A Chandra study of the massive,distant galaxy cluster SDSS J0150–1005

We present a study of a fossil cluster,SDSS J0150–1005（z 0.364）,with high spatial resolution based on the imaging spectroscopic analysis of Chandra observations.The Chandra X-ray image shows a relaxed and symmetric morphology,which indicates that SDSS J0150–1005 is a well-developed galaxy cluster with no sign of a recent merger.According to the isothermal model,its global gas temperature is 5.73±0.80 keV,and the virial mass is 6.23±1.34×1014M⊙.Compared with the polytropic temperature model,the mass calculated based on the isothermal model is overestimated by 49%±11.The central gas entropy,S0.1 r200=143.9±18.3 keV cm2,is significantly lower than the average value of normal galaxy clusters with similar temperatures.Our results indicate that SDSS J0150–1005 formed during an early epoch.     

The timing behavior of magnetar Swift J1822.3—1606： timing noise or a decreasing period derivative？

The different timing results of the magnetar Swift J1822.3—1606 are analyzed and understood theoretically.It is noted that different timing solutions are caused not only by timing noise,but also because the period derivative is decreasing after the outburst.Both the decreasing period derivative and the large timing noise may originate from wind braking associated with the magnetar.Future timing of Swift J1822.3—1606 will help clarify whether or not its period derivative is decreasing with time.     

Study on the Spin Characteristics of the Flora Asteroid Family

Asteroid families are the remnants of catastrophic collisions, and their fundamental physical properties provide us the information of their parent bodies and thereafter dynamical evolutions. Especially, the orbit and spin characteristics can reveal the influences of the Yarkovsky effect and the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect on the evolution of the asteroid family, respectively. Based on the Asteroid Lightcurve Database (LCDB), the spin rate distribution of the Flora asteroid family is studied, and a tendency that the spin rates of the small Flora family members concentrate primarily in the range of 3–5 d^?1 is found. The analysis on the spin states of the Flora family asteroids tells that most of these asteroid family members are in the prograde spinning state. However, for the Flora family members with an orbital semi-major axis smaller than 2.2 au, the ratio between the number of prograde spinning members and that of retrograde ones is close to that of the near-Earth asteroids, namely 1 : 3. Furthermore, for those prograde spinning Flora family asteroids with an orbital semi-major axis larger than 2.2 au, a portion of them exhibit the aggregation in the distribution of orbital semi-major axis against the absolute magnitude, and in which nine members show the features similar to the Slivan state.     

Effect of Orbital Distance on the Atmospheric Escape of Exoplanets

Atmospheric escape is an important sector in the evolution of planetary atmosphere, and its energy is mainly originated from the radiation of the host star at the high energy band. The radiation flux drops dramatically with the increase of orbital distance, there is a large difference of planetary atmospheric escape in different orbits, so it is necessary to study the impact of orbital distance on the atmospheric escape of an exoplanet. We consider the radiation transfer and the photochemical reactions of multiple kinds of particles to study the variation of planetary atmospheric escape with the orbital distance by using a 1-D hydrodynamic model. Due to the large differences of the spectra of host stars in different evolution stages, the Astrophysical Plasma Emission Code (APEC) in the X-Ray Spectral Fitting Package (XSPEC) is used to obtain the spectra of solar-type stars with different ages as the input spectra of the model. The results indicate that the escape rates of the exoplanets in different orbits are different significantly, and the escape mechanism is converted from the drastic hydrodynamic escape into the moderate Jeans escape as the orbital distance increases, the smaller the planetary gravitational potential, the younger the star-planet system, the larger the distance of this conversion. The correlation between the escape rate and the radiation flux decreases for the short-period exoplanets in a younger star-planet system. It is shown that the classical energy-limited escape theory is not suitable for this kind of exoplanets. These results have enriched the studies on the atmospheric escape of exoplanets, especially, extended the studies on the escape mechanism and energy conversion under different orbital distances and stellar ages.