Research 7: P Chote

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