A survey for variable young stars with small telescopes – V. Analysis of TX Ori, V505 Ori, and V510 Ori, the HST ULLYSES targets in the σ Ori cluster

Investigations of the formation young stellar objects (YSOs) and planets require detailed analysis individual sources as well statistical a larger number objects. The Hubble UV Legacy Library Young Stars Essential Standards (ULLYSES) project provides such unique opportunity by establishing spectroscopic library high- low-mass stars in local universe. Here we analyse optical photometry three ULLYSES targets (TXOri, V505Ori, V510Ori) other YSOs $\sigma$Ori cluster taken at time HST observations to provide reference for those spectra. We identify populations along line sight $\sigma$Ori, separated parallax proper motion space. show typical YSO behaviour with pronounced variability mass accretion rates order 10$^{-8}$M$_\odot$/yr. Optical colours do not agree standard interstellar reddening suggest significant contribution scattered light. They are also amongst most variable strongest accretors cluster. V505\,Ori shows seven day period, indicating an inner disk warp co-rotation radius. Uncovering exact nature will improved modelling spectra context available photometry, including light contributions non-standard reddening.