Modeling low mass stellar populations, like clusters and dwarf galaxies, with population synthesis models requires that we evaluate the role played by stochastic fluctuations in the sampling of the IMF on the spectro-photometric properties of these sparse populations. Interacting binaries may also modify the integrated spectra of these systems depending on the final product of the binary interaction and on the frequency of binary stars. In this work we compare the relative importance of stochastic fluctuations and binary evolution on low mass galaxy properties as a function of the population age and total mass. In most cases the effects of stochastic fluctuations dominate those produced by binary interactions. We explore and quantify the relative importance of these effects through cosmic times.

Because of their small angular size < 1 mas, spatial information on High-mass X-ray binaries (HMXB) has typically been inferred from photometry or spectroscopy. Optical interferometry offers the possibility to spatially resolve such systems, but has been traditionally limited to bright targets or low spectral resolution. The VLTI instrument GRAVITY, working in the near-infrared K band, achieves unprecedented precision in differential interferometric quantities at high spectral resolution, allowing to study HMXBs through the lens of optical interferometry for the first time. We present GRAVITY observations on two X-ray binaries: the microquasar SS 433 and the supergiant HMXB BP Cru. The former is the only known steady super-Eddington accretor in the Galaxy and is in a unique stage of binary evolution, with probable ties to at least part of the ULX population. With GRAVITY, we resolve its massive winds and optical baryonic jets for the first time, finding evidence for powerful equatorial outflows and photoionization as the main heating process along the jets. BP Cru harbors an X-ray pulsar accreting from the wind of its early-blue hypergiant companion Wray 977. The GRAVITY observations resolve the inner parts of the stellar wind and allow probing the influence of the orbiting pulsar on the circumstellar environment.

Studies of the presence of magnetic fields in Herbig Ae/Be stars are extremely important because they enable us to improve our insight into how the magnetic fields of these stars are generated and how they interact with their environment, including their impact on the planet formation process and the planet-disk interaction. We report new detections of weak mean longitudinal magnetic fields in the close Herbig Ae double-lined spectroscopic binary AK Sco and in the presumed spectroscopic Herbig Ae binary HD 95881 (Järvinen et al. 2018) based on observations obtained with HARPSpol attached to ESO’s 3.6 m telescope. Such studies are important because only very few close spectroscopic binaries with orbital periods below 20 d are known among Herbig Ae stars. Our detections favour the conclusion that the previously suggested low incidence (5-10%) of magnetic Herbig Ae stars can be explained by the weakness of these fields and the limited accuracy of the published measurements. The search for magnetic fields and the determination of their geometries in close binary systems will play an important role for understanding the mechanisms that are responsible for the magnetic field generation.

The lowest metallicity massive stars in the Local Universe with $Z\sim \left( {{Z}_{\odot }}/50-{{Z}_{\odot }}/30 \right)$ are the crucial objects to test the validity of assumptions in the modern models of very low-metallicity massive star evolution. These models, in turn, have major implications for our understanding of galaxy and massive star formation in the early epochs. DDO68-V1 in a void galaxy DDO68 is a unique extremely metal-poor massive star. Discovered by us in 2008 in the HII region Knot3 with $Z={{Z}_{\odot }}/35\,\left[ 12+\log \left( \text{O/H} \right)\sim 7.14 \right]$, DDO68-V1 was identified as an LBV star. We present here the LBV lightcurve in V band, combining own new data and the last archive and/or literature data on the light of Knot3 over the 30 years. We find that during the years 2008-2011 the LBV have experienced a very rare event of ‘giant eruption’ with V-band amplitude of 4.5 mag ($V\sim {{24.5}^{m}}-{{20}^{m}}$).

Physical conditions and chemical abundances of two H II regions and a planetary nebula in the dIrr galaxy Leo A are presented. These determinations were performed using the direct method (Te measured) and the ONS method. We also constructed photoionization models for the three nebulae to determine the abundances and to analyse the ionizing stars. The O abundance was determined to be 12+log(O/H) = 7.4±0.2 in all cases.

The progenitors of many core-collapse supernovae (CCSNe) are expected to be in binary systems. By performing a series of three-dimensional hydrodynamical simulations, we investigate how CCSN explosions affect their binary companion. We find that the amount of removed stellar mass, the resulting impact velocity, and the chemical contamination of the companion that results from the impact of the SN ejecta, strongly increases with decreasing binary separation and increasing explosion energy. Also, it is foud that the impact effects of CCSN ejecta on the structure of main-sequence (MS) companions, and thus their long term post-explosion evolution, are in general not dramatic.

Thanks especially to the ALMA interferometer, there are several new detections of CO gas in debris disks. Based on our own and archival ALMA observations, we found that the presence of CO gas in dust-rich debris disks around young (10–50 Myr) A-type stars is common. Interestingly, similarly dust-rich debris disks around young F-K type stars exhibit significantly lower gas incidence. The main difference between the two subsamples is related to a special population of gaseous debris disks whose total CO gas quantity is comparable to that of the less massive Herbig Ae disks. The origin of gas in these CO-rich debris systems is not fully clarified yet.

Amongst the most tantalizing questions in science are those relating to the life issue. What is it, how did it emerge, does it exist beyond our planet? In this review some central themes that have governed this debate over past decades will be described. Through the newly proposed Persistence Principle, it is argued that material stability can be achieved through either kinetic or thermodynamic means, opening up the possibility for life to be understood as a kinetic, rather than a thermodynamic, phenomenon. That insight allows the evolutionary process from inanimate to animate to be understood as one that was initiated with the emergence of a kinetically stable prebiotic replicative chemical system. Such a chemical system, once established, was able to evolve and complexify toward increasingly stable replicative forms, toward life. With a clearer understanding of what life is, the search for life in the universe can become more clearly directed.

Gaia Data Release 2 (DR2; April 25, 2018) provides astrometric and photometric data for more than a billion stars - among them many AGB stars. As part of DR2 the light curves of several hundreds of thousand variable stars, including many long-period variable (LPV) candidates, are made available. The publication of the light curves and LPV-specific attributes in addition to the standard DR2 products offers a unique opportunity to study AGB stars. In this contribution, we present the first results for AGB stars based on the analysis of the Gaia data performed after their release. As an immediate result of the Gaia DR2 LPV database we introduce a new photometric index capable of efficiently distinguishing AGB stars of different masses and chemical 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.

We theoretically investigate the impact of feedback and its metallicity dependence in massive star formation from prestellar cores at all metallicity range. We include the feedback by MHD disk winds, radiation pressure, and photoevaporation solving the evolution of protostars and accretion flows self-consistently. Interestingly, we find that the feedback does not set the upper mass limit of stellar birth mass at any metallicity. At the solar metallicity, the MHD disk wind is the dominant feedback to set the star formation efficiencies (SFEs) from the prestellar cores similar to low-mass star formation. The SFE is found to be lower at lower surface density environment. The photoevaporation becomes significant at the low metallicity of Z < 10−2 Z⊙. Considering this efficient photoevaporation, we conclude that the IMF slope is steeper, i.e., massive stars are rarer at the extremely metal-poor environment of 10−5 − 10−3Z⊙. Our study raises a question on the common assumption of the universal IMF with a truncated at 100M⊙. Since the total feedback strength in the cluster/galaxy scale is sensitive to the number fraction of massive stars, the re-evaluations of IMF at various environments are necessary.

A Last affiliation changed 3 to 4 against MS. Please check and confirm if it is fine. small number of the sample of 184 carbon stars in the Magellanic Clouds show signs that they are in the act of evolving off of the asymptotic giant branch. Most carbon stars grow progressively redder in all infrared colors and develop stronger pulsation amplitudes as their circumstellar dust shells become optically thicker. The reddest sources, however, have unexpectedly low pulsation amplitudes, and some even show blue excesses that could point to deviations from spherical symmetry as they eject the last of their envelopes. Previously, all dusty carbon-rich AGB stars have been labeled “extreme,” but that term should be reserved for the truly extreme carbon stars. These objects may well hold the clues needed to disentangle what actually happens when a star ejects the last of its envelope and evolves off of the AGB.

Young low-mass protostellar sources are known to show significant chemical diversity in their envelopes at a few 1000s au scale; two distinct cases are hot corino chemistry and warm carbon-chain chemistry (WCCC). It is of great interest how the chemical diversity is inherited to chemistry of disk-forming regions. With the recent ALMA observations, we found that the chemical diversity in envelopes is indeed delivered into the disk-forming regions at a 100 au scale. Moreover, the chemical composition changes drastically from envelopes to disks. We also found sources with the hybrid chemical characteristics; both hot corino chemistry and WCCC occur in spatially separated parts of a single source. This hybrid case may be a common occurrence, while hot corinos and WCCC sources are regarded as distinct cases. This unified view of chemistry in disk-forming regions will be an important clue to tracing the chemical evolution from protostellar cores to protoplanetary disks.

In the last decade observations have been able to probe the evolution of the galaxy luminosity function, in particular showing a variation of its faint-end with redshift. We employ the data of the Cluster-EAGLE project, a set of cosmological, hydrodynamical zoom-in simulations of 30 galaxy clusters, to study the evolution of the galaxy luminostity functions in clusters with redshift. We compile a catalogue of simulated galaxies’ luminosities in the SDSS bands using the E-MILES spectra database, and taking into account dust attenuation. Stacked luminosity functions present little evolution with redshift of the faint-end slope from z=3.5 to z=0, regardless of the cluster mass.

Prolate rotation (i.e. rotation around the long axis) has been reported for two Local Group dwarf galaxies: Andromeda II, a dwarf spheroidal satellite of M31, and Phoenix, a transition type dwarf galaxy. The prolate rotation may be an exceptional indicator of a past major merger between dwarf galaxies. We showed that this type of rotation cannot be obtained in the tidal stirring scenario, in which the satellite is transformed from disky to spheroidal by tidal forces of the host galaxy. However, we successfully reproduced the observed Andromeda II kinematics in controlled, self-consistent simulations of mergers between equal-mass disky dwarf galaxies on a radial or close-to-radial orbit. In simulations including gas dynamics, star formation and ram pressure stripping, we are able to reproduce more of the observed properties of Andromeda II: the unusual rotation, the bimodal star formation history and the spatial distribution of the two stellar populations, as well as the lack of gas. We support this scenario by demonstrating the merger origin of prolate rotation in the cosmological context for sufficiently resolved galaxies in the Illustris large-scale cosmological hydrodynamical simulation.

Jets often display bends and knots at which the flows change character. Extreme distortions have implications for the nature of jet flows and their interactions. We present the results of three radio mapping campaigns. The distortion of 3CRR radio galaxy NGC 7385 is caused by a collision with a foreground magnetised gas cloud which causes Faraday rotation and free-free absorption, and is triggered into star formation. For NGC 6109 the distortion is more extreme, creating a ring-shaped structure, but no deflector can be identified in cold or hot gas. Similar distortions in NGC 7016 are apparently associated with an X-ray gas cavity, and the adjacent NGC 7018 shows filaments drawn out beyond 100 kpc. Encounters with substructures in low-density, magnetised, intergalactic gas are likely causes of many of these features.

We have modeled the luminosity-displacement correlation of high-mass X-ray binaries (HMXBs) with an evolutionary population synthesis (EPS) code. Detailed properties including offsets of simulated HMXBs are presented under both common envelope prescriptions usually adopted (i.e., the αCE formalism and the γ algorithm), and several theoretical models describing the natal kicks. We suggest that the distinct observational properties may be used as potential evidence to discriminate between models.

We are performing systematic observation studies on the Galactic interstellar isotopic ratios, including 18O/17O, 12C/13C, 14N/15N and 32S/34S. Our strategy focuses on combination of multi-transition observation data toward large samples with different Galactocentric distances. Our preliminary results show positive Galactic radial gradients of 18O/17O and 12C/13C. In both cases, the ratio increases with the Galactocentric distance, which agrees with the inside-out scenario of our Galaxy. Observations of other isotopes such as 14N/15N and 32S/34S are on-going.

The carbon-rich AGB star V Hya is believed to be in the very brief transition phase between the AGB and a planetary nebula (PN). Using HST/STIS, we previously found a high-velocity (> 200 kms−1) jet or blob of gas ejected only a few years ago from near (< 0.3 arcsec or 150 AU) the star (Sahai et al. 2003, Sahai et al. 2016). From multi-epoch high-resolution spectroscopy we found time-variable high-velocity absorption features in the CO 4.6 μm vibration-rotation lines of V Hya (Sahai et al. 2009). Modeling shows that these are produced in compact clumps of outflowing gas with significant radial temperature gradients consistent with strong shocks. Here, we present very high resolution (∼100 milliarcsecond) imaging of the central region of V Hya using the coronagraphic mode of the Gemini Planet Imager (GPI) in the 1 μm band and spectral-spatial imaging of 4.6 μm CO 1-0 transitions using the Phoenix spectrometer. We report the detection of a compact central dust disk from GPI, and molecular emission from the Phoenix observations at relatively larger scales. We discuss models for the central structures in V Hya, in particular disks and outflows, using these and complementary images in the optical and radio.