# Presentation: 797329

## Instrument Observation Strategy

**Chris Bebek**
**Lawrence Berkeley National Laboratory**
**10 July 2002**

## Photometry illustration

**Photometry illustration**

- Wavelength

- Flux

- U        B        V        R

- Color:
- K correction1
- Photo z
- Classification2

- 1+z spaced B-band filters

- 1A. Kim
- 2J. Lamoureux

- Light curve S/N requirements

- B

- ~V

- ~R

## Spectroscopy illustration

**Spectroscopy illustration**

**SII “W”**

**SiII**

**Metallicity**

## Fixed filter concept

- Note the ability to weight integrated exposure time in a particular filter.

## Focal plane gymnastics

## Focal plane concept

**Focal plane concept**

## Repetitive program
Step the focal plane through the observation field.
N steps in each CCD filter; 2N steps in each HgCdTe filter.
Fixed length exposures determined by a shutter.
The multiple exposures per filter are used
to implement dithering/drizzle;
to eliminate cosmic ray pollution.
S/N assists
NIR filters have twice the area of visible filters
time dilation gives more points on the light curve for increasing z.
All stars see all filters (modulo scan field edge effects).
Fields revisited with fixed cadence, 4 days.
SNe automatically discovered and their evolution followed for 100’s of days.

- Step the focal plane through the observation field.
- N steps in each CCD filter; 2N steps in each HgCdTe filter.
- Fixed length exposures determined by a shutter.
- The multiple exposures per filter are used
- to implement dithering/drizzle;
- to eliminate cosmic ray pollution.
- S/N assists
- NIR filters have twice the area of visible filters
- time dilation gives more points on the light curve for increasing z.
- All stars see all filters (modulo scan field edge effects).
- Fields revisited with fixed cadence, 4 days.
- SNe automatically discovered and their evolution followed for 100’s of days.

**Observation concept**

## Observation concept

**Observation concept**

**Targeted program**
- SNe candidates are scheduled for spectrographic measurement near peak luminosity.
- Light curve and color analysis done on ground to identify Type Ia and roughly determine *z*.
- Note peak luminosity is 14 days to 40 days after discovery for *z *= 0.3 and 1.7 respectively.
- Star is steered into spectrograph port.
- Imager exposures can be taken during spectroscopy albeit with longer exposure times and non-standard orientation to the observational fields.

## Signal-to-noise

- Input
- SNe luminosity as a function of z and epoch.
- Zodiacal background
- Detector specs
- Sum noise and signal over 4 effective pixels
- Solve for S/N
- Vary exposure time
- Number of exposures.
- Find 300 s exposures with 4 in the CCDs and 8 in the HgCdTe meet S/N requirements.

## SNe flux

- CCD
- HgCdTe

## Zodiacal background light

## Imager Sensors Specs

|  | Visible | NIR | Units |
| --- | --- | --- | --- |
| FOV | 0.34 | 0.34 | deg2 |
| Plate scale (nominal) | 0.10 | 0.17 | asec |
| Wavelength | 350-1000 | 900-1700 | nm |
| <Quantum efficiency> | 80 | 60 | % |
| Read noise
(multiple reads) | 4 | 5 | e |
| Dark current | 0.002 | 0.02 | e/s/pixel |
| Filters 
(1+z spaced B-band) | 6 | 3 |  |
| Read time time. | 20 | 20 | s |

## S/N achieved

**S/N>30**

**S/N>30**

**S/N>20**

**S/N>15**

**S/N>10**

**S/N>3**

**Requirement**

- mag attenuation

## SNe yield

- Input
- Spectroscopy time as a function of z
- SNe production rate
- Focal plane scan strategy
- 4 day cadence
- Time allocation: 60% photometry, 40% spectroscopy
- Plot SNe yield per year in 0.1 z bins

## Spectrograph Sensors Specs

|  | Visible | NIR | Units |
| --- | --- | --- | --- |
| Wavelength  coverage | 350-980 | 980-1700 | nm |
| Plate scale | 0.15 | 0.15 |  asec |
| Spatial resolution | 0.15 | 0.15 |  asec |
| Field-of-View | 3 x 3 | 3 x 3 | asec2 |
| Resolution | 100 | 100 |  |
| <Quantum  Efficiency> | 80 | 60 | % |
| Read Noise | 2 | 5 | e- |
| Dark  Current | 0.001 | 0.02 | e-/s/pixel |

- With these specs, total integration time (w/ 1000 s exposures) is

## SNe production rate

## SNe yield

- SNe discovered
- SNe w/ spectroscopy

- 2200 SNe discovered in 7.5 sq. deg.
- 1600 w/ spectroscopic follow-up

## Summary

- This tool can be turned around by fixing the S/N at a particular z and fixing the exposure time and number of exposures to establish margins on detector performance specs.
- Better left to advanced modeling and simulation tools that make use of light curve fitting – note, the study shown synthesizes S/N points on the light curve at the required epochs.
- This Excel spreadsheet study is superceded by
- Fisher matrix approach of Gary Bernstein
- SNAP simulators
- The simulator is best used for the specification margining to establish detector goals and requirements.