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  • 1
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    Induced massive star formation in the trifid nebula? (1998)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1998-10-17
    Description: The Trifid nebula is a young (10(5) years) galactic HII region where several protostellar sources have been detected with the infrared space observatory. The sources are massive (17 to 60 solar masses) and are associated with molecular gas condensations at the edges or inside the nebula. They appear to be in an early evolutionary stage and may represent the most recent generation of stars in the Trifid. These sources range from dense, apparently still inactive cores to more evolved sources, undergoing violent mass ejection episodes, including a source that powers an optical jet. These observations suggest that the protostellar sources may have evolved by induced star formation in the Trifid nebula.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cernicharo -- Lefloch -- Cox -- Cesarsky -- Esteban -- Yusef-Zadeh -- Mendez -- Acosta-Pulido -- Garcia Lopez RJ -- Heras -- New York, N.Y. -- Science. 1998 Oct 16;282(5388):462-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉J. Cernicharo, Instituto de Estructura de la Materia, Dpto. Fisica Molecular, Consejo Superior de Investigaciones Cientificas, (CSIC), Serrano 123, 28006 Madrid, Spain. B. Lefloch, Instituto de Estructura de la Materia, Dpto. Fisica Molecu.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9774270" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Windows through the dusty disks surrounding the youngest low-mass protostellar objects (2000)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2000-04-28
    Description: The formation and evolution of young low-mass stars are characterized by important processes of mass loss and accretion occurring in the innermost regions of their placentary circumstellar disks. Because of the large obscuration of these disks at optical and infrared wavelengths in the early protostellar stages (class 0 sources), they were previously detected only at radio wavelengths using interferometric techniques. We have detected with the Infrared Space Observatory the mid-infrared (mid-IR) emission associated with the class 0 protostar VLA1 in the HH1-HH2 region located in the Orion nebula. The emission arises in three wavelength windows (at 5. 3, 6.6, and 7.5 micrometers) where the absorption due to ices and silicates has a local minimum that exposes the central part of the young protostellar system to mid-IR investigations. The mid-IR emission arises from a central source with a diameter of 4 astronomical units at an averaged temperature of approximately 700 K, deeply embedded in a dense region with a visual extinction of 80 to 100 magnitudes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cernicharo, J -- Noriega-Crespo, A -- Cesarsky, D -- Lefloch, B -- Gonzalez-Alfonso, E -- Najarro, F -- Dartois, E -- Cabrit, S -- New York, N.Y. -- Science. 2000 Apr 28;288(5466):649-52.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Consejo Superior de Investigaciones Cientificas, Instituto de Estructura de la Materia, Departamento Fisica Molecular, Serrano 121, 28006 Madrid, Spain. cerni@astro.iem.csic.es〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10784443" target="_blank"〉PubMed〈/a〉
    Keywords: Astronomical Phenomena ; *Astronomy ; Carbon Dioxide ; Ice ; Methane ; Methanol ; Silicates ; Spectrophotometry, Infrared ; Temperature ; Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
    Electronic Resource
    Electronic Resource
    Far-Infrared CO Rotational Lines in the Orion Molecular Cloud (1998)
    Springer
    Astrophysics and space science 263 (1998), S. 205-208 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a high signal-to-noise grating spectrum between 43-196.9 μm of the Orion molecular cloud towards the massive star-forming region IRc2, obtained with the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). CO lines up to J=20-19 have been detected around Orion-IRc2, while in the central position higher quantum numbers have been found. Lines of the 13CO isotopic species have also been observed in several directions. In addition, high quality LWS-FP observations of some CO lines have been performed towards IRc2. The data analysis suggest that at least two regions of Orion-IRc2 contribute to the observed CO emission: the ridge, responsible of the spatial extension, and the plateau, dominating the line flux observed towards the center of the map. CO emission through the Orion molecular cloud has been studied in terms of temperature, column density and H2 volume density, using and Large Velocity Gradient (LVG) model. We find that the flux ratio of the several CO lines can not be explained in terms of an homogeneous source, but a gradient in temperature and density must be involved. Besides the CO lines, several molecular and fine-structure atomic lines have been detected in all observed positions. A detailed discussion of other molecular species rather than CO (H2O, OH...) can be found in the contribution by Cernicharo et al (1998).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002158210794
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  • 4
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    Gas-phase formation of the prebiotic molecule formamide: insights from new quantum computations (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-14
    Description: New insights into the formation of interstellar formamide, a species of great relevance in prebiotic chemistry, are provided by electronic structure and kinetic calculations for the reaction NH 2 + H 2 CO -〉 NH 2 CHO + H. Contrarily to what previously suggested, this reaction is essentially barrierless and can, therefore, occur under the low temperature conditions of intestellar objects thus providing a facile formation route of formamide. The rate coefficient parameters for the reaction channel leading to NH 2 CHO + H have been calculated to be A = 2.6 x 10 –12  cm 3  s –1 , β = –2.1 and = 26.9 K in the range of temperatures 10–300 K. Including these new kinetic data in a refined astrochemical model, we show that the proposed mechanism can well reproduce the abundances of formamide observed in two very different interstellar objects: the cold envelope of the Sun-like protostar IRAS16293–2422 and the molecular shock L1157-B2. Therefore, the major conclusion of this Letter is that there is no need to invoke grain-surface chemistry to explain the presence of formamide provided that its precursors, NH 2 and H 2 CO, are available in the gas phase.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Hot and dense water in the inner 25 au of SVS13-A (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-22
    Description: In the context of the ASAI (Astrochemical Surveys At IRAM) project, we carried out an unbiased spectral survey in the millimetre window towards the well known low-mass Class I source SVS13-A. The high sensitivity reached (3–12 mK) allowed us to detect at least six HDO broad (full width at half-maximum ~4–5 km s –1 ) emission lines with upper level energies up to E u = 837 K. A non-local thermodynamic equilibrium Large Velocity Gradient (LVG) analysis implies the presence of very hot (150–260 K) and dense (≥3  x  10 7  cm –3 ) gas inside a small radius (~25 au) around the star, supporting, for the first time, the occurrence of a hot corino around a Class I protostar. The temperature is higher than expected for water molecules are sublimated from the icy dust mantles (~100 K). Although we cannot exclude we are observing the effects of shocks and/or winds at such small scales, this could imply that the observed HDO emission is tracing the water abundance jump expected at temperatures ~220–250 K, when the activation barrier of the gas phase reactions leading to the formation of water can be overcome. We derive X ( HDO ) ~ 3  x  10 –6 , and a H 2 O deuteration ≥1.5  x  10 –2 , suggesting that water deuteration does not decrease as the protostar evolves from the Class 0 to the Class I stage.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Phosphorus-bearing molecules in solar-type star-forming regions: first PO detection (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-03
    Description: As part of the Large Program Astrochemical Surveys At IRAM, we have used the IRAM 30 m telescope to lead a systematic search for the emission of rotational transitions of P-bearing species between 80 and 350 GHz towards L1157-B1, a shock position in the solar-type star-forming region L1157. We report the detection of several transitions of PN and, for the first time, of pre-biotic molecule PO. None of these species are detected towards the driving protostar of the outflow L1157-mm. Analysis of the line profiles shows that PN arises from the outflow cavity, where SiO, a strong shock tracer, is produced. Radiative transfer analysis yields an abundance of 2.5  x  10 –9 and 0.9  x  10 –9 for PO and PN, respectively. These results imply a strong depletion (100) of phosphorus in the quiescent cloud gas. Shock modelling shows that atomic N plays a major role in the chemistry of PO and PN. The relative abundance of PO and PN brings constraints both on the duration of the pre-shock phase, which has to be ~10 6 yr, and on the shock parameters. The maximum temperature in the shock has to be larger than 4000 K, which implies a shock velocity of 40 km s –1 .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Shedding light on the formation of the pre-biotic molecule formamide with ASAI (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-10
    Description: Formamide (NH 2 CHO) has been proposed as a pre-biotic precursor with a key role in the emergence of life on Earth. While this molecule has been observed in space, most of its detections correspond to high-mass star-forming regions. Motivated by this lack of investigation in the low-mass regime, we searched for formamide, as well as isocyanic acid (HNCO), in 10 low- and intermediate-mass pre-stellar and protostellar objects. The present work is part of the IRAM Large Programme ASAI (Astrochemical Surveys At IRAM), which makes use of unbiased broad-band spectral surveys at millimetre wavelengths. We detected HNCO in all the sources and NH 2 CHO in five of them. We derived their abundances and analysed them together with those reported in the literature for high-mass sources. For those sources with formamide detection, we found a tight and almost linear correlation between HNCO and NH 2 CHO abundances, with their ratio being roughly constant – between 3 and 10 – across 6 orders of magnitude in luminosity. This suggests the two species are chemically related. The sources without formamide detection, which are also the coldest and devoid of hot corinos, fall well off the correlation, displaying a much larger amount of HNCO relative to NH 2 CHO. Our results suggest that, while HNCO can be formed in the gas-phase during the cold stages of star formation, NH 2 CHO forms most efficiently on the mantles of dust grains at these temperatures, where it remains frozen until the temperature rises enough to sublimate the icy grain mantles. We propose hydrogenation of HNCO as a likely formation route leading to NH 2 CHO.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Molecules with a peptide link in protostellar shocks: a comprehensive study of L1157 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-25
    Description: Interstellar molecules with a peptide link (–NH–C(=O)–), like formamide (NH 2 CHO), acetamide (NH 2 COCH 3 ) and isocyanic acid (HNCO), are particularly interesting for their potential role in pre-biotic chemistry. We have studied their emission in the protostellar shock regions L1157-B1 and L1157-B2, with the IRAM 30 m telescope, as part of the ASAI Large Programme. Analysis of the line profiles shows that the emission arises from the outflow cavities associated with B1 and B2. Molecular abundances of (0.4–1.1) 10 –8 and (3.3–8.8) 10 –8 are derived for formamide and isocyanic acid, respectively, from a simple rotational diagram analysis. Conversely, NH 2 COCH 3 was not detected down to a relative abundance of a few ≤10 –10 . B1 and B2 appear to be among the richest Galactic sources of HNCO and NH 2 CHO molecules. A tight linear correlation between their abundances is observed, suggesting that the two species are chemically related. Comparison with astrochemical models favours molecule formation on icy grain mantles, with NH 2 CHO generated from hydrogenation of HNCO.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    The density structure of the L1157 molecular outflow (2014)
    Oxford University Press
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    Publication Date: 2014-12-10
    Description: We present a multiline CS survey towards the brightest bow-shock B1 in the prototypical chemically active protostellar outflow L1157. We made use of (sub-)mm data obtained in the framework of the Chemical HErschel Surveys of Star forming regions and Astrochemical Surveys at IRAM (ASAI) key science programs. We detected 12 C 32 S, 12 C 34 S, 13 C 32 S, and 12 C 33 S emissions, for a total of 18 transitions, with E u up to ~180 K. The unprecedented sensitivity of the survey allows us to carefully analyse the line profiles, revealing high-velocity emission, up to 20 km s –1 with respect to the systemic. The profiles can be well fitted by a combination of two exponential laws that are remarkably similar to what previously found using CO. These components have been related to the cavity walls produced by the ~2000 yr B1 shock and the older (~4000 yr) B2 shock, respectively. The combination of low- and high-excitation CS emission was used to properly sample the different physical components expected in a shocked region. Our CS observations show that this molecule is highlighting the dense, n H 2 = 1–5 10 5  cm –3 , cavity walls produced by the episodic outflow in L1157. In addition, the highest excitation ( E u  ≥ 130 K) CS lines provide us with the signature of denser (1–5 10 6  cm –3 ) gas, associated with a molecular reformation zone of a dissociative J -type shock, which is expected to arise where the precessing jet impacting the molecular cavities. The CS fractional abundance increases up to ~10 –7 in all the kinematical components. This value is consistent with what previously found for prototypical protostars and it is in agreement with the prediction of the abundances obtained via the chemical code Astrochem.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Diagnosing shock temperature with NH3 and H2O profiles (2016)
    Oxford University Press
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    Publication Date: 2016-08-21
    Description: In a previous study of the L1157 B1 shocked cavity, a comparison between NH 3 (1 0 –0 0 ) and H 2 O(1 10 –1 01 ) transitions showed a striking difference in the profiles, with H 2 O emitting at definitely higher velocities. This behaviour was explained as a result of the high-temperature gas-phase chemistry occurring in the post-shock gas in the B1 cavity of this outflow. If the differences in behaviour between ammonia and water are indeed a consequence of the high gas temperatures reached during the passage of a shock, then one should find such differences to be ubiquitous among chemically rich outflows. In order to determine whether the difference in profiles observed between NH 3 and H 2 O is unique to L1157 or a common characteristic of chemically rich outflows, we have performed Herschel -HIFI observations of the NH 3 (1 0 –0 0 ) line at 572.5 GHz in a sample of eight bright low-mass outflow spots already observed in the H 2 O(1 10 –1 01 ) line within the Water In Star-forming regions with Herschel Key Programme. We detected the ammonia emission at high velocities at most of the outflows positions. In all cases, the water emission reaches higher velocities than NH 3 , proving that this behaviour is not exclusive of the L1157-B1 position. Comparisons with a gas–grain chemical and shock model confirms, for this larger sample, that the behaviour of ammonia is determined principally by the temperature of the gas.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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