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NGST/NEXUS Operations Jane Morrison October 19, 2000

NGST/NEXUS Operations Jane Morrison October 19, 2000. NGST. Nexus. NGST at a Glance. 8m primary mirror 0.6-10+ µm wavelength range 5 year mission life (10 year goal) passively cooled to <50K L2 orbit Launch 2009. Logical successor to HST Key part of the Origins Program.

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NGST/NEXUS Operations Jane Morrison October 19, 2000

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  1. NGST/NEXUS OperationsJane MorrisonOctober 19, 2000 NGST Nexus

  2. NGST at a Glance • 8m primary mirror • 0.6-10+ µm wavelength range • 5 year mission life (10 year goal) • passively cooled to <50K • L2 orbit • Launch 2009 • Logical successor to HST • Key part of the Origins Program Formulation Phase (A/B) Implementation Phase 99 00 01 02 03 04 05 06 07 08 09 LRD Select Prime PDR/NAR Launch CDR

  3. Guiding with NGST • Guider is part of NIRCAM • NIRCAM: 0.6 to 5.3 microns • Camera composed of 4 sub cameras each covering a field of 2  2 arc minutes. • Guiding with: • Large bandpass filters - a portion of sub-camera used for guiding • Narrow bandpass filters- entire sub-camera used for guiding.

  4. Guiding using NIRCAM 10 10 pixel area around guide star is read at 30 Hz. The 512  512 readout area is excluded from science observations 2' 4'

  5. Requirements of Guide Star Catalog • All Sky catalog • At least 1 arc second positional accuracy • Sufficient density to ensure a 95% probability of finding a suitable guide star. • Limiting magnitude corresponding to a 95 % probability of finding NGS > 1 IJ 17.0 JJ 16.2 KJ 15.5

  6. Guide Star Catalogs for NGST • Guide Star Catalog: GSC-2 supplemented with 2MASS • 2MASS • 300 million stars and other unresolved objects • For unconfused sources outside the |b| < 10 • J = 15.8 , H = 15.1 and Ks = 14.3 • Positional accuracy better than 0. 5 arc seconds

  7. Guide Star Catalogs for NGST cont. • GSC-2 • 2 billion stars, galaxies and other objects • All sky catalog of position, magnitudes, proper motions and colors • Positional accuracy better than 0. 3 arc seconds • Limiting magnitude needed to meet goal of 95% probability of finding a guide star in the FOV of NIRCAM (Spagna) • J385 < 19.5 F610 < 18.5

  8. Areas of Concern • Uncertainty in predicting NIR magnitudes from Photographic J, F and N bands. • Contamination of the stellar population with galaxies (problem alleviated somewhat in galactic plane relax magnitude limit for guide star). • Contamination by unresolved blends • Gaps in Coverage • Over-exposed regions • Crowded regions

  9. Summary: Guide Star Catalog for NGST GSC-2 + 2MASS  sufficient density and accuracy to be used as the guide star catalog for NGST.

  10. Nexus • Pathfinder for NGST - flight demonstration testbed for NGST Technology • Prior to launch, each phase of Nexus will reduce risk & help NGST. • Actual Nexus flight/mission will be final validation with enough time to fix problems for NGST. • Launch Date: late 2004/early 2005. • Mission Orbit: L2.

  11. Nexus Targets Nexus must validate critical NGST wavefront sensing and control and guiding procedures. Search for targets and associated guide stars to ensure there will be an adequate number of pairs for WS testing.

  12. 1.3’ 1.3’ 1.3’ Target Area(on sky) WSC Detector Guider Detector initial location of target 0.92’ 0.38’ 0.92’ 0.38’ - area covered by field diversity experiment (50%) - initial allowable area for guide star

  13. Catalog Search • The Catalog • Tycho-2 Catalog • 2.5 million stars with positions, proper motion, and magnitudes (BT and VT) • Observations from the ESA Hipparcos satellite in combination with the Astrographic Catalog and 143 other ground-based star catalogs • Density: 25 stars deg-2 (Galactic poles), 150 stars deg-2 (Galactic plane). • Positional accuracy: 60 mas • Photometric accuracy: 0.10 mag • Limiting magnitude: K~10-11

  14. Query: Selection Criteria • Target Stars • Magnitude: K<10 • No nearby neighbors within 27” and brighter than Kprimary+5 • Guide Stars • Magnitude range: 8<K<14 • No nearby neighbors within 5” • Separation • Annulus with radius=2.6’±0.19’

  15. Process of Selection • Sort catalog (in declination) • Convert to K magnitude • Reject objects • Color • Magnitude error above tolerance • No mean position given (no ground-based position) • Find target objects • Search for nearby spoiler stars • Search for guide stars • If match found – search for spoiler stars for GS

  16. Color Transformations (VT – K) (BT – VT) data from Gunn and Struker (ApJ Supp. 52 June 1983)

  17. Results of Selection • Number of objects in catalog: 2 539 913 • Rejected objects: • No mean position given 122 543 • B-V > 1.3 472 566 • B-V < -0.39 12 080 • Magnitude error > 0.5m 25 796 • Total number rejected 632 985 • Number of objects remaining: 1 906 928 • Target/GS pairs found: 82 755

  18. Magnitude of Target Stars # Pairs 2-3 11 3-4 52 4-5 184 5-6 769 6-7 2525 7-8 7683 8-9 22375 9-10 49156 Histogram of Pairs found

  19. Tycho-2 magnitude distribution

  20. Distribution of Pairs on Sky # pairs =1016

  21. Distribution of Pairs on Sky # pairs =2525

  22. Distribution of Pairs on Sky # pairs =7683

  23. Distribution of Pairs on Sky # pairs =22315

  24. Distribution of Pairs on Sky # pairs =49156

  25. Conclusions • We find about 82,000 qualified target pairs (Nqual) • Number of instantaneously available target pairs (Ninst) is Nqual multiplied by following factors: • 10/360 (orientation) • 0.8 (spectral type) • 1/3 (field-of-regard) • Ninst=600 • Continue with study- Use a catalog with a fainter limiting magnitude ( GSC-2); this could have a dramatic effect in adding spoilers

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