We have measured the periods and light curves of 148 RR Lyrae variables from V=13.5 to 19.7 from the first 100 deg 2 of the QUEST 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 37.5 • by 3.5 • in α and δ (≥ 30 by ≥ 3kpc), lies ∼ 50 kpc from the Sun, and has a depth along the line of sight of ∼ 5 kpc (1σ). These properties are consistent with the recent models that suggest it is a tidal stream from the Sgr dSph galaxy. The mean period of the type ab variables, 0.58 d , is also consistent. In addition, we have found two smaller over-densities in the halo, one of which may be related to the globular cluster Pal 5.

A method is described to perform ensemble stellar photometry on a series of CCD images for which the number and identity of the comparison stars vary throughout the set of exposures. The technique is particularly useful for the production of light curves of variable stars from long-term photometric programs where the inhomogeneity of the data set can be large. The linear least-squares solution is derived, paying particular attention to the evaluation of errors. Examples are presented of the use of two interactive computer programs which implement this technique.

With the 1 m Schmidt telescope of the Llano del Hato Observatory and the QUEST CCD camera, 380 deg 2 of the sky have been surveyed for RR Lyrae variables in a band 2 .3 wide in declination (centered at = À1) and covering right ascensions from 4C1 to 6C1 and from 8C0 to 17C0. The bright limit (due to CCD saturation) and the faint limit are V $13.5 and $19.7, respectively, which correspond to $4 and $60 kpc from the Sun. We present a catalog of the positions, amplitudes, mean magnitudes, periods, and light curves of the 498 RR Lyrae variables that have been identified in this region of the sky. The majority of these stars (86%) are new discoveries. The completeness of the survey has been estimated from simulations that model the periods and light curves of real RR Lyrae variables and take into account the pattern of epochs of observation. While the completeness of the survey varies with apparent magnitude and with position, almost everywhere in the surveyed region it is quite high (>80%) for the type ab RR Lyrae variables and between 30% and 90% for the lowamplitude type c variables.

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We call attention to a small group of cataclysmic variable stars (whose prototype might be considered RZ LMi) that have complex light curves of 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 similarities and differences between these RZ LMi stars and SU UMa systems are summarized and discussed in the context of extant models for the superoutbursts of SU UMa-type dwarf novae.

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