Author name code: severino ADS astronomy entries on 2022-09-14 author:"Severino, Giuseppe" ------------------------------------------------------------------------ Title: The Structure and Evolution of the Sun Authors: Severino, Giuseppe Bibcode: 2017ses..book.....S Altcode: No abstract at ADS Title: The Intensity-Velocity Phase Spectra of Evanescent Oscillations and Acoustic Sources Authors: Severino, G.; Straus, T.; Oliviero, M.; Steffen, M.; Fleck, B. Bibcode: 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. Title: Acoustic-Gravity Waves in the Solar Atmosphere: Comparing Hinode/SP Observations with Numerical Simulations Authors: Fleck, Bernard; Straus, T.; Severino, G. Bibcode: 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 CO5BOLD. 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 Mm3, the lower resolution simulation a cube of size 11.2 x 11.2 x 5.2 Mm3. 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. Title: The intensity effect in magneto-optical filters Authors: Oliviero, M.; Severino, G.; Berrilli, F.; Moretti, P. F.; Jefferies, S. M. Bibcode: 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. 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. Bibcode: 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. Title: High-frequency Waves in Numerical Simulations of the Solar Atmosphere Authors: Fleck, Bernard; Straus, T.; Severino, G. Bibcode: 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. Title: What does the Sun suggest about global oscillation amplitudes in solar-like stars? Authors: Severino, G.; Straus, Th.; Oliviero, M.; Steffen, M. Bibcode: 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. Title: Planning magneto-optical filters for the study of magnetic oscillations of the Sun Authors: Oliviero, M.; Severino, G.; Esposito, G. Bibcode: 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. 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. Bibcode: 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. Title: High frequency waves in the solar atmosphere?. Authors: Fleck, B.; Straus, T.; Carlsson, M.; Jefferies, S. M.; Severino, G.; Tarbell, T. D. Bibcode: 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 0o 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 CO5BOLD). 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. 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. Bibcode: 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. Title: On The Interpretation Of Hinode NFI Filtergrams Authors: Fleck, Bernard; Straus, T.; Jefferies, S. M.; Severino, G.; Tarbell, T. D. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. Title: Velocity and Intensity Power and Cross Spectra in Numerical Simulations of Solar Convection Authors: Severino, G.; Straus, T.; Steffen, M. Bibcode: 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. 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 Bibcode: 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-2. 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. Title: Accurate Intensity Velocity Phase Difference in the Potassium Resonance Line Obtained with VAMOS Authors: Magrı, M.; Oliviero, M.; Severino, G. Bibcode: 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. 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. Bibcode: 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. Title: Simulation of Magneto-Optical Filter Transmission Profiles Authors: Severino, G.; Oliviero, M.; Landi Degl'Innocenti, E. Bibcode: 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. Title: Resonant Oscillation Modes and Background in Realistic Hydrodynamical Simulations of Solar Surface Convection Authors: Straus, T.; Severino, G.; Steffen, M. Bibcode: 2006ESASP.617E...4S Altcode: 2006soho...17E...4S No abstract at ADS 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. Bibcode: 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. Title: A new method to calibrate MOF-based instruments Authors: Magrí, M.; Oliviero, M.; Severino, G. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. Title: An Observational Method to Prevent Cross-Talk and Calibrate Mof-Based Instruments Authors: Magrı, Maria; Oliviero, Maurizio; Severino, Giuseppe Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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. Title: CASTEL: Capodimonte Antarctic Solar TELescope Authors: Moretti, P. F.; Severino, G. Bibcode: 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). Title: Atmospheric Gravity Waves Authors: Severino, G.; Oliviero, M.; Straus, Th.; Ulrich, R. K. Bibcode: 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. 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 Bibcode: 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. Bibcode: 2003MSAIS...2..181S Altcode: CONCORDIASTRO is the Nice-Napoli joint project for site testing of the Dome C for solar and stellar astronomy in the visible. CONCORDIASTRO/Italy is the solar physics part of this project, whose the Napoli team has the principal responsibility. Beyond the well-known interest for the helioseismology, CONCORDIASTRO/Italy pointed out that, because of its special atmospheric conditions, Dome C promises to be one of the best sites on Earth to perform high-resolution solar physics. Here we review the basis for this statement and the solar observations program planned by CONCORDIASTRO/Italy. Title: EGSO - The European Grid of Solar Observations Authors: Reardon, K.; Antonucci, E.; Giordano, S.; Severino, G.; Messerotti, M.; EGSO Team Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 2000NIMPA.443..342B Altcode: A 50 m2 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. Bibcode: 2000MmSAI..71..999O Altcode: No abstract at ADS Title: Calibration of VAMOS Magnetic Data Authors: Vogt, E.; Oliviero, M.; Severino, G.; Straus, T. Bibcode: 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. Bibcode: 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 Bibcode: 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.

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. Bibcode: 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. Bibcode: 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.

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. Bibcode: 1999A&A...345..915T Altcode: We have measured the equivalent width WK 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 WK vs. Teff 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 WNa vs. Teff has a maximum for Teff ~ 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 WK 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 Teff <~ 3800 K these models in general underestimate WK. The discrepancies between observed and computed WK and WNa 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. Bibcode: 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. Bibcode: 1998MmSAI..69..615S Altcode: No abstract at ADS Title: Modelling the background of the solar oscillations Authors: Severino, G.; Straus, Th. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1998MmSAI..69..567G Altcode: No abstract at ADS Title: The VAMOS Data Analysis Pipeline Authors: Oliviero, M.; Severino, G.; Straus, Th. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 D1 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1996joso.proc..160M Altcode: No abstract at ADS Title: Magnetic Noise Simulations in Velocity Authors: Marmolino, C.; Oliviero, M.; Severino, G.; Smaldone, L. A. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 kx - 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. Bibcode: 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.

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.

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:

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;

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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1990IAUS..138..251M Altcode: No abstract at ADS Title: Book-Review - Solar and Stallar Granulation Authors: Rutten, R. J.; Severino, G. Bibcode: 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. Bibcode: 1989MmSAI..60..181M Altcode: No abstract at ADS Title: Solar and stellar granulation Authors: Rutten, Robert J.; Severino, Giuseppe Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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/Ic < 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 K2 peak separation, W2, and of the full width at half-maximum, W0. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.