We present a detailed spectroscopic analysis of the luminous blue variable AG Carinae during the last two visual minimum phases of its S-Dor cycle (1985-1990 and 2000-2003). The analysis reveals an overabundance of He, N, and Na, and a depletion of H, C, and O, on the surface of AG Car, indicating the presence of CNO-processed material. Furthermore, the ratio N/O is higher on the stellar surface than in the nebula. We found that the minimum phases of AG Car are not equal to each other, since we derived a noticeable difference between the maximum effective temperature achieved during 1985-1990 (22, 800 K) and 2000-2001 (17, 000 K). Significant differences between the wind parameters in these two epochs were also noticed. While the wind terminal velocity was 300 km s −1 in 1985-1990, it was as low as 105 km s −1 in 2001. The mass-loss rate, however, was lower from 1985-1990 (1.5 × 10 −5 M ⊙ yr −1 ) than from 2000-2001 (3.7 × 10 −5 M ⊙ yr −1 ). We found that the wind of AG Car is significantly clumped (f ≃ 0.10 − 0.25) and that clumps must be formed deep in the wind. We derived a bolometric luminosity of 1.5 × 10 6 L ⊙ during both minimum phases which, contrary to the common assumption, decreases to 1.0 × 10 6 L ⊙ as the star moves towards maximum flux in the V band. Assuming that the decrease in the bolometric luminosity of AG Car is due to the energy used to expand the outer layers of the star (Lamers 1995), we found that the expanding layers contain roughly 0.6 − 2 M ⊙ . Such an amount of mass is an order of magnitude lower than the nebular mass around AG Car, but is comparable to the nebular mass found around lower-luminosity LBVs and to that of the Little Homunculus of Eta Car. If such a large amount of mass is indeed involved in the S Dor-type variability, we speculate that such instability could be a failed Giant Eruption, with several solar masses never becoming unbound from the star.

The dust formation process in the winds of Asymptotic Giant Branch stars is discussed, based on full evolutionary models of stars with mass in the range 1M ⊙ M 8M ⊙ , and metallicities 0.001 < Z < 0.008. Dust grains are assumed to form in an isotropically expanding wind, by growth of pre-existing seed nuclei.Convection, for what concerns the treatment of convective borders and the efficiency of the schematization adopted, turns out to be the physical ingredient used to calculate the evolutionary sequences with the highest impact on the results obtained.Low-mass stars with M 3M ⊙ produce carbon type dust with also traces of silicon carbide. The mass of solid carbon formed, fairly independently of metallicity, ranges from a few 10 −4 M ⊙ , for stars of initial mass 1 − 1.5M ⊙ , to ∼ 10 −2 M ⊙ for M∼ 2 − 2.5M ⊙ ; the size of dust particles is in the range 0.1µm a C 0.2µm. On the contrary, the production of silicon carbide (SiC) depends on metallicity. For 10 −3 Z 8 × 10 −3 the size of SiC grains varies in the range 0.05µm < a SiC < 0.1µm, while the mass of SiC formed is 10 −5 M ⊙ < M SiC < 10 −3 M ⊙ .Models of higher mass experience Hot Bottom Burning, which prevents the formation of carbon stars, and favours the formation of silicates and corundum. In this case the results scale with metallicity, owing to the larger silicon and aluminium contained in higher-Z models. At Z=8 × 10 −3 we find that the most massive stars produce dust masses m d ∼ 0.01M ⊙ , whereas models of smaller mass produce a dust mass ten times smaller. The main component of dust are silicates, although corundum is also formed, in not negligible quantities (∼ 10 − 20%).

Context. The First Byurakan Survey (FBS), also known as the Markarian Survey, is the largest low resolution spectroscopic survey of the sky and led to the discovery of 1500 UV-excess (UVX) galaxies and starburst galaxies. The FBS plates have also been used to search for UVX stellar objects, late-type stars, and for the identification of unusual infrared sources. Aims. The Digitized First Byurakan Survey (DFBS) provides the astronomical community with a digitized version of the FBS images and with the extracted spectra for the objects present in the plates. Methods. Nearly 2000 plates have been scanned and stored and programs were developed to compute the astrometric solution, extract the spectra, and apply wavelength and photometric calibration for the objects present in the plates. Results. The DFBS database and catalog of objects has been assembled. The DFBS database contains data for 20 000 000 objects present in the survey and provides tools for accessing the DFBS. Conclusions. New scientific projects as well as existing surveys will benefit by the digitized images and the ready-to-use extracted spectra which will allow an efficient computer-based analysis of the dataset.

We present the historical light curve of the BL Lac object S5 0716+714, spanning the time interval from 1953 to 2003, built using Asiago archive plates and our recent CCD observations, together with literature data. The source shows an evident long-term variability, over which well-known short-term variations are superposed. In particular, in the period from 1961 to 1983 the mean brightness of S5 0716+714 remained significantly fainter than that observed after 1994. Assuming a constant variation rate of the mean magnitude, we can estimate a value of about 0.11 mag yr À1 . The simultaneous occurrence of decreasing ejection velocities of superluminal moving components in the jet reported by Bach and coworkers suggests that both phenomena are related to the change of the direction of the jet to the line of sight from about 5 to 0N7 for an approximately constant bulk Lorentz factor of about 12. A simple explanation is a precessing relativistic jet, which should at present be close to the smallest orientation angle. One can therefore in the next 10 years expect a decrease of the mean brightness of about 1 magnitude.

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