George W. Turner

RZ LEONIS MINORIS, PG 0943+521, AND V1159 ORIONIS: THREE CATACLYSMIC VARIABLES WITH SIMILAR AND UNUSUAL OUTBURST BEHAVIOR

We call attention to a small group of cataclysmic variable stars (whose prototype might be considered RZ LMi) that have complex light curves fo similar shape which repeat with typical periods of a few weeks. The predictability of the time of each superoutburst and the stability of the shape of the light curve is unexpectedly high for cataclysmic variables, which are well-known for erratic variations in both the timing and the shape of their outbursts. The phenomenon appears to be closely related to SU Ursae Majoris-type superoutbursts, especially since superhumps appear in these stars. The similiarities and differences between these RZ LMi stars and SU UMa systems are summerized and discussed in the context of extant models for the superoutbursts of SU UMa-type dwarf novae.

The 65 Day Period in 3C 66A during Bright State

Historically, 3C 66A has been considered a relative quiescent blazar. For that reason, 3C 66A was selected as a comparison source for OJ 287 in the OJ-94 project. However, after more detailed observation it turns out that the variability of 3C 66A itself is very interesting. We have analyzed the entire project data set of 3C 66A from fall of 1993 to spring of 1998 by using structure function analysis, Deeming periodograms, Scargle periodograms, and the folded light curves. Here we present the first preliminary evidence for the 65 day period in 3C 66A observed during the bright state. Our analysis indicates that this period is slowly slowing down. We will also discuss the possible physical mechanism producing the observed periodicity.

Are Z Camelopardalis–Type Dwarf Novae Brighter at Standstill?

Average V-band brightnesses over multiple outbursting and standstill intervals are computed for the light curves of five Z Cam-type dwarf novae: RX And, Z Cam, SY Cnc, AH Her, and HX Peg. Both CCD photometry from RoboScope and AAVSO visual estimates are used in the analysis, with consistent results from the two databases for the stars in common. In four of the five stars, the standstills are as bright as or brighter than the mean V-band brightness during outbursting intervals. This is consistent with Z Cam stars being near the upper stability boundary in for operation of the thermal limit cycle that is thought to be responsible for ˙ M dwarf nova outbursts. However, the unusual standstills or hesitations observed in SY Cnc are sometimes fainter than the mean brightness during outbursting intervals. From several well-observed examples we describe the light curves of Z Cam stars as they enter standstill. During this characteristic damped oscillation the amplitude decreases with a timescale approximately equal to the mean outburst recurrence interval, and the period of the oscillation decreases with as standstill is approached. The exits from standstill usually change abruptly ˙ P. 20.4 into outbursting mode by emerging from standstill into a decline from outburst.

Outburst Characteristics in the Dwarf Nova SU Ursae Majoris

The 1973E1999 V -band light curve from AAVSO visual estimates and RoboScope CCD exposures is examined to study the systematic properties of normal outbursts and superoutbursts in this prototype of the SU UMaEtype dwarf novae. A number of the outburstsI correlations previously reported in VW Hyi and in SU UMa are not present in these data. Several lines of evidence suggest that, during this 26 year interval, variations in the mass-transfer rate served to obscure some of the expected correlations. The M 0 variation apparently caused a nearly complete cessation of outbursting in 1980E1983. We do Ðnd a corre- lation of the time since the last superoutburst with the mean brightness in the interval since the last superoutburst, supporting the notion that superoutbursts are a disk-initiated phenomenon that occurs when the gas remaining in the disk after each normal outburst has accumulated to some critical value.

Light Curve of CR Bootis 1990-2012 from the Indiana Long-Term Monitoring Program

Two telescopes are used at the Morgan-Monroe Observatory of Indiana University for autonomous long-term photometric monitoring of stellar sources, mostly cataclysmic variable stars. The instrumentation is designed and implemented to be appropriate for multiyear automated monitoring. The capabilities and limitations of the equipment are described, along with accounts of the software, the reduction procedures, the motivations for the scientific programs, and the execution of the observing campaigns. Data on the AM CVn-type cataclysmic variable CR Boo are presented and discussed as an example of the kinds of light curves generated at this facility. The He-rich disk in CR Boo has SU UMa-type outburst behavior, with both superoutbursts and what appear to be dwarf nova outbursts. However, the light curve is quite irregular and displays a wide variety of unusual features such as switching among several superoutburst recurrence intervals, and having intervals of dwarf nova-like outbursts that seem to come and go. We discuss the likelihood that deterministic chaos is responsible for these irregularities.

Periodic and Near-Periodic Decaday Lightcurves in Old Nova and Nova-Like CVs

Several CVs classified as old nova or nova-like systems have been found to have photometric variations with stable or near-stable periods of tens of days. In RW Tri, DI Lac, and V841 Oph the ~ 0.5 mag variations are sine-like and not always present. In V446 Her the ~ 1.5 mag variations have been present for four years and have the form of outbursts. RZ LMi and PG0943+521 have large variations with a complex but very similar shape to the periodic lightcurves. If these decaday variations have a common cause it is likely to involve a periodic modulation of the mass transfer rate.

The unusual 1992 outburst of V630 Cassiopeiae

A two magnitude outburst of the cataclysmic variable (CV) V630 Cas was observed in late 1992. A low-amplitude, slow rise, long duration event is unlike the outbursts seen in the various recognized outburst classes of CVs and related objects.

UNATTENDED H-ALPHA SPECTROSCOPY OF P CYGNI AND BETA LYRAE

An experiment in automated, unattended fiber-optic stellar spectroscopy is described. Particular attention is paid to the critical technique for placing the program star in the optical fiber. As a feasibility demonstration study, the equipment and technique have been used to acquire H-alpha spectra of P Cyg and beta Lyrae over a 6-week period. The P Cyg spectra show little systematic variability with time. The beta Lyr spectra are assembled into a gray-scale phase-resolved spectral image. When displayed in this manner, the H-alpha and He I lines bear a resemblance to the spectra of cataclysmic variable stars that display a third emission component, or S-wave.

Variability Characteristics of Blazar OJ 287

Blazar OJ 287 is one of the best observed extragalactic objects. It’s historical light curve goes back to 1890’s. Based on the historical behaviour Sillanpaa et al. (1988) showed that OJ 287 displays large periodic outbursts, with a period of 11.7 years. We have monitored OJ 287 intensively for two years, during the OJ-94 project. This project was created for monitoring OJ 287 during its predicted new outburst in 1994. In the data archive we have over 7000 observations on OJ 287, in the radio, infrared and optical bands. This data archive contains the best ever obtained light curves for any extragalactic object. The optical light curve shows continuous variability down to time scales of tens of minutes. The variability observed in OJ 287 can be broken down to (at least) four different categories: 1. The large outbursts that occur every 11.7 years. The last one of these happened during November 1994, almost at the predicted time. These outbursts can be due to the binary black hole model proposed by Sillanpaa et al. (1988).