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The c2d Spitzer Spectroscopic Survey of Ices Around Low-mass Young Stellar Objects. IV. NH_3 and CH_3OH

Bottinelli, Sandrine and Boogert, A. C. Adwin and Bouwman, Jordy and Beckwith, Martha and van Dishoeck, Ewine F. and Öberg, Karin I. and Pontoppidan, Klaus M. and Linnartz, Harold and Blake, Geoffrey A. and Evans, Neal J. and Lahuis, Fred (2010) The c2d Spitzer Spectroscopic Survey of Ices Around Low-mass Young Stellar Objects. IV. NH_3 and CH_3OH. Astrophysical Journal, 718 (2). pp. 1100-1117. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20100806-081927930

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Abstract

NH_3 and CH_3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and CH3OCH3. Despite a number of recent studies, little is known about their abundances in the solid state. This is particularly the case for low-mass protostars, for which only the launch of the Spitzer Space Telescope has permitted high-sensitivity observations of the ices around these objects. In this work, we investigate the ~8–10μm region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass young stellar objects (YSOs). These data are part of a survey of interstellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10μm silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH_(3-) and CH_3OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ~9μm in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH_3 ν_2 umbrella mode and derive abundances with respect to water between ~2% and 15%. Simultaneously, we also revisited the case of CH_3OH ice by studying the ν_4 C–O stretch mode of this molecule at ~9.7μm in 16 objects, yielding abundances consistent with those derived by Boogert et al. based on a simultaneous 9.75 and 3.53μm data analysis. Our study indicates that NH_3 is present primarily in H_2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH_3OH being in an almost pure methanol ice, or mixed mainly with CO or CO_2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH_3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10%–20% of nitrogen is locked up in known ices.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-637X/718/2/1100DOIArticle
http://iopscience.iop.org/0004-637X/718/2/1100PublisherArticle
ORCID:
AuthorORCID
van Dishoeck, Ewine F.0000-0001-7591-1907
Pontoppidan, Klaus M.0000-0001-7552-1562
Blake, Geoffrey A.0000-0003-0787-1610
Additional Information:© 2010 The American Astronomical Society. Received 2010 January 4; accepted 2010 May 6; published 2010 July 13. We thank Karoliina Isokoski (Leiden) for recording additional laboratory spectra during the completion of this study. We are also thankful to Helen Fraser and the c2d team for stimulating discussions and useful comments on the manuscript. Support for this work, part of the Spitzer Legacy Science Program, was provided by NASA through contracts 1224608, 1230779, 1230782, 1256316, and 1279952 issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Astrochemistry in Leiden is supported by a Spinoza grant of The Netherlands Organization for Scientific Research (NWO) and by a NOVA grant. The laboratory work is financially supported by “Stichting voor Fundamenteel Onderzoek der Materie” (FOM) and “The Netherlands Research School for Astronomy” (NOVA). Funding for K.I.Ö. was provided by a grant from the European Early Stage Training Network (MEST-CT-2004-504604). Support for K.M.P. was provided by NASA through Hubble Fellowship grant 1201.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.
Funders:
Funding AgencyGrant Number
NASA/JPL1224608
NASA/JPL1230779
NASA/JPL1230782
NASA/JPL1256316
NASA/JPL1279952
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
European Early Stage Training NetworkMEST-CT-2004-504604
NASA Hubble Fellowship1201.01
Subject Keywords:astrochemistry; infrared: ISM; ISM: abundances; ISM: molecules; stars: formation
Classification Code:PACS: 95.80.+p; 95.30.Ft; 97.21.+a; 98.58.Bz; 98.38.Bn
Record Number:CaltechAUTHORS:20100806-081927930
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20100806-081927930
Official Citation:Sandrine Bottinelli et al 2010 ApJ 718 1100 doi: 10.1088/0004-637X/718/2/1100
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:19311
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:06 Aug 2010 16:47
Last Modified:22 Aug 2017 19:59

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