2023/12/06 by J. Davy Kirkpatrick, Federico Marocco, Kirkpatrick, J. Davy +190 · 1 voice
Physics and Astronomy · #Astronomy and Astrophysical Research #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies #astro-ph.EP #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.48550/arxiv.2312.03639
openalex publication_date 2023/12/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
A complete accounting of nearby objects -- from the highest-mass white dwarf progenitors down to low-mass brown dwarfs -- is now possible, thanks to an almost complete set of trigonometric parallax determinations from Gaia, ground-based surveys, and Spitzer follow-up. We create a census of objects within a Sun-centered sphere of 20-pc radius and check published literature to decompose each binary or higher-order system into its separate components. The result is a volume-limited census of ∼3,600 individual star formation products useful in measuring the initial mass function across the stellar (<8 M_\odot) and substellar (\gtrsim 5 MJup) regimes. Comparing our resulting initial mass function to previous measurements shows good agreement above 0.8M_\odot and a divergence at lower masses. Our 20-pc space densities are best fit with a quadripartite power law, ξ(M) = dN/dM ∝ M-α with long-established values of α= 2.3 at high masses (0.55 < M < 8.00 M_\odot) and α= 1.3 at intermediate masses (0.22 < M < 0.55 M_\odot), but at lower masses we find α= 0.25 for 0.05 < M <0.22 M_\odot and α= 0.6 for 0.01 < M < 0.05 M_\odot. This implies that the rate of production as a function of decreasing mass diminishes in the low-mass star/high-mass brown dwarf regime before increasing again in the low-mass brown dwarf regime. Correcting for completeness, we find a star to brown dwarf number ratio of, currently, 4:1, and an average mass per object of 0.41 M_\odot.