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Context. Betelgeuse is one the largest stars in the sky in terms of angular diameter. Structures on the stellar photosphere have been detected in the visible and near-infrared as well as a compact molecular environment called the MOLsphere. Mid-infrared observations have revealed the nature of some of the molecules in the MOLsphere, some being the precursor of dust.

Context. Red supergiant (RSG) stars exhibit significant mass loss by means of a slow, dense wind. They are often considered to be the more massive counterparts of Asymptotic Giant Branch (AGB) stars. While AGB mass loss is related to their strong pulsations, the RSG are often only weakly variable. This raises the question of whether their wind-driving mechanism and the dust composition of the wind are the same.

Context.The study of the atmosphere of red supergiant stars in general and of Betelgeuse(αOrionis) in particular is of prime importance to understand dust formation and how mass is lost to the interstellar medium in evolved massive stars.

Aims.In order to gain new insight into the unidentified identity of the diffuse interstellar band (DIB) carriers, this paper describes research into possible links between the shape of the interstellar extinction curve (including the 2175 Å bump and far-UV rise), the presence or absence of DIBs, and physical and chemical conditions of the diffuse interstellar medium (gas and dust) in the Small Magellanic Cloud (SMC).

Aims.To study the nature of Bulge AGB stars and in particular their circumstellar dust, we have analysed mid-infrared spectra obtained with the ISOCAM CVF spectrometer in three Bulge fields.

The Large Magellanic Cloud (LMC) offers a unique laboratory to study the diffuse interstellar bands (DIBs) under conditions that are profoundly different from those in the Galaxy. DIB carrier abundances depend on several environmental factors, in particular the local UV radiation field. In this paper we present measurements of twelve DIBs in five lines of sight to early-type stars in the LMC, including the 30 Doradusregion. From the high resolution spectra obtained with VLT/UVES we also derive environmental parameters that characterise the local interstellar medium (ISM) in the probed LMC clouds. These include the column density components (including total column density) for the atomic resonance lines of $\ion{Na}{i}$, $\ion{Ca}{ii}$, $\ion{Ti}{ii}$, $\ion{K}{i}$. In addition, we derive the $\ion{H}{i}$column density from 21 cm line profiles, the total-to-selective visual extinction RVand the gas-to-dust ratio N($\ion{H}{i}$)/AV. Furthermore, from atomic line ratios we derive the ionisation balance and relative UV field strength in these environments. We discuss the properties of the LMC ISM in the context of DIB carrier formation. The behaviour of DIBs in the LMC is compared to that of DIBs in different local environmental conditions in the Milky Way. A key result is that in most cases the diffuse band strengths are weak (up to factor 5) with respect to Galactic lines of sight of comparable reddening, EB-V. In the line of sight towards Sk –69 223the 5780 and 5797 Å DIBs are very similar in strength and profile to those observed towards HD 144217, which is typical of an environment exposed to a strong UV field. From the velocity analysis we find that DIB carriers (towards Sk –69 243) are better correlated with the ionised species like $\ion{Ca}{ii}$than with neutrals (like $\ion{Na}{i}$and CO). The most significant parameter that governs the behaviour of the DIB carrier is the strength of the UV field.

In this paper we study the extended atmosphere of the late-type supergiant αOrionis. Infrared spectroscopy of red supergiants reveals strong molecular bands, some of which do not originate in the photosphere but in a cooler layer of molecular material above it. Lately, these layers have been spatially resolved by near and mid-IR interferometry. In this paper, we try to reconcile the IR interferometric and ISO-SWS spectroscopic results on αOrioniswith a thorough modelling of the photosphere, molecular layer(s) and dust shell. From the ISO and near-IR interferometric observations, we find that αOrionishas only a very low density water layer close above the photosphere. However, mid-IR interferometric observations and a narrow-slit N-band spectrum suggest much larger extra-photospheric opacity close to the photosphere at those wavelengths, even when taking into account the detached dust shell. We argue that this cannot be due to the water layer, and that another source of mid-IR opacity must be present. We show that this opacity source is probably neither molecular nor chromospheric. Rather, we present amorphous alumina (Al2O3) as the best candidate and discuss this hypothesis in the framework of dust-condensation scenarios.

We provide direct observational evidence for a link between photospheric activity and perturbations in the dense inner-most stellar wind regions of the B supergiant star ϵOri. The results, which are relevant to our understanding of the origin of wind structure, are based on a multi-spectral line analysis of optical time-series data secured in 1998 using the HEROS spectrograph on the ESO Dutch 0.9-m telescope in La Silla. A period of ~1.9 days is consistently identified in Balmer, He iabsorption, and weak metal lines such as Si iiiand C ii. The primary characteristic is a large-amplitude swaying of the central absorption trough of the line, with differential velocities in lines formed at varying depths in the atmosphere. The variance resulting from the “S-wave” velocity behaviour of the lines is constrained within ±the projected rotation velocity (~80 km s-1) in the weakest absorption lines, but extends blue-ward to over -200 km s-1in Hα. A second (superimposed) 1.9 day signal is present at more extended blue-ward velocities (to ~-300 km s-1) in lines containing stronger circumstellar components. Inspection of archival optical data from 1996 provides evidence that this modulation signal has persisted for at least 2.5 years. Non-radial pulsational modelling is carried out in an attempt to reproduce the key observational characteristics of the line profile variability. Only limited success is obtained with prograde ($m=-1$) modes. The principal S-wave pattern cannot be matched by these models and remains enigmatic.

We analyse ISO–SWS 01 ($R \sim 1500$) $12{-}27.5\,\mu$m (band 3) spectra of the 10 standard calibration stars with the highest flux using synthetic spectra generated from (marcs) atmosphere models. The comparison between the observed and synthetic spectra reveals the quality of (1) the atmospheric model construction and subsequent synthetic spectra computation and of (2) the (OLP 10.1) calibration and data reduction of the spectrometer at these wavelengths.
The models represent the general features of the observations, but the synthetic spectrum computation is hampered by the lack of comprehensive molecular and atomic line lists. We also suspect some problems with the temperature distribution in the outer layers of the model and inaccuracies in the extrapolation of the collision-induced absorption coefficients of H2pairs. We detect baseline ripples and fringes in the observed spectra, that survive the calibration and detailed reduction process. Photometric calibration uncertainties are estimated by means of the scaling factors between the synthetic and observed spectra.

The composition of ice grains provides an important tool for the study of the molecular environment of star forming regions. Using ISAAC at the VLT to obtain spectra around 4.65 μm we have detected for the first time “XCN” and CO ice in an extragalactic environment: the nuclear region of the nearby dusty starburst/AGN galaxy NGC 4945. The profile of the solid CO band reveals the importance of thermal processing of the ice while the prominence of the XCN band attests to the importance of energetic processing of the ice by FUV radiation and/or energetic particles. In analogy to the processing of ices by embedded protostars in our Galaxy, we attribute the processing of the ices in the center of NGC 4945 to ongoing massive star formation. Our M-band spectrum also shows strong HI Pfβand H20–0 S(9) line emission and gas phase CO absorption lines. The HI, H2, PAH, gas phase CO and the ices seem to be embedded in a rotating molecular disk which is undergoing vigorous star formation. Recently, strong OCN-absorption has been detected in the spectrum of the Galactic center star GC: IRS 19. The most likely environment for the OCN-absorption is the strongly UV-exposed GC molecular ring. The presence of processed ice in the center of NGC 4945 and our Galactic center leads us to believe that processed ice may be a common characteristic of dense molecular material in star forming galactic nuclei.

We present the Spectral Energy Distribution of HR 4049 based on literature data and new continuum measurements at 850 μm. The SED shows variable absorption in the UV, and a large IR excess, both caused by circumstellar dust. The shape of the IR excess from 1 μmall the way down to 850 μmcan be nearly perfectly fitted with a single blackbody function at $T \approx 1150$K or alternatively with a sum of blackbodies in a narrow temperature range. The energy emitted in this IR continuum radiation is about one-third of the stellar luminosity. We show that this blackbody radiation must be due to the presence of a circumbinary disk with a large height. This disk must also be gas-rich, in agreement with the observations of molecular bands in the ISO-SWS spectrum. We present two possible scenario's for explaining the shape and the intensity of the IR excess. The first scenario involves large grains ($a \ge 1$mm) that each radiate like a blackbody. The second scenario argues that the blackbody radiation is due to a very optically thick circumbinary disk. We investigate if such a disk would indeed produce blackbody radiation by presenting results from radiative transfer calculations. We further quantify the properties of such a disk and its stability in the framework of (hydro)dynamics, grain settling, radiation pressure and grain drift. The virtues and shortcomings of both models for the origin of the IR blackbody are discussed by contrasting them with other observations and assessing them in the framework of (binary) (post-)AGB evolution.

We present simultaneous and continuous observations of the Hα, Hβ, He iD3, Na iD1,D2doublet and the Ca iiH & K lines for the RS CVn system HR 1099. The spectroscopic observations were obtained during the MUSICOS 1998 campaign involving several observatories and instruments, both echelle and long-slit spectrographs. During this campaign, HR 1099 was observed almost continuously for more than 8 orbits of $2\fd8$. Two large optical flares were observed, both showing an increase in the emission of Hα, Ca iiH & K, Hβand He iD3and a strong filling-in of the Na iD1, D2doublet. Contemporary photometric observations were carried out with the robotic telescopes APT-80 of Catania and Phoenix-25 of Fairborn Observatories. Maps of the distribution of the spotted regions on the photosphere of the binary components were derived using the Maximum Entropy and Tikhonov photometric regularization criteria. Rotational modulation was observed in Hαand He iD3in anti-correlation with the photometric light curves. Both flares occurred at the same binary phase (0.85), suggesting that these events took place in the same active region. Simultaneous X-ray observations, performed by ASM on board RXTE, show several flare-like events, some of which correlate well with the observed optical flares. Rotational modulation in the X-ray light curve has been detected with minimum flux when the less active G5 V star was in front. A possible periodicity in the X-ray flare-like events was also found.

ωOri(HD 37490, HR 1934) is a Be star known to have presented variations. In order to investigate the nature and origin of its short-term and mid-term variability, a study is performed of several spectral lines (Hα, Hδ, $\ion{He}{i}$4471, 4713, 4921, 5876, 6678, $\ion{C}{ii}$4267, 6578, 6583, $\ion{Mg}{ii}$4481, $\ion{Si}{iii}$4553 and $\ion{Si}{ii}$6347), based on 249 high signal-to-noise high-resolution spectra taken with 8 telescopes over 22 consecutive nights during the MuSiCoS (Multi SIte COntinuous Spectroscopy) campaign in November-December 1998. The stellar parameters are revisited and the projected rotational velocity ($v\sin i = 179$km s-1) is redetermined using several methods. With the MuSiCoS 98 dataset, a time series analysis of line-profile variations (LPVs) is performed using the Restricted Local Cleanest (RLC) algorithm and a least squares method. The behaviour of the velocity of the centroid of the lines, the equivalent widths and the apparent vsinifor several lines, as well as Violet and Red components of photospheric lines affected by emission (red $\ion{He}{i}$lines, $\ion{Si}{ii}$6347, $\ion{C}{ii}$6578, 6583) are analyzed. The non-radial pulsation (NRP) model is examined using phase diagrams and the Fourier-Doppler Imaging (FDI) method. The LPVs are consistent with a NRP mode with $l = 2$or 3, $|m| = 2$with frequency 1.03 c d-1. It is shown that an emission line outburst occurred in the middle of the campaign. Two scenarios are proposed to explain the behaviour of a dense cloud, temporarily orbiting around the star with a frequency 0.46 c d-1, in relation to the outburst.

The time variation in the water-vapour bands in oxygen-rich Mira variables has been investigated using multi-epoch ISO/SWS spectra of four Mira variables in the 2.5–4.0 μm region. All four stars show H2O bands in absorption around minimum in the visual light curve. At maximum, H2O emission features appear in the ~3.5–4.0 μm region, while the features at shorter wavelengths remain in absorption. These H2O bands in the 2.5–4.0 μm region originate from the extended atmosphere. The analysis has been carried out with a disk shape, slab geometry model. The observed H2O bands are reproduced by two layers; a “hot” layer with an excitation temperature of 2000 K and a “cool” layer with an excitation temperature of 1000–1400 K. The column densities of the “hot” layer are $6\times10^{20}$–$3\times10^{22}$cm-2, and exceed $3\times10^{21}$cm-2when the features are observed in emission. The radii of the “hot” layer () are ~1 $R_*$at visual minimum and 2 $R_*$at maximum, where $R_*$is a radius of background source of the model, in practical, the radius of a 3000 K black body. The “cool” layer has the column density () of $7\times10^{20}$–$5\times10^{22}$cm-2, and is located at 2.5–4.0 $R_*$.  depends on the object rather than the variability phase. The time variation of Rhotfrom 1 to 2 is attributed to the actual variation in the radius of the H2O layer, since the variation in  far exceeds the variation in the “continuum” stellar radius. A high H2O density shell occurs near the surface of the star around minimum, and moves out with the stellar pulsation. This shell gradually fades away after maximum, and a new high H2O density shell is formed in the inner region again at the next minimum. Due to large optical depth of H2O, the near-infrared variability is dominated by the H2O layer, and the L'-band flux correlates with the area of the H2O shell. The infrared molecular bands trace the structure of the extended atmosphere and impose appreciable effects on near-infrared light curve of Mira variables.

We analyze ISO archive data of the nearby bright emission-line star 51 Oph, previously classified as a proto-planetary system similar to βPic. The infrared spectrum reveals the presence of gas-phase emission bands of hot (~850 K) CO, CO2, H2O and NO. In addition to this, partially crystalline silicate dust is present. The solid-state bands and the energy distribution are indicative of dust that has formed recently, rather than of debris dust. The presence of hot molecular gas and the composition of the circumstellar dust are highly unusual for a young star and are reminiscent of what is found around evolved (AGB) stars, although we exclude the possibility of 51 Oph belonging to this group. We suggest several explanations for the nature of 51 Oph, including a recent episode of mass loss from a Be star, and the recent destruction of a planet-sized body around a young star.

We report the discovery in the ISO/SWS spectrum of the post-AGB star HR 4049of emission bands due to 17O and 18O isotopes locked up in CO2molecules. It is the first time these isotopomers are detected outside the solar system. Isotopic ratios derived in the optically thin limit are as low as 16O/17O $= 8.3\pm 2.3$and 16O/$^{18}{\rm O} = 6.9 \pm 0.9$. These values are at least one order of magnitude lower than any previously determined isotopic ratio in any type of evolved star.

Context.The circumstellar environment of evolved stars is generally rich in molecular gas and dust. Typically, the entire environment is either oxygen-rich or carbon-rich, depending on the evolution of the central star.

Context.The origin of the narrow optical emission bands seen towards the Red Rectangle is not yet understood. We investigate the proposal that these are caused by luminescence of large carbonaceous molecules.

Context.Mass-loss occurring in red supergiants (RSGs) is a major contributor to the enrichment of the interstellar medium in dust and molecules. The physical mechanism of this mass loss is however relatively poorly known. Betelgeuse is the nearest RSG, and as such a prime object for high angular resolution observations of its surface (by interferometry) and close circumstellar environment.

Context.Studying the composition of dust in the interstellar medium (ISM) is crucial for understanding the cycle of dust in our galaxy.