Variable Stars of Globular Clusters in the Large Magellanic Cloud

Evan McClellan (FSU)

Horace Smith (advisor) (MSU)

Charles Kuehn (MSU)

August 6th, 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?

Catelan2005

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/0507464

• Catelan, M. 2006, astro-ph/0604035

• De Lee, N. Variable Stars in NGC6304, MSU 2004

• MSU, 2005, http://www.pa.msu.edu/soarmsu/

• NASA/ESA, 2008, http://www.spacetelescope.org/

• SMARTS Consortium Website, 2008, http://www.astro.yale.edu/smarts/

• Smith, H.A. RR Lyrae Stars, Cambridge University Press, 1995

Thanks

• Special thanks to Dr. Horace Smith and Charles Kuehn