EX Lupi in quiescence

Abstract

Aims. EX Lupi is the prototype of EXors, a subclass of low-mass pre-main sequence stars whose episodic eruptions are attributed to temporarily increased accretion. In quiescence the optical and near-infrared properties of EX Lup cannot be distinguished from those of normal T Tau stars. Here we investigate whether it is the circumstellar disk structure that makes EX Lup an atypical Class II object. During outburst the disk might undergo structural changes. Our characterization of the quiescent disk is intended to serve as a reference for studying the physical changes related to one of EX Lupi's strongest known eruptions in 2008 Jan-Sep. Methods. We searched the literature for photometric and spectroscopic observations including ground-based, IRAS, ISO, and Spitzer data. After constructing the optical-infrared spectral energy distribution (SED), we compared it with the typical SEDs of other young stellar objects and modeled it using the Monte Carlo radiative transfer code RADMC. We determined the mineralogical composition of the 10 μm silicate emission feature and also gave a description of the optical and near-infrared spectra. Results. The SED is similar to that of a typical T Tauri star in most aspects, though EX Lup emits higher flux above 7 μm. The quiescent phase data suggest low-level variability in the optical-mid-infrared domain. By integrating the optical and infrared fluxes, we derived a bolometric luminosity of 0.7 L . The 10 μm silicate profile could be fitted by a mixture consisting of amorphous silicates, but no crystalline silicates were found. A modestly flaring disk model with a total mass of 0.025 M and an outer radius of 150 AU was able to reproduce the observed SED. The derived inner radius of 0.2 AU is larger than the sublimation radius, and this inner gap sets EX Lup apart from typical T Tauri stars.

Accretion dynamics of EX Lupi in quiescence

“…The luminosity is highly variable owing to variations in the accretion rate. The estimated stellar radius is ∼1.6 R (Sipos et al 2009). The rotational velocity (v sin i) is consistent with the value of 4.4 ± 2.0 km s −1 (Sipos et al 2009).…”

“…The lack of near-infrared (near-IR) excess is interpreted as a small, dust-depleted hole in the disk, with size ∼0.3 AU (Sipos et al 2009). Observations of CO Banzatti et al 2015) are also in agreement with a sub-AU hole, mostly devoid of dust.…”

“…Observations of CO Banzatti et al 2015) are also in agreement with a sub-AU hole, mostly devoid of dust. It had been suggested that the disk was relatively massive (0.025 M for a star with mass ∼0.6 M ) based on disk models containing only small dust grains (Sipos et al 2009). If instead we assume a more typical maximum grain size of 100 µm, as is usually found in other T Tauri stars (D'Alessio et al 2001(D'Alessio et al , 2006Andrews & Williams 2007), the disk mass does not need to be so extreme and could be below 1% of the stellar mass (Appendix B).…”

“…Estimates of the accretion rate based on Pa β (Sipos et al 2009) and on multiple emission lines (using the relations of Alcalá et al 2014; Appendix C) result in a value of 4 ± 2 × 10 −10 M /yr. The observed Hα width at 10% of the peak ) during our quiescence data are in agreement with these values, although for some of the spectra with stronger lines, the accretion rate increases up to ∼10 −9 M /yr.…”

First X-ray detection of the young variable V1180 Cassiopeiae

“…Lorenzetti et al 2007;Sipos et al 2009;Antoniucci et al 2013), is still very uncertain. Although there is general consensus about the nature of the outbursts (i.e.…”