Table of contents

In the present work, we reconstruct different f(T)-gravity models corresponding to the original and entropy-corrected versions of the holographic and new agegraphic dark energy models. We also obtain the equation of state parameters of the corresponding f(T)-gravity models. We conclude that the original holographic and new agegraphic f(T)-gravity models behave like the phantom or quintessence model, whereas in the entropy-corrected models, the equation of state parameter can justify the transition from the quintessence state to the phantom regime as indicated by the recent observations.

We present the model of an anisotropic universe with string fluid as the source of matter within the framework of the scalar-tensor theory of gravitation. An exact solution of field equations is obtained by applying Berman's law of variation to Hubble's parameter which yields a constant value of the deceleration parameter. The nature of classical potential is examined for the model under consideration. It has also been found that the massive strings dominate in the early universe and finally disappear from the universe. This is in agreement with current astronomical observations. The physical and dynamical properties of the model are also discussed.

The kinematics of ten superluminal components (C11– C16, C18, C20, C21 and C24) of blazar 3C 279 are studied from VLBI observations. It is shown that their initial trajectory, distance from the core and apparent speed can be well fitted by the precession model proposed by Qian. Combined with the results of the model fit for the six superluminal components (C3, C4, C7a, C8, C9 and C10) already published, the kinematics of sixteen superluminal components can now be consistently interpreted in the precession scenario with their ejection times spanning more than 25 yr (or more than one precession period). The results from model fitting show the possible existence of a common precessing trajectory for these knots within a projected core distance of ∼0.2–0.4 mas. In the framework of the jet-precession scenario, we can, for the first time, identify three classes of trajectories which are characterized by their collimation parameters. These different trajectories could be related to the helical structure of magnetic fields in the jet. Through fitting the model, the bulk Lorentz factor, Doppler factor and viewing angle of these knots are derived. It is found that there is no evidence for any correlation between the bulk Lorentz factor of the components and their precession phase (or ejection time). In a companion paper, the kinematics of another seven components (C5a, C6, C7, C17, C19, C22 and C23) have been derived from model fitting, and a binary black-hole/jet scenario was envisaged. The precession model proposed by Qian would be useful for understanding the kinematics of superluminal components in blazar 3C 279 derived from VLBI observations, by disentangling different mechanisms and ingredients. More generally, it might also be helpful for studying the mechanism of jet swing (wobbling) in other blazars.

After a brief reminder of the mechanism of gravitational lensing of extended sources, the particular case of the host galaxy of QSO RXJ0911, a high redshift (z ∼ 2.8) quadruply imaged quasar, is explored. The non linearity of the problem, together with the proximity of the source to a cusp of the lens inner caustic, has important consequences on the dependence of the image appearance on the size and shape of the source. Their expected main features and their interpretation in terms of source extension and shape are investigated in a spirit of simplicity and in preparation for the analysis of high sensitivity and spatial resolution images that will soon be within reach with the completion of the Atacama Large Millimeter/submillimeter Array (ALMA). In particular, the information on source size carried by relative image brightness is discussed. Extension of the results to other types of quadruply imaged quasars is briefly considered.

We report the internal proper motions of 12 GHz methanol masers in massive star-forming region G35.20–0.74 observed with the Very Long Baseline Array (VLBA) at four epochs spanning about 1.5 yr. Two groups of maser features were detected, groups A and B, and the latter that had a V-shaped spatial distribution is likely tracing the north outflow in G35.20–0.74. We present a three-dimensional model for the kinematics of these masers, by assuming the interstellar medium was blown by the stellar wind from the driving source (G35.2N) of the outflow. Adopting a position angle of ∼ 81° for the main axis of the outflow from previous studies, we estimate an inclination of 35° ± 5.5°, a velocity of 8.1 ± 0.7 km s⁻¹ for the stellar wind along the main axis and an expansion speed gradient of 0.05 ± 0.016 km s⁻¹ AU⁻¹. From the model, we derive the age of the north outflow in G35.20–0.74 to be ∼ 1.6 × 10⁴ yr.

We analyzed the B and V light curves of two EA-type binaries V211 and NV358 for the first time using the Wilson-Devinney code. Our analysis shows that V211 is a typical Algol-type binary and NV358 is a well detached binary system. As the two binaries are definite members of ω Centauri due to their proper motion, we estimated their physical parameters, obtaining M₁ = 1.13 ± 0.03 M_⊙, R₁ = 0.98 ± 0.01 R_⊙, M₂ = 0.33 ± 0.01 M_⊙ and R₂ = 0.92 ± 0.01 R_⊙ for V211; M₁ = 1.30±0.05 M_⊙, R₁ = 1.03±0.01 R_⊙, M₂ = 0.58±0.02 M_⊙ and R₂ = 0.78±0.01 R_⊙ for NV358. On the color-magnitude diagram of ω Centauri, V211 is located in the faint blue straggler region and its primary component is more massive than a star at the main-sequence turnoff. Therefore, V211 is a blue straggler and was formed by mass transfer from the secondary component to the primary. The age of NV358 is less than 1.93 Gyr, indicating that it is much younger than the first generation of stars in ω Centauri. Like NV364 in ω Centauri, NV358 should be a second-generation binary.

The magnetar Swift J1834.9–0846 is observed using the Nanshan 25 m radio telescope. No pulsed radio emission is detected. The upper limit on the pulsed radio emission from this source is 0.5 mJy. According to the "fundamental plane" for radio magnetars, this source should have radio emission. Therefore, our results put constraints on the existence of a fundamental plane of magnetar radio emission. We argue that a magnetar's ability to emit radio emission may have little to do with the spin down luminosity and is related to the magnetar's X-ray luminosity. The only necessary condition is a relatively low X-ray luminosity.

We present modeling work on three young stellar objects that are promising targets for future high-resolution observations to investigate circumstellar disk evolution. The currently available data comprise the spectral energy distribution from optical to millimeter wavelengths which allow constraining the structure of the circumstellar disk using self-consistent radiative transfer models. The results suggest that the assumption of well-mixed dust and gas leads to overestimation of flux in the far-infrared. Observational and theoretical arguments suggest that an overall decrease in far-infrared excess can be explained by dust settling towards the midplane. A new disk model is hence employed to take the effect of dust sedimentation into account. The extended model satisfactorily reproduces all existing observations. The three targets studied here therefore deserve follow-up observations to reveal the evolutionary state of their protoplanetary disks.

We reconstruct the rotation curve of the Milky Way using the new trigonometric parallax and proper motion data for masers in 43 high-mass star-forming regions obtained by VLBI, as well as the existing data from the literature, based on a new set of galactic constants (R₀, Θ₀) = (8.4 kpc, 254 km s⁻¹) measured by Reid et al. The revised rotation curve of the Milky Way is almost flat or slightly rising in the region from about 15 to 6 kpc. The rotation velocities within 5 kpc of the Galactic center, as determined by VLBI, differ from those obtained by measurement of the HI- and CO-line tangent velocities. We fitted the revised rotation curve arising from three mass components: the bulge, disk and dark matter halo. The total mass of the Milky Way is found to be 2.3 × 10¹¹M_⊙ (20 kpc). This is about 10% larger than that from Sofue et al, and is comparable with the mass of M31, 3.4 × 10¹¹M_⊙ (35 kpc), given by Carignan et al. The limited accurate observational data, especially the VLBI data, do not permit a fully satisfactory fit to the rotation curve. The extensive parallax and proper motion data that will be produced by the Bar and Spiral Structure Legacy Survey project in the next few years should lead to considerable progress in understanding the rotation curve and dark matter halo of the Milky Way.

The second phase of the Chang'E Program (also named Chang'E-3) has the goal to land and perform in-situ detection on the lunar surface. A VIS/NIR imaging spectrometer (VNIS) will be carried on the Chang'E-3 lunar rover to detect the distribution of lunar minerals and resources. VNIS is the first mission in history to perform in-situ spectral measurement on the surface of the Moon, the reflectance data of which are fundamental for interpretation of lunar composition, whose quality would greatly affect the accuracy of lunar element and mineral determination. Until now, in-situ detection by imaging spectrometers was only performed by rovers on Mars. We firstly review reflectance conversion methods for rovers on Mars (Viking landers, Pathfinder and Mars Exploration rovers, etc). Secondly, we discuss whether these conversion methods used on Mars can be applied to lunar in-situ detection. We also applied data from a laboratory bidirectional reflectance distribution function (BRDF) using simulated lunar soil to test the availability of this method. Finally, we modify reflectance conversion methods used on Mars by considering differences between environments on the Moon and Mars and apply the methods to experimental data obtained from the ground validation of VNIS. These results were obtained by comparing reflectance data from the VNIS measured in the laboratory with those from a standard spectrometer obtained at the same time and under the same observing conditions. The shape and amplitude of the spectrum fits well, and the spectral uncertainty parameters for most samples are within 8%, except for the ilmenite sample which has a low albedo. In conclusion, our reflectance conversion method is suitable for lunar in-situ detection.

Ground Layer Adaptive Optics (GLAO) is a recently developed technique extensively applied to ground-based telescopes, which mainly compensates for the wavefront errors induced by ground-layer turbulence to get an appropriate point spread function in a wide field of view. The compensation results mainly depend on the turbulence distribution. The atmospheric turbulence at Dome A in the Antarctic is mainly distributed below 15 meters, which is an ideal site for applications of GLAO. The GLAO system has been simulated for the Kunlun Dark Universe Survey Telescope, which will be set up at Dome A, and uses a rotating mirror to generate several laser guide stars and a wavefront sensor with a wide field of view to sequentially measure the wavefronts from different laser guide stars. The system is simulated on a computer and parameters of the system are given, which provide detailed information about the design of a practical GLAO system.