Massive stellar systems: observational challenges and perspectives in the E-ELT era

We introduce the empirical framework concerning optical and near-infrared (NIR) photometry of crowded stellar fields. In particular, we address the impact that linear detectors and analytical PSF played in improving the accuracy and the precision of multi-band color-magnitude diagrams (CMDs). We focus our attention on recent findings based on deep NIR images collected with Adaptive Optics (AO) systems at the 8-10m class telescopes and discuss pros and cons of the different approaches. We also discuss the estimate of the absolute age of globular clusters using a well defined knee along the lower main sequence. We mention the role which the current AO-assisted instruments will have in addressing longstanding astrophysical problems of the Galactic center. Finally, we outline the role of first generation of E-ELT instruments upon photometry and spectroscopy of crowded stellar fields

Observations of field and cluster RR Lyræ with Spitzer. Towards high precision distances with Population II stellar tracers

Indexación: Scopus.We present our project to calibrate the RR Lyræ period-luminosity-metallicity relation using a sample of Galactic calibrators in the halo and globular clusters.https://www.epj-conferences.org/articles/epjconf/pdf/2017/21/epjconf_puls2017_07004.pd

Do the dominant plant species impact the substrate and vegetation composition of post-coal mining spoil heaps?

This is an accepted manuscript of an article published by Elsevier in Ecological Engineering on 03/12/2019, available online: https://doi.org/10.1016/j.ecoleng.2019.105685 The accepted version of the publication may differ from the final published version�� 2019 Dominant species influence both species and functional composition of the vegetation as well as soil properties of the substrate. However, knowledge about the role played by dominant species in the process of shaping their habitat within post-industrial ecosystems is still limited. We aimed to assess the impact of four dominant species (Calamagrostis epigejos, Daucus carota, Poa compressa and Tussilago farfara) on soil abiotic and biotic properties, and to detect differences in species and functional composition of the vegetation types studied. We hypothesized that (1) dominant species of higher mean biomass cause lower aboveground biodiversity and (2) dominant species of higher mean biomass have a higher impact than the others on soil properties. We measured soil chemistry (TOC, N, P, K, Na, Mg content, EC, pH and enzyme activities) as well as biomass, species diversity and functional diversity of vegetation on 15 study plots (28.3 m2) for each species studied. The DCA analysis revealed a clear distinction between the patches dominated by studied species. Vegetation patches dominated by Calamagrostis epigejos were correlated with amount of biomass, canopy height CWM and specific leaf CWM. Patches dominated by Daucus carota were related to the light requirements (EIV-L), Total Organic Carbon (TOC) and K content. The vegetation patches dominated by Poa compressa were related to dehydrogenase activity, higher Mg content and species richness of the vegetation patches. The highest TOC content was recorded for T. farfara substrates, and the lowest for C. epigejos substrates. The content of potassium does not differ statistically significantly in the substrates from sites dominated by D. carota and P. compressa. The highest values of Mg content were recorded for D. carota and were statistically different from Poa compressa sites, while the higher phosphorus content (statistically significantly different) was recorded for patches dominated by T. farfara and P. compressa. Despite our assumptions, the species with the highest mean biomass (Calamagrostis epigejos) did not cause lower species or functional diversity. In contrast, Tussilago farfara has the highest impact on postindustrial site habitats on coal mine heaps, as extreme values of four soil substratum parameters were recorded on these plots. This species also decreased both species and functional diversity of vegetation. The knowledge about relationship existing between plants (aboveground vegetation) and soil organisms seems important in order to undertake suitable reclamation measures and to restore variety of functions as well as to create diverse vegetation based on native species.Published versio

On a New Theoretical Framework for RR Lyrae Stars. II. Mid-infrared Period-Luminosity-Metallicity Relations

We present new theoretical period-luminosity-metallicity (PLZ) relations for RR Lyrae stars (RRL) at Spitzer and WISE wavelengths. The PLZ relations were derived using nonlinear, time-dependent convective hydrodynamical models for a broad range in metal abundances (Z=0.0001 to 0.0198). In deriving the light curves, we tested two sets of atmospheric models (Brott & Hauschildt 2005, Castelli & Kurucz 2003) and found no significant difference between the resulting mean magnitudes. We also compare our theoretical relations to empirical relations derived from RRL in both the field and in the globular cluster M4. Our theoretical PLZ relations were combined with multi-wavelength observations to simultaneously fit the distance modulus, mu_0, and extinction, Av, of both the individual Galactic RRL and of the cluster M4. The results for the Galactic RRL are consistent with trigonometric parallax measurements from Gaia's first data release. For M4, we find a distance modulus of $\mu_0=11.257 \pm 0.035$ mag with $A_V = 1.45 \pm 0.12$ mag, which is consistent with measurements from other distance indicators. This analysis has shown that when considering a sample covering a range of iron abundances, the metallicity spread introduces a dispersion in the PL relation on the order of 0.13 mag. However, if this metallicity component is accounted for in a PLZ relation, the dispersion is reduced to ~0.02 mag at MIR wavelengths

Metallicity Distribution of Galactic Halo Field RR Lyræ, and the Effect of Metallicity on Their Pulsation Properties

We present our analysis of a large sample (over 150k) of candidate Galactic RR Lyrae (RRL) stars for which we derived high quality photometry at UV, optical and infrared wavelengths, using data from publicly available surveys. For a sub-sample of these stars (∼ 2,400 fundamental mode field RRLs) we have measured their individual metallicity using the ΔS method, resulting in the largest and most homogeneous spectroscopic data set collected for RRLs. We use this sample to study the metallicity distribution in the Galactic Halo, including the long-standing problem of the Oosterhoff dichotomy among Galactic globular clusters. We also analyze the dependence of their pulsation properties, and in particular the shape of their infrared light curves, from their [Fe/H] abundance

On the Use of Field RR Lyrae As Galactic Probes: IV. New Insights Into and Around the Oosterhoff Dichotomy*

We discuss the largest and most homogeneous spectroscopic data set of field RR Lyrae variables (RRLs) available to date. We estimated abundances using both high-resolution and low-resolution (ΔS method) spectra for fundamental (RRab) and first overtone (RRc) RRLs. The iron abundances for 7941 RRLs were supplemented with similar estimates that are available in the literature, ending up with 9015 RRLs (6150 RRab, 2865 RRc). The metallicity distribution shows a mean value of 〈[Fe/H]〉 = −1.51 ± 0.01, and σ(standard deviation) = 0.41 dex with a long metal-poor tail approaching [Fe/H] ≃ − 3 and a sharp metal-rich tail approaching solar iron abundance. The RRab variables are more metal-rich (〈[Fe/H]〉ab = −1.48 ± 0.01, σ = 0.41 dex) than RRc variables (〈[Fe/H]〉c = −1.58 ± 0.01, σ = 0.40 dex). The relative fraction of RRab variables in the Bailey diagram (visual amplitude versus period) located along the short-period (more metal-rich) and the long-period (more metal-poor) sequences are 80% and 20%, while RRc variables display an opposite trend, namely 30% and 70%, respectively. We found that the pulsation period of both RRab and RRc variables steadily decreases when moving from the metal-poor to the metal-rich regime. The visual amplitude shows the same trend, but RRc amplitudes are almost two times more sensitive than RRab amplitudes to metallicity. We also investigated the dependence of the population ratio (Nc/Ntot) of field RRLs on the metallicity and we found that the distribution is more complex than in globular clusters. The population ratio steadily increases from ∼0.25 to ∼0.36 in the metal-poor regime, it decreases from ∼0.36 to ∼0.18 for −1.8 ≤ [Fe/H] ≤ −0.9 and it increases to a value of ∼0.3 approaching solar iron abundance