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NASA NTRS1985

The 1982-1984 Eclipse of Epsilon Aurigae

A workshop proceedings concerned with the new data collected during the 1982-1984 eclipse period of the 27-year system Epsilon Aurigae is presented. This binary star has been a classic problem in astrophysics because the opaque eclipsing object is nonstellar, and probably disk shaped. Invited papers concerning the history of the system, optical, infrared and ultraviolet photometry, optical polarimetry and ultraviolet spectroscopy are included. An invited paper concerning comprehensive theoretical interpretation in the context of stellar evolution also is included. The information collected herein is unparalleled in scope and will remain a standard reference until the next eclipse cycle in the year 2009 A.D., in all probability.

Stencel, R. E.↗

NASA NTRS1985

The newly discovered eclipsing supergiant 22 Vulpeculae

Spectra obtained with the IUE satellite have led to the discovery that 22 Vul is an atmospheric eclipsing binary belonging to the zeta Aurigae class of stars. The system is the first found with a G-type primary (G3 Ib-II), while the spectral type of the secondary is the latest (B9) and its period is the shortest (249 days) of any of the classical members of the group. Out-of-eclipse spectra, atmospheric eclipse phases and totality observations are discussed. Comparisons are made with other systems.

Ake, T. B.↗

NASA NTRS1986

Discovery of a new short-period, eclipsing cataclysmic variable

Photometry and spectroscopy of a newly recognized 14th mag eclipsing cataclysmic variable, KPD 1911 + 1212 (= SVS 8130, V1315 Agl) are reported. The system exhibits deep (1.7 mag) eclipses with period 0.1397 day. The spectrum is that of a high-excitation old nova and shows dramatic variability of the emission line strengths through the eclipse. The profiles of the Balmer emission lines are also phase-dependent, with prominent absorption cores appearing briefly near the inferior conjunction of the emission line source. There is no direct evidence for the secondary. A preliminary determination of radial velocity variations at modest spectral resolution yields K = 132 + or - 26 km/s for the Balmer emission lines. A model is presented for the system consistent with current data, which implies a mass for the primary and secondary stars of 0.9 and 0.4 solar mass respectively and in inclination of i = 78 deg.

Downes, R. A.↗

NASA NTRS1986

Fifteen years of solar eclipses - 1986-2000

The dates of occurrence and the paths of observability of the three total eclipses and 30 partial eclipses of the sun which will occur over the period 1986-2000 AD are identified. Data are provided for the times and duration of local maxima, the extent of coverage of the solar disk, and the breadth of the footprint of the eclipses on the earth's surface.

Espenak, Fred↗

NASA NTRS1987

Predictions for the total solar eclipse of 1988

A total eclipse of the sun will be widely visible from the East Indies on March 18, 1988. Detailed predictions for this event are presented which include tables of geographic coordinates for the northern limit, center line and southern limit of the path of totality, local circumstances for 40 cities within the total and partial eclipse paths, the lunar-limb profile, and maps depicting the path of totality. The author discusses the general characteristics of the eclipse, local circumstances from various points along the central path and the Saros-series history.

Espenak, Fred↗

NASA NTRS1988

Circular polarimetry of EXO 033319-2554.2 - A new eclipsing AM Herculis star

This Letter presents circular polarimetry that unequivocally identifies EXO 033319-2554.2 as only the third eclipsing AM Her star and brings the total number of AM Her stars now identified to 14. The orbital period is 126.4 minutes, as previously reported, and defines a new short-period edge to the period gap seen in all classes of cataclysmic variable stars. EXO 033319-2554.2 shows 2.5 mag deep eclipses of the predominantly accreting magnetic pole on the white dwarf. Before the eclipse, the pole rotates into the line of sight and shows white-light circular polarization, due to cyclotron radiation, that reaches values as high as 10 percent. There is some evidence that the second pole is emitting cyclotron radiation too. How high time resolution photometry, linear polarimetry, and spectroscopy will be of great value in understanding this system.

Berriman, Graham↗

NASA NTRS1988

US 943 - A 19th mag eclipsing cataclysmic variable with a period of 2 hr 3.8 min

The high-latitude, V equals about 19.5, blue variable star US 943 is found to be an eclipsing binary with an orbital period of 2.06 hr. The light curve is dominated by an orbital hump which has an amplitude of 0.9 mag in V and is centered about 0.17 orbital cycles before the 1.5-mag deep eclipse. There is evidence that the eclipse has at least two components. The overall appearance of the star is that of a dwarf nova in quiescence, a conclusion that is supported by the observation of a subsequent bright state (V equals about 15) suggesting a dwarf nova outburst.

Howell, S. B.↗

NASA NTRS1990

A search for eclipses of HD 114762 by a low-mass companion

HD 114762 has an unseen companion with a dynamical mass that satisfies the constraint mass sin i = 2.5 x 10 to the 31st gm. The companion is a good candidate for a planetary-mass object, but the inclination of its orbit is unknown and its mass is indeterminate. Tests were conducted for the specific case of a nearly edge-on orbit by looking for eclipses of HD 114762 by the companion. Although the a priori probability of an eclipse is low, this is a crucial case because the companion has its minimum mass if the orbit is edge on. No eclipses were found with a depth greater than 0.01 mag and, therefore, the inclination of the orbit of HD 114762 is less than 89 deg.

Robinson, Edward L.↗

NASA NTRS1989

Predictions for the total solar eclipse of 1991

A total eclipse of the sun will be widely visible from the Western Hemisphere on July 11, 1991. Detailed predictions for this event are presented which include tables of geographic coordinates for the northern limit, southern limit and center line of the path of totality, local circumstances on the center line and for 95 cities within the partial and total eclipse paths, maps depicting the path of totality, the sky during totality and the lunar limb profile. The author discusses the general characteristics of the eclipse including local circumstances from various points along the central path, the Saros series history and effects caused by the lunar limb profile.

Espenak, Fred↗

NASA NTRS1990

Electron-positron heating and the eclipsing millisecond pulsar PSR 1957 + 20

The companion in the eclipsing millisecond PSR 1957 + 20 appears to be strongly heated by the pulsar and may also be rapidly losing mass due to that heating. A new mechanism is presented by which the heating may be accomplished: diffusion of mildly relativistic electron-positron pairs from the pulsar's relativistic wind through a thermal wind issuing from the companion. Wave-particle scattering regulates the depth at which the pairs deposit their energy; requirements of self-consistency place bounds on the wave spectrum and pair distribution function. If the pairs carry over about 10 percent of the pulsar spin-down luminosity, and the companion's heavy element abundance is subsolar, the heating rate can be adequate to drive a wind with sufficient momentum flux to explain the eclipse geometry. Annihilation photons then heat the companion beneath its photosphere and supply a significant part of the power for the optical luminosity. This model also suggests that the eclipse duration decreases sharply above a critical photon frequency.

Krolik, Julian H.↗

NASA NTRS1991

The orbital ephemeris and eclipse transitions of the low-mass X-ray binary EXO 0748 - 676

Using the eclipses as fiducial markers, an updated ephemeris for EXO 0748 - 676 is derived and evidence is found that between February 1985 and March 1989 the 3.82-h orbital period of EXO 0748 - 676 decreased with a time scale of -5 x 10 to the 6th yr. The sense of this change is the same as that predicted by simple models for the evolution of low-mass X-ray binaries containing main-sequence companions, but is a factor about 100 faster than expected. This rapid change in orbital period could result from the expansion of the companion due to the effects of X-ray heating. The eclipse transition durations are variable, with the shortest observed taking 1.5 s and the longest 40 s. This latter figure is about an order of magnitude too large to be due to absorption effects in the atmosphere of the secondary assuming a Roche geometry and likely stellar temperature. Either flaring activity or the presence of an X-ray heated evaporative wind or a corona may enhance the scale height of the companion's atmosphere producing the extended eclipse transitions.

Parmar, A. N.↗

NASA NTRS1991

The eclipsing AM Herculis variable H1907 + 690

The discovery is reported of an eclipsing cataclysmic variable that exhibits up to 10 percent circular polarization at optical wavelengths, securing its classification as an AM Herculis type binary. The object, H1907 + 609, was located with the guidance of X-ray positions from the HEAO 1 survey. Optical CCD photometry exhibits deep eclipses, from which is derived a precise orbital period of 1.743750 hr. The eclipse duration suggests an inclination angle about 80 deg for a main-sequence secondary star. The optical flux has been persistently faint during observations spanning 1987-1990, while the X-ray measurements suggest long-term X-ray variability. The polarization and photometric light curves can be interpreted with a geometric model in which most of the accretion is directed toward a single magnetic pole, with an accretion spot displaced about 17 deg in longitude from the projection of the secondary star on the white dwarf surface.

Remillard, R. A.↗

NASA NTRS1993

Gravity wave forcing in the middle atmosphere due to reduced ozone heating during a solar eclipse

We present an analysis of the gravity wave structure and the associated forcing of the middle atmosphere induced by the screening of the ozone layer from solar heating during a solar eclipse. Fourier integral techniques and numerical evaluation of the integral solutions were used to assess the wave field structure and to compute the gravity wave forcing of the atmosphere at greater heights. Our solutions reveal dominant periods of a few hours, characteristic horizontal and vertical scales of about 5000 to 10,000 km and 200 km, respectively, and an integrated momentum flux in the direction of eclipse motion of about 5.6 x 10 exp 8 N at each height above the forcing level. These results suggest that responses to solar eclipses may be difficult to detect above background gravity wave and tidal fluctuations until well into the thermosphere. Conversely, the induced body forces may penetrate to considerable heights because of the large wave scales and will have significant effects at levels where the wave field is dissipated.

Fritts, David C.↗

NASA NTRS1994

Variation of stratospheric NO2 during the solar eclipse

The numerical modeling of the changes of the concentration of trace gases in the atmosphere during the eclipse shows that the NO2 total content in the vertical column increases approximately by 80 percent. The first observations of the NO2 total content during the eclipse of 1981 have given 60 plus or minus 20 percent. In the observations of 1990 the more precise methods and instruments for stratospheric NO2 measurements were used. The surface ozone, NO, and NO2 concentrations were under control. The results of the observations give the increasing of the stratospheric NO2 during the eclipse by 55 plus or minus 6 percent. The maximum increasing of the NO2 content is observed at the moment of the maximum phase.

Elansky, Nikolay F.↗

NASA NTRS1994

The two variables in the triple system HR 6469 = V819 Her: One eclipsing, one spotted

A complete BV light curve, from 14 nights of good data obtained with the Vanderbilt University-Tennessee State University (VU-TSU) automatic telescope, are presented and solved with the Wilson-Devinney program. Third light is evaluated, with the companion star brighter by 0.58(sup m) in V and 0.11(sup m) in B. The eclipses are partial. Inferred color indices yield F2 V and F8 V for the eclipsing pair and G8 IV-III for the distant companion star. After removing the variability due to eclipses, we study the residual variability of the G8 IV-III star over the ten years 1982 to 1992. Each yearly light curve is fit with a two-spot model. Three relatively long-lived spots are identified, with rotation periods of 85.9(sup d), 85.9(sup d), and 86.1(sup d). The weak and intermittent variability is understood because the G8 IV-III star has a Rossby number at the threshold for the onset of heavy spottedness.

Van Hamme, Walter V.↗

NASA NTRS1994

Optical, IUE, and ROSAT observations of the eclipsing nova-like variable V347 Puppis (LB 1800)

Using time-resolved optical spectroscopy and UBVRI and high-speed photometry obtained at Mount Stromlo Observatory, Mount John University Observatory, and the South African Astronomical Observatory; International Ultraviolet Explorer (IUE) ultraviolet spectroscopy; and Roentgen Satellite (ROSAT) survey X-ray fluxes, we present a study of the accretion disk, hot spot, and emission line regions in the bright eclipsing nova-like variable V347 Pup (LB 1800). In the optical and UV, V347 Pup is a strong emission line source with a continuum spectrum which is remarkably red for a high-M cataclysmic variable. Consistent with its high inclination, we interpret the continuum spectrum as the superposition of the spectrum of the cool (T(sub eff) approximately 7000 K) outer edge and the hot (T(sub eff) approximately 100,000 K) inner regions of a self-eclipsed accretion disk. For the assumed parameters, the model matches the level and shape of the observed spectrum for an inclination of approximately 88 and a distance of approximately 300 pc. The prominent hump in the optical and UV light curves just before eclipse manifests the presence of the hot spot where the accretion stream strikes the edge of the disk. The wavelength dependence of the amplitude of the hump is best modeled by a spot having an effective temperature of approximately 25,000 K and an area of approximately 3 x 10(exp 18) sq cm if the spot radiates like a blackbody, or an effective temperatue of approximately 14,000 K and an area of approximately 3 x 10(exp 19) sq cm if it radiates with a stellar spectrum. In either case, the hot spot produces only one-tenth of the predicted luminosity for the assumed mass-transfer rate of 10(exp -8) solar mass/yr. Either the hot spot is 'buried' in the edge of the accretion disk, or a significant fraction of its luminosity is radiated away in lines. The difference in azimuth between the peak of the hump and the dynamically expected location of the hot spot suggests that the spot's emitting surface is rotated forward by approximately 36 deg relative to the edge of the disk.

Mauche, Christopher W.↗

NASA NTRS1994

Line profiles variations from atmospheric eclipses: Constraints on the wind structure in Wolf-Rayet stars

Binary systems in which one of the components has a stellar wind may present a phenomenon known as 'wind' or 'atmospheric eclipse', in which that wind occults the luminous disk of the companion. The enhanced absorption profile, relative to the spectrum at uneclipsed orbital phases, can be be modeled to yield constraints on the spatial structure of the eclipsing wind. A new, very efficient approach to the radiative transfer problem, which makes no requirements with respect to monotonicity of the velocity gradient or size of that gradient, is presented. The technique recovers both the comoving frame calculation and the Sobolev approximation in the appropiate limits. Sample computer simulations of the line profile variations induced by wind eclipses are presented. It is shown that the location of the wind absorption features in frequency is a diagnostic tool for identifying the size of the wind acceleration region. Comparison of the model profile variations with the observed variations in the Wolf-Rayet (W-R)+6 binary system V444 Cyg illustrate how the method can be used to derive information on the structure of the wind of the W-R star constrain the size of the W-R core radius.

Auer, L. H.↗

NASA NTRS1995

Eclipse timings of the low-mass X-ray binary EXO 0748-676: Statistical arguments against orbital period changes

EXO 0748-676, an eclipsing low-mass X-ray binary, is one of only about four or five low-mass X-ray binaries for which orbital period evolution has been reported. We observed a single eclipse egress with ROSAT . The time of this egress is consistent with the apparent increase in P(sub orb) previously reported on the basis of EXOSAT and Ginga observations. Standard analysis, in which O-C (observed minus calculated) timing residuals are examined for deviations from a constant period, implicitly assume that the only uncertainty in each residual is measurement error and that these errors are independent. We argue that the variable eclipse durations and profiles observed in EXO 0748-676 imply that there is an additional source of uncertainty in timing measurements, that this uncertainty is intrinsic to the binary system, and that it is correlated from observation to observation with a variance which increases as a function of the number of binary cycles between observations. This intrinsic variability gives rise to spurious trends in O-C residuals which are misinterpreted as changes in the orbital period. We describe several statistics tests which can be used to test for the presence of intrinsic variability. We apply those statistical tests which are suitable to the EXO 0748-676 observations. The apparent changes in the orbital period of EXO 0748-676 can be completely accounted for by intrinsic variability with an rms variability of approximately 0.35 s per orbital cycle. The variability appears to be correlated from cycle-to-cycle on timescales of less than 1 yr. We suggest that the intrinsic variability is related to slow changes in either the source's X-ray luminosity or the structure of the companion star's atmosphere. We note that several other X-ray binaries and cataclysmic variables have previously reported orbital period changes which may also be due to intrinsic variability rather than orbital period evolution.

Hertz, Paul↗