Dynamics and collisions of episodic jets from black holes and accretion disk systems

In many astrophysical black hole systems, episodic jets of plasma blobs have been observed, which are much faster and more powerful than continuous jets. A magnetohydrodynamical model was proposed by Yuan et al. to study the formation of episodic jets in Sgr A*. By taking Sgr A* and a stellar mass black hole as examples, we modify the model of Yuan et al. by including the effects of relativity, and further study the relativistic motion and expansion of episodic jets of plasma blobs. Then we study the collision between two consecutive ejections in the modified model, and calculate the magnetic energy released in the collision. Our results show two consecutive blobs can collide with each other, and the released magnetic energy is more than 1050 erg,which supports the idea that a gamma-ray burst is powered by the collision of episodic jets, as suggested by Yuan & Zhang.     

Modern comprehensive study of the W UMa system TY Boo

New three color light curves of TY Boo were acquired during five nights from February to May 2006 in the BV R bandpass using a 50-cm F/8.4 RitcheyChr′etien telescope(Ba50)at the Baja Astronomical Observatory(Hungary),with a512×512 Apogee AP-7 CCD camera.A photometric solution of these light curves was obtained by means of the Wilson-Devinney code.The results showed that the less massive component is hotter than the more massive one,and the temperature difference between the components is △T～249 K.Long term investigation of the system based on all available data shows two stages of increase and a similar trend for decrease,which appears to be periodic behavior.A set of new light elements yields a new period(P=0.3171506d)and shows a periodic decrease with the rate d P/d E=5.858×10-12d cycle-1,6.742×10-9d yr-1or 0.058 s century-1.The evolutionary status of the system is discussed.     

Hints of a second explosion(a quark nova) in Cassiopeia A supernova

We show that the explosive transition of the neutron star(NS)to a quark star(QS)(a Quark Nova)in Cassiopeia A(Cas A)a few days following the supernova(SN)proper can account for several of the puzzling kinematic and nucleosynthetic features that are observed.The observed decoupling between Fe and44Ti and the lack of Fe emission within44Ti regions is expected in the QN model owing to the spallation of the inner SN ejecta by relativistic QN neutrons.Our model predicts the44Ti to be more prominent to the NW of the central compact object(CCO)than in the SE and little of it along the NE-SW jets,in agreement with Nu Star observations.Other intriguing features of Cas A are addressed,such as the lack of a pulsar wind nebula and the reported few percent drop in the CCO temperature over a period of 10 yr.     

Kinematics of solar neighborhood stars and its dependence on age and metallicity

We have constructed a catalog containing the best available astrometric,photometric, radial velocity and astrophysical data for mainly F-type and G-type stars(called the Astrometric Catalog associated with Astrophysical Data, ACAD). This contains 27 553 records and is used for the purpose of analyzing stellar kinematics in the solar neighborhood. Using the Lindblad-Oort model and compiled ACAD, we calculated the solar motion and Oort constants in different age–metallicity bins. The evolution of kinematical parameters with stellar age and metallicity was investigated directly. The results show that the component of the solar motion in the direction of Galactic rotation(denoted S2) linearly increases with age, which may be a consequence of the scattering processes, and its value for a dynamical cold disk was found to be 8.0 ± 1.2 km s-1. S2 also linearly increases with metallicity, which indicates that radial migration is correlated to the metallicity gradient. On the other hand, the rotational velocity of the Sun around the Galactic center has no clear correlation with ages or metallicities of stars used in the estimation.     

Numerical simulation of superhalo electrons generated by magnetic reconnection in the solar wind source region

Superhalo electrons appear to be continuously present in the interplanetary medium, even during very quiet times, with a power-law spectrum at energies above ～2 ke V. Here we numerically investigate the generation of superhalo electrons by magnetic reconnection in the solar wind source region, using magnetohydrodynamics and test particle simulations for both single X-line reconnection and multiple X-line reconnection. We find that the direct current electric field, produced in the magnetic reconnection region, can accelerate electrons from an initial thermal energy of T ～ 105 K up to hundreds of ke V. After acceleration, some of the accelerated electrons, together with the nascent solar wind flow driven by the reconnection, propagate upwards along the newly-opened magnetic field lines into interplanetary space, while the rest move downwards into the lower atmosphere. Similar to the observed superhalo electrons at 1 AU, the flux of upward-traveling accelerated electrons versus energy displays a power-law distribution at ～ 2-100 ke V, f(E) ～ E-δ, with a δ of ～ 1.5- 2.4.For single(multiple) X-line reconnection, the spectrum becomes harder(softer) as the anomalous resistivity parameter α(uniform resistivity η) increases. These modeling results suggest that the acceleration in the solar wind source region may contribute to superhalo electrons.     

Characterizing motion types of G-band bright points in the quiet Sun

We study the motion of G-band bright points(GBPs)in the quiet Sun to obtain the characteristics of different motion types.A high resolution image sequence taken with the Hinode/Solar Optical Telescope(SOT)is used,and GBPs are automatically tracked by segmenting 3D evolutional structures in a space-time cube.After putting the GBPs that do not move during their lifetimes aside,the non-stationary GBPs are categorized into three types based on an index of their motion type.Most GBPs that move in straight or nearly straight lines are categorized as a straight motion type,a few moving in rotary paths into rotary motion,and the others fall into a motion type we called erratic.The mean horizontal velocities are 2.18±0.08 km s-1,1.63±0.09 km s-1and 1.33±0.07 km s-1for straight,erratic and rotary motion types,respectively.We find that a GBP drifts at a higher and constant velocity during its whole life if it moves in a straight line.However,it has a lower and variational velocity if it moves on a rotary path.The diffusive process is ballistic-,super-and sub-diffusion for straight,erratic and rotary motion types,respectively.The corresponding diffusion index(γ)and coefficients(K)are 2.13±0.09 and 850±37 km2s-1,1.82±0.07 and331±24 km2s-1,and 0.73±0.19 and 13±9 km2s-1.In terms of direction of motion,it is homogeneous and isotropic,and usually persists between neighboring frames,no matter what motion type a GBP is classified as.     

Suzaku observation of Be / X-ray binary pulsar EXO 2030+375

We study the timing and spectral properties of Be/X-ray binary pulsar EXO 2030+375 using a Suzaku observation taken on 2012 May 23,during a less intense Type I outburst.Pulsations were clearly detected in the X-ray light curves at a barycentric period of 41.2852 s,which suggest that the pulsar is spinning-up.The pulse profiles were found to be peculiar,e.g.unlike those obtained from the earlier Suzaku observation acquired on 2007 May 14.A single-peaked narrow profile at soft X-rays(0.5–10 ke V range)changed to a double-peaked broad profile in the 12–55 ke V energy range and again reverted back to a smooth single-peaked profile at hard X-rays(55–70 ke V range).The 1.0–100.0 ke V broadband spectrum of the pulsar was found to be well described by three continuum models described as(i)a partial covering high energy cut-off power-law model,(ii)a partially absorbed power-law with highenergy exponential rolloff and(iii)a partial covering Negative and Positive power law with EXponential(NPEX)continuum model.Unlike the earlier Suzaku observation during which several low energy emission lines were detected,a weak and narrow Iron Kαemission line at 6.4 ke V was only present in the pulsar spectrum during the2012 May outburst.Non-detection of any absorption like feature in the 1–100 ke V energy range supports the claim of the absence of the cyclotron resonance scattering feature in EXO 2030+375 from the earlier Suzaku observation.Pulse-phase resolved spectroscopy revealed the presence of additional dense matter causing the absence of a second peak from the soft X-ray pulse profiles.The details of the results are described in the paper.     

Long-term transit timing monitoring and homogenous study of WASP-32

We report new photometric observations of the transiting exoplanetary system WASP-32 made by using CCD cameras at Yunnan Observatories and Ho Koon Nature Education cum Astronomical Centre, China from 2010 to 2012. Following our usual procedure, the observed data are corrected for systematic errors according to the coarse decorrelation and SYSREM algorithms so as to enhance the signal of the transit events. Combined with radial velocity data presented in the literature, our newly observed data and earlier photometric data in the literature are simultaneously analyzed to derive the physical parameters describing the system by employing the Markov chain Monte Carlo technique. The derived parameters are consistent with the result published in the original paper about WASP-32b, but the uncertainties of the new parameters are smaller than those in the original paper. Moreover, our modeling result supports a circular orbit for WASP-32b. Through the analysis of all available mid-transit times, we have refined the orbital period of WASP-32b; no evident transit timing variation is found in these transit events.     

Sensitivity study of high eccentricity orbits for Mars gravity recovery

By linear perturbation theory, a sensitivity study is presented to calculate the contribution of the Mars gravity field to the orbital perturbations in velocity for spacecrafts in both low eccentricity Mars orbits and high eccentricity orbits(HEOs). In order to improve the solution of some low degree/order gravity coefficients, a method of choosing an appropriate semimajor axis is often used to calculate an expected orbital resonance, which will significantly amplify the magnitude of the position and velocity perturbations produced by certain gravity coefficients. We can then assess to what degree/order gravity coefficients can be recovered from the tracking data of the spacecraft. However, this existing method can only be applied to a low eccentricity orbit, and is not valid for an HEO. A new approach to choosing an appropriate semimajor axis is proposed here to analyze an orbital resonance. This approach can be applied to both low eccentricity orbits and HEOs. This small adjustment in the semimajor axis can improve the precision of gravity field coefficients and does not affect other scientific objectives.