Some of these elements (P, Cl, K, Ti, Cr, and Mn) have no

coronal spectroscopic measurements available.Hence, for

these elementsMTOFis in some sense providing the first

"coronalobservations",asthe solar wind isthe interplan-

etaryextension of thecorona.The MTOFsensor isrou-

tinelymeasuringisotopicabundancevariationsforsev-

eral elements (neon, magnesium, silicon, sulfur, argon, cal-

cium,iron,andnickel),someofwhichhaveneverbeen

previously observedin the solar wind,in solarenergetic

particle (SEP) populations, nor spectroscopically in the sun.

Among the brand new isotopes are those of silicon, sulfur,

calcium, chromium, and nickel.MTOFhaspresented the

firstfinetime resolution ofsolarwind abundancevaria-

tions for the elements Cr and Fe, and Fe isotopes.

Itisalready established thatsolar wind and suprathermal

(SEP) ion composition,both elementalandchargestate,

vary according to the source conditions.The so-called first

ionization potential(FIP) effect,which reflectselemental

fractionationincoronalandsolarwindelementalabun-

dances compared to photospheric values for elements with

low FIP's ( <10 eV ),hasbeen observed using long time

averages for slow and CME-related solar wind.The effect

Figure 8.A SOHO-CELIAS/MTOF spectrum accumulated over three

days period (uncorrected for efficiencies, but with the sensor set in a

mode optimized for observing solar wind specieswith masses above

thatofsulfur).Unshadedpeaksrepresenttheelementscommonly

observed byin situsolar wind experiments; elements and isotopes in

greenarenotobservedroutinelybyconve ntionalsolarwind

experiments;and elements andisotopes for which SOHO hasmade

the firstin situspacecraft solar wind observations are inred.

ismuch reduced

in coronalhole solarwind.

The reason

for the "FIP effect" isnotknown,nor why itdependson

solar wind flow type, but some of the currenttheoriescan

be distinguished by what they predict for different elements based on differentphysical constants (e.g., in addition to FIP, there

are theories involving the first ionization time, the ionization diffusion length, etc.).MTOF is making a unique contribution to

thisstudy, both inthe number of elementsthatareobservable forthe firsttime by a solarwind experimentand by the time

resolution of measurements.These include pivotal elements such as K, Na, Al, which have extremely low FIP's (< 6 eV), and

S, P, and Cwhich have FIPsin the transitional FIP region (near 10 eV).

Both chromiumand iron are low FIP elements.The MTOF hasobtained a slow solar wind elementalabundance ratio of⁵²Cr/

56_{Fe = 0.015[!]0.003.This is similar to photospheric values and indicates that chromium behaves in the same manner as iron in}

the FIP fractionation process.

Solar Wind Isotopic AbundancesSolar wind isotopic measurements by CELIAS/MTOF are unique.Previous spacecraft mea-

surements have been restricted to helium, and foil measurements from the manned lunar expeditions have given results only for

helium, neon,and argon.The Apollo FoilExperimentindicated significantvariationsin the helium isotopic composition, but

none were observed in the neon isotopic composition. Itis generally assumed that the solar wind givesan unbiased sample of

isotopic composition of the corona,and thereforethephotosphere,which in turn isassumed to be representative of the outer

solar convective zone.These compositions should then be close to the primordial composition of the solar nebula.

Astrong isotopicfractionationinthesolarwindisnotexpected,althoughweakeffectsmaybecausedbytheion-neutral

separation process that takes place in the upper chromosphere/transition region, andpotentially fractionation could result in the

inner corona due to differences in Coulomb drag.The measurements from MTOF are being used to determine whether there are

differences in relative isotopic abundances among different solar wind regimes (CME-related, coronal hole, or slow solar wind)

or for thesame type of solarwind,butasa function of solar cycle.Differencesbetween differentsolar wind regimesor the

absence of such differences can be taken as indicators of the faithfulness of solar wind particles of the solar surface composition.

Solar Wind Charge State AbundancesThe relative ionization statesof ionsin the corona depend on the localelectron tem-

perature and density, the ions' collisionalionization and radiative and dielectronic recombination rates,and the ions' outflow

velocities.The local coronaldensity and temperature change with altitude, as observed by UVCS.As the solar wind expands

outward,the coronalelectron density decreasesto the extentthatthe solar wind ion expansion time scale isshort compared to

the ionization and recombination time scales.The relative ionization statesbecomeconstant,forever reflective ofthe condi-

tionsatthefreezing-in altitude.Thesolar wind ionsmaintaintheir chemicalandchargestateidentity asthey continue to

Proposal forSOHO SolarMaximum Science Program-

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