Simulations predict that hot super-Earth sized exoplanets can have their envelopes stripped by photoevaporation, which would present itself as a lack of these exoplanets. However, this absence in the ...exoplanet population has escaped a firm detection. Here we demonstrate, using asteroseismology on a sample of exoplanets and exoplanet candidates observed during the Kepler mission that, while there is an abundance of super-Earth sized exoplanets with low incident fluxes, none are found with high incident fluxes. We do not find any exoplanets with radii between 2.2 and 3.8 Earth radii with incident flux above 650 times the incident flux on Earth. This gap in the population of exoplanets is explained by evaporation of volatile elements and thus supports the predictions. The confirmation of a hot-super-Earth desert caused by evaporation will add an important constraint on simulations of planetary systems, since they must be able to reproduce the dearth of close-in super-Earths.
ABSTRACT
We perform an asteroseismic investigation of giant stars in the field of NGC 6791 with previous indications of atypical evolution. The analysis uses observations from Kepler and Gaia in ...combination with ground-based photometry, a literature radial-velocity study, and measurements of eclipsing binaries in the cluster. We derive mass, radius, effective temperature, evolutionary stage, and apparent distance modulus of each target. Among the investigated cluster giants we find clear evidence of overmassive and undermassive members, and non-members with strong hints of potential past membership. Our results indicate that about 10 per cent of the red giants in the cluster have experienced mass transfer or a merger. High-resolution high-S/N spectroscopic follow-up could confirm potential past membership of the non-members, and reveal whether certain element abundances might expose the non-standard evolution of overmassive and undermassive stars. If so, field stars of similar type could be identified as what they are, i.e. overmassive or undermassive stars, and not mistakenly classified as younger or older than they are.
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens of thousands of field stars. Tests against independent estimates of these properties are however scarce, ...especially in the metal-poor regime. Here, we report the detection of solar-like oscillations in eight stars belonging to the red-giant branch (RGB) and red-horizontal branch (RHB) of the globular cluster M4. The detections were made in photometric observations from the K2 Mission during its Campaign 2. Making use of independent constraints on the distance, we estimate masses of the eight stars by utilizing different combinations of seismic and non-seismic inputs. When introducing a correction to the Δν scaling relation as suggested by stellar models, for RGB stars we find excellent agreement with the expected masses from isochrone fitting, and with a distance modulus derived using independent methods. The offset with respect to independent masses is lower, or comparable with, the uncertainties on the average RGB mass (4–10 per cent, depending on the combination of constraints used). Our results lend confidence to asteroseismic masses in the metal-poor regime. We note that a larger sample will be needed to allow more stringent tests to be made of systematic uncertainties in all the observables (both seismic and non-seismic), and to explore the properties of RHB stars, and of different populations in the cluster.
HD 187547 was the first candidate that led to the suggestion that solar-like oscillations are present in delta Scuti stars. Longer observations, however, show that the modes interpreted as solar-like ...oscillations have either very long mode lifetimes, longer than 960 days, or are coherent. These results are incompatible with the nature of "pure" stochastic excitation as observed in solar-like stars. Nonetheless, one point is certain: the opacity mechanism alone cannot explain the oscillation spectrum of HD 187547. Here we present new theoretical investigations showing that convection dynamics can intrinsically excite coherent pulsations in the chemically peculiar delta Scuti star HD 187547. More precisely, it is the perturbations of the mean Reynold stresses (turbulent pressure) that drives the pulsations and the excitation takes place predominantly in the hydrogen ionization zone.
We combine results from interferometry, asteroseismology and spectroscopy to determine accurate fundamental parameters of 23 bright solar-type stars, from spectral type F5 to K2 and luminosity ...classes III–V. For some stars we can use direct techniques to determine the mass, radius, luminosity and effective temperature, and we compare with indirect methods that rely on photometric calibrations or spectroscopic analyses. We use the asteroseismic information available in the literature to infer an indirect mass with an accuracy of 4–15 per cent. From indirect methods we determine luminosity and radius to 3 per cent. We find evidence that the luminosity from the indirect method is slightly overestimated (≈ 5 per cent) for the coolest stars, indicating that their bolometric corrections (BCs) are too negative. For Teff we find a slight offset of −40 ± 20 K between the spectroscopic method and the direct method, meaning the spectroscopic temperatures are too high. From the spectroscopic analysis we determine the detailed chemical composition for 13 elements, including Li, C and O. The metallicity ranges from Fe/H=−1.7 to +0.4, and there is clear evidence for α-element enhancement in the metal-poor stars. We find no significant offset between the spectroscopic surface gravity and the value from combining asteroseismology with radius estimates. From the spectroscopy we also determine v sin i and we present a new calibration of macroturbulence and microturbulence. From the comparison between the results from the direct and spectroscopic methods we claim that we can determine Teff, log g and Fe/H with absolute accuracies of 80 K, 0.08 and 0.07 dex. Photometric calibrations of Strömgren indices provide accurate results for Teff and Fe/H but will be more uncertain for distant stars when interstellar reddening becomes important. The indirect methods are important to obtain reliable estimates of the fundamental parameters of relatively faint stars when interferometry cannot be used. This paper is the first to compare direct and indirect methods for a large sample of stars, and we conclude that indirect methods are valid, although slight corrections may be needed.
Abstract
We report the first asteroseismic results obtained with the Hertzsprung Stellar Observations Network Group Telescope from an extensive high-precision radial-velocity observing campaign of ...the subgiant
μ
Herculis. The data set was collected during 215 nights in 2014 and 2015. We detected a total of 49 oscillation modes with
l
values from zero to three, including some
l
= 1 mixed modes. Based on the rotational splitting observed in
l
= 1 modes, we determine a rotational period of 52 days and a stellar inclination angle of 63°. The parameters obtained through modeling of the observed oscillation frequencies agree very well with independent observations and imply a stellar mass between 1.11 and 1.15
M
⊙
and an age of
Gyr. Furthermore, the high-quality data allowed us to determine the acoustic depths of the He
ii
ionization layer and the base of the convection zone.
Context.
Asteroseismic investigations of solar-like oscillations in giant stars allow for the derivation of their masses and radii. For members of open clusters, this allows us to obtain an age ...estimate of the cluster that is expected to be identical to the age estimate given by the colour-magnitude diagram, but independent of the uncertainties that are present for that type of analysis. Thus, a more precise and accurate age estimate can be obtained.
Aims.
We aim to identify and measure the asteroseismic properties of oscillating giant members of the open cluster NGC 6866 and utilise them for a cluster age estimate. Model comparisons also allow constraints to be placed on the stellar physics. Here, we investigate the efficiency of convective-core overshoot during the main sequence evolution, which has a significant influence on the age estimations for these relatively massive giants. The effects of rotation and core overshoot are similar, but not identical, and so, we also investigated the potential of our measurements to distinguish between these effects.
Methods.
We identified six giant members of NGC 6866 via photometry, proper motions, and parallaxes from
Gaia
, and spectroscopic literature measurements. These were combined with asteroseismic measurements, which we derived using photometric data from the
Kepler
mission for five of the stars. Comparisons to stellar-model isochrones constrained the convective-core overshoot and enable a more precise and accurate age estimate than previously possible.
Results.
A significant amount of differential reddening is found for NGC 6866. Asteroseismology establishes the helium-core burning evolutionary phase for the giants, which have a mean mass of 2.8
M
⊙
. Their radii are significantly smaller than predicted by current 1D stellar models unless the amount of convective-core overshoot on the main sequence is reduced to
α
ov
≤ 0.1 ⋅
H
p
in the step-overshoot description. Our measurements also suggest that rotation has affected the evolution of the stars in NGC 6866 in a way that is consistent with 3D simulations, but not with current 1D stellar models. The age of NGC 6866 is estimated to be 0.43 ± 0.05 Gyr, which is significantly younger and more precise than most previous estimates.
Conclusions.
We derive a precise cluster age while constraining convective-core overshooting and the effects of rotation in the stellar models. A comparison to age estimates from machine learning methods of the same and similar giant stars uncovers potential biases for automated asteroseismic and non-asteroseismic age estimates of helium-core burning stars.
Context. Helioseismology has enabled us to better understand the solar interior, while also allowing us to better constrain solar models. But now is a tremendous epoch for asteroseismology as space ...missions dedicated to studying stellar oscillations have been launched within the last years (MOST and CoRoT). CoRoT has already proved valuable results for many types of stars, while Kepler, which was launched in March 2009, will provide us with a huge number of seismic data very soon. This is an opportunity to better constrain stellar models and to finally understand stellar structure and evolution. Aims. The goal of this research work is to estimate the global parameters of any solar-like oscillating target in an automatic manner. We want to determine the global parameters of the acoustic modes (large separation, range of excited pressure modes, maximum amplitude, and its corresponding frequency), retrieve the surface rotation period of the star and use these results to estimate the global parameters of the star (radius and mass). Methods. To prepare for the arrival and the analysis of hundreds of solar-like oscillating stars, we have developed a robust and automatic pipeline, which was partially adapted from helioseismic methods. The pipeline consists of data analysis techniques, such as Fast Fourier Transform, wavelets, autocorrelation, as well as the application of minimisation algorithms for stellar-modelling. Results. We apply our pipeline to some simulated lightcurves from the asteroFLAG team and the Aarhus-asteroFLAG simulator, and obtain results that are consistent with the input data to the simulations. Our strategy gives correct results for stars with magnitudes below 11 with only a few 10% of bad determinations among the reliable results. We then apply the pipeline to the Sun and three CoRoT targets. In particular we determine the large separation and radius of the Sun, HD49933, HD181906, and HD181420.
The number of main-sequence stars for which we can observe solar-like oscillations is expected to increase considerably with the short-cadence high-precision photometric observations from the NASA ...Kepler satellite. Because of this increase in the number of stars, automated tools are needed to analyse these data in a reasonable amount of time. In the framework of the asteroFLAG consortium, we present an automated pipeline which extracts frequencies and other parameters of solar-like oscillations in main-sequence and subgiant stars. The pipeline uses only the time series data as input and does not require any other input information. Tests on 353 artificial stars reveal that we can obtain accurate frequencies and oscillation parameters for about three quarters of the stars. We conclude that our methods are well suited for the analysis of main-sequence stars, which show mainly p-mode oscillations.
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