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Gaia calibrated UV luminous stars in LAMOST

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Research in Astronomy and Astrophysics 2018年第12期18卷 123-130页

作者： Yu Bai ji-feng liu Song Wang Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences College of Astronomy and Space Sciences University of Chinese Academy of Sciences

We take advantage of Gaia Data Release 2 to present 275 and 1774 ultraviolet luminous stars in the far ultraviolet(FUV) and near ultraviolet(NUV), *** stars exceed their expected values by 5σ with respect to over one million ultraviolet stars in the log g *** extinction is corrected with a 3 D dust *** order to limit the Lutz-Kelker bias to an insignificant level, we select stars with relative uncertainties in luminosity less than 40% and trigonometric parallaxes less than 20%.We cross-identified our sample with the catalogs of RR Lyr stars and possible white dwarf main-sequence binaries, and find they compose ～62% and ～16% of our sample in the FUV and NUV, *** catalog provides a unique sample to study stellar activity, spectrally unresolved compact main-sequence binaries and variable stars.

关键词： stars:activity stars:general ultraviolet:stars

Sharp Chandra View of ROSAT All-Sky Survey Bright Sources I. Improvement of Positional Accuracy

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Research in Astronomy and Astrophysics 2016年第12期16卷 67-74页

作者： Shuang Gao Song Wang ji-feng liu Department of Astronomy Beijing Normal University Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences College of Astronomy and Space Sciences University of Chinese Academy of Sciences

The ROSAT All-Sky Survey （RASS） represents one of the most complete and sensitive soft X- ray all-sky surveys to date. However, the deficient positional accuracy of the RASS Bright Source Catalog （BSC） and subsequent lack of firm optical identifications affect multi-wavelength studies of X-ray sources. The widely used positional errors σpos based on the Tycho Reference Catalog （Tycho-1） have previously been applied for identifying objects in the optical band. The considerably sharper Chandra view covers a fraction of RASS sources, whose ~rpos could be improved by utilizing the sub-arcsec positional accuracy of Chandra observations. We cross-match X-ray objects between the BSC and Chandra sources extracted from the Advanced CCD Imaging Spectrometer （ACIS） archival observations. A combined list of counter- parts （BSCxACIS） with Chandra spatial positions weighted by the X-ray flux of multiple counterparts is employed to evaluate and improve the former identifications of BSC when used with other surveys. Based on these identification evaluations, we suggest that the point-source likeness of BSC sources and INS （iso- lated neutron star） candidates should be carefully reconsidered.

关键词： catalogs -- surveys -- X-rays: general -- X-rays: stars

Machine learning classification of Gaia Data Release 2

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Research in Astronomy and Astrophysics 2018年第10期18卷 1-4页

Machine learning has increasingly gained more popularity with its incredibly powerful ability to make predictions or calculate suggestions for large amounts of data. We apply machine learning clas-sification to 85 613 922 objects in the Gala Data Release 2, based on a combination of Pan-STARRS I and AI1WISE data. The classification results are cross-matched with the Simbad database, and the to-tal accuracy is 91.9%. Our sample is dominated by stars, ~98%, and galaxies make up 2%. For the objects with negative parallaxes, about 2.5% are galaxies and QSOs, while about 99.9% are stars if the relative parallax uncertainties are smaller than 0.2. Our result implies that using the threshold of 0 〈 σπ/π 〈 0.2 could yield a very clean stellar sample.

关键词： methods data analysis - stars general - Gaia catalog

An investigation of a magnetic cataclysmic variable with a period of 14.1 ks

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Research in Astronomy and Astrophysics 2017年第1期17卷 103-112页

作者： Song Wang Yu Bai Chuan-Peng Zhang ji-feng liu Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China College of Astronomy and Space Sciences University of Chinese Academy of Sciences Beijing 100049 China

Magnetic cataclysmic variables （CVs） contain a white dwarf （WD） with a magnetic field strong enough to control the accretion flow from a late type secondary. In this paper, we identify a magnetic CV （CXOGSG J215544.4＋380116） from the Chandra archive data. The X-ray light curves show a significant period of 14.1 ks, and the X-ray spectra can be described by a multi-temperature hot thermal plasma, suggesting the source is a magnetic CV. The broad dip in the X-ray light curve is due to the eclipse of the primary magnetic pole, and the additional dip in the bright phase of the soft and medium bands may be caused by the accretion stream crossing our line of sight to the primary pole. Follow-up optical spectra show features of an M2-M4 dwarf dominating the red band and a WD which is responsible for the weak upturn in the blue band. The mass （~ 0.4 34⊙） and radius （~0.4 R⊙） for the M dwarf are obtained using CV evolution models and empirical relations between the orbital period and the mass/radius. The estimated low X-ray luminosity and accretion rate may suggest the source is a low-accretion-rate polar. In addition, Very Large Array observations reveal a possible radio counterpart to the X-ray source, but with a low significance. Further radio observations with high quality are needed to confirm the radio counterpart and explore the properties of this binary system.

关键词： novae, cataclysmic variables - stars late-type - stars magnetic field

An active M star with X-ray double flares disguised as an ultra-luminous X-ray source

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Research in Astronomy and Astrophysics 2016年第2期16卷 119-126页

作者： jin-Cheng Guo ji-feng liu Song Wang Yue Wu Yu-Xiang Qin Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China University of Chinese Academy of Sciences Beijing 100049China School of Physics The University of MelbourneParkvilleVictoria 3010Australia

Here we present research on an ultra-luminous X-ray source （ULX） candidate 2XMM J 140229.91＋542118.8. The X-ray light curves of this ULX candidate in M 101 exhibit features of a flare star. More importantly, the Chandra light curve displays unusual X-ray double flares, which is comprised of two close peaks. The X-ray （0.3-11.0 keV） flux of the first peak was derived from the two-temperature APEC model as ～ 1.1 ±0.1× 10-12 ergcm-2 s-1. The observed flux at its first peak increased by about two orders of magnitude in X-ray as compared to quiescence. The slope of the second fast decay phase is steeper than the slope of the first fast decay phase, indicating that the appearance of a second flare accelerated the cooling of the first flare in a way we do not understand yet. We also observed its optical counterpart using a 2.16 m telescope administered by National Astronomical Observatories, Chinese Academy of Sciences. By optical spectral fitting, it is confirmed to be a late type dMe2.5 star. According to the spectral type and apparent magnitude of its optical counterpart, we estimate the photometric distance to be ～ 133.4 ±14.2 pc. According to the X-ray spectral fitting, a possible explanation is provided. However, more similar close double flares are needed to confirm whether this accelerated cooling event is a unique coincidence or a common physical process during double flaring.

关键词： stars flare -- X-ray stars -- galaxies individual (M101)

Three X-ray flares near primary eclipse of the RS CVn binary XY UMa

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Research in Astronomy and Astrophysics 2016年第8期16卷 127-134页

作者： Hang Gong Rachel Osten Thomas Maccarone Fabio Reale ji-feng liu Paul A. Heckert Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Space Telescope Science Institute 3700 San Martin Drive Baltimore MD 21218 USA Center for Astrophysical Sciences Johns Hopkins University Baltimore MD 21218 USA Department of Physics Texas Tech University Lubbock TX 79409 USA Dipartimento di Fisica e Chimica Universita di Palermo Piazza del Parlamento 1 90134 Palermo Italy INAF/Osservatorio Astronomico di Palermo Piazza del Parlamento 1 90134 Palermo Italy College of Astronomy and Space Science University of Chinese Academy of Sciences Beijing 100049 China department of chemistry and physics western carolina university，Cullowhee，NC 28723，USA

We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa （Porb≈0.48 d）. In two Chandra ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no evidence for eclipses in the X-ray flux. The flares took place around times of primary eclipse, with one flare occurring shortly （〈 0.125 Porb） after a primary eclipse, and the other two happening shortly （〈 0.05/9orb） before a primary eclipse. Two flares occurred within roughly one orbital period （△Ф≈ 1.024 Porb） of each other. We analyze the light curve and spectra of the system, and investigate coronal length scales during both quiescence and flares, as well as the timing of the flares. We explore the possibility that the flares are orbit-induced by introducing a small orbital eccentricity, which is quite challenging for this close binary.

关键词： stars binaries -- stars flare -- stars activity -- X-rays stars

Synthesis and Biological Activities of Novel Anthranilic Diamides Analogues Containing Benzo[b]thiophene

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Chemical Research in Chinese Universities 2013年第4期29卷 714-720页

作者： ZHANG ji-feng liu Chen liu Peng-fei YAN Tao WANG Bao-lei XIONG Li-xia LI Zheng-ming State Key Laboratory of Elemento-Organic Chemistry Institute of Elemento-Organic Chemistry Nankai University Tianjin 300071 P.. R. China

A series of novel anthranilic diamides analogues containing benzo[b]thiophenyl ring was designed and synthesized. Their structures were characterized by melting points, 1H nuclear magnetic resonance（IH NMR） and high-resolution mass spectrometry（HRMS）. The bioassay tests indicate that their insecticidal activities were weak to moderate. Antibacterial tests indicate that some of the compounds showed favourable activity in vitro against Physa- lospora piricola, Alternaria solani, Cercospora arachidicola, Gibberella sanbinetti and Phytophthora infestans at a dosage of 50 mg/L.

关键词： Anthranilic diamide Benzo[b]thiophene Insecticidal activity Antibacterial activity

Stellar activity cycles as revealed by long-term beat-like patterns from light curves of Kepler

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Research in Astronomy and Astrophysics 2021年第6期21卷 301-313页

作者： Heng-Geng Han Kai-Ming Cui ji-feng liu Hui-Qin Yang Xuan Fang Rui-Ning Zhao CAS Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China School of Astronomy and Space Sciences University of Chinese Academy of SciencesBeijing 100049China WHU-NAOC Joint Center for Astronomy Wuhan UniversityWuhan 430072China Department of Physics&Laboratory for Space Research Faculty of Sciencethe University of Hong KongHong KongChina

Stellar activity cycles have been found on many stars through different *** in debate,an empirical relation has been found where a period of stellar activity cycle Pcyc is positively correlated with rotation period Prot along some segregated *** this work,we built a systematic process to search for the Kepler objects that are analogous to the long-term solar brightness variations and investigate their possible *** a rigorous selection,we obtained 43 objects that all exhibit clear long-term beat-like patterns and their variability(amplitude of rotational modulation)periods and rotation periods were *** to the 4-year duration of the Kepler mission,our targets are located in the region where the cycle periods are longer than~1 yr and shorter than~2.5 ***,all of our targets exhibit clear and notable quasi-periodic variations in variability,yet we cannot confirm any linear trends that were predicted by previous research *** may suggest that in the Kepler realm of the Pcyc-Prot diagram,these relations would mix with each other or the beat-like patterns may not be related to the stellar cycle unless other evidence is provided.

关键词： stars:activity starspots stars:rotation

Epidemiological Investigation of Human Papillomavirus Infection in Men Attending a Sexually Transmitted Disease Clinic in Hangzhou Area

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Biomedical and Environmental Sciences 2006年第2期19卷 153-157页

作者： XU TANG AI-E XU XIAO-PING DONG XIU-KUN SUN HONG SHEN ji-feng liu Department of Dermatology the 3rd Hospital of Hangzhou Hangzhou 310009 Zhejiang China Prion s Laboratory National Institute for Viral Disease Control and Prevention Chinese Center for Disease Control and Prevention Beijing 100052 China

Objective To investigate the epidemiological characteristics of human papillomavirus （HPV） infection in men attending a sexually transmitted diseases （STD） clinic in Hangzhou area. Methods Male subjects （n=375） aged 18-70 years, attending the STD clinic were recruited. Urethral swabs were assessed for HPV DNA using polymerase chain reaction （PCR） with the consensus primers MY09/11. HPV genotypes of positive PCR products were determined by restriction fragment length polymorphisms and direct sequence analysis. Results Of the 375 swabs collected, 305 （81.3%） yielded sufficient DNA for the subsequent HPV analysis. Among the 305 subjects, the prevalence of HPV was 13.8%. Nononcogenic HPV types were found in 8.5% （26/305） of subjects, oncogenic types in 4.3% （13/305）, and multiple types in 1.0% （3/305）. The prevalence of HPV infection was higher in subjects from urban area than in those from rural area （P〈0.05）. The prevalence was also higher in those who received fewer years of education （P〈0.05） and those who had more sex partners （P〈0.05）. Conclusions HPV infection among men at high risk is not uncommon. The detection rate of HPV DNA is significantly related to some sociodemographic factors, such as residence, educational level and the number of sex partners.

关键词： Human papillomavirus Men Sexually transmitted diseases