Context. Transiting planets around stars are discovered mostly through photometric surveys. Unlike radial velocity surveys, photometric surveys do not tend to target slow rotators, inactive or ...metal-rich stars. Nevertheless, we suspect that observational biases could also impact transiting-planet hosts. Aims. This paper aims to evaluate how selection effects reflect on the evolutionary stage of both a limited sample of transiting-planet host stars (TPH) and a wider sample of planet-hosting stars detected through radial velocity analysis. Then, thanks to uniform derivation of stellar ages, a homogeneous comparison between exoplanet hosts and field star age distributions is developed. Methods. Stellar parameters have been computed through our custom-developed isochrone placement algorithm, according to Padova evolutionary models. The notable aspects of our algorithm include the treatment of element diffusion, activity checks in terms of \hbox{$\log{R'_{HK}}$}logRHK′ and vsini, and the evaluation of the stellar evolutionary speed in the Hertzsprung-Russel diagram in order to better constrain age. Working with TPH, the observational stellar mean density ρ⋆ allows us to compute stellar luminosity even if the distance is not available, by combining ρ⋆ with the spectroscopic log g. Results. The median value of the TPH ages is ~5 Gyr. Even if this sample is not very large, however the result is very similar to what we found for the sample of spectroscopic hosts, whose modal and median values are 3, 3.5) Gyr and ~4.8 Gyr, respectively. Thus, these stellar samples suffer almost the same selection effects. An analysis of MS stars of the solar neighbourhood belonging to the same spectral types bring to an age distribution similar to the previous ones and centered around solar age value. Therefore, the age of our Sun is consistent with the age distribution of solar neighbourhood stars with spectral types from late F to early K, regardless of whether they harbour planets or not. We considered the possibility that our selected samples are older than the average disc population.
In this study, we report an electrochemical study based on nanocellulose (NC) and single-walled carbon nanohorns (SWCNH). SWCNH and NC ensure large surface area, good conductivity, high porosity and ...chemical stability, becoming attractive for electrodes. The materials were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Scanning Electron Micrograph (SEM), Transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential. Using XRD and FTIR it was possible to observe particular characteristics of NC and SWCNH. The presence of dahlia-like assemblies on the NC surface was observed by MEV and TEM. Then, we investigated the electrochemical behavior of NC-SWCNH, which showed the excellent results when it was used guanine and adenine, as proof of concept, by using cyclic and linear sweep voltammetry (LSV). LSV was also employed for simultaneous detection resulting in limits of detection of 1.7 × 10−7 mol L−1 and 1.4 × 10−6 mol L−1, for guanine and adenine, respectively. In addition, the proposed electrode was applied for determination of both bases in synthetic human serum and fish sperm. We demonstrate that it is possible to use NC, a renewable material, in conducting thin films with SWCNH, and due to simplicity in the preparation and high conductivity, this new thin film could be extended for others electrochemical purposes such as sensing and biosensing.
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Aims. This article aims to measure the age of stars with planets (SWP) through stellar tracks and isochrones computed with the PAdova and TRieste Stellar Evolutionary Code (PARSEC). Methods. We ...developed algorithms based on two different techniques for determining the ages of field stars: isochrone placement and Bayesian estimation. Their application to a synthetic sample of coeval stars shows the intrinsic limits of each method. For instance, the Bayesian computation of the modal age tends to select the extreme age values in the isochrones grid. Therefore, we used the isochrone placement technique to measure the ages of 317 SWP. Results. We found that ~6% of SWP have ages lower than 0.5 Gyr. The age distribution peaks in the interval 1.5, 2) Gyr, then it decreases. However, ~7% of the stars are older than 11 Gyr. The Sun turns out to be a common star that hosts planets, when considering its evolutionary stage. Our SWP age distribution is less peaked and slightly shifted towards lower ages if compared with ages in the literature and based on the isochrone fit. In particular, there are no ages below 0.5 Gyr in the literature.
We use high-precision photometry of red-giant-branch (RGB) stars in 57 Galactic globular clusters (GCs), mostly from the 'Hubble Space Telescope (HST) UV Legacy Survey of Galactic GCs', to identify ...and characterize their multiple stellar populations. For each cluster the pseudo-two-colour diagram (or 'chromosome map') is presented, built with a suitable combination of stellar magnitudes in the F275W, F336W, F438W, and F814W filters that maximizes the separation between multiple populations. In the chromosome map of most GCs (type-I clusters), stars separate in two distinct groups that we identify with the first (1G) and the second generation (2G). This identification is further supported by noticing that 1G stars have primordial (oxygen-rich, sodium-poor) chemical composition, whereas 2G stars are enhanced in sodium and depleted in oxygen. This 1G-2G separation is not possible for a few GCs where the two sequences have apparently merged into an extended, continuous sequence. In some GCs (type-II clusters) the 1G and/or the 2G sequences appear to be split, hence displaying more complex chromosome maps. These clusters exhibit multiple subgiant branches (SGBs) also in purely optical colour-magnitude diagrams, with the fainter SGB joining into a red RGB which is populated by stars with enhanced heavy-element abundance. We measure the RGB width by using appropriate colours and pseudo-colours. When the metallicity dependence is removed, the RGB width correlates with the cluster mass. The fraction of 1G stars ranges from ~8 per cent to ~67 per cent and anticorrelates with the cluster mass, indicating that incidence and complexity of the multiple population phenomenon both increase with cluster mass.
Aims. We seek to constrain the formation of the Galactic bulge by analysing the detailed chemical composition of a large sample of red clump stars in Baade’s window. These stars were selected to ...minimise the contamination by other Galactic components, so they are good tracers of the bulge metallicity distribution in Baade’s window, at least for stars more metal-rich than ~−1.5. Methods. We used an automatic procedure to measure Fe/H differentially with respect to the metal-rich star μLeo in a sample of 219 bulge red clump stars from R = 20 000 resolution spectra obtained with FLAMES/GIRAFFE at the VLT. For a subsample of 162 stars, we also derived Mg/H from spectral synthesis around the Mg i triplet at λ 6319 Å. Results. The Fe and Mg metallicity distributions are both asymmetric with median values of +0.16 and +0.21, respectively. They show only a small proportion of stars at low metallicities, extending down to Fe/H = −1.1 or Mg/H = −0.7. The iron distribution is clearly bimodal, as revealed both by a deconvolution (from observational errors) and a Gaussian decomposition. The decomposition of the observed Fe and Mg metallicity distributions into Gaussian components yields two populations of equal sizes (50% each): a metal-poor component centred on Fe/H = −0.30 and Mg/H = −0.06 with a large dispersion and a narrow metal-rich component centred on Fe/H = +0.32 and Mg/H = +0.35. The metal-poor component shows high Mg/Fe ratios (around 0.3), while stars in the metal-rich component are found to have nearly solar ratios. Kinematical differences between the two components have also been found: the metal-poor component shows kinematics compatible with an old spheroid, while the metal-rich component is consistent with a population supporting a bar. In view of their chemical and kinematical properties, we suggest different formation scenarii for the two populations: a rapid formation time scale as an old spheroid for the metal-poor component (old bulge) and for the metal-rich component, a formation on a longer time scale driven by the evolution of the bar (pseudo-bulge). The observations are described well by a simple model consisting of two components: a simple closed box model to predict the metal-poor population contribution and a local thin disc metallicity distribution, shifted in metallicity, to represent the metal-rich population. The pseudo-bulge is compatible with its being formed from the inner thin disc, assuming high (but plausible) values of the gradients in the early Galactic disc.
Abstract
Bulge globular clusters (GCs) with metallicities Fe/H ≲ −1.0 and blue horizontal branches are candidates to harbor the oldest populations in the Galaxy. Based on the analysis of
HST
...proper-motion-cleaned color–magnitude diagrams in filters F435W and F625W, we determine physical parameters for the old bulge GCs NGC 6522 and NGC 6626 (M28), both with well-defined blue horizontal branches. We compare these results with similar data for the inner halo cluster NGC 6362. These clusters have similar metallicities (−1.3 ≤ Fe/H ≤ −1.0) obtained from high-resolution spectroscopy. We derive ages, distance moduli, and reddening values by means of statistical comparisons between observed and synthetic fiducial lines employing likelihood statistics and the Markov chain Monte Carlo method. The synthetic fiducial lines were generated using
α
-enhanced BaSTI and Dartmouth stellar evolutionary models, adopting both canonical (
Y
∼ 0.25) and enhanced (
Y
∼ 0.30–0.33) helium abundances. RR Lyrae stars were employed to determine the HB magnitude level, providing an independent indicator to constrain the apparent distance modulus and the helium enhancement. The shape of the observed fiducial line could be compatible with some helium enhancement for NGC 6522 and NGC 6626, but the average magnitudes of RR Lyrae stars tend to rule out this hypothesis. Assuming canonical helium abundances, BaSTI and Dartmouth models indicate that all three clusters are coeval, with ages between ∼12.5 and 13.0 Gyr. The present study also reveals that NGC 6522 has at least two stellar populations, since its CMD shows a significantly wide subgiant branch compatible with 14% ± 2% and 86% ± 5% for first and second generations, respectively.
Context. Globular clusters trace the formation and evolution of the Milky Way and surrounding galaxies, and outline their chemical enrichment history. To accomplish these tasks it is important to ...have large samples of clusters with homogeneous data and analysis to derive kinematics, chemical abundances, ages and locations. Aims. We obtain homogeneous metallicities and alpha-element enhancement for 51 Galactic bulge, disc, and halo globular clusters that are among the most distant and/or highly reddened in the Galaxy's globular cluster system. We also provide membership selection based on stellar radial velocities and atmospheric parameters. The implications of our results are discussed. Methods. We observed R~ 2000 spectra in the wavelength interval 456-586 nm for over 800 red giant stars in 51 Galactic globular clusters. We applied full spectrum fitting with the code ETOILE together with libraries of observed and synthetic spectra. We compared the mean abundances of all clusters with previous work and with field stars. We used the relation between mean metallicity and horizontal branch morphology defined by all clusters to select outliers for discussion. Results. Fe/H, Mg/Fe, and alpha/Fe were derived in a consistent way for almost one-third of all Galactic globular clusters. We find our metallicities are comparable to those derived from high-resolution data to within sigma= 0.08 dex over the interval -2.5< Fe/H < 0.0. Furthermore, a comparison of previous metallicity scales with our values yields sigma< 0.16 dex. We also find that the distribution of Mg/Fe and alpha/Fe with Fe/H for the 51 clusters follows the general trend exhibited by field stars. It is the first time that the following clusters have been included in a large sample of homogeneous stellar spectroscopic observations and metallicity derivation: BH 176, Djorg 2, Pal 10, NGC 6426, Lynga 7, and Terzan 8. In particular, only photometric metallicities were available previously for the first three clusters, and the available metallicity for NGC 6426 was based on integrated spectroscopy and photometry. Two other clusters, HP 1 and NGC 6558, are confirmed as candidates for the oldest globular clusters in the Milky Way. Conclusions. Stellar spectroscopy in the visible at R~ 2000 for a large sample of globular clusters is a robust and efficient way to trace the chemical evolution of the host galaxy and to detect interesting objects for follow-up at higher resolution and with forthcoming giant telescopes. The technique used here can also be applied to globular cluster systems in nearby galaxies with current instruments and to distant galaxies with the advent of ELTs.
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