bluuebunny/crossref_metadata_2025 huggingface dataset:
Photometric characteristics of the Be stars: almost twenty years of UBV monitoring at the Hvar observatory
Authors: Pavlovski K. , Božić H. , Ružić Ž. , Harmanec P. , Horn J. , Koubský P. , Juza K. , Hadrava P. , Kříž S. , Štefl S. , Žďársky F.
Published: July 2016

Since their discovery (by Father Secchi in 1866) until the end of sixties, Be stars were not a subject of any systematic studies of their possible light and colour variations. Already at that time, the astronomical literature contained ample evidence showing that a number of Be stars were light variables. However, almost all such findings resulted as by-products of studies of different or wider groups of objects. Feinstein (1968) was probably the first who pointed out explicitly that many Be stars are light variables. A pioneering study which was aimed at the detection of light variations of a large group of Be stars by means of differential photoelectric photometry was carried out by Haupt & Schroll (1974).
Rapid multicolour variations of selected southern Be stars
Authors: Štefl S. , Harmanec P. , Baade D.
Published: July 2016

Many previous surveys of the rapid variability of Be stars (e.g., Balona et al. 1987, Cuypers et al. 1989, Balona et al 1992) were limited to the Strömgren b-band only. We have undertaken a new observational effort with the specific aim of studying colour variations. A search for new rapidly variable stars should provide us with statistical material needed to generalize properties of the phenomenon with respect to the stellar parameters. Some preliminary results of these items are presented here.
An improved model of the B0.5e + Be binary system φ Per
Authors: Harmanec P. , Horn J. , Koubský P. , Juza K. , Božić H. , Pavlovski K. , Hubert A.-M , Hubert H.
Published: July 2016

φ Per (HD 10516) is a spectroscopic binary with a 126.699-day period (Ludendorff 1910, Cannon 1910, Harmanec 1985). However, most of the published RV curves of the primary are based on H I shell lines and exhibit a typical distortion with a sharp maximum, shallow minimum and a bump at 0.P4 after the RV maximum (c.f., e.g., Harmanec 1985). There has been controversy on the nature of the secondary. Hynek (1940) and Hendry (1976) concluded that the binary was composed of two B stars. Peters (1976) suggested that the secondary of φ Per is a Roche-lobe filling K giant. Poeckert (1981) reported the discovery of a weak He II 4686 emission which moved in antiphase to the Be primary and suggested that it originated in the disk around the secondary. In his interpretation, the secondary is a helium star, a remnant of an originally more massive star which in the past transferred its mass to the present Be star. There is now no mass tranfer in the system according to Poeckert. Using RVs of the broad absorptions for primary, and of the He II 4686 emission for the secondary, Poeckert obtained two roughly sinusoidal RV curves and M1sin3i = 21.1 m⊙ and M2sin3i = 3.4 m⊙.
Physics of the phase changes of Be stars
Authors: Ghosh K.K.
Published: July 2016

Based on spectroscopic observations of more than 100 Be stars, we present the results of the phase changes of Be stars.
Phase changes in Be stars: The Be-shell and Be phases of Pleione
Authors: Doazan V. , de La Fuente A. , Cramer N. , Barylak M.
Published: July 2016

Phase changes from Be to Be-shell and/or B normal, and conversely, presently remain unpredictable in Be stars (except in some binaries where the transition to a shell phase seems to be associated with the orbital period). Because of their unpredictable character, these phenomena have been monitored in very few cases and are still very poorly understood. However, the existence of phase transitions have strong modelling implications. Under the disk model, the inclination of the star's rotation axis determines the type of spectrum, Be or Be-shell, that a given Be star may exhibit. It is obvious that this picture is contradicted by phase transitions (Doazan 1982).
The photosphere of Pleione
Authors: Zorec J.
Published: July 2016

In this paper we report results concerning the photospheric Balmer discontinuity of Pleione. They show that after the Be → Be-shell phase transitions, the stellar photosphere keeps its characteristics unchanged.
MWC 314 – A new galactic B[e] supergiant
Authors: Miroshnichenko Anatoly S.
Published: July 2016

We present a new study of MWC 314 = BD +14°3887 – a poorly investigated object with strong emission lines and IR excesses. Merrill (1927) payed attention to it because of the presence of hydrogen and Fe II emissions in its spectrum. Swensson (1942) also detected interstellar lines H and K CaII and 4430 Å band, Balmer emissions from Hα to H8, NaI 5890 and 5896 Å emissions and estimated its spectral type as gG2-3 or dG4-5 from the SED in continuum, and B2 from the excitation degree. Photospheric lines and spectral features of late-type stars were not observed. Allen (1973) noted that the object's SED corresponds to that of a late-type star but it might be a symbiotic system or a reddened normal star. The IRAS fluxes were obtained only at 12 and 25 μm. The object is unknown as a radio source. From this we can conclude that this system consists of, at least, a hot star surrounded by a gaseous envelope.
The Structure of the Circumstellar Material in Be Stars
Authors: Waters L.B.F.M. , Marlborough J.M.
Published: July 2016

We review observations that are relevant for the determination of the structure and geometry of the circumstellar envelopes of Be stars. Evidence is summarized suggesting that Be stars have rotating discs. Infrared and radio continuum and line measurements and their interpretation are discussed.
Structure of the circumstellar envelope of Ψ Persei at large radii
Authors: Dougherty S.M. , Taylor A.R.
Published: July 2016

The radiative transfer equation is solved for a generalised disc model of the circumstellar envelope around Ψ Persei to investigate the nature of the long wavelength turndown in the continuum spectrum of Be stars. The flux density and source dimensions at 15 GHz rule out truncation of the circumstellar envelope around Ψ Persei as the cause of the turndown.
A hidden class of Be stars?
Authors: Zaal P.A. , Waters L.B.F.M. , Marlborough J.M. , Geballe T.R.
Published: July 2016

Recently, Brα and Brγ emission was detected in the infrared spectrum of the B0.2V star τ Scorpii, without noticeable emission in Hα (Waters et al. A&A 272, L9-L12, 1993). Here we present simple HI recombination line calculations in the infrared and in the optical that demonstrate that there could be a class of B stars with low-density discs, a factor of 100 lower in density compared to normal Be stars, which may have escaped detection so far.
Continuous spectra of circumstellar envelopes of Be stars
Authors: Rohe-Koths D. , Dachs J.
Published: July 2016

Line emission in Be star spectra is accompanied by continuous emission both in the Balmer continuum and in the infrared spectral region, due to the same process that is responsible for Balmer line emission, i.e. to recombination radiation from ionized hydrogen in the extended circumstellar disks surrounding the hot central stars.
Optical Resolution of Be Star Envelopes
Authors: Vakili F. , Mourard D. , Stee P.
Published: July 2016

Probing the atmospheres of Be stars by means of Optical Long Baseline Interferometry (OLBI) is a method still in its infancy. Published observational results in this field can be counted on one hand. In this paper we introduce the principles of OLBI as they apply to observations of Be stars and review results from existing long baseline interferometers. Regular operation of OLBI is most effective when carried out in conjunction with standard techniques such as photometry and spectroscopy. With the next generation of synthetic arrays combining sub-milliarcsecond resolution and a spectral resolution better than 10000, OLBI should be able to address the direct detection of pulsation and magnetic fields.
Smooth winds and clumped winds for early-type stars
Authors: Blomme R. , Runacres M.
Published: July 2016

The use of the IR and radio continuum as a clumping indicator for the stellar wind of early-type stars is investigated.
Line profiles in expanding atmospheres
Authors: Cidale L.
Published: July 2016

The analysis of the UV resonance transitions of superionized species observed in early-type stars suggests the presence of a high temperature region and an outward flow of matter (Snow & Marlborough 1976).
The hard life of clumps in atmospheres of early-type stars
Authors: Kholtygin A.F.
Published: July 2016

As has been recently established, the atmospheres of early-type stars are strongly disheveled. These atmospheres consist of dense clumps and a more rarefied interclump medium. We consider the forces that determine the motion of the clumps. We show that the main force is gravitational attraction of the clumps to the star. For stars with a high effective temperature (Teff ≥ 6 · 104 K) it appears that the clump/interclump gas number density ratio is ≥ 30. In this case we can conclude that the clumps are formed by shock waves. Some evidence as to the existence of gas jets in the atmospheres of Wolf-Rayet stars have recently been presented. We propose that such jets may be a common feature of all early-type stars. Profiles of HeI lines in spectra of clumped atmospheres with jets have been calculated.
High resolution spectroscopy at the ESO 50 cm telescope: spectroscopic monitoring of luminous hot stars
Authors: Kaufer A. , Mandel H. , Stahl O. , Wolf B. , Szeifert Th. , Gäng Th , Gummersbach C.A. , Kovacs J.
Published: July 2016

Galactic Luminous Blue Variables and A- and B-type supergiants were monitored spectroscopically with high resolution in wavelength and time. Line profile variations on different timescales are found.
The stellar wind of χ2 Ori and its variability
Authors: Sapar L. , Sapar A.
Published: July 2016

The resonance spectral lines of high-resolution IUE spectra of χ2 Ori (B2I) have been studied with the aim to determine in more detail the physical status of the stellar wind and its variability due to shell outbursts and clumps superimposed on the isotropic stellar wind. Some general features of resonance spectral line profiles have been studied and explained in physical terms using χ2 Ori as a specimen.
CORALIE–ELODIE new planets and planetary systems. Looking for fossil traces of formation and evolution
Authors: Udry S. , Mayor M. , Queloz D.
Published: July 2016

6 new extra-solar planet candidates (HD 6434 b, HD 19994 b, HD 83443c, HD 92788b, HD 121504b, HD 190228b) are announced as part of our planet-search programmes in the northern and southern hemispheres. HD 83443 c is member of a 2-planet system with Saturnian and sub-Saturnian masses. Another system including a planet + a very low-mass brown dwarf orbiting HD 168443 is also presented. These 2 new systems and the new planetary detections rise to 25 the number of ELODIE and CORALIE candidates with minimum masses ≤20MJup. The orbital element distributions of giant-planet candidates, like the secondary mass function, the eccentricity and period distributions, compared to the equivalent distributions for spectroscopic binaries, strongly suggest different formation mechanisms for the two populations.
Results from Microlensing Searches for Extrasolar Planets
Authors: Sackett Penny D.
Published: July 2016

Specially-designed microlensing searches, some of which have been underway for several years, are sensitive to extrasolar planets orbiting the most common stars in our Galaxy. Microlensing is particularly well-suited to the detection of Jupiter-mass planets orbiting their parent stars at several AU. Since Jovian analogs are thought to influence the subsequent evolution of most planetary systems, they are particularly important to study. The orbital radii and distances to the planetary systems probed by microlensing are larger than those currently studied by radial velocity techniques; the two methods are thus complementary. Recent results from microlensing searches are discussed, including constraints on Jovian analogs orbiting typical Galactic stars. Benefits and drawbacks of the technique for the characterization of planetary systems, and future prospects are briefly reviewed.
Search of extra-solar planets with the spectrograph EMILIE and AAA system
Authors: Bouchy F. , Schmitt J. , Bertaux J. L. , Connes P.
Published: July 2016

The method of stellar velocity variations measurement has recently shown its capability by discovering tens of extra-solar planets. Accuracies achieved today are in the range of 3 to 10 m/s. The spectrograph EMILIE coupled to the Absolute Astronomical Accelerometer (AAA) system and established at the 1.52 m telescope of the Observatoire de Haute Provence is an instrument which aims at reaching an accuracy better than 1 m/s, long term. Results on some typical stars are presented.
Probing the Outskirts of an Extrasolar Planet with HST Time-Series Photometry
Authors: Charbonneau David , Brown Timothy M. , Gilliland Ronald L. , Noyes Robert W. , Burrows Adam
Published: July 2016

We observed 4 planetary transits of HD 209458 with the STIS spectrograph on HST, and generated a photometric time series with extremely rapid cadence and high precision. We use these data to better constrain the orbital, stellar, and planetary parameters, and to search for circumplanetary rings and planetary satellites.
Are there Jupiters in the α Centauri system?
Authors: Endl Michael , Kürster Martin , Els Sebastian , Hatzes Artie P. , Cochran William D. , Dennerl Konrad , Döbereiner Stefan
Published: July 2016

We present the results of five years of high precision radial velocity (RV) monitoring of the α Centauri system. Observations were performed with the ESO 1.4m CAT telescope and the Coudé Echelle Spectrometer (CES) on La Silla. From the achieved RV precision we establish the detection threshold for Jovian planets in orbit around α Centauri A & B. Together with the known dynamical limits for stable planetary orbits we can set strong constraints on the presence of giant planets in our neighbouring binary system.
Timescales of Disk Evolution and Planet Formation
Authors: Jayawardhana Ray
Published: July 2016

It has been suggested that circumstellar disks evolve from dense, actively accreting structures to low-mass, replenished remnants. During this transition, grains may assemble into planetesimals, or the disk may be cleared by newborn planets. Recently identified nearby groups of young stars provide valuable laboratories for probing disk evolution. I discuss the properties of dust disks in the TW Hydrae Association and the MBM 12 cloud, and compare the results to other studies of disk evolution and planet formation timescales.
Modal structure of earth-like planets in the presence of magnetic field
Authors: Nasiri S.
Published: July 2016

Free oscillations of the earth received much attention by the pioneering work of Benioff (1954). He observed an oscillation period of 57 minutes by investigating the data of Kamchatka earthquake and assumed the free oscillations of the earth as its origin. Since then many aspects of the problem has been investigated by different authors.
Orbital Eccentricity Growth through Disc–Companion Tidal Interactions
Authors: Nelson Richard P. , Papaloizou John C.B. , Masset Frédéric
Published: July 2016

We present the results of 2–D non linear hydrodynamic simulations performed to examine the driving of orbital eccentricity through disc-companion tidal interaction. We examine the eccentricity evolution for companion masses, mp, in the range 1 > mp >; 30 MJupiter. The disc model we employ is similar to a minimum mass solar nebula model.

We find that there is a transition in behaviour, characterised by a rapid growth in eccentricity, for companion masses mp ≳ 20 MJupiter. Companions with masses below this limit show essentially no growth in eccentricity, for the disc model parameters that we examine. Our results suggest that if giant planets form from protostellar discs with properties similar to those studied in this paper, then the observed orbital eccentricities of the extrasolar planets are not a consequence of tidal interaction with their protostellar discs during formation.
Semi-Analytic Formulas of Velocity Stirring Rates in Particle Disks
Authors: Ohtsuki Keiji , Stewart Glen R. , Ida Shigeru
Published: July 2016

We have obtained viscous stirring and dynamical friction rates of planetesimals based on three-body orbital integrations, taking into account the Rayleigh distribution of eccentricities and inclinations. We have found that the evolution of root mean square eccentricities and inclinations calculated by using these rates agrees with N-body simulations quite well.
General-relativistic Linear Perturbation Theory on Elastical Astronomical Bodies
Authors: Wu Xuejun , Xu Chongming , Soffel Michael
Published: July 2016

The general relativistic perturbations of a uniformly rotating and axisymmetric elastic deformable astronomical body in the first post-Newtonian approximation of Einstein's general relativity is discussed in a co-rotating coordinates. The main new results presented here are the post-Newtonian variations of the energy and Euler equation, which at the Newtonian level of accuracy is so called Jeffreys-Vicente equation and it play a fundamental role for the description of global geodynamics in the classical geophysics. Our results will be useful to treat the relativistic nutation and precession of the Earth and other planets.
The Role of Clouds in Brown Dwarf and Extrasolar Giant Planet Atmospheres
Authors: Marley Mark S. , Ackerman Andrew S.
Published: July 2016

Clouds and hazes are important throughout our solar system and in the atmospheres of brown dwarfs and extrasolar giant planets. Among the brown dwarfs, clouds control the colors and spectra of the L-dwarfs; the disappearance of clouds helps herald the arrival of the T-dwarfs. The structure and composition of clouds will be among the first remote-sensing results from the direct detection of extrasolar giant planets.
Radiative equilibrium models of “hot Jupiters”
Authors: Goukenleuque Cédric , Bézard Bruno , Lellouch Emmanuel
Published: July 2016

We present an extension of our equilibrium model, initially applied to 51 Peg b (Goukenleuque et al. 2000), to other irradiated extrasolar planets with different orbital distances (up to 1 AU). The model yields the mean atmospheric thermal structure and predicts the reflected spectral flux as well as the thermal flux emerging from such planets, in the visible and in the infrared wavelength ranges.
The inner 1 AU of circumstellar disks
Authors: Akeson R. L. , Ciardi D. R. , van Belle G.T. , Creech-Eakman M.J. , Lada E. A.
Published: July 2016

Infrared observations of two T Tauri stars, T Tau and SU Aur, were obtained using long-baseline interferometry with the Palomar Testbed Interferometer (PTI). For both sources, the 2.2 micron emission is resolved at PTF's nominal fringe spacing of 4 milliarcsec. Using simple circumstellar material distributions, we find that the infrared emission region is tenths of AU in size. We also compare our results from PTI with accretion disk models inferred from spectral energy distributions.
Penetration of Interstellar Dust Aggregates Into Circumstellar Dust Disks
Authors: Kimura Hiroshi , Mann Ingrid
Published: July 2016

Interstellar dust particles, which are supposedly aggregates, penetrate dust disks around stars because of the star's motion relative to the surrounding interstellar medium (ISM). We discuss the interrelation of the physical properties of local interstellar dust, the relative motion of the star and the surrounding ISM, and the evolution of the circumstellar disk.
Spectroscopic study of stars with dusty disks
Authors: Sivarani T. , Parthasarathy M.
Published: July 2016

We have selected several stars with far-IR (IRAS) fluxes indicating the presence of circumstellar dust shells and disks. In this paper we present an analysis of the spectra of these stars. In several of these stars we find evidence for gaseous envelopes in addition to dusty disks. In some of these stars we find complex and variable Ha profiles indicating the variations in the circumstellar envelopes and disks.
Gas evolution in protoplanetary disks
Authors: Thi W. F. , van Dishoeck E.F. , van Zadelhoff G.J. , Blake G. A. , Mannings V. , Sargent A. I. , Horn J. , Becklin E. E. , van den Ancker M.E. , Natta A.
Published: July 2016

We present the results of a study of the evolution of the gas and dust in disks around T Tauri, Herbig Ae and Vega-like stars. We observed the two lowest rotational lines of H2 with the ISO-SWS as well as 12CO 3–2 and 13CO 3–2 with the JCMT, and CO 6–5 with the CSO. The H2 lines trace the warm (∽ 100 K) inner region whereas the CO lines probe the colder outer disks. Substantial amounts of H2 have been detected toward T Tauri and Herbig Ae stars, and, surprisingly, also around three Vega-like objects (49 Cet, HD 135344 and β Pictoris). In contrast with previous conclusions derived from CO data, a significant mass of warm gas is found to persist up to ages of several tens of Myrs, suggesting that slow formation of gas-rich giant planets is possible.
Observations of YSO Circumstellar Discs
Authors: Ward-Thompson D. , André P. , Lay O. P.
Published: July 2016

We present the results of short baseline interferometry observations at submillimetre wavelengths, using a two-element interferometer comprising the JCMT/CSO, of circumstellar discs around young YSOs. We model data for the Class 0 protostar IRAS03282 and the Class I protostar L1709B with discs and compare them with previously published results. We find evidence for the ratio of the disc to envelope mass to increase as the objects evolve.
The Drake equation may need new factors based on peculiarities of planets of Sun-like stars
Authors: Ksanfomality L. V.
Published: July 2016

N = RsfpneflfifcL. This well known Drake equation denoting the number N of civilizations in the Galaxy, includes a factor fp that is the fraction of stars that have planetary systems, and another factor ne that is the mean number of planets suitable for life. The latter is usually understood as the number of planets within the habitable zone. When the Solar system remained a unique object of its kind the sense of fp and ne seemed to be clear. There is now a limited statistic in hand about the features of other planetary systems, permitting a rough estimation of fp and ne (based on the list of 32 star companions, compiled by G. Marcy, 14.02.2000).
Ground-based exoplanet near-infrared search by imaging and spectroscopy: 3 new companion candidates in TWA
Authors: Neuhäuser Ralph , Huélamo Nuria , Guenther Eike W. , Brandner Wolfgang , Alves João , Comerón Fernando , Petr Monika G. , Cuby Jean-Gabriel
Published: July 2016

We report first results from our ground-based infrared imaging search for sub-stellar companions (brown dwarfs and giant planets) of young (up to 100 Myrs) nearby (up to 100 pc) stars, where companions should be well separated from the central stars and still relatively bright due to ongoing accretion and/or contraction. Our observations are performed mainly with SOFI and SHARP at the ESO 3.5m NTT on La Silla (imaging) and with ISAAC at the ESO 8.2m Antu (VLT-UT1) on Cerro Paranal (imaging and spectroscopy), all in the H- and K-bands. Here, we present new companion candidates1 around three T Tauri stars (TWA-8 A, RXJ1121.1-3845, and RXJ1121.3-3447 N) in the TW Hya group, which would have been sub-stellar if at the same distance and age as the T Tauri stars, but are found to be background stars by spectroscopy.
Precision Astrometry with the Space Interferometry Mission
Authors: Unwin Stephen C.
Published: July 2016

SIM - the Space Interferometry Mission - will be the first of a new generation of space instruments using interferometry. Designed for precision astrometry, it will be a 10-meter optical interferometer providing 4 microarcsecond (μas) absolute position measurements over the whole sky, using a grid of stars (and quasars) for a reference frame. Maintaining its astrometric precision on stars as faint as 20 magnitude, it will far surpass the capability of ground-based astrometry, opening up a new era of space-based astrometry. A wide range of astrophysics problems will be addressed by SIM, including formation and dynamics of our Galaxy, calibration of the cosmic distance scale, and fundamental stellar astrophysics. SIM will search for planetary companions to nearby stars, by detecting the well-known astrometric ‘wobble’ signature with a single-measurement precision of 1 μas, enabling the detection of planets down to about an Earth mass. SIM will serve as a technology pathfinder for NA8A's Terrestrial Planet Finder. Launch is currently planned for 2008, with a mission duration of 5 years.
Simulations of Relativistic Jet Formation in Compact Radio Sources
Authors: Meier David L.
Published: July 2016

I review recent numerical and analytic work on the magnetohydrodynamic (MHD) model of jet formation in active galactic nuclei, with an emphasis on producing the highly relativistic outflows and high radio luminosities observed in the most powerful sources.
The Central Dark Mass of the Milky Way
Authors: Eckart A. , Genzel R. , Ott T.
Published: July 2016

Measurements of the proper motions and radial velocities of stars in the central cluster of the Milky Way have revealed the presence of a 2-3 million solar mass black hole at the position of the compact radio source Sagittarius A* (SgrA*). The overall stellar motions do not deviate strongly from isotropy and are consistent with a spherical isothermal stellar cluster. Speckle spectroscopy with SHARP at the NTT and slit spectroscopy with ISAAC at the VLT suggests that several of them are early type stars. This is consistent with the idea that these stars are members of an early type cluster with small angular momentum and therefore are now in the immediate vicinity of SgrA*. Most recent data now allows to measure the curvatures of the stellar orbits for a few of the stars that are closest to the center and have the largest proper motions of up to 1400 km/s. The curvatures indicate that the stars indeed orbit the central compact object and will allow to further determine its mass and compactness.
The Sub-Parsec Structure of Accretion Disks as Revealed by VLBI Imaging of Free-Free Absorption
Authors: Jones D.L. , Wehrle A.E. , Piner B.G. , Meier D.L.
Published: July 2016

The physical conditions in the inner parsec of accretion disks believed to orbit the central black holes in active galactic nuclei can be probed by imaging the absorption of background radio emission by ionized gas in the disk. High angular resolution radio observations of several nearby galaxies at multiple frequencies have revealed evidence for free-free absorption by disks or tori of ionized gas. The depth and angular width of the absorption increases with decreasing frequency. The longest possible baselines are needed to provide adequate angular resolution at low frequencies where the effects of free-free absorption are most evident. Recent results from VSOP as well as ground-based VLBI observations of the nearby galaxy NGC 4261 illustrate the critical importance of high angular resolution at frequencies below 10 GHz.
VLBA Studies of the Accretion Region in NGC 1275
Authors: Walker R. C. , Kellermann K. I. , Dhawan V. , Romney J. D. , Anantharamaiah K. R. , Vermeulen R. C. , Alef W.
Published: July 2016

VLBA observations of the two-sided emission structures in 3C 84 have been used to study the ionized gas in the vicinity of the presumed accretion disk on parsec scales. Strong free-free absorption is seen with a radial gradient, but only upper limits have been obtained on a stimulated recombination line at 23 GHz.
Definitive Measurements of a Supermassive Black Hole and Its Surrounding Mass
Authors: Dressel Linda
Published: July 2016

A discrete thin rotating emission-line disk is ideal for determining the mass of a supermassive black hole in the nucleus of a galaxy. One can use high resolution imaging in combination with a matrix of spatially resolved velocity measurements to confirm the simple geometry and kinematics of the disk. If the disk remains bright and orderly beyond the sphere of influence of the black hole, with motion driven predominantly by gravitational force, one can also measure the density of the surrounding matter in the nucleus. This is being done for the bright Liner galaxy NGC 3998.
Intraday Variability and Microarcsecond Structure in Blazar Cores
Authors: Jauncey David L. , Kedziora-Chudczer Lucyna , Lovell J. E. J. , Macquart Jean-Pierre , Nicolson George D. , Perley Rick A. , Reynolds John E. , Tzioumis A.K. , Wieringa Mark A. , Bignall Hayley E.
Published: July 2016

The accumulation of evidence now strongly favours interstellar scintillation (ISS) as the principal mechanism causing intra-day variability (IDV) at cm wavelengths. While ISS reduces the implied brightness temperatures, they remain uncomfortably high. The distance to the scattering screen is an important parameter in determining the actual brightness temperature encountered. The high brightness temperatures, the presence of strong and variable circular polarization and the observed lifetimes of a decade or more for several IDV sources, pose significant problems for synchrotron theory.

“The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.” William Shakespeare, Julius Caesar
Circular Polarization in Scintillating Sources
Authors: Macquart Jean-Pierre , Kedziora-Chudczer Lucyna , Jauncey David L. , Sault R. , Rayner David P.
Published: July 2016

We discuss the detection of variable circular polarization (CP) in several scintillating radio sources: PKS 1519-273, PKS 0405-385 and Sgr A*. In all cases the CP is variable, with the fractional variability in the CP greatly exceeding that in total intensity.
The GB6 4.85 GHz Radio Variability Catalog
Authors: Gregory P.C. , Capak P. , Gasson D. , Scott W.K.
Published: July 2016

The NRAO seven-beam receiver was used on the former Green Bank 91 m telescope, during 1986 November and 1987 October, to repeatedly survey the declination band (0° < δ < +75°) at 4.85 GHz. This data base has been used to extract variability information for sources in the GB6 catalog, a large unbiased sample of sources derived from the combined survey images. Long term variability information (one year time base) is available for 97% of the 75,162 GB6 sources and short term variability (few day) is available for 20,963 sources. This large variability data base is available to the astronomical community through http://pulsar.physics.ubc.ca/gregory/index.html.
CJ-F: The Kinematics of 241 AGN
Authors: Britzen S. , Vermeulen R.C. , Taylor G.B. , Campbell R.M. , Browne I.W. , Wilkinson P. , Pearson T.J. , Readhead A. C. S.
Published: July 2016

We present first results from the analysis of multi-epoch VLBI observations of 241 sources in the CJ-F sample (Caltech Jodrell-Flat-spectrum, Taylor et al. 1996). We have been obtaining 5 GHz VLBI (global and VLBA) snapshot observations of the CJ-F sources (complete with 293 sources) since 1990 in order to create a valid database for thorough statistical tests of pc-scale jet motion in AGN. All 241 CJ-F AGN have been observed at least three times with the VLBA, which enables us to investigate jet component motions and paths. In particular, we concentrate on the analysis of those properties supposed to be essential for gamma-ray production, i.e., superluminal motion and bending.
Co-ordinated VSOP and Chandra Observations of 0836+710
Authors: Murphy D.W. , Preston R.A. , Piner G.B. , Lister M.L. , Marshall H.L. , Edwards P.G.
Published: July 2016

We briefly describe the radio observations that form part of co-ordinated Chandra, HALCA+VLBA, and VLBA-only observations of the superluminal gamma-ray loud quasar 0836+710. The radio observations were at 6 frequencies (1.6, 5, 8, 15, 22, and 43 GHz) with the two lowest frequency observations being undertaken with the VLBA co-observing with the HALCA spacecraft (the space element of the Japanese VSOP mission). Combining the radio and X-ray data will allow constraints to be placed on the jet Doppler factor.
Milli-arcsecond Scale Rotation Measure in Two CSSs
Authors: Mantovani F. , Ricci R. , Junor W. , Saikia D.J. , Salter C.
Published: July 2016

Two Compact Steep-spectrum Sources (CSSs), 0548+165 and 1524-136, have been observed in dual polarization with the VLBA at 4.9 and 8.4 GHz. Rotation measures (RMs) up to 104 rad m−2 were derived for the jets of both sources. These high values possibly arise due to the external medium interacting with the radio jets, with measured depolarization being due to small-scale inhomogeneities in the medium.
Correlation Between Extended Radio and Line Emission for a Radio-loud Quasar Sample
Authors: Cao Xinwu , Jiang D.R.
Published: July 2016

A strong correlation is present between the extended radio and broad-line emission for a radio-loud quasar sample. The statistic behaviour on the core emission of lobe-dominated quasars is rather different from that of core-dominated quasars. The extended radio luminosity is a good tracer for jet power, while the core luminosity can only be a jet power tracer for core-dominated quasars.
A z = 2.72 Galaxy Gravitationally Lensed by the Cluster MS 1512+36: Reconstruction and Near-infrared Spectroscopy
Authors: Labbé Ivo , Franx Marijn
Published: July 2016

Using archival HST/WFPC2 optical data and near-infrared VLT/ISAAC spectroscopy, the properties of the Lyman-break galaxy cB58 are analyzed. The z = 0.37 galaxy cluster MS1512+36 lenses it into strongly magnified arcs with ample substructure. The data enables an accurate reconstruction of the source, yielding milliarcseconds resolution; an unparalleled view of the central kpc of the z = 2.72 starburst galaxy.
Hyper-Fine Features of the Dust Distribution in the Central Region of the Seyfert Galaxy NGC 4151
Authors: Ohtani Hiroshi , Hattori Takashi , Miyazaki Satoshi , lye Masanori , Komiyama Yutaka , Sasaki Toshiyuki , Kosugi George , team Subaru
Published: July 2016

Fine features of the dust distribution in the central region of NGC 4151 have been studied from high resolution images obtained by the Subaru Telescope. The two dust lanes lying along a circum-nuclear ellipse of 40“ ×20” have been recognized to consist of a number of fine filaments and knots. In the inner region, there has been found dust distributed in a bipolar cone region extending to 5” from the nucleus. This cone is exactly complementary to the well-known bipolar ionized gaseous region. A dense knot is seen at 2” SE from the nucleus, but no torus-like feature is recognized. The masses of neutral gas in the outer lanes and in the inner region are estimated as 106M⊙ and 105M⊙ respectively. These observational results are compared with results of numerical simulations of gas dynamics.
Star Formation in NGC 4038/4039
Authors: Mengel Sabine , Thatte Niranjan , Lehnert Matthew , Genzel Reinhard
Published: July 2016

We performed near infrared integral field spectroscopy of several star clusters and the nuclei of the prototypical merger NGC 4038/39 (“The Antennae”). Near infrared (NIR) images covered both galaxies. The collision of the two gas-rich spiral galaxies has triggered a starburst obvious from a large number of young star clusters. ISO data suggest that the most active star formation occurs in the region where the two galaxy disks overlap. A significant fraction of the total bolometric luminosity of the system is produced there. Since this region is heavily extincted in the optical, the investigation was made in the NIR. Using Brγ emission and CO absorption features as age indicators, we derive the ages and mass estimates of the star clusters from a comparison with stellar synthesis models. Extinction is calculated from the Brγ/Hα ratio. The young, bright star clusters have ages ranging from 4-12 Myrs, while the nuclear starbursts are much older (50-80 Myrs). The overlap region hosts most of the youngest star clusters below ∼8 Myrs, while the northwestern region is dominated by star clusters in the age range between 8 and 12 Myrs. Several regions, including the northern nucleus, show evidence for sequential star formation on small spatial scales (< 100pc).
Molecular ISM and Star Formation Efficiency in the Central Kpc
Authors: Jogee Shardha
Published: July 2016

Why do the circumnuclear (inner 1-2 kpc) regions of some spirals develop starbursts, which are intense short-lived (t ≪ 1 Gyr) episodes of star formation characterized by a high star formation rate per unit mass of molecular gas (SFR/MH2), which I refer to as the star formation efficiency (SFE), while others with comparable gas content become non-starbursts? I address this question and other issues on circumnuclear evolution using high resolution (2” or 100-200 pc) CO (J=1>0) observations from the Owens Valley Radio Observatory, optical and NIR images, along with radio continuum (RC) and Brγ data. The sample galaxies are all nearby, moderately inclined, and include the brightest nearby starbursts comparable to M82 and control non-starbursts. Detailed results are in Jogee (1999) and Jogee, Kenney, & Scoville 2000 (in prep.)
The 3D Structure of the Galactic Bulge from the MACHO Red Clump Stars
Authors: Fux R. , Axelrod T. , Popowski P.
Published: July 2016

Many evidences demonstrate that the Milky Way is a barred galaxy with the near end of the bar pointing in the first Galactic quadrant (e.g. Gerhard 1999 for a review), thus offering an exceptional chance to study the detailed three-dimensional structure and dynamics of a real bar. One of the best tracer of the Galactic bulge/bar are the red clump stars: they are very numerous, sufficiently bright to be detected throughout the bulge, and their absolute I-magnitude has an intrinsic dispersion of only 0.2 magnitude, with a mean value almost independent of colour and metallicity (Paczyński & Stanek 1998, Udalski 2000). Here we outline an ongoing project aiming to recover the 3D bulge stellar distribution as primarily traced by these stars, as in Stanek et al. (1997), but in a non-parametric way and from the VR database of the MACHO experiment within an almost fully observed ∼ 8° × 8° bulge area centred on (l, b) ≈ (4°, − 6°) (e.g. Alcock et al. 1997), soon complemented with I-band photometry.
Small-Scale Structure Deduced from X- and γ-ray Timing Measurements
Authors: Miller M. Coleman
Published: July 2016

X-ray timing observations of neutron stars and black holes are among the few available probes of ultrastrong magnetic fields, strong gravity, high densities, and the propagation of thermonuclear burning. Here we review the evidence for these effects revealed with data from the Rossi Explorer in the last five years. We also discuss the exciting prospects for making the first quantitative tests of strong-gravity general relativistic predictions with a large-area X-ray timing mission.
The Accretion Discs and Bipolar Jets in Orion KL
Authors: Matveyenko L. I. , Diamond P. J. , Graham D. A.
Published: July 2016

The fine structure of active regions in Orion KL has been studied. It is shown that accretion disks and bipolar outflows accompany star formation. The accretion disks are divided into protoplanetary rings. The H2O super maser emission is associated with the rings and bipolar outflows. The surrounding medium (VLSR=7.74 km/s) amplifies the emission within the maser window by more than two orders of magnitude.
Microquasar Jets: A Comparison with Extragalactic Jets
Authors: Spencer Ralph , De La Force Chris , Stirling Alastair
Published: July 2016

We compare the properties of jets found in extragalactic sources with those recently discovered in the much lower luminosity microquasars in our galaxy.
Face-on SS 433 Stars as a Possible New Type of Extragalactic X-Ray Sources
Authors: Fabrika S. , Mescheryakov A.
Published: July 2016

The object SS433 is a well-known source of relativistic jets, which are formed in supercritical accretion disk. It is very probable that the disk has polar channels and their radiation is collimated (the photo-cones). A face-on SS433 object can appear as ultra-bright and highly variable X-ray source, Lx ˜ 1040 − 1042 erg/s. We discuss the properties of these hypothetical objects and their frequency expected in galaxies. We describe a search for such objects using the ROSAT All Sky Survey and RC3 catalog of galaxies. Among the total 418 positive correlations we find that 142 sources in S and Irr galaxies are unknown as AGNs. Nuclear sources among them still contain many AGNs. Non-nuclear (offset) sources are rather hard, their X-ray luminosities are 1039 − 1041 erg/s. Their observed frequency is about 4–5% per galaxy, that is in agreement with expected frequency of the face-on SS 433 stars. The only way to recognize such stars is their expected violent variability in X rays.
On the Bowshocks Associated with the Orion Proplyds
Authors: Arthur S.J. , Henney W.J. , García-Arredondo F.
Published: July 2016

We investigate the global stellar wind dynamics of the exciting star of the Orion Nebula by using the “proplyds” and their bowshocks as probes of the ram pressure balance conditions in the nebula. This careful analysis is only possible if high resolution data are available, since the proplyds are so small and the bowshocks are so faint.
Evidence of Clumpy Dust Shell Structure in IRC+10216 from K Band Lunar Occultation Observations
Authors: Chandrasekhar T. , Mondal Soumen
Published: July 2016

Lunar occultation observations at 2.2 microns of the inner dust shell of the carbon rich long period variable IRC + 10216 yield a clumpy structure with atleast four components. Comparison with concurrent and earlier speckle observations confirm the presence of these components and show that real spatial changes are taking place at the level of milli arcseconds on time scales of a few years in the inner dust shell of IRC + 10216.
Multi-wavelength Observations of the Red Giant R Doradus with the MAPPIT Interferometer
Authors: Jacob A.P. , Bedding T.R. , Robertson J.G. , Barton J.R. , Haniff C.A. , Marson R.G. , Scholz M.
Published: July 2016

We present visibility measurements of the nearby Mira-like star R Doradus taken over a wide range of wavelengths (650-990 nm). The observations were made using MAPPIT (Masked APerture-Plane Interference Telescope), an interferometer operating at the 3.9-m Anglo-Australian Telescope. We used a slit to mask the telescope aperture and prism to disperse the interference pattern in wavelength. We observed in R Dor strong decreases in visibility within the TiO absorption bands. The results are in general agreement with theory but differ in detail, suggesting that further work is needed to refine the theoretical models.
Cool Giant Stars are Bigger at 712 nm than at 754 nm
Authors: Quirrenbach A. , Mozurkewich D. , Armstrong T. , Buscher D. , Hummel C.
Published: July 2016

We used the Mark III Optical Interferometer on Mt. Wilson in 1991 and 1992 to measure the diameters of 42 stars with 10 nm wide filters centered at 712 nm and at 754 nm. These filters probe the stellar atmosphere in a strong TiO band (712 nm) and in a “continuum” band relatively free of TiO absorption (754 nm). The data were taken on a North-South baseline that could be configured to lengths between 3.0 m and 31.5 m. Observations of the target stars were interleaved with frequent measurements of calibrator stars. The square of the calibrated visibility amplitude V2 was determined as a function of baseline length, and a uniform disk model fitted to these data (for details see Mozurkewich et al. 1991). The average formal error of the diameter measurements - derived from the χ2 of the model fits - is 2.5%. Data for a subset of 12 stars have already been published (Quirrenbach et al. 1993).
Molecular Excitation at the Nucleus of the QSO I Zw 1
Authors: Eckart A. , Schinnerer E. , Staguhn J.
Published: July 2016

We present results from the most recent Plateau de Bure observation of the 12CO(2-1) line towards the nearby QSO I Zw 1.
Molecular Gas Rich Galaxy Pair Unveiled in the Lensed Quasar 0957+561
Authors: Planesas P. , Martin-Pintado J. , Neri R. , Colina L.
Published: July 2016

Molecular gas in the host galaxy of the lensed quasar QSO 0957+561 has been detected at the redshift of 1.414 using the IRAM Plateau de Bure interferometer. This detection shows the extended nature of the molecular gas distribution. The molecular gas mass is 2-4 109 M⊙ and it is distributed in a disk that is several kiloparsecs in diameter. A second, weaker component of CO is interpreted as arising from a close companion galaxy moving at a velocity 440 km s−1 higher than the host galaxy.
Molecular Gas and Star Formation in BIMA SONG Bars
Authors: Sheth Kartik , Vogel S.N. , Harris A.I. , Regan M.W. , Thornley M.D. , Heifer T.T. , Wong T. , Blitz L. , Bock D. C-J.
Published: July 2016

Using a sample of 7 barred spirals from the BIMA Survey of Nearby Galaxies (SONG), we compare the molecular gas distribution in the bar, to recent massive star formation activity. In all 7 galaxies, Hα is offset azimuthally from the CO on the downstream side. The maximum offset, at the bar ends, ranges from 170-570 pc, with an average of 320±120 pc. We discuss whether the observed offsets are consistent with the description of gas flows in bars provided by the two main classes of models: n-body models and hydrodynamic models.
CO Mapping of Spiral Galaxies in the Ursa Major Cluster: An Atlas
Authors: Rhee Myung-Hyun , Chung Aeree , Verheijen Marc , Yun Min S.
Published: July 2016

We present the first results of the OTF CO (J=1-0) mapping of spiral galaxies in the Ursa Major cluster, obtained with the NRAO 12m radio telescope during June 20-27, 1999 and March 23-30, 2000.
Mass Spectrum of the Galactic Center Molecular Clouds
Authors: Miyazaki Atsushi , Tsuboi Masato
Published: July 2016

We have observed three molecular clumps in the Galactic center region in the CS J=2-1 line with the Nobeyama Millimeter Array. We have determined the mass spectrum and other statistical relations for the Galactic center cloud cores. The derived mass spectrum is somewhat steeper than for galactic cloud cores based on molecular line observations. In addition, the spectrum is steeper than that of the large scale Galactic center clumps.
Chandra Studies of Supernova Remnants and Pulsars
Authors: Slane Patrick , Hughes John P. , Rakowski Cara E. , Burrows David N. , Nousek John A. , Garmire Gordon P. , Gaensler Bryan M.
Published: July 2016

With sub-arcsecond angular resolution accompanied by fast time resolution and spatially resolved spectral capabilities, the Chandra X-ray Observatory provides a unique capability for the study of supernova remnants (SNRs) and pulsars. Though in its relative infancy, Chandra has already returned stunning images of SNRs which reveal the distribution of ejecta synthesized in the stellar explosions, the distinct properties of the forward and reverse shocks, and the presence of faint shells surrounding compact remnants. Pulsar observations have uncovered jet features as well as small-scaled structures in synchrotron nebulae. In this brief review we discuss results from early Chandra studies of pulsars and SNRs.
Global VLBI Observations of M82
Authors: McDonald A.R. , B. Muxlow T.W. , Pedlar A. , Garrett M.A. , Wills K.A.
Published: July 2016

Images are presented of the starburst galaxy M82 from a 20-station global VLBI experiment with an angular resolution of up to 3 mas. These images resolve several of the sources into a number of components and with future VLBI experiments the expansion of these components may be tracked on a ∼2 year timescale. Expansion of one of the brightest remnants in M82 has already been measured on a ∼10 year timescale using the European VLBI Network (EVN) alone and an expansion rate of 10,000 km s−1 calculated. Furthermore, limits on the deceleration of this remnant have been deduced. Further VLBI experiments will be able to better constrain the deceleration of the remnants on a ∼10 year timescale as they continue to interact with the interstellar medium in M82.