Star Distances

Hurt wrote:
******************************

Just how far are the stars?

snip

I've actually wondered about "standard candles"- cephid variables,
type-Ia supernovae, etc. None of the articles I have seen really
explain *why* they are so uniform, what are the error bounds, etc. etc.


--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University

In article , Andy Resnick
wrote:

Hurt wrote:
******************************

Just how far are the stars?

snip

I've actually wondered about "standard candles"- cephid variables,
type-Ia supernovae, etc. None of the articles I have seen really
explain *why* they are so uniform, what are the error bounds, etc. etc.

In a nutshell

Cepheids have a period luminosity relationship, whereas type 1a have a
known brightness curve.

--
The greatest enemy of science is pseudoscience.

Jaffa cakes. Sweet delicious orangey jaffa goodness, and an abject lesson why
parroting information from the web will not teach you cosmology.

Official emperor of sci.physics. Please pay no attention to my butt poking
forward, it is expanding.

Relf's Law?
"Bull**** repeated to the limit of infinity asymptotically approaches
the odour of roses."

Phineas T Puddleduck wrote:
In article , Andy Resnick
wrote:


Hurt wrote:

******************************

Just how far are the stars?


snip

I've actually wondered about "standard candles"- cephid variables,
type-Ia supernovae, etc. None of the articles I have seen really
explain *why* they are so uniform, what are the error bounds, etc. etc.


In a nutshell

Cepheids have a period luminosity relationship, whereas type 1a have a
known brightness curve.

Well, I guess my question is more specifically- how has that been
established? We have no way of creating these systems in a lab and
carefully measuring them. Presumably the invariant quantities have been
established by theoretical considerations, but I don't know the reference.


--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University

In article , Andy Resnick
wrote:



Well, I guess my question is more specifically- how has that been
established? We have no way of creating these systems in a lab and
carefully measuring them. Presumably the invariant quantities have been
established by theoretical considerations, but I don't know the reference.

Cepheids was through work done by Leavitt
http://en.wikipedia.org/wiki/Period-...y_relationship

Much better is
http://www.astro.livjm.ac.uk/courses...kington/cepinp
1.htm

Light curves were plotted for various supernovae and they were also
seen to show a similar form

http://en.wikipedia.org/wiki/Supernova#Type_Ia

http://www.citebase.org/cgi-bin/cita...:astro-ph/0208
059

--
The greatest enemy of science is pseudoscience.

Jaffa cakes. Sweet delicious orangey jaffa goodness, and an abject lesson why
parroting information from the web will not teach you cosmology.

Official emperor of sci.physics. Please pay no attention to my butt poking
forward, it is expanding.

Relf's Law?
"Bull**** repeated to the limit of infinity asymptotically approaches
the odour of roses."

Andy Resnick wrote in news:e78quk$qve$1
@eeyore.INS.cwru.edu:

Hurt wrote:
******************************

Just how far are the stars?

snip

I've actually wondered about "standard candles"- cephid variables,
type-Ia supernovae, etc. None of the articles I have seen really
explain *why* they are so uniform, what are the error bounds, etc. etc.



In the case of Type Ia supernova, the progenitor is supposedly always a
white dwarf with a mass equal to the Chandrasekhar limit. So the fuel
quantity is always the same if that proposition is true. The relatively
small variation in the light curves of these is thought to depend on how
complete the deflagration develops until it changes over to supersonic
detonation. The more the deflagration completes the greater quantity of Ni
56 and Co 56 are produced. It is primarily the decay of these isotope that
powers the luminosity of the supernova debris. The peak brightness is
mostly powered by Ni 56 decay.

The Cepheid thing is a bit trickier. These are callibrated by getting
parallax fixes of near by examples but there aren't actually very many
within range. Luckily the supernova 1987A in the Large Magellanic Cloud
happenned to illuminate a debris ring about a year after the initial
supernova was seen. This allowed a fix on the LMC via the so called 'light
echo distance' method. The LMC contains many Cepheids and as the distance
to the LMC is well established from the above at 167,000 ly quite good
calibration is obtained. Ned Wright gives a summary of the different
methods of getting interstellar distances and explains why Cepheids work as
standard candles. You would have to read the primary literature or a text
book to get the error bound info you are after.

http://www.astro.ucla.edu/~wright/distance.htm

Klazmon.