Resolving the nature of the Rosette HH 1 jet facing strong UV dissipation

The Rosette HH 1 jet is a collimated flow immersed in the strong UV radiation field of the Rosette Nebula. We investigate the physical properties of the Rosette HH 1 jet using high-quality narrowband images and high-dispersion spectroscopy. The new images show that the axis of the jet is not precisely aligned with the star near the base of the jet. The high resolution of the spectra allows us to accurately determine the contributions from the H II region, jet, and star. The approaching and receding sides of the expanding shell of the Rosette Nebula are at heliocentric velocities of 13 and 40 km s ^-1, while the jet reaches a maximum velocity offset at a heliocentric velocity of -30 km s^-1. The [S II] doublet ratios indicate an electron density of ∼1000 cm^-3 in the jet and ≤100 cm ^-3 in the H II region. With a careful subtraction of the nebular and jet components, we find the stellar Ha line is dominated by a broad absorption profile with little or no emission component, indicating a lack of substantial circumstellar material. The circumstellar material has most likely been photoevaporated by the strong UV radiation field in the Rosette Nebula. The evaporation timescale is 10³-10⁴ yr. The Rosette HH 1 jet source provides evidence for an accelerated evolution from a CTTS to a WTTS due to the strong UV radiation field; therefore, both CTTSs and WTTSs can be spatially mixed in regions with massive star formation.