bluuebunny/crossref_metadata_2025 huggingface dataset:
Interferometry and Lunar Occultations: Status and Prospects of Ground-Based Milliarcsecond Resolution Observations
Authors: Richichi A.
Published: June 2019

Lunar occultations and long-baseline interferometry are two direct observational methods capable of delivering milliarcsecond resolution of binary stars. We will review the status of these two techniques, particularly with reference to their respective advantages, limitations, and accessibility for binary star research programs. We will also illustrate the near-term prospects, in connection with the availability of large modern interferometric facilities such as the VLTI.
Observational Properties of Synthetic Visual Binary
Authors: Nurmi P.
Published: June 2019

Forthcoming astrometric missions will observe a huge number of new binaries from which a large fraction will be visual binaries. Detailed planning of optimal detection procedures requires pre-launch information about the observational properties of expected visual binaries. Hence, a synthetic binary catalog is created and analyzed for observational properties of visual binary stars. These results help to understand what kind of binaries we expect to find in the final output catalogs of astrometric missions. These results represent ‘true’ binary distributions if all of them would be observed. All real observational projects or astrometric satellites sample only small fractions of these populations depending on the observational capabilities of the missions. In this study we consider only relative numbers with respect to the total number of binary stars assumed to exist in the sky down to the magnitude limit depending on the astrometric mission.
Nine Years of VLBI Imaging of Supernova 1993J
Authors: Bietenholz M.F. , Bartel N. , Rupen M.P. , Beasley A.J. , Graham D.A. , V.I. Altunin , Venturi T. , Umana G. , Cannon W.H. , Conway J.E.
Published: June 2019

We present a selection of our VLBI images of SN 1993J, along with our latest results on its expansion and its shell structure.
Optical, Ultraviolet, and Infrared Observations of SN 1993J
Authors: Filippenko Alexei V. , Matheson Thomas
Published: June 2019

We review the existing set of optical/UV/IR observations of Supernova 1993J, concentrating heavily on optical data because these are by far the most plentiful. Some results from theoretical modeling of the observations are also discussed. SN 1993J has provided the best observational evidence for the transformation of a SN from one spectral type to another, thereby providing a link between Type II and Type Ib supernovae (SNe). This has strengthened the argument that SNe Ib (and, by extension, SNe Ic) are core-collapse events. SN 1993J has remained relatively bright for 10 years; its late-time emission comes from the collision of supernova ejecta with circumstellar gas that was released by the progenitor prior to the explosion. The circumstellar material shows strong evidence of CNO processing.
Simulated Radio Images and Light Curves of SN 1993J
Authors: Dwarkadas Vikram V. , Mioduszewski Amy J. , Ball Lewis T.
Published: June 2019

We present calculations of the radio images and light curves from supernovae, based on high-resolution numerical simulations of the hydrodynamics and radiation transfer in a spherically symmetric medium. As a specific example we model the emission from SN1993J. This supernova does not appear to be expanding in a self-similar fashion, and cannot be adequately fitted with the often-used analytic mini-shell model. We present a good fit to the radio evolution at a single frequency. Both free-free absorption and synchrotron self-absorption are needed to fit the light curve at early times, and a circumstellar density profile of ρ ~ r−1.7 provides the best fit to the later data. Comparisons of VLBI images of SN1993J with synthetic model images suggest that internal free-free absorption completely obscures emission at 8.4 GHz passing through the center of the supernova for the first few tens of years after explosion.
The Early Spectroscopy of Supernovae
Authors: Yamaoka Hitoshi , Ayani Kazuya , Hashimoto Tetsuya
Published: June 2019

The spectroscopy of a supernova (SN) just after its discovery is quite important not only for the spectral type classification but also for the planning further follow-up observations or the target-of-opportunity observations (ToOs). The early spectroscopy is needed also because the information from the outermost envelope of such exploding objects as SNe cannot be obtained in the later phase. In order to obtain the early spectrum, the quick circulation of the discovery information is important. We introduce our contributions with the public astronomical observatories in Japan, including the case of “hypernova” SN 2002ap discovered by a Japanese amateur astronomer. We summarize the time interval between the discoveries, the announcements, and the first spectral classifications of recent SNe, and discuss what would be required for the early spectroscopy.
Photometric Observations of Recent Supernovae
Authors: Tsvetkov D.Yu.
Published: June 2019

Regular photometric observations of sufficiently bright northern supernovae are carried out at Sternberg Astronomical Institute’s observatories. Since 1998 the observations of more than 60 supernovae were obtained on about 150 nights with different telescopes and detectors. We present the data of the observation program, the parameters of light curves for 18 SNe and the light curves for SNe 1999aa, 2001B, 2002bo.
Radio Observations of Supernova Remnants in the M82 Starburst
Authors: Pedlar Alan , Muxlow Tom , Riley Jon
Published: June 2019

We report on recent MERLIN, VLA and VLBI observations of the compact radio sources in the nearby starburst M82, with angular resolutions ranging from arcseconds to milliarcseconds. The spectral properties of the compact sources have been investigated by 15 GHz VLA-Pie Town observations which show that 16 of the less luminous compact sources are, in fact, HII regions. However the steep non-thermal spectrum, parsec size and small variability of the remaining sources is consistent with their being supernova remnants. Several show clear shell structures at MERLIN resolution (~50 mas) and 5 have been resolved further using VLBI. Measurements of the most compact source (41.95+575) shows an expansion velocity of ~ 2000 km s-1, and one of the best defined SNR shells (43.31+592) shows an expansion velocity of ~ 104 km s-1. Recent VLBI and MERLIN measurements confirm this expansion velocity and show little evidence for deceleration. We comment on the discrepancy between this measured expansion velocity and the low expansion velocities predicted theoretically for remnants in M82.
Understanding Type II Supernovae
Authors: Zampieri L. , Ramina M. , Pastorello A.
Published: June 2019

We present the results of a systematic analysis of a group of Type II plateau supernovae that span a large range in luminosities, from faint objects like SN 1997D and 1999br to very luminous events like SN 1992am. The physical properties of the supernovae appear to be related to the plateau luminosity or the expansion velocity. The simultaneous analysis of the observed light curves, line velocities and continuum temperatures leads us to robust estimates of the physical parameters of the ejected envelope. We find strong correlations among several parameters. The implications of these results regarding the nature of the progenitor, the central remnant and the Ni yield are also addressed.
Magnetorotational Mechanism of Supernova Type II Explosion
Authors: Moiseenko S.G. , Bisnovatyi-Kogan G.S. , Ardeljan N.V.
Published: June 2019

Results of 2D simulations of the magnetorotational mechanism of supernova type II are presented. Amplification of toroidal magnetic field of the star due to differential rotation of the star leads to the transformation of the rotational (gravitational) energy to the energy of the supernova explosion. In our simulation the energy of the explosion is 1.12 - 1051 erg. The explosion ejects about 0.11 M⊙.
Explosion Models for Thermonuclear Supernovae Resulting from Different Ignition Conditions
Authors: Bravo Eduardo , García-Senz Domingo
Published: June 2019

We have explored in three dimensions the fate of a white dwarf of mass of 1.38 M⊙ as a function of different initial locations of carbon ignition, with the aid of a SPH code. The calculated models cover a variety of possibilities ranging from the simultaneous ignition of the central volume of the star to the off-center ignition in multiple scattered spots. In the former case, the possibility of a transition to a detonation when the mean density of the nuclear flame decreases to ρ ≃ 2 × 107 g cm−3 and its consequences are discussed. In the last case, the dependence of the results as a function of the number of initial igniting spots and the chance of some of these models to evolve to the pulsating delayed detonation scenario are also outlined.
Using Multi-Band Photometry to Classify Supernovae
Authors: Poznanski Dovi , Gal-Yam Avishay , Maoz Dan , Filippenko Alexei V. , Leonard Douglas C. , Matheson Thomas
Published: June 2019

Large numbers of supernovae (SNe) have been discovered in recent years, and many more will be found in the near future. Once discovered, further study of a SN and its possible use as an astronomical tool (e.g., as a distance estimator) require knowledge of the SN type. Current classification methods rely almost solely on the analysis of SN spectra to determine their type. However, spectroscopy may not be possible or practical. We present a classification method for SNe based on the comparison of their observed colors with synthetic ones, calculated from a large database of multi-epoch optical spectra of nearby events. Broadband photometry at optical wavelengths allows classification of SNe up to z = 0.75, and the use of infrared bands extends it further to z = 2.5. We demonstrate the applicability of this method, outline the observational data required to further improve the usefulness of the method, and discuss prospects for its use on future SN samples. Community access to the tools developed is provided by a dedicated website.
Optical Bumps in Cosmological GRBs as Supernovae
Authors: Bloom J.S.
Published: June 2019

From both photometric and broadband spectral monitoring of γ-ray burst (GRB) lightcurve “bumps,” particularly in GRB 011121, a strong case grew for a supernova (SN) origin. The GRB-SN connection was finally solidified beyond a reasonable doubt with the discovery that the bump in GRB 030329 was spectroscopically similar to a bright Type Ic SN. In light of this result, I re-assess the previous SN bump claims and conclude that: 1) the distribution of GRB-SN bump peak magnitudes is consistent with the local Type Ib/c SNe peak distribution and 2) the late-time bumps in all long-duration GRBs are likely supernovae.
Cosmic Gamma-Ray Bursts: The Big Picture
Authors: Hurley Kevin
Published: June 2019

A “typical” GRB occurs in a star-forming region of a galaxy at a redshift z~1. In currently popular models, it is caused by the collapse of a massive star which has exhausted its nuclear fuel supply. The star collapses to a black hole threaded by a strong magnetic field, and possibly fed by an accretion torus. Through a variety of processes, electrons are accelerated and gamma-rays, X-rays, optical light, and radio emission ensue, with durations from seconds to years. In this talk, I will review the general observational properties of bursts, their afterglows and host galaxies, and some of the open questions about them.
Physical Restrictions to Cosmological Gamma-Ray Burst Models
Authors: Bisnovatyi-Kogan G.S.
Published: June 2019

The present common view about GRB origin is related to cosmology, and is based on statistical analysis, and on measurements of the redshifts in the GRB optical afterglows of long GRB. No correlation is found between redshifts, GRB spectrum, and total GRB fluence. Comparison of KONUS and BATSE data about statistics and hard X-ray lines is done, and some differences are noted. Hard gamma-ray afterglows, prompt optical spectra, hard X-ray lines, polarization measurements could be very important for farther insight into GRB origin. Possible connection of short GRB with soft gamma repeaters is discussed.
Observations of Type Ia Supernovae and Challenges for Cosmology
Authors: Li Weidong , Filippenko Alexei V.
Published: June 2019

Observations of Type Ia supernovae (SNe Ia) reveal correlations between their luminosities and light-curve shapes, and between their spectral sequence and photometric sequence. Assuming SNe Ia do not evolve at different redshifts, the Hubble diagram of SNe Ia may indicate an accelerating Universe, the signature of a cosmological constant or other forms of dark energy. Several studies raise concerns about the evolution of SNe Ia (e.g., the peculiarity rate, the rise time, and the color of SNe Ia at different redshifts), but all these studies suffer from the difficulties of obtaining high-quality spectroscopy and photometry for SNe Ia at high redshifts. There are also some troubling cases of SNe Ia that provide counter examples to the observed correlations, suggesting that a secondary parameter is necessary to describe the whole SN Ia family. Understanding SNe Ia both observationally and theoretically will be the key to boosting confidence in the SN Ia cosmological results.
India
Authors: Narlikar J. V. , Rana N.C.
Published: June 2019

A summary of work related to astronomy education carried out during the last three years in India is presented here. Since India is a huge country and many educational efforts are made by individuals alone, this report cannot be regarded as complete, but a specific sampling.

India has more than 200 Universities, 8000 colleges, and about 100,000 schools, 33 planetaria, more than 100 museums and about 60 well known amateur astronomers’ clubs. Scores of dedicated astronomy oriented school teachers, act as nuclei of astronomy education for the general public and school children .The astronomical almanac, used in a typical household is in some way related to the stars in the sky and the movements of the Sun, the Moon and the planets. Traditionally, a rudimentary knowledge of the celestial sphere is common. The recent developments in space technology have brought a fascination and glamour to modern astronomy for all age groups, and this is noticeably reflected in the number of media coverages of astronomy.
The European Astrophysics Doctoral Network
Authors: Ray Thomas Patrick
Published: June 2019

In 1986, a group of university astrophysics institutes in eleven Western European countries established a federation known as the European Astrophysics Doctoral Network (EADN). The aims of the EADN, then and now, are to stimulate the mobility of postgraduate students in astrophysics within Europe, and to organize pre-doctoral astrophysics schools for graduate students at the beginning of their PhD research. The network has by now expanded to include about 30 institutes in 17 Western European countries, and ways are being actively sought for expanding the EADN even further to include Eastern and Central Europe. The coordinators have been Prof. Jean Heyvaerts (France) until 1992, Prof. Loukas Vlahos (Greece) 1992–1993 and myself since 1993. The network is financially supported by the European Union “ERASMUS” and the “Human Capital & Mobility” programmes as well as by national funds.
Mathwise Astronomy and the TLTP: aiding or degrading education?
Authors: McCabe E.M.
Published: June 2019

The Teaching and Learning Technology Programme (TLTP) in the UK was launched in 1992 to “develop innovations in teaching and learning through the power of technology”. Increasing numbers of students with mixed abilities and backgrounds were entering into higher education. Flexible course structures and the need for remedial teaching added further motivation in the search for methods of improving productivity and efficiency.

Since 1992 over 33 million of funding has been awarded to 76 projects spanning the university curriculum. When support from host institutions is taken into account, overall funding for the TLTP is estimated at 75 million. TLTP materials are now becoming available to assist institutions in maintaining and enhancing the quality of their teaching provision. The successful implementation of this new technology is requiring each institution to rethink its teaching and learning strategies (Laurillard, 1993).
Teaching/Learning Astronomy at the Elementary School Level
Authors: Lanciano Nicoletta
Published: June 2019

There are those who argue that children have little familiarity with the sky and that the study of astronomy should be put off until they're older. We believe, on the other hand, that children have an intimate daily rapport with the sky, the sun and moon especially, based on genuine affection for these celestial bodies which is often expressed in their fantasies, reminiscent of ancient mythology and present-day primitive cultures. Their initial conceptions of celestial objects and phenomena bring to mind ancient philosophical conceptions and the kind of erroneous thinking induced by present-day culture and mass media, and make us aware of how difficult it is to develop personal perceptions and of the powerful emotions that prevent or inhibit us from building new ones.
The Influences of the National Curriculum on Children's Misconceptions about Astronomy and the Use of these Misconceptions in the Development of Interactive Teaching Materials
Authors: Baxter John H.
Published: June 2019

It is now well established that children construct their own explanations for the easily observed astronomical events before they receive any formal education in astronomy (see Mali & Howe, 1985; Nussbaum & Novak, 1976; Vosnaidou, 1991. It is also generally accepted that childrens notions, or ‘alternative frameworks’ are tenacious and frequently pass into adulthood (Gunstone et al, 1981). Baxter's (1989) survey revealed a hierarchy of alternative frameworks about astronomy that became less naive as age increases, but also revealed that many pupils leaving school at the age of 16 years did not explain the easily observed astronomical events within a post-Copernican framework.
Role of Novel Scientific Results in Learning
Authors: Vujnović V.
Published: June 2019

Introductory remarks on astronomy education in Croatia are given. Since the learning process is a complex intellectual and emotional process which should be supported during the interaction with the teacher, different approaches should be used. Tests could give useful insight into preconceptions. The following approaches should be balanced: historical approach, discovery approach (by the use of self-made tools and courtyard observations), and thorough inclusion of novel scientific results and views (to which a special precaution has been paid).
The Jupiter-Comet Collision: some conceptual implications
Authors: Sathe Dileep V.
Published: June 2019

A typical science course at the high school level includes some information on planets and their moons. For example, it is well-known that Jupiter has 16 moons and Saturn has 18 moons. Add to this the enthusiasm of the public in the collision of comet Shoemaker-Levy 9 with Jupiter in July 1994. This immediately raises the possibility of a collision of a comet with a moon of Jupiter. Due to this possibility a strange fact about these moons comes into the picture, that is some of them are prograde in nature and some are retrograde. Can these two types of moons pose any problems in teaching ? The present situation in education leads us to believe that they can pose some problems. It is described below, in support of this answer.
The Use of the Planetarium in Nautical and Field Astronomy Education
Authors: Seymour P.A.H.
Published: June 2019

The universe of marine navigators and surveyors is basically a geocentric one. All calculations necessary for reducing celestial observations to obtain directional or positional information can be carried out within the pre- Copernican two sphere hypothesis. Some mature students on the degree courses have practical experience of navigation at sea but are not used to more abstract ways of thinking. However, most courses in navigation require students to understand the many corrections that have to be applied in astro-navigation. The planetarium can be used to illustrate the basic concepts of the two sphere hypothesis, although other methods are needed to understand the nautical almanac and the principles used in its calculation.
Astronomy to understand a human environment
Authors: Isobe S.
Published: June 2019

Astronomy is an important science in understanding a human environment. However, it is thought by most politicians, economists, and members of the public that astronomy is a pure science having no contribution to daily human activities except a few matters relating to time. The Japanese government is studying a reorganisation of our school system to have 5 school days per week, instead of 6 days per week, and this July its committee made a recommendation to reduce school hours for science and set up new courses for practical computers and environmental science. I currently made a proposal. It is very difficult for most of the school pupils, who will have non-scientific jobs, to understand science courses currently taught in school, because each science is taught independently from the other sciences. Therefore, their knowledge of sciences obtained during their school period does not greatly help their understanding of global environmental problems.
Teaching Astronomy at Sydney Observatory
Authors: Lomb N.R. , Kitchener J.
Published: June 2019

Sydney Observatory is a museum of astronomy and a public observatory. It is Australia's oldest existing observatory and is now a branch of the Powerhouse Museum, the largest museum in the southern hemisphere. With 65,000 visitors each year, the observatory is popular with the public. Visitors can come during the day to see exhibits and audiovisuals and in the evenings on telescope viewing sessions. They can also take part in school holiday workshops, adult education courses or a telescope-making course. In addition, many school groups come along during the school terms to extend the astronomical knowledge of their students. Other professional services provided by the observatory include an annual guidebook with up-to-date information for the sky as seen from Sydney and an astronomical information service for the public and the media.
Developing Science Education and Outreach Partnerships at Research Institutions
Authors: Dow K. L.
Published: June 2019

Like many research institutions, the Harvard-Smithsonian Center for Astrophysicsf (CfA), has been actively engaged in education and public outreach activities for many years. The Harvard University Department of Astronomy, the formal higher education arm of the CfA, offers an undergraduate concentration and a doctoral program. In our Science Education Department, educational researchers manage ten programs that address the needs of teachers and students (K-12 and college), through advanced technology, teacher enhancement programs, and the development of curriculum materials. The Editorial and Public Affairs Department offers several public lecture series, recorded sky information, children's nights, and runs the Whipple Observatory Visitors Center in Amado, AZ. In this environment of successful programs, the High Energy Astrophysics (HEA) division, one of seven research divisions at the CfA, has initiated, or partnered with other institutions, development of several new education and outreach programs. Some of these programs involve partnerships with the education community, but all of them have been initiated by and involve scientists.
Literature for Amateur Astronomers
Authors: Kudashkina L.S. , Andronov I.L.
Published: June 2019

The experience of working with amateur astronomers in the countries of the Commonwealth of Independent States and in Ukraine shows a noticeable lack of literature, especially educational and methodological. The amateurs, possessing an observational base, do not know what best to observe at a given moment, and those, who are not yet ready for practical work in astronomy, do not know how to be prepared.
U.S. Science education reforms: is astronomy being overlooked?
Authors: Hoff D.B.
Published: June 2019

In 1981, in response to growing concerns that the United States was falling behind the rest of the world educationally, the federal Secretary of Education created a national commission on excellence in education. This commission was charged with gathering data about the status of U.S. education compared to the rest of the developed world and to define the problems which would have to be faced to successfully pursue the course of excellence in education.
The Life in the Universe Series
Authors: Billingham J. , DeVore E. , Milne D. , O'Sullivan K. , Stoneburner C. , Tarter J.
Published: June 2019

Students, young and old, find the existence of extraterrestrial life one of the most intriguing of all science topics. The theme of searching for life in the universe lends itself naturally to the integration of many scientific disciplines for thematic science education. Based upon the search for extraterrestrial intelligence (SETI), the Life in the Universe (LITU) curriculum project at the SETI Institute developed a series of six teachers guides, with ancillary materials, for use in elementary and middle school classrooms, grades 3 through 9. Lessons address topics such as the formation of planetary systems, the origin and nature of life, the rise of intelligence and culture, spectroscopy, scales of distance and size, communication and the search for extraterrestrial intelligence. Each guide is structured to present a challenge as the students work through the lessons. The six LITU teachers guides may be used individually or as a multi-grade curriculum for a school.
Fundamental Parameters of the Underlying Be Stars (Review Paper)
Authors: Slettebak Arne
Published: June 2019

The various methods for determining masses, radii, luminosities, effective temperatures, spectral types, and rotational velocities of the underlying Be stars are reviewed, and representative values listed for each.
Differential Rotation in B and Be Stars
Authors: Zorec J. , Divan L. , Mochkovitch R. , Garcia A.
Published: June 2019

In this paper we present two kinds of results which show that differential rotation is a highly probable phenomenon in B and Be stars. These results show that angular momentum is an important parameter which must be taken into account for interpreting the observed parameters of B and Be stars and for studying their structure.
An Infrared Study of Southern Be Stars: Ground-Based and Iras Observations
Authors: Persi P. , Ferrari-Toniolo M.
Published: June 2019

Infrared observations represent a powerful tool in understanding the physical conditions of the circumstellar matter around Be stars. Previous IR studies have been reported by different authors (i.e. Gehrz et al. 1974, Persi et al. 1982, Ashok et al. 1984, and Waters, 1986).

For this purpose, we have undertaken an IR study of 21 southern Be stars including JHKLM photometry, CVF spectra at resolution R=100 around the IR HI emission lines Brγ, Brα, and Pfγ and IRAS data at 12 and 25 microns taken from the Point Sources Catalogue. The IRAS flux densities were corrected following the procedure described in the IRAS Explanatory Supplement.

The near-IR observations were obtained in March 1985 at the lm ESO (La Silla, Chile) telescope, equipped with the InSb Spectrophotometer. In the next section we discuss the nature of the observed IR excesses, and from the measured Brα/Brγ intensity line ratios for three Be stars, we derive the mass-loss rates.
The Relation Between Mass Loss and Luminosity For Be Stars
Authors: Waters L.B.F.M. , Lamers H.J.G.L.M. , Coté J.
Published: June 2019

The mass loss rates of a large sample of Be stars derived from the UV and the IR are compared. The IR rates were derived using a simple equatorial disc model, and are typically a factor 100 larger than those derived from the UV. In terms of mass fluxes, the mass flux in the polar regions (derived from the UV observations) is about a factor 103 smaller than the mass flux in the equatorial regions. The dependence of MIR and Muv on stellar luminosity is studied. It is shown that MIR depends weaker on L than Muv. This suggests that two different mechanisms are responsible for the mass flux in polar and equatorial regions.
Emission Line Variability in the Be Star X-Ray Binaries 4U1258-61 and 4U2206+54
Authors: Corbet Robin H.D.
Published: June 2019

Results of programs to monitor Ha emission line variability in two Be star X-ray binaries are presented. These systems provide a means of investigating the influence of a binary companion on the circumstellar envelope of a Be star.
Pole-On Cataclysmic Variables as Be Stars
Authors: Garrison R. F.
Published: June 2019

Cataclysmic-variable stars (CVs) are technically Be stars, since Balmer emission lines appear in their spectra. In general, CV spectra are so unusual that they are easily recognized. The main features are extremely broad, shallow hydrogen lines with broad, faint emission cores. The Balmer emission decrement is very slow, more like that of an H II region than that of a normal Be star. The Balmer decrement in cataclysmic variable stars has been discussed by Elitzur, et al.

If a CV were viewed pole-on, the spectrum might be quite different. It could exhibit a smooth continuum or may even resemble a normal Be star, except for the Balmer decrement. In this case, there may be a bright cataclysmic variable lurking in the Be star class. A possible example is the star NS 274-67, an 03e star described by Conti et al. (1986), which has Balmer emission from H-beta to H-ep-silon, but no nebular emission at [0 II] or [0 III].
Spectral Transients in the Line Profiles of λ Eridani
Authors: Smith Myron A. , Gies D.R. , Donald Penrod G.
Published: June 2019

Recently we have monitored the absorption line profile variations of a number of rapidly rotating B stars. These variations are observed as alternating quasi-absorption and -emission bumps that travel blue-to-red across the profile with a local period defined by the time to move one bump spacing. This type of pattern can be modelled successfully by assuming the presence of one or two active nonradial pulsation (NRP) modes in the photosphere of the star. Many observations show significant departures from the simple expectations of the models: successive bumps can have different amplitudes (which may vary on timescales of hours), and individual bumps can occasionally appear just ahead or behind the position predicted from a mean period. Nevertheless, we believe these anomalies can be treated as perturbations from a time-averaged pulsation model.
The Evolution of Rapidly Rotating B Stars (Review Paper)
Authors: Smith Robert Connon
Published: June 2019

Be stars are located in or near the main-sequence band for non-rotating stars. Although this stage of evolution is relatively well understood, there are two main effects that make it impossible to say whether all Be stars are in the same stage of evolution and, if so, what that stage is. One effect is the spread in observed magnitude and colour as a result of rotation. Correction for rotation is not possible because of the unknown inclination of any particular star's rotation axis to the line of sight and because it is not clear what the internal angular momentum distribution is or how it changes as a result of evolution. The other effect is that there are uncertainties in the theoretical evolutionary tracks because the amount of convective overshooting is unclear. Other mixing mechanisms that might in principle also confuse the tracks seem to be small near the main sequence. If Be stars are related to theβCephei and 53 Persei stars in the same part of the HR diagram, then the non-radial pulsation properties of Be stars may give a clue to their evolutionary state. The existence of a circumstellar disc or ring, however, tells us very little about the evolutionary stage of the underlying star. A useful way forward may be to try to understand individual stars in as much detail as possible.
Be Stars as Members of Open Clusters
Authors: Feinstein A.
Published: June 2019

A list of 124 Be-type stars belonging to 52 open clusters has been compiled. All of them have photometric UBV data, and many of them spectral classification in the MK system. Besides, the cluster's distance modulus and the mean color excess from the member stars are known. Then, we have computed the absolute magnitude and the intrinsic colors of each Be star.

The observed color-color diagram (Figure 1) shows clearly that nearly all Be stars appear to be reddened. In Figure 2 is given the color-magnitude diagram, (B-V)o versus Mv, in whicn the ZAMS (Blaauw, 1963) is also included. A few stars to the left of the main sequence belong to the young open clusters: NGC 869, 6167, 6530 and 6611. This effect may be due to wrong correction of the color indices because of abnormal values of the reddening law.
Variable Be Stars in h and χ Persei
Authors: Waelkens C.L. , Lampens P. , Cuypers J. , Denoyelle J. , Heynderickx D. , Rufener F. , Smeyers P.
Published: June 2019

The double cluster h and χ Persei has since long been known to be rich in Be stars (Trumpler, 1926). It belongs to an age group in which various types of variable stars occur (Mermilliod, 1981). Other clusters of this age group are NGC 3293, the cluster that is richest in β Cephei variables (Balona and Engelbrecht, 1983), IC 2581, NGC 4755, and NGC 6871. The comparison of the characteristics of variable stars in all these clusters and in clusters of other age groups could reveal to which extent the cluster stellar content is determined by age and by other parameters, such as galactic location, and so metallicity. Since h and χ Persei are very rich clusters that have not yet been studied intensively as far as stellar variability is concerned (Percy, 1972), we have undertaken a study of the photometric variability of the brightest stars in the double cluster. Our first interest was to detect β Cephei variables, but it rapidly turned out that the double cluster contains a considerable amount of highly variable Be stars.
The Oosterhoff Period Effect and the Age of the Galactic Globular Cluster System
Authors: Sandage Allan
Published: June 2019

The Oosterhoff division of globular clusters into two dichotomous mean period groups is a result of the variation with metallicity of the combined effects of (1) a mean increase in period with decreasing metallicity, and (2) the change of globular cluster horizontal branch (HB) morphology from the M3 to the M13 HB type within the instability strip in the metallicity range of [Fe/H] between -1.7 and -1.9. A new representation of the Oosterhoff period effect showing this property is made from the individual cluster data in Figure 1. The relation between period and metallicity for cluster and for field RR Lyraes at the blue fundamental edge of the instability strip in the HR diagram as read from this figure is

log Pab = -0.122(±0.02)([Fe/H]) - 0.500(±0.01)

using the metallicity scale of Butler.

The high slope coefficient is consistent with the extant models of the HB when they are read at the varing temperature of the fundamental blue edge given by equation (3) of the text. Most of the current literature treats only the constant temperature condition, which is manifestly incorrect. It is this temperature effect that reconciles the observations and the models.

A new calibration of the absolute magnitudes of RR Lyrae stars as a function of metallicity, combined with new oxygen enhanced isochrones for globular clusters (Bergbusch & VandenBerg 1992) reduces the age of the Galactic globular cluster system to 14.1 ± 0.3 Gyr (internal error). The resulting lower age of the universe which, when combined with a Hubble constant near 50 km s-1 Mpc-1 determined from type I supernovae, shows that the cosmological expansion has been decelerated by an amount consistent with the closure density, permitting Ω ∼ 1 now from the timing test.
Recent improvements to the Cepheid distance scale
Authors: Freedman Wendy L. , Madore Barry F.
Published: June 2019

In the course of the last decade significant advances have been made in the observations of Cepheid variables and in their successful application to the extragalactic distance scale. Much of this progress has come about as a result of new CCD and near-infrared photometry. These recent improvements are discussed, and a comparison is given of Population I Cepheids and Population II distances. The correspondence is good, with the zero points agreeing at a level of better than 15% in distance. At this same level of significance, a systematic difference between these distances scales may exist, in the sense that the RR Lyrae distances appear to be smaller than the Cepheid distances (if it is assumed, as has generally been done for extragalactic studies of RR Lyraes, that Mv(RR) = 0.77 mag, independent of [Fe/H]). However, several recently-published calibrations of Mv(RR) significantly reduce this discrepancy. Finally, new Cepheid data for the nearby galaxy M81 are presented based on recent Hubble Space Telescope observations.
Cepheid and Long – Period Variables in Virgo Cluster Galaxies
Authors: Pierce M.J. , McClure R.D. , Welch D.L. , Racine R. , van den Bergh S.
Published: June 2019

We are currently undertaking a ground-based imaging survey which attempts to discover and determine periods for variable stars in Virgo Cluster galaxies. Such a survey is now feasible thanks to the high resolution imaging (FWHM ≤ 0.50 arcsec) routinely obtained with the High Resolution Camera on the Canada-France-Hawaii Telescope. The Virgo Cluster has long been considered a crucial “stepping-stone” in the extragalactic distance scale problem given that the cluster is at a “cosmologically interesting” distance and that there is little controversy in the relative distance between Virgo and more distant clusters, such as Coma. Consequently, much of the controversy regarding the extragalactic distance scale and the Hubble Constant can be eliminated with a determination of the Virgo Cluster distance. Some preliminary results and the prospects for establishing the distance to the Virgo Cluster using Cepheids and LPVs are discussed.
An Adjustment to Cepheid Distances Calculated Using Model Atmospheres
Authors: Hindsley Robert , Bell R.A.
Published: June 2019

Hindsley and Bell (1989, Ap. J., 341, 1004) determined distances for 23 Cepheids using the surface brightness method. The color V – IC on the Cousins system or V – RJ on the Johnson system was used to measure visual surface brightness. Combined with the observed visual magnitudes, angular diameters were then calculated. Comparison of angular diameters with radius differences in linear units, obtained by integrating the radial velocity curve, yielded each Cepheid's distance.

Hindsley and Bell calibrated the relationship between color and surface brightness using model atmospheres. The zero point of the relationship was found using observations of Vega and an appropriate model. More recently the spectral scans of Gunn and Strycker (1983, Ap. J. Suppl., 52, 121) and the Cousins filter response curves of Hindsley and Bell were used to calculate colors and these were compared to the corresponding observed colors.
The Effect of a Vertical Magnetic Field on the Periods of Trapped g-modes in White Dwarfs
Authors: Carroll Bradley W.
Published: June 2019

A white dwarf model with cylindrical symmetry is used to investigate the effect of a uniform vertical magnetic field on the periods of g-modes trapped in the compositionally stratified surface layers. For those modes for which trapping is most effective, the periods wander by approximately 10% about their zero-field values as B0 increases. As the field strength increases further, the period may abruptly increase by some 25% to a new, more stable value; see Figure 1. The periods of less efficiently trapped modes do not show this sensitivity for field strengths up to 1 MG, the upper limit examined.
Fourier Analysis of Line-Profile Variations: Toward Stellar m – v Diagrams?
Authors: Merryfield W.J. , Kennelly E.J.
Published: June 2019

Numerous rapidly rotating δ Scuti stars exhibit variable line profiles containing traveling subfeatures [l]-[2], which may be signatures of nonradial pulsations having relatively high azimuthal order |m| We describe a procedure whereby a time series of spectral line profiles is Fourier analysed both in time and in a wavelength variable that is presumed to correspond to azimuthal position Φ on the star. What such an analysis can tell us is examined by analysing artificially-generated data. For an ideal example in which sin i = 1 and a single mode having is present, the two-dimensional Fourier transform yields a power spectrum in frequency and an apparent azimuthal order that provides a good indication of the actual and m. Such a straightforward interpretation is also possible when sin i < 1, and when multiple sectoral modes are present. For tesseral modes may correspond more closely to than to m.
Interpretations of Solar Oscillations
Authors: Cox Arthur N.
Published: June 2019

The current theoretical status of understanding solar oscillations is reviewed. Interpretation of the thousands of well-determined frequencies refines our knowledge of the composition and convection structure of the Sun, since its mass, radius, luminosity, and age are better known from other sources. Recent issues that have been discussed are the solar center structure, bearing on the missing solar neutrino problem, the convection zone helium content, validating helium settling by diffusion, the variations of the oscillation frequencies over the solar cycle, indicating cyclical structure changes in the very outer magnetic layers, and the fine structure splittings of mode frequencies, revealing the internal rotation. Our ability to match observed frequencies to now within only a few microhertz has been enhanced by the recently improved MHD equation of state and the new Livermore OPAL opacities. Thus solar oscillations not only reveal solar structure data, but also they guide improvements for stellar astrophysics material properties. A new discussion of current investigations of the convection zone helium abundance and its depth is presented.
New Opacities and the Beta Cephei Stars
Authors: Balona L.A.
Published: June 2019

The recent revision of metal opacities has opened up the possibility that the long-sought mechanism for driving pulsations in these stars has at last, been found. This hypothesis makes a testable prediction — that noβCep variables should exist among metal-poor B-type stars. We report on the results of an intensive CCD monitoring campaign to test this prediction. The question of the pulsation mode ofβCep stars and the consequence of a revision of the absolute magnitudes to accommodate the fundamental radial mode among these stars is also discussed. Pulsational instability due to driving by ionization of metals has many other repercussions for the incidence of pulsation among the B-type stars. A classification scheme for other intrinsically variable B-type stars is suggested. It is shown that if, as generally supposed, pulsation is common among B-type stars then at least two different mechanisms must be in operation.
Did Beta Canis Majoris Quit Pulsating?
Authors: Odell Andrew P. , Watson Robert D.
Published: June 2019

The star β CMa, prototype of the β CMa variables, is known to have been a double mode pulsator since the beginning of the century, with amplitudes of 12 and 7 km/sec for the 6.00 and 6.03 hour oscillations (Shobbrook, 1973). Recently, Dziembowski, Moskalik, and Pamyatnykh (1992) have produced models of B stars using OPAL opacities which have many radial and non-radial modes unstable. As only a few modes are observed in these stars, these authors suggest that modes might change amplitude in such a way that modes can appear, disappear, or be replaced by other modes. Based on unsubstantiated rumour that β CMa had, like α Vir, quit pulsating (Pesnell, priv. comm.), we undertook observations with the Mt. John University Observatory (New Zealand) echelle spectrograph and CCD camera on the 1-m McLelland telescope. We found that β CMa is still pulsating, but with reduced amplitude and substantial period change compared with earlier data.

In particular, quadratic ephemerides fit to all known times of spectroscopic maxima agree with our times of maxima [P1: HJD 2448611.8436; P2: HJD 2448611.8278] to better than two minutes, but an earlier linear ephemeris by Chappelier (1985) disagrees by over two hours. Our data is best fit with amplitudes of about 7 km/sec for both modes-this gives a nominal beat amplitude of nearly zero at the 49-day beat minimum (at a time when the linear ephemeris would have predicted a maximum amplitude). This may be the cause of the rumour mentioned above. Additional support for our conclusion of continuing pulsation comes from the fact that obvious line profile changes occur on the pulsation time scale.
An Extraordinary Early-Type Eclipsing Binary
Authors: Balona L.A. , Cuypers J.
Published: June 2019

HR 2680 (B5V) was used as a comparison star in a multi-site (ESO & SAAO) campaign organised in 1988 to observe Be stars. We found that the star is an eclipsing binary with a period of 8.1 days. The eclipse is partial with a depth of 0.18 mag. Radial velocity observations confirmed the period.

A light variation with an amplitude of as much as 0.03 mag was seen outside the eclipse (Fig. 1). This variation can be interpreted as two oscillations with approximate periods of 1.19 and 1.28 days. Further photometric observations were obtained in 1989, 1990 and 1991 at SAAO. The multiperiodicity was confirmed, but the periods were not constant from season to season.

We suspect that the star is a pulsator of the 53 Per class of line-profile variables. Being an eclipsing binary, this unique system is of potentially great importance as a test bed for stellar dynamics and nonradial pulsations.
Pulsation Properties of Hydrodynamic Models with Dimensional Analysis
Authors: Aikawa Toshiki
Published: June 2019

We demonstrate that the dimension deduced from time series data of hydro-dynamic models for chaotic pulsation is a function of luminosity. The dimension is proposed as a good quantity to guess stellar parameters and the physics of stellar envelopes like as the pulsation periods and light curve shapes used for regular variables.
The Evolution of Hα Profiles in S-type Mira Stars
Authors: Woodsworth A.W.
Published: June 2019

Past attempts to model the Hα emission profiles from Mira stars have been hampered by the strong absorption bands produced by TiO (M-type Miras) or carbon-based molecules (C-type Miras). The S-type Miras, however, exhibit relatively clean emission lines. As part of a larger study of Mira variables, I have obtained a series of high-dispersion Hα profiles of S-type Miras at different phases, using the DAO 48” coudé spectrograph. Although most profiles were obtained from different stars, their shapes develop in a regular way with advancing phase, so it appears that the observations can be used together to provide a good data base for the fitting of evolutionary (rather than static) models for the shock waves in S-type Miras.

Initial experiments with fitting simple models to the profiles have been extremely encouraging. The profiles can be represented very well by three Gaussian components.
OPAL Opacities
Authors: Rogers F. J. , Iglesias C. A.
Published: June 2019

We have continued to improve and update the OPAL opacity code. Addition of intermediate coupling has further increased the opacity over earlier LS coupling results. A ‘corresponding states’ method has been used to extend the tables in both X and Z. This has allowed the calculation and distribution of extensive opacity tables for several different sets of metal abundance.