SMART-1 Impact Observation at the Canada-France-Hawaii Telescope
SMART-1 Impact Observation at the Canada-France-Hawaii Telescope
复制标题
加拿大-法国-夏威夷望远镜的 SMART-1 撞击观测
DOI：
--
复制
发表时间：
2007
期刊：
影响因子：
--
通讯作者：
B. Foing
中科院分区：
文献类型：
--
作者：
C. Veillet;B. Foing
简介：由于其使命计划周密，SMART-1号航天器于2006年9月3日在月球近侧坠毁，坠毁地点没有太阳照射，美洲和太平洋地区的许多大型天文台都能看到。SMART-1小组协调的观测活动促使专业和业余天文学家多次尝试从地球观测撞击。由于许多观测地点的天气恶劣，而且很难在离太阳照射的月球表面如此近的地方观测到地球光照射的撞击地点，因此加拿大-法国-夏威夷望远镜只成功观测到一次，新墨西哥州的一名业余爱好者可能探测到了撞击闪光。CFHT近实时提供的撞击闪光图像为一次非常成功的使命画上了视觉上的句号，在随后的图像中探测到撞击羽流，为首次研究撞击月球土壤的喷出物动态提供了可能性。观测装置：撞击时CFHT 3.6米望远镜上的仪器是一台全新的宽视场红外照相机WIRCam。每个WIRCam图像覆盖20'x20'的领域，这要归功于四个非常敏感的夏威夷-2 RG探测器的拼接。16个MPixels图像在几秒钟内读取。图像比例为0.3”/像素。由于图像之间有5秒的间隔，并且不知道撞击的确切时间，因此决定将曝光时间设置为10秒，从而给出实际观察到撞击的2/3概率。由于太阳光照射的月球表面接近撞击点，而地球光照射的撞击区域相对较亮（WIRCam），因此相机使用了最亮的滤光片：2130 nm处的氢分子发射滤光片H2 v=1-0 S（1）。在撞击前一天拍摄了撞击现场的测试图像，以便对撞击区域和地貌特征进行侦察，作为撞击观察的参考。撞击闪光：撞击并没有发生在两张照片之间，幸运的是，它被记录了下来。望远镜是指向这样的马赛克的最小的部分将看到阳光照亮的地区。因此，撞击的位置非常接近马赛克的一个角落。在图1中可以看到示出在该角上的整个检测器的相应图像。在真实的时间内对图像进行并行处理允许在观察到闪光图像之后的短时间内释放闪光图像。这些数据实际上是一长串10秒的图像，覆盖了近一个小时（撞击前20分钟，撞击后40分钟）。由于地辉照亮的月球具有非常低的对比度，特征不容易被看到。在这方面，虚拟月谱就非常有用。撞击发生在SMART-1撞击区图像上看到的山坡上（图3）。图1用于撞击观测的2Kx 2K探测器。阳光照射的月亮位于探测器的右上角（饱和-因此是黑色的）。大地之光照亮的月亮被认为是与星空的背景。在许多地方都可以看到明亮的月亮的各种丑陋的反射。撞击闪光是图像顶部的亮点，靠近终结者。
Introduction: Thanks to a well-planed ending of its mission, the SMART-1 spacecraft crashed on the near side of the Moon on the 3 of September 2006 at a site not illuminated by the Sun and visible from many large observatories in the Americas and the Pacific region. An observing campaign coordinated by the SMART-1 team triggered many attempts by both professional and amateur astronomers to observe the impact from the Earth. Bad weather in many observing sites and the difficulty to observe the Earthshine-lit crash site so close to the Sun-illuminated lunar surface led to only one successful observation at CanadaFrance-Hawaii Telescope and a possible detection of the impact flash by an amateur in New Mexico. The image of the impact flash, made available in near real-time by CFHT, brought visual closure to a very successful mission, and the detection of the impact plume on subsequent frames opened the possibility to study for the first time the dynamics of the ejecta from an impact on the lunar soil. Observing setup: The instrument available on the CFHT 3.6-m telescope at the time of impact was a brand new wide-field infrared camera, WIRCam. Each WIRCam image covers a 20’x20’ field, thanks to a mosaic of four very sensitive Hawaii-2 RG detectors. The 16 MPixels images are read in a few seconds. Image scale is 0.3”/pixel. With a 5-second gap between images and not knowing the exact time of impact, it was decided to set the exposure time at 10 seconds, giving a 2/3 probability of actually observing the impact. With the sunshine lit lunar surface close to the impact site and the relatively bright (for WIRCam) Earthshine lit impact area, the narrowest filter available in the camera was used: a molecular hydrogen emission filter H2 v=1-0 S(1) at 2130nm. Test images were made of the crash site the day preceding the impact, allowing a reconnaissance of the impact area and the landscape features to be used as reference for the impact observation. The impact flash: The impact did not happen between two images and was, luckily, recorded. The telescope was pointed so that the smallest portion of the mosaic would see the Sunshine lit area. The impact was therefore located very close to a corner of the mosaic. he corresponding image showing the whole detector on that corner is seen on Fig 1. Scripts processing the images in real time allowed a release of the flash image a short time after it was observed. The data actually consist in a long sequence of 10s images covering nearly an hour (20mn before the impact and 40mn after). As the Earthshine lit Moon has a very low contrast, features are not easily seen. For this work, the Virtual Moon Atlas [1] was very useful. The impact was localized on the slopes of a mountain seen on the SMART-1 image of the impact zone (Fig 3). Fig 1 The 2Kx2K detector used for the impact observation. The sunshine lit Moon is at the extreme upper right of the detector (saturated – hence black). The Earthshine lit Moon is seen with the starry sky in the background. Various ugly reflexions from the bright Moon are seen in many places... The impact flash is the bright spot at the top of the image, close to the terminator.