The Evolution of the FU Orionis Disk, and the Seeds of Planet Formation
Abstract
Young stars form new planetary systems during the collapse of a giant cloud of gas and dust. Tiny dust particles and gas parcels collide and stick together, growing slowly into planetary cores and then full-size planets. But is this process a steady and slow one, or are there bumps in the road to planet construction? In 1936, the young star FU Orionis (FU Ori) became 100 times brighter in only a few short months. Although astronomers didn't realize at the time, FU Ori was undergoing a "burst" of accretion -- instead of a slow trickle of material falling into the central star, nearly 20 Jupiters worth of material have fallen in and burned since 1936. This sustained flow is a large fraction of the entire measureable disk mass (both gas and dust) surrounding FU Ori. FU Ori has slowly faded over the past 80 years, reducing by approximately 1 mag. in B. But what changes did this increased brightness wreak upon FU Ori's disk, and what implications would it have for any planets that might have formed or form later? Unlike most observed young stars, FU Ori and its (~ 10) brethren with similar behavior show no evidence of crystalline dust grains like forsterite (peridot), and the temperatures at an Earth-equivalent distance would have risen from room temperature to a scalding 1000 degrees Kelvin.Our study with SOFIA/FORCAST, in comparison with our previous study with Spitzer/IRS, provides the first multi-epoch infrared spectroscopic study of an FUor, as it appeared in 2004 and 2016. First, the continuum (the energy emitted by viscous heating in the disk) has decreased by 13% but is still fit by a 7200 K blackbody at 13% less strength; second, the heating source behind disk's atmosphere (similar to a stellar atmosphere, as the superheated inner disk is at the same temperature as a typical star) has also decreased, exciting less high temperature water vapor. This change has not completely propagated to the rest of the disk. The silicate dust remains unchanged. We conclude that the material in the innermost portion of the disk, which has been cascading onto the central star, has been slowly reducing, or cooling, and is not being resupplied on this timescale.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #48
- Pub Date:
- October 2016
- Bibcode:
- 2016DPS....4811105G