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We use the stellar evolution code BPASS and the gravitational wave simulation code LEGWORK to simulate populations of compact binaries that may be detected by the in-development space-based gravitational wave (GW) detector LISA. Specifically, we simulate the Magellanic Clouds and binary populations mimicking several globular clusters, neglecting dynamical effects. We find that the Magellanic Clouds would have a handful of detectable sources each, but for globular clusters the amount of detectable sources would be less than one. We compare our results to earlier research and find that our predicted numbers are several tens of times lower than calculations using the stellar evolution code BSE that take dynamical effects into account, but also calculations using the stellar evolution code SeBa for the Magellanic Clouds. This correlates with earlier research which compared BPASS models for GW sources in the Galactic disk with BSE models and found a similarly sized discrepancy. We analyse and explain this discrepancy as being caused by differences between the stellar evolution codes, particularly in the treatment of mass transfer and common-envelope events in binaries, where in BPASS mass transfer is more likely to be stable and tends to lead to less orbital shrinkage in the common-envelope phase than in other codes. This difference results in fewer compact binaries with periods short enough to be detected by LISA existing in the BPASS population. For globular clusters, we conclude that the impact of dynamical effects is uncertain from the literature, but the differences in stellar evolution have an effect of a factor of a few tens.

Galactic white dwarf binaries (WDBs) and black hole binaries (BHBs) will be gravitational wave (GW) sources for LISA. Their detection will provide insights into binary evolution and the evolution of our Galaxy through cosmic history. Here, we make predictions of the expected WDB and BHB population within our Galaxy. We combine predictions of the compact remnant binary populations expected by stellar evolution by using the detailed Binary Population and Spectral Synthesis code (BPASS) with a Milky Way analogue galaxy model from the Feedback In Realistic Environment (FIRE) simulations. We use \textscPhenomA and \textscLEGWORK to simulate LISA observations. Both packages make similar predictions that on average four Galactic BHBs and 673 Galactic WDBs above the signal-to-noise ratio (SNR) threshold of 7 after a four-year mission. We compare these predictions to earlier results using the Binary Star Evolution (BSE) code with the same FIRE model galaxy. We find that BPASS predicts a few more LISA observable Galactic BHBs and a twentieth of the Galactic WDBs. The differences are due to the different physical assumptions that have gone into the binary evolution calculations. These results indicate that the expected population of compact binaries that LISA will detect depends very sensitively on the binary population synthesis models used and thus observations of the LISA population will provide tight constraints on our modelling of binary stars. Finally, from our synthetic populations we have created mock LISA signals that can be used to test and refine data processing methods of the eventual LISA observations.

We study the LISA sources that arise from isolated binary evolution, and how these depend on age and metallicity, using model stellar populations from BPASS. We model these as single-aged populations which are analogous to star clusters. We calculate the combined GW spectrum of all the binaries within these model clusters, including all types of compact binaries as well as those with living stars. These results allow us to evaluate the detectability of star clusters with LISA. We find at late times the dominant sources are WD-WD binaries by factors of 50-200, but at times between $10^8$ and $10^9$ years we find a significant population of NS-WD and BH-WD binaries (2-40 per $10^6$ M$_{\odot}$), which is related to the treatment of mass transfer and common envelope events in BPASS, wherein mass transfer is relatively likely to be stable. Metallicity also has an effect on the GW spectrum and on the relative dominance of different types of binaries. Using the information about known star clusters will aid the identification of sky locations where one could expect LISA to find GW sources.

We present forward modeling from the BPASS code suite of the population of observed gravitational wave (GW) transients reported by the LIGO/VIRGO consortium (LVC) during their third observing run, O3(a+b). Specifically, we predict the expected chirp mass and mass ratio distributions for GW transients, taking account of detector sensitivity to determine how many events should have been detected by the current detector network in O3(a+b). We investigate how these predictions change by alternating between four different remnant mass estimation schemes and two supernovae (SNe) kick prescriptions. We find that none of the model populations resulting from these variations accurately match the whole O3(a+b) GW transient catalog. However, agreement from some models to part of the catalog suggests ways to achieve a more complete fit. These include reducing the number of low mass black holes (BHs) close to the mass gap, while also increasing the number of higher mass BHs below the pair-instability SN limit. Finally, we find that the interaction between the value of the remnant mass from a stellar model and the choice of SN kick is complex and different kick prescriptions may be required depending on whether a neutron star or BH is formed.