2 Observations

The targets were given by the locations of the Lex/B absorption. Four by four square degree regions were centered on the shadows. The clouds were expected to be local due to the small emission in the shadows. Fairly bright stars have to be chosen in the temperature, log(g) and [Fe/H] range where the $uvby\beta$ data may be transformed to intrinsic properties. The problem was that no immediate target stars were available, a situation now remedied with the publication of the Tycho Catalog, ESA (1997). The PPM Catalog , Röser & Bastian (1993), provides a rough one dimensional spectral classification and all stars with a classification earlier than G5 were included but PPM is of course not complete. The PPM candidates were supplemented with all stars from the Space Telescope Guide Star Catalog brighter than $V\approx$11.5$\rm ^m$. The GSC provides, however, only a magnitude and a position but no color information, (Lasker et al. 1990). The resulting observing lists ended up containing hundreds of stars for each region. Most of the stars have been identified in the recently published Tycho Catalog, ESA (1997).

The observations were carried out with the SAT, La Silla. SAT is a 50 cm telescope with a permanent six channel photometer designed for efficient work in the $uvby\beta$system. The telescope may be operated in a fully automated mode but was used in a semiautomatic way. Only letting the telescope center the star in a diaphragm. The integrations were followed manually since the temperature of most of the candidate stars were unknown. Any standard error or minimum count condition in all four bands could have left the telescope measuring only a few K, M stars in a night. The uvby observations were performed first in order to select a list of stars to have $\beta$observations, $\beta$ looses its sensitivity in the mid G star range.

On uvby nigths $\sim$50 standards from the lists of Crawford & Barnes (1970), Grønbech et al. (1976), Olsen (1983, 1993) were observed. The large number is necessary to cover the B, A, F, G, K, M range for dwarfs and evolved stars and with a spread in metallicity. Special care was taken to determine the atmospheric extinction since the lb165-32 shadow has a rather northern latitude.

After the uvby observations the $\beta$ data were taken. In principle much simpler but a little hampered but the narrowness $\sim$30 Å of the narrow band. In the March 1995 run there were some further problems with the wide band running wild at times due to sparks caused by oil leaking into the multiplier's socket. Apart from standards taken from the uvby standards mentioned above primary standards from Crawford & Mander (1966) were observed. In a $\beta$ night $\sim$25 standards are observed.

The observations were carried out during three observing runs in December 1993, November 1994 and March 1995. A total of seven weeks were spent at the telescope. The bulk of stars from the original list turned out to be later than the validity of the accurate distance, intrinsic color calibration of the $uvby\beta$ system. It is hoped that these late type stars eventually may be used to determine lower distance limits for the three shadowing clouds. Their location in front of the clouds will be confirmed by the absence of polarization and with one parameter less, E_b-y is known to be zero, their distance may be determined from the uvby photometry alone. Data for these late type stars are not included in the present catalog.