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

By August Muench, E. Lada, C. Lada, Joao F. Alves, U. Florida, Smithsonian Astrophysical Observatory, E. Observatory. 2002

321 citations recorded by the source corpus.

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 M☉ 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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/15e091971dd8961e469826939b10357d9870d670

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TOWARD A UNIFICATION OF STAR FORMATION RATE DETERMINATIONS IN THE MILKY WAY AND OTHER GALAXIES (2011, methodology): “Povich et al. (2009) showed that Npop as reported by Broos et al. (2007) for NGC 6618 translates to a SFR based on star counts of SFRSC = 0.008–0.01 M⊙ yr −1, using the Muench et al. (2002) IMF to convert Npop to Mpop.”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, unknown): “…star (Kroupa 2001, 2002; Chabrier 2003, 2005; Covey et al. 2008; Deacon et al. 2008; Bochanski et al. 2010; Parravano et al. 2011), young cluster (Muench et al. 2002; Chabrier 2003, 2005; Sabbi et al. 2008; Andersen et al. 2009; Sung & Bessell 2010; Lodieu et al. 2011, 2012a,b; Da Rio et al.…”
Herschel-Planck dust optical-depth and column-density maps - I. Method description and results for Orion (2014, unknown): “It contains the nearest massive star-forming cluster to Earth, the Trapezium cluster (e.g. Hillenbrand 1997; Lada et al. 2000; Muench et al. 2002; Da Rio et al. 2012), at a distance of 414 pc Menten et al. 2007).”
EVOLUTIONARY SIGNATURES IN THE FORMATION OF LOW-MASS PROTOSTARS. II. TOWARD RECONCILING MODELS AND OBSERVATIONS (2005, methodology): “Finally, if we assume the same efficiency but instead use the IMF found by Muench et al. (2002) for the Trapezium cluster shown by Alves et al. (2007) to match (with the 30% scaling) the dense core mass function in the pipe nebula, we find N1/N3 = 1.1 and N1/N0.”
The Formation and Early Evolution of Low-Mass Stars and Brown Dwarfs (2012, background): “…to the Trapezium Cluster at the center of the ONC because it is very compact and is located in front of a dense molecular cloud, reducing the contamination from background stars (Hillenbrand & Carpenter 2000; Lucas & Roche 2000; Lucas, Roche & Tamura 2005; Luhman et al. 2000; Muench et al. 2002).”
New Brown Dwarfs and an Updated Initial Mass Function in Taurus (2004, methodology): “As described above, the IMF for Taurus differs significantly from that of IC 348, which in turn closely matches the IMF for the Trapezium at stellar masses (Muench et al. 2002, 2003; Slesnick et al. 2004).”
Stellar and dynamical masses of ellipticals in the Sloan Digital Sky Survey (2003, result): “Our results suggest that a cutoff at M > 0.1M⊙ is required, consistent with IMF measurements from young embedded clusters (Muench et al. 2002).”
The Formation of Massive Stars from Turbulent Cores (2002, background): “In the Trapezium, the IMF has a broad maximum between 0.6 M⊙ and the hydrogen burning limit (Muench et al. 2002).”
STAR FORMATION EFFICIENCIES AND LIFETIMES OF GIANT MOLECULAR CLOUDS IN THE MILKY WAY (2010, background): “…dN d lnm d lnm, (1) where 〈q〉 ≡ ∫ mU mL q(m∗) dN d lnm d lnm. (2) The quantitydN/d lnm is the stellar initial mass function (IMF), which we take to be either that of Muench et al. (2002) modified to have a high mass slope of−1.35 rather than their −1.21, or the IMF of Chabrier (2005).”
The Initial Configuration of Young Stellar Clusters: A K-Band Number Counts Analysis of the Surface Density of Stars (2004, methodology): “…this analysis, we assume M∗ = 0.5M⊙ as an appropriate median stellar mass from young cluster initial mass functions reported in the literature (e.g., Muench et al. 2002; Luhman et al. 2003), and vdisp = 1 km s −1 based on Maxwellian velocity dispersions derived from C18O linewidths for these…”
THE FIRST HUNDRED BROWN DWARFS DISCOVERED BY THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE) (2011, result): “This result is in accordance with findings in young star formation regions (e.g., Luhman et al. 2000, Muench et al. 2002, Lucas et al. 2006, Luhman 2007), but the derived masses for those objects should be considered cautiously, as discussed in Baraffe et al. (2003), because models with ages of ∼1…”
The APOGEE-2 Survey of the Orion Star-forming Complex. II. Six-dimensional Structure (2018, methodology): “The masses for both the cluster and field stars are drawn from the Initial Mass Function (IMF) from Muench et al. (2002).”
The mass function of dense molecular cores and the origin of the IMF (2006, methodology): “Also plotted are the field star IMFs of Kroupa (2001) (solid grey) and Chabrier (2003) (dotted grey), and the Muench et al. (2002) (dashed grey) IMF all scaled up by a factor of∼ 3 in mass. therefore the stellar and core mass functions should be of similar overall functional form.”
Inverse dynamical population synthesis: Constraining the initial conditions of young stellar clusters by studying their binary populations (2012, unknown): “Brown dwarfs have since been detected in the centre of the cluster (Hillenbrand & Carpenter 2000; Luhman et al. 2000; Lucas et al. 2001; Muench et al. 2002), so that the mean mass may decreases to 0.5M⊙ (Scally et al. 2005), in good agreement with the canonical IMF.”
The Mass Distribution and Lifetime of Prestellar Cores in Perseus, Serpens, and Ophiuchus (2008, background): “Alves et al. (2007) find a turnover in the CMD of the Pipe Nebula at M ∼ 3× the turnover in the Trapezium IMF (Muench et al. 2002), and suggest that the stellar IMF is a direct product of the CMD, with a uniform core-tostar efficiency of 30%±10%.”