Cosmic Origins Spectrograph Instrument Handbook for Cycle 17

2.2 Observing Considerations for Cycle 17

---

2.2.1 The COS GTO Program

The COS Investigation Definition Team (IDT) is responsible for the development, management, and scientific oversight of COS prior to launch. As Guaranteed Time Observers (GTOs) the COS IDT has 555 orbits of guaranteed observing time with the instrument. The IDT observing time will occur primarily in Cycle 17, with a portion of the time remaining for observations in Cycles 18 and 19. The members of the COS IDT are listed in Acknowledgments.

As GTOs, the COS IDT is permitted to have exclusive access to the targets they will observe for the science they proposed. The COS GTO target list may be found at:

 http://www.stsci.edu/hst/proposing/docs/COS-GTO

GTO target protection policy is more fully explained in the HST Call for Proposals.

2.2.2 Survey and SNAP Programs with COS

The detectors in COS are photon counters and can be harmed by exposure to bright light. All COS observations must be checked at STScI by an Instrument Scientist to confirm both that the intended target is within safe limits for brightness and that no potentially too-bright objects exist nearby. Because of this, the combined total number of targets accepted from all Survey and SNAP programs for COS and STIS/MAMA will not exceed 300. For more information on this and other policies pertaining to HST observing, please see the Call for Proposals.

2.2.3 Non-point Sources Uses of COS

COS offers dramatic improvement in sensitivity to faint objects compared to previous UV spectroscopic instruments flown aboard HST. COS achieves high sensitivity, particularly in the FUV, by minimizing the number of reflections, which leads to an inherently simple design. Accordingly, COS was optimized for observing faint point sources (objects less than 0.1 arcsec in diameter), for which it delivers full throughput and spectral resolution performance. Observations of extended sources will result in degraded spectral resolution, although COS can be used to detect faint, diffuse sources.

2.2.4 Three-Gyro Observing with HST

We anticipate that all observations in Cycle 17 will be done in 3-gyro science mode, providing greater scheduling flexibility and greater sky coverage (at a given time) than in recent Cycles. Proposers should plan their observations accordingly, using information in the HST Primer and visibility tools on-line at: http://apst.stsci.edu/apt/external/help/roadmap1.html