bluuebunny/crossref_metadata_2025 huggingface dataset:
A High School Astronomy Course for a Wide Range of Student Abilities
Authors: Sampson G. E.
Published: June 2019

Astronomy is, inherently, a high-interest subject. However, at the high school level there is a tendency to teach astronomy using higher- level abstractions and complex mathematics. This teaching approach thus eliminates a large number of students who have difficulties with abstractions and complex mathematics, thereby restricting the study of astronomy to a rather select group of students.

The astronomy course offered since 1976 at Wauwatosa West High School was developed to reach a wide range of students with differing abilities. The prerequisite for this one-semester elective course is the successful completion of one year of high school science. Most of the students enrolled in this course are high school juniors and seniors, ages 16–18. Since algebra is not a prerequisite, the “math phobic“students have been attracted to the course.
Astronomy Teaching in the Astronautics Club
Authors: Aleshkina E.Yu.
Published: June 2019

There is no necessity to argue about a vital need of an extension of astronomy and space knowledge equivalent to a modern state of the natural sciences. Astronomy teaching both professionally and for amateurs in the form of general courses is particularly needed nowadays because of the spread of various forms of mysticism in Russia.

The main goal of astronomy teaching is to help students to become aware of the place of humanity in the Universe. In this connection it is necessary to study not only astronomy but also other relevant courses simultaneously. Such complex astronomy study plays a significant role. It is necessary to show a close interaction of astronomy with other sciences such as traditionally mathematics, physics, chemistry and also biology and psychology, which just begin to be integrated in the field of space sciences.
The Short-Period Photometric Variability of Be Stars
Authors: Balona L.A. , Engelbrecht C.A.
Published: June 2019

The fact that some Be stars have periodic light vanations with time scales of the order of one day is well established (eg. Balona and Engelbrecht 1986). The cause of this variability is not yet understood. The explanation which seems to have gained the most acceptance is nonradial pulsation (NRP). It is of great importance to ascertain the proportion of Be stars which are short-period variables and to determine the link between the variations and the emission-line phase. We have started a photometric project to investigate these problems. In this note we present some preliminary results and tentative conclusions.
Spectral Energy Distribution and Interstellar Reddening (Review Paper)
Authors: Houziaux L. , Manfroid J.
Published: June 2019

We review the recent results on flux distribution of Be stars from 320 to 850nm. It appears that data are available for only 10 to 15 % of the objects recognized as “normal” Be stars. The main current problems appear to be the variability of the continuous radiation, and the correction for interstellar reddening. Various attempts to solve these matters are discussed. We stress the need for fairly high (lnm) resolution spectral scans obtained simultaneously with data in other spectral ranges, repeated at appropriate intervals of time. Such requirements make it necessary to restrict the observing programmes to a limited sample of carefully chosen objects.
Structure of the Envelope of EW Lac in 1971–1984
Authors: Kogure T. , Suzuki M.
Published: June 2019

Kogure and Suzuki (1984) have noticed that EW Lac (HD217050, B2 III pe) has revealed the long-term variation notably different before and after about 1976. Before 1976, the profiles of spectral lines were sufficiently symmetric and stable, suggesting a circular disk or ring for the structure of envelope. In contrast, since 1977, EW Lac entered a phase of anomalous V/R variation.

We have obtained about 180 coudé spectra in 16 years by 1985 with the 188 cm reflector at the Okayama Astrophysical Observatory. Most of them were measured using the PDS densitometer at the Kwasan Observatory, University of Kyoto for the radial velocities and line profiles. A part of results were reported by Suzuki and Kogure (1986).
Red and Infrared Photometry of Be Stars
Authors: Kilambi G. C. , Vivekananda Rao P. , Sarma M. B. K.
Published: June 2019

All programme stars including standard stars were observed with the standard RI filters of the Johnson system with a 20-arcsec diaphragm for 4 nights during the 1982–83 observing season. A photoelectric photometer attached to the 1.2 meter reflecting telescope of the Japal— Rangapur Observatory was used for these observations. A dry-ice cooled EMI 9558B photomultiplier tube was used as the detector and the photo-current was recorded by means of a GR 1230A DC-amplifier and a Honeywell Brown chart recorder.

The extinction coefficients for R and (R-I) were determined from the observations of standard stars taken from the list of Johnson (1966) and also from the observations of an early and a late spectral type star on each night and all the observations were corrected for atmospheric extinction. The instrumental magnitudes of a programme star were transformed to the standard system through normal procedures.
High-Resolution Emission-Line Spectroscopy of Be Stars: Comparison of Hα and Weak Emission Lines
Authors: Hanuschik Reinhard W.
Published: June 2019

For a number of bright southern Be stars, high-resolution, high S/N spectroscopy has been performed for Hα, Si II λ6371 and four Fe II emission lines. With the exception of four stars, both Hα and weak emission line profiles exhibit resolved double-peak structure. Peak separation increases with stellar projected rotational velocity. In many cases, Hα profiles (but not Fe II lines) show resolved fine-structure (inflections in the flanks) indicating a two-component structure of the disk. Envelope models with arbitrary density and rotational velocity laws have been fitted to the Fe II line profiles with satisfactory results. It is found that the innermost Hα disk component also emits the Fe II lines and has an average outer radius of 5 r*; density falls off as r-l.5 or more rapidly. The outer disk component emits the faint and narrow secondary component of Hα lines with average outer radius 20 r*. The envelopes of the four stars with a strong, dominating single peak both in Hα and Fe II either are dominated by strong radial motions or, more likely, have elliptical disk-like structure.
Interstellar Absorption of Some Be Stars
Authors: Briot D. , Zorec J.
Published: June 2019

It is well known that the intrinsic colors of Be stars are not the same as those of “normal” B stars and they are often redder. So interstellar absorption of Be stars determined from photometric indices may be overestimated. In order to avoid this, a method often used to determine the interstellar absorption of Be stars is based on the ultraviolet interstellar absorption bump at 2200 Å (Dorschner 1975; Nandy et al. 1975, 1976). However some peculiar Be stars exist whose circumstellar matter contributes to the 2200 Å bump (Savage et al. 1978). The aim of this work is to test the deredenning method from the 2200 Å bump for “classical” Be stars, in determining the interstellar absorption in the region of the Be star, using the surrounding normal stars.
Infrared Observations of Be Stars (Review Paper)
Authors: Lamers Henny J.G.L.M.
Published: June 2019

The first indication that Be stars have an excess near-IR radiation, compared to normal stars of the same spectral type was found by Johnson et al. (1966). Johnson (1967) noticed that in his sample of 85 early type stars all the Be stars and shell stars had an excess in K-L and he concluded that this is due to IR emission from circumstellar shells. Woolf et al. (1970) suggested that the IR excess of Be stars might be due to free-free emission in the ionized circumstellar envelope which also produces the Balmer emission lines, but their observations at 5 and 10 µ could not rule out the possibility that circumstellar dust contributed to the excess. The observations by Allen (1973) of a large number of Be stars up to a wavelength of 3.5 µ could not make the distiction between free-free or dust emission either.
Near Infrared Spectra of 103 Bright Be Stars
Authors: Andrillat Y.
Published: June 2019

We have observed 103 bright Be stars in the near infrared up to 10500 A with a dispersion of 230 and 50 A mm-1. The observations were performed with a Reticon (1024 diodes) attached to the ROUCAS spectrograph at the 193 cm telescope of the Haute Provence Observatory.

In this spectral range, the Be stars are characterized by the lines of HI (Paschen series), 0I(7772-74-75, 8446 A), CaII(8542, 8662, 8498 A), FeII(7712, 9997 A) and NI(8686-83-80, 8719-12-03, 8629 A).

On our spectra, the CaII triplet is always blended with P13, P15, P16, and only the enhancement of these lines permits to conclude to the CaII presence. The 0I 8446 A is perturbed by the Paschen lines P17 and P18 (low dispersion spectra) and P18 (high dispersion spectra). The NI 8686-83-80 A lines also perturb the P13 profile.
Voyager Observations of Zeta Tau
Authors: Carone T. E. , Polidan R. S.
Published: June 2019

Zeta Tau (HD 37202) is a well known Be/shell star of spectral type B1 IVe and vsin(i) = 220 km/sec (Slettebak 1982). Its visual and UV variability have been studied extensively (Heap 1975; Hubert-Delplace and van der Hucht 1978; Hubert-Delplace et al. 1983; Dawanas and Hirata 1984; Harmanec 1984). Zeta Tau has also been found to be a binary with an orbital period of 132.97 days (Harmanec 1984). Irregular light variations have been observed (Hoffleit 1982) and long term variations not associated with the 132.97 day period have also been seen (Hubert-Delplace et al. 1983).
Long-Termed Variability in the Far Ultraviolet Flux of Be Stars
Authors: Peters G. J. , Polidan R. S.
Published: June 2019

Optical light variability appears to be commonplace in Be stars, on time scales from days to decades, but the phenomenon has yet to be satisfactorily explained. Some possible causes include changes in 1) the star's photospheric temperature or radius, or 2) the envelope's opacity or continuous emission. To investigate the nature of the photometric variability in Be stars, we have been monitoring the FUV flux of selected objects with the ultraviolet spectrometers (UVS) on the Voyager 1 and 2 spacecrafts (cf. Broadfoot, et al. 1977, and Holberg, et al. 1982, respectively, for information on the instrumentation and calibration, and Drilling, et al. 1984 and Polidan, et al. 1987 for a discussion of data reduction techniques), and report the initial results from these observations in this paper.
Be Binary Systems with a Cool Companion: Are they Interacting?
Authors: Floquet M. , Hubert A.M. , Maillard J.P. , Chauville J.
Published: June 2019

High resolution spectrograms of the two well known Be binary systems ζ Tau and KX And were obtained , in the IR ( 2-2.5µ ), with the Fourier Transform Spectrometer of the CFHT. They do not reveal evidence of a cool giant companion.
A Photometric Study of Herbig Ae/Be Stars
Authors: E. Eugenio , V. Mendoza
Published: June 2019

It is well known (cf. Mendoza 1983) that “classical“ Be stars, and Herbig Ae/Be objects, in addition to hydrogen lines in emission, also share at least two photometric characteristics, namely, light varitions, and infrared color excesses.

We have selected the α(16)⋀(9) {Mendoza 1979}, and the JHKL-photometric systems, in order to study some photometric properties of Be stars. The observations have been carried out at the National Astronomical Observatory (San Pedro Martir, B.C.N., and Tonantzintla, Pue.), Mexico, from 1976 to 1986.
I-band Cepheid Distance to NGC 6822
Authors: Lee Myung Gyoon , Freedman Wendy L. , Madore Barry F.
Published: June 2019

NGC 6822 was the first galaxy outside the Galaxy where the Cepheid period-luminosity relation was applied as a distance indicator (Hubble 1925, ApJ, 62, 409). Later, thirteen Cepheids in this galaxy were studied by Kayser (1967, AJ, 72, 134) using BV photographic photometry. We have obtained BVRI CCD photometry of stars in two 2.2' X 3.5' fields of NGC 6822. Field 3) using Figure 1 shows an I – (V – I) diagram of ∼ 6,400 measured stars in NGC 6822 including seven known Cepheids. The reddening is estimated to E(B – V) = 0.28 ± 0.03 from the (B – V)-(V – I) diagram of the stars with V < 20 mag. The distance to NGC 6822 has been estimated using the random-phase I band photometry of seven Cepheids (V7(I=16.31), V5(I=18.97), V6(I=18.44), V3(I=17.88), V1(I=18.05), V28(I=17.61), and V2(I=17.29)) combined with their periods given by Kayser.
A Preliminary Distance to the Small Magellanic Cloud by the Surface Brightness Technique
Authors: Barnes Thomas G. , Moffett Thomas J. , Gieren Wolfgang P.
Published: June 2019

We present a new distance determination to the Small Magellanic Cloud from the surface brightness technique applied to the Cepheid variable HV 829. Although this is a preliminary distance based on only one star, it illustrates the power of the surface brightness technique to extragalactic Cepheid distances, it develops the technique which we will apply to additional SMC and LMC Cepheids, and the distance is of intrinsic interest because of the current controvery concerning distances for the Magellanic Clouds.

For HV 829 itself we obtain a distance modulus of 18.91 ± 0.20 mag. From other evidence we infer that HV 829 is slightly in front of the SMC centroid distance. Correcting to the SMC centroid yields a distance to the SMC of 19.05 ± 0.20 mag. We stress that this distance modulus is fully independent of any other distance modulus for the SMC, including those based upon Cepheids. Even so, our result agrees more closely with other, independent Cepheid distances than with RR Lyrae distances and main sequence fitting distances.
Studies of Large-Amplitude δ Scuti Variables
Authors: Wilson W. J. F. , Milone E. F. , Fry D. J. I.
Published: June 2019

The determination of Baade-Wesselink radii and luminosities for pulsating stars are long-standing and highly desired goals since they provide the promise of being standard candles. In a modest contribution towards these goals, we have undertaken a programme to determine the radii and luminosities of the large-amplitude δ Scuti stars DY Herculis, EH Librae and DY Pegasi from optical and infrared photometry and cross-correlated radial velocity data. We use Fourier representations for V, I and J light curves and for the radial velocity curves in Baade-Wesselink analyses to derive minimum radii over the pulsation cycles. These radii and their errors and the mean bolometric luminosities and absolute magnitudes will be discussed here and in papers to follow. As a check, we also apply our method to the data and results of other groups.
White Dwarf Seismology at the Université de Montréal
Authors: Fontaine G. , Brassard P. , Bergeron P. , Wesemael F.
Published: June 2019

Over the last several years, we have developed a comprehensive program aimed at better understanding the properties of pulsating DA white dwarfs (or ZZ Ceti stars). These stars are nonradial pulsators of the g-type, and their study can lead to inferences about their internal structure. For instance, the period spectrum of a white dwarf is most sensitive to its vertical chemical stratification, and one of the major goals of white dwarf seismology is to determine the thickness of the hydrogen layer that sits on top of a star. This can be done, in principle, by comparing in detail theoretical period spectra with the periods of the observed excited modes. Likewise, because the cooling rate of a white dwarf is very sensitive to the specific heat of its core material (and hence to its composition), it is possible to infer the core composition through measurements and interpretations of rates of period change in a pulsator.
HR 8762: Low-amplitude Photometric Variation in a Pre-shell Phase
Authors: Gonzàlez-Bedolla S. , Sareyan J. P. , Chauville J. , Morel P. J. , Alvarez M.
Published: June 2019

Longitude-coordinated high-precision photometry has been obtained a few weeks before the beginning of a strong Be and shell phase (1988) in HR 8762 (o And). The star showed variations of a few millimagnitudes in amplitude; i.e., just over the detection threshold. The classical 1.57-day double-wave period is still detected, showing that it probably never fades out completely, whatever the phase of the star. These variations can be interpreted as normal photospheric activity in a regular rotating B star. Although the variations of HR 8762 during our campaign were quite small, we could detect their amplitudes at a level of a few mmag.

We still have to check whether they are still “in phase” with previous photometric observations: if this is the case, it means that in the “spot” hypothesis, these (superficial?) features would remain in the same position on the photosphere, changing only in surface area and/or brightness with the star's activity.
NLTE Synthetic Spectra of Mira-Type Variable Stars
Authors: Luttermoser Donald G. , Bowen George H. , Willson Lee Anne
Published: June 2019

We present NLTE radiative transfer in hydrodynamic models representative of Mira-type variable stars. Calculations were carried out with the PANDORA code of the Bowen models using a snapshot approximation.
A Photometric and Spectroscopic Study of Southern RV Tauri Stars
Authors: Pollard Karen , Kilmartin P.M. , Gilmore A.C. , Cottrell P.L.
Published: June 2019

A program to obtain photometric and spectroscopic (high and medium resolution) observations of a number of southern RV Tauri stars has been undertaken over the past two years at the Mount John University Observatory (MJUO). Eleven RV Tauri stars of both RVa (constant mean magnitude) and RVb (varying mean magnitude) photometric type have been chosen as well as normal and weak metal lined RV Tauri stars.

Most program stars display the alternating deep and shallow semi-regular light variations as well as the light curve - colour curve phase lag characteristic of RV Tauri stars. Fourier analyses of the light curves have revealed the dominant periodicities (see figure 1) and allowed phasing of the spectroscopic observations.

High resolution échelle spectra obtained of these stars around the Hα region display the complex emission and absorption structure of the Hα line at various phases. Metallic lines show emission and line doubling or ‘splitting’ - profiles characteristic of the shock wave that propagates through the line-formation regions of these stars during a pulsational cycle. Spectra at specific phases will be used in an abundance analysis of selected RV Tauri stars.
The Bump Cepheid Mass Discrepancy Laid to Rest (?)
Authors: Moskalik P. , Buchler J. R.
Published: June 2019

The beat and bump mass discrepancies have been a long standing, unsolved difficulty in the Cepheid modelling (Cox 1980). The new opacities of Rogers & Iglesias (1992) has provided a partial solution to the problem, bringing the beat masses into good agreement with other mass determinations (Moskalik, Buchler & Marom 1992; herafter MBM). The discrepancy for the bump masses has also been greatly reduced, nevertheless it has not been eliminated entirely.

Recently, the new version of the Livermore tables has been released (Iglesias, Rogers & Wilson 1992). The new calculations take into account previously disregarded spin-orbit coupling in the iron atoms. The inclusion of this effect leeds to a further enhancement of the “metal opacity bump” around 2-5xl05K. In the following we repeat the calculations of MBM to assess the consequences of this enhancement for the bump mass calibration.
A survey of RR Lyrae models
Authors: Bono G. , Stellingwerf R.F.
Published: June 2019

An extensive grid of non-linear pulsating models of RR Lyrae stars have been computed. To simulate the outer regions of these variables a non-local and time-dependent treatment of convective transport has been adopted. In this poster we briefly describe some new features of the instability strip (IS).
Nonlinear Radiative RR Lyrae Models: A Search for Double-Mode Behavior
Authors: Guzik Joyce A. , Cox Arthur N.
Published: June 2019

Cox (1991), Kovacs, Buchler, and Marom (1991), and Kovacs et al. (1992) showed that opacity changes indicated by the Livermore OPAL opacities increase the pulsation masses of double-mode RR Lyrae variables. We calculated limiting amplitude solutions for radiative RR Lyrae models of 0.75 M⊙, 51 L⊙, and Z=0.0001 (Oosterhoff II) to investigate the effects of the mass increase and opacity changes suggested by the OPAL opacities. In particular, we modified the Stellingwerf analytical fit (1975) to the Cox-Tabor (1976) tables to decrease the opacity by 20% between 20,000 and 30,000 K. The Stellingwerf periodic relaxation method was used to converge the models to a limit cycle, and the Floquet matrix analysed to search for a tendency of the fundamental mode to grow from the full-amplitude overtone solution, and the overtone to grow from the full-amplitude fundamental mode solution, thereby predicting double-mode behavior.
Double-mode RR Lyrae models
Authors: Bono G. , Stellingwerf R.F.
Published: June 2019

Double-mode RR Lyrae stars (RRd) represent a fundamental testing ground for the theory of stellar pulsation because they play an important role in understanding the interaction between different pulsation modes. In spite of the fact that from an observational point of view the identification of the fundamental (F) and first overtone (IO) periods needs only few periods of light curve coverage (Sandage et al. 1981, Nemec 1985), the theoretical models of double-mode and mixed-mode variables dating back to the original papers of Cox et al. (1983) and Stellingwerf (1975) were not integrated for long enough times to ensure proper mode identification. Recently Kovacs and Buchler (1992) using a standard radiative hydrodynamical code investigated the theoretical properties of RRd stars in more detail. This paper represents a brief description of the results of few cases computed adopting a non-linear, non-local treatment of convective transport, and long integration times to enable positive mode identification.
New results on field and cluster RR Lyraes
Authors: Clementini G. , Merighi R. , Tosi M. , Gratton R. , Carretta E.
Published: June 2019

RR Lyrae stars both in the field and in clusters can be used to derive the metal abundance of the regions and systems where they are found.

(1) New data have been collected on a sample of field ab-type RR Lyraes with the aim of studying the composition of the halo and the disk of the galaxy, (Clementini et al. 1992a, in preparation), using the relation found by Clementini et al. (1991), (hereafter CTM91), between [Fe/H] and the equivalent width of the Ca II K-line W‘(K). (2) A quantitative chemical abundance analysis of the ab type RR Lyrae (V29) in the globular cluster M4 has been performed using high resolution, high S/N spectroscopy. We obtain [Fe/H]=–1.3 ± 0.2 and the α– elements (Mg and Ti) are overabundant by 0.6 dex. These results are in good agreement with determinations from high resolution spectra of giants and blue horizontal branch stars (Clementini et al. 1992b, in preparation).
On Period Ratios and Resonance Sequences
Authors: Petersen J.O.
Published: June 2019

Basic features of calibrations of period ratio diagrams in terms of mass or radius can be understood from two facts: (1) The pulsation Q-parameter for the fundamental mode of Cepheid-type models increases by a factor of about 3 from periods of about 0.05 days to 100 days, whereas Q for overtones vary much less. Therefore period ratios usually decrease with increasing pulsation period in a group of variable stars or in a model sequence (calibration curve). (2) Mass over radius (M/R) is a good pulsation parameter determining Q-values and therefore also period ratios (e.g. Cogan 1970). Using the pulsation criterion with constant Q, it is easy to show that this implies that periods of models with a fixed period ratio, e.g. 0.70, to a first approximation is proportional to both M and R. Thus all calibration curves in period ratio diagrams should move towards increasing period with increasing M or R. This is confirmed in numerous cases.
Asymmetry of metallic spectral lines in Cepheids
Authors: Albrow Michael , Cottrel P.L.
Published: June 2019

A program of high resolution spectroscopic observations of Cepheids has been carried out at Mt John University Observatory for several years. Radial velocities and asymmetries have been measured for selected metallic lines using the method of Wallerstein et al (1992).

The line profiles show the largest asymmetry at phases of maximum inward velocity. The asymmetry at phases of maximum outward velocity is smaller and sometimes in the same direction as for the inward velocity maxima. Enhanced asymmetry is also noticed at phases where the bump appears on the radial velocity curve.

To date our models are unable to predict such behaviour. It is important that a satisfactory explaination for these observations be found so that the accuracy of Baade-Wesselink radius solutions for such stars can be assessed.
Investigation of the Double-mode Cepheid TU Cas: Atmospheric Parameters and Chemical Composition
Authors: Andrievsky S. M. , Kovtyukh V. V. , Makarenko E. N. , Usenko I. A.
Published: June 2019

Atmospheric parameters and abundances of 25 elements were determined from two spectrograms of TU Cas (with dispersion 9 Å/mm) obtained in 1977 and 1990. We find Teff= 5860 - 6000K; logg = 1.0 - 1.5; and vt = 2.9 - 5.3 km/s.

The value of [Fe/H] ∼ -0.5 testifies to the fact that TU Cas is deficient in metals compared with other double-mode Cepheids. More exact values of [Fe/H] for 9 double-mode Cepheids in the Southern Hemisphere (Barrell 1982), V367 Set (a member of the open cluster NGC 6649) and our value for TU Cas all show a good correlation with P1/P0. As the atmospheric Fe abundance increases, the ratio P1/P0 decreases.

Our measured values for abundances (in brackets) of various elements in the atmosphere of TU Cas are: C (8.26), Na (6.32), Mg (7.07), Si (6.85), S (6.96), Ca (5.88), Sc (2.71), Ti (4.34), V (3.35), Cr (5.29), Mn (4.92), Fe (6.94), Co (4.47), Ni (5.70), Zn (3.63), Sr (2.00), Y (2.17), Zr (2.21), Ba (1.41), La (1.08), Ce (0.96), Nd (0.82), Sm (0.42), Eu (1.04), and Gd (0.92).
The RV Variability of Yellow Giants
Authors: Larson A.M. , Irwin A.W. , Yang S.L.S. , Goodenough C. , Walker G.A.H. , Bohlender D.A. , Walker A.R.
Published: June 2019

The hydrogen fluoride (HF) absorption cell technique has been used at the Canada-France-Hawaii Telescope for over a decade to monitor the radial velocity variability of nearby, solar-type stars in a search for substellar companions. As a complement to this program, we have also been monitoring a select group of G and K subgiants, giants and supergiants, which have all proved variable. We present here a brief summary of our analysis.
RR Lyrae Variables in the Second-Parameter Globular Cluster NGC 7006
Authors: Wehlau Amelia , Nemec James M.
Published: June 2019

The distant globular cluster NGC7006 was one of the first clusters studied for which the distribution of stars along the horizontal branch of its C-M diagram showed evidence for a “second parameter” in addition to metallicity. Studies of the more than 60 known RR Lyrae stars in this cluster should yield some statistically significant trends or correlations which might help to identify the second parameter. In the first stage of this study (Wehlau, Nemec, Han-Ian $ Rich 1992, AJ, 103, 1583) photographic data from 1984 were combined with previously published data from the 1930's and 1950's and used to obtain period change rates for 46 variables. The median rate was found to fall one standard error below that predicted by the Yale evolutionary HB models. In addition, statistically significant evidence was found for a radial gradient in period change rates in the sense that rates for variables in the outer region of the cluster were more negative.

In the second stage of the investigation B and V magnitudes derived from CCD frames of the cluster are being used to obtain colors and to increase the number of variables for which good periods are known, in particular variables in the inner region of this centrally concentrated cluster.
Observations of Interstellar Reddening in Cygnus and Perseus
Authors: Nandy K
Published: June 2019

The Object of the Edinburgh Spectrophotometry Survey is to determine the interstellar extinction law as precisely as possible and to search for intrinsic variations in it. The observations have been extended to early type stars up to a limiting magnitude of 11ṃ0 in regions extending from lII = 50° to lII = 200°. The 16/24/60-inch Schmidt telescope of the Royal Observatory has been used in conjunction with an objective prism and grating. Spectra extend from λ = 3300 Å to λ = 9000 Å with a dispersion of 1000 Å/mm at Hγ. Since few stars fainter than 9m have been measured in earlier investigations, the present survey extends considerably the amount of information available.

In determining the extinction from a comparison of pairs of stars, one reddened and the other unreddened, one is faced by the problem of having to find two intrinsically similar stars in the same galactic region.
Dispersion of Polarization in Reflection Nebulae
Authors: Gehrels Thomas
Published: June 2019

A Few Observations Were Made in NGC 7023 with filters at 0.36, 0.56, and 0.74 μ The wavelength dependence of polarization fitted with a straight line shows an appreciable rise with longer wavelengths. (See refs. 1 and 2.) The observations at the three filters were compared with Mie calculations obtained from Dr. B. M. Herman and General S. R. Browning of the University of Arizona for various refractive indices and particle sizes. Only single particle sizes have been considered, and therefore the results are preliminary. The present work represents a first reconnaissance to learn the techniques and some of the geometrical conditions.

A firm conclusion, however, is reached in ruling out purely graphitic and purely metallic interstellar grains. The reasoning is as follows: The polarizations in various reflection nebulae (observed by Elvius and Hall) are “positive” and strong, and the color dependence is strong, with a fairly steep rise toward longer wavelengths; this behavior occurs for scattering angles from 20° to 70°. Such behavior is found in the Mie calculations at 2<a/λ ≅ 1.5. (See ref. 3.)
Formation of Molecular Hydrogen in Interstellar Space
Authors: Knaap H. F. P. , Van Den Meijdenberg C. J. N. , Beenakker J. J. M. , Van De Hulst H. C.
Published: June 2019

Although Several Attempts at observing the interstellar hydrogen molecules in the ultraviolet or infrared are in preparation (ref. 1), these molecules are still undetected. They may form the most abundant unobserved constituent of the interstellar gas. The strongest indirect argument for the presence of these molecules lies in the fact that the density of atomic hydrogen observed by the 21-cm line goes down in some dark clouds, where the dust density and, presumably, the total gas density goes up by a large factor.

Inasmuch as the density in the interstellar clouds is of the order of 10 atoms/cm3 and the temperature is only of the order of 100° K, any formation of molecules by atom-atom collisions is too slow to be of importance. The most eligible process for H2 formation is recombination on the surface of an interstellar dust grain. Rate estimates of this process have been made in various degrees of detail, as reported in references 2 to 4.
Near Infrared Interferometry of the Galilean Satellites
Authors: Howell R
Published: June 2019

Some of the Galilean satellites show evidence of two distinct surface types, a high albedo frost and a dark, presumably silicate material. We are beginning a program to map the spatial distribution of these components with a Michel son spatial interferometer. This will be done both in and next to the 2.0µm frost absorption band. While the mapping program is just beginning, this investigation has already yielded new information on the wavelength dependence of seeing in the infrared.
Parallaxes And Detection Of Dark Companions: The Case Of Interferometry Versus Imaging.
Authors: Connes Pierre
Published: June 2019

One tries to define an optimal method for the measurement of small apparent stellar motions. The available or proposed techniques and atmospheric disturbances are studied first. A special purpose interferometer is then devised; it is found far more complex and not in any way better than a previously described direct imaging system.
UV Absorption Spectra of Molecules and the Connection with Pumping Mechanisms for Astrophysical Masers
Authors: Viney J.C.
Published: June 2019

Since interstellar masers were first discovered in 1965, various attempts have been made to account for the variety of behaviour observed. In particular a number of theoretical models have been advanced to account for the pumping mechanisms but none have gained a wide acceptance.

Over forty molecules have now been identified in the interstellar medium, of these five exhibit maser action; they are detected by virtue of their small angular diameter and very large brightness temperatures > 1013°K. The molecules in question are H20, OH, SiO, CH3OH and CH, of these the Hydroxyl maser presents the widest range of behaviour and therefore if the physical mechanisms involved could be understood these masers could be used to probe the interstellar environment and obtain more information about this important region where new stars are formed
New Emission Resonances in Laser-Produced Plasmas on Cesium, Barium and the Lanthanides
Authors: Carrol P.K. , Kennedy E.T. , O'Sullivan G.D.
Published: June 2019

Emission spectra of laser-produced plasmas on targets of Cs, Ba and the lanthanides have been studied systematically in the region from 40 - 300Å. In the lighter of these elements the most characteristic feature is a strong emission maximum consisting of a mixture of continuum and discrete lines. The maximum is centered at 102 Å for cesium and moves to shorter wavelength with increasing Z. At praeseodymium a second maximum appears at longer wavelengths and with increasing Z both maxima broaden and eventually form a single continuum. The resonances are interpreted as excitation of 4d10 4fN9 to 4d 4fN+1 followed by re-emission modified by the presence of the exciting electron. The extensive continua which appear with the progressive filling of the f shell, are attributed to brehmstrahlung radiation.
Stark Broadening of Isolated Lines from Multiply Charged Ions
Authors: Hey J. D.
Published: June 2019

When calculating the Stark widths of isolated lines of multiply charged ions with several bound electrons, radiated by dense, hot plasmas, the existing theories of Stark broadening which have been applied mainly to lower-temperature measurements on singly-ionized species, need to be modified in several respects. These modifications involve taking more careful account of the complexities of the particular atomic structure: e.g. deviations from LS coupling, configuration mixing, and optically forbidden transitons. Earlier work, showing explicitly the relationship between the Stark widths and the oscillator strengths for the collision-induced transitions Which contribute to the width, is extended. Some of the principles involved will be discussed and, if time permits, comparison will be made between calculations and the results of several critically selected experiments on spectral lines in the near UV (2000-3500 Å).
The Problem of the UV Interstellar Absorption Band at 2200A
Authors: Carnochan D.J. , Nandy K. , Willis A.J. , Wilson R.
Published: June 2019

The ultraviolet interstellar extinction curve from 2740Å to 1350Å has been obtained using data from the S2/68 satellite experiment. The extinction increases into the ultraviolet and shows a pronounced peak at 2200Å. This is interpreted as a general scattering continuum with a strong absorption feature superposed on it at 2200Å. The profile of the feature appears to be symmetrical and has a half-width of 360Å. There is a strong correlation between the strength of the feature and the scattering part of the curve in both the ultraviolet and the visible. On a broad scale the shape of the extinction curve is constant showing no variation with distance from the sun, direction around the galaxy, and height above the galactic plane.
O VI Profiles of Solar Quiet and Active Areas Recorded by OSO-8 L.P.S.P. Experiment
Authors: Lemaire P. , McWhirter P. , Artzner G. , Vial J. C. , Bonnet R.M. , Gouttebroze P. , Jouchoux A. , Leibacher J. , Skumanich A. , Vidal-Madjar A.
Published: June 2019

O VI resonance line (2s2S - 2p2PO , 103.19 nm) is formed in the chromosphere-corona transition zone with a temperature of maximum ionization of 350 000°C (Jordan, 1969). The OSO-8/LPSP experiment has observed this line with a 0.006 nm resolution, few arcseconds angular resolution and a time resolution up to few seconds. We present the shape of the line in different areas on the sun (quiet and active). As transition lines are used to determine propagation of wave from chromosphere to corona, we compare width of the O VI line with other measurements obtained with lines of lower ionization temperature. From successive profiles we consider the possibility of direct measurements of wave propagating.
Possibility of a White Dwarf as the Accreting Compact Star in CI Cam (XTE J0421+560)
Authors: Ishida Manabu , Morio Kazuyuki , Ueda Yoshihiro
Published: June 2019

Although CI Cam, which showed an outburst in April 1998, has been regarded as a soft X-ray transient (SXT) harboring a, black hole, it has some characteristics that can hardly be reconciled with the SXT picture. In this paper, we propose a white dwarf as the central accreting star in CI Cam.
1RXS J232953.9+062814: A Possible Progenitor of AM CVn Stars
Authors: Uemura M.
Published: June 2019

We revealed that the hydrogen-rich cataclysmic variable lRXS J232953.9+062814 is an SU UMa-type dwarf nova with a superbump period of 66.774±0.010 min. A photometric orbital period is determined to be 64.184± 0.003 min, which is below the period minimum. Although the standard evolutionary scenario of cataclysmic variables predicts lower mass-transfer rates in systems with shorter orbital periods, its short recurrence time of outbursts and bright apparent magnitude indicate that this object has a relatively high mass-transfer rate. With the analogous system V485 Cen, these objects establish the first subpopulation in hydrogen-rich cataclysmic variables below the period minimum. Concerning the evolutionary status of them, we propose that they are progenitors of AM CVn stars on evolutionary courses in which systems have an evolved secondary star with a hydrogen-exhausted core.
Spectroscopic Diagnostics of Precessing Discs: The Stream-Disc Impact in XTE J1118+480 (= KV UMA) in Outburst
Authors: Haswell С. A. , Foulkes S. B. , Rolfe D. J. , Murray J. R. , Tovmassian G. H. , Zharikov S. V. , Maxted P. F. L. , North R. , Charles P. A. , Hynes R. I.
Published: June 2019

We present orbital trailed spectrograms of XTE J1118+480 taken at the rise to outburst maximum in 2000. These show an evolving S-wave feature arising from the stream impact on the edge of the eccentric precessing disc. By comparing the observed S-waves with those generated in an SPH simulation, we deduce the disc precession phases corresponding to our observations. Hence we infer changes in the disc precession period around the outburst maximum: taken at face value our spectroscopy suggests a precession period temporarily as short as 20 days.
UBV Photometry of CYG X-1 from 1996 to 2003
Authors: Voloshina I. B. , Lyuty V. M.
Published: June 2019

The preliminary results of analysis of UBV-photometry of the black hole candidate Cyg X-l in primary minimum are presented. These observations were carried out with the main goal of studying in detail the variability that was detected by Lyuty in 1985 in the optical light curve of this system near orbital phase 0.00.
Proper Motions in the Faint Sky Variability Survey
Authors: Besselaar E. J. M. van den , Groot P. J.
Published: June 2019

The Faint Sky Variability Survey (FSVS) is aimed at rinding photometrically and astrometrically variable objects. The main goal is to get a better understanding of binary evolution. This survey consists of 78 fields, which covers a total area of 21 deg2 in the sky and it is sensitive for objects in the magnitude range of 17 < V < 24. (For a description see Groot et al. 2003).
High Time Resolution Spectroscopy of Short Period Variable Objects
Authors: Michel R. , Fordham J. L. A.
Published: June 2019

Photon counting detector technology allows high time resolution spectroscopy on sources such as pulsars and cataclysmic variables. Here we report on first observing trials on Cvs in a high time resolution mode undertaken with the MIC photon counting detector (Fordham et al. 2000) on the 2.1m telescope at San Pedro Martir Observatory.
Hydrodynamic Models of the Accretion Stream in Magnetic Cataclysmic Variables
Authors: Belle Kunegunda F.
Published: June 2019

Hero I use the MHD code, FLASH, from the University of Chicago ASCI Center for Astrophysical Thermonuclear Flashes, to simulate initial two-dimensional simple models of accretion streams in magnetic CVs. These models explore the evolution of inflowing material for two white dwarf masses; 0.5M⊙ and 0.9M⊙. It is seen that a discontinuity forms at a height of 6.1 X 108 cm above the white dwarf ‘surface’ for MWD = 0.5M⊙ and at 1.6 X 109 cm for MWD = 0.9M⊙. These models will be developed further with the ultimate goal of completing a three-dimensional model of magnetic accretion onto a WD surface.
New Spectroscopic Observations of Dwarf Nova BZ Ursae Majoris with Extremely Unusual Emission Lines Profiles
Authors: Neustroev V. V. , Zharikov S. V. , Medvedev A. , Shearer A.
Published: June 2019

We present preliminary results of new spectroscopic observations of dwarf nova BZ UMa in quiescence. Fifty medium resolution spectra allow us to reproduce the radial velocity curve from the Hα emission line. We confirm that BZ UMa shows extremely unusual emission lines profiles, Unlike the classical single or the double-peaked profiles usually observed in spectra of dwarf novae, emission lines of BZ UMa consist of at least five peaks.
Dynamic Populations of Dust in Interplanetary Space
Authors: Grün E. , Staubach P.
Published: June 2019

Information on the dynamics of interplanetary dust is obtained by observations of radio-meteors, zodiacal light, thermal infrared emission, and by measurements with in-situ detectors on board Earth satellites and deep spaceprobes. These methods are sensitive to different meteoroid sizes (mm- to sub-micron sized) and refer to different regions of space. Bigger particles (> 10-9 g) move on bound Keplerian orbits and are dynamically dominated by solar gravity, while the trajectories of particles smaller than 10-10 g are strongly influenced by radiation pressure and electromagnetic interactions. Modelling interplanetary dust is done by dividing the whole meteoritic complex into dynamically distinct populations. Divine's (1993) model identifies five dynamically different populations of interplanetary meteoroids: bigger particles are described by the “core”, and “asteroidal”-populations, intermediate sizes by the “halo”-population, and small particles are included in the “eccentric” and the “inclined”-populations. The intermediate and the small particle populations, in particular, have to be redefined for several reasons: new data are available which require the consideration of hyperbolic orbits and the inclusion of radiation pressure and electromagnetic forces. New small particle populations are interstellar dust and beta-meteoroids.
Orbital Evolution of the Lunar Ejecta
Authors: Yamamoto S. , Mukai T.
Published: June 2019

We have estimated the flux of lunar ejecta near the Earth, e.g., the cumulative flux of ejecta larger than 10-13g is 10-10particles cm-2s-1. In addition, our numerical simulations for the orbital evolution of lunar ejecta lead to the orbital characterization of these ejecta. Since our calculations suggest that the incident direction of lunar ejecta onto the Earth is nearly isotropic, it is expected that the dynamical properties of lunar ejecta make it possible to distinguish them from other IDPs.
Fragmenting Particles During 1989-1994 Perseid Radar Observations
Authors: Šimek M.
Published: June 2019

The occurrence of fragmenting particles was investigated from radar observations of the Perseids at Ondřejov Observatory. Diurnal patterns of fragmenting meteoroids are presented. Their minimum occurrence coincides with the culmination of the Perseid radiant while the maximum appears at the time of sunset at meteor heights. Solar longitude of the main contribution of fragmenting meteoroids at L⊙ = 138°86±0°04 (equinox 1950.0) fits with the peak activity of the new filament in the stream. This supports the concept of the low age of the filament. The maximum proportion of fragmenting particles occurred in 1991.
Modelling the Orbital Evolution of the Perseid Meteoroids
Authors: Jones J. , Brown P.
Published: June 2019

We have modelled the evolution in the distribution of orbits of 1.5 x 106 particles released at the 1862, 1737 and 1610 apparitions of 109P/Swift-Tuttle for a range of particle masses and for a range of ejection angles about the comet-solar line. The evolution of the stream is dominated by the influence of planetary perturbations, most notably those due to Jupiter. A periodicity of approximately 12 years in Perseid activity is noted in the material ejected during the 1862 apparition. Without Jovian perturbations, the nodes of these recently released Perseid particles would not cross the Earth's orbit. Activity from 1862 is notable in the simulations for 1991-1994 and also for the early 1980's. Ejections in 1737 and to a lesser extent in 1610 contribute material seen at the Earth in the late 1980's.
Sources of Interplanetary Dust
Authors: Dermott S.F. , Grogan K. , Gustafson B.Å.S. , Jayaraman S. , Kortenkamp S.J. , Xu Y.L.
Published: June 2019

Asteroids, comets and interstellar dust are possible sources of the particles that constitute the dust in the inner solar system. Each of these components gives rise to particular, characteristic features, the amplitudes of which can be used to estimate the size of the associated source. The asteroidal component feeds the dust bands and the Earth's resonant ring, while the cometary component may account for the large scale height of the zodiacal cloud observed at 1 AU Previous discussions of the observed strengths of these various features indicated that the source of about one third of the thermal flux observed, for example, in the IRAS 25μm waveband is asteroidal, while two thirds is cometary. However, a variety of assumptions go into this calculation (the size-frequency distribution of the particles is particularly significant) and we now know that the result is highly dependent on these assumptions. The zodiacal cloud is also the source of the IDPs collected on Earth. Because of strong gravitational focusing by the Earth of particles in low e and I orbits, it is probable that the majority of IDPs originate from asteroids, particularly those asteroids in the Themis and Koronis families.