共查询到20条相似文献，搜索用时 46 毫秒
1.
Guo-Liang Lü 《中国天文和天体物理学报》2007,7(1):101-110
1 INTRODUCTION Symbiotic stars (SSs) are interacting binaries consisting of a cool giant, a hot compact companion and an H II region (Berman 1932; Boyarchuk 1967; Boyarchuk 1968). The cool component is a red giant (RG) that belongs either to the first gia… 相似文献
2.
Xiao-Bin Zhang Rong-Xian ZhangNational Astronomical Observatories Chinese Academy of Sciences Beijing xzhang@bao. ac. cnCAS-PKU Joint Beijing Astrophysics Center Beijing 《中国天文和天体物理学报》2003,3(4):311-315
Four stars, GSC 1258-0143, GSC 1986-1665, GSC 3045-0892 and GSC 2983-1597 were found to be new variables during a campaign of CCD photometric monitoring of short-period eclipsing binary stars. The variabilities of these new variables are reported. The main characteristics and probable classifications of the variables are discussed through a preliminary analysis on their light curves. Among these stars, GSC 1258-0143 is classified as a RR Lyr star of sub-type a. Its pulsation period is determined to be about 0.5206 days. The other three stars, are definite variables, but their periods and types of light variations remain unknown. 相似文献
3.
B. Novakovic 《中国天文和天体物理学报》2007,7(3):415-420
We present the orbits of ten visual binary stars: WDS 01015 6922, WDS 01424– 0645, WDS 01461 6349, WDS 04374–0951, WDS 04478 5318, WDS 05255–0033, WDS 05491 6248, WDS 06404 4058, WDS 07479–1212, and WDS 18384 0850. We have also determined their masses, dynamical parallaxes and ephemerides. 相似文献
4.
Ji Li Gang Zhao National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Physics Hebei Normal University Shijiazhuang 《中国天文和天体物理学报》2004,4(1):75-87
The abundances of long-lived radioactive elements Th and U observed in metal-poor halo stars can be used as chronometers to determine the age of individual stars, and hence set a lower limit on the age of the Galaxy and hence of the universe. This radioactive dating requires the zero-decay productions of Th and U, which involves complicated r-process nucleosynthesis calculations. Several parametric r-process models have been used to calculate the initial abundance ratios of Th/Eu and U/Th, but, due to the sharp sensitivity of these models to nuclear physics inputs, the calculations have relatively large uncertainties which lead to large uncertainties in the age determinations. In order to reduce these uncertainties, we present a simple method to estimate the initial productions of Th and U, which only depends on the solar system abundances and the stellar abundances of stable r-process elements. From our calculations of the initial abundance ratios of Th/Eu and U/Th, we re-estimate the ages of those ver 相似文献
5.
The methods used to derive effective temperatures, projected rotational velocities and surface gravities of a sample of low
and high-amplitude δ Sct stars are presented here. Effective temperatures were derived using Hα and Hβ line profiles whereas
rotational velocities were calculated following the method described in Solano & Fernley (1997). Surface gravities were obtained
using Hipparcos parallaxes and evolutionary models (Claret 1995). The results of this analysis will be published in a subsequent
paper (Solano & Pintado 1999).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
E. Paunzen 《Astrophysics and Space Science》1999,266(3):379-387
In this article the current status of the knowledge forthe group of λ Bootis stars is reviewed. These metal poor objectsare
quite outstanding compared to other chemically peculiar stars of theupper main sequence. Up to now no conclusive theory has
been developedwhich is able to explain the majority of observational results. There is,however, an increasing interest in
observational as well as theoreticalresults in order to develop and test astrophysical models such asaccretion of circumstellar
matter and diffusion processes in stellaratmospheres.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Based on the Hipparcos proper motions and available radial velocity data of O-B stars, we have re-examined the local kinematical structure of the young disk population of-1500 O-B stars not including the Gould-belt stars. A systematic warping motion of the stars about the direction to the Galactic center has been reconfirmed. A negative K-term implying a systematic contraction of stars in the solar vicinity has been detected. Two different distance scales are used in order to find out their impact on the kinematical parameters, and we conclude that the adopted distance scale plays an important role in characterizing the kinematical parameters at the present level of the measurement uncertainty. 相似文献
8.
Hua-Wei Zhang Gang Zhao National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Astronomy School of Physics Peking University Beijing Chinese Academy of Sciences-Peking University Joint Beijing Astrophysical Center Beijing 《中国天文和天体物理学报》2003,3(5):453-457
High-resolution, high signal-to-noise ratio spectra have been obtained for 32 metal-poor stars. The equivalent widths of Li A6708 A were measured and the lithium abundances were derived. The average lithium abundance of 21 stars on the lithium plateau is 2.33±0.02 dex. The Lithium plateau exhibits a marginal trend along metallicity, dA(Li)/d[Fe/H] ?0.12±0.06, and no clear trend with the effective temperature. The trend indicates that the abundance of lithium plateau may not be primordial and that a part of the lithium was produced in Galactic Chemical Evolution (GCE). 相似文献
9.
Gang Zhao Yu-Qin Chen Hong-Mei QiuNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,2(4)
We present the equivalent widths of 15 extrasolar-planet host stars. These data were based on the high-resolution, high signal-to-noise ratio spectra obtained with the 2.16m telescope at Xinglong station. The error in the Xinglong equivalent width is estimated by a comparison of these data with those given in previous studies of common stars. 相似文献
10.
Vincenzo Ripepi 《Astrophysics and Space Science》2003,284(1):69-72
We present time series observations of the intermediate mass Pre-Main Sequence star H254 belonging to the young star cluster IC 348 and of the Herbig Ae star V351 Ori.Both these stars present light variation on short time scale (a few hours) typical of the Scuti pulsation. The new data are briefly described together with the plan for future observational campaigns on PMS Scuti stars. 相似文献
11.
Claude Catala 《Astrophysics and Space Science》2003,284(1):53-60
Intermediate mass pre-main sequence stars (1.5 to 5 M
)cross the instability strip on their way to the main sequence.They are therefore expected to be pulsating in a similar way as the Scuti stars. In this review, I present the status of observational studies ofpulsations in these stars, and comment on prospects for futureinvestigations of these pulsations from the ground and from space. 相似文献
12.
Li-Feng Xing Shuang-Yi Zhao Wei Su Yan Shen Xiao-Bin Zhang Jian-Yan Wei 《中国天文和天体物理学报》2007,7(4):551-557
We monitored 16 X-ray selected young solar-type stars for light variation and found appreciable periodic light variability with amplitudes of a few hundredths of a magni-tude in nine of the objects. Using the method of Phase Dispersion Minimization (PDM) and Fourier analysis (software PERIOD04), the rotation periods of these stars were determined from the photometric data. The rotation periods of all nine stars are shorter than about 3days. It is suggested that, as with the Pleiades cluster, small amplitude light variations are quite common among young solar-type stars with rotation periods around 3 days or less. This gives further evidence for the spin up of solar-type stars predicted by models of angular momentum evolution of pre-main sequence stars. 相似文献
13.
R.G. Gratton 《Astrophysics and Space Science》1999,265(1-4):157-164
Since about thirty years it is known that Oxygen and other α-elementsare overabundant in metal-poor stars. In this talk I
briefly review thehistorical and theoretical background, discuss reliability of presentabundance determinations for O, and
finally comment about the implicationsrelevant to galactic chemical evolution.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
V G Klochkova Gang Zhao V E Panchuk S V Ermakov National Astronomical Observatories Chinese Academy of Sciences Beijing Special Astrophysical Observatory Russian Academy of Sciences Nizhnij Arkhyz Karachai-Cherkessia Russia 《中国天文和天体物理学报》2004,4(3):279-283
We present an atlas of a group of bright stars in the range of spectral classes F-G and luminosity classes I-V. The spectra were obtained with spectral resolution R ～ 15 000 within spectral region 4500-6620/A Typical spectra of stars with different metallicity [Fe/H] are included. We also show the digital version of the spectral data in FITS format. 相似文献
15.
16.
We use the flexibility of the concept of a fermion–boson star to explore different configurations, ranging from objects of
atomic size and masses of the order 1018 g, up to objects of galactic masses and gigantic halos around a smaller core, with possible interesting applications to astrophysics
and cosmology, particularly in the context of dark matter.
PACS codes: 04.40.−b, 95.35.+d 相似文献
17.
An analysis of the stars included in the catalogue of λ Bootis by Paunzen et al. (1997) and with IUE Low Resolution observations
is presented here. Using line-ratios of carbon to heavier elements (Al and Ni) allows us to establish unambiguous membership
criteria for the λ Bootis group. These criteria have been used to look for new λ Bootis candidates in the IUE Final Archive.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
T.P. Ray 《Astrophysics and Space Science》2000,272(1-3):115-125
After briefly reviewing observations of molecular outflows from young stars, we discuss current ideas as to how they might
be accelerated. Broadly speaking it is thought that such outflows represented either deflected accreted gas, or ambient material
that has been pushed by a poorly collimated wind or accelerated by a highly collimated jet. Observations tend to favour the
latter model, with jets being the clear favourite at least for the youngest flows. Jets from young stars may accelerate ambient
gas either through the development of a boundary layer, where ambient and jet material are turbulently mixed, or at the working
surface of the jet, i.e. the bow shock, via the prompt entrainment mechanism. Recently, we (Downes and Ray, 1999) have investigated,
through simulations, the efficiency of prompt entrainment in jets from young stars as a means of accelerating ambient molecular
gas without causing dissociation. Prompt entrainment was found to be very poor at transferring momentum from the jet to its surroundings in both the case
of ``heavy' (not surprizingly) but also ``equi-density' (with respect to the ambient environment) jets. Moreover the transfer
efficiency decreases with increasing density as the bow shock takes on a more aerodynamic shape. Models, however, in which
jets are the ultimate prime movers, do have the advantage that they can reproduce several observational features of molecular
outflows. In particular a power law relationship for mass versus velocity, similar to what is observed, is predicted by the
simulations and the so-called ``Hubble Law' for molecular outflows is naturally explained. Pulsing of the jet, i.e. varying
its velocity, is found to have little effect on the momentum transfer efficiency at least for the dynamically young jets we
have studied.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Yu-Qin Chen Gang Zhao National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,2(2):151-160
1 INTRODUCTION In the past years, we were thrilled to the reports of discoveries of many planets around stars.These planetary systems outside the solar system (if exist) provide not only an independenttest of the formation theory of the solar system but also a chance to search for extraterrestriallife in the universe. Many studies have been made to identify the particularities of these stars,among which spectroscopic studies (e.g. Gonzalez et al. 2001; Santos et al. 2001; Zhao etaL. 2001… 相似文献
20.
Li-Feng Xing Xiao-Bin Zhang Jian-Yan Wei National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Technology Physics Zhengzhou University of Light Industry Zhengzhou Graduate School of Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2006,6(6):716-722
We monitored the light curves of 22 weak-line T Tauri stars (WTTSs) discovered among the X-ray sources in the field of the Taurus-Auriga cloud. For 12 of the 22 WTTSs photometric periodic variability is confirmed and their rational periods are determined using Phase Dispersion Minimization (PDM) and Fourier analysis. Most of them are found to have periods shorter than one day. This gives further evidence for the spin up of solar-type stars predicted by the models of angular momentum evolution of pre-main sequence stars. 相似文献