Context. The unparalleled photometric data obtained by NASA's Kepler Space Telescope has led to improved understanding of red giant stars and binary stars. Seismology allows us to constrain the properties of red giants. In addition to eclipsing binaries, eccentric non-eclipsing binaries that exhibit ellipsoidal modulations have been detected with Kepler. Aims. We aim to study the properties of eccentric binary systems containing a red giant star and to derive the parameters of the primary giant component. Methods. We applied asteroseismic techniques to determine the masses and radii of the primary component of each system. For a selected target, light and radial velocity curve modelling techniques were applied to extract the parameters of the system and its primary component. Stellar evolution and its effects on the evolution of the binary system were studied from theoretical models. Results. The paper presents the asteroseismic analysis of 18 pulsating red giants in eccentric binary systems, for which masses and radii were constrained. The orbital periods of these systems range from 20 to 440 days. The results of our ongoing radial velocity monitoring programme with the Hermes spectrograph reveal an eccentricity range of e = 0.2 to 0.76. As a case study we present a detailed analysis of KIC 5006817, whose rich oscillation spectrum allows for detailed seismic analysis. From seismology we constrain the rotational period of the envelope to be at least 165 d, which is roughly twice the orbital period. The stellar core rotates 13 times faster than the surface. From the spectrum and radial velocities we expect that the Doppler beaming signal should have a maximum amplitude of 300 ppm in the light curve. Fixing the mass and radius to the asteroseismically determined values, we find from our binary modelling a value of the gravity darkening exponent that is significantly larger than expected. Through binary modelling, we determine the mass of the secondary component to be 0.29 ± 0.03 M . Conclusions. For KIC 5006817 we exclude pseudo-synchronous rotation of the red giant with the orbit. The comparison of the results from seismology and modelling of the light curve shows a possible alignment of the rotational and orbital axis at the 2σ level. Red giant eccentric systems could be progenitors of cataclysmic variables and hot subdwarf B stars.

Context. Low-and intermediate-mass stars go through a period of intense mass-loss at the end of their lives, during the asymptotic giant branch (AGB) phase. While on the AGB a significant part, or even most, of their initial mass is expelled in a stellar wind. This process controls the final stages of the evolution of these stars and contributes to the chemical evolution of galaxies. However, the wind-driving mechanism of AGB stars is not yet well understood, especially so for oxygen-rich sources. Characterizing both the present-day mass-loss rate and wind structure and the evolution of the mass-loss rate of such stars is paramount to advancing our understanding of this processes. Aims. We study the dusty wind of the oxygen-rich AGB star W Hya to understand its composition and structure and shed light on the mass-loss mechanism. Methods. We modelled the dust envelope of W Hya using an advanced radiative transfer code. We analysed our dust model in the light of a previously calculated gas-phase wind model and compared it with measurements available in the literature, such as infrared spectra, infrared images, and optical scattered light fractions. Results. We find that the dust spectrum of W Hya can partly be explained by a gravitationally bound dust shell that probably is responsible for most of the amorphous Al 2 O 3 emission. The composition of the large (∼0.3 μm) grains needed to explain the scattered light cannot be constrained, but probably is dominated by silicates. Silicate emission in the thermal infrared was found to originate from beyond 40 AU from the star. In our model, the silicates need to have substantial near-infrared opacities to be visible at such large distances. The increase in near-infrared opacity of the dust at these distances roughly coincides with a sudden increase in expansion velocity as deduced from the gas-phase CO lines. The dust envelope of W Hya probably contains an important amount of calcium but we were not able to obtain a dust model that reproduces the observed emission while respecting the limit set by the gas mass-loss rate. Finally, the recent mass loss of W Hya is confirmed to be highly variable and we identify a strong peak in the mass-loss rate that occurred about 3500 years ago and lasted for a few hundred years.

Context. The launches of the MOST, CoRoT, and Kepler missions opened up a new era in asteroseismology, the study of stellar interiors via interpretation of pulsation patterns observed at the surfaces of large groups of stars. These space-missions deliver a huge amount of high-quality photometric data suitable to study numerous pulsating stars. Aims. Our ultimate goal is a detection and analysis of an extended sample of γ Dor-type pulsating stars with the aim to search for observational evidence of non-uniform period spacings and rotational splittings of gravity modes in main-sequence stars typically twice as massive as the Sun. This kind of diagnostic can be used to deduce the internal rotation law and to estimate the amount of rotational mixing in the near core regions. Methods. We applied an automated supervised photometric classification method to select a sample of 69 Gamma Doradus (γ Dor) candidate stars. We used an advanced method to extract the Kepler light curves from the pixel data information using custom masks. For 36 of the stars, we obtained high-resolution spectroscopy with the HERMES spectrograph installed at the Mercator telescope. The spectroscopic data are analysed to determine the fundamental parameters like T eff , log g, v sin i, and [M/H]. Results. We find that all stars for which spectroscopic estimates of T eff and log g are available fall into the region of the HR diagram where the γ Dor and δ Sct instability strips overlap. The stars cluster in a 700 K window in effective temperature, log g measurements suggest luminosity class IV-V, i.e. sub-giant or main-sequence stars. From the Kepler photometry, we identify 45 γ Dor-type pulsators, 14 γ Dor/δ Sct hybrids, and 10 stars which are classified as "possibly γ Dor/δ Sct hybrid pulsators". We find a clear correlation between the spectroscopically derived v sin i and the frequencies of independent pulsation modes. Conclusions. We have shown that our photometric classification based on the light curve morphology and colour information is very robust. The results of spectroscopic classification are in perfect agreement with the photometric classification. We show that the detected correlation between v sin i and frequencies has nothing to do with rotational modulation of the stars but is related to their stellar pulsations. Our sample and frequency determinations offer a good starting point for seismic modelling of slow to moderately rotating γ Dor stars.

The debris disk around β Pictoris is known to contain gas. Previous ALMA observations revealed a CO belt at ∼85 au with a distinct clump, interpreted as a location of enhanced gas production. Photodissociation converts CO into C and O within ∼50 years. We resolve C I emission at 492 GHz using ALMA and study its spatial distribution. C I shows the same clump as seen for CO. This is surprising, as C is expected to quickly spread in azimuth. We derive a low C mass (between 5 × 10 −4 and 3.1 × 10 −3 M ⊕ ), indicating that gas production started only recently (within ∼5 000 years). No evidence is seen for an atomic accretion disk inwards of the CO belt, perhaps because the gas did not yet have time to spread radially. The fact that C and CO share the same asymmetry argues against a previously proposed scenario where the clump is due to an outward migrating planet trapping planetesimals in an resonance; nor can the observations be explained by an eccentric planetesimal belt secularly forced by a planet. Instead, we suggest that the dust and gas disks should be eccentric. Such a configuration, we further speculate, might be produced by a recent tidal disruption event. Assuming that the disrupted body has had a CO mass fraction of 10%, its total mass would be 3 M Moon .

Context. Many post-asymptotic giant branch (post-AGB) stars in binary systems have an infrared (IR) excess arising from a dusty circumbinary disk. The disk formation, current structure, and further evolution are, however, poorly understood. Aims. We aim to constrain the structure of the circumstellar material around the post-AGB binary and RV Tauri pulsator AC Her. We want to constrain the spatial distribution of the amorphous and of the crystalline dust. Methods. We present very high-quality mid-IR interferometric data that were obtained with the MIDI/VLTI instrument. We analyze the MIDI visibilities and differential phases in combination with the full spectral energy distribution, using the MCMax radiative transfer code, to find a good structure model of AC Her's circumbinary disk. We include a grain size distribution and midplane settling of dust self-consistently in our models. The spatial distribution of crystalline forsterite in the disk is investigated with the mid-IR features, the 69 µm band and the 11.3 µm signatures in the interferometric data. Results. All the data are well fitted by our best model. The inclination and position angle of the disk are precisely determined at i = 50 ± 8• and PA = 305 ± 10 • . We firmly establish that the inner disk radius is about an order of magnitude larger than the dust sublimation radius. The best-fit dust grain size distribution shows that significant grain growth has occurred, with a significant amount of mm-sized grains now being settled to the midplane of the disk. A large total dust mass ≥10 −3 M is needed to fit the mm fluxes. By assuming α turb = 0.01, a good fit is obtained with a small grain size power law index of 3.25, combined with a small gas/dust ratio ≤10. The resulting gas mass is compatible with recent estimates employing direct gas diagnostics. The spatial distribution of the forsterite is different from the amorphous dust, as more warm forsterite is needed in the surface layers of the inner disk. Conclusions. The disk in the AC Her system is in a very evolved state, as shown by its small gas/dust ratio and large inner hole. Mid-IR interferometry offers unique constraints, complementary to mid-IR features, for studying the mineralogy in disks. A better uv coverage is needed to constrain in detail the distribution of the crystalline forsterite in the disk of AC Her, but we find strong similarities with the protoplanetary disk HD 100546.

Far-infrared Herschel images of the Eridani system, seen at a fifth of the Sun's present age, resolve two belts of debris emission. Fits to the 160 μm PACS image yield radial spans for these belts of 12-16 and 54-68 AU. The south end of the outer belt is ≈10% brighter than the north end in the PACS+SPIRE images at 160, 250, and 350 μm, indicating a pericenter glow attributable to a planet "c." From this asymmetry and an upper bound on the offset of the belt center, this second planet should be mildly eccentric (e c ≈ 0.03-0.3). Compared to the asteroid and Kuiper Belts of the young Sun, the Eri belts are intermediate in brightness and more similar to each other, with up to 20 km sized collisional fragments in the inner belt totaling ≈5% of an Earth mass. This reservoir may feed the hot dust close to the star and could send many impactors through the Habitable Zone, especially if it is being perturbed by the suspected planet Eri b, at semi-major axis ≈3 AU.

Aims. We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent β for spatial and/or temporal variations. Methods. Using mapping observations of the very dense ρ Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N 2 H + , which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N 2 H + (J = 3−2) and (J = 6−5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H 2 ), hence the surface density distribution of the gas. Results. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, =88, is not far from the canonical value of 100, however. In ρ Oph A, the exponent β of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. β assumes intermediate values for evolutionary classes in between. Conclusions. Since β is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C 18 O, also N 2 H + is frozen onto the grains.

We present far-infrared and submillimeter maps from the Herschel Space Observatory and the James Clerk Maxwell Telescope of the debris disk host star AU Microscopii. Disk emission is detected at 70, 160, 250, 350, 450, 500 and 850 µm. The disk is resolved at 70, 160 and 450 µm. In addition to the planetesimal belt, we detect thermal emission from AU Mic's halo for the first time. In contrast to the scattered light images, no asymmetries are evident in the disk. The fractional luminosity of the disk is 3.9 × 10 −4 and its mm-grain dust mass is 0.01 M ⊕ (±20%). We create a simple spatial model that reconciles the disk SED as a blackbody of 53 ± 2 K (a composite of 39 and 50 K components) and the presence of small (non-blackbody) grains which populate the extended halo. The best fit model is consistent with the "birth ring" model explored in earlier works, i.e., an edge-on dust belt extending from 8.8-40 AU, but with an additional halo component with an r −1.5 surface density profile extending to the limits of sensitivity (140 AU). We confirm that AU Mic does not exert enough radiation force to blow out grains. For stellar mass loss rates of 10-100x solar, compact (zero porosity) grains can only be removed if they are very small; consistently with previous work, if the porosity is 0.9, then grains approaching 0.1 µm can be removed via corpuscular forces (i.e., the stellar wind).