The Young Population of the Chamaeleon II Dark Cloud

We discuss the results of the optical spectroscopic follow-up of pre-main-sequence (PMS) objects and candidates selected in the Chamaeleon II dark cloud based on data from the Spitzer Legacy survey “From Molecular Cores to Planet Forming Disks” (c2d) and from previous surveys. Our sample includes both objects with infrared excess selected according to c2d criteria and referred to as young stellar objects and other cloud members and candidates selected from complementary optical and near-infrared data. We characterize the sample of objects by deriving their physical parameters. The vast majority of objects have masses M ⩽ 1 M☉ and ages <6 Myr. Several of the PMS objects and candidates lie very close to or below the hydrogen-burning limit. A first estimate of the slope of the initial mass function in Cha II is consistent with that of other T associations. The star formation efficiency in the cloud (1%-4%) is consistent with our own estimates for Taurus and Lupus, but significantly lower than for Cha I. This might mean that different star formation activities in the Chamaeleon clouds may reflect a different history of star formation. We also find that the Cha II cloud is turning some 8 M☉ into stars every megayear, which is less than the star formation rate in the other c2d clouds. However, the star formation rate is not steady and evidence is found that the star formation in Cha II might have occurred very rapidly. The Hα emission of the Cha II PMS objects, as well as possible correlations between their stellar and disk properties, is also investigated.

[1]  K. Stapelfeldt,et al.  The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. X. The Chamaeleon II Pre-Main-Sequence Population as Observed with IRAC and MIPS , 2008, 0802.1424.

[2]  F. Leone.  Magnetic Intensification of the Li I λ6708 Line and the Abundance and Age Spread in Young Cool Stars , 2007 .

[3]  Jonathan P. Williams,et al.  A Submillimeter View of Circumstellar Dust Disks in ρ Ophiuchi , 2007, 0708.4185.

[4]  B. Merín,et al.  The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. IX. The Serpens YSO Population as Observed with IRAC and MIPS , 2007, 0704.0009.

[5]  E. Covino,et al.  A WFI survey in the Chamaeleon II dark cloud , 2007, astro-ph/0702230.

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

[7]  Andrew A. West,et al.  Low-Mass Dwarf Template Spectra from the Sloan Digital Sky Survey , 2006, astro-ph/0610639.

[8]  R. Indebetouw,et al.  Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A Grid of 200,000 YSO Model SEDs , 2006, astro-ph/0608234.

[9]  R. Jayawardhana,et al.  Spectroscopy of Young Planetary Mass Candidates with Disks , 2006, astro-ph/0607152.

[10]  B. Merín,et al.  The first brown dwarf with a disk in Chamaeleon II , 2006 .

[11]  C. Briceño,et al.  Bown dwarf and very low mass stars search in orion ob1a and ob1b asociations , 2006 .

[12]  D. T. Jaffe,et al.  Young, Low-Mass Brown Dwarfs with Mid-Infrared Excesses , 2006, astro-ph/0602249.

[13]  Heidelberg,et al.  The very low-mass population of the Corona Australis and Chamaeleon II star forming regions ⋆ , 2005, astro-ph/0511672.

[14]  G. Rieke,et al.  Spitzer Observations of IC 348: The Disk Population at 2-3 Million Years , 2005, astro-ph/0511638.

[15]  E. Young,et al.  The Disk Fractions of Brown Dwarfs in IC 348 and Chamaeleon I , 2005, astro-ph/0510664.

[16]  Instituto de Astrof'isica de Canarias,et al.  Seventeen new very low-mass members in Taurus. The brown dwarf deficit revisited , 2005, astro-ph/0509317.

[17]  N. Evans,et al.  Evidence for J- and H-Band Excess in Classical T Tauri Stars and the Implications for Disk Structure and Estimated Ages , 2005, astro-ph/0509036.

[18]  D. Padgett,et al.  The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. V. Chamaeleon II Observed with IRAC , 2005, astro-ph/0610849.

[19]  Subhanjoy Mohanty,et al.  The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs , 2005, astro-ph/0502155.

[20]  L. Hartmann,et al.  Measuring Accretion in Young Substellar Objects: Approaching the Planetary Mass Regime , 2005, astro-ph/0502023.

[21]  G. Fazio,et al.  Spitzer Identification of the Least Massive Known Brown Dwarf with a Circumstellar Disk , 2005, astro-ph/0502100.

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

[23]  R. Jayawardhana,et al.  A New Classical T Tauri Object at the Substellar Boundary in Chamaeleon II , 2004 .

[24]  Canada.,et al.  A new Classical T Tauri object at the sub-stellar boundary in Chamaeleon II , 2004, astro-ph/0407427.

[25]  L. Testi,et al.  Accretion in brown dwarfs: An infrared view , 2004, astro-ph/0406106.

[26]  K. Luhman.  A Census of the Chamaeleon I Star-forming Region , 2004, astro-ph/0402509.

[27]  Harinder P. Singh,et al.  The Indo-US Library of Coudé Feed Stellar Spectra , 2004, astro-ph/0402435.

[28]  P. Mauas,et al.  Library of flux-calibrated echelle spectra of southern late-type dwarfs with different activity levels ? , 2004 .

[29]  Thuringer Landessternwarte Tautenburg,et al.  The brown dwarf population in the Chamaeleon I cloud , 2003, astro-ph/0312026.

[30]  C. Ledoux,et al.  The UVES Paranal Observatory Project: A Library of High- Resolution Spectra of Stars across the Hertzsprung-Russell Diagram , 2003 .

[31]  T. Preibisch,et al.  Constraints on the IMF and the brown dwarf population of the young cluster IC 348 , 2003 .

[32]  E. Covino,et al.  Further identification of ROSAT all-sky survey sources in Orion , 2003 .

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

[34]  E. al.,et al.  From molecular cores to planet-forming disks: An SIRTF legacy program , 2003, astro-ph/0305127.

[35]  G. Rieke,et al.  A Census of the Young Cluster IC 348 , 2003, astro-ph/0304409.

[36]  G. Chabrier.  Galactic Stellar and Substellar Initial Mass Function , 2003, astro-ph/0304382.

[37]  L. Hillenbrand,et al.  Accretion in Young Stellar/Substellar Objects , 2003, astro-ph/0304078.

[38]  R. Jayawardhana,et al.  Evidence for a T Tauri Phase in Young Brown Dwarfs , 2003, astro-ph/0303565.

[39]  G. Olofsson,et al.  Near–infrared and ISOCAM observations of the Chamaeleon II dark cloud , 2003 .

[40]  R. Pelló,et al.  STELIB: A library of stellar spectra at R 2000 ?;?? , 2003, astro-ph/0302334.

[41]  S. N. Raines,et al.  A Study of the Luminosity and Mass Functions of the Young IC 348 Cluster Using FLAMINGOS Wide-Field Near-Infrared Images , 2003, The Astronomical Journal.

[42]  France,et al.  Brown dwarfs in the Pleiades cluster: Clues to the substellar mass function , , 2002, astro-ph/0212571.

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

[44]  Suzanne L. Hawley,et al.  The Palomar/MSU Nearby Star Spectroscopic Survey. IV. The Luminosity Function in the Solar Neighborhood and M Dwarf Kinematics , 2002 .

[45]  Michael C. Liu,et al.  A Survey for Circumstellar Disks around Young Substellar Objects , 2002, astro-ph/0210523.

[46]  Caltech,et al.  Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga , 2002, astro-ph/0209164.

[47]  K. Sahu,et al.  Substellar Mass Function of Young Open Clusters as Determined through a Statistical Approach Using Two Micron All Sky Survey and Guide Star Catalog Data , 2002, astro-ph/0206325.

[48]  J. Carpenter.  Constraints on the Circumstellar Disk Masses in the IC 348 Cluster , 2002, astro-ph/0205554.

[49]  Johns Hopkins University,et al.  Characterization of M, L, and T Dwarfs in the Sloan Digital Sky Survey , 2002, astro-ph/0204065.

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

[51]  P. Kroupa.  The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems , 2002, Science.

[52]  Y. Fukui,et al.  A Large Scale 12CO (J=1−0) Survey toward the Chamaeleon Region with NANTEN , 2001 .

[53]  Brazil.,et al.  Chromospherically young, kinematically old stars , 2001, astro-ph/0112452.

[54]  N. Epchtein,et al.  Low mass T Tauri and young brown dwarf candidates in the Chamaeleon II dark cloud found by DENIS , 2001, astro-ph/0109427.

[55]  R. Koehler.  Multiplicity of X-Ray-selected T Tauri Stars in Chamaeleon , 2001, astro-ph/0109103.

[56]  C. Dominik,et al.  Passive Irradiated Circumstellar Disks with an Inner Hole , 2001, astro-ph/0106470.

[57]  M. Osorio,et al.  The Substellar Mass Function in σ Orionis , 2001, astro-ph/0104097.

[58]  J. Weingartner,et al.  Dust Grain-Size Distributions and Extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud , 2001 .

[59]  N. Hambly,et al.  Very Low-Mass Stars and Brown Dwarfs of the Young Open Cluster IC 2391 , 2000, astro-ph/0011492.

[60]  P. Kroupa.  On the variation of the initial mass function , 2000, astro-ph/0009005.

[61]  Lynne A. Hillenbrand,et al.  Detection of Disk Accretion at the Substellar Limit , 2000 .

[62]  F. Allard,et al.  TiO and H2O Absorption Lines in Cool Stellar Atmospheres , 2000, astro-ph/0008465.

[63]  J. Weingartner,et al.  Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC , 2000, astro-ph/0008146.

[64]  F. Allard,et al.  Evolutionary Models for Very Low-Mass Stars and Brown Dwarfs with Dusty Atmospheres , 2000, astro-ph/0005557.

[65]  G. Rieke,et al.  The Initial Mass Function of Low-Mass Stars and Brown Dwarfs in Young Clusters , 2000, astro-ph/0004386.

[66]  L. Hillenbrand,et al.  Constraints on the Stellar/Substellar Mass Function in the Inner Orion Nebula Cluster , 2000, astro-ph/0003293.

[67]  A. Kawamura,et al.  Dense Cores and Star-Formation Activities in the Chamaeleon Dark-Cloud Complex , 1999 .

[68]  Francesco Palla,et al.  Star Formation in the Orion Nebula Cluster , 1999 .

[69]  Thierry Forveille,et al.  Spectroscopic Classification of Late-M and L Field Dwarfs , 1999 .

[70]  E. Feigelson,et al.  High-Energy Processes in Young Stellar Objects , 1999 .

[71]  L. Hartmann,et al.  Accretion processes in star formation , 1999 .

[72]  G. Rieke,et al.  Low-Mass Star Formation and the Initial Mass Function in the ρ Ophiuchi Cloud Core , 1999, astro-ph/9905286.

[73]  Telemachos Ch. Mouschovias,et al.  in The Origin of Stars and Planetary Systems , 1999 .

[74]  Sabine Frink,et al.  The History of Low-Mass Star Formation in the Upper Scorpius OB Association , 1999 .

[75]  F. Allard,et al.  The NextGen Model Atmosphere Grid for 3000 ≤ Teff ≤ 10,000 K , 1998, astro-ph/9807286.

[76]  D. B. Navascués,et al.  The Mass Function at the End of the Main Sequence: The M35 Open Cluster , 1998, astro-ph/9905230.

[77]  E. Palazzi,et al.  Optical polarimetry, high–resolution spectroscopy and IR analysis of the Chamaeleon I dark cloud , 1997 .

[78]  Y. Fukui,et al.  13CO (J= 1–0) Observations of the Lupus Molecular Clouds , 1996 .

[79]  L. Hartmann,et al.  Pre-Main-Sequence Evolution in the Taurus-Auriga Molecular Cloud , 1995 .

[80]  L. Mundy,et al.  Constraints on Circumstellar Disk Masses in the Trapezium Cluster , 1995 .

[81]  Y. Fukui,et al.  Overall Distribution of Dense Molecular Gas and Star Formation in the Taurus Cloud Complex , 1995 .

[82]  S. Beckwith,et al.  Millimeter-wave continuum measurements of young stars , 1995 .

[83]  P. Hartigan.  New T Tauri stars in Chamaeleon I and Chamaeleon II , 1993 .

[84]  P. Hartigan,et al.  Chamaeleon II: Distance Determination and HR Diagram , 1992 .

[85]  K. Strom,et al.  A study of the stellar population in the Chamaeleon dark clouds , 1992 .

[86]  Alexander Brown,et al.  A search for evidence of cold dust around naked T Tauri stars , 1991 .

[87]  S. Beckwith,et al.  A Survey for Circumstellar Disks around Young Stellar Objects , 1990 .

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

[89]  Blair D. Savage,et al.  Observed Properties of Interstellar Dust , 1979 .

[90]  R. Schwartz.  A survey of southern dark clouds for Herbig-Haro objects and H-alpha emission stars. , 1977 .

[91]  Michael D. Smith.  Astrophysics and space science , 1970 .

[92]  P. Bodenheimer.  Studies in Stellar Evolution. II. Lithium Depletion during the Pre-Main Contraction. , 1965 .