explanation blue bibcodes open ADS page with paths to full text
Author name code: merenda
ADS astronomy entries on 2022-09-14
author:"Merenda, Laura"
---------------------------------------------------------
Title: Configuración magnética preeruptiva de la región NOAA
12127 mediante extrapolación no lineal del campo
Authors: Merenda, L. A.; Iglesias, F. A.; Mandrini, C. H.; Cremades, H.
2021BAAA...62...19M Altcode:
We studied the magnetic properties of active region NOAA 12127 previous
to a M1.5-class flare, that was accompanied by a coronal mass ejection,
on the August 1, 2014. We estimated the pre-eruptive coronal magnetic
field using a non-linear force-free extrapolation, and compared the
results with images in Hα and 171 Å. The extrapolated field is able
to reproduce the general morphology of the magnetic configurations
linked to a filament and several coronal loops identified.
---------------------------------------------------------
Title: Asymmetric expansion of coronal mass ejections in the low
corona
Authors: Cremades, H.; Iglesias, F. A.; Merenda, L. A.
2020A&A...635A.100C Altcode: 2020arXiv200110085C
<BR /> Aims: Understanding how magnetic fields are structured within
coronal mass ejections (CMEs), and how they evolve from the low
corona into the heliosphere, is a major challenge for space weather
forecasting and for solar physics. The study of CME morphology is a
particularly auspicious approach to this problem, given that it holds a
close relationship with the CME magnetic field configuration. Although
earlier studies have suggested an asymmetry in the width of CMEs in
orthogonal directions, this has not been inspected using multi-viewpoint
observations. <BR /> Methods: The improved spatial, temporal, and
spectral resolution, added to the multiple vantage points offered
by missions of the Heliophysics System Observatory, constitute a
unique opportunity to gain insight into this regard. We inspect the
early evolution (below ten solar radii) of the morphology of a dozen
CMEs occurring under specific conditions of observing spacecraft
location and CME trajectory, favorable to reduce uncertainties
typically involved in the 3D reconstruction used here. These events
are carefully reconstructed by means of a forward modeling tool using
simultaneous observations of the Solar-Terrestrial Relations Observatory
(STEREO) Extreme Ultraviolet Imager and the Solar Dynamics Observatory
Atmospheric Imaging Assembly as input when originating low in the
corona, and followed up in the outer fields of view of the STEREO and
the Solar and Heliospheric Observatory coronagraphs. We then examine
the height evolution of the morphological parameters arising from the
reconstructions. <BR /> Results: The multi-viewpoint analysis of this
set of CMEs revealed that their initial expansion - below three solar
radii - is considerably asymmetric and non-self-similar. Both angular
widths, namely along the main axes of CMEs (AW<SUB>L</SUB>) and in
the orthogonal direction (AW<SUB>D</SUB>, representative of the flux
rope diameter), exhibit much steeper change rates below this height,
with the growth rate of AW<SUB>L</SUB> found to be larger than that of
AW<SUB>D</SUB>, also below that height. Angular widths along the main
axes of CMEs are on average ≈1.8 times larger than widths in the
orthogonal direction AW<SUB>D</SUB>. The ratios of the two expansion
speeds, namely in the directions of CMEs main axes and in their
orthogonal, are nearly constant in time after ∼4 solar radii, with an
average ratio ≈1.6. Heights at which the width change rate is defined
to stabilize are greater for AW<SUB>L</SUB> than for AW<SUB>D</SUB>.
---------------------------------------------------------
Title: Expansión y autosimilitud de eyecciones coronales de masa
a partir de observaciones estereoscópicas
Authors: Cremades, H.; Iglesias, F. A.; Merenda, L. A.; López, F. M.;
Cabello, I.
2019BAAA...61...41C Altcode:
Coronal mass ejections (CMEs) constitute the most spectacular dynamic
events in the solar system, and are key players in determining
space weather conditions. Given that the ocurrence of a CME has
so far been impossible to predict, the best attempt at forecasting
is then to assess their impact with the best possible accuracy. In
this respect, understanding how magnetic fields are organized within
CMEs, and how they evolve from the low corona into the heliosphere,
is crucial. Exceptional ongoing solar missions, such as STEREO,
SOHO, and SDO, provide a unique opportunity to shed light into this
aspect. The STEREOscopic-view images provided by the STEREO/SECCHI
suite in combination with images from Earth’s perspective recorded
by SDO/AIA and SOHO/LASCO enable the analysis of CME evolution from
their birth in the low corona. The set of CMEs uder study arises from an
appropriate combination of spacecraft vantage points and CME propagation
direction, which is helpful to reduce uncertainties in their forward
modeling. These events are carefully analyzed as they originate low
in the corona by means of simultaneous observations of STEREO/EUVI and
SDO/AIA, and followed up to the outer fields of view of the STEREO and
SOHO coronagraphs. In particular, we examine the evolution of their
global magnetic field configuration, and how CMEs expand along the
direction of their main symmetry axis and orthogonal to it.
---------------------------------------------------------
Title: A long-duration active region: Evolution and quadrature
observations of ejective events
Authors: Cremades, H.; Mandrini, C. H.; Fuentes, M. C. López; Merenda,
L.; Cabello, I.; López, F. M.; Poisson, M.
2017IAUS..327...60C Altcode:
Unknown aspects of the initiation, evolution, and associated phenomena
of coronal mass ejections (CMEs), together with their capability of
perturbing the fragile technological equilibrium on which nowadays
society depends, turn them a compelling subject of study. While
space weather forecasts are thus far not able to predict when and
where in the Sun will the next CME take place, various CME triggering
mechanisms have been proposed, without reaching consensus on which
is the predominant one. To improve our knowledge in these respects,
we investigate a long-duration active region throughout its life, from
birth until decay along five solar rotations, in connection with its
production of ejective events. We benefit from the wealth of solar
remote-sensing data with improved temporal, spatial, and spectral
resolution provided by the ground-breaking space missions STEREO,
SDO, and SOHO. During the investigated time interval, which covers
the months July - November 2010, the STEREO spacecraft were nearly
180 degrees apart, allowing for the uninterrupted tracking of the
active region and its ensuing CMEs. The ejective aspect is examined
from multi-viewpoint coronagraphic images, while the dynamics of the
active region photospheric magnetic field are inspected by means of
SDO/HMI data for specific subintervals of interest. The ultimate goal
of this work in progress is to identify common patterns in the ejective
aspect that can be connected with the active region characteristics.
---------------------------------------------------------
Title: Erratum:"Convective Nature of Sunspot Penumbral
Filaments: Discovery of Downflows in the Deep Photosphere" <A
href="/abs/2011ApJ...734L..18J">(2011, ApJ, 734, L18)</A>
Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.;
Aznar Cuadrado, R.; Merenda, L.
2011ApJ...740L..55J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The height of chromospheric loops in an emerging flux region
Authors: Merenda, L.; Lagg, A.; Solanki, S. K.
2011A&A...532A..63M Altcode: 2012arXiv1202.1113M
Context. The chromospheric layer observable with the He i 10 830 Å
triplet is strongly warped. The analysis of the magnetic morphology of
this layer therefore requires a reliable technique to determine the
height at which the He i absorption takes place. <BR /> Aims: The He
i absorption signature connecting two pores of opposite polarity in an
emerging flux region is investigated. This signature is suggestive of a
loop system connecting the two pores. We aim to show that limits can be
set on the height of this chromospheric loop system. <BR /> Methods: The
increasing anisotropy in the illumination of a thin, magnetic structure
intensifies the linear polarization signal observed in the He i triplet
with height. This signal is altered by the Hanle effect. We apply an
inversion technique incorporating the joint action of the Hanle and
Zeeman effects, with the absorption layer height being one of the
free parameters. <BR /> Results: The observed linear polarization
signal can be explained only if the loop apex is higher than ≈ 5
Mm. Best agreement with the observations is achieved for a height of
6.3 Mm. <BR /> Conclusions: The strength of the linear polarization
signal in the loop apex is inconsistent with the assumption of a He
i absorption layer at a constant height level. The determined height
supports the earlier conclusion that dark He 10 830 Å filaments in
emerging flux regions trace emerging loops.
---------------------------------------------------------
Title: Convective Nature of Sunspot Penumbral Filaments: Discovery
of Downflows in the Deep Photosphere
Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.;
Aznar Cuadrado, R.; Merenda, L.
2011ApJ...734L..18J Altcode: 2011arXiv1105.1877J
We study the velocity structure of penumbral filaments in the deep
photosphere to obtain direct evidence for the convective nature of
sunspot penumbrae. A sunspot was observed at high spatial resolution
with the 1 m Swedish Solar Telescope in the deep photospheric C I 5380
Å absorption line. The Multi-Object Multi-Frame Blind Deconvolution
method is used for image restoration and straylight is filtered out. We
report here the discovery of clear redshifts in the C I 5380 Å line
at multiple locations in sunspot penumbral filaments. For example,
bright head of filaments show larger concentrated blueshift and are
surrounded by darker, redshifted regions, suggestive of overturning
convection. Elongated downflow lanes are also located beside bright
penumbral fibrils. Our results provide the strongest evidence yet
for the presence of overturning convection in penumbral filaments and
highlight the need to observe the deepest layers of the penumbra in
order to uncover the energy transport processes taking place there.
---------------------------------------------------------
Title: Internetwork Horizontal Magnetic Fields in the Quiet Sun
Chromosphere: Results from a Joint Hinode/VTT Study
Authors: Lagg, A.; Ishikawa, R.; Merenda, L.; Wiegelmann, T.; Tsuneta,
S.; Solanki, S. K.
2009ASPC..415..327L Altcode:
We present results from a joint Hinode/VTT campaign (May
2008). Spectropolarimetric data of a quiet Sun super-granular network
cell at a heliocentric angle of 28° in the He I 10830 Å line were
analyzed using an inversion code incorporating Hanle and Zeeman effects
(HeLIx^+) to retrieve magnetic field strength and direction in the upper
chromosphere. Simultaneously recorded Hinode SOT/SP data reveal the
photospheric magnetic field morphology, clearly showing magnetic flux
concentrations in the internetwork. The photospheric magnetic field
maps are used to feed potential field extrapolations similar to the
work by Schrijver & Title (2003). The extrapolated magnetic field
structure is compared with the magnetic field configuration resulting
from the He 10830 inversions. These inversions also reveal horizontal
magnetic structures extending over a length of up to 20 Mm above the
internetwork, indicative of the presence of a magnetic canopy. The
photospheric magnetic flux concentrations in the internetwork are
obviously not sufficiently strong to prevent the formation of a canopy
at chromospheric heights.
---------------------------------------------------------
Title: Diagnóstico de campos magnéticos en estructuras de la
cormosfera y corona del sol mediante los efectos Hanle y Zeeman Title:
Diagnóstico de campos magnéticos en estructuras de la cormosfera y
corona del sol mediante los efectos Hanle y Zeeman
---------------------------------------------------------
Title: Diagnosis
of magnetic fields in structures of the solar cormosphere and corona
through the Hanle and Zeeman effects;
Authors: Merenda, Laura
2008PhDT.......407M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Magnetic Map of a Solar Filament
Authors: Merenda, L.; Trujillo Bueno, J.; Collados, M.
2007ASPC..368..347M Altcode:
One of the most useful diagnostic tools for the detection of inclined
magnetic fields in solar chromospheric and coronal structures is
that based on the fact that the Hanle effect in forward scattering
at the solar disk center creates linear polarization in some spectral
lines, such as those of the He I 10830 Å multiplet. Here we show the
preliminary results of an ongoing investigation on the magnetic field
of a solar filament, based on the inversion of spectropolarimetric
observations obtained with the Tenerife Infrared Polarimeter.
---------------------------------------------------------
Title: The Magnetic Field of Solar Chromospheric Spicules
Authors: Trujillo Bueno, J.; Ramelli, R.; Merenda, L.; Bianda, M.
2007ASPC..368..161T Altcode:
A suitable diagnostic tool for investigating the magnetism of the
solar chromosphere is the observation and theoretical modeling of
the Hanle and Zeeman effects in solar spicules. In our presentation
we highlighted the great scientific interest of this new diagnostic
window by showing how the magnetic field vector can be inferred from
spectropolarimetric observations of solar chromospheric spicules
in several spectral lines, such as those of the 10830 Å and 5876
Å multiplets of neutral helium. Our off-limb spectropolarimetric
observations of the He I 10830 Å multiplet were obtained with the
Tenerife Infrared Polarimeter (TIP) attached to the Vacuum Tower
Telescope at the Observatorio del Teide (Tenerife), while those of the
5876 Å multiplet resulted from observations with the Zurich Imaging
Polarimeter (ZIMPOL) at the Gregory Coudé Telescope of the Istituto
Ricerche Solari Locarno. The application of a Stokes profiles inversion
technique led to the following conclusion. In quiet Sun spicules the
magnetic field vector at a height of about 2000 km above the solar
visible “surface" has a typical strength of the order to 10 G and is
inclined by approximately 35° with respect to the solar local vertical
direction. In spicules observed close to active regions the strength
of the magnetic field was of the order of 50 G. The two figures below
show the off-limb Stokes profiles of the He I 5876 Å multiplet observed
in a quiet region (upper figure) and close to an active region (lower
figure). Note that in both cases Stokes U is non-zero, which is the
observational signature of the Hanle effect of an inclined magnetic
field. The change of sign in Stokes U along the spatial direction
of the spectrograph's slit can be explained by variations in the
azimuth of the magnetic field vector. Interestingly, while the Stokes
V profiles corresponding to the observed quiet region are caused by
the alignment-to-orientation transfer mechanism (see, e.g., page 607
of Landi Degl'Innocenti & Landolfi 2004), that observed in the
spicules close to the active region is dominated by the longitudinal
Zeeman effect. The interested reader will find more information in
the papers by Trujillo Bueno et al. (2005) and by Ramelli et al. (2006).
---------------------------------------------------------
Title: Spectro-Polarimetry of Solar Prominences
Authors: Ramelli, R.; Bianda, M.; Trujillo Bueno, J.; Merenda, L.;
Stenflo, J. O.
2006ASPC..358..471R Altcode: 2009arXiv0906.2342R
A large set of high-precision, full-Stokes spectro-polarimetric
observations of prominences in He I D<SUB>3</SUB>, Hα, and Hβ lines
has been recorded with the ZIMPOL polarimeter at the Gregory-Coudé
Telescope in Locarno. The observational technique allows us to
obtain measurements free from seeing-induced spurious effects. The
instrumental polarization is well under control and taken into account
in the data analysis. We present our observational results for each
of the lines mentioned above. Of particular interest is that most
of our Hα measurements show <P />antisymmetric V profiles that are
a characteristic signature of the Zeeman effect in the prominence
plasma. A Stokes inversion technique based on the quantum theory of the
Hanle and Zeeman effects is being applied on observed Stokes profiles
in the He I D<SUB>3</SUB> line in order to obtain information on the
magnetic field vector that confines the prominence plasma.
---------------------------------------------------------
Title: The Hanle and Zeeman Effects in Solar Spicules
Authors: Ramelli, R.; Bianda, M.; Merenda, L.; Trujillo Bueno, T.
2006ASPC..358..448R Altcode: 2009arXiv0906.2340R
A large set of high precision full-Stokes spectro-polarimetric
observations of the He I D<SUB>3</SUB> line in spicules has been
recorded with the ZIMPOL polarimeter at the Gregory-Coudé Telescope in
Locarno. The observational technique allows us to obtain measurements
free from seeing-induced spurious effects. The instrumental polarization
is well under control and taken into account in the data analysis. The
observed Stokes profiles are interpreted according to the quantum theory
of the Hanle and Zeeman effects with the aim of obtaining information on
the magnetic field vector. To this end, we make use of a suitable Stokes
inversion technique. The results are presented giving emphasis on a few
particularly interesting measurements which show clearly the operation
of the Hanle and Zeeman effects in solar chromospheric spicules.
---------------------------------------------------------
Title: Determination of the Magnetic Field Vector via the Hanle and
Zeeman Effects in the He I λ10830 Multiplet: Evidence for Nearly
Vertical Magnetic Fields in a Polar Crown Prominence
Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.;
Collados, M.
2006ApJ...642..554M Altcode:
The magnetic field is the key physical quantity responsible for the
formation, stability, and evolution of solar prominences (ribbons of
cool dense gas embedded in the hot tenuous corona). Therefore, it is
important to obtain good empirical knowledge of the three-dimensional
structure of prominence magnetic fields. Here we show how the magnetic
field vector can be inferred via the physical interpretation of
spectropolarimetric observations in the He I λ10830 multiplet. To this
end, we have developed an inversion code based on the quantum theory
of the Hanle and Zeeman effects and on a few modeling assumptions. We
show an application to full Stokes vector observations of a polar crown
prominence that, in the slit-jaw Hα image, showed nearly vertical
plasma structures. Our results provide evidence for magnetic fields
on the order of 30 G inclined by about 25° with respect to the local
solar vertical direction. Of additional interest is that the inferred
nearly vertical magnetic field vector appears to be slightly rotating
around a fixed direction in space as one proceeds along the direction
of the spectrograph's slit. While these results provide new light on
the three-dimensional geometry of the magnetic fields that confine the
plasma of polar crown prominences, they also urge us to develop improved
solar prominence models and to pursue new diagnostic investigations.
---------------------------------------------------------
Title: Determination of the Magnetic Field Vector in a Polar Crown
Prominence via the Hanle and Zeeman Effects in the He I 10830 Å
Multiplet.
Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.;
Collados, M.
2005ESASP.596E..18M Altcode: 2005ccmf.confE..18M
No abstract at ADS
---------------------------------------------------------
Title: Spectropolarimetric Observations of Prominences and Spicules,
and Magnetic Field Diagnostics
Authors: Ramelli, R.; Bianda, M.; Trujillo Bueno, J.; Merenda, L.;
Stenflo, J. O.
2005ESASP.596E..82R Altcode: 2005ccmf.confE..82R
No abstract at ADS
---------------------------------------------------------
Title: The Hanle and Zeeman Effects in Solar Spicules: A Novel
Diagnostic Window on Chromospheric Magnetism
Authors: Trujillo Bueno, J.; Merenda, L.; Centeno, R.; Collados, M.;
Landi Degl'Innocenti, E.
2005ApJ...619L.191T Altcode: 2005astro.ph..1533T; 2005astro.ph..1533B
An attractive diagnostic tool for investigating the magnetism of the
solar chromosphere is the observation and theoretical modeling of
the Hanle and Zeeman effects in spicules, as shown in this Letter for
the first time. Here we report on spectropolarimetric observations of
solar chromospheric spicules in the He I λ10830 multiplet and on their
theoretical modeling accounting for radiative transfer effects. We find
that the magnetic field in the observed (quiet-Sun) spicular material at
a height of about 2000 km above the visible solar surface has a strength
of the order of 10 G and is inclined by approximately 35<SUP>deg</SUP>
with respect to the local vertical direction. Our empirical finding
based on full Stokes vector spectropolarimetry should be taken into
account in future magnetohydrodynamical simulations of spicules.
---------------------------------------------------------
Title: Selective absorption processes as the origin of puzzling
spectral line polarization from the Sun
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M.;
Merenda, L.; Manso Sainz, R.
2002Natur.415..403T Altcode: 2002astro.ph..1409T
Magnetic fields play a key role in most astrophysical systems, from
the Sun to active galactic nuclei. They can be studied through their
effects on atomic energy levels, which produce polarized spectral
lines. In particular, anisotropic radiation `pumping' processes (which
send electrons to higher atomic levels) induce population imbalances
that are modified by weak magnetic fields. Here we report peculiarly
polarized light in the HeI 10,830-Å multiplet observed in a coronal
filament located at the centre of the solar disk. We show that the
polarized light arises from selective absorption from the ground level
of the triplet system of helium, and that it implies the presence of
magnetic fields of the order of a few gauss that are highly inclined
with respect to the solar radius vector. This disproves the common
belief that population imbalances in long-lived atomic levels are
insignificant in the presence of inclined fields of the order of a few
gauss, and opens up a new diagnostic window for the investigation of
solar magnetic fields.
---------------------------------------------------------
Title: A study of AE UMa: Is it a δ Scuti variable?
Authors: Martín-Luis, F.; García, A.; Rey, M.; Merenda, L.
2001hsa..conf..388M Altcode:
No abstract at ADS
