Asteroid properties from SuperWASP light curves

“超级黄蜂”项目主要是对太阳系外行星凌日的超广角搜索，十多年来，当明亮的小行星经过调查区域时，它一直在偶然地观察它们。多个宽视场（北半球和南半球各有8台7.8 × 7.8视场的摄像机），每晚每分钟观测几个小时，持续数周，提供了一个理想的组合，可以获得亮度超过15等的小行星的旋转光曲线。用于识别小行星探测和光度测定的软件工具已经开发出来。仅2004年和2006年的有限观测数据就提供了270颗小行星的570条光曲线，加上123颗小行星的相位曲线和绝对星等，其中93颗小行星以前没有值[2]。该项目将包括完成数据缩减（从2010年开始），并通过以下一项或多项方法利用这个庞大、无偏、星等有限的小行星光曲线数据集：-确定自旋极方向：10年时间跨度内的广泛观测几何形状允许同时提取自旋周期、形状和自旋极方向[3,4]。虽然明亮小行星的周期通常有很好的特征，但该数据集将提供几倍的自旋方向，从而允许研究依赖于大小的进化效应。-双星的识别：广泛的观测几何形状也最大限度地提高了观测双星小行星日食的可能性[综述，5]，从中可以得出小行星的密度。我们将进行可行性研究，以确定是否可以使用SuperWASP数据集检测双星。-密度测定的另一种技术是使用平衡形状[6]。该方法似乎对具有较大光曲线振幅的大型物体（SuperWASP数据中最好记录的物体）很有效，可能是因为碎石堆物体的撞击碰撞暂时消除了压力引起的剪切强度。-探测活动：在极少数情况下，小行星会因碰撞[例7]或短暂放气而出现一次性或零星的增亮事件。大的时间覆盖范围将允许搜索异常增亮。相位曲线（亮度变化作为太阳相位角的函数）与表面散射特性有着复杂的关系。配合新的IAU H-G1-G2系统[8]需要良好的相位覆盖，特别是在零相角附近。与许多已发表的相位曲线不同，SuperWASP提供的连续、长期覆盖符合这一标准。可靠相位曲线的显著增加将用于研究光谱类型、反照率、尺寸或自旋之间可能存在的相关性。参考文献：1)Parley N et al.（2005）利用SuperWASP进行偶然小行星光曲线调查。Parley N（2008）利用超级黄蜂对太阳系的偶然调查。地球，月球和行星，97,261-268.2。3) Kaasalainen M., Torppa J.（2001）小行星光曲线反演的优化方法ⅰ：形状确定。李建军，张建军，张建军，等。（2001）小行星光曲线反演方法研究[J] .地球物理学报（自然科学版）。完整的反问题。Margot J-L et al.（2016）小行星系统：双星、三元组和对。钱德拉塞卡（1963）罗氏椭球体的平衡和稳定性。Snodgrass C等（2010）2009年小行星P/2010 A2的碰撞残骸轨迹起源。（2010）小行星的三参数星等相位函数。地球物理学报，41(6):814-816。Li et al.（2016）小行星测光。《小行星4》，亚利桑那大学出版社，第129-150页。

The SuperWASP project, primarily an ultra-wide angle search for extra-solar planetary transits, has serendipitously observed bright asteroids for over 10 years as they pass through the survey fields. The multiple wide fields (Northern and southern hemisphere sites, each with 8 cameras with 7.8 x 7.8 fields), with observations every minute for several hours per night over several weeks at a time, provide an ideal combination to obtain rotational light curves of asteroids brighter than magnitude 15. Software tools to identify asteroid detections and perform photometry have already been developed [1]. Data from limited observations in 2004 and 2006 alone have provided 570 light curves for 270 asteroids, plus phase curves and absolute magnitudes for 123 asteroids, 93 of which had no previous values [2].This project will involve completion of the data reduction (from 2010 onwards) and exploitation of this massive, unbiased, magnitude-limited asteroid light curve dataset through one or more of the following: - Determination of spin pole orientations: The wide range of viewing geometries over the 10 year timespan allows simultaneous extraction of spin period, shape and spin pole orientation [3,4]. While periods are generally well-characterised for bright asteroids, the dataset will provide a several-fold increase in spin orientations, allowing investigation of size-dependent evolutionary effects. - Identification of binaries: The wide range of viewing geometries also maximises the possibility of observing eclipses of binary asteroids [review, 5], from which asteroid densities can be derived. We will undertake a feasibility study to determine if binaries can be detected using the SuperWASP dataset. - An alternative technique for density determination is the use of equilibrium shapes [6]. The method appears to work well for large objects with large light curve amplitudes (the objects best recorded in SuperWASP data), perhaps because impact jostling of rubble pile objects temporarily removes pressure-induced shear strength. - Detection of activity: In rare cases, asteroids have exhibited one-off or sporadic brightening events, due to collisions [e.g. 7] or transient outgassing. The large temporal coverage will allow a search for anomalous brightening. - Phase curves (brightness variation as a function of solar phase angle) are related in a complex way to surface scattering properties. Fitting with the new IAU H-G1-G2 system [8] requires good phase coverage, particularly near zero phase angle. Unlike many published phase curves, the continuous, long term coverage provided by SuperWASP fulfils this criterion. The significant increase in reliable phase curves will be used to investigate possible correlations with spectral type [review in 9], albedo, size or spin.References: 1) Parley N et al. (2005) Serendipitous asteroid lightcurve survey using SuperWASP. Earth, Moon & Planets, 97, 261-268.2) Parley N (2008) Serendipitous surveys of the Solar System using SuperWASP. PhD Thesis, The Open University.3) Kaasalainen M. & Torppa J. (2001) Optimisation methods for asteroid lightcurve inversion I: Shape determination. Icarus 153, 24-36.4) Kaasalainen M, Torppa J & Piironen J (2001) Optimisation methods for asteroid lightcurve inversion II. The complete inverse problem. Icarus 153, 37-51.5) Margot J-L et al. (2016) Asteroid systems: Binaries, triples and pairs. In Asteroids IV, Univ. Arizona Press, p355-373.6) Chandrasekhar S (1963) The Equilibrium and the stability of the Roche ellipsoids. Ap. J. 138, 1182-1213.7) Snodgrass C et al. (2010) A collision in 2009 as the origin of the debris trail of asteroid P/2010 A2. Nature, 467, 814-8168) Muinonen K. et al., (2010) A three-parameter magnitude phase function for asteroids. Icarus 209, 542-555.9) Li et al. (2016) Asteroid photometry. In Asteroids IV, Univ. Arizona Press, p129-150.