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Author name code: severino
ADS astronomy entries on 2022-09-14
author:"Severino, Giuseppe"
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Title: The Structure and Evolution of the Sun
Authors: Severino, Giuseppe
2017ses..book.....S Altcode:
No abstract at ADS
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Title: The Intensity-Velocity Phase Spectra of Evanescent Oscillations
and Acoustic Sources
Authors: Severino, G.; Straus, T.; Oliviero, M.; Steffen, M.; Fleck, B.
2013SoPh..284..297S Altcode: 2012SoPh..tmp..295S
There are three major issues in modeling solar evanescent oscillations:
the variation of the intensity [I]-velocity [V] phase difference of
p-modes close to the base of photosphere; the existence of a plateau
of negative I-V phase differences below and between the ridges of the
low-frequency p-modes; the explanation of the I-V cross-spectra of
the evanescent oscillations. We present new interpretations for the
first two issues, based on modeling intensity fluctuations taking steep
temperature gradients, opacity, and non-adiabatic cooling into account.
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Title: Acoustic-Gravity Waves in the Solar Atmosphere: Comparing
Hinode/SP Observations with Numerical Simulations
Authors: Fleck, Bernard; Straus, T.; Severino, G.
2012AAS...22020121F Altcode:
We investigate the signatures of acoustic-gravity waves in Hinode/SP
observations and compare them to those found in line spectra synthesized
from high-resolution 3D radiation-hydrodynamics simulations. The
Hinode/SP time series extends over 4 hours, with a cadence of 16 s and a
spatial resolution of 0.16 arcsec/pixel. The observations are compared
to two numerical simulations of the Sun’s surface layers, both
computed with the radiation hydrodynamics code CO<SUP>5</SUP>BOLD. The
higher resolution simulation has a fixed 3D Cartesian grid with 400
x 400 x 300 cells, each of size 14 km x 14 km x 7.5 km, the lower
resolution simulation 200 x 200 x 250 cells, each of size 56 km x 56
km x 21 km. The higher resolution simulation thus covers a cube of 5.6
x 5.6 x 2.3 Mm<SUP>3</SUP>, the lower resolution simulation a cube of
size 11.2 x 11.2 x 5.2 Mm<SUP>3</SUP>. A line-synthesis code, based
on the assumption of local thermodynamic equilibrium (LTE), was fed
with the physical parameters of the simulations to produce synthetic,
two-dimensional spectra of the photospheric lines of Fe 6301/6302 Å
(Hinode/SP), Fe 6173 Å (SDO/ HMI), and Ni 6768 Å (SOHO/MDI). The
resulting Doppler velocity time series are analyzed using Fourier
techniques and compared to the observed Hinode/SP spectra. The
height-dependent energy flux in the simulations is determined in the
acoustic, evanescent and internal gravity wave regime and compared to
energy flux estimates from the Hinode observations and the synthesized
Doppler velocities of the simulations.
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Title: The intensity effect in magneto-optical filters
Authors: Oliviero, M.; Severino, G.; Berrilli, F.; Moretti, P. F.;
Jefferies, S. M.
2011SPIE.8148E..0VO Altcode: 2011SPIE.8148E..27O
We used a laser system for determining the bandpasses of the two
vapour cells, the Magneto-Optical Filter (MOF) and the Wing Selector
(WS), which are the core of solar narrow-band filters based on the
MOF technology. A new result, which we called the Intensity Effect,
was found: the MOF and WS bandpasses depend not only on the temperature
at which the cell is heated and the external magnetic field in which
the cell is embedded, but also on the radiation intensity entering
the cell. A theoretical interpretation of the Intensity Effect is
proposed in terms of the kinetic equilibrium of the potassium atomic
populations inside the vapour cell. We need to take the Intensity
Effect into account for setting-up MOF based instruments for solar and
stellar observations as well as for modelling the MOF and WS spectral
transmissions.
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Title: DIMMI-2h a MOF-based instrument for Solar Satellite ADAHELI
Authors: Stangalini, M.; Moretti, P. F.; Berrilli, F.; Del Moro, D.;
Jefferies, S. M.; Severino, G.; Oliviero, M.
2011SPIE.8148E..0US Altcode: 2011SPIE.8148E..26S
The Doppler-Intensity-Magnetograms with a Magneto-optical filter
Instrument at two heights (DIMMI-2h) is a double channel imager using
Magneto Optical Filters (MOF) in the potassium 770 nm and sodium
589 nm lines. The instrument will provide simultaneous dopplergrams
(velocity fields), continuum intensity and longitudinal magnetic flux
images at two heights in the solar atmosphere corresponding to low
and high photosphere. Dimmi- 2h is the possible piggy-back payload on
ADAHELI satellite. The spatial resolution (approximately 4 arcsec) and
the high temporal cadence (15 s) will permit to investigate low and
medium oscillating modes (from 0 to below 1000) up to approximately
32 mHz in the frequency spectrum. The acquisition of long-term
simultaneous velocity, intensity and magnetic information up to these
high frequencies will permit also the study of the propagation and
excitation of the waves with a frequency resolution never obtained
before.
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Title: High-frequency Waves in Numerical Simulations of the Solar
Atmosphere
Authors: Fleck, Bernard; Straus, T.; Severino, G.
2011SPD....42.1720F Altcode: 2011BAAS..43S.1720F
We investigate the excitation processes, propagation characteristics,
and energy transport of high-frequency waves in the solar atmosphere
with the help of high-resolution 3D radiation-hydrodynamics
simulations. Time series of synthetic spectra of four photospheric
Fraunhofer lines (Fe 6302, Fe 6301, Fe 6173, Ni 6768) from these
simulations are analyzed in order to evaluate the diagnostic power of
spectroscopic observations.
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Title: What does the Sun suggest about global oscillation amplitudes
in solar-like stars?
Authors: Severino, G.; Straus, Th.; Oliviero, M.; Steffen, M.
2010AN....331..896S Altcode:
Motivated by the results of CoRoT and based on the solar experience,
we develop a new stellar scaling law for the intensity-velocity
amplitude ratio (gain) of resonant oscillations, which is a quantity
independent of the excitation model. The comparison of our approach
with observations gives new interesting results for the Sun as a
star. Moreover, for a sample of three solar-like stars observed
by CoRoT, we found that our scaling law provides an explanation of
the low observed luminosity amplitudes which is an alternative to
non-adiabatic effects.
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Title: Planning magneto-optical filters for the study of magnetic
oscillations of the Sun
Authors: Oliviero, M.; Severino, G.; Esposito, G.
2010Ap&SS.328..325O Altcode: 2010Ap&SS.tmp..134O
VAMOS is a Magneto-Optical Filter (MOF) that can acquire nearly
simultaneous Dopplergrams and magnetograms with high cadence in the K
I 7699 Å line. We performed an accurate set-up of this instrument
in view of its use for studying oscillations in solar magnetic
regions. The optimal set-up for VAMOS was achieved and an extra result
of the spectral transmission measurements was found. The MOF and Wing
Selector (WS) bandpasses depend not only on the cell temperature and
magnetic field but also on the radiation intensity entering the cell,
when this radiation exceeds a suitable level. We call this effect The
Intensity Effect.
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Title: On the Origin of High-Frequency "Acoustic” Power in
Photospheric and Chromospheric Velocity Power Spectra
Authors: Fleck, Bernard; Straus, T.; Carlsson, M.; Jefferies, S. M.;
Severino, G.; Tarbell, T. D.
2010AAS...21640309F Altcode: 2010BAAS...41..879F
In a recent paper (Fleck et al., 2010) we compared observed Dopplergram
time series from Hinode with results from 3-D numerical simulations
based on the Oslo "Stagger” and CO5BOLD codes. Given the rapid falloff
of atmospheric modulation transfer functions at high frequencies due
to the extended widths of typical velocity response functions, one
would expect the high-frequency tail of Doppler power spectra to drop
significantly below those of actual velocities at the corresponding
heights in the simulations. Surprisingly, our analysis of power spectra
of Doppler shifts of simulated line profiles did not reveal such a
steep falloff at high frequencies. Instead, they are comparable to
(and in some cases even larger than) those of the actual velocities,
making estimates of the energy flux of high frequency acoustic
waves questionable, in particular those that apply atmospheric MTF
corrections. In this work we study the cause of this unexpected
behavior in detail, with particular emphasis on the role of rapidly
changing velocity response functions in a dynamic atmosphere with
strong vertical velocity gradients.
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Title: High frequency waves in the solar atmosphere?.
Authors: Fleck, B.; Straus, T.; Carlsson, M.; Jefferies, S. M.;
Severino, G.; Tarbell, T. D.
2010MmSAI..81..777F Altcode: 2010arXiv1002.3285F
The present study addresses the following questions: How representative
of the actual velocities in the solar atmosphere are the Doppler
shifts of spectral lines? How reliable is the velocity signal derived
from narrowband filtergrams? How well defined is the height of the
measured Doppler signal? Why do phase difference spectra always pull
to 0<SUP>o</SUP> phase lag at high frequencies? Can we actually observe
high frequency waves (P< 70 s)? What is the atmospheric MTF of high
frequency waves? How reliably can we determine the energy flux of high
frequency waves? We address these questions by comparing observations
obtained with Hinode/NFI with results from two 3D numerical simulations
(Oslo Stagger and CO<SUP>5</SUP>BOLD). Our results suggest that the
observed high frequency Doppler velocity signal is caused by rapid
height variations of the velocity response function in an atmosphere
with strong velocity gradients and cannot be interpreted as evidence of
propagating high frequency acoustic waves. Estimates of the energy flux
of high frequency waves should be treated with caution, in particular
those that apply atmospheric MTF corrections.
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Title: On the Role of Acoustic-Gravity Waves in the Energetics of
the Solar Atmosphere
Authors: Straus, T.; Fleck, B.; Jefferies, S. M.; McIntosh, S. W.;
Severino, G.; Steffen, M.; Tarbell, T. D.
2009ASPC..415...95S Altcode: 2010arXiv1003.3773S
In a recent paper (Straus et al. 2008) we determined the energy
flux of internal gravity waves in the lower solar atmosphere using
a combination of 3D numerical simulations and observations obtained
with the IBIS instrument operated at the Dunn Solar Telescope and
the Michelson Doppler Imager (MDI) on SOHO. In this paper we extend
these studies using coordinated observations from SOT/NFI and SOT/SP
on Hinode and MDI. The new measurements confirm that gravity waves
are the dominant phenomenon in the quiet middle/upper photosphere and
that they transport more mechanical energy than the high-frequency
(> 5 mHz) acoustic waves, even though we find an acoustic flux 3-5
times larger than the upper limit estimate of Fossum & Carlsson
(2006). It therefore appears justified to reconsider the significance of
(non-M)HD waves for the energy balance of the solar chromosphere.
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Title: On The Interpretation Of Hinode NFI Filtergrams
Authors: Fleck, Bernard; Straus, T.; Jefferies, S. M.; Severino, G.;
Tarbell, T. D.
2009SPD....40.0927F Altcode:
Phase difference spectra between the velocity signals at two
different heights represent a powerful tool to study the propagation
characteristics of acoustic-gravity waves in the solar atmosphere. In
our efforts to study the dynamics and energetics of these waves we
have acquired high-resolution, high-cadence time series with Hinode
SOT/NFI at two different levels in the Mg b2 or Na D1 lines. The
observed phase spectra between the velocity signals derived from the
"wing" and "core" filtergrams of these lines do not show the expected
behavior. This points to (a) a fundamental lack of understanding of
the propagation characteristics of acoustic waves, which may be more
complex than commonly assumed, or (b) significant difficulties in
interpreting filtergrams taken at fixed wavelengths in the wings of an
absorption line, possibly limiting the diagnostic potential of Doppler
"velocity" measurements from such filtergrams. The present work aims
at disentangling these effects with the help of numerical simulations.
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Title: High Frequency Acoustic Waves in the Sun's Atmosphere
Authors: Fleck, B.; Jefferies, S. M.; McIntosh, S. W.; Severino, G.;
Straus, T.; Tarbell, T. D.
2008ESPM...12.2.39F Altcode:
This year marks the 60th anniversary of two pioneering papers by
Schwarzschild (1948) and Biermann (1948), who independently proposed
that acoustic waves generated in the turbulent convection zone play
an important role in the heating of the chromosphere and corona. High
frequency acoustic waves have remained one of the leading contenders
for solving the heating problem of the non-magnetic chromospheres of
the Sun and late-type stars ever since. Earlier attempts to determine
the acoustic energy flux from ground were compromised by atmospheric
seeing, which has its biggest effect on the high frequency parts
of the observed signal. Recently, based on a comparison of TRACE
observations and 1-D simulations, Fossum & Carlsson (2005, 2006)
concluded that high-frequency acoustic waves are not sufficient
to heat the solar chromosphere. The same conclusion was reached by
Carlsson et al. (2007) from an analysis of Hinode SOT/BFI Ca II H and
blue continuum observations. Other authors (e.g. Cuntz et al. 2007;
Wedemeyer-Boehm et al. 2007, Kalkofen 2007), however, questioned
these results for a number of reasons. Because of its limited spatial
resolution and limited sensitivity there are inherent difficulties
when comparing TRACE observations with numerical simulations. Further,
intensity oscillations are difficult to interpret, as they result from
a phase-sensitive mix of temperature and pressure fluctuations, and
non-local radiation transfer effects may complicate the picture even
more. Here we revisit the role of high frequency acoustic waves in the
dynamics and energetics of the Sun's atmosphere using high cadence,
high resolution Doppler velocity measurements obtained with SOT/SP
and SOT/NFI on Hinode.
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Title: On the Role of Acoustic-gravity Waves in the Energetics of
the Solar Atmosphere
Authors: Straus, T.; Fleck, B.; Jefferies, S. M.; Cauzzi, G.; McIntosh,
S. W.; Reardon, K.; Severino, G.; Steffen, M.; Suter, M.; Tarbell,
T. D.
2008ESPM...12.2.11S Altcode:
We revisit the dynamics and energetics of the solar atmosphere, using a
combination of high-quality observations and 3D numerical simulations
of the overshoot region of compressible convection into the stable
photosphere. We discuss the contribution of acoustic-gravity waves
to the energy balance of the photosphere and low chromosphere. We
demonstrate the presence of propagating internal gravity waves at
low frequencies (< 5mHz). Surprisingly, these waves are found
to be the dominant phenomenon in the quiet middle/upper photosphere
and to transport a significant amount of mechanical energy into the
atmosphere outweighing the contribution of high-frequency (> 5mHz)
acoustic waves by more than an order of magnitude. We compare the
properties of high-frequency waves in the simulations with results
of recent high cadence, high resolution Doppler velocity measurements
obtained with SOT/SP and SOT/NFI on Hinode. Our results seem to be in
conflict with the simple picture of upward propagating sound waves. We
discuss the implications of our findings on the energy flux estimate
at high-frequencies.
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Title: Velocity and Intensity Power and Cross Spectra in Numerical
Simulations of Solar Convection
Authors: Severino, G.; Straus, T.; Steffen, M.
2008SoPh..251..549S Altcode: 2008SoPh..tmp...54S
Fitting observed power and cross spectra of medium-degree p modes
in velocity (V) and intensity (I) has been widely used for getting
information about the p-mode excitation process and, in particular,
for trying to determine the type and location of the acoustic
sources. Numerical simulations of solar convection allow one to
"observe" velocity and temperature (T, used as proxy for I) fluctuations
in different reference frames. Sampling the oscillations on planes of
constant optical depth (τ-frame) closely corresponds to the observer's
point of view, whereas sampling the oscillations at constant geometrical
height (z-frame) is more appropriate for comparison with predictions
from theoretical models based on Eulerian hydrodynamics. The results of
the analysis in the two frames show significant differences. Considering
the effects introduced on oscillations by the steep temperature gradient
of the photosphere and by the temperature- and pressure-dependent
continuum opacity, we develop a new model for fitting the simulated V
and T power and cross spectra both in the τ- and z-frames and discuss
its merits and limitations.
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Title: The Energy Flux of Internal Gravity Waves in the Lower Solar
Atmosphere
Authors: Straus, Thomas; Fleck, Bernhard; Jefferies, Stuart M.;
Cauzzi, Gianna; McIntosh, Scott W.; Reardon, Kevin; Severino, Giuseppe;
Steffen, Matthias
2008ApJ...681L.125S Altcode:
Stably stratified fluids, such as stellar and planetary atmospheres,
can support and propagate gravity waves. On Earth these waves,
which can transport energy and momentum over large distances and can
trigger convection, contribute to the formation of our weather and
global climate. Gravity waves also play a pivotal role in planetary
sciences and modern stellar physics. They have also been proposed
as an agent for the heating of stellar atmospheres and coronae, the
exact mechanism behind which is one of the outstanding puzzles in solar
and stellar physics. Using a combination of high-quality observations
and 3D numerical simulations we have the first unambiguous detection
of propagating gravity waves in the Sun's (and hence a stellar)
atmosphere. Moreover, we are able to determine the height dependence of
their energy flux and find that at the base of the Sun's chromosphere it
is around 5 kW m<SUP>-2</SUP>. This amount of energy is comparable to
the radiative losses of the entire chromosphere and points to internal
gravity waves as a key mediator of energy into the solar atmosphere.
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Title: Accurate Intensity Velocity Phase Difference in the Potassium
Resonance Line Obtained with VAMOS
Authors: Magrı, M.; Oliviero, M.; Severino, G.
2008SoPh..247...15M Altcode:
We present new results about the phase difference between the intensity
and velocity fluctuations of the solar photosphere obtained with the
Velocity And Magnetic Observations of the Sun (VAMOS) instrument, which
uses the magneto-optical filter (MOF) technique. Before this observing
run, we applied the calibration method described in Magrì, Oliviero,
and Severino (Solar Phys.232, 159, 2005) to reduce the instrumental
cross-talk which was present in previous VAMOS data. The quality of this
calibration, which can be easily applied to any MOF-based instrument,
has been confirmed by comparing with the MOF transmission-profile
measurements obtained with a diode laser system. Finally, we discuss the
new VAMOS phase-difference value in relation to data obtained by other
authors in the same potassium spectral line and in other lines that
can be used to study nonadiabatic effects of solar global oscillations.
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Title: Internal Gravity Waves and their Role in the Energetics of
the Solar Atmosphere
Authors: Fleck, Bernard; Straus, T.; Jefferies, S.; McIntosh, S. W.;
Severino, G.; Steffen, M.
2007AAS...210.2410F Altcode: 2007BAAS...39..130F
Internal gravity waves are believed to be excited by convective
overshoot in the solar atmosphere. We compare the results from numerical
simulations of the overshoot region of compressible convection into a
stable photosphere, with observations of the velocity field at several
heights in the solar atmosphere. We find a consistent picture for the
quiet middle/upper photosphere in which internal gravity waves are the
dominant phenomenon at low frequencies (< 2.5 mHz). We estimate the
contribution of these waves to the energy balance in the photosphere
and low chromosphere.
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Title: Simulation of Magneto-Optical Filter Transmission Profiles
Authors: Severino, G.; Oliviero, M.; Landi Degl'Innocenti, E.
2007ASPC..368..617S Altcode:
We present a numerical simulation of a potassium Magneto-Optical Filter
(MOF) enabling to compute the filter transmission. The results of the
simulation are compared with experimental transmission profiles at
different heating temperatures, measured with a diode laser system. The
comparison reveals a significant amount of agreement but also shows
some important differences.
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Title: Resonant Oscillation Modes and Background in Realistic
Hydrodynamical Simulations of Solar Surface Convection
Authors: Straus, T.; Severino, G.; Steffen, M.
2006ESASP.617E...4S Altcode: 2006soho...17E...4S
No abstract at ADS
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Title: SINERGIES (Sun, INterplanetary, EaRth Ground-based InstrumEntS)
or the potential of the Italian Network for Ground-Based Observations
of Sun-Earth Phenomena.
Authors: Amata, E.; Candidi, M.; Centrone, M.; Consolini, G.;
Contarino, L.; Criscuoli, S.; De Lauretis, M.; Diego, P.; Ermolli,
I.; Francia, P.; Giorgi, F.; Laurenza, M.; Magrí, M.; Marcucci, F.;
Massetti, S.; Messerotti, M.; Oliviero, M.; Penza, V.; Perna, C.;
Pietropaolo, E.; Romano, P.; Severino, G.; Spadaro, D.; Storini, M.;
Vellante, M.; Villante, U.; Zlobec, P.; Zuccarello, F.
2006MSAIS...9...82A Altcode:
The Italian Network for Ground-Based Observations of Sun-Earth
Phenomena, whose instruments monitor the Sun, the Interplanetary
Space, and the Earth's Magnetosphere, has recently started to operate
in a coordinated scheme. In this paper, we describe few significant
examples of this coordination effort. 1) During the year 2003, several
coordinated observational campaigns were carried out in order to study
the solar photospheric dynamics. 2) Reconstruction of TSI in time, for
periods spanning from a solar rotation up to the whole current solar
cycle. 3) Extreme solar events occurring during the late October -
early November 2003.
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Title: A new method to calibrate MOF-based instruments
Authors: Magrí, M.; Oliviero, M.; Severino, G.
2006MSAIS...9..112M Altcode:
We present a method for calibrating every instruments based on the
magneto-optical filter (MOF) technology \citep{cacciani78}. The method
allows to determine the operating characteristics of the filter and to
find if spurious transmissions are present in the transmission profile
due to an incorrect operating temperature or to the degradation of the
filter. These characteristics are inferred by modelling the blue and/or
red line intensity images acquired with the MOF system. We applied
the method to the observations performed with the VAMOS instrument.
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Title: SINERGIES, the Italian Network for Ground-Based Observations
of Sun-Earth Phenomena .
Authors: Amata, E.; Berrilli, F.; Candidi, M.; Cantarano, S.; Centrone,
M.; Consolini, G.; Contarino, L.; Criscuoli, S.; De Lauretis, M.;
Del Moro, D.; Egidi, A.; Ermolli, I.; Francia, P.; Giordano, S.;
Giorgi, F.; Oliviero, M.; Magrí, M.; Marcucci, F.; Massetti, S.;
Messerotti, M.; Parisi, M.; Perna, C.; Pietropaolo, E.; Romano, P.;
Severino, G.; Spadaro, D.; Storini, M.; Vellante, M.; Villante, U.;
Zlobec, P.; Zuccarello, F.
2006MSAIS...9...79A Altcode:
Since many years, the complex phenomena occurring on the Sun have
been continuously monitored by different and complementary ground
based instruments managed by groups of the Italian Astrophysics
Community. Recently some of these instruments have started to operate in
a coordinated scheme, the Italian Network for Ground-Based Observations
of Sun-Earth Phenomena. In this paper, we describe the characteristics
of the nodes belonging to the Network, called SINERGIES, the scientific
objectives, the facilities and the data storage system of the Network
itself. Due to its capabilities, the Network allows the Italian Solar
Terrestrial Physics Community to monitor solar activity and its effect
on the Earth.
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Title: SOLARNET-Italian Solar Archive Federation. The First Italian
Virtual Observatory Application
Authors: Volpicelli, C. A.; Antonucci, E.; Cora, A.; Giordano, S.;
Messerotti, M.; Santin, A.; Zlobec, P.; Severino, G.; Oliviero, M.;
DeMarino, I.; Alvino, R.; Straus, T.; Ermolli, I.; Centrone, C.;
Perna, C.; Zuccarello, F.; Romano, P.; Spadaro, D.; Contarino, L.
2006MSAIS...9..129V Altcode:
We describe the implementation of the national project SOLARNET (SOLar
ARchive NETwork) aimed at federating the heterogeneous Italian solar
data archives into a VO (Virtual Observatory) framework as a single
integrated database, and providing users with tools to search and
retrieve specific data sets. It interoperates using the SOAP/XML
Web Services exposed by each single node and managed via a unified
Portal.This project is the first real Italian Virtual Observatory
application using the standard defined by the IVOA (International
Virtual Observatory Alliance) working groups.
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Title: An Observational Method to Prevent Cross-Talk and Calibrate
Mof-Based Instruments
Authors: Magrı, Maria; Oliviero, Maurizio; Severino, Giuseppe
2005SoPh..232..159M Altcode:
We present a method for calibrating every instrument working with
magneto-optical filter (MOF) technology, in order to take into account
the effect in the observations due to the aging of the vapour cells. The
method allows the evaluation of some characteristics of the transmission
profile by modelling the blue and/or the red line intensity images
acquired with the MOF system. In particular, it reveals the presence
of unwanted spurious transmissions and prevents cross-talk between the
intensity and velocity fluctuations. The method also gives information
about the position of the "working point" of the instrument, i.e. the
average wavelength position of its transmission profile, which is
necessary for estimating the right solar atmospheric layer observed
by the MOF. This analysis is powerful and fast: applied before every
observing campaign, it enables setting Q the most suitable value for
the cell temperature, which is one of the parameters that controls
the MOF transmission profile.
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Title: A model to interpret the intensity-velocity and
velocity-velocity phase differences from solar observations obtained
with magneto-optical filters
Authors: Moretti, P. F.; Severino, G.
2004A&A...421..729M Altcode:
The intensity (I) and velocity (V) signals obtained using
magneto-optical filters (MOF), are not independent of each other. The
induced spurious signals affect the intensity-velocity phase difference
measurements and the effect is referred to as a I-V crosstalk (Moretti
& Severino \cite{Moretti02}). We show a new model to interpret
the I-V phase measurements and, in particular, its application to the
interpretation of the data obtained with sodium MOF systems. The model
can also be applied to correct the velocity-velocity phase from multi
layer observations.
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Title: How Well Can We Infer the Properties of the Solar Acoustic
Sources?
Authors: Jefferies, Stuart M.; Severino, Giuseppe; Moretti,
Pier-Francesco; Oliviero, Maurizio; Giebink, Cynthia
2003ApJ...596L.117J Altcode:
Measurements of the p-mode line asymmetry in the solar oscillation
velocity power spectrum have been used on several occasions to infer
the properties of the acoustic sources. These inferences are based on
the assumption that, unlike the observed intensity signal, the velocity
signal does not contain a nonresonant (background) component that is
correlated with the p-mode signal. Line asymmetry measurements have also
been used to draw inferences on the nature of the correlated background
signal that is present in intensity observations. By simultaneously
modeling the observed velocity and intensity power spectra and the
intensity-velocity cross spectrum, we enforce strict observational
constraints on the properties of the fitting model. We find that in
order to accurately describe the observed data, we have to include
a correlated background component in both our models for the V and
I signals at low frequencies. Our results also show that we cannot
uniquely determine the acoustic source depth for low-frequency waves
or the detailed properties of the correlated background signals. It
appears that further physical and/or observational constraints are
needed before we can obtain this information.
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Title: CASTEL: Capodimonte Antarctic Solar TELescope
Authors: Moretti, P. F.; Severino, G.
2003MSAIS...2..186M Altcode:
The program of the CONCORDIASTRO/Italy project consists of the
installation of a 40 cm telescope at Dome C. This telescope will be
used to acquire time-series of filtergrams in the visible at both
medium and high spatial resolution, with the aim to qualify Dome C
for solar observations. In case the expectation of very good seeing
at Dome C will be confirmed, this site will allow long-lasting, high
spatial resolution data that are needed for many scientific purposes;
one example, of interest for our group, is the study of small seismic
events that are considered the best candidate to excite the solar
global oscillations. This contribution focuses on the project planning
of CONCORDIASTRO/Italy and on the telescope named CASTEL (Capodimonte
(or Concordia) Antarctic Solar TELescope).
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Title: Atmospheric Gravity Waves
Authors: Severino, G.; Oliviero, M.; Straus, Th.; Ulrich, R. K.
2003MmSAI..74..595S Altcode:
We compared a theoretical model for atmospheric gravity waves with
observations of both intensity (I) and velocity (V) fluctuations of
the solar photosphere. The preliminary results confirm the presence
of g-waves in this part of solar atmosphere and rise new questions
which deserve further investigation.
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Title: The Italian solar data archives: national and European
perspectives
Authors: Messerotti, M.; Coretti, I.; Padovan, S.; Zlobec, P.;
Antonucci, E.; Cora, A.; Volpicelli, C. A.; Dimitoglou, G.; Reardon,
K.; Tripicchio, A.; Severino, G.; EGSO Team
2003MmSAI..74..391M Altcode:
We discuss the present status of the solar data archives geographically
distributed in the Italian Astronomical Observatories of the National
Institute for Astrophysics (INAF). In particular, we describe the
national project SOLARNET (SOLAR NETwork) aimed at federating all the
Italian solar archives as a distributed database, the first step toward
an Italian Virtual Solar Observatory (IVSO), and the European Grid
for Solar Observations (EGSO) project, which is under implementation
to construct the basis for a large solar archive federation based on
the Grid architecture to provide the scientific user with advanced
resources such as a solar feature catalogue.
---------------------------------------------------------
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.
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: EGSO - The European Grid of Solar Observations
Authors: Reardon, K.; Antonucci, E.; Giordano, S.; Severino, G.;
Messerotti, M.; EGSO Team
2003MmSAI..74..823R Altcode:
The European Grid of Solar Observations (EGSO) project aims to
produce the framework for a coordinated community-wide resource for
obtaining and reducing solar observations. The EGSO will be capable of
sharing resources coming from all types of providers, while ensuring
scalability, security, and compatibility among all datasets. The user
will be provided with a customizable search interface from which to
simultaneously browse or data mine a range of solar and heliospheric
data archives. In essence, the EGSO will create the fabric of a virtual
solar observatory.
---------------------------------------------------------
Title: Preliminary Results on the Solar Photospheric Dynamics Observed
with Vamos
Authors: Oliviero, M.; Moretti, P. F.; Severino, G.; Straus, Th.;
Magrı, M.; Tripicchio, A.
2002SoPh..209...21O Altcode:
The intensity and velocity fluctuations, observed simultaneously, are a
powerful diagnostic tool of the dynamics of the solar atmosphere. The
phase relation between the fluctuations can improve our knowledge of
the solar background, its relation with the acoustic sources, and
its interaction with the solar acoustic oscillations. Furthermore,
the opposite asymmetries observed along the p-mode line profiles in
the intensity and velocity power spectra contain information about
the source of the solar acoustic oscillations. For these reasons,
it is relevant to study the height dependence of the asymmetries and
phases in the solar atmosphere. In this paper, we present the results
from the analysis of observations performed by the VAMOS instrument in
the potassium 769.9 nm line and Na i D lines, and compare the measured
phases with those obtained at different layers in the solar atmosphere
by different instruments, spanning from the base of the photosphere
to the low chromosphere.
---------------------------------------------------------
Title: The intensity-velocity phase difference with Magneto-Optical
Filters
Authors: Moretti, P. F.; Severino, G.
2002A&A...384..638M Altcode:
The phase difference between the intensity and velocity signals is
a powerful diagnostic for the dynamics of the solar atmosphere. The
phases are used to quantify the nonadiabatic degree of the acoustic
modes and, recently, to infer the characteristics of the source of
the solar oscillations. For this reason, the error attributed to
the phase obtained from the observations plays an important role in
distinguishing between different phenomena. In this paper we discuss
the results obtained with the systems using a Magneto-Optical Filter. A
model to correct for the contamination induced by the velocity in the
intensity signal is described and the phases in the sodium D lines
presented. We also discuss the difference between the results obtained
when the phase values are computed with a local analysis or when the
l -nu diagram is obtained.
---------------------------------------------------------
Title: The Solar Intensity-Velocity Cross Spectrum: A Powerful
Diagnostic for Helioseismology
Authors: Severino, G.; Magrì, M.; Oliviero, M.; Straus, Th.;
Jefferies, S. M.
2001ApJ...561..444S Altcode:
We show that the solar intensity-velocity cross spectrum provides
a sensitive diagnostic for the interaction between the oscillatory
and nonoscillatory components of the solar velocity and intensity
signals. In particular, we demonstrate that to simultaneously model the
V and I power spectra, the I-V coherence spectrum, and the I-V phase
difference spectrum requires a coherent, correlated background signal
and a coherent, uncorrelated signal in both intensity and velocity. We
speculate that these signals may be related to the “acoustic events”
observed recently by Goode and colleagues. We also show why caution
should be exercised in the interpretation of model fit parameters
based only on measurements of the velocity or intensity power spectra,
or both: specifically, the parameters associated with the oscillation
source characteristics.
---------------------------------------------------------
Title: Analysis of high resolution and full disk solar images
Authors: Berrilli, F.; Caccin, B.; Cantarano, S.; Egidi, A.; Penza,
V.; Criscuoli, S.; del Moro, D.; Pietropaolo, E.; Consolini, G.;
Ermolli, I.; Lepreti, F.; Mainella, G.; Severino, G.; Zuccarello, F.
2001ESASP.493..173B Altcode: 2001sefs.work..173B
No abstract at ADS
---------------------------------------------------------
Title: The source of the solar oscillations: Convective or magnetic?
Authors: Moretti, P. F.; Cacciani, A.; Hanslmeier, A.; Messerotti,
M.; Oliviero, M.; Otruba, W.; Severino, G.; Warmuth, A.
2001A&A...372.1038M Altcode:
The origin of solar oscillations has not yet been clearly
determined. The downflows due to convective rapid cooling at the surface
have been invoked as a possible source. In this paper we investigate
the properties of the source as inferred from the local analysis of
the intensity-velocity phase differences. The same spatial and temporal
characteristics of other observed events and their correlation with the
Hα bright points suggests downward plasma jets related to explosive
chromospheric evaporation to be another possible candidate.
---------------------------------------------------------
Title: The effect of stellar activity on the Li I 6708, Na I 5896
and K I 7699 Å lines. A comparison with the Pleiades, field stars
and the Sun
Authors: Barrado y Navascués, D.; García López, R. J.; Severino,
G.; Gomez, M. T.
2001A&A...371..652B Altcode: 2001astro.ph..3419N; 2001astro.ph..3419B
An analytical model has been developed to empirically study the effects
of stellar spots and faculae on the observed equivalent widths of Li
i 6708, Na i 5896 and K i 7699 Å lines (and abundances in the case
of lithium) in late-type stars, taking into account the changes in
the observed magnitudes and colors. Solar spectra corresponding
to different active regions are used as input data and a range
of filling factors are applied to simulate the surfaces of stars
with different levels of activity. Detailed comparisons between
predicted and observed photometric colors and equivalent widths are
made for late-type stars of the Pleiades and the field. The observed
dispersions in K i and Li i equivalent widths for Pleiades stars can
be partially accounted by the simultaneous effects of activity on
colors and the line formation, indicating that the lithium-rotation
connection suggested for ~ 0.7-0.9 M_sun Pleiades stars could be due
in part to the stellar activity. However, under realistic values for
the filling factors, only a small portion of the observed spread could
be explained by these effects. Based on observations collected with
the Gregory-Coudé telescope, operated on the island of Tenerife by
the Universitäts-Sternwarte Göttingen in the Spanish Observatorio
del Teide of the Instituto de Astrofísica de Canarias.
---------------------------------------------------------
Title: A model of intensity and velocity power and I-V phase
difference across p-mode line profile based on a forced damped
harmonic oscillator and on the observed coherence spectrum
Authors: Magri, Maria; Oliviero, Maurizio; Severino, Giuseppe;
Straus, Thomas
2001MmSAI..72..511M Altcode:
We develop a simple model, based on a damped harmonic oscillator excited
by a random forcing, with the aim to reproduce the observed trends in
the intensity I and velocity V power and in the I-V phase difference and
coherence spectra. The model accounts for an oscillation mode embedded
in a solar background which is partly correlated to the mode. The
complex vectors I and V and the corresponding power spectra and I-V
phase difference are computed. The observed power spectra and the I-V
phase difference in the frequencies range 2.245 - 2.275 mHz for l = 17
(GONG data) are used as a comparison. We can also reproduce the trend
of the observed coherence. The obtained results are quite stimulating to
understand how the correlated convective background affects the data and
what fraction of the convective background is correlated to the mode.
---------------------------------------------------------
Title: Recent results on the solar photospheric dynamics
Authors: Severino, Giuseppe; Magri, Maria; Oliviero, Maurizio;
Straus, Thomas
2001MmSAI..72..677S Altcode:
The solar photosphere is a relatively small atmospheric layer, that
is a boundary between the convective interior and the optically thin
and magnetic outer atmosphere, where convection overshoots into and
different types of waves are excited and damped. Such a system cannot
be described by a simple dynamical model. Recent progress in the study
of the solar photospheric dynamics has been obtained thanks to the
space-time analysis of the velocity (V) and intensity (I) fluctuations
measured by the GONG, MDI/SOHO and VAMOS experiments. In particular,
it is claimed that the I-V phase differences and coherence can allow
to identify the seismic events which are thought to excite the solar
global oscillations.
---------------------------------------------------------
Title: A new model to reproduce the I-V phase difference and the
coherence spectra of the p-mode solar oscillation
Authors: Magri, M.; Oliviero, M.; Severino, G.; Straus, Th.
2001ESASP.464..653M Altcode: 2001soho...10..653M
We develop a simple model based on a dumped harmonic oscillator excited
by a random forcing, with the aim to reproduce the observed trends
in the intensity (I) and velocity (V) phase difference and coherence
spectra. The model accounts for an oscillation mode embedded in a
solar background which is partly correlated to the mode. The complex
vectors I and V and the corresponding I-V phase difference and coherence
spectra are computed. We also computed the I and V power spectra. For
comparison we used the GONG data at l = 17 and the average of the data
at n = 2 from l = 160 to l = 200 computed by Oliviero et al. (2001),
these proceedings. The obtained results are interesting to understand
how the convective solar background affects the spectra and in what
fraction it is correlated to the modes.
---------------------------------------------------------
Title: A high frequency and high l resolution intensity-velocity
phase differences from GONG data
Authors: Oliviero, M.; Severino, G.; Straus, Th.
2001ESASP.464..669O Altcode: 2001soho...10..669O
We analysed 9 GONG months (324 days) of intensity (I) and velocity
(V) data to produce I and V power, I-V phase difference and coherence
spectra with high resolution in both frequency and spherical harmonic
degree l, for the frequency range 0 - 8.3mHz and for l = 0 - 50. This
analysis confirms that the steplike behaviour of the solar background
phase differences, with negative values below ~3.3mHz and positive
values above ~4mHz, extends to low-l values, at least down to l =
4. The two-dimensional (frequency and degree l) phase differences and
coherence are particularly suitable to isolate the p-modes and the
background at low-l values and low frequencies, where the leakage peaks
are resolved. In this way, we can better estimate the phase difference
and the power of the solar background. Furthermore, we used one GONG
month of data to compute the l-averaged profiles of I and V power, I-V
phase difference and coherence, for the p-modes with radial order n =
2 and l = 160 - 200. These new high resolution measurements and the
p-mode mean profiles can be used to improve our knowledge of the nature
of the solar background and its relation with the acoustic p-modes.
---------------------------------------------------------
Title: The Velocity And Magnetic Observations of the Sun (VAMOS)
project: status and future prospects
Authors: Severino, G.; Moretti, P. F.; Oliviero, M.; Vamos Team
2001ESASP.464..337S Altcode: 2001soho...10..337S
The Velocity And Magnetic Observations of the Sun (VAMOS) is a project
by the Solar group at the Osservatorio Astronomico di Capodimonte
(OAC), to conduct a full-disk study of solar photospheric dynamics and
longitudinal magnetic field. To reach this goal, VAMOS has developed
a solar imager, based on the technology of the magneto-optical filter
(MOF), to obtain high cadence observations of the Sun's intensity (I)
and velocity (V) fluctuations, and longitudinal magnetic field (B)
component at the photospheric level. The instrument, with two potassium
vapour cells, became operational in May 1999, and it has been used
for campaign observations since then. Data reduction software has been
developed for both the Doppler images calibration and the V and I images
spherical harmonic decomposition. Progress is underway to perform the B
images calibration, and to improve the instrument stability. Currently,
the science done by VAMOS deals with the analysis of power, phase
difference and coherence l-v diagrams in the potassium resonance line.
---------------------------------------------------------
Title: The local I-V phase difference to investigate the background
spatial distribution
Authors: Moretti, P. F.; Oliviero, M.; Severino, G.; Mof Development
Group
2001ESASP.464..661M Altcode: 2001soho...10..661M
The phase difference between the intensity and velocity (I-V) is
claimed to be a powerful tool for understanding the nature of the
solar oscillations. The identification of a solar background in the
intensity-velocity l-ν diagram has been associated to a possible
signature of the source of the resonant oscillations. Many attempts have
been accomplished to match the results from the models to the recent
I-V values obtained from the observations. In this paper we present the
I-V phase computed with a different approach: the local analysis. The
global behaviour enhanced by the spherical harmonic decomposition is
now mixed to the local, non-resonant, phenomena. Nevertheless, where
convection is negligible, still two phase regimes, or populations, are
significant. The advantage of this method consists of the capability
to follow the distribution on the disk of I-V at different frequencies
and correlate to the solar structures. The background locations are
found where the velocity power is low. The results from some days of
full-disk images with a 4"/pixel resolution in the sodium D lines are
shown and a possible source of the solar background is suggested.
---------------------------------------------------------
Title: The local analysis to investigate the source of the solar
oscillations
Authors: Moretti, P. F.; Oliviero, M.; Severino, G.; Mof Development
Group
2001MmSAI..72..522M Altcode:
The phase difference between the intensity and velocity (I-V) is claimed
to be a powerful tool in the understanding the nature of the solar
oscillations. The identification of a solar "background" in the I-V
l-ν diagrams has been associated to a possible signature of the source
of the resonant oscillations. Many attempts have been accomplished
to match the results from the models to the recent I-V trait obtained
from the obervations. In this paper we present the I-V from a different
point of view: the local analysis. We expect that this approach can
reveal the local, non-resonant, phenomena, in addition to the global
behavior enhanced by the spherical harmonic decomposition. Nevertheless,
when convection is negligible, still two populations of phase values
are significant, likewise in the l-ν diagram. The advantage of this
method consists of the capability to follow the distribution on the
disk of the I-V phase at different frequencies and correlate to the
solar structures. The results address, in the five-minute band, the
"background" locations to those points where the velocity power is
low. The analysis is new and the results put some constraints to the
characteristics of the source of the five-minute oscillations.
---------------------------------------------------------
Title: The solar p-mode background - how correlated is it?
Authors: Straus, Th.; Severino, G.; Magri, M.; Oliviero, M.
2001ESASP.464..607S Altcode: 2001soho...10..607S
Two observational facts have enforced the interest in the solar p-mode
backbground spectrum in the recent past: the opposite asymmetry of the
p-mode profiles in intensity and velocity, and the particular behavior
of the I-V phase difference in the transition from the background to the
p-mode across the line profiles. The latter fact has been demonstrated
to be consistent with a superposition of the p-mode signal with a
coherent background, probably the signal of the source of excitation
itself, whereas the first has been attributed or to the geometrical
position of the source inside the cavity, or to a background signal
which is correlated to the p-mode signal. Different models identify this
correlated background mainly or in the velocity of in the intensity
signal. By including also the I-V coherence into our study we try to
answer the question how correlated the solar p-mode background is.
---------------------------------------------------------
Title: The photosphere - region of reflection and excitation of
solar oscillations
Authors: Straus, Thomas; Severino, Giuseppe
2001MmSAI..72..533S Altcode:
Two observational facts have enforced the interest in the solar p-mode
background spectrum in the recent past: the opposite asymmetry of the
p-mode profiles in intensity and velocity, and the particular behavior
of the I-V phase difference in the transition from the background to
the p-mode across the line profiles. We give a short review on the
current status of the investigation of the solar background.
---------------------------------------------------------
Title: High altitude test of RPCs for the Argo YBJ experiment
Authors: Bacci, C.; Bao, K. Z.; Barone, F.; Bartoli, B.; Bernardini,
P.; Buonomo, R.; Bussino, S.; Calloni, E.; Cao, B. Y.; Cardarelli, R.;
Catalanotti, S.; Cavaliere, A.; Cesaroni, F.; Creti, P.; Danzengluobu,
M.; D'Ettorre Piazzoli, B.; Vincenzi, M. D.; Girolamo, T. D.; Sciascio,
G. D.; Feng, Z. Y.; Fu, Y.; Gao, X. Y.; Geng, Q. X.; Guo, H. W.; He,
H. H.; He, M.; Huang, Q.; Iacovacci, M.; Iucci, N.; Jai, H. Y.; Kong,
F. M.; Kuang, H. H.; Labaciren,; Li, B.; Li, J. Y.; Liu, Z. Q.; Lu, H.;
Ma, X. H.; Mancarella, G.; Mari, S. M.; Marsella, G.; Martello, D.;
Mei, D. M.; Meng, X. R.; Milano, L.; Morselli, A.; Mu, J.; Panareo,
M.; Parisi, M.; Pellizzoni, G.; Peng, Z. R.; Pinto, C.; Pistilli,
P.; Reali, E.; Santonico, R.; Severino, G.; Shen, P. R.; Stanescu,
C.; Su, J.; Sun, L. R.; Sun, S. C.; Surdo, A.; Tan, Y. H.; Vernetto,
S.; Wang, C. R.; Wang, H.; Wang, H. Y.; Wei, Y. N.; Yang, H. T.; Yao,
Q. K.; Yu, G. C.; Yue, X. D.; Yuan, A. F.; Zhang, H. M.; Zhang, J. L.;
Zhang, N. J.; Zhang, T. J.; Zhang, X. Y.; Zhaxisangzhu,; Zhaxiciren,;
Zhu, Q. Q.
2000NIMPA.443..342B Altcode:
A 50 m<SUP>2</SUP> RPC carpet was operated at the YanBaJin Cosmic
Ray Laboratory (Tibet) located 4300 m a.s.l. The performance of
RPCs in detecting Extensive Air Showers was studied. Efficiency and
time-resolution measurements at the pressure and temperature conditions
typical of high mountain laboratories, are reported.
---------------------------------------------------------
Title: I-V phase difference and gain analysis of GONG full-disk data
Authors: Oliviero, M.; Severino, G.; Straus, T.; Jefferies, S. M.;
Appourchaux, T.
2000MmSAI..71..999O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Calibration of VAMOS Magnetic Data
Authors: Vogt, E.; Oliviero, M.; Severino, G.; Straus, T.
1999ESASP.448..405V Altcode: 1999ESPM....9..405V; 1999mfsp.conf..405V
No abstract at ADS
---------------------------------------------------------
Title: The Solar p-Mode Background: Observations and Hydrodynamical
Models
Authors: Straus, Th.; Steffen, M.; Severino, G.; Freytag, B.
1999ESASP.448..203S Altcode: 1999mfsp.conf..203S; 1999ESPM....9..203S
No abstract at ADS
---------------------------------------------------------
Title: Phase Differences and Gains between Intensity and Velocity
in Low-Degree Acoustic Modes Measured by SOHO
Authors: Jiménez, Antonio; Roca Cortés, Teodoro; Severino, Giuseppe;
Marmolino, Ciro
1999ApJ...525.1042J Altcode:
Helioseismic instruments aboard SOHO are making possible a more accurate
way of investigating the internal structure of the Sun. Making use of
the different techniques and characteristics of these instruments,
it is possible to measure solar oscillations as variations of the
photospheric velocity (GOLF, MDI) or as irradiance and radiance
fluctuations (VIRGO, MDI). Among the other advantages of observing solar
oscillations simultaneously with different instruments and techniques,
the study of velocity and irradiance measurements provides information
on nonadiabatic effects in the radiatively cooled solar atmosphere. The
thermodynamical properties of the atmosphere determine a phase shift
between intensity and velocity (downward positive) oscillations of
-90° in the case of an adiabatic atmosphere. Here we compute the phase
differences and gains between intensity and velocity acoustic modes
measured by SOHO to quantify the nonadiabatic degree of the solar
atmosphere. After correcting the observed phase differences of the
solar background influence, we find not exactly an adiabactic behavior,
but close to it. Finally, we compare our results with three different
theoretical models of the solar atmosphere, finding the best agreement
with a model that includes turbulent pressure associated with convection
and fluctuations of the superadiabatic temperature gradient. <P />Based
on observations with the VIRGO, GOLF, and MDI instruments on board SOHO.
---------------------------------------------------------
Title: The ARGO-YBJ detector and high energy GRBs
Authors: Bacci, C.; Bao, K. Z.; Barone, F.; Bartoli, B.; Bastieri,
D.; Bernardini, P.; Buonomo, R.; Bussino, S.; Calloni, E.; Cao,
B. Y.; Cardarelli, R.; Catalanotti, S.; Cavaliere, A.; Cesaroni, F.;
Creti, P.; Danzengluobu; D'Ettorre Piazzoli, B.; de Vincenzi, M.;
di Girolamo, T.; di Sciascio, G.; Feng, Z. Y.; Fu, Y.; Gao, X. Y.;
Geng, Q. X.; Guo, H. W.; He, H. H.; He, M.; Huang, Q.; Iacovacci,
M.; Iucci, N.; Jai, H. Y.; Kong, F. M.; Kuang, H. H.; Labaciren; Li,
B.; Li, J. Y.; Liu, Z. Q.; Lu, H.; Ma, X. H.; Mancarella, G.; Mari,
S. M.; Marsella, G.; Martello, D.; Mei, D. M.; Meng, X. R.; Milano,
L.; Morselli, A.; Mu, J.; Oliviero, M.; Padovani, P.; Panareo, M.;
Parisi, M.; Pellizzoni, G.; Peng, Z. R.; Pistilli, P.; Santonico,
R.; Sartori, G.; Sbarra, C.; Severino, G.; Shen, P. R.; Sparvoli, R.;
Stanescu, C.; Su, J.; Sun, L. R.; Sun, S. C.; Surdo, A.; Tan, Y. H.;
Vernetto, S.; Vietri, M.; Wang, C. R.; Wang, H.; Wang, H. Y.; Wei,
Y. N.; Yang, H. T.; Yao, Q. K.; Yu, G. C.; Yue, X. D.; Yuan, A. F.;
Zhang, H. M.; Zhang, J. L.; Zhang, N. J.; Zhang, T. J.; Zhang, X. Y.;
Zhaxisangzhu; Zhaxiciren; Zhu, Q. Q.
1999A&AS..138..597B Altcode:
ARGO-YBJ (Astrophysical Radiation with Ground-based Observatory at
YangBaJing) is a detector optimized to study small size air showers. It
consists of a layer of Resistive Plate Counters (RPCs) covering an
area of ~ 6500 m(2) and will be located in the Yangbajing Laboratory
(Tibet, China) at 4300 m a.s.l. ARGO-YBJ will be devoted to a wide
range of fundamental issues in cosmic rays and astroparticle physics,
including in particular gamma-ray astronomy and gamma-ray bursts
physics in the range 10 GeV /500 TeV. The sensitivity of ARGO-YBJ to
detect high energy GRBs is presented.
---------------------------------------------------------
Title: Observational Constraints on Models of the Solar Background
Spectrum
Authors: Straus, Th.; Severino, G.; Deubner, F. -L.; Fleck, B.;
Jefferies, S. M.; Tarbell, T.
1999ApJ...516..939S Altcode:
We discuss the properties of the solar background signal as observed in
high-quality, l-ν power and phase difference spectra of the continuum
(C), velocity (V), and line intensity (I) fluctuations of the Ni
I 6768 Å line. These spectra were generated from high-resolution
images acquired by the Michelson Doppler Imager on board SOHO. <P />We
confirm that the background signal in the velocity power spectra can be
reproduced by a composite model with two quasi-stationary components,
describing large-scale and small-scale convective motions, and a
periodic component. The line and continuum intensity power spectra
require additional quasi-stationary and periodic components. The
extra quasi-stationary component dominates the intensity and
continuum background signals over the spectral region where the I-V
phase difference spectra show essentially constant negative phase
difference: i.e., below and in between the p-mode ridges (called the
plateau-interridge regime by Deubner et al.). Since the I-V phase
between the p-mode ridges is not random, the solar background beneath
the p-modes must be considered as coherent. We thus speculate that
the negative phase regime may be the manifestation of a correlated
background. Such a background has been proposed to explain the opposite
sense of the asymmetries of the p-mode line profiles in velocity and
brightness oscillations.
---------------------------------------------------------
Title: Probing the {Na} BT I D and {K} BT I lambda 7699 resonance
lines sensitivity to background opacity in late-type stars
Authors: Tripicchio, A.; Gomez, M. T.; Severino, G.; Covino, E.;
García López, R. J.; Terranegra, L.
1999A&A...345..915T Altcode:
We have measured the equivalent width W<SUB>K</SUB> of the K i resonance
line at 7699 Angstroms for a large sample of low activity late-type
stars observed with high spectral resolution and we have verified
that the relation W<SUB>K</SUB> vs. T<SUB>eff</SUB> is monotonically
decreasing, for both dwarf and giant stars. This behaviour is different
from that of the Na I D lines for stars of the same type, which showed
that the relation W<SUB>Na</SUB> vs. T<SUB>eff</SUB> has a maximum for
T<SUB>eff</SUB> ~ 4000 K, which is better defined for giants than for
dwarfs (Tripicchio et al. 1997). The fit of the observed K I equivalent
widths by means of a NLTE spectral line synthesis using conventional
background opacity shows that, for dwarf stars, the adopted models
overestimate the observed W<SUB>K</SUB> for temperatures <~ 4000
K. This result is similar to that discussed for the Na I D lines in our
previous paper. On the other hand, for giant stars with T<SUB>eff</SUB>
<~ 3800 K these models in general underestimate W<SUB>K</SUB>. The
discrepancies between observed and computed W<SUB>K</SUB> and
W<SUB>Na</SUB> for cool stars are much stronger than the variations
due to uncertainties in either atmospheric model or line parameters,
like effective temperature and surface gravity, or Van der Waals
broadening. For M dwarf stars, the most convincing explanation for
the disagreement is the lack of atomic and molecular line opacity in
the adopted models. In fact, a NLTE spectral synthesis including an
additional background opacity reproduces with a good level of accuracy
the equivalent widths, as well as the general shape of the profiles for
both the Na I D and K I lines, in a subsample of early-M dwarfs. Based
on observations collected at the European Southern Observatory (ESO),
La Silla, Chile, and at the McDonald Observatory, Mt. Locke, Texas, USA
---------------------------------------------------------
Title: Space and Time Analysis of the Solar Photospheric Dynamics
at Moderate-l Values
Authors: Oliviero, M.; Severino, G.; Straus, Th.; Jefferies, S. M.;
Appourchaux, T.
1999ApJ...516L..45O Altcode:
A space-time analysis of 36 days' worth of full-disk intensity and
velocity images, obtained by the Global Oscillation Network Group,
is used to produce a high-resolution l-ν phase-difference spectrum
for the spectral range (4<=l<=2000, 0<=ν<=8.3 mHz). This
is the first time a phase-difference spectrum has been produced for
intermediate-l values. The phase differences on the p-mode ridges
are found to linearly increase from ~65° at 2 mHz up to ~95°
at 4.7 mHz. Only near 3.9 mHz are the differences close to 90°,
the theoretically expected phase for adiabatic evanescent waves. The
phases between the ridges exhibit a steplike behavior in frequency with
negative values at low frequency and positive values (greater than 90°)
at high frequency. The negative phase values are consistent with the
extension to low- and moderate-l values of the plateau-interridge regime
discovered by Deubner et al. in 1990. However, positive phase values,
which represent higher phase for the solar background than for the
acoustic modes, were not expected. An understanding of this observed
phase-difference behavior will improve our knowledge of the nature of
the solar background and its interaction with the acoustic p-modes.
---------------------------------------------------------
Title: Observations of the background of solar oscillations
Authors: Straus, Th.; Severino, G.
1998MmSAI..69..615S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modelling the background of the solar oscillations
Authors: Severino, G.; Straus, Th.
1998MmSAI..69..611S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: VAMOS: Velocity and Magnetic Observations of the Sun
Authors: Oliviero, M.; Dolci, M.; Severino, G.; Straus, Th.; Cacciani,
A.; Moretti, P. F.
1998IAUS..185...53O Altcode:
The VAMOS is an instrument, based on two sodium resonance cells,
that acquires full disc Doppler and magnetic images of the sun,
and is operative at the Osservatorio Astronomico di Capodimonte
in Napoli. The importance of a careful control of the two cells
temperatures is emphasized. The two approaches for calibrating velocity
data, based on the knowledge of both the solar rotation and the earth
- sun relative velocity, are applied. Doppler and magnetic data are
used to study some of the effects that solar active regions can have
on global oscillations.
---------------------------------------------------------
Title: VAMOS: velocity and intensity data analysis and first results
on I-V phase difference at low l
Authors: Oliviero, M.; Severino, G.; Straus, Th.
1998MmSAI..69..623O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Power of acoustic oscillations during the solar activity minima
Authors: Gavryuseva, E.; Gavryusev, V.; Severino, G.
1998MmSAI..69..567G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The VAMOS Data Analysis Pipeline
Authors: Oliviero, M.; Severino, G.; Straus, Th.
1998ESASP.418..275O Altcode: 1998soho....6..275O
This poster illustrates the calibration procedure and the spherical
harmonics analysis pipeline developed for the helioseismology data
acquired with the VAMOS (Velocity And Magnetic Observations of
the Sun) instrument. Calibration is performed in essentially three
steps. First, a theoretical solar image is constructed containing
all the contributions to the Earth-Sun line-of-sight relative
velocity for each observing time. Then the observed Doppler images
are fitted to the simulated velocity images. To take into account
the center-to-limb dependence of the solar line profiles, the solar
disk is divided into concentric rings, and in each of these annuli the
observed signal is fitted to the simulated velocity with a second order
polynomial. Finally, the Doppler images are effectively calibrated to
produce residual images in absolute velocity units. The two-dimensional
residual images are decomposed into spherical harmonics and the
resulting coefficients are Fourier transformed to produce the solar
oscillation power spectra. The spherical harmonics analysis routines,
as well as the calibration routines for the VAMOS, have been developed
in IDL, version 4.0.1. We show the l- ν diagram of the velocity and of
the phase difference I-V between intensity and velocity oscillations,
obtained by applying our analysis pipeline to 256 solar Doppler and
intensity images in the NaI D lines acquired once per minute with
the VAMOS in Napoli on February 20, 1997. In particular, the results
regarding the phase difference are interesting because they cover a
range of degrees in l (50-200) that up to now has been little explored.
---------------------------------------------------------
Title: Phase spectra seen from space
Authors: Straus, Th.; Deubner, F. -L.; Fleck, B.; Marmolino, C.;
Severino, G.; Tarbell, T.
1998IAUS..185..455S Altcode:
We discuss preliminary results of a study of the dynamics of the solar
atmosphere including a first space based investigation of k-omega phase
difference spectra between velocity and intensity perturbations. The
data, including simultaneous line shift, line depth, and continuum
intensity measurements at disk center, have been obtained from a MDI
time series in its high resolution mode. Line depth and continuum
intensity are used to calculate the line intensity which is the more
frequently used parameter in phase difference studies. We compare the
results to ground based observations.
---------------------------------------------------------
Title: The Solar Background Spectrum: a Gold Mine of Information
Authors: Severino, G.; Straus, Th.; Jefferies, S. M.
1998ESASP.418...53S Altcode: 1998soho....6...53S
We discuss the properties of the intensity-velocity (I-V) phase
difference spectra generated from 15 hours of high resolution MDI
observations. These spectra provide a spectacular demonstration of the
wealth of untapped information that is available on the nature of the
solar background. In this context, the regimes of coherent phase in
between the modes (“interridges”) and between the f mode and the
Lamb waves (“plateau”), first discovered by Deubner et al. 1990,
is of extreme interest. Understanding the background is important for
several reasons: (i) it contains information about the convection
processes and the wave propagation characteristics of the solar
atmosphere in addition to that provided by the resonant oscillations,
(ii) its interaction with the p-modes may explain why the sense of the
asymmetry in the p-mode line profiles depends on the dynamic variable
observed (Roxburgh & Vorontsov 1997, Nigam et al. 1998), (iii)
estimates for the p-mode line asymmetries are sensitive to errors in
the background determination, and (iv) the background limits the g-mode
and low frequency p-mode visibilities. We also propose a new model
for the solar background which uses the observed phase information:
previous models (e.g. Harvey 1985) are restricted to power information
only. Currently, our model is limited to low frequencies (1 mHz <=
ν <= 3.5 mHz) and intermediate to high ell values, however, it
still demonstrates the potential of the phase information to improve
our estimates of the background components of both the velocity and
intensity signals. A superposition of a correlated background and the
p-mode signal succeeds in reproducing the observed I-V phase transition
from negative (background) to positive (p-mode) values. Moreover,
the model suggests that the background is responsible for the values
of I-V phase, equal to or less than the adiabatic values observed in
the low photosphere (Hill et al, 1991).
---------------------------------------------------------
Title: K-ϖ Phase Spectra Obtained from Space
Authors: Straus, Th.; Fleck, B.; Severino, G.; Deubner, F. -L.;
Marmolino, C.; Tarbell, T.
1998ESASP.417..293S Altcode: 1998cesh.conf..293S
No abstract at ADS
---------------------------------------------------------
Title: The Magneto-Optical Filter in Napoli: Perspectives and Test
Observations
Authors: Moretti, P. F.; Severino, G.; Cauzzi, G.; Reardon, K.;
Straus, T.; Cacciani, A.; Marmolino, C.; Oliviero, M.; Smaldone, L. A.
1997ASSL..225..293M Altcode: 1997scor.proc..293M
An observing station based on the Magneto-Optical-Filter (MOF)
technology is being installed at Osservatorio Astronomico di
Capodimonte, in Napoli. In this paper, the main characteristics and
goals of this new instrument are discussed, and several velocity and
magnetic observations from a test campaign are shown.
---------------------------------------------------------
Title: The NaI resonance lines as a spectroscopic test of late-type
stellar atmospheres.
Authors: Tripicchio, A.; Severino, G.; Covino, E.; Terranegra, L.;
Garcia Lopez, R. J.
1997A&A...327..681T Altcode:
We have tested current models for the atmospheres (including photosphere
and low chromosphere) of late-type stars using the D resonance lines
of neutral sodium as a diagnostic. To this end, we have measured
the equivalent widths of the D lines for a sample of 39 dwarf and
45 giant late-type stars observed with high spectral resolution. We
constructed photospheric models over a grid in effective temperature
and surface gravity spanning the spectral types F to M, and luminosity
classes V and III of the sample stars. The model photospheres were
extended into the chromosphere by assuming a suitable scaling from
the Sun, and theoretical Nai D equivalent widths were computed over
the grid of models including the deviations from local thermodynamic
equilibrium. By taking into account both the experimental errors and
the possible variations of stellar parameters (effective temperature,
surface gravity, sodium abundance and microturbulence), the comparison
between observed and computed equivalent widths allows us to state that
the model atmospheres we have used can reproduce the observations for
the two luminosity classes and for all the spectral types except for
the M-type stars. We have discussed the importance of line blanketing
in the spectral analysis of these stars, but at present we cannot
conclude that this effect would reduce the discrepancy.
---------------------------------------------------------
Title: Active region effects on solar irradiance at NA I D lines
Authors: Marmolino, C.; Oliviero, M.; Severino, G.; Smaldone, L. A.
1997A&AS..125..381M Altcode:
The possibility to detect solar oscillations in the low frequency domain
depends crucially on the power contrast among the oscillation signal and
other time dependent signals in the same frequency range. The signal to
noise ratio is increased by our ability to understand and remove solar
sources of noise. In measurements of the mean Doppler velocity shift of
the integrated solar disk, the solar noise has a line component spectrum
with a major peak at 13.1 days, and a second less prominent peak at 27.2
days. Active region modulation is believed almost completely responsible
for this signal. We develop simulations of the flux and velocity
fluctuations produced by different solar active region distributions,
based on an analytical description of their action. From a grid of
models of active regions and from their spatial distribution over the
disk, we calculate the synthetic flux profile in the Na I D<SUB>1</SUB>
line and determine the velocity measure of a resonance spectrometer. Our
velocity results are compared with the offset velocities from the IRIS
network. There is a rather good agreement between the observed and
computed velocities, and the plage contribution to the noise appears to
be dominant. The simulation allows to test calibration procedures and
to study the effect on the spurious velocities of different parameters,
such as the intensity thresholds used to determine the areas of spots
and plages, and the contrast of the active regions. In particular, we
find that the inclusion of intrinsic line shifts in plages can change
strongly both the amplitude and the shape of the simulated signal,
and then may be an important source of uncertainty for the simulation.
---------------------------------------------------------
Title: The ARGO full Coverage Detector
Authors: Bacci, C.; Bartoli, B.; Barone, F.; Dai, Behzhong; Bernardini,
P.; Calloni, E.; Cardarelli, R.; Catalanotti, S.; Cavaliere, A.;
Cessaroni, F.; Xu, Chunxian; Creti, P.; Banzengluobu; D'Ettorre
Pizaaoli, B.; De Vincenzi, M.; Di Sciascio, G.; Cai, Dong; Grado, A.;
Yu, Guangce; Kuang, Haohuai; Jia, Hunayu; He, Huilin; He, Huihai; Guo,
Hongwei; Lee, Huidong; Iacovacci, M.; Iucci, N.; Li, Jinyu; Le, Meng;
Marmolino, C.; Manearella, G.; Mari, S. M.; Martello, D.; Morselli,
A.; Milano, L.; Oliviero, M.; PAdovani, P.; Panareo, M.; Parisi, M.;
Shen, Peiruo; Pistilli, P.; Saavedra, O.; Santonico, R.; Severino,
G.; Sparvolli, R.; Stanescu, C.; Storini, M.; Surdo, A.; Vernetto,
S.; Villoresi, G.; Zhao, Xin; Zhang, Xueyao; Jiang, Yinlin; Chen,
Yongzhong; Tan, Youheng; Fu, Yu; Feng, Zhenyong
1997ICRC....5..265B Altcode: 1997ICRC...25e.265B
No abstract at ADS
---------------------------------------------------------
Title: ARTHEMIS: The Archive Project for the IPM and THEMIS
Authors: Reardon, K.; Severino, G.; Cauzzi, G.; Gomez, M. T.; Straus,
T.; Russo, G.; Smaldone, G.; Marmolino, C.
1997ASPC..118..398R Altcode: 1997fasp.conf..398R
We describe the plan for ARTHEMIS, the italian archive for THEMIS, from
the point of view of the prospective users of the archive. This archive
is designed to store the data from the Italian Panoramic Monochromator
(IPM) instrument installed on THEMIS as well as the full-disk images
obtained by the telescope. We break the expected users down into
seven categories: a) prospective IPM users; b) campaign planners; c)
data analysts, d) external collaborators; e) instrument monitors, f)
archival observers; and g) the general public.
---------------------------------------------------------
Title: ARTHEMIS: The archive project for the Italian Panoramic
Monochromator
Authors: Reardon, K.; Severino, G.; Cauzzi, G.; Gomez, M. T.; Straus,
T.; Russo, G.; Smaldone, L. A.; Marmolino, C.
1997MmSAI..68..499R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous Doppler and magnetic solar maps from a MOF
installed at the Osservatorio di Capodimonte
Authors: Cacciani, A.; Marmolino, C.; Moretti, P. F.; Oliviero, M.;
Severino, G.; Smaldone, L. A.
1997MmSAI..68..467C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Li I resonance lines in a solar active region.
Authors: Cauzzi, G.; Gomez, M. T.; Severino, G.
1997joso.proc...57C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The NA I resonance lines as a spectroscopic test of cool
stars atmospheres
Authors: Tripicchio, A.; Covino, E.; Gomez, M. T.; Severino, G.;
Terranegra, L.
1996ASPC..109..575T Altcode: 1996csss....9..575T
No abstract at ADS
---------------------------------------------------------
Title: Active regions effects on global oscillation measurements.
Authors: Marmolino, C.; Oliviero, M.; Severino, G.; Smaldone, L. A.
1996joso.proc..160M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Noise Simulations in Velocity
Authors: Marmolino, C.; Oliviero, M.; Severino, G.; Smaldone, L. A.
1995ESASP.376b.407M Altcode: 1995help.confP.407M; 1995soho....2..407M
No abstract at ADS
---------------------------------------------------------
Title: Galactic evolution of beryllium. I. NLTE effects and accuracy
of beryllium abundances in metal-poor stars.
Authors: Garcia Lopez, R. J.; Severino, G.; Gomez, M. T.
1995A&A...297..787G Altcode:
We have investigated in detail the uncertainties in deriving
beryllium abundances for metal-poor stars from the BeII resonance
doublet at λ 3131A. These uncertainties are related to the quality
of the observations, the physical data used, and the adopted stellar
parameters. We have taken into account the NLTE effects on the lines
formation for the Sun and a sample of six stars with metallicities
in the range -0.4>=[Fe/H]>=-2.7. NLTE and LTE calculations give
nearly the same equivalent widths for the Sun, confirming the previous
results of Chmielewski et al. (1975). The extension of the NLTE analysis
to metal-poor stars indicates that the absolute NLTE corrections
to the beryllium abundances are lower than 0.1dex. The six selected
metal-poor stars have been previously observed by other authors, and
show a dispersion of ~0.2-0.5dex in their Be abundances (which can be
as large as ~1dex when including the error bars). Our analysis of these
stars provides consistent abundances with uncertainties in the range
0.2-0.3dex, which are basically related to the errors in the adopted
stellar parameters (mainly surface gravity). These uncertainties and
NLTE corrections <~0.1dex should be taken into account when using
LTE beryllium abundances for primordial nucleosynthesis and Galactic
chemical evolution studies.
---------------------------------------------------------
Title: Modelling umbrae
Authors: Severino, G.; Gomez, M. -T.; Caccin, B.
1994ASIC..433..169S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Signatures of proton beams in the Ly-alpha profile: sensitivity
of the diagnostics
Authors: Messerotti, M.; Gomez, M. T.; Severino, G.
1994LNP...432..279M Altcode: 1994LNPM...11..279M
We modelled the effects on the Ly-alpha emission caused by an
accelerated proton beam impacting onto the chromosphere to estimate its
detection threshold as an effective diagnostics for protons. Chosen
a model chromosphere and a HI model atom with 3 bound levels plus a
continuum, we computed the background Ly-alpha flux profile and the
superthermal contribution in the red wing due to the beam. The profiles
computed for different model parameters show that a source with a radius
exceeding 1000 km and producing a total proton flux greater than 5 x
10^10 erg cm^-2 s^-1 should be detectable in irradiance observations.
---------------------------------------------------------
Title: Phases and amplitudes of acoustic-gravity waves. 2: The
effects of reflection
Authors: Marmolino, C.; Severino, G.; Deubner, F. -L.; Fleck, B.
1993A&A...278..617M Altcode:
We study wave reflection caused by the temperature stratification
of the solar atmosphere, assumed to be a succession of two layers
of different temperatures and radiative decay times. Considering
waves which propagate energy upward in the atmosphere, we compute
the complex amplitude reflection and transmission coefficients and
investigate the effects that reflection introduces on the phases of
acoustic-gravity waves. In the evanescent region of the k<SUB>x</SUB>
- omega diagram, between the Lamb waves and the acoustic cut-off
frequency, the reflection coefficient is small, in particular zero on
the fundamental mode. Therefore, in this region, the reflected wave
has a small amplitude and its superposition to the incident wave does
not affect the latter in a significant way. In particular, the T - V
phase differences of the total wave are very similar to those of the
incident wave. Furthermore, a heruisitic formula is presented which
describes the observed coexistence of two different phase regimes
between velocity and intensity oscillations in the evanescent area
above the fundamental mode.
---------------------------------------------------------
Title: The formation of the alkali resonance lines in cool
atmospheres. I. NaI and KI in a sunspot umbra
Authors: Caccin, B.; Gomez, M. T.; Severino, G.
1993A&A...276..219C Altcode:
We have studied the formation of the Na I and K I resonance lines
in a sunspot umbra looking at their diagnostic value. <P />We have
computed different cross-sections and rates for the excitation
of the alkali atoms by collisions with neutral hydrogen atoms in
addition to electrons, and we have evaluated their effects on the
emergent line profiles. <P />The main results of the line synthesis,
which allowed for different temperature structures, line blend, the
Zeeman broadening produced by a constant vertical magnetic field, and
a possible overcorrection for stray light of the observed spectrum,
are that: <P />i) the comparison between the observed and the computed
inner wings of the sodium profiles suggests that the umbral upper
photosphere is cooler than in a standard model; <P />ii) there is
no satisfactory fit of the reversed and asymmetric line cores of the
sodium and potassium resonance lines in the umbral spectrum.
---------------------------------------------------------
Title: Atmospheric structure of sunspots
Authors: Gomez, M. T.; Caccin, B.; Severino, G.
1993MmSAI..64..519G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The importance of collisional excitations by HI in cool
atmospheres
Authors: Severino, G.; Caccin, B.; Gomez, M. T.
1993MmSAI..64..565S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar astronomy: the GOLF experiment on board of SOHO
Authors: Severino, G.; Gomez, M. T.; Andretta, V.; Marmolino, C.
1993MmSAI..64..790S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High S/N NaI D line profiles in late-type MS stars and their
importance for stellar modelling
Authors: Covino, E.; Gomez, M. T.; Severino, G.; Franchini, M.
1993ASPC...40..190C Altcode: 1993IAUCo.137..190C; 1993ist..proc..190C
No abstract at ADS
---------------------------------------------------------
Title: The center-to-limb variations of four Ca i lines in the
photospheric spectrum at λ6500
Authors: Ambruoso, P.; Marmolino, C.; Gomez, M. T.; Severino, G.
1992SoPh..141...35A Altcode:
We study the center-limb (CL) variation of the average profiles of four
Ca I lines near λ6500 and compare these observations with synthetic
data obtained from several line formation models having different
thermal structures, line parameters, LTE and non-LTE conditions,
and micro and macroturbulence values, to assess the formation
characteristics of our Ca I lines in the solar photosphere.
---------------------------------------------------------
Title: Optical signatures of beam-plasma interactions in the solar
atmosphere: simulation results
Authors: Messerotti, M.; Gomez, M. T.; Severino, G.
1992pdta.proc...77M Altcode:
On the Sun acceleration processes occurring in flaring regions during
reconnection can originate particle beams. Driven by the magnetic
topology of the site, such beams can travel both upwards to the corona,
where electron beams are known to produce observable radio emission
through beam instability, and downwards to the chromosphere, where
electron beams interact with the ambient plasma to procedure radio waves
and X-rays depending on their energy spectrum and proton beams trigger
nuclear reactions which results in gamma-ray lines formation. In reality
no clear diagnostics for proton (or neutral) beams generation has been
identified yet. A theoretical model, not yet confirmed by experimental
evidences, provides the appearance of a non-thermal emission in the red
wing of the Ly-alpha line due to the process a proton beam undergoes
after impacting upon the chromospheric plasma. If detectable, this
emission could be a good indicator for proton beams formation. In
the present work we performed some simulations of such a process with
different parameters for the impacting proton beams in order to define
a detectability threshold of the non-thermal effect. Parameters' range
is discussed in the frame of possible observations from space and the
extension of the simulations to the neutral beam case is considered.
---------------------------------------------------------
Title: Photospheric dynamics and the NLTE formation of the solar K
I 769.9 NM line
Authors: Gomez, M. T.; Severino, G.; Rutten, R. J.
1991A&A...244..501G Altcode:
Earlier analyses of the K I 769.9 nm resonance line are extended
as a diagnostic of dynamical phenomena in the solar photosphere by
evaluating the effects of dynamical variations on departures from LTE
in the K I spectrum. Representative models for the solar granulation
and the solar five-minute oscillation are used to estimate dynamical
NLTE departures in the K I populations and to compare these to standarad
plane-parallel NLTE modeling. Various NLTE mechanisms operate together
in K I simultaneously with fortuitous cancellations; the resulting
population departures vary less than 30 percent between dynamical
perturbations. These results validate the assumption of departure
invariance, i.e., adopting NLTE population departure coefficients from
a standard static model for use in dynamical perturbations, as a good
first-order approximation in K I 769.9 nm formation studies.
---------------------------------------------------------
Title: Book-Review - Solar and Stellar Granulation
Authors: Rutten, R. J.; Severino, G.; Rudiger, G.
1991AN....312..147R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Phases and amplitudes of acoustic-gravity waves. I - Upward
and downward solutions
Authors: Marmolino, C.; Severino, G.
1991A&A...242..271M Altcode:
A study is presented of the phases and amplitudes of acoustic-gravity
waves in the kx-omega diagram. Waves which propagate energy both upward
and downward in the solar atmosphere are considered. The wave model
considers linear perturbations in a compressible medium assumed to be
a perfect gas stably stratified at uniform temperature and radiatively
damped. The kx-omega diagrams are also displayed for the temperature
and pressure amplitudes relative to velocity. The results from the
model are discussed and compared with recent observations of the phase
relations between velocity and brightness oscillations.
---------------------------------------------------------
Title: Collisional Broadening and Shift of the Alkali Resonance Lines
Authors: Andretta, V.; Gomez, M. T.; Severino, G.
1991SoPh..131....1A Altcode:
We use the 6-8-12 interatomic potential, with a suitable scaling
for the relevant atomic radii, to reproduce the measured broadening
and shift of the alkali resonance lines perturbed by noble gases,
at temperatures of ∼ 500 K.
---------------------------------------------------------
Title: Formation of the KI 7699A Line in Sunspots
Authors: Caccin, B.; Carlsson, M.; Gomez, M. T.; Severino, G.
1991ASIC..341..415C Altcode: 1991sabc.conf..415C
No abstract at ADS
---------------------------------------------------------
Title: Dynamics of the solar atmosphere. IV - Evanescent waves of
small amplitude
Authors: Deubner, F. -L.; Fleck, B.; Marmolino, C.; Severino, G.
1990A&A...236..509D Altcode:
The phase spectra of velocity and brightness perturbations in the quiet
photosphere have been studied in the evanescent domain of the k-omega
diagram. A regime of low-amplitude evanescent motions, occupying a
large sector of the diagnostic diagram bordered by the Lamb and the
fundamental mode, has been discovered. This regime forms a continuum
in the k-omega plane, in contrast to the 5-min oscillations. Beyond the
fundamental mode, it extends to much higher frequencies in between the
power ridges of the resonant p-modes. It is suggested that the observed
V-I phase is characteristic of evanescent waves, whose progressive
part carries energy downward, and that a continuum of such waves is
produced through scattering of ordinary resonant p-modes at higher
levels in the atmosphere.
---------------------------------------------------------
Title: On the 5-MINUTE Photospheric Oscillation and its Modeling
Authors: Marmolino, C.; Severino, G.
1990IAUS..138..251M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Solar and Stallar Granulation
Authors: Rutten, R. J.; Severino, G.
1989Sci...246..137R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The signature of the 5-minute photospheric oscillation on
the solar spectral line profiles
Authors: Marmolino, C.; Severino, G.
1989MmSAI..60..181M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar and stellar granulation
Authors: Rutten, Robert J.; Severino, Giuseppe
1989ASIC..263.....R Altcode: 1989ssg..conf.....R
No abstract at ADS
---------------------------------------------------------
Title: Granulation and the NLTE Formation of K I 769. 9
Authors: Gomez, M. T.; Severino, G.; Rutten, R. J.
1989ASIC..263..565G Altcode: 1989ssg..conf..565G
No abstract at ADS
---------------------------------------------------------
Title: The solar spectral lines as a diagnostic tool of the
atmospheric structure: numerical advances and new applications
Authors: Gomez, M. T.; Severino, G.
1989MmSAI..60..177G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The granulation sensitivity of helioseismology lines.
Authors: Rutten, R. J.; Bruls, J. H. M. J.; Gomez, M. T.; Severino, G.
1988ESASP.286..251R Altcode: 1988ssls.rept..251R
The authors address the sensitivity of the Ni I 676.78 nm GONG line and
the K I 769.9 nm resonance line to the temperature fluctuations present
in the solar granulation. The temperature contrasts due to granulation
are probably small in the upper photosphere where the cores of these
two helioseismology lines are formed. However, the cores are sensitive
also to the granulation temperature contrasts in the deep photosphere,
through non-local NLTE effects in their formation. The largest effects
are due to the ultraviolet radiation field, which is strongly modulated
by the granulation in the deep layers where it escapes and carries these
contrasts upwards to the line formation height. The authors discuss
the resulting NLTE mechanisms and their influence on the two lines.
---------------------------------------------------------
Title: Solution of Radiative Transfer Problems with non-LTE and
Velocity Fields in the Solar Atmosphere
Authors: Gomez, M. T.; Severino, G.
1988sca..conf...62G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fe II lines in the presence of photospheric oscillations
Authors: Marmolino, C.; Roberti, G.; Severino, G.
1988ASSL..138..217M Altcode: 1988pffl.proc..217M; 1988IAUCo..94..217M
The synthesis of the Fe II 6516 A line in the solar photosphere in the
presence of granulation and five-minute oscillation is described. The
asymmetry of the spatially resolved profiles in the presence of
granulation is much stronger than that of the mean, unresolved
profile. There is a blueshift of the spatially averaged line profile
corresponding to a velocity of 360 m/s in the center of gravity. The
line bisector produced by the five-minute oscillation are plotted as
a function of time. When both granulation and five-minute oscillation
are present, the general behavior of the spatially averaged line
bisector vs. time is just the temporal fluctuation of the spatially
mean C-shape due to the granulation. When granulation is present, the
blue flank in the line profiles oscillates with a velocity amplitude
lower than the red flank does.
---------------------------------------------------------
Title: Temporal variations of solar spectral line profiles induced
by the 5-minute photospheric oscillation
Authors: Gomez, M. T.; Severino, G.; Marmolino, C.; Roberti, G.
1987A&A...188..169G Altcode:
The authors simulated the variations induced by the 5 min photospheric
oscillation on the line profiles. They found that a phase lag of the
order of 150 degree between temperature and velocity wave perturbations
can explain the observed differences between the oscillations of the
line flanks at residual intensity levels I/I<SUB>c</SUB> < 0.7. Such
a phase relation in the 5 min oscillation differs from that of the
adiabatic case in which the temperature and pressure fluctuations are 90
degrees out of phase with respect to the velocity. It is shown that a
simple model of radiative damping in the solar photosphere can produce
the required phase lag between temperature and velocity. Finally,
it is also shown that the granulation can affect differentially the
oscillations of the line flanks. This effect, however, does not fit
the observed behaviour of the flank oscillations.
---------------------------------------------------------
Title: Broadening and shift of Fe i lines perturbed by atomic
hydrogen
Authors: Gomez, M. T.; Marmolino, C.; Roberti, G.; Severino, G.
1987SoPh..112..227G Altcode:
The broadening and shift parameters for a number of FeI lines perturbed
by atomic hydrogen are computed using the interatomic potential due to
Hindmarsh et al. (1967, 1970). It is also shown that the rms radius
and the effective radius of the radiating atom, which determine the
force constants in the interatomic potential, can be simply related
each other, depending on the orbital quantum number of the atomic level.
---------------------------------------------------------
Title: Line asymmetries and shifts in the presence of granulation
and oscillations: The CLV of the K i 7699 resonance line
Authors: Marmolino, C.; Roberti, G.; Severino, G.
1987SoPh..108...21M Altcode:
We study the effects of both the solar granulation and short-period
oscillations on the solar profile of the KI 7699 resonance line and
its center-to-limb variations.
---------------------------------------------------------
Title: Velocity Variations of Small Scale Solar Structures, and
Physical Problems Related to the Overshoot Layers
Authors: Nesis, Anastasios; Severino, Giuseppe
1987LNP...291..154N Altcode: 1987csss....5..154N
We compare our results about the variation of the vertical and
horizontal velocity with height in the Solar photosphere with the
theoretical granulation model by Nelson. The comparison shows, (i)
that the mixing length derived by Nelson corresponds to the height
of the overshoot-layers derived by Nesis, and (ii) that the large
spatial structures with large horizontal velocities dominate the
continuum layers.
---------------------------------------------------------
Title: Velocity Variations of Small Scale Solar Structures, and
Physical Problems Related to the Overshoot Layers
Authors: Nesis, A.; Severino, G.
1987MitAG..70..330N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Differences between Line Bisectors in Quiet and
Active Sun
Authors: Marmolino, C.; Roberti, G.; Severino, G.
1987rfsm.conf...30M Altcode:
The asymmetry and shift of solar lines show systematic variations
between quiet and active regions. Marmolino et al. (1984, 1986) studied
the effects produced by photospheric motions (waves and granulation)
on the K I 7699 Å line in the quiet Sun. In this paper the authors
extend this study to the synthesis of line bisectors in plages.
---------------------------------------------------------
Title: The effects of acoustic-gravity waves on the K i 7699 line
Authors: Severino, G.; Roberti, G.; Marmolino, C.; Gomez, M. T.
1986SoPh..104..259S Altcode:
We examine the effects of acoustic-gravity waves with long and short
periods on the solar profile of the K I7699 line using a dynamic model
of line formation.
---------------------------------------------------------
Title: Line Asymmetries and Shifts in Presence of Granulation and
Oscillations - the CLV of the KI7699 Resonance Line
Authors: Marmolino, C.; Roberti, G.; Severino, G.
1985tphr.conf...89M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Line asymmetries and shifts in presence of granulation and
oscillations: the CLV of the K I 7699 resonance line.
Authors: Marmolino, C.; Roberti, G.; Severino, G.
1985MPARp.212...89M Altcode:
The authors study the effects of both the solar granulation and a
monochromatic acoustic-gravity wave on the solar profile of the K I
7699 resonance line and its center-to-limb variations (CLV).
---------------------------------------------------------
Title: The response of the line KI 7699 to the solar oscillations
Authors: Marmolino, C.; Roberti, G.; Severino, G.; Vazquez, M.;
Woehl, H.
1984ESASP.220..191M Altcode: 1984ESPM....4..191M
The time behavior of the KI 7699 line profile in presence of
acoustic-gravity waves with periods of 300, 180, and 30 sec was
studied. The response of the line to the waves depends strongly on
the period and is not linear for the 30 sec wave. The height increase
of the amplitude in the longer period waves explains the observed
anticorrelation between line asymmetry and line core shift. The time
averaged profile for the 30 sec wave has a red shifted line core. This
could account for the lowest part of the C shaped solar bisectors.
---------------------------------------------------------
Title: CA II K emission diagnostics. I - The widths and the strengths
in a one-dimensional model
Authors: Marmolino, C.; Severino, G.
1983A&A...127...33M Altcode:
The authors modeled the widths and the strengths of the Ca II K
emission from a one-dimensional atmosphere in terms of a limited set of
parameters. Partial frequency redistribution (PRD) in the scattering
process was correctly accounted for. The emission characteristics
depend generally on several model parameters. However the dependence
on chromospheric microturbulence appears to fit easily the observed
behaviour of the K<SUB>2</SUB> peak separation, W<SUB>2</SUB>, and of
the full width at half-maximum, W<SUB>0</SUB>. The authors remark that
emission in the core of the K line can occur as a PRD effect, without
any chromospheric temperature rise, and discuss some implications of
this event.
---------------------------------------------------------
Title: On the widths of the CA II K emission in late-type stars
Authors: Severino, G.
1982A&A...109...90S Altcode:
Consideration is given to the parameters controlling the widths of the
emission core in the Ca II K line found in most late-type stars. A
model of Ca II K core formation which takes into account partial
redistribution effects in the scattering process is developed and used
to calculate emission widths as a function of a limited set of stellar
parameters. It is found that the K2 peak separation and the full width
at half maximum of the core feature depend essentially on the amplitude
of chromospheric turbulent velocities, while the K1 dip separation
depends on partial redistribution effects as well as turbulent velocity
amplitude. Results also cast doubt on the previously claimed dependence
of the K1 dip on the square root of the temperature minimum.
---------------------------------------------------------
Title: Magnetic Fine-Structures and Granular Velocities
Authors: Caccin, B.; Falciani, R.; Gomez, M. T.; Marmolino, C.;
Roberti, G.; Severino, G.; Smaldone, L. A.
1981SSRv...29..373C Altcode:
In the last years we have gained some experience in the diagnostics
of small-scale structures, both on the interpretative and on the
observational point of view. We report here the conclusions and the
suggestions for future developments attained in two main fields of
interest.
---------------------------------------------------------
Title: The third central moment of photospheric lines as a measure
of velocity gradients and line shifts
Authors: Marmolino, C.; Severino, G.
1981A&A...100..191M Altcode:
The significance of the third central moment (M3) of photospheric
line profiles as an indicator of velocity, temperature and pressure
perturbations is analyzed. A linear inversion method is applied to the
third central moments of a set of synthetic lines computed using the
temperature structures of the B2 and D2 models of Altrock and Musman
(1976) for the granular and intergranular atmospheres, respectively,
in order to derive mean photospheric velocity gradients. It is found
that for data taken with infinite spatial resolution, M3 is a nearly
linear measure of the velocity gradients, whereas at finite resolution
it is essentially determined by the different weights of the shifted
granular and intergranular line components. Results also suggest a
means of disentangling velocity gradients and the horizontal integration
of inhomogeneities.
---------------------------------------------------------
Title: On the continuum diagnostics of photospheric faculae.
Authors: Caccin, B.; Severino, G.
1979ApJ...232..297C Altcode:
Maps reproducing the intensity contrast in the continuum (wavelength of
5000 A) are obtained for a facular point at different positions on the
solar disk, and the contribution function of the emergent intensity is
analyzed for several representative lines of sight. A two-component
axially symmetric model is used whose thermodynamic structure is
derived from that of a magnetostatic flux tube representative of a
small filigree element. The wall of the flux tube appears to have
a dominant role, with respect to the interior, in determining the
observable contrast: Hence the reliability of the semiempirical models
obtained by inversion of continuum data is seriously questioned. The
center-to-limb variation of the average contrast does not vary with
the shape of the flux tube (a cylinder and a funnel are considered),
the only difference being that the map at mu equals 1.0 for the
funnel shows a thin very bright ring. The two-component approximation,
neglecting the precise structure of the wall, causes an overestimate
of the contrast; a discussion of this effect is given.
---------------------------------------------------------
Title: Response functions and contribution functions of photospheric
lines.
Authors: Caccin, B.; Gomez, M. T.; Marmolino, C.; Severino, G.
1977A&A....54..227C Altcode:
An attempt is made to obtain the response function (RF) of a
photospheric Fraunhofer line by solving the equation of radiative
transfer in LTE using an appropriate perturbation method. A first-order
expression for the RF is derived with which effects of arbitrary
perturbations in thermodynamic quantities or velocity-field parameters
on emergent line intensity can be evaluated. Perturbations considered
to be amenable to such treatment include line-opacity Doppler shifts
due to velocity fields, microturbulence variations, and temperature
variations at constant electron density. Some examples of RFs for
photospheric lines are presented, and an attempt is made to define
the contribution function (CF) of a line depression in full analogy
with that of the emergent intensity. It is noted that a CF should not
be employed in place of the appropriate RF to predict the sensitivity
of a Fraunhofer line to a perturbation at a given depth.
