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We examine the e †ects of di †erent assumptions about the initial conditions, angular momentum loss law, and angular momentum transport on the angular momentum evolution of 0.5È1.2 solar mass stars. We Ðrst perform a parameter variation study to test the sensitivity of the surface rotation rate as a function of mass and age to changes in the initial conditions and input physics. We then check to see if the distribution of initial conditions for a given physical scenario is consistent for open clusters of di †er-ent ages.The behavior of the rapid rotators is highly sensitive to the saturation threshold for angular momentum loss above which angular momentum loss scales linearly with the rotation rate. Very high (u crit ), values for suppress rapid rotation prior to the main sequence, and very low values permit rapid u crit rotation to survive for too long. For solid-body (SB) and di †erential rotation (DR) models, higher mass models rotate more rapidly than lower mass models for the same initial conditions and DR models u crit . di †er from SB models in both the direct e †ect of core-envelope decoupling and a change in the calibration of the angular momentum loss law needed to reproduce the solar rotation at the age of the Sun ; the e †ects of both are discussed. Slow rotation in young clusters can be achieved with modest disk lifetimes (3È10 Myr) for the DR models and longer disk lifetimes for the SB models (10 or more Myr). In addition, the slowly rotating DR models spin down during the early main sequence more than the slowly rotating SB models do.When compared with the cluster data, the observed mass dependence of the rapid rotator phenomenon can be reproduced only with a mass-dependent for both the SB and DR models. A scaling of u crit inversely proportional to the convective overturn timescale can reproduce the observed massu crit dependent spindown. The observed spindown of the slow rotators in the young open clusters is in better agreement with the DR than the SB models. We also discuss observational tests to distinguish di †erent classes of models using low-mass stars and rotation periods in open clusters.

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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.