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- Taquet, V., et al.
(författare)
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Linking interstellar and cometary O2: A deep search for 16O18O in the solar-Type protostar IRAS 16293b-2422
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 618
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Tidskriftsartikel (refereegranskat)abstract
- Recent measurements carried out at comet 67P/Churyumov-Gerasimenko (67P) with the Rosetta probe revealed that molecular oxygen, O2, is the fourth most abundant molecule in comets. Models show that O2 is likely of primordial nature, coming from the interstellar cloud from which our solar system was formed. However, gaseous O2 is an elusive molecule in the interstellar medium with only one detection towards quiescent molecular clouds, in the ρ Oph A core. We perform a deep search for molecular oxygen, through the 21-01 rotational transition at 234 GHz of its 16O18O isotopologue, towards the warm compact gas surrounding the nearby Class 0 protostar IRAS 16293-2422 B with the ALMA interferometer. We also look for the chemical daughters of O2, HO2, and H2O2. Unfortunately, the H2O2 rotational transition is dominated by ethylene oxide c-C2H4O while HO2 is not detected. The targeted 16O18O transition is surrounded by two brighter transitions at ± 1 km s-1 relative to the expected 16O18O transition frequency. After subtraction of these two transitions, residual emission at a 3σ level remains, but with a velocity offset of 0.3-0.5 km s-1 relative to the source velocity, rendering the detection "tentative". We derive the O2 column density for two excitation temperatures Tex of 125 and 300 K, as indicated by other molecules, in order to compare the O2 abundance between IRAS 16293 and comet 67P. Assuming that 16O18O is not detected and using methanol CH3OH as a reference species, we obtain a [O2]/[CH3OH] abundance ratio lower than 2-5, depending on the assumed Tex, a three to four times lower abundance than the [O2]/[CH3OH] ratio of 5-15 found in comet 67P. Such a low O2 abundance could be explained by the lower temperature of the dense cloud precursor of IRAS 16293 with respect to the one at the origin of our solar system that prevented efficient formation of O2 in interstellar ices.
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| 2. |
- van't Hoff, Merel L. R., et al.
(författare)
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Temperature profiles of young disk-like structures The case of IRAS 16293A star
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 633
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Tidskriftsartikel (refereegranskat)abstract
- Context. Temperature is a crucial parameter in circumstellar disk evolution and planet formation because it governs the resistance of the gas to gravitational instability and sets the chemical composition of the planet-forming material. Aims. We set out to determine the gas temperature of the young disk-like structure around the Class 0 protostar IRAS 16293-2422A. Methods. We used Atacama Large Millimeter/submillimeter Array (ALMA) observations of multiple H2CS J = 7 - 6 and J = 10 - 9 lines from the Protostellar Interferometric Line Survey (PILS) to create a temperature map for the inner similar to 200 AU of the disk-like structure. This molecule is a particularly useful temperature probe because transitions between energy levels with different K-a quantum numbers operate only through collisions. Results. Based on the H2CS line ratios, the temperature is between similar to 100-175 K in the inner similar to 150 AU, and drops to similar to 75 K at similar to 200 AU. At the current resolution (0.5 ''similar to 70 AU), no jump is seen in the temperature at the disk-envelope interface. Conclusions. The temperature structure derived from H2CS is consistent with envelope temperature profiles that constrain the temperature from 1000 AU scales down to similar to 100 AU, but does not follow the temperature rise seen in these profiles at smaller radii. Higher angular resolution observations of optically thin temperature tracers are needed to establish whether cooling by gas-phase water, the presence of a putative disk, or the dust optical depth influences the gas temperature at less than or similar to 100 AU scales. The temperature at 100 AU is higher in IRAS 16293A than in the embedded Class 0/I disk L1527, consistent with the higher luminosity of the former.
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