# # Program information file # PROGRAM_ID 2024A032 PROGRAM_TITLE Gas Dynamics in the Dipper Star EPIC 205151387, using the He I Line at 1.08 microns PROGRAM_INV1 Michael Sitko PROGRAM_INV2 Ray Russell PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG EPIC 205151387 is a K2V 'dipper' star, with frequent drops in brightness thought to be due to changes in dust extinction along the line of sight. The most likely scenario is one where the line of sight passes though the surface layers of its circumstellar disk. Changes in extinction can occur when the disk scale height changes, perhaps due to ripples in the surface of the disk. In the case of EPIC 205151387, gas flows produce a line profile in the He I 1.083 micron line, whose strength increases when the dust extinction increases - the gas and dust are mixed together. Most pre-main sequence A and F stars exhibit line profiles of outflowing gas with a P Cygni-like profile. In EPIC 20515138, the gas is characterized by an inverse P Cygni-like profile, that is, inflowing gas. toward the star, and more pronounced that in most other low-mass star [such as T Tauri stars]. In this object, the He I line profile changes from epoch to epoch, and even changes dramatically from night to night. This makes it an excellent object to probe the dynamics near the disk surface. This proposal requests time to monitor the changes in the He I line [and dust extinction] using the SpeX SXD mode and K band imaging. PROGRAM_ABSTRACT_END