First detection of ND in the solar-mass protostar IRAS16293-2422 (original) (raw)
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Interstellar deuterated ammonia: from NH3 to ND3
Astronomy & Astrophysics, 2005
We use spectra and maps of NH 2 D, ND 2 H, and ND 3 , obtained with the CSO, IRAM 30 m and Arecibo telescopes, to study deuteration processes in dense cores. The data include the first detection of the hyperfine structure in ND 2 H. The emission of NH 2 D and ND 3 does not seem to peak at the positions of the embedded protostars, but instead at offset positions, where outflow interactions may occur. A constant ammonia fractionation ratio in star-forming regions is generally assumed to be consistent with an origin on dust grains. However, in the pre-stellar cores studied here, the fractionation varies significantly when going from NH 3 to ND 3. We present a steady state model of the gas-phase chemistry for these sources, which includes passive depletion onto dust grains and multiply saturated deuterated species up to five deuterium atoms (e.g. CD + 5). The observed column density ratios of all four ammonia isotopologues are reproduced within a factor of 3 for a gas temperature of 10 K. We also predict that deuterium fractionation remains significant at temperatures up to about 20 K. ND and NHD, which have rotational transitions in the submillimeter domain are predicted to be abundant.
Detection of doubly-deuterated methanol in the solar-type protostar IRAS?16293-2422
Astronomy and Astrophysics, 2002
We report the first detection of doublydeuterated methanol (CHD 2 OH), as well as firm detections of the two singly-deuterated isotopomers of methanol (CH 2 DOH and CH 3 OD), towards the solar-type protostar IRAS16293−2422. From the present multifrequency observations, we derive the following abundance ratios:
Geochimica et Cosmochimica Acta, 2008
The insoluble organic matter of the carbonaceous meteorites contains radicals having a polyaromatic structure and a heterogeneous distribution. By using Hyperfine Sublevel Correlation spectroscopy (HYSCORE) in pulsed Electron Paramagnetic Resonance (pulsed-EPR), whereby nuclear frequencies of magnetic nuclei and their hyperfine interaction with electron spin of radicals are detected with high resolution, the radicals are shown to be considerably enriched in deuterium in the Orgueil meteorite, with a D/H ratio of 1.5 ± 0.5 Â 10 À2 . These radicals hold 3.6 ± 1.2 Â 10 À3 H relative to total organic H.
A study of deuterated water in the low-mass protostar IRAS 16293-2422
Astronomy & Astrophysics, 2012
Context. Water is a primordial species in the emergence of life, and comets may have brought a large fraction to Earth to form the oceans. To understand the evolution of water from the first stages of star formation to the formation of planets and comets, the HDO/H 2 O ratio is a powerful diagnostic. Aims. Our aim is to determine precisely the abundance distribution of HDO towards the low-mass protostar IRAS16293-2422 and learn more about the water formation mechanisms by determining the HDO/H 2 O abundance ratio. Methods. A spectral survey of the source IRAS16293-2422 was carried out in the framework of the CHESS (Chemical HErschel Surveys of Star forming regions) Herschel Key program with the HIFI (Heterodyne Instrument for the Far-Infrared) instrument, allowing detection of numerous HDO lines. Other transitions have been observed previously with ground-based telescopes. The spherical Monte Carlo radiative transfer code RATRAN was used to reproduce the observed line profiles of HDO by assuming an abundance jump. To determine the H 2 O abundance throughout the envelope, a similar study was made of the H 18 2 O observed lines, as the H 2 O main isotope lines are contaminated by the outflows. Results. It is the first time that so many HDO and H 18 2 O transitions have been detected towards the same source with high spectral resolution. We derive an inner HDO abundance (T ≥ 100 K) of about 1.7 × 10 −7 and an outer HDO abundance (T < 100 K) of about 8 × 10 −11 . To reproduce the HDO absorption lines observed at 894 and 465 GHz, it is necessary to add an absorbing layer in front of the envelope. It may correspond to a water-rich layer created by the photodesorption of the ices at the edges of the molecular cloud. At a 3σ uncertainty, the HDO/H 2 O ratio is 1.4-5.8% in the hot corino, whereas it is 0.2-2.2% in the outer envelope. It is estimated at ∼4.8% in the added absorbing layer. Conclusions. Although it is clearly higher than the cosmic D/H abundance, the HDO/H 2 O ratio remains lower than the D/H ratio derived for other deuterated molecules observed in the same source. The similarity of the ratios derived in the hot corino and in the added absorbing layer suggests that water formed before the gravitational collapse of the protostar, contrary to formaldehyde and methanol, which formed later once the CO molecules had depleted on the grains.
Nitrogen hydrides in the cold envelope of IRAS 16293-2422
Astronomy & Astrophysics, 2010
Nitrogen is the fifth most abundant element in the Universe, yet the gas-phase chemistry of N-bearing species remains poorly understood. Nitrogen hydrides are key molecules of nitrogen chemistry. Their abundance ratios place strong constraints on the production pathways and reaction rates of nitrogen-bearing molecules. We observed the class 0 protostar IRAS16293-2422 with the heterodyne instrument HIFI, covering most of the frequency range from 0.48 to 1.78 THz at high spectral resolution. The hyperfine structure of the amidogen radical o-NH 2 is resolved and seen in absorption against the continuum of the protostar. Several transitions of ammonia from 1.2 to 1.8 THz are also seen in absorption. These lines trace the low-density envelope of the protostar. Column densities and abundances are estimated for each hydride. We find that NH:NH 2 :NH 3 ≈5:1:300. Dark clouds chemical models predict steady-state abundances of NH 2 and NH 3 in reasonable agreement with the present observations, whilst that of NH is underpredicted by more than one order of magnitude, even using updated kinetic rates. Additional modelling of the nitrogen gas-phase chemistry in dark-cloud conditions is necessary before having recourse to heterogen processes.
Stratified NH and ND emission in the prestellar core 16293E in L1689N
Astronomy & Astrophysics, 2015
Context. High degrees of deuterium fractionation are commonly found in cold prestellar cores and in the envelopes around young protostars. As it brings strong constraints to chemical models, deuterium chemistry is often used to infer core history or molecule formation pathways. Whereas a large number of observations are available regarding interstellar deuterated stable molecules, relatively little is known about the deuteration of hydride radicals, as their fundamental rotational transitions are at high frequencies where the atmosphere is mostly opaque. Aims. Nitrogen hydride radicals are important species in nitrogen chemistry, as they are thought to be related to ammonia formation. Observations have shown that ammonia is strongly deuterated, with [NH 2 D]/[NH 3 ] ∼ 10%. Models predict similarly high [ND]/[NH] ratios, but so far only one observational determination of this ratio is available, towards the envelope of the protostar IRAS16293-2422. To test model predictions, we aim here to determine [ND]/[NH] in a dense, starless core. Methods. We observed NH and ND in 16293E with the HIFI spectrometer on board the Herschel Space Observatory as part of the CHESS guaranteed time key programme, and derived the abundances of these two species using a non local thermodynamic equilibrium radiative transfer model. Results. Both NH and ND are detected in the source, with ND in emission and NH in absorption against the continuum that arises from the cold dust emission. Our model shows, however, that the ND emission and the NH absorption originate from different layers in the cloud, as further evidenced by their different velocities. In the central region of the core, we can set a lower limit to the [ND]/[NH] ratio of > ∼ 2%. This estimate is consistent with recent pure gas-phase models of nitrogen chemistry.
Deuterated interstellar and circumstellar molecules: D/H ratio and dominant formation processes
There are several constraints associated with the different models used in accounting for the D/H ratio observed of singly and multiply deuterated interstellar and circumstellar molecular species. Thermodynamically, the most distinctive difference between a molecule and its deuterated analogue is the zero point energy (ZPE). Applying high level quantum chemical calculations, the ZPE for all H-containing and their corresponding D-analogues for all interstellar/circumstellar molecular species considered in this study are determined. From the difference in the ZPE between the H-containing and the corresponding D-analogue, Boltzmann factor is computed for all the systems using the excitation tempera-ture/molecular cloud temperature for the known D-molecules and a range of temperature for others. From the results, there is a direct correlation between the Boltzmann factors and the D/H ratios. Pronounced deuterium fractionation occurs at larger values of Boltzmann factor resulting in the observed high D/H ratios. Increased deuterium fractionation at low temperature suggests that grain surface reactions are the major formation processes for deuterated molecules. This implies that at lower temperature (higher Boltzmann factor), the exchange reaction involving deuterium or deuterium fractionation is much pronounced resulting in the distribution and redistribution of deuterium among various species. The implications of these results and the possibility of detecting more D-molecules are discussed. Graphic abstract
Astronomy & Astrophysics, 2022
Context. Di-deuterated molecules are observed in the earliest stages of star formation at abundances of a few percent relative to their nondeuterated isotopologs, which is unexpected considering the scarcity of deuterium in the interstellar medium. With sensitive observations leading to the detection of a steadily increasing number of di-deuterated species, it is becoming possible to explore successive deuteration chains. Aims. The accurate quantification of the column density of di-deuterated methanol is a key piece of the puzzle that is missing in the otherwise thoroughly constrained family of D-bearing methanol in the deeply embedded low-mass protostellar system and astrochemical template source IRAS 16293-2422. A spectroscopic dataset for astrophysical purposes was built for CHD2OH and made publicly available to facilitate the accurate characterization of this species in astrochemical surveys. Methods. The newly computed line list and partition function were used to search for C...
Astronomy and Astrophysics, 2010
Context. The deuterium fractionation, D frac , has been proposed as an evolutionary indicator in pre-protostellar and protostellar cores of low-mass star-forming regions. Aims. We investigate D frac , with high angular resolution, in the cluster environment surrounding the UCH ii region IRAS 20293+3952. Methods. We performed high angular resolution observations with the IRAM Plateau de Bure Interferometer (PdBI) of the ortho-NH 2 D 1 11-1 01 line at 85.926 GHz and compared them with previously reported VLA NH 3 data. Results. We detected strong NH 2 D emission toward the pre-protostellar cores identified in NH 3 and dust emission, all located in the vicinity of the UCH ii region IRAS 20293+3952. We found high values of D frac 0.1-0.8 in all the pre-protostellar cores and low values, D frac < 0.1, associated with young stellar objects. Conclusions. The high values of D frac in pre-protostellar cores could be indicative of evolution, although outflow interactions and UV radiation could also play a role.
Detection of Interstellar H[TINF]2[/TINF]D[TSUP]+[/TSUP] Emission
The Astrophysical Journal, 1999
We report the detection of the 1 10-1 11 ground-state transition of ortho-H 2 D ϩ at 372.421 GHz in emission from the young stellar object NGC 1333 IRAS 4A. Detailed excitation models with a power-law temperature and density structure yield a beam-averaged H 2 D ϩ abundance of with an uncertainty of a factor of 2. The Ϫ12 3 # 10 line was not detected toward W33A, GL 2591, and NGC 2264 IRS (in the latter source at a level that is 3-8 times lower than previous observations). The H 2 D ϩ data provide direct evidence in support of low-temperature chemical models in which H 2 D ϩ is enhanced by the reaction of and HD. The H 2 D ϩ enhancement toward ϩ H 3 NGC 1333 IRAS 4A is also reflected in the high DCO ϩ /HCO ϩ abundance ratio. Simultaneous observations of the N 2 H ϩ 4-3 line show that its abundance is about 50-100 times lower in NGC 1333 IRAS 4A than in the other sources, suggesting significant depletion of N 2. The N 2 H ϩ data provide independent lower limits on the abundance that are consistent with the abundances derived from H 2 D ϩ. The corresponding limits on the ϩ H 3 column density agree with recent near-infrared absorption measurements of toward W33A and GL 2591.