NGST/NEXUS Operations Jane Morrison October 19, 2000 Nexus NGST

NGST at a Glance Formulation Phase (A/B)Implementation Phase -Logical successor to HST -Key part of the Origins Program -Logical successor to HST -Key part of the Origins Program Select Prime PDR/NAR CDR Launch 8m primary mirror µm wavelength range 5 year mission life (10 year goal) passively cooled to <50K L2 orbit Launch 2009 LRD

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. Guiding with NGST

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 2'2' 4'4'

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 N GS > 1 I J  17.0 J J  16.2 K J  15.5

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 K s = 14.3 Positional accuracy better than 0. 5 arc seconds

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

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

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

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 Mission Orbit: L2.

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.

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

Catalog Search The Catalog –Tycho-2 Catalog –2.5 million stars with positions, proper motion, and magnitudes (B T and V T ) –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

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

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

Color Transformations (B T – V T ) (V T – K) data from Gunn and Struker (ApJ Supp. 52 June 1983 )

Results of Selection Number of objects in catalog: Rejected objects: –No mean position given –B-V > –B-V < –Magnitude error > 0.5 m –Total number rejected Number of objects remaining: Target/GS pairs found:

Histogram of Pairs found # Pairs Magnitude of Target Stars

Tycho-2 magnitude distribution

Distribution of Pairs on Sky # pairs =1016

# pairs =2525 Distribution of Pairs on Sky

# pairs =7683 Distribution of Pairs on Sky

# pairs =22315 Distribution of Pairs on Sky

# pairs =49156 Distribution of Pairs on Sky

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