Showing papers in "Astronomy and Astrophysics in 1985"

A simple maximum entropy deconvolution algorithm

Abstract: On decrit l'algorithme de deconvolution implante dans le systeme de traitement d'image astronomique AIPS. Exemples d'application

Are polycyclic aromatic hydrocarbons the carriers of the diffuse interstellar bands in the visible

Abstract: On montre que ces molecules possedent des transitions optiquement actives dans le domaine visible; qu'elles peuvent survivre aux photons UV dans le milieu interstellaire diffus et qu'elles sont les especes moleculaires les plus abondantes apres H 2 et CO Ce sont de meilleurs candidats que les longues chaines carbonees

Time dependent chemistry in dense molecular clouds. I - Grain surface reactions, gas/grain interactions and infrared spectroscopy

Abstract: For the fist time, a time-dependent model is described which includes the role of grains in the production of molecules in dense clouds including ion-molecule gas phase chemistry. The approach provides information regarding the coupling between the two phases. Although the coupling between the two chemistries is extremely strong, the two domains maintain their own identities. While H2O, CH4, and NH3 are made efficiently, with a high production rate on grains and released back to the gas phase, the gas phase is essentially responsible for the formation of CO, a very stable molecule which may or may not react on grains with atomic oxygen and may or may not form CO2.

Polycyclic aromatic hydrocarbons and the diffuse interstellar bands

Abstract: The profiles, widths and positions of the Diffuse Interstellar Bands (DIB’s) are discussed. It is shown that the carriers of the DIB’s are molecular rather than impurities in grains. Polycyclic Aromatic Hydrocarbons (PAH’s) are attractive candidates for the DIB’s, in view of their likely abundance, their extreme stability, and the fact that these molecules, and their corresponding radicals, show visible transitions.

Desorption from interstellar grains

Abstract: Different desorption mechanisms from interstellar grains are considered to resolve the conflict between the observed presence of gaseous species in molecular clouds and their expected depletion onto grains. The physics of desorption is discussed with particular reference to the process of grain heating and the specific heat of the dust material. Impulsive heating by X-rays and cosmic rays is addressed. Spot heating of the grains by cosmic rays and how this can lead to desorption of mantles from very large grains is considered. It is concluded that CO depletion on grains will be small in regions with A(V) less than five from the cloud surface and n(H) less than 10,000, in agreement with observations and in contrast to expectations from pure thermal equilibrium. Even in very dense and obscured regions and in the absence of internal ultraviolet sources, the classical evaporation of CO or N2 and O2-rich mantles by cosmic rays is important.

Comptonization of low-frequency radiation in accretion disks: angular distribution and polarization of hard radiation

Abstract: Calcul de la distribution angulaire et de la polarisation pour plusieurs epaisseurs optiques de disques, dans le cas d'une diffusion de Thomson

Magnetic stellar winds: a 2-D generalization of the Weber-Davis model.

Abstract: Methode numerique de calcul de modeles de vent stable a symetrie axiale avec des champs magnetiques geles a l'interieur

The triple alpha reaction at low temperatures in accreting white dwarfs and neutron stars.

Abstract: Formules generales du taux de la reaction α triple dans des conditions de faible temperature et forte densite se produisant dans les naines blanches et etoiles a neutrons

Formation environment of cometary nuclei in the primordial solar nebula

Abstract: Etude de l'environnement de la formation des cometes dans la nebuleuse solaire primordiale, du point de vue composition chimique des glaces du noyau cometaire

The ionisation of the primeval plasma at the time of recombination

Abstract: On a deduit de nouveau les equations pour l'ionisation du plasma cosmique pendant la periode de recombinaison en corrigeant les travaux anterieurs et en admettant la possibilite que l'Univers contienne des quantites substantielles de matiere non baryonique (le parametre de densite cosmique Ω T pouvant etre plus grand que la contribution baryonique Ω B ) Les resultats sont presentes sous forme de tables pour diverses valeurs de Ω T h 2 et Ω B h 2 et une temperature actuelle de T o =2,7 K On donne deux approximations analytiques: l'une valable pour z>1500, est une modification de la formule standard de Saha, l'autre, valable pour 800

Evolution of massive stars with semiconvective diffusion

Abstract: Etudes des sequences d'evolution a masse constante pour des etoiles de population I de 15 M ○. et 30 M ○. depuis le debut de la combustion du carbone du cœur

Point and interval estimation of the true unbiased degree of linear polarization in the presence of low signal-to-noise ratios

Abstract: Estimations du degre de polarisation lineaire lorsque les erreurs sur une observation des parametres de Stokes normalises q et u sont connus et donnes egaux a σ

Evidence of scattering effects on the sizes of interplanetary Type III radio bursts

Abstract: An analysis is conducted of 162 interplanetary Type III radio bursts; some of these bursts have been observed in association with fast electrons and Langmuir wave events at 1 AU and, in addition, have been subjected to in situ plasma parameter measurements. It is noted that the sizes of burst sources are anomalously large, compared to what one would anticipate on the basis of the interplanetary plasma density distribution, and that the variation of source size with frequency, when compared with the plasma frequency variation measured in situ, implies that the source sizes expand with decreasing frequency to fill a cone whose apex is at the sun. It is also found that some local phenomenon near the earth controls the apparent size of low frequency Type III sources.

Accurate methods in general planetary theory

Abstract: On developpe un formalisme et un algorithme qui permettent de calculer avec une grande precision relative (10 −6 ) le systeme autonome qui regule les variations a tres longue periode (>50000 ans) des 8 elements orbitaux des planetes, jusqu'au degre 5 en excentricite-inclinaison et jusqu'au second ordre par rapport aux masses

Henyey-Greenstein representation of the mean volume scattering phase function for zodiacal dust

Abstract: Determination des caracteristiques de diffusion des particules interplanetaires a partir de l'integrale de brillance de la lumiere zodiacale

Propagation of nonlinear, radiatively damped longitudinal waves along magnetic flux tubes in the solar atmosphere

Abstract: For solar magnetic flux tubes three types of waves are compared: longitudinal MHD tube waves, acoustic tube waves propagating in the same tube geometry but with rigid walls and ordinary acoustic waves in plane geometry. It is found that the effect of the distensibility of the tube is small and that longitudinal waves are essentially acoustic tube waves. Due to the tube geometry there is considerable difference between longitudinal waves or acoustic tube waves and ordinary acoustic waves. Longitudinal waves as well as acoustic tube waves show a smaller amplitude growth, larger shock formation heights, smaller mean chromospheric temperature but a steeper dependence of the temperature gradient on wave period.

Inhomogeneous synchrotron-self-compton models and the problem of relativistic beaming of BL Lac objects.

Abstract: On presente un formalisme pour le calcul du spectre synchrotron auto-Compton d'une large classe de sources heterogenes allongees (jets). La densite des electrons relativistes, l'energie maximum des electrons et le champ magnetique sont supposes etre des lois de puissance d'une coordonnee radiale. Application a PKS 2155-304 et PKS 0537-441. Les resultats sont compares a ceux d'un modele homogene

Do we observe light curves of binary asteroids

Abstract: Etude des courbes de lumiere anormales de 10 asteroides pouvant etre binaires: 15 Eunomia, 39 Laetitia, 43 Ariadne, 44 Nysa, 61 Danae, 63 Ausonia, 82 Alkmene, 192 Nausikaa, 216 Kleopatra et 624 Hektor

Possible parents for the cometary CN radical - Photochemistry and excitation conditions

Abstract: Afin de determiner quelle molecule parente pourrait etre responsable de la production du radical CN observe dans les atmospheres cometaires, on passe en revue les proprietes photochimiques des molecules HCN, C 2 N 2 , HC 3 N et CH 3 CN

Estimates of galactic cosmic ray spectra at low energies

Abstract: Modele incluant l'acceleration par choc, les pertes d'energie et la perte par propagation, permettant de calculer le spectre energetique des protons, particule α, noyaux moyens et lourds, et electrons dans le rayonnement cosmique entre quelques MeV/nucleon et 100 GeV/nucleon

Irradiation-induced mass-overflow instability as a possible cause of superoutbursts in SU UMa stars.

Abstract: On suggere que l'instabilite du flux s'ecoulant et de la masse induisant un rayonnement pourrait etre une cause des supereruptions observees dans les etoiles SU UMa