Found 34 talks width keyword stellar populations

Monday May 18, 2009
Instituto de Astrofísica de Andalucía, Spain


In the next decade astronomers will attempt to constrain the nature of dark matter, dark energy and the (perhaps inflationary) processes which generated structure as well as understanding the astrophysics of galaxy evolution and the formation and evolution of our Milky Way and Local Group. Large-scale spectroscopic surveys on large telescopes will be critical to achieving reliable results in all these areas. The desideratum is a survey which obtains the spectra of a few times 105 galaxies from the visible into the near IR at each of a sufficient number of redshift slices that one can follow the evolution of all interesting populations. Large samples of different stellar populations in different Local Group environments will also be targeted. I will summarize the outline of a multi-object 0.4-1.7 μ spectrograph for GTC and discuss the status of miniSIDE. MiniSIDE has been conceived as a pathfinder for a large fiber-fed survey spectrograph but will be a scientific instrument on its own, capable of providing high quality science data and be competitive within the instrumentation suite of GTC. A Letter of Intent has been submitted recently to propose miniSIDE as a facility science instrument for GTC.

Tuesday April 21, 2009
INAF-Osservatorio Astronomico di Teramo, Italy


The last few years have witnessed a growing amount of empirical evidence pointing to the existence of multiple stellar populations in some Galactic globular clusters. It is also becoming more and more clear that clusters, hosting multiple stellar populations, do share some common properties, but also differ from each other in various aspects. In this talk, I will review the recent results concerning the presence of multiple stellar populations in stellar clusters, emphasizing the (different) properties of the subpopulations in the various clusters, and how they have been interpreted so far. I will discuss also the global characteristics of "peculiar" clusters - hosting multiple populations - from different points of view, and compare them with "normal" clusters, to try and shed some light on their nature and origin.

Thursday March 19, 2009
European Southern Observatory, Garching, Germany


Most studies of the stellar and substellar populations of star forming regions rely on the identification of the signatures of accretion, outflows, circumstellar dust, or activity characteristic of the early stages of stellar evolution. However, the decay of these observational signatures with time limits our ability to understand the complete star forming history of young aggregates, and to obtain unbiased samples of young stellar objects at different stages of disk evolution. I will present the results of a wide-area study of the stellar population of selected clouds in the nearby Lupus star forming region, initially defined to complement the data obtained by the Spitzer Space Observatory Legacy Program “From molecular cores to planet-forming disks”. When combined with 2MASS photometry, our data allow us to fit the spectral energy distributions of well over 150,000 sources seen in that direction, and to identify possible new members based on their photospheric fluxes alone, with independence of the display of signposts of youth. In this way we identify a very clear signature of the existence of a surprisingly numerous and thus far unrecognized population of cool members of Lupus 1 and 3, which is absent from Lupus 4.
The approximately 130 new members that we identify show that Lupus 1 and 3 have been forming low mass stars in numbers comparable to, or even exceeding in Lupus 1, those revealed by recent sensitive surveys based on the signposts of youth. We hypothesize on several possibilities for the origin of this population that may account for its puzzling properties of general lack of disks, coevality with the disk-bearing population, and preferential off-cloud location, which hint at a picture more complex and interesting than the quiescent formation inside dense molecular clouds.

Friday October 24, 2008
Instituto de Astrofísica de Canarias, Spain


(1) We present SAURON integral-field stellar velocity and velocity dispersion maps for four double-barred early-type galaxies: NGC2859, NGC3941,NGC4725 and NGC5850. The presence of the nuclear bar is not evident from the radial velocity, but it appears to have an important effect in the stellar velocity dispersion maps: we find two sigma-hollows of amplitudes between 10 and 40 km/s at either sides of the center, at the ends of the nuclear bars. We have performed numerical simulations to explain these features. Ruling out other possibilities, we finally conclude that, although the sigma-hollows may be originated by a younger stellar population component with low velocity dispersion, more likely they are an effect of the contrast between two kinematically different components: the high velocity dispersion of the bulge and the ordered motion (low velocity dispersion) of the nuclear bar.

(2) We have explored radial color and stellar surface mass density profiles for a sample of 85 late-type galaxies with available deep (down to ~27.0 mag/arcsec2 SDSS g'- and r'-band surface brightness profiles. About 90% of the light profiles have been classified as broken exponentials, exhibiting either truncations (Type II galaxies) or antitruncations (Type III galaxies). Their associated color profiles show significantly different behavior. For the truncated galaxies a radial inside-out bluing reaches a minimum of (g' - r') = 0.47 +/- 0.02 mag at the position of the break radius, this is followed by a reddening outwards. The anti-truncated galaxies reveal a more complex behavior: at the break position (calculated from the light profiles) the color profile reaches a plateau region - preceded with a reddening - with a mean color of about (g' - r') = 0.57 +/- 0.02 mag. Using the color to calculate the stellar surface mass density profiles reveals a surprising result. The breaks, well established in the light profiles of the Type II galaxies, are almost gone, and the mass profiles resemble now those of the pure exponential Type I galaxies. This result suggests that the origin of the break in Type II galaxies are most likely to be a radial change in stellar population, rather than being caused by an actual drop in the distribution of mass. The anti-truncated galaxies on the other hand preserve their shape to some extent in the stellar surface mass density profiles. We find that the stellar surface mass density at the break for truncated (Type II) galaxies is 13.6 +/- 1.6 Msun/pc2 and 9.9 +/- 1.3 Msun/pc2 for the anti-truncated (Type III) ones. We estimate that ~15% of the total stellar mass in case of Type II galaxies and ~9% in case of Type III galaxies are to be found beyond the measured break radii.

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