1. RR Lyrae Stars
By: Mike Lundquist

2. What Are They Old Stars, Over 10 Billion Years Old
Helium Burning, Horizontal Branch Stars
Variable Stars With Periods of 0.2 to 1.1 days
~0.7 Solar Masses
~4-6 Solar Radii
Metal Poor Stars

3. RR Lyrae Stars In M3

4. Evolution Ascend RGB Helium Flash onto HB Enter Instability Strip
Ascend AGB
Forms Planetary Nebula
Becomes a White Dwarf

5. Types of RR Lyrae Stars
RRab -- Fundamental Mode --Rapid Increase to the Peak of the Light Curve, with a Relatively Slow Decrease
RRc -- Overtone Mode -- Increase in the Light Curve Nearly Equal to the Decrease
RRd – Pulsate in both the RRab and RRc modes.

6. RRab Type Stars Have Longer Periods
RRab Type Stars Are Easier to Find than RRc
Most RR Lyrae stars found are RRab Type
RR Lyrae Stars are Very Common in Globular Clusters

7. Pulsation Ionized Helium Layers Absorb Heat
Pressure and Luminosity Increase
Star Expands and Cools
Pressure and Luminosity Decrease
Star Compresses
Ionized Helium Absorbs Heat
Cycle Continues

8. The Blazhko Effect

9. The Blazhko Effect
Periodic Variations in Light Curve
Only Mostly in RRab Type.
Leading Theories
Result of Resonance
Result of Magnetic Field and Rotation

10. Other Important Uses Standard Candles Accurate to ~10% Distance
Real Time Stellar Evolution

11. Standard Candles Absolute magnitudes: MV ~ 0.6
Accurate Distance Measurements

12. Metallicity Relationship

13. Real Time Stellar Evolution?
RR Lyrae Star V79
Between 1962 and 1996, Pulsations in the First Overtone Increased Significantly, while the Period has Decreased.
Decrease in Period Suggests Blueward Stellar Evolution

14. Summary Good For Calculating Distances
Good For Testing Pulsation Models
Insight into Stellar Evolution of Low Mass Stars
RR Lyrae Properties
Period days
Mv 0.6 ± 0.2
Te K – 6100 K
Log g
[Fe/H] 0.0 – -2.5
Mass ~0.7 Solar Masses
Radius ~4-6 Solar Radii

15. For More Information
Principles of Stellar Evolution and Nucleosynthesis By Donald D. Clayton
RR Lyrae Stars By Horace A. Smith