Site testing campaign for the Large Optical/infrared Telescope of China:overview

The Large Optical/infrared Telescope(LOT) is a ground-based 12 m diameter optical/infrared telescope which is proposed to be built in the western part of China in the next decade.Based on satellite remote sensing data,along with geographical,logistical and political considerations,three candidate sites were chosen for ground-based astronomical performance monitoring.These sites include:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.Up until now,all three sites have continuously collected data for two years.In this paper,we will introduce this site testing campaign,and present its monitoring results obtained during the period between March 2017 and March 2019.     

Data processing and data products from 2017 to 2019 campaign of astronomical site testing at Ali,Daocheng and Muztagh-ata

Based on previous site testing and satellite cloud data,Ali,Daocheng and Muztagh-ata have been selected as candidate sites for the Large Optical/Infrared Telescope(LOT) in China.We present the data collection,processing,management and quality analysis for our site testing based on using similar hardware.We analyze meteorological data,seeing,background light,cloud and precipitable water vapor data from 2017 March 10 to 2019 March 10.We also investigated the relative usefulness of our all-sky camera data in comparison to that from the meteorological TERRA satellite data based on a night-by-night comparison of the correlation and consistency between them.We find a 6% discrepancy arising from a wide range of factors.     

Site-testing at Muztagh-ata site Ⅰ:ground meteorology and sky brightness

Site-testing is crucial for achieving the goal of scientific research and analysis of meteorological and optical observing conditions,one of the associated basic tasks.As one of three potential sites to host the 12-meter Large Optical/infrared Telescope(LOT),the Muztagh-ata site,which is located on the Pamir Plateau in Xinjiang,in west China,began its site-testing task in the spring of 2017.In this paper,we firstly start with an introduction to the site and then present a statistical analysis of the ground-level meteorological properties such as air temperature,barometric pressure,relative humidity,and wind speed and direction,recorded by an automatic weather station with standard meteorological sensors for a two-year duration.We also show the monitoring results of sky brightness during this period.     

现代日晕光度计多波段测光系统初步测试结果分析

现代日晕光度计是用于精确测定监测址点的多种大气参量的精密仪器,它已列为我国西部太阳设备选址工作中的重要设备。利用同一架日晕光度计首先对昭通大山包进行了多波段数据采集。在仔细分析初步测光结果的基础上,进一步完善日晕光度计的光学系统。使用改进后的设备对昆明凤凰山址点进行了多次数据采集,都获得了理想数据。这表明日晕光度计的多波段测光系统已能够用于西部太阳选址工作中。     

Simulation and analysis of co-phasing errors of the segmented primary mirror tiled by hexagonal segments in LOT

In this paper, co-phasing errors of a segmented primary mirror tiled by hexagonal segments are successfully calculated for the 12-meter Large aperture Optical/infrared Telescope(LOT). Co-phasing errors including out-of-plane errors are simulated separately and comprehensively based on several software simulation platforms. PAOLA simulation results show that the Strehl Ratio(SR) of LOT is larger than 0.8 when the RMS value of tip-tilt obeying a normal distribution is less than 0.018 arcsec, and the SR of LOT is larger than 0.8 when the RMS value of piston obeying a normal distribution is less than 40 nm. Besides,simulation results of Zemax show that the SR of LOT is larger than 0.8 when the RMS value of tip-tilt obeying a normal distribution is less than 0.02 arcsec, and the SR of LOT is larger than 0.8 when the RMS value of piston obeying a normal distribution is less than 40 nm. These simulation results successfully lay a solid foundation for LOT(especially the segmented primary mirror with active optics).     

Preface:Site testing campaign for the Large Optical/infrared Telescope of China

The Large Optical/infrared Telescope of China is a 12 meter diameter ground-based optical/infrared telescope which is proposed to be constructed in the western part of China in favor of its arid climate,and clear,dark nights.A site testing campaign was initiated between November 2016 and March2019 in order to investigate long term astronomical weather conditions in the western part of China,specifically,at three sites:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.This is the first attempt to evaluate long term performances of three candidate sites with uniformly calibrated instruments and data collecting/processing methods for a two-year span in China.In this special issue,we present nine papers that describe the whole site testing campaign,including preparation,data collecting/processing methods,instrument set up at three candidate sites as well as detailed statistics for the measurement results from March 2017 to March 2019.     

Site testing at Muztagh-ata site Ⅱ:seeing statistics

In this article,we present a detailed analysis of the statistical properties of seeing for the Muztaghata site which is a candidate site for hosting the future Chinese Large Optical/infrared Telescope(LOT)project.The measurements were obtained with differential image motion monitors(DIMMs) from April2017 to November 2018 at different heights during different periods.The median seeings at 11 m and6 m are very close but significantly different from that on the ground.We mainly analyzed the seeing at11 m monthly and hourly,having found that the best season for observing was from late autumn to early winter and seeing tended to improve during the night only in autumn.The analysis of the dependence on temperature inversion,wind speed and direction also was made and the best meteorological conditions for seeing are given.     

中国第三次天文台选址高潮及对丽江高美古地区天文观测条件的初步估计

本文介绍了中国第三次天文台选址高潮的背景及最近这次台址调研的进展情况。天文气候条件普查的结果认为在中国挑选出受局部地形影响的较好台址是有可能的。报道了对华北和西北若干候选点进行踏勘和测量的结果。详细介绍了在滇西地区的选址普查和丽江高美古选址观测的经过。据云量和ＤＩＭＭ视宁度观测的初步结果来看，高美古是一个很有希望的潜在优良台址。     

CCD离焦对现代日晕光度计测量结果影响分析

现代日晕光度计（Sky Brightness Monitor,SBM）是一种测定天文址点白昼大气参量的精密仪器,它已成为国际上太阳选址工作的重要设备之一。与国外同类设备不同的是,云南天文台研制的现代日晕光度计上的CCD相机系统可以被简单拆卸并保存,有利于选址踏勘阶段的携带和运输。为获取组装现代日晕光度计设备时可能存在的CCD离焦所导致的测量误差,于2011年6月在新疆奇台县和宁夏石嘴山市利用当地稳定的日照条件做了多次CCD大离焦量快变试验。统计结果表明,现代日晕光度计的CCD显著离焦可造成的相对测量误差约在6％之内。在正常情况下,即观测者基本按照物镜旋筒刻线标志在望远镜上安装CCD设备时,日晕测量的相对误差一般远小于6％。因此认为这种系统误差对优良址点的测量影响基本可以忽略。     

Modeling the formation of the K-Pg boundary layer

In this paper we investigate the formation of the Cretaceous-Paleogene (K-Pg) boundary layer through numerical modeling. The K-Pg layer is widely agreed to be composed of meteoritic material and target rock from the Chicxulub impact site, that has been ejected around the globe and mixed with local material during final deposition. The observed composition and thickness of the K-Pg boundary layer changes with azimuth and distance from the impact site. We have run a suite of numerical simulations to investigate whether we can replicate the observational data, with a focus on the distal K-Pg layer and the impact glasses at proximal sites such as Beloc, Haiti. Previous models of the K-Pg ejecta have assumed an initial velocity distribution and tracked the ejecta to its final destination. Here, we attempt to model the entire process, from impact to the arrival of the ejecta around the globe. Our models replicate the observed ejecta thickness at proximal sites, and the modeled ejecta is composed of sediments and silicate basement rocks, in agreement with observational data. Models that use a 45° impact angle are able to replicate the total ejecta and iridium volume at distal sites, and the majority of the ejecta is composed of meteorite and target sediments. Sub-vertical impacts generate too little iridium, and oblique impacts of ?30 degrees generate too much. However, in contrast to observations, models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance, and are unable to transport shocked minerals (quartz and zircon) from the Chicxulub basement rocks around the globe. We suggest that much of the K-Pg ejecta is transported non-ballistically, and that the most plausible mechanism is through re-distribution from a hot, expanding atmosphere. The results are important for future investigations of the environmental effects of the Chicxulub impact.     

日晕光度计图像日心自动定位方法

现代日晕光度计是用于精确测定日间天文监测址点多种大气参量的精密仪器,它已列为我国西部太阳设备选址工作中的重要设备之一。在数据处理中日心坐标的选取对处理结果有决定性影响,但由于观测过程中日面中心坐标在图像上随时间变化,因此发展了两种用于日面中心自动定位的方法:日面总强度法和傅里叶变换相关法。详细介绍了这两种方法,并对比取得的结果差别及其对测量结果的影响。     

日晕测量与日晕光度计外缘杂散光抑制试验

为配合大型太阳设备西部选址工作,研制了一架现代日晕光度计(Sky Brightness Monitor,SBM).前期实验对日晕光度计性能进行了测试,同时积累了云南部分址点的日晕数据.资料分析结果显示,轿子雪山正午前后的日晕水平最低可至日面中心强度百万分之几的量级(蓝波段).这表明该日晕光度计内部杂散光水平已达到了国际同类产品的标准.日晕光度计的内部杂散光源主要来自两部分:镜筒前端中性滤光片(ND4)固定套圈的边缘衍射(视场靠内区域)和镜筒内置光阑的边缘衍射(视场靠外区域).针对后者进行的变换光阑孔径大小试验结果证实,适当缩小光阑孔径可有效减小数据中视场靠外区域的衍射光干扰.     

光学天文台址的高度探讨

本文对全球现有天文台址的海拔高度、大望远镜所在地的高度和近十年来的光学天文台的选址在海拔高度上的考虑进行了综述和分析,并对云南境内候选点的高度提出看法。     

Light pollution and night sky brightness at the site of Kottamia Observatory

Photoelectric measurements of the night sky brightness and the light pollution of Kottamia Observatory have been carried out and the deduced results are expressed in mag/sec². The maximum brightness of the sky in the direction of Cairo city at zenith distance 45° and azimuth 70° when the sun is almost 60° below the horizon are 22.68; 21.54 and 19.82 mag/sec² for blue, yellow and red colours respectively. The corresponding values of night sky background are 22.94; 21.85 and 20.14 mag/sec² respectively.The isophotes of the sky brightness at Kottamia Observatory have been drawn for blue, yellow and red colours. The variations of the night sky brightness and the (B-V) colour index with altitude of the observed point have been studied.The light pollution and the night sky brightness at the site of Kottamia Observatory is compared with that deduced by different investigators at other sites. It has been shown that the sky brightness at zenith distance 45° at Kottamia Observatory site is similar to Kitt Peak and Palomar Observatory sites. Kottamia Observatory site is slightly brighter than Junipero Serra while it is darker than Mount Hamilton and San Jose sites. The comparative results have been carried out at blue and yellow colours. No comparison is obtained at red as there is no data published for the red colour.     

Slippage of Jets Explained by the Magnetic Topology of NOAA Active Region 12035

We present the investigation of 11 recurring solar jets that originated from two different sites (site 1 and site 2) close to each other (\({\approx}\,11~\text{Mm}\)) in NOAA active region (AR) 12035 during 15?–?16 April 2014. The jets were observed by the Atmospheric Imaging Assembly (AIA) telescope on board the Solar Dynamics Observatory (SDO) satellite. Two jets were observed by the telescope of the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, India, in H\(\upalpha\). On 15 April, flux emergence is strong in site 1, while on 16 April, flux emergence and cancellation mechanisms are involved in both sites. The jets of both sites have parallel trajectories and move to the south with a speed between 100 and 360 km?s^?1. The jets of site 2 occurred during the second day have a tendency to move toward the jets of site 1 and merge with them. We conjecture that the slippage of the jets could be explained by the complex topology of the region, which included a few low-altitude null points and many quasi-separatrix layers (QSLs), which could intersect with one another.     

Development of solar scintillometer

The index of scintillation measurement is a good parameter to compare different sites for image quality or ‘seeing’. We have developed a scintillometer, which is deployed on the high resolution SPAR telescope in the island site of Udaipur Solar Observatory, for the site characterization to specify the proposed MAST (Multi Application Solar Telescope). The scintillometer consists of a miniature telescope, termed as micro telescope (4 mm aperture, 15 mm focal length) mounted on a drive which tracks the Sun continuously, associated amplifiers and a data acquisition system. A photodiode is used as the detector. The telescope along with detector was obtained from National Solar Observatory (NSO), and is similar to the one used for Advanced Technology Solar Telescope (ATST) site survey. At USO we developed the amplifier and data acquisition system for the scintillometer. A 24-bit analog to digital converter based system was designed, assembled, tested and used as the data acquisition system (DAS). In this paper, we discuss the instrumentation and present the initial results.     

A survey of the selenochemistry of major,minor and trace elements

Average data for igneous and/or metaigneous rocks and soils from seven lunar sites are presented. There are compositional similarities between Apollo 11 and Luna 16 eastern maria, Ap 12 and 15 western maria and between Ap 16 and L 20 highlands. Subtle differences do exist between the paired mare sites and the two highland sites and striking differences between the eastern and western maria. Chondritic normalized REE (rare earth element) patterns for igneous rocks and soils from all sites range from 7-350 generally with negative Eu anomalies. Anorthositic gabbroes to anorthosites, presumably highland material, exhibit a positive Eu anomaly. The REE patterns or Sr isotopic ratios suggest two lava flows each for the L 16 and Ap 14 sites, at least four lava flows for the Ap 11 and 12 site and about six for the Ap 15 site. Paucity of lunar andesites suggests rather limited lunar chemical differentiation. Norite-KREEP is a prominent component at Ap 12, 14 and 15, less at Ap 11 and 16 and L 16 and apparently very low at the L 20 highland site. Derivation of lunar soils can be best explained using multi-component mixing systems. Characterization of meteoritic impacting bodies is also observed in addition to a steady state veil of 1.9% carbonaceous Cl like material in soils. Interelement correlations impose constraints on the primitive composition of the Moon and on magmatic processes like selective volatilization.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.     

Imaging polarimetry of Comet 9P/Tempel before and after the Deep Impact

The NASA's Deep Impact mission was the first impact experiment to a cometary nucleus. The target of the mission was Comet 9P/Tempel, one of the Jupiter family comets. The impact was performed on July 4th, 2005. Imaging polarimetric observations were carried out by Polarimetric Imager for COmets (PICO) mounted on the Lulin One-meter Telescope (LOT) at Lulin Observatory, Taiwan. Intensity and linear polarization degree maps were obtained on July 3-5, 2005. Impact ejecta plume was clearly recognized in the enhanced intensity map. Furthermore, arc-shaped region of high polarization was recognized in the polarization map. Dust grains in this region had larger expansion velocity than the grains which provided the brightest area in the intensity map. comparing our results with the MIR spectroscopy obtained by Subaru Telescope we conclude that very small carbonaceous grains might be responsible for the region of high polarization.     

High-altitude wind velocity at Oukaimeden observatory

This paper aims at studying the wind at 200 mbar over the Moroccan observatory Oukaimeden, as high-altitude winds have been adopted as a useful parameter for site characterization in terms of the suitability of a site for the development of some adaptive optics techniques. The data used come from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data base, which is widely acknowledged as being reliable. Statistical analyses of 200-mbar wind speed since 1983 are performed. Comparison with some of the main observatory sites worldwide qualifies Oukaimeden as one of the best observatory sites in terms of 200-mbar wind statistics. Our analysis of a record of seeing measurements during the years 2003 and 2004 concludes that while 200-mbar wind speed can be used as a parameter for ranking astronomical sites in term of their suitability for adaptive optics, it cannot be used for the whole atmospheric seeing prediction. A comparison of monthly values of the seeing parameter at Oukaimeden, La Silla and Paranal demonstrates the high seeing quality of Oukaimeden, as the seeing values measured were lower than those of La Silla and Paranal for most of the time during the comparison period. Furthermore, a statistical analysis of atmospheric stratified seeing, wavefront coherence time and isoplanatic angle measured with a Multi-Aperture Scintillation Sensor instrument over Paranal from 2004 to 2007 have been performed. We found good correlations between 200-mbar wind velocity and levels 4, 5 and 6 seeing, wavefront coherence time and isoplanatic angle, with corresponding correlation coefficients of 0.74, 0.79, 0.70, 0.97 and 0.78.