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Abstract: EX Lup is the prototype of EXors, a subclass of low-mass pre-main sequencestars whose episodic eruptions are attributed to temporarily increasedaccretion. In quiescence the optical and near-infrared properties of EX Lupcannot be distinguished from those of normal T Tau stars. Here we investigatewhether it is the circumstellar disk structure which makes EX Lup an atypicalClass II object. During outburst the disk might undergo structural changes. Ourcharacterization of the quiescent disk is intended to serve as a reference tostudy the physical changes related to one of EX Lupi-s strongest knowneruptions in 2008 Jan-Sep. We searched the literature for photometric andspectroscopic observations including ground-based, IRAS, ISO and Spitzer data.After constructing the optical-infrared spectral energy distribution SED, wecompared it with the typical SEDs of other young stellar objects and modeled itusing the Monte Carlo radiative transfer code RADMC. A mineralogicaldecomposition of the 10 micron silicate emission feature and also thedescription of the optical and near-infrared spectra were performed. The SED isin general similar to that of a typical T Tauri star, though above 7 micron EXLup emits higher flux. The quiescent phase data suggest low level variabilityin the optical-mid-infrared domain. Integrating the optical and infrared fluxeswe derived a bolometric luminosity of 0.7 L Sun. The 10 micron silicate profilecould be fitted by a mixture consisting of amorphous silicates, no crystallinesilicates were found. A modestly flaring disk model with a total mass of 0.025M Sun and an outer radius of 150 AU was able to reproduce the observed SED. Thederived inner radius of 0.2 AU is larger than the sublimation radius, and thisinner gap sets EX Lup aside from typical T Tauri stars.

Author: N. Sipos, P. Ábrahám, J. Acosta-Pulido, A. Juhász, Á. Kóspál, M. Kun, A. Moór, J. Setiawan

Source: https://arxiv.org/

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