Spitzer Space Telescope - General Observer Proposal #50654


Testing the Evolution of Young Stars with FU Orionis Objects

Principal Investigator: Marc Audard
           Institution: Observatoire de Geneve

     Technical Contact: Marc Audard, Observatoire de Geneve

Co-Investigators: 
Carla Baldovin Saavedra, University of Geneva                         
Andres Carmona, University of Geneva                                  
Thierry Lanz, University of Maryland                                  

Science Category: young stellar objects 
 Observing Modes: IrsStare 
  Hours Approved: 2.7 

Abstract:
FU Orionis objects (FUors) play a central role in the study of the evolution of
young stars. They undergo accretion outbursts that can bring up to about 0.01
solar masses per outburst, therefore providing a significant amount of mass in
the pre-main sequence life of a star. Spitzer IRS observations of FUors have
shown either silicate features in absorption and ice bands or silicates in
emission with no ice bands. This led some authors to propose an evolutionary
paradigm in which the former FUors are younger than the latter FUors. The FUor
phase might be a common but rarely observed phase (about 20 FUors known) of most
young low-mass stars and might be the link between Class I and Class II sources.
So far, Spitzer has obtained IRS spectra of about half of the FUor catalog,
focusing on its most famous class members. With this short Spitzer proposal, we
aim to observe FUors that have not yet been observed with the IRS or had no
high-resolution module spectra. We will study the composition and evolution of
dust grains and of ices in FUors surrounded by envelopes, and we aim at
detecting faint molecular hydrogen and atomic lines with the high-resolution
module spectra. The IRS spectra will probe the stellar environment, and thus
test the above evolutionary paradigm and the different theories for the origin
of FUor outburst. The Spitzer IRS observations of our sample of FUors will
therefore provide additional insights about a significant phase in the life of
young stars with the aim to better describe the evolutionary sequence from Class
I star to Class II sources.