bluuebunny/crossref_metadata_2025 huggingface dataset:
Water on Venus?
Authors: Libby W. F. , Corneil P.
Published: July 2016

It is proposed that Venus may have polar seas which are acidic and thus cannot precipitate calcium carbonate. This leaves the carbon dioxide in the atmosphere. The argument is that the great equatorial land masses always have been too hot for liquid water and thus could not be weathered to give the sea salts necessary to form the precipitate. The action of steam on rocks is to liberate acids which are volatile and would dissolve in the polar seas. The volcanic vapors issuing in the early times consisting mainly of water and carbon dioxide would have begun polar seas at once since the expected equatorial (black body) surface temperature of the bare planet is too high (464 K) due to proximity of the sun. The accumulation of carbon dioxide in the atmosphere would have ensured the continued increase of the temperature due to the greenhouse effect. On earth, on the contrary, condensation over most of the planetary surface probably was possible from the beginning. Liquid water, ice-weathering, and river transport of salts to the seas all probably occurred from the beginning.

As the pressure at the surface probably approximates 100 atm (Venera 5 and 6) we can expect the polar seas to be below the boiling point although possibly hot. An isothermal layer of some thickness is naturally established over liquid water heated by infrared from above. Evaporation and condensation to form rain constitutes an efficient heat transport mechanism. Such a layer naturally would move toward lower latitude carrying moisture which then will rise and eventually move poleward in the high atmosphere causing rain and possibly the planet wide cloud cover. The atmosphere containing volatiles such as hydrochloric and hydrofluoric and sulfurous and sulfuric acids as well as carbon dioxide will form clouds which might be expected to consist of concentrated acid solutions. The main rain over the poles probably falls from altitudes well below the cloud top seen from earth. It is possible that the Venus clouds seen from earth are non aqueous just as our stratosphere carries dust clouds apparently of ammonium sulfate. At the moment it is very difficult to decide between these alternatives.

In the more polar regions the seas might conceivably be as cool as 50 °C.
On the nature of the Venus clouds
Authors: Kuiper Gerard P.
Published: July 2016

A comparison of a wide range of Venus observations with the ultraviolet, visible, and infrared reflection spectra and thermodynamic properties of a variety of candidate materials indicates that the principal constituent of the Venus clouds is partially hydrated FeCl2.
The Trouble with Venus
Authors: Sagan Carl
Published: July 2016

Venus is the closest planet. Its surface has never been seen at optical frequencies; nevertheless we now know with at least fair reliability, and in some cases with remarkable accuracy, its surface temperature and pressure, its atmospheric structure, its period of rotation, the obliquity of its rotation axis, the mean surface dielectric constant, its ionospheric structure, and even a little about its surface topography. And yet the clouds of Venus, visible to the naked eye and known to be clouds since the time of Lomonsov, continue to elude our efforts to understand them comprehensively. Not only do we disagree on the chemical composition of the clouds, but it is not even settled whether they are condensation clouds or non-condensable aerosols. And yet there is a very wide variety of relevant data on the clouds. Indeed, the ratio of potentially diagnostic data points to mutually exclusive hypotheses is of the order unity.
Mars: Occurrence of liquid water
Authors: Ingersoll Andrew P.
Published: July 2016

In the absence of juvenile liquid water, condensation and subsequent melting of ice are the only means of producing liquid water on the Martian surface. However, the evaporation rate is so high that the available heat sources cannot melt ice on Mars. Melting might occur only in concentrated solutions of strongly deliquescent salts.
Atmospheric depths of Jupiter, Saturn, and Uranus
Authors: Dermott S. F.
Published: July 2016

The presence of numerous near-commensurabilities among pairs of mean motions and the strong correlation between orbital radius and mass in the satellite systems of the three major planets (particularly in the Saturn system) suggest that the orbits of the satellites have evolved considerably under the action of tides. It is shown that the source of dissipation could be boundary layer turbulence at the base of the planetary atmosphere. If this is the source of dissipation then it should be possible to estimate the depths of these atmospheres from the mean rates of energy dissipation.
The Present State of Gamma-Ray Astronomy
Authors: Clark G.
Published: July 2016

The current state of gamma-ray astronomy is reviewed in terms of the most recent experimental results that define, in either measured fluxes or upper limits, the cosmic photon spectrum in the energy range from 0.5 MeV to 1016 eV. Methods of research developed during the last 10 yr are discussed and specific results are cited. Cosmic gamma rays have been observed in two regions of the spectrum – from 0.5 to 6 MeV and from about 50 MeV to several hundred MeV. Above 50 MeV a strong concentration of intensity is observed in a band of directions around the galactic equator. In both spectral regions a diffuse background gamma ray flux, apparently isotropic and of extragalactic origin, is observed. Evidence of ~ 50 MeV gamma-ray pulses from the Crab pulsar has been reported. No definite evidence of any other discrete gamma-ray source besides the galaxy itself has been observed at any energy.
A Large-Area Gas-Čerenkov Detector for High-Energy Gamma-Ray Astronomy
Authors: Delvaille J. , Greisen K. , Koch D. , McBreen B. , Fazio G. , Hearn D. , Helmken H.
Published: July 2016

Experimental upper limits of the high-energy gamma-ray flux (above 100 MeV) from point sources are about 10−5 cm−2 s−1, and realistic theoretical predictions for the strongest sources are an order of magnitude lower than this, while the diffuse background flux is about 4 × 10−5 cm−2 s−1 sr−1 in space, and 100 times higher at balloon altitudes. To meet the need for instrumental sensitivity and angular resolution adequate to measure the small but important gamma-ray source strengths, a telescope of large area (5 m2) and fine angular discrimination (0.5 deg at 300 MeV, 0.3 deg at energies above 1 GeV) has been developed.
Studies of the Solar X-Ray Spectrum as a Function of Position on the Disk
Authors: Brabban D. H. , Glencross W. M. , Herring J. R. H.
Published: July 2016

Work has been in progress for many years at University College London to determine how the intensity spectrum of emitted X-rays changes as a function of time and position on the solar disk. Early spectroheliographs consisted of grazing incidence parabolic mirrors which focussed radiation onto proportional counters from which spectral data were obtained. Such instruments, built in collaboration with the University of Leicester Group, have been flown on two rockets (Negus et al., 1969) and on the OSO V satellite (Herring et al., 1971).
Measurement of the Polarisation, Spectra and Accurate Locations of Cosmic X-Ray Sources
Authors: Pounds K. A.
Published: July 2016

Following the successful flights of large area survey experiments on three unstabilised Skylark rockets in 1967, 8 and 9, the Leicester Group has now changed the emphasis of its Cosmic X-ray Astronomy programme to the detailed observation of specific sources using attitude-controlled vehicles. Two new Skylark experiments for flights in the current year are described and some details are also given of an X-ray polarimeter/spectrometer being prepared for launch in 1973 on the UK-5 satellite.
A Gas Proportional Chamber for use in Cosmic X-Ray Research
Authors: Serlemitsos P.
Published: July 2016

Multi-anode gas proportional counters, when used in cosmic X-ray research, offer several advantages over more conventional large area detectors. Some of these are:

1.

Low detector background, effected by excluding from the sensitive volume, areas in the proximity of the counter walls, and by requiring that the region of interaction is localized inside the counter.

2.

Uniform response which makes possible energy resolution limited primarily by the statistics on the number of electron-ion pairs in the interaction, rather than by partial charge collection due to weak field regions inside the counter.

3.

Information relating to the interaction depth within the gas, which may be used in applying consistency checks regarding the nature of the incident radiation.

Methods have been devised for the modular construction of such counters, with particular emphasis on such items as, large areas, ease of assembly, matching of the many counter modules, accurate collimation, window supports, and shape integrity under differing amounts of differential pressure. Detector background at rocket altitudes was found to be flat above 2 keV, and less than 10−3 cm−2 s −1keV−1.
Spectroheliographs for the Ultraviolet
Authors: Öhman Y.
Published: July 2016

A brief survey is presented and ground based observations are reported aiming at the design of simple spectroheliographs for space research, particularly in the range 1.500–3.000 Å.
A Tunable Birefringent Filter for the UV Region
Authors: Fredga Kerstin , Högbom J. A.
Published: July 2016

In the near ultraviolet part of the spectrum filters with narrow bandpasses (smaller than a few Ångströms) are difficult to manufacture. Ordinary birefringent filters suffer from low transmission because of the great number of polarizers usually needed. From this point of view the Šolc-type birefringent filter offers a solution since it only employs two polarizers. With a suitable arrangement of the angles of the optic axes of the birefringent plates adjacent secondary maxima can be suppressed to any desired value.

It is shown that by modulating the distribution of the angles by a cosine function a normal transmission peak may be split into two peaks. The distance of the two peaks depends on the frequency of the modulation function. In this manner the filter can easily be tuned over half the free spectral range without appreciable change of the transmission profile. The theoretical results have been experimentally verified.
Fabry-Pérot Interferometers as Narrow Band Optical Filters
Authors: Title Alan M.
Published: July 2016

We have constructed solid Fabry-Pérot narrow-band filters that can be used in systems having one arc second or better resolution. Our filters operate at Hα, have a three-inch aperture, and typical transmission of 70%. However, the same technology can be applied to construction of filters as narrow as 0.05 Å at any wavelength from 4200 to 11000 Å.
Solutions of Some High Potential Problems in Rocket Experiments
Authors: Hessberg H. , Niekerke J.
Published: July 2016

Corona-problems severely can effect absolute calibrated photomultiplier-experiments in sounding rockets. Solutions in case of experiment R-130 (absolute spectral photometry of B-stars in the vacuum UV-region) are presented.

(To be published in Raumfahrtforschung, Berlin/Stuttgart/München.)
Housing of Photoelectric Equipment in Rocket Experiments
Authors: Hessberg H.
Published: July 2016

The housing of photoelectric equipment in rocket experiments results among others in the following demands: Stability of the structure and nevertheless little weight, exact geometrical alignment and at the same time soft, vibration- and shock-protecting supportings (in case of photomultipliers for instance).
Absolute UV Calibration of Rocket Photometers Used to Up-Date the OAO Calibration
Authors: Gaide Albert
Published: July 2016

Accurate rocket observations are needed to estimate the post-launch sensitivity of the Wisconsin OAO instruments and to set the absolute scale of the OAO broad-band photometry and spectrophotometry. Seven broad-band photometers, equipping a pointable Aerobee rocket, are calibrated against a source of synchrotron radiation in an attempt to determine, as accurately as possible, the absolute energy distribution of OAO reference stars. The first flight (July 1st, 1970) failed for technical reasons but the experiment will be repeated in 1971.
Fluctuations and secular changes in the earth's rotation
Authors: Brouwer Dirk
Published: July 2016

Geophysical considerations favor seeking the cause of the random changes in the earth's rate of rotation in the turbulent motion in the core of the earth. Professor van der Waerden's analysis applies to this interpretation. The observational evidence indicates that the character of the fluctuation curve may be intermediate between that expected on the basis of a theory with frictional couple and one without. If confirmed, this would indicate that two different causes contribute to the changes in the earth's rate of rotation.
Détermination de la constants de l'aberration
Authors: Potter H. I.
Published: July 2016

Preliminary results on the observation of the constant of aberration by the photographic polar tube of Pulkovo Observatory are presented.
The motion of Mars 1751-1956
Authors: Duncombe R. L.
Published: July 2016

Report on the work in progress using Clemence's theory of the motion of Mars.
Radar observations of venus in 1962
Authors: Ponsonby J. E. B. , Thomson J. H. , Imrie K. S.
Published: July 2016

Results of observations made at Jodrell-Bank with the radio-telescope.
Relations among some important astronomical constants
Authors: Brouwer Dirk
Published: July 2016

The availability of accurate values of the coefficients J2, J4, … in the Earth's potential and radar determinations of the distances Earth-Moon and Earth-Venus provides relations among astronomical constants different in form from those used in previous efforts to construct a consistent system of astronomical constants. Some of the important relations have gained in simplicity.
Stability of spiral motion
Authors: Szebehely V.
Published: July 2016

The stability of the motion of particles in spiral orbits is investigated. The force field is represented by the potential functionf=C(expaφ)/rnlimiting case of which is the Newtonian gravitational field (n= 1,a= 0). Particular solutions of the equations of motion are shown to be logarithmic spirals. A linearized stability analysis leads to a fourth order system of differential equations with variable coefficients. Complete solution of this system is obtained showing a rather complex stability situation in which outward motions are always associated with instability while inward motions might be stable or unstable depending on the value of the constantsaandnoccurring in the above potential function.
A kinematical study of field supergiants near the Sun
Authors: Steffey P. C.
Published: July 2016

This paper deals with an attempt to use computations of galactic orbits to trace supergiant stars back to their points of origin. The data consist of the observed space velocities of the stars and their ages as determined from stellar evolution theory. The local galactic potential field is assumed known, as well as the Sun's motion relative to the circular velocity. The results place the origin ofαLep, and possiblyαCar, in the association II Sco. BothαandβOri appear to have started in the association I Ori, although the motions in the galactic plane are not completely consistent. The high latitude supergiants 89 Her andρLeo can be traced backward very plausibly to an origin in the layer presently occupied by stellar associations.
Orbits of binary systems with decreasing mass
Authors: Hadjidemetriou J.
Published: July 2016

The effect of the isotropic loss of mass from either component of a binary system on the elements of the orbit was studied. The period increases secularly, while the behaviour of the eccentricity depends on the particular way the mass decreases. Several functions for the mass were studied and an attempt was made to explain the observed dependence of the period on the eccentricity under the assumption that mass was lost.
Irreversibility and cooperative phenomena in small stellar dynamical systems
Authors: Miller R. H.
Published: July 2016

Stellar dynamical systems were shown to possess the macroscopic irreversibility characteristic of statistical mechanical systems by means of a computer calculation of anN-body system. The irreversibility, corresponding to a linear increase of entropy with the time (over short times), has implications concerning the reliability ofN-body calculations in the sense of numerical analysis. The same calculation indicates the existence of strong cooperative phenomena in stellar systems.
Dynamical evolution of small stellar systems
Authors: Aarseth S. J.
Published: July 2016

The evolution of an isolatedN-body system withN= 100 has been studied numerically for about 30 mean relaxation times. The equipartition effect leads to pronounced mass segregation with the formation of a dense nucleus of heavy members and an extended halo of mainly light bodies. The total integration time would correspond to ∼ 108years for a mean cluster radius of 1 pc and a mean mass of 1⊙, but even so only 10 per cent of the cluster members escape to infinity.
The equations of variation in a numerical lunar theory
Authors: Eckert W. J. , Smith H. F.
Published: July 2016

This paper concerns a new solution, with increased precision, of the “main problem” of the lunar theory, i.e. the three-body problem where the Sun, Earth, and Moon behave as mass particles and the Sun moves about the center of gravity of the Earth-Moon system according to Kepler's laws. The solution gives the coordinates as harmonic series with constant coefficients and with arguments that are linear functions of the time with four fundamental frequencies. The method of solution is a numerical one in which the best previous solution is substituted into the differential equations and the resulting residuals are used to determine corrections to the substituted solution. Brown's series were used as a first approximation and the goal was to improve the coefficients by at least 2 orders of magnitude to 10–10. The process involved the solution of a set of 6325 variation equations with as many unknowns. The emphasis in this paper is upon the techniques of separating the equations and for treating the notorious small divisors in such a manner that a relaxation scheme is effective. The numerical results are analyzed, not for their astronomical implications, but for their consistency; and it is concluded that the method has not only succeeded thus far but may be extended further with certain adjustments for the worst cases of the divisors.
Satellite motion for all inclinations around an oblate planet
Authors: Eckstein M. , Shi Y. , Kevorkian J.
Published: July 2016

A uniformly valid solution for the motion of a satellite around an oblate planet is presented. The Two-Variable Expansion Procedure was applied to obtain a solution valid for all inclinations including the critical. This solution is correct to order ε, where ε is a small parameter proportional to the oblateness parameterJ2. The reciprocal of the radius vector, eccentricity, perigee, inclination, and node of the satellite orbit are given as functions of the central angleφbetween node and satellite. The results are based on a potential which includes the second and fourth zonal harmonics. The solution for the case of critical inclination is first obtained separately and then matched with the solution of the noncritical case to establish a solution uniformly valid for all inclinations.
Surprise and Sociology in Multi-Disciplinary Sciences: A Public Lecture
Authors: Townes Charles H.
Published: July 2016

This lecture is being given as part of an international meeting on astronomical imaging. It is, in fact, the first major meeting of people with backgrounds in both optical and radio imaging, and has attracted 200 people from all around the world. One of those is a man who has been an active researcher in microwave and infrared spectroscopy for over half a century. It is my pleasure to introduce that man, Professor Charles Townes from the Space Science Laboratory, University of California, Berkeley. It is clear that throughout his life Professor Townes has been attracted by a series of fundamental challenges. He was already an acknowledged molecular spectroscopist when, in 1951, to solve the problem of short wavelength oscillators, he conceived a system for using excited ammonia molecules that became the ammonia beam maser oscillator. He followed this in 1958 by publishing a paper with his brother-in-law, Arthur Schawlow, that laid the foundations for the development of the laser. These two activities, flowing as they did from the pursuit of the most fundamental physics, paved the way for some of the key elements of modern communications.
The Sydney University Stellar Interferometer (SUSI)
Authors: Davis J.
Published: July 2016

The Sydney University Stellar Interferometer has been designed and constructed as a two aperture, single ro, long baseline, optical interferometer with wavefront-tilt compensation and dynamic optical path length compensation. Initially it will operate in the blue part of the visual spectrum but provision has been made for the addition of an additional beam-combining system for a second spectral band. The rationale behind the choice of instrumental parameters, the potential developments which have been taken into account in its construction, and the current status of SUSI are outlined.
The VLT Interferometer
Authors: Bedding T. R. , Beckers J. M. , Faucherre M. , Hubin N. , Koehler B. , von der Lühe O. , Merkle F. , Zhu N.
Published: July 2016

One of the observing modes available with the ESO Very Large Telescope will be coherent combination of the light received by up to four 8 m unit telescopes and several 1.8 m auxiliary telescopes. The location of the main telescopes is fixed, while auxiliary telescopes can be moved among some 30 observing stations. The locations of these stations were chosen to augment the (u, v) coverage of the unit telescopes as well as to function as an independent interferometric array.

The 8 m telescopes will be equipped with adaptive optics to correct for seeing-induced wavefront aberrations. This wavefront correction will be complete at near-infrared wavelengths, giving the interferometer very high sensitivity in this spectral regime. This paper gives a brief description of the VLT Interferometer and an update on its status.
CIROI Project
Authors: Xu J.Y. , Wang Z.M.
Published: July 2016

CIROI (China InfraRed Optical Interferometry) Project would be probably divided into three stages: prototype, moderate aperture, and large aperture. The prototype with two collection apertures of 10 cm and baseline of 12 m for first testing stage is being manufactured.
An Overview of the SUSI Control System
Authors: Minard R. A. , Booth A. J. , Tango W. J. , Brummelaar T. Ten , Bennis H. , Owens S. M.
Published: July 2016

The SUSI control system is a distributed real-time system currently consisting of 17 processors. A custom real-time operating system and network protocols ensure synchronous operation of servo loops across multiple processors.
Phase and Image Reconstruction from Pupil-Plane Observations in the Near Infrared: Integration of the Phasors
Authors: Monin J.-L. , Ageorges N. , Desbat L. , Perrier C.
Published: July 2016

A new method to reconstruct the phase of bidimensional interferograms, obtained through pupil-plane interferometry is presented. We compute the average complex phasor components of the cross-spectrum on a data set to reconstruct the original unperturbed phase. We present preliminary results on simulated images which visibility phases are distorted using a model of atmospheric perturbed wavefronts.
Restoration Over Fields of View Wider than the Isoplanatic Patch
Authors: Thorpe G. , Fraser D.
Published: July 2016

This paper presents the results of a preliminary investigation into the problems in through-the-atmosphere image restoration which are more suited to data from a small telescope, i.e., one having a diameter of about 0.5 m, using techniques of image geometric transformation (and eventually, parallel image processing) in their solution. We have imaged bright objects, over fields of view which subtend angles greater than those in most “large” telescope experiments, i.e., between 40 and 100 arc sec, for example, where the isoplanatic assumptions are less valid.
AIPS++: A New Astronomical Imaging Package
Authors: Norris Ray P.
Published: July 2016

In this paper I describe a new software package (“AIPS++”) being written by a consortium of seven astronomical institutions spread over four continents. I start by describing the background to the project, followed by a summary detailing what AIPS++ is and why it is being written in this way. Section 3 describes the challenge of running a globally distributed project spread over four continents. Finally I describe the current status and an estimated completion date.
Integrated Optics in Astronomical Interferometry
Authors: Coudé du Foresto V.
Published: July 2016

Integrated optical components (mostly single-mode fibers and couplers) can be used to achieve several functions that are needed in interferometry: coherent beam transportation and recombination, pathlength modulation and control for fringe tracking and double Fourier interferometry, spatial filtering of the wavefront and interferogram calibration. Their potential is assessed and the main problems encountered in their implementation are discussed: dispersion, polarization behavior, and especially starlight injection.
Laser Guide Star Adaptive Optics: Present and Future
Authors: Olivier S. S. , Max C. E.
Published: July 2016

Feasibility demonstrations using one to two meter telescopes have confirmed the utility of laser beacons as wavefront references for adaptive optics systems. Laser beacon architectures suitable for the new generation of eight and ten meter telescopes are presently under study. This paper reviews the concept of laser guide star adaptive optics and the progress that has been made by groups around the world in implementing such systems. A description of the laser guide star program at LLNL and some experimental results is also presented.
Observations of Seeing at 0.5 and 12.4 μm
Authors: Livingston W. , Kopp G. , Gezari D. , Varosi F.
Published: July 2016

A variety of observations have been made of solar features (sunspots, faculae, the limb) using both array and single element scanning techniques. The telescope was the 1.6 m McMath-Pierce on Kitt Peak. Array data were acquired with a 58×62 pixel Si:Ga detector at 4.8, 7.8, 12.4, and 18 μm, while a CCD camera recorded the same image position at 0.5 μm. In a separate experiment, a nutating mirror device was used to generate a raster scan of solar disk areas, the output being fed to a Si PIN diode (0.5 μm filter) and a As:Si diode (12.4 μm filter). The scanner data yield simultaneous images at the two wavelengths and was essentially a repeat of the 1970 Turon-Léna experiment with updated equipment. Examples of images at the various wavelengths are given in the poster. Analysis of the data is incomplete at this time. We can report that the effects of seeing were encountered at all wavelengths, including 18μm, even though conditions were deemed good at times (for example, penumbral filaments were resolved in sunspots). We have thus been unable to verify, as yet, the conditions reported by Bester et al, in which exceptional seeing is realized in the infrared.
High Resolution Imaging at mm-Wavelengths with the Hat Creek Array
Authors: Erickson W. C. , Mundy L. G. , Grossman A.
Published: July 2016

The Hat Creek mm-wavelength array, operated by the Berkeley-Illinois-Maryland Association (BIMA), is undergoing an expansion to nine telescopes. The first six of these telescopes will be operational in January, 1993. The telescopes are relatively small, 6 m in diameter, and are moved on rubber-tired dollies so it will be possible to transport them on roads in the vicinity of the main array. Initially, we plan to place two of the telescopes at outrigger sites located 0.5 and 1.0 km from the main array. Use of these outrigger telescopes will yield angular resolutions of 0.45 arc-sec at 2.7 mm wavelength and 0.21 arc-sec at 1.2 mm wavelength. When all nine telescopes are operational, reasonable image quality will be obtained with a single 12-hour observation. The maximum sidelobe amplitude depends upon source declination, but is about 16%. Figures 1, 2, and 3 show the uv coverage and beamshapes which will be achieved at various declinations.
The Present Status of Astrometry at Optical and Radio Wavelengths
Authors: Johnston K. J.
Published: July 2016

A Review is presented of the present status of astrometry towards defining a radio/optical reference frame.
The USNO Astrometric Interferometer
Authors: Hutter Donald J.
Published: July 2016

The U.S. Naval Observatory Astrometric Interferometer (USNOAI) will be the dedicated astrometric sub-array of the new Navy Prototype Optical Interferometer (NPOI) at Lowell Observatory, which is being built in collaboration with the Naval Research Laboratory. The USNOAI will be in operation on Anderson Mesa, near Flagstaff, Arizona, in late 1993. The instrument will incorporate four siderostats which will be located in a Y-shaped configuration, and will feature state-of-the-art delay lines, a real-time zeroth-order fringe tracking algorithm, a full-array laser metrology system to monitor baseline motion, and a limiting magnitude of 10. The instrument will be capable of simultaneous observations on six baselines, and will produce star positions accurate to a few mas. With it, we will be able to maintain the HIPPARCOS reference frame with matching accuracy over the next few decades.
High Precision Differential Astrometry in Large Angular Separation Pairs of Radiosources
Authors: Marcaide J.M. , Guirado J.C.
Published: July 2016

We show preliminary results of three of the four radiosource pairs with angular separations ranging from 0.01° to 6° where we have determined such a separation with a typical fractional precision of 10−8 using phase delays corrected for structural and ionospheric contributions. In the radiosource 4C39.25 we measure a motion with respect to an external radiosource which is compatible with previously reported internal superluminal motion.
Radar Imaging of the Planets Using the Very Large Array
Authors: Muhleman Duane O. , Butler Bryan J. , Slade Martin A. , Grossman Arie W.
Published: July 2016

We have used the VLA to make images of the planets which are continuously illuminated by the high power planetary radar transmitter on the 70 meter antenna at Goldstone, CA. That instrument is capable of transmitting up to 460,000 watts of continuous power near 8.5 GHz. Radar imaging experiments became possible after the installation of the 8.5 GHz receivers on all VLA antennas by NASA for the encounter of the Voyager spacecraft with Uranus. A similar radar may be configured with the Australia Telescope (array) at Narrabri and the Goldstone 70 m at S-band which may be important for experiments on Venus whose atmosphere strongly absorbs at X-band. Highly successful experiments have been carried out at the VLA on Mercury, Venus, Mars, Saturn's rings and Titan, the giant satellite of Saturn.
Limitations to Optical/IR Interferometry from the Ground and Space
Authors: Colavita M. M.
Published: July 2016

The primary limitation to ground-based optical/IR interferometry is the turbulent atmosphere, which limits sensitivity by restricting the coherence volume, limits imaging accuracy by corrupting the fringe phase, and limits astrometric accuracy by corrupting the angle of arrival. Various advanced techniques can be used to circumvent these limits to some extent. Sensitivity can be increased with adaptive optics and laser guide stars, which should eventually be able to phase the individual apertures of an interferometer down to some cutoff wavelength, limited by tilt sensing. However, the sky coverage for cophasing the interferometer on an arbitrary object will remain limited at short wavelengths. For imaging, closure-phase techniques, well established in radio interferometry, will be used in next-generation instruments. However, for maximum sensitivity on extended objects, redundant arrays will be needed to cophase the interferometer. For astrometry, the limits to wide-field astrometry set by the atmosphere can be reduced somewhat with two-color techniques, but otherwise do not seem reducible by the techniques now being discussed. However, over narrow fields, the astrometric performance of an interferometer can be quite good. In space, without the corruptions of the atmosphere, the fundamental limitation is photon noise. However, technical issues such as metrology accuracy and practical issues such as maximum affordable baseline length will also limit performance.
A Review of High-Redshift Merger Observations
Authors: Abraham R.G.
Published: July 2016

Evolution in the merger rate as a function of redshift isin principlethe key observable testing hierarchical models for the formation and evolution of galaxies. However,in practice, direct measurement of this quantity has proven difficult. In this opening review I outline the current best estimates for the merger rate as a function of cosmic epoch, focusing mostly upon recent advances made possible by deep ground-based redshift surveys and morphological studies undertaken withHST.I argue that a marriage of these techniques, in an attempt to determine the space density of mergers amongst the abundant morphologically peculiar population at high redshifts, is probably the most promising currently-available avenue for determining the prevalence of mergers at high redshifts. However, resolved kinematical studies, which seem set to become available in the next few years, are probably the best hope for a definitive determination of the space density of mergers at high redshifts.
Total Mass and Luminosity of Star Forming Regions in the LMC: Predicted Infrared Fluxes
Authors: Missoulis V. , Dapergolas A. , Kontizas E. , Kontizas M. , Oliver S.
Published: July 2016

We have investigated 4 Shapley constellations (1996, A&A, 308, 40) to define the associated stellar complexes and their properties. From observed star counts and recent spectral classification we derive an age estimate and the upper mass limit of individual stars in these regions.
Counterrotation in Galaxies
Authors: Bertola F. , Corsini E.M.
Published: July 2016

The phenomenon of counterrotation is observed when two galaxy components have their angular momenta projected antiparallel onto the sky. It follows that if the two components rotate around the same axis, the counter-rotation is intrinsic. On the contrary the counterrotation is only apparent if the rotation axes are misaligned and the line-of-sight lies in between the two vectors or their antivectors. In the case of intrinsic counterrotation the two components can be superimposed or radially separated.
Stellar Counter-Rotation Along the Hubble Sequence: A Probe for Galaxy Formation Scenarios
Authors: Prada F. , Gutiérrez C.M.
Published: July 2016

We present some preliminary results of an on-going project to investigate the phenomenon of counter-rotation in galaxies. The analysis of two Sb and two barred galaxies shows the presence of stellar counter-rotating components in the central 1 to 3 kpc of each galaxy. This, along with similar structures found in ellipticals and early-type spirals, demonstrate that the counter-rotation extends along the Hubble sequence. The physical origin of these features is briefly discussed stressing the possible relevance of this phenomenon in understanding the general problem of galaxy formation.
Shell Formation in NGC 474
Authors: Turnbull A.J. , Carter D. , Bridges T.J. , Thomson R. C.
Published: July 2016

We present broad band photometry (B and R) of the classic shell galaxy NGC 474. Preliminary results indicate that the shells have a similar colour to and follow the same trend of colour with radius as the underlying galaxy.
The Character of Embedded Rings
Authors: Chatterjee Tapan K.
Published: July 2016

It is well known that, under favorable conditions, tidal interactions between a spiral galaxy and a more compact elliptical leads to the formation of embedded rings in the disk (e.g. Chatterjee 1979, Bull. Astron. Soc. India, 7, 32); in addition there are also nuclear rings whcih do not seem to have a tidal origin (e.g. Buta 1986, ApJ, 306, 768). The two types of rings occur in different regions of the spirals, which can be explained on the basis of the tidal hypothesis by extending the previous research work of Chatterjee (1984, Ap&SS, 106, 309). In this context, using the same theory, we study many normal on-axis collisions (as rings are best formed for this orientation) between a disk galaxy, modeled as an exponential disk with a polytropic n = 0,3,4, bulge (mass being equally distributed amongst the polytropic indices), and a compact spherical intruder, modeled with a polytropic n = 2, 3, 4, distribution (mass being equally distributed amongst the polytropic indices). The internal energy changes suffered by the disk, have a direct bearing on the sharpness of the rings, and are directly obtained from the relationship, for the fractional change in internal energy of the disk, as fE = γβ, where β is a function of the galactic models and the collision parameter γ = G(σs/V2) ∝ σs/V2 (where σs is the projected velocity of collision). We find that sharp rings form for fE ≥ 0.5; beyond this value of fE the intensity contrast of the rings diminish. However, fairly sharp rings (from an observational point of view) form for fE ≥ 1/3, which corresponds to 7 ≥ 0.01; which corresponds to a density maximum near a region ~ (1/3)R (R being the radius of the disk galaxy), so that rings of tidal origin are not expected to be prominent at a distance interior to ~ 1/3 of the radius of the disk galaxy. They are not expected to form interior to ~ 1/10 of the radius of the disk.
Angular Momentum Transfer Due to Galactic Winds and Cooling Flows
Authors: Missoulis V.
Published: July 2016

We examine a model of galaxy formation where the bulge is formed at very early stages and this burst of star formation leads to a galactic wind which interacts with a huge surrounding gaseous envelope.
Stellar Populations in High-z Galaxy Mergers
Authors: Shioya Yasuhiro , Bekki Kenji
Published: July 2016

We investigate the nature of stellar populations of major galaxy mergers between late-type spirals considerably abundant in interstellar medium by performing numerical simulations designed to solve both the dynamical and chemical evolution in a self-consistent manner. We particularly consider that the star formation history of galaxy mergers is a crucial determinant for the nature of stellar populations of merger remnants, and therefore investigate how the difference in star formation history between galaxy mergers affects the chemical evolution of galaxy mergers.
Fueling Nuclear Starbursts
Authors: Gerritsen Jeroen P.E. , Icke Vincent
Published: July 2016

We present a numerical simulation of two merging equal-mass, gas-rich disk galaxies. Special emphasis is given to an accurate treatment of the interstellar medium physics and star formation with its feedback. We will explain how the negative feedback from young stars restricts the bulk of the star formation during the merger-induced starburst to the nucleus.
Molecular Gas and Star Formation in Interacting and Isolated Galaxies
Authors: Young J.S.
Published: July 2016

The results of the FCRAO Extragalactic CO Survey are used to examine the trends regarding the molecular gas distribution, the star formation efficiency, and the global gas surface densities (HI and H2) in galaxies as a function of environment. Relative to a sample of isolated Sbc-Scd galaxies, the strongly interacting galaxies have more compact gas distributions, a higher mean value for the global star formation efficiency, and a larger fraction of gas in molecular form. Not only is the molecular gas redistributed during interactions, but evidence is presented for an enhanced conversion of atomic to molecular gas as well.
The Evolution of Young Star Clusters in Merging Galaxies
Authors: Whitmore Bradley C.
Published: July 2016

The formation of young star clusters in merging galaxies is, by now, well established. The new challenge is to use these young clusters as a tool to address some of the outstanding questions. For example, what fraction of these young clusters become globular clusters? Is this enough to explain the difference in the specific globular cluster frequencies for spirals and ellipticals? What is it about the collision between two gas-rich galaxies that triggers giant molecular clouds to form star clusters? Can the star clusters be used to age date merger remnants and establish a convincing evolutionary connection between merging spirals and elliptical galaxies? This review will focus on the last of these items.
Spectroscopy of Luminous Infrared Galaxies
Authors: Veilleux S.
Published: July 2016

A review of recent optical and infrared spectroscopic results on luminous infrared galaxies is presented. The main emphasis is on the ultraluminous objects. Possible correlations with infrared luminosity are identified. These results are used to constrain the nature of the dominant energy source in luminous infrared galaxies, and to test whether these objects may represent an evolutionary phase between starburst galaxies and active galactic nuclei.
The Fate of Ultraluminous Mergers
Authors: Baker A.C. , Clements D.L.
Published: July 2016

Galaxy formation is a diverse range of ongoing processes. Numerical simulations suggest that disk galaxies in collision pass through a massive burst of star formation, and produce ‘elliptical–like’ remnants similar to bone fide elliptical galaxies. The observed relative numbers of merging systems and elliptical galaxies are consistent with this picture (Toomre 1977). We here investigate further by studying the distribution of old stars in a sample of merging galaxies : the ultraluminous IR galaxies (ULIRGs). We selected ten ULIRGs from the literature (Clements & Baker 1996; Leech et al. 1994; Zhenglong et al. 1991; Melnick & Mirabel 1990) by two criteria: proximity (redshifts z < 0.15), for good spatial resolution; and confirmed signs of merging. We obtained deep K–band images (tint ~ 1000 - 2700s) in good seeing using MAGIC on the Calar Alto 3.5m telescope. Our data have a field–of–view roughly equivalent to 10 - 20 effective radii for the galaxies. We have fitted analytic surface brightness profiles to the data for the exponential disk and the de Vaucouleurs r1/4 elliptical descriptions. We strongly favour the elliptical-like description in 8 out of 10 cases, supporting the picture that collision and merger of classical spiral galaxies can produce classical elliptical galaxies, through tidal disruption, violent star formation accompanied by prodigious infrared emission, and gravitational relaxation. These data can also constrain the properties of the ULIRG (double) nuclei and hence the lifetime of the ULIRG phase (Baker & Clements 1998).
The Interacting Seyfert 2 Galaxy UGC 3995A
Authors: Dultzin-Hacyan D. , Marziani P. , D' Onofrio M.
Published: July 2016

Direct observational evidence of interaction driven inflow of gas toward a Seyfert nucleus remains scant. UGC 3995 is one of the rare systems of galaxies that, at a first glance, offers direct evidence of this phenomenon: a bright filament appears to connect the bar of the spiral galaxy UGC 3995A (whose nucleus shows a Seyfert 2 spectrum) to the nucleus of a smaller spiral companion (UGC 3995B) whose radial velocity exceeds by only 30 km s−1 that of UGC 3995A. Narrow (redshifted Hα) and broad band (R, B) images of UGC 3995, along with long slit spectra in the Hα region were collected at the 2.1 m telescope of the Observatorio Astronómico Nacional at San Pedro Mártir (SPM), México, in January-February 1995. From the B-R color map we infer that UGC 3995B is partially obscuring UGC 3995A. It is likely that a conspiracy of chance alignments and obscuration is giving the bar of UGC 3995A a disrupted appearance suggestive of stripping. The fairly regular profile of the HI 21 cm line suggests that the neutral hydrogen disks of both UGC 3995A and B have not yet undergone strong perturbations. However, while on the eastern side of UGC 3995A we observe HII region gas approximately following the rotation of the HI gas, on the western side we may be observing shock-heated “minority” gas whose motion is not exclusively rotational. We conclude that most of the morphological peculiarities observed in UGC 3995 cannot be easily related to infall of gas toward the Seyfert nucleus. Nevertheless, the kinematics of ionized gas in the western part of the disk of UGC 3995A has been affected by the intruder, probably because UGC 3995B is already physically in contact with UGC 3995A.
Radiative Avalanche Driven by Spherical Starbursts
Authors: Fukue J. , Umemura M. , Mineshige S.
Published: July 2016

As a solid physical mechanism to link between starburst activity and AGNs, we have proposed a radiative avalanche, where the mass accretion is driven by radiation drag exerted by stellar radiation from circumnuclear (ring-like) starburst regions (Umemura et al. 1997a,b). We here examine a radiative avalanche for a case of spherically distributed sources (Fukue et al. 1997). The results of the present spherical case are qualitatively similar to those of the ring-like case. For example, the drift timescale tdrift is found to be tdrift = 1.86×109 yr (m+1)(b/100 pc)2 (L∗/1012L⊙)−1g(r)−1, where m is the power of rotational velocity (vϕ ∝ rm), L∗ the starburst luminosity, b the radius of the starburst region, and g(r) a function of the order unity. This timescale is sufficiently shorter than the viscous timescale of the relevant region. In contrast to ring-like starbursts, the advantage of spherical starbursts is the large solid angle subtended by the starburst region. Hence, the luminosity of the starburst region is fully available to avalanche on the surface of the disk. Furthermore, the radiation field of the starburst region has no angular momentum, which is in favor for the avalanche.
Environmental Extremists in the Virgo Cluster
Authors: Kenney Jeffrey , Koopmann Rebecca
Published: July 2016

Many types of galaxy interactions have been posited to occur in clusters, although it remains unclear which processes actually occur, and which ones might help explain the tendency for early type galaxies to inhabit high density environments, or cause the rapid evolution of cluster galaxies (e.g., Dressler et al. 1997). With these questions in mind, we have been conducting an environmental inventory of galaxies in the Virgo Cluster. Our approach is to combine surveys of spirals and S0s with detailed studies of the most interesting and peculiar galaxies. In this paper, we describe two main points. 1.) There is a population of spiral galaxies in the Virgo cluster with the small central light concentrations (bulge-to-disk ratios, or B/D's) characteristic of isolated Sb and Sc galaxies, but global star formation rates lower than those of isolated spirals of any Hubble class (Sa-Sc). These Virgo galaxies are generally classified as “early type” (e.g. Sa), and thus contribute to the morphology-density relationship. 2.) There areseveral typesof environmental interactions occurring in Virgo, including low velocity tidal interactions and mergers, high velocity tidal interactions and collisions, HI accretion, and ICM-ISM stripping. We discuss examples of some of these interactions.