The Accreting Object Database: Probing the Formation Mechanisms of Planets and (Sub-)Stellar Objects

Comparing the relationship between accretion rate and mass in the stellar and substellar regimes is an effective strategy to identify the point at which the formation pathway for brown dwarfs diverges between planet-like and star-like formation mechanisms. To this end, we have assembled a comprehensive database of published accretion diagnostics for over 500 observations of almost 400 unique objects with masses ranging from 0.005 to 2 solar masses (including 64 brown dwarfs and 4 giant planets). The studies compiled in our database reveal a scatter of 4 orders of magnitude in the accretion rate vs. mass relationship in the brown dwarf regime. To explore the extent to which third variables, such as age, multiplicity, and intrinsic accretion variability explain the observed scatter, systematic errors due to differences in methodology must be eliminated. Using a uniform evolutionary model, we re-estimated masses and radii for brown dwarfs in the database using published spectral types and age estimates. We then re-estimated the accretion rate for each object by applying a uniform set of scaling relations and Gaia DR2 parallaxes to reported line fluxes and equivalent widths. Ongoing analyses seek to bolster the statistical sample in the database by incorporating additional studies, thoroughly account for and minimize systematic sources of error, calibrate different accretion diagnostics, and robustly analyze third effects with variable distributions now corrected for methodological differences. This database represents the most thorough compilation of literature studies of low-mass accretors to date, and is a valuable tool for future exploration of how formation properties vary across the substellar regime.