Symbiotic stars (SySts) are long-period interacting binaries composed of a hot compact star, an evolved giant star, and a tangled network of gas and dust nebulae. Presently, we know 252 SySts in the Milky Way and 62 in external galaxies. However, these numbers are still in striking contrast with the predicted population of SySts in our Galaxy. In this contribution, I present the concept and the early results from RAMSES II (Raman Search for Extragalactic Symbiotic Stars), a Gemini/GMOS Upgrade Project which makes use of the Raman OVI 6830Å band as a powerful photometric tool to identify new SySts, within and beyond the Galaxy.

Massive stars are the drivers of the chemical evolution of dwarf galaxies. We review here the basics of massive star evolution and the specificities of stellar evolution in low-Z environment. We discuss nucleosynthetic aspects and what observations could constrain our view on the first generations of stars.

Dwarf galaxies with stellar masses around 109M⊙ can be explored at high and low redshifts and they give a glimpse of the different conditions of galaxy formation at different epochs. Using a large sample of about 300 zoom-in cosmological hydrodynamical simulations of galaxy formation I will briefly describe the formation of dwarfs at this mass scale at 3 different epochs: cosmic dawn (Ceverino, Klessen, Glover 2018), cosmic noon (Ceverino, Primack, Dekel 2015), and today (Ceverino et al. 2017). I will describe the FirstLight simulations of first galaxies at redshifts 5-15. These first dwarfs have extremely high star formation efficiencies due to high gas fractions and high gas accretion rates. These simulations will make predictions that will be tested for the first time with the James Webb Space Telescope (JWST). At cosmic noon, z = 2, galaxy formation is still a very violent and dynamic process. The VELA simulations have generated a set of dispersion-dominated dwarfs that show an elongated morphology due to their prolate dark-matter halos. Between z = 1 and 0, the AGORA simulation shows the formation of a low-mass disc due to slow gas accretion. The disc agrees with many local scaling relations, such as the stellar-mass-halo-mass and the baryonic Tully-Fisher relation.

Stellar magnetic field manifestations such as stellar winds and EUV radiation are the key drivers of planetary atmospheric loss and escape. To understand how the central star influences habitability, it is very important to perform detailed investigation of the star’s magnetic field. We investigate the surface magnetic field geometry and chromospheric activity of 51 sun-like stars. The magnetic geometry is reconstructed using Zeeman Doppler imaging. Chromospheric activity is measured using the Ca II H& K lines. We confirm that the Sun’s large-scale geometry is dominantly poloidal, which is also true for slowly rotating stars. Contrary to the Sun, rapidly rotating stars can have a strong toroidal field and a weak poloidal field. This separation in field geometry appears at Ro=1. Our results show that detailed investigation of stellar magnetic field is important to understand its influence on planetary habitability.

We compare the properties of stellar populations for globular clusters (GCs) and field stars in two dwarf spheroidal galaxies (dSphs): ESO269-66, a close neighbour of NGC5128, and KKs3, one of the few isolated dSphs within 10 Mpc. We analyse the surface density profiles of low and high metallicity (blue and red) stars in two galaxies using the Sersic law. We argue that 1) the density profiles of red stars are steeper than those of blue stars, which evidences in favour of the metallicity and age gradients in dSphs; 2) globular clusters in KKs3 and ESO 269-66 contain 4 and 40 percent of all stars with [Fe / H] ~ 1.6 dex and the age of 12 Gyr, correspondingly. Therefore, GCs are relics of the first powerful star-forming bursts in the central regions of the galaxies. KKs 3 has lost a smaller percentage of old low-metallicity stars than ESO269-66, probably, thanks to its isolation.

Recent theories on the formation of the Solar System turned the attention to the study of low mass cloud cores in massive star forming regions. The Rosette Molecular Cloud is a well-known star forming area having highly filamentary structure with dense cores covering a wide range of masses. These pre- and protostellar cores were observed by Herschel and key core properties were derived from its data. With the Effelsberg 100m telescope a sample of these cores with masses ranging between 3-40 M⊙ were observed in ammonia inversion lines. In this work we are examining the correlations between these two datasets with the aim of gaining insight of the processes behind the star formation of the region.

We present initial results from three-dimensional (3-D) radiation hydrodynamical simulations for the Sun and targeted Sun-like stars. We plan to extend these simulations up to several stellar days to study p-mode excitation and damping processes. The level of variation of irradiance on the time scales spanned by our 3-D simulations will be studied too. Here we show results from a first analysis of the computational data we produced so far.

The community of massive stars is working intensively on Local Group dwarf irregular galaxies (dIrr). They are a reservoir of metal-poor massive stars that serve to understand the physics of their higher redshift siblings and population III stars, interpret the farthest, most energetic SNe and GRBs, and compute feedback through Cosmic History. Along the way, we became interested in the recent star-formation history and initial mass-function of the host dIrr’s, their chemical evolution, and gas and dust content. Our team is working to unveil and characterize with spectroscopy the OB-stars in IC 1613, Sextans A and SagDIG, that form a sequence of decreasing metal content. We showcase some results to stimulate synergies between both communities.

I review the insights emerging from recent large kinematic surveys of galaxies at low redshift, with particular reference to the SAMI, CALIFA and MaNGA surveys. These new observations provide a more comprehensive picture of the angular momentum properties of galaxies over wide ranges in mass, morphology and environment in the present-day universe. I focus on the distribution of angular momentum within galaxies of various types and the relationship between mass, morphology and specific angular momentum. I discuss the implications of the new results for models of galaxy assembly.

Self-interacting dark matter (SIDM) can create sufficiently large cores in dark matter haloes of dwarf galaxies if the self-interaction cross-section is sufficiently large on scales of dwarf galaxies. Such a large cross-section can be realized without changing the densities and shapes of cluster-size haloes by introducing a velocity dependent cross-section. Lowering the central densities of dwarf-size haloes, however, may change the strength of stellar feedback required to reproduce observed properties of dwarf galaxies such as the luminosity function of the Milky Way’s satellite galaxies. We perform simulations of galaxy formation by employing such a velocity dependent self-interaction cross-section to investigate the coupled effect of SIDM and feedback.

We studied Planetary Nebulae (PNe) metallicity gradients using Ar abundances. We compared them with H ii regions in the galaxies of the local universe M 31, M 33, NGC 300 and in the Milky Way. Galactocentric radio (RG) and chemical abundances were collected from the literature, carefully selecting an homogeneous sample for each galaxy. In these galaxies, metallicity gradients computed with PNe abundances are flatter than those of H ii regions.

We report on the successful search for CO (2-1) and (3-2) emission associated with OH/IR stars in the Galactic Bulge. We observed a sample of eight extremely red AGB stars with the APEX telescope and detected seven. The sources were selected at sufficient high Galactic latitude to avoid interference by interstellar CO, which hampered previous studies of inner galaxy stars. We also collected photometric data and Spitzer IRS spectroscopy to construct the SEDs, which were analysed through radiative transfer modelling. We derived variability periods of our stars from the VVV and WISE surveys. Through dynamical modelling we then retrieve the total mass loss rates (MLR) and the gas-to-dust ratios. The luminosities range between approximately 4,000 and 5,500 L⊙ and periods are below 700 days. The total MLR ranges between 10−5 and 10−4 M⊙ yr−1. The results are presented in Blommaert et al. 2018 and summarized below.

Herbig Ae/Be-type stars are analogs of T Tauri stars at higher masses. Since the confirmation of magnetospheric accretion using Balmer and sodium line profiles in the Herbig Ae star UX Ori, a number of magnetic studies have been attempted, indicating that about 20 Herbig Ae/Be stars likely have globally organized magnetic fields. The low detection rate of magnetic fields in Herbig Ae stars can be explained by the weakness of these fields and rather large measurement uncertainties. The obtained density distribution of the root mean square longitudinal magnetic field values revealed that only a few stars have magnetic fields stronger than 200 G, and half of the sample possesses magnetic fields of about 100 G or less. We report on the results of our analysis of a sample of presumably single Herbig Ae/Be stars based on recent observations obtained with HARPSpol attached to ESO’s 3.6m telescope. Knowledge of the magnetic field structure combined with the determination of the chemical composition are indispensable to constrain theories on star formation and magnetospheric accretion in intermediate-mass stars. As of today, magnetic phase curves have been obtained only for two Herbig Ae/Be stars, HD 101412 and V380 Ori.

The Atacama Large Millimeter/submillimeter Array (ALMA) is providing important advances in studies of star formation. In particular, polarimetry can reveal the disk magnetic configuration, a crucial ingredient in many processes, as, for example, the transport of angular momentum. We analized ALMA Band 7 (870 μm) polarimetric data at 0.”2 resolution for the young rotating disk/jet systems DG Tau and CW Tau, to find magnetic signatures. From the Stokes I, U, Q maps, we derive the linear polarization intensity, $P = \sqrt {{Q^2} + {U^2}} $, the linear polarization fraction, and the polarization angle. The alignment of the latter with the disk minor axis (Fig. 1) shows that self-scattering of dust thermal emission rather than magnetic alignment dominates the polarization in both targets (Bacciotti et al. 2018). However, several dust properties can be diagnosed comparing the polarization data with the models of self-scattering (e.g. Kataoke et al. 2017, Yang et al. 2017). The maximum grain size turns out to be in the range 50 - 70 μm for DG Tau and 100 - 150 μm for CW Tau. The asymmetry of the polarized intensity in DG Tau, observed for the first time around a T Tauri star, indicates that the disk is flared. Moreover, the observed belt-like feature may betray the presence of a disk substructure. In contrast, the polarization maps of CW Tau indicate that here the grains have settled to the disk midplane. Polarimetry is thus very important in studies of the dust evolution.

Certain types of large amplitude AGB variable are proving to be powerful distance indicators that will rival Cepheids in the James Webb Space Telescope era of high precision infrared photometry. These are predominantly found in old populations and have low mass progenitors. At the other end of the AGB mass-scale, large amplitude variables, particularly those undergoing hot bottom burning, are the most luminous representatives of their population. These stars are < 1 Gyr old, are often losing mass copiously and are vital to our understanding of the integrated light of distant galaxies as well as to chemical enrichment. However, the evolution of such very luminous AGB variables is rapid and remains poorly understood. Here I discuss recent infrared observations of both low- and intermediate-mass Mira variables in the Local Group and beyond.

We investigate dynamics of slender magnetic flux tubes (MFT) in the accretion disks of young stars. Simulations show that MFT rise from the disk and can accelerate to 20-30 km/s causing periodic outflows. Magnetic field of the disk counteracts the buoyancy, and the MFT oscillate near the disk’s surface with periods of 10-100 days. We demonstrate that rising and oscillating MFT can cause the IR-variability of the accretion disks of young stars.