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====== SONG Science ======

A detailed understanding of stars underpins much of astrophysics. Stars are the most fundamental astrophysical objects, they are the basic constituents of galaxies, and, to a large extent, the overall properties of the universe are controlled by their evolution.  Stars are huge balls of gas, and turbulent motions within them generate sound waves that cause the majority of them to wobble and ring like bells. The measurement and analysis of these acoustic oscillations is the only way to peer into the interior of a star.  We propose to acquire and assemble a telescope and spectrograph instrument that will be part of a world-wide network dedicated to `listening' to stars 24 hours per day. Constant monitoring is the only way to directly observe the workings of their interiors.



===== Background: seismology of stars and stellar astrophysics =====

The past decade has seen the re-emergence of observational stellar astrophysics. Consider just three large-scale surveys, out of many: (1) the spectroscopic survey of the Milky Way with APOGEE [{majewski2010}]; the astrometric survey of Gaia [{gilmore2012}]; and the photometric time-domain survey of Kepler [{koch2010}]. The data from these experiments have increased, by orders of magnitude, the number of stars for which we now have knowledge of their composition, pulsation properties, masses, radii, ages, motions, positions, orbiting planets, multiplicity, etc. spanning across much of the Galaxy. These surveys have provided key insights into how the Milky Way was formed and has evolved, as well as new constraints on theories of stellar structure and evolution beyond what has been learned from star clusters.  They have also provided targets that can be followed up with more detailed observations to probe poorly understood physics. 

This proposal focuses on asteroseismology, a unique tool that opens a window into stellar interiors from observations of stellar oscillations. Asteroseismology of stars displaying solar-like oscillations has also been revolutionized as an observational science in the past decade, due to a flood of high-precision photometry from the CoRoT, Kepler, and now TESS space missions \citep{chaplin2013,hekker2013b,ricker2015,hekker2017}. For example, Kepler provided oscillation spectra derived from four years of continuous data for hundreds of main-sequence and tens of thousands of giant stars, comprising the largest existing dataset for seismology. These observations have enabled detailed and profound astrophysical studies \citep[e.g.,][]{garcia2019,jackiewicz2021}.




===== SONG results so far =====


===== References =====

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