Structure Effects on Coulomb Dissociation of 8^8B

Coulomb Dissociation provides an alternative method for determining the radiative capture cross sections at astrophysically relevant low relative energies. For the breakup of $^8$B on $^{58}$Ni, we calculate the total Coulomb Dissociation cross section and the angular distribution for E1, E2 and M1. Our calculations are performed first within the standard first order semiclassical theory of Coulomb Excitation, including the correct three body kinematics, and later including the projectile-target nuclear interactions.Comment: 6 pages, proceedings from International Workshop on RNB, Puri, India, January 1998 - to be published in J. Phys.

Structure effects on the Coulomb dissociation of 8B at relativistic energies

We investigate the Coulomb dissociation of 8B on 208Pb target at the beam energy of 250 MeV/nucleon, employing the cross sections for the radiative capture reaction 7Be(p,gamma)8B calculated within the Shell Model Embedded in the Continuum (SMEC) approach. In contrast to the situation at lower beam energies, the Coulomb breakup cross sections are found to be sensitive to the M1 transitions. Comparisons of SMEC and single-particle potential model predictions show that the Coulomb breakup cross sections at these high energies are sensitive to the structure model of 8B. Analysis of the preliminary data taken recently at GSI reveal that E2 multipolarity contributes up to 25 % to the cross sections even for the relative energies of p - 7Be below 0.25 MeV.Comment: 22 pages, 7 figure

Measurement of E2 Transitions in the Coulomb Dissociation of 8B

In an effort to understand the implications of Coulomb dissociation experiments for the determination of the 7Be(p,gamma)8B reaction rate, longitudinal momentum distributions of 7Be fragments produced in the Coulomb dissociation of 44 and 81 MeV/nucleon 8B beams on a Pb target were measured. These distributions are characterized by asymmetries interpreted as the result of interference between E1 and E2 transition amplitudes in the Coulomb breakup. At the lower beam energy, both the asymmetries and the measured cross sections are well reproduced by perturbation theory calculations, allowing a determination of the E2 strength.Comment: 8 pages, 3 figure

Coulomb and nuclear breakup of 8^8B

The cross sections for the ($^8$B,$^7$Be-$p$) breakup reaction on $^{58}$Ni and $^{208}$Pb targets at the beam energies of 25.8 MeV and 415 MeV have been calculated within a one-step prior-form distorted-wave Born approximation. The relative contributions of Coulomb and nuclear breakup of dipole and quadrupole multipolarities as well as their interference have been determined. The nuclear breakup contributions are found to be substantial in the angular distributions of the $^7$Be fragment for angles in the range of 30$^\circ$ - 80$^\circ$ at 25.8 MeV beam energy. The Coulomb-nuclear interference terms make the dipole cross section larger than that of quadrupole even at this low beam energy. However, at the incident energy of 415 MeV, these effects are almost negligible in the angular distributions of the ($^7$Be-p) coincidence cross sections at angles below 4$^\circ$.Comment: Revised version, accepted for publication in Phys. Rev.

E1−E2E1-E2 interference in the Coulomb dissociation of 8^8B

We investigate the effects arising out of the $E1 - E2$ interference in the Coulomb dissociation of $^8$B at beam energies below and around 50 MeV/nucleon. The theory has been formulated within a first order semiclassical scheme of Coulomb excitation, in which both the ground state and the continuum state wave functions of $^8$B enter as inputs. We find that the magnitude of the interference could be large in some cases. However, there are some specific observables which are free from the effects of the $E1 - E2$ interference, which is independent of the models used to describe the structure of $^8$B. This will be useful for the analysis of the breakup data in relation to the extraction of the astrophysical factor $S_{17}(0)$.Comment: Revised version to appear in Physical Review

Calculations of three-body observables in ^8B breakup

We discuss calculations of three-body observables for the breakup of ^8B on a ^{58}Ni target at low energy using the coupled discretised continuum channels approach. Calculations of both the angular distribution of the ^7Be fragments and their energy distributions are compared with those measured at several laboratory angles. In these observables there is interference between the breakup amplitudes from different spin-parity excitations of the projectile. The resulting angle and the energy distributions reveal the importance of the higher-order continuum state couplings for an understanding of the measurements.Comment: 22 pages (postscript), accepted in Phys. Rev.

Nuclear and Coulomb Interaction in the 8B to 7Be + p Breakup Reaction at sub-Coulomb Energies

The angular distribution for the breakup of 8B into 7Be+p on a 58Ni target has been measured at an incident energy of 25.75 MeV. The data are inconsistent with first-order theories but are remarkably well described by calculations including higher-order effects. The comparison with theory illustrates the importance of the exotic proton halo structure of 8B in accounting for the observed breakup angular distribution.Comment: 4 pages, 3 figures, Phys. Rev. Letters (accepted). This is the version that will appear in the journal article. It contains minor changes and a new referenc

KIC 3858884: a hybrid {\delta} Sct pulsator in a highly eccentric eclipsing binary

The analysis of eclipsing binaries containing non-radial pulsators allows: i) to combine two different and independent sources of information on the internal structure and evolutionary status of the components, and ii) to study the effects of tidal forces on pulsations. KIC 3858884 is a bright Kepler target whose light curve shows deep eclipses, complex pulsation patterns with pulsation frequencies typical of {\delta} Sct, and a highly eccentric orbit. We present the result of the analysis of Kepler photometry and of high resolution phaseresolved spectroscopy. Spectroscopy yielded both the radial velocity curves and, after spectral disentangling, the primary component effective temperature and metallicity, and line-of-sight projected rotational velocities. The Kepler light curve was analyzed with an iterative procedure devised to disentangle eclipses from pulsations which takes into account the visibility of the pulsating star during eclipses. The search for the best set of binary parameters was performed combining the synthetic light curve models with a genetic minimization algorithm, which yielded a robust and accurate determination of the system parameters. The binary components have very similar masses (1.88 and 1.86 Msun) and effective temperatures (6800 and 6600 K), but different radii (3.45 and 3.05 Rsun). The comparison with the theoretical models evidenced a somewhat different evolutionary status of the components and the need of introducing overshooting in the models. The pulsation analysis indicates a hybrid nature of the pulsating (secondary) component, the corresponding high order g-modes might be excited by an intrinsic mechanism or by tidal forces.Comment: 18 pages, 14 figures, accepted for publication on Astronomy & Astrophysic

Asteroseismology and Interferometry

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within Astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume 14, Issue 3-4, pp. 217-36