bluuebunny/crossref_metadata_2025 huggingface dataset:
Gravitational lenses
Authors: Hewitt J. N.
Published: July 2016

In approximately half the systems currently recognized as strongly gravitationally lensed, the background object is an extragalactic radio source. Radio observations have played an important role in the identification of lensed systems, and the properties of radio sources allow some of the astrophysical applications of lensing to be realized. High redshift galaxies can be studied through lens modeling and by observing more than one ray path through the lens. The morphological, spectral, and polarization information of high resolution radio images provides strong constraints on the mass distribution in the lensing galaxies. On cosmological scales, radio variability has been applied to the time delay measurement of angular diameter distance.
A VLA Study of Ooty Small Diameter Sources
Authors: Menon T.K.
Published: July 2016

In the Ooty lunar occultation survey of about 711 sources at 327 MHz over 200 sources were classified as unresolved with upper limits of about 4″ (Kapahi(1986)). In order to study the nature of these sources I have observed a sub-sample of 71 sources with the VLA in the A-Configuration at 6 cm. The angular resolution ranged from 0.4 to 0.8 arc second. My observations show that of the above 71 sources 56% are well resolved doubles and triples resembling FRII sources with angular separations of 0″.4 to 8″. The flux density ratios of well separated doubles and triples range from 1 to about 8. However the LAS of sources with ratios of less than 2 is found to increase with decreasing flux density. Since most of the low flux density sources are in blank fields in the PSS prints no redshift information is available at present. Being FRII sources they are likely to be very distant sources at comologically interesting ranges of redshift. In order to test whether the above observed increase in the angular size is of cosmological significance we need optical identification and redshift information. These are being planned.
First millimeter Mapping of the jet and nucleus of M87
Authors: Despringre V. , Fraix-Burnet D.
Published: July 2016

An intriguing question about extragalactic jets is why they are so few being seen at optical wavelengths, or equivalently, why the cutoff frequency of the synchrotron radiation is generally not in the optical, but rather in the infrared or even in the sub- millimeter domain. The answer is undoubtedly related to the efficiency of the acceleration of the relativistic electrons responsible for the synchrotron emission. The presence of a break at low frequency somewhere in the synchrotron spectrum is another feature that constrains the model parameters, but its precise location is unknown for most jets, because of the lack of photometry in the millimeter domain. It was thus necessary to fill the gap between radio and optical wavelengths in the synchrotron spectrum of optical jets. The required observation had to be of high sensitivity and high spatial resolution (of the order of 1″). Another reason for observing at millimeter wavelengths is that molecular lines and thermal emission from cold dust are detectable in this frequency range.
Hubble Space Telescope Observations of Extragalactic Jets
Authors: Macchetto F. Duccio
Published: July 2016

The study of the optical counterparts to the radio jets has been the subject of a number of observing programs with the Hubble Space Telescope (HST). We know that these jets play a fundamental role in transporting energy from the central source to the extended radio lobes. Observations at optical and ultraviolet wavelengths with the HST are essential to obtain spatial resolutions similar to, or better than, those achieved in the radio band and, thus, provide the possibility of directly comparing the sites and mechanisms responsible for the emission at these different wavelengths.
Can BL Lac Nuclei and Broad Line Regions Coexist? or When is an Object a BL Lac?
Authors: Marchã M.J.M.
Published: July 2016

The problem of BL Lac classification is a long standing one and it is mainly due to the subjectiveness of selection criteria used in the definition of BL Lac samples. For instance, an object will undoubtedly be classified as a BL Lac if it shows flat radio spectrum, high optical and radio polarization, featureless optical continuum with weak or absent emission lines, and variable flux and polarization. However, the problem arises when the object shows some but not all of these properties. In face of this difficulty, different authors (Stickel et al. 1991, Stocke et al. 1991) have tried to make a systematic analysis of the data and it has been common to classify as BL Lacs those objects whose strongest emission lines have equivalent width (EW) ≤ 5 Å. Another common criterion is to require the 4000 Å break contrast to be ≤ 0.25. Nevertheless, both of these criteria are rather arbitrary and more directly related to practical observational considerations, than they are to any physical distinction between objects. What is proposed here is a slightly different approach; it is proposed that we take a step back from common classification and that instead of imposing strict selection criteria, we create a multi-observational parameter space to investigate any breaks in the distribution of observed properties that will help clarify the distinction between BL Lacs and other flat radio spectrum sources.
A Possible Fundamental Difference Between Radio Loud and Radio Quiet AGN
Authors: Calvani M. , Sulentic J.W. , Marziani P. , Dultzin-Hacyan D. , Moles M.
Published: July 2016

We report on some striking differences between radio loud and quiet emitters that we found in a comparative analysis of the high and low ionization lines for 52 low redshift AGN (31 loud; 21 quiet).

The broad components of Civλ1549 and Hβ were chosen as representative of the high and low ionization lines respectively. CIVλ1549 observations were obtained with the Faint Object Spectrograph on the HST. They were retrieved from the HST data archive and matching optical spectra for the region of Hβ were obtained at several ground based observatories. Details on observations, narrow/broad component deconvolution and profile cleaning from satellite lines (especially FeII) can be found in Marziani et al. (1995). The rest frame for each quasar was determined from the radial velocity of strong narrow lines, typically [Oiii]λλ4959,5007.
The Radio and Optical Properties of Quasars
Authors: Impey C.D. , Hooper E.J. , Foltz C.B. , Hewett P.C.
Published: July 2016

The relationship between the radio and optical emission of quasars was first studied using radio-selected objects, which generally had high radio luminosities due to the relatively low sensitivity limits of the surveys. More recently, radio follow-up observations have been made of optical surveys surveys in other wavebands. Taken together, the two survey methods have detected quasars with a range of over 6 orders of magnitude in radio luminosity. We report here new observations with the Very Large Array (VLA) of 103 quasars from the Large Bright Quasar Survey (LBQS), with absolute magnitudes in the range −25 < MB < −23 and redshifts in the range 0.2 < z < 1.1. This can be combined with our previous LBQS observations (Paper I, Paper II) to yield 359 quasars, the largest sample of sensitive radio observations of optically-selected quasars in a single survey.
Inverse Compton X-Rays from Giant Radio Galaxies
Authors: Tsakiris D. , Leahy J.P. , Strom R.G. , Barber C.R.
Published: July 2016

The X-ray radiation from inverse Compton scattering of CMB photons by the relativistic electrons in ‘radio’ lobes provides a direct measure of their column density at a known energy, unlike synchrotron radiation which also depends on the unknown magnetic field. Thus by combining inverse Compton and radio data we can separately determine the particle energies and field strengths, rather than having to rely on uncertain estimates like minimum energy. The predicted flux is

and strong IC signal requires high radio flux and low magnetic field, properties of giant radio galaxies. On the other hand the minimum detectable count rate, Imin, increases with the target size due to the larger background contribution. As a result the detectability of IC X-rays for ROSAT PSPC B measurements is roughly,
assuming a spectral index of 0.75. After making detailed prediction of SIC for a number of objects of the 3CR sample, the best candidates were 3C 236, 3C 326, and 4C 73.08.
Optical Identifications for a Sample of REXs: Search for BL Lac Objects
Authors: Ruscica C. , Caccianiga A. , Maccacaro T. , Wolter A.
Published: July 2016

Twenty six Radio Emitting X-ray Sources (REXs) have been observed in two observing runs as part of a project aimed at selecting a new and large sample of BL Lac objects (see Wolter et al. this conference). Sources were selected by cross-correlating ROSAT-PSPC public images against VLA radio surveys. Here we present results from the first observations of 14 sources conducted in April 1995 with a B&C spectrograph in longslit mode using a CCD-Tektronix TK-1024 AB detector at the 2.1m San Pedro Martir telescope (Mexico). Table 1 shows the data derived for the 8 confirmed REXs. X-ray fluxes are in units of erg cm–2 sec–1 in the 0.1-2.4 keV band, radio fluxes are in mJy at 5 GHz, X-ray luminosities are in erg sec–1 in the energy range 0.1-2.4 keV and radio luminosities are in erg sec–1 at 5 GHz. We assumed Ho = 50 km sec–1 Mpc–1 and qo = 0. A more detailed description of individual sources will be published elsewhere.
Optical Monitoring of the Gamma–Ray Loud BL Lac Object S5 0716+714
Authors: Latini G. , Bosio S. , DE FRANCESCO G. , Villata M. , Ghisellini G. , Raiteri C.M. , Tosti G. , Fiorucci M. , Maesano M. , Massaro E. , Montagni F. , Nesci R.
Published: July 2016

We monitored the γ-ray loud BL Lac object S5 0716+714 between November 1994 and April 1995 (J.D. 2449671–2449838), from the Observatories of Torino, Perugia and Roma. The source was always active in the R and B bands, showing a particularly high optical state during the period of the CGRO pointing (February 14–28, 1995). The lightcurve in the R band is presented in Fig. 1. The complete set of observations is discussed in Ghisellini et al. (1995).
Radio Source Environments at Redshifts > 0.5
Authors: Lacy M. , Rawlings S. , Wold M. , Bunker A. , Blundell K.M. , Eales S.A. , Lilje P.B.
Published: July 2016

The most powerful radio sources in the local Universe are found in giant elliptical galaxies. Looking back to a redshift of 0.5 (≈ half the age of the Universe for ω = 1), we see that these host galaxies are increasingly found in moderately rich clusters. This fact gives us hope that radio sources can be used as tracers of high density environments at high redshift. By exploiting radio source samples selected over a wide range in luminosity (Blundell et al., these proceedings), we will also be able to test whether the luminosities of radio sources are correlated with their environments.
Radio-Optical Alignments in Nearby Cooling Flow Cluster Central Galaxies
Authors: Mcnamara B.R.
Published: July 2016

The centers of dominant cluster galaxies in cooling flows are often unusually blue, they have spatially extended nebular line emission and bright, FR I radio sources (Fabian 1994). As a class, they are the most rapidly evolving giant elliptical galaxies known. Among the most interesting of these objects, the Abell 1795 (z = 0.06) and Abell 2597 (z = 0.08) central cluster galaxies have very blue, lobe-like structures that are located along their FR I radio lobes (McNamara & O'Connell 1993). This discovery was surprising because correlations between the radio source and blue optical continuum were thought to occur exclusively in powerful, FR II radio galaxies at redshifts z > 0.6 that show the alignment effect. By analogy with the distant radio galaxies, the blue lobes are thought to be regions of star formation that were triggered by the passage of the radio source (De Young 1995), or scattered light from an obscured, anisotropically radiating active nucleus that is beaming its light obliquely to the line of sight (Sarazin & Wise 1993; Crawford & Fabian 1993; Sarazin et al. 1995). Scattered light is usually polarized. Therefore, polarization measurements of the aligned optical continuum should provide a strong test of the scattering hypothesis.

McNamara et al. (1995) have obtained U-band polarimetry of the blue lobes in the Abell 1795 cluster central galaxy. They found an upper limit to the degree of polarization of the light emitted from the lobes of < 7%. The accuracy of this measurement is limited by the presence of diluting background starlight. This limit is inconsistent with the lobes being scattered light that originated in an obscured, anisotropically radiating nucleus, unless the radiation is beamed and is viewed at an angle < 22° to the line of sight, which is unlikely. The absence of a detailed correspondence between the radio lobes and optical lobes and the absence of a polarized signal is also inconsistent with synchrotron light.

The blue optical lobes are probably regions of vigorous star formation. If a burst of star formation were triggered by the expanding radio lobes, the age of the burst population should be ≃ 107 yr. The star formation rate in both lobes, assuming the Local IMF, would then be ≃ 20 M⊙ yr–1 and the stellar mass of the lobes would be ≃ 108 M⊙. The large cooling flow in A1795 may be fueling the star formation and the radio source or the fuel may have originated from one or more gaseous cluster galaxies that recently fell into the cluster's core. This result strongly suggests that the radio sources in central cluster galaxies may be a significant factor driving the evolution of their stellar populations.
The Unification of Quasars and Radio Galaxies
Authors: Alighieri Sperello Di Serego
Published: July 2016

The evidence for misdirected quasars in the nuclei of powerful radio galaxies (PRG) is now solid: 1. strong perpendicular polarization of the UV continuum, produced by the scattering of light from the hidden nucleus, has been observed in 10 (out of 11) PRG with z > 0.7 (Cimatti et al. 1993); 2. polarized broad MgII2800 has been seen in 6 PRG (di Serego Alighieri et al. 1994, Antonucci et al. 1994), showing that the hidden nucleus is indeed a quasar. These findings are receiving authoritative confirmation from observations with the Keck telescope (Cimatti, Cohen and van Breugel in these Proceedings). Here I would like to concentrate on recent developments of our understanding of the unification between quasars and PRG.
The Evolutionary Unified Scheme, Jet Asymmetry, and Superluminal Motion
Authors: Vagnetti Fausto
Published: July 2016

The evolutionary unified scheme (Vagnetti et al., 1991; Vagnetti and Spera, 1994) is the first attempt to describe the radio source populations accounting at the same time for their cosmic evolution and their anisotropic phenomena. It achieves an interconnection between anisotropy and evolution through a changing balance between two optical components, an isotropic “thermal” one and a relativistic beam. It predicts an evolution of the radio-optical ratio, interpreted as a slow increase of the Lorentz factor with the cosmic time (Vagnetti et al., 1991). It also predicts a link between the high and low-power unified schemes, and in particular between high and low-redshift blazars, and between high and low-redshift radio galaxies.
Comptonization as Blazar High Energy Emission
Authors: Dreissigacker Oliver
Published: July 2016

We explain the overall continuous Grazar (Gamma Ray Blazar) spectrum from the synchrotron turnover to the EGRET GeV detections by means of Comptonization in the parsec scale jet's substructures.

While making use of the constraints on the synchrotron spectrum and other measurable quantities, no exotic particle acceleration is needed to achieve the high energy output.

We show, that the “Lighthouse Model” of blobs of relativistic electrons, travelling with the jet plasma at relativistic speeds, produce both, correct timescales and shapes for the lightcurve, and correct ratios and slopes of the synchrotron, X-ray and γ-ray branches.
A Numerical Study of Relativistic Jets
Authors: Font J.A. , Marti J.M. , Ibáñez J.M. , Müller E.
Published: July 2016

Numerical simulations of supersonic jets are able to explain the structures observed in many VLA images of radio sources. The improvements achieved in classical simulations (see Hardee, these proceedings) are in contrast with the almost complete lack of relativistic simulations the reason being that numerical difficulties arise from the highly relativistic flows typical of extragalactic jets. For our study, we have developed a two-dimensional code which is based on (i) an explicit conservative differencing of the special relativistic hydrodynamics (SRH) equations and (ii) the use of an approximate Riemann solver (see Martí et al. 1995a,b and references therein).
Viewing Angle and the Appearance of Superluminal Jets
Authors: Aller H. D. , Aller M. F. , Hughes P. A. , Mioduszewski A.
Published: July 2016

The time history of BL Lacertae has shown clear evidence of changes in jet orientation both in the plane of the sky and in the angle to the line of sight (see Figure 1). Models based on transverse shocks in a relativistic flow quantitatively fit the polarization and flux density data well and permit one to determine parameters of the flow such as the bulk Lorentz factor and the angle of the flow to the line of sight (Hughes, Aller and Aller 1989). The orientation of the jet flow to the line of sight changed by approximately 6° between the early 1980 bursts and one in 1991. There have been comparable changes in the orientation of the jet on the plane of the sky. Such changes in jet orientation may be due to a helical flow pattern arising from precession or instability.
MHD Self-Similar Solutions for Collimated Jets
Authors: Trussoni E. , Sauty C. , Tsinganos K.
Published: July 2016

The MHD modelling of jets in axisymmetric geometry requires the treatment of the Bernoulli and the transfield equations, that can be treated following a self-similar approach. This technique is based on two main assumptions: i) the physical variables are factorized; ii) a suitable scaling law in one direction is prescribed. Solutions self-similar in the r direction (in a spherical frame of reference) have been studied to model collimated winds from disks (Blandford and Payne 1982). Here we present solutions self-similar in the θ direction, suitable to study the collimated wind around the polar axis of a rotating object (Tsinganos and Trussoni 1991, Sauty and Tsinganos 1994). Our basic assumptions are:

–

The magnetic flux function, that describes the poloidal components of velocity and magnetic field, is expressed as A(r, θ) ∝ f(r)sin2θ.

–

The density and the pressure of the plasma are assumed to scale linearly with A: ρ(r, θ) ∝ 1 + δA and P(r, θ) ∝ Po(r) (1 + KfA). Accordingly, the surfaces with equal poloidal Alfvén number M are spherical.
MHD equilibria of Helical Jets
Authors: Villata M. , Ferrari A.
Published: July 2016

From recent high angular resolution (≃ 0.1 arcsec) observations of some extragalactic jets (in particular we refer to the radio, optical, and ultraviolet images of the M 87 jet, of 3C 66B, and 3C 264) it can be inferred that the synchrotron emission from the jet comes mainly from an external, quasi-cylindrical surface on which bright helical filamentary structures can be clearly recognized.
Fractal Properties of Extragalactic Jets: Evidence of Turbulence?
Authors: Bodo G. , Massaglia S. , Feretti L. , Ferrari A. , Dall'Anese D.
Published: July 2016

Several different properties of extragalactic radio sources have been attributed to the effects of turbulence. The morphological appearance of FRI sources has been often interpreted as the result of turbulent entrainment in subsonic or transonic flows (Bicknell 1984, 1986). Moreover, particle acceleration by MHD turbulence via a second order Fermi process is one of the possible ways for accelerating the synchrotron emitting relativistic particles (see Ferrari, Trussoni & Zaninetti 1979). Turbulence appears therefore as an important ingredient in the theoretical modelling of extragalactic radio sources; however, we do not have, unfortunately, any direct evidence of it.
The VSOP Mission for Extragalactic Radio Sources
Authors: Hirabayashi Hisashi
Published: July 2016

The VSOP (VLBI Space Observatory Programme) mission is being developed by the Institute of Space and Astronautical Science (ISAS), in close collaboration with the National Astronomical Observatory (NAO) of Japan. NASA and NRAO of the USA are key collaborating institutions, and most radio-telescopes world-wide will participate in some VSOP observations.
Radio Luminosity Functions
Authors: Condon J.J.
Published: July 2016

Luminosity functions give the space densities of source populations as functions of spectral luminosity. They constrain source physics, clustering, cosmological evolution, and contributions to the radiation background. Extragalactic radio sources span eight decades of luminosity, so dividing them into luminosity ranges effectively separates them by energy generation mechanism and other fundamental properties. Multivariate luminosity functions divide the source population in additional ways (e.g., by optical morphology, optical absolute magnitude, or radio spectral index) selected to emphasize particular source characteristics.
The Radio Sky at Micro-Jy Levels
Authors: Fomalont E. B.
Published: July 2016

The properties of the μJy radio sources are described in this paper. The results were obtained from deep VLA observations of four fields, shown in Table 1. Deep optical images have been obtained for the Bootes and Lilly 1 fields.
Distant Radio Galaxies: the Strong Link between the Radio and Optical Emission
Authors: Röttgering Huub
Published: July 2016

Recent observations of distant radio galaxies show that there is a strong link between the radio source and the optical continuum and Lyα line emission from the galaxy. This link is discussed in terms of differences in age, orientation and environment between the radio sources.
Stellar Population Models of Distant Radio Galaxies
Authors: Villani D. , Alighieri S. Di Serego
Published: July 2016

Stellar populations of high redshift radio galaxies (HzRG) (z up to 4.2) are the oldest stellar systems known, that is the ones formed at the earliest cosmological epochs. Therefore they are the best objects for providing us with information about the epoch of galaxy formation. The information on the stellar populations in HzRG are obtained from the study of their Integrated Spectral Energy Distribution (ISED) which are gathered both from spectra and integrated magnitudes. The most common approach for the interpretation of colors and spectral features of the energy distribution of galaxies is the Evolutionary Population Synthesis (EPS), which has been introduced for the first time by Tinsley in 1972. EPS models have often been used in the past to interpret the ISED of HzRG (Chambers & Charlot 1990; Lilly & Longair 1984; di Serego Alighieri et al. 1994) in order to draw conclusions on the age of the stellar populations and therefore on the epoch of galaxy formation. The results are sometimes conflicting and a number of very recent EPS models have become available (Bressan et al. 1995; Bruzual & Charlot 1993; Buzzoni 1989; Guiderdoni & Rocca-Volmerange 1987): we are therefore analysing the differences between the various EPS models with the aim of assessing their suitability to study the stellar population at early epochs. The EPS models assume for stars a given Initial Mass Function(IMF) as well as a Star Formation Rate (SFR). Then one can compute the number of stars with given mass present in the galaxy as a function of time. The position of each star in the HR diagram is determined by means of the isochrones, which are calculated from stellar evolutionary models. The ISED of a galaxy is obtained from the superposition of the spectra of single stars obtained from a stellar spectral library. Thus these models describe the galaxy ISED as a function of the time, giving a complete evolutionary picture.
Faint Radio Sources and the Cosmic Microwave Background
Authors: Richards Eric A.
Published: July 2016

We have mapped a single field with the VLA to an unprecedented rms sensitivity of 1.5 μJy. Our observations reveal that the excess μJy population (see Windhorst et al (1993), Fomalont et al. (1993)) is continuous down to 1 μJy. In addition, we measure a microwave sky temperature of ΔT/T = (1.4 ± 1.2) x 10–5, consistent with microwave decrements we discovered near the center of our map.
FSRQ and the Gamma-Ray Background
Authors: Di Girolamo T. , Comastri A. , Setti G.
Published: July 2016

The contribution of Flat Spectrum Radio Quasars (FSRQ) to the γ-ray background (GRB) is modeled. FSRQ are known to make a substantial contribution to the hard (E>100 MeV) background. The so called “MeV bump”, however, cannot be accounted for in terms of this class of sources even taking into account the newly discovered class of FSRQ with a broad band spectrum sharply peaked in the MeV range (“MeV blazars”). This is in agreement with the recent results obtained by Kappadath et al. (1995) using COMPTEL data.
The magnetic field of the nearest cool starA Paradigm for Stellar Activity
Authors: Schrijver Carolus J.
Published: July 2016

Looking at the Sun forges the framework within which we try to interpret stellar observations. The stellar counterparts of spots, plages, flux tubes, chromospheres, coronae, etc., are readily invoked when attempting to interpret stellar data. This review discusses a selection of solar phenomena that are crucial to understand stellar atmospheric activity. Topics include the interaction of magnetic fields and flows, the relationships between fluxes from different temperature regimes in stellar atmospheres, the photospheric flux budget and its impact on the measurement of the dynamo strength, and the measurement of stellar differential rotation.
Doppler imaging of eclipsing binaries
Authors: Piskunov N.
Published: July 2016

We describe the extension of our Doppler imaging technique to the case of eclipsing binary systems. Using numerical experiments, we show that the simultaneous imaging of both components breaks the north-south ambiguity that occurs for single stars with high inclination. Characteristic map distortions can be used to correct errors in the orbital parameters of the binary.

We apply this technique to ER Vul – an active RS CVn type binary. Our preliminary results show the presence of the hot spots on the substellar sides of both components, perhaps due to the reflection effect.

We also discuss application of the same technique to contact binaries, where non-sphericity is significant.
HST imaging of Betelgeuse
Authors: Gilliland Ronald L. , Dupree Andrea K.
Published: July 2016

We have obtained the first direct image of the surface of a star with HST in March 1995. Our near-ultraviolet images of the M2 Iab supergiant-star Betelgeuse (Alpha Orionis) taken with the COSTAR-corrected Faint Object Camera show about 10 resolution elements over the stellar disk. With direct resolution of Betelgeuse the following discoveries resulted: 1) The apparent size of the disk in the UV (≃ λ 2550) is larger by a factor of ≃2.1 than in the optical, demonstrating the extent of the supergiant atmosphere. 2) An unresolved hot spot (higher temperature than the disk by a few thousand degrees) dominates the spatial structure of the atmosphere. 3) The atmosphere at 2550 å extends to 125 milliarcsec (FWHM 108 mas) with a limb-darkening coefficient of about 1.0.
VLBI for probing large-scale magnetic structures of stars
Authors: Lestrade J.-F.
Published: July 2016

By VLBI astrometry, we show that the two RSCVn type binaries, UX Ari and σ2 CrB, have a preferred site of radio emission which is the intra-system region. It is known that radio emission from these stars is from the gyro-synchrotron process associated with large-scale magnetic fields. High gravity in the intra-system region might favor dense magnetic loops. Interactions in this region between loops attached to the surfaces of the two stellar components might produce reconnections required for electron acceleration.
Current studies and future prospects in stellar-structure imaging with the GI2T
Authors: Stee Ph. , Bonneau D. , Morand F. , Mourard D. , Vakili F.
Published: July 2016

The capability of optical long baseline interferometry for measuring the angular diameter of stars or binary separation is now well established. However, for the imaging of photospheric disk structures one needs very long baseline interferometers operated in the multi-telescope phase-closure technique. In this paper we will stress the capability of spectro-interferometric measurements to constrain the physics of hot stars. We will report our study of the interacting binary, β Lyrae, and the mass-losing Be star γ Cassiopeiae. We will look at the interpretation of both the modulus and phase data recorded by the long baseline interferometer GI2T in the southern France. The performances and limitations of spectro-interferometric techniques will also be discussed through some of the most exciting prospects within the reach of current interferometers.
What we don't know about starspots
Authors: Hall Douglas S.
Published: July 2016

The scope of this paper will be starspots, and by that I mean regions cooler than the surrounding photosphere (like sunspots) but I also mean the whole range from very small (like sunspots) to very large (such as seen on very active stars like RS CVn).
Recent measurements of stellar magnetic fields
Authors: Saar S. H.
Published: July 2016

High resolution, high S/N spectra have been successfully modeled to yield information on the magnetic properties of cool stars for some 15 years now. These analyses yield estimates of the intensity weighted surface filling factor of active regions, f, and the mean unsigned field strength in these regions), B. The measurements are difficult, though, hampered by the small magnitude of the Zeeman effect, small f values for most stars, and the unknown spatial and thermodynamic properties of the active regions. Recent data, mostly in the infrared (IR) where the Zeeman effect (∞ λ2) is larger, are yielding better measurements than ever before. I summarize the new observations here, and show how they are expanding and modifying our understanding of magnetic fields on cool stars.
Surface properties of T Tauri stars
Authors: Bertout Claude , Mennessier Catherine
Published: July 2016

We focus here on those T Tauri star properties that make it worthwhile to Doppler-image these young stellar objects, namely magnetic structures and accretion features. We then comment on recent results obtained for two bright, fast rotating weak-line T Tauri stars.
Doppler images of the Pleiades ZAMS stars HII 686 and HII 3163
Authors: Stout–Batalha N. M. , Vogt S. S.
Published: July 2016

Of the steadily increasing number of Doppler Images appearing in the literature, the majority are of the RS CVn subclass of binary stars. The large rotational velocities and dynamo action of these stars is probably attributable to tidal spin-up of the active subgiant star by its binary companion. Their dynamos and resultant surface features (starspots) are thus almost certainly influenced by the companion. As such, these objects are not the ideal testing ground for comparison with single-star solar-like activity. Recently, a handful of Doppler images of single late-type main sequence and pre-main sequence stars have appeared in the literature. Pre-main sequence stars include V410 Tau (Joncour, Bertout, & Menard 1994), (Strassmeier, Welty, & Rice 1994), (Hatzes 1995) and HD 283572 (Joncour, Bertout, & Bouvier 1994). The main sequence stars include AB Dor (Collier Cameron & Unruh 1994), (Kürster, Schmitt, & Cutispoto 1994) and LQ Hya (Strassmeier, et al. 1993), (Saar & Piskunov 1994). These studies suggest that high-latitude dark spots are common to all rapidly-rotating stars, although, the spots found in the above work do not symmetrically straddle the pole as do polar spots of rapidly-rotating RS CVn binary stars.
Chromospheric heating in late–type stars: evidence for magnetic and nonmagnetic surface structure
Authors: Cuntz Manfred
Published: July 2016

The aim of this paper is to evaluate recent observational and theoretical results concerning the physics of chromospheric heating as inferred from IUE, HST-GHRS and ROSAT data. These results are discussed in conjunction with theoretical model calculations based on acoustic and magnetic heating to infer some conclusions about the magnetic and nonmagnetic surface structure of cool luminous stars. I find that most types of stars may exhibit both magnetic and nonmagnetic structures. Candidates for pure nonmagnetic surface structure include M-type giants and supergiants. M-type supergiants are also ideal candidates for identifying direct links between the appearance of hot spots on the stellar surface (perhaps caused by large convective bubbles) and temporarily increased chromospheric heating and emission.
Stellar prominences
Authors: Cameron Andrew Collier
Published: July 2016

Stellar coronae, like the interstellar medium, are multi-phase media. Physical conditions in different parts of the corona allow material to exist in thermal equilibrium either as a tenuous X-ray plasma at temperatures of several million degrees, or in a denser form at temperatures low enough for hydrogen to recombine.
Relations between photospheric structure and X-ray emission
Authors: Kürster M.
Published: July 2016

The relation between photospheric and coronal active regions in late–type stars is studied from two different points of departure. First, I report on 5 years of ROSAT X–ray monitoring of the active young K–star AB Dor. I compare the X–ray data with 16 years of V–band brightness monitoring showing a 10–year decline between 1978 and 1989 and a subsequent rise phase. Quite differently, the X–ray flux of AB Dor (while exhibiting strong variability on time scales of minutes to weeks) reveals no pronounced long–term trend over the 5 years of the program. This supports the concept of a saturated corona. Second, I present rotationally modulated ROSAT X–ray light curves of three active stars (AB Dor, CF Tuc, YY Men) and compare them with contemporaneous Doppler images. I demonstrate that it is possible to explain the X–ray light curves by coronal emission regions that are spatially related with photospheric active regions. I discuss the concept of X–ray bright loops connecting the major star spot complexes.
On radio emission and related X-rays in solar-like stellar coronae
Authors: Güdel M.
Published: July 2016

Selected results relevant to coronal structuring in solar-like single stars based on combined radio and X-ray information are presented. Nonthermal radio and thermal soft X-ray emissions from coronal solar-like stars provide direct information on particle acceleration and coronal heating in the magnetically confined outer atmospheres. The structural relationship between the emission sources is mostly inferred from indirect arguments such as rotational modulation or gyroresonance emission. Direct VLBI provides evidence of resolved, extended coronae on solar-like stars.
New models for the convective flux in stellar atmospheres
Authors: Kupka F.
Published: July 2016

Over the past decades various forms of the mixing length theory (MLT) have been used to describe convection in stellar atmospheres. Recent advances in turbulence theory now allow for major improvements in modelling thermal convection. We review several models for convection which have been derived from turbulence theory, and describe one of them, the “CM model”, in detail. The CM model has been used in several stellar evolution and helioseismology codes during the last four years and has now been applied to model atmospheres. An overwiew comparing stellar atmosphere models based on the CM formulation with its MLT predecessors indicates improvements on model atmospheres for A and F stars.
The Legacy of the Struves for the Establishment of an Inertial Coordinate System on the Sky
Authors: Batten Alan H.
Published: July 2016

Contributions made by Vassily Yakovlevich Struve and his son Otto Vassilyevich to the eventual establishment of an inertial frame of reference on the sky are discussed under five heads: (i) the foundation of Pulkovo Observatory, (ii) instrumentation, (iii) Vassily Yakovlevich's determination of the constant of aberration, (iv) Otto Vassilyevich's determination of the coefficient of precession and (v) international cooperation.
Pulkovo Observatory's Status in 19th Century Positional Astronomy
Authors: Krisciunas Kevin
Published: July 2016

The most significant basis of the reputation of a scientific organization is the accuracy and influence of its work. From a comparison of values of certain astronomical constants and stellar parallaxes obtained at Pulkovo and elsewhere, the extremely high weight given to the Pulkovo values (e.g. by Newcomb) is further justified in retrospect given the small deviations between Pulkovo values and the “modern” values accepted a century later.
The IAU Working Group on Reference Systems
Authors: Hughes James A.
Published: July 2016

The IAU Working Group on Reference Systems (WG) was founded by a Commission Resolution passed at the XXth General Assembly in Baltimore in 1988. Since most, if not all, participants in this meeting are familiar with that resolution, it will not be discussed here. Background material may be found, for example, in Highlights of Astronomy, XX General Assembly (1988, Ed. D. McNally). Particular attention is called to the reports by B. Morando, R. Duncombe and J.A. Hughes (pp. 482-500) which were given as part of the Joint Commission Meeting, Towards Milliarcsecond Accuracy, chaired by P.K. Seidelmann. This short presentation will provide a description of the current state of affairs of the WG, which is chaired by the speaker.
CONFOR: A New Program for Determining the Connection Between Radio and Optical Reference Frames
Authors: Gubanov V.S. , Kumkova I.I. , Tel'Nyuk-Adamchuk V.V.
Published: July 2016

The program for establishment of a link between the fundamental system FK5 and the radioastronomical coordinate system is described. The program includes photographic and meridian observations of extragalactic radio/optical sources and intermediate reference stars. Observatories of the USSR, GDR and Yugoslavia are participating in the project.
The Nikolaev Axial Meridian Circle: The Present and Future Status
Authors: Shornikov O.E. , Shulga A.V. , Liadovoi N.S. , Kashtalian S.L. , Maigurov P.V.
Published: July 2016

Some information on the construction of the AMC was given at IAU Colloquium 100 in Belgrade. The present paper reports the first results of trial observations of star right ascensions. At present the instrument is being prepared for semiautomatic absolute and relative night-time and day-time observations. The scheme of the instrument, principal units and calculations of their parameters are estimated and an observational programme is proposed.
Constructions of Astrometric Instrumentation at Pulkovo Observatory
Authors: Yershov V.N. , Streletsky Yu.S. , Lebedev N.V.
Published: July 2016

Past and present construction of astrometric instrumentation at Pulkovo is discussed.
Positional Observations of Components of Triple Stars for the Hipparcos and HST Missions
Authors: Anosova J. P. , Orlov V. V.
Published: July 2016

This work has been made in accordance with the plan of the International Working Group “Double Stars: HIPPARCOS Input Catalogue Consortium.” The precise coordinates for the components of the triple stars from the programs of the Astronomical Observatory (AO) of Leningrad State University (LSU) and the Uccle zone (declination from +30° to +50°) are determined. The work has been made by two methods: (1) special astrometrical observations for about 70 triple stars; some colleagues from the observatories in Pulkovo, Nikolaev, and Goloseevo (USSR), as well as from Belgrade (Yugoslavia) have taken part in this work; (2) statistical treatment for about 200 triple stars, using the data of the catalogues ADS and WDS—all available positional observations of the relative coordinates of the components.

Also, the special observations of the triple stars in Pulkovo and Belgrade have been used, as well as the data from the catalogue by Ch. Worley from 1820 to 1988. The old observations by W. Struve in 1820-1830 play an important role. The data obtained are used for the compilation of the observational programs of the AO of LSU by the HIPPARCOS and HST.
Problem of Using Lunar Positional Observations for Determination of Zero-Points of Fundamental Star Catalogues
Authors: Fomin V. A.
Published: July 2016

The long series of meridian observations of the Moon can be used for the precise determination of the equinox- and equator-corrections of a star catalogue. Systematic errors of different charts of the lunar marginal zone used for the reduction of the lunar limb observations have no influence on the determination of the secular variations of the zero-points of the fundamental coordinate system.

From meridian observations of the lunar limb made during the interval 1923-1977 in Washington, Greenwich, Cape and Tokyo the following estimate is found for the correction to the right ascension system of the FK4 catalogue:

which is in disagreement with the values used for the compilation of the FK5 catalogue.
On the Definition of an “Inertial Coordinate System”
Authors: Peruansky S. S.
Published: July 2016

Astrometry is a branch of science which develops methods for the quantitative descriptions of places and time instants of astronomical events on the basis of observations of celestial bodies. For this purpose a theoretical coordinate system is introduced (e.g. equatorial a, α, δ). The aim of astrometry is to apply this system to the observed reference objects (stars, planets etc.) so that their coordinates α(t), δ(t) can be calculated according to the relations α(t) =f1(Pk, t-to) and δ(t) =f2(Pk, t-to) where Pk are parameters, to is the conventional time instant and t is the current time. In order to understand the term inertial coordinate system assume that the coordinates α(t), δ(ti), i=1,2,…n are used for plotting the coordinate origins. If these coincide then the system is conventional-fixed and therefore inertial. Thus, the inertial coordinate system in astrometry is a conventional-fixed reference frame reproduced with the use of celestial bodies whose law of motion is known with sufficient accuracy.
The Optimum Conventional Terrestrial System Determined by VLBI and SLR Stations
Authors: Kosek W. , Kolaczek B.
Published: July 2016

The optimum Conventional Terrestrial System (CTS) can be defined by accurate coordinates of some number of stations distributed homogeneously all over the world. There are scores of laser and VLBI stations whose coordinates are known with high accuracy of the order of 1-2 cm. There are many CTS defined by the sets of station coordinates determined in the process of determination of the Earth rotation paramaters and the Earth gravity field. Presently existing stations are not distributed homogeneously on the Earth. They are located mostly in Europe and in North America. In this situation, the errors of orientation of axes and origin positions are not equal. Some of them, based on a small number of not homogeneously distributed stations, are not well-defined (stable).
Reference Surfaces and Global Figure Parameters of the Terrestrial Planetary Bodies
Authors: Kamensky K.K.
Published: July 2016

For connecting the inertial coordinate system with the non-inertial planetocentric one we need to know values of the fundamental astronomical constants as well as global figure parameters of the planet. We distinguish among planetary figures a dynamical, a level, and hypsometric figures.
The Tycho Project On-Board the Hipparcos Satellite
Authors: Høg E.
Published: July 2016

The Hipparcos mission had to be revised because the satellite did not reach the circular geostationary orbit. Observations from the elliptical transfer orbit will be degraded in the sense that good quality observations are expected, but only during less than 50 percent of the total time, and the mission duration will probably be less than 2.5 years. If the mission lasts 12 months a Tycho catalogue is expected containing at least 200 000 stars with typical accuracies of 0.10 arcsec for positions and 0.10 mag for B and V magnitudes.
A Strategy for Linking HIPPARCOS to an Extra-Galactic Reference Frame
Authors: Argue A. N.
Published: July 2016

The strategy for linking the HIPPARCOS Catalogue to extragalactic objects originally devised for the geostationary orbit, is no longer adequate for the elliptical orbit to which the satellite is now confined, but useful improvements in the rotation matrix may be obtained by incorporating proper motions from certain other catalogues and from ground based absolute proper motions.
Regatta-Astro Project: Astrometric Studies From Small Space Laboratory
Authors: Avanesov G. , Vavaev V. , Ziman Ya. , Kogan A. , Kostenko V. , Krasikov V. , Fedotov V. , Heifets V. , Chesnokov Yu.
Published: July 2016

The REGATTA-ASTRO project provides a great set of astrometric and photometric measurements from Small Space Laboratory (SSL). SSL is a special spacecraft being designed at the Space Research Institute, USSR Academy of Sciences. The main feature of this spacecraft is the attitude control by solar light pressure. The main objective of the project is to compile precise global catalogues of star positions, parallaxes and proper motion containing stars with magnitude up to 8-9 and a position accuracy of 0.″01. The astrometric concept of the project is based on a highly deterministic spacecraft angular motion and numerous observations of each star using wide-angle TV cameras with CCD detectors. The SSL computer provides measurement data pre-processing, photometric referencing and data compression. Ground-based computers process the data statistically. The estimated vector includes star coordinates, SSL angular motion parameters and generalized distortion of the instruments used.
Celestial Coordinate System and the FK5 Catalogue
Authors: Gulyaev A. P.
Published: July 2016

To study the motion of the celestial objects in a reference frame one should Know the evolution of the frame itself, In our case it the motion of the origin of coordinates and the proper motions of the objects, the system is based upon.
First Results From the New Micrometer on the Carlsberg Automatic Meridian Circle
Authors: Fabricius C. , Helmer L. , Einicke O. H. , Morrison L. V. , Buontempo M. E. , Argyle R. W. , Quijano L. , Muiños J.L.
Published: July 2016

A new micrometer has been in operation on the Carlsberg Automatic Meridian Circle since May 1988. The zenith mean error for one observation has improved from O.″19 to 0.″14 and the limiting magnitude from 13m.2 to 14m.8. The first meridian observations of Pluto and observations of nine extragalactic objects are briefly discussed.
The SRS Catalog of 20,488 Star Positions Culmination of an International Cooperative Effort
Authors: Smith C. A. , Corbin T. E. , Hughes J. A. , Jackson E. S. , Khrutskaya E. V. , Polozhentsev A. D. , Polozhentsev D. D. , Yagudin L. I. , Zverev M. S.
Published: July 2016

A major international effort to observe and compile the results of observations from many transit circle programs into a single catalog of positions referred to the FK4 system came to a conclusion with the completion and distribution of the Southern Reference Star (SRS) catalog of 20,488 stars. Previous discussions focussed on the adjustments to the observational material to refer it to the FK4 system and on the random errors as estimated from residual differences. In the present discussion, we give the results of internal comparisons which have been made between the individual contributing catalogs and the final combined SRS catalog. Also, results of a comparison between the SRS catalog and the AGK3R catalog are given where they overlap in the declination zone from +5 to −5 degrees. The possibility of magnitude equation and color error in the SRS catalog is discussed.

The reduction procedure used to transform the version of the SRS catalog based on the FK4/B1950.0 system to the version based on the FK5/J2000.0 system is given.