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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

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RR Lyrae Stars

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  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 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

  15. 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

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