Speaker
Description
The mechanism behind Long Secondary Periods (LSPs) in variable red giants remains unexplained, although recent evidence suggests they may be caused by periodic obscuration from a dusty cloud associated with a close-orbiting substellar companion, supported by observations of secondary eclipses in the mid-infrared. As one of the tests of this hypothesis, we conducted a two-year monitoring campaign of four LSP stars exhibiting mid-infrared secondary minima, for which we have collected high quality lightcurves and high-resolution spectra at multiple phases of their LSP variability cycle. We present a phase-dependent analysis of spectral diagnostics tracing the stellar atmosphere and circumstellar environment. These data allow us to investigate the structure, kinematics, and variability of the obscuring material and to assess its consistency with an orbiting dusty structure associated with a substellar companion.