The Solar Twin Planet Search

Abstract

Context. We are carrying out a search for planets around a sample of solar twin stars using the HARPS spectrograph. The goal of this project is to exploit the advantage offered by solar twins to obtain chemical abundances of unmatched precision. This survey will enable new studies of the stellar composition -planet connection. Aims. We determine the fundamental parameters of the 88 solar twin stars that have been chosen as targets for our experiment. Methods. We used the MIKE spectrograph on the Magellan Clay Telescope to acquire high resolution, high signal-to-noise ratio spectra of our sample stars. We measured the equivalent widths of iron lines and used strict differential excitation/ionization balance analysis to determine atmospheric parameters of unprecedented internal precision: σ(T eff ) = 7 K, σ(log g) = 0.019, σ([Fe/H]) = 0.006 dex, σ(v t ) = 0.016 km s −1 . Reliable relative ages and highly precise masses were then estimated using theoretical isochrones. Results. The spectroscopic parameters we derived are in good agreement with those measured using other independent techniques. There is even better agreement if the sample is restricted to those stars with the most internally precise determinations of stellar parameters in every technique involved. The root-mean-square scatter of the differences seen is fully compatible with the observational errors, demonstrating, as assumed thus far, that systematic uncertainties in the stellar parameters are negligible in the study of solar twins. We find a tight activity-age relation for our sample stars, which validates the internal precision of our dating method. Furthermore, we find that the solar cycle is perfectly consistent both with this trend and its star-to-star scatter. Conclusions. We present the largest sample of solar twins analyzed homogeneously using high quality spectra. The fundamental parameters derived from this work will be employed in subsequent work that aims to explore the connections between planet formation and stellar chemical composition.

High-precision abundances of elements in solar twin stars

“…6, the stellar ages agree very well with the values of Ramírez et al (2014b), who also determined ages from Yonsei-Yale isochrones in the T eff -log g diagram. The small systematic deviation for the three oldest stars may be due to their enhanced [α/Fe] values ([α/Fe] 0.08), which were taken into account when deriving their ages in the present paper, but apparently not by Ramírez et al (2014b). Table 6 together with standard deviations and reduced 0.07 dex) at a given age may be explained by infall of metal-poor gas onto the Galactic disk followed by star formation before mixing evens out the chemical inhomogeneities.…”

“…A comparison with ages derived by Ramírez et al (2014b) indicates that the ages have internal errors ranging from 0.4 to 0.8 Gyr.…”

“…The deviations in T eff and [Fe/H] are compatible with the small errors quoted above, but the rms deviation in log g is larger than expected; stars with log g < 4.35 turn out to have systematically higher log g values in Sousa et al (2008) than in the present paper. These deviations are not seen when comparing with log g values from Ramírez et al (2014b).…”

Shallow extra mixing in solar twins inferred from Be abundances

“…We adopted the ages previously derived by our group (Monroe et al 2013(Monroe et al , 2015Melendez et al 2014a) using the algorithm described in Ramírez et al (Ramírez et al , 2014, which computes the age probability distribution function by comparing the location of the star on the T eff , log g, [Fe/H] parameter space with the values predicted by theory. For the two youngest stars, we also used other age indicators, as described in Monroe et al (2015).…”

The Solar Twin Planet Search

“…HIP11915 was previously established as a solar twin in Ramírez et al (2014) based on its fundamental properties (T eff = 5760 ± 4 K, log g = 4.46 ± 0.01, and [Fe/H] = −0.059 ± 0.004). Its age, estimated from isochrone fitting to be 4.0 ± 0.6 Gyr, is also in keeping with the solar value (Ramírez et al 2014). HIP11915 is a bright (m V = 8.6) star with relatively low activity (log(R HK ) < −4.8), making it an excellent target for highprecision RV monitoring.…”