# Presentation: 868699

## Calibration Program

- Susana E. Deustua
- American Astronomical Society
- 12 November 2003

## Science Driver:  w and w(z)

- To standardize SNe, we need to know
- the **RATIO** of SNe fluxes in any two filters:  e.g. **f****B****/f****J**
- this is equivalent to the **COLOR**:  e.g. **B-J = -2.5 log f****B****/f****J**
- But not the absolute flux.

- B-band filter

- z=0 Type Ia SN

- z=1.4 Type Ia SN

- redshifted B-band filter

## Science Driver	

- The science requires observations of nearby and distant SNe Ia.
- At redshift z=0,
- SNe Ia restframe B-band flux is measured in a B filter
- SNe Ia are bright at peak, m~19 mag
- At high redshifts, e.g z=1.4
- SNe Ia restframe B-band flux shifted to longer wavelengths, e.g. is observed in J filter.
- SNe Ia are faint at peak, m~25 mag
- To standardize SNe, we need to know
- the flux **RATIO** in any two filters:  e.g. fB/fJ
- this is equivalent to the **COLOR**:  e.g. B-J = -2.5 log fB/fJ
- The problem to solve is how to accurately measure the ratio for faint objects, and in the near infrared (NIR).
- Do not need to know the absolute flux, just the slope.

## Elements

- Standard stars are bright
- Science targets are faint
- Spectral energy distribution of SNe are different than stars
- Need multiple band pass measurements
- For high precision need lots of flux at all wavelengths
- Ideal:  one very bright blackbody because it covers the entire wavelength span

## Science Driver: w0 and w

*What effect does calibration error have on the uncertainty in w****0**** and w********?*
- Assuming uncertainty solely in the temperature of the calibrator:
-  A single calibrator gives rise to a negligible increase in systematics: the extinction correction effectively corrects for a one-parameter miscalibration.
- B) Two calibrators: at T=35000 and at T=6000, calibrating different wavelength regimes.  The uncertainty in w**0** and w**** increases by ~ 20% for temperature errors ~ 3%.
- If there is miscalibration of the spectra (i.e. mismatch in the overlap region) this is inferior to a single star spanning the entire spectral range.
- The simulations specify color_ _calibration of 2% in optical, 3% in NIR with 4% miscalibration.

- A)

- B)

- w**0**

- w**1**

- w**1**

##      Methodology                        Approach

- The instrument sensitivity, sins() is a function of *s*tel, *s*opt and *s*det, and can be determined through direct comparison with a calibrated light source. F() is the flux of a known light source (ergs cm-2 s-1 Å-1) and C is the counts at the detector.
- 	if s() is a constant, s, in a given bandpass, Δ this simplifies to s=Counts/Flux

- Use a calibrated light source
- On the ground:
- NIST traceable light source
- In space
- Fly a blackbody
- Use calibrated, stable, astrophysical sources

##        Methodology                        Approach

- The photometric zeropoint sets the brightness scale of the instrument system in a given bandpass.
- 	It is determined by observations of calibrated, spectrophotometric standard stars which allows conversion
- from counts to magnitudes
-  or counts to flux units

- Use many stars
- Range of spectral energy distributions (colors)
- Calibrated with reference to a light source
- Measure each star with each instrument
- Imager
- Each Filter + detector
- Spectrograph
- Each Slice + detector

## Current State of Calibration

**Current State of Calibration**

- From the Ground:
- Sloan Digital Sky Survey (u,g,r,i,z to 23rd mag)
- 30 filters + CCDs
- Goal: photometric accuracy 2% in magnitudes and colors with errors in primaries of 1.5% at *u, *1% in *g*, *r*, *i*  &1.5% in *z, relative to F subdwarf BD +17°4708*
- Results:  3% in u’, z’, 1.5% in g’,r’,i’ (Smith, Tucker, Kent, Richmond et al. 2002 AJ 123, 2121) using 158 stars.
- 2MASS (J <15.8, H < 15.1, Ks< 14.3)
- 3 filters + HgCdTe
- Goal:  Photometric precision <5% for point sources with SNR >20, Repeatability 5-10%
- Results:  Observation of set of stars relative to Kurucz model of Vega is 1.6%, 1.7% and 1.7% (Cohen, Wheaton and Megeath 2003) using 33 stars
- Measurement precision is 0.01 – 0.02 mag
- UKIRT, faint JHK *magnitude* standards (K = 9.5 to 14),
*Internal* (repeatability) errors for K are < 0.005mag

## Current State of Calibration

- Space-based
- Hubble Space Telescope
- Multiple instruments:  WF/PC, WF/PC2, STIS, ACS and filters
- STIS:
- Goal: 5% imaging and spectrographic photometry (UV & optical)
- Achieved ~1% optical (Bohlin, 2002 HST Calib. Conference) referenced to stellar atmosphere models of hot white dwarfs
- ACS:
- Goal:  WFC 3%, HRC 2%, SBC 5% limited by absolute calibration of flux standards
- NICMOS:
- Goal:  near infrared imaging 2-4 % photometric zeropoint (relative) but awaits observations of standard stars.
- Bohlin, Dickinson, and Calzetti (2001, AJ, 122, 2218).
- IRAS & SIRTF are not relevant (too far in the IR)
- Bottom line:  SNAP calibration specs are in the ballpark of these efforts.
- => achievable.

## The challenge 1

- Targets range over a wide range of brightness and so do the standard stars

## The challenge 2

- 4 3x3 HgCdTe arrays
- 4 3x3 CCD arrays each with 4 filters
-  = 36+4x36 = 180 filter + detector combinations
- 12 each: NIR (e.g.  J, H, K-like)
- 24 each: Optical (e.g. U, B, V, R, I, Z)
- Effects filter shifts, stellar type.
- 2-channel integral field spectrograph
- 2 optical and 2 NIR detectors

- Guider
- HgCdTe

- Spectrograph
- Spectr. port

- CCDs

## Lifetime frequency 

- Calibration starts before launch and ends with de-orbiting
- fundamental calibration of one or more stable stars can be done once
- identification of spectrophotometric standards should occur ahead of time
- measurement/observation of standards is continuous, ongoing operation because
- systems change
- detectors change:  heat up/cool down, charge transfer inefficiencies, cosmic ray hits,
- filters change:  bandpass shifts, transmission changes
- optics may change:  focus drifts, outgassing
- more frequently obtain
- flat fields, dark frames, bias frames
- once in a while
- astrometrical calibration obtained after launch and periodically checked
- to catalog positions of sources
- determine geometrical distortions:  due to e.g. varying spatial scale over focal plane, offsets in chip surfaces/tilts

## Steps to Spectrophotometric Calibration

- Establish calibrated fundamental flux standards
- In the optical and near infrared to about V~12 mag.
- tied to MKS calibration scale
- Establish primary spectrophotometric stars,
- transfer calibration from fundamentals
- used for optical and near infrared
- White Dwarfs, Solar Analogs  to 16 to 18 mag
- hot OV to cool MIII to ~19.5 mag
- may be in SNAP fields,
- Establish secondary stars in SNAP fields,  transfer calibration
- To fainter stars, m > 19.5  mag
- With wide color range
- Calibrate instrument(s) from 350 nm to 1700 nm
- flat fields, filter function etc
- Science measurements

## SNAP Spectrophotometric Calibration

**Standards**

**SNAP Science**
**Measurements**

**Fundamental**
**Standards**

**Secondary**
**Field**
**Standards**

**Calibrate **
**Instruments**

**Calibration Transfer**

_**Calibration Transfer:**_
**MKS calibration**
** ****Fundamental Standards**
**   ****observed spectroscopically**

-  **Primary Field Standards**
-    **observed spectroscopically**

-  **Primary Field Standards**
-    **observed photometrically**

-  **Secondary Field Standards**
-    **observed photometrically**

**SNAP Spectrophotometric Calibration**

***SNAP Spectrograph required to calibrate fundamentals and transfer calibration to primaries and to imager***
***=>Results in well calibrated spectrograph and imager***

**MKS **
**calibration**

***1***

***3***

***5***

***4***

***2***

## Calibration R&D Plans

**Calibration R&D Plans**

- Identify good calibration standards
- Establish standard star network
- Construct calibration error budget
- (iterative process with simulation and instrumentation teams)
- Investigate optimal telescope platforms:  balloons, space, ground
- Develop pre-launch and in-orbit calibration strategies
- Develop 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
- pre-launch calibration program
- in-orbit when calibration included in observatory management

## Need to Check

- How well are fundamental flux standards calibrated?
- Uncertainties in calibration transfer (“error transfer”)
- from fundamental flux standards to spectrophotometric primaries
- from primaries to secondary standards
- from secondary standards to science targets
- Requirements on flat fields
- Uncertainties introduced by other effects
- filter properties
- position on focal plane
- numbers/types of standards

## Approach

- White dwarf stellar (WD) atmosphere models:  simplest spectra
- Studies of
- of hot (20000 to 60000 K), WD  models
- in the optical concordance is ~1% (cf. Bohlin etal)
- compare to observations in the NIR
- Current work with HST/NICMOS
- NICMOS-3 Observation/Calibration of Faint Spectrophotometric Standards in NIR (0.8-1.9microns) Current HST Spectrophotometric Standards
- G191B2B, GD71 (White Dwarfs)
- P041C, P330E, P177D (Solar Analogs)
- Fainter White Dwarfs and Candidate Solar Analogs from SDSS:  4 White Dwarfs and 6 Solar Analogs (V=11.8-18.8)
- Future work
- Verify physics inputs into models (check with modelers)
- double check NIR standards (e.g. trade study)

***See Ralph Bohlin’s talk during breakout session***

## 1

- Different models are within 1% and less than 2% in the NIR, even in the worst case (for  the hottest white dwarfs)
- Model inputs:  effective temperature and surface gravity obtained from H Balmer lines (Finley), Landolt V-band normalization.  Results:  LTE  non-LTE

***Optical***

***Near Infrared***

***SNAP wavelength range: 350nm to 1.7 microns***

***G1912B***

***HZ43***

***GD153***

***GD71***

## Approach

- White dwarf stellar (WD) atmosphere models:  simplest spectra
- Studies of
- of hot (20000 to 60000 K), WD  models
- in the optical concordance is ~1% (cf. Bohlin etal)
- compare to observations in the NIR
- Current work with HST/NICMOS
- NICMOS-3 Observation/Calibration of Faint Spectrophotometric Standards in NIR (0.8-1.9microns) Current HST Spectrophotometric Standards
- G191B2B, GD71 (White Dwarfs)
- P041C, P330E, P177D (Solar Analogs)
- Fainter White Dwarfs and Candidate Solar Analogs from SDSS:  4 White Dwarfs and 6 Solar Analogs (V=11.8-18.8)
- Future work
- Verify physics inputs into models (check with modelers)
- double check NIR standards (e.g. trade study)

***See Ralph Bohlin’s talk during breakout session***

## Calibration R&D Plans

**Calibration R&D Plans**

- Identify good calibration standards
- Establish standard star network
- Construct calibration error budget
- (iterative process with simulation and instrumentation teams)
- Investigate optimal telescope platforms
- Develop pre-launch and in-orbit calibration strategies
- Develop 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
- pre-launch calibration program
- in-orbit when calibration included in observatory management

## SNAP North Field (SNAP-N)
Perform initial photometric survey down to r=16.5 (and, if possible, down to r=22)
Characterize stellar populations as a function of apparent magnitude down to r=16.5 (and, if possible, down to r=22), based upon the above photometric survey
Find suitable faint (r>16) candidate spectrophometric standard stars and obtain followup spectra for classification
Understand errors in calibration transfer from fundamental to secondary standards
Monitor the field for variables (future)
SNAP South Field (SNAP-S)
choose south field
repeat as for SNAP-N

**Perform initial photometric survey down to r=16.5 (and, if possible, down to r=22)**
**Characterize stellar populations as a function of apparent magnitude down to r=16.5 (and, if possible, down to r=22), based upon the above photometric survey**
**Find suitable faint (r>16) candidate spectrophometric standard stars and obtain followup spectra for classification**
**Understand errors in calibration transfer from fundamental to secondary standards**
**Monitor the field for variables (future)**
- SNAP South Field (SNAP-S)
**choose south field**
**repeat as for SNAP-N**

***More in Allyn Smith’s breakout session talk***

**Establish Standard Star Network**

## SNAP-N Primary Standards

- Currently:
- Candidate White Dwarfs and Solar Analogs for primary standards selected by 5-color photometry from SDSS database.
- Follow up
- Apache Point Observatory 3.5m spectroscopy for spectral type identification.
- Future:
- WIYN 0.9m at KPNO survey of entire SNAP-N field to identify fainter primary and secondary standards
- pilot in 2002/2003, broadband and narrow band search for KIII giants in SNAP-N field.
- KPNO Proposal to use WIYN + Hydra (multi-fiber spectrograph) to identify stars in SNAP-N field using positions from SDSS database. (Limited because SDSS does not cover the north ecliptic pole)

***Allam, Kent, Tucker, Smith,  Mostek, Mufson, Richmond, Deustua***

## SDSS Data in the SNAP North Field

- SDSS Stripe 38 photometry

- O stars -- cyan line
- B stars -- white line
- A stars -- green line
- F stars -- yellow-green line
- G stars -- yellow line
- K stars -- orange line
- M stars -- red line

## SNAP-N Primary Standards

- Currently:
- Candidate White Dwarfs and Solar Analogs for primary standards selected by 5-color photometry from SDSS database.
- Follow up
- Apache Point Observatory 3.5m spectroscopy for spectral type identification.
- Future:
- WIYN 0.9m at KPNO survey of entire SNAP-N field to identify fainter primary and secondary standards
- pilot in 2002/2003, broadband and narrow band search for KIII giants in SNAP-N field.
- KPNO Proposal to use WIYN + Hydra (multi-fiber spectrograph) to identify stars in SNAP-N field using positions from SDSS database. (Limited because SDSS does not cover the north ecliptic pole)

***Allam, Kent, Tucker, Smith,  Mostek, Mufson, Richmond, Deustua***

## SNAP-N Primary Standards

- Currently:
- Candidate White Dwarfs and Solar Analogs for primary standards selected by 5-color photometry from SDSS database.
- Follow up
- Apache Point Observatory 3.5m spectroscopy for spectral type identification.
- Future:
- WIYN 0.9m survey of entire SNAP-N field to identify fainter primary and secondary standards
- pilot in 2002/2003, broadband and narrow band search for KIII giants in SNAP-N field.
- KPNO Proposal to use WIYN + Hydra (multi-fiber spectrograph) to identify stars in SNAP-N field using positions from SDSS database. (Limited because SDSS does not cover the north ecliptic pole)

## SNAP-N Primary Standards

**SNAP-N Primary Standards**

- Identify primary stars in the SNAP northern field
- Magnitude range: V=16-19 within the capabilities of the SNAP spectrograph and imager
- Monitor primary stars for variability on both short and long timescales
- Minimize survey color for field coverage, depth, and repeatability
- Choose one broadband filter to perform majority of the survey
- Observe each field in a second broadband filter only once for photometric solution
- Subsequent observations made only in primary broadband filter; variability through ensemble photometry
- B-R color provides best S/N and efficiency given repeated two band observations
- Final product is a position list of non-variable stars with a range of B-R color, magnitudes, and errors

***Mostek, Mufson, Richmond***

## SNAP North Field Coverage

** **

**SNAP North Field Coverage**

- 6.5°

- 1.2°

## Issues to be determined...

**Issues to be determined...**

- Trade studies with color bands, repeatability, and field coverage
- How many primaries required? One per detector somewhere in the SNAP survey?
- Optimal observing sequence in the course of a run?
- Observing cadence of weeks – months sufficient to catch most variability? Are years required?

## Calibration R&D Plans

**Calibration R&D Plans**

- Identify good calibration standards
- Establish standard star network
- Construct calibration error budget
- (iterative process with simulation and instrumentation teams)
- Investigate optimal telescope platforms
- Develop pre-launch and in-orbit calibration strategies
- Develop 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
- pre-launch calibration program
- in-orbit when calibration included in observatory management

## Calibration Error Budget Framework

**Color **
**calibration**

**Zero point **
**(sets scale) **

**Secondary star field calibration**

**Flatfields**

**Primary standards **
**calibration**

**Aperture **
**corrections**

**Scattered  light**

**Detector **

**Telescope **

**linearity**

**intra-pixel **

**Calibration Error Budget Framework**

- How do calibration transfer errors propagate down the network?
- How well do filters+detectors, integral field spectrograph need to be calibrated?

**Optics**

**Filter **

**Imager/**
**Spectrograph**

**band pass shifts**

**non-****uniformity**

## Calibration Error Budget Framework

**Color **
**calibration**

**Zero point **
**(sets scale) **

**Secondary star field calibration**

**Flatfields**

**Primary standards **
**calibration**

**Aperture **
**corrections**

**Scattered  light**

**Detector **

**Telescope **

**linearity**

**intra-pixel **

**Calibration Error Budget Framework**

- How do calibration transfer errors propagate down the network?
- How well do filters+detectors, integral field spectrograph need to be calibrated?

**Optics**

**Filter **

**Imager/**
**Spectrograph**

**band pass shifts**

**non-****uniformity**

## Zeropoint Uncertainties

- Simulation: Transfer calibration from fundamental flux standards to primary calibrators
- Inputs assume:
- fundamentals and primary standards with the SNAP spectrograph and also with the imager
- sources of uncertainty are:
- fundamental standard calibration:
- errors in stellar atmosphere models
- repeatability errors
- errors in the spectrograph per spec.
- S/N
- uncertainties in filter transmission calibration of 2-3%, and angle of incidence to 0.25 degrees, measured in the lab.
- Results are ~1% errors.

***More in S. Mufson’s talk in breakout session***

## White Dwarf Transfer: 19 to 22 mag.

- White Dwarf at m=19

## White Dwarf Transfer: 19 to 22 mag.

- White Dwarf at m=22

## FV star transfer 19 to 22 mag

- F8V at m=19

## FV star transfer 19 to 22 mag

- F8V at m=22

## Filter Passband Shifts

- Simulations of passband shifts to answer: What is the effect of passband shifts on photometry of science targets?
- Assumes range of calibrating stars
- Calculates observed vs. synthetic (true) magnitudes for calibrating stars in a  filter assuming
- pass band is shifted by N angstroms
- different detector positions effect varies with colors of stars, uncertainties < 2%

***Results discussed in Kent’s talk during breakout session***

## At Present

- List of technical reports and papers
*Calibrating SNAP* SPIE Proceedings, submitted August 2003
- Internal memos
- _[http://spiff.](http://spiff.rit.edu/richmond/snap/pipeline/)__[rit](http://spiff.rit.edu/richmond/snap/pipeline/)__[.](http://spiff.rit.edu/richmond/snap/pipeline/)__[edu](http://spiff.rit.edu/richmond/snap/pipeline/)__[/](http://spiff.rit.edu/richmond/snap/pipeline/)__[richmond](http://spiff.rit.edu/richmond/snap/pipeline/)__[/snap/pipeline/](http://spiff.rit.edu/richmond/snap/pipeline/)_
- _[http://mimosa.](http://mimosa.astro.indiana.edu/snap/docs/preliminary_calibration_plan.htm)__[astro](http://mimosa.astro.indiana.edu/snap/docs/preliminary_calibration_plan.htm)__[.](http://mimosa.astro.indiana.edu/snap/docs/preliminary_calibration_plan.htm)__[indiana](http://mimosa.astro.indiana.edu/snap/docs/preliminary_calibration_plan.htm)__[.](http://mimosa.astro.indiana.edu/snap/docs/preliminary_calibration_plan.htm)__[edu](http://mimosa.astro.indiana.edu/snap/docs/preliminary_calibration_plan.htm)__[/snap/docs/preliminary_calibration_plan.](http://mimosa.astro.indiana.edu/snap/docs/preliminary_calibration_plan.htm)__[htm](http://mimosa.astro.indiana.edu/snap/docs/preliminary_calibration_plan.htm)_
- http://mimosa.astro.indiana.edu/snap/cosmosim.html
- _[http://home.](http://home.fnal.gov/~dtucker/snap/pt/)__[fnal](http://home.fnal.gov/~dtucker/snap/pt/)__[.](http://home.fnal.gov/~dtucker/snap/pt/)__[gov](http://home.fnal.gov/~dtucker/snap/pt/)__[/~](http://home.fnal.gov/~dtucker/snap/pt/)__[dtucker](http://home.fnal.gov/~dtucker/snap/pt/)__[/snap/pt/](http://home.fnal.gov/~dtucker/snap/pt/)_
-  Maps of the Cosmos, International Astronomical Union. Symposium no. 216, held 14-17 July, 2003 in Sydney, Australia
- Calibration of the SNAP Program
- Supernova/Acceleration Probe Error Budget
- The SNAP Standard Star Program
- AAS Annual Meetings January 2003, June 2002, January 2002.

## Calibration R&D Plans

**Calibration R&D Plans**

- Identify good calibration standards
- Establish standard star network
- Construct calibration error budget
- (iterative process with simulation and instrumentation teams)
- Investigate optimal telescope platforms
- Develop pre-launch and in-orbit calibration strategies
- Develop 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
- pre-launch calibration program
- in-orbit when calibration included in observatory management

## Calibration R&D Plans

**Calibration R&D Plans**

- Identify good calibration standards
- Establish standard star network
- Construct calibration error budget
- (iterative process with simulation and instrumentation teams)
- Investigate optimal telescope platforms
- Develop pre-launch and in-orbit calibration strategies
- Develop 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
- pre-launch calibration program
- in-orbit when calibration included in observatory management

## Future Studies

- On-board calibration observing program follows standard protocols:
- observing cadence for acquisition of calibration data
- flat fields for each filter
- frequency of fundamental primary standard star observations
- in the spectrograph
- in the imager
- e.g. HST allocated < 10% time to calibration
- development of in-flight calibration diagnostics
- e.g. repeated observations of stars in SNAP fields to check instrument behavior
- Impact of calibration hardware on instrument design
- flat field lamps
- wavelength calibration lamps
- etc.

## Future Studies

- Selection of Standard Calibrator
- Finish studies of model atmospheres
- NIST traceable sources
- Good NIR standards
- Understand uncertainties in “cross-over” between optical and NIR
- Match different detector systems
- Obtain fainter NIR standard stars

## Conclusion

- On track to a Standard Star Network with 2% Optical, 3% NIR color calibration just need to develop SNAP calibration plan
- Best catalog of faint “red-shifted” standards in existence.
- 9 filters plus spectrophotometry
- Suitable for work out to 1.7μ  (z = 1.7)
- Long baseline of variable observations (in the SNAP fields).
- Highest precision faint NIR standards
- Science:  simultaneous space and ground observations of SNe. Better understanding of atmospheric transmission and flux recovery
- Will be useful for
- large ground-based telescopes: GMST, Gemini, etc
- space-borne: JWST, WF3

## Calibration Team

## R&D Milestones

- THE END