University of Birmingham The K2 Galactic Archaeology Program Data Release 2 Zinn, Joel C.; Stello, Dennis; Elsworth, Yvonne; García, Rafael A.; Kallinger, Thomas; Mathur, Savita; Mosser, Benoît; Bugnet, Lisa; Jones, Caitlin; Hon, Marc; Sharma, Sanjib; Schönrich, Ralph; Warfield, Jack T.; Luger, Rodrigo; Pinsonneault, Marc H.; Johnson, Jennifer A.; Huber, Daniel; Aguirre, Victor Silva; Chaplin, William J.; Davies, Guy R. DOI: 10.3847/1538-4365/abbee3 Citation for published version (Harvard): Zinn, JC, Stello, D, Elsworth, Y, García, RA, Kallinger, T, Mathur, S, Mosser, B, Bugnet, L, Jones, C, Hon, M, Sharma, S, Schönrich, R, Warfield, JT, Luger, R, Pinsonneault, MH, Johnson, JA, Huber, D, Aguirre, VS, Chaplin, WJ, Davies, GR & Miglio, A 2020, 'The K2 Galactic Archaeology Program Data Release 2: Asteroseismic results from campaigns 4, 6, & 7', The Astrophysical Journal Supplement Series, Volume, vol. 251, no. 2. https://doi.org/10.3847/1538-4365/abbee3 Link to publication on Research at Birmingham portal 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. 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Chaplin,7, 5 Guy R. Davies,7, 5 and Andrea Miglio5, 7 1Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA 2School of Physics, University of New South Wales, Barker Street, Sydney, NSW 2052, Australia 3Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA 4Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006, Australia 5Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark 6Center of Excellence for Astrophysics in Three Dimensions (ASTRO-3D), Australia 7School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK 8AIM, CEA, CNRS, Universit´eParis-Saclay, Universit´eParis Diderot, Sorbonne Paris Cit´e, F-91191 Gif-sur-Yvette, France 9Institute of Astrophysics, University of Vienna, Turkenschanzstrasse¨ 17, Vienna 1180, Austria 10Space Science Institute, 4750 Walnut Street Suite #205, Boulder, CO 80301, USA 11Instituto de Astrof´ısica de Canarias, La Laguna, Tenerife, Spain 12Dpto. de Astrof´ısica, Universidad de La Laguna, La Laguna, Tenerife, Spain 13LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universit´e, Universit´ede Paris Diderot, 92195 Meudon, France 14IRFU, CEA, Universit´eParis-Saclay, 91191 Gif-sur-Yvette, France 15School of Physics, University of New South Whales, Barker Street, Sydney, NSW 2052, Australia 16Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT, UK 17Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus OH 43210, USA 18Department of Physics, The Ohio State University, 191 West Woodruff Avenue, Columbus OH 43210 19Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA 20Virtual Planetary Laboratory, University of Washington, Seattle, WA, USA 21 Institute for Astronomy, University of Hawai`i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA ABSTRACT Studies of Galactic structure and evolution have benefitted enormously from Gaia kinematic infor- mation, though additional, intrinsic stellar parameters like age are required to best constrain Galactic models. Asteroseismology is the most precise method of providing such information for field star pop- ulations en masse, but existing samples for the most part have been limited to a few narrow fields of view by the CoRoT and Kepler missions. In an effort to provide well-characterized stellar parameters across a wide range in Galactic position, we present the second data release of red giant asteroseismic parameters for the K2 Galactic Archaeology Program (GAP). We provide νmax and ∆ν based on six independent pipeline analyses; first-ascent red giant branch (RGB) and red clump (RC) evolutionary arXiv:2012.04051v1 [astro-ph.SR] 7 Dec 2020 state classifications from machine learning; and ready-to-use radius & mass coefficients, κR & κM , which, when appropriately multiplied by a solar-scaled effective temperature factor, yield physical stellar radii and masses. In total, we report 4395 radius and mass coefficients, with typical uncertain- ties of 3:3% (stat:) ± 1% (syst:) for κR and 7:7% (stat:) ± 2% (syst:) for κM among RGB stars, and 5:0% (stat:) ± 1% (syst:) for κR and 10:5% (stat:) ± 2% (syst:) for κM among RC stars. We verify that the sample is nearly complete | except for a dearth of stars with νmax . 10 − 20µHz | by comparing Corresponding author: Joel C. Zinn [email protected] 2 to Galactic models and visual inspection. Our asteroseismic radii agree with radii derived from Gaia Data Release 2 parallaxes to within 2:2 ± 0:3% for RGB stars and 2:0 ± 0:6% for RC stars. 1. INTRODUCTION We have previously released a collection of νmax and The Galactic Archaeology Program (GAP; Stello et al. ∆ν values for 1210 K2 GAP red giants in Stello et al. 2015) has taken advantage of the multidirectional view (2017). The present release covers campaigns 4, 6, & of the Galaxy offered by the re-purposed Kepler mission, 7, and comprises 4395 stars. In addition to the global K2. With hundreds of thousands of stars observed, K2's asteroseismic parameters, νmax and ∆ν, we also provide potential for studying the Galaxy is significant. Instead scaling-relation quantities that, when combined with an of a single snapshot of the Galaxy with Kepler (Borucki effective temperature, yield radii and masses. We also et al. 2008), K2 (Howell et al. 2014) observed along the provide estimates of systematic and statistical errors on ecliptic, including the local disk, the bulge, and even dis- the asteroseismic quantities, and establish the complete- tant regions of the halo. Importantly for this work, the ness of observed targets in order to ensure a well-defined K2 mission has delivered the quality of data necessary selection function. for asteroseismic analysis. The K2 GAP aims to provide fundamental stellar pa- 2. DATA rameters for red giants across the Galaxy. In combina- 2.1. Target selection tion with temperature and metallicity information, as- In the context of the GAP, analysis of the campaigns teroseismology can provide stellar radii, masses, and, presented here were prioritized due to their coverage when combined with stellar models, ages. Kepler red gi- of the sky: the Galactic center (C7) the Galactic anti- ant asteroseismology has yielded important findings for center (C4) and out of the Galactic plane (C6). These Galactic archaeology, including verifying the presence results will ultimately be joined with a forthcoming anal- of a vertical age gradient in the Galactic disc (Miglio ysis of the rest of the K2 campaigns for which GAP tar- et al. 2013; Casagrande et al. 2016); testing Galactic gets have been observed. The GAP targets red giants chemical evolution models (e.g., Spitoni et al. 2020); because they are bright (probing far into the Galaxy) and confirming an age difference between chemically- and because their oscillations are detectable from the and kinematically-defined thin and thick discs (Silva K2 long-cadence data, which has a Nyquist frequency Aguirre et al. 2018). Nevertheless, the Kepler aster- of ∼ 280µHz. All GAP targets for campaigns 4, 6 & oseismic sample was not curated for Galactic studies, 7 were selected from 2MASS (Skrutskie et al. 2006) to and so GAP's deliberate and well-understood target se- have J − K > 0:5 and good photometric quality based lection for Galactic archaeology purposes sets up K2 to on 2MASS flags.1 The proposed targets passing these be a more useful tool for Galactic archaeology, particu- selection criteria were prioritized based on a rank or- larly in light of its expanded view of the Galaxy. Indeed, dering in V -band magnitude from bright to faint.2 C4 the K2 data is providing interesting insights into the rel- and C6 targets were chosen to have 9 < V < 15, and ative ages of chemically-defined stellar populations be- C7 targets were chosen to have 9 < V < 14:5, with yond the solar vicinity (Rendle et al.