Defocused PSF-fitting Photometrystar.herts.ac.uk/RoPACS/Files/mpwShop/Parviainen.pdf · Why PSF...
Transcript of Defocused PSF-fitting Photometrystar.herts.ac.uk/RoPACS/Files/mpwShop/Parviainen.pdf · Why PSF...
Introduction Observations PSF fitting Photometry Results
Defocused PSF-fitting PhotometryRoPACS Network Workshop - May 2010
Hannu Parviainen
Instituto de Astrof́ısica de Canarias
11.05.2010
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results
1 IntroductionThe light curveDefocused PSF
2 ObservationsObservations
3 PSF fitting PhotometryPSF model 1PSF model 2Fitting
4 Results
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results The light curve Defocused PSF
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results The light curve Defocused PSF
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results The light curve Defocused PSF
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results The light curve Defocused PSF
PSF
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results The light curve Defocused PSF
PSF
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results Observations
Observations
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results Observations
Observations
GJ436(b)
Bright (6.3 in H)
Distance 10.2 pc
Observations - 13.03.2010
H filter
1.5 s. integration
Defocused to ≈ 8 pix ring
200 images / cube
W-setup (4.6’ fow)
40 cubes → 8000 images
Challenges (problems)
No comparison star
Misbehaving dome →vignetting
Defocusing
Reduces the noise due topixel-to-pixel variation
Smooths out the noise due tosky variation
Allows for longer integration ofbright targets
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results PSF model 1 PSF model 2 Fitting
PSF Fitting Photometry
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results PSF model 1 PSF model 2 Fitting
Why?
What
Model the shape of the psf
Fit the model to the data
Calculate flux from the model
Why
PSF spread over a large numberof pixels
Vignetted part can be excluded
But only if the effects due tothe vignetting are confinedLess pixels to fit → increasesscatter
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results PSF model 1 PSF model 2 Fitting
PSF model
PSF model
Center (x ,y)n concentric rings
AmplitudeWidthRadius
Rings
Gaussians
Evaluation of exp is slow!Infinite support
Quartic polynomials
Only multiplicationsLess elegant but fastClipping → finite support
Quartic polynomial
fi(r) = a+4a(r4/4w − r2/2w
)
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results PSF model 1 PSF model 2 Fitting
PSF model
PSF model
Center (x ,y)n concentric rings
AmplitudeWidthRadius
Rings
Gaussians
Evaluation of exp is slow!Infinite support
Quartic polynomials
Only multiplicationsLess elegant but fastClipping → finite support
Amplitude
Center
Width
Quartic polynomial
fi(r) = a+4a(r4/4w − r2/2w
)
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results PSF model 1 PSF model 2 Fitting
PSF model
PSF model
PSF(r) =n
∑i
fi(r)
Flux
F(r) = 2π
∫rPSF(r)dr
F(r) = 2π
∫r
n
∑i
fi(r)dr
F(r) = 2π
n
∑i
∫r fi(r)dr
0 2 4 6 8 10 12 14 16
Flux integration
Flux is a sum of polynomials
Fast, minimizes numerical errors
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results PSF model 1 PSF model 2 Fitting
Fitting
Differential evolution (DE)
Global optimization algorithm
Fast, robust, easy to implement
Price, Storn, and Lampinen(2005)
Implementation
Fortran, Python, NumPy, andPyFITS
Trivial parallelization with MPI
Implementation
Iterative optimization ofparameter space bounds
Increases stability
Performance
0.2 - 0.8 sec/image for the 3ring model (11 free parameters)
Other
Calculates centers of defocusedpsf’s → aperture photometry
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results
Results
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results
PSF fitting example
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results
Final light curve
Hannu Parviainen Defocused PSF-fitting Photometry
Introduction Observations PSF fitting Photometry Results
Thank you!
Hannu Parviainen Defocused PSF-fitting Photometry