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Scientific Impact of Descopes

Scientific Impact of Descopes. Rick Perley Version 3may06, 12PM. The Problem. Contingency is getting short. It may be necessary to consider descoping aspects of the EVLA We can consider descopes in one or both: Hardware Software Alternatively, there are some ‘delay’ options.

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Scientific Impact of Descopes

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  1. Scientific Impact of Descopes Rick Perley Version 3may06, 12PM EVLA Advisory Committee Meeting May 8-9, 2006

  2. The Problem • Contingency is getting short. • It may be necessary to consider descoping aspects of the EVLA • We can consider descopes in one or both: • Hardware • Software • Alternatively, there are some ‘delay’ options. • I review here the impact of these options on the scientific productivity of the EVLA. EVLA Advisory Committee Meeting May 8-9, 2006

  3. Hardware Descopes We have considered: • Removal of one or more bands • X, Ku, S, Ka are the possibilities • Reduction of bandwidth from 16 to 8 GHz. • Reduce number of outfitted antennas. • Removal of special solar observing hardware. • Items 1 and 2 were discussed last year. EVLA Advisory Committee Meeting May 8-9, 2006

  4. Bandwidth Reduction • Significant savings possible – but mostly in correlator. Not our money to save, and politically very tricky. • Our savings come from DTS system. But, much of the needed components for all antennas already purchased. • Scientific impact: 40% loss of continuum sensitivity per unit time at K, Ka and Q bands, less on Ku. None other bands. • It is too late to obtain significant savings through this descope option. EVLA Advisory Committee Meeting May 8-9, 2006

  5. Band Descopes • Bands we could consider: Total Parts Only • S-Band $1.4M $400K • X-Band $1.0M $200K • Ku-Band $1.3M $200K • Ka-Band $1.2M $200K • I consider the scientific implications of each band listed. EVLA Advisory Committee Meeting May 8-9, 2006

  6. X-Band • The VLA has a good X-band system – operating from 7.8 – 8.8 GHz. • It has been argued that simply leaving this legacy system in place would be sufficient. • This is a poor argument: • Continuum sensitivity will be less than half that of C-band. • Only spectral observations of transitions lying between 8 and 8.8 GHz would be useful. • X-band would become both legacy and vestigial. • Nevertheless – this is the easiest band descope. EVLA Advisory Committee Meeting May 8-9, 2006

  7. S-Band vs. U-Band? • Removal of X-band might be considered an easy decision – but the decision of which band is next to go will not be easy. • The debate of which is more scientifically productive will surely pit ‘non-thermal’ vs. ‘thermal’ science interests. • Who is to say what is more valuable? • Consider the following: EVLA Advisory Committee Meeting May 8-9, 2006

  8. S-Band • This band will become the band of choice for non-thermal imaging: • Likely better than twice the sensitivity of L-band. • Twice the total bandwidth, • At least three times the available (RFI-free) bandwidth • Nearly 1.5 times the efficiency. • We anticipate superb performance from this band. EVLA Advisory Committee Meeting May 8-9, 2006

  9. Examples of Key Lost Science • TBD? (Do we need to)? EVLA Advisory Committee Meeting May 8-9, 2006

  10. Ku-Band • This is a key ‘thermal science’ band. • Transition zone (from optically thick to optically thin) for the highest EM HII regions. • Dozens of molecular and atomic spectral transitions. • Lowest frequency where precise dust emission observations can be made (lowest optical depth to dust extinction). • Lowest frequency (= highest redshift) for key high frequency molecular studies (e.g. CO 1-0 at z – 5.8). • Could be argued this is the highest ‘really good’ band for non-thermal science. EVLA Advisory Committee Meeting May 8-9, 2006

  11. Examples of Key Lost Science EVLA Advisory Committee Meeting May 8-9, 2006

  12. Ka-Band? • Early in the project, this badn was identified for accelerated development – rich science mine! • Relatively unexplored spectral region, esp. good for thermal emission processes. • Hundreds of molecular spectral transitions. • Low sky emission – between H2O and O2 emission. Decent efficiency, excellent Tsys. • Testing of the designed horn/polarizer is about to begin. • We could review this decision, if necessary. EVLA Advisory Committee Meeting May 8-9, 2006

  13. Ka-Band Science • Thermal Science! • HII regions, dusty obscured disks, star forming regions. • Hundreds of spectral transitions. • Hi-z lines. • Excellent continuum sensitivity – far better than Q-band, even for optically thick thermal emission. EVLA Advisory Committee Meeting May 8-9, 2006

  14. My Opinion • Full Frequency Coverage a Primary Goal of this project. • Any retreat is an admission of failure by NRAO (and by AUI!) • The science impact of band descopes is enormous. At least 10 years would be needed to recover a descoped band. • If we must cut back, then an acceptable compromise is to simply purchase the parts, and build the new systems in post-construction years. • This, in essence, shifts the implementation costs to operations. EVLA Advisory Committee Meeting May 8-9, 2006

  15. Solar Mode Descopes • Not a lot of money (~$200K) • Scientific impact limited to the ‘solar community’ and solar science. • Solar community use of VLA is now very light (nearly non-existent). • Only two bands (L-band and one other, currently not identified) budgeted for special solar mode systems. EVLA Advisory Committee Meeting May 8-9, 2006

  16. Implementation Descope? • A suggestion has been made to reduce the number of EVLA-outfitted antennas. • Savings limited – in many areas we have already bought ‘in bulk’ for the whole project. • Very strong science impact: • Point-source sensitivity reduced by linear fraction. • Imaging capability (particularly for complex fields) reduced by a greater fractions – baselines rise as N2. • This descope would affect all bands, all observers, all programs, all science. • I think this idea is a ‘non-starter’. It should be dismissed at the highest level, now. EVLA Advisory Committee Meeting May 8-9, 2006

  17. Software Descopes • Software in three major areas: • M&C • E2E • Post-Processing. • We consider M&C as sacrosanct. The group is of just-sufficient size. • Post-processing group already minimal – sub-critical. No fat here! • We look at ‘e2e’ for descope opportunities. EVLA Advisory Committee Meeting May 8-9, 2006

  18. Descopes in e2e? • Level 2 and Level 3 software e2e deliverables already descoped. • Budget is currently unable to provide all ‘Level 1’ deliverables. • Three more staff needed to achieve Level 1 deliverables. • This does not include extra staff for imaging algorithm R&D. • Approximately $1M of contingency already utilized in addressing shortfalls in `e2e’. • Could review ‘Level 1’, for further descopes. • Probable course of action is to delay some deliverables. • Effect would be to move some to operations. EVLA Advisory Committee Meeting May 8-9, 2006

  19. E2E Descope Options • (A list of Level 1 deliverables which would be deferred/removed, should we have to go this route …) • (Perhaps a reminder that e2e, and the One Observatory, is an NRAO/AUI obligation, and that the failure of the 2000 DMD model is not the fault of the EVLA Project). • (Hence, more resources from NRAO/CV, and AUI, are needed). EVLA Advisory Committee Meeting May 8-9, 2006

  20. Deferment Options • Although not formally a ‘descope’, perhaps the best options are to defer planned capability. • Hardware: Already mentioned that costs could be offset into future operations by purchasing early, with implementation deferred until post 2012. • Not a great option, but doable, deferring $xxxK to future generations. • Risk: Much better receivers might be available later? (I doubt this, given the existing capabilities). EVLA Advisory Committee Meeting May 8-9, 2006

  21. Deferment Options • Software. • Clearly an area where deferment is possible – even likely: • Real-time scheduling: Can be done by a person indefinitely, until good software can be written. • Automatic image generation: Can be done by trained individuals until more automated systems can cover harder and harder configuration/frequency/weather combinations. • Post-processing software. Although development of improved algorithms is non-deferrable, we can match scheduling of tough experiments (full-field, noise-limited, high-resolution polarimetric imaging at L-band, for example) until the software is ready. • Nothing new in this – done by the VLA. • Other examples… EVLA Advisory Committee Meeting May 8-9, 2006

  22. Summary • Advertised scientific productivity of EVLA requires all hardware and software deliverables to be met. • It is unwise policy to remove frequency bands. History shows recovery will be at least a decade away. • All software deliverables in e2e are key for full scientific usage – especially by those not trained to be ‘radio astronomers’. • The preferred solution is an increase in the budget sufficient to keep us on track and on time. Estimate of this: $5M. (… only 6% of total EVLA1 budget). • The acceptable, but not preferable, means is deferment of promised capability into the operational years. EVLA Advisory Committee Meeting May 8-9, 2006

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