1.3 COS Quick Reference Guide
Table 1.1: COS Instrument Characteristics
Property | FUV channel | NUV channel |
---|---|---|
Entrance apertures | 2.5 arcsec diameter circle: clear (PSA) or attenuated (BOA) | |
Detector plate scale | ~0.11 arcsec per pixel1 | 23.5 mas per pixel |
0.0285 arcsec per pixel | 23.8 mas per pixel |
1 Exact value of plate scale depends on grating and lifetime position.
2 Raw plate scale.
Table 1.2: COS Detector Characteristics
FUV XDL (A/B) | NUV MAMA | |
---|---|---|
Photocathode | CsI (opaque) | Cs2Te (semi-transparent) |
Window | None | MgF2 (re-entrant) |
Wavelength range | < 900–2150 Å | 1650–3200 Å |
Active area | 85 × 10 mm (two) | 25.6 × 25.6 mm |
Pixel format (full detector) | 16,384 × 1,024 (two) | 1,024 × 1,024 |
Image size recorded per spectrum | 16,384 × 128 (two, | 1,024 × 1,024 |
Pixel size | 6 × 24 μm | 25 × 25 μm |
Spectral resolution element size (= resel) | 6 × 10 pix | 3 × 3 pix |
Quantum efficiency | ~26% at 1335 Å | ~10% at 2200 Å |
Typical dark-count rate (away from SAA)1 | 1.38 counts s–1 cm–2 | 180.80 counts s–1 cm–2 |
Detector Global Count rate limit2 | 60,000 counts s–1 | 770,000 counts s–1 |
~1.67 counts s–1 pix–1 | ~200 counts s–1 pix–1 | |
Screening limits for bright objects | see Table 10.1 | |
Dead-time constant | 7.4 μs | 280 ns |
1 The dark rate varies with time. The reported values are measured as of September 2020. FUVA and FUVB values differ slightly (see Table 7.1). See also COS Dark Rate Monitoring for updated values.
2 Count rates higher than these limits will trigger a detector shut-down. Bright-object screening limits are lower. See Chapter 10.
3 The FUV values are not applicable to the COS FUV G130M blue cenwaves, 1055 and 1096. The local count rate limit for these two modes is 0.2 counts s−1 pix−1.
Table 1.3: COS Calibration Accuracies
Property | FUV channel | NUV channel |
---|---|---|
Wavelength zero point: M gratings | 15 km s–1 | 15 km s–1 |
Wavelength zero point: L gratings | 150 km s–1 | 175 km s–1 |
Wavelength scale1 | 15 km s–1 | 15 km s–1 |
Absolute photometry2 | 5% | 5% |
Relative photometry (same object at a different times)2 | 2% | 2% |
Flat field quality (spectral S/N) per resel, using standard techniques | 35:1 | 100:1 |
Flat field quality (spectral S/N) per resel, using special techniques | 100:13 | 100:1 |
1 With updated dispersion solutions, the wavelength scales for the FUV M gratings are now accurate to 7 km s–1. See the COS ISR 2018-22 for more details.
2 Value for the NUV channel applies to spectroscopy, not imaging.
3 See Section 5.8.1.
Table 1.4: Useful Figures and Tables
Topic | Source | Content |
---|---|---|
Usage planning | Grating parameters | |
FUV grating wavelength ranges | ||
NUV grating wavelength ranges | ||
Count-rate screening limits | ||
Aperture parameters and PSFs | BOA transmission | |
Model LSFs for the COS FUV channel | ||
Model LSFs for the COS NUV channel | ||
Resolving Power of FUV gratings | ||
Cross section of the COS imaging PSF | ||
Relative transmission of the COS PSA in the NUV | ||
HST focal plane and COS aperture | ||
Effective Area | FUV spectroscopy | |
NUV spectroscopy | ||
NUV imaging | ||
Acquisitions | Examples of spiral search patterns | |
Point-source images with all apertures and mirrors | ||
ACQ/IMAGE exposure times | ||
Dispersed-light exposure times | ||
Detector characteristics | FUV XDL detector schematic layout | |
NUV MAMA detector layout | ||
Detector background count rates | ||
Overheads and observing parameters | TAGFLASH exposure durations | |
Overhead estimates for Phase | ||
Generic observatory overhead times | ||
Overhead times for OSM1 movements | ||
Overhead times for OSM2 movements | ||
Science exposure overhead times | ||
Celestial backgrounds | Sky background versus wavelength | |
Moon, Earth and zodiacal-light background levels | ||
Galactic extinction model | ||
Earthshine and zodiacal light fluxes | ||
Strengths of airglow lines | ||
Data quality | FUV flat-field example | |
NUV flat-field example |
-
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