Cosmic Origins Spectrograph

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					             HST Field of View                                                  COS Optical Design
                                                               Calibration Lamp Platform


                                                                                                     Optic Select
                                                                                                                        NUV Detector
                                                                                                                                                          C OS
                                                              FUV Detector
                                                                                                     Mechanism 2                            Cosmic Origins Spectrograph

                                                                                                                                               Far Ultraviolet (FUV) Channel
                                                              Entrance Aperture                                                            1-reflection; aberration-corrected along dispersion
                                                                                                                         Optic Select      2 side-by-side 16k x 1k pixel delay line MCPs
                                                                                                                         Mechanism 1
                                                                                                                                           TIME-TAG; pulse-height recording
                                                               External light enters at lower left; common path to first element at        3 gratings; 300-800 Ǻ spectral coverage
                                                               lower right. FUV path in green; NUV path in blue; PtNe and D2               R=3000; 20,000 [1150-2050 Å]
                                                               input calibration beams in tan.
                                                                                                                                              Near Ultraviolet (NUV) Channel
                                                                   COS Spectroscopic Mode Summary                                          Fully corrected optical design
                                                                                                  
                                                                                                                                           1k x 1k 25µm/pixel MAMA
                                                                               Nominal           Wavelength             Resolving          TIME-TAG recording
 The HST focal plane showing the instrument                     Spectral      Wavelength          Coverage               Power             4 gratings, 1 imaging mirror and filter
 complement after Servicing Mission 4. The COS FUV              Element        Range             per exp (Å)             ()            100-800 Ǻ non-contiguous spectral coverage
 and NUV channels view the same 2.5 arcsec patch of                                                                                        R=2000; 20,000 [1700-3200 Å]
 sky, but not simultaneously. Instrument apertures and           G130M        1150 - 1450              300          20000-24000
 separations are shown to scale.                                                                                                        The Cosmic Origins Spectrograph has been built
                                                                 G160M        1405 - 1775              375          20000-24000
                                                                                                                                        through a collaborative effort between the University
                                                                 G140L        1230 - 2050              820              2400-3500       of Colorado, Ball Aerospace, and Goddard Space
COS Wavelength Coverage by Mode
  Mode                                                                                                                                  Flight Center. COS will be installed on the Hubble
                                                                 G185M        1700 - 2100             3 x 35        16000-20000         Space Telescope (HST) during HST Servicing
                                                                 G225M        2100 - 2500             3 x 35        20000-24000         Mission 4. The COS principal investigator is James
 G230L                                                                                                                                  Green (University of Colorado).
                                                                 G285M        2500 - 3200             3 x 41        20000-24000
 G285M                                                                                                                                  COS is designed to primarily observe point sources.
 G225M                                                           G230L        1700 - 3200        1 or 2 x 400           1500-2800       Equipped with state-of-the art detectors and optics
                                                           
 G185M                                                                                                                                  and optimized for maximum FUV throughput, COS
                                                                                                                                        provides moderate and low resolution spectroscopy
 G140L                                                                                                                                  throughout the HST-accessible satellite ultraviolet,
 G160M                                                                                                                                  dramatically increasing faint object discovery power
 G130M
                                                                                                                                        and the spectroscopic efficiency of HST.
                                                                                                                                        For further information, please visit:
             1500      2000        2500    3000                                                                                         http://www.stsci.edu/hst/cos
                       Wavelength (Ǻ)
                                                                                                                                        http://www.stsci.edu/hst/cos
 Wavelength coverages available with common COS
 spectroscopic modes. The ranges for different grating
 tilts are offset in the vertical direction. Additional
 settings may be available for some modes. Notice non-
 continuous spectral ranges for NUV modes.
                                                                                                                                                                             v3 - January 2008
                                                     FUV Lim iting Flux for S/N=10 in 3600 sec (R~20,000 (0.08 Ǻ) binning)
                                               COS and STIS FUV Limiting Flux Comparison                                                                            COS FUV Format                              COS and STIS Detector Characteristic Comparison
                                       -12.5

                                                                STIS E140M + 0.2x0.2 aperture                                                                             Internal PtNe Wavecal                                      COS/FUV          STIS/FUV         COS/NUV              STIS/NUV
              sec -1 Ǻ-1 )




                                       -13.0                    R=45,000

                                                                                                                                                                                                             Spectral               1150-1775(M)
                                                                                                                                                                                                                                                      1150-1700        1700-3200             1600-3200
                                       -13.5                                                                                                                                                                 coverage (Ǻ)           1230-2050(L)
              -2
                    log Flux (erg cm




                                                                                                                                                                                                                                       2800 (M)         400 (M)          600 (M)               350 (M)
                                       -14.0
                                                                                                                                                                             External Source
                                                                                                                                                                                                             Effective Area            2000 (L)        1700 (L)          575 (L)               900 (L)
                                                              COS G130M                                                                                                                                      (cm2)                    (at 1300)      (at 1300)       (at 2500)            (at 2500)
                                       -14.5                  R~20,000-24,000
                                                                                                                COS G160M
                                                                                                                R~20,000-24,000                                                                              Resolution         H     N/A       110000                    N/A                 110000
                                       -15.0
                                                                                                                                                                                                             ()             M 20000-24000 10000-40000             16000-24000           10000-30000
                                                                                                                                                                                                                                L 2400-3500      1000                  1500-2800                500
                                                                                                                                                    The figure above shows the typical spectrum format
                                       -15.5                                                                                                        for a single COS FUV MCP detector segment. The           Number of pixels                                                                  1024
                                           1100        1200        1300          1400          1500      1600        1700         1800              COS FUV detector consists of two such segments                                     32768          1024 (2048)         1024
                                                                                                                                                                                                             along dispersion                                                                 (2048)
                                                                                   Wavelength (Ǻ)                                                   separated by a small gap. Two spectra may be
                                                                                                                                                    recorded as shown above. The lower spectrum is           Background                      -5                 -5               -3                 -3
                                                                                                                                                    from an external source illuminating the prime                                    4.3 x10          350 x10          1.9 x10               17 x10
                                                                                                                                                                                                             (cts/sec/resel)
                                                                                                                                                    science aperture (PSA); the upper spectrum is from
                                       The figures above and below compare COS Primary
                                                                                                                                                    the internal PtNe wavelength calibration lamp which      Background
                                       Science Aperture (PSA) and STIS medium resolution                                                            illuminates the wavelength calibration aperture                                             -18          -18                      -16              -16
                                                                                                                                                                                                             equivalent F           0.5-8 x10         20 x10         1.3-3.8 x10            13.8 x10
                                       (M mode) performance by indicating the limiting flux for                                                     (WCA).                                                          -2    -1
                                                                                                                                                                                                             (erg cm sec Ǻ )   -1
                                                     †
                                       which S/N=10 can be achieved in 3600 sec exposures
                                       with uniform binning corresponding to R~20,000 (bins of                                                      The figure below shows the typical spectrum format
                                       0.08 Å for FUV and 0.12 Å for NUV. The superior light                                                        for the COS NUV MAMA detector. Three separate
                                       gathering power of COS provides >10x the FUV                                                                 segments – labeled A, B, and C - of the dispersed
                                                                                                                                                                                                                                    COS Time-TAG Mode Summary
                                       throughput of STIS and up to 70x STIS FUV observing                                                          first-order spectrum are directed by separate pickoff
                                       speed.                                                                                                       mirrors to illuminate slightly offset positions on the        Default mode for FUV and NUV; 32 msec sampling
                                                                                                                                                    detector. The left-most three stripes are from the            FUV pulse-heights improve background removal
                                       Note: COS Bright Object Aperture (BOA) performance                                                                                                                         Unique TAGFLASH mode acquires wavecal spectra
                                                                                                                                                    internal PtNe wavelength calibration lamp. The
                                       limits are ≥150x brighter due to the BOA attenuation.                                                                                                                        during science exposures; no on-target time lost
                                                                                                                                                    three stripes to the right are from an external source
                                       †
                                        COS flat fields will support S/N=30 and for FP-split                                                        illuminating the PSA.                                         Fully processed photon list product; can be binned or
                                       observations in certain circumstances S/N~100.                                                                                                                               time-sliced to user requirements
                                                                                                                                                                  PtNe wavecal        External source
                                                  newNUV Limiting Flux for S/N=10 in 3600 sec (R~20,000 (0.12 Ǻ) binning)                                         C     B   A         C      B    A
                                               COS and STIS NUV Limiting Flux Comparison
                                -12.5
                                                                                                                                                                                                                                     COS Imaging Mode Summary
                                                                                                                                                                                                                                 Imaging
                                                                                                                                                                                                                                                                     COS/NUV
                                -13.0
                                                                                                                                                                                                                               Characteristic
                                                                                                                                                                                                                           FOV area                     12.5 (full diameter)
                                                           STIS E230M + 0.2x0.2 aperture
                                                           R=30,000                                                                                                                                                        (arcsec2)                     4.9 (un-vignetted)
                                -13.5
log Flux (erg cm-2 sec-1 Ǻ-1)




                                                                                                                                                                                                                           Broadband                     0.07 (2300)
                                                                                                                                          Y (pix)




                                                                                                                                                                                                                           throughput                    0.02 (3300)
                                -14.0
                                                                                                                                                                                                                           Pixel scale (arcsec)          0.024
                                                                                                                                                                                                                                                        166 (full diameter)
                                                                                                                                                                                                                           Number of pixels
                                -14.5
                                                    COS G185M
                                                                                                                    COS G285M                                                                                                                           100 (un-vignetted)
                                                                                                                    R~20,000-24,000
                                                    R~16,000-20,000         COS G225M
                                                                            R~20,000-24,000                                                                                                                                Background
                                -15.0                                                                                                                                                                                      equivalent F                ~5 x10-19 (HSTMAG ~ 24.5)
                                                                                                                                                                                                                           (erg cm-2 sec-1 Ǻ-1)
                                                                                                                                                                                                                                                        1
                                -15.5                                                                                                                                            X (pix)                                   Number of filters
                                                                                                                                                                                                                                                        (broad-band, 1700-3200 Ǻ.)
                                     1600           1800       2000       2200          2400      2600     2800         3000       3200
                                                                                                                                                                     COS NUV Format
                                                                                  Wavelength (Ǻ)
                                       For the most current COS sensitivities, please refer to the COS
                                       ETC at http://etc.stsci.edu/webetc/index.jsp

				
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