Star Formation in Space and Time: Taurus‐Auriga

To understand the formation of stellar groups, one must first documentcarefully the birth pattern within real clusters and associations. In thisstudy of Taurus-Auriga, we combine pre-main-sequence ages from our ownevolutionary tracks with stellar positions from observational surveys. Aided bythe extensive, millimeter data on the molecular clouds, we develop a picture ofthe region's history. Star formation began, at a relatively low level and in aspatially diffuse manner, at least 10 Myr in the past. Within the last fewmillion years, new stars have been produced at an accelerating rate, almostexclusively within a confined group of striated cloud filaments. The gas bothinside and around the filaments appears to be in force balance. Thus, theappearance of the filaments is due to global, quasi-static contraction of theparent cloud material. Gravity drives this contraction and shock dissipationmediates it, but the internal motion of the gas does not appear to beturbulent. The accelerating nature of recent star formation means that thecondensation of cloud cores is a threshold phenomenon, requiring a minimumbackground density. Other, nearby cloud regions, including Lupus andChamaeleon, contain some locales that have attained this density, and othersthat have not. In the latter, we find extensive and sometimes massive moleculargas that is still devoid of young stars.Comment: 19 pages, 7 figures, to be published in ApJ - December 20, 200