Mass Loss and Jet Outflow in the Orion Nebula Proplyd LV 2*

摘要

We have obtained Hubble Space Telescope (HST) Space Telescope Imaging Spectrometer high-resolution spectra of the Orion proplyd LV 2 in the C III doublet at 1906.68 and 1908.73 ?. New images at the 6 cm wavelength with MERLIN complement earlier HST images at a similar spatial resolution. This object is one of the closest proplyds to θ1 Ori C, the source of the photoionizing and photoevaporating radiation. Combining the spectra with the HST images and detailed theoretical models has allowed a determination of the mass-loss rate as 8.2 × 10-7 M☉ yr-1 ±10%. This rate of mass loss is used to address the conundrum of the continued existence of proplyds. Even though they should be photoevaporated in only about 105 yr, there is no evidence for their destruction. It is concluded that the only explanation is that the age of θ1 Ori C is less than 105 yr. These spectra and previously unpublished ground-based spectra in [O III] also show the presence of a monopolar microjet, redshifted by about 100 km s-1 with respect to the systemic velocity. This jet is more visible in the 6 cm MERLIN images than in HST images, and this image together with the spectra are used to determine the flow parameters for the jet. Our spectra also include the stand-off shock that lies between LV 2 and θ1 Ori C. This is the result of the high-velocity wind coming from the hot star θ1 Ori C with the low-velocity wind coming from the proplyd. As expected, this shock is at rest with respect to the two objects.