SOFIA Science Teleconference

  • Date: Thursday, May 5
  • Time: 1-2pm EDT
  • Location NTC-200

Agenda

Science Case (star formation, extragalactic, planetary, etc.); in particular, how each flows down to technical requirements (# of pixels, 2SB or DSB, spectrometer range/resolution, RF band).

Participants

Astronomers:
  • Al Wooten (NRAO)
  • Mark Gurwell (Harvard)
  • Tony Remijan (NRAO)
  • Ted Bergin (University of Michigan), called in to delta-telecon next day
  • Gary Melnick (Harvard), called in to delta-telecon next day

Several engineers from NRAO

Summary

Tony talked some about searching for metal hydrides (MgH, FeH, CaH, NiH, etc.). HIFI hasn’t been successful, he’s thinking they’re looking in the wrong places. These have linewidths 20-30 km/sec and extents up to about an arcminute. We then talked a bit about solar system objects, in particular mapping of the comas of comets (water isotopes or CH) and what instrument specs you’d want for that. Talked about dual sideband versus double sideband. While dual-sideband with image rejection would be a nice feature, algorithms using LO frequency switching make double sideband okay. Certainly, given the hypothetical choice between 4 pixels dual-sideband or 8 pixels double-sideband, there was no hesitation in going with the 8 pixels. There was then some more discussion on general spectrometer requirements. We’ll be limited in range here to ~2 GHz in using a HEB mixer. We are further limited to 1.5 GHz only if we want to stick with what’s currently available “off-the-shelf” with CASPER hardware. Regarding extragalactic, I asked if we were sensitive enough to detect CII in the z=0.3 to 0.6 range. Al seemed to think yes, but he was going to run the calculations to confirm. Didn’t really touch much on star formation, other than I asked if high-J transitions of CO, HCN, etc. would be extended or limited to small dense areas, in which case it doesn’t drive having more pixels. H2D+ also came up again as a must-do.

Ted and Gary had conflicts on Thursday, so called in to "delta-telecon" the following afternoon. Ted stressed that without large sensitivity improvement in using SIS, we may not have enough of a leap over GREAT in capability to justify a new instrument. We really need at least an order-of-magnitude improvement. If we go to 8 pixels, then we have the factor of 8 mapping speed improvement plus the 1000/1400 squared decrease in integration time from the improved HEB to give a total mapping speed improvement of 16x. If we can do this without sacrificing the total tuning bandwidth of the low-frequency GREAT channel, then we may have enough of a jump. This is in contrast to higher frequency FPAs, e.g. 1.9 or 2.7 THz, where the LO power requirements of an array will necessarily limit the tuning bandwidth to single-line surveys. Ted would really like to see sensitivity calculations for SOFIA with the proposed receiver temperatures (I will ask Al to provide this).
Topic revision: r1 - 2011-05-09, EricBryerton
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