Robo-AO Kepler Asteroseismic Survey. I. Adaptive Optics Imaging of 99 Asteroseismic Kepler Dwarfs and Subgiants

Schonhut-Stasik, Jessica; Baranec, Christoph; Huber, Daniel; Ziegler, Carl; Atkinson, Dani; Gaidos, Eric; Law, Nicholas M.; Riddle, Reed; Hagelberg, J.; Marel, Nienke van der; Hodapp, Klaus W.

doi:10.3847/1538-4357/aa886f

Cited by 6 publications

(8 citation statements)

References 54 publications

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“…We conclude that the companions do not contribute to more than ∼10% to the flux in the optical. No visual companions have been detected in ten of our targets (including KIC 7871531 and KIC 12317678) from adaptive optics imaging in the visible (Schonhut-Stasik et al 2017). If confirmed, the composite nature of the spectra is expected to bias our abundances by about 0.05 dex at most Notes.…”

Section: Selection Of Targets and Basic Propertiesmentioning

confidence: 76%

Testing abundance-age relations beyond solar analogues with Kepler LEGACY stars

Morel,

Creevey,

Montalban

et al. 2020

Preprint

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The prospects of using abundance ratios as stellar age indicators appear promising for solar analogues, but the usefulness of this technique for stars spanning a much wider parameter space remains to be established. We present abundances of 21 elements in a sample of 13 bright FG dwarfs drawn from the Kepler LEGACY sample to examine the applicability of the abundance-age relations to stars with properties strongly departing from solar. These stars have precise asteroseismic ages that can be compared to the abundancebased estimates. We analyse the well-known binary 16 Cyg AB for validation purposes and confirm the existence of a slight metal enhancement (∼0.02 dex) in the primary, which might arise from planetary formation/ingestion. We draw attention to systematic errors in some widely-used catalogues of non-seismic parameters that may significantly bias asteroseismic inferences. In particular, we find evidence that the ASPCAP T eff scale used for the APOKASC catalogue is too cool for dwarfs and that the [Fe/H] values are underestimated by ∼0.1 dex. In addition, a new seismic analysis of the early F-type star KIC 9965715 based on our spectroscopic constraints shows that the star is more massive and younger than previously thought. We compare seismic ages to those inferred from empirical abundance-age relations based on ages from PARSEC isochrones and abundances obtained in the framework of the HARPS-GTO program. These calibrations take into account a dependency with the stellar effective temperature, metallicity, and/or mass. We find that the seismic and abundance-based ages differ on average by 1.5-2 Gyrs, while taking into account a dependency with one or two stellar parameters in the calibrations leads to a global improvement of up to ∼0.5 Gyr. However, even in that case we find that seismic ages are systematically larger by ∼0.7 Gyr. We argue that it may be ascribed to a variety of causes including the presence of small zero-point offsets between our abundances and those used to construct the calibrations or to the choice of the set of theoretical isochrones. The conclusions above are supported by the analysis of literature data for a larger number of Kepler targets. For this extended sample, we find that incorporating a T eff dependency largely corrects for the fact that the abundance-based ages are lower/larger with respect to the seismic estimates for the cooler/hotter stars. Although investigating age dating methods relying on abundance data is worth pursuing, we conclude that further work is needed to improve both their precision and accuracy for stars that are not solar analogues.

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Section: Selection Of Targets and Basic Propertiesmentioning

confidence: 76%

Testing abundance-age relations beyond solar analogues with Kepler LEGACY stars

Morel,

Creevey,

Montalban

et al. 2020

Preprint

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“…We have checked those stars and found that some have low S/N power spectra, with Kepler time series that are only a few quarters long. The low-amplitude stars could also be contaminated by nearby stars or diluted by their companions in binary systems (Ziegler et al 2017;Schonhut-Stasik et al 2017) or be exotic stars. Figure 10a also shows that high-mass HeB stars have overall lower amplitudes compared to RGB stars at a given ν max .…”

Section: Mass Effectmentioning

confidence: 99%

Asteroseismology of 16,000 Kepler Red Giants: Global Oscillation Parameters, Masses, and Radii

Jiang

Huber

Bedding

et al. 2018

ApJS

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237

350

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The Kepler mission has provided exquisite data to perform an ensemble asteroseismic analysis on evolved stars. In this work we systematically characterize solar-like oscillations and granulation for 16,094 oscillating red giants, using end-of-mission long-cadence data. We produced a homogeneous catalog of the frequency of maximum power (typical uncertainty σ νmax =1.6%), the mean large frequency separation (σ ∆ν =0.6%), oscillation amplitude (σ A =4.7%), granulation power (σ gran =8.6%), power excess width (σ width =8.8%), seismically derived stellar mass (σ M =7.8%), radius (σ R =2.9%), and thus surface gravity (σ log g =0.01 dex). Thanks to the large red giant sample, we confirm that redgiant-branch (RGB) and helium-core-burning (HeB) stars collectively differ in the distribution of oscillation amplitude, granulation power, and width of power excess, which is mainly due to the mass difference. The distribution of oscillation amplitudes shows an extremely sharp upper edge at fixed ν max , which might hold clues for understanding the excitation and damping mechanisms of the oscillation modes. We find that both oscillation amplitude and granulation power depend on metallicity, causing a spread of 15% in oscillation amplitudes and a spread of 25% in granulation power from [Fe/H]=-0.7 to 0.5 dex. Our asteroseismic stellar properties can be used as reliable distance indicators and age proxies for mapping and dating galactic stellar populations observed by Kepler . They will also provide an excellent opportunity to test asteroseismology using Gaia parallaxes, and lift degeneracies in deriving atmospheric parameters in large spectroscopic surveys such as APOGEE and LAMOST.

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“…We calculated separation and position angle between the primary and secondary stars with the same technique as Schonhut-Stasik et al (2017), adapted for Robo-AO at Kitt Peak. We tested this method with Palomar data from Baranec et al (2016) and Kitt Peak data from Ziegler et al (2018a) reproducing separation, position angle and uncertainty values.…”

Section: Separation and Position Anglementioning

confidence: 99%

“…To compare our companion fraction with a similar sample also observed with Robo-AO, we used values from their KOI survey (Ziegler et al 2018a). We combined the oscillating dwarfs in our work with a sample of 99 oscillating Kepler dwarfs and subgiants from Schonhut-Stasik et al (2017) to produce a companion fraction representing dwarf and subgiant solar-like oscillators. Excluding giants makes the asteroseismic sample more consistent with the KOI sample.…”

Section: Comparison To Other Surveysmentioning

confidence: 99%

“…A lack of oscillations could also be attributed to multiplicity; either via the dilution of amplitudes caused by contaminating flux (Schonhut-Stasik et al 2017), or by spectroscopic binaries 3 , inhibiting oscillations through tidal interaction. Tidal interactions between stars are believed to increase magnetic activity and subsequently decreases the efficiency of the surface convection that drives oscillations, inducing amplitude suppression.…”

Section: Introductionmentioning

confidence: 99%

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ROBO-AO Kepler Asteroseismic Survey. II. Do Stellar Companions Inhibit Stellar Oscillations?

Schonhut-Stasik

Huber

Baranec

et al. 2020

ApJ

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The Kepler space telescope observed over 15,000 stars for asteroseismic studies. Of these, 75% of dwarfs (and 8% of giants) were found to show anomalous behavior: such as suppressed oscillations (low amplitude) or no oscillations at all. The lack of solar-like oscillations may be a consequence of multiplicity, due to physical interactions with spectroscopic companions or due to the dilution of oscillation amplitudes from "wide" (AO detected; visual) or spectroscopic companions introducing contaminating flux. We present a search for stellar companions to 327 of the Kepler asteroseismic sample, which were expected to display solar-like oscillations. We used direct imaging with Robo-AO, which can resolve secondary sources at ∼0. 15, and followed up detected companions with Keck AO. Directly imaged companion systems with both separations of ≤ 0. 5 and amplitude dilutions >10% all have anomalous primaries, suggesting these oscillation signals are diluted by a sufficient amount of excess flux. We also used the high-resolution spectrometer ESPaDOnS at CFHT to search for spectroscopic binaries. We find tentative evidence for a higher fraction of spectroscopic binaries with high radial velocity scatter in anomalous systems, which would be consistent with previous results suggesting that oscillations are suppressed by tidal interactions in close eclipsing binaries.2 Because the period of oscillation is longer in red giant stars (log(g)<3.5) this allows the use of long cadence observations.

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Robo-AO Kepler Asteroseismic Survey. I. Adaptive Optics Imaging of 99 Asteroseismic Kepler Dwarfs and Subgiants

Cited by 6 publications

References 54 publications

Testing abundance-age relations beyond solar analogues with Kepler LEGACY stars

Testing abundance-age relations beyond solar analogues with Kepler LEGACY stars

Asteroseismology of 16,000 Kepler Red Giants: Global Oscillation Parameters, Masses, and Radii

ROBO-AO Kepler Asteroseismic Survey. II. Do Stellar Companions Inhibit Stellar Oscillations?

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