Does IRAS 16293–2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment

By F. Schoeier, J. Jørgensen, E. F. Dishoeck, G. Blake. 2002

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A detailed radiative transfer analysis of the observed continuum and molecular line emission toward the deeply embedded young stellar object IRAS 16293-2422 is performed. Accurate molecular abundances and abundance changes with radius are presented. The continuum modelling is used to constrain the temperature and density distributions in the envelope, enabling quantitative estimates of various molecular abundances. The density structure is well described by a single power-law falling off as r^(-1.7), i.e., in the range of values predicted by infall models. A detailed analysis of the molecular line emission strengthens the adopted physical model and lends further support that parts of the circumstellar surroundings of IRAS are in a state of collapse. The molecular excitation analysis reveals that the emission from some molecular species is well reproduced assuming a constant fractional abundance throughout the envelope. The abundances and isotope ratios are generally close to typical values found in cold molecular clouds in these cases, and there is a high degree of deuterium fractionation. There are, however, a number of notable exceptions. Lines covering a wide range of excitation conditions indicate for some molecules, e.g., H_2CO, CH_3OH, SO, SO_2 and OCS, a drastic increase in their abundances in the warm and dense inner region of the circumstellar envelope. The location at which this increase occurs is consistent with the radius at which ices are expected to thermally evaporate off the grains. In all, there is strong evidence for the presence of a "hot core" close to the protostar, whose physical properties are similar to those detected towards most high mass protostars except for a scaling factor. However, the small scale of the hot gas and the infalling nature of the envelope lead to very different chemical time scales between low mass and high mass hot cores, such that only very rapidly produced second-generation complex molecules can be formed in IRAS 16293-2422 . Alternatively, the ices may be liberated due to grain-grain collisions in turbulent shear zones where the outflow interacts with the envelope. Higher angular resolution observations are needed to pinpoint the origin of the abundance enhancements and distinguish these two scenarios. The accurate molecular abundances presented for this low-mass protostar serve as a reference for comparison with other objects, in particular circumstellar disks and comets.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/d55c6f67d013bf4b21a21a8dab25973d420b183f

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Citations in the corpus

An atomic and molecular database for analysis of submillimetre line observations (2004, methodology): “Indeed, it is becoming increasingly clear that more information — including chemical gradients throughout the source — can be inferred from the data if a good molecular excitation model is available (e.g., Schöier et al. 2002; Maret et al. 2004).”
Grain Surface Models and Data for Astrochemistry (2017, result): “Finally, the correlation found between the abundances of HC(O)CH2OH and H2C(OH)CH2O with those of formaldehyde and methanol is as expected typically in ratios of the order of a few percent and in good agreement with observations (Jørgensen et al. 2012; Schöier et al. 2002).”
A laboratory survey of the thermal desorption of astrophysically relevant molecules (2004, background): “Schöier et al. (2002) suggest that many of the observational traits towards IRAS 16293–2422 are consistent with CO trapping.”
First detection of triply-deuterated methanol (2003, background): “A more recent study of the spatial distribution of CH3OH was performed by Schoier et al. (2002), and showed evidence for an abundance jump of methanol of two orders of magnitude in the inner part of the envelope (≤ 150 AU).”
Near-Arcsecond Resolution Observations of the Hot Corino of the Solar-Type Protostar IRAS 16293–2422 (2004, background): “…far the existence of inner warm regions with evaporated mantles in solartype protostars has been argued indirectly from the sophisticated analysis of molecular multifrequency single-dish observations (Ceccarelli et al. 2000a, 2000b; Scho¨ier et al. 2002; Maret et al. 2002, 2004; Doty et al. 2004).”
The chemical history of molecules in circumstellar disks - I. Ices (2009, background): “However, the material in the hot inner envelope in our model is essentially n freefall towards the star or the inner disk, and its transit time of a few 100 yr is too short for complex organics to be formed abundantly (see also Schöier et al. 2002).”
Complex Chemistry in Star-forming Regions: An Expanded Gas-Grain Warm-up Chemical Model (2008, background): “The detection of complex molecules in hot corinos also points to grain-surface production, as gas-phase chemical timescales are greater than the transit time of the infalling gas in these sources (Schöier et al. 2002; Bottinelli et al. 2004a; Aikawa et al. 2007).”
Mechanistical Studies on the Irradiation of Methanol in Extraterrestrial Ices (2007, background): “…has recently been noted, however, that molecules subliming from these grains will have lifetimes of only a few hundred years before collapsing into the protostar; unlikely enough time to form complex molecules by methanol-induced gas-phase chemistry (Schöier et al. 2002; Rodgers & Charnley 2003).”
Sulphur-bearing species in the coma of comet 67P/Churyumov–Gerasimenko (2016, background): “The most simple MNRAS 462, S253–S273 (2016) nloaded from https://academ ic.oup.com /m nras/article-abstract/462/Suppl_1/S253/2633389 by guest on 16 M arch 2020 organo-sulphur molecule H2CS has been detected in the low-mass protostar IRAS 16293−2422 (Schöier et al. 2002).”
Our astrochemical heritage (2012, unknown): “References: for comets [309] and[49]; for IRAS16293-2422 [96], [391] and [89].”
Water in star-forming regions with Herschel (WISH). II. Evolution of 557 GHz 110-101 emission in low-mass protostars (2012, methodology): “…the large-scale physical structure of the envelopes and to compare the water emission to envelope parameters, each source is modelled using the 1D dust radiative transfer code DUSTY (Ivezić & Elitzur 1997) following the prescriptions outlined in Schöier et al. (2002) and Jørgensen et al. (2002).”
DETECTION OF THE SIMPLEST SUGAR, GLYCOLALDEHYDE, IN A SOLAR-TYPE PROTOSTAR WITH ALMA (2012, background): “…be the best low-mass protostellar testbed for astrochemical studies (see, e.g., Blake et al. 1994; van Dishoeck et al.1995; Ceccarelli et al. 2000; Schöier et al. 2002), a status that has been further bolstered by the detection of awealth complex organic molecules toward this source (Cazaux et…”
A computer program for fast non-LTE analysis of interstellar line spectra With diagnostic plots to interpret observed line intensity ratios (2007, methodology): “…et al. 2002; Jakob et al. 2007), and, if enough observations are available, even molecular abundance profiles (e.g., Van der Tak et al. 2000a; Schöier et al. 2002; Maret et al. 2005), especially when coupled to chemical networks (e.g., Doty et al. 2004; Evans et al. 2005; Goicoechea et al.…”
Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores (2007, background): “Radio observations find gaseous CH3OH to be abundant in the central regions of protostars (Schöier et al. 2002a).”
Resetting chemical clocks of hot cores based on S-bearing molecules (2004, unknown): “…multifrequency observations of H2S, OCS, SO and SO2 have been reported and analyzed by sophisticated models, which take into account the density and temperature structure of the source, as well as the abundance profile of each studied molecule (Schöier et al. 2002; Wakelam et al. 2004).”
Organic molecules in protoplanetary disks around T Tauri and Herbig Ae stars (2004, methodology): “The H2CO/CH3OH abundance ratio of > 0.15 for LkCa 15 is consistent with values found for embedded YSOs (see Table 8 of Schöier et al. 2002 for IRAS 16293–2422 and van der Tak et al. 2000 for the case of massive protostars).”
Complex Molecules in the Hot Core of the Low-Mass Protostar NGC 1333 IRAS 4A (2004, background): “…(> 100 K) and high densities (> 107 cm−3: Ceccarelli et al. 2000a), high abundances of hydrides (CH3OH, H2CO, H2O: Ceccarelli et al. 2000a, b; Schöier et al. 2002), high deuteration levels (> 10%: Ceccarelli et al. 1998, 2001; Parise et al. 2002; Roberts et al. 2002), and complex…”
Experimental evidence for glycolaldehyde and ethylene glycol formation by surface hydrogenation of CO molecules under dense molecular cloud conditions (2015, background): “Observations towards the same source performed by Schöier et al. (2002) reported a gas-phase H2CO abundance of 6×10−8 and a solid-state abundance of (1–4) ×10−6 relative to H2, yielding a gas-phase HC(O)CH2OH/H2CO ratio of 10 per cent, comparable within the uncertainties to the 3–5 per cent value…”