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We present time-resolved, high signal-to-noise intensity spectra for the magnetic white dwarf Feige 7. On the basis of these data, we show, using computer models for magnetic stars, that the magnetic field in Feige 7 cannot be represented by a centered dipole geometry. We find that a good approximation to the field is a dipole of strength 35 MG displaced by 0.15 white dwarf radii from the stellar center, viewed at different angles as the star rotates. Furthermore, we find it necessary to use a model with variable surface abundances of hydrogen and helium to reproduce the variation, due to stellar rotation, in the Zeeman absorption lines of these elements

Time-series photometric observations of the binary star V471 Tauri were conducted using the Whole Earth Telescope observing network. The purpose was to determine the mechanism responsible for causing the 555 and 277 s periodic luminosity variations exhibited by the white dwarf in this binary. Previous observers have proposed that either g-mode pulsations or rotation of an accreting magnetic white dwarf could cause the variations, but were unable to decide which was the correct model. The present observations have answered this question. Learning the cause of the white dwarf variations has been possible because of the discovery of a periodic signal at 562 s in the Johnson U-band flux of the binary. By identifying this signal as reprocessed radiation and using its phase to infer the phase of the shorter wavelength radiation which produces it, made it possible to compare the phase of the 555 s U-band variations to the phase of the X-ray variations. It was found that U-band maximum coincides with X-ray minimum. From this result it was concluded that the magnetic rotator model accurately describes the variations observed, but that models involving g-mode pulsations do not.

Results are reported from 264.1 hr of nearly continuous time-series photometry on the pulsating prewhite dwarf star (DPV) PG 1159 - 035. The power spectrum of the data set is completely resolved into 125 individual frequencies; 101 of them are identified with specific quantized pulsation modes, and the rest are completely consistent with such modal assignment. It is argued that the luminosity variations are certainly the result of g-mode pulsations. Although the amplitudes of some of the peaks exhibit significant variations on the time scales of a year or so, the underlying frequency structure of the pulsations is stable over much longer intervals. The existing linear theory is invoked to determine, or strongly constrain, many of the fundamental physical parameters describing this star. Its mass is found to be 0.586 solar mass, is rotation period 1.38 days, its magnetic field less than 6000 G, its pulsation and rotation axes to be aligned, and its outer layers to be compositionally stratified.

We report the discovery of low-amplitude pulsation modes in the faint variable DO white dwarf PG 1707+427 (V817 Her). With the large aperture of the CFHT, enough modes were uncovered to allow us to derive a preliminary asteroseismological estimate of the mass of the star of approximately 0.7 M ⊙ . This assumes that the modes observed have a spherical harmonic index l=1

An extensive set of high-speed photometric observations obtained with the Whole Earth Telescope network is used to show that the complex light curve of the ZZ Zeti (DAV) star G29-38 is dominated by a single, constant amplitude period of 615 s during the time span of these observations. The pulse arrival times for this period exhibit a systematic variation in phase readily explained by light-travel time effects produced by reflex orbital motion about an unseen companion. The best-fit model to the observations indicates a highly eccentric orbit, a period of 109 + or - 13 days and a minimum mass of 0.5 solar mass for the companion.

L'analyse des observations photometriques et des vitesses radiales derivees des observations spectroscopiques de l'ex-nova CP Pup fournit une periode de modulation en desaccord avec des donnees anterieures, suggerant la presence de plus d'une periodicite photometrique. L'etude presente ne permet pas de classifier CP Pup comme une variable cataclysmique magnetique et une etude plus complete du comportement de la modulation photometrique est suggeree

Les timings de 37 eclipses de la nova naine IP Peg, obtenus de 1986 a 1988, sont presentes et combines avec les timings publies anterieurement afin de remettre a jour l'ephemeride orbitale et d'examiner le comportement du rayon du disque d'accretion tout le long du cycle de sursaut. Les resultats montrent un accroissement rapide de la periode orbitale et des explications possibles sont suggerees

The results of forty-eight resection arthroplasties (Girdlestone procedures) in forty-three patients were analyzed. The indications were sepsis after a total hip replacement (thirty-three procedures), aseptic loosening of a total hip replacement (ten procedures), and primary septic arthritis (five procedures). The resection arthroplasty effectively eradicated the sepsis in all but three patients, who had a recurrence. Pain was alleviated in nearly all of the patients, but the ability to walk and the level of activity improved only slightly. Shortening of the limb ranged from three to eleven centimeters, and all patients used a support for walking. The six patients who had a bilateral procedure were able to walk using double supports. With regard to relief of pain, walking, and function, the results were significantly poorer in the women, particularly the older ones. The results were also significantly inferior in the patients who had had sepsis after a total hip replacement. Generally, walking, function, and the level of activity were better when much of the proximal end of the femur had been retained. Resection arthroplasty should spare as much of the proximal end of the femur as possible if a future replacement of the hip is contemplated.

The grid radiograph, a new technique for radiographic evaluation of total hip replacements, ensures reproducible positioning of the hip and the x-ray beam. When this method was used, the images of stable acetabular and femoral components on one radiograph could be superimposed perfectly on the images of these components on subsequent radiographs. Subtle shifts in the positions of the components, such as tilting of the femoral surface replacement, subsidence of the femoral component, or migration of the acetabular component, were detected. When used with high-contrast radiographic technique and film, the implant-bone interfaces were depicted better by this method than by others. Grid radiographs can be used for detailed prospective evaluation of total hip replacements and are of practical value in counseling patients about the probable durability of the replacement.

Many college physics departments would welcome the opportunity to initiate a modest research program which could involve their undergraduate students. Astronomical photoelectric photometry is a field in which it is possible to initiate a useful undergraduate oriented research program with relatively modest equipment, some of which can commonly be found in a college physics department. A sketch of the equipment necessary, opportunities, and challenges in this work are presented.

White dwarf stars provide important boundary conditions for the understanding of stellar evolution. An adequate understanding of even these simple stars is impossible without detailed knowledge of their interiors. PG1346+082, an interacting binary white dwarf system, provides a unique opportunity to view the interior of one degenerate as it is brought to light in the accretion disk of the second star as the primary strips material from its less massive companion (see Wood et at. 1987).PG1346+082 is a photometric variable with a four magnitude variation over a four to five day quasi-period. A fast Fourier transform (FFT) of the light curve shows a complex, time-dependent structure of harmonics. PG1346+082 exhibits flickering – the signature of mass transfer. The optical spectra of the system contain weak emission features during minimum and broad absorption at all other times. This could be attributed to pressure broadening in the atmosphere of a compact object, or to a combination of pressure broadening and doppler broadening in a disk surrounding the compact accretor. No hydrogen lines are observed and the spectra are dominated by neutral helium. The spectra also display variable asymmetric line profiles.

A computer model is developed using infinitely long concentric cylindrical shells to represent the neutral atoms, ions and electrons in the barium cloud. The neutral shells are given a distribution of positions and velocities whose parameters are chosen to be consistent with the dynamics of the release. From this distribution, the ion and electron shells are generated at random using the observed time constant for photoionization. The ion and electron shells thus formed are followed using self-consistent equations of motion. Various averages which could be compared with observation of the actual cloud are calculated at regular time intervals. An unexpected result is the predicted very early return of the magnetic field within the cloud to its ambient value.

An experimental procedure is presented which enables the beginning or intermediate student of mechanics to use linear air track apparatus to determine the functional relationship between the period, mass, and spring constant for small amplitude oscillatory motion. The results of a typical set of experiments as well as two different methods for obtaining the desired mathematical expression are included. The resulting expression agrees well with that which can be derived analytically from Hooke's law.

The initial phase of the free expansion of a one-dimensional plasma is studied by the use of the computer experiment technique. Three models are utilized, using ion and electron sheets in the form of infinite plane sheets, concentric infinite cylindrical shells and concentric spherical shells respectively. In each case electron sheets and one-component ion sheets move in a self-consistent electric field. The dynamics of each expansion is analyzed in terms of average expansion velocities, oscillation frequencies and relative distribution of energy between thermal, flow and electric field energies. Comparison of pertinent quantities is made between the three models. Over the first few plasma periods the expansions are similar, but with significant differences which can be attributed to the geometry of the model. The use of the symmetry most nearly like that of the physical problem which is being modeled is indicated.

PG 1707+427 was identified in the Palomar-Green survey (Green Schmidt and Liebert, 1986) as an object with a significant ultraviolet excess. Observations by Bond and Grauer in 1982 showed it to be a pulsating variable (Bond, Grauer, Green and Liebert, 1984). Fourier transforms of the discovery time-series photometric runs revealed power in PG 1707+427’s light curves in two bands with periods near 450-s and 333-s. The longer period peak was observed to have a variable amplitude while the other one appeared relatively constant in strength. Wesemael, Green and Liebert (1985) placed PG 1707+427 in the spectroscopic class of PG 1159–035 (DOV) pulsating variables.

The results of forty-eight resection arthroplasties (Girdlestone procedures) in forty-three patients were analyzed. The indications were sepsis after a total hip replacement (thirty-three procedures), aseptic loosening of a total hip replacement (ten procedures), and primary septic arthritis (five procedures). The resection arthroplasty effectively eradicated the sepsis in all but three patients, who had a recurrence. Pain was alleviated in nearly all of the patients, but the ability to walk and the level of activity improved only slightly. Shortening of the limb ranged from three to eleven centimeters, and all patients used a support for walking. The six patients who had a bilateral procedure were able to walk using double supports. With regard to relief of pain, walking, and function, the results were significantly poorer in the women, particularly the older ones. The results were also significantly inferior in the patients who had had sepsis after a total hip replacement. Generally, walking, function, and the level of activity were better when much of the proximal end of the femur had been retained. Resection arthroplasty should spare as much of the proximal end of the femur as possible if a future replacement of the hip is contemplated.

An established rabbit hindlimb model was used to determine the effects of systemic steroid administration on posttraumatic limb swelling and joint stiffness. Dexamethasone acetate was administered intramuscularly to the test rabbits in one of four doses two hours following fracture as well as one and two weeks later. Dexamethasone did not produce a significant decrease in swelling but did produce a statistically significant dose-dependent decrease in ankle stiffness compared to controls. Tibia torsional strength to failure was not adversely affected.

The central star of the planetary nebula Abell 41 has been found to be a detached binary star system with a period of 2 hours 43 minutes. Photometric observations which support this conclusion were carried out at Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), and Louisiana State University (LSU) Observatory.

To determine the effects of intermittent passive motion on joint stiffness following periarticular fracture, bilateral distal tibia fractures were produced in 31 rabbits. Following immobilization and fracture union at three weeks, one ankle on each rabbit underwent passive exercise daily until sacrifice at six weeks. The contralateral ankle remained immobile, except for weekly stiffness determinations. Passive exercise produced limb swelling and resulted in temporarily decreased ankle stiffness to, but not significantly below, control values. Between exercise sessions, the exercised ankles became significantly stiffer than the contralateral immobilized ankles. The cause of stiffness was not determined, but extrapolation from other work would suggest that the regimens of intermittent passive exercise tested in this study additionally traumatized the healing tissues surrounding the fracture.

HFG1 (136+5°1) is a large, low-surface-brightness planetary nebula that was discovered by Heckathorn, Fesen, and Gull (Astron. Astrophys., 114, 414, 1982). In the autumn of 1986, photoelectric photometry by A.D.G. and H.E.B. showed that the 14th-mag central star of HFG1 is a large-amplitude variable. Subsequent CCD photometry by R.C. and H.E.B. reveals a sinusoidal variation with a period of 13.96 hr and an amplitude of 1.1 mag in the B band.

The grid radiograph, a new technique for radiographic evaluation of total hip replacements, ensures reproducible positioning of the hip and the x-ray beam. When this method was used, the images of stable acetabular and femoral components on one radiograph could be superimposed perfectly on the images of these components on subsequent radiographs. Subtle shifts in the positions of the components, such as tilting of the femoral surface replacement, subsidence of the femoral component, or migration of the acetabular component, were detected. When used with high-contrast radiographic technique and film, the implant-bone interfaces were depicted better by this method than by others. Grid radiographs can be used for detailed prospective evaluation of total hip replacements and are of practical value in counseling patients about the probable durability of the replacement.

6th Whole Earth Telescope Workshop (WET) -- JUN 20-21, 2002 -- NAPLES, ITALY, WOS: 000184698800009, The Multi-site spectroscopic telescope is a virtual instrument and the name of a collaboration that opens up a new observational window by combining continuous observations of spectroscopic variations and simultaneous photometric monitoring. This constitutes an enormous observational effort, but in return promises to finally provide access to a mode identification for and an asteroseismological analysis of the pulsating sdB star PG 1605+072. Multi-Site Spectroscopic Telescope observations for this object have been secured during a large coordinated campaign in May and June of the year 2002. The frequency resolution and coverage of the photometric time series has been noticeably enhanced by a significant contribution from the Whole Earth Telescope, which was used to observe PG 1605+072 as an alternate target during the WET XCov22 campaign, also conducted in May 2002. This paper briefly outlines the motivation for the MSST project and tries to give a first assessment of the overall quality of the data obtained, with a focus on the Whole Earth Telescope observations.

The detection of soft X-ray pulsations from the hot, helium-rich, degenerate object, PG 1159-035 is reported. These observations, obtained with the Low Energy experiment on EXOSAT, show the presence of large-amplitude soft X-ray (44-150 A) pulsations analogous to several of the low-amplitude, nonradial, g-mode pulsations which are observed in the optical. These soft X-ray pulsations, with periods of 516 s, 524 s, and 539 s, arise from the photosphere of PG 1159-035 and constitute the first observations of stellar atmospheric pulsational phenomena in the X-ray band.

High speed photometry of the extremely hot, nearly degenerate stars PG 1707 + 427 and PG 2131 + 066 reveals that they are low-amplitude pulsating variables. Power spectral analysis shows both to be multiperiodic, with dominant periods of 7.5 and 6.4-6.9 minutes, respectively. Together with the known pulsators PG 1159 - 035 and the central star of the planetary nebula Kohoutek 1-16, these objects define a new pulsational instability strip at the hot edge of the H-R diagram. The variations of these objects closely resemble those of the much cooler pulsating ZZ Ceti DA white dwarfs; both groups are probably nonradial g-mode pulsators. Evolutionary contraction of the PG 1159 - 035 variables may lead to period changes that would be detectable in as little as 1 year. The optical and IUE spectra of the PG 1159 - 035 variables are characterized by absorption lines of C IV and other CNO ions, indicating radiative levitation of species heavier than helium. He II is also present in the spectra, but the hydrogen Balmer lines are absent. Effective temperatures near 100,000 K are required, and the He II 4686 A profiles indicate log g greater than 6. These helium-rich pulsators form the hottest known subgroup of the DO white dwarfs.

The central star of the planetary nebula VV 47 (164 +31deg1, occasionally known as NGC 2474-5) exhibits an optical spectrum similar to those of the pulsating PG1159-035 stars with somewhat broader absorption lines than those of the pulsating nucleus of the planetary nebula K1-16. Broad absorption features of He II, C IV, and O VI are observed, with narrow emission reversals in some cases. UBV photometry confirms that this is a very hot star, with little reddening. Several long runs of time-series photometry appear to show irregular variations, but we cannot present a conclusive case that this relatively faint object is a pulsating variable. The similarity to the PG1159-035 variables suggests a distance of 1060 (+1000,-600) pc. Our results are consistent with the distance, Zanstra temperature, and luminosity estimates derived by Kaler.

A small group of stars near the edge of the IC 1805 (W4) H II region has been studied partly for evidence of a physical association with the nebula. The two brightest stars have pronounced shell spectra and evidence of hydrogen emission lines. A B8 V star with weak Hg lines, two normal B stars, and four fainter stars in the field were studied. UBV, H-beta, and Stromgren four-color photometry of nine stars yield a reddening of E(B - V) = 0.54 m, a distance of 485 pc, and an age of not greater than 10 to the 7.4th yr. The two shell stars and two normal B stars fall on the ZAMS but the Hg star is either a multiple or foreground star and the three fainter stars are probably background stars. The group is not associated with the more distant (2200 pc) IC 1805.

HFG1 (136+5°1) is a large, low-surface-brightness planetary nebula that was discovered by Heckathorn, Fesen, and Gull (Astrpn. Astronphys., 114, 414, 1982). in the autumn of 1986, photoelectric photometry by A.D.G. and H.E.B. showed that the 14th-mag central star of HFG1 is a large-amplitude variable. Subsequent CCD photometry by R.C. and H.E.B. reveals a sinusoidal variation with a period of 13.96 hr and an amplitude of 1.1 mag in the B band.

Observations photometriques de 15 etoiles pouvant presenter les proprietes de pulsateurs chauds, deficients en hydrogene, tels que PG 1159-035 et le noyau de la nebuleuse planetaire K 1-16

Multicolor photometry of the hydrogen-deficient star BD -9°4395 has shown the star to be variable in light at optical wavelengths. Analysis indicates that any possible periods which exist must be longer than one hour.

UBV observations and a light curve are presented for a new variable star, chosen to be a companion star for the very hot degenerate dwarf PG 1520 + 525, and these data are found to be consistent with the interpretation that the new variable is a halo RR Lyrae variable of Bailey's type 'c'. Under the assumption that its absolute magnitude is +0.6, the UBV observations place it 2.2 kpc above the galactic plane, 8.5 kpc from the galactic center, and 2.8 kpc from the sun.

Photometric monitoring has revealed brightness variations of 0.1 m on a time scale of weeks for HD 46703, a metal-deficient F-type field analog of the stars lying above the horizontal branch in globular clusters. It is suggested that HD 46703 belongs to the '89 Her' class of luminous F-type variables. Since HD 46703 is unquestionably a halo object, it is almost certainly a low-mass star. It is suggested that it, and probably the other 89 Her variables, are masquerading as supergiants during their final evolution off the asymptotic giant branch.

Two dual-channel photometers have been constructed which enable the simultaneous observation of a rapid variable star and a nearby comparison star under conditions of variable atmospheric transparency. Photometer design is based on that of the McDonald Observatory high-speed photometer, with an on-axis main channel of standard design and a second channel consisting of a miniature photometer riding on the offset-guider stage. During observations, sky background measurements are taken periodically by briefly moving the telescope of the two stars, allowing the subtraction of sky contributions to each data point; the effects of extinction and variations in sky transparency are then removed from the sky-subtracted channel-one data by dividing by comparison star data. Data obtained under a variety of observing conditions at the Louisiana State University Observatory and at Kitt Peak National Observatory has demonstrated that precision high-speed photometry can be obtained under nonphotometric conditions with the two-star photometer.

The bright soft X-ray source E2003 + 225, originally discovered by the HEAO 1 low-energy detectors, has been found to be a new AM Herculis type binary. The optical counterpart shows a rich emission spectrum of He II, He I, and H as well as circular and linear polarization. Larger polarization in the near-infrared than in the ultraviolet argues for its origin as high harmonic cyclotron emission. Optical photometry, polarimetry, spectroscopy, and the X-ray light curves are all consistent with an orbital period of 222.51 m, the longest period known for AM Herculis systems, and only the second on the long side of the 2-3 hour cataclysmic variable period gap.

Spectra of the pulsating white dwarf ZZ Psc (= G29-38) were obtained using the International Ultraviolet Explorer. By using a multiple-exposure technique in conjunction with simultaneous ground-based exposure-metering photometry, it was possible to obtain mean on-pulse and off-pulse spectra in the 1950-1310 A wavelength range. The ratio of the time-averaged on-pulse to off-pulse spectra is best fitted by a temperature variation that is in phase with the optical light variation. This result is consistent with the hypothesis that the observed variation is due to a high-order nonradial pulsation. Conventional ultraviolet spectra of ZZ Psc showed broad absorption features at 1390 and 1600 A. These features are also found in the spectra of the cool DA-type white dwarfs G226-29 and G67-23, and appear to increase in strength with decreasing temperature. A possible explanation for the 1600 A feature is absorption by the satellite band of resonance-broadened hydrogen Ly-alpha. Such absorption would also help explain a discrepancy between the observed pulsation amplitude shortward of 1650 A and the predicted amplitudes based on model atmospheres.

La photometrie de l'etoile centrale de la nebuleuse planetaire Kohoutek 1-16 montre que c'est une variable pulsante de faible amplitude. La periode dominante est de 28,3 minutes, avec une semi-amplitude qui est habituellement voisine de 0,01 mag. Toutefois plusieurs periodes additionnelles apparaissent parfois dans les spectres de puissance calcules a partir des courbes de lumiere. On prevoit que la contraction de K 1-16 doit conduire a une diminution de periode si rapide qu'elle sera detectable sur un intervalle d'environ 2 ans

High-speed photometry of Hamuy's (Hamuy and Maza, 1986) blue variable star in Orion, obtained on September 26 and 28, 1986 with the two-star photometer of the University of Arkansas at Little Rock attached to the 1.3-m Kitt Peak National Observatory reflector, are presented. Both the short-time-scale flickering and the spectroscopic appearance of the star are found to be typical of the class of nova-like (UX UMa-type) variables. The data suggest that Hamuy's variable does not range over more than a few tenths of a magnitude.

The 5.2 hr X-ray binary 4U 2129+47 was observed for a full orbital cycle using the imaging proportional counter detector and the monitor proportional counter detector aboard the Einstein Observatory, as well as a 0.9 m reflector for 5 hrs continuous optical photometry. The X-ray and optical light curves, the X-ray spectrum, and the times of optical and X-ray minimum were determined. The shape of the 5.2 hr X-ray light curve is independent of energy. A partial X-ray eclipse occurred which was centered on the time of optical minimum and which lasted 20 percent of the orbital period. During this interval the X-ray intensity varied smoothly by a factor of three, and the light curve was symmetric relative to the time of minimum. These findings argue that the X-ray emitting region is extended and highly ionized. A model is presented in which an accretion disk corona scatters radiation from a central accreting neutron star.

Time-series photometry is reported that shows that KUV 05134 + 2605 is a pulsating DB white dwarf. The light curve shows sharply peaked pulses with a complicated mode structure including periods between 350 and 900 sec. The optical spectrum appears to be that of a star near the hot end of the DB sequence, consistent with theoretical predictions and the temperature range estimated empirically for previously known DBV stars. 21 refs.

On a obtenu quatre series d'observations photometriques de 4C 29.45 pendant un sursaut optique. Elles indiquent des variations de brillance rapides de l'ordre de 0,02 j ou moins. Plusieurs descriptions theoriques d'un quasar impliqent un trou noir tres massif entoure par un disque d'accretion. Elles permettent d'expliquer la variabilite rapide observee ici avec un choix realiste des parametres du modele