An Asymmetric Outflow from the Herbig Ae Star HD 163296

Abstract

We present an observational picture of the HH 409 bipolar outflow including the detection of six previously unreported Herbig-Haro knots from the Herbig Ae star HD 163296. This study combines seven years of data from ground-based Fabry-Pérot and HST coronagraphic imagery, as well as HST long-slit spectral imagery. The redshifted counterjet includes a chain of six Herbig-Haro knots spanning >27" to the northeast (P.A.~42^deg) of the source and has been active for >80 yr. The brightest knot in the counterjet is HH 409 C, a low-excitation bow shock with a shock velocity V_s~50 km s^-1 and total space motion V_jet~260 km s^-1. The presence of additional knots in the counterjet beyond the bow shock may indicate precession of the jet axis. The blueshifted jet includes two closely spaced knots within 10" and a distant bow shock (~21") southwest (P.A.~223^deg) of the source. The brightest knot in the jet is HH 409 A, a higher excitation more bullet-like shock with V_s~90 km s^-1 and V_jet~360 km s^-1. The average opening angles for both the jet and counterjet are similar, α_a~2^deg, and consistent with opening angles of lower mass T Tauri stars. The mass-loss rates in both lobes of the flow, despite the asymmetry of the knots, are also comparable, M˙_out~1.0×10^-8 M_solar yr^-1. This suggests that variations in the mass outflow rate are not more than a factor of ~2.