Gas-phase CO2 toward massive protostars

被引:63
作者
Boonman, AMS
van Dishoeck, EF
Lahuis, F
Doty, SD
机构
[1] Sterrewacht Leiden, NL-2300 RA Leiden, Netherlands
[2] Univ Groningen, SRON Natl Inst Space Res, NL-9700 AV Groningen, Netherlands
[3] Denison Univ, Dept Phys & Astron, Granville, OH 43023 USA
关键词
stars : formation; ISM : abundances; ISM : molecules; infrared : ISM; ISM : lines and bands; molecular processes;
D O I
10.1051/0004-6361:20021868
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We present infrared spectra of gas-phase CO2 around 15 mum toward 14 deeply embedded massive protostars obtained with the Short Wavelength Spectrometer on board the Infrared Space Observatory. Gas-phase CO2 has been detected toward 8 of the sources. The excitation temperature and the gas/solid ratio increase with the temperature of the warm gas. Detailed radiative transfer models show that a jump in the abundance of two orders of magnitude is present in the envelope of AFGL 2591 at T>300 K. No such jump is seen toward the colder source NGC 7538 IRS9. Together, these data indicate that gas-phase CO2 shows the same evolutionary trends as CO2 ice and other species, such as HCN, C2H2, H2O, and CH3OH. The gas-phase CO2 abundance toward cold sources can be explained by gas-phase chemistry and possible freeze-out in the outer envelope. Different chemical scenarios are proposed to explain the gas-phase CO2 abundance of 1-2x10(-6) for T>300 K and of similar to10(-8) for T<300 K toward AFGL 2591. The best explanation for the low abundance in the warm exterior is provided by destruction of CO2 caused by the passage of a shock in the past, combined with freeze-out in the coldest part at T<100 K. The high abundance in the interior at temperatures where all oxygen should be driven into H2O is unexpected, but may be explained either by production of OH through X-ray ionization leading to the formation of abundant gas-phase CO2, or by incomplete destruction of evaporated CO2 for T>300 K.
引用
收藏
页码:1063 / 1072
页数:10
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