What are RR Lyrae stars used to determine?
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What are RR Lyrae stars used to determine?
RR Lyrae variables are periodic variable stars, commonly found in globular clusters. They are used as standard candles to measure (extra) galactic distances, assisting with the cosmic distance ladder.
Why are RR Lyrae important?
The importance of the study of RR Lyrae stars is at least threefold: first they can be used as “standard candles” in distance determinations, and secondly they provide us with information on the chemical composition (helium and heavy element abundance) in the halo and old disk popula- tion of our galaxy.
What are RR Lyrae and Cepheid stars?
Cepheid stars and RR Lyrae star are examples of pulsating variable stars. The greater the luminosity of a Cepheid star, the longer its period of oscillation.
Who first used RR Lyrae variable stars to determine distances in the Milky Way?
How did Harlow Shapley use the period-luminosity relationship of RR Lyrae variables to determine the size of the Milky Way galaxy? He found the distances to globular clusters distributed about the center of the galaxy.
What are RR Lyrae stars quizlet?
RR Lyrae variables are horizontal-branch stars that all have roughly the same average luminosity of about 100 L.
What important measurement did RR Lyrae variables allow astronomers to get?
RR Lyrae’s brightness (between 7th and 8th magnitude) made it bright enough to observe spectroscopically in such a way that the changes in its spectrum could be traced throughout its cycle of variability. This enabled astronomers to measure changes in spectral type, as well as to detect the presence of emission lines.
What does RR stand for in RR Lyrae?
This scheme provides 334 letter combinations. After that variable stars are numbered, with the letter V before, e.g. V 404 Cygni. So, R Coronae Borealis was the first variable star to be discovered in its constellation, and RR Lyrae was the 10th variable found in Lyra.
What is one important difference between Cepheids and RR Lyrae variables?
What is one of the differences between Cepheid variables and RR Lyrae variables? All Cepheids have the same luminosity, while RR Lyrae stars vary greatly in brightness. RR Lyrae variables pulsate irregularly as compared to Cepheids which are very regular.
How far are RR Lyrae stars?
RR Lyrae
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Proper motion (μ) | RA: -109.68 mas/yr Dec.: -195.75 mas/yr |
| Parallax (π) | 3.64 ± 0.23 mas |
| Distance | 900 ± 60 ly (270 ± 20 pc) |
| Absolute magnitude (MV) | 0.600 ± 0.126 |
What is the most important important difference between Cepheids and RR Lyrae variable stars?
What is one of the differences between Cepheid variables and RR Lyrae variables? All Cepheids have the same luminosity, while RR Lyrae stars vary greatly in brightness.
Are RR Lyrae on the main sequence?
RR Lyrae stars have evolved off the main sequence. They lie in a region of the HR diagram which has roughly yellow color, in a sort of gap between the main sequence and red giant branch.
How do astronomers measure the distance to RR Lyrae stars?
The period of pulsation of an RR Lyrae variable depends on its mass, luminosity and temperature, while the difference between the measured luminosity and the actual luminosity allows its distance to be determined via the inverse-square law.
Why are RR Lyrae stars considered to be standard candles for measuring distance?
Another feature of RR Lyrae stars is that they exhibit a period-luminosity relation similar to that of Cepheid variable stars. Although this means that they can be used as standard candles to measure distances, they are much fainter than Cepheids and are generally used only to measure distances to globular clusters.
Which can you see farther away RR Lyrae and Cepheid variable stars Why?
Q: What could explain that difference? Because Cepheids are more luminous than RR Lyrae, we can use them to extend our reach farther into the depths of space, reaching more distant galaxies. In particular, Cepheids allow us to measure the distance to the nearest big cluster of galaxies, known as the Virgo Cluster.
Are RR Lyrae stars on the main sequence?
What is one difference between Cepheids and RR Lyrae stars?
Cepheids are higher luminosity stars than RR Lyrae variables, and have longer periods. Cepheids are higher luminosity stars than RR Lyrae variables, and have longer periods.
How do astronomers tell RR Lyrae and Cepheid stars apart?
If you look on the diagram below, you’ll see that a different class of pulsing variable star, the Cepheids, lies far above the RR Lyrae on the luminosity scale. Cepheids may be 100 times more luminous than RR Lyr stars, which means that astronomers can detect and measure them in much more distant galaxies.
