What are RR Lyrae and Cepheid variable stars?
RR Lyraes are old, relatively low mass, Population II stars, in common with W Virginis and BL Herculis variables, the type II Cepheids. Classical Cepheid variables are higher mass population I stars. RR Lyrae variables are much more common than Cepheids, but also much less luminous.
What are RR Lyrae and Cepheid variable stars and why are they important to understanding the universe?
Cepheids and RR Lyrae stars are two types of pulsating variable stars. 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.
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 type of star is RR Lyrae?
RR Lyrae are low metallicity (population II) stars that begin their lives with a mass and size similar to that of our Sun. They become RR Lyrae stars during the red giant phase, late in the evoluton of the star, and so have typical ages of around 10 billion years.
What is the most important important difference between Cepheids and RR Lyrae variable stars?
RR Lyrae variables pulsate irregularly as compared to Cepheids which are very regular. Cepheids vary because they pulsate; RR Lyrae variables vary because they are binaries. Cepheids are higher luminosity stars than RR Lyrae variables, and have longer periods.
Why are RR Lyrae variables not used to find distances to distant galaxies quizlet?
Why are RR-Lyrae variables not used to find distances to distant galaxies? They are not bright enough to be seen at large distances. Type Ia supernovae are frequently used as standard candles for the measurement of distances to galaxies, but they are not all equally luminous.
What are the differences between an RR Lyrae variable and an Cepheid variable star?
RR Lyrae variables pulsate irregularly as compared to Cepheids which are very regular. 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.
What makes RR Lyrae variables different from Cepheid variables?
What are RR Lyrae variables and how are they related to the instability strip?
RR Lyrae are variable, horizontal branch stars with periods ranging from a few hours to 2 days, and optical brightnesses that typically vary between 0.3 and 2 magnitudes. They lie in the instability strip of the Hertzsprung-Russell diagram and suffer instabilities that cause their size to periodically change.
What property of RR Lyrae stars makes them useful for measuring distances?
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.
What are RR Lyrae variables used for in astronomy?
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.
How does blending affect the RR Lyrae variable?
The effect of blending can impact RR Lyrae variables sampled near the cores of globular clusters, which are so dense that in low-resolution observations multiple (unresolved) stars may appear as a single target.
Where do RR Lyrae stars fall on the diagram?
The RR Lyrae variable stars fall in a particular area on a Hertzsprung–Russell diagram of color versus brightness. RR Lyrae variables are periodic variable stars, commonly found in globular clusters.
How are RR Lyrae stars similar to Cepheid variables?
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.