413 research outputs found

    Exoplanets: Gaia and the importance of ground based spectroscopy follow-up

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    The search for extrasolar planets has developed rapidly and, today, more than 1700 planets have been found orbiting stars. Thanks to Gaia, we will collect high-accuracy astrometric orbits of thousands of new low-mass celestial objects, such as extra-solar planets and brown dwarfs. These measurements in combination with spectroscopy and with present day and future extrasolar planet search programs (like HARPS, ESPRESSO) will have a crucial contribution to several aspects of planetary astrophysics (formation theories, dynamical evolution, etc.). Moreover, Gaia will have a strong contribution on the stellar chemical and kinematic characterisation studies. In this paper we present a short overview of the importance of Gaia in the context of exoplanet research. As preparatory work for Gaia, we will then present a study where we derived stellar parameters for a sample of field giant stars

    Revisiting the correlation between stellar activity and planetary surface gravity

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    Aims: We re-evaluate the correlation between planetary surface gravity and stellar host activity as measured by the index log(RHKÔÇ▓R'_{HK}). This correlation, previously identified by Hartman (2010), is now analyzed in light of an extended measurements dataset, roughly 3 times larger than the original one. Methods: We calculated the Spearman's rank correlation coefficient between the two quantities and its associated p-value. The correlation coefficient was calculated for both the full dataset and the star-planet pairs that follow the conditions proposed by Hartman (2010). In order to do so, we considered effective temperatures both as collected from the literature and from the SWEET-Cat catalog, which provides a more homogeneous and accurate effective temperature determination. Results: The analysis delivers significant correlation coefficients, but with a lower value than those obtained by Hartman (2010). Yet, the two datasets are compatible, and we show that a correlation coefficient as large as previously published can arise naturally from a small-number statistics analysis of the current dataset. The correlation is recovered for star-planet pairs selected using the different conditions proposed by Hartman (2010). Remarkably, the usage of SWEET-Cat temperatures leads to larger correlation coefficient values. We highlight and discuss the role of the correlation betwen different parameters such as effective temperature and activity index. Several additional effects on top of those discussed previously were considered, but none fully explains the detected correlation. In light of the complex issue discussed here, we encourage the different follow-up teams to publish their activity index values in the form of log(RHKÔÇ▓R'_{HK}) index so that a comparison across stars and instruments can be pursued.Comment: 11 pages, 3 figures, accepted for publication in A&

    ARES v2 - new features and improved performance

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    Aims: We present a new upgraded version of ARES. The new version includes a series of interesting new features such as automatic radial velocity correction, a fully automatic continuum determination, and an estimation of the errors for the equivalent widths. Methods: The automatic correction of the radial velocity is achieved with a simple cross-correlation function, and the automatic continuum determination, as well as the estimation of the errors, relies on a new approach to evaluating the spectral noise at the continuum level. Results: ARES v2 is totally compatible with its predecessor. We show that the fully automatic continuum determination is consistent with the previous methods applied for this task. It also presents a significant improvement on its performance thanks to the implementation of a parallel computation using the OpenMP library.Comment: 4 pages, 2 Figures; accepted in A&A; ARES Webpage: www.astro.up.pt/~sousasag/are

    Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program II: Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu

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    To understand the formation and evolution of the different stellar populations within our Galaxy it is essential to combine detailed kinematical and chemical information for large samples of stars. We derive chemical abundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu for a large sample of more than 1000 FGK dwarf stars with high-resolution (RÔł╝R \sim\,115000) and high-quality spectra from the HARPS-GTO program. The abundances are derived by a standard Local Thermodinamyc Equilibrium (LTE) analysis using measured Equivalent Widths (EWs) injected to the code MOOG and a grid of Kurucz ATLAS9 atmospheres. We find that thick disk stars are chemically disjunct for Zn and Eu and also show on average higher Zr but lower Ba and Y when compared to the thin disk stars. We also discovered that the previously identified high-╬▒\alpha metal-rich population is also enhanced in Cu, Zn, Nd and Eu with respect to the thin disk but presents Ba and Y abundances lower on average, following the trend of thick disk stars towards higher metallities and further supporting the different chemical composition of this population. The ratio of heavy-s to light-s elements of thin disk stars presents the expected behaviour (increasing towards lower metallicities) and can be explained by a major contribution of low-mass AGB stars for s-process production at disk metallicities. However, the opposite trend found for thick disk stars suggests that intermediate-mass AGB stars played an important role in the enrichment of the gas from where these stars formed. Previous works in the literature also point to a possible primary production of light-s elements at low metallicities to explain this trend. Finally, we also find an enhancement of light-s elements in the thin disk at super solar metallicities which could be caused by the contribution of metal-rich AGB stars. (short version)Comment: 20 pages, 19 figures, accepted by A&

    Searching for solar siblings among the HARPS data

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    The search for the solar siblings has been particularly fruitful in the last few years. Until now, there are four plausible candidates pointed out in the literature: HIP21158, HIP87382, HIP47399, and HIP92831. In this study we conduct a search for solar siblings among the HARPS high-resolution FGK dwarfs sample, which includes precise chemical abundances and kinematics for 1111 stars. Using a new approach based on chemical abundance trends with the condensation temperature, kinematics, and ages we found one (additional) potential solar sibling candidate: HIP97507.Comment: 4 pages, 2 figures, 1 table. Accepted in A&

    The impact of bars on the radial distribution of supernovae in disc galaxies

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    We present an analysis of the impact of bars on the radial distributions of the different types of supernovae (SNe) in the stellar discs of host galaxies with various morphologies. We find that in Sa-Sbc galaxies, the radial distribution of core-collapse (CC) SNe in barred hosts is inconsistent with that in unbarred ones, while the distributions of SNe Ia are not significantly different. At the same time, the radial distributions of both types of SNe in Sc-Sm galaxies are not affected by bars. We propose that the additional mechanism shaping the distributions of Type Ia and CC SNe can be explained within the framework of substantial suppression of massive star formation in the radial range swept by strong bars, particularly in early-type spirals. The radial distribution of CC SNe in unbarred Sa-Sbc galaxies is more centrally peaked and inconsistent with that in unbarred Sc-Sm hosts, while the distribution of SNe Ia in unbarred galaxies is not affected by host morphology. These results can be explained by the distinct distributions of massive stars in the discs of early-and late-type spirals.Comment: 3 pages, 1 figure. This is a brief summary of arXiv:1511.08896, written for a short contribution in the EWASS-2016 Symposium 16 "Frontiers of massive-star evolution and core-collapse supernovae

    Supernovae and their host galaxies - V. The vertical distribution of supernovae in disc galaxies

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    We present an analysis of the height distributions of the different types of supernovae (SNe) from the plane of their host galaxies. We use a well-defined sample of 102 nearby SNe appeared inside high-inclined (i > 85 deg), morphologically non-disturbed S0-Sd host galaxies from the Sloan Digital Sky Survey. For the first time, we show that in all the subsamples of spirals, the vertical distribution of core-collapse (CC) SNe is about twice closer to the plane of host disc than the distribution of SNe Ia. In Sb-Sc hosts, the exponential scale height of CC SNe is consistent with those of the younger stellar population in the Milky Way (MW) thin disc, while the scale height of SNe Ia is consistent with those of the old population in the MW thick disc. We show that the ratio of scale lengths to scale heights of the distribution of CC SNe is consistent with those of the resolved young stars with ages from ~ 10 Myr up to ~ 100 Myr in nearby edge-on galaxies and the unresolved stellar population of extragalactic thin discs. The corresponding ratio for SNe Ia is consistent with the same ratios of the two populations of resolved stars with ages from a few 100 Myr up to a few Gyr and from a few Gyr up to ~ 10 Gyr, as well as with the unresolved population of the thick disc. These results can be explained considering the age-scale height relation of the distribution of stellar population and the mean age difference between Type Ia and CC SNe progenitors.Comment: 11 pages, 6 figures, 6 tables, accepted for publication in MNRA

    CNO behaviour in planet-harbouring stars. II. Carbon abundances in stars with and without planets using the CH band

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    Context. Carbon, oxygen and nitrogen (CNO) are key elements in stellar formation and evolution, and their abundances should also have a significant impact on planetary formation and evolution. Aims. We present a detailed spectroscopic analysis of 1110 solar-type stars, 143 of which are known to have planetary companions. We have determined the carbon abundances of these stars and investigate a possible connection between C and the presence of planetary companions. Methods. We used the HARPS spectrograph to obtain high-resolution optical spectra of our targets. Spectral synthesis of the CH band at 4300\AA was performed with the spectral synthesis codes MOOG and FITTING. Results. We have studied carbon in several reliable spectral windows and have obtained abundances and distributions that show that planet host stars are carbon rich when compared to single stars, a signature caused by the known metal-rich nature of stars with planets. We find no different behaviour when separating the stars by the mass of the planetary companion. Conclusions. We conclude that reliable carbon abundances can be derived for solar-type stars from the CH band at 4300\AA. We confirm two different slope trends for [C/Fe] with [Fe/H] because the behaviour is opposite for stars above and below solar values. We observe a flat distribution of the [C/Fe] ratio for all planetary masses, a finding that apparently excludes any clear connection between the [C/Fe] abundance ratio and planetary mass.Comment: 10 pages, 10 figures. Accepted to A&
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