Abundance difference between components of wide binaries

Abstract

Abstract. We present iron abundance analysis for 23 wide binaries with main sequence components in the temperture range 4900-6300 K, taken from the sample of the pairs currently included in the radial velocity planet search on going at the Telescopio Nazionale Galileo (TNG) using the high resolution spectrograph SARG. The use of a line-by-line differential analysis technique between the components of each pair allows us to reach errors of about 0.02 dex in the iron content difference. Most of the pairs have abundance differences lower than 0.02 dex and there are no pairs with differences larger than 0.07 dex. The four cases of differences larger than 0.02 dex may be spurious because of the larger error bars affecting pairs with large temperature difference, cold stars and rotating stars. The pair HD 219542, previously reported by us to have a different composition, here is shown to be normal. For non-rotating stars warmer than 5500 K, characterized by a thinner convective envelope and for which our analyis appears to be of higher accuracy, we are able to exclude in most cases the consumption of more than 1 Earth Mass of iron (about 5 Earth masses of meteoritic material) during the main sequence lifetime of the stars, placing more stringent limits (about 0.4 Earth masses of iron) in five cases of warm stars. This latter limit is similar to the estimates of rocky material accreted by the Sun during its main sequence lifetime. Combining the results of the present analysis with those for the Hyades and Pleiades, we conclude that the hypothesis that pollution by planetary material is the only mechanism responsible for the highest metallicity of the stars with planets may be rejected at more than 99% level of confidence if the incidence of planets in these samples is as high as 8% and similar to the field stars included in current radial velocity surveys. However, the significance of this result drops considerably if the incidence of planets around stars in binary systems and clusters is less than a half of that around normal field stars.

The GAPS programme with HARPS-N at TNG

“…This is a rare occurrence among binary systems, as in most cases the two components have very similar metal abundances (Desidera et al 2004(Desidera et al , 2006. This result seems to be in contrast with the work by Teske et al (2013), who found the two stars to be similar in physical properties and in iron and nickel abundances, with some evidence of enrichment in C and O abundance of XO-2N compared to XO-2S.…”

“…Elemental abundances 5 were measured using the differential spectral analysis described in Paper II, which is based on the prescriptions reported in detail by Gratton et al (2001) and Desidera et al (2004Desidera et al ( , 2006. In particular, this method gives very accurate results when the binary components are very similar in stellar parameters, as is the case of the XO-2 system.…”

“…We estimated how many heavy elements were being accreted or depleted in one of the components following the prescriptions of Murray et al (2001), as in Desidera et al (2004Desidera et al ( , 2006 Table 2, the difference of iron within the convective zone is ∼10 M ⊕ . Assuming to first order a similar composition of meteoritic material, this corresponds to 50 M ⊕ of heavy elements.…”

“…Obtaining accurate differential abundances is easier for members of stellar clusters (e.g., Yong et al 2013) and binary systems (Gratton et al 2001;Laws & Gonzalez 2001;Desidera et al 2004Desidera et al , 2006Ramírez et al 2011;Liu et al 2014) because here many observational uncertainties related to distances and reddening can be considered common-mode effects. In addition, the most accurate results are obtained from comparing stars that are very similar to each other (Gratton et al 2001;Desidera et al 2004;Liu et al 2014). At the same time, it is also crucial that such stellar samples are accurately scrutinized to determine whether planets exist around them.…”

Catalogs of Wide Binaries: Impact on Galactic Astronomy

“…• studying the impact of planetary systems on the evolution of their host stars via the detailed surface abundances of stars in wide binaries (Desidera et al 2004).…”