HST survey of the Orion Nebula Cluster in the H2O 1.4 µm absorption band: I. A census of substellar and planetary mass objects

Massimo Robberto, Mario Gennaro, Maria Giulia Ubeira Gabellini, Lynne A. Hillenbrand, Camilla Pacifici, Leonardo Ubeda, Morten Andersen, Travis Barman, Andrea Bellini, Nicola Da Rio, Selma E. de Mink, Giuseppe Lodato, Carlo Felice Manara, Imants Platais, Laurent Pueyo, Giovanni Maria Strampelli, Jonathan C. Tan, L. Testi

Research output: Contribution to journalArticlepeer-review


In order to obtain a complete census of the stellar and sub-stellar population, down to a few MJup in the ∼ 1 Myr old Orion Nebula Cluster, we used the infrared channel of the Wide Field Camera 3 of the Hubble Space Telescope with the F139M and F130N filters. These bandpasses correspond to the 1.4 µm H2O absorption feature and an adjacent line-free continuum region. Out of 4,504 detected sources, 3,352 (about 75%) appear fainter than m130 = 14 (Vega mag) in the F130N filter, a brightness corresponding to the hydrogen-burning limit mass (M ≃ 0.072 M⊙) at ∼ 1 Myr. Of these, however, only 742 sources have a negative F130M-139N color index, indicative of the presence of H2O vapor in absorption, and can therefore be classified as bona-fide M and L dwarfs, with effective temperatures T ≲ 2850 K at an assumed 1 Myr cluster age. On our color-magnitude diagram, this population of sources with H2O absorption appears clearly distinct from the larger background population of highly reddened stars and galaxies with positive F130M-F139N color index, and can be traced down to the sensitivity limit of our survey, m130 ≃ 21.5, corresponding to a 1 Myr old ≃ 3 MJup planetary mass object under about 2 magnitudes of visual extinction. Theoretical models of the BT-Settl family predicting substellar isochrones of 1, 2 and 3 Myr down to ∼ 1 MJup fail to reproduce the observed H2O color index at M ≲ 20 MJup. We perform a Bayesian analysis to determine extinction, mass and effective temperature of each sub-stellar member of our sample, together with its membership probability.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Apr 28 2020


  • Associations: individual (M42, Orion Nebula Cluster)
  • Brown dwarfs
  • Open clusters
  • Stars: atmospheres
  • Stars: pre-main sequence

ASJC Scopus subject areas

  • General

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