Jonathan Mushkin and Sabina Sagynbayeva

From the calendar

In the search of study of gravitational waves emitted during the coalescence of binaries, an important "atom" is the evaluation of the likelihood (that is, the probability of the observed data, given some model parameters). This evaluation repeats during the search itself and within the parameter-estimation process, which can require tens to hundreds CPU hours per transient. We propose a new method to evaluate the likelihood, by factorizing the likelihood function to components that depend either on the intrinsic binary parameters (parameters of the binary evolution itself) or extrinsic parameters (relative positions and orientations between the observatories and the binary). By computing the components, we can then evaluate the likelihood at all possible combinations extremely efficiently, practically covering the entire relevant phase space, providing both a speed-up (minutes per event, with prospects of going to seconds) and robustness. In this talk I will present the work, and how it fits in the wider context of GW transient astronomy.

Stellar magnetic activity poses a major challenge to the characterization of exoplanet atmospheres. Evolving starspots can introduce astrophysical noise that masks or mimics atmospheric signals, potentially leading to false positive detections or biased measurements. This is especially pertinent for ongoing observatories like JWST, which studies the atmospheres of small planets orbiting Sun-like stars that often exhibit strong magnetic activity. Disentangling stellar and planetary signals is therefore critical for robustly measuring exoplanet atmospheric properties.In this talk, I will showcase the novel technique for mapping the evolving starspot distributions on exoplanet host stars observed by Kepler and TESS. Our hierarchical Bayesian approach uses Gaussian processes to infer key starspot properties like typical sizes, active latitudes, and lifetimes from the photometric variability induced by spots rotating in and out of view. Crucially, by leveraging the abundant transits of exoplanets, some of which cross over spots, we can break degeneracies in the spot modeling to infer stellar and starspots parameters. Simultaneously, transiting exoplanets provide a novel probe of stellar magnetic activity and spin-orbit misalignments, illuminating the formation and evolution of planetary systems. I will discuss the implications of our results for both fields and highlight the potential of our flexible technique in the era of precise time-domain photometry.