Evolution of dust and ice features around FU Orionis objects

Abstract

(abridged) We present spectroscopy data for a sample of 14 FUors and 2 TTauri stars observed with the Spitzer Space Telescope or with the Infrared Space Observatory (ISO). Based on the appearance of the 10 micron silicate feature we define 2 categories of FUors. Objects showing the silicate feature in absorption (Category 1) are still embedded in a dusty and icy envelope. The shape of the 10 micron silicate absorption bands is compared to typical dust compositions of the interstellar medium and found to be in general agreement. Only one object (RNO 1B) appears to be too rich in amorphous pyroxene dust, but a superposed emission feature can explain the observed shape. We derive optical depths and extinction values from the silicate band and additional ice bands at 6.0, 6.8 and 15.2 micron. In particular the analysis of the CO_2 ice band at 15.2 micron allows us to search for evidence for ice processing and constrains whether the absorbing material is physically linked to the central object or in the foreground. For objects showing the silicate feature in emission (Category 2), we argue that the emission comes from the surface layer of accretion disks. Analyzing the dust composition reveals that significant grain growth has already taken place within the accretion disks, but no clear indications for crystallization are present. We discuss how these observational results can be explained in the picture of a young, and highly active accretion disk. Finally, a framework is proposed as to how the two categories of FUors can be understood in a general paradigm of the evolution of young, low-mass stars. Only one object (Parsamian 21) shows PAH emission features. Their shapes, however, are often seen toward evolved stars and we question the object's status as a FUor and discuss other possible classifications.

accepted for publication in ApJ; 63 pages preprint style including 8 tables and 24 figures

References in corpus (6)

• The Burst Mode of Protostellar Accretion
• The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks III. Simulations with Radiative Cooling and Realistic Opacities
• The unusual hydrocarbon emission from the early carbon star HD 100764: The connection between aromatics and aliphatics
• Binarity as a key factor in protoplanetary disk evolution: Spitzer disk census of the eta Chamaeleontis cluster
• The outburst of the eruptive young star OO Serpentis between 1995 and 2006
• Deeply embedded objects and shocked molecular hydrogen: The environment of the FU Orionis stars RNO 1B/1C

Cited by in corpus (4)

• Long-wavelength excesses of FU Orionis objects: flared outer disks or infalling envelopes?
• Encounter-driven accretion in young stellar clusters - A connection to FUors?
• High-resolution polarimetry of Parsamian 21: revealing the structure of an edge-on FU Ori disc
• 2MASS J17112318-2724315: A Deeply-Embedded Low-Mass Protostellar System in the B59 Molecular Cloud