Herschel far-infrared photometric monitoring of protostars in the Orion Nebula Cluster

TL;DR

This study presents the first wide-field far-infrared monitoring of protostars in the Orion Nebula Cluster, revealing significant short-term variability likely caused by changes in protostellar accretion processes.

Contribution

It provides the first high-resolution, time-series far-infrared observations of a star-forming region, demonstrating rapid protostellar variability and its potential link to accretion dynamics.

Findings

Detected 43 protostars with complex structures

Observed >20% brightness variations over weeks

Variability likely driven by inner accretion processes

Abstract

We have obtained time series observations of the Orion Nebula Cluster at 70 microns and 160 microns from the Herschel/PACS Photometer. This represents the first wide-field far-infrared photometric monitoring of a young star forming region. The acquired 35'x35' maps show complex extended structures, with unprecedented details, that trace the interaction between the molecular gas and the young hot stars. We detect 43 protostars, most of which are situated along the integral-shaped filament extending from the Orion nebula, through OMC2 and to OMC3. We present high-reliability light curves for some of these objects using the first six epochs of our observing program spread over 6 weeks. We find amplitude variations in excess of 20% for a fraction of the detected protostars over periods as short as a few weeks. This is inconsistent with the dynamical time-scales of cool far-IR emitting material that orbits at hundreds of AU from the protostar, and it suggests that the mechanism(s) responsible for the observed variability originates from the inner region of the protostars, likely driven by variable mass accretion.