A critical reassessment of the fundamental properties of Gas Giant Host Star Gliese 504

A critical reassessment of the fundamental properties of GJ 504: Chemical composition and age

Authors:

D'Orazi et al

Abstract:

The recent development of brand new observational techniques and theoretical models have greatly advanced the exoplanet research field. Despite significant achievements, which have allowed the detection of thousands extrasolar systems, a comprehensive understanding of planetary formation and evolution mechanisms is still desired. One relevant limitation is given by the accuracy in the measurements of planet-host star ages. The star GJ 504 has been found to host a substellar companion whose nature is strongly debated. There has been a recent difference of opinion in the literature owing to the uncertainty on the age of the system: a young age of ∼ 160 Myr would imply a giant planet as a companion, but a recent revision pointing to a solar age (∼ 4 Gyr) instead suggests a brown dwarf. With the aim of shedding light on this debated topic, we have carried out a high-resolution spectroscopic study of GJ 504 to derive stellar parameters, metallicity, and abundances of both light and heavy elements, providing a full chemical characterisation. The main objective is to infer clues on the evolutionary stage (hence the age) of this system. We performed a strictly differential (line-by-line) analysis of GJ 504 with respect to two reference stars, that is the planet-host dwarf ι Hor and the subgiant HIP 84827. The former is crucial in this context because its stellar parameters (hence the evolutionary stage) is well constrained from asteroseismic observations. Regardless of the zero point offsets, our differential approach allows us to put tight constraints on the age of GJ 504 with respect to ι Hor, thereby minimising the internal uncertainties. We found that the surface gravity of GJ 504 is 0.2 ± 0.07 dex lower than that of the main-sequence star ι Hor, suggesting a past turn-off evolution[...]

κ Andromedae Hosts a 22 Jupiter Mass SuperJupiter

The Age of the Directly-Imaged Planet Host Star κ Andromedae Determined From Interferometric Observations

Authors:

Jones et al

Abstract:

κ Andromedae, an early type star that hosts a directly imaged low mass companion, is expected to be oblate due to its rapid rotational velocity (vsini = ∼162 km s−1). We observed the star with the CHARA Array's optical beam combiner, PAVO, measuring its size at multiple orientations and determining its oblateness. The interferometric measurements, combined with photometry and this vsini value are used to constrain an oblate star model that yields the fundamental properties of the star and finds a rotation speed that is ∼85\% of the critical rate and a low inclination of ∼30∘. Three modeled properties (the average radius, bolometric luminosity, and equatorial velocity) are compared to MESA evolution models to determine an age and mass for the star. In doing so, we determine an age for the system of 47+27−40 Myr. Based on this age and previous measurements of the companion's temperature, the BHAC15 evolution models imply a mass for the companion of 22+8−9 MJ.

Eating Planets Can Make Stars Appear Older Than They are

Effect of planet ingestion on low-mass stars evolution: the case of 2MASS J08095427–4721419 star in the Gamma Velorum cluster

Authors:

Tognelli et al

Abstract:

We analysed the effects of planet ingestion on the characteristics of a pre-MS star similar to the Gamma Velorum cluster member 2MASS J08095427–4721419 (#52). We discussed the effects of changing the age t0 at which the accretion episode occurs, the mass of the ingested planet and its chemical composition. We showed that the mass of the ingested planet required to explain the current [Fe/H]#52 increases by decreasing the age t0 and/or by decreasing the Iron content of the accreted matter. We compared the predictions of a simplified accretion method – where only the variation of the surface chemical composition is considered – with that of a full accretion model that properly accounts for the modification of the stellar structure. We showed that the two approaches result in different convective envelope extension which can vary up to 10 percent. We discussed the impact of the planet ingestion on a stellar model in the colour-magnitude diagram, showing that a maximum shift of about 0.06 dex in the colour and 0.07 dex in magnitude are expected and that such variations persist even much later the accretion episode. We also analysed the systematic bias in the stellar mass and age inferred by using a grid of standard non accreting models to recover the characteristics of an accreting star. We found that standard non accreting models can safely be adopted for mass estimate, as the bias is \la6 percent, while much more caution should be used for age estimate where the differences can reach about 60 percent.

Taurus Stars Have Long Lasting Protoplanetary Disks

The age of Taurus - environmental effects on disc lifetimes

Authors:

Rees et al

Abstract:

Using semi-empirical isochrones, we find the age of the Taurus star-forming region to be 3-4 Myr. Comparing the disc fraction in Taurus to young massive clusters suggests discs survive longer in this low density environment. We also present a method of photometrically de-reddening young stars using iZJH data.

Rotation, differential rotation, and gyrochronology of active Kepler stars

Rotation, differential rotation, and gyrochronology of active Kepler stars

Authors:

Reinhold et al

Abstract:

The high-precision photometry from the CoRoT and Kepler satellites has led to measurements of surface rotation periods for tens of thousands of stars. Our main goal is to derive ages of thousands of field stars using consistent rotation period measurements in different gyrochronology relations. Multiple rotation periods are interpreted as surface differential rotation (DR). We re-analyze the sample of 24,124 Kepler stars from Reinhold et al. (2013) using different approaches based on the Lomb-Scargle periodogram. Each quarter (Q1-Q14) is treated individually using a prewhitening approach. Additionally, the full time series, and different segments thereof are analyzed. For more than 18,500 stars our results are consistent with the rotation periods from McQuillan et al. (2014). Thereof, more than 12,300 stars show multiple significant peaks, which we interpret as DR. Gyrochronology ages between 100 Myr and 10 Gyr were derived for more than 17,000 stars using different gyrochronology relations. We find a bimodal age distribution for Teff between 3200-4700 K. The derived ages reveal an empirical activity-age relation using photometric variability as stellar activity proxy. Additionally, we found 1079 stars with extremely stable (mostly short) periods. Half of these periods may be associated with rotation stabilized by non-eclipsing companions, the other half might be due to pulsations. The derived gyrochronology ages are well constrained since more than 93.0 % of the stars seem to be younger than the Sun where calibration is most reliable. Explaining the bimodality in the age distribution is challenging, and limits accurate stellar age predictions. The existence of cool stars with almost constant rotation period over more than three years of observation might be explained by synchronization with stellar companions, or a dynamo mechanism keeping the spot configurations extremely stable.

Determing the Ages of Exoplanetary Host Stars Through Stromgren Photometric Methods

THE AGES OF EARLY-TYPE STARS: STRÖMGREN PHOTOMETRIC METHODS CALIBRATED, VALIDATED, TESTED, AND APPLIED TO HOSTS AND PROSPECTIVE HOSTS OF DIRECTLY IMAGED EXOPLANETS

Authors:

David et al

Abstract:

Age determination is undertaken for nearby early type (BAF) stars, which constitute attractive targets for high-contrast debris disk and planet imaging surveys. Our analysis sequence consists of acquisition of $uvby\beta $ photometry from catalogs, correction for the effects of extinction, interpolation of the photometry onto model atmosphere grids from which atmospheric parameters are determined, and finally, comparison to the theoretical isochrones from pre-main sequence through post-main sequence stellar evolution models, accounting for the effects of stellar rotation. We calibrate and validate our methods at the atmospheric parameter stage by comparing our results to fundamentally determined ${{T}_{{\rm eff}}}$ and ${\rm log} g$ values. We validate and test our methods at the evolutionary model stage by comparing our results on ages to the accepted ages of several benchmark open clusters (IC 2602, α Persei, Pleiades, Hyades). Finally, we apply our methods to estimate stellar ages for 3493 field stars, including several with directly imaged exoplanet candidates.