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 Principles of Stellar Evolution and Nucleosynthesis By Donald D. Clayton RR Lyrae Stars By Horace A. Smith http://www.aavso.org/ http://www.journals.uchicago.edu/doi/pdf/10.1086/316352 http://www.astronomy.ohio-state.edu/~ryden/ast162_4/notes16.html 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 http://www.aanda.org/index.php?option=article&access=bibcode&bibcode=2006A%2526A...459..577KPDF http://www.journals.uchicago.edu/doi/pdf/10.1086/506198 http://www.aanda.org/index.php?option=article&access=bibcode&bibcode=2007A%2526A...474..557MPDF http://adsabs.harvard.edu/abs/2004rrls.book.....S http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1998ASPC..135..385F&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf