STUDY SUMMARY - IPMU

More documents

Recommendations

Info

<strong>SUMMARY</strong> REPORT WIDE FIELD FIBER-FED OPTICAL MULTI-OBJECT SPECTROMETER (WFMOS) allocation success rate will be high. If there are few targets, then most positioner elements will not have a target available. At intermediate target density, the success rate will be moderate, and will depend on the degree of overlap of adjacent patrol regions. A full discussion of the allocation efficiency issues and trade-offs appears in the OCDD, Section 6. 4.4 Exposure Times and Survey Time Estimate As discussed above, WFMOS provides high throughput and high positioner allocation efficiency, allowing the primary surveys to be accomplished in modest telescope time. Table 4.4-1 summarizes the required exposure times and survey times for the primary surveys. More extensive detail of the survey efficiency and exposure time calculator appear in the OCDD. Table 4.4-1: Exposure and survey times for the low-redshift Dark Energy survey (DELZ), the high-redshift Dark Energy survey (DEHZ), the low-resolution Galactic Archaeology survey (GALR), and the high-resolution Galactic Archaeology survey (GAHR). Survey Resolution Mag S/N Obs (min) Survey time (hrs) DELZ 3500 RAB < 23.0 Line = 7 15 832 DEHZ 1500 RAB < 25 Cont = 4 240 286 GALR 5000 V = 20 10–15 / Å 30 765 GAHR 20,000 V = 17 150 / Å 60 1125 4.5 System Versatility and Upgrades The conceptual design of the current instrument has been tuned to delivery optimal performance for the Gemini surveys (DE/GA) while attempting to keep costs low. However, as introduced in Section 2, as the unique capabilities of WFMOS will have major impact in many areas of auxiliary science, we have borne this in mind in our design study. There are significant features in the major elements of this design, the fiber positioner assembly and the spectrograph, that ensure versatility and permit possible upgrades. The key to keeping upgrade options open is clean interfaces between subsystems and design modularity. The highlights of potential upgrades are: • Increase in the total number of positioners—possible because of the design of the individual positioner and the spectrograph design. • Increase in spectral resolution of the spectrographs. • Survey changes with different gratings. 4.5.1 Positioner The current design has 2,400 positioners arranged in a hexagonal pattern centered on the focal plane that covers 1.2 to 1.4 degree field. This configuration was selected to optimize the data collected with respect to cost. The outer edges of the 1.5 degree focal plane are affected by vignetting reducing the throughput and subsequently making those fibers beyond 1.4 degrees less efficient (Figure 3.10-3). However, even taking this vignetting effect into account, a decrease in observation time can be obtained by fully populating the focal plane with positioners. The number of positioners can be increased to 3,200 with no change in the design of the existing Cobra positioner, its control system, or its electronics architecture. 4.5.2 Spectrograph The spectrograph design easily allows an increase in the number of positioners as well as other design upgrades. Since each spectrograph is identical, adding a fourth spectrograph would 61
<strong>SUMMARY</strong> REPORT WIDE FIELD FIBER-FED OPTICAL MULTI-OBJECT SPECTROMETER (WFMOS) accommodate more positioners. No recurring engineering costs are added. The spectrograph beam size is 500 mm in diameter, and the range of camera-collimator angles is 0 to 110 degrees. A grating can be designed for any angle in this range, giving a range of spectral resolutions from 0 to 30,000. The width of the detector in SREs (spectral resolution elements) is constant—there are always 1724 of them. So as the resolution increases the wavelength coverage decreases. The whole wavelength range 420 nm–970 nm is obtained at R ~2178 at 12 deg, whereas 31.6 nm of spectral coverage in a single order is obtained at R ~30,000 at 100 degree. The spectrographs can, therefore, be used to do other science programs if new gratings are purchased. Furthermore, the gratings purchased for the four surveys can be used at different angles to give different wavelength ranges. Our system will have significant sensitivity below 420 nm and above 970 nm, which will definitely be of great interest for auxiliary science. 62
Page 1 and 2:
WIDE FIELD FIBER-FED OPTICAL MULTI-
Page 3 and 4:
One of three identical Schmidt Spec
Page 5 and 6:
SUMMARY REPORT WIDE FIELD FIBER-FED
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20: SUMMARY REPORT WIDE FIELD FIBER-FED
Page 69: SUMMARY REPORT WIDE FIELD FIBER-FED
Page 99: SUMMARY REPORT WIDE FIELD FIBER-FED
show all

STUDY SUMMARY - IPMU

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?