光谱波长位置的确定

波长位置在光谱工作中至关重要。本文讨论和介绍了利用恒星光谱谱线，夜天光谱线，大气吸收线及摄谱仪标准谱灯谱线确定波长位置的方法。     

基于样条函数的恒星光谱自动归一化方法

恒星的观测谱一般由连续谱、谱线和噪声组成,其中连续谱是黑体辐射导致的辐射流量随波长变化的光滑连续光谱。光谱分类及恒星物理参数估计等研究依赖于连续谱及谱线信息的准确提取。因此光谱数据处理的工作主要是拟合连续谱,并通过对光谱进行归一化来提取谱线特征。连续谱拟合的方法主要有多项式拟合、中值滤波、小波滤波等。已有的方法在低信噪比、宇宙线信号干扰、存在发射线等情况下,有不同程度的局限性,体现在鲁棒性和准确度上。目前,针对郭守敬望远镜的10 7条光谱没有自动化方法应用到归一化上的问题,研究并开发一种适用于不同的温度、信噪比及波长覆盖范围,并能够自动化处理的恒星光谱归一化方法,显得十分迫切。在仔细分析不同类型光谱的基础上,提出了一种基于固定窗口划分的连续谱拟合方法。该方法对光谱中能够体现连续谱特征的数据点进行筛选提取,通过细微地控制样条函数平滑度产生更加准确的连续谱。使用郭守敬望远镜中不同光谱型、温度范围、波长覆盖范围的光谱进行实验,结果表明,该方法具有良好的精度和普适性。     

中国丽江积分视场光纤光谱仪分辨能力实验室测试结果

中国丽江积分视场光纤光谱仪(China Lijiang Integral Field Unit,简称CHILI)是中国第一台用于夜天文观测的科学级积分视场光纤光谱仪,安装在丽江天文观测站2.4 m光学望远镜上。CHILI运输到中国前,在美国德克萨斯大学奥斯汀分校(University of Texas at Austin)进行了实验室测试。本次实验主要针对CHILI的蓝端,主要测试内容有本底、平场、暗场和波长定标。为了明确知道谱线在像素位置上的精准波长和CHILI探测器的分辨能力,对测试数据进行了波长定标和光谱分辨能力的计算。结果显示,CHILI蓝端的波长范围约为3 500～5 300,在此波长范围内,光谱分辨本领FW H M■5,其对应的光谱分辨率R=λ/?λ约为600～1 000,符合CHILI预期要求。     

云台一米镜卡焦摄谱仪重力弯沉的谱线位移及展宽效应

本文在理论上着重分析了云台一米镜卡焦摄谱仪中准直镜和照相机的重力弯沉效应。并拍摄了一米镜处于四十五个不同指向时的铁谱,测量重力弯沉效应引起谱线位移的大小。表明,重力弯沉引起谱线位移为μ的数量级,在观测中的连续变化产生特殊的谱线展宽效应。实验与理论分析的拟合基本一致。并讨论了重力弯沉对波长测量、谱线轮廓测量、光谱分辨率测量的影响以及克服的方法。     

使用小波技术自动搜寻天体谱线

使用小波技术对包括恒星、近邻星系和ＡＧＮ等不同的天体光谱进行了自动处理．用小波滤波的方法将光谱中的连续谱与诸线分离;然后使用小波域隐含马尔可夫模型（ＨＭＭ）,对已去掉连续谱的光谱进行降噪,同时得到了噪声在每个光谱中的分布;在训练ＨＭＭ的过程中,使用改进的Ｔｙｉｎｇ方法增加训练数据以保证训练的可靠性;利用噪声分布确定出谱线信号的局部阈值,在已经降噪的光谱中找到吸收线和发射线;用高斯函数拟会出谱线的形状,标出线心的波长值,作为自动证认的基础．     

赛弗特星系恒星速度弥散度的测量

星系中心黑洞质量和核球恒星速度弥散度的紧密关系揭示出准确测量恒星速度弥散度对测定星系中心黑洞质量尤为重要.文中提供了一种利用SDSS(Sloan Digital SkySurvey)光谱测定速度弥散度及其不确定性的方法.通过对像素空间包含显著特征吸收线的4个不同谱区的拟合,得到准确测量恒星速度弥散度σ的光谱区域.文中4个拟合波段主要包含的吸收线为CaⅡK,MgⅠb三重线(波长5167.5,5172.7,5183.6(?))和CaT(CaⅡ三重线,波长8498.0,8542.1,8662.1(?)).不同区域结果表明,MgⅠb区由于受到铁族发射线影响,拟合的σ值偏低;CaⅡK线区谱线强度很弱,易受限于最小二乘法搜索算法;CaT+CaⅡK联合区得出的速度弥散度和只计算CaT区域的结果相当.利用该方法,测试了一个红移小于0.05的赛弗特星系样本,发现CaT区是测速度弥散度的最佳谱区.     

彗星光谱的证认与氨的光谱的分析

我们使用氨的光谱来研究彗星光谱的谱线,这些谱线的成因是氮与氢所构成的分子,特别是 NH_2。我们从低压下,轻微激发所得的氨光谱,比较从别的氨光谱,能更完全地证认彗星的光谱。从彗星各种光谱里所证认出的谱线的情观的研究,得知这些光谱更可利用来研究氨的光谱的细节。由我们所得的谱线的分群表现氨光谱的 NH_2光带的结构;有些彗星的光带还分裂为二,这种分裂现象是在实验室里所观测不到的。     

基于兴隆观测基地80厘米望远镜的CSST无缝光谱地面测试

我国预计2025年发射的巡天空间望远镜(Chinese Space Station Telescope, CSST),主要用于开展大规模的多色成像与无缝光谱巡天工作。发射前需要利用地基望远镜对空间望远镜的光学成像系统、探测器,以及设备长时间运行稳定性进行地面测试。设计了兴隆观测基地80 cm望远镜的无缝光谱地面测试,利用A型恒星、B型恒星和沃尔夫拉叶星HD4004的强吸收和发射线特征,拟合色散方程,并发现色散方程具有空间分布特征。对HR3173的53条数据的零级谱位置信息及色散方程系数进行了二次曲面拟合,并利用该曲面对HR3173零级像位置范围内的HR718数据进行了波长定标,得到的CCD上8×13 pixels范围内的平均视向速度精度为51 km/s。     

1980年日全食色球闪光光谱观测和初步结果

1980年2月16日日全食时,我们在云南省瑞丽县用一架无缝光谱仪成功地进行了一次闪光光谱观测。仪器由定天镜供光,平均色散度为5.7/mm。光谱底片的高度分辨率为185 km。 观测资料初步分析如下:在4799—5845波段内,证认了1042条色球谱线,其中72条是文献[1]和[2]中未见列出的;确定了色球底的位置;用食既前的太阳边缘的无缝光谱和日食前一天的日心有缝光谱进行了绝对强度定标;测量计算了各条谱线在色球底层附近的强度。 此外,还拍摄到了5303(FeXIV),5445和5694(CaXV)三条日冕线。     

使用小波技术自动搜寻天体谱线

使用小波技术对包括恒星、近邻星系和ＡＧＮ等不同的天体光谱进行了自动处理,用小波滤波的方法将光谱中的连续谱与谱线分离,然后使用小波域隐含马尔可夫模型（ＨＭＭ）,对已去掉连续谱的光谱进行降噪,同时得到了噪声在每个光谱中的分布;在训练ＨＭＭ的过程中,使用改进的Ｔｙｉｎｇ方法增加训练数据以保证训练的可靠性,利用噪声分布确定出谱线信号的局部阈值,在已经降噪的光谱中找到吸收线和发射线,用高斯函数拟合出谱线的形     

High Resolution Spectral Atlas of Telluric Lines

Before reaching our telescopes, stellar radiation passes through Earth's atmosphere. This interaction causes the formation of a number of telluric lines in registered stellar spectra. In this paper an atlas of atmospheric lines is reported. Observations have been carried out at the 91 cm cassegrain telescope of the M. G. Fracastoro observing station of the Catania Astrophysical Observatory equipped with a Czerney-Turner echelle spectrograph. The spectral region examined is between 6800 Å and 7800 Å. The possibility of using this atlas either to recognize telluric lines or as a wavelength calibration source is also discussed.     

Soho Cds–nis in-flight intensity calibration using a plasma diagnostic method

The internal intensity calibration of the Coronal Diagnostic Spectrometer (CDS) – Normal Incidence Spectrometer (NIS) is studied using the Arcetri diagnostic method. A large number of spectral lines observed by the CDS–NIS 1 and NIS 2 windows in a solar active region is analysed in order to determine the intensity calibration curve for both channels. The plasma diagnostic method developed in Arcetri allows the measurement of the correction factors to the preliminary CDS–NIS internal intensity calibration curves and the determination of the relative calibration between NIS 1 and NIS 2. A further correction factor of approximately three is found to be necessary for a correct intercalibration of the two wavelength windows. Also the NIS 2 second-order sensitivity is measured. The Arcetri diagnostic method proves to be a powerful tool for intensity calibration studies.     

The High-Resolution Solar Reference Spectrum between 250 and 550 nm and its Application to Measurements with the Ozone Monitoring Instrument

We have constructed a new high resolution solar reference spectrum in the spectral range between 250 and 550 nm. The primary use of this spectrum is for the calibration of the Dutch – Finnish Ozone Monitoring Instrument (OMI), but other applications are mentioned. The incentive for deriving a new high resolution solar reference spectrum is that available spectra do not meet our requirements on radiometric accuracy or spectral resolution. In this paper we explain the steps involved in constructing the new spectrum, based on available low and high resolution spectra and discuss the main sources of uncertainty. We compare the result with solar measurements obtained with the OMI as well as with other UV-VIS space-borne spectrometers with a similar spectral resolution. We obtain excellent agreement with the OMI measurements, which indicates that both the newly derived solar reference spectrum and our characterization of the OMI instrument are well understood. We also find good agreement with previously published low resolution spectra. The absolute intensity scale, wavelength calibration and representation of the strength of the Fraunhofer lines have been investigated and optimized to obtain the resulting high resolution solar reference spectrum.     

Wavelength calibration by combining arc and night sky lines for LAMOST

A novel method is presented for the wavelength calibration of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). The proposed method combines the arc lines and night sky lines, and can achieve high performance. Firstly, the initial wavelength calibration is performed by employing arc lines. Afterwards, the centroids of sky lines are calculated by the initial calibration results and adjusted by the gravity method iteratively. Finally, the ultimate wavelength calibration is obtained by fitting the centroids of arc lines and sky lines with their corresponding wavelengths. Experiments are performed on the data observed by LAMOST, and the results of the proposed method are more accurate than that of the calibration only by arc lines or sky lines. The calibration sky lines are dense in the red channel (5,700–9,000 Å) of LAMOST, but only a few ones are in the blue channel (3,700–5,900 Å). The new method achieves excellent results in the red channel as the substantial sky lines are employed, and the calibration accuracy of the blue channel is also enhanced in some degree by the scare sky lines.     

On the reliability of C iv λ1549 as an abundance indicator for high-redshift star-forming galaxies

We reconsider the use of the equivalent width of C  iv  λ1549, EW(C  iv ), as an indicator of the oxygen abundance in star-forming galaxies, as proposed by Heckman et al. for nearby starbursts. We refine the local calibration of EW(C  iv ) versus log (O/H) by using a restricted wavelength window which minimizes blending with interstellar absorption lines. When applied to the stellar component only of the complex C  iv  λ1549 features in two high-redshift galaxies with good quality spectra,  MS 1512−cB58 ( z = 2.7268)  and  Q1307−BM1163 ( z = 1.4105)  , the local calibration gives values of the oxygen abundance which are in good agreement with other metallicity determinations based on nebular emission and interstellar absorption lines. Our main conclusion is that for this method to give reliable results at high redshifts, it should only be used on data of sufficiently high spectral resolution  ( R ≳ 1000)  for stellar and interstellar C  iv components to be clearly separated. Oxygen abundances will be systematically overestimated if the local calibration is applied to spectra of high-redshift galaxies obtained with the low resolving powers  ( R ≃ 200–300)  of many current wide-field surveys. It will also be necessary to understand better the causes of the scatter in the local relation, before we can be confident of inferences from it at high z .     

Prominence atlas in the SUMER range 800–1250 Å: I. Observations, data reduction and preliminary results

The aim of this work is to build an EUV-UV spectral catalogue of a prominence. Here we focus on the preparatory work for the final result and we give an example of the results obtained. As a first step, we present the information needed for a full understanding of the results that will form the final entire catalogue. The data are composed of a full SUMER spectrum in the range 800–1250 Å of a prominence observed on 8 October 1999. A quiet-Sun area was also observed in the same spectral range in order to have a reference spectrum. Beside the standard corrections, we give details of the estimated stray light and the wavelength calibration of both datasets. We also present a short list of lines as an example of the results from the line-fitting procedure we applied to the data. For each line we give the measured position, the total intensity and the FWHM in the quiet Sun and at two different spatial positions in the prominence. With a final atlas of the prominence it will be possible to investigate several properties of the feature such as mass motion, differential emission measure, density, and elemental composition.     

Absolute brightness temperature measurements at 2.1-mm wavelength

Absolute measurements of the brightness temperatures of the Sun, new Moon, Venus, Mars, Jupiter, Saturn, and Uranus, and of the flux density of DR21 at 2.1-mm wavelength are reported. Relative measurements at 3.5-mm wavelength are also presented which resolve the absolute calibration discrepancy between The University of Texas 16-ft radio telescope and the Aerospace Corporation 15-ft antenna. The use of the bright planets and DR21 as absolute calibration sources at millimeter wavelengths is discussed in the light of recent observations.     

Photometric and Thermal Cross-calibration of Solar EUV Instruments

We present an assessment of the accuracy of the calibration measurements and atomic physics models that go into calculating the SDO/AIA response as a function of wavelength and temperature. The wavelength response is tested by convolving SDO/EVE and Hinode/EIS spectral data with the AIA effective area functions and by comparing the predictions with AIA observations. For most channels, the AIA intensities summed over the disk agree with the corresponding measurements derived from the current version (V2) of the EVE data to within the estimated 25 % calibration error. This agreement indicates that the AIA effective areas are generally stable in time. The AIA 304 Å channel, however, does show degradation by a factor of almost 3 from May 2010 through September 2011, when the throughput apparently reached a minimum. We also found some inconsistencies in the 335 Å passband, possibly due to higher-order contamination of the EVE data. The intensities in the AIA 193 Å channel agree to within the uncertainties with the corresponding measurements from EIS full CCD observations. Analysis of high-resolution X-ray spectra of the solar-like corona of Procyon and of EVE spectra allowed us to investigate the accuracy and completeness of the CHIANTI database in the AIA shorter wavelength passbands. We found that in the 94 Å channel, the spectral model significantly underestimates the plasma emission owing to a multitude of missing lines. We derived an empirical correction for the AIA temperature responses by performing differential emission measure (DEM) inversion on a broad set of EVE spectra and adjusting the AIA response functions so that the count rates predicted by the full-disk DEMs match the observations.     

Near-IR spectral evolution of dusty starburst galaxies

We propose a multicomponent analysis of starburst galaxies, based on a model that takes into account the young and evolved stellar components and the gas emission, with their respective extinction, in the frame of a coherent dust distribution pattern. Near-IR signatures are preferentially investigated, in order to penetrate as deep as possible into the dusty starburst cores. We computed the 1.4-2.5 μm spectra of synthetic stellar populations evolving through strong, short timescale bursts of star formation (continuum and lines, R ? 500). The evolution model is specifically sensitive to cool stellar populations (AGB and red supergiant stars). It takes advantage of the stellar library of Lançon & Rocca-Volmerange (1992) [A&ASS, 96, 593], observed with the same instrument (FTS/CFHT) as the analysed galaxy sample, so that the instrumental effects are minimised. The main near-IR observable constraints are the molecular signatures of CO and H₂O and the slope of the continuum, observed over a range exceptionally broad for spectroscopic data. The H - K colour determined from the spectra measures the intrinsic stellar energy distribution but also differential extinction, which is further constrained by optical emission line ratios. Other observational constraints are the near-IR emission lines (Brγ, He I 2.06 μm, [Fe II] 1.64 μm, H₂ 2.12 μm) and the far-IR luminosity. The coherence of the results relies on the interpretation in terms of stellar populations from which all observable properties are derived, so that the link between the various wavelength ranges is secured. The luminosity L_K is used for the absolute calibration.We apply this approach to the typical spectrum of the core of NGC 1614. Consistent solutions for the starburst characteristics (star-formation rate, IMF, burst age, morphology) are found and the role of each observational constraint in deriving satisfactory models is extensively discussed. The acceptable contamination of the K band light by the underlying population amounts ≥ 15% even through a 5 arcsec aperture. The model leads to a limit on the direct absorption of Lyman continuum photons by dust situated inside the ionised areas, which in turn, with standard gas-to-dust ratios, translates into small characteristic sizes for the individual coexisting H II regions of the massive starburst area (clusters containing ∼ 10² ionising stars). We show that room is left for IMFs extending to 120 M_⊙, rather than truncated at ∼ 60 M_⊙ as most conservative studies conclude. High internal velocity dispersions (≥ 20 km s⁻¹) are then needed for the H II regions. An original feature of this work is to base the analysis of near-infrared spectral galaxy observations on a large wavelength range, using models constructed with spectral stellar data observed with the same instrument. However a broader use of this spectral evolution model on other spectral or photometric data samples is possible if the spectral resolution of the model is adapted to observations or if colours are derived from the energy distributions.Catherine J. Cesarsky