AstroChemical Newsletter #98

January 2024

You can access the full abstracts by clicking the paper titles. Submit your abstracts before the 25th of each month for inclusion in the following newsletter.


The GUAPOS project: G31.41+0.31 Unbiased ALMA sPectral Observational Survey. IV. Phosphorus-bearing molecules and their relation with shock tracers

Fontani, F., Mininni, C., Beltran, M.T., Rivilla, V.M., Colzi, L., et al.

The astrochemistry of the important biogenic element phosphorus (P) is still poorly understood, but observational evidence indicates that P-bearing molecules are likely associated with shocks. We study P-bearing molecules, as well as some shock tracers, towards one of the chemically richest hot molecular core, G31.41+0.31, in the framework of the project "G31.41+0.31 Unbiased ALMA sPectral Observational Survey" (GUAPOS), observed with the Atacama Large Millimeter Array (ALMA). We have observed the molecules PN, PO, SO, SO2, SiO, and SiS, through their rotational lines in the spectral range 84.05-115.91 GHz, covered by the GUAPOS project. PN is clearly detected while PO is tentatively detected. The PN emission arises from two regions southwest of the hot core peak, "1" and "2", and is undetected or tentatively detected towards the hot core peak. the PN and SiO lines are very similar both in spatial emission morphology and spectral shape. Region "1" is in part overlapping with the hot core and it is warmer than region "2", which is well separated from the hot core and located along the outflows identified in previous studies. The column density ratio SiO/PN remains constant in regions "1" and "2", while SO/PN, SiS/PN, and SO2/PN decrease by about an order of magnitude from region "1" to region "2", indicating that SiO and PN have a common origin even in regions with different physical conditions. Our study firmly confirms previous observational evidence that PN emission is tightly associated with SiO and it is likely a product of shock-chemistry. We propose the PN emitting region "2" as a new astrophysical laboratory for shock-chemistry studies

accepted for publication in Astronomy & Astrophysics
DOI: 10.48550/arXiv.2311.13367
Full-text URL:

Observational Chemical Signatures of the Past FU Ori Outbursts

L. Zwicky, T. Molyarova, V. Akimkin, G.V. Smirnov-Pinchukov, D. Semenov, Á. Kóspál, P. Ábrahám

FU Ori-type stars are young stellar objects (YSOs) experiencing luminosity outbursts by a few orders of magnitude, which last for ~10^2 years. A dozen of FUors are known up to date, but many more currently quiescent YSOs could have experienced such outbursts in the last ~10^3 years. To find observational signatures of possible past outbursts, we utilise ANDES, RADMC-3D code as well as CASA ALMA simulator to model the impact of the outburst on the physical and chemical structure of typical FU Ori systems and how it translates to the molecular lines' fluxes. We identify several combinations of molecular lines that may trace past FU Ori objects both with and without envelopes. The most promising outburst tracers from an observational perspective are the molecular flux combinations of the N2H+ J = 3 - 2, C18O J = 2 - 1, H2CO (J_{K_a, K_c}) = 4_{04}-3_{03}, and HCN J = 3 - 2 lines. We analyse the processes leading to molecular flux changes and show that they are linked with either thermal desorption or enhanced chemical reactions in the molecular layer. Using observed CO, HCN, N2H+ and H2CO line fluxes from the literature, we identify ten nearby disc systems that might have undergone FU Ori outbursts in the past ~10^3 years: [MGM2012] 556, [MGM2012] 371 and [MGM2012] 907 YSOs in L1641, Class II protoplanetary discs around CI Tau, AS 209 and IM Lup and transitional discs DM Tau, GM Aur, LkCa 15 and J1640-2130.

accepted in MNRAS
DOI: 10.1093/mnras/stad3713
Full-text URL:

JWST: Deuterated PAHs, PAH-nitriles, and PAH Overtone and Combination Bands I: Program Description and First Look

Boersma, C., Allamandola, L.J., Esposito, V.J., Maragkoudakis, A., Bregman, J.D., Temi, P., Lee, T.J., Fortenberry, R.C., Peeters, E.

A first look is taken at the NIRSpec 1–5 μm observations from James Webb Space Telescope program 1591 that targets seven objects along the low-mass stellar life cycle with polycyclic aromatic hydrocarbon (PAH) emission. Spectra extracted from a 1''.5 radius circular aperture are explored, showing a wealth of features, including the 3 μm PAH complex, the PAH continuum, and atomic and molecular emission lines from H i, He, H2, and other species. CO2- and H2O-ice absorption and CO emission is also seen. Focusing on the bright-PDR position in M17, the PAH CH stretch falls at 3.29 μm (FWHM = 0.04 μm). Signs of its 1.68 μm overtone are confused by line emission in all targets. Multicomponent decomposition reveals a possible aliphatic deuterated PAH feature centered at 4.65 μm (FWHM = 0.02 μm), giving [D/H]alip. = 31% ± 12.7%. However, there is little sign of its aromatic counterpart between 4.36 and 4.43 μm. There is also little sign of PAH nitrile emission between 4.34 and 4.39 μm. A PAH continuum rises from ∼1 to 3.2 μm, after which it jumps by about a factor of 2.5 at 3.6 μm, with bumps at 3.8, 4.04, and 4.34 μm adding structure. The CO2 absorption band in M17 is matched with 10:1 H2O:CO2 ice at 10 K. The v = 0 pure rotational molecular hydrogen population diagram reveals >2200 K UV-pumped gas. The hydrogen Pfund series runs from levels 10 to >30. Considering Brα/Brβ = 0.381 ± 0.01966 and Case B recombination results in AV ≃ 8. CO emission in IRAS 21282+5050 originates from 258 K gas. In-depth spectral–spatial analysis of all features and targets is planned for a series of forthcoming papers.

2023 The Astrophysical Journal, 959, 74
DOI: 10.3847/1538-4357/ad022b
Full-text URL:

JOYS+: mid-infrared detection of gas-phase SO2 emission in a low-mass protostar. The case of NGC 1333 IRAS2A: hot core or accretion shock?

M. L. van Gelder, M. E. Ressler, E. F. van Dishoeck, P. Nazari, B. Tabone, J. H. Black, Ł. Tychoniec, L. Francis, M. Barsony, H. Beuther, A. Caratti o Garatti, Y. Chen, C. Gieser, V. J. M. le Gouellec, P. J. Kavanagh, P. D. Klaassen, B. W. P. Lew, H. Linnartz, L. Majumdar, G. Perotti, W. R. M. Rocha

JWST/MIRI has sharpened our infrared eyes toward the star formation process. This paper presents the first mid-infrared detection of gaseous SO2 emission in an embedded low-mass protostellar system. MIRI-MRS observations of the low-mass protostellar binary NGC 1333 IRAS2A are presented from the JWST Observations of Young protoStars (JOYS+) program, revealing emission from the SO2 ν3 asymmetric stretching mode at 7.35 micron. The results are compared to those derived from high-angular resolution SO2 data obtained with ALMA. The SO2 emission from the ν3 band is predominantly located on ∼50−100 au scales around the main component of the binary, IRAS2A1. A rotational temperature of 92±8 K is derived from the ν3 lines. This is in good agreement with the rotational temperature derived from pure rotational lines in the vibrational ground state (i.e., ν=0) with ALMA (104±5 K). However, the emission of the ν3 lines is not in LTE given that the total number of molecules predicted by a LTE model is found to be a factor 2×104 higher than what is derived for the ν=0 state. This difference can be explained by a vibrational temperature that is ∼100 K higher than the derived rotational temperature of the ν=0 state. The brightness temperature derived from the continuum around the ν3 band of SO2 is ∼180 K, which confirms that the ν3=1 level is not collisionally populated but rather infrared pumped by scattered radiation. This is also consistent with the non-detection of the ν2 bending mode at 18-20 micron. Given the rotational temperature, the extent of the emission (∼100 au in radius), and the narrow line widths in the ALMA data (3.5 km/s), the SO2 in IRAS2A likely originates from ice sublimation in the central hot core around the protostar rather than from an accretion shock at the disk-envelope boundary.

Accepted for publication in Astronomy & Astrophysics
DOI: 10.1051/0004-6361/202348118
Full-text URL:

Single-atom catalysis in space: Computational exploration of Fischer–Tropsch reactions in astrophysical environments

Pareras, Cabedo, McCoustra & Rimola

Gas-phase chemistry at extreme conditions (low densities and temperatures) is difficult, so the presence of interstellar grains is especially important for the synthesis of molecules that cannot form in the gas phase. Interstellar grains are advocated to enhance the encounter rate of the reactive species on their surfaces and to dissipate the energy excess of largely exothermic reactions, but less is known of their role as chemical catalysts that provide low activation energy pathways with enhanced reaction rates. Different materials with catalytic properties are present in interstellar environments, like refractory grains containing space-abundant d-block transition metals. In this work we report for first time mechanistic insights on the Fischer–Tropsch methanol (CH3OH) synthesis under astrophysical conditions using single-atom Fe-containing silica surfaces as interstellar heterogeneous catalysts. Quantum chemical calculations considering extended periodic surfaces were carried out in order to search for the stationary points and transitions states to finally construct the reaction potential energy surfaces. Binding energy and kinetic calculations based on the Rice–Ramsperger–Kassel–Marcus (RRKM) scheme were also performed to evaluate the catalytical capacity of the grain and to allocate those reaction processes within the astrochemical framework. Our mechanistic studies demonstrate that astrocatalysis is feasible in astrophysical environments. Thermodynamically the proposed process is largely exergonic, but kinetically it shows energy barriers that would need from an energy input in order to go through. Kinetic calculations also demonstrate the strong temperature dependency of the reaction process as tunnelling is not relevant in the involved energetic barriers. The present results can explain the presence of CH3OH in diverse regions where current models fail to reproduce its observational quantity. The evidence of astrocatalysis opens a completely new spectrum of synthetic routes triggering chemical evolution in space. From the mechanistic point of view the formation of methanol catalysed by a single atom of Fe0 is feasible; however, its dependency on the temperature makes the energetics a key issue in this scenario.

A&A, 680 (2023) A57
DOI: 10.1051/0004-6361/202347877
Full-text URL:

α-enhanced astrochemistry: the carbon cycle in extreme galactic conditions

Bisbas, T.G., Zhang, Z-Y., Gjergo, E., Zhao, Y-H., Luo, G., Quan, D., Jiang X-J., Sun, Y., Topkaras, T., Li, D., and Guo, Z.

Astrochemistry has been widely developed as a power tool to probe physical properties of the interstellar medium (ISM) in various conditions of the Milky Way (MW) Galaxy, and in near and distant galaxies. Most current studies conventionally apply linear scaling to all elemental abundances based on the gas-phase metallicity. However, these elements, including carbon and oxygen, are enriched differentially by stellar nucleosynthesis and the overall galactic chemical evolution, evident from α-enhancement in multiple galactic observations such as starbursts, high-redshift star-forming galaxies, and low-metallicity dwarfs. We perform astrochemical modeling to simulate the impact of an α-enhanced ISM gas cloud on the abundances of the three phases of carbon (C+, C, CO) dubbed as `the carbon cycle'. The ISM environmental parameters considered include two cosmic-ray ionization rates (ζcr=1e-17 and 1e-15 s−1), two isotropic FUV radiation field strengths (χ/χ0=1 and 1e2), and (sub-)linear dust-to-gas relations against metallicity, mimicking the ISM conditions of different galaxy types. In galaxies with [C/O]<0, CO, C and C+ all decrease in both abundances and emission, though with differential biases. The low-J CO emission is found to be the most stable tracer for the molecular gas, while C and C+ trace H2 gas only under limited conditions, in line with recent discoveries of [CI]-dark galaxies. We call for caution when using [CII]~158μm and [CI](1-0) as alternative H2-gas tracers for both diffuse and dense gas with non-zero [C/O] ratios.

MNRAS accepted
DOI: 10.1093/mnras/stad3782
Full-text URL:

JWST Observations of Young protoStars (JOYS+): Detection of icy complex organic molecules and ions. I. CH4, SO2, HCOO−, OCN−, H2CO, HCOOH, CH3CH2OH, CH3CHO, CH3OCHO, CH3COOH

W. R. M. Rocha, E. F. van Dishoeck, M. E. Ressler, M. L. van Gelder, K. Slavicinska, N. G. C. Brunken, H. Linnartz, T. P. Ray, H. Beuther, A. Caratti o Garatti, V. Geers, P. J. Kavanagh, P. D. Klaassen, K. Justannont, Y. Chen, L. Francis, C. Gieser, G. Perotti, Ł. Tychoniec, M. Barsony, L. Majumdar, V. J. M. le Gouellec, L. E. U. Chu, B. W. P. Lew, Th. Henning, G. Wright

Complex organic molecules (COMs) detected in the gas phase are thought to be mostly formed on icy grains, but no unambiguous detection of icy COMs larger than CH3OH has been reported so far. Exploring this matter in more detail has become possible with the JWST the critical 5-10 μm range. In the JOYS+ program, more than 30 protostars are being observed with the MIRI/MRS. This study explores the COMs ice signatures in the low and high-mass protostar, IRAS 2A and IRAS 23385, respectively. We fit continuum and silicate subtracted observational data with IR laboratory ice spectra. We use the ENIIGMA fitting tool to find the best fit between the lab data and the observations and to performs statistical analysis of the solutions. We report the best fits for the spectral ranges between 6.8 and 8.6 μm in IRAS 2A and IRAS 23385, originating from simple molecules, COMs, and negative ions. The strongest feature in this range (7.7 μm) is dominated by CH4 and has contributions of SO2 and OCN-. Our results indicate that the 7.2 and 7.4 μm bands are mostly dominated by HCOO-. We find statistically robust detections of COMs based on multiple bands, most notably CH3CHO, CH3CH2OH, and CH3OCHO. The likely detection of CH3COOH is also reported. The ice column density ratios between CH3CH2OH and CH3CHO of IRAS 2A and IRAS 23385, suggests that these COMs are formed on icy grains. Finally, the derived ice abundances for IRAS 2A correlate well with those in comet 67P/GC within a factor of 5. Based on the MIRI/MRS data, we conclude that COMs are present in interstellar ices, thus providing additional proof for a solid-state origin of these species in star-forming regions. The good correlation between the ice abundances in comet 67P and IRAS 2A is in line with the idea that cometary COMs can be inherited from the early protostellar phases.

Accepted for publication in A&A
Full-text URL:

Sulphur ion implantation into O2, CO, and CO2 ices: Implications for the formation of sulphur-bearing molecules in the Kuiper Belt

Duncan V. Mifsud, Zuzana Kaňuchová, Péter Herczku, Zoltán Juhász, Sándor T.S. Kovács, Gergő Lakatos, K.K. Rahul, Richárd Rácz, Béla Sulik, Sándor Biri, István Rajta, István Vajda, Sergio Ioppolo, Robert W. McCullough, Nigel J. Mason

Previous experimental work has systematically investigated the radiolytic sulphur chemistry arising as a result of the implantation of reactive sulphur ions into various oxygen-bearing molecular ices (e.g., H2O, CO2) so as to better understand the surface chemistry of the Galilean moons of Jupiter, where sulphur ions are sourced from the giant Jovian magnetosphere. However, significantly less attention has been paid to analogous sulphur chemistry occurring under conditions relevant to the Kuiper Belt, where sulphur ions supplied by the solar wind may implant into the surfaces of icy bodies that are rich in volatile oxygen-bearing molecular ices such as O2, CO, or CO2. This paper presents the results of a study on the implantation of 290–400 keV S+ ions into pure O2, CO, and CO2 ices under temperature, pressure, radiation dose, and ice deposition conditions relevant to the Kuiper Belt, with a particular focus on the potential synthesis of simple inorganic sulphur-bearing molecules (e.g., SO2, OCS, CS2). Experiments involving CO2 ices were also performed at higher temperatures more typically associated with the Galilean moon system so as to determine whether there exist any differences in the chemistry resulting from the implantation of reactive sulphur ions in these two regions of the Solar System. Our results constitute the first systematic investigation of solid-phase sulphur chemistry in the Kuiper Belt mediated by the sulphur ion component of the solar wind, and thus represent an important step forward in our understanding of the astrochemical processes occurring in the outermost depths of the Solar System.

Icarus, 2024, 411, 115926
DOI: 10.1016/j.icarus.2023.115926
Full-text URL: