Deuterated Ammonia in Galactic Protostellar Cores
نویسندگان
چکیده
We report on a survey of NH2D towards protostellar cores in low–mass star formation and quiescent regions in the Galaxy. Twenty–three out of thirty-two observed sources have significant (∼5σ) NH2D emission. Ion–molecule chemistry, which preferentially enhances deuterium in molecules above its cosmological value of 1.6× 10 sufficiently explains these abundances. NH2D/NH3 ratios towards Class 0 sources yields information about the “fossil remnants” from the era prior to the onset of core collapse and star formation. We compare our observations with predictions of gas–phase chemical networks. Subject headings: Molecular Processes; ISM: abundances; ISM: general; ISM: clouds; ISM: molecules; ISM:deuterium; radio lines: ISM
منابع مشابه
Deuterium enrichment of ammonia produced by surface N+H/D addition reactions at low temperature
The surface formation of NH3 and its deuterated isotopologues – NH2D, NHD2, and ND3 – is investigated at low temperatures through the simultaneous addition of hydrogen and deuterium atoms to nitrogen atoms in CO-rich interstellar ice analogues. The formation of all four ammonia isotopologues is only observed up to 15 K, and drops below the detection limit for higher temperatures. Differences be...
متن کاملMassive Protostellar Cores: Galactic Distribution and Dynamics
Massive stars are born in very obscured regions, far away from us and within dense (proto)stellar clusters. For these reasons, the study of the earliest phases of massive star formation requires the use of high angular resolution tools and cold gas probes. Methanol masers and (sub)millimetre continuum emission satisfy these requirements. Methanol masers are exclusively associated with the earli...
متن کاملHigh NH2D/NH3 ratios in protostellar cores
Observations of low mass protostars which probe small enough size scales to be within likely CO depletion regions show the highest [NH2D]/[NH3] ratios yet measured, of 4–33%. These molecular D/H ratios are higher than those measured on larger scales, showing that deuterium fractionation increases towards protostellar cores. As in cold clouds, such high ratios can be produced by gas-phase ion-mo...
متن کاملHigh - Mass Starless Cores
We report the identification of a sample of potential High-Mass Starless Cores (HMSCs). The cores were discovered by comparing images of the fields containing candidate High-Mass Protostellar Objects (HMPOs) at 1.2mm and mid-infrared (8.3µm; MIR) wavelengths. While the HMPOs are detected at both wavelengths, several cores emitting at 1.2mm in the same fields show absorption or no emission at th...
متن کاملChemical differentiation in regions of massive star formation.
We have reexamined the origin of the apparent differentiation between nitrogen-bearing molecules and complex oxygen-bearing molecules that is observed in hot molecular cores associated with massive protostars. Observations show that methanol is an ubiquitous and abundant component of protostellar ices. Recent observations suggest that ammonia may constitute an appreciable fraction of the ices t...
متن کامل