Showing papers in "Astronomy and Astrophysics in 1983"

Fundamental relationships relevant to the transfer of polarized light in a scattering atmosphere.

Abstract: Le pulsar radio et RX, 4U 1510-59, a un âge caracteristique plusieurs fois inferieur a celui du reste de supernova associe MSH 15-52. Cette divergence peut etre resolue si l'on considere que l'etoile a neutrons a ete formee de facon calme et que le reste de supernova a ete forme par un vent relativiste plutot que par une enveloppe de debris. 4U 1510-59 pourrait etre membre d'objets incluant PSR 0820+02 et les amas globulaires sources RX. Cette hypothese conduit a des predictions verifiables concernant le mouvement propre de ces objets et la dynamique des amas globulaires

DE 102: a numerically integrated ephemeris of the moon and planets spanning forty-four centuries.

Abstract: It is pointed out that the 1960's were the turning point for the generation of lunar and planetary ephemerides All previous measurements of the positions of solar system bodies were optical angular measurements New technological improvements leading to immense changes in observational accuracy are related to developments concerning radar, Viking landers on Mars, and laser ranges to lunar corner cube retroreflectors Suitable numerical integration techniques and more comprehensive physical models were developed to match the accuracy of the modern data types The present investigation is concerned with the first integrated ephemeris, DE 102, which covers the entire span of the historical astronomical observations of usable accuracy which are known The fit is made to modern data The integration spans the time period from 1411 BC to 3002 AD

Interstellar radiation field and dust temperatures in the diffuse interstellar matter and in giant molecular clouds.

Abstract: In Paper I (Mezger et al, 1982) we have investigated the emission spectrum of dust in both the diffuse interstellar matter (ISM) and in Giant Molecular Clouds (GMC's) This included an estimation of dust absorption cross sections from the Lyman continuum to the submm range and a redetermination of the interstellar radiation field (ISRF) using the most recent observations In this paper we reevaluate the ISRF as a function of galactocentric distance D G , taking into account the results of recent surveys of the galactic 24 μm and 34 μm emission as well as of FIR surveys of the galactic plane as discussed in Paper I, and using an improved model of the variation of dust opacity in the galactic plane We then determine the radiation field inside GMC's, including the radiation from the GMC itself, as a function of both D G and the extinction A V measured from the surface of the cloud Next, we calculate the dust temperatures of the MRN composite graphite/silicate dust model (Mathis et al, 1977) in the radiation field within the cloud The main results are: (i) The ISRF between 009 and 8 μm is dominated by stellar radiation and between 8 and 1000 μm is dominated by reemitted radiation from dust grains The total energy density of the ISRF between D G = 10 and 5 kpc increases by a factor seven The ISRF attains its intensity maximum at ∼ 1 μm (ii) The dominant sources of heating in GMC's are stellar radiation for graphite grains and FIR heating for silicate grains The contribution of normal field stars embedded in GMC's to the heating of dust is normally negligible This may be different in a cloud which contains many low-mass pre-MS stars While the temperatures of graphite grains in the diffuse ISM and in the outer sheaths of GMC's are twice as high as the temperatures of silicate grains, both types of grains attain approximately equal temperatures between 5 and 7 K deep inside GMC's (iii) The stellar radiation absorbed in the outer layers of GMC's is practically all converted into FIR radiation whose integrated mean intensity is about five times that of the diffuse galactic FIR emission

The excitation of type II radio bursts in the corona

Abstract: Simultaneous radioheliograph and orbital coronagraph observation of coronal transient activity shows metric type II radio emission originating early in the event, well below the visible white light transient. It is suggested that the shock which excites the type II emission is independent of the transient, in the sense that it is initiated in the low corona (probably in association with a flare) and travels through the already-existing transient disturbance with a propagation speed significantly greater than that of the front edge of the transient itself. Radio emission then results when the flare shock overtakes, first, the region of principal density pile-up along the sides of the expanding transient and only later the top of the transient.

Search for pulsed γ-ray emission from radio pulsars in the COS-B data.

Abstract: On n'a detecte aucun signal Rγ provenant des pulsars PSR 0740―28, PSR 0950+08, PSR 1055―52 et PSR 1929+10

Near-infrared photometry. II. Intrinsic colours and the absolute calibration from one to five micron.

Abstract: On continue la description de l'unification et de la reparametrisation des resultats de plusieurs auteurs au sujet de la photometrie IR proche, en derivant les couleurs intrinseques et les valeurs de calibrage absolu du systeme photometrique decrit dans un precedent article

Fine time structure in the 1979 March 5 gamma ray burst

Abstract: Data on the impulsive phase of the 1979 March 5 gamma ray burst, taken by three identical detectors aboard the Prognoz 7, Venera 11, and Venera 12 spacecraft with 2 ms time resolution, are presented. The first 200 ms of the time history may be described by an exponential decay with time constant of approximately 120 ms up to approximately 100 ms, and time constant of approximately 30 ms thereafter; at low energies, a pulsating component with a period of approximately 23 ms appears. The data could be consistent with torsional vibrations of a neutron star, the rotation of a rapidly spinning neutron star, or oscillations caused by interactions between hot plasma and a magnetic field.