Variable Stars of Globular Clusters in the Large Magellanic Cloud Evan McClellan (FSU) Horace Smith (advisor) (MSU) Charles Kuehn (MSU) August 6 th, 2008

Outline Background- –RR Lyrae Variables –The Hertzsprung-Russell diagram –Globular Clusters –Satellite Galaxies –Galaxy Formation –Oosterhoff Dichotomy NGC2210- –Instruments –Procedure –Results

RR Lyrae Variables Low mass ~0.8 solar masses Population II - ~10Gyr old Radial Pulsation RRab example: Fundamental Mode

RRc First Overtone:

The Hertzsprung-Russell Diagram Temperature vs. Luminosity

Globular Clusters Globular Cluster H-R Diagram Soar image of NGC2210 (Smith 1995)

Satellite Galaxies Large and Small Magellanic Clouds, other dwarf spheroidal galaxies Role in formation of Galactic Halo? NASA/ESA 2008

Oosterhoff Dichotomy Bimodal Period Distribution for Galactic GCs OoI: average ‘ab’ P~0.55 days OoII: average ‘ab’ P~0.65 days Oosterhoff Gap: 0.58 < P < 0.62 What about globular clusters in satellite galaxies? Catelan 2005

NGC2210-Instruments SOAR- –4.1m mirror –Feb. 5-18, 2008 SMARTS- –1.3m mirror –Sep. 4-Dec. 31, 2006 MSU 2005 SMARTS Consortium 2008

Procedure For each set of data- –Define “star” –Find stars –Align images –Combine –Make CMD Putting it all together- –Synch star names –Calibrate brightness –Find “variables” –Filter out non-RR-Lyrae –Combine lightcurves –Plot period vs. amplitude

Lightcurves Type “ab” lightcurve

Lightcurves Type “c” lightcurve

Results Soar Color-Magnitude Diagram

Results Smarts Color-Magnitude Diagram

Results Average ‘ab’ Period=0.596 days

References Carrol and Ostlie, An Introduction to Modern Astrophysics, Addison-Wesley, 2007 Catelan, M. 2005, astro-ph/ Catelan, M. 2006, astro-ph/ De Lee, N. Variable Stars in NGC6304, MSU 2004 MSU, 2005, NASA/ESA, 2008, SMARTS Consortium Website, 2008, Smith, H.A. RR Lyrae Stars, Cambridge University Press, 1995

Thanks Special thanks to Dr. Horace Smith and Charles Kuehn