Parkinson’s research helped establish the field of “laboratory astrophysics.” He contributed fundamental UV spectral atomic and molecular data and lead space-based observational studies of the Sun.

Solar abundances have been historically assumed to be representative of cosmic abundances. However, our knowledge of the solar abundance of helium, the second most abundant element, relies mainly on models 1 and indirect measurements through helioseismic observations 2 , because actual measurements of helium in the solar atmosphere are very scarce. Helium cannot be directly measured in the photosphere because of its high first ionization potential, and measurements of its abundance in the inner corona have been sporadic 3 , 4 . In this Letter, we present simultaneous global images of the helium (out to a heliocentric distance of 3 R ⊙ (solar radii)) and hydrogen emission in the solar corona during the minimum of solar activity of cycle 23 and directly derive the helium abundance in the streamer region and surrounding corona (out to 2.2 R ⊙ ). The morphology of the He + corona is markedly different from that of the H corona, owing to significant spatial variations in helium abundance. The observations show that the helium abundance is shaped according to and modulated by the structure of the large-scale coronal magnetic field and that helium is almost completely depleted in the equatorial regions during the quiet Sun. This measurement provides a trace back to the coronal source of the anomalously slow solar wind observed in the heliosphere at the Sun–Earth Lagrangian point L1 in 2009, during the exceptionally long-lasting minimum of solar activity cycle 23.

Instrumentation and plasma diagnostic techniques are being developed to obtain a detailed empirical description of solar wind acceleration regions at heights between the coronal base and about 10 solar radii from sun center (R⊙). The goal of this work is to determine a sufficient number of observational parameters to constrain, significantly, theories of solar wind acceleration, coronal heating, and solar wind composition. Although a substantial amount of data on the electron density structure of the corona already exists, there are only isolated measurements of other critical plasma parameters, except for observations of regions near the base of the corona. Ultraviolet spectroscopy provides a capability to expand greatly the number of plasma parameters that can be specified by means of remote sensing techniques. Ultraviolet measurements of spectral line profiles determine the random velocity distributions and effective temperature of protons, minor ions, and electrons. Ion densities and chemical abundances are derivable from the collisional component of the observed resonant line intensities. Outflow velocities can be determined from Doppler shifts and Doppler dimming of spectral lines. The instruments which are being developed for remote sensing of the extended corona consist of an occulted telescope system and a high resolution spectrometer. The basic design was proven on three sounding rocket flights. Initial data on proton temperatures and solar wind outflow velocities for heliospheric heights between 1.5 and 3.5 solar radii from sun center have been obtained. More powerful instruments are being developed for Spartan (a Shuttle-deployed subsatellite) and for the Solar Heliospheric Observatory mission.

We present preliminary results of a. study to create coronal outflow velocity maps for the period from 1996 to 2005. The velocities are derived from the UVCS/SOHO synoptic observations of the O VI 103.2 ran and 103.7 nm intensities. The maps are made at a constant heliocentric height of 2.3 R-circle dot, near the traditional coronal source surface height of 2.5 R-circle dot. Our results for the Cycle 22/23 minimum show that the classic solar minimum conditions, where highspeed wind dominates the polar regions, lasted only until May 1997. However, during the same time period there was very little change in the fraction of fast or slow speed wind at low heliographic latitudes (< 30 degrees). When completed, the coronal velocity maps will be used to show the connections between structures in the corona and solar wind streams at greater distances from the Sun. It will also help clarify how variations in the spatial distribution of outflow velocities are controlled by the coronal magnetic field and plasma conditions at the source regions.

This paper reviews our growing understanding of the physics behind coronal heating (in open-field regions) and the acceleration of the solar wind. Many new insights have come from the last solar cycle's worth of observations and theoretical work. Measurements of the plasma properties in the extended corona, where the primary solar wind acceleration occurs; have been key to discriminating between competing theories. We describe how UVCS/SOHO measurements of coronal holes and streamers over the last 14 years have provided clues about the detailed kinetic processes that energize both fast and slow wind regions. We also present a brief survey of current ideas involving the coronal source regions of fast and slow wind streams, and how these change over the solar cycle. These source regions are discussed in the context of recent theoretical models (based on Alfven waves and MHD turbulence) that have begun to successfully predict both the heating and acceleration in fast and slow wind regions with essentially no free parameters. Some new results regarding these models-including a quantitative prediction of the lower density and temperature at 1 AU seen during the present solar minimum in comparison to the prior minimum-are also shown.

We present a detailed analysis of oxygen ion velocity distributions in the extended solar corona, based on observations made with the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO spacecraft. Polar coronal holes exhibit broad line widths and unusual intensity ratios of the O VI λλ1032, 1037 emission-line doublet. A traditional interpretation of these features is that oxygen ions have a strong temperature anisotropy, with the temperature perpendicular to the magnetic field being much larger than the temperature parallel to the field. However, recent work by Raouafi and Solanki suggested it may be possible to model the observations using an isotropic velocity distribution. In this paper we analyze an expanded data set to show that the original interpretation of an anisotropic distribution is the only one fully consistent with the observations. It is necessary to search the full range of ion plasma parameters to determine the values with the highest probability of agreement with the UVCS data. The derived ion outflow speeds and perpendicular kinetic temperatures are consistent with earlier results, and there continues to be strong evidence for preferential ion heating and acceleration with respect to hydrogen. At heliocentric heights above 2.1 solar radii, every UVCS data point is more consistent with an anisotropic distribution than with an isotropic distribution. At heights above 3 solar radii, the exact probability of isotropy depends on the electron density chosen to simulate the line-of-sight distribution of O VI emissivity. The most realistic electron densities (which decrease steeply from 3 to 6 solar radii) produce the lowest probabilities of isotropy and most probable temperature anisotropy ratios that exceed 10.

Ultraviolet coronagraph observations of the extended solar corona (defined here as 1.5 to 10 solar radii from Sun-center) have become a powerful tool for obtaining detailed empirical descriptions of coronal holes, streamers, and coronal mass ejections. The empirical models resulting from ultraviolet coronagraph observations provide the constraints needed to test and guide theoretical models aimed at determining the physical processes that control solar wind acceleration, CME heating and acceleration, and solar energetic particle (SEP) acceleration. Measurements to date from sounding rockets, the shuttle deployed Spartan 201 satellite and the Solar and Heliospheric Observatory (SOHO) have utilized high resolution spectroscopy over a very limited instantaneous field of view. New concepts for next generation instrumentation include imaging ultraviolet spectro-coronagraphs and large aperture ultraviolet coronagraph spectrometers. An imaging instrument would be the first to obtain absolute spectral line intensities of the extended corona over a wide field of view. Such images would provide the absolute intensities of spectral lines that can be used to determine densities and outflow velocities of specific coronal ions. Measurements from several charge states of a given element will allow electron temperatures to be determined. These measurements combined with observations of H I Ly α provide absolute chemical abundances (relative to hydrogen) for observed elements. Ultraviolet imaging would be highly complementary to a large-aperture ultraviolet coronagraph spectrometer designed for high spectral resolution observations over a small instantaneous field of view. The images would be used to select targets for more detailed spectroscopic studies with the large aperture UV coronagraph spectrometer and to provide time dependent empirical descriptions of the regions surrounding the narrow instantaneous field of view of the large aperture instrument. Descriptions of both the imaging ultraviole spectro-coronagraph and the large aperture ultraviolet coronagraph spectrometer are provided. Recommended co-observing instruments are described.

We have tracked the spectral responsivity of the ultraviolet channels of the UVCS (Ultraviolet Coronagraph Spectrometer) instrument on SOHO by repeated observations of a stable hot star. We demonstrate first that the ultraviolet spectral irradiance of the Be star ζ Tau (HD 37202) for the 100-  to 125-nm wavelength range has been sufficiently constant for our purposes when measured periodically over the course of the SOHO mission. We then use ζ Tau as a radiometric transfer standard to determine an average decrease beginning in November of 1998 of 13.0% per year in the responsivity of the UVCS O vi channel for wavelengths near H i Ly α and for a particular UVCS unvignetted aperture used for science observations. The calibration tracking method involves separating two ζ Tau spectral regions that are overlapped on part of the detector. The change in the responsivity of UVCS/SOHO began in late 1998 as determined by comparison of simultaneous observations of the corona carried out with UVCS/SOHO and the freshly-calibrated UVCS instrument on the Spartan 201 satellite in early November of 1998.

We have measured the absolute energy-averaged cross section for the electron impact excitation of ${\mathrm{C}}^{2+}(2s2p\phantom{\rule{0.2em}{0ex}}^{3}P^{o}\ensuremath{\rightarrow}2{p}^{2}\phantom{\rule{0.2em}{0ex}}^{3}P)$ from energies below threshold to $17\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ above, and present the measured absolute rate coefficients for this transition, for temperatures from ${10}^{4}$ to ${10}^{5}\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. These rate coefficients are required for diagnostics of plasmas such as those found in astrophysical environments. The synchronous photon detection method with beams modulation and inclined electron and ion beams was used. Radiation at $117.6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ from the decay of the excited ions back to the metastable state was detected using an absolutely calibrated optical system. The fractional population of metastable ${\mathrm{C}}^{2+}(2s2p\phantom{\rule{0.2em}{0ex}}^{3}P^{o})$ in the incident ion beam was determined to be $0.42\ifmmode\pm\else\textpm\fi{}0.03(1.65\phantom{\rule{0.2em}{0ex}}\ensuremath{\sigma})$. The rate coefficient for ${\mathrm{log}}_{10}\phantom{\rule{0.3em}{0ex}}\mathrm{T}=4.8$ was determined to be $1.01\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}\ifmmode\pm\else\textpm\fi{}14%$ at a 90% confidence $(1.65\phantom{\rule{0.2em}{0ex}}\ensuremath{\sigma})$ level. The measured cross section is in agreement within experimental uncertainty with 6-term close-coupling $R$-matrix calculations and 90-term $R$ matrix with pseudostates calculations.

We have measured the absolute energy-averaged cross section for the electron impact excitation of C{sup 2+}(2s2p {sup 3}P{sup o}{yields}2p{sup 2} {sup 3}P) from energies below threshold to 17 eV above, and present the measured absolute rate coefficients for this transition, for temperatures from 10{sup 4} to 10{sup 5} K. These rate coefficients are required for diagnostics of plasmas such as those found in astrophysical environments. The synchronous photon detection method with beams modulation and inclined electron and ion beams was used. Radiation at 117.6 nm from the decay of the excited ions back to the metastable state was detected using an absolutely calibrated optical system. The fractional population of metastable C{sup 2+}(2s2p {sup 3}P{sup o}) in the incident ion beam was determined to be 0.42{+-}0.03(1.65 {sigma}). The rate coefficient for log{sub 10} T=4.8 was determined to be 1.01x10{sup -8} cm{sup 3} s{sup -1}{+-}14% at a 90% confidence (1.65 {sigma}) level. The measured cross section is in agreement within experimental uncertainty with 6-term close-coupling R-matrix calculations and 90-term R matrix with pseudostates calculations.