The ITRF coordinates of the spherical center of FAST

球坐标系中的一种新型轨道参数化方法

A Novel Orbit Parameterization in Spherical Coordinates

本文提出一种球坐标系下的新型轨道参数化方法，通过混合可变与不变轨道参数来简化合成天体群体的精确定位，适用于巡天设计与模拟研究。

A 3D radiative transfer framework: IV. spherical & cylindrical coordinate systems

We extend our framework for 3D radiative transfer calculations with a non-local operator splitting methods along (full) characteristics to spherical and cylindrical coordinate systems. These coordinate systems are better suited to a number of physical problems than Cartesian coordinates. The scattering problem for line transfer is solved via means of an operator splitting (OS) technique. The formal solution is based on a full characteristics method. The approximate $Λ$ operator is constructed considering nearest neighbors exactly. The code is parallelized over both wavelength and solid angle u…

BSSN equations in spherical coordinates without regularization: vacuum and non-vacuum spherically symmetric spacetimes

Brown has recently introduced a covariant formulation of the BSSN equations which is well suited for curvilinear coordinate systems. This is particularly desirable as many astrophysical phenomena are symmetric with respect to the rotation axis or are such that curvilinear coordinates adapt better to their geometry. However, the singularities associated with such coordinate systems are known to lead to numerical instabilities unless special care is taken (e.g., regularization at the origin). Cordero-Carrion will present a rigorous derivation of partially implicit Runge-Kutta methods in forthcom…

An axis-free overset grid in spherical polar coordinates for simulating 3D self-gravitating flows

A type of overlapping grid in spherical coordinates called the Yin-Yang grid is successfully implemented into a 3D version of the explicit Eulerian grid-based code PROMETHEUS including self-gravity. The modified code successfully passed several standard hydrodynamic tests producing results which are in very good agreement with analytic solutions. Moreover, the solutions obtained with the Yin-Yang grid exhibit no peculiar behaviour at the boundary between the two grid patches. The code has also been successfully used to model astrophysically relevant situations, namely equilibrium polytropes, a…

球极坐标中的快速二阶精度泊松求解器

A Fast, Second-Order Accurate Poisson Solver in Spherical Polar Coordinates

提出一种基于分治策略和James算法的球极坐标泊松方程求解器，利用预计算核矩阵和离散格林函数，实现$O(N^3\log N)$复杂度，并在FARGO3D中验证了二阶精度。

Visualising three-dimensional volumetric data with an arbitrary coordinate system

Astronomical data does not always use Cartesian coordinates. Both all-sky observational data and simulations of rotationally symmetric systems, such as accretion and protoplanetary discs, may use spherical polar or other coordinate systems. Standard displays rely on Cartesian coordinates, but converting non-Cartesian data into Cartesian format causes distortion of the data and loss of detail. I here demonstrate a method using standard techniques from computer graphics that avoids these problems with 3D data in arbitrary coordinate systems. The method adds minimum computational cost to the disp…