共查询到20条相似文献，搜索用时 203 毫秒
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介绍了丽江高美古二期选址的筛选工作，经过踏勘确定高美古周围山头的10个点为筛选点，采用小型轻便望远镜于1998年10月16至1999年1月27日进行目视衍射环观测，并对取得的资料作了处理、分析和初步探讨。观测发现各点的视宁度没有明显差别，6 相似文献
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介绍了丽江高美古二期选址在踏勘和筛选工作的基础上 ,对 3 # 点和6# 点的视宁度进行了对比观测。通过对 1 999年 2月 6日～ 1 999年 1 2月 3 1日 2个点共 4 756组同时段观测数据的统计和处理得到 :3 # 点的视宁度平均值为 1 1 .2 62 3cm ,6# 点的视宁度平均值为 1 1 .5952cm。经F分布检验和t分布检验假设成立 ,作出 3 # 点和 6# 点的视宁度无显著性差异的推断 ,与初期用衍射环观测视宁度的结果一致 ,进一步说明了高美古整个山头的视宁度都是优良的 相似文献
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E. Brannigan M. Takami A. Chrysostomou J. Bailey 《Monthly notices of the Royal Astronomical Society》2006,367(1):315-322
We demonstrate that artificial bipolar structure can be detected using spectro-astrometry when the point spread function (PSF) of a point source suffers distortion in a relatively wide slit. Spectro-astrometry is a technique which allows us to probe the spatial structure of astronomical sources on milliarcsec (mas) scales making it possible to detect close binaries and to study the geometry and kinematics of outflowing gas on scales much smaller than the seeing or the diffraction limit of the telescope. It is demonstrated that a distorted PSF, caused by tracking errors of the telescope or unstable active optics during an exposure, can induce artificial signals which may be misinterpreted as a real spectro-astrometric signal. Using simulations, we show that these may be minimized by using a narrow slit relative to the seeing. Spectra should be obtained at antiparallel slit position angles (e.g. 0° and 180°) for comparison in order to allow artificial signatures to be identified. 相似文献
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Starting November 1999 we are carrying out simultaneous seeing observations with the Solar Differential Image Motion Monitor (S-DIMM) at the Fuxian Lake station of the Yunnan Observatory and a solar scintillometer of the type used in the recent site survey by one of us (Beckers et al., 1997). The purpose was to compare the two methods of assessing the daytime atmospheric seeing for a lake site. We report here the first results of this comparison. We find that the relation between the seeing as measured by the S-DIMM (the Fried parameter r
0) and the scintillation in the solar irradiance (I) differs greatly from the relation found by Seykora (1993) for NSO/Sac Peak. We conclude that the I measurements give a good indication for the amount of near-Earth seeing but that they are a poor proxy for the total atmospheric seeing. We interpret the simultaneous (r
0, I) observations in terms of an atmospheric seeing model and find good quantitative agreement with a model in which a fraction () of the seeing originated near the Earth (ground or water) and the rest (1–) originates at higher layers. For lake sites is small all day and the seeing is determined primarily by the refractive index variations at higher atmospheric layers. For land sites is small in the early morning but rapidly increases as the day progresses, near-Earth seeing dominating there most of the time. 相似文献
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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
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A.J. Horton D.F. Buscher C.A. Haniff 《Monthly notices of the Royal Astronomical Society》2001,327(1):217-226
We present a numerical analysis of free-space propagation of the beams inside a long-baseline optical/infrared interferometer. Unlike the models of beam propagation used in most previous studies, our analysis incorporates the effects of atmospheric seeing on the wavefronts entering the interferometer. We derive results for the changes in throughput, coherence loss and fringe-detection signal-to-noise ratio arising from diffraction along the propagation path. Our results for conditions of moderate seeing show that although the flux throughput decreases with propagation distance for a given beam diameter, the fringe contrast increases at the same time. In this case it becomes possible for diffraction to increase the signal-to-noise ratio of the fringe measurements. Previous studies have only considered an arrangement where all the apertures in the beam-propagation system have the same diameter. If the light at the end of the propagation path is collected with a fixed size aperture, we find that in many cases the signal-to-noise ratio for fringe detection is maximized when the initial beam diameter is approximately 30 per cent smaller than the final collector diameter. We discuss the implications of our results in the context of future interferometer designs. 相似文献
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Winifred Sawtell Cameron 《Earth, Moon, and Planets》1975,14(1):187-199
Several different manifestations of lunar transient phenomena (LTP) have been reported. These include: (1) brightenings - both sudden and slow, (2) reddish - both bright and dull, (3) bluish -both bright and dull, (4) fairly abrupt dimmings or darkenings, and (5) obscurations, which may be accompanied by any of the other four manifestations. Approximately 200 lunar features exhibiting such anomalies have been reported at least once, but 80% of all observations are found in less than a dozen sites and 60% are found in about one-half dozen sites. An observing program is being conducted for the Association of Lunar and Planetary Observers which is designed to monitor the LTP sites, the seismic epicenter sites and non-LTP comparison sites. It addresses the ‘brightenings’ category of observations and is designed to establish normal brightness of each observed feature for all phases of a lunation. It also seeks to establish a quantified ‘seeing’ scale. About one-half dozen observers have reported albedo measures (estimated from an albedo scale set up by each observer). The most extensive new data on albedo versus age (phase of Moon) are for the crater Dawes. Several LTP effects have been discerned in Dawes. In addition, seeing estimates, based on the behavior of a star's diffraction disk, provided some unexpected results when disk behavior is compared with other subjective estimates of seeing. 相似文献
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Ewen A. Whitaker 《Icarus》1979,40(3):406-417
The phase relations of several asteroids. Mercury, and the Moon display the same basic characteristics, but differ slightly in detail. An improved treatment of the photometric function for open-work particulate layers shows that for phase angles greater than about 7°, the shape of the curves is diagnostic of the presence of such layers, and that both the shape and slope of the curves is dependent primarily upon the bulk density of these layers. This treatment also strongly indicates that the “opposition effect” is not due to shadow hiding in a regolith of very low bulk density. Other data support the idea that this effect is unrelated to shadow-hiding phenomena, and that it may thus be a diffraction/scattering effect with or without internal reflection phenomena also. 相似文献
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Th. Berkefeld D. Schmidt D. Soltau O. von der Lühe F. Heidecke 《Astronomische Nachrichten》2012,333(9):863-871
The new 1.5‐m German solar telescope GREGOR at the Observatorio del Teide, Tenerife, is equipped with an integrated adaptive optics system. Although partly still in the commissioning phase, the system is already being used used for most science observations. It is designed to provide diffraction‐limited observations in the visible‐light regime for seeing better than 1.2″. We describe the AO system including the optical design, software, wavefront reconstruction, and performance (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Modulation transfer functions (MTFs), generated as a by-product of the analysis of low-resolution solar images taken for the Global Oscillation Network Group, were used to estimate the quality of seeing at its six sites. These MTFs, after approximate correction for the effects of the instrumental point spread function, were fitted with physically-motived functional forms representing the effects of seeing and scattering. It was found that the estimates of seeing quality were relatively robust to the effects of scattering, but were severely biased by effects caused by changes in instrumental focus. Relative trends in seeing quality are preserved on time scales shorter than a few months and it is found that local topography dominates the observed trends in daytime seeing quality. 相似文献
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We investigate the influence of seeing upon measurement of magnetic flux of photospheric fields. For this purpose we quantify seeing variation in one day's observation at Big Bear Solar Observatory in terms of the Fried function, a Modulation Transfer Function for the atmospheric seeing. The temporal variation of seeing quality is compared with that of magnetic flux measured in a quiet region with size 5 \times 4 near the solar disk center. A good correlation is found between the seeing change and apparent evolution of magnetic flux values, implying, as a possibility, that magnetic flux measurement might have been modulated by seeing. Based on a simple model of ensembles of Gaussian magnetic elements we argue that even the net flux as well as the total flux can change due to seeing variation if the magnetograph has a finite detection threshold and if the intrinsic fluxes in one and the other polarities are unbalanced. 相似文献
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John C. Webber 《Solar physics》1971,16(2):340-361
The sunspot spectrum shows many molecular lines, of which some have been identified. These lines are formed farther out in the sunspot atmosphere than the atomic lines or the continuum, and are thus useful for probing the outer layers. Photographic spectrograms were obtained for three different sunspots under carefully selected seeing conditions, showing molecular absorption lines due to MgH, CaH, and TiO. Analysis led to estimates of the effective rotational temperatures of each; in the case of CaH, no definite conclusions could be drawn. Predicted rotational temperatures and observational f-values were calculated on the basis of model umbral atmospheres due to several authors. A new model was derived from the molecular lines measured here, and shown to differ widely from previous models. The usefulness of photographic spectra for this purpose is seriously questioned, and suggestions are made for new observations. 相似文献
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讨论了经过大气后天文图象的象质衰减,研究了对这种衰减进行描述的视宁度参数ｒ０及其它几个大气光学参数,介绍了几种测量象质衰减参数的方法,重点介绍了我们将差分像运动法运用于白日视宁度测量的尝试以及新设计的可兼顾昼夜的视宁度测量仪,仪器已用于云台白日的视宁度测量。最后对近场近似假设进行了定量分析,在此基础上给出了新确定的近场近似成立的范围,这一范围比以前所给的要更大些。 相似文献
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R. W. Wilson N. O'Mahony C. Packham M. Azzaro 《Monthly notices of the Royal Astronomical Society》1999,309(2):379-387
We present results from a study of the seeing quality at the 4.2-m William Herschel telescope at La Palma. The median intrinsic seeing at the site is found to be excellent, and is comparable to that at the Paranal and Mauna Kea observatories. Contributions to the seeing from turbulence within the telescope dome are insignificant. Furthermore, the optical quality and tracking stability of the telescope are good, so that long-exposure image widths close to the limit imposed by the site seeing can be expected. 相似文献
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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