The effect of a strong external radiation field on protostellar envelopes in Orion

被引:41
作者
Jorgensen, JK
Johnstone, D
van Dishoeck, EF
Doty, SD
机构
[1] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[2] Leiden Observ, NL-2300 RA Leiden, Netherlands
[3] Natl Res Council Canada, Herzberg Inst Astrophys, Victoria, BC V9E 2E7, Canada
[4] Univ Victoria, Dept Phys & Astron, Victoria, BC V8P 1A1, Canada
[5] Denison Univ, Dept Phys & Astron, Granville, OH 43023 USA
关键词
stars : formation; radiative transfer; astrochemistry;
D O I
10.1051/0004-6361:20053011
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We discuss the effects of an enhanced interstellar radiation field (ISRF) on the observables of protostellar cores in the Orion cloud region. Dust radiative transfer is used to constrain the envelope physical structure by reproducing SCUBA 850 mu m emission. Previously reported (CO)-C-13, (CO)-O-17 and H2CO line observations are reproduced through detailed Monte Carlo line radiative transfer models. It is found that the (CO)-C-13 line emission is marginally optically thick and sensitive to the physical conditions in the outer envelope. An increased temperature in this region is needed in order to reproduce the (CO)-C-13 line strengths and it is suggested to be caused by a strong heating from the exterior, corresponding to an ISRF in Orion 10(3) times stronger than the "standard" ISRF. The typical temperatures in the outer envelope are higher than the desorption temperature for CO. The (CO)-O-17 emission is less sensitive to this increased temperature but rather traces the bulk envelope material. The data are only fit by a model where CO is depleted, except in the inner and outermost regions where the temperature increases above 30 - 40 K. The fact that the temperatures do not drop below approximate to 25 K in any of the envelopes whereas a significant fraction of CO is frozen- out suggest that the interstellar radiation field has changed through the evolution of the cores. The H2CO lines are successfully reproduced in the model of an increased ISRF with constant abundances of 3 - 5 x 10(-10).
引用
收藏
页码:609 / 619
页数:11
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