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Laboratory validation of the dual-zone phase mask coronagraph in broadband light at the high-contrast imaging THD testbed
摘要： Context. Speci?c high-contrast imaging instruments are mandatory to characterize circumstellar disks and exoplanets around nearby stars. Coronagraphs are commonly used in these facilities to reject the di?racted light of an observed star and enable direct imaging and spectroscopy of its circumstellar environment. One important property of the coronagraph is to be able to work in broadband light. Aims. Among several proposed coronagraphs, the dual-zone phase mask coronagraph is a promising solution for starlight rejection in broadband light. In this paper, we perform the ?rst validation of this concept in laboratory. Methods. First, we consider the principle of the dual-zone phase mask coronagraph. Then, we describe the high-contrast imaging THD testbed, the manufacturing of the components, and the quality control procedures. Finally, we study the sensitivity of our coronagraph to low-order aberrations (inner working angle and defocus) and estimate its contrast performance. Our experimental broadband light results are compared with numerical simulations to check agreement with the performance predictions. Results. With the manufactured prototype and using a dark hole technique based on the self-coherent camera, we obtain contrast levels down to 2 × 10?8 between 5 and 17 λ0/D in monochromatic light (640 nm). We also reach contrast levels of 4 × 10?8 between 7 and 17 λ0/D in broadband (λ0 = 675 nm, ?λ = 250 and ?λ/λ0 = 40%), which demonstrates the excellent chromatic performance of the dual-zone phase mask coronagraph. Conclusions. The performance reached by the dual-zone phase mask coronagraph is promising for future high-contrast imaging instruments that aim to detect and spectrally characterize old or light gaseous planets.
关键词： techniques: high angular resolution,instrumentation: high angular resolution,planets and satellites: detection
更新于2025-09-04 15:30:14
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Encyclopedia of Spectroscopy and Spectrometry || Terahertz Imaging and Spectroscopy Methods and Instrumentation
摘要： Terahertz Imaging and Spectroscopy Methods and Instrumentation
关键词： Instrumentation,Terahertz,Spectroscopy,Imaging
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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Methane on Mars: New insights into the sensitivity of CH4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration
摘要： The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1σ sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5 × 5° bins. Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate.
关键词： NOMAD,Instrumentation,Infrared spectroscopy,Mars atmosphere,Methane
更新于2025-09-04 15:30:14
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Digital compensation of the sideband-rejection ratio in a fully analog 2SB sub-millimeter receiver
摘要： Context. In observational radio astronomy, sideband-separating receivers are preferred, particularly under high atmospheric noise, which is usually the case in the sub-millimeter range. However, obtaining a good rejection ratio between the two sidebands is dif?cult since, unavoidably, imbalances in the different analog components appear. Aims. We describe a method to correct these imbalances without making any change in the analog part of the sideband-separating receiver, speci?cally, keeping the intermediate-frequency (IF) hybrid in place. This opens the possibility of implementing the method in any existing receiver. Methods. (i) We have built hardware to demonstrate the validity of the method and tested it on a fully analog receiver operating between 600 and 720 GHz. (ii) We have tested the stability of calibration and performance versus time and after full resets of the receiver. (iii) We have performed an error analysis to compare the digital compensation in two con?gurations of analog receivers, with and without intermediate-frequency hybrid. Results. (i) An average compensated sideband-rejection ratio of 46 dB is obtained. (ii) Degradation of the compensated sideband rejection ratio on time and after several resets of the receiver is minimal. (iii) A receiver with an IF hybrid is more robust to systematic errors. Moreover, we have shown that the intrinsic random errors in calibration have the same impact for con?guration without IF hybrid and for a con?guration with IF hybrid with analog rejection ratio better than 10 dB. Conclusions. We demonstrate that compensated rejection ratios above 40 dB are obtained even in the presence of high analog rejec- tion. Further, we demonstrate that the method is robust allowing its use under normal operational conditions at any telescope. We also demonstrate that a full analog receiver is more robust against systematic errors. Finally, the error bars associated with the compensated rejection ratio are almost independent of whether IF hybrid is present or not.
关键词： methods: miscellaneous,instrumentation: miscellaneous,techniques: miscellaneous
更新于2025-09-04 15:30:14
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NIR spectroscopy research in the Ozaki group for the last 30 years
摘要： The purpose of this article is to introduce NIR spectroscopy research in the Ozaki group for the last 30 years. It might be interesting for some readers to know how and why our group pursued NIR spectroscopy for the last three decades. Perhaps, the readers can learn research purpose, research direction, strategy and tactics of NIR studies of our lab. For the last 30 years or so NIR spectroscopy has made fantastic progress in theory, instrumentation, spectral analysis, and application. Thus, the history of the Ozaki group strongly reflects the history of NIR spectroscopy. We have run after the rapid progress of NIR spectroscopy, and at the same time, probably we have created some novel advances of NIR spectroscopy.
关键词： NIR spectroscopy,research history,spectral analysis,instrumentation,Ozaki group
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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A High-precision Technique to Correct for Residual Atmospheric Dispersion in High-contrast Imaging Systems
摘要： Direct detection and spectroscopy of exoplanets requires high-contrast imaging. For habitable exoplanets in particular, located at a small angular separation from the host star, it is crucial to employ small inner working angle (IWA) coronagraphs that ef?ciently suppress starlight. These coronagraphs, in turn, require careful control of the wavefront that directly impacts their performance. For ground-based telescopes, atmospheric refraction is also an important factor, since it results in a smearing of the point-spread function (PSF), that can no longer be ef?ciently suppressed by the coronagraph. Traditionally, atmospheric refraction is compensated for by an atmospheric dispersion compensator (ADC). ADC control relies on an a priori model of the atmosphere whose parameters are solely based on the pointing of the telescope, which can result in imperfect compensation. For a high-contrast instrument like the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system, which employs very small IWA coronagraphs, refraction-induced smearing of the PSF has to be less than 1 mas in the science band for the ?rst on-sky measurement and correction of residual optimum performance. In this paper, we present atmospheric dispersion. Atmospheric dispersion is measured from the science image directly, using an adaptive grid of arti?cially introduced speckles as a diagnostic to feedback to the telescope’s ADC. With our current setup, we were able to reduce the initial residual atmospheric dispersion from 18.8 mas to 4.2 in broadband light (y- to H-band) and to 1.4 mas in the H-band only. This work is particularly relevant to the upcoming extremely large telescopes (ELTs) that will require ?ne control of their ADC to reach their full high-contrast imaging potential.
关键词： atmospheric effects,planets and satellites: detection,instrumentation: adaptive optics
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
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An Imaging Algorithm for a Lunar Orbit Interferometer Array
摘要： Radio astronomical observations below 30 MHz are hampered by the refraction and absorption of the ionosphere as well as the radio frequency interference (RFI), and thus, high angular resolution sky intensity map is not yet available. An interferometer array on lunar orbit provides a perfect observatory in this frequency band: it is out of the ionosphere, and the Moon helps to block the RFIs from the Earth. The satellites can make observations on the far side of the Moon and then send back the data on the near-side part of the orbit. However, for such arrays, the traditional imaging algorithm is not applicable: the ?eld of view is very wide (almost whole-sky), and for baselines distributed on a plane, there is a mirror symmetry between the two sides of the plane. A further complication is that for each baseline, the Moon blocks part of the sky, but as the satellites orbit the Moon, both the direction of the baseline and the blocked sky change, so even imaging algorithms that can deal with a noncoplanar baseline may not work in this case. Here, we present an imaging algorithm based on solving the linear mapping equations relating the sky intensity to the visibilities. We show that the mirror symmetry can be broken by the three-dimensional baseline distribution generated naturally by the precession of the orbital plane of the satellites. The algorithm is applicable and good maps can be reconstructed, even though the sky blocking by the Moon is different for each baseline. We also investigate how the map-making is affected by inhomogeneous baseline distributions.
关键词： space vehicles: instruments,?rst stars,radio continuum: general,dark ages,reionization,techniques: interferometric,instrumentation: interferometers,methods: data analysis
更新于2025-09-04 15:30:14