# # Program information file # PROGRAM_ID 2024A026 PROGRAM_TITLE Dust Extinction and Gas Flows in 'Dippers' PROGRAM_INV1 Michael Sitko PROGRAM_INV2 Ray Russell PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Dippers are stars exhibiting variations [usually irregular in nature] in brightness at visible wavelengths detected by the Kepler facility A significant population was detected in the Sco-Oph Association during the K2 extended mission. Most of these 'dips' are likely the results of variable dust extinction, and the dips range from a few % to 40%. The extinction in a few systems has been determined, and found to be due to dust grains that have grown significantly in size from those in the general interstellar medium and giant molecular clouds. Unlike most pre-main sequence stars, that exhibit line profiles consistent with outflowing gas, the dippers often exhibit line profiles consistent with inflowing gas toward the star. And these profiles change from epoch to epoch. It seems likely that during a dip, we see through more dust, perhaps due to irregularities in the disk surface. Lines such as the He I line at 1.08 microns vary with the extinction, indicating that the gas and dust are mixed together. In this proposal, the spectral variability will be extended to a larger [and on average, brighter] sample that has ben previously examine in tis manner. PROGRAM_ABSTRACT_END