B. Lemasle

On the metallicity gradient of the Galactic disk

Aims. The iron abundance gradient in the Galactic stellar disk provides fundamental constraints on the chemical evolution of this important Galaxy component, however the spread around the mean slope is, at fixed Galactocentric distance, more than the estimated uncertainties. Methods. To provide quantitative constraints on these trends, we adopted iron abundances for 265 classical Cepheids (more than 50% of the currently known sample) based either on high-resolution spectra or on photometric metallicity indices. Homogeneous distances were estimated using near-infrared period-luminosity relations. The sample covers the four disk quadrants, and their Galactocentric distances range from similar to 5 to similar to 17 kpc. We provided a new theoretical calibration of the metallicity-index-color (MIC) relation based on Walraven and NIR photometric passbands. Results. We estimated the photometric metallicity of 124 Cepheids. Among them 66 Cepheids also have spectroscopic iron abundances and we found that the mean difference is -0.03 +/- 0.15 dex. We also provide new iron abundances, based on high-resolution spectra, for four metal-rich Cepheids located in the inner disk. The remaining iron abundances are based on high-resolution spectra collected by our group (73) or available in the literature (130). A linear regression over the entire sample provides an iron gradient of -0.051 +/- 0.004 dex kpc(-1). The above slope agrees quite well, within the errors, with previous estimates based either on Cepheids or on open clusters covering similar Galactocentric distances. However, Cepheids located in the inner disk systematically appear more metal-rich than the mean metallicity gradient. Once we split the sample into inner (R(G) <8 kpc) and outer disk Cepheids, the slope (-0.130 +/- 0.015 dex kpc(-1)) in the former region is approximate to 3 times steeper than the slope in the latter one (-0.042 +/- 0.004 dex kpc(-1)). In the outer disk the radial distribution of metal-poor (MP, [Fe/H] <-0.02 dex) and metal-rich (MR) Cepheids across the four disk quadrants does not show a clear trend when moving from the innermost to the external disk regions. The relative fractions of MP and MR Cepheids in the 1st and in the 3rd quadrants differ at the 8 sigma (MP) and 15 sigma (MR) levels. Finally, we found that iron abundances in two local overdensities of the 2nd and of the 4th quadrant cover individually a range in iron abundance of approximate to 0.5 dex. Conclusions. Current findings indicate that the recent chemical enrichment across the Galactic disk shows a clumpy distribution.

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

We present homogeneous and accurate iron abundances for 42 Galactic Cepheids based on high resolution (R ~ 38 000) high signal-to-noise ratio (S/N ≥ 100) optical spectra collected with UVES at VLT (128 spectra). The above abundances were complemented with high-quality iron abundances provided either by our group (86) or available in the literature. We were careful to derive a common metallicity scale and ended up with a sample of 450 Cepheids. We also estimated accurate individual distances for the entire sample by using homogeneous near-infrared photometry and the reddening free period-Wesenheit relations. The new metallicity gradient is linear over a broad range of Galactocentric distances (RG ~ 5-19 kpc) and agrees quite well with similar estimates available in the literature (-0.060 ± 0.002 dex/kpc). We also uncover evidence that suggests that the residuals of the metallicity gradient are tightly correlated with candidate Cepheid groups (CGs). The candidate CGs have been identified as spatial overdensities of Cepheids located across the thin disk. They account for a significant fraction of the residual fluctuations, and also for the large intrinsic dispersion of the metallicity gradient. We performed a detailed comparison with metallicity gradients based on different tracers: OB stars and open clusters. We found very similar metallicity gradients for ages younger than 3 Gyr, while for older ages we found a shallower slope and an increase in the intrinsic spread. The above findings rely on homogeneous age, metallicity, and distance scales. Finally, by using a large sample of Galactic and Magellanic Cepheids for which accurate iron abundances are available, we found that the dependence of the luminosity amplitude on metallicity is vanishing.

Galactic abundance gradients from Cepheids - On the iron abundance gradient around 10–12 kpc

Context. Classical Cepheids are excellent tracers of intermediate-mass stars, since their distances can be estimated with very high accuracy. In particular, they can be adopted to trace the chemical evolution of the Galactic disk. Aims. Homogeneous iron abundance measurements for 33 Galactic Cepheids located in the outer disk together with accurate distance determinations based on near-infrared photometry are adopted to constrain the Galactic iron gradient beyond 10 kpc. Methods. Iron abundances were determined using high resolution Cepheid spectra collected with three different observational instruments: ESPaDOnS@CFHT, Narval@TBL and FEROS@2.2m ESO/MPG telescope. Cepheid distances were estimated using nearinfrared (J,H,K-band) period-luminosity relations and data from SAAO and the 2MASS catalog. Results. The least squares solution over the entire data set indicates that the iron gradient in the Galactic disk presents a slope of –0.052 ± 0.003 dex kpc −1 in the 5–17 kpc range. However, the change of the iron abundance across the disk seems to be better described by a linear regime inside the solar circle and a flattening of the gradient toward the outer disk (beyond 10 kpc). In the latter region the iron gradient presents a shallower slope, i.e. –0.012 ± 0.014 dex kpc −1 . In the outer disk (10–12 kpc) we also found that Cepheids present an increase in the spread in iron abundance. Current evidence indicates that the spread in metallicity depends on the Galactocentric longitude. Finally, current data do not support the hypothesis of a discontinuity in the iron gradient at Galactocentric distances of 10–12 kpc. Conclusions. The occurrence of a spread in iron abundance as a function of the Galactocentric longitude indicates that linear radial gradients should be cautiously treated to constrain the chemical evolution across the disk.

On the metallicity distribution of classical Cepheids in the Galactic inner disk

We present homogeneous and accurate iron abundances for almost four dozen (47) of Galactic Cepheids using high-spectral resolution (R ~ 40 000) high signal-to-noise ratio (S/N ≥ 100) optical spectra collected with UVES at VLT. A significant fraction of the sample (32) is located in the inner disk (RG ≤ 6.9 kpc) and for half of them we provide new iron abundances. Current findings indicate a steady increase in iron abundance when approaching the innermost regions of the thin disk. The metallicity is super-solar and ranges from 0.2 dex for RG ~ 6.5 kpc to 0.4 dex for RG ~ 5.5 kpc. Moreover, we do not find evidence of correlation between iron abundance and distance from the Galactic plane. We collected similar data available in the literature and ended up with a sample of 420 Cepheids. Current data suggest that the mean metallicity and the metallicity dispersion in the four quadrants of the Galactic disk attain similar values. The first-second quadrants show a more extended metal-poor tail, while the third-fourth quadrants show a more extended metal-rich tail, but the bulk of the sample is at solar iron abundance. Finally, we found a significant difference between the iron abundance of Cepheids located close to the edge of the inner disk ([Fe/H] ~ 0.4) and young stars located either along the Galactic bar or in the nuclear bulge ([Fe/H] ~ 0). Thus suggesting that the above regions have had different chemical enrichment histories. The same outcome applies to the metallicity gradient of the Galactic bulge, since mounting empirical evidence indicates that the mean metallicity increases when moving from the outer to the inner bulge regions.

THE PANCHROMATIC VIEW OF THE MAGELLANIC CLOUDS FROM CLASSICAL CEPHEIDS. I. DISTANCE, REDDENING, AND GEOMETRY OF THE LARGE MAGELLANIC CLOUD DISK

We present a detailed investigation of the Large Magellanic Cloud (LMC) disk using classical Cepheids. Our analysis is based on optical (I,V; OGLE-IV), near-infrared (NIR: J,H,Ks) and mid-infrared (MIR: w1; WISE) mean magnitudes. By adopting new templates to estimate the NIR mean magnitudes from single-epoch measurements, we build the currently most accurate, largest and homogeneous multi-band dataset of LMC Cepheids. We determine Cepheid individual distances using optical and NIR Period-Wesenheit relations (PWRs), to measure the geometry of the LMC disk and its viewing angles. Cepheid distances based on optical PWRs are precise at 3%, but accurate to 7, while the ones based on NIR PWRs are more accurate (to 3%), but less precise (2%-15%), given the higher photometric error on the observed magnitudes. We found an inclination i=25.05

New NIR light-curve templates for classical Cepheids

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Detailed chemical composition of classical Cepheids in the LMC cluster NGC 1866 and in the field of the SMC

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Discovery of blue companions to two southern Cepheids: WW Car and FN Vel

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The Dependency of the Cepheid Period‐Luminosity Relation on Chemical Composition

0.55 (syst.) deg, and a position angle of the lines of nodes P.A.=150.76

A new and homogeneous metallicity scale for Galactic classical Cepheids: I. Physical parameters⋆⋆⋆⋆⋆⋆

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