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WISH VI. Constraints on UV and X-ray irradiation from a survey of hydrides in low- to high-mass YSOs | | A. O. Benz
; S. Bruderer
; E. F. van Dishoeck
; M. Melchior
; S. F. Wampfler
; F. van der Tak
; J. R. Goicoechea
; N. Indriolo
; L. E. Kristensen
; D.C. Lis
; J. C. Mottram
; E. A. Bergin
; P. Caselli
; F. Herpin
; M. R. Hogerheijde
; D. Johnstone
; R. Liseau
; B. Nisini
; M. Tafalla
; R. Visser
; F. Wyrowski
; | | Date: |
29 Mar 2016 | | Abstract: | Hydrides are simple compounds containing one or a few hydrogen atoms bonded
to a heavier atom. They are fundamental precursor molecules in cosmic chemistry
and many hydride ions have become observable in high quality for the first time
thanks to the Herschel Space Observatory. Ionized hydrides, such as CH+ and
OH+, and also HCO+ that affect the chemistry of molecules such as water,
provide complementary information on irradiation by far UV (FUV) or X-rays and
gas temperature. The targeted lines of CH+, OH+, H2O+, C+ and CH are detected
mostly in blue-shifted absorption. H3O+ and SH+ are detected in emission and
only toward some high-mass objects. The observed line parameters and
correlations suggest two different origins, related to gas entrained by the
outflows and to the circumstellar envelope. The column density ratios of
CH+/OH+ are estimated from chemical slab models, assuming that the H2 density
is given by the specific density model of each object at the beam radius. For
the low-mass YSOs the observed ratio can be reproduced for an FUV flux of 2-400
times the ISRF at the location of the molecules. In two high-mass objects, the
UV flux is 20-200 times the ISRF derived from absorption lines, and 300-600
ISRF using emission lines. If the FUV flux required for low-mass objects
originates at the central protostar, a substantial FUV luminosity, up to 1.5
L_sun, is required. There is no molecular evidence for X-ray induced chemistry
in the low-mass objects on the observed scales of a few 1000 AU. For high-mass
regions, the FUV flux required to produce the observed molecular ratios is
smaller than the unattenuated flux expected from the central object(s) at the
Herschel beam radius. This is consistent with an FUV flux reduced by
circumstellar extinction or by bloating of the protostar. | | Source: | arXiv, 1603.8721 | | Services: | Forum | Review | PDF | Favorites | |
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