Metallicities and activities of southern stars

Bluhm

et al. 2014

A&A

Self Cite

Context. More than 50 exoplanets have been found around giant stars, revealing different properties when compared to planets orbiting solar-type stars. In particular, they are super-Jupiters and are not found orbiting interior to ∼0.5 AU. Aims. We are conducting a radial velocity study of a sample of 166 giant stars aimed at studying the population of close-in planets orbiting giant stars and how their orbital and physical properties are influenced by the post-MS evolution of the host star. Methods. We have collected multiepoch spectra for all of the targets in our sample. We have computed precision radial velocities from FECH/CHIRON and FEROS spectra, using the I 2 cell technique and the simultaneous calibration method, respectively. Results. We present the discovery of a massive planet around the giant star HIP 105854. The best Keplerian fit to the data leads to an orbital distance of 0.81 ± 0.03 AU, an eccentricity of 0.02 ± 0.03 and a projected mass of 8.2 ± 0.2 M J . With the addition of this new planet discovery, we performed a detailed analysis of the orbital properties and mass distribution of the planets orbiting giant stars. We show that there is an overabundance of planets around giant stars with a ∼ 0.5−0.9 AU, which might be attributed to tidal decay. Additionally, these planets are significantly more massive than those around MS and subgiant stars, suggesting that they grow via accretion either from the stellar wind or by mass transfer from the host star. Finally, we show that planets around evolved stars have lower orbital eccentricities than those orbiting solar-type stars, which suggests that they are either formed in different conditions or that their orbits are efficiently circularized by interactions with the host star.

Section: Line Profile Analysis and Stellar Photometric Variabilitymentioning

confidence: 99%

The properties of planets around giant stars

Jones

Bluhm

et al. 2014

A&A

Self Cite

“…This was determined using the distance from the Hipparcos main sequence as a function of B − V colour where we set all subgiants to have a distance from the main sequence of 1 or greater. The full selection details are explained in Jenkins et al (2008), hereafter referred too as Paper I. Therefore, this plot merely serves to highlight the sample distribution we will discuss in the chapters that follow.…”

Section: Observations and Reductionmentioning

confidence: 99%

“…Such fundamental characterisation is also necessary for a more complete understanding of stellar populations and galactic structure. Studies of stellar chromospheric activity in large samples of nearby stars (Duncan et al 1991;Henry et al 1996;Wright 2004;Jenkins et al 2006Jenkins et al , 2008 have found that the magnetic activity of solar type dwarfs and subgiants follows a bimodal distribution. In addition, the activity of Based on observations made with the ESO telescopes at the La Silla Paranal observatory under programme ID's 076.C-0578(B), 077.C-0192(A), 082.C-0446(A) and 082.C-0446(B).…”

Section: Introductionmentioning

confidence: 99%

Chromospheric activities and kinematics for solar type dwarfs and subgiants: analysis of the activity distribution and the AVR

Murgas

Rojo

et al. 2011

A&A

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111

105

Aims. In this work we present chromospheric activity indices, kinematics, radial-velocities, and rotational velocities for more than 850 FGK-type dwarfs and subgiant stars in the southern hemisphere and test how best to calibrate and measure S -indices from echelle spectra. Methods. We measured our parameters using the high-resolution and high-S /N FEROS echelle spectra acquired for this purpose. Results. We confirm the bimodal distribution of chromospheric activities for such stars and highlight the role that the more active K-dwarfs play in biasing the number of active stars. We show that the age-activity relationship does appear to continue to ages older than the Sun if we simply compare main sequence stars and subgiant stars with an offset of around 2.5 Gyr between the peaks of both distributions. Also we show evidence of an increased spin-down timescale for cool K dwarfs compared with earlier F and G type stars. We highlight that activities drawn from low-resolution spectra (R < 2500) significantly increase the rms scatter when calibrating onto common systems of measurements like the Mt. Wilson system. Also we show that older and widely used catalogues of activities in the south appear to be offset compared to more recent works at the ∼0.1 dex level in log R HK through calibrator drift. In addition, we show how kinematics can be used to preselect inactive stars for future planet search projects. We see the well known trend between projected rotational velocity and activity, however we also find a correlation between kinematic space velocity and chromospheric activity. It appears that after the Vaughan-Preston gap there is a quick step function in the kinematic space motion towards a significantly broader spread in velocities. We speculate on reasons for this correlation and provide some model scenarios to describe the bimodal activity distribution through magnetic saturation, residual low level gas accretion, or accretion by the star of planets or planetesimals. Finally, we provide a new empirical measurement for the disk-heating law, using the latest age-activity relationships to reconstruct the age-velocity distribution for local disk stars. We find a value of 0.337 ± 0.045 for the exponent of this power law (i.e. σ tot ∝ t 0.337 ), in excellent agreement with those found using isochrone fitting methods and with theoretical disk-heating models.

“…FEROS has a resolving power of R ∼ 48 000, an efficiency of ∼20% and provides an almost complete optical spectral coverage (∼3500−9200 Å), which allows us to study many absorption lines in the optical range (used in the chemical analisys and in our radial velocity computations) and also to study the emission in the core of the Ca ii HK lines (3933 and 3968 Å), which are used as chromospheric activity indicators (e.g. Jenkins et al 2008, and references therein). The echelle spectrograph mounted on the 1.5 m telescope, can reach a maximum resolution of R ∼ 45 000 with an efficiency of ∼1% and covers a spectral region between 4020 Å and 7100 Å.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Study of the impact of the post-MS evolution of the host star on the orbits of close-in planets

Jones

Rojo

et al. 2011

A&A

Self Cite

Context. To date, more than 30 planets have been discovered around giant stars, but only one of them has been found to be orbiting within 0.6 AU from the host star, in direct contrast to what is observed for FGK dwarfs. This result suggests that evolved stars destroy/engulf close-in planets during the red giant phase. Aims. We are conducting a radial velocity survey of 164 bright G and K giant stars in the southern hemisphere with the aim of studying the effect of the host star evolution on the inner structure of planetary systems. In this paper we present the spectroscopic atmospheric parameters (T eff , log g, ξ, [Fe/H]) and the physical properties (mass, radius, evolutionary status) of the program stars. In addition, rotational velocities for all of our targets were derived. Methods. We used high resolution and high S/N spectra to measure the equivalent widths of many Fe i and Fe ii lines, which were used to derive the atmospheric parameters by imposing local thermodynamic and ionization equilibrium. The effective temperatures and metallicities were used, along with stellar evolutionary tracks to determine the physical properties and evolutionary status of each star. Results. We found that our targets are on average metal rich and they have masses between ∼1.0 M and 3.5 M . In addition, we found that 122 of our targets are ascending the RGB, while 42 of them are on the HB phase.