UVCS/SOHO ABSTRACTS
AAS/SPD MEETINGS

Empirically Determined Anisotropic Velocity Distributions and Outflows of O⁵⁺ Ions in a Coronal Streamer at Solar Minimum

Frazin, R. A.; Cranmer, S. R.; Kohl, J. L.

Empirical constraints on the O⁵⁺ velocity distributions and outflow speeds in a solar minimum equatorial streamer between 2.6 and 5.1 R_sun are determined using a spectral synthesis code that includes O VI Doppler dimming. These constraints follow directly from UV spectra taken on 12 October 1996 with the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO satellite and 3D electron densities derived from tomography applied to a time series of polarized white-light images taken with the Large Angle Spectrometric Coronagraph Experiment (LASCO) on SOHO. Four conclusions result from this work: 1) Our analysis shows O⁵⁺ velocity distribution anisotropy in the streamer legs and stalk and that the microscopic velocity distribution (which excludes wave motions that equally affect all charged particles) is also anisotropic, where the most probable speed perpendicular to the magnetic field direction exceeds that in the parallel direction. 2) There is no evidence of anisotropy in the streamer core. 3) There is preferential heating of the O⁵⁺ ions over the protons in the streamer stalk and legs, but not in the core. 4) The outflow velocity of the O⁵⁺ ions is determined at heights above 4.6 Rsun. All results have a confidence level of at least 70%. The evidence for microscopic anisotropy in the O⁵⁺ velocity distributions and preferential heating of the O⁵⁺ ions over the protons presented here is reminiscent of that provided for coronal holes by Cranmer et al. (1999). One particularly favorable candidate mechanism to explain these phenomena is ion cyclotron resonance, in which high frequency Alfven waves are absorbed by the heavy ions. Cranmer et al. discuss the relevance of this process to an empirical model of a polar coronal hole. Our data suggest that the dominant processes that heat the heavy ions in coronal holes may also be important in streamers. Reference: Cranmer, S.R., et al. 1999, ApJ, 511, 481

Halo CMEs in the Ultraviolet

Raymond, J. C.; Ciaravella, A.; van Ballegooijen, A. A.

Halo CMEs are especially important for connecting remote sensing observations with in situ measurements, as well as for Space Weather. However, analysis of coronagraphic observations of halo CMEs is complicated by relatively severe projection effects. We discuss the use of Doppler shifts to constrain CME structure and evolution along the line-of-sight, and we discuss the excitation of UV emission lines at high velocities and large heights above the Sun. This work was supported by NASA Grant NAG5-11420.

Empirical densities, kinetic temperatures, and outflow velocities in the equatorial streamer belt at solar minimum

Strachan, L.; Suleiman, R.; Panasyuk, A. V.; Biesecker, D. A.; Kohl, J. L.

We use combined Ultraviolet Coronagraph Spectrometer (UVCS) and Large Angle Spectroscopic Coronagraph (LASCO) data to determine the O(5+) outflow velocities as a function of height along the axis of an equatorial streamer at solar minimum and as a function of latitude (at 2.3 solar radii from sun center). The results show that outflow increases rather abruptly in the region between 3.6 and 4.1 solar radii near the streamer cusp, and gradually increases to 90 km/s at about 5 solar radii in the streamer stalk beyond the cusp. The latitudinal variation at 2.3 solar radii shows that there is no outflow (within the measurement uncertainties) in the center of the streamer called the core, and that a steep increase in outflow occurs just beyond the streamer legs, where the O VI 1032 intensity relative to H I 1216 (Ly alpha) is higer than in the core. Velocity variations in both height and latitude show that the transitions from no measurable outflow to positive outflow are relatively sharp and thus can be used to infer the location of the transition from closed to open field lines in streamer magnetic field topologies. Such information, including the densities and kinetic temperatures derived from the observations, provides hard constraints for realistic theoretical models of streamers and the source regions of the slow solar wind. This work is supported by NASA Grant NAG5-11420 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by the ESA PRODEX program (Swiss contribution). do not accept author defined LaTeX macros.

Solar and Heliospheric Observatory Observations of a Helical Coronal Mass Ejection

A.Ciaravella, J.C. Raymond, B. Thompson, A van Ballegooijen, L. Strachan, J. Li, L. Gardner, R. O'Neal, E. Antonucci, J. Kohl, and G. Noci.

The Feb 12, 2000 CME: spectroscopic and white light observations. The CME occurred on Feb 12, 2000 on the NW is an excellent set of data in which the UVCS entrance slit was centered at 2.3 Rsun inside the LASCO C2 for 36 hours providing a unique set of data to study all the phases of a typical flux rope CME and the changes in the structure of the underlying  corona. Spectral lines such as H I (1216, 1026 A), OVI (1032,1037 A), SiXII (520 A) were imaged during the event and from their Doppler shifts the component of  velocity along the line of sight is obtained. We present the UVCS spectra and the plasma diagnostics of the CME plasma and  compare the spectroscopic results with the more classical visible light  scenario.
This event is unusual in that UVCS detected an enhanced Si XII intensity at the leading edge and a gradual dimming of the coronal brightness by 50%.

Comparison of UVCS and EISCAT observations of a mid- and high-latitude streamer during the Third Whole Sun Month Campaign

L. Strachan, A. V. Panasyuk, J. L. Kohl, A. Breen

We compare the plasma properties of two different streamer regions in the extended corona (1.5 to 6 solar radii) with solar wind velocity measurements made at larger distances during the Third Whole Sun Month Campaign. Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) measurements were made of H Ly-alpha intensities and profiles and O VI 1032/1037 intensities in order to put constraints on the plasma conditions in these regions. The UVCS/SOHO measurements were centered at position angles 70 deg (CCW from NHP) during 12-21 Sept. 1999 and 190 deg during 22-25 Sept. 1999. Streamer kinetic temperatures and outflow velocities are compared with measurements of outflow velocities determined by EISCAT interplanetary scintillation observations at the same position angles. The EISCAT measurements showed slow flow above the streamers at 25 to 80 solar radii, with steep gradients on the boundaries as flow speeds increased above the inter-streamer regions. Comparisons of EISCAT measurements from 25-35 solar radii and UVCS/SOHO coronal measurements should cast light on the acceleration of the slow solar wind.

This work is supported by NASA under Grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

SOHO/UVCS Observations of a Coronal Jet During the Third Whole Sun Month Campaign

Y.-K. Ko, J. Raymond, S. Gibson, L. Strachan, D. Alexander, L. Fletcher, T. Holzer, H. Gilbert, J. Burkepile, C. St. Cyr, B. Thompson

On August 26 1999, a coronal jet occurred at the north west limb near a sigmoid active region which has been the target for a joint observation plan during the third Whole Sun Month Campaign. This jet was observed by several instruments at the limb (SOHO/CDS, SOHO/EIT, TRACE, MLSO/CHIP, MLSO/PICS), at 1.7 Ro (SOHO/UVCS), and at the outer corona (SOHO/LASCO). At 1.7 Ro, the intensities of Lyman alpha, Lyman beta in the jet increased by as large a factor of 100 compared with the background corona, while those for O VI 1032 and O VI 1037 increased by a factor of 2. C III 977 line also brightened significantly. The line shift in the lines indicates that the line-of-sight velocity in the jet started from ~150 km/sec blue shift and ended at ~120 km/sec red shift. This line-of-sight motion seen at 1.7 Ro apparently was opposite that observed when the jet emerged from the limb. In this paper, we present the observation by SOHO/UVCS and discuss the dynamic structure and physical properties of this jet as it passed through 1.7 Ro. Comparisons will be shown with the observations from other instruments. This work is supported by NASA Grant number NAG5-7822.

New Insights on CMEs from Spectroscopic observations of UltraViolet Coronagraph Spectrometer

Angela Ciaravella, J.C. Raymond, A. van Ballegooijen, O.C. St. Cyr, S.P. Plunkett, UVCS Mission Operations Team

Since the SOHO launch spectroscopic observations of Coronal Mass Ejections have been performed with the Ultraviolet Coronagraph Spectrometer (UVCS). The data provide new insights on the physical and dynamical conditions of the ejected material which can in turn be used to put constraints on the theoretical models. Detailed diagnostics of temperatures, densities, abundances have been obtained for some events observed by UVCS. Energetics, heating and evolution during the propagation through the corona have been derived as well. The component along the line of sight can be measures from the Doppler shift of the spectral lines which together with white light observations can be used to derive a three dimensional picture of the event. We present the results of the spectroscopic analysis of a CME observed with UVCS and a comparison with LASCO white light observations. ~

Surf's Still Up: UVCS/SOHO Observations as Strong Constraints on Coronal Heating Theories

S. R. Cranmer, J. L. Kohl

In 1996, the Ultraviolet Coronagraph Spectrometer (UVCS) instrument aboard SOHO observed surprisingly broad line profiles of the O VI 1032, 1037 doublet in polar coronal holes. These measurements indicated perpendicular ion temperatures of at least 100--200 million K above two solar radii in the nascent high-speed solar wind. Since then, these observations have been supplemented by profiles of other ions, Doppler dimming measurements made possible by Spartan 201, and a great deal of theoretical work. This talk outlines the current state of understanding about coronal heating and solar wind acceleration that has been facilitated by UVCS.

The most promising mechanism for heating and accelerating minor ions remains the dissipation of high-frequency (10 to 10,000 Hz) ion cyclotron waves, but heating the protons is a more open question. The physics of the ion cyclotron interaction in the corona has only begun to be explored, and we will discuss recent insights into the generation and damping of these waves. A self-consistent theory of wave damping and turbulent cascade ``replenishment'' would allow the question of proton heating to be answered more definitively. Also, a kinetic approach to ion cyclotron heating yields non-bi-Maxwellian ``resonant shell'' velocity distributions that could produce emission line profiles narrower than expected from their most probable speeds. Thus, the UVCS measurements of 100--200 million K ion temperatures may only be lower limits.

This work is supported by the National Aeronautics and Space Administration under grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program (Swiss contribution).

New Diagnostics of Coronal Heating and Solar Wind Acceleration Processes Achievable With The Advanced Solar Coronal Explorer (ASCE)

S. R. Cranmer, J. L. Kohl, L. D. Gardner, J. C. Raymond, L. Strachan, P. L. Smith, R. A. Howard, J. M. Davila, R. R. Fisher, G. Noci, G. Tondello, D. G. Socker, D. Moses

The Advanced Solar Coronal Explorer (ASCE) is a proposed NASA Medium-class Explorer (MIDEX) mission that underwent a detailed Concept Study in 1999. The science payload includes large aperture EUV and visible light coronagraphs. ASCE's unprecedented spectral range, spatial resolution, and sensitivity (30 to 100 times the EUV sensitivity of UVCS/SOHO) provide measurements needed to investigate the role of high-frequency and low-frequency waves in heating and accelerating the fast and slow speed solar wind. This presentation will outline the advanced capabilities of ASCE for obtaining detailed empirical descriptions of solar wind acceleration regions, specifying coronal temperatures, flow speeds, densities, and elemental abundances. Velocity distributions for electrons and more than 10 to 20 ion species with mass-to-charge ratios from 4 to 1 (including singly ionized helium) can be measured by ASCE in coronal holes and streamers. This information is sufficient to derive the wavenumber power spectrum of magnetic fluctuations that affect the primary electron/proton plasma. The main goal is to identify the physical processes responsible for heating and acceleration of the primary particles and minor ions in the fast and slow speed solar wind.

Results from the 2 November 1998 SwRI/LASP Sounding Rocket Campaign

D.M. Hassler, F. Auchere, B. Handy, L. Strachan, D. Slater, T.N. Woods

We present results from the November 2, 1998 SwRI/LASP sounding rocket campaign with the dual purpose of providing inter-calibration for the SOHO/EIT and TRACE instruments and providing a measure of the coronal helium abundance by direct comparison of the coronal Ly-alpha lines of He II (304 angstroms) and H I (1216 angstroms). The sounding rocket payload provided full-disk solar images of Fe IX/X 171 and H I Ly-alpha 1216 for inter-calibration with the SOHO/EIT and TRACE instruments, respectively, as well as off-limb observations of the He II 304 line to be compared with off-limb SOHO/UVCS observations of the H I 1216 line to provide a constraint on the coronal helium abundance. This work has been funded in part by NASA under grant NAG5-5140 to Southwest Research Institute.

UVCS/SOHO Observations of Equatorial and Polar Coronal Holes
  
J. L. Kohl, M. P. Miralles, S. R. Cranmer, and R. M. Suleiman
  
A large equatorial coronal hole was observed above the west limb with the Ultraviolet Coronagraph Spectrometer (UVCS)  on SOHO from November 1999 to March 2000. Observations in H I Lyalpha and O VI 103.2, 103.7 nm provided spectroscopic diagnostics of proton and O5 velocity distributions and outflow velocities. These properties will be compared to those of the large polar coronal holes observed near solar minimum. The equatorial coronal hole corresponded to a high-speed solar wind stream at 1 AU, but there were significant differences between the interplanetary properties of this stream and the steady high-speed wind seen over the poles at solar minimum. The several obvious differences between the two structures in the extended corona may be associated with the different densities and magnetic field configurations and flux tube expansion factors. Preliminary results from a detailed empirical model of the equatorial coronal hole will be presented.
This work is supported by NASA under Grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

Solar Cycle Variations of O VI and H I Lyman Alpha Intensities in the Solar Corona 

M. P. Miralles, A. Panasyuk, L. Strachan, L. D. Gardner, R. Suleiman, P. L. Smith, J. L. Kohl

UVCS/SOHO measurements of O VI (103.2 and 103.7 nm) and H I Lyman alpha  intensities in the solar corona have been made from 1996 to the present spanning the rising phase of cycle 23. During solar minimum the corona consisted of large coronal holes at the poles and quiescent streamers at the equator. During the ascending phase of the cycle, the corona presented high latitude streamers and finally polar streamers as the Sun approached solar maximum. Recent observations of the solar corona show the presence of coronal holes at the equator and streamers at the poles. Our observations provide descriptions of these structures over the rising  phase of the solar cycle. We compare the properties of quiescent equatorial streamers which occurred at solar minimum to high latitude and polar streamers observed toward solar maximum. We also compare solar minimum polar coronal holes to equatorial coronal holes present at solar maximum. We discuss how these results are related to the plasma properties.
This work is supported by NASA under Grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

New Insights into Solar Coronal Plasma Kinetics from UVCS/SOHO
 

S. R. Cranmer

Bull. Am. Astron. Soc., 31, 871 (meeting 194, poster 32.06)

The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) has measured anisotropic temperatures and differential outflow velocities for hydrogen, oxygen, and magnesium ions in polar coronal holes. Line widths of the O VI 1032, 1037 doublet indicate perpendicular temperatures of at least 200 million K above 2 solar radii. We present theoretical models of the dissipation of high frequency (10 to 10,000 Hz) ion cyclotron resonant Alfv\'en waves, and we find that it is possible to explain many of the observed kinetic properties of the plasma with relatively small wave amplitudes. There is suggestive evidence that such waves should be generated gradually throughout the wind rather than propagated up from the base of the corona. We also discuss how additional insight into the ion cyclotron resonance interaction can be obtained by considering the process as an analogue of Sobolev-theory radiative transfer.

This work is supported by the National Aeronautics and Space Administration under grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program (Swiss contribution).

SOHO Observations of a Helical Coronal Mass Ejection

J.C. Raymond, A. Ciaravella, A. van Ballegooijen, B. Thompson

The EIT, LASCO and UVCS instruments aboard SOHO observed a CME on Dec. 11/12 1997. The ejected prominence material rose relatively slowly, averaging 150 km/s, but Doppler shifts as great at -300 km/s were seen in the O VI lines. The observed gas spans the temperature range from about 30,000 K to 300,000 K. The observations can be modeled as left-handed helix which untwists at about 0.0009 radians/sec. Considerable heating as the plasma moves from the solar surface to 1.7 solar radii is required to explain the observed temperature range.

Joint HI Lyman alpha Observations with UVCS/Spartan and UVCS/SOHO During the STS-95 Mission 

D. Dobrzycka, J. L. Kohl, L.D. Gardner,L. Strachan, M.P. Miralles, P. L. Smith, R. Suleiman, A. Panasyuk, J. 
Michels, Y.-K. Ko 

The Spartan 201 Ultraviolet Coronal Spectrometer (UVCS/Spartan) is an instrument developed to conduct 
spectroscopic studies of the extended solar corona and its expansion into the solar wind. It was designed to be Shuttle deployed and retrieved and has already flown in 1993, 1994, 1995, 1997, and 1998 providing a consistent set of data that span several years of the declining and rising phases of the solar cycle. The advantage of this instrument is that its inflight performance characteristics can be determined from the preflight and postflight laboratory calibration. The last, Spartan 201-5 mission was launched aboard the Space Shuttle Discovery (STS-95) on 29 October 1998 at 2:19:20 PM (EST). Spartan 201 made autonomous observations of the Sun and its corona for approximately 43 hours during 26 orbits around the Earth. These observations were coordinated with the Ultraviolet Coronagraph Spectrometer on board the Solar and Heliospheric Observatory (UVCS/SOHO). One of the main goals of the Spartan 201-5 mission was to update calibration of the UVCS/SOHO and to provide continuity of measurements from the period before and after solar minimum. We review the successfully accomplished goals of the UVCS/Spartan on the Spartan 201-5 flight and describe the radiometric and spectrometric comparison of the streamer data to that of UVCS/SOHO. 

Far UV Spectroscopy: Atmospheric Processes in Cool Stars 

Brickhouse, N. S. 

Bull. American Astron. Soc., 192, #63.04 

New results from the far ultraviolet are increasing our understanding of the structure and dynamics of cool star atmospheres. The far UV spectrum bridges the gap between the chromospheric ultraviolet and the X-ray corona. The important O VI ion spans the range of activity from a diverse group of systems, and is formed near the peak of the emission measure distribution of less active stars like the Sun, while it is formed at the minimum of the distribution for the highly active RS CVn binaries and rapidly rotating young stars. Density diagnostics from C III, newly accessible with the lambda 977/lambda 1176 line ratio from ORFEUS, indicate a wide spread in transition region pressure among different systems as well. In active (i.e. closed field) regions, magnetic pressure confinement overcomes fluid domination in the transition region and allows quasi-static structures to support the steep temperature gradients, while in open field line regions (e.g. coronal holes) the wind begins its acceleration through steep gradients. New results from ORFEUS show the first evidence for warm winds in luminous hybrid stars, providing the critical link between solar-like stars with hot coronae and cooler stars with cool winds. Closer to home, the UVCS experiment on SOHO probes the diagnostic O VI doublet throughout the inner coronal region of the Sun. Observed line profiles indicate that ion temperatures in solar coronal holes are hotter than electron temperatures, demonstrating the importance of ion heating and acceleration processes.  

The Impact of Ion-Cyclotron Wave Dissipation on Minor Ion Velocity Distributions in the Solar Corona 

CRANMER, S. R.; FIELD, G. B.; NOCI, G.; KOHL, J. L. 

Bull. American Astron. Soc., 191, #74.11 

We present theoretical models of the acceleration and heating of minor ions in the solar wind, as well as detailed anisotropic velocity distribution functions computed numerically by solving the Boltzmann transport equation. We examine the compatibility between these models and spectroscopic measurements of the velocities and kinetic temperatures of various particle species in the solar corona. The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) has measured hydrogen kinetic temperatures in polar coronal holes in excess of 3 million K, and O VI ion kinetic temperatures of at least 200 million K. In addition, the velocity distributions parallel to the open magnetic field are smaller than those perpendicular to the field, possibly implying temperature anisotropy ratios of order 100 for minor ions.
We examine various features of plasma heating by the dissipation of high-frequency ion-cyclotron resonance Alfven waves, which may be the most natural physical mechanism to produce the observed plasma conditions. The modeled ion velocity distributions depend sensitively on the assumed amplitudes and frequencies of the waves, and these computations can be used to accurately predict many quantitative features of the wave power spectrum. Indeed, the more ionic species that are observed spectroscopically, the greater the extent in frequency space the wave spectrum can be inferred.
This work is supported by the National Aeronautics and Space Administration under grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by Swiss funding agencies. 

A User's Guide to UVCS/SOHO 

KOHL, J. L.; NOCI, G.; CRANMER, S. R.; FINESCHI, S.; GARDNER, L. D.; HALAS, C. D.; SMITH, P. L.; STRACHAN, L.; SULEIMAN, R. M.
Bull. American Astron. Soc., 191, #73.09 

The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is currently being used to observe the extended solar corona between 1 and 10 heliocentric radii. In its first two years of operation, UVCS/SOHO has made spectroscopic measurements leading to the determination of densities, velocities, temperatures, and elemental abundances in coronal holes, equatorial streamers, and coronal mass ejections. Observations of selected non-solar targets, such as near-ecliptic stars, planets, comets, and interplanetary hydrogen and helium, have also produced interesting astronomical results. This poster presents a brief review of the UVCS/SOHO spectroscopic and polarimetric diagnostic capabilities, highlighted by pertinent observational data. Most importantly, we summarize the procedures that have been designed to allow UVCS/SOHO data to be used by a wide array of researchers, and invite participation in this unique investigation. Scientists interested in UVCS/SOHO observations are encouraged to fill out the ``Get Involved'' questionnaire located on the WWW at: http://cfa-www.harvard.edu/uvcs/
This work is supported by the National Aeronautics and Space Administration under grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by Swiss funding agencies.

Absolute Elemental Abundances in Streamers 

J. Raymond, J. Kohl, R. Suleiman, A. Ciaravella, S. Fineschi, L. Gardner, A. Panasyuk, L. Strachan (CfA), G. 
Noci (Universita di Firenze), E. Antonucci (Osservatorio di Torino), P. Nicolosi, G. Naletto (Universita di 
Padova), S. Giordano, C. Benna (Universita di Torino) 

The UVCS instrument aboard the SOHO satellite has measured the intensities of emission lines of H, N, O, Mg, Al, S, Ar, Ca ,Fe and Ni at 1.5 solar radii in a quiescent equatorial helmet streamer and in an active region 
streamer. The First Ionization Potential (FIP) effect is clearly seen. Low FIP elements show nearly 
photospheric abundances above the active region and along the edges of the equatorial streamer, while high 
FIP elements are depleted by a factor of 2-3. Near the center of the streamer, presumably the closed field 
region, the low-FIP elements are at about 1/3 photospheric abundances, and the high FIP elements are near 
1/10 their photospheric values. 

Ultraviolet Spectroscopy of Coronal Mass Ejection

A. Ciaravella (European Space Agency and Smithsonian Astrophysical Observatory), J. C. Raymond 
(Harvard-Smithsonian Center for Astrophysics), S. Fineschi (Smithsonian Astrophisical Observatory), M. 
Romoli (University of Florence - Italy), E. Antonucci (University of Torino - Italy) 

The Ultraviolet Coronagraph Spectrometer (UVCS) observed a spectacular coronal mass ejection (CME) on December 23 1996, caused by a prominence eruption. The evolution of the ejected plasma was followed for 
about 2h in both ultraviolet and visible light channels. The observation consists of a series of 5 minutes exposures, at heliocentric distance of 1.5 R_?ødot. Excursions of more than two orders of magnitude are detected in the Ly\alpha (1216 ?Å\/), Ly\beta (1026 ?Å\/), Ly\gamma (972 ?Å\/) and Ly\delta (949 ?Å\/) lines of hydrogen. The C III (977 A) is very bright during the CME evolution, but many other more weak low temperature lines, like N III (991 ?Å\/, 991 ?Å\/), N II (1085 ?Å\/), N V (1242 ?Å\/), have been detected. Line intensities and profiles have been measured providing important diagnostics for a very detailed study of physical and dynamical parameters of CME. Lines widths show non-thermal line broadening due to an expansion of plasma with velocity larger than 50 km/sec. The Ly\alpha spatial pattern of the line shift appears very structured with red and blue shifts, along the line of sight, up to 0.2 ?Å\/ ( 50km/sec) and 1 ?Åkm/sec) respectively. The data also provide the emission measure in the LogT range 4.0 - 5.5. A variation of one order of magnitude has been observed in the polarized brightness. 

UVCS/SOHO Synoptic Observations of the Extended Corona during the Whole Sun Month Campaign 

L. Strachan, S. Fineschi, L. D. Gardner, A. V. Panasyuk, J. L. Kohl (CfA), E. Antonucci, S. Giordano (U.Turin), M. Romoli (U.Florence) 

Daily synoptic observations were made with UVCS/SOHO during the Whole Sun Month (10 August to 8 September 1996) in order to characterize the large-scale spatial distributions of plasma parameters in the solar corona from 1.5 to 3 solar radii. We use observed line profiles and intensities of H I Lyman alpha and O VI 1032/1037 ?Åand white light polarized brightness measurements to derive physical properties of the plasma in the solar wind acceleration region. Line of sight velocity distributions and bulk outflow velocities for neutral hydrogen and for O^5 +, and electron densities can be derived from these measurements. We show some results from the on-going effort and present some of these data as synoptic maps. The ultimated goal of this work is to produce a data set that can be used in developing empirical models that describe the solar minimum conditions of the extended corona. This work is supported by NASA under Grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by Swiss funding sources. 

Empirical Models of the Extended Solar Corona 

J. L. Kohl (Harvard-Smithsonian Center for Astrophysics), G. Noci (University of Florence), E. Antonucci (Astronomical Observatory of Turin), A. Ciaravella (European Space Agency), S. Cranmer, D. Dobrzycka, S. Fineschi, L. D. Gardner (Harvard-Smithsonian Center for Astrophysics), M. C. E. Huber (European Space Agency), A. Panasyuk, J. C. Raymond, L. Strachan (Harvard-Smithsonian Center for Astrophysics) 

Ultraviolet spectroscopy is being used to produce self consistent empirical models of polar coronal holes and equatorial streamers in the extended solar corona. The models are intended to provide experimental values for many of the primary plasma parameters of the extended corona, which can then be used to constrain theoretical coronal and solar wind models. The empirical models are based on synoptic observations and other measurements of spectral line profiles and intensities of H I Ly\alpha, O VI 1032 ?Å\ and 1037 ?ÅFe XII 1242 ?ÅMg X 625 ?Å\ and several others. Information about velocity distributions, outflow velocities, densities and elemental abundances as derived from the observations are specified in the models. The models used to specify the empirically derived parameters include a description of well established theoretical processes such as those controlling ionization balance, collisional excitation, and resonant scattering. They do not include any descriptions of less well established processes such as heating functions, transverse wave motions or direct momentum deposition by waves. The intent is to provide, to the maximum extent possible, empirical descriptions that can be used, together with theoretical models, to help identify the dominant physical processes responsible for coronal heating, solar wind acceleration and the chemical composition of the solar wind. This work is supported by NASA Grant NAG5-3192 to the Smithsonian Astrophysical Observatory, the Italian Space Agency and Swiss funding sources. 

Thermal Coupling of Protons and Neutral Hydrogen in the Fast Solar Wind

L. Allen, S. R. Habbal (Harvard-Smithsonian Center for Astrophysics) 

Motivated by the recent Spartan and UVCS observations [Kohl et al. 1996] of hot protons with temperatures exceeding 4 \times 10^6 K below 3.5 R_s in coronal holes, as inferred from the measured broadening of the Lyman \alpha spectral line profile, we studied the thermal coupling of neutral hydrogen to protons in the presence of Alfv?én waves in the solar wind. The approach used is adopted from Olsen et al. [1994] in which the neutral hydrogen atoms are treated as test particles in a background electron-proton solar wind. The model computations show that an anisotropy in the neutral hydrogen temperature in the directions parallel and perpendicular to the magnetic field develops in the inner corona well below 5 R_s for background solar wind solutions consistent with observational constraints of the high speed wind. In particular, we find that the neutral hydrogen temperature parallel to the magnetic field direction remains strongly coupled to the proton temperature, T_p, while the perpendicular neutral hydrogen temperature exceeds this by \sim 10^6 K for a wide range of proton flow speeds, densities and temperatures for a spectrum of Alfv?én waves. The neutral hydrogen effective temperature, T_H(eff)^\perp, incorporating both random thermal motion and wave motion of the particles, is found to be independent of frequency and significantly less than the proton effective temperature, T_p(eff), in the inner corona. Thus, without additional information about the waves, which would allow T_H^\perp and T_p to be extracted from the models, T_H(eff)^\perp provides an upper limit on T_p and a lower limit on T_p(eff). However, with increasing proton temperature, the anisotropy in the inner corona decreases, with a temperature difference of < 8 \times 10^5 K between the protons and neutrals below 3 R_s when the latter reach 6 \times 10^6 K. 

Model Computations of the Line Profiles of O VI 1032 and 1037 ?Åin the Fast Solar Wind and Comparison with UVCS Observations 

X. Li, S. R. Habbal, R. Esser (Harvard-Smithsonian Center for Astrophysics) 

The profiles of the O VI 1032 and 1037 ?Å\ spectral lines are calculated for the fast solar wind. The computed theoretical line profiles are based on high speed solar wind models where the O^+5 ions are treated as test particles in a three-fluid (electrons, protons and alphas) background solar wind flow. The background solar wind model matches the observational constraints of particle flux, flow speeds and temperatures at 1 AU, and the electron density profiles in the inner corona. Line of sight effects are included in the calculations of the line profile. Preferential heating is applied to the oxygen ions to produce an ion temperature in the inner corona around 2 \times 10^8 K, as inferred from the UVCS observations on SOHO, and a flow speed exceeding that of the protons beyond several solar radii. Both resonantly scattered and collisionally excited components of the oxygen 1032 and 1037 ?Å\ lines are computed. We find that for flow speeds below 100 km/s, the two> components have approximately the same width. However, once the speed exceeds 150 km/s, the collisionally excited component becomes much wider than the resonantly scattered component. This effect can be explained by the strong Doppler dimming of the resonantly scattered component as the flow speed increases. Consequently, when the integration along the line of sight is taken into account, ions traveling along trajectories away from the plane of the sky will contribute to the the broadening of the collisionally excited component and to the dimming of the resonantly scattered component. The model computations thus suggest that the broad oxygen line profiles observed by the UVCS instrument on SOHO reflect the existence of very high oxygen flow speeds very close to the coronal base, in addition to the high kinetic temperatures. 

Expansion Factors in Coronal Holes and Plume/Interplume UVCS Observations 

G. Poletto, G. Corti (Osservatorio Astrofisico, Firenze, ITALY), G. Noci (Universita di Firenze, ITALY), J. Kohl (Center for Astrophysics, Boston, MA), S. Suess (NASA Marshall Space Flight Center, AL) 

We show that expansion factors in plumes and coronal hole areas devoid of plumes are nearly equal because the plasma beta is <<1. Hence, the overall coronal hole expansion factor is equal to the expansion factors of its densest structures. UVCS plume and interplume observations of coronal holes are illustrated, with the purpose of showing the data capabilities. Integration along the line of sight, through a medium containing high and low pressure regions, and the rapid decrease with heliocentric distance of vvplume intensity, presently hinder an observational determination of the expansion factors between 1.5 and 2 solar radii.

Ultraviolet Spectroscopy -- First Results From SOHO 

Kjeldseth-Moe, O. 

The Solar and Heliospheric Observatory, SOHO, has several instruments observing in the ultraviolet wavelength range, 15 - 160 nm. These include the spectrometers, CDS and SUMER, and the UV coronagraph, UVCS which also has spectroscopic capability. The solar radiation in this wavelength range is formed at temperatures between 5000 K and 15 MK. They are therefore well suited to study the solar atmosphere, from the chromosphere to the corona in active regions. All the instruments have the capability of mapping the structure of the hot corona and measure intensities, profiles and velocity shifted wavelengths of individual UV spectral lines. With their great spectral range the spectrometers may also be used to determine pressure, temperature, element abundances and other gas parameters. To this is added the capability of observing virtually uninterrupted the time variations of the coronal radiation on several time scales. In this talk we describe some of the first results from the ultraviolet observations of the sun with SOHO and discuss briefly some of the scientific implications 'go for it resulting from the observations.