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A Baseline Correction Algorithm for FAST

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Research in astronomy and Astrophysics 2022年第8期22卷 1-5页

作者： De-Jian Liu Ye Xu Ying-Jie Li Ze-Hao Lin Shuai-Bo Bian Chao-Jie Hao Purple Mountain Observatory Chinese Academy of SciencesNanjing 210008China School of astronomy and Space Science University of Science and Technology of ChinaHefei 230026China

The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the most sensitive ground-based,singledish radio telescope on ***,the original HⅠspectra produced by FAST are affected by standing *** maximize the power of FAST for high-sensitivity observations,we proposed an algorithm that combines fast Fourier transforms and extreme envelope curves to automatically correct the baselines of FAST HⅠspectra and remove standing waves from the *** algorithm can reduce the amplified noise level caused by standing waves to a near-ideal level without losing signals or introducing false *** root mean square of the average baseline reaches~8 mK,approaching the theoretical sensitivity of an HⅠspectrum produced by FAST for an integration time of 335 minutes,i.e.,~6 m K.

关键词： methods:observational techniques:spectroscopic telescopes

A Fast radio Burst Backend for the Tianlai Dish Pathfinder Array

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Research in astronomy and Astrophysics 2022年第12期22卷 211-223页

作者： Zijie Yu Furen Deng Shijie Sun Chenhui Niu Jixia Li Fengquan Wu Wei-Yang Wang Yougang Wang Hui Feng Lin Shu Jie Hao Reza Ansari Albert Stebbins Xuelei Chen National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China Department of astronomy Peking UniversityBeijing 100871China Kavli Institute for astronomy and Astrophysics Peking UniversityBeijing 100871China Institute of Automation Chinese Academy of SciencesBeijing 100190China Guangdong Institute of Artificial Intelligence and Advanced Computing Guangzhou 510535China UniversitéParis-Saclay CNRS/IN2P3IJCLabF-91405 OrsayFrance Fermi National Accelerator laboratory P.O.Box 500BataviaIL 60510-5011United States of America Department of Physics College of SciencesNortheastern UniversityShenyang 110819China Center of High Energy Physics Peking UniversityBeijing 100871China

The Tianlai Dish Pathfinder Array is a radio interferometer array consisting of 16 six-meter dish *** original digital backend integration time is at the seconds level,designed for H I intensity mapping experiment.A new digital backend with millisecond response is added to enable it to search for fast radio burst during its *** design and calibration of this backend,and the real time search pipeline for it are described in this *** is capable of forming 16 digital beams for each linear polarization,covering an area of 19.6 square *** search pipeline is capable of searching for,recording and classifying FRBs automatically in real *** commissioning,we succeeded in capturing the signal pulses from the pulsars PSR B0329+54 and B2021+51.

关键词： instrumentation:miscellaneous techniques:interferometric telescopes radio continuum:general (stars:)pulsars:general

A catalogue of 74 new open clusters found in Gaia Data-Release 2

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Research in astronomy and Astrophysics 2021年第4期21卷 216-224页

作者： Zhi-Hong He Ye Xu Chao-Jie Hao Zhen-Yu Wu Jing-Jing Li Purple Mountain Observatory Chinese Academy of SciencesNanjing 210023China University of Science and Technology of China Hefei 230026China National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China key laboratory of Optical astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China

Based on astrometric data from Gaia Data-Release 2(DR2),we employ an unsupervised machine learning method to blindly search for open star clusters in the Milky Way within the Galactic latitude range of|b|<20°.In addition to 2080 known clusters,74 new open cluster candidates are *** this work,we present the positions,apparent radii,parallaxes,proper motions and member stars of these ***,to obtain the physical parameters of each candidate cluster,stellar isochrones are fit to the photometric *** results show that the apparent radii and the observed proper motion dispersions of these new candidates are consistent with those of open clusters previously identified in Gaia DR2.

关键词： Galaxy:open clusters and associations methods:data analysis surveys

A 95 GHz methanol emission survey toward eight small supernova remnants

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Research in astronomy and Astrophysics 2017年第12期17卷 65-76页

作者： Ying-Jie Li Ye Xu Xi Chen Deng-Rong Lu Yan Sun Xin-Yu Du Zhi-Qiang Shen Purple Mountain Observatory Chinese Academy of SciencesNanjing 210008China University of Science and Technology of China Chinese Academy of SciencesHefei 230026China Center for Astrophysics Guangzhou UniversityGuangzhou 51006China Shanghai Astronomical Observatory Chinese Academy of SciencesShanghai 200030China University of the Chinese Academy of Sciences Beijing 100049China

We report on a 95 GHz（80-71A＋） methanol（CH3OH） emission survey with the Purple Mountain Observatory Delingha 13.7 m telescope. Eight supernova remnants（SNRs） with angular size〈10′ were observed, but emission was only detected in three SNRs near the Galactic center（Sgr A East,G 0.1–0.1 and G 359.92–0.09）. CH3OH emission mainly surrounds the SNRs and can be decomposed into nine spatial peaks with the velocity range of eight peaks being（-30, 70） km s-1, and the other is（70, 120） km s-1. They are probably excited by interaction with these SNRs and adjacent molecular gas in the central molecular zone（CMZ）, although star formation may play an important role in exciting CH3OH emission in some regions of CMZ. We infer that tidal action is unlikely to be an excitation source for CH3OH emission.

关键词： ISM:molecules ISM:supernova remnants Galaxy:center ISM:kinematics and dynamics ISM:clouds

Position and attitude determination by integrated GPS/SINS/TS for feed support system of FAST

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Research in astronomy and Astrophysics 2020年第9期20卷 192-200页

作者： Ming-Hui Li Peng Jiang Dong Jun Yul Jing Hai Sun National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China

This paper presents a new measurement system based on integration method that can provide all-weather dependability and higher precision for the measurement of FAST's feed support *** measurement system consists of three types of measuring equipments,and a processing software with the core data fusion *** Strapdown Inertial Navigation System(SINS)can autonomously measure the position,speed and attitude of the *** own shortcoming is that the measurement data diverge rapidly over *** must combine the Global Positioning System(GPS)and the Total Station(TS)to obtain high-precision measurement *** Kalman filtering algorithm is adopted for the integration measurement system,which is an optimal algorithm to estimate the measurement errors.A series of tests are carried out to evaluate the *** the feed cabin,the maximum RMS of the position is 14.56 mm,the maximum RMS of the attitude is 0.095,these values are less than 15 mm and 0.1°as the precision for measuring the feed *** the Stewart manipulator,the maximum RMS of the position is 2.99 mm,the maximum RMS of the attitude is 0.093°,these values are less than 3 mm and 0.1°as the precision for measuring the Stewart *** a result,the new measurement meets the requirement of measurement precision for FAST's feed support system.

关键词： FAST Integration measurement system GPS/SINS/TS Kalman Filter

The Electromagnetic Characteristics of the Tianlai Cylindrical Pathfinder Array

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Research in astronomy and Astrophysics 2022年第6期22卷 234-255页

作者： Shijie Sun Jixia Li Fengquan Wu Peter Timbie Reza Ansari Jingchao Geng Huli Shi Albert Stebbins Yougang Wang Juyong Zhang Xuelei Chen National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China Department of Physics University of Wisconsin Madison1150 University AveMadison WI 53703united States of America IJC Lab CNRS/IN2P3&UniversitéParis-Saclay15 rue Georges ClemenceauF-91405 OrsayFrance The 54th Research Institute China Electronics Technology Group CorporationShijiazhuangHebei 050051China Fermi National Accelerator laboratory P.O.Box 500Batavia IL 60510-5011United States of America School of Mechanical Engineering Hangzhou Dianzi UniversityHangzhou 310017China Department of Physics College of SciencesNortheastern UniversityShenyang 110819China Center of High Energy Physics Peking UniversityBeijing 100871China

A great challenge for 21 cm intensity mapping experiments is the strong foreground radiation which is orders of magnitude brighter than the 21 cm *** of the foreground takes advantage of the fact that its frequency spectrum is smooth while the redshifted 21 cm signal spectrum is ***,a complication is the nonsmoothness of the instrument *** paper describes the electromagnetic simulation of the Tianlai cylinder array,a pathfinder for 21 cm intensity mapping *** to the vast scales involved,a direct simulation requires a large amount of computing *** have made the simulation practical by using a combination of methods:first simulate a single feed,then an array of feed units,finally with the feed array and a cylindrical reflector together,obtain the response for a single *** studied its radiation pattern,bandpass response and the effects of mutual coupling between feed units,and compared the results with *** features seen in the measurement result are reproduced well in the simulation,especially the oscillatory features which are associated with the standing waves on the *** mutual coupling between feed units is quantified with Sparameters,which decrease as the distance between the two feeds *** on the simulated S-parameters,we estimate the correlated noise which has been seen in the visibility data,and the results show very good agreement with the data in both magnitude and frequency *** results provide useful insights on the problem of 21 cm signal extraction for real instruments.

关键词： instrumentation interferometers-methods numerical-methods observational-cosmology observations-(cosmology:)dark ages-reionization-first stars-(cosmology:)diffuse radiation

The role of magnetic damping in the r-mode evolution of accreting neutron stars

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Science China(Physics,Mechanics & astronomy) 2015年第3期58卷 90-95页

作者： CAO GuoJie ZHOU Xia WANG Na Xinjiang Astronomical Observatory Chinese Academy of Sciences University of Chinese Academy of Sciences key laboratory of radio astronomy Chinese Academy of Sciences

The magnetic damping rate was introduced in the evolution equations of r-modes,which shows that r-modes can generate strong toroidal magnetic fields in the core of accreting millisecond pulsars inducing by differential *** consideration of the coupling evolution of r-modes,spin and thermal evolution,we investigated the influence of the magnetic damping on the differential rotation of nonlinear r-modes of accreting neutron *** derived the coupling evolution equations of the star involving the magnetic damping rate in the framework of second-order r-mode *** numerical results show that the magnetic damping suppressed the nonlinear evolution of r-modes since the saturation amplitude is reduced to a great *** particular,because of the presence of the generated toroidal magnetic field,the spin-down of the stars is terminated and the viscous heating effects are also ***,we could obtain a stronger generated toroidal magnetic field in the second-order r-mode *** gravitational radiation may be detected by the advanced laser interferometer detector LIGO if the amount of differential rotation is small when the r-mode instability becomes active and the accretion rate is not very high.

关键词：模式演变阻尼率中子星吸积磁性非线性演化环形磁场演化方程

Astrophysical constraints on the proton-to-electron mass ratio with FAST

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Research in astronomy and Astrophysics 2019年第2期19卷 15-24页

作者： Xi Chen Simon P.Ellingsen Ying Mei Center for Astrophysics Guangzhou University Shanghai Astronomical Observatory Chinese Academy of Sciences School of Physical Sciences University of Tasmania

That the laws of physics are the same at all times and places throughout the Universe is one of the basic assumptions of physics. Astronomical observations provide the only means to test this basic assumption on cosmological time and distance scales. The possibility of variations in the dimensionless physical constant μ-the proton-to-electron mass ratio, can be tested by comparing astronomical measurements of the rest frequency of certain spectral lines at radio wavelengths with laboratory determinations. Different types of molecular transitions have different dependencies on μ and so observations of two or more spectral lines towards the same astronomical source can be used to test whether there is any evidence for either temporal or spatial changes in the physical fundamental constants. μ will change if the relative strength of the strong nuclear force compared to the electromagnetic force varies. Theoretical studies have shown that the rotational transitions of some molecules which have transitions in the frequency range that will be covered by FAST(e.g., CH_3 OH, OH and CH) are sensitive to changes in μ. A number of studies looking for possible variations in μ have been undertaken with existing telescopes, however, the greater sensitivity of FAST means it will open new opportunities to significantly improve upon measurements made to *** this paper, we discuss which molecular transitions and sources(both in the Galaxy and external galaxies)are likely targets for providing improved constraints on μ with FAST.

关键词： ISM:molecules radio lines:ISM techniques:radial velocities elementary particles

Differential correction method applied to measurement of the FAST reflector

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Research in astronomy and Astrophysics 2016年第8期16卷 25-32页

作者： Xin-Yi Li Li-Chun Zhu Jin-Wen Hu Zhi-Heng Li National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China University of Chinese Academy of Sciences Beijing 100049 China

The Five-hundred-meter Aperture Spherical radio Telescope （FAST） adopts an active deformable main reflector which is composed of 4450 triangular panels. During an observation, the illuminated area of the reflector is deformed into a 300-m diameter paraboloid and directed toward a source. To achieve accurate control of the reflector shape, positions of 2226 nodes distributed around the entire reflector must be measured with sufficient precision within a limited time, which is a challenging task because of the large scale. Measurement of the FAST reflector makes use of stations and node targets. However, in this case the effect of the atmosphere on measurement accuracy is a significant issue. This paper investigates a differen- tial correction method for total stations measurement of the FAST reflector. A multi-benchmark differential correction method, including a scheme for benchmark selection and weight assignment, is proposed. On- site evaluation experiments show there is an improvement of 70%-80% in measurement accuracy compared with the uncorrected measurement, verifying the effectiveness of the proposed method.

关键词： telescopes -- FAST -- measurement -- differential correction