Friday, June 13 - Plenary Session

Name:  Viki Joergens

Affiliation:  Max-Planck-Institut for Astronomy

Title:  The Coolest 'Stars' are Free-Floating Planets

We show that the coolest known object that is formed in a star-like mode is a free-floating planet. We discovered recently that the free-floating planetary mass object OTS44 (M9.5, ~12 Jupiter masses, age ~2 Myr) has significant accretion and a substantial disk. This demonstrates that the processes that characterize the canonical star-like mode of formation apply to isolated objects down to a few Jupiter masses. We detected in VLT/SINFONI spectra that OTS44 has strong, broad, and variable Paschen beta emission. This is the first evidence for active accretion of a free-floating planet. The object allows us to study accretion and disk physics at the extreme and can be seen as free-floating analog of accreting planets that orbit stars. Our analysis of OTS44 shows that the mass-accretion rate decreases continuously from stars of several solar masses down to free-floating planets. We determined, furthermore, the disk mass (30 Earth masses) and further disk properties of OTS44 through SED modeling based on far-IR Herschel data. We find that objects between 14 solar masses and 0.01 solar masses have the same ratio of the disk-to-central-mass of about 0.01. Our results indicate that OTS44 is formed like a star and suggest that the increasing number of young free-floating planets and ultra-cool field T and Y dwarfs are the low-mass extension of the stellar population.