Lithium in field Am and normal A-F-type stars

Preliminary abundances of lithium and a few other elements have been obtained for 31 field Am stars with good Hipparcos parallaxes, as well as for 36 normal A and F stars. Radial and projected rotational velocities were determined as well. We examine the Li abundance as a function of the stellar parameters: for normal stars, it is clearly bimodal for Teff < 7500 K, while Am-Fm stars are all somewhat Li-deficient in this range. The most Li-deficient stars - either Am or normal - tend to be at least slightly evolved, but the reverse is not true.Comment: 4 pages, 2 figures, poster presented at the conference "Element stratification in stars, 40 years of atomic diffusion", eds. G. Alecian, O. Richard and S. Vauclair, EAS Publication Series, in pres

Would humans without language be apes?

The bedrock of comparative psychology of cognition, especially where nonhuman primates are concerned, rests on Darwin's famous account according to which continuity would be the main trait leading from the animal to the human mind. This idea was popularized through the statement in which Darwin postulated only quantitative differences between humans and the other species, namely "the difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind" (Darwin, 1871, p. 128)..

Asteroseismic signatures of helium gradients in late F-type stars

Element diffusion is expected to occur in all kinds of stars : according to the relative effect of gravitation and radiative acceleration, they can fall or be pushed up in the atmospheres. Helium sinks in all cases, thereby creating a gradient at the bottom of the convective zones. This can have important consequences for the sound velocity, as has been proved in the sun with helioseismology. We investigate signatures of helium diffusion in late F-type stars by asteroseismology. Stellar models were computed with different physical inputs (with or without element diffusion) and iterated in order to fit close-by evolutionary tracks for each mass. The theoretical oscillation frequencies were computed and compared for pairs of models along the tracks. Various asteroseismic tests (large separations, small separations, second differences) were used and studied for the comparisons. The results show that element diffusion leads to changes in the frequencies for masses larger than 1.2 Msun. In particular the helium gradient below the convective zone should be detectable through the second differences.Comment: 8 pages, 11 figures, 2 tables Accepted for publication in Astronomy and Astrophysics. The official date of acceptance is 03/05/200

Categories as paradigms for comparative cognition

Forming categories is a basic cognitive operation allowing animals to attain concepts, i.e. to represent various classes of objects, natural or artificial, physical or social. Categories can also be formed about the relations holding among these objects, notably similarity and identity. Some of the cognitive processes involved in categorisation will be enumerated. Also, special reference will be made to a much neglected area of research, that of social representations. Here, animals conceive the natural class of their conspecifics as well as the relationships established between them in groups. Two types of social categories were mentioned: (1) intraspecies recognition including recognition of individual conspecifics; and (2) representation of dominance hierarchies and of their transitivity in linear orders

Self-regulated hydrodynamical process in halo stars : a possible explanation of the lithium plateau

It has been known for a long time (Mestel~1953) that the meridional circulation velocity in stars, in the presence of mu-gradients, is the sum of two terms, one due to the classical thermal imbalance (Omega-currents) and the other one due to the induced horizontal mu-gradients (mu-induced currents, or mu-currents in short). In the most general cases, mu-currents are opposite to Omega-currents. Vauclair (1999) has shown that such processes can, in specific cases, lead to a quasi-equilibrium stage in which both the circulation and the helium settling is frozen. Here we present computations of the circulation currents in halo star models, along the whole evolutionary sequences for four stellar masses with a metallicity of [Fe/H] = -2. We show that such a self-regulated process can account for the constancy of the lithium abundances and the small dispersion in the Spite plateau.Comment: to appear in "The Light Elements and their Evolution", ASP conf. Serie

Spots structure and stratification of helium and silicon in the atmosphere of He-weak star HD 21699

The magnetic star HD 21699 possesses a unique magnetic field structure where the magnetic dipole is displaced from the centre by 0.4 +/- 0.1 of the stellar radius (perpendicularly to the magnetic axis), as a result, the magnetic poles are situated close to one another on the stellar surface with an angular separation of 55$^o$ and not 180$^o$ as seen in the case of a centred dipole. Respectively, the two magnetic poles form a large "magnetic spot". High-resolution spectra were obtained allowing He I and Si II abundance variations to be studied as a function of rotational phase. The results show that the helium abundance is concentrated in one hemisphere of the star, near the magnetic poles and it is comparatively weaker in another hemisphere, where magnetic field lines are horizontal with respect to the stellar surface. At the same time, the silicon abundance is greatest between longitudes of 180 - 320$^o$, the same place where the helium abundance is the weakest. These abundance variations (with rotational phase) support predictions made by the theory of atomic diffusion in the presence of a magnetic field. Simultaneously, these result support the possibility of the formation of unusual structures in stellar magnetic fields. Analysis of vertical stratification of the silicon and helium abundances shows that the boundaries of an abundance jump (in the two step model) are similar for each element; $\tau_{5000}$ = 0.8-1.2 for helium and 0.5-1.3 for silicon. The elemental abundances in the layers of effective formation of selected absorption lines for various phases are also correlated with the excitation energies of low transition levels: abundances are enhanced for higher excitation energy and higher optical depth within the applied model atmosphere.Comment: accepted by MN, 7 pagers, 10 figs, 3 table

Reaction to spatial novelty and exploratory strategies in baboons

Exploratory activity was examined in 4 young baboons with the aim of investigating the type of spatial coding (purely geometric and/or by taking into account the identity of the object) used for the configuration of objects. Animals were individually tested in an outdoor enclosure for their exploratory reactions (contact time and order of spontaneous visits) to changes brought about to a configuration of different objects. Two kinds of spatial changes were made: a modification (1) of the shape of the configuration (by displacement of one object) and (2) of the spatial arrangement without changing the initial shape (exchanging the location of two objects). In the second experiment, the effect of a spatial modification of the global geometry constituted by four identical objects was investigated. Finally, in the third experiment, a substitution of a familiar object with a novel one was performed without changing the objects' configuration. The baboons strongly reacted to geometrical modifications of the configuration. In contrast, they were less sensitive to modifications of local features that did not affect the initial spatial configuration. Analyses of spontaneous exploratory activities revealed two types of exploratory strategies (cyclic and back-and-forth). These data are discussed in relation to (1) the distinction between the encoding of geometric versus local spatial features and (2) the spatial function of exploratory activity