43 research outputs found
Low-mass and sub-stellar eclipsing binaries in stellar clusters
We highlight the importance of eclipsing double-line binaries in our
understanding on star formation and evolution. We review the recent discoveries
of low-mass and sub-stellar eclipsing binaries belonging to star-forming
regions, open clusters, and globular clusters identified by ground-based
surveys and space missions with high-resolution spectroscopic follow-up. These
discoveries provide benchmark systems with known distances, metallicities, and
ages to calibrate masses and radii predicted by state-of-the-art evolutionary
models to a few percent. We report their density and discuss current
limitations on the accuracy of the physical parameters. We discuss future
opportunities and highlight future guidelines to fill gaps in age and
metallicity to improve further our knowledge of low-mass stars and brown
dwarfs.Comment: 30 pages, 5 figures, no table. Review pape
Dwarf Galaxies of the Local Group
The Local Group (LG) dwarf galaxies offer a unique window to the detailed
properties of the most common type of galaxy in the Universe. In this review, I
update the census of LG dwarfs based on the most recent distance and radial
velocity determinations. I then discuss the detailed properties of this sample,
including (a) the integrated photometric parameters and optical structures of
these galaxies, (b) the content, nature and distribution of their ISM, (c)
their heavy-element abundances derived from both stars and nebulae, (d) the
complex and varied star-formation histories of these dwarfs, (e) their internal
kinematics, stressing the relevance of these galaxies to the dark-matter
problem and to alternative interpretations, and (f) evidence for past, ongoing
and future interactions of these dwarfs with other galaxies in the Local Group
and beyond. To complement the discussion and to serve as a foundation for
future work, I present an extensive set of basic observational data in tables
that summarize much of what we know, and what we still do not know, about these
nearby dwarfs. Our understanding of these galaxies has grown impressively in
the past decade, but fundamental puzzles remain that will keep the Local Group
at the forefront of galaxy evolution studies for some time.Comment: 66 pages; 9 figures; 8 table
Evolution of mass segregation in open clusters : some observational evidences.
On the basis of the best available member list and duplicity information, we have studied the radial structure of Praesepe and of the very young open cluster NGC 6231. We have found mass segregation among the cluster members and between binaries and single stars, which is explained by the greater average mass of the multiple systems. However, the degree of mass segregation for stars between 1.5 and 2.3 M_sun is less pronounced in Praesepe than in the Pleiades. Furthermore, mass segregation is already present in the very young open cluster NGC 6231 although this cluster is likely still not dynamically relaxed. We discuss the implications of these results and propose a qualitative scenario for the evolution of mass segregation in open clusters. In Praesepe the mass function of single stars and primaries appears to be significantly different, like in the Pleiades. We observe an absence of ellipticity of the outer part of Praesepe