bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance of the Medicina Radiotelescope and the New S/X Receiver for Geodynamics VLBI
Authors: Grueff G. , Comoretto G. , Mantovani F. , Tomasi P. 
Published: June 2019

At the beginning of 1980 the Istituto di Radioastronomia of the Consiglio Nazionale delle Ricerche (C.N.R.) started the Italian VLBI Project.The first antenna was completed in October 1983 (see Table 1 for telescope characteristics). The first VLBI Mark2 experiment was performed in March 1984. In December 1984 we had the first Mark3 experiment. From that time our Institute is officially member of the European VLBI Network (EVN) and since January 1986 it is also Associate Member of the US Network.
4 Years of Radio to X-ray Observations of 3C 273
Authors: Courvoisier T.J.-L. , Robson E. I. , Blecha A. , Bouchet P. 
Published: June 2019

The quasar 3C273 has been repeatedly observed at radio, mm, IR, optical, UV and X-ray frequencies since December 1983. A complex pattern of continuum variations has been discovered, which can be used to provide model independent physical parameters, and to constrain different models. The main features revealed by our set of observations are:
(i)A flux decrease by 40% in the 2–10 kev flux in 20 days in early 1984 (Courvoisier et al. 1987).(ii)Differences between the X-ray light curves at 0.5 keV and 2–10 keV.(iii)A drop in the mm to mid-IR emission by factors 2–4 in early 1986, while the near infrared flux remained stable (Robson et al. 1986).(iv)A decrease in the ultraviolet intensity of ∼40% in about 6 months in 1987 (Ulrich, Courvoisier and Wamsteker 1988).(v)Rapid variability in the infrared and optical emission on timescales as short as one day in 1988 (Courvoisier et al. 1988 and Robson, Courvoisier and Bouchet this conference).
TAURUS observations of active galaxies: NGC 1275 and NGC 4151
Authors: Unger S.W. , Taylor K. , Pedlar A. , Ghataure H. , Penston M.V. , Axon D.J. 
Published: June 2019

We have used the TAURUS technique to study the morphology and velocity field of spatially extended emission–line gas in a number of active galaxies. This paper describes our results for NGC 1275 and NGC 4151. The emission line maps of NGC 1275 are the first scientific data from the new 4.2-m William Herschel Telescope, and show that the morphology of the foreground galaxy falling into the Perseus cluster bears a close relationship to that of NGC 1275 itself, implying that the two galaxies are physically associated.In the case of NGC 4151, we find the emission line region is elongated along the same axis as the nuclear radio source. This cannot be due to emission-line gas being accelerated by radio ejecta, since the emission-line gas rotates with the galactic disk. We suggest that the emission-line gas is being ionized by a highly anisotropic nuclear continuum source, UV photons escaping from the nucleus preferentially along the radio axis.
X-ray Constraints on AGN Clustering
Authors: De Zotti G. , Persic M. , Franceschini A. , Danese L. , Palumbo G.G.C. , Boldt E. A. , Marshall F. E. 
Published: June 2019

Studies of the HEAO–1 A2 all–sky survey data have established that the level of anisotropy of the extragalactic X–ray background (XRB) is relatively low:
–The cell–to–cell XRB intensity variations can be entirely accounted for by Poisson fluctuations in the space distribution of known classes of sources; the 90% confidence upper limit to any additional contribution on a scale of 26 square degrees is 2.3% (Shafer and Fabian 1983).–No significant correlations of XRB intensity fluctuations appear to be present; the formal 90% confidence upper limit on the amplitude of autocorrelations, relative to the mean background intensity, for an angular scale of 3° is Γ(3°) ≤ 1.9 × 10−2 (Persic et al. 1988).
New 45M Radio Telescope and Fourier-Transform Type Spectrometer at Nobeyama Radio Observatory
Authors: Hirabayashi Hisashi 
Published: June 2019

The 45m radiotelescope of Nobeyama Radio Observatory (NRO) is now in operation. It has a surface accuracy of 0.2 mm (rms) and a pointing accuracy of 0.001 degrees. Two types of spectrometers were designed for the telescope. One type is an Acousto-Optical-Spectrometer (AOS) with a 16,384 channel, 2000 MHz full-bandwidth spectrometer, and a 8192 channel, 160 MHz full-bandwidth spectrometer. The other type is a direct Fourier transform type spectrometer called “FX”. One FX is designed for a 10 meter, 5 element supersynthesis interferometer and another for the 45m radio telescope. The “interferometer FX” is a spectro-correlator that processes 5 inputs of 320 MHz bandwidth signals into correlations with 1024 frequency channels. The “45m FX” has 4 sets of 10 MHz bandwidth, 1024 channel spectrometers.It has been pointed out by Morimoto, Hirabayashi, and Jugaku (1978) that formaldehyde anti-maser absorption lines in the direction of dark clouds would be suitable for SETI (Search for Extra-Terrestrial Intelligence). The Nobeyama 45m radiotelescope is suited for such targeted deep SETI.
Theoretical and observational efforts in order to obtain high precision positions of the Galilean satellites of Jupiter
Authors: Thuillot W. , Vu D. T. , Arlot J. E. 
Published: June 2019

The two manners to improve the knowledge of the motions of the galilean satellites are the elaboration of a new theory and the use of high precision observations. In this paper, we present new results on these subjects.We have applied the Sagnier's method in order to get a new theory of the motions and we describe here the second approximation which leads to a third order solution. In this solution appear coupled terms in longitude of the perijoves and longitudes of the nodes. The de Haerdtl's inequalities, which come from the 3-7 commensurability between satellites 3 and 4 are included in this solution. These developments, first computed by de Heardtl, have been improved by Lieske (1973). In our solution we introduce the use of the variables in inclination, and some new terms appear.In order to get the best precision for the final ephemerides, the accuracy of the observations have to be improved: best results may be obtained with the use of the observations of mutual events. Simulations have shown the interest to take into account the variations of the albedo as a function of geographic longitudes and latitudes on the satellites themselves. So, the theoretical flux of light is closer to the observed one and the accuracy is improved. In 1985, mutual events occur and we have organized a campaign in order to obtain results of high precision.
Relativistic effects in geodynamics
Authors: Boucher C. 
Published: June 2019

Geodesy has now reached such an accuracy in both measuring and modelling that time variations of the size, shape and gravity field of the Earth must be basically considered under the name of Geodynamics. The objective is therefore the description of point positions and gravity field functions in a terrestrial reference frame, together with their time variations.For this purpose, relativistic effects must be taken into account in models. Currently viable theories of gravitation such as Einstein's General Relativity can be expressed in the solar system into the parametrized post-newtonian (PPN) formalism. Basic problems such as the motion of a test particle give a satisfactory answer to the relativistic modelling in Geodynamics.The relativistic effects occur in the definition of a terrestrial reference frame and gravity field. They also appear widely into terrestrial (gravimetry, inertial techniques) and space (satellite laser, Lunar laser, VLBI, satellite radioelectric tracking …) measurements.
Inertial modes trapped in the solar convective envelope
Authors: Dziembowski W. , Kosovichev A. , Kozlowski. M. 
Published: June 2019

Due to their efficient trapping in the outer layers such modes may reach observable amplitudes of the order of 1–10 m/s, even if their energies are as those of the “five minute” oscillations. The modes that are most likely to be seen correspond to the lowest radial orders.The paper will be published in Acta Astronomica.
The effect of toroidal magnetic fields in the overshoot layer on the eigenfrequencies of stellar oscillations
Authors: Belvedere Gaetano 
Published: June 2019

The overshoot layer in stellar convection zones is slightly subadiabatic and can be considered as a stable region for storage of magnetic flux. Belvedere, Pidatella and Stix (1986) estimated the size of the overshoot layer and computed the magnetic field strength, beyond which toroidal flux tubes become unstable to buoyancy, for a number of main sequence spectral types ranging from F5 to K0. Here we estimate the relative frequency perturbation of high order acoustic modes due to the presence of a non-oblique axisymmetric magnetic field in the overshoot layer. We find that increases with the advancing spectral type, the predicted frequency splitting being large enough to be detected by observations, at least for the Sun.We conclude that magnetic field induced frequency splitting of high order acoustic modes may well be due to a toroidal field of relatively moderate strength just beneath the bottom of the convection zone.
Evidence for global pressure oscillations in Procyon and α Centauri
Authors: Gellt B. , Grec G. , Fossat E. 
Published: June 2019

Helioseismology bas proved to be a powerful tool to probe the internal structure of the sun. With a new adapted optical resonance spectrophotometer, an extension has been attempted to two bright stars, namely α Centauri Å and Procyon. Results obtained from two observing runs on α Centauri Å in May 1983 and May 1984 at La Silla, and one observing run on Procyon in February 1984 at Hawaii are presented. In both cases, solar-like pressure oscillations have been detected. The complete analysis is presented, which leads to determine essentially five parameters: the frequency range, the amplitudes, the mean equidistance Δν, the departure around this equidistance (curvature of the echelle-diagram) and the fine frequency spacing between modes of degree 0 and 2. For Procyon, all results are consistent with theoretical predictions, including excitation of oscillations, mass, radius, and age of the star. For α Centauri, all the results are consistent together and are confirmed by the 1984 observations. They suggest that α Cen might be younger than estimated, consistent with a zero age main sequence star.This is the abstract of a paper recently published in Astronomy and Astrophysics. We have selected here under some parts of this paper. For more detail, it is recommended to refer to this journal.
Overview of the conference: implications of seismological data for astrophysics
Authors: Cox Arthur N. 
Published: June 2019

This review of the conference will necessarily consider the seismological data implications for only stellar astrophysics. While there are some aspects of this conference that interface with subjects like relativity, gravity, stellar systems, studies of chaos, etc., these will not be discussed here. What we are doing here is discussing the interiors of stars. We want to learn about their masses and composition structures. Pulsation periods can be used to measure stellar mean densities. Further details that seem accessible are the solar rotation speed versus depth and latitude and the structure of both solar and stellar atmospheres.Most of the contributions at this conference dealt with the hard problems of our understanding oscillations of the sun. As we shall see in many cases, the problems in understanding the stars by observing their pulsation periods are even more difficult. Similarities and differences between helioseismology and asteroseismology will be a principal theme of this review.
Results from Space
Authors: Heap Sara R. 
Published: June 2019

Space astronomy has made major and ever increasing contributions to planetary nebula research. Three astronomical satellites – Rosat, Hubble, and EUVE – have been launched since our last meeting five years ago. In addition, SpaceLab experiments flying on the NASA Shuttle have now observed a planetary nebula. After fourteen years, the IUE satellite is still going strong, and IRAS data continue to provide new results on planetaries and their antecedents.With such a large volume of space data and a broad range in research topics, it is impossible to describe all the results from these instruments. Fortunately, other reviews at this conference by Perinotto (IUE observations of stellar winds) and Zhang (broadband flux distributions) will cover some of these topics. I will limit this review to five topics: (1) the first far-UV spectrum of a planetary, (2) new observations concerning the interaction of a stellar wind and the nebula, (3) the first high-resolution pictures of planetaries made by Hubble, (4) new observational evidence on the masses of planetary nuclei, and (5) recent advances in UV spectroscopy of central stars.
The Southern Deep Near Infrared Survey (DENIS) a Prospect of PN Exploration
Authors: Kimeswenger Stefan , Kienel Christoph 
Published: June 2019

The near infrared light is important for the exploration of proto-planetary nebulae as well as for the planetary nebulae in early phases (Persi et. al. 1986, in Planetary and Proto-Planetary Nebulae: From IRAS to ISO, ed A. P. Martinez). Numerous work on the fluxes of the well known planetary nebulae was already done in the late 80's, but a sky survey will give a large sample of data to provide more detailed statistics.The present work presents an overview of the data on planetary nebulae expected from the European project of a deep near infrared survey of the southern sky (denis) (IAP and DESPA Paris, Heidelberg, Leiden, IAC Tenerife, Grenoble, Lyon, Frascati, Innsbruck, Vienna) in the I, J and K band with a limiting magnitude of 14.5 to 15 for point sources and 17 mag arcsec−1 for the surface brightness. The angular resolution for identification of non–point source objects will be about 5″.
Star formation: relationship between the maser species
Authors: Caswell Jim L. 
Published: June 2019

Masers in Star Formation Regions arise chiefly from the molecules of methanol, hydroxyl, and water; in the case of methanol and hydroxyl, masing transitions are numerous. Exploring the relationship between the maser species (and their relationship to any associated ultracompact HII region detectable at radio wavelengths) can be made at two levels: first, at the general level, assessing whether the occurrence together of some species, and the absence of others, reveals significant properties of the site as a whole; second, at a deeper level, to assess whether the masing spots are coincident in both velocity and space.The first may be used as a diagnostic of the evolutionary state of the embedded young massive star. The second reveals physical conditions.New studies relevant to these issues are discussed here. Substantial unbiased surveys of the major masing transitions are especially valuable in allowing a more effective interpretation of existing targeted observations.
Sydney Work on 21-cm Observations of the HI Galactic Disk
Authors: Kerr F. J. 
Published: June 2019

This paper reports briefly on the provisional results of the 21-cm galactic work at the Radiophysics Laboratory, Sydney. Observations were made with a 36-ft, transit-type radio-telescope whose beam width at half-power is 1°.5 and a 4-channel receiver whose band width, 40 kcps, is equivalent to 8 km/sec.The large scale structure of the galaxy has been studied by Kerr, Hindman, and Carpenter. They derive a general picture of the spiral structure in the southern hemisphere extending the Leiden results (see Fig. 1) and, in addition, a “relief map” of the galaxy showing the location of the densest parts of the hydrogen layer with respect to a central plane (see Fig. 2). Analysis of the spiral structure is for the present limited to regions beyond 3 kpc from the center. The Sydney and Leiden data agree well where they overlap, but location of spiral arms is sensitive to the choice of rotational model. Four or five spiral arms, or sections of arms, are indicated in the longitude interval l= 170° to l= 320°. The arms are clearly trailing in the rotation.
Validity of the Cloud Model of the Interstellar Medium
Authors: Donn Bertram 
Published: June 2019

Because of the extreme irregularity in distribution of interstellar matter, some idealized model must be adopted in discussing the interstellar medium. Three simple models have been considered. The original one, long-since discarded, was a uniform distribution. This has been largely replaced by the random cloud picture in which space is visualized as filled with isolated clouds, 5–10 per kpc, about 10 pc in diameter, the array having an exponential velocity distribution with a mean of about 8 km/sec. Lastly, there is a turbulent or a random density fluctuation model.Although the random cloud hypothesis has received most attenuation from astronomers, it has been well recognized that it is an over simplified model and should be used with some caution. This point of view has been clearly stated by many workers in this field, as the following statements by Oort and by Minkowski, respectively, demonstrate.
Microstructure of the Galactic Magnetic Field
Authors: Serkowski K. 
Published: June 2019

The polarization of the stars in open clusters, explained on the basis of the Davis-Greenstein theory, gives some information on the microstructure of the galactic magnetic field.The polarization is most conveniently described by the parameters Q, U, proportional to the Stokes parameters and defined by

where p is the amount of polarization, θ is the position angle of the electric vector, and θ̄ is the mean value of θ for the region under consideration.
Internal Motions in the Orion Nebula
Authors: Münch G. 
Published: June 2019

In the first and second Symposia of this series von Weizsäcker and von Hoerner discussed the problem of turbulence in the Orion Nebula, while in the second Symposium Courtès has further treated the problem. Von Hoerner has presented a detailed discussion of the methodologies of the treatment. It was suggested that the observed variations in radial velocity in the nebula are consistent with the predictions of the Kolmogoroff equilibrium theory of turbulence, which is valid at sufficiently high Reynolds numbers. However, their results to some extent were inconclusive, mainly because the observations which they analyzed were not sufficiently numerous and accurate. With the purpose of reanalyzing the whole problem, Dr. O. C. Wilson and I undertook the task of determining radial velocities and profiles of selected emission lines in the spectrum of the nebula, using the largest practical resolving power in angle and frequency available with the 200-in. telescope. In order to use advantageously the efficiency of the instrument, we have photographed the brighter parts of the nebula (roughly subtending a solid angle of about 6′ aperture) with the Coudé spectrograph fitted with 31 parallel entrance slits, which are separated from each other by a distance of 1 mm in the focal plane or 1″.3 in the sky. In this manner we obtain in one exposure the spectrum of an area about 40″X40″ with a dispersion such that 1 μ = 0.27 km/sec. In each of these plates about 600 Doppler shifts of the lines [OII] λ3726, Hγ, and [OII] λ5007 have been measured, each of which represents some average value (not necessarily the same for the three lines) of the velocities of nebular matter along the line of sight. Altogether we have about 50 000 radial velocities measured. The accuracy with which a radial velocity may be determined is set by the intrinsic shape of the lines, which reflects the distribution of velocities along the line of sight. To give an idea of the orders of magnitude of the quantities involved, I may mention here that typical values of the mean widths h at half-intensity of the hydrogen, [OIII], and Fe—comparison lines are h(H) = 28.6 km/sec, h(OIII) = 20.0 km/sec, h(Fe) = 8.3 km/sec. The bisection of a line with a cross wire to an accuracy around 0.5 km/sec is thus feasible; repeated measurements have, indeed, shown such precision. On the assumption that the profiles to which the above widths correspond are Gaussian, we may easily disentangle the thermal and turbulent components of the mean square radial velocities, through the dependence on atomic weight of the former. We find from the representative values given aboveThe corresponding kinetic temperature is 9700°K, in close agreement with the value of the electron temperature determined by other methods.
The Observational Evidence
Authors: Eggen O. J. 
Published: June 2019

The domain in the (U, V) plane of old-disk-population stars is defined by a sample of F- and G-type stars brighter than visual magnitude 6.5 for which luminosities are available from intermediate-band photometry. The majority of these old-disk stars avoid the domain of the young-disk population in the (U, V) plane except for (1) several objects with V near − 17 km s–1 and (2) a half dozen possible members of a solar group. The sample of stars used to define the old-disk population is confined to distances less than 100 parsec from the Sun and those with V near − 17 km s–1 may represent several generations of the objects formed in what is now the solar neighbourhood and which keep returning to this neighbourhood because they are isoperiodic (V near − 17 km s–1) with the local standard of rest. The half dozen possible members of a solar group indicate an evolutionary age of some 5 × 109 yr. In addition to some of the previously recognized stellar groups in the old-disk population (e.g. Wolf 630 and ζ Her), a new group with U = +40 to 50 km s–1 and V = −36 km s–1 is also discussed. The sample of red giants: (VE≤5m.0 and (R–I)0 > + 0m.42) contains eight probable members of the halo population of which five are members of the Arcturus group. Possible structure in the old-disk-population giant sequence is discussed on the basis of published narrow-band indices, and the luminosity functions of the old- and the young-disk-population red giants are compared.Most of the material presented can be found in Eggen, O. J.: 1973, Publ. Astron. Soc. Pacific85, 542.
Recent Studies of the Brightest Stars in the Magellanic Clouds
Authors: Osmer Patrick S. 
Published: June 2019

The objective prism surveys carried out by Sanduleak (1968, 1969) make available for the first time a relatively complete and homogeneous list of the brightest stars in both Magellanic Clouds for the range of spectral types O–G5. Photometric observations in the four color, Hβ system of the 169 candidates in the SMC and the 45 brightest stars in the LMC as well as spectroscopic observations of the most luminous early-type stars, lead to the following picture of the stability and evolution of very massive stars:
(1)The reddening is the same for the most luminous stars in both Clouds and there is a sharply defined upper limit to the stellar luminosity, which is also the same in both Clouds. This limit corresponds to Mbol = −11 ± 1 or 90 in good agreement with the classic study of Feast et al. (1960).(2)The stars of highest total luminosity are the blue supergiants, and in both Clouds the high temperature limit corresponds to type B1.5 or Te ~ 25000 K for Mv ~ −8. The SMC appears to be deficient in luminous F5–G5 supergiants.(3)With few exceptions the most luminous stars are not known to show more than low amplitude variations in light. They do show Hβ emission as expected, and four stars in the LMC have anomalously strong emission, indicative of unusual atmospheric activity. Bright Wolf-Rayet stars have long been known in the Clouds; in addition, several candidate Of stars are indicated by the photometry.(4)The brightest B-type supergiants in the SMC appear to be deficient in N, Si, O, and probably Mg and C, although helium is normal, a result worth pursuing in the less luminous stars.(5)Judging from the numbers of the brightest stars, the recent rate of star formation in both galaxies per unit mass is quite similar despite the fact that the SMC has a larger fraction of neutral hydrogen and the LMC a more conspicuous display of Hii regions.