RR Lyrae stars. These are lower-luminosity stars, where the instability strip crosses the horizontal branch. They may appear on cluster H-R diagrams by omission in the "RR Lyrae gap", since variables are usually not plotted.
RR Lyrae Stars
A large class of pulsating (amplitude variation about 1 mag) blue giants of anomalous spectral type (A2-F6) with periods of less than 1 day. Their average absolute magnitude is about +0.8.
RR LYRAE STARS
Variable stars similar to the cepheids. They are blue giants with periods of about ten to fifteen hours and they change in brightness by about one magnitude.
R TYPE STARS ...
RR Lyrae stars were first discovered in the late nineteenth century, where they were found in great numbers in globular clusters. They were first called ``cluster variables,'' a name which they retained for many decades.
RR Lyrae stars can be used as standard candles to measure distances out to about 760,000 parsecs (about 2.5 million light years).
RR Lyrae stars are a sub-classification of Cephied variables. They have a much shorter oscillation period - usually less than a day - and are all about 90 times brighter than the Sun.
2. RR Lyrae stars are a type of cataclysmic variable. (Hint)
3. The Galactic halo contains about as much gas and dust as the Galactic disk. (Hint)
4. The Galactic disk contains only old stars. (Hint) ...
Cepheids and RR Lyrae Stars.
Figure 3. Light variation of a Cepheid variable. It is plotted so that two cycles of pulsation are shown.
Another feature of RR Lyrae stars is that they exhibit a period-luminosity relation similar to that of Cepheid variable stars.
A classification of RR Lyrae stars according to the shape and amplitude of their light variation (a, b, and c, although today types a and b are usually combined). The c-type stars have the smallest amplitude.
RR Lyrae stars are pulsating stars like Cepheids, but they are low mass stars with short periods (less than a day). They are seen in globular clusters, and appear to all have the same luminosity.
They become RR Lyrae stars during the red giant phase, late in the evolution of the star, and so have typical ages of around 10 billion years.
Period-luminosity relationship for Cepheids and RR Lyrae stars.
Let us now see how this relationship can be used to determine the distance to a Cepheid.
Accurate knowledge of open cluster distances is vital for calibrating the period-luminosity relationship shown by variable stars such as cepheid and RR Lyrae stars, which allows them to be used as standard candles.
RR: RR Lyrae stars, low mass pulsating stars with helium-fusing cores. They have variation amplitudes of a few tenths of a magnitude and periods under a day. Their uniform absolute magnitudes make them good distance indicators.
Among A-type peculiar stars are Ae stars, Am stars, and Ap stars. Also, two of the main kinds of pulsating variables, RR Lyrae stars and Delta Scuti stars, have surface temperatures in the A-star range.
Related category
- TYPES OF STAR ...
The Cepheids and RR Lyrae stars are typical examples of such variables. The explosive (or eruptive) variables include novas, supernovas, and similar stars that undergo sudden outbursts of radiant energy, which results in rapid brightening.
Instability Strip - A region of the H-R diagram occupied by pulsating stars, including Cepheid variables and RR Lyrae stars
Intercrater Plain - Smooth portions of the surface of Mercury that lie between and around clusters of large craters ...
In the H-R diagram of a globular cluster, the sequence of stars extending from the red giants toward the blue side of the diagram; includes RR Lyrae stars.
Horoscope ...
horizontal branch: In the H-R diagram of a globular cluster, the sequence of stars extending from the red giants toward the blue side of the diagram; includes RR Lyrae stars.
Another prominent feature is Hertzsprung gap located in the region between A5 and G0 spectral type and between +1 and -3 absolute magnitudes (i.e. between the top of main sequence and the giants in the horizontal branch). RR Lyrae stars can be found ...
As we have seen Cepheid variables and RR Lyrae stars provide another means of obtaining distances, so long as we have calibrated the Period-Luminosity curves with variable stars whose distances have been obtained through other means.
A famous and well-studied variable star, RR Lyrae is the prototype for it's class. Over a period of about 13 hours, the star dims by more than a factor of two and then returns to it's initial brightness. RR Lyrae stars are old stars and are often ...
RR Lyrae stars allow measurement of distances to globular clusters.spectroscopic parallax: the distance obtained by observing a star's color, correcting for Doppler shift, inferring the star's luminosity from a calibrated HR diagram, ...
These are located at the low luminosity end of the instability strip and they have periods less than a day. RR lyrae stars are good for relatively near by distances.
 See also: Rr lyrae star, RR Lyrae, Star, Sun, Cluster
  
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