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LAMOST Time-Domain survey:first results of four K2 plates

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Research in Astronomy and Astrophysics 2021年第11期21卷 213-232页

作者： Song Wang Hao-Tong Zhang Zhong-Rui Bai Hai-Long Yuan Mao-Sheng Xiang Bo Zhang Wen Hou Fang Zuo Bing Du Tan-Da Li Fan Yang Kai-Ming Cui Yi-Lun Wang Jiao Li Mikhail Kovalev Chun-Qian Li Hao Tian Wei-Kai Zong Heng-Geng Han Chao Liu A-Li Luo Jian-Rong Shi Jian-Ning Fu Shao-Lan Bi Zhan-Wen Han Ji-Feng Liu Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Max-Planck Institute for Astronomy Konigstuhl 17D-69117 HeidelbergGermany Department of Astronomy Beijing Normal UniversityBeijing 100875China School of Physics and Astronomy University of BirminghamBirmingham B152TTUK Stellar Astrophysics Centre Department of Physics and AstronomyAarhus UniversityNy Munkegade 120DK-8000 Aarhus CDenmark College of Astronomy and Space Sciences University of Chinese Academy of SciencesBeijing 100049China Yunnan Astronomical Observatory Chinese Academy of SciencesKunming 650216China Key Lab of Space Astronomy and Technology National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China WHU-NAOC Joint Center for Astronomy Wuhan UniversityWuhan 430072China

From Oct.2019 to Apr.2020,LAMOST performed a time-domain(TD)spectroscopic survey of four K2 plates with both low-and medium-resolution observations.The low-resolution spectroscopic survey acquired 282 exposures(≈46.6 h)over 25 nights,yielding a total of about 767000 spectra,and the medium-resolution survey took 177 exposures(≈49.1 h)over 27 nights,collecting about 478000 spectra.More than 70%/50%of low-resolution/medium-resolution spectra have signal-to-noise ratio higher than 10.We determine stellar parameters(e.g.,Teff,log g,[Fe/H])and radial velocity(RV)with different methods,including LASP,DD-Payne and SLAM.In general,these parameter estimations from different methods show good agreement,and the stellar parameter values are consistent with those of APOGEE.We use the Gaia DR2 RV values to calculate a median RV zero point(RVZP)for each spectrograph exposure by exposure,and the RVZP-corrected RVs agree well with the APOGEE data.The stellar evolutionary and spectroscopic masses are estimated based on the stellar parameters,multi-band magnitudes,distances and extinction values.Finally,we construct a binary catalog including about 2700 candidates by analyzing their light curves,fitting the RV data,calculating the binarity parameters from medium-resolution spectra and cross-matching the spatially resolved binary catalog from Gaia EDR3.The LAMOST TD survey is expected to represent a breakthrough in various scientific topics,such as binary systems,stellar activity,stellar pulsation,etc.

关键词： astronomical database:miscellaneous catalogs stars:fundamental parameters binaries:general binaries:spectroscopic

The fractions of post-binary-interaction stars and evolved blue straggler stars on the red giant branch of globular clusters

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Research in Astronomy and Astrophysics 2021年第9期21卷 101-110页

作者： Dan-Dan Wei Bo Wang Hai-Liang Chen Hai-Feng Wang Xiao-Bo Gong Dong-Dong Liu Deng-Kai Jiang Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of ScienceKunming 650216China University of Chinese Academy of Science Beijing 100049China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China South-Western Institute for Astronomy Research Yunnan UniversityKunming 650500China LAMOST

The red giant branch(RGB)of globular clusters(GCs)is home to some exotic stars,which may provide clues on the formation of multiple stellar populations in GCs.It is well known that binary interactions are responsible for many exotic stars.Thus,it is important to understand what fraction of stars on the RGB of GCs is the result of binary interactions.In this paper,we performed a binary population synthesis study to track the number of post-binary-interaction(post-BI)stars that appear on the RGB,with particular emphasis on the evolved blue straggler stars(E-BSSs).Assuming an initial binary fraction of nearly 50%,we find that about half of the objects on the RGB(called giants)underwent the binary interactions,and that E-BSSs account for around 10%of the giants in our standard simulation.We also compare the properties of post-BI giants that evolved from different channels.We find that the initial orbital period and mass ratio distributions significantly affect the fraction of post-BI giants.Our results imply that the non-standard stars from binary interactions provide a non-negligible contribution to the RGB stars in GCs,which should be considered in future investigations of the origin of multiple stellar populations.

关键词： blue stragglers stars:chemically peculiar globular clusters:general binaries:general

A diagnostic of the orbital spectrum of LS 5039 with Fermi-LAT

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Research in Astronomy and Astrophysics 2019年第12期19卷 281-286页

作者： Zhi Chang Shu Zhang Yu-Peng Chen Long Ji Ling-Da Kong Key Laboratory of Particle Astrophysics Institute of High Energy PhysicsChinese Academy of SciencesBejjing 100049China University of Chinese Academy of Sciences Beijing 100049China Institut fur Astronomie und Astrophysik Kepler Center for Astro and Particle PhysicsEberhard Karls UniversitatSand 172076 TibingenGermany

LS 5039 is a well-known γ-ray binary system which consists of an unknown compact object and a massive companion O star. It shows rather stable emissions at high energies over years and hence serves as an ideal laboratory to investigate the emission mechanism for such peculiar systems which emit prominent γ-rays. To this end, we take the orbital phase resolved energy spectrum as observed by Fermi-LAT over 10 years. We divide the orbit into four orbital phases, each with an orbital phase range of 0.25,centered at 0.00, 0.25, 0.50 and 0.75 respectively, where the phase 0.0 is the periastron and phase 0.5 is the apastron. The phases around 0.25 and 0.75 are symmetric and hence are supposed to have identical local acceleration environment. The spectral analysis shows that the Fermi-LAT spectra are largely different from these two symmetric orbital phases: the emission from orbital phase 0.25 turns out to be significantly stronger than that from 0.75. This result does not fit a scenario that γ-rays are Doppler boosted emission from bow shock tails if LS 5039 has a shock configuration similar to PSR B1259-63, and indicates that the inverse Compton scatterings between the shock accelerated plasma and the stellar particle environment is the underline procedure. We also find that the previous report for a disappearance of the orbital modulation at 3–20 GeV is due to the similar spectral turn-over energies of the different orbital phases. The spectral properties of periastron and apastron regions are addressed in the context of the measurements in phase regions around 0.25 and 0.75.

关键词： binaries:general gamma rays:general