bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Host Galaxies of High-Redshift Type Ia Supernovae
Authors: Sullivan Mark , Ellis Richard ,   the Supernova Cosmology Project_a3
Published: June 2019

SummaryWe present new results on the Hubble diagram of distant type Ia supernovae (SNe Ia) segregated according to the type of host galaxy. This makes it possible to check earlier evidence for a cosmological constant by explicitly comparing SNe residing in galaxies likely to contain negligible dust with the larger sample. The cosmological parameters derived from these SNe Ia hosted by presumed dust-free early-type galaxies support earlier claims for a cosmological constant, which we demonstrate at ≃ 5σ significance, and the internal extinction implied is small even for late-type systems (AB < 0.2). Furthermore, the scatter observed in the SNe Ia Hubble diagrams correlates closely with host galaxy morphology. We find this scatter is smallest for SNe Ia occurring in early-type hosts and largest for those in late-type galaxies. Moreover, SNe residing in late-type hosts appear fainter in their light-curve-width-corrected luminosity than those in early-type hosts, as expected if a modest amount of dust extinction is a contributing factor. Thus, our data demonstrate that host galaxy extinction is unlikely to systematically dim distant SNe Ia in a manner that would produce a spurious cosmological constant.
Constraints on SN Ia Progenitors and ICM Enrichment from Field and Cluster SN Rates
Authors: Maoz D. , Gal-Yam A. 
Published: June 2019

SummaryThe iron mass in galaxy clusters is about 6 times larger than could have been produced by core-collapse SNe, assuming the stars in cluster galaxies formed with a standard IMF. Type-Ia SNe have been proposed as the alternative dominant iron source. We use our HST measurements of the cluster SN-Ia rate at high redshift to study the cluster iron enrichment scenario. The measurements can constrain the star-formation epoch and the SN-Ia progenitor models via the mean delay time between the formation of a stellar population and the explosion of some of its members as SNe-Ia. The low observed rate of cluster SNe-Ia at z ~ 1 pushes back the star-formation epoch in clusters to z > 2, and implies a short delay time. We also show a related analysis for high-z field SNe which implies, under some conditions, a long SN-Ia delay time. Thus, cluster enrichment by core-collapse SNe from a top-heavy IMF may remain the only viable option.
Dark Energy: Nature and Robustness
Authors: Blanchard A. , Zolnierowski Y. 
Published: June 2019

SummarySupernovae have provided the evidence for the existence of a dominant dark energy component of the Universe. The commonly accepted form of such a component is the quintessence. Here, we show that the possible nature of this component is rather well constrained by combining the various existing observational cosmological data. However, relaxing some of the various hypothesis can lead to somewhat different results.
Desktop Space Exploration
Authors: Martin-Smith M. , Buckland R. 
Published: June 2019

The Humble Space Telescope project aims to launch a small space telescope for educational and recreational purposes, in time for the New Millennium.The arrival of the 3rd Millennium, accompanied in the United Kingdom by a Millennium Commission distributing 250 million per year of National Lottery funds for good causes and imaginative projects which would otherwise require direct funding by the taxpayer, provides a unique opportunity to design, build and operate a small but capable version of the pioneering Hubble Space Telescope.In July 1994, a leading British newspaper with a long history of covering developments in science, launched a competition for members of the public to propose science projects to be funded by the Millennium Commission.
New Trends in Astronomy Teaching
Authors: Abati L.E. 
Published: June 2019

We are all aware of the fact that Astronomy teaching is not an easy task for many different reasons which we are going to examine during this Colloquium. The present contribution focuses on one of these reasons we consider of major importance for Astronomy in the school: Teacher Training.Teacher training has been debated extensively for a long time and discussion is being presently livened up.
Optical Emission-Line Spectra of Be Stars (Review Paper)
Authors: Dachs Joachim 
Published: June 2019

AbstractRecent observational work on spectra obtained at optical and near-infrared wavelengths is reviewed for “ordinary” (non-supergiant non-peculiar) Be and Be-shell stars, with particular emphasis on comparison between high-resolution spectral measurements and current Be star models. Emission-line profiles are interpreted in terms of geometry, dimensions and dynamics of a dense (N ≃ 1011 cm-3), cool (T ≃ 104 k) line-emitting region in the circumstellar envelope, separated from the thin, hot expanding stellar wind region. Present observations support a rotating-disk model for the cool, line-emitting region. Indications pointing towards structuring of cool circumstellar envelope regions are reported. Significant spectral variations are detected both on short (less than one day) and long time scales (months to years). Typical cycle times for large-amplitude V/R variations and intervals between shell episodes depend on spectral type, increasing with decreasing effective temperature of the central stars and ranging from a few years for early-Be type stars to a few decades for late Be stars.
FeII And FeIII Lines As a Diagnostic of the Physical Conditions in the Atmospheres of Be Stars
Authors: Baratta G.B. , Friedjung M. , Muratorio G. , Viotti R. 
Published: June 2019

AbstractFell lines are frequently observed in the optical spectra of early type emission line stars. Space observations of their ultraviolet spectra led to the discovery of a considerable line absorption due to ionized metal lines formed in the stellar envelopes. We describe some examples and show that spectral synthesis is required especially for the analysis of the low resolution spectra, and may provide information about the structure of the envelopes and the mass loss rates. We also discuss the Felll lines in the UV spectra of a Herbig Be star and of β Lyrae.
RR Lyraes in the Magellanic Clouds
Authors: Walker Alistair R. 
Published: June 2019

AbstractRecent work on the Magellanic Cloud RR Lyrae stars is reviewed. The absolute magnitudes of LMC RR Lyraes, when calibrated from a distance modulus of 18.5 mag, disagrees with the Galactic calibration. The revised distance scale makes distances greater, and ages younger, within our galaxy. Field star studies show that the “halo” population of the LMC is very similar to that of our own Galaxy outside of the solar circle. This result supports a Searle and Zinn model of galaxy formation.
White Dwarf and Pre-White Dwarf Oscillations
Authors: Cox Arthur N. 
Published: June 2019

AbstractCompact stars that result from extreme mass loss on the asymptotic giant branch and planetary nebula formation are observed to pulsate in a very large surface effective temperature range as they cool to become the classical white dwarfs. The hottest and most luminous of these display periods in excess of 1000 seconds because they are large, but when the stars arrive on the cooling line on the Hertzsprung-Russell diagram, their periods become generally less than 1000 seconds. Then the stars have masses near 0.6 M⊙ and radii near 109 cm. Their luminosity depends then almost entirely on the surface effective temperature as the entire star with its legacy of complicated internal luminosity peaks cools to the classical simple electron degenerate structure. Very thin surface layers of hydrogen and helium cover the bulk of the carbon- and oxygen-rich mass that results from hydrogen and helium burning in earlier intermediate mass stellar evolution. The cause of the nonradial pulsations of low angular degree, but rather high radial order, for the most luminous of these stars is the cyclical ionization of carbon and oxygen in layers not too deep that their effectiveness is limited by a long luminosity time scale. Thus the surface hydrogen and helium must be thin, probably thinner than the current period spacings interpretation for PG 1159-035 suggests. For the classical DBV and DAV pulsators, it appears that neither the hydrogen ionization K and γ effects or convection blocking at the bottom of a hydrogen convection zone can destabilize the observed pulsations when the overriding short time scale effects of time-dependent convection are included. It appears, however, that a thin CO convection shell can produce pulsations by its time-dependent effects, but again only very thin H and He surface layers are allowed. This new pulsation mechanism can alleviate the serious problem that DAV variables are observed hotter than the hydrogen K and γ effects and convection blocking can predict. The appearance of non-pulsators in the DAV and DBV instability strips can be explained by a too-thick hydrogen and helium surface layer that interferes with (poisons) the CO ionization convection zone. Finally time-dependent convection predicts that only a few of the many possible modes exist due to their internal amplitude structure that can result in both strong driving and strong damping. Thus actually observed pulsating modes can assist in mapping individual internal white dwarf composition structures, not only by their periods but also the fact that they pulsate.
Nonradial Pulsation amongδScuti Stars
Authors: Breger Michel 
Published: June 2019

AbstractThe review examines recent observational and theoretical results on the nonradial pulsation ofδScuti stars. The dominant pulsation modes are rotationally split p modes with= 1 and 2, and radial orders 1 to 4. Line-profile analyses also reveal the existence of additional high-degree modes. Nonradial pulsation is usually accompanied by slow amplitude and period variability. The small-amplitude single-mode variables are shown to be typical nonradial pulsators.The interesting cases of 1 Mon andθ2Tau are examined in more detail. The present status of asteroseismolgy of theδScuti stars is reviewed.The periods of the four evolvedδScuti variables studied are found to be decreasing, although stellar evolution predicts period increases due to larger radii. New work on the multiple periods of AI Vel shows that, apart from stellar evolution, an additional mechanism must exist to cause temporary period changes. It is argued that for a larger sample of stars the average period change must nevertheless reflect evolutionary changes.
Frequency analysis of multiperiodic δ Scuti stars
Authors: Mantegazza L. , Poretti E. , Zerbi F.M. 
Published: June 2019

We report some of the recent results of our studies on δ Scuti star pulsation which are based on observations made at Merate and La Silla Observatories, sometimes in two site campaigns. Our recent experiences on X Caeli and 44 Tauri have shown that quite complicate light curves can be resolved even with observations obtained from one site only, if compact and accurate datasets are collected on sufficiently long time baselines (Mantegazza and Poretti, 1992; Poretti et al., 1992). Here we report the preliminary results of the light curve analysis of three more stars surveyed for more than 120 hours each: BI CMi, HD 18878 and HD 224639.BI CMi has been observed in a two-site campaign in January-February 1991, the observations being collected during 17 nights. The frequency analysis of the light curve allowed us to identify unambiguously 4 pulsation modes at 8.247, 8.863, 8.514 and 7.424 c/d with semi-amplitudes of 22, 19, 5 and 5 mmag respectively.
A Striking Similarity Between the Sun, Binary Systems and RR Lyrae Stars
Authors: Kotov V. A. 
Published: June 2019

AbstractThe periodicity of P0=160.0101 (±1) min discovered in the Sun's global oscillations, then in rapid variability of active galactic nuclei (AGNs) (Kotov & Lyuty 1990), might have a cosmological origin. Analysing the distribution of periods of ∼4000 close binaries we found that the most commensurate (with an odd-even parity taken into account) period of galactic binaries is equal to 160.0(±1) min (∼ 4σ). Accordingly, it is argued that the famous 2-3 hr gap of cataclysmic binaries might be closely associated with the “universal” P0- oscillation. A similar analysis applied to the ∼1200 RR Lyrae variables in galactic globular clusters (GCs) and 72 RR Lyraes in the LMC GCs (Graham 1985; Nemec et al. 1985) showed that for all those stars the P0- period appears to be the most “resonant” one (Fig. 1). This strongly supports the cosmological origin of the P0- oscillation. Since the P0- resonance for RR Lyraes appears to be most pronounced when the “odd-even” parity is taken into account, it is hypothesized that variability in the majority of GC RR Lyraes should be related to their binary nature and may be relevant to explanation of Blazhko effect.
Time-Series Spectroscopy of ζ Ophiuchi
Authors: Reid A.H.N. , Bolton C.T. , Crowe R.A. , Fieldus M.S. , Fullerton A.W. , Gies D.R. , Howarth I.D. , McDavid D. , Prinja R.K. , Smith K.C. 
Published: June 2019

AbstractWe have undertaken a multi-site, multi-wavelength observing campaign on the archetypal O stars ζ Puppis (O4 I(n)f) and ζ Ophiuchi (O9.5 V). Both stars are well known for the strength of their line profile variations (lpv's), and represent extremes of O spectral type and luminosity class. UV time-series spectroscopy of ζ Pup and ζ Oph is described by Prinja et al. (Ap.J. 1992, 390, 266), and Howarth et al. (Ap.J. 1992, submitted) respectively. The optical spectroscopic results of ζ Oph are reported by Reid et al. (1992, ApJ submitted), of which some of the principal results are given here.During late April, and early May, 1989, we obtained high-resolution, high signal-to-noise optical spectra of the late O-type, rapid rotator ζ Oph. Time-series analysis, using the CLEAN algorithm, has shown that the characteristic lpv seen in HeI λ447lÅ, Si III λλ4552, 4567, 4575Å, and MgII λ448lÅ can be satisfactorily represented as a set of 4 sinusoids. No substantial variation is observed in HeII λ4541, or NIII λ4517Å. We attribute this behaviour to a combination of equatorial gravity-darkening and a latitudinally-confined origin for the lpv.The phase changes over the line profiles indicate repetitive patterns of axial symmetry, rotating prograde in the co-rotating frame of the star. The periods are 3.339 hours (-m = 4), 2.435 hours (-m = 5 or -m = 6), 1.859 hours (-m = 9 ± 1), and either 1.366 hours or 1.292 hours (-m = 11 ± 1); -m represents the spatial frequency around the stellar equator. The first three periods confirm those found at earlier epochs, and we conclude that some lpv characteristics are reproduced over at least a 2-year interval.Since no commensurate superperiod (|m|P) exists, and since the super-periods are less than our estimated minimum rotation period for ζ Oph (> 18 hours), we reject a rotational modulation origin for the lpv and conclude that the star is undergoing multi-mode, sectorial, non-radial pulsations.
Dust Induced Dynamics of Circumstellar Shells around Long—Period Variables
Authors: Gauger A. , Fleischer A.J. , Sedlmayr E. 
Published: June 2019

The presence of dust essentially affects the optical appearance and the dynamics of circumstellar shells around LPVs, while in turn the formation of solid particles as well as their properties critically depend on the actual local conditions. Thus, a reliable modelling of the structure and dynamics of such shells requires a detailed treatment of the dust complex.In our hydrocode, which is described in more detail in Fleischer et al. (1992), the time evolution of the dust component is treated consistently by means of a moment method (Gauger et al. 1990). For the solution of the hydrodynamical and thermodynamical problem we essentially follow the approach of Bowen (1988), except for the shocks, which so far are assumed to be isothermal.
A spectroscopic study of RCB stars in the Galaxy and the LMC
Authors: Pollard Karen , Cottrell P.L. , Lawson W.A. 
Published: June 2019

AbstractHigh resolution échelle spectra have been obtained of two Large Magellanic Cloud (LMC) and one galactic R Coronae Borealis (RCB) star with the Anglo-Australian Telescope. An analysis of these data using He- and C-rich models and the model atmosphere code WIDTH6 of Kurucz indicates that the galactic RCB star SU Tau and the two LMC stars, W Men and HV12842, have similar atmospheric parameters to the warmer galactic RCB and hydrogen-deficient Carbon (HdC) stars e.g., R CrB and XX Cam. Specifically, the new stars have Teff ∼7000 K, log g = 0.5-1.0, microturbulent velocities between 6 and 8 km.s-1 and C/He ratios from 0.004 to 0.006.An abundance analysis has been performed on these stars for a wide range of species. Special emphasis has been placed on particular elements H, He, Li, C, N, O, & Fe (see figure 1), which are key indicators of the extent and relative importance of nuclear processes such as the CNO cycle and triple-alpha process, and also of the physical processes such as convective mixing and mass loss. Specific values for the abundances of [H/He], [Li/Fe] and [Fe/total] (expressed relative to the total abundance of all species) in SU Tau and HV12842 are -5.4 & -6.4, +2.5 & +2.4, -0.4 & -0.8.
Oosterhoff I and II RR Lyrae Variable Masses
Authors: Cox Arthur N. 
Published: June 2019

AbstractThe anomalously low theoretical masses for double-mode RR Lyrae variable stars obtained from accurately observed period ratios recently have been increased by using stellar models constructed with the new Livermore OPAL opacities. These new models appear to the lowest order radial modes to be less concentrated in density, and they thus produce longer periods. Since the fundamental mode is increased in period more than the first overtone, this period ratio from the model is decreased. Cox (1991) showed that now these pulsation-based masses agree with evolution masses, and all RR Lyrae variable stars show little mass loss from the red giant tip in earlier evolution. This investigation has been validated by two additional papers that use more directly the OPAL opacities rather than simple adjustments to the Stellingwerf (1975ab) fit. These new papers (Kovacs, Buchler, and Marom, 1991, and Kovacs, Buchler, Marom, Iglesias, and Rogers, 1992) also display composition effects for Population II mixtures.My new study uses directly the latest OPAL intermediate coupling opacities for the Oosterhoff I and II (Z=0.0003 and 0.0001, respectively) compositions in frozen-in convection (mixing length/pressure scale height ratio=1.25) models to see if there is any difference between the masses of variable stars in these two globular cluster classes. Derived masses are just over 0.65 and 0.75 M⊙, respectively. The Oosterhoff I mass could be as large as the Oosterhoff II mass only if the iron abundance in the Z mixture is increased by more than 30% over that for the solar mixture.The Sandage effect of higher periods for variables in Oosterhoff II clusters at lower Z than for the Oosterhoff I clusters might be explained with my new masses by having the Oosterhoff II variables born much to the blue of the instability strip and evolving at increasing luminosity to the red. For Oosterhoff I variables, they can be born at their lower mass and higher Z inside the instability strip at lower luminosity, evolving both to the red and blue with little evolutionary luminosity increase before they become red nonvariables.
A Full-Amplitude Nonlinear Model for RR Lyr: Pulsations, Shock Waves and Hα Peculiarities
Authors: Fokin Andrew 
Published: June 2019

AbstractThe shock phenomena and Hα formation in the atmosphere of RR Lyrae are investigated by means of numerical simulations. The full-amplitude hydrodynamical model is generated, adopting M = 0.578M⊙, L = 62L⊙, Teff = 7175K and Population II composition. The Hα profiles are obtained by solution of the non-LTE line transfer problem for the multilevel hydrogen atom. In the course of pulsations an extended (about 16 static scales) low-density atmosphere is produced with nearly exponential density decrease. Two shocks, propagating outwards, are successively generated during one period. The shock amplitude reaches 140 km/s. No mass loss has been found. These results confirm the earlier results of S. Hill (1972). The main shock develops very high, at mass depths near 0.001 g per area, whereas computations for W Vir yield 100. An analysis of the Fe I and Ti II lines shows that this difference is sufficient to explain the lack of metallic line-doubling in RR Lyrae stars. The bump on the light curve is due to a weak shock, propagating below the photosphere, which is generated with the early shock at the stage of expansion at the H-recombination front. The central intensities, Dopplerian shifts, amplitudes and phases of splitting of the computed Hα profiles agree well with the observed values (Gillet & Crowe 1988). The lack of strong emission also fits the observations, resulting from strong scattering processes near the shock. The predicted Lyman lines show strong emission, reaching maximum at the maximum light.
Mass-Loss During the RR Lyrae Phase of the HB: Mass Dispersion on the HB and RR Lyrae Period Changes
Authors: Koopmann Rebecca A. , Lee Young-Wook , Demarque Pierre , Howard Jamie M. 
Published: June 2019

Horizontal branch (HB) models were evolved using the Yale stellar evolution code, YREC, to test the possibility that mass loss during the RR Lyrae phase is able to produce the observed color (mass) dispersion on the HB (Willson and Bowen 1984) and the anomalous period changes in RR Lyrae stars (Laskarides 1974). Models of total mass 0.64, 0.66, 0.68, 0.70, and 0.72 M⊙ (YMS = 0.23, Z = 0.001) were evolved with constant mass loss rates of 0, 10-10, and 10-9 M⊙ yr-1. Mass loss was assumed to occur only in the RR Lyrae phase, and the instability strip was defined by 3.800 < log Teff < 3.875.HB stars which lose mass evolve further to the blue. Low mass loss rates do not affect the shape of the tracks significantly. Stars, which without mass loss could not become blue HB stars, were able to emerge from the instability strip on the blue side.
The Masses and Luminosities of Globular Cluster RRc Stars
Authors: Simon Norman R. , Clement Christine M. 
Published: June 2019

AbstractA large number of hydrodynamic pulsation models are converged in the first overtone, and their mean properties compared with observations of RRc stars in six globular clusters. The two observed quantities, period and Fourier parameter ϕ31, lead, via the models, to inferred values for mean mass, luminosity and temperature of the RRc sample in each cluster. We find a narrow range in intracluster RRc luminosity and temperature, but a wider range in mass. At the same time, the intercluster spread is wide in all three parameters. A full discussion of our techniques and results will be given elsewhere (Simon and Clement, in preparation).
CCD Photometry of RR Lyrae Stars in M3
Authors: Cacciari C. , Carretta E. , Ferraro F. , Fusi Pecci F. , Tessicini G. , Nemec J.M. , Walker A.R. 
Published: June 2019

AbstractNew CCD BVI observations of RR Lyrae variables in M3 are presented. Mean magnitudes and colours are derived, as well as their relations with periods and amplitudes, and comparisons are made with previous data (Sandage 1981, 1990). Preliminary results are presented on the temperature distribution of the variables and the period-shift effect with respect to M15 and M68.