Searching transients in large-scale surveys. A method based on the Abbe value

(Abridged) A new method is presented to identify transient candidates in large-scale surveys based on the variability pattern in their light curves. The method is based on the Abbe value, that estimates the smoothness of a light curve, and on a newly introduced value called the excess Abbe that estimates the regularity of the light curve variability pattern over the duration of the observations. Based on simulated light curves, transients are shown to occupy a specific region in the Abbe versus Excess Abbe diagram, distinct from sources presenting pulsating-like features in their light curves or having featureless light curves. The method is tested on real light curves taken from EROS-2 and OGLE-II surveys in a 0.50deg x 0.17deg field of the sky in the LMC. The method identifies 43 EROS-2 transient candidates out of a total of ~1300 variable stars, and 19 more OGLE-II candidates. The efficiency of the method is further tested by comparing the list of transient candidates with known Be stars in the literature. It is shown that all Be stars known in the studied field of view with detectable bursts or outbursts are successfully extracted by the method. In addition, four new transient candidates displaying bursts and/or outbursts are found in the field, of which at least two are good new Be candidates. The new method proves to be a potentially powerful tool to extract transient candidates from large-scale multi-epoch surveys. The better the photometric measurement uncertainties are, the cleaner the list of detected transient candidates is. In addition, the diagram is shown to be a good diagnostic tool to check the data quality of multi-epoch photometric surveys. A trend of instrumental and/or data reduction origin, for example, will manifest itself by an unexpected distribution of points in the diagram.Comment: Accepted for publication in A&

A Method to Extract the Structural Strata and Elements of Landscape Using GIS

Analyzing the landscape with using large three-dimensional database is well noted as the new method. In applying the method, the measure to divide the database into several densities of data to adjust many places and to analyze in mainframe computer is in need. The purpose of this study is to clarify the method of dividing spaces into structural layer, which can be measured in its quantity._ The theoretical method to extract the landscape elements by the distance from the viewpoint has been recognized by the previous studies, which based on the human phenomenon philosophy. However, the quantities of distance, which defines the space as a whole environment around viewpoint is not yet applicable for practical design. Because, the quantities have not been clearly found to apply to the real space since, feelings of distance varies by personal image. The cause of differences are due to some factors such as physical factors including the topography, the vegetation, and the building surroundings. Furthermore, there are other factors for example, psychological and social._ In this study, the physically caused distance definition is to be cleared through the method to extract the structural strata and the elements of landscape._ As an initial analysis, the angle of gaze from viewpoint, based on human engineering, the heights of the layers were examined and clearly found. The relationship between the eyesight and the angle of gaze are analyzed. Secondly, the continuity of figure from viewpoint are measured. It applied the fifty meters mesh digital map, the topographic vector data, the aerial photograph, and the building form vector data, to the Geographic Information System; the SIS and the ArcGIS. It proved that three scale of view; the close, the distance, and the background divides the real landscape. With this result, the method to extract the structural strata are found._ Preliminary, the methodsÕ application was tried to real spaces for further analysis. The results encouraged the analysis of physical quantity related with the human image including the time-space, and the relationship between the view and the other sense, which are under processes._

Diffusion in stellar interiors: critical tests of three numerical methods

We describe and discuss the properties of three numerical methods for solving the diffusion equation for the transport of the chemical species and of the angular momentum in stellar interiors. We study through numerical experiments both their accuracy and their ability to provide physical solutions. On the basis of new tests and analyses applied to the stellar astrophysical context, we show that the most robust method to follow the secular evolution is the implicit finite differences method. The importance of correctly estimating the diffusion coefficient between mesh points is emphasized and a procedure for estimating the average diffusion coefficient between a convective and a radiative zone is described.Comment: 15 pages, 8 figures. accepted for publication in Astronomy and Astrophysic

The survival of 205Pb in intermediate-mass AGB stars

The now extinct 205Pb is a pure s-process radionuclide (t_{1/2} = 1.5x10^7 y) of possible substantial cosmochemical interest. As a necessary complement to the detailed theoretical study of the nuclear physics and astrophysics aspects of the 205Pb - 205Tl pair carried out by Yokoi et al. (1985), and to the recent calculation of the 205Pb production in Wolf-Rayet stars by Arnould et al. (1997), this paper addresses for the first time in some detail the question of the survival of this radionuclide in thermally pulsing AGB stars. This problem is made difficult by the high sensitivity to temperature and density of the rates of the weak interaction processes that are able to produce or destroy 205Pb. In view of this sensitivity, a recourse to detailed stellar models is mandatory. With the help of some simplifying assumptions concerning in particular the third dredge-up characteristics, some of which (like its depth) being considered as free parameters, predictions are made for the 205Pb contamination of the stellar surface at the end of a pulse-interpulse cycle following a series of a dozen of pulses in three different intermediate-mass stars (M=3M_sun,Z=0.02; M=6M_sun,Z=0.02; M=3M_sun,Z=0.001). It is concluded that the chances for a significant 205Pb surface enrichment are likely to increase with M for a given Z, or to increase with decreasing Z for a given M. More specifically, following the considered pulses at least, the enrichment appears to be rather unlikely in the 3M_sun star with Z=0.02, while it seems to be much more probable in the other two considered stars. It is also speculated that the (3M_sun,Z=0.02) star could possibly experience some 205Pb enrichment following later pulses than the ones considered in this paper.Comment: 10 pages, 10 figures, Latex A&A, ps file available at ftp://obsftp.unige.ch/pub/mowlavi/pbtl.ps; accepted for publication in A&