Annu. Rev. Astron. Astrophys. 1981. 19: 77-113
Copyright © 1981 by . All rights reserved

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2. THE SOLAR NEIGHBORHOOD

We regard the solar neighborhood, somewhat loosely, as the region within which fairly accurate abundances of elements can be determined by stellar spectroscopy, i.e. that within a distance of the order of a kiloparsec. Important topics are (a) the standard abundance distribution in stars and the interstellar medium (ISM) and its uniformity (or otherwise); (b) the age-metallicity relation; (c) the statistical distribution of metallicities in long-lived stars; and (d) abundance anomalies of individual elements or isotopes that are considered as population-related, rather than due to processing in the observed stars themselves.

2.1. Standard Abundance Distribution

Most of our "standard" abundances come from observations within the Solar System (e.g. Cameron 1980), but a comparison with abundances in the ISM and in hot young stars gives an idea of the degree to which solar abundances are truly "cosmic" and provides some insight into the uncertainties in all three sources of data. Recent abundance determinations for some common elements are compared in Table 1, which shows that there is little difference between the Sun, young stars, and the local present-day ISM. The most disturbing discrepancy is that oxygen and nitrogen seem to be underabundant in Orion (and other nearby galactic HII regions) and in the Cygnus Loop SNR by a factor of 2 or so, which needs to be borne in mind when one tries to put together stellar and nebular data in order to study large-scale trends within and between galaxies. The discrepancy in Orion has been discussed by Meyer (1979), who finds that condensation on grains could account for part (but probably not all) of the discrepancy. [There is evidence for a stronger depletion of iron (Peimbert 1979a) and presumably other refractory elements.] Isotope ratios of C, N, O, Si, and S in the local ISM (Penzias 1980, Wannier 1980) differ from solar-system values by factors that are significant in the first three cases, but always less than 2. The interstellar D/H ratio, while on average consistent with the solar-system value, shows large local variations (Vidal-Madjar et al. 1978 and references therein, Laurent, Vidal-Madjar & York 1979).

Table 1. "Cosmic" abundances of some common elements

  12+ 12+         12+
  log He/H log O/H log O/C log O/N log O/Ne log O/S log Fe/H

Sun              
         Photosphere a   8.9 0.2 0.9   1.7 7.6  
         Prominences b 10.8            
         Corona c       0.9 1.1    
B stars 11.0 d 8.9 e 0.5 f 1.0 e 0.9 g   7.5 f
Orion Nebula 11.0 h 8.6 i 0.1 i, j 0.9 h 0.7 k 1.3 l 6.7 m
Cygnus Loopn   8.5 0.2 0.7   1.8  
Disk planetary              
         nebulaeo   8.7          

a Lambert 1978, Lambert & Luck 1978, Blackwell & Shallis 1979
b Hirayama 1971
c Walker, Rugge & Weiss 1974
d Leckrone 1971
e Kane, McKeith & Dufton 1980, Dufton, Kane & McKeith 1981
f Hardorp & Scholz 1970, Kodaira and Scholz 1970
g Auer & Mihalas 1973
h Peimbert & Torres-Peimbert 1977
i Torres-Peimbert, Peimbert & Daltabuit 1980
j Bohlin et al. 1980
k Meyer 1979
l Lester, Dinerstein & Rank 1979
m Peimbert 1979a
n D'Odorico & Dopita 1980
o Kaler 1980

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