L1599B: Cloud Envelope and C+ Emission in a Region of Moderately Enhanced Radiation Field

TL;DR

This study investigates how an asymmetric radiation field from a nearby star affects the chemical and physical properties of a molecular cloud, revealing localized enhanced emission and potential differential motion within the cloud.

Contribution

It provides detailed observational analysis of the effects of asymmetric radiation on molecular cloud envelopes, combining multiple spectral lines to understand physical and chemical variations.

Findings

Enhanced [CII] emission on the side facing the star

Cloud interior shows typical molecular properties

Velocity tracking suggests differential radial motion

Abstract

We study the effects of an asymmetric radiation field on the properties of a molecular cloud envelope. We employ observations of carbon monoxide (12CO and 13CO), atomic carbon, ionized carbon, and atomic hydrogen to analyze the chemical and physical properties of the core and envelope of L1599B, a molecular cloud forming a portion of the ring at approximately 27 pc from the star Lambda Ori. The O III star provides an asymmetric radiation field that produces a moderate enhancement of the external radiation field. Observations of the [CII] fine structure line with the GREAT instrument on SOFIA indicate a significant enhanced emission on the side of the cloud facing the star, while the [Ci], 12CO and 13CO J = 1-0 and 2-1, and 12CO J = 3-2 data from the PMO and APEX telescopes suggest a relatively typical cloud interior. The atomic, ionic, and molecular line centroid velocities track each other very closely, and indicate that the cloud may be undergoing differential radial motion. The HI data from the Arecibo GALFA survey and the SOFIA/GREAT [CII] data do not suggest any systematic motion of the halo gas, relative to the dense central portion of the cloud traced by 12CO and 13CO.