Grain growth in newly discovered young eruptive stars

Abstract

FU Orionis-type stars are young stellar objects showing large outbursts due to highly enhanced accretion from the circumstellar disk onto the protostar. FUor-type outbursts happen in a wide variety of sources from the very embedded ones to those with almost no sign of extended emission beyond the disk. The subsequent eruptions might gradually clear up the obscuring envelope material and drive the protostar on its way to become a disk-only T Tauri star. We used VLT/VISIR to obtain the first spectra that cover the 8-13 $\mu$m mid-infrared wavelength range in low-resolution of five recently discovered FUors. Four objects from our sample show the 10 $\mu$m silicate feature in emission. We study the shape and strength of the silicate feature in these objects and find that they mostly contain large amorphous grains, suggesting that large grains are typically not settled to the midplane in FUor disks. This is a general characteristic of FUors, as opposed to regular T Tauri-type stars whose disks display anything from pristine small grains to significant grain growth. We classify our targets by determining whether the silicate feature is in emission or in absorption, and confront them with the evolutionary scenarios on the dispersal of the envelopes around young stars. In our sample, all Class II objects exhibit silicate emission, while for Class I objects, the appearance of the feature in emission or absorption depends on the viewing angle with respect to the outflow cavity. This highlights the importance of geometric effects when interpreting the silicate feature.

7 pages, 1 table, 3 figures, accepted for publication in the Astrophysical Journal Letters

References in corpus (11)

• Crystalline silicates and dust processing in the protoplanetary disks of the Taurus young cluster
• Spitzer IRS Spectra and Envelope Models of Class I Protostars in Taurus
• Spitzer-IRS Observations of FU Orionis Objects
• Evolution of dust and ice features around FU Orionis objects
• The ALMA early science view of FUor/EXor objects - V: continuum disc masses and sizes
• V346 Nor: the post-outburst life of a peculiar young eruptive star
• Mass transport from the envelope to the disk of V346 Nor: a case study for the luminosity problem in an FUor-type young eruptive star
• Brightness variations of the FUor-type eruptive star V346 Nor
• The progenitor of the FUor-type young eruptive star 2MASS J06593158-0405277
• Interferometric view of the circumstellar envelopes of northern FU Orionis-type stars
• The weakening outburst of the young eruptive star V582 Aur

Cited by in corpus (8)

• Massive compact disks around FU Orionis-type young eruptive stars revealed by ALMA
• Discovery of a mid-infrared protostellar outburst of exceptional amplitude
• V899 Mon: a peculiar eruptive young star close to the end of its outburst
• An APEX study of molecular outflows in FUor-type stars
• A complex dust morphology in the high-luminosity AGN Mrk 876
• Accretion Burst Crystallizes Silicates in a Planet-Forming Disk
• Gaia20bdk -- a new FUor in Sh 2-301 Star Forming Region
• A gap at 1 au in the disk of DI Cha A revealed by infrared interferometry