We present Spitzer IRS spectroscopy of CO2 ice toward 19 young stellar objects (YSOs) with luminosity lower than 1L⊙ . Pure CO2 ice forms only at elevated temperatures, T > 20 K, and thus at higher luminosities. Current internal luminosities of YSOs with L < 1L⊙ do not provide such conditions out to radii of typical envelopes. Significant amounts of pure CO2 ice would signify a higher past luminosity. We analyze 15.2 μm CO2 ice bending mode absorption lines in comparison to the laboratory data. We decompose pure CO2 ice from 12 out of 19 young low luminosity sources. The presence of the pure CO2 ice component indicates high dust temperature and hence high luminosity in the past. The sum of all the ice components (total CO2 ice amount) can be explained by a long period of low luminosity stage between episodic accretion bursts as predicted in an episodic accretion scenario. Chemical modeling shows that the episodic accretion scenario explains the observed total CO2 ice amount best.

ABSTRACT
1. INTRODUCTION
2. OBSERVATIONS, ANALYSIS AND MODELING
REFERENCES

• HYO JEONG KIM(Department of Astronomy, The University of Texas at Austin)
• NEAL J. EVANS Ⅱ(Department of Astronomy, The University of Texas at Austin)
• MICHAEL M. DUNHAM(Department of Astronomy, Yale University)
• JEONG-EUN LEE(Department of Astronomy and Space Science, Kyung Hee University)
• KLAUS M. PONTOPPIDAN(Space Telescope Science Institute)