THE SPITZER ICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS

By K. Oberg, A. Boogert, K. Pontoppidan, S. V. D. Broek, E. V. van Dishoeck, S. Bottinelli, G. Blake, N. Evans II. 2011

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Ices regulate much of the chemistry during star formation and account for up to 80% of the available oxygen and carbon. In this paper, we use the Spitzer c2d Legacy ice survey, complimented with data sets on ices in cloud cores and high-mass protostars, to determine standard ice abundances and to present a coherent picture of the evolution of ices during low- and high-mass star formation. The median ice composition H2O:CO:CO2:CH3OH:NH3:CH4:XCN is 100:29:29:3:5:5:0.3 and 100:13:13:4:5:2:0.6 toward low- and high-mass protostars, respectively, and 100:31:38:4:–:–:– in cloud cores. In the low-mass sample, the ice abundances with respect to H2O of CH4, NH3, and the component of CO2 mixed with H2O typically vary by <25%, indicative of co-formation with H2O. In contrast, some CO and CO2 ice components, XCN, and CH3OH vary by factors 2–10 between the lower and upper quartile. The XCN band correlates with CO, consistent with its OCN− identification. The origin(s) of the different levels of ice abundance variations are constrained by comparing ice inventories toward different types of protostars and background stars, through ice mapping, analysis of cloud-to-cloud variations, and ice (anti-)correlations. Based on the analysis, the first ice formation phase is driven by hydrogenation of atoms, which results in an H2O-dominated ice. At later prestellar times, CO freezes out and variations in CO freezeout levels and the subsequent CO-based chemistry can explain most of the observed ice abundance variations. The last important ice evolution stage is thermal and UV processing around protostars, resulting in CO desorption, ice segregation, and the formation of complex organic molecules. The distribution of cometary ice abundances is consistent with the idea that most cometary ices have a protostellar origin.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/ec09a928b663f4f11836aa2c5cd699d0d33c9da0

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Citations in the corpus

Formation of Complex Molecules in Prestellar Cores: A Multilayer Approach (2017, background): “…in the gas phase in our model is their overproduction on grains that is translated into gas via reactive desorption, which also leads to the somewhat increased fractions of CH3OH and H2CO in the ice bulk (see lower panel of Figure 5, Table 2) as compared to observed values (Öberg et al. 2011).”
Detection of complex organic molecules in a prestellar core: a new challenge for astrochemical models (2012, background): “According to Öberg et al. (2011), COMs could form sequentially and CH3OCHO and CH3CHO are formed by UV irradiation of cold CO-rich ices and CH3OCH3 forms in warmer (CH3OH-rich) ice after CO has evaporated (see also Öberg et al. 2009).”
The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime (2015, background): “We opt to use initial abundances at a time of 3.2 ×105 years which corresponds to an ice ratio of 100:15:6:1 for H2O:CO:CO2:CH3OH and 100:7:22 for H2O:NH3:CH4.”
H-atom addition and abstraction reactions in mixed CO, H2CO and CH3OH ices – an extended view on complex organic molecule formation (2016, background): “…show that rather than mixing with H2O, the bulk of the CO accretes on top of a previously formed H2O-rich polar ice, forming an apolar COrich ice layer (Tielens et al. 1991, Öberg et al. 2011a; Boogert & Ehrenfreund 2004; Gibb et al. 2004; Mathews et al. 2013, Boogert, Gerakines & Whittet 2015).”
Observations of the Icy Universe (2015, methodology): “The overview by Öberg et al. (2011) does not include extragalactic and GC ices, which are particularly well studied in CO2.”
Gas and grain chemical composition in cold cores as predicted by the Nautilus three-phase model (2016, result): “Since comets could reflect (at least partially) the primordial material that formed them (Öberg et al. 2011; Boogert et al. 2015), it is interesting to compare qualitatively our results with observations in these objects.”
Grain Surface Models and Data for Astrochemistry (2017, background): “High sensitivity observations have shown that complex organic molecules are also present in the gas phase in cold environments (∼ 10 K), albeit at a low level with respect to molecular hydrogen (Öberg et al. 2010, 2011; Cernicharo et al. 2012; Bacmann et al. 2012; Vastel et al. 2014).”
The Disk Substructures at High Angular Resolution Project (DSHARP). II. Characteristics of Annular Substructures (2018, methodology): “…expected to be abundant in disks based on cometary measurements and ice observations toward star-forming regions (e.g., Mumma & Charnley 2011; Öberg et al. 2011a), their binding energies are so high that their snowline locations are expected to be below the resolution limit of the DSHARP…”
Our astrochemical heritage (2012, background): “(6) The midplane, characterized by cold and dense regions, with large amounts of molecular freeze-out, where only light species can survive (Öberg et al. 2011b), in analogy with the central 1000 AU of prestellar cores (Sect.”
REACTIVE DESORPTION AND RADIATIVE ASSOCIATION AS POSSIBLE DRIVERS OF COMPLEX MOLECULE FORMATION IN THE COLD INTERSTELLAR MEDIUM (2013, result): “As expected, our chemical model produces a typical ice composition which is similar to that calculated in a number of previous studies (Garrod & Pauly 2011; Vasyunin & Herbst 2013), and which is also generally similar to observed ice abundances toward protostars (Öberg et al. 2011).”