bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multifrequency Polarization Variations in 0917+624
Authors: Qian S.J. , Kraus A. , Krichbaum T.P. , Witzel A. , Zensus J.A. 
Published: July 2016

AbstractIntraday variability in compact flat-spectrum radio sources has been intensively studied in recent years. For most IDV events the apparent brightness temperatures derived from the observed timescales are in the range of Tb,app ~ 1016−18 K. For extremely rapid variations, Tb,app can reach up to ~ 1021 K (e.g. Kedziora-Chudczer et al., 1997). Refractive interstellar scintillation may be the most likely extrinsic mechanism (Rickett et al., 1995; Qian, 1994a; Qian, 1994b). Especially for the case of extreme Tb,app (> 1018 K) RISS may be dominant (Dennet-Thorpe and de Bruyn, 2000). However, some IDV events with Tapp ~ 1017−18 K show evidence for an intrinsic origin e.g. the correlated radio-optical intraday variations observed in the BL Lac object 0716+714 (Wagner and Witzel, 1995, Qian et al, 1996). It seems important to distinguish between IDV which is a phenomenon intrinsic to the compact radio sources and IDV which is primarily due to RISS. Multifrequency polarization and VLB I observations would be most helpful (Gabuzda and Kochanev, 1997).
ISS of Polarized Compact Extragalactic Radio Sources
Authors: Rickett Barney 
Published: July 2016

AbstractIt is shown that the detailed inter-relations of the 8.6 GHz IDV in Stokes’ parameters I, Q and U of the quasar 0405-385, as quantified by their auto and cross correlations, can be successfully modelled by interstellar scintillation (ISS) of a double source with two components separated by about 10 micro-arcseconds. Though this is not a unique source model it confirms that ISS can explain quantitatively the rapid variations in both flux and linear polarization. Thus there is no evidence in support of an intrinsic component in the IDV.
VLA Observations of Angular Broadening Close to the Sun
Authors: Gothoskar Pradeep , Anantharamahaia K.R. , Desai Ketan , Rao A.P. 
Published: July 2016

AbstractWe present synthesis imaging of scatter-broadening of radio sources carried out using the Very Large Array (VLA) at six radio frequencies during the period of solar minimum. Three compact radio sources were observed from 2 to 16 solar radii around the sun. The data indicate highly anisotropic scattering. The scatter-broadening was estimated from the area of the scattered image and was found to be factor of two lower and orientation of magnetic fields was closer to the radial direction. Present observations confirm the variation of scatter-broadening with solar elongation.
Trying to Enlarge the Sky Coverage of the FAST
Authors: Wu Shengyin , Wang Shouguan , Mao Yukuan , Su Yan 
Published: July 2016

AbstractThe proposed FAST project is a novel giant spherical radio telescope, with active elements which form a temporary paraboloid to track radio objects in the sky. Efforts have been made to extend the limited sky coverage that is a characteristic disadvantage of Arecibo-style radio telescopes. Three measures under investigation are introduced in this paper. The expected performance of the telescope is described, and a brief comparison is made with some of the largest existing radio telescopes.
V652 Her: Evidence that White Dwarf Mergers Really do Happen
Authors: Jeffery C. Simon 
Published: July 2016

AbstractV652 Herculis is a pulsating B star with a mass of about 0.6 M⊙ and a luminosity of some 1000 L⊙. Its uniqueness is defined by a surface which is predominantly (99%) CNO-processed helium. Precise measurements of its pulsation properties have provided direct tests for stellar pulsation and evolution models. Simulations of the merger of two helium white dwarfs are very successful in explaining its origin.
Criterion for Dynamical Instability of Mass Transfer in Binary Evolution
Authors: Han Zhanwen , Podsiadlowski Philipp , Tout Christopher A. 
Published: July 2016

AbstractUsing Eggleton’s code, we performed a series of binary evolution calculations in order to investigate the criterion for dynamical instability of mass transfer in binaries. In these calculations, we took the donor’s mass on the zero-age main sequence (ZAMS) from 0.8 to 1.9 M⊙. For each mass, we systematically varied the mass of the core at the beginning of mass transfer and the mass of the companion star. We assumed that mass transfer was completely non-conservative and that all the mass that was lost from the system carried with it the orbital angular momentum of the accreting component. We found that the critical mass ratio, above which mass transfer is dynamically unstable, is from 1.1 to 1.3 in these red-giant binary systems.
TU Muscae and the Early-type Overcontact Binaries
Authors: Terrell Dirk 
Published: July 2016

AbstractA simultaneous photometric and spectroscopic analysis of the purported early-type overcontact binary TU Muscae is presented. With a well-behaved light curve and a mass ratio far from unity, if TU Mus is indeed an overcontact system, it presents an interesting challenge for 3-D stellar evolution codes, like the Djehuty code, that will be applied to early-type overcontact binaries. The analysis shows TU Mus is slightly overcontact and that a detailed treatment of the reflection effect is important for modeling the light curves.
V838 Monocerotis — a Newly Discovered, Very Peculiar, Slow Nova-Like Object
Authors: Rauch Thomas , Hauschildt Peter , Asplund Martin , Gredel R. , Käufl H.-U. , Kerber Florian , Rosa Michael , Starrfield Sumner G. , Wagner R. Mark , Williams Robert E. 
Published: July 2016

AbstractThe eruptive variable V838 Mon was discovered on Jan 6, 2002. Due to a subsequent phase of almost constant brightness and a spectral appearance which is unlike classical novae, speculations have been made about its nature. Either it was a very peculiar, slow nova defining a new class, an eruptive event in an evolved star as in the case of Sakurai’s Object but in a much earlier phase, or something completely different.
Strange New Magnetics from the Sloan Digital Sky Survey
Authors: Szkody Paula 
Published: July 2016

AbstractThe first two years of the Sloan Digital Sky Survey have discovered over 50 new cataclysmic variables, of which four are confirmed Polars, two others are likely candidates and several others are good candidates for Intermediate Polars or SW Sex stars. Several systems have unusual characteristics, including large amplitude, narrow cyclotron humps indicating a very low temperature shock on a cool white dwarf, or very deep eclipses. Although SDSS is finding a variety of systems, it is ideal for picking up the low mass transfer rate magnetic systems missed in X-ray surveys and in past optical surveys with brighter limits. Thus, it is providing us with a clearer picture of the range of conditions existing in magnetics CVs.
Two Types of X-ray Spectra in Cataclysmic Variables
Authors: Mukai K. , Kinkhabwala A. , Peterson J. R. , Kahn S. M. , Paerels F. 
Published: July 2016

AbstractWe present Chandra HETG spectra of seven cataclysmic variables, including four intermediate polars. We find that they divide unambiguously into two distinct types. Spectra of the first type (nonmagnetic systems and EX Hya) are remarkably well fit by a simple cooling flow model, which assumes only steady-state isobaric radiative cooling. The maximum temperature, kTmax, and the normalization, which provides a highly precise measurement of the accretion rate, are the only free parameters of this model. Spectra of the second type (the three other IPs) are grossly inconsistent with a cooling flow model. They instead exhibit a hard continuum, and show strong H-like and He-like ion emission but little Fe L-shell emission, which is consistent with expectations for line emission from a photoionized plasma. Using a simple photoionization model, we argue that the observed line emission for these sources can be driven entirely by the hard continuum. The physical significance of these two distinct types of X-ray spectra is also explored.
The Fe XXII I(11.92 Å)/I(11.77 Å) Density Diagnostic
Authors: Mauche Christopher W. , Liedahl Duane A. , Fournier Kevin B. 
Published: July 2016

AbstractUsing the Livermore X-ray Spectral Synthesizer, which calculates spectral models of highly charged ions based on HULLAC atomic data, we investigate the temperature, density, and photoexcitation dependence of the I(11.92 Å)/I(11.77 Å) line ratio of Fe XXII. Applied to the Chandra HETG spectrum of the intermediate polar EX Hya, we find that the electron density of its Te ≈ 12 MK plasma is orders of magnitude greater than that observed in the Sun or other late-type stars.
Spectroscopic and Photometric Observations of the Magnetic Cataclysmic Variable TX Col
Authors: Mhlahlo Nceba , Potter Stephen B. , Buckley David 
Published: July 2016

AbstractSimultaneous photometry and spectroscopy of the Intermediate Polar TX Col were obtained in order to investigate its accretion mode and dynamics. The spectroscopic and photometric power spectra of TX Col are observed to change on relatively short timescales. Spectroscopy reveals a dominant periodicity at the orbital period (5.69 hr) and a spin period of 1909 s in radial velocities, while line equivalent widths show a strong periodicity at the beat period (2106 s). It is the first time that the orbital period has been detected in optical wavelengths.
FUSE Results on Magnetic CVs: VV Pup, YY Dra, LS Peg and DW UMa
Authors: Szkody Paula , Hoard Donald W. , Linnell Albert P. , Long Knox , Schmidt Gary , Sion Edward M. 
Published: July 2016

AbstractIn Cycles 2 and 3, we obtained FUSE observations of the Polar VV Pup, and the IP/SW Sex stars YY Dra, LS Peg and DW UMa. The spectra show a wide range of line intensities and structure. The phase-resolved spectra in each case reveal interesting properties about the hot accretion zones.
Radiation-hydrodynamic Models of the Accretion Spots in Magnetic Cataclysmic Variables
Authors: Beuermann K. 
Published: July 2016

AbstractThe structure of the near-polar accretion spots on accreting magnetic white dwarfs has been studied theoretically and observationally in numerous papers over the last decade. Detailed treatments are available for the regime of low mass flux, usually termed the bombardment case, and for higher mass fluxes which create a strong shock standing above the photosphere of the white dwarf. No general treatment is so far available for the case of shocks buried deep in the photosphere. I review the theoretical foundations, present some applications of theory, and discuss in short the open questions which still need to be addressed.
Tomography of AM Her and QQ Vul
Authors: Staude A. , Schwope A. D. , Hedelt P. , Rau A. , Schwarz R. 
Published: July 2016

AbstractWe present optical high-resolution spectroscopy of AM Her and QQ Vul. Making use of indirect imaging techniques (Doppler and Roche tomography), we are able to make details visible, which a model of these systems has to be able to account for. Especially the emission line data cannot be explained by current models of polars.
On the Evolution of the Nova-like Variable AE Aquarii
Authors: Meintjes P. J. 
Published: July 2016

AbstractIt is shown here that the peculiar properties of AE Aqr can can be accounted for if the mass transfer from an evolved 0.7M⊙ secondary K4-5 star (qi ≈ 0.8, i.e. < 1) initiated when the orbital period of the binary was Porb,i ≈ 8.5 hours and the white dwarf period P*,i ≈ 1 hour. This resulted in a significant amount of orbital angular momentum being accreted by the white dwarf in an initial discless spin-up phase towards P* ≈ 0.1 Porb,i. This destabilized the mass transfer, resulting in a run-away mass transfer from the secondary that lasted for approximately 104 years, with the orbital period evolving to Porb ≈ 11 hours until a critical mass ratio of qcrit = 0.73 had been reached. In this phase the mass transfer from the secondary occurred at a rapid rate of approximately Ṁ2 ≈ 1020 g s-1, resulting in an accretion disc which spun-up the white dwarf to a period of approximately P* ≈ 33 s. For all q ≤ qcrit = 0.73 the mass transfer proceeded on the thermal time scale of the secondary star, i.e. at a much slower rate, resulting in the binary converging and forcing AE Aqr into the propeller phase. Applying stellar wind theory, this allow an estimate of the polar magnetic field of the secondary star, which is of the order of B° ≈ (1600 – 2000) G. It has been shown here that the duration of mass transfer phase q = qcrit → 0.67 (now) lasted for approximately tṀ2 ~ 107 years, similar to the spin-down time scale of the white dwarf, tsd = P*/P* ≈ 107 years. The propeller ejection of matter in the current phase results in the dissipation of mhd power of Lmhd ≈ 1034 erg s-1, probably channeled into mass ejection and non-thermal activity. This explains the non-thermal outbursts that are observed in radio wavelengths, and occasionally also in TeV energies, from AE Aqr.
Note About a New Evaluation of the Direct Perturbations of the Planets on the Moon’s Motion
Authors: Standaert D. 
Published: July 2016

The aim of this paper is to present the principal features of a new evaluation of the direct perturbations of the planets on the Moon’s motion. Using the method already published in Celestial Mechanics (Standaert, 1980), we compute “a first-order theory” aiming at an accuracy of the order of the meter for all periodic terms of period less than 3 500 years.From an external point of view, we mean by that:
a)keplerian orbits for the planets,b)the ELP-2000 solution of the Main Problem proposed by Mrs. Chapront (Chapront-Touzë, 1980),c)the first-order derivatives with respect to the constants of motion of the SALE theory of Henrard (Henrard, 1979).On the other hand, from an internal point of view, the computations include:
d)the development in Legendre polynomials not only to the first-order in (a/a'), but also the following ones (up to the sixth-order for Venus, for example),e)the contributions of the second-order in the Lie triangle,f)second-order contributions coming from the corrections of the mean motions due to the planetary action.
Comments on the Effect of Adopting New Precession and Equinox Corrections
Authors: Williams J. G. , Melbourne W. G. 
Published: July 2016

AbstractThe new astronomical constants being introduced for 1984 affect the derived values of UT1 and terrestrial longitudes differently for the space techniques than for the optical techniques. The new sidereal time equation has been defined to avoid a discontinuity in UT1 as obtained by the established techniques. However, this definition does introduce a discontinuity in both the terrestrial longitude system and the UT1 rate derived by the space techniques which have an inertial celestial reference frame rather than a stellar catalog frame. The use of consistent expressions for precession and Greenwich Mean Sidereal Time will not eliminate differences between the inertial and classical optical techniques. Only improvements in the accuracy of the precession constant and equinox offset and drift will bring about consistency. Improvements in the precession constant can be expected in the next few years. The inertial techniques will exhibit shifts in the derived UT1 rate and terrestrial longitude system with each change in the precession constant if Greenwich Mean Sidereal Time is referenced to the mean equinox of date, as is the present practice, but would be stable if the reference is a fixed equinox. The latter choice is recommended.
Determination of Coordinates for the Orroral Lunar Ranging Station
Authors: Morgan P. , King R.W. 
Published: July 2016

AbstractUsing models of the Earth-Moon system developed from analysis of 10 years of laser ranging observations from the McDonald Observatory, we have analyzed observations obtained by the Orroral Lunar Ranging Station since April 1978. Normal point residuals from many of the observations performed before April 1980 using a 20 ns, mi tiple-mode laser pulse are discreetly spaced, as multiples of 6 ns, and may have been corrupted by variations in pulse shape. Further evaluation is required before these observations are used in scientific analyses. Observations performed during the MERIT Short Campaign (August - October 1980) using a 6 ns, single-mode pulse are apparently reliable. Using 27 single photoelectron events, obtained on 7 nights during this period, we have estimated the coordinates of Orroral, with respect to McDonald, with uncertainties of 1-2 m in cylindrical radius and longitude and 5-10 m in z-axis distance.
VLBI Measurements of Radio Source Positions at Three U.S. Stations
Authors: Ye Shu-Hua 
Published: July 2016

AbstractResults of VLBI measurement of 14 radio source positions at three U.S. stations during the MERIT short campaign is presented. Comparisons with other solutions are given, together with the comparisons between several radio source catalogues.During the MERIT short campaign, several observatories cooperated in VLBI measurements organized jointly by the U.S. National Geodetic Survey (NGS) and the National Aeronautics and Space Administration (NASA). There were two 7-day observations arranged from Sept. 26 to Oct. 2 and from Oct. 16 to Oct. 22, with time span nearly 23 hours per day. Details of the observation and data reduction have been published elsewhere (1). This paper deals with radio source positions determined by three U.S. stations, the Haystack Observatory, the Harvard Radio Astronomy Station (HRAS) and the Owens Valley Radio Observatory (OVRO).
Expansion of the Disturbing Function by Factorization
Authors: Broucke R. , Presler W. 
Published: July 2016

AbstractWe present an expansion of the disturbing function for the third-body perturbations in the form , where ε is the ratio of semi-major axes (a/a’) and Xnm and Ynm depend only on the five elements e, i, ω, Ω, of the satellite while and depend on the corresponding elements of the perturbing body. Each one of the four functions X and Y is represented as a product of two factors as opposed to three factors in our previous publication of this subject (Broucke, 1981). We develop several relations for the construction of the X and Y-series. These series are relatively short and can be computed in advance and stored on magnetic tape, for instance.
Resource Sharing in the CSIRO Division of Radiophysics Library
Authors: Davies Jenny 
Published: July 2016

The CSIRO Divison of Radiophysics was established as the CSIRO Radiophysics Laboratory in 1939 to conduct radar research. After World War 2 experimental radar instruments were applied to the developing field of radio astronomy. Current areas of research for the Division, which is host to the new Australia Telescope (AT), are radio astronomy, antenna technology, satellite communications, signal processing and microelectronics.The AT has three observatory sites, all in New South Wales: six antennas near Narrabri, over 500 km from Sydney, the 27-year-old Parkes observatory, 350 km from Sydney, and one antenna near Coonabarabran, between Parkes and Narrabri. Most staff are located at the Division’s headquarters in Sydney, where the main library is also located, and small collections are maintained at the Parkes and Narrabri observatories.
Resource Sharing: Information Sharing
Authors: Motais de Narbonne Anne-Marie 
Published: July 2016

When we speak of resource sharing, we mostly mean document sharing through union catalogues, list exchanges, interlibrary loans, cooperative acquisition programs... Yet, the first and primary condition of the library network efficiency is information sharing.Libraries have been quite successful in this field for the last decades but, nowadays, new technology such as electronic mail or telefax offers unequaled facilities to set up and promote a permanent and world wide program of information exchanges liable to meet the increasing needs of punctual responses. From an eight year experience at Paris Observatory library which has been hosting the French national service CADIST [Centre d’acquisition et d’information scientifique et technique], we can assert that, outer demands of informations being at the same time useful information sources, such a quick answer service does participate to the improvement of the inner service efficiency.
Milestones of Information Exchange in Astronomy from Prehistory to the Present
Authors:   Magda Vargha Konkoly Observatory
Published: July 2016

“That tho’ a Man were admitted into Heaven to view the wonderful Fabrick of the World, and the Beauty of the Stars, yet what would be otherwise be Rapture and Extasie would be but a melancholy Amazement if he had not a Friend to communicate it to.”Attributed to Archytas by Christian HuygensThe Beginnigs. The origins of astronomy as a science can be traced back to the time when watchers of the sky first began to record the results of their observations and transmit them succeeding generations. The media used by these earliest astronomers were various, from great megalithic monuments like Stonehenge to the clay tablets of the Babylonian ephemerists and the papyrus rolls of the Egyptians.Even in Antiquity such records were the foundation for the advance of astronomical knowledge. Thus the Chaldean Tables of the Babylonian had a great influence on the development of Greek astronomy. And in 130 B.C. Hipparchus discovered the precession of the equinoxes by comparing his own observations with those of Timocharis a century and a half earlier. Later even Copernicus himself used the results of Timocharis, Ptolemy, and al-Battani.
Earth at Night: An Image of the Nighttime Earth Based on Cloud-Free Satellite Photographs
Authors: Sullivan Woodruff T. 
Published: July 2016

ABSTRACTAn image of the entire earth at nighttime is assembled for the first time. It consists of a mosaic of photographs, all taken at local midnight in the 400-1100 nm band, made by the Defense Meteorological Satellite Program over the period 1974-84. Photographs were selected for freedom from clouds, lack of moonlight, high sensitivity, and suitability to illustrate various temporal phenomena. The image primarily reveals activities of humankind such as urban street lighting, rangeland burning, slash-and-burn agriculture, natural gas burnoffs in oilfields, and squidding. Although light pollution in urban areas creates a striking map, at the same time it devastates astronomical observation and removes much of humankind from any familiarity with the night sky.
Pollution and Pollution Control in the Third World
Authors: Stock J. , Marin Z. 
Published: July 2016

ABSTRACTIn developing countries in Latin America, Asia, and Africa, light pollution takes a particular aspect due to the social and economical situation. The official reluctance to solve unpopular problems combined with a generalized ignorance create a hostile climate for any campaign in favor of astronomical observatories or amateur associations. The tropical climate makes most energy savings measures unnecessary. Obsolete industrial installations make the application of particle output control difficult or impossible. The most important contribution to air pollution, however, comes from forest fires, some of them as a cheap clearing method, others as an expressions of political discontent. To this must be added that most countries do not have yet a legislature which would permit the imposition of pollution control.