The line-of-sight velocities of OB associations and molecular clouds in a wide solar neighborhood: The streaming motions of stars and gas in the Perseus arm     

T. G. Sitnik 《Astronomy Letters》2003,29(5):311-320

We compare the line-of-sight velocities of stars in OB associations within 3 kpc of the Sun and the molecular clouds closest to them. The Perseus arm is used as an example to show that the line-of-sight velocity ranges in which OB-association stars, molecular clouds, and H II regions ionized by these association stars are observed overlap. The streaming motions produced by density waves in the (l, V_LSR) plane were found to lead to an inversion of the distances to objects of the Perseus arm and the interarm space beyond this arm.  相似文献   

A hard X-ray survey of the Galactic-Center region with the IBIS telescope of the INTEGRAL observatory: A catalog of sources     

M. G. Revnivtsev  R. A. Sunyaev  D. A. Varshalovich  V. V. Zheleznyakov  A. M. Cherepashchuk  A. A. Lutovinov  E. M. Churazov  S. A. Grebenev  M. R. Gilfanov 《Astronomy Letters》2004,30(6):382-389

From August 23 through September 24, 2003, the INTEGRAL Observatory conducted a deep survey of the Galactic-Center region with a record-breaking sensitivity at energies above 20 keV. We have analyzed the images of the Galactic-Center region obtained with the ISGRI detector of the IBIS telescope (15–200 keV) and give a catalog of detected sources. We detected a total of 60 sources with fluxes above 1.5 mCrab, 44 and 3 of which were previously identified as binary systems of different classes in our Galaxy and as extragalactic objects, respectively. We discovered one new source.  相似文献   

Radio continuum surveys     

Justin L. Jonas  Eddie E. Baart 《Astrophysics and Space Science》1995,230(1-2):351-358

The Rhodes University radio astronomy group has been involved in radio continuum mapping of southern extended radio sources since 1976. We describe the various mapping projects undertaken with the HartRAO telescope, particularly the Rhodes/HartRAO 2300 MHz all-sky survey, and speculate on future projects.  相似文献   

Formation of galactic subsystems in light of the magnesium abundance in field stars: The thick disk     

V. A. Marsakov  T. V. Borkova 《Astronomy Letters》2005,31(8):515-527

The space velocities and Galactic orbital elements of stars calculated from the currently available high-accuracy observations in our compiled catalog of spectroscopic magnesium abundances in dwarfs and subgiants in the solar neighborhood are used to identify thick-disk objects. We analyze the relations between chemical, spatial, and kinematic parameters of F–G stars in the identified subsystem. The relative magnesium abundances in thick-disk stars are shown to lie within the range 0.0 < [Mg/Fe] < 0.5 and to decrease with increasingmetallicity starting from [Fe/H] ≈ ?1.0. This is interpreted as evidence for a longer duration of the star formation process in the thick disk. We have found vertical gradients in metallicity (grad_Z[Fe/H] = ?0.13 ± 0.04 kpc^?1) and relative magnesium abundance (grad_Z[Mg/Fe] = 0.06 ± 0.02 kpc^?1), which can be present in the subsystem only in the case of its formation in a slowly collapsing protogalaxy. However, the gradients in the thick disk disappear if the stars whose orbits lie in the Galactic plane, but have high eccentricities and low azimuthal space velocities atypical of the thin-disk stars are excluded from the sample. The large spread in relative magnesium abundance (?0.3 < [Mg/Fe] < 0.5) in the stars of the metal-poor “tail” of the thick disk, which constitute ≈8% of the subsystem, can be explained in terms of their formation inside isolated interstellar clouds that interacted weakly with the matter of a single protogalactic cloud. We have found a statistically significant negative radial gradient in relative magnesium abundance in the thick disk (grad_R[Mg/Fe] = ?0.03 ± 0.01 kpc^{? 1}) instead of the expected positive gradient. The smaller perigalactic orbital radii and the higher eccentricities for magnesium-richer stars, which, among other stars, are currently located in a small volume of the Galactic space near the Sun, are assumed to be responsible for the gradient inversion. A similar, but statistically less significant inversion is also observed in the subsystem for the radial metallicity gradient.  相似文献   

Generation of daylight reference years for two European cities with different climate: Athens, Greece and Bratislava, Slovakia     

M.T. Markou  H.D. Kambezidis  A. Bartzokas  S. Darula  R. Kittler 《Atmospheric Research》2007,86(3-4):315-329

In this work, daylight reference years (DRYs), based on daylight and solar radiation measurements, are designed for two European cities, Athens, Greece and Bratislava, Slovakia, by using the Danish method, the Festa–Ratto technique and the Modified Sandia National Laboratories methodology. The data basis consists of 5-minute values of global and diffuse horizontal illuminance, global and diffuse horizontal irradiance, zenith luminance and solar altitude as well as of daily values of sunshine duration for 5 years for Athens and 8 years for Bratislava. Moreover, Linke's turbidity factor, luminous turbidity factor and relative sunshine duration are calculated and utilized. Then, for each DRY, the predominant sky-luminance distributions over Athens and Bratislava are identified, by using the methodology of Kittler et al., who corresponded the main sky conditions to 15 theoretical sky standards in diagrams of the ratio of zenith luminance to diffuse horizontal illuminance against solar altitude.For both cities the three aforementioned methods do not create identical DRYs. Despite the differences, the sky types defined for each of the two places seem not to depend on the choice of DRY. The predominant sky standard, for all of them, is a cloudless, polluted sky with a broad solar corona for Athens and an overcast sky with slight brightening towards the sun as well as very clear sky with low atmospheric turbidity for Bratislava. However, the selection of the DRY, which represents best the daylight conditions, is necessary for studies in saving energy in buildings. The DRY, which is created by the Modified Sandia National Laboratories method, is chosen for most cases, while the one created by the Danish method is also useful on certain occasions.  相似文献   

加强"十五"重点项目管理 ,努力促进地震科技进步     

林趾祥 《国际地震动态》2002,(9):7-11

总结了山东省防震减灾“九五”期间主要成功的经验和教训,提出了加强“十五”防震减灾重点项目管理的几点意见。  相似文献   

Radio Emission from Galactic Disks     

Lesch  H. 《Studia Geophysica et Geodaetica》1998,42(3):364-372

This paper gives a short overview of the observational results on galactic magnetic fields. Interstellar magnetic fields, as deduced from multi-frequency polarization observations, show a well-ordered structure largely following the spiral arms. In some galaxies an axisymmetric spiral pattern dominates (the field being directed inwards), while others exhibit a dominant bisymmetric spiral field or mixed modes, as predicted from non-linear dynamo theory. As long as star formation activity is low, the magnetic fields are rather regular. Strong star formation leads to turbulent cloud motions and supernova explosions, which tangle the field, so that the radio emission is only weakly polarized. As a consequence the highest fractional polarizations and polarized intensities at centimeter wavelengths are found in interarm regions. At decimeter wavelengths, galactic disks become optically thick for polarized emission. In NGC 6946 the regular field is concentrated in narrow magnetic arms located in between the optical spiral arms. The field cannot simply be frozen into the gas and oriented by a density-wave flow. A galactic dynamo may provide a stable spiral pattern of the field, but non-axisymmetric models are still being developed.  相似文献   

GIS能平安度过2000年吗     

石伟伟  杨国东 《测绘与空间地理信息》1998,(4)

本文论述了2000年的问题对GIS产业发展的不利影响,分析了它所产生的根源,阐述了解决这一问题的方案。  相似文献   

The statistical effects of galactic tides on the Oort cloud     

Piotr A. Dybczyski  Halina Pretka 《Earth, Moon, and Planets》1995,71(3):13-18

This report is a comment on two papers by Matese and Whitman (1989, 1992). We discuss here the applicability of uniform probability densities for the orbital parameters of the Oort cloud comets.  相似文献   

基于ESDA的中国年画网络店铺区位演化     

段然  李仁杰  王守成  张军海  李照航 《热带地理》2012,32(6):626-632

通过收集淘宝网络店铺中的中国年画店铺基本信息,基于地级市空间统计单元,运用探索性空间数据分析理论中的全局自相关、局部自相关和热区分析等方法,对中国年画网络店铺区位的演化特征进行定量分析与挖掘。研究结果表明：1）中国年画网络店铺的区位演化整体上具有显著的空间自相关性,空间聚集特征明显;2）店铺区位局部差异明显,京、津、冀、鲁等省市构成了店铺区位选择的区域中心,并对周边城市产生辐射;3）店铺区位选择的热区从呈斑块状、阶梯状地域分布,逐渐演化为京、津、冀、鲁等稳定连片热区;4）总结了影响年画网络店铺区位选择的3个主要因素：区域经济因素、传统文化因素和消费者个性化需求因素。  相似文献