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University of Birmingham the TESS Light Curve of AI Phoenicis University of Birmingham The TESS light curve of AI Phoenicis Maxted, P. F. L.; Gaulme, Patrick; Graczyk, D.; Heminiak, K. G.; Johnston, C.; Orosz, Jerome A.; Prša, Andrej; Southworth, John; Torres, Guillermo; Davies, Guy R.; Ball, Warrick; Chaplin, William J DOI: 10.1093/mnras/staa1662 License: None: All rights reserved Document Version Publisher's PDF, also known as Version of record Citation for published version (Harvard): Maxted, PFL, Gaulme, P, Graczyk, D, Heminiak, KG, Johnston, C, Orosz, JA, Prša, A, Southworth, J, Torres, G, Davies, GR, Ball, W & Chaplin, WJ 2020, 'The TESS light curve of AI Phoenicis', Monthly Notices of the Royal Astronomical Society, vol. 498, no. 1, pp. 332–343. https://doi.org/10.1093/mnras/staa1662 Link to publication on Research at Birmingham portal Publisher Rights Statement: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. General rights Unless a licence is specified above, all rights (including copyright and moral rights) in this document are retained by the authors and/or the copyright holders. The express permission of the copyright holder must be obtained for any use of this material other than for purposes permitted by law. •Users may freely distribute the URL that is used to identify this publication. •Users may download and/or print one copy of the publication from the University of Birmingham research portal for the purpose of private study or non-commercial research. •User may use extracts from the document in line with the concept of ‘fair dealing’ under the Copyright, Designs and Patents Act 1988 (?) •Users may not further distribute the material nor use it for the purposes of commercial gain. Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document. When citing, please reference the published version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive. If you believe that this is the case for this document, please contact [email protected] providing details and we will remove access to the work immediately and investigate. Download date: 28. Sep. 2021 MNRAS 498, 332–343 (2020) doi:10.1093/mnras/staa1662 Advance Access publication 2020 June 12 The TESS light curve of AI Phoenicis P. F. L. Maxted, 1‹ Patrick Gaulme,2 D. Graczyk,3 K. G. Hełminiak ,3 C. Johnston ,4 Jerome A. Orosz,5 Andrej Prsa,ˇ 6 John Southworth,1 Guillermo Torres,7 Guy R. Davies,8,9 Warrick Ball 8,9 and William J Chaplin8,9 1 Astrophysics group, Keele University, Keele, Staordshire ST5 5BG, UK Downloaded from https://academic.oup.com/mnras/article/498/1/332/5856568 by University of Birmingham user on 09 October 2020 2Max-Planck-Institut fur¨ Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Gottingen,¨ Germany 3Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Rabianska´ 8, PL-87-100 Torun,´ Poland 4Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium 5Astronomy Department, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1221, USA 6Villanova University, Department of Astrophysics and Planetary Science, 800 Lancaster Avenue, Villanova, PA 19085, USA 7Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA 8School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK 9Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark Accepted 2020 June 8. Received 2020 June 6; in original form 2020 March 20 ABSTRACT Accurate masses and radii for normal stars derived from observations of detached eclipsing binary stars are of fundamental importance for testing stellar models and may be useful for calibrating free parameters in these model if the masses and radii are sufficiently precise and accurate. We aim to measure precise masses and radii for the stars in the bright eclipsing binary AI Phe, and to quantify the level of systematic error in these estimates. We use several different methods to model the Transiting Exoplanet Survey Satellite (TESS) light curve of AI Phe combined with spectroscopic orbits from multiple sources to estimate precisely the stellar masses and radii together with robust error estimates. We find that the agreement between different methods for the light-curve analysis is very good but some methods underestimate the errors on the model parameters. The semi-amplitudes of the spectroscopic orbits derived from spectra obtained with modern echelle´ spectrographs are consistent to within 0.1 per cent. The masses of the stars in AI Phe are M1 = 1.1938 ± 0.0008 M and M2 = 1.2438 ± 0.0008 M, and the radii are R1 = 1.8050 ± 0.0022 R and R2 = 2.9332 ± 0.0023 R. We conclude that it is possible to measure accurate masses and radii for stars in bright eclipsing binary stars to a precision of 0.2 per cent or better using photometry from TESS and spectroscopy obtained with modern echelle´ spectrographs. We provide recommendations for publishing masses and radii of eclipsing binary stars at this level of precision. Key words: binaries: eclipsing – stars: fundamental parameters – stars: individual: AI Phe – stars: solar-type. and new uvby light curves, and a spectroscopic estimate of the metal 1 INTRODUCTION abundance ([Fe/H] =−0.14 ± 0.1). The analysis by Andersen et al. AI Phe is a moderately bright (V = 8.6) star that was first noted as an has been the definitive observational study of AI Phe until recently eclipsing binary by Strohmeier (1972). Photometric monitoring by and the absolute parameters derived therein have often been used Reipurth (1978) established that the orbital period is approximately as a benchmark for testing stellar evolution models of single stars 24.59 d and that the primary eclipse is total. Hrivnak & Milone (e.g. Andersen et al. 1988;Polsetal.1997; Ribas, Jordi & Gimenez´ (1984) obtained UBVRI light curves of AI Phe, covering both 2000; Lastennet & Valls-Gabaud 2002; Spada et al. 2013;Ghezzi& eclipses and combined their analysis of these light curves with the Johnson 2015; Higl & Weiss 2017). spectroscopic orbits for both stars published by Imbert (1979)to Kirkby-Kent et al. (2016) used light curves obtained during the measure the masses and radii of both components. They found that WASP exoplanet transit survey together with improved spectroscopic the stars in AI Phe are slightly more massive than the Sun, and both orbits for both components by Hełminiak et al. (2009) to improve have evolved away from the zero-age main sequence, with the more the precision of the radius measurements for both components of massive star being a subgiant. A much-improved spectroscopic orbit AI Phe to better than 1 per cent. Sybilski et al. (2018) also obtained for AI Phe was published by Andersen et al. (1988) together with a spectroscopic orbits for both components of AI Phe together with re-analysis of the UBVRI light curves by Hrivnak & Milone (1984) spectroscopic observations obtained during the secondary eclipse that show that the rotation axis of the subgiant component is not aligned with the orbital axis of the binary system. Gallenne et al. E-mail: [email protected] (2019) have used the VLTI interferometer to measure the astrometric C 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society The TESS light curve of AI Phoenicis 333 light curves from ground-based observatories. For any mid-latitude observing site it will be necessary to patch together eclipses observed on different nights, or even from different observing seasons, to obtain complete coverage of both eclipses. Kirkby-Kent et al. (2016) found that the orbital period of AI Phe is not constant, presumably due to the presence of a third body in the system. The orbit of the presumed third body is not well characterized, so it is possible that there is a systematic error in the published radius estimates for this binary due to inaccuracies in the orbital phases assigned to different parts of the light curve. This problem of phasing the light curve may Downloaded from https://academic.oup.com/mnras/article/498/1/332/5856568 by University of Birmingham user on 09 October 2020 explain the small discrepancies between the values of the orbital eccentricity, e, and longitude of periastron, ω, obtained in different studies (Kirkby-Kent et al. 2016). The launch of the Transiting Exoplanet Survey Satellite (TESS; Ricker et al. 2015) afforded us the opportunity to obtain a high- precision light curve of AI Phe with complete coverage of both eclipses observed over a single orbital period of the binary system. Accordingly, we applied for and were awarded guest-observer status Figure 1. Skymapper r-band image of AI Phe overlaid with the aperture to observe AI Phe using the 2-min cadence mode of TESS (G011130, used to calculate the TESS light curve of AI Phe. Pixels used to measure the P.I. Maxted; G011083, P.I. Hełminiak; G011154, P.I. Prsa).ˇ TESS is flux are plotted in blue and pixels used to calculate the background value are designed to produce very high-quality photometry of bright stars plotted in green. The Skymapper data are displayed as an inverse logarithmic (100 ppm per hour or better for stars with Ic ≈ 8) and AI Phe grey-scale image. shows very well-defined total eclipses, so we expect a very small random error on the parameters derived from the analysis of the TESS light curve.
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