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We present MUSE deep integral-field unit spectroscopy of three planetary nebulae(PNe) with high abundance discrepancy factors (ADF > 20): NGC 6778, M 1-42 and Hf 2-2. We have constructed flux maps for more than 40 emission lines, and use them to build extinction, electron temperature (T$_e$), electron density (n$_e$), and ionic abundances maps of a number of ionic species. The effects of the contribution of recombination to the auroral [N II] and [O II] lines on T$_e$ and the abundance maps of low-ionization species are evaluated using recombination diagnostics. As a result, low T$_e$ values and a downward gradient of T$_e$ are found toward the inner zones of each PN. Spatially, this nearly coincides with the increase of abundances of heavy elements measured using recombination lines in the inner regions of PNe, and strongly supports the presence of two distinct gas phases: a cold and metal-rich and a warm one with "normal" metal content. We have simultaneously constructed, for the first time, the ADF maps of O$^+$ and O$^{2+}$ and found that they centrally peak for all three PNe under study. We show that the main issue when trying to compute realistic abundances from either ORLs or CELs is to estimate the relative contribution of each gas component to the H I emission, and we present a method to evaluate it. It is also found that, for the studied high-ADF PNe, the amount of oxygen in the cold and warm regions is of the same order., 20 pages, 10 Tables, 16 Figures. Additional material in appendix, 1 Table and 22 Figures. This article has been accepted for publication in MNRAS, Published by Oxford University Press on behalf of the Royal Astronomical Society

56 UMa is a wide binary system that contains a chemically peculiar red giant and a faint companion. Due to its surface chemical abundances, the red giant was classified as a barium (Ba) star. This implies that the companion has to be a white dwarf, since Ba stars form when mass is transferred to them from an s-process rich Asymptotic Giant Branch (AGB) star. However, in the case of 56 UMa, the companion might be too massive to be the progeny of an AGB star that efficiently produced s-process elements such as barium. In this Letter, we revisit the orbital parameters of the system and perform a full spectral analysis with the goal of investigating the Ba-star classification of the giant and unravelling the nature of its faint companion. We combined radial-velocity and astrometric data to refine the orbital parameters of the system, including the orbital inclination and the companion mass. Then, we re-determined the stellar parameters of the giant and its chemical abundances using high-resolution HERMES spectra. Finally, we investigated the morphology of the interstellar gas in the vicinity of the system. The faint component in 56 UMa has a mass of $1.31 \pm 0.12$ M$_{\odot}$, which, together with the mixed s+r abundance profile of the red giant, confirms that the giant is not a standard barium star. Additionally, the clear identification of a cavity surrounding 56 UMa could indicate that a supernova explosion occurred about 10 5 years ago in the system, suggesting that the faint companion might be a neutron star. However, finding an evolutionary scenario that explains all the observables is not trivial, so we discuss different possible configurations of the system and their respective merits., Comment: Accepted for publication in A&AL

The FORS Upgrade project (FORS-Up) aims at bringing a new life to the highly demanded workhorse instrument attached to ESO's Very Large Telescope (VLT). FORS2 is a multimode optical instrument, which started regular science operations in 2000 and since then, together with its twin, FORS1, has been one of the most demanded and most productive instruments of the VLT. In order to ensure that a FORS shall remain operational for at least another 15 years, an upgrade has been planned. This is required as FORS2 is using technology and software that is now obsolete and cannot be put and maintained to the standards in use at the Observatory. The project - carried out as a collaboration between ESO and INAF-Astronomical Observatory of Trieste - aims at bringing to the telescope in 2023/2024 a refurbished instrument with a new scientific detector, an upgrade of the instrument control software and electronics, a new calibration unit, as well as additional filters and grisms. The new FORS will also serve as a test bench for the Extremely Large Telescope (ELT) standard technologies (among them the use of programmable logic controllers and of the features of the ELT Control Software). The project aims at minimising the downtime of the instrument by performing the upgrade on the currently decommissioned instrument FORS1 and retrofitting the Mask Exchange Unit and polarisation optics from FORS2 to FORS1., Comment: Author version of a paper presented at SPIE Ground-based and Airborne Instrumentation for Astronomy VIII; corrected one statement

Variability of CzeV843 Cen was detected 31 March 2016 in the FOV of V834 Cen using Dk154 telescope at La Silla.

The role of mass loss, especially episodic mass loss, in evolved massive stars is one of the outstanding questions in stellar evolution theory. IFU observations can provide superb information on the recent mass-loss history and the evolutionary stages. With VLT MUSE we have observed a representative sample of massive stars from different evolved stellar classes that underwent episodic mass loss, which gave rise to extended nebulae. The structural inhomogeneities and associated velocity differences in the nebulae are tracers of the mass-loss history. The simultaneous observation of all lines at each position in the nebulae provides very accurate line ratios for physical diagnostics.

CCD photometry of the newly discovered eclipsing dwarf nova IY Ursae Majoris is used to study the physical properties of the accretion disc in the late decline and quiescence stages. Eclipse mapping analysis shows that in these stages the accretion disc is cool with approximately flat radial brightness temperature distribution and $T_{\rm BR}\sim5000-5500$ K. The hot spot is found to lie close along the stream trajectory at distance $0.36a$ and $0.25a$ from the disc center in February and March. The orbital hump strength decreases by ∼ 30% in a month. Taking the smallest possible size of the hot spot, we derive an upper limit for its brightness temperature, ∼ 15 900 K and ∼ 13 800 K, respectively.

It is expected that an average protostar will undergo at least one impulsive interaction with a neighbouring protostar whilst a large fraction of its mass is still in a massive, extended disc. If protostars are formed individually within a cluster before falling together and interacting, there should be no preferred orientation for such interactions. As star formation within clusters is believed to be coeval, it is probable that during interactions, both protostars possess massive, extended discs. We have used an SPH code to carry out a series of simulations of non-colpanar disc-disc interactions. We find that non-coplanar interactions trigger gravitational instabilities in the discs, which may then fragment to form new companions to the existing stars. (This is different from coplanar interactions, in which most of the new companion stars form after material in the discs has been swept up into a shock layer, and this then fragments.) The original stars may also capture each other, leading to the formation of a small-N cluster. If every star undergoes a randomly oriented disc-disc interaction, then the outcome will be the birth of many new stars. Approximately two-thirds of the stars will end up in multiple systems., 12 pages, submitted to MNRAS; low resolution figures only

Aims. The role of episodic mass loss is one of the outstanding questions in massive star evolution. The structural inhomogeneities and kinematics of their nebulae are tracers of their mass-loss history. We conduct a three-dimensional morpho-kinematic analysis of the ejecta of η Car outside its famous Homunculus nebula. Methods. We carried out the first large-scale integral field unit observations of η Car in the optical, covering a field of view of 1′× 1′ centered on the star. Observations with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT) reveal the detailed three-dimensional structure of η Car’s outer ejecta. Morpho-kinematic modeling of these ejecta is conducted with the code SHAPE. Results. The largest coherent structure in η Car’s outer ejecta can be described as a bent cylinder with roughly the same symmetry axis as the Homunculus nebula. This large outer shell is interacting with the surrounding medium, creating soft X-ray emission. Doppler velocities of up to 3000 km s-1 are observed. We establish the shape and extent of the ghost shell in front of the southern Homunculus lobe and confirm that the NN condensation can best be modeled as a bowshock in the orbital/equatorial plane. Conclusions. The SHAPE modeling of the MUSE observations provides a significant gain in the study of the three-dimensional structure of η Car’s outer ejecta. Our SHAPE modeling indicates that the kinematics of the outer ejecta measured with MUSE can be described by a spatially coherent structure, and that this structure also correlates with the extended soft X-ray emission associated with the outer debris field. The ghost shell immediately outside the southern Homunculus lobe hints at a sequence of eruptions within the time frame of the Great Eruption from 1837–1858 or possibly a later shock/reverse shock velocity separation. Our 3D morpho-kinematic modeling and the MUSE observations constitute an invaluable dataset to be confronted with future radiation-hydrodynamics simulations. Such a comparison may shed light on the yet elusive physical mechanism responsible for η Car-like eruptions.

The role of episodic mass loss in evolved massive stars is one of the outstanding questions in stellar evolution theory. Integral field spectroscopy of nebulae around massive stars provide information on their recent mass-loss history. η Car is one of the most massive evolved stars and is surrounded by a complex circumstellar environment. We have conducted a three-dimensional morpho-kinematic analysis of η Car’s ejecta outside its famous Homunculus nebula. SHAPE modelling of VLT MUSE data establish unequivocally the spatial cohesion of the outer ejecta and the correlation of ejecta with the soft X-ray emission.

We perform 2D and 3D numerical simulations of an accretion disc in a close binary with a mass ratio of 0.5, corresponding to the dwarf nova IP Pegasi. We do not include artificial nor α-viscosity and supply gas from the inner L1 point. We construct Doppler maps and artificial trailed spectrograms. In the 2D calculation, the results agree very well with those observed in IP Peg. In the 3D calculations, the stream from the L1 point penetrates into the accretion disc. The resulting flow pattern, therefore, is different from the 2D results.

We simulate numerically the surface flow of a gas-supplying companion star in a semi-detached binary system. Calculations are carried out for a region including only the mass-losing star, thus not the mass accreting star. The equation of state is that of an ideal gas characterized by a specific heat ratio gamma, and the case with gamma=5/3 is mainly studied. A system of eddies appears on the surface of the companion star: an eddy in the low pressure region near the L1 point, one around the high pressure at the north pole, and one or two eddies around the low pressure at the opposite side of the L1 point. Gas elements starting near the pole region rotate clockwise around the north pole (here the binary system rotates counter-clockwise as seen from the north pole). Because of viscosity, the gas drifts to the equatorial region, switches to the counter-clockwise eddy near the L1 point and flows through the L1 point to finally form the L1 stream. The flow field in the L1 region and the structure of the L1 stream are also considered., Comment: 10 pages, 22 figures, Accepted for publication in A&A

The well-known recurrent nova T Pyx has brightened by 7 magnitudes, starting on 2011 April 14, its first eruption since 1966. T Pyx is unique amongst recurrent novæ in being surrounded by a nebula formed of material ejected during previous eruptions. The latest eruption therefore offers the rare opportunity to observe a light echo sweeping through the existing shell, and a new one forming. The sudden exposure of the existing shell to high-energy light is expected to result in a change of the dust morphology as well as in the part destruction of molecules. We observe this process in the near- and mid-IR during several epochs using ESO's VLT instruments Sinfoni, Visir and Isaac. Unfortunately, in the data analysed so far we only have a tentative detection in Brα from the shell, so might in the end have to be content with upper limits for the emission from the various molecular bands and ionised lines.

We numerically simulate the surface flow of a gas-supplying companion star in a semi-detached binary system and construct the Doppler map. Our numerical results indicate an eddy configuration composed of a Heddy, a L1-eddy, and a L2-eddy associated with high/low pressures on the surface of the companion star. We find that the formation of these eddies can be explained in terms of the astrostrophic wind. We apply our calculations to the Galactic supersoft X-ray source RX J0019.8+2156. This object is very attractive for the present study since the observed Doppler map might reflect the surface flow on the companion star. We have constructed the Doppler map of RX J0019.8+2156 and compare it with observations.

Ba II stars are red giants showing an enhancement of carbon and s-process elements. The elucidation of their nature seems to require a mass transfer, either by wind or Roche lobe overflow, during their past evolution. Were it really the case, all Ba II stars would be binaries with a white dwarf as companion. To better understand the exact role of their binarity, more orbits are definitely needed. They can be obtained by monitoring the radial velocity variations of those stars. However, a quicker way to find new Ba II stars with orbital elements would be to search for their existence among known spectroscopic binaries. This would also crucially test whether mass transfer is a necessary and sufficient condition to explain Ba II stars. If it is indeed the case, then all spectroscopic binaries, made of a giant and a white dwarf, in a reasonable range of periods, would exhibit the Ba II pecularity. However, the discovery of a peculiar giant+main sequence binary system would imply a revision of our ideas about Ba II stars. To this end have we begun a systematic spectral survey of spectroscopic binaries with orbital periods in the range characteristic of known Ba II stars and containing a red giant. The realization that some stars of the catalogue we compiled were already identified as semibariium stars encourages us to pursue our investigation. Coude spectra were taken with the 152 cm telescope, at a dispersion of 12 Å mm−1 . Until now, 2 stars out of a sample of 31 present a slight enhancement of s-process elements (their anomaly being in the range Ba 0.3 to 0.5), and 2 more appear to be good candidates. The study of a larger sample is currently in progress. A discussion of the nature of the companion to the 2 newly discovered semibarium stars is presented on grounds of their mass function and photometric indices.