The c2d Spitzer Spectroscopic Survey of Ices around Low-Mass Young Stellar Objects. I. H2O and the 5-8 μm Bands

By K. Pontoppidan, A. Boogert, Helen J. Fraser, E. F. Dishoeck, G. Blake, F. Lahuis, K. Oberg, N. Evans, C. Salyk. 2007

473 citations recorded by the source corpus.

To study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low-luminosity YSOs (L ∼ 0.1–10 L☉) using 3-38 μm Spitzer and ground-based spectra. The sample is complemented with previously published Spitzer spectra of background stars and with ISO spectra of well-studied massive YSOs (L ∼ 105 L☉). The long-known 6.0 and 6.85 μm bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. The 6.0 μm band is often deeper than expected from the bending mode of pure solid H2O. The additional 5-7 μm absorption consists of five independent components, which, by comparison to laboratory studies, must be from at least eight different carriers. Much of this absorption is due to simple species likely formed by grain surface chemistry, at abundances of 1%-30% for CH3OH, 3%-8% for NH3, 1%-5% for HCOOH, ~6% for H2CO, and ~0.3% for HCOO− relative to solid H2O. The 6.85 μm band has one or two carriers, of which one may be less volatile than H2O. Its carrier(s) formed early in the molecular cloud evolution and do not survive in the diffuse ISM. If an NH4+-containing salt is the carrier, its abundance relative to solid H2O is ~7%, demonstrating the efficiency of low-temperature acid-base chemistry or cosmic-ray-induced reactions. Possible origins are discussed for enigmatic, very broad absorption between 5 and 8 μm. Finally, the same ices are observed toward massive and low-mass YSOs, indicating that processing by internal UV radiation fields is a minor factor in their early chemical evolution.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/26c2500333d67e47d069a57ea79c54db8567c576

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In Astronomy and Astrophysics

1. R. Garrod
2. N. Evans II
3. P. Caselli
4. E. Dishoeck
5. E. Bergin
6. P. Myers
7. E. Herbst
8. M. Tafalla

In Atmospheric Science

1. R. Garrod
2. P. Caselli
3. E. Dishoeck
4. E. Herbst
5. E. Bergin
6. A. Tielens
7. M. Tafalla
8. H. Cuppen

In Spectroscopy

1. R. Garrod
2. P. Caselli
3. E. Dishoeck
4. E. Herbst
5. E. Bergin
6. N. Evans II
7. K. Oberg
8. A. Tielens

Citations in the corpus

• Star Formation in the Milky Way and Nearby Galaxies (2012, background): “Freeze-out of CO and conversion to CO2 ice causes further complications in cold regions of high column density (Lee et al. 2003; Pontoppidan et al. 2008; Whittet et al. 2007), but other issues likely dominate the interpretational uncertainties for most extragalactic CO observations.”
• THE HERSCHEL ORION PROTOSTAR SURVEY: SPECTRAL ENERGY DISTRIBUTIONS AND FITS USING A GRID OF PROTOSTELLAR MODELS (2016, background): “Near 10 µm and 18 µm, absorption by sub-micron-sized silicate grains causes broad absorption features; in addition, there are several ice absorption features across the infrared spectral range (Boogert et al. 2008; Pontoppidan et al. 2008).”
• Observations of the Icy Universe (2015, methodology): “The 5- component fits applied to LYSOs and Galactic MYSOs (Pontoppidan et al., 2008) were also applied to MYSOs in the GC CMZ (An et al., 2011) and in the LMC (Seale et al., 2011).”
• ON THE FORMATION OF CO2 AND OTHER INTERSTELLAR ICES (2011, background): “Such conditions could explain the particularly high methanol-ice fractions detected in low-mass star-forming cores (Boogert et al. 2008).”
• Hydrogenation reactions in interstellar CO ice analogues A combined experimental/theoretical approach (2009, background): “CH3OH ice has also been detected toward low-mass YSOs with abundances ranging from <1% to more than 25% of the H2O ice abundance (Pontoppidan et al. 2003; Boogert et al. 2008).”
• Complex Chemistry in Star-forming Regions: An Expanded Gas-Grain Warm-up Chemical Model (2008, background): “Table 5 shows observationally determined ice compositions towards two embedded YSOs, and towards the galactic center infrared source, Sgr A* (Gibb et al. 2000).”
• Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results (2010, methodology): “Finally, submillimeter continuum maps obtained with JCMTSCUBA, IRAM-MAMBO, and/or APEX-LABOCA are available at 10–20″ resolution for most embedded sources (e.g., Di Francesco et al. 2008), as are ground-based and mid-IR Spitzer observations of ices (Gibb et al. 2004b; Boogert et al. 2008).”
• A COLD COMPLEX CHEMISTRY TOWARD THE LOW-MASS PROTOSTAR B1-b: EVIDENCE FOR COMPLEX MOLECULE PRODUCTION IN ICES (2010, background): “Still, 0.5% of the CH3OH ice must evaporate to account for the observed CH3OH abundance of ∼2×10−9 toward the ‘core’, assuming a H2O abundance of ∼ 5× 10 −5 with respect to H2.”
• Photodesorption of ices I: CO, N₂, and CO₂ (2008, background): “This remains to be investigated, especially for the astrophysically relevant cases of CO ice on top of CO2 ice, and CO:CO2 and CO2:H2O mixtures (Pontoppidan et al. 2008).”
• THE SPITZER c2d LEGACY RESULTS: STAR-FORMATION RATES AND EFFICIENCIES; EVOLUTION AND LIFETIMES (2008, background): “…part to geometry of the envelope-disk interface, the inner radius of the envelope (Jørgensen et al. 2005), different amounts of scattered light, emission from jets in the 4.5 µm band, and deep ice features (see, e.g., Huard et al. 2006; Dunham et al. 2006; Bourke et al. 2006; Boogert et al. 2008).”
• Astrochemistry and compositions of planetary systems (2020, background): “Figure 8 shows ice spectra observed towards protostars in ρ-Oph F, and how the ice composition changes with distance from the central dense core (Pontoppidan et al. 2008b).”
• WATER, O2, AND ICE IN MOLECULAR CLOUDS (2008, background): “However, there is some evidence that either pure CO ice pockets form, or the CO accretes on top of an already formed layer of water ice (Tielens et al. 1991; Lee et al. 2005; Pontoppidan et al. 2004, 2008).”
• THE SPITZER ICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS (2011, unknown): “The c2d program (Evans et al. 2003) obtained IRS spectra of 50 lowmass protostars (Boogert et al. 2008; Pontoppidan et al. 2008; Öberg et al. 2008; Bottinelli et al. 2010, from now on Paper I-IV), providing an unprecedented sample size that complements the ISO data on high-mass protostars.”