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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
S H J Wallström, E Lagadec, S Muller, J H Black, N L J Cox, R Galván-Madrid, K Justtanont, S Longmore, H Olofsson, R D Oudmaijer, G Quintana-Lacaci, R Szczerba, W Vlemmings, H van Winckel, A Zijlstra
Yellow hypergiants are rare and represent a fast evolutionary stage of massive evolved stars. That evolutionary phase is characterised by a very intense mass loss, the understanding of which is still very limited. Here we report ALMA Compact Array observations of a 50″-mosaic toward the Fried Egg nebula, around one of the few Galactic yellow hypergiants IRAS 17163-3907. The emission from the (12)CO J=2-1 line, H30α recombination line, and continuum is imaged at a resolution of ~8″, revealing the morphology of the molecular environment around the star...
January 10, 2017: Astronomy and Astrophysics
M Santander-García, V Bujarrabal, J Alcolea, A Castro-Carrizo, C Sánchez Contreras, G Quintana-Lacaci, R L M Corradi, R Neri
CONTEXT: The mechanism behind the shaping of bipolar planetary nebulae is still poorly understood. It is becoming increasingly clear that the main agents must operate at their innermost regions, where a significant equatorial density enhancement should be present and related to the collimation of light and jet launching from the central star preferentially towards the polar directions. Most of the material in this equatorial condensation must be lost during the asymptotic giant branch as stellar wind and later released from the surface of dust grains to the gas phase in molecular form...
January 2017: Astronomy and Astrophysics
L Velilla Prieto, C Sánchez Contreras, J Cernicharo, M Agúndez, G Quintana-Lacaci, V Bujarrabal, J Alcolea, C Balança, F Herpin, K M Menten, F Wyrowski
AIMS: We aim to investigate the physical and chemical properties of the molecular envelope of the oxygen-rich AGB star IK Tau. METHODS: We carried out a millimeter wavelength line survey between ~79 and 356 GHz with the IRAM-30 m telescope. We analysed the molecular lines detected in IK Tau using the population diagram technique to derive rotational temperatures and column densities. We conducted a radiative transfer analysis of the SO2 lines, which also helped us to verify the validity of the approximated method of the population diagram for the rest of the molecules...
January 2017: Astronomy and Astrophysics
S Cuadrado, J R Goicoechea, O Roncero, A Aguado, B Tercero, J Cernicharo
As many organic molecules, formic acid (HCOOH) has two conformers (trans and cis). The energy barrier to internal conversion from trans to cis is much higher than the thermal energy available in molecular clouds. Thus, only the most stable conformer (trans) is expected to exist in detectable amounts. We report the first interstellar detection of cis-HCOOH. Its presence in ultraviolet (UV) irradiated gas exclusively (the Orion Bar photodissociation region), with a low trans-to-cis abundance ratio of 2.8 ± 1...
December 2016: Astronomy and Astrophysics
S P Treviño-Morales, A Fuente, Á Sánchez-Monge, P Pilleri, J R Goicoechea, V Ossenkopf-Okada, E Roueff, J R Rizzo, M Gerin, O Berné, J Cernicharo, M Gónzalez-García, C Kramer, S García-Burillo, J Pety
The CO(+) reactive ion is thought to be a tracer of the boundary between a HII region and the hot molecular gas. In this study, we present the spatial distribution of the CO(+) rotational emission toward the Mon R2 star-forming region. The CO(+) emission presents a clumpy ring-like morphology, arising from a narrow dense layer around the HII region. We compare the CO(+) distribution with other species present in photon-dominated regions (PDR), such as [CII] 158 µm, H2 S(3) rotational line at 9.3 µm, polycyclic aromatic hydrocarbons (PAHs) and HCO(+)...
September 15, 2016: Astronomy and Astrophysics
V Bujarrabal, A Castro-Carrizo, J Alcolea, M Santander-García, H Van Winckel, C Sánchez Contreras
AIMS: We aim to study the rotating and expanding gas in the Red Rectangle, which is a well known object that recently left the asymptotic giant branch (AGB) phase. We analyze the properties of both components and the relation between them. Rotating disks have been very elusive in post-AGB nebulae, in which gas is almost always found to be in expansion. METHODS: We present new high-quality ALMA observations of C(17)O J=6-5 and H(13)CN J=4-3 line emission and results from a new reduction of already published (13)CO J=3-2 data...
September 2016: Astronomy and Astrophysics
A Fuente, J Cernicharo, E Roueff, M Gerin, J Pety, N Marcelino, R Bachiller, B Lefloch, O Roncero, A Aguado
CONTEXT: Barnard B1b has revealed as one of the most interesting globules from the chemical and dynamical point of view. It presents a rich molecular chemistry characterized by large abundances of deuterated and complex molecules. Furthermore, it hosts an extremely young Class 0 object and one candidate to First Hydrostatic Core (FHSC) proving the youth of this star forming region. AIMS: Our aim is to determine the cosmic ray ionization rate, [Formula: see text], and the depletion factors in this extremely young star forming region...
September 2016: Astronomy and Astrophysics
M R Schmidt, J H He, R Szczerba, V Bujarrabal, J Alcolea, J Cernicharo, L Decin, K Justtanont, D Teyssier, K M Menten, D A Neufeld, H Olofsson, P Planesas, A P Marston, A M Sobolev, A de Koter, F L Schöier
CONTEXT: A discrepancy exists between the abundance of ammonia (NH3) derived previously for the circumstellar envelope (CSE) of IRC+10216 from far-IR submillimeter rotational lines and that inferred from radio inversion or mid-infrared (MIR) absorption transitions. AIMS: To address the discrepancy described above, new high-resolution far-infrared (FIR) observations of both ortho- and para-NH3 transitions toward IRC+10216 were obtained with Herschel, with the goal of determining the ammonia abundance and constraining the distribution of NH3 in the envelope of IRC+10216...
August 2016: Astronomy and Astrophysics
S B Bteich, B Tercero, J Cernicharo, R A Motiyenko, L Margulès, J-C Guillemin
CONTEXT: More than 30 cyanide derivatives of simple organic molecules have been detected in the interstellar medium, but only one dicarbonitrile has been found and that very recently. There is still a lack of high-resolution spectroscopic data particularly for dinitriles derivatives. The carbonyl cyanide molecule is a new and interesting candidate for astrophysical detection. It could be formed by the reaction of CO and CN radicals, or by substitution of the hydrogen atom by a cyano group in cyanoformaldehyde, HC(=O)CN, that has already been detected in the interstellar medium...
August 2016: Astronomy and Astrophysics
G Quintana-Lacaci, M Agúndez, J Cernicharo, V Bujarrabal, C Sánchez Contreras, A Castro-Carrizo, J Alcolea
AIMS: Our knowledge of the chemical properties of the circumstellar ejecta of the most massive evolved stars is particularly poor. We aim to study the chemical characteristics of the prototypical yellow hypergiant star, IRC +10420. For this purpose, we obtained full line surveys at 1 and 3 mm atmospheric windows. METHODS: We have identified 106 molecular emission lines from 22 molecular species. Approximately half of the molecules detected are N-bearing species, in particular HCN, HNC, CN, NO, NS, PN, and N2H(+)...
August 2016: Astronomy and Astrophysics
L Kolesniková, J L Alonso, C Bermúdez, E R Alonso, B Tercero, J Cernicharo, J-C Guillemin
AIMS: The recent discovery of methyl isocyanate (CH3NCO) in Sgr B2(N) and Orion KL makes methyl cyanate (CH3OCN) a potential molecule in the interstellar medium. The aim of this work is to fulfill the first requirement for its unequivocal identification in space, i.e. the availability of transition frequencies with high accuracy. METHODS: The room-temperature rotational spectrum of methyl cyanate was recorded in the millimeter wave domain from 130 to 350 GHz. All rotational transitions revealed A-E splitting owing to methyl internal rotation and were globally analyzed using the ERHAM program...
July 2016: Astronomy and Astrophysics
Gabriele Cazzoli, Valerio Lattanzi, Till Kirsch, Jürgen Gauss, Belén Tercero, José Cernicharo, Cristina Puzzarini
CONTEXT: Despite the fact that many sulfur-bearing molecules, ranging from simple diatomic species up to astronomical complex molecules, have been detected in the interstellar medium, the sulfur chemistry in space is largely unknown and a depletion in the abundance of S-containing species has been observed in the cold, dense interstellar medium (ISM). The chemical form of the missing sulfur has yet to be identified. AIMS: For these reasons, in view of the fact that there is a large abundance of triatomic species harbouring sulfur, oxygen, and hydrogen, we decided to investigate the HSO radical in the laboratory to try its astronomical detection...
July 2016: Astronomy and Astrophysics
S Pacheco-Vázquez, A Fuente, C Baruteau, O Berné, M Agúndez, R Neri, J R Goicoechea, J Cernicharo, R Bachiller
CONTEXT: Transitional disks are structures of dust and gas around young stars with large inner cavities in which planet formation may occur. Lopsided dust distributions are observed in the dust continuum emission at millimeter wavelengths. These asymmetrical structures can be explained as being the result of an enhanced gas density vortex where the dust is trapped, potentially promoting the rapid growth to the planetesimal scale. AIMS: AB Aur hosts a transitional disk with a clear horseshoe morphology which strongly suggests the presence of a dust trap...
May 2016: Astronomy and Astrophysics
J Cernicharo, Z Kisiel, B Tercero, L Kolesniková, I R Medvedev, A López, S Fortman, M Winnewisser, F C de Lucia, J L Alonso, J-C Guillemin
The recent analysis of the composition of the frozen surface of comet 67P/Churyumov-Gerasimenko has revealed a significant number of complex organic molecules. Methyl isocyanate (CH3NCO) is one of the more abundant species detected on the comet surface. In this work we report extensive characterization of its rotational spectrum resulting in a list of 1269 confidently assigned laboratory lines and its detection in space towards the Orion clouds where 399 lines of the molecule have been unambiguously identified...
March 2016: Astronomy and Astrophysics
B Tercero, J Cernicharo, A López, N Brouillet, L Kolesniková, R A Motiyenko, L Margulès, J L Alonso, J-C Guillemin
We report on the tentative detection of trans ethyl methyl ether (tEME), t-CH3CH2OCH3, through the identification of a large number of rotational lines from each one of the spin states of the molecule towards Orion KL. We also search for gauche-trans-n-propanol, Gt-n-CH3CH2CH2OH, an isomer of tEME in the same source. We have identified lines of both species in the IRAM 30 m line survey and in the ALMA Science Verification data. We have obtained ALMA maps to establish the spatial distribution of these species...
October 1, 2015: Astronomy and Astrophysics
M Agúndez, J Cernicharo, P de Vicente, N Marcelino, E Roueff, A Fuente, M Gerin, M Guélin, C Albo, A Barcia, L Barbas, R Bolaño, F Colomer, M C Diez, J D Gallego, J Gómez-González, I López-Fernández, J A López-Fernández, J A López-Pérez, I Malo, J M Serna, F Tercero
Cyanogen (NCCN) is the simplest member of the series of dicyanopolyynes. It has been hypothesized that this family of molecules can be important constituents of interstellar and circumstellar media, although the lack of a permanent electric dipole moment prevents its detection through radioastronomical techniques. Here we present the first solid evidence of the presence of cyanogen in interstellar clouds through the detection of its protonated form toward the cold dark clouds TMC-1 and L483. Protonated cyanogen (NCCNH(+)) has been identified through the J = 5 - 4 and J = 10 - 9 rotational transitions using the 40m radiotelescope of Yebes and the IRAM 30m telescope...
July 1, 2015: Astronomy and Astrophysics
O Berné, J Montillaud, C Joblin
Fullerenes have been recently detected in various circumstellar and interstellar environments, raising the question of their formation pathway. It has been proposed that they can form at the low densities found in the interstellar medium by the photo-chemical processing of large polycyclic aromatic hydrocarbons (PAHs). Following our previous work on the evolution of PAHs in the NGC 7023 reflection nebula, we evaluate, using photochemical modeling, the possibility that the PAH C66H20 (i.e. circumovalene) can lead to the formation of C60 upon irradiation by ultraviolet photons...
May 1, 2015: Astronomy and Astrophysics
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