Tracing the evolutionary stage of Bok globules: CCS and NH3

Abstract

We pursue the investigation of a previously proposed correlation between chemical properties and physical evolutionary stage of isolated low-mass star-forming regions. In the past, the NH3/CCS abundance ratio was suggested to be a potentially useful indicator for the evolutionary stage of cloud cores. We aim to study its applicability for isolated Bok globules. A sample of 42 Bok globules with and without signs of current star formation was searched for CCS(2-1) emission, the observations were complemented with NH3 measurements available in the literature and own observations. The abundance ratio of both molecules is discussed with respect to the evolutionary stage of the objects and in the context of chemical models. The NH3/CCS ratio could be assessed for 18 Bok globules and is found to be moderately high and roughly similar across all evolutionary stages from starless and prestellar cores towards internally heated cores harbouring protostars of Class 0, Class I or later. Bok globules with extremely high CCS abundance analogous to carbon-chain producing regions in dark cloud cores are not found. The observed range of NH3/CCS hints towards a relatively evolved chemical state of all observed Bok globules.

12 pages, 6 figures, accepted for publication in Astronomy & Astrophysics

References in corpus (9)

• Observing the gas temperature drop in the high-density nucleus of L 1544
• Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores
• Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions
• An Ammonia Spectral Atlas of Dense Cores in Perseus
• Modeling the Lukewarm Corino Phase - is L1527 unique?
• Ethynyl (C2H) in massive star formation: Tracing the initial conditions?
• The Thermal Structure of Gas in Pre-Stellar Cores: A Case Study of Barnard 68
• Observational study of sites of triggered star formation: CO and mid-infrared observations
• A 2MASS Analysis of the Stability of Southern Bok Globules

Cited by in corpus (14)

• Chemistry of Dark Clouds: Databases, Networks, and Models
• Cluster Formation Triggered by Filament Collisions in Serpens South
• Nobeyama 45-m mapping observations toward nearby molecular clouds, Orion A, Aquila Rift, and M17: Project overview
• Physical Conditions of the Earliest Phases of Massive Star Formation: Single-Dish and Interferometric Observations of Ammonia and CCS in Infrared Dark Clouds
• An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud: II CCS & HC${}_7$N Chemistry and Three Modes of Star Formation in the Filaments
• Precise observations of the 12C/13C ratios of HC3N in the low-mass star-forming region L1527
• Chemical Variation in Molecular Cloud Cores in the Orion A Cloud. II
• Intensity-Corrected Herschel Observations of Nearby Isolated Low-Mass Clouds
• Molecular Cloud Cores with High Deuterium Fractions: Nobeyama Mapping Survey
• Nobeyama 45-m Mapping Observations toward Orion A. III. Multi-Line Observations toward an Outflow-shocked Region, OMC-2 FIR
• First clear detection of the CCS Zeeman splitting toward the pre-stellar core, Taurus Molecular Cloud-1
• An ALCHEMI inspection of sulphur-bearing species towards the central molecular zone of NGC 253
• Characterising the physical and chemical properties of a young Class 0 protostellar core embedded in the Orion B9 filament
• A Survey of Magnetic Field Properties in Bok Globules