A Hectospec Spectroscopic Census of Kinematic Members in the Orion Nebula Cluster

Abstract

We present a comprehensive spectroscopic census of the Orion Nebula Cluster (ONC), based primarily on low-resolution optical spectroscopy obtained with MMT/Hectospec. We derive spectral types, youth indicators, and accretion diagnostics for 1513 stars located in the ONC region, enabling the identification and characterization of pre-main-sequence stars. We combine these measurements with a kinematic membership analysis based on Gaia Data Release 3 astrometry to identify and confirm cluster members. Using these combined diagnostics, we identify and characterize 780 bona fide T Tauri stars associated with the ONC. In addition, we construct a census of protoplanetary discs using infrared photometry obtained with the IRAC and MIPS instruments aboard the Spitzer Space Telescope. We further derive stellar masses, ages, and extinctions using the MassAge code, which combines photometric and spectroscopic inputs with stellar evolutionary models, and employs a Monte Carlo approach for uncertainty propagation. The resulting homogeneous catalogue of ONC members provides spectroscopic characterizations, kinematic membership constraints, disc diagnostics, and self-consistent estimates of stellar physical parameters. This dataset offers a refined view of the stellar population of the ONC and provides a robust foundation for investigating its kinematic structure, age distribution, and protoplanetary disc population.