Emission line variability of young 10-30 M_Jup companions.I. The case of GQ Lup b and GSC 06214-00210 b

Context. Emission lines that are indicative of active accretion have been observed for a number low-mass companions ( M < 30 Jup ) to stars. Line variability is ubiquitous on stellar accretors, but it has never characterized in detail companions. Such characterizations can offer insights into the mechanism at play. Aims. We aim characterize short-to-long-term H I Paschen β emission line two 10 wide orbits: GQ Lup b and GSC 06214-00210 b. also clarify their mechanisms. Methods. used J-band observations R = 1800–2360, obtained with VLT/SINFONI 2017, record time-series investigations hours-to-weeks (1.282 µm). Contrary ∝ , should be less affected by chromospheric activity contamination. The photospheric was analyzed each epoch removed ForMoSA forward-modeling tool, using new grids ATMO models exploring different C/O [M/H] values. time series profiles intensities were compared those more massive accretors predictions from latest magnetospheric shock models. To complement these results, we re-investigated archival spectroscopic near-infrared wavelengths target increase frame up decade build comprehensive understanding processes Results. For b, find timescales several months decades, whereas within acceptable noise levels shorter timescales. tens minutes all way decade. partially resolved least one epoch. Both objects show flux moderate (<50%), below rotation period, significant longer (up ~1000% decade-long timescales). This behavior resembles classical T Tauri blue-shifted only reproduced models, while fairly well both except which model highly favored. values broadly consistent solar Conclusions. While favored higher resolution (R > 000) required disentangle (non-exclusive) emitting similar low mass stars may support high amplitude over month found could key explaining yield imaging campaigns.