Edward G. Schmidt

Evidence favoring nonevolutionary cepheid masses

It is suggested that the bumps on the velocity curves of nonlinear Cepheid models may be understood as the consequence of a resonance between the fundamental and the second overtone modes of the pulsating star. Thus the presence of bumps can be inferred from linear calculations. The region of the observational instability strip containing bumps is compared with the location of the calculated resonances. As was the case for the nonlinear calculations, it is found that masses considerably less than evolutionary values are required to bring agreement between the observations and the theory. (AIP)

THE BEHLEN OBSERVATORY VARIABLE STAR SURVEY: FIRST RESULTS

Various light curve parameters are presented for the first 93 objects in a photometric survey of poorly studied variable stars. Stars from the General Catalogue of Variable Stars (GVCS) fainter than tenth magnitude, north of the equator which were classified as pulsating variables (but excluding the long period, semiregular, and irregular variables) were included. It is shown that two parameters, the acuteness and the rise time, are useful for characterizing the light curves. Several criteria are applied to the photometric data to test the classification of the stars. For 26 stars new or improved classifications are suggested. In particular, there are six eclipsing or ellipsoidal variables among the 79 stars classed in the GCVS as RR Lyrae stars

Photometry of Type II Cepheids. I. The Long-Period Stars

We present 1256 new photometric observations of 36 Cepheids with periods longer than 8 days. The majority are likely type II Cepheids, but we have included about a dozen classical Cepheids for comparison purposes, a few stars of uncertain type, and one putative RV Tauri star. We discuss the appearance of the light curves, the Fourier parameters, and the light-curve stability in terms of differentiation between type I and type II Cepheids. Although we encounter the same difficulties as previous investigators in using these parameters for this purpose, we are able to identify some stars of particular interest, including several likely type I Cepheids at large distances from the Galactic plane. Six stars with especially large period changes are identified and discussed.

THE LUMINOSITY SCALE OF CEPHEID VARIABLE STARS: A REVISION

The period-luminosity-color relation for classical Cepheids is discussed in terms of a recent redeterminations of the distance moduli of open clusters with Cepheid members. The distance moduli of eight clusters with well established Cepheid members were determined from Stromgren four-color and Hp photometry of the B stars. Possible sources of systematic errors in these distance moduli are discussed. Zero points are derived from these data for the period-luminosity-color (PLC) relation on the UBV system and the period-luminosity relations for near-infrared magnitudes. The present relations yield absolute magnitudes which are fainter by 0.4-0.6 mag than those now commonly used. The source of this discrepancy is discussed. These lower luminosities cause the pulsational masses of the Cepheids to be less than the evolutionary masses by up to a factor of 2.5 but bring them into good agreement with the masses of beat and bump Cepheids. Thus, the predictions of the pulsation theory are made more consistent but the Cepheid mass discrepancy is reintroduced. This revision of the Cepheid luminosity scale will directly affect distances of galaxies based on the Cepheids, but its effect on the Hubble constant depends on how much weight was placed on the Cepheids in the establishment of the distance scale in the Local Group. A comparison of distance moduli for the Large Magellanic Cloud based on various indicators with those for the Cepheids from the present calibration shows no serious discrepancy. Subject headings: cosmology galaxies: Magellanic Clouds stars: Cepheids stars: pulsation

The behlen observatory variable star survey. IV

Finding charts, accurate coordinates, and light curves are presented for 106 variable stars including 6 which are newly discovered. Parameters descriptive of the light curves are tabulated including periods for 16 stars which lacked them. The periods from the General Catalog of Variable Stars for ten stars were found to be seriously in error. The classification of the stars is discussed. Revisions or refinements of the classifications from the General Catalogue of Variable Stars are suggested for 20 stars and classifications are given for 7 which were previously unclassified. 15%-23% of the Bailey type ab RR Lyrae stars show scatter in their light curves which is suggestive of the Blazhko effect. O 1996 American Astronomical Society.

PHOTOMETRY OF TYPE II CEPHEID CANDIDATES FROM THE NORTHERN PART OF THE ALL SKY AUTOMATED SURVEY

We have obtained VR photometry of 282 Cepheid variable star candidates from the northern part of the All Sky Automated Survey (ASAS). These together with data from the ASAS and the Northern Sky Variability Survey (NSVS) were used to redetermine the periods of the stars. We divided the stars into four groups based on location in a plot of mean color, V-R, versus period. Two of the groups fell within the region of the diagram containing known type II Cepheids and yielded 14 new highly probable type II Cepheids. The properties of the remaining stars in these two groups are discussed but their nature remains uncertain. Unexplained differences exist between the sample of stars studied here and a previous sample drawn from the NSVS by Akerlof et al. This suggests serious biases in the identification of variables in different surveys.

Investigation of radius anomalies among short-period Cepheids

Simultaneous photometric and spectroscopic observations have been obtained of two short-period Cepheids, SU Cas and TU Cas. The Wesselink method of Barnes et al. was used to obtain radii. The radii are found to agree, within the expected error, with evolutionary values. This strengthens the argument that the beat Cepheids are normal Cepheids in mixed-mode behavior rather than a separate class of objects and that evolutionary masses and radii are correct.

PHOTOMETRY OF TYPE II CEPHEIDS. III. THE INTERMEDIATE-PERIOD STARS

We present 741 new photometric observations for 22 Cepheids with periods between 3 and 8 days. Many of the stars are probable type II Cepheids, but we have included some type I Cepheids for comparison. The shapes and stability of the shapes of the light curves, the stability of the periods, and the scatter of individual data points are discussed. Although none of these proves to be a reliable discriminator between type I and type II Cepheids, they do permit the identification of several unusual stars.

The Spectra of Type II Cepheids. III. The Hα Line and Helium Emission in Long-Period Stars*

We have obtained Hα profiles from 175 spectra of 37 Cepheids with periods longer than 8 days. About two-thirds of the stars are likely type II Cepheids. In contrast to the situation among short-period stars, the velocity of Hα relative to the metal-line spectrum is not a useful parameter for distinguishing type I and type II Cepheids. On the other hand, at periods longer than 11 days and shorter than 34 days strong emission is observed in many stars and appears to be a good discriminator of type. On this basis we identify one probable type I Cepheid at a large distance from the Galactic plane. We have found He λ5876 emission in seven Cepheids among the long-period stars discussed here and in one star with a short period, bringing to nine the number of type II Cepheids known to exhibit He emission.

The Blazhko Effect of the RR Lyrae Star DR Andromedae

We have obtained 551 new V and R observations of the RR Lyrae star DR Andromedae. Our data set is consistent with a primary period of 0.563118 days; however, the light curve of DR And cannot be well described by a single period. We conclude that DR And demonstrates the Blazhko effect with a Blazhko period of approximately 57.5 days.