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°) 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 Vs ~ 50 km s-1 and total space motion Vjet ≈ 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°) of the source. The brightest knot in the jet is HH 409 A, a higher excitation more bullet-like shock with Vs ~ 90 km s-1 and Vjet ≈ 360 km s-1. The average opening angles for both the jet and counterjet are similar, αa ~ 2°, 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, out ~ 1.0 × 10-8 M☉ yr-1. This suggests that variations in the mass outflow rate are not more than a factor of ~2.