<p><em>Note: By "progenitor", I mean "the star as it was when it was still main sequence". Please correct me if I've got the terminology wrong.</em></p>

<p>Most B-type subdwarfs have mass roughly half that of the Sun. Prior to becoming blue-white subdwarfs, they went through the red giant phase, so their main sequence masses would have been between <span class="math-container">$0.3$</span> and <span class="math-container">$8M_{\odot}$</span>. Since they went on to fuse helium, we can raise that lower bound to <span class="math-container">$0.5 M_{\odot}$</span>. Since helium fusion in these stars begins with a "helium flash", then they would be <span class="math-container">$&lt; 2M_{\odot}$</span> during the main sequence.</p>

<p>Is anything more known about the masses of main-sequence stars that can become B-type subdwarfs? The narrow range of masses observed for the subdwarfs derives from the narrow range of viable core masses. However, the papers I have read indicate that the progenitor stars may have masses in a much wider range than that of their cores. So the <span class="math-container">$0.5M_{\odot} \leq M \leq 2M_{\odot}$</span> range given above may be the tightest-known bounds for the mass of such a star, but if anyone is able to provide a reliable source for tighter bounds, I would be very interested.</p>

<p><strong>Source for the <span class="math-container">$0.5M_{\odot}$</span> lower bound:</strong></p>

<p><a href="https://iopscience.iop.org/article/10.1086/304125/pdf" rel="nofollow noreferrer">Laughlin, G., Bodenheimer, P., &amp; Adams, F. C. (1997). The end of the main sequence. The Astrophysical Journal, 482(1), 420.</a></p>

<p><strong>Source for the <span class="math-container">$2M_{\odot}$</span> upper bound:</strong></p>

<p><a href="https://books.google.co.uk/books?id=A2G1DwAAQBAJ&amp;pg=PA52&amp;dq=Harpaz,+Amos+%22Helium+Flash%22&amp;hl=en&amp;sa=X&amp;ved=0ahUKEwjetMH757jnAhWWShUIHRA2Dk8QuwUIMDAA#v=onepage&amp;q=Harpaz%2C%20Amos%20%22Helium%20Flash%22&amp;f=false" rel="nofollow noreferrer">Harpaz, A. (1993). Stellar evolution. AK Peters/CRC Press.</a></p>

CC BY-SA 4.0
2020-01-28T08:27:38.387Z
I realise this may be a bit of a difficult question, as there doesn't seem to be much information about this in the scientific literature. (Well, not as far as I can tell.) But if someone knows the answer in the specific case of a one-solar-mass star (e.g. our Sun) I'd be particularly interested in that.
Astrid_Redfern
CC BY-SA 4.0
2020-02-07T22:13:01.417Z
I've been reading a paper called "The Origin of Subdwarf B Stars (I) - the Formation Channels" (Han et al., 2002, very heavily cited). In it, there are evolutionary diagrams for sdB stars with various different zero-age main sequence (ZAMS) masses. These are: 1M⊙ (becoming an 0.496M⊙ sdB), 0.8M⊙, 1.26M⊙, 1.6M⊙ and 1.9M⊙. Many actual observed sdB stars were shown to be in graph positions that might correspond to these evolutionary tracks. So I now have a sub-range of viable main sequence masses! Maybe enough to post an answer.
Astrid_Redfern
<star><stellar-evolution><main-sequence>
The mass of Subdwarf B progenitors in the main sequence
Astrid_Redfern
# The mass of Subdwarf B progenitors in the main sequence

(Asked by: username_0 on 2020-01-26)

*Note: By "progenitor", I mean "the star as it was when it was still main sequence". Please correct me if I've got the terminology wrong.*

Most B-type subdwarfs have mass roughly half that of the Sun. Prior to becoming blue-white subdwarfs, they went through the red giant phase, so their main sequence masses would have been between $0.3$ and $8M\_{\odot}$. Since they went on to fuse helium, we can raise that lower bound to $0.5 M\_{\odot}$. Since helium fusion in these stars begins with a "helium flash", then they would be $< 2M\_{\odot}$ during the main sequence.

Is anything more known about the masses of main-sequence stars that can become B-type subdwarfs? The narrow range of masses observed for the subdwarfs derives from the narrow range of viable core masses. However, the papers I have read indicate that the progenitor stars may have masses in a much wider range than that of their cores. So the $0.5M\_{\odot} \leq M \leq 2M\_{\odot}$ range given above may be the tightest-known bounds for the mass of such a star, but if anyone is able to provide a reliable source for tighter bounds, I would be very interested.

**Source for the $0.5M\_{\odot}$ lower bound:**

[Laughlin, G., Bodenheimer, P., & Adams, F. C. (1997). The end of the main sequence. The Astrophysical Journal, 482(1), 420.](https://iopscience.iop.org/article/10.1086/304125/pdf)

**Source for the $2M\_{\odot}$ upper bound:**

[Harpaz, A. (1993). Stellar evolution. AK Peters/CRC Press.](https://books.google.co.uk/books?id=A2G1DwAAQBAJ&pg=PA52&dq=Harpaz,+Amos+%22Helium+Flash%22&hl=en&sa=X&ved=0ahUKEwjetMH757jnAhWWShUIHRA2Dk8QuwUIMDAA#v=onepage&q=Harpaz%2C%20Amos%20%22Helium%20Flash%22&f=false)

**Tags:** star, stellar-evolution, main-sequence

> **Comments:**
> **username_0**: I realise this may be a bit of a difficult question, as there doesn't seem to be much information about this in the scientific literature. (Well, not as far as I can tell.) But if someone knows the answer in the specific case of a one-solar-mass star (e.g. our Sun) I'd be particularly interested in that.  
> **username_0**: I've been reading a paper called "The Origin of Subdwarf B Stars (I) - the Formation Channels" (Han et al., 2002, very heavily cited). In it, there are evolutionary diagrams for sdB stars with various different zero-age main sequence (ZAMS) masses. These are: 1M⊙ (becoming an 0.496M⊙ sdB), 0.8M⊙, 1.26M⊙, 1.6M⊙ and 1.9M⊙. Many actual observed sdB stars were shown to be in graph positions that might correspond to these evolutionary tracks. So I now have a sub-range of viable main sequence masses! Maybe enough to post an answer.  

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## 0 answers

