A Spectral Investigation into the Properties and Evolutionary Status of Radial-Mode Hot-Subdwarf Pulsators and Blue Large-Amplitude Pulsators

Hot subdwarfs are a unique class of stellar objects that provide insight into late stages of stellar evolution as well as compact binary studies and astroseismology. These stars have high temperatures and luminosities which fall below the main sequence. They have been shown to evolve through binary interaction, where a significant portion of the stellar envelope has been stripped. In addition, instabilities in the interior of these stars can lead to stellar pulsations that can be observed through variability of their atmospheric parameters. Non-radial pulsations in these stars has been theorized and observed, providing additional details into the stellar interior of hot subdwarfs. Recently, radial-mode pulsations have been discovered in these stars, leading to new, seemingly independent, classes of pulsators. These classes are known as blue large-amplitude pulsators (BLAPs) and B-type radial-mode subdwarf variables (sdBVs). BLAPs have large amplitude pulsations (200 - 400 mmag) and short pulsation periods (10 - 40 min) while radial-mode sdBVs have lower amplitudes (20 - 70 mmag) and even shorter pulsation periods (5 - 16 min). Little is known about the fundamental properties and evolutionary status of these objects, since there are few spectroscopic observations. Presented here is a case study for one of the originally discovered BLAPs which was found during the Optical Gravitational Lensing Experiment (OGLE) survey, named OGLE-BLAP-009. In addition, a comparison case study for one radial-mode sdBV, named ZTF-sdBV-08, which was discovered during the Zwicky Transient Facility (ZTF) survey is presented. The aim of these studies is to use time-series photometry and spectroscopy to estimate the fundamental properties of these stars, such as mass and radius, and to place constraints on their evolutionary status using stellar evolution models developed with MESA and GYRE. This will serve as a test for future analysis on more of these objects in order to try and characterise the classes as a whole.