一米新真空太阳望远镜多波段光谱仪CaⅡ通道杂散光研究

观测目标的亮度越小,杂散光对其的影响越大。在光谱观测中,由于谱线线心的剩余能量较小,所以杂散光对光谱观测的影响显著。在用抚仙湖1 m太阳望远镜多波段光谱仪进行光谱观测时发现,CaⅡ光谱图像在855.6 nm吸收线右侧的亮度有肉眼可见的明显下降,针对此现象分析产生光谱图像色散方向上亮度左右差异的原因,结合杂散光的理论用实验的方法找出杂散光的来源及传输路径。分析结果表明,产生此种现象是由于狭缝的次极大衍射光照亮成像镜后反射到CCD,形成一个弧形的杂散光亮斑,强度约为光谱图像平均光子数的20.9%,对CaⅡ通道的光谱图像产生了严重的影响。对分析的结果进行了理论验证。利用遮挡杂散光传输路径与图像处理两种抑制杂散光的方法对其进行消除,使CaⅡ通道杂散光恢复到正常水平。     

兴隆1m光学望远镜杂散光效应研究

兴隆1m光学望远镜采取了加装挡板等基于经验和定性分析的杂散光抑制措施。用Tracepro光学分析软件对圆顶内1m望远镜的杂散光传播路径做了计算和分析,提出了对1m望远镜的杂散光抑制的改进措施,通过在Tracepro中计算的系统杂散光"归一化点源辐照度透过率(PSNIT)"函数对改进措施进行了评价。计算结果表明:对于有效视场外30°范围的杂散源,改进措施可使得1m望远镜的PSNIT全部下降到10-10;模拟1m望远镜在满月条件下对偏月25°的天体观测(R波段、15等星、t=15~150s),1m望远镜观测信噪比可提高约147%。     

一米新真空红外太阳望远镜多波段光谱仪光谱弯曲分析

在太阳长狭缝光谱观测中,光谱的狭缝方向和色散方向应该分别与CCD探测器的两个边缘平行。但实际上,由于狭缝、光栅、CCD探测器的机械安装精度等原因,会造成他们之间的位置关系不匹配,导致得到的太阳光谱总是存在一定的倾斜和变形。即使有时这些倾斜很微小,也会对太阳光谱的平场计算造成严重影响,从而影响整个光谱数据的处理过程。对抚仙湖1 m新真空红外太阳望远镜多波段光谱仪得到的一组Hα光谱数据的倾斜量做了测量和分析,并讨论了其对太阳光谱平场计算的影响。     

大气色散对太阳多波段同步高分辨图像重建的影响

抚仙湖1 m新真空太阳望远镜(New Vacuum Solar Telescope,NVST)利用多波段成像系统对太阳光球和色球同时进行高分辨成像观测,并对观测图像进行多波段同步高分辨统计重建,以大幅度降低重建所需的计算量,并改善低信噪比波段的高分辨重建效果。大气色散是影响多波段同步高分辨重建效果的主要因素。借助多层湍流大气的模拟,通过比较不同天顶角下色散引起的波像差、相对谱比,分析了大气色散对多波段同步高分辨重建的影响。分析结果表明对于1 m太阳望远镜,当天顶角在60°以内时,色散对近红外以及波长相差不大的可见光波段的多波段同步高分辨重建的影响较小,而393.3 nm波段受色散的影响明显,天顶角超过45°时分辨率明显下降。     

一米新真空太阳望远镜多波段光谱仪杂散光及空间PSF的测量

杂散光由于光学表面散射和地球大气散射引起,降低了光谱图像的空间分辨率。光学系统都存在杂散光,要获得高分辨的光谱图像需要对杂散光进行抑制。多波段光谱仪的杂散光分为两类:(1)光谱桶内由于光机结构引起的杂射光;(2)混在成像光路中并参与色散的杂散光。第1种杂散光可直接测量,约占光谱能量的3%左右。第2种杂散光由于受多种因素影响,所以很难精确测量。从日食光谱测量中测得在观测目标周围对目标产生的杂散光的下限约为10%,并对空间方向的点扩散函数进行测量,为光谱的高分辨重建提供参考。     

云南天文台Hα全日面观测数据服务系统

云南天文台Hα全日面望远镜是云南天文台太阳观测的主要仪器之一。经过十几年的运行,望远镜积累了大量的观测数据,并且这些数据还在以每天1～2Gbyte的速度增长。为了保存这些数据,便于进行数据共享,建立了Hα全日面观测数据服务系统。硬件方面,采用DAS+NAS的存储方案;软件方面采用PHP+MySQL的方案。本系统的基本功能包括数据存储、数据备份、数据查询和数据下载,并已经正常运行了半年左右。介绍了这一系统的设计方案和基本结构。由于这一系统更多的是为澄江1m红外太阳塔的有关系统的设计提供经验和参照,因此在文中相关部分初步讨论了某些针对澄江1m红外太阳塔有关系统的考虑。     

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.     

红外波段太阳观测技术方法研究

1m红外太阳塔是我国未来重点发展的地面太阳观测设备，本文的所有工作均围绕着与此相关的红外波段太阳观测技术方法展开。1．针对望远镜实验平台－云台太阳光谱仪，建立了光谱仪分光流量,工用多种实验手段验证了其可靠性。利用该模型计算了Fe Ⅰ1.56μm红外太阳光 谱的分光流量，分析了实验观测的可行性及改进方案。2．针对探测器实验平台－PtSi红外焦平面阵列相机，建立了FeⅠ1.56μm光谱观测信噪比模型，模拟了各种噪声对观测的影响。在此基础上，在国内首次成功进行了FeⅠ1.56μm红外太阳光谱的面阵观测实验。3．在红外观测实验所处的高背景低对比度条件下，讨论了红外太阳光谱观测的图像处理方法，分析了观测中出现的干涉条纹的来源及解决办法，初步建立起了一整套红外太阳光谱与成像的定标方法和图像处理方法。4．首次利用PVA材料，设计研制了一套FeⅠ1.56μm近红外Stokes参量偏振仪，并将该偏振仪安装在美国国立天文台McMath望远镜上进行了观测实验。针对一太阳黑子，通过扫描进行了二维的Stokes参量观测。同时建立了一套从Stokes参量反演磁矢量场的方法，并将反演的结果与怀柔太阳磁场望远镜的观测结果进行了比对。5．针对1m红外太阳塔的太阳光谱仪系统，给出了垂直多波段光谱仪和红外大色散光谱仪的光、机初步设计。6．针对1m红外太阳塔的科学目标，提出了多波段光谱仪探测器系统方案，对红外大色散光谱仪所使用的红外探测器也进行了初步方案设计。     

NVST高分辨窄带成像系统视场频漂的实测与分析

1 m新真空太阳望远镜的成像系统包括Hα,Ca Ⅱ和He Ⅰ三个窄带成像通道,三者均使用里奥滤光器系统进行单色像观测。以Hα通道实测图像为例,探讨了在线心-线翼的偏带观测出现的太阳像亮度空间分布不均匀问题的原因。该不均匀性不同于杂散光,其空间分布形式与变化程度随观测波长点的不同而不同。通过对多组实测数据的分析认为,出现亮度不均现象的根本原因是滤光器的视场效应,视场边缘区域的工作波长相对中心区域发生频率漂移。频漂的程度和空间分布特征与光路装调密切相关,通过分析对比2017年3月光路调整前后频漂情况得出结论:在目前Hα成像通道2.2'的视场范围内,视场频漂量最大为0.005 nm,小于透过带带宽,且仅出现在视场左下角边缘。     

基于Lyot滤光器的NVST磁像仪光学系统设计

我国1 m新真空太阳望远镜(New Vacuum Solar Telescope, NVST)能够实现优于0.2″的高分辨成像观测,但还不具备高分辨磁场的常规观测能力。很多磁结构和太阳活动都存在于较小的尺度,需要进行高分辨磁场测量。1 m新真空太阳望远镜的台址具备优良的视宁度,若磁像仪具备快速调制能力,并配合高分辨统计重建技术,有望实现亚角秒分辨率的太阳磁场测量。1 m新真空太阳望远镜测量磁场面临的主要问题包括折轴光路带来的时变偏振、望远镜姿态变化和风载带来的光轴偏移以及湍流的影响等多种问题。针对太阳磁场高分辨观测的需求及1 m新真空太阳望远镜面临的太阳磁场测量问题,详细分析了1 m新真空太阳望远镜太阳光球磁场的测量需求,制定了磁像仪的基本参数,提出了偏振分析器需求,设计了光球磁场的高分辨观测方案。最后利用ZEMAX光学设计软件为磁像仪设计了光路,结果显示光学设计能够满足高分辨成像的需求。     

Optimizing CCDs for spectrographs

For a spectrograph giving a fixed format spectrum,the quantum efficiency (QE) can be optimized for the different wavelengthsacross the CCD. It is shown that a slight modification of the conventionalsingle layer anti-reflection coating can give major improvements in QE forsuch instruments, while at the same time minimizing problems with fringingand stray light from the CCD.     

Correction of solar observations for stray light by numerical integration,with application to Mercury's drop

A numerical method for correction of stray light in solar observations has been developed. In particular a regular sunspot, where the circular contours of penumbra and umbra are projected as ellipses, has been studied. When a specified set of values for the stray light parameters is given, and also tentative values for the relative intensities of penumbra and umbra, the integration of stray light can be performed in any point. The result will be the observable intensity if the conditions were as given by these initial values.By means of limb observations the stray light parameters may be improved, and finally a variation of the penumbra- and umbra intensities in the computation, enables a determination of these quantities by comparison with observations.The method is tested on observations of the transit of Mercury, May 9, 1970. Calculation of isophotes with Mercury close to the limb shows the black drop phenomenon; which thus may be explained as an effect of stray light only.It is also shown that the Wilson effect on a sunspot cannot be produced by stray light alone.     

Mercury Transit for Stray Light Evaluation: IPM-THEMIS Case

Mercury's transit on the solar disk offers ideal conditions to determine the stray light level of instruments. We present here the results on the stray light level deduced from the observation of the Mercury transit on 2003 May 7th at the secondary focus of the THEMIS telescope with the broad-band and spectral channels of the IPM instrument. The scattered light in the broad-band channel is about 17% and about 25% in the spectral channel. The spread function was deduced for the two channels taking into account the observations on the limb and on Mercury's disk. The goal of this paper is to underline the limits of determining the spread function from limb measurements to correct disk observations. Indeed, we show that if a diaphragm is located in the optical path of scattering surfaces, then the spread function deduced from limb measurements can be underestimated compared to the one required for disk observations. The case is illustrated with the results of the IPM-THEMIS instrument. The spread function deduced from limb measurements is able to correct disk observations in the broad-band channel but not in the spectral channel, even if the two channels are illuminated through the same telescope configuration.     

A Model for the Stray-Light Contamination of the UVCS Instrument on SOHO

We present a detailed model of stray-light suppression in the spectrometer channels of the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO spacecraft. The control of diffracted and scattered stray light from the bright solar disk is one of the most important tasks of a coronagraph. We compute the fractions of light that diffract past the UVCS external occulter and non-specularly pass into the spectrometer slit. The diffracted component of the stray light depends on the finite aperture of the primary mirror and on its figure. The amount of non-specular scattering depends mainly on the micro-roughness of the mirror. For reasonable choices of these quantities, the modeled stray-light fraction agrees well with measurements of stray light made both in the laboratory and during the UVCS mission. The models were constructed for the bright H i Lyα emission line, but they are applicable to other spectral lines as well.     

Stray-Light Effect on Magnetograph Observations

To examine the stray-light effect in magnetograph observations, we have determined the point spread functions of the vector magnetograph mounted on the Japanese Solar Flare Telescope based on two indirect methods, one analyzing the solar limb intensity profile, and the other using the Fourier power spectra of photospheric intensity distributions. Point spread functions consist of two parts: a blurring part which describes seeing and small-spread-angle stray light, and a scattering part which describes large-spread-angle stray light. The FWHM spatial resolution is typically 3.0, and the amount of scattered light is about 15% on clear days. We find that the blurring part is well described by a Moffat function whose Fourier transform is given by an exponential function. Our results indicate that polarization measurements of low-intensity magnetic elements like sunspots may be significantly underestimated due to the large-spread-angle stray light, and polarization measurements of magnetic elements which are smaller than 5–7 appear to be disturbed by small-spread-angle stray light.     

Measurement of Aureole and Suppression of Internal Stray Light of Aureole Photometer

A modern aureole photometer (AP) was developed for the site survey inWest China, in preparation for the installation of future large solar equipments. The performance of this new AP was tested in preliminary observations, and a lot of sky brightness data were accumulated at a few sites in Yunnan Province. The result of data analysis shows that the aureole near the noon time on Jiaozi Snow Mountain is as low as a few millionths of the intensity at the solar disk center, indicating the low internal stray light level of our instrument. The internal stray light of the AP comes mainly from two parts: the edge diffraction of the ferrule for fixing the ND4 filter in the front end of the telescope tube, causing the stray light distributed in the inner region of the field of view, and the edge diffractions of the diaphragms placed inside the telescope tube, causing the stray light distributed in the outer region of the field of view. In order to suppress the stray light of the latter part, the experiment to change the aperture size of an additional diaphragm was performed. The result shows that the stray light in the outer region of the field of view can be effectively suppressed by reducing properly the aperture size of the diaphragm.     

YNST光电导行镜机械设计

YNST(云南1m太阳望远镜)光电导行系统的作用除了获取足够清晰的太阳像用作光电导行外,还参与望远镜光轴的校正.介绍了YNST光电导行镜的光学要求、机械设计结果及镜体设计所采用的被动无热化技术.校核了导行镜在阳光辐照下的热变形,计算了导行镜镜筒的最大弯沉,结果表明,所采用的无热化设计是有效的,导行镜刚度满足导行系统要求...     

1m红外太阳望远镜光电导行系统中像场旋转的分析

云南天文台1m红外太阳望远镜(YNST)光电导行系统是基于检测太阳像在面阵CMOS图像传感器上的偏移量作为反馈控制信号的高精度闭环跟踪系统[1]。由于YNST是一个地平式装置,在太阳像偏移检测量中存在着像场旋转量,为了获取稳定清晰的太阳像,必须对检测量进行消旋[2]才能达到光电导行系统的跟踪要求。根据球面天文学及天体测量学的知识并结合导行镜的光学系统,推导了光电导行系统中像场旋转的变化规律并对其进行模拟分析。     

Solar and Heliospheric Observatory/Large Angle Spectrometric Coronagraph Polarimetric Calibration

We present a polarimetric characterization and correction for the Solar and Heliospheric Observatory/Large Angle Spectrometric Coronagraph (SOHO/LASCO) C2 and C3 white light coronagraphs. By measuring the uncorrected polarization angles in solar minimum C2 coronal images, we have determined that the coronagraph acts as an optical phase retarder which converts a small fraction of the incoming radiation polarization from linear to circular. In addition, from the measurements of polarization angle in C3 coronal images we have determined that a component of the instrumentally scattered light in that instrument is polarized. We infer the retardation angle for C2 and compute the corresponding Mueller matrix, and determine the polarized stray light spatial profile in C3. The C2 Mueller matrix and C3 polarized stray light profiles are used to correct for instrumental effects in solar minimum coronal observations to obtain polarized brightness between two and thirty-two solar radii, which show deep polar coronal holes extending to the limit of the field of view.     

Point spread function tails and the measurements of diffuse stellar halo light around edge-on disc galaxies

Measuring the integrated stellar halo light around galaxies is very challenging. The surface brightness of these haloes is expected to be many magnitudes below dark sky and the central brightness of the galaxy. Here, I show that in some of the recent literature the effect of very extended Point Spread Function (PSF) tails on the measurements of halo light has been underestimated; especially in the case of edge-on disc galaxies. The detection of a halo along the minor axis of an edge-on galaxy in the Hubble Ultra Deep Field can largely be explained by scattered galaxy light. Similarly, depending on filter and the shape one assumes for the uncertain extended PSF, 20–80 per cent of the halo light found along the minor axis of scaled and stacked Sloan Digital Sky Survey (SDSS) edge-on galaxy images can be explained by scattered galaxy light. Scattered light also significantly contributes to the anomalous halo colours of stacked SDSS images. The scattered light fraction decreases when looking in the quadrants away from the minor axis. The remaining excess light is well modelled with a Sérsic profile halo with shape parameters based on star count halo detections of nearby galaxies. Even though, the contribution from PSF scattered light does not fully remove the need for extended components around these edge-on galaxies, it will be very challenging to make accurate halo light shape and colour measurements from integrated light without very careful PSF measurements and scattered light modelling.