FS CMa type binaries

FS CMa type stars is a group of ~70 objects formerly known as unclassified stars with the B[e] phenomenon. Their very strong emission-line spectra in combination with a nearly main-sequence luminosity suggest the binary nature for them. They possess strong IR excesses due to radiation of circumstellar dust that implies a compact distribution probably in a circumbinary disk. Our long-term spectroscopic monitoring revealed neutral metal lines, which always include that of Li I 6708 \AA, in the spectra of some FS CMa objects indicating the presence of a cool star. We present a summary of our results with a first overview of FS CMa type binaries and review possible implications for the nature and evolutionary status of the entire group.Comment: 4 pages, 1 figure, to appear in EAS Publication Series, in proceedings of the "Physics Of Evolved Star 2015" conferenc

The B[e] phenomenon in the Milky Way and Magellanic Clouds

Discovered over 30 years ago, the B[e] phenomenon has not yet revealed all its puzzles. New objects that exhibit it are being discovered in the Milky Way, and properties of known objects are being constrained. We review recent findings about objects of this class and their subgroups as well as discuss new results from studies of the objects with yet unknown nature. In the Magellanic Clouds, the population of such objects has been restricted to supergiants. We present new candidates with apparently lower luminosities found in the LMC.Comment: 5 pages, 2 figures, IAU Symposium 272, Active OB stars: structure, evolution, mass loss and critical limit

On Protostellar Disks in Herbig Ae/Be Stars

The spectral shape of IR emission from Herbig Ae/Be stars has been invoked as evidence for accretion disks around high-mass protostars. Instead, we present here models based on spherical envelopes with $r^{-1.5}$ dust density profile that successfully explain the observed spectral shapes. The spectral energy distributions (SEDs) of eight primary candidates for protostellar disks are fitted in detail for all wavelengths available, from visual to far IR. The only envelope property adjusted in individual sources is the overall visual optical depth, and it ranges from 0.3 to 3. In each case, our models properly reproduce the data for both IR excess, visual extinction and reddening. The success of our models shows that accretion disks cannot make a significant contribution to the radiation observed in these pre-main sequence stars.Comment: 10 pages, 2 Postscript figures (included), uses aaspp4.sty. To appear in Astrophysical Journal Letter

VY Mon - the twin of Z CMa?

In 1985-1990 we obtained photometric, polarimetric and spectroscopic observations of the peculiar emission-line star VY Mon. These observational data were compared with those of Z CMa. To our opinion the similarity of the observational features of these stars is due to their similar nature

The remarkable outburst of the highly evolved post-period-minimum dwarf nova SSS J122221.7-311525

We report extensive 3-yr multiwavelength observations of the WZ Sge-type dwarf nova SSS J122221.7-311525 during its unusual double superoutburst, the following decline and in quiescence. The second segment of the superoutburst had a long duration of 33 d and a very gentle decline with a rate of 0.02 mag d-1, and it displayed an extended post-outburst decline lasting at least 500 d. Simultaneously with the start of the rapid fading from the superoutburst plateau, the system showed the appearance of a strong near-infrared excess resulting in very red colours, which reached extreme values (B - I ? 1.4) about 20 d later. The colours then became bluer again, but it took at least 250 d to acquire a stable level. Superhumps were clearly visible in the light curve from our very first time-resolved observations until at least 420 d after the rapid fading from the superoutburst. The spectroscopic and photometric data revealed an orbital period of 109.80 min and a fractional superhump period excess ?0.8 per cent, indicating a very low mass ratio q ? 0.045. With such a small mass ratio the donor mass should be below the hydrogen-burning minimum mass limit. The observed infrared flux in quiescence is indeed much lower than is expected from a cataclysmic variable with a near-main-sequence donor star. This strongly suggests a brown-dwarf-like nature for the donor and that SSS J122221.7-311525 has already evolved away from the period minimum towards longer periods, with the donor now extremely dim

Properties of galactic B[e] supergiants III. MWC 300

We present the results of optical and near-IR spectroscopic and mid-IR imaging observations of the emission-line star MWC 300. Its properties and evolutionary state are still under debate (a B[e] supergiant or a Herbig Be star)