THE COSMIC ORIGINS SPECTROGRAPH

Abstract

The Cosmic Origins Spectrograph (COS) is a moderate-resolution spectrograph\nwith unprecedented sensitivity that was installed into the Hubble Space\nTelescope (HST) in May 2009, during HST Servicing Mission 4 (STS-125). We\npresent the design philosophy and summarize the key characteristics of the\ninstrument that will be of interest to potential observers. For faint targets,\nwith flux F_lambda ~ 1.0E10-14 ergs/s/cm2/Angstrom, COS can achieve comparable\nsignal to noise (when compared to STIS echelle modes) in 1-2% of the observing\ntime. This has led to a significant increase in the total data volume and data\nquality available to the community. For example, in the first 20 months of\nscience operation (September 2009 - June 2011) the cumulative redshift\npathlength of extragalactic sight lines sampled by COS is 9 times that sampled\nat moderate resolution in 19 previous years of Hubble observations. COS\nprograms have observed 214 distinct lines of sight suitable for study of the\nintergalactic medium as of June 2011. COS has measured, for the first time with\nhigh reliability, broad Lya absorbers and Ne VIII in the intergalactic medium,\nand observed the HeII reionization epoch along multiple sightlines. COS has\ndetected the first CO emission and absorption in the UV spectra of low-mass\ncircumstellar disks at the epoch of giant planet formation, and detected\nmultiple ionization states of metals in extra-solar planetary atmospheres. In\nthe coming years, COS will continue its census of intergalactic gas, probe\ngalactic and cosmic structure, and explore physics in our solar system and\nGalaxy.\n