Re: Prominences on Other Stars
From: Martin Brown (|||newspam|||_at_nezumi.demon.co.uk)
Date: 06/30/04
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Date: Wed, 30 Jun 2004 11:51:25 +0100
In message <989139d7.0406291739.21111723@posting.google.com>, Barry
Simon <bsimon615@aol.com> writes
>I am in the process of putting together a digital slideshow comprised
>of h-alpha images of the Sun that I have taken and simulated images to
>scale of other stars. The simulated images are being made from solar
>images I have taken that are scaled up or down as appropriate and
>"recolored" as appropriate.
It is an interesting question.
Have any speckle images of Betelgeuse been made in H-alpha ?
>this. Primarily I am interested in hearing speculation as to how
>large prominences could be on other stars. How do the laws of physics
>apply? Given that a good prominence on our Sun can frequently extend
>outward 50,000 miles and it is not that uncome to capture one
>extending out to even 100,000 miles, can a good prominence on
>Betelguese extend out proportionally as far (an amazing 50 million
>miles or further) or would the limits for prominence size on other
>stars be much like on our Sun? If so, a 50,000 mile to 100,000 mile
>prominence extending above the limb of Betelquese, Antares or other
>super red giant would barely be a bump on the surface.
>
>What is the speculation of others, or better yet how would physical
>laws and gravity apply?
Surface gravity on a sphere of uniform density rho scales with its
radius. And for a main sequence star mass scales with radius cubed. Very
crudely:
g = GM/r^2
M = 4/3 pi rho r^3
so g = 4/3 pi rho G r
This is bad news for your would be prominence on a massive giant main
sequence star. It would get smaller as the stars mass increases like
1/M^(1/3).
However, red giants are vastly expanded and will not be as dense as the
sun so they can do some very interesting things. Planetary nebulae
result when stars lose their grip on the outer layers.
AGB or Mira class variable stars would be a good place to look for
interesting behaviour. Are any close enough or big enough to resolve?
Regards,
-- Martin Brown
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