The star-formation process in molecular clouds associated with Herbig Be/Ae stars. I - LK H-alpha 198, BD + 40 deg 4124, and NGC 7129

Abstract

view Abstract Citations (65) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The star-formation process in molecular clouds associated with Herbig Be/Ae stars. I. LkHalpha 198, BD +40 4124, and NGC 7129. Loren, R. B. Abstract Three molecular clouds associated with the young, rapidly evolving Herbig Be/Ae stars are examined in an attempt to determine the triggering mechanism of star formation. Self-gravitation of an isolated massive cloud, with no enhancement of the external pressure, could account for collapse and subsequent star formation in only the case of the NGC 7129 cloud. An external source of cloud compression must occur in the other two cases. In the LkHa 198 cloud this may be the result of a cloud-cloud collision. The source of increased external pressure in the BD +4004124 cloud is not clearly identified, but may be the result of expansion of a nearby H ii region. In the BD +4004124 and NGC 7129 clouds, the TA*(CO) peaks are not just surface heating of the cloud but are coincident with enhanced 7('3CO) and high-density cores detectable in HCN and 2 mm H2CO emission. In the LkHa 198 cloud the TA*(CO) peaks are associated with stars at the surface of the cloud, while a region of enhanced CO line broadening is at a position that may be self-absorbed in CO. The observed spatial variations of CO line profiles in the LkHa 198 cloud are compared to the four major models for radiative line transfer in molecular clouds. Both the V r collapse and microturbulent models fail to account for observed CO profiles, while a V r -112 collapse can account for all of the observations, and macroturbulence can account for the observations if it is driven by a V r -112 collapse. The variation of CO line extent in the NGC 7129 cloud is also in conflict with the microturbulent or V r collapse models but could be the result of macroturbulent broadening. Subject headings: interstellar: molecules - nebulae: general - stars: emission-line - stars: formation Publication: The Astrophysical Journal Pub Date: December 1977 DOI: 10.1086/155728 Bibcode: 1977ApJ...218..716L Keywords: Interstellar Matter; Microwave Emission; Molecular Spectra; Star Formation; A Stars; Astronomical Models; B Stars; Millimeter Waves; Molecular Excitation; Radio Sources (Astronomy); Stellar Spectra; Astrophysics full text sources ADS | data products SIMBAD (3)