山东中部一条明显的北西向中强地震带   总被引：1，自引：0，他引：1  

晃洪太  李家灵 《华北地震科学》1998,16(2):23-29

长清－临沂地震带是山东中部一条明显的北西向中强地震带,由９次中强地震组成。这些地震沿北西向展布,主要分布在四个震源区,大致呈５０￣５５ｋｍ等间距分布。除１６６８年郯城地震与北北东向的郯庐断裂带有关外,其它地震受北西向蒙山断裂控制,是该断裂各为层段新活动的结果。另外,该地城带内地震的发生还有一定深部构造背景。未来应注意研究该带内再次发生中强地震的可能。  相似文献   

太白维山火山岩系序列相划分及火山活动特征   总被引：4，自引：0，他引：4  

王建新  李景春 《华北地质矿产杂志》1998,13(2):118-125

太白维山火山岩系为晋东北地区中生代火山断陷盆地产物。通过工作研究,确定陈我内岩系的岩石类型及空间分布;指出了两大岩系为两个岩浆源的产物及各序列相的成因类型;确定了水下火山碎屑涌流相的存在,并提出了对形成岩浆蒸气爆发岩的新认识。  相似文献   

辽西地区中生代义县旋回火山活动特征分析   总被引：6，自引：0，他引：6  

史卜庆  吴智平 《高校地质学报》1998,4(4):413-422

辽西地区广泛发育中生代火山岩,其中以义县旋回火山岩最为发育。本文在对辽西地区义县旋回火山岩微量元素地球化学特征研究的基础上,认为义县旋回火山岩具有同源性质,由壳幔混溶物质作用于统一的火山活动过程中产生。  相似文献   

宝石颜色的命名与判定方法评述     

张庆麟 《上海国土资源》1998,(3):24-29

较系统评述了现有的各种命名与判定宝石颜色的方法,如命名法中的二名法、类似法、色度法和三要素法;判定法中的目测法、仪器测量法和对比法。指出它们均存在有不同程度的缺点,但相对比较起来,用色谱图系的对比法是目前较好的方法。  相似文献   

A new population of brown dwarfs     

M. R. S. Hawkins  C. Ducourant  H. R. A. Jones  & M. Rapaport 《Monthly notices of the Royal Astronomical Society》1998,294(3):505-512

In this paper we report the first results from a survey for low-mass stars and brown dwarfs, based on a photographic stack of around 100 Schmidt plates. This survey extends photographic searches by about 2 mag, and covers an area of 25 deg². Some 30 faint objects with large R − I colours were selected for further study, and were found to have very strong molecular absorption in their spectra, but only moderately red infrared colours. Five of these stars were selected for a parallax programme; three of these were found to be at a distance of around 45 pc, implying a very low luminosity. On the basis of their luminosity alone it is clear that these stars are field brown dwarfs, and we discuss their likely evolutionary status in the context of current models of low-mass stellar evolution.  相似文献   

The light curves of soft X-ray transients     

King  & Ritter 《Monthly notices of the Royal Astronomical Society》1998,293(1):L42-L48

We show that the light curves of soft X-ray transients (SXTs) follow naturally from the disc instability picture, adapted to take account of irradiation by the central X-ray source during the outburst. Irradiation prevents the disc from returning to the cool state until central accretion is greatly reduced. This happens only after most of the disc mass has been accreted by the central object, on a viscous time-scale, accounting naturally for the exponential decay of the outburst on a far longer time-scale (τ20–40 d) than seen in dwarf novae, without any need to manipulate the viscosity parameter α. The accretion of most of the disc mass in outburst explains the much longer recurrence time of SXTs compared with dwarf novae. This picture also suggests an explanation of the secondary maximum seen in SXT light curves about 50–75 d after the start of each outburst, since central irradiation triggers the thermal instability of the outer disc, adding to the central accretion rate one viscous time later. The X-ray outburst decay constant τ should on average increase with orbital period, but saturate at a roughly constant value ∼40 d for orbital periods longer than about a day. The bolometric light curve should show a linear rather than an exponential decay at late times (a few times τ). Outbursts of long-period systems should be entirely in the linear decay regime, as is observed in GRO J1744−28. UV and optical light curves should resemble the X-rays but have decay time-scales up to 2–4 times longer.  相似文献   

The dwarf galaxy population of the Coma cluster to M_R=−11: a detailed description     

Neil Trentham 《Monthly notices of the Royal Astronomical Society》1998,293(1):71-88

We present the luminosity function and measurements of the scalelengths, colours and radial distribution of dwarf galaxies in the Coma cluster down to R =24. Our survey area is 674 arcmin²; this is the deepest and most detailed survey covering such a large area.
Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are as follows.
(1) Galaxies in the Coma cluster have a luminosity function φ( L )∝ L ^α that is steep (α∼−1.7) for −15< M_R <−11, and is shallower brighter than this. The curvature in the luminosity function at M_R ∼−15 is statistically significant.
(2) The galaxies that contribute most strongly to the luminosity function at −14< M_R <−12 have colours and scalelengths that are consistent with those of local dwarf spheroidal galaxies placed at the distance of Coma.
(3) These galaxies with −14< M_R <−12 have a colour distribution that is very strongly peaked at B − R =1.3. This is suggestive of a substantial degree of homogeneity in their star formation histories and metallicities.
(4) These galaxies with −14< M_R <−12 also appear to be more confined to the cluster core ( r ∼200 kpc) than the brighter galaxies. Alternatively, this observation may be explained in part or whole by the presence of an anomalously high number of background galaxies behind the cluster core. Velocity measurements of these galaxies would distinguish between these two possibilities.  相似文献   

The galaxy luminosity function in clusters and the field     

Neil Trentham 《Monthly notices of the Royal Astronomical Society》1998,294(2):193-200

We present the results from a CCD survey of the B -band luminosity function of nine clusters of galaxies, and compare them to published photographic luminosity functions of nearby poor clusters like Virgo and Fornax, and also to the field luminosity function. We derive a composite luminosity function by taking the weighted mean of all the individual cluster luminosity functions; this composite luminosity function is steep at bright and faint magnitudes and is shallow in-between.
All clusters have luminosity functions consistent with this single composite function. This is true both for rich clusters like Coma and for poor clusters like Virgo.
This same composite function is also individually consistent with the deep field luminosity functions found by Cowie et al. and Ellis et al., and also with the faint end of the Las Campanas Redshift Survey R -band luminosity function, shifted by 1.5 mag. A comparison with the Loveday et al. field luminosity function, which is well determined at the bright end, shows that the composite function, which fits the field data well fainter than M _B=−19, drops too steeply between M _B=−19 and −22 to fit the field data there.  相似文献   

A Ca ii H&K survey of γ Doradus candidates     

Anthony B. Kaye  & Klaus G. Strassmeier 《Monthly notices of the Royal Astronomical Society》1998,294(2):L35-L39

In an investigation of the starspot hypothesis as it applies to the 'slowly variable' F-type dwarfs, we spectroscopically observed eight promising γ Doradus candidates to search for Ca  ii H&K emission. We found that there are no significant emission reversals in the cores of these resonance lines. Based on the ceiling flux calculations of the Ca  ii K line and on calculations of the Rossby number, we conclude that there is no support for the presence of strong magnetic activity and the starspot hypothesis in these objects.  相似文献   

The biconical kiloparsec structure generated by nuclear starbursts     

Guillermo Tenorio-Tagle  & Casiana Muñoz-Tuñón 《Monthly notices of the Royal Astronomical Society》1998,293(3):299-305

Two-dimensional calculations of the hydrodynamics produced by nuclear starbursts, taking into consideration the accretion or infall of disc matter on to the heart of the starburst, are here shown to lead to stationary solutions that naturally account for the kpc-scale biconical X-ray and optically detected filamentary structure. The calculated flows are critically compared with former models and with observations of nuclear starbursts. For the infall models, we find that the mechanical energy power of the nuclear cluster must exceed a threshold value, imposed by the rate of disc mass accretion, to undergo blowout. This, combined with an initial mass function (IMF), is shown to regulate the minimum amount of mass that a starburst needs to generate kpc-scale outflows.  相似文献