Fundamental parameters of RR Lyrae stars from multicolour photometry and Kurucz atmospheric models -- II. Adaptation to double-mode stars

Our photometric-hydrodynamic method is generalized to determine fundamental parameters of multiperiodic radially pulsating stars. We report 302 UBV(RI)_C Johnson-Kron-Cousins observations of GSC 4868-0831. Using these and published photometric data of V372 Ser, their metallicity, reddening, distance, mass, radius, equilibrium luminosity, effective temperature are determined. The results underline the necessity of using multicolour photometry including an ultraviolet band to classify properly subgroups of RR Lyrae stars: our U observations could reveal that GSC 4868-0831 is a subgiant star pulsating in two radial modes, V372 Ser is a giant star with size and mass of an RRd star.Comment: 10 pages, 4 figures, 5 tables. Accepted for publication in Monthly Notices RA

Fundamental parameters of RR Lyrae stars from multicolour photometry and Kurucz atmospheric models. I. Theory and practical implementation

A photometric calibration of Kurucz static model atmospheres is used to obtain the following parameters of RR Lyrae stars: variation of stellar angular radius $\vartheta$, effective temperature $T_{\rm e}$, gravity $g_{\rm e}$ as a function of phase, interstellar reddening $E(B-V)$ towards the star and atmospheric metallicity $M$. Photometric and hydrodynamic conditions are given to find the phases of pulsation when the quasi-static atmosphere approximation (QSAA) can be applied. The QSAA is generalized to a non-uniformly moving spherical atmosphere, and the distance $d$, mass ${\cal M}$ and atmospheric motion are derived from the laws of mass and momentum conservation. To demonstrate the efficiency of the method, the $UBV(RI)_C$ photometry of SU Dra was used to derive the following parameters: $[M]=-1.60\pm .10$~dex, $E(B-V)=0.015\pm .010$, $d=663\pm 67$~pc, ${\cal M}=(0.68\pm .03){\cal M}_\odot$, equilibrium luminosity $L_{\rm eq}=45.9\pm 9.3L_\odot$ and $T_{\rm eq}=6813\pm 20$~K.Comment: 8 pages, 3 figure

Investigation of metal-insulator like transition through the ab initio density matrix renormalization group approach

We have studied the Metal-Insulator like Transition (MIT) in lithium and beryllium ring-shaped clusters through ab initio Density Matrix Renormalization Group (DMRG) method. Performing accurate calculations for different interatomic distances and using Quantum Information Theory (QIT) we investigated the changes occurring in the wavefunction between a metallic-like state and an insulating state built from free atoms. We also discuss entanglement and relevant excitations among the molecular orbitals in the Li and Be rings and show that the transition bond length can be detected using orbital entropy functions. Also, the effect of different orbital basis on the effectiveness of the DMRG procedure is analyzed comparing the convergence behavior.Comment: 12 pages, 14 figure

Phase Separation of Superfluids in the Chain of Four-Component Ultracold Atoms

We investigate the competition of various exotic superfluid states in a chain of spin-polarized ultracold fermionic atoms with hyperfine spin $F = 3/2$ and s-wave contact interactions. We show that the ground state is an exotic inhomogeneous mixture in which two distinct superfluid phases --- spin-carrying pairs and singlet quartets --- form alternating domains in an extended region of the parameter space

A NUMERICAL METHOD FOR SOLUTION OF LINEAR TRANSIENT HEAT CONDUCTION EQUATIONS

A new numerical integrating method is compared in this paper with the most popular two-level schemes, as the Crank-Nicolson (C.-N.), the Galerkin (G.), the EulerCauchy (E.-C.), the Backward Difference (B.-D.), and the 4th order Runge-Kutta (R-K.4). This procedure, the Weighting-Function Method (W.-F. M.) uses not a constant weighting factor (like 1/2 in C.-N. scheme) but a weighting function. The weighting function depends on the actual problem and on the time step. The approximating weighting function is calculated in the first few steps until it reaches a constant value; after that, the calculation will be continued using this constant weight. The W.-F. M. was tested on different simple examples, and was compared with the analytical solution and with the results of other schemes. The W.-F. M. has the best accuracy