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3. RR Lyrae Stars
The prototype for this class
of stars, RR Lyrae (also known as RR Lyra), was discovered to be
a short period variable star by Williamina Fleming (1857-1911)
at Harvard in 1899. She noted its changing brightness on
photographic plates taken over a period of several days. It was
also noted to have a period nearly the same as a large number of
similar such stars found in globular clusters by Solon Bailey
(1854-1931) in 1893 (EAA; Moore, 2002). RR Lyrae itself was at
first thought to have escaped from a globular cluster, but later
other RR Lyrae like stars were found as isolated stars apart
from the many RR Lyrae stars associated with globular clusters
(Moore, 2002). RR Lyrae has a period of 13 hours and 36
minutes. It varies from magnitude 7.1 to 8.1 (Dibon-Smith,
2000). Figure 2A shows RR Lyrae’s location with respect to the
constellation Lyra. Figure 3 compares the periods of Cepheid
and RR Lyrae stars. Figure 4 shows a typical period of a
Cepheid variable star, and figure 5 shows a typical period for a
RR Lyrae variable star.
Figure 2A. RR Lyrae and environs.
From:
http://www.exn.ca/Stories/1998/06/22/55.asp
Figure 2B.
Close-up view of RR Lyrae (arrow pointing upward) and nearby
stars. North is at the top and East is to the left. The
central star marked with the arrow pointing to the right has a
magnitude of ~ 8.8. The star marked with the arrow pointing to
the left has a magnitude of 7.2. Ninety-second exposure with
Canon 20Da digital camera using an 85 mm f/3.5 lens, ISO 800.
Image
courtesy James McGaha.
Figure 3.
Comparison of Cepheid and RR Lyrae stars.
From: http://www.earth.uni.edu/~morgan/astro/course/Notes/section3/new11.html
Figure 4. Typical light curve for a Type I (Classical)
Cepheid variable star.
From: http://www.earth.uni.edu/~morgan/astro/course/Notes/section3/new11.html
Figure 5.
Typical light curve for a RR Lyrae variable star.
From: http://www.earth.uni.edu/~morgan/astro/course/Notes/section3/new11.html
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