MARINE AND NORMARINE TRACE FOSSILS AND PLANT ROOTS IN A REGRESSIONAL SETTING (PLEISTOCENE, ITALY)

The sedimentary structures occurring in one of the Pleistocene marine terraces at the Ionian coast, indicate a shoaling upward trend from the shoreface of a sandy beach to nonmarine conditions. Four main facies have been recognized. Facies A consists of hummocky cross-bedded sands representing a wave-dominated nearshore environment. Physical and biological structures of facies B are suggestive of an abrupt reduction in energy level, possibly related to the establishment of shallow protected environments. Features of facies C suggest a stable environment of upper shoreface but strongly influenced by continental supplies. Upward, this facies passes into sediments deposited in continental conditions. The last facies (D) is related to moist or wet terrestrial environments. Bioturbation levels of facies A to C are in general low. Facies D, however, is well bioturbated, having an ichnofabric dominated by Taenidium isp. Sparse, vertical roots of vascular plants extended in many cases to at least 3 m below the base of facies D. Particularly unusual is the close association of large Taenidium isp. and vertical roots, where the trace fossil is clustered tightly around the plant, in some cases to more than 1 m below the water-sediment interface

The existence of a 2Po excited state for the e+Ca system

The Configuration Interaction method is used to demonstrate that there is an electronically stable state of positronic calcium with an orbital angular momentum of L=1. This prediction relies on the use of an asymptotic series to estimate the variational limit of the energy. The best estimate of the binding energy is 37 meV. A discussion of the structure of the system is also presented.Comment: 4 pages, 2 figures, in press PR

An Alternative Origin for Hypervelocity Stars

Halo stars with unusually high radial velocity ("hypervelocity" stars, or HVS) are thought to be stars unbound to the Milky Way that originate from the gravitational interaction of stellar systems with the supermassive black hole at the Galactic center. We examine the latest HVS compilation and find peculiarities that are unexpected in this black hole-ejection scenario. For example, a large fraction of HVS cluster around the constellation of Leo and share a common travel time of $\sim 100$-200 Myr. Furthermore, their velocities are not really extreme if, as suggested by recent galaxy formation models, the Milky Way is embedded within a $2.5\times 10^{12} h^{-1} M_{\odot}$ dark halo with virial velocity of $\sim 220$ km/s. In this case, the escape velocity at $\sim 50$ kpc would be $\sim 600$ km/s and very few HVS would be truly unbound. We use numerical simulations to show that disrupting dwarf galaxies may contribute halo stars with velocities up to and sometimes exceeding the nominal escape speed of the system. These stars are arranged in a thinly-collimated outgoing ``tidal tail'' stripped from the dwarf during its latest pericentric passage. We speculate that some HVS may therefore be tidal debris from a dwarf recently disrupted near the center of the Galaxy. In this interpretation, the angular clustering of HVS results because from our perspective the tail is seen nearly ``end on'', whereas the common travel time simply reflects the fact that these stars were stripped simultaneously from the dwarf during a single pericentric passage. This proposal is eminently falsifiable, since it makes a number of predictions that are distinct from the black-hole ejection mechanism and that should be testable with improved HVS datasets.Comment: 4 pages, 4 figures. Replacement to match version accepted to ApJ

Large dimension Configuration Interaction calculations of positron binding to the group II atoms

The Configuration Interaction (CI) method is applied to the calculation of the structures of a number of positron binding systems, including e+Be, e+Mg, e+Ca and e+Sr. These calculations were carried out in orbital spaces containing about 200 electron and 200 positron orbitals up to l = 12. Despite the very large dimensions, the binding energy and annihilation rate converge slowly with l, and the final values do contain an appreciable correction obtained by extrapolating the calculation to the l to infinity limit. The binding energies were 0.00317 hartree for e+Be, 0.0170 hartree for e+Mg, 0.0189 hartree for e+Ca, and 0.0131 hartree for e+Sr.Comment: 13 pages, no figs, revtex format, Submitted to PhysRev

Line Emission from an Accretion Disk around a Rotating Black Hole: Toward a Measurement of Frame Dragging

Line emission from an accretion disk and a corotating hot spot about a rotating black hole are considered for possible signatures of the frame-dragging effect. We explicitly compare integrated line profiles from a geometrically thin disk about a Schwarzschild and an extreme Kerr black hole, and show that the line profile differences are small if the inner radius of the disk is near or above the Schwarzschild stable-orbit limit of radius 6GM/c^2. However, if the inner disk radius extends below this limit, as is possible in the extreme Kerr spacetime, then differences can become significant, especially if the disk emissivity is stronger near the inner regions. We demonstrate that the first three moments of a line profile define a three-dimensional space in which the presence of material at small radii becomes quantitatively evident in broad classes of disk models. In the context of the simple, thin disk paradigm, this moment-mapping scheme suggests formally that the iron line detected by the Advanced Satellite for Cosmology and Astrophysics mission from MCG-6-30-15 (Tanaka et al. 1995) is 3 times more likely to originate from a disk about a rotating black hole than from a Schwarzschild system. A statistically significant detection of black hole rotation in this way may be achieved after only modest improvements in the quality of data. We also consider light curves and frequency shifts in line emission as a function of time for corotating hot spots in extreme Kerr and Schwarzschild geometries. Both the frequency-shift profile and the light curve from a hot spot are valuable measures of orbital parameters and might possibly be used to detect frame dragging even at radii approaching 6GM/c^2 if the inclination angle of the orbital plane is large.Comment: 15 pages (LaTex), 7 postscript figures; color plot (Figure 1) available at http://cfata2.harvard.edu/bromley/nu_nofun.html (This version contains a new subsection as well as minor corrections.

Properties of the triplet metastable states of the alkaline-earth-metal atoms

A configuration interaction approach with a semiempirical model potential for the core was used to study the static and dynamic properties of the alkaline-earth-metal atoms. The alkaline-earth-metal atoms properties determined were the scalar and tensor polarizabilities, the quadrupole moment, some of the oscillator strengths and the dispersion coefficents of the van der Waals intearaction. It was observed that the use of a polarization potential to the experimental binding energy consider the influence of relativistic effects upon the core electron distribution. The resulting polarizabilities, and dispersion parameters for homonuclear pairs of atoms were within 0.1% and within 1-2 % for heavier atoms

Line Emission from an Accretion Disk around a Black hole: Effects of Disk Structure

The observed iron K-alpha fluorescence lines in Seyfert-1 galaxies provide strong evidence for an accretion disk near a supermassive black hole as a source of the line emission. These lines serve as powerful probes for examining the structure of inner regions of accretion disks. Previous studies of line emission have considered geometrically thin disks only, where the gas moves along geodesics in the equatorial plane of a black hole. Here we extend this work to consider effects on line profiles from finite disk thickness, radial accretion flow and turbulence. We adopt the Novikov and Thorne (1973) solution, and find that within this framework, turbulent broadening is the dominant new effect. The most prominent change in the skewed, double-horned line profiles is a substantial reduction in the maximum flux at both red and blue peaks. The effect is most pronounced when the inclination angle is large, and when the accretion rate is high. Thus, the effects discussed here may be important for future detailed modeling of high quality observational data.Comment: 21 pages including 8 figures; LaTeX; ApJ format; accepted by ApJ; short results of this paper appeared before as a conference proceedings (astro-ph/9711214

The Periodic Standing-Wave Approximation: Overview and Three Dimensional Scalar Models

The periodic standing-wave method for binary inspiral computes the exact numerical solution for periodic binary motion with standing gravitational waves, and uses it as an approximation to slow binary inspiral with outgoing waves. Important features of this method presented here are: (i) the mathematical nature of the ``mixed'' partial differential equations to be solved, (ii) the meaning of standing waves in the method, (iii) computational difficulties, and (iv) the ``effective linearity'' that ultimately justifies the approximation. The method is applied to three dimensional nonlinear scalar model problems, and the numerical results are used to demonstrate extraction of the outgoing solution from the standing-wave solution, and the role of effective linearity.Comment: 13 pages RevTeX, 5 figures. New version. A revised form of the nonlinearity produces better result

Dynamic Stark shift of the Li-7(2s -> 3s) transition

The dynamic dipole polarizabilities for the 3s state of the Li atom are computed using Hylleraas and semiempirical approaches. This enables the calculation of the 7Li(2s→3s) Stark shift at photon wavelengths of 610.5 nm and 735.1 nm. They are calculated to be 834.7(5) and -686.7(25) a03, respectively. The first two tune-out frequencies for the 7Li(2s) ground state are determined to be 670.971626(1) nm and 324.192(2) nm, respectively