The Galactic abundance gradient from Cepheids

Abstract

Abstract. 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. 2002c;Luck et al. 2003) 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 R G, = 7.9 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 R G ≈ 11 kpc can be interpreted as a change of metallicity level in the vicinity of the galactic corotation resonance.

Chemical abundance analysis of the open clusters Cr 110, NGC 2099 (M 37), NGC 2420, NGC 7789, and M 67 (NGC 2682)

“…However, our sample contains ∼15 more OC than that of Sestito et al (2008), and most of them (including our five determinations) fall into the gap around 9 < R GC < 12 kpc, discussed above. With the addition of these clusters, we find a gentler slope of −0.05 ± 0.01 dex kpc −1 , in good agreement with previous work (Friel 1995;Friel et al 2002) and with the disk Cepheids within R GC 11 kps (Andrievsky et al 2004;Lemasle et al 2008). If we exclude the clusters outside R GC = 12 kpc and remove the low resolution OC data from Friel et al (2002), the slope does not steepen significantly, becoming −0.06 ± 0.02 dex kpc −1 .…”

Observational studies of Cepheid amplitudes

“…For Cepheids belonging to spectroscopic binary systems, the amplitude of the radial velocity variations of pulsational origin was determined by removing the orbital effect from the radial velocity data based on the orbital elements available in the online database 1 of binary Cepheids (Szabados 2003b Giridhar (1983), Fry & Carney (1997), Groenewegen et al (2004), Andrievsky et al (2002a,b,c), Luck et al (2003), Andrievsky et al (2004Andrievsky et al ( , 2005, Kovtyukh et al (2005a,b), Romaniello et al (2005), Mottini (2006), Yong et al (2006), and Lemasle et al (2007).…”

“…To homogenize the scale of [Fe/H] values, data were shifted to a common solar metallicity, log[n(Fe)] = 7.45 on a scale where log[n(H)] = 12 (Grevesse et al 2007). Most [Fe/H] data have been taken from Andrievsky and his collaborators' papers (Andrievsky et al 2002a,b,c;Luck et al 2003;Andrievsky et al 2004Andrievsky et al , 2005Kovtyukh et al 2005a,b). Their scale was shifted by 0.05 because they used an earlier [Fe/H] value for the solar chemical composition (Grevesse et al 1996).…”

On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk

“…The iron gradients traced by stellar populations younger than a few hundred Myr show a well-defined trend when moving from the inner to the outer disk regions. The iron abundances in the innermost disk regions (R G ∼ 5 kpc) are well above solar ([Fe/H] ∼ 0.4, Andrievsky et al 2002;Pedicelli et al 2009;Luck & Lambert 2011;Genovali et al 2013, hereafter G13), while in the outer disk (R G ∼ 15 kpc) they are significantly more metal-poor ([Fe/H] ∼ -0.2/-0.5, Andrievsky et al 2004;Yong et al 2006; Lemasle et al 2008). However, the young stellar populations in the two innermost Galactic regions showing ongoing star formation activity -the bar and the nuclear bulge -attain solar A&A 566, A37 (2014) iron abundances, thus suggesting that the above regions have experienced different chemical enrichment histories .…”