Stars of low to intermediate mass in the Orion Nebula

Specially filtered photographs in the red or near-IR of the Orion Nebula reveal the Trapezium Cluster of about 67 stars brighter than V = 16, centered on Theta-1 Ori. The spectra of 12 known variables in, or very near, the Trapezium cluster indicate that they are not conventional T Tauri stars, leading to the suggestion that the cluster is a sample of post-T Tauri stars that have been gravitationally trapped for a relatively long time in the massive Orion Molecular Cloud, and are now observable only because Theta-1 Ori has removed the obscuring dust from that volume. Since the masses of the cluster members are unknown, it is not possible to say whether or not it is through the past dissipation of such molecular clouds and the release of their stellar components that the large number of low-mass stars in the solar neighborhood has been accumulated.