bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cepheids in IC 4182, Calibration of SNIa 1937C and the Hubble constant
Authors: Saha A. , Sandage A. , Panagia N. , Tammann G. A. , Labhardt L. , Schwengeler H. , Macchetto F. D. 
Published: June 2019

AbstractObservations with the Wide Field Camera on HST were examined, and 27 Cepheids were discovered. Photometry and period analysis have produced unambiguous light curves free of alias. The observed P-L relation has a slope consistent with seminal calibration studies of Galactic and LMC Cepheids. An apparent distance modulus (in V) of 28.47 ± 0.10 to IC 4182 is derived. This implies that Mv(max) for SNIa 1937C is -19.92 ± 0.2 mag, independent of everything except differential absorption between the Cepheids and the supernova. Using this to calibrate Hubble diagrams for SNIa by several authors, and allowing for a 1-σ uncertainty in the absolute magnitude from the calibration of only one SNIa, we obtain H0 = 45 ± 14kms-1Mpc-1.
The Internal Structure of White Dwarf Stars Using the Whole Earth Telescope
Authors: Bradley P.A. 
Published: June 2019

AbstractWhite dwarfs are the final end state for the majority of stars, and hold clues to help solve many current pressing astrophysical problems. We can perform asteroseismology on the pulsating white dwarfs to better understand their internal structure and input physics, paving the way to a better understanding of astrophysics, stellar evolution, and the history of our Galaxy. I describe briefly the potential of asteroseismology by using it to infer the internal structure of PG1159-035.
Chaos in Pulsating Variable Stars: Preliminary Analysis of Photometric Photometry and Observational Constraints of Detection
Authors: Kreidl T.J. 
Published: June 2019

AbstractChaos theory has been applied to a variety of variable stars, but few convincing candidates for chaos have been identified. Here, well-established analysis methods have been applied to some very extensive data sets of rapidly oscillating Ap (roAp) stars and one white dwarf. It it shown that in spite of the amount of data, the signal-to-noise ratio makes positive detection of chaos extremely difficult, especially due to scintillation noise. A new form of dimension computation is presented and discussed. Simple models were constructed to show what noise levels can be tolerated before the detection of chaos is no longer possible and comparisons are drawn with data that could be obtained in the future from space. The lack of phase and amplitude stability in HD 134214 and mode switching in HD217522 and HD 137949 are pointed out as the possible results of chaos, making frequent monitoring of roAp stars desirable.
The Pulsation Characteristics of HD 93044
Authors: Zong-li Liu , Zhi-ping Li 
Published: June 2019

AbstractThe amplitude and period of the first frequency increased, but the amplitude and period of the second frequency decreased. Two new frequencies (10.5011 and 2.0484 c/d) were found. The frequency (2.0484 c/d) might be an interaction term from which resonances can occur and then lead amplitude and period variations.
Line Profile Variations of Rotating Pulsating Stars
Authors: Aerts C. , De Pauw M. 
Published: June 2019

Line-profile variations (LPVs) are often seen in early-type stars. They were first detected in the β Cephei stars, where they are due to radial as well as to nonradial pulsations (NRP). It is still a matter of debate whether NRP is also the cause of LPVs in broad-lined B- and Be stars.The study of LPVs of nonradially pulsating stars is often considered to be especially interesting in the case of rapid rotators, because in such stars the line profiles may offer a Doppler image of the stellar surface. Almost all investigators conclude that only sectorial modes with high -values can properly account for the observations of LPVs in broad-lined stars; on the other hand, high-degree modes are almost never seen in slowly rotating stars.We point out here that the expression for the velocity field which is usually adopted, is not valid for rapid rotators.
β Cephei Pulsation Anomalies: Potential New Windows into the Instabilities and Evolution of Early B Stars
Authors: Goldberg B.A. , Polidan R.S. , Crowe R.A. , Aikman G.C.L. , Bambery R.J. , Gathright J.T. , Odgers G.J. 
Published: June 2019

AbstractWe have obtained Voyager Ultraviolet Spectrometer (UVS) measurements of well-known β Cephei stars, which now total more than 1500 hours (> 300 pulsation cycles!) and which constitute the most comprehensive coherent data set that can address fundamental pulsation properties of a significant cross-section of the group. The extended measurement sequences for individual stars, which cover many successive pulsation cycles at wavelengths where pulsation amplitudes reach a maximum, can provide more comprehensive tests of pulsation stability than any ground-based data. During 1990-91, we acquired more than 100 hours of ground-based high-resolution spectroscopic observations and UBV photometric observations, simultaneous and near-simultaneous with the UVS data set. Analysis has been initiated at NASA's Goddard Spaceflight Center (NASA/GSFC), the University of Hawaii at Hilo (UH Hilo), and the Dominion Astrophysical Observatory (DAO).
Variable UV Line Emission in S Carinae: Miras Do Not Fear Change
Authors: Brugel E.W. , Davis R. , Bookbinder J. 
Published: June 2019

AbstractThe object S Carinae is a bright, relatively hot, short (149d) period mira. As expected, the Mg II h and k lines dominate the ultraviolet line spectra during a large fraction of the pulsation cycle. There are also numerous emission lines of Fe I and Fe II produced by either fluorescense or possibly collisional excitation. The unifying “theme” for all the ultraviolet line emission is variability - during a pulsation cycle one observes changes in the intensity, the central wavelength and (for the stronger lines) the line profile.
Pulsations and declines of RCB stars
Authors: Cottrell P.L. , Lawson W.A. 
Published: June 2019

AbstractWe have continued to observe many of the R Coronae Borealis (RCB) stars and other related hydrogen-deficient carbon stars. We wish to more fully investigate the photometric and spectroscopic properties of these peculiar stars.The UBVRI photometric data (acquired at Mount John University Observatory, MJUO) are being used to investigate whether the periods determined by Lawson et al. (1990), based on time intervals of up to 1100 d, are still evident in the larger datasets which now cover time intervals of up to 2200 d.The long time baseline of photometric observations that we have been able to acquire has enabled us to accumulate an extensive database of decline photometry. These are used to investigate links with the pulsations at maximum light in order to get a better understanding of this remarkable phenomenon.
Pulsations of Proto-Giant-Planets
Authors: Wuchterl G. 
Published: June 2019

AbstractNonlinear oscillations of proto-giant-planets have been found in recent numerical calculations relevant to planetary formation. Pulsations are excited in two phases of the protoplanetary evolution, (a) In an ‘instability strip’ at core masses of typically 0.2M⊙ (M⊕ is the earth mass). Perturbations grow into the nonlinear domain and saturate into perodic variations with relative luminosity-amplitudes of 0.2m (b) At the so called critical mass (typically at Mcore ≈ 15M⊕). There the pulsations drive a strong mass loss. A large portion of the envelope is ejected. Then the mass loss fades and the envelope settles into a new quasi-equilibrium. This remnant — a post nucleated instability protoplanet — has a compact envelope and is in core and envelope mass similar to Uranus and Neptune.
Time Dependent Convection and the Pulsations of Polaris
Authors: Morgan Siobahn M. , Cox Arthur N. 
Published: June 2019

The low amplitude radially pulsating classical Cepheid Polaris (α UMi) has well observed decreasing radial velocity and light amplitudes and an increasing period. Recent work indicates that Polaris may stop pulsating by 1995 (Dinshaw et al, 1989), which would make it an excellent indicator for the red edge of the Cepheid instability strip in the Hertzsprung-Russell diagram.We have calculated Population I envelope models with 200 mass shells of a 5.5 M⊙ star near Teff = 5700 K and log(L/L⊙) = 3.11 which match Polaris’ characteristics (Arellano Ferro, 1984). Models were calculated using the Linear Non Adiabatic pulsation analysis code of Castor (1971). The effects of convection on the pulsational stability were calculated with the time dependent convection theory of Cox, Brownlee and Eilers (1966) as discussed by Cox and Guili (1968). The characteristics of the models were altered until the appropriate period, temperature and luminosity were obtained.
Pulsation Variables in the AF stars of the Case Low-Dispersion Survey
Authors: Kinman T.D. 
Published: June 2019

AbstractThe AF stars are those of spectral types A and F that have been discovered on objective-prism plates taken with the Burrell Schmidt in the Case Low-Dispersion Northern Sky Survey (Pesch and Sanduleak, 1983). In SA 57, this survey is complete to V = 16.5. In this field and also in the Lick Astrograph RR Lyrae survey field RR 7 (in the anticenter) the AF stars comprise (a) blue horizontal branch stars and RR Lyrae stars of the halo and (b) stars which have the higher surface gravities of main sequence stars. The two groups can be separated primarily by their differing Balmer jumps and Balmer line-widths. The latter group (which may well include blue stragglers of both Pop I and Pop II) extends some 10 kpc above the galactic plane and shows a wide range of metallicity. Photoelectric photometry of this AF star sample has allowed the detection field RR Lyrae stars of lower-amplitudes than could have been found by conventional blinking techniques; this has led to a significant increase in the number of RR Lyrae stars that are known in SA 57 and RR 7. The cooler main sequence and/or blue straggler AF stars lie in the zone of pulsational instability and one higher-amplitude δ-Scuti star was detected in field RR 7. It is suggested that these AF stars provide a good sample for studying the incidence of pulsation in the population of older stars that extends beyond the thin disk.
Fundamental Mode and First Overtone Mode Cepheids in the Small Magellanic Cloud
Authors: Smith H.A. , Silbermann N.A. , Baird S.R. , Graham J.A. 
Published: June 2019

AbstractWe report results of a new photographic survey of variable stars in a 1 x 1.3 degree region near the Northeast Arm of the Small Magellanic Cloud. We have discovered 133 new variable stars in this field and have determined periods and B lightcurves for 78 new and 72 previously known variables. At periods shorter than about 3 days, the Cepheid period-luminosity relation splits into two sequences. The brighter sequence is believed to be populated by stars pulsating in the first overtone radial mode, wherecis the fainter sequence is populated by fundamental mode pulsators. The peak in the Cepheid period-frequency distribution occurs near a period of 1.8 days. The surface density of RR Lyrae stars in this field is comparable to that in an outlying SMC field near NGC 121.
CCD Observations of Forgotten Cepheids
Authors: DuPuy David L. , Todd Viar W. , Bloomer Raymond H. , Ward Bradley J. 
Published: June 2019

AbstractCCD observations have been obtained of eight Cepheids which have few recent observations, or an uncertain period, or an uncertain finder chart. All CCD images were flat-fielded, with 4-min exposures (0.5-m telescope) or 6-min exposures (0.4-m telescope). The stars chosen for observation were CY Aqr, EV Aur, V395 Cas, V588 Cas, DW Per, HZ Per, MM Per, and SX Per.Photometry shows clean, Cepheid light curves for six of these eight stars, with the results for MM Per shown as an example below. V588 Cas did not show a periodicity in our data set (only 9 points), and the results for EV Aur will be published separately. We obtained standard deviations of comparison-star differences for all useable stars in our CCD images, to aid future observers in choosing suitable comparisons.
New Ways of Revealing Cepheid Binaries
Authors: Szabados L. 
Published: June 2019

AbstractTwo methods involving the observed amplitudes of radial velocity and UBVR light variations for classical Cepheids have been analysed, both being implicitly known: their principle is trivial but these methods had not yet been used systematically as indicators of duplicity.The slope method is based on the alteration of the wavelength dependence of the light variation amplitude if either a blue or a red companion is added to the light of the Cepheid. The amplitude ratio (AR) method makes use of the fact that the companion reduces the amplitude of the light variation without observable effect on the pulsational radial velocity amplitude. This means that the ratio of these two amplitudes (Arad.vel./AB) has a larger value for binary Cepheids as compared with the single pulsators.Each method has been applied to more than 100 Cepheids, thus allowing to study how the uncontaminated parameters (amplitude ratio and slope) depend on the pulsation period. Binary Cepheids deviate from the regular pattern in these diagrams, and a number of new binaries can be discovered in this way. The effect of duplicity is revealed by both methods independently for VZ CMa, FM Cas, CR Cep, V402 Cyg, VI154 Cyg, V440 Per and DR Vel.
The Periods of RR Lyrae
Authors: Cox Arthur N. 
Published: June 2019

AbstractRR Lyrae (0.566 day period) exhibits the Blasko effect that suggests another natural mode with almost the same period as the accepted fundamental radial mode. This mode might be nonradial, but no one has done an extensive evaluation of this idea. An investigation requires a model that includes the deep composition structure where g-modes of low angular (observable) degree have weight and amplitude. An RR Lyrae model including the outer half of the mass and more than 99% of the radius, based on an asymptotic giant branch model from Hollowell (private communication), see below, was used for this study. It includes composition gradient ramps between the primordial surface hydrogen and helium and the almost pure helium shell and the one between this helium shell and the convective core that is burning helium.Nonradial mode periods almost resonant with the radial fundamental mode period seem to occur for all low ℓ values. In addition to significant pulsation amplitudes in the composition gradient regions where the Brunt Väisälä frequency is large, these low degree and low radial order modes have near-surface amplitudes very similar to the low order radial modes. These modes are evanescent in the convective core. Classical K and γ effects give enough driving in the very low mass surface layers, so that important deep radiative damping for these modes does not completely stabilize nonradial g-mode pulsations. The g4, ℓ=1 mode gives a. double-mode RR Lyrae with Blasko effect.A nonradial mode may not always be visible, depending on how rotation presents the nonspherical pulsations to the observer. Thus the Blasko effect might come and go, as observed for maybe 20% of all RR Lyrae variables. For many, the Blasko effect may not be observable, even when a nonradial mode is there.
The m1 Index in RR Lyrae Stars
Authors: Eloy Rodríguez  , Rolland Angel , de Coca Pilar López 
Published: June 2019

AbstractWe have carried out simultaneous uvbyβ photometry for several RR Lyrae stars. For each of these stars, the observed m1 index variation along the pulsation cycle is compared with that expected variation from the (Δm1*,β) grids of Rodriguez et al. (1991) for the corresponding temperatures, gravities and metallicities. The m1 index variations are also calculated using the Kurucz's models. Good agreement is found
Period Variation of the Pop.II Cepheid AU Peg
Authors: Vinko J. 
Published: June 2019

AbstractAU Peg, a short period BL Her-type variable, is unique among short period Cepheids. It is a member of a close binary system with an unseen companion. In t his paper the pulsational period variation is presented. It is shown that the period variation is very rapid and highly non-linear. It seems that there is no simple explanation of this phenomena by standard evolution or tidal interaction.
Long-Term Brightness Changes in Cool Pulsating Variables
Authors: Percy John R. 
Published: June 2019

AbstractSeveral types of cool pulsating variables show unexplained long-term changes in brightness, typically on time scales of 10 to 20 times the basic (pulsational) period. The visual and photoelectric programs of the American Association of Variable Star Observers (AAVSO) are well-suited for detecting and studying these changes. Some examples are given here, including yellow hypergiants, RV Tauri stars, small- and large-amplitude red giant and super giant variables. The study of pulsating variables on long time scales provides “new perspectives” on their behavior.
Period Changes in the SX Phoenicis Star CY Aquarii
Authors: Joner Michael D. , Powell John M. 
Published: June 2019

AbstractCY Aquarii is a Population II dwarf Cepheid that has been observed on a regular basis since 1930. We present evidence from unpublished times of maximum light from Brigham Young University observations secured in the mid-1970s to the present that indicate that the period of CY Aqr has changed in a discontinuous manner. Furthermore, we find that the period has changed significantly since the epoch of the last published investigation (1988). Finally, contrary to some past claims, examination of our high time resolution light curves yields no indication of multi-periodic pulsation in CY Aqr.
28 And: Simultaneous Strömgren Photometry
Authors: Rodríguez E. , A. Rolland  , López de Coca P. , Garrido R. , Mendoza E.E. 
Published: June 2019

AbstractWe have carried out simultaneous uvby photometry of the low amplitude δ Set star 28 And. Analysis of the data, using the Fourier Transform method, establishes 28 And as a monoperiodic pulsator. Using the classical O-C method, it is found that the pulsation of this star can be well described by means of a linear ephemeris with a period of P=0.d069304118 over the last twenty-four years. Amplitude variations are also shown to be present from season to season. The physical parameters of this star are determined and the nature of radial or nonradial pulsation is discussed on the basis on the derived phase shifts and amplitude ratios between Strömgren colours. The results indicate that 28 And pulsates in a nonradial mode with ℓ = 2.
ρ Pup: A Monoperiodic Radially Pulsating δ Set Star
Authors: Rodríguez Eloy , Rolland Angel , de Coca Pilar López 
Published: June 2019

Abstractρ Pup is a δ Scuti type pulsator with relatively low amplitude (ΔV∼0.m09). Analysis of the data from different sources, using the Fourier Transform method, establishes ρ Pup as a monoperiodic pulsator. Using the classical O-C method, it is found that the pulsation of this star can be well described by means of a linear ephemeris with a period of P=0.d140881372 over more than eighty years. The nature of radial or nonradial pulsation is discussed on the basis on the derived phase shifts and amplitude ratios between different colours. The results indicate that ρ Pup is a radial pulsator.
A Search for the Regional Variations in the Wavelength Dependence of Interstellar Polarization
Authors: Serkowski K. , Chojnacki W. , Rucinski S. 
Published: June 2019

The Polarization of 19 Bright, Highly Polarized Stars was measured from March until July 1965, with a differential polarimeter installed at the Cassegrain focus of the 90-cm telescope of the Toruń Observatory in Poland. The stellar light was split by the calcite Wollaston prism into two beams falling upon the cathodes of the photomultipliers. The observations were made at eight position angles of the polarimeter differing by 45°, alternately with and without the quartz depolarizer. The yellow 2-mm Schott GG 14 and the blue Schott BG 12 (l-mm) + GG 13 (2-mm) filters were used. No optical elements except the depolarizer were placed between the Wollaston prism and the telescope mirrors.Usually only the Stokes parameters having the larger absolute values were accurately measured. The resulting polarization ratios pv/pB of the Stokes parameters expressed in magnitudes, measured with yellow and blue filters, are given in the ninth column of table I.
Scanner Observations of λ4430
Authors: Joseph Wampler E. 
Published: June 2019

The Interstellar Band at λ4430 has been observed in over 100 stars by using the Lick Observatory scanning spectrograph mounted on both the 120-inch telescope and on the Crossley telescope. Although in some instances the feature is badly blended with stellar lines, particularly with early B supergiants, in general the central depth of λ4430 has been determined to an accuracy exceeding 0.5 percent of the stellar continuum.The feature has been found to have a fairly symmetrical profile, although there may be changes in the profile from star to star. The extended wings reported by other observers were not detected, and also the feature does not seem to be polarized.The correlation between the absorption band at A.4430 and color excess is not one-to-one. Even field stars lying in the galactic plane show much intrinsic scatter in the ratio of this absorption band to color excess.
Infrared Radiation From Interstellar Grains
Authors: Stein Wayne A. 
Published: June 2019

The Past Several Years there has been a growing interest in the possibility of observing infrared radiation at wavelengths greater than 10 μ, from various astronomical objects. For example, Gould in references 1 and 2 has suggested trying to observe several lines in the infrared with emphasis on the 12.8-μ line of Ne+ and the 28-μ line of molecular hydrogen. The possibility of being able to observe the emission from interstellar grains in the wavelength region between 10 μ and 100 μ was suggested in a discussion presented in references 3 and 4. The intensity expected from thermal emission by the grains has also been investigated by F. D. Kahn at Manchester.The present paper indicates information about interstellar grains that could be gained by measuring the intensity as a function of wavelength and the polarization of radiation emitted by the grains in the far infrared.
The Application of High Angular Resolution Stellar Interferometry to the Study of Single Objects in the Visual Region of the Spectrum
Authors: Davis John 
Published: June 2019

AbstractA brief review of existing angular diameter measurements of single objects is given. Potential astronomical programmes for high angular resolution stellar interferometry in the visual region of the spectrum are discussed with particular regard to the sensitivity, resolution, and accuracy required for significant astrophysical results to be obtained. This discussion is used as a basis for suggesting the minimum requirements for future high angular resolution stellar interferometers.