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ABSTRACT We present Spitzer IRS spectroscopy of CO 2 ice toward 19 young stellar objects (YSOs) withluminosity lower than 1 L  . Pure CO 2 ice forms only at elevated temperatures, T > 20 K, and thusat higher luminosities. Current internal luminosities of YSOs with L < 1 L  do not provide suchconditions out to radii of typical envelopes. Signicant amounts of pure CO 2 ice would signify ahigher past luminosity. We analyze 15.2 „ m CO 2 ice bending mode absorption lines in comparisonto the laboratory data. We decompose pure CO 2 ice from 12 out of 19 young low luminositysources. The presence of the pure CO 2 ice component indicates high dust temperature and hencehigh luminosity in the past. The sum of all the ice components (total CO 2 ice amount) can beexplained by a long period of low luminosity stage between episodic accretion bursts as predictedin an episodic accretion scenario. Chemical modeling shows that the episodic accretion scenarioexplains the observed total CO 2 ice amount best.

EVIDENCES OF EPISODIC MASS ACCRETION IN LOW-LUMINOSITY EMBEDDED PROTOSTARS