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Avoided crossings between non-radial modes in low mass RGB stars

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Research in Astronomy and Astrophysics 2012年第12期12卷 1655-1665页

作者： Jun-Jun Guo1,2.3,yan Li1,2.and Xiang-Jun Lai1,2.1 National Astronomical Observatories/yunnan Observatory,chinese academy of sciences, kunming 650011,{2. 2.Key laboratory for the structure and evolution of celestial objects,chinese academy of sciences,kunming 650011,china 3 graduate university of chinese academy of sciences,beijing 100049,{2. National Astronomical Observatories/yunnan Observatory Chinese Academy of Sciences Kunming 650011 China Key laboratory for the structure and {2. of celestial objects Chinese Academy of Sciences Kunming 650011 China graduate university of {2. Beijing 100049 China

Non-radial p modes and g modes appear simultaneously in red giant stars. Their frequencies have different variation rates,causing their frequencies to become close during stellar evolution so that avoided crossings *** separation between regions where acoustic waves and gravity waves propagate for l=1,2.and 3 is different,which results in the coupling efficiency also being *** present the results of numerical computations of the models we *** find that the two kinds of modes for l=2.and 3 need to be closer in frequency in order for a complete exchange to occur,compared to the case for modes with l=*** scaled oscillation frequencies also present better regularity with evolution than modes with l=1. In order to study the effect of the avoided crossings in detail,we set the mode which has the smallest mode inertia to be the p *** plot the two kinds of modes for l =1,2.and 3 in frequency and periodéchelle diagrams and find modes of l=2.and 3 fit the two relations better;they are more equally spaced in frequency and period than modes with l=*** careful observation of the two kinds oféchelle diagrams for l=2.and 3,we still find that some p modes shift a little from being equally spaced in frequency and some g modes,which are close to those p modes in period,shift a little from being equally spaced in ***,we study the relation between the deviation from period being equally spaced and the mode inertia of g modes for different *** g modes of l=1 with a period closer to the p mode have less inertia and the deviation is bigger in the periodéchelle *** deviation is also obvious. However g modes of l=2.and 3 shift a little or have almost no deviation from being equally spaced in period,even though some of them may have strong coupling and close mode inertia like in the p ***,we suggest a possible method for measuring period spacing of g modes precisely using mixed g modes with l=2.and 3 that have fewer observed mixed g m

关键词： stars:oscillations-stars:red giants

Birthrates and delay times of Type Ia supernovae

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Science china(Physics,Mechanics & Astronomy) 2010年第3期53卷 586-590页

作者： WANG Bo1,2.3, LIU ZhengWei1,2.3, HAN yunKun1,2.3, LEI ZhenXin1,2.3, LUO yangPing1,2.3 & HAN ZhanWen1,2.1National Astronomical Observatories/yunnan Observatory, chinese academy of sciences, kunming 650011, {2. 2.ey laboratory for the structure and evolution of celestial objects, chinese academy of sciences, kunming 650011, {2. 3graduate {12. of chinese academy of sciences, beijing 100049, {2. National Astronomical Observatories/yunnan Observatory Chinese Academy of Sciences Kunming China Key laboratory for the structure and {2. of celestial objects Chinese Academy of Sciences Kunming China graduate university of {2. Beijing China

Type Ia supernovae (SNe Ia) play an important role in diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology. However, the nature of the progenitors of SNe Ia is still unclear. In this paper, according to a detailed binary population synthesis study, we obtained SN Ia birthrates and delay times from different progenitor models, and compared them with observations. We find that the Galactic SN Ia birthrate from the double-degenerate (DD) model is close to those inferred from observations, while the birthrate from the single-degenerate (SD) model accounts for only about 1/2.2.3 of the observations. If a single starburst is assumed, the distribution of the delay times of SNe Ia from the SD model is a weak bimodality, where the WD + He channel contributes to the SNe Ia with delay times shorter than 100 Myr, and the WD + MS and WD + RG channels to those with age longer than 1 Gyr.

关键词： binaries: close stars: evolution supernovae: general white dwarfs

A statistical study of the relation between soft X-ray excess and accretion disk

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Science china(Physics,Mechanics & Astronomy) 2010年第S1期53卷 102-105页

作者： LIU Jieying1,2.3 & QIAO ErLin1,2.1 National Astronomical Observatories/yunnan Observatory,chinese academy of Science,{2.,china 2.Key laboratory for the structure and evolution of celestial objects,chinese academy of sciences,{2.,china 3 {12. university of chinese academy of sciences,beijing 100049,china National Astronomical Observatories/yunnan Observatory Chinese Academy of Science Kunming China Key laboratory for the structure and {2. of celestial objects Chinese Academy of Sciences Kunming China graduate university of {2. Beijing China

To study the origin of the soft X-ray excess,we compile a sample of 94 unobscured,radio-quiet QSOs and Seyfert galaxies with available data from GALEX and *** find that 50 sources show strong soft X-ray excess and the other 44 show weak/no soft X-ray *** analyses of the data indicate that the difference in soft X-rays is mainly but not only resulting from different accretion rates(in units of Eddington rate).The statistical study of the sources with soft X-ray excess shows that the strength of soft X-ray excess weakly and positively correlates with the Eddington ratio and increases with the increase of the strength of UV radiations relative to the *** that the UV emissions are from the thin disk,the correlations imply that the origin of soft X-ray excess is associated with the thin disk,either by means of Comptonization of the disk photons or in some other ways.

关键词： accretion:accretion disks ultraviolet:galaxies X-rays:galaxies

Genetic structure and phylogeography of a relict tree fern,Sphaeropteris brunoniana (Cyatheaceae) from china and Laos inferred from cpDNA sequence variations:Implications for conservation

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Journal of Systematics and evolution 2011年第1期49卷 72-79页

作者： 1,2.Zi-Juan WANG 1 Kai-yun GUAN 1 (kunming Institute of Botany, chinese academy of sciences, kunming 6502.4, china) 2.(graduate university of chinese academy of sciences, beijing 100049, china) (kunming Institute of Botany Chinese Academy of Sciences Kunming 650204 China) (graduate university of {2. Beijing 100049 China)

In this study, we analyzed the genetic structure and phylogeography of Sphaeropteris brunoniana from china and Laos. Combining cpDNA trnL-trnF and atpB-rbcL sequence variations, five haplotypes were identi- fied from the 10 investigated populations. Moderate haplotype diversity (h = 0.66580) and low nucleotide diver- sity (π = 0.2. × 10 ?3 ) were detected. The S. brunoniana in yunnan region had much higher genetic diversity (h = 0.60195, π = 0.35 × 10 ?3 ) than that of Hainan–Laos (h = 0.00000, π = 0.00). A high level of genetic differentiation (94.74%) between the two regions was revealed by AMOVA. Nested clade analysis identified two major clusters of the five haplotypes, one clade in the yunnan region and the other in Hainan–Laos. The analysis indicated that restricted gene flow with isolation by distance and allopatric fragmentation were likely the major processes that shaped the spatial distribution of the haplotypes. The isolated distribution of clades implied the emergence of independent refugia of this species in each region during Quaternary glaciations. The yunnan populations frequently contained an ancestral haplotype, and most of them harbored other descendent haplotypes. Based on the distribution pattern of haplotypes and the nested clade analysis results, the yunnan region potentially had several refugia of this species during glacial periods, whereas the Hainan populations were probable new colonizations.

关键词： atpB-rbcL Hainan–Laos phylogeography Sphaeropteris brunoniana trnL-trnF yunnan.

Ionization state of cosmic hydrogen by early stars and quasars

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Research in Astronomy and Astrophysics 2009年第6期9卷 665-681页

作者： Xiao-Chun Mao1,2.1 National Astronomical Observatories, chinese academy of sciences, beijing 100012. {2. 2.graduate university of chinese academy of sciences, beijing 100049, {2. National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China graduate university of {2. Beijing 100049 China

Cosmic hydrogen is reionized and maintained in its highly ionized state by the ultraviolet emission attributed to an early generation of stars and quasars. The Lyα opacity observed in absorption spectra of high-redshift quasars permits more stringent constraints on the ionization state of cosmic hydrogen. Based on density perturbation and structure formation theory, we develop an analytic model to trace the evolution of the ionization state in the post-overlap epoch of reionization, in which the bias factor is taken into account. For quasars, we represent an improved luminosity function by utilizing a hybrid approach for the halo formation rate that is in reasonable agreement with the published measurements at 2.≤ z ≤ 6. Comparison with the classic Press-Schechter mass function of dark matter halos, we demonstrate that the biased mass distribution indeed enhances star formation efficiency in the overdense environment by more than 2. per cent following the overlap of ionized bubbles. In addition, an alternative way is introduced to derive robust estimates of the mean free path for ionizing photons. In our model, star-forming galaxies are likely to dominate the ionizing background radiation beyond z = 3, and quasars contribute equally above a redshift of z ～ 2.5. From 5 ≤ z ≤ 6, the lack of evolution in photoionization rate can thus be explained by the relatively flat evolution in star formation efficiency, although the mean free path of ionizing photons increases rapidly. Moreover, in the redshift interval z ～ 2.- 6, the expected mean free path and Gunn-Peterson optical depth obviously evolve by a factor of ～ 500 and ～50 respectively. We find that the relative values of critical overdensities for hydrogen ionization and collapse could be 430% at z ≈2.and 2. at z ≈6, suggesting a rapid overlap process in the overdense regions around instant quasars following reionization. We further illustrate that the absolute estimates of the fraction of neutral hydrogen computed fr

关键词： cosmology theory -- formation galaxies -- quasars general -- diffuse radiation -- intergalactic medium

Multi-epoch X-ray observations of the narrow-line Seyfert 1 galaxy SDSS J160508.87+32.92..4 with XMM-Newton

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Science china(Physics,Mechanics & Astronomy) 2010年第S1期53卷 207-211页

作者： AI yanLi1,2.3,yUAN WeiMin1,2.ZHOU Hongyan4,5 & WANG JianGuo1,2.3 1 National Astronomical Observatories/yunnan Observatory,chinese academy of sciences,kunming 650011,{2. 2.Key laboratory for the structure and evolution of celestial objects,chinese academy of sciences,kunming 650011,{2. 3 graduate {12. of the chinese academy of sciences,beijing 100049,{2. 4 Center for Astrophysics,{12. of Science and Technology of {2.,Hefei 2.002.,{2. 5 Joint Institute of Galaxies and Cosmology,SHAO and USTC,Shanghai 2.0030,{2. National Astronomical Observatories/yunnan Observatory Chinese Academy of Sciences Kunming China Key laboratory for the structure and {2. of celestial objects Chinese Academy of Sciences Kunming China graduate university of the {2. Beijing China Center for Astrophysics University of Science and Technology of China Hefei China Joint Institute of Galaxies and Cosmology SHAO and USTC Shanghai China

We present results of multi-epoch XMM-Newton observations separated by several years of the narrow-line Seyfert 1(NLS1) galaxy,SDSS J160508.87+*** NLS1 showed X-ray flux variations on timescales of years as well as low amplitude variations on timescales as short as hours,while the X-ray spectral shape remained essentially *** spectrum shows a significant soft X-ray *** model of reflection from an ionized disc,that is dominant in the whole XMM-Newton bandpass,provides the best description of the observed spectra for all the observations,though alternatives such as Compton scattering(T-0.2. keV) cannot be ruled out in a statistical *** the disc reflection model,the observed variations may originate either from the change in the reflection fraction,or from the variability of the intrinsic X-ray luminosity.

关键词： galaxies:active Seyfert X-rays individual

The deep thermal characteristic of continental margin of the northern South china Sea

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chinese Science Bulletin 2000年第18期45卷 1717-1722页

作者： ZHANG Jian & WANG Jiyang1. graduate School, university of Science and Technology of {2., chinese academy of sciences, beijing 100039, {2. 2. Institute of Geology, chinese academy of sciences, beijing 10002., {2. graduate School University of Science and Technology of China Chinese Academy of Sciences Beijing China Institute of Geology Chinese Academy of Sciences Beijing China

Heat flow plays an important role in the study ot thermal structure and thermal evolutionof continental margin of the northern South {2. Sea. The analysis of heat flow value shows that margin heat flow in the northern South {2. Sea is relatively high setting, but the percentage of crustal heat flow is lower than 35% in terrestrial heat flow. The terrestrial heat flow exhibited a current of rise from the Northern Continental Margin to the Southern Central Basin. However, the proportion of crustal heat flow in terrestrial heat flow slowly dropped down in the same direction. It is suggested that the main factor causing high heat flow setting is the moving up of hot material from asthenosphere.

关键词： margin of northern South china Sea terrestrial heat flow thermal structures.

Anatomy and ontogeny of unisexual flowers in dioecious Woonyoungia septentrionalis (Dandy) Law (Magnoliaceae)

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Journal of Systematics and evolution 2009年第4期47卷 263-272页

作者： ~(1,2.Lin FU ~1Qing-Wen ZENG ~1Jing-Ping LIAO ~1Feng-Xia XU~* 1(South china Botanical Garden,chinese academy of sciences,Guangzhou 510650,china) 2.graduate university of chinese academy of sciences,beijing 100049,china) (South china Botanical Garden Chinese Academy of Sciences Guangzhou 510650 China) (graduate university of {2. Beijing 100049 China)

Woonyoungia septentrionalis(Dandy)Law is a dioecious species with unisexual flowers in Magnoliaceae. The floral morphology and structure of the species are conspicuously different from other species and are important to the study of floral phylogeny in this *** floral anatomy and ontogeny were investigated to evaluate the systematic position of ***,using scanning electron microscopy and light microscopy. All of the floral organs are initiated acropetally and *** carpels are of conduplicated type without the differentiation of stigma and *** degenerated stamens in the female flowers have the same structures as the normal stamens at the earlier developmental stages,but they do not undergo successive development and eventually *** male floral apex was observed to have the remnants of carpels in a few investigated *** the bisexual flower features could be traced both in the male and female flowers in ***,it suggests that the flower sex in Magnoliaceae tends toward *** well as the unisexual flowers,the reduced tepals and carpels and concrescence of carpels conform to the specialized tendency in Magnoliaceae,which confirms the derived position of *** in this *** the initiation pattern of floral parts of *** is very similar to other species in this family,it needs further investigation and especially comparison with species in Kmeria to evaluate the separation of Woonyoungia.

关键词： floral anatomy Magnoliaceae ontogeny Woonyoungia septentrionalis(Dandy)Law.

Genetic differentiation of Wolffia globosa in china

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Journal of Systematics and evolution 2011年第6期49卷 509-517页

作者： 1,2.un-Xia yUAN 1Jin PAN 1Bao-Sheng WANG 1Da-Ming ZHANG 1(State Key laboratory of Systematic and evolutionary Botany,Institute of Botany,{2.,beijing 100093,china) 2.graduate university of {2.,beijing 100049,china) (State Key laboratory of Systematic and evolutionary Botany Institute of Botany Chinese Academy of Sciences Beijing 100093 China) (graduate university of {2. Beijing 100049 China)

Wolffia Horkel ex Schleid.(Lemnaceae) includes the world’s smallest ***,their bodies are extremely simplified,making classification difficult and *** reports about the genetic structure of these clonal-dominant aquatic plants have been published until *** this study,of 2.7 samples from 42.populations spanning representative locations in china,two chloroplast haplotypes(glo-cp and un-cp) and 66 amplified fragment length polymorphism genotypes were *** on wide sampling,cpDNA haplotypes,and amplified fragment length polymorphism profiles,we found that there are two genetic lineages(glo-and unlineages) of Wolffia species in *** and genetic diversity of Wolffia species are high compared with other clonal plants(Simpson’s index,D = 0.97;Nei’s diversity,H = 0.1835).Different spatial structure patterns were detected between glo-and *** autocorrelation at short distances(y negative autocorrelations at larger distances(>1500 km) were detected within the glo-lineage,but no significant spatial genetic structure was detected beyond 100 km within the ***,spatial genetic analysis of *** revealed significant autocorrelation within short distances,indicating that restricted gene flow might be one of the most important factors in shaping genetic structure.

关键词： AFLP chloroplast DNA genetic differentiation spatial genetic structure Wolffia.