Nossas perspectivas s˜ao de avan¸car as publica¸c˜oes sobre o processo de redetermina¸c˜ao diferencial dos parˆametros fundamentais para novas estrelas an´alogas e gˆemeas solares.
Pretendemos realizar tamb´em o acompanhamento espectropolarim´etrico de alguns alvos j´a selecionados. Tal procedimento ser´a fundamental para a determina¸c˜ao e investiga¸c˜ao
do ciclo de atividade magn´etica das estrelas an´alogas e gˆemeas solares.
Outros trabalhos est˜ao baseados na determina¸c˜ao dos elementos qu´ımicos (elementos
vol´ateis e refrat´arios) que podem estar associados com a assinatura espectrosc´opica de planetas em tornos das estrelas an´alogas. De acordo comMel´endez et al.(2009) eRam´ırez
et al.(2009), a abundˆancia dos elementos vol´ateis e refrat´arios no espectro do Sol refletem uma poss´ıvel assinatura da forma¸c˜ao dos planetas rochosos no nosso sistema solar. Para
esse tipo de an´alise se faz necess´ario a utiliza¸c˜ao de espectros de alta resolu¸c˜ao e elevada rela¸c˜ao de sinal ru´ıdo para obten¸c˜ao de abundˆancias qu´ımicas de alt´ıssima precis˜ao (0,01
dex). Seguindo nessa linha, pretendemos ainda utilizar os nossos espectros do BCool para derivar esses elementos nas nossas estrelas an´alogas e gˆemeas solares, visando identificar
a presen¸ca de poss´ıveis planetas em torno dessas estrelas.
Uma outra possibilidade de trabalho est´a associada a minha participa¸c˜ao no projeto
SP IRou (sigla em francˆes para “Le Spectro Polarim`etre infra Rouge”). Esse instrumento consiste em um espectropolar´ımetro de alta resolu¸c˜ao (R ≈ 75000) que cobrir´a toda a
regi˜ao do infravermelho pr´oximo, ou seja, comprimentos de onda desde 0,98 at´e 2,35 µm, e ser´a instalado no telesc´opio de 3,6 m do CFHT. A parte espectrogr´afica desse
instrumento ser´a fundamental para a detec¸c˜ao de planetas habit´aveis parecidos com a Terra e que estejam orbitando an˜as vermelhas pr´oximas. J´a em modo polarim´etrico o
SP IRou ser´a um instrumento, ´unico, capaz de obter espectros de polariza¸c˜ao (Stokes Q, U e V) de regi˜oes internas de forma¸c˜ao estelar, estrelas jovens e sistemas planet´arios em
forma¸c˜ao. Assim, inserido nesse projeto, irei me dedicar a duas frentes de trabalho, uma voltada para busca e caracteriza¸c˜ao de exoplanetas em torno de estrelas de pouca massa,
como por exemplo, an˜as do tipo espectral M, e outra, preocupada em explorar o impacto do campo magn´etico sobre as estrelas e sua influˆencia na forma¸c˜ao planet´aria.
CAP´ITULO 8. CONCLUS ˜OES E PERSPECTIVAS
os dados obtidos pelos sat´elites TESS − N ASA e PLAT O − ESA nos pr´oximos anos.
Al´em dos dados obtidos a partir dos telesc´opios em terra SP IRou e outros instrumentos brasileiros.
Cap´ıtulo
9
Astronomy & Astrophysicsmanuscript no. beck_solarAnalogueLithium_final ESO 2016c September 30, 2016
Lithium abundance and rotation of seismic solar analogues
Solar and stellar connection fromKepler and Hermes observations
⋆P. G. Beck1, J.-D. do Nascimento Jr.2, 3, T. Duarte2, D. Salabert1, A. Tkachenko4, S. Mathis1, S. Mathur5, R. A. García1, M. Castro2, P. L. Pallé6, 7, R. Egeland8, 9, D. Montes7, O. Creevey11,
M. F. Andersen12, D. Kamath4, and H. van Winckel4
1 Laboratoire AIM, CEA/DRF - CNRS - Univ. Paris Diderot - IRFU/SAp, Centre de Saclay, 91191 Gif-sur-Yvette Cedex, France
e-mail: [email protected]
2 Departamento de Física, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, RN, Brazil 3 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
4 Instituut voor Sterrenkunde, KU Leuven, B-3001 Leuven, Belgium
5 Space Science Institute, 4750 Walnut street Suite 205, Boulder, CO 80301, USA 6 Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
7 Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
8 High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000, USA 9 Department of Physics, Montana State University, Bozeman, MT 59717-3840, USA
10 Dpto. Astrofísica, Facultad de CC. Físicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain
11 Laboratoire Lagrange, Université de Nice Sophia-Antipolis, UMR 7293, CNRS, Observatoire de la Côte d’Azur, Nice, France 12 Stellar Astrophysics Centre, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
version of September 30, 2016
ABSTRACT
Context.Lithium and surface rotation are good diagnostic tools to probe the internal mixing and angular momentum transfer in stars.
Aims.We aim to explore the relation between surface rotation, lithium abundances A(Li) and age in a sample of solar-analogue stars
and study their possible binary nature.
Methods.A sample of 18 solar-analogue stars, observed by the NASA Kepler satellite was selected for an in-depth analysis. Their seis-
mic properties and surface rotation rates are well constrained from previous studies. About 53 hours of high-resolution spectroscopy were obtained to derive the fundamental parameters from spectroscopy and A(Li). These values are combined and confronted with seismic masses, radii and ages as well as surface rotation periods measured from Kepler photometry.
Results.From radial velocities, we identify and confirm a total of 6 binary star systems. For each star, a signal-to-noise ratio of
typically 80.S/N.210 in the final spectrum was achieved around the lithium line. Fundamental parameters and A(Li) are reported. By using the surface rotation period derived from Kepler photometry, a well-defined law between A(Li) and rotation rates higher than the solar value is obtained. The seismic radius translates the surface rotation period into surface velocity. With models constrained by the characterization of the individual mode frequencies for single stars, we identify a sequence of three solar analogues with similar mass (∼1.1 M⊙) and stellar ages ranging between 1 to 9 Gyr. Within the realistic estimate of ∼7% for the mass uncertainty, we find
a good agreement of the measured A(Li) compared to the predicted evolution from a grid of models calculated with the Toulouse- Geneva stellar evolution code, which includes rotational internal mixing, calibrated to reproduce solar chemical properties. The scatter in ages inferred from the global seismic parameters is too large to be compared to A(Li).
Conclusions.We present a consistent spectroscopic survey of the Li-abundance in solar-analogue stars with a mass of 1.00±0.15 M⊙,
and characterised through asteroseismology and surface rotation rates, based on Kepler observations. The correlation between A(Li) and Protsupports the gyrochronological concept for stars younger than the Sun and becomes clearer, if the confirmed binaries are
excluded. The consensus between measured A(Li) for solar analogues with model grids, calibrated onto the Sun’s chemical properties suggests that these targets share the same internal physics. In this light, the solar Li-value appears to be normal for a star like the Sun.
Key words. stars: fundamental parameters − stars: solar-type − stars: rotation − stars: evolution − Methods: observational − Tech- niques: spectroscopic
1. Introduction
In the last decade, numerous studies focused on the ques- tion whether the rotation and chemical abundances of the Sun are typical for a solar-type star, i.e. a star of a solar ⋆ Based on observations made with the NASA Kepler space telescope
and the Hermes spectrograph mounted on the 1.2 m Mercator Tele- scope at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
mass and age (e.g. Gustafsson 1998; Allende Prieto et al. 2006; 5
Delgado Mena et al. 2014; Datson et al. 2014; Ramírez et al. 2014; Carlos et al. 2016; dos Santos et al. 2016). These stud- ies compared the Sun with solar-like stars and were inconclu- sive due to relatively large systematic errors (Gustafsson 2008;
Robles et al. 2008; Reddy et al. 2003). 10
The fragile element lithium is a distinguished tracer of mix- ing processes and loss of angular momentum inside a star (Talon & Charbonnel 1998). Its abundance in stars changes con-
arXiv:1603.08809v1 [astro-ph.SR] 29 Mar 2016
Astronomy & Astrophysicsmanuscript no. 27583_MB �cESO 2016
March 30, 2016
Mass effect on the lithium abundance evolution of open clusters:
Hyades, NGC 752, and M67
M. Castro1, T. Duarte1, G. Pace2, and J. -D. do Nascimento Jr.1, 3
1 Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, CEP: 59072-970 Natal, RN, Brazil 2 Instituto de Astrofísica e Ciência do Espaço, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
3 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA Received : Accepted :
ABSTRACT
Lithium abundances in open clusters provide an effective way of probing mixing processes in the interior of solar-type stars and convection is not the only mixing mechanism at work. To understand which mixing mechanisms are occurring in low-mass stars, we test non-standard models, which were calibrated using the Sun, with observations of three open clusters of different ages, the Hyades, NGC 752, and M67. We collected all available data, and for the open cluster NGC 752, we redetermine the equivalent widths and the lithium abundances. Two sets of evolutionary models were computed, one grid of only standard models with microscopic diffusion and one grid with rotation-induced mixing, at metallicity [Fe/H] = 0.13, 0.0, and 0.01 dex, respectively, using the Toulouse-Geneva evolution code. We compare observations with models in a color-magnitude diagram for each cluster to infer a cluster age and a stellar mass for each cluster member. Then, for each cluster we analyze the lithium abundance of each star as a function of mass. The data for the open clusters Hyades, NGC 752, and M67, are compatible with lithium abundance being a function of both age and mass for stars in these clusters. Our models with meridional circulation qualitatively reproduce the general trend of lithium abundance evolution as a function of stellar mass in all three clusters. This study points out the importance of mass dependence in the evolution of lithium abundance as a function of age. Comparison between models with and without rotation-induced mixing shows that the inclusion of meridional circulation is essential to account for lithium depletion in low-mass stars. However, our results suggest that other mechanisms should be included to explain the Li-dip and the lithium dispersion in low-mass stars.
Key words. stars: fundamental parameters - stars: abundances - stars: evolution - stars: interiors - stars: solar-type
1. Introduction
Lithium (7Li) is a fragile element that is destroyed at temper-
atures above ∼2.5 × 106 K. The lithium depletion in stars de-
pends on several factors such as mass, age, metallicity, rota- tion, magnetic fields, mass loss, and mixing mechanisms (e.g.
D’Antona & Mazzitelli 1984;Deliyannis & Pinsonnault 1997;
Ventura et al. 1998;Charbonnel & Talon 2005). Abundance mea- surements of this element in open cluster stars allow us to in- vestigate mixing in stellar interior and to put constraints on the non-convective mixing processes as a function of mass, age, ro- tation, and metallicity for coeval stars. To understand the mix- ing mechanisms and to explain the complex evolution of stellar chemical elements, we need to constrain the effect of mass. As a part of this complexity, several unexpected results related to the depletion of lithium in stars have been found and reveal our limited understanding of the physics acting in the stars’ interi- ors. One of these unexpected results concerns the measurements of lithium abundance in late-F and early G-type stars, show- ing empirical evidence that is in contradiction with the standard model predictions, which only include convection. For stars in these spectral classes, authors have shown lithium depletion dur- ing the main sequence (Boesgaard & Tripicco 1986;Boesgaard 1987;Pilachowski & Hobbs 1988). However, convective zones of low-mass main sequence (MS) stars do not reach regions in the stellar interior, where the temperature is sufficiently high to drive lithium destruction (see e.g.Randich et al. 2006, and refer-
Send offprint requests to: M. Castro, email: [email protected]
ences therein). This depletion is mass-age dependent (do Nasci- mento et al. 2009;Meléndez et al. 2010;Pace et al. 2012). For stars of one solar mass, including the Sun and those stars, which are spectroscopically indistinguishable from the Sun called solar twins (Cayrel de Strobel 1996), the extremely low lithium abun- dance of about one hundred times lower than its original value as measured in meteorites, represents a long-standing puzzle.
During the pre-main-sequence (PMS), studies showed that Li destruction in stars with mass that is equal or larger to the so- lar one should be weak (Martin et al. 1993;Jones et al. 1997).
Randich et al. (1997) determined the lithium abundance in 28 stars of the 28 Myr old cluster IC 2602. They compared the lithium abundance distribution as a function of stellar mass of this sample with those of the α Persei (50 Myr old) and the Pleiades (70 Myr old) clusters, and showed that only latest-type stars present a significant lithium depletion during the PMS. Early-K and G-type stars have a slightly lower lithium abun- dance in the oldest clusters, and F-type stars do not present any significant lithium depletion.
According to the standard stellar models, lithium depletion should be a unique function of mass, age, and chemical compo- sition. Stars with close effective temperature in a given cluster should have undergone the same amount of lithium depletion. In this context, lithium abundances have been studied extensively in open clusters of different ages and revealed a complex behav- ior with an important scattering (see e.g.Pinsonneault 1997, and references therein). The star-to-star scatter in lithium abundance exists among solar-type stars of the ∼2 Gyr old cluster NGC 752,
Astronomy & Astrophysics manuscript no. 88_solar_twins ESO 2016c May 6, 2016
On the link between rotation, chromospheric activity and lithium
abundance in solar twins
T. S. S. Duarte1, J. S. da Costa2, M. Castro1, and J. D. do Nascimento Jr.1, 3
1 Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, CEP: 59072-970 Natal, RN, Brazil 2 Escola de Ciência e Tecnologia, Universidade Federal do Rio Grande do Norte, CEP: 59072-970 Natal, RN, Brazil
3 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA Received : Accepted :
ABSTRACT
Context.Rotation period, chromospheric activity, lithium abundance, and depth of the outer convective zone play an important role in the study of the processes at work in the stellar interior and exterior, in particular we have been investigating the link between these parametes and solar twins stars.
Aims.Our sample consists of 80 solar twin field stars with surface lithium abundance for 67 stars. These objects were selected from literature. This sample allows us to investigate whether the surface lithium abundance of solar twins can be described in terms of the chromospheric activity, rotation period and convective zone mass deepening. We have also analyzed the link among this parameters and the stellar age in this sample.
Methods.We derived an extensive grid of stellar evolutionary models, suitable to solar twins stars, for a thin set of mass and metallic- ity. From these models, the mass depth of the outer convective zone were estimated for these solar twins, the stellar mass and age have recalculated. The Te f f, logR0
HKand [Fe/H] values were obtained from literature, the luminosity was estimated from HIPPARCOS trigonometric parallax measurements and we use R0
HKvalues to derive rotation periods.
Results.Our determination of stellar parameters is in good agreement with the measurements published in the literature. Our theo- retical models provide a good description for increasing lithium depletion with respect to age for solar twins. We also realized that all these parameters are closely related for this sample.
Conclusions.These results illustrate that solar twins stars present a closely and reciprocal relation between A(Li) and the stellar parameters, Age, chromospheric activity, convective zone mass deepening and rotation period. From this we can consider that the Sun behaves really as a solar twin star, within the observational uncertainties.
Key words. stars: fundamental parameters - stars: abundances - stars: evolution - stars: interiors - stars: solar twins
1. Introduction
Over the last twenty years, the number of solar twins have been huge increased (Pasquini et al. 2008), Takeda stood at about one hundred. Cayrel de Strobel (1996) defines a solar twin as a dwarf star with effective temperature, surface gravity, microturbulent velocity indistinguishable from the Sun values. Porto de Mello & da Silva (1997) discovered the first solar twins has been used for different purposes such as studies of asteroid mineralogy or set the zero-point of fundamental calibrations of color-temperature relations (e.g., Porto de Mello & da Silva 1997; Lazzaro et al. 2004; Holmberg et al. 2006; Casagrande et al. 2010; Melendez et al. 2010; Ramirez et al. 2012; Casagrande et al. 2012; Jasmim et al. 2013; Datson et al. 2014). Solar twins are suitable for testing chemical evolution of the Galactic disk (Nissen 2015; Spina et al. 2015) and studies of evolutionary stellar physics modeling (e.g., do Nascimento et al. 2009; Castro et al. 2011; Tucci Maia et al. 2015). Recently, studies of measuring distances using spectro- scopically identified solar twins has been proposed by Jofre et al. (2015). Except for some solar twin from open clusters (Pasquini et al. 1994), ages for field solar twin stars are particularly noto- riously difficult to derive (e.g., Barnes 2007; Soderblom 2010). Consequently, the classical distinction between solar-type and analogs or twins does not include age constraints.
Send offprint requests to: T. Duarte, email: [email protected]
The study of the true rotation or rotation period evolution of solar twins (do Nascimento et al. 2013, 2014) point out to the possibility of ages can be estimated using gyrochronology (Barnes 2007). However, even if recent works have increased the number of solar twins and studied their fundamental param- eters and chemical abundances surface magnetic activity in de- tail, (e.g., Garcia et al. 2014a; Baumann et al. 2010; Schrijver & Zwaan 2008) their Prot are mostly unknown, except for the two solar twins 18 Sco (Porto de Mello & da Silva 1997) and CoRoT Sol 1 (do Nascimento et al. 2013). The unprecedented continu- ous photometric observation over 6 years with CoRoT (Baglin et al. 2006) and 4 years with Kepler (Borucki et al. 2010) has been led to a small revolution in the understanding of the stellar ro- tation. These satellites allow us to study a larger sample of cool solar-like stars. Among the stars studied by these space missions, there are low mass stars as similar as possible with the Sun and with measurements of rotation periods.
Prime examples in this field, was the characterization of some solar analogs such as 16 Cyg A& B from Kepler obser- vations (e.g., Metcalfe et al. 2012; do Nascimento et al. 2014; Davies et al. 2015) and CoRoT 102684698 (do Nascimento et al. 2013). Stellar surface rotation is a key ingredient to our under- standing of stellar activity and mixing mechanism in low mass stars. Rotational has a major impact on the stellar evolution and can change properties of solar-type stars by reducing the effects Article number, page 1 of 8
Draft version May 6, 2016
Preprint typeset using LATEX style emulateapj v. 12/16/11
SEISMIC AND SPECTROSCOPIC ANALYSIS OF 10 BRIGHT RED GIANTS OBSERVED BY KEPLER H. R. Coelho1,2, D. Bossini1,2, W. J. Chaplin1,2, S. Degl’Innocenti3,20, M. Dell’Omodarme3,20, T. Duarte4, R. Garcia5, L. Girardi6,7, R. Handberg2,1, S. Hekker8, D. Huber9,10,2, N. Lagarde1, M. N. Lund2,1, S. Mathur21,
A. Miglio1,2, P. G. P. Moroni3, B. Mosser12, J. D. do Nascimento4,13, E. Poretti14,15,16, M. Rainer14, T. Rodrigues6,7,17, A. Serenelli18, V. Silva Aguirre2, G. Valle19,20,3,
Draft version May 6, 2016
ABSTRACT
Subject headings: Asteroseismology – Stars: red giants – Stars: fundamental parameters – Stars: abundances
1. INTRODUCTION
[short intro on relevance of testing seismically inferred distances, masses radii and of testing model predictions of internal mixing in red giant stars]
In this work we present the seismic and spectroscopic study of 10 bright red giant stars observed by the Kepler space telescope. The data obtained for the target stars have high signal to noise ratio, allowing a detailed study of chemical abundances coupled with high quality seis-
1
School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
2
Stellar Astrophysics Centre (SAC), Department of Physics a nd Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
3
Dipartimento di Fisica ”Enrico Fermi”, Universit di Pisa, Largo Pontecorvo 3, Pisa 56127, Italy
4
Universidade Federal do Rio Grande do Norte, UFRN, De-