help needed asap for hr diagrams (1 Viewer)

[melllyy]

i am confused about how to determine the age of a star on the main sequence. if the star is at the top of the main sequence is it old or young? i am just confused about the whole thing. i have one source which shows a star at the top of the main sequence and it says it is a very young star, but i cant remember what my teacher told me whether the starts coming in from the top are old or young. and for some reason i think the are young at the bottom? can anyone help meeeee?

 

[alcalder]

OK Melllyy it's been a while, let me see...

A star drops onto the main sequence as it is forming. Where it drops on depends on how massive it is. The higher up the main sequence, the bigger the star.

The star's evolution then follows a path dependent on how massive it is. Those stars that are medium to small ( 1 Solar mass and lower) do seem to have a path that brings them back onto the main sequence but HIGHER.

Now, if you look at the stars in a cluster. A young cluster will have a majority of stars that live up on the high end of the main sequence. As the cluster gets older, these stars die out and stars are forming that live lower down on the main sequence. Thus a young cluster will have most stars high up on the main sequence and older clusters have most stars lower down on the main sequence.

I hope that helps.

 

[tennille]

Alcader is correct. Larger stars are situated at the top of the main sequence band, whilst smaller stars are located towards the bottom of the main sequence band. The HR diagram is a plot of temperature (or spectral class) against luminosity (or magnitude) of the star. Larger stars have a higher luminosity and are higher in temperature, therefore, they lie towards the top of the main sequence band (remember that the x-axis consists of decreasing temperature). Smaller stars have lower luminosity and also a lower temperature and are situated at the bottom. As stars age, they move off the main sequence band. The more massive stars go to the top right hand corner of the HR diagram as a super giant, and the smaller stars move above the main sequence band to the "giant" stage, and then finally become a white dwarf towards the bottom of the HR diagram (the movement from a giant to a white dwarf means that the star passes through the main sequence stage, as Alcader mentioned).

 

[Nick_kirk]

Isn't it easier to just look at the turn-off points rather than "where the majority of the stars are"?

I actually have a question about this.

In the syllabus it says we have to know the evolutionary tracks for 1,5 and 10 solar masses. I know the paths up to the AGB (giant or supergiant) and I know the path that the 1 solar mass takes to get down to white dwarf.

For 5 and 10 do you only have to know up to the AGB stage? It doesn't seem like Neutron stars or pulsars or novae or blackholes would go on the HR diagram.

 

[ThomasF]

Isn't it easier to just look at the turn-off points rather than "where the majority of the stars are"?

I actually have a question about this.

In the syllabus it says we have to know the evolutionary tracks for 1,5 and 10 solar masses. I know the paths up to the AGB (giant or supergiant) and I know the path that the 1 solar mass takes to get down to white dwarf.

For 5 and 10 do you only have to know up to the AGB stage? It doesn't seem like Neutron stars or pulsars or novae or black holes would go on the HR diagram.

You are correct there. However, for the 5 and 10 solar mass stars, you would have to show how they move to the top left hand corner of the HR diagram and go super novae. You should then give a detailed description of what happens to the stars after the supernovae. So say something along these lines;

I would draw an HR diagram and show (in different colours) the life of the 1, 5 and 10 solar mass stars.

On it, I would show the path the protostar takes to go onto the main sequence (For 1, 5 and 10 SM the paths would come from varying intensity) I would then show how the 1 solar mass star would eventually become a red giant (going to the top right hand section, then after is triple alpha reactions and post helium burning becoming a white dwarf.

For the 5 and 10 SM stars, I would show them going to the near top left corner at this stage (for the 5 SM star, say a temp of 23,000K and a luminosity of 10^4) (the 10SM star, maybe 27,000K and a luminosity of 10^5)

After this I would say, Both stars would go supernovae. After the super novae of either star, if what was left was between .4-3.0 SM, then that will become a neutron star (Neutron, because of the intense heat and gravity, electron repulsion forces can not prevent the star collapsing in upon it self, only neutron atomic force prevent the star from falling in upon itself (Then maybe something about pulsars / rotating, emitting neutron stars)

I would then also say, However if after the explosion, what remained was Greater then 3.0 SM, this star will become a black hole. This is because even neutron atomic forces cannot prevent the intense heat and gravity, and thus, the entire star falls in upon itself creating the black hole.

Thats just me and what I would do though but I don't have the context of the question, so I couldn't exactly explain it very well.


*edit* wow, realised how late this answer was. Well, at least people can refer to this if they come in here