The Homogeneous Study of Transiting Systems (HoSTS) – II. The influence of the line list on stellar parameters

Doyle, A. P.; Smalley, B.; Faedi, F.; Pollacco, D.; Chew, Y. Gómez Maqueo

doi:10.1093/mnras/stx1180

Cited by 10 publications

(19 citation statements)

References 26 publications

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“…We checked these results for Kepler-278 by recomputing their fundamental parameters with log g fixed to the accurate value estimated from asteroseismology 16 , obtaining T eff = 4967 ± 49 K and [Fe/H]= 0.24 ± 0.04 K, which represent a difference of only 2 K and 0.02 dex when compared to the parameters obtained with no constraints on log g. Therefore, in agreement with the results of Mortier et al (2014) and Doyle et al (2017), we find that T eff and [Fe/H] are not significantly altered when log g is fixed and, hence, in the next sections we adopt the unconstrained set of fundamental stellar parameters.…”

Section: Consistency Checks On T Eff and Log Gsupporting

confidence: 72%

“…Surface gravity from Mg i b, Na i D, and Ca lines. We obtained log g values from the spectral synthesis of the wings of several strong features using the iSpec spectral analysis tool 14 (Blanco-Cuaresma et al 2014), following a similar method as described in Bruntt et al (2010), Doyle et al (2017). The lines analyzed include Mg i b (λ5180 Å), Na i D (λ5889, 5895 Å), and Ca i (λ6122, 6162, 6439 Å) from which we obtained an average value of log g = 3.66 ± 0.10 dex for Kepler-278 and log g = 3.70 ± 0.08 dex for Kepler-391.…”

Section: Consistency Checks On T Eff and Log Gmentioning

confidence: 99%

“…To avoid this degeneracy and improve stellar parameters, it has been pointed out that fixing log g to an external accurate value (e.g., from asteroseismic data or transits) improves the final stellar parameters. However, it has also been noticed that fixing log g to an external value has no significant effect on the temperatures or metallicities when working with methods based on EWs, and then it is sufficient to use the unconstrained values (Mortier et al 2014;Doyle et al 2017).…”

Section: Consistency Checks On T Eff and Log Gmentioning

confidence: 99%

“…For Kepler-391 the differences are a little bit smaller, but still the largest in comparison with any of the other studies: ∆T eff = 93 K, ∆ log g = 0.32 dex, and ∆[Fe/H] = −0.17 dex. The most probable sources for these discrepancies are the quality of the spectra, especially resolution, and the analysis technique, in which log g values are not constrained (e.g., Doyle et al 2017).…”

Section: Comparison With Previous Workmentioning

confidence: 99%

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Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting planets I. Detailed characterization of multi-planet systems Kepler-278 and Kepler-391

Jofré,

Almenara,

Petrucci

et al. 2019

Preprint

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Aims. Kepler-278 and Kepler-391 are two of the three evolved stars known to date on the red giant branch (RGB) to host multiple short-period transiting planets. Moreover, the planets orbiting Kepler-278 and Kepler-391 are among the smallest discovered around RGB stars. Here we present a detailed stellar and planetary characterization of these remarkable systems. Methods. Based on high-quality spectra from Gemini-GRACES for Kepler-278 and Kepler-391, we obtained refined stellar parameters and precise chemical abundances for 25 elements. Nine of these elements and the carbon isotopic ratios, 12 C/ 13 C, had not previously been measured. Also, combining our new stellar parameters with a photodynamical analysis of the Kepler light curves, we determined accurate planetary properties of both systems. Results. Our revised stellar parameters agree reasonably well with most of the previous results, although we find that Kepler-278 is ∼15% less massive than previously reported. The abundances of C,

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Section: Consistency Checks On T Eff and Log Gsupporting

confidence: 72%

Section: Consistency Checks On T Eff and Log Gmentioning

confidence: 99%

Section: Consistency Checks On T Eff and Log Gmentioning

confidence: 99%

Section: Comparison With Previous Workmentioning

confidence: 99%

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Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting planets I. Detailed characterization of multi-planet systems Kepler-278 and Kepler-391

Jofré,

Almenara,

Petrucci

et al. 2019

Preprint

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“…There is still no consensus among the community as to whether such an analysis has to be preferred for seismic targets (e.g. Doyle et al 2017). A constrained analysis is undoubtedly more precise, but whether it is also more accurate is unclear.…”

Section: Determination Of Atmospheric Parametersmentioning

confidence: 99%

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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The atmospheric parameters of FGK stars using wavelet analysis of CORALIE spectra

Gill

Maxted

Smalley

2018

A&A

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Context. Atmospheric properties of F-,G-and K-type stars can be measured by spectral model fitting or from the analysis of equivalent width measurements. These methods require data with good signal-to-noise ratio and reliable continuum normalisation. This is particularly challenging for the spectra we have obtained with the CORALIE échelle spectrograph for FGK stars with transiting M-dwarf companions. The spectra tend to have low signal-to-noise ratios, which makes it difficult to analyse them using existing methods. Aims. Our aim is to create a reliable automated spectral analysis routine to determine T eff , [Fe/H], V sin i from the CORALIE spectra of FGK stars. Methods. We use wavelet decomposition to distinguish between noise, continuum trends, and stellar spectral features in the CORALIE spectra. A subset of wavelet coefficients from the target spectrum are compared to those from a grid of models in a Bayesian framework to determine the posterior probability distributions of the atmospheric parameters. Results. By testing our method using synthetic spectra we found that our method converges on the best fitting atmospheric parameters. We test the wavelet method on 20 FGK exoplanet host stars for which higher quality data have been independently analysed using equivalent width measurements. We find that we can determine T eff to a precision of 85 K, [Fe/H] to a precision of 0.06 dex and V sin i to a precision of 1.35 km s −1 for stars with V sin i ≥ 5 km s −1 . We find an offset in metallicity ≈ −0.18 dex relative to the equivelent width fitting method. We can determine log g to a precision of 0.13 dex but find systematic trends with T eff . Measurements of log g are only reliable to confirm dwarf-like surface gravity (log g ≈ 4.5).Conclusions. The wavelet method can be used to determine T eff , [Fe/H] and V sin i for FGK stars from CORALIE échelle spectra. Measurements of log g are unreliable but can confirm dwarf-like surface gravity. We find that our method is self consistent, and robust for spectra with SNR 40.

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The Homogeneous Study of Transiting Systems (HoSTS) – II. The influence of the line list on stellar parameters

Cited by 10 publications

References 26 publications

Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting planets I. Detailed characterization of multi-planet systems Kepler-278 and Kepler-391

Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting planets I. Detailed characterization of multi-planet systems Kepler-278 and Kepler-391

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

The atmospheric parameters of FGK stars using wavelet analysis of CORALIE spectra

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