AKARI observations of ice absorption bands towards edge-on young stellar objects

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

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55 Scopus citations


Context. Circumstellar disks and envelopes of low-mass young stellar objects (YSOs) contain significant amounts of ice. Such icy material will evolve to become volatile components of planetary systems, such as comets in our solar system. Aims. To investigate the composition and evolution of circumstellar ice around low-mass young stellar objects (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. Methods. 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 μm to 5 μm, including the CO 2 band and the blue wing of the H 2O band, which are inaccessible from the ground. We developed procedures to carefully process the spectra of targets with nebulosity. 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. Results. Towards the class 0-I sources (L1527, IRC-L1041-2, and IRAS 04302), absorption bands of H 2O, CO 2, CO, and XCN are clearly detected. Column density ratios of CO 2 ice and CO ice relative to H 2O ice are 21-28% and 13-46%, respectively. If XCN is OCN -, its column density is as high as 2-6% relative to H 2O ice. The HDO ice feature at 4.1 μm is tentatively detected towards the class 0-I sources and HV Tau. Non-detections of the CH-stretching mode features around 3.5 μm provide upper limits to the CH 3OH abundance of 26% (L1527) and 42% (IRAS 04302) relative to H 2O. 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 2O ice band towards ASR41 and 2MASSJ 1628137-243139, which are edge-on class II disks. We also detect H 2O 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.

Original languageEnglish
Article numberA57
JournalAstronomy and Astrophysics
StatePublished - 2012
Externally publishedYes


  • astrochemistry
  • circumstellar matter
  • infrared: ISM
  • stars: formation


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