Galactic distribution of WR stars     

Karel A. van der Hucht 《Astrophysics and Space Science》2002,281(1-2):199-202

The recent VIIth Catalogue of Galactic Wolf-Rayet Stars lists 227 Population I WR stars, comprising 127 WN, 87 WC, 10 WN/WC and 3 WO stars. Additional discoveries bring the census to 234 WR stars. A re-determination of the optical photometric distances and the galactic distribution of WR stars shows in the solar neighbourhood a projected surface density of 2.7 WR stars per kpc², a N _WC/N _WN number ratio of 1.3, and a WR binary frequency of 40 %.The galactocentric distance (R _WR) distribution per subtype showsR _WN and R _WC decreasing with WN and WC subtypes. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Persistent and transient blank field sources     

A. Treves  S. Campana  M. Chieregato  A. Moretti  T. Nelson  M. Orio 《Astrophysics and Space Science》2007,308(1-4):167-169

Blank field sources (BFS) are good candidates for hosting dim isolated neutron stars (DINS). The results of a search of BFS in the ROSAT HRI images are revised. We then focus on transient BFS, arguing that they belong to a rather large population. The perspectives of future research on DINS are then discussed.   相似文献   

Mira变星拱星包层速度流场的二流模型   总被引：1，自引：0，他引：1  

俞志尧 《中国天文和天体物理学报》1986,(4)

我们研究了Mira变星拱星包层速度流场的二流模型。根据拱星包层中尘埃颗粒及气体的连续性方程和动量方程,并假定气体的膨胀过程为多方膨胀过程,通过计算,我们分别得到尘埃颗粒及气体的速度流场、以及尘埃颗粒和气体之间的牵连速度。与观测事实比较后表明,我们得到的尘埃颗粒及气体的速度流场都与观测事实相一致。用我们得到的气体的速度流场估算了Mira变星的质量损失率为1.19×10~(-6)M_⊙/年,这也与已知的观测事实相符。  相似文献   

晚期恒星坍缩时磁轴的变化规律     

张家铝  龚瑞生 《中国天文和天体物理学报》1987,(3)

本文导出了磁偏轴椭球在坍缩时磁轴的变化公式。计算结果表明,磁轴和自转轴重合的情况在坍缩时是不稳定的,稍有偏离,磁轴与自转轴间的夹角就要增大。这有助于说明脉冲星磁轴与自转轴偏离的原因以及通常在研究中假定两者相互垂直的合理性。  相似文献   

The winds of WC10 central stars of planetary nebulae     

Orsola De Marco  M. J. Barlow  P. J. Storey 《Astrophysics and Space Science》1996,238(1):91-96

We present the results of an analysis of the winds of two WC10 central stars of planetary nebulae, CPD-56°8032 and He 2-113. These two stars have remarkably similar spectra, although the former exhibits somewhat broader emission line widths. High resolution spectra (up to R=50 000) were obtained in May 1993 for both objects at the 3.9 m AAT, using the UCL Echelle Spectrograph. The fluxes in individual Cii auto-ionising multiplet components, many of which were blended, were derived. Lines originating from auto-ionising resonance states situated in the C²⁺ continuum are very sensitive to the electron temperature, since the population of the these levels is close to LTE. The measured widths and profile shapes of these transitions are presented and are in excellent agreement with those predicted on the basis of their calculated auto-ionising lifetimes. The wind electron temperature is derived for both stars from the ratio of the fluxes in four such transitions (T _e =18 500 K±1 500 K for CPD-56° 8032 andT _e =13 600 K±800 K for He 2-113). Optical depth effects are investigated using normal recombination lines to obtain an independent wind electron temperature estimate in excellent agreement with the dielectronic line analysis.  相似文献   

仙王VV1976—1978年食的UBV光电测光     

黄永伟  郭子和 《中国天文和天体物理学报》1987,(2)

本文发表1976—1978年食期间,对VVCep进行UBV光电测光的结果。从我们自己观测的B-V和U-B色指数曲线得到了第二,三,四接触时刻,其对应的食甚时刻为JD2443361,与预报的日期相符合。文中,我们用M型子星的气流来解释色指数曲线的下降段和上升段深度不等的现象。从我们解释食的物理模型得到M型超巨星的半径为1860R_⊙,其大气的厚度达450R_⊙,约为半径的四分之一。  相似文献   

A spectrophotometric study of the Wolf-Rayet star HD 50896     

B. S. Shylaja 《Journal of Astrophysics and Astronomy》1986,7(4):305-316

New spectrophotometric observations of the Wolf-Rayet system HD 50896 are presented and interpreted in terms of its binary nature. The lines of N V, N IV and C IV show moderate variations, which can be explained using a binary model with a compact companion. He n λ4686 appears to arise from a larger region compared to other lines. The distortion caused by the wind can partly explain its flux variations. The emission fluxes of He I lines are generally constant indicating their non-participation in the orbit. The results are compared with other Wolf-Rayet binaries (V444 Cyg and CQ Cep) and the evolutionary status is discussed.  相似文献   

Photoelectric photometry of eclipsing binary V375 cassiopeiae     

Zhang Rong-Xian  Zhang Ji-tong  Li Qi-sheng  Zhai Di-sheng 《Chinese Astronomy and Astrophysics》1986,10(4):265-271

Some 604 photoelectric BV observations of the eclipsing binary V375 Cas were obtained at Beijing Observatory from August to November 1982. Photometric solution was carried out using the Wilson-Devinney program for the BV light curves. The system is found to be a semidetached binary in which the less massive component fills its Roche lobe and the more massive component nearly does so. It is very similar to RZ Dra. This very interesting system is important for the understanding of the evolution of close binaries.  相似文献   

Wind Ionization Structure of the Short-Period Eclipsing LMC Wolf-Rayet Binary BAT99-129: Preliminary Results     

C. Foellmi  A. F. J. Moffat  S. V. Marchenko 《Astrophysics and Space Science》2006,304(1-4):85-88

BAT99-129 is a rare, short-period eclipsing Wolf-Rayet binary in the Large Magellanic Cloud. We present here medium-resolution NTT/EMMI spectra that allow us to disentangle the spectra of the two components and find the orbital parameters of the binary. We also present VLT/FORS1 spectra of this binary taken during the secondary eclipse, i.e. when the companion star passes in front of the Wolf-Rayet star. With these data we are able to extract, for the first time in absolute units for a WR + O binary, the sizes of the line emitting regions.Based on observations obtained at the La Silla and Paranal Observatories, European Southern Observatory (Chile).  相似文献   

Modeling the evolution of Sakurai's Object     

Falk Herwig 《Astrophysics and Space Science》2002,279(1-2):103-113

Sakurai's Object is a born again AGBstar of the very late thermal pulse flavor. In thiscontribution I will discuss new models of stellar evolution andnucleosynthesis models of this phase. Two most intriguing properties ofSakurai's Object have so far not been understood theoretically: the peculiar chemical appearance, in particular the high lithiumabundance, and the short time scale of only a few years on which thetransition from the dwarf configuration into the born again giantappearance has occurred. A new nucleosynthesis mode of hot hydrogen-deficient ³He burning can explain the extraordinarylithium abundance. During the thermal pulse ³He is ingested fromthe envelope together with the protons into the hot He-flashconvection zone. The first network calculations show that, due to thelarge ¹²C abundance protons are captured rather by carbon, thandestroy newly formed ⁷Be and ultimately ⁷Li. Moreover, the shortevolution time scale has been reproduced by making the assumption that the convective efficiency forelement mixing is smaller by two to three orders of magnitude thanpredicted by the mixing-length theory. As a result the main energygeneration from fast convective proton capture will occur at a largermass coordinate, closer to the surface and the expansion to the giantstate is accelerated to a few years, in excellent agreement with thebehavior of Sakurai's Object. This result represents an independent empiricalconstraint on the poorly known efficiency of element mixing inconvective zones of the stellar interior.  相似文献