The order of the Galactic cosmic ray source (GCRS) composition in terms of first ionization potential (FIP) was examined. For most elements, the degree of volatility is (positively) correlated with the value of the FIP, so that it is not easy to distinguish a correlation of GCRS abundances anomalies with FIP from a correlation with volatility. Only a few permit to distinguish between the two kinds of ordering: if they are depleted relative to refractory metals, volatility must be relevant, if not, FIP is relevant. Among them Cu and Zn would seem to favor FIP. Among the best indicators are Ge and Pb. The abundance anomalies in GCRS are defined relative to a standard which, for the heavy elements concerned, is commonly taken as C1 Carbonaceous Chondrites. Photospheric abundances are more directly representative of the protosolar nebula, and hence of ordinary local galactic (LG) matter. The Ge and Pb reference abundance determinations in the Photosphere and in C1 meteorites are examined and their relevance to the problem with FIP vs. volatility in GCRs is discussed

Grevesse, N.

Meyer, J. P.

English

NASA Technical Reports Server

OG 7.1-2
S
GEIWANIL!_{ANDLEAD : SIGNIFICANT DIFFEKENUES BEIWEEN_ITIC
AND PIiUIDSPHERIC_AI_ES ?
NicolasGREVESSE
Institut d'Astrophysique, Universit6 de Liege, Belgium
Jean-Paul MEYER
Service d'Astrophysique, Centre d'Etudes Nucl6aires de Saclay, France
I. Introduction. A key question at present is whether the Galactic Cosmic
Ray Source (GCRS) composition is ordered in terms of First Ionization
Potential (FIP) (in which case the _ composition resembles that of the
Solar Corona and of Solar Energetic Particles (SEP)/II,12,31,33,39/, and
GCR's have probably been first injected by flaring F to M stars /33/), or
in terms of volatility (in which case (:_'_'smust be largely interstellar
grain destruction products and their similarity to SEP's is purely for-
tuitous /10,15,4/).
The problem is that, for most elements, the degree of volatility
is (positively) correlated with the value of the FIP, so that it is not
easy to distinguish a correlation of GCRS abundances anomalies with FIP
from a correlation with volatility. Only a few volatile, though low_FIP,
elements that are exceptions to the general rule permit to distinguish
between the two kinds of ordering : if they are depleted relative to
refractory metals, volatility must be relevant, if not, FIP is relevant
/32/. P_nong them Cu (semi-volatile ; not depleted) and Zn (very volatile;
only slightly depleted in accordance with its intermediate FIP) would
seem to favour FIP. But among the best indicators are Ge and Pb.
Surprizingly enough, Ge and Pb have recently been found deficient
relative to refractory elements with similar FIP /6,7,23,16,8,28,17,18/.
Is this observation compelling, in the sense that volatility must indeed
be the key parameter ?
The abundance anomalies in GCRS are defined relative to a standard
which, for the heavy elements concerned, is conmonly taken as C1 Carbona-
ceous Chondrites. While for most elements Cl's are certainly not far from
being an unbiased sample of the protosolar nebula (their morphology makes
it plausible ; good agreement with photosphere whenever check possible ;
continuity of abundances beyond Fe), we do not know precisely to within
which _ccuracy this is the case, especially for volatile elements /1,29,
30,2,14,20,21/. Photospheric abundances, though often less accurately
determined, are certainly more directly representative of the protosolar
nebula, and hence of ordinary local galactic (I.G)matter. (As regards C2
carbonaceous chondrites, which are a mixture of 50% C1-1ike material,
plausibly unfractionated, and of 50% highly fractionated material, there
is no reason whatsoever to believe that their bulk composition might have
any relevance as a standard /1,29,30,2,14/.)
Here we shall more closely look into the Ge and Pb reference abun-
dance determinations in the Photosphere and in CI meteorites, and discuss
their relevance to the problem of FIP vs. volatility in GCR's.
2. The meteoritic and photospheric abundances of Germanium. The Ge abun-
dance in C1's is very reproducible /14/, and the value for Cl's quoted in
/2/, Ge = 118 (I.I0), should therefore be reliable (fig. I; see Table I
for notations).
https://ntrs.nasa.gov/search.jsp?R=19850026551 2020-03-20T17:00:22+00:00Z
6 OG 7.1-2
On the other hand, photospheric abundance measurements have now
reached a high degree of accuracy for those elements for which well
measurable lines are present in the solar spectrum and accurate atomic
data are available. The systematic, model dependent errors, as well as
the errors related to departure from LTE, have indeed been reduced to the
few % level. With the Holweger_M6ller model atmosphere and a
microturbulence parameter _0.85 km/s, a high degree of consistency is
obtained from a very large number of lines sampling wide ranges of
wavelengths, optical depths, and excitation temperatures. In particular,
various lines of different ionization states of particular elements, as
well as molecular lines, yield very closely consistent abundances. These
points are discussed in /20/.
As regards Ge in the photosphere, see /25,35/ for previous
studies, and revisions by /5,20/. Five Gel lines can be identified in the
solar spectrum : _3039, 3124, 3269, 4226 and 4685 A. The 13124 and 4226
lines are too strongly blended to be of any use. We are thus left with
three lines.
In Table 1 we give the measured equivalent widths Wk . The value
for the 13039 UV line is based on the spectrum of /35/, which is of good
quality. But the line is quite perturbed, partly by an unidentified
feature. The 13269 line is much less perturbed, and the WA value can
accordingly be determined much more precisely (see fig. in /35/). Values
obtained from older Jungfraujoch spectra, from /35/ and from the atlas of
/13/ agree within 4%. As for the blue 14685 feature, the atlas of /13/
yields an extremely precise value of WA = 5..5±0.2 m_. But there are two
problems. First, the feature is the sum of the Ge I and of a Co I line at
about the same wavelength. The Co I contribution to WA can be estimated
quite reliably to Wk (Co I)=1.5±0.4 n_ based on the accurate transition
probabilities of /9/. We are) left with WA (Gel = 4.0±0.5 m_ for the
contribution of Ge to the feature. In addition, the k 4685 feature shows
a slight asymmetry on the red side, which implies an unidentified blend.
The above value of WA is therefore an upper limit to the true WA (Gel).
The oscillator strengths log gf given in Table I are based on
branching ratio measurements by /26/ normalized to beam foil lifetime
measurements. They should be accurate to within 20%.
Our adopted photospheric Ge abundance, Ge = 72 (l.38)(Table I,
Fig.l) is lower than the C1 value by a factor of 0.61 (1.40).
3. The meteoritic and photospheric abundances of Lead. The abundance of
Pb in Cl's is rather well defined : Pb = 3.15 (1.08) /2/ (Table 2,
fig.2).
As regards the photosphere, see /36, 25, 19/, and especially /.22/
for previous studies. Five Pb I lines can be identified in the solar
spectrum : _ 3639, 3683, 3739, 4057 and 7229 A. The latter two are
extremely doubtful. The i 3639 and _ 3739 lines will be considered, but
they are seriously blended with much more intense lines. Only the I 3683
line is a really good abundance indicator (see fig. in /19/).
In Table 2 we give the equivalent widths WL obtained on the atlas
of /13/. The k 3683 value is in excellent agreement with earlier
determinations /19/. The other two values are very uncertain, and the
previous determinations indeed diverge.
The oscillator strengths log gf given in table 2 are based on
lifetime measurements for several Pb I states (to within 5%) combined
with branching ratio measurements (to within 8%) by /27/. The overall
accuracy is 10%. The validity of the data is confirmed by the relative
7 OG7.1-2
oscillator strengths measurements of /34/ which agree within 0.7% with
/27/ for the ratio of the gf values for the k 3683 and 3639 lines.
Our adopted photospheric Pb abundance, Pb = 1.97 (1.12) (Table 2,
fig.2) is lower than the C1 value by a factor of 0.63 (1.15).
4. General discussion of photospheric vs. CI abundances. We have found
that the photospheric abundance determinations of both Ge and Pb are
lower than their C1 abundance. How does this fit into a more general
comparison between CI and photospheric abundances ? Ge is a moderately
volatile element (Tcond _ 900 K), and /2/ consider that elements of this
class may be on average N 25% lower in the Photosphere than in Cl's. But
the agreement between Photosphere and Cl's is generally improved in the
updated assessment of /20/. The smoothness of the abundance curve of
odd-A (r+s) isotopes vs. mass in the Ga,Ge,As,Se region, as derived from
C1 data, tends to support the C1 value for Ge /1,29,2/. The situation is
1000 _ oD PREOICTED
g  kll "
,,, t • ""
1
- t
t -- t l
,oo , .,1 t<,.l i
!iit ,l'Z "7 _
Z Z a.
In rn o
_ < _
Ge _ Pb _ ,,, c,...,o.c,_,_J,..
ISi = 106 ISi E 10 ll_, P • illli,d on Phltolll_*
10 0.1 _ 0.1
Table 1 - Photospheric and meteoritic abundances of C-enminitan
Line [,ll] W_, [m_i log gf lOgNGellogNH=12] Ge [Si=1061
3039 61.5 + 8.5 0.017 +_ 0.080 3.28 +0.24 53.(1"7_)
3269 43.3 +II'_ -0.921 + 0.080 3.46___'_ 80.(I.'23)
4685 < 4.0 +_ 0.5 -2.013 +_ 0.080 <3.86+0.10 <202.(1.26)
Adopted Photospheric 3.41+_0.14 72. (I. 38)
Meteoritic C1 3.63+0.04 118.(1.10)
Notations : In parenthesis : error factors ; "log Ne_": scale log Nil= 12;
"Ge" : scale Si = 106, based on log NSi-=7.555 /20/.
Table 2 - Photospheric and meteoritic abundances of Lead
Line [_] W). [m_] log gf logNpb [lOgNH=12 ] Pb [Si=106]
3639 [6.4] -0. 700+0. 040 [2.00] [2.8]
3683 7.7+0.4 -0. 513+-0. 040 1.85+_0.05 1.97 (1.12)
3739 [0.8] -0.117+-0.040 [1.96] [2.5]
Adopted Photospheric 1.85+_0.05 1.97 (1.12)
Meteoritic C1 2.05+-0.03 3.15 (1.08)
Notations : see Table I ; [ ]: highly doubtful.
8
OG7.1-2
however, not simple as regards r and s nucleosynthesis in this range of
mass /24/. As regards Pb, it is a highly volatile element (T_^.A _ 400 K)
for which fractionation could easily take place in C1's. For'_'{_hly vola-
tile elements, the observed C1/photospheric ratios scatter a lot /2920/.
The scatter may be real, or be due to poor photospheric determinations.
To muddle up the situation a little more, note also the totally unexpec-
ted but probably reliable overabundances of Fe and Ti by ~ 45% and 25%
in the photosphere relative to C1's, while the agreement between photos-
pheric and C1 data is very close for all neighbouring elements, both
refractory and siderophile /20,21/.
5. Discussion of the Cosmic-Ra_,Ge and Pb abundances. GCRS abundances of
Ge = 66 (1.19) and 64 (1.45) relative to Si = 105 have been obtained b}
/7/ and /28/. It is obvious from fig. I that these values, while low with
respect to the CI abundance of Ge, are prefectly consistent with its
photospheric abundance relative to Si and other low FIP metals.
As regards Pb, we shall compare the (Pb-group)/(Pt-group) = (Z=81
to 83)/(Z=74 to 80) ratio observed in GCR's to that predicted near earth,
starting from I_ abundances based on, either meteoritic, or photospheric
data. The LG abundances for the Pt-group and the Pb-group are respective-
ly 3.46 (1.07) and 3.47 (1.08) based on meteorites, and 3.88 (1.08) and
2.29 (I.11) based mainly on the photosphere (Si = 106) /2,20,21,this
paper,3,38/. So the LG Pb-group/Pt-group ratio is 1.00 (1.11) based on
meteorites and 0.59 (1.14) based on the Photosphere (fig.3). Applying a
bias related to FIP enhances this ratio by a factor of 1.50 (1.25) /33/
(fig.3). Taking into account spallation in the interstellar medium and
instrumental effects on the HF_AO_C3data reduces the predicted observable
ratio by a factor of ~0.43 /7/ (fig.3). (Pure interstellar spallation
calculations by /37/ yield a reduction by a factor of 0.58 to 0.73,
depending on the model, the models with the larger reductions being
favoured in view of the high fluxes of nuclei in the range Z=61 to 75 ;
dashed on fig. 3). The ratios obtained might be compared with the obser-
ved ratios 0.25 (1.35) by /7/ and 0.38 (1.33) by /18/. It is clear from
fig. 3 that the data are inconsistent with the FIP hypothesis if C1
meteorites are taken as a standard, but are not inconsistent if photos-
pheric values are adopted instead.
6. Conclusion. There is an apparently significant discrepancy between the
photospheric and the CI abundances of Ge and Pb. The Ge and Pb abundances
in GCR's are consistent with the ordering in terms of FIP if referred to
the photospheric values.
References
I. Anders, E. 1971, GCA, 35,516. 20. Grevesse, N. 1984a, Phys. Seripta T8, 492. Anders, E. et al. 196"2_,GC.A46,2363 21. Grevesse, . 1984b, in Frontiers oT-'Astr.& Ap.,ed.
3. Beer, H. et el. 1982, Astr.Ap. I05,270 R. Pallavlcini (Florence ..Ital. Astr.Soc.), p.71
4. Bibring, J.P. et al. 1981, 17th"T-CRC,Paris,2,289 22. Beuge, O. et al. 1973, Solar Phys. 30, 301
5. Bi_mont, E. et al. 1977, Phys. Seripta 16,39 23. Israel,M.H. et al. 1983, 18th ICl_C,Bengalore,9,305
6. Blnns, W.R. et aI. 1983, 18th ICl_C,Bang_ore,9,1O6 24. Kappeler, F. et al. 1982, Ap.J. 257, 821
7. Binns, W.R. et al. 1984,Adv. Space Res. 4,N'2--3,26 26. Lmnbert, D.L. et al. 1969, [V_?_AS--f_2,88
8. Byrnak, B. et al. 1983,18th ICl_C,Bangalore,2, 29 26. Lotrian, J. et al. 1978, J.Phys. ]_-T3,2273
9. Cardon, B.L. et al. 1982, Ap.J. 260, 395 -- 27. Lotrian, J. et al. 1979, JQSK'r,21,T43
10. Cesarsky, C.J. et al. 1980, IAU S--ymp.N°94, 28. Lund, N. 1984, Adv. Space Res. _ N°2-3,5
Origin of Cosmic Rays, G. Setti et al. ed., p.361 29. Meyer, J.P. 1979a, "Les El_ment's'et leurs Isotopes
11. Cook, W.R. et al. 1990, Ap.J. Letters 238, L97 dans l'Unlvers" (U. of Liege Press), p.153
12. Cook, W.R. et al. 1994, Ap. J. 279, 827 30. Meyer, J.P. 1979b, 16th ICI_C, Kyoto, 2, 115
13. Delboullle, L. et al. 1973, Atla-s-'of the Solar 31. Meyer, J.P. 1981a, 17th IC_, Paris, __, 266
Spectrum, Universlt_ de Liege 32. Meyer, J.P. 1981b, 17th ICItC, Paris, 2, 281
14. Ebihara, M. et al. 1982,GCA 46, 1949 33. Meyer, J.P. 1965, Ap.J. Suppl. 57, 173"
15. I_pstein, R.I. 1980, 1_ _ 723 34. Muradov, V.G. et al. 1982, Opt.S'pec.(USSR) 52, 25216. Fixsen, D.J. et al. 1963, ICBC,Bangalore,9,119 35. Ross, J.E. et al. 1974, Solar Phys. 35, 281--
17. Fowler, P.H. et al. 1983, 18th ICeC,Bangalore,9,11O 36. Ross, J.E. et el. 1968, Proc.Natl.Aca'd.Sei. 59, 1
19. Fowler, P.H. et al. 1984, 9th European Cosmic Ray 37. Tsao, C.H. et al. 1993, 16th ICl_,Bangalore, 2, 225
Syrup., Kosice 36. Walter, G. et al. 1983, Astr. Ap. 123, 279
19. Grevesse, N. 1969, Solar Phys. 6, 391 39. Webber, W.R. 1982, Ap.J. 255, 329


Germanium and lead: Significant differences between meteoritic and photospheric abundances?

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