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Creators/Authors contains: "Ho, Anna Y. Q."

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  1. ABSTRACT

    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 $z_{\rm h}=0.634 \pm {0.063}\, \mathrm{kpc}$, comparable with values in the literature. A comparison with yields from asymptotic giant branch (AGB)more »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 $1\!-\!3\, \mathrm{M}_{\odot }$.

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  2. Abstract

    The Zwicky Transient Facility (ZTF), a public–private enterprise, is a new time-domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg2field of view and an 8 second readout time. It is well positioned in the development of time-domain astronomy, offering operations at 10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a single 1-m class survey telescope. The public surveys will cover the observable northern sky every three nights ingandrfilters and the visible Galactic plane every night ingandr. Alerts generated by these surveys are sent in real time to brokers. A consortium of universities that provided funding (“partnership”) are undertaking several boutique surveys. The combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter thanr ∼ 20.5 on timescales of minutes to years. We describe the primary science objectives driving ZTF, including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei, and tidal disruption events, stellar variability, and solar system objects.