The Megamaser Cosmology Project (MCP) measures the Hubble Constant by determining geometric distances to circumnuclear 22 GHz H2O megamasers in galaxies at low redshift (z < 0.05) but well into the Hubble flow. In combination with the recent, exquisite observations of the Cosmic Microwave Background by WMAP and Planck, these measurements provide a direct test of the standard cosmological model and constrain the equation of state of dark energy. The MCP is a multi-year project that has recently completed observations and is currently working on final analysis. Based on distance measurements to the first four published megamasers in the sample, the MCP currently determines H0 = 69.3 ± 4.2 km s−1 Mpc−1. The project is finalizing analysis for five additional galaxies. When complete, we expect to achieve a ~4% measurement. Given the tension between the Planck prediction of H0 in the context of the standard cosmological model and astrophysical measurements based on standard candles, the MCP provides a critical and independent geometric measurement that does not rely on external calibrations or a distance ladder.

Pulsar polarization has been a fruitful area of study since the first discovery of pulsars 50 years ago. Polarization gives information on the geometry of the star, the location of the radio emission in the magnetosphere, the physics behind the radio emission mechanism and a plethora of phenomenology. Here, I will restrict myself to a brief outline of recent work in pulsar polarization using observations taken with the Parkes radio telescope over the past decade.

Nicolae Donitch gave a special role to Romania’s membership of the IAU, even though it had basically adhered to it in 1922, but only on the 12th of July 1928 was Romania’s membership in the IAU recognized. He was a passionate observer of eclipses, of the zodiacal light, and a good instrument builder. His tortuous destiny was somehow similar to the destiny of many Romanians from Eastern Moldova: he was born in Chişinău, the capital of Bessarabia at that time; he studied in Odessa; after the first revolution in February 1917 he left Russia and remained in Odessa until the arrival of the Bolsheviks in 1920, who would completely destroy his laboratory. He then moved to his private Astrophysics Observatory in Dubăsarii Vechi, which he had set up in 1908, and stayed until 1940, when Bessarabia was once again torn away from Romania. He relocated to Bucharest, but soon after, when communists came to power, he had to leave the country on a permanent basis. As he severed all the ties with people from the country that had fallen into the red zone of communism, we completely lost track of him. It was only recently that, after thorough research, we could discover his traces, and learn of his last years of life.

From the derived stellar density profile using LAMOST giant stars, we find that the Galactic disk does not show truncation or break, but smoothly transit to the halo from 19 kpc. The scale length of the outer disk is only 1.6 ± 0.1 kpc, substantially smaller than previous results. This implies that the shapes of the inner and outer disk are different. Meanwhile, the disk flaring is not only found in older populations, but also in younger population. Moreover, the vertical oscillations of the disk are identified in a wide range or R from 8 to 14 kpc. We also find that the velocity dispersion profile as a function of the Galactocentric radius is flat with scale length of 26.3 ± 3.2 kpc. We confirm that the radial velocity profile in outer disk is significantly affected by asymmetric motion. The bar with either a slower or a faster pattern speed can induce the similar radial asymmetric motion.

The polarization measurement of coronal forbidden emission lines is the most promising method of determining the direction of magnetic fields in the corona. A classical theory for the forbidden lines was presented in Megha et al. (2017) for the case of arbitrary strength magnetic fields. Here we apply that theoretical formalism to study the effect of density distributions, magnetic field configurations, and velocity fields on the Stokes profiles formed in corona. For illustrations we use the atomic parameters of the [Fe xiii] 10747 Å coronal forbidden line.

The overall goal of the ESA Rosetta mission was to help decipher the origin and evolution of our solar system. Looking at the chemical composition of comet 67P/Churyumov-Gerasimenko is one way of doing this. The amount of very volatile species found and the insight into their isotopic abundances show that at least some presolar ice has survived the formation of the solar system. It shows that the solar nebula was not homogenized in the region where comets formed. The D/H ratio in water furthermore indicates that Jupiter family comets and Oort cloud comets probably formed in the same regions and their difference is then purely due to their different dynamical history. The organics found in 67P are very diverse, with abundant CH- and CHO- bearing species. Sulphur bearing species like S3 and S4 and others show evidence of dust grain chemistry in molecular clouds.

This paper addresses the relationships between Arthur S. Eddington, former director of the Cambridge Observatory (1914-1944), with the International Astronomical Union. It is demonstrated that the Union was related to every major moment in Eddington’s scientific career. New historical elements are brought forward, in the last section of the paper, to demonstrate Eddington’s action in favour of German colleagues during the Second World War.

A radio polarization study of gamma-ray-detected pulsars reveals a surprising tendency for the magnetic and rotation axes to be relatively aligned. This provides tension with gamma-ray models, which disfavour such alignment. The lack of correlation between these findings and those derived from the gamma-ray light curves suggests problems in the models. To make the data consistent with a random orientation of the magnetic field the emission regions could be assumed to extend outside what is traditionally thought to be the open-field-line region in a magnetic inclination angle dependent way. Both acceptance and rejection of this hypothesis has important consequences. Finally, a unification scheme is proposed to explain the observational differences between gamma-ray loud and gamma-ray quiet radio pulsars. This unification scheme takes the orientation of the line of sight and the magnetic inclination angle to be key parameters affecting both the radio and gamma-ray light-curve morphology.

The 5th RAVE data release is based on 520,781 spectra (R ≈ 7500 in the CaT region at 8410 - 8795Å) of 457,588 unique stars. RAVE DR5 provides radial velocities, stellar parameters and individual abundances for up to seven elements and distances found using isochrones for a considerable subset of these objects. In particular, RAVE DR5 has 255,922 stellar observations that also have parallaxes and proper motions from the Tycho-Gaia astrometric solution (TGAS) in Gaia DR1. The combination of RAVE and TGAS thus provides the currently largest overlap of spectroscopic and space-based astrometric data and thus can serve as a formidable preview of what Gaia is going to deliver in coming data releases. Basic properties of the RAVE+TGAS survey and its derived data products are presented as well as first applications w.r.t wave-like patterns in the disk structure. An outlook to the 6th RAVE data release is given.

The level of isotopic fractionation in molecules provides insights into their formation environments and how they formed. In this article, we review hydrogen and nitrogen isotopic fractionation in low-mass star-forming regions. Interstellar molecules are significantly enriched in deuterium. The importance of the nuclear spin states of light species on deuterium fractionation and the usefulness of singly and doubly deuterated molecules as chemical tracers are discussed. Observations have revealed that molecules in prestellar cores are enriched in or depleted in 15N depending on molecules. Compared with deuterium fractionation chemistry, our understanding of 15N fractionation chemistry is not well established. We briefly discuss potential 15N fractionation routes, i.e., isotopic-exchange reactions and isotopic selective photodissociation of N2. In addition, the selective freeze-out of 15N atoms onto dust grains around the transition between N atoms and N2 is discussed as a potential mechanism that causes the depletion of 15N in the gas phase.

We present a new technique to study joint observations of EUV spectral line intensities and in situ charge states of the fast solar wind. We solve the time-dependent equation for ionization and recombination for a chosen element and calculate the charge state evolution along the open magnetic fields for elements such as C, O, Ne, Mg, Si and Fe. Comparing predicted spectral lines intensities above the limb and in situ charge states to observations from SOHO/SUMER and Ulysses/SWICS, we test how well the modelled thermodynamic parameters of the solar wind reproduce observations. We outline the application of this method to Solar Orbiter data.

Analyzing archival data from different telescopes, H2O megamaser Seyfert 2s appeared to exhibit higher nuclear radio luminosities than non-masing Seyfert 2s (Zhang et al. 2012). This has been confirmed by our follow-up study on multi-band (11, 6, 3.6, 2, 1.3 cm) radio properties of maser host Seyfert 2s, through systematic Effelsberg observations (Liu et al. 2017). The nuclear radio luminosity was supposed to be a suitable indicator to guide future AGN maser searches. Thus we performed a pilot survey with the Effelsberg telescope on H2O maser emission toward a small sample of radio-bright Seyfert 2 galaxies with relatively higher redshift (>0.04). Our pilot survey led to one new megamaser source and one additional possible detection, which reflects our success in selecting H2O megamaser candidates compared to previous observations (higher detection rate, larger distance). Our successful selection technique choosing Seyfert 2s with radio-bright nuclei may provide good guiding for future H2O megamaser surveys. Therefore we are conducting a large systematic survey toward a big Seyfert 2 sample with such radio-bright nuclei. Detections of luminous H2O masers at large distance (z>0.04) may hold the great potential to increase our knowledge on the central highly obscured but still very enigmatic regions of active Seyfert galaxies (Zhang et al. 2017).

The process of the magnetic polarity reversal of the Sun has been an important subject in the solar physics. The objective of this study is to investigate how solar global magnetic field change over solar cycle by tracking the migration of open magnetic flux regions. The results show that the open magnetic fluxes migrate from one pole to the other crossing the equator during a solar cycle. The migration rate is approximately 10 m s−1, comparable to meridional flow. The results have been published in Scientific Reports (Huang et al. (2017)).

A number of complex systems arising in diverse disciplines may have certain quantitative features that are surprisingly similar which are classified under the paradigm of “universality”. The non-extensive Tsallis stastical mechanics and Lévy flight patterns provide a novel basis for analyzing non-equilibrium complex systems that may exhibit long-range correlations. The present work studies the scope of employing non-extensive Gutenberg-Richter (G-R) type law for the magnitude distribution of energy of solar wind, in order to investigate the existence of a universal behavior as well as to compute the relations of degree of non-extensivity and Lévy statistics in solar wind turbulence with heliographic distance during different solar cycles.

Water megamaser emission is powerful in tracing the inner region of active nuclei, mapping accretion disks and providing important clues on their absorption properties. From the X-ray spectra of AGN it is possible to estimate the intrinsic power of the central engine and the obscuring column density. The synergy between X-ray and water maser studies allows us to tackle the AGN inner physics from different perspectives. For a complete sample of AGN selected in the 20-40 keV energy range, we have investigated the presence of water maser emission and its connection to the X-ray emission, absorption and accretion rate. The hard X-ray selection of the sample results in a water maser detection rate much higher than those obtained from optically-selected samples.

Relying on the complementarity of Gaia proper motions with radial velocities of the RAVE survey, we attempt to constrain the kinematics of the Milky Way disc. Based on the population synthesis model, we simulate the observations, applying the detailed selection functions of the observations. The dynamics is described using a global gravitational potential computed from the mass distribution of the population model, approximated by a Stäckel potential (Bienaymé et al. 2015). We explore a set of free parameters (solar motion, age - velocity dispersion of the disc as a function of age, the velocity gradients, vertex deviation) using a Markov Chain Monte Carlo method. We show that the fitted model reproduces very well the radial velocity and proper motion distributions, allowing to constrain the thin and thick disc secular evolution with time.

Detecting and studying pulsars above a few GHz in the radio band is challenging due to the typical faintness of pulsar radio emission, their steep spectra, and the lack of observatories with sufficient sensitivity operating at high frequency ranges. Despite the difficulty, the observations of pulsars at high radio frequencies are valuable because they can help us to understand the radio emission process, complete a census of the Galactic pulsar population, and possibly discover the elusive population in the Galactic Centre, where low-frequency observations have problems due to the strong scattering. During the decades of the 1990s and 2000s, the availability of sensitive instrumentation allowed for the detection of a small sample of pulsars above 10 GHz, and for the first time in the millimetre band. Recently, new attempts between 3 and 1 mm (≈86 − 300 GHz) have resulted in the detections of a pulsar and a magnetar up to the highest radio frequencies to date, reaching 291 GHz (1.03 mm). The efforts continue, and the advent of new or upgraded millimetre facilities like the IRAM 30-m, NOEMA, the LMT, and ALMA, warrants a new era of high-sensitivity millimetre pulsar astronomy in the upcoming years.

A century of existence: it may seem short on the time-scale of the evolution of the universe, but very consequential to that of a scientific association. The fact that the IAU may be able to celebrate such a milestone is in itself a meritorious collective achievement, for it was not obvious at the very beginning that this organization was going to last more than a decade. Drawing on the historical sociology of scientific institutions, my paper will discuss the moral economy through which the IAU – and its dated but persistent form of scientific internationalism – has stabilized and maintained its identity since its creation in 1919, under the unifying auspices of a global scientific object to be known as: Under One Sky.

Using the appropriate kinetic equation, we considered the problem of propagation of accelerated electrons into the solar corona and chromosphere. Its analytical solution was used for modelling the M7.7 class limb flare occurred on July 19, 2012. Coronal above-the-loop-top hard X-Ray source was interpreted in the thin-target approximation, the foot-point source - in the thick-target approximation with account of the reverse-current electric field. For the foot-point source we found a good accordance with the RHESSI observations. For the coronal source we also got very accurate estimate of the power-law spectral index, but significant differences between the modelled and observed hard X-ray intensities were noticed. The last discrepancy was solved by adding the coronal magnetic trap model to the thin target model. The former one implies that the trap collapses in two dimensions, locks and accelerates particles inside itself. In our report, we confirm an existence and high efficiency of the electron acceleration in collapsing magnetic traps during solar flares. Our new results represent (e.g. for RHESSI observations) the theoretical prediction of the double step particle acceleration in solar flares, when the first step is the acceleration in reconnection area and the second one – the acceleration in coronal trap.