This contract supports the investigation of elemental abundances in the solar corona, principally through analysis of high-resolution soft x ray spectra from the Flat Crystal Spectrometer on NASA's Solar Maximum Mission. The goals of the study are a characterization of the mean values of relative abundances of elements accessible in the FCS data, and information on the extent and circumstances of their variability. A summation of the data analysis and reporting activities which occurred during the months of June to December 1993 is reported

Saba, Julia L. R.

English

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NA SA-CR- 19481.1.1
SEMI.ANNUAL PROGRESS REPORT
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FOR CONTRACT NASW-4814
CORONAL ABUNDANCES AND THEIR VARIATION
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Date: 15 December 1993
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Principal Investigator and Author:
Julia L.R. Saba (Lockheed Organization 91-3H)
Author's address (Lockheed Remote Site):
Code 682.2, NASA/Goddard Space Flight Center
Greenbelt, Maryland 20771
Institution address:
Lockheed Palo Alto Research Laboratory
Organization 91-30, Building 252
3251 Hanover Street
Palo Alto, California 93404
ABSTRACT
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This contract supports the investigation of elemental abundances in the solar corona,
principally through analysis of high-resolution soft X-ray spectra from the Flat Crystal
Spectrometer on the 8olaf Mazirnara Mi_io.. The goals of the study are a characteri-
zation of the mean values of relative abundances of elements accessible in the FCS data,
and information on the extent and circumstances of their variability. This report is a sum-
mation of the data analysis and _eporting activities which occurred during the months of
June to December 1993.
Subject termm Solar corona, X-ray spectra, elemental abundances, abundance variability
https://ntrs.nasa.gov/search.jsp?R=19940018803 2020-06-16T16:09: 9+00:00Z
1_-17-£993 1i:55 30± 286 i6i7 GSFC-CODE 685/682 P.03
I. INTRODUCTION
This is the first semi-annual report for contract NASW-4814. The contract resulted from
an award under NASA's Supporting Research & Technology Program after peer review
o_ a proposal submitted by the Principal Investigator (PI) in August 1992 in response to
NASA Reseach Announcement NRA-92-OSSA-10. Yotiflcation o_ the award was given in
February 1993 and funding began in June 1993. The current investigation is a continuation
and an extenulon of a pilot study of coronal abundances begun as a So/Gr Mazimum MiJaion
Guest Investigation (GI) by the same PI.
The contract supports an investigation of elemental abundances in the outer atmosphere
of the Sun, principally through analysis of hlgh-resolution soft X-ray spectra from the Flat
Crystal Spectrometer (FCS) on the Solar Maximum Minion ($MM), a NASA mission ded-
icated to solar observations from 1980 through 1989. This instrument acquired an excellent
data base for studying the relative amounts of oxygen, neon, magnesium, and iron in solar
active regions in various states of evolution and activity. The project includes analysis of
this data base to decouple the ei_ects of temperature and abundance, to assess different
theoretical calculations of spectral line intensities for use in the study, and to account for
the possible effects of opacity due to resonance scattering of certain bright lines. The goals
of the study are a characterization of the mean values of relative abundances of elements
accessible in the FCS data, information on the extent of their variability, identi£eatlon
of possible correlations of variability with active region properties, and clarification of a
possible association between abundance variability and active region dynamics.
II. SCIENTIFIC BACKGROUND
Knowledge of solar elemental abundances is essential for correct interpretation of plasma
diagnostic information from spectral and image data. Also, an assumed set of abundances
is implicit in many aspects of astrophysical data analysis, such as calculations of energetics
and radiative loss rates, and comparisons of relative emission in dii_erent wavebands to
assess possible emission mechanisms. It has recently become apparent that a single set of
abundances does not apply throughout the solar atmosphere, and that in some cases order
of masnltude variability is found, so that many previous analyses must be reconsidered.
In addition to these practical problems, it now appears that systematic differences in
the average composition of the corona compared to the photosphere, and some details of
coronal abundance variability might give important clues to the fundamental problems of
coronal heating and mass supply.
A pattern is emerging that much of the observed variation in abundance8 between the
photosphere and the solar wind and solar energetic particles (SEPs) is associated with the
first ionization potential (FIP) of the elements, in the sense that elements with low FIP
are enhanced in SEPs and the solar wind relative to high-FIP elements, as compared with
photospheric composition. Although there is no convlnclng model yet available, the idea
is that some element separation mechanism operates in a temperature regime of about
10,000 K where low-FIP elements are ionized while high-FIP elements remain neutral.
The 5._'M GI pilot study examined the behaviors of two low-FIP elements, M 8 and Fe,
and two high-PIP elements, O and Ne. A statistical analysis showed that the ratio of the
12-17-IS_ 11:55 30i doo i5i7 o_rc-_oum oom/oo_ P.04
low-PIP Pe to the high-PIP Ne appeared to vary by a factor of 5 or more, spanning a range
which included the photospheric and the nominal coronal values. The other low-PIP/high-
PIP ratios also seemed to vary at least between the photospheric and nominal coronal
values and both the low-PIP/low-PIP ratio Fe/Mg and the high-PIP/high-PIP ratio O/Ne
also showed significant variability. Several issues arose which needed to be addressed in a
more extensive study before the work could progress. The present investigation has been
attacking two of those issues.
III. CURRENT Pl_OGRESS
A. Fu XVII Resonance Scattering
During the reporting period, 15 June to 15 December 1993, the PI has concentrated on
diagnosing and understanding the role of resonance scattering of Fe XVII. The bright Fe
XVII line at 15.01 ._., which featured heavily in the pilot study analysis was discovered by
Schmalz, Saba, and Strong (1992 Astrophys. J., 398, Ll15) to be much more ai_ected by
resonance scattering than previous work by Itugge and McKenzie (1985 Astrophys. J., 297,
338) had suggested. At the center of bright active regions, where the abundance data were
acquired, resonance scattering can deplete the observed flux in a line. The magnitude of the
effect of resonance scattering and the impact on the derived abundance variability is being
assessed in several ways. A fraction of the analysis was repeated using another Fe XVII
line (at 16.78 ._.) which is much less affected by scatter. In parallel, the various theoretical
calculations available for the six bright Fe XVII lines covered by the PCS spectra are being
examined with the assistance of Dr. Anand Bhatia at the Laboratory for A,tronomy and
Solar Physics at Goddard, who has made some of the calculations. At present comparing
different pairs of the lines yield different answers. However, the initial analysis implies
that resonance scattering cannot account for the bulk of the observed variability although
it can introduce a systematic offset in the actual abundance ratios. Work on resonance
scattering will continue in the next reporting period.
B. Diagnostic Tools
Work has begun on comparing the various temperature diagnostic line ratios available in
the FCS data base. The most sensitive temperature diagnostic to use is a ratio of the Fe
XVIII llne at 14.24 ._. with one of the Fe XVII lines. However, to make use of this ratio,
one needs to have good values for the fractions of iron in the ioni_ation states Fe+17 and
Fe+l& Unfortunately, the ionization balance calculations that predict these ion fractions
as a function of temperature have recently come into question. New calculations have been
proposed by Arnaud and Raymond (1992 Astrophys. J., 398, 394) as an improvement over
the previous calculations of Arnaud and Rothent_ug (1985 Astrophys. J. Suppl. Series,
60, 425), which were used in the pilot study. The two sets of calculations yield values of
temperature for a given Fe XVIII/Pe XVII Rux ratio, which translates into dlf_erent relative
abundance ratios for given values of flux ratios for the lines used in the study. An effort to
compare the Fe XVIII/Pe XVII temperature diagnostic with diagnostics from the M s XI
and Ne IX triplets and with the ratio of Mg XII/Mg XI are underway. Although these ratios
are less sensitive to temperature, they ,hould give a handle on which of the two sets of iron
±2-i7-Z995 ii;56 3Oi 286 i6i7 GSFC-CODE 685/682 _,_s
ionization balance calculations are more consistent with the FCS data. Ongoing dialogues
have also been established with several other groups who are comparing predictions oi"
the iron ionization balance calculations with their own data or who are examining the
calculations from i_rBt principles. This work will continue in the next reporting period,
The goal is to be able to convert the various Une _ux ratios to relative abundance ratios
by divi_ng out the temperature response.
IV. PRESENTATIONSs
During the reporting period, the following presentations were made under this contract, to
report and publicize initial findings and to obtain feedback from the community to refine
plans for future work:
5MM Fla_ Crl]j_al Spectrometer Mealurementa of Solar Active Region AbundanceJ: Vari.
ationJ on the PIP theme: J.L.R. Saba and K.T. Strong, 24th meeting of the Solar Physics
Division of the A.A.S., Stanford, California, 13-10 July 1993.
An Abundance of New Information for A_troph_JicJ _om the Solar Corona: J.L.R. Saba,
Laboratory for Astronomy & Solar Physics sendnaz at Goddard Space Flight Center, 30
September 1993.
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NASA ...... RE;ORT'DOCUMENTATiON'PAG£'4"-
(IN LIEU OF NASA FORM 1626)
" [....ACCESSION NO. CATALOG NO.
........................
Coronal Abundances and their Variations 15 December 1993
.....
CODE: 0/gi-30
i_.Um_i-- .... .miimw_m.i------ii m mmm_--------
J. L. R. Saba TION REPORT NO:
.............. 10 WORK UNIT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Lockheed Palo Alto Research Labs B/252
Solar & Astrophysics Laboratgry 0/91-30 .......
3251 Hanover Street , Palo Alto Ca. 94304 NASW-4814
...............................................
i2T SPONSORING AGENCY NAME AND ADDRESS PERIOD COVERED
NASA Headquarters
Solar Physics Branch Semi-annual report for the
Spac e Physics Division period June - December 1993
i__inIiii_...----_IIimi.--------_IIIII
Washington, D.C. 20546 14. SPONSORING AGENCY CODE
NASA HQ/ CODE SS
........................
...........................
This contract supports the investiqation of elemental abundances in the solar
corona, pr!nci ally through analysls of high.resolution soft X-ray spectra
from the Flat _rystal Spectrometer on_NASA_s Solar Maximum M!ss!on. The goals
of the study are a characterization of the mean values oT relative a_unoances
of elements accessible in the FCS datac and information on the extent and
circumstances of their variability. Th_s report _s a summation of the data
analysis and reporting activities which occurred during the months of june to
December 1993.
..................17 KEY WORDS (SuG&E_EB'_-AG÷GER'S"I-iBT'SiS_Ri&G÷iEN'S_A_E"E"T,(1) ..............
X-Ray, Spectra, Corona, (,omposition Space Science, Solar Physics
(OF THIS REPORT) (OF THIS PAGE) I 4 I
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For sale by: Superintentent of Documents, U.S. Government Printing Office,
Washington, D.C. 20402-0001
Semi-annual progress report^: for the
months of june - Decemoer _vv_


Coronal abundances and their variation

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