NEW RESULTS
Discovery of thionylimide, HNSO, in space: the first N-, S- and O-bearing interstellar molecule (
The Astrophysical Journal Letters, 2024, just accepted; DOI: 10.48550/arXiv.2404.01044)
Abstract
We present the first detection in space of thionylimide (HNSO) toward the Galactic Center molecular cloud G+0.693-0.027, thanks to the superb sensitivity of an ultradeep molecular line survey carried out with the Yebes 40m and IRAM 30m telescopes. This molecule is the first species detected in the interstellar medium containing, simultaneously, N, S and O. We have identified numerous Ka = 0, 1 and 2 transitions belonging to HNSO covering from Jup = 2 to Jup = 10, including several completely unblended features. We derive a molecular column density of N = (8 ± 1)×1013 cm-2, yielding a fractional abundance relative to H2 of ∼6 × 10-10, which is about ∼37 and ∼4.8 times less abundant than SO and SO2, respectively. Although there are still many unknowns in the interstellar chemistry of NSO-bearing molecules, we propose that HNSO is likely formed through the reaction of the NSO radical and atomic H on the surface of icy grains, with alternative routes also deserving exploration. Finally, HNSO appears as a promising link between N- , S- and O- interstellar chemistry and its discovery paves the route to the detection of a new family of molecules in space.
Graphical Abstract
The GUAPOS project. V: The chemical ingredients of a massive stellar protocluster in the making (
Monthly Notices of the Royal Astronomical Society, 2024, just accepted; DOI:
https://arxiv.org/abs/2403.02191 )
Abstract
Most stars, including the Sun, are born in rich stellar clusters containing massive stars. Therefore, the study of the chemical reservoir of massive star-forming regions is crucial to understand the basic chemical ingredients available at the dawn of planetary systems. We present a detailed study of the molecular inventory of the hot molecular core G31.41+0.31 from the project GUAPOS (G31.41+0.31 Unbiased ALMA sPectral Observational Survey). We analyze 34 species for the first time plus 20 species analyzed in previous GUAPOS works, including oxygen, nitrogen, sulfur, phosphorus, and chlorine species. We compare the abundances derived in G31.41+0.31 with those observed in other chemically-rich sources that represent the initial and last stages of the formation of stars and planets: the hot corino in the Solar-like protostar IRAS 16293-2422 B, and the comets 67P/Churyumov-Gerasimenko and 46P/Wirtanen. The comparative analysis reveals that the chemical feedstock of the two star-forming regions are similar. The abundances of oxygen- and nitrogen-bearing molecules exhibit a good correlation for all pair of sources, including the two comets, suggesting a chemical heritage of these species during the process of star formation, and hence an early phase formation of the molecules. However, sulfur- and phosphorus-bearing species present worse correlations, being more abundant in comets. This suggests that while sulfur- and phosphorus-bearing species are predominantly trapped on the surface of icy grains in the hot close surroundings of protostars, they could be more easily released into gas phase in comets, allowing their cosmic abundances to be almost recovered.
Graphical Abstract
Interstellar detection of O-protonated carbonyl sulfide, HOCS+ (
The Astrophysical Journal, 2024, just accepted; DOI:
https://arxiv.org/abs/2402.15405 )
Abstract
We present the first detection in space of O-protonated carbonyl sulfide (HOCS+), in the midst of an ultradeep molecular line survey toward the G+0.693-0.027 molecular cloud. From the observation of all Ka = 0 transitions ranging from Jlo = 2 to Jlo = 13 of HOCS+ covered by our survey, we derive a column density of N = (9 ± 2) × 10 12 cm-2, translating into a fractional abundance relative to H2 of 7 × 10-11. Conversely, the S-protonated HSCO+ isomer remains undetected, and we derive an upper limit to its abundance with respect to H2 of ≤ 3×10sup>-11, a factor of ≥ 2.3 less abundant than HOCS+. We obtain a HOCS+/OCS ratio of ∼2.5×10-3, in good agreement with the prediction of astrochemical models. These models show that one of the main chemical routes to the interstellar formation of HOCS+ is likely the protonation of OCS, which appears to be more efficient at the oxygen end. Also, we find that high values of cosmic-ray ionisation rates (10-15-10-14 s-1) are needed to reproduce the observed abundance of HOCS+. In addition, we compare the O/S ratio across different interstellar environments. G+0.693-0.027 appears as the source with the lowest O/S ratio. We find a HOCO+/HOCS+ ratio of ∼31, in accordance with other O/S molecular pairs detected toward this region and also close to the O/S solar value (∼37). This fact indicates that S is not significantly depleted within this cloud due to the action of large-scale shocks, unlike in other sources where S-bearing species remain trapped on icy dust grains.
Graphical Abstract
Detection of the elusive carbonic acid (HOCOOH) in space (
The Astrophysical Journal, 2023, 954, 3. DOI: 10.3847/1538-4357/ace523)
Abstract
After a quarter century since the detection of the last interstellar carboxylic acid, acetic acid (CH3COOH), we report the discovery of a new one, the cis-trans form of carbonic acid (HOCOOH), toward the Galactic Center molecular cloud G+0.693-0.027. HOCOOH stands as the first interstellar molecule containing three oxygen atoms and also the third carboxylic acid detected so far in the interstellar medium. Albeit the limited available laboratory measurements (up to 65 GHz), we have also identified several pairs of unblended lines directly in the astronomical data (between 75-120 GHz), which allowed us to slightly improve the set of spectroscopic constants. We derive a column density for cis-trans HOCOOH of N = 6.4 × 1012 cm-2, which yields an abundance with respect to molecular H2 of 4.7 × 10-11. Meanwhile, the extremely low dipole moment (about fifteen times lower) of the lower-energy conformer, cis-cis HOCOOH, precludes its detection. We obtain an upper limit to its abundance with respect to H2 of ≤ 1.2 × 10-9, which suggests that cis-cis HOCOOH might be fairly abundant in interstellar space, although it is nearly undetectable by radio astronomical observations. We derive a cis-cis/cis-trans ratio ≤ 25, consistent with the smaller energy difference between both conformers compared with the relative stability of trans- and cis-formic acid (HCOOH). Finally, we compare the abundance of these acids in different astronomical environments, further suggesting a relationship between the chemical content found in the interstellar medium and the chemical composition of the minor bodies of the Solar System, which could be inherited during the star formation process.
Graphical Abstract
H2CN/H2NC abundance ratio: a new potential temperature tracer for the interstellar medium (
Monthly Notices of the Royal Astronomical Society, 2023, 523, 3239-3250. DOI:
10.1093/mnras/stad1385)
Abstract
The H2NC radical is the high-energy metastable isomer of H2CN radical, which has been recently detected for the first time in the interstellar medium towards a handful of cold galactic sources, besides a warm galaxy in front of the PKS 1830-211 quasar. These detections have shown that the H2CN/H2NC isomeric ratio, likewise the HCN/HNC ratio, might increase with the kinetic temperature (Tkin), but the shortage of them in warm sources still prevents us to confirm this hypothesis and shed light about their chemistry. In this work, we present the first detection of H2CN and H2NC towards a warm galactic source, the G+0.693-0.027 molecular cloud (with Tkin > 70 K), using IRAM 30m observations. We have detected multiple hyperfine components of the NKaKc = 101 - 000 and 202 - 101 transitions. We derived molecular abundances with respect to H2 of (6.8±1.3)×10-11 for H2CN and of (3.1±0.7)×10-11 for H2NC, and a H2CN/H2NC abundance ratio of 2.2±0.5. These detections confirm that the H2CN/H2NC ratio is ≳2 for sources with Tkin > 70 K, larger than the ∼1 ratios previously found in colder cores (Tkin ∼ 10 K). This isomeric ratio dependence with temperature cannot be fully explained with the currently proposed gas-phase formation and destruction pathways. Grain surface reactions, including the H2NC → H2CN isomerization, deserve consideration to explain the higher isomeric ratios and H2CN abundances observed in warm sources, where the molecules can be desorbed into the gas phase through thermal and/or shock-induced mechanisms.
Graphical Abstract
