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## On the Multiplicity of the O-Star Cyg OB2 #8a and its Contribution to the γ-ray Source 3EG J2033+4118

### Astrophysics and Space Science (2005-06-01) 297: 291-298 , June 01, 2005

We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 #8A is an O6+O5.5 binary system with a period of about 21.9 days. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal radio emitter. We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the radio waveband to γ-rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for a putative γ-ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified EGRET source 3EG J2033+4118.

## Temperature of Polar Corona of the Sun According to Kislovodsk Observations During 1957–2002

### Solar Physics (2006-08-01) 237: 201-210 , August 01, 2006

We continued a study of the long-term variations of temperature in the solar corona at all latitudes (Makarov, Tlatov, and Callebaut, 2002a). The series of the green (Fe xiv 530.3 nm; KI_{5303}) and red (Fe x 637.4 nm; KI_{6374}) coronal intensities for 1957–2002 has been obtained using the coronal observations at the Kislovodsk Solar Station. The mean monthly coronal intensities have been calculated at all latitudes (0–90^{˚}) and in the high latitude (45–90^{˚}) zones. It was found that the value of KI_{6374}/KI_{5303}increased about 2.0 times at the high latitudes during the last 45 years. This corresponds to a decrease of the average temperature by 0.1 ×10^{6}K of the polar corona. We suppose that a polar decrease of coronal temperature is connected with an increase of the area of polar zones *A*_{PZ}occupied by unipolar magnetic fields (Makarov *et al*., 2002) and, probably, with an increase of the area of polar coronal holes. The maximum ratio KI_{6374}/KI_{5303}is observed during the minimum sunspot activity.

## A combination of SPH andN-body 2 for gas dynamics in star clusters

### Astrophysics and Space Science (1990-08-01) 170: 221-224 , August 01, 1990

When stars are being formed in a region of a molecular cloud, the presence of the gas of this cloud will influence the dynamics of these newly formed stars. We discuss an implementation of SPH or Smooth Particle Hydrodynamics within the framework of*N*-body2, which will permit the study of this kind of mixed systems. It is our intention to include various gas removal processes, and to study their influence on the behaviour of stars and gas.

## Kinetic Models of Solar and Polar Winds

### Astrophysics and Space Science (2001-06-01) 277: 169-180 , June 01, 2001

The study of the solar corona has been strewn with great discoveries, surprises and controversies. The major steps since van de Hulst's (1953)and Chapman's (1957) early hydrostatic models of the extended corona, until the most recent generations of kinetic models of the coronal expansion and of the supersonic solar wind flows, are presented. These models are compared to in-situ observations. Progress in polar wind models went through a somewhat similar evolution that is outlined also. The advantages and limitations of the successive brands of solar wind and polar wind models are considered.

## Resonantly Damped Surface and Body MHD Waves in a Solar Coronal Slab with Oblique Propagation

### Solar Physics (2007-11-01) 246: 213-230 , November 01, 2007

The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a zero-*β* configuration and for parallel propagation of waves does not allow the existence of surface waves. When oblique propagation of perturbations is considered, both surface and body waves are able to propagate. When the perpendicular wavenumber is larger than a certain value, the body kink mode becomes a surface wave. In addition, a sausage surface mode is found below the internal cutoff frequency. When nonuniformity in the equilibrium is included, surface and body modes are damped by resonant absorption. In this paper, first, a normal-mode analysis is performed and the period, the damping rate, and the spatial structure of the eigenfunctions are obtained. Then, the time-dependent problem is solved, and the conditions under which one or the other type of mode is excited are investigated.

## A semi-numerical perturbation method for separable hamiltonian systems

### Celestial Mechanics and Dynamical Astronomy (1990-03-01) 49: 43-67 , March 01, 1990

A detailed account is given of a semi-numerical perturbation method which has been proposed and improved upon in a succession of previous papers. The method analyses the first order effect of a small perturbation applied to a non-trivial two-degreeof-freedom separable Hamiltonian system (including the description of resonances) and construct approximate surfaces of section of the perturbed system. When the separable Hamiltonian system is already the description of a resonance, as it is the case in the problems we have investigated in the previous papers, these resonances are actually secondary resonances. The key role of the method is the numerical description of the angle-action variables of the separable system. The method is thus able to describe the perturbations of non-trivial separable systems and is not confined to the analysis of a small neigborhood of their periodic orbits.

## Book reviews

### Space Science Reviews (1969-12-01) 10: 455-456 , December 01, 1969

## On the precession constant: Values and constraints on the dynamical ellipticity; link with Oppolzer terms and tilt-over-mode

### Celestial Mechanics and Dynamical Astronomy (1996-12-01) 65: 439-458 , December 01, 1996

The luni-solar precession, derived by theoretical considerations from the precession of the equator, is one of the most important parameters for computing not only precession but also nutations, due to its relation to the dynamical flattening. In this paper, we review the numerical values of this parameter, from the geodynamical point of view as well as the astronomical point of view, from the observational point of view as well as from the theoretical point of view. In particular, we point out a difference of about 1 percent between the global Earth dynamical flattening derived from the astronomical observations and the values derived from the different geophysical computations. The nutation amplitudes depend on the Earth dynamical flattening and this dependence is amplified by a resonance at an important normal mode, the Tilt-Over-Mode (TOM). Since the astronomical point of view as well as the geophysical one are confronted, we also take the opportunity to make the link between the TOM and the expressions of the nutations of the different axes which, in turn, are related with one another by the Oppolzer terms. Both, the Oppolzer terms and the TOM originate from a reference frame tilt effect. In writing the link between the nutational motions of the different axes, and so, in writing the Oppolzer terms, we also make the link with the precessional motion.

## ISO's View on AFGL 4106

### Astrophysics and Space Science (1997-01-01) 255: 469-475 , January 01, 1997

## Additions to the Theory of the Rotation of Europa

### Celestial Mechanics and Dynamical Astronomy (2005-09-01) 93: 101-112 , September 01, 2005

In a previous paper (*The Rotation of Europa*, Henrard, *Celest. Mech. Dyn. Astr*., *91*, 131–149, 2005) we have developed a semi-analytical theory of Europa, one of the Galilean satellites of Jupiter. It is based on a synthetic theory of the orbit of Europa and is developed in the framework of Hamiltonian formalism. It was assumed that Europa is a rigid body and Jupiter a point mass. Several additional effects should be investigated in order to complete the theory. The present contribution considers the effect of the shape of Jupiter and of the gravitational pull of Io. The sensitivity of the main theory to a change in the values of the moments of inertia of Europa is also considered.