bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heterodyne Interferometry in the Infrared
Authors: Townes C.H. , Bester M. , Danchi W.C. , Degiacomi C.G. , Greenhill L.J. 
Published: July 2016

The University of California Infrared Spatial Interferometer (ISI) for the 10 μm wavelength region is briefly described along with results obtained on prominent stars and on atmospheric phenomena. The system has two movable telescopes of 1.65 m aperture. It operates in principle like a modern radio interferometer, using heterodyne detection, CO2 laser local oscillators, RF delay lines, and lobe rotation to maintain a fixed-frequency fringe rate.Rather extensive measurements have been made on atmospheric pathlength or phase fluctuation characteristics which show substantial deviations from the Kolmogorov-Taylor model, fortunately in a direction favoring adaptive optics, long baselines, and the use of infrared wavelengths. Outer scales as small as about 10 meters occur under good seeing conditions. Visibility results on 13 stars show that 6 of them have dust shells rather far from the star and give evidence for episodic emission of gas. Others of the 13 stars also vary with time, but are characterized by more continuous emission and dust formation near the stars at temperatures as high as 1300 K.
Mass Measurement of Accreting Magnetic White Dwarfs with Hard X-Ray Spectroscopy
Authors: Ishida M. , Fujimoto R. 
Published: July 2016

Accreting magnetic white dwarfs are usually found as component stars in Magnetic Cataclysmic Variables (MCVs), in which a white dwarf with B = 105-8 G accepts mass from a late type (secondary) star via Roche Lobe overflow. Matter from the secondary is funneled by the magnetic field and concentrates on the magnetic pole(s) of the white dwarf. Since the accretion flow becomes highly supersonic, a standing shock wave is formed close to the white dwarf. The temperature of the plasma at the shock front reflects the gravitational potential and can be denoted as a function of the mass (M) and the radius (R) of the white dwarf as:
Note here that the height of the shock is expected to be within 10% of the white dwarf radius, and hence neglected here.
The Hipparcos results
Authors: Turon C. 
Published: July 2016

After a brief presentation of the Hipparcos mission, and an overview of the astrometric and photometric results obtained from the main mission and from Tycho, more details are given on the parallaxes. Absolute parallaxes have been obtained for 117 955 entries of the Hipparcos Catalogue, out of a total of 118 218, with a median precision of 0.97 mas for stars brighter than 9. This precision varies with apparent magnitude and ecliptic latitude. The estimated systematic error is smaller than 0.1 mas. The distances of more than 20 000 stars are determined to better than 10 %. Some more statistics are presented.A few applications of this fantastic amount of new and accurate data are presented, in the fields of absolute magnitude calibrations, stellar physics, distance scale determination.
The Mpifr Radio Continuum Surveys and Their WWW Distribution
Authors: Fürst E. , Reich W. , Reich P. , Uyaniker B. , Wielebinski R. 
Published: July 2016

The observation of an area of 120° × 56° centered on RA=8h DEC=20° at 408 MHz was the first astronomical use of the MPIfR 100-m telescope (1970) and was designed to compile a complete sky survey using also data from Jodrell Bank and Parkes (Haslam et al., 1982). The observation of the northern sky at 1420 MHz started in 1972 using the Stockert 25-m telescope and was finished in 1976 (Reich and Reich 1986). This survey has been completed to an all sky survey using data from Villa Elisa (Argentina). The two surveys are absolutely calibrated. The angular resolutions are 0.8° and 0.59°, respectively. A number of surveys of the Galactic plane have been made with the 100-m telescope at arc minute angular resolution. Surveys at 2695 MHz (|b| ≤ 5°) (Reich et al. 1990, Fürst et al. 1990) and at 1410 MHz (|b| < 4°) (Reich et al. 1990) are public.At medium Galactic latitudes (up to |b| = 20°) the emission consists mainly of faint extended ridges or arcs superimposed on the still dominating, about 10 times stronger, diffuse Galactic emission. They have never been investigated in a systematic way although they provide important clues for the understanding of the “disk-halo connection”. This region is covered by new observations at 1400 MHz with the 100-m telescope.
Solar Surface Magnetoconvection
Authors: Stein Robert F. , Nordlund Åke 
Published: July 2016

Magnetoconvection simulations on meso-granule and granule scales near the solar surface are used to study small scale dynamo activity, the emergence and disappearance of magnetic flux tubes, and the formation and evolution of micropores.From weak seed fields, convective motions produce highly intermittent magnetic fields in the intergranular lanes which collect over the boundaries of the underlying meso-granular scale cells. Instances of both emerging magnetic flux loops and magnetic flux disappearing from the surface occur in the simulations. We show an example of a flux tube collapsing to kG field strength and discuss how the nature of flux disappearance can be investigated. Observed Stokes profiles of small magnetic structures are severely distorted by telescope diffraction and seeing.Because of the strong stratification, there is little recycling of plasma and field in the surface layers. Recycling instead occurs by exchange with the deep layers of the convection zone. Plasma and field from the surface descend through the convection zone and rise again toward the surface. Because only a tiny fraction of plasma rising up from deep in the convection zone reaches the surface due to mass conservation, little of the magnetic energy resides in the near surface layers. Thus the dynamo acting on weak incoherent fields is global, rather than a local surface dynamo.
Galaxy Haloes and the Missing Mass Problem
Authors: van den Bergh Sidney 
Published: July 2016

Available evidence on the mass-to-light ratios in binary galaxies, small clusters and in rich clusters is reviewed. The interpretation of the binary data remains ambiguous. The relative velocity of M81 and M82 implies thatm/LV> 12. The Local Group data also appear to favour the existence of some hidden mass associated with M31 and the Galaxy. In the Virgo cluster a significant fraction of the virial mass may be concentrated in the halo of M87. In Coma the missing mass was probably stripped from the haloes of the two dominant E galaxies and is now distributed throughout the cluster.It is suggested that metal-poor stars in the galactic disc have a higher CNO abundance than do halo stars of similar metallicity. This may explain why globular cluster stars lie on taller red giant branches than do moderately high-velocity stars near the Sun. The dominant old red giant population in the disc of M31 appears to be similar to that in the Galaxy. Most of the red giants in M33, NGC 6822 and in the LMC lie on taller red giant branches than do those in the Galaxy and M31. This suggests that old evolved stars in these relatively low-luminosity galaxies have a lower heavy element abundance than do their counterparts in the galactic disc. The red giants in M32 appear to be intermediate between those in M31 and M33. This supports the idea that M32 was once much more luminous than it is at present.
Absolute Magnitudes by Statistical Parallaxes
Authors: Heck André 
Published: July 2016

Our algorithm for stellar luminosity calibrations (based on the principle of maximum likelihood) allows the calibration of relations of the type:Where n is the size of the sample at hand,Mi, are the individual absolute magnitudes,Cijare observational quantities (j = 1, …, N), andqjare the coefficients to be determined.If we put N = 1 and CiN= 1, we havethe mean absolute magnitude of the sample. As additional output, the algorithm provides us also with the dispersion in magnitude of the sample σM, the mean solar motion (U, V, W) and the corresponding velocity ellipsoid (σu, σV, σw).
Fundamental Parameters and the Helium Content of Eclipsing Spectroscopic Binaries
Authors: Jørgensen H.E. 
Published: July 2016

Today we know accurate masses, radii, surface gravities and luminosities or effective temperatures of a very small number of stars. There are several reasons for deriving accurate parameters of stars. I shall mention only four problems:(i)checking stellar evolution calculations, particularly calculations of isochrones, using binaries,(ii)derivation of helium content in stars of different age,(iii)checking log g derived from photometry and stellar atmosphere calculations,(iv)determination of accurate positions in the HR diagram to get an independent check on calibrations of photometric systems.
Quasar Surveys
Authors: Smith M. G. 
Published: July 2016

A review is given of progress in surveys for quasars at frequencies from radio to x-ray. Radio results show evidence for a decline in the radio luminosity function for flat-spectrum radio sources at redshifts z > 2. The IRAS survey is uncovering hitherto unknown dusty Seyfert galaxies. Optical surveys, which yield the largest number of QSOs per square degree, may suffer from selection effects which depend on intrinsic luminosity, redshift, and spectral evolution - particularly above redshift 2. Below redshifts of about 2.3, the optical magnitude-redshift plane is being filled in to the point where the evolution of the luminosity function can be seen directly. The statistics of quasar pair separations provide the best evidence so far for quasar clustering.The existence of many potentially significant selection effects means that a multi-frequency approach to quasar surveys is likely to prove essential to an understanding of the evolutionary behaviour of the quasar population as a whole.
On the QSO Content of the First Byurakan Survey and the Completeness of the Palomar Green Survey
Authors: Véron P. , Mickaelian A.M. , Gonçalves A.C. , Véron-Cetty M.P. 
Published: July 2016

The second part of the First Byurakan Survey is aimed at detecting all bright (B < 16.5) UV-excess starlike objects in a large area of the sky. By comparison with major X-ray and radio surveys we tentatively identified as QSOs 11 FBS objects. We made spectroscopic observations of nine of them. We found six new QSOs bringing the total number of known QSOs in this survey to 42.By comparison with the Palomar Green (PG) QSO survey, we found that the completeness of this last survey is of the order of 70% rather than 30–50% as suggested by several authors.
Are There Quasars at Non-Cosmological Distances?
Authors: Harutyunian Haik A. 
Published: July 2016

In Dravskikh & Dravskikh (1996) the results of a statistical analysis of quasar luminosity as a function of redshift, if it is assumed to be cosmological, are given (see Fig.1). Three quasar samples were analyzed separately:
•quasars with absorption lines;•quasars associated with galaxies or association-quasars not having absorption lines (from Burbidge et al. 1996);•other quasars not included in the first two groups.
Hard X-ray Spectrum of the Above-the-Looptop Source in Impulsive Solar Flares
Authors: Masuda S. 
Published: July 2016

Extended AbstractThe Hard X-ray Telescope (HXT: Kosugi et al. 1991) onboard Yohkoh has observed that, in impulsive solar flares, a hard X-ray source is located above the apex of a soft X-ray flaring loop, in addition to double footpoint sources (Masuda et al. 1994, 1995). This observation suggests that flare energy-release, probably magnetic reconnection, takes place not in the soft X-ray loop but above the loop. It is important to derive the hard X-ray spectrum of the above-the-looptop source accurately in order to understand how electrons are energized there. The above-the-looptop source was most clearly observed during the 13 January 1992 flare. However, the count rate, especially in the H-band (53–93 keV), is too small to synthesize high-quality images and to derive an accurate spectrum.
Excitation of H2 and HD in Shocks and PDRs
Authors: Bertoldi F. , Draine B. T. , Rosenthal D. , Timmermann R. , Howat S. K. Ramsay , Geballe T. , Feuchtgruber H. , Drapatz S. 
Published: July 2016

Photodissociation regions (PDRs) and shocks give rise to conspicuous emission from rotationally and vibrationally excited molecular hydrogen. This line emission has now been studied with ISO and from the ground in great detail. A remarkable discovery has been that toward the Orion outflow and other shock-excited regions, the H2 level populations show a very high excitation component. We suggest that these high-excitation populations may arise from non-thermal pumping processes, such as H2 formation and high-velocity ion-molecule collision in partially dissociative shocks. In PDRs such as NGC 7023 however, formation pumping is always less important than fluorescent pumping.We furthermore present two HD emission line detections toward Orion Peak 1. This enables the first comparison of the H2 and the HD excitation, which surprisingly turn out to be identical.
Measurements of The Primordial D/H Abundance Towards Quasars
Authors: Tytler David , O'Meara John M. , Suzuki Nao , Lubin Dan , Burles Scott , Kirkman David 
Published: July 2016

Big Bang Nucleosynthesis (BBN) is the synthesis of the light nuclei, Deuterium (D or 2H), 3He, 4He and 7Li during the first few minutes of the universe. In this review we concentrate on recent data which give the primordial deuterium (D) abundance.We have measured the primordial D/H in gas with very nearly primordial abundances. We use the Lyman series absorption lines seen in the spectra of quasars. We have measured D/H towards three QSOs, while a fourth gives a consistent upper limit. All QSO spectra are consistent with a single value for D/H: 3.325+0.22−0.25X10−5. From about 1994 − 1996, there was much discussion of the possibility that some QSOs show much higher D/H, but the best such example was shown to be contaminated by H, and no other no convincing examples have been found. Since high D/H should be much easier to detect, and hence it must be extremely rare or non-existent.The new D/H measurements give the most accurate value for the baryon to photon ratio, η, and hence the cosmological baryon density: ωb = 0.0190 ± 0.0009 (1σ) A similar density is required to explain the amount of Lyα absorption from neutral Hydrogen in the intergalactic medium (IGM) at redshift z ≃ 3, and to explain the fraction of baryons in local clusters of galaxies. The D/H measurements lead to predictions for the abundances of the other light nuclei, which generally agree with measurements. The remaining differences with some measurements can be explained by a combination of measurement and analysis errors or changes in the abundances after BBN. The measurements do not require physics beyond the standard BBN model. Instead, the agreement between the abundances is used to limit the non-standard physics.
The Origin of Continuum Emission in Active Galactic Nuclei
Authors: Bregman Joel N. 
Published: July 2016

The general understanding of the continuum emission from AGN has changed from the picture where nonthermal processes were responsible for all of the emission. The current body of observation indicates that there are two types of objects, one being the blazar class (or blazar component), where nearly all of the emission is nonthermal, due primarily to synchrotron and inverse Compton emission. Variability studies indicate that the emitting region decreases with size from the radio through the X-ray region, where the size of the X-ray region is of order a light hour. More than two dozen of these radio-loud AGNs have been detected at GeV energies (one source at TeV energies), for which the radiation mechanism may be inverse Compton mechanism.In the other class, the radio-quiet AGN (component), the emission is almost entirely thermal, with radiation from dust dominating the near infrared to submillimeter region. The optical to soft X-ray emission is often ascribed to black body emission from an opaque accretion disk, but variability studies may not be consistent with expectations. Another attractive model has free-free emission being responsible for the optical to soft X-ray emission. The highest frequencies at which these AGN are detected is the MeV range, and these data should help to determine if this emission is produced in a scattering atmosphere, such as that around an accretion disk, or by another model involving an opaque pair plasma.
ROSAT Observations of Active Galactic Nuclei
Authors: Brinkmann W. 
Published: July 2016

The large number of Active Galactive Nuclei detected for the first time through their X-ray emission in the ROSAT All Sky Survey as well as the first measurements of the X-ray emission of many previously known AGN provide a new unprecedented large basis for the statistical and morphological exploration of these objects.The soft energy range of the X-Ray Telescope, the good energy resolution of the PSPC detector, and the high sensitivity of the instrument further allows an investigation of the spectral properties of sources in this energetically important energy band.A short overview is given of the actual ongoing research concentrating on the study of the soft X-ray class properties of the various types of AGN.
Review of GRANAT Observations of AGNs
Authors: Churazov E. , Gilfanov M. , Finoguenov A. , Sunyaev R. , Chernyakova M. , Apalkov Yu. , Grebenev S. , Lagunov I. , Jourdain E. , Roques J.P. , Mandrou P. , Bouchet L. , Ballet J. , Claret A. , Laurent P. , Lebrun F. 
Published: July 2016

Brief review of AGNs observations in the X-ray / soft gamma-ray bands with the orbital observatory GRANAT is presented.For three well known bright objects (3C273, NGC4151 and Cen A) broad band (3 keV–few hundreds keV) spectra have been obtained. Imaging capabilities allowed accurate (several arcminutes) identification of these objects with sources of hard X-rays.The spectrum of NGC4151 above ≈ 50 keV was found to be much steeper than that in most of the previous observations, while in standard X-ray band the spectrum agrees with observed previously. The comparison of the observed spectra with that of the X-Ray Background (XRB) indicates that sources similar to NGC4151 could reproduce the shape of XRB spectrum in 3–60 keV band.Cen A was observed in the very low state during most of observations in 1990–1993, except for two observations in 1991. The variability of the hard X-ray flux has been detected on the time scales of several days.
The Soft X-ray Excesses Observed by ROSAT
Authors: Walter R. , Fink H.H. 
Published: July 2016

The properties of the soft X-ray excesses of bright Seyfert 1 galaxies and Quasars are described using the observations obtained with the PSPC (0.1–2.4 keV) detector of the XRT telescope aboard ROSAT during the ROSAT all sky survey (RASS). The sample consists of 58 Seyfert 1 type AGN detected with more than 300 counts during the RASS and observed at least once with IUE.The soft X-ray photon indices of our sample members range from 1.6 to 3.4 in a wide distribution (< Γ > = 2.50, σ = 0.48). The width of the distribution is considerably larger than the mean statistical uncertainty on the individual spectral slopes (σ = 0.33). Excepting for IC 4329A and Mrk 766, the mean contribution of absorbing cold matter intrinsic to the Seyfert galaxies of our sample to the absorbing column density is less than 1020cm−2. In IC 4329A and Mrk 766 intrinsic absorbtion is observed at soft X-ray. Both sources are also strongly reddened by dust.An excess of soft X-ray flux is detected in 90% of the sources above the exptrapolation of the hard X-ray power law. It can be shown that the PSPC spectral slope is a measure of the strength of the soft X-ray excess. If the reddened sources are excluded, a correlation appears between the strength of the ultraviolet blue bump and the soft X-ray photon index (figure 1). The ratio of the ultraviolet to infrared fluxes and the ultraviolet spectral slope are also related to the strength of the blue bump. The observations are compatible with a model where most of the spectral variations arising among the sources studied are driven by the strength of the bump component, which varies by a factor of 100 from object to object. A bump model consisting of a power law with a high energy cutoff at 80 eV can fit most of the sources. In any case, the spectral energy distribution of the ultraviolet to soft X-ray bump is characterised by vFv(1375 Å) = (1–5) ∫ε > 150eVFεdε.
The Nuclear Region of the Sbc Spiral Galaxy NGC 5055: A Mildly Active Nucleus
Authors: Pişmiş P. , Manteiga M. , Mampaso A. , Recillas-Cruz E. , Cruz-Gonzàlez G. 
Published: July 2016

NGC 5055 is one of a list of nearby large spiral galaxies we have selected for a morphological and kinematic study of their bulges. CCD images are obtained at various spectral bands and in the Hα line using the 2.1 m reflector at San Pedro Martir observatory in México, while long-slit spectra at four different PA's are secured with the IDS spectrograph of the Isaac Newton Telescope of the observatory Roque de los Muchachos at La Palma, Spain. Some of the galaxies on our list for which observations are already performed are, aside from NGC 5055, NGC 3351, 4314, 5383 and 5915. These galaxies are not known to have active nuclei. However, we believe that activity may be a common phenomenon spanning a wide range of energetics, from the most active quasars and radio-galaxies (with jets) down to the mildest cases like our Galaxy or M31. The latter may be designated as MAGN (mildly active galactic nuclei). These ideas are treated in a review by Pişmiş (1987, Rev. Mex. Astron. Astrof. 14). The MAGN are usually nearby, and hence offer the possibility to study them in sufficient detail. It is reasonable to expect that the physical phenomenon underlying activity in galactic nuclei is one and the same, and it is essentially the global parameters such as energy at the nucleus that give rise to the different classes of AGN. Thus by studying the nearby mildly active galaxies one can construct a physically acceptable model supported by observation; such model, based on firmer grounds, can then be applied to all AGN.NGC 5055 (Sbc) with an adopted distance of 8.2 Mpc has a very bright bulge with a tenuous multiple arm structure around it, extending to 8 arcmin. Our velocity field and morphology of NGC 5055 lead to the following conclusions.1. The galaxy presents a north-south asymmetry; the southern approaching side has its isophotes closer together than at the farther side. We adopt PA 101° for the line of nodes. Our long-slit spectra cover the position angles: 58°, 101°, 112° and 155°.2. The rotation curve shows a linear region around the nucleus. At PA 101°, the line of nodes, the amplitude is 270 km s−1 between points ±5 arcsec on either side of the nucleus.3. There is high concentration of mass at the nuclear region (the bulge of the galaxy). An estimate of the mass for the region where the rotation curve is linear ±5 arcsec, is 1.5 × 108 M⊙. Burbidge et al. (1960) give a total mass of 7.6 × 1010 M⊙. The bulge density is thus found to be 500 times the average density of this galaxy.Analysis of the general velocity field based on four long-slit spectra shows an asymmetry between the East and West sides, ±5 arcsec around the nucleus of NGC 5055, suggestive of the existence of non-circular motion. Indeed evidence is found of an outflow on the west side of the Galaxy within a cone emanating from the center towards the NW with a projected radial velocity of around 80 km s−1. Thus this galaxy shows activity at its center and is a candidate for the MAGN group.