Michael Todd May 4, 2011 M. Todd 1 , D. Coward 2 and M.G. Zadnik 1 - PowerPoint PPT Presentation

An optimal search strategy for Trojan asteroids and science follow-up of GAIA alerts with the Zadko Telescope, Western Australia Michael Todd May 4, 2011 M. Todd 1 , D. Coward 2 and M.G. Zadnik 1 Email: michael.todd@icrar.org 1 Curtin University, Western Australia 2 The University of Western Australia

Part 1 The Zadko Telescope 1 GREAT-SSO, Pisa, 4 May 2011

Zadko Telescope - Introduction Rapid response optical telescope Fully robotic Unique location 2 GREAT-SSO, Pisa, 4 May 2011

Zadko Telescope – Specifications Telescope: Primary mirror aperture 1.0 m Focal length 4.0 m Focal ratio f/4.0 Camera: Model Andor iKon DW436BV CCD array 2048 x 2048 pixels Pixel size 13.5 x 13.5 µm -50 ° C Operating temperature Field of view 23.5 x 23.5 arc-minutes Limiting magnitude R≈21 (180 s exposure) Location: 115 ° 42’47.2” E Longitude 31 ° 21’21.5” S Latitude Altitude 50 m ASL (Coward et al. 2010) 3 GREAT-SSO, Pisa, 4 May 2011

Zadko Telescope - Location About 70 km north from Perth 4 GREAT-SSO, Pisa, 4 May 2011

Zadko Telescope - Location Co-located with Australian LIGO, the Gravity Discovery Centre (a science education outreach facility) and the Leaning Tower of Gingin (Torre pendente di Gingin) 5 GREAT-SSO, Pisa, 4 May 2011

TAROT TAROT (Télescopes à Action Rapide pour les Objets Transitoires)  a network of fully robotic rapid response telescopes (Klotz et al. 2008) Zadko Telescope + TAROT  a global fast response robotic telescope network for the study of multispectra transients and potentially dangerous Earth-orbiting space debris 6 GREAT-SSO, Pisa, 4 May 2011

TAROT TAROT Calern: first light 1998. 15 GRBs observed since 2004. TAROT La Silla: first light 2006. 6 GRBs observed since 2006. (http://tarot.obs-hp.fr) Zadko Telescope: first light 2009. 7 GRBs observed since 2009.  robotised and networked with TAROT in 2010 1998 2006 2010 7 GREAT-SSO, Pisa, 4 May 2011

Automatic vs Robotic Automatic telescope • Surveys • Scheduling done before night • Routine Supernova search, variable stars • 1+ operators • e.g. OGLE, EROS, LSST Can interrupt schedule from Robotic telescope } external triggers • Targets of Opportunity -GRB • -Gravity Wave Rescheduling during the night -Neutrino... • GRB (early detections), confirmations • no operator required • e.g. ROTSE, TAROT, ASAS (Klotz 2008) 8 GREAT-SSO, Pisa, 4 May 2011

Robotic Software Structure Not telescope dependent! 9 GREAT-SSO, Pisa, 4 May 2011

Current Projects Research projects Spectrum Partners Status Gamma ray bursts GRB optical TAROT (France), UWA, Current follow-up Curtin Gamma ray bursts GRB astrophysics TAROT/NASA Current Gravitational waves GW triggers LIGO/VIRGO Current searches MOU in place Extra-Galactic Neutrino Neutrino triggers ANTARES, TAROT Pilot program 2011 searches Binary asteroid studies Optical UWA, OCA, Curtin Current Education outreach Optical UWA, Curtin, Current Polly Farmer Foundation 10 GREAT-SSO, Pisa, 4 May 2011

Future Projects Research projects Spectrum Partners Status Optical follow-up of Radio triggers ICRAR/ASKAP Proposed 2012 radio transients (Australian SKA Pathfinder) GAIA Satellite follow-up Optical ESA, OCA, Obs. Paris Proposed 2012 GBOT (GAIA) Optical ESA, OCA, Obs. Paris Proposed 2012 Space-debris tracking Optical TAROT, ICRAR, CNRES, Pilot program 2010 ESA Proposed 2012 11 GREAT-SSO, Pisa, 4 May 2011

Part 2 Trojan asteroids in the inner Solar System 12 GREAT-SSO, Pisa, 4 May 2011

Trojans - Introduction There are about 570,958 known 1 asteroids in the Solar System Of these, there are:  Jupiter Trojans: 4832  Mars Trojans: 4 (predicted ~50)  Earth Trojans: 0 (predicted ~17) 1 as of April 18, 2011 (www.minorplanetcenter.org) 13 GREAT-SSO, Pisa, 4 May 2011

What is a Trojan? Trojans are those asteroids which: • share an orbit with a planet, and • are located in regions around L4 and L5 Lagrangian points These have 1:1 mean motion resonance (coorbital), which only occurs if the semi-major axis is similar to the planet and the eccentricity must be close to e = 0 for them to remain in the Lagrangian region during their orbits and so be considered to be Trojans. 14 GREAT-SSO, Pisa, 4 May 2011

Earth Trojans Earth Trojans (may) exist near the L4 and L5 Lagrangian points of Earth’s orbit. Known: 0 Predicted: 0.65 ± 0.12 (diam. > 1 km) 16.3 ± 3.0 (diam. > 100 m) (Morais & Morbidelli 2002) Known asteroids having a ≈1 AU (grey) compared to Regions in which a body may exist in co-orbital motion with a planet stable inclinations for Earth Trojans (red), from Morais & Morbidelli (2002) 15 GREAT-SSO, Pisa, 4 May 2011

Earth Trojans Synthesis of orbit inclination model (Morais & Morbidelli 2002) and heliocentric longitude model (Tabachnik & Evans 2000) to identify probability regions Earth Trojan (L4) target field. Normalised probability contour for Earth Trojan bodies by Inclination and Heliocentric Longitude. >63% probability that Trojan will occupy this region. 16 GREAT-SSO, Pisa, 4 May 2011

Earth Trojans Earth Trojans – Observing Constraints • Need to observe at elongations close to the Sun • Small observing window after sunset and before sunrise (Image: NASA) 17 GREAT-SSO, Pisa, 4 May 2011

Earth Trojans Earth Trojans – Field survey options Option 1: Survey entire field Solid angle of field is 3490 deg 2 . Telescope Limiting Exp. FOV FOVs Time mag. Zadko R ~ 21 180s 0.15 deg 2 23267 1160h 3.5 deg 2 TAROT R ~ 18 60s 998 16.6h 5.7 deg 2 SkyMapper g ~ 21.9 110s 613 18.7h 8.0 deg 2 Catalina V ~ 20 30s 437 3.6h PTF 1.2m R ~ 20.6 60s 8.1 deg 2 431 7.2h Pan-STARRS R ~ 24 30s 7.0 deg 2 499 4.2h 9.6 deg 2 LSST r ~ 24.7 30s 364 3.0h 0.45 deg 2 GAIA V ~ 20 7756 Note 1 Note 1: GAIA to operate in continuous scanning mode Only possible to observe entire field with large survey telescope! Will take several days. 18 GREAT-SSO, Pisa, 4 May 2011

Earth Trojans Earth Trojans – Field survey options Option 2: Survey field within inclination limits Solid angle of field is 1300 deg 2 . Telescope Limiting Exp. FOV FOVs Time Whole mag. field Zadko R ~ 21 180s 0.15 deg 2 8667 433h 1160h 3.5 deg 2 TAROT R ~ 18 60s 372 6.2h 16.6h 5.7 deg 2 SkyMapper g ~ 21.9 110s 228 7.0h 18.7h 8.0 deg 2 Catalina V ~ 20 30s 163 1.4h 3.6h PTF 1.2m R ~ 20.6 60s 8.1 deg 2 161 2.7h 7.2h Pan-STARRS R ~ 24 30s 7.0 deg 2 186 1.6h 4.2h 9.6 deg 2 LSST r ~ 24.7 30s 136 1.2h 3.0h 0.45 deg 2 GAIA V ~ 20 2889 Note 1 Note 1: GAIA to operate in continuous scanning mode Can be done in 1 day with large survey telescope. Requires pairs of observations, repeated at 3-month intervals.. 19 GREAT-SSO, Pisa, 4 May 2011

Earth Trojans Earth Trojans – Field survey options Option 3: Survey in ecliptic plane ± 10 ° Solid angle of field is ~900 deg 2 Telescope Limiting Exp. FOV FOVs Time Whole mag. field Zadko R ~ 21 180s 0.15 deg 2 5840 292h 1160h 3.5 deg 2 TAROT R ~ 18 60s 257 4.3h 16.6h 5.7 deg 2 SkyMapper g ~ 21.9 110s 157 4.8h 18.7h 8.0 deg 2 Catalina V ~ 20 30s 112 56m 3.6h PTF 1.2m R ~ 20.6 60s 8.1 deg 2 111 111m 7.2h Pan-STARRS R ~ 24 30s 7.0 deg 2 128 64m 4.2h 9.6 deg 2 LSST r ~ 24.7 30s 94 47m 3.0h 0.45 deg 2 GAIA V ~ 20 400 • Look for Trojans crossing ecliptic plane • Requires 2 observing sessions per 2-3 weeks for half a year • Less time per session compared to whole field survey • Still requires large FOV telescope 20 GREAT-SSO, Pisa, 4 May 2011

Earth Trojans Earth Trojans – Field survey options Option 4: Survey a swath of the field For a 10˚ swath, area ~90 - 140 deg 2 Telescope Limiting Exp. FOV FOVs Time mag. 590 – 930 29.5 – 46.5h Zadko R ~ 21 180s 0.15 deg 2 26 – 40 26 – 40m 3.5 deg 2 TAROT R ~ 18 60s 16 – 25 30 – 46m 5.7 deg 2 SkyMapper g ~ 21.9 110s 12 – 18 6 – 9m 8.0 deg 2 Catalina V ~ 20 30s 12 – 18 12 – 18m PTF 1.2m R ~ 20.6 60s 8.1 deg 2 13 – 20 7 – 10m Pan-STARRS R ~ 24 30s 7.0 deg 2 10 – 15 5 – 8m 9.6 deg 2 LSST r ~ 24.7 30s 0.45 deg 2 GAIA V ~ 20 200 - 300 • Use Earth’s revolution about Sun to sweep out field • Requires 2 observing sessions per week for up to a year • Minimal time per session compared to whole field survey • Observations made at end of twilight before/after primary science 21 GREAT-SSO, Pisa, 4 May 2011

Earth Trojans – Variation in magnitude • Apparent magnitude for 1 km object ranges from 17.9 to 19.5 • Assumed albedo 0.20 • No atmospheric extinction Variation in apparent magnitude across field. Earth Trojan (L4) target field. Inverse square law dominant over phase angle. 22 GREAT-SSO, Pisa, 4 May 2011

Mars Trojans Mars Trojans exist near the L4 and L5 Lagrangian points of Mars’ orbit. Known: 4 Predicted: ~50 (diam. > 1 km) (Tabachnik & Evans 1999) Inclinations of 72 known asteroids (grey) with 𝑏 ≈1.52 AU (similar to Mars) compared to prediction from Trojan model (red [L4] / blue [L5] lines), from Tabachnik and Evans (1999) 23 GREAT-SSO, Pisa, 4 May 2011