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

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

Dec 27, 2022 318 likes •620 views

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

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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. Todd1, D. Coward2 and M.G. Zadnik1

Email: michael.todd@icrar.org

1 Curtin University, Western Australia 2 The University of Western Australia

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GREAT-SSO, Pisa, 4 May 2011 1

Part 1 The Zadko Telescope

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Zadko Telescope - Introduction

Rapid response optical telescope Fully robotic Unique location

2 GREAT-SSO, Pisa, 4 May 2011

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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

Zadko Telescope – Specifications

(Coward et al. 2010)

3 GREAT-SSO, Pisa, 4 May 2011

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Zadko Telescope - Location

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About 70 km north from Perth

GREAT-SSO, Pisa, 4 May 2011

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Zadko Telescope - Location

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Co-located with Australian LIGO, the Gravity Discovery Centre (a science education

  • utreach facility) and the Leaning Tower of Gingin (Torre pendente di Gingin)

GREAT-SSO, Pisa, 4 May 2011

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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

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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

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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

Can interrupt schedule from external triggers

  • GRB
  • Gravity Wave
  • Neutrino...

}

(Klotz 2008)

8 GREAT-SSO, Pisa, 4 May 2011

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Robotic Software Structure

Not telescope dependent!

9 GREAT-SSO, Pisa, 4 May 2011

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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 GW triggers LIGO/VIRGO Current MOU in place Extra-Galactic Neutrino searches Neutrino triggers ANTARES, TAROT Pilot program 2011 Binary asteroid studies Optical UWA, OCA, Curtin Current Education outreach Optical UWA, Curtin, Polly Farmer Foundation Current

Current Projects

10 GREAT-SSO, Pisa, 4 May 2011

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Future Projects

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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

GREAT-SSO, Pisa, 4 May 2011

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Part 2 Trojan asteroids in the inner Solar System

GREAT-SSO, Pisa, 4 May 2011

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There are about 570,958 known1 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)

Trojans - Introduction

13 GREAT-SSO, Pisa, 4 May 2011

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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

  • ccurs 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.

What is a Trojan?

14 GREAT-SSO, Pisa, 4 May 2011

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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)

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Earth Trojans

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

GREAT-SSO, Pisa, 4 May 2011

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Synthesis of orbit inclination model (Morais & Morbidelli 2002) and heliocentric longitude model (Tabachnik & Evans 2000) to identify probability regions

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Earth Trojans

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.

GREAT-SSO, Pisa, 4 May 2011

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Earth Trojans

  • Need to observe at elongations close to the Sun
  • Small observing window after sunset and before sunrise

(Image: NASA)

Earth Trojans – Observing Constraints

17 GREAT-SSO, Pisa, 4 May 2011

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Earth Trojans Earth Trojans – Field survey options

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Telescope Limiting mag. Exp. FOV FOVs Time

Zadko R ~ 21 180s 0.15 deg2 23267 1160h TAROT R ~ 18 60s 3.5 deg2 998 16.6h SkyMapper g ~ 21.9 110s 5.7 deg2 613 18.7h Catalina V ~ 20 30s 8.0 deg2 437 3.6h PTF 1.2m R ~ 20.6 60s 8.1 deg2 431 7.2h Pan-STARRS R ~ 24 30s 7.0 deg2 499 4.2h LSST r ~ 24.7 30s 9.6 deg2 364 3.0h GAIA V ~ 20

Note 1

0.45 deg2 7756

Note 1: GAIA to operate in continuous scanning mode

Only possible to observe entire field with large survey telescope! Will take several days. Option 1: Survey entire field Solid angle of field is 3490 deg2.

GREAT-SSO, Pisa, 4 May 2011

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Earth Trojans Earth Trojans – Field survey options

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Telescope Limiting mag. Exp. FOV FOVs Time Whole field

Zadko R ~ 21 180s 0.15 deg2 8667 433h 1160h TAROT R ~ 18 60s 3.5 deg2 372 6.2h 16.6h SkyMapper g ~ 21.9 110s 5.7 deg2 228 7.0h 18.7h Catalina V ~ 20 30s 8.0 deg2 163 1.4h 3.6h PTF 1.2m R ~ 20.6 60s 8.1 deg2 161 2.7h 7.2h Pan-STARRS R ~ 24 30s 7.0 deg2 186 1.6h 4.2h LSST r ~ 24.7 30s 9.6 deg2 136 1.2h 3.0h GAIA V ~ 20

Note 1

0.45 deg2 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.. Option 2: Survey field within inclination limits Solid angle of field is 1300 deg2.

GREAT-SSO, Pisa, 4 May 2011

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Earth Trojans Earth Trojans – Field survey options

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Option 3: Survey in ecliptic plane ±10°

  • 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

Solid angle of field is ~900 deg2

Telescope Limiting mag. Exp. FOV FOVs Time Whole field

Zadko R ~ 21 180s 0.15 deg2 5840 292h 1160h TAROT R ~ 18 60s 3.5 deg2 257 4.3h 16.6h SkyMapper g ~ 21.9 110s 5.7 deg2 157 4.8h 18.7h Catalina V ~ 20 30s 8.0 deg2 112 56m 3.6h PTF 1.2m R ~ 20.6 60s 8.1 deg2 111 111m 7.2h Pan-STARRS R ~ 24 30s 7.0 deg2 128 64m 4.2h LSST r ~ 24.7 30s 9.6 deg2 94 47m 3.0h GAIA V ~ 20 0.45 deg2 400

GREAT-SSO, Pisa, 4 May 2011

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Telescope Limiting mag. Exp. FOV FOVs Time

Zadko R ~ 21 180s 0.15 deg2 590 – 930 29.5 – 46.5h TAROT R ~ 18 60s 3.5 deg2 26 – 40 26 – 40m SkyMapper g ~ 21.9 110s 5.7 deg2 16 – 25 30 – 46m Catalina V ~ 20 30s 8.0 deg2 12 – 18 6 – 9m PTF 1.2m R ~ 20.6 60s 8.1 deg2 12 – 18 12 – 18m Pan-STARRS R ~ 24 30s 7.0 deg2 13 – 20 7 – 10m LSST r ~ 24.7 30s 9.6 deg2 10 – 15 5 – 8m GAIA V ~ 20 0.45 deg2 200 - 300

Earth Trojans Earth Trojans – Field survey options

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Option 4: Survey a swath of the field For a 10˚ swath, area ~90 - 140 deg2

  • 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

GREAT-SSO, Pisa, 4 May 2011

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  • Apparent magnitude for 1 km object ranges from 17.9 to 19.5
  • Assumed albedo 0.20
  • No atmospheric extinction

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Earth Trojans – Variation in magnitude

Variation in apparent magnitude across field. Inverse square law dominant over phase angle. Earth Trojan (L4) target field.

GREAT-SSO, Pisa, 4 May 2011

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Mars Trojans exist near the L4 and L5 Lagrangian points

  • f Mars’ orbit.

Known: 4 Predicted: ~50 (diam. > 1 km) (Tabachnik & Evans 1999)

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Mars Trojans

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)

GREAT-SSO, Pisa, 4 May 2011

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Synthesis of orbit inclination model (Scholl, Marzari & Tricarico 2005) and heliocentric longitude model (Tabachnik & Evans 2000) to identify probability regions.

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Mars Trojans

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.

GREAT-SSO, Pisa, 4 May 2011

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Earth Trojans Mars Trojans – Field survey options

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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
  • ut the field during the ~4 months the fields are visible.

Mars Trojan target field at opposition. Indicated angles of longitude and latitude are heliocentric angles.

Apparent magnitude for 1km

  • bject ranges from 16.9 to 19.3

across field

  • Assumed albedo 0.20
  • No atmospheric extinction

GREAT-SSO, Pisa, 4 May 2011

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Earth Trojans Conclusions

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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

GREAT-SSO, Pisa, 4 May 2011

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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