Showing papers in "The Astrophysical Journal in 1984"
3,313 citations
TL;DR: In this article, the authors explored the role of mass transfer in the evolution of double degenerate systems and found that low-mass helium/helium pairs are unstable to dynamical time-scale mass transfer and probably coalesce to form helium-burning sdO stars.
Abstract: Close double white dwarfs should arise from the second phase of mass exchagne in close binaries which first encountered mass exchange while the more massive star was crossing the Hertzprung gap. Tidal mass transfer in these double degenerate systems is explored. The sequence of double white dwarf divides naturally into three segments. (1) Low-mass helium/helium pairs are unstable to dynamical time-scale mass transfer and probably coalesce to form helium-burning sdO stars. (2) In helium/carbon-oxygen pairs, mass transfer occurs on the time scale for gravitational radiation losses (approx.10/sup -4/ M/sub sun/ yr/sup -1/); the accreted helium is quickly ignited, and the accretor expands to dimensions characteristic of R CrB stars, engulfing its companion star. (3) Carbon-oxygen/carbon-oxygen pairs are again unstable to dynamical time-scale mass transfer and, since their total masses exceed the Chandrasekhar limit, are destined to become supernovae. Inactive lifetimes in these latter systems between creation and interaction can exceed 10/sup 10/ years. Birthrates of R CrB stars and Type I supernovae by evolution of double white dwarfs are in reasonable agreement with observational estimates.
2,234 citations
TL;DR: In this paper, the mean level of Ca n H and K emission (averaged over 15 years) is correlated with rotation period, as expected, but there is a further dependence of the emission on spectral type.
Abstract: Rotation periods are reported for 14 main-sequence stars, bringing the total number of such stars with well-determined rotation periods to 41. It is found that the mean level of their Ca n H and K emission (averaged over 15 years) is correlated with rotation period, as expected. However, there is a further dependence of the emission on spectral type. When expressed as the ratio of chromospheric flux to total bolometric flux, the emission is well correlated with the parameter Pohs/Tc, where Pohs is the observed rotation period and tc(B—V) is a theoretically-derived convective overturn time, calculated assuming a mixing length to scale height ratio a ~ 2. This finding is consonant with general predictions of dynamo theory, if the relation between chromospheric emission and dynamo-generated magnetic fields is essentially independent of rotation rate and spectral type for the stars considered. The dependence of mean chromospheric emission on rotation and spectral type is essentially the same for stars above and below the Vaughan-Preston “gap,” thus casting doubt on explanations of the gap in terms of a discontinuity in dynamo characteristics. Subject headings: Ca n emission — convection — stai
1,650 citations
TL;DR: In this article, the carbon deflagration model was proposed for Type I supernovae. But it is not a plausible model for Type II supernova, as the model is not suitable for the case of large nuclear energy release and the star is disrupted completely leaving no compact star remnant behind.
Abstract: The carbon deflagration models in accreting C+O white dwarfs are presented as a plausible model for Type I supernovae. The evolution of the white dwarf is calculated from the beginning of accretion. The relatively rapid accretion studied here (M> or approx. =4 x 10/sup -8/ M/sub sun/ yr/sup -1/) leads to the initiation of the carbon deflagration at the center. Subsequent propagation of the convective carbon deflagration wave and associated explosive nucleosynthesis are calculated for several cases of mixing length in the convection theory. The deflagration wave synthesizes 0.5-0.6 M/sub sun/ /sup 56/Ni in the inner layer of the star; this amount is sufficient to power the light curve of Type I supernovae by the radioactive decays of /sup 56/Ni and /sup 56/Co. In the outer layers, substantial amount of intermediate mass elements, Ca, Ar, S, Si, Mg, and O are synthesized in the decaying deflagration wave; this is consistent with the spectra of Type I supernovae near maximum light. As a result of large nuclear energy release, the star is disrupted completely, leaving no compact star remnant behind. Thus the carbon deflagration model can account for many of the observed features of Type I supernovae.
1,335 citations
TL;DR: In this article, it was shown that if rich clusters formed where the primordial density enhancement, when averaged over an appropriate volume, was unusually large, then they give a biased measure of the large-scale density correlation function determiend by the probability distribution of the density fluctuations on a rich cluster mass scale.
Abstract: If rich clusters formed where the primordial density enhancement, when averaged over an appropriate volume, was unusually large, then they give a biased measure of the large-scale density correlation function determiend by the probability distribution of the density fluctuations on a rich cluster mass scale. If this distribution was Gaussian, the correlation function is amplified. The amplification for rich clusters is estimated to be eaual about ten and predicted trend of amplification with richness agrees qualitatively with that observed. Some implications of these results for the large-scale density correlations are discussed.
1,220 citations
TL;DR: The Infrared Astronomical Satellite (IRAS) as discussed by the authors consists of a spacecraft and a liquid helium cryostat that contains a cooled IR telescope, whose focal plane assembly is cooled to less than 3 K, and contains 62 IR detectors in the survey array.
Abstract: The Infrared Astronomical Satellite (IRAS) consists of a spacecraft and a liquid helium cryostat that contains a cooled IR telescope. The telescope's focal plane assembly is cooled to less than 3 K, and contains 62 IR detectors in the survey array which are arranged so that every source crossing the field of view can be seen by at least two detectors in each of four wavelength bands. The satellite was launched into a 900 km-altitude near-polar orbit, and its cryogenic helium supply was exhausted on November 22, 1983. By mission's end, 72 percent of the sky had been observed with three or more hours-confirming scans, and 95 percent with two or more hours-confirming scans. About 2000 stars detected at 12 and 25 microns early in the mission, and identified in the SAO (1966) catalog, have a positional uncertainty ellipse whose axes are 45 x 9 arcsec for an hours-confirmed source.
1,008 citations
TL;DR: In this article, a steady state, spherically symmetric, magnetohydrodynamic model of the Crab nebula is constructed, where a highly relativistic positronic positronic pulsar wind is terminated by a strong MHD shock that decelerates the flow and increases its pressure to match boundary conditions imposed by the recently discovered supernova remnant that surrounds the nebula.
Abstract: A steady state, spherically symmetric, magnetohydrodynamic model of the Crab nebula is constructed. A highly relativistic positronic pulsar wind is terminated by a strong MHD shock that decelerates the flow and increases its pressure to match boundary conditions imposed by the recently discovered supernova remnant that surrounds the nebula. If the magnetic luminosity of the pulsar wind upstream of the shock is about 0.3 percent of its particle luminosity, the pressure and velocity boundary conditions imposed by the remnant place the shock where it is inferred to be: near the outer boundary of an underluminous region observed to surround the pulsar. It is necessary to include the weak magnetization of the wind to satisfy the boundary conditions and to calculate the regular synchrotron radiation self-consistently.
927 citations
TL;DR: In this paper, a nonrelativistic potential theory for gravity is proposed, which is built on the basic assumptions of the modified dynamics, which were shown earlier to reproduce dynamical properties of galaxies and galaxy aggregates without having to assume the existence of hidden mass.
Abstract: We consider a nonrelativistic potential theory for gravity which differs from the Newtonian theory. The theory is built on the basic assumptions of the modified dynamics, which were shown earlier to reproduce dynamical properties of galaxies and galaxy aggregates without having to assume the existence of hidden mass. The theory involves a modification of the Poisson equation and can be derived from a Lagrangian. The total momentum, angular momentum, and (properly defined) energy of an isolated system are conserved. The center-of-mass acceleration of an arbitrary bound system in a constant external gravitational field is independent of any property of the system. In other words, all isolated objects fall in exactly the same way in a constant external gravitational field (the weak equivalence principle is satisfied). However, the internal dynamics of a system in a constant external field is different from that of the same system in the absence of the external field, in violation of the strong principle of equivalence. These two results are consistent with the phenomenological requirements of the modified dynamics. We sketch a toy relativistic theory which has a nonrelativistic limit satisfying the requirements of the modified dynamics.
887 citations
TL;DR: In this paper, a photometry of 33 clusters of galaxies, with redshifts between 0.003 (the Virgo Cluster) and 0.54 (Cl 0016+16) to search for evolution of the colors of cluster populations.
Abstract: In this paper we analyze photometry of 33 clusters of galaxies, with redshifts between 0.003 (the Virgo Cluster) and 0.54 (Cl 0016+16) to search for evolution of the colors of cluster populations. In each cluster we select these galaxies brighter than M/sub V/ = -20 which are within the circular area containing the inner 30% of the total Jupiter population. From the distribution of these galaxies in the color-magnitude plane, we determine the fraction of galaxies whose rest-frame B-V colors are at least 0.2 mag bluer than the ridge line of the early type galaxies at that magnitude. We define this to be the blue galaxy population, f/sub B/, and find it to have the following characteristics in compact, concentrated clusters: (1) For z or approx. =0.1 f/sub B/ increases with redshift reaching f/sub B/approx.0.25 at z = 0.5. (3) The values of f/sub B/ seen in clusters at a particular redshift are mostly consistent with clusters being random samples of one homogeneous galaxy population, but there is some evidence that processes within individual clusters may also affect the galaxy content.
812 citations
TL;DR: In this article, a generalized model for the spherical collapse of a singular isothermal sphere such as protosolar and binary nebulae is defined for a sound speed of 0.35 km/sec and a rotation rate of 10 to 14th/sec.
Abstract: A generalized model which accounts for the effects of initially uniform and slow rotation is defined for the spherical collapse of a singular isothermal sphere such as protosolar and binary nebulae. An initial unstable equilibrium state is described for a sound speed of 0.35 km/sec and a rotation rate of 10 to the -14th/sec for the molecular cloud surrounding the accreting core. The total angular momentum and mass of the inner cloud is set equal to solar system values. The evolution of the collapse is traced by applying a perturbation analysis to the similarity solution for a nonrotating condition, and matched asymptotic expansions solve the hydrodynamic equations. The model is concluded a valid tool for studying star and nebular disk formation.
TL;DR: The relationship between galaxy morphology and local density is derived from two complete galaxy redshift surveys as mentioned in this paper, which is completely consistent with the one derived by Dressler for a sample of 55 rich clusters.
Abstract: The relationship between galaxy morphology and local density is derived from two complete galaxy redshift surveys. This relationship is completely consistent with the one derived by Dressler for a sample of 55 rich clusters. The apparently universal morphology-density relation extends over six orders of magnitude in galaxy space density. There is no dependence of galaxy morphology on density in regions where the dynamical time scale is comparable with or greater than the Hubble time. At densities greater than about 600 galaxies/cu Mpc, S0's dominate the galaxy population. At these densities, stripping mechanisms are likely to affect the galaxy population. At densities greater than about 3000 galaxies/cu Mpc, the fraction of elliptical galaxies rises steeply. In these regions, the collapse time is short compared with typical time scales for the formation of disks.
TL;DR: The first detection of a large infrared excess from a main-sequence star without significant mass loss was reported in this article. But this was only for the case of Alpha Lyrae, which has a diameter of about 20 arcsec.
Abstract: IRAS observations of Alpha Lyrae reveal a large infrared excess beyond 12 microns. The excess over an extrapolation of a 10,000 K blackbody is a factor of 1.3 at 25 microns, 7 at 60 microns, and 16 at 100 microns. The source of 60 microns emission has a diameter of about 20 arcsec. This is the first detection of a large infrared excess from a main-sequence star without significant mass loss. The most likely origin of the excess is thermal radiation from solid particles more than a millimeter in radius, located approximately 85 AU from Alpha Lyr and heated by the star to an equilibrium temperature of 85 K. These results provide the first direct evidence outside of the solar system for the growth of large particles from the residual of the prenatal cloud of gas and dust.
TL;DR: In this article, the authors applied the hydrostatic-isothermal gas model to obtain the cluster core radius, the limiting slope of the X-ray surface brightness distribution, and the presence and magnitude of a central luminosity excess above that predicted from the model when fit to the outer regions of the cluster.
Abstract: Imaging observations from the Einstein Observatory are used to determine properties of galactic clusters and the intracluster gas. The hydrostatic-isothermal gas model is applied to obtain the cluster core radius, the limiting slope of the X-ray surface brightness distribution, and the presence and magnitude of a central luminosity excess above that predicted from the model when fit to the outer regions of the cluster. It is concluded that clusters can be divided into two basic families, one with small core radii and X-ray emission centered on a central dominant galaxy, and one with larger core radii and generally no central, stationary bright galaxy. The former type probably begins to form in the early stages of a cluster's dynamical evolution. The intracluster gas has a larger scale height than that of the galaxies based on the fit of the hydrostatic-isothermal model to the X-ray surface brightness profiles.
TL;DR: In this paper, the outer edge of the core is fitted to the boundary conditions at the bottom of the hydrogen-rich envelope, and two cases with initial helium core mass of M/sub H//sup(/sup 0/) = 2.6 and 2.4 m/sub sun/
Abstract: Helium cores in stars with masses near 10 M/sub sun/ are evolved from the helium burning phase; the outer edge of the core is fitted to the boundary conditions at the bottom of the hydrogen-rich envelope. Two cases with initial helium core mass of M/sub H//sup(/sup 0/) = 2.6 M/sub sun/ (case 2.6) and 2.4 M/sub sun/ (case 2.4) are studied. Both cores spend the carbon burning phase under nondegenerate condition and leave O+Ne+Mg cores. Further evolution depends on the mass of the O+Ne+Mg core, M/sub C/.
TL;DR: In this article, the temperature fluctuations in the cosmic background radiation for universes dominated by massive collisionless relics of the big bang are analyzed and an initially adiabatic constant curvature perturbation spectrum is assumed.
Abstract: Detailed calculations of the temperature fluctuations in the cosmic background radiation for universes dominated by massive collisionless relics of the big bang are presented. An initially adiabatic constant curvature perturbation spectrum is assumed. In models with cold dark matter, the simplest hypothesis - that galaxies follow the mass distribution leads to small-scale anisotropies which exceed current observational limits if omega is less than 0.2 h to the -4/3. Since low values of omega are indicated by dynamical studies of galaxy clustering, cold particle models in which light traces mass are probably incorrect. Reheating of the pregalactic medium is unlikely to modify this conclusion. In cold particle or neutrino-dominated universes with omega = 1, presented predictions for small-scale and quadrupole anisotropies are below current limits. In all cases, the small-scale fluctuations are predicted to be about 10 percent linearly polarized.
TL;DR: In this paper, the properties of the synchrotron continuum were calculated on the basis of a steady spherically symmetric MHD model of the flow in the Crab nebula.
Abstract: The properties of the synchrotron continuum are calculated on the basis of a steady spherically symmetric MHD model of the flow in the Crab nebula. The model accounts for the spectral distribution of the continuum from the optical to gamma-rays, and semiquantitatively for its observed spatial distribution. The model does not account for the radio portion of the Crab nebula's spectrum.
TL;DR: In this article, an analytical calculation is presented which determines the probability that the light from a distant quasar can be lensed by objects in a different redshift range, and a number of recommendations are offered with respect to VLA and Space Telescope observations of quasars lensed.
Abstract: An analytical calculation is presented which determines the probability that the light from a distant quasar can be lensed by objects in a different redshift range. Three types of information are used to make the calculation: (1) the physical properties of the intervening scattering lenses; (2) the intrinsic properties of the quasars and (3) the selection procedures by which the quasar samples are acquired. A series of differential equations is given in which the probability is derived, and a number of recommendations are offered with respect to VLA and Space Telescope observations of quasars lensed in this way.
TL;DR: In this paper, it was shown that the angular momentum of galaxies grows to first order (in proportion to t) during the linear phases of protogalactic evolution, and this result is confirmed in N-body simulations of the formation of structure.
Abstract: An analysis by Doroshkevich (1970) which shows that the angular momentum of galaxies grew to first order (in proportion to t) during the linear phases of protogalactic evolution is expanded. This result is confirmed in N-body simulations of the formation of structure. The well-known study of Peebles (1969) found growth at second order only (in proportion to t to the 5/3-power) because its analysis was restricted to spherical regions. In such regions growth occurs purely as a result of convective effects on the bounding surface; the material initially within a spherical volume gains no angular momentum in second-order perturbation theory. These considerations do not affect estimates of the total angular momentum acquired by a galaxy in the gravitational instability picture.
TL;DR: In this paper, the authors derived similarity solutions which describe the collapse of cold, collisionless matter in a perturbed Einstein-de Sitter universe, and they obtained three classes of solutions, one each with planar, cylindrical, and spherical symmetry.
Abstract: We derive similarity solutions which describe the collapse of cold, collisionless matter in a perturbed Einstein-de Sitter universe. We obtain three classes of solutions, one each with planar, cylindrical, and spherical symmetry. Our solutions can be computed to arbitrary accuracy, and they follow the development of structure in both the linear and nonlinear regimes.
TL;DR: In this article, observations of three classical visual reflection nebulae were conducted in the wavelength range from 1.25 to 2.2 microns, taking into account NGC 7023, 2023, and 2068.
Abstract: In the past, reflection nebulae have provided an astrophysical laboratory well suited for the study of the reflection properties of interstellar dust grains at visual and ultraviolet wavelengths. The present investigation is concerned with observations which were begun with the objective to extend to near-infrared wavelengths the study of grains in reflection. Observations of three classical visual reflection nebulae were conducted in the wavelength range from 1.25 to 2.2 microns, taking into account NGC 7023, 2023, and 2068. All three nebulae were found to have similar near-infrared colors, despite widely different colors of their illuminating stars. The brightness level shown by two of the nebulae at 2.2 microns was too high to be easily accounted for on the basis of reflected light. Attention is given to a wide variety of possible emission mechanisms.
TL;DR: In this paper, the authors used 10-20 micron observations of previously identified members of the embedded population of the Rho Ophiuchi dark cloud to make determinations of the broadband energy distributions for 32 of the 44 sources.
Abstract: In combination with previous IR and optical data, the present 10-20 micron observations of previously identified members of the embedded population of the Rho Ophiuchi dark cloud allow determinations to be made of the broadband energy distributions for 32 of the 44 sources. The majority of the sources are found to emit the bulk of their luminosity in the 1-20 micron range, and to be surrounded by dust shells. Because they are, in light of these characteristics, probably premain-sequence in nature, relatively accurate bolometric luminosities for these objects can be obtained through integration of their energy distributions. It is found that 44 percent of the sources are less luminous than the sun, and are among the lowest luminosity premain-sequence/protostellar objects observed to date.
TL;DR: In this article, the nucleon-to-photon ratio of primordial nucleosynthesis is re-examined in the context of a detailed comparison of theory and observation, and a new argument is presented to show how the observed abundances of D and /sup 3/He can be used to derive a lower bound to the nucleus density.
Abstract: Primordial nucleosynthesis is reexamined in the context of a detailed comparison of theory and observation. A new argument is presented to show how the observed abundances of D and /sup 3/He can be used to derive a lower bound to the nucleon density. In concert with the previously known upper bound from D alone, we define a conservative (''safe bet'') range for the nucleon-to-photon ratio: eta = (3-10) x 10/sup -10/. New observations of /sup 7/Li are consistent with the abundances of D and /sup 3/He and help us sto define a reasonable (''best bet'') range: eta = (4-7) x 10/sup -10/. In either of these ranges the predicted and observed abundances of D, /sup 3/He, and /sup 7/Li re all in concordance. The upper bounds correspond to ..cap omega../sub N/ or =0.24 if N/sub v/> or =3 and tau/sub 1/2/> or =10.4 minutes.« less
TL;DR: In this paper, a set of models from local and high-redshift observations were compared to the Friedmann-Lemaitre cosmological constant π 1.0.
Abstract: The inflationary scenario requires that the universe have negligible curvature along constant-density surfaces. In the Friedmann-Lemaitre cosmology that leaves us with two free parameters, Hubble's constant H/sub 0/ and the density parameter ..cap omega../sub 0/ (or, equivalently, the cosmological constant ..lambda..). I discuss here tests of this set of models from local and high-redshift observations. The data agree reasonably well with ..cap omega../sub 0/approx.0.2.
TL;DR: Extended sources of far-infrared emission superposed on the zodiacal and galactic backgrounds are found at high galactic latitudes and near the ecliptic plane as discussed by the authors.
Abstract: Extended sources of far-infrared emission superposed on the zodiacal and galactic backgrounds are found at high galactic latitudes and near the ecliptic plane. Clouds of interstellar dust at color temperatures as high as 35 K account for much of this complex structure, but the relationship to H I column density is not simple. Other features of the extended emission show the existence of warm structures within the solar system. Three bands of dust clouds at temperatures of 150-200 K appear within 10 deg on both sides of the ecliptic plane. Their ecliptic latitudes and derived distances suggest that they are associated with the main asteroid belt. A third component of the 100-micron cirrus, poorly correlated with H I, may represent cold material in the outer solar system or a new component of the interstellar medium.
TL;DR: In this article, the authors calculate the evolution of cosmological density correlation functions to lowest nonvanishing order in perturbation theory for an initially random Gaussian distribution, which is consistent with observations in the nonperturbative regime.
Abstract: I calculate the evolution of cosmological density correlation functions to lowest nonvanishing order in perturbation theory for an initially random Gaussian distribution. The three-point function so obtained scales with size as in the continuous hierarchy model, but there is a residual nontrival dependence on shape of the reduced three-point amplitude Q. The average value Q-bar = 34/21-(1/6)..gamma.. is consistent with observations in the nonperturbative regime. The four-point function is also hierarchical in form, with amplitudes R/sub a/ = (34/21)/sup 2/ and R-bar/sub b/ = 682/189. The perturbation expansion in fact gives kappa/sub N/proportionalxi/sup N/-1 for the reduced correlation function kappa/sub N/ to all orders N. A graphical technique enumerates the terms which appear in kappa/sub N/.
TL;DR: In this paper, the structure and evolution of very massive objects (stars of mass approx.10/sup 2/-10/Sup 5/M/sub sun/) are discussed in terms of simple semianalytic models.
Abstract: The structure and evolution of Very Massive Objects (stars of mass approx.10/sup 2/-10/sup 5/ M/sub sun/) are discussed in terms of simple semianalytic models. We estimate the helium enrichment due to mass loss, and present evidence for a dynamical instability arising in the hydrogen shell burning phase of a 500 M/sub sun/ Population I star. The fate of a VMO is decided in its oxygen core phase, Calculations of the effects of the pair instability, oxygen and silicon burning, and alpha-quenching on the global binding energy of initially isentropic polytropic cores allow us to predict the critical oxygen core mass above which complete collapse to a black hole occurs: M/sub O//sub c/roughly-equal10/sup 2/ M/sub sun/ corresponding to an initial star mass greater than 200 M/sub sun/. Cores smaller than this explode; we estimate the kinetic energy liberated.
TL;DR: In this article, the authors used balloon-borne instrumentation of very high sensitivity to detect 25 hard X-ray bursts with peak fluxes of above 7 x 10 to the -3rd/(sq cm s keV) at 20 keV.
Abstract: Using balloon-borne instrumentation of very high sensitivity, approximately 25 hard X-ray bursts with peak fluxes of above 7 x 10 to the -3rd/(sq cm s keV) at 20 keV have been detected, in 141 minutes of observation of the sun on June 27, 1980. These hard X-ray microflares last from a few seconds to several tens of seconds and have power-law energy spectra. They are generally accompanied by small soft X-ray bursts, but H-alpha flares and solar radio bursts are reported for only a few of these hard X-ray bursts. The integral number of events varies approximately as the inverse of the peak flux, down to the limits of the measurements. These observations suggest that even very small transient releases of energy by the sun may be primarily nonthermal in character. It is speculated that the energy released in accelerated electrons for these microflares, averaged over time, may contribute significantly to the heating of the active corona.