Tracing the origins of permitted emission lines in RU Lupi down to AU scales^*

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: [lindapod;fran]@arcetri.astro.it
² Centro de Astrofísica da Universidade do Porto, Rua das Estrelas s/n, 4150-762 Porto, Portugal e-mail: pgarcia@astro.up.pt
³ Departamento de Engenharia Física, Faculdade de Engenharia da Universidade do Porto, Portugal
⁴ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy e-mail: [nisini;antoniucci]@mporzio.astro.it
⁵ Laboratoire d'Astrophysique de Grenoble, BP 53, 38041 Grenoble Cedex, France e-mail: dougados@obs.ujf-grenoble.fr
⁶ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, Taipei 10617, Taiwan, R.O.C. e-mail: hiro@asiaa.sinica.edu.tw

Received: 17 September 2007
Accepted: 13 November 2007

Abstract

Context.Most of the observed emission lines and continuum excess from young accreting low mass stars (Classical T Tauri stars – CTTSs) take place in the star-disk or inner disk region. These regions have a complex emission topology that is still largely unknown.

Aims.In this paper the magnetospheric accretion and inner wind contributions to the observed permitted He and H near infrared (NIR) lines of the bright southern CTTS RU Lupi are investigated for the first time.

Methods.Previous optical observations of RU Lupi have shown a strong Hα profile, due to the emission from a wind in the line wings, and a micro-jet detected in forbidden lines. We extend this analysis to NIR lines through the seeing-limited, high spectral-resolution spectra taken with VLT/ISAAC, and narrow-band imaging and low spectral-resolution spectroscopy acquired with the adaptive optics (AO) aided telescope VLT/NACO. Using spectro-astrometric analysis we investigate the presence of extended emission down to very low spatial scales (a few AU).

Results.The HeI λ10830 line presents a P Cygni profile whose absorption feature indicates the presence of an inner stellar wind. Moreover, the spectro-astrometric analysis proves the presence of an extended emission superimposed on the absorption feature and likely coming from the micro-jet detected in the optical. In contrast, the origin of the hydrogen Paschen and Brackett lines is difficult to address. We tried to explain the observed line profiles and flux ratios with both accretion and wind models showing the limits of both approaches. The lack of a spectro-astrometric signal indicates that the HI emission is either compact or symmetric. Our analysis confirms the sensitivity of the HeI line to the faint extended emission regions in the close proximity of the star.