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Non-Spherical Stars
An anonymous reader writes "Now that the large interferometers are coming on line, the stars are no longer dots. Achernar (Alpha Eridani), is a huge ellipsoid whose polar radius (due to fast spinning) is 50% smaller than the equatorial one!"
More details at the press release:
1 4-03.html
http://www.eso.org/outreach/press-rel/pr-2003/pr-
Including more technical drawings.
-molo
Using your sig line to advertise for friends is lame.
The oblateness of Altair was measured using the Palomar Testbed Interferometer (PTI) in 1999-2000.
This site describes the telescopes that comprise the interferometer used to make the observations:
http://www.eso.org/projects/vlti/
Quote:
The Very Large Telescope Interferometer (VLTI) consists in the coherent combination of the four VLT Unit Telescopes and of several moveable 1.8m Auxiliary Telescopes. Once fully operational, the VLTI will provide both a high sensitivity as well as milli-arcsec angular resolution provided by baselines of up to 200m length.
Actually, I think they mean "solid-body" as "cohesive object" in this case.
While I'm getting technical, Plasma can't be considered a fluid either, as it's not a liquid, it's a different state of matter altogether.
This exchange is about on par with "How is a liquid not a fluid?" "Because it's a liquid."
"Fluid" is not a state of matter, no one's claiming it's a state of matter, saying plasma can't be a fluid because plasma is the 4th state of matter is a category error. Liquid is the second state of matter. Gas is the third state of matter. Both are fluids.
A fluid is any substance which undergoes continuous deformation when subjected to a shear stress. The problem we're probably having is that the obvious sources for the shear stresses in the couse of, say, water being poured from a cup (normal force of the side of the cup vs gravity) are paralleled for the case of plasma by electromagnetic feilds. It just don't grok intuitively but, plasma behaves like a fluid... ergo, it is a fluid.
Simple Machines in Higher Dimensions
In the more recent surveys of bright stars in a cluster, they've seen that faster rotating stars (seen indirectly by the rotational broadening of spectral lines of the star) of the same spectral type have a wider scatter of observed brightnesses. The explanation for this is that:
(i) Faster rotating stars are brighter at their poles than their equators (because of centripetal force slightly expanding the distance of the equator from the core of the star), and:
(ii) The spin axes of stars are randomly oriented with respect to telescopes on Earth, so:
(iii) For a large sample of fast rotating stars, you sample all the brightnesses from the equator to the poles, hence a large scatter in measured brightness. You can assume that all stars are effectively at the same distance if they are in a distant cluster.
Hope that's reasonably clear,
Dr Fish