Expansion Timescale Research Articles

General Relativistic Effects in the Neutrino-driven Wind and [CLC][ITAL]r[/ITAL][/CLC]-Process Nucleosynthesis

We discuss general relativistic effects in the steady state neutrino-driven "wind" that may arise from nascent neutron stars. In particular, we generalize previous analytic estimates of the entropy per baryon S, the mass outflow rate , and the dynamical expansion timescale τdyn. We show that S increases and τdyn decreases with increasing values of the mass-to-radius ratio describing the supernova core. Both of these trends indicate that a more compact core will lead to a higher number of neutrons per seed nucleus. Such an enhancement in the neutron/seed ratio may be required for successful r-process nucleosynthesis in neutrino-heated supernova ejecta.

R-Process surveys

We survey the r-process of nucleosynthesis in matter flowing out radially from a nascent neutron star. We parameterize the expansion of the matter according to the entropy per baryon, the initial electron-to-baryon ratio, and the expansion timescale. We present here constraints on r-process conditions based on successful synthesis of the A = 195 abundance peak.

Comment on “Substorm recurrence during steady and variable solar wind driving: Evidence for a normal mode in the unloading dynamics of the magnetosphere” by A. J. Klimas, D. N. Baker, D. Vassiliadis, and D. A. Roberts

Comment on “Substorm recurrence during steady and variable solar wind driving: Evidence for a normal mode in the unloading dynamics of the magnetosphere” by A. J. Klimas, D. N. Baker, D. Vassiliadis, and D. A. Roberts

How does magnetospheric convection relate to the expansion onset of substorms?

The suddenness of substorm expansions suggests that they are instabilities in the magnetosphere. The convection during the growth phase of isolated substorms is examined with the intent of determining conditions leading to the instability. Properties of the large-scale two-celled convection considered are the intensity of the convection, the size of the convection cells and the time rate of change of both of these. There is considerable variation in values of the intensity, its rate of change, and the size of the convection cells just before expansion onset. On the other hand, onsets frequently occur when the rate of increase of the size of the convection cell is slowing down or has reached zero. Since the time-scale of this ‘slowing down’ is an order of magnitude greater than the time-scale of expansion, the slowing down is not a result of the instability, but is one of the conditions leading up to the onset of instability. A number of examples of this behaviour of the growth of the size of the convection cells are discussed. The following interpretation is proposed. The slowing down indicates that the magnetospheric convection cells are approaching a steady-state size which corresponds to the enhanced dayside merging rate that exists in growth phases. However, the steady-state is unstable against contractions in size and this is the cause of expansions. Triggered substorms and substorms without growth phases occur when a decrease in the dayside merging rate requires a contraction of the cell size. Theories of substorms compatible with this behaviour include the ballooning instability theory and a model in which magnetospheric dipolar convection controls merging in the tail.

Can neutrino decay-driven mock gravity save hot dark matter?

The radiative decay of a 30 eV neutrino with a lifetime of order 10^23-24^ s has recently been shown to yield a satisfactory explanation of a wide range of problems in astrophysics. Melott in 1985 showed how such a decay can explain morphological features of dwarf satellite galaxies. Melott, McKay, and Ralston in 1988 demonstrated that such a decay process can ionize the IGM to the Gunn-Peterson limit. Finally, in a series of papers Sciama has addressed the issue of radiative neutrino decay and successfully applied it to an even broader range of problems. In this paper we investigate whether the photon flux generated by the radiative decay of a massive neutrino is capable of generating sufficient radiation pressure to cause a "mock gravitational" collapse of primordial hydrogen clouds. We show that when using neutral hydrogen as a source of opacity for mock gravity the time scale for mock gravitational collapse is significantly larger than the expansion time scale. Thus, the model fails as a source of galactic seed perturbations. Furthermore, we argue that nonlinear feedback mechanisms will be unable to increase the collapse rate of the cloud under mock gravity.

OH maser proper motions in Cepheus A

MERLIN measurements made between 1982 and 1989 reveal proper motions of OH masers in the source Cepheus A. The proper motions are typically a few milliarcsec per year, and are mainly directed away from the central H II regions. Statistical analysis of the data suggests an expansion time-scale of some 300 yr. The distance of the source implied by the proper motions is 320 pc, assuming that the expansion is isotropic. The proper motions can be reconciled with the larger distance of 730 pc which is generally accepted, provided that the masers are moving at large angles to the line of sight

Inflation and compactification from Galaxy redshifts?

The distribution of galaxies in the pencil-beam surveys of Broadhurstet al. which proved periodical across 8–10 consecutive steps in a flat dust model withq0=0.5 is found to reveal extended periodicity up to 16–17 phase-coherent steps, covering the total sample, in a flat, moderately inflationary model withq0=−0.5 (vacuum/dust ratio 2/1). In the latter model the vacuum component helps to reach the critical density and lengthens the expansion time-scale. It is shown that the explanation of the found periodicity as a consequence of space compactification as suggested by G. Paal twenty years ago in connection with apparent quasar periodicities is still possible.

Charmonium absorption in hadronic matter by coherent multiple scattering

A quantum mechanical model for a heavy quark pair as produced in hadronic collisions is presented. It describes the dynamical time evolution of the pair, using a potential model, and simultaneously takes into account the interaction of the pair with surrounding hadronic matter while leaving the reaction zone. The physical concepts involved like coherence effects are studied and an expansion time scale is introduced for bound-state formation. The properties of the so modeled charmonium are described and compared to experimental observations in hadron-hadron, hadron-nucleus and nucleus-nucleus collisions.

Changes in the optical remnant of Kepler's supernova during the period 1942-1989

Images of the optical nebulosity associated with Kepler's supernova have been obtained at the Mount Wilson Observatory in 1941-1943, at the Palomar Observatory in 1950-1983, and on La Silla in 1989. These data have been used to study the luminosity evolution of individual knots and the expansion and translation of the optical remnant of Kepler's supernova of 1604. From the study of the motions of 50 long-lived knots, expansion is {minus}0.623 + or {minus} 0.045 arcsec/century, translation is 0.484 + or {minus} 0.049 arcsec/century, and expansion time scale of 32,000 + or {minus} 12,000 yr. For an assumed distance of 4.5 kpc the centroid of the nebulosity tangential velocity is 117 + or {minus} 10 km/s to the W and 105 + or {minus} 11 km/s to the N. By combining astrometric and spectroscopic information, a space velocity of 278 + or {minus} 12 km/s is estimated. This indicates that the progenitor of SN 1604 was a high-velocity object. It could have been either a Population II star or a massive high-velocity runaway star. 30 refs.

Theories of inflation and conformal transformation

We show that seberal different theories of inflation including R 2, Brans-Dicke, and induced-gravity inflation are all related to generalized or power-law inflation by means of conformal transformations. These theories all involve non-standard gravity, and the use of conformal transformations allows one to obtain standard inflationary predictions such as the expansion time-scale, reheating and density perturbations in each case very simply. We also discuss the possibilities of this method to be applied to string theory.

Molecular gas bar and expanding molecular ring in the nucleus of the spiral galaxy Maffei 2

view Abstract Citations (48) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular Gas Bar and Expanding Molecular Ring in the Nucleus of the Spiral Galaxy Maffei 2 Ishiguro, M. ; Kawabe, R. ; Morita, K. -I. ; Okumura, S. ; Chikada, Y. ; Kasuga, T. ; Kanzawa, T. ; Iwashita, H. ; Handa, K. ; Takahashi, T. ; Kobayashi, H. ; Murata, Y. ; Ishizuki, S. ; Nakai, N. Abstract Aperture synthesis observations of the central 1.5 kpc region of the spiral galaxy Maffei 2 (d ~ 5 Mpc) have been made in CO(J = 1-0) line with 5.8" x 5.0" resolution (~ 135 pc) using the Nobeyama Millimeter Array. We have found a central narrow ridge of molecular gas with a size 1000 pc x 200 pc and a ringlike feature with a large noncircular motion (60 km s^-1^) with a size 500 pc x 240 pc. The narrow ridge is interpreted as a bar of molecular gas in shocks generated at the leading edges in the bar potential. The molecular bar has a mass of (1-5) x 10^8^ M_sun_, and there is a depression in the molecular gas distribution within 100 pc of the nucleus. The observational results suggest that the ring is an expanding and rotating ring of molecular gas in the plane of the galaxy, V_exp_ ~ 60 km s^-1^ and M_sun_ (3-13) x 10^7^ M_sun_. The kinetic energy of expansion is >(1-5) x 10^54^ ergs and a dynamical expansion time scale is ~ 5 x 10^6^ yr (resultant kinetic luminosity is [1-8] x 10^6^ L_sun_). This energy and luminosity require an explosive event at the nucleus. The ring may have been formed by a starburst induced by the efficient gas supply in the bar potential. Publication: The Astrophysical Journal Pub Date: September 1989 DOI: 10.1086/167840 Bibcode: 1989ApJ...344..763I Keywords: Galactic Nuclei; Interstellar Gas; Line Spectra; Molecular Gases; Spiral Galaxies; Galactic Structure; Gas Dynamics; Infrared Sources (Astronomy); Astrophysics; GALAXIES: INDIVIDUAL NAME: MAFFEI 2; GALAXIES: INTERNAL MOTIONS; GALAXIES: INTERSTELLAR MATTER; GALAXIES: NUCLEI; GALAXIES: STRUCTURE; INTERFEROMETRY full text sources ADS | data products SIMBAD (7) NED (6)

Time scales of expansion and contraction of the auroral oval

The auroral boundary index calculated by Gussenhoven et al. [1983] on the basis of Defense Meteorological Satellite Program precipitating electron data is used to examine the dynamics of the auroral oval in the midnight sector. The equatorward boundary of the oval expands equatorward and contracts poleward corresponding to southward and northward turnings, respectively, of the interplanetary magnetic field (IMF). The time scales are found to be, on the average, 45 min for the expansion and 8 hours for the contraction. A general empirical formula to predict the oval location for any IMF variation is devised. Physical processes in the magnetosphere consistent with the “rapid” expansion and “slow” contraction of the auroral oval are discussed.

CN abundance variations in the shell of IRC +10216

view Abstract Citations (65) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CN abundance variations in the shell of IRC +10216 Wootten, A. ; Lichten, S. M. ; Sahai, R. ; Wannier, P. G. Abstract First observations of the N = 2-1 line of CN at 226.9 GHz are reported. High-resolution maps of IRC + 10216 and OMC-1 show that the peak in both sources is compact but resolved in a 30 arcsec beam. In IRC + 10216 the emission extends approximately 70 arcsec at the line center velocity. A model for CN excitation and the absence of infrared vibration-rotation absorption lines suggest the presence of a source of CN molecules in the outer circumstellar shell. Examination of chemical, expansion, and photodissociation time scales in the outer shell leads to the identification of HCN photodissociation by the interstellar radiation field as a plausible source. This model explains the large discrepancy in the CN abundance predicted by chemical equilibrium models of the shell and confirms the importance of photo-dissociation in the chemistry of circumstellar shells. Maps and spectra were also made in OMC-1 and OMC-2. In OMC-1, CN emission lies along a narrow ridge, peaking in the BN/KL region. Publication: The Astrophysical Journal Pub Date: June 1982 DOI: 10.1086/159973 Bibcode: 1982ApJ...257..151W Keywords: Abundance; Cyanogen; Interstellar Chemistry; Nebulae; Stellar Envelopes; Carbon Stars; Hydrocyanic Acid; Infrared Astronomy; Molecular Clouds; Molecular Structure; Photodissociation; Astrophysics full text sources ADS | data products SIMBAD (2)

Synthesis of Al-26 in explosive hydrogen burning

The possibility of Al-26 synthesis during the explosive processing of hydrogen-rich material in the outer layers of a supernova or in nova envelopes is investigated. It is found that in the peak temperature range of 1-3 x 10 to the 8th deg K and for expansion time scales of the order of 1-1000 s, values of (Al-26)/(Al-27) as high as 0.1-1 can be obtained for values of 0.001-100,000 for the product of the peak density in g/cu cm and the proton mass fraction. Such a level of Al-26 production is considerably higher than that of recent carbon/neon burning nucleosynthesis models, and is sufficient to account for the magnesium anomalies detected in certain inclusions from the Leoville and Allende meteorites. Al abundances resulting from a hydrodynamical calculation performed on the grounds of a 25 solar mass presupernova model are also presented, and the influence of uncertainties in the input physics is discussed; in particular, the rates of the (Mg-25)(p,gamma)(Al-26) and (Al-26)(p,gamma)(Si-27) key reactions are studied.

Explosive nucleosynthesis, equilibrium thermodynamics, and relativistic heavy-ion collisions

A description of the formation of composite nuclei observed in relativistic heavy-ion collisions is developed. The description is analogous to that used in accounting for the formation of nuclei under explosive conditions, as encountered in the expansion of an isotropic and homogeneous universe and in imploding-exploding supermassive stars. The model studied is one in which composite nuclei are formed in the space-time evolution of a rapidly expanding system of nucleons. Within the framework of this model, it is shown that reaction rates may initially be fast compared to expansion time scales, that detailed balance can then be met and a quasiequilibrium established for a short period of time and limited volume of space in this space-time evolution. An idealized equilibrium model is then proposed which contains a sharp cutoff from equilibrium to free expansion. In such a model the observed properties of the composite particles reflect a "frozen in" equilibrium state. A simple discussion is then presented showing that the volume at which the transition occurs is related to the finite size of the correlated structures in the system. A key result in the approach developed is that properties of the composite particle cross sections can be used to obtain information on the size of the emitting region without resorting to a Hanbury-Brown-Twiss correlation measurement. Another important result is that cross sections for composite nuclei are characterized by Maxwell-Boltzmann distributions in some rest system and recent data will be discussed from this viewpoint. The thermodynamic properties of the system, such as the equation of state and the energy-temperature relationship are investigated. The effect of continuum correlations from resonances and echoes will also be discussed.NUCLEAR REACTIONS Thermodynamic model of heavy-ion collisions at relativistic energies. Theory of formation of composite nuclei in space-time evolution of an expanding system of nucleons.

OH-IR stars. I - Physical properties of circumstellar envelopes

view Abstract Citations (364) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS OH-IR stars. I. Physical properties of circumstellar envelopes. Goldreich, P. ; Scoville, N. Abstract A theoretical model of the circumstellar envelope which surrounds a OH-IR star is developed. The circumstellar gas is ejected by radiation pressure which acts on dust grains that condense in the atmosphere of the central star. The dust grains transfer momentum to the gas by collisions with the gas molecules. These collisions are the dominant source of heat input to the circumstellar gas. The major sources of cooling are the emission of radiation by H20 molecules and adiabatic expansion. The gas temperature decreases from T 2 x l0 K near the stellar surface at r 6 x 1013 cm, to T 8 x 102 K at r = 1015 cm and to T 102 K at r = 1016 cm. The OH molecule abundance in the circumstellar envelope is controlled by chemical exchange reactions and by the dissociation of H20 molecules. The reaction OH + H2 H20 + H + 0.69 eV, which has an activation energy of 0.3 eV, rapidly converts OH molecules into H20 molecules in the warm (T > 5 x 102 K) inner (r <% 2 x 1015 cm) region of the circumstellar envelope. Beyond r 2 x 1015 cm, T is so low that the exchange reaction is very slow and the mean lifetime of an OH molecule is greater than the expansion time scale for the circumstellar envelope. In the outer region of the circumstellar envelope, OH molecules are produced from the photodissociation of H20 molecules by the interstellar ultraviolet radiation and from the dissociation of H20 molecules by collisions with dust grains. These processes are capable of producing OH number densities greater than 1 at r 1016 cm. The predicted values of the gas temperature, T, and the OH abundance, o , depend upon the rate of mass loss from the central star, (t) The results quoted above are based on a calculation with = 3 x l0- M0 yr-1. In general, T varies inversely and o varies directly with (I). Subject headings: infrared: sources - stars: circumstellar shells Publication: The Astrophysical Journal Pub Date: April 1976 DOI: 10.1086/154257 Bibcode: 1976ApJ...205..144G Keywords: Atmospheric Models; Hydroxyl Emission; Infrared Astronomy; Interstellar Masers; Stellar Envelopes; Abundance; Dust; Gas Temperature; M Stars; Photodissociation; Stellar Mass Ejection; Water; Astrophysics full text sources ADS | data products SIMBAD (1)

Grain Formation in the Expanding Envelopes of T Tauri Stars

The possibility of the nucleation in the expanding envelopes of T Tauri stars is investigated by using the nucleation theory by Becker and Doring. The nucleation time scale r,. in .the gas is investigated assuming that only graphite is condensable. The expansion time scale roxo of the gas ejected from a T Tauri star is calculated assuming that the gas flow is steady and spherically symmetric. The time scale r,. is compared with roxp for Xo=l0- 2 (Xo is the concentration of carbori by mass) assuming that the gas expands adiabatically, and the mass­ loss rate needed for nucleation is found to be larger than those observed in T Tauri stars. Thi~ suggests that nucleation around T Tauri stars is rather difficult. § I, Introduction It is generally believed that grains ·are contained m interstellar and proto­ planetary gas clouds. The importance of the existence of grains has been pointed out in connection with the cooling mechanism during the contraction of the gas cloud and with the origin of protoplanets. 1> In spite of the importance, however, the formation of grains has not yet been understood well. A few authors have .Pointed out the possibility that grains are formed in atmospheres of cool stars or in expanding shells of active stars such as T Tauri stars, planetary nebulae, novae and supernovae.2>-4> This is a:lso suggested by the infrared excesses of active stars. 5>-u> Hoyle and Wickramasinghe 2>•8> have investigated the conditions for the forma­ tio'n and the growth of solid particles in the static stellar atmospheres of N-type stars. Kamijo14) and Donn et al. 15> have re-examined Hoyle and Wickramasinghe's mechanism in cool carbon stars. On the other hand, Fix16 > has studied the forma­ tion of grains in the adiabatically . pulsating atmosphere. He has shown that if the pulsation period is longer than a few months, the grains are condensed in expanding phases of pulsation. In this paper we will investigate the possibility of the formation of grains in the expanding envelopes of T Tauri stars using the nucleation theory by Becker and Doring 17> and others. 18>-20> The reasons why we take notice ofT Tauri stars are as follows: Firstly, some of them are known as infrared stars 11> so that grains may exist in the circumstellar spaces around T Tauri stars. The mass-loss rates are known from the observations together with the initial velocities of ejected matter and stellar radii. 21 > Hence we can easily compare our estimation with

Nucleosynthesis in neutron rich supernova ejecta

A nuclear reaction network of 903 different, strong and electromagnetic reactions, linking 107 chemical constituents is used to study the elements synthesized in the neutron rich material, ejected in supernova explosions. A large number of three body reactions virtually eliminates the usual bottle neck at theA=5 mass gap. For initially high temperatures and densities,T=1010K and ϱ=7×108 gm/cm3, with expansion time scales of 10−3–10−2 sec, three differentn top ratios,n/p=4,n/p=3/2, andn/p∼1, are considered for the ejected matter. In all three cases, the material synthesized is preponderantly heavy. For then/p=4 model, the conditions at the charged particle freeze-out are ideal for the ‘r-process’. The onset of this rapid neutron capture phase is explicitly shown with a sequence of time lapse abundance plots.

Nucleosynthesis in Explosive Oxygen Burning

view Abstract Citations (65) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Nucleosynthesis in Explosive Oxygen Burning Truran, J. W. ; Arnett, W. David Abstract A preliminary investigation of the conditions appropriate to the synthesis of nuclei of intermediate mass (28 < A <42) by explosive oxygen burning is presented. These calculations make use of the recent measurements the 100 + 100 reaction rate by Patterson, Winkler, and Spinka. The resulting abundance distributions are found to be sensitive to the temperature and density of the medium, to the time scale of expansion, and to the degree of neutron enrichment. Encouragingly good fits to both the elemental and isotopic abundance features in the silicon-to-calcium region are obtained for explosive oxygen burning in a rather restricted temperature range (3.5 X 10 < T < 3.7 X 10' K) for densities in the range 10' < p < 10' g cm Publication: The Astrophysical Journal Pub Date: April 1970 DOI: 10.1086/150415 Bibcode: 1970ApJ...160..181T full text sources ADS |

On Antimatter and Cosmology

A cosmological model based on a gravitational plasma of matter and antimatter is discussed. The antigravitational interaction of matter and antimatter leads to segregation and an expansion of the plasma universe. The expansion time scale is controlled by the aggregation time scale.