Against the biases in spins and shapes of asteroids
A. Marciniak, F. Pilcher, D. Oszkiewicz, T. Santana-Ros, S. Urakawa, S. Fauvaud, P. Kankiewicz, Ł. Tychoniec, M. Fauvaud, R. Hirsch, J. Horbowicz, K. Kamiński, … 展开作者
A. Marciniak, F. Pilcher, D. Oszkiewicz, T. Santana-Ros, S. Urakawa, S. Fauvaud, P. Kankiewicz, Ł. Tychoniec, M. Fauvaud, R. Hirsch, J. Horbowicz, K. Kamiński, I. Konstanciak, E. Kosturkiewicz, M. Murawiecka, J. Nadolny, K. Nishiyama, S. Okumura, M. Polińska, F. Richard, T. Sakamoto, K. Sobkowiak, G. Stachowski, P. Trela
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Published in Planetary and Space Science. 13 pages, 20 figures
Physical studies of asteroids depend on an availability of lightcurve data. Targets that are easy to observe and analyse naturally have more data available, so their synodic periods are confirmed from multiple sources. Also, thanks to availability of data from a number of apparitions, their spin and shape models can often be obtained.
Almost half of bright (H<=11 mag) main-belt asteroid population with known lightcurve parameters have rotation periods considered long (P>12 hours) and are rarely chosen for photometric observations. There is a similar selection effect against asteroids with low lightcurve amplitudes (a_max<=0.25 mag). As a result such targets, though numerous in this brightness range, are underrepresented in the sample of spin and shape modelled asteroids. In the range of fainter targets such effects are stronger. These selection effects can influence what is now known about asteroid spin vs. size distribution, on asteroid internal structure and densities and on spatial orientation of asteroid spin axes.
To reduce both biases at the same time, we started a photometric survey of a substantial sample of those bright main-belt asteroids that displayed both features: periods longer than 12 hours, and amplitudes that did not exceed 0.25 magnitude. First we aim at finding synodic periods of rotation, and after a few observed apparitions, obtaining spin and shape models.
As an initial result of our survey we found that a quarter of the studied sample (8 out of 34 targets) have rotation periods different from those widely accepted. We publish here these newly found period values with the lightcurves.
The size/frequency plot might in reality look different in the long-period range. Further studies of asteroid spins, shapes, and structure should take into account serious biases that are present in the parameters available today.
A practical re-weighting scheme of data fitting: application to asteroids orbit determination with Gaia
LTE, Observatoire de Paris, Université PSL, Sorbonne Université, Université de Lille, LNE, CNRS（巴黎天文台，巴黎文理研究大学，索邦大学，里尔大学）；Institute of Applied Astronomy, Russian Academy of Sciences（俄罗斯科学院应用天文学研究所）；DiRAC Institute and the Department of Astronomy, University of Washington（华盛顿大学天文学系及DIRAC研究所）；Institut Polytechnique des Sciences Avancées (IPSA)（高等科学理工学院）
On the orbital evolution of 2020 AV2, the first asteroid ever observed to go around the Sun inside the orbit of Venus
太阳系的最内层尚未得到广泛的研究，因为在地球轨道内运动的小天体往往在其恒星轨道周期的大部分时间里处于非常低的太阳伸长，远离搜索近地天体的方案经常观测到的区域。从兹威基瞬变设施进行的调查是第一个能够探测到与地月系统直接引力扰动分离的多个小行星的调查。ZTF的发现包括2019 AQ 3和2019 LF 6，这两颗Atiras是已知小行星中周期最短的。在这里，我们对2020 AV 2的轨道演化进行了评估，这是ZTF发现的Atira，具有类似的短周期，但遵循完全包含在金星轨道内的路径。这一特性使它成为难以捉摸的瓦蒂拉种群的第一个已知成员。真正的Vatiras，那些长期动态稳定的，被认为是受到所谓的冯齐佩尔-利多夫-科扎伊振荡，保护他们免受近距离接触水星和金星。然而，2020 AV 2似乎是前Atira，最近进入Vatira轨道域。它显示出偏心率和倾角值的反耦合振荡，但近日点辐角的值可能会循环。模拟显示，2020年AV 2可能会在未来与金星达到3：2的共振轨道，激活冯齐佩尔-利多夫-科扎伊机制，这反过来又为长期稳定的Vatiras种群的存在打开了可能性。
Thermal properties of slowly rotating asteroids: Results from a targeted survey
上下文早期的研究表明，缓慢旋转的小行星应该比快速旋转的小行星具有更高的热惯性，因为热浪穿透更深的次表面。然而，热惯性已被确定主要是快速转子由于选择效应，在现有的光度法用于获得热物理建模（TPM）所需的形状模型。目的。我们的目标是减轻这些选择的影响，通过生产形状模型的慢转子，缩放它们，并计算其热惯性与TPM，并验证是否热惯性随旋转周期的增加。方法.为了减少对慢旋转小行星的偏见，我们从世界各地的多个站对周期超过12小时的主带小行星进行了光度观测活动，在某些情况下还增加了WISE和开普勒太空望远镜的数据。对于自旋和形状的重建，我们使用的光变曲线反演方法，并推导出热惯性，我们应用热物理模型，以适应现有的红外数据从IRAS，AKARI，和WISE。结果我们提出了11个慢转子，提供了一个很好的适合的热数据的新模型。在两种情况下，TPM分析显示出对两种可能的镜像解决方案之一的明显偏好。我们导出了目标的直径和半径以及它们的热惯性，其范围在3 $^{+33}_{-3}$和45 $^{+60}_{-30}$ Jm $^{-2}$ s $^{-1/2}$ K $^{-1}$之间。结论.加上我们以前的工作，我们已经分析了16个慢旋转器，从我们的密集调查与大小之间的30和150公里。目前的样品的热惯性变化很大，这并不证实较早的建议，较慢的转子有较高的热惯性。
