New merlin observations of OH/IR stars: OH357.31-1.33 and OH0.9+1.3     

V. Migenes  E. Lüdke  R. J. Cohen  M. Shepherd  P. F. Bowers 《Astrophysics and Space Science》1995,224(1-2):515-516

We present recent radio interferometer measurements of the OH 1612 MHz maser emission from the OH/IR sources OH0.9+1.3 and OH357.31 obtained with the enhanced MERLIN. Some preliminary results are briefly discussed. These results are part of an on-going observational campaign to obtain the best radio maps of bright OH/IR stars with MERLIN, VLA and VLBA, in order to understand the nature and dynamics of their circumstellar matter and evolution.  相似文献   

Pulsations in subdwarf B stars     

C. Simon Jeffery 《Journal of Astrophysics and Astronomy》2005,26(2-3):261-271

Subdwarf B stars play a significant role in close binary evolution and in the hot star content of old stellar populations, in particular in giant elliptical galaxies. While the question of their origin poses several problems for stellar evolution theory, one of their most fascinating properties is the presence of multi-periodic 2–3 minute oscillations. Interpreting these oscillations optimally requires the correct identification of the modes. Partial identifications can be obtained using high-speed observations of radial velocity and colour variations. We review some of the several attempts to make such observations, most recently with the Multi-Site Spectroscopic Telescope campaign and withULTRACAM.  相似文献   

Pre-main-sequence outflows     

Colin R. Masson 《Astrophysics and Space Science》1995,224(1-2):99-108

In the 3 decades since winds from young stars were discovered, there have been many observations of bipolar molecular flows and ionized jets, and it has been recognized that outflows are intimately linked to star formation. Despite many observational clues and theoretical ideas, we still do not have a fully coherent picture of the outflow process.  相似文献   

18颗双星的自转测量     

谭徽松 《中国天文和天体物理学报》1986,(2)

用美国McDonald天文台2.1米反射镜的折轴Reticon观测HeI 5875谱线,由标准星的观测轮廓与Gray的转致轮廓卷积后同被测星的观测轮廓进行拟合,测得了18颗双星的Vsini,并结合以前测得的20个双星系统的结果,同Slettebak老系统进行了比较,得到了它们的近似关系:在Vsini<100 kms~(-1)时,两者的值比较一致;当Vsini>100kms~(-1)时,本方法得出的值明显偏低。这一关系间接说明,我们的结果与Slettebak新系统的趋势是一致的。  相似文献   

Infrared speckle imaging: Data reduction with application to binary stars     

J. C. Christou 《Experimental Astronomy》1991,2(1):27-56

The extended Knox-Thompson reduction scheme currently in use at Kitt Peak National Observatory and Steward Observatory for the reduction of infrared speckle interferometry is described in detail. Applications of this algorithm and the less computationally intensive shift-and-add analysis to both simulated and real binary star data is presented demonstrating that the latter may be successfully used for image reconstruction by using a separately measured point source. The performance of both techniques is shown to improve by application of an iterative deconvolution algorithm to apply a priori image constraints without degradation of photometric information.Operated by the Association of Universities for Research in Astronomy Inc. (AURA) under cooperative agreement with the National Science Foundation  相似文献   

A numerical survey of neutron star crustal density profiles     

B. Datta  A. V. Thampan  D. Bhattacharya 《Journal of Astrophysics and Astronomy》1995,16(3-4):375-391

An accurate numerical survey of the density profiles corresponding to the crusts of neutron stars for representative equation of state models is presented. This will find application in calculations of thermal and magnetic evolution of neutron stars.  相似文献   

Magnetic fields at the surfaces of stars     

J. D. Landstreet 《Astronomy and Astrophysics Review》1992,4(1):35-77

Summary Magnetic fields have now been detected in stars in several parts of the Hertzsprung-Russell diagram. Roughly dipolar fields ranging in strength between 3× 10² and 3×10⁴ G are found in many chemically peculiar A and B main sequence stars. Dipolar fields are also found in some 2–3% of white dwarfs, but with strengths between 1×10⁶ and 5×10⁸ G. In both these types of stars, the observed fields vary as the underlying star turns, but do not change in a secular manner. In solartype stars, structurally complex fields of a few kG are found with filling factors of the order of 0.1 to 0.8. Further indirect evidence of fields in cool main sequence stars is provided by detection of visible and ultraviolet line emission (chromospheric activity), x radiation (coronal matter), and giant starspots. In this review, we survey the observations of stellar magnetism in all these types of stars, as well as efforts to model the observed magnetic fields and associated photospheric peculiarities and activity.This article was processed by the author using the Springer-Verlag T_EX AAR macro package 1991.  相似文献   

Shocks and shells in hot star winds     

A. Feldmeier  J. Puls  C. Reile  A. W. A. Pauldrach  R. P. Kudritzki  S. P. Owocki 《Astrophysics and Space Science》1995,233(1-2):293-299

Radiation-driven winds of hot, massive stars showvariability in UV and optical line profiles on time scales of hours to days.Shock heating of wind material is indicated by the observed X-ray emission. We present time-dependent hydrodynamical models of these winds, where flowstructures originate from a strong instability of the radiative driving. Recent calculations (Owocki 1992) of the unstable growth of perturbations were restricted by the assumptions of 1-D spherical symmetry and isothermality of the wind. We drop the latter assumption and include the energy transfer in the wind. This leads to a severe numerical shortcoming, whereby all radiative cooling zones collapse and the shocks become isothermal again. We propose a method to hinder this collapse. Calculations for dense supergiant winds then show: (1) The wind consists of a sequence of narrow and dense shells, which are enclosed by strong reverse shocks (with temperatures of 10⁶ to 10⁷ K) on their starward facing side. (2) Collisions of shells are frequent up to 6 to 7 stellar radii. (3) Radiative cooling is efficient only up to 4 to 6R _*. Beyond these radii, cooling zones behind shocks become broad and alter the wind structure drastically: all reverse shocks disappear, leaving regions ofpreviously heated gas.  相似文献   

Spectral analyses of [WCL]-type central stars     

Uwe Leuenhagen 《Astrophysics and Space Science》1996,238(1):75-78

The optical spectra of the seven late-type Wolf-Rayet central stars NGC-40 (PNG 120.0+09.8, subtype [WC8]), He 2-99 (PNG 309.0–04.2, [WC9]), BD+30°3639 (PN G 064.7+05.0, [WC9]), CPD-56°8032 (PNG 332.9–09.9, [WC11]), He2-113 (PNG 321.0+03.9, [WC11]), M4-18 (PNG 146.7+07.6, [WC11]) and K2-16 (PNG 352.9+11.4, [WC11]) are analyzed by means of spherically expanding model atmospheres. The NLTE simulations account for the elements hydrogen, helium, carbon and oxygen. As main results effective temperature, element abundances and final velocity of the wind are determined for each star. Assuming distances or luminosities for the objects, also the stellar radii and the mass-loss rates can be fixed. The results of these analyses establish empirical constraints for the evolutionary status of WC-type central stars as post-AGB objects and provide input for modeling their planetary nebulae.  相似文献   

AB Dor: A single star with RSCVn like activity in X-ray band     

M. Alev  M. A. Alpar  A. Esendemir  Ü. Kiziloğlu 《Astrophysics and Space Science》1996,245(1):15-25

Using the archival ROSAT PSPC observations, AB Dor is found to be variable in X-rays. The periodic variations are consistent with previously reported rotational period of 0 ^d .514. The average spectrum of AB Dor is best represented with two-temperature Raymond-Smith model with kT values of 0.19±0.07 and 1.17±0.02 keV. The quiescent luminosity of the system is found to be 4.36±0.6×10³⁰ ergs s^–1. A flare with a rise time of 350 seconds is detected during which X-ray luminosity rises from 5.8±1.6×10³⁰ to 15.8±4.9×10³⁰ ergs s^–1. We conclude that AB Dor is very similar to the active components of RS CVn binaries and other active classes. In view of the wide separation from the binary companion Rst 137B, this activity must be intrinsic to the active star.  相似文献