  Young T Tauri stars (TTS) are surrounded by an accretion disk, which over
time disperses due to photoevaporation, accretion, and possibly planet
formation. The accretion shock on the central star produces an UV/optical
veiling continuum, line emission, and X-ray signatures. As the accretion rate
decreases, the impact on the central star must change. In this article we study
MN Lup, a young star where no indications of a disk are seen in IR
observations. We present XMM-Newton and VLT/UVES observations, some of them
taken simultaneously. The X-ray data show that MN Lup is an active star with
L_X/L_bol close to the saturation limit. However, we find high densities (n_e >
3e10 /cm^3) in the X-ray grating spectrum. This can be well fitted using an
accretion shock model with an accretion rate of 2e-11 M_sun/yr. Despite the
simple Halpha line profile which has a broad component, but no absorption
signatures as typically seen on accreting TTS, we find rotational modulation in
Ca II K and in photospheric absorption lines. In the Halpha line we see a
prominence in absorption about 2R_* above the stellar surface - the first of
its kind on a TTS. MN Lup is also the only TTS where accretion is seen, but no
dust disk is detected that could fuel it. We suggest that MN Lup presents a
unique and short-lived state in the disk evolution. It may have lost its dust
disk only recently and is now accreting the remaining gas at a very low rate.
