共查询到20条相似文献，搜索用时 31 毫秒
1.
Mark Chun Richard Wilson Remy Avila Tim Butterley Jose-Luis Aviles Don Wier Sam Benigni 《Monthly notices of the Royal Astronomical Society》2009,394(3):1121-1130
We present the results of an 18-month study to characterize the optical turbulence in the boundary layer and in the free atmosphere above the summit of Mauna Kea in Hawaii. This survey combined the Slope-Detection and Ranging (SLODAR) and Low-Layer SCIntillation Detection And Ranging (SCIDAR) (LOLAS) instruments into a single manually operated instrument capable of measuring the integrated seeing and the optical turbulence profile within the first kilometre with spatial and temporal resolutions of 40–80 m and 1 min (SLODAR) or 10–20 m and 5 min (LOLAS). The campaign began in the fall of 2006 and observed for roughly 50–60 h per month. The optical turbulence within the boundary layer is found to be confined within an extremely thin layer (≤80 m), and the optical turbulence arising within the region from 80 to 650 m is normally very weak. Exponential fits to the SLODAR profiles give an upper limit on the exponential scaleheight of between 25 and 40 m. The thickness of this layer shows a dependence on the turbulence strength near the ground, and under median conditions the scaleheight is <28 m. The LOLAS profiles show a multiplicity of layers very close to the ground but all within the first 40 m. The free-atmosphere seeing measured by the SLODAR is 0.42 arcsec (median) at 0.5 μm and is, importantly, significantly better than the typical delivered image quality at the larger telescopes on the mountain. This suggests that the current suite of telescopes on Mauna Kea is largely dominated by a very local seeing either from internal seeing, seeing induced by the flow in/around the enclosures, or from an atmospheric layer very close to the ground. The results from our campaign suggest that ground-layer adaptive optics can be very effective in correcting this turbulence and, in principle, can provide very large corrected fields of view on Mauna Kea. 相似文献
2.
Jenkins 《Monthly notices of the Royal Astronomical Society》1998,294(1):69-92
Fast guiding may improve the images delivered by telescopes. It may be implemented fairly cheaply and offers an upgrade path to smaller telescopes, which will make them more useful in the 8-m era. However, the detailed performance of a fast guiding system must depend on many parameters and this makes it difficult to assess its precise scientific benefits. This paper provides a comprehensive mathematical framework for calculating the performance of fast guiding systems. A range of models has been calculated that illustrates the benefits for telescopes of various sizes in various wavelength ranges. Three measures of performance have been examined: FWHM, 50 per cent encircled energy diameter and energy concentration in a 0.35-arcsec aperture. Typical gains over natural seeing are found to be in the 20 to 40 per cent range at useful levels of sky coverage. Other things being equal, small telescopes do not benefit as much as large ones from fast guiding. The sensitivity of these benefits to assumptions has also been examined, and this highlights the need to operate in the correct wavelength range for the aperture in question. The largest perturbations to ideal models are likely to be the result of telescope windshake and the outer scale of turbulence. If there is appreciable windshake, fast guiding will yield larger benefits than expected from the natural seeing. A short outer scale (a few hundred metres) will, however, lose most of the gains. 相似文献
3.
L. Kleint S.V. Berdyugina D. Gisler A.I. Shapiro M. Bianda 《Astronomische Nachrichten》2010,331(6):644-647
Upcoming large solar telescopes will offer the possibility of unprecedented high resolution observations. However, during periods of non‐ideal seeing such measurements are impossible and alternative programs should be considered to best use the available observing time. We present a synoptic program, currently carried out at the Istituto Ricerche Solari Locarno (IRSOL), to monitor turbulent magnetic fields employing the differential Hanle effect in atomic and molecular lines. This program can be easily adapted for the use at large telescopes exploring new science goals, nowadays impossible to achieve with smaller telescopes. The current, interesting scientific results prove that such programs are worthwhile to be continued and expanded in the future. We calculate the approximately achievable spatial resolution at a large telescope like ATST for polarimetric measurements with a noise level below 5 × 10‐5 and a temporal resolution which is sufficient to explore variations on the granular scale. We show that it would be important to optimize the system for maximal photon throughput and to install a high‐speed camera system to be able to study turbulent magnetic fields with unprecedented accuracy (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
In early January 1888, James E. Keeler was one of the first astronomers to work with the very new Lick Observatory 36-in. refractor. On January 7 while observing Saturn visually on a night of very fine seeing, he discovered a narrow, dark “division” in the outer part of the A ring. Despite repeated attempts, neither Keeler nor any of the other Lick observers saw this gap again until over a year later, on March 2, 1889, another night of extremely good seeing. On that occasion not only Keeler, but also E. S. Holden, J. M. Schaeberle, and E. E. Barnard all observed “Mr. Keeler's division,” as Barnard called it. It could only be seen using very high magnification with this large telescope, at a site known to be excellent, on the nights of very best definition. This gap is not the same as the feature which J. F. Encke had earlier discovered and described as a low-contrast division nearly in the middle of the A ring, and had drawn as nearly the same width as Cassini's division. Later visual observations by B. Lyot and A. Dollfus, again on nights of fine seeing with large telescopes, showed that the Encke division is complex. To them, with the best resolution, it appeared as three wide minima of light, fuzzy, and of low contrast, with a narrow, well-marked minimum of light at its outer edge. The outer edge is just where Keeler placed his gap, although he did not see the low-contrast structure in the Encke division. The images, with much superior resolution obtained from the Pioneer and Voyager space probes, show that the Encke division is even more complex than Lyot and Dollfus realized, but confirm the narrow Keeler feature as a true gap in the outer part of the A ring. 相似文献
5.
受地球大气影响, 使用地基光学望远镜观测角距离较小的双星系统或主卫星系统时往往会出现星象不可分辨的情况. 因此, 系统光心位置与系统质心位置可能存在一定的偏差. 准确地测量太阳系天体系统质心位置可以改进其轨道参数, 有助于揭示太阳系的形成与演化. 以矮行星Haumea及其亮卫星Hiíaka的运动为例, 仿真系统光心围绕质心扰动的过程, 探究视宁度(用星象的半高全宽表示)变化对准确测量光心位置的影响. 仿真结果表明, 使用二维高斯定心算法测定的系统光心位置随视宁度变化, 而修正矩定心算法的定心结果不受视宁度的影响. 根据仿真结果, 研究能够有效减少视宁度变化对光心位置准确测量影响的定心算法十分必要; 同时, 新的定心算法还需考虑主星光度变化的影响. 使用云南天文台2.4m望远镜, 1m望远镜以及紫金山天文台姚安观测站0.8m望远镜从2022年2月7日至2022年5月25日观测矮行星Haumea系统, 得到29晚共463幅CCD图像. 新定心算法确定的光心位置与使用二维高斯定心算法的结果相比具有更好的位置拟合效果. 此外, 还发现亮卫星Hiíaka在Jet Propulsion Laboratory (JPL)历表与Institut de Mécanique Céleste et de Calcul des ''Ephémérides (IMCCE)历表中的位置存在较大偏差. 相似文献
6.
7.
We describe the Caltech solar site survey in 1965–1967 directed by R. B. Leighton. The solar seeing at 102 locations in 34 sites in Southern California was evaluated by 6009 visual estimates with portable telescopes. Cloud cover and other meteorological factors were also measured, and sunlight recorders were operated at several sites. We have reanalyzed much of the data to determine its consistency and learn what else we could about the sites. The visual estimates show good internal consistency and correlation with photographic data.The seeing was found to be best at various sites associated with water, and we point out the importance of the Bowen ratio in determining the influence of water vapor on seeing. It was found that seeing at the different sites was not well correlated in time.The seeing was found to be best at Lake Elsinore, an inland sink. Good seeing was also found on the Caltech campus and at Big Bear Lake in the San Bernardino Mountains. Taking into account the better sky transparency and the feasibility of constructing an observatory in the lake, we chose Big Bear Lake for the site of a new observatory. The lack of correlation of seeing with transparency suggests the benefits of several smaller telescopes, targeted at specific goals, located at sites chosen for those goals. 相似文献
8.
Instrumentation built to record seeing data automatically via image motion measurements of bright stars in small telescopes is described. The centroid of the star image is found 256 times s-1 in one dimension and is analyzed on-line. The device works over a range of FWHM values as would be seen through a large telescope between <0.1 and 3.0 arcsec. The first results for two identical instruments set up at two locations near the duPont Telescope at Las Campanas Observatory are reported. For a total of 61 nights of data (450 h at each site), the median seeing is 0.6 arcsec, with quartiles at 0.4 and 0.8 arcsec. These are FWHM values referred to 5000 Å at the zenith. So far, the two sites are indistinguishable on average. 相似文献
9.
Alessandro Berton Markus Feldt Raffaele Gratton Stefan Hippler Thomas Henning 《New Astronomy Reviews》2006,49(10-12):661
We present here simulations of extrasolar planets detections obtained using a combination of extreme adaptive optics and integral field spectroscopy. The simulation code, written for IDL, provides images and, in particular, spectra, taking into account realistic Speckle Noise, AO correction effects and specific instrumental features. A detailed study has been done for ESO VLT telescopes (8.2 m), within the Phase A of the CHEOPS project, but the code is particularly flexible and can be updated for larger telescope diameters (ELTs) in order to give a realistic estimate of the detection limits, for giant telescopes, in standard conditions of seeing. 相似文献
10.
天文光学望远镜轴系驱动方式发展概述 总被引：4，自引：0，他引：4
该文首先介绍了已投入使用的2.5米口径以上的25架地平式光学望远镜和11架赤道式光学望远镜轴系驱动方式,并概述了天文光学望远镜轴系驱动及其相关技术的发展过程;然后对目前国际上在研的6架大型光学望远镜和预研的10架极大光学望远镜轴系所采用的驱动形式进行了归类;最后分析了未来极大光学望远镜轴系驱动的发展趋势和与之相关的研究内容. 相似文献
11.
A previously described microthermal measurement technique is applied to diagnose the causes and locations of sources of harmful ‘seeing’ effects in solar telescopes. Examples of the investigation of a compact 30-cm refractor at Culgoora Observatory and the massive 60-in. McMath reflector at Kitt Peak Observatory are described. The separate contributions from various parts of the telescopes and their immediate environments to the overall modulation transfer function and to the rms wavefront deformation are determined. The effectiveness of ventilation equipment fitted to these telescopes is assessed. In particular, it is shown that rms wavefront deformations ranging from λ/8 to 2λ may originate within the immediate atmospheric environments of these telescopes. Since the locations of these disturbances are determined there is a possibility of effecting improvements for example by mounting a telescope adequately high above the floor of its supporting tower. In the McMath reflector the major contribution to bad ‘seeing’ generally arises in the upper part of the instrument in the vicinity of the heliostat.
相似文献12.
Coupling the JNLT with the Keck telescope is of considerable interest. Further enhancement may be possible with auxiliary small telescopes, as planned for ESO's VLT. Current plans for installing the optical very large array at Mauna Kea provide opportunities for extra OVLA telescopes near the JNLT.A coudé field slicer is proposed for interferometric observing of a reference star together with the main object. Additions to the JNLT coudé spectrograph are also suggested for use as a speckle camera with multiple spectral channels.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
13.
Woodruff T. Sullivan III 《Experimental Astronomy》2009,25(1-3):107-124
Forged by the development of radar during World War II, radio astronomy revolutionized astronomy during the decade after the war. A new universe was revealed, centered not on stars and planets, but on the gas between the stars, on explosive sources of unprecedented luminosity, and on hundreds of mysterious discrete sources with no optical identifications. Using “radio telescopes” that looked nothing like traditional (optical) telescopes, radio astronomers were a very different breed from traditional (optical) astronomers. This pathbreaking of radio astronomy also made it much easier for later “astronomies” and their “telescopes” (X-ray, ultraviolet, infrared, gamma-ray) to become integrated into astronomy after the launch of the space age in the 1960s. This paper traces the history of radio telescopes from 1945 through about 1990, from the era of converted small-sized, military radar antennas to that of large interferometric arrays connected by complex electronics and computers; from the era of strip-chart recordings measured by rulers to powerful computers and display graphics; from the era of individuals and small groups building their own equipment to that of Big Science, large collaborations and national observatories. 相似文献
14.
近代天文圆顶发展概况 总被引：2，自引：0，他引：2
综述了国内外天文圆顶的各种设计方案，比较了各种方案的性能，并介绍了为改善圆顶性能，降低造价进行的相关研究，以及为下一代巨型地面望远镜圆顶进行的预研究．结合目前正在研制的大天区多目标光纤光谱望远镜——LAMOST，简述了我国LAMOST望远镜圆顶的设计方案及其相关研究的概况。 相似文献
15.
PaulHickson 《Monthly notices of the Royal Astronomical Society》2002,330(3):540-546
Equipped with a suitable optical relay system, telescopes employing low-cost fixed primary mirrors could point and track while delivering high-quality images to a fixed location. Such an optical tracking system would enable liquid-mirror telescopes to access a large area of sky and employ infrared detectors and adaptive optics. Such telescopes could also form the elements of an array in which light is combined either incoherently or interferometrically. Tracking of an extended field requires correction of all aberrations including distortion, field curvature and tilt. A specific design is developed that allows a 10-m liquid-mirror telescope to track objects for as long as 30 min and to point as far as 4° from the zenith, delivering a distortion-free diffraction-limited image to a stationary detector, spectrograph or interferometric beam combiner. 相似文献
16.
KONG Xu LIN Lin LI Jin-rong ZHOU Xu ZOU Hu LI Hong-yu CHEN Fu-zhen DU Wei FAN Zhou MAO Ye-wei WANG Jing ZHU Yi-nan ZHOU Zhi-min 《Chinese Astronomy and Astrophysics》2014
In recent years the number of worldwide 8∼10 m-class ground-based telescopes is continually increased, the 4 m-diameter or smaller telescopes have become the small and medium-sized telescopes. In order to obtain some noticeable scientific results by using these existing small and medium-sized telescopes, we have to consider very carefully what we can do, and what we can not. For this reason, the Time Allocation Committee of the 2.16 m telescope of the National Astronomical observatories of China (NAOC) has decided to support some key projects since 2013. The long-term project “Spectroscopic Observations of the Star Formation Regions in Nearby Galaxies” proposed by us is one of three key projects, it is supported by the committee with 30 dark/grey nights in each of three years. 相似文献
17.
A. Tokovinin † 《Monthly notices of the Royal Astronomical Society》2000,316(3):637-641
Vibrations of telescopes can be successfully corrected in real time using a seismometer as an inertial reference. A prototype pendular seismometer is described that is suitable for angular vibration measurements at frequencies from a few tenths to several tens of Hz. The average pendulum position is maintained by a slow servo system that also damps its resonance. The prototype instrument has an rms noise of 3 milliarcsec in the 0–25-Hz band. It was tested on a 1-m telescope, and a good agreement of the seismometer signal with the direct optical measurements of the optical axis fluctuations of the telescope was found. A frequency response of the seismometer is studied, an expression for the rms amplitude of residual (uncompensated) vibrations is given. In space applications it is suggested that a pendular mirror in front of the telescope is used as an inertial reference for vibration correction. 相似文献
18.
Russell Cannon 《Astrophysics and Space Science》1989,160(1-2):275-280
Many of the major British telescopes are described in this volume by other speakers directly involved with those facilities, so this contribution will concentrate on aspects of the operation of the Anglo-Australian Observatory (AAO) which seem particularly relevant to the JNLT. Some requirements for the success of the new very large optical telescopes are also discussed.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
19.
The European Very Large Telescope program has been approved in 1987. It aims to consists of an array of four 8 m telescopes, plus two additional 2 m class auxiliary telescopes, the latter being fully dedicated to optical (infrared and visible) interferometry, with possible combination of some and, in the long term, all large telescopes. We discuss the implementation of this program in the next ten years.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
20.
David L. Crawford 《Experimental Astronomy》1994,5(1-2):87-89
New generation small telescopes can and should be very complementary facilities for the new large telescopes and for space astronomy. With CCD imaging detectors as part of their instrumentation package, they are most efficient research tools for many research programs. In addition, linking a number of them together into a "global network of astronomical telescopes" appears to make a good deal of sense. A new non-profit organization, GNAT, Inc., has been established to be the catalyst for such a network.Operated by AURA, Inc. under cooperative agreement with the National Science Foundation, Washington D.C. 相似文献