L. E. González

SN 1991bg - A type Ia supernova with a difference

We present 13 spectra and 31 photometric observations covering the first 150 days of SN 1991bg in NGC 4374 (M 84). Although SN 1991bg was a type Ia supernova displaying the characteristic Si II absorption at 6150 A near maximum and the Fe emission lines at late phases, it varied from the well-defined norm for SNe Ia in several important respects. The peculiarities include faster declines in the B and V light curves after maximum, a distinct color evolution, a very red B−V color near maximum, relatively faint peak luminosity, a distinct spectral evolution, and a short peak phase

The 1990 Calán/Tololo supernova search

We have started a search for supernovae as a collaboration between the University of Chile and the Cerro Tololo Inter-American Observatory, with the aim of producing a moderately distant (0.01<z<0.10) sample of Type Ia and Type II supernovae suitable for cosmological studies. The project began in mid-1990 and continues to the present. This paper reports on the Calan/Tololo discoveries in the course of 1990, and on the spectroscopic and photometric observations gathered for these objects. All of these observations were obtained with CCDs, with the extensive collaboration of visiting astronomers. Great care was exercised in the reduction of the light curves in order to properly correct for the background light of the host galaxy of each supernova

Dynamical properties of liquid Al near melting: An orbital-free molecular dynamics study

The static and dynamic structure of liquid Al is studied using the orbital free ab initio molecular dynamics method. Two thermodynamic states along the coexistence line are considered, namely T=943 and 1323 K, for which x-ray and neutron scattering data are available. A kinetic-energy functional which fulfills a number of physically relevant conditions is employed, along with a local first-principles pseudopotential. In addition to a comparison with experiment, we also compare our ab initio results with those obtained from conventional molecular-dynamics simulations using effective interionic pair potentials derived from second-order pseudopotential perturbation theory.

THE FAST DECLINING TYPE Ia SUPERNOVA 2003gs, AND EVIDENCE FOR A SIGNIFICANT DISPERSION IN NEAR-INFRARED ABSOLUTE MAGNITUDES OF FAST DECLINERS AT MAXIMUM LIGHT*

We obtained optical photometry of SN 2003gs on 49 nights, from 2 to 494 days after T(B_(max)). We also obtained near-IR photometry on 21 nights. SN 2003gs was the first fast declining Type Ia SN that has been well observed since SN 1999by. While it was subluminous in optical bands compared to more slowly declining Type Ia SNe, it was not subluminous at maximum light in the near-IR bands. There appears to be a bimodal distribution in the near-IR absolute magnitudes of Type Ia SNe at maximum light. Those that peak in the near-IR after T(B_(max)) are subluminous in the all bands. Those that peak in the near-IR prior to T(B_(max)), such as SN 2003gs, have effectively the same near-IR absolute magnitudes at maximum light regardless of the decline rate Δm_(15)(B). Near-IR spectral evidence suggests that opacities in the outer layers of SN 2003gs are reduced much earlier than for normal Type Ia SNe. That may allow γ rays that power the luminosity to escape more rapidly and accelerate the decline rate. This conclusion is consistent with the photometric behavior of SN 2003gs in the IR, which indicates a faster than normal decline from approximately normal peak brightness.

Optical Photometry of the Type I[CLC]a[/CLC] Supernova 1999[CLC]ee[/CLC] and the Type I[CLC]b[/CLC]/[CLC]c[/CLC] Supernova 1999[CLC]ex[/CLC] in IC 5179

We present UBVRIz lightcurves of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex, both located in the galaxy IC 5179. SN 1999ee has an extremely well sampled lightcurve spanning from 10 days before Bmax through 53 days after peak. Near maximum we find systematic differences ~0.05 mag in photometry measured with two different telescopes, even though the photometry is reduced to the same local standards around the supernova using the specific color terms for each instrumental system. We use models for our bandpasses and spectrophotometry of SN 1999ee to derive magnitude corrections (S-corrections) and remedy this problem. This exercise demonstrates the need of accurately characterizing the instrumental system before great photometric accuracies of Type Ia supernovae can be claimed. It also shows that this effect can have important astrophysical consequences since a small systematic shift of 0.02 mag in the B-V color can introduce a 0.08 mag error in the extinction corrected peak B magnitudes of a supernova and thus lead to biased cosmological parameters. The data for the Type Ib/c SN 1999ex present us with the first ever observed shock breakout of a supernova of this class. These observations show that shock breakout occurred 18 days before Bmax and support the idea that Type Ib/c supernovae are due to core collapse of massive stars rather than thermonuclear disruption of white dwarfs.

A theoretical study of the static structure and thermodynamics of liquid lithium

The authors have studied the static structure and some thermodynamic properties of liquid lithium by using the variational modified hypernetted chain (VMHNC) approximation as the liquid state theory and several effective interatomic pair potentials, derived from different pseudopotentials already proposed in the literature. They also propose a new interatomic pair potential derived from the neutral pseudoatom method (NPA).

Molecular dynamics simulation of liquid lithium

Liquid 7Li at 470 K is studied by molecular dynamics simulation. A recently proposed interionic effective potential with no adjustable parameters is assumed. Both structural and dynamical properties show very good agreement with the available experimental information.

Structural, dynamic, and electronic properties of liquid tin: An ab initio molecular dynamics study

We report on a study of several structural, dynamic, and electronic properties of liquid Sn at a thermodynamic state close to the triple point (573 K) and another one at a higher temperature (1273 K). This study has been performed by ab initio molecular dynamics simulations using 205 atoms and around 20 ps of simulation time. The calculated static structures show a good agreement with the available experimental data. The dynamic structure factors fairly agree with their experimental counterparts obtained by inelastic x-ray scattering experiments, which display inelastic side peaks. The calculated dispersion relations exhibit a positive dispersion, although not so marked as suggested by the experiment; moreover, its slope at the long-wavelength limit compares favorably with the experimental sound velocity. Electron densities near selected triplets of atoms are similar to those appearing in the solid phases, but these features have an extremely short lifetime, so they should not be considered as solid remnants in the melt.

Orbital free ab initio molecular dynamics study of liquid Al near melting

The orbital free ab initio molecular dynamics method is applied to study the static and dynamic structure of liquid Al near the triple point. The method uses a new kinetic energy functional, along with a local pseudopotential constructed within the same kinetic energy functional. The results obtained for the dynamic structure factor are compared with recent experimental data.

Structure and thermodynamics of hard D-dimensional spheres : overlap volume function approach

A very simple ansatz for the direct correlation functions of hard D-dimensional spheres is presented. For D = 1 and 3, it reduces exactly to the Percus-Yevick (PY) theory, yielding results which are very close to the PY theory for the other dimensions. A generalized Carnahan-Starling equation of state is proposed, which is in excellent agreement with the available computer simulation results. Finally, a generalized Verlet-Weis procedure for the pair distribution function g(r, η), is proposed. The important case of hard discs (D = 2) is studied in detail, leading to excellent results for g(r, η).