Chandra and Spitzer Imaging of the Infrared Cluster in NGC 2071

TL;DR

This study combines Chandra X-ray and Spitzer IR observations to analyze the star-forming region NGC 2071-IR, identifying protostars, their classes, and X-ray characteristics, revealing insights into early stellar evolution and ionization mechanisms.

Contribution

First combined X-ray and mid-IR imaging of NGC 2071-IR, identifying protostars and analyzing their properties and X-ray spectra, including fluorescent Fe emission.

Findings

IRS 1 is a class I protostar driving a bipolar outflow.

Detection of fluorescent Fe line at 6.4 keV in IRS 1.

Identification of deeply embedded, possibly younger protostar VLA 1.

Abstract

We present results of a sensitive Chandra X-ray observation and Spitzer mid-IR observations of the infrared cluster lying north of the NGC 2071 reflection nebula in the Orion B molecular cloud. We focus on the dense cluster core known as NGC 2071-IR which contains at least nine IR sources within a 40 x 40 arcsecond region. This region shows clear signs of active star formation including powerful molecular outflows, Herbig-Haro objects, and both OH and H2O masers. We use Spitzer IRAC images to aid in X-ray source identification and to determine YSO classes using mid-IR colors. Spitzer IRAC colors show that the luminous source IRS 1 is a class I protostar. IRS 1 is believed to be driving a powerful bipolar molecular outflow and may be an embedded B-type star or its progenitor. Its X-ray spectrum reveals a fluorescent Fe emission line at 6.4 keV, arising in cold material near the protostar. The line is present even in the absence of large flares, raising questions about the nature of the ionizing mechanism responsible for producing the 6.4 keV fluorescent line. Chandra also detects X-ray sources at or near the positions of IRS 2, IRS 3, IRS 4, and IRS 6 and a variable X-ray source coincident with the radio source VLA 1, located just 2 arcsec north of IRS 1. No IR data are yet available to determine a YSO classification for VLA 1, but its high X-ray absorption shows that it is even more deeply-embedded than IRS 1, suggesting that it could be an even younger, less-evolved protostar.