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Leonardo Sidis
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What is behind the pulsation of the light of a Cepheid?
These sites explain quite well.Leonardo Sidis said:What is behind the pulsation of the light of a Cepheid?
Labguy said:These sites explain quite well.
http://www.madsci.org/posts/archives/2004-02/1076556627.As.r.html
http://www.peripatus.gen.nz/Astronomy/CepVar.html
http://www.fofweb.com/Subscription/Science/Helicon.asp?SID=2&iPin=ffdastron2630
http://josephhall.org/ho/
The second paragraph in the first link I gave explains this in a roundabout way. Parallax can be used to find the distance to only nearby stars, Cepheid or otherwise. The first accurate distance measurements (a long time ago) were by the parallax method, but at long distances the parallax angle shift is too small to measure. So, some of the first parallax measurements happened to be for a few Cepheids and it was then noticed that the Cepheids pulsate in brightness (Magnitude) over regular periods and reach very near the same magnitude highs and lows.Leonardo Sidis said:Thanks for the help!
I was also wondering how the pulsation of a Cepheid star would help us determine the distance from Earth of it or another star. Wouldn't we first have to find how far the Cepheid is away from us before being able to determine the distances of other objects from us based on this distance? If parallax was used to find the distance to a Cepheid, why can't we use the same method to determine the distance of another star from Earth?
Leonardo Sidis said:Thanks, that cleared things up for me. It seems kind of weird though, that there are two exact types of a star that hold true in every circumstance.
SpaceTiger said:They're not all exactly the same. In fact, astronomers expend a great deal effort trying to quantify the differences between one Cepheid (for example) and the next. Labguy split Cepheids into two groups, Pop I and Pop II, and this is an excellent approximation for some purposes, but one might want to take this further and establish a continuum relationship for age, heavy element content, etc. And even once this is done, stars will never be exactly as we predict them to be -- there will always be some natural variation. We do our best to figure out how much variation there is so that we can estimate the typical error in our distance measurement.
Space Tiger is correct in:Leonardo Sidis said:Thanks, that cleared things up for me. It seems kind of weird though, that there are two exact types of a star that hold true in every circumstance. Shouldn't the magnitude, size, density, etc. of a star vary indeterminably?
which is what I was referring to in my earlier post (#4) when I said:Space Tiger said:but one might want to take this further and establish a continuum relationship for age, heavy element content, etc.
But, I didn't know if you wanted the detail at that point.. There is a lot more to add, but it is called a "book". I type way too slowly to try to post it here..Labguy said:(with several adjustments needing to be made for other factors)
The pulsation of a Cepheid is caused by the expansion and contraction of its outer layers. This pulsation is a result of the balance between the outward pressure of radiation and the inward pull of gravity.
The pulsation of a Cepheid causes it to vary in brightness, with a regular period of a few days to a few weeks. As the star expands, it cools and becomes dimmer, and as it contracts, it heats up and becomes brighter.
Cepheids have a well-known relationship between their period and their luminosity, which allows astronomers to accurately determine their distance from Earth. This makes them valuable tools for measuring distances to far-off galaxies and other objects in the universe.
Yes, the pulsation of Cepheids is linked to their mass and age, so studying their pulsation can provide insight into the evolution of stars. In fact, the discovery of the period-luminosity relationship of Cepheids was a crucial step in understanding the life cycle of stars.
Yes, there are two main types of Cepheid stars: classical Cepheids and type II Cepheids. Classical Cepheids are larger and more luminous, while type II Cepheids are smaller and less luminous. They have different pulsation periods and are found in different types of galaxies.