During the Epoch of Reionization (EoR), feedback effects reduce the efficiency of star formation process in small halos or even fully quench it. The galaxy luminosity function (LF) may then turn over at the faint-end. We analyze the number counts of z > 5 galaxies observed in the fields of four Frontier Fields (FFs) clusters and obtain constraints on the LF faint-end: for the turn-over magnitude at z ∼ 6, MUVT ≳-13.3; for the circular velocity threshold of quenching star formation process, vc* ≲ 47 km s−1. We have not yet found significant evidence of the presence of feedback effects suppressing the star formation in small galaxies.

Recent work (Corradi et al. 2015; Jones et al. 2016) has shown that the phenomenon of extreme abundance discrepancies, where recombination line abundances exceed collisionally excited line abundances by factors of 10 or more, seem to be strongly associated with planetary nebulae with close binary central stars. To further investigate, we have obtained spectra of a sample of nebulae with known close binary central stars, using FORS2 on the VLT, and we have discovered several new extreme abundance discrepancy objects. We did not find any non-extreme discrepancies, suggesting that a very high fraction of nebulae with close binary central stars also have an extreme abundance discrepancy.

Magnetic instability is a key consideration for filament eruptions and subsequent CMEs. In this contribution we are considering different magnetic conditions for active and non-active regions, such as coronal hole regions and quiet sun, and also active regions of a simple magnetic configuration. The aim is to assess magnetic instability through potential and non-potential field modelling and 3D evaluation of the magnetic decay index. Some eruptive examples from solar cycle 24 using HMI/SDO data are presented, complemented with observations of AIA/SDO.

Evidence of surface magnetism is now observed on an increasing number of cool stars. The detailed manner by which dynamo-generated magnetic fields giving rise to starspots traverse the convection zone still remains unclear. Some insight into this flux emergence mechanism has been gained by assuming bundles of magnetic field can be represented by idealized thin flux tubes (TFTs). Weber & Browning (2016) have recently investigated how individual flux tubes might evolve in a 0.3M⊙ M dwarf by effectively embedding TFTs in time-dependent flows representative of a fully convective star. We expand upon this work by initiating flux tubes at various depths in the upper ~50-75% of the star in order to sample the differing convective flow pattern and differential rotation across this region. Specifically, we comment on the role of differential rotation and time-varying flows in both the suppression and promotion of the magnetic flux emergence process.

Since the first investigations into accretion onto black holes, astrophysicists have proposed effective Newtonian-like potentials to mimic the strong-field behavior of matter near a Schwarzschild or Kerr black hole. On the other hand, the fields of neutron stars or black holes in many of the alternative gravity theories differ from the idealized Schwarzschild or Kerr field which would require a number of new potentials. To resolve this, we give a Newtonian-like Hamiltonian which almost perfectly mimics the behavior of test particles in any given stationary space-time. The properties of the Hamiltonian are excellent in static space-times such as the Schwarzschild black hole, but become worse for space-times with gravito-magnetic or dragging effects such as near the Kerr black hole.

Each CCD of LAMOST accommodates 250 spectra, while about 40 are used to observe sky background during real observations. How to estimate the unknown sky background information hidden in the observed 210 celestial spectra by using the known 40 sky spectra is the problem we solve. In order to model the sky background, usually a pre-observation is performed with all fibers observing sky background. We use the observed 250 skylight spectra as training data, where those observed by the 40 fibers are considered as a base vector set. The Locality-constrained Linear Coding (LLC) technique is utilized to represent the skylight spectra observed by the 210 fibers with the base vector set. We also segment each spectrum into small parts, and establish the local sky background model for each part. Experimental results validate the proposed method, and show the local model is better than the global model.

The radio non-detection of two Type Ia supernovae (SNe) SN 2011fe and SN 2014J has been modeled considering synchrotron radiation from shock accelerated electrons in the SN shock fronts. With 10% each of the bulk kinetic energy in electric and magnetic fields, a very low density of the medium around both the SNe has been estimated from the null detection of radio emission, around 1 and 4 years after the explosion of SNe 2014J and 2011fe, respectively. Keeping the fraction of energy in electrons fixed at 10%, a medium with particle density ~ 1cm−3 is found when 1% of the post shock energy is in magnetic fields. In case of a wind medium, the former predicts the mass loss rate Ṁ to be <10−9M⊙ yr−1, and the latter gives an upper limit ~10−9M⊙ yr−1, for wind velocity of 100 kms−1, for both the SNe. The tenuous media obtained from this study favor the double degenerate as well as a spin up/down model for both SNe 2011fe and 2014J.

We gathered a multiwavelength dataset of two well-known LBVs. We found a complex mass-loss, with evidence of variability, such as has been seen previously. In addition, our data reveal signatures of collimated stellar winds. We propose a new scenario for these two stars where the nebula shaping is influenced by the presence of a companion star and/or fast rotation.

With the launch of Gaia in December 2013, Europe entered a new era of space astrometry following in the footsteps of the very successful Hipparcos mission. A weakness of Gaia is that it only operates at optical wavelengths. However, much of the Galactic centre and the spiral arm regions are obscured by interstellar extinction. An obvious improvement on Gaia is to include the Near-Infra-Red (NIR) which requires the use of new types of detectors. Additionally, to scan the entire sky and measure global absolute parallaxes the spacecraft must have a constant rotation resulting in a moving image that must be compensated for by, for example, operating the detectors in Time Delayed Integration (TDI) mode. If these technical issues can be solved a new Gaia-like mission separated by a 20 year interval would give; 1) NIR all-sky astrometry and photometry to penetrate the obscured regions and to observe intrinsically red objects with almost diffraction limited resolution; 2) improved proper motions with fourteen times smaller errors than from Gaia alone opening up new science cases, such as long period exoplanets and accurate halo measurements; 3) allow the slowly degrading accuracy of the Gaia reference frame, which will be the basis for future astronomical measurements, to be reset.

Super star clusters (SSCs) represent the youngest and most massive form of known gravitationally bound star clusters in the Universe. They are born abundantly in environments that trigger strong and violent star formation. We investigate the properties of these massive SSCs in a sample of 42 nearby starbursts and luminous infrared galaxies. The targets form the sample of the SUperNovae and starBursts in the InfraReD (SUNBIRD) survey that were imaged using near-infrared (NIR) K-band adaptive optics mounted on the Gemini/NIRI and the VLT/NaCo instruments. Results from i) the fitted power-laws to the SSC K-band luminosity functions, ii) the NIR brightest star cluster magnitude − star formation rate (SFR) relation and iii) the star cluster age and mass distributions have shown the importance of studying SSC host galaxies with high SFR levels to determine the role of the galactic environments in the star cluster formation, evolution and disruption mechanisms.

Neutron(n)-capture elements are produced by s-process nucleosynthesis in low- and intermediate-mass AGB stars, and therefore can be enriched in planetary nebulae (PNe). In the last ten years, n-capture elements have been detected in more than 100 PNe in the Milky Way and nearby galaxies. In some objects, several different n-capture elements have been detected, providing valuable constraints to models of AGB nucleosynthesis and evolution. These detections have motivated theoretical and experimental investigations of the atomic data needed to derive accurate n-capture element abundances. In this review, I discuss the methods and results of these atomic data studies, and their application to abundance determinations in PNe.

Compressive Sensing is an emerging technology for data compression and simultaneous data acquisition. This is an enabling technique for significant reduction in data bandwidth, and transmission power and hence, can greatly benefit space-flight instruments. We apply this process to detect exoplanets via gravitational microlensing. We experiment with various impact parameters that describe microlensing curves to determine the effectiveness and uncertainty caused by Compressive Sensing. Finally, we describe implications for space-flight missions.

In 1964 (Solar Cycle 20; SC 20), Patrick McIntosh began creating hand-drawn synoptic maps of solar magnetic features, based on Hα images. These synoptic maps were unique in that they traced magnetic polarity inversion lines, and connected widely separated filaments, fibril patterns, and plage corridors to reveal the large-scale organization of the solar magnetic field. Coronal hole boundaries were later added to the maps, which were produced, more or less continuously, into 2009 (i.e., the start of SC 24). The result was a record of ~45 years (~570 Carrington rotations), or nearly four complete solar cycles of synoptic maps. We are currently scanning, digitizing and archiving these maps, with the final, searchable versions publicly available at NOAA's National Centers for Environmental Information. In this paper we present preliminary scientific studies using the archived maps from SC 23. We show the global evolution of closed magnetic structures (e.g., sunspots, plage, and filaments) in relation to open magnetic structures (e.g., coronal holes), and examine how both relate to the shifting patterns of large-scale positive and negative polarity regions.

The distributions of supernovae of different types and subtypes along the radius and in z coordinate of galaxies have been studied. We show that among SNe Ia in spiral galaxies, SNe Iax and Ia-norm have, respectively, the largest and smallest concentration to the center; the distributions of SNe Ia-91bg and Ia-91T are similar. A strong concentration of SNe Ibc to the central regions has been confirmed. In spiral galaxies, the supernovae of all types strongly concentrate to the galactic plane; the slight differences in scale height correlate with the extent to which the classes of supernovae are associated with star formation.

Our understanding of gamma-ray bursts (GRBs) has come a long way in the past fifty years since their first detection. We now know that GRBs arise in distant galaxies and that there are at least two distinct sub-classes, the long-duration class being produced by some rare massive star core collapse and the short-duration class likely by compact binary mergers involved neutron stars. In both cases, the final remnant will be a stellar-mass black-hole or a massive neutron star. The bursts themselves are associated with ultra-relativistic jetted outflows created by these events, and their afterglows by the impact of these outflows on the surrounding circumburst material. Increasingly GRBs are also being used as probes of the universe, both for understanding galaxy evolution back to the era of reionization, and for the physics of gravitational wave sources. However, many aspects of GRBs remain poorly understood, some pointers to which are given here.

Using a magnetic carpet as model for the near surface solar magnetic field we study its effects on the propagation of energy injectected by photospheric footpoint motions. Such a magnetic carpet structure is topologically highly non-trivial and with its magnetic nulls exhibits qualitatively different behavior than simpler magnetic fields. We show that the presence of magnetic fields connecting back to the photosphere inhibits the propagation of energy into higher layers of the solar atmosphere, like the solar corona. By applying certain types of footpoint motions the magnetic field topology is is greatly reduced through magnetic field reconnection which facilitates the propagation of energy and disturbances from the photosphere.

We study a model of cosmic reionization where quasars (QSOs) are the dominant source of ionizing photons at all relevant epochs. We employ a suite of adaptive hydrodynamical simulations post-processed with a multi-wavelength Monte Carlo radiative-transfer code and calibrate them in order to accurately reproduce the observed quasar luminosity function and emissivity evolution. Our results show that the QSO-only model fails in reproducing key observables linked to the Helium reionization, as the temperature evolution of the inter-galactic medium (IGM) and the HeII effective optical depth in synthetic Lyα spectra. Nevertheless, we find hints that an increased quasar contribution can explain recent measurements of a large inhomogeneity in the IGM at redshift z ≈ 5. Finally, we devise a method capable of constraining the QSOs contribution to the reionization from the properties of the HeII Lyα forest at z ≈ 3.5.

We perform hydrodynamic supernova (SN) simulations in spherical symmetry for progenitor models with solar metallicity across the stellar mass range from 9.0 to 120 M⊙ to explore the progenitor-explosion and progenitor-remnant connections based on the neutrino-driven mechanism. We use an approximative treatment of neutrino transport and replace the high-density interior of the neutron star (NS) by an inner boundary condition based on an analytic proto-NS core-cooling model, whose free parameters are chosen to reproduce the observables of SN 1987A and the Crab SN for theoretical models of their progenitor stars.

Judging the fate of a massive star, either a neutron star (NS) or a black hole (BH), solely by its structure prior to collapse has been ambiguous. Our work and previous attempts find a non-monotonic variation of successful and failed supernovae with zero-age main-sequence mass. We identify two parameters based on the “critical luminosity” concept for neutrino-driven explosions, which in combination allows for a clear separation of exploding and non-exploding cases.

Continuing our simulations beyond shock break-out, we are able to determine nucleosynthesis, light curves, explosion energies, and remnant masses. The resulting NS initial mass function has a mean gravitational mass near 1.4 M⊙. The average BH mass is about 9 M⊙ if only the helium core implodes, and 14 M⊙ if the entire pre-SN star collapses. Only ~10% of SNe come from stars over 20 M⊙, and some of these are Type Ib or Ic.

Comparison of the Gaia DR1 auxiliary quasar solution to recent ground based VLBI solutions for ICRF2 sources.

I will present new results on the star formation history of 30 Doradus in the Large Magellanic Cloud based on the panchromatic imaging survey Hubble Tarantula Treasury Project (HTTP). Here the focus is on the starburst cluster NGC2070. The star formation history is derived by comparing the deepest ever optical and NIR color-magnitude diagrams (CMDs) with state-of-the-art synthetic CMDs generated with the latest PARSEC models, which include all stellar phases from pre-main sequence to post-main sequence. For the first time in this region we are able to measure the star formation using intermediate and low mass stars simultaneously. Our results suggest that NGC2070 experienced a prolonged activity. I will discuss the detailed star formation history, initial mass function and reddening distribution.