View Full Version : Episode 22: Variable Stars

2007-Feb-05, 04:30 PM
Our Sun has been around for billions of years, and will last for billions more. We're lucky, it's pretty stable and regular as stars go, only changing in brightness a little now and then. ...

Read the full blog entry (http://www.astronomycast.com/star-formation/episode-22-variable-stars/)

2007-Feb-07, 08:08 PM
Question about Variable stars:
A current, more favored, theory of Nova formation is the, "Disk Instability Model"
In this model the transfer of matter from the low mass star to its binary companion white dwarf is fairly constant.
It is postulated that, as the matter is accreted on the disk, a critical point of density is achieved in the disk. At this point thermal instabilities within the disk cause matter to be accreted onto the white dwarf. This causes a sudden increase in light.
I’m not clear on this point.
Is the light caused by matter being accreted on the white dwarf or is it caused by matter on the accretion disk undergoing fusion?

2007-Feb-09, 04:58 AM
Hello Fraser & Folks:

I've listened to the podcast for a few weeks after I got myself a new iPod. Pamela was a former graduate project advisor.

With regard to your last Variable Star episode, I may have missed it but its worth noting that variable star astronomy is one of the areas where people can make some significant contributions with respect to data gathering.

Interested folks should explore the American Association of Variable Star Observers at <www.aavso.org>, the British Astronomical Association's Variable Star Section at <www.britastro.org/vss/>, or the Astronomical Society of South Australia's Variable Star Section at <www.assa.org.au/sig/variables/>.

Just a thought.
Doc Kinne, MSc.
AAVSO, ALPO, Cornell Astronomical Society

2007-Feb-09, 07:12 AM
Frazer and Doctor Gay,

Thanks for another great episode of your podcast. I have been anticipating this topic for awhile. Being very new to astonomy I have really enjoyed the episodes which enhance my observation experiecnce. For instance Betelguese looks more awesome now that I've learned a little about the different types of stars. And the Orion nebula and Pleiades are even more interesting after learning about star formation and their stages of progression.

This Topic is especially interesting for me because it gives me an opportunity to observe actual variable star cycles and compare the results to those predicted Astronomers. I have been to the AAVSO site and plan to explore this opportunity a little more thoroughly when the weather clears again.

Thanks again for a great show and I look forward to more. I do have just one question. I seem to percieve the Orange stars as being brighter that the blue/white ones. For instance Betelguese looks much brighter than Rigel. I realize that Betelgeuse is slightly variable but as far as I can tell, Rigel should always be as bright as if not brighter that Betelgeuse. Do you have any tips concerning comparing red/orange stars to blue/white ones. This is an area where my observations don't match the charts always.

TIA Larry

2007-Sep-05, 05:22 PM
Thanks for another great show. I really have found the Astro Casts informative and entertaining.

As Pamela was talking about the effects of one start transiting another, I was thinking about the effects of micro gravitational lensing. That effect was explained in earlier shows. We would expect star A passing in front of star B, to block the light from star B. If star A was dmiier, then we would expect the overall light be be a little dimmer from this effect.

However, we would also expect star A to bend some of star B's light which would have not have otherwise made it to our observer's position. Thus, this effect would make things appear a little brighter.

How are these effects taken into account when determing the relative luminosities and other information about the two stars involved in the transit?