PDA

View Full Version here: : Nothing lasts for ever - cepheids that are no more


bojan
01-03-2011, 08:38 AM
http://www.universetoday.com/83600/another-ceasin-cepheid/#more-83600

renormalised
01-03-2011, 09:19 AM
Interesting. They've known about the changes in these stars for quite some time. These changes are probably due to some adjustment of the internal structure as these stars age.

CraigS
01-03-2011, 09:37 AM
Maybe the pulsations of these stars, (across the broader set of known Cepheids), have never been as accurate as they'd like to think.

As telescopes are get more precise, you'd kind of expect that the variations in pulsations, would become more noticeable. (After all, all observations contain uncertainties. These are also a moving target).

Still, chalk another one up for the stellar evolution theory in its never-ending 'tug-o-war' with the stellar pulsation theory. Last time we looked at this (http://www.iceinspace.com.au/forum/showthread.php?p=660724&highlight=cepheid#post660724), the report was that stellar pulsation had produced highly accurate estimates in the mass predictions for an eclipsing binary cepheid.

The period vs luminosity relationship has really only been known for about 100 years, and the ionised Helium mechanism was only proposed in 1953.

Is this really sufficient time for us to expect that all known Cepheid pulsations should be as expected ?

Cheers

renormalised
01-03-2011, 10:52 AM
The basis of the stellar pulsation and evolutionary theories are pretty well understood, but the details vary and there is still a lot to learn. Every star is an example to itself and whilst they should generally follow the basic rules as we know them, it would be foolish to say that we completely understand what's going on....there are always exceptions to the rule and new, surprising things turn up all the time. Even some of the basics are going to change as we learn more about the mechanisms driving the pulsations and how that fits into stellar evolution. Both theories are going to change over time. That is a given.