RR LyraesRR Lyraes

Bi-Qing ForBi-Qing For

Chris Sneden (UT) Chris Sneden (UT)

George Preston (Carnegie Observatory)George Preston (Carnegie Observatory)

What are RR Lyrae stars?What are RR Lyrae stars?

APOD 23 Feb 2001

What happens when stars cross What happens when stars cross the instability strip? the instability strip?

They pulsate like a jello!

Scientific Computing in the School of Physics at the University of Sydney

RR LyraesRR Lyraes

Max radius

Typical time scale = 0.57 day

Different types of RR LyraesDifferent types of RR Lyraes

What drives stellar pulsations?What drives stellar pulsations?

• Kappa-mechanism (RR Lyrs)– “steam engine”

Absorb heat

Restore the balance inside the star

Release heat / cool off

Contract Expand

Why RR Lyraes are interesting? Why RR Lyraes are interesting?

• Most of RR Lyraes have – stable pulsation – stable pulsational period– high luminosity

• Easy to be identified at large distances

• Standard candles for distance scale

• Tracers for Studying Galactic structure

Distance scale to Globular ClustersDistance scale to Globular Clusters

https://www.cfa.harvard.edu/~jhartman/M3_movies.html

M 3

Duffau et al. (2006)

Tracers for studying Galactic structureTracers for studying Galactic structure

Special: Blazhko effectSpecial: Blazhko effect

Sergey Blazhko

created by D. Welch based on MACHO project data, Alcock et al. 2000

What am I studying?What am I studying?• Chemical compositions throughout the

pulsational cycle.

• Line profile variation

• Where do we get the spectra?

George Preston

LCO

Du Pont 100 inch

What do we learn?What do we learn?

Line profile variationLine profile variation

Chemical CompositionsChemical Compositions

Current MissionsCurrent Missions

CoRoT - COnvection, ROtation & Transits planétaires

Kepler Space Telescope

Many new RR Lyrs have been discovered

New properties have been found in the lightcurves of RR Lyrs