Sun-Like Stars Unlike the Sun: Clues for Chemical Anomalies of Cool Stars

Astronomische Nachrichten, 13 August 2018

Sun-like stars unlike the Sun Clues for chemical anomalies of cool stars

V. Adibekyan1,?, E. Delgado-Mena1, S. Feltzing2, J. I. Gonzalez´ Hernandez´ 3,4, N. R. Hinkel5,6, A. J. Korn7, M. Asplund8, P.G. Beck9, M. Deal10,11, B. Gustafsson7,12, S. Honda13, K. Lind14,7, P.E. Nissen15, and L. Spina16

1 Instituto de Astrof´ısica e Cienciasˆ do Espac¸o, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal 2 Department of Astronomy and Theoretical Physics, Lund Observatory, Box 43, SE-22100 Lund, Sweden 3 Instituto de Astrof´ısica de Canarias, 38200 La Laguna, Tenerife, Spain 4 Departamento de Astrof´ısica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain 5 School of Earth & Space Exploration, Arizona State University, Tempe, AZ 85287, USA 6 Vanderbilt University, Department of Physics and Astronomy, 6301 Stevenson Center Lane, Nashville, TN 37235, USA 7 Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden 8 The Australian National University, Research School of Astronomy and Astrophysics, Cotter Road, Weston, ACT, 2611, Australia 9 Laboratoire AIM, CEA/DRF-CNRS-Univ. Paris Diderot-IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex, France 10 Laboratoire Univers et Particules de Montpellier (LUPM), UMR 5299, Universite´ de Montpellier, CNRS, place Eugene` Bataillon, 34095 Montpellier Cedex 5, France 11 CNRS, IRAP, 14 avenue Edouard Belin, 31400 Toulouse, France 12 NORDITA, Roslagstullsbacken 23, SE-106 91 Stockholm, Sweden 13 Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo, 407-2 Nishigaichi, Sayo-cho, Sayo, Hyogo 679-5313, Japan 14 Max-Planck Institut fur¨ Astronomie, Konigstuhl¨ 17, 69117 Heidelberg, Germany 15 Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus C, Denmark 16 Universidade de Sao˜ Paulo, Departamento de Astronomia do IAG/USP, Rua do Matao˜ 1226, Sao˜ Paulo, 05509-900, SP, Brasil

Received XXXX, accepted XXXX Published online XXXX

Key words stars: abundances – stars: chemically peculiar – (stars:) planetary systems – Galaxy: abundances – (Galaxy:) solar neighborhood We present a summary of the splinter session “Sun-like stars unlike the Sun“ that was held on 09 June 2016 as part of the Cool Stars 19 conference (Uppsala, Sweden). We discussed the main limitations (in the theory and observations) in the derivation of very precise stellar parameters and chemical abundances of Sun-like stars. We outlined and discussed the most important and most debated processes that can produce chemical peculiarities in solar-type stars. Finally, in an open discussion between all the participants we tried to identify new pathways and prospects towards future solutions of the currently open questions.

1 Motivation quence stars with spectral types of later than about F0 have a bisectors with a so-called classical C shape, while hotter In stellar astronomy, we sometimes divide stars into two stars show reversed C shape. This boundary is called ”gran- wide groups and colloquially refer to them as cool stars ulation boundary“ (e.g. Gray & Nagel 1989; Gray & Toner (late-type stars) and hot stars (early-type stars), although 1986) and practically divides the Hertzsprung–Russell di- there is no sharp division between these two groups. These agram into cool and hot stars (Gray 2005). In this work, kinds of deﬁnitions are lexical and have only a descriptive, adopting the deﬁnition of Gray we refer to stars later than qualitative character. A more quantitative boundary between F0 when saying ”cool stars“. These low-mass stars have cool and hot stars was suggested by Gray (2005) based on long lifetimes and their envelopes contain information about the shape of the bisectors of the spectral lines. Main se- their stellar evolution and the history of the evolution of chemical abundances in the Galaxy. ? Corresponding author: [email protected]

During the last decade, noticeable advances were made et al. 2014; Ram´ırez et al. 2009). For more discussion on in the characterization of atmospheric properties (e.g. effec- different definitions we refer the reader to Datson (2014). tive temperature, metallicity, surface gravity) and chemical In the splinter session the following definitions for so- abundances of cool stars. The high precision in stellar atmo- lar twins, analogs and Sun-like stars in terms of stellar spheric parameters is crucial for precise characterization of parameters were presented and used. Solar twins: Teff = physical properties of stars such as their mass and age. 57771±100 K, log g = 4.44±0.10 dex, [Fe/H] = 0.00±0.10 The extremely high precision in chemical abundance dex (e.g. Adibekyan et al. 2014; Ram´ırez et al. 2009), solar derivations allowed observers to study subtle chemical pe- analogs: Teff = 5777±200 K, log g = 4.44±0.20 dex, [Fe/H] culiarities in Sun-like stars. Given the nature of the detailed = 0.00±0.20 dex (e.g. Adibekyan et al. 2014), and solar- chemical abundance derivations, it is likely that many phys- type: main sequence or subgiant stars with 5000 K < Teff < ical processes determine the chemical characteristics of the 6500 K. stars. Understanding the origin of these anomalies is very With the recent advances of asteroseismology, thanks to important for the further advancement of Galactic and stel- Kepler (Borucki et al. 2010) and CoRoT (Convection, Rota- lar astronomy, as well as the very fast advancing field of tion, and planetary Transits – Baglin et al. 2006) missions, exoplanetary research. parameters determined by astroseismology have also been In June 2016, we organized a Splinter Session at the included in the definition of solar analogues and twins. In Cool Stars 19 workshop with the goal to bring together ex- particular, the presence of solar-like oscillations can be used perts of stellar, Galactic and planetary astrophysics to high- to consider a star as a solar analog, or a seismic solar analog light the latest results and discuss what may make Sun-like (e.g. Beck et al. 2016b; do Nascimento et al. 2013; Metcalfe stars unlike the Sun. We had six invited review talks and et al. 2012; Salabert et al. 2016a). four contributed talks, which were followed by an open discussion between speakers and participants. The main scien- 2.1 Accuracy and precision in stellar parameters and tific questions discussed during the session were: chemical abundances I. Abundances of the Sun and Sun-like stars. What is the highest precision and accuracy we actually can expect cur- High-precision and high-accuracy stellar abundances are rent analysis methods to deliver? What are the limitations crucial for many fields of stellar, planetary and galactic as- in the theory (e.g. model of atmospheres, 1D, hydrostatic, trophysics. However, precise and accurate derivation of stel- LTE) and observations (e.g. spectral resolution, signal-to- lar atmospheric abundances is a difficult challenge which is noise ratio, atmospheric observational conditions)? obvious when comparing different techniques and measure- II. Abundance characteristics of stars. How is the inho- ments (Hinkel et al. 2016; Jofre et al. 2017). mogeneous Galactic chemical evolution, the star- and planetary formation history, and the stellar evolution reflected in 2.1.1 High-resolution spectroscopy the surface abundances of Sun-like stars? How can we study these different aspects by analyzing the elemental abun- If past analyses of large, homogeneous and high-quality dances in stellar spectra? data reached abundance precisions of 0.03-0.07 dex (e.g. Adibekyan et al. 2015b, 2012c; Bensby et al. 2003, 2014; In this paper we summarize the presentations and the Gilli et al. 2006; Nissen & Schuster 2010; Reddy et al. discussions of this splinter session. 2006; Takeda 2007; Valenti & Fischer 2005), the latest works on solar twins that are based on differential line- 2 Solar twins, analogs and solar-type stars by-line analysis report even higher precision of .0.01 dex (e.g. Adibekyan et al. 2016a,b; Bedell et al. 2014; Gonzalez´ Hernandez´ et al. 2013, 2010; Melendez´ et al. 2009, 2012; Classifying a star as solar-type, solar analog, or solar twin Nissen 2015, 2016; Ram´ırez et al. 2010; Saffe et al. 2016; depends on the degree of similarity between the star and Spina et al. 2016a,b; Tucci Maia et al. 2014). Consequently, the Sun. The categorization also reflects the evolution of the precision in atmospheric parameters reported for the so- astronomical instrumentation and observational techniques. lar twins is very high: ∼10 K for T , ∼0.02 dex for log g, Cayrel de Strobel (1996) defined a solar twin as a star that eff and ∼0.01 dex for [Fe/H] (e.g. Adibekyan et al. 2016a; Be- has the same atmospheric and physical properties as the dell et al. 2014; Ram´ırez et al. 2014; Spina et al. 2016a,b; Sun within the observational errors. This definition obvi- Tucci Maia et al. 2014). ously depends on the uncertainties of the derived parame- Recently, Bedell et al. (2014) analyzed solar spectra ob- ters. Soderblom & King (1998) provided a more practical served with different instruments, from different asteroids, definition of these three categories of stars. While the lit- and at different times, i.e, conditions. The authors reached a erature is full of quantitatively different definitions of solar conclusion that a major effect on differential relative abun- twins, analogs and sun-like (solar type) stars, these defini- dances is caused by the use of different instruments (up to tions are qualitatively similar (e.g. Adibekyan et al. 2014; Datson et al. 2015; do Nascimento et al. 2014; Gonzalez´ 1 We note that the value of the nominal solar effective temperature re- Hernandez´ et al. 2010; Melendez´ et al. 2009; Porto de Mello comended by IAU 2015 resolution B3 is 5772±0.8K (Prsaˇ et al. 2016).

(2014) for 14 stars in common obtained an average difference and rms deviation of: ∆Teff = 0±10 K, ∆log g = 0.002±0.020 dex, and ∆[Fe/H] = 0.000±0.014 dex. The same author, when comparing his results with that of Sousa et al. (2008) for the 21 solar twins in common found the following average differences and rms deviations: ∆Teff = -1±8 K, ∆log g = 0.018±0.033 dex, and ∆[Fe/H] = -0.003±0.009 dex. Comparison of chemical abundances of individual elements, and abundance ratios is also usually small. For example, the average offset and rms deviation in [Y/Mg] abundance ratio observed between Nissen (2016) and Tucci Maia et al. (2016) is 0.012±0.016 dex (see Fig. 1).

Fig. 1 Comparision of [Y/Mg] abundance ratios derived by Nis- sen (2016) and Tucci Maia et al. (2016) for 14 solar twin stars. 2.1.2 3D and non-LTE effects (Courtesy of Poul Erik Nissen). Most of the studies, when deriving stellar parameters and elemental abundances used classical 1D hydrostatic mod- 0.04 dex). They found that the choice of asteroids to ob- els with an assumption of local thermodynamic equilib- tain the solar reflected spectra and time-dependent effects rium (LTE). Thanks to the exponentially increasing level of (observations at different epochs) are smaller than 0.01 dex. computational power, huge progress has been made in the Bensby et al. (2014) have also analyzed (applying exactly last decade in developing 3D hydrodynamical model atmo- the same analysis techniques) different spectra of the Sun spheres (e.g. Beeck et al. 2013; Freytag et al. 2012; Magic (scattered solar light from the afternoon sky, the Moon, et al. 2013; Trampedach et al. 2013). Furthermore, non-LTE Jupiter’s moon Ganymede, and the asteroids Vesta and calculations and corrections are now available for more than Ceres) obtained during a period of six years with different 20 elements e.g. Li, O, Na, Mg, Si, Ca, Ti, Fe, Sr, Ba (e.g. instruments. The maximum observed differences for solar Amarsi et al. 2015, 2016; Bergemann 2011; Korotin et al. parameters were 49 K for Teff, 0.03 dex for log g, and 0.03 2015; Lind et al. 2009, 2012; Merle et al. 2011; Osorio et al. dex for solar metallicity. In turn, Adibekyan et al. (2016a) 2015; Prakapaviciusˇ et al. 2013; Shi et al. 2011; Spite et al. showed that the average difference in chemical abundances 2012). For a detailed discussion of non-LTE effects in the observed for two different high-quality (signal-to-noise ra- lines of different elements we refer the reader to Mashonk- tio of about 400) spectra obtained during the same night for ina (2014). the same star is usually small .0.01±0.03 dex, but can reach For most elements with complex atoms, non-LTE effects up to 0.06 dex depending on the element. are not very strong in solar-twins. The amplitude of these ef- Most of the reported uncertainties are in fact precision, fects are different for different species (species sensitive to or internal (random) errors (e.g., uncertainties in the contin- over-ionisation or collision-dominated species) and depends uum setting, in the log g f values). Systematic errors, due to on atmospheric parameters of the stars. For example in the the model atmospheres and atomic data are more difficult to case of iron (see Fig. 2) and other neutral Fe-peak atoms, estimate and can be much larger than the random errors. Re- the non-LTE effects increase as temperature increases, sur- cently, Bensby et al. (2014) evaluated the external precision face gravity decreases, and the metallicity decreases (e.g. of their abundance derivation by comparing their results for Bergemann & Nordlander 2014). Obviously, when compar- solar-type stars with those from the literature (Adibekyan ing stars with very similar parameters, such as solar twins, et al. 2012c; Reddy et al. 2006, 2003; Valenti & Fischer the differential non-LTE effects are very small (e.g. Nissen 2005). The authors found that the differences (average for 2015; Spina et al. 2016a). They become non-negligible for all stars in common) in stellar parameters and abundances of high-precision work on solar analogs and should be consid- individual elements observed between different works range ered when solar-type stars are intercompared. from -10K to +120 K for Teff, from -0.05 to -0.07 dex for log g, from -0.02 to +0.03 dex for [Fe/H], and from -0.09 2.1.3 Asteroseismology to 0.10 dex for different elements. For more complete and extensive comparison of more than 80 data sets we refer the Comparison of physical parameters derived with different, reader to Hinkel et al. (2014). They found that the varia- independent methods help us to understand and estimate the tion between studies per element has a mean of 0.14 dex for accuracy of the derivations. A combination of different as- all elements in all stars in their compiled catalog, called the tronomical tools and methods also helps to improve the ac- Hypatia Catalog. curacy of the determinations. In particular, asteroseismol- The comparison between different studies of solar twin ogy combined with high-resolution spectroscopy allows us stars shows higher agreement. In particular, Nissen (2015) to substantially improve the accuracy of the stellar parame- when comparing his results with those of Ram´ırez et al. ters (e.g. Chaplin et al. 2014; Creevey et al. 2016; Lebreton

0.5 log(g)=1.0 log(g)=1.5 log(g)=2.0

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0.3

0.2

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0.5 log(g)=2.5 log(g)=3.0 log(g)=3.5

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I 0.3

A(Fe) 0.2 ∆

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0.5 log(g)=4.0 log(g)=4.5 log(g)=5.0 4000 0.4 4500 5000 0.3 5500 6000 0.2 6500 7000 0.1

0.0 −5 −4 −3 −2 −1 0 −5 −4 −3 −2 −1 0 −5 −4 −3 −2 −1 0 [Fe/H]

Fig. 2 The dependence of typical NLTE corrections for high-excitation (Eexc > 2.5 eV), unsaturated (Wλ < 50 mÅ) Fe I lines on stellar 1 parameters. All models have ξt = 2.0 km s . The ﬁgure is from Lind et al. (2012).

& Goupil 2014; Metcalfe et al. 2014). The role of astero- evolution of lithium for the asteroseismic mass. TGEC in- seismology is particularly invaluable for derivation of stellar cludes complete atomic diffusion (including radiative accel- ages, which is usually very difficult to determine with high erations) and non-standard mixing processes. Then the au- accuracy using spectroscopy. Asteroseismology can provide thors compared it to the spectroscopically measured lithium ages of solar-like stars with a relative precision of 10 to 15 abundance and seismically determined age. For all the stars % (e.g. Chaplin et al. 2014). they found a good agreement within the realistic uncertain- Such improved stellar parameters are beneficial to study ties of stellar mass and age derived by Lebreton & Goupil aspects of stellar structure and evolution such as rotation, (2014). Such agreement between theory and observations activity or the lithium abundance. Examples of such an ef- suggests that for these solar analogues, the same physical fort are the works of Salabert et al. (2016a) and Beck et al. processes are driving internal mixing. (2016a) where the authors carefully selected 18 seismic solar analogs to study different properties of these stars2. Beck 3 Galactic chemical evolution and et al. (2016a) used the Toulouse-Geneva Evolutionary Code nucleosynthesis with solar twins (TGEC, Hui-Bon-Hoa 2008), to compute the theoretical Important information about the formation and evolution of 2 A summary of the current work on this sample of 18 solar analogues is described in dedicated proceeding articles by Beck et al. (2016c) and galaxies are locked into the chemical compositions of stars. Salabert et al. (2016b). All the metals, or elements heavier than Boron, originate

Copyright line will be provided by the publisher asna header will be provided by the publisher 5 from stars that enrich the interstellar medium with their own unique pattern of elements depending on their mass and ini- tial metallicity. In fact, each specific element has been produced by different sites of nucleosynthesis that contribute to the chemical evolution of galaxies with different timescales (e.g. Pagel 2009). The chemical abundances, measured as [X/Fe] vs. [Fe/H] for solar-type stars are traditionally used to study the Galactic chemical evolution because iron has been assumed to be a good chronological indicator of nucleosynthesis (e.g. Adibekyan et al. 2012c; Bensby et al. 2003; Chiappini et al. 1997; Edvardsson et al. 1993; Romano et al. 2010; Smil- janic et al. 2014, 2016). Obviously, the studies of the relations between the abundance ratios and age would provide more direct information about the nucleosynthetic history of elements and chemical evolution of our Galaxy. Recently, Nissen (2015, 2016) used relatively high- precision ages (derived from evolutionary tracks) and chemical abundances of 18 elements (from O to Ba) determined for 21 solar twins to study the correlations between these two parameters. For stars younger than 6 Gyr, Nissen found that some elements show very tight correlation with stellar age. Nissen showed that this linear correlation breaks down at 6 Gyr and the stars with ages between 6 and 9 Gyr Fig. 3 [Y/Mg] and [Y/Al] versus stellar age. Stars younger than split up into two groups with high and low values of [X/Fe] 6 Gyr are marked with black filled circles. Old stars with low for the odd-Z elements Na, Al, Sc, and Cu. Nissen (2016) [Na/Fe] and high [Na/Fe] are shown in red and green filled circles, respectively. Three [α/Fe]-enhanced stars are shown with open concluded that the younger stars were formed from a well- blue circles and the Sun is shown with its typical symbol. The mixed interstellar gas while older stars formed in regions figure is from Nissen (2016). that were enriched by supernovae with different neutron ex- cesses. He also showed that due to very tight linear correlation with age, [Y/Mg] and [Y/Al] abundance ratios can be lowed by a decrease towards the youngest stars. The [X/Fe] used to derive stellar ages with a precision reaching 1 Gyr for the n-capture elements decrease with age. (see Fig. 3). This result on solar twins was later confirmed Knowledge of the [X/Fe]-age relations is a gold mine by other authors (Spina et al. 2016a; Tucci Maia et al. 2016) from which we can achieve considerable understanding and was extended to solar analogs (Adibekyan et al. 2016b). about the processes that governed the formation and evo- Interestingly, Feltzing et al. (2016) recently showed that the lution of the Milky Way: the nature of the star formation correlation between [Y/Mg] and age is a function of metal- history, the supernovae (SNe) rates, the stellar yields, and licity and gets flat at metallicities below -0.5 dex. the variety of the SNe progenitors, etc. This approach has More recently, Spina et al. (2016a) studied a sample of been already successfully applied before to low(er) preci- 41 thin disk and four thick disk stars for which superb abun- sion data (e.g. Edvardsson et al. 1993) and demonstrated its dances with 0.01 dex precision and accurate stellar ages power. These types of studies are of fundamental signifi- have been obtained through a line-by-line differential anal- cance in efforts to reconstruct the nucleosynthethis history ysis of the EWs relative to the solar spectrum (see Bedell of the Galactic disk through chemical evolution models. et al. 2014; Spina et al. 2016b). Based on this data set, Spina et al. (2016a) outlined the [X/Fe]-age relations over a time interval of 10 Gyr (see Fig. 4). They presented the [X/Fe] - 4 Chemical abundances of Sun-like stars age relations for 23 elements (C, O, Na, Mg, Al, Si, S, Ca, with and without planets Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Ba, La, Ce, Nd, and Eu). Their main results revealed that each different class of The connection (probably bi-directional) between stellar elements showed distinct evolution with time that relies on and planetary properties has been widely explored. In par- the different characteristics, rates and timescales of the nu- ticular, the very first correlation observed in the field of ex- cleosynthesis sites from which they are produced. The α- oplanetary research was the correlation between the giant- elements are characterized by a [X/Fe] decrement as time planet occurence and stellar metallicity (usually iron con- goes on. Strikingly, an opposite behavior is observed for Ca. tent was used as a proxy for overall metallicity) (e.g. Fischer The iron-peak elements show an early [X/Fe] increase fol- & Valenti 2005; Gonzalez 1997; Santos et al. 2001, 2004;

hosts will lay the groundwork to answer many questions related to formation and evolution of both planets and stars.

4.1 Tc trend

After the first planets were discovered, astronomers tried to search for chemical signatures of planet formation and planet engulfment on the planet-host stars. Several studies, starting from Gonzalez (1997) and Smith et al. (2001), explored a possible trend between the abundances of chemical elements and the condensation temperature (Tc) of the elements. This trend is usually called ”Tc trend“, and the slope of the correlation (slope of the linear fit) of [X/Fe] vs. condensation temperature is usually named ”Tc slope“. Melendez´ et al. (2009) were the first to report a statistically significant deficit of refractory elements (high-Tc) with respect to volatiles (low-Tc) in the Sun compared to solar twin stars (see Fig. 5). The authors suggested that these missing elements were trapped in the terrestrial planets in our solar system. The same conclusion was also reached by Ram´ırez et al. (2009), who analyzed a larger number of solar twins and analogs with and without detected planets. However, these results and explanations were strongly con- tested by Gonzalez´ Hernandez´ et al. (2010) and Gonzalez´ Hernandez´ et al. (2013), who did not find a statistically sig- Fig. 4 [Al/Fe] and [Ni/Fe] ratios as a function of stellar ages. nificant and consistent T trend when comparing stars with The red triangles represent the thick disk stars, while the black c symbols are the thin disk stars. The [X/Fe]-age relations have and without planets, even when evaluating these Tc trends been fitted by linear, hyperbolic and two-segmented line functions for stars with detected super-Earth like planets (see Fig. 6). shown as blue dashed, red solid and green dashed lines, respec- This very exciting possible connection between chemical tively. (Courtesy of Lorenzo Spina). peculiarities of parent stars and formation of planets has also been examined in other works (e.g. Biazzo et al. 2015; Ecuvillon et al. 2006; Hinkel & Kane 2013; Maldonado et al. 2015; Mishenina et al. 2016; Nissen 2015; Saffe et al. Sousa et al. 2011). Later, studies based on large and ho- 2015, 2016; Schuler et al. 2011b; Sozzetti et al. 2006; Spina mogeneous data-sets showed that elements other than iron, et al. 2016a,b; Takeda et al. 2001), but contradictory con- such as, C, O, Mg, and Si, may play a very important role clusions were reached. for planet formation (e.g. Adibekyan et al. 2015a, 2012a,b; Brugamyer et al. 2011; Delgado Mena et al. 2010; Haywood Together with the rocky material accretion (e.g. Schuler 2009; Robinson et al. 2006). et al. 2011b; Spina et al. 2015) and/or rocky material trap (e.g. Melendez´ et al. 2009) in terrestrial planets, several ex- Interestingly, the importance of stellar (and disk) metal- planations are proposed to explain the Tc trend. Adibekyan licity is likely not only limited to the formation of planets. et al. (2014) suggested that the Tc trend strongly depends It is now becoming clear that the architecture, structure and on the stellar age (see Fig. 7) and they found a tentative de- even habitability of planets strongly depend on the chem- pendence on the galactocentric distances of the stars. The ical properties of their hosts (e.g. Adibekyan et al. 2016c, correlation with stellar age was later confirmed by several 2013; Dawson & Murray-Clay 2013; Dorn et al. 2015; San- authors (e.g. Nissen 2015; Spina et al. 2016b), while the tos et al. 2015). In particular we see that the position of plan- possible relation with the galactocentric distances is more ets in the period-mass diagram depends on the metallicity challenging (see Adibekyan et al. 2016b; Maldonado et al. of the host star (Adibekyan et al. 2013; Beauge´ & Nesvorny´ 2015) probably because of its very complex nature or be- 2013). We learned that the presence or absence of gaseous cause the galactocentric distances were estimated indirectly. atmosphere of small-sized planets probably depends on the Maldonado et al. (2015) and Maldonado & Villaver (2016) metallicity (Dawson et al. 2015)and we know that miner- further suggested a significant correlation with the stellar alogical ratios, such as Mg/Si and Fe/Si, may control the radius and mass. Onehag¨ et al. (2014) in turn showed that structure and composition of terrestrial planets (e.g. Bond while the Sun shows a different Tc trend when compared et al. 2010; Dorn et al. 2015; Grasset et al. 2009; Thiabaud to the solar-field twins, it shows a very similar abundance et al. 2014). These results imply that the study of the link trend with Tc when compared to the stars from the open between planet formation processes and properties of their cluster M67. They suggested that the Sun, unlike most stars,

0.15 0.1 O Eu Nd Y 0.10 C S Cu Eu Sr Nd Zr C Zn NaCu Zr O Na Mn Mg VCe Y SiMg BaVSr SUN-STARS 0.05 CrSiCoNi BaCaTi Sc S Mn CrNi CeCa AlSc 0.00 Zn Al 0.0∆ [X/Fe] SUN-STARS Co Ti -0.05 -0.10 -0.1 [X/Fe]

∆ -0.15 HD 93385 ([Fe/H]=+0.02, mp= 8.4 MEARTH, NP = 2) HD 134060 ([Fe/H]=+0.14, mp=11.2 MEARTH, NP = 2)

0 500 T C(K) 1000 1500 0 500 T C(K) 1000 1500 Zn 0.15 O Cu Eu Zn Al 0.1 Sr Y 0.10 C Na Co V Sc Zr Mn Ni Ti Ba Zr

SUN-STARS Mn 0.05 S CrSiMg SrCa Nd O NaCu CrNi Ca

0.0∆ [X/Fe] SUN-STARS Sc Ce S SiMgCo V TiAl 0.00 Ba C Ce Nd -0.05 Y -0.10 -0.1 Eu [X/Fe]

∆ -0.15 HD 45184 ([Fe/H]=+0.05, mp=12.7 MEARTH, NP = 1) HD 189567 ([Fe/H]=-0.24, mp=10.0 MEARTH, NP = 1) 0 O 500 T C(K) 1000 1500 Zr 0 500 T C(K) 1000 Eu 1500 0.15 Ce C Sr Zr Zn Eu BaSr Nd 0.1 0.10 S Ca Y S BaVCe Y Cu Mg Zn Cu Mn CrMgCo TiAl

SUN-STARS Si Ca 0.05 C Na CrCoNi V TiAl Na SiNi NdSc Sc 0.0∆ [X/Fe] SUN-STARS 0.00 Mn O -0.05 -0.10 -0.1 [X/Fe]

∆ -0.15 HD 1461 ([Fe/H]=+0.20, mp= 5.9 MEARTH, NP = 2) HD 96700 ([Fe/H]=-0.18, mp= 9.0 MEARTH, NP = 2)

0 500 T C(K) 1000 1500 0 500 T C(K) 1000 1500

0.15 Sr SZn Nd 0.1 Zn 0.10 O MgEu Zr Mn BaCa Sc Y Cu VSr AlSc O Eu Ce SUN-STARS Ti 0.05 C Mn CrSiNi BaCeCa Y Cu CrNi Ti Zr Na Co 0.0∆ [X/Fe] SUN-STARS SiMg V 0.00 C Na Co NdAl -0.05 S -0.10 -0.1 [X/Fe] Ba

∆ -0.15 HD 31527 ([Fe/H]=-0.17, mp=11.5 MEARTH, NP = 3) HD 134606 ([Fe/H]=+0.27, mp= 9.3 MEARTH, NP = 3)

0 500 T C(K) 1000 1500 0 500 T C(K) 1000 1500 Nd Sr 0.15 MgEu Sr Na Zn Ce Al Zr 0.1 Nd Y Zr 0.10 O Cu V O Eu CeCa Ba Ti Sc Cu Mn Ni V SUN-STARS 0.05 Mn CrCoNi Ca SZn CrSiCo TiAlSc C Na Si Y 0.0∆ [X/Fe] SUN-STARS C Mg 0.00 S -0.05 -0.10 -0.1 [X/Fe]

∆ -0.15 HD 10180 ([Fe/H]=+0.08, mp=11.8 MEARTH, NP > 3) HD 160691 ([Fe/H]=+0.30, mp=10.6 MEARTH, NP > 3) 0 500 1000 1500 0 500 1000 1500

TC (K) TC (K)

Fig. 6 Abundance differences, ∆[X/Fe]SUN−S T ARS , between the Sun and 10 stars hosting super-Earth-like planets (circles). Diamonds show the average abundances in bins of ∆Tc = 150 K. Linear fits to the data points (solid line) and to the mean data points (dashed-dotted line) weighted with the error bars are also displayed. The figure is from Gonzalez´ Hernandez´ et al. (2013). was formed in a dense stellar environment where the proto- However, the comparison of binary systems of twin stars stellar disk was already depleted in refractory elements by should not be affected by the above mentioned processes radiative pressure on dust grains from bright stars before the and effects (e.g. formation time and place) and the only Sun formed (see Gustafsson et al. 2016, for further discus- complications can be related to stellar evolution (if the stars sion). Gustafsson, at this meeting and in a forthcoming pa- do not have exactly the same physical properties e.g. mass). per, has demonstrated that it is difficult in this way to cleanse Several authors studied the Tc trend in binary stars with and enough material for forming a full cluster with such abun- without planetary companions (e.g. Liu et al. 2014; Mack dance characteristics – the photoionization of the gas limits et al. 2016; Saffe et al. 2015) or in binary stars where both the amount of cleansed gas that is cool enough for star for- components host planets (e.g. Biazzo et al. 2015; Ram´ırez mation severely. Gaidos (2015) also suggested that gas-dust et al. 2015; Teske et al. 2015, 2016). Although some sig- segregation in the disk can produce the Tc trend, although nificant differences between the twin pairs in some sys- only a qualitative analysis and discussion was made. tems were reported, in general the results and conclusions of To separate the possible chemical signatures of planet these studies point in different directions. Thus, as a whole, formation from the effects of Galactic chemical evolution, it is difficult to conclude that there are systematic differences in the chemical abundances of stars with and without plan- several authors tried to correct the Tc slope by using the [X/Fe]–age relation (e.g. Spina et al. 2016b; Yana Galarza ets in the binary systems. Moreover, there are discrepancies et al. 2016). However, such kind of corrections are not easy in the results even for the same individual systems such as to perform because of the intrinsic scatter in the [X/Fe]– 16 Cyg AB (e.g. Laws & Gonzalez 2001; Schuler et al. age distributions due, for instance, to migration processes 2011a; Takeda 2005; Tucci Maia et al. 2014). It should be in the Galaxy (e.g. Haywood 2008; Haywood et al. 2013; noted also that there are not many high-precision abundance Minchev et al. 2013; Sellwood & Binney 2002) and possible intercorrelation between different parameters.

studies of binary stars where none of the stars host planets3. These kind of studies might help us to understand what is the largest detectable chemical anomaly not related to terrestrial planet formation.

4.2 Li abundance Lithium, being a light element, can be easily destroyed in the inner layers of solar-type stars, extending to the outer layers if an efficient mixing process is at work. The Li abundance is very sensitive to different process such as rotation- induced and overshooting mixing (e.g. Pinsonneault et al. 1992; Xiong & Deng 2009; Zhang 2012). It also strongly depends on many parameters such as effective temperature, metallicity and age (e.g. Baumann et al. 2010; Carlos et al. 2016; Delgado Mena et al. 2015, 2014; Pinsonneault et al. 1992; Takeda et al. 2010). The presence of stellar compan- ion can also affect the lithium abundance through interac- tions of the components (e.g. Zahn 1994). Even the possibil- ity of the Li production by stellar flares have been discussed in the literature (Canal 1974; Montes & Ramsey 1998), although the recent observations by Honda et al. (2015) does Fig. 5 Differences between [X/Fe] of the Sun and the mean val- not provide any evidence of Li production by superflares. ues in the solar twins (with no detected planets) as a function of Together with the aforementioned processes, it was sug- Tcond. The abundance pattern shows a break at Tcond ∼ 1200 K. The gested that the presence of planets and/or formation of plan- solid lines are fits to the abundance pattern, while the dashed lines ets can also affect the Li content. In particular, several represent the standard deviation from the fits. The figure is from works, starting from King et al. (1997), showed that solar Melendez´ et al. (2009). analogs (in the temperature range of Teff= T ± 80K but a relatively large range of metallicities) with detected planets are systematically more depleted in Li than their ’single’ counterparts (e.g. Castro et al. 2009; Chen & Zhao 2006; Delgado Mena et al. 2014; Figueira et al. 2014; Gonza- lez 2008, 2015; Gonzalez et al. 2010; Israelian et al. 2009, 2004; Takeda et al. 2010). This relation, however, was con- tested by several authors (e.g. Baumann et al. 2010; Car- los et al. 2016; Ghezzi et al. 2010; Luck & Heiter 2006; Ram´ırez et al. 2012; Ryan 2000) arguing that the reported Li depletion in planet hosts relative to the non-hosts can be related to the bias in age, mass and metallicity. Figueira et al. (2014) applied a multivariable regression to simultaneously consider the impact of different parameters (age, metallicity, Teff) on Li abundances. The authors reached the conclusion that planet-hosting stars display a depletion in lithium. As in the case of Tc trend, studying stellar twins in binary systems can help to understand the origin of Li depletion. Probably the most suitable system for this kind of studies is the 16 Cyg binary system. The 16 Cyg system is composed of two solar-type stars which are two of the best observed Kepler targets. A red dwarf is in orbit around 16 Cyg A, and 16 Cyg B hosts a giant planet. The Li abundance is much more depleted in 16 Cyg B than in 16 Cyg A, by a factor of at least 4.7 (King et al. 1997). The interesting as-

Fig. 7 Tc slopes versus ages for the full sample (top) and for the pect of studying the 16 Cyg system is that the two stars have solar analogs (bottom). Gray solid lines provide linear ﬁts to the 3 data points. The ﬁgure is from Adibekyan et al. (2014). One should always bear in mind that detection of low-mass/small- sized planets, especially at large separations, is very hard and the presence of this undetected planets is always possible and very probable since these planets are very common (e.g. Mayor et al. 2014; Mulders et al. 2016).

ferential approach with respect to another star. The results from these varying methods produce abundances that can be highly precise, approaching . 0.01 dex, with exciting new findings as discussed above. Deal et al. (2015) used the TGEC, which includes complete atomic diffusion (including radiative accelerations). By testing the accretion of planetary matter with the same chemical composition as the bulk Earth (Allegre` et al. 1995), they found that the more massive the accreted mass, the more Li depletion occurs at the surface (see Fig. 8) i.e. opposite to a common expectation that the accretion of planetary material should increase the Li abundance. The accretion of a fraction of an Earth mass is enough to explain a Li ratio of 4.7 in the 16 Cyg system. The authors concluded that such a process may be frequent in planet-hosting stars and should be studied in other cases in the future. Fig. 8 Li abundance profiles after the accretion of different It is difficult to determine the highest achievable ac- masses at the beginning of the main sequence in the model of 16 curacy in stellar abundance determinations due to the fact Cyg B (Courtesy of Morgan Deal). An accreted mass lower than that different models and analyses are not always in agree- 0.6⊕ practically does not affect the lithium abundance, while an ac- ment. Additionally, it is complicated to calculate the as- ⊕ cretion of Earth-like chemical composition matter of 0.66 mass sociated error budget including systematics. Going beyond is enough to explain the lithium abundance difference observed 0.01 dex will likely require modelling of stellar (magnetic) between the two stars. activity (e.g. Fabbian & Moreno-Insertis 2015) in some cases even time-dependent phenomena4 like diffusion (e.g. the same age and may be assumed to have the same chemi- Onehag¨ et al. 2014). Employing these techniques requires cal composition. Since the observable parameter difference meticulous work and will be limited to relatively small data between the two stars is very small (e.g. . 0.05M in mass, sets in order to enable extremely high accuracy. It is impor- . 80K in temperature), the currently observed differences tant, for the sake of measuring the true surface abundances in Li abundance is likely to be due to their different evolu- of stars, that we continue to work on high precision spec- tion, related to the fact that one of them hosts a giant planet troscopy while developing the modelling techniques to a while the other does not. higher degree of self-consistency. The fact that 16 Cyg B has a planet suggests that a disk Studying stellar abundances allows a deep insight into may have been in interaction with the star at the beginning the formation and evolution of stars and stellar systems. of its evolution. Recently Deal et al. (2015) studied the im- Namely, [X/Fe]-age correlations can relate whether stars pact of the accretion of metal rich planetary matter onto this were formed from well-mixed molecular clouds or within star. The accretion modifies the surface chemical composi- areas that were enriched to varying degrees by supernovae tion of the star and may trigger an instability called finger- (Nissen 2016). By looking at the abundances with age, it ing (or thermohaline) convection (Deal et al. 2013; Garaud is possible to get a clearer picture of the nucleosynthetic 2011; Theado´ & Vauclair 2012; Vauclair 2004). This insta- enrichment timescales for different element classes (Spina bility occurs in the case of a stable temperature gradient and et al. 2016a). However, studying how stellar abundances an unstable mean molecular weight gradient when the ther- vary when a star hosts planets is not straightforward. There mal diffusivity is larger than the molecular one. This mixing is an on-going controversy as to whether refractory ele- process dilutes the accreted matter and may transport light ments are locked up inside of planets as they form, as shown elements down to their nuclear destruction layers and lead by the Tc trend from some studies, but not from others. The to an extra depletion at the surface. The authors used the solution may be correlated with stellar age, Galactocentric Brown et al. (2013) 1D prescription (determined from 3D distance, or due to a molecular cloud already depleted in re- simulations) to compute the effect of fingering convection. fractory elements prior to star formation. The Li content, in particular, may be depleted in planetary hosts compared to non-hosts. These questions are intriguing because the solu- 5 Summary tions offer a wide range of stellar and planetary evolution scenarios. With a coordination between accurate observed Determining both precise and accurate stellar abundances stellar abundances and detailed models for both stars and is a truly difficult task. There are many different choices planets, we are optimistic that the mysteries underlying the to make: telescopes and instruments, atomic and molecular varying abundance characteristics of Sun-like stars unlike data, 1D or 3D model atmospheres that incorporate either the Sun may be revealed in the future. LTE or NLTE line formation, and techniques that determine abundances with respect to the Sun or in a (line-by-line) dif- 4 See Dupree et al. (2016) for an extreme case.

Acknowledgements. We thank the science organizing committee Baglin, A., Auvergne, M., Barge, P., et al. 2006, in ESA Special of Cool Stars 19 for selecting this splinter session and the local Publication, Vol. 1306, ESA Special Publication, ed. M. Frid- organizing committee for the provided support in organization of lund, A. Baglin, J. Lochard, & L. Conroy, 33 the splinter. We also thank all the participants of the splinter ses- Baumann, P., Ram´ırez, I., Melendez,´ J., Asplund, M., & Lind, K. sion for very active and productive discussion. V.A. and E.D.M 2010, A&A, 519, A87 acknowledge the support from Fundaçao˜ para a Cienciaˆ e Tec- Beauge,´ C. & Nesvorny,´ D. 2013, ApJ, 763, 12 nologia (FCT) through national funds and from FEDER through Beck, P. G., do Nascimento, J., Salabert, D., et al. 2016a, A&A COMPETE2020 by the following grants UID/FIS/04434/2013 (under rev.) & POCI-01-0145-FEDER-007672, PTDC/FIS-AST/7073/2014 & Beck, P. G., Allende Prieto, C., Van Reeth, T., et al. 2016b, A&A, POCI-01-0145-FEDER-016880 and PTDC/FIS-AST/1526/2014 589, A27 & POCI-01-0145-FEDER-016886. V.A. also acknowledges the Beck, P. G., Salabert, D., Garc´ıa, R. A., et al. 2016c, ArXiv support from FCT through Investigador FCT contracts of ref- 1611.04329 erence IF/00650/2015/CP1273/CT0001. E.D.M further acknowl- Bedell, M., Melendez,´ J., Bean, J. L., et al. 2014, ApJ, 795, 23 edges the support of the FCT (Portugal) in the form of the grant Beeck, B., Cameron, R. H., Reiners, A., & Schussler,¨ M. 2013, SFRH/BPD/76606/2011. NRH acknowledges that the results re- A&A, 558, A48 ported herein benefited from collaborations and/or information Bensby, T., Feltzing, S., & Lundstrom,¨ I. 2003, A&A, 410, 527 exchange within NASA’s Nexus for Exoplanet System Science Bensby, T., Feltzing, S., & Oey, M. S. 2014, A&A, 562, A71 (NExSS) research coordination network sponsored by NASA’s Bergemann, M. 2011, MNRAS, 413, 2184 Science Mission Directorate. In addition, N.R.H. also benefited Bergemann, M. & Nordlander, T. 2014, NLTE Radiative Transfer from support of the Vanderbilt Office of the Provost through the in Cool Stars, ed. E. Niemczura, B. Smalley, & W. Pych, 169– Vanderbilt Initiative in Data-intensive Astrophysics (VIDA) fel- 185 lowship. JIGH acknowledges financial support from the Spanish Biazzo, K., Gratton, R., Desidera, S., et al. 2015, A&A, 583, A135 Ministry of Economy and Competitiveness (MINECO) under the Bond, J. C., O’Brien, D. P., & Lauretta, D. S. 2010, Astrophys J, 2 013 Ramon´ y Cajal program MINECO RYC-2013-14875, and 715, 1050 the Spanish ministry project MINECO AYA2014-56359-P. Fund- Borucki, W. J., Koch, D., Basri, G., et al. 2010, Science, 327, 977 ing for the Stellar Astrophysics Centre is provided by The Danish Brown, J. M., Garaud, P., & Stellmach, S. 2013, ApJ, 768, 34 National Research Foundation (Grant DNRF106). PGB acknowl- Brugamyer, E., Dodson-Robinson, S. E., Cochran, W. D., & Sne- edges the ANR (Agence Nationale de la Recherche, France) pro- den, C. 2011, ApJ, 738, 97 gram IDEE (n◦ ANR-12-BS05-0008) ”Interaction Des Etoiles et Canal, R. 1974, ApJ, 189, 531 des Exoplanetes” and received funding from the CNES grants at Carlos, M., Nissen, P. E., & Melendez,´ J. 2016, A&A, 587, A100 CEA. Castro, M., Vauclair, S., Richard, O., & Santos, N. C. 2009, A&A, 494, 663 Cayrel de Strobel, G. 1996, A&A Rev., 7, 243 Chaplin, W. J., Basu, S., Huber, D., et al. 2014, ApJS, 210, 1 References Chen, Y. Q. & Zhao, G. 2006, AJ, 131, 1816 Chiappini, C., Matteucci, F., & Gratton, R. 1997, ApJ, 477, 765 Adibekyan, V., Delgado-Mena, E., Figueira, P., et al. 2016a, A&A, Creevey, O. L., Metcalfe, T. S., Schultheis, M., et al. 2016, A&A 591, A34 (under rev.) Adibekyan, V., Delgado-Mena, E., Figueira, P., et al. 2016b, A&A, Datson, J. 2014, PhD thesis, University of Turku 592, A87 Datson, J., Flynn, C., & Portinari, L. 2015, A&A, 574, A124 Adibekyan, V., Figueira, P., & Santos, N. C. 2016c, Origins of Life Dawson, R. I., Chiang, E., & Lee, E. J. 2015, Mon Not R Astron and Evolution of the Biosphere, 46, 351 Soc, 453, 1471 Adibekyan, V., Santos, N. C., Figueira, P., et al. 2015a, A&A, 581, Dawson, R. I. & Murray-Clay, R. A. 2013, ApJ, 767, L24 L2 Deal, M., Deheuvels, S., Vauclair, G., Vauclair, S., & Wachlin, Adibekyan, V. Z., Benamati, L., Santos, N. C., et al. 2015b, MN- F. C. 2013, A&A, 557, L12 RAS, 450, 1900 Deal, M., Richard, O., & Vauclair, S. 2015, A&A, 584, A105 Adibekyan, V. Z., Delgado Mena, E., Sousa, S. G., et al. 2012a, Delgado Mena, E., Bertran´ de Lis, S., Adibekyan, V.Z., et al. 2015, A&A, 547, A36 A&A, 576, A69 Adibekyan, V. Z., Figueira, P., Santos, N. C., et al. 2013, A&A, Delgado Mena, E., Israelian, G., Gonzalez´ Hernandez,´ J. I., et al. 560, A51 2010, ApJ, 725, 2349 Adibekyan, V. Z., Gonzalez´ Hernandez,´ J. I., Delgado Mena, E., Delgado Mena, E., Israelian, G., Gonzalez´ Hernandez,´ J. I., et al. et al. 2014, A&A, 564, L15 2014, A&A, 562, A92 Adibekyan, V. Z., Santos, N. C., Sousa, S. G., et al. 2012b, A&A, do Nascimento, Jr., J.-D., Garc´ıa, R. A., Mathur, S., et al. 2014, 543, A89 ApJ, 790, L23 Adibekyan, V. Z., Sousa, S. G., Santos, N. C., et al. 2012c, A&A, do Nascimento, Jr., J.-D., Takeda, Y., Melendez,´ J., et al. 2013, 545, A32 ApJl, 771, L31 Allegre,` C. J., Poirier, J.-P., Humler, E., & Hofmann, A. W. 1995, Dorn, C., Khan, A., Heng, K., et al. 2015, A&A, 577, A83 Earth and Planetary Science Letters, 134, 515 Dupree, A. K., Avrett, E. H., & Kurucz, R. L. 2016, ApJ, 821, L7 Amarsi, A. M., Asplund, M., Collet, R., & Leenaarts, J. 2015, MN- Ecuvillon, A., Israelian, G., Santos, N. C., Mayor, M., & Gilli, G. RAS, 454, L11 2006, A&A, 449, 809 Amarsi, A. M., Lind, K., Asplund, M., Barklem, P. S., & Collet, Edvardsson, B., Andersen, J., Gustafsson, B., et al. 1993, A&A, R. 2016, MNRAS, 463, 1518

275, 101 Maldonado, J., Eiroa, C., Villaver, E., Montesinos, B., & Mora, A. Fabbian, D. & Moreno-Insertis, F. 2015, ApJ, 802, 96 2015, A&A, 579, A20 Feltzing, S., Howes, L. M., McMillan, P. J., & Stonkute, E. 2016, Maldonado, J. & Villaver, E. 2016, A&A, 588, A98 ArXiv e-prints Mashonkina, L. 2014, in IAU Symposium, Vol. 298, Setting the Figueira, P., Faria, J. P., Delgado-Mena, E., et al. 2014, A&A, 570, scene for Gaia and LAMOST, ed. S. Feltzing, G. Zhao, N. A. A21 Walton, & P. Whitelock, 355–365 Fischer, D. A. & Valenti, J. 2005, ApJ, 622, 1102 Mayor, M., Lovis, C., & Santos, N. C. 2014, Nature, 513, 328 Freytag, B., Steffen, M., Ludwig, H.-G., et al. 2012, Journal of Melendez,´ J., Asplund, M., Gustafsson, B., & Yong, D. 2009, ApJ, Computational Physics, 231, 919 704, L66 Gaidos, E. 2015, ApJ, 804, 40 Melendez,´ J., Bergemann, M., Cohen, J. G., et al. 2012, A&A, 543, Garaud, P. 2011, ApJl, 728, L30 A29 Ghezzi, L., Cunha, K., Smith, V. V., & de la Reza, R. 2010, ApJ, Merle, T., Thevenin,´ F., Pichon, B., & Bigot, L. 2011, MNRAS, 724, 154 418, 863 Gilli, G., Israelian, G., Ecuvillon, A., Santos, N. C., & Mayor, M. Metcalfe, T. S., Chaplin, W. J., Appourchaux, T., et al. 2012, ApJL, 2006, A&A, 449, 723 748, L10 Gonzalez, G. 1997, MNRAS, 285, 403 Metcalfe, T. S., Creevey, O. L., Dogan,˘ G., et al. 2014, ApJS, 214, Gonzalez, G. 2008, MNRAS, 386, 928 27 Gonzalez, G. 2015, MNRAS, 446, 1020 Minchev, I., Chiappini, C., & Martig, M. 2013, A&A, 558, A9 Gonzalez, G., Carlson, M. K., & Tobin, R. W. 2010, MNRAS, 403, Mishenina, T., Kovtyukh, V., Soubiran, C., & Adibekyan, V. Z. 1368 2016, MNRAS, 462, 1563 Gonzalez´ Hernandez,´ J. I., Delgado-Mena, E., Sousa, S. G., et al. Montes, D. & Ramsey, L. W. 1998, A&A, 340, L5 2013, A&A, 552, A6 Mulders, G. D., Pascucci, I., Apai, D., Frasca, A., & Molenda- Gonzalez´ Hernandez,´ J. I., Israelian, G., Santos, N. C., et al. 2010, Zakowicz, J. 2016, ArXiv e-prints ApJ, 720, 1592 Nissen, P. E. 2015, A&A, 579, A52 Grasset, O., Schneider, J., & Sotin, C. 2009, Astrophys J, 693, 722 Nissen, P. E. 2016, A&A, 593, A65 Gray, D. F. 2005, The Observation and Analysis of Stellar Photo- Nissen, P. E. & Schuster, W. J. 2010, A&A, 511, L10 spheres Onehag,¨ A., Gustafsson, B., & Korn, A. 2014, A&A, 562, A102 Gray, D. F. & Nagel, T. 1989, ApJ, 341, 421 Osorio, Y., Barklem, P. S., Lind, K., et al. 2015, A&A, 579, A53 Gray, D. F. & Toner, C. G. 1986, PASP, 98, 499 Pagel, B. E. J. 2009, Nucleosynthesis and Chemical Evolution of Gustafsson, B., Church, R. P., Davies, M. B., & Rickman, H. 2016, Galaxies A&A, 593, A85 Pinsonneault, M. H., Deliyannis, C. P., & Demarque, P. 1992, Haywood, M. 2008, MNRAS, 388, 1175 ApJS, 78, 179 Haywood, M. 2009, ApJ, 698, L1 Porto de Mello, G. F., da Silva, R., da Silva, L., & de Nader, R. V. Haywood, M., Di Matteo, P., Lehnert, M. D., Katz, D., & Gomez,´ 2014, A&A, 563, A52 A. 2013, A&A, 560, A109 Prakapavicius,ˇ D., Steffen, M., Kucinskas,ˇ A., et al. 2013, Memo- Hinkel, N. R. & Kane, S. R. 2013, MNRAS, 432, 36 rie della Societa Astronomica Italiana Supplementi, 24, 111 Hinkel, N. R., Timmes, F. X., Young, P. A., Pagano, M. D., & Prsa,ˇ A., Harmanec, P., Torres, G., et al. 2016, AJ, 152, 41 Turnbull, M. C. 2014, AJ, 148, 54 Ram´ırez, I., Asplund, M., Baumann, P., Melendez,´ J., & Bensby, Hinkel, N. R., Young, P. A., Pagano, M. D., et al. 2016, ApJS, 226, T. 2010, A&A, 521, A33 4 Ram´ırez, I., Fish, J. R., Lambert, D. L., & Allende Prieto, C. 2012, Honda, S., Notsu, Y., Maehara, H., et al. 2015, PASJ, 67, 85 ApJ, 756, 46 Hui-Bon-Hoa, A. 2008, Ap&SS, 316, 55 Ram´ırez, I., Khanal, S., Aleo, P., et al. 2015, ApJ, 808, 13 Israelian, G., Delgado Mena, E., Santos, N. C., et al. 2009, Nature, Ram´ırez, I., Melendez,´ J., & Asplund, M. 2009, A&A, 508, L17 462, 189 Ram´ırez, I., Melendez,´ J., Bean, J., et al. 2014, A&A, 572, A48 Israelian, G., Santos, N. C., Mayor, M., & Rebolo, R. 2004, A&A, Reddy, B. E., Lambert, D. L., & Allende Prieto, C. 2006, MNRAS, 414, 601 367, 1329 Jofre, P., Heiter, U., Worley, C. C., et al. 2017, A&A, submitted Reddy, B. E., Tomkin, J., Lambert, D. L., & Allende Prieto, C. King, J. R., Deliyannis, C. P., Hiltgen, D. D., et al. 1997, AJ, 113, 2003, MNRAS, 340, 304 1871 Robinson, S. E., Laughlin, G., Bodenheimer, P., & Fischer, D. Korotin, S. A., Andrievsky, S. M., Hansen, C. J., et al. 2015, A&A, 2006, ApJ, 643, 484 581, A70 Romano, D., Karakas, A. I., Tosi, M., & Matteucci, F. 2010, A&A, Laws, C. & Gonzalez, G. 2001, ApJ, 553, 405 522, A32 Lebreton, Y. & Goupil, M. J. 2014, A&A, 569, A21 Ryan, S. G. 2000, MNRAS, 316, L35 Lind, K., Asplund, M., & Barklem, P. S. 2009, A&A, 503, 541 Saffe, C., Flores, M., & Buccino, A. 2015, A&A, 582, A17 Lind, K., Bergemann, M., & Asplund, M. 2012, MNRAS, 427, 50 Saffe, C., Flores, M., Jaque Arancibia, M., Buccino, A., & Jofre,´ Liu, F., Asplund, M., Ram´ırez, I., Yong, D., & Melendez,´ J. 2014, E. 2016, A&A, 588, A81 MNRAS, 442, L51 Salabert, D., Garcia, R. A., Beck, P. G., et al. 2016a, ArXiv Luck, R. E. & Heiter, U. 2006, AJ, 131, 3069 1608.01489 Mack, III, C. E., Stassun, K. G., Schuler, S. C., Hebb, L., & Pepper, Salabert, D., Garcia, R. A., Beck, P. G., et al. 2016b, ArXiv e-prints J. A. 2016, [arXiv:1601.00018] Santos, N. C., Adibekyan, V., Mordasini, C., et al. 2015, A&A, Magic, Z., Collet, R., Asplund, M., et al. 2013, A&A, 557, A26 580, L13

Santos, N. C., Israelian, G., & Mayor, M. 2001, A&A, 373, 1019 Santos, N. C., Israelian, G., & Mayor, M. 2004, A&A, 415, 1153 Schuler, S. C., Cunha, K., Smith, V. V., et al. 2011a, ApJ, 737, L32 Schuler, S. C., Flateau, D., Cunha, K., et al. 2011b, ApJ, 732, 55 Sellwood, J. A. & Binney, J. J. 2002, MNRAS, 336, 785 Shi, J. R., Gehren, T., & Zhao, G. 2011, A&A, 534, A103 Smiljanic, R., Korn, A. J., Bergemann, M., et al. 2014, A&A, 570, A122 Smiljanic, R., Romano, D., Bragaglia, A., et al. 2016, A&A, 589, A115 Smith, V. V., Cunha, K., & Lazzaro, D. 2001, AJ, 121, 3207 Soderblom, D. R. & King, J. R. 1998, in Solar Analogs: Charac- teristics and Optimum Candidates., ed. J. C. Hall, 41 Sousa, S. G., Santos, N. C., Israelian, G., Mayor, M., & Udry, S. 2011, A&A, 533, A141 Sousa, S. G., Santos, N. C., Mayor, M., et al. 2008, A&A, 487, 373 Sozzetti, A., Yong, D., Carney, B. W., et al. 2006, AJ, 131, 2274 Spina, L., Melendez,´ J., Karakas, A. I., et al. 2016a, A&A, 593, A125 Spina, L., Melendez,´ J., & Ram´ırez, I. 2016b, A&A, 585, A152 Spina, L., Palla, F., Randich, S., et al. 2015, A&A, 582, L6 Spite, M., Andrievsky, S. M., Spite, F., et al. 2012, A&A, 541, A143 Takeda, Y. 2005, PASJ, 57, 83 Takeda, Y. 2007, PASJ, 59, 335 Takeda, Y., Honda, S., Kawanomoto, S., Ando, H., & Sakurai, T. 2010, A&A, 515, A93 Takeda, Y., Sato, B., Kambe, E., et al. 2001, PASJ, 53, 1211 Teske, J. K., Ghezzi, L., Cunha, K., et al. 2015, ApJ, 801, L10 Teske, J. K., Khanal, S., & Ram´ırez, I. 2016, ApJ, 819, 19 Theado,´ S. & Vauclair, S. 2012, ApJ, 744, 123 Thiabaud, A., Marboeuf, U., Alibert, Y., et al. 2014, Astron Astro- phys, 562, A27 Trampedach, R., Asplund, M., Collet, R., Nordlund, Å., & Stein, R. F. 2013, ApJ, 769, 18 Tucci Maia, M., Melendez,´ J., & Ram´ırez, I. 2014, ApJ, 790, L25 Tucci Maia, M., Ram´ırez, I., Melendez,´ J., et al. 2016, A&A, 590, A32 Valenti, J. A. & Fischer, D. A. 2005, ApJS, 159, 141 Vauclair, S. 2004, ApJ, 605, 874 Xiong, D. R. & Deng, L. 2009, MNRAS, 395, 2013 Yana Galarza, J., Melendez,´ J., Ram´ırez, I., et al. 2016, A&A, 589, A17 Zahn, J.-P. 1994, A&A, 288, 829 Zhang, Q. S. 2012, MNRAS, 427, 1441