A photometric study of the ULLYSES/PENELLOPE T Tauri star sample in Ori OB1 and 𝛔 Ori: the accretion process at the highest time resolution

In order to build up a legacy spectroscopy survey of accreting low-mass pre-main sequence stars, synchronized HST and ESO/VLT observational campaigns, named ULLYSES and PENELLOPE, respectively, were carried out in the Orion star forming region in late 2020. The spectroscopic program was supported by an extensive multi-band photometric monitoring at different ground-based observatories, including our domestic telescopes at Konkoly Observatory, Hungary, as well as by simultaneous TESS observations. Here we report on our ongoing analysis aiming at characterizing the accretion process of the targeted objects based on multi-filter photometry. We observed BVr'i' light curves with an approximately daily cadence, and derived the brightness and color evolution of 13 T Tauri-type stars. We developed a novel method to estimate the accretion rate from simultaneous optical data, utilizing a grid of slab modeling. Using the high time resolution TESS light curves as temporal variability templates, we interpolated the BVr'i' multicolor data sets to a time resolution of 10 min. We also produced accretion rate curves with this cadence, and could define the exact variability state of the stars at the precise epochs of the spectroscopy. We analysed the amplitudes and timescales present in the accretion rate curves, and proposed to connect the different characteristic timescales with physical mechanisms. The photometry-based results on the accretion process will be later combined with HST and VLT spectroscopy of the same sample. The results, together with the similar T Tauri samples from other star forming regions, will make ULLYSES/PENELLOPE one of the highest impact study of the stellar accretion process of today.