region NOAA 8990 is presented. The observations were
recorded with the La Palma Stokes Polarimeter attached to the Swedish
Vacuum Solar Telescope. The stratification of different physical
parameters is retrieved using the Stokes Inversion based on Response
functions (SIR). Our results confirm the decrease of magnetic field
strength and the increase of inclination in light bridges. We find a
complex temperature stratification in these structures Coming out from
the stratification of the magnetic field strength and the orientation
of the magnetic field vector, we suggest a canopy structure above the
light bridge. We derive the vertical component of electric current
density (Jz). The increase of Jz corresponds to
temperature enhancements that might be caused by the energy dissipation
stored in the magnetic field.
Title: The Magnetic Configuration in Light Bridges
Authors: Jurčák, J.; Sobotka, M.; Martínez Pillet, V.
Bibcode: 2005ESASP.600E...8J
Altcode: 2005dysu.confE...8J; 2005ESPM...11....8J
No abstract at ADS
Title: The scientific case for spectropolarimetry from space:
a novel diagnostic window on cosmic magnetic fields
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Casini, R.;
Martínez Pillet, V.
Bibcode: 2005ESASP.588..203T
Altcode: 2005tssc.conf..203T
No abstract at ADS
Title: The Scientific Case for Quantum Spectropolarimetry from Space
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Casini, R.;
Martínez Pillet, V.
Bibcode: 2005ESASP.596E...4T
Altcode: 2005ccmf.confE...4T
No abstract at ADS
Title: Moving Magnetic Features as Prolongation of Penumbral Filaments
Authors: Sainz Dalda, A.; Martínez Pillet, V.
Bibcode: 2005ApJ...632.1176S
Altcode:
A sequence of 633 high spatial resolution magnetograms and continuum
images from SOHO MDI of NOAA AR 0330 is used to study moving magnetic
feature (MMF) activity in the moat surrounding a mature leader
sunspot. The time-averaged frame shows that the moat region is covered
by a magnetic field that exhibits the same polarity distribution as that
observed in the penumbra. The moat field displays the true polarity
of the spot in the sector where the penumbra displays it. Similarly,
on the side where the penumbra shows a polarity opposite the true one
(due to projection effects after the so-called apparent neutral line),
the moat field also displays a polarity opposite the true one. This is
only compatible with a moat field that is horizontal almost everywhere,
as in the outer penumbra. Indeed, this horizontal moat field is seen
to be physically connected with the penumbra. This connection is
made evident when analyzing the individual structures detected in the
averaged images, which we call moat filaments. The filaments stretch
out for 12" in the moat and can be traced back into the penumbra. The
observed polarity distribution along them is only compatible with mean
inclinations in the range of 80°-90°. Inside the spot, these filaments
are linked to the more horizontal magnetic field component that is
thought to carry a large part of the Evershed flow. Several bipolar
MMFs are seen to originate inside the penumbra and cross the sunspot
outer boundary to enter the moat region, following the paths outlined
by the moat filaments. These results are discussed in the frame of our
current theoretical understanding of the Evershed flow and MMF activity.
Title: Velocity Fields in an Irregular Sunspot
Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V.
Bibcode: 2005ASSL..320..227J
Altcode: 2005smp..conf..227J
No abstract at ADS
Title: SUNRISE: high-resolution UV/VIS observations of the Sun from
the stratosphere
Authors: Gandorfer, Achim M.; Solanki, Sami K.; Schüssler, Manfred;
Curdt, Werner; Lites, Bruce W.; Martínez Pillet, Valentin; Schmidt,
Wolfgang; Title, Alan M.
Bibcode: 2004SPIE.5489..732G
Altcode:
SUNRISE is a balloon-borne solar telescope with an aperture of 1m,
working in the UV/VIS optical domain. The main scientific goal
of SUNRISE is to understand the structure and dynamics of the
magnetic field in the atmosphere of the Sun. SUNRISE will provide
diffraction-limited images of the photosphere and chromosphere with
an unpredecented resolution down to 35km at wavelengths around
220nm. Focal-plane instruments are a spectrograph/polarimeter,
a Fabry-Perot filter magnetograph, and a filter imager. The first
stratospheric long-duration balloon flight of SUNRISE over Antarctica
is planned in winter 2006/2007. SUNRISE is a joint project of the
Max-Planck-Institut fur Sonnensystemforschung (MPS), Katlenburg-Lindau,
with the Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, the
High-Altitude Observatory (HAO), Boulder, the Lockheed-Martin Solar and
Astrophysics Lab. (LMSAL), Palo Alto, and the Instituto de Astrofisica
de Canarias, La Laguna, Tenerife. In this paper we will present an
overview on the mission and give a description of the instrumentation,
now, at the beginning of the hardware construction phase.
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.
Bibcode: 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: The imaging magnetograph eXperiment for the SUNRISE balloon
Antarctica project
Authors: Martinez Pillet, Valentin; Bonet, Jose A.; Collados, Manuel
V.; Jochum, Lieselotte; Mathew, S.; Medina Trujillo, J. L.; Ruiz Cobo,
B.; del Toro Iniesta, Jose Carlos; Lopez Jimenez, A. C.; Castillo
Lorenzo, J.; Herranz, M.; Jeronimo, J. M.; Mellado, P.; Morales, R.;
Rodriguez, J.; Alvarez-Herrero, Alberto; Belenguer, Tomas; Heredero,
R. L.; Menendez, M.; Ramos, G.; Reina, Manuel; Pastor, C.; Sanchez,
A.; Villanueva, J.; Domingo, Vicente; Gasent, J. L.; Rodriguez, P.
Bibcode: 2004SPIE.5487.1152M
Altcode:
The SUNRISE balloon project is a high-resolution mission to study solar
magnetic fields able to resolve the critical scale of 100 km in the
solar photosphere, or about one photon mean free path. The Imaging
Magnetograph eXperiment (IMaX) is one of the three instruments that
will fly in the balloon and will receive light from the 1m aperture
telescope of the mission. IMaX should take advantage of the 15 days
of uninterrupted solar observations and the exceptional resolution
to help clarifying our understanding of the small-scale magnetic
concentrations that pervade the solar surface. For this, IMaX should
act as a diffraction limited imager able to carry out spectroscopic
analysis with resolutions in the 50.000-100.000 range and capable
to perform polarization measurements. The solutions adopted by the
project to achieve all these three demanding goals are explained in this
article. They include the use of Liquid Crystal Variable Retarders for
the polarization modulation, one LiNbO3 etalon in double pass
and two modern CCD detectors that allow for the application of phase
diversity techniques by slightly changing the focus of one of the CCDs.
Title: Magnetic Properties of the Solar Internetwork
Authors: Socas-Navarro, H.; Martínez Pillet, V.; Lites, B. W.
Bibcode: 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: Flux Cancellation in a Decaying Active Region
Authors: Martinez Pillet, V.; Sainz Dalda, A.; van Driel-Gesztelyi, L.
Bibcode: 2004cosp...35.1133M
Altcode: 2004cosp.meet.1133M
Flux Cancellation in a Decaying Active Region Flux cancellation
is observed in many regions on the Sun as internetwork, network
and active regions fields. It clearly plays a crucial role in the
constant flux processing observed in the solar surface. During the
decay of an active region, we have observed the in-situ dissapearance
of 70 % of its flux (from SOHO/MDI). Active region flux decay is a
global, large-scale, process crucial to the solar cycle. But the
flux cancellations, where the flux actually disappears, do take
place in very small scale regions. There opposite polarities meet and
vanish. The process needs of observations with sufficient sensitivity
and angular resolution. In the example presented here, we show how
up to 4 of these cancellations are associated with outward moving
material in the Corona (as observed by TRACE), including a major
active region filament eruption. Solar Orbiter, profiting from the
advantage observing position and near-corotation can follow these
subtle, but crucial, processes with the necessary set of instruments:
Magnetographs, Coronal imagers and spectrographs. For those events
occurring in the spacecraft solar vertical, one should not exclude
the detection of the phenomena in the in-situ instruments.
Title: Velocity fields in an irregular sunspot
Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V.
Bibcode: 2003ESASP.535..109J
Altcode: 2003iscs.symp..109J
Line-of-sight velocity fields in an irregular sunspot (NOAA 8990)
have been determined from Stokes-I spectra of the line Fe I 630.15
nm, obtained with the La Palma Stokes Polarimeter at the Swedish
Vacuum Solar Telescope on May 13, 2000. We show and discuss the
resulting velocity maps, the dependence of velocities on the
continuum intensities, and the correlation between velocities and
line asymmetries.
Title: SUNRISE: Balloon-borne High-Resolution Observation of the Sun
Authors: Solanki, S. K.; Curdt, W.; Gandorfer, A.; Schüssler,
M.; Lites, B. W.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.;
Sunrise Team
Bibcode: 2003ANS...324..113S
Altcode: 2003ANS...324..P20S
No abstract at ADS
Title: SUNRISE: a balloon-borne telescope for high resolution solar
observations in the visible and UV
Authors: Solanki, Sami K.; Gandorfer, Achim M.; Schuessler, Manfred;
Curdt, W.; Lites, Bruce W.; Martinez-Pillet, Valentin; Schmidt,
Wolfgang; Title, Alan M.
Bibcode: 2003SPIE.4853..129S
Altcode:
Sunrise is a light-weight solar telescope with a 1 m aperture for
spectro-polarimetric observations of the solar atmosphere. The telescope
is planned to be operated during a series of long-duration balloon
flights in order to obtain time series of spectra and images at the
diffraction-limit and to study the UV spectral region down to ~200 nm,
which is not accessible from the ground. The central aim of Sunrise
is to understand the structure and dynamics of the magnetic field in
the solar atmosphere. Through its interaction with the convective flow
field, the magnetic field in the solar photosphere develops intense
field concentrations on scales below 100 km, which are crucial for the
dynamics and energetics of the whole solar atmosphere. In addition,
Sunrise aims to provide information on the structure and dynamics
of the solar chromosphere and on the physics of solar irradiance
changes. Sunrise is a joint project of the Max-Planck-Institut fuer
Aeronomie (MPAe), Katlenburg-Lindau, with the Kiepenheuer-Institut fuer
Sonnenphysik (KIS), Freiburg, the High-Altitude Observatory (HAO),
Boulder, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL),
Palo Alto, and the Instituto de Astrofi sica de Canarias, La Laguna,
Tenerife. In addition, there are close contacts with associated
scientists from a variety of institutes.
Title: Liquid crystal optical retarders for IMaX to fly with SUNRISE
Authors: Jochum, Lieselotte; Herrero, Pilar; Collados, Manuel;
Martinez Pillet, Valentin; Rodriguez, Javier; Lopez, Manuel
Bibcode: 2003SPIE.4843...30J
Altcode:
The Instituto de Astrofísica de Canarias (IAC), Spain, together with
the Spanish company Tecdis Displays Ibérica, S.A., are developing
voltage tunable optical retarders using liquid crystals as phase
retarding medium. The ROCLIs are built for being used in the Imaging
Magnetograph eXperiment (IMaX), which is one of the instruments aboard
of the SUNRISE balloon mission (details about IMaX are described
in a different paper in this session). A big advantage of using
voltage tuned retarder plates is that no mechanisms are needed, which
reduces significantly failure risk, weight, power and cost, aspects
of particular importance in the SUNRISE balloon mission and for many
future space borne applications. A set of prototypes has already
been fabricated by Tecdis S.A. and is being characterized in the
IAC laboratories. The purpose of these prototypes is to evaluate and
demonstrate conceptually the suitability of the chosen liquid crystal
for our use in IMaX. First results are very promising. In this paper
we will present a full technical description of the ROCLIs for IMaX
together with the laboratory test and verification results.
Title: IMax: a visible magnetograph for SUNRISE
Authors: Jochum, Lieselotte; Collados, Manuel; Martínez Pillet,
Valentin; Bonet, Jose A.; del Toro Iniesta, Jose Carlos; Lopez,
Antonio; Alvarez-Herrero, Alberto; Reina, Manuel; Fabregat, Juan;
Domingo, Vicente
Bibcode: 2003SPIE.4843...20J
Altcode:
The description of the Imaging Magnetograph eXperiment (IMaX) is
presented in this contribution. This is a magnetograph which will
fly by the end of 2006 on a stratospheric balloon, together with
other instruments (to be described elsewhere). Especial emphasis
is put on the scientific requirements to obtain diffraction-limited
visible magnetograms, on the optical design and several constraining
characteristics, such as the wavelength tuning or the crosstalk between
the Stokes parameters.
Title: Sunrise: a 1-m balloon borne solar telescope
Authors: Solanki, S. K.; Schüssler, M.; Curdt, W.; Lites, B. W.;
Martinez Pillet, V.; Schmidt, W.; Title, A. M.; Sunrise Team
Bibcode: 2002ESASP.505...27S
Altcode: 2002solm.conf...27S; 2002IAUCo.188...27S
Sunrise is a light-weight solar telescope with a 1 m aperture
for spectro-polarimetric observations of the solar atmosphere. The
telescope is planned to be operated during a series of long-duration
balloon flights in order to obtain time series of spectra and images
at the diffraction-limit and to study the UV spectral region down to
≅200 nm, which is not accessible from the ground. The central aim of
Sunrise is to understand the structure and dynamics of the magnetic
field in the solar atmosphere. Interacting with the convective flow
field, the magnetic field in the solar photosphere develops intense
field concentrations on scales below 100 km, which are crucial for the
dynamics and energetics of the whole solar atmosphere. In addition,
Sunrise aims to provide information on the structure and dynamics of
the solar chromosphere and on the physics of solar irradiance changes.
Title: Decay of sunspots
Authors: Martínez Pillet, V.
Bibcode: 2002AN....323..342M
Altcode:
The photometric decay of sunspots is studied in some detail. Aspects
related to leader vs. follower sunspot decay are presented and our
current understanding of the physical mechanisms involved critically
reviewed. The intrinsic instability of follower spots to form a stable
sunspot cannot be understood in terms of the fluting stability as
proposed long time ago. For leader sunspots, the slow decay phase
is considered in the light of diffusive models that spread the flux
of the spot over a larger area. It is shown that the Moving Magnetic
Feature (MMF) phenomenon, while probably part of the decay process,
has an origin not related to the decay process itself. Magnetic flux
losses from leader sunspots are 3 to 8 times slower than the pace of
net flux generation seen in the moat region. It is argued that MMFs
are originated from the interaction of the field free convection
(moat flows) and the Evershed magnetized channels outside the spot.
Title: Small-Scale Magnetic Structure in the Photosphere: Relevance
to Space Weather Phenomena
Authors: Martínez Pillet, V.
Bibcode: 2002stma.conf....9M
Altcode:
No abstract at ADS
Title: High-resolution solar polarimetry with Sunrise
Authors: Schmidt, W.; Solanki, S. K.; Lites, B. W.; Title, A. M.;
Martínez Pillet, V.
Bibcode: 2001AN....322..363S
Altcode:
Sunrise is a solar telescope with an aperture of 1 m, and is dedicated
for spectropolarimetric measurements in the visible and the near
UV. The total wavelength range is 200 to 1000 nm for narrowband imaging
and diagnostic spectroscopy. Sunrise is planned as a stratospheric
long-duration balloon mission with a first flight in 2006
Title: A proposal for the visible-light imager magnetograph
Authors: von der Lühe, O.; Martinez Pillet, V.; Schmidt, W.;
Collados, M.
Bibcode: 2001ESASP.493..421V
Altcode: 2001sefs.work..421V
No abstract at ADS
Title: Solar encounter
Authors: Battrick, Bruce; Sawaya-Lacoste, H.; Marsch, E.; Martinez
Pillet, V.; Fleck, B.; Marsden, R.
Bibcode: 2001ESASP.493.....B
Altcode: 2001sefs.work.....B
The prime objectives of the workshop were to: inform the community
about the science opportunities of the Solar Orbiter mission; to
provide a forum for sharpening and focussing the science goals; allow
the hardware groups and instrument proposers to critically review the
payload; establish international contacts and collaborations.
Title: Intercomparison of SOUP, ASP, LPSP, and MDI magnetograms
Authors: Berger, T.; Lites, B.; Martinez-Pillet, V.; Tarbell, T.;
Title, A.
Bibcode: 2001AGUSM..SP51B12B
Altcode:
We compare simultaneous magnetograms of a solar active region taken by
the Advanced Stokes Polarimeter (ASP) and the Solar Optical Universal
Polimeter (SOUP) in 1998. In addition we compare magnetograms taken by
the La Palma Stokes Polarimeter (LPSP), the Michelson Doppler Imager
(MDI) on SOHO, and the SOUP instrument in 2000. The SOUP instrument on
the Swedish Vacuum Solar Telescope (SVST) attains the highest spatial
resolution but has the least understood calibration; the ASP on the Dunn
Solar Telescope (DST) at Sacramento Peak attains the highest magnetic
field precision. The goal of the program is to better quantify the
SOUP magnetograms and thereby study magnetic element dynamics in the
photosphere with higher precision.
Title: A Photometric and Magnetic Analysis of the Wilson Effect
Authors: Steinegger, M.; Bonet, J. A.; Vázquez, M.; Martinez
Pillet, V.
Bibcode: 2001ASSL..259..279S
Altcode: 2001dysu.conf..279S
For two sunspot groups observed in June 1992 we analyze the
center-to-limb variation and height dependence of various geometrical
parameters describing the Wilson effect by using continuum observations
and simultaneously obtained images of the degree of polarization.
Title: Spectral signature of uncombed penumbral magnetic fields. Reply
Authors: Martínez Pillet, V.
Bibcode: 2001A&A...369..644M
Altcode:
A combination of two penumbral models similar to those used by
Martínez Pillet (2000) is presented. One matches the observed
rms fluctuations perfectly while the other reproduces the observed
Net Circular Polarization. No factor three mismatch exists in this
case. The rationale of using two different, but strongly coupled,
models is explained.
Title: Optical Tomography of a Sunspot. II. Vector Magnetic Field
and Temperature Stratification
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 2001ApJ...547.1130W
Altcode:
An observational determination of the three-dimensional magnetic
and thermal structure of a sunspot is presented. It has been
obtained through the application of the SIR inversion technique
(Stokes Inversion based on Response functions) on a low-noise, full
Stokes profile two-dimensional map of the sunspot as observed with
the Advanced Stokes Polarimeter. As a result of the inversion, maps
of the magnetic field strength, B, zenith angle, γ, azimuth, χ, and
temperature, T, over 25 layers at given optical depths (i.e., an optical
tomography) are obtained, of which those between logτ5=0 and
logτ5=-2.8 are considered to provide accurate information on
the physical parameters. All over the penumbra γ increases with depth,
while B is larger at the bottom layers of the inner penumbra (as in
the umbra) but larger at the top layers of the outer penumbra (as in
the canopy). The corrugation of the penumbral magnetic field already
observed by other authors has been confirmed by our different inversion
technique. Such a corrugation is especially evident in the zenith angle
maps of the intermediate layers, featuring the presence of the so-called
spines that we further characterize: spines are warmer and have a less
inclined magnetic field than the spaces between them and tend to have a
smaller gradient of γ with optical depth over the entire penumbra, but
with a field strength which is locally stronger in the middle penumbra
and locally weaker in the outer penumbra and beyond in the canopy. In
the lower layers of these external parts of the sunspot, most of the
field lines are seen to return to the solar surface, a result that is
closely connected with the Evershed effect (e.g., Westendorp et al.,
the third paper in this series). The Stokes V net area asymmetry map
as well as the average B, γ, and T radial distributions (and that
of the line-of-sight velocities; see the third paper in this series)
show a border between an inner and an outer penumbra with different
three-dimensional structure. We suggest that it is in this middle zone
where most of a new family of penumbral flux tubes (some of them with
Evershed flow) emerge interlaced (both horizontally and vertically)
among themselves and with the ``background'' magnetic field of the
penumbra. The interlacing along the line of sight is witnessed by
the indication of many points in the outer penumbra showing rapid
transitions with height between two structures, one with very weak
and inclined magnetic field at the bottom of the photosphere and the
other with a stronger and less inclined magnetic field. Over the whole
penumbra, and at all optical layers, a constant but weak deviation from
radiality of some 5° is detected for the azimuth of the vector magnetic
field, which may be in agreement with former detections but which is
not significantly higher than the size of the errors for this parameter.
Title: Optical Tomography of a Sunspot. III. Velocity Stratification
and the Evershed Effect
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martínez Pillet, V.
Bibcode: 2001ApJ...547.1148W
Altcode:
The stratification with optical depth of the line-of-sight (LOS)
velocity of a simple, isolated, round sunspot observed with the Advanced
Stokes Polarimeter (ASP; Elmore et al.) presented here completes this
series of papers that investigates the stratification in optical depths
of such a typical sunspot. These results have been obtained through the
use of the SIR technique (Stokes Inversion based on Response functions
of Ruiz Cobo & del Toro Iniesta). From these data we have confirmed
that there are strong downflowing velocities at logτ5=0
that coincide spatially with the places where the magnetic field points
downward (Westendorp Plaza et al.). Further confirmation is obtained
by the application of the same method on a different sunspot, already
analyzed with the Milne-Eddington inversion technique (Stanchfield,
Thomas, & Lites). These downflows reconcile observations that have
detected Evershed velocities outside sunspots together with suggestions
of the possible return of the flow within the penumbra. The Evershed
flow seems to be concentrated in elevated channels not thicker than 1 or
2 scale heights that are mostly located in the space between magnetic
spines, i.e., in places where the magnetic field is more inclined,
weaker in the inner-middle penumbra, and stronger in the outer penumbra
and beyond the visible limits of the sunspot. This conclusion is
based upon the tight correlation found between LOS velocities and
the (reported in the second paper of this series) magnetic field
strength and zenith angle. The upstreaming material is seen in the
inner penumbra and the downstreaming in the outer penumbra. A strong
increase with optical depth has been obtained for the LOS velocities
that provides indications of the superposition of Evershed channels
along the LOS. The differential opacity effect between the center-side
and the limb-side penumbra, already reported in the second paper in
this series, is also seen in the velocity maps and has suggested the
comparison of the vertical mass flux through the upstreaming zones
(mostly seen in the center side) and the downstreaming zones (mostly
seen in the limb side), obtaining a fairly good balance between the two.
Title: Full Stokes LPSP Observations of the Na D1 and
D2 Lines in Magnetized Regions close to the Solar Limb
Authors: Martínez Pillet, V.; Trujillo Bueno, J.; Collados, M.
Bibcode: 2001ASPC..236..133M
Altcode: 2001aspt.conf..133M
No abstract at ADS
Title: ASP Observations - First Analysis of Mgb2 Stokes
Parameters
Authors: Briand, C.; Martínez Pillet, V.
Bibcode: 2001ASPC..236..565B
Altcode: 2001aspt.conf..565B
No abstract at ADS
Title: High-resolution Solar Polarimetry with Sunrise
Authors: Schmidt, W.; Solanki, S. K.; Schüssler, M.; Curdt, W.;
Lites, B. W.; Title, A. M.; Martinez Pillet, V.
Bibcode: 2001AGM....18S1001S
Altcode:
Sunrise is a 1m balloon-borne solar telescope. It is equipped with
a spectrograph polarimeter which combines vector-polarimetry in the
visible with diagnostic spectroscopy in the visible and the UV, down
to 200 nm. The instrumentation includes a filter-magnetograph and a
medium-band filtergraph. The wavelength bands of the latter include
the CH-band (430.6 nm) and a UV continuum at 205 nm. Diffraction
limited resolution in the UV will be achieved by employing a phase
diversity technique. The main telescope is based on a lightweight
silicon-carbide mirror, developed within the Solar Lite program. During
the long-duration flight at Antarctica, foreseen for late 2005, Sunrise
will continuously observe the sun for a period of about ten days,
with constant image quality across the full field of view. In-flight
alignment of the telescope optics will be controlled by a wavefront
sensor. The main goal of Sunrise is to understand the structure and
dynamics of the magnetic field in the atmosphere of the sun. To this
end, Sunrise will observe small magnetic flux concentrations with
dimensions of less than 70 km with high polarimetric accuracy. At the
same time, Sunrise will provide diffraction-limited filtergrams of
the photosphere and chromosphere with a resolution down to 35 km at
a wavelength of 200 nm.
Title: Chromosphere: Emerging Flux Regions
Authors: Martínez Pillet, V.
Bibcode: 2000eaa..bookE2000M
Altcode:
A description of the emergence of large concentrations of magnetic
fields (active regions) at the solar surface is presented. The dark
structures known as SUNSPOTS are a consequence of this process....
Title: Spectral signature of uncombed penumbral magnetic fields
Authors: Martínez Pillet, V.
Bibcode: 2000A&A...361..734M
Altcode:
The uncombed penumbral model proposed by Solanki & Montavon
(\cite{sol93a}) is used to understand some recent observational
results found in penumbrae. This model uses a penumbral magnetic
field structured into horizontal flux tubes embedded in a more
vertical background field. A modified version of this model, with
a weaker field strength in the horizontal tubes, is used to explain
the gradient with height of field strength and inclination found in
studies using inversion techniques. These studies have found that
over a range of 300 km, the field strength of the outer penumbra
increases with height by more than 500 G. Similarly, the field
inclination decreases with height by 30o in the same range
of heights. We show that spectra generated by the uncombed model
can give rise to these two effects as long as the horizontal tubes
(of ~ 100 km diameter) remain unresolved. We also study the linear,
quadratic and rms fluctuations of the inclination gradients that can
be generated by the uncombed model. These gradients are found to be
compatible with those obtained from the null divergence condition and
those derived from observations of net circular polarization. A key
ingredient to explain these gradients is the contribution of the two
boundary layers that enclose the horizontal magnetic tubes as seen by
the line-of-sight. Our realization of the uncombed model also predicts
values of the net circular polarization observed with the Advanced
Stokes Polarimeter. The existence of a pure background penumbral field
as proposed by the model is, however, put into question.
Title: Long-Term Observations of Solar Active Regions at the VNT
Authors: Bonet, J. A.; Casas, R.; Giammanco, C.; Martinez Pillet,
V.; Vazquez
Bibcode: 2000ESASP.463..635B
Altcode: 2000sctc.proc..635B
No abstract at ADS
Title: Working Group 1: Magnetic Field Structuring
Authors: van Driel-Gesztelyi, L.; Martinez Pillet, V.
Bibcode: 1999ESASP.446...71V
Altcode: 1999soho....8...71V
No abstract at ADS
Title: Making sense of sunspot decay - II. Deviations from the Mean
Law and Plage Effects
Authors: Petrovay, K.; Martínez Pillet, V.; van Driel-Gesztelyi, L.
Bibcode: 1999SoPh..188..315P
Altcode: 1999astro.ph..6258P
In a statistical analysis of Debrecen Photoheliographic Results sunspot
area data we find that the logarithmic deviation (log D)' of the area
decay rate D from the parabolic mean decay law (derived in the first
paper in this series) follows a Gaussian probability distribution. As
a consequence, the actual decay rate D and the time-averaged decay
rate are also characterized by approximately lognormal distributions,
as found in an earlier work. The correlation time of (log D)' is about
3 days. We find a significant physical anticorrelation between (log
D)' and the amount of plage magnetic flux of the same polarity in an
annulus around the spot on Kitt Peak magnetograms. The anticorrelation
is interpreted in terms of a generalization of the turbulent erosion
model of sunspot decay to the case when the flux tube is embedded in
a preexisting homogeneous `plage' field. The decay rate is found to
depend inversely on the value of this plage field, the relation being
very close to logarithmic, i.e., the plage field acts as multiplicative
noise in the decay process. A Gaussian probability distribution of
the field strength in the surrounding plage will then naturally lead
to a lognormal distribution of the decay rates, as observed. It is
thus suggested that, beside other multiplicative noise sources, the
environmental effect of surrounding plage fields is a major factor
in the origin of lognormally distributed large random deviations from
the mean law in the sunspot decay rates.
Title: TIP: The Tenerife Infrared Polarimeter
Authors: Martínez Pillet, V.; Collados, M.; Bellot Rubio, L. R.;
Rodríiguez Hidalgo, I.; Ruiz Cobo, B.; Soltau, D.
Bibcode: 1999AGAb...15...89M
Altcode: 1999AGM....15..P05M
The aim of the IAC Tenerife Infrared Polarimeter is to obtain
quantitative measurements of the polarization state of the solar
radiation collected in near-infrared wavelengths by the Gregory Coudé
Telescope and the Vacuum Tower Telescope of the Observatorio del Teide
(Spain). In this contribution we describe the analyzer, instrumental
calibration, and detector subsystems of TIP, and give details concerning
the specifications of the instrument.
Title: Measurements of the solar aureole at the Teide Observatory
Authors: González Jorge, H.; Martínez Pillet, V.; Vázquez, M.;
Pallé, P.; McGovern, F.; Raes, F.
Bibcode: 1998NewAR..42..515G
Altcode:
Daily measurements of the solar aureole were made at the Vacuum Newton
Telescope ( D=40 cm) at the Teide Observatory (Tenerife) for various
airmasses. We use these measurements to understand how the aureole
is produced and to extrapolate visible measurements to the infrared
range (1.6 μm). This information will be used to correct sunspot
photometric measurements. This programme is included in the second
Aerosol Characterization Experiment (ACE-2) held on Tenerife from
mid June to July 1997. During this period a large variety of aerosol
measurements were made at different altitudes on the island and by
aircraft flying over this area of the North Atlantic Ocean. This
information will be used to constrain the physical parameters of the
aerosols needed for our extrapolation.
Title: Velocity Oscillations in Active Sunspot Groups
Authors: Balthasar, H.; Martínez Pillet, V.; Schleicher, H.; Wöhl, H.
Bibcode: 1998SoPh..182...65B
Altcode:
Time series of two-dimensional spectra were taken with the Göttingen
2D spectrometer at the VTT on Tenerife in 1996. They were investigated
for Doppler velocities and velocity oscillations in small spots and
pores of rapidly evolving sunspot groups. For the present measurements
the magnetically insensitive lines Fe i 557.6 nm and Fe i 709.0 nm
were selected.
Title: Vector magnetic fields of emerging solar flux. I. Properties
at the site of emergence
Authors: Lites, B. W.; Skumanich, A.; Martinez Pillet, V.
Bibcode: 1998A&A...333.1053L
Altcode:
Several small emerging bipolar regions have been observed with
the Advanced Stokes Polarimeter (ASP), including extensive time
series measurements of one small region. Both new and previously
recognized properties of the actual site of first emergence, where
the magnetic field is nearly horizontal to the surface, are revealed
by these observations. They provide the most complete and accurate
observational description to date of newly emerging vector magnetic
fields. We find that: 1) the strength of the magnetic field at the site
of the emergence (where the vector field is nearly parallel to the
solar surface) ranges from about 200 to 600 G, 2) as individual flux
elements migrate rapidly away from the emergence zone, they attain
kiloGauss strengths only after becoming oriented nearly vertically,
3) the emergence zone is dotted by small, transient, upward rising ( ~
1 km s(-1) ) horizontal magnetic elements as indicated by the Doppler
shift of the polarized spectral profiles, 4) the leading polarity flux
coalesces immediately into a compact region which forms a pore, but the
emerging following polarity flux is spatially much less compact, 5) some
``moving magnetic features'' having the same magnetic polarity as the
growing pore, but on the opposite side of the pore from the emergence
zone, coalesce with the pore during the observation period, and 6)
the observations suggest a low canopy of weak horizontal magnetic
fields arches over the emergence zone. These observations support a
widely accepted picture of emerging bipolar flux: the buoyantly rising
flux transports mass from the photosphere into the chromosphere, where
it then may drain downward along arched magnetic loops. The observed
formation of a pore suggests that emergence of subsurface structure,
not organized flows near the surface, is largely responsible for the
apparent coalescence of sunspots from more diffuse fields viewed at
the solar surface. These observations neither confirm nor refute the
operation of convective collapse of flux tubes.
Title: Optical Tomography of a Sunspot. I. Comparison between Two
Inversion Techniques
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1998ApJ...494..453W
Altcode:
A quantitative comparison between the Milne-Eddington (ME) inversion
technique implemented by Skumanich & Lites and the SIR (Stokes
Inversion based on Response Functions) proposed by Ruiz Cobo &
del Toro Iniesta is presented. Numerical experiments are carried
out to explore the capabilities and limitations of both diagnostic
techniques. Such experiments consist of inversions of Stokes profiles
previously synthesized in ``realistic'' solar atmospheric models. The
results show that the ME inversion provides accurate, line-of-sight
(LOS) averaged values for the input stratification of the vector
magnetic field. Its greater speed compared to SIR makes it useful for
quick analysis of large quantities of data (such as those currently
provided by modern spectropolarimeters) if one is only interested
in LOS-averaged quantities. However, the higher order description
of the atmosphere used by SIR (which acknowledges variation of the
thermal, dynamic, and magnetic parameters through the photosphere)
allows retrieval of the stratification of all these parameters to good
accuracy. This is so even in the presence of discontinuities such
as those foreseen in magnetic canopies of sunspots. The trade-offs
between thermodynamic and magnetic parameters observed in some ME
inversions are reduced considerably in the case of SIR inversions
because of the more realistic treatment of the thermodynamics in this
analysis. Notably, both allow one to extract quantitative inferences of
fairly weak magnetic fields (below 500 G), even when they are applied
to Zeeman-sensitive lines in the visible spectrum; i.e., well below
the commonly accepted limit of 500 G. The thermodynamic parameters
resulting from the ME inversion are understood theoretically in terms
of the generalized response functions introduced by Ruiz Cobo &
del Toro Iniesta and through the concept of height of formation
for inferred values proposed by Sánchez Almeida, Ruiz Cobo, &
del Toro Iniesta. The present comparison and verification of
the reliability of inversion methods is a natural first step toward
the ongoing analysis of the three-dimensional magnetic structure of
a sunspot. By using SIR (with ME results for initialization) on maps
of a whole sunspot observed by the Advanced Stokes Polarimeter, we
obtain maps at different optical layers (i.e., an optical tomography)
of the temperature, vector magnetic field, and LOS velocity. Such a
tomography will appear in subsequent papers of the present series. To
illustrate fits to the observed Stokes profiles, we show here actual
inversion results for three points observed within a sunspot: one
within the umbra, another from the outermost parts of the penumbra,
and a third from the magnetic canopy surrounding the sunspot.
Title: Vector Magnetic Fields of Emerging Solar Flux
Authors: Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1998ESASP.417..259M
Altcode: 1998cesh.conf..259M
No abstract at ADS
Title: Evidence for a downward mass flux in the penumbral region of
a sunspot
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martinez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1997Natur.389...47W
Altcode:
No abstract at ADS
Title: The Calibration of the Advanced Stokes Polarimeter
Authors: Skumanich, A.; Lites, B. W.; Martínez Pillet, V.;
Seagraves, P.
Bibcode: 1997ApJS..110..357S
Altcode:
We describe and apply the methods that have been developed to calibrate
the Advanced Stokes Polarimeter and to compensate for the polarization
effects introduced by the Vacuum Tower Telescope at the National Solar
Observatory/Sunspot. A seven-parameter model of the telescope is fitted
to data obtained at a variety of mirror angles using observations
of both the center of the solar disk and that point within a sunspot
umbra at which the magnetic field is oriented as close to the line of
sight as possible. The response matrix of the polarimeter itself is
determined by the use of polarizing calibration optics that modify
the polarization state of the beam exiting the telescope but before
entering the polarimeter. A global least-squares solution is obtained
simultaneously for the response matrix and the telescope parameters. A
detailed gain-correction procedure is described that reduces the
multiplicative gain errors in the spectral images to typically less
than 1%. We have successfully recovered net-linear polarization
profiles with peak amplitudes of 1 × 10-3Ic
against an instrumentally produced background polarization of ~=1-5 ×
10-2Ic. Net-polarization signals smaller than
~=3 × 10-4Ic are lost, even with sufficient
averaging, in a background due to photometric and other calibration
errors.
Title: Space Certifiability of LCVRs
Authors: del Toro Iniesta, J. C.; Martinez Pillet, V.; Gonzalez
Escalera, V.
Bibcode: 1997ASPC..118..356D
Altcode: 1997fasp.conf..356D
This contribution is a report on a test campaign carried out by the
IAC, in collaboration with Construcciones Aeronauticas, S.A. (CASA) as
a main contrac tor, for exploring the capabilities of liquid crystal
variable retarders (LCVRs) to be u sed in future space missions as
the core of the modulation package of a polarimetric device, used as
a post-focus instrument of a visible solar telescope.
Title: Active Region Magnetic Fields. I. Plage Fields
Authors: Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1997ApJ...474..810M
Altcode:
We present observations taken with the Advanced Stokes Polarimeter
(ASP) in active-region plages and study the frequency distribution of
the magnetic field strength (B), inclination with respect to vertical
(γ), azimuthal orientation (χ), and filling factor (f). The
most common values at disk center are B = 1400 G, γ < 10°,
no preferred east-west orientation, and f = 15%. At disk center,
there is a component of weak (<1000 G), more horizontal fields
that corresponds to arching field lines connecting footpoints of
different polarities. The center-to-limb variation (CLV) of the
field strength shows that, close to the limb (μ = 0.3), the field
strength is reduced to 800 G from its disk-center value. This can be
interpreted as a gradient of B with height in solar plages of around
-3 G km-1. From this CLV study, we also deduce that magnetic
field lines remain vertical for the entire range of heights involved. A
similar analysis is performed for structures found in active regions
that show a continuous distribution of azimuths (resembling sunspots)
but that do not have a darkening in continuum. These ``azimuth centers''
show slightly larger values of B than normal plages, in particular
at their magnetic center. Filling factors are also larger on average
for these structures. The velocities in the magnetic component
of active regions have been studied for both averaged Stokes profiles
over the entire active region and for the spatially resolved data. The
averaged profiles (more representative of high filling factor regions)
do not show any significant mean velocities. However, the spatial
average of Doppler velocities derived from the spatially resolved
profiles (i.e., unweighted by filling factor) show a net redshift at
disk center of 200 m s-1. The spatially resolved velocities
show a strong dependence on filling factor. Both mean velocities and
standard deviations are reduced when the filling factor increases. This
is interpreted as a reduction of the p-mode amplitude within the
magnetic component. Strong evidence for velocities transverse to the
magnetic field lines has been found. Typical rms values are between
200 and 300 m s-1, depending on the filling factor. The
possible importance of these transverse motions for the dynamics of
the upper atmospheric layers is discussed. The asymmetries of the
Stokes profiles and their CLV have been studied. The averaged Stokes
V profiles show amplitude and area asymmetries that are positive
at disk center and become negative at the limb. Both asymmetries,
and for the two Fe I lines, are maximized away from disk center. The
spatially resolved amplitude asymmetries show a clear dependence on
filling factor: the larger the filling factor, the smaller the amplitude
asymmetry. On the other hand, the area asymmetry is almost independent
of the filling factor. The only observed dependence is the existence
of negative area-asymmetry profiles at disk center for filling factors
smaller than 0.2. Around 20% of the observed points in a given plage
have negative area asymmetry. The amplitude asymmetry of Stokes V is,
on the other hand, always positive. The amplitude asymmetries of the
linear polarization profiles are observed to have the same sign as
the Stokes V profiles. Similarly, the same CLV variation of the linear
polarization amplitude asymmetries as for Stokes V has been found. The
scenarios in which this similarity can exist are studied in some detail.
Title: Polarimetric Measurements of Sunspots
Authors: Martinez Pillet, V.
Bibcode: 1997ASPC..118..212M
Altcode: 1997fasp.conf..212M
Making emphasis on observations that have included some type of
polarization analysis, I concentrate on two subjects. First, the vector
magnetic field configuration of structures with different sizes is
reviewed. I cover from magnetic knots, and their relation to small scale
magnetic elements, to large sunspots. In doing so, a different concept
of how a pore should be described is proposed. Second, the fibril
organization of the magnetic field in penumbrae is reviewed. Both,
field strength and inclination fluctuations in the azimuthal direction
are seen. The necessary gas pressure fluctuations needed to achieve
force balance are analyzed. As a solution to the missing Evershed
flow problem, the findings of a return flux surrounding sunspots by
Westendorp et al. (1997b) are considered.
Title: The IAC Solar Polarimeters: Goals and Review of Two Ongoing
Projects
Authors: Sanchez Almeida, J.; Collados, M.; Martinez Pillet, V.;
Gonzalez Escalera, V.; Scharmer, G. B.; Shand, M.; Moll, L.; Joven,
E.; Cruz, A.; Diaz, J. J.; Rodriguez, L. F.; Fuentes, J.; Jochum,
L.; Paez, E.; Ronquillo, B.; Carranza, J. M.; Escudero-Sanz, I.
Bibcode: 1997ASPC..118..366S
Altcode: 1997fasp.conf..366S
The IAC is currently developing two similar polarimeters, one for
optical wavelengths and one for near infra-red wavelengths (1.5
mu m). Both instruments will provide spectra of the four Stokes
parameters over 2D solar regions. The visible spectro-polarimeter will
be operated at the Swedish Tower (La Palma), and it is being developed
in collaboration with the Royal Swedish Academy of Sciences. We intend
to take advantage of the excellent seeing conditions at this telescope,
while maintaining high polarimetric precision. The IR polarimeter
is being designed for the German VTT (Tenerife) which has better
angular resolution in the near infra-red. This report describes the
goals and technical solutions. It also briefs on the current status
of the projects.
Title: Velocity oscillations in active sunspot groups.
Authors: Balthasar, H.; Martínez Pillet, V.; Schleicher, H.; Wöhl, H.
Bibcode: 1997AGAb...13...12B
Altcode:
No abstract at ADS
Title: Inversion Techniques Applied to Sunspot Spectropolarimetric
Data
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martinez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1997ASPC..118..197W
Altcode: 1997fasp.conf..197W
Two inversion techniques are compared: the Unno-Rachkov\-sky fitting
method (UR) and the Stokes Inversion based on Response functions
(SIR). Results with synthetic profiles in sunspot model atmospheres and
real data show that whilst UR is well suited for recovering a constant
vec B, SIR enables us to know the run with depth of vec B and the line
of sight velocity together with the temperature stratification.
Title: Optical Tomography of a Sunspot: Preliminary Results
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martinez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1997ASPC..118..202W
Altcode: 1997fasp.conf..202W
Preliminary results of the inversion of spectropolarimetric maps
of a sunspot observed with the Advanced Stokes Polarimeter (ASP) are
presented. The method used, Stokes Inversion based on Response functions
(SIR), does not assume constancy of the different parameters with
depth, thus enabling us to embark on an analysis of the information at
different layers in continuum optical depth (i.e. optical tomography),
of a sunspot's photosphere. Maps of the vector magnetic field and
other physical quantities like temperature or line-of-sight velocity at
several optical depths show a new and promising view of the structure
of a sunspot, casting light on long standing debates as those over
penumbral `corrugated' fields (spines), superpenumbral canopies,
return flux, or the nature of the Evershed effect.
Title: The magnetic structure of pores and sunspots derived from
Advanced Stokes Polarimeter data.
Authors: Keppens, R.; Martinez Pillet, V.
Bibcode: 1996A&A...316..229K
Altcode:
We investigate the radial variation of the magnetic field structure
across sunspots, pores and azimuth centers (ACs). We define ACs as
magnetic structures of about the same size as pores (all structures
studied here are larger than 3 Mm diameter), but without a clear
(at least 5%) continuum decrease associated with them. We start
from the full 3D vector fields as observed with the Advanced Stokes
Polarimeter (ASP), and perform a statistical study of the azimuthally
averaged field components in the local cylindrical reference frame
centered on the structures. Our statistical study comprises a sample
of 16 sunspot observations, a sample of 51 pores, and a sample of
22 ACs. For all structures, we derive mean radial profiles and their
standard deviations. Due to the relatively large sample of pores, we
are able to investigate variations of this mean radial field structure
with the size of the pores. On the basis of our statistics, we identify
systematic changes in the magnetic field structure over a considerable
size range. We suggest how this may be the natural consequence of a
formation scenario for the largest pores, by a lateral clustering of
magnetic elements. Indeed, in this process, an AC may develop into a
dark pore and gradually grow in size through the incremental addition of
magnetic flux. Several observations where ACs turn into pores provide
an estimate of about 4-5x10^19^Mx for the critical magnetic flux at
which such transitions occur. We confirm the existence of a magnetic
canopy for pores of all sizes, as their magnetic extent is virtually
always larger than the associated continuum darkening. We observe
a relatively rapid change in the continuum appearance of a large
pore in the sample. We identify the associated changes in the field
structure, and confront it with the determined mean field variation
across sunspots. It appears that we have witnessed the formation of
a partial penumbra.
Title: Line Asymmetries and the Microstructure of Photospheric
Magnetic Fields
Authors: Sanchez Almeida, J.; Landi Degl'Innocenti, E.; Martinez
Pillet, V.; Lites, B. W.
Bibcode: 1996ApJ...466..537S
Altcode:
A systematic structuring of magnetic fields over scales much smaller
than the mean free path of photospheric photons may be responsible for
the observed asymmetrical Stokes profiles. We explore this possibility
by deriving the radiative transfer equation for microstructured magnetic
atmospheres (the MISMA approximation). This equation is subsequently
employed to show that very schematic MISMA scenarios for the penumbrae
of sunspots, plage and network regions, and internetwork regions produce
Stokes profiles that have the observed asymmetries. The details of
these model atmospheres are of secondary importance, but the ease of
generating the type of observed asymmetries with MISMAs is significant,
so the existence of MISMAs deserves serious consideration. Should such
microstructures exist, the techniques currently employed to infer
properties of the solar photosphere need to be revised. MISMAs are
also of concern for the physics of the photosphere itself. These two
topics are briefly discussed.
Title: Magnetic Flux Emergence Observed with the Advanced Stokes
Polarimeter
Authors: Lites, B.; Martinez Pillet, V.
Bibcode: 1996AAS...188.3313L
Altcode: 1996BAAS...28Q.870L
We have carried out quantitative observations of the vector magnetic
field during the emergence of three small bipolar active regions in
June, 1992, July 1993, and September 1994 using the Advanced Stokes
Polarimeter (ASP). The region of horizontal magnetic field at the actual
site of emergence is always characterized by low magnetic field strength
(i.e. considerably less than 1000 Gauss). We find a strong relationship
between field strength and inclination in these regions. This suggests
that 1) flux emerging from below the photosphere does not coalesce
into strong flux tubes until it reaches the photosphere, becomes
nearly vertical as a result of magnetic buoyancy, and is then acted
upon by convective collapse, and 2) the field strength of flux rising
through the convection zone may be in rough equipartition with the fluid
motions. We find the flux emergence zone to be characterized by highly
variable (both spatially and temporally) fill factors for the magnetic
field, suggesting that the flux below the surface is filamentary,
that it rises rapidly through the photosphere to form a magnetic
canopy above the emergence region. Sequences of Hα on- and off-band
images obtained with the ASP reveal the accompanying development of
the arch-filament system, and suggest that the material within the
Hα structures is supplied by a siphon flow as evidenced by apparent
chromospheric red shifts on the sides of the loops closest to a large
pore, and blue shifts where the fields anchor in plage regions. Proper
motions of the magnetic flux images throughout a day's observation
indicate the presence of a persistent vortex flow on a small scale
(a few arcseconds). The National Center for Atmospheric Research is
sponsored by the National Science Foundation.
Title: Small-Scale Horizontal Magnetic Fields in the Solar Photosphere
Authors: Lites, B. W.; Leka, K. D.; Skumanich, A.; Martinez Pillet,
V.; Shimizu, T.
Bibcode: 1996ApJ...460.1019L
Altcode:
We present recent observations of quiet regions near the center
of the solar disk using the Advanced Stokes Polarimeter. These
observations reveal a component of the solar magnetic field heretofore
unobserved: isolated, small-scale (typically 1"-2" or smaller),
predominantly horizontal magnetic flux structures in the solar
photosphere. These features occur in isolation of the well-known,
nearly vertical flux concentrations usually seen in the photospheric
"network." Hence we ascribe this horizontal flux to the photospheric
"internetwork." They reveal themselves by the distinct signature
of the Stokes Q and U polarization profiles, which are symmetric
about the line center. The polarization signals are weak, with peak
amplitudes typically ∼0.1%-0.2% of the continuum intensity in the
resolved spectral profiles, but they are well above the noise level
of these observations (≍0.05%). Such magnetic fields are weak
(significantly less than 1000 G) and largely horizontal owing to
the absence, or near absence, of accompanying Stokes V polarization
when observed at the center of the solar disk. These horizontal field
elements are often associated with blueshifted Stokes line profiles,
and they often occur between regions of opposite polarity (but weak)
Stokes V profiles. The horizontal elements are short-lived, typically
lasting ∼5 minutes. Our observations suggest that we are viewing the
emergence of small, concentrated loops of flux, carried upward either
by granular convection or magnetic buoyancy. Even though these entities
show weak field strengths, they also seem to be fairly common, implying
that they could carry the order of 1024 Mx of magnetic flux
to the surface on a daily basis. However, further observational study
is needed to identify the specific nature of this phenomenon.
Title: A proposal for a low instrumental polarization coude
telescope. II. The German Gregory-Coude Telescope at the Observatorio
del Teide.
Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Kneer, F.
Bibcode: 1995A&AS..113..359S
Altcode:
We have put into practice the technique to minimize the instrumental
polarization (IP) of coude telescopes proposed by Martinez Pillet &
Sanchez Almeida (1991): a λ/2-plate inserted into the optical path,
with the proper orientation, cancels the IP. The compensation of the
Gregory-Coude Telescope at the Observatorio del Teide turns out to
fulfil theoretical expectations. Empirical tests at 630nm demonstrate
that its IP decreases by a factor ~4. We show that the residual IP is
not intrinsic to the method but it is due to the limited precision of
the retarder presently used. In addition, observations indicate that
the insertion of the λ/2-plate does not noticeably deteriorate the
optical quality of the whole telescope. In short, this work proves
the practical soundness of the λ/2-plate technique to reduce IP.
Title: The Possible Ascent of a Closed Magnetic System through
the Photosphere
Authors: Lites, B. W.; Low, B. C.; Martinez Pillet, V.; Seagraves,
P.; Skumanich, A.; Frank, Z. A.; Shine, R. A.; Tsuneta, S.
Bibcode: 1995ApJ...446..877L
Altcode:
We present a comprehensive interpretation of the evolution of a small
magnetic region observed during its entire disk passage. The vector
magnetic field measurements from the Advanced Stokes Polarimeter,
along with Hα and magnetogram measurements from the Lockheed SOUP
instrument operating at the Swedish Solar Observatory on La Palma,
and soft X-ray images from the Yohkoh satellite support the hypothesis
that we have observed the passage of a nearly closed magnetic system
through the photosphere into the corona. The observations suggest that
as the magnetic flux begins to emerge into the photosphere it shows a
rather simple geometry, but it subsequently develops a small δ-sunspot
configuration with a highly sheared vector field along the polarity
inversion line running through it. At that stage, the vector field is
consistent with a concave upward magnetic topology, indicative of strong
electric currents above the photosphere. An Hα prominence is found
above this inversion line when the δ-sunspot is fully formed. These
observed features and the sequence of events are interpreted in terms
of a nearly closed magnetic system that rises through the photosphere
into the corona as a result of magnetic buoyancy. The magnetic system
persists in the corona well after the dark δ-sunspot has disappeared
in the photosphere We suggest that this coronal structure is in
quasi-static equilibrium with its buoyancy partially countered by
the weight of the plasma trapped at the bottom of closed magnetic
loops. The plausibility of such a scenario is demonstrated by a
three-dimensional magnetostatic model of the emergence of a closed,
spheroidal magnetic system in the corona, in which the Lorentz force
arising from cross-field currents is balanced by the gravitational
and pressure forces. This theoretical model carries many features in
common with the observed morphology of our active region.
Title: Small scale horizontal magnetic fields in the solar photosphere
Authors: Leka, K. D.; Lites, B. W.; Skumanich, A.; Martínez Pillet,
V.; Shimizu, T.
Bibcode: 1995IAUS..176P.120L
Altcode:
No abstract at ADS
Title: Observed differences between large and small sunspots.
Authors: Collados, M.; Martinez Pillet, V.; Ruiz Cobo, B.; del Toro
Iniesta, J. C.; Vazquez, M.
Bibcode: 1994A&A...291..622C
Altcode:
We confirm recent results about the differences in temperature
and magnetic field strength between the umbra of large and small
sunspots. Five Stokes I- and V-spectra from the darkest cores of
three different umbrae have been analysed with the inversion code
of the radiative transfer equation by Ruiz Cobo & del Toro
Iniesta (1992). The run with depth of temperature, magnetic field
(strength and inclination) and velocity along the line of sight are
obtained. The larger sunspots turn out to be cooler and possesing
a larger magnetic field strength, practically throughout the whole
atmosphere. Neither significant gradients of the line-of-sight velocity,
nor of the magnetic field inclination, are detected in any of the
spots analysed. Two model atmospheres are given corresponding to hot
(small) and cool (large) sunspots. The models are, to a large extent,
free from effects of penumbral/photospheric stray-light because it is
nearly absent in the large spots and because in the small one, where
it is important for the Stokes I-profile, only Stokes V is considered
to obtain the model atmosphere. These are the first umbral models in
the literature for which a simultaneous determination of the magnetic
field and thermodynamic stratifications is presented. The implications
of these stratifications for the energy transport in sunspot umbrae
are discussed.
Title: A Quantitative Comparison of Vector Magnetic Field Measurement
and Analysis Techniques
Authors: Lites, B. W.; Martinez Pillet, V.; Skumanich, A.
Bibcode: 1994SoPh..155....1L
Altcode:
We make a quantitative comparison between spectral vs filter measurement
and analysis techniques for extraction of solar vector magnetic fields
from polarimetric data using as a basis the accurately calibrated,
high angular resolution Stokes profile data from the Advanced Stokes
Polarimeter. It is shown that filter-based measurements deliver
qualitative images of the field alignment for sunspots that are visually
similar to images derived from the more detailed analysis of the Stokes
profiles. However, quantitative comparison with least-squares fits
to the full Stokes profiles show that both the strength of the field
predicted by the filter-based analysis and its orientation contain
substantial errors. These errors are largest for plage regions
outside of sunspots, where the field strengths are inferred to be
only a fraction of their true values, and errors in the orientation of
40-50° are common. Within sunspots, errors of 20° are commonplace. The
greatest source of these errors is the inability of the filter-based
measurements to account for the small fill fraction of magnetic fields
or, equivalently, scattered light in the instrument, which reduce the
degree of polarization. The uncertainties of the full profile fitting
methods are also discussed, along with the errors introduced by coarser
wavelength sampling of the observed Stokes profiles. The least-squares
fitting procedure operates best when the profiles are sampled at least
as frequently as one Doppler width of the line.
Title: Evidence for Supersonic Downflows in the Photosphere of a
Delta Sunspot
Authors: Martinez Pillet, V.; Lites, B. W.; Skumanich, A.; Degenhardt,
D.
Bibcode: 1994ApJ...425L.113M
Altcode: 1994ApJ...425L.113P
We present polarization profiles observed with the High Altitude
Observatory/National Solar Observatory (HAO/NSO) Advanced Stokes
Polarimeter (ASP) that demonstrate, in a model-independent way,
the presence of strong downflows close to the neutral line of a
delta sunspot (a spot with both polarities contained within the
same penumbra). The flows are as large as 14 km/s, a velocity that,
at photospheric levels, strongly suggests the presence of supersonic
compressive fluid flows in a region only 100-200 km above the visible
surface. These velocities are probably the largest ever reported at
photospheric levels. The region containing the downflows is large enough
(about 2 sec on a side) to be resolved, although it is likely to contain
fine structure at or below our spatial resolution. The origin of these
flows is discussed in terms of the funneling of material through an
isolated magnetic nozzle in an otherwise closed magnetic system which
is rising through the surface.
Title: The Inclination of Network Magnetic Fields
Authors: Sanchez Almeida, J.; Martinez Pillet, V.
Bibcode: 1994ApJ...424.1014S
Altcode:
We have observed the linear polarization of 21 bright grains of the
photospheric network close to the disk center. The linear polarization
of Fe I 6302.5 A was always lower than 1.9 x 10-3 (referred
to continuum intensity). This level of linear polarization implies a
very small magnetic field inclination with respect to the vertical,
which we estimate below 10 deg. Our finding is in apparent disagreement
with previous studies which claim large inclinations; however, it
fulfills theoretical expectations. Plage regions close to sunspots
might show inclination, but isolated network elements do not.
Title: Vector spectropolarimetry with the Advanced Stokes Polarimeter
(ASP) for quantitative solar magnetometry
Authors: Skumanich, A.; Lites, B. W.; Martínez Pillet, V.
Bibcode: 1994ASIC..433...99S
Altcode:
No abstract at ADS
Title: Magnetic Configuration of a Short-Lived Delta SPOT
Authors: Martinez Pillet, V.; Lites, B. W.; Skumanich, A. P.;
Seagraves, P.
Bibcode: 1994ASPC...68..244M
Altcode: 1994sare.conf..244M
No abstract at ADS
Title: The inclination of magnetic fields in small-scale flux
concentrations
Authors: Sánchez Almeida, J.; Martínez Pillet, V.
Bibcode: 1994smf..conf..316S
Altcode:
No abstract at ADS
Title: Physical conditions in magnetic elements of different
polarities surrounding sunspots
Authors: Martínez Pillet, V.; Lites, B. W.; Skumanich, A. P.; Elmore,
D. F.; Seagraves, P.
Bibcode: 1994smf..conf..219M
Altcode:
No abstract at ADS
Title: Instrumental polarization of telescopes: a laboratory test
of the diffraction model
Authors: Sánchez Almeida, J.; Martínez Pillet, V.
Bibcode: 1994smf..conf..343S
Altcode:
No abstract at ADS
Title: Polarizing properties of grazing-incidence X-ray mirrors
- Comment
Authors: Sanchez Almeida, J.; Martinez Pillet, V.
Bibcode: 1993ApOpt..32.4231S
Altcode:
We show that grazing-incidence telescopes, like those used for X-ray
imaging, present negligible instrumental polarization. This property
does not depend on the number of reflections the telescope employs
to lead light from the entrance pupil to the focal plane. The result
applies to the various mirrors of the advanced X-ray astrophysics
facility satellite. In this particular case we have quantified the
residual instrumental polarization to be between 10 exp -3 and 5 x 10
exp -5, depending on the size of the resolution elements.
Title: The distribution of sunspot decay rates.
Authors: Martinez Pillet, V.; Moreno-Insertis, F.; Vazquez, M.
Bibcode: 1993A&A...274..521M
Altcode:
The distribution of sunspot decay rates is studied using the Greenwich
Photoheliographic Results (GPR) for a total of approximately hundred
years between 1874 and 1976. The decay rates are seen to be
lognormally distributed. The discrepancies between the decay rates
given in the past by different authors are shown to originate as
a consequence of this asymmetric distribution. It is pointed out
that the extended tails shown by the lognormal distributions are
associated to spots decaying much faster than suggested by Bumba's
(1963) work. A cycle by cycle analysis of the lognormal distributions
associated with each sunspot group type and for single spots is
presented. The differences between the nine solar cycles involved are
studied. As a remarkable property of the decay process, we show
that it happens at a nearly constant total to umbral area ratio. This
property holds for decaying spots which are still large enough to
show a penumbra. We have studied the suitability of a decay law
with the instantaneous decay rate proportional to the length of the
spot boundary. This law predicts a parabolic decay pattern with some
specific characteristics. No definite conclusion in favour of this
law is reached, but it is suggested that a linear decay is as weakly
supported by the GPR data as a peripheral one. On the other hand, weak
non-linearities are seen in the decay of isolated spots with a clear
tendency to produce a convex pattern in the area vs. time diagram. The
implication is that sunspot decay is braked as time proceeds.
Title: The continuum intensity-magnetic field relation in sunspot
umbrae
Authors: Martinez Pillet, V.; Vazquez, M.
Bibcode: 1993A&A...270..494M
Altcode:
We describe the work carried out to obtain observational evidence
of a local relation between the temperature and the magnetic field in
different regions of several sunspots. Information about the temperature
is extracted from the continuum intensity. The magnetic field is
deduced by using the Stokes V profile of lines with different excitation
potentials. A scaling relation between Stokes V and continuum intensity
is used to estimate the stray-light contamination. The observed local
relation between continuum intensity and magnetic field can be adapted
to the equations describing magnetostatic horizontal force balance. The
commonly accepted value for the Wilson depression suggests that the
tension forces are as important as the magnetic pressure in defining
horizontal equilibrium. The local relation observed holds for spatial
scales larger than 1 arcsec. Evidence of unresolved hot magnetic regions
inside the umbra is presented. Our study provides clues pointing to a
dependence of continuum intensity with sunspot area. Small spots are
seen to be brighter than big ones.
Title: The Continuum Intensity Magnetic Field Relation in Sunspot
Umbrae
Authors: Martinez Pillet, V.; Vazquez, M.
Bibcode: 1993ASPC...46...60M
Altcode: 1993mvfs.conf...60M; 1993IAUCo.141...60M
No abstract at ADS
Title: Atomic orientation in chromospheric lines.
Authors: Trujillo Bueno, J.; Martínez Pillet, V.; Sánchez Almeida,
J.; Landi Degl'Innocenti, E.
Bibcode: 1993ASPC...46..526T
Altcode: 1993ASPC...46..526B; 1993mvfs.conf..526T; 1993IAUCo.141..526T
Observations of the Stokes I and V profiles of the Ca II H and K lines
in solar magnetic regions are presented. Least-squares fits of dI/dλ
to V are obtained and the wavelength variation of the residuals,
i.e. V-kdI/dλ, calculated. The authors find significant symmetric
residuals in umbrae, which are in agreement with the effect on the
V profiles due to atomic orientation, i.e. with the existence of an
unequal population of the Zeeman sublevels with M > 0 with respect
to those with M < 0.
Title: The Distribution of Sunspot Decay Rates
Authors: Martinez Pillet, V.; Moreno-Insertis, F.; Vazquez, M.
Bibcode: 1993ASPC...46...67M
Altcode: 1993mvfs.conf...67M; 1993IAUCo.141...67M
No abstract at ADS
Title: High Angular Resolution Stokes V Spectra in Penumbrae
Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Lites, J. T. Buenol
B. W.
Bibcode: 1993ASPC...46..192S
Altcode: 1993mvfs.conf..192S; 1993IAUCo.141..192S
No abstract at ADS
Title: Stray Light Effects on the Solar Intensity Distribution
Authors: Martinez Pillet, V.
Bibcode: 1992SoPh..140..207M
Altcode:
A description of the stray-light problem based on a radiative transfer
approach is presented. The two-dimensional convolution that describes
the effect of the stray-light is recovered in this formalism. On the
other hand, the normalization condition used for the spread function in
our procedure is different from the one used in the old approach. The
controversy raised by the old normalization condition is satisfactorily
eliminated within our description. We have applied our formalism to
aureole observations and derived the spread function parameters. These
parameters are similar to the ones used in the standard approach
but now a new quantity appears. It is derived consistently within
our formalism and it allows a description of different atmospheric
quality conditions without changing the actual shape of the spread
function. This possibility is also a new characteristic of our formalism
that has no analogy to the old one. Finally, the information derived
from limb profiles is used to correct sunspot images. The correction
does not need to make any assumption about the shape of the spot but it
uses the information contained on the image itself. It is shown how,
for large spots, the contamination of stray-light can be considered
as an added constant level of light throughout the umbra.
Title: Instrumental polarization in the focal plane of telescopes
Authors: Sanchez Almeida, J.; Martinez Pillet, V.
Bibcode: 1992A&A...260..543S
Altcode:
We present a technique to model the instrumental polarization in
the focal plane of a telescope. It takes into account that different
rays of an incoming beam suffer different variation of the original
polarization in their paths through the system. It also considers that
the net effect depends on the way in which the different rays interfere
with each other. We show that the Mueller matrix which describes this
instrumental polarization greatly simplifies if the polarimetric
measurements have poor spatial resolution. The Mueller matrices
corresponding to a pair of academic cases are worked out: a diffraction
limited telescope when the source lies on its axis and an axisymmetric
mirror with the source off the axis. We discuss the consequences of
these mathematical results on real telescopes (e.g. LEST). Finally,
we briefly consider the seeing-induced instrumental polarization.
Title: Relations between fundamental parameters of sunspots
Authors: Martínez Pillet, Valentín Juan
Bibcode: 1992PhDT.......298M
Altcode:
No abstract at ADS
Title: A proposal for a low instrumental polarization coude telescope
Authors: Martinez Pillet, V.; Sanchez Almeida, J.
Bibcode: 1991A&A...252..861M
Altcode: 1991A&A...252..861P
A technique for obtaining an ideal two-mirror coude system with no
instrumental polarization is described. A half-wave plate positioned
between the two mirrors with the proper orientation produces the
desired effect. The level of spurious polarization is limited by the
characteristics of the retarder and the similarity of the mirrors. The
telescope design and accuracy are discussed.
Title: Spectrograph distortion in sunspot line profiles
Authors: Martinez Pillet, V.; Sanchez Almeida, J.
Bibcode: 1991SoPh..134..403M
Altcode:
We show empirically how the effect of the instrumental polarization
of the spectrograph can distort the shape of the intensity profiles
in sunspots. In order to avoid the problems an analysis of the
polarization of the light should be performed at the entrance slit of
the spectrograph.
Title: The instrumental polarization of a Gregory-Coudé telescope
Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Wittmann, A. D.
Bibcode: 1991SoPh..134....1A
Altcode:
We calculate a theoretical model of the polarization properties of
a Gregory-Coudé telescope to predict the behaviour of the German
Gregory-Coudé Telescope installed at the Observatorio del Teide
(Spain). Measurements of the real effects produced by this telescope
acting upon light of known polarization are compared with the model. We
estimate an uncertainty in its predictions of about 10%, which is
produced by the uncertainties of the (complex) refractive index of the
metallic layers covering the mirrors. The paper concludes by briefly
considering the way in which the plain telescope changes the Stokes'
profiles.
Title: Performance of the IAC Stokes I and V analyzer.
Authors: Sánchez Almeida, J.; Martínez Pillet, V.
Bibcode: 1991sopo.work..191S
Altcode:
The chromatic behaviour of the IAC analyzer, commonly used at the German
Vacuum Gregory-Coude telesope at the Spanish Observatorio del Teide
(Canary Islands), is investigated. It is shown that, through careful
alignment of the optical components, a nearly perfect circular analysis
can be obtained at wavelengths of 4000 Å and 6000 Å. For other visible
regions the crosstalk between linear and circular polarization can be
always made lower than 10%.
Title: Spectropolarimetry of active regions.
Authors: Del Toro Iniesta, J. C.; Martínez Pillet, V.; Vázquez, M.
Bibcode: 1991sopo.work..224D
Altcode:
A circular analyzer has been used at the focal plane of a telescope in
days of absence of instrumental polarization to simultaneously record
I±V spectrograms at two different wavelength ranges: ≡6300 Å and
≡3930 - 3970 Å. The observations have been analyzed within two,
also different, frames: on the one hand, an empirical relationship
between brightness temperature and the magnetic field strength has been
found for sunspot umbrae, which allows a determination of the Wilson
depression; on the other, estimates of the chromospheric longitudinal
component of the magnetic field (magnetic flux if the filling factor
is not unity) in two umbrae, in a penumbra, and in a plage have been
found by using profiles of the resonance lines H and K of Ca II. A
ratio of order 2 - 3 between the longitudinal components of the field
at the chromospheric height of formation of the Ca II lines and the
photospheric height of formation of the 6302.5 Å Fe I line is also
found in umbrae.
Title: Circular Polarization of the CA II H and K Lines in Solar
Quiet and Active Regions
Authors: Martinez Pillet, V.; Garcia Lopez, R. J.; del Toro Iniesta,
J. C.; Rebolo, R.; Vazquez, M.; Beckman, J. E.; Char, S.
Bibcode: 1990ApJ...361L..81M
Altcode:
A representative set of profiles is presented for the Ca II H resonace
line in Stokes V and I, for the quiet sun, plages, sunspot umbrae,
and a flare, as well as one example of the Ca II K line in a sunspot
penumbra. The degree of polarization is highest in the spots and zero
in the quiet sun, within error limits. The V profile asymmetries are,
however, highest in the flare. The spectra of the Ca II K line are
used to obtain a linear relation between V(lambda) and -dI/d(lambda)
and a value for B(parallel) of 820 + or - 40 G using the weak-field
approximation.
Title: Decay rates of sunspot groups from 1874 to 1976
Authors: Martinez Pillet, V.; Moreno-Insertis, F.; Vazquez, M.
Bibcode: 1990Ap&SS.170....3M
Altcode:
The global behaviour and fine structure of the distribution of sunspot
decay rates from activity cycle 13 to 20 are presented. It is shown
that the distribution of this parameter is lognormal. Statistically
significantly lower values of decay rates are found in cycles 13,
14, and 18 for isolated spots. The complex groups had no appreciable
changes.
Title: On the Continuum Intensity Magnetic Field Relation Along the
Decay Phase of Sunspots
Authors: Martinez Pillet, V.; Vazquez, M.
Bibcode: 1990Ap&SS.170...75M
Altcode:
We present continuum intensity-magnetic field distributions for a
decaying sunspot. It is shown that a very simple model accounts for
the observed correlation. The Wilson depression is determined.
Title: Facular points and small-scale magnetic elements
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Martinez Pillet, V.; Ruiz Cobo, B.
Bibcode: 1990Ap&SS.170....9D
Altcode:
We present spectroscopic observations, with high spatial resolution, of
Ca ii K bright points very near the disc centre. Magnetic concentrations
have been detected in these network (facular) points by only using
intensity profiles of the well-known pair of lines Fe i5250.22 Å and
5247.06 Å. No brightening of these structures with respect to the quiet
photosphere can be ascertained within an accuracy threshold of 1.2%.
Title: Are small-scale magnetic concentrations spatially coincident
with bright facular points?
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Martinez Pillet, V.; Ruiz Cobo, B.
Bibcode: 1990A&A...233..570D
Altcode:
The usually assumed identification of small-scale magnetic
concentrations with bright facular or network points on the photosphere
is observationally checked by using high spatial resolution spectra
of Ca II K bright points very near the disk center. The detection of
spatially unresolved magnetic structures is made via a new differential
analysis of the well-known pair of Fe I lines 5247.06 A and 5250.22
A; these concentrations are present in the central part of a line
weakening zone, which is of some 2 arcsec wide. No continuum intensity
enhancement with respect to the quiet photosphere can be ascertained of
these structures, within an accuracy threshold of 1.2 percent. In spite
of this, magnetic concentrations brighter than the quiet photosphere
are compatible with the observations, but if so, they must be narrower
than 0.2 arcsec.
Title: Stray-light measurements at the Observatorio del Teide
Authors: Martinez Pillet, V.; Ruiz Cobo, B.; Vazquez, M.
Bibcode: 1990SoPh..125..211M
Altcode:
A new procedure to separate the instrumental and atmospheric components
of stray light is presented. It is based on the dependence of the
aureole's atmospheric component on the air mass and is applied to
measurements taken with the Vacuum Newton Telescope (VNT) at the
Observatorio del Teide (Tenerife). The resulting instrumental part
is independent of the air mass. The variation of both components
with wavelength is also studied. The instrumental component shows no
dependence on wavelength, in contrast to the atmospheric one which is
greater in the blue than in the red. It is concluded that observations
with air masses larger than two will probably be strongly affected by
stray light.