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ABSTRACT We present new photometric and spectroscopic observations of an unusual luminous blue variable (LBV) in NGC 3432, covering three major outbursts in 2008 October, 2009 April and 2009 November. Previously, this star experienced an outburst also in 2000 (known as SN 2000ch). During outbursts the star reached an absolute magnitude between −12.1 and −12.8. Its spectrum showed H, He i and Fe ii lines with P-Cygni profiles during and soon after the eruptive phases, while only intermediate-width lines in pure emission (including He iiλ4686) were visible during quiescence. The fast-evolving light curve soon after the outbursts, the quasi-modulated light curve, the peak magnitude and the overall spectral properties are consistent with multiple episodes of variability of an extremely active LBV. However, the widths of the spectral lines indicate unusually high wind velocities (1500-2800 km s−1), similar to those observed in Wolf-Rayet stars. Although modulated light curves are typical of LBVs during the S-Dor variability phase, the luminous maxima and the high frequency of outbursts are unexpected in S-Dor variables. Such extreme variability may be associated with repeated ejection episodes during a giant eruption of an LBV. Alternatively, it may be indicative of a high level of instability shortly preceding the core-collapse or due to interaction with a massive, binary companion. In this context, the variable in NGC 3432 shares some similarities with the famous stellar system HD 5980 in the Small Magellanic Cloud, which includes an erupting LBV and an early Wolf-Rayet star. [ABSTRACT FROM AUTHOR]

The spectral distributions of Be/X-ray binaries in the Large Magellanic Cloud and Galaxy have been shown to differ significantly from the distribution of isolated Be stars in the Galaxy. Population synthesis models can explain this difference in spectral distributions through substantial angular momentum loss from the binary system. In this work, we explore the spectral distribution of Be/X-ray binaries in the Small Magellanic Cloud (SMC) using high signal-to-noise ratio spectroscopy of a sample of 37 optical counterparts to known X-ray pulsars. Our results show that the spectral distribution of Be/X-ray binaries in the SMC is consistent with that of the Galaxy, despite the lower metallicity environment of the SMC. This may indicate that, although the metallicity of the SMC is conducive to the formation of a large number of high-mass X-ray binaries, the spectral distribution of these systems is likely to be most strongly influenced by angular momentum losses during binary evolution, which are not particularly dependent on the local metallicity. [ABSTRACT FROM AUTHOR]

Dust radiative transfer models are presented for 60 carbon stars in the Magellanic Clouds (MCs) for which 5–35 μm Spitzer infrared spectrograph (IRS) spectra and quasi-simultaneous ground-based JHKL photometry are available. From the modelling, the luminosity and mass-loss rate are derived (under the assumption of a fixed expansion velocity and dust-to-gas ratio), and the ratio of silicon carbide (SiC) to amorphous carbon (AMC) dust is also derived. This ratio is smaller than observed in Galactic carbon stars, as has been noted before. Light curves for 36 objects can be retrieved from the massive compact halo object (MACHO) and optical gravitational lensing experiment (OGLE) data bases, and periods can be derived for all but two of these. Including data from the literature, periods are available for 53 stars. There is significant scatter in a diagram where the mass-loss rates are plotted against luminosity, and this is partly due to the fact that the luminosities are derived from single-epoch data. The mass-loss rates for the MC objects roughly scatter around the mean relation for Galactic C-stars. The situation is better defined when the mass-loss rate is plotted against pulsation period. For a given period, most of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) stars have mass-loss rates that are in agreement with that observed in Galactic carbon stars (under the assumption that these objects have an expansion velocity and dust-to-gas ratio typical of the mean observed in Galactic carbon Miras). For some SMC sources only, the IRS spectrum at longer wavelengths falls clearly below the model flux predicted by a constant mass-loss rate. An alternative model with a substantial increase of the mass-loss rate to its present-day value over a time-scale of a few tens of years is able to explain the spectral energy distribution (SED) and IRS spectra of these sources. However, the probability to have two such cases in a sample of 60 is small, and makes this not a likely explanation (and testable by re-observing these objects near the end of the lifetime of Spitzer). Alternative explanations are (ad hoc) changes to the dust emissivity at longer wavelengths, and/or deviations from spherical symmetry. [ABSTRACT FROM AUTHOR]

We present spectroscopic observations, taken with the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph telescope/instrument, of the unusual Small Magellanic Cloud X-ray binary system SXP 323 = AX J0051−733. This system shows a clear modulation at 0.71 d in long-term optical photometry, which has been proposed as the binary period of this system. The high-resolution optical spectra, taken at a range of phases during the 0.71-d cycle, rule out this possibility. Instead it is suggested that this long-term effect is due to non-radial pulsations in the Be star companion to SXP 323. In addition, the spectra show clear evidence for major changes in the ( V/ R) ratio of the double peaks of the Balmer lines indicative of asymmetries in the circumstellar disc. The complex structure of the interstellar lines is also discussed in the context of the SMC structure. [ABSTRACT FROM AUTHOR]

We present synthetic spectra for circumstellar discs that are heated by radiation from a central brown dwarf. Under the assumption of vertical hydrostatic equilibrium, our models yield scaleheights for brown dwarf discs in excess of three times those derived for classical T Tauri (CTTS) discs. If the near-IR excess emission observed from brown dwarfs is indeed due to circumstellar discs, then the large scaleheights we find could have a significant impact on the optical and near-IR detectability of such systems. Our radiation transfer calculations show that such highly flared discs around brown dwarfs will result in a large fraction of obscured sources due to extinction of direct starlight by the disc over a wide range of sightlines. The obscured fraction for a ‘typical’ CTTS is less than 20 per cent. We show that the obscured fraction for brown dwarfs may be double that for CTTS, but this depends on stellar and disc mass. We also comment on possible confusion in identifying brown dwarfs via colour–magnitude diagrams: edge-on CTTS display similar colours and magnitudes to face-on brown dwarf plus disc systems. [ABSTRACT FROM AUTHOR]

We address the relationship between spectral type and physical properties for A-type supergiants in the Small Magellanic Cloud (SMC). First, we construct a self-consistent classification scheme for A supergiants, employing the calcium K to Hε line ratio as a temperature-sequence discriminant. Following the precepts of the ‘MK process’, the same morphological criteria are applied to Galactic and SMC spectra, with the understanding that there may not be a correspondence in physical properties between spectral counterparts in different environments. Then we discuss the temperature scale, concluding that A supergiants in the SMC are systematically cooler than their Galactic counterparts at the same spectral type, by up to ∼10 per cent. Considering the relative line strengths of Hγ and the CH G band, we extend our study to F- and early G-type supergiants, for which similar effects are found. We note the implications for analyses of luminous extragalactic supergiants, for the flux-weighted gravity–luminosity relationship and for population synthesis studies in unresolved stellar systems. [ABSTRACT FROM AUTHOR]