We examine 15 orbits of Hubble Space Telescope observations of the nearby post-core-collapsed globular cluster NGC 6397 using narrowband photometry in Ha with broadband photometry in V, R, and I. We recover the candidate helium white dwarfs (He WDs) recently discovered by Cool et al., of which one was examined spectroscopically by Edmonds et al., along with a sequence of these objects extending down to the magnitude limit of the survey. We also find a sequence of stars with weak Ha emission and magnitudes characteristic of BY Draconis stars; their offset above the main sequence also suggests they are probable binaries. The radial distributions for both the He WD and BY Dra candidates are significantly more centrally concentrated than the main-sequence stars, suggesting that indeed both populations are in binary systems.

Gravitational microlensing events are powerful tools for the study of stellar populations. In particular, they can be used to discover and study a variety of binary systems. A large number of binary lenses have already been found through microlensing surveys and a few of these systems show strong evidence of orbital motion on the timescale of the lensing event. We expect that more binary lenses of this kind will be detected in the future. For binaries whose orbital period is comparable to the event duration, the orbital motion can cause the lensing signal to deviate drastically from that of a static binary lens. The most striking property of such light curves is the presence of quasi-periodic features, which are produced as the source traverses the same regions in the rotating lens plane. These repeating features contain information about the orbital period of the lens. If this period can be extracted, then much can be learned about the lensing system even without performing time-consuming, detailed light curve modeling. However, the relative transverse motion between the source and the lens significantly complicates the problem of period extraction. To resolve this difficulty, we present a modification of the standard LombScargle periodogram analysis. We test our method for four representative binary lens systems and demonstrate its efficiency in correctly extracting binary orbital periods.