Spectroheliograms of quiet regions obtained by the OSO-G satellite in chromospheric, transition zone, and coronal lines indicate that the chromospheric network as seen in Ca K can be resolved despite the low resolution (30 arc s) of OSO-G. The network pattern becomes more diffuse with increasing height, indicating that the magnetic field pattern spreads with height.

The dynamical evolution of open star clusters has been studied successfully by numerical N-body simulations. We compare in detail the theoretically predicted lifetimes with those derived from the observed age distribution of open clusters. Rare but efficient encounters between clusters and giant molecular clouds are probably responsible for the sudden disruption of many open clusters. Massive black holes from the galactic corona would, on the average, affect only old open clusters.

Establishing accurate morphological measurements of galaxies in a reasonable amount of time for future big-data surveys such as EUCLID, the Large Synoptic Survey Telescope or the Wide Field Infrared Survey Telescope is a challenge. Because of its high level of abstraction with little human intervention, deep learning appears to be a promising approach. Deep learning is a rapidly growing discipline that models high-level patterns in data as complex multilayered networks. In this work we test the ability of deep convolutional networks to provide parametric properties of Hubble Space Telescope like galaxies (half-light radii, Sérsic indices, total flux etc..). We simulate a set of galaxies including point spread function and realistic noise from the CANDELS survey and try to recover the main galaxy parameters using deep-learning. We compare the results with the ones obtained with the commonly used profile fitting based software GALFIT. This way showing that with our method we obtain results at least equally good as the ones obtained with GALFIT but, once trained, with a factor 5 hundred time faster.

The major stumbling block in the determination of a rotation curve beyond the solar circle has been the lack of a suitable set of objects with well defined and independently measured distances and velocities which can be observed to large galactocentric radii. Two things have changed this situation. The first was the realization that essentially all local HII regions have associated molecular material. The second was the acquisition of reliable distances to the stars exciting a sizable number of HII regions at large galactocentric radii (Moffat, FitzGerald, and Jackson 1979). Because the velocity of the associated molecular gas can be measured very accurately by means of radio observations of CO, we have been able to overcome the past difficulties and have measured the rotation curve of the Galaxy to a galactocentric distance of 18 kpc.

The orbital evolution of the whole sample sample of short-period comets was computed by numerical integrations for a time interval of 2000 yr centered on the present epoch. This data base is intended to serve in various studies involving the statistics of orbital evolution and correlation with physical parameters or discovery circumstances. We present some results concerning the following aspects: the evolution of the orbital elements and their past-future asymmetry, statistics on the discovery of comets and on the encounters of comets with Jupiter.

The Magellanic Clouds are unique in providing sites to study the interstellar medium (ISM) and its components at all scales. To promote the pursuit of such studies, we have begun the Magellanic Cloud Emission-line Survey (MCELS), a deep imaging survey of both of these nearby galaxies in the emission of Hα, [S II], and [O III]. The emission-line images will be used in detailed optical and multiwavelength studies of H II regions, supernova remnants, planetary nebulae, superbubbles, and supergiant shells. Together with parallel surveys at other wavelengths, this survey will provide the foundation upon which to build a deeper understanding of the ISM in the Clouds and other galaxies, from small scales (~1 pc) all the way up to global scales. We present a sample of recent and current work using the MCELS dataset.

Two periods can be distinguished in the past history of our subject. The first period, which begun about 100 years ago, was dominated by intensive studies of novae and U Gem type stars at their outbursts and led to a fairly detailed, photometric and — particularly — spectroscopic description of these phenomena. The faintness of all these objects at minimum was a seriously hampering circumstance for observing them spectroscopically outside of their outbursts and it was only about 30 years ago that two pioneering surveys — of novae by HUMASON (1938) and of U Gem type stars by ELVEY and BABCOCK (1943) — begun to unravel their true nature.

The nature of dark matter is one of the outstanding questions of astrophysics. The internal motions of member stars reveal that the lowest luminosity galaxies in the Local Group are the most dark-matter dominated. New large datasets allow one to go further, and determine systematic properties of their dark matter haloes. We summarise recent results, emphasising the critical role of the dwarf spheroidal galaxies in understanding both dark matter and baryonic processes that shape galaxy evolution.

I review our knowledge about effective temperatures and masses of massive OB stars paying special attention to results recently obtained using new atmospheric models including sphericity, mass-loss and line-blanketing. The new temperature scales for O dwarfs and supergiants are lower than previously accepted. No systematic mass discrepancy is found among O supergiants, although individual problematic cases still remain. It is shown that model atmospheres give answers consistent with binary systems. Good agreement is found between theoretical predictions and observations of the Wind Momentum-Luminosity relationship for Galactic O-type supergiants. Finally, I review the status of the WLR in M33.

We review properties of all known collisionally pumped (class I) methanol maser series based on observations with the Australia Telescope Compact Array (ATCA) and the Mopra radio telescope. Masers at 36, 84, 44 and 95 GHz are most widespread, while 9.9, 25, 23.4 and 104 GHz masers are much rarer, tracing the most energetic shocks. A survey of many southern masers at 36 and 44 GHz suggests that these two transitions are highly complementary. The 23.4 GHz maser is a new type of rare class I methanol maser, detected only in two high-mass star-forming regions, G357.97-0.16 and G343.12-0.06, and showing a behaviour similar to 9.9, 25 and 104 GHz masers. Interferometric positions suggest that shocks responsible for class I masers could arise from a range of phenomena, not merely an outflow scenario. For example, some masers might be caused by interaction of an expanding Hii region with its surrounding molecular cloud. This has implications for evolutionary sequences incorporating class I methanol masers if they appear more than once during the evolution of the star-forming region. We also make predictions for candidate maser transitions in the ALMA frequency range.

Using an homogeneous sample of $v\sin i$ values for A-type main sequence stars (Royer et al. 2002), the equatorial velocity ($v$) distributions are determined as function of spectral class, from B9 to F2. The chemically peculiar and binary stars are discarded. These distributions of “normal” stars are discussed in terms of stellar formation and evolution, in particular the remaining bimodality observed for the earliest spectral types of the sample. We show that late B and early A-type main-sequence stars have genuine bimodal distributions of true equatorial rotational velocities probably due to the phenomena of angular momentum loss and of redistribution the star underwent before reaching the main sequence. A striking lack of slow rotators is noticed among intermediate and late A-type stars. The bimodal-like shape of their true equatorial rotational velocity distributions could be due to evolutionary effects.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Gas-phase methanol was recently detected in a protoplanetary disk for the first time with ALMA. The peak abundance and distribution of methanol observed in TW Hya differed from that predicted by chemical models. Here, the chemistry of methanol gas and ice is calculated using a physical model tailored for TW Hya with the aim to contrast the results with the recent detection in this source. New pathways for the formation of larger complex molecules (e.g., ethylene glycol) are included in an updated chemical model, as well as the fragmentation of methanol ice upon photodesorption. It is found that including fragmentation upon photodesorption improves the agreement between the peak abundance reached in the chemical models with that observed in TW Hya (∼10−11 with respect to H2); however, the model predicts that the peak in emission resides a factor of 2 − 3 farther out in the disk than the ALMA images. Reasons for the persistent differences in the gas-phase methanol distribution between models and the observations of TW Hya are discussed. These include the location of the ice reservoir which may coincide with the compact mm-dust disk (≲ 60 au) and sources of gas-phase methanol which have not yet been considered in models. The possibility of detecting larger molecules with ALMA is also explored. Calculations of the rotational spectra of complex molecules other than methanol using a parametric model constrained by the TW Hya observations suggest that the detection of individual emission lines of complex molecules with ALMA remains challenging. However, the signal-to-noise ratio can be enhanced via stacking of multiple transitions which have similar upper energy levels.

We provide results from an extended 3D numerical simulation study of Reynolds stress models of stellar convection and probe the modelling of compressibility, pressure fluctuations, and dissipation of turbulent kinetic energy.

The class ‘bulges’ contains objects with very different formation and evolution paths and very different properties. I review two types of ‘bulges’, the boxy/peanut bulges (B/Ps) and the discy bulges. The former are parts of bars seen edge-on, have their origin in vertical instabilities of the disc and are somewhat shorter in extent than bars. Their stellar population is similar to that of the inner part of the disc from which they formed. Discy bulges have a disc-like outline, i.e., seen face-on they are circular or oval and seen edge-on they are thin. Their extent is of the order of 5 times smaller than that of the boxy/peanut bulges. They form from the inflow of mainly gaseous material to the centre of the galaxy and from subsequent star formation. They thus contain a lot of young stars and gas. Bulges of different types often coexist in the same galaxy. I review the main known results on these two types of bulges and present new simulation results.

B/Ps form about 1Gyr after the bar, via a vertical buckling. At that time the bar strength decreases, its inner part becomes thicker – forming the peanut or boxy shape – and the ratio increases. A second buckling episode is seen in simulations with strong bars, also accompanied by a thickening of the peanut and a weakening of the bar. The properties of the B/Ps correlate strongly with those of the bar: stronger bars have stronger peanuts, a more flat-topped vertical density distribution and have experienced more bucklings.

I also present simulations of disc galaxy formation, which include the formation of a discy bulge. Decomposition of their radial density profile into an exponential disc and a Sérsic bulge gives realistic values for the disc and bulge scale-lengths and mass ratios, and a Sérsic shape index of the order of 1.

It is thus clear that classical bulges, B/P bulges and discy bulges are three distinct classes of objects and that lumping them together can lead to confusion. To avoid this, the two latter could be called B/P features and inner discs, respectively.

Recent studies of the nearest star-forming clouds of the Galaxy at submillimeter wavelengths with the Herschel Space Observatory have provided us with unprecedented images of the initial conditions and early phases of the star formation process. The Herschel images reveal an intricate network of filamentary structure in every interstellar cloud. These filaments all exhibit remarkably similar widths - about a tenth of a parsec - but only the densest ones contain prestellar cores, the seeds of future stars. The Herschel results favor a scenario in which interstellar filaments and prestellar cores represent two key steps in the star formation process: first turbulence stirs up the gas, giving rise to a universal web-like structure in the interstellar medium, then gravity takes over and controls the further fragmentation of filaments into prestellar cores and ultimately protostars. This scenario provides new insight into the inefficiency of star formation, the origin of stellar masses, and the global rate of star formation in galaxies. Despite an apparent complexity, global star formation may be governed by relatively simple universal laws from filament to galactic scales.

Analysing mid–infrared ISOCAM images of the cluster of galaxies J1888.16CL, we identified among its members several particularly active galaxies with total infrared luminosities well above $10^{11}~\Lo$. If powered by dust enshrouded starbursts, as suggested by their optical spectra, these Luminous Infrared Galaxies would exhibit star formation rates surprisingly high in the cluster environment. The triggering mechanism is unclear but could be tidal collisions within sub-structures or infalling groups.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present two 3D Large Eddy Simulations (LES) of the convection-radiation transition layer for both the A and the B component of the α Centauri binary system. Theoretical oscillation spectra are then calculated from stellar evolutionary models that include the effects of turbulence based on the LES simulations. By taking both non-seismic and seismic observational constraints into account we discuss the possibility to probe turbulence beyond standard 5mixing-length-theory in a star other than Sun.

Among the current sample of over 2000 radio pulsars known primarily in the disk of our Galaxy, millisecond pulsars now number almost 200. Due to the phenomenal success of blind surveys of the Galactic field, and targeted searches of Fermi gamma-ray sources, for the first time in over a decade, Galactic millisecond pulsars now outnumber their counterparts in globular clusters! In this paper, I briefly review earlier results from studies of the Galactic millisecond pulsar population and present new constraints based on a sample of 60 millisecond pulsars discovered by 20 cm Parkes multibeam surveys. I present a simple model of the population containing ~ 30,000 potentially observable millisecond pulsars with a luminosity function, radial distribution and scale height that matches the observed sample of objects. This study represents only a first step towards a more complete understanding of the parent population of millisecond pulsars in the Galaxy and I conclude with some suggestions for further study in this area.

The atmosphere of Venus was discovered for the first time by the Russian scientist Mikhail V. Lomonosov at the St Petersburg Observatory in 1761. Lomonosov detected the refraction of solar rays while observing the transit of the planet across the disk of the Sun. From these observations he correctly inferred that only the presence of refraction in a sufficiently thick atmosphere could explain the appearance of a light (‘fire’) ring around the night disk of Venus during the initial phase of transit, on the side opposite from the direction of motion. Lomonosov described this phenomenon, which carries his name, as the appearance ‘of a hair-thin luminescence’, which encircled a portion of the planet's disk that had not yet contacted the solar disk. He also observed a bulge set up at the edge of the Sun during the egress phase of the Venus transit. ‘This bears witness to nothing less than the refraction of solar rays in the Venusian atmosphere’, he wrote. This paper is based on the original Lomonosov publications and describes historical approaches to the study involving procedure, drawings, and implications.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html