7.1 The COS Exposure Time Calculators
To help with proposal preparation, four COS Exposure Time Calculators (ETCs) are available on the STScI ETC webpage:
http://etc.stsci.edu
These calculators model spectroscopic and imaging exposures for both target acquisitions and scientific observations. They estimate count rates for given source and background parameters, and calculate either the signal-to-noise ratio for a given exposure time or the exposure time needed to achieve a desired signal-to-noise ratio. If you have a calibrated spectrum of your source you can upload it to the Exposure Time Calculators. The ETCs warn you if your observations exceed local or global brightness limits (see Table 10.1). The ETCs offer extensive on-line help that provides instructions and explains their calculations.
A unique exposure ID is assigned to each calculation performed by the ETCs, allowing results from previous calculations to be retrieved easily. This number must be included in the appropriate box in your Phase II
proposal to document your work and to facilitate Phase II
review. Proposers are urged to check the COS ETC webpage for any updates or issues related to the COS ETCs before performing ETC simulations.
The spectroscopic ETC can display the input spectrum, a simulated one-dimensional output spectrum, the S/N as a function of wavelength, and the number of counts per resolution element for the selected instrument configuration and source. These outputs can be downloaded in ASCII format. The ETC also computes the BUFFER-TIME
, which is required for TIME-TAG
observations. Scale this value by 2/3 and, following the discussion in Section 5.4, enter it in the Astronomer’s Proposal Tool.
The imaging ETC allows for the selection of either the PSA or BOA and either MIRRORA or MIRRORB. It reports the count rate in the brightest pixel, total counts in the detector, and S/N per resolution element.
The target-acquisition ETCs return the acquisition exposure time to be entered in APT for both imaging and spectroscopic acquisitions. Target acquisition is described in Chapter 8.
-
COS Instrument Handbook
- Acknowledgments
- Chapter 1: An Introduction to COS
-
Chapter 2: Special Considerations for Cycle 29
- • 2.1 COS FUV Detector Lifetime Positions
- • 2.2 Visit Length
- • 2.3 Central Wavelength Settings Added in Cycle 26
- • 2.4 The G285M Grating is Available but Unsupported
- • 2.5 COS Observations Below 1150 Angstroms: Resolution and Wavelength Calibration Issues
- • 2.6 Time-Dependent Sensitivity Changes
- • 2.7 Spectroscopic Use of the Bright Object Aperture
- • 2.8 Non-Optimal Observing Scenarios
- • 2.9 NUV Spectroscopic Acquisitions
- • 2.10 SNAP, TOO, and Unpredictable Source Programs with COS
- • 2.11 Choosing between COS and STIS
- Chapter 3: Description and Performance of the COS Optics
- Chapter 4: Description and Performance of the COS Detectors
-
Chapter 5: Spectroscopy with COS
- • 5.1 The Capabilities of COS
- • 5.2 TIME-TAG vs. ACCUM Mode
- • 5.3 Valid Exposure Times
- • 5.4 Estimating the BUFFER-TIME in TIME-TAG Mode
- • 5.5 Spanning the Gap with Multiple CENWAVE Settings
- • 5.6 FUV Single-Segment Observations
- • 5.7 Internal Wavelength Calibration Exposures
- • 5.8 Fixed-Pattern Noise
- • 5.9 COS Spectroscopy of Extended Sources
- • 5.10 Wavelength Settings and Ranges
- Chapter 6: Imaging with COS
- Chapter 7: Exposure-Time Calculator - ETC
-
Chapter 8: Target Acquisitions
- • 8.1 Introduction
- • 8.2 Target Acquisition Overview
- • 8.3 ACQ SEARCH Acquisition Mode
- • 8.4 ACQ IMAGE Acquisition Mode
- • 8.5 ACQ PEAKXD Acquisition Mode
- • 8.6 ACQ PEAKD Acquisition Mode
- • 8.7 Exposure Times
- • 8.8 Centering Accuracy and Data Quality
- • 8.9 Recommended Parameters for all COS TA Modes
- • 8.10 Special Cases
- Chapter 9: Scheduling Observations
- Chapter 10: Bright-Object Protection
- Chapter 11: Data Products and Data Reduction
-
Chapter 12: The COS Calibration Program
- • 12.1 Introduction
- • 12.2 Ground Testing and Calibration
- • 12.3 SMOV4 Testing and Calibration
- • 12.4 COS Monitoring Programs
- • 12.5 Cycle 17 Calibration Program
- • 12.6 Cycle 18 Calibration Program
- • 12.7 Cycle 19 Calibration Program
- • 12.8 Cycle 20 Calibration Program
- • 12.9 Cycle 21 Calibration Program
- • 12.10 Cycle 22 Calibration Program
- • 12.11 Cycle 23 Calibration Program
- • 12.12 Cycle 24 Calibration Program
- • 12.13 Cycle 25 Calibration Program
- • 12.14 Cycle 26 Calibration Program
- • 12.15 Cycle 27 Calibration Program
- • 12.16 Cycle 28 Calibration Program
- Chapter 13: Spectroscopic Reference Material
- • Glossary