2003PASP..115..334M

To gain insight into the nature of the peculiar Herbig-Haro object HH 255 (also called Burnham's nebula), we use previously published observations to derive information about the emission-line fluxes as a function of position within HH 255 and compare them with the well-studied and relatively well behaved bow shock HH 1. There are some qualitative similarities in the Hα and [O III] λ5007 lines in both objects. However, in contrast to the expectation of the standard bow-shock model, the fluxes of the [O I] λ6300, [S II] λ6731, and [N II] λ6583 lines are essentially constant along the axis of the flow, while the electron density decreases, over a large distance within HH 255. We also explore the possibility that HH 255 represents the emission behind a standing or quasi-stationary shock. The shock faces upwind, and we suggest, using theoretical arguments, that it may be associated with the collimation of the southern outflow from T Tauri. Using a simplified magnetohydrodynamic simulation to illustrate the basic concept, we demonstrate that the existence of such a shock at the north edge of HH 255 could indeed explain its unusual kinematic and ionization properties. Whether or not such a shock can explain the detailed emission-line stratification remains an open question.