The degree of CO depletion in pre-stellar cores ?

By A. Bacmann, Bertrand Lefloch, Cecilia Ceccarelli, A. Castets, J. Steinacker, Laurent Loinard Aiu Jena, Observatoire de Grenoble, O. Bordeaux, U. Mexico. 2002

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We present new results on CO depletion in a sample of nearby pre-stellar cores, based on observations of the millimeter C 17 O and C 18 O lines and the 1.3 mm dust emission with the IRAM 30 m telescope. In most cases, the distribution of CO is much flatter than that of the dust, whereas other tracers, like $\rm N_2H^{+}$, still probe the latter. In the centre of these objects, we estimate CO to be underabundant by a factor 4–15 depending on the cores. The CO underabundance is more pronounced in the central regions and appears to decrease with increasing distance from the core centre. This underabundance is most likely due to the freezing out of CO onto the dust grains in the cold, dense parts of the cores. We find evidence for an increase of the CO depletion degree with the core density.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/974968f619fdb648751d0bfd4f7852c07ac39b31

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Citations in the corpus

On The Internal Structure Of Starless Cores. Physical and Chemical Properties of L1498 and L1517B (2004, unknown): “…interiors (Kuiper et al. 1996; Willacy et al. 1998; Kramer et al. 1999; Alves et al. 1999; Send offprint requests to: M. Tafalla, e-mail: m.tafalla@oan.es Caselli et al. 1999; Bergin et al. 2001; Jessop & WardThompson 2001; Tafalla et al. 2002; Bergin et al. 2002; Bacmann et al. 2002).”
A gallery of bubbles. The nature of the bubbles observed by Spitzer and what ATLASGAL tells us about the surrounding neutral material (2010, background): “…i) the CO (3−2) emission is insensitive to high densities; ii) the condensations are probably optically thick in 12CO; and iii) the CO molecule is probably depleted in the gaseous phase because it condenses onto the dust grains in cold dense cores (Caselli et al. 1999; Bacmann et al. 2002).”
First detection of triply-deuterated methanol (2003, background): “Meantime, observations of doubly deuterated formaldehyde in a sample of pre-stellar cores showed that the degree of deuteration increases with increasing CO depletion (Bacmann et al. 2002, 2003).”
Cold Dark Clouds: The Initial Conditions for Star Formation (2007, background): “A comparative study of CO suggest freeze-out dominates when densities exceed ∼ 3 × 104 cm−3(Bacmann et al. 2002).”
REACTIVE DESORPTION AND RADIATIVE ASSOCIATION AS POSSIBLE DRIVERS OF COMPLEX MOLECULE FORMATION IN THE COLD INTERSTELLAR MEDIUM (2013, background): “In addition to these molecules, several other simple species were observed toward B1-b and L1689b such as CO, HCO+, N2H+, NH3, CS, and HNCO/HCNO (Hirano et al. 1999; Bacmann et al. 2002; Marcelino et al. 2009; Öberg et al. 2010).”
Testing grain surface chemistry : a survey of deuterated formaldehyde and methanol in low-mass Class 0 protostars (2006, result): “We also plotted in this figure the result for prestellar cores observed by Bacmann et al. (2002).”
The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse (2006, background): “…, which suggest that, during an initial, approximately isothermal phase of the collapse process, molecular species containing the heavy elements, notably carbon and oxygen , are removed from the gas phase by 'freeze–out' on to the surfaces of grains (Bacmann et al. 2002, Tafalla et al. 2004).”
Enhanced Deuterium Fractionation in Dense Interstellar Cores Resulting from Multiply Deuterated H3+ (2003, methodology): “The prestellar cores observed by Bacmann et al. (2002, 2003) indicate that D2CO fractionation increases with CO depletion.”
The chemistry of multiply deuterated species in cold, dense interstellar cores (2004, background): “Additionally, CO depletions have now been observed in many different sources (e.g., Caselli et al. 1999; Bergin et al. 2002; Redman et al. 2002; Bacmann et al. 2002; Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20040441 Tafalla et…”
Our astrochemical heritage (2012, background): “CO freeze-out has been measured in starless and pre-stellar cores at a 80-90% level ([461]; [82]; [23]; [368]).”
Chemical modeling of L183 (= L134N) : an estimate of the ortho/para H2 ratio (2008, background): “CO is expected to freeze-out onto the grain mantles at high densities (a few 104 cm−3) and low temperatures (≤ 20 K) (e.g. Caselli et al. 1999, Bergin et al. 2001, Bacmann et al. 2002, Tafalla et al. 2002, Pagani et al. 2005).”
PHYSICAL PROPERTIES AND GALACTIC DISTRIBUTION OF MOLECULAR CLOUDS IDENTIFIED IN THE GALACTIC RING SURVEY (2010, methodology): “Indeed, using other molecules such as N2H + and the dust continuum as a tracer for the densest molecular phase, Bacmann et al. (2002) have measured a CO under-abundance of 5-15 in molecular cores of density 105-106 cm−3.”
On the internal structure of starless cores II. A molecular survey of L1498 and L1517B (2006, background): “Most dense cores, in fact, suffer from severe depletion (e.g., Bacmann et al. 2002; Tafalla et al. 2002), while only a minority seem unaffected by it (Hirota et al. 2002; Tafalla & Santiago 2004).”
Probing the Evolutionary Status of Starless Cores through N2H+ and N2D+ Observations (2004, background): “C18O data were already available for L1544 (Caselli et al. 1999), Oph D, L328, L429 (Bacmann et al. 2002), L1495, L1498, L1517B (Tafalla et al. 2002), B68 (Bergin et al. 2002), and L1521F (Crapsi et al. 2004).”
Probing the formation of intermediate- to high-mass stars in protoclusters - A detailed millimeter study of the NGC 2264 clumps (2005, background): “The spherical abundance profiles are thus fixed to standard values, i.e. [CS]/[H2]=1×10−9 (i.e. Tafalla et al. 2002) and [HCO+]/[H2]=1.5×10−9 (i.e. Bergin et al. 1997), in the low-density outer regions and are assumed to scale as n−0.4H2 with density (cf. Bacmann et al. 2002).”
CO Depletion and Deuterium Fractionation in Prestellar Cores (2003, background): “We recently studied the degree of CO depletion in a sample of pre-stellar cores, and showed that the depletion degree increases with density (Bacmann et al. 2002).”