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PILOT overview Pathfinder for an International Large Optical Telescope

This design study proposes a joint Australian/European facility, the PILOT, as the first major optical/infrared telescope in Antarctica. It discusses the advantages of Antarctica and Dome C as a telescope site, and highlights the benefits of a 2.5-meter telescope. The study also covers the challenges of operating in Antarctica and the design features required to ensure optimal performance.

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PILOT overview Pathfinder for an International Large Optical Telescope

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  1. The PILOT Design StudyWill Saunders, Peter Gillingham, Andrew McGrath, Roger Haynes, AAOJohn Storey, Jon Lawrence, UNSWASA, July 2008

  2. PILOT overviewPathfinder for an International Large Optical Telescope Dome C 3250m altitude – First major Optical/Infrared telescope in Antarctica– Proposed as joint Australian/European facility– To be sited at Dome C (3250m, 123E 75S) – First light 2013– 2.5 metre Optical/Infrared telescope– NCRIS-funded design study now almost complete– Twin science and pathfinder role “Australia’s top priorities for new infrastructure funding this decade are to commence 10% participation in the SKA and an ELT, maintain 20% access to 8-m class optical/infrared telescopes, continue operations of the AAO and Australia Telescope, and carry out the PILOT program.”Decadal Plan, 2006

  3. 104 Jy/"2 0.2" 10-6 μm 1 10 1 0 Sky/telescope backgrounds 1 Transparency 0 40 μm 2 10 DC 0.27" DC 7.0 ms DC 5.4" Seeing Isoplanatic angle Coherence timescale CP 2.5" CP 0.8" CP 3.4 ms Why Antarctica? Compared with best temperate sites: • Free atmospheric seeing  2-3  median seeing ~0.27" above 60m  best < 0.1" • Isoplanatic angle  2-3 • Coherence timescale  2-3 • Scintillation noise  3-4 • Thermal IR backgrounds  10-100 • Precipitable Water Vapour  4 • Cloud  2

  4. Why Dome C? Existing Concordia French/Italian station Well-characterised site Regular traverse route Can see geostationary satellites Low Auroral emission Relatively high sky coverage

  5. Why Australia? Dome C ● ●Casey Hobart● No good O/IR astronomical sitesNo space programProximityHistory of Antarctic AstronomyLarge Antarctic ProgramAustralian Antarctic Territory

  6. Why 2.5m? AO D/r0 ~ 1 at 2.4μm – diffraction-limited with fast guiding D/r0 ~ 4 at 0.8μm – optimal size for fast guiding Available from multiple vendors – reduced timecales, cost and risk Limit for passive support and ion-polishing Limit for convenient shipping Allows world-beating science Tip-Tilt Natural seeing D/r0=1 D/r0=4

  7. Antarctic 'Challenges' Seeing vs height 100m Temperature vs height 235 K 200 Temperature vs time and height for 1 day -80 C -30  Temperature -85°C to -30° Humidity ~150% Diamond dust (Ice crystals) Very turbulent and variable surface layer up to ~60m dT/dt up to 10°C/hour dT/dZ = 0.2-1°C/m Less dark time? Less sky coverage Limited real-time data transfer Inaccessible in winter

  8. PILOT Design Overview – 2.5 metre Ritchey-Chrétien telescope – Twin f/10 Nasmyth foci– Infrared optimised, but can use 0.35μm-350μm – Diffraction-limited optics over 1° field– Wide-field pixel scale matched to median free seeing – Diffraction limited imaging over small fields at all wavelengths > 0.5μm– Fast tip-tilt secondary – f/1.5 meniscus Zerodur primary, actively ventilated – Active ventilation of mirror and telescope main structure – Installed on a 30m tower to get above ground layer– Enclosure for temperature and humidity control – 24 hour remote operation with minimal human interventionOptics, thermal differentials, windshake, guiding, must all be twice as good as other terrestrial telescopes to do justice to the site

  9. Tower – Get above worst of turbulent layer – Reduce air temperature gradient – But ~15°C warmer – Also windier, median ~7m/s – Lowest mode 2-3Hz – Windshake < 0.25", will clean up with tip-tilt – Probably aluminium – Assembled and built at site 1 year before telescope arrives Windshake

  10. PILOT with air T=-48C 150mg/m3 150% RH T=-48C 75mg/m3 75% RH +5 T=-53C 75mg/m3 150% RH ΔT (°C) 3 2 1 Must protect telescope from:(a) diamond dust(b) frost – 150% RH(c) wind shake(d) temperature gradientPut telescope in dome, aperture as small as possible, ventilate continuously with dry air warmed to same temperature as apertureAlso ventilate primary mirror, to (a) speed up thermalisation and (b) allow temperature differences 1C or more

  11. Delivered image quality Tip-tilt removes most windshake and residual ground-layer turbulence. Using balloon or MASS/SNODAR values makes little difference to delivered image quality.Budget for entire PILOT system is 0.2" d80 (~0.13" FWHM)Median delivered wide-field image quality ~0.3" for izYJHKMedian delivered narrow-field image quality < 0.25" for izYJHK

  12. Sensitivities Optical sensitivity comparable with 8m.Greatest sensitivity gains over temperate sites at K,L,M, and mid-infrared.At K, background is 30-40 times less thanbest temperate sites, image quality 2-3 times as good. =>70 times faster than VISTA to given depth, 10 times faster than seeing-limited 8-m.Only possibility to get NIR data of resolution and depth comparable to big optical surveys.Only possibility to get high resolution matching photometry for Spitzer warm mission (3.6+4.5μm).No comparison with JWST, but JWST takes 50 hrs/deg2 just for slewing => wide-field

  13. Science Drivers for PILOT: Science drivers must be driven by at least one of: – resolution over wide fields– low IR background– photometric stability– continuous coverageFour identified big science drivers so far:– H2 in our Galaxy– The first light in the Universe– The earliest stellar populations– The equation of state of the Universe

  14. Proposed Instrumentation 1. Fast optical camera, 0.35-1μm, 0.02"/pix, 20" x 20". Diffraction-limited imaging over small fields.2. Wide-field MIR camera, 10-40μm, 1"/pix, 10' x 10', grisms/Fabry-Perot filter, R>10,000. Terahertz?3. Wide-field NIR camera: 1-5μm, 0.15"/pix, 4K x 4K, 11'x11'. Also allows narrow-field diffraction limited zYJHK imaging: 1-2.5μm, 0.06"/pix, 4'x4'.4. Wide-field Optical camera, 0.35-1μm, 0.08"/pix, 32K x 32K, 40' x 40'. Orthogonal Transfer Array CCDs?Overall, allows both wide-field and diffraction-limited imaging from 0.4μm - 40μm.

  15. Science Driver: Galactic ecology S(1) 160K 17.0µm S(2) 185K 12.3µm AV=1 Molecular clouds are stellar nurseries, but H2 very hard to detect directly. Best lines in mid-infrared, but sensitivity from ground is very poor.Use Fabry-Perot filter to carry out survey of H2 0-0 S(1) & S(2) 12+17µm lines (ground state lines of molecular hydrogen). Use phase shift to build up velocity cube with ~10km/s  2" resolution.Will detect AV=1 clouds to < 200K, enough to map surfaces of normal MC's Can do 12μm during daytime

  16. Science Driver: Highest redshift stellar populations PILOT Kdark Spitzer warm mission will cover large areas at 3.6μm+4.5μm (7500 hours). Need K-band data to find 4000Ǻ break at z>6. Too hard for VISTA. PILOT survey speed comparable to Spitzer.Takes few hundred Myear to develop 4000Ǻ break. Detection at z~6-7 pushes => galaxy formation at z>10 Re-ionisationepoch, Population III. Expect 103-104 galsCan maybe get 3μm data with PILOT VLT K-band Spitzer

  17. Science Driver: First light in the UniversePair-Instability SuperNovae at z>10 SN2006gy brightest ever detectedMetal-poor, Pair-Instability SuperNovaExpect similar supernovae from Pop IIICan see 250Msol in 1 hour at Kd to z=15Expect to see few/yearVISTA not sensitive enoughJWST FOV too small (~1/deg2)

  18. 0.7" 0.3" 0.3" 0.1"FWHM 0.5" FWHM Science Driver: Equation of State of the Universe via a large weak lensing survey – Measures evolution of equation of state of Universe, hence nature of Dark Energy – Most promising route to understanding Dark Energy (NASA, NSF, ESA…) – Need large sky coverage, very stable PSF, resolution limited– Antarctica gives 10-100 fold advantage– As good as DUNE and much sooner

  19. Other science: PILOT 4 hrs – Lensing masses for South Pole Telescope S-Z clusters– Near-field cosmology - g-K colours for ~109 stars in Milky Way and nearby galaxies– Star formation rate of the Universe via type II SN rate– Star cluster astroseismology– Exoplanet secondary transits– Microlensing by ice-giant and terrestrial planets– H2 surveys of nearby galaxies– Pop III Gamma Ray Burst followup in K,L,M– Lucky imaging - Hubble from the ground– Source finder for GMT/JWST spectroscopy– Your idea here– Breakout session Tuesday lunchtime– PILOT science case poster

  20. Beyond PILOT WHAT? GMT-A LAPCAT In general, can always do Adaptive Optics to < ½ the wavelength in Antarctica. So highest resolution is always comparable to telescope with twice the diameterAt Kd (only), sensitivity is greater thana telescope with twice the diameter8m-class telescope would be more sensitive and MUCH faster surveying than ELT at KCompetitive with JDEM (exSNAP), similar timescale 20m-class telescopemeets many original goals of OWL (Originally Was Larger)

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