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
Zadko Telescope - Introduction Rapid response optical telescope Fully robotic Unique location 2
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 Operating temperature -50 C Field of view 23.5 x 23.5 arc-minutes Limiting magnitude R 21 (180 s exposure) Location: Longitude 115 42 47.2 E Latitude 31 21 21.5 S Altitude 50 m ASL (Coward et al. 2010) 3
Zadko Telescope - Location About 70 km north from Perth 4
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
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
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
Automatic vs Robotic Automatic telescope Surveys Scheduling done before night Routine Supernova search, variable stars 1+ operators e.g. OGLE, EROS, LSST Robotic telescope Targets of Opportunity Rescheduling during the night GRB (early detections), confirmations no operator required e.g. ROTSE, TAROT, ASAS } -Neutrino... Can interrupt schedule from external triggers -GRB -Gravity Wave (Klotz 2008) 8
Robotic Software Structure Not telescope dependent! 9
Current Projects Research projects Spectrum Partners Status Gamma ray bursts GRB optical follow-up TAROT (France), UWA, Curtin Current Gamma ray bursts GRB astrophysics TAROT/NASA Current Gravitational waves searches Extra-Galactic Neutrino searches GW triggers LIGO/VIRGO Current MOU in place Neutrino triggers ANTARES, TAROT Pilot program 2011 Binary asteroid studies Optical UWA, OCA, Curtin Current Education outreach Optical UWA, Curtin, Polly Farmer Foundation Current 10
Future Projects Research projects Spectrum Partners Status Optical follow-up of radio transients Radio triggers ICRAR/ASKAP (Australian SKA Pathfinder) Proposed 2012 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, ESA Pilot program 2010 Proposed 2012 11
Part 2 Trojan asteroids in the inner Solar System 12
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
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
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 stable inclinations for Earth Trojans (red), from Morais & Morbidelli (2002) Regions in which a body may exist in co-orbital motion with a planet 15
Earth Trojans Synthesis of orbit inclination model (Morais & Morbidelli 2002) and heliocentric longitude model (Tabachnik & Evans 2000) to identify probability regions Normalised probability contour for Earth Trojan bodies by Inclination and Heliocentric Longitude. Earth Trojan (L4) target field. >63% probability that Trojan will occupy this region. 16
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
Earth Trojans Earth Trojans Field survey options Option 1: Survey entire field Telescope Solid angle of field is 3490 deg 2. Limiting mag. Exp. FOV FOVs Time Zadko R ~ 21 180s 0.15 deg 2 23267 1160h TAROT R ~ 18 60s 3.5 deg 2 998 16.6h SkyMapper g ~ 21.9 110s 5.7 deg 2 613 18.7h Catalina V ~ 20 30s 8.0 deg 2 437 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 LSST r ~ 24.7 30s 9.6 deg 2 364 3.0h GAIA V ~ 20 Note 1 0.45 deg 2 7756 Note 1: GAIA to operate in continuous scanning mode Only possible to observe entire field with large survey telescope! Will take several days. 18
Earth Trojans Earth Trojans Field survey options Option 2: Survey field within inclination limits Telescope Limiting mag. Solid angle of field is 1300 deg 2. Exp. FOV FOVs Time Whole field Zadko R ~ 21 180s 0.15 deg 2 8667 433h 1160h TAROT R ~ 18 60s 3.5 deg 2 372 6.2h 16.6h SkyMapper g ~ 21.9 110s 5.7 deg 2 228 7.0h 18.7h Catalina V ~ 20 30s 8.0 deg 2 163 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 LSST r ~ 24.7 30s 9.6 deg 2 136 1.2h 3.0h GAIA V ~ 20 Note 1 0.45 deg 2 2889 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
Earth Trojans Earth Trojans Field survey options Option 3: Survey in ecliptic plane ±10 Telescope Solid angle of field is ~900 deg 2 Limiting mag. Exp. FOV FOVs Time Whole field Zadko R ~ 21 180s 0.15 deg 2 5840 292h 1160h TAROT R ~ 18 60s 3.5 deg 2 257 4.3h 16.6h SkyMapper g ~ 21.9 110s 5.7 deg 2 157 4.8h 18.7h Catalina V ~ 20 30s 8.0 deg 2 112 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 LSST r ~ 24.7 30s 9.6 deg 2 94 47m 3.0h GAIA V ~ 20 0.45 deg 2 400 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
Earth Trojans Earth Trojans Field survey options Option 4: Survey a swath of the field Telescope For a 10 swath, area ~90-140 deg 2 Limiting mag. Exp. FOV FOVs Time Zadko R ~ 21 180s 0.15 deg 2 590 930 29.5 46.5h TAROT R ~ 18 60s 3.5 deg 2 26 40 26 40m SkyMapper g ~ 21.9 110s 5.7 deg 2 16 25 30 46m Catalina V ~ 20 30s 8.0 deg 2 12 18 6 9m PTF 1.2m R ~ 20.6 60s 8.1 deg 2 12 18 12 18m Pan-STARRS R ~ 24 30s 7.0 deg 2 13 20 7 10m LSST r ~ 24.7 30s 9.6 deg 2 10 15 5 8m GAIA V ~ 20 0.45 deg 2 200-300 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
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. Inverse square law dominant over phase angle. Earth Trojan (L4) target field. 22
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 a 1.52 AU (similar to Mars) compared to prediction from Trojan model (red [L4] / blue [L5] lines), from Tabachnik and Evans (1999) 23
Mars Trojans Synthesis of orbit inclination model (Scholl, Marzari & Tricarico 2005) and heliocentric longitude model (Tabachnik & Evans 2000) to identify probability regions. Normalised probability contour for Mars Trojan bodies by Inclination and Heliocentric Longitude. Mars Trojan target field at opposition. >48% probability that Trojan will occupy this region. 24
Earth Trojans Mars Trojans Field survey options Field at opposition subtends 9450 - nearly 3x larger than Earth Trojan field! Best approach: survey a swath of the field (L4 / L5) use Earth s and Mars revolutions about the Sun to sweep out the field during the ~4 months the fields are visible. Apparent magnitude for 1km object ranges from 16.9 to 19.3 across field Assumed albedo 0.20 No atmospheric extinction Mars Trojan target field at opposition. Indicated angles of longitude and latitude are heliocentric angles. 25
Earth Trojans Conclusions Zadko Telescope Unique location in the Southern Hemisphere Most suited for optical follow-up tasks With TAROT forms a global network of robotic telescopes Can respond to external triggers automatic scheduling Trojan asteroid search Trojan fields occupy significant sky area Most efficient use of telescope time: divide search field into strips use Earth s revolution about Sun to sweep out area 27
Thanks for your attention Zadko Telescope http://www.zt.science.uwa.edu.au/ Key contacts: David Coward (Director) UWA Email: coward@physics.uwa.edu.au