出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We present Spitzer IRS, SH mode spectroscopy toward 21 young stellar objects (YSOs) with luminosity lower than 1 L (4 with luminosity lower than 0.1 L ). While the standard star formation model predicts protostars to have a luminosity higher than 1.6 L , Spitzer Legacy Project, From Molecular Cores to Planet Forming Disks (c2d) survey shows that 59 % of the 112 embedded protostars have luminosity lower than 1.6 L . One possible explanation is that mass accretion is not a constant process. If accretion is episodic, sources that currently are low luminosity may have had much higher accretion rates, and thus luminosities, in the past. In that case, imprints of the high luminosity stage in low luminosity YSOs would support the idea of episodic mass accretion. Evidence may be found in their 15.2 mm CO2 ice features. Pure CO2 ice can be formed only at elevated temperatures and thus higher luminosity. Current internal luminosities of YSOs with L 1 L do not provide such conditions. We analyze 15.2 mm CO2 ice bending mode absorption lines in comparison to laboratory data. Preliminary analysis indicates that the low luminosityYSOs may harbor pure CO2 ice components. A detailed analysis is ongoing and the results are presented here.
