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Title: The evolution of accretion in young stellar objects: Strong accretors at 3-10 Myr

While the rate of accretion onto T Tauri stars is predicted to decline with age, objects with strong accretion have been detected at ages of up to 10 Myr. We analyze a sample of these old accretors, identified by having a significant U band excess and infrared emission from a circumstellar disk. Objects were selected from the ∼3 Myr σ Ori, 4-6 Myr Orion OB1b, and 7-10 Myr Orion OB1a star forming associations. We use high-resolution spectra from the Magellan Inamori Kyocera Echelle to estimate the veiling of absorption lines and calculate extinction for our T Tauri sample. We also use observations obtained with the Magellan Echellette and, in a few cases, the SWIFT Ultraviolet and Optical Telescope to estimate the excess produced in the accretion shock, which is then fit with accretion shock models to estimate the accretion rate. We find that even objects as old as 10 Myr may have high accretion rates, up to ∼10{sup –8} M{sub ☉} yr{sup –1}. These objects cannot be explained by viscous evolution models, which would deplete the disk in shorter timescales unless the initial disk mass is very high, a situation that is unstable. We show that the infrared spectral energymore » distribution of one object, CVSO 206, does not reveal evidence of significant dust evolution, which would be expected during the 10 Myr lifetime. We compare this object to predictions from photoevaporation and planet formation models and suggest that neither of these processes have had a strong impact on the disk of CVSO 206.« less
Authors:
; ; ; ;  [1] ; ;  [2] ;  [3]
  1. Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States)
  2. Centro de Investigaciones de Astronomía (CIDA), Mérida, 5101-A (Venezuela, Bolivarian Republic of)
  3. Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)
Publication Date:
OSTI Identifier:
22365583
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 790; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ACCRETION DISKS; DUSTS; EMISSION; ENERGY SPECTRA; EVOLUTION; LIFETIME; MASS; RESOLUTION; STARS; T TAURI STARS; TELESCOPES; ULTRAVIOLET RADIATION