| 1. |
- Van Gelder, M. L., et al.
(författare)
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JOYS+: Mid-infrared detection of gas-phase SO 2 emission in a low-mass protostar
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 682
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Tidskriftsartikel (refereegranskat)abstract
- Context. Thanks to the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST), our ability to observe the star formation process in the infrared has greatly improved. Due to its unprecedented spatial and spectral resolution and sensitivity in the mid-infrared, JWST/MIRI can see through highly extincted protostellar envelopes and probe the warm inner regions. An abundant molecule in these warm inner regions is SO2, which is a common tracer of both outflow and accretion shocks as well as hot core chemistry. Aims. This paper presents the first mid-infrared detection of gaseous SO2 emission in an embedded low-mass protostellar system rich in complex molecules and aims to determine the physical origin of the SO2 emission. Methods. JWST/MIRI observations taken with the Medium Resolution Spectrometer (MRS) of the low-mass protostellar binary NGC 1333 IRAS 2A in the JWST Observations of Young protoStars (JOYS+) program are presented. The observations reveal emission from the SO2 ν3 asymmetric stretching mode at 7.35 µm. Using simple slab models and assuming local thermodynamic equilibrium (LTE), we derived the rotational temperature and total number of SO2 molecules. We then compared the results to those derived from high-angular-resolution SO2 data on the same scales (∼50−100 au) obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). Results. The SO2 emission from the ν3 band is predominantly located on ∼50−100 au scales around the mid-infrared continuum peak of the main component of the binary, IRAS 2A1. 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), which are extended over similar scales. However, the emission of the ν3 lines in the MIRI-MRS spectrum is not in LTE given that the total number of molecules predicted by a LTE model is found to be a factor of 2 × 104 higher than what is derived for the ν = 0 state from the ALMA data. This difference can be explained by a vibrational temperature that is ∼100 K higher than the derived rotational temperature of the ν = 0 state: Tvib ∼ 200 K versus Trot = 104 ± 5 K. The brightness temperature derived from the continuum around the ν3 band (∼7.35 µm) 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 µm. The similar rotational temperature derived from the MIRI-MRS and ALMA data implies that they are in fact tracing the same molecular gas. The inferred abundance of SO2 , determined using the LTE fit to the lines of the vibrational ground state in the ALMA data, is 1.0 ± 0.3 × 10−8 with respect to H2, which is on the lower side compared to interstellar and cometary ices (10−8−10−7). Conclusions. 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−1), the SO2 in IRAS 2A likely originates from ice sublimation in the central hot core around the protostar rather than from an accretion shock at the disk–envelope boundary. Furthermore, this paper shows the importance of radiative pumping and of combining JWST observations with those from millimeter interferometers such as ALMA to probe the physics on disk scales and to infer molecular abundances.
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| 2. |
- Beuther, H., et al.
(författare)
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JWST Observations of Young protoStars (JOYS): Outflows and accretion in the high-mass star-forming region IRAS 23385+6053
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 673
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Tidskriftsartikel (refereegranskat)abstract
- Context. Understanding the earliest stages of star formation, and setting it in the context of the general cycle of matter in the interstellar medium, is a central aspect of research with the James Webb Space Telescope (JWST). Aims. The JWST program JOYS (JWST Observations of Young protoStars) aims to characterize the physical and chemical properties of young high- and low-mass star-forming regions, in particular the unique mid-infrared diagnostics of the warmer gas and solid-state components. We present early results from the high-mass star formation region IRAS 23385+6053. Methods. The JOYS program uses the Mid-Infrared Instrument (MIRI) Medium Resolution Spectrometer (MRS) with its integral field unit (IFU) to investigate a sample of high- and low-mass star-forming protostellar systems. Results. The full 5-? 28 μm MIRI MRS spectrum of IRAS 23385+6053 shows a plethora of interesting features. While the general spectrum is typical for an embedded protostar, we see many atomic and molecular gas lines boosted by the higher spectral resolution and sensitivity compared to previous space missions. Furthermore, ice and dust absorption features are also present. Here, we focus on the continuum emission, outflow tracers such as the H2(0-? 0)S(7), [FeII](4F9/2-6D9/2), and [NeII](2P1/2-2P3/2) lines, and the potential accretion tracer Humphreys α H I(7-6). The short-wavelength MIRI data resolve two continuum sources, A and B; mid-infrared source A is associated with the main millimeter continuum peak. The combination of mid-infrared and millimeter data reveals a young cluster in the making. Combining the mid-infrared outflow tracers H2, [FeII], and [NeII] with millimeter SiO data reveals a complex interplay of at least three molecular outflows driven by protostars in the forming cluster. Furthermore, the Humphreys α line is detected at a 3-?4σ? level toward the mid-infrared sources A and B. One can roughly estimate both accretion luminosities and corresponding accretion rates to be between ∼2.6 × 10-6 and ∼0.9 × 10-4 Mo yr-1. This is discussed in the context of the observed outflow rates. Conclusions. The analysis of the MIRI MRS observations for this young high-mass star-forming region reveals connected outflow and accretion signatures, as well as the enormous potential of JWST to boost our understanding of the physical and chemical processes at play during star formation.
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| 3. |
- Francis, L., et al.
(författare)
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JOYS: MIRI/MRS spectroscopy of gas-phase molecules from the high-mass star-forming region IRAS 23385+6053
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 683
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Tidskriftsartikel (refereegranskat)abstract
- Context. Space-based mid-infrared (IR) spectroscopy is a powerful tool for the characterization of important star formation tracers of warm gas which are unobservable from the ground. The previous mid-IR spectra of bright high-mass protostars with the Infrared Space Observatory (ISO) in the hot-core phase typically show strong absorption features from molecules such as CO2, C2H2, and HCN. However, little is known about their fainter counterparts at earlier stages. Aims. We aim to characterize the gas-phase molecular features in James Webb Space Telescope Mid-Infrared Instrument Medium Resolution Spectrometer (MIRI/MRS) spectra of the young and clustered high-mass star-forming region IRAS 23385+6053. Methods. Spectra were extracted from several locations in the MIRI/MRS field of view, targeting two mid-IR sources tracing embedded massive protostars as well as three H2 bright outflow knots at distances of >8000 au from the multiple. Molecular features in the spectra were fit with local thermodynamic equilibrium (LTE) slab models, with their caveats discussed in detail. Results. Rich molecular spectra with emission from CO, H2, HD, H2O, C2H2, HCN, CO2, and OH are detected towards the two mid-IR sources. However, only CO and OH are seen towards the brightest H2 knot positions, suggesting that the majority of the observed species are associated with disks or hot core regions rather than outflows or shocks. The LTE model fits to 12CO2, C2H2, HCN emission suggest warm 120a-200 K emission arising from a disk surface around one or both protostars. The abundances of CO2 and C2H2 of ~10âà  à  7 are consistent with previous observations of high-mass protostars. Weak ~500 K H2O emission at ~6a-7 μm is detected towards one mid-IR source, whereas 250a-1050 K H2O absorption is found in the other. The H2O absorption may occur in the disk atmosphere due to strong accretion-heating of the midplane, or in a disk wind viewed at an ideal angle for absorption. CO emission may originate in the hot inner disk or outflow shocks, but NIRSpec data covering the 4.6 μm band head are required to determine the physical conditions of the CO gas, as the high temperatures seen in the MIRI data may be due to optical depth. OH emission is detected towards both mid-IR source positions and one of the shocks, and is likely excited by water photodissociation or chemical formation pumping in a highly non-LTE manner. Conclusions. The observed molecular spectra are consistent with disks having already formed around two protostars in the young IRAS 23385+6054 system. Molecular features mostly appear in emission from a variety of species, in contrast to the more evolved hot core phase protostars which typically show only absorption; however, further observations of young high-mass protostars are needed to disentangle geometry and viewing angle effects from evolution.
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| 4. |
- Gieser, C., et al.
(författare)
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JOYS: Disentangling the warm and cold material in the high-mass IRAS 23385+6053 cluster
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 679
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Tidskriftsartikel (refereegranskat)abstract
- Context. High-mass star formation occurs in a clustered mode where fragmentation is observed from an early stage onward. Young protostars can now be studied in great detail with the recently launched James Webb Space Telescope (JWST). Aims. We study and compare the warm (>100 K) and cold (<100 K) material toward the high-mass star-forming region (HMSFR) IRAS 23385+6053 (IRAS 23385 hereafter) combining high-angular-resolution observations in the mid-infrared (MIR) with the JWST Observations of Young protoStars (JOYS) project and with the NOrthern Extended Millimeter Array (NOEMA) at millimeter (mm) wavelengths at angular resolutions of 0.a2 1.a0. Methods. We investigated the spatial morphology of atomic and molecular species using line-integrated intensity maps. We estimated the temperature and column density of different gas components using H2 transitions (warm and hot component) and a series of CH3CN transitions as well as 3 mm continuum emission (cold component). Results. Toward the central dense core of IRAS 23385, the material consists of relatively cold gas and dust ( 50 K), while multiple outflows create heated and/or shocked H2 and show enhanced temperatures ( 400 K) along the outflow structures. An energetic outflow with enhanced emission knots of [FeII] and [NiII] suggests J-type shocks, while two other outflows have enhanced emission of only H2 and [SI] caused by C-type shocks. The latter two outflows are also more prominent in molecular line emission at mm wavelengths (e.g., SiO, SO, H2CO, and CH3OH). Data of even higher angular resolution are needed to unambiguously identify the outflow-driving sources given the clustered nature of IRAS 23385. While most of the forbidden fine structure transitions are blueshifted, [NeII] and [NeIII] peak at the source velocity toward the MIR source A/mmA2 suggesting that the emission is originating from closer to the protostar. Conclusions. The warm and cold gas traced by MIR and mm observations, respectively, are strongly linked in IRAS 23385. The outflows traced by MIR H2 lines have molecular counterparts in the mm regime. Despite the presence of multiple powerful outflows that cause dense and hot shocks, a cold dense envelope still allows star formation to further proceed. To study and fully understand the spatially resolved MIR properties, a representative sample of low- and high-mass protostars has to be probed using JWST.
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| 5. |
- Rocha, W. R.M., et al.
(författare)
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JWST Observations of Young protoStars (JOYS+): Detecting icy complex organic molecules and ions: I. CH4, SO2, HCOO, OCN, H2CO, HCOOH, CH3CH2OH, CH3CHO, CH3OCHO, and CH3COOH
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 683
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Tidskriftsartikel (refereegranskat)abstract
- Context. Complex organic molecules (COMs) are ubiquitously detected in the gas phase and thought to be mostly formed on icy grains. Nevertheless, there have not been any unambiguous detections of COMs larger than CH3OH in ices reported thus far. Exploring this matter in greater detail has now become possible with the unprecedented possibilities offered by the James Webb Space Telescope (JWST) within the infrared (IR) spectral range with its very high sensitivity and spectral resolution in the critical 5 10 μm range, the fingerprint region of oxygen-bearing COMs. Aims. In the JWST Observations of Young protoStars (JOYS+) program, more than 30 protostars are undergoing observation with the Medium Resolution Spectrograph (MRS) of the Mid-IR Instrument (MIRI). The goal of this study is to comprehensively explore the COMs ice signatures in one low- and one high-mass protostar: NGC 1333 IRAS 2A and IRAS 23385+6053, respectively. Methods. We performed global continuum and silicate subtractions of the MIRI-MRS spectra, followed by a local continuum subtraction in optical depth scale in the range around 6.8 and 8.6 μm, the ice COM fingerprint region. We explored different choices for the local continuum and silicate subtraction. Next, we fit the observational data with a large sample of available IR laboratory ice spectra. We used the ENIIGMA fitting tool, a genetic algorithm-based code that not only finds the best fit between the lab data and the observations, but also performs a statistical analysis of the solutions, such as deriving the confidence intervals and quantifying fit degeneracy. Results. We report the best fits for the spectral ranges between 6.8 and 8.6 μm in NGC 1333 IRAS 2A and IRAS 23385+6053, originating from simple molecules and COMs, as well as negative ions. Overall, we find that ten chemical species are needed to reproduce the astronomical data. The strongest feature in this range (7.7 μm) is dominated by CH4, with contributions from SO2 and OCN. Our results indicate that the 7.2 and 7.4 μm bands are mostly dominated by HCOO. We also find statistically robust detections of COMs based on multiple bands, most notably, CH3CHO, CH3CH2OH, and CH3OCHO. We also report a likely detection of CH3COOH. Based on the ice column density ratios between CH3CH2OH and CH3CHO of NGC 1333 IRAS 2A and IRAS 23385+6053, we find compelling evidence that these COMs are formed on icy grains. Finally, the derived ice abundances for NGC 1333 IRAS 2A correlate well with those in comet 67P/GC within a factor of 5. Conclusions. Based on the high-quality JWST (MIRI-MRS) spectra, we conclude that COMs are present in interstellar ices, thus providing additional proof for the solid-state origin of these species in star-forming regions. In addition, the good correlation between the ice abundances in comet 67P and NGC 1333 IRAS 2A is fully in line with the idea that cometary COMs may be inherited from the early protostellar phases to a significant extent.
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| 6. |
- Wakelam, V., et al.
(författare)
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Reaction Networks for Interstellar Chemical Modelling : Improvements and Challenges
- 2010
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Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 156:04-jan, s. 13-72
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Forskningsöversikt (refereegranskat)abstract
- We survey the current situation regarding chemical modelling of the synthesis of molecules in the interstellar medium. The present state of knowledge concerning the rate coefficients and their uncertainties for the major gas-phase processes-ion-neutral reactions, neutral-neutral reactions, radiative association, and dissociative recombination-is reviewed. Emphasis is placed on those key reactions that have been identified, by sensitivity analyses, as 'crucial' in determining the predicted abundances of the species observed in the interstellar medium. These sensitivity analyses have been carried out for gas-phase models of three representative, molecule-rich, astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the expanding circumstellar envelope IRC +10216. Our review has led to the proposal of new values and uncertainties for the rate coefficients of many of the key reactions. The impact of these new data on the predicted abundances in TMC-1 and L134N is reported. Interstellar dust particles also influence the observed abundances of molecules in the interstellar medium. Their role is included in gas-grain, as distinct from gas-phase only, models. We review the methods for incorporating both accretion onto, and reactions on, the surfaces of grains in such models, as well as describing some recent experimental efforts to simulate and examine relevant processes in the laboratory. These efforts include experiments on the surface-catalyzed recombination of hydrogen atoms, on chemical processing on and in the ices that are known to exist on the surface of interstellar grains, and on desorption processes, which may enable species formed on grains to return to the gas-phase.
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| 7. |
- Chen, Tao, et al.
(författare)
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From planes to bowls : Photodissociation of the bisanthenequinone cation
- 2018
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Ingår i: Chemical Physics Letters. - : Elsevier B.V.. - 0009-2614 .- 1873-4448. ; 692, s. 298-303
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined experimental and theoretical study of the photodissociation of the bisanthenequinone (C28H12O2) cation, Bq+. The experiments show that, upon photolysis, the Bq+ cation does not dehydrogenate, but instead fragments through the sequential loss of the two neutral carbonyl groups, causing the formation of five-membered carbon cycles. Quantum chemical calculations confirm this Bq+ → [Bq - CO]+ → [Bq - 2CO]+ sequence as the energetically most favorable reaction pathway. For the first CO loss, a transition state with a barrier of ∼3.2 eV is found, substantially lower than the lowest calculated H loss dissociation pathway (∼4.9 eV). A similar situation applies for the second CO loss channel (∼3.8 eV vs. ∼4.7 eV), but where the first dissociation step does not strongly alter the planar PAH geometry, the second step transforms the molecule into a bowl-shaped one.
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| 8. |
- Chen, Tao, et al.
(författare)
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Photodissociation processes of Bisanthenquinone cation
- 2017
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Ingår i: Proceedings of the International Astronomical Union. - : Cambridge University Press. - 1743-9213. ; :S332, s. 353-359
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Tidskriftsartikel (refereegranskat)abstract
- A systematic study, using ion trap time-of-flight mass spectrometry, is presented for the photo-dissociation processes of Bisanthenquinone (Bq) cations, C28H12O2+, a ketone substituted Polycyclic Aromatic Hydrocarbon (PAH). The Bq cation fragments through sequential loss of the two neutral carbonyl (CO) units upon laser (626nm) irradiation, resulting in a PAH-like derivative C26H12+. Upon further irradiation, C26H12+ exhibits both stepwise dehydrogenation and C2/C2H2 loss fragmentation channels. Quantum chemistry calculations reveal a detailed picture for the first CO-loss, which involves a transition state with a barrier of ∼ 3.4 eV, which is lower than the energy required for the lowest H-loss pathway (∼ 5.0 eV). The barrier for the second CO-loss is higher (∼ 4.9 eV). The subsequent loss of this unit changes the Bq geometry from a planar to a bent one. It is concluded that the photodissociation mechanism of the substituted PAH cations studied here is site selective in the substituted subunit. This work also shows that an acetone substituted PAH cation is not photo-stable upon irradiation.
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| 9. |
- Ligterink, N. F W, et al.
(författare)
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The prebiotic molecular inventory of Serpens SMM1: I. An investigation of the isomers CH 3 NCO and HOCH 2 CN
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 647
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Methyl isocyanate (CH3NCO) and glycolonitrile (HOCH2CN) are isomers and prebiotic molecules that are involved in the formation of peptide structures and the nucleobase adenine, respectively. These two species are investigated to study the interstellar chemistry of cyanides (CN) and isocyanates (NCO) and to gain insight into the reservoir of interstellar prebiotic molecules. Methods. ALMA observations of the intermediate-mass Class 0 protostar Serpens SMM1-a and ALMA-PILS data of the low-mass Class 0 protostar IRAS 16293B are used. Spectra are analysed with the CASSIS line analysis software package in order to identify and characterise molecules. Results. CH3NCO, HOCH2CN, and various other molecules are detected towards SMM1-a. HOCH2CN is identified in the PILS data towards IRAS 16293B in a spectrum extracted at a half-beam offset position from the peak continuum. CH3NCO and HOCH2CN are equally abundant in SMM1-a at [X]/[CH3OH] of 5.3 × 10-4 and 6.2 × 10-4, respectively. A comparison between SMM1-a and IRAS 16293B shows that HOCH2CN and HNCO are more abundant in the former source, but CH3NCO abundances do not differ significantly. Data from other sources are used to show that the [CH3NCO]/[HNCO] ratio is similar in all these sources within ~10%. Conclusions. The new detections of CH3NCO and HOCH2CN are additional evidence for a large interstellar reservoir of prebiotic molecules that can contribute to the formation of biomolecules on planets. The equal abundances of these molecules in SMM1-a indicate that their formation is driven by kinetic processes instead of thermodynamic equilibrium, which would drive the chemistry to one product. HOCH2CN is found to be much more abundant in SMM1-a than in IRAS 16293B. From the observational data, it is difficult to indicate a formation pathway for HOCH2CN, but the thermal Strecker-like reaction of CN- with H2CO is a possibility. The similar [CH3NCO]/[HNCO] ratios found in the available sample of studied interstellar sources indicate that these two species are either chemically related or their formation is affected by physical conditions in the same way. Both species likely form early during star formation, presumably via ice mantle reactions taking place in the dark cloud or when ice mantles are being heated in the hot core. The relatively high abundances of HOCH2CN and HNCO in SMM1-a may be explained by a prolonged stage of relatively warm ice mantles, where thermal and energetic processing of HCN in the ice results in the efficient formation of both species.
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| 10. |
- Linnartz, H., et al.
(författare)
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C-60(+) as a diffuse interstellar band carrier; a spectroscopic story in 6 acts
- 2020
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Ingår i: Journal of Molecular Spectroscopy. - : Elsevier BV. - 0022-2852 .- 1096-083X. ; 367
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Tidskriftsartikel (refereegranskat)abstract
- In 2019 it was exactly 100 years ago that the first two DIBs, diffuse interstellar bands, were discovered by Mary Lea Heger. Today some 500 + DIBs are known. In numerous observational, modelling and laboratory studies, efforts have been made to identify the carriers of these absorption features that are observed in the light of reddened stars crossing diffuse and translucent clouds. Despite several claims over the years that specific DIBs could be assigned to specific species, not one of these withstood dedicated follow-up studies. An exception is C-60(+). In 2015, Campbell et al. showed that two strong bands, recorded in the laboratory around 960 nm, coincided precisely with known DIBs and in follow-up studies three more matches between C-60(+) transitions and new observational DIB studies were claimed. Over the last four years the evidence for C-60(+) as the first identified DIB carrier - including new laboratory data and Hubble Space Telescope observations - has been accumulating, but not all open issues have been solved yet. This article summarizes 6 spectroscopic achievements that sequentially contributed to what seems to become the first DIB story with a happy end.
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