2012ApJ...758...38K -
Astrophys. J., 758, 38 (2012/October-2)
CO2 ice toward low-luminosity embedded protostars: evidence for episodic mass accretion via chemical history.
KIM H.J., EVANS II N.J., DUNHAM M.M., LEE J.-E. and PONTOPPIDAN K.M.
Abstract (from CDS):
We present Spitzer IRS spectroscopy of CO2 ice bending mode spectra at 15.2 µm toward 19 young stellar objects (YSOs) with luminosity lower than 1 L☉(3 with luminosity lower than 0.1 L☉). Ice on dust grain surfaces can encode the history of heating because pure CO2 ice forms only at elevated temperature, T > 20 K, and thus around protostars of higher luminosity. Current internal luminosities of YSOs with L < 1L☉ do not provide the conditions needed to produce pure CO2 ice at radii where typical envelopes begin. The presence of detectable amounts of pure CO2 ice would signify a higher past luminosity. Many of the spectra require a contribution from a pure, crystalline CO2component, traced by the presence of a characteristic band splitting in the 15.2 µm bending mode. About half of the sources (9 out of 19) in the low-luminosity sample have evidence for pure CO2ice, and 6 of these have significant double-peaked features, which are very strong evidence of pure CO2ice. The presence of the pure CO2 ice component indicates that the dust temperature, and hence luminosity of the central star/accretion disk system, must have been higher in the past. An episodic accretion scenario, in which mixed CO-CO2 ice is converted to pure CO2 ice during each high-luminosity phase, explains the presence of pure CO2ice, the total amount of CO2ice, and the observed residual C18O gas.
Abstract Copyright:
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Journal keyword(s):
astrochemistry - ISM: molecules - stars: formation - stars: low-mass - stars: protostars
Simbad objects:
33
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