Peculiarities of the UV continuum energy distribution for T Tauri stars     

A. S. Kravtsova  S. A. Lamzin 《Astronomy Letters》2003,29(9):612-620

In the UV spectra of BP Tau, GW Ori, T Tau, and RY Tau obtained with the Hubble Space Telescope, we detected an inflection near 2000 Å in the F _λ ^c (λ) curve that describes the continuum energy distribution. The inflection probably stems from the fact that the UV continuum in these stars consists of two components: the emission from an optically thick gas with T<8000 K and the emission from a gas with a much higher temperature. The total luminosity of the hot component is much lower than that of the cool component, but the hot-gas radiation dominates at λ<1800 Å. Previously, other authors have drawn a similar conclusion for several young stars from low-resolution IUE spectra. However, we show that the short-wavelength continuum is determined from these spectra with large errors. We also show that, for three of the stars studied (BP Tau, GW Ori, and T Tau), the accretion-shock radiation cannot account for the observed dependence F _λ ^c (λ) in the ultraviolet. We argue that more than 90% of the emission continuum in BP Tau at λ>2000 Å originates not in the accretion shock but in the inner accretion disk. Previously, a similar conclusion was reached for six more classical T Tau stars. Therefore, we believe that the high-temperature continuum can be associated with the radiation from the disk chromosphere. However, it may well be that the stellar chromosphere is its source.  相似文献   

太阳系早期的短寿期放射性核素   总被引：2，自引：0，他引：2  

徐伟彪 《天文学报》2003,44(3):231-239

较详细地介绍全新的太阳系起源理论——X-wind模式,天体化学实验发现太阳系早期存在大量的短寿期放射性核素(半衰期小于100Ma),这些核素对太阳系的形成和演化有重要的影响,一种理论认为,这些核素是在恒星内部合成,并由星风注入原太阳分子云,星风产生的激波诱发分子云核的塌缩而形成原太阳,另一种理论认为,这些核素是高能粒子与原太阳分子云或太阳星云中的气体和尘埃相互作用的产物。  相似文献   

Scale invariant theory for Bianchi Type VIII and IX space-times with perfect fluid     

G. Mohanty  B. Mishra 《Astrophysics and Space Science》2003,283(1):67-74

In this paper we have taken an attempt to study the feasibility of scale invariant theory (Wesson, 1981a,b) in Bianchi type VIII and IX space-times with a time dependent gauge function (Dirac Gauge i.e. βα )and a matter field in the form of a perfect fluid. It is found that Bianchi type VIII (δ=1) space-time is feasible in this theory whereas Bianchi type IX (δ=-1) space-time is not feasible. In this feasible case a radiating model is constructed and its physical behaviour is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Giant Vibrations in Dip     

T.C. Teixeira  J. Christensen-Dalsgaard  F. Carrier  C. Aerts  S. Frandsen  D. Stello  T. Maas  M. Burnet  H. Bruntt  J.R. de Medeiros  F. Bouchy  H. Kjeldsen  F. Pijpers 《Astrophysics and Space Science》2003,284(1):233-236

This work reports the discovery of solar-type oscillations in thegiant star Hydrae.  相似文献   

1.2米地平式望远镜指向模型的研究 (1.全天指向模型的建立)   总被引：4，自引：1，他引：3  

郑向明  王武  张云成  冯和生 《天文学报》2003,44(3):330-336

介绍了云南天文台1.2米地平式望远镜用于天文观测和图像采集处理的方法,建立了新的、独特的全天指向模型,大大提高了该望远镜的指向精度,达到1″,并在多年的实际应用中得到验证。  相似文献   

Mode Identification from Line Profiles using the Direct Fitting Technique     

Luis A. Balona 《Astrophysics and Space Science》2003,284(1):121-124

The method of moments and the direct fitting method are the onlyspectroscopic methods of mode identification which allow a determination ofall pulsational parameters. The pulsation parameters are required to predictthe light amplitude and phase which can be important discriminants in modeidentification. The direct fitting method has several advantages over themethod of moments. It is not restricted to low spherical harmonic degree or form of the eigenfunction and is not sensitive to the placement of the continuum. In the last few years the method has been applied to several different types of stars. We briefly describe the method and give someexamples of its application.  相似文献   

低质量X射线双星的毫秒级准周期信号——最近的进展     

YU Wen-fei 《天文研究与技术》2003,(1):12-15

最近对低质量X射线双星中的千赫兹准周期振动的研究表明 ,是辐射压力 ,而不是盘和磁球的相互作用以及处于盘内边界的广义相对论效应在短时标的盘切断机制上起作用。本文给出了一些研究结果及讨论。  相似文献   

Ice flow direction during late Paleozoic glaciation in western Paraná Basin, Brazil     

A. L. D. Gesicki  C. Riccomini  P. C. Boggiani   《Journal of South American Earth Sciences》2002,14(8)

The recent discovery of ice-striated surfaces associated with the late Paleozoic Aquidauana Formation suggests that glaciers coming from southwest Africa reached westernmost parts of the Paraná Basin in central Brazil. Abrasion features were developed by glaciers moving from SSE towards NNW, mainly on an unconsolidated bed. These records expand to about 1,050,000 km², the coverage of the late Paleozoic glaciation in the region of the Paraná Basin in Western Gondwana.

Resumen

A recente descoberta de superfícies estriadas associadas à Formação Aquidauana, de idade permocarbonífera, sugere que as geleiras provenientes do sudoeste da África alcançaram as porções ocidentais da Bacia do Paraná, na região central do Brasil. As feições de abrasão foram geradas pelo deslocamento de geleiras de SSE para NNW, principalmente sobre substrato inconsolidado. Estes novos registros evidenciam que a glaciação neopaleozóica cobriu uma área de pelo menos de 1.050.000 km² na região ocupada pela Bacia do Paraná no Gondwana Ocidental.  相似文献   

The pegmatites of the Nova Era–Itabira–Ferros pegmatite district and the emerald mineralisation of Capoeirana and Belmont (Minas Gerais, Brazil): geochemistry and Rb–Sr dating     

Preinfalk  Y. Kostitsyn  G. Morteani   《Journal of South American Earth Sciences》2002,14(8)

The chemical composition and Rb–Sr ages of mica, feldspar, and whole rock samples from the emerald mineralisation of Capoeirana and Belmont, from emerald-barren pegmatites and of the Borrachudos granitic gneiss, Monlevade banded and granitic gneisses from the area of Nova Era–Itabira–Ferros (Minas Gerais, Brazil) as well as from the Guanhães gneiss (Minas Gerais, Brazil) have been determined. The Borrachudos granitic and Monlevade banded gneiss with connected pegmatitic schlieren and pegmatite veins, as well as the Guanhães gneiss, got their actual textures and mineralogical composition at about 1.9 Ga in the context of the Transamazonic tectonothermal event.The Monlevade banded gneiss belongs to a volcano-metasedimentary greenstone belt sequence, which is the typical country rock of the emerald occurrences. The main emerald-forming event at Belmont and Capoeirana was a metasomatic reaction of Be-rich anatectic pegmatites with Cr-rich ultrabasic rocks during the Transamazonic event. At Capoeirana, K–feldspar-bearing Be-rich pegmatites were transformed during the emerald-forming process into plagioclase–quartz rocks. Rb–Sr ages on biotite of about 480 Ma from the emerald mineralisation result from the rejuvenation of Transamazonic biotite by the Brasiliano event.The widespread macroscopically unmetamorphosed pegmatites of the study area formed in the Brasiliano event at 477±14 Ma. These pegmatites resulted to be emerald-barren although the differentiation degree, as given by diagrams such as Cs vs. K/Rb for muscovite and K–feldspar, starts from ceramic and ends with Be pegmatites. Some pegmatites display a marked internal differentiation.

Abstract

Foram determinadas as composições químicas e as idades Rb–Sr de mica branca, feldspato potássico e de rochas totais das mineralizações de esmeraldas de Capoeirana e Belmont, de pegmatitos sem esmeraldas e dos gnaisses Borrachudos, Monlevade e Guanhães da região de Nova Era–Itabira–Ferros (Minas Gerais, Brazil). Os gnaisses graníticos Borrachudos, os gnaisses bandados Monlevade, seus respectivos pegmatitos e veios/schlieren pegmatóides, e os gnaisses Guanhães, adquiriram suas texturas e composições mineralógicas atuais há cerca de 1.9 Ga no contexto do evento Transamazônico.As rochas regionais encaixantes típicas das ocorrências de esmeraldas são os gnaisses Monlevade que pertencem a uma sequência metavulcano-sedimentar de tipo greenstone belt. O evento principal de formação de esmeraldas em Belmont e Capoeirana foi uma reação metassomática dos pegmatitos anatéticos ricos em Be com rochas ultrabásicas ricas em Cr durante o evento Transamazônico em torno de 1.9 Ga. Em Capoeirana nesse contexto os pegmatitos com feldspato potássico ricos em Be foram transformados em rochas de plagioclasio–quartzo. As idades Rb–Sr de cerca de 480 Ma de minerais das mineralizações de esmeralda resultaram da reequilibração de biotitas e feldspatos Transamazônicos durante o evento Brasiliano.Os pegmatitos não-metamórficos e sem esmeralda da região estudada foram formados no evento Brasiliano há 477±14 Ma. O grau de diferenciação dos pegmatitos, estudado em diagramas indicadores específicos como por exemplo Cs vs. K/Rb de micas brancas e feldspatos potássicos, varia desde pegmatitos cerámicos até muscovita-pegmatitos, à pegmatitos de metais raros e até berilíferos. Alguns dos pegmatitos apresentam marcante diferenciação interna.  相似文献   

Evaluation of pre-CHAMP gravity models `GRIM5-S1' and `GRIM5-C1' with satellite crossover altimetry     

J. Klokočník  Ch. Reigber  P. Schwintzer  C. A. Wagner  J. Kostelecký 《Journal of Geodesy》2002,76(4):189-198

 The new GFZ/GRGS gravity field models GRIM5-S1 and GRIM5-C1, currently used as initial models for the CHAMP mission, have been compared with other recent models (JGM 3, EGM 96) for radial orbit accuracy (by means of latitude lumped coefficients) in computations on altimetry satellite orbits. The bases for accuracy judgements are multi-year averages of crossover sea height differences from Geosat and ERS 1/2 missions. This radially sensitive data is fully independent of the data used to develop these gravity models. There is good agreement between the observed differences in all of the world's oceans and projections of the same errors from the scaled covariance matrix of their harmonic geopotential coefficients. It was found that the tentative scale factor of five for the formal standard deviations of the harmonic coefficients of the new GRIM fields is justified, i.e. the accuracy estimates, provided together with the GRIM geopotential coefficients, are realistic. Received: 20 February 2001 / Accepted: 24 October 2001  相似文献