YSOVAR: the first sensitive, wide-area, mid-IR photometric monitoring of the ONC

TL;DR

This study presents the first wide-area, sensitive mid-infrared photometric monitoring of the Orion Nebula Cluster, revealing variability related to inner disk structures in young stellar objects using Spitzer data.

Contribution

It provides the first extensive mid-infrared time series data of the ONC, enabling new insights into disk processes and stellar variability in young stars.

Findings

Detection of variability in young stellar objects at 3.6 and 4.5 microns.

Identification of AA-Tau analogs with flux dips likely caused by disk structures.

Data set useful for studying stellar rotation, eclipsing binaries, and disk evolution.

Abstract

We present initial results from time series imaging at infrared wavelengths of 0.9 sq. degrees in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5 micron data over 40 consecutive days. We extracted light curves with ~3% photometric accuracy for ~2000 ONC members ranging from several solar masses down to well below the hydrogen burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (Ic) and/or near-infrared (JKs) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence (PMS) eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 & 4.5 micron variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009, and we highlight our light curves for AA-Tau analogs - YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.