302 NOTES from OBSERVATORIES in Both Cycles, During the Year

302 NOTES FROM OBSERVATORIES

In both cycles, during the year following conjunction, conspicuous emission was present at H and K. It was about 1.5 A wide, and on two of the best Perkins plates it has a very fine central absorption line. The emission was more conspicuous in 1940 than in the next cycle (1950). Fine Κ absorption has appeared on a few plates at odd times throughout the orbital cycle, with no apparent regularity. The data do not rule out an actual eclipse, though it is considered improbable. The star should be followed closely at the next conjunction, which will occur late in 1959.

ι A p. /.,83, 433,1936. 2 Pub. Lick Obs., 16,291,1928. 3 Dom. Αρ. Obs., 6,191,1933.

EMISSION LINES OF Can IN CLASSICAL CEPHEID VARIABLES

George H. Herbig Lick Observatory, University of California

The first published observation of emission lines of Can in classical cepheid variables of Baade's population type I1 was that of W. S. Adams and A. H. Joy,2 who found shortward-displaced emission components in the Η and Κ lines of the cepheid ζ Gemi- norum (period = 10.2d). These bright lines are present for ap- proximately four days around the time of maximum light. In 1948 A. Van Hoof3 found similar emission lines displaced shortward of the centers of the Η and Κ lines in the cepheid X Cygni (P — 16.4d) ; in this star, the bright lines apparently appear twice during the cycle: on the lower part of the rising branch of the light-curve, and again shortly after maximum light. Since then, the same type of emission has been observed in the cepheids η Aquilae4 (P = 7.2d) and S Sagittae5 (P = 8.4d) during phases on the rising branches of their light-curves ; it has also been found by R. F. Sanford in Τ Monocerotis {P = 27.0d),e but the phase of appearance has not been announced. The question immediately arises : is the presence of these emission lines a general characteristic of classical cepheids? If so,

detailed investigation of the properties and occurrence of the bright lines may provide worth-while information on the cepheid phenomenon. The present note reports an effort to provide a pre- liminary answer to this question by spectrographic observation of a small number of representative cepheids in the region of the H and Κ lines of Can. The observations were made with the two-prism spectrograph and 6-inch camera of the 36-inch refractor. The prisms are set for minimum deviation at λ 3950; the dispersion is 53 A/mm at that wave length. The low transmission of the 36-inch objective in the near ultraviolet made it necessary to confine the work to the brighter variables. The stars for which adequate spectrograms were obtained are listed in Table I. Since this program was in

TABLE I Cepheids with Bright Co ii Lines No. Plates Period Showing Mean AV* Phaset Star (Days) Emission (km/sec) (Periods) δ Cephei 5.37 5 -39 0.84-0.88 Y Sagittarii 5.77 1 -52 0.89 U Sagittarii 6.74 1 -79 0.88 X Sagittarii 7.01 2 -53 0.94, 0.94 U Aquilae 7.02 2 -60 0.89, 0.89 W Sagittarii 7.59 1 -43 0.96 TT Aquilae 13.75 1 -59 0.09 • Displacement of emission with respect to absorption spectrum. t The phase, referred to maximum light, at which the plates showing emission were obtained. The phases are computed from the elements given in the 1948 edition of Kukarkin and Parenago's General Catalogue of Variable Stars, and have been corrected when necessary to make maximum light as recently observed by Eggen (Ref. 7) occur at phase zero. No recent observations of W and X Sagittarii were known to the writer, and hence such corrections could not be made for those variables.

the nature of a reconnaissance, no attempt was made to obtain an extensive series of plates for each star. Rather, the observations were made on the rising branches of the light-curves and generally were discontinued after one good plate showing emission had been obtained. Several stars other than those listed in Table I were observed less thoroughly and no emission lines were found, but this result could as easily have been due to the small number of good spectrograms as to a real absence of emission.

The results can be summarized as follows : 1. The temporary presence of shortward-displaced emission lines of Can appears to be a general characteristic of classical cepheid variables, at least those of Eggen's types7 A and B, with periods between five and sixteen days. 2. In all of the variables listed in Table I, with the exception of TT Aquilae, calcium emission was found for a portion of the time that the stars were on the rising branches of their light- curves. The longest period cepheid observed, TT Aquilae, shows H and Κ emission after maximum light, and hence is similar to X Cygni in this respect. The material now available is too sparse to prove that emission is not present at any other times during the cycles of these particular variables. The more extensive data available on S Sagittae indicate that any recurrence of emission is not conspicuous, but all cepheids may not behave precisely the same in this respect. 3. The emission line in H is often equal in intensity to, or stronger than, that in K. This is a general feature of the phenomenon that was observed, and for which an explanation was advanced, in the study of S Sagittae.5 4. There is nothing in the present material that does not fit in with the interpretation of the emission-line phenomenon, in terms of the self-absorption of a broad, displaced emission line by overlying cooler gas, that has been advanced for S Sagittae.5

1 The W Virginis-like cepheids of population II show strong emission lines of hydrogen at certain phases, but those objects are not considered here. tPuh.A.AS., 9,254,1939. 108,160,1948. 4 T. S. Jacobsen, Pub. AS.P., 62,269,1950. 5 G. H. Herbig, Ap. /., in press *Ap. /.,109,231,1949. 7 Ap. /., 113,367,1951 ; Contr. Lick Obs., Ser. II, No. 32.