view Abstract Citations (35) References (91) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H i, CO, and IRAS Observations of NGC 7023 Rogers, C. ; Heyer, Mark H. ; Dewdney, P. E. Abstract We describe observations toward the reflection nebula NGC 7023 and the Herbig Be star HD 200775 of neutral hydrogen, carbon monoxide, and thermal dust emission all at a resolution of approximately 1 arcmin. These observations reveal a region of atomic gas that fills a well-defined, double-lobed void of molecular emission. The column density of H I is a factor of 35 smaller on average than the surrounding molecular cloud; the space density contrast is probably similar. The distribution of H I is not uniformed but tends to concentrate in a rim interior to the surrounding molecular rim. The thermal dust emission is of the same extent as the optical nebula and atomic region. There must be a population of cold dust outside this region that is not detected in IRAS bands. Within the atomic region, the far-infrared emissivity of the dust relative to gas is 25 times greater than expected. The morphology of dust optical depth may suggest that the excessive emissivity can be accounted for by H2 in the interface between regions of H I and (13)CO emission. Our H I observations also support the hypothesis that extended red emission (ERE) arises from hydrogenated amorphous carbon (HAC) material on dust. One of the main goals of this work is to compare photodisassociation and gas outflows as mechanisms for altering young stellar environments. Equilibrium photodisassociation region (PDR) models are not tested well by our observations because of geometrical uncertainties. For example, the observed H I-H2 and H I-(12)CO interfaces, which are viewed tangentially, appear to be in conflict with predictions of the standard model. Aslo, the selective photodisassociation of C(18)O relative to (13)CO appears to be more widespread than predicted. Time-dependent models, under the constraint of age estimates for HD 200775, cannot easily reproduce both the observed mass and the extent of atomic gas in NGC 7023. A challenge for future time-dependent models, which include dynamics, is to explain the observed high-density contrast between the atomic and molecular regions. We argue that not enough time has elapsed for there to have been any dynamical expansion of the PDR. A bipolar outflow, now defunct, could have produced the hourglass-shaped molecular rim and the density contrast between the atomic and molecular regions. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175475 Bibcode: 1995ApJ...442..694R Keywords: B Stars; Carbon Monoxide; Cosmic Dust; Emission Spectra; Gas Jets; H I Regions; Molecular Clouds; Radio Astronomy; Reflection Nebulae; Stellar Evolution; Data Reduction; Gas Flow; Image Analysis; Infrared Astronomy Satellite; Interstellar Extinction; Photodissociation; Radio Observation; Radio Telescopes; Spectrum Analysis; Astronomy; ISM: ABUNDANCES; ISM: DUST; EXTINCTION; ISM: INDIVIDUAL NGC NUMBER: NGC 7023; ISM: JETS AND OUTFLOWS; ISM: MOLECULES; ISM: REFLECTION NEBULAE; STARS: EMISSION-LINE; BE; STARS: PRE--MAIN-SEQUENCE; STARS: INDIVIDUAL HENRY DRAPER NUMBER: HD 200775 full text sources ADS | data products SIMBAD (9)