<p>The HR diagram is a sort-of &quot;phase diagram&quot; (in a very rough sense) for stars, where a particular star's location on the diagram says something about what &quot;kind&quot; of star it is.  However, because age is not on the axes of a HR diagram, stars trace out complex paths through it as they evolve.</p>
<p>For my purposes, I'd like to be able to very quickly reference what kind of star I'm looking at based on its age and mass.  I'm just trying to simulate more-or-less realistic stellar populations; I'm not doing research or anything and so I'm not really accounting for things like mass loss (or gain in binaries).  For this purpose it would be useful to have a &quot;phase diagram&quot; where age (perhaps relative to ZAMS) is on an axis, letting me use it as a sort of look-up table based on the mass of the star.  (Maybe it could also be 3D to include metallicity, but that could be a future step).  Ideally I'd just like to be realistic enough to capture different types of end-of-life behaviors (different types of giants, whether the star will go supernova or not, etc...)</p>
<p>I think this should be possible to do in principle using a stellar evolution code like MESA.  You'd need to define what you consider to be different &quot;types&quot; of stars and decide where to draw boundaries (maybe possible with something like k-means or support vector analysis?).  I've messed around with MESA-web a bit, but I'm no astrophysicist and I have no idea if I'm doing things right, e.g. if I'm picking sufficiently realistic nuclear reaction networks.</p>
<p>So, my question is: has anybody done something like this before, and/or is there some fundamental limitation to this approach that I don't know about?</p>

CC BY-SA 4.0
2021-12-28T16:43:34.980Z
Well the more conventional approach is to plot mass tracks and isochrones on the HR diagram. As I understand it, you want to plot mass vs age on a mass vs age diagram without allowing for mass loss? Well those are just horizontal lines that terminate at the end of a star's life but not including mass-loss is totally unrealistic. Or perhaps you want to plot stars on the diagram? The problem is that you don't know the ages or masses of of stars since these are not observables (except mass in some binary systems). Do you mean something like https://www.jpl.nasa.gov/infographics/stellar-evolution
ProfRob
CC BY-SA 4.0
2021-12-28T17:17:04.220Z
I want the track of a particular star to be vertical, yes, but I was thinking of a phase diagram like the kind you see in e.g. chemistry, so there would be regions on the plot where different "types" of stars would be found.  Mass/age not being observable is not a problem: I'm generating populations from whole cloth, picking random masses (via IMF) and random ages (guassian).  The issue with the HR diagram is that I'd like to be able to shift the whole pop up/down in age, which is non-trivial when the tracks aren't vertical.  Then I could switch individual star "types" as they cross bounds.
realityChemist
CC BY-SA 4.0
2021-12-28T22:02:36.007Z
I get it. Well what you would do is plot age on the y-axis and mass on the x-axis and you could colour code the lines based on the gravity. This would enable a division between PMS, MS, giant, supergiant and white dwarf, based on some arbitrary division, or perhaps more meaningfully, based on $dg/dt$ (a large value indicating a "phase transition"). No, I've never seen such a diagram.
ProfRob
CC BY-SA 4.0
2021-12-29T09:18:36.467Z
For what you want to achieve the Mesa web defaults would be sufficient. The basic nuclear network will adapt as the star evolves so it will be good enough.
Rob
CC BY-SA 4.0
2021-12-29T14:50:04.930Z
Thank you for the feedback!  By "gravity" do you mean the surface gravity?  And if so, what is the reason for using this rather than some other measure (e.g. radius or luminosity)?
realityChemist
<star><stellar-evolution><stellar-astrophysics>
Mass-age stellar phase diagram
realityChemist
# Mass-age stellar phase diagram

(Asked by: username_0 on 2021-12-28)

The HR diagram is a sort-of "phase diagram" (in a very rough sense) for stars, where a particular star's location on the diagram says something about what "kind" of star it is. However, because age is not on the axes of a HR diagram, stars trace out complex paths through it as they evolve.

For my purposes, I'd like to be able to very quickly reference what kind of star I'm looking at based on its age and mass. I'm just trying to simulate more-or-less realistic stellar populations; I'm not doing research or anything and so I'm not really accounting for things like mass loss (or gain in binaries). For this purpose it would be useful to have a "phase diagram" where age (perhaps relative to ZAMS) is on an axis, letting me use it as a sort of look-up table based on the mass of the star. (Maybe it could also be 3D to include metallicity, but that could be a future step). Ideally I'd just like to be realistic enough to capture different types of end-of-life behaviors (different types of giants, whether the star will go supernova or not, etc...)

I think this should be possible to do in principle using a stellar evolution code like MESA. You'd need to define what you consider to be different "types" of stars and decide where to draw boundaries (maybe possible with something like k-means or support vector analysis?). I've messed around with MESA-web a bit, but I'm no astrophysicist and I have no idea if I'm doing things right, e.g. if I'm picking sufficiently realistic nuclear reaction networks.

So, my question is: has anybody done something like this before, and/or is there some fundamental limitation to this approach that I don't know about?

**Tags:** star, stellar-evolution, stellar-astrophysics
> **Comments:**
> **username_1**: Well the more conventional approach is to plot mass tracks and isochrones on the HR diagram. As I understand it, you want to plot mass vs age on a mass vs age diagram without allowing for mass loss? Well those are just horizontal lines that terminate at the end of a star's life but not including mass-loss is totally unrealistic. Or perhaps you want to plot stars on the diagram? The problem is that you don't know the ages or masses of of stars since these are not observables (except mass in some binary systems). Do you mean something like https://www.jpl.nasa.gov/infographics/stellar-evolution  
> **username_0**: I want the track of a particular star to be vertical, yes, but I was thinking of a phase diagram like the kind you see in e.g. chemistry, so there would be regions on the plot where different "types" of stars would be found.  Mass/age not being observable is not a problem: I'm generating populations from whole cloth, picking random masses (via IMF) and random ages (guassian).  The issue with the HR diagram is that I'd like to be able to shift the whole pop up/down in age, which is non-trivial when the tracks aren't vertical.  Then I could switch individual star "types" as they cross bounds.  
> **username_1**: I get it. Well what you would do is plot age on the y-axis and mass on the x-axis and you could colour code the lines based on the gravity. This would enable a division between PMS, MS, giant, supergiant and white dwarf, based on some arbitrary division, or perhaps more meaningfully, based on $dg/dt$ (a large value indicating a "phase transition"). No, I've never seen such a diagram.  
> **username_2**: For what you want to achieve the Mesa web defaults would be sufficient. The basic nuclear network will adapt as the star evolves so it will be good enough.  
> **username_0**: Thank you for the feedback!  By "gravity" do you mean the surface gravity?  And if so, what is the reason for using this rather than some other measure (e.g. radius or luminosity)?  

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## 0 answers

