bluuebunny/crossref_metadata_2025 huggingface dataset:
Speckle Observations of Binary Stars with the MAMA Detector
Authors: Horch E. , Morgan J.S. , Giaretta G. , Timothy John G. , Kasle D.B.
Published: July 2016

We have made two sets of speckle observations of binary stars with the Multi-Anode Microchannel Array (MAMA) detector. Our observing system is a true photon counting imaging device which records the arrival time of every detected photon. We present speckle autocorrelation analyses of five binary systems, two observed with the 3.6-m telescope at the European Southern Observatory and three observed with the 40-in reflector at Lick Observatory. These five systems represent a wide variation in separation and magnitude difference that indicate that the MAMA detector is capable of recording high quality speckle data at extremely low count rates and can recover image features very near the diffraction limit of the telescope. In one case, only 10 photons per frame were recorded for the dim companion of the system, and in another case, a separation of 0″.157±0″.031 was derived for a system observed with the 40-in telescope where the diffraction limit is about 0″.125. Future prospects for this system are discussed.
Towards a Comprehensive View of Binary and Multiple Systems
Authors: Batten Alan H.
Published: July 2016

First, I wish to express my appreciation of the honour implied by the dedication to me of the proceedings of this Colloquium. It is, of course, gratifying that colleagues should wish to make such a gesture, but I can think of many others in the field, many participants in this meeting, who are at least as worthy of a similar honour. I can only be grateful that the Scientific Organizing Committee chose me. I would also like to thank both it and the Local Organizing Committee, on your behalf as well as my own, for all the hard work that has made this Colloquium possible. I know enough of organizing meetings to guess at what has been involved in making this one run so smoothly. I have organized both IAU Colloquia and a meeting of the AAS, but I have never tried to do the two within three months of each other, as our hosts have done on this occasion!
The Homogeneity of the UBV(RI)C System
Authors: Menzies J W
Published: July 2016

There are two large sets of high precision standard star photometry which claim to represent the UBV(RI)c system, one in the E regions in the south established by Cousins and one at the equator due to Landolt. There appear to be systematic differences between them. Astrophysical interpretations which depend on photometric data may in consequence depend on which set of standards was used.
Irriducible Elements of Quality in High-Precision Photometry
Authors: Sterken C.
Published: July 2016

A consise overview of the errors related to transformations of data from one photometric system to another is given.
Accuracy in variable star work: The three-star single-channel technique
Authors: Breger Michel
Published: July 2016

The three-star technique for photoelectric photometers is discussed. The technique is used to study millimag variations of variable stars with periods in the range of 30 minutes to a few days. It is emphasized that for highest precision two comparison stars should be used and observed as often as the variable star. The different types of numbers used to express the precision of measurement are discussed together with possible misinterpretations.

Finally, the successful use of an extinction coefficient derived from differential extinction between the three stars is illustrated with measurements showing an extreme amount of instrumental sensitivity drift.
Photometry with Infrared Arrays
Authors: Glass I.S.
Published: July 2016

Infrared arrays have been in use at a number of observatories for several years. They are more complicated in their construction than optical ones and more problems arise in obtaining good photometry from them. The types of arrays currently available are described together with the observational techniques and the problems encountered in obtaining accurate photometric results.
An Intimate Relation with Two Automatic Telescopes for Almost Nine Years
Authors: Hall Douglas S. , Henry Gregory W.
Published: July 2016

From Oct. 1983 through Dec. 1987 most of the observing capacity of the Boyd-Genet prototype 10-inch APT was devoted to a program of 92 variable stars the output of which was sent to us for analysis. From Nov. 1987 through the present the entire observing capacity of the VU-TSU 16-inch APT has been devoted to a program of 136 mostly magnetically active variables. We review the technical performance of both APTs in terms of malfunctions, down-time, resulting photometric accuracy, phase coverage, and scientific results to date.
High-Precision Photometry with CCDSs on Small Telescopes
Authors: Zeilik Michael
Published: July 2016

From the theory of CCD operation and our experience since 1986 with a Photometries CCD camera, we provide practical suggestions for achieving high-precision photometry on a small telescope (61-cm).
SNIa Diversity: Theory and Diagnostics
Authors: Canal R. , Ruiz-Lapuente P.
Published: July 2016

Existing evidence of photometric and spectroscopic diversity among Type la supernovae is compared with the predictions from physical modeling of the explosions. Concerning light curves, changes in the central ignition density of massive (M ≃ Mch) C+O white dwarfs alone do not give appreciable variation. Spectroscopic diversity has been found in the nebular phase, the underluminous SN 1991bg providing an extreme case. A range of 0.4-0.8 Mʘ of 56Ni synthesized in the explosions is derived from the nebular spectra of a sample of SNe la. For SN 1991bg, however, a 56Ni mass of ∼ 0.1 Mʘ only is obtained. That leads us to explore models based on the detonation of low-mass WDs for this SN. Additionally, a nebular spectrum of SN 1991bg shows narrow Hα emission at the position of the SN. If this emission is confirmed against background contamination from the galaxy, it would be first evidence of a nondegenerate, H-rich companion in a SNIa.
Dynamics of Type-II Supernovae
Authors: Janka H.-Th. , Müller E. M.
Published: July 2016

Hydrodynamical simulations of type-II supernovae in one and two dimensions are performed for the revival phase of the delayed shock by neutrino energy deposition. Starting with a post-collapse model of the 1.31 Mʘ iron core of a 15 Mʘ star immediately after the stagnation of the prompt shock about 10 ms after core bounce, the models are followed for several hundred milliseconds with varied neutrino fluxes from the neutrino sphere. The variation of the neutrino luminosities is motivated by the considerable increase of the neutrino emission due to convective processes inside and close to the neutrino sphere (see Janka 1993), which are driven by negative gradients of entropy and electron concentration left behind by the prompt shock (Burrows & Fryxell 1992, Janka & Müller 1992). The size of this luminosity increase remains to be quantitatively analyzed yet and may require multi-dimensional neutrino transport. However, in the presented simulations the region below the neutrino sphere is cut out and replaced by an inner boundary condition, so that the convective zone is only partially included and the neutrino flows are treated as a freely changeable energy source.

For small neutrino luminosities the energy transfer to the matter is insufficient to revive the stalled shock. However, there is a sharp transition to successful explosions, when the neutrino luminosities lie above some ‘threshold value’. Once the shock is driven out and the density and temperature of the matter between neutrino sphere and shock start to decrease during the expansion, suitable conditions for further neutrino energy deposition are maintained, and an explosion results. With the neutrino energy deposition the entropy per nucleon in the region between neutrino sphere and shock grows, and convective overturn will set in. Multi-dimensional simulations show that due to the large pressure scale height a large-scale pattern of up-flows and down-flows with velocities close to the local speed of sound develops. Consequently, cold, postshock material is advected down into the neutrino heating layer close to the neutrino sphere and hot material is transported outwards, thus reducing energy losses by re-emission of neutrinos and increasing the pressure behind the shock. Therefore these convective processes are found to be a very important aid to the delayed supernova explosion. In fact, two-dimensional models explode even in cases where spherically symmetrical computations fail.
Progenitors and Hydrodynamics of Type II and lb Supernovae
Authors: Woosley S. E. , Weaver T. A. , Eastman R. G.
Published: July 2016

We review critical physics affecting the observational characteristics of those supernovae that occur in massive stars. Particular emphasis is given to 1) how mass loss, either to a binary companion or by a radiatively driven wind, affects the type and light curve of the supernova, and 2) the interaction of the outgoing supernova shock with regions of increasing pr3 in the stellar mantle. One conclusion is that Type II-L supernovae may occur in mass exchanging binaries very similar to the one that produced SN 1993J, but with slightly larger initial separations and residual hydrogen envelopes (∼1 Mʘ and radius ∼ several AU). The shock interaction, on the other hand, has important implications for the formation of black holes in explosions that are, near peak light, observationally indistinguishable from ordinary Type II-p and lb supernovae.
Statistical Analysis of Supernovae and the Progenitors of SN lb and SN Ic
Authors: Li Zongwei
Published: July 2016

We review the fundamental classification scheme and statistical analysis of supernovae, emphasizing recently introduced subtypes, SN1987K, and SN1993J. Type Ib/Ic and Type II supernovae are of interest for starburst galaxies. We discuss possible progenitors of SNIb and SN Ic, and the possibility that they may be Wolf-Rayet stars.
SN 1987A: Observations at Later Phases
Authors: Bouchet P. , Danziger I. J. , Gouiffes C. , Della Valle M. , Moneti A.
Published: July 2016

The last observations (until April 1993) of SN 1987A made at ESO, La Silla, are presented. Our data show that: (i) the criterion of line shifts proves that dust is still present and is absorbing more strongly than ever; (ii) the I magnitude decreases faster than the other ones after day ∼1700; (iii) the 1.3mm flux is constant at about 9mJy, and comes most probably from free-free emission produced by the cooling of the former star envelope still weakly ionized. Previous analyses of the bolometric light curve until day 1444 are briefly reviewed. In spite of the large uncertainties, the flattening of the light curve, observed after day ∼900, extends until our latest data points (day 2172). This can be explained by theoretical models including time-dependent effects due to long recombination and cooling times (Fransson and Kozma 1993). However, one cannot rule out the presence of a compact object such as a neutron star, radiating as a pulsar or accreting matter from a disk either continuously or intermittently.
Freeze out, IR-catastrophes and Non-thermal Emission in SNe
Authors: Fransson Claes , Houck John , Kozma Cecilia
Published: July 2016

Freeze out effects and the IR-catastrophe are discussed for SN 1987A and for Type la SNe. We show that the light curves of the optical lines in SN 1987A provide strong evidence for the IR-catastrophe. We also argue that most optical lines are dominated by non-thermal excitation after ∼ 800 days. The level of this emission is set mainly by the total mass of the elements. Models of the [OI]λλ6300 — 64 light curve show that an oxygen mass of ∼ 1.5Mʘ is needed. Light curve models for Type la SNe display a sharp decrease in the optical flux as a result of the IR-catastrophe at ∼ 500 days, producing UBV-photometry inconsistent with observations of SN1972E by Kirshner & Oke (1975).
Radio Emission from SN 1987A
Authors: Staveley-Smith L. , Manchester R. N. , Tzioumis A. K. , Reynolds J. E. , Briggs D. S.
Published: July 2016

We review the first six years of radio observations of Supernova 1987A. The evolution can be divided into two phases: the initial radio outburst which lasted a few weeks, and the period from mid-1990 to the present, during which the radio emission has steadily increased. Both phases can be explained by a small fraction (0.1-0.5%) of the post-shock thermal energy being converted to energy in relativistic particles and magnetic fields, which give rise to synchrotron radiation. The optical depths, densities and density profiles for the pre-shocked circumstellar material are somewhat different for the two phases, but consistent with models of the density structure of the material within the circumstellar ring. New high-resolution radio observations show that the SN shock front is already at about three-quarters of the radius of the circumstellar ring, and that there exists a bright equatorial component of emission aligned with this ring which is probably due to a polar density gradient in the ‘hourglass’ structure.
The Distribution of Supernova Remnants in the Galaxy
Authors: Green D.A.
Published: July 2016

Observational selection effects and the lack of accurate distances for most Galactic SNRs pose problems for studies of the distribution of SNRs in the Galaxy. However, by comparing the observed Galactic longitude distribution of high surface brightness SNRs with that expected from simple models — which avoids some of the problems with selection effects and the lack of distances — a Gaussian scale length of ≈ 7 kpc in Galactocentric radius is obtained for SNRs.
Far-Ultraviolet Observations of Supernova Remnants
Authors: Blair William P.
Published: July 2016

New observations of supernova remnants in the far ultraviolet, especially in the sub-Ly α region, are changing the way we look at the interaction between blast waves and the interstellar medium. I briefly review some of the recent FUV observations of supernova remnants from the Hopkins Ultraviolet Telescope, the Voyager Ultraviolet Spectrometers, as well as IUE and HST.
The Hertzsprung Multiple Exposure Technique and its Application to 61 Cygni
Authors: Josties F. J.
Published: July 2016

E. Hertzsprung developed the multiple exposure technique for observing double stars photographically around 1914 at Potsdam (Hertzsprung, 1920). The technique consists in taking one or more rows of 17 to 35 exposures of a small field which normally includes only the double star itself. The total number of exposures on a plate can vary from 17 to 140, depending primarily on the separation of the double star and the anticipated systematic effects in the observational system. An important feature of the technique is the use of objective gratings to substantially reduce the problem of magnitude error. The large number of exposures serve to reduce the random error, while the objective gratings, together with other innovations introduced by Hertzsprung, help to minimize the systematic errors. In this way Hertzsprung provided us with an observational technique of considerably higher accuracy than the traditional visual micrometer work.
Detection of Double Stars with the Two-Color Refractometer
Authors: Christy James W. , Wellnitz Dennis D. , Currie Douglas G.
Published: July 2016

Attempts to detect double stars are being made with the Two-Color Refractometer (TCR). The refractometer is an instrument developed by the Quantum Electronics Group of the University of Maryland to measure atmospheric refraction.

During check-out observations using the U.S. Naval Observatory’s (USNO’s) 24“ reflecting telescope, the refractometer is being used to detect the astrometric separation of the ultraviolet and red photocenters of the combined light from a double star, differentially referenced to nearby stars. The refractometer contains two dispersive wedges which null the incoming dispersion; the positions of the wedges then provide a measure of the dispersion of the incoming light. The angular part of this measure immediately gives the position angle of the double. The angular distance between the two components of the pair is a combined function of the measured quantity and of the magnitude and color differences of the components of the double star, and is therefore obtainable only with additional information.
Review of the Occultation Technique for the Study of Binaries
Authors: White Nathaniel M.
Published: July 2016

The systematic search for stellar multiplicity by observations of lunar occultations began in 1969. David Evans will review a large portion of the data collected since then in the second paper of this session. Here we will outline the historical development of the technique and comment on its limitations, contributions to double star research, and future improvements.

Sir John Herschel (1865) may have been the first to suggest that “a double star, too close to be seen divided with any telescope, may yet be detected to be double by the mode of its disappearance.” However, the visual discovery of duplicity by occultation is not sufficient, for the observations are not subject to analysis after the fact. The power of the occultation technique was realized more than 100 years after the suggestion, with the application of photomultipliers and electronic digital data handling. Whitford (1939) took the first step in using a cesium photo tube, oscilloscope, and moving film to record the occultations of Beta Capricorni and Upsilon Aquarii. The resolution of the spectroscopic binary Beta Capricorni was discussed, but he concluded his data were not able to resolve it, an observation which was later accomplished at several observatories and summarized by Evans and Fekel (1979).
Radial Velocity Observations of Binary Stars
Authors: Scarfe C. D.
Published: July 2016

This review considers three main areas, leaving several others to be discussed in more detail in the contributed papers of this session.

1.

The need for spectrographs and measuring instruments of great stability for long-term projects such as radial velocity observations of visual binary stars.

2.

The use of cross-correlation devices, both analog (radial velocity scanners) and digital, for radial velocity measurement.

3.

The use of comparison spectra impressed directly onto the starlight and of polarisation instruments as means to very precise radial velocities.
Spectral Classification of Composite Spectrum Stars
Authors: Schmidtke Paul C.
Published: July 2016

Classifying the spectral types of individual components of composite spectrum stars can be a difficult task. Markowitz (1969) discussed the problems of blended and veiled lines associated with the visual assessment of blue spectrograms. Although synthetic spectra (i.e. formed by the intentional superposition of two different spectra) can be used as a means of calibration, the classification of composites with slit spectrograms is a subjective process. Classifications based upon broad- and intermediate-band photometry (Young 1971) can be highly objective, but the lack of spectral resolution introduces other complications. For example, colors in the UBVR system measure the gross behavior of a star's energy distribution. Results based upon this information are not only affected by interstellar reddening but also are incapable of identifying common spectral peculiarities. The use of spectrophotometric indices (Beavers and Cook 1980) avoids the major difficulties of other techniques. The results are not influenced by the veiling or blending of lines, nor are the results influenced by interstellar reddening. If a sufficient number of features are observed, common types of spectral peculiarities can be identified.
Present and Past Space Programs
Authors: Rakos Karl D.
Published: July 2016

The increase in accuracy of astrometric results has been very limited in the last half century, and improvements of more than about a factor of 3 at best for ground-based observations are not expected for the next two decades. This is largely due to well known error-sources connected with the Earth atmosphere. By moving the observing equipment to a platform aboard a satellite many of these errors would disappear completely, or to a large extent. Unfortunately till now no space astrometric project has been realised. Consequently there are no astrometric observations of visual binary stars from space. Of course, the astrophysical parameters of double stars are as important as their astrometric data. A large number of double stars has been observed from space by measuring their radiation and spectra in different wavelengths regions not attainable from ground based telescopes. A good example is HZ Hercules (Her X-1).
Astrometry with the Space Telescope Wide-Field/Planetary Camera
Authors: Baum W. A.
Published: July 2016

Although the Space Telescope Wide-Field/Planetary Camera is not primarily an astrometric instrument, it is expected to have some astrometric capability. Moreover, one of its possible astrometric applications is of unusually high scientific importance, namely, an attempt to detect the presence of planets around nearby stars. Let me therefore adopt that application as an example for discussing the anticipated astrometric performance of the camera system. It will be expeditious to make use of some diagrams that I have presented previously elsewhere, so part of the story may sound familiar (Baum 1979a, 1979b, 1980a, 1980b; Baum, Thomsen, and Kreidl 1981).
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

We 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

Cepheid 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

The 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

We 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

Masers 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.
AGB stars in the Magellanic Clouds and in other members of the Local Group
Authors: Cioni Maria-Rosa L.
Published: July 2016

Results obtained in the Magellanic Clouds using the latest near-IR DENIS survey are briefly reviewed. This sets the stage for a similar study of AGB stars in other galaxies in the Local Group and, in particular, in NGC 6822.
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

We 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.
AGB variables as distance indicators
Authors: Feast Michael
Published: July 2016

Evidence for the existence of Mira Period-Luminosity relations is reviewed including recent work on Miras with thick circumstellar shells. The calibration of the relation at K is discussed in detail. The nature of variables deviating from the PL relation and possible metallicity effects are also discussed.
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

More 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

Spectroscopy 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

S 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

The 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

20 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

The 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

The 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

We 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

We 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

Studying 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

We 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

By 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

The 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

In 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

The 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

Mean 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 - as a temperature indicator. Where  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 - 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

The 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

The 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

Accretion 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

We 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

We 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.
JET-X A Joint European X-ray Telescope for SPECTRUM-X
Authors: Wells A. , Lumb D.H. , Pounds K.A. , Stewart G.C. , Aschenbach B. , Brauninger H. , Hasinger G. , Trumper J. , Citterio O. , Scarsi L. , Peacock A. , Taylor B.
Published: July 2016

The Joint European X-Ray Telescope, JET-X, is one of the core instruments of the scientific payload of the USSR SPECTRUM-X astrophysics mission due for launch in 1993. The JET-X instrument concept is described and its scientific performance and capability discussed.
Thermal Detectors for X-ray Astronomy
Authors: Holt Stephen S.
Published: July 2016

Spectroscopy is traditionally characterized by the sacrifice of quantum efficiency for high spectral resolution. Since X-ray astronomy is a photon-limited discipline, the choice between high resolution for very few sources versus much lower resolution for many more has not always been an easy one. The development of new thermal detectors offers the opportunity to “have one’s cake and eat it, too.”