{
  "id": "1205.4950",
  "version": "v1",
  "published": "2012-05-20T18:10:03.000Z",
  "updated": "2012-05-20T18:10:03.000Z",
  "title": "New isolated planetary mass objects and the stellar and substellar mass function of the sigma Orionis cluster",
  "authors": [
    "K. Peña Ramírez",
    "V. J. S. Béjar",
    "M. R. Zapatero Osorio",
    "M. G. Petr-Gotzens",
    "E. L. Martín"
  ],
  "comment": "Accepted for publication in ApJ. 69 pages, 15 figures",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We report on our analysis of the VISTA Orion ZYJHKs photometric data (completeness magnitudes Z=22.6 and J=21.0mag) focusing on a circular area of 2798.4 arcmin^2 around the young sigma Orionis star cluster (~3Myr, ~352pc, solar metallicity). The combination of the VISTA photometry with optical, WISE and Spitzer data allows us to identify a total of 210 cluster member candidates with masses in the interval 0.25-0.004Msun, 23 of which are new planetary-mass object findings. These discoveries double the number of cluster planetary-mass candidates known so far. One object has colors compatible with a T spectral type. The cluster harbors about as many brown dwarfs (69, 0.072-0.012Msun) and planetary-mass objects (37, 0.012-0.004Msun) as very low-mass stars (104, 0.25-0.072Msun). Based on Spitzer data, we derive a disk frequency of ~40% for very low-mass stars, brown dwarfs, and planetary mass objects in sigma Orionis. The radial density distributions of these three mass intervals are alike: all are spatially concentrated within an effective radius of 12arcmin (1.2pc) around the multiple star sigma Ori, and no obvious segregation between disk-bearing and diskless objects is observed. Using the VISTA data and the Mayrit catalog, we derive the cluster mass spectrum (DeltaN/DeltaM ~ M^{-alpha}) from ~19 to 0.006Msun (VISTA ZJ completeness), which is reasonably described by two power-law expressions with indices of alpha=1.7+/-0.2 for M>0.35Msun, and alpha=0.6+/-0.2 for M<0.35Msun. The sigma Orionis mass spectrum smoothly extends into the planetary-mass regime down to 0.004Msun. Our findings of T-type sources (<0.004Msun) in the VISTA sigma Orionis exploration appear to be smaller than what is predicted by the extrapolation of the cluster mass spectrum down to the survey J-band completeness.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2012-05-20T18:10:03.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "isolated planetary mass objects",
      "substellar mass function",
      "sigma orionis cluster",
      "sigma orionis star cluster",
      "sigma orionis exploration appear"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/0004-637X/754/1/30",
      "journal": "The Astrophysical Journal",
      "year": 2012,
      "month": "Jul",
      "volume": 754,
      "number": 1,
      "pages": 30
    },
    "note": {
      "typesetting": "TeX",
      "pages": 69,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1115592,
      "adsabs": "2012ApJ...754...30P"
    }
  }
}