# # Program information file # PROGRAM_ID 2024B072 PROGRAM_TITLE Using iSHELL To Measure the Magnetic Field Strengths of Chemically Peculiar Ap/Bp Stars PROGRAM_INV1 Stephen Chojnowski PROGRAM_INV2 Pamela Marcum PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Ap stars host global magnetic fields that can reach extraordinary strengths up to 34 kG. The field origins are enigmatic considering that A/B main sequence stars lack the surface convection zones in which the [considerably weaker] fields of low-mass stars are generated. The fact that Ap stars are not rare, representing some 10-15% of the A/B stellar population, highlights the importance in addressing this long-standing mystery of stellar astrophysics. Little is known about how Ap stars work, how they were formed, and what they will evolve into. Of the 3652 known Ap stars as of 2009, only 84 were known to have the combination of very slow rotation and strong fields needed for the Zeeman effect to be observed in unpolarized light. For these stars, the separations of magnetically split lines [RMSL] provide minimally ambiguous, largely model-independent measures of their intrinsic surface field strengths. Whereas the vast majority of past Ap+RMSL studies were optical-based, the NIR has a major advantage due to the wavelength dependencies of the Doppler and Zeeman effects [lambda and lambda^2, respectively] conspiring to increase the NIR line separation relative to optical for a given rotational velocity and field strength. This advantage was recently demonstrated thanks to H-band spectra from the SDSS/APOGEE survey, in which numerous new examples of stars with RMSL have been discovered even at the modest resolution of the APOGEE instruments. We propose to exploit iSHELL's considerably higher resolution both for follow-up of Ap stars already known to exhibit RMSL in the NIR as well as for discovering new examples of RMSL that are hinted at in the APOGEE spectra. PROGRAM_ABSTRACT_END