We examine three analytic theories of magnetospheric accretion onto classical T Tauri stars (CTTSs) under the assumption that the magnetic field strength does not vary appreciably from star to star. From these investigations we derive predicted relationships among the stellar mass, radius, rotation period, and disk accretion rate. Data from five studies of the accretion parameters of CTTSs are used to test the predicted correlations. We generally find that the data do not display the predicted correlations except for that predicted by the model of Shu et al. as detailed by Ostriker & Shu and extended here to include nondipole field topologies. Their identification of the trapped flux as an important quantity in the model appears to be critical for reconciling the observed data to the theory. While the data do generally support the extended Ostriker & Shu predictions, only one of the two studies for which the requisite data exist shows the highest correlation when considering all the relevant parameters. This suggests that great care must be taken when trying to use existing observations to test the theory.

We present results of a search for optical counterparts of X-ray sources in and toward the globular cluster Omega Centauri (NGC 5139) using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. The ACS data consist of a mosaic of Wide Field Channel (WFC) images obtained using F625W, F435W, and F658N filters; with 9 pointings we cover the central ∼10 ′ ×10 ′ of the cluster and encompass 109 known Chandra sources. We find promising optical counterparts for 59 of the sources, ∼40 of which are likely to be associated with the cluster. These include 27 candidate cataclysmic variables (CVs), 24 of which are reported here for the first time. Fourteen of the CV candidates are very faint, with absolute magnitudes in the range M 625 = 10.4 − 12.6, making them comparable in brightness to field CVs near the period minimum discovered in the SDSS (Gänsicke et al. 2009). Additional optical counterparts include three BY Dra candidates, a possible blue straggler, and a previously-reported quiescent low-mass X-ray binary (Haggard et al. 2004). We also identify three foreground stars and 11 probable active galactic nuclei. Finally, we report the discovery of a group of seven stars whose X-ray properties are suggestive of magnetically active binaries, and whose optical counterparts lie on or very near the metal-rich anomalous giant and subgiant branches in ω Cen. If the apparent association between these seven stars and the RGB/SGB-a stars is real, then the frequency of X-ray sources in this metal-rich population is enhanced by a factor of at least five relative to the other giant and subgiant populations in the cluster. If these stars are not members of the metal-rich population, then they bring to 20 the total number of red stragglers (also known as sub-subgiants) that have been identified in ω Cen, the largest number yet known in any globular cluster.