Optical spectroscopy of EX Lupi during quiescence and outburst

Abstract

Context. EX Lupi is the prototype of EXor variables. After 50 years of mild variability and smaller outbursts, the object again experienced a large outburst in 2008. Aims. We explore the accretion mechanisms in EX Lupi during its pre-outburst, outburst, and post-outburst phases. Methods. We analyze 10 high-resolution optical spectra of EX Lupi, taken before, during, and after the 2008 outburst. In both quiescence and outburst, the star presents many permitted emission lines. These include lines typical of accreting T Tauri stars, plus a large number of neutral and ionized metallic lines (mostly Fe I and Fe II). During the outburst, the number of emission lines increases to about a thousand, and their structure shows a narrow and a broad component (NC and BC). We study the structure of the BC, which is highly variable on short timescales (24−72 h).Results. An active chromosphere can explain the metallic lines in quiescence and the outburst NC. The dynamics of the BC line profiles suggest that these profiles originate in a hot, dense, non-axisymmetric, and non-uniform accretion column that suffers velocity variations along the line-of-sight on timescales of days. Assuming Keplerian rotation, the emitting region would be located at ∼0.1−0.2 AU, which is consistent with the location of the inner disk rim, but the velocity profiles of the lines reveal a combination of rotation and infall. Line ratios of ions and neutrals can be reproduced assuming a temperature of T ∼ 6500 K for electron densities of a few times 10 12 cm −3 in the line-emitting region. The line profiles also indicate that there is an accretion-related inner disk wind. Conclusions. The data confirm that the 2008 outburst was an episode of increased accretion, albeit much stronger than previous EX Lupi and typical EXors outbursts. The line profiles are consistent with the infall/rotation of a non-axisymmetric structure that could be produced by clumpy accretion during the outburst phase. A strong inner disk wind appears in the epochs of higher accretion. The rapid recovery of the system after the outburst and the similarity between the pre-outburst and post-outburst states suggest that the accretion channels are similar during the whole period, and only the accretion rate varies, providing a superb environment for studying the accretion processes.

High-resolution TNG spectra of T Tauri stars

“…On the other hand, gas from the accretion funnel is expected to be ionised and to produce broader lines, such as the HI lines. The observed widths of the neutral metallic lines are consistent with an origin in the post-shock region of the accretion columns or in the inner disk, where the gas is heated to a few thousand K (Berinstain et al 1998;Sicilia-Aguilar et al 2012;Giannini et al 2017).…”

Radial velocity variations in the young eruptive star EX Lupi

“…This study is the continuation of a series of papers by our group investigating the quiescent state and the extreme outburst of EX Lup in 2008 (Sipos et al 2009;Ábrahám et al 2009;Goto et al 2011;Kóspál et al 2011;Juhász et al 2012;Sicilia-Aguilar et al 2012). In Sect.…”

“…Because EX Lup is a highly active star, special care had to be taken when determining its RV. During the 2008 outburst, except for a very veiled Li 6708 Å line, no photospheric absorption lines were visible in the optical and nearinfrared spectra of EX Lup (Sicilia-Aguilar et al 2012;Kóspál et al 2011). Thus RV determination was not possible from those spectra.…”

LBT/LUCIFER near-infrared spectroscopy of PV Cephei

“…We can now compare our results with the circumstellar environment of the EXor prototype EX Lup (Kóspál et al 2011b;Sicilia-Aguilar et al 2012) to get a more quantitative evaluation. Our analysis shows many similarities between the two objects, both in the physical structure and the observed spectra.…”