SpectroPhotometric Calibration of MicroChannel Plate UV Detectors using White Dwarf Data

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Spectro-Photometric Calibration of Micro-Channel
Plate UV Detectors using White Dwarf Data (Flux
and Wavelength Calibration of UV Spectra)
by Mudit K. Srivastava Under the guidance of
Dr. Norbert Kappelmann
Inter-University Centre for Astronomy and
Astrophysics (IUCAA), India
13th June 2008 COSPAR Capacity Building Workshop
- 2008 Kuala Lumpur, Malaysia
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Introduction

• White Dwarfs as Flux Standard due to

• Nearly Featureless Spectra

• Virtually pure Hydrogen atmosphere Easy to
  model

• Enough Bright Good SNR in short integration
  time

• Negligible interstellar extinction

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Introduction

• White Dwarfs as Flux Standard due to

• Nearly Featureless Spectra

• Virtually pure Hydrogen atmosphere Easy to
  model

• Enough Bright Good SNR in short integration
  time

• Negligible interstellar extinction

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Introduction

• White Dwarfs as Flux Standard due to

• Nearly Featureless Spectra

• Virtually pure Hydrogen atmosphere Easy to
  model

• Enough Bright Good SNR in short integration
  time

• Negligible interstellar extinction

• Objectives (1.) Flux Calibration of the
  observed (wavelength calibrated )UV Spectra of
  G191-B2B using White Dwarf model.

(2.) Reduction and Wavelength Calibration of
the Spectra of star HD93521 using reference data
from Barnstedt et al, AAS, 2000, 143, 193
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Introduction..

• ORFEUS (Orbiting and Retrievable Far and Extreme
  Ultraviolet Spectrometer) Telescope, with Echelle
  Spectrograph, during Nov/Dec 1996.

• Echelle Grating

• Diffraction Order 40 to 61

• Wavelength range 900-1400 Angstroms

• Resolution 10000

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Introduction..

• ORFEUS (Orbiting and Retrievable Far and Extreme
  Ultraviolet Spectrometer) Telescope, with Echelle
  Spectrograph, during Nov/Dec 1996.

• Echelle Grating

• Diffraction Order 40 to 61

• Wavelength range 900-1400 Angstroms

• Resolution 10000

L

S

Order 40
Order 61
Echelle Spectra of HD93521

• Overlapping of Spectra near edges.

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Reduction and Wavelength Calibration of HD93521

• Archival raw data is used

• Reduction

• Identifying each spectral order

• Determination of 'number of counts' in a
  'slit' of 1X7 pixels centred at the peak of the
  spectrum

• Estimation and subtraction of background

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Reduction and Wavelength Calibration of HD93521

• Archival raw data is used

• Reduction

• Identifying each spectral order

• Determination of 'number of counts' in a
  'slit' of 1X7 pixels centred at the peak of the
  spectrum

• Estimation and subtraction of background

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Wavelength-calibration..

• Wavelength Calibration

• Identifying a pixel with a wavelength

• Reference Spectra is used to identify lines in
  each spectral order

• Wavelength at each Pixel is estimated through
  linear interpolation/extrapolation.

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Wavelength-calibration..

• Wavelength Calibration

• Identifying a pixel with a wavelength

• Reference Spectra is used to identify lines in
  each spectral order

• Wavelength at each Pixel is estimated through
  linear interpolation/extrapolation.

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Wavelength-calibration..

• Wavelength Calibration

• Identifying a pixel with a wavelength

• Reference Spectra is used to identify lines in
  each spectral order

• Wavelength at each Pixel is estimated through
  linear interpolation/extrapolation.

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Flux Calibration of G191-B2B

• Archival Wavelength Calibrated data is used

• Flux Calibration Convert y-axis (counts) into
  Flux by removing all the instrumental effects

e.g. Grating response near the edges of the
spectra
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flux-calibration..

• Grating response could not be removed as 'flat
  fields' were not available.

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flux-calibration..

• Grating response could not be removed as 'flat
  fields' were not available.

• Model Spectrum is used to flux Calibrate the
  reduced spectra.

• Model Spectrum is fit to the combined reduced
  spectrum (of all orders) using chi square
  minimization.

• A conversion factor is obtained to calibrate the
  input spectrum.

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flux-calibration..

• Results

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flux-calibration..

• Results

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flux-calibration..

• Results

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Thank you