arXiv subjects

A. Youdin

Publications and source records attributed to A. Youdin.

3 recordsLinked to original sources

arXiv2012

M dwarf stars in the light of (future) exoplanet searches

We present a brief overview of a splinter session on M dwarf stars as planet hosts that was organized as part of the Cool Stars 17 conference. The session was devoted to reviewing our current knowledge of M dwarf stars and exoplanets in order to prepare for current and future exoplanet searches focusing in low mass stars. We review the observational and theoretical challenges to characterize M dwarf stars and the importance of accurate fundamental parameters for the proper characterization of their exoplanets and our understanding on planet formation.

astro-ph.SR↗

arXiv2011

Roadmap For Small Bodies Exploration: Theoretical Studies

This document covers five broad topics from theory of small bodies: planetesimal formation, cosmochemistry, thermal evolution, collisions and dynamics. Each of these topics is described in a separate section, where we prioritize selected main issues over completeness. The text points out the principal unresolved problems in each area, and suggests ways how progress can be made. This includes support for new code development, observations and experimental work that can be used to constrain theory, new research directions, and studies of cross-over regimes where the system's behavior is determined by several competing processes. The suggested development areas are placed in the context of NASA space exploration.

astro-ph.EP↗

arXiv2009

Forming Planetesimals in Solar and Extrasolar Nebulae

Planets are built from planetesimals: solids larger than a kilometer which grow by colliding pairwise. Planetesimals themselves are unlikely to form by two-body collisions; sub-km objects have gravitational fields individually too weak, and electrostatic attraction is too feeble for growth beyond a few cm. We review the possibility that planetesimals form when self-gravity brings together vast ensembles of small particles. Even when self-gravity is weak, aerodynamic processes can accumulate solids relative to gas, paving the way for gravitational collapse. Particles pile up as they drift radially inward. Gas turbulence stirs particles, but can also seed collapse by clumping them. While the feedback of solids on gas triggers vertical shear instabilities that obstruct self-gravity, this same feedback triggers streaming instabilities that strongly concentrate particles. Numerical simulations find that solids 10-100 cm in size gravitationally collapse in turbulent disks. We outline areas for progress, including the possibility that still smaller objects self-gravitate.

astro-ph.EP↗