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Register a new userDetailed elemental abundances of binary stars: Searching for signatures of planet formation and atomic diffusion
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Binary star systems are assumed to be co-natal and coeval, thus to have identical chemical composition. In this work we aim to test the hypothesis that there is a connection between observed element abundance patterns and the formation of planets using binary stars. Moreover, we also want to test how atomic diffusion might influence the observed abundance patterns. We conduct a strictly line-by-line differential chemical abundance analysis of 7 binary systems. Stellar atmospheric parameters and elemental abundances are obtained with extremely high precision (< 3.5%) using the high quality spectra from VLT/UVES and Keck/HIRES. We find that 4 of 7 binary systems show subtle abundance differences (0.01 - 0.03 dex) without clear correlations with the condensation temperature, including two planet-hosting pairs. The other 3 binary systems exhibit similar degree of abundance differences correlating with the condensation temperature. We do not find any clear relation between the abundance differences and the occurrence of known planets in our systems. Instead, the overall abundance offsets observed in the binary systems (4 of 7) could be due to the effects of atomic diffusion. Although giant planet formation does not necessarily imprint chemical signatures onto the host star, the differences in the observed abundance trends with condensation temperature, on the other hand, are likely associated with diverse histories of planet formation (e.g., formation location). Furthermore, we find a weak correlation between abundance differences and binary separation, which may provide a new constraint on the formation of binary systems.
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We present a line-by-line differential analysis of a sample of 16 planet hosting stars and 68 comparison stars using high resolution, high signal-to-noise ratio spectra gathered using Keck. We obtained accurate stellar parameters and high-precision relative chemical abundances with average uncertainties in teff, logg, [Fe/H] and [X/H] of 15 K, 0.034 [cgs], 0.012 dex and 0.025 dex, respectively. For each planet host, we identify a set of comparison stars and examine the abundance differences (corrected for Galactic chemical evolution effect) as a function of the dust condensation temperature, tcond, of the individual elements. While we confirm that the Sun exhibits a negative trend between abundance and tcond, we also confirm that the remaining planet hosts exhibit a variety of abundance $-$ tcond trends with no clear dependence upon age, metallicity or teff. The diversity in the chemical compositions of planet hosting stars relative to their comparison stars could reflect the range of possible planet-induced effects present in these planet hosts, from the sequestration of rocky material (refractory poor), to the possible ingestion of planets (refractory rich). Other possible explanations include differences in the timescale, efficiency and degree of planet formation or inhomogeneous chemical evolution. Although we do not find an unambiguous chemical signature of planet formation among our sample, the high-precision chemical abundances of the host stars are essential for constraining the composition and structure of their exoplanets.
We present a detailed chemical abundance analysis of 15 elements in the planet-hosting wide binary system HD80606 + HD80607 using Keck/HIRES spectra. As in our previous analysis of the planet-hosting wide binary HD20782 + HD20781, we presume that these two G5 dwarf stars formed together and therefore had identical primordial abundances. In this binary, HD80606 hosts an eccentric ($eapprox0.93$) giant planet at $sim$0.5 AU, but HD80607 has no detected planets. If close-in giant planets on eccentric orbits are efficient at scattering rocky planetary material into their host stars, then HD80606 should show evidence of having accreted rocky material while HD80607 should not. Here we show that the trends of abundance versus element condensation temperature for HD80606 and HD80607 are statistically indistinguishable, corroborating the recent result of Saffe et al. This could suggest that both stars accreted similar amounts of rocky material; indeed, our model for the chemical signature of rocky planet accretion indicates that HD80606 could have accreted up to 2.5~$M_{oplus}$ of rocky material---about half that contained in the Solar System and primordial asteroid belt---relative to HD80607 and still be consistent with the data. Since HD80607 has no known giant planets that might have pushed rocky planet material via migration onto that star, we consider it more likely that HD80606/07 experienced essentially no rocky planet accretion. This in turn suggests that the migration history of the HD80606 giant planet must have been such that it ejected any close-in planetary material that might have otherwise been shepherded onto the star.
We obtained high-resolution near-IR spectra of 45 AGB stars located in the Galactic bulge. The aim of the project is to determine key elemental abundances in these stars to help constrain the formation history of the bulge. A further aim is to link the photospheric abundances to the dust species found in the winds of the stars. Here we present a progress report of the analysis of the spectra.
Using high-resolution echelle spectra obtained with Magellan/MIKE, we present a chemical abundance analysis of both stars in the planet-hosting wide binary system HD20782 + HD20781. Both stars are G dwarfs, and presumably coeval, forming in the same molecular cloud. Therefore we expect that they should possess the same bulk metallicities. Furthermore, both stars also host giant planets on eccentric orbits with pericenters $lesssim 0.2,$ AU. We investigate if planets with such orbits could lead to the host stars ingesting material, which in turn may leave similar chemical imprints in their atmospheric abundances. We derived abundances of 15 elements spanning a range of condensation temperatures ($T_{C}approx 40-1660,$ K). The two stars are found to have a mean element-to-element abundance difference of $0.04pm0.07,$ dex, which is consistent with both stars having identical bulk metallicities. In addition, for both stars, the refractory elements ($T_{C} > 900,$ K) exhibit a positive correlation between abundance (relative to solar) and $T_{C}$, with similar slopes of $approx$ $1times10^{-4},$ dex K$^{-1}$. The measured positive correlations are not perfect; both stars exhibit a scatter of $approx$ $5times10^{-5},$ dex K$^{-1}$ about the mean trend, and certain elements (Na, Al, Sc) are similarly deviant in both stars. These findings are discussed in the context of models for giant planet migration that predict the accretion of H-depleted rocky material by the host star. We show that a simple simulation of a solar-type star accreting material with Earth-like composition predicts a positive---but imperfect---correlation between refractory elemental abundances and $T_{C}$. Our measured slopes for HD 20782/81 are consistent with what is predicted for the ingestion of 10--20 Earths by both stars.
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