共查询到20条相似文献，搜索用时 46 毫秒
1.
半个世纪以前,Ｒｏｂｅｒｔｓ 和Ｓａｎｄａｇｅ 在验证Ｓｃｈｗａｒｚｓｃｈｉｌｄ 的理论发现时,在水平支ＲＲＬｙｒａｅ 变星缺口段的红端发现了两颗小变幅的变星。当时定不出类型,标以“？”。以后Ｓａｎｄａｇｅ 在做ＲＲ Ｌｙｒａｅ 变星统计研究时,竟不加解释地当作ＲＲａｂ 型星处理。半个世纪之间,没有人对这颗星的反常加以注意。我们用国内的ＣＣＤ 观测,又发现了一颗类似的小变幅变星,但变幅更小,周期更长。这颗星与以前发现的两颗一起,似乎构成ＲＲ Ｌｙｒａｅ 星的又一个次型。现有的变星脉动理论还不能对之加以解释。我们预计,这将再一次推动脉动理论发展。 相似文献
2.
The infrared properties of ULIRGs in samples from the Sloan Digital Sky Survey, 2dF Galaxy Redshift Survey and 6dF Galaxy
Survey (SDSS-2dF-6dF Survey) and ULIRGs in the IRAS 1 Jy sample are compared. We find that the infrared properties are quite
similar in both the far infrared and the near infrared for those two samples. By using the IRAS two-color diagram and the
2MASS two-color diagram we find that 24 sources in the SDSS-2dF-6dF Survey are candidate Seyfert 1-like sources indicative
of strong AGN-dominant nature. 相似文献
3.
V.S. Avedisova 《Astrophysics and Space Science》1997,252(1-2):261-272
The main kinematic characteristics of our Galaxy are analyzed using a catalog of about 2700 Galactic star-forming regions. The terminal velocities of the star-forming regions confirm that the rotation curve for the inner Galaxy is flat from |l| 23°. Bends in the rotation curve are probably due to motions in spiral arms. The Galaxy rotates with a circular velocity of 200 ± 10 km s-1. Evidence for an expanding ring-like structure at 3 kpc is presented. An l - v diagram for the catalog sources in the first and fourth Galactic quadrants is constructed. Density wave theory is used to show that a two-spiral model with a pitch angle of -9° and large-amplitude velocity perturbations in the region of 3 kpc can satisfactory describe the main features of the l - v diagram to Galactocentric radii of 6-7 kpc. 相似文献
4.
A family of high-velocity stars (Energy-19000 km2/sec2, angular momentum 1150 kpc km/sec) were computed using Innanen's (1966) mass model of the Galaxy. The stars were set initially on the curve of zero velocity. The inclination diagram indicates a quasi-isolating third integral. 相似文献
5.
On the basis of 30 observations the period of the new cepheid in M31,P=75.487 is obtained. Ths cepheid has an extremely long period and gives a possibility to determine the period-amplitude envelope toward the long-period region in M31 galaxy. A comparison of the period-amplitude diagrams in various galaxies is made. 相似文献
6.
I. Meinunger 《Astronomische Nachrichten》1977,298(3):171-177
For the derivation of distances and of the density distribution of the RR Lyrae stars in the Sonneberg fields near the north galactic pole (comprising 355 □°) we determined their photographic B-brightnesses. The density distribution of the RR Lyrae stars in each of the fields is almost identical with the density distribution given by KINMAN , WIRTANEN , and JANES (1966). Furthermore we derived the period-amplitude relations for RR Lyrae stars with 11mg·<mpg < 16m·7, which in the extended fields 92/93 Leo and 1 Boo turned out to be similar to those in the fields of KINMAN et al. near the pole. In the extended field 26 Com we found a slightly different period-amplitude relation pointing perhaps to a less homogeneous population. 相似文献
7.
An NUV-optical diagram composed from sources from the second Galaxy Evolution Explorer(GALEX) Ultraviolet Variability(GUVV-2) Catalog provides us with a method to tentatively classify the unknown GUVV-2 sources by their NUV-optical magnitudes.For the purpose of testing the correctness and generality of the method,we carry out a program on the spectroscopic observations of the unidentified GUVV-2 sources.The spectroscopic identification of these 37 sources are 19 type-A to-F stars,10 type-G to-K stars and 7 ... 相似文献
8.
The IceCube experiment has detected two neutrinos with energies between 1 and 10 PeV. They might have originated from Galactic or extragalactic sources of cosmic rays. In the present work we consider hadronic interactions of the diffuse very high energy cosmic rays with the interstellar matter within our Galaxy to explain the PeV neutrino events detected in IceCube. We also expect PeV gamma ray events along with the PeV neutrino events if the observed PeV neutrinos were produced within our Galaxy in hadronic interactions. PeV gamma rays are unlikely to reach us from sources outside our Galaxy due to pair production with cosmic background radiation fields. We suggest that in future with simultaneous detections of PeV gamma rays and neutrinos it would be possible to distinguish between Galactic and extragalactic origins of very high energy neutrinos. 相似文献
9.
《New Astronomy Reviews》2002,46(2-7):365-379
Relationships between jet physics and the evolutionary phases of radio galaxies are discussed. This includes the connection between the properties of relativistic jets and the Fanaroff–Riley classes of radio galaxies and the interaction of jets with the interstellar medium in Gigahertz Peak Spectrum and Compact Steep Spectrum Radio Sources. Jets in Seyfert galaxies are compared with those in classical radio galaxies and recent work suggesting that there are major differences between the two types of jets is summarized. The proposed major differences are principally that Seyfert jets are thermally dominated with subrelativistic speeds whereas Radio Galaxy jets are relativistic electron/positron flows. Hence, the production of jets in Seyferts and radio galaxies are fundamentally different. 相似文献
10.
11.
A comparison of the observed distribution of absolute proper motions with a kinematical model of the Galaxy is presented. Proper motions with respect to galaxies were obtained for about 40 000 stars along the main Galactic meridian and in two fields near the North Galactic pole (programme MEGA). The Galaxy is considered as composed of the disk (main sequence and disk red giants), the thick disk and spheroid populations. For each subsystem, spatial velocity components and their dispersions were computed. The distribution of kinematical parameters were modelled for stars located in different directions of the Galaxy. 相似文献
12.
Annie C. Robin 《Astrophysics and Space Science》1994,217(1-2):163-168
Models of population synthesis for the Galaxy have been developed in order to understand galactic structure and evolution. They allow to test scenarii of evolution by comparisons between model predictions and observed distributions. Forthcoming near-infrared surveys will enormously increase the amount of information about the distributions of late type stars in the Galaxy. We show here how population synthesis models will help to analyse these surveys and to interprete them in terms of mass function, star formation history and stellar evolution. 相似文献
13.
In this work a model has been proposed to explain how the nucleus of a Galaxy can accumulate mass and becomes supermassive — ultimately giving way to gravitational instability leading to an explosion in the nucleus. The process may be repeated many times during the life-span of a Galaxy. The mass shed by the evolved stars populating the central region of the Galaxy can be attracted toward the nuclear core by gravitational pull. Since the incident gas possesses rotational velocity, the centrifugal repulsion of the gas may balance the gravitational pull of the nucleus; thus infall of mass into the nucleus will ordinarily be inhibited. But dissipative agents — such as the prevailing magnetic field and the viscosity of gas — may be sufficient to destroy the rotational velocity of the incident gas and keep the accretion process efficient. The correlation between rotational velocity of gas and its distance from the centre of the Galaxy has been deduced. The radial equation of motion has been solved and the time-scale during which the nucleus accumulates mass sufficient for explosion, has been estimated. 相似文献
14.
Sami Dib C. Jakob Walcher Mark Heyer Edouard Audit Laurent Loinard 《Monthly notices of the Royal Astronomical Society》2009,398(3):1201-1206
Supernova (SN) explosions inject a considerable amount of energy into the interstellar medium (ISM) in regions with high-to-moderate star formation rates. In order to assess whether the driving of turbulence by supernovae is also important in the outer Galactic disc, where the star formation rates are lower, we study the spatial distribution of molecular cloud (MC) inclinations with respect to the Galactic plane. The latter contains important information on the nature of the mechanism of energy injection into the ISM. We analyse the spatial correlations between the position angles (PAs) of a selected sample of MCs (the largest clouds in the catalogue of the outer Galaxy published by Heyer et al). Our results show that when the PAs of the clouds are all mapped to values into the [0°, 90°] interval, there is a significant degree of spatial correlation between the PAs on spatial scales in the range of 100–800 pc. These scales are of the order of the sizes of individual SN shells in low-density environments such as those prevailing in the outer Galaxy and where the metallicity of the ambient gas is of the order of the solar value or smaller. These findings suggest that individual SN explosions, occurring in the outer regions of the Galaxy and in likewise spiral galaxies, albeit at lower rates, continue to play an important role in shaping the structure and dynamics of the ISM in those regions. The SN explosions we postulate here are likely associated with the existence of young stellar clusters in the far outer regions of the Galaxy and the ultraviolet emission and low levels of star formation observed with the Galaxy Evolution Explorer (GALEX) satellite in the outer regions of local galaxies. 相似文献
15.
朱紫 《紫金山天文台台刊》2003,(1)
针对地面FK5和空间依巴谷自行系统 ,采用银河系运动学分析方法发现 ,即使考虑了岁差改正的影响 ,两种自行系统之间仍存在很大差异。用建立在FK5系统上的PPM和ACRS自行与依巴谷自行比较 ,发现FK5自行系统内部存在非刚性运动 ;同时无法用VLBI及LLR所测定的岁差改正值来解释FK5与依巴谷自行系统的关系。 相似文献
16.
In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants.
In the present study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. The
determination of atmospheric parameters is based on analyses of silicon ionisation balance.
Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si
and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral
standards in our Galaxy.
We compare our results with the abundances expected from studies of HII regions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Mauri J. Valtonen Kimmo A. Innanen Leena Tähtinen 《Astrophysics and Space Science》1984,107(2):209-222
Numerical simulations have been performed in order to study the gravitational interaction between the outlying population of the Galaxy and the Large Magellanic Cloud (LMC). The following effects have been noted: (1) halo objects are partially removed from the orbital distance of the LMC such that a local minimum is created in the radial density profile; (2) a large number of halo objects go into escape orbits. This possibility makes the determination of the mass of the Galaxy by virial theorem arguments unreliable; (3) the orbit of the LMC decays faster than what one would expect on the basis of the classical dynamical friction calculation. The excess friction derives from three-body effects, which are not accounted for in the classical dynamical friction. Finally, the fates of globular clusters and dwarf galaxies near the Galaxy and the LMC are discussed. 相似文献
18.
M. I. Wilkinson A. Vallenari C. Turon U. Munari D. Katz G. Bono M. Cropper A. Helmi N. Robichon F. Thévenin S. Vidrih T. Zwitter F. Arenou M.-O. Baylac G. Bertelli A. Bijaoui F. Boschi F. Castelli F. Crifo M. David A. Gomboc A. Gómez M. Haywood U. Jauregi P. de Laverny Y. Lebreton P. Marrese T. Marsh S. Mignot D. Morin S. Pasetto M. Perryman A. Pr&#;a A. Recio-Blanco F. Royer A. Sellier A. Siviero R. Sordo C. Soubiran L. Tomasella Y. Viala 《Monthly notices of the Royal Astronomical Society》2005,359(4):1306-1335
19.
S. Ninkovi&#x; 《Astronomische Nachrichten》1992,313(2):83-89
The total kinetic energy of the Galaxy is estimated from the potential energy by applying the virial theorem. The limits of the potential energy depend strongly on the value of the local escape velocity. They are estimated to be between −7. 1016 MȮ km2s−2 and −1. 1016 MȮ km2s−2 (escape velocity approximately between 450 km s−1 and 600 km s−1). The specific kinetic energy of the Galaxy as a whole is most likely about 21 000 km2s−2, being equally distributed among the subsystems if the local escape velocity is near its lower limit; the higher the local escape velocity is, the higher is the specific kinetic energy of the Galaxy due to the influence of the dark corona. The specific kinetic energy of the dark corona tends to become equal to that of the Galaxy as a whole for very high values of the local escape velocity. For the purpose of estimating the totl potential energy of the Galaxy, inter alia, a new model of the Milky Way is developed, which yields both the potential and the density analytically so that it is suitale for calculating the galactocentric orbits. 相似文献
20.
As the origin of the soft X-ray background, emission of soft X-rays from shocks occurred in the accretion of intergalactic gas onto the Galaxy is studied. Infall of discrete gas clouds cannot explain the diffuse component of soft X-rays. If intergalactic gas rich in heavy elements as the cosmic abundance continously flows into the Galaxy and forms a standing shock surrounding the Galaxy, the line emissions by heavy elements from the shocked gas explain the soft X-ray background. Formation of the high velocity cloud by thermal instability in the shocked gas is also discussed briefly. 相似文献