Stellar Disk Destruction by Dynamical Interactions in the Orion Trapezium Star Cluster

Stellar disk destruction by dynamical interactions in the Orion Trapezium star cluster

Authors:

Zwart et al

Abstract:

We compare the observed size distribution of circum stellar disks in the Orion Trapezium cluster with the results of N-body simulations in which we incorporated an heuristic prescription for the evolution of these disks. In our simulations, the sizes of stellar disks are affected by close encounters with other stars (with disks). We find that the observed distribution of disk sizes in the Orion Trapezium cluster is excellently reproduced by truncation due to dynamical encounters alone. The observed distribution appears to be a sensitive measure of the past dynamical history of the cluster, and therewith on the conditions of the cluster at birth. The best comparison between the observed disk size distribution and the simulated distribution is realized with a cluster of N=2500±500 stars with a half-mass radius of about 0.5\,pc in virial equilibrium (with a virial ratio of Q=0.5, or somewhat colder Q≃0.3), and with a density structure according to a fractal dimension of F≃1.6. Simulations with these parameters reproduce the observed distribution of circum stellar disks in about 0.2--0.5\,Myr.

Brown Dwarfs Detected in Near-IR Sprectroscopy of the Orion Trapezium Cluster

NEAR-INFRARED (JHK) SPECTROSCOPY OF YOUNG STELLAR AND SUBSTELLAR OBJECTS IN ORION

Authors:

Ingraham et al

Abstract:

We performed low-resolution (R ~ 40) near-infrared (0.9-2.4 μm) multi-object spectroscopy of 240 isolated point sources having apparent H-band magnitudes between 9 and 18 in the central 5' × 6' of the Orion Trapezium cluster. The observations were performed over four nights at the Canada-France-Hawaii Telescope using the visiting instrument SIMON, an infrared imager and multi-object spectrograph. We present the spectra of 104 objects with accurately derived spectral types including 7 new objects having masses below the hydrogen-burning limit, and 6 objects with masses below the deuterium-burning limit. The spectral classification is performed by fitting previously classified spectral templates of dwarf stars (K4-M3) and optically classified young stellar and substellar objects (M4-L0), to the entire 0.9-2.4 μm spectral energy distribution in order to assign a spectral type and visual extinction for each object. Of the 104 objects studied, 44 have been previously classified spectroscopically using various techniques. We perform a rigorous comparison between the previous classifications and our own and find them to be in good agreement. Using the dereddened H-band magnitudes, the classified objects are used to create an Hertzsprung-Russell diagram for the cluster. We find that the previous age estimates of ~1 Myr to be consistent with our results. Consistent with previous studies, numerous objects are observed to have luminosities several magnitudes above the 1 Myr isochrone. Numerous objects exhibiting emission features in the J band are also reported.