THE SPECTRUM OF R CORONÆ AT MINIMUM

The observing conditions were evidently not very good and Barnard's attention was mainly directed upon the red-focus disk, but even so it is hard to understand how the companion could have escaped Barnard's eye. The pair is unquestionably a binary system for the annual proper motion of the variable is 0."23 in about 186°. It may be in rapid orbital motion and just at present at its maximum angular separation. Whether the companion is also a variable star remains to be determined, but the probabilities do not favor this explanation. It is apparent that this discovery affects the interpretation of all phenomena hitherto observed in o Ceti at or near its minimum brightness. The light-curve, for example ; for, when Mira is at minimum the observed apparent magnitude (9.2 in the present minimum) must be corrected by approximately half a magnitude to allow for the effect of the companion, provided the latter does not also vary in brightness. When the variable is bright, the companion's share in the intregrated light is, of course, negligible. The range of variability is therefore greater than has been supposed. Again, as Joy points out, by reason of its early spectral class and consequent difference of color index, the companion must be considerably brighter, photographically, than Mira, and the observed spectrum must be that of the companion rather than that of the variable—“on our spectrograms hardly a trace of the M-type spectrum remains after the star has passed below magnitude 9.2." This remark doubtless applies to the spectral peculiarities observed at earlier minima, unless the companion is also a variable. November 12, 1923. Robert G. Aitken.