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

<p><span>Understanding the interstellar and potentially circumstellar extinction in sight lines of classical TTauri stars is an important ingredient</span><br><span>for constructing reliable spectral energy distributions, which catalyze for example protoplanetary disk chemistry. Therefore, some</span><br><span>attempts of measuring</span><span> </span><span>A</span><span>V</span><span> </span><span>towards individual stars have been made using partly di</span><span>ff</span><span>erent wavelength regimes and di</span><span>ff</span><span>erent under-</span><br><span>lying assumptions. Here, we use strong lines of Ly</span><span>&alpha;</span><span> </span><span>fluorescent H</span><span>2</span><span> </span><span>and derive extinction based on the assumption of optically thin</span><br><span>transitions. We investigate a sample of 72 classical TTauri stars observed with the Hubble Space Telescope in the framework of the</span><br><span>ULLYSES programme. We compute</span><span> </span><span>A</span><span>V</span><span> </span><span>and</span><span> </span><span>R</span><span>V</span><span> </span><span>values for the 34 with su</span><span>ffi</span><span>cient data quality as well as an additionally</span><span> </span><span>A</span><span>V</span><span> </span><span>value for</span><br><span>the canonical</span><span> </span><span>R</span><span>V</span><span> </span><span>=</span><span> </span><span>3</span><span>.</span><span>1-value. Our results agree largely with values obtained from optical data. Moreover, we confirm the degeneracy</span><br><span>between</span><span> </span><span>A</span><span>V</span><span> </span><span>and</span><span> </span><span>R</span><span>V</span><span> </span><span>and present possibilities to break this. Finally, we discuss the validity of the assumption of optical thin lines.</span></p> <p><span>Here we show the used line fits and A_V modelling.</span></p> <p>Appendix of the publication in Astronomy and Astrophysics:&nbsp; <span>Measurement of interstellar extinction for classical TTauri stars</span>&nbsp;<span>using FUV H</span><span>2</span><span> </span><span>line fluxes</span></p>