Transcript RR Lyrae Stars

RR Lyrae Stars
By: Mike Lundquist
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
RR Lyrae Stars In M3
Evolution
• Ascend RGB
• Helium Flash onto HB
• Enter Instability Strip
• Ascend AGB
• Forms Planetary Nebula
• Becomes a White Dwarf
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.
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
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
The Blazhko Effect
The Blazhko Effect
• Periodic Variations in Light Curve
• Only Mostly in RRab Type.
Leading Theories
• Result of Resonance
• Result of Magnetic Field and
Rotation
Other Important Uses
• Standard Candles
Accurate to ~10% Distance
• Real Time Stellar Evolution
Standard Candles
• Absolute magnitudes: MV ~ 0.6
• Accurate Distance Measurements
Metallicity Relationship
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
Summary
•Good For Calculating Distances
•Good For Testing Pulsation Models
•Insight into Stellar Evolution of Low Mass Stars
RR Lyrae Properties
Period
0.2-1.1 days
Mv
0.6 ± 0.2
Te
7400 K – 6100 K
Log g
2.5-3.0
[Fe/H]
0.0 – -2.5
Mass
~0.7 Solar Masses
Radius
~4-6 Solar Radii
For More Information
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Principles of Stellar Evolution and Nucleosynthesis By Donald D. Clayton
RR Lyrae Stars By Horace A. Smith
http://www.aavso.org/
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http://www.pa.msu.edu/people/smith/
http://spiff.rit.edu/classes/phys230/lectures/mw_size/mw_size.html
http://antwrp.gsfc.nasa.gov/apod/ap041012.html
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http://www.journals.uchicago.edu/doi/pdf/10.1086/506198
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2007A%2526A...474..557MPDF
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