An analytical averaged model of orbital resonance

After having examined the characteristics of some models used at present in the study of orbital resonance, we propose an analytical averaged model, which offers certain convenience in the study of both the characteristics and the evolution of resonance.     

Poynting-Robertson drag and orbital resonance

Both the Poynting-Robertson drag and resonant orbits appear to be very important for the motion of small grains in the early solar system. While orbital resonances are very often stable and tend to force bodies into noncircular orbits, the Poynting-Robertson drag produces secular variations in the semimajor axis and tends to circularize the orbits. We study numerically the competition between the Poynting-Robertson drag and the gravitational interaction of grains with Jupiter near the 2/1 resonance. Computations are based on the plane-restricted problem. Numerical investigations show that the grains always cross the resonance region without any oscillation, except in the special case where the grains were initially inside the resonance. In both cases the variations of the osculating elements exhibit a drastic step, which can be explained by Greenberg's and Schubart's theories.     

The orbital resonance amongst the Galilean satellites of Jupiter

The resonance amongst three of the Galilean satellites is described in a way intended to demonstrate the similarities it has to the normal two-satellite resonance. The hypothesis that the resonance was formed by the action of tidal forces is discussed. The problem is too complicated to reach any firm conclusions, but the tidal hypothesis does not seem to be a satisfactory explanation.

     

Dependence on the observational time intervals and domain of convergence of orbital determination methods

In the framework of the orbital determination methods, we study some properties related to the algorithms developed by Gauss, Laplace and Mossotti. In particular, we investigate the dependence of such methods upon the size of the intervals between successive observations, encompassing also the case of two nearby observations performed within the same night. Moreover we study the convergence of Gauss algorithm by computing the maximal eigenvalue of the jacobian matrix associated to the Gauss map. Applications to asteroids and Kuiper belt objects are considered.     

An observational determination of the principal nutation constants

The longitude and obliquity components of the principal nutation terms were derived from observations made in 1955–1977 of 43 star-pairs common to the ILS Programmes VI and VII. The observations were reduced to a uniform system appropriate to these 43 star-pairs. The results are 6'.'850 for the longitude component and 9'.'212 for the obliquity component.     

An observational search for large-scale organization of five-minute oscillations on the Sun

The large-scale solar velocity field has been measured over an aperture of radius 0.8 R on 121 days between April and September, 1976. Measurements are made in the line Fei 5123.730 Å, employing a velocity subtraction technique similar to that of Severny et al. (1976). Comparisons of the amplitude and frequency of the five-minute resonant oscillation with the geomagnetic C9 index and magnetic sector boundaries show no evidence of any relationship between the oscillations and coronal holes or sector structure.     

An observational program for a unified optical-radio reference frame

An observational pilot program is described which provides a first step towards the construction of an inertial extragalactic reference frame from optical and radio measurements. Candidate objects will be selected from extragalactic compact radio sources which display optical counterparts. Galactic radio stars will be secondary reference objects. The reference frame will be defined by the radio positions of the extragalactic objects. Based on a coordinated effort in both hemispheres, a global homogeneous net of about 400 quasars and 100 radio stars is expected to result from a five year campaign.     

An observational examination of models for sunspot magnetic field configurations

The magnetic field configuration for an isolated, nearly circular sunspot has been obtained from measurements at some 100 points in the spot. The observations are compared with theoretical models for the field configuration of an isolated, axially-symmetric sunspot. The results support the Schlüter, Temesváry model with no return flux and a limiting field line inclination of ~70°.     

An ionospheric origin for Pi 1 micropulsations

Cosmic noise absorption pulsation events observed with fast response riometers at Macquarie Island in the southern auroral zone have almost always been accompanied by Pi 1 micropulsations. A cross-spectral analysis of fast response riometer data and vertical component induction magnetometer data for one such event showed that, after the low frequency components are removed, the absorption A(t) is better correlated with the absolute value of the field Z(t) than with the recorded quantity $\text{d}\text{Z}\text{dt}$. The peaks in Z(t) lag those in A(t) by one second while A(t) lags $\text{d}\text{Z}\text{d}\text{t}$ by abou second. Furthermore, many of the pulsations in Z(t) show a similar time asymmetry to that commonly observed in c.n.a. pulsations, viz. a more rapid onset time than decay time.These results are taken as evidence that the Pi 1 micropulsations observed from the ground during the recovery phase of an auroral substorm are brought about by fluctuations in the ionospheric currents which give rise to the magnetic bay, these fluctuations being due to conductivity changes resulting from particle precipitation. The lag between A(t) and Z > (t) is attributed to the self-inductance of the electrojet.     

An investigation of the orbital identity of some new asteriods

Starting from over one hundred preliminary orbits of minor planets discovered at our observatory and a collection of over 7000 positions, we used a computer to make a systematic study of their identity. From the preliminary identification, we proceed to improve the orbits with all the data available, taking into consideration the perturbations of the major planets. There are eight asteriods which have passed the rigid test of identification. Their accurate orbits and opposition ephemerides have been computed.Also, there are four other asteriods discovered at Purple Mountain Observatory, which have been assigned permanent numbers. In this paper, we suggested the following names of Chinese scientists for these planets: Planet (1802) 1964 TW₁, be given the name Zhang Heng (AD78-139), a prominent scientist of the Later Han Dynasty; Planet (1888) 1964 VO₁, be given the name Zu Chong-zhi (429–500), the great mathematician of The Southern Dynasty; Planet (1972) 1964 VQ₁, be designated Yi Xing, to commemorate the famous astronomer of Tang Dynasty, Zhang Sui (Monk Yi Xing 683–727); Planet (2012) 1964 TE₂, be named Guo Shou-jing, (1231–1316) the talented astronomer of the Yuan Dynasty.     

An observational approach to the early stages of stellar evolution

During the last three decades an observational approach has been applied at the Byurakan Astrophysical Observatory to the problems of the evolution of astronomical bodies and systems. In contradiction to the traditional point of view, assuming that the processes of condensation are dominant in the Universe, this approach makes use of the observed predominance of expansions, ejections, and explosions.In the past, the observational approach has led to the prediction of an expansion of some stellar associations confirmed later by the analysis of observations. It became clear that the stellar associations are very young systems where the star-formation process is still continuing. The new approach has also led to the concept of the activity of galactic nuclei. The observational approach considers as a phenomenon of primary importance the formation of nebulae as a consequence of the activity of dense bodies (nebulae surrounding the novae, planetary nebulae, supernova remnants, cometary nebulae, and the diffuse nebulae in OB-associations).The new approach in application to the early stages of stellar evolution is discussed. The T Tauri-stage is considered as a phase following the more dense protostellar state. The flare stars are regarded as the next phase of evolution. The phenomena of fuors (FU Ori-type brightenings) can be considered as an expression of the same tendency (the transformation of dense matter into a rarefied state).     

Seeable universe and its accelerated expansion: an observational test

From the equivalence principle, one gets the strength of the gravitational effect of a mass M on the metric at position r from it. It is proportional to the dimensionless parameter β ²=2GM/rc ², which normally is ?1. Here G is the gravitational constant, M the mass of the gravitating body, r the position of the metric from the gravitating body and c the speed of light. The seeable universe is the sphere, with center at the observer, having a size such that it shall contain all light emitted within it. For this to occur one can impose that the gravitational effect on the velocity of light at r is zero for the radial component, and non zero for the tangential one. Light is then trapped. The condition is given by the equality R _g =2GM/c ², where R _g represents the radius of the seeable universe. It is the gravitational radius of the mass M. The result has been presented elsewhere as the condition for the universe to be treated as a black hole. According to present observations, for the case of our universe taken as flat (k=0), and the equation of state as p=?ρc ², we prove here from the Einstein’s cosmological equations that the universe is expanding in an accelerated way as t ², a constant acceleration as has been observed. This implies that the gravitational radius of the universe (at the event horizon) expands as t ². Taking c as constant, observing the galaxies deep in space this means deep in time as ct, linear. Then, far away galaxies from the observer that we see today will disappear in time as they get out of the distance ct that is <R _g . The accelerated expanding vacuum will drag them out of sight. This may be a valid test for the present ideas in cosmology. Previous calculations are here halved by our results.     

An observational study of coronal hole rotation over the sunspot cycle

An analysis of the rotation of coronal holes (CHs) spanning 18 years was done based on data from theCatalogue of Coronal Holes (Sanchez-Ibarra and Barraza-Paredes, 1992). A differential rotation of CHs is confirmed for the totality of CHs, but a different behavior was found when those were separated as equatorial or isolated, and polar hole extensions, such as in theCatalogue. Isolated CHs show a typical differential rotation, but polar hole extensions display two different types of behavior: a rotation rate below 40° ± 5° of heliographic latitude, increasing to the equator, and a rotation rate above the same heliographic latitude but increasing to the poles. Also discussed here is how this last result agrees with other studies that indicate the mostly rigid rotation of the corona at higher latitudes.     

An observational constraint on the existence of proto-superclsuters atz=3.3

The online version of the original article can be found at     

An orbital period investigation of the Algol-type eclipsing binary VW Hydrae

Orbital period variations of the Algol-type eclipsing binary, VW Hydrae, are analyzed based on one newly determined eclipse time and the other times of light minima collected from the literature. It is discovered that the orbital period shows a continuous increase at a rate of dP/dt = +6.34×10-7 d yr-1 while it undergoes a cyclic change with an amplitude of 0.0639 d and a period of 51.5 yr. After the long-term period increase and the large-amphtude period oscillation were subtracted from the O-C curve, the residuals of the photoelectric and CCD data indicate a small-amplitude cyclic variation with a period of 8.75 yr and a small amplitude of 0.0048d. The continuous period increase indicates a conservative mass transfer at a rate of dM2/dt = 7.89×10-8 M⊙ yr-1 from the secondary to the primary. The period increase may be caused by a combination of the mass transfer from the secondary to the primary and the angular momentum transfer from the binary system to the circumbinary disk. The two cyclic period oscillations can be explained by light-travel time effects via the presence of additional bodies. The small-amplitude periodic change indicates the existence of a less massive component with mass M3 > 0.53 M⊙, while the large-amplitude one is caused by the presence of a more massive component with mass M4 > 2.84 M⊙. The ultraviolet source in the system reported by Kviz & Rufener (1987) may be one of the additional components, and it is possible that the more massive one may be an unseen neutron star or black hole. The rapid period increase and the possibility of the presence of two additional components in the binary make it a very interesting system to study. New photometric and high-resolution spectroscopic observations and a detailed investigation of those data are required in the future.