Homogeneous observational data on four photometric systems which cover the spectral range from 0.14 to 4 microns through narrow, intermediate and broad passband filters are used to review and derive some photometric characteristics of Be stars. We find that 60% of the stars under discussion have ultraviolet and infrared excesses.

Variations of Balmer emission line strength for Be stars are compared to simultaneously measured photometric light-curves in the visual and infrared regions of the spectrum. Three different types of correlations between photometric and spectrometric variations are described. Variable intensity of continuous recombination radiation from ionized hydrogen in the circumstellar envelope is shown to be a major source of light variations for Be stars.

By the end of 1980, the total number of Be stars discovered in the field of open clusters amounted to 180 stars distributed in 60 clusters. Among these, 110 Be stars belong to 32 clusters included in the sample I studied, which contains 75 open clusters younger than the Hyades. But only 88 stars with complete UBV photoelectric photometry have been taken into consideration here. The concept of age groups, defined elsewhere (Mermilliod 1981a), is used throughout the present analysis, as well as the new estimate of the colour excesses and distance moduli I obtained for these 32 clusters. Under the assumption of uniform reddening across the clusters, absolute magnitudes and dereddened colour indices have been calculated for the 88 Be stars.

A comprehensive catalogue of more than 1100 Be stars with known MK classification has been prepared at the Strasbourg Stellar Data Center, and is described in an other session of this Symposium (Jaschek and Egret, 1982). The compilation of photometric and spectroscopic data available for these stars has made possible a general statistical approach of the Be star spectral group.

101 normal Be stars, probable members of 56 galactic clusters and OB-associations, and more than 20 extreme Be stars in the Large Magellanic Cloud were used to derive intrinsic colours of 09-B9 (III-V)e stars. Furthermore, the correlation between the intrinsic colour (U-B)0 and the absolute magnitude of non-supergiant Be stars was confirmed to be and

The aim of the present investigation is to enlarge the basis for the determination of intrinsic colours and absolute magnitudes by providing a large sample from the southern sky.

The absolute luminosity of most Be stars can be determined by using Balmer line narrow band photometry with an accuracy of about 0.4 mag. The few cases in which this method fails can be detected.

The ratios α=ΔV/Δ(B-V) and β=Δ(U-B)/Δ(B-V) for the long-term variation of Be stars have been derived. The inclination effect on α is found. The dependence of α on the spectral type is also inferred. The signs of α and β are essentially the same.

Eight years ago a program was started at the Vatican Observatory to search for faint emission-line stars close to the galactic plane. Indeed at that time few early type emission stars were known fainter than V = 12. This survey consists in a double program:the search for emission line stars with the Vatican Schmidt using the objective prism and an appropriate combination of plate and filter in order to have a narrow passband around Hα(McCarthy Treanor 1970);and UBVRI photometry at the Mt. Lemmon facilities of the Univ. of Arizona observatories. Five papers have already been published(Coyne et al 1974, 1975, 1978;Wisniewski et al 1976, 1977). Two more will be published later this year. The Vatican Emission Star Survey(VES) resulted in the discovery of about 1000 new emission-line stars; for 700 of those the photometry is finished.

In our photoelectric searches for the β Cephei variables (JS77, JS79, and J82) several early B stars with nebulous lines were included. A summary of their photometric behaviour is presented in Table 1, columns four to six. Two of the stars, HR 2963 and HR 3476, are

apparently constant in light, HR 3213 is a short-period β Cephei star, HR 3462 shews ellipsoidal variations with a period of Od.563, which implies an orbital period twice that long (cf. also Shobbrook 1981), and HR 8854 is an eclipsing binary with P = 2d.3913.

One of the greatest difficulties in interpreting the continuous spectrum of Be stars is to separate the effects of interstellar reddening from the effects due to the presence of the envelope. This difficulty has been avoided in the two types of correlations considered here. In the first one, parameters not affected by interstellar reddening are used (the Balmer jump and the Balmer decrement). In the second one, the parameters used can be affected by the interstellar extinction but comparisons are made only between values which correspond to the same (but variable) Be star, at different epochs, with different amounts of emission.

The intrinsic reddening and its relation with Hα emission has been determined for 32 Be/Shell stars observed simultaneously at high dispersion at Hα and between λλ3000-and 6200 Å with the Chalonge spectrograph. A trend toward higher reddenings when Hα emission is stronger is observed, together with a large scatter which indicates that for a given emission at Hα, intrinsic reddening can be quite different for different stars.

The spectrophotometric behavior of the Be/shell stars seems to be different when their second Balmer discontinuity is in emission from that when it is in absorption. We have analysed here a particular case in which the second Balmer jump is in absorption. In this note we compare the results of a BCD analysis concerning the variations of the Be-Shell star 88 Her (HD162732), to the results of the UBV photometry.

Based upon a sample of 140 B0-A0 emission-line stars contained in “A Photographic Atlas of Be stars” statistical relationships between variable stars and Be stars are examined. It is found that 44 % of all the stars of the sample show some kind of photometric variations. The stars with narrow metallic absorption lines display relatively more intense photometric activity. Proceeding from this conclusion, the photometric variability of two stars HD 50138 and HD 193182 can be predicted.

Results of photoelectric observations of HDE 245770 spreaded over six years are presented. No variations greater than some hundreths of magnitudes are evident in contrast with the ancient light history, which is more complex. A sensible variation of the colour indices is present on a time scale of tens of years. The temporal analysis of these data shows some evidence of orbital periodicity.

A review of the most recent developments in polarization studies of Be stars is presented. New polarization techniques for high-resolution spectropolarimetry and for near infrared polarimetry are described and a wide range of new observations are discussed. These include broadband, intermediate-band and multichannel observations of the continuum polarization of Be stars in the wavelenght interval 0.3–2.2 microns, high resolution (0.5 Å) line profile polarimetry of a few stars and surveys of many stars for the purposes of statistical analyses. The physical significance of the observational material is discussed in the light of recent theoretical models. Emphasis is placed on the physical and geometrical parameters of Be star envelopes which polarimetry helps to determine.

Simultaneous spectroscopic and polarimetric observations of about 40 bright southern Be stars have been carried out by Dr. Pöllitsch and myself with the ESO 1.5m coudé spectrograph and with the ESO two channel polarimeter.