Solar Abundance of Osmium (Spectroscopy/Cosmochemistry) GEORGE JACOBY and LAWRENCE H

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Proc. Nati. Acad. Sci. USA Vol. 73, No. 5, pp. 1382-1383, May 1976 Astronomy Solar abundance of osmium (spectroscopy/cosmochemistry) GEORGE JACOBY AND LAWRENCE H. ALLER Department of Astronomy, University of California, Los Angeles, Calif. 90024 Contributed by L. H. Aller, February 17, 1976

ABSTRACT The abundance parameter, log gfA, where g Table 1. Synthesis of osmium X 4420 A line is the statistical weight of the lower level, f is the oscillator strength, and A is the abundance (by numbers of atoms with X2 Element Xlower Log gfA respect to hydrogen), has been derived for three lines of osmium r/Pcoll by a method of spectrum synthesis. An apparent discordance 4419.270 FeI 3.63 3 4.90 of the derived abundance with that found from the carbonaceous chondrites is probably to be attributed primarily to errors 4419.520 FeI 4.00 3 4.51 in the f-values, and blending with unknown contributors. 4419.607 (FeI) 4.00 3 4.33 4419.778 FeI 3.30 3 4.56 The goal of the method of spectrum synthesis is to reproduce 4419.840 (FeI) 4.00 3 4.75 accurately the absolute intensity at the center of the disk, 4419.938 VI 0.28 3 2.32 Ix(O,O), and the "limb darkening" Ix(O,)/Ix(OO) in the local 4420.105 (Fel) 4.00 3 4.18 continuum over a limited wavelength interval X1 to X2 that 4420.285 (FeI) 4.00 5 5.83 includes a spectral line or lines of the element of interest. Here 4420.460 OsI 0.00 3 0.45 O 4420.526 SmII 0.33 5 0.75 is the angle between the outward-directed normal to the solar 4420.665 ScII 0.62 5 0.88 photosphere and the direction to the observer. We follow ex- 4420.929 (FeI) 4.00 3 4.43 actly the procedures described in previous papers on the solar 4421.125 SmII 0.38 3 0.58 abundances of platinum (1) and iridium (2). At the outset we must emphasize that the quantity determined is the product log gfA, where g is the statistical weight of the lower level, f few instances, we have employed factors as high as five. We is the Ladenburgf or oscillator strength, and A is the elemental have not allowed for hyperfine structure. To some extent, it can abundance, normally expressed on the scale log A(H) = 12.00. be simulated empirically by an enhanced macroturbulence or Although log gfA can often be established within an accuracy damping constant, provided the pattern is not too broad. A +0.02, blends of the observed line with unknown contributors macroturbulent velocity of 2.5 km/sec has been employed. (particularly molecules or high-level transitions of metals like Note that the Os X 3301.579 and PtI 3301.86 lines fall in the iron) can vitiate the results. In particular, the abundance can same spectral region; data are presented in Table 4 of ref. 1. be established only when the f-values are known; g is always A check on the program is provided by the center-to-limb known. variations in the continuum at X 4420 and Ix(O,O) near 3301 and Observational data were taken from the Kitt Peak Solar 3059. Satisfactory agreement between theory and observation Spectrum Atlas (3) and digitized for treatment in the computer. is found for X 4420 with limb-darkening data of Peytureaux (8) The adopted model solar atmosphere and auxiliary treatment and at X 3059 with the intensity at the center of the disk as of the ultraviolet opacity have been described previously (1). measured by Houtgast (9). At X 3301, there is a discrepancy of Three lines of osmium have been examined: XX 3058.706, about 10%, which, however, does not affect the abundance 3301.579, and 4420.460 (all wavelengths in A). The line of determination. shortest wavelength falls in a strongly blended region, not far from the extremely strong X 3059.09 Fel line; The residual intensity of the iron-line wing upon which the osmium line falls 0.80_ is 0.25 of the continuum. In this region the continuum is strongly depressed by pressure-dependent opacity sources (4). The X Z 0.60 3301.579 line was attributed by Goldberg et al. (5) to a ruthenium transition a5F5-z5G05, the weakest line of this multi- z plet! The equivalent width is greater than those of stronger RuI lines; an empirical curve of growth (6) shows that ruthenium 040 must be a minor contributor to this feature and we can neglect it. The 4420.460 line falls on the wing of the SmII X 4420.526 line. The blending is not severe and should permit a reliable determination of the osmium abundance. Detailed data re- quired for line synthesis are given in Table 1. Successive col- 0.00 umns give the wavelength, the element, the excitation potential 3301.2 3301.4 3301.6 3301.8 3302.0 3302.2 of the lower level in eV, the ratio of the damping parameter WAVELENGTH (A) to that (7), and log FIG. 1. Spectral synthesis of the osmium line X 3301.58. The re- employed computed by elementary theory sidual intensity refers to the continuum (taken as 1.0). The solid curve gfA. Unidentified features are treated as though they were iron is the observed spectrum at the center of the solar disk; the dots refer lines; hence they are indicated by (Fe). to the computed points. Note that the platinum X 3301.87 line falls Normally, collisional damping constants up to about three in the same region. For identifications of individual lines see Table times the value computed by simple theory are expected. In a 4 in ref. 1. 1382 Downloaded by guest on September 23, 2021 Astronomy: Jacoby and Aller Proc. Natl. Acad. Sci. USA 73 (1976) 1383 Table 2. Solar abundance of osmium with Corliss-Bozman f-values H U)z o LuI X Log gf Log A z 3058.706 0.02 2.10 IJo 3301.579 -0.23 0.70 :D 4420.460 -1.05 0.70

O' result. Both numbers are in disaccord with values obtained by 4419.8 4420.0 44202 442Q4 4420.6 4420.8 Urey for carbonaceous chondrites (12) or "solar system values" WAVELENGTH (A) recommended by Cameron (13). We are inclined to favor the abundances derived from carbonaceous chondrites and at- FIG. 2. Spectral synthesis of the osmium X 4420.46 line at the tribute the discordance of a factor of 5 to systematic errors in center of the solar disk. The position of the OsI line which falls near the SmII feature is indicated by the arrow. thef-values. We have assumed log A(Si) = 7.65 for the sun, in this comparison. An even more severe discordance is suggested by the work Fig. 1 shows the spectral synthesis fit for the osmium and of Suess and Zeh (14), who quote 0.85 as the most probable platinum lines near A 3301 at the center of the solar disk. Un- abundance of osmium on the scale N(Si) = 106. With log A(Si) fortunately, no center-limb comparisons are available. Ap- = 7.65 there results log A(Os) = 1.60. Line blending with un- parently, an as yet unidentified line falls between SrI A 3301.782 known contributors as well as inaccuracies in thef-values may and PtI 3301.869. The contribution of ruthenium to the osmium have to be invoked to explain this discrepancy. line is probably at most 10%. The fit for A 4420.46 near the limb (see Figs. 2 and 3) is disappointing; the predicted line depths This program was supported in part by National Science Foundation are greater than the observed. The effect on the abundance Grant AST 71-03362 A04 to University of California, Los Angeles. We to are grateful to Mr. Charles Keyes for helpful advice and to the Campus determination ought be small, however. Table 2 gives the Computing Network for their cooperation. final abundance results. The 3058 line seems to be severely blended with some unknown contributor. Accordingly, we have 1. Burger, H. & Aller, L. H. (1975) Proc. Natl. Acad. Sci. USA 72, adopted an osmium abundance of log A(Os) = 0.70. The log 4193-4195. gf values are taken from the work of Corliss and Bozman (10). 2. Drake, S. & Aller, L. H. (1976) Proc. Natl. Acad. Sci. USA 73, Some years ago, Grevesse et al. (11) derived an osmium 269-270. abundance, log A(Os) = 0.75, in good accord with the present 3. Brault, J. & Testerman, L. (1972) Preliminary Edition of Kitt Peak Solar Atlas, microfilm version. 4. Aller, L. H. (1961) in Physics and Chemistry of the Earth (MacMillan-Pergamon, New York), Vol. 4, pp. 1-25. 5. Goldberg, L., Muller, E. & Aller, L. H. (1960) Astrophys. J. Suppl. Ser. 5, 1-137. z 6. Aller, L. H. (1965) Adv. Astron. Astrophys. 3, 1-25. 7. Uns6ld, A. (1955) in Physik der Sternatmosphiren (Springer- z Verlag, Berlin), pp. 331-334. U) 8. Peytureaux, R. (1955) Ann. Astrophys. 18, 34-41. 9. Houtgast, J. (1968) Sol. Physics. 3,47-54. cr 10. Corliss, C. & Bozman, W. R. (1962) in Experimental Transition Probabilities for Spectral Lines [Nat. Bur. Stds. (USA) Mono- graph 53], 276-282. 11. Grevesse, N., Blanquet, G. & Boury A. (1968) in Origin and 4419.8 4420.0 4420.2 4420.4 4420.6 4420.8 Distribution of the Elements, ed. Ahrens, L. M. (Pergamon, New WAVELENGTH (A) York), p. 177. FIG. 3. Spectral synthesis of the osmium A 4420.46 line near the 12. Urey, H. C. (1972) Ann. N.Y. Acad. Sci. 194,35-44. solar limb (cos = 0.2). The predicted profiles tend to be shallower 13. Cameron, A. G. W. (1973) in Explosive Nucleosynthesis, eds. than the observed ones. Some of these lines are of unknown origin Schramm, D. N. & Arnett, W. D. (University of Texas Press, and/or were synthesized as iron lines. The effect on the abundance Austin, Texas) pp. 3-21. determination is small. 14. Suess, H. E. & Zeh, H. D, (1973) Astrophys. Sp. Sci. 23,173-187. Downloaded by guest on September 23, 2021