The radio remnant of SN 1993J: an instrumental explanation for the evolving complex structure

We present simulated images of Supernova 1993J at 8.4 GHz using Very Long Baseline Interferometry (VLBI) techniques. A spherically symmetric source model is convolved with realistic u v -plane distributions, together with standard imaging procedures, to assess the extent of instrumental effects on the recovered brightness distribution. In order to facilitate direct comparisons between the simulations and published VLBI images of SN 1993J, the observed u v -coverage is determined from actual VLBI observations made in the years following its discovery.
The underlying source model only exhibits radial variation in its density profile, with no azimuthal dependence and, even though this model is morphologically simple, the simulated VLBI observations qualitatively reproduce many of the azimuthal features of the reported VLBI observations, such as appearance and evolution of complex azimuthal structure and apparent rotation of the shell. We demonstrate that such features are inexorably coupled to the u v -plane sampling.
The brightness contrast between the peaks and the surrounding shell material are not as prominent in the simulations (which of course assume no antenna- or baseline-based amplitude or phase errors, meaning no self-calibration procedures will have incorporated any such features in models). It is conclusive that incomplete u v -plane sampling has a drastic effect on the final images for observations of this nature. Difference imaging reveals residual emission up to the 8σ level. Extreme care should be taken when using interferometric observations to directly infer the structure of objects such as supernovae.     

Progress in spectral studies of the FBS blue stellar objects

Spectral observations of 10 FBS blue stellar objects (BSO) with the OHP 1.93-m and BAO 2.6.m telescopes are reported, and overall progress in all the spectral observations and classifications of FBS BSO over 1987–2000 and in the classification of these objects based on all the accessible sources-- in all, 753 out of 1103 objects-- is discussed. Representative slit spectra for the major types of objects are presented and compared with digitized low dispersion spectra from the DFBS. The nature of the FBS objects is examined in terms of advances in the spectral studies. Two-color diagrams are constructed from the SDSS data and are used to find the regions occupied by the various types for further identification of objects of unknown type. Translated from Astrofizika, Vol. 52, No. 1, pp. 85–97 (February 2009).     

Gaia, an unprecedented observatory for Solar System dynamics

The mission Gaia by European Space Agency (ESA) is expected to fly at the end of 2011 and to perform an all-sky, magnitude-limited survey for 5 years. The probe will not use an input catalogue, and will get high accuracy astrometry and photometry for all sources of magnitude V<20. Low-resolution spectra will also be available. Moving Solar System objects will be observed as well, and their observations will be processed by a specific pipeline in order to retrieve the physical and dynamical characteristics of each object. In this contribution we will mainly focus on the impact of Gaia observations on asteroid dynamics. A dramatic improvement of orbital elements is expected, as well as the measurement of subtle effects such as those related to general relativity (GR). Gaia observations will also be supported by a network of ground-based observation sites, capable of providing follow-up for newly discovered objects that will not receive an adequate coverage from space. Specific strategies for follow-up are being planned and tested. These will need to take into account the peculiar observing geometry (large parallax effect due to the orbit of Gaia around L2) and the time constraints dictated by data processing.     

Simulations and interpretation of the 6-cm MERLIN images of the classical nova V723 Cas

We compare the predictions of simple models for the radio emission from classical novae with the MERLIN radio observations of nova V723 Cas (Nova Cas 1995). Spherically symmetric and ellipsoidal radiative transfer models are implemented in order to generate synthetic emission maps. These are then convolved with an accurate representation of the u v coverage of MERLIN. The parameters and geometry of the shell model are based on those returned by fitting models to the observed light curve. This allows direct comparison of the model images with the nine 6-cm MERLIN images of V723 Cas.
It is found that the seemingly complex structure (clumping, apparent rotation) evident in the observations can actually be reproduced with a simple spherical emission model. The simulations show that a 24-h track greatly reduces the instrumental effects and the synthetic radio map is a closer representation of the true (model) sky brightness distribution. It is clear that interferometric arrays with sparse u v coverage (e.g. MERLIN, VLBA) will be more prone to these instrumental effects especially when imaging ring-like objects with time-dependent structure variations. A modelling approach such as that adopted here is essential when interpreting observations.     

Complex of Meteoroid Orbits with Eccentricities Near 1 and Higher

In our work, the method that can help to predict the existence of distant objects in the Solar system is demonstrated. This method is connected with statistical properties of a heliocentric orbital complex of meteoroids with high eccentricities. Heliocentric meteoroid orbits with high eccentricities are escape routes for dust material from distant parental objects with near-circular orbits to Earth-crossing orbits. Ground-based meteor observations yield trajectory information from which we can derive their place of possible origin: comets, asteroids, and other objects (e.g. Kuiper Objects) in the Solar system or even interstellar space. Statistical distributions of radius vectors of nodes, and other parameters of orbits of meteoroids contain key information about position of greater bodies. We analyze meteor orbits with high eccentricities that were registered in 1975–1976 in Kharkiv (Ukraine). The orbital data of the Kharkiv electronic catalogue are received from observations of radiometeors with masses 10⁻⁶−10⁻³ g.     

Magnetic fields in the nearby Universe,as observed in solar and planetary realms,stars, and interstellar starforming nurseries

Here I present a survey of planetary, stellar and clumpy interstellar magnetic fields, with an emphasis on discoveries made in the last decade. Ground-based and Earth–satellite observations of magnetic fields in astronomical objects are cataloged, as obtained at all multiple electromagnetic wavelengths.For each type of object, the basic observational properties are summarized, and the best theoretical scenario which accounts for the large body of observations is discussed. There is no single unifying magnetic model for all objects (although dynamo theory comes close for many compact objects, and helical theory for many extended objects).The strength of the observed magnetic fields reaches exagauss values (10¹⁸ G) in compact objects such as magnetars, and decreases to microgauss values (10^?6 G) in the clumpy interstellar medium.     

On Rotation of an Isolated Globule

During CO observations of new Southern objects with the 15-m SEST mm telescope (Cerro La Silla, Chile) we have found that the globule connected with the object CLN127-128 rotates with an angular velocity 4.3 · 10^-14 s^-1, which corresponds to the velocity of extremely fast rotating globules. The object CLN127-128 is a chain of three stars; two of them are connected with bright nebulae, and the third is a suspected Herbig Ae/Be star. All three stars are bright in near IR, which is specific for the existence of circumstellar shells (or disks) around them. The specific angular momentum of the globule confirms that it is in virial equilibrium. Besides the finding of a rotating globule, CO observations suggest the presence of a blue-shifted outflow from CLN127-128 with a velocity of -1.1 km/s (in the system connected with the globule).     

Determination of the red shifts of selected IVS program objects. I

The spectroscopic red shifts of seven optical objects whose coordinates coincide with those of radio sources in the IVS (International VLBI Service for Geodesy and Astrometry) program list are determined from observations with the 6-m BTA telescope at the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences. A comparison of these spectra and red shifts with data in the radio frequency range shows that four of the objects discussed here are correctly identified, while the other three require further study. The distances to the radio sources derived from our measurements yield more accurate estimates of the cosmological model parameters than those based on the proper motions of these objects derived from geodesic VLBI observations.     

A study of optically featureless objects from the EC Survey: searching for new southern BL Lac objects

In an attempt to discover new southern BL Lac objects, 14 optically featureless objects from the Edinburgh–Cape Survey were selected. Optical polarimetry and spectroscopy, radio and IR observations were carried out in order to improve their classifications. The 14 objects were examined according to special criteria that are described. Their UBV and JHK colour–colour distributions, spectrograms, radio observations and visible-region polarimetry were utilized to conclude that the selected objects are not BL Lacs. Most of them are apparently not extragalactic objects. It is suggested that four of the 14 candidates are DC white dwarfs, one is a QSO, three are DA white dwarfs or sdB subdwarfs, one is a cataclysmic variable, one is a DAO/sdO and another is possibly a DA+dM binary (composite system with a 'primary' hot white dwarf and a 'secondary' M-type main-sequence dwarf) or a cataclysmic variable. One object is likely to be a subdwarf, while two remain unclassifiable.     

Asteroid polarimetric observations using the Torino UBVRI photopolarimeter

A long-term project of polarimetric observations of minor planets has been carried out since 1995 at the 2.15-m telescope of the El Leoncito Observatory (San Juan, Argentina) using the Torino photopolarimeter. We present here an updated summary of the results, including many measurements obtained during the most recent observing runs. The main purpose of the observations has been to obtain albedo estimates and compare them with previous IRAS radiometric determinations, mainly for objects having small (<50 km) IRAS diameters. Another field of investigation is the measurement of the degree of linear polarization at very small phase angles (less than 1°). The latter observations can be a useful input for modern theoretical models of light scattering from asteroid surfaces. In general, we have obtained a wealth of new results, including objects exhibiting a peculiar polarimetric behavior.     

Evidence for an Extended Scattered Disk

By telescopic tracking, we have established that the transneptunian object (TNO) 2000 CR₁₀₅ has a semimajor axis of 220±1 AU and perihelion distance of 44.14±0.02 AU, beyond the domain which has heretofore been associated with the “scattered disk” of Kuiper Belt objects interacting via gravitational encounters with Neptune. We have also firmly established that the TNO 1995 TL₈ has a high perihelion (of 40.08±0.02 AU). These objects, and two other recent discoveries which appear to have perihelia outside 40 AU, have probably been placed on these orbits by a gravitational interaction which is not strong gravitational scattering off of any of the giant planets on their current orbits. Their existence may thus have profound cosmogonic implications for our understanding of the formation of the outer Solar System. We discuss some viable scenarios which could have produced these objects, including long-term diffusive chaos and scattering off of other massive bodies in the outer Solar System. This discovery implies that there must be a large population of TNOs in an “extended scattered disk” with perihelia above the previously suggested 38 AU boundary. The total population is difficult to estimate due to the ease with which such objects would have been lost. This illustrates the great value of frequent and well time-sampled recovery observations of trans-neptunian objects within their discovery opposition.     

Monsters and babies from the first / iras survey

Radio continuum emission at cm wavelengths is relatively little affectedby extinction. When combined with far-infrared (FIR) surveys thisprovides for a convenient and unbiased method to select (radio-loud)AGN and starbursts deeply embedded in gas and dust–rich galaxies. Suchradio-selected FIR samples are useful for detailed investigations ofthe complex relationships between (radio) galaxy and starburst activity, and to determine whether ULIRGs are powered by hidden quasars (monsters) or young stars (babies).We present the results of a large program to obtain identifications andspectra of radio-selected, optically faint IRAS/FSC objects using theFIRST/VLA 20 cm survey (Becker, White and Helfand 1995). These objects are all radio-`quiet' in the sense that their radiopower / FIR luminosities follow the well-known radio/FIR relationshipfor star forming galaxies.We compare these results to a previous study by our group of a sampleof radio-`loud' IRAS/FSC ULIRGs selected from the Texas 365 MHzsurvey (Douglas etal. 1996). Many of these objects alsoshow evidence for dominant, A-type stellar populations, as well as highionization lines usually associated with AGN. These radio-loud ULIRGshave properties intermediate between those of starbursts and quasars,suggesting a possible evolutionary connection.Deep Keck spectroscopic observations of three ULIRGs from these samplesare presented, including high signal-to-noise spectropolarimetry.The polarimetry observations failed to show evidence of a hidden quasar inpolarized (scattered) light in the two systems in which the stellar lightwas dominated by A-type stars. Although observations of a larger samplewould be needed to allow a general conclusion, our current data suggestthat a large fraction of ULIRGs may be powered by luminous starbursts,not by hidden, luminous AGN (quasars).     

The case for asymmetric dust around a C-rich asymptotic giant branch star

JHKL observations of the mass-losing carbon Mira variable IRAS 15194–5115 (II Lup) extending over about 18 yr are presented and discussed. The pulsation period is 575 d and has remained essentially constant over this time span. The star has undergone an extensive obscuration minimum during this time. This is complex and, like such minima in similar objects (e.g. R For), does not fit the model predictions of a simple long-term periodicity. Together with the high-resolution observations of Lopez et al., the results suggest that the obscuration changes are caused by the formation of dust clouds of limited extent in the line of sight. This is an R Coronae Borealis-type (RCB-type) model. The effective reddening law at J and H is similar to that found for R For.     

Light pressure effect on the orbital evolution of objects moving in the neighborhood of low-order resonances

The hardware-software complex of the SBG telescope of the Kourovka astronomical observatory of the Ural Federal University is described. The area-to-mass ratio of high-orbit objects was estimated from the results of positional observations at the SBG telescope. Positions and sizes of resonance zones are determined from the numerical simulation results depending on the area-to-mass ratio in the case of low-order resonances (1 : 1, 1 : 2, and 1 : 3). Secular perturbations of semimajor axes of orbits, caused by the Poynting-Robertson effect, are estimated in the neighborhood of low-order resonance zones at different area-to-mass ratios.     

Unusual radio properties of the BL Lac object 0820+225

We present the results of simultaneous VLBA polarization observations of the BL Lacertae object 0820+225 at 5, 8 and 15 GHz, together with earlier images at 5 GHz. This source has an unusually rich total intensity and polarization structure compared with other objects with comparable redshifts. The magnetic field in the inner part of the complex and highly twisted VLBI jet is transverse, as is typical of BL Lacertae objects, but becomes roughly longitudinal further from the core, possibly as a result of shear. Although the integrated rotation measure of 0820+225 is modest, the rotation-measure distribution on parsec scales is non-uniform, and clearly shows regions where the rotation measure is substantially higher than the integrated value.     

Asteroids 1 ceres and 4 vesta: Objects of the Dawn space mission

The Dawn spacecraft of the NASA space mission to asteroids 1 Ceres and 4 Vesta was launched in September 2007. The choice of these two asteroids is deeply grounded: they are the largest and most massive objects of the main belt that are completely different in material composition, evolution history, and internal structure. Recently, the results of observations and numerical modeling have shown their amazing uniqueness: they both have experienced the complex process of thermal evolution and differentiation of their internal mineral resources, but have a completely different internal structure. Being the largest bodies, have they managed to resist the process of collisional evolution in the asteroid belt and have survived in their “primitive form.” Because of this, their study is very important from the point of view of cosmogonic problems regarding the asteroid belt and the Solar System as a whole. The present paper shortly reviews the recent progress in the study of Ceres and Vesta achieved due to observations performed on the Earth (including the polarimetric observations made by the authors) and from the Hubble Space Telescope (HST) before the long-term orbital investigations performed by the Dawn spacecraft.     

Analysis of λ = 6 cm VLBI polarization observations of a complete sample of northern BL Lacertae objects

The results of very long baseline interferometry (VLBI) total intensity ( I ) and linear polarization ( P ) observations at     are presented for 10 radio bright BL Lacertae objects. These images complete first-epoch polarization observations for the 1-Jy sample of northern BL Lacertae objects defined by Kühr & Schmidt. Estimates of superluminal speeds are presented for several sources, bringing the total number of sources in the sample for which such estimates are available to 16. Second-epoch observations currently being reduced should yield speed estimates for VLBI features in essentially all the sources in the sample. The jet magnetic fields of these BL Lacertae objects are usually transverse to the local jet direction, but a sizeable minority (about 30 per cent) have VLBI jet components with longitudinal magnetic fields. This may suggest that the conditions in the VLBI jets of BL Lacertae objects are favourable for the formation of relativistic shocks; alternatively, it may be that the toroidal component of the intrinsic jet magnetic field is characteristically dominant in these sources.     

Ultra-Compact H II Regions

This article reviews how observations of dense molecular gas can help us understand the dynamics and evolution of ultra-compact H II (UCHII) regions. Particular attention is paid to the cometary objects, which it is argued are likely to be the dominant class. Thermal molecular lines in emission and absorption are considered as well as the mainly dynamical information from masers. Most of the UCHII regions studied at high resolution have hot cores ahead them which makes interpretation of molecular observations much more complex. Significant support for the champagne flow model for cometary regions can been seen, adding to the evidence from studies of the ionised gas. How the prevalence of cometary objects may fit into a triggered, sequential picture of massive star formation is outlined.