Kevin M. Lee

AH Cam: A metal-rich RR Lyrae star with the shortest known Blazhko period

Analysis of 746 new V-band observations of the RR Lyrae star AH Cam obtained during 1989 - 1992 clearly show that its light curve cannot be described by a single period. In fact, at first glance, the Fourier spectrum of the photometry resembles that of a double-mode pulsator, with peaks at a fundamental period of 0.3686 d and an apparent secondary period of 0.2628 d. Nevertheless, the dual-mode solution is a poor fit to the data. Rather, we believe that AH Cam is a single-mode RR Lyrae star undergoing the Blazhko effect: periodic modulation of the amplitude and shape of its light curve. What was originally taken to be the period of the second mode is instead the 1-cycle/d alias of a modulation sidelobe in the Fourier spectrum. The data are well described by a modulation period of just under 11 d, which is the shortest Blazhko period reported to date in the literature and confirms the earlier suggestion by Goranskii. A low-resolution spectrum of AH Cam indicates that it is relatively metal rich, with delta-S less than or = 2. Its high metallicity and short modulation period may provide a critical test of at least one theory for the Blazhko effect. Moskaliks internal resonance model makes specific predictions of the growth rate of the fundamental model vs fundamental period. AH Cam falls outside the regime of other known Blazhko variables and resonance model predictions, but these are appropriate for metal-poor RR Lyrae stars. If the theory matches the behavior of AH Cam for a metal-rich stellar model, this would bolster the resonance hypothesis.

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.

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.

The RR Lyrae Star V442 Herculis: An Extreme Case of Light‐Curve Modulation

We have obtained photometric observations of the peculiar RR Lyrae star V442 Her during six observing seasons spanning an elapsed time of nearly 9 years. The period has undergone two large, abrupt changes in the past 5 years. Although light-curve modulation is fairly common among RR Lyrae stars, the modulation of the light curve of V442 Her is highly unusual for its large amplitude, long period, extreme alterations in light-curve shape, and large period changes.

The Blazhko Effect of the RR Lyrae Star FM Persei

We have obtained 615 new V and R observations of the RR Lyrae star FM Per. A period search identified a primary period of 0.489256 days; however, the light curve of FM Per cannot be well described by a single period. We conclude that FM Per demonstrates the Blazhko effect with a Blazhko period of approximately 122 days.

The Spectra of Type II Cepheids. II. The Hα Line in Intermediate-Period Stars*

We present 98 Hα profiles for 21 pulsating variable stars with periods from 3 to 8 days. The strength, depth, and shape of Hα vary throughout the cycles of the stars in a way consistent with the temperature changes. Otherwise, they are quite uniform among all the stars, with a single exception. In FM Del, Hα is weaker and has a smaller central depth than in the other stars. This and the wavelength shifts of the core are attributed to incipient emission. The differential velocity of Hα relative to the metal lines is less than 25 km s-1 for all the stars except QY Cyg, FM Del, and EF Tau. We suggest that this indicates that only these stars are type II Cepheids despite the large distances of some of the others from the Galactic plane.

The Spectra of Type II Cepheids. I. The Hα Line in Short-Period Stars*

We present 88 Hα profiles for 24 pulsating variable stars with periods between 1 and 3 days in order to explore the behavior of this line in type II as compared with classical Cepheids. Surprisingly, large velocity differences were found between Hα and the metal lines in some type II Cepheids. Strong emission was observed in three stars, VZ Aql, NW Lyr, and V439 Oph, while line filling by incipient emission is present in seven others. All of the stars with emission and most with incipient emission belong to Diethelms AHB2 class, and the emission is associated with the secondary bump on the rising branch of the light curve. Two stars, BF Ser and MQ Aql, show doubling of the core near maximum light, and asymmetry of the line is noted in some spectra.

The Blazhko Effect of the RR Lyrae Star V421 Herculis

We have obtained new V-band photometry of the RR Lyrae Star V421 Her to test the suggestion of Tsessevich and Mandel (1985) that V421 Her is a double model RR Lyrae with the unusual period ratio of 0.79. We confirm the finding of Tsessevich and Mandel that the light curve of V421 Her is not well described by a single period. However, although the primary period we find agrees well with that of Tsessevich and Mandel, we are unable to confim their 0.43812 day secondary period. Instead, we suggest that V421 Her exhibits the classical Blazhko effect.