Near-to-far Infrared Variability of EX Lup-type Stars: Clues to Disk Structure and Accretion
First Author:
Agnes Kospal
Email: kospal AT strw.leidenuniv.nl
Leiden Observatory, Leiden, The Netherlands
Niels Bohrweg 2
Leiden, NL-2333 CA, The Netherlands
Coauthors:
Abraham, Peter, Konkoly Observatory, Budapest, Hungary
Ardila, David, NASA Herschel Science Center, Pasadena, CA
Abstract
EX Lupi-type stars (EXors) are low-mass pre-main sequence stars exhibiting large, repetitive optical outbursts, thought to be powered by enhanced accretion from the circumstellar disk to the star. The brightness evolution of EXors in the near-to-far infrared regime has never been studied, although this is the wavelength range where the emission is dominated by the circumstellar material. By analyzing how changing accretion and illumination affect different parts of the disk, infrared flux variations help us to gather information on disk structure and energetics and to clarify the role of the circumstellar material in the eruption. We investigate the brightness evolution of four well-kown EXors: the prototype EX Lup, as well as DR Tau, VY Tau and UZ Tau E. Using archival Spitzer data to obtain their spectral energy distributions (SEDs), we compare these SEDs with ones derived from IRAS, ISO, 2MASS, and ground-based measurements taken in the last 25 years. We report, for the first time, clear flux changes at infrared wavelengths for several targets. The wavelength dependence of the flux changes varies considerably from star to star. By modelling the wavelength dependence of the flux changes with a radiative transfer code, we test whether variable accretion can account for the observations or geometric changes should also be invoked.
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