Measurement of interstellar extinction for classical TTauri stars using FUV H2 line fluxes

Understanding the interstellar and potentially circumstellar extinction in sight lines of classical TTauri stars is an important ingredient
for constructing reliable spectral energy distributions, which catalyze for example protoplanetary disk chemistry. Therefore, some
attempts of measuring AV towards individual stars have been made using partly different wavelength regimes and different under-
lying assumptions. Here, we use strong lines of Lyα fluorescent H2 and derive extinction based on the assumption of optically thin
transitions. We investigate a sample of 72 classical TTauri stars observed with the Hubble Space Telescope in the framework of the
ULLYSES programme. We compute AV and RV values for the 34 with sufficient data quality as well as an additionally AV value for
the canonical RV = 3.1-value. Our results agree largely with values obtained from optical data. Moreover, we confirm the degeneracy
between AV and RV and present possibilities to break this. Finally, we discuss the validity of the assumption of optical thin lines.

Here we show the used line fits and A_V modelling.

Appendix of the publication in Astronomy and Astrophysics:  Measurement of interstellar extinction for classical TTauri stars using FUV H2 line fluxes