Lower limits for the ratio C^(12)/C^(13) have been determined for eight metal-deficient stars. These limits are inconsistent with the predictions of nearly all of the universal models considered by Wagoner, Fowler, and Hoyle (1967) unless at least one generation of massive, rapidly evolving stars existed before the formation of any of the program stars

Cohen, J. G.

Grasdalen, G. L.

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The Astrophysical Journal, Vol. 151, January 1968 
LIMITS ON THE C12/C13 RATIO IN METAL-DEFICIENT STARS 
J. G. Cohen 
Mount Wilson and Palomar Observatories, Carnegie Institution of Washington, 
California Institute of Technology 
G. L. Grasdalen* 
Harvard College Observatory and Smithsonian Astrophysical Observatory 
Received October 25, 1967 
ABSTRACT 
Lower limits for the ratio C12/C13 have been determined for eight metal-deficient stars. These limits 
are inconsistent with the predictions of nearly all of the universal models considered by Wagoner, Fowler, 
and Hoyle (1967) unless at least one generation of massive, rapidly evolving stars existed before the 
formation of any of the program stars. 
Wagoner, Fowler, and Hoyle (1967) have completed an analysis of the synthesis of 
elements at high temperature in the initial universe and in certain types of supermassive 
stars. In both cases, for all values of the adjustable parameters, the isotopic ratio C12/C13 
is very close to unity, except the case of a supermassive star which initially consists 
entirely of He4, where only C12 is produced. Furthermore in some cases the mass fraction 
C/H is comparable to that observed in the most metal-deficient stars. 
We have attempted to obtain lower limits for the ratio C12/C13 in siibdwarfs, which are 
among the oldest objects in the Galaxy. It is possible that the gas from which these 
weak-line stars condensed had already been contaminated by material processed in an 
earlier generation of stars; we would then expect an isotopic ratio Cu/Cn greater than 
4.3 as a result of stellar nucleosynthesis. If synthesis has proceeded as described by 
Wagoner et d. (excluding the one case noted above for which no C13 is produced) and if 
there was no previous generation of massive, rapidly evolving 0 stars, we should obtain 
an average isotopic ratio close to unity. 
We have computed the isotopic shifts between the rotational lines K = 10 to = 30 
of each branch of the (0,0), (1,1), and (2,2) ^42A-X2II CH bands near 4200 Â, with the 
aid of formulae given by Herzberg (1950). We have included terms of up to order 
(1 — p4) where 
P = V H12/Hn 
and pi2 and nn are the reduced masses for C^H and C13H, respectively. These shifts 
range in absolute value from 0.2 to 1.0 Â. The shifts calculated for the R-branch of the 
(0,0) band differ by less than 0.1 Â from those measured by Richter and Tonner (1967). 
Tracings were made of Palomar plates exposed by J. L. Greenstein from 4222 to 
4300 Â for each of the program stars fisted in Table 1. We used the David Mann micro- 
photometer of the Harvard College Observatory, which has a device for the digital out- 
put of the density. The density readings were then plotted by a computer, together with 
the wavelength for each sample, and any entries on a fine fist close to the sample wave- 
length. The identification fine fist consisted of all fines from the Revised Multiplet Table 
(Moore 1959) in the wavelength region under consideration (excluding only those of 
very high excitation such as Cl n), the C^H rotational fines in this region, whose wave- 
lengths were taken from the Revised Rowland Table (Moore, Minnaert, and Houtgast 
1966), and the C13H fines, whose wavelengths we had predicted. In some cases we have 
* Present address: Department of Geology, California Institute of Technology. 
L41 
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L42 J. G. COHEN AND G. L. GRASDALEN Vol. 151 
also looked for features of the C13N14 band near 3874 Â (Ganiaris, Bashkin, and Waddell 
1966). Although the CN band is very strong in spectra of late-type stars for solar metal 
content, it is reduced in strength in subdwarfs by a factor of approximately (Z/ZSUn)2, 
and hence its absence cannot significantly increase the lower limit for C]2/C13 obtained 
from examination of the CH band. 
No definite indication of the presence of C13 was obtained for any of the program 
stars. We have assigned the lower limits for C12/C13 given in the sixth column of Table 1 
on the basis of the depression below the apparent continuum at the positions of several 
relatively unblended C13H features. Because of severe problems of overlapping lines, 
even in these metal-deficient cool objects, we cannot assign higher lower limits in spite 
of the high dispersion of the plate material. The limits to some extent reflect the strength 
TABLE 1 
Lower Limits of the Ratio C^/C13 
Star Plate Dispersion (Â/ mm) Teff (ZO/Z) Lower Limit C12/C18 Ref.* 
HD 2665  
HD 5916  
HD 6582 Cas) 
HD 6755  
HD 19445  
HD 65583  
HD 122563  
HD 140283  
Pc 8253 
Pb 5329a 
Pb 5323 
Pc 8253 
Pb 2345 
Pb 43602 
Pb 3230a 
Pb 4609 
Pb 3176 
9 
4.5 
4.5 
9 
4.5 
4.5 
4.5 
4.5 
4800 
4400 
5100 
5200 
5800 
5300 
4200 
5600 
37 
10 
4 
11 
60 
2 
200-600 
150 
7 
8 
6 
8 
4 
13 
5 
3 
K 
Rt 
c 
K 
CS 
SSf 
p 
CS 
* References for reff and Zq/Z: C, J. G. Cohen (1967), unpublished. 
CS, J. G. Cohen, and S. E. Strom, Ap. /., in press. 
K, D. Koelbloed (1967), Ap. 149, 299. 
P, B. E. J. Pagel (1965), No. 104. 
R, N. Roman (1955), J. Suppl, 2, 195. 
SS, S. E. Strom and K. M. Strom Í1967), Ap. J., 150, 501. 
t These are stars for which no detailed abundance analysis has been performed. The reference is for values oi U — B and B — V, which have been transformed into reff by a method described in SS, and into Z/ZQ with the aid of Wallerstein’s (1961) 
correlation. 
of the C12H band, which increases as the effective temperature decreases. It is unfortu- 
nate that two of the three most metal-deficient stars have Teu greater than 5500° K, 
so that the C12H band is very weak. 
We have obtained tracings of several Balmer lines for HD 140283 only. Since the 
hydrogen lines are quite narrow, we can deduce an upper limit for the deuterium abun- 
dance. No shift in the line-center wavelength was seen for H7, HÔ, or H8. In addition, 
though any line over 15 mÂ would be clearly detectable, no lines were observed at the 
wavelengths of the corresponding deuterium lines. We therefore conclude that the ratio 
D/H is less than 1/150 for this very metal-poor star. This is not surprising, since any 
deuterium initially present in the atmosphere will be carried by convection to a depth 
where it is destroyed during the phase of contraction toward the main sequence (Boden- 
heimer 1965). 
Our lower limits to C12/C13, together with the large metal deficiency of many of the 
program stars, are inconsistent with the predictions of the models considered by Wagon- 
er et al. except for the case of a supermassive star composed of initially He4, where only 
C12 is produced. Therefore if any of the other universal models described by Wagoner 
et al. are valid, a previous generation of rapidly evolving massive stars must have existed 
before the condensation of any of the program stars. 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
No. 1, 1968 C12/C13 RATIO L43 
This research has been supported in part by grant NGR 22-024-001 from the National 
Aeronautics and Space Administration and grant GP 7030 of the National Science 
Foundation. 
We should like to thank Prof. W. A. Fowler and Dr. R. Wagoner for helpful discus- 
sions. We thank Prof. Jesse L. Greenstein for the plate material. We are very grateful 
to Dr. Stephen E. Strom, who suggested the problem and provided funds and encourage- 
ment. 
REFERENCES 
Bodenheimer, P., in Peimbert, M., and Wallerstein, G. 1965, Ap. 142,1024. 
Ganiaris, N., Bashkin, S., and Waddell, J. H. 1966, Ap. J., 146, 308. 
Herzberg, G. 1950, The Spectra of Diatomic Molecules (New York: D. Van Nostrand Co.). 
Moore, C. E. 1959, Revised Multiplet Table (NBS Tech. Note 36). 
Moore, C. E., Minnaert, M. G. J., and Houtgast, J. 1966, Revised Rowland Table (NBS Monog. 61). 
Richter, J., and Tonner, K. 1967, Zs.f. Ap., 67, 155. 
Wagoner, R. B., Fowler, W. A., and Hoyle, F. 1967, Ap. J., 148, 3. 
Wallerstein, G. 1961, Ap. J. Suppl., 6, 407. 
Copyright 1968. The University of Chicago. Printed in U.S.A. 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 


Limits on the C^(12)/C^(13)Ratio in Metal-Deficient Stars

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Limits on the C^(12)/C^(13)Ratio in Metal-Deficient Stars

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