# # Program information file # PROGRAM_ID 2021B080 PROGRAM_TITLE LAERTES: L-Band Accretion Estimator Reconnaissance of TTS Emission Spectra PROGRAM_INV1 Will Fischer PROGRAM_INV2 Tracy Beck PROGRAM_INV3 James Muzerolle PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG The disk accretion rates of accreting young stars are important inputs for understanding how stars and planets get their masses. These are best measured from the UV/optical continuum, but these wavelengths are not accessible for the most embedded T Tauri stars [TTS] or in their precursors, the protostars. Instead, IR emission lines can be used as indirect tracers. At 4.05 microns, Brackett alpha is a strong emission line in accreting young stars and will be readily accessible to JWST spectroscopy even in young, deeply embedded protostars where near-IR lines are invisible, but it has not been fully calibrated as an accretion indicator. In 2021B, the ULLYSES public director's discretionary program with Hubble will measure the UV/optical continuum in three bright T Tauri stars, 12 times per star over three consecutive rotation periods to track their short-term variability. We propose 1.7-4.2 micron SpeX LXD_short spectroscopy of these TTS with the 0.8 arcsec slit, three times per star. This will allow [1] calibration of Brackett alpha with the same techniques as for previous single-epoch Hubble targets that we are observing with IRTF in 2020B and 2021A and [2] an initial look at how tightly any mid-IR variability is tied to UV variability. It will also provide an important archival dataset for the community by extending the wavelength coverage of the Hubble observations to the thermal IR. PROGRAM_ABSTRACT_END