Article

# Time variation of radial gradients in the galactic disk: electron temperatures and abundances

• ##### C. Quireza
Astronomy and Astrophysics (Impact Factor: 5.08). 02/2007; DOI: 10.1051/0004-6361:20066916
Source: arXiv

ABSTRACT We investigate the electron temperature gradient in the galactic disk as measured by young HII regions on the basis of radio recombination lines and the corresponding gradient in planetary nebulae (PN) based on [OIII] electron temperatures. The main goal is to investigate the time evolution of the electron temperature gradient and of the radial abundance gradient, which is essentially a mirror image of the temperature gradient. The recently derived electron temperature gradient from radio recombination lines in HII regions is compared with a new determination of the corresponding gradient from planetary nebulae for which the progenitor star ages have been determined. The newly derived electron temperature gradient for PN with progenitor stars with ages in the 4-5 Gyr range is much steeper than the corresponding gradient for HII regions. These electron temperature gradients are converted into O/H gradients in order to make comparisons with previous estimates of the flattening rate of the abundance gradient. It is concluded that the O/H gradient has flattened out in the past 5 Gyr at a rate of about 0.0094 dex kpc-1 Gyr-1, in good agreement with our previous estimates.

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##### Article: Multi‐Conjugate Adaptive Optics VLT imaging of the distant old open cluster FSR 1415
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ABSTRACT: We employ the recently installed near-infrared Multi-Conjugate Adaptive Optics demonstrator (MAD) to determine the basic properties of a newly identified, old and distant, Galactic open cluster (FSR 1415). The MAD facility remarkably approaches the diffraction limit, reaching a resolution of 0.07 arcsec (in K), that is also uniform in a field of ∼1.8 arcmin in diameter. The MAD facility provides photometry that is 50 per cent complete at K∼ 19. This corresponds to about 2.5 mag below the cluster main-sequence turn-off. This high-quality data set allows us to derive an accurate heliocentric distance of 8.6 kpc, a metallicity close to solar and an age of ∼2.5 Gyr. On the other hand, the deepness of the data allows us to reconstruct (completeness-corrected) mass functions (MFs) indicating a relatively massive cluster, with a flat core MF. The Very Large Telescope/MAD capabilities will therefore provide fundamental data for identifying/analysing other faint and distant open clusters in the Galaxy III and IV quadrants.
Monthly Notices of the Royal Astronomical Society 12/2008; 391(4):1650 - 1658. · 5.52 Impact Factor
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ABSTRACT: Radial metallicity gradients are observed in the disks of the Milky Way and in several other spiral galaxies. In the case of the Milky Way, many objects can be used to determine the gradients, such as HII regions, B stars, Cepheids, open clusters and planetary nebulae. Several elements can be studied, such as oxygen, sulphur, neon, and argon in photoionized nebulae, and iron and other elements in cepheids, open clusters and stars. As a consequence, the number of observational characteristics inferred from the study of abundance gradients is very large, so that in the past few years they have become one of the main observational constraints of chemical evolution models. In this paper, we present some recent observational evidences of abundance gradients based on several classes of objects. We will focus on (i) the magnitude of the gradients, (ii) the space variations, and (iii) the evidences of a time variation of the abundance gradients. Some comments on recent theoretical models are also given, in an effort to highlight their predictions concerning abundance gradients and their variations. Comment: 8 pages, 3 figures, uses iaus.cls, in press, IAU Symp. 265, Chemical abundances in the Universe: Connecting the first Stars to Planets, Ed. K. Cunha, M. Spite, B. Barbuy
Proceedings of the International Astronomical Union 11/2009;
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##### Article: The evolution of the Galactic metallicity gradient from high-resolution spectroscopy of open clusters
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