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129 results on '"Do Nascimento, J. D."'

2. Seismic and spectroscopic analysis of 9 bright red giants observed by Kepler

Author

Coelho, H R, primary, Miglio, A, additional, Morel, T, additional, Lagarde, N, additional, Bossini, D, additional, Chaplin, W J, additional, Degl’Innocenti, S, additional, Dell’Omodarme, M, additional, Garcia, R A, additional, Handberg, R, additional, Hekker, S, additional, Huber, D, additional, Lund, M N, additional, Mathur, S, additional, Prada Moroni, P G, additional, Mosser, B, additional, Serenelli, A, additional, Rainer, M, additional, do Nascimento, J D, additional, Poretti, E, additional, Mathias, P, additional, Valle, G, additional, Dal Tio, P, additional, and Duarte, T, additional

Published
2023
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3. A Hale-like Cycle in the Solar Twin 18 Scorpii

Author

do Nascimento, J.-D., primary, Barnes, S. A., additional, Saar, S. H., additional, de Mello, G. F. Porto, additional, Hall, J. C., additional, Anthony, F., additional, de Almeida, L., additional, Velloso, E. N., additional, da Costa, J. S., additional, Petit, P., additional, Strugarek, A., additional, Wargelin, B. J., additional, Castro, M., additional, Strassmeier, K. G., additional, and Brun, A. S., additional

Published
2023
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5. Stellar rotations and the disentanglement of the Galactic thin and thick discs.

Author

da Silva, M P, Alves-Brito, A, and do Nascimento, J D

Subjects
STELLAR rotation, DWARF stars, LOW mass stars, STELLAR populations, STARS, GALAXY formation, AGE of stars
Abstract

The kinematics, mean α-elements, and ages of the stars reveal two distinct disc populations observed in the Solar neighbourhood. Although several studies have been carried out to characterize abundances of chemical elements and kinematic identifications in these populations, there are few studies that dealt with the analysis of stellar rotation and characteristics of populations focused on low-mass stars of the F and G types. In this work, we propose a new approach to classify stellar populations from the thin and thick disc for F and G dwarf stars by relating chemical abundance and rotation (v  sin  i) of these stars in the rotational–chemical–plane (v  sin  i –[α/Fe]–[Fe/H] plot). Our results show that the two rotational-chemical sequences disentangled, high- and low-[α/Fe] components, present properties (α-enhanced, ages, kinematics, space velocity gradients, local density ratio) closely linked to the stars of the chemically and kinematically defined as thin and thick disc components. This study has an impact on calibrations that relate ages to rotation (gyro-chronology) as well as age to chemical abundances (chemochronology), as well as sheds light on the understanding of the processes of Galactic disc formation. [ABSTRACT FROM AUTHOR]

Published
2024
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7. Far beyond the sun: II. Probing the stellar magnetism of the young Sun ι Horologii from the photosphere to its corona

Author

Amazo-Gómez, E M, primary, Alvarado-Gómez, J D, additional, Poppenhaeger, K, additional, Hussain, G A J, additional, Wood, B E, additional, Drake, J J, additional, do Nascimento, J D, additional, Anthony, F, additional, Sanz-Forcada, J, additional, Stelzer, B, additional, Del Sordo, F, additional, Damasso, M, additional, Redfield, S, additional, Donati, J F, additional, König, P C, additional, Hébrard, G, additional, and Miles-Páez, P A, additional

Published
2023
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8. Seismic and spectroscopic analysis of nine bright red giants observed by Kepler.

Author

Coelho, H R, Miglio, A, Morel, T, Lagarde, N, Bossini, D, Chaplin, W J, Degl'Innocenti, S, Dell'Omodarme, M, Garcia, R A, Handberg, R, Hekker, S, Huber, D, Lund, M N, Mathur, S, Prada Moroni, P G, Mosser, B, Serenelli, A, Rainer, M, do Nascimento, J D, and Poretti, E

Subjects
RED giants, ASTRONOMICAL photometry, PARALLAX, CARBON isotopes, SPACE telescopes, DATA release
Abstract

Photometric time series gathered by space telescopes such as CoRoT and Kepler allow to detect solar-like oscillations in red giant stars and to measure their global seismic constraints, which can be used to infer global stellar properties (e.g. masses, radii, and evolutionary states). Combining such precise constraints with photospheric abundances provides a means of testing mixing processes that occur inside red-giant stars. In this work, we conduct a detailed spectroscopic and seismic analysis of nine nearby (d < 200 pc) red giant stars observed by Kepler. Both seismic constraints and grid-based modelling approaches are used to determine precise fundamental parameters for those evolved stars. We compare distances and radii derived from Gaia Data Release 3 parallaxes with those inferred by a combination of seismic, spectroscopic, and photometric constraints. We find no deviations within errors bars, however the small sample size and the associated uncertainties are a limiting factor for such comparison. We use the period spacing of mixed modes to distinguish between ascending red-giants and red clump stars. Based on the evolutionary status, we apply corrections to the values of Δν for some stars, resulting in a slight improvement to the agreement between seismic and photometric distances. Finally, we couple constraints on detailed chemical abundances with the inferred masses, radii, and evolutionary states. Our results corroborate previous studies that show that observed abundances of lithium and carbon isotopic ratio are in contrast with predictions from standard models, giving robust evidence for the occurrence of additional mixing during the red-giant phase. [ABSTRACT FROM AUTHOR]

Published
2024
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10. Far beyond the Sun − II. Probing the stellar magnetism of the young Sun ι Horologii from the photosphere to its corona.

Author

Amazo-Gómez, E M, Alvarado-Gómez, J D, Poppenhäger, K, Hussain, G A J, Wood, B E, Drake, J J, do Nascimento, J-D, Anthony, F, Sanz-Forcada, J, Stelzer, B, Del Sordo, F, Damasso, M, Redfield, S, Donati, J F, König, P C, Hébrard, G, and Miles-Páez, P A

Subjects
STELLAR activity, STELLAR rotation, STELLAR magnetic fields, SPACE telescopes, LIGHT curves, SOLAR flares, SOLAR atmosphere, POWER spectra
Abstract

A comprehensive multiwavelength campaign has been carried out to probe stellar activity and variability in the young Sun-like star ι-Horologii. We present the results from long-term spectropolarimetric monitoring of the system by using the ultra-stable spectropolarimeter/velocimeter HARPS at the ESO 3.6-m telescope. Additionally, we included high-precision photometry from the NASA Transiting Exoplanet Survey Satellite (TESS) and observations in the far- and near-ultraviolet spectral regions using the STIS instrument on the NASA/ESA Hubble Space Telescope (HST). The high-quality data set allows a robust characterization of the star's rotation period, as well as a probe of the variability using a range of spectroscopic and photometric activity proxies. By analysing the gradient of the power spectra (GPS) in the TESS light curves, we constrained the faculae-to-spot driver ratio (⁠|$\rm S_{fac}/S_{spot}$|⁠) to 0.510 ± 0.023, which indicates that the stellar surface is spot dominated during the time of the observations. We compared the photospheric activity properties derived from the GPS method with a magnetic field map of the star derived using Zeeman–Doppler imaging (ZDI) from simultaneous spectropolarimetric data for the first time. Different stellar activity proxies enable a more complete interpretation of the observed variability. For example, we observed enhanced emission in the HST transition line diagnostics C  iv and C  iii , suggesting a flaring event. From the analysis of TESS data acquired simultaneously with the HST data, we investigate the photometric variability at the precise moment that the emission increased and derive correlations between different observables, probing the star from its photosphere to its corona. [ABSTRACT FROM AUTHOR]

Published
2023
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12. TOI-1452 b: SPIRou and TESS Reveal a Super-Earth in a Temperate Orbit Transiting an M4 Dwarf

Author

Cadieux, Charles, primary, Doyon, René, additional, Plotnykov, Mykhaylo, additional, Hébrard, Guillaume, additional, Jahandar, Farbod, additional, Artigau, Étienne, additional, Valencia, Diana, additional, Cook, Neil J., additional, Martioli, Eder, additional, Vandal, Thomas, additional, Donati, Jean-François, additional, Cloutier, Ryan, additional, Narita, Norio, additional, Fukui, Akihiko, additional, Hirano, Teruyuki, additional, Bouchy, François, additional, Cowan, Nicolas B., additional, Gonzales, Erica J., additional, Ciardi, David R., additional, Stassun, Keivan G., additional, Arnold, Luc, additional, Benneke, Björn, additional, Boisse, Isabelle, additional, Bonfils, Xavier, additional, Carmona, Andrés, additional, Cortés-Zuleta, Pía, additional, Delfosse, Xavier, additional, Forveille, Thierry, additional, Fouqué, Pascal, additional, da Silva, João Gomes, additional, Jenkins, Jon M., additional, Kiefer, Flavien, additional, Kóspál, Ágnes, additional, Lafrenière, David, additional, Martins, Jorge H. C., additional, Moutou, Claire, additional, do Nascimento, J.-D., additional, Ould-Elhkim, Merwan, additional, Pelletier, Stefan, additional, Twicken, Joseph D., additional, Bouma, Luke G., additional, Cartwright, Scott, additional, Darveau-Bernier, Antoine, additional, Grankin, Konstantin, additional, Ikoma, Masahiro, additional, Kagetani, Taiki, additional, Kawauchi, Kiyoe, additional, Kodama, Takanori, additional, Kotani, Takayuki, additional, Latham, David W., additional, Menou, Kristen, additional, Ricker, George, additional, Seager, Sara, additional, Tamura, Motohide, additional, Vanderspek, Roland, additional, and Watanabe, Noriharu, additional

Published
2022
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13. TOI-1759 b: A transiting sub-Neptune around a low mass star characterized with SPIRou and TESS

Author

Martioli, E., primary, Hébrard, G., additional, Fouqué, P., additional, Artigau, É., additional, Donati, J.-F., additional, Cadieux, C., additional, Bellotti, S., additional, Lecavelier des Etangs, A., additional, Doyon, R., additional, do Nascimento, J.-D., additional, Arnold, L., additional, Carmona, A., additional, Cook, N. J., additional, Cortes-Zuleta, P., additional, de Almeida, L., additional, Delfosse, X., additional, Folsom, C. P., additional, König, P.-C., additional, Moutou, C., additional, Ould-Elhkim, M., additional, Petit, P., additional, Stassun, K. G., additional, Vidotto, A. A., additional, Vandal, T., additional, Benneke, B., additional, Boisse, I., additional, Bonfils, X., additional, Boyd, P., additional, Brasseur, C., additional, Charbonneau, D., additional, Cloutier, R., additional, Collins, K., additional, Cristofari, P., additional, Crossfield, I., additional, Díaz, R. F., additional, Fausnaugh, M., additional, Figueira, P., additional, Forveille, T., additional, Furlan, E., additional, Girardin, E., additional, Gnilka, C. L., additional, Gomes da Silva, J., additional, Gu, P.-G., additional, Guerra, P., additional, Howell, S. B., additional, Hussain, G. A. J., additional, Jenkins, J. M., additional, Kiefer, F., additional, Latham, D. W., additional, Matson, R. A., additional, Matthews, E. C., additional, Morin, J., additional, Naves, R., additional, Ricker, G., additional, Seager, S., additional, Takami, M., additional, Twicken, J. D., additional, Vanderburg, A., additional, Vanderspek, R., additional, and Winn, J., additional

Published
2022
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14. Activity and Rotation of Nearby Field M Dwarfs in the TESS Southern Continuous Viewing Zone

Author

Newton, E.R., Agüeros, M.A., Machado, J.M., Anthony, F., Do Nascimento, J.-D., Wood, M.L., Núñez, A., Curtis, J.L., Rampalli, R., Mann, A.W., and Thao, P.C.

Abstract

The evolution of magnetism in late-type dwarfs remains murky, as we can only weakly predict levels of activity for M dwarfs of a given mass and age. We report results from our spectroscopic survey of M dwarfs in the Southern Continuous Viewing Zone (CVZ) of the Transiting Exoplanet Survey Satellite (TESS). As the TESS CVZs overlap with those of the James Webb Space Telescope, our targets constitute a legacy sample for studies of nearby M dwarfs. For 122 stars, we obtained at least one R ≈ 2000 optical spectrum with which we measure chromospheric Hα emission, a proxy for magnetic field strength. The fraction of active stars is consistent with what is expected for field M dwarfs; as in previous studies, we find that late-type M dwarfs remain active for longer than their early-type counterparts. While the TESS light curves for ≈20% of our targets show modulations consistent with rotation, TESS systematics are not well enough understood for confident measurements of rotation periods (P rot) longer than half the length of an observing sector. We report periods for 12 stars for which we measure P rot ≲ 15 days or find confirmation for the TESS-derived P rot in the literature. Our sample of 21 P rot, which includes periods from the literature, is consistent with our targets being spun-down field stars. Finally, we examine the Hα-to-bolometric luminosity distribution for our sample. Two stars are rotating fast enough to be magnetically saturated, but are not, hinting at the possibility that fast rotators may appear inactive in Hα.

Published
2022
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15. OGLE-2019-BLG-0033/MOA-2019-BLG-035

Author

Herald, A., Udalski, A., Bozza, V., Rota, P., Bond, I. A., Yee, J. C., Sajadian, S., Mróz, P., Poleski, R., Skowron, J., Szymański, M. K., Soszyński, I., Pietrukowicz, P., Kozłowski, S., Ulaczyk, K., Rybicki, K. A., Iwanek, P., Wrona, M., Gromadzki, M., Abe, F., Barry, R., Bennett, D. P., Bhattacharya, A., Fukui, A., Fujii, H., Hirao, Y., Itow, Y., Kirikawa, R., Kondo, I., Koshimoto, N., Matsubara, Y., Matsumoto, S., Miyazaki, S., Muraki, Y., Olmschenk, G., Ranc, C., Okamura, A., Rattenbury, N. J., Satoh, Y., Sumi, T., Suzuki, D., Silva, S. Ishitani, Toda, T., Tristram, P. J., Vandorou, A., Yama, H., Beichman, C. A., Bryden, G., Novati, S. Calchi, Carey, S., Gaudi, B. S., Gould, A., Henderson, C. B., Johnson, S., Shvartzvald, Y., Zhu, W., Dominik, M., Hundertmark, M., Jørgensen, U. G., Longa-Peña, P., Skottfelt, J., Tregloan-Reed, J., Bach-Møller, N., Burgdorf, M., D’Ago, G., Haikala, L., Hitchcock, J., Khalouei, E., Peixinho, N., Rahvar, S., Snodgrass, C., Southworth, J., Spyratos, P., Zang, W., Yang, H., Mao, S., Bachelet, E., Maoz, D., Street, R. A., Tsapras, Y., Christie, G. W., Cooper, T., de Almeida, L., do Nascimento, J.-D., Green, J., Han, C., Hennerley, S., Marmont, A., McCormick, J., Monard, L. A. G., Natusch, T., and Pogge, R.

Subjects
binaries: general, stars: low-mass, gravitational lensing: micro, brown dwarfs
Abstract

Context Brown dwarfs are transition objects between stars and planets that are still poorly understood, for which several competing mechanisms have been proposed to describe their formation. Mass measurements are generally difficult to carry out for isolated objects as well as for brown dwarfs orbiting low-mass stars, which are often too faint for a spectroscopic follow-up. \ud \ud Aims Microlensing provides an alternative tool for the discovery and investigation of such faint systems. Here, we present an analysis of the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035, which is caused by a binary system composed of a brown dwarf orbiting a red dwarf. \ud \ud Methods Thanks to extensive ground observations and the availability of space observations from Spitzer, it has been possible to obtain accurate estimates of all microlensing parameters, including the parallax, source radius, and orbital motion of the binary lens. \ud \ud Results Following an accurate modeling process, we found that the lens is composed of a red dwarf with a mass of M1 = 0.149 ± 0.010 M⊙ and a brown dwarf with a mass of M2 = 0.0463 ± 0.0031 M⊙at a projected separation of a⊥ = 0.585 au. The system has a peculiar velocity that is typical of old metal-poor populations in the thick disk. A percent-level precision in the mass measurement of brown dwarfs has been achieved only in a few microlensing events up to now, but will likely become more common in the future thanks to the Roman space telescope.

Published
2022

16. Estimating fundamental parameters of nearby M dwarfs from SPIRou spectra

Author

Cristofari, P I, primary, Donati, J-F, additional, Masseron, T, additional, Fouqué, P, additional, Moutou, C, additional, Delfosse, X, additional, Artigau, E, additional, Folsom, C P, additional, Carmona, A, additional, Gaidos, E, additional, do Nascimento, J-D, additional, Jahandar, F, additional, and Hébrard, G, additional

Published
2021
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17. Constraining stellar physics from red-giant stars in binaries – stellar rotation, mixing processes and stellar activity

Author

Beck P. G., Kallinger T., Pavlovski K., Palacios A., Tkachenko A., García R. A., Mathis S., Corsaro E., Johnston C., Mosser B., Ceillier T., do Nascimento J.-D., and Raskin G.

Subjects
Physics, QC1-999
Abstract

The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to an improved understanding of stellar structure and evolution - in particular for solar-like oscillators in this context. Binary stars are fascinating objects. Because they were formed together, binary systems provide a set of two stars with very well constrained parameters. Those can be used to study properties and physical processes, such as the stellar rotation, dynamics and rotational mixing of elements and allows us to learn from the differences we find between the two components. In this work, we discussed a detailed study of the binary system KIC 9163796, discovered through Kepler photometry. The ground-based follow-up spectroscopy showed that this system is a double-lined spectroscopic binary, with a mass ratio close to unity. However, the fundamental parameters of the components of this system as well as their lithium abundances differ substantially. Kepler photometry of this system allows to perform a detailed seismic analysis as well as to derive the orbital period and the surface rotation rate of the primary component of the system. Indications of the seismic signature of the secondary are found. The differing parameters are best explained with both components located in the early and the late phase of the first dredge up at the bottom of the red-giant branch. Observed lithium abundances in both components are in good agreement with prediction of stellar models including rotational mixing. By combining observations and theory, a comprehensive picture of the system can be drawn.

Published
2017
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27. Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Author

Beck, P. G., primary, Kallinger, T., additional, Pavlovski, K., additional, Palacios, A., additional, Tkachenko, A., additional, Mathis, S., additional, García, R. A., additional, Corsaro, E., additional, Johnston, C., additional, Mosser, B., additional, Ceillier, T., additional, do Nascimento, J.-D., additional, and Raskin, G., additional

Published
2018
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29. The energy budget of stellar magnetic fields

Author

See, V., Jardine, M., Vidotto, A. A., Donati, J.-F, Folsom, C. P., Boro Saikia, S., Bouvier, J., Fares, R., Gregory, S. G., Hussain, G., Jeffers, S. V., Marsden, S. C., Morin, J., Moutou, C., do Nascimento, J. D., Petit, P., Rosén, L., Waite, I. A., See, V., Jardine, M., Vidotto, A. A., Donati, J.-F, Folsom, C. P., Boro Saikia, S., Bouvier, J., Fares, R., Gregory, S. G., Hussain, G., Jeffers, S. V., Marsden, S. C., Morin, J., Moutou, C., do Nascimento, J. D., Petit, P., Rosén, L., and Waite, I. A.

Abstract

Spectropolarimetric observations have been used to map stellar magnetic fields, many of which display strong bands of azimuthal fields that are toroidal. A number of explanations have been proposed to explain how such fields might be generated though none are definitive. In this paper, we examine the toroidal fields of a sample of 55 stars with magnetic maps, with masses in the range 0.1-1.5 M⊙. We find that the energy contained in toroidal fields has a power-law dependence on the energy contained in poloidal fields. However the power index is not constant across our sample, with stars less and more massive than 0.5 M⊙ having power indices of 0.72±0.08 and 1.25±0.06, respectively. There is some evidence that these two power laws correspond to stars in the saturated and unsaturated regimes of the rotation-activity relation. Additionally, our sample shows that strong toroidal fields must be generated axisymmetrically. The latitudes at which these bands appear depend on the stellar rotation period with fast rotators displaying higher latitude bands than slow rotators. The results in this paper present new constraints for future dynamo studies

Published
2017

30. What can we Learn About Stellar Activity Cycles from ZDI?

Author

See, Victor, Jardine, M., Vidotto, A., Donati, J.-F., Boro Saikia, S., Bouvier, J., Fares, R., Folsom, C., Gregory, S., Hussain, G., Jeffers, S., Marsden, S., Morin, J., Moutou, C., do Nascimento, J. D., Petit, P., Waite, I., +BCool Collaboration, Feiden, Gregory, Fabbian, Damian, Simoniello, Rosaria, Collet, Remo, Criscuoli, Serena, Korhonen, Heidi, Krivova, Natalie, Oláh, Katalin, Shapiro, Alexander, Vidotto, Aline, Vitas, Nikola, Science & Technology Facilities Council, and University of St Andrews. School of Physics and Astronomy

Subjects
QC Physics, QB Astronomy, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, QC, QB
Abstract

It is known that activity cycles, similar to the 11 year cycle of the Sun, can exist on other stars. Previous work suggests that stars may lie on two branches in a cycle period vs rotation period diagram though there is no definitive explanation for why this should be the case.Fundamentally, activity cycles occur as a result of the underlying dynamo. Indeed, a great deal has been learnt about the Sun's activity cycle by studying how its magnetic field evolves over each activity cycle. In the same way, we should be able to learn about the activity cycles of other stars by studying their magnetic field properties. In this talk, I will present new insights into stellar activity cycles by analysing the magnetic maps of stars that are known to present activity cycles. I will show that stars along each of the branches appear to have different magnetic field topologies. Publisher PDF

Published
2016
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31. Lithium abundance and rotation of seismic solar analogues

Author

Beck, P. G., primary, do Nascimento, J.-D., additional, Duarte, T., additional, Salabert, D., additional, Tkachenko, A., additional, Mathis, S., additional, Mathur, S., additional, García, R. A., additional, Castro, M., additional, Pallé, P. L., additional, Egeland, R., additional, Montes, D., additional, Creevey, O., additional, Andersen, M. F., additional, Kamath, D., additional, and van Winckel, H., additional

Published
2017
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33. The solar wind in time – II. 3D stellar wind structure and radio emission.

Author

Ó Fionnagáin, D, Vidotto, A A, Petit, P, Folsom, C P, Jeffers, S V, Marsden, S C, Morin, J, do Nascimento, J-D, and the BCool Collaboration

Subjects
SOLAR wind, STELLAR winds, SOLAR activity, SOLAR radio emission, ELECTROMAGNETIC waves
Abstract

In this work, we simulate the evolution of the solar wind along its main-sequence lifetime and compute its thermal radio emission. To study the evolution of the solar wind, we use a sample of solar mass stars at different ages. All these stars have observationally reconstructed magnetic maps, which are incorporated in our 3D magnetohydrodynamic simulations of their winds. We show that angular-momentum loss and mass-loss rates decrease steadily on evolutionary time-scales, although they can vary in a magnetic cycle time-scale. Stellar winds are known to emit radiation in the form of thermal bremsstrahlung in the radio spectrum. To calculate the expected radio fluxes from these winds, we solve the radiative transfer equation numerically from first principles. We compute continuum spectra across the frequency range 100 MHz to 100 GHz and find maximum radio flux densities ranging from 0.05 to 2.2 |$\mu$| Jy. At a frequency of 1 GHz and a normalized distance of d  = 10 pc, the radio flux density follows 0.24 (Ω/Ω⊙)0.9 (d /[10pc])-2 |$\mu$| Jy, where Ω is the rotation rate. This means that the best candidates for stellar wind observations in the radio regime are faster rotators within distances of 10 pc, such as κ1 Ceti (0.73 |$\mu$| Jy) and χ1 Ori (2.2 |$\mu$| Jy). These flux predictions provide a guide to observing solar-type stars across the frequency range 0.1–100 GHz in the future using the next generation of radio telescopes, such as ngVLA and Square Kilometre Array. [ABSTRACT FROM AUTHOR]

Published
2019
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34. The connection between stellar activity cycles and magnetic field topology

Author

See, V., primary, Jardine, M., additional, Vidotto, A. A., additional, Donati, J.-F., additional, Boro Saikia, S., additional, Bouvier, J., additional, Fares, R., additional, Folsom, C. P., additional, Gregory, S. G., additional, Hussain, G., additional, Jeffers, S. V., additional, Marsden, S. C., additional, Morin, J., additional, Moutou, C., additional, do Nascimento, J. D., additional, Petit, P., additional, and Waite, I. A., additional

Published
2016
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36. The energy budget of stellar magnetic fields

Author

See, V., Jardine, M., Vidotto, A. A., Donati, J. -F, Folsom, C. P., Saikia, S. Boro, Bouvier, J., Fares, R., Gregory, S. G., Hussain, G., Jeffers, S. V., Marsden, S. C., Morin, J., Moutou, C., do Nascimento, J. D., Jr., Petit, P., Rosén, Lisa, Waite, I. A., See, V., Jardine, M., Vidotto, A. A., Donati, J. -F, Folsom, C. P., Saikia, S. Boro, Bouvier, J., Fares, R., Gregory, S. G., Hussain, G., Jeffers, S. V., Marsden, S. C., Morin, J., Moutou, C., do Nascimento, J. D., Jr., Petit, P., Rosén, Lisa, and Waite, I. A.

Abstract

Spectropolarimetric observations have been used to map stellar magnetic fields, many of which display strong bands of azimuthal fields that are toroidal. A number of explanations have been proposed to explain how such fields might be generated though none are definitive. In this paper, we examine the toroidal fields of a sample of 55 stars with magnetic maps, with masses in the range 0.1-1.5M(circle dot). We find that the energy contained in toroidal fields has a power-law dependence on the energy contained in poloidal fields. However the power index is not constant across our sample, with stars less and more massive than 0.5M(circle dot) having power indices of 0.72 +/- 0.08 and 1.25 +/- 0.06, respectively. There is some evidence that these two power laws correspond to stars in the saturated and unsaturated regimes of the rotation-activity relation. Additionally, our sample shows that strong toroidal fields must be generated axisymmetrically. The latitudes at which these bands appear depend on the stellar rotation period with fast rotators displaying higher latitude bands than slow rotators. The results in this paper present new constraints for future dynamo studies.

Published
2015
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37. INTERPLAY OF TIDAL EVOLUTION AND STELLAR WIND BRAKING IN THE ROTATION OF STARS HOSTING MASSIVE CLOSE-IN PLANETS

Author

Ferraz-Mello, S., Dos Santos, M. Tadeu, Folonier, H., Czismadia, Sz., Do Nascimento, J. -D., Jr., Paetzold, M., Ferraz-Mello, S., Dos Santos, M. Tadeu, Folonier, H., Czismadia, Sz., Do Nascimento, J. -D., Jr., and Paetzold, M.

Abstract

This paper deals with the application of the creep tide theory (Ferraz-Mello) to the study of the rotation of stars hosting massive close-in planets. The stars have nearly the same tidal relaxation factors as gaseous planets and the evolution of their rotation is similar to that of close-in hot Jupiters: they tidally evolve toward a stationary solution. However, stellar rotation may also be affected by stellar wind braking. Thus, while the rotation of a quiet host star evolves toward a stationary attractor with a frequency (1+6e(2)) times the orbital mean motion of the companion, the continuous loss of angular momentum in an active star displaces the stationary solution toward slower values: active host stars with big close-in companions tend to have rotational periods longer than the orbital periods of their companions. The study of some hypothetical examples shows that, because of tidal evolution, the rules of gyrochronology cannot be used to estimate the age of one system with a large close-in companion, no matter if the star is quiet or active, if the current semimajor axis of the companion is smaller than 0.03-0.04 AU. Details on the evolution of the systems: CoRoT LRc06E21637, CoRoT-27, Kepler-75, CoRoT-2, CoRoT-18, CoRoT-14 and on hypothetical systems with planets of mass 1-4 M-Jup in orbit around a star similar to the Sun are given.

Published
2015

38. HIP 10725: The first solar twin/analogue field blue straggler

Author

Schirbel, L, Meléndez, J, Karakas, Amanda, Ramírez, I, Castro, Matthieu, Faria, Marcos A, Lugaro, Maria, Asplund, Martin, Tucci Maia, M, Yong, David, Howes, Louise, Do Nascimento, J. D., Schirbel, L, Meléndez, J, Karakas, Amanda, Ramírez, I, Castro, Matthieu, Faria, Marcos A, Lugaro, Maria, Asplund, Martin, Tucci Maia, M, Yong, David, Howes, Louise, and Do Nascimento, J. D.

Abstract

Context. Blue stragglers are easy to identify in globular clusters, but are much harder to identify in the field. Here we present the serendipitous discovery of one field blue straggler, HIP 10725, that closely matches the Sun in mass and age, but with a metallicity slightly lower than solar. Aims. We characterise the solar twin/analogue HIP 10725 to assess whether this star is a blue straggler. Methods. We employed spectra with high resolution (R ~ 105) and high signal-to-noise ratio (330) obtained with UVES at the VLT to perform a differential abundance analysis of the solar analogue HIP 10725. Radial velocities obtained by other instruments were also used to check for binarity. We also studied its chromospheric activity, age, and rotational velocity. Results. HIP 10725 is severely depleted in beryllium ([ Be/H ] ≤ −1.2 dex) for its stellar parameters and age. The abundances relative to solar of the elements with Z ≤ 30 show a correlation with condensation temperature, and the neutron capture elements produced by the s-process are greatly enhanced, while the r-process elements seem normal. We found its projected rotational velocity (vsini = 3.3 ± 0.1 km s-1) to be significantly higher than solar and incompatible with its isochrone-derived age. Radial velocity monitoring shows that the star has a binary companion. Conclusions. Based on the high s-process element enhancements and low beryllium abundance, we suggest that HIP 10725 has been polluted by mass transfer from an AGB star that probably had an initial mass of about 2 M⊙. The radial velocity variations suggest the presence of an unseen binary companion, probably the remnant of a former AGB star. Isochrones predict a solar-age star, but this disagrees with the high projected rotational velocity and high chromospheric activity. We conclude that HIP 10725 is a field blue straggler, rejuvenated by the mass-transfer process of its former AGB companion.

Published
2015

39. Shallow extra mixing in solar twins inferred from Be abundances

Author

Tucci Maia, M., Meléndez, J., Castro, M., Asplund, M., Ramírez, I., Monroe, T. R., Do Nascimento, J. D., Yong, D., Tucci Maia, M., Meléndez, J., Castro, M., Asplund, M., Ramírez, I., Monroe, T. R., Do Nascimento, J. D., and Yong, D.

Abstract

Lithium and beryllium are destroyed at different temperatures in stellar interiors. As such, their relative abundances offer excellent probes of the nature and extent of mixing processes within and below the convection zone. We determine Be abundances for a sample of eight solar twins for which Li abundances have previously been determined. The analyzed solar twins span a very wide range of age, 0.5-8.2 Gyr, which enables us to study secular evolution of Li and Be depletion. We gathered high-quality UVES/VLT spectra and obtained Be abundances by spectral synthesis of the Be II 313 nm doublet. The derived beryllium abundances exhibit no significant variation with age. The more fragile Li, however, exhibits a monotonically decreasing abundance with increasing age. Therefore, relatively shallow extra mixing below the convection zone is necessary to simultaneously account for the observed Li and Be behavior in the Sun and solar twins.

Published
2015

40. The energy budget of stellar magnetic fields

Author

See, V., primary, Jardine, M., additional, Vidotto, A. A., additional, Donati, J.-F., additional, Folsom, C. P., additional, Boro Saikia, S., additional, Bouvier, J., additional, Fares, R., additional, Gregory, S. G., additional, Hussain, G., additional, Jeffers, S. V., additional, Marsden, S. C., additional, Morin, J., additional, Moutou, C., additional, do Nascimento, J. D., additional, Petit, P., additional, Rosén, L., additional, and Waite, I. A., additional

Published
2015
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44. 18 Sco: A solar twin rich in refractory and neutron-capture elements. Implications for chemical tagging

Author

Melendez, Jorge, Ramirez, Ivan, Karakas, Amanda, Yong, David, Monroe, Tala Wanda R., Bedell, Megan, Bergemann, Maria, Asplund, Martin, Maia, Marcelo Tucci, Bean, Jacob, Do Nascimento, J. D., Bazot, M., Alves-Brito, A, Melendez, Jorge, Ramirez, Ivan, Karakas, Amanda, Yong, David, Monroe, Tala Wanda R., Bedell, Megan, Bergemann, Maria, Asplund, Martin, Maia, Marcelo Tucci, Bean, Jacob, Do Nascimento, J. D., Bazot, M., and Alves-Brito, A

Abstract

We study with unprecedented detail the chemical composition and stellar parameters of the solar twin 18 Sco in a strictly differential sense relative to the Sun. Our study is mainly based on high-resolution (R ∼ 110,000), high signal-to-noise ratio (800

Published
2014

46. Stellar magnetism: empirical trends with age and rotation

Author

Vidotto, A. A., primary, Gregory, S. G., additional, Jardine, M., additional, Donati, J. F., additional, Petit, P., additional, Morin, J., additional, Folsom, C. P., additional, Bouvier, J., additional, Cameron, A. C., additional, Hussain, G., additional, Marsden, S., additional, Waite, I. A., additional, Fares, R., additional, Jeffers, S., additional, and do Nascimento, J. D., additional

Published
2014
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47. High precision abundances of the old solar twin HIP 102152: Insights on Li depletion from the oldest sun

Author

Monroe, Tala Wanda R., Melendez, Jorge, Ramirez, I, Yong, David, Bergemann, Maria, Asplund, Martin, Bedell, Megan, Maia, Marcelo Tucci, Bean, Jacob, Lind, Karin, Alves-Brito, Alan, Casagrande, Luca, Castro, Matthieu, Do Nascimento, J. D., Bazot, M., Freitas, Fabrıcio C., Monroe, Tala Wanda R., Melendez, Jorge, Ramirez, I, Yong, David, Bergemann, Maria, Asplund, Martin, Bedell, Megan, Maia, Marcelo Tucci, Bean, Jacob, Lind, Karin, Alves-Brito, Alan, Casagrande, Luca, Castro, Matthieu, Do Nascimento, J. D., Bazot, M., and Freitas, Fabrıcio C.

Abstract

We present the first detailed chemical abundance analysis of the old 8.2 Gyr solar twin, HIP 102152. We derive differential abundances of 21 elements relative to the Sun with precisions as high as 0.004 dex (≲1%), using ultra high-resolution (R = 110,00

Published
2013

48. The solar, exoplanet and cosmological lithium problems

Author

Melendez, J., Ramirez, I., Casagrande, L., Asplund, M., Gustafsson, Bengt, Yong, D., do Nascimento, J. D., Jr., Castro, M., Bazot, M., Melendez, J., Ramirez, I., Casagrande, L., Asplund, M., Gustafsson, Bengt, Yong, D., do Nascimento, J. D., Jr., Castro, M., and Bazot, M.

Abstract

We review three Li problems. First, the Li problem in the Sun, for which some previous studies have argued that it may be Li-poor compared to other Suns. Second, we discuss the Li problem in planet hosting stars, which are claimed to be Li-poor when compared to field stars. Third, we discuss the cosmological Li problem, i.e. the discrepancy between the Li abundance in metal-poor stars (Spite plateau stars) and the predictions from standard Big Bang Nucleosynthesis. In all three cases we find that the "problems" are naturally explained by non-standard mixing in stars.

Published
2010
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49. The solar, exoplanet and cosmological lithium problems

Author

Melendez, Jorge, Ramirez, I, Casagrande, L, Asplund, Martin, Gustafsson, Bengt, Yong, David, Do Nascimento, J. D., Castro, M., Bazot, M., Melendez, Jorge, Ramirez, I, Casagrande, L, Asplund, Martin, Gustafsson, Bengt, Yong, David, Do Nascimento, J. D., Castro, M., and Bazot, M.

Abstract

We review three Li problems. First, the Li problem in the Sun, for which some previous studies have argued that it may be Li-poor compared to other Suns. Second, we discuss the Li problem in planet hosting stars, which are claimed to be Li-poor when compared to field stars. Third, we discuss the cosmological Li problem, i. e. the discrepancy between the Li abundance in metal-poor stars (Spite plateau stars) and the predictions from standard Big Bang Nucleosynthesis. In all three cases we find that the "problems" are naturally explained by non-standard mixing in stars.

Published
2009

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