Observations of water vapor toward Orion BN/KL

Citation
Gj. Melnick et al., Observations of water vapor toward Orion BN/KL, ASTROPHYS J, 539(2), 2000, pp. L87-L91
Citations number
27
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004637X → ACNP
Volume
539
Issue
2
Year of publication
2000
Part
2
Pages
L87 - L91
Database
ISI
SICI code
0004-637X(20000820)539:2<L87:OOWVTO>2.0.ZU;2-4
Abstract
We have obtained spectra of the rotational ground-state 1(10)-1(01) 556.936 GHz ortho-(H2O)-O-16 and 1(10)-1(01) 547.676 GHz ortho-(H2O)-O-18 transiti ons toward Orion BN/KL using the Submillimeter Wave Astronomy Satellite (SW AS). The ortho-(H2O)-O-16 spectrum shows strong evidence for both a broad ( Delta v similar or equal to 48 km s(-1)) and a narrow (Delta v similar or e qual to 7.5 km s(-1)) component, while the ortho-(H2O)-O-18 shows evidence for only a broad (Delta v similar or equal to 24 km s(-1)) component. The b road component emission in both ortho-(H2O)-O-16 and ortho-(H2O)-O-18 arise s primarily from gas heated within the low- and high-velocity outflows and shocked gas surrounding IRc2 in which the ortho-(H2O)-O-16 and ortho-(H2O)- O-18 fractional abundances are estimated to be 3.5 x 10(-4) and 7 x 10(-7), respectively. This finding provides further confirmation that water is eff iciently and abundantly produced within warm shock-heated gas. We estimate that the hot core plus the compact ridge contribute less than or similar to 10% to the ortho-(H2O)-O-16 integrated intensity within the SWAS beam. The narrow component seen in the ortho-(H2O)-O-16 spectrum is best fitted by o rtho-water emission from the extended ridge (ER) and the higher temperature core of the extended ridge (CER) with a common fractional abundance of 3.3 x 10(-8). The absence of any discernible narrow component in the ortho-(H2 O)-O-18 spectrum is used to set 3 sigma upper limits on the ortho-water fra ctional abundance within the ER of 7 x 10(-8) and within the CER of 5.2 x 1 0(-7). This implies that within the dense extended quiescent region, gas-ph ase water is neither a major repository of oxygen nor a major coolant in Or ion BN/KL.