Chinese Astronomy最新文献

Nine records on a new star of 1408 have been gathered from Chinese historical books. A careful examination of these records leads one to interpret confidently the event as a supernova. Its recorded position strongly suggests that the X-ray source Cygnus X-1 is the remnant of this supernova.

In this paper a new semi-analytical, semi-numerical method for computing the second order perturbation of artificial satellites is presented. The basic ideas are the following:

• 1.

  1. We adopt as fundamental elements $\text{σ}{}^{\mathrm{\ast }}$, which are the mean elements obtained after subtracting the short-period terms Δσ_s from the osculating elements.

• 2.

  2. The secular and long-period rates (up to third order) of $\text{σ}{}^{\mathrm{\ast }}$ are found by numerically averaging the rates of the osculating elements.

• 3.

  3. The osculating elements in computing dσ/dt are found by adding to $\text{σ}{}^{\mathrm{\ast }}$ the short-period termsΔσ_s, in which the first-order terms are obtained by analytical method, and the second-order terms by Fourier analysis.

By using $\text{σ}{}^{\mathrm{\ast }}$, we have overcome the shortcoming in the numerical method, due to the use of short integration steps, while our numerical computation of $\text{dσ}{}^{\mathrm{\ast }}\text{/dt}$ and Δσ_s⁽²⁾ obviates the development of complicated formulae.

Our computing time of the second-order perturbation is only $\text{1}\text{10}$ that of the classical numerical method, and our required memory is about $\text{1}\text{5}$ of the purely analytical method.

In the numerical method, an improved Chebychev iteration process is developed to better serve the needs of satellite dynamical geodesy.

Detailed formulae for computing the perturbating forces and some numerical results of computation by our method are given. These show that the radius and across-track errors are less than 0.1m, and that the along-track errors are less than 1m.

For an axisymmetric galaxy with an exponential density decrease along the z-direction, the relation between the projected surface density and the rotation curve is investigated. The peculiar motions of stars are neglected. Revised forms of Toomre's formulae for an infinitely thin disk galaxy are obtained. It is found that with a finite thickness, matter is more concentrated towards the centre; the projected surface density in the central part of our Galaxy comes out about 9% higher than is given by Toomre's model.

After reviewing the various methods used so far in the long-term prediction of solar activity, we have opted to use methods based on the 80-year period and probability considerations. Our predictions for Cycle No. 21 are:

• 1.

  Maximum of the annual average Wolf number: 54 – 94

• 2.

  Minimum of the annual average Wolf number: 0 – 4

• 3.

  Epoch of maximum: first half of 1981 - first half of 1983

• 4.

  Epoch of minimum: first half of 1976 - first half of 1977

A comparison of our predictions with others is made.

In this paper, a localised region of the corona which generates a noise storm on meter waves (Type-1 bursts) is called a Type-1 source, and we investigate statistically any evolutionary relation between the production of Type-1 source and the flare activity in the associated plage region. Our data are provided by interferometer (working at 146 MHz) of the Miyun Station of Peking Observatory and our methods consist in a comparison of the evolutionary curves (Time variations) of the intensity of a Type-1 source and of the flare activity as characterized by the f-number. We found that (1) there is indeed an evolutionary relation with typical time lags of 1–2 days between the Type-1 source and the flare activity, (2) some small flares of Class “--” may also be related to Type-1 sources, (3) the S-component at cm waves is related to flare activity, the rise in the f-number before the onset of a proton flare suggesting a pre-heating of the S-component source, and (4) a Type-1 source can be regarded as the after-effect of flare activity.

Based on Lee-Wick's theory of abnormal nuclear state, the possible existence of a new type of neutron stars of abnormal state is discussed. Calculation shows that there may be some stable and/or metastable abnormal neutron stars with M ∼ M_⊙.