Showing papers in "The Astrophysical Journal in 1980"
TL;DR: In this paper, a study of the galaxy populations in 55 rich clusters is presented together with a discussion of the implications for the formation and/or evolution of different morphological types.
Abstract: A study of the galaxy populations in 55 rich clusters is presented together with a discussion of the implications for the formation and/or evolution of different morphological types. A well-defined relationship is found between local galaxy density and galaxy type, which, in agreement with previous studies, indicates an increasing elliptical and SO population and a corresponding decrease in spirals with increasing density.
3,368 citations
TL;DR: In this article, the authors calculate the rate at which angular momentum and energy are transferred between a disk and a satellite which orbit the same central mass, and show that substantial changes in both the structure of the disk and the orbit of Jupiter must have taken place on a time scale of a few thousand years.
Abstract: We calculate the rate at which angular momentum and energy are transferred between a disk and a satellite which orbit the same central mass. A satellite which moves on a circular orbit exerts a torque on the disk only in the immediate vicinity of its Lindblad resonances. The direction of angular momentum transport is outward, from disk material inside the satellite's orbit to the
satellite and from the satellite to disk material outside its orbit. A satellite with an eccentric orbit exerts a torque on the disk at corotation resonances as well as at Lindblad resonances. The angular momentum and energy transfer at Lindblad resonances tends to increase the satellite's orbit eccentricity whereas the transfer at corotation resonances tends to decrease it. In a Keplerian disk, to lowest order in eccentricity and in the absence of nonlinear effects, the corotation resonances dominate by a slight margin and the eccentricity damps. However, if the strongest corotation resonances saturate due to particle trapping, then the eccentricity grows. We present an illustrative application of our results to the interaction between Jupiter and the protoplanetary disk. The angular momentum transfer is shown to be so rapid that substantial
changes in both the structure of the disk and the orbit of Jupiter must have taken place on a time scale of a few thousand years.
1,601 citations
TL;DR: In this article, the relation between spiral and SO galaxies in the light of recent data on the colors and morphology of disk systems, and on the content of clusters at different redshifts was investigated.
Abstract: We reconsider the relation between spiral and SO galaxies in the light of recent data on the colors and morphology of disk systems, and on the content of clusters at different redshifts. Star formation will strongly deplete the gas in most spirals in a fraction of the Hubble time, so we suggest that the gas in spirals has been replenished by infall from residual envelopes, probably including gas-rich companions and tidal debris. SO's may then be disk systems that lost their gas-rich envelopes at an early stage and consumed their remaining gas by star formation. This picture is consistent with the color of SO's if most of their star formation stopped at least a few gigayears ago, and it is consistent with their small disk-to-bulge ratios relative to spirals, since this is a direct result of the early truncation of star formation. Numerical simulations show that the gas envelopes of disk galaxies in clusters are largely stripped away when the clusters collapse, but star formation can continue in the spirals for several gigayears while their remaining disk gas is consumed. These results can explain the blue galaxies observed by Butcher and Oemler in two condensed clusters at zapprox.0.4: these clustersmore » are seen just before most of their galaxies run out of gas, so that star formation is still occurring in them but will soon die out, causing the spirals to evolve into SO's with normal present colors. A rapid evolution of the galaxy content of condensed clusters is predicted at moderate redshifts, ranging from a large fraction of blue galaxies at zapprox.0.4 to very few at zapprox.0.« less
1,537 citations
TL;DR: In this article, major axis spectra extending to the faint outer regions of the galaxies were used to deduce rotation curves for 21 galaxies whose properties encompass a wide range of radii, masses, and luminosities.
Abstract: For 21 Sc galaxies whose properties encompass a wide range of radii, masses, and luminosities, we have obtained major axis spectra extending to the faint outer regions, and have deduced rotation curves. The galaxies are of high inclination, so uncertainties in the angle of inclination to the line of sight and in the position angle of the major axis are minimized. Their radii range from 4 to 122 kpc (H = 50km s-1 Mpc-1); in general, the rotation curves extend to 83% or R25i.b. When plotted on a linear scale with no scaling, the rotation curves for the smallest galaxies fall upon the initial parts of the rotation curves for the larger galaxies. All curves show a fairly rapid velocity rise to V ˜ 125 km s-1 at R ˜ 5 kpc, and a slower rise thereafter. Most rotation curves are rising slowly even at the farthest measured point. Neither high nor low luminosity Sc galaxies have falling rotation curves. Sc galaxies of all luminosities must have significant mass located beyond the optical image. A linear relation between log Vmax and log R follows from the shape of the common rotation curve for all Sc's, and the tendency of smaller galaxies, at any R, to have lower velocities than the large galaxies at that R. The significantly shallower slope discovered for this relation by Tully and Fisher is attributed to their use of galaxies of various Hubble types and the known correlation of Vmax with Hubble type. The galaxies with very large central velocity gradients tend to be large, of high luminosity, with massive, dense nuclei. Often their nuclear spectra show a strong stellar continuum in the red, with emission lines of [N II] stronger than Halpha. These galaxies also tend to be 13 cm radio continuum sources. Because of the form of the rotation curves, small galaxies undergo many short-period, very differential, rotations. Large galaxies undergo (in their outer parts) few, only slightly differential, rotations. This suggests a relation between morphology, rotational properties, and the van den Bergh luminosity classification, which is discussed. UGC 2885, the largest Sc in the sample, has undergone fewer than 10 rotations in its outer parts since the origin of the universe but has a regular two-armed spiral pattern and no significant velocity asymmetries. This observation puts constraints on models of galaxy formation and evolution.
1,434 citations
TL;DR: In this paper, it was shown that the presence of a phase transition early in the history of the universe, associated with spontaneous symmetry breaking (believed to take place at very high temperatures at which the various fundamental interactions unify), significantly modifies its dynamics and evolution.
Abstract: It is shown that the presence of a phase transition early in the history of the universe, associated with spontaneous symmetry breaking (believed to take place at very high temperatures at which the various fundamental interactions unify), significantly modifies its dynamics and evolution. This is due to the energy 'pumping' during the phase transition from the vacuum to the substance, rather than the gravitating effects of the vacuum. The expansion law of the universe then differs substantially from the relation considered so far for the very early time expansion. In particular it is shown that under certain conditions this expansion law is exponential. It is further argued that under reasonable assumptions for the mass of the associated Higgs boson this expansion stage could last long enough to potentially account for the observed isotropy of the universe.
606 citations
TL;DR: In this article, the authors examined whether clouds of neutral hydrogen can condense from a hot, dynamic corona above the plane of the Galaxy and showed that it is consistent with current values for the supernova heating rate above the disk.
Abstract: We examine whether high-velocity clouds of neutral hydrogen (not the Magellanic Stream), observed in every longitude quadrant of the sky, can condense from a hot, dynamic corona above the plane of the Galaxy. Supernova-heated gas that arises above the disk must either flow outward as a wind or remain bound to the Galaxy in a dynamic corona in which gas is constantly in motion: a static corona is not stable. Since clouds cannot condense in a wind, we favor a corona and show that it is consistent with current values for the supernova heating rate above the disk. Gas continuously entering the corona from the disk rises up (in Z) and outward (in ..omega..) in an attempt to reach static equilibrium with the corona. The gas behaves adiabatically until radiative losses become important. Then, coronal gas is susceptible to thermal instabilities and neutral clouds condense from the corona. Clouds form toward the top of the corona at about one density scale height because thermal instabilities grow most rapidly there. After formation, clouds fall ballistically toward their point of origin.
586 citations
TL;DR: A torsional wave pattern with alternating latitude zones of slow and fast rotation is found, after subtracting a differentially rotating frame as mentioned in this paper, which evidently represents a deep-seated circulation pattern and is the first evidence of the association of mass motions with large-scale characteristics of the solar activity cycle.
Abstract: Twelve years of full-disk Mount Wilson velocity data have been analyzed to study horizontal east-west motions. A torsional wave pattern with alternating latitude zones of slow and fast rotation is found, after subtracting a differentially rotating frame. Amplitudes of the flow pattern average about 3 m/s. It requires about 22 years for zones to drift from the poles, where they originate, to the equator, where they disappear. The pattern is symmetric about the equator. The zones representing the next solar cycle (No. 22) are seen now at high solar latitudes. Solar active regions are formed in a latitude strip centered on the boundary of fast- and slow-velocity zones. This pattern evidently represents a deep-seated circulation pattern and is the first evidence of the association of mass motions with large-scale characteristics of the solar activity cycle.
448 citations
TL;DR: In this paper, the authors argue that the mass of molecular gas in the Galaxy has been considerably overestimated and that the ages of the giant molecular complexes do not exceed a few times 10/sup 7/ years.
Abstract: From the available observational and theoretical evidence we argue that the mass of molecular gas in the Galaxy has been considerably overestimated and that the ages of the giant molecular complexes do not exceed a few times 10/sup 7/ years. We derive an expression for the collisional time scale for clumps in a complex and show that it has a maximum value of 1 x 10/sup 7/ yr. We argue that the formation of giant complexes by random collisional agglomeration of small molecular clouds is incompatible with several firm observational results. We discuss the Parker instability as a possible formation mechanism which can explain many of the observed properties of the complexes.
396 citations
TL;DR: If half or more of the mass of a virialized system is lost in less than one dynamical crossing time, the system dissocites if the mass loss occurs in a collapsing protosystem with uniform density, no angular momentum, and relatively little radiation of energy as mentioned in this paper.
Abstract: If half or more of the mass of a virialized system is lost in less than one dynamical crossing time, the system dissocites If the mass loss occurs in a collapsing protosystem with uniform density, no angular momentum, and relatively little radiation of energy, the minimum fractional mass loss required for dissociation is reduced to deltaM/M/sub 0/=R/sub c//(2R/sub 0/) Here R/sub c/ is the radius of the system when the mass loss occurs and R/sub 0/ is the radius it would have attained after virialization if no mass loss had occurred A situation of this type is expected in a protocluster that forms from a collapsing interstellar cloud The stars form when the protocluster is near its point of maximum compression Any newly formed OB stars produce an H II region whose expansion dissipates the residual gas in the protosystem before the system reaches dynamical equilibrium The angular momentum of the protosystem and any radiative losses from it prior to star formation will tend to stabilize it against mass loss by limiting the compression factor 2R/sub 0//R/sub c/ The angular momentum places a lower limit on the radius R/sub c/, and the radiative losses reduce the final equilibrium radius R/submore » 0/ However, observed infantile clusters such as the Trapezium are sufficiently compressed at the present time that a loss of as little as 10% of their mass is sufficient to dissociate them This may explain why most young stars are not located in gravitationally bound clusters If the protocluster gas contains an appreciable magnetic field, the compression of this field in the collapsing cloud drains off some of the gravitational energy that otherwise would go into the kinetic energy of collapse This increases the minimum mass loss required to dissociate the system, but it is still very small for most systems« less
391 citations
379 citations
TL;DR: In this article, the structure of steady, radiative, one-dimensional shock waves in partially ionized gas with a transverse magnetic field B/sub 0/ is investigated under a broad range of conditions applicable to the interstellar medium.
Abstract: The structure of steady, radiative, one-dimensional shock waves in partially ionized gas with a transverse magnetic field B/sub 0/ is investigated. Under a broad range of conditions applicable to the interstellar medium it is found that such shocks may be preceded by a magnetic precursor which heats and compresses the medium ahead of the front where the neutral gas undergoes a discontinuous change of state; indeed, if B/sub 0/ is sufficiently large, a shock can exist with no discontinuities in hydrodynamical variables. Within this magnetic precursor both ions and electrons stream through the neutral fluid with velocities which may be a significant fraction of the shock speed. The physical processes operative in such shocks are examined, including the effects of charged dust grains in dense molecular clouds. Numerical examples are shown for v/sub s/ = 10 km s/sup -1/ shocks propagating into diffuse H I or H/sub 2/. Shocks with magnetic precursors may have important consequences for the interstellar medium, some of which are briefly considered.
TL;DR: In this article, it was shown that relativistic secondary particles can be entirely responsible for the observed radio halo in Coma, if it is assumed that the ratio of the energy-dependent production rate of primary protons to primary electrons is the same as that apparent from cosmic rays in our Galaxy.
Abstract: Relativistic protons produced in radio galaxies in a cluster can diffuse over distances approx.1 Mpc in the intracluster medium before suffering inelastic collisions with thermal protons. This results in a population of relativistic secondary electrons and positrons formed in situ on this scale. It is shown that these secondary particles can be entirely responsible for the observed radio halo in Coma, if it is assumed that the ratio of the energy-dependent production rate of primary protons to primary electrons is the same as that apparent from cosmic rays in our Galaxy, and that the intracluster magnetic field is in approximate equipartition (approx.2 microgauss) with relativistic particles. Clearly, this model eliminates the theoretical difficulties involved in the transport of primary electrons at speeds orders of magnitude in excess of the Alfven speed, as required to reach the outer halo in less than a radiative lifetime. In addition, low-energy protons may play a significant role in heating the intracluster gas through Coulomb collisions.
TL;DR: In this paper, the age-metallicty relation for the disk in the neighborhood of the Sun is derived from four-color and H..beta.. photometry of a large sample of southern F dwarfs, analyzed in combination with theoretical isochrones.
Abstract: The age-metallicty relation for the disk in the neighborhood of the Sun is derived from four-color and H..beta.. photometry of a large sample of southern F dwarfs, analyzed in combination with theoretical isochrones. It is found that the mean metallicity of the disk increased by about a factor of 5 between 12 and 5 billion years ago and has increased only slightly since then; this conclusion is independent of the helium abundance assumed for the models.
TL;DR: In this paper, the authors give a new formulation for the evolution of protostars and derive the jump conditions of the radiative accretion shock which joins the hydrostatic mass-gaining core to the dynamic inner cloud envelope.
Abstract: We review the controversy and give a new formulation for the problem of the evolution of protostars. Our method entails the division of the global problem into a set of more manageable subproblems. We derive the jump conditions of the radiative accretion shock which joins the hydrostatic mass-gaining core to the dynamic inner cloud envelope. Different approximations hold with high accuracy in the regions that we call the dust envelope, the opacity gap, the radiative precusor, the accretion shock, and the hydrostatic core. In no region do we need to solve equations more complicated than ordinary differential equations. Thus, standard integration schemes yield the high accuracy needed to resolve complex spatial structures which span many orders of magnitude in density and temperature. Our 1 M/sub sun/ protostar ends its main accretion phase moderately high up in the H-R diagram. This star begins it pre--main-sequence phase of quasi-static contraction on a convective Hayashi track.
TL;DR: In this paper, a new variable, V(e)/V(a), which is superior to V/Vmax when sufficient observational data are available, is introduced, and statistically independent complete samples can be generated from partially overlapping samples such that each observed object appears only once in the analysis.
Abstract: Methods are derived for applying the V/Vmax variable when several complete samples are analyzed simultaneously. A new, related, variable, V(e)/V(a), which is superior to V/Vmax when sufficient observational data are available, is introduced. It is shown how statistically independent complete samples can be generated from partially overlapping samples such that each observed object appears only once in the analysis. These methods make it possible to combine the information from different complete samples, and to make an efficient use of all available data. Illustrative examples for quasars are given. It is shown how the generalized V/Vmax and V(e)/V(a) can be used to find the amount of cosmological evolution of quasars and its associated range of uncertainty.
TL;DR: The GSFC Cosmic X-ray Experiment on HEAO 1 for regions of the sky away from known point sources and more than 20 deg from the galactic plane is available at present.
Abstract: The spectrum of the extragalactic diffuse X-ray background has been measured with the GSFC Cosmic X-ray Experiment on HEAO 1 for regions of the sky away from known point sources and more than 20 deg from the galactic plane. A total exposure of 80 sq m-s-sr is available at present. Free-free emission from an optically thin plasma of 40 plus or minus 5 keV provides an excellent description of the observed spectrum from 3 to 50 keV. This spectral shape is confirmed by measurements from five separate layers of three independent detectors. With an estimated absolute precision of about 10%, the intensity of the emission at 10keV is 3.2 keV/keV/sq cm/s/sr, a value consistent with the average of previously reported spectra. A uniform hot intergalactic medium of approximately 36% of the closure density of the universe would produce such a flux, although nonuniform models indicating less total matter are probably more realistic.
TL;DR: In this paper, a model is proposed which can account for the longevity, energetics, and dynamical structure of dark molecular clouds, and it is found that star formation occurs on a relatively slow time scale, comparable to the cloud lifetime.
Abstract: A model is proposed which can account for the longevity, energetics, and dynamical structure of dark molecular clouds. Recent observations of a high space density of T Tauri stars in some dark clouds provide the basis for the assertion that high-velocity winds from these low mass pre-main-sequence stars provide a continuous dynamic input into molecular clouds. It is postulated that as clumps are driven above the Jeans mass, both by coalescence and the enhancement of ram pressure through continuing acceleration by protostellar winds, collapse is followed by the formation of low-mass stars that generate additional protostellar winds. Finally, it is found that star formation occurs on a relatively slow time scale, comparable to the cloud lifetime
TL;DR: In this paper, the spectrum of Tycho's supernova remnant has been observed in terms of a shock wave model, where the shock wave is presumably encountering neutral atoms that have some probability of giving line emission before being ionized by the post-shock gas.
Abstract: We have observed the spectrum of Tycho's supernova remnant and have detected only the H..cap alpha.., H..beta.., and H..gamma.. lines. The H..cap alpha.. line profile can be divided into two components: one with a width consistent with the instrumental resolution and one with a full width at half-maximum (FWHM) of 1800 +- 200 km s/sup -1/. The two components have similar intensities. The observations are interpreted in terms of a shock wave model. The shock wave is presumably encountering neutral atoms that have some probability of giving line emission before being ionized by the post-shock gas. Charge exchange can occur in the post-shock region, giving rise to a broad emission component from a population of fast neutral atoms. The ratio of broad to narrow emission components is a sensitive function of shock velocity because the charge-exchange cross section depends strongly on the proton velocity. For Tycho's remnant, both the ratio of broad to narrow emission and the FWHM of the broad emission can be fitted if the shock velocity is 2300 +- 500 km s/sup -1/. Combined with the proper motion of the filament as found by Kamper and van den Bergh, the distance to Tycho's remnant is about 2.3more » +- 0.5 kpc. The absolute photographic magnitude of Tycho's supernova at maximum is then -18.8 +- 1.3, which is consistent with the absolute magnitudes of extragalactic Type I supernovae at maximum light.The shock model can be applied to some other emission nebulae. We predict that a broad emission component should be present in the H..cap alpha.. line profile of the remnant of SN 1006. If the model applies to the high-velocity emission regions in the Cygnus Loop observed by Kirshner and Taylor, we expect the high-velocity components to have a width approximately equal to half their velocity shift and to be unobservable in forbidden emission lines of heavy elements. The model may also apply to the high-velocity emission region observed by Elliott near eta Carinae.« less
TL;DR: In this article, the partial differential equations describing a Type II supernova are reduced to the time-dependent diffusion equation, and the behavior of luminosity, effective temperature, B--V color, and fluid velocity is explicitly presented, with dependence on mass, energy of explosion, initial radius, and opacity shown.
Abstract: By suitable tranformations, primarily made to remove homologous expansion, the partial differential equations describing a Type II supernova are reduced to the time-dependent diffusion equation. The behavior of luminosity, effective temperature, B--V color, and fluid velocity is explicitly presented, with dependence on mass, energy of explosion, initial radius, and opacity shown. The solutions allow crude estimates of the mass of ejected matter (Mapprox. =8 M/sub sun/) and of /sup 56/Co synthesized (approx.0.5 M/sub sun/ in one case) to be made from observational data. From such solutions it may be possible to infer absolute luminosity from distance-independent characteristics of the event.
TL;DR: In this paper, it was shown that the conversion of CO to methane and of N2 to ammonia in the primitive solar nebula was probably so slow relative to radial mixing rates or nebula evolutionary rates that only small amounts of NH3 and CH4 could have been present.
Abstract: It is shown that the conversion of CO to methane and of N2 to ammonia in the primitive solar nebula was probably so slow relative to radial mixing rates or nebula evolutionary rates that only small amounts of NH3 and CH4 could have been present. Thus most of the nitrogen was present as N2 and most of the carbon as CO and CO2 throughout the nebula. The consequences of this kinetic effect upon the composition of cometary ices and of the Jovian planets, the melting and outgassing behavior of ice rich planetary satellites, and the abundance of carbon in the terrestrial planets are briefly discussed.
TL;DR: In this paper, the authors investigate the collapse of nonrotating gas spheres with a polytropic equation of state: n = 3, corresponding to y = 4/3, and find a family of exact and homologously collapsing configurations.
Abstract: We investigate the collapse of nonrotating gas spheres with a polytropic equation of state: n = 3, corresponding to y = 4/3. Such polytropes provide a reasonable approximation to collapsing stellar cores during the early phase before nuclear density is reached. We find a family of exact
homologously collapsing configurations. Homologous collapse of the entire core is possible if the pressure at a given density is reduced by up to 3% from the value for a marginally stable static core. For a greater pressure reduction, an inner core can collapse homologously, the mass of which varies as the 3/2 power of the reduced pressure at the onset of collapse. Linear perturbations of
these homologously collapsing solutions are separable in space and time. Low order radial and nonradial modes are calculated, and it is found that all modes are essentially stable.
TL;DR: In this paper, it was shown that substantial Ly-alpha radiative heating occurs in the upper chromosphere resulting from the conductive energy flux in the transition zone where the Ly alpha line cools the gas.
Abstract: Homogeneous plane-parallel semiempirical flare model atmospheres which reproduce observations in lines and continua of H I, Si I, C I, Ca II, and Mg II have a thin transition zone at the top of the enhanced chromosphere, indicating a significant amount of heating from the zone to the temperature minimum level. The minimum temperature is located deeper and is higher than in the quiet-sun and active-region models. The results do not agree with the particle-heated theoretical models, and it is suggested that the models of Brown (1973) and Henoux and Nakagawa (1977, 1978) do not include an essential term for heat conduction in their energy balance equations. It is concluded that substantial Ly-alpha radiative heating occurs in the upper chromosphere resulting from the conductive energy flux in the transition zone where the Ly-alpha line cools the gas.
TL;DR: In this article, a simple shock model for the acceleration of energetic particles in corotating interaction regions (CIRs) in the solar wind is presented, where particles are accelerated at the forward and reverse shocks which bound the CIR by being compressed between the shock fronts and magnetic irregularities upstream from the shocks, or by being accelerated between upstream irregularities and those downstream from shocks.
Abstract: A simple shock model for the acceleration of energetic particles in corotating interaction regions (CIRs) in the solar wind is presented. Particles are accelerated at the forward and reverse shocks which bound the CIR by being compressed between the shock fronts and magnetic irregularities upstream from the shocks, or by being compressed between upstream irregularities and those downstream from the shocks. Particles also suffer adiabatic deceleration in the expanding solar wind, an effect not included in previous shock models for acceleration in CIRs. The model is able to account for the observed exponential spectra at earth, the observed behavior of the spectra with radial distance, the observed radial gradients in the intensity, and the observed differences in the intensity and spectra at the forward and reverse shocks.
TL;DR: In this article, a phenomenological theory for the structure of the unstable line-driven winds of early-type stars is proposed, where the winds are conjectured to break up into a population of blobs that are being radiatively driven through, and confined by ram pressure of an ambient gas that is not itself being driven.
Abstract: A phenomenological theory is proposed for the structure of the unstable line-driven winds of early-type stars. These winds are conjectured to break up into a population of blobs that are being radiatively driven through, and confined by ram pressure of an ambient gas that is not itself being radiatively driven. Radiation from the bow shocks preceding the blobs can account for the X-ray luminosity of zeta Puppis. The theory breaks down when used to model the much lower density wind of tau Scorpii, for then the blobs are destroyed by heat conduction from shocked gas. This effect explains why the profiles of this star's UV resonance lines depart from classical P Cygni form.
TL;DR: In this paper, the authors compare the X-ray polarization features of geometrically thick clouds surrounding a black hole and the standard accretion disk model, and show that general-relativistic corrections can lead to large rotations in the plane of Xray polarization and to changes in the degree of polarization.
Abstract: We compare the X-ray polarization features of geometrically thick clouds surrounding a black hole and the standard accretion disk model. The calculations include a fully general-relativistic treatment of the radiation transfer problem. In both cases general-relativistic corrections can lead to large rotations in the plane of X-ray polarization and to changes in the degree of polarization. Such differences are potentially observable and can be used to distinguish between the two models. The polarization features can indicated whether a black hole is present in a compact X-ray source.