Paper

The Initial Mass Function Based on the Full-sky 20-pc Census of \\(\\sim\\)3,600 Stars and Brown Dwarfs

Grant, Kristin, Kiwy, Frank, Hsu, Chih-Chun, Low, Ryan, Caselden, Dan, Hamlet, Leslie K, Zurek, David, Jonkeren, Alexander, Suárez, Genaro, Deen, Sam, Burgasser, Adam J, Li, Guodong, Kiman, Rocio, Wedracki, Zbigniew, Rees, Jon M, Planet 9 Collaboration, Vos, Johanna M, Sun, Guoyou, Allers, Katelyn N, Aganze, Christian, Rothermich, Austin, Sainio, Arttu, Walla, Jim, Dereveanco, Alexandru, Durantini Luca, Hugo A, Frazer, Anya, Stern, Daniel, Schurr, Steven D, Mamajek, Eric, Kuchner, Marc J, Raddi, Roberto, Thévenot, Melina, Pantoja, Blake M, Casewell, S L, Chao-Wei, Tsai, Tanner, Christopher, Kabatnik, Martin, J Davy Kirkpatrick, Marocco, Federico, Smart, R L, Voloshin, Nikita V, Kesseli, Aurora, Guillaume, Colin, Russwurm, Rebekah, Calamari, Emily, Gonzales, Eileen C, Selg-Mann, Karl, Connor, Thomas, Antonini, Edoardo, Faherty, Jacqueline K, Ventura, Maurizio, Higashimura, Hiro, Sapelkin-Tambling, Fyodor Theo, Adorno, Jose I, Yadukrishna Raghu, Apps, Kevin, Schümann, Jörg, Gantier, Jean Marc, Meisner, Aaron M, Pumphrey, Benjamin, Popinchalk, Mark, Pendrill, William, Eisenhardt, Peter R, Theissen, Christopher, Ma

2023

Overview

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 \\(\\sim\\)3,600 individual star formation products useful in measuring the initial mass function across the stellar (\\(<8 M_\\odot\\)) and substellar (\\(\\gtrsim 5 M_{Jup}\\)) regimes. Comparing our resulting initial mass function to previous measurements shows good agreement above 0.8\\(M_\\odot\\) and a divergence at lower masses. Our 20-pc space densities are best fit with a quadripartite power law, \\(\\xi(M) = dN/dM \\propto M^{-\\alpha}\\) with long-established values of \\(\\alpha = 2.3\\) at high masses (\\(0.55 < M < 8.00 M_\\odot\\)) and \\(\\alpha = 1.3\\) at intermediate masses (\\(0.22 < M < 0.55 M_\\odot\\)), but at lower masses we find \\(\\alpha = 0.25\\) for \\(0.05 < M <0.22 M_\\odot\\) and \\(\\alpha = 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\\).

• Publisher: Cornell University Library, arXiv.org
• Subject: Binary stars / Brown dwarf stars / Census / Censuses / Initial mass function / Low mass stars / Parallax / Star & galaxy formation / Star formation / White dwarf stars