The c2d Spitzer Spectroscopic Survey of Ices Around Low-Mass Young Stellar Objects. IV. NH3 and CH3OH

Дата и время публикации : 2010-05-12T23:19:00Z

Авторы публикации и институты :
Sandrine Bottinelli (Leiden Observatory, Leiden University, Centre d’Etude Spatiale des Rayonnements, CESR, Université de Toulouse)
A. C. Adwin Boogert (IPAC, NASA Herschel Science Center)
Jordy Bouwman (Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden)
Martha Beckwith (Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, Department of Chemistry and Chemical Biology, Cornell University)
Ewine F. van Dishoeck (Leiden Observatory, Leiden University, Max-Planck Institute für Extraterrestrische Physik)
Karin I. Oberg (Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, Harvard-Smithsonian Center for Astrophysics)
Klaus M. Pontoppidan (California Institute of Technology, Division of Geological and Planetary Sciences)
Harold Linnartz (Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden)
Geoffrey A. Blake (California Institute of Technology, Division of Geological and Planetary Sciences)
Neal J. Evans II (Department of Astronomy, University of Texas at Austin)
Fred Lahuis (SRON Netherlands Institute for Space Research, Leiden Observatory, Leiden University)

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: 31 pages, 15 figures, accepted for publication in ApJ
Первичная категория: astro-ph.GA

Все категории : astro-ph.GA

Краткий обзор статьи: NH3 and CH3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and HCOOCH3. Despite a number of recent studies, little is known about their abundances in the solid state. (…) In this work, we investigate the ~ 8-10 micron 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 10 micron silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH3- and CH3OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ~9 micron in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH3 nu_2 umbrella mode, and derive abundances with respect to water between ~2 and 15%. Simultaneously, we also revisited the case of CH3OH ice by studying the nu_4 C-O stretch mode of this molecule at ~9.7 micron in 16 objects, yielding abundances consistent with those derived by Boogert et al. 2008 (hereafter paper I) based on a simultaneous 9.75 and 3.53 micron data analysis. Our study indicates that NH3 is present primarily in H2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH3OH being in an almost pure methanol ice, or mixed mainly with CO or CO2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH3 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.

Category: Physics