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- 摘要
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Thermal structure of a hot non-flaring corona from Hinode/EIS
摘要： Aims. In previous studies, a very hot plasma component has been diagnosed in solar active regions through the images in three different narrow-band channels of Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). This diagnostic from extreme ultraviolet (EUV) imaging data has also been supported by the matching morphology of emission in the hot Ca XVII line, as observed with Extreme-Ultraviolet Imaging Spectrometer (EIS) on board Hinode. This evidence is debated because of the unknown distribution of the emission measure along the line of sight. Here we investigate in detail the thermal distribution of one such region using EUV spectroscopic data. Methods. In an active region observed with SDO/AIA, Hinode/EIS, and X-ray telescope (XRT), we select a sub-region with a very hot plasma component and another cooler sub-region for comparison. The average spectrum is extracted for both, and 14 intense lines are selected for analysis that probe the 5.5 < log T < 7 temperature range uniformly. From these lines, the emission measure distributions are reconstructed with the Markov-chain Monte Carlo method. Results are cross-checked in comparison with the two sub-regions, with a different inversion method, with the morphology of the images, and with the addition of fluxes measured with narrow, and broadband imagers. Results. We find that, whereas the cool region has a flat and featureless distribution that drops at temperature log T ≥ 6.3, the distribution of the hot region shows a well-defined peak at log T = 6.6 and gradually decreasing trends on both sides, thus supporting the very hot nature of the hot component diagnosed with imagers. The other cross-checks are consistent with this result. Conclusions. This study provides a completion of the analysis of active region components, and the resulting scenario supports the presence of a minor very hot plasma component in the core, with temperatures log T > 6.6.
关键词： techniques: imaging spectroscopy,Sun: UV radiation,Sun: corona,techniques: spectroscopic,Sun: X-rays, gamma rays
更新于2025-09-23 15:23:52
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Spatial and Temporal Stability of Airglow Measured in the Meinel Band Window at 1191.3 nm
摘要： We report on the temporal and spatial fluctuations in the atmospheric brightness in the narrow band between Meinel emission lines at 1191.3 nm using a λ/Δλ = 320 near-infrared instrument. We present the instrument design and implementation, followed by a detailed analysis of data taken over the course of a night from Table Mountain Observatory. At low airmasses, the absolute sky brightness at this wavelength is found to be 5330 ± 30 nW m?2 sr?1, consistent with previous measurements of the inter-band airglow at these wavelengths. This amplitude is larger than simple models of the continuum component of the airglow emission at these wavelengths, confirming that an extra emissive or scattering component is required to explain the observations. We perform a detailed investigation of the noise properties of the data and find no evidence for a noise component associated with temporal instability in the inter-line continuum. This result demonstrates that in several hours of ～100 s integrations the noise performance of the instrument does not appear to significantly degrade from expectations, giving a proof of concept that near-infrared line intensity mapping may be feasible from ground-based sites.
关键词： techniques: imaging spectroscopy,site testing,atmospheric effects
更新于2025-09-23 15:23:52
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First survey of Wolf-Rayet star populations over the full extension of nearby galaxies observed with CALIFA
摘要： The search of extragalactic regions with conspicuous presence of Wolf-Rayet (WR) stars outside the Local Group is challenging task owing to the di?culty in detecting their faint spectral features. In this exploratory work, we develop a methodology to perform an automated search of WR signatures through a pixel-by-pixel analysis of integral ?eld spectroscopy (IFS) data belonging to the Calar Alto Legacy Integral Field Area survey, CALIFA. This procedure has been applied to a sample of nearby galaxies spanning a wide range of physical, morphological, and environmental properties. This technique allowed us to build the ?rst catalogue of regions rich in WR stars with spatially resolved information, and enabled us to study the properties of these complexes in a two-dimensional (2D) context. The detection technique is based on the identi?cation of the blue WR bump (around He ii λ4686 ?, mainly associated with nitrogen-rich WR stars; WN) and the red WR bump (around C iv λ5808 ?, mainly associated with carbon-rich WR stars; WC) using a pixel-by-pixel analysis that maximizes the number of independent regions within a given galaxy. We identi?ed 44 WR-rich regions with blue bumps distributed in 25 out of a total of 558 galaxies. The red WR bump was identi?ed only in 5 of those regions. Most of the WR regions are located within one e?ective radius from the galaxy centre, and around one-third are located within ～1 kpc or less from the centre. We found that the majority of the galaxies hosting WR populations in our sample are involved in some kind of interaction process. Half of the host galaxies share some properties with gamma-ray burst (GRB) hosts where WR stars, such as potential candidates to the progenitors of GRBs, are found. We also compared the WR properties derived from the CALIFA data with stellar population synthesis models, and con?rm that simple star models are generally not able to reproduce the observations. We conclude that other e?ects, such as binary star channel (which could extend the WR phase up to 10 Myr), fast rotation, or other physical processes that cause the loss of observed Lyman continuum photons, very likely a?ect the derived WR properties, and hence should be considered when modelling the evolution of massive stars.
关键词： techniques: imaging spectroscopy,galaxies: ISM,galaxies: starburst,stars: Wolf-Rayet
更新于2025-09-23 15:21:21
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LAMOST CCD camera-control system based on RTS2
摘要： The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is the largest existing spectroscopic survey telescope, having 32 scientific charge-coupled-device (CCD) cameras for acquiring spectra. Stability and automation of the camera-control software are essential, but cannot be provided by the existing system. The Remote Telescope System 2nd Version (RTS2) is an open-source and automatic observatory-control system. However, all previous RTS2 applications were developed for small telescopes. This paper focuses on implementation of an RTS2-based camera-control system for the 32 CCDs of LAMOST. A virtual camera module inherited from the RTS2 camera module is built as a device component working on the RTS2 framework. To improve the controllability and robustness, a virtualized layer is designed using the master-slave software paradigm, and the virtual camera module is mapped to the 32 real cameras of LAMOST. The new system is deployed in the actual environment and experimentally tested. Finally, multiple observations are conducted using this new RTS2-framework-based control system. The new camera-control system is found to satisfy the requirements for automatic camera control in LAMOST. This is the first time that RTS2 has been applied to a large telescope, and provides a referential solution for full RTS2 introduction to the LAMOST observatory control system.
关键词： telescopes,methods: observational,techniques: imaging spectroscopy,instrumentation: detectors
更新于2025-09-19 17:15:36
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LEMONY – a library of empirical medium-resolution spectra by observations with the NAOC Xinglong 2.16-m and YNAO Gaomeigu 2.4-m telescopes
摘要： In this study, we expand the coverage and improve the homogeneity of the distribution of MILES template stars in the parameter space, as well as extend the wavelength coverage of the template spectra to the far red beyond the CaII triplet. To achieve this, we have carried out a major observational campaign using two long-slit spectrographs: the OMR mounted on the National Astronomy Observatory of China (NAOC) 2.16-m telescope and the Yunnan Faint Object Spectrograph and Camera (YFOSC) mounted on the Yunnan Astronomical Observatory (YNAO) 2.4-m telescope. The original sample is based on the MILES library, supplemented by 918 stars selected from the PASTEL data base. In total, 822 OMR and 1324 YFOSC spectra have been collected and reduced, covering the wavelength ranges λλ3800–5180 and λλ5150–9000, respectively. The spectra have a mean resolution full width at half-maximum of ～3.3 ? and are wavelength- and ?ux-calibrated to an accuracy of ～20 km s?1 and ～5 per cent, respectively. The spectra are further corrected for systematic errors in the wavelength calibration to an accuracy of ～4 km s?1 by cross-correlating with the theoretical spectra. Almost all the spectra have an average signal-to-noise ratio better than 100 per pixel. Combined with the MILES spectra, there are now 1731, 1542, 1324 and 1273 stars with spectra covering λλ3800–5180, λλ3800–7500, λλ5150–9000 and λλ3800–9000, respectively. In this paper, we describe our template star selection, the observation and data reduction, and we present the reduced spectra collected hitherto.
关键词： stars: fundamental parameters,techniques: imaging spectroscopy
更新于2025-09-19 17:15:36
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Performance of the VLT Planet Finder SPHERE
摘要： Context. The new planet finder for the Very Large Telescope (VLT), the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE), just had its first light in Paranal. A dedicated instrument for the direct detection of planets, SPHERE, is composed of a polarimetric camera in visible light, the Zurich IMager POLarimeter (ZIMPOL), and two near-infrared sub-systems: the Infra-Red Dual-beam Imager and Spectrograph (IRDIS), a multi-purpose camera for imaging, polarimetry, and long-slit spectroscopy, and the integral field spectrograph (IFS), an integral field spectrograph. Aims. We present the results obtained from the analysis of data taken during the laboratory integration and validation phase, after the injection of synthetic planets. Since no continuous field rotation could be performed in the laboratory, this analysis presents results obtained using reduction techniques that do not use the angular differential imaging (ADI) technique. Methods. To perform the simulations, we used the instrumental point spread function (PSF) and model spectra of L and T-type objects scaled in contrast with respect to the host star. We evaluated the expected error in astrometry and photometry as a function of the signal to noise of companions, after spectral differential imaging (SDI) reduction for IRDIS and spectral deconvolution (SD) or principal component analysis (PCA) data reductions for IFS. Results. We deduced from our analysis, for example, that β Picb, a 12 Myr old planet of ～10 MJup and semi-major axis of 9–10 AU, would be detected with IRDIS with a photometric error of 0.16 mag and with a relative astrometric position error of 1.1 mas. With IFS, we could retrieve a spectrum with error bars of about 0.15 mag on each channel and astrometric relative position error of 0.6 mas. For a fainter object such as HR 8799d, a 13 MJup planet at a distance of 27 AU, IRDIS could obtain a relative astrometric error of 3 mas.
关键词： techniques: imaging spectroscopy,planetary systems,instrumentation: spectrographs,methods: data analysis,instrumentation: high angular resolution
更新于2025-09-19 17:15:36
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Properties of the dust in the coma of 67P/Churyumov-Gerasimenko observed with VIRTIS- M
摘要： An investigation is presented of the dust scattering in the coma of 67P/Churyumov–Gerasimenko for the dates of 2015 February 28, March 15 and April 27. A comparison of the morphology of dust continuum maps at 1.1 μm and gas emission shows that for the above dates the spatial distribution of the dust is strongly correlated with H2O but not with CO2 emission. For April 27, the radial pro?le on the illuminated side of the nucleus in the inner coma agrees well with the direct simulation Monte Carlo (DSMC) calculations as the dust is accelerating and ?ows outwards but follows a 1/ρ distribution at distances larger than 4 km from the nucleus. The azimuthal distribution of the dust is narrower than the broader emission of the gas. Afρ values are 1.13 m for 2015 February 28, 2.02 m for April 27, while local values for March 15 are 2.3–5.3 m, depending on the nucleus illumination. In the inner coma, the spectral re?ectivity from 0.35 to 3.5 μm displays a red slope with a change at around 1 μm. From 0.35 to 0.8 μm, the values range from 9 to 12 ± 1 per cent per 100 nm both on the sunlit side and on the dark side. From 1 to 2.5 μm, the values are 1.7 ± 0.2 per cent per 100 nm on the sunlit side and 3 ± 1 per cent per 100 nm on the dark side. For the August 26 jet, no signi?cant increase of the colour gradient with distance from the nucleus could be observed, nor any signi?cant difference detected between the jet and the background coma.
关键词： methods: data analysis – methods: observational – techniques: imaging spectroscopy – comets: individual: 67P/Churyumov–Gerasimenko.
更新于2025-09-11 14:15:04
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Mode identification based on time-series spectrophotometry for the bright rapid sdB pulsator EC 01541?1409
摘要： We present an analysis of time-resolved spectrophotometry gathered with FORS/VLT for the rapidly pulsating hot B subdwarf EC 01541?1409 with the aim of identifying the degree index (cid:2) of the larger amplitude modes. This mode identi?cation can be extremely useful in detailed searches for viable asteroseismic models in parameter space, and can be crucial for testing the validity of a solution a posteriori. To achieve it, we exploit the (cid:2)-dependence of the monochromatic amplitude, phase, and velocity-to-amplitude ratio of a mode as a function of wavelength. We use the (cid:2)-sensitive phase lag between the ?ux perturbation and the radial velocity as an additional diagnostic tool. On this basis, we are able to unambiguously identify the dominant 140.5 s pulsation of our target as a radial mode, and the second-highest amplitude periodicity at 145.8 s as an (cid:2) = 2 mode. We further exploit the exceptionally high-sensitivity data that we gathered for the dominant mode to infer modal properties that are usually quite di?cult to estimate in sdB pulsators, namely the physical values of the dimensionless radius, temperature, and surface gravity perturbations.
关键词： stars: oscillations,stars: individual: EC 01541-1409,techniques: imaging spectroscopy,stars: atmospheres,stars: variables: general,asteroseismology
更新于2025-09-10 09:29:36
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67P/Churyumov-Gerasimenko active areas before perihelion identified by GIADA and VIRTIS data fusion
摘要： We characterised 67P/Churyumov-Gerasimenko?s cometary activity during its inbound arc before perihelion (August 2014-January 2015). We focused on the geomorphological regions of the Northern hemisphere observed by the ESA/Rosetta space probe during this time period. The GIADA dust detector characterised the physical properties of the fluffy and compact particles ejected from the nucleus; the VIRTIS imaging spectrometer detected exposed water ice. We identified specific cometary active areas by adopting the following GIADA and VIRTIS indicators: a) The decrease with increasing temperature of the centre of the 3.2-?m absorption band and of the spectral slope between 1.1 and 1.9??m, as measured by VIRTIS, which are both possible effects of water ice exposition. b) The number of fluffy and compact particles ejected from a specific region, which we determined by tracing dust particles in the coma, as detected by GIADA, back down to the nucleus. The correlation between GIADA and VIRTIS indicators led us to conclude that dust emission causes exposition of water ice on the surface of the nucleus, and fluffy and compact particles have common ejection regions; their lack of correlation in the coma is due to spread induced by their different velocities. We find that the most active regions are located in the neck (Hapi and Seth) and in the body (Ash, Babi and Aten) of the comet. These regions are also the ones most illuminated during the considered observation period, indicating that insolation is the main, if not only, driver of cometary activity.
关键词： Methods: data analysis,Instrumentation: detectors,Comets: Churyumov-Gerasimenko,Techniques: imaging spectroscopy
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