Xing Li

Minor Ions in the High Speed Solar Wind,

University of Science & Technology of China, 1998
 

We present the results of a parameter study of the influence of heavy ions on the background solar wind, choosing doubly ionized helium, or alpha particles, and O+6, as examples. Using a three-fluid solar wind model, we keep the input parameters to the electrons and protons unchanged, and investigate the effects of changing the input energy flux to the heavy ions and their coronal abundance, i.e. their abundance at 1 R_sun, on the background electron-proton solar wind. Our results confirm earlier studies that alpha particles can have a dramatic effect on the thermodynamic and flow properties of the protons in the solar wind. The maximum coronal abundance for which the changes in the energy input to the heavy ions has no effect on the protons is 5*10^-4 for the alphas, and 5*10^-5 for the oxygen ions, which are well below the photospheric values. For larger coronal abundances, the sensitivity of the changes of the flow speed and proton mass flux to changes in the energy input to the heavy ions increases sharply with increasing abundance. When the heavy ions are not heated, the increase in the coronal abundance leads to an increase in flow speed, a decrease in proton mass flux, and an increase in proton temperature at 1 AU. However, as the heat input to the heavy ions increases, the dependence of these parameters on the abundance goes through a transition and starts to follow the opposite pattern, namely a decrease in flow speed and proton temperature at 1 AU, and an increase in proton mass flux. This study shows that, for currently known photospheric elemental abundances, the flow properties of heavy ions cannot be investigated independently of those of the bulk proton-electron solar wind when the energy transfer between them becomes significant. The effect of heavy ions on the electron-proton bulk solar wind is determined primarily by the collisions occurring very close to the coronal base. Hence, including physical processes responsible for the preferential heating of heavy ions to temperatures exceeding those of protons in the inner corona, cannot be done without considering the subsequent implications for the protons and electrons in a self-consistent manner.

Self-consistent, one-dimensional, multi-fluid wave-driven solar wind models are presented. The energy from wave damping or turbulence dissipation is assumed to be apportioned to different ions. The Alfven waves have a remarkable effect on the minor ions in the solar wind: minor ions can almost exactly surf on the Alfven waves in the high speed solar wind. Alfven waves tend to decrease the velocity difference between minor ions and protons. When minor ions surpass the proton speed because of their preferential heating and reach the local Alfven wave phase speed, the minor ions will suffer a drag force from Alfven waves which makes them flow slower. The two observation facts, that heavy ions flow faster than protons, and that they are hotter than protons, are linked by a common explanation. The temperatures of heavy ions at 1AU are reasonable compared to observations. The well-known mass proportional temperatures of heavy ions are found in our models.

Recent observations of the spectral line profiles and intensity ratio of the O VI 1032 {\AA} and 1037.6 {\AA} doublet by the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO), made in coronal holes below 3.5 R_sun, provided evidence for Doppler dimming of the O VI 1037.6 {\AA} line and pumping by the chromospheric C II 1037.0182 {\AA} line. Evidence for a significant kinetic temperature anisotropy of O^5+ ions was also derived from these observations. We show in this Letter how the component of the kinetic temperature in the direction perpendicular to the magnetic field, for both isotropic and anisotropic temperature distributions, affects both the amount of Doppler dimming and pumping. Taking this component into account, we further show that the observed intensity ratio of the O VI doublet less than one can be accounted for only if pumping by C II 1036.3367 {\AA} in addition to C II 1037.0182 {\AA} is in effect. The inclusion of the C II 1036.3367 {\AA} pumping implies that the speed of the O^5+ ions reaches 370 km/s around 3 R_sun and that these ions are much faster than protons at that heliocentric distance.

 
 
  L. Abbo

Studi di vento solare lento con i dati dell'Ultraviolet Coronagraph Spectrometer della Missione Spaziale SOHO.

University of Torino.
 

 
 
  S. Giordano

Ultraviolet Spectroscopic Observations of the Solar Corona with UVCS --Origin of the Fast Solar Wind.

University of Torino, 1999.
 

 
 
  E. Landi

Spectroscopic Diagnostic of Optically Thin Plasmas, 

PhD in Astronomy, University of Firenze, 1998
 

 
 
  S. Fineschi

Polarimetry and Spectroscopy from Space-Borne Coronagraphs

PhD in Astronomy,     University of Firenze, 1994.
 

One new generation of instruments spaces is rendering them the spectroscopic and polarimetrica observation of the solar corona possible.  A coronale spectrograph for the ultraviolet one -- `` the Ultraviolet Coronagraph and Spectrometer' ' (UVCS) -- gia' has flown to edge of one mission SPARTAN with the Space Shuttle.  One sophisticated version piu' of the same launch instrument sara' in 1995 with probe ESA/nasa `` Solar and Heliospheric Observatory' ' (SOHO). A coronografo/polarimetro for the observation of the line Lyman-alpha (Ly-a) of coronale hydrogen e' under construction and sara' included in the scientific cargo of a sounding rocket NASA.  In this seminary e' illustrated the theoretical contribution and it experiences them of my search of Doctorate to these three missions spaces them. The scientific obbiettivo of the Ly-a coronografo/polarimetro e' the measure of the linear polarization of the Ly-a (1216 Ang.)  coronale to eliocentriche heights comprised between 1.1 and 2 solar beams.  In corona, this line e' formed and polarized from the dissemination for resonance of the below cromosferica Ly-a cancellation that illuminates coronale neutral hydrogen anisotropicamente. The presence of a magnetic field coronale modification this polarization through the Hanle effect.  From the measure of the polarization of the Ly-a e' therefore possible to deduce only information on the magnetic fields of the crown, than to tutt' today pressoche' they are disowned.  The theory of the Hanle effect of the coronale Ly-a and requirement orchestrate them for the observation of this effect will come introduce to you in this seminary, thus like one description of the instrument. The UVCS/soho e' a coronografo that consists of three telescopes (``canali' '), hidden externally and inner, that they operate in conjunction with two spectrometers UV and a polarimetro to wide band in the visible one.  The UVCS e' designed for the determination of the fundamental physical parameters (temperatures, density, velocity' of the solar wind) of the corona comprised between 1.2 and 10 solar beams.  The seminary descrivera' the attivita' experiences them of characterization of the members of spectrometers UV, and of integration and test white woman works them of the light channel.

The UVCS/spartan e' a reduced version of the UVCS/soho and has flown in opens them 1993.  The SPARTAN e' a sub-satellite put in orbit and received to earth from the Space Shuttle.  In the verrano seminary some of the observations carried out during this mission SPARTAN  

 
 
  M. Romoli

The UVCS/SOHO Coronagraph Polarimeter,

PhD in Astronomy, University of Firenze, 1992
 

Subject of the PhD Thesis is the development of the Ultraviolet Coronagraph Spectometer (UVCS) of the scientific payload of SOHO
(SOlar Heliospheric Observatory), dedicated to the study of the heliosphere by means of helioseismologic experiments, coronal remote sensing and in situ monitoring of the solar wind. The spacecraft  will be sent in orbit in July 1995.

The research activity has been carried out at the Dipartimento di Astronomia e Scienza dello Spazio of the University of Firenze, under the supervision of Prof. Giancarlo Noci, UVCS Co-PI, and at the Harvard-Smithsonian Center for Astrophysics in Cambridge, USA (April
1989 - October 1990), under the supervision of Dr. John Kohl, UVCS PI.

UVCS is a three channel coronagraph consisting of two UV spectrometers, optimized to measure intensities and profiles of spectral lines in the 60 - 140 nm range, in particular Lya e OVI 1032/37, and a polarimeter in the broadband visible light (450 - 600 nm) to measure the linearly polarized coronal radiation.

A preliminary discussion of the theoretical and instrumental aspects connected to the experiment, is followed by the description of  the reasearch activity, which is focused on the development of the coronagraph polarimeter. In particular, the following topics are described:
- Definition of the scientific requirements and specifications of
the characteristics of the optical and
detective components.

- Computer simulation of the detectable polarized signal.

- Analysis of the techniques for the stray light suppression in
a coronagraph, with both theoretical and experimental approaches.

- Laboratory tests to measure the characteristics of different
linear polarizer and the scattering off the sunlight trap.

- In flight intensity calibration procedure.
 

MS Theses:

This thesis is proposed to determine the physical parameters of the regions of the solar atmosphere in which the solar wind is originated, that is that one plasma current to high velocita' that propaga from the Sun towards interplanetary means.  The proprieta' of the solar wind, to distances of the order of the distance Sole-Terra (approx. 150 million km), are notes from measures completed in situ from experiments space them.  To the contrary, very little it is known on the regions of origin of the wind, within the solar corona, and therefore on their characteristics and the physical processes that determine the proprieta' of the wind.  The scarsita' of information on this region it derives from the difficolta' of observation of spectral lines to eliocentriche heights of the order of little solar beams. The recent mission spaces them SOHO (Solar Heliospheric Observatory) door to edge experiment UVCS (Ultraviolet Coronograph Spectrometer) that it observes lines in the ultraviolet one in an interval of heights comprised between 1.4 and 10 solar beams.  They give you of recent acquired from UVCS have been analyzes to you, in this job, with spectroscopic techniques and they have allowed to obtain information us on the physical parameters of the coronale plasma between 1.5 and 2,3 solar beams. In particular, holding account that to the intensita' of observed lines HI 103À Lya 121Ã and OVI - 1037A) contribute processes radiati to you and processes collide them, have calculated the intensita' previewed for these from theoretical models and we have confronted it with turns out to you observed, obtaining an only partial agreement to you.  To this point they have been used technical diagnostic spectroscopic, that they preview the separation between members due to processes radiati to you and to processes collides them, in order to gain information on the physical parameters of the coronale plasma. The originalita' of this study it resides in the fact that for before the time e' which could gain the course with the fuoruscita eliocentrica height of the velocita' of of the plasma from the analysis of the phenomenon of the Doppler Dimming.  Moreover e' gained the profile of densita' electronic with the eliocentrica height, up to now acquired exclusively beginning from observations in the visible one, also from the observations in the UV available from UVCS, obtaining a good agreement with turns out to you gia' famous.  E' then derived, from the study of the spectral profiles, the kinetic temperature along the line of sight for Hydrogen and OVI and, from the conservation of the flow of mass, indications on geometry of expansion of the solar wind.  The comparison between turns out obtained and the theoretical predizioni to you door to assert the inconsistenza between gives to you observed and responsible processes to you commonly thought of the coronale heating and the acceleration of the wind.  On the base of this comparison e' be possible to indicate those that they seem the promising lines of development piu' in the study of the origin of the solar wind.

This thesis discusses a mechanism for the heating of the solar corona and the acceleration of the solar wind, based on the dissipation of Alfven waves by gravity damping. This mechanism was proposed by Khabibrakhmanov and Mullan (1994) but has not previously been applied in modeling efforts. After extending Khabibrakhmanov and Mullan theory to give an expression for the evolution of the Alfven wave amplitude as a function of the local parameters of the atmosphere, the thesis shows how gravity damping compares with other mechanisms which have been proposed for the dissipation of the Alfven waves. Then a wind model is calculated: this includes, in the energy equation, a gravity dissipation term, and, in the momentum equation, a different wave acceleration term from that which is usually adopted. Initial conditions for the integration of the equations are compatible with recentUlysses measurements. The integration proceeds from 1AU towards the base of the solar corona, and into the transition region (where T = (1-2)x10^5 K). The thesis results show that the gravity damping of Alfven waves heats protons in the solar plasma to several million degrees, and accelerates the solar wind to 600-700 km/s. Model predictions at low heliocentric distances compare favorably with recently acquired data. One prediction of the model is that the damping process is most effective in regions where the Alfven speed is low. Another prediction is that although the energy is deposited mainly into protons, the deposition occurs close enough to the Sun that collisional coupling also leads to effective heating of the electrons (to T_e  ~10^6K). Finally, the model results are compared with those obtained from models based on ion-cyclotron resonant processes.

L. Maccari, HI Lyman-alpha Emission from Coronal Transients,  Doctor Degree Thesis in Physics, 1995, University of Firenze, 1995.