  Studies of patterns of abundance enhancements of elements, relative to
solar-coronal abundances, in large solar energetic-particle (SEP) events, and
of their power-law dependence on the mass-to-charge ratio A/Q of the ions, have
been used to determine the effective source-plasma temperature T that defines
the Q-values of the ions. We find that a single assumed value for the coronal
reference He/O ratio in all SEP events is often inconsistent with the
transport-induced power-law trend of the other elements. In fact, the coronal
He/O actually varies rather widely from one SEP event to another. In the large
Fe-rich SEP events with T = 3 MK, where shock waves, driven out by coronal mass
ejections (CMEs), have reaccelerated residual ions from impulsive suprathermal
events that occur earlier in solar active regions, He/O = 90, a ratio similar
to that in the slow solar wind, which may also originate from active regions.
Ions in the large SEP events with T < 2 MK may be accelerated outside active
regions, and have values of 40 < He/O < 60. Mechanisms that determine coronal
abundances, including variations of He/O, are likely to occur near the base of
the corona (at ~ 1.1 RS) and thus to affect both SEPs (at ~2 - 3 RS) and the
solar wind. Other than He, reference coronal abundances for heavier elements
show little temperature dependence or systematic difference between SEP events;
He, the element with the highest first ionization potential, is unique. The
CME-driven shock waves probe the same regions of space, at ~2 RS near active
regions, which are also likely sources of the slow solar wind, providing
complementary information on conditions in those regions.
