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Astronomy and Astrophysics

Sarah Massalkhi, M Agúndez, J Cernicharo, L Velilla Prieto, J R Goicoechea, G Quintana-Lacaci, J P Fonfría, J Alcolea, V Bujarrabal
Context: Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si-C bond detected in C-rich AGB stars are SiC2 , SiC, and Si2 C. To date, the ring molecule SiC2 has been observed in a handful of evolved stars, while SiC and Si2 C have only been detected in the C-star envelope IRC +10216...
March 2018: Astronomy and Astrophysics
M Guélin, N A Patel, M Bremer, J Cernicharo, A Castro-Carrizo, J Pety, J P Fonfría, M Agúndez, M Santander-García, G Quintana-Lacaci, L Velilla Prieto, R Blundell, P Thaddeus
During their late pulsating phase, AGB stars expel most of their mass in the form of massive dusty envelopes, an event that largely controls the composition of interstellar matter. The envelopes, however, are distant and opaque to visible and NIR radiation: their structure remains poorly known and the mass-loss process poorly understood. Millimeter-wave interferometry, which combines the advantages of longer wavelength, high angular resolution and very high spectral resolution is the optimal investigative tool for this purpose...
February 2018: Astronomy and Astrophysics
Emeric Bron, Chloé Daudon, Jérôme Pety, François Levrier, Maryvonne Gerin, Pierre Gratier, Jan H Orkisz, Viviana Guzman, Sébastien Bardeau, Javier R Goicoechea, Harvey Liszt, Karin Öberg, Nicolas Peretto, Albrecht Sievers, Pascal Tremblin
Context: Previous attempts at segmenting molecular line maps of molecular clouds have focused on using position-position-velocity data cubes of a single molecular line to separate the spatial components of the cloud. In contrast, wide field spectral imaging over a large spectral bandwidth in the (sub)mm domain now allows one to combine multiple molecular tracers to understand the different physical and chemical phases that constitute giant molecular clouds (GMCs). Aims: We aim at using multiple tracers (sensitive to different physical processes and conditions) to segment a molecular cloud into physically/chemically similar regions (rather than spatially connected components), thus disentangling the different physical/chemical phases present in the cloud...
February 2018: Astronomy and Astrophysics
I Tanarro, B Alemán, P de Vicente, J D Gallego, J R Pardo, G Santoro, K Lauwaet, F Tercero, A Díaz-Pulido, E Moreno, M Agúndez, J R Goicoechea, J M Sobrado, J A López, L Martínez, J L Doménech, V J Herrero, J M Hernández, R J Peláez, J A López-Pérez, J Gómez-González, J L Alonso, E Jiménez, D Teyssier, K Makasheva, M Castellanos, C Joblin, J A Martín-Gago, J Cernicharo
We present a proof of concept on the coupling of radio astronomical receivers and spectrometers with chemical reactors and the performances of the resulting setup for spectroscopy and chemical simulations in laboratory astrophysics. Several experiments including cold plasma generation and UV photochemistry were performed in a 40 cm long gas cell placed in the beam path of the Aries 40 m radio telescope receivers operating in the 41-49 GHz frequency range interfaced with fast Fourier transform spectrometers providing 2 GHz bandwidth and 38 kHz resolution...
January 2018: Astronomy and Astrophysics
G Quintana-Lacaci, J Cernicharo, L Velilla Prieto, M Agúndez, A Castro-Carrizo, J P Fonfría, S Massalkhi, J R Pardo
Context: ALMA is providing us essential information on where certain molecules form. Observing where these molecules emission arises from, the physical conditions of the gas, and how this relates with the presence of other species allows us to understand the formation of many species, and to significantly improve our knowledge of the chemistry that occurs in the space. Aims: We studied the molecular distribution of NaCN around IRC +10216, a molecule detected previously, but whose origin is not clear...
November 2017: Astronomy and Astrophysics
Nick L J Cox, Jan Cami, Amin Farhang, Jonathan Smoker, Ana Monreal-Ibero, Rosine Lallement, Peter J Sarre, Charlotte C M Marshall, Keith T Smith, Christopher J Evans, Pierre Royer, Harold Linnartz, Martin A Cordiner, Christine Joblin, Jacco Th van Loon, Bernard H Foing, Neil H Bhatt, Emeric Bron, Meriem Elyajouri, Alex de Koter, Pascale Ehrenfreund, Atefeh Javadi, Lex Kaper, Habib G Khosroshadi, Mike Laverick, Franck Le Petit, Giacomo Mulas, Evelyne Roueff, Farid Salama, Marco Spaans
The carriers of the diffuse interstellar bands (DIBs) are largely unidentified molecules ubiquitously present in the interstellar medium (ISM). After decades of study, two strong and possibly three weak near-infrared DIBs have recently been attributed to the [Formula: see text] fullerene based on observational and laboratory measurements. There is great promise for the identification of the over 400 other known DIBs, as this result could provide chemical hints towards other possible carriers. In an effort to systematically study the properties of the DIB carriers, we have initiated a new large-scale observational survey: the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES)...
October 2017: Astronomy and Astrophysics
M Gerin, J Pety, B Commerçon, A Fuente, J Cernicharo, N Marcelino, A Ciardi, D C Lis, E Roueff, H A Wootten, E Chapillon
Aims: The formation epoch of protostellar disks is debated because of the competing roles of rotation, turbulence, and magnetic fields in the early stages of low-mass star formation. Magnetohydrodynamics simulations of collapsing cores predict that rotationally supported disks may form in strongly magnetized cores through ambipolar diffusion or misalignment between the rotation axis and the magnetic field orientation. Detailed studies of individual sources are needed to cross check the theoretical predictions...
October 2017: Astronomy and Astrophysics
J Cernicharo, M Agúndez, L Velilla Prieto, M Guélin, J R Pardo, C Kahane, C Marka, C Kramer, S Navarro, G Quintana-Lacaci, J P Fonfría, N Marcelino, B Tercero, E Moreno, S Massalkhi, M Santander-García, M C McCarthy, C A Gottlieb, J L Alonso
We report the discovery in space of methyl silane, CH3 SiH3 , from observations of ten rotational transitions between 80 and 350 GHz ( J u from 4 to 16) with the IRAM 30 m radio telescope. The molecule was observed in the envelope of the C-star IRC +10216. The observed profiles and our models for the expected emission of methyl silane suggest that the it is formed in the inner zones of the circumstellar envelope, 1-40 R * , with an abundance of (0.5-1) × 10-8 relative to H2 . We also observed several rotational transitions of silyl cyanide (SiH3 CN), confirming its presence in IRC +10216 in particular, and in space in general...
October 2017: Astronomy and Astrophysics
A Fuente, M Gerin, J Pety, B Commerçon, M Agúndez, J Cernicharo, N Marcelino, E Roueff, D C Lis, H A Wootten
The extremely young Class 0 object B1b-S and the first hydrostatic core (FSHC) candidate, B1b-N, provide a unique opportunity to study the chemical changes produced in the elusive transition from the prestellar core to the protostellar phase. We present 40"×70" images of Barnard 1b in the13 CO 1→0, C18 O 1→0, NH2 D 11,1 a →10,1 s , and SO 32 →21 lines obtained with the NOEMA interferometer. The observed chemical segregation allows us to unveil the physical structure of this young protostellar system down to scales of ∼500 au...
October 2017: Astronomy and Astrophysics
C H M Pabst, J R Goicoechea, D Teyssier, O Berné, B B Ochsendorf, M G Wolfire, R D Higgins, D Riquelme, C Risacher, J Pety, F Le Petit, E Roueff, E Bron, A G G M Tielens
CONTEXT: L1630 in the Orion B molecular cloud, which includes the iconic Horsehead Nebula, illuminated by the star system σ Ori, is an example of a photodissociation region (PDR). In PDRs, stellar radiation impinges on the surface of dense material, often a molecular cloud, thereby inducing a complex network of chemical reactions and physical processes. AIMS: Observations toward L1630 allow us to study the interplay between stellar radiation and a molecular cloud under relatively benign conditions, that is, intermediate densities and an intermediate UV radiation field...
October 2017: Astronomy and Astrophysics
S Ramstedt, S Mohamed, W H T Vlemmings, T Danilovich, M Brunner, E De Beck, E M L Humphreys, M Lindqvist, M Maercker, H Olofsson, F Kerschbaum, G Quintana-Lacaci
Context: Recent observations at subarcsecond resolution, now possible also at submillimeter wavelengths, have shown intricate circumstellar structures around asymptotic giant branch (AGB) stars, mostly attributed to binary interaction. The results presented here are part of a larger project aimed at investigating the effects of a binary companion on the morphology of circumstellar envelopes (CSEs) of AGB stars. Aims: AGB stars are characterized by intense stellar winds that build CSEs around the stars...
September 21, 2017: Astronomy and Astrophysics
Gabriele Cazzoli, Valerio Lattanzi, Sonia Coriani, Jürgen Gauss, Claudio Codella, Andrés Asensio Ramos, José Cernicharo, Cristina Puzzarini
Context: Magnetic fields play a fundamental role in star formation processes and the best method to evaluate their intensity is to measure the Zeeman effect of atomic and molecular lines. However, a direct measurement of the Zeeman spectral pattern from interstellar molecular species is challenging due to the high sensitivity and high spectral resolution required. So far, the Zeeman effect has been detected unambiguously in star forming regions for very few non-masing species, such as OH and CN...
September 2017: Astronomy and Astrophysics
J R Rizzo, B Tercero, J Cernicharo
Context: The nearby massive star-forming region Orion KL is one of the richest molecular reservoirs known in our Galaxy. The region hosts newly formed protostars, and the strong interaction between their radiation and their outflows with the environment results in a series of complex chemical processes leading to a high diversity of interstellar tracers. The region is therefore one of the most frequently observed sources, and the site where many molecular species have been discovered for the first time...
September 2017: Astronomy and Astrophysics
O Berné, N L J Cox, G Mulas, C Joblin
Emission of fullerenes in their infrared vibrational bands has been detected in space near hot stars. The proposed attribution of the diffuse interstellar bands at 9577 and 9632 Å to electronic transitions of the buckminsterfullerene cation (i.e. [Formula: see text]) was recently supported by new laboratory data, confirming the presence of this species in the diffuse interstellar medium (ISM). In this letter, we present the detection, also in the diffuse ISM, of the 17.4 and 18.9 μm emission bands commonly attributed to vibrational bands of neutral C60...
September 2017: Astronomy and Astrophysics
J Champion, O Berné, S Vicente, I Kamp, F Le Petit, A Gusdorf, C Joblin, J R Goicoechea
Context: Protoplanetary disks undergo substantial mass-loss by photoevaporation, a mechanism which is crucial to their dynamical evolution. However, the processes regulating the gas energetics have not been well constrained by observations so far. Aims: We aim at studying the processes involved in disk photoevaporation when it is driven by far-UV photons (i.e. 6 < E < 13.6 eV). Methods: We present a unique Herschel survey and new ALMA observations of four externally-illuminated photoevaporating disks (a...
August 2017: Astronomy and Astrophysics
S Cuadrado, J R Goicoechea, J Cernicharo, A Fuente, J Pety, B Tercero
We investigate the presence of complex organic molecules (COMs) in strongly UV-irradiated interstellar molecular gas. We have carried out a complete millimetre (mm) line survey using the IRAM 30 m telescope towards the edge of the Orion Bar photodissociation region (PDR), close to the H2 dissociation front, a position irradiated by a very intense far-UV (FUV) radiation field. These observations have been complemented with 8.5″ resolution maps of the H2 CO J K a , K c = 51,5 → 41,4 and C18 O J = 3 → 2 emission at 0...
July 2017: Astronomy and Astrophysics
S König, S Martín, S Muller, J Cernicharo, K Sakamoto, L K Zschaechner, E M L Humphreys, T Mroczkowski, M Krips, M Galametz, S Aalto, W H T Vlemmings, J Ott, D S Meier, A Fuente, S García-Burillo, R Neri
Aims: Extragalactic observations of water emission can provide valuable insights into the excitation of the interstellar medium. In particular they allow us to investigate the excitation mechanisms in obscured nuclei, i.e. whether an active galactic nucleus or a starburst dominate. Methods: We use sub-arcsecond resolution observations to tackle the nature of the water emission in Arp 220. ALMA Band 5 science verification observations of the 183 GHz H2 O 313 -220 line, in conjunction with new ALMA Band 7 H2 O 515 -422 data at 325 GHz, and supplementary 22 GHz H2 O 616 - 523 VLA observations, are used to better constrain the parameter space in the excitation modelling of the water lines...
June 2017: Astronomy and Astrophysics
Javier R Goicoechea, Sara Cuadrado, Jérôme Pety, Emeric Bron, John H Black, José Cernicharo, Edwige Chapillon, Asunción Fuente, Maryvonne Gerin
We report high angular resolution (4.9″×3.0″) images of reactive ions SH(+), HOC(+), and SO(+) toward the Orion Bar photodissociation region (PDR). We used ALMA-ACA to map several rotational lines at 0.8 mm, complemented with multi-line observations obtained with the IRAM 30 m telescope. The SH(+) and HOC(+) emission is restricted to a narrow layer of 2″- to 10″-width (≈800 to 4000 AU depending on the assumed PDR geometry) that follows the vibrationally excited [Formula: see text] emission. Both ions efficiently form very close to the H/H2 transition zone, at a depth of Av≲1 mag into the neutral cloud, where abundant C(+), S(+), and [Formula: see text] coexist...
May 2017: Astronomy and Astrophysics
M Agúndez, J Cernicharo, G Quintana-Lacaci, A Castro-Carrizo, L Velilla Prieto, N Marcelino, M Guélin, C Joblin, J A Martín-Gago, C A Gottlieb, N A Patel, M C McCarthy
Linear carbon chains are common in various types of astronomical molecular sources. Possible formation mechanisms involve both bottom-up and top-down routes. We have carried out a combined observational and modeling study of the formation of carbon chains in the C-star envelope IRC +10216, where the polymerization of acetylene and hydrogen cyanide induced by ultraviolet photons can drive the formation of linear carbon chains of increasing length. We have used ALMA to map the emission of λ 3 mm rotational lines of the hydrocarbon radicals C2H, C4H, and C6H, and the CN-containing species CN, C3N, HC3N, and HC5N with an angular resolution of ~1″...
May 2017: Astronomy and Astrophysics
A Parikka, E Habart, J Bernard-Salas, J R Goicoechea, A Abergel, P Pilleri, E Dartois, C Joblin, M Gerin, B Godard
CONTEXT: The methylidyne cation (CH(+)) and hydroxyl (OH) are key molecules in the warm interstellar chemistry, but their formation and excitation mechanisms are not well understood. Their abundance and excitation are predicted to be enhanced by the presence of vibrationally excited H2 or hot gas (~500-1000 K) in photodissociation regions with high incident FUV radiation field. The excitation may also originate in dense gas (> 10(5) cm(-3)) followed by nonreactive collisions with H2, H, and electrons...
March 2017: Astronomy and Astrophysics
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