Spectrograph slit is conventionally used to enhance the spectral resolution and manage how much light can be allowed to enter spectrograph. A narrower slit provides a higher resolution but sacrifices efficiency of spectrograph and results in a low signal to noise ratio (S/N) spectra product. We take GuoShouJing telescope as an example and carry out a series of experiments to study how its 2/3 slit mode affects the precision of stellar radial velocity measurement and atmosphere parameters estimate. By transforming the resolution and adding a Gaussian White Noise to the extremely high quality spectra from the Sloan Digital Sky Survey, we generate synthetic stellar spectra of various brightness with different S/Ns. Comparing the measurements on these noise added spectra with the original high quality ones, we summarize the influences of the 2/3 slit mode on the measurement accuracy of stellar radial velocity and atmospheric parameters.
We derive an analytic expression for the instrument profile of a slit spectrograph, also known as the line spread function. While this problem is not new, our treatment relies on the operatorial approach to the description of diffractive optical systems, which provides a general framework for the analysis of the performance of slit spectrographs under different illumination conditions. Based on our results, we propose an approximation to the spectral resolution of slit spectrographs, taking into account diffraction effects and sampling by the detector, which improves upon the often adopted app…
We have studied the Residual Blaze Functions (RBF) resulting from division of individual echelle orders by extracted flat-field in spectra obtained by slit-fed OES spectrograph of 2m telescope of Ondřejov observatory, Czech Republic. We have eliminated the dependence on target and observation conditions by semiautomatic fitting of global response function, thus getting the instrument-only dependent part, which may be easily incorporated into data reduction pipeline. The improvement of reliability of estimation of continuum on spectra of targets with wide and shallow lines is noticeable and the…
We present the wide field slitless spectroscopy mode of the NIRISS instrument on the James Webb Space Telescope. This mode employs two orthogonal low-resolution (resolving power $\approx 150$) grisms in combination with a set of six blocking filters in the wavelength range 0.8 to $2.3\,μ$m to provide a spectrum of almost every source across the field-of-view. When combined with the low background, high sensitivity and high spatial resolution afforded by the telescope, this mode will enable unprecedented studies of the structure and evolution of distant galaxies. We describe the performance of …
A Slit Mask Integral Field Unit for the Robert Stobie Spectrograph on the Southern African Large Telescope: I. Instrument Development
Space Science and Engineering Initiative, College of Engineering, University of Hawai’i at Manoa（夏威夷大学马诺阿分校工程学院空间科学与工程倡议）；Centre for Space Research, North-West University（西北大学太空研究中心）；South African Astronomical Observatory（南非天文台）；University of Wisconsin（威斯康星大学）
We present a method to determine the static aberrations in a nearly diffraction-limited spectrograph introduced, for example, by alignment or manufacturing errors. We consider an instrument with two stages separated by a slit or image slicer located in the intermediate focal plane. In such a spectrograph, it is not trivial to distinguish aberrations in the first stage, before the slit, from those in the second, after the slit. However, our method achieves this. Measuring these aberrations separately opens the possibility of reducing them, by realignment or other means, and thereby improving th…
The MMT and Magellan infrared spectrograph (MMIRS) is a cryogenic multiple slit spectrograph operating in the wavelength range 0.9-2.4 micron. MMIRS' refractive optics offer a 6.9 by 6.9 arcmin field of view for imaging with a spatial resolution of 0.2 arcsec per pixel on a HAWAII-2 array. For spectroscopy, MMIRS can be used with long slits up to 6.9 arcmin long, or with custom slit masks having slitlets distributed over a 4 by 6.9 arcmin area. A range of dispersers offer spectral resolutions of 800 to 3000. MMIRS is designed to be used at the f/5 foci of the MMT or Magellan Clay 6.5m telescop…
CYCLOPS2 is an upgrade for the UCLES high resolution spectrograph on the Anglo-Australian Telescope, scheduled for commissioning in semester 2012A. By replacing the 5 mirror Coudé train with a Cassegrain mounted fibre-based image slicer CYCLOPS2 simultaneously provides improved throughput, reduced aperture losses and increased spectral resolution. Sixteen optical fibres collect light from a 5.0 arcsecond^2 area of sky and reformat it into the equivalent of a 0.6 arcsecond wide slit, delivering a spectral resolution of R = 70000 and up to twice as much flux as the standard 1 arcsecond slit of t…
The Fiber Optical Cable and Connector System, FOCCoS, subsystem of the Prime Focus Spectrograph, PFS, for Subaru telescope, is responsible to feed four spectrographs with a set of optical fibers cables. The light injection for each spectrograph is assured by a convex curved slit with a linear array of 616 optical fibers. In this paper we present a design of a slit that ensures the right direction of the fibers by using masks of micro holes. This kind of mask is made by a technique called electroforming, which is able to produce a nickel plate with holes in a linear sequence. The precision erro…
We present a conceptual design for the atmospheric dispersion corrector (ADC) for TMT's Infrared Imaging Spectrograph (IRIS). The severe requirements of this ADC are reviewed, as are limitations to observing caused by uncorrectable atmospheric effects. The requirement of residual dispersion less than 1 milliarcsecond can be met with certain glass combinations. The design decisions are discussed and the performance of the design ADC is described. Alternative options and their performance tradeoffs are also presented.
SpectraPy is an Astropy affiliated package for spectroscopic data reduction. It collects algorithms and methods for data reduction of astronomical spectra obtained by through-slits spectrographs. It has been created to fill the gap in Astropy between the already existing data handling libraries and those for spectra analysis. SpectraPy combines Astropy facilities with SAOImageDS9 features, providing a set of tools for spectra calibration and 2D extraction. It starts from raw frames, and using configuration files which describe the optical setup of the instrument, it automatically locates and e…
We report in this paper the test of a plane holographic optical element to be used as an aberration-corrected grating for a slitless spectrograph, inserted in a convergent telescope beam. Our long term objective is the optimisation of a specific hologram to switch the auxiliary telescope imager of the Vera Rubin Observatory into an accurate slitless spectrograph, dedicated to the atmospheric transmission measurement. We present and discuss here the promising results of tests performed with prototype holograms at the CTIO $0.9\,$m telescope during a run of 17 nights in May-June 2017. After thei…
Stray light caused by scattering on optical surfaces and in the Earth's atmosphere degrades the spatial resolution of observations. We study the contribution of stray light to the two channels of POLIS. We test the performance of different methods of stray-light correction and spatial deconvolution to improve the spatial resolution post-facto. We model the stray light as having two components: a spectrally dispersed component and a component of parasitic light caused by scattering inside the spectrograph. We use several measurements to estimate the two contributions: observations with a (partl…
We describe the design, construction and commissioning of LOTUS; a simple, low-cost long-slit spectrograph for the Liverpool Telescope. The design is optimized for near-UV and visible wavelengths and uses all transmitting optics. It exploits the instrument focal plane field curvature to partially correct axial chromatic aberration. A stepped slit provides narrow (2.5x95 arcsec) and wide (5x25 arcsec) options that are optimized for spectral resolution and flux calibration respectively. On sky testing shows a wavelength range of 3200-6300 Angstroms with a peak system throughput (including detect…
SARG is the high resolution spectrograph of TNG. It has been in operation since late spring 2000. SARG is a cross dispersed echelle spectrograph; it offers both single object and long slit (up to 26 arcsec) observing modes covering a spectral range from λ=0.37 up to 1 μm, with resolution ranging from R=29,000 up to R=164,000. Cross dispersion is provided by means of a selection of four grisms; interference filters may be used for the long slit mode (up to 26 arcsec). A dioptric camera images the cross dispersed spectra onto a mosaic of two 2048x4096 EEV CCDs (pixel size: 13.5 μm) allowing comp…
The Transient Double-beam Spectrograph (TDS) is designed for optical low-resolution observations of non-stationary and extragalactic sources with the 2.5-m telescope of Caucasus Mountain Observatory of the Sternberg Astronomical Institute. It operates simultaneously in a short-wavelength (360--577 nm, reciprocal dispersion 1.21 A/pixel, resolving power R=1300 with a 1 arcsec slit) and long-wavelength (567--746 nm, 0.87 A/pixel, R=2500) channels. The light is split by a dichroic mirror with a 50% transmission at 574 nm. In the "blue" channel, the automatic replacement of the grating by a grism …
The Multi-slit Solar Explorer (MUSE) is a proposed NASA MIDEX mission, currently in Phase A, composed of a multi-slit EUV spectrograph (in three narrow spectral bands centered around 171A, 284A, and 108A) and an EUV context imager (in two narrow passbands around 195A and 304A). MUSE will provide unprecedented spectral and imaging diagnostics of the solar corona at high spatial (<0.5 arcsec), and temporal resolution (down to ~0.5s) thanks to its innovative multi-slit design. By obtaining spectra in 4 bright EUV lines (Fe IX 171A , Fe XV 284A, Fe XIX-Fe XXI 108A) covering a wide range of transit…
We have designed a fiber scrambler as a prototype for the Keck HIRES spectrograph, using double scrambling to stabilize illumination of the spectrometer and a pupil slicer to increase spectral resolution to R = 70,000 with minimal slit losses. We find that the spectral line spread function (SLSF) for the double scrambler observations is 18 times more stable than the SLSF for comparable slit observations and 9 times more stable than the SLSF for a single fiber scrambler that we tested in 2010. For the double scrambler test data, we further reduced the radial velocity scatter from an average of …
Differential atmospheric dispersion is a wavelength-dependent effect introduced by the atmosphere. It is one of the instrumental errors that can affect the position of the target as perceived on the sky and its flux distribution. This effect will affect the results of astronomical observations if not corrected by an atmospheric dispersion corrector (ADC). In high-resolution spectrographs, in order to reach a radial velocity (RV) precision of 10 cm/s, an ADC is expected to return residuals at only a few tens of milli-arcseconds (mas). In fact, current state-of-the-art spectrographs conservative…
Radial velocity and atmospheric parameter calculations for the GaiaNIR spectrograph
ELTE Eötvös Loránd University（罗兰大学）；Gothard Astrophysical Observatory（戈特哈德天体物理观测站）；HUN-REN CSFK, Konkoly Observatory（匈牙利研究网络科学院孔科利天文台）；Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台，巴黎文理研究大学，索邦大学，巴黎西岱大学，塞吉-蓬图瓦兹大学，法国国家科学研究中心）；Leiden Observatory, Leiden University（莱顿大学莱登天文台）；Mullard Space Science Laboratory, University College London（伦敦大学学院穆拉德空间科学实验室）；Royal Observatory of Belgium（比利时皇家天文台）
We present the current results from the development of a wide integral field infrared spectrograph (WIFIS). WIFIS offers an unprecedented combination of etendue and spectral resolving power for seeing-limited, integral field observations in the 0.9-1.8 um range and is most sensitive in the 0.9-1.35 um range. Its optical design consists of front-end re-imaging optics, an all-reflective image slicer-type, integral field unit (IFU) called FISICA, and a long-slit grating spectrograph back-end that is coupled with a HAWAII 2RG focal plane array. The full wavelength range is achieved by selecting be…
One source of error in high-precision radial velocity measurements of exoplanet host stars is chromatic change in Earth's atmospheric transmission during observations. Mitigation of this error requires that the photon-weighted barycentric correction be applied as a function of wavelength across the stellar spectrum. We have designed a system for chromatic photon-weighted barycentric corrections with the EXtreme PREcision Spectrograph (EXPRES) and present results from the first year of operations, based on radial velocity measurements of more than $10^3$ high-resolution stellar spectra. For obs…
Update on the Magellan InfraRed Multi-Object Spectrograph (MIRMOS)
Carnegie Science, The Observatories（卡内基科学学会，天文台）；Turion Space（图里奥太空）；LCS Optics LLC（LCS光学有限责任公司）；The Ohio State University（俄亥俄州立大学）；CSEM SA (Centre Suisse d’Electronique et de Microtechnique)（瑞士电子与微技术中心）；Johns Hopkins University（约翰斯·霍普金斯大学）；Capella Space（卡佩拉太空）；Penn State University（宾夕法尼亚州立大学）；Giant Magellan Telescope Organization（大型麦哲伦望远镜组织）
(Abridged) Atmospheric dispersion and field differential refraction impose severe constraints on widefield MOS observations. Flux reduction and spectral distortions must be minimised by a careful planning of the observations -- which is especially true for instruments that use slits instead of fibres. This is the case of VIMOS at the VLT, where MOS observations have been restricted, since the start of operations, to a narrow two-hour range from the meridian to minimise slit losses. We revisit in detail the impact of atmospheric effects on the quality of VIMOS-MOS spectra. We model slit losses …
HARMONI at ELT: line spread functions in a diffraction limited spectrometer
UKATC, Royal Observatory Edinburgh（英国天文技术控制中心，爱丁堡皇家天文台）；Oxford University（牛津大学）；Aix-Marseille Université, CNRS, CNES, LAM（艾克斯-马赛大学，法国国家科学研究中心，法国国家空间研究中心，拉格朗日实验室）；Université Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon (CRAL)（里昂第一大学，法国国家科学研究中心，里昂天体物理研究中心）；Instituto de Astrofísica de Canarias (IAC)（加那利天体物理学研究所）；Department of Physics, Durham University（杜伦大学物理系）
OCTOCAM is a multi-channel imager and spectrograph that has been proposed for the 10.4m GTC telescope. It will use dichroics to split the incoming light to produce simultaneous observations in 8 different bands, ranging from the ultraviolet to the near-infrared. The imaging mode will have a field of view of 2' x 2' in u, g, r, i, z, J, H and Ks bands, whereas the long-slit spectroscopic mode will cover the complete range from 4,000 to 23,000 Å with a resolution of 700 - 1,700 (depending on the arm and slit width). An additional mode, using an image slicer, will deliver a spectral resolution of…
The spectral resolution of a dispersive astronomical spectrograph is limited by the trade-off between throughput and the width of the entrance slit. Photonic guided-wave transitions have been proposed as a route to bypass this trade-off, by enabling the efficient reformatting of incoherent seeing-limited light collected by the telescope into a linear array of single modes: a pseudo-slit which is highly multimode in one axis but diffraction-limited in the dispersion axis of the spectrograph. It is anticipated that the size of a single-object spectrograph fed with light in this manner would be e…
The RISTRETTO project is aiming to build an instrument that will detect the reflected light from close-by exoplanet. It is a two stage instrument: An extreme AO system in the visible, followed by a seven spaxel single mode High resolution Spectrograph. In this paper we present the design of this spectrograph: a classical echelle spectrograph fed with single mode fibers. Standard single mode fibers have been chosen and are forming a long tilted slit in order to have the right order spacing on the detector. The instrument will be under vacuum and thermally controlled in order to make it stable.
We describe the design, construction and measured performance of the Kitt Peak Ohio State Multi-Object Spectrograph (KOSMOS) for the 4-m Mayall telescope and the Cerro Tololo Ohio State Multi-Object Spectrograph (COSMOS) for the 4-m Blanco telescope. These nearly identical imaging spectrographs are modified versions of the OSMOS instrument; they provide a pair of new, high-efficiency instruments to the NOAO user community. KOSMOS and COSMOS may be used for imaging, long-slit, and multi-slit spectroscopy over a 100 square arcminute field of view with a pixel scale of 0.29 arcseconds. Each conta…
Fibre-fed spectrographs now have throughputs equivalent to slit spectrographs. However, the sky subtraction accuracy that can be reached has often been pinpointed as one of the major issues associated with the use of fibres. Using technical time observations with FLAMES-GIRAFFE, two observing techniques, namely dual staring and cross beam-switching, were tested and the resulting sky subtraction accuracy reached in both cases was quantified. Results indicate that an accuracy of 0.6% on sky subtraction can be reached, provided that the cross beam-switching mode is used. This is very encouraging …
We present a new scheme of a moderate-resolution spectrograph based on a cascade of serial holographic gratings each of which produces an individual spectrum with a resolution of about 6000 and a bandwidth of 80 nm. The gratings ensure centering of each part of the spectrum they produce so as to provide uniform coverage of the broadest possible wavelength interval. In this study we manage to simultaneously cover the 430-680 nm interval without gaps using three gratings. Efficiency of the spectrograph optical system itself from the entrance slit to the CCD detector is typically of about 60 % wi…
We present the calibration of the spectroscopic Lick/IDS standard line-index system for measurements obtained with the Gemini Multi-Object Spectrographs known as GMOS-North and GMOS- South. We provide linear correction functions for each of the 25 standard Lick line indices for the B600 grism and two instrumental setups, one with 0.5 arcsecond slit width and 1x1 CCD pixel binning (corresponding to ~2.5 Angstroem spectral resolution) and the other with 0.75 arcsecond slit width and 2x2 binning (~4 Angstroem). We find small and well-defined correction terms for the set of Balmer indices Hbeta, H…
We present EMIR, a powerful near-infrared (NIR) camera and multi-object spectrograph (MOS) installed at the Nasmyth focus of the 10.4 m GTC. EMIR was commissioned in mid-2016 and is offered as a common-user instrument. It provides spectral coverage of 0.9 to 2.5 $μm$ over a field of view (FOV) of 6.67x6.67 squared arcmin in imaging mode, and 6.67x4 squared arcmin in spectroscopy. EMIR delivers up to 53 spectra of different objects thanks to a robotic configurable cold slit mask system that is located inside the cryogenic chamber, allowing rapid reconfiguration of the observing mask. The imagin…
Two fibre integral field units (IFU) are being built in the SAAO fibre-lab for the Robert Stobie Spectrograph's visible arm and the future red arm. Each IFU sits in its own slit-mask cassette and is referred to as a slit-mask IFU (SMI). They will be available some time in 2022. The smaller, 200 micron fibre IFU has 309 X 0.9 arcsec diameter spatial elements covering an elongated hexagonal footprint of 18 X 23 arcsec. The larger, 400 micron fibre IFU has 178 X 1.8 arcsec diameter spatial elements covering an on-sky area of 21 X 44 arcsec. In both cases there are two groups of 13 fibres offset b…
Image slicing is a powerful technique in astronomy. It allows the instrument designer to reduce the slit width of the spectrograph, increasing spectral resolving power whilst retaining throughput. Conventionally this is done using bulk optics, such as mirrors and prisms, however more recently astrophotonic components known as photonic lanterns (PLs) and photonic reformatters have also been used. These devices reformat the multi-mode (MM) input light from a telescope into single-mode (SM) outputs, which can then be re-arranged to suit the spectrograph. The photonic dicer (PD) is one such device…
We present SIPGI, a spectroscopic pipeline to reduce optical/near-infrared data from slit-based spectrographs. SIPGI is a complete spectroscopic data reduction environment which retains the high level of flexibility and accuracy typical of the standard "by-hand" reduction methods but is characterized by a significantly higher level of efficiency. This is obtained by exploiting three main concepts: $i)$ the instrument model: at the core of the data reduction is an analytic description of the main calibration relations (e.g. spectra location and wavelength calibration) that can be easily checked…
Measuring the stellar position angle provides valuable information on binary stellar formation or stellar spin axis evolution. We aim to develop a method for determining the absolute stellar position angle using spectro-astrometric analysis of high resolution long-slit spectra. The method has been designed in particular for slowly rotating stars. We investigate its applicability to existing dispersive long-slit spectrographs, identified here by their plate scale, and the size of the resulting stellar sample. The stellar rotation induces a tilt in the stellar lines whose angle depends on the st…
In this paper we describe the echelle spectrograph of the 2 meter telescope of the Rozhen National Astronomical Observatory. The spectrograph is a cross-dispersed, bench-mounted, fiber-fed instrument giving a resolution from $\sim$30000 to $\sim$45000. The spectral range obtained in one single image is from 3900 to 9000 Å. We describe the parameters of the fiber injection and the guiding unit, of the spectrograph itself, and of the detector. The identified orders and the resulting resolving power are presented. The opportunity to increase of the resolution by using a narrower slit is discussed…
In the era of vast spectroscopic surveys focusing on Galactic stellar populations, astronomers want to exploit the large quantity and good quality of data to derive their atmospheric parameters without losing precision from automatic procedures. In this work, we developed a new spectral package, FASMA, to estimate the stellar atmospheric parameters (namely effective temperature, surface gravity, and metallicity) in a fast and robust way. This method is suitable for spectra of FGK-type stars in medium and high resolution. The spectroscopic analysis is based on the spectral synthesis technique u…
To achieve its ambitious scientific goals, the Near-Infrared Spectrograph, NIRSpec, on board the Webb Space Telescope, needs to meet very demanding throughput requirements, here quantified in terms of photon-conversion efficiency (PCE). During the calibration activities performed for the instrument commissioning, we have obtained the first in-flight measurements of its PCE and also updated the modeling of the light losses occurring in the NIRSpec slit devices. The measured PCE of NIRSpec fixed-slit and multi-object spectroscopy modes overall meets or exceeds the pre-launch model predictions. T…
The spectral resolution of a dispersive spectrograph is dependent on the width of the entrance slit. This means that astronomical spectrographs trade-off throughput with spectral resolving power. Recently, optical guided-wave transitions known as photonic lanterns have been proposed to circumvent this trade-off, by enabling the efficient reformatting of multimode light into a pseudo-slit which is highly multimode in one axis, but diffraction-limited in the other. Here, we demonstrate the successful reformatting of a telescope point spread function into such a slit using a three-dimensional int…
SIPGI is a spectroscopic pipeline for the data reduction of optical/near-infrared data acquired by slit-based spectrographs. SIPGI is a complete spectroscopic data reduction environment retaining the high level of flexibility and accuracy typical of the standard "by-hand" reduction methods but with a significantly higher level of efficiency. This is obtained exploiting three main concepts: 1) a built-in data organiser to classify the data, together with a graphical interface; 2) the instrument model (analytic description of the main calibration relations); 3) the design and flexibility of the …
