分类： 天文学 >> 天文学 提交时间： 2023-02-19
Li-Li Wang
Shi-Yin Shen
A-Li Luo
Guang-Jun Yang
Ning Gai
Yan-Ke Tang
Meng-Xin Wang
Li Qin
Jin-Shu Han
Li-Xia Rong
摘要： We firstly derive the stellar population properties: age and metallicity for $\sim$ 43,000 low redshift galaxies in the seventh data release (DR7) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey, which have no spectroscopic observations in the Sloan Digital Sky Survey(SDSS). We employ a fitting procedure based on the small-scale features of galaxy spectra so as to avoid possible biases from the uncertain flux calibration of the LAMOST spectroscopy. We show that our algorithm can successfully recover the average age and metallicity of the stellar populations of galaxies down to signal-to-noise$\geq$5 through testing on both mock galaxies and real galaxies comprising LAMOST and their SDSS counterparts. We provide a catalogue of the age and metallicity for $\sim$ 43,000 LAMOST galaxies online. As a demonstration of the scientific application of this catalogue, we present the Holmberg effect on both age and metallicity of a sample of galaxies in galaxy pairs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yan Lu
A-Li Luo
Li-Li Wang
Li Qin
Rui Wang
Xiang-Lei Chen
Bing Du
Fang Zuo
Wen Hou
Jian-Jun Chen
Yan-Ke Tang
Jin-Shu Han
Yong-Heng Zhao
摘要： To study the quality of stellar spectra of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and the correctness of the corresponding stellar parameters derived by the LASP (LAMOST Stellar Parameter Pipeline), the outlier analysis method is applied to the archived AFGK stars in the fifth data release (DR5) of LAMOST. The outlier factor is defined in order to sort more than 3 million stellar spectra selected from the DR5 Stellar Parameter catalog. We propose an improved Local Outlier Factor (LOF) method based on Principal Component Analysis and Monte Carlo to enable the computation of the LOF rankings for randomly picked sub-samples that are computed in parallel by multiple computers, and finally to obtain the outlier ranking of each spectrum in the entire dataset. Totally 3,627 most outlier ranked spectra, around one-thousandth of all spectra, are selected and clustered into 10 groups, and the parameter density distribution of them conforms to the parameter distribution of LAMOST DR5, which suggests that in the whole parameter space the probability of bad spectra is uniformly distributed. By cross-matching the 3,627 spectra with APOGEE, we obtain 122 common ones. The published parameters calculated from LASP agree with APOGEE for the 122 spectra although there are bad pixels or bad flux calibrations in them. On the other hand, some outlier spectra show strong nebular contamination warning the corresponding parameters should be carefully used. A catalog and a spectral atlas of all the 3,627 outliers can be found at the link http://paperdata.china-vo.org/LY_paper/dr5Outlier/dr5Outlier_resource.zip.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Li Qin
A-Li Luo
Wen Hou
Yin-Bi Li
Kai-Ming Cui
Fang Zuo
Shuo Zhang
Rui Wang
Jin-Shu Han
Li-Li Wang
Yan Lu
Xiang-Lei Chen
摘要： Rotation is a critical physical process operating in the formation of Am stars. There is a strong correlation between low-velocity rotation and chemical peculiarity. However, the existence of many non-CP slow rotators challenges the understanding of Am stars. The purpose of our work is to search for low-velocity rotating non-CP A-type stars and Am stars and to make a comparative analysis. In this paper, we pick out a sample from the LAMOST-Kepler project, including 21 Am stars, 125 non-CP slow rotators, and 53 non-CP fast rotators. We calculate the rotational frequencies through periodic change of light curves caused by inhomogeneous stellar surfaces and then obtain the rotational velocities. For slow rotators, the age of Am stars is statistically younger than that of non-CP stars in the same temperature bin. In the comparison of the period, the average amplitude, and stellar mass of Am and non-CP stars, we discover that there is no difference in the photometric variability between Am and non-CP stars, which implies similar inhomogeneities on the surfaces. The average amplitude of non-CP stars has a downward trend with the increase of effective temperature and stellar mass, which is consistent with the theoretical prediction caused by weak dynamo-generated magnetic fields in A-type stars. In addition, we confirm four non-non-CP stars which have flares by checking FOV images, 24 pixel images, and pixel-level light curves.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We derive a catalog of early-type emission-line stars including 30,048 spectra of 25,886 stars from LAMOST DR7, in which 3,922 have Simbad records. The sample is obtained using K-Nearest Neighbor and Random Forest methods and visually inspected. The spectra are classified into 3 morphological types (10 subtypes) based on H$\alpha$ emission line profiles. Some spectra contaminated by nebula emission lines such as from HII regions are flagged in the catalog. We also provide a specific sub-catalog of 101 stars with the stellar wind by calculating stellar wind or accretion flow velocities based on P Cygni or inverse P Cygni profiles, in which 74\% of them having velocities below 400km/s. More important, with two color-color diagrams (H-K, K- W1) and (H-K, J-H) of a collection of known Herbig Ae/Be stars (HAeBes) and classical Ae/Be stars (CAeBes), we propose an updated criterion to separate HAeBes from CAeBes. By the criterion, we select 201 HAeBes candidates and 5,547 CAeBes candidates from the sample. We confirmed 66 of the 201 HAeBes by using both WISE images and LAMOST spectra and present a specific HAeBe sub-catalog, in which 58 are newly identified. In addition, the WISE colors (W1-W2, W1- W3, and W1-W4) show the distribution consistency between our confirmed HAeBes and that of the known HAeBes. Most of the 66 confirmed HAeBes locate in the lower edge of the main sequence of hot end in the HR diagram, while the distances of about 77\% exceed 1Kpc, which enlarges the number of far distant known HAeBes.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： In this paper, we propose a MIM (metallic metasurface-insulator-metal) stacked structure to realize perfect absorption in mid- and far- infrared bandwidth. A large number of metallic composite metallic units placed on a uniform layer of insulator Ge which is deposited on a uniform metallic Ti surface. Each of units consists of four right-angled triangular cubes in middle of four sides of a square. Three resonant absorption peaks can be discrete or levelling dependent to thickness of cubes. Once metallic cubes are thinner than its skin depth, an effective ultra-broadband absorber is realizable with average absorption over 90% percent ranging from 8-14{\mu}m. We build a four-level cavity-dipole interacting model to explain phenomena of plasma absorption levelling. This is created by strong phase coherence from meta-surface since three hybrid modes are coupled by common cavity photons in arrays of micro-cavities between top and below metallic layers. The structure is polarization-selective to infrared light. It has great potential in infrared detection and imaging.
分类： 生物学 >> 生物医药 提交时间： 2017-05-10
摘要： The synergy of the activities between chloroquine and various human immunodeficiency virus protease inhibitors was investigated in chloroquine-resistant and -sensitive malaria parasites. In both in vitro and in vivo assay systems, ritonavir was found to be the most potent in potentiating the antimalarial action of chloroquine.
分类： 生物学 >> 生物医药 提交时间： 2017-05-10
摘要： Signal transducer and activator of transcription (STAT) proteins play an important role in cytokine signaling pathways and regulation of immune responses. The balance of the phosphorylated (activated) STAT1 (pSTAT1) and STAT3 (pSTAT3) has been documented in cancer immunology. In this study, we investigated the dynamic balance of pSTAT1 and pSTAT3 in C57BL/6 mice infected with either a nonlethal (Py17XNL) or lethal (Py17XL) strain of Plasmodium yoelii. Both Py17XNL and Py17XL infections induced a maximum activation of STAT1 and STAT3 on the first day after parasite inoculation. Additionally, the Py17XNL infection induced a pSTAT1-dominant response in mice during the early stage of infection, with the resolution of parasitemia. In contrast, Py17XL infection induced a pSTAT3-dominant response during the early phase of infection, with the death of the animals. Our results indicated that maximum activation of STAT1 and STAT3 occurred much earlier than the peak levels of cytokines induced by Plasmodium yoelii infection based on previous reports and that infection with Py17XNL and Py17XL induced different dynamic patterns of pSTAT1 and pSTAT3 balance. Cellular & Molecular Immunology
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