A number of studies of abundance gradients in the galactic disk have been performed in recent years. The results obtained are rather disparate: from no detectable gradient to a rather significant slope of about -0.1 dex kpc-1. The present study concerns the abundance gradient based on the spectroscopic analysis of a sample of classical Cepheids. These stars enable one to obtain reliable abundances of a variety of chemical elements. Additionally, they have well determined distances which allow an accurate determination of abundance distributions in the galactic disc. Using 236 high resolution spectra of 77 galactic Cepheids, the radial elemental distribution in the galactic disc between galactocentric distances in the range 6–11 kpc has been investigated. Gradients for 25 chemical elements (from carbon to gadolinium) are derived. The following results were obtained in this study. Almost all investigated elements show rather flat abundance distributions in the middle part of galactic disc. Typical values for iron-group elements lie within an interval from -0.02 to -0.04 dex kpc-1 (in particular, for iron we obtained d[Fe/H]/d dex kpc-1). Similar gradients were also obtained for O, Mg, Al, Si, and Ca. For sulphur we have found a steeper gradient (-0.05 dex kpc-1). For elements from Zr to Gd we obtained (within the error bars) a near to zero gradient value. This result is reported for the first time. Those elements whose abundance is not expected to be altered during the early stellar evolution (e.g. the iron-group elements) show at the solar galactocentric distance [El/H] values which are essentially solar. Therefore, there is no apparent reason to consider our Sun as a metal-rich star. The gradient values obtained in the present study indicate that the radial abundance distribution within 6–11 kpc is quite homogeneous, and this result favors a galactic model including a bar structure which may induce radial flows in the disc, and thus may be responsible for abundance homogenization.

This paper reports on the spectroscopic investigation of 12 Cepheids which are situated in the crucial region of galactocentric distances from 9 kpc to 12 kpc, where according to our previous results (Andrievsky et al. [CITE]; Luck et al. [CITE]) the radial metallicity distribution experiences an obvious change. In particular, the wriggle in the iron abundance distribution is found to fall approximately at galactocentric distances 10–11 kpc (assuming galactocentric distance of the Sun kpc). Within the transition zone from 10 to 11 kpc the relative-to-solar iron abundance decreases approximately to –0.2 dex. The new sample of stars, analyzed in present paper, gives results supporting the previous conclusion about the multimodal character of the metallicity distribution in galactic disc. Using a quite simple consideration of galactic chemical evolution we show that the observed distribution can be explained in the framework of a model which includes the spiral arms. In particular, the wriggle feature associated with 11 kpc can be interpreted as a change of metallicity level in the vicinity of the galactic corotation resonance.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

As a continuation of our previous work, which concerned the radial abundance distribution in the galactic disc over the distances 4–10 kpc this paper presents the first results on the metallicity in the outer disc ( kpc). Based on high-resolution spectra obtained for 19 distant Cepheids we sampled galactocentric distances from 10 to 12 kpc. Combined with the results of our previous work on the inner and middle parts of the galactic disc, the present data enable one to study the structure of the radial abundance distribution over a large baseline. In particular, we find indications of a discontinuity in the radial abundance distribution for iron as well as a number of the other elements. The discontinuity is seen at a galactocentric distance kpc. This finding supports the results reported earlier by Twarog et al. ([CITE]).