The Evolution of Disk Winds from a Combined Study of Optical and Infrared Forbidden Lines

Abstract

We analyze high-resolution (Δ v  ≤ 10 km s −1 ) optical and infrared spectra covering the [O i ] λ 6300 and [Ne ii ] 12.81 μ m lines from a sample of 31 disks in different evolutionary stages. Following work at optical wavelengths, we use Gaussian profiles to fit the [Ne ii ] lines and classify them into high-velocity component (HVC) or low-velocity component (LVC) if the line centroid is more or less blueshifted than 30 km s −1 with respect to the stellar radial velocity, respectively. Unlike for the [O i ], where an HVC is often accompanied by an LVC, all 17 sources with an [Ne ii ] detection have either an HVC or an LVC. [Ne ii ] HVCs are preferentially detected toward high accretors ( M ⊙ yr −1 ), while LVCs are found in sources with low , low [O i ] luminosity, and large infrared spectral index ( n 13–31 ). Interestingly, the [Ne ii ] and [O i ] LVC luminosities display an opposite behavior with n 13–31 : as the inner dust disk depletes (higher n 13–31 ), the [Ne ii ] luminosity increases while the [O i ] weakens. The [Ne ii ] and [O i ] HVC profiles are generally similar, with centroids and FWHMs showing the expected behavior from shocked gas in microjets. In contrast, the [Ne ii ] LVC profiles are typically more blueshifted and narrower than the [O i ] profiles. The FWHM and centroid versus disk inclination suggest that the [Ne ii ] LVC predominantly traces unbound gas from a slow, wide-angle wind that has not lost completely the Keplerian signature from its launching region. We sketch an evolutionary scenario that could explain the combined [O i ] and [Ne ii ] results and includes screening of hard (∼1 keV) X-rays in inner, mostly molecular, MHD winds.