行星(月球)自转监测望远镜的原理样机地面验证实验

类地行星(月球)自转监测望远镜的科学目标是在行星(月球)表面现场测量行星(月球)自转并研究其内部结构和物理性质.为了验证全新的观测原理和资料处理方法,项目团队设计制造了一套原理样机,在一台商用天文望远镜的光路前端增加3面反射镜组,使其具有同时观测3个视场的能力.自2017年起在地面上开展了观测实验,获得了混合有3视场星象的图像.通过计算星象在前后图像上的位移实现了归属视场识别,使得观测效果与分视场独立观测等同,证明了用一台设备同时观测多视场的可行性.处理图像并通过3个视场中心的指向变化归算地球自转轴的空间指向,与理论值比较偏差平均约1′′,证明了观测原理和数据处理方法有效.对各种观测误差来源进行了分析,包含大气折射、仪器热稳定性和光学分辨能力的影响等,指出采用更长焦距的望远镜可以提高空间分辨率,优化形变控制可以提高观测稳定性.改进多视场同时观测中的光学设计也有助于精度的提高.     

A flat FLRW model with dynamical Λ as function of matter and geometry

We revisit the evolution of the scale factor in a flat FLRW spacetime with a new generalized decay rule for the dynamic $\Lambda$-term under modified theories of gravity. It analyzes certain cosmological parameters and examines their behaviours in this generalized setting which includes several decay laws in the literature. We have also obtained observational constraints on various model parameters and estimated the present values of cosmological parameters $\{{\Omega }_{m_0}$, ${\Omega }_{{\Lambda }_0}$, $q_0,t_0$, ${\omega }_0\}$ and have discussed with various observational results. Finite time past and future singularities in this model are also discussed.     

Estimations of Planetary Occurrence Rates for Solar-type Stars with Data Release 25 from Kepler Q1–Q17 Observations

The detection of exoplanets in the past three decades has revealed the fact that planets are ubiquitous in the universe. In order to deeply study the ubiquity of habitable planets, on one hand, we need to understand the characteristics of habitable planets; on the other hand, we can analyze the the distribution characteristics of exoplanets have been found, and to calculate the probability of occurrence of such planets around stars. Among the exoplanets that have been found so far, most of them are discovered by the transit method. For example, the number of the planets detected by the Kepler space telescope is 2344. Kepler telescope officially retired in 2018, and the Kepler team released the final version of Kepler Data Release (DR25), including a total of 198709 stars observed quarterly Q1–Q17. Here we analyze the Kepler data by using two different methods, Inverse Detection Efficiency Method (IDEM) and Maximum Likelihood Analysis (ML), to estimate planet occurrence rates in the space of the parameters of radius and orbital period. At the same time, the samples were classified according to the spectral types of stars, and the planet occurrence rates around F, G, and K Kepler stars as well as its overall formation rate were estimated respectively. We estimate the planetary occurrence rates for planets among radius range of 1–20 $R_{\oplus }$ ($R_{\oplus }$ is one radius of the Earth) and orbital period range of 0.4–400 days by IDEM and ML, for which around F stars are respectively $0.36\pm 0.02$ and $0.47\pm 0.02$. The rates around G stars by IDEM and ML are respectively $1.62\pm 0.05$ and $1.23\pm 0.04$. The rates around K stars by IDEM and ML are respectively $2.61\pm 0.12$ and $2.73\pm 0.13$. And the overall occurrence rate of such planets around F, G, K stars by IDEM and ML are respectively $1.16\pm 0.03$ and $0.90\pm 0.02$. According to our estimation, we further show the results for the planet occurrence rates around stars with different spectral types by different methods, and discuss the reliability of the results in comparison with the previous studies.     

Tsallis holographic dark energy model with observational constraints in the higher derivative theory of gravity

The present study deals with a Tsallis holographic dark energy model in a flat Friedmann-Lamatire-Rbertson-Walker space-time geometry in the context of higher derivative theory of gravity. We have solved the field equations by applying energy conservation-law in non-interacting case and have obtained such a scale factor $a\left(\tau \right)={\left[\sinh \left(\sqrt{2a_1}\tau \right)\right]}^{\frac{1}{2}}$ where $a_1$ is called as model parameter which shows transit phase evolution of the universe (decelerating to accelerating). Using this scale factor we have obtained the various cosmological parameters viz. Hubble parameter $H$, deceleration parameter (DP) $q$, jerk $j$, snap $s$, lerk $l$ and max-out $m$. Constraining on Hubble parameters $H\left(z\right)$ by the observational data of $H\left(z\right)$ we have obtained the present values of $H_0$, $a_0$ and $a_1$ and by using these constrained values, we have studied other cosmological parameters. Taking the constant equation of state (EoS) ${\omega }_m$ for ordinary matter, we have investigated the effective behaviour of various cosmological parameters and energy conditions in our model. We have observed the present values of $\{t_0,H_0,q_0,j_0,s_0,l_0,m_0,{\omega }_{d{e}_0},{\omega }_0^{\left(eff\right)}\}$ and discussed with $\Lambda$CDM model. We have found the age of the present universe $t_0=13.05$ Gyrs, present value of DP $q_0=-0.8065$ and transition point $z_t=0.748$ which are compatible with several observational results.     

Study on 21 cm Signal of High Redshift Quasars

We use the results of high resolution numerical simulations to fix the theoretical model of high redshift quasars (QSOs) ionizing and heating neutral gas, and predict the signal characteristics and signal/noise (S/N) ratios for Five-hundred-meter Aperture Spherical Telescope (FAST) to observe the 21 cm radiation around QSO. Our conclusions are summarized as: (1) the 21 cm frequency spectrum under the FAST field has full HII region for the QSO at $z=8$ and with luminosity similar to ULAS J1120+0641, while has only a small trough for the QSO at $z=10$ and with low luminosity; (2) the effect of Finite Light Travel Time (FLTT) obviously changes the 21 cm frequency spectrum of high redshift QSOs, makes the transition curve at lower frequency much steeper than that at higher frequency; (3) the FAST telescope can observe the 21 cm radiation of high redshift QSO with very high S/N ratio as high as $～12$, thus can identify the HII regions and the FLTT effect.