bluuebunny/crossref_metadata_2025_split huggingface dataset:
Using Local Group galaxies to investigate the influence of blending on Cepheid distances and the cosmological distance scale
Authors: Mochejska Barbara J. , Macri Lucas M. , Sasselov Dimitar D. , Stanek Krzysztof Z. 
Published: July 2016

AbstractWe investigate the influence of blending on the Cepheid distance scale using two Local Group galaxies, M31 and M33. Blending leads to systematically low distances to galaxies observed with the HST, and therefore to systematically high estimates of H0. High-resolution HST images are compared to our ground-based data, obtained as part of the DIRECT project, for a sample of 22 Cepheids in M31 and 102 Cepheids in M33. For a sample of 22 Cepheids in M31, the average (median) flux contribution from luminous companions not resolved on the ground-based images in the V-band, SV, is about 19% (12%) of the flux of the Cepheid. For 102 Cepheids in M33 the average (median) values of SV, SI, SB are 23% (13%), 28% (20%), 28% (15%). For 64 Cepheids in M33 with periods in excess of 10 days the average (median) SV, SI, SB are 16% (7%), 23% (12%), 20% (10%).
Radial velocities, metallicities, and distances of Cepheids in M31 and M33
Authors: Forestell Amy D. , Barnes Thomas G. , Sneden Christopher , Moffett Thomas J. 
Published: July 2016

AbstractCepheid variable stars are fundamental to the calibration of the extragalactic distance scale. We present radial velocities, preliminary metallicities, and preliminary surface brightness distances of Cepheids in Local Group galaxies M31 and M33 using data obtained with the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. These data are the first step toward surface brightness distance measurements and metallicity calibrations of these extragalactic Cepheids.
Light curves and absolute magnitudes of four recent fast LMC novae
Authors: Hearnshaw J.B. , Livingston C.M. , Gilmore A.C. , Kilmartin P.M. 
Published: July 2016

AbstractThe light curves of four recent fast LMC novae (Nova LMC 1988a, 1992, 1995, 2000) have been analysed to obtain the parameter t2 the time for a two magnitude decline below maximum light. Using the calibration of Della Valle & Livio (1995), values of MV at maximum are obtained. The weighted mean distance modulus to the LMC based on these novae is 18.89 ± 0.16. This differs significantly from the distance modulus adopted by Della Valle & Livio of 18.50, but only differs at the 1σ-level from Feast’s (1999) value of 18.70 ± 0.10. The evidence based on these novae suggests that either: (i) DMLMC = 18.50 is too close for the LMC; or (ii) some novae in the LMC, including these four, are significantly underluminous at maximum light compared with those in M31, by about 0.4 mag. This could be a metallicity effect, given that more metal-rich M31 novae were predominantly used by Della Valle & Livio to obtain their calibration.
Short and long period variable stars in the Carina dwarf Spheroidal galaxy
Authors: Monelli M. , Walker A.R. , Bono G. , Buonanno R. , Caputo F. , Castellani M. , Castellani V. , Corsi C.E. , Dall’Ora M. , Pulone L. , Marconi M. , Nonino M. , Smith H.A. , Stetson P.B 
Published: July 2016

AbstractWe present first results concerning the detection of variable stars in the Carina dwarf Spheroidal from B, V images collected with the 4-m CTIO telescope. We show a sample of candidate variables spanning from the tip of the Red Giant Branch down to the Main Sequence turn off. Finally, we discuss the future photometric and spectroscopic developments of this project.
AGB maser stars as tracers of stellar populations
Authors: Habing H.J. 
Published: July 2016

AbstractMasers are known to occur in circumstellar envelopes of AGB stars that are long-period variables and have entered the TP-AGB phase. The maser radiation is intrinsically weak and detection limits prevent us from seeing maser stars much beyond the Galactic Center. Very deep searches have led to the detection of a handful of maser stars in the Large Magellanic Cloud. Some 1000 stellar masers are known. They trace a population of stars with main sequence masses between 1 and 6 M⊙ and ages between 2 and 8 Gyr, the same population that is traced by Cepheids. Their distribution in our Galaxy is the same as that of the red giants, and therefore the stars trace the galactic bar. An outstanding feature is a small disk of radius 150 pc around the galactic center. The disk is in rapid, solid body rotation and leads to a good measurement of the mass density within that distance for Sgr A.
Near-Infrared photometry of the LMC cluster Reticulum
Authors: Dall’Ora M. , Bono G. , Storm J. , Ripepi V. , Testa V. , Andreuzzi G. , Buonanno R. , Caputo F. , Castellani V. , Corsi C.E. , Degl’Innocenti S. , Marconi G. , Marconi M. , Monelli M. 
Published: July 2016

AbstractWe present U, B, V, I (SUSI@NTT) and J,Ks (SOFI@NTT) photometry of the Large Magellanic Cloud (LMC) cluster Reticulum. The observing strategy and data reduction (DAOPHOTII/ALLFRAME) allowed us to reach an accuracy of the order of 0.01 – 0.03 mag in all the bands at limiting magnitudes typical of RR Lyrae stars. Reticulum hosts a sizable sample of RR Lyrae stars (32), and we supply an accurate distance estimate using the RR Lyrae K-band Period-Luminosity-Metallicity (PLZK) relation. This method presents several advantages when compared with the MV vs [Fe/H] relation, since it is only marginally affected by off-ZAHB evolutionary effects and reddening corrections.
Observational properties of red variables in the LMC
Authors: Takeuti M. , Noda S. , Abe F. , Bond I.A. , Dodd R.J. , Hearnshaw J.B. , Honda M. , Honma M. , Jugaku J. , Kan-ya Y. , Kato Y. , Kilmartin P.M. , Matsubara Y. , Masuda K. , Muraki Y. , Nakamura T. , Ohnishi K. , Reid M. , Rattenbury N.J. , Saito To. , Saito Y. , Sato H. , Sekiguchi M. , Skuljan J. , Sullivan D.J. , Sumi T. , Yamada R. , Yanagisawa T. , Yock P.C.M. , Yoshizawa M. 
Published: July 2016

AbstractMore than 4000 stars observed in both MOA and DENIS projects showing periodic or quasi-periodic light curves are studied. Almost all Mira stars are located on the classical period-luminosity relation, and the multiplicity of the period-luminosity relation is confirmed for small-amplitude stars. The colour-magnitude diagrams based on the MOA red band, Rm, and Ks constructed for the sequences, form a single strip with small successive shifts.
Spectroscopic and photometric properties of red stars in the bar of the Large Magellanic Cloud
Authors: Evans Tom Lloyd 
Published: July 2016

AbstractSpectroscopy and variability studies of red stars in the Bar of the LMC enable the stars to be classed as spectral type M, S or C and as variables of class L, SR or Mira. The results are compared with data for Magellanic Cloud star clusters and for the galactic field. The number of S stars relative to carbon stars is generally high in comparison to theoretical expectation.
Cepheid Masses: FUSE Observations of S Mus
Authors: Evans Nancy Remage , Massa Derck , Fullerton Alexander , Sonneborn George , Iping Rosina 
Published: July 2016

AbstractS Mus is the Cepheid with the hottest known companion. As a benefit, the large ultraviolet flux made it the only Cepheid companion for which the velocity amplitude could be measured with the echelle mode of the HST GHRS. Unfortunately, the high temperature is difficult to constrain at wavelengths longer than 1200 Å because of the degeneracy between temperature and reddening. We have now obtained a FUSE spectrum in order to determine the temperature of the companion better. We have identified two regions which are temperature sensitive near 16 000 K, but are relatively unaffected by H2 absorption (940 Å, and the Ly β wings). By comparing S Mus B with other FUSE spectra, we have determined a temperature of 17 000 K. The resultant Cepheid mass is 6.0 ± 0.4 M⊙
The Be star omicron Cassiopeiae
Authors: Koubský Pavel , Ak Hasan , Harmanec Petr , Yang Stephenson , Božić Hrvoje 
Published: July 2016

AbstractThe analysis of radial velocities (RVs) of the Be star ο Cas from 27 high S/N spectra allowed us to revive the binary nature of this star, first suggested by Abt & Levy (1978, “AL”), but later refuted by several authors. The period search in our RV data based on measurements of Hα emission and He I λ6678 Å absorption profiles detected a dominant peak close to the 1033-d period found by AL. The resulting curves are very smooth. The rms error of the solution for the emission RVs is nearly 5 times lower than the scatter of the solution by AL. If the RV variations are due to orbital motion, then ο Cas turns out to be a challenging system with an unseen secondary component with mass comparable to, or even more massive than the primary.
High resolution spectroscopy of the triple system 20 Leo
Authors: Frémat Y. , Lampens P. , Hensberge H. , Arentoft T. , De Cat P. , Garrido R. , Parrao L. , Peña J.H. , Mathias P. , Van Cauteren P. 
Published: July 2016

Abstract20 Leo is a spectroscopic triple system composed of 3 very similar stars, one of which seems to be aδSct star. Observations at high spectral and high time resolution have been obtained at the Observatoire de Haute Provence with the ELODIE spectrograph on the 1.9-m telescope. The spectra were taken during 7 nights in 2003 January and cover the whole optical domain from 3900 to 6800 Å. We used a Fourier transform technique recently developed by P. Hadrava to disentangle the combined spectrum. Application of the method allows the derivation of radial velocities at all orbital phases (even at phases of complete blending), as well as individual spectra for each component. From these computations we deduced more accurate individual radial velocities and improved orbital parameters describing the motion of the inner binary. Model atmospheres were used to analyze each individual spectrum and determine stellar fundamental parameters of the three components such as effective temperature, surface gravity and projected rotation velocity.
Determining The Metallicity of Cepheid Stars in The SMC, LMC and The Galaxy
Authors: Mottini Marta , Primas Francesca , Romaniello Martino , Groenewegen Martin 
Published: July 2016

AbstractThe Cepheid Period-Luminosity relation is unquestionably one of the most powerful tools at our disposal for determining the extragalactic distance scale. While significant progress has been made in the past few years towards its understanding and characterisation, both on the observational (e.g. the HST Key Project) and theoretical (e.g. non-linear pulsation models, non-LTE atmospheres etc.) sides, the debate on the influence that chemical composition may have on the Period-Luminosity relation is still unsettled. Current estimates lead to differences in the distance as large as 15%, effectively limiting the accuracy of Cepheids as distance indicators. To further tackle this problem, we have obtained high resolution spectra of a large sample of Cepheids in our Galaxy and the Magellanic Clouds. The superb quality of the data allow us to probe the detailed effects of chemical composition (alpha, iron-group, and heavy elements) over more than a factor of ten in metallicity. Here, we present the first preliminary results of the analysis of iron abundances in a sub-sample of Cepheids.
Application of The Riccati Method to The Adiabatic Oscillations of Stars
Authors: Takata M. , Löffler W. 
Published: July 2016

AbstractThe eigenmodes of the adiabatic oscillations of stars are usually calculated numerically by solving the system of the four linear first-order differential equations using either the relaxation method or the shooting method. Finding some shortcomings in these conventional methods, we adopt another method, namely the Riccati method, in which it is not the system of the linear differential equations but the nonlinear matrix Riccati equation that is solved numerically. After describing the method, we discuss its advantages and give some demonstrations.
Evolutionary Properties of Intermediate-Mass Stars
Authors: Cassisi Santi 
Published: July 2016

AbstractWe briefly review the main problems related to the computation of the evolution of intermediate-mass stars: the treatment of turbulent convection and the occurrence of blue loops during the core He-burning phase. It is shown that, in order to obtain more accurate and reliable stellar models for this class of stars, one has to consider all possible theoretical and observational constraints. These include observations of low-mass stars to constrain the treatment of envelope convection, and the analysis of the pulsational behaviour of Cepheid stars.
The Luminosities of Horizontal Branches and RR Lyrae Stars in Globular Clusters
Authors: McNamara D.H. , Rose M.B. , Brown P.J. , Ketcheson D.I. , Maxwell J.E. , Smith K.M. , Wooley R.C. 
Published: July 2016

AbstractWe have utilized the latest stellar models of the Y2 (Yonsei-Yale) collaborators and color-magnitude diagrams of globular clusters to infer ages and absolute magnitudes of their horizontal branches (HB). The intrinsic (B – V) color indices of the turn-offs, of the globular clusters were used to find ages. For 47 clusters that appear to be coeval (within ±0.7 Gyr), we find an average age of 12.5 Gyr. We adopt this age and infer the absolute magnitudes of the turn-offs, from the clusters [Fe/H] values. The absolute magnitude of the horizontal branches or RR Lyrae stars are then determined from the difference between the apparent magnitudes of the horizontal branches (or RR Lyrae stars) and the apparent magnitude of the turn-offs, VTO. We conclude: 1) The slope of the MV(HB), [Fe/H] relation is ~0.3 for clusters with [Fe/H] values between —0.5 to —1.5. The relation has zero slope for [Fe/H] values smaller than −1.5. 2) For [Fe/H] < -1.3, the MV(HB) or MV values of RRLyrae stars are not only a function of [Fe/H], but the horizontal-branch type in the sense that the clusters with the blue horizontal branches have more luminous horizontal branches than clusters with red horizontal branches. The same results are found by inferring the luminosities of the HBs from pulsating blue stragglers.
Magellanic Cloud novae and the peak magnitude vs rate-of-decline relationship
Authors: Liller William , Yumi Shida Raquel 
Published: July 2016

AbstractStudying classical novae in the Magellanic Clouds has at least three huge advantages: (1) their distances are well-known; (2) the interstellar extinction is small and reasonably well known; and (3) an abundance of novae (47 as of 2003 September 15) have been discovered in the two clouds. Consequently, we will investigate in this paper one of the most important characteristics of novae: the relationship between the absolute magnitudes of the nova outbursts at maximum brightness and their rate of decline, often referred to as the MMRD.
Magnetic Models Can Not Explain The Blazhko Effect in RR Lyrae Stars
Authors: Chadid M. , Shorlin S.L.S. , Landstreet J.D. 
Published: July 2016

AbstractWe report a new series of high-precision Stokes V profiles and longitudinal magnetic field measurements of RR Lyrae, obtained with the MuSiCoS spectropolarimeter over a period of four years. These data provide no evidence whatsoever for a strong magnetic field in the photosphere of RRLyrae, which is consistent with Preston’s (1967) results, but inconsistent with apparent magnetic field detections by Babcock (1958) and Romanov et al. (1987, 1994). Following discussion of these disparate results, we conclude that RR Lyrae is a bona fide non-magnetic star, a conclusion which leads to the general falsification of models of the Blazkho effect requiring strong photospheric magnetic fields.
Dynamical Phasing of Type II Cepheids
Authors: McSaveney J.A. , Pollard K.R. , Cottrell P.L. 
Published: July 2016

AbstractBy phasing using the minimum of the acceleration curve of a selection of Type II Cepheids of a range of periods, a clearer understanding of the pulsational dynamics of the stars is obtained. BVRI photometry and a selection of metallic line velocities and Hα equivalent widths are presented using this phasing.
Asteroseismology with COROT
Authors: Vauclair Gérard , Catala Claude , Baglin Annie , Auvergne Michel , Michel Eric 
Published: July 2016

AbstractThe COROT project has been developed in the framework of the CNES small satellite programme, with European and Brazilian cooperation. It will be launched in 2006. It is dedicated to seismology and detection of telluric planets. It will perform relative broad-band photometry in visible light during very long (150 d) observing runs in the same direction, plus a number of short (10-20 d) observing runs. Both programmes will work simultaneously on the same region of the sky. The seismology programme aims to map the HR diagram and study in detail approximately 50 targets brighter than magnitude 9. The exoplanet programme will search for telluric planets slightly larger than the Earth orbiting around stars of magnitude 12 to 16, located in the habitable zone and closer. The data collected will also allow valuable seismic studies. A number of additional scientific programmes will also be conducted. The mission characteristics derived from the scientific objectives, the instrument and its performances for seismology, as well as preliminary observing plans, are presented.
Horizontal Branch Evolution
Authors: Rood R.T. , Crocker D.A. 
Published: July 2016

AbstractIn 1973 the outstanding problems confronting the theory of horizontal branch evolution were the “second parameter” problem and the Oosterhoff Effect. Despite significant progress, particularly in the observations and in the observation/theory interface, they remain as the outstanding problems of 1988. The Oosterhoff Effect is now discussed primarily in the guise of the Sandage Period Shift Effect. The morphology of the HB seems more complicated than ever. E.g., many clusters show bimodal distributions along the HB. Here we will tentatively consider those to be manifestations of the second parameter problem. We will indicate why we feel that all previously suggested solutions have all been chimeras.
On the Irregular Light Variation of the RV Tau Star R Scuti
Authors: Kollath Z. , Kovacs G. 
Published: July 2016

AbstractThe nature of irregular light variation in giants and supergiants has long been a matter of dispute. Our lack of understanding has two main sources: (i) a paucity of long, continuous, high quality observations and thorough analysis of the available data and (ii) until very recently, a lack of systematic nonlinear hydrodynamic studies for these stars.
RR Lyrae Stars and the Sandage Period-Shift Effect Examined Using IR-Derived Temperatures
Authors: Longmore A.J. , Dixon R. , Skillen I. , Jameson R.F. , Fernley J.A. 
Published: July 2016

AbstractMean temperatures for RR Lyrae stars in 7 globular clusters (M3, M4, M5, M15, M107, ω Cen and NGC 5466) have been determined using the optical-infrared colour <V>-<K> as a temperature indicator. Where <K> has been relatively well determined, from means of 3 or more observations, the scatter in relationships such as Log P’ vs log (temperature) and log (temperature) vs (blue amplitude) is significantly reduced when IR-derived temperatures are used instead of those derived from (B-V). Within the observational errors, the gradient in the log P’ vs log (temperature) diagram is the same for each cluster. Temperatures derived from <V>-<K> should also be less sensitive to metallicity differences than their optically derived counterparts. The Sandage Period-Shift Effect has therefore been re-examined using 6 of the 7 clusters (NGC 5466 was excluded because of too few data). A strong correlation between period-shift and metallicity is found; a smaller shift (but in the same sense) is also found for the temperature – amplitude relationship.
Pulsation of α Cir (HD 128898)
Authors: Weiss Werner W. , Schneider Hartmut 
Published: July 2016

AbstractThe group of pulsating CP2-stars (also called “rapidly oscillating Ap stars” provides asteroseismology with oscillation spectra of high accuracy. The potential as a diagnostic tool for modelling stellar interiors is widely appreciated. The identification of pulsation modes is important for such an analysis. However, this is rarely possible in an unambiguous manner. To improve the situation and to make use of additional information, we observed HD 128898 simultaneously spectroscopically and photometrically at ESO. For each of our individual CAT-CES spectra (1 minute integration time) it was thus possible to determine the pulsation phase at mid-exposure. A total of 887 spectra (R = 50000) were binned according to their pulsation phase and coadded to improve significantly the signal to noise ratio.
Features in the Soft X-ray Background
Authors: Rothenflug R. 
Published: July 2016

AbstractThe soft X-ray background is explained in terms of emission coming from hot gas. Most of these soft X-ray data were obtained by proportional counters with a poor energy resolution. Instruments having the capability to resolve lines were only flown by two groups: a GSPC by a Japanese group and a SSD by a french-american collaboration. They both detected the 0 VII line emission coming from the soft X-ray background and so proved the thermal nature of the emission. The implications of these results on possible models for the local hot medium will be discussed. The same detectors observed part of the North Polar Spur. They detected emission lines coming from different species (0 VII,Fe XVII,Ne IX). Spatial variations of line ratios for this object could be due to non-equilibrium ionization effects.
Theory of Accretion Disk Coronae
Authors: Kallman T. R. 
Published: July 2016

AbstractAccretion disk coronae are likely to be the dominant site for X-ray absorption and reprocessed emission in low mass X-ray binaries, and may be present in other classes of compact X-ray sources such as active galactic nuclei and cataclysmic variables. In spite of this fact, and in spite of the observational evidence for their existence, there remain many uncertainties about the structure of accretion disk coronae. This paper will discuss the coronal structure and dynamics, their X-ray spectral signatures including coupling to the variability behavior of compact X-ray sources, and the major unsolved theoretical issues surrounding them.
X-ray Absorption by Ionized Gas in EXOSAT Spectra from the Binary System 4U1700-37/HD153919
Authors: Haberl F. , Kallman T.R. , White N.E. 
Published: July 2016

AbstractWe observed the 3.41 day eclipsing, massive binary system 4U1700-37/HD153919 with EXOSAT for more than one complete binary period to investigate the spectral variations during the orbital cycle of the neutron star. The spectra show a low energy excess below ~ 3 keV when modelled by a powerlaw spectrum attenuated by photoelectric absorption by neutral gas, suggesting partial ionization of the absorbing gas. The column density derived from spectra above 3 keV shows an asymmetric distribution around orbital phase 0.5 with higher absorption before eclipse ingress. We approximated the with distance to the X-ray source gradually decreasing ionization of the wind by two zones. One of higher ionized wind around the X-ray source for which X-ray opacities of a gas in photoionization equilibrium were used and a zone of neutral gas further away from the X-ray source. We find that our spectra below 3 keV can be well fitted by a powerlaw which is attenuated first by photoelectric absorption of ionized gas and then by neutral gas. Since around phase 0.5 the major contribution of the wind column density along the line of sight arises from the ionized part we found that the total column density can be higher up to a factor of about 4 taking ionization into account.
The Evolution of Cooling Flow and the Mass Deposition Process
Authors: Hattori Makoto , Habe Asao 
Published: July 2016

AbstractWe perform the numerical hydrodynamical calculation of cluster cooling flow including the mass deposition process and examine evolution of cooling flow. We take two mass deposition models. In one model, mass deposition occurs in large extent. In other model, mass deposition occurs only in central region. In any model, diagnostics of X-ray surface brightness do not agree with observation in any evolutional phases.