TY - JOUR

T1 - Testing grain-surface chemistry in massive hot-core regions

AU - Bisschop, S. E.

AU - Jørgensen, J. K.

AU - Van Dishoeck, E. F.

AU - De Wachter, E. B.M.

PY - 2007/4/1

Y1 - 2007/4/1

N2 - Aims. We study the chemical origin of a set of complex organic molecules thought to be produced by grain surface chemistry in high mass young stellar objects (YSOs). Methods. A partial submillimeter line-survey was performed toward 7 high-mass YSOs aimed at detecting H2CO, CH3OH, CH2CO, CH3CHO, C2H5OH, HCOOH, HNCO and NH2CHO. In addition, lines of CH3CN, C 2H5CN, CH3CCH, HCOOCH3, and CH 3OCH3 were observed. Rotation temperatures and beam-averaged column densities are determined. To correct for beam dilution and determine abundances for hot gas, the radius and H2 column densities of gas at temperatures >100 K are computed using 850 μm dust continuum data and source luminosity. Results. Based on their rotation diagrams, molecules can be classified as either cold (<100 K) or hot (>100 K). This implies that complex organics are present in at least two distinct regions. Furthermore, the abundances of the hot oxygen-bearing species are correlated, as are those of HNCO and NH2CHO. This is suggestive of chemical relationships within, but not between, those two groups of molecules. Conclusions. The most likely explanation for the observed correlations of the various hot molecules is that they are "first generation" species that originate from solid-state chemistry. This includes H2CO, CH3OH, C 2H5OH, HCOOCH3, CH3OCH3, HNCO, NH2CHO, and possibly CH3CN, and C2H 5CN. The correlations between sources implies very similar conditions during their formation or very similar doses of energetic processing. Cold species such as CH2CO, CH3CHO, and HCOOH, some of which are seen as ices along the same lines of sight, are probably formed in the solid state as well, but appear to be destroyed at higher temperatures. A low level of non-thermal desorption by cosmic rays can explain their low rotation temperatures and relatively low abundances in the gas phase compared to the solid state. The CH3CCH abundances can be fully explained by low temperature gas phase chemistry. No cold N-containing molecules are found.

AB - Aims. We study the chemical origin of a set of complex organic molecules thought to be produced by grain surface chemistry in high mass young stellar objects (YSOs). Methods. A partial submillimeter line-survey was performed toward 7 high-mass YSOs aimed at detecting H2CO, CH3OH, CH2CO, CH3CHO, C2H5OH, HCOOH, HNCO and NH2CHO. In addition, lines of CH3CN, C 2H5CN, CH3CCH, HCOOCH3, and CH 3OCH3 were observed. Rotation temperatures and beam-averaged column densities are determined. To correct for beam dilution and determine abundances for hot gas, the radius and H2 column densities of gas at temperatures >100 K are computed using 850 μm dust continuum data and source luminosity. Results. Based on their rotation diagrams, molecules can be classified as either cold (<100 K) or hot (>100 K). This implies that complex organics are present in at least two distinct regions. Furthermore, the abundances of the hot oxygen-bearing species are correlated, as are those of HNCO and NH2CHO. This is suggestive of chemical relationships within, but not between, those two groups of molecules. Conclusions. The most likely explanation for the observed correlations of the various hot molecules is that they are "first generation" species that originate from solid-state chemistry. This includes H2CO, CH3OH, C 2H5OH, HCOOCH3, CH3OCH3, HNCO, NH2CHO, and possibly CH3CN, and C2H 5CN. The correlations between sources implies very similar conditions during their formation or very similar doses of energetic processing. Cold species such as CH2CO, CH3CHO, and HCOOH, some of which are seen as ices along the same lines of sight, are probably formed in the solid state as well, but appear to be destroyed at higher temperatures. A low level of non-thermal desorption by cosmic rays can explain their low rotation temperatures and relatively low abundances in the gas phase compared to the solid state. The CH3CCH abundances can be fully explained by low temperature gas phase chemistry. No cold N-containing molecules are found.

KW - Astrochemistry

KW - ISM: abundances

KW - ISM: molecules

KW - Line: identification

KW - Methods: observational

KW - Stars: formation

UR - http://www.scopus.com/inward/record.url?scp=34247242788&partnerID=8YFLogxK

U2 - 10.1051/0004-6361:20065963

DO - 10.1051/0004-6361:20065963

M3 - Journal article

AN - SCOPUS:34247242788

VL - 465

SP - 913

EP - 929

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

IS - 3

ER -