For the search of Herbig Ae/Be objects in the extremely young open cluster NGC 6611 we have selected a sample of 52 pre-main sequence candidates, discovered by Walker (1961), Sagar & Joshi (1979), Chini & Wargau (1990) and The et al. (1990). We continue the approach of the last paper by studying each star individually with new and unpublished Walraven WULBV, Johnson/Cousins UBV(RI)(C) and Johnson JHKLM photometric data as well as low resolution spectroscopy.Each object is shown to have its own extinction law, which is investigated using their spectral energy distribution (SED). There does not seem to be a clear relationship between the location of a star and the extinction law. This means that the extinction is generated locally and its correction must be taken individually. For each object accurate astrophysical parameters are then derived. Plotting the objects in an HR-diagram, together with the values for the E(B - V), the probability of membership value P and the extinction characteristics, helps to discriminate between cluster members and non-cluster members.Most foreground stars are of late spectral type and are labeled as Group III objects. Group I, to which most members of this cluster belong, contains objects of early spectral type. Part of them seem to be in their post ZAMS phase and the other part in their pre-ZAMS stage. By comparing the evolutionary tracks of Palla & Stahler (1993) for pre-MS objects and of Maeder & Meyenet (1988) for post-MS stars we have concluded that the cluster contains objects of a few 0.1 Myr as well as objects of about 6 Myr. As most of the Group I objects do not show well-known Herbig Ae/Be characteristics, the time scale of clearing the disk material must be typically less than about 0.1 Myr for the more massive objects. Objects that show an IR-excess are found among the less luminous ones. They could still be in their pre-ZAMS phase, having an age of about 1 Myr. Such an age is appropriate for the Group II objects, which are of intermediate spectral type. As they are located close to the stellar birthline they should have been formed recently. It seems that an efficient clearing mechanism must have taken place, because not many of these objects are embedded and show only some IR-anomalies. This could be the reason that we have found no more than four typical Herbig Ae/Be candidates.We support the hypothesis of Hillenbrand et al. (1993) that there is an age spread in NGC 6611. The stars with the highest Av values are located in the centre of the cluster, somewhat to the northwest. This coincides with the location of many embedded sources more towards the northwest, a region in which star-formation is probably still taking place. The age of the most evolved objects is about 6 Myr.It would be interesting to study these regions and the Group II objects since investigating the youngest objects which are still partly embedded may help us to understand the first phases of star formation and the rapid cleaning of the circumstellar material. Young ''naked'' stars can also be formed by evaporating gaseous globules (EGGs) as was recently discovered in dark regions of this cluster (Hester & Scowen 1995). The lack of angular momentum of such objects could explain the paucity of HAeBe candidates.

The spectral classification of 42 southern metallic-line and peculiar A- type stars is described. (auth)

Using data obtained with the IRAS and groundbased telescopes, the spectral energy distribution of the pre-main sequence stars HD 176386, TY CrA, R CrA and T CrA were constructed and analysed. For all stars two possible models, one based on a normal extinction law and another one with an extinction law characterized by R > 3.1 are considered. Only the latter model turns out to be acceptable. HD 176386 and TY CrA have excess radiation in the far infrared only. This excess is caused by rather cool dust (T approximately 95 K) located at quite a distance from the central star (up to about 1000 AU). The stars R CrA and T CrA not only have excess radiation in the far-IR but in the near-IR as well. This near-IR excess is caused by a dust shell located close to the star (within 2 AU) with an average temperature of 1310 K (R CrA) and 1370 K (T CrA). Analysis of the properties of these hot dust shells, based on a spherical symmetric model, indicate large particles of iron and/or graphite to be the most likely constituents. HD 176386 is constant in brightness, whereas TY - CrA shows only minor (< 0.m15) fluctuations. R and T CrA are both variable stars (maximum DELTA-V = 4.m4 and 2.m6, respectively). We believe that this difference is due to the presence or absence of dust close to the central star. In the HR diagram all four stars are located in the region where intermediate mass pre-main sequence stars are theoretically predicted to be found (Palla & Stahler 1990). With Iben (1965) it is seen that the variable stars R CrA and T CrA are relatively younger compared to the not or hardly variable stars HD 176386 and TY CrA. Therefore, we believe the presence of hot dust relatively close to these stars to represent a (very) young stage of pre-stellar evolution. HD 176386 and TY CrA are probably in a more evolved stage of evolution, one in which this dust has already been cleared away.

Intermediate and narrow band photometry of SN 1987 A are presented. All observations are carried out at the Danish 0.5 m telescope at European Southern Observatory (ESO), La Silla, and presented in the instrument system. The bands in the Stromgren system are uvby, βW, a wide H β filter, and βN, a narrow H β filter. Flux calibrations are derived for the first time for the H β passbands, and improved flux calibrations are given for the uvby passbands

We present a list of 23 Herbig Ae/Be stars and Herbig Ae/Be star candidates. All stars have been observed for 2 up to 8 years in the Stromgren photometric system, making it possible to gain more insight in the nature of their variability. The results of our study are the following: 1) Spectral type A0 separates the stars showing large variations in their brightness (0.m65 less-than-or-equal-to DELTA-y less-than-or-equal-to 3.m0) from those showing small variations (DELTA-y < 0.m20), with the later spectral type stars being the more variable. For stars of spectral type A0 both small and large variations are observed. 2) The behaviour of the stars in the colour-magnitude diagram can be divided into three classes: one in which there is a monotonic dependence of the colour index on visual brightness (class R), one in which this dependence is non-monotonic (class CR), and a third in which there does not seem to be such a dependence (class RB). The latter is mostly found among the stars showing small variations in their brightness. Among the stronger variables there is only one star that belongs to this class. 3) The behaviour in the colour-magnitude diagram is spectral type independent but does seem to depend on the size of the variation in brightness: all stars of class CR have DELTA-y greater-than-or-equal-to 1.m70. All those belonging to the other two classes have DELTA-y less-than-or-equal-to 1.m70. 4) A majority of the variable stars show a preference to be near maximum brightness. However, irrespective of such a preference, these stars can be divided into two groups according to their type of variability: stars showing periods of calmness (i.e. periods in which the luminosity of the star stays almost constant) and those that do not. Furthermore, the time scale on which the latter group displays variations in brightness of several tenths of a magnitude is, in general, much shorter than that displayed by stars of the first group.

We present intermediate and narrow band photometry of SN 1987 A. All observations are carried out at the Danish 0.5m telescope at European Southern Observatory (ESO), La Silla, and presented in the instrumental system. The bands in the Stromgren system are u (lambda-eff = 3505 angstrom, FWHM = 325 angstrom), v (4110 angstrom, 170 angstrom), b (4685 angstrom), 185 angstrom), y (5488 angstrom, 225 angstrom), beta-W, a wide H-beta filter (4864 angstrom, 135 angstrom), and beta-N, a narrow H-beta filter (4865 angstrom, 30 angstrom). Flux calibrations are derived for the first time for the H-beta passbands, and improved flux calibrations are given for the uvby passbands.

aration is an average of 4 measures of the double distance. It is possible now, after nearly four years and seven observing missions at La Silla, to make the first conclusions on the work done. Regarding the air tranquillity, La Silla is largely superior to the average of European sites of which I have direct observing experience. 51 % of the nights have been completely utilizable or in part (26% "good quality" nights and 25% "sufficient quality" nights), while during the remaining 49% of nights, bad seeing or covered sky have prevented the observations. A comparison with the seeing measurements made at Cerro Vizcachas has allowed to establish that, when the value measured there is better than 0'!7, generally, the images at the GPO can be considered good; in these conditions the diffraction image presents itself as stable and the "turbulence" is less than 0V14 (for the definition of "turbulence", see Danjon and Couder, 1935, or Texereau, 1958). Up till now, a total of 1840 measurements of 432 systems, down to separations of 01.'18, have been made at La Silla. Figure 5 shows the histogram of the percentages of the measurements made by class of separation. From these first results, it is my firm belief that La Silla is a very valid site for the observation of visual double stars. The contribution that a good observer (who could rely full time, for this kind of observations, on the GPO astrograph, or on an instrument of superior class) could give to the astronomy of visual double stars and to the knowledge of stellar masses, would be fundamental.

Le comportement de l'etoile variable irreguliere UX Ori dans le diagramme magnitude-couleur montre que la courbe se separe en 2 parties distinctes, une branche rouge (partie de la courbe allant du maximum jusqu'a un certain point de rebroussement) et une branche bleue (partie allant du point de rebroussement jusqu'au minimum). De plus, il semblerait que selon le comportement de l'etoile dans une branche particuliere, ces branches elles-memes peuvent etre sectionnees en 2 parties. L'exces IR observe pour UX Ori peut etre explique comme une re-emission thermique par les grains de poussiere circumstellaire.