Detection of interstellar ortho-D2H+ with SOFIA

Abstract

We report on the detection of the ground-state rotational line of ortho-D2H+ at 1.477 THz (203 micron) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) onboard the Stratospheric Observatory For Infrared Astronomy (SOFIA). The line is seen in absorption against far-infrared continuum from the protostellar binary IRAS 16293-2422 in Ophiuchus. The para-D2H+ line at 691.7 GHz was not detected with the APEX telescope toward this position. These D2H+ observations complement our previous detections of para-H2D+ and ortho-H2D+ using SOFIA and APEX. By modeling chemistry and radiative transfer in the dense core surrounding the protostars, we find that the ortho-D2H+ and para-H2D+ absorption features mainly originate in the cool (T<18 K) outer envelope of the core. In contrast, the ortho-H2D+ emission from the core is significantly absorbed by the ambient molecular cloud. Analyses of the combined D2H+ and H2D+ data result in an age estimate of ~500 000 yr for the core, with an uncertainty of ~200 000 yr. The core material has probably been pre-processed for another 500 000 years in conditions corresponding to those in the ambient molecular cloud. The inferred time scale is more than ten times the age of the embedded protobinary. The D2H+ and H2D+ ions have large and nearly equal total (ortho+para) fractional abundances of ~$10^{-9}$ in the outer envelope. This confirms the central role of H3+ in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also D3+ should be abundant in these conditions.

19 pages, 12 figures, accepted for publication in The Astrophysical Journal

References in corpus (14)

• The ALMA Protostellar Interferometric Line Survey (PILS): First results from an unbiased submillimeter wavelength line survey of the Class 0 protostellar binary IRAS 16293-2422 with ALMA
• The 2014 KIDA network for interstellar chemistry
• The Mass Distribution and Lifetime of Prestellar Cores in Perseus, Serpens, and Ophiuchus
• Polycylcic Aromatic Hydrocarbons (PAH's) in dense cloud chemistry
• Early Science with SOFIA, the Stratospheric Observatory for Infrared Astronomy
• GREAT: the SOFIA high-frequency heterodyne instrument
• The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse
• Hipparcos distances of Ophiuchus and Lupus cloud complexes
• Survey of ortho-H2D+(1_{1,0}-1_{1,1}) in dense cloud cores
• The upGREAT 1.9 THz multi-pixel high resolution spectrometer for the SOFIA Observatory
• Benchmarking spin-state chemistry in starless core models
• A SCUBA survey of L1689 - The dog that didn't bark
• Infrared H3+ and CO Studies of the Galactic Core: GCIRS 3 and GCIRS 1W
• CH in absorption in IRAS16293-2422

Cited by in corpus (22)

• The ALMA-PILS survey: Isotopic composition of oxygen-containing complex organic molecules toward IRAS 16293-2422B
• Ingredients for Solar-like Systems: protostar IRAS 16293-2422 B versus comet 67P/Churyumov-Gerasimenko
• Hydrodynamics with gas-grain chemistry and radiative transfer: comparing dynamical and static models
• Modeling deuterium chemistry in starless cores: full scrambling versus proton hop
• Successive deuteration in low-mass star-forming regions: the case of D${}_2$-methanol (CHD${}_2$OH) in IRAS 16293-2422
• The ortho-to-para ratio of water in interstellar clouds
• First detection of NHD and ND${}_2$ in the interstellar medium
• Rotational spectroscopy of mono-deuterated oxirane ($c$-C${}_2$H${}_3$DO) and its detection towards IRAS 16293$-$2422 B
• ExoMol line lists -- L: High-resolution line lists of H${}_3^{+}$, H${}_2$D${}^{+}$, D${}_2$H${}^{+}$ and D${}_3^{+}$
• Modelling the abundance structure of isocyanic acid (HNCO) toward the low-mass solar type protostar IRAS 16293-2422
• Similar levels of deuteration in the pre-stellar core L1544 and the protostellar core HH211
• Species-to-species rate coefficients for the ${\mathrm{H}}_3^{+}+{\mathrm{H}}_2$ reacting system
• SOFIA/EXES observations of warm H${}_2$ at high spectral resolution: witnessing para-to-ortho conversion behind a molecular shock wave in HH7
• APEX observations of ortho-H${}_2$D${}^{+}$ towards dense cores in the Orion B9 filament
• First map of D${}_2$H${}^{+}$ emission revealing the true centre of a prestellar core: further insights into deuterium chemistry
• Rotational spectroscopy of oxirane-\textit{2,2}-$d_2$, $c$-CD${}_2$CH${}_2$O, and its tentative detection toward IRAS 16293$-$2422~B
• Rotational spectroscopy of CH${}_3$OD with a reanalysis of CH${}_3$OD toward IRAS 16293$-$2422
• PRODIGE - envelope to disk with NOEMA: V. Low 12C/13C ratios for CH3OH and CH3CN in hot corinos
• Search for H${}_3^{+}$ isotopologues toward CRL 2136 IRS 1
• Isotopic fractionation in interstellar molecules
• Role of NH3 Binding Energy in the Early Evolution of Protostellar Cores
• Chemical analysis of prestellar cores in Ophiuchus yields short timescales and rapid collapse