Site Map
Follow us on Facebook Follow us on Twitter YouTube channel
Centro de Astrofísica da Universidade do Porto

Exploring the α-enhancement of metal-poor planet-hosting stars.
The Kepler and HARPS samples
(Research Note)

V. Zh. Adibekyan, E. Delgado Mena, S. G. Sousa, N. C. Santos, G. Israelian, J. I. González Hernández, M. Mayor, A. A. Hakobyan

Recent studies have shown that at low metallicities Doppler-detected planet-hosting stars tend to have high a-content and to belong to the thick disk. We used the reconnaissance spectra of 87 Kepler planet candidates and data available from the HARPS planet search survey to explore this phenomenon. Using the traditional spectroscopic abundance analysis methods, we derived Ti, Ca, and Cr abundances for the Kepler stars. In the metallicity region –0.65 < [Fe/H] < –0.3 dex, the fraction of Ti-enhanced thick-disk HARPS planet harboring stars is 12.3 ± 4.1%, and for their thin-disk counterparts this fraction is 2.2 ± 1.3%. Binomial statistics give a probability of 0.008 that this could have occurred by chance. Combining the two samples (HARPS and Kepler) reinforces the significance of this result (P ~ 99.97%). Since most of these stars harbor small sized or low-mass planets we can assume that, although terrestrial planets can be found in a low-iron regime, they are mostly enhanced by α-elements. This implies that early formation of rocky planets could start in the Galactic thick disk, where the chemical conditions for their formation are more favorable.

stars: abundances – planetary systems

Table with chemical abundances is only available at the CDS via anonymous ftp to ( or via

Astronomy and Astrophysics
Volume 547, Page A36_1
November 2012

>> PDF>> ADS>> DOI

Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

Proceed on CAUP's website|Go to IA website