bluuebunny/crossref_metadata_2025 huggingface dataset:
Environmental Effects in the Stellar Populations of Elliptical Galaxies
Authors: Lucey J. R.
Published: June 2019

While early work successfully modelled the stellar population of elliptical galaxies as old, single-age, metal-rich systems, there is evidence that a small amount of recent (i.e. a few Gyrs ago) star formation has occurred in some nearby ellipticals (O'Connell, 1980; Rose, 1985; Pickles, 1985; Bica, 1988). Elliptical galaxies reside in environments ranging from the dense cores of rich clusters to isolated field regions. It has long been suggested that the global properties of ellipticals depend on environment. For example, McClure and Van den Bergh (1968) noted apparent differences in the 380-450nm colours between a set of cluster ellipticals and three from the field. Recent work has tended to support the view that the properties of ellipticals depend on environment (e.g. de Carvalho and Djorgovski, 1992). The most likely cause of these differences is the presence of a small amount of recent star formation in the field ellipticals. This environmental dependency may have important consequences for the use of ellipticals as distance indicators.
Supergiant Stars as Tracers of Galactic Chemical Composition
Authors: Ferro A Arellano , Parrao L , Mantegazza L
Published: June 2019

A photometric reddening-free calibration for [Fe/H] valid for giant and supergiant stars of intermediate temperature, has been obtained using the Strömgren uvbyß system. Galactic supergiants, supergiants in Magellanic Clouds and galactic metal deficient red giants with spectroscopic determinations of [Fe/H] were used as calibrators. The calibration can be used to predict [Fe/H] with an accuracy of 0.33 dex and shows the potential of supergiant stars as tracers of iron abundances in other galaxies.
Colours and Teff of Main Sequence Stars Covering the Galactic Metallicity Range
Authors: Alonso A. , Arribas S. , Martínez-Roger C.
Published: June 2019

We present the results of a general programme aimed to study the effects of metallicity on the temperature scale of late main sequence stars (F0-K5). A sample of approximately 400 stars with published UBV(RI) and ubvy – β photometry has been collected from the literature. A three years campaign of observations (Alonso et al. 1994b) was carried out to obtain JHK photometry in order to apply the InfraRed Flux Method (IRFM) to derive effective temperatures. The effect of metallicity on Colour-Colour IR diagrams is discussed. The absolute flux calibration in the IR was revised in Alonso et al. (1994a). The effect of metallicity on the bolometric correction has been studied in Alonso et al. (1995) in order to derive bolometric fluxes. The temperatures have been derived by applying the IRFM using new Kurucz models. Teff = f(Colours, [Fe/H], log(g)) relations are obtained for dwarfs covering the ranges 4000K ≤ Teff ≤ 8000K, 3.5 ≤ logg ≤ 5.00, +0.5 ≤ [Fe/H] ≤ −3.00 which expands considerably the database of previous works. These relations are used to check atmosphere models through the analysis of UBV RIJH Kubvy – β synthetic photometry in combination with the IRFM. The transformation from the theoretical HR diagram into an observational one is analyzed with the new relations. The influence of these points on the study of the evolution of the Galaxy is briefly discussed.
Binaries in the Universe. Dynamical Mechanisms of Formation and Evolution of Different Kinds of Constituents of the Universe
Authors: Anosova J. , Tanikawa K. , Funato Y.
Published: June 2019

We study the dynamics of extended shells of relatively low-mass particles around and inside the orbit of two heavy centres of gravity (a binary) by computer simulations. The binary components are surrounded by N=16000 small mass particles in a uniform random distribution on a few spherical envelopes with different radii expanding with some velocity. Some shells are inside the orbit of the binary.
Isolated Binaries and Triples in N-body Systems
Authors: Anosova J. , Kiseleva L.
Published: June 2019

Stars show a marked tendency to form the systems of different multiplicity starting from the smallest systems as binary and triple stars up to clusters with a significantly larger number of objects (N ~ 107 for globular cluster s). Different investigators have used different methods of binary stars identificati on but modern observations give a frequency of binary and multiple stars in the Galactic field up to 70% Binary and multiple stars are also often present within star clusters. It is therefore very important to be able to identify such systems as rather isolated substructures in which the dynamical evolution is not significantly affected by other stars (at least, during some considerab le time interval).
BVRI CCD Photometry of IC 166
Authors: Outeiro M. Manteiga , Rodriguez J.R. Acarreta , Roger C. Martinez , Straniero O.
Published: June 2019

The first results of BVRI CCD photometry of the cluster IC 166, obtained at the new telescope IAC80 at the Observatorio del Teide (Tenerife, Spain) are presented. Using the Daophot crowded field photometric package, different color-magnitude diagrams were constructed and some cluster properties (reddening, distance and age) studied.
Emission-Line Stars in the Outer Part of the Orion Star-Forming Region
Authors: Wiramihardja Suhardja D , Nakano Makoto , Kogure Tomokazu
Published: June 2019

In a series of emission-line star survey programs we have conducted wide and deep survey observations for Hα emission stars in the Orion star-forming region. The first result for the Kiso area A-0904 (5°x5°, centered at α = 5h40m and δ = +0°) was presented in Paper I (Wiramihardja et al., 1989), followed by Paper II (Kogure et al., 1989) for the area A-0903 (α = 5h20m, δ = −5° and A-0976 (α = 5h40m, δ = −5°). In Paper IV the results for the areas A-1047 (α = 5h20m, δ = −10° and A-1048 (α = 5h40m, δ = −10°) are given.
Another Source of Local Missing Mass
Authors: Malkov O.Yu.
Published: June 2019

It is well-known that the velocities and distributions of stars perpendicular to the Galactic plane indicate the presence of unseen or missing mass in the local disk of the Milky Way. In spite of an abundance of papers on this subject, no consensus seems to have been reached on not only the amount of dark matter, but even on a “correct” method of analysis.
The Asymmetric Drift of the Thick Disk Population
Authors: Ojha Devendra , Robin Annie C. , Bienaymé Olivier
Published: June 2019

We investigate the kinematics of the thick disk population using photometric and astrometric sample surveys towards two opposite directions at intermediate latitude. A multivariate discriminant analysis (MDA) is used to distinguish the ‘Thick Disk’ from other populations with the help of the Besançon model of population synthesis. The data constrain the asymmetric drift of the thick disk population, which is found to be 40±10 km/s and does not depend on the galactic radius.
A New Sample of Thick Disk and Halo Stars
Authors: Soubiran C. , Perrin M.N. , Cayrel R. , Chereul E.
Published: June 2019

The aim of our stellar population study is to investigate the kinematical and chemical characteristics of the thin disk, thick disk and halo of the Galaxy. We have selected 51 stars in 2 astrometric and photometric surveys at l = 42°, b = +79° (Soubiran 1992) and l = 167°, b = +47° (Ojha et al. 1994), on the basis of the Reduced Proper Motion Diagram. They were observed with the 193cm telescope at Observatoire de Haute-Provence, with the CARELEC spectrograph (dispersion of 66Å/mm, FWHM of 3.0Å, range λλ4600 – 5500Å), together with 43 comparison stars with known fundamental parameters. The derivation of Teff, logg and [Fe/H] was done differentially using a grid of synthetic spectra and the comparison stars, as described in Cayrel et al. (1991). Twenty of the target stars were found to be more deficient than −0.5. In the (V, [Fe/H]) distribution, the halo stars are clearly separated from the other stars with a mean of (V, [Fe/H]) ≃ (−210km/s, – 1.4dex). Because of the small size of the sample, it was not possible to discriminate the thick disk from the thin disk. We have taken 200 more spectra, and with these new observations, we hope to be able to deconvolve the 3 populations in the (U, V, W, [Fe/H]) space as we did previously with the (U, V) velocity (Soubiran 1993).
The Thick Disc Population of the Galaxy
Authors: Robin A.C. , Haywood M. , Ojha D.K. , Bienaymé O. , Crézé M.
Published: June 2019

The availability of photometric and astrometric star counts on large fields well distributed in the Galaxy allows us to measure the characteristics of the thick disc population. We use a total of 19 data sets in UBV towards a dozen directions in order to measure the scale height, scale length, local density and metallicity of the intermediate population.
The Transition from Disk to Halo as seen from Correlations between Kinematics and Metallicity
Authors: Bartašiūtė S.
Published: June 2019

An investigation has been made to determine the relationship between kinematic and chemical properties of stars covering nearly all population types in the Galaxy. For this purpose, a sample has been taken of about 1150 high-galactic-latitude F–K stars down to V = 14.0, for which photoelectric seven-color data in the Vilnius medium-band system were collected at the Maidanak Observatory in Uzbekistan, Central Asia. Combining the obtained photometric material with the proper motion and radial velocity data enabled us to compute kinematic parameters of the sample stars and then to make plots of the galactic orbital eccentricities, angular momenta, and velocity dispersions versus [Fe/H], with much attention drawn to the region where the transition between the thin disk and halo occurs.
Are there Two Populations of subdwarf B Stars Visible in Kinematic Samples?
Authors: De Boer K.S. , Geffert M. , Odenkirchen M. , Schmidt J.H.K. , Theissen A. , Colin J. , Ducourant C. , Lecampion J.-F.
Published: June 2019

The discussions about stellar populations and their spatial distribution can be best advanced by studies of special and well defined star types. The study of subdwarf B stars provides great promise: it is relatively easy both to find sdB stars and to determine their physical parameters.
Chemical Content of Nine F-Supergiants from Different Regions of the LMC
Authors: Hill V.
Published: June 2019

In order to extend the available abundance information in the Magellanic Clouds, and particularly the elemental ratios, we have undertaken a homogenous sudy of supergiants stars in both Clouds using high resolution spectroscopy. We compare the abundance ratios obtained for nine LMC F-supergiants (Hill et al., 1994) with those for three SMC similar stars (Spite et al., 1989).
Metallicity of Stars and Gas in Galaxies of Different Hubble Types
Authors: Möller C. , Fritze-V. Alvensleben U. , Fricke K.J.
Published: June 2019

Many observations point out the great difference in metallicities determined from broad band colors of various wavelength regimes.
Edge-on Spiral Galaxies – Dust Influence and Thick Disks
Authors: De Grijs R. , Van Der Kruit P.C.
Published: June 2019

We have fitted exponential, isothermal (“sech2”) and intermediate (“sech”) model distributions to the observed vertical light profiles in edge-on galaxies.
Discovery of Cepheids in M100 and M101
Authors: Mould Jeremy , Freedman Wendy , Ferrarese Laura , Kelson Dan
Published: June 2019

The Hubble Space Telescope key project to determine the extragalactic distance scale aims to measure H0 to 10%. To achieve this goal will require Cepheid distance measurements for some 20 galaxies within a redshift of approximately 103 km/s. These galaxies in turn will calibrate five secondary distance indicators which will extend the volume over which the expansion rate has been measured to some 106 Mpc3.
New Metallicity Scale of Elliptical Galaxies
Authors: Sil'chenko O.K.
Published: June 2019

This work presents a new calibration of the metallicity scale for elliptical galaxies based on new observational data. I use my observations with the 1000-channel IPCS of the 6m telescope. The spectra for 100 galaxies are published elsewhere (Sil'chenko & Shapovalova, 1989; Sil'chenko, 1990). A subsample of 30 ellipticals has become a base for the new metallicity scale.
The Globular Cluster System of M87
Authors: Cohen J.G.
Published: June 2019

We have begun a program with the Low Resolution Imaging Spectrograph, operating with 30 multi-slits per exposure (Oke et al 1994, Cohen et al 1993) on the ten – meter W. M. Keck telescope located on Mauna Kea, Hawaii to observe the globular cluster systems of the Virgo ellipticals. We expect to learn about the dark matter content of galaxy halos, the formation of these halos and their cluster systems, possibly the formation of the galaxy's themselves, the interaction of the cluster system with the galaxy's gravitational potential (i.e. rotation and spinup), and the homogeneity of chemical evolution in various places. The metallicity of the globular clusters versus the metallicity of the underlying galaxy can also by analyzed. In addition the dynamics (i.e. in practice, the rotation and velocity dispersion) of the halo of the parent galaxy versus the globular cluster system can be determined.
The Age Spread Among Galaxies and the Origin of the UV Radiation from Elliptical Galaxies
Authors: Lee Young-Wook , Park Jang-Hyun
Published: June 2019

Recent UV observations of elliptical galaxies are interpreted as evidence for the global second parameter phenomenon of horizontal-branch (HB) morphology within, as well as between, these galaxies. In this picture, the origin of the UV radiation is mostly due to hot HB stars and their post-HB progeny produced by the metal-poor tail of the wide metallicity distribution expected to be present in these systems. The attractive feature of this model is that the bimodal temperature distributions of HB stars (and their progeny), required to generate the 2000 Å dip of the spectral energy distribution (SED), can naturally be reproduced from the standard HB population models with large range of metal abundance (see Lee 1994, ApJ, 430, L113). Detailed population synthesis models are presented, which reproduce the systematic variation of UV upturn among elliptical galaxies (Fig 1). If age is the major second parameter, as suggested by the fossil record in our Galaxy, the observed UV color gradient and the UV upturn-total mass (mean metallicity) correlation, within and between the early-type systems, would imply, respectively, (1) that most galaxies formed from the inside out, and (2) that there is age spread among galaxies, in the sense that more massive galaxies are older (and more metal-rich in the mean) than less massive galaxies as a result of more efficient star formation (and metal enrichment) in denser environments.
Radio Source Counts at Ultra Low Frequencies: Results, Significance and Implication for Observational Cosmology
Authors: Sokolov K.P.
Published: June 2019

Analysis of cosmological evolution effects in the low-frequency source counts at 25 MHz obtained with the UTR-2 radio telescope and conclusions on the large-scale extragalactic radio source space distribution are presented. The data require the existence of a decrease in the space distribution of the most distant extended radio sources.
The Nature of the Emission Galaxies in the Canada France Redshift Survey (CFRS)
Authors: Rola C. , Tresse L. , Stasińska G. , Hammer F.
Published: June 2019

The nature of the emission-line galaxies up to z ≈ 0.3 in the CFRS was analysed. The (4500–8500Å) spectral range allowed us to measure the Hα line intensity until z ≈ 0.3 and to correct for reddening. This permitted us to examine the physical properties of these galaxies in the light of a new grid of photoionisation models, obtained with the code PHOTO (Stasińska 1990). This grid was used to define the loci for photoionisation by hot main sequence stars in two diagnostic diagrams. As ionisation source we used the Kurucz (1992) log g = 5 stellar model atmospheres with abundances consistent with those of the model nebulae. The photoionisation models reproduce the separation zone between the objects thermally and non-thermally excited in the [S II] λ6725/Hα versus [O III]λ5007/Hβ diagnostic diagram, which Veilleux and Osterbrock (1987) determined empirically. A equivalent separation zone was defined for the [O III] λ5007/Hβ versus [O II] λ3727/Hβ diagram. In spite of its reddening dependence, this diagram is useful to separate the H II region-like galaxies from the non-thermally excited ones. Using both diagrams the analysis of the CFRS data allowed us to obtain the following statistics about the nature of the objects: about 20 % of all the galaxies with z ≤ 0.3 have spectra with properties intermediate between Seyfert 2 galaxies and LINERs (compared to 2 % found in the local Universe; Huchra & Burg 1992). More details of this work are given in Tresse et al. (1994). A full version will be submitted to MNRAS.
Reference frames in relativistic space-time
Authors: Soffel M. , Herold H. , Ruder H. , Schneider M.
Published: June 2019

Three fundamental concepts of reference frames in relativistic space-time are confronted: 1. the gravitational compass, 2. the stellar compass and 3. the inertial compass. It is argued that under certain conditions asymptotically fixed (stellar) reference frames can be introduced with the same rigour as local Fermi frames, thereby eliminating one possible psychological reason why the importance of Fermi frames frequently has been overestimated in the past. As applications of these three concepts we discuss: 1. a relativistic definition of the geoid, 2. a relativistic astrometric problem and 3. the post-Newtonian theory of a laser gyroscope fixed to the Earth's surface.
Coordinate system in general relativity
Authors: Fukushima Toshio
Published: June 2019

The proper reference frame comoving with a system of mass-points is defined as a general relativistic extension of the relative coordinate system in the Newtonian mechanics. The coordinate transformation connecting this and the background coordinate systems is presented explicitly in the post-Newtonian formalism. The conversion formulas of some physical quantities caused by this coordinate transformation are discussed. The concept of the rotating coordinate system is reexamined within the relativistic framework. A modification of the introduced proper reference frame named the Natural Coordinate System (NCS) is proposed as the basic coordinate system in the astrometry. By means of the concept of the natural coordinate system, the relation between the solar system barycentric coordinate system and the terrestrial coordinate system is given explicitly. To illustrate the concept of NCS, we quote in the following the definition of the non-rotating NCS comoving with the Earth, i.e. the Terrestrial Coordinate System (TCS) (Fukushima et al., 1986a, 1986b):

1) Consider a fictitious spacetime with the metric obtained by subtracting the direct terms due to the Earth from the true metric in the solar system Barycentric Coordinate System (BCS).

2) The time coordinate axis of the TCS is defined as the worldline of the geocenter, i.e. the timelike geodesic of the geocenter in the above ficititious spacetime.

3) The unit of time in the TCS, terrestrial second sT, is defined as the unit of time in the BCS, barycentric second, multiplied by a certain factor so that there exist periodic differences only between the time coordinate of any event in the TCS, i.e. TDT, and the corresponding time coordinate in the BCS, i.e. TDB.

4) The space coordinate axes of the TCS are defined as three geometrically straight lines satisfying that they and the time coordinate axis of the TCS are orthogonal to each other at the geocenter in the above fictitious spacetime, and that the coordinate triad constructed by them is symmetric.

5) The unit of length in the TCS, terrestrial meter mT, is defined as the length so that c = 299792458 mT/sT.
Preliminary evaluation of Doppler-determined pole positions computed using World Geodetic System 1984
Authors: Bangert John A. , Cunningham James P.
Published: June 2019

Since 1975, the Defense Mapping Agency (DMA) has been determining polar motion as a byproduct of computing the precise orbits of the Navy Navigation Satellite System (NNSS) satellites. The orbit determination process currently incorporates the NSWC 9Z2 terrestrial reference system and the NWL 10E-1 Earth Gravitational Model (EGM) to degree 28 and order 27. The World Geodetic System 1984 (WGS 84), developed by DMA, will replace the NSWC 9Z2/10E-1 system for NNSS orbit determination. The WGS 84 EGM to degree and order 41 will be utilized. This paper presents the results of two experiments which compared pole positions computed in the two systems. These comparisons indicate that use of WGS 84 improves agreement between pole position values resulting from the Nova-class satellite orbit solutions and the values determined by other modern techniques.
Simultaneous determination of the Earth rotation parameters and coordinates of the optical astrometric stations
Authors: Manabe Seiji , Tanikawa Kiyotaka , Yokoyama Koichi
Published: June 2019

The earth rotation parameters and coordinates of optical astrometric stations from 1962. O to 1986. O are estimated simultaneously on the assumption that the system of selected standard stations does not rotate. Longitudes and latitudes of the stations are determined every 2 months. Disagreement of the ERPs with those obtained by the space techniques decreased much compared with the published ERPs of the IPMS. It is expected that the ERPs in the whole period are also improved significantly.
Consistency of CDP and IRIS VLBI Earth orientation results
Authors: Mallama A. , Clark T. A. , Ryan J. W.
Published: June 2019

This study compares the earth orientation results obtained by the NASA CDP and the NGS IRIS experiments. The results agree at about one combined formal error (two milliarcseconds) after small biases (one to three milliarcseconds) have been removed from each component. Furthermore the biases are found to correspond to small rotations between the reference frames, principally the terrestrial frame, for the two sets of experiments. In the past the CDP data has not been used in combined solutions of earth orientation parameters prepared by the data centers at the U.S.N.O. and the B.I.H. The authors propose that these data should be included because they are distinct from the IRIS data and represent an important supplement to those data. We also point out that the total number of observations is about equal in the CDP and IRIS experiment sets.
Review of the achievements of project MERIT for the intercomparison of techniques for monitoring the rotation of the Earth
Authors: Wilkins G. A.
Published: June 2019

It is generally recognised that the Working Group on the Rotation of the Earth that was set up after IAU Symposium No. 82 has successfully achieved its principal objectives, namely: “to make recommendations on … future international services on earth-rotation” and “to obtain and analyse data on earth-rotation by both current and new methods …”. In particular, by organising Project MERIT, it has stimulated the development and use of new techniques and it has brought together in fruitful collaboration scientists from many countries and disciplines. Other subsidiary objectives have also been achieved and the project has been extended through cooperation with the COTES Working Group on the terrestrial reference system. The possible reasons for this success are also reviewed in the expectation that the conclusions will be relevant to other future projects.
Recent improvements in the U.S.N.O. combined solution for Earth rotation parameters
Authors: Babcock A. K.
Published: June 2019

The USNO combined solution for Earth rotation parameters, commonly known as CORE has recently been made more sensitive to high-frequency signals in the various types of input data. This is particularly important in the estimation of the variation in UT1—UTC which has recently been shown to have real fluctuations over time intervals of less than a week. A second modification was introduced to tailor the data smoothing to the particular noise characteristics of the individual techniques. This has resulted in a redistribution of the weights of these techniques, and in improved time-resolution and accuracy of the CORE solution.
Weights for prediction of Earth orientation Parameters
Authors: Sekiguchi N.
Published: June 2019

The most important factor in getting accurate predictions of Earth orientation parameters (EOP) is choosing suitable input data. Also, we must choose a proper statistical model for the noise in these data. The weights of the data are determined on the basis of these models. Finally, we must determine suitable values of parameters in the computation of EOP predictions.
Forecasting length-of-day using numerical weather prediction models
Authors: Rosen R. D. , Salstein D. A. , Nehrkorn T. , Dickey J. O. , Eubanks T. M. , Steppe J. A. , McCalla M.R.P. , Miller A. J.
Published: June 2019

A new approach to forecasting changes in length-of-day (δl.o.d) with lead times from one to ten days is examined. The approach is based on the high correlation that has been shown to exist between high frequency changes in l.o.d. and those in the atmosphere's angular momentum (M). Because forecasts of tropospheric values of M can be calculated from the zonal wind fields produced by operational numerical weather prediction models, it seems worth investigating whether these forecasts are sufficiently skillful to use to infer the evolution of δl.o.d. Here, we examine the quality of M forecasts made by the Medium Range Forecast (MRF) model of the U.S. National Meteorological Center (NMC). By comparing these forecasts against those based on a simple model of persistence, we find that skillful forecasts of M are being achieved on average by the MRF, although there has been much month-to-month variability in forecast quality. Overall, our results indicate that for prediction lead times of 1–10 days, dynamically-based forecasts of δl.o.d. represent a viable alternative to the empirical approaches currently in use.
The post - Newtonian rotation of Earth: a first approach
Authors: Schastok J. , Soffel M. , Ruder H. , Schneider M.
Published: June 2019

The problems of dynamics of extended bodies in metric theories of gravity are reviewed. In a first approach towards the relativistic description of the Earth's rotational motion the post - Newtonian treatment of the free precession of a pseudo - rigid and axially symmetric model Earth is presented. Definitions of angular momentum, pseudo - rigidity, the corotating frame, tensor of inertia and axial symmetry of the rotating body are based upon the choice of the standard post - Newtonian (PN) coordinates and the full PN energy momentum complex. In this framework, the relation between angular momentum and angular (coordinate) velocity is obtained. Since the PN Euler equations for the angular velocity here formally take their usual Newtonian form it is concluded that apart from PN modifications (renormalizations) of the inertia tensor, the rotational motion of our pseudo - rigid and axially symmetric model Earth essentially is “Newtonian”.
Geophysical models of the surface global vorticity vector
Authors: Grafarend Erik W.
Published: June 2019

Within the framework of Newtonian kinematics the local vorticity vector is introduced and averaged with respect to global earth geometry, namely the ellipsoid of revolution. For a deformable body like the earth the global vorticity vector is defined as the earth rotation. A decomposition of the Lagrangean displacement and of the Lagrangean vorticity vector into vector spherical harmonics, namely into spheroidal and toroidal parts, proves that the global vorticity vector only contains toroidal coefficients of degree and order one (polar motion) and toroidal coefficients of degree one and order zero (length of the day) in the case of an ellipsoidal earth. Once we assume an earth model of type ellipsoid of revolution the earth rotation is also slightly dependent on the ellipsoidal flattening and the radial derivative of the spheroidal coefficients of degree two and order one.
Comparisons of ET(solar), ET(lunar), UT, and TDT
Authors: Markowitz Wm.
Published: June 2019

A fundamental dynamical scale, ET(solar), was formed from absolute, meridian circle observations, from 1835 to 1982. At 1967.0 the ET(solar) and SI seconds were equal to 1 part in 109 and, from Morrison's (1979 a) ET(lunar) scale, the ET(ILE) and SI seconds were equal to 1 part in 1010. The long term fluctuation in the Earth's rotation has been parabolic, instead of sinusoidal, for at least 350 y.
The time transformation TDB–TDT: an analytical formula and related problem of convention
Authors: Fairhead L. , Bretagnon P. , Lestrade J.-F.
Published: June 2019

An analytical formula for the time transformation TDB–TDT valid over a few thousand years around J2000 has been computed with an accuracy at the 1 ns level. The coefficients for a formula accurate at the 100 ns level are provided here. The numerical and analytical procedures to compute this transformation are discussed. We note that these procedures cannot comply with recommendation 5 of the 1976 IAU meeting. Furthermore, these procedures yield different units for the corresponding TDB time scales. We also note that this transformation is independent of the two PPN parameters γ and β and of the 3 most commonly used coordinate systems (isotropic, standard-Schwarzschild, Painlevé) at least at the 1 ns level.
Effects of variations in Earth rotation on extended use of GPS orbits
Authors: Klepczynski W. J.
Published: June 2019

Time transfer data, derived from single frequency observations of GPS satellites, have shown a unique bowing characteristic in the residuals with an amplitude which sometimes amounts to about 80 ns. Investigations attempting to explain this characteristic have so far been unsuccessful. The studies have been concerned with hardware and software effects. The hardware studies have:

(a) compared data obtained with single frequency receivers with data obtained simultaneously with dual frequency receivers which eliminate the effects of the ionosphere;

(b) compared data obtained with different kinds of single frequency receivers; and

(c) compared data obtained simultaneously with different kinds of antennas, including one designed to minimize the effects of multipath.
Evidence for the Earth's gravitational time delay in VLBI experiments
Authors: Schuh H. , Fellbaum M. , Campbell J. , Soffel M. , Ruder H. , Schneider M.
Published: June 2019

Evidence is found that in IRIS experiments the gravitational time delay due to the gravitational field of the Earth can be seen. Influences of this time delay upon baseline determinations are discussed.
Interaction Beyond the Main Sequence: One Recipe?
Authors: De Greve Jean-Pierre
Published: June 2019

We investigate the different aspects that govern the interaction of post-main-sequence evolution of binaries, using a new, homogeneous set of computations. The set describes the evolution of both components through the phase of mass transfer, till the end of the core helium burning of the primary. The mass range is 9 to 40 Mo, the mass ratios are 0.9 and 0.6 (and introducing 0.99 as a newcomer). Both for small and large masses we discuss the consequences of non-conservative mass transfer. Using a simple concept for the fraction β of transferred matter, we look to its value at the onset of mass transfer for various mass ratios and periods. Exploration of the phase space of interacting binaries reveals the influence of the various parameters on the dimensions of the resulting systems after mass transfer. Special attention is given to binaries with mass ratios very close to one. Their secondaries evolve directly into yellow supergiants such as observed in the LMC.
Zeta Aurigae Type Binaries
Authors: Carpenter Kenneth G.
Published: June 2019

Recent progress in the study of ζ Aur and VV Cep systems is reviewed, with an emphasis on what has been learned about the extended atmospheres and winds around the cooler components.
Aspects of Mass Loss and Angular Momentum Loss in Binaries Containing Cool Components
Authors: Eggleton Peter P.
Published: June 2019

Cool stars show evidence of dynamo activity which is stronger with more rapid rotation. Tidal friction in a moderately close binary can be a cause of relatively rapid rotation, so that cool components in such binaries are presumably liable to stronger stellar winds than single cool stars. As a consequence, the binary can be subject to orbital angular momentum loss. Both the mass loss and the orbital angular momentum loss can be on a timescale comparable to nuclear evolution in a red subgiant, or even faster. RS CVn stars probably give the best possibility of measuring these processes, although some observational data are difficult to reconcile with simple theories.

Barium stars, and symbiotics, may both be affected by these processes. They must be the products of evolution of moderately wide binaries, as must such objects as cataclysmic variables. I attempt to define the ranges of zero-age parameters necessary to produce such varied objects. A simplistic model of the distribution of stars brighter than 6th magnitude (a ‘Theoretical Bright Star Catalogue’) suggests that for every three Ba stars with a measurable orbit, there should be one main sequence ‘Ba star’.
Circularization and Synchronization Times in Detached Main-Sequence Eclipsing Binaries
Authors: Claret A. , Gimenez A.
Published: June 2019

We have studied a sample of selected eclipsing binaries with accurate absolute dimensions in order to check the validity of available theories of tidal evolution in terms of synchronization and circularization time scales. The use of integrated values, using theoretical evolutionary tracks to compute the change with time of radius, luminosity and internal structure, provides a powerful tool for the prediction of observable parameters. Pseudo-synchronization at periastron is the best approximation to stellar rotation in eccentric systems. While most systems are found to show synchronized velocities, the presence of eccentric orbits shows that circularization process are still active during the main sequence stage.
Carbon Depletion in Case B Mass Transfer Algol-Type Binaries
Authors: Yoon Tae S. , Honeycutt Kent
Published: June 2019

The surface carbon abundances of Algol secondaries are known to be low compared to field stars of similar type. The C and N anomalies of these G and K subgiants are undoubtedly due to the exposure of CN cycle processed material as mass transfer removes the outer layers of the star. Therefore the carbon abundance is a promising tool for helping fix the evolutionary state of Algols, particularly the amount of mass which has been lost from the secondary. We report here the carbon abundance of 12 Algol secondaries as deduced from the g-band in spectra obtained during photometric totality. We compare the abundances to those from models of single stars of appropriate age and mass. The values of log ∊(C) for this sample fall 0.25–0.75 dex below field G and K giants, and 1.25–1.75 dex above “stripped” single star models. This larger sample supports the conclusions of Parthasarthy et al. regarding mixing and mass loss, which they deduced from a smaller sample of carbon abundances.
Analysis of Period Changes of YY Eridani
Authors: Kim Chun-Hwey
Published: June 2019

Four times of minimum lights from six nights photoelectric observations of YY Eri during the observing seasons from 1983 to 1984 are derived. With these and previously published photoelectric minima, new light elements are determined. A detailed numerical investigation of times of minima shows that the orbital period has changed sinusoidally with a period of about 24 years. These changes of period are investigated in terms of two plausible causes : a light-time effect due to an unseen third body and asymmetries of light curves due to stellar activities of one component or both.
Test of the Optimization Techniques for the Photometric Analysis of Contact Binaries
Authors: Lapasset E. , Gomez M. , Fariñas R.
Published: June 2019

We present light curve analyses of contact binaries and comparisons with previously published cross-correlations radial velocity data. The critical parameter q (mass-ratio) obtained from a grid technique is confronted with the spectroscopic value. For total eclipsing systems, both values are always in a good or reasonable agreement, including some stars with shallow light curves. For partial eclipsing systems, convergent photometric and spectroscopic results are obtained for an important set of stars. Two exceptions are V523 Cas and XY Boo for which some arguments are suggested. We concluded that reliable parameter determinations can be obtained from pure photometric solutions, by means of grid techniques.
HD 46407: The First Eclipsing-Binary Barium Star
Authors: Jorissen A. , Manfroid J. , Sterken C.
Published: June 2019

A long-term, high-accuracy, differential uvby monitoring of a sample of 19 barium stars revealed that HD 46407, a well known barium star with an orbital period of 458 d, is an eclipsing binary. The eclipse (of the companion by the barium star) was most clearly seen in November 1988, when a dip of 0.02 mag (in y) having a FWHM of about 10 d was recorded in the lightcurve. Confirmation of the eclipsing nature of HD 46407 was also obtained in February 1985 and in February 1990. A shallow secondary eclipse (extending over about 50% of the orbital period) seems to be present as well. The b – y index is marginally variable, while v – b color variations are correlated with the y variations, in the sense that the system appears redder when it is fainter. We suggest that these variations originate in the scattering of the red-giant light by dust particles trapped (in a wide ring or shell?) around the (compact) companion. The eclipsed light would then be the light of the red giant backscattered by the dust around the companion.
Aspects of the Angular Momentum Loss Problem for Cool Close Binary Systems
Authors: Budding E. , Slee O. B. , Stewart R. T.
Published: June 2019

We concentrate on the application of centimeter wavelength observational data to the coronae of rapidly rotating active dwarf stars. In particular we seek insight into coronal loop geometries, and their possible relevance to the magnetic braking mechanism, which must play a key role in binary evolution scenarios for such stars.
MWC 560: Its Spectroscopic and Photometric Development in 1990
Authors: Buckley D.A.H.
Published: June 2019

Optical spectroscopic, photometric, and infrared photometric observations of the symbiotic-like star MWC560, which underwent a prolonged ‘outburst’ during 1990, are presented. Both the magnitudes and timescales of outbursts are similar to other symbiotics, and related systems. The large ejection velocities observed, and the transient nature of the highly blue shifted absorption components, are quite atypical, however.
Irradiation-Driven Mass Transfer in Low-Mass X-Ray Binaries
Authors: Podsiadlowski Philipp
Published: June 2019

External irradiation can completely alter the internal structure of the secondary in a low-mass X-ray binary (LMXB). For radiation fluxes as are typically found in LMXBs, the secondary expands by a factor of 2 to 3 in order to relax towards a new state of thermal equilibrium. This relaxation process provides a new mass-transfer driving mechanism for LMXBs, which can drastically alter the evolution of these systems.
On the Masses and on the Mass Transfer in the Interactive Binary SS 433
Authors: Zwitter Tomaž , D'Odorico Sandro , Oosterloo Tom , Calvani Massimo
Published: June 2019

Recent spectroscopic observations of the interactive binary SS 433 with the ESO's New Technology Telescope show that the compact object is a neutron star. We note that the huge mass transfer rate (which may well be the reason for the uniqueness of SS 433) suggests that a significant fraction of the mass lost from the normal star actually settles on the neutron star. This may have important consequences for the structure of the accretion disk and for the formation of jets in this peculiar system.
The Eclipsing Binaries in NGC 5466 and Implications for Close Binary Evolution
Authors: Milone E. F. , Stagg C. R. , Kallrath J.
Published: June 2019

The three eclipsing binaries among the blue stragglers of the globular cluster NGC 5466 have been modeled. Two of the systems are contact systems and the third is a short-period Algol system. The results indicate that the systems are well on their way to merger, but the implications for the origin of blue-stragglers are less clear.
Supernovae in Massive Interacting Binaries
Authors: Joss P. C. , Hsu J. J. L. , Podsiadlowski Ph. , Ross R. R.
Published: June 2019

We here report the results of a systematic investigation of how binary interaction affects the presupernova evolution of massive stars and the resulting supernova explosions. We summarize the various types of binary interaction and the evolutionary scenarios in which they are realized. We also present the results of a series of hydrodynamical calculations which model the supernova explosion for various progenitor types and discuss their observable characteristics.
Interferometry of Solar Flares at 3-mm Wavelength
Authors: Kundu M. R. , White S. M. , Gopalswamy N. , Lim J.
Published: June 2019

We describe a set of millimeter interferometric observations of solar flares carried out in conjunction with GRO experiments during the 1991 June Campaign of the Max'91 Program. We show evidence that millimeter emission probes the most energetic (MeV) electrons in solar flares; we also find that in the same flare there can be both impulsive nonthermal and gradual thermal millimeter emission. Millimeter emission usually occurs at the steep rise phase of the hard X-ray emitting electrons (25-100 KeV). There appears to exist some delay between BIMA mm-emission onset and GRO-BATSE 25-100 KeV X-ray emission. Both results have implications for the particle acceleration process.
12-μM Observations at the 1991 Eclipse
Authors: Jennings D. E. , Deming D. , Mccabe G. , Noyes R. , Wiedemann G. , Espenak F.
Published: June 2019

The 11 July 1991 total solar eclipse over Mauna Kea was a unique opportunity to study the limb profile of the 12.32 μm MgI emission line. Our observations used the NASA 3-meter Infrared Telescope Facility,1 and a new Goddard large cryogenic grating spectrometer. Spectra of the line were taken in the slitless mode at second contact. The results show that the emission peaks within ~ 300 km of the 12-μm continuum limb. This agrees with recent theoretical predictions for this line as a NLTE upper photospheric emission feature. However, the increase in optical depth for this extreme limb-viewing situation means that most of the observed emission arises from above Tmin, and we find that this emission is extended to altitudes well in excess of the model predictions. The line emission can be traced to altitudes as high as 2000 km above the 12-μm continuum limb, whereas theory predicts it to remain observable no higher than 500 km above the continuum limb. The substantial limb-extension observed in this line is qualitatively consistent with limb-extensions seen by other observers in the far-IR continuum, and may be indicative of departures from gravitational hydrostatic equilibrium in the upper solar atmosphere, and/or may result from temperature and density inhomogeneities. The extended altitude of formation of this line enhances its value as a Zeeman probe of magnetic fields.
The Structure of the White-Light Corona at the 1991 Eclipse
Authors: Sanchez-Ibarra A. , Cisneros-Molina M. , Hinojosa-Palafox G. , Cisneros-Peña F. , Torre J. Guerrero de La , Norzagaray-Cosío M. , Tapia-Fonllem C.
Published: June 2019

The total solar eclipse of July 11, 1991 was observed from “La Matanza”, Baja California Sur, México, only 5 km south of the center line of totality, with several small instruments intended to obtain images of the corona during totality, and using a range of exposure times which allowed us to detect both the inner and outer corona. Relations between large and fine scale structures of the corona, the photospheric and chromospheric activity, and the presence of coronal holes are presented.
On Sunspot and Facular Contrast Variations Near 2 μm and 4 μm
Authors: Kotov V. A. , Koutchmy S.
Published: June 2019

Observations of the Sun at 2.2 and 3.75 μm have been made at the Pic-du-Midi and Crimean observatories. High resolution (~ 1″) records of the sunspot and facular contrasts at various heliocentric distances as well as those at the extreme solar limb are presented. We find substantial variations in the sunspot-core relative intensity caused by magnetic activity of the spot. The extreme-limb contrasts of faculae at 3.75 μm are strong thus support flux-tube models which result in an enhancement of the extreme-limb facular brightness.
Ground-Based Near-Infrared Observations of Global Solar Oscillations
Authors: Didkovsky L. V. , Kotov V. A.
Published: June 2019

Near-infrared (0.7-1.0 μm) observations of solar brightness oscillations were performed in 1983-1991 at the Crimean Solar Tower with the use of two (16 × 16 and 32 × 32) photodiode arrays. In 1991 new observations of p-modes were made simultaneously in two spectral ranges, near 0.7 and 1.0 μm. The data is analysed to check for the presence of solar variation with the 160-min period. It is found that the mean relative amplitude for the 160-min solar irradiance variation at 0.73 - 1.65 μm wavelengths, ~ 2 × 10–6, is much lower than the upper limits set by the ACRIM and IPHIR space experiments.
On the Ion Broadening of the 12 μm lines of Atomic Magnesium
Authors: Hoang-Binh D. , Van Regemorter H.
Published: June 2019

We have investigated the impact broadening of the 12 μm lines. Ion broadening is found to follow the adiabatic theory, whereas electron broadening needs a non-adiabatic treatment. This relaxes the fixed width/shift ratio, as found by Chang and Schoenfeld (1991), using a pure adiabatic analysis.
Vector Magnetometry Using the 12-μm Emission Lines
Authors: Deming D. , Hewagama T. , Jennings D. E. , McCabe G. , Wiedemann G.
Published: June 2019

Recent polarimetric observations of the 12.32-μm emission line have provided the observational basis for deriving vector magnetic fields in the upper photosphere with great sensitivity. We use a line source function from the non-LTE model of Carlsson, Rutten and Shchukina, and calculate the radiative transfer of the Stokes I, Q, U, and V profiles. The results show that the profiles are not significantly affected by magneto-optical effects or by saturation, and reliable vector fields can be extracted by simply fitting the Seares relations to the Stokes profiles. Vector field observations for sunspots have shown that the field extends well beyond the photometric boundary of the sunspot, but that the field strength at the penumbral/photospheric boundary is less than half of the sunspot-center value. Within a mature sunspot, the 12-μm line profiles contain essentially no unpolarized radiation, indicating that the field is not intermittent in the sense of containing discrete flux tubes separated by field-free regions. We describe the design of a 12-μm Stokes polarimeter incorporating a high-resolution Fabry-Perot etalon and a 128 × 128 infrared array detector.
Flux Tube Shredding and its Infrared Signature
Authors: Bünte M. , Steiner O. , Solanki S.K. , Pizzo V.J.
Published: June 2019

The interchange instability of solar magnetic flux tubes and possible stabilization mechanisms are reviewed. Special attention is paid to the influence of magnetic tension forces and the internal atmosphere, both of which were neglected in earlier studies of this instability. It is found that whirl flows with velocities of only 2.2 km s–1 are strong enough to stabilize the flux tubes. However, their absence or the excitation of other instabilities might lead to a shredding of the tubes. The observability of such a scenario in the infrared is briefly discussed.