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Discovery of s-process enhanced stars in the LAMOST survey

Norfolk, Brodie J. and Casey, Andrew R. and Karakas, Amanda I. and Miles, Matthew T. and Kemp, Alex J. and Schlaufman, Kevin C. and Ness, Melissa and Ho, Anna Y. Q. and Lattanzio, John C. and Ji, Alexander P. (2019) Discovery of s-process enhanced stars in the LAMOST survey. Monthly Notices of the Royal Astronomical Society, 490 (2). pp. 2219-2227. ISSN 0035-8711. doi:10.1093/mnras/stz2630.

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Here we present the discovery of 895 s-process-rich candidates from 454 180 giant stars observed by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) using a data-driven approach. This sample constitutes the largest number of s-process enhanced stars ever discovered. Our sample includes 187 s-process-rich candidates that are enhanced in both barium and strontium, 49 stars with significant barium enhancement only and 659 stars that show only a strontium enhancement. Most of the stars in our sample are in the range of effective temperature and log g typical of red giant branch (RGB) populations, which is consistent with our observational selection bias towards finding RGB stars. We estimate that only a small fraction (∼0.5 per cent) of binary configurations are favourable for s-process enriched stars. The majority of our s-process-rich candidates (95 per cent) show strong carbon enhancements, whereas only five candidates (<3  per cent) show evidence of sodium enhancement. Our kinematic analysis reveals that 97 per cent of our sample are disc stars, with the other 3 per cent showing velocities consistent with the Galactic halo. The scaleheight of the disc is estimated to be z_h = 0.634±0.063kpc⁠, comparable with values in the literature. A comparison with yields from asymptotic giant branch (AGB) models suggests that the main neutron source responsible for the Ba and Sr enhancements is the ¹³C(α,n)¹⁶O reaction. We conclude that s-process-rich candidates may have received their overabundances via mass transfer from a previous AGB companion with an initial mass in the range 1−3M_⊙.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Casey, Andrew R.0000-0003-0174-0564
Karakas, Amanda I.0000-0002-3625-6951
Schlaufman, Kevin C.0000-0001-5761-6779
Ness, Melissa0000-0001-5082-6693
Ho, Anna Y. Q.0000-0002-9017-3567
Lattanzio, John C.0000-0003-2952-859X
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 September 13. Received 2019 September 13; in original form 2018 March 2. Published: 22 October 2019. This paper includes data gathered with the 6.5-m Magellan Telescope located at Las Campanas Observatory, Chile. We thank David W. Hogg (NYU) and Hans-Walter Rix (MPIA) for useful discussions. ARC is supported through an Australian Research Council Discovery Project under grant DP160100637. AIK acknowledges financial support from the Australian Research Council (DP170100521). AYQH was supported by the GROWTH project funded by the National Science Foundation under PIRE Grant No 1545949, and a National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144469. APJ is supported by NASA through Hubble Fellowship grant HST-HF2-51393.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This research has made use of NASA’s Astrophysics Data System. The Guoshoujing Telescope (LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
Funding AgencyGrant Number
Australian Research CouncilDP160100637
Australian Research CouncilDP170100521
NSF Graduate Research FellowshipDGE-1144469
NASA Hubble FellowshipHST-HF2-51393.001
National Development and Reform CommissionUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:stars: abundances – stars: chemically peculiar
Issue or Number:2
Record Number:CaltechAUTHORS:20191120-080724331
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Official Citation:Brodie J Norfolk, Andrew R Casey, Amanda I Karakas, Matthew T Miles, Alex J Kemp, Kevin C Schlaufman, Melissa Ness, Anna Y Q Ho, John C Lattanzio, Alexander P Ji, Discovery of s-process enhanced stars in the LAMOST survey, Monthly Notices of the Royal Astronomical Society, Volume 490, Issue 2, December 2019, Pages 2219–2227,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99943
Deposited By: Tony Diaz
Deposited On:20 Nov 2019 19:04
Last Modified:16 Nov 2021 17:50

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