The Luminosity and Mass Function of the Trapezium Cluster: From B Stars to the Deuterium-burning Limit

August A. Muench, Elizabeth A. Lada, Charles J. Lada, João Alves

We use the results of a new multiepoch, multiwavelength, near-infrared

census of the Trapezium cluster in Orion to construct and analyze the

structure of its infrared (K-band) luminosity function. Specifically, we

employ an improved set of model luminosity functions to derive this

cluster's underlying initial mass function (IMF) across the entire range

of mass from OB stars to substellar objects down to near the

deuterium-burning limit. We derive an IMF for the Trapezium cluster that

rises with decreasing mass, having a Salpeter-like IMF slope until near

~0.6 Msolar where the IMF flattens and forms a broad peak

extending to the hydrogen-burning limit, below which the IMF declines

into the substellar regime. Independent of the details, we find that

substellar objects account for no more than ~22% of the total number of

likely cluster members. Further, the substellar Trapezium IMF breaks

from a steady power-law decline and forms a significant secondary peak

at the lowest masses (10-20 times the mass of Jupiter). This secondary

peak may contain as many as ~30% of the substellar objects in the

cluster. Below this substellar IMF peak, our K-band luminosity function

(KLF) modeling requires a subsequent sharp decline toward the planetary

mass regime. Lastly, we investigate the robustness of pre-main-sequence

luminosity evolution as predicted by current evolutionary models, and we

discuss possible origins for the IMF of brown dwarfs.

Department of Astrophysics
External organisation(s)
Harvard-Smithsonian Center for Astrophysics, University of Florida, Gainesville
The Astrophysical Journal
Publication date
Peer reviewed
Austrian Fields of Science 2012
103004 Astrophysics
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