arXiv subjects

Emmanuel Davoust

Publications and source records attributed to Emmanuel Davoust.

24 records · Page 2Linked to original sources

arXiv1998

The Massive Nearby SBNGs: Young Galaxies in Formation

We discuss the implications of the recent discovery that Starburst Nucleus Galaxies (SBNGs) have lower oxygen abundances than "normal galaxies" of the same morphological type. Our interpretation of this result is that SBNGs are young galaxies, still in the process of formation. We consider several alternatives, but none of them provides a viable explanation. This new result has important consequences for our understanding of galaxy evolution, as it confirms the scenario of hierarchical formation of galaxies, and explains recent observations of the Hubble Space Telescope.

astro-ph↗

arXiv1997

A hundred years of science at the Pic du Midi Observatory

The Pic du Midi Observatory, situated at an altitude of 2890 meters, was always very hard to reach, and living there was difficult. Its history is a lesson in courage. It is also a lesson in creativity, because astronomers took advantage of the remarkable quality of the site in many ways, to study planets and, later, to prepare for the Apollo missions. They also invited geophysicists, botanists, and cosmic ray physicists to conduct experiments there, and the Observatory became a successful center for multidisciplinary studies. The heroic period, which ended in 1952, is reviewed through the accomplishments of four directors, Celestin Vaussenat, Emile Marchand, Camille Dauzere and Jules Baillaud.

astro-ph↗

arXiv1996

Structural classification of galaxies in clusters

The traditional method of morphological classification, by visual inspection of images of uniform quality and by reference to standards for each type, is critically examined. The rate of agreement among traditional morphologists on the morphological type of galaxies is estimated from published classification works, and is estimated at about 20 %, when galaxies are classified into three bins (E, S0, S+Irr). The advantages of the quantitative method of structural classification for classifying galaxies in clusters are outlined. This method is based on the isophotal analysis of galaxy images, and on the examination of quantitative structural parameters derived from this analysis, such as the profiles of luminosity, ellipticity and deviations from ellipticity of the galaxy. The structural and traditional methods are compared on a complete sample of 190 galaxies in the Coma cluster. The morphological types derived by both methods agree to within 15 or 20 %, the same rate as among traditional morphologists alone, thus showing that our morphological classes do coincide with the traditional ones. The galaxies with discrepant types are mostly faint (mag_B > 16.0), or have features typical of spirals, but which have not been detected, noticed or taken into account by traditional morphologists. The rate of agreement is also good for galaxies in a distant cluster (z ~0.4). The structural method, gives highly reproducible results, never reached by traditional estimations of the morphological type. Thus, the morphological types obtained with this method should be preferred. The advantages of the method are further demonstrated by new results on the properties of galaxies in clusters.

astro-ph↗

arXiv1995

Software for producing trichromatic images in astronomy

We present a software package for combining three monochromatic images of an astronomical object into a trichromatic color image. We first discuss the meaning of "true" colors in astronomical images. We then describe the different steps of our method, choosing the relevant dynamic intensity range in each filter, inventorying the different colors, optimizing the color map, modifying the balance of colors, and enhancing contrasts at low intensity levels. While the first steps are automatic, the last two are interactive.

astro-ph↗

arXiv1995

The purpose of astronomy

This is a presentation of the purpose of astronomy in the context of modern society. After exposing two misconceptions about astronomy, I detail its role in five domains, certified knowledge, incorporated abilities, innovations, collective goods, and popular science; with each domain is associated an institution, an incentive, and a method of evaluation. Finally, I point out the role of astronomy as a source of inspiration in other fields than science.

astro-ph↗

arXiv1995

Starbursts in barred spiral galaxies. I. Mrk 712: a new Wolf-Rayet galaxy

We report the discovery of emission from Wolf-Rayet stars in a giant HII region 4.5 arcsec South of the nucleus of the IRAS barred spiral galaxy Mrk 712. The ratio of WNL to OV stars, estimated from the luminosity of the HeII 4686 line, is 0.2. By comparison with starburst and stellar evolution models, we find that this high value is only compatible with a very young starburst episode (3 - 4 Myr) and a flat initial mass function (Gamma = -1). The presence of the [ArV] line reveals that the HII region is strongly ionized by the hot Wolf-Rayet stars. The comparison with other barred Wolf-Rayet galaxies suggests that the detection of Wolf-Rayet stars depends on the dust content and orientation of the galaxy.

astro-ph↗