Context. Tidal interactions between planets and their host stars are not well understood, but may be an important factor in their formation, structure, and evolution. Previous studies suggest that ...these tidal interactions may be responsible for discrepancies between the ages of exoplanet host stars estimated using stellar models (isochronal age estimates) and age estimates based on the stars’ rotation periods (gyrochronological age estimates). Recent improvements in our understanding of the rotational evolution of single stars and a substantial increase in the number of exoplanet host stars with accurate rotation period measurements make it worthwhile to revisit this question. Aims. Our aim is to determine whether the gyrochronological age estimates for transiting exoplanet host stars with accurate rotation period measurements are consistent with their isochronal age estimates, and whether this is indicative of tidal interaction between the planets and their host stars. Methods. We have compiled a sample of 28 transiting exoplanet host stars with measured rotation periods, including two stars (HAT-P-21 and WASP-5) for which the rotation period based on the light curve modulation is reported here for the first time. We use our recently developed Bayesian Markov chain Monte Carlo method to determine the joint posterior distribution for the mass and age of each star in the sample. We extend our Bayesian method to include a calculation of the posterior distribution of the gyrochronological age estimate that accounts for the uncertainties in the mass and age, the strong correlation between these values, and the uncertainties in the mass-rotation-age calibration. Results. The gyrochronological age estimate (τgyro) is significantly lower than the isochronal age estimate for about half of the stars in our sample. Tidal interactions between the star and planet are a reasonable explanation for this discrepancy in some cases, but not all. The distribution of τgyro values is evenly spread from very young ages up to a maximum value of a few Gyr, i.e. there is no obvious pile-up of stars at very low or very high values of τgyro as might be expected if some evolutionary or selection effect were biasing the age distribution of the stars in this sample. There is no clear correlation between τgyro and the strength of the tidal force on the star due to the innermost planet. There is clear evidence that the isochronal age estimates for some K-type stars are too high, and this may also be the case for some G-type stars. This may be the result of magnetic inhibition of convection. The densities of HAT-P-11 and WASP-84 are too high to be reproduced by any stellar models within the observed constraints on effective temperature and metallicity. These stars may have strongly enhanced helium abundances. There is currently no satisfactory explanation for the discrepancy between the young age for CoRoT-2 estimated from either gyrochronology or its high lithium abundance, and the extremely old age for its K-type stellar companion inferred from its very low X-ray flux. Conclusions. There is now strong evidence that the gyrochronological age estimates for some transiting exoplanet host stars are significantly lower than the isochronal age estimates, but it is not always clear that this is good evidence for tidal interactions between the star and the planet.
Context.
Eclipsing, spectroscopic double-lined binary star systems are excellent laboratories for calibrating theories of stellar interior structure and evolution. Their precise and accurate masses ...and radii measured from binary dynamics offer model-independent constraints and challenge current theories of stellar evolution.
Aims.
We aim to investigate the mass discrepancy in binary stars. This is the significant difference between stellar components’ masses measured from binary dynamics and those inferred from models of stellar evolution via positions of the components in the
T
eff
− log
g
Kiel diagram. We study the effect of near-core mixing on the mass of the convective core of the stars and interpret the results in the context of the mass discrepancy.
Methods.
We fitted stellar isochrones computed from a grid of
MESA
stellar evolution models to a homogeneous sample of eleven high-mass binary systems. Two scenarios are considered where individual stellar components of a binary system are treated independent of each other and where they are forced to have the same age and initial chemical composition. We also study the effect of the microturbulent velocity and turbulent pressure on the atmosphere model structure and stellar spectral lines, and its link with the mass discrepancy.
Results.
We find that the mass discrepancy is present in our sample and that it is anti-correlated with the surface gravity of the star. No correlations are found with other fundamental and atmospheric parameters, including the stellar mass. The mass discrepancy can be partially accounted for by increasing the amount of near-core mixing in stellar evolution models. We also find that ignoring the microturbulent velocity and turbulent pressure in stellar atmosphere models of hot evolved stars results in the overestimation of their effective temperature by up to 8%. Together with enhanced near-core mixing, this can almost entirely account for the ∼30% mass discrepancy found for the evolved primary component of V380 Cyg.
Conclusions.
We find a strong link between the mass discrepancy and the convective core mass. The mass discrepancy can be solved by considering the combined effect of extra near-core boundary mixing and the consistent treatment in the spectrum analysis of hot evolved stars. Our binary modelling results in convective core masses between 17 and 35% of the stellar mass, which is in excellent agreement with the results from gravity-mode asteroseismology of single stars. This implies larger helium core masses near the end of the main sequence than have been anticipated so far.
Context. Two independent investigations of the atmosphere of the hot Jupiter HAT-P-12b by two different groups resulted in discrepant solutions. Using broad-band photometry from the ground, one study ...found a flat and featureless transmission spectrum that was interpreted as gray absorption by dense cloud coverage. The second study made use of Hubble Space Telescope (HST) observations and found Rayleigh scattering at optical wavelengths caused by haze. Aims. The main purpose of this work is to determine the source of this inconsistency and provide feedback to prevent similar discrepancies in future analyses of other exoplanetary atmospheres. Methods. We studied the observed discrepancy via two methods. With further broad-band observations in the optical wavelength regions, we strengthened the previous measurements in precision, and with a homogeneous reanalysis of the published data, we were able to assess the systematic errors and the independent analyses of the two different groups. Results. Repeating the analysis steps of both works, we found that deviating values for the orbital parameters are the reason for the aforementioned discrepancy. Our work showed a degeneracy of the planetary spectral slope with these parameters. In a homogeneous reanalysis of all data, the two literature data sets and the new observations converge to a consistent transmission spectrum, showing a low-amplitude spectral slope and a tentative detection of potassium absorption.
Abstract
We announce the detection of recurring sets of recurring starspot occultation events in the short-cadence K2 light curve of Qatar-2, a K dwarf star transited every 1.34 d by a hot Jupiter. ...In total, we detect 34 individual starspot occultation events, caused by five different starspots, occulted in up to five consecutive transits or after a full stellar rotation. The longest recurring set of recurring starspot occultations spans over three stellar rotations, setting a lower limit for the longest starspot lifetime of 58 d. Starspot analysis provided a robust stellar rotational period measurement of 18.0 ± 0.2 d and indicates that the system is aligned, having a sky-projected obliquity of 0° ± 8°. A pronounced rotational modulation in the light curve has a period of 18.2 ± 1.6 d, in agreement with the rotational period derived from the starspot occultations. We tentatively detect an ellipsoidal modulation in the phase curve, with a semi-amplitude of 18 ppm, but cannot exclude the possibility that this is the result of red noise or imperfect removal of the rotational modulation. We detect no transit-timing and transit-duration variations with upper limits of 15 s and 1 min, respectively. We also reject any additional transiting planets with transit depths above 280 ppm in the orbital period region 0.5–30 d.
ABSTRACT Given the potential of ensemble asteroseismology for understanding fundamental properties of large numbers of stars, it is critical to determine the accuracy of the scaling relations on ...which these measurements are based. From several powerful validation techniques, all indications so far show that stellar radius estimates from the asteroseismic scaling relations are accurate to within a few percent. Eclipsing binary systems hosting at least one star with detectable solar-like oscillations constitute the ideal test objects for validating asteroseismic radius and mass inferences. By combining radial velocity (RV) measurements and photometric time series of eclipses, it is possible to determine the masses and radii of each component of a double-lined spectroscopic binary. We report the results of a four-year RV survey performed with the échelle spectrometer of the Astrophysical Research Consortium's 3.5 m telescope and the APOGEE spectrometer at Apache Point Observatory. We compare the masses and radii of 10 red giants (RGs) obtained by combining radial velocities and eclipse photometry with the estimates from the asteroseismic scaling relations. We find that the asteroseismic scaling relations overestimate RG radii by about 5% on average and masses by about 15% for stars at various stages of RG evolution. Systematic overestimation of mass leads to underestimation of stellar age, which can have important implications for ensemble asteroseismology used for Galactic studies. As part of a second objective, where asteroseismology is used for understanding binary systems, we confirm that oscillations of RGs in close binaries can be suppressed enough to be undetectable, a hypothesis that was proposed in a previous work.
The eclipsing binary LL Aqr consists of two late-type stars in an eccentric orbit with a period of 20.17 d. We use an extensive light curve from the SuperWASP survey augmented by published radial ...velocities and UBV light curves to measure the physical properties of the system. The primary star has a mass of 1.167 ± 0.009 M⊙ and a radius of 1.305 ± 0.007 R⊙. The secondary star is an analogue of the Sun, with a mass and radius of 1.014 ± 0.006 M⊙ and 0.990 ± 0.008 R⊙ respectively. The system shows no signs of stellar activity: the upper limit on spot-induced rotational modulation is 3 mmag, it is slowly rotating, has not been detected at X-ray wavelengths, and the calcium H and K lines exhibit no emission. Theoretical stellar models provide a good match to its properties for a sub-solar metal abundance of Z = 0.008 and an age of 2.5 Gyr. Most low-mass eclipsing binary systems are found to have radii larger than expected from theoretical predictions, blamed on tidally-enhanced magnetic fields in these short-period systems. The properties of LL Aqr support this scenario: it exhibits negligible tidal effects, shows no signs of magnetic activity, and matches theoretical models well.
WASP-104b is Darker Than Charcoal Mo nik, T.; Hellier, C.; Southworth, J.
The Astronomical journal,
08/2018, Letnik:
156, Številka:
2
Journal Article
Recenzirano
Odprti dostop
By analyzing the K2 short-cadence data from Campaign 14, we detect phase-curve modulation in the light curve of the hot-Jupiter host star WASP-104. The ellipsoidal modulation is detected with high ...significance and in agreement with theoretical expectations, while Doppler beaming and reflection modulations are detected tentatively. We show that the visual geometric albedo is lower than 0.03 at 95% confidence, making it one of the least-reflective planets found to date. The light curve also exhibits a rotational modulation, implying a stellar rotational period likely to be near 23 or 46 days. In addition, we refine the system parameters and place tight upper limits for transit timing and duration variations, starspot occultation events, and additional transiting planets.
ABSTRACT
Stars that are both pulsating and eclipsing offer an important opportunity to better understand many of the physical phenomena that occur in stars, because it is possible to measure the ...pulsation frequencies of stars for which the masses and radii are known precisely and accurately. KIC 9851944 is a double-lined detached eclipsing binary containing two F-stars which show both pressure and gravity mode pulsations. We present an analysis of new high-resolution spectroscopy of the system and high-quality light curves from the Kepler and TESS space missions. We determine the masses and effective temperatures of the stars to 0.6 per cent precision, and their radii to 1.0 and 1.5 per cent precision. The secondary component is cooler, but larger and more massive than the primary so is more evolved; both lie inside the δ Scuti and γ Doradus instability strips. We measure a total of 133 significant pulsation frequencies in the light curve, including 14 multiplets that each contain between 3 and 19 frequencies. We find evidence for tidal perturbations to some of the p and g modes, attribute a subset of the frequencies to either the primary or secondary star, and measure a buoyancy radius and near-core rotational frequency for the primary component. KIC 9851944 is mildly metal-rich and MIST isochrones from the MESA evolutionary code agree well with the observed properties of the system for an age of 1.25 Gyr.
We describe seven exoplanets transiting stars of brightness V = 10.1-12.4. WASP-130b is a 'warm Jupiter' having an orbital period of 11.6 d around a metal-rich G6 star. Its mass and radius (1.23 plus ...or minus 0.04 M sub( Jup) and 0.89 plus or minus 0.03 R sub( Jup)) support the trend that warm Jupiters have smaller radii than hot Jupiters. WASP-131b is a bloated Saturn-mass planet (0.27 M sub( Jup) and 1.22 R sub( Jup)). Its large scaleheight and bright (V = 10.1) host star make it a good target for atmospheric characterization. WASP-132b (0.41 M sub( Jup) and 0.87 R sub( Jup)) is among the least irradiated and coolest of WASP planets, having a 7.1-d orbit around a K4 star. WASP-139b is a 'super-Neptune' akin to HATS-7b and HATS-8b, being the lowest mass planet yet found by WASP (0.12 M sub( Jup) and 0.80 R sub( Jup)). The metal-rich K0 host star appears to be anomalously dense, akin to HAT-P-11. WASP-140b is a 2.4-M sub( Jup) planet in an eccentric (e = 0.047 plus or minus 0.004) 2.2-d orbit. The planet's radius is large (1.4 R sub( Jup)), but uncertain owing to the grazing transit (b = 0.93). The 10.4-d rotation period of the K0 host star suggests a young age, and the time-scale for tidal circularization is likely to be the lowest of all known eccentric hot Jupiters. WASP-141b (2.7 M sub( Jup), 1.2 R sub( Jup) and P = 3.3 d) and WASP-142b (0.84 M sub( Jup), 1.53 R sub( Jup) and P = 2.1 d) are typical hot Jupiters orbiting metal-rich F stars. We show that the period distribution within the hot-Jupiter bulge does not depend on the metallicity of the host star.
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