We present recent results obtained using old variable RR Lyrae stars on the Galactic halo structure and its connection with nearby dwarf galaxies. We compare the period and period-amplitude distributions for a sizeable sample of fundamental mode RR Lyrae stars (RRab) in dwarf spheroidals (~1300 stars) with those in the Galactic halo (~16'000 stars) and globular clusters (~1000 stars). RRab in dwarfs –as observed today– do not appear to follow the pulsation properties shown by those in the Galactic halo, nor they have the same properties as RRab in globulars. Thanks to the OGLE experiment we extended our comparison to massive metal–rich satellites like the dwarf irregular Large Magellanic Cloud (LMC) and the Sagittarius (Sgr) dwarf spheroidal. These massive and more metal–rich stellar systems likely have contributed to the Galactic halo formation more than classical dwarf spheroidals.

Finally, exploiting the intrinsic nature of RR Lyrae as distance indicators we were able to study the period and period amplitude distributions of RRab within the Halo. It turned out that the inner and the outer Halo do show a difference that may suggest a different formation scenario (in situ vs accreted).

Following the discovery of quantum phenomena at laboratory scale (Couder & Fort 2006), de Broglie pilot wave theory (De Broglie 1962) has been revived under a hydrodynamic guise (Bush 2015). Theoretically, it boils down to solving the transport equations for the energy and linear momentum densities of a postulated fundamental fluid in terms of classical wave equations, which inherently are Lorentz-invariant and scale-invariant. Instead of the conventional harmonic solutions, for astronomical and gravitational problems the novel solutions for the homogeneous wave equation in spherical coordinates are more suitable (Munera et al. 1995, Munera & Guzman 1997, and Munera 2000). Two groups of solutions are particularly relevant: (a) The inherently-quantized helicoidal solutions that may be applicable to describe spiral galaxies, and (b) The non-harmonic solutions with time (t) and distance (r) entangled in the single variable q = Ct/r (C is the two-way local electromagnetic speed). When these functions are plotted against 1/q they manifestly depict quantum effects in the near field, and Newtonian-like gravity in the far-field. The near-field predicts quantized effects similar to ring structures and to Titius-Bode structures, both in our own solar system and in exoplanets, the correlation between predicted and observed structures being typically larger than 99 per cent. In the far-field, some non-harmonic functions have a rate of decrement with distance slower than inverse-square thus explaining the flat rotation rate of galaxies. Additional implications for Trojan orbits, and quantized effects in photon deflection were also noted.

The centers of galaxies host two distinct, compact components: massive black holes and nuclear star clusters. Nuclear star clusters are the densest stellar systems in the universe, with masses of ~ 107M⊙ and sizes of ~ 5pc. They are almost ubiquitous at the centres of nearby galaxies with masses similar to, or lower than the Milky Way. Their occurrence both in spirals and dwarf elliptical galaxies appears to be a strong function of total galaxy light or mass. Nucleation fractions are up to 100% for total galaxy magnitudes of MB = −19mag or total galaxy luminosities of about LB = 1010 L ⊙ and falling nucleation fractions for both smaller and higher galaxy masses. Although nuclear star clusters are so common, their formation mechanisms are still under debate. The two main formation scenarios proposed are the infall and subsequent merging of star clusters and the in-situ formation of stars at the center of a galaxy. Here, I review the state-of-the-art of nuclear star cluster observations concerning their structure, stellar populations and kinematics. These observations are used to constrain the proposed formation scenarios for nuclear star clusters. Constraints from observations show, that likely both cluster infall and in-situ star formation are at work. The relative importance of these two mechanisms is still subject of investigation.

Diverse variable phenomena in the Universe are periodic. Astonishingly many of the periodic signals present in stars have timescales coinciding with human ones (from minutes to years). The periods of signals often have to be deduced from time series which are irregularly sampled and sparse, furthermore correlations between the brightness measurements and their estimated uncertainties are common. The uncertainty on the frequency estimation is reviewed. We explore the astronomical and statistical literature, in both cases of regular and irregular samplings. The frequency uncertainty is depending on signal to noise ratio, the frequency, the observational timespan. The shape of the light curve should also intervene, since sharp features such as exoplanet transits, stellar eclipses, raising branches of pulsation stars give stringent constraints. We propose several procedures (parametric and nonparametric) to estimate the uncertainty on the frequency which are subsequently tested against simulated data to assess their performances.

International Astronomical Union was formed after the First World War although it became truly international only after the Second World War. Its Commission 41 on History of Astronomy (C41) was set up in 1948 and in a few years established itself as an active and influential unit. It has the distinction of being a joint Commission, the other partner being International Union of History and Philosophy of Science and Technology (IUHPS). Since IAU is an internationally respected body of professional astronomers, its support for history of astronomy enhances the credibility of the discipline in the eyes of scientists as well as science establishments of individual countries. C41 is committed to advancing objective and rigorous world history of astronomy taking into account all its aspects.

Close-in massive planets transfer angular momentum to their host stars and influence their rotation through the torques associated with the tides raised on the star by the planet. For a star hosting a hot Jupiter, the limit of distance below which tidal torques cannot be neglected grows from a ~0.04 to a ~0.07 AU as the mass of the planet grows from 0.5 to 4MJup.

The past few years have witnessed a large increase in the number of extrasolar planets. Thanks to successful surveys from the ground and from space, there are now over 1000 confirmed exoplanets and more then 3000 planetary candidates. More than 130 of these systems host multiple planets. Many of these systems demonstrate physical and orbital characteristics fundamentally different from those of our solar system. The challenges associated with the diversity of planetary systems have raised many interesting questions on planet formation and orbital dynamics.

We use the SDSS Stripe 82 to study the stellar-mass growth that is triggered by minor mergers in local disk galaxies. Since major mergers destroy disks and create spheroids, morphologically disturbed spirals are likely remnants of minor mergers (since the disk remains intact). Disturbed spirals exhibit enhanced specific star formation rates (SSFRs), with the enhancement increasing in galaxies with ‘later’ morphological type (that have larger gas reservoirs and smaller bulges). By combining the SSFR enhancements with the fraction of time spirals in various morphological classes spend in this ‘enhanced’ mode, we estimate that ~40% of the star formation activity in local spirals is directly triggered by minor mergers. Combining our results with the star formation in local early-type galaxies – which is almost completely driven by minor mergers – suggests that around half the star formation activity at the present day is likely to be triggered by the minor-merger process.

We present the 12CO J=1–0, 13CO J=1–0, and C18O J=1–0 maps of the M17 giant molecular clouds (GMCs) obtained as a part of the Nobeyama 45m CO Galactic Plane Survey. The observations cover the entire area of M17 SW and M17 N clouds at an angular resolution of ~ 15″ which corresponds to ~ 0.15 pc. We found that the N cloud consists of a couple of twisted filaments, they are extended in parallel toward the Hii region. The typicall width of the filaments is ~0.5 pc in 13CO intensity map. Most of young stellar objects (YSOs) are located on the filaments which have a bright rim structure in 8μm at the filament edge facing the Hii region. Furthermore, the time scale of the YSOs formation on the bright rim is comparable with that of NGC 6618 cluster which provides UV photons for the region. This fact indicates that the cluster triggered to form YSOs in N cloud. We also investigated the geometry of the Hii region and GMCs by comparing spatial distribution of 12CO velocity channel map and infrared dark cloud, and then found that NGC 6618 is possibly formed by the cloud cloud colision.

The standard paradigm of structure formation in the universe, the cold dark matter cosmology, contains several crucial unsolved problems such as “cusp-core problem” and “too-big-to-fail problem”. To solve these problems, we study about the dynamical response of a virialized system with a central cusp to the energy feedback driven by periodic supernova feedback using collisionless N-body simulations with the Nested-Particle-Mesh code. The resonance between dark matter particles and the density wave excited by the oscillating potential plays a significant role in the cusp-core transition of dark matter halos. Furthermore, we show that the cusp-core transition with periodic supernova feedback can solve the too-big-to-fail problem.

We investigate the sputtering and thermal desorption of various grain-surface species in one dimensional steady-state shock models motivated by the recent detection of SO emission towards class 0-I protostars. We find that the thermal desorption is more efficient at higher densities, while the efficiency of sputtering is independent of density. SO is completely desorbed, if the accretion velocity is higher than ~ 2 km s−1 and ~ 4 km s−1, with the pre-shock density of 109 cm−3 and 108 cm−3, respectively. The column density of warm post-shock gas is found to be N ~ 1021 cm−2. If the abundance of SO ice is ~ 10−7 relative to hydrogen in the pre-shock material, SO emission around L1527 can be explained by the sublimation at the accretion shock.

The construction of viable and physically-realistic interstellar dust models is only possible if the constraints imposed by laboratory data on interstellar dust analogue materials are respected and used within a meaningful theoretical framework. These “physical” dust models can then be directly compared to observations without the need for any tuning to fit the observations. Such models will generally fail to achieve the excellent fits to observations that “empirical” models are able to achieve. However, the physically-realistic approach will necessarily lead to a deeper insight and a fuller understanding of the nature and evolution of interstellar dust. The THEMIS modelling approach, based on (hydrogenated) amorphous carbons and amorphous silicates with metallic Fe and/or FeS nano-inclusions appears to be a promising move in this direction.

To better understand the differences between coronal cloud prominences and channel prominences, we systematically identified and analyzed coronal cloud prominences recorded in SDO/AIA images at 304 Å from 2010 May 20 through 2012 April 28. For the 225 cases identified, their numbers vary directly with the sunspot number. Their durations are typically less than 3 days. Their most frequent maximum height is 90,000 + and - 10,000 km. We offer our hypothesis that many coronal cloud prominences originate from some of the mass of previously erupted filaments ejected high out of their filament channels; subsequently part of this mass falls and collects in leaky magnetic troughs among coronal magnetic fields which constrain the leaked mass to slowly drain downward along curved trajectories where it appears as coronal rain. Currently there is inadequate evidence for a convincing correspondence between either coronal cloud prominences or channel prominences with stellar prominences detected to date.

The number of confirmed, high-redshift galaxy clusters is very low compared to the number of well-studied clusters nearby. Bent, double-lobed radio sources are frequently found in galaxy clusters, and thus can be used as tracers for efficiently locating high-redshift clusters. Using our Spitzer Snapshot Survey, we have identified approximately 300 potential new clusters with redshifts 0.7 < z < 3. These objects make up the high-redshift portion of the Cluster Occupied by Bent Radio AGN (COBRA) survey. We have created color-magnitude diagrams using infrared and optical data. Using the colors of the radio source host and the red sequence we can estimate redshifts for our clusters, as well as examine the evolution of the cluster galaxies over a large range of cosmic time.

Colliding plasmas are ubiquitous in astrophysical environments and allow conversion of kinetic energy into heat and, most importantly, the acceleration of particles to extremely high energies to form the cosmic ray spectrum. In collisionless astrophysical plasmas, kinetic plasma processes govern the interaction and particle acceleration processes, including shock formation, self-generation of magnetic fields by kinetic plasma instabilities, and magnetic field compression and reconnection. How each of these contribute to the observed spectra of cosmic rays is not fully understood, in particular both shock acceleration processes and magnetic reconnection have been proposed. We will review recent results of laboratory astrophysics experiments conducted at high-power, inertial-fusion-class laser facilities, which have uncovered significant results relevant to these processes. Recent experiments have now observed the long-sought Weibel instability between two interpenetrating high temperature plasma plumes, which has been proposed to generate the magnetic field necessary for shock formation in unmagnetized regimes. Secondly, magnetic reconnection has been studied in systems of colliding plasmas using either self-generated magnetic fields or externally applied magnetic fields, and show extremely fast reconnection rates, indicating fast destruction of magnetic energy and further possibilities to accelerate particles. Finally, we highlight kinetic plasma simulations, which have proven to be essential tools in the design and interpretation of these experiments.

Commission 45 is solidly anchored in the beginnings of the IAU. It evolved out of Commission 29, which was one of the original commissions and whose title and emphasis was the Spectral Classification of Stars (Transactions of the IAU, Volume I, 1922). C29 was formed with W.S. Adams (Pasadena) as president. Its first members were Miss Cannon, R.H. Curtiss, A. Fowler, A. de Gramont, M. Hamy, H.F. Newall, J.S. Plaskett, H.N. Russell, all very much part of the history of stellar spectroscopy. In the 1922 Transactions report it was recognized the Harvard System of spectral classification “has already been adopted by international agreement. . .”

Asteroseismology is among the most powerful observational tools to determine fundamental properties of stars. Space-based photometry has recently enabled the systematic detection of oscillations in exoplanet host stars, allowing a combination of asteroseismology with transit and radial-velocity measurements to characterize planetary systems. In this contribution I will review the key synergies between asteroseismology and exoplanet science such as the precise determination of radii and ages of exoplanet host stars, as well as applications of asteroseismology to measure spin-orbit inclinations in multiplanet systems and orbital eccentricities of small planets. Finally I will give a brief outlook on asteroseismic studies of exoplanet hosts with current and future space-based missions such as K2 and TESS.

We still do not know the timescale for the merging of binary black holes (BHs). This timescale has important implications for gravitational wave predictions and our understanding of BH demographics. Here we discuss efforts to constrain the fraction of BH pairs on kpc scales using observations of dual active galactic nuclei.