Recent far-infrared (FIR) observations have revealed the presence of freshly formed dust with the masses exceeding 0.1 M⊙ in young remnants of core-collapse supernovae (CCSNe) such as SN 1987A and Cassiopeia A. Meanwhile, dust masses derived from near- to mid-infrared (N/MIR) observations of CCSNe a few years after explosions are on the order of 10−5–10−3M⊙. Here, we demonstrate that such small dust masses as seen from N/MIR observations would not necessarily reflect the formation history of dust but could be just limited by the luminosity of the SN that can heat up dust formed in the ejecta.

The detection of thousands of planets orbiting stars other than the Sun has shown that planets are common throughout the Galaxy. However, the diversity of systems found has also raised many questions regarding the process of planet formation and evolution. Interestingly, but perhaps not unexpectedly, crucial information to constraint the planet formation models comes from the analysis of the planet-host stars. In this talk I will review why it is so important to study and understand the stars when finding and characterising exoplanets. I will then present some of the most relevant star-planet relations found to date, and how they are helping us to understand planet formation and evolution. I will end with a presentation of the future steps in this field, including what Gaia will bring to help constrain the properties of planet-host stars, as well as to the star-planet connection.

Stellar occultations by solar system objects allow kilometric accuracy, permit the detection of tenuous atmospheres (at nbar level), and the discovery of rings. The main limitation was the prediction accuracy, typically 40 mas, corresponding to about 1,000 km projected at the body. This lead to large time dedicated to astrometry, tedious logistical issues, and more often than not, mere miss of the event. The Gaia catalog, with sub-mas accuracy, hugely improves both the star positions, resulting in achievable accuracies of about 1 mas for the shadow track on Earth. This permits much more carefully planned campaigns, with success rate approaching 100%, weather permitting. Scientific perspectives are presented, e.g. central flashes caused by Plutos atmosphere revealing hazes and winds near its surface, grazing occultations showing topographic features, occultations by Chariklos rings unveiling dynamical features such as proper mode “breathing”.

About one half of high-mass X-ray binaries host a Be star [an OB star with a viscous decretion (slowly outflowing) disk]. These Be/X-ray binaries exhibit two types of X-ray outbursts (Stella et al. 1986), normal X-ray outbursts (LX~1036−37 erg s−1) and occasional giant X-ray outbursts (LX > 1037 erg s−1). The origin of giant X-ray outbursts is unknown. On the other hand, a half of gamma-ray binaries have a Be star as the optical counterpart. One of these systems [LS I +61 303 (Porb = 26.5 d)] shows the superorbital (1,667 d) modulation in radio through X-ray bands. No consensus has been obtained for its origin. In this paper, we study a possibility that both phenomena are caused by a long-term, cyclic evolution of a highly misaligned Be disk under the influence of a compact object, by performing 3D hydrodynamic simulations. We find that the Be disk cyclically evolves in mildly eccentric, short-period systems. Each cycle consists of the following stages:

1. 1) As the Be disk grows with time, the initially circular disk becomes eccentric by the Kozai-Lidov mechanism.

2. 2) At some point, the disk is tidally torn off near the base and starts precession.

3. 3) Due to precession, a gap opens between the disk base and mass ejection region, which allows the formation of a new disk in the stellar equatorial plane (see Figure 1).

4. 4) The newly formed disk finally replaces the precessing old disk. Such a cyclic disk evolution has interesting implications for the long-term behavior of high energy emission in Be/X-ray and gamma-ray binaries.

Magnetic fields play an important role in shaping the circumstellar environment of hot, massive stars. Observational diagnostics give clues to the presence of magnetism across the entire electromagnetic spectrum. Infrared features can show more complex structure, indicating they may probe deeper opacities than optical features. Optical and infrared features mimic each other, with identical blue and red peak variations and identical peak velocity of material. These comparisons indicate the location of the infrared and optical emitting material is similar. Longer wavelength diagnostics are currently being developed and tested. IR spectroscopy is a viable tool to detect magnetic candidates in the Galactic center and star forming regions.

Stellar occultations are a unique technique to access physical characteristics of distant solar system objects from the ground. They allow the measure of the size and the shape at kilometric level, the detection of tenuous atmospheres (few nanobars), and the investigation of close vicinity (satellites, rings) of Transneptunian objects and Centaurs. This technique is made successful thanks to accurate predictions of occultations. Accuracy of the predictions depends on the uncertainty in the position of the occulted star and the object's orbit. The Gaia stellar catalogue (Gaia Collaboration (2017)) now allows to get accurate astrometric stellar positions (to the mas level). The main uncertainty remains on the orbit. In this context, we now take advantage of the NIMA method (Desmars et al.(2015)) for the orbit determination and of the Gaia DR1 catalogue for the astrometry. In this document, we show how the orbit determination is improved by reducing current and some past observations with Gaia DR1. Moreover, we also use more than 45 past positive occultations observed in the 2009-2017 period to derive very accurate astrometric positions only depending on the position of the occulted stars (about few mas with Gaia DR1). We use the case of (10199) Chariklo as an illustration. The main limitation lies in the imprecision of the proper motions which is going to be solved by the Gaia DR2 release.

We present a catalog of potential candidates for asteroid mass determination based on mutual close encounters of numbered asteroids with massive perturbers (D>20 km). Using a novel geometric approach tuned to optimize observability, we predict optimal epochs for mass determination observations. In contrast to previous studies that often used simplified dynamical models, we have numerically propagated the trajectories of all numbered asteroids over the time interval from 2013 to 2023 using relativistic equations of motion including planetary perturbations, J2 of the Sun, the 16 major asteroid perturbers and the perturbations due to non-sphericities of the planets. We compiled a catalog of close encounters between asteroids where the observable perturbation of the sky plane trajectory is greater than 0.5 mas so that astrometric measurements of the perturbed asteroids in the Gaia data can be leveraged. The catalog v1.0 is available at ftp://dosya.akdeniz.edu.tr/ivantsov.

Turbulent transport and mixing generated by hydrodynamic instabilities triggered by rotation gradients are key mechanisms in the evolution of massive stars. We present here a summary of the progresses on shear-induced mixing obtained with numerical simulations, along with a new prescription for horizontal turbulence.

Some studies suggested that the chemical abundance trend with the condensation temperature, Tc, is a signature of rocky planet formation. Very recently, a strong Tc trend was reported in ζ2 Ret relative to its companion (ζ1 Ret) and was explained by the presence of a debris disk around ζ2 Ret. We re-evaluated the presence and variability of the Tc trend in this system with a goal to understand the impact of the presence of the debris disk on a star. Our results confirm the reported abundance difference between ζ2 Ret and ζ1 Ret and its dependence on the Tc. However, we also found that the Tc trends depend on the individual spectrum used. We conclude that for the ζ Reticuli system, for example, nonphysical factors can be at the root of the Tc trends for the case of individual spectra. For more details see Adibekyan et al. (2016b).

FASTWIND is a unified NLTE atmosphere/spectrum synthesis code originally designed (and frequently used) for the optical/IR spectroscopic analysis of massive stars with winds. Until the previous version (v10), the line transfer for background elements (mostly from the iron-group) was performed in an approximate way, by calculating the individual line-transitions in a single-line Sobolev or comoving frame approach, and by adding up the individual opacities and source functions to quasi-continuum quantities that are used to determine the radiation field for the complete spectrum (see Puls et al. 2005, A&A 435, 669, and updates).

We have now updated this approach (v11) and calculate, for all contributing lines (from elements H to Zn), the radiative transfer in the comoving frame, thus also accounting for line-overlap effects in an “exact” way. Related quantities such as temperature, radiative acceleration and formal integral have been improved in parallel. For a typical massive star atmospheric model, the computation times (from scratch, and for a modern desktop computer) are 1.5 h for the atmosphere/NLTE part, and 30 to 45 minutes (when not parallelized) for the formal integral (i.e., SED and normalized flux) in the ranges 900 to 2000 and 3800 to 7000 Å(Δλ = 0.03 Å).

We compare our new with analogous results from the alternative code CMFGEN (Hillier & Miller 1998, ApJ 496, 407, and updates), for a grid consisting of 5 O-dwarf and 5 O-supergiant models of different spectral subtype. In most cases, the agreement is very good or even excellent (i.e., for the radiative acceleration), though also certain differences can be spotted. A comparison with results from the previous, approximate method shows equally good agreement, though also here some differences become obvious. Besides the possibility to calculate the (total) radiative acceleration, the new FASTWIND version will allow us to investigate the UV-part of the spectrum in parallel with the optical/IR domain.

Knowledge of the spin and shape parameters of the asteroids is very important for understanding of the conditions during the creation of our planetary system and formation of asteroid populations. The main belt asteroid and Flora family member 967 Helionape was observed during five apparitions. The observations were made at the Bulgarian National Astronomical Observatory (BNAO) Rozhen, since March 2006 to March 2016. Lihtcurve inversion method (Kaasalainen et al. (2001)), applied on 12 relative lightcurves obtained at various geometric conditions of the asteroid, reveals the spin vector, the sense of rotation and the preliminary shape model of the asteroid. Our aim is to contribute in increasing the set of asteroids with known spin and shape parameters. This could be done with dense lightcurves, obtained during small number of apparitions, in combination with sparse data produced by photometric asteroid surveys such as the Gaia satellite (Hanush (2011)).

The formation of massive stars remains one of the most intriguing questions in astrophysics today. The main limitations result from the difficulty to obtain direct observational constraints on the formation process itself. In this context, the Carina High-contrast Imaging Project of massive Stars (CHIPS) aims to observe all 80+ O stars in the Carina nebula using the new VLT 2nd-generation extreme-AO instrument SPHERE. This instrument offers unprecedented imaging contrast allowing us to detect the faintest companions around massive stars. These novel observational constraints will help to discriminate between the different formation scenarios by comparing their predictions for companion statistics and properties.

We discuss the stellar and wind properties of 72 presumably single O-type giants, bright giants, and supergiants in the 30 Doradus region. This sample constitutes the largest and most homogeneous sample of such stars ever analyzed and offers the opportunity to test models describing their main-sequence evolution.

We are presenting the first results of low dispersion spectroscopic observation of asteroids at Bulgarian National Astronomical Observatory Rozhen. Asteroids with unclassified spectra and brighter than 15 magnitude have been chosen. Besides just presenting the asteroid reflectance, classification according to Bus S. J. et al. (2012) has been done. The asteroid spectra of 590 Tomyris, 703 Noemi, 1596 Itzigsohn and 1826 Miller are presented together with standard spectra corresponding to the three best matches given by the public software tool M4AST (Popescu M. et al. (2012)). Our aim is to participate in the coordinated program of asteroids spectroscopy complementary to the observations of Gaia.

The role of massive stars in the Galactic evolution is crucial. During their lifetime these stars change the kinematics around them through stellar winds, affect the formation of new stars, ionise and chemically enrich the media with the final supernova explosion. But the census of both massive stars and their host clusters is still poor. We expect that still ~100 of galactic massive stellar clusters remains unknown (Hanson & Popescu, 2008).

The stellar occultation technique is a powerful tool to study distant small solar system bodies. Currently, around 2 500 trans-neptunian objects (TNOs) and Centaurs are known. With the astrometry from Gaia and large surveys like the Large Synoptic Survey Telescope (LSST), accurate predictions of occultation events will be available to tens of thousands of TNOs and Centaurs and boost the knowledge of the outer solar system.

We obtained VLT/X-shooter spectra of twelve candidate young massive stars previously selected by Hanson et al. (1997) in the giant Hii region M17. An analysis of their spectra using FASTWIND models (Puls et al. 2005) shows that they span a mass range of 6 - 20 M⊙. We identify the presence of gaseous and dusty disks around six sources based on emission lines in the spectrum and infrared continuum excess.

A new asteroid taxonomy will be an important result of Gaia observations of Solar System objects. Since Gaia observes asteroids in observing conditions and in an interval of wavelength which are slightly different with respect to normal ground-based observations, a dedicated observing campaign has been carried out at the Telescopio Nazionale Galileo in La Palma (Canary Islands, Spain). The obtained spectra have been used to generate a large number of synthetic clones, each one having slight changes with respect to its parent spectrum. These synthetic spectra are then used to feed the algorithm of taxonomic classification developed to reduce Gaia asteroid spectra. Processing of these data is in progress.

Since 2015, scientific activities at the Terskol Observatory have been aimed at optical follow-up of stellar objects and asteroids detected within the framework of the Gaia mission. Two years of successful research have yielded new data and findings in this field. Photometric observations of Gaia transients allowed us to reveal physical characteristics of a good few of them. Moreover, we detected positions of dozens of asteroids which were reported by the GBOT group. In this paper, some results obtained from observations of transients Gaia16bkf, Gaia16bkn, Gaia17asz and newly detected asteroids are presented.

Luminous Blue Variables (LBVs) are a brief phase in the evolution of massive stars, but a very important one. The giant eruptions remain enigmatic, but the discovery of the flagship LBV η Car to be a five-year highly eccentric binary put focus on possible binarity induced mechanism for these outbursts, and prompted binarity searches among LBVs. While several wide LBV binaries were identified, HR Car is the first system found to be similar to η Car, i.e., relatively close & eccentric.