FABRY-PEROT OBSERVATIONS AND NEW MODELS OF THE HH 47A AND HH 47D BOW SHOCKS

We present new models for the HH 47A and HH 47D bow shocks based on li ne flux and velocity maps obtained with an imaging Fabry-Perot spectro meter. We confirm that HH 47A and HH 47D each show a bow shock/Mach di sk morphology, and that velocity variability in the outflow can accoun t for the observed structures. While it was suggested a decade ago tha t the inner working surface HH 47A appears to be traveling into the wa ke of HH 47D, we find kinematic evidence that the outer bow shock HH 4 7D is also not the primary ejection event in the outflow but follows i n the wake of previously ejected material. By comparing the observed l ine ratios and line profiles to those predicted by our bow shock model s, we find that both bow shocks have substantially lower shock velocit ies than their space motions would imply, and that the emission from e ach bow shock is systematically blueshifted from the rest-frame veloci ty of the ambient emission, indicating a comoving preshock medium. We derive kinematic ages of similar to 1150 yr for HH 47D and similar to 550 yr for HH 47A, which implies that the stellar driving source may u ndergo repetitive eruptions similar to FU Orionis-type outbursts every several hundred years. This timescale is similar to estimates made by Reipurth and collaborators for the separation between major outbursts in the HH 34 and HH 111 stellar jets.