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AKARI observations of ice absorption bands towards edge-on YSOs | | Y. Aikawa
; D. Kamuro
; I. Sakon
; Y. Itoh
; H. Terada
; J.A. Noble
; K.M. Pontoppidan
; H.J. Fraser
; M. Tamura
; R. Kandori
; A. Kawamura
; M. Ueno
; | | Date: |
16 Dec 2011 | | Abstract: | To investigate the composition and evolution of circumstellar ice around
low-mass YSOs, we observed ice absorption bands in the near infrared (NIR)
towards eight YSOs ranging from class 0 to class II, among which seven are
associated with edge-on disks. We performed slit-less spectroscopic
observations using the grism mode of the Infrared Camera (IRC) on board AKARI,
which enables us to obtain full NIR spectra from 2.5 $mu$m to 5 $mu$m. The
spectra were fitted with polynomial baselines to derive the absorption spectra.
The molecular absorption bands were then fitted with the laboratory database of
ice absorption bands, considering the instrumental line profile and the
spectral resolution of the grism dispersion element. Towards the class 0-I
sources (L1527, IRC-L1041-2, and IRAS04302), absorption bands of H$_2$O,
CO$_2$, CO, and XCN are clearly detected. Column density ratios of CO$_2$ ice
and CO ice relative to H$_2$O ice are 21-28% and 13-46%, respectively. If XCN
is OCN$^-$, its column density is as high as 2-6% relative to H$_2$O ice. The
HDO ice feature at 4.1 $mu$m is tentatively detected towards the class 0-I
sources and HV Tau. Non-detections of the CH-stretching mode features around
3.5 $mu$m provide upper limits to the CH$_3$OH abundance of 26% (L1527) and
42% (IRAS04302) relative to H$_2$O. We tentatively detect OCS ice absorption
towards IRC-L1041-2. Towards class 0-I sources, the detected features should
mostly originate in the cold envelope, while CO gas and OCN$^-$ could originate
in the region close to the protostar, where there are warm temperatures and UV
radiation. We detect H$_2$O ice band towards ASR41 and 2MASSJ1628137-243139,
which are edge-on class II disks. We also detect H$_2$O ice and CO$_2$ ice
towards HV Tau, HK Tau, and UY Aur, and tentatively detect CO gas features
towards HK Tau and UY Aur. | | Source: | arXiv, 1112.3736 | | Services: | Forum | Review | PDF | Favorites | |
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