# # Program information file # PROGRAM_ID 2022B085 PROGRAM_TITLE Studying the Formation and Dissipation of Transient Decretion Disks in Newly Discovered Be Stars PROGRAM_INV1 Guy Stringfellow PROGRAM_INV2 PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Be stars are rare objects believed to be rapidly rotating B-stars undergoing non-radial pulsations that eject matter into the circumstellar environment temporarily forming a decretion disk. How this process works, and the physics and time scales driving the formation of decretion disks remain elusive. Historically, a star is classified as a Be-star if the observed stellar optical spectrum resembles that of a B-type star displaying mostly normal absorption lines, but with some [primarily H-alpha or other Balmer lines] displaying emission. Disks are now being found around hot massive stars of other spectral types, ranging from A-O. Further, many previously observed normal B-stars have subsequently been found to display emission lines, emphasizing the transient nature of these decretion disks. Large surveys are discovering hundreds of previously unknown Be-stars, making their prevalence and importance in the evolution of massive stars more impactful. These serendipitous discoveries often have no previous spectra, so their classification and evolutionary state remain unclear. To make progress in understanding the underlying physics responsible for the formation and dissipation of these decretion disks, the intervals of quiescence between outbursts, the longevity of these disks, their formation and dissipation events need to be well studied. This requires spectral classification and concerted time domain studies with cadences enabling coverage of the disk events. Optical-IR spectral and optical photometric monitoring observations [approved or proposed] of a sample of Be-stars already displaying evidence of transitory disks over timescales of days to months will be studied. This unprecedented dataset will provide unique insight into the formation and dissipation of these disks through measuring emission line ratios, line-profile variability/structure analysis, rotation/angular momentum diagnostics, and binarity through radial velocities and their timescales. Single optical+IR spectra of newly discovered Be-stars will also be obtained to perform spectral typing and evolutionary assessment. PROGRAM_ABSTRACT_END