The Cosmic Origins Spectrograph
Instrument Overview
Steve Osterman1, J. Green1, C. Froning1, T. Ake2, A. Aloisi2, S. Béland1, E. Burgh1, C. Danforth1, T. Delker3, K. France1, S. Friedman2,
P. Ghavamian2, P. Goudfrooij2, G. Hartig2, B. Keeney1, C. Keyes2, G. Kriss2, D. Lennon2, D. Massa2, J. McPhate4, C. Oliveira2,
R. Osten2, S. Penton1, C. Proffitt2, D. Sahnow5, O. Siegmund4, K. Sembach2, E. Smith2, D. Soderblom2, E. Wilkinson6, L. Winter1
1University of Colorado, 2Space Telescope Science Institute, 3Ball Aerospace and Technologies Corporation,
4University of California, Berkeley, 5Johns Hopkins University, 6Southwest Research Corporation.
Abstract
The Cosmic Origins Spectrograph (COS) is a fourth generation instrument installed aboard the Hubble Space Telescope in May 2009
as part of Servicing Mission 4. COS is an ultraviolet spectrograph optimized for observing faint point sources with moderate spectral
resolution λ/Δλ greater than 16,000 between 1150Å and 3200Å. COS is the most sensitive ultraviolet spectrograph flown to date, with a
peak effective area of 3000 cm2 and as much as 10 cm2 at wavelengths as short as 950Å in the low resolution channel. COS’s
sensitivity advantage is particularly evident in the far ultraviolet channel, where COS is 10 to 30 times more sensitive than STIS.
COS DESIGN
G160M-C
•  COS is optimized to provide high sensitivity, moderate
resolution NUV and FUV spectroscopy for point-like objects.
•  COS has two modes providing medium and low resolution
spectroscopy: FUV (~900-1775Å) and NUV (1700-3200Å).
•  Reflections minimized to maximize FUV throughput.
•  2.5ʺ″ entrance aperture admits >97% of light from point
source targets.
•  Wavelength calibration and stability monitoring provided by
on-board Pt/Ne lamp.
•  Target acquisition algorithm centers isolated objects to
<0.05ʺ″ in all modes, with results as good as 0.003ʺ″.
Aperture Mechanism:
Primary Science Aperture,
Bright Object Aperture
1150-1775Å, G130M, G160M, G140L
1700-3200Å, G185M, G225M, G285M, G230L
•  Two segment windowless cross delay line detector (XDL)
sensitive from < 900Å to ~2200Å (two 10x85mm segments).
•  Dispersion provided by low scatter holographically ruled
diffraction gratings which simultaneously correct for HST
aberration and minimize astigmatism in one reflection.
•  300-370Å coverage per grating position (~16Å central gap)
•  Background: 1.8cts/sec/cm2 (0.16 cts/resl/ksec, or 1 count/
pixel in 4.3 days).
•  Resolution (M gratings): 16,000-21,000
•  Supports S/N > 50 per resolution element.
FUV Sensitivity (cm2)
800
1000
3000
Performance as described in
original proposal (HDC1 and
HDC2 modes)
G130M
2000
1000
G160M
G140L
100
FUSE Effective Area
(Sahnow, et al, 2000)
10 cm2
SiC1
10
SiC2
LiF1
(STIS E140M)
0
1000
1200
600
400
200
LiF2
1400
1600
Wavelength (Å)
1800
2000
2200
1
900
950Å
950
1000
1050
Wavelength (Å)
1100
1150Å
0
1500
1150
o  FUV sensitivity extends to 900Å using G140L.
o  COS effective area comparable to FUSE.
Optical bench:
Recycled GHRS
bench
2000
2500
Wavelength (Å)
3000
o  NUV sensitivity close to prelaunch predictions.
o  NUV detector background much lower than STIS
COS sensitivity is
apparent in this spectrum
of PKS0405-123 – Note
relative S/N and
observing times
Channel H1821+643, G130M, 580sec
NUV Sensitivity (cm2)
4000
o  FUV sensitivity matches prelaunch (thermal vac, or TVAC)
expectations and provides gains >10 in sensitivity, 70 in
observing speed.
o  COS gains: faint targets (discovery), observing times (survey)
Wavelength Resolu0on Limi0ng Vmag* Range (λ/Δλ) (S/N 10 in 10 Ksec) G130M (FUV) 1150-­‐1450Å 16,000-­‐21,000 19.1 [16.3] G160M (FUV) 1405-­‐1775Å 16,000-­‐21,000 16.7 [14.1] G140L (FUV) 900-­‐2050Å 1500-­‐4000 20.6 [17.8] G185M (NUV) 1700-­‐2100Å 22,000-­‐28,000 17.8 [15.7] G225M (NUV) 2100-­‐2500Å >25,000 17.5 [15.8] G285M (NUV) 2500-­‐3200Å >25,000 16.9 [15.6] G240L (NUV) 1650-­‐3200Å 2100-­‐3900 20.4 [18.7] TA1 (NUV) 1700-­‐3200Å 0.05˝ (Targ.Acq.) * S/N 10 per resl in 10Ksec at central λ, assuming B5V star (Castelli-­‐
Kurucz model) [Vmag assuming a flat (Fλ) con:nuum] •  1024x1024 pixel NUV MAMA detector (STIS spare).
•  Holographically ruled gratings with ~ 4000 - 4800l/mm
provide 16,000-24,000 Resolution from 1700-3200Å in
medium resolution modes.
•  34-40Å per stripe, 3 stripes per grating position with 65
-70 Å gaps. Full covrage possible with multiple settings.
•  Background: ~200cts/sec global (1.7 cts/resl/ksec).
•  Resolution: Spectral (M gratings): >22,000
Angular (TA mode): ~0.05″
•  Supports S/N >115 per resl without focal plane splits.
Effective Area (cm2)
OSM1:
G130M,
G160M,
G140L,
NCM1
COS NUV CHANNEL
Effective Area (cm2)
FUV
XDL
Detector
OSM2: G185M,
G225M, G285M,
G230L, TA1
COS FUV CHANNEL
FUV Sensitivity (cm2)
Effective Area (cm2)
Calibration
Platform
NUV
MAMA
Detector
(STIS
spare)
Photo credit: Jason B. McPhate, 2009
0.3ʺ″
TA1 target
acquisition
imaging mode
provides ~0.05ʺ″
NUV imaging
11473 Visit 1; 900sec image, G2 B star
P330E (~52,000 cts
peak pixel)
(Goudfrooij)
Related Posters
Wavelength (Å)
(See 464.24: COS Observations of Intergalactic O VI Systems in the Spectrum of PKS 0405-123 )
464.02.
464.03.
464.05.
464.07.
464.08.
464.10.
464.12.
464.14.
464.16.
464.20.
464.25.
The Cosmic Origins Spectrograph: NUV Imaging Performance
Cosmic Origins Spectrograph : Target Acquisition Performance and Updated Guidelines
Cosmic Origins Spectrograph: On-Orbit Structural and Thermal Stability.
Effective Area of the Cosmic Origins Spectrograph below 1150 Å
Preliminary Characterization of the On-Orbit Line Spread Function of COS
COS SMOV Calibration: Detector Background Performance
Wavelength Calibration of the Cosmic Origins Spectrograph
Cosmic Origins Spectrograph: Servicing Mission Observatory Verification Overview
Cosmic Origins Spectrograph: Spectroscopic Sensitivity of the Cosmic Origins Spectrograph
Time-Dependent Spectroscopic Sensitivity Monitoring of the Cosmic Origins Spectrograph
Cosmic Origins Spectrograph: Flat Fields And Signal-to-noise Characteristics
H1821+643, G160M, 530sec
Poster 464.22