A technique is proposed for specifically determining the relative solar coronal abundance of neon and magnesium. The relative abundance is calculated directly from the relative intensity of the resonance lines of Ne X (12.134A) and Mg XI (9.169A) without the need for the development of a detailed model of the thermal structure of the corona. Moderate resolution Bragg crystal spectrometer results from the OVI-10 satellite were used to determine a coronal neon to magnesium relative abundance of 1.47 + or - 0.38. The application of this technique to a recent higher resolution rocket observation gave an abundance ratio of approximately 0.93 + or - 0.15

Rugge, H. R.

Walker, A. B. C., Jr.

English

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https://ntrs.nasa.gov/search.jsp?R=19760010939 2020-03-22T16:28:35+00:00Z
9V
SUIPR Report No. 650
The Relative Abundance
Of Neon and Magnesium
in the Solar Corona
(NASA-CP -1 46194) THE 1: 73LATIVr, ABUNDA INCE OF	
N76-18027
N EON AND 14 ,^ G Y ESTU m IN THP SOL A P COPOMA
(Stanford Univ.)	 18 F HC $3.50	 CSCT- 03B	 Tinclais
G3/92 14235
by
H. R. Rugge
A. B. C. Walker, Jr.
January 1976
MAP,
RECEIVED 
k' "
"Sh %I fpco
National Aeronautics and Space Administration
Grants NSG-2049 and NSG-7099
:z^f	 aGyp'`;
..........
INSTITUTE FOR PLASMA RESEARCH
STANFORD UNIVERSITY, STANFORD, CALIFORNIA
V N ZED
A4
ABSTRACT
A technique is proposed for specifically determining the relative
solar coronal abundance of neon and magnesium. The relative abundance
is calculated directly from the relative intensity of the resonance
lines of Ne X (12.1341) and Mg XI (9.1691) without the need for the
development of a detailed model of the thermal structure of the corona.
Moderate resolution Bragg crystal spectrometer results from the OVI-10
satellite are used to determine a coronal neon to magnesium relative
abundance of 1.47 f 0.38. The application of this technique to a
recent higher resolution rocket observation gives an abundance ratio
of= 0.93±0,.15.
I. INTRODUCTION
Solar abundances determined from the analysis of chromospheric
line intensities are subject to uncertainties owing to the particular
atmospheric models and the values of the atomic rate constants used.
In addition, they are incomplete since the chromospheric spectrum
contains no lines from the important noble gasses. Published compi-
lations of solar system abundances are frequently strongly weighted
by meteoric data for the nonvolatile elements (Urey, 1972; Cameron,
1974). Recent determinations of solar abundances using other techniques
such as the analysis of permitted coronal lines (Pottasch, 1967; Walker,
1975), the solar wind (Barre, Ashbridge, Hundhausen and Montgomery,
1970) and solar cosmic rays (Bertsch, Fichtel and Reames, 1972;
Crawford, Price, Cartwright and Sullivan, 1975) have confirmed the
general abundance models derived from chromospheric and meteoric
studies, but have raised questions about the abundances of specific
elements, in particular neon, argon and oxygen.
In the present paper, we use an approach developed by Walker (1972)
which specifically allows the relative abundance of neon and magnesium
to be calculated directly from the relative intensity of the resonance
lines of Ne X (12.1341) and Mg XI (9.169A' ) without the development of
a detailed model of the thermal structure of the corona. The intensity
ratio of these linesis not sensitive to temperature over the temperature
range where these active region 77nes are efficiently excited. The
close proximity of the two lines in wavelength also minimizes the error
introduced by uncertainties in spectrometer calibration curves.
	 d
The most comprehensive set of observations, obtained on the
OVI-10 satellite, are only of moderate spectral resolution, so that
it is necessary to correct the neon and magnesium line intensities
for line blends in order to carry out the analysis. However, even
with these limitations, the present analysis has allowed us to establish
l
the Ne/Mg abundance ratio to ±30%. The technique has also been applied
i
to high resolution data obtained by Parkinson (1975). The Ne/Mg
abundance ratios recently quoted in the literature have varied by a
factor of 4. While the abundance of magnesium relative to silicon
(which has been used as a standard by the workers studying meteoric
abundances) is subject to some uncertainty, the variation in the most
recently published work is relatively small, so that the improved Ne/Mg
ratios derived in the present paper can be converted to an absolute
II. THEORY
The relative flux of the Ne X and Mg XI resonance lines can be
k written (Walker, Rugge and Weiss, 1974a), 	 1
C A^F Ne	 'M	 - Ne fdTe (Te)aNe X^Te)JNe X ls2-ls2 ^Te)_	 _
R
	 F(	
Ne
Ne AM
	 dTeM Te)aMg XI(Te)JMg XI 1s2-1s2p (Te ) 	(1)
r^
g
where	 F	 is in units of ergs cm 2 sec-1,	 AZ	is the abundance of
element	 Z	 with respect to hydrogen, and	 aZz (Te )	 is the fractional
population of ion	 z	 of element	 Z.	 The function	 J(Te)	 depends only
on atomic .rate constants and is, to first order, simply equal to the
collisional excitation rate. 	 We have calculated the emission functions
aZz(Te)JZz(Te)	 (Walker, 1972; Walker and McKenzie, 1975) including all
relevant collisional and radiative and dielectronic recombination
processes and cascades up to levels with 	 n = 6.	 Earlier calculations
of these emission functions carried out by Tucker and Koren (1971)
agree with our latest calculations to within = 10% when normalized to
the same abundances.	 For the simple, highly charged ions of interest
here, the theoretical excitation rates, often a serious source of error
in this type of analysis, should be accurate to ±20%, or better.
i
The results of our calculations are presented in Figure 1, from
which it can be seen that the ratio	 INe/IMg	 is approximately indepen-
x
°K	 106 °K.dent of temperature for 	 3 X 106 	5 T < 9 . 5 X	 The emission
I
' functions for the Ne X and Mg XI resonance lines have their maxima
well within the temperature range where the ratio remains approximately
. constant.	 Thus, relative abundances calculated from the observed line
I. intensity ratios, using equation (1), will depend only weakly on the
shape assumed for the emission measure function:
3
For the lines under consideration here, the relatively complicated
active region emission measure function found by Walker, Rugge and
Weiss (1974a,b) reduces to the form proposed by Chambe (1971) and used
by Batstone et al. (1970) and Acton et al. (1972) to characterize
active regions;
M(T) = C 10-T/Ti	 (2)
Walker, Rugge and Weiss found T1 = 3.5 X 106 °K and T1 =
f,
4.0 X 106 °K, Batstone et al. found T1 — 7 X 106 OK and Acton et al.,
using lower energy lines, found T1  3.2 X 106 °K for a large active
region of the type most commonly observed by the OVI-10 satellite. We
f
have evaluated equation (1) using the differential emission measure
functional form given in equation (2) for a number of values of Tl.
The results are given in Table 1. In the region which best characterizesi
the OVI-10 active regions, T l Z 3 X 106 OK, the variation in R
derived from equations (1) and (2) is but a few percent. We conclude 	 {
that variations in active region structure should result in an
uncertainty of < ±5% in the relative Ne/Mg abundance derived from the
Ne X and Mg XI line ratio.
4
0TABLE 1
Dependence of the Ne X/Mg XI Intensity Ratio (R) on Active Region
Emission-Measure*
T Ti T1
(106 o K) R	 (106 o K)	 R (106 o K) R
1.5 0.9	 2.5	 1.06 4.0 1.10
2.0 1.01	 3.0	 1.10 w 1.10
III. RESONANCE LINE OBSERVATIONS
The accuracy of the technique described in Section II is improved
if a reasonably large body of observations can be used to establish
the intensity ratio of the Ne X and Mg XI resonance lines, since the
minor effects of variations in the emission measure function will be
averaged out. The largest body of well calibrated observations with
sufficient resolution appears to be the observations obtained with the
KAP Bragg crystal spectrometer on board the OVI-10 satellite (Rugge
and Walker, 1963). The calibration of the 017I-10 spectrometer and the
procedure used to correct the observations for scattered light and to
subtract the x-ray continuum and background from lines is described
in detail by Walker, Rugge and Weiss (1974b). However, the moderate
resolution of the spectrometer results in the blending of closely
spaced lines and, when several strong localized sources are visible
i
on the _solar disk, in confusion owing to the overlapping of the spectra
from each source. Because of this latter difficulty, only scans in
which the solar x-ray spectrum was dominated by a single active region
were used in the analysis. As a result of this weeding process, 14
orbits of data, obtained between December 1966 and April 1967, were
selected for analysis.
The Mg XI resonance line at 9.169A is not clearly resolved from
the intercombination line ls2 1S 1s2s 3P, and from the close dielectronic
satellite lines in the OVI-10 spectra. To overcome this difficulty we
1
have chosen to integrate the total number of counts above background
1
between 9.165 and 9.320A, thereby including the intensities of the
resonance, intercombination, '
 and forbidden lines of Mg XI, as well as
6
all of the nearby satellite lines of Mg X. This total intensity is
then corrected to yield the resonance line intensity in the following
way. Parkinson's (1972) Mg XI spectrum is used to determine the
p	 relative contribution of the Mg XI lines in the wavelength interval
directly. His measurements of the intensity of these He-like lines
is in good agreement with recent theory (Gabriel, 1972; Bhalla,
Gabriel and Presnyakov, 1974) and other observations of He-like lines
(e.g., Rugge and Walker, 1971; Acton et al., 1972). The relative
intensities of all the satellite lines in the wavelength interval for
the OVI-10 data are calculated from the relative intensities of these
lines observed by Parkinson, corrected for a temperature difference
using the Bhalla et al. theory. The somewhat lower effective tempera-
tures obtained from the OVI-10 data compared to the Parkinson data
(3.2 X 106 OK to 4.0 X 106 OK, respectively) raise the satellite line
fractional contribution somewhat in our spectra compared to that obtained
by Parkinson. The Mg XI resonance line intensity is obtained by
correcting for these additional lines in the wavelength interval. The
a
uncertainty in this correction results primarily from the calculation 	 s
of the temperature correction to the Mg X satellite line relative
intensities. It is estimated to be - +15%.
The two strongest lines closest to the Ne X resonance line at	 i
12.134A are the Fe XVII lines at 72.12! (2p 6 1S-2p54d 1Pl) and at
12.26! (2p6 1S-2p54d 3Dl). The 12.261 line can be separated from the
Ne X resonance line for the OVI-10 spectra, but the 12.12k line cannot.
a
To obtain the intensity of the 72.12A Fe y7JII line, we have chosen to
establish the value of the (presumed) constant ratio between the 72.72!
dine 'and the much stronger and easily resolved lines of Fe XVII at
15.01! (2p6 1S-2p53d 1P1) and at 16.77! (2p6 1S-2p53s 1P1)
7
UN
't f! 3
i1,
1
To obtain these ratios we have analyzed several orbits of higher
w
resolution KAP crystal spectrometer data, obtained with the OVI -17
satellite (Walker, Rugge and Weiss, 1974c), and used the high resolu-
tion rocket spectrum obtained by Parkinson (1975). The observed
ratios are in reasonable agreement with the calculations of Loulergue
and Nussbaumer (1975). Thus, we calculate the line intensity of the
0
12.12A Fe XVII line, which must be subtracted from the blended lines
0
at 12.13A to obtain the Ne X resonance line intensity, using measured
ratios between this line and other strong and easily resolved Fe XVII
lines also measured with the OVI-10 spectrometer. The total uncer-
tainty in correctly assessing the intensity of the Ne X resonance line
after subtracting the blended 12.121 line is estimated to be N ±25%.,
The ratios of the Ne X resonance line intensity (in ergs cm 2sec-1)
3
to the Mg XI resonance line intensity (in the same units), R, obtained 	 r
from the OVI-10 data are shown inFigure 2, plotted against the relative
intensity (in counts) of the Mg lines near 9.21. As can be seen from
the figure, there is little, if any, correlation between the ratio R
o
and the total 9.21 intensity. This should be the case if the ratio
if
is, as expected, essentially temperature independent for the observa- 	 j
3
tions used. The scatter in the data is consistent with a constant
ratio having the uncertainties discussed earlier. If we assume the
ratio is, in fact, constant, we may average the data and obtain a
i
ratio of the Ne X resonance line intensity to that of the Mg XI
resonance line of 0.90 ± 0.24. Using the result of equation (1), this
a	
leads directly to a relative solar coronal neon to magnesium abundance
of '1.47 ± 0.38.
8
f	 'z ) 1
Very recently, data which do not require corrections for
blending of lines with the Ne X or Mg XI resonance lines have become
available. We have applied the technique described in Section II to
this single high resolution spectrum obtained by Parkinson (1975)
from a rocket. The ratio of Parkinson's Ne X/Mg XI resonance line
fluxes is 0.57 ± 0.10, which leads to a relative Ne/Mg abundance
ratio of 0.93 f 0.15 independent of whether or not we use his derived
active region emission measure function or the function expressed in
equation (2). This further emphasizes the independence of the tech-
nique from the detailed thermal structure of the active region for the
Ne to Mg abundance determination.
tr
i
IV. DISCUSSION
The technique described in this paper has been applied to 14 orbits
of moderate resolution x-ray data obtained on the OVI-10 satellite. The
relative solar coronal neon to magnesium abundance has been found to be
1.47 f 0.38. Application of this technique to a single high resolution
x-ray spectrum obtained by Parkinson (1975) yields a relative abundance
of 0.93 t 0.15. These values compare with a value recently obtained by
the authors, using a less direct technique, of 1.8 (Walker, Rugge and
Weiss, 1974a) b). Other recent solar results have ranged from an
Ne/Mg ratio of — 0.6 obtained from the analysis of the Li-like lines in
the solar XUV spectrum (Flower and Nussbaumer, 1975), — 0.8 obtained
from solar cosmic ray measurements(Crawford et al., 1975), — 0.9
(Withbroe, 1971; Dupree, 1972) and 1.75 (Malinovsky and Heroux, 1972)
obtained from coronal XUV measurements, to a ratio of - 2.9 (Bertsch
et al_., 1972) obtained from other solar cosmic ray measurements.
Since, as mentioned above, most recent measurements of the Mg
abundance have been found to be between 30 and 35 X 10-6 relative to H,
the OVI-10 Ne/Mg ratio obtained in this paper may be used to derive an
w	 Ne abundance relative _H of = 47 X 10-6 . Parkinson's data, used in the
same way, lead to an Ne abundance of 30 X 10 -6.
We would like to again empbasize the basic simplicity of the
technique described in this paper when it is applied to high resolution
solar crystal spectrometer data easily obtainable with presently flown
instrumentation.' The ultimate accuracy of the Ne/Mg results obtained
are limited only by the uncertainties in resonance line calculations
and the slight variations in the resonance line intensity ratios with
active region temperature.
10
a
IREFERENCES
Acton, L. W., Catura, R. C., Meyerott, A. J., Wolfson, C. J., and
Culhane, J. L., 1972, Solar Phys., 26, 183.
Bame, S. J., Asbridge, J. R., Hundhausen, A. J., and Montgomery,
M. P., 1970, J. Geophys. Res., ,M, 6370.
Batstone, R. M., Evans, K., Parkinson, J. H., and Pounds, K. A.,
1970, Solar Phys., 2^, 389.
Bertsch, D. L., Fichtel, C. E., and Reames, D. V., 1972, Ap. J.,
?7?, 169•
Bhalla, C. P., Gabriel, A. H., and Presnyakov, L. P., 1975, to be
published in Mon. Not. R. Astr. Soc.
Cameron, A. G. W., 1974, Space Sci. Rev., Z^, 121.
Chambe, G., 1971, Astron. Astrophys., 12 1 210.
Crawford, H. J., Price, P. B., Cartwright, B. G., and Sullivan, J. D.,
1975, Ap. J . ,	 213.
Dupree, A. K., 1972, Ap. J., ,,;178 527•
Flower, D. R., and Nussbaumer, H., 1975, Astron. Astrophys.,, 295•
Gabriel, A. H., 1972, Mon. Not. R. Astr. Soc., 160, 99•
Loulergue, M., and Nussbaumer, H., 1975, preprint, to be submitted
to Astron. Astrophys.
Malinovsky, M., and Heroux, L., 1973, Ap. J., 181, 1009.	 {
Parkinson, J. H., 1972, Nature Phys. Sci., 236, 68.
Parkinson, J. H., 1975, Solar Phys., 22, 183.
Pottasch, S. R., 1967, Bull. Astron. Soc. Neth., 19, 113.
Rugge, H. R., and Walker, A. B. C., Jr., 1968, Space Research VIII,
	
a
Ed. A. P. Mitra, North Holland Publishing Co., Amsterdam, p. 439.
11
11
i
{f Rugge, H. R., and Walker, A. B. C., Jr., 1971, Solar Phys., 18, 244.
r
Tucker, W. H., and Koren, M., 1971, Ap. J., 168, 283.
i
Urey, H. C., 1972, Ann. of the New York Acad. cf Sci.,, 35•
Walker, A. B. C., Jr., 1972, Space Sci. Rev., 13, 672.
Walker, A. B. C., Jr., 1975, Solar Gamma-, X and EUV Radiation,
i
Ed. S. R. Kane, D. Reidel Publishing Co., p. 73.
i
Walr.er, A. B. C., Jr., and McKenzie, D. L., 1975, private communication.
Walker, A. B. C., Jr., Rugge, H. R., and Weiss, K. S., 1974a, Ap. J.,
188, 423.
Walker, A. B. C., Jr., Rugge, H. R., and Weiss, K. S., 1974b, Ap. J.,
,
^^92, 169
Walker, i. B. C., Jr., Rugge, H. R., and Weiss, K. S., 1974c, Ap. J.,
94, 471.
Withbroe, G. L., 1971, NBS Special Pub., No- 353, P. 17•
tFIGURE CAPTIONS
Figure 1. The intensities of the Ne X and Mg XI resonance lines (left
hand scale) and the ratio of the Ne X to the Mg XI
resonance line intensities (right hand side) plotted versus
temperature. The calculations are carried out for an
assumed neon to magnesium relative abundance of 1.8.
Figure 2. The measured energy ratio of the Ne X resonance line to
the Mg XI resonance line plotted against the average Mg
intensity per scan (in counts. Each data point represents
the average of several scans; the majority represent the
average of a full orbit of data.
1
i
a
a
13
,E
j
	
10-52	 ^—	 10.0
1LEFT-HAND	 ^i /• ^^,
SCALE --^— ;.y	 ^ \
U	 ^
RIGHT-HAND SCALE
r
	
10-53	 /	 1.0
co
1.2
CIO 1.0cu
E
0.8
u-
u
0.6
0.4
. 9
--'\- AVERAGE VALUE
i
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The relative abundance of neon and magnesium in the solar corona

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