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We present the analysis of time-resolved spectroscopy of the pulsating subdwarf B (sdB) star PG 1605+072. From our main observing run of 16 nights we have detected velocity variations at five frequencies that correspond to those found in photometry. Based on these data, there appears to be change in amplitude of the dominant modes over about a year. However, when we include extra observations to improve the frequency resolution, we find that some of the frequencies are split into two or three. Simulations suggest that the apparent amplitude variation can be at least partially explained by a series of very closely spaced frequencies around the two strongest modes. By combining observations taken over ∼300 d we conclude that some of the closely spaced modes are caused by one mode the amplitude of which is varying, however this frequency is still within ∼1 μHz of an apparently stable frequency. Because of this kind of complexity and uncertainty we advise caution when trying to identify oscillation modes in this star. [ABSTRACT FROM AUTHOR]

We explore the occurrence of dust in M-type Mira atmospheres and its effect on limb darkening under schematic assumptions about dust temperatures and dust particle properties. Dust particles that are thermodynamically coupled to the surrounding gas may form and may affect limb darkening, though only by very little in infrared continuum bandpasses. Dust particles that assume the equilibrium temperature given by the mean intensity of the radiation field only form under rare circumstances. Unexpectedly large or wavelength-dependent infrared continuum radii observed by interferometry are unlikely to be caused by atmospheric dust, except possibly near 1 μm; however, radius measurements may be significantly affected by molecular band contamination. [ABSTRACT FROM AUTHOR]

We discuss the wavelength dependence of angular diameters of M giants from an observational perspective. Observers cannot directly measure an optical-depth radius for a star, despite this being a common theoretical definition. Instead, they can use an interferometer to measure the square of the fringe visibility. We present new plots of the wavelength-dependent centre-to-limb variation (CLV) of intensity of the stellar disc as well as visibility for Mira and non-Mira M giant models. We use the terms ‘CLV spectra’ and ‘visibility spectra’ for these plots. We discuss a model-predicted extreme limb-darkening effect (also called the narrow-bright-core effect) in very strong TiO bands which can lead to a misinterpretation of the size of a star in these bands. We find no evidence as yet that this effect occurs in real stars. Our CLV spectra can explain the similarity in visibilities of R Dor (M8IIIe) that have been observed recently, despite the use of two different passbands. We compare several observations with models, and find that the models generally underestimate the observed variation in visibility with wavelength. We present CLV and visibility spectra for a model that is applicable to the M supergiant α Ori. [ABSTRACT FROM AUTHOR]

Presents bisector measurements of the H[alpha] line of oscillating Ap (roAp) star [alpha] Cir, obtained from dual-site observations. Use of spectrographs on dual site observation; Changes of the velocity amplitude and phase of principal pulsation depending on the height of H[alpha]line; Effects on the blending of metal lines on the H[alpha] bisector results.

Presents the interferometric observations with the 3.9 meter Anglo-Australian Telescope. Exposition of high-resolution spectra taken over five nights with the ESO CAT showing double-lined spectroscopic binary beta Cen; Identification of two pulsation frequencies in the primary; Determination of orbital parameters and component masses of double-star.