Amelia Wehlau

Two-Color CCD Photometry of Variable Stars in NGC 7006

B and V CCD photometry from 1984 through 1994 is presented for 50 RR Lyrae stars and two red variable stars in the globular cluster NGC 7006. New determinations of pulsation periods and period change rates are given and used to plot B light curves. The new photometry is combined with previously published photometry obtained from photographic plates taken in the 1930s, the 1950s and 1984 and used to derive O - C diagrams and new period change rates. V light curves based on the CCD data are also displayed, and colors derived from mean values of B and V are given. Period-amplitude diagrams and the color-magnitude diagram for the variables are shown. The dereddened blue and red edges to the instability strip in the cluster are found to be at (B-V)0 = 0.14 and 0.38. The period change rates have been revised from those given in an earlier paper and the new median period change rate is found to be +0.03, close to that predicted by the Yale evolutionary models.

Period change rates for 46 RR Lyrae stars in NGC 7006

Period change rates are presented for 46 RR Lyrae stars in the globular cluster NGC 7006 based on previously published photometry of photographic plates taken in the 1930s and 1950s by Hubble and Sandage, and new photometry of 35 photographic plates taken in 1984 with the Palomar 60 in. telescope. The mean period change rate for the 42 RRab stars is = −0.06 ± 0.04 d/Myr and the median is −0.04, which, for the horizontal branch (HB) type of NGC 7006, is one standard error below the median value of β predicted by the Yale evolutionary HB models. Statistically significant evidence for a radial gradient in the values (in the sense that the β values are more negative in the outer region of the cluster than in the inner) is also presented and discussed

Observations of variable stars in the globular cluster M80

Observations of the globular cluster M80 obtained between 1939 and 1987 are examined. The observations have resulted in the discovery of ten variable stars in or near the cluster. The colors and periods of these variable stars are discussed. For the nine stars with known periods, blue light curves are obtained. The light curves of the five variables farthest from the cluster center are obtained. Consideration is given to the shape of the light curve and position in the period-luminosity diagram of V1, a W Virginis star whose light curve and period have not changed over the 50 yrs of observations. Also, the nova T Sco 1860 is discussed, noting the possibility of searching for the nova using modern technology. 32 refs.

Magnitudes and colors of variables in the globular cluster NGC 5897

Magnitudes for the seven RR Lyr variables and one red variable in NGC 5897 have been derived from 213 B plates taken from 1939 through 1987 and from 38 V plates taken from 1956 through 1987. Blue light curves have been constructed for all the periodic variables and visual light curves for all but one star (V4) with a badly blended image. The period distribution of the RR Lyr stars is rather unusual, with three periods from 0.797 to 0.856 day, two at 0.420 and 0.454 day, and two more at 0.342 and 0.349 day. No variation to within + or - 0.1 mag can be seen for SK 120, a star which appears to be a cluster member lying within the instability strip. 26 refs.

First optical candidate for a recovered classical nova in a globular cluster - Nova 1938 in M14

U, B, V, R, and H-alpha CCD frames of the field of the nova which appeared in the globular cluster M14 in 1938 have been compared with the nova discovery images. On the basis of positional coincidence, brightness, and blue color, a candidate nova was identified and its right ascension and declination to within 1 arcsec each. Confirmation of the candidate and detailed study of the quiescent nova will probably require Hubble Space Telescope observations.

Two-color photographic photometry of variables in the globular cluster M28

Visual magnitudes have been measured for 20 variables on 32 plates of M28. These have been combined with previously published as well as newly determined blue magnitudes in order to obtain colors for the variables. Blue and visual light curves are presented for 15 of the the variables, including one W Virginis star V4, one RV Tauri star V17, one field Mira variable V7, nine cluster RR Lyrae stars, and three field RR Lyrae stars. It is shown that V14, previously thought to be a c type RR Lyrae star, is to the red of the instability strip. The visual light curve of V9 suggests that the star may be a member of a binary or a very close optical double. Possible evidence for differential reddening in the vicinity of M28 is presented. The bimodal distribution of the periods of the RR Lyrae stars in M28 may indicate a spread in metallicity among the RR Lyrae variables. 16 refs.

A Candidate for the Recovered Nova of 1938 in the Globular Cluster M 14

Although close binaries are believed to be of importance in the dynamical evolution of globular clusters, searches for such binaries have produced mostly negative results, aside from x-ray sources. Two dwarf novae which are possible cluster members are known (Margon and Downes 1983) and two classical nova candidates have been found. The crowded field around the nova observed in 1860 close to the center of M80 makes ground-based recovery of that star impossible with present techniques. Here we report on our attempt to recover the star which erupted in 1938 about 30″ (0.8 core radii) from the center of M14.

The LongTerm Behaviour of Two Pulsating Variables in M56

Of twelve variables known in Messier 56 in Lyra, two, V1 and V6 are the subject of this paper. VI was discovered by Shapley (1920) and first determined by Sawyer Hogg (1942) to be a Cepheid with a period of 1.5 days. V6 was discovered by Sawyer Hogg (1940) from her early plates at the David Dunlap Observatory. Later Sawyer Hogg (1949) showed it to be an RV Tauri type with a period of 90.02 days, one of the first such to be identified in a globular cluster. A.H.Joy (1949) determined spectral type and radial velocity for both of these variables.

SOLAR TURBULENT VELOCITIES

Amelia W. Wehlau and William H. Wehlau* University of Western Ontario London, Canada The differences in the half -widths of Fraunhofer lines as observed at the center and at the limb of the solar disk may be explained in several ways. One way is by the assumption of a variation of turbulent velocity with depth. The higher layers of the solar atmosphere contribute more to the formation of lines at * Post-Doctoral Fellow, National Research Council of Canada.