Period-Luminosity Relationship of Type I Cepheids - Need Better Formula

In summary, the conversation discusses the difficulties in finding a more detailed formula for the Period-luminosity relationship of Type I Cepheids. The Wikipedia description and graphical approach in the book do not seem to match, and a better formula/relationship is sought out. The conversation also mentions that Cepheid variables are divided into two subclasses, Population I and Population II, and they follow different period-luminosity relationships. The formula for Population I Cepheids is given as Mv = -2.81 log10(P) - 1.43 (+/- 1). However, the book makes a distinction between type and population, causing some confusion.
  • #1
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This is related to a HW post I made over in the HW forum. I am stuck trying to find a more detailed formula for the Period-luminosity relationship of Type I Cepheids.

Wikipedias description doesn't seem to match with the book (or include any mention of type I or type II), and frankly the graphical approach in my book isn't cutting it for me. Is there a better formula/relationship out there.

It seems I might be able to get a decent estimate by taking making my own linear/log function from the graph, but when I do so the answer varies quite a bit depending on which values for the points on the graph I estimate.
 
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  • #2
Read Wiki more carefully.

Cepheid variables are divided into at least two subclasses: Population I or classical Cepheids, and Population II or W Virginis Cepheids. The former are young massive stars, whereas the latter are older fainter stars.[13] Population I and II Cepheids follow different period-luminosity relationships. The luminosity of Population II Cepheids is, on average, less than classical Cepheids by about 1.5 magnitudes (but still brighter than RR Lyrae stars).

Also from the Wiki article,

Mv = -2.81 log10(P) - 1.43( +/- 1)

where:

Mv = absolute magnitude (Population 1 Cepheids)
P = period in days

http://en.wikipedia.org/wiki/Cepheid_variable
 
  • #3
I went ahead and used that as well. However the book makes a distinction between type and population. O well, thanks though.
 

1. What is the Period-Luminosity Relationship of Type I Cepheids?

The Period-Luminosity Relationship of Type I Cepheids is a relationship between the pulsation period and the intrinsic luminosity of a specific type of variable star. It was first discovered by Henrietta Swan Leavitt in the early 1900s and is used to measure the distances to galaxies and determine their expansion rate.

2. Why is a better formula needed for the Period-Luminosity Relationship of Type I Cepheids?

The current formula for the Period-Luminosity Relationship of Type I Cepheids is based on observations from a small sample of stars and may not accurately represent the relationship for all Type I Cepheids. A better formula is needed to improve the accuracy of distance measurements and to better understand the physics behind this relationship.

3. How is the Period-Luminosity Relationship of Type I Cepheids used in astronomy?

The Period-Luminosity Relationship of Type I Cepheids is an important tool for measuring the distances to galaxies. By determining the pulsation period of a Type I Cepheid, astronomers can calculate its intrinsic luminosity and use this to calculate its distance from Earth. This relationship is also used to study the expansion rate of the universe and the evolution of galaxies.

4. What factors affect the Period-Luminosity Relationship of Type I Cepheids?

The Period-Luminosity Relationship of Type I Cepheids is affected by several factors, including the metallicity of the star (the amount of elements other than hydrogen and helium), the temperature and mass of the star, and the presence of binary companions. These factors can impact the pulsation period and intrinsic luminosity of the star and therefore affect the accuracy of the relationship.

5. How can a better formula for the Period-Luminosity Relationship of Type I Cepheids be determined?

To develop a better formula for the Period-Luminosity Relationship of Type I Cepheids, astronomers use observations from a larger sample of stars and take into account the various factors that can affect the relationship. They also use theoretical models and simulations to understand the physics behind the relationship and improve its accuracy. Collaboration among scientists and continued research in this field will help to refine the formula and improve our understanding of these important stars.

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