thank you for your consideration. 1978940241 Assigned ID: 7251 ----- Attempting Submission 1 (Thu Apr 16 00:58:25 GMT 2026) ----- A main goal of the major HST/ULLYSES science program was to study accretion activity and its variability in low-mass pre-main sequence stars. This requires isolating emission processes that are due solely to accretion, from the other contributions to observed ultra-violet, optical, and near-infrared fluxes for these objects. A relatively recent revelation, is that the underlying stellar photospheres of young pre-main sequence stars are themselves multi-temperature, with a significant contribution coming from starspots that occupy 50-80% of the stellar surface, and contribute 20-70% of the total flux across the red optical portion of the spectrum. However, this is exactly the wavelength region used to anchor our knowledge of the star, and thereby predict towards the blue optical and ultraviolet wavelength ranges, the underlying stellar contribution. Without correct assessment of the spectral energy distribution of the underlying star, estimates of stellar accretion rates are biased by factors of a few to ten. Through this archival proposal award, we will re-analyze ULYSSES data for at least 24 and ideally up to 109 stars, re-deriving accretion rates that correctly account for the effects of the ubiquitous starspots. PI Lynne Hillenbrand has several decades of experience working in the fields of star formation, young stellar popuations, stellar multiplicity, individual YSOs, time-variable phenomena, accretion/outflow processes, disk lifetimes, pre-main sequence stellar evolution, the initial mass function, stellar ages, and stellar activity. She has worked with spectroscopy from ultraviolet to mid-infrared wavelengths of young stars and has deep experience in the field. She is familiar with both the data sets and the analysis described in the proposal. Graduate Student Facundo Perez Paolino has published five first-author papers on reproducing young stellar object spectrophotometry with models that incorporate starspots, accretion, and disk excess emission, resulting in a mature, end to end computational workflow for extracting physical parameters from low, moderate, and high resolution spectra from optical to near infrared wavelengths. This includes: prior starspot modelling of X-Shooter data used as the templates for ODYSSEUS, measuring magnetic fields originating in both the starspots and the photospheres of young stellar objects, and modelling accretion shcok excesses in broadband near-infrared spectra of accreting young stellar objects. He also has substantial experience with (mainly near infrared) stellar spectroscopy both as an archival data user and as an observer, including leading and participating in multiple accepted telescope proposals and observing campaigns. He is therefore an expert practitioner of the analysis described in the proposal and is familiar with the data sets. His experience dealing with the inherent degeneracies associated with modelling starspots are especially important for the proposed work. Stellar Physics and Stellar Types 0 false true false false false false false SUPPORTED