Stellar occultations for asteroid astrometry


The high-quality astrometry of Gaia offers unique opportunities for solar system science. Apart from the astrometry of ~150,000 asteroid at ~1 mas accuracy expected in DR3, an additional way of collecting ultra-precise asteroid astrometry can be devised, based on the utilization of the extremely precise positions and parallaxes of stars (~20 μas, for mag<15) in the Gaia catalog.

Stars are often occulted by asteroids, which cast a moving ‘shadow’ path upon the Earth, with cross-track width equal to their diameters. Combining the immense accuracy of Gaia stellar data with precision timing of predicted occultations, one can deduce asteroid positions with an accuracy well below the Gaia nominal ~1 mas!

Occultation astrometry can be a game-changer for asteroid astrometry, extending the time-coverage of Gaia. In the pre-Gaia era the only prediction with a reasonable reliability concerned, in general, asteroids several tens of km in size. This limit is brought down to a few km thanks to Gaia astrometry. A single site, that before could hope in a few positive events per year, can target several 10s per month (mag<14 stars; good for ~40 cm telescopes). We use different telescopes for our observations, ranging from portable instruments to the 1 m C2PU telescopes at Plateau de Calern (OCA). We are also implementing a project of continuous monitoring at the universCity robotic 0.5 m telescope, under construction at that same site.

Main science goals

Specific Campaigns

The Team

  • L. Abe
  • M. Conjat
  • J. Ferreira
  • E. Lagadec
  • M. N'Diaye
  • R. Leiva
  • L. Liberato
  • J.P. Rivet
  • P. Tanga
  • D. Vernet
  • M. Buie (SWRI, CO, USA)
  • S. Bouquillon (SYRTE, France)
  • F. Colas (IMCCE, Paris)
  • J. Desmars (IMCCE, France)
  • K. Tsiganis (University of Tessalonica, Greece)
  • P. Machado (University of Lisbon, Portugal)
  • B. Sicardy (LESIA, Paris)
  • F. Spoto (Minor Planet Center, MA, USA)
  • D. Souami (NAXIS, Belgium)


  • Ferreira, J. F., Tanga, P., Machado, P., & Corsaro, E. (2020), A survey for occultation astrometry of main belt: expected astrometric performances, Astronomy and Astrophysics, 641, A81.
  • Buie, M. W., et al. (2020), Size and Shape Constraints of (486958) Arrokoth from Stellar Occultations, The Astronomical Journal, 159, 130.
  • Dias-Oliveira, A., et al. (2017), Study of the Plutino Object (208996) 2003 AZ84 from Stellar Occultations: Size, Shape, and Topographic Features, The Astronomical Journal, 154, 22.
  • Arlot, J.-E., et al. (2013), Astrometric results of observations of mutual occultations and eclipses of the Uranian satellites in 2007, Astronomy and Astrophysics, 557, A4.
  • Braga-Ribas, F., et al. (2013), The Size, Shape, Albedo, Density, and Atmospheric Limit of Transneptunian Object (50000) Quaoar from Multi-chord Stellar Occultations, The Astrophysical Journal, 773, 26.
  • Tanga, P., & Delbo, M. (2007), Asteroid occultations today and tomorrow: toward the GAIA era, Astronomy and Astrophysics, 474, 1015.
  • Young, L., et al. (2019), The Gaia-based prediction of the 2019 May 1 occultation of elongated KBO (33128) 1998 BU48, EPSC-DPS Joint Meeting 2019, 2019, EPSC-DPS2019-1321.
  • Ferreira, J., Tanga, P., & Machado, P. (2019), A Bayesian approach to the processing of stellar occultations, EPSC-DPS Joint Meeting 2019, 2019, EPSC-DPS2019-71.
  • Ferreira, J., Tanga, P., & Machado, P. (2019), Occultation Astrometry with DR2: Assessing the capabilities of robotic telescopes, The Gaia Universe, 30.
  • Tanga, P., Spoto, F., Hestroffer, D., Altmann, M., Bouquillon, S., & Desmars, J. (2017), Asteroid astrometry with Gaia: stellar occultations and beyond, AAS/Division for Planetary Sciences Meeting Abstracts #49, 117.11.
  • Spoto, F., Tanga, P., Mignard, F., & Carry, B. (2016), Investigating the contribution of Gaia to orbit improvement and stellar occultation prediction, AAS/Division for Planetary Sciences Meeting Abstracts #48, 327.09.
  • Berthier, J., et al. (2013), Detection of a Stellar Occultation by (87) Sylvia I (Romulus), Central Bureau Electronic Telegrams, 3398, 1.
  • Braga Ribas, F., et al. (2012), Stellar Occultations by Large TNOs on 2012: The February 3rd by (208996) 2003 AZ84, and the February 17th by (50000) Quaoar, AAS/Division for Planetary Sciences Meeting Abstracts #44, 402.01.
  • Maris, M., Hestroffer, D., Delbo, M., Mueller, M., Grundy, W., Stansberry, J., Tozzi, G. P., Tanga, P., & Thuillot, W. (2008), Post eclipse thermal response of Uranian satellites with SINFONI: a status report ., Memorie della Societa Astronomica Italiana Supplementi, 12, 34.
  • Tanga, P., & Delbo, M. (2007), Asteroid Size Harvest: A Bright Future For Star Occultations, AAS/Division for Planetary Sciences Meeting Abstracts #39, 35.08.
  • Delbo, M., & Tanga, P. (2006), The future of asteroid occultations: the post-GAIA era, European Planetary Science Congress 2006, 147.
Topic revision: r12 - 08 Apr 2021, PaoloTanga
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