Function Of Orbital Phase Research Articles

Simultaneous Extreme-Ultraviolet and Infrared Observations of the Eclipsing Polar HU Aquarii

We present simultaneous EUV and infrared (J, K) observations of the polar HU Aquarii obtained during 1998 August when the star was in a high mass accretion state. EUV and IR light curves and EUV spectra are presented and compared with previous observations. The accretion region on the white dwarf has increased in temperature (124,000 to 240,000 K) and radius (0.04RWD to 0.06RWD) compared with previous EUV observations made during low mass accretion states. The EUV and IR photometric observations are shown to have a similar appearance as a function of orbital phase. The EUV photometry shows rapid changes and provides evidence for mass accretion via blobs. The high-state IR light curves present an asymmetric double-humped shape with J = 14.8 and K = 14.1. We applied an ellipsoidal model fit to the observations, and the result indicates that the cause of the modulated shape is due to both ellipsoidal variations from the Roche lobe filling secondary star and a complex flux combination probably dominated at all orbital phases by cyclotron emission. The source of maximum cyclotron emission appears to be in the accretion column high above the white dwarf surface.

UV spectroscopy of the peculiar binary V Sagittae in a low state

ABSTRA C T In this paper we present the first phase-resolved, high-resolution, UV spectroscopy of V Sge. HST GHRS observations were obtained covering 1.5 orbital cycles of V Sge in a low state. We covered the He ii 1640 line and the C iv 1550 doublet alternately, and also obtained one spectrum covering Mg ii 2800. We create continuum and line flux light curves for the He ii and C iv spectra. A secular decrease in continuum and line strength occurs throughout our observation. The continuum light curves show a deep primary eclipse but no obvious secondary eclipse. The line fluxes show no significant changes during primary or secondary eclipses. The He ii line shows dramatic orbital variations in shape, but it is always purely an emission line, i.e., it shows no sign of a P Cygni profile. The C iv doublet shows a P Cygni profile in which the absorption vanishes at primary mid-eclipse. This locates the source of the P Cygni line in the primary star wind. The maximum velocity of absorption in the P Cygni profile is 700 km s 21 , much smaller than the HWZI of the C iv emission which is 1500 km s 21 . We attribute this to the presence of a broad C iv emission component underlying the primary star P Cygni profile. The C iv line also varies with orbital phase. In particular, the velocity at the blue edge of the absorption varies between 2700 and 2250 km s 21 as a function of orbital phase. The red and blue peaks of the profile also vary around the orbit, with the red peak at maximum strength near phases 0.5‐0.7. The blue peak is at maximum strength near phases 0.1‐0.2. We can explain the detailed behaviour of the He ii and C iv line profiles in the context of a colliding wind model. Here the winds from each star collide, forming a shock which, due to the rapid rotation of the binary, is wrapped around both stars. The C iv P Cygni line comes from the primary star wind, which has a terminal velocity of ,700 km s 21 . We attribute the He ii line and the broad C iv emission to a fast, optically thin wind from the secondary star. This wind has a terminal velocity of ,1500 km s 21 . Interstellar lines due to C i ,C i*, C iv ,M gii and P ii are detected. Column densities are measured for C i and P ii. The C i column density is used to estimate the hydrogen column density. We find that nH is of order 10 19 atom cm 22 .

BeppoSAX observations of an orbital cycle of the X-ray binary pulsar GX 301-2

We present preliminary results on our campaign of observations of the X-ray binary pulsar GX301-2. BeppoSAX observed this source six times in January/February 1998: at the periastron and apoastron, and at other four, intermediate, orbital phases. We present preliminary results on the GX 301-2 spectral and temporal behaviour as a function of orbital phase.

The Far‐Ultraviolet Spectrum and Short‐Timescale Variability of AM Herculis from Observations with the Hopkins Ultraviolet Telescope

Using the Hopkins Ultraviolet Telescope (HUT), we have obtained 850-1850 A spectra of the magnetic cataclysmic variable star AM Her in the high state. These observations provide high time resolution spectra of AM Her in the far-ultraviolet and sample much of the orbital period of the system. The spectra are not well modeled in terms of simple white dwarf (WD) atmospheres, especially at wavelengths shortward of Lyα. The continuum flux changes by a factor of 2 near the Lyman limit as a function of orbital phase; the peak fluxes are observed near magnetic phase 0.6 when the accreting pole of the WD is most clearly visible. The spectrum of the hot spot can be modeled in terms of a 100,000 K WD atmosphere covering 2% of the WD surface. The high time resolution of the HUT data allows an analysis of the short-term variability and shows the UV luminosity to change by as much as 50% on timescales as short as 10 s. This rapid variability is shown to be inconsistent with the clumpy accretion model proposed to account for the soft X-ray excess in polars. We see an increase in narrow-line emission during these flares when the heated face of the secondary is in view. The He II narrow-line flux is partially eclipsed at secondary conjunction, implying that the inclination of the system is greater than 45°. We also present results from models of the heated face of the secondary. These models show that reprocessing on the face of the secondary star of X-ray/EUV emission from the accretion region near the WD can account for the intensities and kinematics of most of the narrow-line components observed.

Concerning the Reported Phase‐modulated Changes in the Spectrum of 41 Sextantis

ABSTRACTSreedhar Rao et al. have reported that the metallic‐line star 41 Sextantis exhibits significant changes in the depths and equivalent widths of its spectral lines and that these changes are coupled with the orbital motion of this spectroscopic binary. Based on their discovery, they suggest that 41 Sex is a possible evolutionary link between the Am and Ap stars. High‐dispersion CCD spectra of 41 Sex, obtained in 1991 with the 0.9 m feed telescope and coudé spectrograph at the Kitt Peak National Observatory, were measured to determine the equivalent widths and depths of several metallic lines and the depths of Ca ii K and H8 as a function of orbital phase. The spectrum changes that Sreedhar Rao et al. observed could not be verified with these data. Possible explanations for this lack of confirmation might be that the star was in a quiescent state in 1991 or that the reported changes to the spectrum happen on a timescale much greater than the orbital period. An updated solution for the spectroscopic orbital elements is also presented.

Eclipse Mapping of the Accretion Disk Wind in the Cataclysmic Variable UX Ursae Majoris

We present the results of an effort to model recent HST eclipse observations of the C IV 1550 A resonance line in the high-inclination nova-like cataclysmic variable UX UMa. Assuming this line to be predominantly wind-formed, we are able to roughly reproduce the shapes and strengths of the observed line profiles (both away from and during eclipse) within the framework of a simple kinematic model in which the outflow is described as a rotating, biconical accretion disk wind. Our preferred model also matches most of the detailed behavior of different parts of the C IV line profile (blue wing, line center, and red wing) as a function of orbital phase. The most important result of our modeling is that it strongly suggests the presence of a high column (NH ~ 1023 cm-2), relatively dense (ne 4 × 1012 cm-3), and only slowly outflowing (vpoloidal vescape) transition region between the disk photosphere and the fast-moving wind. We also find that the outflow from UX UMa is probably only moderately collimated (the outer opening angle of our preferred model is θmax 65°). Finally, the rotational disturbance seen in the data is fitted reasonably well by our model, in which the rotational component of motion in the wind is fixed by conserving the specific angular momentum of the outflowing material. The implications of these results for dynamical models of disk-driven winds are discussed.

Optical photometry of the eclipsing Large Magellanic Cloud supersoft source CAL 87

We present optical photometry of the eclipsing supersoft source, CAL87. These observations comprise long term data accumulated as a by-product of the MACHO Project, and high speed white light photometry of a single eclipse. We (i) derive an improved ephemeris of To = HJD 2450111.5144(3) + 0.44267714(6)E for the time of minimum light, (ii) find the eclipse structure to be stable over a period of 4 years, and (iii) investigate the colour variation as a function of orbital phase. The resolution afforded by the high speed nature of the white light observations enables us to see new structure in the light curve morphology.

Eclipse Mapping of the Accretion Disk Wind in the Cataclysmic Variable UX UMa

AbstractWe present the results of an effort to model recent HST eclipse observations of the wind-formed C, ɪv 1550Å resonance line in the high-inclination nova-like variable UX UMa (Mason et al. 1995, Baptista et al. 1995). Within the framework of a simple kinematic model, in which the outflow is described as a rotating, biconical accretion disk wind (Knigge et al. 1995), we are able to reproduce not only the shapes and strengths of the observed line profiles both away from and during eclipse, but also most of the detailed behaviour of different parts of the line (blue wing, line centre and red wing) as a function of orbital phase (Figure 1).The most important result of our modeling is that it strongly suggests the presence of a vertically extended (H ~ few × 10 RWD), relatively dense (ne ~ 1013 cm−3) and only slowly-outflowing (υpoloidal << υescape) transition region between the disk photosphere and the fast-moving wind. Thus the best current data already demand that the simplified picture of accretion disks and winds as quasi-independent physical phenomena should be replaced by a unified theory of accretion disk atmospheres. It may be important in this context that, barring strong contamination of the observed C ɪv wind line by an underlying disk-formed component, the evidence for rotation in the outflow is unambiguous: the observed line flux light curves clearly exhibit a rotational disturbance that is well matched by our simple model of a rotating disk wind.

Cross-correlation characteristics of OB stars from IUE spectroscopy

We present a catalogue of homogeneous measures of the linewidth parameter, v(e) sin i, for 373 O-type stars and early B supergiants (including the separate components of 25 binary and three triple systems), produced by cross-correlating high-resolution, short-wavelength IUE spectra against a 'template' spectrum of tau Sco. We also tabulate terminal velocities. There are no O supergiants in our sample with v(e) sin i < 65 km s(-1), and only one supergiant earlier than B5 has v(e) sin i < 50 km s(-1), confirming that an important line broadening mechanism in addition to rotation must be present in these objects. A calibration of the area under the cross-correlation peak against spectral type is used to obtain estimates of continuum intensity ratios of the components in 28 spectroscopically binary or multiple systems. At least seven SB2 systems show evidence for the 'Struve-Sahade effect', a systematic variation in relative line strength as a function of orbital phase. The stellar wind profiles of the most rapid rotator in our sample, the O9 III:n* star HD 191423 (v(e) sin i = 436 km s(-1)), show it to have a 'wind-compressed disc' similar to that of HD 93521; this star and other rapid rotators are good candidates for studies of non-radial pulsation.

The Place of Origin of the Flickering in Z Cha

The variability in the observable light curve of a CV can be attributed to (i) orbital and long-term variations; (ii) flickering, (iii) photon noise, (iv) scintillation (negligible) and (v) any residual noise. Calculating the rms-scatter of the count rates in a light curve as a function of orbital phase, ϕ, through accretion disk eclipse of high inclination CVs – after subtraction of a smoothed light curve to remove orbital and long-term variations, and applying a correction for photon noise – permits one to confine the place of origin of the flickering if its visibility is phase dependent or if eclipses take place (assuming any residual source of noise to be constant in time). The rms-scatter curve is then defined as the function where is the variance due to flickering and the variance due to residual noise.

ASCA measurements of the grain-scattered X-ray halos of eclipsing massive X-ray binaries: VELA X-1 and Centaurus X-3

view Abstract Citations (34) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS ASCA Measurements of the Grain-scattered X-Ray Halos of Eclipsing Massive X-Ray Binaries: VELA X-1 and Centaurus X-3 Woo, Jonathan W. ; Clark, George W. ; Day, Charles S. R. ; Nagase, Fumiaki ; Takeshima, Toshiaki Abstract We have measured the decaying dust-scattered X-ray halo of Cen X-3 during its binary eclipse with the ASCA solid-state imaging spectrometer (SIS). The surface brightness profile (SBP) of the image in the low-energy band (0.5-3 keV) lies substantially above the point-spread function (PSF) of the X-ray telescope, while the SBP in the high-energy band (5-10 keV) exhibits no significant deviation. By contrast, the SBPs of Vela X-1 during its eclipse are consistent with the PSF in both the low- and high-energy bands -- strong evidence that a dust halo is indeed present in Cen X-3. Accordingly, we modeled the SBP of Cen X-3 taken from six consecutive time segments under the principal assumptions that the dust is distributed uniformly along a segment of the line of sight, the grains have a power-law size distribution, and the low-energy source flux was the same function of orbital phase before as during our observation. The best-fit set of parameters included a grain density value of 1.3 g/cu cm, substanially less than the density of 'astronomical silicate.' This result supports the idea that interstellar grains are 'fluffy' aggregates of smaller solid particles. We attribute the failure to detect a halo of Vela X-1 during its eclipse phase to extended strong circumsource absorption that probably occurred before the eclipse and allowed the halo to decay away before the observation began. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/187620 Bibcode: 1994ApJ...436L...5W Keywords: Eclipsing Binary Stars; Halos; Massive Stars; Pulsars; X Ray Binaries; X Ray Scattering; Imaging Spectrometers; Interstellar Matter; Light Curve; Astrophysics; STARS: BINARIES: ECLIPSING; ISM: DUST; EXTINCTION; STARS: PULSARS: INDIVIDUAL NAME: VELA X-1; STARS: PULSARS: INDIVIDUAL NAME: CENTAURUS X-3; X-RAYS: STARS full text sources ADS | data products SIMBAD (3) HEASARC (1)

Evidence for a gas stream in GX301 – 2

Model calculations are used to study observed variations of column density and X-ray luminosity as a function of orbital phase. The models include a spherically symmetric stellar wind, and the wind plus three types of gas streams. The comparisons of the models with the data by least-squares fitting demonstrate that a gas stream is a necessary part of the models. A gas stream in systems like GX301-2 may be expected, based on the results of Stevens' model (1988, Mont. Not. Roy. ast. Soc. 232) of enhanced stellar wind accretion for eccentric X-ray binaries

Spin Period Variations of the White Dwarf in FO Aqr/H2215-086

AbstractAn investigation of the rotation period variation of the white dwarf in FO Aqr/H2215-086 is presented. A cubic ephemeris is derived for the arrival times of maxima of the pulse light curve which is associated with the white dwarf rotation. Potential problems, resulting from variations of the pulse arrival time as function of orbital phase, and from the change with wavelength of the pulse light curve shape, are investigated. A possible explanation is given for the second effect, being caused by a variable contribution of a modulation at the beat period (of the pulse and orbital periods) as a function of orbital phase.

THE ORBITAL INCLINATION OF A0620-00 MEASURED POLARIMETRICALLY

ABSTRACT The mass of the degenerate primary in A0620 - 00 is inferred from its spectroscopic mass function to be not less than 3.2 solar masses, making it an excellent candidate for a black hole. The exact value of the mass depends on the orbital inclination. The inclination of a binary system can be determined from the shape of its Stokes parameter light curves if the linear polarization of the system varies as a function of orbital phase. A0620 - 00 over one 8-hour binary period was observed with the 4.5-m equivalent MMT. Its polarization in the visible is variable with orbital phase. The standard theory of Brown et al. (1978) was used to derive an orbital inclination of i = 57 deg (+20 deg, -50 deg), where the error is the 90-percent confidence interval. An inclination of i = 57 deg corresponds to a mass of the compact primary of 6.6 solar masses, but the large uncertainty in the measured value of the inclination allows the derived mass of A0620 - 00 to be as low as 3.8 solar masses. If this is taken to be the maximum mass of any degenerate configuration consistent with general relativity except a black hole, then the mass of A0620 - 00 is still not well enough determined to conclude that it must be a black hole.

An EXOSAT X-ray observation of one orbital cycle of 4U 1700-37/HD 153919

Exosat observations of close to one complete binary cycle of 4U 1700-37/HD 153919 are presented, and X-ray absorption variations are determined as a function of orbital phase in order to study the properties of the stellar wind of the companion HD 153919. The decrease noted in absorption between eclipse egress and phase 0.5 may be due to X-rays from a neutron star being absorbed by an inner wind with a radial velocity law close to that predicted by Castor et al. (1975). Under the assumption that the X-ray source is powered by material captured from the steller wind, the absorption variations with orbital phase and the time-average luminosity have been modeled to investigate the suppression of the radiative acceleration of the wind via the ionization of the wind by the X-ray source.

What is causing the eclipse in the millisecond binary pulsar?

Possible physical mechanisms for explaining the radio eclipses in the millisecond binary pulsar PSR 1957 + 20 are discussed. If, as recent observations suggest, the duration of the eclipses depends on the observing frequency, a plausible mechanism is free-free absorption of the radio pulses by a low-density ionized wind surrounding the companion. Detailed numerical calculations are performed for this case, and it is found that all of the observations made at 430 MHz can be reliably reproduced, including the asymmetry in the excess time delay of the pulses. The model leads to definite predictions for the duration of the eclipse at other observing frequencies, as well as the radio intensity and excess time delay of the pulses as a function of orbital phase. If the duration of the eclipses were found to be independent of frequency, then the likely mechanism would be reflection of the radio signal at a contact discontinuity between a high-density wind and the pulsar radiation. In this case, however, it is difficult to explain the observed symmetry of the eclipse.

The radial velocity curve and peculiar TiO distribution of the red secondary star in Z Chamaeleontis

view Abstract Citations (414) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Radial Velocity Curve and Peculiar TiO Distribution of the Red Secondary Star in Z Chamaeleontis Wade, Richard A. ; Horne, Keith Abstract The secondary star of the dwarf nova Z Cha has been detected with the CCD spectrograph of the CTIO 4 m telescope. The TiO λ7150/λ7650 band ratio implies a Boeshaar spectral type of M5.5 for the secondary star, which contributes ≡15% of the light at λ7500. The absolute absorption strength of TiO is very weak on the side of the star that faces the white dwarf and accretion disk. The authors use cross-correlation techniques to measure the velocity of the secondary star as a function of orbital phase, and examine the photometric variations of spectral features with orbital phase. They also model the phase variations of the absorption features in terms of their surface distribution on the secondary star, evaluate a correction to the observed K velocity to account for the nonuniform line strength, and derive physical parameters of the Z Cha system. Publication: The Astrophysical Journal Pub Date: January 1988 DOI: 10.1086/165905 Bibcode: 1988ApJ...324..411W Keywords: Dwarf Novae; Eclipsing Binary Stars; Radial Velocity; Spatial Distribution; Titanium Oxides; Velocity Distribution; Absorption Spectra; Accretion Disks; Charge Coupled Devices; M Stars; Stellar Luminosity; Stellar Spectrophotometry; Astrophysics full text sources ADS | data products SIMBAD (17)

The variable iron line in cygnus X-3

Cygnus X-3 was observed with the GSPC on board EXOSAT on several occasions, one observation lasting for 7 orbital cycles. The width W and centroid energy E of the iron emission feature near 6.7 keV show a smooth, correlated, sinusoidal-type modulation, the iron line being widest and E being lowest just before X-ray maximum. The line profile may show a low-energy wing, but apart from this does not deviate strongly from a symmetric, Gaussian-type shape. The continuum at higher energies than the line is not completely smooth, but shows ‘bumps’ which remain stable in time. Two possible explanations are discussed for the correlated variation of E and W as a function of orbital phase.

Constraints on the inclination and masses of the HDE 226868/Cygnus X-1 system from the observations

Analyses of two high-dispersions IUE spectra of HDE 226868 (the optical counterpart of Cygnus X-1) are combined with studies of low-dispersion IUE spectra to provide a more accurate determination of the variation of C IV stellar wind absorption as a function of orbital phase. By incorporating these observational results into an analysis of the structure of the X-ray ionization cavity in the stellar wind, it is found that the orbital inclination must lie between 36 and 67 deg, leading to a mass for the compact object between 5.7 and 11.2 solar masses.

The anomalous X-ray absorption spectrum of VELA X-1

The HEAO 2 satellite's Solid State Spectrometer and Monitor Proportional Counter was used to observe one orbit of the massive X-ray binary Vela X-1. Using spectral fits to the data as a function of orbital phase, the column density and state of the material along the line of sight to the X-ray source has been inferred. The spectrum near orbital phase 0.2 compares favorably with absorption by neutral material with a column density corresponding to plausible values of stellar wind velocity law and total primary mass loss rate. Spectra at later orbital phases, which show unexpected strong absorption features near 2.0 and 2.5 keV, are interpreted as due to absorption by material with suppressed opacity below 2.0 keV. The opacity required to produce the observed features implies either the presence of an intense soft X-ray flux, or altered elemental abundances in the gas near Vela X-1.