2007/10/05 by Jose A. Caballero, J. A. Caballero · 4 citations
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2007.12555.x
MNRAS, accepted
arxiv created 2007/10/05 · openalex publication_date 2007/12/05 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29
I have re-visited the spatial distribution of stars and high-mass brown dwarfs in the σ Orionis (σ Ori) cluster (∼3 Ma, ∼360 pc). The input was a catalogue of 340 cluster members and candidates at separations less than 30 arcmin to σ Ori AB. Of them, 70 per cent have features of extreme youth. I fitted the normalized cumulative number of objects counting from the cluster centre to several power-law, exponential and King radial distributions. The cluster seems to have two components: a dense core that extends from the centre to r≈ 20 arcmin and a rarified halo at larger separations. The radial distribution in the core follows a power law proportional to r1, which corresponds to a volume density proportional to r−2. This is consistent with the collapse of an isothermal spherical molecular cloud. The stars more massive than 3.7 M⊙ concentrate, however, towards the cluster centre, where there is also an apparent deficit of very low mass objects (M < 0.16 M⊙). Last, I demonstrated through Monte Carlo simulations that the cluster is azimuthally asymmetric, with a filamentary overdensity of objects that runs from the cluster centre to the Horsehead Nebula.