Author name code: andretta
ADS astronomy entries on 2022-09-14
author:"Andretta, Vincenzo"
------------------------------------------------------------------------
Title: Coronal mass ejection followed by a prominence eruption and
a plasma blob as observed by Solar Orbiter
Authors: Bemporad, A.; Andretta, V.; Susino, R.; Mancuso, S.; Spadaro,
D.; Mierla, M.; Berghmans, D.; D'Huys, E.; Zhukov, A. N.; Talpeanu,
D. -C.; Colaninno, R.; Hess, P.; Koza, J.; Jejčič, S.; Heinzel,
P.; Antonucci, E.; Da Deppo, V.; Fineschi, S.; Frassati, F.; Jerse,
G.; Landini, F.; Naletto, G.; Nicolini, G.; Pancrazzi, M.; Romoli,
M.; Sasso, C.; Slemer, A.; Stangalini, M.; Teriaca, L.
Bibcode: 2022A&A...665A...7B
Altcode: 2022arXiv220210294B
Context. On 2021 February 12, two subsequent eruptions occurred above
the western limb of the Sun, as seen along the Sun-Earth line. The
first event was a typical slow coronal mass ejection (CME), followed
∼7 h later by a smaller and collimated prominence eruption,
originating south of the CME, followed by a plasma blob. These
events were observed not only by the SOHO and STEREO-A missions,
but also by the suite of remote-sensing instruments on board Solar
Orbiter.
Aims: We show how data acquired by the Full Sun
Imager (FSI), the Metis coronagraph, and the Heliospheric Imager
(HI) from the Solar Orbiter perspective can be combined to study
the eruptions and different source regions. Moreover, we show how
Metis data can be analyzed to provide new information about solar
eruptions.
Methods: Different 3D reconstruction methods were
applied to the data acquired by different spacecraft, including
remote-sensing instruments on board Solar Orbiter. Images acquired
by the two Metis channels in the visible light (VL) and H I Ly-α
line (UV) were combined to derive physical information about the
expanding plasma. The polarization ratio technique was also applied
for the first time to Metis images acquired in the VL channel.
Results: The two eruptions were followed in 3D from their source
region to their expansion in the intermediate corona. By combining
VL and UV Metis data, the formation of a post-CME current sheet (CS)
was followed for the first time in the intermediate corona. The
plasma temperature gradient across a post-CME blob propagating
along the CS was also measured for the first time. Application
of the polarization ratio technique to Metis data shows that by
combining four different polarization measurements, the errors are
reduced by ∼5 − 7%. This constrains the 3D plasma distribution
better. Movies associated to Figs. 4-7 are available at https://www.aanda.org
Title: Linking Small-scale Solar Wind Properties with Large-scale
Coronal Source Regions through Joint Parker Solar Probe-Metis/Solar
Orbiter Observations
Authors: Telloni, Daniele; Zank, Gary P.; Sorriso-Valvo, Luca;
D'Amicis, Raffaella; Panasenco, Olga; Susino, Roberto; Bruno, Roberto;
Perrone, Denise; Adhikari, Laxman; Liang, Haoming; Nakanotani, Masaru;
Zhao, Lingling; Hadid, Lina Z.; Sánchez-Cano, Beatriz; Verscharen,
Daniel; Velli, Marco; Grimani, Catia; Marino, Raffaele; Carbone,
Francesco; Mancuso, Salvatore; Biondo, Ruggero; Pagano, Paolo; Reale,
Fabio; Bale, Stuart D.; Kasper, Justin C.; Case, Anthony W.; de Wit,
Thierry Dudok; Goetz, Keith; Harvey, Peter R.; Korreck, Kelly E.;
Larson, Davin; Livi, Roberto; MacDowall, Robert J.; Malaspina, David
M.; Pulupa, Marc; Stevens, Michael L.; Whittlesey, Phyllis; Romoli,
Marco; Andretta, Vincenzo; Deppo, Vania Da; Fineschi, Silvano; Heinzel,
Petr; Moses, John D.; Naletto, Giampiero; Nicolini, Gianalfredo;
Spadaro, Daniele; Stangalini, Marco; Teriaca, Luca; Capobianco,
Gerardo; Capuano, Giuseppe E.; Casini, Chiara; Casti, Marta; Chioetto,
Paolo; Corso, Alain J.; Leo, Yara De; Fabi, Michele; Frassati,
Federica; Frassetto, Fabio; Giordano, Silvio; Guglielmino, Salvo L.;
Jerse, Giovanna; Landini, Federico; Liberatore, Alessandro; Magli,
Enrico; Massone, Giuseppe; Messerotti, Mauro; Pancrazzi, Maurizio;
Pelizzo, Maria G.; Romano, Paolo; Sasso, Clementina; Schühle, Udo;
Slemer, Alessandra; Straus, Thomas; Uslenghi, Michela; Volpicelli,
Cosimo A.; Zangrilli, Luca; Zuppella, Paola; Abbo, Lucia; Auchère,
Frédéric; Cuadrado, Regina Aznar; Berlicki, Arkadiusz; Ciaravella,
Angela; Lamy, Philippe; Lanzafame, Alessandro; Malvezzi, Marco;
Nicolosi, Piergiorgio; Nisticò, Giuseppe; Peter, Hardi; Solanki,
Sami K.; Strachan, Leonard; Tsinganos, Kanaris; Ventura, Rita; Vial,
Jean-Claude; Woch, Joachim; Zimbardo, Gaetano
Bibcode: 2022ApJ...935..112T
Altcode:
The solar wind measured in situ by Parker Solar Probe in the very
inner heliosphere is studied in combination with the remote-sensing
observation of the coronal source region provided by the METIS
coronagraph aboard Solar Orbiter. The coronal outflows observed near
the ecliptic by Metis on 2021 January 17 at 16:30 UT, between 3.5 and
6.3 R ⊙ above the eastern solar limb, can be associated
with the streams sampled by PSP at 0.11 and 0.26 au from the Sun,
in two time intervals almost 5 days apart. The two plasma flows
come from two distinct source regions, characterized by different
magnetic field polarity and intensity at the coronal base. It follows
that both the global and local properties of the two streams are
different. Specifically, the solar wind emanating from the stronger
magnetic field region has a lower bulk flux density, as expected,
and is in a state of well-developed Alfvénic turbulence, with low
intermittency. This is interpreted in terms of slab turbulence in the
context of nearly incompressible magnetohydrodynamics. Conversely,
the highly intermittent and poorly developed turbulent behavior of the
solar wind from the weaker magnetic field region is presumably due to
large magnetic deflections most likely attributed to the presence of
switchbacks of interchange reconnection origin.
Title: The first two years of Metis, the Solar Orbiter coronagraph
Authors: Andretta, Vincenzo
Bibcode: 2022cosp...44.1337A
Altcode:
The Solar Orbiter spacecraft was launched on 10 February 2020 carrying
on board a suite of remote-sensing and in-situ instruments designed
to explore from up close the Sun and the heliosphere. The suite of
instruments includes Metis, a multi-channel imaging coronagraph capable
of simultaneously observe the solar corona in a narrow band centered on
the Ly-$\alpha$ line, at 121.6 nm, and in polarized visible light, in
the band 580-640 nm. Since its first-light observations in early 2020,
Metis has been carrying out many observations throughout the mission
Cruise Phase. With the beginning of the nominal science phase in 2022,
Metis has then reached an important milestone, almost two years after
its first light. Here I will describe the Metis instrument, review
the observations carried out in these two years, and highlight the
main results already obtained, emphasising those especially relevant
for our understanding of the cradle of the solar wind.
Title: The observed large scale equatorial UV corona: new perspectives
with 'recent', 'future' and 'old' data
Authors: Abbo, Lucia; Fineschi, Silvano; Parenti, Susanna; Romoli,
Marco; Pancrazzi, Maurizio; Andretta, Vincenzo; Auchère, Frédéric;
Susino, Roberto; Spadaro, Daniele; Nicolini, Gianalfredo; Giordano,
Silvio; Zangrilli, Luca
Bibcode: 2022cosp...44.1327A
Altcode:
In order to understand the sources and the physical mechanisms for the
propagation of the Slow Solar Wind (SSW), it is essential to analyze
solar data in the region which shapes the large scale structure in
corona where the SSW is accelerated, such as streamers and boundaries
coronal hole/streamer. The focus of this work is to trace the channels
where the SSW escapes from the solar disk up to 5 solar radii in
corona. We give an overview on how Solar Orbiter observations (remote
sensing and in-situ) together with other space missions (i.e. SPP and
PROBA-3) can give a major contribution to the study of the evolution
of the streamer belt and global corona, of the role of the coronal
magnetic field topology in controlling the solar wind dynamics and
abundance, and of abundance anomalies in streamers and in boundaries
CH/streamer. In particular, we study how to trace back some equatorial
features from the extended corona to the disk. We analyse recent Metis
observations in corona together with the Extreme Ultraviolet Imager
(EUI) observations on disk and corona (by using the occulter). We also
present results from SOHO observations in 1996-1997 (solar minimum),
during which was observed a stable equatorial streamer belt with a
typical dipole magnetic structure. We have analyzed data by UVCS,
SUMER, CDS to trace large scale features and also sub-structures at
very high spatial resolution from the disk up to 3 solar radii. This
comparison and overlapping is still unique in solar physics and it can
improve our knowledge about the origin, acceleration and propagation
of the solar wind.
Title: Following prominences eruption from Sun to Parker Solar Probe
with multi-spacecraft observations
Authors: Niembro, Tatiana; Reeves, Kathy; Berghmans, David; Seaton,
Daniel; Andretta, Vincenzo; Hess, Phillip
Bibcode: 2022cosp...44.1464N
Altcode:
In the early hours of 2021 April 25, Solar Probe Cup on-board Parker
Solar Probe (PSP) registered the passage of a solar wind structure
characterized by a clear and constant alpha to proton density ratio
above 6% during three hours that remained present but faint and
intermittently within a twelve-hour window. PSP was behind the Sun
relative to the Earth, but the spacecraft location was visible to
both Solar Orbiter (SO) and STEREO-A (STA). SO and PSP were in nearly
perfect quadrature. In this work, we report the helium-enriched plasma
structure from the Sun to PSP combining multi-spacecraft remote sensing
and in situ measurements. We identify a prominence as the likely source,
visible in both STA/EUVI and SO/EUI. The associated CME was observed in
STA/COR2, and SO/Metis and SoloHI and reached PSP when it was located
at 46 solar radii, 8 hours after the spacecraft registered a crossing
of the heliospheric current sheet. Except for the extraordinary alpha
ratio enhancement, the CME showed ordinary plasma signatures and a
complex magnetic field with an overall enhancement. The PSP/WISPR
images show a structure entering the field of view a few hours before
the in situ crossing followed by repetitive transient structures that
are the result of flying through the CME body. We believe this to be
the first example of a CME being imaged by PSP/WISPR directly before
and during being detected in situ.
Title: UV coronagraphic observations of an erupting prominence in
the H I Ly-alpha line by Metis on-board Solar Orbiter
Authors: Russano, Giuliana; Teriaca, Luca; Andretta, Vincenzo; Sasso,
Clementina; de Leo, Yara; Uslenghi, Michela
Bibcode: 2022cosp...44.2412R
Altcode:
We show an erupting prominence event occurred on October 25, 2021 above
the South-Est limb of the Sun, observed by the Solar Orbiter (SolO)
Metis coronagraph UV channel, a narrow-band filter around the H I Ly
$\alpha$ line at 121.567 nm. The event, associated to a Coronal Mass
Ejection (CME), was visible also in the Metis visible light channel
and was also observed by other coronagraphs in orbit around the Sun,
like STEREO-A SECCHI COR1 and COR2 and SOHO/LASCO-C2. The observed CME
had a projected speed on the order of ∼ 220 km s‑1, as provided
by the CACTUS catalog. The event first appears in the STEREO-A EUVI
304 Å images as a typical limb prominence starting at 06:15 UT,
then it crossed the fields-of-view (FOVs) of STEREO-A SECCHI COR1
and SOHO/LASCO-C2 (respectively at 8:00 UT and 9:00 UT), until it
shows up in the Metis FOV at 14:00 UT where the prominence eruption
can be followed as far as ~ 10.2 solar radii. From the Solar Orbiter
perspective (very similar to that of SOHO and SDO since the separation
angle SolO-Sun-Earth was 5 deg), the source region of the eruption
was located just behind the Est limb, as suggested by STEREO-A EUVI
304 Å images (the separation angle STEREO-A-Sun-Earth was ~38 deg),
and by the fact that no significant associated signature is seen in
the AIA/SDO coronal imagers. This presentation will summarize the
ongoing analysis to derive geometrical and physical parameters of the
prominence as well as the expanding plasma magnetic field profiles of
this interesting event.
Title: Gaia Data Release 3. Stellar chromospheric activity and mass
accretion from Ca II IRT observed by the Radial Velocity Spectrometer
Authors: Lanzafame, A. C.; Brugaletta, E.; Frémat, Y.; Sordo, R.;
Creevey, O. L.; Andretta, V.; Scandariato, G.; Busà, I.; Distefano,
E.; Korn, A. J.; de Laverny, P.; Recio-Blanco, A.; Abreu Aramburu,
A.; Álvarez, M. A.; Andrae, R.; Bailer-Jones, C. A. L.; Bakker,
J.; Bellas-Velidis, I.; Bijaoui, A.; Brouillet, N.; Burlacu, A.;
Carballo, R.; Casamiquela, L.; Chaoul, L.; Chiavassa, A.; Contursi,
G.; Cooper, W. J.; Dafonte, C.; Dapergolas, A.; Delchambre, L.;
Demouchy, C.; Dharmawardena, T. E.; Drimmel, R.; Edvardsson, B.;
Fouesneau, M.; Garabato, D.; García-Lario, P.; García-Torres, M.;
Gavel, A.; Gomez, A.; González-Santamaría, I.; Hatzidimitriou,
D.; Heiter, U.; Jean-Antoine Piccolo, A.; Kontizas, M.; Kordopatis,
G.; Lebreton, Y.; Licata, E. L.; Lindstrøm, H. E. P.; Livanou, E.;
Lobel, A.; Lorca, A.; Magdaleno Romeo, A.; Manteiga, M.; Marocco, F.;
Marshall, D. J.; Mary, N.; Nicolas, C.; Ordenovic, C.; Pailler, F.;
Palicio, P. A.; Pallas-Quintela, L.; Panem, C.; Pichon, B.; Poggio,
E.; Riclet, F.; Robin, C.; Rybizki, J.; Santoveña, R.; Sarro, L. M.;
Schultheis, M. S.; Segol, M.; Silvelo, A.; Slezak, I.; Smart, R. L.;
Soubiran, C.; Süveges, M.; Thévenin, F.; Torralba Elipe, G.; Ulla,
A.; Utrilla, E.; Vallenari, A.; van Dillen, E.; Zhao, H.; Zorec, J.
Bibcode: 2022arXiv220605766L
Altcode:
The Gaia Radial Velocity Spectrometer provides the unique opportunity
of a spectroscopic analysis of millions of stars at medium-resolution
in the near-infrared. This wavelength range includes the Ca II infrared
triplet (IRT), which is a good diagnostics of magnetic activity in the
chromosphere of late-type stars. Here we present the method devised for
inferring the Gaia stellar activity index together with its scientific
validation. A sample of well studied PMS stars is considered to identify
the regime in which the Gaia stellar activity index may be affected by
mass accretion. The position of these stars in the colour-magnitude
diagram and the correlation with the amplitude of the photometric
rotational modulation is also scrutinised. Three regimes of the
chromospheric stellar activity are identified, confirming suggestions
made by previous authors on much smaller $R'_{\rm HK}$ datasets. The
highest stellar activity regime is associated with PMS stars and RS
CVn systems, in which activity is enhanced by tidal interaction. Some
evidence of a bimodal distribution in MS stars with $T_{\rm eff}\ge$
5000 K is also found, which defines the two other regimes, without a
clear gap in between. Stars with 3500 K$\le T_{\rm eff} \le$ 5000 K
are found to be either very active PMS stars or active MS stars with
a unimodal distribution in chromospheric activity. A dramatic change
in the activity distribution is found for $T_{\rm eff}\le$3500 K,
with a dominance of low activity stars close to the transition between
partially- and fully-convective stars and a rise in activity down into
the fully-convective regime.
Title: Prominence eruption observed in He II 304 Å up to >6
R⊙ by EUI/FSI aboard Solar Orbiter
Authors: Mierla, M.; Zhukov, A. N.; Berghmans, D.; Parenti, S.;
Auchère, F.; Heinzel, P.; Seaton, D. B.; Palmerio, E.; Jejčič, S.;
Janssens, J.; Kraaikamp, E.; Nicula, B.; Long, D. M.; Hayes, L. A.;
Jebaraj, I. C.; Talpeanu, D. -C.; D'Huys, E.; Dolla, L.; Gissot, S.;
Magdalenić, J.; Rodriguez, L.; Shestov, S.; Stegen, K.; Verbeeck,
C.; Sasso, C.; Romoli, M.; Andretta, V.
Bibcode: 2022A&A...662L...5M
Altcode: 2022arXiv220515214M
Aims: We report observations of a unique, large prominence
eruption that was observed in the He II 304 Å passband of the Extreme
Ultraviolet Imager/Full Sun Imager telescope aboard Solar Orbiter on
15-16 February 2022.
Methods: Observations from several vantage
points - Solar Orbiter, the Solar-Terrestrial Relations Observatory,
the Solar and Heliospheric Observatory, and Earth-orbiting satellites -
were used to measure the kinematics of the erupting prominence and the
associated coronal mass ejection. Three-dimensional reconstruction was
used to calculate the deprojected positions and speeds of different
parts of the prominence. Observations in several passbands allowed us
to analyse the radiative properties of the erupting prominence.
Results: The leading parts of the erupting prominence and the leading
edge of the corresponding coronal mass ejection propagate at speeds
of around 1700 km s−1 and 2200 km s−1,
respectively, while the trailing parts of the prominence are
significantly slower (around 500 km s−1). Parts of the
prominence are tracked up to heights of over 6 R⊙. The
He II emission is probably produced via collisional excitation rather
than scattering. Surprisingly, the brightness of a trailing feature
increases with height.
Conclusions: The reported prominence
is the first observed in He II 304 Å emission at such a great
height (above 6 R⊙). Movies are available at https://www.aanda.org
Title: Observation of Magnetic Switchback in the Solar Corona
Authors: Telloni, Daniele; Zank, Gary P.; Stangalini, Marco;
Downs, Cooper; Liang, Haoming; Nakanotani, Masaru; Andretta,
Vincenzo; Antonucci, Ester; Sorriso-Valvo, Luca; Adhikari, Laxman;
Zhao, Lingling; Marino, Raffaele; Susino, Roberto; Grimani, Catia;
Fabi, Michele; D'Amicis, Raffaella; Perrone, Denise; Bruno, Roberto;
Carbone, Francesco; Mancuso, Salvatore; Romoli, Marco; Da Deppo, Vania;
Fineschi, Silvano; Heinzel, Petr; Moses, John D.; Naletto, Giampiero;
Nicolini, Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Frassati,
Federica; Jerse, Giovanna; Landini, Federico; Pancrazzi, Maurizio;
Russano, Giuliana; Sasso, Clementina; Berghmans, David; Auchère,
Frédéric; Aznar Cuadrado, Regina; Chitta, Lakshmi P.; Harra, Louise;
Kraaikamp, Emil; Long, David M.; Mandal, Sudip; Parenti, Susanna;
Pelouze, Gabriel; Peter, Hardi; Rodriguez, Luciano; Schühle, Udo;
Schwanitz, Conrad; Smith, Phil J.; Verbeeck, Cis; Zhukov, Andrei N.
Bibcode: 2022arXiv220603090T
Altcode:
Switchbacks are sudden, large radial deflections of the solar wind
magnetic field, widely revealed in interplanetary space by the Parker
Solar Probe. The switchbacks' formation mechanism and sources are still
unresolved, although candidate mechanisms include Alfvénic turbulence,
shear-driven Kelvin-Helmholtz instabilities, interchange reconnection,
and geometrical effects related to the Parker spiral. This Letter
presents observations from the Metis coronagraph onboard Solar Orbiter
of a single large propagating S-shaped vortex, interpreted as first
evidence of a switchback in the solar corona. It originated above
an active region with the related loop system bounded by open-field
regions to the East and West. Observations, modeling, and theory provide
strong arguments in favor of the interchange reconnection origin of
switchbacks. Metis measurements suggest that the initiation of the
switchback may also be an indicator of the origin of slow solar wind.
Title: The first coronal mass ejection observed in both visible-light
and UV H I Ly-α channels of the Metis coronagraph on board Solar
Orbiter
Authors: Andretta, V.; Bemporad, A.; De Leo, Y.; Jerse, G.; Landini,
F.; Mierla, M.; Naletto, G.; Romoli, M.; Sasso, C.; Slemer, A.;
Spadaro, D.; Susino, R.; Talpeanu, D. -C.; Telloni, D.; Teriaca, L.;
Uslenghi, M.; Antonucci, E.; Auchère, F.; Berghmans, D.; Berlicki,
A.; Capobianco, G.; Capuano, G. E.; Casini, C.; Casti, M.; Chioetto,
P.; Da Deppo, V.; Fabi, M.; Fineschi, S.; Frassati, F.; Frassetto,
F.; Giordano, S.; Grimani, C.; Heinzel, P.; Liberatore, A.; Magli, E.;
Massone, G.; Messerotti, M.; Moses, D.; Nicolini, G.; Pancrazzi, M.;
Pelizzo, M. -G.; Romano, P.; Schühle, U.; Stangalini, M.; Straus,
Th.; Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Aznar
Cuadrado, R.; Bruno, R.; Ciaravella, A.; D'Amicis, R.; Lamy, P.;
Lanzafame, A.; Malvezzi, A. M.; Nicolosi, P.; Nisticò, G.; Peter,
H.; Plainaki, C.; Poletto, L.; Reale, F.; Solanki, S. K.; Strachan,
L.; Tondello, G.; Tsinganos, K.; Velli, M.; Ventura, R.; Vial, J. -C.;
Woch, J.; Zimbardo, G.
Bibcode: 2021A&A...656L..14A
Altcode:
Context. The Metis coronagraph on board Solar Orbiter offers a new
view of coronal mass ejections (CMEs), observing them for the first
time with simultaneous images acquired with a broad-band filter in
the visible-light interval and with a narrow-band filter around the
H I Ly-α line at 121.567 nm, the so-called Metis UV channel.
Aims: We show the first Metis observations of a CME, obtained on 16
and 17 January 2021. The event was also observed by the EUI/FSI imager
on board Solar Orbiter, as well as by other space-based coronagraphs,
such as STEREO-A/COR2 and SOHO/LASCO/C2, whose images are combined here
with Metis data.
Methods: Different images are analysed here
to reconstruct the 3D orientation of the expanding CME flux rope using
the graduated cylindrical shell model. This also allows us to identify
the possible location of the source region. Measurements of the CME
kinematics allow us to quantify the expected Doppler dimming in the
Ly-α channel.
Results: Observations show that most CME features
seen in the visible-light images are also seen in the Ly-α images,
although some features in the latter channel appear more structured
than their visible-light counterparts. We estimated the expansion
velocity of this event to be below 140 km s−1. Hence,
these observations can be understood by assuming that Doppler dimming
effects do not strongly reduce the Ly-α emission from the CME. These
velocities are comparable with or smaller than the radial velocities
inferred from the same data in a similar coronal structure on the
east side of the Sun.
Conclusions: The first observations by
Metis of a CME demonstrate the capability of the instrument to provide
valuable and novel information on the structure and dynamics of these
coronal events. Considering also its diagnostics capabilities regarding
the conditions of the ambient corona, Metis promises to significantly
advance our knowledge of such phenomena. Movies are available at https://www.aanda.org
Title: Cosmic-ray flux predictions and observations for and with
Metis on board Solar Orbiter
Authors: Grimani, C.; Andretta, V.; Chioetto, P.; Da Deppo, V.; Fabi,
M.; Gissot, S.; Naletto, G.; Persici, A.; Plainaki, C.; Romoli, M.;
Sabbatini, F.; Spadaro, D.; Stangalini, M.; Telloni, D.; Uslenghi, M.;
Antonucci, E.; Bemporad, A.; Capobianco, G.; Capuano, G.; Casti, M.;
De Leo, Y.; Fineschi, S.; Frassati, F.; Frassetto, F.; Heinzel, P.;
Jerse, G.; Landini, F.; Liberatore, A.; Magli, E.; Messerotti, M.;
Moses, D.; Nicolini, G.; Pancrazzi, M.; Pelizzo, M. G.; Romano, P.;
Sasso, C.; Schühle, U.; Slemer, A.; Straus, T.; Susino, R.; Teriaca,
L.; Volpicelli, C. A.; Freiherr von Forstner, J. L.; Zuppella, P.
Bibcode: 2021A&A...656A..15G
Altcode: 2021arXiv210413700G
Context. The Metis coronagraph is one of the remote sensing instruments
hosted on board the ESA/NASA Solar Orbiter mission. Metis is devoted
to carry out the first simultaneous imaging of the solar corona in
both visible light (VL) and ultraviolet (UV). High-energy particles
can penetrate spacecraft materials and may limit the performance of
the on-board instruments. A study of the galactic cosmic-ray (GCR)
tracks observed in the first VL images gathered by Metis during the
commissioning phase is presented here. A similar analysis is planned
for the UV channel.
Aims: We aim to formulate a prediction of
the GCR flux up to hundreds of GeV for the first part of the Solar
Orbiter mission to study the performance of the Metis coronagraph.
Methods: The GCR model predictions are compared to observations
gathered on board Solar Orbiter by the High-Energy Telescope in the
range between 10 MeV and 100 MeV in the summer of 2020 as well as with
the previous measurements. Estimated cosmic-ray fluxes above 70 MeV
n−1 have been also parameterized and used for Monte Carlo
simulations aimed at reproducing the cosmic-ray track observations in
the Metis coronagraph VL images. The same parameterizations can also
be used to study the performance of other detectors.
Results:
By comparing observations of cosmic-ray tracks in the Metis VL images
with FLUKA Monte Carlo simulations of cosmic-ray interactions in
the VL detector, we find that cosmic rays fire only a fraction, on
the order of 10−4, of the whole image pixel sample. We
also find that the overall efficiency for cosmic-ray identification
in the Metis VL images is approximately equal to the contribution
of Z ≥ 2 GCR particles. A similar study will be carried out during
the whole of the Solar Orbiter's mission duration for the purposes of
instrument diagnostics and to verify whether the Metis data and Monte
Carlo simulations would allow for a long-term monitoring of the GCR
proton flux.
Title: First light observations of the solar wind in the outer corona
with the Metis coronagraph
Authors: Romoli, M.; Antonucci, E.; Andretta, V.; Capuano, G. E.; Da
Deppo, V.; De Leo, Y.; Downs, C.; Fineschi, S.; Heinzel, P.; Landini,
F.; Liberatore, A.; Naletto, G.; Nicolini, G.; Pancrazzi, M.; Sasso,
C.; Spadaro, D.; Susino, R.; Telloni, D.; Teriaca, L.; Uslenghi,
M.; Wang, Y. -M.; Bemporad, A.; Capobianco, G.; Casti, M.; Fabi, M.;
Frassati, F.; Frassetto, F.; Giordano, S.; Grimani, C.; Jerse, G.;
Magli, E.; Massone, G.; Messerotti, M.; Moses, D.; Pelizzo, M. -G.;
Romano, P.; Schühle, U.; Slemer, A.; Stangalini, M.; Straus, T.;
Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Auchère,
F.; Aznar Cuadrado, R.; Berlicki, A.; Bruno, R.; Ciaravella, A.;
D'Amicis, R.; Lamy, P.; Lanzafame, A.; Malvezzi, A. M.; Nicolosi,
P.; Nisticò, G.; Peter, H.; Plainaki, C.; Poletto, L.; Reale, F.;
Solanki, S. K.; Strachan, L.; Tondello, G.; Tsinganos, K.; Velli,
M.; Ventura, R.; Vial, J. -C.; Woch, J.; Zimbardo, G.
Bibcode: 2021A&A...656A..32R
Altcode: 2021arXiv210613344R
In this work, we present an investigation of the wind in the solar
corona that has been initiated by observations of the resonantly
scattered ultraviolet emission of the coronal plasma obtained with
UVCS-SOHO, designed to measure the wind outflow speed by applying
Doppler dimming diagnostics. Metis on Solar Orbiter complements the
UVCS spectroscopic observations that were performed during solar
activity cycle 23 by simultaneously imaging the polarized visible
light and the H I Lyman-α corona in order to obtain high spatial and
temporal resolution maps of the outward velocity of the continuously
expanding solar atmosphere. The Metis observations, taken on May 15,
2020, provide the first H I Lyman-α images of the extended corona
and the first instantaneous map of the speed of the coronal plasma
outflows during the minimum of solar activity and allow us to identify
the layer where the slow wind flow is observed. The polarized visible
light (580-640 nm) and the ultraviolet H I Lyα (121.6 nm) coronal
emissions, obtained with the two Metis channels, were combined in
order to measure the dimming of the UV emission relative to a static
corona. This effect is caused by the outward motion of the coronal
plasma along the direction of incidence of the chromospheric photons
on the coronal neutral hydrogen. The plasma outflow velocity was then
derived as a function of the measured Doppler dimming. The static
corona UV emission was simulated on the basis of the plasma electron
density inferred from the polarized visible light. This study leads
to the identification, in the velocity maps of the solar corona, of
the high-density layer about ±10° wide, centered on the extension
of a quiet equatorial streamer present at the east limb - the coronal
origin of the heliospheric current sheet - where the slowest wind
flows at about 160 ± 18 km s−1 from 4 R⊙
to 6 R⊙. Beyond the boundaries of the high-density layer,
the wind velocity rapidly increases, marking the transition between
slow and fast wind in the corona.
Title: Exploring the Solar Wind from Its Source on the Corona into
the Inner Heliosphere during the First Solar Orbiter-Parker Solar
Probe Quadrature
Authors: Telloni, Daniele; Andretta, Vincenzo; Antonucci, Ester;
Bemporad, Alessandro; Capuano, Giuseppe E.; Fineschi, Silvano;
Giordano, Silvio; Habbal, Shadia; Perrone, Denise; Pinto, Rui F.;
Sorriso-Valvo, Luca; Spadaro, Daniele; Susino, Roberto; Woodham, Lloyd
D.; Zank, Gary P.; Romoli, Marco; Bale, Stuart D.; Kasper, Justin C.;
Auchère, Frédéric; Bruno, Roberto; Capobianco, Gerardo; Case,
Anthony W.; Casini, Chiara; Casti, Marta; Chioetto, Paolo; Corso,
Alain J.; Da Deppo, Vania; De Leo, Yara; Dudok de Wit, Thierry;
Frassati, Federica; Frassetto, Fabio; Goetz, Keith; Guglielmino,
Salvo L.; Harvey, Peter R.; Heinzel, Petr; Jerse, Giovanna; Korreck,
Kelly E.; Landini, Federico; Larson, Davin; Liberatore, Alessandro;
Livi, Roberto; MacDowall, Robert J.; Magli, Enrico; Malaspina, David
M.; Massone, Giuseppe; Messerotti, Mauro; Moses, John D.; Naletto,
Giampiero; Nicolini, Gianalfredo; Nisticò, Giuseppe; Panasenco,
Olga; Pancrazzi, Maurizio; Pelizzo, Maria G.; Pulupa, Marc; Reale,
Fabio; Romano, Paolo; Sasso, Clementina; Schühle, Udo; Stangalini,
Marco; Stevens, Michael L.; Strachan, Leonard; Straus, Thomas; Teriaca,
Luca; Uslenghi, Michela; Velli, Marco; Verscharen, Daniel; Volpicelli,
Cosimo A.; Whittlesey, Phyllis; Zangrilli, Luca; Zimbardo, Gaetano;
Zuppella, Paola
Bibcode: 2021ApJ...920L..14T
Altcode: 2021arXiv211011031T
This Letter addresses the first Solar Orbiter (SO)-Parker Solar
Probe (PSP) quadrature, occurring on 2021 January 18 to investigate
the evolution of solar wind from the extended corona to the inner
heliosphere. Assuming ballistic propagation, the same plasma volume
observed remotely in the corona at altitudes between 3.5 and 6.3
solar radii above the solar limb with the Metis coronagraph on SO
can be tracked to PSP, orbiting at 0.1 au, thus allowing the local
properties of the solar wind to be linked to the coronal source region
from where it originated. Thanks to the close approach of PSP to the
Sun and the simultaneous Metis observation of the solar corona, the
flow-aligned magnetic field and the bulk kinetic energy flux density
can be empirically inferred along the coronal current sheet with an
unprecedented accuracy, allowing in particular estimation of the Alfvén
radius at 8.7 solar radii during the time of this event. This is thus
the very first study of the same solar wind plasma as it expands from
the sub-Alfvénic solar corona to just above the Alfvén surface.
Title: Effects of the chromospheric Lyα line profile shape on
the determination of the solar wind H I outflow velocity using the
Doppler dimming technique
Authors: Capuano, G. E.; Dolei, S.; Spadaro, D.; Guglielmino, S. L.;
Romano, P.; Ventura, R.; Andretta, V.; Bemporad, A.; Sasso, C.;
Susino, R.; Da Deppo, V.; Frassetto, F.; Giordano, S. M.; Landini,
F.; Nicolini, G.; Pancrazzi, M.; Romoli, M.; Zangrilli, L.
Bibcode: 2021A&A...652A..85C
Altcode: 2021arXiv210805957C
Context. The determination of solar wind H I outflow velocity is
fundamental to shedding light on the mechanisms of wind acceleration
occurring in the corona. Moreover, it has implications in various
astrophysical contexts, such as in the heliosphere and in cometary
and planetary atmospheres.
Aims: We aim to study the effects
of the chromospheric Lyα line profile shape on the determination
of the outflow speed of coronal H I atoms via the Doppler dimming
technique. This is of particular interest in view of the upcoming
measurements of the Metis coronagraph aboard the Solar Orbiter
mission.
Methods: The Doppler dimming technique exploits the
decrease of coronal Lyα radiation in regions where H I atoms flow out
in the solar wind. Starting from UV observations of the coronal Lyα
line from the Solar and Heliospheric Observatory (SOHO), aboard the
UltraViolet Coronagraph Spectrometer, and simultaneous measurements
of coronal electron densities from pB coronagraphic observations, we
explored the effect of the profile of the pumping chromospheric Lyα
line. We used measurements from the Solar UV Measurement of Emitted
Radiation, aboard SOHO, the Ultraviolet Spectrometer and Polarimeter,
aboard the Solar Maximum Mission, and the Laboratoire de Physique
Stellaire et Planetaire, aboard the Eight Orbiting Solar Observatory,
both from representative on-disc regions, such as coronal holes
and quiet Sun and active regions, and as a function of time during
the solar activity cycle. In particular, we considered the effect
of four chromospheric line parameters: line width, reversal depth,
asymmetry, and distance of the peaks.
Results: We find that
the range of variability of the four line parameters is of about 50%
for the width, 69% for the reversal depth, and 35% and 50% for the
asymmetry and distance of the peaks, respectively. We then find that
the variability of the pumping Lyα profile affects the estimates of
the coronal H I velocity by about 9−12%. This uncertainty is smaller
than the uncertainties due to variations of other physical quantities,
such as electron density, electron temperature, H I temperature, and
integrated chromospheric Lyα radiance.
Conclusions: Our work
suggests that the observed variations in the chromospheric Lyα line
profile parameters along a cycle and in specific regions negligibly
affect the determination of the solar wind speed of H I atoms. Due
to this weak dependence, a unique shape of the Lyα profile over
the solar disc that is constant in time can be adopted to obtain the
values of the solar wind H I outflow velocity. Moreover, the use of an
empirical analytical chromospheric profile of the Lyα, assumed uniform
over the solar disc and constant in time, is justifiable in order to
obtain a good estimate of the coronal wind H I outflow velocity using
coronagraphic UV images.
Title: Magnetic imaging of the outer solar atmosphere (MImOSA)
Authors: Peter, H.; Ballester, E. Alsina; Andretta, V.; Auchère, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; Alemán, T. del Pino; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Štěpán, J.; Teriaca, L.; Bueno, J. Trujillo
Bibcode: 2021ExA...tmp...95P
Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability of
planets orbiting these host stars. Although the magnetic field at the
surface of the Sun is reasonably well characterised by observations,
the information on the magnetic field in the higher atmospheric layers
is mainly indirect. This lack of information hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution
and high sensitivity. (b) An extreme-UV-to-IR coronagraph that is
designed to measure the large-scale magnetic field in the corona with
an aperture of about 40 cm. (c) An extreme-UV imaging polarimeter
based on a 30 cm telescope that combines high throughput in the
extreme UV with polarimetry to connect the magnetic measurements
of the other two instruments. Placed in a near-Earth orbit, the data
downlink would be maximised, while a location at L4 or L5 would provide
stereoscopic observations of the Sun in combination with Earth-based
observatories. This mission to measure the magnetic field will finally
unlock the driver of the dynamics in the outer solar atmosphere and
thereby will greatly advance our understanding of the Sun and the
heliosphere.
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: In-flight optical performance assessment for the Metis solar
coronagraph
Authors: Da Deppo, Vania; Chioetto, Paolo; Andretta, Vincenzo; Casini,
Chiara; Frassetto, Fabio; Slemer, Alessandra; Zuppella, Paola; Romoli,
Marco; Fineschi, Silvano; Heinzel, Petr; Naletto, Giampiero; Nicolini,
Gianalfredo; Spadaro, Daniele; Stangalini, Marco; Teriaca, Luca;
Bemporad, Alessandro; Casti, Marta; Fabi, Michele; Grimani, Catia;
Heerlein, Klaus; Jerse, Giovanna; Landini, Federico; Liberatore,
Alessandro; Magli, Enrico; Melich, Radek; Pancrazzi, Maurizio; Pelizzo,
Maria-G.; Romano, Paolo; Sasso, Clementina; Straus, Thomas; Susino,
Roberto; Uslenghi, Michela; Volpicelli, Cosimo Antonio
Bibcode: 2021SPIE11852E..10D
Altcode:
Metis is a multi-wavelength coronagraph onboard the European Space
Agency (ESA) Solar Orbiter mission. The instrument features an
innovative instrument design conceived for simultaneously imaging the
Sun's corona in the visible and ultraviolet range. The Metis visible
channel employs broad-band, polarized imaging of the visible K-corona,
while the UV one uses narrow-band imaging at the HI Ly , i.e. 121.6
nm. During the commissioning different acquisitions and activities,
performed with both the Metis channels, have been carried out with the
aim to check the functioning and the performance of the instrument. In
particular, specific observations of stars have been devised to assess
the optical alignment of the telescope and to derive the instrument
optical parameters such as focal length, PSF and possibly check the
optical distortion and the vignetting function. In this paper, the
preliminary results obtained for the PSF of both channels and the
determination of the scale for the visible channel will be described
and discussed. The in-flight obtained data will be compared to those
obtained on-ground during the calibration campaign.
Title: On-ground flat-field calibration of the Metis coronagraph
onboard the Solar Orbiter ESA mission
Authors: Casini, C.; Da Deppo, V.; Zuppella, P.; Chioetto, P.; Slemer,
A.; Frassetto, F.; Romoli, M.; Landini, F.; Pancrazzi, M.; Andretta,
V.; De Leo, Y.; Bemporad, A.; Fabi, M.; Fineschi, S.; Frassati, F.;
Grimani, C.; Jerse, G.; Heerlein, K.; Liberatore, A.; Magli, E.;
Naletto, G.; Nicolini, G.; Pelizzo, M. G.; Romano, P.; Sasso, C.;
Spadaro, D.; Stangalini, M.; Straus, T.; Susino, R.; Teriaca, L.;
Uslenghi, M.; Casti, M.; Heinzel, P.; Volpicelli, A.
Bibcode: 2021SPIE11852E..5BC
Altcode:
Solar Orbiter, launched on February 9th 2020, is an
ESA/NASA mission conceived to study the Sun. This work presents
the embedded Metis coronagraph and its on-ground calibration in the
580-640 nm wavelength range using a flat field panel. It provides
a uniform illumination to evaluate the response of each pixel of
the detector; and to characterize the Field of View (FoV) of the
coronagraph. Different images with different exposure times were
acquired during the on-ground calibration campaign. They were analyzed
to verify the linearity response of the instrument and the requirements
for the FoV: the maximum area of the sky that Metis can acquire.
Title: In-flight calibration of Metis coronagraph on board of
Solar Orbiter
Authors: Liberatore, A.; Fineschi, S.; Casti, M.; Capobianco, G.;
Romoli, M.; Andretta, V.; Bemporad, A.; Da Deppo, V.; De Leo, Y.; Fabi,
M.; Frassetto, F.; Grimani, C.; Heerlein, K.; Heinzel, P.; Jerse,
G.; Landini, F.; Magli, E.; Naletto, G.; Nicolini, G.; Pancrazzi,
M.; Pelizzo, M. G.; Romano, P.; Sasso, C.; Slemer, A.; Spadaro, D.;
Straus, T.; Susino, R.; Teriaca, L.; Uslenghi, M.; Volpicelli, C. A.;
Zuppella, P.
Bibcode: 2021SPIE11852E..48L
Altcode:
Metis coronagraph is one of the remote-sensing instruments of the Solar
Orbiter mission launched at the begin of 2020. The mission profile will
allow for the first time the remote-sensing observation of the Sun
from a very close distance and increasing the latitude with respect
to the ecliptic plane. In particular, Metis is aimed at the overall
characterization and study of the solar corona and solar wind. Metis
instrument acquires images of the solar corona in two different
wavelengths simultaneously; ultraviolet (UV) and visible-light (VL). The
VL channel includes a polarimeter with an electro-optically modulating
Liquid Crystal Variable Retarder (LCVR) to measure the linearly
polarized brighness pB) of the K-corona. This paper presents part of
the in-flight calibration results for both wavelength channels together
with a comparison with on-ground calibrations. The orientation of the
K-corona linear polarization was used for the in-flight calibration
of the Metis polarimeter. This paper describes the correction of the
on-ground VL vignetting function after the in-flight adjustment of
the internal occulter. The same vignetting function was adaptated to
the UV channel.
Title: Challenges during Metis-Solar Orbiter commissioning phase
Authors: Romoli, Marco; Andretta, Vincenzo; Bemporad, Alessandro;
Casti, Marta; Da Deppo, Vania; De Leo, Yara; Fabi, Michele; Fineschi,
Silvano; Frassetto, Fabio; Grimani, Catia; Heerlein, Klaus; Heinzel,
Petr; Jerse, Giovanna; Landini, Federico; Liberatore, Alessandro;
Magli, Enrico; Naletto, Giampiero; Nicolini, Gianalfredo; Pancrazzi,
Maurizio; Pelizzo, Maria Guglielmina; Romano, Paolo; Sasso, Clementina;
Schühle, Udo; Slemer, Alessandra; Spadaro, Daniele; Straus, Thomas;
Susino, Roberto; Teriaca, Luca; Uslenghi, Michela; Volpicelli, Cosimo
Antonio; Zupella, Paola
Bibcode: 2021SPIE11852E..5AR
Altcode:
Metis is the visible light and UV light imaging coronagraph on board
the ESA-NASA mission Solar Orbiter that has been launched February 10th,
2020, from Cape Canaveral. Scope of the mission is to study the Sun up
close, taking high-resolution images of the Sun's poles for the first
time, and understanding the Sun-Earth connection. Metis coronagraph
will image the solar corona in the linearly polarized broadband visible
radiation and in the UV HI Ly-α line from 1.6 to 3 solar radii when at
Solar Orbiter perihelion, providing a diagnostics, with unprecedented
temporal coverage and spatial resolution, of the structures and dynamics
of the full corona. Solar Orbiter commissioning phase big challenge was
Covid-19 social distancing phase that affected the way commissioning
of a spacecraft and its payload is typically done. Metis coronagraph
on-board Solar Orbiter had its additional challenges: to wake up and
check the performance of the optical, electrical and thermal subsystems,
most of them unchecked since Metis delivery to spacecraft prime, Airbus,
in May 2017. The roadmap to the fully commissioned coronagraph is here
described throughout the steps from the software functional test,
the switch on of the detectors of the two channels, UV and visible,
to the optimization of the occulting system and the characterization
of the instrumental stray light, one of the most challenging features
in a coronagraph.
Title: First-light Science Observations of the Metis Solar Coronagraph
Authors: Fineschi, S.; Romoli, M.; Andretta, V.; Bemporad, A.;
Capobianco, G.; Casti, M.; Da Deppo, V.; De Leo, Y.; Fabi, M.;
Frassetto, F.
Bibcode: 2021SPIE11852E..11F
Altcode:
Metis coronagraph is one of the remote-sensing instruments of the Solar
Orbiter mission launched in February 2020. The mission profile will
allow for the first time the remote-sensing observation of the Sun from
as close as 0.28 AU and from ecliptic latitudes as high as 30?. Metis,
in particular, is aimed at the study and the overall characterization
of the solar corona and solar wind. This instrument is an innovative
inverted-occultation coronagraph that will image the solar corona for
the first time simultaneously in two different wavelength band-passes:
in the linearly-polarized visible-light (VL), between 580 and 640 nm,
and in the ultraviolet (UV) Lyman-a line of hydrogen, HI at 121.6 nm
by combining in the same telescope UV interference mirror coatings
(Al/MgF2) and spectral bandpass filters. The visible channel includes
a broad-band polarimeter to observe the linearly polarized component of
the K corona. These measurements will allow a complete characterization
of the physical parameters, such as density and outflow speed, of
the two major plasma components of the corona and the solar wind:
electrons (protons) and hydrogen. After a period of commissioning, by
the summer of 2020, Metis will have performed the First-light Science
Observations during the "Remote-Sensing Check-out Window" (RSCW) that
is a telemetry contact period, specifically allocated before entering
the operational phase at the end of 2021. This presentation will report
the first-light science observations of Metis represented by the UV
and polarized VL images of the corona. The calibration results from
the commissioning will be used for the correction of the instrumental
effects. The resulting first-light maps of the coronal electron and
hydrogen distributions will be presented.
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: High resolution soft X-ray spectroscopy and the quest for
the hot (5-10 MK) plasma in solar active regions
Authors: Del Zanna, Giulio; Andretta, Vincenzo; Cargill, Peter J.;
Corso, Alain J.; Daw, Adrian N.; Golub, Leon; Klimchuk, James A.;
Mason, Helen E.
Bibcode: 2021FrASS...8...33D
Altcode: 2021arXiv210306156D
We discuss the diagnostics available to study the 5--10 MK plasma in
the solar corona, which is key to understanding the heating in the
cores of solar active regions. We present several simulated spectra,
and show that excellent diagnostics are available in the soft X-rays,
around 100 Angstroms, as six ionisation stages of Fe can simultaneously
be observed, and electron densities derived, within a narrow spectral
region. As this spectral range is almost unexplored, we present an
analysis of available and simulated spectra, to compare the hot emission
with the cooler component. We adopt recently designed multilayers to
present estimates of count rates in the hot lines, with a baseline
spectrometer design. Excellent count rates are found, opening up
the exciting opportunity to obtain high-resolution spectroscopy of
hot plasma.
Title: Magnetic Imaging of the Outer Solar Atmosphere (MImOSA):
Unlocking the driver of the dynamics in the upper solar atmosphere
Authors: Peter, H.; Alsina Ballester, E.; Andretta, V.; Auchere, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; del Pino Aleman, T.; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Stepan, J.; Teriaca, L.; Trujillo Bueno, J.
Bibcode: 2021arXiv210101566P
Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability
of planets orbiting these host stars. The lack of information on the
magnetic field in the higher atmospheric layers hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution and high
sensitivity. (b) An extreme-UV-to-IR coronagraph that is designed to
measure the large-scale magnetic field in the corona with an aperture
of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30
cm telescope that combines high throughput in the extreme UV with
polarimetry to connect the magnetic measurements of the other two
instruments. This mission to measure the magnetic field will unlock
the driver of the dynamics in the outer solar atmosphere and thereby
greatly advance our understanding of the Sun and the heliosphere.
Title: The MDOR/PDOR on-line module for MISO, the planning software
of Solar Orbiter instruments
Authors: Volpicelli, Cosimo; Landini, Federico; Pancrazzi, Maurizio;
Straus, Thomas; Susino, Roberto; Nicolini, Gianalfredo; Sasso,
Clementina; Fabi, Michele; De Leo, Yara; Casini, Chiara; Naletto,
Giampiero; Nicolosi, Piergiorgio; Spadaro, Daniele; Andretta, Vincenzo;
Antonucci, Ester; Fineschi, Silvano; Da Deppo, Vania; Zuppella, Paola;
Frassetto, Fabio; Slemer, Alessandra; Mercier, Claude; Kouliche,
Dimitri; Caminade, Stephane; Picard, David; Buchlin, Eric; Auchère,
Frédéric; Romoli, Marco
Bibcode: 2020SPIE11452E..0SV
Altcode:
Solar Orbiter is a solar mission that will approach the Sun down to a
minimum perihelion of 0.28 AU and will increase its orbit inclination
with respect to the ecliptic up to a maximum angle of 34 deg. For
imagers aboard Solar Orbiter there will be three 10-days remote sensing
windows per orbit. Observations shall be carefully planned at least 6
months in advance. The Multi Instrument Sequence Organizer (MISO) is
a web based platform developed by the SPICE group and made available
to support Solar Orbiter instruments teams in planning observations
by assembling Mission Database sequences. Metis is the UV and visible
light coronagraph aboard Solar Orbiter. Metis is a complex instrument
characterized by a rich variety of observing modes, which required a
careful commissioning activity and will need support for potential
maintenance operations throughout the mission. In order to support
commissioning and maintenance activities, the Metis team developed
a PDOR (Payload Direct Operation Request) and MDOR (Memory Direct
Operation Request) module integrated in MISO and made available to all
Solar Orbiter instruments. An effort was made in order to interpret
the coding philosophy of the main project and to make the additional
module as homogeneous as possible both to the web interface and to the
algorithm logic, while integrating characteristics which are peculiar
to PDORs and MDORs. An user friendly web based interface allows the
operator to build the operation request and to successively modify or
integrate it with further or alternative information. In the present
work we describe the PDOR/MDOR module for MISO by addressing its logic
and main characteristics.
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: The Solar-C (EUVST) mission: the latest status
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko; Suematsu,
Yoshinori; Hara, Hirohisa; Tsuzuki, Toshihiro; Katsukawa, Yukio; Kubo,
Masahito; Ishikawa, Ryoko; Watanabe, Tetsuya; Toriumi, Shin; Ichimoto,
Kiyoshi; Nagata, Shin'ichi; Hasegawa, Takahiro; Yokoyama, Takaaki;
Watanabe, Kyoko; Tsuno, Katsuhiko; Korendyke, Clarence M.; Warren,
Harry; De Pontieu, Bart; Boerner, Paul; Solanki, Sami K.; Teriaca,
Luca; Schuehle, Udo; Matthews, Sarah; Long, David; Thomas, William;
Hancock, Barry; Reid, Hamish; Fludra, Andrzej; Auchère, Frederic;
Andretta, Vincenzo; Naletto, Giampiero; Poletto, Luca; Harra, Louise
Bibcode: 2020SPIE11444E..0NS
Altcode:
Solar-C (EUVST) is the next Japanese solar physics mission to
be developed with significant contributions from US and European
countries. The mission carries an EUV imaging spectrometer with
slit-jaw imaging system called EUVST (EUV High-Throughput Spectroscopic
Telescope) as the mission payload, to take a fundamental step towards
answering how the plasma universe is created and evolves and how the
Sun influences the Earth and other planets in our solar system. In
April 2020, ISAS (Institute of Space and Astronautical Science) of JAXA
(Japan Aerospace Exploration Agency) has made the final down-selection
for this mission as the 4th in the series of competitively chosen
M-class mission to be launched with an Epsilon launch vehicle in mid
2020s. NASA (National Aeronautics and Space Administration) has selected
this mission concept for Phase A concept study in September 2019 and
is in the process leading to final selection. For European countries,
the team has (or is in the process of confirming) confirmed endorsement
for hardware contributions to the EUVST from the national agencies. A
recent update to the mission instrumentation is to add a UV spectral
irradiance monitor capability for EUVST calibration and scientific
purpose. This presentation provides the latest status of the mission
with an overall description of the mission concept emphasizing on key
roles of the mission in heliophysics research from mid 2020s.
Title: A Radiation Environmental Study for the Metis Coronagraph on
board Solar Orbiter
Authors: Grimani, C.; Andretta, V.; Chioetto, P.; Da Deppo, V.; Fabi,
M.; Gissot, S.; Naletto, G.; Plainaki, C.; Romoli, M.; Spadaro, D.;
Stangalini, M.; Telloni, D.; Uslenghi, M.
Bibcode: 2020AGUFMSH038..08G
Altcode:
The solar cycle 24 was the weakest of the last hundred years. All
predictions available in the literature for the solar cycle 25 indicate
a similar or even weaker period of solar activity. As a result,
the highest galactic cosmic-ray flux of the last century will strike
the Solar Orbiter spacecraft along its orbit. Conversely, only one
solar energetic particle event (SEP) per year (average predictions)
is expected during the cruise phase of the mission in the fluence range
106-107 protons cm-2 above 30 MeV.An
instrument dedicated radiation environmental study will be carried out
for Metis, the coronagraph on board Solar Orbiter. Pre-launch Monte
Carlo simulations aiming to estimate the overall dose absorbed by the
Cerium treated polarimeter lenses indicated an average dose absorption
of 2000 Gy for the extended mission, while the lenses showed a few %
transmittance loss with a 106 Gy of gamma radiation. Monte Carlo simulations will be also performed to study energetic
particle single hits and tracks in the images of the visible light and
ultraviolet detectors. On the other hand, dark images provide precious
clues for cosmic-ray monitoring and images background estimates for both
Metis and EUI (Extreme-Ultraviolet Imager) detectors. Collaboration with
the EPD (Energetic Particle Detector) instrument scientists and data
from cosmic-ray experiments in orbit during the Solar Orbiter mission
will allow us to study cosmic-ray variations along the spacecraft
orbit and their effects on the instrument performance.
Title: First results from the EUI and SPICE observations of Alpha
Leo near Solar Orbiter first perihelion
Authors: Buchlin, E.; Teriaca, L.; Giunta, A. S.; Grundy, T.; Andretta,
V.; Auchere, F.; Peter, H.; Berghmans, D.; Carlsson, M.; Fludra, A.;
Harra, L.; Hassler, D.; Long, D.; Rochus, P. L.; Schühle, U.; Aznar
Cuadrado, R.; Caldwell, M.; Caminade, S.; DeForest, C.; Fredvik, T.;
Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp, E.; Kucera, T. A.;
Müller, D.; Parenti, S.; Schmutz, W. K.; Sidher, S.; Smith, P.;
Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
Bibcode: 2020AGUFMSH0360024B
Altcode:
On June 16th 2020 Solar Orbiter made a dedicated observing campaign
where the spacecraft pointed to the solar limb to allow some of the
high resolution instruments to observe the ingress (at the east limb)
and later the egress (west limb) of the occultation of the star Alpha
Leonis by the solar disk. The star was chosen because its luminosity and
early spectral type ensure high and stable flux at wavelengths between
100 and 122 nanometers, a range observed by the High Resolution EUI
Lyman alpha telescope (HRI-LYA) and by the long wavelength channel
of the SPICE spectrograph. Star observations, when feasible, allow
to gather a great deal of information on the instrument performances,
such as the radiometric performance and the instrument optical point
spread function (PSF). We report here the first results from the
above campaign for the two instruments.
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: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
A. N.
Bibcode: 2020A&A...642A...2R
Altcode:
Context. The Solar Orbiter spacecraft will be equipped with a wide
range of remote-sensing (RS) and in situ (IS) instruments to record
novel and unprecedented measurements of the solar atmosphere and
the inner heliosphere. To take full advantage of these new datasets,
tools and techniques must be developed to ease multi-instrument and
multi-spacecraft studies. In particular the currently inaccessible
low solar corona below two solar radii can only be observed
remotely. Furthermore techniques must be used to retrieve coronal
plasma properties in time and in three dimensional (3D) space. Solar
Orbiter will run complex observation campaigns that provide interesting
opportunities to maximise the likelihood of linking IS data to their
source region near the Sun. Several RS instruments can be directed
to specific targets situated on the solar disk just days before
data acquisition. To compare IS and RS, data we must improve our
understanding of how heliospheric probes magnetically connect to the
solar disk.
Aims: The aim of the present paper is to briefly
review how the current modelling of the Sun and its atmosphere
can support Solar Orbiter science. We describe the results of a
community-led effort by European Space Agency's Modelling and Data
Analysis Working Group (MADAWG) to develop different models, tools,
and techniques deemed necessary to test different theories for the
physical processes that may occur in the solar plasma. The focus here
is on the large scales and little is described with regards to kinetic
processes. To exploit future IS and RS data fully, many techniques have
been adapted to model the evolving 3D solar magneto-plasma from the
solar interior to the solar wind. A particular focus in the paper is
placed on techniques that can estimate how Solar Orbiter will connect
magnetically through the complex coronal magnetic fields to various
photospheric and coronal features in support of spacecraft operations
and future scientific studies.
Methods: Recent missions such as
STEREO, provided great opportunities for RS, IS, and multi-spacecraft
studies. We summarise the achievements and highlight the challenges
faced during these investigations, many of which motivated the Solar
Orbiter mission. We present the new tools and techniques developed
by the MADAWG to support the science operations and the analysis of
the data from the many instruments on Solar Orbiter.
Results:
This article reviews current modelling and tool developments that ease
the comparison of model results with RS and IS data made available
by current and upcoming missions. It also describes the modelling
strategy to support the science operations and subsequent exploitation
of Solar Orbiter data in order to maximise the scientific output
of the mission.
Conclusions: The on-going community effort
presented in this paper has provided new models and tools necessary
to support mission operations as well as the science exploitation of
the Solar Orbiter data. The tools and techniques will no doubt evolve
significantly as we refine our procedure and methodology during the
first year of operations of this highly promising mission.
Title: Metis: the Solar Orbiter visible light and ultraviolet
coronal imager
Authors: Antonucci, Ester; Romoli, Marco; Andretta, Vincenzo; Fineschi,
Silvano; Heinzel, Petr; Moses, J. Daniel; Naletto, Giampiero; Nicolini,
Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Berlicki, Arkadiusz;
Capobianco, Gerardo; Crescenzio, Giuseppe; Da Deppo, Vania; Focardi,
Mauro; Frassetto, Fabio; Heerlein, Klaus; Landini, Federico; Magli,
Enrico; Marco Malvezzi, Andrea; Massone, Giuseppe; Melich, Radek;
Nicolosi, Piergiorgio; Noci, Giancarlo; Pancrazzi, Maurizio; Pelizzo,
Maria G.; Poletto, Luca; Sasso, Clementina; Schühle, Udo; Solanki,
Sami K.; Strachan, Leonard; Susino, Roberto; Tondello, Giuseppe;
Uslenghi, Michela; Woch, Joachim; Abbo, Lucia; Bemporad, Alessandro;
Casti, Marta; Dolei, Sergio; Grimani, Catia; Messerotti, Mauro;
Ricci, Marco; Straus, Thomas; Telloni, Daniele; Zuppella, Paola;
Auchère, Frederic; Bruno, Roberto; Ciaravella, Angela; Corso,
Alain J.; Alvarez Copano, Miguel; Aznar Cuadrado, Regina; D'Amicis,
Raffaella; Enge, Reiner; Gravina, Alessio; Jejčič, Sonja; Lamy,
Philippe; Lanzafame, Alessandro; Meierdierks, Thimo; Papagiannaki,
Ioanna; Peter, Hardi; Fernandez Rico, German; Giday Sertsu, Mewael;
Staub, Jan; Tsinganos, Kanaris; Velli, Marco; Ventura, Rita; Verroi,
Enrico; Vial, Jean-Claude; Vives, Sebastien; Volpicelli, Antonio;
Werner, Stephan; Zerr, Andreas; Negri, Barbara; Castronuovo, Marco;
Gabrielli, Alessandro; Bertacin, Roberto; Carpentiero, Rita; Natalucci,
Silvia; Marliani, Filippo; Cesa, Marco; Laget, Philippe; Morea, Danilo;
Pieraccini, Stefano; Radaelli, Paolo; Sandri, Paolo; Sarra, Paolo;
Cesare, Stefano; Del Forno, Felice; Massa, Ernesto; Montabone, Mauro;
Mottini, Sergio; Quattropani, Daniele; Schillaci, Tiziano; Boccardo,
Roberto; Brando, Rosario; Pandi, Arianna; Baietto, Cristian; Bertone,
Riccardo; Alvarez-Herrero, Alberto; García Parejo, Pilar; Cebollero,
María; Amoruso, Mauro; Centonze, Vito
Bibcode: 2020A&A...642A..10A
Altcode: 2019arXiv191108462A
Aims: Metis is the first solar coronagraph designed for a
space mission and is capable of performing simultaneous imaging of the
off-limb solar corona in both visible and UV light. The observations
obtained with Metis aboard the Solar Orbiter ESA-NASA observatory
will enable us to diagnose, with unprecedented temporal coverage and
spatial resolution, the structures and dynamics of the full corona
in a square field of view (FoV) of ±2.9° in width, with an inner
circular FoV at 1.6°, thus spanning the solar atmosphere from 1.7
R⊙ to about 9 R⊙, owing to the eccentricity
of the spacecraft orbit. Due to the uniqueness of the Solar Orbiter
mission profile, Metis will be able to observe the solar corona
from a close (0.28 AU, at the closest perihelion) vantage point,
achieving increasing out-of-ecliptic views with the increase of the
orbit inclination over time. Moreover, observations near perihelion,
during the phase of lower rotational velocity of the solar surface
relative to the spacecraft, allow longer-term studies of the off-limb
coronal features, thus finally disentangling their intrinsic evolution
from effects due to solar rotation.
Methods: Thanks to a novel
occultation design and a combination of a UV interference coating of
the mirrors and a spectral bandpass filter, Metis images the solar
corona simultaneously in the visible light band, between 580 and 640
nm, and in the UV H I Lyman-α line at 121.6 nm. The visible light
channel also includes a broadband polarimeter able to observe the
linearly polarised component of the K corona. The coronal images in
both the UV H I Lyman-α and polarised visible light are obtained at
high spatial resolution with a spatial scale down to about 2000 km
and 15 000 km at perihelion, in the cases of the visible and UV light,
respectively. A temporal resolution down to 1 s can be achieved when
observing coronal fluctuations in visible light.
Results: The
Metis measurements, obtained from different latitudes, will allow for
complete characterisation of the main physical parameters and dynamics
of the electron and neutral hydrogen/proton plasma components of the
corona in the region where the solar wind undergoes the acceleration
process and where the onset and initial propagation of coronal mass
ejections (CMEs) take place. The near-Sun multi-wavelength coronal
imaging performed with Metis, combined with the unique opportunities
offered by the Solar Orbiter mission, can effectively address crucial
issues of solar physics such as: the origin and heating/acceleration
of the fast and slow solar wind streams; the origin, acceleration,
and transport of the solar energetic particles; and the transient
ejection of coronal mass and its evolution in the inner heliosphere,
thus significantly improving our understanding of the region connecting
the Sun to the heliosphere and of the processes generating and driving
the solar wind and coronal mass ejections.
Conclusions: This
paper presents the scientific objectives and requirements, the overall
optical design of the Metis instrument, the thermo-mechanical design,
and the processing and power unit; reports on the results of the
campaigns dedicated to integration, alignment, and tests, and to
the characterisation of the instrument performance; describes the
operation concept, data handling, and software tools; and, finally,
the diagnostic techniques to be applied to the data, as well as a brief
description of the expected scientific products. The performance of the
instrument measured during calibrations ensures that the scientific
objectives of Metis can be pursued with success. Metis website:
http://metis.oato.inaf.it
Title: The GAPS programme at TNG. XXII. The GIARPS view of the
extended helium atmosphere of HD 189733 b accounting for stellar
activity
Authors: Guilluy, G.; Andretta, V.; Borsa, F.; Giacobbe, P.; Sozzetti,
A.; Covino, E.; Bourrier, V.; Fossati, L.; Bonomo, A. S.; Esposito,
M.; Giampapa, M. S.; Harutyunyan, A.; Rainer, M.; Brogi, M.; Bruno,
G.; Claudi, R.; Frustagli, G.; Lanza, A. F.; Mancini, L.; Pino, L.;
Poretti, E.; Scandariato, G.; Affer, L.; Baffa, C.; Baruffolo, A.;
Benatti, S.; Biazzo, K.; Bignamini, A.; Boschin, W.; Carleo, I.;
Cecconi, M.; Cosentino, R.; Damasso, M.; Desidera, S.; Falcini,
G.; Martinez Fiorenzano, A. F.; Ghedina, A.; González-Álvarez,
E.; Guerra, J.; Hernandez, N.; Leto, G.; Maggio, A.; Malavolta, L.;
Maldonado, J.; Micela, G.; Molinari, E.; Nascimbeni, V.; Pagano, I.;
Pedani, M.; Piotto, G.; Reiners, A.
Bibcode: 2020A&A...639A..49G
Altcode: 2020arXiv200505676G
Context. Exoplanets orbiting very close to their parent star are
strongly irradiated. This can lead the upper atmospheric layers to
expand and evaporate into space. The metastable helium (He I) triplet
at 1083.3 nm has recently been shown to be a powerful diagnostic
to probe extended and escaping exoplanetary atmospheres.
Aims: We perform high-resolution transmission spectroscopy of the
transiting hot Jupiter HD 189733 b with the GIARPS (GIANO-B + HARPS-N)
observing mode of the Telescopio Nazionale Galileo, taking advantage
of the simultaneous optical+near infrared spectral coverage to detect
He I in the planet's extended atmosphere and to gauge the impact of
stellar magnetic activity on the planetary absorption signal.
Methods: Observations were performed during five transit events of HD
189733 b. By comparison of the in-transit and out-of-transit GIANO-B
observations, we computed high-resolution transmission spectra. We
then used them to perform equivalent width measurements and carry
out light-curves analyses in order to consistently gauge the excess
in-transit absorption in correspondence with the He I triplet.
Results: We spectrally resolve the He I triplet and detect an absorption
signal during all five transits. The mean in-transit absorption depth
amounts to 0.75 ± 0.03% (25σ) in the core of the strongest helium
triplet component. We detect night-to-night variations in the He I
absorption signal likely due to the transit events occurring in the
presence of stellar surface inhomogeneities. We evaluate the impact of
stellar-activity pseudo-signals on the true planetary absorption using
a comparative analysis of the He I 1083.3 nm (in the near-infrared)
and the Hα (in the visible) lines. Using a 3D atmospheric code, we
interpret the time series of the He I absorption lines in the three
nights not affected by stellar contamination, which exhibit a mean
in-transit absorption depth of 0.77 ± 0.04% (19σ) in full agreement
with the one derived from the full dataset. In agreement with previous
results, our simulations suggest that the helium layers only fill part
of the Roche lobe. Observations can be explained with a thermosphere
heated to ~12 000 K, expanding up to ~1.2 planetary radii, and losing ~1
g s-1 of metastable helium.
Conclusions: Our results
reinforce the importance of simultaneous optical plus near infrared
monitoring when performing high-resolution transmission spectroscopy of
the extended and escaping atmospheres of hot planets in the presence
of stellar activity. Based on observations made with the Italian
Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo
Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the
Observatorio del Roque de los Muchachos (La Palma, Canary Islands,
Spain).
Title: Helium Line Emissivities in the Solar Corona
Authors: Del Zanna, G.; Storey, P. J.; Badnell, N. R.; Andretta, V.
Bibcode: 2020ApJ...898...72D
Altcode: 2020arXiv200608971D
We present new collisional-radiative models (CRMs) for helium in
the quiescent solar corona and predict the emissivities of the He
and He+ lines to be observed by DKIST, Solar Orbiter, and
Proba-3. We discuss in detail the rates we selected for these models,
highlighting several shortcomings we have found in previous work. As no
previous complete and self-consistent coronal CRM for helium existed,
we have benchmarked our largest model at a density of 106
cm-3 and temperature of 20,000 K against recent CRMs
developed for photoionized nebulae. We then present results for the
outer solar corona, using new dielectronic recombination rates we have
calculated, which increase the abundance of neutral helium by about
a factor of 2. We also find that all optical triplet He I lines,
and in particular the well-known He I 10830 and 5876 Å lines, are
strongly affected by both photoexcitation and photoionization from the
disk radiation and that extensive CRMs are required to obtain correct
estimates. Close to the Sun, at an electron density of 108
cm-3 and temperature of 1 MK, we predict the emissivity of
He I 10830 Å to be comparable to that of the strong Fe XIII coronal
line at 10798 Å. However, we expect the He I emissivity to sharply
fall in the outer corona, with respect to Fe XIII. We confirm that
the He+ Lyα at 304 Å is also significantly affected by
photoexcitation and is expected to be detectable as a strong coronal
line up to several solar radii.
Title: Optical design of the multi-wavelength imaging coronagraph
Metis for the solar orbiter mission
Authors: Fineschi, S.; Naletto, G.; Romoli, M.; Da Deppo, V.;
Antonucci, E.; Moses, D.; Malvezzi, A. M.; Nicolini, G.; Spadaro,
D.; Teriaca, L.; Andretta, V.; Capobianco, G.; Crescenzio, G.;
Focardi, M.; Frassetto, F.; Landini, F.; Massone, G.; Melich, R.;
Nicolosi, P.; Pancrazzi, M.; Pelizzo, M. G.; Poletto, L.; Schühle,
U.; Uslenghi, M.; Vives, S.; Solanki, S. K.; Heinzel, P.; Berlicki,
A.; Cesare, S.; Morea, D.; Mottini, S.; Sandri, P.; Alvarez-Herrero,
A.; Castronuovo, M.
Bibcode: 2020ExA....49..239F
Altcode: 2020ExA...tmp...14F
This paper describes the innovative optical design of the Metis
coronagraph for the Solar Orbiter ESA-NASA mission. Metis is a
multi-wavelength, externally occulted telescope for the imaging
of the solar corona in both the visible and ultraviolet wavelength
ranges. Metis adopts a novel occultation scheme for the solar disk,
that we named "inverse external occulter", for reducing the extremely
high thermal load on the instrument at the spacecraft perihelion. The
core of the Metis optical design is an aplanatic Gregorian telescope
common to both the visible and ultraviolet channels. A suitable
dichroic beam-splitter, optimized for transmitting a narrow-band in
the ultraviolet (121.6 nm, HI Lyman-α) and reflecting a broadband
in the visible (580-640 nm) spectral range, is used to separate the
two optical paths. Along the visible light optical path, a liquid
crystal electro-optical modulator, used for the first time in space,
allows making polarimetric measurements.
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: The Solar-C_EUVST mission
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko;
Ichimoto, Kiyoshi; Suematsu, Yoshinori; Hara, Hirohisa; Katsukawa,
Yukio; Kubo, Masahito; Toriumi, Shin; Watanabe, Tetsuya; Yokoyama,
Takaaki; Korendyke, Clarence M.; Warren, Harry P.; Tarbell, Ted; De
Pontieu, Bart; Teriaca, Luca; Schühle, Udo H.; Solanki, Sami; Harra,
Louise K.; Matthews, Sarah; Fludra, A.; Auchère, F.; Andretta, V.;
Naletto, G.; Zhukov, A.
Bibcode: 2019SPIE11118E..07S
Altcode:
Solar-C EUVST (EUV High-Throughput Spectroscopic Telescope) is a
solar physics mission concept that was selected as a candidate for
JAXA competitive M-class missions in July 2018. The onboard science
instrument, EUVST, is an EUV spectrometer with slit-jaw imaging
system that will simultaneously observe the solar atmosphere from the
photosphere/chromosphere up to the corona with seamless temperature
coverage, high spatial resolution, and high throughput for the first
time. The mission is designed to provide a conclusive answer to the
most fundamental questions in solar physics: how fundamental processes
lead to the formation of the solar atmosphere and the solar wind, and
how the solar atmosphere becomes unstable, releasing the energy that
drives solar flares and eruptions. The entire instrument structure
and the primary mirror assembly with scanning and tip-tilt fine
pointing capability for the EUVST are being developed in Japan, with
spectrograph and slit-jaw imaging hardware and science contributions
from US and European countries. The mission will be launched and
installed in a sun-synchronous polar orbit by a JAXA Epsilon vehicle in
2025. ISAS/JAXA coordinates the conceptual study activities during the
current mission definition phase in collaboration with NAOJ and other
universities. The team is currently working towards the JAXA final
down-selection expected at the end of 2019, with strong support from
US and European colleagues. The paper provides an overall description
of the mission concept, key technologies, and the latest status.
Title: Comparing extrapolations of the coronal magnetic field
structure at 2.5 R⊙ with multi-viewpoint coronagraphic
observations
Authors: Sasso, C.; Pinto, R. F.; Andretta, V.; Howard, R. A.;
Vourlidas, A.; Bemporad, A.; Dolei, S.; Spadaro, D.; Susino, R.;
Antonucci, E.; Abbo, L.; Da Deppo, V.; Fineschi, S.; Frassetto, F.;
Landini, F.; Naletto, G.; Nicolini, G.; Nicolosi, P.; Pancrazzi, M.;
Romoli, M.; Telloni, D.; Ventura, R.
Bibcode: 2019A&A...627A...9S
Altcode: 2019arXiv190509005S
The magnetic field shapes the structure of the solar corona, but we
still know little about the interrelationships between the coronal
magnetic field configurations and the resulting quasi-stationary
structures observed in coronagraphic images (such as streamers,
plumes, and coronal holes). One way to obtain information on the
large-scale structure of the coronal magnetic field is to extrapolate
it from photospheric data and compare the results with coronagraphic
images. Our aim is to verify whether this comparison can be a fast
method to systematically determine the reliability of the many methods
that are available for modeling the coronal magnetic field. Coronal
fields are usually extrapolated from photospheric measurements that
are typically obtained in a region close to the central meridian on
the solar disk and are then compared with coronagraphic images at the
limbs, acquired at least seven days before or after to account for solar
rotation. This implicitly assumes that no significant changes occurred
in the corona during that period. In this work, we combine images from
three coronagraphs (SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) that
observe the Sun from different viewing angles to build Carrington maps
that cover the entire corona to reduce the effect of temporal evolution
to about five days. We then compare the position of the observed
streamers in these Carrington maps with that of the neutral lines
obtained from four different magnetic field extrapolations to evaluate
the performances of the latter in the solar corona. Our results show
that the location of coronal streamers can provide important indications
to distinguish between different magnetic field extrapolations.
Title: OPSys: optical payload systems facility for space
instrumentation integration and calibration
Authors: Capobianco, Gerardo; Fineschi, Silvano; Massone, Giuseppe;
Landini, Federico; Casti, Marta; Bellomo, Alessandro; Deffacis,
Maurizio; Romoli, Marco; Antonucci, Ester; Andretta, Vincenzo; Naletto,
Giampiero; Nicolini, Gianalfredo; Spadaro, Daniele
Bibcode: 2019SPIE11180E..7MC
Altcode:
The Optical Payload System (OPSys) is an INAF (italian National
Institute for Astrophysics) facility hosted by Aerospace Logistics
Technology Engineering Company (ALTEC SpA) in Turin, Italy. The facility
is composed by three clean rooms having different cleanliness levels,
a thermo-vacuum chamber (SPOCC, Space Optics calibration Chamber)
with a motorized optical bench and several light sources covering the
range from the extreme ultraviolet to the red light wavelengths. The
SPOCC has been designed having in mind the very stringent requirements
of the calibration of solar coronagraphs and the suppression of
the stray-light. The facility and the optical performances will be
described here. The calibration campaign performed on Metis space
coronagraph will be reported as a case study.
Title: Optical performance of the Metis coronagraph on the Solar
Orbiter ESA mission
Authors: Frassetto, Fabio; Da Deppo, Vania; Zuppella, Paola; Romoli,
Marco; Fineschi, Silvano; Antonucci, Ester; Nicolini, Giana; Naletto,
Giampiero; Nicolosi, Piergiorgio; Spadaro, Daniele; Andretta, Vincenzo;
Castronuovo, Marco; Casti, Marta; Capobianco, Gerardo; Massone,
Giuseppe; Susino, Roberto; Landini, Federico; Pancrazzi, Maurizio;
Teriaca, Luca; Schühle, Udo; Heerlein, Klaus; Uslenghi, Michela
Bibcode: 2019SPIE11180E..6YF
Altcode:
The Metis coronagraph aboard the Solar Orbiter ESA spacecraft is
expected to provide new insights into the solar dynamics. In detail,
it is designed to address three main questions: the energy deposition
mechanism at the poles (where the fast wind is originated), the
source of the slow wind at lower altitude, and how the global corona
evolves, in particular in relation to the huge plasma ejections that
occasionally are produced. To obtain the required optical performance,
not only the Metis optical design has been highly optimized, but the
alignment procedure has also been subjected to an accurate evaluation
in order to fulfill the integration specifications. The telescope
assembling sequence has been constructed considering all the subsystems
manufacturing, alignment and integration tolerances. The performance
verification activity is an important milestone in the instrument
characterization and the obtained results will assure the fulfillment
of the science requirements for its operation in space. The entire
alignment and verification phase has been performed by the Metis team in
collaboration with Thales Alenia Space Torino and took place in ALTEC
(Turin) at the Optical Payload System Facility using the Space Optics
Calibration Chamber infrastructure, a vacuum chamber especially built
and tested for the alignment and calibration of the Metis coronagraph,
and suitable for tests of future payloads. The goal of the alignment,
integration, verification and calibration processes is to measure
the parameters of the telescope, and the characteristics of the two
Metis channels: visible and ultraviolet. They work in parallel thanks
to the peculiar optical layout. The focusing and alignment performance
of the two channels must be well understood, and the results need to be
easily compared to the requirements. For this, a dedicated illumination
method, with both channels fed by the same source, has been developed;
and a procedure to perform a simultaneous through focus analysis has
been adopted. In this paper the final optical performance achieved by
Metis is reported and commented.
Title: Alignment procedure for the Gregorian telescope of the Metis
coronagraph for the Solar Orbiter ESA mission
Authors: Da Deppo, Vania; Mottini, Sergio; Naletto, Giampiero;
Frassetto, Fabio; Zuppella, Paola; Sertsu, Mewael G.; Romoli, Marco;
Fineschi, Silvano; Antonucci, Ester; Nicolini, Gianalfredo; Nicolosi,
Piergiorgio; Spadaro, Daniele; Andretta, Vincenzo; Castronuovo, Marco;
Casti, Marta; Capobianco, Gerardo; Massone, Giuseppe; Susino, Roberto;
Landini, Federico; Pancrazzi, Maurizio; Casini, Chiara; Teriaca,
Luca; Uslenghi, Michela
Bibcode: 2019SPIE11180E..76D
Altcode:
Metis is a solar coronagraph mounted on-board the Solar Orbiter ESA
spacecraft. Solar Orbiter is scheduled for launch in February 2020
and it is dedicated to study the solar and heliospheric physics from a
privileged close and inclined orbit around the Sun. Perihelion passages
with a minimum distance of 0.28 AU are foreseen. Metis features two
channels to image the solar corona in two different spectral bands:
in the HI Lyman at 121.6 nm, and in the polarized visible light band
(580 - 640 nm). Metis is a solar coronagraph adopting an "inverted
occulted" configuration. The inverted external occulter (IEO) is a
circular aperture followed by a spherical mirror which back rejects
the disk light. The reflected disk light exits the instrument through
the IEO aperture itself, while the passing coronal light is collected
by the Metis telescope. Common to both channels, the Gregorian on-axis
telescope is centrally occulted and both the primary and the secondary
mirror have annular shape. Classic alignment methods adopted for on-axis
telescope cannot be used, since the on-axis field is not available. A
novel and ad hoc alignment set-up has been developed for the telescope
alignment. An auxiliary visible optical ground support equipment source
has been conceived for the telescope alignment. It is made up by four
collimated beams inclined and dimensioned to illuminate different
sections of the annular primary mirror without being vignetted by
other optical or mechanical elements of the instrument.
Title: Metis/Solar Orbiter polarimetric visible light channel
calibration
Authors: Casti, M.; Fineschi, S.; Capobianco, G.; Romoli, M.;
Antonucci, E.; Nicolini, G.; Naletto, G.; Nicolosi, P.; Spadaro, D.;
Andretta, V.; Castronuovo, M.; Massone, G.; Susino, R.; Da Deppo, V.;
Frassetto, F.; Landini, F.; Pancrazzi, M.; Teriaca, L.; Uslenghi, M.
Bibcode: 2019SPIE11180E..3CC
Altcode:
Metis is the solar coronagraph of the ESA mission Solar Orbiter. For
the first time, Metis will acquire simultaneous images of the solar
corona in linearly polarized, broadband visible light (580-640 nm) and
in the narrow-band HI Ly-α line (121.6 nm). The visible light path
includes a polarimeter, designed to observe and analyse the K-corona
linearly polarized by Thomson scattering. The polarimeter comprises a
liquid crystal Polarization Modulation Package (PMP) together with a
quarter-wave retarder and a linear polarizer. The Metis PMP consists of
two Anti-Parallel Nematic Liquid Crystal Variable Retarders (LCVRs) with
their fast axis parallel with respect to each other and a pre-tilted
angle of the molecules in opposite direction. This configuration results
in an instrumental wide field of view (+/-7°). The LCVRs provide an
electro-optical modulation of the input polarized light by applying an
electric field to the liquid crystal molecules inside the cells. A given
optical retardance can be induced in the LCVRs by selecting a suitable
voltage value. This paper reports the polarimetric characterization of
the Visible-light channel for the Metis/Solar Orbiter coronagraph. The
retardance-to-voltage calibration of the electro-optical polarimeter was
characterized over the entire field of view of the coronagraph yielding
a complete "polarimetric flat-field" of the Metis Visible-light channel.
Title: Stray light calibration for the Solar Orbiter/Metis solar
coronagraph
Authors: Landini, F.; Romoli, M.; Fineschi, S.; Casini, C.; Baccani,
C.; Antonucci, E.; Nicolini, G.; Naletto, G.; Nicolosi, P.; Spadaro,
D.; Andretta, V.; Castronuovo, M.; Casti, M.; Capobianco, G.; Massone,
G.; Susino, R.; Da Deppo, V.; Frassetto, F.; Pancrazzi, M.; Teriaca,
L.; Schuehle, U.; Heerlein, K.; Uslenghi, M.
Bibcode: 2019SPIE11180E..2IL
Altcode:
The Solar Orbiter/Metis visible and UV solar coronagraph redefines
the concept of external occultation in solar coronagraphy. Classical
externally occulted coronagraphs are characterized by an occulter in
front of the telescope entrance aperture. Solar Orbiter will approach
the Sun down to 0.28 AU: in order to reduce the thermal load, the
Metis design switches the positions of the entrance aperture and the
external occulter thus achieving what is called the inverted external
occultation. The inverted external occulter (IEO) consists of a circular
aperture on the Solar Orbiter thermal shield that acts as coronagraph
entrance pupil. A spherical mirror, located 800 mm behind the IEO, back
rejects the disklight through the IEO itself. To pursue the goal of
maximizing the reduction of the stray light level on the focal plane,
an optimization of the IEO shape was implemented. The stray light
calibration was performed in a clean environment in front of the OPSys
solar disk divergence simulator (at ALTEC, in Torino, Italy), which is
able to emulate different heliocentric distances. Ground calibrations
were a unique opportunity to map the Metis stray light level thanks to
a pure solar disk simulator without the solar corona. The stray light
calibration was limited to the visible light case, being the most
stringent. This work is focused on the description of the laboratory
facility that was used to perform the stray light calibration and on
the calibration results.
Title: Effect of the non-uniform solar chromospheric Lyα radiation
on determining the coronal H I outflow velocity
Authors: Dolei, S.; Spadaro, D.; Ventura, R.; Bemporad, A.; Andretta,
V.; Sasso, C.; Susino, R.; Antonucci, E.; Da Deppo, V.; Fineschi,
S.; Frassetto, F.; Landini, F.; Naletto, G.; Nicolini, G.; Pancrazzi,
M.; Romoli, M.
Bibcode: 2019A&A...627A..18D
Altcode:
We derived maps of the solar wind outflow velocity of coronal
neutral hydrogen atoms at solar minimum in the altitude range
1.5-4.0 R⊙. We applied the Doppler dimming technique to
coronagraphic observations in the UV H I Lyα line at 121.6 nm. The
technique exploits the intensity reduction in the coronal line with
increasing velocities of the outflowing plasma to determine the
solar wind velocity by iterative modelling. The Lyα line intensity
is sensitive to the wind outflow velocity and also depends on the
physical properties of coronal particles and underlying chromospheric
emission. Measurements of irradiance by the chromospheric Lyα
radiation in the corona are required for a rigorous application of
the Doppler dimming technique, but they are not provided by past
and current instrumentations. A correlation function between the H
I 121.6 nm and He II 30.4 nm line intensities was used to construct
Carrington rotation maps of the non-uniform solar chromospheric Lyα
radiation and thus to compute the Lyα line irradiance throughout
the outer corona. Approximations concerning the temperature of
the scattering H I atoms and exciting solar disc radiation were
also adopted to significantly reduce the computational time and
obtain a faster procedure for a quick-look data analysis of future
coronagraphic observations. The effect of the chromospheric Lyα
brightness distribution on the resulting H I outflow velocities
was quantified. In particular, we found that the usual uniform-disc
approximation systematically leads to an overestimated velocity in
the polar and mid-latitude coronal regions up to a maximum of about
50-60 km s-1 closer to the Sun. This difference decreases at
higher altitudes, where an increasingly larger chromospheric portion,
including both brighter and darker disc features, contributes to
illuminate the solar corona, and the non-uniform radiation condition
progressively approaches the uniform-disc approximation.
Title: Helium emission in the near-Sun corona
Authors: Andretta, Vincenzo; DelZanna, Giulio
Bibcode: 2019shin.confE..82A
Altcode:
We compute the emission from the strongest He I and He II lines in
the corona within 2.0 R_Sun. We compute in particular the emission
of the near-IR He I 10830 line as well as the emission of the EUV
He I 584 and He II 304 lines, in the optically thin regime. We use a
collisional-radiative model, including processes such as photoionization
and photoexcitation from the solar disk. We also assess the relevance
of dielectronic recombination into neutral helium in the coronal
environment.
Title: Predicting the COSIE-C Signal from the Outer Corona up to 3
Solar Radii
Authors: Del Zanna, Giulio; Raymond, John; Andretta, Vincenzo; Telloni,
Daniele; Golub, Leon
Bibcode: 2018ApJ...865..132D
Altcode: 2018arXiv180807951D
We present estimates of the signal to be expected in quiescent solar
conditions, as would be obtained with the COronal Spectrographic
Imager in the EUV in its coronagraphic mode (COSIE-C). COSIE-C has been
proposed to routinely observe the relatively unexplored outer corona,
where we know that many fundamental processes affecting both the lower
corona and the solar wind are taking place. The COSIE-C spectral band,
186-205 Å, is well-known as it has been observed with Hinode EIS. We
present Hinode EIS observations that we obtained in 2007 out to 1.5 R
⊙, to show that this spectral band in quiescent streamers
is dominated by Fe XII and Fe XI and that the ionization temperature
is nearly constant. To estimate the COSIE-C signal in the 1.5-3.1
R ⊙ region we use a model based on CHIANTI atomic data
and SoHO UVCS observations in the Si XII and Mg X coronal lines of
two quiescent 1996 streamers. We reproduce the observed EUV radiances
with a simple density model, photospheric abundances, and a constant
temperature of 1.4 MK. We show that other theoretical or semi-empirical
models fail to reproduce the observations. We find that the coronal
COSIE-C signal at 3 R ⊙ should be about 5 counts/s per
3.″1 pixel in quiescent streamers. This is unprecedented and opens
up a significant discovery space. We also briefly discuss stray light
and the visibility of other solar features. In particular, we present
UVCS observations of an active region streamer, indicating increased
signal compared to the quiet Sun cases.
Title: Wide field of view liquid crystals-based modulator for the
polarimeter of the Metis/Solar Orbiter
Authors: Capobianco, Gerardo; Casti, Marta; Fineschi, Silvano;
Massone, Giuseppe; Sertsu, Mewael G.; Landini, Federico; Romoli,
Marco; Antonucci, Ester; Andretta, Vincenzo; Naletto, Giampiero;
Nicolini, Gianalfredo; Spadaro, Daniele; Alvarez Herrero, Alberto;
Garcia Parejo, Pilar; Marmonti, Matteo
Bibcode: 2018SPIE10698E..30C
Altcode:
Metis is an inverted occulted coronagraph on-board the ESA/Solar
Orbiter mission. The visible light path of the instrument will observe
the "white" light (580-640 nm) linearly-polarized emission from the
solar corona. The coronal polarized brightness allows retrieval of
physical parameters such as the electron density and temperature of
the K-corona. The Metis polarimeter comprises a quarter-wave retarder,
the liquid crystal polarization modulation package (PMP) and a linear
polarizer working as polarization analyser. The PMP consists of two
Anti-Parallel Nematic Liquid Crystal Variable Retarders (LCVRs) with
the fast axes parallels one to each other and a pre-tilted angle of the
molecules in opposite direction, in order to maximize the homogeneity of
the retardance across instrumental wide field of view: +/-7 deg. This
presentation reports the characterization of the PMP breadboard
(BB), fully representative of the optical/polarimetric performances
of the flight model. This characterization consisted in determining
the performances of the device in terms of retardance as function of
the applied voltage at different temperatures, angle of incidence and
the variation of the retardance as a function of the wavelength. The
calibrations were performed by measuring the complete Mueller matrix
of the PMP-BB. The experimental results have been compared with the
parameters of the theoretical model (e.g., depolarization, effective
retardance, cells misalignment).
Title: Calibration of the liquid crystal visible-light polarimeter
for the Metis/Solar Orbiter coronagraph
Authors: Casti, M.; Fineschi, S.; Capobianco, G.; Landini, F.; Romoli,
M.; Antonucci, E.; Andretta, V.; Naletto, G.; Nicolini, G.; Spadaro,
D.; Alvarez-Herrero, A.; Garcia-Parejo, P.; Marmonti, M.
Bibcode: 2018SPIE10698E..31C
Altcode:
Metis is the solar coronagraph selected for the payload of the ESA
Solar Orbiter mission. Metis will acquire simultaneous imaging in
linearly polarized, broadband visible light (580-640 nm) and in the
narrow-band HI Ly-α line (121.6 nm). The METIS visible light path
includes a polarimeter, designed to observe and analyse the K-corona
linearly polarized by Thomson scattering. The polarimeter comprises a
liquid crystal Polarization Modulation Package (PMP) together with a
quarter-wave retarder and a linear polarizer. The Metis PMP consists of
two Anti-Parallel Nematic Liquid Crystal Variable Retarders (LCVRs) with
their fast axis parallel with respect to each other and a pre-tilted
angle of the molecules in opposite direction. The LCVRs provide an
electro-optical modulation of the input polarized light by applying
an electric field to the liquid crystal molecules inside the cells. A
given optical retardance can be induced in the LCVRs by selecting a
suitable voltage value. This presentation will report the polarimetric
characterization of the Flight Model of the Metis polarimeter and the
voltage-to-retardance calibration.
Title: Mapping the solar wind HI outflow velocity in the inner
heliosphere by coronagraphic ultraviolet and visible-light
observations
Authors: Dolei, S.; Susino, R.; Sasso, C.; Bemporad, A.; Andretta,
V.; Spadaro, D.; Ventura, R.; Antonucci, E.; Abbo, L.; Da Deppo, V.;
Fineschi, S.; Focardi, M.; Frassetto, F.; Giordano, S.; Landini, F.;
Naletto, G.; Nicolini, G.; Nicolosi, P.; Pancrazzi, M.; Romoli, M.;
Telloni, D.
Bibcode: 2018A&A...612A..84D
Altcode:
We investigated the capability of mapping the solar wind outflow
velocity of neutral hydrogen atoms by using synergistic visible-light
and ultraviolet observations. We used polarised brightness images
acquired by the LASCO/SOHO and Mk3/MLSO coronagraphs, and synoptic Lyα
line observations of the UVCS/SOHO spectrometer to obtain daily maps
of solar wind H I outflow velocity between 1.5 and 4.0 R⊙
on the SOHO plane of the sky during a complete solar rotation (from
1997 June 1 to 1997 June 28). The 28-days data sequence allows us to
construct coronal off-limb Carrington maps of the resulting velocities
at different heliocentric distances to investigate the space and time
evolution of the outflowing solar plasma. In addition, we performed
a parameter space exploration in order to study the dependence of the
derived outflow velocities on the physical quantities characterising
the Lyα emitting process in the corona. Our results are important
in anticipation of the future science with the Metis instrument,
selected to be part of the Solar Orbiter scientific payload. It was
conceived to carry out near-sun coronagraphy, performing for the first
time simultaneous imaging in polarised visible-light and ultraviolet
H I Lyα line, so providing an unprecedented view of the solar wind
acceleration region in the inner corona. The movie (see Sect. 4.2)
is available at https://www.aanda.org
Title: Exoplanet Transits of Stellar Active Regions
Authors: Giampapa, Mark S.; Andretta, Vincenzo; Covino, Elvira;
Reiners, Ansgar; Esposito, Massimiliano
Bibcode: 2018AAS...23123402G
Altcode:
We report preliminary results of a program to obtain high spectral-
and temporal-resolution observations of the neutral helium triplet
line at 1083.0 nm in transiting exoplanet systems. The principal
objective of our program is to gain insight on the properties of
active regions, analogous to solar plages, on late-type dwarfs by
essentially using exoplanet transits as high spatial resolution
probes of the stellar surface within the transit chord. The 1083 nm
helium line is a particularly appropriate diagnostic of magnetized
areas since it is weak in the quiet photosphere of solar-type stars
but appears strongly in absorption in active regions. Therefore,
during an exoplanet transit over the stellar surface, variations in
its absorption equivalent width can arise that are functions of the
intrinsic strength of the feature in the active region and the known
relative size of the exoplanet. We utilized the Galileo Telescope and
the GIANO-B near-IR echelle spectrograph to obtain 1083 nm spectra
during transits in bright, well-known systems that include HD 189733,
HD 209458, and HD 147506 (HAT-P-2). We also obtained simultaneous
auxiliary data on the same telescope with the HARPS-N UV-Visible
echelle spectrograph. We will present preliminary results from our
analysis of the observed variability of the strength of the He I
1083 nm line during transits.Acknowledgements: Based on observations
made with the Italian Telescopio Nazionale Galileo (TNG) operated on
the island of La Palma by the Fundación Galileo Galilei of the INAF
(Istituto Nazionale di Astrofisica) at the Spanish Observatorio del
Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The
NSO is operated by AURA under a cooperative agreement with the NSF.
Title: METIS, the Multi Element Telescope for Imaging and
Spectroscopy: an instrument proposed for the solar orbiter mission
Authors: Antonucci, E.; Andretta, V.; Cesare, S.; Ciaravella, A.;
Doschek, G.; Fineschi, S.; Giordano, S.; Lamy, P.; Moses, D.; Naletto,
G.; Newmark, J.; Poletto, L.; Romoli, M.; Solanki, S.; Spadaro, D.;
Teriaca, L.; Zangrilli, L.
Bibcode: 2017SPIE10566E..0LA
Altcode:
METIS, the Multi Element Telescope for Imaging and Spectroscopy,
is an instrument proposed to the European Space Agency to be part of
the payload of the Solar Orbiter mission. The instrument design has
been conceived for performing extreme ultraviolet (EUV) spectroscopy
both on the solar disk and off-limb, and near-Sun coronagraphy
and spectroscopy. The proposed instrument suite consists of three
different interconnected elements, COR, EUS and SOCS, sharing the
same optical bench, electronics, and S/C heat shield aperture. COR is
a visible-EUV multiband coronagraph based on a classical externally
occulted design. EUS is the component of the METIS EUV disk spectrometer
which includes the telescope and all the related mechanisms. Finally,
SOCS is the METIS spectroscopic component including the dispersive
system and the detectors. The capability of inserting a small telescope
collecting coronal light has been added to perform also EUV coronal
spectroscopy. METIS can simultaneously image the visible and ultraviolet
emission of the solar corona and diagnose, with unprecedented temporal
coverage and space resolution the structure and dynamics of the full
corona in the range from 1.2 to 3.0 (1.6 to 4.1) solar radii (R⊙,
measured from Sun centre) at minimum (maximum) perihelion during the
nominal mission. It can also perform spectroscopic observations of the
solar disk and out to 1.4 R⊙ within the 50-150 nm spectral region,
and of the geo-effective coronal region 1.7-2.7 R⊙ within the 30-125
nm spectral band.
Title: METIS: the visible and UV coronagraph for solar orbiter
Authors: Romoli, M.; Landini, F.; Antonucci, E.; Andretta, V.;
Berlicki, A.; Fineschi, S.; Moses, J. D.; Naletto, G.; Nicolosi, P.;
Nicolini, G.; Spadaro, D.; Teriaca, L.; Baccani, C.; Focardi, M.;
Pancrazzi, M.; Pucci, S.; Abbo, L.; Bemporad, A.; Capobianco, G.;
Massone, G.; Telloni, D.; Magli, E.; Da Deppo, V.; Frassetto, F.;
Pelizzo, M. G.; Poletto, L.; Uslenghi, M.; Vives, S.; Malvezzi, M.
Bibcode: 2017SPIE10563E..1MR
Altcode:
METIS coronagraph is designed to observe the solar corona with an
annular field of view from 1.5 to 2.9 degrees in the visible broadband
(580-640 nm) and in the UV HI Lyman-alpha, during the Sun close
approaching and high latitude tilting orbit of Solar Orbiter. The
big challenge for a coronagraph is the stray light rejection. In
this paper after a description of the present METIS optical design,
the stray light rejection design is presented in detail together with
METIS off-pointing strategies throughout the mission. Data shown in this
paper derive from the optimization of the optical design performed with
Zemax ray tracing and from laboratory breadboards of the occultation
system and of the polarimeter.
Title: VizieR Online Data Catalog: HeI 5876 & 10830Å EWs of
solar-type stars (Andretta+, 2017)
Authors: Andretta, V.; Giampapa, M. S.; Covino, E.; Reiners, A.;
Beeck, B.
Bibcode: 2017yCat..18390097A
Altcode:
A total of 134 FEROS spectra (R=48000) of our targets (including
telluric standards) were acquired on the night of UT 2011 December
6-7; spectral coverage from 3500 to 9200Å. The Fiber Extended-range
Optical Spectrograph (FEROS) was mounted at the 2.2m Max-Planck
Gesellschaft/European Southern Observatory (MPG/ESO) telescope at La
Silla (Chile). The HeIλ10830 spectroscopic observations were
carried out on the same night as the FEROS D3 observations,
using the CRyogenic high-resolution InfraRed Echelle Spectrograph
(CRIRES), mounted at Unit Telescope 1 (Antu) of the VLT array at Cerro
Paranal. The details of the observations is given in table 1. (3 data files).
Title: The Mg I b triplet and the 4571 Å line as diagnostics of
stellar chromospheric activity
Authors: Sasso, C.; Andretta, V.; Terranegra, L.; Gomez, M. T.
Bibcode: 2017A&A...604A..50S
Altcode: 2017arXiv170604421S
Context. The Mg I 4571 Å line and the b triplet are denoted in
the literature as diagnostics of solar and stellar activity since
their formation is in the low chromosphere.
Aims: We aim to
investigate the potential of these four spectral lines as diagnostics
of chromospheric activity in solar-like stars, studying the dependence
of the intensity of these lines from local atmospheric changes by
varying atmospheric models and stellar parameters.
Methods:
Starting with Next-Gen photospheric models, we build a grid of
atmospheric models including photosphere, chromosphere and transition
region and solve the radiative transfer to obtain synthetic profiles
to compare with observed spectra of main-sequence, solar like stars
with effective temperatures in the range 4800-6400 K, solar gravity
and solar metallicity.
Results: We find that the Mg I 4571 Å
line is significantly sensitive to local changes in the atmospheric
model around the minimum temperature. Conversely, the lines of the
b triplet do not show significant responses to changes on the local
atmospheric structure.
Title: Estimates of Active Region Area Coverage through Simultaneous
Measurements of the He I λλ 5876 and 10830 Lines
Authors: Andretta, Vincenzo; Giampapa, Mark S.; Covino, Elvira;
Reiners, Ansgar; Beeck, Benjamin
Bibcode: 2017ApJ...839...97A
Altcode: 2017arXiv170310060A
Simultaneous, high-quality measurements of the neutral helium triplet
features at 5876 Å and 10830 Å in a sample of solar-type stars are
presented. The observations were made with ESO telescopes at the La
Silla Paranal Observatory under program ID 088.D-0028(A) and MPG Utility
Run for Fiber Extended-range Optical Spectrograph 088.A-9029(A). The
equivalent widths of these features combined with chromospheric models
are utilized to infer the fractional area coverage, or filling factor,
of magnetic regions outside of spots. We find that the majority of the
sample is characterized by filling factors less than unity. However,
discrepancies occur among the coolest K-type and the warmest and
most rapidly rotating F-type dwarf stars. We discuss these apparently
anomalous results and find that in the case of K-type stars, they are
an artifact of the application of chromospheric models best suited to
the Sun than to stars with significantly lower T eff. The
case of the F-type rapid rotators can be explained by the measurement
uncertainties of the equivalent widths, but they may also be due
to a non-magnetic heating component in their atmospheres. With the
exceptions noted above, preliminary results suggest that the average
heating rates in the active regions are the same from one star to
the other, differing in the spatially integrated, observed level of
activity due to the area coverage. Hence, differences in activity in
this sample are mainly due to the filling factor of active regions.
Title: Validating coronal magnetic field reconstruction methods
using solar wind simulations and synthetic imagery
Authors: Pinto, Rui; Rouillard, Alexis; Génot, Vincent; Amari, Tahar;
Buchlin, Eric; Arge, Nick; Sasso, Clementina; Andretta, Vincenzo;
Bemporad, Alessandro
Bibcode: 2017EGUGA..1913650P
Altcode:
We present an ongoing effort within the ESA Modeling and Data Analysis
Working Group (MADAWG) to determine automatically the magnetic
connectivity between the solar surface and any point in interplanetary
space. The goal is to produce predictions of the paths and propagation
delays of plasma and energetic particle propagation. This is a key
point for the data exploitation of the Solar Orbiter and Solar Probe
Plus missions, and for establishing connections between remote and
in-situ data. The background coronal magnetic field is currently
determined via existing surface magnetograms and PFSS extrapolations,
but the interface is ready to include different combinations of coronal
field reconstruction methods (NLFFF, Solar Models), wind models (WSA,
MULTI-VP), heliospheric models (Parker spiral, ENLIL, EUHFORIA). Some
model realisations are also based on advanced magnetograms based on
data assimilation techniques (ADAPT) and the HELCATS catalogue of
simulations. The results from the different models will be combined in
order to better assess the modelling uncertainties. The wind models
provide synthetic white-light and EUV images which are compared to
coronographic imagery, and the heliospheric models provide estimations
of synthetic in-situ data wich are compared to spacecraft data. A part
of this is work (wind modelling) is supported by the FP7 project #606692
(HELCATS).
Title: A virtual appliance as proxy pipeline for the Solar
Orbiter/Metis coronagraph
Authors: Pancrazzi, M.; Straus, T.; Andretta, V.; Spadaro, D.; Haugan,
S. V.; de Groof, A.; Carr, R.; Focardi, M.; Nicolini, G.; Landini,
F.; Baccani, C.; Romoli, M.; Antonucci, E.
Bibcode: 2016SPIE.9913E..4LP
Altcode:
Metis is the coronagraph on board Solar Orbiter, the ESA mission devoted
to the study of the Sun that will be launched in October 2018. Metis is
designed to perform imaging of the solar corona in the UV at 121.6 nm
and in the visible range where it will accomplish polarimetry studies
thanks to a variable retarder plate. Due to mission constraints, the
telemetry downlink on the spacecraft will be limited and data will be
downloaded with delays that could reach, in the worst case, several
months. In order to have a quick overview on the ongoing operations
and to check the safety of the 10 instruments on board, a high-priority
downlink channel has been foreseen to download a restricted amount of
data. These so-called Low Latency Data will be downloaded daily and,
since they could trigger possible actions, they have to be quickly
processed on ground as soon as they are delivered. To do so, a proper
processing pipeline has to be developed by each instrument. This
tool will then be integrated in a single system at the ESA Science
Operation Center that will receive the downloaded data by the Mission
Operation Center. This paper will provide a brief overview of the on
board processing and data produced by Metis and it will describe the
proxy-pipeline currently under development to deal with the Metis
low-latency data.
Title: The EUV spectrum of the Sun: Irradiances during 1998-2014
Authors: Del Zanna, G.; Andretta, V.
Bibcode: 2015A&A...584A..29D
Altcode:
We present calibrated EUV spectral irradiances obtained from
observations with the Solar and Heliospheric Observatory (SOHO) Coronal
Diagnostics Spectrometer (CDS) Normal Incidence Spectrometer (NIS)
during the 1998-2014 period, which spans the cycle 23 maximum and
minimum and the cycle 24 maximum. We revise the corrections for the
burn-in of the strong lines and our previous long-term calibration of
the NIS. We find no indications of further overall degradation of the
instrument responsivities after 2010. We compare the CDS irradiances
with those obtained by the prototype and flight instruments aboard
the Solar Dynamics Observatory (SDO) Extreme ultraviolet Variability
Experiment (EVE) and the Thermosphere Ionosphere Mesosphere
Energetics Dynamics (TIMED) Solar EUV Experiment (SEE) EUV Grating
Spectrograph (EGS). We find overall excellent agreement (to within
a relative 10-20%) with the EVE data (especially during 2010-2012),
but point out inconsistencies in some of the prototype and flight
EVE irradiances. There is overall agreement with some of the TIMED
SEE EGS data. We confirm the small variations in the irradiances of
low-temperature lines (except the helium lines) and show that the
irradiances in the hot (2-3 MK) lines are significantly lower for the
cycle 24 maximum compared to the previous one.
Title: Modelling low-lying, cool solar loops with optically thick
radiative losses
Authors: Sasso, C.; Andretta, V.; Spadaro, D.
Bibcode: 2015A&A...583A..54S
Altcode: 2015arXiv150805792S
Aims: We investigate the increase of the differential emission
measure (DEM) towards the chromosphere due to small and cool magnetic
loops (height ≲8 Mm, T ≲ 105 K). In a previous paper,
we analysed the conditions of existence and stability of these loops
through hydrodynamic simulations, focussing on their dependence on the
details of the optically thin radiative loss function.
Methods:
In this paper, we extend those hydrodynamic simulations to verify
if this class of loops exists and is stable when using an optically
thick radiative loss function. We study two cases: constant background
heating and a heating depending on the density. The contribution to the
transition region extreme-UV output of these loops is also calculated
and presented.
Results: We find that stable, quasi-static cool
loops can be obtained using an optically thick radiative loss function
and a background heating depending on the density. The DEMs of these
loops, however, fail to reproduce the observed DEM for temperatures
between 4.6 < log T < 4.8. We also show the transient phase of
a dynamic loop obtained by considering constant heating rate and find
that its average DEM, interpreted as a set of evolving dynamic loops,
reproduces the observed DEM very well.
Title: A steady-state supersonic downflow in the transition region
above a sunspot umbra
Authors: Straus, Thomas; Fleck, Bernhard; Andretta, Vincenzo
Bibcode: 2015A&A...582A.116S
Altcode: 2015arXiv150704279S
We investigate a small-scale (~1.5 Mm along the slit), supersonic
downflow of about 90 km s-1 in the transition region
above the lightbridged sunspot umbra in AR 11836. The observations
were obtained with the Interface Region Spectrograph (IRIS) on
2013 September 2 from 16:40 to 17:59 UT. The downflow shows up as
redshifted "satellite" lines of the Si iv and O iv transition region
lines and is remarkably steady over the observing period of nearly
80 min. The downflow is not visible in the chromospheric lines,
which only show an intensity enhancement at the location of the
downflow. The density inferred from the line ratio of the redshifted
satellites of the O iv lines (Ne = 1010.6 ± 0.25
cm-3) is only a factor 2 smaller than the one inferred
from the main components (Ne = 1010.95 ± 0.20
cm-3). Consequently, this implies a substantial mass flux
(~5 × 10-7 g cm-2 s-1), which would
evacuate the overlying corona on timescales close to 10 s. We interpret
these findings as evidence of a stationary termination shock of a
supersonic siphon flow in a cool loop that is rooted in the central
umbra of the spot. The movie is available in electronic form at http://www.aanda.org
Title: The EUV spectrum of the Sun: SOHO, SEM, and CDS irradiances
Authors: Del Zanna, G.; Wieman, S. R.; Andretta, V.; Didkovsky, L.
Bibcode: 2015A&A...581A..25D
Altcode:
We use calibrated extreme-UV (EUV) spectral irradiances obtained from
observations with the Solar & Heliospheric Observatory (SOHO)
Coronal Diagnostics Spectrometer Normal Incidence Spectrometer (NIS) to
estimate the signal measured by the Solar EUV Monitor (SEM) first-order
band, 260 to 340 Å (SEM 1). The NIS observes the resonance lines He
ii 304 Å and Si xi 303 Å directly in second order. The irradiances of
the other lines in the band are estimated with a differential emission
measure (DEM) modelling, using updated atomic data. The observations
analysed here were obtained during 1998-2011, which means that they span
the maximum and minimum of Cycle 23. The current knowledge of the SEM 1
degradation is used to find effective areas during the dates of the NIS
observations and to predict the SEM 1 count rates across the band. The
total count rates, estimated by folding the NIS-based spectra with the
SEM 1 effective areas, agree very well (within 10-20%) with the observed
ones during solar minimum conditions, when the He ii 304 Å is the
dominant contribution to the band. Excellent agreement with the Solar
Dynamics Observatory (SDO) Extreme ultraviolet Variability Experiment
(EVE) observations is also found. On the other hand, the predicted
SEM 1 count rates during the Cycle-23 maximum are significantly (by
about 30%) lower than the observed ones. The solar spectrum in the
SEM 1 band changes significantly during maximum conditions, with the
He ii 304 Å only contributing about 40%. A significant fraction of
the observed count rates comes from coronal emission in an off-band
spectral region that has recently been discovered. An explanation for
the discrepancy needs further investigation.
Title: Stray-light analyses of the METIS coronagraph on Solar Orbiter
Authors: Fineschi, S.; Sandri, P.; Landini, F.; Romoli, M.; DaDeppo,
V.; Frassetto, F.; Verroi, E.; Naletto, G.; Morea, D.; Antonucci,
E.; Spadaro, D.; Andretta, V.
Bibcode: 2015SPIE.9604E..0KF
Altcode:
The METIS coronagraph on board the Solar Orbiter mission will have the
unique opportunity of observing the solar outer atmosphere as close
to the Sun as 0.28 A.U., and from up to 35° out-of-ecliptic. The
telescope design of the METIS coronagraph includes two optical paths:
i) broad-band imaging of the full corona in linearly polarized
visible-light (VL: 580-640 nm), ii) narrow-band imaging of the full
corona in the ultraviolet (UV) Lyman α (121.6 nm). This paper describes
the stray-light analyses performed on the UV and VL channels of the
METIS Telescope with the nonsequential modality of Zemax OpticStudio. A
detailed opto-mechanical model of the METIS Telescope is simulated
by placing the CAD parts of all the sub-assemblies at the nominal
position. Each surface, mechanical and optical, is provided with a
modelled coating and BSDF reproducing the optical and the diffusing
properties. The geometric model allows for the verification of the
correct functioning of the blocking elements inside the telescope
and for an evaluation of the stray-light level due to surface
roughness. The diffraction off the inner edge of the IEO on the plane
of the IO is modelled separately from the contributor of the surface
micro-roughness. The contributors due to particle contamination and
cosmetic defects are also analysed. The results obtained are merged
together and compared to the requirements of stray-light. The results
of this analysis together with those from two different analyses based
on a Montecarlo ray-trace and a semi-analytical model are consistent
with each other and indicate that the METIS design meets the stray-light
level requirements
Title: A Method for Measuring Active Region Filling Factors on
Solar-Type Stars
Authors: Giampapa, Mark Steven; Andretta, Vincenzo; Beeck, Benjamin;
Reiners, Ansgar; Schussler, Manfred
Bibcode: 2015TESS....120101G
Altcode:
Radiative diagnostics of “activity” in the Sun and solar-type stars
are spatially associated with sites of emergent magnetic flux. The
magnetic fields themselves are widely regarded as the surface
manifestations of a dynamo mechanism. The further development of
both dynamo theory and models of the non-radiative heating of outer
stellar atmospheres requires a knowledge of stellar magnetic field
properties. In this context, it becomes important to determine the
surface distribution, or at least the fractional coverage of, magnetic
active regions as one critical constraint for dynamo models. But,
while information on the spatial distribution of activity on stellar
surfaces can be gathered in some special cases (mostly rapid rotators),
such measurements have always been elusive in more solar-like stars. We
discuss the challenges and results obtained from a method that relies
on the non-linear response of the two principal He I triplet lines
(at 1083 nm and 587.6 nm) to infer useful constraints on the fractional
area coverage of magnetic active regions on solar-type stars.
Title: Observations of a Steady-State Supersonic Downflow in the
Transition Region above a Sunspot Umbra
Authors: Fleck, Bernhard; Straus, Thomas; Andretta, Vincenzo
Bibcode: 2015TESS....120311F
Altcode:
Sunspots have been an area of intense research ever since Hale's
discovery of strong magnetic fields in these structures. Here we report
on the detection of a particular sunspot phenomenon: a small-scale (~
1.5 Mm), supersonic downflow of about 90 km/s in the transition region
above a light-bridged sunspot umbra. The observations were obtained with
the Interface Imaging Region Spectrograph (IRIS) on 2 September 2013
from 16:39 to 17:58 UT in the sunspot of AR 11836 near disk center. Slit
length and width were 68” and 0.166”, respectively. The cadence of
the time series was 3 s, with exposure times of 2 s. The observations
comprise nine spectral windows: C II 1336, Fe XII 1349, Cl I 1352,
O I 1356, Si IV 1394, Si IV 1403, NUV at 2786 and 2831, and Mg II h
and k 2796. The spectral window containing the Si IV 1403 line also
includes the O IV 1400, 1401, and 1405 lines, the last one blended
with a S IV line. The downflow shows up as red-shifted, well-separated
“satellite” lines of the Si IV and O IV transition region lines and
is remarkably steady over the observing period of nearly 80 min. The
satellite lines do not participate in the 3-min shock wave Doppler
maneuvres of the main component. The downflow is not visible in the
chromospheric lines, which only show an intensity enhancement at the
location of the downflow. The density inferred from the line ratio of
the redshifted satellites of the O IV lines (Ne=1010.5
±0.3 cm-3) is only a factor 2.5 smaller than the
one inferred from the main components (Ne=1010.9 ±0.2
cm-3). Consequently, this implies a substantial mass
flux (~ 4×10-7 g cm-2 s-1), which
would evacuate the overlying corona on time scales of the order of 10
s. We interpret these findings as evidence of a stationary termination
shock of a supersonic siphon flow in a cool loop rooted in the central
umbra of the spot. Such stationary shocks have been predicted for
siphon flows in hot coronal loops by Noci (1981).
Title: Polarimetric calibrations and astronomical polarimetry in
the V-band with Solar Orbiter/METIS instrument
Authors: Capobianco, Gerardo; Fineschi, Silvano; Focardi, Mauro;
Andretta, Vincenzo; Massone, Giuseppe; Bemporad, Alessandro; Romoli,
Marco; Antonucci, Ester; Naletto, Giampiero; Nicolini, Gianalfredo;
Nicolosi, Piergiorgio; Spadaro, Daniele
Bibcode: 2014SPIE.9143E..4VC
Altcode:
METIS is one of the remote sensing instruments on board the ESA-
Solar Orbiter mission, that will be launched in July 2017. The Visible
Light Channel (VLC) of the instrument is composed by an achromatic
LC-based polarimeter for the study of the linearly polarized solar
K-corona in the 580-640 nm bandpass. The laboratory calibrations with
spectropolarimetric techniques and the in-flight calibrations of this
channel, using some well knows linearly polarized stars in the FoV
of the instrument with a degree of linear polarization DOLP > 10%
are here discussed. The selection of the stars and the use of other
astronomical targets (i.e. planets, comets,…) and the opportunity
of measurements of the degree of linear polarization in the visible
bandpass of some astronomical objects (i.e. Earth, comets,…) are
also objects of this paper.
Title: On-board CME detection algorithm for the Solar Orbiter-METIS
coronagraph
Authors: Bemporad, A.; Andretta, V.; Pancrazzi, M.; Focardi, M.;
Straus, T.; Sasso, C.; Spadaro, D.; Uslenghi, M.; Antonucci, E.;
Fineschi, S.; Abbo, L.; Nicolini, G.; Landini, F.; Romoli, M.; Naletto,
G.; Nicolosi, P.
Bibcode: 2014SPIE.9152E..0KB
Altcode:
The METIS coronagraph is one of the instruments part of the payload of
the ESA - Solar Orbiter mission to be launched in 2017. The spacecraft
will operate much like a planetary encounter mission, with the main
scientific activity taking place with the remote-sensing instruments
during three 10-days intervals per orbit: optimization of the different
instrument observing modes will be crucial. One of the key scientific
targets of METIS will be the study of transient ejections of mass
through the solar corona (Coronal Mass Ejections - CMEs) and their
heliospheric evolution. METIS will provide for the first time imaging of
CMEs in two different wavelengths: VL (visible light 580- 640 nm) and UV
(Lyman-α line of HI at 121.6 nm). The detection of transient phenomena
shall be managed directly by the METIS Processing and Power Unit (MPPU)
by means of both external triggers ("flags") coming from other Solar
Orbiter instruments, and internal "flags" produced directly by the METIS
on-board software. METIS on-board algorithm for the automatic detection
of CMEs will be based on running differences between consecutive images
re-binned to very low resolution and thresholded for significant changes
over a minimum value. Given the small relative variation of white light
intensity during CMEs, the algorithm will take advantage of VL images
acquired with different polarization angles to maximize the detection
capability: possible false detections should be automatically managed
by the algorithm. The algorithm will be able to provide the CME first
detection time, latitudinal direction of propagation on the plane
of the sky (within 45 degrees), a binary flag indicating whether a
"halo CME" has been detected.
Title: In-flight UV and polarized-VL radiometric calibrations of
the solar orbiter/METIS imaging coronagraph
Authors: Focardi, M.; Capobianco, G.; Andretta, V.; Sasso, C.; Romoli,
M.; Landini, F.; Fineschi, S.; Pancrazzi, M.; Bemporad, A.; Nicolini,
G.; Pucci, S.; Uslenghi, M.; Naletto, G.; Nicolosi, P.; Spadaro, D.;
Teriaca, L.; SchuÌhle, U. H.; Antonucci, E.
Bibcode: 2014SPIE.9144E..09F
Altcode:
METIS is an innovative inverted occulted solar coronagraph capable of
obtaining for the first time simultaneous imaging of the full corona
in linearly polarized visible-light (580-640 nm) and narrow-band
(+/- 10 nm) ultraviolet H I Ly-α (121.6 nm). It has been selected to
fly aboard the Solar Orbiter1 spacecraft, whose launch is
foreseen in July 2017. Thanks to its own capabilities and exploiting
the peculiar opportunities offered by the Solar Orbiter planned orbit,
METIS will address some of the still open issues in understanding the
physical processes in the corona and inner heliosphere. The Solar
Orbiter Nominal Mission Phase (NMP) will be characterized by three
scientific observing windows per orbit and METIS will perform at least
one in-flight calibration per observing window. The two imaging channels
of METIS will be calibrated on ground and periodically checked, verified
and re-calibrated in-flight. In particular, radiometric calibration
images will be needed to determine the absolute brightness of the solar
corona. For UV radiometric calibration a set of targets is represented
by continuum-emitting early type bright stars (e.g. A and B spectral
types) whose photospheres produce a bright far-ultraviolet continuum
spectrum stable over long timescales. These stars represent an important
reference standard not only for METIS in-flight calibrations but
also for other Solar Orbiter instruments and they will be crucial for
instruments cross-calibrations as well. For VL radiometric calibration,
a set of linearly polarized stars will be used. These targets shall
have a minimum degree of linear polarization (DoLP > 5%) and a
detectable magnitude, compatible with the instrument integration times
constrained by the desired S/N ratio and the characteristics of the
spacecraft orbit dynamics.
Title: Hardware and software architecture on board solar
orbiter/METIS: an update
Authors: Pancrazzi, M.; Focardi, M.; Nicolini, G.; Andretta, V.;
Uslenghi, M.; Magli, E.; Ricci, M.; Bemporad, A.; Spadaro, D.; Landini,
F.; Romoli, M.; Antonucci, E.; Fineschi, S.; Naletto, G.; Nicolosi,
P.; Teriaca, L.
Bibcode: 2014SPIE.9144E..3FP
Altcode:
METIS, is one of the ten instruments selected to be part of the Solar
Orbiter payload; it is a coronagraph that will investigate the inner
part of the heliosphere performing imaging in the visible band and in
the hydrogen Lyman α line @ 121.6 nm. METIS has recently undergone
throughout a revision to simplify the instrument design. This paper
will provide an overview of the updated hardware and software design of
the coronagraph as presented at the Instrument Delta-Preliminary Design
Review occurred in April 2014. The current configuration foresees two
detectors, an Intensified APS for the UV channel and an APS for the
visible light equipped with a Liquid Crystal Variable Retarder (LCVR)
plate to perform broadband visible polarimetry. Each detector has a
proximity electronics generating the control and readout signals for
the sensor but the operations of the two devices are in charge of a
centralized unit, the METIS Processing and Power Unit (MPPU). The MPPU
operates the remaining electrical subsystems supplying them with power
and providing on board storage and processing capabilities. Its design
foresees the redundancy of the most critical parts, thus mitigating the
effects of possible failures of the electronics subsystems. The central
monitoring unit is also in charge of providing the communication with
the S/C, handling the telemetry and telecommand exchange with the
platform. The data acquired by the detectors shall undergo through
a preliminary on-board processing to maximize the scientific return
and to provide the necessary information to validate the results on
ground. Operations as images summing, compression and cosmic rays
monitoring and removal will be fundamental not only to mitigate the
effects of the main sources of noise on the acquired data, but also to
maximize the data volume to be transferred to the spacecraft in order to
fully exploit the limited bandwidth telemetry downlink. Finally, being
Solar Orbiter a deep-space mission, some METIS procedures have been
designed to provide the instrument an efficient autonomous behavior
in case of an immediate reaction is required as for the arising of
transient events or the occurrence of safety hazards conditions.
Title: On-board detection and removal of cosmic ray and solar
energetic particle signatures for the Solar Orbiter-METIS coronagraph
Authors: Andretta, V.; Bemporad, A.; Focardi, M.; Grimani, C.;
Landini, F.; Pancrazzi, M.; Sasso, C.; Spadaro, D.; Straus, T.;
Uslenghi, M. C.; Antonucci, E.; Fineschi, S.; Naletto, G.; Nicolini,
G.; Nicolosi, P.; Romoli, M.
Bibcode: 2014SPIE.9152E..2QA
Altcode:
METIS is part of the science payload of Solar Orbiter. It is a
coronagraph designed to obtain images of the outer solar corona both in
the visible 580-640 nm band and in the UV, in a narrow band centered
around the hydrogen Lyman-α line. We describe the main features of
the procedures to remove signatures due to cosmic rays (CRs) and to
solar energetic particles (SEPs) comparing them with alternatives in
other contexts and in other solar coronagraphic missions. Our analysis
starts from a realistic assessment of the radiation environment where
the instrument is expected to operate, which is characteristic of the
interplanetary space of the inner solar system, but quite unusual for
most solar missions.
Title: The EUV spectrum of the Sun: SOHO CDS NIS radiances during
solar cycle 23
Authors: Andretta, V.; Del Zanna, G.
Bibcode: 2014A&A...563A..26A
Altcode: 2014arXiv1401.7570A
For the first time, we present and discuss EUV radiances of the solar
transition region (TR) and corona obtained during a solar cycle. The
measurements were obtained with the SOHO/coronal diagnostic spectrometer
(CDS) during the period from 1996 to 2010. We find that limb-brightening
significantly affects any characterisation of the solar radiances. We
present the limb-brightening function for the main lines and find that
it does not change measurably during the cycle. We confirm earlier
findings that the radiance histogram of the cooler lines have a well
defined, log-normal quiet-Sun component, although our results differ
from previous ones. The width of the lowest-radiance log-normal
distribution is constant along the cycle. Both the analysis of the
centre-to-limb variation and of the radiance statistical distribution
point to a constant quiet Sun emission along solar cycle 23. Lines
formed above 1 MK are dramatically affected by the presence of active
regions, and indeed, no "quiet Sun" region can be defined during
periods of maximum activity. Much of the irradiance variability in lines
formed below 1.5 MK is due to a change in the emitting area. For hotter
lines, the emitting area saturates to almost 100% of full solar disk
at the maximum of activity, while simultaneously the emission due to
active regions increases by more than an order of magnitude. We show
that structures around active regions, sometimes referred to as dark
halos or dark canopies, are common and discuss their similarities and
differences with coronal holes. In particular, we show how they are
well visible in TR lines, contrary to coronal holes.
Title: On-Orbit Degradation of Solar Instruments
Authors: BenMoussa, A.; Gissot, S.; Schühle, U.; Del Zanna, G.;
Auchère, F.; Mekaoui, S.; Jones, A. R.; Walton, D.; Eyles, C. J.;
Thuillier, G.; Seaton, D.; Dammasch, I. E.; Cessateur, G.; Meftah,
M.; Andretta, V.; Berghmans, D.; Bewsher, D.; Bolsée, D.; Bradley,
L.; Brown, D. S.; Chamberlin, P. C.; Dewitte, S.; Didkovsky, L. V.;
Dominique, M.; Eparvier, F. G.; Foujols, T.; Gillotay, D.; Giordanengo,
B.; Halain, J. P.; Hock, R. A.; Irbah, A.; Jeppesen, C.; Judge,
D. L.; Kretzschmar, M.; McMullin, D. R.; Nicula, B.; Schmutz, W.;
Ucker, G.; Wieman, S.; Woodraska, D.; Woods, T. N.
Bibcode: 2013SoPh..288..389B
Altcode: 2013arXiv1304.5488B
We present the lessons learned about the degradation observed in
several space solar missions, based on contributions at the Workshop
about On-Orbit Degradation of Solar and Space Weather Instruments
that took place at the Solar Terrestrial Centre of Excellence (Royal
Observatory of Belgium) in Brussels on 3 May 2012. The aim of this
workshop was to open discussions related to the degradation observed
in Sun-observing instruments exposed to the effects of the space
environment. This article summarizes the various lessons learned
and offers recommendations to reduce or correct expected degradation
with the goal of increasing the useful lifespan of future and ongoing
space missions.
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: Multi Element Telescope for Imaging and Spectroscopy (METIS)
coronagraph for the Solar Orbiter mission
Authors: Antonucci, Ester; Fineschi, Silvano; Naletto, Giampiero;
Romoli, Marco; Spadaro, Daniele; Nicolini, Gianalfredo; Nicolosi,
Piergiorgio; Abbo, Lucia; Andretta, Vincenzo; Bemporad, Alessandro;
Auchère, Frédéric; Berlicki, Arkadiusz; Bruno, Roberto; Capobianco,
Gerardo; Ciaravella, Angela; Crescenzio, Giuseppe; Da Deppo, Vania;
D'Amicis, Raffaella; Focardi, Mauro; Frassetto, Fabio; Heinzel,
Peter; Lamy, Philippe L.; Landini, Federico; Massone, Giuseppe;
Malvezzi, Marco A.; Moses, J. Dan; Pancrazzi, Maurizio; Pelizzo,
Maria-Guglielmina; Poletto, Luca; Schühle, Udo H.; Solanki, Sami K.;
Telloni, Daniele; Teriaca, Luca; Uslenghi, Michela
Bibcode: 2012SPIE.8443E..09A
Altcode:
METIS, the “Multi Element Telescope for Imaging and Spectroscopy”,
is a coronagraph selected by the European Space Agency to be part of
the payload of the Solar Orbiter mission to be launched in 2017. The
unique profile of this mission will allow 1) a close approach to the
Sun (up to 0.28 A.U.) thus leading to a significant improvement in
spatial resolution; 2) quasi co-rotation with the Sun, resulting in
observations that nearly freeze for several days the large-scale outer
corona in the plane of the sky and 3) unprecedented out-of-ecliptic
view of the solar corona. This paper describes the experiment concept
and the observational tools required to achieve the science drivers
of METIS. METIS will be capable of obtaining for the first time: •
simultaneous imaging of the full corona in polarized visible-light
(590-650 nm) and narrow-band ultraviolet HI Lyman α (121.6 nm); •
monochromatic imaging of the full corona in the extreme ultraviolet
He II Lyman α (30.4 nm); • spectrographic observations of the HI
and He II Ly α in corona. These measurements will allow a complete
characterization of the three most important plasma components of
the corona and the solar wind, that is, electrons, hydrogen, and
helium. This presentation gives an overview of the METIS imaging and
spectroscopic observational capabilities to carry out such measurements.
Title: The processing and power unit of the METIS coronagraph aboard
the Solar Orbiter space mission
Authors: Focardi, M.; Pancrazzi, M.; Uslenghi, M.; Nicolini, G.;
Magli, E.; Landini, F.; Romoli, M.; Antonucci, E.; Fineschi, S.;
Naletto, G.; Nicolosi, P.; Spadaro, D.; Andretta, V.; Gennaro, C.;
Zoppo, G. P.; Stevoli, A.; Battistelli, E.; Rusconi, A.
Bibcode: 2012SPIE.8442E..4IF
Altcode:
The Multi Element Telescope for Imaging and Spectroscopy (METIS) is the
coronagraph selected for the Solar Orbiter payload, adopted in October
2011 by ESA for the following Implementation Phase. The instrument
design has been conceived by a team composed by several research
institutes with the aim to perform both VIS and EUV narrow-band
imaging and spectroscopy of the solar corona. METIS, owing to its
multi-wavelength capability, will address some of the major open issues
in understanding the physical processes in the corona and the solar
wind origin and properties, exploiting the unique opportunities offered
by the SO mission profile. The METIS Processing and Power Unit (MPPU)
is the Instrument's power supply and on-board data handling modular
electronics, designed to address all the scientific requirements of
the METIS Coronagraph. MPPU manages data and command flows, the timing
and power distribution networks and its architecture reflects several
trade-off solutions with respect to the allocated resources in order
to reduce any possible electronics single-point failure. This paper
reports on the selected HW and SW architectures adopted after the
Preliminary Design Review (PDR), performed by ESA in early 2012.
Title: MESSI: the METIS instrument software simulator
Authors: Nicolini, G.; Andretta, V.; Abbo, L.; Antonucci, E.; Bemporad,
A.; Capobianco, G.; Crescenzio, G.; Fineschi, S.; Focardi, M.; Magli,
E.; Naletto, G.; Nicolosi, G.; Pancrazzi, M.; Ricci, M.; Romoli, M.;
Uslenghi, M.; Volpicelli, A.
Bibcode: 2012SPIE.8449E..1LN
Altcode:
Instrument software simulators are becoming essential both for
supporting the instrument design and for planning the future
operations. In this paper we present the Software Simulator developed
for the METIS coronagraph, an instrument of the Solar Orbiter ESA
mission. We describe its architecture and the modules it is composed
of, and how they interchange data to simulate the whole acquisition
chain from the photons entering the front window to the stream
of telemetry? data received and analysed on ground. Each software
module simulates an instrument subsystem by combining theoretical
models and measured subsystem properties. A web-based application
handles the remote user interfaces of the Institutions of the METIS
Consortium, allowing users from various sites to overview and interact
with the data flow, making possible for instance input and output at
intermediate nodes. Description of the modes of use of the simulator,
both present and future, are given with examples of results. These
include not only design-aid tasks, as the evaluation and the tuning
of the image compression algorithms, but also those tasks aimed to
plan the in-flight observing sequences, based on the capability of
the simulator of performing end to end simulations of science cases.
Title: METIS: a novel coronagraph design for the Solar Orbiter mission
Authors: Fineschi, Silvano; Antonucci, Ester; Naletto, Giampiero;
Romoli, Marco; Spadaro, Daniele; Nicolini, Gianalfredo; Abbo, Lucia;
Andretta, Vincenzo; Bemporad, Alessandro; Berlicki, Arkadiusz;
Capobianco, Gerardo; Crescenzio, Giuseppe; Da Deppo, Vania; Focardi,
Mauro; Landini, Federico; Massone, Giuseppe; Malvezzi, Marco A.;
Moses, J. Dan; Nicolosi, Piergiorgio; Pancrazzi, Maurizio; Pelizzo,
Maria-Guglielmina; Poletto, Luca; Schühle, Udo H.; Solanki, Sami K.;
Telloni, Daniele; Teriaca, Luca; Uslenghi, Michela
Bibcode: 2012SPIE.8443E..3HF
Altcode:
METIS (Multi Element Telescope for Imaging and Spectroscopy) METIS,
the “Multi Element Telescope for Imaging and Spectroscopy”,
is a coronagraph selected by the European Space Agency to be part
of the payload of the Solar Orbiter mission to be launched in
2017. The mission profile will bring the Solar Orbiter spacecraft
as close to the Sun as 0.3 A.U., and up to 35° out-of-ecliptic
providing a unique platform for helio-synchronous observations of
the Sun and its polar regions. METIS coronagraph is designed for
multi-wavelength imaging and spectroscopy of the solar corona. This
presentation gives an overview of the innovative design elements of
the METIS coronagraph. These elements include: i) multi-wavelength,
reflecting Gregorian-telescope; ii) multilayer coating optimized for
the extreme UV (30.4 nm, HeII Lyman-α) with a reflecting cap-layer
for the UV (121.6 nm, HI Lyman-α) and visible-light (590-650); iii)
inverse external-occulter scheme for reduced thermal load at spacecraft
peri-helion; iv) EUV/UV spectrograph using the telescope primary mirror
to feed a 1st and 4th-order spherical varied
line-spaced (SVLS) grating placed on a section of the secondary mirror;
v) liquid crystals electro-optic polarimeter for observations of the
visible-light K-corona. The expected performances are also presented.
Title: Coronal Diagnostics from Narrowband Images Around 30.4 nm
Authors: Andretta, V.; Telloni, D.; Del Zanna, G.
Bibcode: 2012SoPh..279...53A
Altcode: 2012SoPh..tmp...73A; 2012arXiv1203.4091A
Images taken in the band centered at 30.4 nm are routinely used to map
the radiance of the He II Ly α line on the solar disk. That line is
one of the strongest, if not the strongest, line in the EUV observed in
the solar spectrum, and one of the few lines in that wavelength range
providing information on the upper chromosphere or lower transition
region. However, when observing the off-limb corona, the contribution
from the nearby Si XI 30.3 nm line can become significant. In this
work we aim at estimating the relative contribution of those two
lines in the solar corona around the minimum of solar activity. We
combine measurements from CDS taken in August 2008 with temperature
and density profiles from semiempirical models of the corona to
compute the radiances of the two lines, and of other representative
coronal lines (e.g. Mg X 62.5 nm, Si XII 52.1 nm). Considering both
diagnosed quantities from line ratios (temperatures and densities)
and line radiances in absolute units, we obtain a good overall match
between observations and models. We find that the Si XI line dominates
the He II line from just above the limb up to ≈ 2 R⊙
in streamers, while its contribution to narrowband imaging in the 30.4
nm band is expected to become smaller, even negligible in the corona
beyond ≈ 2 - 3 R⊙, the precise value being strongly
dependent on the coronal temperature profile.
Title: Joint Response of the Helium Lines to Chromospheric Heating
in Solar-type Stars
Authors: Giampapa, Mark S.; Andretta, V.; Beeck, B.; Reiners, A.;
Schussler, M.
Bibcode: 2012AAS...22020314G
Altcode:
We present a preliminary report on simultaneous observations of
the He I 5876 and 10830 triplet lines, respectively, in a sample of
solar-type stars. The near-IR spectra were obtained with the VLT and
CRIRES instrument while the visible spectra were acquired with the
MPG/ESO 2.2-m telescope in conjunction with the FEROS spectrograph. The
correlation of the observed strengths of these lines will be examined
and their potential as diagnostics of active region area coverage in
solar-type stars will be discussed. The NSO is operated by AURA
under a cooperative agreement with the National Science Foundation.
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 low-lying cool loops and their contribution to the
transition region EUV output
Authors: Sasso, C.; Andretta, V.; Spadaro, D.; Susino, R.
Bibcode: 2012A&A...537A.150S
Altcode: 2011arXiv1112.0309S
Aims: We aim to investigate the increase of the differential
emission measure (DEM) towards the chromosphere. In the past 30 years,
small and cool magnetic loops (height ≲ 8 Mm, T ≲ 105 K)
have been proposed as an explanation for this effect.
Methods:
We present hydrodynamic simulations of low-lying cool loops in which
we studied the loops' conditions of existence and stability, and their
contribution to the transition region EUV output.
Results:
We find that stable, quasi-static cool loops (with velocities <1
km s-1) can be obtained under different and more realistic
assumptions on the radiative loss function with respect to previous
works. A mixture of the DEMs of these cool loops plus intermediate
loops with temperatures between 105 and 106
K can reproduce the observed emission of the lower transition region
at the critical turn-up temperature point (T ~ 2 × 105 K)
and below T = 105 K.
Title: Preliminar Determination of the Basal Chromospheric Emission
for Late-Type Stars.
Authors: Terranegra, L.; Oliviero, M.; Andretta, V.
Bibcode: 2012MSAIS..19..209T
Altcode:
We present a preliminar determinations of the basal emission for
chromospheric very inactive dwarf and giant late type stars using
data collected from the literature. We also derive the activity
indeces SHK and RHK for about 550 solar
type dwarf and giant using the 1Å, FWHM resolution spectra of the
Indo-U.S. library. All the sample stars where in addition selected
in the distance range 20< d <100 pc. The new fitting curves of
the basal emission extend previous calibrations of the activity index
RHK to the range \mbox{0.2< B-V <2.2 .
Title: Physical structure of solar cool loops.
Authors: Sasso, C.; Susino, R.; Andretta, V.; Spadaro, D.
Bibcode: 2012MSAIS..19...81S
Altcode:
Recently, studies and observations focused on the solar transition
region and the low corona have shown the importance of small and
cool magnetic loops in producing most of the solar EUV output at
temperatures below 1 MK. This kind of structures has remained only
poorly characterized in terms of physical properties. We study the
possibility of obtaining cool loops using unidimensional hydrodynamic
simulations, performed with a state-of-the-art numerical code with a
fully adaptive grid. The dependence of their physical structures on
the form of the radiative losses function has been explored. We find,
as a first result, that the shape of the radiative losses function for
T<105 K imposes restrictive conditions on the existence
and the stability of such cool loops.
Title: Estimating the Fractional Area Coverage of Active Regions in
Dwarf Stars
Authors: Andretta, V.; Giampapa, M.
Bibcode: 2011ASPC..448.1111A
Altcode: 2011csss...16.1111A
It has been shown (Andretta & Giampapa 1995) that the two He I
triplet lines at 1.083 μm and 587.6 nm, respectively, can be utilized
to infer the area coverage of active (plage-like) regions on stellar
surfaces by exploiting their different responses to chromospheric
heating. This kind of information, which is very difficult to obtain
through other methods, can serve as a fundamental constraint for
the development of stellar dynamo theory. We discuss the application
and limitations of this approach to the interpretation of spatially
resolved solar data along with some preliminary stellar observations.
Title: The solar orbiter METIS coronagraph data signal processing
chain
Authors: Pancrazzi, M.; Focardi, M.; Uslenghi, M.; Nicolini, G.;
Magli, E.; Landini, F.; Romoli, M.; Bemporad, A.; Antonucci, E.;
Fineschi, S.; Naletto, G.; Nicolosi, P.; Spadaro, D.; Andretta, V.
Bibcode: 2011SPIE.8167E..2CP
Altcode: 2011SPIE.8167E..66P
METIS, the Multi Element Telescope for Imaging and Spectroscopy,
is one of the instruments selected in 2009 by ESA to be part of the
payload of the Solar Orbiter mission. The instrument design has been
conceived to perform both multiband imaging and UV spectroscopy of
the solar corona. The two sensors of the detecting system will produce
images in visible light and in two narrow UV bands, at 121.6 and 30.4
nm. The instrument is constituted by several subunits that have to be
properly controlled and synchronized in order to provide the expected
performances. Moreover, the large amount of data collected by METIS has
to be processed by the on board electronics to reduce the data volume
to be delivered to ground by telemetry. These functionalities will be
realized by a dedicated electronics, the Main Power and Processing Unit
(MPPU). This paper will provide an overview of the METIS data handling
system and the expected on board data processing.
Title: The EUV spectrum of the Sun: SOHO CDS NIS irradiances from
1998 until 2010
Authors: Del Zanna, G.; Andretta, V.
Bibcode: 2011A&A...528A.139D
Altcode:
We present extreme-ultraviolet (EUV) irradiances of the Sun taken during
the 1998-2010 period from the Solar and Heliospheric Observatory (SoHO)
Coronal Diagnostic Spectrometer (CDS) Normal Incidence Spectrograph
(NIS). They were obtained from NIS full-Sun radiance observations, and
represent the first set of EUV spectral observations spanning a solar
cycle. We compare the CDS line irradiances with those obtained from
rocket measurements, one that flew in May 1997 and one in April 2008,
together with the Thermosphere Ionosphere Mesosphere Energetics Dynamics
(TIMED) Solar EUV Experiment (SEE) EUV Grating Spectrograph (EGS) and
various historical records. Excellent agreement (to within a relative
20%) is found in most cases, with a few notable exceptions. Lines formed
in the transition region show very small changes with the solar cycle,
with the exception of the helium lines. The irradiances of lines formed
around 1 MK already change during the cycle by a factor ~5; for hotter
lines (2.5 MK) the variability reaches factors of the order of 40. For
lines formed around 1-3 MK, and to a less extent, the helium lines,
we find a good linear correlation between CDS irradiances and the 10.7
cm radio flux, although each line has a different coefficient. No
correlation is found for the transition-region lines. Significant
discrepancies between the observed irradiances and those modelled
is found. This confirms the importance in obtaining EUV spectral
measurements of the solar irradiance.
Title: Evolution of the Magnetic Fields of Magnetic Ap Stars During
the Main Sequence Phase
Authors: Landstreet, J. D.; Bagnulo, S.; Andretta, V.; Silaj, J.;
Fossati, L.; Wade, G. A.
Bibcode: 2011mast.conf...14L
Altcode:
This paper discusses the results of our survey of magnetic fields
among Ap stars that are members of open clusters. Such stars are unlike
field Ap stars in that they have relatively well-determined ages, both
absolutely (in years) and as a fraction of the main sequence lifetime
elapsed. By measuring the fields of such stars once or a few times per
star, we can estimate the RMS longitudinal field strength of each star,
and study how this quantity varies with age through the 10^8 to 10^9,yr
of main sequence life. Dividing our sample of some 80 stars into mass
bins of 2 - 3, 3 - 4, and 4 - 5 M_⊙, we find that both the typical
field strength and the total magnetic flux, emerging from the surface
of stars decline on time scales that are a modest fraction of the main
sequence lifetime in each of the three mass bins.
Title: The EUV spectrum of the Sun: long-term variations in the SOHO
CDS NIS spectral responsivities
Authors: Del Zanna, G.; Andretta, V.; Chamberlin, P. C.; Woods, T. N.;
Thompson, W. T.
Bibcode: 2010A&A...518A..49D
Altcode:
We present SOHO Coronal Diagnostic Spectrometer (CDS) normal incidence,
extreme-ultraviolet spectra of the Sun taken from the beginning of
the mission in 1996 until now. We use various methods to study the
performance of the instrument during such a long time span. Assuming
that the basal chromospheric-transition region emission in the quiet
parts of the Sun does not vary over the cycle, we find a slow decrease
in the instrument sensitivity over time. We applied a correction to the
NIS (Normal Incidence Spectrograph) data, using as a starting reference
the NIS absolute calibration obtained from a comparison with a rocket
flight in May 1997. We then obtained NIS full-Sun spectral irradiances
from observations in 2008 and compared them with the EUV irradiances
obtained from the rocket that flew on April 14, 2008 a prototype of
the Solar Dynamics Observatory EVE instrument. Excellent agreement is
found between the EUV irradiances from NIS and from the EVE-prototype,
confirming the NIS radiometric calibration. The NIS instrument over
13 years has performed exceptionally well, with only a factor of about
2 decrease in responsivity for most wavelengths.
Title: The EUV spectral irradiance of the Sun from 1997 to date
Authors: Del Zanna, Giulio; Andretta, Vincenzo
Bibcode: 2010IAUS..264...78D
Altcode:
We present measurements of the EUV spectral irradiance we have
obtained from radiance measurements with the SOHO Coronal Diagnostic
Spectrometer, from 1997 to date. We discuss the contribution of
the various regions of the Sun to the total EUV irradiance, and how
they varied dramatically between the last two solar minima. These
observations allow us to interpret spectral irradiance measurements in
the EUV which have been available since 2002 with the TIMED mission. We
also briefly discuss how changes in various activity indices compare
with the EUV spectral variability, and the limitations of spectral
modelling.
Title: ARENA Solar Astrophysics Working Group Reporting on Dome C
Exceptional Potential for Solar Observations
Authors: Damé, L.; Andretta, V.; Arena Solar Astrophysics Working
Group Members
Bibcode: 2010EAS....40..451D
Altcode:
The ARENA Solar Astrophysics Working Group (WG6) is reviewing the
exceptional site conditions prevailing at Dome C/Concordia making it
a unique place on Earth for solar observations: excellent seeing, low
sky brightness, low water vapour and high duty cycle. These qualities
open science programmes which can combine very high resolution,
coronagraphy, infrared access, and long time series (continuity). Major
objectives accessible are the chromosphere-corona interface at very
high resolution, direct magnetic field measurements in the chromosphere
(prominences) and in the corona, 2D imaging spectroscopy and waves. A
first mid-size facility is proposed and described, AFSIIC (Antarctica
Facility for Solar Interferometric Imaging and Coronagraphy),
using 3×Ø50 cm off-axis telescopes (1.4 m equivalent telescope)
to access these objectives with the proper flux, angular resolution
and coronagraphic potential. Support infrastructure and logistics have
been studied and are discussed, noticeably a 30 m tower to place the
observatory over the very thin surface turbulent layer of Dome C.
Title: An Erupting Filament and Associated CME Observed by Hinode,
STEREO and SOHO
Authors: Bemporad, A.; Del Zanna, G.; Andretta, V.; Magrí, M.;
Poletto, G.; Ko, Y. -K.
Bibcode: 2009ASPC..415..385B
Altcode:
A multi-spacecraft campaign was set up in May 2007 to observe the
off-limb corona with Hinode, STEREO and SOHO instruments (Hinode
HOP 7). During this campaign, a filament eruption and a coronal
mass ejection (CME) occurred on May 9 from NOAA 10953 at the West
limb. The filament eruption starts around 13:40 UT and results in a
CME at 4°SW latitude. Remarkably, the event was observed by STEREO
(EUVI and COR1) and by the Hinode/EIS and SOHO/UVCS spectrometers. We
present results from all these instruments. High-cadence data from
Stereo/EUVI A and B in the He II λ304 line were used to study the
3-D expansion of the filament. A slow rising phase, during which the
filament moved southward, was followed by an impulsive phase during
which the filament appeared to change direction and then contribute
to the westward-expanding CME as seen in STEREO/COR 1. Hinode/EIS was
scanning with the 2'' slit the region where the filament erupted. The
EIS spectra show remarkable non-thermal broadening in lines emitted at
different temperatures at the location of the filament eruption. The
CME was also observed by the SOHO/UVCS instrument: the spectrograph
slit was centered at 1.7 solar radii, at a latitude of 5°SW and
recorded a sudden increase in the O VI λλ 1032-1037 and Si XI λ520
spectral line intensities. We discuss the overall morphology of this
interesting eruptive event, and provide a preliminary assessment of
its temperature and density structure.
Title: Multi-Instrument Campaigns to Observe the Off-Limb Corona
Authors: Del Zanna, G.; Andretta, V.; Poletto, G.; Teriaca, L.; Ko,
Y. -K.; Mason, H. E.; Vourdilas, A.; Bemporad, A.; Magri, M.
Bibcode: 2009ASPC..415..315D
Altcode:
We briefly describe two multi-instrument campaigns we coordinated to
observe the off-limb corona in 2007, with some preliminary results. The
first one (Hinode HOP 7) was a SOHO/Hinode/TRACE/STEREO/Ulysses
week-long campaign during the SOHO-Ulysses quadrature in 2007 May. We
could not achieve all of our goals, however we were very fortunate in
that the ``Del Zanna'' active region appeared on the Sun at the right
longitude, and that a filament eruption and a CME were observed. Of
particular significance is the finding of large (100 km s-1)
non-thermal broadenings in all coronal lines observed by Hinode/EIS
in the region where the filament was erupting. The second campaign
(Hinode HOP 44) involved SOHO (CDS, SUMER, UVCS), Hinode, and TRACE to
measure the physical parameters of plume/interplume regions in the polar
coronal holes from the low corona to 1.7 solar radii, on 30/10-4/11. We
obtained a good set of observations, however various instrumental
constraints and the lack of fully developed plumes limited our goals.
Title: Multispacecraft observations of a prominence eruption
Authors: Bemporad, A.; Del Zanna, G.; Andretta, V.; Poletto, G.;
Magrí, M.
Bibcode: 2009AnGeo..27.3841B
Altcode:
On 9 May 2007 a prominence eruption occurred at the West
limb. Remarkably, the event was observed by the STEREO/EUVI telescopes
and by the HINODE/EIS and SOHO/UVCS spectrometers. We present results
from all these instruments. High-cadence (~37 s) data from STEREO/EUVI
A and B in the He II λ304 line were used to study the 3-D shape and
expansion of the prominence. The high spatial resolution EUVI images
(~1.5"/pixel) have been used to infer via triangulation the 3-D shape
and orientation of the prominence 12 min after the eruption onset. At
this time the prominence has mainly the shape of a "hook" highly
inclined southward, has an average thickness of 0.068 R⊙,
a length of 0.43 R⊙ and lies, in first approximation,
on a plane. Hence, the prominence is mainly a 2-D structure and there
is no evidence for a twisted flux rope configuration. HINODE/EIS was
scanning with the 2" slit the region where the filament erupted. The
EIS spectra show during the eruption remarkable non-thermal broadening
(up to ~100 km s-1) in the region crossed by the filament
in spectral lines emitted at different temperatures, possibly with
differences among lines from higher Fe ionization stages. The CME was
also observed by the SOHO/UVCS instrument: the spectrograph slit was
centered at 1.7 R⊙, at a latitude of 5° SW and recorded
a sudden increase in the O VI λλ1032-1037 and Si XII λ520 spectral
line intensities, representative of the CME front transit.
Title: Evolution of Global Magnetic Fields in Main Sequence A and
B Stars
Authors: Landstreet, J. D.; Bagnulo, S.; Andretta, V.; Fossati, L.;
Mason, E.; Silaj, J.; Wade, G. A.
Bibcode: 2009ASPC..405..505L
Altcode:
Some main sequence A and B stars (``magnetic Ap stars") possess
kG-strength global fields of simple geometry. These fields are
expected to evolve during the main sequence lifetime of the stars
due to ohmic decay, large-scale circulation flows, and the changing
stellar structure caused by stellar evolution. We are attempting to
obtain useful observational constraints on field evolution by observing
the fields of a large sample of magnetic Ap stars in open clusters,
from which we derive stellar ages. Our data to date indicate that
the fields of these stars decline with stellar age more rapidly than
would be expected from magnetic flux conservation as the stars expand
with evolution.
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: Helium Line Formation and Abundance during a C-Class Flare
Authors: Andretta, Vincenzo; Mauas, Pablo J. D.; Falchi, Ambretta;
Teriaca, Luca
Bibcode: 2008ApJ...681..650A
Altcode: 2008arXiv0803.0418A
During a coordinated campaign that took place in 2001 May, a C-class
flare was observed both with SOHO instruments and with the Dunn Solar
Telescope of the National Solar Observatory at Sacramento Peak. In
two previous papers we described the observations and discussed some
dynamical aspects of the earlier phases of the flare, as well as the
helium line formation in the active region prior to the event. Here we
extend the analysis of the helium line formation to the later phases
of the flare in two different locations of the flaring area. We have
devised a new technique, exploiting all available information from
various SOHO instruments, to determine the spectral distribution of
the photoionizing EUV radiation produced by the corona overlying the
two target regions. In order to find semiempirical models matching
all of our observables, we analyzed the effect on the calculated
helium spectrum, both of AHe (the He abundance) and of
the uncertainties in the incident EUV radiation (level and spectral
distribution). We found that the abundance has in most cases (but not
in all) a larger effect than the coronal back-radiation. The result
of our analysis is that, considering the error of the measured lines
and adopting our best estimate for the coronal EUV illumination, the
value AHe = 0.075 +/- 0.010 in the chromosphere (for T >
6300 K) and transition region yields reasonably good matches for all
the observed lines. This value is marginally consistent with the most
commonly accepted photospheric value, AHe = 0.085.
Title: Searching for links between magnetic fields and stellar
evolution. III. Measurement of magnetic fields in open cluster Ap
stars with ESPaDOnS
Authors: Landstreet, J. D.; Silaj, J.; Andretta, V.; Bagnulo, S.;
Berdyugina, S. V.; Donati, J. -F.; Fossati, L.; Petit, P.; Silvester,
J.; Wade, G. A.
Bibcode: 2008A&A...481..465L
Altcode: 2008arXiv0803.0877L
Context: A small fraction of upper main sequence stars have strong,
highly structured magnetic fields. The origin and evolution
of these fields are not adequately understood.
Aims: We
are carrying out a survey of magnetic fields in Ap stars in open
clusters in order to obtain the first sample of magnetic upper main
sequence stars with precisely known ages. These data will constrain
theories of field evolution in these stars.
Methods: A survey
of candidate open cluster magnetic Ap stars was carried out using
the new ESPaDOnS spectropolarimeter at the CFHT. This instrument
provides an alternative to the FORS1 spectropolarimeter used up to
now for this survey.
Results: We have obtained 44 measurements
of the mean longitudinal fields < Bz > of 23 B6-A2
stars that have been identified as possible Ap stars and that are
possible members of open clusters, with a median uncertainty of about
45 G. Of these stars, 10 have definite field detections. Nine stars of
our sample are found not to be magnetic Ap stars. These observations
significantly increase the information available about low-mass stars
near the TAMS compared to our previous sample.
Conclusions:
We find that ESPaDOnS provides field measurements comparable to those
that we have previously obtained with FORS1, and that these data also
contain a large amount of useful information not readily obtained from
lower resolution spectropolarimetry. With the new data we are able to
expand the available data on low-mass, relatively evolved Ap stars,
and identify more robustly which observed stars are actually magnetic
Ap stars and cluster members. Re-analysis of the enlarged data set
of cluster Ap stars indicates that such stars with masses in the
range of 2-5 {M_⊙} show rms fields larger than about 1 kG only when
they are near the ZAMS. The time scale on which these large fields
disappear varies strongly with mass, ranging from about 250 Myr for
stars of 2-3 {M_⊙} to 15 Myr for stars of 4-5 {M_⊙}. Our data are
consistent either with emergent flux conservation for most (but not
all) Ap stars, or with modest decline in flux with age. Based
on observations made with the Canada-France-Hawaii Telescope,
operated by the National Research Council of Canada, the Centre
National de Recherche Scientifique of France, and the University
of Hawaii, under programme 05A-C19.
Title: Evolution of global magnetic fields in main sequence A and
B stars
Authors: Landstreet, J. D.; Bagnulo, S.; Andretta, V.; Fossati, L.;
Mason, E.; Silaj, J.; Wade, G. A.
Bibcode: 2008CoSka..38..391L
Altcode:
The (presumably fossil) magnetic fields in magnetic Ap stars
are expected to evolve as the stars pass through the main
sequence. Virtually no observational evidence currently constrains this
process, because ages of field Ap stars cannot be determined accurately
at present. To provide data about field evolution as a function of age,
we are studying the fields of Ap stars in clusters. It is found that
the fields, and probably the emergent magnetic flux, decline with
increasing age for Ap stars in the range of 2 - 5 M⊙.
Title: Searching for links between magnetic fields and stellar
evolution: II. The evolution of magnetic fields as revealed by
observations of Ap stars in open clusters and associations
Authors: Landstreet, J. D.; Bagnulo, S.; Andretta, V.; Fossati, L.;
Mason, E.; Silaj, J.; Wade, G. A.
Bibcode: 2007A&A...470..685L
Altcode: 2007arXiv0706.0330L
Context: The evolution of magnetic fields in Ap stars during the
main sequence phase is presently mostly unconstrained by observation
because of the difficulty of assigning accurate ages to known field
Ap stars.
Aims: We are carrying out a large survey of magnetic
fields in cluster Ap stars with the goal of obtaining a sample of
these stars with well-determined ages. In this paper we analyse the
information available from the survey as it currently stands.
Methods: We select from the available observational sample the stars
that are probably (1) cluster or association members and (2) magnetic
Ap stars. For the stars in this subsample we determine the fundamental
parameters T{eff}, L/L_⊙, and M/M_⊙. With these data
and the cluster ages we assign both absolute age and fractional age
(the fraction of the main sequence lifetime completed). For this
purpose we have derived new bolometric corrections for Ap stars.
Results: Magnetic fields are present at the surfaces of Ap stars from
the ZAMS to the TAMS. Statistically for the stars with M > 3 M_⊙
the fields decline with advancing age approximately as expected from
flux conservation together with increased stellar radius, or perhaps
even faster than this rate, on a time scale of about 3×107
yr. In contrast, lower mass stars show no compelling evidence for field
decrease even on a timescale of several times 108 yr.
Conclusions: Study of magnetic cluster stars is now a powerful tool
for obtaining constraints on evolution of Ap stars through the main
sequence. Enlarging the sample of known cluster magnetic stars, and
obtaining more precise rms fields, will help to clarify the results
obtained so far. Further field observations are in progress. Tables
2 and 3 are only available in electronic form at http://www.aanda.org
Title: The Ca II infrared triplet as a stellar activity
diagnostic. II. Test and calibration with high resolution observations
Authors: Busà, I.; Aznar Cuadrado, R.; Terranegra, L.; Andretta,
V.; Gomez, M. T.
Bibcode: 2007A&A...466.1089B
Altcode:
Aims:We report on our analysis of the high resolution spectra
(R≈86 000) of a sample of 42 late-type active stars (with measured
{log{R'_HK}} spanning from ≈{ -}3 to ≈{ -}5) acquired with the
Italian 3.6 m Telescopio Nazionale Galileo (TNG) using the SARG
spectrometer in the 4960-10 110 Å range. The high quality of the
spectra and the good activity-level coverage allow us to measure
two different chromospheric indicators that can be derived from the
Ca ii infrared triplet (Ca ii IRT) lines: the residual equivalent
width (EQW) and the chromospheric indicator {R_IRT}. The aim of this
work is determine and test the best way of deriving activity-level
information and errors from the Ca ii IRT lines, in preparation of the
GAIA Cornerstone mission by ESA, by which the Ca ii IRT spectral range
will be spectroscopically observed for millions of stars.
Methods:
The {R_IRT} index is calculated for each observed star as the difference
between the calculated NLTE photospheric central intensity and the
observed one. The residual EQW, {Δ W_IRT}, is calculated as the area of
the positive profile obtained as the difference between the calculated
NLTE photospheric and the observed profiles. We correlate {log{R'_HK}}
with {R_IRT} and the {Δ W_IRT}.
Results: This analysis indicates
that Ca ii IRT lines are good chromospheric diagnostics. We find
that both {Δ W_IRT} and the {R_IRT} quantities can be used as
chromospheric indicators, although the former exhibits a tighter
correlation with the {log{R'_HK}} index. Furthermore, we find that
the total chromospheric excess EQW in the Ca ii IRT is almost linearly
correlated with the excess in the Ca ii H & K doublet, as estimated
through the {log{R'_HK}} index. Based on observations made with
the Italian Telescopio Nazionale Galileo (TNG) operated on the island
of La Palma by the Centro Galileo Galilei of the Consorzio Nazionale
per l'Astronomia e l'Astrofisica at the Spanish Observatorio del Roque
de los Muchachos of the Instituto de Astrofísica de Canarias. Table
4 is only available in electronic form at http://www.aanda.org
Title: The magnetic fields of peculiar A and B stars in open clusters
Authors: Landstreet, J. D.; Andretta, V.; Bagnulo, S.; Mason, E.;
Silaj, J.; Wade, G. A.
Bibcode: 2007pms..conf...25L
Altcode:
This paper discusses our recent efforts to observe magnetic fields
in a large sample of A and B stars in a number of open clusters. The
aim of this project is to obtain a statistically significant sample
of magnetic Ap and Bp stars, for which we can characterise the
magnetic field structures and chemical abundances, and for which we
have reasonably well-determined masses and ages. We expect that this
sample will provide valuable constraints on the evolution of magnetic
fields and chemical peculiarities in these stars.
Title: The EUV Spectral Irradiance and the Physical Characteristics
of the Solar Corona During the 10 Years of SOHO Measurements
Authors: Del Zanna, G.; Andretta, V.
Bibcode: 2006ESASP.617E.124D
Altcode: 2006soho...17E.124D
No abstract at ADS
Title: Helium Line Formation During the Decay Phase of a Small
Two-Ribbon Flare
Authors: Andretta, V.; Mauas, P. J. D.; Falchi, A.; Teriaca, L.
Bibcode: 2006ESASP.617E.151A
Altcode: 2006soho...17E.151A
No abstract at ADS
Title: Searching for links between magnetic fields and stellar
evolution. I. A survey of magnetic fields in open cluster A- and
B-type stars with FORS1
Authors: Bagnulo, S.; Landstreet, J. D.; Mason, E.; Andretta, V.;
Silaj, J.; Wade, G. A.
Bibcode: 2006A&A...450..777B
Altcode: 2006astro.ph..1516B
Context: .About 5% of upper main sequence stars are permeated
by a strong magnetic field, the origin of which is still matter
of debate.
Aims: . With this work we provide observational
material to study how magnetic fields change with the evolution of
stars on the main sequence, and to constrain theory explaining the
presence of magnetic fields in A and B-type stars.
Methods:
. Using FORS1 in spectropolarimetric mode at the ESO VLT, we have
carried out a survey of magnetic fields in early-type stars belonging
to open clusters and associations of various ages.
Results:
. We have measured the magnetic field of 235 early-type stars with a
typical uncertainty of ∼ 100 G. In our sample, 97 stars are Ap or Bp
stars. For these targets, the median error bar of our field measurements
was ∼ 80 G. A field has been detected in about 41 of these stars,
37 of which were not previously known as magnetic stars. For the 138
normal A and B-type stars, the median error bar was 136 G, and no
field was detected in any of them.
Title: SARG observations of 40 stars with different activity level:
test for the R_{IRT} chromospheric activity indicator .
Authors: Busà, I.; Andretta, V.; Gomez, M. T.; Terranegra, L.;
Aznar Cuadrado, R.
Bibcode: 2006MSAIS...9..229B
Altcode:
We report on preliminary analysis of high resolution spectra
(R≈86,000) of a sample of 42 late-type active stars (with
log{R^{'}_{HK}} spanning from ≈ -3 to ≈ -5) acquired with the
Italian 3.6m Telescopio Nazionale Galileo (TNG) by using the SARG
spectrometer in th e 4960 - 10110 Å range. The high quality
of the spectra and the good activity level coverage allow us to test
and calibrate the new chromospheric indicator R _{IRT} given by the
difference between the calculated NLTE photospheric central intensity
and the observed one \citep{busa00,andretta00}. This analysis
indicate that Ca II IRT lines are good chromospheric diagnostic,
in particular in the low-activity level range.
Title: Searching for Links Between Magnetic Field and Stellar
Evolution: a Survey of Magnetic Stars in Open Clusters with FORS1
at the VLT
Authors: Bagnulo, S.; Mason, E.; Szeifert, T.; Landstreet, J. D.;
Wade, G. A.; Andretta, V.
Bibcode: 2005ASPC..343..369B
Altcode:
We outline a diagnostic technique for stellar magnetic fields based on
spectropolarimetry of H Balmer lines. We present preliminary results
of a survey of magnetic stars in open clusters carried out with FORS1
at the ESO VLT, aimed at examining the characteristics of the magnetic
fields of intermediate-mass stars as they evolve onto and across the
main sequence.
Title: Helium line formation in a solar active region
Authors: Mauas, P. J. D.; Andretta, V.; Falchi, A.; Falciani, R.;
Teriaca, L.; Cauzzi, G.
Bibcode: 2005ESASP.560..811M
Altcode: 2005csss...13..811M
No abstract at ADS
Title: The Ca II Infrared Triplet as a stellar activity diagnostic
. I. Non-LTE photospheric profiles and definition of the
RIRT indicator
Authors: Andretta, V.; Busà, I.; Gomez, M. T.; Terranegra, L.
Bibcode: 2005A&A...430..669A
Altcode:
This work is part of a larger project on the study of activity in
stars of spectral type similar to, or later than the Sun, from PMS
to ZAMS, based on the analysis of the high resolution Ca II InfraRed
Triplet (Ca II IRT: λ= 8498, 8542, 8662 Å) observed profiles. Here,
a preliminary study on the diagnostic power of these calcium lines
has been performed by means of NLTE calculations of the line profiles
with an approximate treatment of UV line-blanketing, for a grid of
photospheric models with Teff = 4200, 5200, 6200 K, log g =
4.0, 4.5, 5.0 and [A/H] = 0.0, -1.0, -2.0. We used these calculations
to estimate the sensitivity of the profiles to changes in stellar
parameters and the effect of departures from LTE. As found by other
authors, the Ca II triplet NLTE EQW s (equivalent widths) are quite
sensitive to photospheric parameters, in particular to Teff
and [A/H]. On the other hand, we find that the dependence of the Ca
II triplet lines central depression (CD = 1-central relative flux) on
log g and Teff, and to a lesser extent to [A/H], is very
weak. The departure from LTE is negligible when we consider EQW s,
unless very metal-poor atmospheres are considered, while CD s can
be affected by NLTE by more than 20%. This analysis indicates that
in the use of these lines as activity indicators (where the details
of the line profile in the core are important), a NLTE treatment is
required. Furthermore, we show that a new chromospheric indicator,
which we denote RIRT, can be derived from measurements of
Ca II IRT line central depressions, provided that rotational broadening
is taken into proper account. In order to facilitate the use of the Ca
II IRT lines as activity diagnostics, we give interpolation formulae
for estimating line CD s within the range of stellar parameters of
our NLTE calculations.
Title: Helium Line Formation and Abundance in a Solar Active Region
Authors: Mauas, P. J. D.; Andretta, V.; Falchi, A.; Falciani, R.;
Teriaca, L.; Cauzzi, G.
Bibcode: 2005ApJ...619..604M
Altcode: 2004astro.ph.12058M
An observing campaign (SOHO JOP 139), coordinated between ground-based
and Solar and Heliospheric Observatory (SOHO) instruments, has been
planned to obtain simultaneous spectroheliograms of the same active
region in several spectral lines. The chromospheric lines Ca II K,
Hα, and Na I D, as well as He I 10830, 5876, 584, and He II 304 Å
lines have been observed. The EUV radiation in the range λ<500
Å and in the range 260<λ<340 Å has also been measured at
the same time. These simultaneous observations allow us to build
semiempirical models of the chromosphere and low transition region of
an active region, taking into account the estimated total number of
photoionizing photons impinging on the target active region and their
spectral distribution. We obtained a model that matches very well all
the observed line profiles, using a standard value for the He abundance
([He]=0.1) and a modified distribution of microturbulence. For this
model we study the influence of the coronal radiation on the computed
helium lines. We find that, even in an active region, the incident
coronal radiation has a limited effect on the UV He lines, while it
is of fundamental importance for the D3 and 10830 Å lines. Finally,
we build two more models, assuming values of He abundance [He]=0.07 and
1.5, only in the region where temperatures are >1×104
K. This region, between the chromosphere and transition region, has been
indicated as a good candidate for processes that might be responsible
for strong variations of [He]. The set of our observables can still be
well reproduced in both cases, changing the atmospheric structure mainly
in the low transition region. This implies that, to choose between
different values of [He], it is necessary to constrain the transition
region with different observables, independent of the He lines.
Title: The EUV spectral irradiance from 1996 to 2003 as obtained
from SOHO
Authors: Del Zanna, G.; Andretta, V.; Beaussier, A.
Bibcode: 2005MmSAI..76..953D
Altcode:
We present EUV (150-800 Å) radiance measurements obtained with the
SOHO/Coronal Diagnostic Spectrometer (CDS) during the period from
1996 to 2003. We complement the CDS measurements with simultaneous
SOHO/EIT EUV images. We use the EIT center-to-limb variations to
obtain an estimate of the EUV spectral irradiance of the 'quiet Sun'
during 1996-2003. We discuss the evolution of the characteristics
of the solar corona from minimum to maximum, and show how it becomes
progressively hotter.
Title: A Non-LTE Analysis of the Ca II Infrared Triplet as a
Diagnostic Tool in Solar-type Stars
Authors: Busà, I.; Andretta, V.; Gomez, M. T.; Terranegra, L.
Bibcode: 2003csss...12.1134B
Altcode:
NLTE calculations of the profiles of the Ca II InfraRed Triplet (IRT:
λ= 8498, 8542, 8662 Å) are performed for a grid of photospheric
models with Teff=4200, 5200, 6200 K, log g=4.0, 4.5, 5.0
and metal=0.0, -1.0, -2.0, showing the sensitivity of the profiles
to changes in stellar parameters and the effect of departures
from LTE. Our analysis shows that the correlation between the
observed line central depression and rhk found, for instance, by
Chmielewski (2000) is mainly due to the effect of v sin i (via the
rotation-activity correlation) instead of being the result of a pure
chromospheric filling-in of the line core. We therefore define
a new activity index, \caindex, given by the difference between the
calculated photospheric central intensity and the observed one. The
correlation we find between this purely chromospheric index and rhk,
for which we give two interpolation expressions, is more directly
related to chromospheric activity.
Title: Solar and Heliospheric Observatory/Coronal Diagnostic
Spectrograph and Ground-based Observations of a Two-Ribbon Flare:
Spatially Resolved Signatures of Chromospheric Evaporation
Authors: Teriaca, L.; Falchi, A.; Cauzzi, G.; Falciani, R.; Smaldone,
L. A.; Andretta, V.
Bibcode: 2003ApJ...588..596T
Altcode:
During a coordinated observing campaign (Solar and Heliospheric
Observatory, SOHO JOP 139), we obtained simultaneous spectroheliograms
of a solar active region in several spectral lines, sampling levels
from the chromosphere to the corona. Ground-based spectroheliograms
were acquired at the Dunn Solar Tower of the National Solar
Observatory/Sacramento Peak in four chromospheric lines, while the
coronal diagnostic spectrograph on board SOHO was used to obtain
rasters of the active region in transition region (TR) and coronal
lines. Such a complete data set allowed us to compare the development
of intensity and velocity fields during a small two-ribbon flare
in the whole atmosphere. In particular, we obtained for the first
time quasi-simultaneous and spatially resolved observations of
velocity fields during the impulsive phase of a flare, in both the
chromosphere and upper atmosphere. In this phase, strong downflows
(up to 40 km s-1) following the shape of the developing
ribbons are measured at chromospheric levels, while strong upward
motions are instead measured in TR (up to -100 km s-1)
and coronal lines (-160 km s-1). The spatial pattern of
these velocities have a common area about 10" wide. This is the first
time that opposite-directed flows at different atmospheric levels
are observed in the same spatial location during a flare. These
signatures are highly suggestive of the chromospheric evaporation
scenario predicted in theoretical models of flares.
Title: The EUV helium spectrum in the quiet Sun: A by-product of
coronal emission?
Authors: Andretta, V.; Del Zanna, G.; Jordan, S. D.
Bibcode: 2003A&A...400..737A
Altcode:
In this paper we test one of the mechanisms proposed to explain the
intensities and other observed properties of the solar helium spectrum,
and in particular of its Extreme-Ultraviolet (EUV) resonance lines. The
so-called Photoionisation-Recombination (P-R) mechanism involves
photoionisation of helium atoms and ions by EUV coronal radiation,
followed by recombination cascades. We present calibrated measurements
of EUV flux obtained with the two CDS spectrometers on board SOHO,
in quiescent solar regions. We were able to obtain an essentially
complete estimate of the total photoionising flux in the wavelength
range below 504 Å (the photoionisation threshold for He I), as well as
simultaneous measurements with the same instruments of the intensities
of the strongest EUV He I and He Ii lines: \specline{He}i{584},
\specline{He}i{537}, and \specline{He}{ii}{304}. We find that there
are not enough EUV ionising photons to account for the observed helium
line intensities. More specifically, we conclude that He Ii intensities
cannot be explained by the P-R mechanism alone. Our results, however,
leave open the possibility that the He I spectrum could be formed by
the P-R mechanism, with the \specline{He}{ii}{304} line as a significant
photoionisating source.
Title: Spatially resolved signatures of chromospheric evaporation
during a small two-ribbon flare
Authors: Teriaca, L.; Falchi, A.; Cauzzi, G.; Falciani, R.; Smaldone,
L. A.; Andretta, V.
Bibcode: 2003MmSAI..74..635T
Altcode:
Ground based spectroheliograms of a solar active region were acquired
in four chromospheric lines simultaneously with rasters in transition
region (TR) and coronal lines obtained with the Coronal Diagnostic
Spectrograph (CDS) aboard SOHO. Such a complete dataset allows us to
study the development of intensity and velocity fields during a small
two-ribbon flare in the whole atmosphere. In particular, we obtain for
the first time quasi-simultaneous and spatially resolved observations
of velocity fields during the impulsive phase of a flare, both in
chromosphere and upper atmosphere. In this phase, strong downflows
(up to 40 km s-1) following the shape of the developing
ribbons are measured at chromospheric levels, while strong upward
motions are measured in TR (up to -100 km s-1) and coronal
lines (-160 km s-1). The spatial pattern of these velocities
have a common area about 10 arcsec wide. This is the first time that
opposite directed flows at different atmospheric levels are observed
in the same spatial location during a flare. These signatures are
highly suggestive of the chromospheric evaporation scenario predicted
in theoretical models of flares.
Title: Behaviour of Hydrogen Lyman lines in a prominence region from
SUMER and CDS
Authors: Aznar Cuadrado, R.; Andretta, V.; Teriaca, L.; Kucera, T. A.
Bibcode: 2003MmSAI..74..611A
Altcode:
We present observations of a prominence, taken on 1998 February 20 in
the framework of SOHO Joint Observing Program no. 63. The instruments
involved were SUMER and the NIS Spectrograph of CDS. The SUMER spectral
range includes the hydrogen Lyman series - starting from Ly-epsilon -
down to the head of the Lyman continuum, while CDS observed a number of
lines from T ~ 104 K to T ~ 2x 106 K. For these
observations, we were able to obtain a satisfactory determination of
the pointing of the SUMER slit relative to CDS. We thus examined - and
compared with information from CDS spectra - the main characteristics of
the hydrogen Lyman series lines and of other strong lines in the SUMER
spectral interval. We also studied the properties (depth, asymmetry)
of the central reversal present in several or all of the Lyman lines
in some regions of the prominence.
Title: The World Space Observatory Project WSO/UV
Authors: Pagano, I.; Rodonò, M.; Bonanno, G.; Buson, L.; Cassatella,
A.; De Martino, D.; Wamsteker, W.; Shustov, B.; Barstow, M.; Brosch,
N.; Fu-Zhen, Cheng; Dennefeld, M.; Gomez de Castro, A. I.; Kappelmann,
N.; Sahade, J.; Van der Hucht, K.; Solheim, J. -E.; Haubold, H.;
Altamore, A.; Andretta, V.; Badiali, M.; Becciani, U.; Busà, I.;
Cappellaro, E.; Cardini, D.; Catalano, S.; Castellani, V.; Chiaberge,
M.; Chieffi, A; Chiuderi, C.; Cosentino, R.; Cremonese, G.; Cutispoto,
G.; Falomo, R.; Ferrini, F.; Franchini, M.; Frasca, A.; Giovannelli,
F.; Gori, L.; Gomez, M.; Hack, M.; Lanza, A. F.; Lanzafame, A.;
Malagnini, M. L.; Marilli, E.; Marziani, P.; Matteucci, F.; Morossi,
C.; Munari, U.; Pace, E.; Panagia, N.; Pasinetti, L.; Piotto, G.;
Polcaro, F.; Radovich, M.; Ragaini, S.; Rifatto, A.; Rossi, C.;
Scuderi, S.; Selvelli, P.; Silvotti, R. L. Terranegra5, M. Turatto3,
M. Uslenghi22, R. Viotti4
Bibcode: 2003MSAIS...3..327P
Altcode: 2003astro.ph..6554P
The World Space Observatory Project is a new space mission concept,
grown out the needs of the Astronomical community to have access to
the part of the electromagnetic spectrum where all known physics can be
studied on all possible time scales: the Ultraviolet range. The physical
diagnostics in this domain supply a richness of new experimental
data unmatched by any other wavelength range, for the studies of the
Universe. As WSO/UV has been driven by the needs of scientists from
many different countries, a new implementation model was needed to
bring the World Space Observatory to reality. The WSO/UV consists of a
single Ultraviolet Telescope in orbit, incorporating a primary mirror
of 1.7 m diameter feeding a UV spectrograph and UV Imagers.
Title: CONCORDIASTRO/Italy: A Solar High-Resolution Observation
Program at Dome-C
Authors: Severino, G.; Andretta, V.; Berrilli, F.; Cascone, E.;
Centrone, M.; Criscuoli, S.; Del Moro, D.; Ermolli, I.; Giorgi, F.;
Jefferies, S. M.; Magri, M.; Moretti, P. F.; Oliviero, M.; Parisi,
L.; V; Porzio; Smaldone, L. A.; Straus, Th.
Bibcode: 2003MSAIS...2..181S
Altcode:
CONCORDIASTRO is the Nice-Napoli joint project for site
testing of the Dome C for solar and stellar astronomy in the
visible. CONCORDIASTRO/Italy is the solar physics part of this project,
whose the Napoli team has the principal responsibility. Beyond the
well-known interest for the helioseismology, CONCORDIASTRO/Italy pointed
out that, because of its special atmospheric conditions, Dome C promises
to be one of the best sites on Earth to perform high-resolution solar
physics. Here we review the basis for this statement and the solar
observations program planned by CONCORDIASTRO/Italy.
Title: GAIA spectroscopy of active solar-type stars
Authors: Ragaini, S.; Andretta, V.; Gomez, M. T.; Terranegra, L.;
Busà, I.; Pagano, I.
Bibcode: 2003ASPC..298..461R
Altcode: 2003gsst.conf..461R
No abstract at ADS
Title: NLTE line-blanketed CaII calculations for evaluation of GAIA
spectroscopic performances
Authors: Busà, I.; Pagano, I.; Rodonò, M.; Gomez, M. T.; Andretta,
V.; Terranegra, L.
Bibcode: 2003ASPC..298..403B
Altcode: 2003gsst.conf..403B
No abstract at ADS
Title: Chromospheric and Transition region He lines during a flare
Authors: Falchi, A.; Mauas, P. J. D.; Andretta, V.; Teriaca, L.;
Cauzzi, G.; Falciani, R.; Smaldone, L. A.
Bibcode: 2003MmSAI..74..639F
Altcode:
An observing campaign (SOHO JOP 139), coordinated between ground
based and SOHO instruments, has been planned to obtain simultaneous
spectroheliograms of the same area in several spectral lines. The
chromospheric lines Ca II K, Hα and Na I D as well as He I 10830,
5876, 584 and 304 Ålines have been observed. These observations allow
us to build semi-empirical models of the atmosphere before and during
a small flare. With these models, constructed to match the observed
line profiles, we can test the He abundance value.
Title: SUMER observations of hydrogen Lyman series and continuum in
a prominence
Authors: Andretta, Vincenzo; Aznar Cuadrado, Regina; Kucera, Therese
A.; Teriaca, Luca
Bibcode: 2002ESASP.506..419A
Altcode: 2002svco.conf..419A; 2002ESPM...10..419A
We present observations of a prominence, taken on February 20, 1998 in
the framework of SOHO Joint Observing Program no. 63. The instruments
involved were SUMER and the Normal Incidence Spectrograph (NIS) of
CDS. The SUMER spectral range includes the hydrogen Lyman series
- starting from Ly-ɛ - down to the head of the Lyman continuum,
while CDS observed a number of lines from T ~ 104K to T ~
2×106K. For these observations, we were able to obtain a
satisfactory determination of the pointing of the SUMER slit relative to
CDS. We thus examined - and compared with information from CDS spectra
- the main characteristics of the hydrogen Lyman series lines and of
other strong lines in the SUMER spectral interval. We also studied
the properties (depth, asymmetry) of the central reversal present in
several or all of the Lyman lines in some regions of the prominence.
Title: Chromospheric evaporation in a two-ribbon flare
Authors: Cauzzi, G.; Falchi, A.; Teriaca, L.; Falciani, R.; Smaldone,
L. A.; Andretta, V.
Bibcode: 2002ESASP.506..561C
Altcode: 2002ESPM...10..561C; 2002svco.conf..561C
We present simultaneous, spatially and temporally resolved
chromospheric, transition region and coronal observations of a small
eruptive flare studied throughout its whole development. We show
that strong and co-spatial plasma motions, oppositely directed in the
chromosphere (downflows) and in upper atmospheric layers (upflows),
develop at the onset of the flare. For the first time, we prove that
such oppositely directed flows originate from the same flaring kernels
in different atmospheric layers. Using realistic values for the plasma
parameters in the flaring loop, we also estimate a balance between
the upward and downward momenta. Our observations confirm in a very
convincing way the scenario of chromospheric evaporation predicted in
theoretical models of flares.
Title: Combined space and ground based observations of a C-1 flare
Authors: Teriaca, L.; Falchi, A.; Cauzzi, G.; Falciani, R.; Smaldone,
L. A.; Andretta, V.
Bibcode: 2002ESASP.508..457T
Altcode: 2002soho...11..457T
We present temporally and spatially resolved space and ground based
observations of a C1 flare. Ground based spectroheliograms were acquired
at the Dunn Solar Tower of NSO/Sacramento Peak in several chromospheric
lines. Simultaneously, the Coronal Diagnostic Spectrograph (CDS)
aboard SoHO was used to obtrain rasters of the same active region
in transiton region (TR) and coronal lines. This unique dataset
provides us, for the first time, with spatially resolved observations
of velocity fields during the impulsive phase of the flare, from the
chromosphere up to the TR and the corona. At the time of the emission
peak, a large area of the flaring kernel observed in TR lines is
characterized by upward velocities. A ~6"×6" kernel displays upflows
velocity above 80 km s-1. In this same area we found, in
data obtained about 3 minutes later, chromospheric downflows of 10 -
20 km s-1. This is the first time that opposite directed
flows at different atmospheric levels are observed in the same spatial
location during a flare.
Title: Simultaneous Hα and sodium observations at the Kanzelhöhe
Solar Observatory
Authors: Moretti, Pier F.; Andretta, V.; Cacciani, A.; Hanslmeier,
A.; Messerotti, M.; Otruba, W.; Warmuth, A.
Bibcode: 2002ESASP.477..147M
Altcode: 2002scsw.conf..147M
At the Kanzelhöhe Solar Observatory, Hα images are currently
obtained simultaneously with sets of intensity, velocity and
longitudinal magnetic images in the sodium D lines. Many flares
have been detected. The preliminary results of the analysis suggest
the events to occur at heights in the solar atmosphere below 1100
km, where the canopy magnetic lines stressed by the photospheric
motions can reconnect. The penetration of the downflowing plasma
jets is investigated in order to justify the solar background in the
photospheric intensity-velocity phase spectrum.
Title: A method to estimate the effect of line blanketing in NLTE
radiative transfer calculations
Authors: Busá, I.; Andretta, V.; Gomez, M. T.; Terranegra, L.
Bibcode: 2001A&A...373..993B
Altcode:
We present a method to estimate the contribution of line opacity to the
total opacity as a function of wavelength. The estimated line-opacity
function can then be used to simulate line-blanketing in NLTE radiative
transfer calculations. Given a reference flux distribution (either
observed or theoretical), our method allows to obtain a good estimate of
the spectrum without the need for considering in detail all the millions
of lines contributing to line blanketing. We applied the method to the
spectra computed from a sample of photospheric models with effective
temperatures Teff = 4200, 5200 and 6200 K, log g = 4.0,
4.5, 5.0 and [A/H] = 0.0, -1.0, -2.0, taken from the NextGen database
(Allard & Hauschildt \cite{allardhauschildt:95}). The computed flux
distributions agree quite well with the corresponding LTE line-blanketed
NextGen fluxes when we introduce the estimated line-opacity contribution
as a multiplicative factor of the continuum opacity in the radiative
transfer calculations. In particular we discuss the importance of a
correct estimate of the continuum flux, mainly in the UV, in the NLTE
formation of the Ca Ii H & K, the Ca Ii InfraRed Triplet (IRT:
lambda = 8498, 8542, 8662), Na I D, Li I and K I resonance lines.
Title: The Role of Velocity Redistribution in Enhancing the Intensity
of the HE II 304 Å Line in the Quiet-Sun Spectrum
Authors: Andretta, Vincenzo; Jordan, Stuart D.; Brosius, Jeffrey W.;
Davila, Joseph M.; Thomas, Roger J.; Behring, William E.; Thompson,
William T.; Garcia, Adriana
Bibcode: 2000ApJ...535..438A
Altcode:
We present observational evidence of the effect of small-scale
(``microturbulent'') velocities in enhancing the intensity of the
He II λ304 line with respect to other transition region emission
lines, a process we call ``velocity redistribution,''. We first show
results from the 1991 and 1993 flights of SERTS (Solar EUV Rocket
Telescope and Spectrograph). The spectral resolution of the SERTS
instrument was sufficient to infer that, at the spatial resolution
of 5", the line profile is nearly Gaussian both in the quiet Sun and
in active regions. We were then able to determine, for the quiet Sun,
a lower limit for the amplitude of nonthermal motions in the region of
formation of the 304 Å line of the order of 10 km s-1. We
estimated that, in the presence of the steep temperature gradients
of the solar transition region (TR), velocities of this magnitude
can significantly enhance the intensity of that line, thus at least
helping to bridge the gap between calculated and observed values. We
also estimated the functional dependence of such an enhancement on
the relevant parameters (nonthermal velocities, temperature gradient,
and pressure). We then present results from a coordinated campaign,
using SOHO/CDS and Hα spectroheliograms from Coimbra Observatory,
aimed at determining the relationship between regions of enhanced
helium emission and chromospheric velocity fields and transition region
emission in the quiescent atmosphere. Using these data, we examined
the behavior of the He II λ304 line in the quiet-Sun supergranular
network and compared it with other TR lines, in particular with O III
λ600. We also examined the association of 304 Å emission with the
so-called coarse dark mottle, chromospheric structures seen in Hα
red-wing images and associated with spicules. We found that all these
observations are consistent with the velocity redistribution picture.
Title: Modelling of Carbon-Rich Stars with Far Infrared Flux Excess
Authors: Bagnulo, Stefano; Doyle, Gerry; Skinner, Chris; Andretta,
Vincenzo
Bibcode: 2000IAUS..177..522B
Altcode:
No abstract at ADS
Title: Diagnostics Constraints on Prominence Parameters from SOHO
and Ground-based Observations
Authors: Schmieder, B.; Kotrč, P.; Heinzel, P.; Kucera, T.;
Andretta, V.
Bibcode: 1999ESASP.448..439S
Altcode: 1999ESPM....9..439S; 1999mfsp.conf..439S
No abstract at ADS
Title: Does Velocity Redistribution Really Enhance the He 304Å Line
to Observed Intensities?
Authors: Jordan, S.; Andretta, V.; Garcia, A.; Brosius, J.; Behring, W.
Bibcode: 1999ESASP.448..303J
Altcode: 1999mfsp.conf..303J; 1999ESPM....9..303J
No abstract at ADS
Title: A Direct Comparison Between EUV Coronal Flux And He Resonance
Line Photon Flux From SOHO/CDS Data
Authors: Andretta, V.; Landi, Enrico; Del Zanna, Giulio; Jordan,
Stuart D.
Bibcode: 1999ESASP.446..123A
Altcode: 1999soho....8..123A
In the wealth of EUV spectroscopic and imaging data gathered by the
SOHO and TRACE missions, a prominent role is played by the helium
resonance emission. For example, He I lines are among the most intense
features in CDS/NIS spectra, while the EIT 304 waveband (dominated by
He II emission) is routinely employed to map the structure of the solar
chromosphere and transition region. However, no 'standard' model has
emerged so far that is able to interpret observed He spectra/images
to a satisfactory degree of self-consistency. Recent research on
the problem of the formation of the solar helium spectrum tends to
rule out a dominant role of coronal radiation in exciting He resonance
lines. However, while evidence for this result is strong, it is based on
indirect tests. Here we present a more direct assessment of this issue
by directly measuring the photon photoionizing EUV flux measured with
CDS/GIS-NIS1. This measure can be directly compared with the observed
flux in the main He I and He II resonance lines observed with CDS/NIS2.
Title: The Role of Velocity Redistribution in Enhancing the Intensity
of the He II 304 A Line in the Quiet Sun Spectrum
Authors: Andretta, Vincenzo; Jordan, Stuart D.; Brosius, Jeffrey W.;
Davila, Joseph M.; Thomas, Roger J.; Behring, William E.; Thompson,
William T.; Garcia, Adriana
Bibcode: 1999STIN...9909151A
Altcode:
We present observational evidence of the effect of small scale
("microturbulent") velocities in enhancing the intensity of the He
II lambda304 line with respect to other transition region emission
lines, a process we call "velocity redistribution". We first show
results from the 1991 and 1993 flights of SERTS (Solar EUV Rocket
Telescope and Spectrograph). The spectral resolution of the SERTS
instrument was sufficient to infer that, at the spatial resolution
of 5", the line profile is nearly gaussian both in the quiet Sun and
in active regions. We were then able to determine, for the quiet Sun,
a lower limit for the amplitude of non-thermal motions in the region
of formation of the 304 A line of the order of 10 km/s. We estimated
that, in the presence of the steep temperature gradients of the solar
Transition Region (TR), velocities of this magnitude can significantly
enhance the intensity of that line, thus at least helping to bridge
the gap between calculated and observed values. We also estimated the
functional dependence of such an enhancement on the relevant parameters
(non-thermal velocities, temperature gradient, and pressure). We then
present results from a coordinated campaign, using SOHO/CDS and H-alpha
spectroheliograms from Coimbra Observatory, aimed at determining
the relationship between regions of enhanced helium emission and
chromospheric velocity fields and transition region emission in the
quiescent atmosphere. Using these data, we examined the behavior of
the He II lambda304 line in the quiet Sun supergranular network and
compared it with other TR lines, in particular with O III lambda600. We
also examined the association of 304 A emission with the so-called
"coarse dark mottle", chromospheric structures seen in H-alpha red
wing images and associated with spicules. We found that all these
observations are consistent with the velocity redistribution picture.
Title: Velocity Redistribution as a He II 304 Intensity Enhancement
Mechanism
Authors: Jordan, S. D.; Andretta, V.; Brosius, J. W.; Behring, W. E.;
Garcia, A.
Bibcode: 1999AAS...194.9310J
Altcode: 1999BAAS...31..990J
Both Skylab and SOHO observations show that the total intensity in
the He II 304 Angstroms line exceeds that predicted by standard NLTE
models by at least a factor of 5. However, the NLTE models do not
include the effect of flows. Carole Jordan showed that a 'velocity
redistribution' of the He II ions in the presence of a sharp temperature
gradient could provide the required enhancement. In earlier studies,
we have reported evidence from the Goddard SERTS sounding rocket for
small-scale nonthermal velocities large enough to enhance the emission
by the required amount if the temperature gradient is large enough
(as given by current transition region models). Here, we assess the
correlation of regions of strong Sun-center quiet-Sun 304 emission
observed with the CDS instrument on SOHO and the dark coarse mottles
observed in the red wing of H-alpha observed at the Coimbra Solar
Observatory. The significant positive correlation supports the picture
of greater velocity mixing in the quiet-Sun regions producing the
highest line intensity. Support for this research is provided by NASA
grant 682-344-17-38 and the Coimbra Solar Observatory.
Title: Observations of Hydrogen and Helium Continua in Solar
Prominences
Authors: Andretta, V.; Kucera, T. A.; Poland, A. I.
Bibcode: 1999ASPC..158..162A
Altcode: 1999ssa..conf..162A
No abstract at ADS
Title: Does Velocity Redistribution Really Enhance the HE 304 A Line
to Observed Intensities?
Authors: Jordan, Stuart; Andretta, Vincenzo; Garcia, Adriana; Brosius,
Jeffrey; Behring, William
Bibcode: 1999STIN...9909149J
Altcode:
Previous work by this group has demonstrated that small-scale
nonthermal velocities probably play a significant role in enhancing the
intensity of the He II 304 A line above values predicted by the static
atmosphere NLTE theories, and more in conformity with Skylab and SOHO
observations. This presentation briefly summarizes the evidence for this
conclusion, emphasizing SOHO and correlated groundbased observations,
of which examples are presented. However, in contrast to the previous
studies, the tact taken here is more critical, asking the question
"Can velocity redistribution fully explain the observations of the 304 A
line, and what counter-indications and problems remain?" The conclusion
reached is that, while velocity redistribution plays a significant
role in the intensity enhancement, it may not be the whole story. Some
other mechanism, associated with velocity filtration, may be at work.
Title: Neutral Hydrogen Column Depths in Prominences Using EUV
Absorption Features
Authors: Kucera, T. A.; Andretta, V.; Poland, A. I.
Bibcode: 1998SoPh..183..107K
Altcode:
Observations of prominence regions in hot coronal lines (≳106 K)
at wavelengths below the hydrogen Lyman absorption limit show what
appear to be absorption features. Other authors have suggested that
these observed features may be due to H and He continuum absorption. But
there has, as yet, been no conclusive evidence that this is indeed the
case. In this paper we present new Solar and Heliospheric Observatory
(SOHO) observations that allow us to address this problem in a
quantitative manner. We find that continuum absorption is the best
explanation for the absorption observed in imaging data from the Coronal
Diagnostic Spectrometer (CDS) on board SOHO. Furthermore, we discuss
a new technique to measure the column depth of neutral hydrogen in a
prominence, and use it to obtain estimates of the prominence filling
factors as well. We calculate the column depth of neutral hydrogen,
ξH∼1018 cm−2, and the filling factor, f≳0.3.
Title: Observations and modelling of spectral energy distributions
of carbon stars with optically thin envelopes
Authors: Bagnulo, S.; Doyle, J. G.; Andretta, V.
Bibcode: 1998MNRAS.296..545B
Altcode:
We present broad-band photometry in the optical, near-infrared and
submillimetre, and mid-infrared spectrophotometry of a selection of
carbon stars with optically thin envelopes. Most of the observations
were carried out simultaneously. Beside the emission feature at 11.3mum
due to silicon carbide grains in the circumstellar environment, many
of our mid-infrared spectra show an emission feature at 8.6mum. All
the observed spectral energy distributions exhibit a very large
far-infrared flux excess. Both these features are indeed common to
many carbon stars surrounded by optically thin envelopes. We have
modelled the observed spectral energy distributions by means of a
full radiative transfer treatment, paying particular attention to the
features quoted above. The peak at 8.6mum is usually ascribed to the
presence of hydrogenated amorphous carbon grains. We find also that
the feature at 8.6mum might be reproduced by assuming that the stars
have a circumstellar environment formed of both carbon- and oxygen-rich
dust grains, although this is in contrast with what one should expect
in a carbon-rich environment. The far-infrared flux excess is usually
explained by the presence of a cool detached dust shell. Following
this hypothesis, our models suggest a time-scale for the modulation
of the mass-loss rate of the order of some 10^3yr.
Title: The Helium Spectrum in the Quiet Sun: The January 16/17 and
May 7-13 1997 Coordinated SOHO/Ground-Based Observational Campaigns
Authors: Andretta, Vincenzo; Jordan, Stuart D.; Muglach, Karin;
Garcia, Adriana; Jones, Harrison P.; Penn, Matthew J.; Soltau, Dirk
Bibcode: 1998ASPC..155..336A
Altcode: 1998sasp.conf..336A
No abstract at ADS
Title: Investigating the Formation of the Helium Spectrum in the
Solar Atmosphere
Authors: Andretta, Vincenzo; Jordan, Stuart D.; Muglach, Karin;
Garcia, Adriana; Jones, Harrison P.; Soltau, Dirk
Bibcode: 1998ASPC..154..559A
Altcode: 1998csss...10..559A
We present the first results of coordinated observations with SOHO
(Solar Heliospheric Observatory) and ground-based observatories aimed
at investigating the mechanisms responsible for the formation of helium
lines in the quiescent solar atmosphere. The observations described
here were taken on 7-13 May 1997; the SOHO instruments involved were
CDS, SUMER and EIT, while ground-based support was provided by the
German Vacuum Tower Telescope on Tenerife (He 1 lambda10830 and Ca 2
lambda8498 spectra-spectroheliograms), Coimbra Solar Observatory (Hα
spectroheliograms), and NASA/NSO Vacuum Tower Telescope on Kitt Peak
(Ca 2 lambda8542 spectra-spectroheliograms and polarimetry).
Title: Comparison of NSO/KPVT 1083 NM and SOHO/CDS/SUMER Observations
of a Coronal Hole.
Authors: Jones, H. P.; Andretta, V.; Jordan, S. D.; Penn, M. J.
Bibcode: 1997AAS...191.7304J
Altcode: 1997BAAS...29.1321J
As part of SOHO Joint Observing Program 16 to study the solar formation
of Helium, coordinated observations of a coronal hole were obtained
on 17 Jan 97. In this paper, we compare the NSO/KPVT full-disk 1083 nm
spectroheliogram and a time sequence of spectra-spectroheliograms of the
coronal hole near the south solar pole with approximately cospatial and
cotemporal SOHO spatial-spectral data taken in He I (58.4 nm, CDS and
SUMER) and He II 30.4 nm (CDS) together with several transition-region
and coronal lines of CIII, OIII, OIV, MgIX, MgX, SiIX, and SiXII. We
have previously reported on correlations of line intensities. Here
we concentrate as well on Doppler shifts and, in particular, line
asymmetry in the He I 1083 nm line which shows augmented absorption
in the blue wing of the line within the coronal hole in the same sense
as reported by Dupree, Penn, and Jones (1996, ApJ 467, L121).
Title: Formation of the Helium II 304 Angstroms Line in the Solar
Atmosphere
Authors: Jordan, S. D.; Andretta, V.
Bibcode: 1997AAS...19112003J
Altcode: 1997BAAS...29.1402J
The problem of the formation of the principle members of the resonance
series of He I and He II at 584 Angstroms and 304 Angstroms remains
a major unsolved problem of the solar atmosphere. Nevertheless,
thanks to observations from the Goddard Solar Extreme Ultraviolet
Rocket Telescope and Spectrograph (SERTS) and from the ESA/NASA
SOHO mission, we now have a data base to address this problem and,
hopefully, to solve it for the quiet atmosphere. This talk will briefly
review alternatives for helium resonance line formation in the Sun,
and will offer a few examples of observations that promise to help
discriminate among them. Specifically, assuming electron collisional
excitation is responsible for the 304 Angstroms line in the quiet Sun,
supported by our earlier studies, evidence from SERTS and SOHO will
be discussed in support of 'velocity redistribution' of the emitting
ions in producing the observed profiles and fluxes.
Title: On the Role of the Solar Corona and Transition Region in the
Excitation of the Spectrum of Neutral Helium
Authors: Andretta, Vincenzo; Jones, Harrison P.
Bibcode: 1997ApJ...489..375A
Altcode:
We investigate the formation of the spectrum of neutral helium in the
solar atmosphere by solving the corresponding non-LTE problem in an
extended grid of model atmospheres. From the results we infer several
general properties and scaling laws that can be used to discriminate
the different proposed formation mechanisms. Some of the scaling laws
have also been tested in a comparison with previous calculations made
with different assumptions. In our models, the excitation of
the spectrum by direct photoionization by EUV radiation shortward
of 504 Å followed by recombinations (PR mechanism), seems to be
capable of influencing significantly the resonance continuum and
the subordinate lines, even in the presence of other (collisional)
excitation mechanisms. While this influence is almost unavoidable in
most atmospheric features, it is hardly justifiable as the only possible
contribution. Moreover, the resonance lines seem inclined to respond
much more effectively to the conditions of the lower transition region,
even in the presence of a significant coronal EUV illumination. With the
help of the detailed non-LTE calculations and of the derived scaling
laws, we explore the interplay of the possible formation mechanisms
and their effect on the individual spectral features.
Title: The NaI λλ5890,5896 resonance doublet as chromospheric
diagnostics in M dwarfs.
Authors: Andretta, V.; Doyle, J. G.; Byrne, P. B.
Bibcode: 1997A&A...322..266A
Altcode:
The Nai D lines at 5890/5896Å are very prominent features in the
spectrum of late-type stars. Nevertheless, little attention has
been devoted to the potential use of those lines as chromospheric
diagnostics. As a case study, we explore the dependence on chromospheric
activity of the D lines in a star with T_eff_=3700K, logg=4.7 and solar
metallicity. The results are compared with the better studied hydrogen
spectrum. We find that the D lines seem to be a promising diagnostic
of the lower-middle chromosphere, that can complement the information
given by lines like Hα. We also find that, for detailed quantitative
studies, it is necessary to include a proper treatment of the background
opacities. Less important, instead, is the need of careful treatment
of transitions induced by collisions with hydrogen atoms. Finally,
our calculations make it clear that, for the most active stars, the
level of coronal emission should also be taken into account.
Title: Measuring the He I/H ratio in a prominence using Lyman
absorption
Authors: Kucera, T. A.; Andretta, V.; Poland, A. I.
Bibcode: 1997SPD....28.0112K
Altcode: 1997BAAS...29Q.881K
We investigate a method for measuring the ratio of neutral helium to
hydrogen in solar prominences. The upper limit to the Lyman continuum
occurs at 911 Angstroms for H, 504 Angstroms for He I, and 228 Angstroms
for He II. Lyman absorption by prominences and other structures is
clearly visible in emission of hot coronal lines observed by the Coronal
Diagnostic Spectrometer (CDS) and Extreme Ultraviolet Imaging Telescope
(EIT) aboard the Solar and Heliospheric Observatory (SOHO). By comparing
the absorption in lines absorbed by H only and by H and He I, the ratio
of He I to H in prominences can be determined. We attempt to do this
by comparing the absorption by a prominence in the Mg X line at 624.9
Angstroms and the Mg IX line at 368.1 Angstroms, both observed by CDS.
Title: The intrinsic LY α to H α ratio in M dwarf stars.
Authors: Doyle, J. G.; Mathioudakis, M.; Andretta, V.; Short, C. I.;
Jelinsky, P.
Bibcode: 1997A&A...318..835D
Altcode:
Using Ly α line profiles generated from a grid of M
dwarf model atmospheres we calculate the attenuation factor
[i.e. Lyα(obs)/Lyα(intrin)] due to the interstellar medium as
a function of hydrogen column density. Then using selected model
atmospheres, attenuation factors were calculated for those M dwarfs with
available Ly α observations. The prime motivation in this work has been
to look afresh at the intrinsic Ly α to H α flux ratio, an important
constraint in the radiative transfer modelling of M dwarfs. For those
active dMe stars where both lines were observed, the intrinsic ratio
is ~3-5 (with ~50% variation). The major uncertainty in this work has
been the interstellar hydrogen column density, emphasizing the need
for further work in this area and in particular an accurate model of
its variation in all directions.
Title: Understanding the Hell 304 Å Resonance Line in the Sun
Authors: Jordan, S.; Andretta, V.; Garcia, A.; Falconer, D.
Bibcode: 1997ESASP.404..439J
Altcode: 1997cswn.conf..439J
No abstract at ADS
Title: Investigating the Formation of the Helium Spectrum with
Coordinated SOHO/Kitt Peak/Sacramento Peak Observations
Authors: Andretta, V.; Jordan, Stuart D.; Jones, Harrison P.; Penn,
Matthew J.
Bibcode: 1997ESASP.404..163A
Altcode: 1997cswn.conf..163A
No abstract at ADS
Title: Simultaneous observations of the He I lambda 1083 and lambda
587.6 lines in the solar atmosphere
Authors: Andretta, V.
Bibcode: 1996AAS...188.3619A
Altcode: 1996BAAS...28..876A
Helium lines are generally a valuable tool to trace activity in the
solar atmosphere. The most prominent lines observable from ground-based
observatories are the triplet lines at 587.6 and 1083 nm, but despite
the wide use of these activity tracer (especially of the latter),
little progress has been made towards the exploitation of their
diagnostic potential. However, recent theoretical investigations
have pointed out that of correlation between the two main triplet
He I lines can discriminate between different scenarios of the line
formation, ultimately giving informations on the structure of the upper
chromosphere/lower transition region. The observations presented here
address such issues for the first time. The spectra were obtained with
the FTS at the McMath/Pierce telescope on Kitt Peak; they constitute
in fact a set of simultaneous observations of the two lines for several
solar features. The observed joint response of lambda 587.6 and lambda
1083 to the level of chromospheric heating can thus be directly compared
with theoretical predictions.
Title: On the diagnostic contents of NA I lines in M dwarfs
Authors: Andretta, V.; Byrne, P. B.; Doyle, J. G.
Bibcode: 1996ASPC..109..559A
Altcode: 1996csss....9..559A
No abstract at ADS
Title: Helium in the Spectrum of the Sun and of Solar-Type Stars
Authors: Andretta, V.; Giampapa, M. S.; Jones, H. P.
Bibcode: 1995IrAJ...22..177A
Altcode:
We present results from detailed non-LTE radiative transfer calculations
of the He I spectrum in the Sun. Using an extended grid of model
chromospheres, we explore the relative importance of, respectively,
the coronal XUV illumination and the thermal structure of the lower
transition region. With reference to the He I lambda 587.6 and lambda
1083.0 triplet lines, we point out some implications for the study of
activity in solar-type stars.
Title: A Method for Estimating the Fractional Area Coverage of Active
Regions on Dwarf F and G Stars
Authors: Andretta, Vincenzo; Giampapa, Mark S.
Bibcode: 1995ApJ...439..405A
Altcode:
The D3 (lambda 5876) and lambda 10830 lines arising from
triplet levels in neutral helium appear in absorption in active
(plage) regions on the Sun and, by implication, in the active
regions on Sun-like (F-early K) stars. These features either do not
occur, or appear only very weakly, in the quite solar (or stellar)
photosphere. Hence, these diagnostics are ideal tracers of magnetic
regions outside of cool spots. The appearance of D3 and
lambda 10830 in absorption immediately suggests that these lines can
be utilized to infer the fractional area coverage, or filling factor,
of active region on stellar surfaces if their intrinsic absorption
strengths in these regions are known. In particular, a meaningful
lower limit to the active filling factor can be deduced if the maximum
absorption equivalent width (Wmax) in D3 or
lambda 10830 as either appears in stellar analogs of solar plages
can be estimated. We develop this approach by constructing a grid
of model chromospheres based on the VAL C model of the quiet solar
chromosphere. This thermal structure is superposed on published models
for F and G dwarf photospheres. We solve for the non-LTE ionization of
hydrogen to infer chromospheric electron densities. We then perform
a multilevel, non-LTE computation of the helium triplet lines in the
sequence of model chromospheres, taking into account the potential
effects of coronal XUV back radiation on the line formation. We
conservatively estimate that Wmax approximately = 100-150
mA for D3 in both F and G dwarfs. The implied lower limits
to the filling factor of plagelike regions can be approximately 20%
among active solar-type stars. We extend this approach by investigating
a method by which the actual filling factor can be deduced through
a study of the joint response of D3 and lambda 10830 to
chromospheric nonradiative heating. We emphasize that our filling factor
estimates indicate the area coverage at the height of formation of
the helium triplet lines in the active chromosphere. Because of field
line spreading with height, filling factors based on chromospheric
lines are expected to exceed estimates based on purely photospheric
lines. Finally, we discuss the relative importance of collisional
and photoionization processes in the formation of these important
diagnostics.
Title: Joint observations of the chromosphere, transition region,
and corona from SOHO and NSO/Kitt Peak
Authors: Jones, H. P.; Harvey, John W.; Andretta, Vincenzo
Bibcode: 1994ESASP.373..345J
Altcode: 1994soho....3..345J
No abstract at ADS