Dust in the disk winds from young stars as a source of the circumstellar extinction

TL;DR

This paper investigates how dust survives in the hot disk winds of young stars, showing that such winds can be opaque and significantly affect stellar radiation, with implications for observed variability and disk structure.

Contribution

It demonstrates that dust can survive in hot T Tauri star winds and significantly influence circumstellar extinction, providing a new perspective on disk wind opacity and variability.

Findings

Dust survives in hot T Tauri star winds due to inefficient heating by gas.

Disk winds can absorb 20-40% of stellar luminosity at certain accretion rates.

Structural inhomogeneity in winds causes variability and shadowing effects.

Abstract

We examine a problem of the dust grains survival in the disk wind in T Tauri stars (TTSs). For consideration we choose the disk wind model described by Garcia et al. (2001), where a gas component of the wind is heated by an ambipolar diffusion up to the temperature of the order of 10$^4$ K. It is shown that the dust grains heating due to collisions with the gas atoms and electrons is inefficient in comparison with heating by the stellar radiation, and thus, dust survives even in the hot wind component. Owing to this, the disk wind may be opaque for the ultraviolet and optical radiation of the star and is capable to absorb its noticeable fraction. Calculations show that at the accretion rate $\dot{M_a} = 10^{-8}-10^{-6} M_\odot$ per year this fraction for TTSs may range from 20% to 40% of a total luminosity of the star correspondingly. This means that the disk wind in TTSs can play the same role as the puffed inner rim considered in the modern models of accretion disks. In Herbig Ae stars (HAEs) inner regions of the disk winds ($r \le 0.5$ AU) are free of dust since there dust grains sublimate under the effect of the radiation of the star. Therefore, in this case a fraction of the absorbed radiation by the disk wind is significantly less, and may be compared with the effect of the "puffed-up inner rim" only at $\dot{M_a} \geq 10^{-6} M_\odot$ yr$^{-1}$. Due to the structural inhomogeneity of the disk wind its optical depth towards an observer may be variable resulting in the photometric activity of the young stars. For the same reason, one can observe moving shadows from the gas and dust streams with the spiral-like structure on the highly resolved circumstellar disk images.