# # Program information file # PROGRAM_ID 2021B036 PROGRAM_TITLE From active to inactive magnetic dynamos in pre-main-sequence stars PROGRAM_INV1 Christian Flores PROGRAM_INV2 Michael connelley PROGRAM_INV3 Bo Reipurth PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Herbig Ae/Be stars are young pre-main-sequence stars with stellar masses ranging from ~3 to 20 solar masses. Most of these stars have weak [B<0.2 kG] or undetected magnetic fields. The lower-mass counterparts of the Herbig Ae/Be stars are the well-studied T~Tauri stars with M < 1.5 Msun. These stars host strong kilogauss magnetic fields on their surfaces, which are thought to be generated by an internal magnetic dynamo mechanism. The exact mass at which this dynamo mechanism stops operating in young stars is not known, yet it contains important clues about the physical conditions necessary to produce and sustain magnetic fields in stars. The goal of this research is to determine the stellar mass at which the dynamo mechanism ceases to work for young stars. We will investigate this problem in two ways; first, by directly measuring the variation of the stars' magnetic field strength as a function of the masses of the stars. Secondly, by monitoring the appearance 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 [M_star ~ 1.5 - 3.0 Msun] with the infrared spectrograph iSHELL on IRTF [this proposal] and the optical spectrograph ESPaDOnS on CFHT [UH proposal submitted]. Stellar parameters will be calculated by modeling the strength of stellar photospheric lines with our magnetic radiative transfer code [Flores et al. 2019]. Once masses, temperatures, and magnetic field strengths are obtained for the stars, 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 then be used to put strong constraints on stellar interior and stellar evolutionary models. PROGRAM_ABSTRACT_END