R. K. Honeycutt

The QUEST RR Lyrae Survey: Confirmation of the Clump at 50 Kiloparsecs and Other Overdensities in the Outer Halo

We have measured the periods and light curves of 148 RR Lyrae variables from V = 13.5 to 19.7 from the first 100 deg2 of the Quasar Equatorial Survey Team RR Lyrae survey. Approximately 55% of these stars belong to the clump of stars detected earlier by the Sloan Digital Sky Survey. According to our measurements, this feature has ~10 times the background density of halo stars, spans at least 375 by 35 in α and δ (≥30 by ≥3 kpc), lies ~50 kpc from the Sun, and has a depth along the line of sight of ~5 kpc (1 σ). These properties are consistent with the recent models that suggest that it is a tidal stream from the Sagittarius dwarf spheroidal galaxy. The mean period of the type ab variables, 0.58 days, is also consistent. In addition, we have found two smaller overdensities in the halo, one of which may be related to the globular cluster Pal 5.

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.

Characteristics of High-State/Low-State Transitions in VY Sculptoris Stars

About 12 years of photometric monitoring of 65 nova-like cataclysmic variables (CVs) have allowed analysis of occasional VY Sculptoris?type low states, which we define as a fading of more than 1.5 mag in less than 150 days. Detailed light curves of eight systems exhibiting these low states are presented and discussed. The data are sufficient to measure the speeds and the shapes of 29 transitions to and from the low state: both single-slope and dual-slope rises and falls are found, with the dual-sloped transitions always being faster when fainter. This behavior is consistent with the low states being due to a starspot on the secondary star, drifting under the inner Lagrangian point, if the two slopes are interpreted as being due to the passage of the umbral and penumbral portions of the starspot.

A MULTIWAVELENGTH STUDY OF AM HERCULIS DURING THE 2002-2004 LOW STATES

We present two epochs of low-state, near-IR spectroscopy of the polar prototype AM Her, along with K-band spectroscopy and JHK photometry. Combining our data with long-term (RoboScope) photometry of the system, we determine a new spectroscopic ephemeris for AM Her. According to the new ephemeris, the primary photometric minimum of the high-state light curve of the system is centered at phase zero. Our K-band spectrum, in which the Brγ and He I (2.06 μm) lines are essentially absent, confirms that during the low state, accretion was negligible. Ellipsoidal variations dominate the J-band light curve, whereas cyclotron harmonics are prominent in the H- and K-band light curves. Cyclotron emission during a time of negligible accretion has been observed in other low- polars. The Hα line is often triple peaked, and all three components follow the motion of the secondary star. The central peak likely originates from the irradiated inner hemisphere of the secondary. The blue/red satellite components reach velocities of ~300 km s-1 with respect to the secondary and coincide in phase with flaring events recently discovered from a photometric campaign. We argue that the satellite behavior is consistent with motions in large loop coronal structures on the secondary star.

Similarities between Stunted Outbursts in Nova-like Cataclysmic Variables and Outbursts in Ordinary Dwarf Novae

Stunted outbursts have been reported in old novae and nova-like cataclysmic variables by Honeycutt, Robertson, and Turner. These 0.4-1 mag outbursts were concluded to be either mass transfer events or disk outbursts similar to dwarf nova eruptions, but seen under unusual conditions. Honeycutt, Robertson, and Turner did not have enough evidence to favor either of these possibilities. This paper uses additional long-term photometry and analysis to argue that the similarities of these stunted outbursts to dwarf nova eruptions are now so numerous that the dwarf nova outburst choice is strongly favored. The similarities discussed here include the range of outburst spacings, the coherence and stability of the outbursts, and the presence of isolated outburst/dip pairs. As part of this discussion we note the presence of unexpectedly stable clocks over 9 years for the repetition interval of dwarf nova outbursts in SY Cnc and of stunted outbursts in FY Per.

High/Low States in Magnetic Cataclysmic Variables

We present long-term photometry of five magnetic cataclysmic variables (MCVs) that displayed pronounced VY Scl–like low states during the interval 1990–2004. A total of 43 transitions to and from the low states are analyzed and compared with the properties of disk VY Scl transitions from an earlier study. We find that the speeds and shapes of the transitions of both disk and magnetic systems above the CV period gap suggest that the low states are due to starspots on the secondary star drifting in front of the L1 point. For systems below the gap, the characteristics of the transitions point to X-ray irradiation on the L1 point for the cause of the low states. Our results are in accord with the nature of the secondary star, which is expected to be fully convective for systems below the gap. Finally, unresolved flaring events present in the low states of the MCVs in our sample are attributed to activity on the secondary, indicating that these secondaries are indeed chromospherically active.

A Large‐Area CCD Camera for the Schmidt Telescope at the Venezuelan National Astronomical Observatory

We have designed, constructed, and put into operation a large-area CCD camera that covers a large fraction of the image plane of the 1 m Schmidt telescope at Llano del Hato in Venezuela. The camera consists of 16 CCD devices arranged in a 4 × 4 mosaic covering 23 × 35 of sky. The CCDs are 2048 × 2048 LORAL devices with 15 μm pixels. The camera is optimized for drift-scan photometry and objective-prism spectroscopy. The design considerations, construction features, and performance parameters are described in the following paper.

New Complexities in the Low-State Line Profiles of AM Herculis

When accretion temporarily ceases in the polar AM Her, the emission-line profiles are known to develop several distinct components, whose origin remains poorly understood. The new low-state spectra reported here have a more favorable combination of spectral resolution (R ~4500), time resolution (~3 minute exposures), and S/N than earlier work, revealing additional details of the orbital dependence of the line profiles. The central strong feature of Hα is found to be composed of two components of similar strength, one having K ~ 100 km s^−1 and phased with the motion of the secondary star, the other having little or no detectable radial velocity variations. We attribute the central line component to gas near the coupling region, perhaps with a contribution from irradiation of the secondary star. The two satellite components have radial velocity offsets of ~±250 km s^−1 on either side of the central strong Hα peak. These satellites most likely arise in large loops of magnetically confined gas near the secondary star due to magnetic activity on the donor star and/or interactions of the magnetic fields of the two stars. Doppler maps show that these two satellite features have concentrations at velocities that match the velocity locations of L4 and L5 in the system.

Spectroscopy of Active and Inactive M Dwarfs in Praesepe

Spectroscopy of 222 late-type dwarfs in the Praesepe open cluster is used to measure the strengths of molecular and atomic features and to examine their sensitivity to chromospheric activity as measured by the strength of H? emission. For this cluster we confirm the results of Hawley and coworkers that some TiO features are selectively weakened among active field stars. However, a similar effect for CaOH is only weakly confirmed. Using differential measures of the strengths of features with respect to the median in narrow color bins, we also find that absorption in the Ca II IR triplet is selectively weakened in more active stars, while absorption at K I and Na I is strengthened. A comparison of the distribution of the H? strengths with V - I color in Praesepe and the similarly aged Hyades cluster indicates that the onset of M dwarf activity occurs at a significantly redder color in Praesepe than in the Hyades. Analysis of similar data on eight clusters from the literature is used to explore the relationship between age and activity in open clusters. We quantify the dependence on cluster age of the location along the main sequence for the onset of activity, confirming that the critical color at which activity becomes prominent is a nearly linear function of the logarithm of the age.

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.