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Showing papers in "Monthly Notices of the Royal Astronomical Society in 1986"



Journal ArticleDOI
TL;DR: The authors adopte les deux constantes R 0 =8,5 kpc and O 0 =220 kms −1, which are the deux constants used in this paper.
Abstract: La commission 33 de l'UAI (Delhi, 21 novembre, 1985) a adopte les deux constantes R 0 =8,5 kpc et O 0 =220 kms −1

736 citations


Journal ArticleDOI
TL;DR: In this article, a variation avec les parametres qui gouvernent la transition de phase and les possibilites de son observation is proposed. André et al. propose une evaluation du spectre du fond stochastique resultant.
Abstract: La cavitation au cours d'une transition de phase du premier ordre peut avoir donne naissance a un rayonnement gravitationnel. On propose une evaluation du spectre du fond stochastique resultant, sa variation avec les parametres qui gouvernent la transition de phase et les possibilites de son observation

333 citations


Journal ArticleDOI
TL;DR: The separation of high-mass pulsators into three clearly defined groups enables some of the properties of a pulsator to be predicted if only a few of its parameters are known as mentioned in this paper.
Abstract: High mass X-ray pulsators are shown to be divisible into three distinct groups on the basis of their observational properties: 1) the Be star systems, 2) non-Be star systems with long pulse periods, (~102 — 103 s), and 3) non-Be star systems with short pulse periods (~100 — 101 s). Differences in mass transfer processes between the groups are invoked to account for the different properties. The separation of high mass pulsators into three clearly defined groups enables some of the properties of a pulsator to be predicted if only a few of its parameters are known. Because of this the optical counterparts of the X-ray sources H0850-42, OAO1653-40 and 1E1048.1-5937 are predicted to be either Be stars or, much less likely, low mass binaries. The orbital (Po) and spin (Ps) periods of the short period systems may be anti-correlated, a phenomenon which is also exhibited by the intermediate polar white dwarf binaries. For the long period systems there is no strong relationship between Po and Ps as there is for the Be star systems. It is shown that for the Be star systems this relationship cannot be accounted for by accretion from a stellar wind if there is equality between the Alfven and corotation radii of the neutron stars in these systems. However, accretion from a non-expanding atmosphere is not excluded. The lack of any correlation between Ps and Po for the supergiant systems is attributed to the low angular momentum of accreted matter. The Be star systems, however, probably accrete significant angular momentum which can result in an accretion disk.

313 citations


Journal ArticleDOI
TL;DR: Examen de la formation des raies d'emission a partir de disques d'accretion et developpement d'expressions simples pour calculer les profils de raies optiquement minces ou epaisses as mentioned in this paper.
Abstract: Examen de la formation des raies d'emission a partir de disques d'accretion et developpement d'expressions simples pour calculer les profils de raies optiquement minces ou epaisses

299 citations


Journal ArticleDOI
TL;DR: On discute de l'eventualite que les premiers objets qui se forment dans un Univers compose de matiere sombre, froide, puissent influer sur la structure subsequente as mentioned in this paper.
Abstract: On discute de l'eventualite que les premiers objets qui se forment dans un Univers compose de matiere sombre, froide, puissent influer sur la structure subsequente. Ces premiers objets auraient ete des etoiles se formant dans des amas de masses ∼10 5 M •

291 citations



Journal ArticleDOI
TL;DR: In this paper, les donnees spectroscopiques concernant 32 galaxies HII were presented, and certain conditions comportent des sursauts de formation stellaire (36 ont ete observes au total) for lesquels on a obtenu les temperatures electroniques and les abondances de loxygene and de lazote.
Abstract: On presente les donnees spectroscopiques concernant 32 galaxies HII. Certaines comportent des sursauts de formation stellaire (36 ont ete observes au total) pour lesquels on a obtenu les temperatures electroniques et les abondances de l'oxygene et de l'azote. On examine les relations existant entre les parametres

238 citations


Journal ArticleDOI
TL;DR: Achlioptas et al. as discussed by the authors compile un echantillon complet de radiosources extragalactiques de densite de flux S≥0,1 Jy a 2,7 GHz for tester la fonction de luminosite radio jusqu'aux deplacements vers le rouge z≃3-4.
Abstract: On a compile un echantillon complet de radiosources extragalactiques de densite de flux S≥0,1 Jy a 2,7 GHz pour tester la fonction de luminosite radio jusqu'aux deplacements vers le rouge z≃3-4. On donne les cartes VLA des 188 sources dans ce domaine des densites de flux

226 citations


Journal ArticleDOI
TL;DR: In this paper, a critere simple permettant de determiner si une fonction de distribution donnee est plus melangee qu'une autre is used for determining whether l'etat initial est froid or a grumeaux.
Abstract: On donne un critere simple permettant de determiner si une fonction de distribution donnee est plus melangee qu'une autre. On utilise ce critere pour montrer qu'une galaxie ayant subi une relaxation violente ne ressemble aux galaxies elliptiques observees que si l'etat initial est froid ou a grumeaux

210 citations



Journal ArticleDOI
TL;DR: The authors pense generalement que tous les univers fermes S 3 en expansion, qui verifient les conditions d'energie standard, s'effondrent a nouveau vers une seconde singularite.
Abstract: On pense generalement que tous les univers fermes S 3 en expansion, qui verifient les conditions d'energie standard, s'effondrent a nouveau vers une seconde singularite. On montre que c'est faux, meme pour des univers de Friedmann

Journal ArticleDOI
TL;DR: Etude numerique de l'influence d'un mouvement aleatoire sur les modes insrables de formation des barres of a type de disques stellaires as discussed by the authors.
Abstract: Etude numerique de l'influence d'un mouvement aleatoire sur les modes insrables de formation des barres d'un type de modeles de disques stellaires. On montre que le taux de croissance des barres est une fonction simple du mouvement aleatoire et de la masse du halo

Journal ArticleDOI
TL;DR: Photometrie en lumiere blanche as mentioned in this paper is a haute vitesse de cette variable cataclysmique, which is used to study the structure of the system and deriver les proprietes de ses composantes.
Abstract: Photometrie en lumiere blanche a haute vitesse de cette variable cataclysmique, afin d'etudier la structure du systeme et de deriver les proprietes de ses composantes


Journal ArticleDOI
TL;DR: In this paper, the inviscid instabilities of an isentropic torus found previously by Papaloizou & Pringle were elucidated. But they did not consider the case where the torus does not have a resonance at corotation.
Abstract: We elucidate the inviscid instabilities of an isentropic torus found previously by Papaloizou & Pringle. The torus is a polytrope of index, n, and has a small ratio of minor radius, ɑ, to orbital radius, r_0. In equilibrium it rotates on cylinders with angular velocity profile Ω,∝r^(-q). Linear modes are proportional to exp i(mO-wt). For small β≡mα/r_0 , we justify the use of height-averaged equations by appealing to approximate vertical hydrostatic equilibrium. The effective polytropic index for the resulting two-dimensional problem is N≡n+½; thus an incompressible torus in three dimensions behaves compressibly in two. Height averaged modes obey an ordinary differential equation, which we solve numerically to obtain the growth rate as a function of q, n, and β. The error made in predicting the growth rate of the actual three-dimensional system is small everywhere along the principal branch even for β~0.5, and is less than 1 per cent for the fastest-growing mode. We analytically solve the artificial case n=-½, which is two-dimensionally incompressible, and show that it has all the qualitative features of the general case, except that it does not have a resonance at corotation. In the general case, with n>-½ and q<2, the corotation resonance absorbs energy and angular momentum, so the growing and decaying modes do not occur in complex-conjugate pairs. We solve a second special case, namely n=2-q=0, almost analytically in three dimensions, without height-averaging. Papaloizou & Pringle asserted that this system is stable but we show that there is an unstable mode for small β just as in the other systems. In fact this principal unstable branch, with corotation at the pressure maximum, is qualitatively the same for all n and is essentially independent both of compressibility and of the gradient in vorticity per unit surface density. Thus the modes are not sonic, nor are they similar to those of the Kelvin-Helmholtz instability. Instead they are composed of two edge waves, akin to surface waves in water although modified by shear and rotation, coupled across a forbidden region around corotation.

Journal ArticleDOI
TL;DR: In this paper, it is argued that gas at different densities in the flow must be largely comoving, and with this assumption an integral set of flow equations are derived and solved approximately.
Abstract: In order to explain the widespread deposition of cooled gas in cooling flows the gas must be significantly inhomogeneous. Equations governing the development of an inhomogeneous flow are set out. It is argued that gas at different densities in the flow must be largely comoving, and with this assumption an integral set of flow equations are derived and solved approximately. The resulting mass deposition profile is sensitively dependent on only the dimensionless ratio of the mass deposition rate to the total radiation rate per unit volume, ξ = 5βp/2ρ R. This result is little affected by the small amount of residual slip in the flow. Plausible values for ξ are confined to a fairly narrow range, including the value required by observations, but still allow considerable latitude in the resulting mass deposition profile. ξ is determined by the initial density distribution of the gas. Low temperature line emission from cooling flows directly maps the distribution of the gas deposition rate, providing a stringent test of cooling flow models.

Journal ArticleDOI
TL;DR: In this paper, the authors analyse les donnees relatives a la periode, la luminosite et la couleur des cepheides du PNM and du GNM.
Abstract: On a analyse les donnees relatives a la periode, la luminosite et la couleur des cepheides du PNM et du GNM. On en deduit un modele geometrique pour les Nuages. On a recalcule le module de distance de chaque Nuage

Journal ArticleDOI
TL;DR: In this article, the vitesse de derive VB des champs magnetiques par rapport au fluide en resolvant les mouvements de nombreuses especes de particules chargees is obtenu.
Abstract: On a obtenu la vitesse de derive V B des champs magnetiques par rapport au fluide en resolvant les mouvements de nombreuses especes de particules chargees. Pour des densites d'hydrogene n H ≤10 11 cm −3 , V B est au moins dix fois plus faible que la vitesse de chute libre, et la dissipation du champ est donc inefficace

Journal ArticleDOI
TL;DR: In this paper, a schema d'evolution galactique is proposed, in which the fonction de masse initiale is bimodale and les etoiles massives se sont formees a un taux plus eleve dans le passe de sorte that les restes stellaires dominent actuellement la masse totale.
Abstract: On propose un nouveau schema d'evolution galactique dans lequel la fonction de masse initiale est bimodale et les etoiles massives se sont formees a un taux plus eleve dans le passe de sorte que les restes stellaires dominent actuellement la masse totale

Journal ArticleDOI
TL;DR: Etude des proprietes spectrales d'un echantillon de six etoiles binaires RX de faible masse, a partir de donnees du satellite EXOSAT as mentioned in this paper, propose differents modeles du continuum de ces sources
Abstract: Etude des proprietes spectrales d'un echantillon de six etoiles binaires RX de faible masse, a partir de donnees du satellite EXOSAT. On propose differents modeles du continuum de ces sources


Journal ArticleDOI
TL;DR: In this paper, les cartes de l'emission maser H 2 O et OH of l'enveloppe circumstellaire de la supergeante VX Sgr are presented.
Abstract: On presente les cartes de l'emission maser H 2 O et OH de l'enveloppe circumstellaire de la supergeante VX Sgr

Journal ArticleDOI
TL;DR: In this paper, a relation periode-luminosite K (2,2 μm) was observed between two amas etudies in the form of P ∞−0,45 M K.
Abstract: Etude de l'utilisation eventuelle de la photometrie dans l'IR proche pour evaluer les distances des amas globulaires On a observe une relation periode-luminosite K (2,2 μm) dans les trois amas etudies; elle est de la forme P ∞−0,45 M K

Journal ArticleDOI
TL;DR: This article propose des techniques numeriques which permettent de calculer des frequences propres and des modes propres a partir de simulations sur ordinateur des disques stellaires.
Abstract: On propose des techniques numeriques qui permettent de calculer des frequences propres et des modes propres a partir de simulations sur ordinateur des disques stellaires

Journal ArticleDOI
TL;DR: Equations differentielles decrivant les ecoulements MHD a multicomposante, avec des champs magnetiques orientes arbitrairement as discussed by the authors.
Abstract: Equations differentielles decrivant les ecoulements MHD a multicomposante, avec des champs magnetiques orientes arbitrairement

Journal ArticleDOI
TL;DR: In this paper, les parametres des raies d'emission de 214 QSOs are presented and a etude preliminaire des proprietes de cet echantillon is presented.
Abstract: On donne les parametres des raies d'emission de 214 QSO. On presente une etude preliminaire des proprietes de cet echantillon


Journal ArticleDOI
TL;DR: In this paper, the results of l'etude de modeles de chocs interstellaires, hydrodynamiques a un fluide and magnetohydrodynamique a trois fluides.
Abstract: Resultats de l'etude de modeles de chocs interstellaires, hydrodynamiques a un fluide et magnetohydrodynamiques a trois fluides. Ont ete incluses 150 reactions chimiques