What distinguishes Pre-main-sequence stars from main sequence stars?

[envanyatar]

I've been reading articles on star formation and would like to know what the Pre-main-sequence actually stands for.

Since more or less each stage of the formation of a star have names what type of star are inclusive in the PMS? How can you point out a PMS star from a main sequence star?

 

[neutrino]

I guess it refers to stars that are still in the nursery, so to speak, i.e. within the nebular material that they started from. The nuclear fusion in the core is not in complete control of the star.

 

[Mariko]

Stars need a initial gravatational collapse over thousands of years then a slow controdiction normally continues over millions of years until nuclear reactions begin once this happens it hits the main sequence.

 

[Chronos]

Stars basically form when there is sufficient local mass density to force gravitational collapse. It is a very inefficient process, so the initial gas mass must be large. Shock waves from neighboring SN are believed to assist the process.

 

[Mariko]

How can you point out a PMS star from a main sequence star?

There's a Diagram or chart if you will that this whole princible is based off of which is called the Hertzsprung-Russell or the (H-R)diagram.This diagram is basically luminosity plotted againsed tempature and as a star goes through it's life the Luminocity and the tempature change according to the diffrent stages it is in its life, you can plot a stars life according to it. stars will hit the main sequence at about 10 million K when it's tempature is high enough to fuse hydrogen to heluim.

 

[SpaceTiger]

How can you point out a PMS star from a main sequence star?

Observationally, young stars tend to lie on the Hayashi track and are red and luminous. Main sequence stars, on the other hand, tend to lie on a particular line (the main sequence) on the Hertzsprung-Russel diagram (as Mariko pointed out), so are distinguishable by their colors and magnitudes. Also, young stars are often enshrouded in dust disks, causing them to shine brightly in the infrared.