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Tidally tilted pulsators (TTPs) are an intriguing new class of oscillatingstars in binary systems; in such stars, the pulsation axis coincides with theline of apsides, or semi-major axis, of the binary. All three TTPs discoveredso far have been $\delta$~Scuti stars. In this Letter, we report the firstconclusive discovery of tidally tilted pulsations in a subdwarf B (sdB) star.HD 265435 is an sdB--white dwarf binary with a 1.65-hr period that has beenidentified and characterized as the nearest potential Type Ia supernovaprogenitor. Using TESS 20-s cadence data from Sectors 44 and 45, we show thatthe pulsation axis of the sdB star has been tidally tilted into the orbitalplane and aligned with the tidal axis of the binary. We identify 31 independentpulsation frequencies, 27 of which have between 1 and 7 sidebands separated bythe orbital frequency ($\nu_{\rm orb}$), or multiples thereof. Using theobserved amplitude and phase variability due to tidal tilting, we assign $\ell$and $m$ values to most of the observed oscillation modes and use these modeidentifications to generate preliminary asteroseismic constraints. Our worksignificantly expands our understanding of TTPs, as we now know that (i) theycan be found in stars other than $\delta$~Scuti pulsators, especiallyhighly-evolved stars that have lost their H-rich envelopes, and (ii) tidallytilted pulsations can be used to probe the interiors of stars in very tightbinaries.

Tidally Tilted Pulsations in HD 265435, a subdwarf B Star with a Close White Dwarf Companion