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X-rays from Stars and Planetary Systems

The Chandra X-ray Observatory has completed a remarkable twenty years in orbit. A large part of the science program of Chandra during this time has involved the study of stars and their planetary systems. This primer aims to give the reader a taste of the enormous range of stellar and planetary astrophysics that Chandra has enabled. Beginning with a tour of the X-ray solar system zoo, including the stunning pulsating X-ray aurorae of Jupiter, we then move on to the hot million-degree outer atmospheres of stars like our own Sun, whose X-ray emission is driven by an internal magnetic dynamo. The same emission processes are also vigorously present in the youngest stars, and we highlight some Chandra observations and results on nascent stellar and planetary systems. Chandra surveys and high-resolution spectroscopy of massive stars have provided a new window on the means by which they scavenge X-ray emission from their radiatively-driven winds, sometimes modulating this output by strong underlying stellar magnetic fields. We touch upon the evanescent X-radiation from intermediate-mass stars before arriving at the inevitable evolutionary endpoints of all but massive stars, first in energized X-ray emitting planetary nebulae, then in the slowly cooling, soft-X-ray emitting photospheres of white dwarfs. We conclude with white dwarfs in close binary systems, rejuvenated by interaction with a companion and where accretion gives play to a new range of energetic behavior even more spectacular and cataclysmic than the coruscant astrophysical road down which they have travelled.