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Asteroseismic Masses of Retired Planet-Hosting A-Stars Using SONG Author(S): Dennis Stello, Daniel Huber, Frank Grundahl Et Al

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Asteroseismic Masses of Retired Planet-Hosting A-Stars Using SONG Author(S): Dennis Stello, Daniel Huber, Frank Grundahl Et Al Coversheet This is the publisher’s PDF (Version of Record) of the article. This is the final published version of the article. How to cite this publication: Dennis Stello, Daniel Huber, Frank Grundahl et al. (2017). ”Asteroseismic masses of retired planet- hosting A-stars using SONG.” Monthly Notices of the Royal Astronomical Society, 472 (4), 4110–4116. https://doi.org/10.1093/mnras/stx2295 Publication metadata Title: Asteroseismic masses of retired planet-hosting A-stars using SONG Author(s): Dennis Stello, Daniel Huber, Frank Grundahl et al. Journal: Monthly Notices of the Royal Astronomical Society DOI/Link: https://doi.org/10.1093/mnras/stx2295 Document version: Publisher’s PDF (Version of Record) This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Redistribution subject to OUP license or copyright; see Terms of Use at https://academic.oup.com/journals/pages/access_purchase/rights_and_permissions/self_archiving _policy_p Use of this article is subject to OUP terms of use and conditions. 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This coversheet template is made available by AU Library Version 1.0, December 2017 MNRAS 472, 4110–4116 (2017) doi:10.1093/mnras/stx2295 Advance Access publication 2017 September 6 Asteroseismic masses of retired planet-hosting A-stars using SONG Dennis Stello,1,2,3‹ Daniel Huber,4,2,5,3 Frank Grundahl,3 James Lloyd,6 Mike Ireland,7 Luca Casagrande,7 Mads Fredslund,3 Timothy R. Bedding,2,3 Pere L. Palle,8 Victoria Antoci,3 Hans Kjeldsen3 and Jørgen Christensen-Dalsgaard3 Downloaded from https://academic.oup.com/mnras/article-abstract/472/4/4110/4107124 by Aarhus University Library user on 22 October 2018 1School of Physics, University of New South Wales, NSW 2052, Australia 2Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006, Australia 3Department of Physics and Astronomy, Stellar Astrophysics Centre, Aarhus University, DK-8000 Aarhus C, Denmark 4Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA 5SETI Institute, 189 Bernardo Avenue, Mountain View, CA 94043, USA 6Department of Astronomy, Cornell University, Ithaca, NY 14850, USA 7Mount Stromlo Observatory, Research School of Astronomy & Astrophysics, The Australian National University, ACT 2611, Australia 8Instituto de Astrof sica de Canarias, E-38200 La Laguna, Tenerife, Spain Accepted 2017 August 31. Received 2017 August 31; in original form 2017 July 25 ABSTRACT To better understand how planets form, it is important to study planet occurrence rates as a function of stellar mass. However, estimating masses of field stars is often difficult. Over the past decade, a controversy has arisen about the inferred occurrence rate of gas-giant planets around evolved intermediate-mass stars – the so-called ‘retired A-stars’. The high masses of these red-giant planet hosts, derived using spectroscopic information and stellar evolution models, have been called into question. Here, we address the controversy by determining the masses of eight evolved planet-hosting stars using asteroseismology. We compare the masses with spectroscopic-based masses from the Exoplanet Orbit Database,which were previously adopted to infer properties of the exoplanets and their hosts. We find a significant one-sided offset between the two sets of masses for stars with spectroscopic masses above roughly 1.6 M, suggestive of an average 15–20 per cent overestimate of the adopted spectroscopic- based masses. The only star in our sample well below this mass limit is also the only one not showing this offset. Finally, we note that the scatter across literature values of spectroscopic- based masses often exceeds their formal uncertainties, making it comparable to the offset we report here. Key words: techniques: radial velocities – stars: fundamental parameters – stars: interiors – stars: oscillations. To estimate stellar mass, they used an isochrone grid-modelling 1 INTRODUCTION approach based on spectroscopic input observables (logg, Teff and One way to understand how planets form is to find relationships be- [Fe/H]). From this, Johnson et al. (2007a,b) reported general in- tween the occurrence rates of exoplanets and the fundamental prop- creased planet occurrence rates but a paucity of planets in short- erties of their host stars, such as mass. The search for exoplanets has period orbits. mainly been focused on cool main-sequence stars below ∼1.4 M However, the mass estimates of the retired A-stars were subse- because their planets are easier to detect (Johnson et al. 2006). To ex- quently called into question by Lloyd (2011), who argued it was tend the mass range of exoplanet host targets, Johnson et al. (2006) statistically unlikely that the sample, which he extracted from the searched for planets around cool evolved intermediate-mass stars, Exoplanet Orbit Database (EOD; Wright et al. 2011), would include dubbed retired A-stars1, which were once hotter main-sequence so many relatively massive stars, given their location in the HR- stars, from which planet occurrence rates could be inferred. diagram. This led to further investigations by Johnson, Morton & Wright (2013), Lloyd (2013) and Schlaufman & Winn (2013), but without a clear resolution. E-mail: [email protected] Sparked by the new space-based era of high-precision time series 1 While not all the retired A-stars are strictly speaking old A-stars (some are photometry, a recent surge of results from the asteroseismology of less massive), we adopt this previously dubbed ‘group-name’ for simplicity. red giants has shown that detailed and highly precise information C 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society Seismic masses of evolved planet hosts 4111 can be obtained about these stars (e.g. Bedding et al. 2011; Beck et al. 2012; Mosser et al. 2012; Stello et al. 2016). In particular, stel- lar mass can be measured (Stello et al. 2008; Kallinger et al. 2010), which makes asteroseismology an obvious way to resolve the dis- pute about the retired A-star planet-host masses. One retired A-star, the red-giant-branch star HD 185351, was ob- served by Kepler. The initial analysis by Johnson et al. (2014) found different masses spanning 1.60–1.99 M depending on the combi- Downloaded from https://academic.oup.com/mnras/article-abstract/472/4/4110/4107124 by Aarhus University Library user on 22 October 2018 nation of seismic and interferometric input, as compared to 1.87 M for the purely spectroscopic-based mass. The seismic inputs were ν, the frequency spacing between overtone modes, and νmax,the frequency of maximum power. Recent results including also the pe- riod spacing between dipole mixed modes (P) as an extra seismic quantity, and non-standard physics provided stronger constraints, indicating more definitively a lower mass of 1.58 ± 0.03 M for this star (Hjørringgaard et al. 2017). Even more recently, Campante et al. (2017)usedK2ob- servations of another retired A-star, HD 212771, to measure its mass from asteroseismology to be 1.45 ± 0.10 M. De- spite this star being in a very similar evolutionary stage to HD 185351, the seismic mass of HD 212771 was larger than the original spectroscopy-based value of 1.15 ± 0.08 M (Johnson et al. 2010). However, subsequent spectroscopic investigations also estimated its mass to be larger (1.51 ± 0.08 M,Mortier et al. 2013; 1.60 ± 0.13 M,Jofreetal.´ 2015) than reported by Johnson et al. (2010). Figure 1. HR-diagram showing MESA (Paxton et al. 2013) stellar evolution With only two seismic targets showing inconclusive results, it is tracks of solar metallicity from Stello et al. (2013). The likelihood of finding still not clear if the stellar masses are systematically overestimated in a star in a given state of evolution (for a given mass) is illustrated by the the planet discovery papers, which would affect conclusions about filled dots along each track, which are equally spaced by 50 Myr in stellar how planet occurrence rates depend on stellar mass, and potentially age. Masses in solar units are shown. The black arrow near the bottom of lead to a different explanation for the high occurrence of planets the 1.0 M red-giant branch illustrates how much the tracks shift if [Fe/H] in the retired A-star sample (currently attributed to the high stellar is increased by 0.2 dex. Dotted fiducial lines are indicative of the transitions mass). from the main sequence to subgiants, and from the rapidly cooling subgiants In this paper, we investigate the retired A-star mass controversy (at roughly constant radius) to the rapidly expanding red giants (at roughly by observing eight planet-hosting red giants using the ground-based constant Teff). The planet-hosting targets are shown with diamonds and the σ SONG telescope to detect solar-like oscillations. This allows us adopted 1 error bars.
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