SUBSTELLAR OBJECTS IN NEARBY YOUNG CLUSTERS (SONYC). V. NEW BROWN DWARFS IN ρ OPHIUCHI

SONYC-Substellar Objects in Nearby Young Clusters-is a survey program to investigate the frequency and properties of substellar objects with masses down to a few times that of Jupiter in nearby star-forming regions. For the {approx}1 Myr old {rho} Ophiuchi cluster, in our earlier paper we reported deep, wide-field optical and near-infrared imaging using Subaru, combined with Two Micron All Sky Survey and Spitzer photometry, as well as follow-up spectroscopy confirming three likely cluster members, including a new brown dwarf with a mass close to the deuterium-burning limit. Here we present the results of extensive new spectroscopy targeting a total of {approx}100 candidates in {rho} Oph, with Fiber Multi Object Spectrograph at the Subaru Telescope and SINFONI at the ESO's Very Large Telescope. We identify 19 objects with effective temperatures at or below 3200 K, eight of which are newly identified very low mass probable members of {rho} Oph. Among these eight, six objects have T{sub eff} {<=} 3000 K, confirming their likely substellar nature. These six new brown dwarfs comprise one-fifth of the known substellar population in {rho} Oph. We estimate that the number of missing substellar objects in our survey area is {approx}15, down to 0.003-0.03 M{sub Sun} andmore » for A{sub V} = 0-15. The upper limit on the low-mass star to brown dwarf ratio in {rho} Oph is 5.1 {+-} 1.4, while the disk fractions are {approx}40% and {approx}60% for stars and brown dwarfs, respectively. Both results are in line with those for other nearby star-forming regions.« less

[1]  John T. Rayner,et al.  An Infrared Spectroscopic Sequence of M, L, and T Dwarfs , 2004, astro-ph/0412313.

[2]  M. Robberto,et al.  The low-mass initial mass function in the Orion nebula cluster based on HST/NICMOS III imaging , 2011, 1108.5581.

[3]  The Luminosity and Mass Function of the Trapezium Cluster: From B Stars to the Deuterium-burning Limit , 2002, astro-ph/0203122.

[4]  A. A. Kaas,et al.  ISOCAM observations of the rho Ophiuchi cloud: Luminosity and mass functions of the pre-main sequence embedded cluster , 2001, astro-ph/0103373.

[5]  The COMPLETE Nature of the Warm Dust Shell in Perseus , 2006, astro-ph/0601692.

[6]  G. Rieke,et al.  The Stellar Population in the rho Ophiuchi Cluster , 1993 .

[7]  Naoyuki Tamura,et al.  Fibre Multi-Object Spectrograph (FMOS) for the Subaru Telescope , 2010 .

[8]  M. Meyer,et al.  THE INITIAL MASS FUNCTION AND DISK FREQUENCY OF THE ρ OPHIUCHI CLOUD: AN EXTINCTION-LIMITED SAMPLE , 2011, 1109.0561.

[9]  K. Ulaczyk,et al.  Unbound or distant planetary mass population detected by gravitational microlensing , 2011, Nature.

[10]  P. H. Hauschildt,et al.  Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458 , 2003 .

[11]  Matthew Bate,et al.  Stellar, brown dwarf and multiple star properties from hydrodynamical simulations of star cluster formation , 2008, 0811.0163.

[12]  Michael C. Liu,et al.  Characterizing Young Brown Dwarfs Using Low-Resolution Near-Infrared Spectra , 2006, astro-ph/0611408.

[13]  M. Cushing,et al.  H- and K-Band Spectra of Brown Dwarf Candidates in the Core of the ρ Ophiuchi Molecular Cloud Complex , 2000 .

[14]  P. Plavchan,et al.  A YOUNG PLANETARY-MASS OBJECT IN THE ρ OPH CLOUD CORE , 2009, 0912.3774.

[15]  C. Tinney,et al.  A METHANE IMAGING SURVEY FOR T DWARF CANDIDATES IN ρ OPHIUCHI , 2010, 1007.2406.

[16]  L. Hartmann,et al.  Disks around Brown Dwarfs in the σ Orionis Cluster , 2008, 0808.0471.

[17]  E. Young,et al.  Near-infrared observations of young stellar objects in the Rho Ophiuchi dark cloud , 1992 .

[18]  University of Leicester,et al.  The potential for Earth‐mass planet formation around brown dwarfs , 2007, 0709.0676.

[19]  F. Allard,et al.  Evolutionary Models for Very Low-Mass Stars and Brown Dwarfs with Dusty Atmospheres , 2000 .

[20]  Michael C. Liu,et al.  Subtle Signatures of Multiplicity in Late-type Dwarf Spectra: The Unresolved M8.5 + T5 Binary 2MASS J03202839–0446358 , 2008, 0803.0295.

[21]  G. Fazio,et al.  Infrared Array Camera (IRAC) Colors of Young Stellar Objects , 2004 .

[22]  R. Jayawardhana,et al.  Infrared Spectroscopy of the Ultra-Low-Mass Binary Oph 162225–240515 , 2006, astro-ph/0610601.

[23]  Rotation and accretion of very low mass objects in the sigma Ori cluster , 2004, astro-ph/0404014.

[24]  David R. Alexander,et al.  THE LIMITING EFFECTS OF DUST IN BROWN DWARF MODEL ATMOSPHERES , 2001 .

[25]  Patrick J. Lowrance,et al.  Discovery of a Very Young Field L Dwarf, 2MASS J01415823-4633574 , 2005 .

[26]  S. Okamura,et al.  Subaru Prime Focus Camera — Suprime-Cam , 2002, astro-ph/0211006.

[27]  Adam J. Burgasser,et al.  The 2MASS Wide-Field T Dwarf Search. III. Seven New T Dwarfs and Other Cool Dwarf Discoveries , 2004, astro-ph/0402325.

[28]  S. Leiden,et al.  A multiplicity survey of the ρ Ophiuchi molecular clouds , 2005, astro-ph/0504593.

[29]  M. Tamura,et al.  SUBSTELLAR OBJECTS IN NEARBY YOUNG CLUSTERS (SONYC): THE BOTTOM OF THE INITIAL MASS FUNCTION IN NGC 1333 , 2009, 0907.2243.

[30]  T. Barman,et al.  A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf “Lithium Test” at Early Ages , 2008, 0808.3153.

[31]  Coryn A. L. Bailer-Jones,et al.  Discovery of Young, Isolated Planetary Mass Objects in the σ Orionis Star Cluster , 2000 .

[32]  L. Allen,et al.  Star Formation in the ρ Ophiuchi Molecular Cloud , 2008 .

[33]  J. Liebert,et al.  Spectroscopy of a Young Brown Dwarf in the ρ Ophiuchi Cluster , 1997 .

[34]  R. Jayawardhana,et al.  A Disk Census for Young Brown Dwarfs , 2003, astro-ph/0305412.

[35]  M. Meyer,et al.  An Electronic Publication Dedicated to Early Stellar Evolution and Molecular Clouds Evidence for a Turnover in the Initial Mass Function of Low–mass Stars and Substellar Objects: Analysis from an Ensemble of Young Clusters , 2022 .

[36]  K. Rice,et al.  Protostars and Planets V , 2005 .

[37]  J. Mathis,et al.  The relationship between infrared, optical, and ultraviolet extinction , 1989 .

[38]  Rotation and variability of very low mass stars and brown dwarfs near epsilon Ori , 2004, astro-ph/0410101.

[39]  M. Tamura,et al.  A deep survey of brown dwarfs in Orion with Gemini , 2005 .

[40]  Low-Mass Star Formation and the Initial Mass Function in the ρ Ophiuchi Cloud Core , 1999, astro-ph/9905286.

[41]  L. Hartmann,et al.  The Initial Mass Function in the Taurus Star-forming Region , 2002 .

[42]  Spectroscopy of Brown Dwarf Candidates in the ρ Ophiuchi Molecular Core , 1998, astro-ph/9810508.

[43]  A Census of the Young Cluster IC 348 , 2003, astro-ph/0304409.

[44]  P. Padoan,et al.  The “Mysterious” Origin of Brown Dwarfs , 2002, astro-ph/0205019.

[45]  R. Jayawardhana,et al.  Discovery of a Young Planetary-Mass Binary , 2006, Science.

[46]  Optical Spectroscopy of the Surface Population of the ρ Ophiuchi Molecular Cloud: The First Wave of Star Formation , 2005, astro-ph/0506251.

[47]  K. Mužić,et al.  SUBSTELLAR OBJECTS IN NEARBY YOUNG CLUSTERS (SONYC). III. CHAMAELEON-I , 2011, 1103.0978.

[48]  M. Skrutskie,et al.  The Two Micron All Sky Survey (2MASS) , 2006 .

[49]  C. Lada,et al.  The discovery of new embedded sources in the centrally condensed core of the Rho Ophiuchi dark cloud - The formation of a bound cluster , 1983 .

[50]  A. Whitworth,et al.  The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation , 2008, 0810.1687.

[51]  Tetsuo Nishimura,et al.  Multi-Object Infrared Camera and Spectrograph (MOIRCS) for the Subaru Telescope* I. Imaging , 2008 .

[52]  David Lafreniere,et al.  SUBSTELLAR OBJECTS IN NEARBY YOUNG CLUSTERS (SONYC). II. THE BROWN DWARF POPULATION OF ρ OPHIUCHI , 2010, 1010.5801.

[53]  R. A. Gutermuth,et al.  The Disk Population of the Chamaeleon I Star-forming Region , 2008, 0803.1019.