Re: escape velocity question

[brian whatcott <inet@INTELLISYS.NET>]

At 17:40 3/15/99 -0500, Larry Cartwright wrote:
> John, you have nicely resolved the order of magnitude error posed
> originally. ... I think you have underestimated the white dwarf radius
> slightly.

> With g = 37000 * g_earth = 3.6E+05 m/s^2 and m = 1 solar mass =
> 2.0E+30 kg, we get R = 1.9E+07 m or about triple the earth's radius.  If
> you assume less mass, say 0.8 solar mass, you get a slightly smaller
> radius, perhaps 1.7E+07 m but still over 2.5 earth radii.  This agrees
> pretty well with what little wd radius data I have seen (e.g. Sirius B and
> Procyon B);  2-3 times wider than Earth, smaller than Neptune.
> ...

> Larry Cartwright

I will be forever in Larry's debt for allowing me the opportunity finally
to quote from the book that has been glowering at me these many years:
Chandrasekhar's Stellar Structure   (1939)

He offers in Table 34d some leading data for white dwarfs, expressed
as log comparisons with the relevant solar quantities:

Name            logM    logL    logR
Sun              0       0       0
o2  Eri B       -0.35   -2.25   -1.74
 Sirius B       -0.01   -2.52   -1.71
Van Maanen #1   +0.53   -3.85   -2.05

(M mass, L luminosity   R radius)

Subrahmanyan was after all the person who originated the upper mass
limit of helium core for white dwarfs equal to 1.44 Sun masses,
beyond which they are destined to collapse he said.
He also had something to say about stellar models which vary material
density with radial depth.

Brian

brian whatcott <inet@intellisys.net>
Altus OK