Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition^⋆

¹ Department of AstronomyYonsei University, 50 Yonsei-ro, Seodaemun-gu, 120-749 Seoul, Korea
e-mail: skarma@galaxy.yonsei.ac.kr
² Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, 305-348 Daejeon, Korea
e-mail: yjchoi@kasi.re.kr
³ Seoul National University, 1 Gwanak-ro, Gwanak-gu, 151-742 Seoul, Korea
⁴ German Aerospace Center (DLR), Rutherfordstraβe 2, 12489 Berlin, Germany
⁵ Akdeniz Universitesi, Fen Fakultesi, Dumlupinar Bulvari, Kampus, 07058 Antalya, Turkey
⁶ Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Asaguchi, 719-0232 Okayama, Japan
⁷ Nishi-Harima Astronomical Observatory, 407-2 Nishigaichi, Sayo-cho, Sayo-gun, 679-5313 Hyogo, Japan

Received: 31 October 2012
Accepted: 3 December 2012

Abstract

Context. Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid sample return missions, not only because of its accessibility but also because of the first C-type asteroid for exploration missions. The lightcurve-related physical properties of this object were investigated during the 2011–2012 apparition.

Aims. We aim to confirm the physical parameters useful for JAXA’s Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase function. Our data complement previous studies that did not cover low phase angles.

Methods. With optical imagers and 1−2 m class telescopes, we acquired the photometric data at different phase angles. We independently derived the rotational lightcurve and the phase curve of the asteroid.

Results. We have analyzed the lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of 7.625 ± 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R = 18.69 ± 0.07 mag and the phase slope of G =  −0.09 ± 0.03 were also obtained based on the observations made during the 2011 − 2012 apparition. These physical properties are in good agreement with the previous results obtained during the 2007−2008 apparition.