The Stripped-Star Ultraviolet Magellanic Cloud Survey (SUMS): The ultraviolet photometric catalog and stripped-star candidate selection

Most massive stars (∼8–25M⊙) interact with a binary companion during their lifetimes. These interactions can remove the hydrogen-rich envelope, producing intermediate-mass (∼2–8M⊙) and helium-rich stars. These “stripped stars” are predicted to emit predominantly in the ultraviolet (UV) and can therefore be identified via a UV excess—provided they are not outshone by their companion. However, despite their importance to binary evolution, supernovae, and ionizing feedback, few stripped stars have been confirmed. This is likely due to the scarcity of wide-field, high angular-resolution, UV surveys of stellar populations with reliable distances and extinction estimates. To address this, we present the Stripped-Star Ultraviolet Magellanic Clouds Survey catalog. We use the Tractor forward modeling software to perform point-spread function photometry on 2420 Swift UVOT images of the LMC and SMC. The resulting catalog contains 734,862 sources in three UV filters to a depth of ∼20 Vega mag. We perform validation tests on the photometry pipeline and highlight the catalog’s broad applicability. We then identify sources with excess UV light compared to main-sequence stars and apply a series of quality cuts. From this, we identify 522 candidate stripped stars in the LMC and 298 in the SMC. We assess the potential contamination from other UV excess systems and argue the dominant uncertainty to be dust: early main-sequence stars can mimic the colors of stripped-star binaries when extinction is overcorrected. This survey lays the groundwork for the first systematic census of stripped stars and opens new windows into binary evolution and massive star populations.