Doubling the Number of Blue Large-Amplitude Pulsators: Final Results of Searches for BLAPs in the OGLE Inner Galactic Bulge Fields

TL;DR

This study leverages two decades of OGLE photometry to perform a comprehensive search for Blue Large-Amplitude Pulsators (BLAPs) in the inner Galactic bulge, substantially expanding the known BLAP population to about 200 with 87 new discoveries. Using a large-scale sinusoid-fitting pipeline and multi-season analyses, the authors extract periods, amplitudes, and colors, classify light-curve morphologies, and identify several BLAPs with multiple pulsation modes. They document extreme period-change events in several objects, apply WWZ frequency analysis to characterize temporal frequency evolution, and assess completeness and purity through simulations, finding near-complete sampling for bright BLAPs and very high catalog purity. The expanded BLAP catalog, including time-series data and finding charts in the OGLE Collection of Variable Stars (OCVS), provides a critical resource for constraining BLAP formation channels, the role of binary interactions, and the evolutionary status of these enigmatic pulsators.

Abstract

Blue Large-Amplitude Pulsators (BLAPs) are rare short-period ($\lesssim$80 min) pulsating variable stars exhibiting large-amplitude brightness variations (typically between 0.1 and 0.4 mag). As a recently discovered class of radial-mode pulsators, the origin and nature of these variables remain the subject of ongoing investigations. Here, we present a comprehensive summary of all BLAPs identified in the data of the Optical Gravitational Lensing Experiment (OGLE), including the discovery of 88 new BLAPs in the inner Galactic bulge fields. We performed a systematic search for periodic signals in the $I$-band light curves of more than 400 million stars with magnitudes down to $I = 21$. Our search effectively doubles the number of these variables to almost 200. The detected BLAPs exhibit pulsation periods between roughly 5 and 76 minutes. The analyzed dataset covers a timespan from 2001 to 2024, with some stars observed up to 20,000 times, providing the temporal coverage needed to study period and amplitude variations. We report on three objects that show enormous period changes, at a rate of $10^{-5}$ yr$^{-1}$, which could provide important clues to the evolutionary status of BLAPs. Full dataset is incorporated into the publicly available OGLE Collection of Variable Stars (OCVS), enabling future studies of these enigmatic objects.

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