Stars in adolescence: wild accretion, manic depression, fits of irrational outbursts, and pimply spots

In this talk, I will review pre-main sequence stellar evolution from birth in a molecular cloud embryo to adulthood on the main sequence, with a particular focus on the Classical T Tauri stars, the adolescents of stellar evolution.  These stars are nearly fully formed, with a remnant disk and ongoing accretion.  The accretion/disk phase typically lasts 2 - 5 Myr, though some stars take as long as 10 Myr before losing their disks and emerging as mature stars, often with little ones to raise.  Strong magnetic activity leads to pimply spots on the stellar surfaces. Some T Tauri stars are still hidden inside their disks, not yet ready to emerge. Manic mood swings change the appearance of the star and are often explained with stochastic accretion. Depression has been seen in lightcurves on timescales of days to years.  Sometimes every classical T Tauri star seems as uniquely precious as a snowflake, but all stars ultimately emerge from this wild period into the uniformity of adulthood.  I will describe the physics that drives the evolution from birth to adulthood, efforts to understand the stellar properties despite the wild teenage facade, and recent observations that are starting to reveal how planets form in circumstellar disks around adolescent stars.