SNAP Calibration Program WBS 2'5 and WBS 3'2'8

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SNAP Calibration Program WBS 2.5 and WBS
3.2.8

• Susana E. Deustua
• American Astronomical Society
• 9-11 July 2002

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Calibration Overview

• Calibration Components
• RD Goals
• Calibration Pipeline
• Spectrophotometric (color) Calibration
• Requirements
• Calibration Methodology
• Calibration Status
• RD Trade Studies
• RD Manpower
• RD Schedule
• RD Budget

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From the last review
This has been, and is being, done as a monte
carlo simulation and requirements have been
relaxed.
A draft calibration plan now exists.
We have already begun identifying experts.
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This is part of the overall strategy.
The instrument and calibration team is aware of
this issue.
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Calibration Components

• Astronomical
• absolute color calibration
• spectrophotometric flux standards
• photometric zeropoints
• for each filter/detector
• flat fields

• Instrument-level
• detector
• linearity, stability
• optics
• wavelength response
• wide field effects
• changes with time, attitude
• spectrograph
• shutter
• speed, timing
• develop diagnostics

Calibration error budget delivers the accuracy of
the photometric solution for each observation
depends on instrument configuration and
performance (OTA Filter Focal Plane Array, OTA
Spectrograph Detector(s))
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Calibration RD Goals

• Trade studies on
• calibration standards
• optimal telescope platforms
• cost-benefit analysis
• standard star network
• Develop SNAP on-board calibration observing
  program
• Study impact of on-board calibration on
• observatory management
• observing strategy, hence SN program
• observatory design
• Design spectrophotometric calibration experiment
• Develop realistic time, cost and manpower
  estimates for calibration program

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Calibration Pipeline WBS 3.2.8

• WBS 3.2.8 Calibration Pipeline
• 3.2.8.1 Image Processing Products
• 3.2.8.2 Spacecraft environmental effects
• Diagnostic Tools
• 3.2.8.3 Calibration Database
• 3.2.8.4 Pipeline Deliverables
• Interface Control Documents (ICD)
• Database
• Instruments
• Image processing

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Simulation
Focal Plane Array
Spectrograph
Calibration
Ground System
Telescope
Operations
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Calibration Pipeline Image Processing

• Image Processing Files
• Imaging Needs
• Bias and dark current constants
• Flat fields
• Photometric zeropoint determination
• Spectroscopy Needs
• Bias and dark current
• Flat fields
• Wavelength calibration
• Spectroscopic standard flux
• Each file (data and processing) needs to carry
• time stamp
• spacecraft position, etc
• detector ID, status etc.

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Calibration Pipeline Instrument Performance

• Time stability
• observing cadence for acquisition of calibration
  data
• e.g. flat fields for each filter
• in-flight calibration diagnostics
• e.g. repeated observations of stars in SNAP
  fields
• Impact of calibration hardware on instrument
  design
• precise shutter
• flat field lamps
• wavelength calibration lamps
• These are standard concerns for telescope systems.

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Calibration Pipeline Archive

• Calibration database
• stores all image processing products
• tracks changes in calibration products with time
• may be subset of the science image/data archive

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Calibration Pipeline RD Deliverables

• Interface Control Documents (ICD) for
• Calibration Database and Archive
• Instrument performance
• Spacecraft environment
• Diagnostic tools
• Image Processing
• Pedestal (bias) and dark current constants
• Flat field constants
• Zeropoint determination
• Spectrophotometric flux standard comparison

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Spectrophotometric Calibration WBS 2.5

• WBS 2.5 Spectrophotometric Calibration
• 2.5.1 Define Color Calibration Requirements
• 2.5.2 Color Calibration RD
• 2.5.2.1 Artifical Point Sources Trade Studies
• 2.5.2.2 Platform Trade Studies
• from the Ground
• from Space
• with Balloons
• with Mixed Platforms
• 2.5.2.3 Cost-Risk-Benefit Analyses
• Number of Transfers
• Systematic effects
• Achievable Precision
• Selection of Calibration Platform
• Selection of optimal instrument concept
• 2.5.3 Standard Stars Network
• 2.5.4 RD - Deliverables

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Spectrophotometric Requirements

• Primary driver is the measurement of the light
  curve at peak brightness of Type Ia Supernova
• with redshifts to z1.7
• across the wavelength range of 350 to 1700 nm
• from 19th to 25th magnitude dynamic range of
  250
• To yield errors on the dark energy equation of
  state parameters w0 to 0.05 and w to 0.3 or
  better
• Desired for other space and ground programs
• NGST faint standard stars, to thermal IR
• Gemini faint standard stars, to mid IR
• possible opportunity for collaboration with
  astronomical community
• Dont need to know the absolute flux, but do need
  to know the absolute color aka spectral shape.
• Use full monte carlo equivalent to color
  calibration of 2 in optical (U-Z), 3 in NIR
  (Z-H), and 4 connecting the two (Zopt Znir).

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Spectrophotometric Requirements
Vega Spectrum
B-band and redshifted B-band filters
z0 Type Ia SN spectrum at maximum z1.4 Type Ia
SN spectrum at maximum
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Color Calibration Methodology

• The instrument sensitivity, sins(?) is a function
  of stel, sopt and sdet, and can be determined
  through direct comparison with a light source
  whose output is known.
• where F(?) is the flux of a known light source
  (ergs cm-2 s-1 Å-1) and R is the response in
  counts.
• The zeropoint (in units of magnitude) of an
  instrument system is determined through
  observations of spectrophotometric standard
  stars, which have previously been calibrated.
• Valuable for other ground and space based programs

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Steps to Spectrophotometric Calibration

• Establish bright primary standard stars
  calibrated
• with NIST light sources 0th magnitude
• e.g. Oke Schild (1970), Oke Gunn (1983),
  Hayes Latham (1975),
• against models 12th -14th mag.
• e.g. Bohlin Colina (1997, 1994), Bohlin,
  Dickinson Calzetti (2001)
• into the NIR (out to 1.7 microns)
• .e.g. Witteborn, Cohen et al (1999)
• Establish secondary stars and transfer
  calibration to fainter stars in 5 magnitude
  steps with the following criteria
• Wide color range
• Several dozen stars per step
• Using standard methods - eg , Landolt, SDSS
• Calibrate instrument(s) from 350 nm to 1700 nm
• photometric accuracy requirement of 2, similar
  to SDSS
• 3 in u, z, 1.5 in g,r,i Smith et al 2002
• verify past 1 micron

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Current Status

• Instrument concepts for calibration developed
• telescope, spectrograph, detectors
• Observing programs identified
• for primary stars space, balloon
• for secondary to nth stars space, ground
• Study of calibration experiments begun
• identification of calibrated light sources
• primary standard stars study
• identification of trade studies
• Error budget analysis started
• monte carlo studies of
• transfer errors from NIST light source to stars
• errors in star-to-star transfer
• Building experienced calibration team
• Draft calibration strategy

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Current Status Instrument Concepts
telescope instruments

• Pros
• fills telescope aperture
• delivers NIST traceable spectral irradiance
  distribution

• Pros
• adapts to any telescope, 1- 4 meter class
• NIST traceable

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Current Status Calibration Steps
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Current Status Solar Spectral Irradiance
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Current Status White Dwarfs
UV optical okay, need to extend to NIR
figures from R. Bohlin
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First Calibration Error Study

• Figure shows the errors assuming calibration is
  directly against a blackbody -- ie. no transfers,
  no systematics.
• 68 confidence level contours
• Errors increase by 20 with respect to no error
  case (black contours)

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Transfer Errors HZ43

• First study of a NIST light source to 13th
  magnitude white dwarf
• primary calibration at balloon altitude, ,
  transfer using two telescopes
• monte carlo realization
• errors are 1.3 in color

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Color Calibration RD Trade Studies Artificial
Point Sources

• Attenuation of bright sources
• Geometry Key issue for precision calibration is
  to simulate distant star using a bright light
  source.
• Attenuation Conceptual design of calibration
  instrumentation to achieve desired attenuation
• Flux Irradiance x geometry/distance2
• Selection of Standard Calibrator
• WD, KIII giants, Sun
• impact on spacecraft design and operation
• NIST traceable sources
• lamp (stability?,operating environment? physics)
• LEDs (wavelength ranges? stability?)
• Blackbody furnace (the gold standard,
  expensive, physics?)
• synchrotron light source (ground only?)

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Color Calibration RD Trade Studies Calibration
Platforms

• Calibration Platform Studies
• Pros and cons of calibration program
• From the ground with existing and/or new
  facilities
• pro stable, accessible
• con systematics due to atmosphere, affects NIR
• In space space shuttle, space station, rocket
• pro accessible
• con long lead time
• With balloons at high earth altitude
• pro above H2O
• con pointing stability concern
• Using mixed platforms ground/space,
  ground/balloon etc.
• pro existing facilities
• con transfer systematics

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Color Calibration RD Trade Studies
Cost-Benefit-Risk Analyses

• For each platform need to understand
• Optimal calibration instrument concept
• Number of Transfers
• Systematic effects
• Understand and account for sources of systematic
  errors between bright stars and NIST light source
• Level of systematic errors in transference from
  primary stars to 20th mag. standards
• linearity of detectors how linear is linear?
  faint target objects bright standard stars
• background dependence
• bright standards against no background (short
  exposure) vs. faint target against high
  background (long exposure)
• shutters, etc.
• Achievable Precision

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Color Calibration RD Trade Studies Network of
Spectrophotometric Standards

• Selection of Spectrophotometric Standard Stars
• Primary Standard Stars
• spectral types
• Hot White Dwarf HZ43
• Solar Analogs
• K0III
• fields
• Secondary through Nth Standard Stars
• select from catalogs, e.g. Sloan Digital Sky
  Survey
• magnitude
• spectral types
• spectral colors
• fields equatorial, SNAP
• monitoring program for variability, companions
• Final selection of Spectrophotometric Standards

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Calibration RD Manpower

• Calibration team has expertise in
• space instrumentation
• astronomical calibration
• establishment of spectrophotometric standard star
  networks
• astronomical spectroscopy and imaging
• astronomical data reduction and analysis
• supernova observations
• instrument calibration
• Expect additions to team over next two years

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Calibration RD Schedule
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Calibration Deliverables
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Spectrophotometric Requirements

• In an ideal universe, a supernovas magnitude is
  
• Thus errors on the observed magnitude, m(z, ?m,
  ??, w0 , w) are
• To put an SN datum on a Hubble diagram, the
  observed magnitude must be corrected for
• photometric error
• extinction due to dust

minimize and identify errors
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Current Status Instrument Concepts

• Instrument concept for balloon based primary
  calibration

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SDSS Photometric Accuracy

• The official accuracy on the SDSS photometry is a
  combination of several things, but the final
  values are
• lt2 at r, (g-r), and (r-i)
• 3 at (u-g) and (i-z).
• To achieve that, the standard star system is
• lt1 at g,r,i and
• lt1.5 at u,z.

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First Calibration Error Study

• Figure shows the errors assuming calibration is
  directly against a blackbody -- ie. no transfers,
  no systematics.
• 68 confidence level contours
• Errors increase by 20 with respect to no error
  case (black contours)

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First Calibration Study
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First Study Calibration Errors Propagated

• Calibration bias from a temperature error in a
  blackbody translates directly into error in the
  distance modulus (black line).

relative
wavelength

• A bias in the calibration translates into a bias
  in color. Extinction correction can reduce
  distance-modulus bias by an order of magnitude.