Non-interacting main-sequence binaries with different chemical compositions: Evidences of infall of rocky material?

Abstract

Abstract. We performed a careful differential abundance analysis of individual components of six main sequence binaries with separations of a few hundreds of AU. To reduce analysis concerns, we selected systems with almost equal mass components. We were able to derive differential abundances of several elements with errors down to 0.01 dex in the best cases. We found that in four systems the two components have the same chemical composition, within these very severe limits. However, clear differences were found for the two remaining systems (HD 219542 and HD 200466), in both cases the primaries being more Fe-rich than the secondaries, by 0.091 ± 0.009 and 0.053 ± 0.024 dex respectively. Similar differences were found for most of the elements considered in our analysis; however, we found no appreciable difference for volatile elements and a trend for increasing abundance differences with increasing condensation temperature for individual elements, a result similar to that found for some single stars with planets by Smith et al. (2001). Finally, we note that HD 219542A has a Li-abundance comparable to those of Li-rich stars in old open clusters, while no Li is detected in the slightly cooler HD 219542B. We suggest that the primaries of these two systems have accreted rocky planets or the inner dust-rich part of a protoplanetary disk, likely due to gravitational perturbation caused by the presence of the companion.

Abundance Analysis of Planetary Host Stars. I. Differential Iron Abundances

“…Results for 12 stars studied by Sadakane et al (2002) average slopes of element abundance versus condensation temperature for five out of 30 planet host stars (most of them from Gonzalez et al 2001). Furthermore, Gratton et al (2001) found differences in element abundances for two noninteracting main-sequence binaries that might suggest infall of rocky material. Abundance determination for elements other than iron are planned for our program stars to further clarify the situation.…”

The GAPS programme with HARPS-N at TNG

“…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.…”

“…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.…”

Stellar Evolution with Enriched Surface Convection Zones. I. General Effects of Planet Consumption

“…Israelian et al (2001Israelian et al ( , 2003 suggest that the presence of 6 Li in stellar atmospheres is an excellent tracer of rocky material accretion, since this isotope should not usually be present in stars whose convection zones once mixed material to depths with T > 2 ; 10 6 K. They have presented evidence for 6 Li in the star HD 82943 (although the result is disputed; see Reddy et al 2002), arguing that it must have been delivered to the stellar surface at some point by infalling material. Further support for pollution has been provided by differential Fe and Li abundance enhancements in binary systems (Gratton et al 2001;Zucker et al 2002, and references therein), although some of these results have since been reconsidered (Desidera et al 2004). Binaries may provide an ideal environment for identifying the signature of pollution, since the surface composition of a pollution candidate may be easily compared with that of its companion, which has presumably preserved the system's primordial abundances.…”

“…Testing planet consumption in stars in the neighborhood of 1 M , they find that pollution is capable of producing observable surface metallicity enhancements, but the percentage of planetary mass dissolved within the convection zone is highly dependent on the structure of both star and planet. In addition to gas giants, smaller rocky planets and planetesimals have also been cited as potential sources of pollutant material (Gratton et al 2001, and references therein). Because of the current lack of constraint on the amount and type of debris that could be accreted onto stars, pollution is best characterized as a change in metallicity; our models make no prior assumptions about the nature of the polluting planets, except to specify the mass of heavy-element enrichment.…”