- 标题
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Detection of Faint Asteroids Based on Image Shifting and Stacking Method
摘要： In order to improve the ability to find the faint and small celestial bodies in the solar system, a method of shifting and stacking images which improves the detection efficiency of faint moving objects is applied to process the sequential optical images. This method determines the existence of moving objects by using the method of false position to pre-estimate the apparent velocities of moving objects, then determines iteratively the accurate positions of moving objects based on the SNR (Signal-to-Noise Ratio) and elongation of stellar image. Using the sequential images of the China Near Earth Object Survey Telescope (CNEOST), we carry out an experiment and succeed in detecting asteroids fainter than 21 magnitude which are invisible on a single image. Thus, the feasibility of this method is verified.
关键词： techniques: image processing,astrometry,instrumentation,methods: data analysis,telescope,methods: observational
更新于2025-09-23 15:23:52
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Photometric and astrometric study of open cluster FSR 814 (Koposov 36) using SDSS/2MASS/PPMXL/Gaia DR2
摘要： We present multi photometric and astrometric study of open cluster FSR 814 (Koposov 36) selected from the FSR catalog in different bands of Sloan Digital Sky Survey (SDSS), 2MASS, PPMXL and Gaia DR2. This study contains new results with a very high accuracy for the first time and generates the multi decontaminated color-magnitude diagrams to estimate the main astrophysical properties (such as: diameter, age, distance, reddening, geometrical projected distances, luminosity and mass functions) of FSR 814. Our results have been compared with other literatures.
关键词： Color-Magnitude Diagram (CMD),Open clusters and associations: individual (FSR 814),Astrometry
更新于2025-09-23 15:23:52
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The SAGE photometric survey: technical description
摘要： To investigate a huge sample of data related to the Stellar Abundance and Galactic Evolution (SAGE) survey in more detail, we are performing a northern sky photometric survey named SAGES with the SAGE photometric system. This system consists of eight filters: Str?mgren-u, SAGE-v, SDSS g, r, i, DDO-51, Hαwide and Hαnarrow, including three Sloan broadband filters, three intermediate-band filters, two narrow-band filters and one newly-designed narrow-band filter. SAGES covers ～12 000 square degrees of the northern sky with δ > ?5?, excluding the Galactic disk (|b| < 10?) and the sky area 12 h <RA <18 h. The photometric detection limit depth at signal-to-noise ratio 5σ can be as deep as V ～20 mag. SAGES will produce a photometric catalog with uniform depth for ～500 million stars with atmospheric parameters including effective temperature Teff, surface gravity log g and metallicity [Fe/H], as well as interstellar extinction to each individual target. In this work, we will briefly introduce the SAGE photometric system, the SAGE survey and a preliminary test field of the open cluster NGC 6791 and its surroundings.
关键词： surveys,astrometry,techniques: photometric,methods: observational,catalogs
更新于2025-09-23 15:23:52
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The impact of ELT distortions and instabilities on future astrometric observations
摘要： The paper discusses an assessment study about the impact of the distortions on the astrometric observations with the Extremely Large Telescope originated from the optics positioning errors and telescope instabilities. Optical simulations combined with Monte Carlo approach reproducing typical inferred opto-mechanical and dynamical instabilities show rms distortions between ～0.1 and 5 mas over 1 arcmin field of view (FoV). Over minutes time-scales the plate scale variations from ELT-M2 caused by wind disturbances and gravity flexures and the field rotation from ELT-M4-M5 induce distortions and PSF jitter at the edge of 1 arcmin FoV (radius 35 arcsec) up to ～ 5 mas comparable to the diffraction-limited PSF size FWHMH = 8.5 mas. The rms distortions inherent to the ELT design are confined to the first to thrid order and reduce to an astrometric rms residual post fit of ～ 10–20 μas for higher order terms. In this paper, we study which calibration effort has to be undertaken to reach an astrometric stability close to this level of higher order residuals. The amplitude and time-scales of the assumed telescope tolerances indicate the need for frequent on-sky calibrations and MCAO stabilization of the plate scale to enable astrometric observations with ELT at the level of ≤50 μas, which is one of the core science missions for the ELT/MICADO instrument.
关键词： astrometry
更新于2025-09-23 15:21:21
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Gaia Astrometry and Fundamental Physics
摘要： Unprecedented astrometric accuracy of Gaia gives a unique opportunity to perform a suite of tests of fundamental physics. The tests range from a test of the Local Lorenz Invariance and the gravitational defection of light to measuring the mass of black hole candidates in certain compact binary systems with visible components. Gaia data can also be used to estimate the energy ?ux of the gravitational waves in certain frequency ranges.
关键词： gravitational waves,fundamental physics,Gaia,general relativity,astrometry
更新于2025-09-23 15:21:01
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Handbook of Exoplanets || Space Astrometry Missions for Exoplanet Science: Gaia and the Legacy of Hipparcos
摘要： Astrometry as a technique has so far proved of limited utility when employed as either a follow-up tool or to independently search for planetary-mass companions around stars in the solar neighborhood. However, the situation is bound to change soon. In this chapter, we provide a brief overview of past and present efforts to detect planets via milli-arcsecond (mas) astrometry, with a special focus on the legacy of the Hipparcos mission. We then focus on the Gaia mission that is poised to become a game changer in the field of exoplanets by unleashing for the first time the power of micro-arcsecond (μas) astrometry. We start by briefly describing the mission status and operation. Next, we address some of the relevant technical issues associated with the precise and accurate determination of astrometric orbits of planetary systems using Gaia data. We then present and discuss the Gaia planet-finding capabilities. We conclude by putting Gaia astrometry in context, illustrating its potential for crucial contributions to exoplanetary science in synergy with other indirect and direct methods for the detection and characterization of planetary systems.
关键词： space vehicles,surveys,planetary systems,methods: data analysis,methods: numerical,astrometry
更新于2025-09-23 15:21:01
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Optical observations of comet 67P/Churyumov-Gerasimenko with the Nordic Optical Telescope
摘要： Context. 67P/Churyumov-Gerasimenko (67P) is a short-period Jupiter-family comet that was chosen as a target for the Rosetta mission by the European Space Agency (ESA). Monitoring of 67P with the Nordic Optical Telescope (NOT; La Palma, Spain) intends to aid this mission by providing ground-based reference information about the overall activity of the target and its astrometric position before the rendezvous. One motivation for our observations was to monitor sudden major increases in activity because they might have affected the Rosetta mission planning. None were observed. Ground-based photometric observations register the global activity of the comet, while the Rosetta spacecraft mostly measures local events. These data combined can lead to new insights into the comet behavior. Aims. The aim of this work is to perform the photometric and the astrometric monitoring of comet 67P with the NOT and to compare the results with the latest predictions for its position and activity. A new method of fitting extended-source components to the target surface brightness distribution was developed and applied to the data to estimate the size and contribution of the coma to the total brightness of the target. Methods. Comet 67P was monitored by the NOT in service mode during the period between 12.5.2013 and 11.11.2014. The very first observations were performed in the V band alone, but in the latest observations, the R band was used as well to estimate the color and nature of activity of the target. We applied a new method for estimating the coma size by deconvolving the point spread function profile from the image, which used Markov chain Monte Carlo and Bayesian statistics. This method will also be used for coma size estimations in further observations after the solar conjunction of 67P. Results. Photometric magnitudes in two colors were monitored during the period of observations. At the end of April 2014, the beginning of activity was observed. In late September 2014, a minor dip in cometary activity was measured. Otherwise, the activity of the comet was close to the expected values. For some of the observations, we were able to determine limits for the physical size and brightness of the coma by studying the surface brightness distribution of the target. The astrometric calibration results we obtained were consistent with the predictions of the ephemerides of the Minor Planet Center, but at the moment these results are superseded with the more precise astrometric data from the Rosetta spacecraft.
关键词： comets: individual: 67P/Churyumov-Gerasimenko,astrometry,techniques: photometric
更新于2025-09-19 17:15:36
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On the importance of astronomical refraction for modern solar astrometric measurements
摘要： In this work we study in details the influence of pure astronomical refraction on solar metrological measurements made from ground-based full disc imagery and provide the tools for correcting the measurements and estimating the associated uncertainties. For a given standard atmospheric model, we first use both analytical and numerical methods in order to test the validity of the commonly or historically used approximations of the differential effect of refraction as a function of zenith distance. For a given refraction model, we provide the exact formulae for correcting solar radius measurements at any heliographic angle and for any zenith distance. Then, using solar images recorded in the near-infrared between 2011 and 2016, we show that these corrections can be applied up to 70° using the usual approximate formulae and can be extended up to 80° of zenith distance provided that a standard atmospheric model and a full numerical integration of the refraction integral are used. We also provide estimates of the absolute uncertainties associated with the differential refraction corrections and show that approximate formulae can be used up to 80° of zenith distance for computing these uncertainties. For a given instrumental setup and the knowledge of the uncertainties associated with local weather records, this can be used to fix the maximum zenith distance one can observe depending on the required astrometric accuracy.
关键词： Astrometry,Atmospheric effects,Sun: fundamental parameters
更新于2025-09-19 17:15:36
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The Power of (Near) Simultaneous Multi-Frequency Observations for mm-VLBI and Astrometry
摘要： Simultaneous or near-simultaneous observations at multiple frequency bands have the potential to overcome the fundamental limitation imposed by the atmospheric propagation in mm-VLBI observations. The propagation effects place a severe limit in the sensitivity achievable in mm-VLBI, reducing the time over which the signals can be coherently combined, and preventing the use of phase referencing and astrometric measurements. We present two demonstrations of the power of (near) simultaneous multi-frequency observations with the KVN and VLBA, and our recently developed analysis strategies to enable new measurements at mm-VLBI. The first case comprises simultaneous observations at 22, 43, 87 and 130 GHz of a group of five AGNs, the weakest of which is ～200 mJy at 130 GHz, with angular separations ranging from 3.6 to 11 degrees, using the KVN. We analysed this data using the Frequency Phase Transfer (FPT) and the Source Frequency Phase Referencing (SFPR) techniques, which use the observations at a lower frequency to correct those at a higher frequency. The results of the analysis provide an empirical demonstration of the increase in the coherence times at 130 GHz from a few tens of seconds to about twenty minutes, with FPT, and up to many hours with SFPR. Moreover the astrometric analysis provides high precision relative position measurements between two frequencies, including, for the first time, astrometry at 130 GHz. The second case is a variation of the above, whereby adding dedicated wide-band cm-wavelength observations to measure the ionosphere eliminates the need for a second, calibrator, source. This addresses the scarcity of calibrators at mm-VLBI. We dubbed this technique Multi Frequency Phase Referencing (MFPR). We present bona fide astrometrically aligned VLBA images of BL Lacertae at 22 and 43 GHz using MFPR, which, combined with results from conventional phase referencing at cm-wavelengths, suggests the VLBI core has a recollimation shock that is revealed at mm-wavelengths. These shocks could be responsible for the γ-ray emission in blazar jets.
关键词： radio continuum,BL Lac,astrometry,galaxies: 1803+784, 1807+698, 1842+681, 1928+738, 2007+777,interferometric
更新于2025-09-09 09:28:46
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Long-term <i>R</i> and <i>V</i> -band monitoring of some suitable targets for the link between ICRF and the future <i>Gaia</i> celestial reference frame
摘要： Context. The Gaia astrometric mission of the European Space Agency was launched on December 2013. It will provide a catalog of 500 000 quasars. Some of these targets will be chosen to build an optical reference system that will be linked to the International Celestial Reference Frame (ICRF). The astrometric coordinates of these sources will have roughly the same uncertainty at both optical and radio wavelengths, and it is then mandatory to observe a common set of targets to build the link. In the ICRF, some targets have been chosen because of their pointlikeness. They are quoted as defining sources, and they ensure very good uncertainty about their astrometric coordinates. At optical wavelengths, a comparable uncertainty could be achieved for targets that do not exhibit strong astrophysical phenomena, which is a potential source of photocenter flickering. A signature of these phenomena is a magnitude variation at optical wavelengths. Aims. The goal of this work is to present the time series of 14 targets suitable for the link between the ICRF and the future Gaia Celestial Reference Frame. The observations have been done systematically by robotic telescopes in France and Chile once every two nights since 2011 and in two filters. These time series are analyzed to search for periodic or quasi-periodic phenomena that must be taken into account when computing the uncertainty about the astrometric coordinates. Methods. Two independent methods were used in this work to analyze the time series. We used the CLEAN algorithm to compare the frequency obtained to those given by the Lomb-Scargle method. It avoids misinterpreting the frequency peaks given in the periodograms. Results. For the 14 targets we determine some periods with a confidence level above 90% in each case. Some of the periods found in this work were not previously known. For the others, we did a comparative study of the periods previously studied by others and always confirm their values. All the periods given by the two methods are in good agreement with the difference always below 7.9% in the worst case. Finally we also present the structure functions for our two sets of objects (BL Lac and Seyfert galaxies). Conclusions. For all but one target, we find variations that could be the signature of periodic or quasi-periodic phenomena. Our time series could allow to bring some constraints on astrophysical models that could explain such variations. Binary black hole system, instabilities in the jet or in the accretion disk, changes in the torus structure are some of these astrophysical phenomena. They must be kept in mind when evaluating the uncertainty about the astrometric position of the targets suitable for the link between reference systems in a conservative way.
关键词： astrometry,reference systems,quasars: general
更新于2025-09-09 09:28:46