bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the nature of OH/IR stars
Authors: Engels Dieter 
Published: June 2019

OH/IR stars are the infrared counterparts of galactic OH maser sources which show a characteristic double-peaked emission-line profile. Their strong radio emission can be detected at large distances, making them excellent tracers of distribution and kinematics of evolved stars in the Milky Way. The OH maser profile is typical for line emission from an expanding circumstellar shell. The circumstellar shells of OH/IR stars absorb the optical emission of the central star nearly completely and reemit the energy in the infrared. Having luminosities ~ 105 L⊙ and energy distributions peaking around 10μm, they may make a major contribution to the interstellar radiation field beyond 5μm. With mass loss rates of 10-5 to 10-4 M⊙/yr they lose several solar masses in a few hundred thousand years. OH/IR stars are therefore important objects for recycling stellar matter into the interstellar medium.Progress has been made in understanding the nature of OH/IR stars. They are Mira-like large-amplitude variables with periods up to 5 years long. It is proposed that they are stars of intermediate mass (2–10 M⊙) on the asymptotic giant branch (AGB). They have not only larger masses than Mira variables proper, but also longer periods of pulsation and larger mass loss rates. As a result optically thick circumstellar dust shells are formed, which prevent the detection of these more massive Mira-like variables at optical wavelengths. Radial pulsation (Mira variability) is thus thought to occur for all intermediate-mass stars in the course of their evolution on the AGB. In view of their high mass-loss rates, these stars may be key objects in the study of the formation of planetary nebulae.
Stellar chemical-abundance gradient in the direction of the South Galactic Pole - preliminary results
Authors: Trefzger Ch. F. , Pel J. W. , Blaauw A. 
Published: June 2019

Using the Walraven VBLUW photometric system, we have studied the metal content of 89 F and G stars in the Galactic South Pole field SA141. Our sample is based on the Basel survey of RGU photometry in Selected Areas, and it contains all stars in SA141 with VJ <14m.5 and (G-R)<1m.15 (spectral types earlier than about G7). The observations were made with the VBLUW photometer and the 90-cm Dutch Telescope at ESO, La Silla.For unreddened intermediate-type stars the VBLUW photometry enables us to separate the effects of temperature, gravity, and metallicity (cf. Lub and Pel, 1977). Since reddening is negligible in SA141, we can therefore determine these three parameters for each program star once the photometric indices are calibrated in terms of Teff, log g, and [Fe/H]. The latter calibration was made in a semi-empirical way, using VBLUW observations of stars with spectroscopic analyses in combination with theoretical colors based on the model spectra by Kurucz (1979). We used the Hyades main-sequence as a zeropoint, adopting [Fe/H] = +0.15 for this cluster.The results in the (V-B)-(B-L) diagram are shown in Fig. 1. This diagram is very sensitive to metallicity, but almost gravity-independent. Fig. 1 indicates that most program stars have metallicities in the range −1 ≦ [Fe/H] ≦ 0. The distribution of the program stars in the gravity-sensitive (V-B)-(L-U) diagram is very narrow, log g =4.2 ± 0.3, which means that these stars are probably all dwarfs, with only very few possible subgiants.The absolute-magnitude calibration was derived by using the data of Cayrel de Strobel et al. (1980) and of Cayrel de Strobel and Bentolila (1983). From their [Fe/H]-catalogue we took all stars with known distances, and within the parameter range of our program stars, to construct an empirical MV - Teff relation. This relation was used to derive distances for the stars in SA141.These distances are plotted against [Fe/H] in Fig. 2. The diagram clearly shows the correlation between distance and metallicity, suggesting for this particular sample a gradient of −0.6 in [Fe/H] over the first 500 pc. Similar values were found in the Basel RGU program (cf. Trefzger, 1981) and by Blaauw and Garmany (1975).
Star counts, local density and KZ force
Authors: Strömgren Bengt 
Published: June 2019

The approach by Bahcall and Soneira to the determination of galactic parameters through the use of star counts is referred to, and tests of the Bahcall-Soneira Galaxy model based on additional observational data are discussed.The determination of the local mass density by Hill, Hilditch and Barnes through studies of A and F stars in the region of the North Galactic Pole is briefly discussed, as is a recent investigation of the problem by Bahcall.In the determination of the galactic force Kz and the local mass density from the density distribution ν(z) and the distribution f(W) of velocities at right angles to the galactic plane for a group of tracer stars, it is important to secure homogeneity of the tracer group. This has led Hill, Hilditch and Barnes in a continuation of their investigation to use photoelectric uvby photometry to segregate homogeneous groups of F stars. A similar approach is followed by Danish astronomers, whose work is briefly described.
V / Disposal of the Dead
Authors: Wheat Joe Ben 
Published: June 2019

Somewhat more than 221 burials have been recovered from Mogollon sites which can be assigned to the periods covered by this study. The precise number cannot be given, nor is it important other than as an index to the validity of our reconstruction of the burial customs represented.Burials of Mogollon 1 have been found at Cave Creek, Chiricahua:3:25, San Simon, SU, Bluff, Crooked Ridge Village, and Tularosa Cave. At Cave Creek two burials, flexed on the side, occurred in pits cut through the floor of an abandoned pithouse; a third, that of an infant, came from a shallow pit outside the house. Two additional burials, an infant and an adult, were placed in shallow depressions in the silt at Chiricahua:3:25. None of these burials, all Penasco Phase, contained grave furniture. Numerical data are not available on Penasco Phase burials at San Simon Village, but according to Sayles (1945:62-64) the body was commonly flexed on the side and placed in a pit sometimes cut through the house floor, but usually outside the house.
Predictions on the Number of Variable Stars for the GAIA Space Mission and for Surveys such as the Ground-Based International Liquid Mirror Telescope
Authors: Eyer Laurent , Cuypers Jan 
Published: June 2019

AbstractFuture space and ground-based survey programmes will produce an impressive amount of photometric data. The GAIA space mission will map the complete sky down to V = 20m, and produce time series for about 1 billion stars. Survey instruments such as the International Liquid Mirror Telescope will observe slices of the sky down to V = 23m. In both experiments, the opportunity exists to discover a huge number of variable stars. Predictions of the expected total number of variable stars and the number of variables in specific subgroups are given.
MONS: Measuring Oscillations in Nearby Stars
Authors: Kjeldsen H. , Bedding T. R. , Christensen-Dalsgaard J. 
Published: June 2019

AbstractMONS is a proposed space mission to study stellar oscillations. We briefly describe the main features of the mission – more details are available at the MONS Home Page (http://www.obs.aau.dk/MONS)
The MOA Project Data Reduction Pipeline and Database
Authors: Reid M. L. , Sullivan D. J. , Dodd R. J. 
Published: June 2019

AbstractThe MOA Project is a collaboration of Japanese and New Zealand (NZ) astronomers and physicists undertaking a survey of stellar variability in the direction of the Galactic bulge and Magellanic Clouds. The primary motivation of the project is detection and monitoring of gravitational microlensing events although a large amount of data is also collected on stellar variability. Surveying the number of stars required to detect gravitational microlensing events is an operation of some magnitude and requires sophisticated data processing software.
Nonlinear Time-Series Analysis of Pulsation of Post-AGB Stars by Genetic Algorithm/Neural Network Hybrid Systems
Authors: Aikawa Toshiki 
Published: June 2019

AbstractSome pulsating post-AGB stars have been observed with an Automatic Photometry Telescope (APT) and a considerable amount of precise photometric data has been accumulated for these stars. The datasets, however, are still sparse, and this is a problem for applying nonlinear time series: for instance, modeling of attractors by the artificial neural networks (NN) to the datasets. We propose the optimization of data interpolations with the genetic algorithm (GA) and the hybrid system combined with NN. We apply this system to the Mackey–Glass equation, and attempt an analysis of the photometric data of post-AGB variables.
Pulsating Variable Stars in Local Group Dwarf Galaxies
Authors: Mateo Mario 
Published: June 2019

AbstractPulsating variables stars have had a long and prominent history in helping to map out the local Universe. Current observational techniques now make it possible to identify examples of all non-degenerate radial pulsating variables throughout much of the Local Group. I review our current knowledge of such variables in the dwarf galaxies of the Local Group. This summary tries to highlight some recent results that help underscore the use of these stars as important tools to study the physical nature of their parent galaxies as well as their continued use as important distance indicators of nearby galaxies.
The Cepheid P–L Relation and Metallicity
Authors: Laney C. D. 
Published: June 2019

AbstractBaade–Wesselink radii derived using VJHK photometry are used to test the metallicity dependence of the Cepheid P–L relation using three collections of metallicity estimates from the literature. The hypothesis that Cepheids at the LMC metallicity ([Fe/H] ~ −0.2) could be several tenths of a magnitude fainter than at solar metallicity is not supported by the evidence.
The Status of the Distance Scale
Authors: Tammann G. A. , Parodi B. R. , Reindl B. 
Published: June 2019

AbstractCepheids are the pillar of the extragalactic distance scale, but their reach in distance is not sufficient to calibrateH0Yet HST has provided Cepheid distances to eight galaxies which have produced SNe la. The latter are used as nearly perfect standard candles to carry the distance scale to 30 000 km s−1, givingH0= 58 ± 5. This determination finds support in other methods, but its range in distance and its weight is unparalleled.
The Pulsation Mode of Polaris
Authors: Moskalik P. , Ogloza W. 
Published: June 2019

AbstractPolaris (α UMi) is the only classical Cepheid withHipparcosparallax determined to better than 10% (Feast & Catchpole 1997). The correct identification of its pulsation mode is therefore crucial for calibrating the Cepheid period–luminosity relation. We show that Polaris is an overtone pulsator. Our analysis confirms the finding of Feast & Catchpole, but is entirely independent of the distance estimation.
On the Existence of Luminosity Differences between HB Field and Cluster Stars
Authors: Carretta E. , Gratton R. G. , Clementini G. 
Published: June 2019

AbstractThe discrepancy between the long distance scale as derived, e.g., from Hipparcos-based distances to globular clusters via main sequence fitting to local subdwarfs, and the short distance scale as derived, e.g., from the absolute magnitude of field RR Lyrae stars via statistical parallaxes and the Baade–Wesselink method, could be accounted for if an intrinsic difference in luminosity of about 0.1−0.2 mag were found to exist between horizontal branch (HB) stars populating the sparse general field and the dense globular clusters.
Theoretical Models for Classical Cepheids: Mean Magnitudes and Colors and the Evaluation of Distance, Reddening and Metallicity
Authors: Marconi Marcella , Caputo Filippina , Ripepi Vincenzo 
Published: June 2019

AbstractWe present a detailed analysis of theoretical period–luminosity (PL) and period–luminosity–color (PLC) relations of classical Cepheids, as derived from nonlinear, nonlocal, time-dependent convective pulsating models with different masses and chemical compositions. The predicted PL and PLC relations turn out to depend on the pulsator metallicity and, to a minor extent, on the adopted averages (magnitude-weighted or intensity-weighted) over the light cycle in different bands. We show that the determination of the reddening and true distance modulus of a galaxy from the observed PL and PLC relations is constrained by the metallicity sensitivity of these relations. Moreover, the metallicity sensitivity itself provides us with a powerful tool for deriving self-consistent evaluations of distance, reddening and metallicity of the host galaxy, once Cepheid measurements in at least three photometric bands are available. To illustrate this point, we apply our relations to the BVK data for Cepheids in the Magellanic Clouds, assuming to be unaware of their metallicities. The three filter method is finally adopted to evaluate the metallicity of galactic Cepheids (BVI data) as a function of their position.
Hydrodynamical Modeling of Double-Mode Pulsation
Authors: Kolláth Zoltán 
Published: June 2019

AbstractThe hydrodynamical modeling of steady double-mode (DM) pulsations has been a long-standing quest. Recent improvements in turbulent-convective pulsation codes provide a natural way to calculate nonlinear DM oscillations. The eddy viscosity plays a crucial role in these models. We present models both for RRd and beat Cepheid variables and for different chemical compositions. Simple nonresonant amplitude equations capture the DM phenomenon, giving an overview of modal selection on the HR diagram.
The Effect of the Solar Cycle on the Resonant Coupling of g Modes
Authors: Jordinson C. , Gough D. O. 
Published: June 2019

AbstractWe consider the effect of the solar cycle on g-mode parametric resonance, and hence on the limiting amplitude of the overstable solar g1(ℓ = 1) mode. We find no change in the expected limiting amplitude from that found by Dziembowski (1983), who ignored cycle variations.
Instabilities in Very Massive Stars
Authors: Jørgen Knut , Ødegaard Røed 
Published: June 2019

AbstractDetailed dynamical models and nucleosynthesis yields of very massive stars from early pre-MS through very late stages have been computed. The recent reduction of mass loss rates for the WR stages can have important consequences for both the evolution, surface composition and stability. Depending on mass and metallicity, in the present models instabilities occur during the accretion phase (pre-ZAMS), LBV stage and very late stages (WC).
Amplitude Variability of Delta Scuti Stars: 4 CVn
Authors: Breger Michel 
Published: June 2019

AbstractThe amplitude variability of δ Scuti stars is demonstrated by the behavior of the evolved δ Scuti star 4 CVn. The data on 4 CVn covering over 30 yr shows the amplitudes of almost all modes to be extremely variable with a time scales of ten years or longer. The most rapid decrease of amplitude in V is shown by the 7.38 d−1 mode of 4 CVn, which collapsed from 15 mmag in 1974 to 4 mmag in 1976, and 1 mmag in 1977. Between 1974–6 and 1977–8 phase jumps of almost half a cycle occurred. While a simple beating model of two close frequencies can be ruled out from the photometric data, the change is compatible with the growth of a new mode between 1976 and 1977.
Photometric Variability of Helium Stars in the Z-bump Instability Strip
Authors: Cuadrado R. Aznar , Rodríguez P. Montañés , Jeffery C. S. , Pollacco D. 
Published: June 2019

AbstractZ-bump opacities are known to excite radial pulsations in helium stars with 102≲L/M≲ 104andTeff∼ 25 000K. Well-studied cases are V652 Her and BX Cir. The absence of variations in the metalpoor star HD 144941 demonstrates the importance of Z-bump opacities to drive these pulsations. Several other helium-rich stars lie close to the theoretical blue-edge of the Z-bump instability strip. One of these, LS IV+6°2, is a known radial velocity variable. We report on recent (1999 June) observations of two helium stars close to the Z-bump instability boundary. Both appear to be variable.
Suppressing g Modes in Shell Hydrogen-Burning δ Scuti Stars
Authors: Bradley P. A. , Guzik J. A. 
Published: June 2019

For shell hydrogen-burning δ Scuti stars, many more unstable modes are predicted than are observed. For example, for 4 CVn and δ Scuti itself, only 18 and 6 modes are observed, respectively, whereas several hundred ℓ = 0, 1 and 2 rotationally-split modes are predicted. The predicted modes have a mixed p- and g-mode character, with many g-type nodes present in the H-exhausted core and shell H-burning region, where the Brunt-Väisälä frequency is large.Here we explore whether the predicted frequency spectrum can be made to agree better with the observed spectrum if the g-mode character of the pulsation modes is partially suppressed. Additional motivation for this approach is provided by the observation by Breger et al. (1999) that 4 modes in 4 CVn identified as ℓ = 1 have nearly equal frequency spacings of ∼14 μHz, reminiscent of consecutive radial orders from a pure p-mode spectrum. We consider 2.1- and 2.3-M⊙ evolutionary models that match the observed Teff, L, and log g, plus an identified radial mode frequency of 4 CVn and δ Scuti. For these models, we experimented with setting the Brunt-Väisälä frequency to zero from the model center to the edge of or beyond H-depleted core, so that the g-type portion of the waves becomes evanescent in this region.
Studies of Non-adiabatic Effects on Radial Pulsations in the Atmospheres of Rapidly Oscillating Ap Stars
Authors: Medupe R. , Kurtz D. W. , Christensen-Dalsgaard J. 
Published: June 2019

AbstractA code for solving non-adiabatic radial pulsation equations with consistent treatment of radiative transfer is used to study the oscillations in the atmospheres of the rapidly oscillating Ap stars. We find that our results are consistent with the presence of an observable node in the temperature eigenfunction.
First Results of the 17th DSN Campaign: Photometry of XX Pyx
Authors: Arentoft T. , Handle G. , Shobbrook R. R. , Wood M. A. , Crause L. , Crake P. , Podmore F. , Habanyama A. , Oswalt T. , Birch P. V. , Lowe G. , Sterken C. , Meintjes P. , Brink J. , Claver C. F. , Medupe R. , Guzik J. A. , Beach T. E. , Martinez P. , Leibowitz E. M. , Ibbetson P. A. , Smith T. , Ashoka B. N. , Raj N. E. , Kurtz D. W. , Balona L. A. , Costa J. E. S. , Breger M. 
Published: June 2019

AbstractWe present the first results from multi-site observations of the δ Scuti star XX Pyx (CD–24°7599). The observations were carried out as the 17th run of the Delta Scuti Network. We collected 583 hr of B, V time-series photometry, resulting in a detection level (4σ) in the amplitude spectrum of 0.5 mmag. We detect 6 new pulsation frequencies, bringing the total number of frequencies known in this star up 19.
On the Amplitude Interferometer Program at the University of Maryland
Authors: Currie Douglas G. 
Published: June 2019

AbstractA coordinated program of instrumental development and astronomical observation in Amplitude Interferometry has been conducted at the University of Maryland for the past ten years. The objective of this overall program will be presented. The method of operation and the fringe detection technique of the University of Maryland Amplitude Interferometer will be described and reviewed from both the theoretical and the instrumental point of view. The relationship between the detection technique of Amplitude Interferometry and the various parameters of the atmospheric model will be described and the measured Modulation Transfer Function of the telescope/atmosphere will be illustrated and compared with the MTF obtained in other techniques. Samples of the data obtained during the Amplitude Interferometry observing program of the past six years will be presented. This has operated to sixth magnitude, and has reproducibility resolved objects to 0.011 arc seconds with precision of better than 0.002 arc seconds. The reproducibility and stability of repeated measurements of the stellar diameters will be presented. The various uses of this data in astronomy will be briefly described.The future application of Amplitude Interferometry will be described, particularly a system to obtain high sensitivity and very high resolution with the same detection system and same signal processing as the current instrument. However, for the immediate future, the two instrumental questions are being addressed separately in the form of the Multi-Aperture Amplitude Interferometer, which operates on a conventional telescope and has an increased data rate (by a factor of 8,000) and the Very Long Baseline Amplitude Interferometer with the increased resolution. These instruments and their current status will be described as well as their relationship to the earlier program and their eventual use in a Multi-Aperture Very Long Baseline Amplitude Interferometer system. Finally the possible applications of these techniques Interferometry to a satellite system will be briefly mentioned.
The Prototype Very Long Baseline Amplitude Interferometer
Authors: Liewer Kurt M. 
Published: June 2019

AbstractAn Amplitude Interferometer based on the design of an earlier interferometer but with two independent telescopes has been built at Maryland, The design and the current status of the instrument will be discussed.This interferometer has been built with automatic guiding in each arm and is intended for use with baselines of 50 meters but can be used with longer baselines at restricted declinations.The visibility detection will be exactly the same as that used in the cassegrain model of the interferometer which has operated successfully for several years on the 100 and 200 inch Hale telescopes. The visibility will be measured simultaneously in three different paths with slightly different delays which will allow for automatic location and tracking of the white light fringe envelope.
The Monteporzio Two Meter Amplitude Interferometer
Authors: Tango William J. 
Published: June 2019

AbstractThe two meter baseline interferometer of the Royal Observatory, Edinburgh, will be described. This instrument was designed specifically for the observation of binary stars which have angular separations intermediate between the classical visual binaries and spectroscopic systems. Observations on bright stars suggest that it should be possible to measure the fringe visibility with an accuracy of a few percent.
Angular Dependence of Atmospheric Turbulence Effect in Speckle Interferometry
Authors: Fried David L. 
Published: June 2019

AbstractThe concepts of speckle interferometry as developed by Labeyrie, and of speckle imagery as formulated by Knox and Thompson are analyzed for dependence on field-of-view size. The preliminary analysis, assuming isoplanatism rederives the results of Korff, and derives the result previously inferred by Knox and Thompson from computer simulation, that allowable spatial frequency separation for difference of phase shift determination must be less than r0/λ When the assumption of isoplanatism is dropped, results are obtained for the expected object power spectrum in speckle interferometry and for the expected bispectrum in speckle imagery, showing the dependence on angular spread for an object consisting of a pair of point sources. An angle, ϑ, is defined (in terms of an integral over the strength of turbulence distribution along the propagation path), which bounds the range within which there are no significant anisoplanatism effects. It is noted that the effect of anisoplanatism is not to attenuate the information bearing signal but rather to impose incorrect information on the signal. Thus anisoplanatism can result in incorrect conclusions with no indication that there is a problem.