Ground-based observations of comets and other small solar system bodies, obtained with a focal reducer in the years 1989 - 2003

The archive consists of ground-based astronomical images, conducted with astronomical telescopes in the years 1989 - 2003. In 1989 CCDs were just becoming available for use in astronomy. As compared with photographic plates, the CCDs of this time had a size of only a few centimeters. But they were about an order of magnitude more sensitive than photographic plates that were traditionally used for astronomical imaging (As an example see the Palomar Sky Survey https://skyserver.sdss.org). This allowed for the first time to take astronomical images in narrow spectral bands transmitting only light emitted by atoms or molecules of a single species and in this way strongly facilitating the interpretation of the observed images. But early CCDs were surrounded by bulky structures for readout and for cooling them to the temperature of liquid nitrogen. Only Cassegrain telescopes had an easily accessible focal plane able to accept the early CCDs. But their focal length is too large for the small-size CCDs. A new device was needed to adapt the CCD to the Cassegrain focal plane of a telescope: the focal reducer. Focal reducers are now commonly used to adapt CCDs to Cassegrain telescopes. They consist of a collimator, a parallel beam and a short-focus camera lens generating an image reduced in size by the ratio of the focal lengths of camera and collimator. The parallel beam provides space for dispersing devices like narrow-band filters or grating prisms. A focal reducer adapts the angular size of the sky recorded by a single pixel of the digital receiver to the size of the average atmospheric seeing element. All images in the present data set are taken with a focal reducer of all lens design. The collimating optics was built by the company Carl Zeiss Jena (German Democratic Republic) and the short focus camera lenses by Carl Zeiss Oberkochen, at that time the western counterpart of Zeiss Jena. In 1995 a color divider was introduced in the parallel beam after the collimating optics. This allowed to generate simultaneously a red and a blue image of the observed object in selected filters (Two-Channel Focal Reducer). A detailed description of the equipment, in particular of the devices that can be put into the parallel beam like filters, Fabry-Perot-Interferometers, and Wollaston prisms used for polarimetry, is contained in Publication 59 (Jockers K. et al.: Exploration of the solar system with the two-channel focal reducer at the 2m-RCC telescope of Pik Terskol Observatory, Kinematics and Physics of Celestial Bodies, Supplement 3, 13-18, 2000). The aims of the observations depend on the objects observed. The main interest was devoted to comets. The cometary ions CO+, H2O+ and CO2+ have important transitions in the visual and near-UV spectral regions and are therefore well observable from the ground in the cometary ion tails. The corresponding neutral molecules are cosmologically important parent molecules of the nucleus. The molecular ions were observed in order to derive their abundances and in this way get information about the abundance of their neutral parents. This necessitated the derivation of the atmospheric extinction as function of wavelength using observations of standard stars. Most of the observed standard stars were taken from the book by Glushneva, I.N., and Voloshina, I.B., Spectrofotometriya yarkikh zvezd', Nauka, Moskva, 1982. From the emission bands of the neutral cometary coma, only CN was observed. Asteroids and planetary satellites have a solid surface and emit in the visual and near-UV spectral region a continuous spectrum. We observed the reddening of the continuum of these bodies with respect to the solar spectrum as function of phase angle Sun-Object-Observer. In addition, we attempted to determine the phase curve of their polarization. From these observations conclusions were drawn on the properties of the regolith on their surfaces. At the start of creation of this archive (2022) the data were located on 25 CD-ROMs (Compact Disk - Read Only Memory) in chronological order. The images on a single CD-ROM have been taken in a comparatively small time-interval. Often, but not always, they correspond to a single observing campaign. The organization of the present archive still reflects the original CD-ROMs including their directory substructure. Data taking at the telescope was computer controlled. This was required as CCDs are digital devices. The images were written in the so-called FITS (Flexible Image Transfer System) format. Metadata and image data are conserved in a single file. First come the metadata in ASCII format. They have standard names. Most important are NAXIS1 and NAXIS2 denoting the dimensions of the image. After the name of the metadatum follows an equality sign "=" and the value. Then follows a "/" and after this as a commentary an explanation of the quantity. The header ends with a single line containing the word "END". After this follow the digital data of the image....

该档案汇集了1989年至2003年间使用天文望远镜在地面上获取的天文图像。1989年，电荷耦合器件（CCD）刚开始在天文学领域得到应用。与传统的用于天文成像的感光板相比，这一时期的CCD尺寸仅有几厘米，但其灵敏度却比传统感光板高出约一个数量级（例如，参见帕洛玛天文台天体调查项目 https://skyserver.sdss.org）。这使得我们首次能够在狭窄的光谱波段中捕捉到仅由单一物种的原子或分子发出的光，从而极大地促进了观测图像的解读。然而，早期的CCD周围环绕着庞大的读取和冷却结构，以降低其至液氮温度。只有卡塞格林望远镜具有易于接入的焦平面，能够容纳早期的CCD。但它们的焦距对于小尺寸的CCD来说过长。因此，需要一个新装置来适配CCD至望远镜的卡塞格林焦平面：焦距缩短器。焦距缩短器现已成为将CCD适配至卡塞格林望远镜的常用设备。它由一个准直器、一个平行光束和一个短焦距相机镜头组成，通过相机和准直器的焦距比来缩小成像尺寸。平行光束为分散装置如窄带滤光器或光栅棱镜等提供了空间。焦距缩短器将单像素数字接收器记录的天空角尺寸适配至平均大气视宁度元素的尺寸。本数据集中的所有图像均使用全镜头设计的焦距缩短器拍摄。准直光学系统由当时的东德公司卡尔·蔡司耶拿（Carl Zeiss Jena）建造，短焦距相机镜头则由卡尔·蔡司奥伯科亨（Carl Zeiss Oberkochen）制造，当时它是耶拿蔡司的西方竞争对手。1995年，在准直光学系统之后的平行光束中引入了一种彩色分离器。这使得在选定的滤光器中同时生成观察对象的红色和蓝色图像（双通道焦距缩短器）。设备（尤其是可放入平行光束中的滤光器、法布里-珀罗干涉仪和用于偏振测量的沃拉斯顿棱镜等装置）的详细描述包含在出版物59中（Jockers K. 等：利用皮克特斯克洛天文台2m-RCC望远镜的双通道焦距缩短器探索太阳系，天体运动学与物理，增刊3，第13-18页，2000年）。观测目标取决于观测对象。主要兴趣集中在彗星上。彗星离子CO+、H2O+和CO2+在可见光和近紫外光谱区域有重要跃迁，因此在彗星离子尾中易于从地面观测。相应的中性分子是宇宙学上重要的核物质母分子。观测分子离子是为了推导它们的丰度，从而获取有关它们中性母体丰度的信息。这需要使用标准恒星的观测来推导大气消光率作为波长的函数。大多数观测的标准恒星均取自Glushneva，I.N.和Voloshina，I.B.所著的《亮星光谱光度学》，科学出版社，莫斯科，1982年。仅从中性彗星尾部的发射带中观测到了CN。小行星和行星卫星具有固态表面，在可见光和近紫外光谱区域发出连续光谱。我们观测了这些天体的连续光谱相对于太阳光谱的消光随相位角（太阳-天体-观测者）的变化。此外，我们还试图确定它们的偏振相位曲线。从这些观测中，得出了有关这些天体表面风化层的性质结论。在创建本档案（2022年）之初，数据位于25张CD-ROM（光盘只读存储器）上，按时间顺序排列。每张CD-ROM上的图像是在相对较短的时间间隔内拍摄的。通常，但并非总是与单一观测活动相对应。本档案的组织结构仍反映了原始CD-ROM及其目录结构。望远镜上的数据采集由计算机控制。图像以所谓的FITS（灵活图像传输系统）格式写入。元数据和图像数据保存在单个文件中。首先是元数据，以ASCII格式呈现，具有标准名称。其中最重要的是NAXIS1和NAXIS2，它们表示图像的维度。在元数据名称之后跟随一个等号“=”，然后是值。之后是一个斜杠“/”，随后是对该数量的解释性注释。头信息以包含单词“END”的单行结束。之后是图像的数字数据。)