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19
Carbon, Nitrogen, Oxygen, and Neon
Our knowledge of the abundance of these elements is
based entirely on spectroanalytical astronomic observations
mostly in other stars than the sun, and in planetary nebulae,
since very high temperatures or high frequency light is required
to excite them to higher energy levels of the neutral
atoms or to Ionize them. Bowen (1948) has studied one line
of oxygen in the sun and secured a somewhat higher abundance
relative to the best estimates for carbon and nitrogen, namely
7 X 10^® atoms cm" as compared with 0.3 and 1.0 x 10^^ atoms cm"
for carbon and nitrogen, respectively. Mlnnaert (1953) summarizes
the work of lfeis31d (1948), Claas (1951) and Hunnaerts (1950) on
the sun and Aller (1953) gives a summary of all stellar data.
We will select the Unsold data for C and N in the sun and the geometric
average of the Uns51d and Claas data for 0 in the sun,
all normalized to log I^ equal to 6.15. Very good agreement
between their data for Na, Mg, Al, Ca and Fe and our selected
values for the elements is secured in this way.
Aller concludes that oxygen and neon have nearly the
same abundance in the stars and planetary nebulae. Traving (1955)
estimates the neon abundance as 1/2.5 that of oxygen. If oxygen
and neon have nearly equal abundances, the logarithm of the abundances
of Ne^^, Ne^^, Mi^ , and Mg^^ fall on nearly a straight line. If
neon is considerably less abundant than oxygen, it could be
ascribed to a fall in abundances after the neutron number 8 of 0