bluuebunny/crossref_metadata_2025 huggingface dataset:
New light on the corrugation phenomenon in our Galaxy
Authors: Feitzinger J. V. , Spicker J.
Published: June 2019

This investigation presents a total picture of the well-known corrugation-phenomenon for the (heliocentric) longitude range 10° ≤ 1 ≤ 240° as derived from HI-studies. For each spiral arm of the spiral pattern of Simonson (1976), we derived the centroid of the HI distribution from the 21-cm line surveys of Weaver and Williams (1974), Sinha (1979), and Westerhout and Wendlandt (1982). The three-component mass model of Rohlfs and Kreitschmann (1981) was used to derive a radial-velocity field, which was supplemented by a radial expansion field and by density-wave kinematics. This combined field served to calculated kinematic distances. The warp was taken into account according to Henderson et al. (1982) and Kulkarni et al. (1982).
Molecular clouds in external galaxies
Authors: Young Judith S.
Published: June 2019

Observations of the large-scale distribution of molecular clouds in external galaxies offer a unique opportunity for investigating galactic evolution. New generations of stars form in these dense regions, and the most massive of these stars recycle their processed interiors into the interstellar medium. Early observations of the CO distribution in the Milky Way (Scoville and Solomon 1975; Burton and Gordon 1976) indicated that there is intense emission at the center of our Galaxy, very little gas between 1 and 4 kpc radius, and a “molecular ring” feature between 4 and 8 kpc. Observations of molecular clouds in external galaxies of a variety of Hubble types and luminosities will enable us to more clearly understand the origin of this distribution. Although no other galaxies are observed to contain CO distributions precisely like that in the Milky Way, the differences which are present provide important clues to the structure and evolution of galaxies.
CH in the Galaxy
Authors: Johansson L.E.B.
Published: June 2019

The distribution of CH in the Galaxy has been investigated via its main-line transition in the 2Π1/2, J=1/2 ground-state Λ-doublet at 3335 MHz. The galactic plane was observed with a spacing between adjacent points of 2°.5 in the longitude ranges 10°-60° and 310°-350°. The northern data (Johansson, 1979) were obtained with the 25.6-m telescope of the Onsala Space Observatory and the southern data with the Parkes 64-m antenna; the corresponding beamwidths are 15′ and , respectively.
High-energy gamma rays and the large-scale distribution of gas and cosmic rays
Authors: Hermsen W. , Bloemen J.B.G.M.
Published: June 2019

The COS-B gamma-ray survey is compared with 12CO and HI surveys in a region containing the Orion complex and in the outer Galaxy. The observed gamma-ray intensities in the Orion region (100 MeV<E<5 GeV) can be ascribed to the interaction of uniformly distributed cosmic rays with the interstellar gas. Calibration of the ratio between H2 column-density and integrated CO line intensity resulted in the value: (3.0±0.7)x102 0 molecules cm-2K -1km -1s. In the outer Galaxy HI column-density maps in three galacto-centric distance ranges are used in combination with COS-B gamma-ray data to determine the radial distribution of the gamma-ray emissivity. A steep negative gradient of the emissivity for the 70 MeV-150 MeV range and an approximately constant (within ~20%) emissivity for the 300 MeV-5 GeV range is found. The result is interpreted as a strong decrease in the cosmic-ray electron density and a near constancy of the nuclear component.
Large-scale Mapping of the Galaxy by IRAS
Authors: Gautier T.N. , Hauser M. G.
Published: June 2019

The Infrared Astronomical Satellite (IRAS), launched 1983 January 25, has been conducting a high-sensitivity, high-resolution all-sky photometric survey at wavelengths of 12, 25, 60, and 100 μm in the infrared. One of the data products from the survey will be a map of the entire Milky Way within latitude limits of 10 degrees at a resolution of 4 arcminutes. Since the IRAS detector system is DC-coupled and has demonstrated excellent stability, this map will contain reliable information on all spatial scales larger than the map resolution. The extremely high sensitivity of the IRAS instrument for the detection of interstellar material in the survey mode is illustrated here in terms of visual extinction and dust and gas column densities.
High-energy Galactic phenomena and the interstellar medium
Authors: Cesarsky Catherine J.
Published: June 2019

Gamma rays of energy in the range 30 MeV-several GeV, observed by the satellites SAS-2 and COS-B, are emitted in the interstellar medium as a result of interactions with gas of cosmic-ray nuclei in the GeV range (π° decay γ rays) and cosmic-ray electrons of energy > 30 MeV (bremsstrahlung γ rays). W. Hermsen has presented at this conference the γ ray maps of the Galaxy in three “colours” constructed by the COS-B collaboration; the information in such maps is supplemented by radio-continuum studies (see lecture by R. Beck), and is a useful tool for studying the distribution of gas, cosmic rays (c.r.) and magnetic fields in the Galaxy. The variables in this problem are many:large-scale (~ 1 kpc) and small-scale (~10 pc) distributions of c.r. nuclei, of c.r. electrons, of atomic and molecular hydrogen, of magnetic fields, fraction of the observed radiation due to localized sources, etc. Of these, only the distribution - or at least the column densities - of atomic hydrogen are determined in a reliable way. Estimates of the amount of molecular hydrogen can be derived from CO observations or from galaxy counts. The radio and gamma-ray data are not sufficient to disentangle all the other variables in a unique fashion, unless a number of assumptions are made (e.g. Paul et al. 1976). Still, the COS-B team has been able to show that :

a) there is a correlation between the gamma-ray emission from local regions, as observed at intermediate latitudes, and the total column density of dust, as measured by galaxy counts. The simplest interpretation is that the density of c.r. nuclei and electrons is uniform within 500 pc of the sun, and that dust and gas are well mixed. Then, γ rays can be used as excellent tracers of local gas complexes (Lebrun et al. 1982, Strong et al. 1982).

b) In the same way, the simplest interpretation of the γ-ray emission at energy > 300 MeV from the inner Galaxy, is that c.r. nuclei and electrons are distributed uniformly as well : there is no need for an enhanced density of c.r. in the 3–6 kpc ring; on the contrary, even assuming a uniform density of c.r., the γ-ray data are in conflict with the highest estimates of molecular hydrogen in the radio-astronomy literature (Mayer-Hasselwander et al. 1982).

c) In the outer Galaxy, the gradient of c.r. which had become apparent in the early SAS-2 data can now, with COS-B data, be studied in three energy ranges. A gradient in the c.r. distribution is only required to explain the low-energy radiation, which is dominated by bremsstrahlung from relativistic electrons (Bloemen et al., in preparation).
Spiral structure and kinematics of HI and HII in external galaxies
Authors: Allen R. J. , Atherton P. D. , Tilanus R.P.J.
Published: June 2019

Compression of the interstellar gas by a passing density-wave is thought to be responsible for triggering the presently observable star formation processes in the arms of spiral galaxies. We present new observations of the distribution and kinematics of the Hβ emission in the spiral arms of M83, obtained with the TAURUS imaging Fabry-Pérot system. These results, when combined with observations of the neutral and molecular components with sufficiently high resolution, should contribute to our understanding of the time sequence by which stars form out of the interstellar gas.
A systematic study of M81
Authors: Bash Frank
Published: June 2019

We describe a series of observational studies of M81 which are presently underway. We hope that these studies will allow improved understanding of this one, simple, density-wave spiral galaxy.
The largest molecular complexes in the first Galactic quadrant
Authors: Dame T. M. , Elmegreen B. G. , Cohen R. S. , Thaddeus P.
Published: June 2019

The CO emission within a few kiloparsecs of the Sun is dominated by a small number of very large molecular complexes, including those associated with the Orion Nebula (Thaddeus 1982), M16 and M17 (Elmegreen, Lada, and Dickinson 1979), and NGC7538 (Cohen et al. 1980). These complexes have masses from several 105 to 106 M⊙ and are generally very well-defined objects. They are also well endowed with HII regions, stellar clusters and associations, masers, and other Population-I objects whose distances can be measured. The complexes are thus valuable probes of the large-scale structure of the Galaxy.
Molecular-cloud clusters and chains
Authors: Sanders D. B. , Clemens D. P. , Scoville N. Z. , Solomon P. M.
Published: June 2019

We report some preliminary results from the Massachusetts - Stony Brook CO survey of the first galactic quadrant using the 14-meter millimeterwave telescope of the Five College Radio Astronomy Observatory. The survey contains approximately 50 000 observations spaced every 3 arcminutes in 1 and b between longitudes 0° and 90° and latitudes −1° and 1°. We have mapped emission from giant molecular clouds (GMC) which we identified, in earlier more limited strip surveys of the galactic plane (Solomon, Sanders and Scoville 1979; Sanders 1981), on size scales from a few parsecs to hundreds of parsecs, in order to determine the degree of clustering and organization into large-scale features. In addition to the characteristic size of 20 – 60 pc for individual GMC, we find clustering of clouds on a scale of from 100 to 300 pc.
Dynamical evolution of the Galactic disk
Authors: Wielen Roland , Fuchs Burkhard
Published: June 2019

After some general remarks on the dynamical evolution of the galactic disk, we review mechanisms which may affect the velocities of disk stars: stochastic heating, deflections, adiabatic cooling or heating. We compare the observed velocities of nearby disk stars with theoretical predictions based on the diffusion of stellar orbits.
Formation and maintenance of spiral structure in galaxies
Authors: Lin C. C. , Bertin G.
Published: June 2019

The formation and maintenance of spiral structure in galaxies is discussed in terms of spiral modes with a general perception consistent with the hypothesis of quasi-stationary spiral structure. The latter is explained in some detail to give it the original proper perspective and to contrast it with recent studies of non-stationary spiral structures. We again emphasize the possible coexistence of fast-evolving spiral features and slow-evolving spiral grand designs. Spiral modes are described in terms of three categories of propagating waves. The reason is given why isolated non-barred galaxies with spiral grand design are found to be mostly two-armed. Some suggestions are made for future research.
Spiral tracers and prestellar incubation periods in a cloudy interstellar medium
Authors: Hausman M. A. , Roberts W W.
Published: June 2019

We present further results of our model of the interstellar medium in spiral galaxies (Roberts and Hausman, 1983; Hausman and Roberts, 1983). The ISM is simulated by a system of particles, representing gas clouds, which orbit ballistically in a spiral-perturbed galactic gravitational field, collide inelastically with one another, and receive velocity impulses from expanding supernova remnants. Star formation may be triggered in the clouds by either collisions or SNR interactions.
Supposed history of our Galaxy
Authors: Iwanowska Wilhelmina
Published: June 2019

Looking back with modern instrumentation like that at Westerbork to possible progenitors of galaxies, we find at increasing redshifts active galaxies, radio galaxies, BL Lac objects and quasars. With improving instrumental sensitivity and resolving power, energetic activity is discovered in these objects: ejecta of millions of solar masses, mostly bipolar, were thrown out from the central bodies to hundreds of kiloparsecs at nearly luminal speeds. The rich variety of their structures and energetics is illustrated in a review paper by Miley (1980). Like miniatures of these phenomena, ejections of 10–100 M⊙ with speeds of 10–100 km s-1 appear in star-forming regions of our Galaxy.
Life in the Galaxy?
Authors: Shostak G. S.
Published: June 2019

It is a decided honor to have the opportunity to address as distinguished a group as is present this evening, and I am particularly grateful for the very complimentary introductory remarks of Harry van der Laan. To paraphrase Einstein's comment on a dissimilar occasion, such a lovely preamble entails a risk that the packaging may prove better than the meat.
The Milky Way: summary and outlook
Authors: Ostriker Jeremiah P.
Published: June 2019

First let me review the historical discussions presented during our symposium: the papers by Paul, Gingerich, Hoskin and Smith. I was greatly impressed by the power of abstract human thought in its confrontation with resistant reality. On the one hand we see again and again extraordinary prescience, where abstract beliefs based on little or no empirical evidence–like the island-universe hypothesis–turn out to be, in their essentials, true. Clearly, we often know more than we know that we know. On the other hand, there are repeated instances of resistance to the most obvious truth due to ingrained beliefs. These may be termed conspiracies of silence. Van Rhijn and Shapley agreed about few things. But one of them was that there was no significant absorption of light in the Galaxy. Yet the most conspicuous feature of the night sky is the Milky Way, and the second most conspicuous feature is the dark rift through its middle. What looks to the most untutored eye like a “sandwich” was modeled as an oblate spheroid. These eminent scientists must have known about the rift, but somehow wished it away in their analyses. I find that very curious. Other examples from earlier times abound. We all know that the Crab supernova was seen from many parts of the globe but, though it was bright enough to be detected by the unaided eye in daylight, its existence was never–so far as we know–recorded in Europe. It did not fit in with the scheme of things, so it was not seen.
Moral Knowledge and Moral Principles
Authors: Schneewind J. B.
Published: June 2019

What is the function of moral principles within the body of moral knowledge? And what must be the nature of moral principles in order for them to carry out this function? A specific set of answers to these questions is widely accepted among moral philosophers – so widely accepted as almost to constitute a sort of orthodoxy. The answers embody a view of the place of principles within the body of morality which crosses the lines between cognitivism and non-cognitivism. Though I have put the question in cognitivist terms and shall discuss it in those terms, I think a similar question and a more or less parallel discussion could be given in non-cognitivist terms. Perhaps the time-honoured debate between the two positions can be suspended, at least temporarily, while we examine, not the nature of morality, but its structure.
III / Summary of Mogollon Branches and Sites
Authors: Wheat Joe Ben
Published: June 2019

The first Mogollon branch defined was the Mimbres. Here, sites have been excavated in the southern part of the Mimbres drainage and in the adjacent part of the Gila drainage.

Harris Village (Haury 1936b) is located about a quarter of a mile east of the Mimbres, New Mexico post office, on a large, flat terrace which rises abruptly some 20 m. above the east bank of the Mimbres River. It is about 1,850 m. above sea level. The village occupied several acres, part of which was not explored. Easily approached from all sides, defense does not seem to have been a factor in selecting the village site. The surrounding countryside is rugged and hilly, but agricultural land is available in small fields along the stream. The area is in the lower part of the pinyon-juniper belt, and a few trees occur on the site. Cottonwood, poplar, and walnut grow along the valley.
VI / Mogollon Pottery
Authors: Wheat Joe Ben
Published: June 2019

The Mogollon Culture begins with the addition of pottery to the last phase of the Cochise Culture. Pottery was the last distinctive element to be added, for architecture and agriculture had been a functioning part of the culture for perhaps a thousand years or more. There can be little doubt that pottery was introduced from outside the area, for the earliest ceramic complex appears as a thriving industry with well established techniques. Technically this pottery is well made, and although only a limited number of shapes occur, it is by no means primitive.

The main outline of Mogollon pottery development can be summarized briefly. The earliest horizon yet known contains polished brown and polished red wares. These wares, or variations of them, continue as basic wares of the ceramic complex throughout Mogollon history.
Prevalence of depression and burden among informal care-givers of people with dementia: a meta-analysis
Authors: Collins Rebecca N. , Kishita Naoko
Published: June 2019

This meta-analysis examined the prevalence of depression and burden among informal care-givers of people with dementia (PwD) and compared the prevalence of depression between male and female, and spousal and non-spousal, care-givers. The quality of studies was evaluated and moderator variables explored. A search of six electronic databases (PsycARTICLES, PsycINFO, MEDLINE Complete, SCOPUS, Web of Science and ProQuest) was conducted from the first available date to the 31 October 2017. Inclusion criteria involved observational studies on the prevalence of burden or depression among informal care-givers of PwD. Forty-three studies were examined with a total of 16,911 participants. The adjusted pooled prevalence of depression was 31.24 per cent (95% confidence interval (CI) = 27.70, 35.01) and burden was 49.26 per cent (95% CI = 37.15, 61.46), although heterogeneity among prevalence estimates was high. Depression prevalence estimates differed according to the instrument used and the continent where the study was conducted. The odds of having depression were almost one and a half times higher in female compared to male care-givers. No significant difference was observed between spouses and non-spouses. Most studies had a medium risk of bias. Results suggest a great need within this population for interventions that are effective at reducing burden and depressive symptoms. It therefore appears imperative for dementia services that are not providing such interventions to do so.
COMERCIO DE MERCANCÍAS LOCALES EN SANTIAGO DE CHILE, 1773–1778
Authors: Martínez Barraza Juan José
Published: June 2019

This article deals with the trade of local merchandise in Santiago's district (Corregimiento) from 1773 to 1778, based on tributary sources. It contributes to the debate on the organization of the colonial internal market. The main traded merchandise, which represented about 80% of Chilean exports, came from the cattle exploitation that was developed in the haciendas around Santiago, whose cattle stocks were complemented from neighboring provinces in the Andes. The largest destination of this trade, in which big merchants acted together with a thousand minor merchants, were the retail channels and the artisan sectors supplying the population of Santiago. The impulse of this demand on the domestic market was so dynamic that it shows a degree of regional autonomy higher than what it is traditionally assumed for the Chilean economy in the late colonial period.
3. Commission Des Notations, Des Unites et de L’Economie Des Publications
Authors: Zagar F.
Published: June 2019

Après la réunion de Rome, on a soumis avant tout à la Commission 3 la question, déjà recommandée par la Joint Commission for Spectroscopy (I.U.P.A.P. et U.A.I.) à Rome, de donner un symbole au numéro d’ onde, et le nom de Kayser (symbole K) à l’unité cm.–1. Les membres de la Commission 3 ne se sont pas trouvés d’accord, et la majorité s’est déclarée contraire à l’adoption des deux propositions. Successivement, la International Organisation for Standardisation (I.S.O.) a communiqué que le Comité technique No. 12 a adopté le nom de Kayser pour l’unité cm.–1, tandis qu’elle a laissé en suspens la decision concernant le symbole K; ainsi que la décision concernant le symbole à adopter pour le numéro d’onde.
Current Status of the Microlensing Surveys
Authors: Paczyński Bohdan
Published: June 2019

The ongoing microlensing searches have generated more photometric measurements of pulsating stars than all previous observing projects combined. In particular, OGLE has made ∼ 340,000 B, V, and I-band measurements of ∼ 1,300 Cepheids in the Large Magellanic Clouds accessible over Internet. Microlensing searches contributed to the development of very efficient image subtraction software which works best in crowded fields. This suggests the use of a period – flux amplitude rather than period – luminosity relation for the Cepheids for distance determination, as the flux amplitude is directly measurable with the image subtraction, and it is not biased by crowding. Future projects will dramatically increase the data rate, will provide all-sky coverage and a complete census of variables, including pulsating stars, to the ever fainter limits. Time will show which approach, a small number of large teams or a large number of small teams, will be more productive.
Photometry of Pulsating Stars in the Magellanic Clouds as Observed in the MOA Project
Authors: Hearnshaw J. B. , Bond I. A. , Rattenbury N. J. , Noda S. , Takeuti M. , Abe F. , Carter B. S. , Dodd R. J. , Honda M. , Jugaku J. , Kabe S. , Kilmartin P. M. , Koribalski B. S. , Matsubara Y. , Masuda K. , Muraki Y. , Nakamura T. , Nankivell G. R. , Reid M. , Rumsey N. J. , Saito To. , Sato H. , Sekiguchi M. , Sullivan D. J. , Sumi T. , Watase Y. , Yanagisawa T. , Yock P. C. M. , Yoshizawa M.
Published: June 2019

A review of the MOA (Microlensing Observations in Astrophysics) project is presented. MOA is a collaboration of approximately 30 astronomers from New Zealand and Japan established with the aim of finding and detecting microlensing events towards the Magellanic Clouds and the Galactic bulge, which may be indicative of either dark matter or of planetary companions. The observing program commenced in 1995, using very wide band blue and red filters and a nine-chip mosaic CCD camera.

As a by-product of these observations a large database of CCD photometry for 1.4 million stars towards both LMC and SMC has been established. In one preliminary analysis 576 bright variable stars were confirmed, nearly half of them being Cepheids. Another analysis has identified large numbers of blue variables, and 205 eclipsing binaries are included in this sample. In addition 351 red variables (AGB stars) have been found. Light curves have been obtained for all these stars. The observations are carried out on a 61-cm f/6.25 telescope at Mt John University Observatory where a new larger CCD camera was installed in 1998 July. From this latitude (44° S) the Magellanic Clouds can be monitored throughout the year.
The Use of Principal Components Analysis in Analysing Variable Star Data
Authors: Kanbur S. M. , Iono D. , Tanvir N. A. , Hendry M. A.
Published: June 2019

We describe the technique of Principal Components Analysis (PCA) as applied to the analysis of variable star data. It is shown that PCA is an efficient way of describing light curve structure.
Blue Variables from the MOA Database
Authors: Noda Sachiyo , Takeuti Mine , Bond I. A. , Rattenbury N. J. , Abe F. , Carter B. S. , Dodd R. J. , Hearnshaw J. B. , Honda M. , Jugaku J. , Kabe S. , Kilmartin P. M. , Masuda K. , Matsubara Y. , Muraki Y. , Nakamura T. , Reid M. , Rumsey N. J. , Saito To. , Sato H. , Sekiguchi M. , Sullivan D. J. , Sumi T. , Watase Y. , Yanagisawa T. , Yock P. C. M. , Yoshizawa M.
Published: June 2019

A large database of CCD photometry for 1.4 million stars towards both the LMC and the SMC, which has been established by the MOA project, is a useful resource to study variable stars. In our preliminary study, variables identified as β Lyrae type stars and Herbig Ae/Be stars have been found amongst blue stars.
Studies of Mira and Semiregular Variables Using Visual Databases
Authors: Bedding T. R. , Conn B. C. , Zijlstra A. A.
Published: June 2019

We used wavelets to investigate period and amplitude changes in Mira and semiregular variables and found a variety of behaviours. Period and amplitude changes often go together, perhaps because changes in amplitude are causing period changes via nonlinear effects.
On the Pulsation Properties of Red Supergiant Variables
Authors: Bono Giuseppe , Panagia Nino
Published: June 2019

We present the preliminary results of a detailed theoretical investigation on the pulsation properties and modal stability of red supergiant (RSG) stars at solar chemical composition and for stellar masses ranging from 10 to 20 M⊙. We find that the main parameter governing their pulsation behavior is the effective temperature, and indeed when moving from the blue edge toward lower effective temperatures the models show an increase in the pulsation amplitudes. For temperatures cooler than 3800 K the pulsation amplitudes are still large but the radial displacements become aperiodic.
New R Coronae Borealis Stars in the LMC Discovered in the MACHO Photometry Database
Authors: Clayton Geoffrey C. , Kilkenny D. , Welch D. L. ,   The MACHO Collaboration
Published: June 2019

An extensive search has been made in the MACHO photometry database for new R Coronae Borealis (RCB) stars in the LMC. Only three such stars were known previously. Nine new LMC RCB stars have been spectroscopically confirmed so far.
Cepheids from the EROS-2 Microlensing Survey
Authors: Beaulieu Jean-Philippe , Marquette Jean-Baptiste
Published: June 2019

Using observations obtained in the pilot campaign of the EROS-2 microlensing survey we observed 290 Cepheids towards the LMC and 590 Cepheids towards the SMC. We present the constraints they give to stellar pulsation theory. We detect a statistically significant break in the slope of the period–luminosity relation for SMC fundamental mode Cepheids with periods shorter than 2 d and discuss its origin.
An Analysis of Cepheid Distances Using Bayesian Statistics
Authors: Barnes Thomas G. , Jefferys William H.
Published: June 2019

We have applied an approximately Bayesian and a fully Bayesian analysis to the calculation of Cepheid distances, radii and absolute magnitudes using the surface brightness (Baade–Wesselink) method. Both methods successfully account for errors in the data, provide unbiased distance estimates, and provide objective model selection for the radial velocity curve. In addition, the fully Bayesian analysis objectively selects a model for the magnitude curve; averages over models of various Fourier orders, properly weighted by the posterior probabilities of the individual models; and includes a Lutz–Kelker correction.

The approximately Bayesian method is that described by Jefferys & Barnes (1999) and Barnes & Jefferys (1999). It is a maximum likelihood approach with objective selection of the order of the Fourier series model of the radial velocities.
The Cepheid Distance to NGC 4414
Authors: Thim Frank
Published: June 2019

A search for Cepheids in NGC 4414 has been performed using HST archive data. Accurate photometry for this galaxy is challenging due to its high surface brightness background with steep gradients and the rather low S/N of stellar point sources. The photometry package ROMAFOT has been used, and the results compare favorably with published photometry reported by Turner et al. (1998). All eleven Cepheids were recovered and nine additional candidates were discovered. The resulting distance modulus of 31ṃ50±0ṃ27 is only 0ṃ1 larger than previously reported.
Evolutionary Changes in the Periods of Cepheids
Authors: Berdnikov L. N. , Ignatova V. V.
Published: June 2019

Our analysis of O – C diagrams for 230 (mainly northern) Cepheids revealed that periods of 67 of them show evolutionary changes. New parabolic elements for these Cepheids are presented.
Critical Complements: Progress on the Orbit of T Mon
Authors: Evans N. R. , Carpenter K. , Robinson R. , Massa D. , Wahlgren G. M. , Vinkó J. , Szabados L.
Published: June 2019

A preliminary orbit has been derived for the high luminosity, 27-d classical Cepheid T Mon. Velocities for the hot companion have been measured from an HST GHRS spectrum and 3 IUE spectra. The companion velocities are inconsistent with binary orbital motion and it is likely that the companion is itself a short period binary. The HST spectrum also shows that the companion is a chemically peculiar star, probably magnetic.
ω Centauri – a Laboratory for Critical Tests of Stellar Structure and Evolution
Authors: Freyhammer L. M. , Petersen J. O. , Andersen M. I.
Published: June 2019

Preliminary results are reported for a monitoring program on ω Cen. We search for multi-mode SX Phe stars and changes in pulsation parameters of the cluster variables in order to test models of stellar evolution. With a periodogram for 10,000 light curves, we estimate that ω Cen hosts several hundred SX Phe stars.
Variable Stars in the Metal-Rich Globular Clusters NGC 6388 and NGC 6441
Authors: Pritzl Barton , Smith Horace A. , Catelan Márcio , Sweigart Allen V.
Published: June 2019

New observations show that RR Lyrae stars in the metal-rich globular clusters NGC 6388 and NGC 6441 have unusually long periods, which indicate that the horizontal branches of these clusters are unusually bright for their metallicities, as predicted by Sweigart & Catelan (1998).
The Petersen Diagram for RR Lyrae Stars in the Magellanic Clouds
Authors: Popielski B. L. , Dziembowski W. A.
Published: June 2019

We show that the spread of the Magellanic Cloud RRd stars in the Petersen diagram may be explained in terms of spread in metallicity by one order of magnitude.
Ground-Based Observations of Short- and Medium-Period Variables Discovered by the Hipparcos Satellite
Authors: Kiss L. L. , Csák B. , Alfaro E. J. , Vinkó J.
Published: June 2019

We present the results of follow-up ground-based photometric and spectroscopic observations of a sample of variable stars discovered by the Hipparcos satellite.
The Oblique Pulsator Model for the Blazhko Effect in RR Lyrae Stars. Theory of Amplitude Modulation I
Authors: Shibahashi Hiromoto
Published: June 2019

By assuming that RR Lyrae stars have fairly strong dipole magnetic fields with symmetry axis oblique to the rotation axis of the star, I show that the oscillation mode which would be a pure radial oscillation in absence of the magnetic field has a quadrupole component, whose symmetry axis coincides with the magnetic axis. The aspect angle of the quadrupole component changes due to the stellar rotation, and this apparent amplitude variation is interpreted as the Blazhko effect in RR Lyrae stars. It is shown that, in the case of off-axis magnetic field, phase modulation is expected. I list up some theoretical predictions based on this model, which would observationally examine this hypothesis.
Long-Term Photometric and Spectroscopic Monitoring of Slowly Pulsating B Stars
Authors: Aerts C. , De Cat P. , De Ridder J. , Kolenberg K. , Waelkens C. , Mathias P. , Briquet M.
Published: June 2019

We review the current status of our long-term monitoring project on slowly pulsating B stars that we started in the course of 1996 and that was recently completed as far as the first part of our plan is concerned. In total, we have selected 17 southern and 8 northern stars. The idea is to fully exploit our current data in the near future and to select the most interesting targets for further very-long-term follow-up monitoring. A first conclusion is that half of the southern targets turn out to be spectroscopic binaries. Some of these have circular orbits and periods of the same order of magnitude as the intrinsic pulsation period(s) of the primary. The eccentric binaries have periods ranging from 12 to 460 d. For most stars the photometric behaviour is dominated by the same frequency as the intrinsic spectroscopic variability. Multiperiodicity in the expected frequency range is found for almost all stars. Two objects, however, turn out to have only one dominant pulsation mode.
The Origin and Interpretation of Line Profile Variations of Pulsating B Stars
Authors: De Bidder J. , Aerts C.
Published: June 2019

We report on an ongoing study on the importance of the contributions of different photospheric variations to the line profile variations of hot pulsating stars.
Binary Slowly Pulsating B Stars
Authors: De Cat P. , Aerts C.
Published: June 2019

The satellite Hipparcos led to the discovery of 267 new variable B-type stars. Some 100 of them were classified as candidate slowly pulsating B stars (SPBs) by Waelkens et al. (1998). Twelve of the brightest southern candidate SPBs were selected together with 5 confirmed SPBs to start a long-term follow-up study (Aerts et al. 1999). From 1996 up to 1998, numerous high-resolution, high signal-to-noise spectra were taken with the CAT/CES combination at La Silla in order to study the line profile variations of the Si II-doublet centered at 4130 Å.

We report our finding that at least 8 of 17 targets turn out to be spectroscopic binaries. We have found a large variety in the obtained orbits. HD 123515 and HD 140873 were known as single-lined spectroscopic binaries, but both turn out to be double-lined. All the others binaries are single-lined. For HD 140873 and HD 177863, we find orbits with large eccentricities of respectively e = 0.731 α 0.006 and e = 0.603 α 0.007. HD 69144, HD 92287 and HD 169978 are three binaries with circular orbits and very short orbital periods (a few days). Since their photometric measurements are dominated by (close to) sinusoidal variations with twice the orbital frequency, these stars are ellipsoidal variables. Their orbital periods are of the same order of magnitude as the expected periods of pulsation.

After removing the orbit, we find the same first frequency in the residual radial velocities as in the gathered photometric measurements for 6 stars. For HD 69144 and HD 169978 we did not yet succeed in deriving an intrinsic period, although HD 69144 has prominent line profile variations. For HD 169978, we have serious doubts about the SPB nature.

For a detailed description, we refer to De Cat et al. (1999).
Z-bump Pulsations in Helium Stars
Authors: Jeffery C. Simon , Saio Hideyuki
Published: June 2019

Radial and nonradial pulsations are excited in low-mass helium stars with effective temperatures between 7000 and 35000 K. In the case of the most luminous stars, these are driven by strange-mode instabilities (Saio & Jeffery 1988). Less luminous helium stars are mostly non-variable, except around 25000 K. V652Her is the prototype radially pulsating helium star, with Teff ~ 25000 K and a pulsation period of 0ḍ08 (Hill et al. 1981). The pulsation was only understood to be driven by the K-mechanism with the introduction of Z-bump opacity (Saio 1993).

The importance of Z-bump instability in low-mass helium stars has been investigated further through a series of pulsation models (Jeffery & Saio 1999a). It is shown that Z-bump pulsations can persist to surprisingly high hydrogen abundances in low-mass stars, and may consequently be excited in several helium-rich hot subdwarfs with Teff ~ 25000 K. Within the Z-bump instability region, both radial and nonradial pulsations are excited, and multi-periodic variability is expected.

Pulsation properties are closely linked to the global dimensions of a pulsating star by the period – mean density relation. When spectroscopic measurements are also available, the twin constraints of period and surface gravity can place very tight limits on the stellar radius (Jeffery & Saio 1999b). These are in excellent agreement with independent measurements for V652 Her and place a lower limit on the mass of the recently discovered Z-bump pulsator BXCir (Kilkenny et al. 1999).
Do Herbig Ae Stars Pulsate?
Authors: Marconi M. , Ripepi V. , Alcalá J. , Covino E. , Terranegra L. , Palla F.
Published: June 2019

We present some preliminary results of a Strömgren photometric survey searching for radially pulsating variables among Herbig Ae stars. These young objects are expected to show a characteristic δ Scuti variability when entering the instability strip along their pre-main sequence evolutionary tracks, according to the theoretical predictions by Marconi & Palla (1998). We identified at least five pulsating Herbig Ae stars with periods in the expected range. On the basis of these encouraging first results, we foresee both new more detailed observations and accurate comparisons with theoretical models.
Spectroscopic Survey of Rapidly Oscillating Ap Stars
Authors: Weiss W. W. , Ryabchikova T. A. , Kupka F. , Lueftinger T. R. , Savanov I. S. , Malanushenko V. P.
Published: June 2019

A spectroscopic survey of roAp stars has been initiated in Vienna in order to determine their fundamental astrophysical parameters and abundances. We report here on our attempt to confirm and elaborate an atmospheric peculiarity recently discovered (Ryabchikova et al. 1999) which should allow to identify roAp stars with a single spectrum.
Pulsation among Λ Bootis Stars
Authors: Weiss Werner W. , Paunzen Ernst , Pamyatnykh A. , Mkrtichian D.
Published: June 2019

We report on the pulsation characteristics of λ Bootis stars as a result of a survey initiated to increase the number of known λ Bootis stars and to improve the definition of this group of peculiar stars.
1995-1998 Large-Scale Campaigns on Λ Boo Star 29 Cygni
Authors: Mkrtichian D. E. , Kusakin A. V. , Koval V. A. , Akan M. C. , Ibanoglu C. , Paunzen E. , Weiss W. W. , de Coca P. Lopez , Rolland A. , Costa V. , Olivares J. I. , Hobart M. A. , Hatzes A. P. , Malanushenko V. P. , Devlen A. , Ozturk A. , Paparó M. , Krisciunas K. , Percy J. , Thompson S. , Handle G. , Burnashev V. I. , Movchan A. I.
Published: June 2019

We present the main results of a photometric and spectroscopic study of the Λ Boo star 29 Cyg carried out from 1995 – 1998.
Observational Proof of the ZZ Ceti Red Edge
Authors: Kanaan A. , Winget D. E. , Kepler S. O. , Montgomery M. H.
Published: June 2019

With a time-series CCD photometry survey, we have demonstrated clearly that the observed red edge for the ZZ Ceti stars instability strip at 11,000 K is not an observational selection effect. Previous surveys for variability among hydrogen atmosphere white dwarfs at around 11,000 K have been carried out using high speed photometry which suffers from variable extinction effects that start becoming important at periods of 15 minutes. In our survey we constantly monitor the sky brightness as well as one or more comparison stars. This is done through the same color filter, therefore minimizing adverse effects of differential extinction. The fact that the theoretical red edge should be around 8,000 K remains, but effects not included in the theory, especially convection-aulsation interaction, could explain it.
Frequency Stability of the Cooler Pulsating White Dwarfs
Authors: Sullivan D. J.
Published: June 2019

Although the frequencies of the pulsating white dwarfs are extremely stable, the evolutionary cooling of these geometrically constrained objects should lead to an observable period change over a sufficiently long time base. Direct measurement of a period change rate for the cooler white dwarfs should provide fundamental data on the core composition of these stellar remnants, and hence their cooling time scales. Progress on attempts to measure the period change rates of two white dwarfs is reported.
Some Remarks on Stellar Pulsation
Authors: Gough Douglas
Published: June 2019

I wondered at first why I had been asked to perform the task of commenting on the scientific discussion of this meeting, until a member of the Scientific Organising Committee pointed out to me that I have not published a serious paper on the subject of the colloquium in his memory (I am not sure whether this is more a statement of the seriousness of my publications, of my publication frequency or of the duration of Jørgen’s memory); however, I am presumably considered to be unbiased by recent advances. Nevertheless, the time allotted (for the oral address) and the corresponding space (in these published proceedings) are inadequate for a complete and balanced review – in any case, that is hardly either desirable or necessary, since the discussions are all still fresh in our minds – and therefore I have been freed to comment personally on some selected issues that have captured my interest.
HST imaging of Jupiter shortly after each impact: Plumes and fresh sites
Authors: Hammel Heidi B.
Published: June 2019

During the first few hours after each impact, numerous phenomena were observed with telescopes on Earth, in orbit, and in space. The primary events in that time were: impacts themselves, rise and fall of large plumes of ejected material, and atmospheric waves; also of interest were the characteristic morphologies of fresh sites. Based on timing from Galileo instruments and ground-based observations, the Hubble Space Telescope (HST) recorded actual impact phenomena for fragments G and W, with the A and E impacts occurring just prior to the HST observation window. For these four events, plumes were directly imaged; plume development and collapse correlated with strong infrared emission near the jovian limb, supporting the interpretation that the IR brightness was created by the fall-back of plume material from high altitude (see chapter by Nicholson). For medium-to-large fresh impact sites imaged by HST within a few hours of impact, expanding rings were detected, caused by horizontal propagation of atmospheric waves (see chapters by Ingersoll and Zahnle). Initial site morphology at visible wavelengths was similar for all medium-to-large impacts: a dark streak surrounded by dark material, dominated by a large crescent-shaped ejecta to the southeast. Smaller impact sites typically only showed a dark patch (no ejecta) which dissipated quickly. This chapter summarizes the most recent measurements and interpretations of plumes and fresh impact sites as observed by HST.
Galileo observations of the impacts
Authors: Chapman Clark R.
Published: June 2019

Galileo observations in the UV, visible, and infrared uniquely characterize the luminous phenomena associated primarily with the early stages of the impacts of SL9 fragments—the bolide and fireball phases—because of the spacecraft's direct view of the impact sites. The single luminous events, typically 1 min in duration at near-IR wavelengths, are interpreted as initial bolide flashes in the stratosphere followed immediately by development of a fireball above the ammonia clouds, which subsequently rises, expands, and cools from ∼ 8000 K to ∼ 1000 K over the first minute. The brightnesses of the bolide phases were remarkably similar for disparate events, including L and N, which were among the biggest and smallest of the impacts as classified by Earth-based phenomena. Subsequent fireball brightnesses differ much more, suggesting that the similar-sized fragments were near the threshold for creating fireballs and large dark features on Jupiter's face. Both bolides and fireballs were much dimmer than had been predicted before the impacts, implying that impactor masses were small (∼0.5km diameter). Galileo data clarify the physical interpretation of the “first precursor,” as observed from Earth: it probably represents a massive meteor storm accompanying the main fragment, peaking ∼10s before the fragment penetrates to the tropopause; hints of behind-the-limb luminous phenomena, recorded from Earth immediately following the peak of the first precursor, may be due to reflection of the late bolide/early fireball stages from comet debris very high in Jupiter's atmosphere.
Models of fragment penetration and fireball evolution
Authors: Crawford David A.
Published: June 2019

A new analytical model that is calibrated against numerical simulations performed with the CTH shock physics code provides a useful description of the entry of Periodic Comet Shoemaker-Levy 9 into the Jovian atmosphere. Mass loss due to radiative heating of fragments larger than 100 m in diameter is insignificant because of energy conservation during the ablative process. Nevertheless, radiative ablation is a major contributor to atmospheric energy deposition at high altitude and plays an important role in early-time fireball evolution. The analytical model provides the initial conditions from which fireball and plume evolution can be calculated using CTH. The results from these simulations suggest that if the tops of the plumes originated from a specific level of the Jovian atmosphere then maximum plume heights are independent of fragment size provided the fragments penetrated at least 30 km below this level. If the tops of the plumes originated from the visible cloud tops, then fragment masses greater than 4 x 1012 g, corresponding to 200 m diameter fully dense water ice, are required to explain the observations. If the plumes originated from the NH4SH layer then masses greater than 3 x 1013 g (400 m water ice) are required. The lateral extent and mass of the observable plume are functions of fragment size and contribute to the lateral extent and albedo of the debris patterns after re-impact with the atmosphere. The apparent gap between the central disturbance of the impact site and the inner front of the crescent-shaped ejecta may reflect the fragment's depth of penetration below the source layer of the visible ejecta.
Active Control for Michelson Stellar Interferometers
Authors: Hardy John W. , Wallner Edward P.
Published: June 2019

The effects of atmospheric turbulence on the image structure in a ground based Michelson Stellar Interferometer are analyzed. A complete system requires compensation both for the wavefront distortions over the collecting apertures and for path length differences between them. Wavefront sensing and compensation have been previously described and analyzed. In this paper, a method of path length compensation and estimation of the mutual coherence function of the source is developed using matched filters in multiple spectral bands. A practical implementation of the resulting system is described and estimates of its performance given.
The Limiting Sensitivity and Visibility Loss in a Small Aperture Amplitude Interferometer
Authors: Tango William J.
Published: June 2019

We analyze the behaviour of an amplitude interferometer with aperture diameters of the order of r0. A simple optical correlator can be used to measure the source coherence function, and the limiting magnitude is found to depend principally on the optical bandwidth. The basic instrument appears to have a limiting magnitude m = +8, but this can be improved by more elaborate correlators. The effects of atmospheric turbulence on such an interferometer can be substantially reduced by an active optical system which compensates for the wavefront tilts in the incident light, and it appears that the limiting magnitude of the interferometer, when atmospheric effects are taken into account, is around m = 7 - 8.
Observational Speckle Interferometry
Authors: Koechlin L.
Published: June 2019

Speckle interferometry techniques have improved appreciably during the past few years. Current progress to be reviewed includes: steps towards a fully digital analysis in the photon counting mode allowing for high resolution on faint astrophysical objects (i.e. quasars), practical prospects for phase recovery procedure, and the design of compact, self-contained interferometers for on-line results at remote sites.