Coordinated Space and Ground Monitoring of Accretion Bursts in a Protoplanetary Disk: MIRI and iSHELL observe the long-term modulation of gas within a small inner disk cavity

DQ Tau is a TTauri eccentric binary with pulsed accretion bursts regulated by its ~ 16-day orbital period. We have monitored this system with seven instruments from ground and space over 40 days. We present results on molecular gas variability from nine JWST-MIRI and nine IRTF-iSHELL epochs over three sequential accretion bursts with accretion luminosity pulses increasing by factors of ~ 9-80. A fundamental new measurement from this analysis is the line broadening of CO (from iSHELL) and H₂O (from MIRI) lines, which we use to estimate Keplerian radii and their variability in parallel to the line luminosity. This unprecedented dataset clearly shows that the molecular emission does not react like HI and the 5-$μ$m continuum with each accretion burst: the line luminosity and width of all hot molecular gas tracers decrease over ~30-35 days, consistent with an emitting region decreasing in temperature and mass as it recedes to larger radii within the ~ 0.2-0.4 au inner cavity perturbed by the binary. The infrared molecular spectrum of DQ Tau is affected more by disk dynamics then by chemical changes triggered by variable accretion, supporting model expectations for chemical relaxation timescales that are much longer than the duration of these accretion bursts (10 days). The variability observed in all tracers in this study is consistent with a scenario where gas mass builds up near the disk edge to modulate the burst peak intensity and gas density in the inner cavity every ~4-5 orbital periods. The origin of this modulation is still unclear.