Constraints on the Stellar/Substellar Mass Function in the Inner Orion Nebula Cluster

By L. Hillenbrand, J. Carpenter. 2000

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We present the results of a 0.″5-0.″9 FWHM imaging survey at K (2.2 μm) and H (1.6 μm) covering ~5.′1 × 5.′1 centered on θ1C Ori, the most massive star in the Orion Nebula Cluster (ONC). At the age and distance of this cluster, and in the absence of extinction, the hydrogen-burning limit (0.08 M☉) occurs at K ≈ 13.5 mag, while an object of mass 0.02 M☉ has K ≈ 16.2 mag. Our photometry is complete for source detection at the 7 σ level to K ≈ 17.5 mag and thus is sensitive to objects as low-mass as 0.02 M☉ seen through visual extinction values as high as 10 mag. We use the observed magnitudes, colors, and star counts to constrain the shape of the inner ONC stellar mass function across the hydrogen-burning limit. After determining the stellar age and near-infrared excess properties of the optically visible stars in this same inner ONC region, we present a new technique that incorporates these distributions when extracting the mass function from the observed density of stars in the K-(H-K) diagram. We find that our data are inconsistent with a mass function that rises across the stellar/substellar boundary. Instead, we find that the most likely form of the inner ONC mass function is one that rises to a peak around 0.15 M☉, and then declines across the hydrogen-burning limit with slope N(log M) ∝ M0.57. We emphasize that our conclusions apply to the inner 0.71 pc × 0.71 pc of the ONC only; they may not apply to the ONC as a whole where some evidence for general mass segregation has been found.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/204528235f7f256407a613374ba7f1ab861e01a6

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Citations in the corpus

Embedded Clusters in Molecular Clouds (2003, methodology): “…AR194-AA41-03.sgm LaTeX2e(2002/01/18) P1: GJB Figure 11 shows a comparison of Trapezium IMFs recently derived from a number of different deep infrared imaging surveys using a variety of methods (Hillenbrand & Carpenter 2000; Lucas & Roche 2000; Luhman et al. 2000; Muench et al. 2000, 2003).”
New Brown Dwarfs and an Updated Initial Mass Function in Taurus (2004, background): “…et al. 2002; Luhman et al. 2003a) and IC 348 (Luhman et al. 2003b) have reported brown dwarf fractions R1 that are a factor of 2 lower than the values derived from luminosity function modeling in the Trapezium cluster in Orion (Luhman et al. 2000; Hillenbrand & Carpenter 2000; Muench et al. 2002).”
The Stellar Population of the Chamaeleon I Star-forming Region (2007, methodology): “Minimum Mass To date, measurements of IMFs in nearby star-forming regions have reached mass limits of ∼ 0.005-0.02 M⊙ through luminosity function modeling (Luhman et al. 2000; Hillenbrand & Carpenter 2000; Muench et al. 2002, 2003; Preibisch et al. 2003; Lucas et al. 2005) and spectroscopy (Hillenbr”
Destruction of protoplanetary discs in the Orion Nebula Cluster (2000, methodology): “The age of the cluster is difficult to determine, but data from Hillenbrand (1997) and Hillenbrand & Carpenter (2000) suggest that perhaps 85 per cent of its stars are less than 2Myr old (with a mean age of ∼ 0.8Myr).”
Low-Luminosity Companions to White Dwarfs (2005, background): “Furthermore, even for only moderately rising mass functions, such as those measured for substellar objects in open clusters (Hillenbrand & Carpenter 2000; Luhman et al. 2000; Hambly et al. 1999; Bouvier et al. 1998), there will be more brown dwarfs than stars if the minimum formed, self-gravitating…”
Infrared Spectroscopy of Substellar Objects in Orion (2001, background): “…yielded objects of planetary mass, in the Chamaeleon I molecular cloud (Tamura et al. 1998; Oasa, Tamura & Sugitani 1999) in the s Orionis cluster (Zapatero-Osorio et al. 2000) and in the Trapezium cluster in Orion (Lucas & Roche 2000, hereafter Paper I; Hillenbrand & Carpenter 2000, hereafter HC).”
The Formation of Brown Dwarfs as Ejected Stellar Embryos (2001, methodology): “For example, Hillenbrand & Carpenter (2000) have shown that in the core of the Orion Nebula Cluster, the mass function turns over at around 0.15 M⊙.”
THE PALOMAR/KECK ADAPTIVE OPTICS SURVEY OF YOUNG SOLAR ANALOGS: EVIDENCE FOR A UNIVERSAL COMPANION MASS FUNCTION (2008, background): “0; Hillenbrand & Carpenter 2000; Slesnick et al. 2004; Luhman 2004).”
The Initial Mass Function in the Taurus Star-forming Region (2002, methodology): “…low-mass stars and brown dwarfs have concentrated on star-forming clusters like the Orion Nebula cluster (Hillenbrand 1997; Luhman et al. 2000; Hillenbrand & Carpenter 2000; Lucas et al. 2001; Muench et al. 2002), Orionis (Barrado y Navascués et al. 2001; Béjar et al. 2001), IC 348 (Herbig…”
The “Mysterious” Origin of Brown Dwarfs (2002, methodology): “Similar IMFs were obtained for the Trapezium cluster in Orion by Luhman et al. (2000) and for the inner region of the Orion Nebula cluster by Hillenbrand & Carpenter (2000) using D’Antona & Mazzitelli’s (1997) evolutionary models.”
The origin of the initial mass function and its dependence on the mean Jeans mass in molecular clouds (2004, background): “These surveys nd that about 20% of the objects are brown dwarfs (Hillenbrand & Carpenter 2000;Slesnick et al.2004).”
Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7 Pre-Main-Sequence Stars (2005, background): “Thus, we exclude a number of obscured stars whose location in the K (H K ) diagram (see e.g., Hillenbrand & Carpenter 2000) predicts a mass around 1M .”
The Luminosity and Mass Function of the Trapezium Cluster: From B Stars to the Deuterium-burning Limit (2002, background): “Vol. 573 not a well-known quantity, and when previously derived, it has depended significantly on additional information derived from the spectral classification of cluster members (Hillenbrand & Carpenter 2000; Hillenbrand et al. 1998).”
The Spectroscopically Determined Substellar Mass Function of the Orion Nebula Cluster (2004, background): “Hillenbrand & Carpenter (2000) (hereafter HC00) present the results of an H and K imaging survey of the inner 5’.1 x 5’.1 region of the ONC.”
2MASS Observations of the Perseus, Orion A, Orion B, and Monoceros R2 Molecular Clouds (2000, methodology): “M _ ) The magnitudes were computed using the preÈmainsequence evolutionary tracks from DÏAntona & Mazzitelli (1997) assuming zero extinction and no near-infrared excess as outlined in Hillenbrand & Carpenter (2000).”
The Initial Mass Function of Low-Mass Stars and Brown Dwarfs in Young Clusters (2000, methodology): “Whereas the results of Hillenbrand (1997) used the models of DM94 and were complete to 0.1 M⊙, the Orion IMF of Hillenbrand & Carpenter (2000) was based on the models of DM97 and reaches 0.02 M⊙.”
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).”
X-Ray-emitting Young Stars in the Orion Nebula (2002, methodology): “%) have JHK but no optical counterparts (Hillenbrand & Carpenter 2000; Carpenter et al. 2001), one has only a mid-infrared counterpart, and 101 (9”