RV Tauri stars are luminous population II Cepheids which show a characteristic light curve of alternating deep and shallow minima. There are 126 RV Tauri variables in our Galaxy. Using WISE [3.4]-[4.6], [12]-[22] diagram we show that Galactic RV Tauri stars show three main types of IR properties in their SEDs; disc-type, non-IR and uncertain, which does not show a clear characteristic in the SED. We also show that there is a strong correlation between disc-type SED and binarity (Gezer et al. 2015). RV Tauri stars were linked to post AGB stars in early studies (Jura 1986), however, recent studies show that their evolutionary nature is more complex than previously thought (Kamath & Van Winckel 2014, and Manick et al. 2018). In this study, we intentionally selected two RV Tauri stars, GK Car (disc-type) and GZ Nor (uncertain), with different IR characteristics to compare their chemical and photometric properties.

Post-AGB stars are the final stage of evolution of low-intermediate mass stars (M < 8 Mʘ). Those in binary systems have stable circumbinary discs. Using data from Herschel (PACS/SPIRE), we extend the SEDs of 50 galactic post-AGB binary systems to sub-millimetre wavelengths and use the slope of the SED as a diagnostic tool to probe the presence of large grains. Using a Monte Carlo radiative transfer code (MCMax), we create a large grid of models to quantify the observed spectral indices, and use the presence of large grains in the disc as a proxy for evolution.

S-type stars are late-type giants enhanced with s-process elements originating either from nucleosynthesis during the Asymptotic Giant Branch (AGB) or from a pollution by a binary companion. The former are called intrinsic S stars, and the latter extrinsic S stars. The intrinsic S stars are on the AGB and have undergone third dredge-up events. The atmospheric parameters of S stars are more numerous than those of M-type giants (C/O ratio and s-process abundances affect the thermal structure and spectral synthesis), and hence they are more difficult to derive. These atmospheric parameters are also entangled within each other. Nevertheless, high-resolution spectroscopic data of S stars combined with the Gaia Data Release 2 (GDR2) parallaxes and with the MARCS model atmospheres for S-type stars were used to derive effective temperatures, surface gravities, and luminosities. These parameters not only allow to locate the intrinsic and extrinsic S stars in the Hertzsprung-Russell (HR) diagram but also allow the accurate abundance analysis of the s-process elements.

Barium (Ba) stars form via mass-transfer in binary systems, and can subsequently interact with their white dwarf companion in a second stage of binary interaction. We used observations of main-sequence Ba systems as input for our evolutionary models, and try to reproduce the orbits of the Ba giants. We show that to explain short and sometimes eccentric orbits, additional interaction mechanisms are needed along the RGB.

To investigate the binary hypothesis in the formation of planetary nebulae, we have been doing long-term photometry and radial velocity (RV) monitoring of bright post-AGB stars which possess bipolar or ellipsoidal nebulae but no indication of a disk in their spectral energy distribution, indicative of a binary companion. RV’s are determined by cross correlating high-resolution spectra with a line mask. Stellar variability and companions both deform the cross correlation function (CCF) and induce periodic variations in the RV. To uniformly quantify the asymmetry of the CCF from a Gaussian, we propose to fit the CCF profile with a Gauss-Hermite series and determine all CCF parameters (RV, skewness, FWHM, and depth) in one single fit. We analyze the correlation and time series of these CCF parameters for V448 Lac and conclude that its RV variability is most likely due to stellar pulsation and not to an orbiting body.

Barium stars are formed via binary interaction with a former AGB companion. Observations are needed to constrain theoretical models and better understand their evolution and surface composition. We present the HR diagram of Ba and related stars, using the recently released TGAS parallaxes, and the mass distribution of the Ba giants that we derived from it.

We carried out an extensive photometric and spectroscopic investigation of the SPB binary, HD 25558 (see Fig. 1 for the time and geographic distribution of the observations). The ~2000 spectra obtained at 13 observatories during 5 observing seasons, the ground-based multi-colour light curves and the photometric data from the MOST satellite revealed that this object is a double-lined spectroscopic binary with a very long orbital period of about 9 years. We determined the physical parameters of the components, and have found that both lie within the SPB instability strip. Accordingly, both components show line-profile variations consistent with stellar pulsations. Altogether, 11 independent frequencies and one harmonic frequency were identified in the data. The observational data do not allow the inference of a reliable orbital solution, thus, disentangling cannot be performed on the spectra. Since the lines of the two components are never completely separated, the analysis is very complicated. Nevertheless, pixel-by-pixel variability analysis of the cross-correlated line profiles was successful, and we were able to attribute all the frequencies to the primary or secondary component. Spectroscopic and photometric mode-identification was also performed for several of these frequencies of both binary components. The spectroscopic mode-identification results suggest that the inclination and rotation of the two components are rather different. While the primary is a slow rotator with ~6 d rotation period, seen at ~60° inclination, the secondary rotates fast with ~1.2 d rotation period, and is seen at ~20° inclination. Our spectropolarimetric measurements revealed that the secondary component has a magnetic field with at least a few hundred Gauss strength, while no magnetic field was detected in the primary.

The detailed analysis and results of this study will be published elsewhere.

The Red Rectangle is a spectacular bipolar nebula centred around the eccentric evolved binary HD 44179. The nebula is rich in spectral signatures: it is the brightest source of the Extended Red Emission (ERE), of the Blue Luminescence (BL) as well as one of the brightest sources of mid-IR PAH bands. Moreover, and unique to this source, a plethora of narrow emission lines is detected on top of the diffuse ERE. Some of these molecular features show rotational contours which become narrower at larger angular separation from the central engine. Some converge to wavelengths and profiles of narrow DIBs. All these observations show that the Red Rectangle is a very rich laboratory to study active astrochemical processes within the nebula. We also address, but fail to answer, the question why this source is so unique among the many observed post-AGB binary analogues.

We present a preliminary analysis of a set of optical (3800-8800 Å) high resolution (R = 80,000) spectra for 69 diffuse interstellar band targets. We carried out a sensitive search for interstellar features in the wavelength range 8470-8740 Å that will be covered by the upcoming GAIA mission. We also investigate how the λ8620Å DIB strength varies as a function of other interstellar parameters (other DIBs, E(B-V) and atomic and molecular column densities).

Binarity is often invoked to explain peculiarities that can not be explained by the standard theory of stellar evolution. Detecting orbital motion via the Doppler effect is the best method to test binarity when direct imaging is not possible. However, when the orbital period exceeds length of a typical observing run, monitoring often becomes problematic. Placing a high-throughput spectrograph on a small semi-robotic telescope allowed us to carry out a radial velocity survey of various types of peculiar evolved stars. In this review we highlight some findings after the first four years of observations. Thus, we detect eccentric binaries among hot subdwarfs, barium, S stars, and post-AGB stars with disks, which are not predicted by the standard binary interaction theory. In disk objects, in addition, we find signs of the on-going mass transfer to the companion, and an intriguing line splitting, which we attribute to the scattered light of the primary.

DV Cam is a triple system showing the diversity of the physics of photospheres of B-type stars at a common age: an SPB star in a wide orbit around a close binary consisting of an ultra-slowly rotating helium-weak star and a much faster rotating mid-B star.

In this paper we give a progress report on the Herschel observations of planetary nebulae that are carried out as part of the MESS guaranteed time key program.

Optical photometry and radial velocities have been obtained for stars whose near- and mid-infrared colours suggest that they have dusty circumstellar discs; many are RV Tauri variables. A subset of six stars have earlier spectral types and smaller light amplitudes than classical RV Tauri stars. All are spectroscopic binaries, with surprisingly short periods.

We report on the first results from observations of 28 variable B stars obtained with the new Mercator telescope (La Palma). Besides confirming the pulsational nature of known and candidate β Cephei and slowly pulsating B stars, we also present new candidate ellipsoidal variables and spotted stars.

We report on the first results from observations of 31 variable A and F stars, obtained with the new Mercator telescope (La Palma). Besides confirming the γ Dor nature of known bonafide and candidate γ Dor stars, we also present new candidate γ Dor stars. In addition, we found a new short-period variable star.

The determination of stellar abundances is the most direct observational test for astronuclear physics. The reliability of such determinations depends on the quality of the observational data, but also critically on a correct understanding of all atmospheric processes as well as on fundamental atomic and molecular data. We illustrate this different aspects with several recent examples which served as a general introduction to the "round table" on this subject.

We present the results of 1.5 years of Spectroscopic monitoring of 10 bright northern SPB candidates discovered from the Hipparcos mission. All stars have line-profile variations and are periodic, with periods corresponding to high-order g-modes. We therefore confirm them to be new SPBs.

Low and intermediate mass stars leave the Asymptotic Giant Branch (AGB) when the mass in their H-rich envelope is less than about 0.01 M⊙, and the high mass loss drops several orders of magnitude. The central star rapidly evolves to the left part of the HR diagram along a track of constant luminosity (e.g. Schönberner 1983). In principle the evolution of the central star to higher Teff and the expansion and cooling of the AGB remnant are easy to calculate. In practice several complicating factors arise which make it much more difficult to predict the morphology and properties of post-AGB stars, such as binarity, post-AGB mass loss and aspherical AGB mass loss. Binarity of post-AGB stars affects the morphology of the circumstellar environment, and it affects evolutionary timescales and surface chemical abundances of the components in the system. This review discusses some properties of binary post-AGB stars.

Eta Orionis is an interesting multiple system of early type stars. It consists of a visual triple system (A, B, C), a spectroscopic triple system (Aabc) and an eclipsing binary Aab. A is a triple system consisting of a 7.989 day eclipsing binary Aab and a gravitationally bound third component Ac with orbital period of about 9.5 years. All components of the pair AB have spectral types in the range 09-B3 (C. Waelkens & P. Lampens 1988). The radial velocity curve is used to constrain the orbital elements and properties of the binary Aab.

The second component Ab is a B-type star that displays rapid absorption line profile variability. Regular patterns are easily visible in the data.

We give a progress report on an observational program intended to determine detailed chemical abundances of β Cephei stars and constant stars with similar temperature and gravity. There is some evidence that non-variable stars have a lower metal content than variables, as the recently found pulsation mechanism would suggest.