RR Lyrae hole in the colour-magnitude diagram

Unlike Cepheids, RR Lyrae do not have a H-burning phase, which is why they do not show the same pattern of more variability during the He-burning phase.
  • #1
FrankPlanck
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RR Lyrae "hole" in the colour-magnitude diagram

Hi everyone,
can someone explain me the RR Lyrae "hole" (or gap) in the colour-magnitude diagram here-->
http://media-2.web.britannica.com/eb-media/22/4422-004-DB07836A.gif
I suppose that the reason is because they rapidly evolve during this phase.
But I know that, generally speaking, stars rapidly evolve during the first passage on the instability strip (H burning) while the second transit on the strip (He burning) is slower.
Hence we can see more variable stars in the He-burnig phase than in the H-burning phase.
This is true for Cepheids, but for RR Lyrae (obviously they have not the H-burning phase)?
Thank you!
 
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  • #2
The RR Lyrae gap in the colour-magnitude diagram is caused by their relatively short period of time spent on the instability strip. As they evolve quickly, they spend a short amount of time at a particular luminosity and temperature, resulting in a gap in the CMD. This gap is also affected by the fact that they have a narrow mass range, which means that they all evolve at the same rate.
 

1. What is an RR Lyrae hole in the colour-magnitude diagram?

An RR Lyrae hole is a gap or deficiency in the distribution of RR Lyrae stars on a colour-magnitude diagram. These stars are pulsating variable stars commonly found in old stellar populations, and their absence in a certain region of the colour-magnitude diagram can provide important insights into the structure and evolution of a galaxy.

2. How is an RR Lyrae hole identified in a colour-magnitude diagram?

An RR Lyrae hole is typically identified by plotting the distribution of RR Lyrae stars on a colour-magnitude diagram for a specific galaxy or stellar population. The absence of these stars in a particular region, usually in the blue and bright end of the diagram, is indicative of an RR Lyrae hole.

3. What causes an RR Lyrae hole?

The formation of an RR Lyrae hole is thought to be caused by various factors, such as the age and metallicity of a stellar population, as well as the dynamical evolution of a galaxy. The exact cause may vary depending on the specific galaxy or population being studied.

4. What can the presence of an RR Lyrae hole tell us about a galaxy?

The presence of an RR Lyrae hole can provide valuable information about the structure and evolution of a galaxy. It can indicate the age and metallicity of the stellar population, as well as the presence of any dynamical processes that may have affected the galaxy. It can also help in understanding the formation and evolution of galaxies in general.

5. Are RR Lyrae holes unique to a certain type of galaxy?

No, RR Lyrae holes have been observed in various types of galaxies, including elliptical galaxies, dwarf galaxies, and globular clusters. However, the exact characteristics and implications of these holes may differ depending on the type of galaxy being studied.

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