Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

Time Series Photometry of Pulsating WhiteDwarf Stars

P. Chote D.J. Sullivan

School of Chemical and Physical SciencesVictoria University of Wellington

NZIP Conference 2011

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

Outline

Pulsating White DwarfsWhat?How?Why?

Puoko-nui CCD PhotometerInstrumentData ReductionExample

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

What?How?Why?

What are White Dwarfs?

I Slowly cooling stellar remnantafter nuclear fusion ceases

I 98% of stars end their life asWhite Dwarfs

I Very faint (difficult to observe)

I First pulsating white dwarfdiscovered accidentally in 1967(Landolt, ApJ, 1968)

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

What?How?Why?

How do they pulsate?

I Complex internal interactions

I Non-radial G-mode pulsations(like water waves)

I Changing Density→Temperature→ Luminosity

I Described by sphericalharmonics that evolve with time

I Periods of 100 - 1000 seconds

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

What?How?Why?

How do they pulsate?

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

What?How?Why?

Why study them?

I Pulsation modes sample internalstructure

I Asteroseismology!

I Laboratories for extreme & exoticphysics

I Core compositionI Convection zone informationI Neutrino coolingI Age determinationsI ...

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Instrument Overview

I Puoko-nui: “Big Sensor”

I 1024x1024px shutterlessFrame Transfer CCD

I ∼ 6 × 6 arcmin field of view

I GPS timing

I Autoguiding

I Portable

I Online data reduction

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Mount John University Observatory

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Frame Transfer

I CCD Readout is slow

I Mask half the chip from light

I Shift charge into masked areaand readout in parallel with nextexposure

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Instrument Overview

TimeDownload

Monitor Configure

Frames

Time

Guiding

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Instrument Overview

Imaging CCD +

Thermo-electric Cooler

Guide

Camera

Control

Electronics

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Instrument Overview

Guide + AcquisitionComputers

To GPSReceiver

ControllerUnit

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Instrument Overview

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Data reduction

T

I

F

I

Converting the raw CCD frames to ameasure of brightness vs time

1. Preprocessing

2. Aperture Photometry

3. Fourier Analysis

4. Modelling

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Preprocessing

Raw CCD Frame Processed CCD Frame

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Aperture Photometry

1. Determine aperture size

2. Estimate & subtract skyintensity (blue annulus)

3. Center aperture over star

4. Sum pixel intensities insideaperture (red circle)

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Lightcurve

I Measurement of intensity vs time

I Divide pulsating star intensity bycomparison to atmosphericeffects

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Fourier AnalysisI Any periodic signal can be

represented as a sum of sinewaves

I The Fourier Transform tells youthe frequency components in agiven signal

I Peaks in FT tell us thefrequencies of the pulsationmodes in the WD

I More data = better identificationof frequencies

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

Fourier AnalysisI Any periodic signal can be

represented as a sum of sinewaves

I The Fourier Transform tells youthe frequency components in agiven signal

I Peaks in FT tell us thefrequencies of the pulsationmodes in the WD

I More data = better identificationof frequencies

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

EC04207-4748: 30 July 2011

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

EC04207-4748

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

EC04207-4748

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

InstrumentData ReductionExample

I Determine ‘real’ frequenciesI Combination frequenciesI Rotational splitting

I Constraints on numerical models

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

Summary

I Pulsating White Dwarfs areinteresting objects

I Pulsations constrain internalstructure

I Specialised instruments forobserving

I Data reduction to determinefrequencies

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars

Pulsating White DwarfsPuoko-nui CCD Photometer

Summary

Acknowledgements

I Marsden Fund

I University of Canterbury

P. Chote, D.J. Sullivan Time Series Photometry of Pulsating White Dwarf Stars