# # Program information file # PROGRAM_ID 2022B035 PROGRAM_TITLE From active to inactive magnetic dynamos in pre-main-sequence stars PROGRAM_INV1 Michael Connelley PROGRAM_INV2 Christian Flores PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG T~Tauri stars are low-mass pre-main sequence stars [M_star < 1.5 M_sun] with strong magnetic fields on their surfaces [B~2kG]. These magnetic fields are thought to be generated in the stellar interior through a dynamo mechanism. The higher-mass counterpart of T~Tauri stars are the Herbig Ae/Be stars [~3 M_sun to 20 M_sun], which have weak [B<0.2 kG] or undetected magnetic fields. The exact point at which the dynamo mechanism stops operating in young stars is not known, but it contains important clues about the internal structure, and even how matter is accreted onto these young stars [magnetospheric vs. boundary layer accretion]. The goal of this research is to determine the stellar mass at which the dynamo mechanism ceases to work in young stars. We will investigate this problem in two ways. First, we will directly measure the stars' magnetic field strength as a function of the masses of the stars. Secondly, we will characterize the impact of starspots on the stellar surface, which manifests as temperature differences between optical and infrared observations. To achieve this, we propose to observe 45 intermediate-mass T~Tauri stars with the optical spectrograph ESPaDOnS on CFHT and the infrared spectrograph iSHELL on IRTF. Stellar parameters will be calculated by modeling the strength of stellar photospheric lines. With the estimated masses, temperatures, and magnetic field strengths, we will be able to directly determine the stellar mass at which the dynamo mechanism starts shutting down for these young stars. This result will indicate how much convection is needed in the stellar outer layers to sustain a magnetic dynamo PROGRAM_ABSTRACT_END