Journal ArticleThe Initial Mass Function Based on the Full-sky 20 pc Census of ∼3600 Stars and Brown DwarfsKirkpatrick, J Davy; Marocco, Federico; Gelino, Christopher R; Raghu, Yadukrishna; Faherty, Jacqueline K; Bardalez_Gagliuffi, Daniella C; Schurr, Steven D; Apps, Kevin; Schneider, Adam C; Meisner, Aaron M; Kuchner, Marc J; Caselden, Dan; Smart, R L; Casewell, S L; Raddi, Roberto; Kesseli, Aurora; Stevnbak_Andersen, Nikolaj; Antonini, Edoardo; Beaulieu, Paul; Bickle, Thomas P; Bilsing, Martin; Chieng, Raymond; Colin, Guillaume; Deen, Sam; Dereveanco, Alexandru; Doll, Katharina; Durantini_Luca, Hugo A; Frazer, Anya; Gantier, Jean Marc; Gramaize, Léopold; Grant, Kristin; Hamlet, Leslie K; Higashimura_東, Hiro_村 滉; Hyogo, Michiharu; Jałowiczor, Peter A; Jonkeren, Alexander; Kabatnik, Martin; Kiwy, Frank; Martin, David W; Michaels, Marianne N; Pendrill, William; Pessanha_Machado, Celso; Pumphrey, Benjamin; Rothermich, Austin; Russwurm, Rebekah; Sainio, Arttu; Sanchez, John; Sapelkin-Tambling, Fyodor Theo; Schümann, Jörg; Selg-Mann, Karl; Singh, Harshdeep; Stenner, Andres; Sun_孙, Guoyou 国佑; Tanner, Christopher; Thévenot, Melina; Ventura, Maurizio; Voloshin, Nikita V; Walla, Jim; Wędracki, Zbigniew; Adorno, Jose I; Aganze, Christian; Allers, Katelyn N; Brooks, Hunter; Burgasser, Adam J; Calamari, Emily; Connor, Thomas; Costa, Edgardo; Eisenhardt, Peter R; Gagné, Jonathan; Gerasimov, Roman; Gonzales, Eileen C; Hsu, Chih-Chun; Kiman, Rocio; Li, Guodong; Low, Ryan; Mamajek, Eric; Pantoja, Blake M; Popinchalk, Mark; Rees, Jon M; Stern, Daniel; Suárez, Genaro; Theissen, Christopher; Tsai, Chao-Wei; Vos, Johanna M; Zurek, DavidThe_Backyard_Worlds_Planet_9_Collaboration<title>Abstract</title> <p>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 ∼3600<italic>individual</italic>star formation products useful in measuring the initial mass function across the stellar (<8<italic>M</italic>_⊙) and substellar (≳5<italic>M</italic>_Jup) regimes. Comparing our resulting initial mass function to previous measurements shows good agreement above 0.8<italic>M</italic>_⊙and a divergence at lower masses. Our 20 pc space densities are best fit with a quadripartite power law,<inline-formula><tex-math><CDATA/></tex-math><math overflow='scroll'><mi>ξ</mi><mo stretchy='false'>(</mo><mi>M</mi><mo stretchy='false'>)</mo><mo>=</mo><mi mathvariant='italic'>dN</mi><mrow><mo stretchy='true'>/</mo></mrow><mi mathvariant='italic'>dM</mi><mo>∝</mo><msup><mrow><mi>M</mi></mrow><mrow><mo>−</mo><mi>α</mi></mrow></msup></math><inline-graphic href='apjsad24e2ieqn1.gif' type='simple'/></inline-formula>, with long-established values of<italic>α</italic>= 2.3 at high masses (0.55 <<italic>M</italic>< 8.00<italic>M</italic>_⊙), and<italic>α</italic>= 1.3 at intermediate masses (0.22 <<italic>M</italic>< 0.55<italic>M</italic>_⊙), but at lower masses, we find<italic>α</italic>= 0.25 for 0.05 <<italic>M</italic>< 0.22<italic>M</italic>_⊙, and<italic>α</italic>= 0.6 for 0.01 <<italic>M</italic>< 0.05<italic>M</italic>_⊙. 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<italic>M</italic>_⊙.</p>IOP2024-04-0110533774The Astrophysical Journal Supplement Series2712550067-0049https://doi.org/10.3847/1538-4365/ad24e22009136; 2009177; 2238468National Science Foundation