| 1. |
- Coutens, A., et al.
(författare)
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VLA cm-wave survey of young stellar objects in the Oph A cluster: Constraining extreme UV- And X-ray-driven disk photoevaporation: A pathfinder for Square Kilometre Array studies
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 631
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Tidskriftsartikel (refereegranskat)abstract
- Observations of young stellar objects (YSOs) in centimeter bands can probe the continuum emission from growing dust grains, ionized winds, and magnetospheric activity that are intimately connected to the evolution of protoplanetary disks and the formation of planets. We carried out sensitive continuum observations toward the Ophiuchus A star-forming region, using the Karl G. Jansky Very Large Array (VLA) at 10 GHz over a field-of-view of 6′ and with a spatial resolution of θmaj ×θmin ∼ 0.′′4 × 0.′′2. We achieved a 5 μJy beam-1 rms noise level at the center of our mosaic field of view. Among the 18 sources we detected, 16 were YSOs (three Class 0, five Class I, six Class II, and two Class III) and two were extragalactic candidates. We find that thermal dust emission generally contributed less than 30% of the emission at 10 GHz. The radio emission is dominated by other types of emission, such as gyro-synchrotron radiation from active magnetospheres, free-free emission from thermal jets, free-free emission from the outflowing photoevaporated disk material, and synchrotron emission from accelerated cosmic-rays in jet or protostellar surface shocks. These different types of emission could not be clearly disentangled. Our non-detections for Class II/III disks suggest that extreme UV-driven photoevaporation is insufficient to explain disk dispersal, assuming that the contribution of UV photoevaporating stellar winds to radio flux does not evolve over time. The sensitivity of our data cannot exclude photoevaporation due to the role of X-ray photons as an efficient mechanism for disk dispersal. Deeper surveys using the Square Kilometre Array (SKA) will have the capacity to provide significant constraints to disk photoevaporation.
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| 2. |
- Fayolle, E. C., et al.
(författare)
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Protostellar and cometary detections of organohalogens
- 2017
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 1:10, s. 703-708
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Tidskriftsartikel (refereegranskat)abstract
- Organohalogens, a class of molecules that contain at least one halogen atom bonded to carbon, are abundant on the Earth where they are mainly produced through industrial and biological processes(1). Consequently, they have been proposed as biomarkers in the search for life on exoplanets(2). Simple halogen hydrides have been detected in interstellar sources and in comets, but the presence and possible incorporation of more complex halogen-containing molecules such as organohalogens into planet-forming regions is uncertain(3,4). Here we report the interstellar detection of two isotopologues of the organohalogen CH3Cl and put some constraints on CH3F in the gas surrounding the low-mass protostar IRAS 16293-2422, using the Atacama Large Millimeter/submillimeter Array (ALMA). We also find CH3Cl in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) by using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. The detections reveal an efficient pre-planetary formation pathway of organohalogens. Cometary impacts may deliver these species to young planets and should thus be included as a potential abiotical production source when interpreting future organohalogen detections in atmospheres of rocky planets.
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| 3. |
- Taquet, V., et al.
(författare)
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Linking interstellar and cometary O2: A deep search for 16O18O in the solar-Type protostar IRAS 16293b-2422
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 618
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Tidskriftsartikel (refereegranskat)abstract
- Recent measurements carried out at comet 67P/Churyumov-Gerasimenko (67P) with the Rosetta probe revealed that molecular oxygen, O2, is the fourth most abundant molecule in comets. Models show that O2 is likely of primordial nature, coming from the interstellar cloud from which our solar system was formed. However, gaseous O2 is an elusive molecule in the interstellar medium with only one detection towards quiescent molecular clouds, in the ρ Oph A core. We perform a deep search for molecular oxygen, through the 21-01 rotational transition at 234 GHz of its 16O18O isotopologue, towards the warm compact gas surrounding the nearby Class 0 protostar IRAS 16293-2422 B with the ALMA interferometer. We also look for the chemical daughters of O2, HO2, and H2O2. Unfortunately, the H2O2 rotational transition is dominated by ethylene oxide c-C2H4O while HO2 is not detected. The targeted 16O18O transition is surrounded by two brighter transitions at ± 1 km s-1 relative to the expected 16O18O transition frequency. After subtraction of these two transitions, residual emission at a 3σ level remains, but with a velocity offset of 0.3-0.5 km s-1 relative to the source velocity, rendering the detection "tentative". We derive the O2 column density for two excitation temperatures Tex of 125 and 300 K, as indicated by other molecules, in order to compare the O2 abundance between IRAS 16293 and comet 67P. Assuming that 16O18O is not detected and using methanol CH3OH as a reference species, we obtain a [O2]/[CH3OH] abundance ratio lower than 2-5, depending on the assumed Tex, a three to four times lower abundance than the [O2]/[CH3OH] ratio of 5-15 found in comet 67P. Such a low O2 abundance could be explained by the lower temperature of the dense cloud precursor of IRAS 16293 with respect to the one at the origin of our solar system that prevented efficient formation of O2 in interstellar ices.
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| 4. |
- Calcutt, H., et al.
(författare)
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The ALMA-PILS survey: complex nitriles towards IRAS 16293-2422
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
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Tidskriftsartikel (refereegranskat)abstract
- Context. Complex organic molecules are readily detected in the inner regions of the gaseous envelopes of forming protostars. Their detection is crucial to understanding the chemical evolution of the Universe and exploring the link between the early stages of star formation and the formation of solar system bodies, where complex organic molecules have been found in abundance. In particular, molecules that contain nitrogen are interesting due to the role nitrogen plays in the development of life and the compact scales such molecules have been found to trace around forming protostars. Aims. The goal of this work is to determine the inventory of one family of nitrogen-bearing organic molecules, complex nitriles (molecules with a -C N functional group) towards two hot corino sources in the low-mass protostellar binary IRAS 16293-2422. This work explores the abundance differences between the two sources, the isotopic ratios, and the spatial extent derived from molecules containing the nitrile functional group. Methods. Using data from the Protostellar Interferometric Line Survey (PILS) obtained with ALMA, we determine abundances and excitation temperatures for the detected nitriles. We also present a new method for determining the spatial structure of sources with high line density and large velocity gradients-Velocity-corrected INtegrated emission (VINE) maps. Results. We detect methyl cyanide (CH3CN) as well as five of its isotopologues, including CHD2CN, which is the first detection in the interstellar medium (ISM). We also detect ethyl cyanide (C2H5CN), vinyl cyanide (C2H3CN), and cyanoacetylene (HC3N). We find that abundances are similar between IRAS 16293A and IRAS 16293B on small scales except for vinyl cyanide which is only detected towards the latter source. This suggests an important difference between the sources either in their evolutionary stage or warm-up timescales. We also detect a spatially double-peaked emission for the first time in molecular emission in the A source, suggesting that this source is showing structure related to a rotating toroid of material. Conclusions. With high-resolution observations, we have been able to show for the first time a number of important similarities and differences in the nitrile chemistry in these objects. These illustrate the utility of nitriles as potential tracers of the physical conditions in star-forming regions.
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| 5. |
- Calcutt, Hannah, 1988, et al.
(författare)
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The ALMA-PILS survey: first detection of methyl isocyanide (CH3NC) in a solar-type protostar
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 617
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Tidskriftsartikel (refereegranskat)abstract
- Methyl isocyanide (CH3NC) is the isocyanide with the largest number of atoms confirmed in the interstellar medium (ISM), but it is not an abundant molecule, having only been detected towards a handful of objects. Conversely, its isomer, methyl cyanide (CH3CN), is one of the most abundant complex organic molecules detected in the ISM, with detections in a variety of low- and high-mass sources. We use ALMA observations from the Protostellar Interferometric Line Survey (PILS) to search for methyl isocyanide and compare its abundance with that of its isomer methyl cyanide. We use a new line catalogue from the Cologne Database for Molecular Spectroscopy (CDMS) to identify methyl isocyanide lines. We also model the chemistry with an updated version of the three-phase chemical kinetics model MAGICKAL, presenting the first chemical modelling of methyl isocyanide to date. We detect methyl isocyanide for the first time in a solar-type protostar, IRAS 16293-2422 B, and present upper limits for its companion protostar, IRAS 16293-2422 A. Methyl isocyanide is found to be at least 20 times more abundant in source B compared to source A, with a CH3CN/CH3NC abundance ratio of 200 in IRAS 16293-2422 B and >5517 in IRAS 16293-2422 A. We also present the results of a chemical model of methyl isocyanide chemistry in both sources, and discuss the implications on methyl isocyanide formation mechanisms and the relative evolutionary stages of both sources.
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| 6. |
- Calcutt, Hannah, 1988, et al.
(författare)
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The ALMA-PILS survey: propyne (CH3CCH) in IRAS 16293–2422
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 631
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Tidskriftsartikel (refereegranskat)abstract
- Context. Propyne (CH3CCH), also known as methyl acetylene, has been detected in a variety of environments, from Galactic star-forming regions to extragalactic sources. These molecules are excellent tracers of the physical conditions in star-forming regions, allowing the temperature and density conditions surrounding a forming star to be determined. Aims. This study explores the emission of CH3CCH in the low-mass protostellar binary, IRAS 16293–2422, and examines the spatial scales traced by this molecule, as well as its formation and destruction pathways. Methods. Atacama Large Millimeter/submillimeter Array (ALMA) observations from the Protostellar Interferometric Line Survey (PILS) were used to determine the abundances and excitation temperatures of CH3CCH towards both protostars. This data allows us to explore spatial scales from 70 to 2400 au. This data is also compared with the three-phase chemical kinetics model MAGICKAL, to explore the chemical reactions of this molecule. Results. CH3CCH is detected towards both IRAS 16293A and IRAS 16293B, and is found the hot corino components, one around each source, in the PILS dataset. Eighteen transitions above 3σ are detected, enabling robust excitation temperatures and column densities to be determined in each source. In IRAS 16293A, an excitation temperature of 90 K and a column density of 7.8 × 1015 cm−2 best fits the spectra. In IRAS 16293B, an excitation temperature of 100 K and 6.8 × 1015 cm−2 best fits the spectra. The chemical modelling finds that in order to reproduce the observed abundances, both gas-phase and grain-surface reactions are needed. The gas-phase reactions are particularly sensitive to the temperature at which CH4 desorbs from the grains. Conclusions. CH3CCH is a molecule whose brightness and abundance in many different regions can be utilised to provide a benchmark of molecular variation with the physical properties of star-forming regions. It is essential when making such comparisons, that the abundances are determined with a good understanding of the spatial scale of the emitting region, to ensure that accurate abundances are derived.
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| 7. |
- Coutens, A., et al.
(författare)
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First detection of cyanamide (NH2CN) towards solar-type protostars
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 612
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Tidskriftsartikel (refereegranskat)abstract
- Searches for the prebiotically relevant cyanamide (NH 2 CN) towards solar-type protostars have not been reported in the literature. We present here the first detection of this species in the warm gas surrounding two solar-type protostars, using data from the Atacama Large Millimeter/Submillimeter Array Protostellar Interferometric Line Survey (PILS) of IRAS 16293-2422 B and observations from the IRAM Plateau de Bure Interferometer of NGC 1333 IRAS2A. We also detected the deuterated and 13 C isotopologs of NH 2 CN towards IRAS 16293-2422 B. This is the first detection of NHDCN in the interstellar medium. Based on a local thermodynamic equilibrium analysis, we find that the deuteration of cyanamide (∼1.7%) is similar to that of formamide (NH 2 CHO), which may suggest that these two molecules share NH 2 as a common precursor. The NH 2 CN/NH 2 CHO abundance ratio is about 0.2 for IRAS 16293-2422 B and 0.02 for IRAS2A, which is comparable to the range of values found for Sgr B2. We explored the possible formation of NH 2 CN on grains through the NH 2 + CN reaction using the chemical model MAGICKAL. Grain-surface chemistry appears capable of reproducing the gas-phase abundance of NH 2 CN with the correct choice of physical parameters.
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| 8. |
- Coutens, A., et al.
(författare)
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The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 623
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen oxides are thought to play a significant role as a nitrogen reservoir and to potentially participate in the formation of more complex species. Until now, only NO, NO, and HNO have been detected in the interstellar medium. We report the first interstellar detection of nitrous acid (HONO). Twelve lines were identified towards component B of the low-mass protostellar binary IRAS 16293-2422 with the Atacama Large Millimeter/submillimeter Array, at the position where NO and NO have previously been seen. A local thermodynamic equilibrium model was used to derive the column density (∼9 × 1014 cm in a 0 .″5 beam) and excitation temperature (∼100 K) of this molecule. HNO, NO, NO+, and HNO3 were also searched for in the data, but not detected. We simulated the HONO formation using an updated version of the chemical code Nautilus and compared the results with the observations. The chemical model is able to reproduce satisfactorily the HONO, NO, and NO abundances, but not the NO, HNO, and NHOH abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting the amount of HNO and NHOH present in the gas phase. Other options are UV photodestruction of these species in ices or missing reactions potentially relevant at protostellar temperatures.
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| 9. |
- Coutens, A., et al.
(författare)
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The ALMA-PILS survey: First detections of deuterated formamide and deuterated isocyanic acid in the interstellar medium
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 590
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Tidskriftsartikel (refereegranskat)abstract
- Formamide (NH2CHO) has previously been detected in several star-forming regions and is thought to be a precursor for different prebiotic molecules. Its formation mechanism is still debated, however. Observations of formamide, related species, and their isopotologues may provide useful clues to the chemical pathways leading to their formation. The Protostellar Interferometric Line Survey (PILS) represents an unbiased, high angular resolution and sensitivity spectral survey of the low-mass protostellar binary IRAS 16293-2422 with the Atacama Large Millimeter/submillimeter Array (ALMA). For the first time, we detect the three singly deuterated forms of NH2CHO (NH2CDO, cis-and trans-NHDCHO), as well as DNCO towards the component B of this binary source. The images reveal that the different isotopologues are all present in the same region. Based on observations of the 13C isotopologues of formamide and a standard 12C/13C ratio, the deuterium fractionation is found to be similar for the three different forms with a value of about 2%. The DNCO/HNCO ratio is also comparable to the D/H ratio of formamide (~1%). These results are in agreement with the hypothesis that NH2CHO and HNCO are chemically related through grain-surface formation.
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| 10. |
- Drozdovskaya, M. N., et al.
(författare)
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The ALMA-PILS survey: The sulphur connection between protostars and comets: IRAS 16293-2422 B and 67P/Churyumov-Gerasimenko
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 476:4, s. 4949-4964
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Tidskriftsartikel (refereegranskat)abstract
- The evolutionary past of our Solar system can be pieced together by comparing analogous lowmass protostars with remnants of our Protosolar Nebula - comets. Sulphur-bearing molecules may be unique tracers of the joint evolution of the volatile and refractory components. ALMA Band 7 data from the large unbiased Protostellar Interferometric Line Survey are used to search for S-bearing molecules in the outer disc-like structure, ~60 au from IRAS 16293-2422 B, and are compared with data on 67P/Churyumov-Gerasimenko (67P/C-G) stemming from the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument aboard Rosetta. Species such as SO 2 , SO, OCS, CS, H 2 CS, H 2 S, and CH 3 SH are detected via at least one of their isotopologues towards IRAS 16293-2422 B. The search reveals a first-time detection of OC 33 S towards this source and a tentative first-time detection of C 36 S towards a low-mass protostar. The data show that IRAS 16293-2422 B contains much more OCS than H 2 S in comparison to 67P/C-G; meanwhile, the SO/SO 2 ratio is in close agreement between the two targets. IRAS 16293-2422 B has a CH 3 SH/H 2 CS ratio in range of that of our Solar system (differences by a factor of 0.7-5.3). It is suggested that the levels of UV radiation during the initial collapse of the systems may have varied and have potentially been higher for IRAS 16293-2422 B due to its binary nature; thereby, converting more H 2 S into OCS. It remains to be conclusively tested if this also promotes the formation of S-bearing complex organics. Elevated UV levels of IRAS 16293-2422 B and a warmer birth cloud of our Solar system may jointly explain the variations between the two low-mass systems.
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