bluuebunny/crossref_metadata_2025_split huggingface dataset:
Instantaneous determination of a variable extinction coefficient in photoelectric photometry
Authors: Poretti E. , Zerbi F. 
Published: July 2016

AbstractObservational evidence was found that even in good photometric sites the extinction coefficient can display large variations during a night. The authors propose a method to determine instantaneous values of the extinction coefficient: it is based on the knowledge of the extra-atmosphere instrumental magnitude m0 for a reference star. An analytical procedure is proposed to determine a reliable value for m0 and results are very satisfactory.
Extended Strömgren Photometry with CCD’s
Authors: Anthony-Twarog B.J. , Twarog B.A. 
Published: July 2016

AbstractCCD’s have made possible the extension of intermediate-band photometric systems, including the Strömgren uvby system, to larger, fainter and cooler stars, with successful applications in old disk and globular clusters. Some of the applications in globular clusters demonstrate the ability to remove foreground stars from photometric diagrams and have enabled a re-evaluation of the evolutionary correction needed for distance modulus determination for metal-poor stars. We have developed an additional index based on measurement of the Ca II H and K lines which retains sensitivity to metallicity changes for extremely metal-poor stars. Finally, we are testing the utility of CCD H/β photometry in the unusual and old open cluster Melotte 66.
Photometry from Space
Authors: Bless R.C. , Taylor M. 
Published: July 2016

AbstractAfter a brief review of the traditional opportunities as well as the problems of doing photometry from space vehicles over a wide variety of wavelength regimes, several topics will be discussed. These include the factors associated with various types of spacecraft orbits (for example, near-earth, geosynchronous, planetary cruise) and with the different kinds of vehicles and platforms used (expendable, shuttle attached payloads, permanent stations, multi-purpose spacecraft, small and large projects). Since ground-based capabilities are constantly improving and expanding, it is necessary to assess those that might compete with space-based photometry. Finally, the present state of space observations as they pertain to “classical,” high precision, high speed and multi-object photometry will be reviewed; possibilities for the future will be addressed briefly.
Recent Results from the High Speed Photometer
Authors: Taylor M. , Bless R.C. , Nelson M. , Percival J. , Bosh A. , Cooke M. , Elliot J. , van Citters W. , Dolan J. , Biggs J. , Wood J. , Robinson E. 
Published: July 2016

AbstractOne of the first stellar photometry programs completed with the High Speed Photometer (HSP) on the Hubble Space Telescope (HST) was visual and ultraviolet observations of the Crab pulsar. We obtained continuous observations on four consecutive days using a visual filter (4000 - 7000 Å) and an additional observation, approximately two months later, using an ultraviolet filter (1600 - 3000 Å). Each observation has a time resolution of 10.7 μsec and spans approximately 30 minutes in duration. In addition to the observations made with the HSP, contemporaneous UBVR observations were also made at Jodrell Bank and McDonald Observatory. Some of the more prominent results include the following: 1) the main pulse arrival time is the same in the UV as it is in the optical and the radio regions of the spectrum, 2) there is essentially no difference in the shape of the optical pulse from one observation to the next, 3) the “flatness” of the peak of the main pulse suggests that the main pulse has been resolved in time, and 4) in accordance with the trend of observations from the radio to infrared wavelengths, the main pulse is slightly narrower in the UV than in the optical.A second HSP science observing program was a long-term program to monitor the eclipsing dwarf nova, Z Chamaeleontis (Porb = 107 minutes). We obtained a total of 42 observations of Z Cha in the UV (1120 - 1580 Å) each with a duration of approximately 45 minutes and separated by approximately three days. Although the majority of the observations cover the eclipse of the white dwarf and hot spot, a few observations were obtained outside-of-eclipse in order to obtain the complete light curve. During the course of this program, Z Cha underwent two “normal” outbursts in which the shape of the light curve changed dramatically. We will present a comparison of the light curve in quiescence with that during a “normal” outburst and quantify such geometrical and physical parameters as temperature and size of the white dwarf, hot spot, and accretion disk.
Historical Supernovae and Supernova Remnants
Authors: Wang Zhenru 
Published: July 2016

The oldest historical supernova (SN), recorded by ancient Chinese in 14th Century B.C. on pieces of tortoise shells or bones, is identified with the aid of modern space γ-ray observations. Hard X-rays with energy up to 20 keV were observed from IC 443 by the X-ray satellite Ginga. We infer from these observations the age of IC 443 is ∼ 1000 — 1400 yrs. The result supports the hypothesis that IC 443 is the remnant of the historical SN 837 that occurred during the Tang Dynasty. The association between the supernova remnant (SNR) CTB 80 and SN 1408 has been hotly debated for about ten years and is briefly reviewed and discussed here. A new picture is presented to explain this association. High energy emission from historical SNRs can persist in a multiphase interstellar medium (ISM). As a result, the study of the relationship between SNRs and ancient guest stars has gained new vitality.
L’Astronomie des Etoiles Doubles face a la Mission Astrometrique du Satellite Hipparcos
Authors: Dommanget J. 
Published: July 2016

SummaryThe Hipparcos satellite is described as well as the scanning process of the sky by its optical design, as a consequence of the satellite’s motion. From these data, the possibilities of the mission is deduced and applied in the case of the binaries.Discussion is made of what may be expected for different double star categories including spectroscopic, astrometric, close visual and wide pairs. Information are given on how proposals should be made for lists of binaries that should be observed.
Reduction of Astrometric Binaries for Low Mass Companions
Authors: Russell Jane L. 
Published: July 2016

AbstractDescribed is the plan of a study just underway to assess the progress so far in the astrometric search for low mass companions. The range of periods which would be discernible, based on the obsprvations’ distribution in time, and the range in amplitude of the detectable orbits, based on careful analysis of the accuracy of the observations, can be used to determine the confidence level of any perturbations as well as to specify what possible companions and orbits for a given star have been ruled out. This study, when completed for several nearby stars, should yield the first comprehensive progress report for the search for astrometric companions.
Long Period Variables in the Magellanic Clouds: the OGLE/MACHO/2MASS/DENIS view
Authors: Groenewegen Martin 
Published: July 2016

AbstractI present a brief analysis of K-band period-luminosity relations for AGB stars in the SMC based on OGLE, 2MASS and DENIS data. I also present, for a selected sample of SMC and LMC stars, a comparison between the analysis of respective MACHO and OGLE data and a method to combine the data from the two surveys.
NGC 6822: short period variable stars, stellar population and distance scale
Authors: Baldacci Lara , Rizzi Luca , Clementini Gisella , Held Enrico V. 
Published: July 2016

AbstractResults are presented on a study of the short period variable stars in the dwarf irregular galaxy NGC 6822. We observed an almost uniformly populated classical instability strip from the Horizontal Branch up to the Classical Cepheid region. The main goal we achieved from the analysis of the faint sample is the first detection of RR Lyrae stars in this galaxy.
An application of Bayesian statistics to the extragalactic Cepheid distance scale
Authors: Barnes Thomas G. , Moffett Thomas J. , Jefferys W.H. , Forestell Amy D. 
Published: July 2016

AbstractWe have determined quasi-geometric distances to the Magellanic Clouds, M31 and M33. Our analysis uses a Bayesian statistical method to provide mathematically rigorous and objective solutions for individual Cepheids. We combine the individual distances with a hierarchical Bayesian model to determine the galactic distances. We obtain distance moduli 18.87 ± 0.07 mag (LMC, 12 stars), 19.14 ± 0.10 (SMC, 8 stars), 23.83 ± 0.35 mag (M33, 1 star) and 25.2 ± 0.6 mag (M31, 1 star) – all uncorrected for metallicity. The M31 and M33 distances are very preliminary. If the PL relations of the LMC, SMC and Galaxy are identical, our results exclude the metallicity effect in the V, (V – R) surface brightness method predicted by Hindsley & Bell (1989) at the 5σ level. Alternately, if Hindsley & Bell’s prediction is adopted as true, we find a metallicity effect intrinsic to the Cepheid PL relation requiring a correction Δ(V – Mv) = (0.36 ± 0.07)Δ[A/H] mag. The latter has the opposite sign to other observational estimates of the Cepheid metallicity effect.
The kinematics and zero point of the log P –〈MK〉 relation for galactic field RR Lyrae variables via statistical parallax
Authors: Dambis A.K. , Vozyakova O.V. 
Published: July 2016

AbstractThe kinematical parameters of the local field RR Lyrae population and the zero point of the log P –〈MK〉 relation for these variables are inferred by applying the statistical parallax (maximum-likelihood) technique to a sample of 379 RR Lyrae stars with known periods, radial-velocities, metallicities, K-band photometry, and absolute proper motions on the ICRS system. Hipparcos, Tycho-2, SPM, UCAC1 and NPM1 were used as the sources of proper motions. The K-band magnitudes were adopted from the 2MASS All-Sky Data Release. The parameters of the velocity distribution are found to be (U0 = −13 ± 9, V0 = −41 ± 7, W0 = −19±4) kms−1, (σU = 66±9, σV = 47±7, σW = 23±5) km s−1 and (U0 = −11±10, V0 = −224±8, W0 = −8±6) km s−1 (σU = 158±9, σV = 95±5, σW = 88±5) km s−1 for the thick-disk (the purest disk sample, 56 stars) and halo (the purest halo sample, 264 stars) objects, respectively. The zero point of the infrared PL relation of Jones et al. (1992 – based on the results obtained using the Baade-Wesselink method) is confirmed: we find 〈MK〉 = −2.33⋅log PF−0.89±0.09, which is only brighter than found using the Baade-Wesselink method (Jones et al. 1992). A conversion of the resulting log P –〈MK〉 relation to V-band luminosities yields the metallicity-luminosity relation 〈MV〉 = +1.12 + 0.18 ⋅ [Fe/H] ± 0.10. Our results imply a solar Galactocentric distance of R0 = 7.8±0.4 kpc and an LMC distance modulus of DMLMC = 18.17 ±0.10 (cluster RR Lyraes) or DMLMC = 18.10±0.10 (field RR Lyraes), thereby favoring the so-called short distance scale.
g-mode pulsations in slowly pulsating B stars
Authors: De Cat P. , Daszyńska-Daszkiewicz J. , Briquet M. , Dupret M.-A. , Scuflaire R. , De Ridder J. , Niemczura E. , Aerts C. 
Published: July 2016

AbstractIn this paper, we give an updated overview of the observed characteristics of g-mode pulsations in slowly pulsating B stars. These characteristics are based on the combined results of linear nonadiabatic analysis of the oscillations and a photometric and spectroscopic mode identification for a sample of 13 members. For 4 stars, at least one mode is stable in all the considered theoretical models.
Pulsating stars in the open cluster NGC 1817
Authors: Arentoft T. , Freyhammer L.M. , Bouzid M.Y. , Sterken C. , Frandsen S. 
Published: July 2016

AbstractWe report on new CCD observations of the open cluster NGC 1817, obtained as part of a program to search for pulsating stars in clusters. In a previous study, several δ Sct stars were found in NGC 1817 and our observations confirm that NGC 1817 is a special cluster, as we detected 19 variable stars. Twelve of these are most likely δ Sct stars of which 11 seem to be cluster members. One is also an eclipsing binary.
Short-term instabilities in γ Velorum: a search for strange modes in variable stars
Authors: Bentley John , Cottrell P.L. 
Published: July 2016

AbstractStrange mode instabilities in Wolf-Rayet stars have been proposed as the cause of clumping in the stellar wind. This, in turn, is suggested as a cause of line profile variations found on short time scales. High-frequency, short-duration, time-series spectroscopy was performed on the Wolf-Rayet star γ Velorum and analysis confirmed the results of a previous study of γ Velorum’s stellar wind which showed that the wind is indeed clumped, most likely from the predicted strange mode pulsations.
First results of Mercator observations of variable A and F stars
Authors: De Ridder J. , Cuypers J. , De Cat P. , Uytterhoeven K. , Schoenaers C. , Davignon G. , Raskin G. , Vanautgaerden J. , Broeders E. , DeMeester W. , Van Malderen R. , De Ruyter S. , Vandenbussche B. , Maas T. , Kolenberg K. , Reyniers M. , Decin G. , Acke B. , Ausseloos M. , Aerts C. , Van Winckel H. , Waelkens C. 
Published: July 2016

AbstractWe report on the first results from observations of 31 variable A and F stars, obtained with the new Mercator telescope (La Palma). Besides confirming the γ Dor nature of known bonafide and candidate γ Dor stars, we also present new candidate γ Dor stars. In addition, we found a new short-period variable star.
Spectra of RV Tauri stars in the Large Magellanic Cloud
Authors: Evans Tom Lloyd , Pollard Karen R. 
Published: July 2016

AbstractLow-resolution (0.6 nm) spectra of 24 RV Tauri stars in the LMC shows that most are of intermediate Preston type, hence intermediate metal deficiency. Two belong to Preston’s class B, with enhanced CH and CN. Higher resolution spectra of the carbon star MACHO 47.2496.8 show that the 12C/13C ratio is high and that the Ball lines at 455.4 and 493.4 nm are enhanced. This suggests that the star has undergone the third dredge-up of helium-burning products on the thermally-pulsing AGB and is now in a post-AGB stage of evolution. JHK photometry from the 2MASS catalogue confirms and extends earlier findings that only moderate infrared excesses occur among this sample of RV Tauri stars.
An overtone Cepheid variable in an LMC eclipsing binary
Authors: Lepischak D. , Welch D.L. 
Published: July 2016

AbstractEclipsing binary systems potentially allow the direct and precise determination of the important properties of their component stars. An eclipsing binary containing a Cepheid variable which is also a double-lined spectroscopic binary would allow, for the first time, the direct measurement of the absolute luminosity and mass of the Cepheid. The MACHO Project LMC database contains five systems whose light curves show variations due to both eclipses and pulsation but only one has been clearly identified as an intermediate-mass, Population I object. This object, MACHO 81.8997.87 (= OGLELMC_SC16 119952) is a 2.035-d overtone Cepheid in an 800.4-d binary system with an M-type companion. Here we present the results of the analysis of the light curve of this system, the implications for its evolutionary history and discuss the prospects for future observations.
A spectroscopic study of southern binary Cepheids
Authors: Petterson O.K.L. , Albrow Michael D. , Cottrell P.L. , Fokin A. 
Published: July 2016

AbstractHigh-resolution spectroscopic observations have been made of a number of southern binary Cepheids to determine their dynamical masses. The stars are part of a long-term programme to observe southern variable stars for which a valuable long-term database has been obtained. The most recent radial velocities have a precision of ~300ms−1, allowing the detection of velocity differences of ~l kms−1 with confidence. Masses were determined for three systems: the 9-day Cepheid S Mus (6.0±0.4M⊙), the double-mode Cepheid Y Car (4.5±1.8M⊙) and the 5-day Cepheid V350Sgr (6.0±0.9M⊙). For five Cepheids (YZCar, AX Cir, V636 Sco, W Sgr and T Mon) new or improved orbital solutions were found. Line level effects have been observed in several species of lines. Most Cepheids were observed to show the same progression of line level effects. Using non-linear radiative hydrodynamical models, we have compared the results of these models with our observations. These have shown that AX Cir and YZ Car have the following properties: L = 2050 L⊙, M = 4.8 M), Teff = 5900 K and L = 9350 L∩, M = 7.7M∩, Teff = 5590 K. Our models show no strong Shockwaves being produced. Good agreement was found between the observed and modelled spectral lines Fe I 5576Å, Si II 6347Å, Ba II 5853Å and Ca II 8542Å.
Seismic Tests of Accretion in Central Stars of Planetary Systems
Authors: Bazot Michaël , Vauclair Sylvie 
Published: July 2016

AbstractCentral stars of extra-solar planetary systems are metal-rich. Planet accretion or initial high metallicity are two models proposed to explain this observational fact that can be tested with asteroseismology. We calculate two stellar models, one with accretion and one with high initial metallicity, in order to obtain the same external parameters for both of them. We then compare their internal structures and their oscillation frequencies.
The effect of metallicity on the Cepheid period-luminosity relation
Authors: Romaniello Martino , Primas Francesca , Mottini Marta , Groenewegen Martin 
Published: July 2016

AbstractWe present preliminary results of an observational campaign devoted to establishing the influence of chemical composition on the Cepheid Period-Luminosity relation. The data are in good agreement with theoretical predictions based on non-linear convective models, suggesting a fairly strong dependence of the Period-Luminosity relation on metallicity in the sense of more metal rich stars being intrinsically fainter than otherwise expected. Our data indicate that the error on the inferred distance can be as large as 10% if the role of metallicity is neglected.
The chemical composition and circumstellar environment of the variable star QY Sge
Authors: Goswami Aruna , Kameswara Rao N. , Lambert D.L. 
Published: July 2016

AbstractChemical composition studies of the variable star QY Sge show abundance anomalies suggestive of the pattern exhibited by the warmer RV Tau variables. Abundance analysis indicates a near-solar atmosphere with highly condensable elements depleted by several factors. Evidence of broad Na D emission features in its spectrum, a characteristic feature of R CrB stars taken at minimum, however, raises the question of its spectral classification. We address this question through a comparative analysis of its spectrum with those of γ Cyg 89 Her and R CrB taken at minimum, in addition to abundance analysis. We also discuss a possible physical scenario of the circumstellar environment accounting for the characteristics of the distinct spectroscopic features.
Does Extreme Mixing Improve Frequency Agreement for δ Scuti Stars?
Authors: Guzik Joyce A. , Austin Benjamin A. , Bradley Paul A. , Cox Arthur N. 
Published: July 2016

Abstractδ Scuti stars that have been observed intensely by the Delta Scuti Network and other campaigns exhibit fewer modes than predicted in the observed frequency range. In addition, some modes are difficult to match by the most likely observable l = 0, 1, and 2 modes, especially considering available spectroscopic mode identifications. Here we examine frequency predictions for stellar models for FG Vir and 4 CVn with extensive core mixing, well beyond the plausible limits of such mixing from convective core overshooting. We find that mixing has the potential to substantially improve frequency agreement, and deserves further investigation.
Structure and Evolution of the Milky Way Galaxy
Authors: Gilmore Gerard , Wyse Rosemary F.G. 
Published: July 2016

AbstractThe combination of chemical abundance, kinematic, and age data for stars near the sun provides important information about the early evolution of the Galaxy. We review available data, with some new analysis, to show that the sum of all available information strongly suggests that the extreme population II subdwarf system formed during a period of rapid collapse of the proto-Galaxy. This subdwarf system now forms a flattened, pressure-supported distribution, with axial ratio ∼2:1. The thick disk formed subsequent to the subdwarf system. At least the metal-poor tail of the thick disk is comparable in age to the globular cluster system. The thick disk is probably kinematically discrete from the Galactic old disk, though the data remain inadequate for robust conclusions.
Type I Intermittent Chaos in Hydrodynamic Pulsation Models
Authors: Aikawa Tohsiki 
Published: July 2016

AbstractWe investigate the cause of the transition from limit cycles to chaotic oscillations in pulsation of less-massive supergiant stars. For this purpose, we examine one of the models which has a limit cycle but is very close to the transition to the type I intermittency (Aikawa 1988, Astrophys. & Space Sci., 139, 214). It is shown that the pulsational driving by the hydrogen ionization with the M type ionization front, which becomes very effective at amplitudes beyond the limit cycle, is responsible for the existence of another unstable fixed point beyond the limit cycle (see Aikawa, 1988, in press Astrophys. & Space Sci.) A merging process of these two fixed points makes the transition.
Double Mode Pulsating Stars and Opacity Changes
Authors: Andreasen G.K. 
Published: July 2016

AbstractThe basic physical properties of double mode Cepheids and double mode δ Scuti stars are still highly controversial. Based on results of very recent opacity calculations a detailed consistent, possible solution of the problem of the nature of double mode variable stars has been developed. Extensive studies have been performed to establish the rules governing the morphology of the period ratio diagrams. An ideal reproduction of the period ratio data for both stellar types are obtained assuming an increase of the Cox-Steward opacity by a factor of about 2.5 in the temperature range from 1.5 X 105K to 8.0 X 105K. Consequences for the mass calibration of Petersen diagrams are evaluated.
Secular Changes in the Light Curve of the Short-Period Cepheid EU Tau
Authors: Matthews J.M. , Gieren W.P. 
Published: July 2016

AbstractUBVRI photometry and radial velocity measurements of EU Tau obtained during three weeks in November/December 1987 have been used to (1) confirm the period, P = 2.1025 days, and epoch established by Fernie (1987, P.A.S.P.,99, 1093) and earlier observers, and (2) investigate apparent phase and/or amplitude discrepancies in the light curve first reported by Gieren and Matthews (1987, A.J.,94, 431). Comparison of these new data with photometry collected by different observers covering over two decades suggests that the light curve of EU Tau undergoes short-lived (less than about 2 pulsation cycles) changes which appear to occur with a period of roughly 19 – 21 days. Various possible sources of modulation – including binarity, double-mode beating and nonradial pulsations – are considered and rejected as unsatisfactory.