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arXiv 1504.00712astro-ph.EP
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近地小行星特征描述的速度需求

The Need for Speed in Near-Earth Asteroid Characterization

J. L. Galache, C. L. Beeson, K. K. McLeod, M. Elvis

摘要:

我们利用小行星中心的数据和工具来探索目前已知的10,000多个近地小行星的发现情况和性质,并量化地面望远镜后续工作的挑战。随着调查变得更加敏感,发现的增长率已经增长到每年约1,000个,每7.5年增加1个。然而,在过去十年中,发现的大型近地小行星(H =< 22)一直稳定在每年约365个,按照这一速度,2005年国会关于在1.4亿近地小行星中发现90%的任务在2030年之前将无法实现。与此同时,特征描述却远远落后:只有不到10%的近地小行星在大小、旋转周期和光谱方面得到了很好的描述,按照目前的跟踪速度,即使是对已知的种群,也需要大约一个世纪的时间才能确定它们。60%以上的近地小行星具有轨道不确定性参数,U >= 4,这使得在发现后一年多的时间里很难重新捕获;对于H > 22的小行星,这一比例超过90%。我们认为,快速的后续行动将是必不可少的特点新发现的近地小行星。大多数新的近地小行星都是在0.5等亮度的峰值内发现的,并且很快就消失了,通常在1/4/6周后消失0.5/3.5/5等。大约80%的行星有小于3年的会合周期,每十年会有几次接近地球。然而,对于大多数新发现的近地小行星来说,对随后出现的现象进行后续观测几乎是不可能的,因为这些近地小行星将是H > 22的近地小行星,它们返回时的亮度往往要比H> 22的小行星暗100倍。我们表明,为了使表征跟上发现的步伐,需要:用专用的> 2米望远镜在几天内获得可见光谱;用> 4米望远镜进行长弧天体测量,也用于相位曲线;用>= 4米望远镜在几天内获得快节奏(<min)光变曲线。对于已知的大近地小行星(H =< 22),可以用1- 2米的望远镜进行双显光谱学、天体测量学和测光学。

英文摘要:

We have used Minor Planet Center data and tools to explore the discovery circumstances and properties of the currently known population of over 10,000 NEAs, and to quantify the challenges for follow-up from ground-based telescopes. The increasing rate of discovery has grown to ~1,000/year as surveys have become more sensitive, by 1mag every ~7.5 years. However, discoveries of large (H =< 22) NEAs have remained stable at ~365/year over the past decade, at which rate the 2005 Congressional mandate to find 90% of 140m NEAs will not be met before 2030. Meanwhile, characterization is falling farther behind: Fewer than 10% of NEAs are well characterized in terms of size, rotation periods, and spectra, and at current rates of follow-up it will take about a century to determine them even for the known population. Over 60% of NEAs have an orbital uncertainty parameter, U >= 4, making reacquisition more than a year following discovery difficult; for H > 22 this fraction is over 90%. We argue that rapid follow-up will be essential to characterize newly-discovered NEAs. Most new NEAs are found within 0.5mag of peak brightness and fade quickly, typically by 0.5/3.5/5mag after 1/4/6 weeks. About 80% have synodic periods of <3 years that bring them close to Earth several times a decade. However, follow-up observations on subsequent apparitions will be near impossible for the bulk of new discoveries, as these will be H > 22 NEAs that tend to return 100 times fainter. We show that for characterization to keep pace with discovery would require: Visible spectroscopy within days with a dedicated >2m telescope; long-arc astrometry, used also for phase curves, with a >4m telescope; and fast-cadence (<min) lightcurves obtained within days with a >= 4m telescope. For the already-known large (H =< 22) NEAs, subsequent-apparition spectroscopy, astrometry, and photometry could be done with 1-2m telescopes.

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