280 one-opposition near-Earth asteroids recovered by the EURONEAR with the Isaac Newton Telescope ^⋆

¹ Isaac Newton Group of Telescopes (ING), Apto. 321, 38700 Santa Cruz de la Palma, Canary Islands, Spain
e-mail: ovidiu.vaduvescu@gmail.com
² Instituto de Astrofísica de Canarias (IAC), C/vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁴ Amateur Astronomer, ROASTERR-1 Observatory, 400645 Cluj Napoca, Romania
⁵ Unidad de Astronomía, Facultad Ciencias Básicas, Universidad de Antofagasta, Chile
⁶ Astronomical Institute of the Romanian Academy, 5 Cutitul de Argint, 040557 Bucharest, Romania
⁷ Dpto. de Física Aplicada I, Escuela de Ingeniería de Bilbao, Universidad del País Vasco, 48940 Bilbao, Spain
⁸ National Solar Observatory, 3665 Discovery Drive, Boulder, CO 80303, USA
⁹ Romanian Society for Meteors and Astronomy (SARM), Str. Tineretului 1, 130029 Targoviste, Romania
¹⁰ Amateur astronomer, 438 Cluj Napoca, Romania
¹¹ Bucharest Astroclub, B-dul Lascar Catargiu 21, sect 1, Bucharest 010662, Romania
¹² Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE) CNRS – UMR 8028, Observatoire de Paris, 77 avenue Denfert-Rochereau, 75014 Paris Cedex, France
¹³ Amateur astronomer, Schela Observatory, 800259 Schela, Romania
¹⁴ Faculty of Sciences, University of Craiova, Str. Alexandru Ioan Cuza 13, 200585 Craiova, Romania
¹⁵ Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH), Str. Reactorului 30, Magurele, Romania
¹⁶ Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK
¹⁷ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁸ Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland
¹⁹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía, S/N, 18008 Granada, Spain
²⁰ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
²¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
²² Qatar Environment and Energy Research Institute (QEERI), HBKU, Qatar Foundation, PO Box 5825, Doha, Qatar
²³ Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
²⁴ Centro de Astrobiología (INTA-CSIC), Dpto. de Astrofísica, ESAC Campus, Camino bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
²⁵ Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
²⁶ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
²⁷ Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
²⁸ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University, Belfast BT7 1NN, UK
²⁹ School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
³⁰ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
³¹ UK Astronomy Technology Centre, Blackford Hill, Edinburgh EH9 3HJ, UK
³² School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
³³ Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK
³⁴ Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands
³⁵ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
³⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³⁷ Department for Geophysics, Astrophysics and Meteorology, Institute of Physics, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
³⁸ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal
³⁹ Department of Physics, The University of Hong Kong, Hong Kong SAR, PR China
⁴⁰ The Laboratory for Space Research, The University of Hong Kong, Hong Kong SAR, PR China
⁴¹ Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
⁴² ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴³ Department of Physics and McGill Space Institute,McGill University, 3600 University Street, Montreal, QC H3A 2T8, Canada

Received: 28 August 2017
Accepted: 11 October 2017

Abstract

Context. One-opposition near-Earth asteroids (NEAs) are growing in number, and they must be recovered to prevent loss and mismatch risk, and to improve their orbits, as they are likely to be too faint for detection in shallow surveys at future apparitions.

Aims. We aimed to recover more than half of the one-opposition NEAs recommended for observations by the Minor Planet Center (MPC) using the Isaac Newton Telescope (INT) in soft-override mode and some fractions of available D-nights. During about 130 h in total between 2013 and 2016, we targeted 368 NEAs, among which 56 potentially hazardous asteroids (PHAs), observing 437 INT Wide Field Camera (WFC) fields and recovering 280 NEAs (76% of all targets).

Methods. Engaging a core team of about ten students and amateurs, we used the THELI, Astrometrica, and the Find_Orb software to identify all moving objects using the blink and track-and-stack method for the faintest targets and plotting the positional uncertainty ellipse from NEODyS.

Results. Most targets and recovered objects had apparent magnitudes centered around V ~ 22.8 mag, with some becoming as faint as V ~ 24 mag. One hundred and three objects (representing 28% of all targets) were recovered by EURONEAR alone by Aug. 2017. Orbital arcs were prolonged typically from a few weeks to a few years; our oldest recoveries reach 16 years. The O−C residuals for our 1854 NEA astrometric positions show that most measurements cluster closely around the origin. In addition to the recovered NEAs, 22 000 positions of about 3500 known minor planets and another 10 000 observations of about 1500 unknown objects (mostly main-belt objects) were promptly reported to the MPC by our team. Four new NEAs were discovered serendipitously in the analyzed fields and were promptly secured with the INT and other telescopes, while two more NEAs were lost due to extremely fast motion and lack of rapid follow-up time. They increase the counting to nine NEAs discovered by the EURONEAR in 2014 and 2015.

Conclusions. Targeted projects to recover one-opposition NEAs are efficient in override access, especially using at least two-meter class and preferably larger field telescopes located in good sites, which appear even more efficient than the existing surveys.