Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program II: Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu

Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program II: Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu

Authors:

Delgado Mena et al

Abstract:

To understand the formation and evolution of the different stellar populations within our Galaxy it is essential to combine detailed kinematical and chemical information for large samples of stars. We derive chemical abundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu for a large sample of more than 1000 FGK dwarf stars with high-resolution (R∼\,115000) and high-quality spectra from the HARPS-GTO program. The abundances are derived by a standard Local Thermodinamyc Equilibrium (LTE) analysis using measured Equivalent Widths (EWs) injected to the code MOOG and a grid of Kurucz ATLAS9 atmospheres. We find that thick disk stars are chemically disjunct for Zn and Eu and also show on average higher Zr but lower Ba and Y when compared to the thin disk stars. We also discovered that the previously identified high-α metal-rich population is also enhanced in Cu, Zn, Nd and Eu with respect to the thin disk but presents Ba and Y abundances lower on average, following the trend of thick disk stars towards higher metallities and further supporting the different chemical composition of this population. The ratio of heavy-s to light-s elements of thin disk stars presents the expected behaviour (increasing towards lower metallicities) and can be explained by a major contribution of low-mass AGB stars for s-process production at disk metallicities. However, the opposite trend found for thick disk stars suggests that intermediate-mass AGB stars played an important role in the enrichment of the gas from where these stars formed. Previous works in the literature also point to a possible primary production of light-s elements at low metallicities to explain this trend. Finally, we also find an enhancement of light-s elements in the thin disk at super solar metallicities which could be caused by the contribution of metal-rich AGB stars.

A Massive Jupiter orbiting the very low metallicity giant star BD+03 2562 and a possible planet around HD 103485

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. V.: A Massive Jupiter orbiting the very low metallicity giant star BD+03 2562 and a possible planet around HD~103485

Authors:

Villaver et al

Abstract:
We present two evolved stars from the TAPAS (Tracking Advanced PlAnetary Systems) with HARPS-N project devoted to RV precision measurements of identified candidates within the PennState - Torun Centre for Astronomy Planet Search. Evolved stars with planets are crucial to understand the dependency of the planet formation mechanism on the mass and metallicity of the parent star and to study star-planet interactions. The paper is based on precise radial velocity (RV) measurements, for HD 103485 we collected 57 epochs over 3317 days with the Hobby-Eberly Telescope and its High Resolution Spectrograph and 18 ultra-precise HARPS-N data over 919 days. For BD+03 2562 we collected 46 epochs of HET data over 3380 days and 19 epochs of HARPS-N data over 919 days. We present the analysis of the data and the search for correlations between the RV signal and stellar activity, stellar rotation and photometric variability. Based on the available data, we interpret the RV variations measured in both stars as Keplerian motion. Both stars have masses close to Solar (1.11 and 1.14), very low metallicities ([Fe/H]=-0.50 and -0.71), and, both have Jupiter planetary mass companions (m sin i=7 and 6.4 Mj), in close to terrestrial orbits (1.4 and 1.3~au), with moderate eccentricities (e=0.34 and 0.2). However, we cannot totally exclude that the signal in the case of HD~103485 is due to rotational modulation of active regions. Based on the current data, we conclude that BD+03 2562 has a bona fide planetary companion while for HD 103485 we cannot totally exclude that the best explanation for the RV signal modulations is not the existence of a planet but stellar activity. If, the interpretation remains that both stars have planetary companions they represent systems orbiting very evolved stars with very low metallicities, a challenge to the conditions required for the formation of massive giant gas planets.

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in massive planets.

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in massive planets. II. Effect of stellar metallicity

Authors:

Bolmont et al

Abstract:
Observations of hot Jupiter type exoplanets suggest that their orbital period distribution depends on the metallicity of their host star. We investigate here whether the impact of the stellar metallicity on the evolution of the tidal dissipation inside the convective envelope of rotating stars and its resulting effect on the planetary migration might be a possible explanation for this observed statistical trend.

We use a frequency-averaged tidal dissipation formalism coupled to an orbital evolution code and to rotating stellar evolution models to estimate the effect of a change of stellar metallicity on the evolution of close-in planets. We consider here two different stellar masses: 0.4 and 1.0 M⊙ evolving from the early pre-main sequence phase up to the red giant branch.

We show that the metallicity of a star has a strong effect on the stellar parameters which in turn strongly influence the tidal dissipation in the convective region. While on the pre-main sequence the dissipation of a metal poor Sun-like star is higher than the dissipation of a metal rich Sun-like star, on the main sequence it is the opposite. However, for the 0.4 M⊙ star, the dependence of the dissipation with metallicity is much less visible.

Using an orbital evolution model, we show that changing the metallicity leads to different orbital evolutions (e.g., planets migrate farther out from an initially fast rotating metal rich star). By using this model, we qualitatively reproduced the observational trends of the population of hot Jupiters with the metallicity of their host stars. However, more steps are needed to improve our model to try to quantitatively fit our results to the observations. Namely, we need to improve the treatment of the rotation evolution in the orbital evolution model and ultimately we need to consistently couple of the orbital model to the stellar evolution model.

DEPENDENCE OF SMALL PLANET FREQUENCY ON STELLAR METALLICITY HIDDEN BY THEIR PREVALENCE

DEPENDENCE OF SMALL PLANET FREQUENCY ON STELLAR METALLICITY HIDDEN BY THEIR PREVALENCE

Authors:

Zhu et al

Abstract:

The dependence of gas giant planet occurrence rate on stellar metallicity has been firmly established. We extend this so-called planet–metallicity correlation to broader ranges of metallicities and planet masses/radii. In particular, we assume that the planet–metallicity correlation is a power law below some critical saturation threshold, and that the probability of hosting at least one planet is unity for stars with metallicity above the threshold. We then are able to explain the discrepancy between the tentative detection and null detection in previous studies regarding the planet–metallicity correlation for small planets. In particular, we find that the null detection of this correlation can be attributed to the combination of high planet occurrence rate and low detection efficiency. Therefore, a planet–metallicity correlation for small planets cannot be ruled out. We propose that stars with metallicities lower than the solar value are better targets for testing the planet–metallicity correlation for small planets.

Is There a Correlation Between hot Jupiters and Host Star Metallicity?

The metallicity distribution and hot Jupiter rate of the Kepler field: Hectochelle High-resolution spectroscopy for 776 Kepler target stars

Authors:

Guo et al

Abstract:

The occurrence rate of hot Jupiters from the Kepler transit survey is roughly half that of radial velocity surveys targeting solar neighborhood stars. One hypothesis to explain this difference is that the two surveys target stars with different stellar metallicity distributions. To test this hypothesis, we measure the metallicity distribution of the Kepler targets using the Hectochelle multi-fiber, high-resolution spectrograph. Limiting our spectroscopic analysis to 610 dwarf stars in our sample with log(g)>3.5, we measure a metallicity distribution characterized by a mean of [M/H]_{mean} = -0.045 +/- 0.00, in agreement with previous studies of the Kepler field target stars. In comparison, the metallicity distribution of the California Planet Search radial velocity sample has a mean of [M/H]_{CPS, mean} = -0.005 +/- 0.006, and the samples come from different parent populations according to a Kolmogorov-Smirnov test. We refit the exponential relation between the fraction of stars hosting a close-in giant planet and the host star metallicity using a sample of dwarf stars from the California Planet Search with updated metallicities. The best-fit relation tells us that the difference in metallicity between the two samples is insufficient to explain the discrepant Hot Jupiter occurrence rates; the metallicity difference would need to be ≃0.2-0.3 dex for perfect agreement. We also show that (sub)giant contamination in the Kepler sample cannot reconcile the two occurrence calculations. We conclude that other factors, such as binary contamination and imperfect stellar properties, must also be at play.

Metal enrichment leads to low atmospheric C/O ratios in transiting giant exoplanets

Metal enrichment leads to low atmospheric C/O ratios in transiting giant exoplanets

Authors:

Espinoza et al

Abstract:

We predict the carbon-to-oxygen (C/O) ratios in the hydrogen-helium envelope and atmospheres of a sample of nearly 50 relatively cool (Teq< 1000 K) transiting gas giant planets. The method involves planetary envelope metallicity estimates that use the structure models of Thorngren et al. (2016) and the disk and planetary accretion model of \"Oberg et al. (2011). We find that nearly all of these planets are strongly metal-enriched which, coupled with the fact that solid material is the main deliverer of metals in the protoplanetary disk, implies that the substellar C/O ratios of their accreted solid material dominate compared to the enhanced C/O ratio of their accreted gaseous component. We predict that these planets will have atmospheres that are typically reduced in their C/O compared to parent star values independent of the assessed formation locations, with C/O

Behaviour of elements from lithium to europium in stars with and without planets

Behaviour of elements from lithium to europium in stars with and without planets

Authors:

Mishenina et al

Abstract:

We conducted an analysis of the distribution of elements from lithium to europium in 200 dwarfs in the solar neighbourhood ~20 pc with temperatures in the range 4800-6200 K and metallicities [Fe/H] higher than -0.5 dex. Determinations of atmospheric parameters and the chemical composition of the dwarfs were taken from our previous studies. We found that the lithium abundances in the planet-hosting solar-analog stars of our sample were lower than those in the stars without planetary systems. Our results reveal no significant differences exceeding the determination errors for the abundances of investigated elements, except for aluminium and barium, which are more and less abundant in the planet-hosting stars, respectively. We did not find confident dependences of the lithium, aluminium and barium abundances on the ages of our target stars (which is probable because of the small number of stars). Furthermore, we found no correlation between the abundance differences in [El/Fe] and the condensation temperature (Tcond) for stars in the 16 Cyg binary system, unlike the case for 51 Peg (HD 217014), for which a slight excess of volatile elements and a deficit of refractories were obtained relative to those of solar twins. We found that one of the components of 16 Cyg exhibits a slightly higher average abundance than its counterpart (<[El/H](A-B)> = 0.08+/-0.02 dex); however, no significant abundance trend versus Tcond was observed. Owing to the relatively large errors, we cannot provide further constraints for this system.

Six New L Class Brown Dwarfs Found

Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric properties

Authors:

Zhang et al

Abstract:

We have conducted a search for L subdwarf candidates within the photometric catalogues of the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Six of our candidates are confirmed as L subdwarfs spectroscopically at optical and/or near infrared wavelengths. We also present new optical spectra of three previously known L subdwarfs (WISEA J001450.17-083823.4, 2MASS J00412179+3547133, ULAS J124425.75+102439.3). We examined the spectral types and metallicity subclasses classification of known L subdwarfs. We summarised the spectroscopic properties of L subdwarfs with different spectral types and subclasses. We classify these new L subdwarfs by comparing their spectra to known L subdwarfs and L dwarf standards. We estimate temperatures and metallicities of 22 late type M and L subdwarfs by comparing their spectra to BT-Settl models. We find that L subdwarfs have temperatures between 1500 K and 2700 K, which are higher than similarly-typed L dwarfs by around 100-400 K depending on different subclasses and subtypes. We constrained the metallicity ranges of subclasses of M, L and T subdwarfs. We also discussed the spectral type and absolute magnitude relationships for L and T subdwarfs.

Zero Age Planetary Orbit of gas giant planets revisited: reinforcement of the link with Stellar Metallicity

Zero Age Planetary Orbit of gas giant planets revisited: reinforcement of the link with Stellar Metallicity

Authors:

Pinotti et al

Abstract:

In 2005 we suggested a relation between the optimal locus of gas giant planet formation, prior to migration, and the metallicity of the host star, based on the core accretion model and radial profiles of dust surface density and gas temperature. At that time, less than two hundred extrasolar planets were known, limiting the scope of our analysis. Here we take into account the expanded statistics allowed by new discoveries, in order to check the validity of some premises. We compare predictions with the present available data and results for different stellar mass ranges. We find that the Zero Age Planetary Orbit (ZAPO) hypothesis continues to hold after a one order of magnitude increase in discovered planets. In particular, the prediction that metal poor stars harbor planets with an average radius distinctively lower than metal rich ones is still evident in the statistics, and cannot be explained away by chaotic planetary formation mechanisms involving migration and gravitational interaction between planets. The ZAPO hypothesis predicts that in metal poor stars the planets are formed nearer their host stars; as a consequence, they are more frequently engulfed by the stars during the migration process or stripped of their gaseous envelops. The depleted number of gas giant planets around metal poor stars would then be the result of the synergy between low formation probability, as predicted by the core accretion model, and high destruction probability, for the ones that are formed.

A Super-Solar Metallicity For Stars With Hot Rocky Exoplanets

A Super-Solar Metallicity For Stars With Hot Rocky Exoplanets

Authors:

Mulders et al

Abstract:

The host star metallicity provide a measure of the conditions in protoplanetary disks at the time of planet formation. Using a sample of over 20,000 Kepler stars with spectroscopic metallicities from the LAMOST survey, we explore how the exoplanet population depends on host star metallicity as a function of orbital period and planet size. We find that exoplanets with orbital periods less than 10 days are preferentially found around metal-rich stars ([Fe/H]~ 0.15 +- 0.05 dex). The occurrence rates of these hot exoplanets increases to ~30% for super-solar metallicity stars from ~10% for stars with a sub-solar metallicity. Cooler exoplanets, that resides at longer orbital periods and constitute the bulk of the exoplanet population with an occurrence rate of >~ 90%, have host-star metallicities consistent with solar. At short orbital periods, P

Behaviour of elements from lithium to europium in stars with and without planets

Behaviour of elements from lithium to europium in stars with and without planets

Authors:

Flock et al

Abstract:

We conducted an analysis of the distribution of elements from lithium to europium in 200 dwarfs in the solar neighbourhood (∼20 pc) with temperatures in the range 4800–6200 K and metallicities [Fe/H] higher than –0.5 dex. Determinations of atmospheric parameters and the chemical compositions of the dwarfs were taken from our previous studies. We found that the lithium abundances in the planet-hosting solar-analogue stars of our sample were lower than those in the stars without planetary systems. Our results reveal no significant differences exceeding the determination errors for the abundances of investigated elements, except for aluminium and barium, which are more and less abundant in the planet-hosting stars, respectively. We did not find confident dependences of the lithium, aluminium and barium abundances on the ages of our target stars (which is probably because of the small number of stars). Furthermore, we found no correlation between the abundance differences in [El/Fe] and the condensation temperature (T_cond) for stars in the 16 Cyg binary system, unlike the case for 51 Peg (HD 217014), for which a slight excess of volatile elements and a deficit of refractories were obtained relative to those of solar twins. We found that one of the components of 16 Cyg exhibits a slightly higher average abundance than its counterpart (<[El/H](A – B)> = 0.08 ±0.02 dex); however, no significant abundance trend versus T_cond was observed. Owing to the relatively large errors, we cannot provide further constraints for this system.

The Correlation Between Host Star Metallicity & Neptune Class Exoplanets

An upper boundary in the mass-metallicity plane of exo-Neptunes

Authors:

Courcol et al

Abstract:

With the progress of detection techniques, the number of low-mass and small-size exoplanets is increasing rapidly. However their characteristics and formation mechanisms are not yet fully understood. The metallicity of the host star is a critical parameter in such processes and can impact the occurence rate or physical properties of these planets. While a frequency-metallicity correlation has been found for giant planets, this is still an ongoing debate for their smaller counterparts. Using the published parameters of a sample of 157 exoplanets lighter than 40 Mearth, we explore the mass-metallicity space of Neptunes and Super-Earths. We show the existence of a maximal mass that increases with metallicity, that also depends on the period of these planets. This seems to favor in situ formation or alternatively a metallicity-driven migration mechanism. It also suggests that the frequency of Neptunes (between 10 and 40 Mearth) is, like giant planets, correlated with the host star metallicity, whereas no correlation is found for Super-Earths (<10 blockquote="" mearth="">

The Correlation Between Metallicity and Debris Disk mass

The Correlation Between Metallicity and Debris Disk mass

Authors:

Gaspar et al

Abstract:

We find that the initial dust masses in planetary debris disks are correlated with the metallicities of their central stars. We compiled a large sample of systems, including Spitzer, the Herschel DUNES and DEBRIS surveys, and WISE debris disk candidates. We also merged 33 metallicity catalogs to provide homogeneous [Fe/H] and σ[Fe/H] values. We analyzed this merged sample, including 222 detected disks (74 warm and 148 cold) around a total of 187 systems (some with multiple components) and 440 disks with only upper limits (125 warm and 315 cold), around a total of 360 systems. The disk dust masses at a common early evolutionary point in time were determined using our numerical disk evolutionary code, evolving a unique model for each of the 662 disks backward to an age of 1 Myr. We find that disk-bearing stars seldom have metallicities less than [Fe/H] = -0.2 and that the distribution of warm component masses lacks examples with large mass around stars of low metallicity ([Fe/H] less than -0.085). Previous efforts to find a correlation have been largely unsuccessful; the primary improvements supporting our result are: 1.) basing the study on dust masses, not just infrared excess detections; 2.) including upper limits on dust mass in a quantitative way; 3.) accounting for the evolution of debris disk excesses as systems age; 4.) accounting fully for the range of uncertainties in metallicity measurements; and 5.) having a statistically large enough sample.

Carbon Enhanced Metal Poor Stars Might Have Hosted Diamond Worlds

CEMP stars: possible hosts to carbon planets in the early universe

Authors:

Mashian et al

Abstract:

We explore the possibility of planet formation in the carbon-rich protoplanetary disks of carbon-enhanced metal-poor (CEMP) stars, possible relics of the early Universe. The chemically anomalous abundance patterns ([C/Fe] ≥ 0.7) in this subset of low-mass stars suggest pollution by primordial core-collapsing supernovae (SNe) ejecta that are particularly rich in carbon dust grains. By comparing the dust-settling timescale in the protoplanetary disks of CEMP stars to the expected disk lifetime (assuming dissipation via photoevaporation), we determine the maximum distance rmax from the host CEMP star at which carbon-rich planetesimal formation is possible, as a function of the host star's [C/H] abundance. We then use our linear relation between rmax and [C/H], along with the theoretical mass-radius relation derived for a solid, pure carbon planet, to characterize potential planetary transits across host CEMP stars. Given that the related transits are detectable with current and upcoming space-based transit surveys, we suggest initiating an observational program to search for carbon planets around CEMP stars in hopes of shedding light on the question of how early planetary systems may have formed after the Big Bang.

13% of Sun-like Stars Have Neptune Class Exoplanets

The HARPS search for southern extra-solar planets XL. Searching for Neptunes around metal-poor stars

Authors:

Faria et al

Abstract:

Stellar metallicity -- as a probe of the metallicity of proto-planetary disks -- is an important ingredient for giant planet formation, likely through its effect on the timescales in which rocky/icy planet cores can form. Giant planets have been found to be more frequent around metal-rich stars, in agreement with predictions based on the core-accretion theory. In the metal-poor regime, however, the frequency of planets, especially low-mass planets, and how it depends on metallicity are still largely unknown. As part of a planet search programme focused on metal-poor stars, we study the targets from this survey that were observed with HARPS on more than 75 nights. The main goals are to assess the presence of low-mass planets and provide a first estimate of the frequency of Neptunes and super-Earths around metal-poor stars. We perform a systematic search for planetary companions, both by analysing the periodograms of the radial-velocities and by comparing, in a statistically-meaningful way, models with an increasing number of Keplerians. A first constraint on the frequency of planets in our metal-poor sample is calculated considering the previous detection (in our sample) of a Neptune-sized planet around HD 175607 and one candidate planet (with an orbital period of 68.42d and minimum mass Mpsini=11.14±2.47M⊕) for HD 87838, announced in the present study. This frequency is determined to be close to 13% and is compared with results for solar-metallicity stars.

Red Giant Host Star Lithium in Open Cluster has Questionable Link With Exoplanet Presence

Lithium in Open Cluster Red Giants Hosting Substellar Companions

Authors:

Carlberg et al

Abstract:

We have measured stellar parameters, [Fe/H], lithium abundances, rotation, and 12C/13C in a small sample of red giants in three open clusters that are each home to a red giant star that hosts a substellar companion (NGC2423 3, NGC4349 127, and BD+12 1917 in M67). Our goal is to explore whether the presence of substellar companions influences the Li content. Both 12C/13C and stellar rotation are measured as additional tracers of stellar mixing. One of the companion hosts, NGC2423 3, is found to be Li-rich with A(Li)_NLTE=1.56 dex, and this abundance is significantly higher than the A(Li) of the two comparison stars in NGC2423. All three substellar companion hosts have the highest A(Li) and 12C/13C when compared to the control red giants in their respective clusters; however, except for NGC2423 3, at least one control star has similarly high abundances within the uncertainties. Higher A(Li) could suggest that the formation or presence of planets plays a role in the degree of internal mixing on or before the red giant branch. However, a multitude of factors affect A(Li) during the red giant phase, and when the abundances of our sample are compared to abundances of red giants in other open clusters available in the literature, we find that they all fall well within a much larger distribution of A(Li) and 12C/13C. Thus, even the high Li in NGC2423 3 cannot be concretely tied to the presence of the substellar companion.

The Mass-Metallicity Relation for Giant Planets

The Mass-Metallicity Relation for Giant Planets

Authors:

Thorngren et al

Abstract:

Exoplanet discoveries of recent years have provided a great deal of new data for studying the bulk compositions of giant planets. Here we identify 38 transiting giant planets (20M⊕less than M less than 20MJ) whose stellar insolation is low enough (F∗ less than 2×108ergs−1cm−2, or roughly Teff less than 1000) that they are not affected by the hot Jupiter radius inflation mechanism(s). We compute a set of new thermal and structural evolution models and use these models in comparison with properties of the 38 transiting planets (mass, radius, age) to determine their heavy element masses. A clear correlation emerges between the planetary heavy element mass Mz and the total planet mass, approximately of the form Mz∝M‾‾√. This finding is consistent with the core accretion model of planet formation. We also study how stellar metallicity [Fe/H] affects planetary metal-enrichment and find a weaker correlation than has been previously reported from studies with smaller sample sizes. Our results suggest that planets with large heavy element masses are more common around stars with a high iron abundance, but are not found there exclusively. We confirm a strong relationship between the planetary metal-enrichment relative to the parent star Zplanet/Zstar and the planetary mass, but see no relation in Zplanet/Zstar with planet orbital properties or stellar mass. Suggestively, circumbinary planets are more enriched in heavy elements than similar mass single-star planets, but with only four such planets the effect is not yet significant. The large heavy element masses of many planets (greater than 50M⊕) suggest significant amounts of heavy elements in H/He envelopes, rather than cores, such that metal-enriched giant planet atmospheres should be the rule.

HD 175607b: a Hot Neptune in a 29 Day Orbit Around Very Metal Poor G Dwarf

The HARPS search for southern extra-solar planets. XXXIX. HD175607 b, the most metal-poor G dwarf with an orbiting sub-Neptune

Authors:

Mortier et al

Abstract:

Context.

The presence of a small-mass planet (Mp less than 0.1\,MJup) seems, to date, not to depend on metallicity, however, theoretical simulations have shown that stars with subsolar metallicities may be favoured for harbouring smaller planets. A large, dedicated survey of metal-poor stars with the HARPS spectrograph has thus been carried out to search for Neptunes and super-Earths.

Aims.

In this paper, we present the analysis of \object{HD175607}, an old G6 star with metallicity [Fe/H] = -0.62. We gathered 119 radial velocity measurements in 110 nights over a time span of more than nine years.

Methods.

The radial velocities were analysed using Lomb-Scargle periodograms, a genetic algorithm, a Markov chain Monte Carlo analysis, and a Gaussian processes analysis. The spectra were also used to derive stellar properties. Several activity indicators were analysed to study the effect of stellar activity on the radial velocities.

Results.

We find evidence for the presence of a small Neptune-mass planet (Mpsini=8.98±1.10\,M⊕) orbiting this star with an orbital period P=29.01±0.02\, days in a slightly eccentric orbit (e=0.11±0.08). The period of this Neptune is close to the estimated rotational period of the star. However, from a detailed analysis of the radial velocities together with the stellar activity, we conclude that the best explanation of the signal is indeed the presence of a planetary companion rather than stellar related. An additional longer period signal (P∼1400\,d) is present in the data, for which more measurements are needed to constrain its nature and its properties.

Conclusions.

HD 175607 is the most metal-poor FGK dwarf with a detected low-mass planet amongst the currently known planet hosts. This discovery may thus have important consequences for planet formation and evolution theories.

The Eccentricity Distribution of Short-Period ExoPlanets

The Eccentricity Distribution of Short-Period Planet Candidates Detected by Kepler in Occultation

Authors:

Shabram et al

Abstract:

We characterize the eccentricity distribution of a sample of ~50 short-period planet candidates using transit and occultation measurements from NASA's Kepler Mission. First, we evaluate the sensitivity of our hierarchical Bayesian modeling and test its robustness to model misspecification using simulated data. When analyzing actual data assuming a Rayleigh distribution for eccentricity, we find that the posterior mode for the dispersion parameter is σ=0.081±0.0140.003. We find that a two-component Gaussian mixture model for ecosω and esinω provides a better model than either a Rayleigh or Beta distribution. Based on our favored model, we find that ∼90% of planet candidates in our sample come from a population with an eccentricity distribution characterized by a small dispersion (∼0.01), and ∼10% come from a population with a larger dispersion (∼0.22). Finally, we investigate how the eccentricity distribution correlates with selected planet and host star parameters. We find evidence that suggests systems around higher metallicity stars and planet candidates with smaller radii come from a more complex eccentricity distribution.

Exoplanet Signatures and Effect on the Chemical Evolution of Their Host Stars

Planet signatures and effect of the chemical evolution of the Galactic thin-disk stars

Authors:

Spina et al

Abstract:

Context:

Studies based on high-precision abundance determinations revealed that chemical patterns of solar twins are characterised by the correlation between the differential abundances relative to the Sun and the condensation temperatures (Tc) of the elements. It has been suggested that the origin of this relation is related to the chemical evolution of the Galactic disk, but other processes, associated with the presence of planets around stars, might also be involved.

Aims:

We analyse HIRES spectra of 14 solar twins and the Sun to provide new insights on the mechanisms that can determine the relation between [X/H] and Tc.

Methods:

Our spectroscopic analysis produced stellar parameters (Teff, log g, [Fe/H], and ξ), ages, masses, and abundances of 22 elements (C, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, and Ba). We used these determinations to place new constraints on the chemical evolution of the Galactic disk and to verify whether this process alone can explain the different [X/H]-Tc slopes observed so far.

Results:

We confirm that the [X/Fe] ratios of all the species correlate with age. The slopes of these relations allow us to describe the effect that the chemical evolution of the Galactic disk has on the chemical patterns of the solar twins. After subtracting the chemical evolution effect, we find that the unevolved [X/H]-Tc slope values do not depend on the stellar ages anymore. However, the wide diversity among these [X/H]-Tc slopes, covering a range of ±4~10−5 dex K−1, indicates that processes in addition to the chemical evolution may affect the [X/H]-Tc slopes.

Conclusions:

The wide range of unevolved [X/H]-Tc slope values spanned at all ages by our sample could reflect the wide diversity among exo-planetary systems observed so far and the variety of fates that the matter in circumstellar disks can experience.