RR Lyrae

Did You Know?

• The variable nature of RR Lyrae was discovered by Scottish astronomer Williamina Fleming at Harvard Observatory in 1901.
• The distance of RR Lyrae was determined within a 5% margin of error in 2002 using the Hubble Space Telescope's fine guidance sensor, yielding 262 pc.
• Combined with Hipparcos satellite data and other sources, the distance estimate is 258 pc.

Variable star class

This low-mass star has exhausted core hydrogen, evolved off the main sequence, and passed through the red giant stage. It now produces energy through helium fusion at its core, placing it on the horizontal branch. As the effective temperature of its outer envelope increases over time, the star enters the instability strip at roughly class A, where its envelope begins to pulsate. RR Lyrae exhibits regular radial pulsations that cause its apparent magnitude to vary between 7.06 and 8.12 over a 0.567-day cycle, with its radius changing between 5.1 and 5.6 solar radii. The star belongs to a subset of RR Lyrae variables displaying the Blazhko effect, a periodic modulation of pulsation strength or phase. Time-series photometric observations in 2014 revealed the physical origin of this effect.

Other stellar classifications

RR Lyrae has low metallicity, with a scarcity of elements heavier than hydrogen and helium, classifying it as a Population II star formed early in the Universe. Its orbit lies close to the Milky Way's plane, never exceeding 680 ly above or below it. The orbit is highly eccentric, bringing the star as close as 6.80 kly to the Galactic Center and as far as 59.9 kly at apapsis.