SOHO Joint Observing Plan Proposal # 112 Coordinated SOHO-Ulysses elemental abundance study Received: October 5, 1999 Authors: G. Poletto, K. Ko, J. Raymond (UVCS), B.J.J. Bromage, S. Parenti (CDS), K. Wilhelm, E. Landi (SUMER), S. Plunkett, Russ Howard (TBC) (LASCO), S. Suess (UVCS-SWOOPS), D. McComas, D. Reisenfeld (SWOOPS), G. Gloeckler, N. Schwadron (SWICS) Scientific Justification and Objectives: The determination of solar abundances has revealed the presence of a variation in the elemental abundance as we move from the photosphere to the corona and into the solar wind, related to the FIP of the element. Although this is nowadays a generally accepted result, how the FIP fractionation effect changes with height is not yet well established. Moreover, there are abundance variation within structures: streamers' abundances are not the same as coronal hole abundances, and streamers' abundances change as one moves from the streamers' legs to the streamer core. In the solar wind, in situ measurements detect a modulation of the low-to-high FIP element ratio that is anticorrelated with the solar wind speed. Moreover, at magnetic sector boundaries, heavy ions abundances have been shown to change abruptly. The behavior of He is more complicated, and there is possibly a second step in the FIP fractionation effect, occurring at about 23 eV. On December 8, there will be an Sun-SOHO-Ulysses quadrature, a situation which occurs every 6 months and provides the best opportunity for coordinated SOHO Ulysses observations: plasma imaged by SOHO at the limb of the Sun will, in due time, be sampled in situ by Ulysses. This geometry motivates our request for coordinated observations aimed at determining the profile of element abundances vs heliocentric distance, from low coronal height out to large distances, and, depending on the morphology of the limb region, aimed also at establishing a direct relation between elemental abundances in structures close to the Sun and abundances measured at different winds. It is worth mentioning that, although our primary objective is the determination of element abundances, the data we will collect allow us also to determine the plasma electron temperature and density. Method and Target Selection: Spectra will be taken in different spectral ranges, depending on the experiment, and at different heliocentric heights -ranging between 1.1/1.2 to ~ 4.5 solar radii- to evaluate the abundance vs. height profile. He, Oxygen, Mg, Fe lines will be observed. The target on which SOHO experiments will focus has to be on the West limb of the Sun at a latitude of 40 degrees below the equator: this is, because of the Ulysses position at the time of observations. The SOHO-Ulysses quadrature will be on December 8: the best observing dates for coordinated observations ranges from Dec 4 to Dec 12. Ulysses SWOOPS and SWICS data referring to the plasma observed by SOHO will be collected 8-25 days later, depending on the solar wind speed. This is obviously related to the source region we will be observing (whether it is a streamer or a coronal hole) and may possibly change during the observing interval, depending on the variability of the region morphology. Integration times on the order of 1-2 days are expected, in order to determine heavy ion abundances, while a higher resolution is achieved in Helium abundance estimates. Operational Details: UVCS: UVCS time from Nov 29 to Dec 12 has been reserved for this project. The days before Dec 4 may be dedicated to test observations, to check how high we can go and still get lines strong enough to be statistically significant. We plan to go as high as 3.5 or even 4.5 solar radii, in a streamer. In the 4 to 12 Dec period, we plan to dedicate one full day to the attempt of observing the He II line at 1085 A. The remaining days, we will take observations with 3-4 different grating position to cover a wide enough spectral range to include Mg, Fe, Si, O, Al lines. The UVCS slit is long enough to cover different regions: the slit will be normal to the solar radius through the -40 degree latitude, the center will be positioned at that latitude. Quite likely, given the present phase of the solar cycle, streamers will be present at that latitude, but the slit edges may cover, possibly, coronal holes, giving us an opportunity for analyzing abundances in different plasma structures and at their interface. SUMER: The SUMER FOV will be centered at the -40 degree position and rastering will be made up to about 1.2 solar radii. The He II 1085 line will most likely be observed, so the spectral range between 1065 and 1105 A will be covered for one or two days, when UVCS as well makes analogous observations. Lines from Ne, Mg and other ions are expected to be observed. CDS: The CDS FOV will be centered at the -40 degree position and rastering will be made up to about 1.2 solar radii. Both the NIS and GIS experiments will be used. A range of locations between the Pole and the -40 degree latitude may be observed, to search for abundance variation with latitude. LASCO: In addition to routine observations, extra pB maps may be taken at the time of observations, to help define the morphology of the region under investigation.