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  • The Initial Mass Function Based on the Full-sky 20-pc Census of $\sim$3,600 Stars and Brown Dwarfs
    Kirkpatrick, J. Davy; Marocco, Federico; Gelino, Christopher R; Raghu, Yadukrishna; Faherty, Jacqueline K; Gagliuffi, Daniella C. Bardalez; 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; Andersen, Nikolaj Stevnbak; Antonini, Edoardo; Beaulieu, Paul; Bickle, Thomas P; Bilsing, Martin; Chieng, Raymond; Colin, Guillaume; Deen, Sam; Dereveanco, Alexandru; Doll, Katharina; Luca, Hugo A. Durantini; Frazer, Anya; Gantier, Jean Marc; Gramaize, Léopold; Grant, Kristin; Hamlet, Leslie K; Higashimura, Hiro; Hyogo, Michiharu; Jałowiczor, Peter A; Jonkeren, Alexander; Kabatnik, Martin; Kiwy, Frank; Martin, David W; Michaels, Marianne N; Pendrill, William; Machado, Celso Pessanha; Pumphrey, Benjamin; Rothermich, Austin; Russwurm, Rebekah; Sainio, Arttu; Sanchez, John; Sapelkin-Tambling, Fyodor Theo; Schümann, Jörg; Selg-Mann, Karl; Singh, Harshdeep; Stenner, Andres; Sun, Guoyou; Tanner, Christopher; Thévenot, Melina; Ventura, Maurizio; Voloshin, Nikita V; Walla, Jim; Wedracki, 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, David; Worlds, The Backyard; :; Collaboration, Planet 9

    12/2023
    Journal Article

    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 $M_\odot$.

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