No Arabic abstract
Direct determination of fundamental stellar parameters has many profound and wide-ranging impacts throughout astrophysics. These determinations are rooted in high angular resolution observations. In particular, as long-baseline optical interferometry has matured over the past decade, increasingly large survey samples are serving to empirically ground the basic parameters of these building blocks of the universe. True imaging and improved parametric fitting are becoming routinely available, an essential component of fully characterizing stars, stellar environments, and planets these stars may host.
This paper outlines the importance of understanding jets from compact binaries for the problem of understanding the broader phenomenology of jet production. Because X-ray binaries are nearby and bright, have well-measured system parameters, and vary by factors of $sim 10^6$ on $sim$ year timescales, they provide a unique opportunity to understand how various aspects of the jet physics change in response to changes in the accretion flow, giving the possibility of looking for trends within individual systems and testing their universality with other systems, rather than trying to interpret large samples of objects on a statistical basis.
High resolution spectroscopy of the lowest-mass stars and brown dwarfs reveals their origins, multiplicity, compositions and physical properties, with implications for the star formation and chemical evolution history of the Milky Way. We motivate the need for high-resolution, infrared spectroscopic surveys to reach these faint sources.
The lowest-mass stars, brown dwarfs and giant exoplanets span a minimum in the mass-radius relationship that probes the fundamental physics of extreme states of matter, magnetism, and fusion. This White Paper outlines scientific opportunities and the necessary resources for modeling and measuring the mass-radius relationship in this regime.
The commercial SmallSat industry is booming and has developed numerous low-cost, capable satellite buses. SmallSats can be used as vehicles for technology development or to host science missions. Missions hosted on SmallSats can answer specific science questions that are difficult or impossible to answer with larger facilities, can be developed relatively quickly, serve to train engineering and scientists, and provide access to space for small institutions. SmallSats complement larger Astrophysics missions and allow the broader community to test new ideas at the bottom of the market, creating new capabilities which find their way to larger missions. Currently, NASA Astrophysics does not provide flight opportunities that would allow technology maturation of instrument systems or concepts of operations. Without flight opportunities to mature technologies, missions hosted on SmallSats are likely to be considered high risk, and face long odds being selected for implementation. Our primary suggestion is that NASA decouples science and technology for SmallSats by creating a technology-based SmallSat AO, modeled after the Earth Sciences InVEST call. Such AO would help reduce the new technology risk for science missions of any size. We also suggest that NASA provides additional science-driven SmallSat opportunities at the ~$12M funding level, provides access to new launchers free of charge to proposers, and re-structures the solicitation AOs so that SmallSats do not compete with other mission classes such as balloons.
We are now in an era where we can image details on the surfaces of stars. When resolving stellar surfaces, we see that every surface is uniquely complicated. Each imaged star provides insight into not only the stellar surface structures, but also the stellar interiors suggesting constraints on evolution and dynamo models. As more resources become operational in the coming years, imaging stellar surfaces should become commonplace for revealing the true nature of stars. Here, we discuss the main types of stars for which imaging surface features is currently useful and what improved observing techniques would provide for imaging stellar surface features.