A&A 463, L13-L16 (2007)
DOI: 10.1051/0004-6361:20066916
Letter
Time variation of radial gradients in the Galactic disk: electron temperatures and abundances
W. J. Maciel1, C. Quireza2, and R. D. D. Costa11 Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG/USP), Universidade de São Paulo, Rua do Matão 1226, 05508-900 São Paulo SP, Brazil
e-mail: [maciel;roberto]@astro.iag.usp.br
2 Observatório Nacional, Rua General José Cristino 77, 20921-400 Rio de Janeiro RJ, Brazil
e-mail: quireza@on.br
(Received 11 December 2006 / Accepted 9 January 2007 )
Abstract
Aims.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.
Methods.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.
Results.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.
Conclusions.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.
Key words: ISM: abundances -- planetary nebulae: general -- Galaxy: abundances -- Galaxy: evolution
© ESO 2007
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