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- 1. Pulsating White Dwarfs Puoko-nui CCD Photometer Summary Time Series Photometry of Pulsating White Dwarf Stars P. Chote D.J. Sullivan School of Chemical and Physical Sciences Victoria University of Wellington NZIP Conference 2011 P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 2. Pulsating White Dwarfs Puoko-nui CCD Photometer Summary Outline Pulsating White Dwarfs What? How? Why? Puoko-nui CCD Photometer Instrument Data Reduction Example P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 3. Pulsating White Dwarfs What? Puoko-nui CCD Photometer How? Summary Why? What are White Dwarfs? Slowly cooling stellar remnant after nuclear fusion ceases 98% of stars end their life as White Dwarfs Very faint (difficult to observe) First pulsating white dwarf discovered accidentally in 1967 (Landolt, ApJ, 1968) P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 4. Pulsating White Dwarfs What? Puoko-nui CCD Photometer How? Summary Why? How do they pulsate? Complex internal interactions Non-radial G-mode pulsations (like water waves) Changing Density → Temperature → Luminosity Described by spherical harmonics that evolve with time Periods of 100 - 1000 seconds P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 5. Pulsating White Dwarfs What? Puoko-nui CCD Photometer How? Summary Why? How do they pulsate? P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 6. Pulsating White Dwarfs What? Puoko-nui CCD Photometer How? Summary Why? Why study them? Pulsation modes sample internal structure Asteroseismology! Laboratories for extreme & exotic physics Core composition Convection zone information Neutrino cooling Age determinations ... P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 7. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Instrument Overview Puoko-nui: “Big Sensor” 1024x1024px shutterless Frame Transfer CCD ∼ 6 × 6 arcmin field of view GPS timing Autoguiding Portable Online data reduction P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 8. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Mount John University Observatory P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 9. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Frame Transfer CCD Readout is slow Mask half the chip from light Shift charge into masked area and readout in parallel with next exposure P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 10. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Instrument Overview Guiding Time Monitor Configure Download Time Frames P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 11. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Instrument Overview Guide Camera Control Electronics Imaging CCD + Thermo-electric Cooler P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 12. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Instrument Overview Controller Unit Guide + Acquisition Computers To GPS Receiver P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 13. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Instrument Overview P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 14. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Data reduction Converting the raw CCD frames to a measure of brightness vs time I 1. Preprocessing 2. Aperture Photometry T 3. Fourier Analysis I 4. Modelling F P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 15. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Preprocessing Raw CCD Frame Processed CCD Frame P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 16. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Aperture Photometry 1. Determine aperture size 2. Estimate & subtract sky intensity (blue annulus) 3. Center aperture over star 4. Sum pixel intensities inside aperture (red circle) P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 17. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Lightcurve Measurement of intensity vs time Divide pulsating star intensity by comparison to atmospheric effects P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 18. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Fourier Analysis Any periodic signal can be represented as a sum of sine waves The Fourier Transform tells you the frequency components in a given signal Peaks in FT tell us the frequencies of the pulsation modes in the WD More data = better identification of frequencies P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 19. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Fourier Analysis Any periodic signal can be represented as a sum of sine waves The Fourier Transform tells you the frequency components in a given signal Peaks in FT tell us the frequencies of the pulsation modes in the WD More data = better identification of frequencies P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 20. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example EC04207-4748: 30 July 2011 P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 21. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example EC04207-4748 P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 22. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example EC04207-4748 P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 23. Pulsating White Dwarfs Instrument Puoko-nui CCD Photometer Data Reduction Summary Example Determine ‘real’ frequencies Combination frequencies Rotational splitting Constraints on numerical models P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 24. Pulsating White Dwarfs Puoko-nui CCD Photometer Summary Summary Pulsating White Dwarfs are interesting objects Pulsations constrain internal structure Specialised instruments for observing Data reduction to determine frequencies P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars
- 25. Pulsating White Dwarfs Puoko-nui CCD Photometer Summary Acknowledgements Marsden Fund University of Canterbury P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars