HST Survey of the Orion Nebula Cluster in ACS/Visible and WFC3/IR Bands. IV. A Bayesian Multiwavelength Study of Stellar Parameters in the Orion Nebula Cluster

Strampelli, Giovanni M.; Robberto, Massimo; Pueyo, Laurent; Gennaro, Mario; Manara, Carlo F.; Sabbi, Elena; Aparicio, Antonio
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The Astrophysical Journal

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We have performed a comprehensive study of the Orion Nebula Cluster (ONC) combining the photometric data obtained by the two Hubble Space Telescope Treasury programs that targeted this region. To consistently analyze the rich data set obtained in a wide variety of filters, we adopted a Bayesian approach to fit the spectral energy distribution of the sources, deriving mass, age, extinction, distance, and accretion for each source in the region. The three-dimensional study of mass distribution for bona fide cluster members shows that mass segregation in the ONC extends to subsolar masses, while the age distribution strongly supports the idea that star formation in the ONC is best described by a major episode of star formation that happened ∼1 Myr ago. For masses ≳0.1 M ⊙, our derived empirical initial mass function (IMF) is in good agreement with a Chabrier system IMF. Both the accretion luminosity (L acc) and mass accretion rates ( ${\dot{M}}_{\mathrm{acc}}$ ) are best described by broken power-law relations. This suggests that for the majority of young circumstellar disks in this cluster the excess emission may be dominated by X-ray-driven photoevaporation by the central star rather than external photoevaporation. If this is the case, the slopes of the power-law relations may be largely determined by the initial conditions set at the onset of the star formation process, which may be quite similar between regions that eventually form clusters of different sizes.