Detector Mosaic Design Considerations for a Wide FOV Drift-Scan Survey Telescope John T. McGraw Mark R. Ackermann Peter C. Zimmer University of New Mexico and Lt. Eric Golden AFRL

The Near Earth Space Surveillance Initiative (NESSI) NESSI is a collaboration between the University of New Mexico (CTI) and McDonald Observatory of The University of Texas at Austin (HET). The project is funded by AFRL.

UNM/USAFA Cooperative Research Design and implementation Data reduction and analysis Follow-up observations RR Lyrae Star W UMa Eclipsing Variable

The CCD/Transit Instrument (CTI) 1.8-m, f/2.2 parabolic primary Paul-Baker optical system 3.96-m focal length 3.96-m focal length 52 arcsec/mm field scale 52 arcsec/mm field scale Existing thermally- compensating structure Existing thermally- compensating structure

The Paul-Baker Optical System Very wide FOV Excellent images Compact design Proposed for LSST

Time-Delay and Integrate (TDI) Readout Mode Advantages: Stable telescope does not move Constant gravity load Instrumental signature averaged over rows “Features:” Meridian TDI adds to the PSF Differential track rate

CTI and HET Survey Geometry E W HET and CTI FOV

Elements of an astronomical survey Discover new objects and phenomena Synoptically monitor objects Motion Motion Variability Variability Provide a statistically significant, unbiased sample of objects Discover targets of opportunity Enable follow up observations Enable follow up observations

The CCD/Transit Instrument (CTI II) Meridian-pointing 1.8-m telescope Images formed on multiple CCDs operated in TDI mode no moving parts no moving parts multiple optical/IR colors each night multiple optical/IR colors each night Fully automated operation Photometric imaging over 1 - 2° FOV surveys ~120° 2 each night surveys ~120° 2 each night V  22.5 nightly detection limit V  22.5 nightly detection limit

Science Drivers Supernova detection AGN Reverberation IR Astrometry

Optical and Near IR Astrometry Single-image astrometry includes stars 90° apart – parallaxes Goal: 3 mas rms per night stellar centroids HET spectra – spectral type and radial velocity

SN Ia: The universe is expanding. Doppler shift measurements give higher recession velocities for more distant galaxies. The rubber band experiment.

The universe is expanding – Hubble’s Law. Hubble’s Constant is the slope of this line. The slope determines the “age” of the universe.

We see the remnant of the Big Bang that initiated the universe in the cosmic microwave background.

One way of visualizing an open, flat or closed universe.

The fate of the universe is determined by what’s in it.

Type Ia supernovae are “standard candles.”

Type Ia supernovae can measure cosmological distances.

Supernovae at large distance map the former conditions of the universe.

The history of cosmic expansion provided by SNe Ia.

Interpreting cosmological parameter space can be tricky.

The annotated version of the previous figure.

Active Galactic Nuclei Discovery of Quasars Quasar Lensing AGN Reverberation

Active Galactic Nuclei The Nature of Quasars

Active Galactic Nuclei The “Standard Model” Accretion disc scale ~ 1 pc Accretion disc scale ~ 1 pc

Active Galactic Nuclei AGN phenomenon is ubiquitous Milky Way? Milky Way? All galaxies? All galaxies? Evolution? Evolution?

Active Galactic Nuclei Mapping: Model, Orientation, Time History Light travel timescale ~ 3 years Light travel timescale ~ 3 years Dynamical timescale ~ r/V ~ 10 – 100 years Dynamical timescale ~ r/V ~ 10 – 100 years

The Obscure Universe The outsider’s view of gravitational lensing:

The Obscure Universe Geometry of Different Optical paths Source geometry Source geometry Lens geometry Lens geometry Source dust chemistry Source dust chemistry Well-sampled light curves Optical path length measurement Optical path length measurement Effects of microlensing Effects of microlensing Dust in lenses Dust in lenses

The Obscure Universe Luminosity variability Days to years Days to years Intrinsic variability Optical path length Microlensing Colley et al Colley et al. 2002

Active Galactic Nuclei AGN Reverberation Mapping the scale, structure, and time-dependent structure changes in the environs of massive black holes Mapping the scale, structure, and time-dependent structure changes in the environs of massive black holes Testing the standard model of AGNs Testing the standard model of AGNs Examples: N1275, N7742 Examples: N1275, N7742

Active Galactic Nuclei Quasars 1° wide strip, α = 8 hours (NGC)  120°² 1° wide strip, α = 8 hours (NGC)  120°² 25 quasars/°² to B = 21  3000 quasars 25 quasars/°² to B = 21  3000 quasars Conservatism: 2° FOV, tilt to cover 10°, B fainter than 22 at S/N = 10, 2df data  all quasars Galaxies (same geometry, B = 19.7)  galaxies  galaxies SNe (same geometry, B = 21 point source)  100 ~ SNe/year  100 ~ SNe/year

PSF Analysis: Motion-induced components Model input: 0.85 arcsec FWHM Moffatt function

Small Pixels Ameliorate Motion-Induced Blur Deconvolution kernel is fully deterministic Blur caused by: 1.Discrete shifting of pixels 2.Curved celestial trajectories – α and δ 3.Differential track rate – all TDI operations

Design Criteria Fully sample the PSF at the R bandpass Include near-IR bandpasses V, R and I optical bandpasses Multiple devices for greater dynamic range Configure optics/focal plane to take advantage of modal 0.85 arcsec seeing at McDonald Observatory Observe Galactic north pole (δ=28°) Strip must intersect HET field of regard

Analysis of Three Optical Designs Paul-Baker And variants involving refractive correctors And variants involving refractive correctors Prime focus Variants include differing numbers of refractive corrector elements Variants include differing numbers of refractive corrector elementsGregorian And variants And variants Astronomical Lidar for Extinction Photometric engineering data Photometric engineering data

The CCD/Transit Instrument (CTI II) Strawman Focal Plane Mosaic Focal Plane Mosaic Strawman Alternatives (EEV CCDs)

The CCD/Transit Instrument (CTI II) Performance CTI S/N (Strawman Mosaic)

The CCD/Transit Instrument (CTI II) Performance S/N at the Detection Limit

Current Survey Comparisons Vital Statistics Survey Name AreaResolutionWavelengthLimitingObs (sq deg) ("/pix)CoverageMagnitude(yearly) Sloan Digital Sky Survey SDSS ugriz r < micron All-Sky Survey 2MASS JHK J < Palomar-Quest Survey PQ UBIR/rizz R < 21 1 PAN-STARRSPS V+R/griz V+R < Large Synoptic Survey Telescope LSST UBVRI R < CCD/Transit Instrument II CTI II BVRIJH R < CTI II Bottom Line: Visible to mid-IR photometry in a single survey Comparable resolution and depth to other surveys Significantly greater repeat observations for variability/astrometry Smaller total area, but widely distributed in galactic latitude and longitude due to nature of transit instrument survey Significant increase in dynamic range Spectroscopic follow-up to same limiting magnitude with HET

The CCD/Transit Instrument (CTI II) Summary CTI II is being designed and built Frontline Research – Science Drivers Frontline Research – Science Drivers Technology transfer to other sky survey telescopes Technology transfer to other sky survey telescopes The “niche” Photometric and astrometric precision Photometric and astrometric precision Repeated observations with one sidereal day cadence Repeated observations with one sidereal day cadence Spectroscopic observations, including real-time targets Spectroscopic observations, including real-time targetsIssues: Final optical design – f/5.5 Final optical design – f/5.5 Detector mosaic Detector mosaic Detector size, pixel size, need for deconvolution Curved channel, OTA devices Curved channel, OTA devices Bandpasses – optical and IR

The CCD/Transit Instrument (CTI) A Sample Sweep East West NorthSouth