Spectroscopic [Fe/H] for 98 extra-solar planet-host stars

Abstract

Abstract. We present stellar parameters and metallicities, obtained from a detailed spectroscopic analysis, for a large sample of 98 stars known to be orbited by planetary mass companions (almost all known targets), as well as for a volume-limited sample of 41 stars not known to host any planet. For most of the stars the stellar parameters are revised versions of the ones presented in our previous work. However, we also present parameters for 18 stars with planets not previously published, and a compilation of stellar parameters for the remaining 4 planet-hosts for which we could not obtain a spectrum. A comparison of our stellar parameters with values of T eff , log g, and [Fe/H] available in the literature shows a remarkable agreement. In particular, our spectroscopic log g values are now very close to trigonometric log g estimates based on Hipparcos parallaxes. The derived [Fe/H] values are then used to confirm the previously known result that planets are more prevalent around metalrich stars. Furthermore, we confirm that the frequency of planets is a strongly rising function of the stellar metallicity, at least for stars with [Fe/H] > 0. While only about 3% of the solar metallicity stars in the CORALIE planet search sample were found to be orbited by a planet, this number increases to more than 25% for stars with [Fe/H] above +0.3. Curiously, our results also suggest that these percentages might remain relatively constant for values of [Fe/H] lower than about solar, increasing then linearly with the mass fraction of heavy elements. These results are discussed in the context of the theories of planetary formation.

Binarity, activity and metallicity among late-type stars

“…The recent observation that (solar-like) stars with planets are on average more metal rich than similar stars without planets (e.g. Santos et al 2001Santos et al , 2004Santos et al , 2005Fischer et al 2003) is at least suggestive that this maybe also the case for binaries. Of particular interest is the fact that the Li abundance seem to differ between single stars and stars which host giant planets , and even between otherwise identical twin-star binaries (Martín et al 2002;Dall et al 2005), possibly related to pre-MS accretion of planetesimals or engulfment of planets.…”

The GAPS programme with HARPS-N at TNG

“…A well-established direct dependence exists between the occurrence rate of giant planets and the metal content of their main-sequence hosts (Gonzalez 1997;Butler et al 2000;Laws et al 2003;Santos et al 2004;Fischer & Valenti 2005;Udry & Santos 2007;Sozzetti et al 2009;Mortier et al 2012). …”

Metallicity and Planet Formation – Observations

“…Santos, Israelian, & Mayor (2004) and demonstrated that giant planet hosts are indeed metal rich compared to the parent sample in planet searches. Santos, Israelian, & Mayor (2004), relative to values from the SPOCS catalog . Systematic difference are evident.…”

“…determined stellar parameters by fitting spectra using SME (Valenti & Piskunov 1996). Santos, Israelian, & Mayor (2004) studied a different sample of stars, using a different spectrograph, different spectral lines, and a different radiative transfer code. They fitted equivalent widths rather than line profiles and adopted a different gravity constraint.…”

“…However, before interpreting these results physically, it is important to check for metallicity bias in the subsample of stars around which Neptune mass planets could have been found. Santos, Israelian, & Mayor (2004) and performed analogous tests for giant planets after Gonzalez (1997) noted that published planet hosts were all metal rich. In this case, Neptunes might only be detectable around stars with low intrinsic velocity variations, which might imply low activity, old age, and hence low metallicity.…”