Astrometric positions for 18 irregular satellites of giant planets from 23 years of observations
Astrometric positions for 18 irregular satellites of giant planets from 23 years of observations
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DOI：
10.1051/0004-6361/201526273
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发表时间：
2015-05
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影响因子：
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通讯作者：
A. R. Gomes-J'unior;M. Assafin;R. Vieira-Martins;J. Arlot;J. Camargo;F. Braga-Ribas;D. D. S. Neto-D.-D.-S.-Net
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作者：
A. R. Gomes-J'unior;M. Assafin;R. Vieira-Martins;J. Arlot;J. Camargo;F. Braga-Ribas;D. D. S. Neto-D.-D.-S.-Net
巨行星的不规则卫星被认为是在太阳系演化过程中被捕获的。了解它们的物理参数，如大小、密度和密度，对于限制它们来自何处以及如何捕获它们非常重要。获得这些参数的最佳方法是由航天器进行现场观测或由天体进行掩星观测。这两种技术都要求轨道是已知的。我们的目标是获得良好的天体测量位置的不规则卫星，以改善他们的轨道和星历。我们从三个数据库中识别并减少了几颗不规则卫星的观测结果，这些数据库包含1992年至2014年在三个站点（Observat\'orio do皮科dos Dias，Observatoire de Haute-Provence和欧洲南方天文台- La Silla）获得的8000多张图像。我们使用PRAIA（天文图像自动归约平台）软件对CCD图像进行了天体测量归约。UCAC 4星表代表国际天球参考系。帧中卫星的识别是通过SPICE/NAIF内核确定的星历完成的。为了克服信息（坐标、日期）缺失或不完整的问题，采取了一些程序，主要是针对较旧的图像。我们设法获得了18颗不规则卫星的6000多个位置：木星的12个，土星的4个，天王星的1个（Sycorax）和海王星的1个（Nereid）。对于某些卫星，获得的位置数超过早期轨道数值积分中使用的位置数的50%。我们的位置与最近的喷气推进实验室星历的比较表明，有一些不规则卫星的轨道系统误差。最明显的情况是错误的倾向Carme。
The irregular satellites of the giant planets are believed to have been captured during the evolution of the solar system. Knowing their physical parameters, such as size, density, and albedo is important for constraining where they came from and how they were captured. The best way to obtain these parameters are observations in situ by spacecrafts or from stellar occultations by the objects. Both techniques demand that the orbits are well known. We aimed to obtain good astrometric positions of irregular satellites to improve their orbits and ephemeris. We identified and reduced observations of several irregular satellites from three databases containing more than 8000 images obtained between 1992 and 2014 at three sites (Observat\'orio do Pico dos Dias, Observatoire de Haute-Provence, and European Southern Observatory - La Silla). We used the software PRAIA (Platform for Reduction of Astronomical Images Automatically) to make the astrometric reduction of the CCD frames. The UCAC4 catalog represented the International Celestial Reference System in the reductions. Identification of the satellites in the frames was done through their ephemerides as determined from the SPICE/NAIF kernels. Some procedures were followed to overcome missing or incomplete information (coordinates, date), mostly for the older images. We managed to obtain more than 6000 positions for 18 irregular satellites: 12 of Jupiter, 4 of Saturn, 1 of Uranus (Sycorax), and 1 of Neptune (Nereid). For some satellites the number of obtained positions is more than 50\% of what was used in earlier orbital numerical integrations. Comparison of our positions with recent JPL ephemeris suggests there are systematic errors in the orbits for some of the irregular satellites. The most evident case was an error in the inclination of Carme.