1 Introduction

RW Aurigae is one of the brightest T Tauri stars (TTSs). It is also a most unusual and extreme object of its kind, and has always played a joker in the exploration of the nature of young low mass pre-main sequence objects.

RW Aur is a resolved triple star system (Ghez et al. 1993), and has a bipolar jet rooted at the brightest component, RW Aur A (e.g. Mundt & Eislöffel 1998; Dougados et al. 2000). Strong and rapid, but irregular brightness variations are common - usually measured for component A, which dominates the flux (see e.g. Gahm et al. 1993; Herbst et al. 1994), and the star is a bright infrared source, with a rather flat spectrum longward of 1 $\mu$m (Cohen & Schwartz 1976; Ghez et al. 1997).

Already Joy (1945) commented on the magnificent spectrum with strong and broad emission lines. Weak, presumably photospheric, absorption lines indicate a star of spectral type K (e.g. Mundt & Giampapa 1982; Valenti et al. 1993), and Hartmann et al. (1986) found that these lines vary in radial velocity. The weakness of the lines indicates the presence of continuous and/or line excess emission - the spectrum is veiled.

The emission line spectrum is very complex, and many lines are blended with each other. Some of the broad emission lines also have narrow emission components, and some have absorption components: broad red-shifted, central and/or slightly blue-shifted in velocity. All these components have been found to undergo strong and rapid (hours/days) changes in fluxes, profiles, and radial velocities (Gahm 1970; Appenzeller & Wolf 1982; Hartmann 1982; Mundt & Giampapa 1982; Appenzeller et al. 1983; Grinin et al. 1983; Stout-Batalha & Batalha 2000).

Many ideas on the cause of the photometric and spectral variability observed on classical TTSs, like RW Aur A, have seen light over the years. Presently, the concept of magnetospheric accretion has been successful in explaining many observed phenomena (see Hartmann 1998, and references therein). Irregular accretion to heated regions at the stellar poles has been recognized as a process for producing irregular light variability (variable veiling hot spots), while gas blobs flowing through the magnetosphere could cause variability of the emission line spectrum (see e.g. Gullbring et al. 1996 and references therein).

The magnetospheric accretion model predicts a correlation between veiling and brightness. Such correlations have been reported (e.g. Gahm et al. 1995; Hessman & Guenther 1997; Chelli et al. 1999), but rather little systematic, long-term spectroscopic and photometric monitoring has been made in order to explore this effect.

The original aim of the present program was to check this particular prediction. One of the selected objects was RW Aur A, which shows clear evidence of variable accretion in several spectral lines along with the chaotic photometric variability. Surprisingly, we found practically no correlation between the degree of veiling and the brightness, as will be discussed below. Instead, we discovered periodic radial velocity changes in the photospheric lines, and also periodic phenomena in practically all other spectral components (Gahm et al. 1999, hereafter called Paper I).

In Paper I, we focussed on the possibility that RW Aur A is a close binary with a secondary of very low mass, possibly a brown dwarf, moving in a nearly circular orbit at less than 10 solar radii from the primary. We reserved a full discussion of all spectral features, and their complex and interwoven variabilities, for a more extensive presentation. In addition, we have also collected a new series of observations of the star at the Nordic Optical Telescope in 1999. The present paper summarizes our findings.