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

Abstract

We analyze high-resolution (Δv ≤ 10 km s⁻¹) optical and infrared spectra covering the [O I] λ6300 and [Ne II] 12.81 μm 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_(acc) > 10⁻⁸M_⊙ yr⁻¹), while LVCs are found in sources with low M_(acc), low [O I] luminosity, and large infrared spectral index (n₁₃₋₃₁). Interestingly, the [Ne II] and [O I] LVC luminosities display an opposite behavior with n₁₃₋₃₁: as the inner dust disk depletes (higher n₁₃₋₃₁), 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.

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