We present long slit spectrophotometric emission line fluxes of bright and extended (< 5 arcsec in diameter) planetary nebulae (PNe), selected from a catalogue with suitable equatorial coordinates for northern hemisphere. In total, 17 planetary nebulae have been chosen and observed in 2008–2010. To measure absolute fluxes, broad slit sizes, ranging from 3.5 to 7.5 arcsec were used and thus equivalent widths (EW) of all observable emission line fluxes were also calculated. Among 17 planetary nebulae observed, line flux measurements of 12 of them were made for the first time. This work also aims to extend the sky coverage of emission line flux standards in northern hemisphere (52 planetary nebulae in southern hemisphere; 6 planetary nebulae in northern hemisphere). Electron temperatures and densities, and chemical abundances of these planetary nebulae were also calculated in this work. These data are expected to lead the photometric or spectrometric further work for absolute emission line flux measurements needed for H ii regions, supernova remnants etc.

Disc fragmentation provides an important mechanism for producing low-mass stars in prestellar cores. Here, we describe smoothed particle hydrodynamics simulations which show how populations of prestellar cores evolve into stars. We find the observed masses and multiplicities of stars can be recovered under certain conditions.

First, protostellar feedback from a star must be episodic. The continuous accretion of disc material on to a central protostar results in local temperatures which are too high for disc fragmentation. If, however, the accretion occurs in intense outbursts, separated by a downtime of ~ 104 yr, gravitational instabilities can develop and the disc can fragment.

Second, a significant amount of the cores’ internal kinetic energy should be in solenoidal turbulent modes. Cores with less than a third of their kinetic energy in solenoidal modes have insufficient angular momentum to form fragmenting discs. In the absence of discs, cores can fragment but results in a top-heavy distribution of masses with very few low-mass objects.

Sheet-like clouds are common in turbulent gas and perhaps form via collisions between turbulent gas flows. Having examined the evolution of an isothermal shocked slab in an earlier contribution, in this work we follow the evolution of a sheet-like cloud confined by (thermal) pressure and gas in it is allowed to cool. The extant purpose of this endeavour is to study the early phases of core-formation. The observed evolution of this cloud supports the conjecture that molecular clouds themselves are three-phase media (comprising viz. a stable cold and warm medium, and a third thermally unstable medium), though it appears, clouds may evolve in this manner irrespective of whether they are gravitationally bound. We report, this sheet fragments initially due to the growth of the thermal instability (TI) and some fragments are elongated, filament-like. Subsequently, relatively large fragments become gravitationally unstable and sub-fragment into smaller cores. The formation of cores appears to be a three stage process: first, growth of the TI leads to rapid fragmentation of the slab; second, relatively small fragments acquire mass via gas-accretion and/or merger and third, sufficiently massive fragments become susceptible to the gravitational instability and sub-fragment to form smaller cores. We investigate typical properties of clumps (and smaller cores) resulting from this fragmentation process. Findings of this work support the suggestion that the weak velocity field usually observed in dense clumps and smaller cores is likely seeded by the growth of dynamic instabilities. Simulations were performed using the smooth particle hydrodynamics algorithm.

The transformation equations from BVRc to g′r′i′ magnitudes and vice versa for the giants were established from a sample of 80 stars collected from Soubiran et al. (2010) with confirmed surface gravity (2 ⩽ logg (cm s− 2) ⩽ 3) at effective temperatures 4000 < Teff(K) < 16000. The photometric observations, all sample stars at g′r′i′ and 65 of them at BVRc, were obtained at TÜBİTAK National Observatory (TUG) 1m (T100) telescope, on the Taurus Mountains in Turkey. The MV absolute magnitudes of the giant stars were estimated from the absolute magnitude-temperature data for the giant stars by Sung et al. (2013) using the Teff from the intrinsic colours considered in this study. The transformation equations could be considered to be valid through the ranges of the following magnitudes and colours involved: 7.10 < V0 < 14.50, 7.30 < g′0 < 14.85, − 0.20 < (B − V)0 < 1.41, − 0.11 < (V − Rc)0 < 0.73, − 0.42 < (g′ − r′)0 < 1.15, and − 0.37 < (r′ − i′)0 < 0.47 mag. The transformations were successfully applied to the synthetic BVRc data of 427 field giants in order to obtain the g′r′i′ magnitudes and colours. Comparisons of these data with the g′r′i′ observations of giants in this study show that the mean residuals and standard deviations lie within [− 0.010, 0.042] and [0.028, 0.068] mag, respectively.

From the observed timings of primary eclipse of HD 5303 we find that its 2.7 day period is increasing at a rate of about one second per year. In this paper we consider the implications of this in terms of mass transfer or mass loss from the system.

This paper discusses problems which have as their uniting theme the need to understand the coupling between a stellar convection zone and a magnetically dominated corona above it. Interest is concentrated on how the convection drives the atmosphere above, loading it with the currents that give rise to flares and other forms of coronal activity. The role of boundary conditions appears to be crucial, suggesting that a global understanding of the magnetic field system is necessary to explain what is observed in the corona. Calculations are presented which suggest that currents flowing up a flux rope return not in the immediate vicinity of the rope but rather in an alternative flux concentration located some distance away.

The Australia Telescope Compact Array has been used in two 6 km configurations to make 12 hour observations of the radio continuum structure of three spiral galaxies at 1380 MHz and 2378 MHz. Radio maps of NGC 1792, 6300 and 1097 are presented here, as part of a survey to find examples of anomalous radio structures in spiral galaxies.

There has been considerable speculation in recent years about the evolution of radio galaxies in clusters. The discovery of powerful X-ray emission with an apparently thermal spectrum from a considerable number of clusters has been attributed to a hot (108K) intracluster gas with an electron density of ∼ 10-3 cm -3 at the cluster centre (see e.g. McHardy 1978). Such a gas surrounding a radio galaxy may conceivably retard the expansion or diffusion of the relativistic electrons and thus allow the source to retain its identity for longer intervals than is the case for field galaxies.

The anomalously high density of the planet Mercury and the higher-than-solar rock-to-ice ratio in Jupiter’s moons Ganymede and Callisto cannot be explained by the conventional disc models of solar system formation. It is shown here that the unusual chemical signature of these bodies is the outcome of a process of chemical fractionation and orbital focussing which is peculiar to gas ring models of planet and regular satellite formation. Good numerical agreement with the observational data is obtained if the temperature of condensation of the planetary system closely followed the law Tn ≃ 680[R⊕/Rn]0.9 K, where Rn denotes the radial distance from the Sun.

Both the radial and the velocity distributions of galaxies within rich clusters are well described by the isothermal distribution (e.g. Lewis 1978 and 1979). It is tempting to ascribe this apparently relaxed state to the operation of Lynden-BeU’s (1967) violent relaxation mechanism, during the initial coherent collapse on the proto-cluster, after it brakes itself against the universal expansion. This scenario explains the isothermal distribution observed in elliptical galaxies and globular clusters. When applied to a cluster of galaxies made up of baryons, however, the timescale for the scenario is comparable with the Hubble time H−1. The situation changes if most of the cluster mass is contributed by neutrinos.

The conventional method of measuring the radiation diagram of an antenna is to rotate it in the field produced by a fixed point source located in its Fraunhofer zone (Hollis et al. (1970)). With the very large antennas typically used in radio astronomy this presents difficulties. For example, to measure the 64 m telescope at ANRAO, Parkes at frequencies in the OH transition lines band (1.6-1.7 GHz), the source, to be located in the Fraunhofer zone, must be located at least 50 km away and then at a sufficiently high angle to allow measurements free from ground effects to be made. Clearly there are no terrestrial means to accomplish this.

The loss-cone-driven electron cyclotron maser instability is widely believed to be responsible for millisecond bursts of intense microwave emission often observed during solar flares. However, the maser radiation is strongly absorbed as it propagates outward from the corona and existing analytical models predict that this absorption should be sufficiently strong to prevent observable levels of the radiation from escaping, except under highly restrictive conditions. In order to address the problem of how microwave spike bursts can be observed at all, we present a numerical ray-tracing analysis which incorporates emission, propagation and absorption of fundamental cyclotron maser radiation in a realistic model of a coronal flux loop. It is found that the radiation can escape to a potential observer and that the physical conditions under which escape occurs are more restrictive for fundamental emission in the extraordinary (x)-mode than in the ordinary (0)-mode. Escaping radiation in the x-mode is found to be highly directional and chiefly observable toward the center of the solar disk, while escaping 0-mode radiation is found to emerge from the corona over a much wider range of directions, with some cases corresponding to observable radiation near the solar limb.

A photometric survey of a central region of the LMC has been undertaken to obtain a magnitude and colour limited sample of bright asymptotic giant branch (AGB) stars; the stars were selected from V and Ic plates taken by the UK Schmidt Telescope Unit (UKSTU) at Coonabarabran. Infrared JHK photometry has been obtained for all the stars in the sample in order to determine bolometric magnitudes, and spectra have been obtained for most of the stars to obtain spectral types. Stars in the sample have bolometric magnitudes up to the AGB limit of Mbol ∼ – 7.1, and many of the stars show evidence for dredge-up of carbon and s-process elements during helium shell flashes. A bolometric luminosity function has been constructed and its behaviour is discussed in terms of possible mass loss scenarios.

Polytropic models have played a significant part in the historical development of stellar structure theory and in other related branches of theoretical astronomy such as stellar pulsations and rotation. In modern astronomy polytropic solutions, because of their wide range of density distributions and our ability to introduce them analytically if necessary, now have an acknowledged role in large scale numerical experiments especially during the developmental stages.

In a technical sense radio astronomers do not use the radio spectrum; they are listeners only, and when the science began they had to listen in the quiet spaces between transmitting services. Radio astronomy was first recognized as a service by the International Telecommunications Union (ITU) in 1959, and the first frequency allocations were then made for it as a ‘passive’ service. In 1963 and 1971 further allocations and frequency protection were obtained at specialized World Administrative Radio Conferences (WARC). The allocations were required for two purposes: (i) to protect the frequencies of the most important spectral lines of atoms and molecules, and (ii) to provide a series of bands for continuum observations. The general protection so far provided has been vital to the growth of the science, and its continuation is of the highest priority to the future life and development of radio astronomy.

Solar flares for which protons of relativistic energies reach Earth are rare events compared with the number in which non-relativistic protons are produced. For instance, Shea and Smart (1978) have listed 139 proton events for the interval 1955-69 of which 17 were GLE’s (i.e. “ground level events” detected by the world network of cosmic ray neutron monitors). We have tentatively identified a further 11 GLE’s in the interval 1970-1977, of which 3 were in 1977 in the sunspot cycle which commenced about mid-1976 (cycle 21). Thus the average rate over the past two solar cycles has been a little over one per year.

Observations of Jupiter’s decametric radio burst have established that above 20 MHz more than 90% of the emission is elliptically polarized in the RH sense, but below this frequency the proportion of the LH polarization increases (Sherrill 1965) until at 10 MHz nearly 40% of the emission is LH polarized (Dowden 1963). The best time and frequency resolutions so far obtained when examining the polarization of the spectra of Jupiter’s bursts have been 10 ms and 50 kHz respectively (Gordon and Warwick 1967, Riihimaa 1975). To study the fine structure of Jupiter’s emission as observed by the linearly polarized Llanherne low frequency radio telescope (Ellis 1972), spectrum analysers with resolutions in the ranges 0.3 — 1 msec and 2–10 kHz have been used (Ellis 1973a, 1973b, 1974, 1975). A new telescope at Llanherne, which is capable of detecting the RH and LH circular components of incident radiation, is being used in conjunction with these analysers to yield information of the hyperfine polarization structure of Jupiter’s decametric radio emission. This paper is a preliminary report of this investigation.

Low frequency radio waves propagating in the interstellar medium are attenuated through absorption by thermal electrons, the optical depth being given by

where f is the radio frequency in MHz, the emission measure in cm-6 pc, and Te the electron temperature.