Prospecting Period Measurements with LSST - Low Mass X-ray Binaries as a Test Case.

The Large Synoptic Survey Telescope (LSST) will provide for unbiased sampling of variability properties of objects with r magnitude < 24. This should allow for those objects whose variations reveal their orbital periods (P-orb), such as low mass X-ray binaries (LMXBs) and related objects, to be examined in much greater detail and with systematic sampling. However, the baseline LSST observing strategy has temporal sampling that is not optimized for such work in the Galaxy. Here, we assess four candidate observing strategies for measurement of P-orb in the range 10 min to 50 d. We simulate multifilter quiescent LMXB light curves including ellipsoidal modulation and stochastic flaring, and then sample these using ',SST's operations simulator (OpSim) over the (mag, P-orb) parameter space, and over five sight-lines sampling a range of possible reddening values. The percentage of simulated parameter space with correctly returned periods ranges from similar to 23 percent, for the current baseline strategy, to similar to 70 per cent for the two simulated strategies without reduced Galactic sampling. Convolving these results with a P-orb distribution, a modelled Galactic spatial distribution and reddening maps, we conservatively estimate that the most recent version of the LSST baseline strategy (baseline2018a) will allow P-orb determination for similar to 18 per cent of the Milky Way's LMXB population, whereas strategies that do not reduce observations of the Galactic Plane can improve this dramatically to similar to 32 per cent. This increase would allow characterization of the full binary population by breaking degeneracies between suggested P-orb distributions in the literature. Our results can be used in the ongoing assessment of the effectiveness of various potential cadencing strategies.