排序方式： 共有116条查询结果，搜索用时 15 毫秒
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We derive the constraints on the mass ratio for a binary system to merge in a violent process. We find that the secondary-to-primary stellar mass ratio should be 0.003 ≲ ( M 2 / M 1 ) ≲ 0.15 . A more massive secondary star will keep the primary stellar envelope in synchronized rotation with the orbital motion until merger occurs. This implies a very small relative velocity between the secondary star and the primary stellar envelope at the moment of merger, and therefore very weak shock waves, and low-flash luminosity. A too low-mass secondary will release small amount of energy, and will expel small amount of mass, which is unable to form an inflated envelope. It can, however, produce a quite luminous but short flash when colliding with a low-mass main-sequence star.
Violent and luminous mergers, which we term mergebursts, can be observed as V838 Monocerotis-type events, where a star undergoes a fast brightening lasting days to months, with a peak luminosity of up to ∼106 L⊙ followed by a slow decline at very low effective temperatures. 相似文献
Violent and luminous mergers, which we term mergebursts, can be observed as V838 Monocerotis-type events, where a star undergoes a fast brightening lasting days to months, with a peak luminosity of up to ∼10
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Z. Fan J. Ma R. de Grijs Y. Yang X. Zhou 《Monthly notices of the Royal Astronomical Society》2006,371(4):1648-1658
The large majority of extragalactic star cluster studies performed to date essentially use multicolour photometry, combined with theoretical stellar synthesis models, to derive ages, masses, extinction estimates and metallicities. M31 offers a unique laboratory for studies of globular cluster (GC) systems. In this paper, we obtain new age estimates for 91 M31 GCs, based on improved photometric data, updated theoretical stellar synthesis models and sophisticated new fitting methods. In particular, we used photometric measurements from the Two Micron All Sky Survey (2MASS), which, in combination with optical photometry, can partially break the well-known age–metallicity degeneracy operating at ages in excess of a few Gyr. We show robustly that previous age determinations based on photometric data were affected significantly by this age–metallicity degeneracy. Except for one cluster, the ages of our other sample GCs are all older than 1 Gyr. Their age distribution shows populations of young- and intermediate-age GCs, peaking at ∼3 and 8 Gyr, respectively, as well as the 'usual' complement of well-known old GCs, i.e. GCs of similar age as the majority of the Galactic GCs. Our results also show that although there is significant scatter in metallicity at any age, there is a notable lack of young metal-poor and old metal-rich GCs, which might be indicative of an underlying age–metallicity relationship among the M31 GC population. 相似文献
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KSS31M型海洋重力仪在动、静态条件下观测到的读数变化及分析 总被引：3，自引：3，他引：0
2002年中国科学院海洋研究所从德国引进了KSS31M型海洋重力仪．为对该重力仪的工作性能有详细的了解,分别在德国重力仪生产厂实验室、中国科学院海洋研究所重力仪实验室进行了静态的定点观测,将重力仪安装在考察船上在黄埔江渔政码头等地进行了动态条件下的定点观测．动、静态的定点观测发现了多种规律性的重力仪读数变化,分析认为这些规律性的读数变化分别是重力仪的随机振荡、月潮的重力效应、海潮的重力效应和重力仪的线性漂移．它们各自有着不同的变化规律,并在海洋重力观测时总是同时存在．重力仪的随机振荡是重力仪自身固有的,其振荡幅度随外界条件的变化而变化,一般为0．04mGal～0．5mGal,周期为2～5min不等,在德国的重力仪厂家实验室和中国科学院海洋研究所重力实验室中观测到了月潮引起的重力变化,其变化幅度为0．2mGal．月潮引起的重力变化和海潮引起的重力变化同步,但相位相反．本文指出,仪器的月漂往往很难精确判定,本文用多种方法计算得到的仪器月漂在1．2mGal到2．3mGal之间． 相似文献
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W. Pietsch 《Astronomische Nachrichten》2008,329(2):170-173
First studies of the X‐ray source population of M 31 were performed with the Einstein Observatory and ROSAT. High resolution Chandra Observatory images not only spatially resolved the center area but also supernova remnants (SNRs) in the galaxy. Source catalogues of restricted areas were presented with high astrometric accuracy. Also luminosity function studies and studies of individual sources based on Chandra and XMM‐Newton observations led to a better knowledge of the X‐ray source population. An XMM‐Newton source catalog based on archival observations revealed more than 850 sources down to a 0.2–4.5 keV luminosity of 1035 erg s–1. EPIC hardness ratios as well as informations from earlier X‐ray, optical, and radio catalogues were used to distinguish between different source classes (SNRs, supersoft sources (SSSs), X‐ray binaries (XRBs), globular cluster sources within M 31, and foreground stars and objects in the background). However, many sources could only be classified as “hard”. These sources may either be XRBs or Crab‐like SNRs in M 31 or background sources. Two of the globular cluster sources could be identified as low mass XRBs with a neutron star as compact object as they showed type I X‐ray bursts. Many of the SSSs were identified as optical novae. Inspired by these results an XMM‐Newton survey of the entire D25 disk of M 31 and a dedicated program to monitor X‐ray counterparts of optical novae in M 31 was started. We discuss implications for further nearby galaxy studies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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The three major large-scale, diffuse γ-ray structures of the Milky Way are the Galactic disk,a bulge-like GeV excess towards the Galactic center, and the Fermi bubble. Whether such structures can also be present in other normal galaxies remains an open question. M31, as the nearest massive normal galaxy, holds promise for spatially-resolving the γ-ray emission. Based on more than 8 years of Fermi-LAT observations, we use(1) disk,(2) bulge, and(3) disk-plus-bulge templates to model the spatial distribution of the γ-ray emission from M31. Among these, the disk-plus-bulge template delivers the best-fit, in which the bulge component has a TS value 25.7 and a photon-index of 2.57 ± 0.17, providing strong evidence for a centrally-concentrated γ-ray emission from M31, that is analogous to the Galactic center excess. The total0.2–300 GeV γ-ray luminosity from this bulge component is(1.16 ± 0.14) × 1038 erg s-1, which would require ～ 1.5 × 105 millisecond pulsars, if they were the dominant source. We also search for a Fermi bubble-like structure in M31 using the full dataset(pass8), but no significant evidence has been found.In addition, a likelihood analysis using only photons with the most accurate reconstructed direction(i.e.,PSF3-only data) reveals a 4.8 σ point-like source located at ～10 kpc to the northwest of the M31 disk, with a luminosity of(0.97 ± 0.27) × 1038 erg s-1 and a pho@ton-$i·nd3 ex of 2.31 ± 0.18. Lacking a counterpart on the southeast side of the disk, the relation between this point-like source and a bubble-like structure remains elusive. 相似文献
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民丰地区是东营凹陷油气勘探中的重要部分,其中物源体系分析对沉积体系研究及储层评价工作的开展具有重要意义。古地貌控制了沉积体系展布的基本格局,陈南断层下降盘、民丰洼陷腹部以及辛镇地区为砂体沉积提供了所需的可容纳空间。特征元素分析以及砂分散体系研究表明,沙三段中下亚段沉积时期,民丰地区发育了三大物源体系,沉积原始组分的供给主要来自北部陈家庄凸起、东部青坨子凸起以及南部盆外水系的注入。在该时期,辛镇地区F1、F2主断裂形成的构造调节带可作为南北向物源输送通道,东部物源体系控制下的沉积体系南端与南部盆外水系的北部分支于辛镇地区发生交汇。由于沉积原始组分是储层发育的基础,因此,不同物源体系控制下的沉积原始组分造成了储层储集空间及物性特征的差异性。混源区与东部物源控制下的储集体为三角洲前缘相带,弱压实,粒间原生孔发育,孔、渗性良好,优于南部以及北部物源体系控制下的储层物性,但南部储层含油性高于东部,混源区储层含油性最好。 相似文献
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天然水体中生物膜对水环境中磷的生物地球化学过程影响 总被引：2，自引：0，他引：2
介绍了生物膜及其发育形成机理,生源要素磷与底泥、悬浮颗粒、藻类及细菌之间的相互作用,生物膜中微生物对生源要素磷循环的作用及其检测方法。通过对该领域近几年最新研究成果的总结,得出生物膜尤其是细菌对元素磷迁移转化的影响起着重要作用;对今后研究重点作出展望,在考虑生物膜存在的条件下,深入研究沉积物、悬浮颗粒、藻类及细菌与磷循环的相互作用机制,将有助于弄清楚水体富营养化发生的过程及机理。 相似文献