The Relative Abundance of Chromium and Iron in the Solar
Wind
J.A. Paquette*, KM. Ipavich*, S.E. Lasley*, P. Bochsler^ and P. Wurzf
"Department of Physics, University of Maryland, College Park, MD, USA 20742
^ Physikalisches Institut der Universitdt Bern, Switzerland, CH3012
Abstract. Chromium and iron are two heavy elements in the solar wind with similar masses. The MTOF (Mass
Time Of Flight) sensor of the CELIAS investigation on the SOHO spacecraft easily allows these two elements to
be resolved from one another. Taking the ratio of the densities of these two elements - as opposed to considering
their absolute abundances - minimizes the effects of uncertainties in instrument efficiency. Measurements of the
abundance ratio are presented here. The First lonization Potential (FIP) of chromium is 6.76 eV, while the FIP of
iron is 7.87 eV. Since Cr and Fe have similar FIPs the ratio of their abundances should not be biased by the FIP
effect which is well known in different solar wind flows. Therefore the Cr/Fe ratio from the MTOF data should
give a good measure of the photospheric abundance ratio. We also compare the ratio measured in this work to the
meteoritic value.
INTRODUCTION
INSTRUMENTATION
Chromium and iron are two heavy elements in the solar
wind with similar properties. In this paper we present a
preliminary study of the chromium to iron abundance ratio in the solar wind using data from the MTOF (Mass
Time of Flight) sensor on SOHO. This is the first measurement of chromium in the solar wind. The abundance
ratio for three short time periods (corresponding to three
different solar wind flow types) and three long (« 1 year
duration) time periods are derived from the data. The
abundance ratio of these two elements can be measured
with sufficient precision using MTOF to allow comparison to photospheric and meteoritic values.
The three short periods were chosen for their relatively
stable bulk speeds, which makes measurment simpler, as
the instrument efficiency is a function of speed. No variation with solar wind flow type in the chromium to iron
abundance ratio was expected a priori, but the choice
of three different flow types allowed the possibility to
be investigated. The three longer time periods were not
explicitly differentiated by flow type. They consisted of
all data during approximately year-long periods in which
the bulk speed was in a narrow range. The study of these
longer periods was intended to test the supposition that
the abundance ratio measured for the shorter periods was
not unusual or atypical.
The MTOF sensor, which is a part of the CELIAS
(Charge Element and Isotope Analysis System) Investigation on SOHO, is shown in Figure 1. It consists of an
energy per charge filter (the WAVE) and a high massresolution (M/AM > 100) spectrometer (the VMass). A
solar wind ion with the requisite E/q to negotiate the
WAVE encounters the carbon foil. After passing through
the foil, a large fraction (the exact value is a function
of both energy and species, but typically from 70% to
more than 99%) of ions will either have been neutralized, or left with charge state +1. Neutrals will travel in a
straight line to the neutral microchannel plate (MCP) detector. Positive ions will be bent towards the ion MCP by
the electric field inside the VMass. In the harmonic electric potential inside the VMass, the time of flight (TOF)
of the ions is proportional to the square root of M/q*
where q* is the charge state after the foil. So in the case
in which q* = 1, the TOF is proportional to ^/M. MTOF
and CELIAS are discussed in greater detail in [1].
In addition, the PM (Proton Monitor) - which is a
subsensor of MTOF - provides solar wind parameters on
a near real time basis. It was used to aid in the analysis
of the MTOF data. The proton monitor consists of a
three-box electrostatic deflection system followed by a
position sensing MicroChannel Plate. The proton monitor
is described in detail in [2].
Instrumental fractionation in MTOF can result from
several sources. Ions whose E/q values are close the up-
CP598, Solar and Galactic Composition, edited by R. F. Wimmer-Schweingruber
© 2001 American Institute of Physics 0-7354-0042-3/017$ 18.00
95
It may be surmised that these two metals have similar
charge state distributions in the solar wind. Hence Cr
ions and Fe ions are likely to have similar E/q distributions at any given time, and so fractionation by the
WAVE will not be important. The small difference in the
masses of the two elements likewise implies similar values for VMass transmission. While the charge state distributions after encountering a carbon foil were measured
for iron, they have not been measured for chromium.
This is a source of uncertainty, but it is unlikely that their
charge states after the carbon foil will be very different
from each other. Therefore, it is likely that instrument
fractionation will be a small effect. It is also likely that
any uncertainty in the ratio of the instrument efficiencies
for the two elements will be less than the uncertainty in
either element's absolute efficiency.
Another consideration in selecting chromium and iron
for study is that the two elements have have similar First
lonization Potentials (FIPs). Chromium's FIP is 6.76 eV,
while the FIP of iron is 7.87 eV. Since both elements
have low FIP, the well-known FIP effect ( see, for example, [6]) will not introduce any fractionation, and the
abundance ratio measured in the solar wind should be directly comparable to the photospheric abundance ratio.
Because both metals have low volatility, the ratio in the
solar wind should also be directly comparable to the meteoritic ratio.
SOLAR WIND ION
E,Q,M
FIGURE 1. Schematic of the MTOF (Mass Time of Flight)
Instrument. Solar wind ions enter through an energy/charge
filter (the WAVE) and pass through a carbon foil, leaving them
with a charge state q*. They then enter a harmonic potential
region in which those with q* > 0 are electrostatically deflected
down to a microchannel plate detector. For an ion of mass M,
the time of flight in this region is °c ^/M/q*.
per or lower limits of the WAVE'S passband are less efficiently transmitted than other ions, but this effect is wellunderstood and can be corrected for. Another fractionation effect is introduced by the carbon foil. The portion
of ions which exit the foil with charge state +1 is a function of both energy and of species. The charge state distribution after exiting a carbon foil has been measured
for many species [3], [4], [5]. While the distribution of
charge states after a carbon foil has been measured for
iron, it has not been done for chromium, and this is therefore a source of uncertainty. Finally, the efficiency of ion
transmission through the VMass region is a function of
energy, since sufficiently energetic ions cannot be turned
back by the electric field and will strike the hyperbola.
Ions of different species in the solar wind (all having
roughly the same speed) will of course have different energies and hence will be fractionated in the VMass. Calibration of MTOF has provided a good understanding of
the details of VMass transmission, although some uncertainty remains.
ANALYSIS TECHNIQUE
The TOF spectra from MTOF are fit using a maximum
likelihood algorithm. The model function has 24 parameters, but fourteen of these are the heights of the peaks of
the various species with masses between 48 and 64. Of
the remaining 10, two describe a linear background, two
are needed to convert from time of flight channel to mass,
two are associated with small subsidiary peaks caused
by electronic "ringing" in the instrument, and the the remaining 4 describe the shape and width of the peaks.
The peak shape (which is identical for all 14 peaks) is a
modified asymmetric Lorenztian. Although this work is
only concerned with masses in the range 52 to 57, a wide
range of time of flight channels was chosen to allow an
adequate fit of the background and other parameters not
related to the heights of the mass peaks.
Figure 2 shows the MTOF data for the relevant range,
together with the model function for the same interval.
The various peaks are labeled with the corresponding
masses. The chromium peak is at mass 52, and the iron
creates peaks at 54, and 56, with a shoulder at 57. The
peak at 48 is titanium, and the peaks at 58,60, and 62 are
primarily nickel.
Two of the parameters provided by the fitting program
CHROMIUM AND IRON
Chromium and iron are close to each other in mass (the
most common isotopes being 52 and 56, respectively).
96
MTOF
TimeTime
of Flight
Spectrum
1996
to April
1997
MTOF
of
Flight
Spectrum April
April
1996
April
1997
MTOF Time
Time of
of Flight
Flight
Spectrum
April
1997
MTOF
Spectrum
April
1996
toto April
380 380
km/skm/s
< V < V< 400
km/s
<
400
km/s
380 km/s
km/s <<
V < 400
400 km/s
km/s
SWV
380
University of Maryland so ho/eel la s/mtof/PM
SW
SW
56 56
56
1 0 0 0 0100001100000000
5 4 55 44
Counts
Counts
Counts
11000000
1 0 0 0 1000-
52 52
o
O
100
5 8 5588
6 0 6600
62
110000
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48
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Observed
Observed Counts
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Time
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Time of
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Channel
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Time of Flight Channel
FIGURE 2.
2. A
A portion
portion of
of
TOF
spectrum
from
MTOF.
The
FIGURE
2.
A
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fromMTOF.
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aa thin
thin
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FIGURE
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are the
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observed
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and
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are
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with
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are
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with
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is the
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atmass
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48is
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52
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at
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and
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and
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60,
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and56
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areis
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peaks are
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primarily nickel.
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and
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theprimarily
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peaks are iron, and the 58, 60,
and 62 peaks are primarily nickel.
52
FIGURE
FIGURE3.
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period.The
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solarwind
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3.3. An
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thechromium
chromium
iron
abundance
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the
chromium
totoiron
iron
abundance
ratio.
the chromium to iron abundance ratio.
56
52 and
correspond to
to the
the peak
peak
heights
of
the
and
the
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peak heights
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of the
the Cr
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and the
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few
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this
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University
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THE CR
CR TO
TO FE
FE
RATIO
IN
DIFFERENT
THE
THE
CR
TO
FE RATIO
RATIO IN
INDIFFERENT
DIFFERENT
FLOW
TYPES
TYPES
FLOW
TYPES
THE CR TO FEFLOW
RATIO
IN DIFFERENT
Three time
time periods
were selected,
selected, each
each corresponding to
FLOW
Three
were
time periods
periods
were TYPES
selected, each corresponding
corresponding to
to
a
different
solar
wind
flow
type.
For
ease
of
analysis,
a different
solar
wind
flow
type.
For
ease
of
different
flow type. For
of analysis,
time
periods
without
large
variations
in
bulk speed
were
Three
time
periods
were large
selected,
each corresponding
to
time
periods
without
variations
in
periods
without
large
variations
in bulk
bulk speed
speed were
were
chosen.
a different
chosen. solar wind flow type. For ease of analysis,
An interstream
time period
period
is shown
shown
in Figure
Figure were
3.
The
An
time
is
in
3.
time periods
without large
variations
in bulk
An interstream
interstream
timeplot
period
shown
in speed
Figure
3. The
The
shaded
region on the
is theistime
period
selected
for
shaded
region
on
the
plot
is
the
time
period
selected
for
chosen.
shaded
region
on
the
plot
is
the
time
period
selected
analysis. This period has a nearly constant velocity. for
This
period
has
aa nearly
constant
velocity.
Ananalysis.
interstream
time
period
is
shown
in
Figure
3.
The
analysis.
This
period
has
nearly
constant
velocity.
A coronal hole time period is shown in Figure 4. The
A
coronal
time
period
is
in Figure
4. The
shaded
onhole
the450-500
plot
the
time
period
Aregion
coronal
hole
time is
period
isisshown
shown
Figure
The
speed
of around
km/s
low
forinaselected
coronal4.for
hole
speed
of
around
450-500
km/s
is
low
for
aa coronal
hole
speed
of
around
450-500
km/s
is
low
for
coronal
hole
analysis.
This
period
has
a
nearly
constant
velocity.
associated wind, but coronal hole flows with speeds in
wind,
but
coronal
flows
with
speeds
in
associated
wind,
butperiod
coronal
hole
flows
with
Aassociated
coronal
time
is hole
shown
in Figure
4. The
this
rangehole
have
previously
been
observed
(see, speeds
e.g.
[7]).in
this
range
have
previously
been
observed
(see,
e.g.
[7]).
have
previously
been
observed
(see,
e.g.
[7]).
speedthis
of range
around
450-500
km/s
is low
forofa acoronal
hole
The
time period
has the
morphology
coronal
hole,
The
time
period
has
the
morphology
of
aa coronal
hole,
The
time
period
has
the
morphology
of
coronal
hole,
associated
wind,
but
coronal
hole
flows
with
speeds
in
with an initial density increase, followed by a subsequent
with
an
initial
density increase,
followed
by
with
anhave
initial
increase,
followed
by aa subsequent
subsequent
this range
been increase
observed
e.g.
[7]).
decrease
andpreviously
adensity
simultaneous
in(see,
both
bulk
speed
decrease and
aa simultaneous
increase
in both
speed
and has
simultaneous
increase
both bulk
bulkhole,
speed
The decrease
time period
the morphology
of in
a coronal
with an initial density increase, followed by a subsequent
decrease and a simultaneous increase in both bulk speed
Date (19
FIGURE 4. PM solar wind parameters for a time period with
FIGURE
4. PM
wind
FIGURE
PMsolar
solarflow.
windparameters
parametersfor
fora atime
timeperiod
periodwith
with
coronal
hole4.associated
coronal
coronalhole
holeassociated
associatedflow.
flow.
A probable CME associated time period is shown in
AAprobable
CME
associated
time
isisshown
inin
FIGURE
PM
solar
wind
parameters
for
aMay
time
period
with
probable
CME
associated
timeperiod
period
shown
Figure
5.4.LASCO
saw
a halo
CME
on
12
1997
Figure
5.
LASCO
saw
a
halo
CME
on
May
12
1997
coronal
hole LASCO
associatedsaw
flow.a halo CME on May 12 1997
atFigure
about5.04:35
UT [9], and
the shock driven by the
atatAabout
04:35
UT
[9],
and
shock
driven
by
the
about
04:35
UT
[9],
and the
the
shock
driven
by
thein
associated
time
period
is on
shown
CMEprobable
arrived atCME
SOHO
slightly
before
01:00
UT
May
CME
atatSOHO
slightly before
01:00 UT
CMEarrived
arrived
SOHO
UTon
onMay
May
Figure
5. LASCO
saw slightly
a halo before
CME 01:00
on May
12
1997
at about 04:35 UT [9], and the shock driven by the
CME arrived at SOHO slightly before 01:00 UT on May
97
15.15.
The
nearly
3-day
period
beginning
just
after
the
15.
The
nearly
3-day
period
beginning
just
after
the
The
nearly
3-day
period
beginning
just
after
the
shock
(shaded
in
gray)
was
the
time
period
selected
for
shock
(shaded
in
gray)
was
the
time
period
selected
for
shock (shaded in gray) was the time period selected for
analysis.
While
thisthis
time
period
bears
some
resemblance
analysis.
While
this
time
period
bears
some
resemblance
analysis.
While
time
period
bears
some
resemblance
to fast
fast
solar
wind,
the
NSO
coronal
hole
show
to
solar
wind,
the
NSO
coronal
hole
maps
show
to fast solar wind, the NSO coronal holemaps
maps
show
Æ of
no no
likely
coronal
hole
within
50°
thethe
equator,
and
no
likely
coronal
hole
within
50
the
equator,
and
likely
coronal
hole
within
50 Æofof
equator,
and
magnetometer
data
from
thethe
ACE
MFI
instrument
shows
magnetometer
data
from
the
ACE
MFI
instrument
shows
magnetometer
data
from
ACE
MFI
instrument
shows
thethe
signature
of aof
a magnetic
magnetic
cloud
time,
the
the
signature
of
cloud
atatthis
time,
sososo
the
signature
a magnetic
cloud
atthis
this
time,
the
identification
of
this
time
period
as
a
CME
associated
identification
of this
time
period
as aasCME
associated
identification
of this
time
period
a CME
associated
oneone
reasonable.
one
isisreasonable.
is reasonable.
University of Maryland
so ho/eel fa s/mtof/PM
2 2
10
was
found.
For
the
coronal
hole
time
period,
2 was
00.30
30
found.
For
the
coronal
hole
time
period,
0
30x10
10 was
found.
For
the
coronal
hole
time
period,
2 2
the
abundance
ratio
was
measured
to
be
1.74
x
10~
74
10
the
abundance
ratio
was
measured
to
be
1
the abundance
ratio was measured to be 174 10 2±
2
2,,and
10~
for
theCME-associated
CME-associatedtime
time
period,
00.31
31
x10
for
the
period,
a aa
031
10 2and
, and
for
time
period,
2 the CME-associated
2
2 2 value
of
1.59
x
10~
±
0.29
x
10~
was
found.
The
2
2
value
of
1
59
10
0
29
10
was
found.
The
ervalue of 159 10 029 10 was found. Theererrors
estimates
are
based
uncertainty
instrument
rors
estimates
are
based
onon
uncertainty
ininin
instrument
re-rerors
estimates
are
based
on
uncertainty
instrument
response,
primarily
due
the
yields
sponse,
primarily
due
totouncertainty
ininin
the
+1+1
yields
forfor
sponse,
primarily
due
touncertainty
uncertainty
the
+1
yields
for
chromium
after
the
carbon
foil.
chromium
after
thethe
carbon
foil.
chromium
after
carbon
foil.
The
results
for
the
comparison
the
three
events
The
results
for
the
comparison
ofofof
the
three
events
ofof
The
results
for
the
comparison
the
three
events
of
different
flow
types
are
shown
in
Figure
6.
As
can
different
flow
types
are
shown
in
Figure
6.
As
can
be
different flow types are shown in Figure 6. As can be
be
seen,
the
values
are
consistent,
within
errors,
with
seen,
the
values
are
allallall
consistent,
within
errors,
with
seen,
the
values
are
consistent,
within
errors,
with
each
other
and
with
both
meteoritic
and
photospheric
each
other
and
with
both
meteoritic
and
photospheric
each
other
and
with
both
meteoritic
and
photospheric
values.
values.
values.
The
result
the
average
the
three
1-year
periods
The
result
ofofof
the
average
ofofof
the
three
1-year
periods
The
result
the
average
the
three
1-year
periods
22
2 2
2.
20
was
0.30
error
estimate
here
was
11.73
73
x10
30
x10
error
estimate
here
was
173
10"
10 ±
030
10~
10 .The
.The
The
error
estimate
here
includes
counting
statistics,
but
was
still
dominated
includes
counting
statistics,
butbut
was
stillstill
dominated
byby
includes
counting
statistics,
was
dominated
by
uncertainty
instrument
efficiency.
This
also
shown
uncertainty
ininin
instrument
efficiency.
This
isisis
also
shown
uncertainty
instrument
efficiency.
This
also
shown
ininFigure
6.6.6.
inFigure
Figure
The
results
from
the
three
time
periods
and
the
average
The
results
from
the
three
time
periods
and
the
average
The
results
from
the
three
time
periods
and
the
average
the
one
year
periods
are
shown
Table
along
ofofof
the
one
year
periods
are
allallall
shown
ininin
Table
1,1,1,
along
the
one
year
periods
are
shown
Table
along
with
values
from
[10]
for
comparison.
with
values
from
[10]
for
comparison.
with
values
from
[10]
for
comparison.
Chromium
to to
Iron
Ratio
Chromium
Iron
Ratio
Chromium
to
Iron
Ratio
Chromium to Iron Abundance Ratio
FIGURE
PMPM
solar
wind
parameters
forfor
time
period
with
FIGURE
solar
wind
parameters
a time
period
with
FIGURE
5.5. 5.PM
solar
wind
parameters
for
aatime
period
with
CME
associated
solar
wind.
LASCO
saw
a halo
CME
about
CME
associated
solar
wind.
LASCO
saw
halo
CME
about
6666
CME
associated
solar
wind.
LASCO
saw
aahalo
CME
about
66
hours
prior
to arrival
the
arrival
of the
shock
near
beginning
of
May
hours
prior
the
arrival
the
shock
near
thethe
beginning
May
hours
prior
totothe
ofofthe
shock
near
the
beginning
ofofMay
12.12.
12.
ONE
YEAR
PERIODS
ONE
YEAR
PERIODS
ONE
YEAR
PERIODS
a one
year
period
beginning
inApril
April
1996,
data
For
aaone
year
period
beginning
ininApril
1996,
allallall
data
ForFor
one
year
period
beginning
1996,
data
with
bulk
speed
determined
PM)
with
the
bulk
speed
(as
determined
by
the
PM)
ininin
aa a
with
thethe
bulk
speed
(as(as
determined
byby
thethe
PM)
narrow
speed
range
(380-400
km/s)
was
summed
over.
narrow
speed
range
(380-400
km/s)
was
summed
over.
narrow
speed
range
(380-400
km/s)
was
summed
over.
This
method
gives
very
good
statistics,
and
efficiency
This
method
gives
very
good
statistics,
and
the
efficiency
This
method
gives
very
good
statistics,
and
thethe
efficiency
(which
is
a
function
of
speed)
varies
very
little
over
the
(which
is
a
function
of
speed)
varies
very
little
over
the
(which is a function of speed) varies very little over
the
small
speed
range.
The
TOF
spectrum
resulting
from
small
speed
range.
The
TOF
spectrum
resulting
from
small speed range. The TOF spectrum resulting from
analyzed
as
described
above.
This
method
does
this
was
analyzed
as
above.
This
method
does
thisthis
waswas
analyzed
asdescribed
described
above.
This
method
does
distinguish
between
data
from
different
flow
types,
not
distinguish
between
data
from
different
flow
types,
notnot
distinguish
between
data
from
different
flow
types,
however.
however.
however.
This
process
was
repeated
time
period
from
This
process
was
repeated
for
the
time
period
from
This
process
was
repeated
forfor
thethe
time
period
from
April
1997
to
April
1998,
and
for
the
period
from
April
April
April1997
1997totoApril
April1998,
1998,and
andfor
forthe
theperiod
periodfrom
fromApril
April
1998
to
September
1999.
Because
of
temporary
loss
1998
totoSeptember
1999.
Because
ofofthe
temporary
loss
1998
September
1999.
Because
thethe
temporary
loss
of
SOHO
in
the
summer
of
1998,
and
the
loss
of
data
of
SOHO
in
the
summer
of
1998,
and
the
loss
of
data
of SOHO in the summer of 1998, and the loss of data
during
December
1998
to
early
February
1999,
the
last
during
December
1998
totoearly
February
1999,
the
last
during
December
1998
early
February
1999,
the
last
time
period
was
actually
of
similar
length
to
the
other
time
period
was
actually
of
similar
length
to
the
other
time period was actually of similar length to the other
two.
two.
two.
RESULTS
RESULTS
RESULTS
Chromium to Iron Abundance Ratio
0.0250.025
0.0200.020
Meteoritic
Meteoritic
0.0150.015
Photospheric
Photospheric
0.0100.010
Interstream
Coronal
Interstream
Coronal
Hole Hole
Average
CME
Average
of of of
CME
CME
Average
1-Year
Periods
Associated
Periods
Associated
Associated 1-Year
1-Year
Periods
Flow Type
Flow
FlowType
Type
FIGURE
Comparison
ofthe
the
chromium
toiron
iron
abundance
FIGURE
6.6.6.Comparison
ofofthe
chromium
totoiron
abundance
FIGURE
Comparison
chromium
abundance
ratio
indifferent
different
solar
wind
flow
types
and
for
the
average
ratio
inindifferent
solar
wind
flow
types
and
for
the
average
ofofof
ratio
solar
wind
flow
types
and
for
the
average
three
one-year
periods
to
the
photospheric
and
meteoritic
valthree
one-year
periods
to
the
photospheric
and
meteoritic
valthree one-year periods to the photospheric and meteoritic values.
Inthis
this
figure,
the
lighter
shaded
region
represents
the
1-σ
ues.
InInthis
figure,
the
lighter
shaded
region
represents
the
1-σ
ues.
figure,
the
lighter
shaded
region
represents
the
1-a
range
of
the
meteoritic
abundance
ratio
reported
by
[10].
The
range
of
the
meteoritic
abundance
ratio
reported
by
[10].
The
range of the meteoritic abundance ratio reported by [10]. The
darker
shaded
region
isthe
the
analogous
photospheric
abundance
darker
shaded
region
isisthe
analogous
photospheric
abundance
darker
shaded
region
analogous
photospheric
abundance
ratio
also
from
[10].
Note
that
the
wider
error
range
of
the
phoratio
also
from
[10].
Note
that
the
wider
error
range
of
the
phoratio also from [10]. Note that the wider error range of the
photospheric
value
completely
encompasses
the
meteoritic
value
tospheric
value
completely
encompasses
the
meteoritic
value
tospheric
value
completely
encompasses
the
meteoritic
value
with
error
range.
The
points
shown
the
plot
are
for
the
with
itsitsits
error
range.
The
points
shown
ononon
the
plot
are
for
the
with
error
range.
The
points
shown
the
plot
are
for
the
average
ofthree
three
periods
ofaproximately
aproximately
year-long
periods
and
average
ofofthree
periods
ofofaproximately
year-long
periods
and
average
periods
year-long
periods
and
three
much
briefer
events;
one
interstream
flow,
another
for
three
much
briefer
events;
one
ananan
interstream
another
forfor
three
much
briefer
events;
one
inter
streamflow,
flow,
another
a coronal
hole
flow,
and
the
last
a CME-associated
flow.
a acoronal
hole
flow,
and
the
last
a aCME-associated
coronal
hole
flow,
and
the
last
CME-associatedflow.
flow.
For the
the interstream
time period,
a value
of the
For
For the
the the
the interstream
interstream time
time period,
period, aa value
value ofof the
the
2
chromium
to
iron
abundance
ratio
of
1
65
10
chromium
65 x1010~2 2± chromium toto iron
iron abundance
abundance ratio
ratio ofof11.65
98
TABLE 1. Chromium to Iron Abundance Ratio
Cr/Fe Abundance Ratio
Photospheric (Grevesse and Sauval, 1998)
Meteoritic (Grevesse and Sauval, 1998)
This Work (Interstream)
This Work (Coronal Hole)
This Work (CME associated)
This Work (1 year beginning Apr 1996)
This Work (1 year beginning Apr 1997)
This Work (1 year beginning Apr 1998)
This Work (Average of three 1-year periods)
CONCLUSIONS
W. I., Livi, S., Marsch, E., Wilken, B., Winterhoff, H. P.,
Ipavich, F. M., Bedini, P., Coplan, M. A., Galvin, A. B.,
Gloeckler, G., Bochsler, P., Balsiger, H., Fischer, J., Geiss,
J., Kallenbach, R., Wurz, P., Reiche, K.-IL, Gliem, K,
Judge, D. L., Ogawa, H. S., Hsieh, K. C, Mobius, E., Lee,
M. A., Managadze, G. G., Verigin, M. L, and Neugebauer,
M., The SOHO Mission, Kluwer Academic Publishers,
Dordrecht, 1995, pp. 441^81.
2. Ipavich, F. M., Galvin, A. B., Lasley, S. E., Paquette, J. A.,
Hefti, S., Reiche, K.-IL, Coplan, M. A., Gloeckler, G.,
Bochsler, P., Hovestadt, D., Griinwaldt, H., Hilchenbach,
M., Gliem, F, Axford, W. L, Balsiger, A., Biirgi, A.,
Geiss, J., Hsieh, K. C., Kallenbach, R., Klecker, B.,
Lee, M. A., Managadze, G. G., Marsch, E., Mobius, E.,
Neugebauer, M., Scholer, M., Verigin, M. I., Wilken, B.,
and Wurz, P., Journal of Geophysical Reasearch, 103,
17205-17213 (1998).
3. Oetliker, M., Charge state distribution, scattering, and
residual energy of ions passing through thin carbon
foils; Basic data for the MTOF mass spectrometer on the
space mission SOHO, Master's thesis, University of Bern,
Switzerland CH3012 (1989).
4. Gonin, M., Interaction of low energy ions with thin
carbon foils; charge exchange, energy loss, and
angular scattering, Master's thesis, University of
Bern, Switzerland CH3012 (1991).
5. Gonin, M., Ein semiempirisches ModeII des
Ladungsaustauches non niederenergetischen lonen
beim Durchang durch dunne Fallen, zur Eichung von
isochronen Flugzeit-Massenspektrometern, Ph.D. thesis,
University of Bern, Switzerland CH3012 (1995).
6. Geiss, J., Space Science reviews, 85, 241-252 (1998).
7. Bohlin, J. D., Coronal Holes and High Speed Streams,
Colorado Associated University Press, Boulder, Colorado,
1977, pp. 27-69.
8. Solar geophysical data prompt reports, Tech. Rep. 623Part I, National Geophysical Data Center, Boulder CO
80303 (1996).
9. Plunkett, S. P., Thompson, B. J., Howard, R. A., Michels,
D. J., Cyr, O. C. S., Tappin, S. J., Schwenn, R., and Lamy,
P. L., Geophysical Research Letters, 25, 2477-2480
(1998).
10. Grevesse, N., and Sauval, A. J., Space Science Reviews,
85, 161-174 (1998).
As can be seen from Table 1, all of the abundance ratios are consistent (within errors) with the photospheric
and meteoritic values. It is also true that all of the values
are slightly higher than both the meteoritic and the photospheric values, but without increased accuracy in the
measurement of the ratio, little can be concluded from
this. It is possible that a small systematic error was introduced in the assumed chromium +1 yields.
Since both chromium and iron are low FIP elements,
the agreement of the values from various flow types with
each other is to be expected. The fact that they also agree
with photospheric values is consistent with the "plateau"
of constant fractionation that is often shown (e.g in [6])
for low FIP elements.
Further study of this question might include consideration of more events of each flow type. Since most of the
uncertainty in the measurement of the ratio is due to uncertainty in the chromium efficiency, precision could be
improved either by measurements of the post-carbon-foil
charge state distributions for chromium, or by calibration
of the the MTOF spare instrument to better determine the
overall chromium efficiency.
ACKNOWLEDGMENTS
This research was supported by NASA grants NAG57678 and NAG5-9282. We would also like to thank the
many individuals at the University of Maryland and at
other CELIAS institutions who contributed to the success of MTOF.
NSO/Kitt Peak data used here are produced cooperatively by NSF/NOAO, NASA/GSFC, and NOAA/SEL.
REFERENCES
1.
1.48 xlO" 2 ±0.19 xl(T 2
1.55 xlO" 2 ±0.051 xlO" 2
1.65 x!0~ 2 ±0.30 x!0~ 2
1.74 xlO" 2 ±0.31 xlO~ 2
1.59xlO" 2 ±0.29xlO~ 2
1.77xlO~ 2
1.75 xlO" 2
1.67xKT 2
1.73 xlO" 2 ±0.30 xlO" 2
Hovestadt, D., Hilchenbach, M., Biirgi, A., Klecker,
B., Laeverenz, P., Scholer, M., Griinwaldt, H., Axford,
99