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Flame : A flexible data reduction pipeline for near-infrared and optical spectroscopy
摘要： We present flame, a pipeline for reducing spectroscopic observations obtained with multislit near-infrared and optical instruments. Because of its ?exible design, flame can be easily applied to data obtained with a wide variety of spectrographs. The ?exibility is due to a modular architecture, which allows changes and customizations to the pipeline, and relegates the instrument-speci?c parts to a single module. At the core of the data reduction is the transformation from observed pixel coordinates (x, y) to recti?ed coordinates (λ, γ ). This transformation consists in the polynomial functions λ(x, y) and γ (x, y) that are derived from arc or sky emission lines and slit edge tracing, respectively. The use of 2D transformations allows one to wavelength calibrate and rectify the data using just one interpolation step. Furthermore, the γ (x, y) transformation includes also the spatial misalignment between frames, which can be measured from a reference star observed simultaneously with the science targets. The misalignment can then be fully corrected during the recti?cation, without having to further resample the data. Sky subtraction can be performed via nodding and/or modelling of the sky spectrum; the combination of the two methods typically yields the best results. We illustrate the pipeline by showing examples of data reduction for a near-infrared instrument (LUCI at the Large Binocular Telescope) and an optical one (LRIS at the Keck telescope).
关键词： techniques: spectroscopic,methods: observational,methods: data analysis,instrumentation: spectrographs
更新于2025-09-09 09:28:46
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Spectroscopy of BL Lacertae objects of extraordinary luminosity
摘要： Aims. We aim to determine the redshift (or stringent lower limits) of a number of bright BL Lacs objects. Methods. We secured optical and near-infrared medium-resolution spectra of four bright BL Lac objects of unknown redshift using the spectrograph X-Shooter at the ESO-VLT. Results. In spite of the high quality of the spectra and the extended spectral range of the observations, we have not detected intrisic spectral features for these sources. However, we are able to provide strigent lower limits to their redshift. In particular, for the two TeV sources PG 1553+113 and H 1722+119, we infer z > 0.30 and z > 0.35 respectively. We also detect an intervening Ca II absorption doublet in the spectrum of MH 2136-428 that is ascribed to the halo of a nearby giant elliptical galaxy at a projected distance of ～100 kpc. Conclusions. Under the hypothesis that all BL Lacs are hosted by a luminous bulge-dominated galaxies, the spectroscopic observations of bright BL Lacs presently indicate that these objects are likely sources with extremely beamed nuclear emission. We present simulations to show under which circumstances it is possible to probe this hypothesis from the detection of very weak absorptions using the next generation of extremely large optical telescopes.
关键词： BL Lacertae objects: general,instrumentation: spectrographs,cosmology: observations
更新于2025-09-09 09:28:46
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Image restoration of solar spectra
摘要： Context. When recording spectra from the ground, atmospheric turbulence causes degradation of the spatial resolution. Aims. We present a data reduction method that restores the spatial resolution of the spectra to their undegraded state. Methods. By assuming that the point spread function (PSF) estimated from a strictly synchronized, broadband slit-jaw camera is the same as the PSF that spatially degraded the spectra, we can quantify what linear combination of undegraded spectra is present in each degraded data point. Results. The set of equations obtained in this way is found to be generally well-conditioned and sufficiently diagonal to be solved using an iterative linear solver. The resulting solution has regained a spatial resolution comparable to that of the restored slit-jaw images. Conclusions. We have developed a new image restoration method for the restoration of ground-based spectral data over a large field of view. The method builds on the PSF information recovered by the MOMFBD code and typically reaches a spatial resolution comparable to that of the broadband slit-jaw images used to recover the PSF.
关键词： techniques: imaging spectroscopy,instrumentation: high angular resolution,techniques: spectroscopic,instrumentation: spectrographs,methods: numerical,techniques: image processing
更新于2025-09-04 15:30:14
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Comprehensive Measurements of the Volume-phase Holographic Gratings for the Dark Energy Spectroscopic Instrument
摘要： The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment that will be employed on the Mayall 4 m Telescope to study the expansion history of the universe. In the era of massively multiplexed fiber-fed spectrographs, DESI will push the boundaries of fiber spectroscopy with a design capable of taking 5000 simultaneous spectra over 360 to 980 nm. The instrument utilizes a suite of three-channel spectrographs, where volume-phase holographic (VPH) gratings provide dispersions. Thirty-six VPH gratings were produced and their performances were evaluated at the Lawrence Berkeley National Laboratory. We present the design and the evaluation tests for the production run of the VPH gratings, verifying the incidence angle, area-weighted efficiency, and wavefront errors (WFEs). We also present the specialized test set-up developed on-site to assess the grating performances. Measurements of the VPH gratings show high consistency in area-weighted efficiency to within an rms of 2% for the red and near-infrared and 6.2% for the blue gratings. Measured WFEs also showed high consistency per bandpass. Comprehensive evaluations show that the VPH gratings meet DESI performance requirements and have been approved for integration.
关键词： dark energy,techniques: spectroscopic,instrumentation: spectrographs
更新于2025-09-04 15:30:14
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Characterizing HR?3549?B using SPHERE
摘要： Aims. In this work, we characterize the low-mass companion of the A0 field star HR 3549. Methods. We observed HR 3549B in imaging mode with the near-infrared branch (IFS and IRDIS) of SPHERE at the VLT, with IFS in Y J mode and IRDIS in the H band. We also acquired a medium-resolution spectrum with the IRDIS long-slit spectroscopy mode. The data were reduced using the dedicated SPHERE GTO pipeline, which is custom-designed for this instrument. We employed algorithms such as PCA and TLOCI to reduce the speckle noise. Results. The companion was clearly visible with both IRDIS and IFS. We obtained photometry in four different bands and also the astrometric position for the companion. Based on our astrometry, we confirm that it is a bound object and set constraints on its orbit. Although several uncertainties still remain, we estimate an age of ～100–150 Myr for this system, yielding a most probable mass for the companion of 40–50 MJup and Teff ～ 2300?2400 K. Compared with template spectra, this points to a spectral type between M9 and L0 for the companion, commensurate with its position on the color–magnitude diagram.
关键词： techniques: imaging spectroscopy,planetary systems,methods: data analysis,instrumentation: spectrographs
更新于2025-09-04 15:30:14
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A New Method for Calibration of Gain Variation in a Detector System
摘要： Transit spectroscopy of habitable planets orbiting late-type stars requires high relative spectrophotometric accuracy between wavelengths during transit/eclipse observation. The spectrophotometric signal is affected not only by image movement and deformation due to wavefront error but also by electrical variation in the detector system. These time-variation components, coupled to the transit signal, distort the measurements of atmospheric composition in transit spectroscopy. Here we propose a new concept for improvement of spectrophotometric accuracy through the calibration of the time-variation components in the detector system by developing densified pupil spectroscopy that provides multiple spectra of the star–planet system. Owing to a group of pixels exposed by the object light (i.e., science pixels), pixel-to-pixel variations can be smoothed out through an averaging operation; thus, only common time-variation components over the science pixels remain. In addition, considering that the detector plane is optically conjugated to the pupil plane, a pupil mask can completely block astronomical light coming into residual pixels. The common time-variation components are reconstructed with the residual pixels and reduced into a random term. Applying the densified pupil spectrograph with a mid-infrared detector system to a large space cryogenic telescope such as the Origins Space Telescope, we show that the system nearly achieves photon noise–limited performance and detects absorption features through transmission spectroscopy and secondary eclipse of terrestrial planets orbiting M-type stars at 10 pc with 60 transit observations. Thus, the proposed method contributes to the measurement of planetary habitability and biosignatures of the nearby transiting habitable candidates.
关键词： techniques: spectroscopic,planets and satellites: atmospheres,methods: data analysis,planets and satellites: terrestrial planets,instrumentation: spectrographs
更新于2025-09-04 15:30:14
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Ultraviolet Solar Spectral Irradiance Variation on Solar Cycle Timescales
摘要： Ultraviolet (UV) Solar spectral Irradiance (SSI) has been measured from orbit on a regular basis since the beginning of the space age. These observations span four Solar Cycles, and they are crucial for our understanding of the Sun-Earth connection and space weather. SSI at these wavelengths are the main drivers for the upper atmosphere including the production and destruction of ozone in the stratosphere. The instruments that measure UV SSI not only require good pre?ight calibration, but also need a robust method to maintain that calibration on orbit. We will give an overview of the catalog of current and former UV SSI measurements along with the calibration philosophy of each instrument and an estimation of the uncertainties in the published irradiances.
关键词： Sun: activity,Sun: UV radiation,instrumentation: spectrographs
更新于2025-09-04 15:30:14