In contemporary astronomy, a period-luminosity relation makes them good standard candles for relatively nearby targets, especially within the Milky Way and Local Group. They are also frequent subjects in the studies of globular clusters and the chemistry (and quantum mechanics) of older stars.
- Why are RR Lyrae standard candles?
- Why are Cepheid variables good standard candles?
- Why are RR Lyrae stars useful for determining the properties of the halo?
- What are RR Lyrae and Cepheid variable stars and why are they important to understanding the universe?
- Why do RR Lyrae pulsate?
- Why do galactic disks appear blue?
- What makes a good standard candle?
- Why are standard candles so important for astronomers?
- Why do RR Lyrae stars pulsate?
Why are RR Lyrae standard candles?
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.
Why are Cepheid variables good standard candles?
It turns out that the rate at which the star pulsates is correlated with how bright the star is. If astronomers can measure the period of a Cepheid variable, they can calculate the absolute magnitude of the star, making Cepheid variables standard candles.
Why are RR Lyrae stars useful for determining the properties of the halo?
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 variable stars and why are they important to understanding the universe?
Key concepts and summary Light curves of these stars show that their luminosities vary with a regularly repeating period. RR Lyrae stars can be used as standard bulbs, and cepheid variables obey a period-luminosity relation, so measuring their periods can tell us their luminosities.
Why do RR Lyrae pulsate?
Properties. RR Lyrae stars pulse in a manner similar to Cepheid variables, but the nature and histories of these stars is thought to be rather different. Like all variables on the Cepheid instability strip, pulsations are caused by the κ-mechanism, when the opacity of ionised helium varies with its temperature.
Why do galactic disks appear blue?
Galactic disks appear blue because: O and B blue giants are much brighter than G, K, or M dwarfs. What perception of the Milky Way Galaxy did astronomers have in 1900? They believed that the Milky Way was the entire universe.
What makes a good standard candle?
(2) Cepheid variable stars and Type Ia supernovae are the most useful standard candles. Cepheid variable stars are good standard candles. First, their luminosity is quite high (the most luminous Cepheids are 40,000 times more luminous than the Sun), so they can be seen to large distances.
Why are standard candles so important for astronomers?
Standard candles are important in astronomy. They allow us to measure distance. If you have two stars of the same type, but one is further away than the other, it looks fainter. Knowing that they should be the same brightness allows us to work out the distances between them.
Why do RR Lyrae stars pulsate?
Properties. RR Lyrae stars pulse in a manner similar to Cepheid variables, but the nature and histories of these stars is thought to be rather different. Like all variables on the Cepheid instability strip, pulsations are caused by the κ-mechanism, when the opacity of ionised helium varies with its temperature.