Using data from the German X-ray satellite ROSAT, we have studied an area of 230 square degrees of the Lupus SFR in search for new WTTS. On the basis of the ROSAT All-Sky Survey, 86 new WTTS and 3 CTTS could be discovered. 47 more TTS were discovered using pointed ROSAT observations of the Lupus 1-3 clouds. Comparing the XLF of the RASS-discovered WTTS in Lupus with an unbiased XLF for non-X-ray discovered WTTS in Taurus (Neuhäuser et al. 1995b), we were able to estimate the completeness of the RASS to about 31%.
Figure 4: Distribution of nearest-neighbour distances for previously known
TTS
(lower panel) and TTS found by the RASS (upper panel). Overplotted are the
expected (Poisson) distributions for a random spatial distribution
Although, due to its limited sensitivity, only a part of the total population is sampled with the RASS, its spatial completeness allowed us to investigate for the first time the spatial distribution of WTTS in the Lupus SFR on a large scale. We find that the numerous WTTS discovered by us are distributed over the whole area of our survey, contrary to the CTTS in the Lupus SFR, which are found almost exclusively in the vicinity of the dark clouds. Moreover, although our survey covers a large area including and surrounding the known concentrations of PMS stars, from the spatial distribution of our new WTTS we presume that we still do not sample all of the WTTS in the Lupus SFR, as WTTS are found up to the borders of our study region. The somewhat lower surface density of WTTS in the southeastern part of our survey area indicates, that the spatial distribution correlates with Gould's Belt rather than with the galactic plane.
The spatial distribution of the new WTTS discovered by the RASS, especially
the observation that many of these stars are found several degrees
away from the dense molecular clouds
of the Lupus SFR, indicates that these stars might be somewhat older than the
hitherto known TTS in Lupus. In this case they could have drifted away from
the dark clouds due to a velocity dispersion of 
as measured
for TTS in Taurus by Jones & Herbig (1979). We cannot
exclude the alternative that these stars were born near their present-day
location, and that their parent clouds have dispersed already. Such a model
for the formation of widely dispersed TTS in short-lived, rapidly
moving cloudlets has recently been proposed by Feigelson (1996).
However, this model also predicts that many of the widely dispersed WTTS
are older than TTS found in or near dark clouds.
In the Lupus 1-3 dark clouds, with our deep raster scan of pointed observations, numerous new WTTS have been discovered as well. The WTTS/CTTS ratio for the Lupus 1-3 clouds was found to be about unity. However, our work shows that the spatial distribution of WTTS differs significantly from that of the CTTS. Therefore the WTTS/CTTS increases significantly, if a larger area is taken into account. For the whole area of our survey we extrapolate a ratio of about 13, which has to be regarded as lower limit only, because most probably there are more WTTS outside the boundaries of our survey. Similar differences between the distribution of CTTS and WTTS have been found in the Taurus-Auriga SFR as well (Wichmann et al. 1996). In Taurus-Auriga as well as in Lupus it has been found, that in the most active part of the SFR, near the dark clouds, there is a WTTS/CTTS ratio of about unity, while these parts of the SFR are surrounded by a large, spatially extended population of WTTS.
Acknowledgements
This research was supported by grant KR 1053/3 from the DFG, Germany, grant 50OR90017 (Verbundforschung Astronomie) from the BMFT, Germany, and from CONACyT, Mexico. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. R. Wichmann would like to thank the staff at ESO, Chile, for the good support during the observations. The ROSAT project has been supported by the BMFT and the MPG, Germany. Many thanks also to the EXSAS and ROSAT teams at MPE.
Figure 5 shows the spectra of the new TTS in the 
and LiI region.
Finding charts are provided for all new TTS. All charts are 
;
north is up and east is left.
Figure 5: Low-dispersion spectra of new WTTS in Lupus. Shown is the 
and Li I region
