bluuebunny/crossref_metadata_2025 huggingface dataset:
New Results for the Linear Stability of the Triangular Points in the Elliptic Restricted Problem
Authors: Meire R.
Published: July 2016

New results are obtained for the linear stability of the triangular points in the elliptic restricted problem using the Hill equations which describe the infinitesimal motion around L4,L5. Also the shape of the 4Π-periodic solutions along the transition curves in the μ-e plane is investigated .
The Planar Inverse Problem for Autonomous Systems
Authors: Xanthopoulos Basilis C. , Bozis George
Published: July 2016

We study the general version of the inverse problem for planar trajectories and for autonomous dynamical systems possessing three integrals, i.e., for a given three-parametric family of curves f(x,y,a,b)=c we find the potential V(x,y) for which these curves are orbits of a unit mass. All possible cases, depending on the preassigned function f, are classified and in each case the necessary and sufficient conditions for the.existence of a solution are established. Among the examples is the case of the Keplerian conic sections which is studied in detail.
Trapping Time of Resonant Orbits in Presence of Poynting - Robertson Drag
Authors: Gonczi R. , Froeschlé Ch. , Froeschlé C.
Published: July 2016

We study numerically the competition between the Poynting-Robertson drag and the gravitational interaction of grains with Jupiter near orbital resonances. The computations are based on the plane elliptic restricted three body problem. Numerical investigations show that the grains always cross the resonance region without any oscillation, except in the special case where the grains were initially inside the resonance. Such grains are temporarily trapped, then due to the drag they are ejected out of the resonance. The trapping time of a particle turns out to be much more important in the 3/2 and 2/1 commensurabilities than in the others.

A numerical exploration of numerous orbits for different initial conditions and different sizes of grains has been performed. The trapping time appears to be closely connected to the size of the librator-type orbits regions; it increases with the initial eccentricity of the orbit, and is also proportional to the radius and the density of the particle.
Visual symbiotic spectra obtained with the Haute Provence multiphot detector
Authors: Muratorio G. , Friedjung M.
Published: July 2016

Spectra of symbiotic stars have been obtained with the Haute Provence Multiplhot detector system. This has 512 pixels, so one can study either a large spectral region at low resolution, or a smaller region with a higher resolution.
A review of the properties of the symbiotic star CH Cygni
Authors: Hack M. , Selvelli P.L.
Published: July 2016

The spectrum of CH Cygni usually has the appearance of a normal M6 III star, but at intervals of several years, it has phases of activity during which it shows the characteristics of a symbiotic star, that is, a blue continuum extending shortward of the Balmer discontinuity, and strong emission lines of He I, Fe II, [Fe II] , [S II], [0 1] , [0 III]; the Balmer lines and the H and K lines of Ca II present emission wings. Outbursts were observed: 1) in September 1963; the star returned to its normal phase by August 1965 (Deutsch, 1964); 2) in June 1967 (Deutsch, 1967); the spectrum was observed by Faraggiana and Hack (1971) until December 1970, when the activity phase was over; 3) another outburst was observed in August 1977 (Morris, 1977; Fehrenbach, 1977), and at the time of our last spectroscopic observations (June 1981) it was still going on. During this last period of activity several observations were made with IUE in both the low and high resolution modes, from 1175 A to 3100 A.
IUE observations of CI Cygni during 1979–1981
Authors: Baratta G.B. , Altamore A. , Cassatella A. , Friedjung M. , Ponz D. , Ricciardi O.
Published: July 2016

High and low resolution IUE spectra of CI Cyg were obtained at VTLSPA during 1979-81 allowing for an analysis of the spectral variations related to the decreasing activity of the star, and to the eclipse (June 1980).

In the high resolution spectra the emission lines have a width slightly larger than the instrumental one. This fact is particularly evident in the HeII 1640 A line and could be related to the peculiar behaviour of this line at low resolution as reported by Michalitsianos et al. (this volume). A systematic radial velocity difference between permitted and intercombination lines was found; this difference should be connected with the structure of the emitting region(s). “Secular” and eclipse varia tion was found in particular in the intercombination line intensities (Viotti et al. 1980). An electron density of ∼ 0.3–1.5×1010 cm–3 was evaluated from the intensity ratios of the NIII] emission lines. No significant difference in these ratios and in the CIII]/NIII] ratio as well was found,during 1979, 1980 (eclipse) and 1981 suggesting no large Ne variation with both the activity phase and eclipse of the star. This result should imply a low density gradient in the partially eclipsed NIII] and CIII] regions. A more detailed analysis of the high resolution data is in course to better clearfy these points, and their implications on the possible models for CI Cyg.
Optical observations of CI Cygni
Authors: Oliversen N.A. , Anderson C.M. , Nordsieck K.H.
Published: July 2016

We report optical emission line variations in CI Cygni during the 1980 eclipse.
Variability of HBV 475 in the near infrared
Authors: Andrillat Y.
Published: July 2016

In the spectral range λλ5800-8750, HBV 475 shows important spectral variations between 1969 and 1974. Sometimes the “hot component” spectrum dominates (many emission lines), sometimes the “cool component” is preponderent (many molecular absorption Ti0 bands) (Andrillat 1973 – Andrillat, Houziaux 1976).

On August 4 1974, June 6 1975 and August 9 1981, we have extended the observations up to l.lμ (fig.l) (Haute Provence Observatory 193 Telescope – Spectro ROUCAS + Image tube – dispersion 230 A.mm-1).
UV time-dependent emission in SY Muscae
Authors: Michalitsianos A.G. , Kafatos M.
Published: July 2016

Ultraviolet spectra acquired with the International Ultraviolet Explorer (IUE) of SY Mus = HD 10036 on 20 September 1980 and 11 June 1981 indicate a substantial enhancement of UV emission over a nine month period. The general UV flux level appears to have increased by approximately one order of magnitude between the first and second observing epochs. The strong ultraviolet continuum evident throughout the entire IUE spectral range λλ1200-3200 A on 11 June 1981 is closely approximated by a star with Teff = 40,000 K, where previously on 20 September 1980 the continuum distribution presented a more complex structure that is possibly explained by a combination of thermal emission from an early type main sequence star, and nebular recombination emission (Michalitsianos et al. 1981).
Determination of the term Symbiotic Star
Authors: Boyarchuk A. A.
Published: July 2016

Symbiotic stars have been studied for many years. But the common determination of the term “symbiotic star” does not exist even now. Merrill (1958) introduced this term in order to emphasize unusual spectral features – absorption TiO bands and emission lines belonging to highly ionized ions.

If we look on the eruptive stars spectra we well see absorption and emission features in the spectra of many stars which we cannot certainly consider as symbiotic stars. For example the U Gem type stars have absorption and emission features in their spectra. A similar situation exists in the case of the old novae. The T Tau type stars have many emission lines, and their spectral type corresponds to G-K. Even the long period variables have some emission lines though their spectral type is M. On the other hand, there are also the BQ[]type stars which are characterized by the presence in their optical spectrum of forbidden emission lines and of a rather hot absorption spectrum.
IUE Observations of the Gaseous Component of the Local Interstellar Medium
Authors: Gilra Daya P.
Published: July 2016

Discovery of interstellar Ge, Ga, and Kr is reported. Several intercombination lines of Fe II are detected. The depletion is most pronounced in Ca, Ti, and V. The highly ionized gas C IV and Si IV is not coextensive with the Si II and C II gas nor with the 0 VI gas. The molecular gas (CO) shows very small velocity dispersion (b~l km/sec).
Optical Observations of Nearby Interstellar Gas
Authors: Frisch P.C. , York D.G.
Published: July 2016

The yellow D lines from neutral sodium are some of the most useful interstellar absorption features for tracing out low density optically thin interstellar material. Hobbs (1978) compared column densities of Nal as determined from the D lines with HI column densities derived from ultraviolet observations and found values of N(NaI)/N(H)<6.3x10-9 in 18 sight-lines with very low reddening, with the exact value of the ratio apparently a function of temperature. If this ratio limit holds for diffuse clouds in nearby space, we expect that observations of the Nal D2 lines at the 3 mA level can be used to trace out nearby clouds with column densities in the range of ≥2.5x1018 cm-2. Thus sensitive measurements of the Nal D lines are a useful way of observing nearby neutral cloud material. With this in mind, we have chosen high-resolution observations of the yellow sodium lines as a means of locating and mapping nearby low density interstellar clouds.
Local Interstellar Extinction With an Emphasis on uvbyβ Results
Authors: Knude Jens
Published: July 2016

Despite only a few percentages of the interstellar mass are contained in solid dust grains knowledge of its distribution is of importance per se, for dereddening purposes and because it probably correlates with the interstellar gas. General information on the bulk of the interstellar mass is thus obtainable from continuum absorption studies. Compared to diffuse emission data interstellar reddenings have the additional advantage by including an upper distance to the material observed.
Do the Arching HI Filaments Show in Local Reddening Data?
Authors: Knude Jens
Published: July 2016

Probable dust counterparts of arching structures are looked for in two cases, (a) the Eridanus expanding shell, Heiles (1976) and (b) the extended Sco-Cen feature, Weaver (1977). Apparently the color excess data may be used to derive distance and dimension estimates of these structures.
The Soft X-Ray Diffuse Background: Implications for the Nature of the Local Interstellar Medium
Authors: McCammon Dan
Published: July 2016

Observations of the diffuse X-ray background in the B and C bands (130-188 eV and 160-284 eV, respectively) provide convincing evidence for the existence of high-temperature interstellar gas. Since the opacity of normal interstellar material is very high, we must assume that the soft X-ray flux observed in the galactic plane originates within a few hundred parsecs of the Sun. The intensity and B/C ratio of this low-latitude flux can be provided by emission from an equilibrium plasma with normal abundances, T = 106.0 K, and 0.0019 cm-6 pc emission measure. More sophisticated nonequilibrium models of material heated by a supernova blast wave would reduce the required emission measure somewhat, but not by so much as a factor of two. Arbitrarily limiting the pressure to 104 cm-3 K gives a maximum density of 0.005 cm-3 and a minimum radius for the emitting region of 75 pc. This fits in well with UV interstellar absorption measurements which indicate that the ISM is very deficient in neutral hydrogen out to ~100 pc from the Sun.

The constancy of the observed B/C ratio implies that there are less than 5x1019 cm-2 variations in any cooler material lying between us and the bulk of the emission. This is consistent with the much smaller column densities of neutral or partially ionized material detected in the solar neighborhood through UV absorption measurements, but the organization of the cooler gas and its interaction with the coronal material require further investigation.

X-ray intensities at high latitudes are larger than those in the plane by as much as a factor of three. The fluctuations show a global anti-correlation with H I column density which suggests that they might be caused by variations in the transmission of X-rays from an extragalactic source, such as a galactic halo or corona. Such models are very difficult to reconcile quantitatively with existing H I measurements, however, and it seems more likely that the bulk of the high-latitude excess is produced by an extension of the unabsorbed interstellar emission in those directions with the remaining fluctuations produced by a combination of absorption and displacement by embedded cooler material, or possibly by transmission of flux from a hot halo.

While it would be most interesting to resolve this point because of its impact on the nature of the galactic halo and the high-latitude H I distribution, it does not greatly affect the amount of hot gas which apparently exists in the solar neighborhood: an isotropic emitting region with only the emission measure required by the average intensity near the galactic plane would account for about two-thirds of the integrated B and C band flux observed at the Earth. The total energy flux is ~1x10-6 ergs cm-2 s-1 if we assume a thermal equilibrium spectrum.
The Nature of the Soft X-Ray Emitting Region in the Direction of the North Polar Spur
Authors: Morrison James P. , Sanders Wilton T.
Published: July 2016

The spatial structure of the X-ray sky in the direction of the North Polar Spur was examined in two energy bands, the B band (0.10 - 0.18 keV) and the C band (0.15 - 0.28 keV). A model with two emitting regions, one local with unabsorbed emission, and the other more distant with emission partially absorbed by spatially varying amounts was investigated.

Using the distribution of atomic hydrogen as a measure of absorbing material, this model was used to predict the flux in the direction of the North Polar Spur. The predicted flux was compared to the data obtained from several sounding rocket flights. The derived flux was found to correlate well with the observed data.
Local Contributions to the 0.6 keV Diffuse X-Ray Background
Authors: Burrows David N.
Published: July 2016

The intensity of the X-ray background between 0.5 and 1.0 keV has surprisingly little dependence on galactic latitude. Possible mechanisms for the production of these X-rays include extragalactic emission and emission from dM stars, both of which should be strongly dependent on galactic latitude, and diffuse emission from hot gas (T ≃ 3 x 106 K) surrounding the Sun. These mechanisms can be distinguished by the presence or absence of absorption by gas within a few hundred parsecs of the Sun. We use X-ray data from the HEA0-1 LED detectors and HI data from the recent Crawford Hill 21 cm survey to place limits on the 0.6 keV intensity originating within 300 pc of the Sun in the general direction of (l,b) = (150°, -30°).
HEAO-1 Diffuse Soft X-Ray Sky Maps
Authors: Nousek John A. , Garmire Gordon P. , Weaver George
Published: July 2016

Maps of the diffuse soft X-ray background intensity are presented, spanning four energy intervals. The lowest energy interval (0.18-0.56 keV) is dominated by local emission, while the next two intervals (0.56-1.0 keV and 1.0-1.4 keV) reveal more distant and more sharply defined structures. Enlarged maps of several of these structures are presented, including the North Polar Spur, the Galactic Center region and the Eridanus Loop.
The Draco Nebula, a Molecular Cloud Associated with a High Velocity Cloud?
Authors: Mebold U. , Kalberla P.W.M.
Published: July 2016

Extended and very faint bright nebulae are found in high (b≳ 30°) galactic latitudes at the Palomar Observatory Sky Survey (POSS) (Lynds, 1965) and even more pronounced at a very sensitive photographic survey of the galactic polar caps by Sandage (1976). Such a nebula, located in the constellation Draco and called “Draco Nebula” or “Dracula”, was found to be in detailed positional coincidence with a 21-cm emission line feature at a LSR velocity of VLSR ≈ -22 km s-1 by Goerigk et al. (1983).
The z-dependence of the Spin Temperature of HI
Authors: Kulkarni Shrinivas R. , Heiles Carl , Van Gorkom J. , Dickey John M.
Published: July 2016

In 1981 we conducted an extensive, low-latitutde, HI 21-cm absorption survey from the VLA. The goal of the survey was to answer the following questions:

(a) What is the vertical distribution of the cold HI clouds?

(b) Do HI clouds get systematically warmer at high |z|?

(c) Does the fraction of warm intercloud medium HI increase with high |z|?

(d) How much HI has been missed in previous HI emission surveys because of optical depth effects?

(e) What is the galactic distribution of cool HI clouds?
Radio and UV Observations of High Latitude HI
Authors: Lockman Felix J. , Hobbs L.M. , Shull J. Michael
Published: July 2016

Interstellar Lyman-α observations toward high latitude stars, which give the column density of HI between us and the star, and 21 cm radio observations, which give the total HI column density to and beyond the star, can be combined to map out the amount of neutral gas as a function of distance from the sun. We present recent observations of the 21 cm and Lyman-α lines made toward ~50 high latitude OB stars, and use these data to discuss the distribution of HI in the solar neighborhood.
Future Studies of the Local Interstellar Medium With Space Telescope and Columbus
Authors: Savage Blair D.
Published: July 2016

The spectrographs aboard Space Telescope and Columbus will provide important new information about the interstellar medium in the immediate vicinity of the sun. The Space Telescope high resolution spectrograph (HRS) will produce resolutions, λ/Δλ, of about 18,000 and 70,000 with high sensitivity between 1200 and 3200 A and greatly reduced sensitivity between 1060 and 1200 A. The highest resolution is adequate to define the multicomponent nature of interstellar absorption lines and to measure thermal line widths exceeding 3 km s-1 . The Columbus mission is in the planning stages. However, it is likely that the spacecraft will contain spectrographs capable of resolutions of 3 x 104 between 912 and 1200 A and 500 between 100 and 900 A. In the longer wavelength region, the very important lines of 0 VI, S VI, H2, H I , and D I are available for study. In the short wavelength region, lines of He I and II, are observable. If the 3x104 resolution spectrograph can provide extended wavelength coverage to 770 A, lines of Ne VIII which are expected from 8x105 K gas are accessible. Astronomers using the ST HRS and Columbus spectrographs will be able to study a wide range of problems relating to cold, warm, and hot gas in the local ISM. Some of the most important observing projects are described.
Observations of Local ISM Emission With the Berkeley EUV/FUV Shuttle Telescope
Authors: Martin Christopher , Bowyer Stuart
Published: July 2016

The Berkeley Extreme Ultraviolet/Far Ultraviolet Shuttle Telescope (BEST) will be launched on the Space Shuttle in November, 1984, as part of the NASA UVX project. The Berkeley spectrometer will make observations of the cosmic diffuse background in the 600-1900 Å band, with a spectral resolution of 10 Å. The sensitivity and spectral resolution of the instrument make it ideal for the study of components of the interstellar medium in the 104 - 106K range.
The LPL Radial Accelerometer
Authors: McMillan R.S. , Smith P.H. , Frecker J.E. , Merline W.J. , Perry M.L.
Published: July 2016

We have begun to observe radial velocities of stars with an optical spectrometer designed for unusually high accuracy. Light from a star image in the focal plane of a telescope is fed to the entrance aperture of the spectrometer by a single optical fiber. Wavelengths are calibrated by transmission of collimated light through a tilt-tunable Fabry-Perot interferometer. The scrambling of incident light rays by the optical fiber and the intrinsic stability of the Fabry-Perot etalon provide immunity to the sources of systematic errors that plague conventional radial velocity meters. The spectrum is dispersed by an echelle grating crossed with another plane reflection grating. Several echelle orders in the vicinity of 4250-4600 Å are imaged in a two-dimensional format on a charge-coupled (CCD) array of detectors. About 350 distinct points on the profile of the stellar spectrum are sampled by successive orders of interferometrie transmission through the etalon. In the vicinity of 4300 Å each interference order is 47 milliangstroms wide and the sample points are 0.64 Å apart, resulting in distinct , widely-spaced monochromatic images of the entrance aperture to be formed in the focal plane of the camera. Changes in Doppler shift cause changes in the relative intensities of these images, according to the slope of the spectral profile at each point sampled. The instrument is being operated as a null-measurement accelerometer, sensitive only to changes in radial velocity, which simplifies operation and enhances sensitivity. With an argon-filled, iron hollow cathode emission line lamp, the interferometer can be calibrated to two parts in 100 million; this corresponds to ± 6 meters/sec in Doppler shift. Calibrations of the interferometer show variations of ± 27 meters/sec on a time scale of months; observations of stars are corrected for such changes. The internal repeatability of observations of the differential Doppler shift of light from the integrated disk of the Sun is ± 6 meters/sec. The corresponding result from about 70 observations of Arcturus (Kl IIIb; B=1.19) is ± 40 meters/sec internal repeatability for each exposure of 20 square-meter seconds. The external repeatability (day-to-day differential accuracy) of nightly averages of stellar observations is ± 20 meters/second. Since the internal precision on the sun and the argon lamp is much better than it is with short exposures on Arcturus, the quality of our observations of stars is limited by the rate of detected photons. This justifies averaging a number of short exposures of a star to approach “laboratory” precision.
A Search for High Velocity Stars
Authors: Florsch A.
Published: July 2016

Fehrenbach’s objective-prism technique for the measurement of radial velocities is well known and has already proved its efficiency. New measuring devices (MESUCOR, FENTOMIX at the O.H.P.) based on the correlation between records make the measurement more rapid and more accurate and will encourage others to use this method. An example is the Hipparcos radial-velocities program. But it is also true that this new process has its limits and does not permit one to get all the information which is on an objective-prism plate, for it is limited by the quality (principally the density) of the images. It will be necessary to continue with the classical visual measurements, especially if one wants to detect faint high-velocity stars quickly, which are often at the density limit of the photographic plate. We must keep in mind that the objective-prism technique is best for this purpose since a three or four hour exposure leads to a great number of spectra (about 60 near the pole, to 200 in the galactic plane in a field of 2X2 degrees).
The Local Galactic Escape Velocity
Authors: Carney Bruce W. , Latham David W. , Peterson Ruth C.
Published: July 2016

We discuss the corrections to the perceived motions of stars due to the disk’s circular velocity, which we determine to be 220 km sec . This implies a Keplerian escape velocity of 310 km sec−1. We discuss upper limits to the rest-frame space velocities of stars from four sources: the summary of Saio and Yoshii (1979); the large new survey of proper motion stars of Carney and Latham (1985); a study of 27 faint proper motion stars near the South Galactic Pole by Carney and Peterson (1984a); and observations by Carney and Peterson (1984b) of stars with possibly extreme velocities identified by Eggen (1969). We find the maximum velocities are near 500 km secc−1, which is likely to be the local value of the escape velocity. This implies a large amount of gravitating matter outside the solar galactic orbit.
Vitesses Radiales Pour Le Programme Hipparcos
Authors: Duflot M.
Published: July 2016

L’étude faite par Ch. Fehrenbach prouve que les Prismes-Objectifs à champ normal (PO) sont les instruments parfaitement adaptés a une étude statistique des mouvements stellaires dans la galaxie.

Les PO souffraient jusqu’à ces dernières années, d’un dépouillement laborieux, inadapté à leur capacité. Les moyens informatisés actuels donnent la possibilité de les utiliser avec le rendement voulu.

Au début de 1982, le groupe du satellite Hipparcos a fait une demande de mesures de vitesses radiales (VR) pour compléter les informations que donnera le satellite. Depuis cette date, nous nous sommes engagés dans la mesure des VR des étoiles brillantes (mg < 9,0) qui sont une partie essentielle du programme Hipparcos. En particulier, nous avons choisi des champs où se groupaient des étoiles des premiers types spectraux (≤ F5) dont la VR était inconnue. Les étoiles des types plus avancés (> F5) peuvent en effet être mesurées, avec plus de précision, avec la méthode de spectrocorrelation directe sur le ciel. Signalons que nous mesurons cependant, dans les champs choisis, les étoiles de tous les types spectraux
A Critical Examination of the Stock Velocity Survey
Authors: Osborn Wayne , MacConnell D.J.
Published: July 2016

The possibility of determining stellar radial velocities for large numbers of stars from objective-prism plates was recognized soon after objective-prism spectroscopy became a common observational technique ; (Pickering, 1887). However, the initial investigations quickly revealed a serious practical problem: how does one determine the rest wavelength position in slitless spectra? This difficulty caused the objective-prism method of obtaining radial velocities to be neglected for many years. It was not until the second half of this century that the method saw a large-scale application. This was the work of Fehrenbach who developed a technique based on a specially designed zero-deviation prism, and successfully used it to isolate members of the Large Magellanic Cloud from foreground field stars (Fehrenbach 1947a, 1947b, 1948; Fehrenbach and Duflot 1970). The Fehrenbach technique has since been applied in a number of other studies; one can mention, as examples, recent work on spectroscopie binaries (Gieseking and Karimie 1982), on cluster membership (Gieseking 1980), and on velocity dispersions at intermediate galactic latitudes (Fehrenbach and Burnage 1982).
Metallic-Line Binaries
Authors: Abt Helmut A.
Published: July 2016

A new radial-velocity study of 55 Am stars reveals 16 SB2s, 20 SBls, and 22 visual or occultation companions for a total of more than one companion per primary. Only about 75% of the primaries are in binaries with periods less than 100 days, even if we allow for unobservable small inclinations and low-mass secondaries. Therefore it may not be true that tidal interactions in close binaries is the only mechanism necessary to produce the low rotational velocities that allow diffusion to act, unless small reductions (factor of 1.4) in rotational velocities occur in binaries of longer periods. The binary frequency of the combined Am plus normal A stars is normal.
Bright Giants with Small Amplitude Long Period Velocity Variability
Authors: Beavers Willet I.
Published: July 2016

Observations during the first eight years of operation of the Fick Observatory photoelectric radial velocity spectrometer have led to the development of a list of approximately seventy bright late giant stars with suspected small amplitude long period velocity variations. Some of these stars have been identified as variable velocity objects by other observers, and a few of them have previous low quality orbit determinations or estimations. Preliminary SB1 orbits are reported for eight of the list members which have been observed through at least one complete cycle. Estimates of the period (P) and velocity semiamplitude (K) are made for other confirmed variables. Generally, the sample contains long P (2 to 8 years), small K (4 to 14 km/sec), late giant systems.
Radial-Velocity Standards
Authors: Batten Alan H.
Published: July 2016

The writer reviews the presently available lists of standard-velocity stars approved by IAU Commission 30 and suggests that the time has arrived for major revisions. Many of the currently adopted standards are known or suspected to be variable in velocity at the level of precision to which we can now work. The writer suggests that we need three levels of standards. Some half-dozen or so bright solar-type stars, visible from all major observatories, should be chosen as fundamental standards, after extensive testing by many observers in various places. A larger group of secondary standards, in various parts of the sky and of a wider range of spectral type and brightness, should be chosen for everyday use by observers working at moderate dispersions. Those stars in the current IAU lists not yet suspected of having variable velocities might form the nucleus of this group. Finally, reference stars should be chosen for special purposes (e.g. cross-correlation, objective-prism determinations) in consultation with the users of these techniques. Standards of accuracy for this last group of stars need not be so strict as for the others.
Summary
Authors: Freeman K.C.
Published: July 2016

We have seen at this meeting how technical advances In devices and detectors have made it possible to measure accurate radial velocities for faint stars and very accurate velocities for brighter stars. People are working on a wide range of frontier problems that were out of reach only a few years ago. Stellar radial velocity work is making an outstanding contribution to our understanding of stars, star clusters and the Galaxy, and I believe that this work has a very rosy future.

I would like now to pick out some topics that seemed particularly important for the present and the future.
Spectroscopy of Globular Clusters in the Remote Halo
Authors: Peterson Ruth C.
Published: July 2016

Spectra from 3800 to 5200 Å with a resolution of 4.5 Å/mm have been obtained for from 4 to 10 stars in each of the remote globular clusters Palomar 1, Eridarm s, NGC 2419, Palomar 3, Palomar 4, Palomar 5, Palomar 14 and Palomar 13. For comparison purposes the moderately distant clusters NGC 1904, NGC 4U7.NGC 5024, NGC 5053, NGC 5466 and NGC 5634 were also observed, along with the nearby globulare M 3, M 5, M 13, M 92, M 71 and M 15. In a1l cases spectra of stars in each cluster were recorded simultaneously, using an aperture plate with the KPNO 4 m telescope, R-C spectrograph, Simmons camera and baked IIIaJ plates. Sky spectra were also obtained at the same time.
The Velocity Dispersion of M 4 Horizontal-Branch Stars
Authors: Peterson Ruth C.
Published: July 2016

Radial velocities have been measured for nine blue horizontal-branch stars in the globular cluster M 4. Their mean velocity is 72.3 ± 0.9 km/s, and their velocity dispersion (after removal of the ±1.5 km/s random error on an individual measurement) is 1.9 ± 0.3 km/s. The observed dispersion is considerably smaller than the value of 4.4 km.s inferred by Peterson and King (1975) from their fit of a King model to the central surface brightness distribution, assuming a solar mass-to-light ratio. This new measurement is more discrepant with such a fit than that noted by Petrson and King, who relied upon the central velocity dispersions measured in integrated light by Illingworth (1976). Of necessity, the clusters studied by Illingworth are highly centrally concentrated, while M 4 is of rather low central concentration. This new result raises the possibility that M 4 in particular, and low-concentration clusters in general, may have mass-to-light ratios that are less than solar. This suggestion should be checked using accurate measurements (to better than 1 km/s) of the velocities of a dozen giants in this and other low-concentration clusters.
High-Velocity Halo Binary Systems
Authors: Ardeberg Arne , Lindgren Harri
Published: July 2016

For our understanding of the earliest phases of galactic star formation we are severely restricted by our lack of relevant samples of stars of early generations. For this reason, it is important to obtain samples of Population II stars, which are as unbiased as possible. Concerning our picture of the first star-formation processes, binary systems with high system velocities are of special interest. Reliable statistics on such objects could give crucial information regarding some key questions connected to the chemical and dynamical state of the early, protostellar matter. Reference is made to a recent discussion of these questions based on photometric data by Carney (1983). We also refer to the binary statistics given by Abt and Levy (1969), by Crampton and Hartwick (1972) and by Abt (1979) indicating a much lower binary frequency for metal-poor stars than for stars belonging to the disk population.
Heavy Remnants in Globular Cluster Cores
Authors: Mayor M. , Meylan G.
Published: July 2016

With a mean precision of 0.6 km/s per measurement, the radial velocities of 169 giants in 47 Tue (published in Mayor et al., 1983) added to the further measures of 25 stars in the core, have permitted the determination of rotation V(r,z) and velocity dispersion σ(r) in this globular cluster. With a mean precison of 0.9 km/s per measurement, the radial velocities of 298 giants in ω Cen (to be published in Mayor et al., 1985), distributed up to the centre, have also permitted the determination of V(r,z) and σ(r) (for both clusters, see Meylan and Mayor, 1984).

The ratios νo/σo of ordered to random motions and the ellipticities of ω Cen and 47 Tue point to a global isotropy of the velocity dispersion.
The Whole Earth Telescope
Authors: Nather R. Edward
Published: July 2016

The history of our galaxy and the detailed history of star formation in the early universe is written in the white dwarf stars. Recently we have learned how to reach beneath their exposed surfaces by observing white dwarfs that are intrinsic variables. We use the stellar equivalent of seismology to probe their interiors, and thus to unravel the history they hold inside. We have designed and placed into operation an observational technique that uses the whole earth as a telescope platform, defeating the effects of daylight which, until now, had seriously limited the length of a single light curve, and therefore the amount of information we could hope to extract from it. This paper describes our new telescope and presents preliminary results from our first observing run in March, 1988.
The Effects of Time Dependant Convection on White Dwarf Radial Pulsations
Authors: Starrfield S. , Cox A. N.
Published: July 2016

We have investigated the effects of relaxing the normal assumption of frozen in convection on studies of radial instabilities in 0.6M⊙ carbon-oxygen white dwarfs with either pure hydrogen layers overlying pure helium layers or 0.6M⊙ carbon-oxygen white dwarfs with pure helium surface layers. In this paper we assume that convection can adjust to the pulsation at a rate determined by the time scale of a convective eddy. Using this assumption in our analysis stabilizes most of the modes in both the DA and DB radial instability strips. We also find that the blue edge of the DA radial instability strip, assuming frozen in convection, is between 12,0O0K and 13,000K. The blue edge for the DB radial instability strip (frozen in convection) is between 32,000K and 33,000K.
Observations of Cold Degenerate Stars
Authors: Ruiz Maria Teresa , Anguita Claudio , Maza Jose
Published: July 2016

Spectrophotometry, BVRI CCD photometry and CCD trigonometric parallaxes of the southern DC stars vB3, ER8 and ESO 439-26 are presented. These stars should be considered among the lowest luminosity degenerates known, with absolute visual magnitudes of 15.4, 16.2 and 17.2 respectively.
An Unsuccessful Search for White Dwarf Companions to Nearby Main Sequence Stars
Authors: Shipman Harry L. , Geczi Jeanne
Published: July 2016

Many of the nearest white dwarf stars (e.g., Sirius B and Procyon B) are in such binaries and would have remained undiscovered if they were even a little bit further away. White dwarfs which are sufficiently hot (T(eff) > 10,000 K) would, if present in binary systems with a relatively cool (F, G, K, or M) main–sequence secondary, be visible in IUE images as a hot companion to the main sequence star. We systematically examined 318 IUE images of 280 different G, K, and M stars which had been observed for other purposes. No previously undiscovered white dwarf stars were found.
A Spectrophotometry Atlas of White Dwarfs Compiled from the IUE Archives
Authors: Swanson Steven R. , Wegner Gary
Published: July 2016

In the past ten years, more than 775 low resolution spectra of white dwarfs have been taken with the International Ultraviolet Explorer satellite (IUE). This wealth of information has yielded many new discoveries in the field of white dwarf research; a few of which include: the λ1400 and λ1600 quasi-molecular features discovered in hydrogen rich DA white dwarfs (Greenstein 1980; Wegner 1982, 1984; Nelan and Wegner 1985; and Koester et. al. 1985), strong C I lines in some DQ white dwarfs (Koester, Weidemann, and Vauclair 1980; Wegner 1981a,b), and the absence of these same lines in hotter DB white dwarfs by Wegner and Nelan (1987) which may indicate convective mixing (Pelletier et al. 1986).
Results of a Spectrophotometric Survey of White Dwarf Suspects in the Solar Neighbourhood
Authors: Bues I.
Published: July 2016

320 blue stars of the Giclas and Luyten catalogues with positions δ 15° and magnitudes have been observed photometrically in UBVRI and Stromgren colours with the ESO lm telescope at La Silla in order to increase the number of close-by white dwarfs. From their Strömgren colours more than 120 stars belong to the white dwarf region. But, as outlined by Rupprecht and Bues (1983), a combination of the photometric systems and the combined two-colour diagrams (R−I)/(U−V) and (R−I) / (u−b) provide additional information on binary components. Fig.1 shows a sample in the (R−I)/(u−b)diagram. For (u−b) <.2 and (R−I) <.2 a second component is present.
Three Double Degenerate Candidates
Authors: Foss Diana
Published: July 2016

This poster reports the results of a search for variable radial velocities in 29 DA white dwarfs. The survey was sensitive to periods between 1h and 66d, although non-ideal sampling limited the longest practically detectable period to 2d. Three stars were discovered to have radial velocity shifts at above the 3σ level. The discovery of these stars, along with that of Saffer, et al. (1988) can put only a lower limit on the space density of close binary white dwarfs, as this survey was less than 100% efficient in detecting radial velocity variations, and its efficiency depended strongly on period.
X-ray Emission from Hot DA White Dwarfs; EXOSAT Results, and Implications for Atmospheric Models
Authors: Paerels Frits , Heise John
Published: July 2016

We present the observations of the photospheric X-ray spectra of hot DA white dwarfs, obtained with the 500 lines mm−1 Transmission Grating Spectrometer on EXOSAT. These spectra cover the full soft X-ray band, at high wavelength resolution and statistical quality. They allow us to do an accurate measurement of the photospheric parameters, particularly of effective temperature and chemical composition of the atmosphere.

We consider the case of HZ 43 in some detail. Model atmospheric spectra that satisfy all measured absolute optical, UV and X-ray fluxes turn out not to fit the shape of the measured X-ray spectrum. However, from a comparison of model spectra calculated with different model atmospheres codes we infer the existence of a 15% systematic uncertainty in the model fluxes at the shortest wavelengths (λ < 100 Å) in current model calculations. This can explain the fitting problem. Since the systematic uncertainty in the models is larger than the statistical uncertainty in the shape of the measured X-ray spectrum of HZ 43, we cannot at present use this measured shape to derive the effective temperature and gravity. We revert to broad band photometry, using the measured integrated soft X-ray flux and the optical flux, to determine Te = 45,000 – 54,000K, R/R⊙ = 0.0140 – 0.0165. From the absence of the He II Ly edge at 227 Å in the measured spectrum, we set a upper limit on the photospheric helium abundance of He/H = 1.0 × 10−5; this upper limit is independent of the uncertainties in the model calculations mentioned above.
Chemical Stratification in White Dwarf Atmospheres and Envelopes
Authors: Koester D.
Published: July 2016

The theory of gravitational separation of elements under the combined influence of gravity and electric fields (Schatzman 1958) has been very successful in explaining the general mono-elemental composition observed in most hot white dwarf atmospheres. Today the exceptions to the rule - DO and DAO with mixed compositions (Wesemael et al.1985), DA with traces of helium (Kahn et al. 1984, Petre et al. 1986, Jordan et al.1987, Paerels 1987), DAB (Liebert et al. 1984), and DBA (Shipman et al. 1987) - pose a problem, because they seem to demand a mechanism that counteracts gravitational separation. Such a mechanism that satisfies the observational constraints is very hard to find, and this has led in recent years to the growing conviction that we indeed observe the equilibrium state of diffusion, but in white dwarfs with extremely thin hydrogen layers that remain transparent (at least in the EUV) in many objects (Jordan and Koester 1986, Liebert et al.1987, Vennes et al. 1987, Fontaine et al.1988, Vennes et al.1988).
An Ultraviolet Look at the Blue Edge of the ZZ Ceti Instability Strip
Authors: Lamontagne R. , Vesemael F. , Fontaine G. , Vegner G. , Nelan E. P.
Published: July 2016

It has already been shown that most, and probably all, of the DA white dwarfs become variable in a narrow temperature range as they cool down (Fontaine et al. 1982). Optical photometry and spectrophotometry has led to several determinations of the boundaries of this instability strip. The strip has been found to cover the range 10300 - 13600 K (McGraw 1979), 10400 - 12100 K (Greenstein 1982), 10000 - 13000 K (Weidemann and Koester 1984) and 11000 - 13000 K (Fontaine et al. 1985). Theoretical calculations show that the location of the blue edge is very sensitive to the efficiency of convection used in the unpertubed models (Winget et al. 1982; Winget and Fontaine 1982; Fontaine, Tassoul, and Wesemael 1984). Also, the sharpness of this boundary depends on the range of stellar mass and thickness of the hydrogen envelope found in ZZ Ceti stars. Recently, Wesemael, Lamontagne, and Fontaine (1986) and Lamontagne, Wesemael, and Fontaine (1987) have obtained and compared ultraviolet observations of several DA white dwarfs, in or near the instability strip, with published model calculations from Nelan and Wegner (1985), hereafter NW, and Koester et al. (1985), hereafter KWZV. They determined the boundaries of the variability region at 11400 - 12500 K or 11700 - 13000 K depending on which grid was used. We present here a reanalysis of these IUE observations with an improved grid of model atmospheres in order to define more precisely the location of the blue edge.
Second-Order Effects due to Rotation in Pulsating Da White Dwarfs
Authors: Brassard P. , Vesemael F. , Fontaine G.
Published: July 2016

The ZZ Ceti star L 19-2 is a stable pulsator whose light curve has now been deciphered with the help of over 300 hours of white light, high-speed photometry (O’Donoghue and Vamer 1982, 1987, hereafter ODV). The analysis indeed reveals the presence in the light curve of five coherent oscillations, with periods ranging from 113s to 350s. Among those, the 192s oscillation possesses three components, almost equally separated in frequency. Most importantly, the slight, but statistically significant, inequality in the frequency spacing of the triplet has been interpreted by these authors as second-order splitting of rotationally-perturbed g-mode oscillations. And indeed, the measured splitting appears consistent with the theoretical predictions of Chlebowski (1978), which are based on somewhat archaic white dwarf models. As pointed out by ODV, it is clearly of great interest to investigate 1) to what extent theoretical predictions based on more realistic, current-generation white dwarf models agree with ODVs identification, and 2) to what extent such second order effects can, eventually, be used to identify individual pulsation modes or constrain the structural parameters of variable white dwarf stars. Motivated by these questions, we have initiated a study of second-order effects due to rotation in ZZ Ceti stars, and we report here the first results of this program.
Discovery of the sixth DBV Star: CBS 114
Authors: Winget D. E. , Claver C. F.
Published: July 2016

Though widely spread across the H-R diagram the compact pulsators have much in common. All are multi-periodic, and most have extremely complex light curves. All appear to be pulsating in nonradial g-modes, with temperature variations responsible for the bulk of the light modulations. The g-modes are global in nature and, typically, many are excited in each pulsator, so they are a rich source of seismological information about the interior regions of the white dwarf stars.

The pulsating DB white dwarf stars (DBV’s) form one of the three distinct classes of pulsating compact objects currently known. We find these classes nearly uniformly distributed in log Te spanning virtually the whole range of the white dwarf cooling sequence, from the hot DOV stars at log Te ~ 5 to the DAV (ZZ Ceti) stars at log Te ~ 4; the DBV stars, with logTe ~ 4.5, fall in the middle.
A New Temperature Determination for Sirius B from IUE: Implications for the Observed Soft X-Ray Fluxes
Authors: Kidder K. , Holberg J.B. , Wesemael F.
Published: July 2016

We have used IUE archive observations to obtain a new and independent estimate of the effective temperature of Sirius B. In this effort we have modeled the observed Lyman alpha profile of Sirius B as a function of effective temperature and find; Teff = 24,500 ± 500 K. This temperature is in good agreement with a recent result obtained from analysis of EXOSAT soft X-ray spectra of Sirius B. In addition to providing confirmation of the soft X-ray result, this temperature implies that Sirius B is significantly cooler and larger in radius than most previous estimates. The radius, R = 0.090 ± 0.005 R⊙, implied by the lower temperature is well in excess of the radius of fully degenerate star having the mass of Sirius B. This investigation employed a unique set of SWP archive spectra, acquired with Sirius B in the small aperture, which have proved to be free of scattered light contamination from Sirius A.