Discovery of a new blue large-amplitude pulsator in the SkyMapper DR2: SMSS J184506.82-300804.7

We report the discovery of a new Blue Large-Amplitude Pulsator (BLAP), SMSS J184506-300804 (SMSS-BLAP-1) in Data Release 2 of the SkyMapper Southern Sky Survey. We conduct high-cadence photometric observations in the u band to confirm a periodic modulation of the light curve. SMSS-BLAP-1 has a ∼19-min pulsation period with an amplitude of 0.2 mag in u band, and is similar to the classical BLAPs found by OGLE. From spectroscopic observations with the Wide-Field Spectrograph on the Australian National University 2.3m telescope, we confirm it as a low-gravity BLAP: best-fitting parameters from the non-LTE tlusty model are estimated as Teff = 29 020 K, logg = 4.661 (cm s-2), and logn(He)/n(H) = -2.722 dex. However, our BLAP exhibits a very He-deficient atmosphere compared to both low- and high-gravity BLAPs, which have logn(He)/n(H) in the range -0.41∼-2.4.