196 NOTES FROM OBSERVATORIES star in their observing programs during the coming season, the following résumé of our findings is presented. day. 1. The improved value of the four-hour period is 0.169165 2. Both the spectroscopic and photometric observations show the presence of a beat period whose elements are min = JD 243 3874.8 -f (17.2 ± 0.1)E. There is some indication that the amplitude of the light-curve drops abruptly to zero at the minimum phase of the beat cycle. This should be carefully checked during the present observing season. The photometric observa- tions of 1950 and 1951 can be combined in two ways. Either the maximum of the beat cycle does not occur halfway between the minima, or the amplitude of the beat curve is itself variable. Thus, accurate photometric observations over the entire cycle would be desirable. 3. The spectroscopic observations show a variation in the gamma velocity of the star, indicating that it is a spectroscopic binary with a period of 12.097 days and a range of 2K = 46.8 km/sec. There seems to be no correlation between this period and any of the features of the light-curves. It would be highly desirable to obtain color observations of the star with an ultraviolet to infrared base line in an effort to detect any possible changes of temperature in the star. The spectroscopic evidence indicates that the temperature cannot change more than about 2000. The high temperature of an early B star makes the ordinary yellow-blue color system very insensitive to temperature changes of this size. COLORS AND MAGNITUDES OF SOME STAR CLUSTERS IN THE MAGELLANIC CLOUDS* S. C. B. Gascoigne Commonwealth Observatory, Canberra, Australia Gerald E. Kron Lick Observatory, University of California Photoelectric colors and magnitudes in the blue and visual spectral regions have been measured for a number of extra-galac- * Presented at the joint meeting of the A.A.S. and the A.S.P. at Victoria, B.C., June 1952.
NOTES FROM OBSERVATORIES 197 tic star clusters, chiefly in the Magellanic Clouds. An RCA-type C-7073B multiplier refrigerated with dry ice was used, attached to the 29-inch Reynolds reflecting telescope at the Commonwealth Observatory. The measurements reported here were made on eight clusters in the Small Cloud, thirteen in the Large Cloud, and two (recognized as being globular clusters) in the Fornax dwarf system. 1 * 2 The magnitude system was standardized as to zero point and color equation by reference to Harvard Standard Region C-12. Each object was measured through four focal-plane apertures of graded sizes ranging from 32 to 110 seconds of arc in diameter. The magnitudes were reduced to the P,V System, 3 equivalent for most practical purposes to the International System. Total magnitudes were estimated by extrapolation with Plummer's formula, 4 with constants determined from our observations. The total apparent magnitudes were converted to absolute magnitudes with Shapley s distance moduli as tabulated by Baade. 5 According to H.C. 275 and 276, and H.B. 889, 899, the objects in the Clouds have been identified as star clusters. The color and magnitude data are given in Table I, and are portrayed in Figure 1, in which the crossed circle represents a normal point for three unreddened galactic globular clusters. We are indebted to Joel Stebbins for converting his published six-color data 6 to the P,V System for this normal point. The dispersion in magnitude and color for these three clusters was 0.5 and 0.1 mag., respectively. In Figure 1, the most striking feature is a strong tendency for a grouping of the colors into a blue group and a red group. The grouping appears so pronounced as to suggest that we have observed clusters of two distinct types. The mean color of the red group agrees with the mean color of the two globular clusters in the Fornax dwarf system, and with the mean color of the three globular clusters in the galaxy (NGC6341, 7078, 7089). The present results, therefore, support Shapley s identification of some of these objects as globular clusters. 7 The blue-color group contains NGC 1866, recently reported by Thackeray 8 to have a spectral type of A3. In this group also are NGC 2107 and 2134, reported by Miss Cannon 7 to have spectral types of A? and A, respectively. The clusters in this group have central condensation properties similar to those of the red
198 NOTES FROM OBSERVATORIES group ; this fact, together with their high luminosities, makes it unlikely that all of them can be identified with the open galactic clusters. The possibility remains, however, that some of these clusters may be similar to open clusters of high luminosity and high central condensation. In their work on the colors of globular TABLE I Name Colors and Magnitudes of Star Clusters (P- V) Absolute P System NGC 1029 Anon. 13.04 14.5 +0.48 +.58-7.8 Ï -6.3 J Fornax NGC 121 339 416 419 458 11.44 12.3 11.86 10.62 11.41 +.70 +.45 +.50 +.54.00-5.6-4.7-5.1-6.4-5.6 Small Cloud IC 1660 HC 275/3 HC 276/81 13.18 12.8 : 13.5 :.00 +.22 +.60: -3.8-4.2: -3.5: NGC 1783 1806 1831 1835 1846 10.55 11.15 10.65 10.58 10.86 +.48 +.60 +.18 +.56 +.58-5.5-5.8 1856 1866 1978 2107 2121 9.96 9.38 10.59 11.36 11.57 +.20 +.07 +.64 +.25 +.72-6.7-7.3-5.3-5.1 Large Cloud 2133 2134 Anon. S Dor 12.26 10.76 9.60 + -12 +.10 0.00-4.4-5.9-7.1 clusters, 9 Stebbins and Whitford found two clusters, NGC 2419 and 7492 that were remarkably blue, and were assigned A-type color classes, evidence that blueness among clusters of globular shape is not unknown.
NOTES FROM OBSERVATORIES 199 Observational selection insured that this sample of Cloud clusters would contain those of higher luminosity. Comparison of the absolute magnitudes in Table I with those for galactic globular clusters shows, however, that these Cloud clusters average about 1.5 magnitudes lower in luminosity. A similar result was found by Hubble 10 for 140 objects in M31 that he provisionally identified as globular clusters; his mean absolute magnitude was 5.3, -S -6 1 1 1 1 1 r X SMC O LMC Fornax & Mean, 3 Glob. -7 O -6-5 O O O 0 X o.? -J J L J I I L -/ O + /.<?.3 A.5 6.7.8 (P-V) Fig. 1. A plot of the colors (P V) against the absolute magnitudes (Mp) of star clusters in the Magellanic Clouds and the Fornax dwarf system. The crossed circle is a normal point for three galactic globular clusters, for which the colors were kindly supplied by Joel Stebbins. with a range from 4 to 7, which agrees with our data. The present results, therefore, provide additional evidence that distances derived from the classical Cepheids observed in the Clouds and in M31 may not be comparable with distances derived from the cluster-type variables observed in the galactic globular clusters and in the Fornax dwarf system. In other words, the present results support current thought regarding a need for revision 11 in
200 NOTES FROM OBSERVATORIES zero point of the period-luminosity law, which now includes the different kinds of variable stars ascribed to Baade s two types of populations. 1 Shapley, Proc. Nat. Acad., 25, 565, 1939. 2 Hubble and Baade, Pub. A.S.P., 51, 40, 1939. 3 Kron and Smith, Ap. J., 113, 334, 1951 ; Contr. L.O., Ser. II, No. 34. 4 H. C. Plummer, M.N., 76,107,1915. 5 W. Baade, Ap. J., 100, 150, 1944; Mt. W. Contr., No. 697. 6 Joel Stebbins, George Darwin Lecture, M.N., 110, 421, 1950. 7 Shapley, Star Clusters, 188, 1930. 8 Quoted by Baade, Pub. Obs. Univ. Mich., 10, 14, 1951. 9 Joel Stebbins and A. E. Whitford, Ap. J., 84, 132,1936 ; Mt. W. Contr., No. 547. E. P. Hubble, Ap. J., 76, 44, 1932; Mt. W. Contr., No. 452. il Cf. Hubble, Proc. Am. Phil. Soc., 95, 464, 1951. FLARING PHENOMENA IN U PEGASI Masaaki Huruhata Tokyo Astronomical Observatory Three-color photometry of the W UMa-type eclipsing variable U Pegasi has been carried out at the Tokyo Astronomical Obser- vatory with a photoelectric photometer attached to the 26-inch refractor. The observations were made on December 2, 3, 13, and 18, 1951, by T. Dambara, T. Nakamura, and the writer. The photometer is furnished with an RCA 1P21 multiplier and the fol- lowing color filters : Matsuda V-Vl, V-B2, and V-Ol, the effec- tive wave lengths of which are 3950 A, 4650 A, and 5550 A, re- spectively. Figure 1 shows the observed three-color light-curves in which ordinates are the magnitude differences from the com- parison star BD+15 4912, and the abscissae are phases reckoned with the light-elements of the star, JD 243 3982.917 0.374784E. The variations of violet light, which amount to 0.3 mag. and continue for about half an hour, show the flaring phenomena near maximum phase. In blue light the tendency can be recognized a little, but in yellow light there is no evidence of corresponding variation. This variation in violet light may be similar to the flar- ing phenomenon that has recently been observed in some late-type dwarf stars. Since the flaring of U Pegasi occurs near the maxi-