Constraining the evolution of the pulsating subdwarf B star Feige 48 (KL UMa).

Pulsating stars allow a direct investigation of their structure and evolutionary history from the evaluation of pulsation modes. However, the observed pulsation frequencies must first be identified with spherical harmonics (modes). For subdwarf B (sdB) stars, such identifications using white-light photometry currently have significant limitations. We propose using time-resolved spectroscopy combined with multicolor photometry to identify pulsation modes and constrain structure models. We propose to observe Feige 48, a unique pulsating sdB star that has a relatively simple pulsation spectrum with constraints other sdB stars don't have: a known binary (and rotation) period, inclination, and some photometrically constrained modes. Our proposed observations will constrain both the star and the binary system. We will measure radial velocity, effective temperature, and gravity variations produced by the pulsations. With simultaneous multicolor photometry, we will calibrate perturbative atmospheric models, identify the remaining pulsation frequencies and apply calibrated models to previously observed sdB stars. This provides an arsenal of seismic tools to test structure and evolution models, constraining stellar parameters including total mass, envelope mass, internal composition discontinuities, and internal rotation.