Lifetime Of Class II Protostar

[leonmate]

Homework Statement

I've been working through coursework set from a module called Sun & Stars.
Basically the concept I understand is that there is a theoretical way of estimating the lifetime of a class II protostar as 2x10^6 years. Using this we can estimate the lifetime of class 0 and class I protostars based on their abundance in comparison to class II (if there are 4x as many class II than class I we assume that class II lifetime is 4x longer also).

Just come across the last question which asks:

How is the lifetime of a class II star estimated?

I've been scouring through my notes and the internet but can't seem to find the theory/derivation/whatever it is they used to figure this out!

I can add that a class II protostar is when the nebula/gas cloud collapses into a protostar with a massive optically thick disc which is correlated with the Classical T Tauri phase

Any help/pointers would be great!

 

[Asim Riaz]

Homework Equations N/A The Attempt at a Solution I'm not sure what the answer is but I think it has something to do with the amount of gas and dust which can be observed around class II protostars, the disc size and the amount of time it takes for the disc to dissipate.