What event marks the transition of a contracting object into a visible T Tauri star?

Answer

When it has ejected or blown away most of its surrounding cocoon of gas

The T Tauri stage is reached when the central object becomes optically visible because intense outflows have cleared away the opaque envelope of dust and gas that previously obscured it.

What event marks the transition of a contracting object into a visible T Tauri star?
astronomyforcegravitystar formationinterstellar cloud