We describe an algorithm that can fit the properties of the dwarf galaxy progenitor of a tidal stream, given the properties of that stream. We show that under ideal conditions (the Milky Way potential, the orbit of the dwarf galaxy progenitor, and the functional form of the dwarf galaxy progenitor are known exactly), the density and angular width of stars along the stream can be used to constrain the mass and radial profile of both the stellar and dark matter components of the progenitor dwarf galaxy that was ripped apart to create the stream. Our provisional fit for the parameters of the dwarf galaxy progenitor of the Orphan Stream indicates that it is less massive and has fewer stars than previous works have indicated.

A recent survey of the far-ultraviolet spectra of 264 B-emission line stars has revealed 16 systems with hot companions that are the stripped down remains of a former mass donor star. Some of these will probably become Be + neutron star X-ray binaries in the future. The actual numbers of such systems may be large, because the detected systems have companions that occupy the brief and bright, He-shell burning stage of evolution.

Quasars with flat radio spectra and one-sided, arc-second scale, ≈ 100 mJy GHz radio jets are found to have similar scale X-ray jets in about 60% of such objects, even in short 5 to 10 ks Chandra observations. Jets emit in the GHz band via synchrotron radiation, as known from polarization measurements. The X-ray emission is explained most simply, i.e. with the fewest additional parameters, as inverse Compton (iC) scattering of cosmic microwave background (cmb) photons by the relativistic electrons in the jet. With physics based assumptions, one can estimate enthalpy fluxes upwards of 1046 erg s−1, sufficient to reverse cooling flows in clusters of galaxies, and play a significant role in the feedback process which correlates the masses of black holes and their host galaxy bulges. On a quasar-by-quasar basis, we can show that the total energy to power these jets can be supplied by the rotational energy of black holes with spin parameters as low as a = 0.3. For a few bright jets at redshifts less than 1, the Fermi gamma ray observatory shows upper limits at 10 Gev which fall below the fluxes predicted by the iC/cmb mechanism, proving the existence of multiple relativistic particle populations. At large redshifts, the cmb energy density is enhanced by a factor (1+z)4, so that iC/cmb must be the dominant mechanism for relativistic jets unless their rest frame magnetic field strength is hundreds of micro-Gauss.

Chondrites are made of a mixture of solids formed at high and low temperatures. This heterogeneity was thought to be produced by large scale transport processes in the Sun’s isolated accretion disk. However, mounting evidences suggest that refractory inclusions in chondrites were produced together with the disk formation.

We present numerical simulations of the formation and transport of rocky materials during the collapse of the Solar Nebula’s parent cloud and the consequent disk assembling.

We find that the interplay between the cloud collapse, the dynamics of gas and dust and thermal processing of different species in the disk, results in a local mixing of solids with different thermal histories. Our simulations return an heterogeneous distribution of refractory material with higher concentration in the outer disk. This refractory material has a short formation timescales, during the first tens of kyr of the Sun (class 0-I). Our results open new frontiers into the origin of the compositional diversity of chondrites.

The outer stellar halo is home to a number of substructures that are remnants of former interactions of the Galaxy with its dwarf satellites. Triangulum-Andromeda (TriAnd) is one of these halo substructures, found as a debris cloud by Rocha-Pinto et al., (2004) using 2MASS M giants. Would be these structures related to dwarf galaxies or to the galactic disk? To uncover the nature of these stars we performed a high-resolution spectroscopic study (R = 40,000) along with a kinematic analysis using Gaia data. We determined the atmospheric parameters and chemical abundances of Ca and Mg for the 13 TriAnd candidate stars along with their respective orbits. Our results indicate that the TriAnd stars analyzed have a galactic nature but that these stars are not from the local thin disk.

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.

In the standard formation scenario of planetary systems, planets form from a protoplanetary disk that consists of gas and dust. The scenario can be divided into three stages: (1) formation of planetesimals from dust, (2) formation of protoplanets from planetesimals, and (3) formation of planets from protoplanets. In stage (1), planetesimals form from dust through coagulation of dust grains and/or some instability of a dust layer. Planetesimals grow by mutual collisions to protoplanets or planetary embryos through runaway and oligarchic growth in stage (2). The final stage (3) of terrestrial planet formation is giant impacts among protoplanets while sweeping residual planetesimals. In the present paper, we review the elementary processes of terrestrial planet formation and discuss the extension of the standard scenario.

The Large Magellanic Cloud (LMC) is the closest massive satellite of the Milky Way (MW), and its proximity allows us to study its stellar populations with great detail, both with resolved photometry and spectroscopy. In turn, this is crucial to unveil its star formation and chemical enrichment histories, and also to investigate the effects that gravitational interactions with other systems (as the Small Magellanic Cloud (SMC) and the MW) may induce on an irregular galaxy. The LMC is characterized by a still on-going star formation activity, as traced by the wide range of ages and metallicities of its stellar populations. However, most of the information about the chemistry and the kinematics of this galaxy has been obtained from low-resolution spectra, which do not allow to draw firm conclusions on many crucial open questions. In particular, (1) we still miss a homogeneous determination of the LMC metallicity distribution; (2) the metal-poor component is still poorly known and described; and (3) we have no conclusive information on the existence of metallicity gradients, which would suggest to spatially inhomegeneous star formation events. To properly address these issues, we analysed nearly 500 high-resolution FLAMES spectra of red giant stars belonging to the LMC field, the largest set of high- resolution spectra of LMC stars analysed so far in a homogeneous way.

Several cool-core clusters are known to host a radio mini-halo, a diffuse, steep-spectrum radio source located in their cores, thus probing the presence of non-thermal components as magnetic field and relativistic particles on scales not directly influenced by the central AGN. The nature of the mechanism that produces a population of radio-emitting relativistic particles on the scale of hundreds of kiloparsecs is still unclear. At the same time, it is still debated if the central AGN may play a role in the formation of mini-halos by providing the seed of the relativistic particles. We aim to investigate these open issues by studying the connection between thermal and non-thermal components of the intra-cluster medium. We performed a point-to-point analysis of the radio and the X-ray surface brightness of a compilation of mini-halos. We find that mini-halos have super-linear scalings between radio and X-rays, with radio brightness declining more steeply than the X-ray brightness. This trend is opposite to that generally observed in giant radio halos, thus marking a possible difference in the physics of the two radio sources. Finally, using the scalings between radio and X-rays and assuming a hadronic origin of mini-halos we derive constraints on the magnetic field in the core of the hosting clusters.

Be/X-ray binaries are a major subclass of high mass X-ray binaries. Two different X-ray outbursts are displayed in the X-ray light curves of such systems. It is generally believed that the X-ray outbursts are connected with the neutron star periastron passage of the circumstellar disk around the Be star. The optical emission of the Be star should be very important to understand the X-ray emission of the compact object. We have monitored several Be/X-ray binaries photometrically and spectroscopically in the optical band. The relationship between the optical emission and X-ray activity is described, which is very useful to explain the X-ray outbursts in Be/X-ray binaries.

Over an 11-year cycle the Sun changes its brightness by less than 0.1%. However, it is an open question how strong the Sun’s photometric variability was in the distant past. One way to answer that is to study other Sun-like stars and compare their photometric variability with that of the Sun. In a recent paper, we presented ground-based spectroscopic observations of a 7.4-year cycle in the solar analogue HD 173701. Complemented with observations from the Kepler space telescope, those data constitute the most complete set of observations of a stellar cycle ever obtained for any Sun-like star. They reveal that HD 173701 has strong solar-like differential rotation and a magnetic cycle comparable to the cycle generated by the solar dynamo, but with a resulting variability twice the amplitude of that observed in the Sun.

We present the recent discovery of new halo structures in the Milky Way (MW) based on the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). HSC is a wide-field imager installed at the prime focus of the Subaru Telescope, and a 300-night survey with this instrument is being carried out in this program. The combination of the superb image quality and depth and the fact that it is a multi-band survey allows us to identify new faint satellites as well as field halo stars in the outskirts of the MW halo beyond the reach of previous surveys. We report here on the new insights into the nature of both stellar and dark halos in the MW as revealed from this on-going survey program and show prospects based on the upcoming large spectroscopic survey with Subaru Prime Focus Spectrograph.

UV radiation plays a critical role in the chemistry of circumstellar envelopes (CSEs) around evolved stars on the asymptotic giant branch (AGB). However, the effects of all potential sources of UV radiation have not been included in models. We present preliminary results of adding an internal source of UV to the CSE chemistry and predict large enhancements of atomic and ionic species arising from photo-destruction of parent species. Observations of atomic carbon towards the UV-bright AGB star o Cet are consistent with the modelling. In addition, we calculate the precise depth dependence of the CO photodissociation rate in an expanding CSE. We incorporate this within a chemical network active in the outflows of AGB stars, which includes 933 species and 15182 reactions. Our results show that the CO envelope size is about 30% smaller at half abundance than the most commonly used radius reported by Mamon et al. (1988).

Dwarf galaxies in the Local Group (LG) represent a distinct as well as diverse family of tracers of the earliest phases of galaxy assembly and the processing resulting from galactic harrassment. Their stellar populations can be resolved and used as probes of the evolution of their host galaxy. In this regard, we present the first reconstruction of the star formation history (SFH) of them using the most evolved AGB stars that are long period variable (LPV). LPV stars trace stellar populations as young as ∼ 30 Myr to as old as the oldest globular clusters. For the nearby, relatively massive and interacting gas-rich dwarf galaxies, the Magellanic Clouds, we found that the bulk of the stars formed ∼ 10 Gyr ago for the LMC, while the strongest episode of star formation in the SMC occurred a few Gyr later. A peak in star formation around 0.7 Gyr ago in both Clouds is likely linked to their recent interaction. The Andromeda satellite pair NGC147/185 show different histories; the main epoch of star formation for NGC 185 occurred 8.3 Gyr ago, followed by a much lower, but relatively constant star formation rate (SFR). In the case of NGC 147, the SFR peaked only 6.9 Gyr ago, staying intense until ∼ 3 Gyr ago. Star formation in the isolated gas-rich dwarf galaxy IC 1613 has proceeded at a steady rate over the past 5 Gyr, without any particular dominant epoch. Due to lack of sufficient data, we have conducted an optical monitoring survey at the Isaac Newton Telescope (INT) of 55 dwarf galaxies in the LG to reconstruct the SFH of them uniformly. The observations are made over ten epochs, spaced approximately three months apart, as the luminosity of LPV stars varies on timescales of months to years. The system of galactic satellites of the large Andromeda spiral galaxy (M31) forms one of the key targets of our monitoring survey. We present the first results in the And I dwarf galaxy, where we discovered 116 LPVs among over 10,000 stars.

Pleione is a classical Be star well known for its cyclic transitions between Be-, shell- and normal B spectral phases. Its nature as a binary system was discussed by McAlister et al. (1989), Gies et al. (1990), Luthardt & Menchenkova (1994) and Nemravova et al (2010). We present the results that trace the evolution of the dimensions of the circumstellar disk of Pleione that are related to the binary system.

With their sizes larger than 0.7 Mpc, Giant Radio Galaxies (GRGs) are the largest individual objects in the Universe. To date, the reason why they reach such enormous extensions is still unclear. One of the proposed scenarios suggests that they are the result of multiple episodes of jet activity. Cross-correlating the INTEGRAL+Swift AGN population with radio catalogues (NVSS, FIRST, SUMSS), we found that 22% of the sources are GRG (a factor four higher than those selected from radio catalogues). Remarkably, all of the sources in the sample show signs of restarting radio activity. The X-ray properties are consistent with this scenario, the sources being in a high-accretion, high-luminosity state with respect to the previous activity responsible for the radio lobes.

The sculpting of the Egg Nebula continues to defy a coherent explanation. Bipolar outflows from the center of the nebula have created bipolar optical lobes that are illuminated by searchlight beams; multiple bipolar outflows orthogonal to the lobes create the appearance of a dark lane; and quasi-circular arcs are imprinted on an approximately spherically-symmetric wind from the progenitorAGB-star. Here, we use archival data from ALMA to study at high angular resolution dust and molecular gas at the center of the nebula. We find that: (i) dust is concentrated in multiple blobs that outline the base of the northern optical lobe; (ii) dense molecular gas forms the wall of a channel swept up and compressed by the outflows that created the bipolar optical lobes; (iii) the expansion and illumination center of the nebula lies at or close to center of the outflow channel. We present a simple working model for the Egg Nebula, and highlight the difficulties that any model face for explaining all the features seen in this nebula.

We performed a new integrated photometry in six passbands on HST M31 PHAT survey mosaics of 1181 star clusters spread over a large range of radial distance. Due to strongly varying background we interactively determined its level based on image and growth-curve analysis. We derived cluster age, mass, extinction, and metallicity by employing stochastic star cluster models.

Trans-Neptunian satellite systems and embryos of the Earth-Moon system could be formed as a result of contraction of rarefied condensations. The angular momenta of rarefied condensations needed for such formation could be acquired at collisions of condensations. The angular momentum of the present Earth-Moon system could be acquired at a collision of two rarefied condensations with a total mass not smaller than 0.1ME, where ME is the mass of the Earth. The mass of the condensation that was a parent for the embryos of the Earth and the Moon could be about 0.01ME, if we take into account the growth of the angular momentum of the embryos with growth of their masses. The Moon embryo could get by an order of magnitude more material ejected from the Earth embryo than that fell directly onto the Moon embryo.

Dwarf galaxies enable us to study early phases of galaxy evolution and are key to many open questions about the hierarchical structure of the Universe. The Large and Small Magellanic Cloud (LMC and SMC) are the most luminous dwarf galaxy satellites of the Milky Way (MW). They are most likely gravitationally bound to each other, and their last interaction occurred about 200 Myr ago. Also, they are in an early phase of minor merging with the MW and will impact the Galactic structure in the future because of their relatively large mass. However, there are still major uncertainties regarding their origin and their interactions with one another and with the Milky Way. We cross-correlated the VMC and Gaia DR2 data to select a sample of stars that likely belong to the Magellanic Bridge, a feature formed of gas and stars which is connecting the LMC and the SMC. We removed potential MW foregound stars using a combination of parallax and colour-magnitude criteria and calculated the proper motions of the Bridge member stars. Our analysis supports a motion of star towards the LMC, which was found to be in good agreement with a dynamical simulation, of the SMC being stripped by the LMC.