I) Extinction ( ) and accretion luminosity ( ) Av Lacc ✓In this analysis we considered the following lines as accretion diagnostics: , , , and lines, together with the Ca II triplet lines. ✓The measured fluxes of these emission lines have been combined with the Gaia DR2 distance (Gaia Collaboration et al. 2018) of pc to derive the line luminosities ( ). ✓From each of them we evaluated the accretion luminosity ( ) by making use of the empirical relations of Alcalá et al. (2017). In this way, we estimated the weighted mean accretion luminosity ( ), as illustrated in Fig. 1. ✓We have developed a new approach to estimate the extinction of our source, which corresponds to the value minimizing the relative error of (Fig. 2). To this end, we corrected the observed spectra for extinction using the extinction law by Weingartner & Draine (2001) that covers the wavelength range of the X-shooter spectra. Hα Hβ Hγ Hδ 151 ± 14 Lline Lacc,line Lacc,line −Lline ⟨Lacc,line⟩ Av ⟨Lacc,line⟩ Variability of the mass accretion rate in the very low-mass star Par-Lup3-4 A. Klutsch1, B. Stelzer1,2, J. M. Alcalá3, A. Frasca4, C. F. Manara5, A. Scholz6 1 IAAT Tübingen, Germany, E-mail : klutsch@astro.uni-tuebingen.de • 2 INAF-OA Palermo, Italy • 3 INAF-OA Capodimonte, Napoli, Italy 4 INAF-OA Catania, Italy • 5 European Southern Observatory, Garching bei München, Germany • 6 SUPA St. Andrews, UK Acknowledgments • This work is supported by the Deutsche Forschungsgemeinschaft (DFG) project number 413113723. References • Alcalá, J. M., et al. 2017, A&A, 600, A20 ; Comerón, F., et al. 2003, A&A, 406, 1001 ; Gaia Collaboration, Brown, A. G. A., et al. 2018, A&A, 616, A1 ; Manara, C. F., et al. 2013, A&A, 558, A114 ; Weingartner, J. C. & Draine, B. T. 2001, ApJ, 548, 296. Virtual conference March 2-4, 2021 Accretion and outflows are key processes in early stellar evolution. The material accreted at the edge of the inner disc is channeled along magnetic funnel flows onto the star. Its kinetic energy is dissipated in standing accretion shocks. The accretion process is therefore sensitive to the spatial and temporal variations of the structure of the magnetic field and its mass load. Due to the change of view of the star-disc system throughout the rotation cycle, geometric effects are superimposed on such intrinsic variability and likely dominate the observed variability. An assessment of changes in the mass accretion rate is essential to understand the structure of the star-disc-magnetosphere system. The young, very low-mass star Par-Lup3-4 displays a rich emission-line spectrum, hosts a disc with an almost edge-on inclination, and is in the critical mass range near the star/brown dwarf transition, where the knowledge of the accretion/outflow connection remains rather poor. These properties make this star a prime target for conducting a variability study of mass accretion. We make use of X-shooter's unique capabilities to monitor its broad-band spectrum in the range from ultraviolet to near-infrared. The sampling of our ten spectra covers timescales of hours, days, weeks, and years. ✓The values are almost constant over time (Fig. 3), with the exception of the spectrum acquired in 2012 (i.e., epoch 2). ✓Due to a bad seeing, the error on is higher and, as a consequence, the determination of is poorer in epochs 3 6. ✓We evaluated the weighted average extinction at: ‣ mag with the method described by Manara et al. (2013). ‣ mag with the approach presented in Sect. I. ✓These values agree with each other within the errors and are consistent with those in the literature for Par-Lup3-4, which range from 2.4 to 5.6 mag (Comerón et al. 2003). ✓We also obtained a good agreement between the values derived with these two methods (Fig. 4). ✓After correcting for the extinction, a small variation of can be seen (Fig. 5). We obtained , which corresponds to a mass accretion rate of or . Av Lacc,line Av − ⟨Av⟩ 1.95 ± 0.25 2.35 ± 0.25 Lacc Lacc log(Lacc/L⊙) = −3.0 ± 0.1 log( ·Macc)