5.3 Valid Exposure Times
The minimum COS exposure duration is 0.1 s (but FLASH=YES TIME-TAG
exposures impose a longer minimum; see Section 5.7.1). The maximum is 6500 s. Between these extremes COS exposure times must be integer multiples of 0.1 s. If the observer specifies an exposure time that is not a multiple of 0.1 s, its value is rounded down to the next lower integer multiple of 0.1 s, (or set to 0.1 s if a smaller value is specified). Exposure times larger than about 3000 s are normally appropriate only for visits with the Continuous Viewing Zone (which is a special requirement that must be requested and justified in the Phase I
proposal) because the visibility period of a typical orbit is ~50 minutes. See the HST Primer for information about HSTʹs orbit and visibility periods.
For TARGET=WAVE
exposures, DEF
(default) must be entered as the exposure time. The value appropriate for the optical configuration will be chosen from a table established at STScI for best performance. At present TARGET=WAVE
flash durations are identical to those given in Table 5.2.
Table 5.2: TAGFLASH
Exposure Durations.
Grating | Central Wavelength (Å) | Flash Duration (s) | Grating | Central Wavelength (Å) | Flash Duration (s) |
---|---|---|---|---|---|
G130M | 1055 | 142 | G225M (cont.) | 2339 | 12 |
1096 | 52 | 2357 | 12 | ||
1222 | 52 | 2373 | 22 | ||
all others | 12 | 2390 | 7 | ||
G160M | all | 12 | 2410 | 7 | |
G140L | all | 7 | G285M | 2617 | 12 |
G185M | 1786 | 12 | 2637 | 12 | |
1817 | 12 | 2657 | 7 | ||
1835 | 12 | 2676 | 22 | ||
1850 | 22 | 2695 | 22 | ||
1864 | 32 | 2709 | 12 | ||
1882 | 17 | 2719 | 7 | ||
1890 | 12 | 2739 | 7 | ||
1900 | 22 | 2850 | 22 | ||
1913 | 17 | 2952 | 7 | ||
1921 | 12 | 2979 | 17 | ||
1941 | 12 | 2996 | 17 | ||
1953 | 17 | 3018 | 22 | ||
1971 | 17 | 3035 | 27 | ||
1986 | 12 | 3057 | 32 | ||
2010 | 12 | 3074 | 32 | ||
G225M | 2186 | 7 | 3094 | 32 | |
2217 | 12 | G230L | 2635 | 7 | |
2233 | 7 | 2950 | 7 | ||
2250 | 22 | 3000 | 7 | ||
2268 | 12 | 3360 | 12 | ||
2283 | 12 | MIRRORA | ... | 7 | |
2306 | 12 | MIRRORB | ... | 12 | |
2325 | 12 |
-
COS Instrument Handbook
- Acknowledgments
- Chapter 1: An Introduction to COS
-
Chapter 2: Special Considerations when Observing with COS
- • 2.1 COS FUV Detector Lifetime Positions
- • 2.2 Visit Length
- • 2.3 Central Wavelength Settings Added in Cycle 26
- • 2.4 ORIENT constraints for Extended Sources
- • 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
- • 5.11 Spectroscopy with Available but Unsupported Settings
- 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
- • 12.17 Cycle 29 Calibration Program
- Chapter 13: Spectroscopic Reference Material
- • Glossary