bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiation Hydrodynamics of the Broad Line Region in Seyfert Galaxies and Quasars
Authors: Mathews William G. 
Published: July 2016

The broad line region in quasars and in the nuclei of active galaxies is the site of remarkable hydrodynamic activity unprecedented elsewhere in the universe. Considerable theoretical effort has been directed to determine how this intense radiation is related to high velocity gas motions in these small regions, which, because of their great distances, cannot be resolved by direct observation. A better theoretical understanding of the nature of the broad line-emitting gas involves many novel aspects of radiation hydrodynamics and may eventually provide insights into the nature of the mysterious quasar phenomenon itself.Continuum and emission line properties of active galaxies and quasars are sufficiently similar that there is little doubt that both can be accounted for by a similar or closely related physical model. The main difference is one of luminosity; typical quasars are considerably brighter than Seyfert galaxies.In the discussion below the relevant observations of quasars and active galaxies are briefly reviewed with an emphasis on the physical properties of the line-emitting gas and its immediate environment. Arguments that support the importance of radiation forces in producing the observed gas velocities are summarized. Finally, the nature of the acceleration process is described with particular attention paid to the various instabilities that may be present and which are generally characteristic of situations in which plasma velocities result directly from the deposition of radiative momentum. In fact, these troublesome instabilities suggest that radiative forces, although very strong, may provide only a partial explanation of the gasdynamical activity observed.
Dynamic Human (Astronomical) Models
Authors: Bishop Jeanne E. 
Published: July 2016

Many educators have found that models can add a lot to the understanding of astronomical concepts. Attractive commercial models of the solar system and celestial globes are readily available. Many models can be constructed of common materials — I found in my doctoral dissertation work that models made and manipulated by students increased retention of concepts of the celestial sphere and rotation, the seasons, lunar phases, and planet motions.But there is another type of model which I have found very successful. I call it the “dynamic human model.” Actually, the concept is not new. I know that many good teachers have a favorite demonstration in which one or more students represent the Earth, sun, or moon. Also, the Elementary-School Science Project of the University of Illinois contained activities for student models to distinguish between Ptolemaic and Copernican systems. However, I do not think the idea has been extended as far as it should be. I would like to suggest ideas for dynamic human models beyond what I have seen elsewhere.
The Universe in the Classroom: A Newsletter on Astronomy for Teachers
Authors: Fraknoi Andrew 
Published: July 2016

Since 1984, the Astronomical Society of the Pacific (ASP) has sponsored a quarterly newsletter on teaching astronomy in grades 3-12. Cosponsored by the American Astronomical Society, the Canadian Astronomical Society, and the International Planetarium Society, the project now reaches over 20,000 teachers and schools in the US and Canada.We would like colleagues overseas to examine the newsletter, and, if they find it useful, to consider translating and distributing it. We will be glad to make it available without charge to anyone who is interested.Since 1978, the summer meetings of the ASP — held in a different city each year — have featured one to three days set aside for workshops on astronomy for teachers. In recent years, between 150 and 200 teachers have come each summer— at their own expense — to take these credit workshops and learn more about astronomical topics, activities, and resources.
A Science and Mathematics Teaching Center
Authors: Bisard Walter 
Published: July 2016

It is widely known that a crisis in science and mathematics teaching exists in the United States. This crisis has reached all levels of education, from elementary to secondary to colleges and universities. The problem, which is easy to define but difficult to resolve, is trifold: there are not enough high-quality science and mathematics teachers; present teachers are teaching out-of field or are out-of-date and in need of subject updating; and the average education graduate is only minimally qualified to teach science and math. These factors have caused national and state “alarms” to be published that point out the increasing mediocrity and an overall lack of science education in our nation’s schools.Central Michigan University, long among the nation’s leaders in the training of teachers at all levels, is taking steps to remedy this alarming situation. A Science and Mathematics Teaching Center, designed to confront the problem head-on, has been founded. The Center’s major purpose is to improve the quality of science and math teaching. This goal is being accomplished through a series of workshops, seminars, in-service programs, conferences, and teacher outreach programs.
The Mills Public Observatory in Dundee
Authors: Vincent Fiona 
Published: July 2016

The only full-time public observatory in Britain is the Mills Observatory in Dundee, Scotland. John Mills was a successful businessman in Victorian Dundee with an interest in astronomy. He bequeathed his money to build a public astronomical observatory in the city, for studying “the wonder and beauty of the works of God in creation.” The Mills Observatory was eventually opened in 1935.Dundee is situated on the northern shore of the River Tay, in central Scotland. The Observatory stands on a wooded hill (an extinct volcano) near the center of the city. The trees shelter it from virtually all direct city light, while leaving an uninterrupted view south across the Firth of Tay. There is some scattered light, but in clear weather the sky can be surprisingly dark, and the Milky Way distinctly visible.
Introductory Astronomy for Mature Students
Authors: Waller William H. 
Published: July 2016

Much of this meeting has been concerned with the teaching of introductory astronomy to children, teenagers, and young adults. Introductory astronomy for working and retired adults has been given short shrift, however. Because the mature population is significant in number and in its influence on governmental support for astronomy, I thought that some mention should be made. My own experience concerns the educational programs that are available to mature students in the United States.Most working adults are restricted by their jobs to taking classes in the evening. Most large universities in the United States provide such classes. These are often administered by organizations that are completely autonomous from the “host” school. A typical arrangement is for the school to provide classroom space, access to audio-visual equipment (sometimes), and university credit for those who register for credit. The “adult education,” “continuing education,” or “university extension” organization handles the rest. It obtains the necessary faculty to teach the courses, advertises the classes, and administers the registration and grading. For the “credit” courses in astronomy, the most common teachers are graduate students and postdoctoral fellows looking for some extra cash and teaching experience. There is no real impetus for regular faculty members to teach these classes. This is an unfortunate circumstance that could be remedied by some private, state, or federal funding of endowed “chairs” in adult education.
Using Teleconferencing for A Planetarium Lesson
Authors: Wasiluk Elizabeth S. 
Published: July 2016

Before coming to West Virginia, I worked for Delaware-Chenango BOCES as their telelearning coordinator. BOCES stands for “Board of Cooperative Educational Services.” Such organizations exist throughout New York State for the purpose of pooling resources of school systems and providing services and equipment they might be unable to afford on their own. Examples of the services they provide include distance learning, vocational education, computer services, etc. Our BOCES owned a portable Starlab planetarium for loan to member school districts.Carol Kwiencinski, from Downsville Central School in Downsville, New York, used the portable planetarium with her students. Her students asked her many questions she could not answer, particularly about black holes. As an add-on to her planetarium session, she approached me to do a teleconference with a planetarium director, Mitch Luman of the Koch Planetarium and Science Center, Evansville, Indiana. To set up the conference, we used a speakerphone, which is basically a set of amplifiers and microphones that allow students to speak and listen to a telephone conversation as a group.
Two Centuries of Study of Algol Systems
Authors: Batten Alan H. 
Published: July 2016

AbstractThe periodicity of the light variation of Algol, discovered just over 200 years ago, may be regarded as the beginning of the study of eclipsing binary systems, especially those of the Algol type. Such studies, however, gained no real momentum until Vogel, 100 years ago, demonstrated by spectroscopy that the binary hypothesis of Algol’s light changes is, in its essentials, correct. Three elements were needed to give us our modern notions of evolution by mass-transfer, namely: (i) results of combined analysis of light-curves and velocity-curves, (ii) evidence of circumstellar matter within binary systems and (iii) the notion that at least one component of an Algol system was near the limit of dynamical stability. All three entered the literature within about a decade, approximately halfway through the second century of eclipsing-binary studies; but it is the computational and instrumental developments of the last 25 years that have made real progress possible. We still lack commensurate theoretical developments, and the whole question of the contribution of Algol systems to the development of the Galaxy has barely been considered.
Time-Resolved Spectroscopy of Accretion Disks in Algols
Authors: Kaitchuck Ronald H. 
Published: July 2016

AbstractTime-resolved spectroscopy during the eclipse of short-period Algol systems, has shown their accretion disks to be small, turbulent structures with non-Keplerian velocity fields and asymmetries between the leading and trailing sides of the disk. These transient disks are produced by the impact of the gas stream on the mass-gaining star, and occur in systems where the star is just large enough to ensure the stream collision is complete. These emission line disks and the excess continuum emission do not always occur together. The permanent accretion disks in at least a few of the long-period Algol systems have features in common with the transient disks including non-Keplerian velocity fields.
Polarizing Gas at Small Optical Depths Around Algols
Authors: Koch R. H. , Elias N. M. , Corcoran M. F. , Holenstein B. D. 
Published: July 2016

AbstractThe origins of visible-band linear polarimetry of Algols and objects related to them are reviewed. It is pointed out, not for the first time, that the polarization signals of these systems can vary sporadically by significant amounts. The difficulty of evaluating the interstellar component of the observed polarization is discussed and these components are evaluated anew for each object studied in this paper. With one possible exception, the polarization signals intrinsic to these binaries derive from electron scattering. A well-defined model is applied to the constant and variable (but phase-locked) polarization signals. Limits to the mass associated with a scattering disk in each binary are derived. Within broad limits, concentrations of scattering mass within and above or below the orbital plane are also developed as are the centroid longitudes of these concentrations within the system. It is pointed out that very few measures of visible-band, circular polarization have been made but that cm-wavelength measures of Algol itself have been very informative.
Circumstellar Matter in Algols and Serpentids
Authors: Plavec Mirek J. 
Published: July 2016

AbstractA systematic search is reported for phenomena associated with circumstellar matter in interacting binary systems of the Algol and W Serpentis type. Ultraviolet emission lines have been detected by the author in 10 Algols and 6 Serpentids. No conspicuous difference exists between systems with disk accretion and those with direct stream impact. Evidence is indicated that the lines are formed predominantly by scattering in an induced stellar wind. Relative intensity of Fe II and Fe III emissions appears to be correlated with the spectral type of the gainer. It is suggested that in the Serpentids we see a thick disk nearly edge–on, but that the emission lines indicate the nature of the gainer inside.
The Relation Between RS CVn and Algol
Authors: Hall Douglas S. 
Published: July 2016

AbstractLate-type secondaries in Algol binaries are rapidly rotating convective stars and thus should be chromospherically active (CA). They are examined with respect to observational manifestations which characterize already known CA stars: Ca II H and K emission cores, photometric variability attributable to starspots, soft x-ray emission, non-thermal radio emission, ultraviolet and infrared excess, and alternating period changes. The conclusion is that they can be regarded as another class of CA stars. In most respects they are literally indistinguishable from other CA stars. Ca II H and K emission cores are observed in the lobe-filling component of six semi-detached binaries: U Cep, RT Lac, RV Lib, AR Mon, S Vel, HR 5110. Alternating period changes are shown to occur only in Algols containing a late-type (convective) star. It is proposed, therefore, that the Matese-Whitmire mechanism explains these changes. Specifically, the interval from one increase (or decrease) to the next can be equated with the star’s magnetic cycle. Cycle lengths for 31 stars, derived in this way, range between 7 years and 109 years, with a median of 50 years.
A Photometric-Spectroscopic Analysis of the Algol-Type Binary U CRB
Authors: van Gent R.H. 
Published: July 2016

U CrB is a well-known Algol-type eclipsing binary (P = 3ḍ522, spectrum B6 V + GO III-IV). Although the system has been closely observed since it’s discovery (Winnecke, 1870), progress in unraveling its true nature has been slow.Early spectroscopic work suggested an early-type spectrum for the secondary which was in variance with the near absence of a secondary eclipse in the lightcurve. Rapid variations were also noted in the lightcurve (Lause, 1938; Batten, 1964; Piotrowski et al., 1974; Olson, 1982), which are only partly attributable to the variability of the commonly used comparison star HD 137147 (Olson, 1980; van Gent, 1982a).
A New Light Synthesis Optimization Program. Test on Simulated Algol Data
Authors: Linnell Albert P. 
Published: July 2016

AbstractSimulation of light curve effects in Algol systems that are near contact or that may evolve into contact requires a different model than the tri-axial ellipsoid used in many current studies. A new light synthesis optimization program, based on the Roche model, satisfies the model requirements and determines system parameters with excellent accuracy, given a sufficiently large set of observations.A widely used criterion for stopping iterative solutions is inadequate. A working criterion is proposed as a replacement.
Reverse Algols
Authors: Leung K.C. 
Published: July 2016

AbstractAn Algol is a binary system having a semidetached configuration where the less massive component is in contact with the critical equipotential surface. A reverse Algol is a binary system having a semidetached configuration where the more massive component is in contact with the critical equipotential surface. In 1985, Leung suggested 5 reverse Algol systems at the Beijing Colloquium. Two more such systems have been discovered recently. The spectral types of these systems range from early B to mid G. There is also a wide spread in mass ratio among these systems. There appear to be two types of reverse Algols, “hot” and “cool” systems. The hot systems have their more massive components as the hotter stars and the cool systems their more massive components as the cooler stars. The mass-radius relation of the reverse Algols is very similar to that of the contact and near-contact systems. It is believed that reverse Algols represent the pre-mass-reversal semidetached phase of close binary evolution. Since selection effects apply to both the regular Algols and reversed Algols in a similar manner, the evolutionary time scale between them would be simply the ratio of the number of confirmed systems of these two types of Algols.
The Effects of Magnetic Fields on Period Changes, Mass Transfer and Evolution of Algol Binaries
Authors: Bolton C. T. 
Published: July 2016

AbstractVariations in the magnetic pressure and flux blocking by starspots during the magnetic cycle of the cool semidetached component of an Algol binary may cause cyclic changes in the quadrupole moment and moment of inertia of the star which can cause alternate period changes. Since several different processes and timescales are involved, the orbital period changes may not correlate strongly with the indicators of magnetic activity. The structural changes in the semidetached component can also modulate the mass transfer rate. Sub-Keplerian velocities, supersonic turbulence, and high temperature regions in circumstellar material around the accreting star may all be a consequence of magnetic fields embedded in the flow. Models for the evolution of Algols which include the effects of angular momentum loss (AML) through a magnetized wind may have underestimated the AML rate by basing it on results from main sequence stars. Evolved stars appear to have higher AML rates, and there may be additional AML in a wind from the accretion disk.
Synthetic Light Curve Analysis of the Close Binary Systems BX Andromedae and RR Leporis
Authors: Samec R.G. , Fuller R.E. , Kaitchuck R. H. , Bookmyer B. B. , Faulkner D. R. 
Published: July 2016

AbstractUnpublished photoelectric observations of the systems BX And and RR Lep were subjected to light curve analysis using the Wilson-Devinney Code.The short-period eclipsing binary system BX And was observed on five nights in 1976 at the Morgan-Monroe station of the Goethe Link Observatory of Indiana University. The observations covering the eclipse portions of the light curves yielded four times of minimum light. A period study covering 89 years of observations confirms that a major period change took place about 1950. The system is suspected of being quite active on a short time scale. Standard magnitudes were derived for BX And and for the comparison star. The corrected color indices indicate that BX And and the comparison star BD+39° 476 are in the spectral range of F3-F5. The light curves, defined by 1092 observations in B, 1097 in V and 971 in the U filter are symmetric. The difference in the eclipse depths are quite large averaging 0.m46. A distinct de-reddening of the light curves occurs during the secondary eclipse. The first synthetic light curve solutions of the system were obtained. The solution of BX And indicates that the system consists of an F-type primary and a K-type secondary component in a state of shallow contact. This result is supported by the location of BX And on the Eggen period-color diagram for contact binaries. The large mass ratio, temperature disparity and period increase are found to be consistent with an early contact phase of thermal relaxation oscillations.
KX Andromedae: Possibly a Strongly Interacting Binary
Authors: Stefl S. , Harmanec P. , Horn J. , Koubský P. , Kriz S. , Hadrava P. , Bozic H. , Pavlovski K. 
Published: July 2016

Although KX And (HD 218393, MWC 397) has been observed since the beginning of our century, we have no reliable model of this peculiar emission-line object. Published papers (e.g. Plavec et al. 1982; Kriz and Harmanec 1975 and references therein) indicate that it is a B+K W Ser-type binary with a period of 38.9 days. This paper presents a summary of intensive observations carried out during the last fifteen years.The observational material used consists of 65 coude spectra obtained with the Ondrejov 2-m telescope, UBV photometry obtained at Hvar Observatory and 28 archival IUE images. The radial-velocity and photometric data are combined with those found in the literature. A PDM period search over the interval 1 to 1000 days unambiguously indicates the 38.9-day period both in RV and photometric data.
Radio Emission from EA Eclipsing Binaries: Evidence for Kilogauss Early- and Late-Type Stars
Authors: Stewart R.T. , Slee O.B. , Budding E. , Coates D.W. , Thompson K. , Bunton John D. 
Published: July 2016

A recent survey of EA eclipsing binaries by the Parkes 64-m telescope operating at 8.4 GHz detected 15 out of 47 systems on at least one out of the 10 nights surveyed. The detected systems were HD 6882 (ξ Phe), HD 36486 (δ Ori A), HD 39780 (TZ Men), HD 57167 (R CMa), HD 58713 (RY Gem), HD 74307 (S Cnc), HD 132742 (δ Lib), HD 147683 (V769 Sco), HD 161741 (V393 Sco), HD 163708 (V1647 Sgr), HD 16871Q(XZ Sgr), HD 183794 (V822 Aql), HD 187949 (V505 Sgr), HD 199005 (KZ Pav), and HD 207098 (δ Cap).A full account of the observations and interpretation has been submitted to The Astrophysical Journal.About one-half of the 15 detections refer to main-sequence pairs of spectral types earlier than F and the remainder are classical Algols.
Evidence for Transient Colour Changes of Algol in the Past
Authors: van Gent R.H. 
Published: July 2016

Most Algol-type variables are believed to be close, semi-detached binaries which have evolved from a rapid mass-transfer phase, which reversed the initial mass-ratio, to a relatively quiescent stage where only small-scale transient events perturb the dynamical and the photo-metrical properties of the system.Of all Algol-systems, only the prototype Algol (β Per) itself is bright enough to be traceable in astronomical records reaching back more than 2000 years. Evidence based on medieval stellar lists and 19th-century visual observations strongly suggest that the intrinsic colour of Algol has been subject to substantial variations within historical times. On a few occasions Algol was apparently observed as reddish, which is at variance with its present blue-white appearance (B-V = −0.05 to +0.10).
Radial Velocity and Profile Variations of the Ultraviolet Circumstellar Lines in ζ Tauri
Authors: Dawanas D. N. , Hirata R. 
Published: July 2016

AbstractThe radial velocity and profile variations of UV lines of the shell star ζ Tau have been examined in the IUE spectra obtained in 1978-1982. The neutral atoms, and once or twice-ionized ions (except C II, Al III, Si III resonance lines) follow the same velocity variations as in the visual spectra, while the Si IV and C IV resonance lines show a constant negative velocity (~ -50 km s− at the core). The Al III, C II resonance lines and probably Fe III (mult. No. 34) are formed in both regions, i.e., in lowly-ionized and highly-ionized regions and the Si III resonance line is formed in a highly-ionized region.