Part 2 — TABLE XXIV
Reading edition
Line Element Predicted Effect Observed Effect
- 0 +
3933 Ca+ * +1 .. .. .. .. 0? +
3944 Al u .. .. +0 + -2 .. .. .. -
3953 Fe n () .. +0 + -2 .. .. .. ..
3961 Al u .. .. +0 + -2 .. .. .. -
3968 Ca+ * +1 .. -1 .. .. 0? +
3999 Ti u .. .. +0 .. -1 .. .. .. ..
4005 Fe n .. .. +0 .. 0 .. .. .. ..
4031 Mn u .. .. -2 -1 -1 .. .. 0 ..
4041 Mn n .. .. -1 -1 -2 .. .. -0 ..
4046 Fe n .. .. -1 -1 0 -1 -1 -2 ..
4064 Fe n .. .. -1 -2 .. +2 0 -2 ..
4068 FeMn n .. .. -1 .. .. +1 -1 .. ..
4072 Fe,- n .. .. 0 +4 .. .. -1 -2 ..
4077 Sr+ * 0 0 +1 s 0 +3 +
4084 Fe n .. .. -1 +1 0 0 .. .. ..
4101 H n .. .. -1 -1 +1 -4 0 -1 +
4132 Fe n .. .. 0 +2 +1 .. +0 -1 ..
4135 Fe n .. .. -1 .. 0 .. +0 .. ..
4144 Fe n .. .. -1 0 +2 0 +0 -1 ..
4167 ? -1 .. -1 -1w 0 .. ..
4172 Fe+ * +1 +1 +3 +1 +0 .. ..
4177 Fe+ * +1 .. +2 .. .. .. ..
4215 Sr+ * 0 0 +2 +3 +0 +1 +
4227 Ca u .. .. -1 -1 0 -2 -0 -2 -
4247 Sc+ * .. 0 .. +1 .. +1 .. ..
4250 Fe n .. .. 0 -2 -1 -2 -1 -2 ..
4254 Cr u .. .. -1 .. -1 -1 -1 -1 ..
4260 Fe n .. .. -1 -2 -1 -2 .. -1 -
4272 Fe n .. .. -1 -2 .. 0 +0 -1 ..
4275 Br u .. .. -1 .. .. 0 +0 -1 ..
4290 Cr u .. .. 0 -2 0 .. +0 -1 ..
4298 Ti, Ca .. .. -1 -2 0 .. 0 .. ..
4308 Fe n .. .. 0 +1 0 .. .. -1 ..
4315 Fe+ * .. 0 +1 +2 .. .. .. ..
4321 Sc+ * .. +1 .. .. s .. .. ..
4326 Fe n .. .. 0 +1 +1 -2w 0 -2 ..
4340 H n .. .. -2 -7 -1 -4 -0 -1 +
4352 CrMg ? .. .. 0 +2 0 +1 +0 -3 ..
4360 Cr n .. .. 0 .. +1 .. .. .. ..
4370 Fe n .. .. +1 .. 0 .. +0 .. ..
4376 Y+ * .. -1 +2 0 .. +1 +2 ..
4383 Fe n .. .. 0 +3 +1 -2 -4 -2 ..
4405 Fe n .. .. -1 .. .. 0 -1 -2 ..
4415 Fe+ * .. +1 0 +3 0 0 -1 ..
4435 Ca n .. .. -1 .. +1 .. 0 -2 -
4444 Ti+ * .. 0 0 +1 s -3 .. ..
4455 Ca n .. .. -2 .. -1 w -1 -3 -
4476 Fe n .. .. -1 .. +1 -1 .. .. ..
4481 Mg+ * .. .. -1 0 0 0 +0 +1 ..
4490 Fe n .. .. 0 .. .. +1 -0 +2 ..
It is seen from the table that the general agreement with the anticipations of theory is satisfactory, and that the deviations, when they occur, rarely exceed one unit. The agreement is not less good than would be expected of the material, since the measures are here used differentially. The majority of the discrepancies are apparently accidental; for example, the deviations shown by the first six entries in the first column are almost certainly the result of better definition in the giant spectrum. There remains, however, the same discrepancy for the lines of Sr+ that was noted in the earlier part of the chapter. There can be no doubt that these lines are stronger in giants than in dwarfs.
The strengthening of the ionized lines of the alkaline earths is explained, when the spectra are examined, by the fact that the neutral lines are still fairly strong long after the ionized lines have passed their maximum—neutral strontium[426] is found at and neutral calcium[427] at . The lowered pressure, then, must increase the concentration of singly ionized atoms at the expense of the residual neutral atoms. There is, however, apparently no satisfactory theoretical explanation of the survival of large quantities of neutral calcium long after the ionized atoms have passed their maximum. The effects predicted above would appear to be the only ones that can be anticipated if the theory holds rigidly. Clearly some factor such as effective level must be further considered.
THE STRONTIUM LINES
The strontium problem is perhaps one that will lead to more comprehensible results when it is treated as a whole. It is impossible to resist the feeling that there is some definite abnormality associated with strontium. The “strontium stars” in the still earlier classes, where the lines 4215, 4077 appear with great intensity, and the stars Circini and Equulei, as well as the apparently erroneous absolute magnitudes obtained by the spectroscopic method for several other stars of low intrinsic luminosity, all point in some such direction.
It may be that these phenomena are a result of an abnormal abundance or distribution of the element. It is not, therefore, entirely necessary to assume that the theory is here at fault, although until the behavior of strontium has been satisfactorily interpreted, that possibility cannot be rejected. It is significant that calcium and barium show similar absolute magnitude behavior. In any case, the ionized strontium lines cannot be cited, as has sometimes been done, in demonstrating that the absolute magnitude effect is due to pressure. What is actually shown is that the concentration of singly ionized atoms is more greatly increased at the expense of the neutral atoms than it is reduced by the formation of doubly ionized atoms. Since a pressure effect operates by the discouragement of recombination, it would be inferred that the recombination of singly ionized atoms with electrons to form neutral atoms is less readily encouraged than the recombination of doubly ionized atoms with electrons to form singly ionized atoms. Evidently the problem is a complex one. If the maximum of the strontium lines were at (where theory first predicted it, and where the earlier measures actually placed it) there would be no anomaly to explain; but two independent observers[428] place it definitely at or , and there can be little doubt that this is actually the correct position of the maximum.
The result of the study of absolute magnitude effects is disappointing. It appears that the observed phenomena are qualitatively explained in a satisfactory manner, as due to lowered pressure, or, more accurately, to low surface gravity. There is, however, a serious discrepancy in the case of the lines whose variation with absolute magnitude is perhaps best established, and upon which the most important results have been based. The results, being empirical, are of course unimpaired, and it would seem that the theory requires to be amended. Furthermore, it does not yet appear to be possible to use the observed changes of intensity for the direct estimation of pressure differences, because of the large number of variables involved and particularly because of the superposition of the pure pressure effect upon the effect of photospheric depth.