the cosmic origins spectrograph

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The Cosmic Origins Spectrograph James C. Green University of Colorado

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The Cosmic Origins Spectrograph. James C. Green University of Colorado. COS Core Team Cynthia Froning Project Scientist Steven Osterman Instrument Scientist J. Michael Shull John Stocke Theodore Snow Jeffrey Linsky Dennis Ebbets Oswald Siegmund Barry Welsh Jason McPhate - PowerPoint PPT Presentation

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Page 1: The Cosmic Origins Spectrograph

The Cosmic Origins Spectrograph

James C. GreenUniversity of Colorado

Page 2: The Cosmic Origins Spectrograph

With a little help from:• COS Core Team

– Cynthia Froning• Project Scientist

– Steven Osterman• Instrument Scientist

– J. Michael Shull– John Stocke – Theodore Snow– Jeffrey Linsky– Dennis Ebbets– Oswald Siegmund– Barry Welsh– Jason McPhate– Stephane Beland– Steven Penton– Kevin France– Eric Burgh– Charles Danforth– Brian Keeney– Lisa Winter– Yangsen Yao– David Sahnow

• Government and Industry– Hsiao Smith– Francis Cepollina– Dave Leckrone– Preston Burch– Malcolm Needner– Don Hood– Rick Higgins– Brian Osborne– Tom Delker– Mark Erikson– Mark LaPole– Ed Shade– Jean Flammand– Francis Bonne-Mason– Bruno Touzet

• Special Thanks to:– Jon Morse– Erik Wilkinson– John Andrews– Ken Brownsberger

Page 3: The Cosmic Origins Spectrograph

COS Performance Philosophy

• Maximum sensitivity with adequate spectral resolution

• Sensitivity depends on both:–Large signal (large effective area)–Low noise (low scatter gratings, low

background detectors )

Page 4: The Cosmic Origins Spectrograph

• COS has 2 channels to provide low and mediumresolution UV spectroscopy– FUV: 1150-1775Å, NUV: 1700-3200Å

• FUV gratings: G130M, G160M, G140L• NUV gratings: G185M, G225M, G285M, G230L

– M gratings have spectral resolution of R ~ 20,000

NUV MAMADetector

(STIS spare)

CalibrationPlatform

FUV XDLDetector

OSM2: G185M, G225M,G285M, G230L, TA1

OSM1: G130M,G160M, G140L,NCM1

Aperture Mechanism:Primary Science Aperture,Bright Object Aperture

Optical bench(not shown):

re-use of GHRSbench

COS Optical Layout

Page 5: The Cosmic Origins Spectrograph

COS Sensitivity Advantages

• Effective Area gains: 10-20 X STIS (more signal)• Background signal ~ 10% of STIS (depends on

source brightness)• Bandpass comparison:

– STIS Echelle: 600 Å | COS FUV: 300 Å

• Net Sensitivity Gain – 10 -100 X• Note: STIS Echelle Modes have much higher

spectral resolution

Page 6: The Cosmic Origins Spectrograph
Page 7: The Cosmic Origins Spectrograph

The Power of COS for IGM StudiesAs of mid-July:87 IGM sightlines observed, 300+ hrs (GO, GTO, ERO)• Total Ly pathlength z = 22.93

COS has already 10x the pathlength and 15x the number of absorbers of all previous GHRS+STIS studies.

Page 8: The Cosmic Origins Spectrograph

He II Reionization: Shull, et al, 2010

Page 9: The Cosmic Origins Spectrograph

COS has performance below 1150 Å

• Effective area comparable to one channel of FUSE at lower spectral resolution

• See poster by Osterman

Page 10: The Cosmic Origins Spectrograph

NUV Imaging

Page 11: The Cosmic Origins Spectrograph
Page 12: The Cosmic Origins Spectrograph
Page 13: The Cosmic Origins Spectrograph

Time Resolved Spectroscopy

• A flare occurred during the observation of a late type (naked) T Tauri Star

Page 14: The Cosmic Origins Spectrograph

Sufficient S/N to see changes in spectral shape and strength of emission features during event and during “low state”

Page 15: The Cosmic Origins Spectrograph

Data Analysis Issues

• Pulse Height Screening– Each photon carries pulse gain information (5 bit)– Never pas through pulse height 0 data. Typical screening

value is 4 (varies with position)

• Grid wire shadows – locations are well known and easily removed

• Co-adding of spectra from different wavelength positions– Software tool available from CU website cos.colorado.edu

Page 16: The Cosmic Origins Spectrograph

On-Orbit Performance Issues• Spectral resolution:

– The spectral resolution of the FUV channel drops to 18,000 at 1150 Å due to the convolution of the HST OTA point spread function with the COS line spread function. The wide aperture of COS allows the wings of the OTA PSF to enter the instrument. (This effect is also seen in the 2” slit on STIS). The effect mitigates slightly as the wavelength increases.

Page 17: The Cosmic Origins Spectrograph

On-Orbit Performance Issues

– This results in a non-Gaussian LSF. The 18,000 resolution is a calculation based on

the modulation transfer function with an imposed Rayleigh criterion, as opposed to a FWHM calculation based on a Gaussian fit to a known non-Gaussian function (which yields R = 16,000)

Page 18: The Cosmic Origins Spectrograph

On-Orbit Performance Issues• Loss of effective area:

– The FUV channels are losing effective area at approximately 5% /year at all wavelengths. (This result is based on a limited number of samplings. The stability and long term trends of the degradation rate are currently unknown.)

– The physical cause of the drop is unknown but atomic oxygen attack on the photocathode is the current leading candidate. If true, this effect may accelerate during solar maximum.

Page 19: The Cosmic Origins Spectrograph

Conclusions

• Despite the unexpected drop in effective area and resolution, COS remains a stunningly effective scientific instrument that is enabling previously impossible observations of multiple phenomena.

• Please look over the many COS posters to appreciate the significant diagnostic capability that has been provided to the community with COS.