bluuebunny/crossref_metadata_2025 huggingface dataset:
The Extragalactic X-Ray and γ-ray Backgrounds
Authors: Setti G.
Published: June 2019

The long-standing problem of the origin of the extragalactic X-ray background (XRB) is reviewed. Although the shape of the spectrum in the 3–100 keV interval is suggestive of an optically thin bremsstrahlung at ~ 40 keV, the interpretation in terms of a hot intergalactic gas (IGG) requires a rather extreme energy supply and a gas density conflicting with the baryon density upper limit derived from primordial nucleosynthesis calculations in the standard hot big-bang model. A summary discussion of the estimated contributions from the integrated X-ray emission of known classes of extragalactic discrete sources at a reference energy of 2 keV is given. Although these estimates are still uncertain, the subtraction of a “minimum” contribution drastically modifies the 40 keV thermal shape, which is the prima facie evidence of a hot IGG. AGNs are the main contributors. Low luminosity AGNs (Seyfert type 1 nuclei) at redshift z = 1 − 2 may in fact saturate the 2 keV XRB, but their observed hard X-ray spectra are on the average unlike (much too steep) that of the XRB. This has led a number of authors to postulate new classes of sources and some exotic models which are briefly summarized. However, if a recently proposed unified scheme of AGNs holds, then the bulk of the XRB intensity can be explained independently of the observed spectral differences and with a mild cosmological evolution. The origin of the extragalactic γ-ray background is briefly commented upon in the concluding remarks.
Modeling Faint Galaxy Counts
Authors: Guiderdoni B. , Rocca-Volmerange B.
Published: June 2019

In this paper, we summarize the results of an analysis of faint galaxy counts presented in Guiderdoni and Rocca-Volmerange (1989). We choose to restrict our analysis here to the examination of pure luminosity evolution.
Optical Search of Faint IRAS Point Sources in the Virgo Cluster Region
Authors: He X. T. , Liang K. , Huang K.
Published: June 2019

The infrared emission in galaxies is strongly connected to star burst processes, while emission from the intergalactic medium results mainly from dust heated by other luminosity sources. The Virgo cluster provides an extensive region in which the properties of such infrared emission can be studied. Galaxies in the Virgo cluster with dust temperatures of 40 K and masses of dust as small as about 5 × 104M⊙ are detectable at the limit of the IRAS survey (Soifer et al., 1987). The IRAS observations of 196 optically selected galaxies in the Virgo cluster have been studied by Helou et al. (Helou et al., 1988; see also Leggett et al., 1988).
Limits on the Energy Density of the Cosmic Infrared Background
Authors: Rephaeli Yoel , Schlickeiser Reinhard
Published: June 2019

One of the least known regions of the cosmic electromagnetic background is in the infrared (IR). This infrared background (IRB) is of considerable astrophysical interest. Early stellar activity, either pregalactic (Bond, Carr and Hogan, 1986), or galactic (Partridge and Peebles, 1967), may have contributed significantly to the IRB. More significant, perhaps, are the superimposed IR emissions from normal galaxies, Seyferts, quasars, and rich clusters of galaxies (e.g., Stecker, Puget and Fazio, 1977). There are only few reported measurements of the IRB, which in general yield energy densities comparable to that of the Cosmic Microwave Background (CMB), ρo ≈4 10−13 erg cm−3. An upper limit on the energy density at 2 μm is δ ≡ ρ/ρo≤1.2 (Hoffman and Lemke, 1978). Matsumoto, Akiba and Murakami (1984) have detected diffuse emission in the 2–5 μm band, with an estimated energy density δ = 1.2.
Observations of Diffuse Infrared Radiation by a Small Cryogenical Telescope, IRTS
Authors: Okuda Haruyuki
Published: June 2019

A small, cryogenically cooled infrared telescope named IRTS (Infrared Telescope in Space) is under development. The telescope is equipped with spectrometers and a photometer with medium spatial and spectral resolution covering the wavelength range from 1 to 1000 μm. The instrument is specially designed for observations of the cosmic background radiation and galactic infrared radiation. It will be flown on board a Japanese reusable free-flyer called SFU (space flyer unit) to be launched in 1994.
Optical Observing Techniques for Faint Extended Surface Brightness
Authors: Schnur Gerhard F. O. , Mattila Kalevi
Published: June 2019

The measurement of faint extended surface brightness at a level of a few S10 is hampered by the disturbingly bright contributions of the Light of the Night Sky (LONS), consisting of, among others, the zodiacal light, airglow, and integrated starlight. Special observing techniques are necessary for investigations of the diffuse light in clusters of galaxies (DLCG) and for the determination of the extragalactic background light (EBL). We argue for the two-telescope method as an effective means to compensate for the bright components of the LONS, which will allow an accurate determination of faint extended surface brightnesses.
Using IRAS Cirrus to Look for X-Ray Shadowing with ROSAT
Authors: Walker Helen J. , Harris Alan W. , Sumner Timothy J.
Published: June 2019

The ROSAT X-ray satellite mission and its X-ray telescope (XRT) are described by Trümper (1984). The characteristics of the Wide Field Camera (WFC) on ROSAT and its potential for studies of the soft X-ray background (SXRB) are discussed by Harris, Sumner, and Walker (1989, this volume). The energy range covered by the WFC is 0.06 keV to 0.21 keV (60 Å to 200 Å), whilst the XRT covers the higher energy range from 0.2 keV to 2 keV. Observations performed to date in this field have given rise to conflicting evidence on the location and nature of the 106 K gas, which is presumed to be the origin of the observed emission (see references in Harris, Sumner, and Walker, 1989, this volume).
Inscriptions from Samos
Authors: Gardner Percy
Published: June 2019

The chief fruit of Mr. Theodore Bent's recent visit to Samos is the discovery of an important agonistic inscription, which gives a list of victors in some games at Samos, probably the Heraea. The limits of date are given on the one hand by the mention of Apameia, founded by Seleucus Nicator, on the other hand by the absence of all Roman names. The forms of the letters with their squareness and strongly marked extremities seem to indicate the second century B.C.

The Heraea were celebrated at Samos from early times. Plutarch tells us that after the battle of Aegospotami the Samians renamed the festival after Lysander. But it soon resumed the older name. In one inscription of imperial times it is called in an inscription of the Antonine age the festival is termed The festival was doubtless a great Ionic πανηγυρίς, attended by all the pleasure-loving people of the coast and worthy of the language in which the Homeric hymn speaks of the Delian festival.
A Summer in Phrygia: Some Corrections and Additions
Authors: Anderson J. G. C.
Published: June 2019

In my second article on Phrygia, Vol. xviii., pp. 101 and 109, mention is made of some Latin inscriptions which were reserved until the stones should be re-examined. I had the opportunity of seeing them again this summer, and I now publish them, together with a few corrections and additions to both papers.

Vol. xvii., p. 401, l. 18. Read ‘the small river nearest but one to Saraï Keui on the east’; see the inset map, Pl. IV.

P. 418 ff. This inscription is discussed by A. Schulten in a paper entitled Libello dei coloni d'un demanio imperiale in Asia in Mitth. des Instituts, Röm. Abtheil., 1898, pp. 231–247. My restorations, which had to be made very hurriedly and with an inadequate knowledge of the special literature of the subject (e.g. of the important inscription of Skaptoparene, which throws so much light on our document), were merely tentative suggestions; but it seemed better to publish the inscription at once for the benefit of scholars than to hoard it up until an exhaustive commentary could be written on it.
Statistics Of Multiple Stars
Authors: Tokovinin A.
Published: June 2019

The statistics of stellar systems of multiplicity three and higher is reviewed. They are frequent, 0.15−0.25 of all stellar systems. Some 700 multiples are expected among the 3383 stars of spectral type F, G, and K within 50 pc, while only 76 of them are actually known. Many (if not all) close binaries have distant tertiary components, indicating that angular momentum exchange within multiple systems was probably critical in forming short-period binaries. The ratio of outer to inner periods in the best-studied nearby multiples and in low-mass pre-main sequence multiples does not exceed 104 at the formation epoch; larger ratios are produced by subsequent orbital evolution. All multiples with well-defined orbits are dynamically stable, the eccentricities of outer orbits obey the empirical stability limit Pout(1 – eout)3/Pin > 5 that is more strict than current theoretical limits. Relative orientation of orbits in triple stars shows some degree of alignment, especially in weakly-hierarchical systems. The statistics support the idea that most multiple stars originated from dynamical interactions in small clusters.
The Spectroscopic orbit of ϕ Cygni, A System with two Late-Type Giants
Authors: Fekel Francis C.
Published: June 2019

Improved orbital elements for ϕ Cygni have been determined from 47 new high-dispersion spectroscopic observations. The period and eccentricity are 434.14 days and 0.559, respectively. Minimum masses plus the inclination of the visual orbit result in masses of 2.16 and 2.06 M⊙ for the two giants. The small magnitude difference of 0.25 mag and a mass ratio of 1.044 indicate that both giants are most likely in the helium-burning phase of their evolution.
Photometry of Eclipsing Binary Stars in the Large and Small Magellanic Clouds
Authors: Bayne G.P. , Tobin W. , Pritchard J.D. , Bond I. , Pollard K.R. , Besier S.C. , Noda S. , Sumi T. , Yanagisawa T. , Sekiguchi M. , Honda M. , Muraki Y. , Takeuti M. , Hearnshaw J.B. , Kilmartin P.M. , Dodd R.J. , Sullivan D.J. , Yock P.C.M.
Published: June 2019

The light curves for three eclipsing binaries in the Magellanic Clouds have been obtained using CCD uVJIC photometry. One target in the LMC, MACHO*05:36:48.7−69:17:00, is an eccentric system, e = 0.20, with a period of 3.853534 ± 0.000005 d. Initial solutions indicate a primary component in the range Teff,1 = 20,000−35,000K and the secondary Teff,2 1000−2000K cooler than the primary, with inclinations ranging i = 84.2° − 86.0°. Two targets in the SMC, MOA J005018.4-723855 and MOA J005623.5−722123, have periods of 1.8399±0.0004 and 2.3199 ± 0.0003 days respectively. Both have circular orbits with the former being a semi-detached system.
Accretion of Protobinary and Evolution of the Mass Ratio
Authors: Hanawa Tomoyuki , Ochi Yasuhiro , Sugimoto Kanako
Published: June 2019

We have reexamined accretion in a protobinary system with two dimensional numerical simulations. We consider protostars which rotate around the center of the mass with circular orbits. The accreting gas is assumed to flow in the orbital plane. It is injected from a circle whose radius is 5 times larger than the orbital separation of the binary. The injected gas has constant surface density, in fall velocity, and specific angular momentum. The accretion depends on the specific angular momentum of the injected gas, jinf. When jinf is small, the binary accretes the gas mainly through two channels: one through the Lagrangian point L2 and the other through L3. When jinf is large, the binary accretes the gas only through the L2 point. The primary accretes more than the secondary in both cases, although the L2 point is closer to the secondary. After flowing through the L2 point, the gas flows half around the secondary and through the L1 point to the primary. Only a small amount of gas flows back to the secondary and the rest forms a circumstellar ring around the primary. The accretion decreases the mass ratio, q = M2/M1, where M1 and M2 denote the masses of the primary and secondary, respectively. The accretion rate increases with time. When jinf is large, it is negligibly small in the first few rotation periods.
IR Geminorum: Complex Disk Behavior During Quiescence
Authors: Li Zongyun , Leung Kam-Ching , Martin Gaskell C.
Published: June 2019

We have carried out nearly continuous V-band photometry from Yunnan Observatory (China) and Behlen Observatory (Nebraska, USA) of IR Gem for over six days starting three days after a normal outburst in January 2002. Our observations show that the behavior of this SU UMa star is unexpectedly complicated, and that for IR Gem, quiescence is potentially more interesting than outbursts. We find a photometric modulation with a period of 98.5 min, exactly equal to the spectroscopically determined orbital period. We tentatively attribute this to heating of the secondary. During the first three days a modulation appeared with a period 5% longer than the orbital period. We suggest that this might be a signature of apsidal precession of an eccentric disk. During the middle of our period of observations a modulation with a period 3% shorter than the orbital period appeared. We invoke nodal precession to explain this. A slower modulation we found with a period of about 1.7 d is roughly consistent with the expected period of nodal precession. There is a puzzling 4.3 d period modulation that we suspect may be the result of beating between apsidal and nodal precession frequencies. We also find inexplicable quasi-periodic cycles on timescales drifting from ~ 0.2 to ~ 0.4 days.
X-ray Observations of SN 1993J
Authors: Zimmermann H.-U.
Published: June 2019

In April 2001 SN1993J was observed with both the PN and MOS cameras of the XMM-Newton observatory. A 2-component thermal emission model assuming ionization equilibrium provides a good fit to the spectrum in the 0.3 to 11 keV energy band, but fits to shock models show also acceptable results. The development of the X-ray temperatures over the first 8 years after the explosion is discussed in the light of the standard SN model. The long term X-ray lightcurve shows a general decline of the luminosity with Lx ∝ t−0.30.
High-Resolution Radio Imaging of Young Supernovae: SN 1979C, SN 1986J, and SN 2001gd
Authors: Pérez-Torres M.A. , Marcaide J.M. , Alberdi A. , Ros E. , Guirado J.C. , Lara L. , Mantovani F. , Stockdale C.J. , Weiler K.W. , Diamond P.J. , Van Dyk S.D. , Lundqvist P. , Panagia N. , Shapiro I.I. , Sramek R.
Published: June 2019

The high resolution obtained through the use of VLBI gives an unique opportunity to directly observe the interaction of an expanding radio supernova with its surrounding medium. We present here results from our VLBI observations of the young supernovae SN 1979C, SN 1986J, and SN 2001gd.
Thermonuclear Supernova Explosions and Their Remnants: The Case of Tycho
Authors: Badenes Carles , Bravo Eduardo , Borkowski Kazimierz J.
Published: June 2019

We propose to use the thermal X-ray emission from young supernova remnants (SNRs) originated in Type Ia supernovae (SNe) to extract relevant information concerning the explosion mechanism. We focus on the differences between numerical 1D and 3D explosion calculations, and the impact that these differences could have on the modeling of young SNRs. We use the remnant of the Tycho supernova (SN 1572) as a test case to compare with our predictions, discussing the observational features that allow to accept or discard a given model.
Weak Interaction Processes in Core-Collapse Supernovae
Authors: Martínez-Pinedo G. , Langanke K. , Sampaio J.M. , Dean D.J. , Hix W.R. , Messer O.E.B. , Mezzacappa A. , Liebendorfer M. , Janka H.-Th. , Rampp M.
Published: June 2019

Supernova simulations to date have assumed that during core collapse electron captures (EC) occur dominantly on free protons, while captures on heavy nuclei are Pauli-blocked and are ignored. Using microscopic calculations we show that the EC rates on heavy nuclei are large enough that, in contrast to previous assumptions, electron capture on nuclei dominates over capture on free protons. This leads to significant changes in core collapse simulations.
The Surroundings of Gamma-Ray Bursts: Constraints on Progenitors
Authors: Chevalier Roger A.
Published: June 2019

The association of a supernova with a gamma-ray burst (GRB 030329) implies a massive star progenitor, which is expected to have an environment formed by pre-burst stellar winds. Although some sources are consistent with the expected wind environment, many are not, being better fit by a uniform density environment. One possibility is that this is a shocked wind, close to the burst because of a high interstellar pressure and a low mass loss density. Alternatively, there is more than one kind of burst progenitor, some of which interact directly with the interstellar medium. Another proposed environment is a pulsar wind bubble that has expanded inside a supernova, which requires that the supernova precede the burst.
The Use of Photographs in Astronomical Instruction
Authors: Brück M.T. , Tritton S.P.
Published: June 2019

For many years, copies on film of photographs, both direct and through objective prisms, taken with the 1.2 m United Kingdom Schmidt Telescope, have provided teaching material suitable for universities and colleges (Brück and Tritton, 1988). Table 1 outlines the various types of application to which the photographs may be put. With additional data, some real physics can be injected into the exercises, allowing students to perform quite elaborate projects.
International Schools for Young Astronomers, Astronomically Developing Countries, and Lonely Astronomers
Authors: Wentzel Donat G.
Published: June 2019

Early in this century, many cities and universities could support telescopes large enough to do serious research. There were significant observatories even in the less accesable parts of the world. Astronomy was very much an international science, and the IAU was founded to aid this international outlook.

In the middle of this century, astronomy changed in two ways. First, the frontier research turned to new topics. It needed telescopes too expensive for most small and many large countries. Second, physics became a more prominent part of astronomy. That left many of the existing small observatories scientifically isolated, especially in developing countries. The scientifically lonely astronomers there needed new alliances to survive.

Simultaneously, the new prominence of physics led to astronomers appearing in physics departments of developing countries. These new astronomers were also isolated and they also needed to build alliances to survive.
Distance education in astronomy: at-a-distance and on-campus, a growing force
Authors: Jones Barrie W.
Published: June 2019

Distance education has a track record in astronomy and is already making a significant contribution worldwide. It will make an even greater contribution in the future, not only at-a-distance, but through greater use of self-study materials on- campus, where it will liberate staff for more appropriate forms of face-to-face teaching, and help overcome the need to do more and more with less and less resource. Distance education offers huge promise in meeting the educational needs of a burgeoning world population, and because low costs can be achieved there is no need for people in areas of material deprivation to face mental deprivation also. The IAU and The Open University can be proactive in promoting the spread of distance education, and of self-study on campus.
A multi-resource system for remote teaching in Astronomy : its aims, its design, the point of view of the learners
Authors: Gerbaldi Michele , Xerri Annie
Published: June 2019

A distance teaching course in Astronomy was developed three years ago by the CNED (Centre National d'Enseignement Distance) in collaboration with professional astronomers from the University of Paris Sud XI.

We wish to present our course with :

•

the conceivers and designers’ point of view

•

the learners’ point of view.
Bringing the Universe into the Laboratory-Project CLEA: Contemporary Laboratory Exercises in Astronomy
Authors: Marschall Laurence A.
Published: June 2019

Were we meeting a century ago to discuss the state of astronomy education, we might have noted that remarkable changes were taking place in our field. The discipline, then regarded as a branch of geometry or mechanics, concerned itself primarily with the determination of positions in the heavens and the mapping of places on the earth. But with the advent of spectroscopy and the construction of large telescopes, astronomy was beginning to probe the how and the why of the heavens as well as the where and when. It was, in short, transforming itself into astrophysics, the study of the physical nature of the universe.
Learning Effectiveness of Lecture Versus Laboratory: are labs worth it?
Authors: Hufnagel B. , Loh E. , Parker J.
Published: June 2019

Michigan State University (MSU) serves a large and diverse student population, ∼ 1000 of whom take the astronomy course for non-science majors each year. Significant resources are also invested in the related astronomy lab, enrolling about half the lecture students. Although this lab is optional, the students are required to complete one lab course for their degree. In the fall of 1995, we undertook an extensive assessment of student learning in these astronomy courses.
The STAR CENTRE at Sheffield Hallam University
Authors: Parkinson John H , Ashton D. , Atkin K. , Harrison B.
Published: June 2019

The Star Centre is a national astronomy and space science base which

facilitates public access to news and information

promotes public awareness, interest, enjoyment and understanding.

The Star Centre meets these twin aims by providing an information service which can be accessed in a variety of ways and by offering a menu of public observing events.

The concept of a national astronomy base developed as part of the Centre for Science Educations growing portfolio of initiatives in both the formal education sector and the wider umbrella of the Public Understanding of Science. In December 1996 the Star Centre was launched with the aid of a Royal Society COPUS development grant and matching funding from Sheffield Hallam University.
Public Information Project of the Total Solar Eclipse of November 3, 1994 in Paraná State, Brazil
Authors: Trevisan R.H.
Published: June 2019

This project had two principal objectives: to communicate safe methods to observe the Sun, so as to prevent ophthalmological accidents to people during the total solar eclipse of 3rd November 1994, and to collaborate with the primary school teachers in the science classroom, illustrating the classes, motivating the students to observe sky phenomena.

In January 1993, a commission called “ECLIPSE 94“Executive Commission, of the Brazilian Astronomical Society was created to coordinate assistance with arrangements for observing the total solar eclipse of 3rd November 1994, that in Brazil was total in the western part of Paraná State, in Santa Catarina State and in a Rio Grande do Sul zone. Professional astronomers from Brazil and from several parts of the world were mobilized to observe this eclipse.
The Role of Amateur Astronomers in Astronomy Education
Authors: Percy J.R.
Published: June 2019

Let us begin by defining “amateur astronomer”. According to a dictionary, an amateur astronomer is “someone who loves astronomy, and cultivates it as a hobby”. At IAU colloquium 98 (The Contributions of Amateurs to Astronomy), Williams (1988) discussed this issue at length. He proposed that, to be an amateur astronomer, one must be an astronomer - able to do astronomy with some degree of skill; he then defined an amateur astronomer as “someone who carries out astronomy with a high degree of skill, but not for pay”.
Selling Our Southern Skies: recent public astronomy developments at the Carter Observatory, New Zealand
Authors: Orchiston W. , Carter B. , Dodd R. , Hall R.
Published: June 2019

Carter Observatory is the gazetted National Observatory of New Zealand, and opened in 1941 December. From the start, the main function of the Observatory was to provide for the astronomical needs of the citizens of, and visitors to, the Wellington region, and today this remains one of its four recognised functions (Orchiston and Dodd, 1995). The other three are to conduct astronomical research of international significance; provide a national astronomy education service for school students, teachers, and trainee teachers; and assist in the preservation of New Zealand's astronomical heritage.
Photometric and H-Alpha Variability in Some Be Stars
Authors: Catalano S. , Umana G.
Published: June 2019

Short-term variations, typically with small amplitude (Δm < 0.1 mag.), time-scales of hours or near one day and in many cases correlated with the rotation period have been found to be commonplace among Be stars (see Harmanec and Pavlovski 1983 for review and papers). Radial and non-radial pulsation modes have been proposed to explain this variability. However, the light curves are often double-peaked, at first suggesting the stars may have large organized dipole magnetic fields and spots not unlike those in the Ap or Bp stars (Harmanec 1983). These rotationally modulated variations are not stable, and seem to vary in both amplitude and period in the sense that intervals with well defined light curves alternate with intervals when variations are absent. This phenomenon is very reminiscent of formation and apparent relative movement in longitude of spots (groups) in some RS CVn binaries (Catalano 1983, Rodono 1986), but on a much more rapid time scale.
The Evidence for Aspect-Dependent Winds in Be Stars
Authors: Grady Carol A. , Bjorkman Karen S. , Snow Theodore P.
Published: June 2019

We present the results of a survey of stellar winds in 62 Be and 43 normal B stars in spectral types B0 to B5 and luminosity classes V-III. We find that in general the wind absorption seen in the resonance lines of C IV and Si IV in Be stars is the result of the superposed absorption from multiple shortward-shifted discrete absorption components. These components are observed in 63% of our Be stars, and are not observed in the normal B stars, confirming the result of Henrichs (1984).
The Flux Distributions of Be Stars in the Far-UV
Authors: Stalio Roberto , Polidan Ronald S. , Peters Geraldine J.
Published: June 2019

The initial results of a program to investigate the far-UV (500-1700 A) spectra of Be stars using the Voyager ultraviolet spectrometers axe presented. Observations of eleven Be stars, with spectral types from B0 through B7, obtained between March 1979 and July 1984 are discussed. The Voyager resolution (∼15 A) allows only limited spectroscopic studies; shortward of 1150 A C III λ977 and LyJβ λ1025 are the most prominent spectral features. Two stars, γ Cas and 59 Cyg, showed enhanced C III λ977 absorption. The flux distributions of the Be stars were intercompared with those of reference stars with low projected rotational velocities and, in a parallel study, to predictions from rotating star models. The model calculations suggest that the observable effects of a high rotational velocity (V≳ 0.9 of critical velocity) on the flux distribution are small except in the FUV (λ < 1150A). The Voyager flux distributions were found to be indistinguishable from those of the low v sin i reference stars. No evidence was found for critical rotation in Be stars. All observations were consistent with Be stars rotating at less than 0.85 of critical velocity.
HD 166596: A Silicon Star With Hα Emission?
Authors: Hirata R. , Dawanas D.N. , Jasniewicz G.
Published: June 2019

The spectral type of HD 166596 (HR 6804) is given as B2.5III in The Bright Star Catalogue (Hoffleit and Jaschek 1982) and as B2HIII by Houk (1978). Its rotational velocity, Vsin i, is 255 km s-1 (Uesugi and Fukuda 1982). Neubauer (1930) noted that its radial velocity is probably variable. Bidelman and MacConnell (1973) designated this star as a silicon star, and thereafter, Renson and Manfroid (1980) found its photometric period, P = 1.67 ± 0.01 days (or 0.83 days) with the amplitudes of 0ṃ04 ∼ 0ṃ05 from their four-color photometry. To the best of our knowledge, there is no report on the presence of any emission line in the foregoing literature.
X-Ray Observations of B-Emission Stars (Review Paper)
Authors: van den Heuvel E.P.J. , Rappaport S.
Published: June 2019

Most evidence on X-ray emission from the vicinity of Be stars concerns the Be/X-ray binaries. Presently some 20 of these systems are known, making them the most numerous class of massive X-ray binaries. Evidence for the binary nature of these systems comes from (i) Doppler modulation of X-ray pulse periods, (ii) periodic X-ray flaring behavior, and (iii) correlated optical and X-ray variability. The correlation between X-ray pulse period and orbital period found by Corbet (1984) can potentially provide important information on the densities and velocities in the circumstellar disks of Be stars.

Evolutionary models indicate that the Be/X-ray binaries represent a later stage in the evolution of normal close binaries with initial primary masses predominantly in the the range 8 to 15 M⊙ . These models indicate that also a class of slightly less massive Be star binaries should exist in which the compact companions are white dwarfs. Be-type blue stragglers in galactic clusters may be such systems.
Discrete Components in OB and Be Stars: The Shocking Truth?
Authors: Barker Paul K.
Published: June 2019

Preliminary calculations of the absorption profiles produced if multiple shells are ejected from the photosphere into a non-monotonic wind, suggest that this geometrical model can reproduce a wide variety of simple and complex profiles observed in the discrete components in OB and Be stars.
Interacting Binaries as Be Stars
Authors: Plavec Mirek J.
Published: June 2019

Semidetached close binary stars of the Algol type often have primary components of spectral type A0 or earlier and display emission at Hα (sometimes also at higher Balmer lines). They are therefore Be stars. Many binaries of this type are not eclipsing and must look like “ordinary” Be stars. We have discovered high-ionization emission lines of N V, C IV, Si IV, Fe III, etc. in the ultraviolet spectra of totally eclipsing Algols. They probably originate in circumstellar turbulent regions at fairly high electron temperatures, of the order of 100 000 K. They are not detectable in most non-eclipsing systems, but may be there and may play an important role in the dynamics of accretion and mass outflow from the systems.
Omicron Andromedae Photometry, Polarimetry, and a Tentative Model of the Light Variability
Authors: Oláh K. , Božić H. , Hadrava P. , Horn J. , Koubský P. , Kříž S. , Minikunov N.H. , Muminović M. , Percy J.R. , Skcherbakov A.G. , Stupar M. , Tarasov A.E.
Published: June 2019

Basic information about the star o and (HR 8762, HD 217675-6) is a bright (V=3.55m, B-V=-0.11m U-B=-0.50m) B6 III-Ve star. Its emission-line and shell spectrum is known to come and go on a time scale of years. In fact, the presence of a strong shell spectrum misled the authors of the HD catalogue to assign the star two HD numbers.

o and is a prototype of Be rapid light variables in the sense that it has the longest record of photoelectric monitoring which goes back to 1915! The long history of attempts to understand the variations of this star has recently been summarized by Harmanec (1983). Collecting and analyzing all historical photoelectric observations, Harmanec (1984) concluded that the light variations of o And can be understood as a superposition of a long-term cyclic (8.5y) variation with an amplitude over 0.1m (the star being faintest at the recorded shell maxima) and a rapid periodic variation with a period of 1.571272 days.
NonRadial Pulsations and the Be Phenomenon
Authors: Penrod G. D.
Published: June 2019

Over the last three years I have obtained about 2000 spectra of a sample of 25 rapidly rotating Bn and Be stars. All but two of the program stars show obvious line-profile variations due to non-radial oscillations. The non-emission stars are each pulsating in one or two short-period high-degree (l = 4 to 10) modes, while the Be stars are in all cases pulsating in a long-period % = 2 mode, and often in a short-period high-Z mode as well. The amplitude of the pulsations in several stars (λ Eri, o And, ζ 0ph, and 2 Vul) is correlated with the occurrence of Be outbursts. The amplitude of the pulsations is largest before the outbursts, declines slowly during the emission phases to a fraction of its previous amplitude, and then slowly recovers to its previous amplitude, a few months before the onset of the next outburst. The correspondence between the presence of a long-period % = 2 mode and Ha emission in rapidly rotating B stars strongly suggests that non-radial pulsation and rapid rotation are the essential components which enable single early B stars to become Be stars. The time scale between Be outbursts probably reflects the relaxation oscillation cycle of the I = 2 mode excitation and damping.
Synthetic uvby-β Photometry of HD 12856 and HD 13890
Authors: Torres A. V. , Garmany C. D.
Published: June 2019

Stromgren and Hβ colors have been measured from spectrophotometric observations of two Be stars without published photometry in Per OB1: HD 12856 (BO pe) and HD 13890 (B1 III:pe). Stellar parameters and improved spectral types are then derived from the color indices and the calibrations of Jakobsen (1986a,b,c). These are compared with the parameters of normal B stars and they are used to estimate the evolutionary status of the stars.
Galactic Cepheid Kinematics as a Probe of Large Scale Non-Axisymmetry of the Galaxy
Authors: Caldwell J. A. R. , Koen C. , Avruch I. M. , Metzger M. R. , Schechter P. L. , Keane M. J.
Published: June 2019

We investigate whether the currently available Galactic Cepheid kinematic data can put interesting constraints on large scale low amplitude non-axisymmetry of the Galactic plane rotation pattern. In this connection we address the experimental design problem of where in the Galactic plane additional Cepheids would prove the most useful for the axisymmetric and the non-axisymmetric modeling of the kinematics.
Mode Determination by Fourier Analysis of Line-Profile Variations: Application to τ Peg
Authors: Kennelly E.J. , Walker G.A.H. , Merryfield W.J. , Matthews J.M.
Published: June 2019

The identification of modes of oscillation is an important first step towards the seismology of stars. Low- and high-degree nonradial modes of oscillation may appear as variations in the line profiles of rapidly rotating δ Scuti stars. We present a technique whereby complex patterns in the line profiles are decomposed into Fourier components in both time and “Doppler space”. The technique is applied to the 7.3-hour time series of high-resolution data obtained from CFHT for the δ Scuti star τ Peg. In addition to the low-degree mode which has been identified in photometric studies (Breger 1991), we find evidence for at least three high-degree modes near 11 and 15. Correcting for the rotation of the star, most of these modes appear to oscillate with frequencies near 17 cycles day-1. Our results are found to be in good agreement with the theoretical limits imposed on the frequencies of oscillation by the models of Dziembowski (1990).
Slowly Pulsating B Stars
Authors: Waelkens C.
Published: June 2019

We discuss two new slowly pulsating B stars for which it can be convincingly shown that they are multiperiodic variables. The group now contains ten confirmed and likely multiperiodic mid-B stars with periods between 0.7 and 4.4 days. The multiperiodicity and the length of the periods point to g-mode pulsations. The very high order of the modes implies that the modes are excited in the core or in the very outer layers of the star. A recently proposed mechanism, in which both the inner and outer layers intervene, is discussed.
β Cep: a Magnetic Be Star?
Authors: Henrichs H.F. , Bauer F. , Hill G.M. , Kaper L. , Nichols-Bohlin J.S. , Veen P.M.
Published: June 2019

Besides the well-known pulsation period of 4h34m, the B1 IV star β Cep has a very significant period of 6 or possibly 12 days in the equivalent width of the ultraviolet resonance lines. This was discovered by Fishel and Sparks (1972) with the OAO-2 satellite, and later confirmed with IUE data. Until now, no explanation has been put forward for this period.

We propose that the UV periodicity arises from a 12 day rotational period of the star and that the stellar wind is modulated by an oblique dipolar magnetic field at the surface.

Support for this hypothesis is given by the striking similarity between the UV-line behavior of β Cep and of known rotating magnetic B stars, for example the B2 V helium-strong star HD 184927 (Barker et al. 1982), and by the measured magnetic field strength of B ± σ = (810 ± 170) G for β Cep itself by Rudy and Kemp (1978). A rotational period of 12 days corresponds well with an adopted radius between 6 and 10 R⊙, given the reported values of 20 - 43 km/s for vsini.

To verify our hypothesis we carried out new magnetic field measurements simultaneously with UV spectroscopy. We confirm the 12 day UV period in the equivalent width of the stellar wind lines of CIV, Si III, Si IV and N V (see Figs. 1 and 2), but find a lower and likely variable field strength (Fig. 3), which is consistent with a 12 day period, but not conclusive.

It remains puzzling why our new magnetic field measurements show a lower field than in 1978. It is interesting to recall the recent discovery (Mathias et al. 1991) that β Cep has entered a new Be phase (July 1990), when Hα turned into emission (see Fig. 4). This opens the suggestion that the lower magnetic field is related to the emission phase. Because the UV period is still the same, the field must still be strong enough to modulate the wind. A possibly higher equivalent width of the 1991 UV data with respect to the 1979 data might also be related to this transition, but this needs to be confirmed.

The star β Cep appears to be the only star in its class which shows this wind variability and in this respect β Cep is an exceptional β Cep star.
Properties of Mira Photospheres
Authors: Scholz M.
Published: June 2019

The first crude pictures of the structure of Mira photospheres were derived from velocity analyses of emission and absorption lines appearing shifted, doubled and doppler-broadened in Mira spectra. Positions and shapes of profiles change with phase and often do not repeat in successive cycles. Non-repeating cycles are also found in colors (e.g., TiO bands in Fig. 9 of Spinrad & Wing 1969) and in light curves and present, of course, a problem in matching specific observed and modeled cycles. The large geometric extension of Mira photospheres was demonstrated by monochromatic radius observations of o Ceti and R Leo by Labeyrie et al. (1977) and Bonneau et al. (1982) which, however, did not systematically follow the stars through different phases and cycles.

The structure of a Mira photosphere is essentially determined by the propagation of shock fronts. A shock front enters the bottom of the photosphere once each cycle and travels outwards.
Convection and the Bump Cepheid Resonance
Authors: Cox Arthur N.
Published: June 2019

Bump Cepheids display a resonance between the fundamental and second overtone modes in the form of a bump on descending light for periods less than 10 days and on the ascending light curve for longer periods. A long-standing problem has been how to explain this resonance for stellar masses consistent with evolution theory, rather than significantly lower ones. New Livermore OPAL intermediate coupling opacities now produce stellar models that are less density concentrated in the outer 1/4 of the radius, and all radial mode periods are increased. The second overtone to fundamental mode period ratio is reduced. This reduction then requires larger masses for the bump resonance, much closer to those from the old Becker, Iben, and Tuggle and the new Stothers and Chin stellar evolution results with no or very little core convection overshooting and the standard (X=0.70 and Z=0.02) composition. This achievement of the OPAL opacities is not adequate, though, because the period ratios have not quite decreased enough. There is another missing ingredient suggested to me by Norman Simon. A second deep “iron line” convection zone now appears between 145,000 and 205,000 K for higher Cepheid luminosities and masses like 7 and 8 M⊙. This convection is necessary to transport the higher luminosities that cannot be carried by radiation alone. An increase in the ratio of the mixing length to the pressure scale height to about 1.5 for 7 M⊙ and 2.0 or more for 8 M⊙ can give an appropriate convection efficiency and the required deep convection zone structure. Thus OPAL opacities, when used with the full physics of convection models all across the instability strip and nonadiabatic pulsation analyses, actually do explain the bump Cepheid puzzle. Further, the unknown convection efficiency for intermediate mass yellow giants can apparently be calibrated as a function of stellar mass.
Classical Models of Cepheid Stars
Authors: Chiosi C.
Published: June 2019

In this paper we summarize recent work on Cepheid stars by Chiosi et al (1992a), who calculated large grids of models at varying mass, effective temperature, mass-luminosity (ML) relation or equivalently underlying evolutionary scheme for intermediate mass stars, i.e. classical models, models with mild core overshoot, and models with large core overshoot, and finally initial chemical composition. The chemical parameters bracket the abundances of the Cepheid stars in the Milky Way and Magellanic Clouds. First, we present the theoretical results limited to the analytical fits of the fundamental period-mass-radius (PMR) relation and the blue and red edges of the instability strip for the fundamental mode and first overtone. Second, we discuss the data converted to magnitudes and colours of the BVRcIc passbands with particular attention to the period-luminosity-colour (PLC) and period-luminosity (PL) relations. Finally, we briefly summarize three studies based on these models, which aimed to explain the shape and width of the observed instability strip (Chiosi et al 1992b), and the main reason for the mass discrepancy of the Cepheid stars (Chiosi et al 1992c) by means of the mass equivalency (ME) method applied to clusters of the Large Magellanic Cloud (LMC). Because the ME method turned out to be sensitive to the distance modulus, the dependence of this on the metallicity has been the subject of the last study by Bertelli et al(1992).
Stellar Structure and RR Lyrae Masses
Authors: Dorman Ben
Published: June 2019

I describe qualitatively the constraints on RR Lyrae masses that arise from consideration of the interior structure of Horizontal Branch (HB) stars. Briefly, the stellar models lying within the temperature range of the instability strip are slightly less massive than those with deep exterior convection zones. I discuss therefore what brings about the existence of these zones in the models.
Period Shifts in RR Lyrae Stars
Authors: Fernley J.
Published: June 2019

Using recently published infrared photometry of RR Lyrae stars from both the field (Fernley et al. 1992) and globular clusters (Longmore et al. 1990), period shifts have been calculated using the mean (V – K) colour rather than the mean (B – V) colour employed in most previous analyses (e.g., Sandage 1990 and references therein). The advantage of using (V – K) rather than (B – V) is the reduced sensitivity to, firstly, metallicity and, secondly, non-LTE radiation. This latter occurs in many RR Lyrae stars near maximum light and clearly should not be included when calculating the mean colour and hence, mean temperature. This, and all other aspects of the present paper, are discussed more fully in Fernley (1992a).

The mean (V – K) colour of both the field and cluster stars were de-reddened using the maps of Burstein and Heiles (1982) and converted to effective temperature using the calibration of Fernley (1989).
A Spectroscopic Abundance Study of Dwarf Cepheid V1719 Cygni
Authors: Kim Chulhee , Sadakane Kozo
Published: June 2019

Spectroscopic CCD observations were carried out for V1719 Cygni and the spectrum in the visual region is analysed relative to the Sun with a line-blanketed convective model atmosphere. Adopted atmospheric parameters are : an effective temperature < Teff > = 7000 K, a surface gravity logg = 3.4. Although our result is dependent on microturbulent velocity and damping constant, it was found that Mg in V1719 Cygni is nearly solar, or underabundent by 0.2 to 0.3 dex according to the analysis of 5172.684 Å MgI line which is relatively free from blending. This is inconsistent with the previous photometric result where VI719 Cygni was known as an abnormally metal rich variable. Because the analysis was given to the single magnesium line which is not a good metallicity indicator and S/N ratio was low due to poor seeing condition, the investigation for iron lines in blue region is undertaken.
RR Lyrae: Shock waves and atmospheric motions.
Authors: Lebre Agnès
Published: June 2019

New high resolution spectroscopic observations of the star RR Lyrae are reported (resolution between 15,000 and 20,000). The spectra were taken in July 1990 with the 1.52m telescope of the Observatoire de Haute Provence, using the AURELIE spectrograph, and were centered around Hβ and NaD. They were distributed in time through almost an entire composite cycle (P = 13.6 hours). Photospheric FeI lines were analysed and their FWHM variations over one luminosity cycle are interpreted in the framework of the propagation of shock waves running through the low atmospheric layers.
On the λ4430 Absorbers in, “Normal” and in Perturbed Clouds
Authors: Dressler Kurt
Published: June 2019

Regions Perturbed By Early-Type Stars are characterized by the occurrence of high Ca II velocities and an increase in the abundance ratio Ca II/Na I (ref. 1), by a decrease in the λ4430 absorption to color excess (ref. 2), and possibly by a deficiency of small relative to large grains (large values of the ratio of total extinction to color excess, A/E). According to reference 3, the grain temperatures in the same regions are expected to be higher, and therefore may lead to selective evaporation of the smallest grains. Since these observations may be connected by way of λ4430 absorption originating in very small grains, it is of interest to compare the value of nf (number of absorbers times flvalue) of the λ4430 absorbers with the number of molecules nmol in the grains responsible for extinction in the visible.
Alinement of Solid Interstellar Particles by a Magnetic Field
Authors: Spitzer Lyman , Jones R. V.
Published: June 2019

For a Long Time the Davis-Greenstein Theory (ref. 1) has been generally considered an adequate explanation of the mechanism responsible for the alinement of interstellar grains and thus for the observed interstellar polarization. The magnetic field required to orient paramagnetic grains is apparently somewhat greater than 10-5 gauss, a relatively large field, but according to reference 2 ferromagnetic grains, proposed by the authors of reference 3, can be oriented by a field of only 10-7 gauss. These results indicate that orientation of interstellar grains is easily explained, even if the magnetic field in interstellar space is relatively weak.

Unfortunately, this relatively satisfactory state of affairs has been upset by two developments. Firstly, the basic mechanism of magnetic relaxation proposed by Davis and Greenstein has been questioned by Dr. C. Kittel of the University of California, who has pointed out that the disorienting effect associated with thermal fluctuations of magnetization within the solid particles is ignored in the formulation of this mechanism.