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|Title:||Deuteration and evolution in the massive star formation process. The role of surface chemistry||Authors:||FONTANI, FRANCESCO
Tan, J. C.
|Issue Date:||2015||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||575||First Page:||A87||Abstract:||Context. An ever growing number of observational and theoretical evidence suggests that the deuterated fraction (column density ratio between a species containing D and its hydrogenated counterpart, D<SUB>frac</SUB>) is an evolutionary indicator both in the low- and the high-mass star formation process. However, the role of surface chemistry in these studies has not been quantified from an observational point of view. <BR /> Aims: Because many abundant species, such as NH<SUB>3</SUB>, H<SUB>2</SUB>CO, and CH<SUB>3</SUB>OH, are actively produced on ice mantles of dust grains during the early cold phases, their D<SUB>frac</SUB> is expected to evolve differently from species formed only (or predominantly) in the gas, such as N<SUB>2</SUB>H<SUP>+</SUP>, HNC, HCN, and their deuterated isotopologues. The differences are expected to be relevant especially after the protostellar birth, in which the temperature rises, causing the evaporation of ice mantles. <BR /> Methods: To compare how the deuterated fractions of species formed only in the gas and partially or uniquely on grain surfaces evolve with time, we observed rotational transitions of CH<SUB>3</SUB>OH, <SUP>13</SUP>CH<SUB>3</SUB>OH, CH<SUB>2</SUB>DOH, and CH<SUB>3</SUB>OD at 3 mm and 1.3 mm, of NH<SUB>2</SUB>D at 3 mm with the IRAM-30 m telescope, and the inversion transitions (1, 1) and (2, 2) of NH<SUB>3</SUB> with the GBT, towards most of the cores already observed in N<SUB>2</SUB>H<SUP>+</SUP>, N<SUB>2</SUB>D<SUP>+</SUP>, HNC, and DNC. <BR /> Results: NH<SUB>2</SUB>D is detected in all but two cores, regardless of the evolutionary stage. D<SUB>frac</SUB>(NH<SUB>3</SUB>) is on average above 0.1 and does not change significantly from the earliest to the most evolved phases, although the highest average value is found in the protostellar phase (~0.3). Few lines of CH<SUB>2</SUB>DOH and CH<SUB>3</SUB>OD are clearly detected, and then only towards protostellar cores or externally heated starless cores. In quiescent starless cores, we have only one doubtful detection of CH<SUB>2</SUB>DOH. <BR /> Conclusions: This work clearly confirms an expected different evolutionary trend of the species formed exclusively in the gas (N<SUB>2</SUB>D<SUP>+</SUP> and N<SUB>2</SUB>H<SUP>+</SUP>) and those formed partially (NH<SUB>2</SUB>D and NH<SUB>3</SUB>) or totally (CH<SUB>2</SUB>DOH and CH<SUB>3</SUB>OH) on grain mantles. It also reinforces the idea that D<SUB>frac</SUB>(N<SUB>2</SUB>H<SUP>+</SUP>) is the best tracer of massive starless cores, while high values of D<SUB>frac</SUB>(CH<SUB>3</SUB>OH) seem fairly good tracers of the early protostellar phases, where the evaporation or sputtering of the grain mantles is most efficient. <P />Tables 3-6, 8, and Appendices are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201424753/olm">http://www.aanda.org</A>IRAM 30 m data (final reduced data used in the paper, in FITS format) are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://184.108.40.206) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/575/A87">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/575/A87</A>||URI:||http://hdl.handle.net/20.500.12386/23496||URL:||http://arxiv.org/abs/1410.7232v1
|Appears in Collections:||1.01 Articoli in rivista|
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