ORCID Profile
0000-0002-4933-2239
Current Organisation
Universidade de São Paulo
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Stellar Astronomy and Planetary Systems | Astronomical and Space Sciences | Space and Solar Physics
Publisher: EDP Sciences
Date: 2016
Publisher: EDP Sciences
Date: 06-05-2008
Publisher: EDP Sciences
Date: 25-10-2011
Publisher: EDP Sciences
Date: 11-2018
DOI: 10.1051/0004-6361/201629294
Abstract: Context . It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1–2 Gyr that is followed by a relatively inactive constant phase. Aims . We revisited the activity-age relation using time-series observations of a large s le of solar twins whose precise isochronal ages and other important physical parameters have been determined. Methods . We measured the Ca II H and K activity indices using ≈9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale ( S MW ), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of T eff , and then computed an improved bolometric flux normalized activity index log R ′ HK ( T eff ) for the entire s le. Results . New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using log R ′ HK ( T eff ). We measured an average solar activity of S MW = 0.1712 ± 0.0017 during solar magnetic cycles 23–24 covered by HARPS observations, and we also inferred an average of S MW = 0.1694 ± 0.0025 for cycles 10–24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6–7 Gyr, in agreement with previous works using open clusters and field stars with precise ages. Conclusions . Our research confirms that Ca II H & K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6–7 Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations effects. The Sun seems to have a normal activity level and variability for its age.
Publisher: American Astronomical Society
Date: 20-04-2017
Publisher: Oxford University Press (OUP)
Date: 19-05-2014
Publisher: American Astronomical Society
Date: 04-04-2018
Publisher: American Astronomical Society
Date: 22-08-2018
Publisher: American Astronomical Society
Date: 14-07-2015
Publisher: Cambridge University Press (CUP)
Date: 07-2017
DOI: 10.1017/S1743921317007426
Abstract: The four main findings about the age and abundance structure of the Milky Way bulge based on microlensed dwarf and subgiant stars are: (1) a wide metallicity distribution with distinct peaks at [Fe/H] = -1.09, -0.63, -0.20, +0.12, +0.41 (2) a high fraction of intermediate-age to young stars where at [Fe/H] & 0 more than 35 % are younger than 8 Gyr, (3) several episodes of significant star formation in the bulge 3, 6, 8, and 11 Gyr ago (4) the ‘knee’ in the α-element abundance trends of the sub-solar metallicity bulge appears to be located at a slightly higher [Fe/H] (about 0.05 to 0.1 dex) than in the local thick disk.
Publisher: Oxford University Press (OUP)
Date: 23-03-2016
DOI: 10.1093/MNRAS/STW676
Publisher: Oxford University Press (OUP)
Date: 21-11-2017
Publisher: Springer Science and Business Media LLC
Date: 10-11-2009
Publisher: Oxford University Press (OUP)
Date: 29-01-2021
Abstract: The abundance patterns observed in the Sun and in metal-poor stars show a clear odd-even effect. An important question is whether the odd-even effect in solar-metallicity stars is similar to the Sun, or if there are variations that can tell us about different chemical enrichment histories. In this work, we report for the first time observational evidence of a differential odd-even effect in the solar twin HIP 11915, relative to the solar odd-even abundance pattern. The spectra of this star were obtained with high-resolving power (140 000) and signal-to-noise ratio (∼420) using the ESPRESSO spectrograph and the VLT telescope. Thanks to the high spectral quality, we obtained extremely precise stellar parameters (σ(Teff) = 2 K, $\\sigma (\\rm {[Fe/H]})$ = 0.003 dex, and σ(log g) = 0.008 dex). We determine the chemical abundance of 20 elements (Z ≤ 39) with high precision (∼0.01 dex), which shows a strong pattern of the odd-even effect even after performing galactic chemical evolution corrections. The odd-even effect is reasonably well-reproduced by a core-collapse supernova of 13 $\\rm {M_{\\odot }}$ and metallicity Z = 0.001 diluted into a metal-poor gas of 1 $\\rm {M_{\\odot }}$. Our results indicate that HIP 11915 has an odd-even effect slightly different than the Sun, thus confirming a different supernova enrichment history.
Publisher: EDP Sciences
Date: 22-06-2012
Publisher: Cambridge University Press (CUP)
Date: 08-2009
DOI: 10.1017/S1743921309991001
Abstract: We present abundance measurements in the tidally disrupted globular cluster NGC 6712. In this cluster, there are large star-to-star variations of the light elements C, N, O, F and Na. While such abundance variations are seen in every well-studied globular cluster, they are not found in field stars and indicate that clusters like NGC 6712 cannot provide many field stars and/or field stars do not form in environments with chemical-enrichment histories like those of NGC 6712. Preliminary analysis of NGC 5466, another tidally disrupted cluster, suggests little (if any) abundance variation for O and Na and the abundance ratios [X/Fe] are comparable to field stars at the same metallicity. Therefore, globular clusters like NGC 5466 may have been Galactic building blocks.
Publisher: American Astronomical Society
Date: 20-12-2008
DOI: 10.1086/592229
Publisher: American Astronomical Society
Date: 23-09-2021
Abstract: Different stellar phenomena affect radial velocities (RVs), causing variations large enough to make it difficult to identify planet signals from the stellar variability. RV variations caused by stellar oscillations and granulation can be reduced through some methods, but the impact of rotationally modulated magnetic activity on RV, due to stellar active regions, is harder to correct. New instrumentation promises an improvement in precision of one order of magnitude, from about 1 m s −1 to about 10 cm s −1 . In this context, we report our first results from 24 spectroscopic Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO)/Very-Large Telescope observations of the solar twin star HIP 11915, spread over 60 nights. We used a Gaussian Process approach and found for HIP 11915 a RV residual rms scatter of about 20 cm s −1 , representing an upper limit for the performance of ESPRESSO.
Publisher: Oxford University Press (OUP)
Date: 08-2013
Publisher: EDP Sciences
Date: 26-05-2011
Publisher: EDP Sciences
Date: 12-2011
Publisher: American Astronomical Society
Date: 20-11-2012
Publisher: EDP Sciences
Date: 12-2015
Publisher: Oxford University Press (OUP)
Date: 29-01-2016
DOI: 10.1093/MNRAS/STW247
Publisher: EDP Sciences
Date: 13-03-2012
Publisher: Oxford University Press (OUP)
Date: 08-03-2019
DOI: 10.1093/MNRAS/STZ681
Publisher: American Astronomical Society
Date: 07-08-2020
Publisher: EDP Sciences
Date: 02-2021
DOI: 10.1051/0004-6361/202039601
Abstract: Context. Sirius-like systems are relatively wide binaries with a separation from a few to hundreds of au they are composed of a white dwarf (WD) and a companion of a spectral type earlier than M0. Here we consider main sequence (MS) companions, where the WD progenitor evolves in isolation, but its wind during the former asymptotic giant branch (AGB) phase pollutes the companion surface and transfers some angular momentum. They are rich laboratories to constrain stellar models and binary evolution. Aims. Within the SpHere INfrared survey for Exoplanet survey that uses the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large Telescope, our goal is to acquire high contrast multi-epoch observations of three Sirius-like systems, HD 2133, HD 114174, and CD-56 7708 and to combine this data with archive high resolution spectra of the primaries, TESS archive, and literature data. Methods. These WDs are easy targets for SPHERE and were used as spectrophotometric standards. We performed very accurate abundance analyses for the MS stars using methods considered for solar analogs. Whenever possible, WD parameters and orbits were obtained using Monte Carlo Markov chain methods. Results. We found brighter J and K magnitudes for HD 114174B than obtained previously and extended the photometry down to 0.95 μ m. Our new data indicate a higher temperature and then shorter cooling age (5.57 ± 0.02 Gyr) and larger mass (0.75 ± 0.03 M ⊙ ) for this WD than previously assumed. Together with the oldest age for the MS star connected to the use of the Gaia DR2 distance, this solved the discrepancy previously found with the age of the MS star. The two other WDs are less massive, indicating progenitors of ∼1.3 M ⊙ and 1.5 − 1.8 M ⊙ for HD 2133B and CD-56 7708B, respectively. In spite of the rather long periods, we were able to derive useful constraints on the orbit for HD 114174 and CD-56 7708. They are both seen close to edge-on, which is in agreement with the inclination of the MS stars that are obtained coupling the rotational periods, stellar radii, and the projected rotational velocity from spectroscopy. The composition of the MS stars agrees fairly well with expectations from pollution by the AGB progenitors of the WDs: HD 2133A has a small enrichment of n-capture elements, which is as expected for pollution by an AGB star with an initial mass 1.5 M ⊙ CD-56 7708A is a previously unrecognized mild Ba-star, which is also expected due to pollution by an AGB star with an initial mass in the range of 1.5 − 3.0 M ⊙ and HD 114174 has a very moderate excess of n-capture elements, which is in agreement with the expectation for a massive AGB star to have an initial mass 3.0 M ⊙ . Conclusions. On the other hand, none of these stars show the excesses of C that are expected to go along with those of n-capture elements. This might be related to the fact that these stars are at the edges of the mass range where we expect nucleosynthesis related to thermal pulses. More work, both theoretical and observational, is required to better understand this issue.
Publisher: Oxford University Press (OUP)
Date: 26-08-2017
Publisher: American Astronomical Society
Date: 29-08-2018
Publisher: EDP Sciences
Date: 12-2014
Publisher: Oxford University Press (OUP)
Date: 31-12-2015
Publisher: Oxford University Press (OUP)
Date: 26-09-2020
Abstract: Abundances of light elements in dwarf stars of different ages are important constraints for stellar yields, Galactic chemical evolution and exoplanet chemical composition studies. We have measured C and N abundances and 12C/13C ratios for a s le of 63 solar twins spanning a wide range in age, based on spectral synthesis of a comprehensive list of CH A-X and CN B-X features using HARPS spectra. The analysis of 55 thin disc solar twins confirms the dependences of [C/Fe] and [N/Fe] on [Fe/H]. [N/Fe] is investigated as a function of [Fe/H] and age for the first time for these stars. Our derived correlation [C/Fe]–age agrees with works for solar-type stars and solar twins, but the [N/Fe]–age correlation does not. The relations [C,N/Fe]–[Fe/H] and [C,N/Fe]–age for the solar twins lay under solar. 12C/13C is found correlated with [Fe/H] and seems to have decreased along the evolution of the local thin disc. Predictions from chemical evolution models for the solar vicinity corroborate the relations [C,N/Fe]–[Fe/H], 12C/13C–age, and [N/O]–[O/H], but do not for the 12C/13C–[Fe/H] and [C/O]–[O/H] relations. The N/O ratio in the Sun is placed at the high end of the homogeneous distribution of solar twins, which suggests uniformity in the N–O budget for the formation of icy planetesimals, watery superearths, and giant planets. C and N had different nucleosynthetic origins along the thin disc evolution, as shown by the relations of [C/N], [C/O], and [N/O] against [O/H] and age. [C/N] and [C/O] are particularly observed increasing in time for solar twins younger than the Sun.
Publisher: EDP Sciences
Date: 18-03-2016
Publisher: EDP Sciences
Date: 06-2013
Publisher: American Astronomical Society
Date: 26-05-2020
Publisher: Oxford University Press (OUP)
Date: 17-10-2018
Publisher: EDP Sciences
Date: 07-2019
DOI: 10.1051/0004-6361/201935306
Abstract: Context. The benchmark open cluster M 67 is known to have solar metallicity and an age similar to that of the Sun. It thus provides us with a great opportunity to study the properties of solar twins, as well as the evolution of Sun-like stars. Aims. Previous spectroscopic studies of M 67 reported possible subtle changes in stellar surface abundances throughout the stellar evolutionary phase, namely the effect of atomic diffusion. In this study we attempt to confirm and quantify more precisely the effect of atomic diffusion, and to explore the level of chemical (in)homogeneity in M 67. Methods. We presented a strictly line-by-line differential chemical abundance analysis of two groups of stars in M 67: three turn-off stars and three subgiants. Stellar atmospheric parameters and elemental abundances were obtained with very high precision using the Keck/HIRES spectra. Results. The subgiants in our s le show negligible abundance variations (≤0.02 dex), which implies that M 67 was born chemically homogeneous. We note that there is a significant abundance difference (~0.1–0.2 dex) between subgiants and turn-off stars, which can be interpreted as the signature of atomic diffusion. Qualitatively stellar models with diffusion agree with the observed abundance results. Some turn-off stars do not follow the general pattern, which suggests that in some cases diffusion can be inhibited, or they might have undergone some sort of mixing event related to planets. Conclusions. Our results pose additional challenges for chemical tagging when using turn-off stars. In particular, the effects of atomic diffusion, which could be as large as 0.1–0.2 dex, must be taken into account in order for chemical tagging to be successfully applied.
Publisher: EDP Sciences
Date: 06-04-2016
Publisher: Oxford University Press (OUP)
Date: 15-08-2016
Publisher: Springer Science and Business Media LLC
Date: 30-08-2021
Publisher: EDP Sciences
Date: 03-2010
Publisher: EDP Sciences
Date: 03-2010
Publisher: EDP Sciences
Date: 11-2010
Publisher: EDP Sciences
Date: 06-2010
Publisher: EDP Sciences
Date: 08-2016
Publisher: EDP Sciences
Date: 06-2018
DOI: 10.1051/0004-6361/201832701
Abstract: Differences in the elemental abundances of planet-hosting stars in binary systems can give important clues and constraints about planet formation and evolution. In this study we performed a high-precision, differential elemental abundance analysis of a wide binary system, HD 80606 / 80607 , based on high-resolution spectra with high signal-to-noise ratio obtained with Keck/HIRES. HD 80606 is known to host a giant planet with the mass of four Jupiters, but no planet has been detected around HD 80607 so far. We determined stellar parameters as well as abundances for 23 elements for these two stars with extremely high precision. Our main results are that (i) we confirmed that the two components share very similar chemical compositions, but HD 80606 is marginally more metal-rich than HD 80607 , with an average difference of +0.013 ± 0.002 dex ( σ = 0.009 dex) and (ii) there is no obvious trend between abundance differences and condensation temperature. Assuming that this binary formed from material with the same chemical composition, it is difficult to understand how giant planet formation could produce the present-day photospheric abundances of the elements we measure. We cannot exclude the possibility that HD 80606 might have accreted about 2.5 to 5 M Earth material onto its surface, possibly from a planet destabilised by the known highly eccentric giant.
Publisher: Cambridge University Press (CUP)
Date: 11-2009
DOI: 10.1017/S174392131000414X
Abstract: We present Li abundances for 73 stars in the metallicity range −3.5 [Fe/H] −1.0 using improved IRFM temperatures (Casagrande et al . 2010) with precise E ( B-V ) values obtained mostly from interstellar NaI D lines, and high-quality equivalent widths (σ EW ~ 3%). At all metallicities we uncover a fine-structure in the Li abundances of Spite plateau stars, which we trace to Li depletion that depends on both metallicity and mass. Models including atomic diffusion and turbulent mixing seem to reproduce the observed Li depletion assuming a primordial Li abundance A Li = 2.64 dex (MARCS models) or 2.72 (Kurucz overshooting models), in good agreement with current predictions ( A Li = 2.72) from standard BBN. We are currently expanding our s le to have a better coverage of different evolutionary stages at the high and low metallicity ends, in order to verify our findings.
Publisher: EDP Sciences
Date: 13-12-2010
Publisher: EDP Sciences
Date: 09-2017
Publisher: American Astronomical Society
Date: 18-05-2012
Publisher: EDP Sciences
Date: 07-2019
DOI: 10.1051/0004-6361/201935156
Abstract: Context. Older models of Galactic chemical evolution (GCE) predict [K/Fe] ratios as much as 1 dex lower than those inferred from stellar observations. Abundances of potassium are mainly based on analyses of the 7698 Å resonance line, and the discrepancy between GCE models and observations is in part caused by the assumption of local thermodynamic equilibrium (LTE) in spectroscopic analyses. Aims. We study the statistical equilibrium of K I , focusing on the non-LTE effects on the 7698 Å line. We aim to determine how non-LTE abundances of potassium can improve the analysis of its chemical evolution, and help to constrain the yields of GCE models. Methods. We construct a new model K I atom that employs the most up-to-date atomic data. In particular, we calculate and present inelastic e+K collisional excitation cross-sections from the convergent close-coupling (CCC) and the B -Spline R -matrix (BSR) methods, and H+K collisions from the two-electron model (LCAO). We constructed a fine, extended grid of non-LTE abundance corrections based on 1D MARCS models that span 4000 T eff ∕K 8000, 0.50 log g 5.00, − 5.00 [Fe/H] + 0.50, and applied the corrections to potassium abundances extracted from the literature. Results. In concordance with previous studies, we find severe non-LTE effects in the 7698 Å line. The line is stronger in non-LTE and the abundance corrections can reach approximately − 0.7 dex for solar-metallicity stars such as Procyon. We determine potassium abundances in six benchmark stars, and obtain consistent results from different optical lines. We explore the effects of atmospheric inhomogeneity by computing for the first time a full 3D non-LTE stellar spectrum of K I lines for a test star. We find that 3D modeling is necessary to predict a correct shape of the resonance 7698 Å line, but the line strength is similar to that found in 1D non-LTE. Conclusions. Our non-LTE abundance corrections reduce the scatter and change the cosmic trends of literature potassium abundances. In the regime [Fe/H] ≲−1.0 the non-LTE abundances show a good agreement with the GCE model with yields from rotating massive stars. The reduced scatter of the non-LTE corrected abundances of a s le of solar twins shows that line-by-line differential analysis techniques cannot fully compensate for systematic LTE modelling errors the scatter introduced by such errors introduces a spurious dispersion to K evolution.
Start Date: 2012
End Date: 12-2015
Amount: $355,000.00
Funder: Australian Research Council
View Funded Activity