RR Lyrae Stars
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Transcript of 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
RRc -- Overtone Mode -- Increase in the Light Curve Nearly Equal to the Decrease
RRd – Pulsate in both the RRab and RRc modes.
RRab -- Fundamental Mode --Rapid Increase to the Peak of the Light Curve, with a Relatively Slow Decrease
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
PulsationIonized 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
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
•Good For Calculating Distances
•Good For Testing Pulsation Models
•Insight into Stellar Evolution of Low Mass Stars
RR Lyrae Properties
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=2
006A%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