Beginning of activity in 67P/Churyumov-Gerasimenko and predictions for 2014–2015
Beginning of activity in 67P/Churyumov-Gerasimenko and predictions for 2014–2015
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DOI：
10.1051/0004-6361/201322020
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发表时间：
2013-07
影响因子：
6.5
通讯作者：
C. Snodgrass;C. Tubiana;D. Bramich;K. Meech;H. Boehnhardt;L. Barrera
中科院分区：
文献类型：
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作者：
C. Snodgrass;C. Tubiana;D. Bramich;K. Meech;H. Boehnhardt;L. Barrera
上下文。67P/丘留莫夫-格拉西门科彗星于2003年被选为罗塞塔号任务的新目标。从那以后，人们对它进行了详细的观察，以描述它的核心和活动。目标。我们展示了这颗彗星在2007/ 2008年活动开始前后，也就是它最后一次通过近日点之前，之前未发表的数据。我们限制了活动开始的时间，并将其与彗星轨道上的其他数据结合起来，预测罗塞塔在2014/5年运行期间的可能行为。方法。在过去的几年里，观测67P的一个相当大的困难是它在大部分时间里都处于朝向银河系中心的拥挤区域。这里展示的2007/8年的数据尤其困难，2014/5年这颗彗星将再次处于不利的位置，无法在地球上进行观测。我们利用在变星和系外行星研究中常用的差分图像分析技术，去除背景源，提取彗星图像。此外，我们重新处理了67P覆盖其整个轨道的大量档案图像，以产生日心光曲线。通过使用一致的还原，测量和校准技术，我们生成了非常干净的光曲线，可用于测量亮度-距离关系并预测彗星未来的亮度。结果。我们确定这颗彗星在2007年11月左右活跃，距离太阳近日点前的距离为4.3天文单位。这颗彗星将到达这个距离，并可能在2014年3月再次活跃起来。我们发现尘埃亮度可以用近日点前α ρ∝r -3.2和近日点后α ρ∝r -3.4来描述，并且彗星的尘气比高于平均值，在r < 2 AU时，log (α fρ /Q(h2o)) = - 24.94±0.22 cm s分子-1。一个适合光度数据的模型表明，只有一小部分（1.4%）的表面是活跃的。
Context . Comet 67P/Churyumov-Gerasimenko was selected in 2003 as the new target of the Rosetta mission. It has since been the subject of a detailed campaign of observations to characterise its nucleus and activity. Aims . We present previously unpublished data taken around the start of activity of the comet in 2007/8, before its last perihelion passage. We constrain the time of the start of activity, and combine this with other data taken throughout the comet’s orbit to make predictions for its likely behaviour during 2014/5 while Rosetta is operating. Methods . A considerable difficulty in observing 67P during the past years has been its position against crowded fields towards the Galactic centre for much of the time. The 2007/8 data presented here were particularly difficult, and the comet will once again be badly placed for Earth-based observations in 2014/5. We make use of the difference image analysis technique, which is commonly used in variable star and exoplanet research, to remove background sources and extract images of the comet. In addition, we reprocess a large quantity of archival images of 67P covering its full orbit, to produce a heliocentric lightcurve. By using consistent reduction, measurement and calibration techniques we generate a remarkably clean lightcurve, which can be used to measure a brightness-distance relationship and to predict the future brightness of the comet. Results . We determine that the comet was active around November 2007, at a pre-perihelion distance from the Sun of 4.3 AU. The comet will reach this distance, and probably become active again, in March 2014. We find that the dust brightness can be well described by A fρ ∝ r -3.2 pre-perihelion and ∝ r -3.4 post-perihelion, and that the comet has a higher dust-to-gas ratio than average, with log (A fρ /Q(H 2 O)) = − 24.94 ± 0.22 cm s molecule -1 at r < 2 AU. A model fit to the photometric data suggests that only a small fraction (1.4%) of the surface is active.