ar X iv : a st ro - p h / 06 02 45 6 v 1 2 1 Fe b 20 06 The dissolving Rosette HH 2 jet bathed in harsh UV radiation of the Rosette Nebula

Herbig-Haro flows discovered in photoionized medium forms a separate category and detailed studies of which become one of the key issues to our understanding of jet production and evolution. The Rosette HH2 jet is the second of such flows that immersed in the spectacular HII region of the Rosette Nebula. However, its disconnected jet components are detached from the proposed energy source, have additional unusual properties and thus a disputable nature. In this paper, we investigate through high-quality echelle spectrographs the physical nature of the jet system. The jet shows distinctly different velocity components. It is believed to be composed of a fast neutral jet with an approaching velocity of-39.5 km −1 as respect to the systemic rest frame, and likely an extensive, photo-evaporated envelope dissolving at roughly the sound speed. This led us to infer a fast dissipating nature of the jet system being bathed in the fully photoionized medium of Rosette. In addition, time series photometric observations provide evidence that the energy source is highly variable, with amplitudes of up to > 1 mag in R & I. This is consistent well with an early evolutionary status of the jet driving star with a red, late type spectrum in the optical.