The Spectroscopically Determined Substellar Mass Function of the Orion Nebula Cluster

By Catherine Slesnick, L. Hillenbrand, J. Carpenter. 2004

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We present a spectroscopic study of candidate brown dwarf members of the Orion Nebula cluster (ONC). We obtained new J- and/or K-band spectra of ~100 objects within the ONC that are expected to be substellar on the basis of their K magnitudes and H-K colors. Spectral classification in the near-infrared of young low-mass objects is described, including the effects of surface gravity, veiling due to circumstellar material, and reddening. From our derived spectral types and existing near-infrared photometry, we construct an H-R diagram for the cluster. Masses are inferred for each object and used to derive the brown dwarf fraction and assess the mass function for the inner 5.′1 × 5.′1 of the ONC, down to ~0.02 M☉. The logarithmic mass function rises to a peak at ~0.2 M☉, similar to previous initial mass function determinations derived from purely photometric methods but falls off more sharply at the hydrogen-burning limit before leveling through the substellar regime. We compare the mass function derived here for the inner ONC with those presented in recent literature for the sparsely populated Taurus cloud members and the rich cluster IC 348. We find good agreement between the shapes and peak values of the ONC and IC 348 mass distributions but little similarity between the ONC and Taurus results.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/74f71c5512a6d32c4fe81a67df6b678116ad53e0

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Citations in the corpus

A NEAR-INFRARED SPECTROSCOPIC STUDY OF YOUNG FIELD ULTRACOOL DWARFS (2013, background): “Overall, we find that the H2O (Allers et al. 2007), H2O-1, H2O-2 (Slesnick et al. 2004) and H2OD 1 (McLean et al. 2003) indices are spectral type sensitive and gravity-insensitive over a broad range in spectral type.”
PLANETS AROUND LOW-MASS STARS (PALMS). IV. THE OUTER ARCHITECTURE OF M DWARF PLANETARY SYSTEMS (2014, background): “The gravity-insensitive indexbased near-infrared classification schemes of Allers et al. (2007) and Slesnick et al. (2004) imply spectral types of M6.”
THE PALOMAR/KECK ADAPTIVE OPTICS SURVEY OF YOUNG SOLAR ANALOGS: EVIDENCE FOR A UNIVERSAL COMPANION MASS FUNCTION (2008, methodology): “0; Hillenbrand & Carpenter 2000; Slesnick et al. 2004; Luhman 2004).”
A Universal Stellar Initial Mass Function? A critical look at variations in extreme environments (2010, background): “Numerous studies of the IMF of the Orion Nebular Cluster have been made over the past decade (Hillenbrand 1997, Hillenbrand & Carpenter 2000, Luhman et al. 2000, Muench et al. 2000, 2002, Slesnick et al. 2004, Lucas et al. 2005, Weights et al. 2009).”
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).”
The stellar and sub-stellar IMF of simple and composite populations (2011, methodology): “Since the new spectroscopic study of Slesnick et al. (2004) also revised the number of BDs per star in the ONC downwards, Luhman (2004) retracts the significance of the claimed difference of the ratio in TaurusAuriga and the ONC.”
Characterizing Young Brown Dwarfs Using Low-Resolution Near-Infrared Spectra (2006, background): “An older population has been suggested as a possible explanation for bifurcation on the H-R diagram of sources in the Orion Nebula cluster (Palla et al. 2005; Slesnick et al. 2004).”
YOUNG L DWARFS IDENTIFIED IN THE FIELD: A PRELIMINARY LOW-GRAVITY, OPTICAL SPECTRAL SEQUENCE FROM L0 TO L5 (2008, background): “…low gravities has been long-established empirically: these lines are not present in the spectra of late-type giants (log(g) ∼ (0)) and weak Na I and K I absorption are commonly seen in late-type M dwarf members of young clusters (e.g., Mart́ın et al. 1996; Luhman et al. 1997; Slesnick et al. 2004).”
The Stellar Population of the Chamaeleon I Star-forming Region (2007, background): “…Muench et al. 2002, 2003; Preibisch et al. 2003; Lucas et al. 2005) and spectroscopy (Hillenbrand 1997; Comerón et al. 2000; Béjar et al. 2001; Luhman et al. 2003b; Briceño et al. 2002; Barrado y Navascués et al. 2004; Luhman 2004d; Slesnick et al. 2004; Levine et al. 2006; Lucas et al. 2006).”
The Evolution of X-Ray Emission in Young Stars (2005, background): “0.2 M⊙) stars, such as reported by Slesnick et al. (2004), may be missing.”
BANYAN. VII. A NEW POPULATION OF YOUNG SUBSTELLAR CANDIDATE MEMBERS OF NEARBY MOVING GROUPS FROM THE BASS SURVEY (2015, unknown): “…Joyce et al. 1998), and it was later demonstrated that the same features could be used to identify young, inflated M-type dwarfs by observing members of star-forming regions (Martín et al. 1996; Luhman et al. 1997; Slesnick et al. 2004; Lucas et al. 2001; Allers et al. 2007; Lodieu et al. 2008).”
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).”