A possible origin of viscosity in Keplerian accretion disks due to secondary perturbation: Turbulent transport without magnetic fields     

Banibrata Mukhopadhyay  Kanak Saha 《中国天文和天体物理学报》2011,11(2)

The origin of hydrodynamic turbulence in rotating shear flow is a long standing puzzle.Resolving it is especially important in astrophysics when the flow's angular momentum profile is Keplerian which forms an accretion disk having negligible molecular viscosity.Hence,any viscosity in such systems must be due to turbulence,arguably governed by magnetorotational instability,especially when temperature T ≥10 5.However,such disks around quiescent cataclysmic variables,protoplanetary and star-forming disks,and t...  相似文献   

First photometric study of the eclipsing binary PS Persei     

Jin-Zhao Yuan 《中国天文和天体物理学报》2011,11(2)

CCD photometric observations of the eclipsing binary PS Persei (PS Per) were obtained on two consecutive days in 2009.The 2003 version of the WilsonDevinney code was used to analyze the first complete light curves in the V and R bands.It is found that PS Per is a short-period Algol-type binary with the less massive component completely filling its inner critical Roche lobe.The mass ratio of q=0.518 and the orbital inclination of i=89.86° are obtained.In addition,based on all available times of primary light...  相似文献   

Dark energy in five-dimensional Brans-Dicke cosmology with dimensional reduction     

Ahmad Rami El-Nabulsi 《中国天文和天体物理学报》2011,(8)

We explore a 5D Brans-Dicke scalar cosmology by conjecturing that the four-dimensional Hubble parameter varies as H = εφs,ε∈ R and s is some unknown power index and that the extra-dimensions compactify as the visible dimensions expand as b(t) ≈ ax(t) ,x ∈ R-. We mainly discuss the case x =-1. For critical values of ε close to unity,it was observed that the acceleration of the universe occurs at redshift close to z = 0.8 which indicates that in our model,accelerated expansion of the universe began only recen...  相似文献   

Solar sail time-optimal interplanetary transfer trajectory design     

Sheng-Ping Gong  Yun-Feng Gao  Jun-Feng Li School of Aerospace  Tsinghua University  Beijing  China 《中国天文和天体物理学报》2011,(8)

The fuel consumption associated with some interplanetary transfer trajectories using chemical propulsion is not affordable. A solar sail is a method of propulsion that does not consume fuel. Transfer time is one of the most pressing problems of solar sail transfer trajectory design. This paper investigates the time-optimal interplanetary transfer trajectories to a circular orbit of given inclination and radius. The optimal control law is derived from the principle of maximization. An indirect method is used...  相似文献   

Photometric analysis of V30 of open cluster NGC 7789     

Yellapragada Ravi Kiron  Kandulapati Sriram  Pasagada Vivekananda Rao 《中国天文和天体物理学报》2011,(9)

We present the photometric solutions of the variable star V30 that is in the foreground of intermediate open cluster NGC 7789.The observations were done in the V passband using the 2 m telescope at the IUCAA-Girawali Observatory in India.The analysis is done using the Wilson-Devinney Code (2003) and the fitted light curve is presented.The photometric solutions reveal a W-subtype contact configuration.The photometric mass ratio is found to be 0.395 and the absolute masses and radii for the components are ded...  相似文献   

The physical origin of optical flares following GRB 110205A and the nature of the outflow     

Wei-Hong Gao 《中国天文和天体物理学报》2011,(11)

The optical emission of GRB 110205A is distinguished by two flares.We examine two possible scenarios for the optical afterglow emission.In the first scenario,the first optical flare is the reverse shock emission of the main outflow and the second one is powered by the prolonged activity of the central engine.However,we find that it is rather hard to reasonably interpret the late(t > 0.1 d) afterglow data unless the GRB efficiency is very high(～ 0.95).In the second scenario,the first optical flare is the low...  相似文献   

On pulsar-driven mass ejection in low-mass X-ray binaries     

Lei Fu  Xiang-Dong Li 《中国天文和天体物理学报》2011,(12)

There is accumulating evidence for mass ejection in low-mass X-ray binaries(LMXBs)driven by radio pulsar activity during X-ray quiescence.We consider the condition for mass ejection by comparing the radiation pressure from a millisecond pulsar,and the gas pressure at the inner Lagrange point or at the surrounding accretion disk.We calculate the critical spin period of the pulsar below which mass ejection is allowed.Combining with the evolution of the mass transfer rate,we present constraints on the orbital ...  相似文献   

CCD photometry of W UMa-type contact binaries in the old open cluster Berkeley 39     

Yellapragada Ravi Kiron  Kandulapati Sriram  Pasagada Vivekananda Rao 《中国天文和天体物理学报》2011,(12)

We present the combined BVI multicolor photometric solutions of seven EW variables in the old open cluster Berkeley 39.The observations were carried out in the B and V passbands from the 2 m telescope at the IUCAA-Girawali Observatory in India.The analysis is done using the 2003 version of the Wilson-Devinney code and the fitted light curves are presented.The light curves appear to be symmetric in all the passbands.The photometric solutions suggest that the variables are W-type systems.The new ephemeris ind...  相似文献   

Relations between integrated and monochromatic luminosities of flat-spectrum radio quasars     

Lian-Zhong Lü 《中国天文和天体物理学报》2011,11(4)

We employ a sample of 362 flat-spectrum radio quasars (FSRQs) to calculate their integrated luminosities by integrating the spectral energy distribution (SED) constructed with multi-band (radio,IR,optical,UV and X-ray) data.We compare these luminosities with those estimated from monochromatic luminosities by multiplying them by the conventional bolometric correction factors.Our analysis shows that the integrated luminosities calculated from the SED are much larger than the bolometric luminosities estimated ...  相似文献   

Strange star candidates revised within a quark model with chiral mass scaling     

Ang Li  Guang-Xiong Peng  Ju-Fu Lu 《中国天文和天体物理学报》2011,11(4)

We calculate the properties of static strange stars using a quark model with chiral mass scaling.The results are characterized by a large maximum mass (～ 1.6 M) and radius (～10 km).Together with a broad collection of modern neutron star models,we discuss some recent astrophysical observational data that could shed new light on the possible presence of strange quark matter in compact stars.We conclude that none of the present astrophysical observations can prove or confute the existence of strange stars.  相似文献