| 1. |
- Bergman, Per, 1960, et al.
(författare)
-
Emission from HCN and CH3OH in comets Onsala 20-m observations and radiative transfer modelling
- 2022
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 660
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. The aim of this work is to characterise HCN and CH3OH emission from recent comets. Methods. We used the Onsala 20-m telescope to search for millimetre transitions of HCN towards a sample of 11 recent and mostly bright comets in the period from December 2016 to November 2019. Also, CH3OH was searched for in two comets. The HCN sample includes the interstellar comet 2I/Borisov. For the short-period comet 46P/Wirtanen, we were able to monitor the variation of HCN emission over a time-span of about one month. We performed radiative transfer modelling for the observed molecular emission by also including time-dependent effects due to the outgassing of molecules. Results. HCN was detected in six comets. Two of these are short-period comets and four are long-period. Six methanol transitions were detected in 46P/Wirtanen, enabling us to determine the gas kinetic temperature. From the observations, we determined the molecular production rates using time-dependent radiative transfer modelling. For five comets, we were able to determine that the HCN mixing ratios lie near 0.1% using contemporary water production rates, Q(H2O), taken from other studies. This HCN mixing ratio was also found to be typical in our monitoring observations of 46P/Wirtanen but here we notice deviations of up to 0.2% on a daily timescale which could indicate short-time changes in outgassing activity. From our radiative transfer modelling of cometary comae, we find that time-dependent effects on the HCN level populations are of the order of 5-15% when Q(H2O) is around 2 x 10(28) mol s(-1). The effects may be stronger for comets with lower Q(H2O). The exact details of the time-dependent effects depend on the amount of neutral and electron collisions, radiative pumping, and molecular parameters such as the spontaneous rate coefficient.
|
|
| 2. |
- Wirström, Eva, 1977, et al.
(författare)
-
Effect of the 3D distribution on water observations made with the SWI: I. Ganymede
- 2020
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 637
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Characterising and understanding the atmospheres of Jovian icy moons is one of the key exploration goals of the Submillimetre Wave Instrument (SWI), which is to be flown on ESA's Jupiter Icy Moons Explorer (JUICE) mission. Aims. The aim of this paper is to investigate how and under which conditions a 3D asymmetric distribution of the atmosphere may affect the SWI observations. In this work we target the role of phase angle for both nadir and limb geometries for unresolved and partially resolved disc observations from large distances.Methods. We adapted the LIME software package, a 3D non-local thermodynamical equilibrium radiative transfer model, to evaluate ortho-H2O populations and synthesise the simulated SWI beam spectra for different study cases of Ganymede's atmosphere. The temperature and density vertical distributions were adopted from a previous work. The study cases presented here were selected according to the distance and operational scenarios of moon monitoring anticipated for SWI during the Jupiter phase of the JUICE mission. Results. We demonstrate that nadir and limb observations at different phase angles will modify the line amplitude and width. Unresolved observations where both absorption against surface continuum and limb emission contributes within the beam will lead to characteristic line wing emission, which may also appear in pure nadir geometry for specific phase angles. We also find that for Ganymede, the 3D non-local thermodynamical equilibrium populations are more highly excited in the upper atmosphere near the sub-solar region than they are in 1D spherically symmetric models. Finally, the 3D radiative transfer is better suited to properly simulate spectral lines for cases where density or population gradients exist along the line of sight.
|
|
| 3. |
- Allen, Veronica, et al.
(författare)
-
High-resolution Study of the Outflow Activity and Chemical Environment of Chamaeleon-MMS1
- 2024
-
Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 971:2
-
Tidskriftsartikel (refereegranskat)abstract
- The earliest stages of low-mass star formation are unclear, with the first hydrostatic core (FHSC) as the transition stage between a prestellar and protostellar core. This work describes the local (∼4000 au) outflow activity associated with candidate FHSC Chamaeleon-MMS1 and its effect on the surrounding material to determine the evolutionary state of this young low-mass source. We observed Chamaeleon-MMS1 with the Atacama Large Millimeter/submillimeter Array at 220 GHz at high spatial (∼75 au) and spectral resolutions (0.1-0.3 km s−1). A low-energy outflow is detected, consisting of two components, a broad spectral feature (Δv ∼ 8 km s−1) to the northeast and narrow spectral features (Δv ∼ 1 km s−1) to both the northeast and southwest. The molecular tracers CS, formaldehyde (H2CO), and methanol (CH3OH) were used to analyze the effect of the outflows on the surrounding gas and determine its rotational temperature. The rotational temperature of H2CO is 40 K toward the continuum source with similarly low temperatures (10-75 K) toward clumps affected by the outflow. CH3OH is only detected toward gas clumps located away from the continuum source, where the methanol is expected to have been released by the energy of the outflow through ice sputtering. While molecular emission and high outflow speeds rule Cha-MMS1 out as an FHSC, its outflow is less energetic than those of other Class 0 objects and its physical properties are within the range covered by other low-luminosity protostars. The inferred gas temperatures toward the continuum source are also relatively low, indicating that Cha-MMS1 is one of the youngest known sources.
|
|
| 4. |
- Bockelée-Morvan, D., et al.
(författare)
-
Cometary Isotopic Measurements
- 2015
-
Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 197:1-4, s. 47-83
-
Forskningsöversikt (refereegranskat)abstract
- Isotopic ratios in comets provide keys for the understanding of the origin of cometary material, and the physical and chemical conditions in the early Solar Nebula. We review here measurements acquired on the D/H, 14N/15N, 16O/18O, 12C/13C, and 32S/34S ratios in cometary grains and gases, and discuss their cosmogonic implications. The review includes analyses of potential cometary material available in collections on Earth, recent measurements achieved with the Herschel Space Observatory, large optical telescopes, and Rosetta, as well as recent results obtained from models of chemical-dynamical deuterium fractionation in the early solar nebula. Prospects for future measurements are presented.
|
|
| 5. |
- Buckle, J. V., et al.
(författare)
-
Observations of chemical differentiation in clumpy molecular clouds
- 2006
-
Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 133, s. 63 - 82
-
Tidskriftsartikel (refereegranskat)abstract
- We have extensively mapped a sample of dense molecular clouds (L1512, TMC-1C, L1262, Per7, L1389, L1251E) in lines of HC 3 N, CH 3 OH, SO and C 18 O. We demonstrate that a high degree of chemical differentiation is present in all of the observed clouds. We analyse the molecular maps for each cloud, demonstrating a systematic chemical differentiation across the sample, which we relate to the evolutionary state of the cloud. We relate our observations to the cloud physical, kinematical and evolutionary properties, and also compare them to the predictions of simple chemical models. The implications of this work for understanding the origin of the clumpy structures and chemical differentiation observed in dense clouds are discussed. © The Royal Society of Chemistry 2006.
|
|
| 6. |
- Carl, Tadeus, 1992, et al.
(författare)
-
Deep search for glycine conformers in Barnard 5
- 2023
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 524:4, s. 5993-6003
-
Tidskriftsartikel (refereegranskat)abstract
- One of the most fundamental hypotheses in astrochemistry and astrobiology states that crucial biotic molecules like glycine (NH2CH2COOH) found in meteorites and comets are inherited from early phases of star formation. Most observational searches for glycine in the interstellar medium have focused on warm high-mass molecular cloud sources. However, recent studies suggest that it might be appropriate to shift the observational focus to cold low-mass sources. We aim to detect glycine towards the so-called methanol hotspot in the Barnard 5 dark cloud. The hotspot is a cold source (Tgas ≈ 7.5 K) with yet high abundances of complex organic molecules (COMs) and water in the gas phase. We carried out deep pointed observations with the Onsala 20 m telescope, targeting several transitions of glycine conformers I and II (Gly-I and Gly-II) in the frequency range 70.2-77.9 GHz. No glycine lines are detected towards the targeted position, but we use a line stacking procedure to derive sensitive abundance upper limits w.r.t. H2 for Gly-I and Gly-II, i.e. ≤(2-5) × 10-10 and ≤(0.7-3) × 10-11, respectively. The obtained Gly-II upper limits are the most stringent for a cold source, while the Gly-I upper limits are mostly on the same order as previously measured limits. The measured abundances w.r.t. H2 of other COMs at the B5 methanol hotspot range from 2 × 10-10 (acetaldehyde) to 2 × 10-8 (methanol). Hence, based on a total glycine upper limit of (2-5) × 10-10, we cannot rule out that glycine is present but undetected.
|
|
| 7. |
- Cordiner, M. A., et al.
(författare)
-
On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation?
- 2016
-
Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 828:1
-
Tidskriftsartikel (refereegranskat)abstract
- IRAS 19312+1950 is a peculiar object that has eluded firm characterization since its discovery, with combined maser properties similar to an evolved star and a young stellar object (YSO). To help determine its true nature, we obtained infrared spectra of IRAS 19312+1950 in the range 5–550 μm using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170 μm, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components: ≈0.22 solar masses of material at 280 ± 18 K, and ≈1.6 solar masses of material at 157 ± 3 K. The O i 63 μm line is detected on-source but no significant emission from atomic ions was found. The HIFI observations display shocked, high-velocity gas with outflow speeds up to 90 km/s along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H2O at 5.8 μm and CO2 at 15 μm. The spectral energy distribution is consistent with a massive, luminous (~2 × 10^4 solar luminosities) central source surrounded by a dense, warm circumstellar disk and envelope of total mass ~500–700 solar masses, with large bipolar outflow cavities. The combination of distinctive far-IR spectral features suggest that IRAS 19312+1950 should be classified as an accreting, high-mass YSO rather than an evolved star. In light of this reclassification, IRAS 19312+1950 becomes only the fifth high-mass protostar known to exhibit SiO maser activity, and demonstrates that 18 cm OH maser line ratios may not be reliable observational discriminators between evolved stars and YSOs.
|
|
| 8. |
- Cordiner, M. A., et al.
(författare)
-
On the ubiquity of molecular anions in the dense interstellar medium
- 2013
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 770:1
-
Tidskriftsartikel (refereegranskat)abstract
- Results are presented from a survey for molecular anions in seven nearby Galactic star-forming cores and molecular clouds. The hydrocarbon anion C6H- is detected in all seven target sources, including four sources where no anions have been previously detected: L1172, L1389, L1495B, and TMC-1C. The C6H-/C6H column density ratio is greater than or similar to 1.0% in every source, with a mean value of 3.0% (and standard deviation 0.92%). Combined with previous detections, our results show that anions are ubiquitous in dense clouds wherever C6H is present. The C6H-/C6H ratio is found to show a positive correlation with molecular hydrogen number density, and with the apparent age of the cloud. We also report the first detection of C4H- in TMC-1 (at 4.8 sigma confidence), and derive an anion-to-neutral ratio C4H-/C4H = (1.2 +/- 0.4) x 10(-5)(= 0.0012% +/- 0.0004%). Such a low value compared with C6H- highlights the need for a revised radiative electron attachment rate for C4H. Chemical model calculations show that the observed C4H- could be produced as a result of reactions of oxygen atoms with C5H- and C6H-.
|
|
| 9. |
- Cordiner, M. A., et al.
(författare)
-
Organic chemistry of low-mass star-forming cores I: 7 mm spectroscopy of Chamaeleon MMS1
- 2012
-
Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 744, s. 131-
-
Tidskriftsartikel (refereegranskat)abstract
- Observations are presented of emission lines from organic molecules at frequencies 32-50 GHz in the vicinity of Chamaeleon MMS1. This chemically rich dense cloud core harbors an extremely young, very low luminosity protostellar object and is a candidate first hydrostatic core. Column densities are derived and emission maps are presented for species including polyynes, cyanopolyynes, sulphuretted carbon chains, and methanol. The polyyne emission peak lies about 5000 AU from the protostar, whereas methanol peaks about 15,000 AU away. Averaged over the telescope beam, the molecular hydrogen number density is calculated to be 106 cm–3 and the gas kinetic temperature is in the range 5-7 K. The abundances of long carbon chains are very large and are indicative of a non-equilibrium carbon chemistry; C6H and HC7N column densities are 5.9+2.9 –1.3 × 1011 cm–2 and 3.3+8.0 –1.5 × 1012 cm–2, respectively, which are similar to the values found in the most carbon-chain-rich protostars and prestellar cores known, and are unusually large for star-forming gas. Column density upper limits were obtained for the carbon-chain anions C4H– and C6H–, with anion-to-neutral ratios [C4H–]/[C4H]
|
|
| 10. |
- Dore, L., et al.
(författare)
-
Doubly 15N-substituted diazenylium: THz laboratory spectra and fractionation models
- 2017
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 604, s. A26-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Isotopic fractionation in dense molecular cores has been suggested as a possible origin of large 14N/15N ratio variations in solar system materials. While chemical models can explain some observed variations with different fractionation patterns for molecules with –NH or –CN functional groups, they fail to reproduce the observed ratios in diazenylium (N2H+).Aims. Observations of doubly 15N-substituted species could provide important constraints and insights for theoretical chemical models of isotopic fractionation. However, spectroscopic data are very scarce.Methods. The rotational spectra of the fully 15N-substituted isopologues of the diazenylium ion, 15N2H+ and 15N2D+, have been investigated in the laboratory well into the THz region by using a source-modulation microwave spectrometer equipped with a negative glow discharge cell. An extended chemical reaction network has been used to estimate what ranges of 15N fractionation in doubly 15N-substituted species could be expected in the interstellar medium (ISM).Results. For each isotopologue of the H- and D-containing pair, nine rotational transitions were accurately measured in the frequency region 88 GHz–1.2 THz. The analysis of the spectrum provided very precise rest frequencies at millimeter and sub-millimeter wavelengths, useful for the radioastronomical identification of the rotational lines of 15N2H+ and 15N2D+ in the ISM.
|
|
| 11. |
- Giers, K., et al.
(författare)
-
Similar levels of deuteration in the pre-stellar core L1544 and the protostellar core HH211
- 2023
-
Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 676
-
Tidskriftsartikel (refereegranskat)abstract
- Context. In the centre of pre-stellar cores, deuterium fractionation is enhanced due to low temperatures and high densities. Therefore, the chemistry of deuterated molecules can be used to probe the evolution and the kinematics in the earliest stages of star formation. Aims. We analyse the deuterium fractionation of simple molecules, comparing the level of deuteration in the envelopes of the prototypical pre-stellar core L1544 in Taurus and the young protostellar core HH211 in Perseus. Methods. We used single-dish observations of CCH, HCN, HNC, and HCO+ and their C-13-, 18O(-), and D-bearing isotopologues, detected with the 20 m telescope at the Onsala Space Observatory. We derived the column densities, and subsequently the carbon isotopic ratios and deuterium fractions of the molecules. Additionally, we used radiative transfer simulations and results from chemical modelling to reproduce the observed molecular lines. We used new collisional rate coefficients for HNC, (HNC)-C-13 DNC, and DCN that consider the hyperfine structure of these molecules. Results. For CCH, we find high levels of deuteration (10%) in both sources, consistent with other carbon chains. We find moderate deuteration of HCN (5-7%), with a slight enhancement towards the protostellar core. Equal levels of deuteration for HNC towards both cores (similar to 8%) indicate that HNC is tracing slightly different layers compared to HCN. We find that the deuterium fraction of HCO+ is enhanced towards HH211, most likely caused by isotope-selective photodissociation of C18O. With radiative transfer, we were able to reproduce the observed lines of CCH, HCN, (HCN)-C-13 HNC, (HNC)-C-13 and DNC towards L1544 as well as CCH, (HCN)-C-13 (HNC)-C-13 DNC, (HCO)-C-13+ HC18O(+) and DCO+ towards HH211. Conclusions. Similar levels of deuteration show that the deuterium fractionation is most probably equally efficient towards both cores, suggesting that the protostellar envelope still retains the chemical composition of the original pre-stellar core. The fact that the two cores are embedded in different molecular clouds also suggests that environmental conditions do not have a significant effect on the deuterium fractionation within dense cores. Our results highlight the uncertainties when dealing with C-13 isotopologues and the influence of the applied carbon isotopic ratio. Radiative transfer modelling shows that it is crucial to include the effects of the hyperfine structure to reproduce the observed line shapes. In addition, to correctly model emission lines from pre-stellar cores, it is necessary to include the outer layers of the core to consider the effects of extended structures. In addition to HCO+ observations, HCN observations towards L1544 also require the presence of an outer diffuse layer where the molecules are relatively abundant.
|
|
| 12. |
- Hajigholi, Mitra, 1986, et al.
(författare)
-
On the accretion process in a high-mass star forming region - A multitransitional THz Herschel-HIFI study of ammonia toward G34.26+0.15
- 2016
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 585:A158, s. 20-
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. Our aim is to explore the gas dynamics and the accretion process in the early phase of high-mass star formation.Methods. The inward motion of molecular gas in the massive star forming region G34.26+0.15 is investigated by using high-resolution profiles of seven transitions of ammonia at THz frequencies observed with Herschel-HIFI. The shapes and intensities of these lines are interpreted in terms of radiative transfer models of a spherical, collapsing molecular envelope. An accelerated Lambda Iteration (ALI) method is used to compute the models.Results. The seven ammonia lines show mixed absorption and emission with inverse P-Cygni-type profiles that suggest infall onto the central source. A trend toward absorption at increasingly higher velocities for higher excitation transitions is clearly seen in the line profiles. The J=3←2 lines show only very weak emission, so these absorption profiles can be used directly to analyze the inward motion of the gas. This is the first time a multitransitional study of spectrally resolved rotational ammonia lines has been used for this purpose. Broad emission is, in addition, mixed with the absorption in the 1_0−0_0 ortho-NH_3 line, possibly tracing a molecular outflow from the star forming region. The best-fitting ALI model reproduces the continuum fluxes and line profiles, but slightly underpredicts the emission and absorption depth in the ground-state ortho line 1_0−0_0. An ammonia abundance on the order of 10^{−9} relative to H_2 is needed to fit the profiles. The derived ortho-to-para ratio is approximately 0.5 throughout the infalling cloud core similar to recent findings for translucent clouds in sight lines toward W31C and W49N. We find evidence of two gas components moving inwards toward the central region with constant velocities: 2.7 and 5.3 km s^{−1}, relative to the source systemic velocity. Attempts to model the inward motion with a single gas cloud in free-fall collapse did not succeed. The inferred mass accretion rates derived rises from 4.1×10^{−3} to 4.5×10^{−2} M⊙ yr^{−1}, which is sufficient to overcome the expected radiation pressure from G34.26+0.15.
|
|
| 13. |
- Olofsson, Henrik, 1972, et al.
(författare)
-
A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite. I. The observational data
- 2007
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 476:number 2, December III, s. 791-806
-
Tidskriftsartikel (refereegranskat)abstract
- Aims.Spectral line surveys are useful since they allow identification of new molecules and new lines in uniformly calibrated data sets. The subsequent multi-transition analysis will provide improved knowledge of molecular abundances, cloud temperatures and densities, and may also reveal previously unsuspected blends of molecular lines, which otherwise may lead to erroneous conclusions. Nonetheless, large portions of the sub-millimetre spectral regime remain unexplored due to severe absorptions by H2O and O2 in the terrestrial atmosphere. The purpose of the measurements presented here is to cover wavelength regions at and around 0.55 mm - regions largely unobservable from the ground.Methods.Using the Odin astronomy/aeronomy satellite, we performed the first spectral survey of the Orion KL molecular cloud core in the bands 486-492 and 541-576 GHz with rather uniform sensitivity (22-25 mK baseline noise). Odin's 1.1 m size telescope, equipped with four cryo-cooled tuneable mixers connected to broad band spectrometers, was used in a satellite position-switching mode. Two mixers simultaneously observed different 1.1 GHz bands using frequency steps of 0.5 GHz (25 h each). An on-source integration time of 20 h was achieved for most bands. The entire campaign consumed ~1100 orbits, each containing one hour of serviceable astro-observation.Results.We identified 280 spectral lines from 38 known interstellar molecules (including isotopologues) having intensities in the range 80 to 0.05 K. An additional 64 weak lines remain unidentified. Apart from the ground state rotational 11,0-10,1 transitions of ortho-H2O, H218O and H217O, the high energy 62,4-71,7 line of para-H2O (Eu=867$\,$K) and the HDO(20,2-11,1) line have been observed, as well as the 10-01 lines from NH3 and its rare isotopologue 15NH3. We suggest assignments for some unidentified features, notably the new interstellar molecules ND and SH-. Severe blends have been detected in the line wings of the H218O, H217O and 13CO lines changing the true linewidths of the outflow emission.
|
|
| 14. |
- Persson, Carina, 1964, et al.
(författare)
-
A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite. II. Data analysis
- 2007
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 476:2, December III, s. 807-827
-
Tidskriftsartikel (refereegranskat)abstract
- Aims.We investigate the physical and chemical conditions in a typical star forming region, including an unbiased search for new molecules in a spectral region previously unobserved.Methods.Due to its proximity, the Orion KL region offers a unique laboratory of molecular astrophysics in a chemically rich, massive star forming region. Several ground-based spectral line surveys have been made, but due to the absorption by water and oxygen, the terrestrial atmosphere is completely opaque at frequencies around 487 and 557 GHz. To cover these frequencies we used the Odin satellite to perform a spectral line survey in the frequency ranges 486-492 GHz and 541-577 GHz, filling the gaps between previous spectral scans. Odin's high main beam efficiency, $\eta_{{\rm mb}}$ = 0.9, and observations performed outside the atmosphere make our intensity scale very well determined.Results.We observed 280 spectral lines from 38 molecules including isotopologues, and, in addition, 64 unidentified lines. A few U-lines have interesting frequency coincidences such as ND and the anion SH-. The beam-averaged emission is dominated by CO, H2O, SO2, SO, 13CO and CH3OH. Species with the largest number of lines are CH3OH, (CH3)2O, SO2, 13CH3OH, CH3CN and NO. Six water lines are detected including the ground state rotational transition 11,0-10,1 of o-H2O, its isotopologues o-H218O and o-H217O, the Hot Core tracing p-H2O transition 62,4-71,7, and the 20, 2-11,1 transition of HDO. Other lines of special interest are the 10-0$_$ transition of NH3 and its isotopologue 15NH3. Isotopologue abundance ratios of D/H, 12C/13C, 32S/34S, 34S/33S, and 18O/17O are estimated. The temperatures, column densities and abundances in the various subregions are estimated, and we find very high gas-phase abundances of H2O, NH3, SO2, SO, NO, and CH3OH. A comparison with the ice inventory of ISO sheds new light on the origin of the abundant gas-phase molecules.
|
|
| 15. |
- Persson, Carina, 1964, et al.
(författare)
-
Ortho-to-para ratio of NH2. Herschel-HIFI observations of ortho- and para-NH2 rotational transitions towards W31C, W49N, W51 and G34.3+0.1
- 2016
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 586, s. Art Nr. A128-
-
Tidskriftsartikel (refereegranskat)abstract
- We have used the Herschel-HIFI instrument to observe both nuclear spin symmetries of amidogen (NH2) towards the high-mass star-forming regions W31C (G10.6-0.4), W49N (G43.2-0.1), W51 (G49.5-0.4) and G34.3+0.1. The aim is to investigate the ratio of nuclear spin types, the ortho-to-para ratio (OPR), of NH2. The excited NH2 transitions are used to construct radiative transfer models of the hot cores and surrounding envelopes in order to investigate the excitation and possible emission of the ground state rotational transitions of ortho-NH2 N_(K_a,K_c} J=1_(1,1) 3/2 - 0_(0,0) 1/2 and para-NH2 2_(1,2) 5/2 - 1_(0,1) 3/2$ used in the OPR calculations. Our best estimate of the average OPR in the envelopes lie above the high temperature limit of three for W49N, specifically 3.5 with formal errors of \pm0.1, but for W31C, W51, and G34.3+0.1 we find lower values of 2.5\pm0.1, 2.7\pm0.1, and 2.3\pm0.1, respectively. Such low values are strictly forbidden in thermodynamical equilibrium since the OPR is expected to increase above three at low temperatures. In the translucent interstellar gas towards W31C, where the excitation effects are low, we find similar values between 2.2\pm0.2 and 2.9\pm0.2. In contrast, we find an OPR of 3.4\pm0.1 in the dense and cold filament connected to W51, and also two lower limits of >4.2 and >5.0 in two other translucent gas components towards W31C and W49N. At low temperatures (T \lesssim 50 K) the OPR of H2 is 20-25 K, depending on time, and values above three at lower temperatures.
|
|
| 16. |
- Persson, Carina, 1964, et al.
(författare)
-
Upper limits to interstellar NH+ and para-NH2- abundances. Herschel-HIFI observations towards Sgr B2 (M) and G10.6-0.4 (W31C)
- 2014
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 567, s. Art. no. A130-
-
Tidskriftsartikel (refereegranskat)abstract
- The understanding of interstellar nitrogen chemistry has improved significantly with recent results from the Herschel Space Observatory. To set even better constraints, we report here on deep searches for the NH+ ground state rotational transition J=1.5-0.5 of the ^2Pi_1/2 lower spin ladder, with fine-structure transitions at 1013 and 1019 GHz, and the para-NH2- 1_1,1-0_0,0 rotational transition at 934 GHz towards Sgr B2(M) and G10.6-0.4 using Herschel-HIFI. No clear detections of NH+ are made and the derived upper limits are
|
|
| 17. |
- Roth, Nathan X., et al.
(författare)
-
Molecular Outgassing in Centaur 29P/Schwassmann-Wachmann 1 during Its Exceptional 2021 Outburst: Coordinated Multiwavelength Observations Using nFLASH at APEX and iSHELL at the NASA-IRTF
- 2023
-
Ingår i: Planetary Science Journal. - 2632-3338. ; 4:9
-
Tidskriftsartikel (refereegranskat)abstract
- The extraordinary 2021 September-October outburst of Centaur 29P/Schwassmann-Wachmann 1 afforded an opportunity to test the composition of primitive Kuiper disk material at high sensitivity. We conducted nearly simultaneous multiwavelength spectroscopic observations of 29P/Schwassmann-Wachmann 1 using iSHELL at the NASA Infrared Telescope Facility (IRTF) and nFLASH at the Atacama Pathfinder EXperiment (APEX) on 2021 October 6, with follow-up APEX/nFLASH observations on 2021 October 7 and 2022 April 3. This coordinated campaign between near-infrared and radio wavelengths enabled us to sample molecular emission from a wealth of coma molecules and to perform measurements that cannot be accomplished at either wavelength alone. We securely detected CO emission on all dates with both facilities, including velocity-resolved spectra of the CO (J = 2-1) transition with APEX/nFLASH and multiple CO (v = 1-0) rovibrational transitions with IRTF/iSHELL. We report rotational temperatures, coma kinematics, and production rates for CO and stringent (3σ) upper limits on abundance ratios relative to CO for CH4, C2H6, CH3OH, H2CO, CS, and OCS. Our upper limits for CS/CO and OCS/CO represent their first values in the literature for this Centaur. Upper limits for CH4, C2H6, CH3OH, and H2CO are the most stringent reported to date, and are most similar to values found in ultra CO-rich Oort cloud comet C/2016 R2 (PanSTARRS), which may have implications for how ices are preserved in cometary nuclei. We demonstrate the superb synergy of coordinated radio and near-infrared measurements, and advocate for future small-body studies that jointly leverage the capabilities of each wavelength.
|
|
| 18. |
- Sewiło, Marta, et al.
(författare)
-
Complex Organic Molecules in Star-Forming Regions of the Magellanic Clouds
- 2019
-
Ingår i: ACS Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 3:10, s. 2088-2109
-
Forskningsöversikt (refereegranskat)abstract
- The Large and Small Magellanic Clouds (LMC and SMC), gas-rich dwarf companions of the Milky Way, are the nearest laboratories for detailed studies on the formation and survival of complex organic molecules (COMs) under metal-poor conditions. To date, only methanol, methyl formate, and dimethyl ether have been detected in these galaxies-all three toward two hot cores in the N113 star-forming region in the LMC, the only extragalactic sources exhibiting complex hot-core chemistry. We describe a small and diverse sample of the LMC and SMC sources associated with COMs or hot-core chemistry, and compare the observations to theoretical model predictions. Theoretical models accounting for the physical conditions and metallicity of hot molecular cores in the Magellanic Clouds have been able to broadly account for the existing observations, but they fail to reproduce the dimethyl ether abundance by more than an order of magnitude. We discuss future prospects for research in the field of complex chemistry in the low-metallicity environment. The detection of COMs in the Magellanic Clouds has important implications for astrobiology. The metallicity of the Magellanic Clouds is similar to that of galaxies in the earlier epochs of the universe; thus, the presence of COMs in the LMC and SMC indicates that a similar prebiotic chemistry leading to the emergence of life, as it happened on Earth, is possible in low-metallicity systems in the earlier universe.
|
|
| 19. |
- Sipilä, O., et al.
(författare)
-
Combined model for 15N, 13C, and spin-state chemistry in molecular clouds
- 2023
-
Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
-
Tidskriftsartikel (refereegranskat)abstract
- We present a new gas-grain chemical model for the combined isotopic fractionation of carbon and nitrogen in molecular clouds. To this end, we have developed gas-phase and grain-surface chemical networks where the isotope chemistry of carbon and nitrogen is coupled with a time-dependent description of spin-state chemistry, which is important for nitrogen chemistry at low temperatures. We updated the rate coefficients of some isotopic exchange reactions considered previously in the literature, and here we present a set of new exchange reactions involving molecules substituted in 13C and 15N simultaneously. We applied the model to a series of zero-dimensional simulations representing a set of physical conditions across a prototypical prestellar core, exploring the deviations of the isotopic abundance ratios in the various molecules from the elemental isotopic ratios as a function of physical conditions and time. We find that the 12C/13C ratio can deviate from the elemental ratio to a high factor depending on the molecule, and that there are highly time-dependent variations in the ratios. The HCN/H13CN ratio, for example, can obtain values of less than ten depending on the simulation time. The 14N/15N ratios tend to remain close to the assumed elemental ratio within approximately 10%, with no clearly discernible trends for the various species as a function of the physical conditions. Abundance ratios between 13C-containing molecules and 13C+15N-containing molecules however show somewhat increased levels of fractionation as a result of the newly included exchange reactions, though they still remain within a few tens of percent of the elemental 14N/15N ratio. Our results imply the existence of gradients in isotopic abundance ratios across prestellar cores, suggesting that detailed simulations are required to interpret observations of isotopically substituted molecules correctly, especially given that the various isotopic forms of a given molecule do not necessarily trace the same gas layers.
|
|
| 20. |
- Taquet, V., et al.
(författare)
-
Chemical complexity induced by efficient ice evaporation in the Barnard 5 molecular cloud
- 2017
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 607, s. 20-
-
Tidskriftsartikel (refereegranskat)abstract
- Cold gas-phase water has recently been detected in a cold dark cloud, Barnard 5 located in the Perseus complex, by targeting methanol peaks as signposts for ice mantle evaporation. Observed morphology and abundances of methanol and water are consistent with a transient non-thermal evaporation process only affecting the outermost ice mantle layers, possibly triggering a more complex chemistry. Here we present the detection of the complex organic molecules (COMs) acetaldehyde (CH3CHO) and methyl formate (CH3OCHO), as well as formic acid (HCOOH) and ketene (CH2CO), and the tentative detection of di-methyl ether (CH3OCH3) towards the "methanol hotspot" of Barnard 5 located between two dense cores using the single dish OSO 20 m, IRAM 30 m, and NRO 45 m telescopes. The high energy cis-conformer of formic acid is detected, suggesting that formic acid is mostly formed at the surface of interstellar grains and then evaporated. The detection of multiple transitions for each species allows us to constrain their abundances through LTE and non-LTE methods. All the considered COMs show similar abundances between 1 and 10% relative to methanol depending on the assumed excitation temperature. The non-detection of glycolaldehyde, an isomer of methyl formate, with a [glycolaldehyde]/[methyl formate] abundance ratio lower than 6%, favours gas phase formation pathways triggered by methanol evaporation. According to their excitation temperatures derived in massive hot cores, formic acid, ketene, and acetaldehyde have been designated as "lukewarm" COMs whereas methyl formate and di-methyl ether were defined as "warm" species. Comparison with previous observations of other types of sources confirms that lukewarm and warm COMs show similar abundances in low-density cold gas whereas the warm COMs tend to be more abundant than the lukewarm species in warm protostellar cores. This abundance evolution suggests either that warm COMs are indeed mostly formed in protostellar environments and/or that lukewarm COMs are efficiently depleted by increased hydrogenation efficiency around protostars.
|
|
| 21. |
- Taquet, V., et al.
(författare)
-
FORMATION AND RECONDENSATION OF COMPLEX ORGANIC MOLECULES DURING PROTOSTELLAR LUMINOSITY OUTBURSTS
- 2016
-
Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 821:1
-
Tidskriftsartikel (refereegranskat)abstract
- During the formation of stars, the accretion of surrounding material toward the central object is thought to undergo strong luminosity outbursts followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas-phase formation and recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas-phase chemical network forming COMs in which ammonia plays a key role. The model calculations presented here demonstrate that ion-molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas-phase reaction branching ratios. In spite of the short outburst timescales of about 100 years, abundance ratios of the considered species higher than 10% with respect to methanol are predicted during outbursts due to their low binding energies relative to water and methanol which delay their recondensation during cooling. Although the current luminosity of most embedded protostars would be too low to produce complex organics in the hot-core regions that are observable with current sub-millimetric interferometers, previous luminosity outburst events would induce the formation of COMs in extended regions of protostellar envelopes with sizes increasing by up to one order of magnitude.
|
|
| 22. |
- Tosi, F., et al.
(författare)
-
Characterization of the Surfaces and Near-Surface Atmospheres of Ganymede, Europa and Callisto by JUICE
- 2024
-
Ingår i: Space Science Reviews. - 0038-6308 .- 1572-9672. ; 220:5
-
Tidskriftsartikel (refereegranskat)abstract
- We present the state of the art on the study of surfaces and tenuous atmospheres of the icy Galilean satellites Ganymede, Europa and Callisto, from past and ongoing space exploration conducted with several spacecraft to recent telescopic observations, and we show how the ESA JUICE mission plans to explore these surfaces and atmospheres in detail with its scientific payload. The surface geology of the moons is the main evidence of their evolution and reflects the internal heating provided by tidal interactions. Surface composition is the result of endogenous and exogenous processes, with the former providing valuable information about the potential composition of shallow subsurface liquid pockets, possibly connected to deeper oceans. Finally, the icy Galilean moons have tenuous atmospheres that arise from charged particle sputtering affecting their surfaces. In the case of Europa, plumes of water vapour have also been reported, whose phenomenology at present is poorly understood and requires future close exploration. In the three main sections of the article, we discuss these topics, highlighting the key scientific objectives and investigations to be achieved by JUICE. Based on a recent predicted trajectory, we also show potential coverage maps and other examples of reference measurements. The scientific discussion and observation planning presented here are the outcome of the JUICE Working Group 2 (WG2): “Surfaces and Near-surface Exospheres of the Satellites, dust and rings”.
|
|
| 23. |
- Willacy, K., et al.
(författare)
-
The Composition of the Protosolar Disk and the Formation Conditions for Comets
- 2015
-
Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 197:1-4, s. 151-190
-
Forskningsöversikt (refereegranskat)abstract
- Conditions in the protosolar nebula have left their mark in the composition of cometary volatiles, thought to be some of the most pristine material in the solar system. Cometary compositions represent the end point of processing that began in the parent molecular cloud core and continued through the collapse of that core to form the protosun and the solar nebula, and finally during the evolution of the solar nebula itself as the cometary bodies were accreting. Disentangling the effects of the various epochs on the final composition of a comet is complicated. But comets are not the only source of information about the solar nebula. Protostellar disks around young stars similar to the protosun provide a way of investigating the evolution of disks similar to the solar nebula while they are in the process of evolving to form their own solar systems. In this way we can learn about the physical and chemical conditions under which comets formed, and about the types of dynamical processing that shaped the solar system we see today.This paper summarizes some recent contributions to our understanding of both cometary volatiles and the composition, structure and evolution of protostellar disks.
|
|
| 24. |
- Wirström, Eva, 1977, et al.
(författare)
-
15N fractionation in star-forming regions and Solar System objects
- 2015
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 11:A29A, s. 271-274
-
Konferensbidrag (refereegranskat)abstract
- We briefly review what is currently known of 14N/15N ratios in interstellar molecules. We summarize the fractionation ratios measured in HCN, HNC, CN, N2 and NH3, and compare these to theoretical predictions and to the isotopic inventory of cometary volatiles.
|
|
| 25. |
- Wirström, Eva, 1977, et al.
(författare)
-
A Radio Astronomical Star Party for those "On The Verge"
- 2013
-
Ingår i: CAP Journal, Ed. S. Reed. - 1996-563X. ; 13, s. 6-8
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Here we describe the Onsala Stjärnträff (Onsala Star Party), an unconventional outreach event that was held during Sweden’s inaugural Day and Night of Astronomy in October 2012. The target group consisted of individuals who are “on the verge” of discovering astronomy; individuals who have a spark of enthusiasm for astronomy, but who have not yet taken this passive interest to the next level. For the event, we adapted the concept of a star party to provide insight, inspiration, hands-on experience and networking opportunities for the participants. Furthermore, the Onsala Space Observatory’s radio telescopes allowed us to compensate for poor weather and to fulfil our role in communicating radio astronomy to a wider public.
|
|
| 26. |
- Wirström, Eva, 1977, et al.
(författare)
-
A Search for O2 in Co-Depleted Molecular Cloud Cores with Herschel
- 2016
-
Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 830:2, s. 102-106
-
Tidskriftsartikel (refereegranskat)abstract
- The general lack of molecular oxygen in molecular clouds is an outstanding problem in astrochemistry. Extensive searches with SWAS, Odin, and Herschel have only produced two detections; upper limits to the O2 abundance in the remaining sources observed are about 1000 times lower than predicted by chemical models. Previous atomic oxygen observations and inferences from observations of other molecules indicated that high abundances of O atoms might be present in dense cores exhibiting large amounts of CO depletion. Theoretical arguments concerning the oxygen gas–grain interaction in cold dense cores suggested that, if O atoms could survive in the gas after most of the rest of the heavy molecular material has frozen out onto dust, then O2 could be formed efficiently in the gas. Using Herschel HIFI, we searched a small sample of four depletion cores — L1544, L694-2, L429, and Oph D — for emission in the low excitation O2 N_J = 33–12 line at 487.249 GHz. Molecular oxygen was not detected and we derive upper limits to its abundance in the range of N(O2)/N(H2)=(0.6— 1.6)*1e-7. We discuss the absence of O2 in the light of recent laboratory and observational studies.
|
|
| 27. |
- Wirström, Eva, 1977, et al.
(författare)
-
A search for pre-biotic molecules in hot cores
- 2007
-
Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 473, s. 177-180
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. Our aim is to better understand the complex chemistry of organic molecules in the interstellar medium, leading to the formation of pre-biotic molecules such as amino acids.Methods. We have performed a search for the pre-biotic molecules amino acetonitrile (H2N CH2 CN) and vinyl acetylene (C2H3 CCH) towards four northern hot core sources using the Onsala 20 m telescope.Results. We have determined upper limits to the column density of amino acetonitrile (1-4*10^13 cm^-2) and vinyl acetylene (2-7*10^14 cm^-2) in the observed sources. In addition, from the absence of other lines within the observed frequency band, we have further constrained the column density of oxiranecarbonitrile (c-C3H3 NO) and amino-ethanol (NH2 CH2 CH2 OH) in these sources.
|
|
| 28. |
- Wirström, Eva, 1977
(författare)
-
Astrochemistry at Millimetre and Submillimetre Wavelengths
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this thesis is a series of observational tests, aiming to clarify the chemical and physical origin of interstellar molecules. Spectral lines at millimetre and submillimetre wavelengths, caused by rotational transitions in CO, H2O, NH3, CH3OH, CH3SH, C2H3CN, and several of their isotopologues, have been observed towards regions of star-formation in the Galaxy. Maps of extended H2O and CO emission from the Orion nebula demonstrate that the water probably is localised to the photon-dominated region at the surface of the molecular cloud, at higher abundances than previously thought. Water is also observed in absorption from its ground-state towards the massive star-forming region Sgr B2. Curiously enough, a water abundance similar to the one reported for Orion is found in the low-excitation gas in one of the Galactic spiral arms. Ammonia absorption was also observed from diffuse spiral arm clouds along the same line-of-sight, but at about an order of magnitude lower abundance. The observed water and ammonia absorptions caused by the Sgr B2 cloud itself are successfully modelled without invoking a morphological component of hot gas.Two independent methods of analysis are applied to observations of methanol (CH3OH) and its 13C isotopologue in the cold envelopes of young stellar objects. Both methods indicate that methanol is mainly formed by hydrogenation of CO on cold dust grains. A study comparing the interstellar abundances of CH3SH (methyl mercaptan) and CH3OH unveil a possible trend of lower relative CH3SH abundances in more evolved objects. However, the significance of this trend, in relation to the chemical origin of these molecules, needs to be further investigated.In addition, searches for two pre-biotic molecules, namely vinyl acetylene (C2H3CCH) and amino acetonitrile (H2NCH2CN), resulting in improved upper abundance limits are presented.A comprehensive conclusion of this thesis is that in order to exploit the full capacity of high-quality observations there is a serious need for additional theoretical and laboratory investigations of processes like proton-exchange reactions, collision rates, freeze-out and desorption, all taking into account different isotopologues and spin-types.
|
|
| 29. |
- Wirström, Eva, 1977, et al.
(författare)
-
COLD WATER VAPOR IN THE BARNARD 5 MOLECULAR CLOUD
- 2014
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 788:2
-
Tidskriftsartikel (refereegranskat)abstract
- After more than 30 yr of investigations, the nature of gas-grain interactions at low temperatures remains an unresolved issue in astrochemistry. Water ice is the dominant ice found in cold molecular clouds; however, there is only one region where cold (similar to 10 K) water vapor has been detected-L1544. This study aims to shed light on ice desorption mechanisms under cold cloud conditions by expanding the sample. The clumpy distribution of methanol in dark clouds testifies to transient desorption processes at work-likely to also disrupt water ice mantles. Therefore, the Herschel HIFI instrument was used to search for cold water in a small sample of prominent methanol emission peaks. We report detections of the ground-state transition of o-H2O (J = 1(10)-1(01)) at 556.9360 GHz toward two positions in the cold molecular cloud, Barnard 5. The relative abundances of methanol and water gas support a desorption mechanism which disrupts the outer ice mantle layers, rather than causing complete mantle removal.
|
|
| 30. |
- Wirström, Eva, 1977, et al.
(författare)
-
Depletion Cores - the O2 hideout?
- 2013
-
Ingår i: The Universe Explored by Herschel, 15 – 18 October 2013, Noordwijk, The Netherlands.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Molecular oxygen has proven to be the most elusive molecule in theinterstellar medium. Despite the fact that it in theory forms easily in both warm and cold dense gas, extensive searches with SWAS, Odin and Herschel have only resulted in detections in a handful of sources. In addition, upper limits in various astronomical environments are at levels of 1000 times less abundant than predicted by chemical models. This situation requires either for atomic carbon to be abundant enough to suppress the O2 by CO formation, or for atomic oxygen to accrete onto grains and remain bound there. However, the binding energies of atoms to grains are highly uncertain and high abundances of OI in depleted gas have both been directly observed and inferred from observations of other molecules. A possible explanation is that OI is bound to grains by fixing (get hydrogenated to form ices) rather than sticking (van der Waals bonding to the surface potential), which will become less efficient in high density gas. We will present a stochastic gas-grain model including the kinetics of OI fixing - demonstrating the possibility of elevated O2 abundances at times when CO is significantly depleted - as well as results from searches for O2 emission in a small sample of starless depletion cores using Herschel HIFI.
|
|
| 31. |
- Wirström, Eva, 1977, et al.
(författare)
-
Ground-state ammonia and water in absorption towards Sgr B2
- 2010
-
Ingår i: Astronomy and Astrophysics. - Paris, France : EDP Sciences. - 0004-6361 .- 1432-0746. ; 522:1, s. A19, 1-9
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Observations of transitions to the ground-state of a molecule are essential to obtain a complete picture of its excitation and chemistry in the interstellar medium, especially in diffuse and/or cold environments. For the important interstellar molecules H2O and NH3, these ground-state transitions are heavily absorbed by the terrestrial atmosphere, hence not observable from the ground.Aims: We attempt to understand the chemistry of nitrogen, oxygen, and their important molecular forms, NH3 and H2O in the interstellar medium of the Galaxy.Methods: We have used the Odin* submillimetre-wave satellite telescope to observe the ground state transitions of ortho-ammonia and ortho-water, including their 15N, 18O, and 17O isotopologues, towards Sgr B2. The extensive simultaneous velocity coverage of the observations, >500 km s-1, ensures that we can probe the conditions of both the warm, dense gas of the molecular cloud Sgr B2 near the Galactic centre, and the more diffuse gas in the Galactic disk clouds along the line-of-sight.Results: We present ground-state NH3 absorption in seven distinct velocity features along the line-of-sight towards Sgr B2. We find a nearly linear correlation between the column densities of NH3 and CS, and a square-root relation to N2H+. The ammonia abundance in these diffuse Galactic disk clouds is estimated to be about 0.5–1 × 10-8, similar to that observed for diffuse clouds in the outer Galaxy. On the basis of the detection of H_218O absorption in the 3 kpc arm, and the absence of such a feature in the H_217O spectrum, we conclude that the water abundance is around 10-7, compared to ~10-8 for NH3. The Sgr B2 molecular cloud itself is seen in absorption in NH3, 15NH3, H2O, H_218O, and H_217O, with emission superimposed on the absorption in the main isotopologues. The non-LTE excitation of NH3 in the environment of Sgr B2 can be explained without invoking an unusually hot (500 K) molecular layer. A hot layer is similarly not required to explain the line profiles of the 11,0≥ts10,1 transition from H2O and its isotopologues. The relatively weak 15NH3 absorption in the Sgr B2 molecular cloud indicates a high [ 14N/15N] isotopic ratio >600. The abundance ratio of H_218O and H_217O is found to be relatively low, 2.5–3. These results together indicate that the dominant nucleosynthesis process in the Galactic centre is CNO hydrogen burning.Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes), and the centre National d'Études Spatiales (CNES, France). The Swedish Space Corporation (SSC) was the industrial prime contractor and is also responsible for the satellite operation.
|
|
| 32. |
- Wirström, Eva, 1977, et al.
(författare)
-
HCN observations of comets C/2013 R1 (Lovejoy) and C/2014 Q2 (Lovejoy)
- 2016
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 588, s. Art. no. A72-
-
Tidskriftsartikel (refereegranskat)abstract
- HCN J = 1-0 emission from the long-period comet C/2013 R1 (Lovejoy) was observed from the Onsala Space Observatory on multiple occasions during the month before its perihelion passage on December 22, 2013. We report detections for seven different dates, spanning heliocentric distances (Rh) decreasing from 0.94 to 0.82 au. Estimated HCN production rates are generally higher than previously reported for the same time period, but the implied increase in production rate with heliocentric distance, QHCN Rh -3.2, represent well the overall documented increase since it was first observed at Rh = 1.35. The implied mean HCN abundance relative to water in R1 Lovejoy is 0.2%. We also report on a detection of HCN with the new 3 mm receiver system at Onsala Space Observatory in comet C/2014 Q2 (Lovejoy) on January 14, 2015, when its heliocentric distance was 1.3 au. Relative to comet C/2013 R1 (Lovejoy), the HCN production rate of C/2014 Q2 (Lovejoy) was more than 5 times higher at similar heliocentric distances, and the implied HCN abundance relative to water 0.09%.
|
|
| 33. |
- Wirström, Eva, 1977, et al.
(författare)
-
ISOTOPIC ANOMALIES IN PRIMITIVE SOLAR SYSTEM MATTER: SPIN-STATE-DEPENDENT FRACTIONATION OF NITROGEN AND DEUTERIUM IN INTERSTELLAR CLOUDS
- 2012
-
Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 757:1, s. L11-
-
Tidskriftsartikel (refereegranskat)abstract
- Organic material found in meteorites and interplanetary dust particles is enriched in D and 15N. This is consistentwith the idea that the functional groups carrying these isotopic anomalies, nitriles and amines, were formed byion–molecule chemistry in the protosolar nebula. Theoretical models of interstellar fractionation at lowtemperaturespredict large enrichments in both D and 15N and can account for the largest isotopic enrichments measured incarbonaceous meteorites. However, more recent measurements have shown that, in some primitive samples, a large15N enrichment does not correlate with one in D, and that some D-enriched primitive material displays little, ifany, 15N enrichment. By considering the spin-state dependence in ion–molecule reactions involving the ortho andpara forms of H2, we show that ammonia and related molecules can exhibit such a wide range of fractionation forboth 15N and D in dense cloud cores.We also show that while the nitriles, HCN and HNC, contain the greatest 15Nenrichment, this is not expected to correlate with extreme D enrichment. These calculations therefore support theview that solar system 15N and D isotopic anomalies have an interstellar heritage. We also compare our results toexisting astronomical observations and briefly discuss future tests of this model.
|
|
| 34. |
- Wirström, Eva, 1977, et al.
(författare)
-
Observational constraints on the formation of interstellar methanol
- 2008
-
Ingår i: in Proceedings of "Organic Matter in Space", Hong Kong Feb. 18-22, 2008, IAU symposium 251, eds. S. Kwok, S. Sandfjord, Cambridge University Press. - 9780521889827 ; , s. 143-144
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The processes by which methanol, one of the most abundant interstellar organics, is formed in the interstellar medium are not yet accurately known. Pure gas-phase chemistry models fail to reproduce observed abundances by orders of magnitude, pointing to formation on grains and subsequent desorption.Observations of methanol and its isotopologue 13CH3OH in several sources have been used to trace the origin, and thus the formation routes of methanol on interstellar grains, by means of isotope labelling a posteriori.
|
|
| 35. |
- Wirström, Eva, 1977, et al.
(författare)
-
Observational tests of interstellar methanol formation
- 2011
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 533, s. A24-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. It has been established that the classical gas-phase production of interstellar methanol (CH(3)OH) cannot explain observed abundances. Instead it is now generally thought that the main formation path has to be by successive hydrogenation of solid CO on interstellar grain surfaces. Aims. While theoretical models and laboratory experiments show that methanol is efficiently formed from CO on cold grains, our aim is to test this scenario by astronomical observations of gas associated with young stellar objects (YSOs). Methods. We have observed the rotational transition quartets J = 2(K) - 1(K) of (12)CH(3)OH and (13)CH(3)OH at 96.7 and 94.4 GHz, respectively, towards a sample of massive YSOs in different stages of evolution. In addition, the J = 1-0 transitions of (12)C(18)O and (13)C(18)O were observed towards some of these sources. We use the (12)C/(13)C ratio to discriminate between gas-phase and grain surface origin: If methanol is formed from CO on grains, the ratios should be similar in CH(3)OH and CO. If not, the ratio should be higher in CH(3)OH due to (13)C fractionation in cold CO gas. We also estimate the abundance ratios between the nuclear spin types of methanol (E and A). If methanol is formed on grains, this ratio is likely to have been thermalized at the low physical temperature of the grain, and therefore show a relative over-abundance of A-methanol. Results. We show that the (12)C/(13)C isotopic ratio is very similar in gas-phase CH(3)OH and C(18)O, on the spatial scale of about 40 '', towards four YSOs. For two of our sources we find an overabundance of A-methanol as compared to E-methanol, corresponding to nuclear spin temperatures of 10 and 16 K. For the remaining five sources, the methanol E/A ratio is less than unity. Conclusions. While the (12)C/(13)C ratio test is consistent with methanol formation from hydrogenation of CO on grain surfaces, the result of the E/A ratio test is inconclusive.
|
|
| 36. |
- Wirström, Eva, 1977, et al.
(författare)
-
Observations of Carbon Isotopic Fractionation in Interstellar Formaldehyde
- 2012
-
Ingår i: 43rd Lunar and Planetary Science Conference. ; 43, s. 1611-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- While solar system organics exhibit small fluctuations in δ^1^3C as compared to δ^1^5N and δD, an interstellar origin cannot be excluded. This study off ^1^3C fractionation in the cold, dense ISM reveals an enrichment in H_2CO that remains to be explained.
|
|
| 37. |
- Wirström, Eva, 1977, et al.
(författare)
-
Odin * CO and 13CO J=5-4 mapping of Orion KL - a step towards accurate water abundances
- 2006
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 453, s. 979-987
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. The very high main beam efficiency (90%) of the telescope on the sub-millimetre wave satellite Odin, in combination with the small calibration errors in the absence of atmospheric attenuation, assures that observed line brightness temperatures are very accurately determined. Based on this, we attempt to determine the column density distribution of H-2, and the ortho-water abundance, in the Orion KL region.Methods. We have, for the first time, mapped the (CO)-C-12 J = 5-4 emission in a 7' x 7' region covering Orion KL, observed simultaneously with a (CO)-C-13 J = 5-4 map. Also presented are (CO)-O-18 J = 5-4 emission data at four different positions and a (CO)-O-17 J = 5-4 emission spectrum detected towards the Orion KL position. The Odin mapping was performed at 1' spacing ( beam full width at half maximum 126'' at 557 GHz).Results. The CO J = 5-4 narrow line emission from this region mainly arises in the warm, dense gas at the interface ( the photon-dominated region) between the M42 HII region and the Orion A molecular cloud, the Orion PDR. The (CO)-C-12 and (CO)-C-13 J = 5-4 emission maps have been used to determine the column density distribution of H-2 gas across the Orion KL region. The results have been verified by comparing to column densities obtained using the decidedly optically thin (CO)-O-18 emission as input to the RADEX radiative transfer code. We find H-2 column densities ranging from 5 x 10(21) cm(-2) at map edges to 7 x 10(22) cm(-2) at the molecular ridge. The mass of the gas in the mapped region is estimated to be 480 M-circle dot, of which 320 M-circle dot is situated towards the molecular ridge. We estimate that about half of this mass belongs to the warm Orion PDR interface layer. Finally, based on data from the positions where (CO)-O-18 J = 5-4 has been observed, we estimate the ortho-water abundance in the Orion PDR layer to be >= 8 x 10(-8), higher than previously estimated.
|
|
| 38. |
- Wirström, Eva, 1977, et al.
(författare)
-
Revised Models of Interstellar Nitrogen Isotopic Fractionation
- 2018
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 474:3, s. 3720-3726
-
Tidskriftsartikel (refereegranskat)abstract
- Nitrogen-bearing molecules in cold molecular clouds exhibit a range of isotopic fractionation ratios and these molecules may be the precursors of 15N enrichments found in comets and meteorites. Chemical model calculations indicate that atom-molecular ion and ion-molecule reactions could account for most of the fractionation patterns observed. However, recent quantum-chemical computations demonstrate that several of the key processes are unlikely to occur in dense clouds. Related model calculations of dense cloud chemistry show that the revised 15N enrichments fail to match observed values. We have investigated the effects of these reaction rate modifications on the chemical model of Wirström et al. (2012) for which there are significant physical and chemical differences with respect to other models. We have included 15N fractionation of CN in neutral-neutral reactions and also updated rate coefficients for key reactions in the nitrogen chemistry. We find that the revised fractionation rates have the effect of suppressing 15N enrichment in ammonia at all times, while the depletion is even more pronounced, reaching 14N/15N ratios of >2000. Taking the updated nitrogen chemistry into account, no significant enrichment occurs in HCN or HNC, contrary to observational evidence in dark clouds and comets, although the 14N/15N ratio can still be below 100 in CN itself. However, such low CN abundances are predicted that the updated model falls short of explaining the bulk 15N enhancements observed in primitive materials. It is clear that alternative fractionating reactions are necessary to reproduce observations, so further laboratory and theoretical studies are urgently needed.
|
|
| 39. |
- Wirström, Eva, 1977
(författare)
-
Studies in Molecular Astrophysics and Astrobiology
- 2006
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The molecules of the interstellar medium (ISM) can be used as probes of the physical conditions in a range of different types of interstellar environment, for example star forming regions. The first chapters of this thesis describe the theory and the observational techniques used to study the rotational transition emission from, and the present knowledge of, these molecules. In particular, models and observations of prebiotic molecules, like the simplest amino acid glycine, have become increasingly interesting in the light of a possible connection to the beginning of life on Earth. Searches for two prebiotic molecules, vinyl acetylene (C2H3 CCH) and amino acetonitrile (H2N CH2 CN), towards hot star-forming cores with the Onsala 20 metre radio telescope are presented. Neither of the molecules has been detected, but towards the richest molecular-line source observed, Orion KL, the upper column density limits are determined to N(C2H3 CCH) 5x10-8.Footnote 1: Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes), and the Centre National d'Etudes Spatiales (CNES, France). The Swedish Space Corporation (SSC) was the industrial prime contractor and is also responsible for the satellite operation.
|
|
| 40. |
- Wirström, Eva, 1977, et al.
(författare)
-
The 12C/13C ratio as a chemistry indicator
- 2011
-
Ingår i: The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Toledo, Spain, May 30-June 3, 2011, #384. ; 280:384
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Isotopic ratios of elements are considered powerful tools, e.g. in tracing the origin of solar system body materials, or the degree of nucleosynthesis processing throughout the Galaxy. In interstellar molecules, some isotopic ratios like H/D and 12C/13C can also be used as indicators of their chemical origin. Isotope fractionation in gas-phase chemical reactions and gas-dust interaction makes observations of the ratio between 12C and 13C isotopologues suitable to distinguish between different formation scenarios. We will present observations of the 12C/13C ratio in methanol (CH3OH) and formaldehyde (CH2O) towards a sample of embedded, massive young stellar objects. In relation to this we also present results from theoretical modeling showing the usefulness of the 12C/13C ratio as a chemistry indicator.
|
|
| 41. |
- Wirström, Eva, 1977, et al.
(författare)
-
Using Methanol Beacons to Find Water in the Dark
- 2013
-
Ingår i: The Universe Explored by Herschel, 15 – 18 October 2013, Noordwijk, The Netherlands.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Interstellar methanol is only formed efficiently from hydrogenation of COmolecules accreted onto grains, and icy grain mantles are observed to consist of 1-30% methanol relative to water. In regions of both low and high mass star formation gas-phase methanol abundances are consistent with partial or complete removal of the ices, either by thermal evaporation or by shock-induced sputtering in outflows. However, the widespread presence of gas-phase methanol in molecular clouds attests to some non-thermal desorption process at work. In particular, distinct peaks of methanol emission at positions significantly offset from protostellar activity implies a transient desorption process, such as clump-clump collisions, rather than a continuous one like photodesorption. Such processes are likely to disrupt a major part of the ice mantles and lead to high gas-phase water abundances clearly distinguishable from what is expected from photodesorption or steady-state gas-phase chemistry.We will report on the first detection of gas-phase water in a cold dark cloud - well offset from protostellar activity - resulting from a small scale survey with Herschel HIFI towards methanol peaks. Physical properties of the sources as well as implications for mantle desorption mechanisms and chemistry in dark clouds will be discussed and compared to those of active star formation.
|
|
