Sustained emission of low energy solar particles with a composition richer in iron than oxygen is observed in the time period 1974 May 7 to 17. Between 0.7 and 4 MeV/nucleon the relative abundances of C:O:Fe are 0.24:1:1.35. It was suggested that these observations provide indication for effects of heavy ion enrichment in the lower corona of the sun

Fan, C. Y.

Gloeckler, G.

Hovestadt, D.

Vollmer, O.

English

NASA Technical Reports Server

UNUSUAL EMISSION OF IRON NUCLEI FROM THE SUN
by
G. Gloeckler, D. Hovestadt, 0. Vollmer,
and C. Y. Fan
Technical Report #75-077
April 25, 1975
(NASA-CR-142712) UNUSUAL EMISSION OF IRON N75-23450
NUCLEI FROM THE SUN (Maryland Univ.) 14 p
HC $3.25 CSCL 03B
3/92 nclas
G3/92 20999
UNIVERSITY OF MARYLAND
DEPARTMENT OF PHYSICS AND ASTRONOMY
COLLEGE PARK, MARYLAND
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https://ntrs.nasa.gov/search.jsp?R=19750015378 2020-03-22T21:15:03+00:00Z
UNUSUAL EMISSION OF IRON NUCLEI FROM TlHE SUN
G. Gloeckler
Department of Physics and Astronomy, University of Maryland
College Park, Maryland 20742
D. Hovestadt,.O. Vollmer
Max Planck Institute, Garching, Cerimaiv
and
C. Y. Fan
Department of Physics, University of Arizonn
Tucson, Arizona 85721
Abstract
Sustained emission of low energy solar particles with a
composition richer in iron than oxygen is observed in the time
period 1974 May 7 to 17. Between 0.7 and 4 MeV/nucleon the relative
abundances of C:O:Fe are 0.24:1:1.35. We suggest that these
observations provide indication for effects of heavy ion enrich-
ment in the lower corona of the sun.
-1-
Overabundance of heavy nuclei. is frequently obh:erved in the
composition of low energy particles accelerated at the sun (Price et al.
1971; Lanzerotti et al.. 1972; Mogro-Compero and Simpson, 1972;
Fleischer and Hart 1973; Hovestadt et al. 1973a; Crawford et al. 1975).
No satisfactory explanation exists as yet to account: for these enhance-
ments, and specifically for Fe/O ratios reported to be as high as 0.1
to 0.6 (Crawford et al. 1975). In this letter we describe a .1.0 day
period of sustained emission of solar particles hav igi a highly unusual
composition. In this "event" iron is more abundant tha-n oxygen and the
composition of nuclei heavier than helium is enriched by a factor of
about 20.
Our data are obtained using the ULET sensor of the University of
Maryland/Max Planck Institute Experiment aboard the IMP 8 earth orbiting
satellite. IMP 8 is in a low eccentricity orbit with perigee of ; 23
earth radii and a period of ' 12 days. ULET is a dl,/dx vs E three
2 2detector telescope with a geometrical factor of 0.53 c:m sr, a 330 vg/cm
flow through proportional counter as the "AE" element, DI, a conventional
surface barrier Au-Si "E" detector, D2, and a plastic scintillator anti-
coincidence cup, A (Hovestadt and Vollmer, 1971). This design allows two
parameter pulse height analysis and unique identification of heavy
particles with energies far below 1 MeV/nucleon as indicated in Table 1.
Every three hours the experiment is automatically switched between a low
and a high threshold mode of operation where either all chemical elements
or only nuclei heavier than helium are counted and analyzed respectively.
The coincidence counting rates of the DID2A detector combination
for the low threshold (protons, alpha particles and heavier elements)
-2-
and the high threshold (nuclei heavier than helimi) modes are plotted
in Fig. 1(a) for the time period 1974 May 5 to 20. The first day and
the last four days represent the typical behavior of low energy
particle fluxes during "relatively quiet" time periods. Ln particular,
the ratio I( . ) plotted in Fig. 1(b) is about 2- x 1.0 and remains
relatively constant. However, beginning about Ma;y 7 the ratio R decreases
by about a factor of 20 and remains relatively constl:;nt for the next ten
days at about 10 to 20 despite large time variations in both rates during
this period (for example, on May 1.4 both rates increase by a factor of
about 103). On May 16-17 the Z > 2 rate drops by about a factor of 10
without a corresponding decrease in the fluxes of proton and alpha
particles.
Analysis of the Dl vs D2 pulse height data allows us to establish
in detail the relative composition and energy spectra of heavy nuclei
during the period of enrichment. In Fig. 2 we display the AE by E matrix
for ULET for data summed from May 7, 12:00 to May 17, 0:00. The curves
labeled C, 0 and Fe are the tracks of carbon, oxygen and iron group
nuclei obtained from inflight calibration and calibrations with heavy
ions from accelerators. There is an unmistakable clustering of points
near the tracks, especially for iron and oxygen, indicating the pre-
dominance of these nuclei. The points in the region between 0 and Fe
correspond to Ne-Ca nuclei, which are also abnormally overabundant. The
abundance of carbon is visibly below that of oxygen.
In table 2 we compare the relative abundances of protons, helium,
and heavier particles between 0.7 and 4 MeV/nucleon derived for this iron
rich event from the high threshold AE vs E matrix to similar ratios for
-3-
high energy solar flare particles, the solar wind, s,Oar corona and
galactic cosmic rays. One can immediately notic4 the large ernhvhacement
of nuclei heavier than oxygen for the iron enriched particle event:.
The differential energy spectra of iron and ox -,n derived from
the high threshold pulse height data summed from 1974 May 7 to 17 are
shown in Fig. 3. In the energy interval 0.65 to ' \ .I McV/nucleon the
flux of iron exceeds that of oxygen by about a fac.lor of two, while at
lower energies the iron enrichment is even larger. W ,~B.twectn 2.3 and 7.5
MeV/nucleon the flux of oxygen is consistent witll the anomalous oygen
hump discovered by llovestadt et al. (1973b). Below 0.7 MeV/nucleon the
iron spectrum includes contributions from Ne-Ca nucle:i for which no
correction has been made for this preliminary report. These corrections
would tend, however, to lower data points labeled (a) and make the turn-
over of the spectrum already noticeable even more pronounced. The oxygen
point labeled (b) has been corrected for contrilutions; from low energy
iron nuclei. In the insert we show the anisotropy of heavy nuclei above
0.7 MeV/nucleon for the 10 day time period. The arrow indicates the
most probable arrival direction (corrected for the Compton-Getting effect)
which is roughly along the average garden hose direction of the inter-
planetary magnetic field.
What mechanisms could produce such enormous enrichments of heavy
nuclei? What causes the enhancement to appear, persist for about. ten
days (despite large intensity variations for both Z > 1 and Z > 2 particles)
and then disappear? In an attempt to answer- the seconid question, -first
we find that the only correlation with the onset of the iron enrichment
is a sudden Forbush decrease at 4 2-5 hours on May 7. During this same
-4-
day solar wind data recorded by the Los Alamos Experiment on IMP 8
indicated presence of a high speed stream and fluctuating densities,
but no abnormal proton to helium abundance (Bame, private communication).
This leads us to propose that on May 7 the IMP 8 satellite entered a
corotating region filled with energetic particles having a composition
superenriched in iron and remained in this region for about 9 to 10 days.
This region is presumably associated with McMath 12906, which also
produced the two small solar flare particle events oni May 9-10 and
May 14-15 respectively. We note with interest that the first of these
events was He3 rich as Mewaldt and Stone (private communication) pointed
out to us and we also observed with our ULET sensor, indicating an
additional anomaly in particle composition.
Although other explanations undoubtedly exist, we suggest that the
particles observed in the 9-10 day period originated aind were accelerated
in regions of the lower solar corona where density enhancements of heavy
ions are likely to exist. Chapman (1958) first pointed out and
subsequently Jokipii (1965, 1966), Nakada (1969), Geiss (1972) and
others (Delache, 1967) have discussed the basic mechanism of ion separation
due to velocity difference of various species which are caused by
combined effects of a strong temperature gradien.t between the photosphere
and the corona and gravitational settling. These authors indeed find
large enrichments of heavy ions in the lower corona of the sun.
Finally we note that the magnitude of this particle event was very
modest. The time averaged intensity of iron at 1 MeV/nucleon was only
-3 22 x 10 /(cm sr sec MeV/nucleon) and much smaller than the average for
solar flare events summarized by Crawford et al. (1975). Perhaps
-5-
subflare particle events such as this will indicate the extent of the
inhomogeneity in the composition of the solar atmosphere and provide
new insights on dynamical processes on the sun.
We are grateful to P. Laeverenz, R. Kuenneth, E. Tums, and J. Cain
for designing and preparing the University of Maryland/MPI experiment for
launch, and acknlowledge the programming effort of John Dalton and the
calibration of tlhe ULET instrument by B. Klecker. We thank S. Bame for
describing to tis solar wind conditions for the time periods of interest,
and E. Stone and R. Mewaldt for.pointing out the lie 3 rich flare.
Discussions with R. Jokipii were of great benefit to us. This work was
supported by NASA under( ontract NAS 5-11063 and by the Gbrman Government.
- - - -
-6-
References
Bame, S. J. 1972, Solar Wind, edited by C. P. Sonett, P. J. Coleman,
Jr., and J. M. Wilcox, NASA pulil.cation SP-308, p. 535.
Chapman, S. 1958, Proc. Phys. Soc. 72, 353.
Crawford, II. J., Price, P. B., Cartwright, B. G., and Sullivan, J. D.
1975, Ap. J., 195, 21.3.
Delache, P. 1967, Ann. Astron., Vol. 30, p. 827.
Fan, C. Y., Cloeckler, C., and Simpson, J. A. 1968, Canadian J. Phys.
46, S458.
Flelscher, R. L. , and Hart, IH. R. 1973, Phys. Rev. Letters, 30, 31.
Garcia-Munoz, M. 1973, Proc. 13th International Cosmic Ray Conference,
University of Denver, August 17-30, Vol. 5, p. 3513.
Geiss, J. 1972, Solar Wind, edited by C. P. Sonett, P. J. Coleman, Jr.,
and J. M. Wilcox, NASA publication SP-308, p. 559.
Hovestadt, D., and Vollmer, 0. 1971, Proc. 12th International Conference
on Cosmic Rays, Hobart, Tasmania,16-25 August, Vol. 4, p.1 6 0 8 .
Hovestadt, D., Vollmer, 0., Gloeckler, G., and Fan, C. Y. 1973a, Proc.
13th International Cosmic Ray Conference, University of Denver, August
17-30, Vol. 2, 1498.
Hovestadt, D., Vollmer, 0., Gloeckler, G., and Fan, C. Y. 1973b, Phys.
Rev. Letters, 31, 650.
Jokipii, J. R. 1965, Thesis, California Institute of Technology.
Jokipii, J. R. 1966, The Solar Wind, edited by R. J. Mackin and
M. Neugebauer, Pergamon Press, New York, p. 215.
Lanzerotti, L. .. , Maclennan, C. G., and Graedel, T. E. 1972, Ap. J.
(Letters), 173, 1.39.
Mogro-Compero, A., and Simpson, J. A. 1972, Ap. J. (Letters), 177, 1,37.
Nakada, M. P. 1969, Solar Phys., 7, 302.
Price, P. B., Hutcheon, I., Cowsik, R., and Barber, D. J. 1971, Phys.
Rev. Letters, 26, 916.
TABLE 1. ENERGY RANGE OF ULET RESPONSE TO VARIOUS N1UCLEI
Chemical Threshold
Element Energy Range (MeV/nucleon) Mode
Protons 0.43 - 1.49 Low Threshold
He •0.31 - 6.6
C 0.19 - 19
0 0.17 - 21 High Threshold
Fe 0.075 - 35
TABLE 2. RELATIVE ABUNDANCES OF PROTONS AND HEAVY PARTICLES NORMALIZED TO OXYGEN
Chemical Iron Rich Event(a) Solar Flare Solar Galactic
Element (0.7 - 4 MeV/n) Particles(b) Solar Find )  orna(b) as- Corona Cosmic Rays
(1 15 MeV/n) (% 100 MeV/n)
Protons (3.20 ± 0.15) x 104 - 5 x 105 1.4 x 105  1.8 x 10 4(g)
He 2470 ± 320 8 40 0 (c) 1.5 x 104 8300 4 5 0 0 (g)
C 65 ± 11 50 ± 4 - 60 100
0 
- 100 2 100 2 100 2 100 100
Ne-Ca 140 ± 22 39 ± 5 31 27 63
Fe 135 ± 21 8 ± 2 17 6 7
(a) present work
(b) from data compiled by Crawford et al. (1975)
(c) variable
(d) Bame (1972)
(e) includes only Ne and Si
(f) Garcia-Munoz (1973)
(g) Fan et al. (1968)
-9-
Figure Captions
Fig. 1i (a) Countring rates of Z > 1 nuclei (primarily protons and
alpha particles) and Z > 2 nuclei for the 1974 May 5-20 t:ime
period.
(b) Iime dependence of the ratio of proton plus alpha to
Z > 2 particles. Note that this ratio is small and remarkably
constant from May 7 to 16 despite large intensity variations
in the counting rates. SEV gives the angle between the earth-
sun and the earth-satellite vectors and shows that between
the onset and disappearance of the iron etnrichment the IMP 8
satellite was in interplanetary space.
Fig. 2 The AE vs E pulseheight analysis matrix for the 1974 May 7 to
17 time period showing the enormous enrichment of iron nuclei.
Fig. 3 Time averaged differential energy spectra for iron and oxygen
during 1974 May 7 to 17. The energy dependent enrichment of
iron over oxygen is evident, with the iron flux exceeding oxygen.
Points labcled (a) include contributions from low energy Ne to
Ca nuclei. Point (b) has been corrected for relatively large
contributions from Z > 8 nuclei below - 0.2 MeV/nucleon. The
insert shows the relative number of heavy particles above 0.7
MeV/nucleon in each of four 900 sectors in the ecliptic plane.
The most probable arrival direction is along the average garden
hose angle of the interplanetary magnetic field.
(a)ULET/MPI DID2A COUNTING RATE
U of Maryland Experiment
IMP 8 Z I NUCLEI
O (LOW THRESHOLD)
0
10
z I
U) -I i: , ,
S-2
10
SEV 60 120 180 240 300 0 60
DAY 5 6 7 8 9 10 11 12 13 14 5 16 17 18 19 20
MAY 1974
(HIGH THRESHOLD)
S2(b) /
I I I t I I I 
DAY 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20
MAY 1974
760 ,
Max Planck Institut / Univ. of Maryland
ULET AE vs. E Matrix
680 I I
2 342 1
I 2 4 5 2 2 2 1 2 3 II
154 113823 14 24 12 1 2 I
3 7 8,10T343 3 13"2-;2,2 2 2 2 2
600 - 15 6/7 4 I 2 I 2 2 2 I I I I 1-- 1 3 I I I
1227.5 1 2 1 1 2 2 i I
,2219"4 I. I I I I F
0 2453 1 I I I I I
-1 12264 2 3 I 2
z 520- 18 9 3 3 I I
Z 2212 4 3 2 I I 1 2
,, 39136 12 1 3
C 12911 25 2 I I
o3 5 8 3 1 1 2 I 1 I 1
=:440 44j3 3 I 2 2 2 2 I I
O 123 I1 2 3 2 2
2438 2 3 1 I 2 I I 2
6574411 2 I 2 I I I
w 15 629 t2 1 2 I I I I
< 360 20 5118e 5 5, 2, 1  I
235,55134 4 55 I I I
14 475112 3 6 7-3 I 2 i I
33615 11 5,1 i 4 43 3 I
4553,15 9 2 21 I 21 I
280 6025 9 5 I 11 1 21 I
41 i12 5 3 I I
33 14 2 1 I 1 I I I
152 11 1 1 ,
42 2 1 1
200 23 1 C 0 
-
I I I I I I I I I
0 80 160 240 320 400 480 560 640 720 800
E- D2 Channel Number
-12-
-I
10
(a) ULET/MPI
U of Maryland Experiment
IMP 8
May 7-17, 1974
10a) Iron
(b)
-3 Oxygen10
U)
U5
10
-6
tO 0.1 I I til
Kinetic Energy (MeV/nucleon)
Figure 3


Unusual emission of iron nuclei from the sun

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