Modelling the closest double degenerate system RXJ0806.3+1527 and its decreasing period

In the hypothesis that the 5.4m binary RXJ0806.3+1527 consists of a low mass helium white dwarf (donor) transferring mass towards its more massive white dwarf companion (primary), we consider as possible donors white dwarfs which are the result of common envelope evolution occurring when the helium core mass of the progenitor giant was still very small (~ 0.2Msun), so that they are surrounded by a quite massive hydrogen envelope (~1/100Msun or larger), and live for a very long time supported by proton--proton burning. Mass transfer from such low mass white dwarfs very probably starts during the hydrogen burning stage, and the donor structure will remain dominated by the burning shell until it loses all the hydrogen envelope and begins transferring helium. We model mass transfer from these low mass white dwarfs, and show that the radius of the donor decreases while they shed the hydrogen envelope. This radius behavior, which is due to the fact that the white dwarf is not fully degenerate, has two important consequences on the evolution of the binary: 1) the orbital period decreases, with a timescale consistent with the period decrease of the binary RXJ0806.3+1527; 2) the mass transfer rate is a factor of about 10 smaller than from a fully degenerate white dwarf, easing the problem connected with the small X-ray luminosity of this object. The possibility that such evolution describes the system RXJ0806.3+1527 is also consistent with the possible presence of hydrogen in the optical spectrum of the star, whose confirmation would become a test of the model.Comment: 13 pages, 4 figures, accepted for publication on ApJ, main journa

A catalog of planetary nebulae in the elliptical galaxy NGC 4697

We present a catalog of 535 planetary nebulae discovered in the flattened elliptical galaxy NGC 4697, using the FORS1 Cassegrain spectrograph of the Very Large Telescope of the European Southern Observatory at Cerro Paranal, Chile. The catalog provides positions (x, y coordinates relative to the center of light of NGC 4697, as well as RA, Dec.), and, for almost all PNs, the magnitude m(5007) and the heliocentric radial velocity in km/s.Comment: 16 pages, 5 figures, ApJS in pres

Internal Migration and Regional Population Dynamics in Europe: Romanian Case Study

The report analyses population migration and change in Romania over the period 1984-1994. The analysis of population change is conducted for 2948 communes and towns, the finest administrative division for which population data are available. The lack of migration data on the level of communes and towns makes in-depth analysis of the migration for small spatial units impossible. For that reason analysis of the patterns of migration is conducted for 40 Judete (also referred to as counties or regions) and the capital city of Bucharest, i.e. 41 units altogether. Council of Europe Publishing, F-67075 Strasbourg - Cedex, France

Were most Low Mass X ray Binaries born in Globular Clusters?

We summarize the status of art of the secular evolution of low mass X-ray binaries (LMXBs) and take a close look at the orbital period distribution of LMXBs and of binary millisecond pulsars (MSP), in the hypothesis that this latter results from the LMXB evolution. The deficiency of systems below the period gap, which in cataclysmic binaries occurs between ~ 2 and 3 hr, points to a very different secular evolution of LMXBs with respect to their counterparts containing a white dwarf compact object. The presence of several ultrashort period LMXBs (some of which are also X-ray millisecond pulsars), the important fraction of binary MSPs at periods between 0.1 and 1 day, the periods (26 and 32hr) of two ``interacting'' MSPs in Globular Clusters are other pieces of the puzzle in the period distribution. We consider the possible explanations for these peculiarities, and point out that Grindlay's old proposal that all (most of) LMXBs in the field were originally born in globular clusters must be carefully reconsidered

Unstable fingering patterns of Hele-Shaw flows as a dispersionless limit of the KdV hierarchy

We show that unstable fingering patterns of two dimensional flows of viscous fluids with open boundary are described by a dispersionless limit of the KdV hierarchy. In this framework, the fingering instability is linked to a known instability leading to regularized shock solutions for nonlinear waves, in dispersive media. The integrable structure of the flow suggests a dispersive regularization of the finite-time singularities.Comment: Published versio

Viscous shocks in Hele-Shaw flow and Stokes phenomena of the Painleve I transcendent

In Hele-Shaw flows at vanishing surface tension, the boundary of a viscous fluid develops cusp-like singularities. In recent papers [1, 2] we have showed that singularities trigger viscous shocks propagating through the viscous fluid. Here we show that the weak solution of the Hele-Shaw problem describing viscous shocks is equivalent to a semiclassical approximation of a special real solution of the Painleve I equation. We argue that the Painleve I equation provides an integrable deformation of the Hele-Shaw problem which describes flow passing through singularities. In this interpretation shocks appear as Stokes level-lines of the Painleve linear problem.Comment: A more detailed derivation is include

Generic critical points of normal matrix ensembles

The evolution of the degenerate complex curve associated with the ensemble at a generic critical point is related to the finite time singularities of Laplacian Growth. It is shown that the scaling behavior at a critical point of singular geometry $x^3 \sim y^2$ is described by the first Painlev\'e transcendent. The regularization of the curve resulting from discretization is discussed.Comment: Based on a talk given at the conference on Random Matrices, Random Processes and Integrable Systems, CRM Montreal, June 200

Simulacija porarizacijskih mjerenja u elektrotvorbi kaona Monte Carlo metodom

Kaon electro-production experiments with polarized electron beam are planed at the Thomas Jefferson National Accelerator Facility (Virginia, USA) in order to complete the information on polarization response functions for the kaon electro-production reactions. The experiment uses the self analyzing property of the Λ recoil. The scattered electrons will be detected in coincidence with the kaons and the decay protons. This paper presents the simulation of this experiment which takes into account the spectrometer acceptances, multiple scattering and radiative corrections. The phase space distribution of the decay protons in the Λ center-of-mass system are generated in order to extract information on the polarization on the three directions. An experimental test with an unpolarized beam has been performed to estimate the efficiency of the method.U Thomas Jefferson National Accelerator Facility (Virginia, USA) predlažu se mjerenja elektrotvorbi s polariziranim elektronima radi cjelovitosti podataka o polarizacijskim funkcijama odziva u elektrotvorbi kaona. Mjerenje rabi samoanalizacijsko svojstvo odboja Λ čestice. Raspršeni elektroni opažat će se sudesno s kaonima i protonima. Ovaj rad predstavlja simulaciju tog eksperimenta u kojoj se uzimaju u obzir prihvati spektrometara, višestruko raspršenje i radijativne popravke. Izvodi se fazna raspodjela protona u centru mase Λ čestice radi dobivanja podataka o polarizaciji u trima smjerovima. Mjerenjem pomoću nepolariziranog snopa ocijenili smo učinkovitost metode