- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Detecting Water in the Atmosphere of HR 8799 c with <i>L</i> -band High-dispersion Spectroscopy Aided by Adaptive Optics
摘要： High-dispersion spectroscopy of brown dwarfs and exoplanets enables exciting science cases, e.g., mapping surface inhomogeneity and measuring spin rate. Here, we present L-band observations of HR 8799 c using Keck NIRSPEC (R = 15,000) in adaptive optics (AO) mode (NIRSPAO). We search for molecular species (H2O and CH4) in the atmosphere of HR 8799 c with a template-matching method, which involves cross-correlation between reduced spectra and a template spectrum. We detect H2O but not CH4, which suggests disequilibrium chemistry in the atmosphere of HR 8799 c, and this is consistent with previous findings. We conduct planet signal injection simulations to estimate the sensitivity of our AO-aided high-dispersion spectroscopy observations. We conclude that 10?4 contrast can be reached in the L band. The sensitivity is mainly limited by the accuracy of line list used in modeling spectra and detector noise. The latter will be alleviated by the NIRSPEC upgrade.
关键词： planets and satellites: atmospheres,planetary systems,methods: observational,planets and satellites: composition,techniques: spectroscopic,techniques: high angular resolution
更新于2025-09-23 15:21:21
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The visible and near-infrared spectra of asteroids in cometary orbits
摘要： Context. Dynamical and albedo properties suggest that asteroids in cometary orbits (ACOs) are dormant or extinct comets. Their study provides new insights for understanding the end-states of comets and the size of the comet population. Aims. We intend to study the visible and near-infrared (NIR) spectral properties of different ACO populations and compare them to the independently determined properties of comets. Methods. We select our ACOs sample based on published dynamical criteria and present our own observational results obtained using the 10.4 m Gran Telescopio Canarias (GTC), the 4.2 m William Herschel Telescope (WHT), the 3.56 m Telescopio Nazionale Galileo (TNG), and the 2.5 m Isaac Newton Telescope (INT), all located at the El Roque de los Muchachos Observatory (La Palma, Spain), and the 3.0 m NASA Infrared Telescope Facility (IRTF), located at the Mauna Kea Observatory, in Hawaii. We include in the analysis the spectra of ACOs obtained from the literature. We derive the spectral class and the visible and NIR spectral slopes. We also study the presence of hydrated minerals by studying the 0.7 μm band and the UV-drop below 0.5 μm associated with phyllosilicates. Results. We present new observations of 17 ACOs, 11 of them observed in the visible, 2 in the NIR and 4 in the visible and NIR. We also discuss the spectra of 12 ACOs obtained from the literature. All but two ACOs have a primitive-like class spectrum (X or D-type). Almost 100% of the ACOs in long-period cometary orbits (Damocloids) are D-types. Those in Jupiter family comet orbits (JFC-ACOs) are ～60% D-types and ～40% X-types. The mean spectral slope S (cid:48) of JFC-ACOs is 9.7 ± 4.6%/1000 ? and for the Damocloids this is 12.2 ± 2.0%/1000 ?. No evidence of hydration on the surface of ACOs is found from their visible spectra. The spectral slope and spectral class distribution of ACOs is similar to that of comets. Conclusions. The spectral taxonomical classification and the spectral slope distribution of ACOs, and the lack of spectral features indicative of the presence of hydrated minerals on their surface, strongly suggest that ACOs are likely dormant or extinct comets.
关键词： minor planets, asteroids: general,comets: general,methods: observational,techniques: spectroscopic
更新于2025-09-23 15:21:01
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Searching for Subsecond Stellar Variability with Wide-field Star Trails and Deep Learning
摘要： We present a method that enables wide-field ground-based telescopes to scan the sky for subsecond stellar variability. The method has operational and image processing components. The operational component takes star trail images. Each trail serves as a light curve for its corresponding source and facilitates subexposure photometry. We train a deep neural network to identify stellar variability in wide-field star trail images. We use the Large Synoptic Survey Telescope Photon Simulator to generate simulated star trail images and include transient bursts as a proxy for variability. The network identifies transient bursts on timescales down to 10 ms. We argue that there are multiple fields of astrophysics that can be advanced by the unique combination of time resolution and observing throughput that our method offers.
关键词： techniques: image processing,methods: observational,techniques: photometric
更新于2025-09-23 15:21:01
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ASTROPOP: the ASTROnomical POlarimetry and Photometry Pipeline
摘要： We developed a new pure-Python pipeline to reduce photometric and polarimetric data: ASTROPOP. It has been designed and optimized to work fully automated with the IAGPOL polarimeter of Pico dos Dias Observatory (OPD; Brazil) and can reduce photometry and polarimetry data from other instruments, especially from SPARC4, a multi-channel polarimeter that has been developed for OPD. We present the results produced by this new code, and compare them with those obtained from PCCDPACK, a traditionally used IRAF package developed for IAGPOL. We also propose to use this code for automatic photometric reduction for the new ROBO40 telescope, also installed at OPD. ASTROPOP is fully open source and distributed under the BSD-3 clause license.
关键词： instrumentation: polarimeters,methods: observational,techniques: polarimetric,techniques: photometric,techniques: image processing
更新于2025-09-23 15:19:57
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Deep SDSS optical spectroscopy of distant halo stars
摘要： Aims. We analyze a sample of tens of thousands of spectra of halo turno? stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population “in situ” out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as ?ux calibrators for the Baryonic Oscillations Spectroscopic Survey (BOSS). Methods. Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that reproduces each observed spectrum best. We used an optimization algorithm and evaluate model ?uxes by means of interpolation in a precomputed grid. In our analysis, we account for the spectrograph’s varying resolution as a function of ?ber and wavelength. Our results for early SDSS (pre-BOSS upgrade) data compare well with those from the SEGUE Stellar Parameter Pipeline (SSPP), except for stars with log g (cgs units) lower than 2.5. Results. An analysis of stars in the globular cluster M 13 reveals a dependence of the inferred metallicity on surface gravity for stars with log g < 2.5, con?rming the systematics identi?ed in the comparison with the SSPP. We ?nd that our metallicity estimates are signi?cantly more precise than the SSPP results. We also ?nd excellent agreement with several independent analyses. We show that the SDSS color criteria for selecting F-type halo turno? stars as ?ux calibrators e?ciently excludes stars with high metallicities, but does not signi?cantly distort the shape of the metallicity distribution at low metallicity. We obtain a halo metallicity distribution that is narrower and more asymmetric than in previous studies. The lowest gravity stars in our sample, at tens of kpc from the Sun, indicate a shift of the metallicity distribution to lower abundances, consistent with what is expected from a dual halo system in the Milky Way.
关键词： techniques: spectroscopic,stars: atmospheres,methods: observational,Galaxy: halo,stars: Population II,stars: fundamental parameters
更新于2025-09-23 15:19:57
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Ground-based Spectroscopy of the Exoplanet XO-2b Using a Systematic Wavelength Calibration
摘要： Exoplanets orbiting close to their host star are expected to support a large ionosphere, which extends to larger pressures than witnessed in our solar system. These ionospheres can be investigated with ground-based transit observations of the optical signatures of alkali metals, which are the source of the ions. However, most ground-based transit spectra do not systematically resolve the wings of the features and continuum, as needed to constrain the alkali abundances. Here we present new observations and analyses of optical transit spectra that cover the Na doublet in the atmosphere of the exoplanet XO-2b. To assess the consistency of our results, observations were obtained from two separate platforms: Gemini/GMOS and Mayall/KOSMOS. To mitigate the systematic errors, we chose XO-2, because it has a binary companion of the same brightness and stellar type, which provides an ideal reference star to model Earth’s atmospheric effects. We find that interpretation of the data is highly sensitive to time-varying translations along the detector, which change according to wavelength and differ between the target and reference star. It was necessary to employ a time-dependent cross-correlation to align our wavelength bins and correct for atmospheric differential refraction. This approach allows us to resolve the wings of the Na line across five wavelength bins at a resolution of ～1.6 nm and limit the abundance of Na. We obtain consistent results from each telescope with an Na amplitude of 521 ± 161 and 403 ± 186 ppm for GMOS and KOSMOS, respectively. The results are analyzed with a radiative transfer model that includes the effects of ionization. The data are consistent with a clear atmosphere between ～1 and 100 mbar that establishes a lower limit on Na at 0.4 +0.3 -0.2 ppm ([Na/H] = -0.64 +0.6 -0.78), consistent with solar. However, we cannot rule out the presence of clouds at ～10 mbar that allow for higher Na abundances, which would be consistent with the stellar metallicity measured for the host star ([Na/H] = 0.485 ± 0.043).
关键词： planets and satellites: atmospheres,planets and satellites: individual (XO-2b),methods: observational,methods: data analysis,techniques: spectroscopic,methods: analytical
更新于2025-09-19 17:15:36
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Mid-infrared interferometry with <i>K</i> band fringe-tracking
摘要： Context. A turbulent atmosphere causes atmospheric piston variations leading to rapid changes in the optical path difference of an interferometer, which causes correlated flux losses. This leads to decreased sensitivity and accuracy in the correlated flux measurement. Aims. To stabilize the N band interferometric signal in MIDI (MID-infrared Interferometric instrument), we use an external fringe tracker working in K band, the so-called FSU-A (fringe sensor unit) of the PRIMA (Phase-Referenced Imaging and Micro-arcsecond Astrometry) facility at VLTI. We present measurements obtained using the newly commissioned and publicly offered MIDI+FSU-A mode. A first characterization of the fringe-tracking performance and resulting gains in the N band are presented. In addition, we demonstrate the possibility of using the FSU-A to measure visibilities in the K band. Methods. We analyzed FSU-A fringe track data of 43 individual observations covering different baselines and object K band magnitudes with respect to the fringe-tracking performance. The N band group delay and phase delay values could be predicted by computing the relative change in the differential water vapor column density from FSU-A data. Visibility measurements in the K band were carried out using a scanning mode of the FSU-A. Results. Using the FSU-A K band group delay and phase delay measurements, we were able to predict the corresponding N band values with high accuracy with residuals of less than 1 μm. This allows the coherent integration of the MIDI fringes of faint or resolved N band targets, respectively. With that method we could decrease the detection limit of correlated fluxes of MIDI down to 0.5 Jy (vs. 5 Jy without FSU-A) and 0.05 Jy (vs. 0.2 Jy without FSU-A) using the ATs and UTs, respectively. The K band visibilities could be measured with a precision down to ≈2%.
关键词： instrumentation: interferometers,methods: observational,techniques: interferometric,methods: data analysis
更新于2025-09-19 17:15:36
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Four winters of photometry with ASTEP South at Dome C, Antarctica
摘要： Context. Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions. Aims. We developed instruments to assess the quality of this site for photometry in the visible and to detect and characterize variable objects through the Antarctic Search for Transiting ExoPlanets (ASTEP) project. Methods. Here, we present the full analysis of four winters of data collected with ASTEP South, a 10 cm refractor pointing continuously toward the celestial south pole. We improved the instrument over the years and developed specific data reduction methods. Results. We achieved nearly continuous observations over the winters. We measure an average sky background of 20 mag arcsec?2 in the 579–642 nm bandpass. We built the lightcurves of 6000 stars and developed a model to infer the photometric quality of Dome C from the lightcurves themselves. The weather is photometric 67.1 ± 4.2% of the time and veiled 21.8 ± 2.0% of the time. The remaining time corresponds to poor quality data or winter storms. We analyzed the lightcurves of σ Oct and HD 184465 and find that the amplitude of their main frequency varies by a factor of 3.5 and 6.7 over the four years, respectively. We also identify 34 new variable stars and eight new eclipsing binaries with periods ranging from 0.17 to 81 days. Conclusion. The phase coverage that we achieved with ASTEP South is exceptional for a ground-based instrument and the data quality enables the detection and study of variable objects. These results demonstrate the high quality of Dome C for photometry in the visible and for time series observations in general.
关键词： site testing,stars: variables: delta Scuti,methods: observational,binaries: eclipsing,methods: data analysis,techniques: photometric
更新于2025-09-19 17:15:36
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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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OmegaWINGS: OmegaCAM-VST observations of WINGS galaxy clusters
摘要： Context. Wide-field observations targeting galaxy clusters at low redshift are complementary to field surveys and provide the local benchmark for detailed studies of the most massive haloes in the local Universe. The Wide-field Nearby Galaxy-cluster Survey (WINGS) is a wide-field multi-wavelength survey of X-ray selected clusters at z = 0.04–0.07. The original 34' × 34' WINGS field of view has now been extended to cover a 1 deg2 field with both photometry and spectroscopy. Aims. We present the Johnson B- and V-band OmegaCAM at the VST observations of 46 WINGS clusters together with the data reduction, data quality, and Sextractor photometric catalogues. Methods. The data reduction was carried out with a modified version of the ESO-MVM (also known as ALAMBIC) reduction package, adding a cross-talk correction, the gain harmonisation, and a control procedure for problematic CCDs. The stray-light component was corrected for by employing our own observations of populated stellar fields. Results. With a median seeing of 1'' in both bands, our 25-min exposures in each band typically reach the 50% completeness level at V = 23.1 mag. The quality of the astrometric and photometric accuracy has been verified by comparison with the 2MASS and SDSS astrometry, and SDSS and previous WINGS imaging. Star-to-galaxy separation and sky-subtraction procedure were tested comparing them with previous WINGS data. Conclusions. The Sextractor photometric catalogues are publicly available at the CDS and will be included in the next release of the WINGS database on the Virtual Observatory together with the OmegaCAM reduced images. These data form the basis for a large ongoing spectroscopic campaign with AAOmega at the AAT and are being employed for a variety of studies.
关键词： galaxies: fundamental parameters,galaxies: clusters: general,galaxies: photometry,methods: observational,catalogs
更新于2025-09-19 17:15:36