# Presentation: 313799

## PreCam Update: SimulationsDouglas Tucker, DES-Calib Telecon, 28 Jan 2008

- Courtesy:  NOAO/AURA/NSF

- UM Curtis-Schmidt

- SMARTS 1m

- SMARTS 1.5m

- SMARTS 0.9m

- Blanco 4m

## PreCam:  Description

- Courtesy:  NOAO/AURA/NSF

- M48 on UM Curtis-Schmidt + Tek2k#5
- FOV:  1.3 deg (2.3 arcsec/pixel)
- 30 sec each in *g*, *r*, *i*

- Credit:  J. Allyn Smith; see Rider et al. (2004)

- For baseline instrument:
- FOV of 1.6o x 1.6o (2.69 sq deg) for baseline instrument at a pixel scale of 1.4 arcsec/pixel
- 1860 fields to cover 5000 sq deg
- At 600 sec per field (see Table), it would take 372 hours, or about 47 nights, to perform a single-pass PreCam Survey in all 5 DES filters

- Baseline instrument:
- 	2x2 mosaic of DECam 2k x 2k CCDs
- Possible upgrades:
- 2x3 mosaic
- DECam 2k x 4k CCDs
- If yield is high enough

**Baseline PreCam Survey Magnitude Limits**

## PreCam:  Benefits to DES (I)(see DES-doc-2373 for more)

- Courtesy:  NOAO/AURA/NSF

- The baseline PreCam Survey -- a single-pass survey of the full DES footprint in all 5 DES filters down to *i*≈18 -- would yield a catalog of several million bright stars calibrated in the DES *grizY* photometric system (typically hundreds per DECam CCD).
- If the PreCam Survey can achieve:
-  5% global relative calibrations (easy), the PreCam star catalog would be useful for “quick look” diagnostics of the DECam data.
- 2% global relative calibrations (do-able), the PreCam star catalog could:
- Start to be used as extinction standards, supplementing the SDSS Stripe 82 standards and the Smith et al. Southern *u’g’r’i’z’* standards (could reduce the amount of time needed for observing standard stars during twilight and/or during middle of night)
- Be used for a robust determination of the transformation relations between the SDSS and DES photometric systems
- Be used as initial *Y*-band standards (see 1b(i))
- <1% global relative calibrations (very challenging), the PreCam star catalog could be used as local standards over the entire DES footprint, obviating the need for observing standard stars during twilight or during the middle of the night
-  All DES twlight observations could be reserved for *z-* and *Y*-band science observations
- This would effectively increase the amount of time for science observations by 1 hour per night, thus increasing DES observing efficiency by about 10%.

## DES Survey Strategy Simulationsby Jim Annis

- Courtesy:  NOAO/AURA/NSF

- DES Simulation T1/A: tileMap-2012.gif

## DES Survey Strategy Simulationsby Jim Annis

- Courtesy:  NOAO/AURA/NSF

- Simulation T1/A: g-band

- Day

- Airmass

## PreCam Extinction Study Simulations:  Toy Model

- Courtesy:  NOAO/AURA/NSF

- Assume each PreCam field has a systematic calibration error
- The accepted magnitudes of all stars in a given PreCam field are all offset by some amount
- Assume that this calibration error is random and Gaussian, with =...
- 0.05mag (easy)
- 0.02mag (do-able)
- 0.01mag (challenging)
- Use the PreCam fields to fit a photometric equation of the form:
- 		 *m**inst** - m**accepted** = a + k*X*
*where **a** = photometric zerpoint, **k**=first order extinction, **X**=airmass*
- Fit the above photometric equation during a DES night using all airmasses *X* from for DES science exposures for that night as tabulated in Jim’s simulations.
- Calculate and plot residuals

## PreCam Extinction Study Simulations:Default (Stripe 82 alone, No PreCam)

- Courtesy:  NOAO/AURA/NSF

- Observe Stripe 82 fields at 3 different airmasses at evening and morning twilight and once in the middle of the night

- (Stripe 82 field-to-field errors ~ 0.01mag)

## PreCam Extinction Study Simulations :PreCam (0.05mag Errors)

- Courtesy:  NOAO/AURA/NSF

- mean still
- comparable due to large # of observations

- Hard to see any trends though

## PreCam Extinction Study Simulations:PreCam (0.02mag Errors)

- Courtesy:  NOAO/AURA/NSF

- mean gets better

- Trends at 0.02 mag level would become noticeable

## PreCam Extinction Study Simulations:PreCam (0.02mag Errors)

- Courtesy:  NOAO/AURA/NSF

- mean gets better

- Trends at 0.02 mag level would become noticeable

- Pat Seitzer already achieves
- 2% photometry on the
- Curtis-Schmidt without any special effort.

## PreCam Extinction Study Simulations:PreCam (0.01mag Errors)

- Courtesy:  NOAO/AURA/NSF

- mean gets even better

- Trends at 0.01 mag level would become noticeable

## PreCam Extinction Study Simulations :PreCam (0.02mag Errors)

- Courtesy:  NOAO/AURA/NSF

- Small number of observations in this filter

- Some nights have only a few obs.
- in a given filter, yielding relatively poor mean

## PreCam Extinction Study Simulations :PreCam (0.02mag Errors) + Stripe 82

- Courtesy:  NOAO/AURA/NSF

- Supplement with twilight observations in Stripe 82 to get better mean

## Extra Slides

- Courtesy:  NOAO/AURA/NSF

## PreCam Extinction Study Simulations

- Courtesy:  NOAO/AURA/NSF

## PreCam Extinction Study Simulations:PreCam (0.05mag Errors) + Stripe 82

- Courtesy:  NOAO/AURA/NSF

## PreCam Extinction Study Simulations:PreCam (0.02mag Errors) + Stripe 82

- Courtesy:  NOAO/AURA/NSF

## PreCam Extinction Study Simulations:PreCam (0.01mag Errors) + Stripe 82

- Courtesy:  NOAO/AURA/NSF

## PreCam Extinction Study Simulations:  Toy Model

- Courtesy:  NOAO/AURA/NSF

- minst - mtrue = a + k*X
- Assume fixed values for a, k, and mtrue
- Assume the values for mtrue have Gaussian errors (due to PreCam field-to-field systematics) of
- 0.05 mag (easy)
- 0.02 mag (do-able)
- 0.01 mag (challenging)
- Calculate minst, assuming zero measurement errors (due to beating down the statistical errors due to the 100’s of stars per DECam chip)
- Do above for all airmasses X from a night as tabulated in Jim’s simulations.
- Fit for a and k
- Calculate residuals