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Jofre E.,Observatorio Astronomico de Cordoba OAC | Jofre E.,CONICET | Petrucci R.,Institute Astronomia Y Fisica del Espacio IAFE | Petrucci R.,CONICET | And 10 more authors.
Astronomy and Astrophysics | Year: 2015

Aims. We present fundamental stellar parameters, chemical abundances, and rotational velocities for a sample of 86 evolved stars with planets (56 giants; 30 subgiants), and for a control sample of 137 stars (101 giants; 36 subgiants) without planets. The analysis was based on both high signal-to-noise and resolution echelle spectra. The main goals of this work are i) to investigate chemical differences between evolved stars that host planets and those of the control sample without planets; ii) to explore potential differences between the properties of the planets around giants and subgiants; and iii) to search for possible correlations between these properties and the chemical abundances of their host stars. Implications for the scenarios of planet formation and evolution are also discussed. Methods. The fundamental stellar parameters (Teff, log g, [Fe/H], ξt) were computed homogeneously using the FUNDPAR code. The chemical abundances of 14 elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Zn, and Ba) were obtained using the MOOG code. Rotational velocities were derived from the full width at half maximum of iron isolated lines. Results. In agreement with previous studies, we find that subgiants with planets are, on average, more metal-rich than subgiants without planets by ∼0.16 dex. The [Fe/H] distribution of giants with planets is centered at slightly subsolar metallicities and there is no metallicity enhancement relative to the [Fe/H] distribution of giants without planets. Furthermore, contrary to recent results, we do not find any clear di fference between the metallicity distributions of stars with and without planets for giants with M∗ > 1. 5 M⊙. With regard to the other chemical elements, the analysis of the [X/Fe] distributions shows differences between giants with and without planets for some elements, particularly V, Co, and Ba. Subgiants with and without planets exhibit similar behavior for most of the elements. On the other hand, we find no evidence of rapid rotation among the giants with planets or among the giants without planets. Finally, analyzing the planet properties, some interesting trends might be emerging: i) multi-planet systems around evolved stars show a slight metallicity enhancement compared with single-planet systems; ii) planets with a ≲ 0.5 AU orbit subgiants with [Fe/H] > 0 and giants hosting planets with a ≲ 1 AU have [Fe/H] < 0; iii) higher-mass planets tend to orbit more metal-poor giants with M∗ ≤ 1.5 M⊙, whereas planets around subgiants seem to follow the planet-mass metallicity trend observed on dwarf hosts; iv) [X/Fe] ratios for Na, Si, and Al seem to increase with the mass of planets around giants; v) planets orbiting giants show lower orbital eccentricities than those orbiting subgiants and dwarfs, suggesting a more efficient tidal circularization or the result of the engulfment of close-in planets with larger eccentricities. © ESO 2015.

Petrucci R.,Institute Astronomia y Fisica Del Espacio IAFE | Jofre E.,Observatorio Astronomico de Cordoba OAC | Schwartz M.,Institute Astronomia y Fisica Del Espacio IAFE | Buccino A.,Institute Astronomia y Fisica Del Espacio IAFE | Mauas P.,Institute Astronomia y Fisica Del Espacio IAFE
Proceedings of the International Astronomical Union | Year: 2011

In this contribution we present 4 complete planetary transits observed with the 40-cm telescope "Horacio Ghielmetti" located in San Juan(Argentina). These objects correspond to a continuous photometric monitoring program of Southern planet host-stars that we are carrying out since mid-2011. The goal of this project is to detect additional planetary mass objects around stars with known transiting-planets through Transit Timing Variations (TTVs). For all 4 transits the depth and duration are in good agreement with the values published in the discovery papers. © 2012 International Astronomical Union.

Saffe C.,CONICET | Saffe C.,National University of San Juan | Flores M.,CONICET | Jaque Arancibia M.,CONICET | And 4 more authors.
Astronomy and Astrophysics | Year: 2016

Context. Detailed abundance studies have reported different trends between samples of stars with and without planets, possibly related to the planet formation process. Whether these differences are still present between samples of stars with and without debris disk is still unclear. Aims. We explore condensation temperature Tc trends in the unique binary system ζ1 Ret -ζ2 Ret to determine whether there is a depletion of refractories that could be related to the planet formation process. The star ζ2 Ret hosts a debris disk which was detected by an IR excess and confirmed by direct imaging and numerical simulations, while ζ1 Ret does not present IR excess or planets. These characteristics convert ζ2 Ret in a remarkable system where their binary nature together with the strong similarity of both components allow us, for the first time, to achieve the highest possible abundance precision in this system. Methods. We carried out a high-precision abundance determination in both components of the binary system via a line-by-line, strictly differential approach. First we used the Sun as a reference and then we used ζ2 Ret. The stellar parameters Teff, log g, [Fe/H], and vturb were determined by imposing differential ionization and excitation equilibrium of Fe I and Fe II lines, with an updated version of the program FUNDPAR, together with plane-parallel local thermodynamic equilibrium ATLAS9 model atmospheres and the MOOG code. We then derived detailed abundances of 24 different species with equivalent widths and spectral synthesis with the MOOG program. The chemical patterns were compared with a recently calculated solar-twins Tc trend, and then mutually between both stars of the binary system. The rocky mass of depleted refractory material was estimated according to recent data. Results. The star ζ1 Ret is found to be slightly more metal rich than ζ2 Ret by ∼0.02 dex. In the differential calculation of ζ1 Ret using ζ2 Ret as reference, the abundances of the refractory elements are higher than the volatile elements, and the trend of the refractory elements with Tc shows a positive slope. These results together show a lack of refractory elements in ζ2 Ret (a debris-disk host) relative to ζ1 Ret. The Tc trend would be in agreement with the proposed signature of planet formation rather than possible galactic chemical evolution or age effects, which are largely diminished here. Then, following the recent interpretation, we propose a scenario in which the refractory elements depleted in ζ2 Ret are possibly locked up in the rocky material that orbits this star and produce the debris disk observed around this object. We estimated a lower limit of Mrock ∼ 3 M⊕ for the rocky mass of depleted material, which is compatible with rough estimations of 3-50 M⊕ of a debris disk mass around a solar-type star. © ESO, 2016.

Jofre E.,Observatorio Astronomico de Cordoba OAC | Jofre E.,CONICET | Petrucci R.,Observatorio Astronomico de Cordoba OAC | Petrucci R.,CONICET | And 3 more authors.
Astronomy and Astrophysics | Year: 2015

We report the discovery of a new exceptional young lithium-rich giant, KIC 9821622, in the Kepler field that exhibits an unusually large enhancement of α, Fe-peak, and r-process elements. From high-resolution spectra obtained with GRACES at Gemini North, we derived fundamental parameters and detailed chemical abundances of 23 elements from equivalent widths and synthesis analysis. By combining atmospheric stellar parameters with available asteroseismic data, we obtained the stellar mass, radius, and age. The data analysis reveals that KIC 9821622 is a Li-rich (A(Li)NLTE = 1.80 ± 0.2) intermediate-mass giant star (M = 1.64 M⊙) located at the red giant branch near the luminosity bump. We find unexpectedly elevated abundances of Fe-peak and r-process elements. In addition, as previously reported, we find that this is a young star (2.37 Gyr) with unusually high abundances of α-elements ([α/Fe] = 0.31). The evolutionary status of KIC 9821622 suggests that its Li-rich nature is the result of internal fresh Li that is synthesized through the Cameron-Fowler mechanism near the luminosity bump. However, its peculiar enhancement of α, Fe-peak, and r-process elements opens the possibility of external contamination by material enriched by a supernova explosion. Although it is less likely, planet accretion cannot be ruled out. © 2015 ESO.

Garcia L.,Observatorio Astronomico de Cordoba OAC | Gomez M.,Observatorio Astronomico de Cordoba OAC
Revista Mexicana de Astronomia y Astrofisica | Year: 2015

We report optical aperture polarimetry for 34 southern hemisphere main-sequence stars with debris disks, in addition to 54 stars without evidence of disk. These sets of stars are combined with another set of 109 stars from the northern hemisphere, obtained from the literature, to build two samples of 51 and 97 solar-type stars with and without debris disks. The distributions of polarization values for the samples with and without disks show no significant statistical difference, within the precision of our observations. However, we identify a sub-sample of 9 stars (d ≲ 50 pc) with disks that have polarization levels above the median for the sample with disk, and that are not appropriately reproduced by Serkowski's interstellar law. These stars are candidates to have intrinsic polarization. In this case the debris disks in these stars may be populated by small dust with sizes of ≈ 0.1μm. © Copyright 2015: Instituto de Astronomía, Universidad Nacional Autónoma de México.

Garcia L.,Observatorio Astronomico de Cordoba OAC | Gomez M.,Observatorio Astronomico de Cordoba OAC
Revista Mexicana de Astronomia y Astrofisica | Year: 2016

Infrared space observatories such as Spitzer and Herschel have allowed the detection of likely analogs to the Kuiper Belt in single as well as binary systems. The aim of this work is to characterize debris disks in single and binary stars and to identify features shared by the disks in both types of systems, as well as possible differences. We compiled a sample of 25 single and 14 binary stars (ages > 100 Myr) with flux measurements at λ> 100m and evidence of infrared excesses attributed to the presence of debris disks. Then, we constructed and modeled the observed spectral energy distributions (SEDs), and compared the parameters of the disks of both samples. Both types of disks are relatively free of dust in the inner region (<3-5 AU) and extend beyond 100 AU. No significant differences in the mass and dust size distributions of both samples are found.

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