V2051 Oph Research Articles

The orbital period of the X-ray binary GX 1+4

A programme has been under way to determine the orbital period of the symbiotic low mass X-ray binary GX 1+4. This programme aims to measure the cyclic variations of the Hα emission line feature of the optical counterpart, V2116 Oph, of this luminous X-ray pulsar. Present results indicate that the orbital period may be significantly greater than the 304 day value previously proposed. Some anomalies in the spectral characteristics of the source are discussed.

A Long-Duration Pre-flare Dip in the Light Curve of V1054 Oph

Photometric observations of V1054 Oph (Wolf 630 AB, mv = 9.69) and of the comparison star HD 152678 (mv = 8.1) were carried out in the UBV bands at Catania Astrophysical Observatory on 1994, June 15, using the 91 cm Cassegrain telescope equipped with an improved version of the twin-beam photometer URSULA (De Biase et al. 1988). We have detected a relatively low-intensity flare event preceded by a pre-flare dip of low amplitude and the exceptionally long duration of 36 min. The integration times were 10, 5 and 5 sec in the U, B and V bands, respectively. The variable and the comparison stars were observed simultaneously in the two independent channels of the twin-beam photometer. The sky background was subtracted from the photon count rates of V1054 Oph and its comparison star in each spectral band, and the flux of the variable was normalized to that of the comparison star.

Eclipse Mapping the Flickering in HT Cas

Flickering is a well-known, though poorly understood, signature of accretion in cataclysmic variables. HT Cas is an excellent system in which to study flickering because its well determined characteristics allow a calibration of the experimental system (see Horne et al. 1991).Patterson (1981) argues that the flickering in HT Cas originates from regions very near the white dwarf. In U Gem, the flickering appears to be associated with the bright spot (Warner & Nather 1971). In RW Tri, the flickering occurs throughout the disk but is centrally concentrated (Horne & Stiening 1985); the same holds true for V2051 Oph (Warner & Cropper 1983).HT Cas is a 16m.4 eclipsing dwarf nova with a binary period of 106 min and an inclination of ∼ 81°. The entire eclipse last about 15 min with the white dwarf totally eclipsed for ∼ 5 min. The mass ratio is 0.15 with the white dwarf having mass ∼ 0.6M⊙ (Horne et al. 1991).We obtained 20 eclipses of HT Cas between 1982 and 1991 in U, B and V at Mt. Palomar and also McDonald Observatory with 0.5 – 2 sec integrations. These data were folded on the ephemeris given by Horne et al. (1991) and corrected for the 30 sec drift in the phasing as noted by Wood et al. (1995).

Flickering in V841 Ophiuchi

Light curves of the nova remnant V841 Oph, obtained on seven nights in 1985, are presented. Flickering occurs on all timescales from at least as short as 100 s to many hours. No periodic modulations were found. Further spectroscopic or infrared observations are recommended in order to verify the orbital period.

Possible radio JETS in GX 1+4

GX 1+4 is an X-ray pulsar with a nominal period of ∼ 2 or 4 min. and has the highest P˙/P of ∼ 0.22 yr−1 among the X-ray pulsars. The source is identified with an optical counterpart V2116 Oph, however no binary period has been reported so far. There are several features of the source like M˙, variable pulse shape, period history and the spectral changes which do not fit well with our present understanding of the source.The radio observation of the galactic center region were made using Molonglo observatory Synthesis Telescope operating at a frequency of 843 MHz. A 12 hr observation was made with the field center at the position coordinates of the optical counterpart. No significant radio emission was seen corresponding to the center position.The synthesis map however, showed the presence of two regions of radio enhancements almost equidistant from the optical source in the diametrically opposite directions/1/. The data is interpreted as due to synchrotron emission produced by the expanding jets of GX 1+4, similar to the radio jets observed in galaxies. Radio jets have been inferred for three galactic X-ray binary sources namely, Sco X-1, Cyg X-3, and SS 433. However, for all these sources no X-ray pulsation has been detected so far. The present observations if confirmed will be the first case of radio jets in a stellar system containing an X-ray pulsar.

A photometric study of V566 ophiuchi

The A-type W UMa system V566 Oph was observed photoelectrically in two wavebands (B andV) in the years 1988-1989 at the Kryonerion Astronomical Station of the National Observatory of Athens, Greece. The light curves of the system are analyzed using frequency-domain techniques and new geometric and photometric elements are derived. These elements are combined with the more recent spectroscopic data based on Reticon observations to yield the absolute parameters of the system. The evolutionary status of the system is considered and it is found that V566 Oph has started its evolution away from the Main Sequence. The period of the system continues to increase.

A period study of V502 Ophiuchus

All available published times of minima of a W-type contact binary V502 Oph have been compiled and critically examined. Ten times of minima were revisted from original observations, and five new times of minima derived from our own observations. A period study covering 53 yr of observations including 84 timings of minima light (63 of them from photoelectric observations) reveals that the orbital period of the system oscillates with a period of about 35 ± 2 yr and amplitude of about 0.020 ± 0.005 day while it undergoes a constant period decrease of about dP/dt ∼ −1.45 10 −7 d/yr

Ginga observations of the dwarf novae BV Pup and V426 Oph

Ginga X-ray observations of the high excitation dwarf nova BV Pup and the suspected DQ Her dwarf nova V426 Oph are presented. The observation of BV Pup took place during optical quiescence and showed no detectable X-ray flux, implying the X-ray luminosity was below that observed by Exosat during the decline from an outburst. An optical spectrum obtained near the time of the X-ray observations showed no high-excitation He II 4686, so that it is not clear if this was an unusual low-excitation time for BV Pup or if this is a normal phase of the outburst cycle. V426 Oph was observed for four days near maximum outburst brightness with overlapping X-ray coverage on three days. The 2-10 keV flux was a factor of 2 below that observed by Exosat during a quiescent state. There is evidence for a 28 min timescale in the X-ray, and optical data which are not strictly periodic in nature.

Spectroscopic Observations of the Southern Old Novae CP Pup and V841 Oph

AbstractNew spectroscopic observations of the old nova CP Pup suggest most probable orbital period of 0.061375 days. First systematic monitoring of the very old nova V841 Oph reveals orbital motion with a most probable period of about 0.6 days. A slightly eccentric solution at P = 0.3755 days is less probable.

Quasi–periodic Outburst Activity of Novae at Minimum

AbstractIn this paper we present the statistical analysis of historical light curves of 8 old novae, performed through a Fourier analysis on ~ 1600 no-equispaced (in the time) observations published by Steavenson between 1921 and 1953. The results seems to support the existence of a semiregular variability on typical timescales of 50d ÷ 100d and amplitude of ~ 0.3 ± 0.1 magnitudes.At present the largest body of data concerning the photometric behaviour of novae at minimum, is due to the pioneering works by Steavenson (1920→1950) and also to Robinson’s compilation (1975) of 33 preeruption lightcurves of novae.Besides testing the evolutionary models, such as the Hibernation Scenario (Shara et al. 1986), the importance of very long term observations of novae at minimum, has been recently pointed out by Bianchini (1987) and Warner (1988) in close connection to the possible detection of solar-type cycles of activity of the secondary. In spite of these considerations an interesting body of ~ 1000 homogenous observations of 5 posteruption lightcurves provided by Steavenson between 1920 to 1950 (published on M.N.R.A.S) has been neglected and only recently recovered (Delia Valle 1988).The aim of our analysis is:a)to verify possible presence of Dwarf Nova activityb)to confirm on the basis of a larger sample of objects, the existence of semiregular variability as observed in Q Cyg 1876 (Shugarov 1983) and v841 Oph (Della Valle and Rosino 1987).In this contribute we present only the preliminary results of our Fourier’s analysis, performed by adopting the procedure suggested by Deeming (1975) to analyse data taken at unequally spaced time intervals, whereas a more complete analysis will be presented in a forthcoming paper.

ANALYSIS OF IUE DATA ON V426 OPHIUCHI: OUTBURST AND ORBITAL VARIABILITY

ABSTRACT Time-resolved IUE spectra throughout two orbits of the dwarf nova V426 Oph during quiescence are presented. It is found that the visual and C IV fluxes remain relatively constant during both orbits, whereas the UV coninua and Mg II lines vary by 20-30 percent. The time scales of this variability are discussed. Analysis of other spectra at brighter optical magnitudes shows that the UV lags the optical during a probable rise to outburst, similar to the behavior of SS Cyg. The reddening of V426 Oph is determined to be E(B-V) = 0.1. The contribution of the white dwarf to the UV flux at quiescence is estimated to be 25 percent, based on the system parameters of Hessman (1988) and the period-temperature relation of Sion (1987).

EXOSAT and IUE observations of contact binaries

view Abstract Citations (30) References (59) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS EXOSAT and IUE Observations of Contact Binaries Vilhu, O. ; Heise, J. Abstract EXOSAT observations are reported of the contact binaries W UMa, VW Cep, 44t Boo, XY Leo, and V566 Oph and the detached short-period RS CVn stars ER Vul and HD 209943. Complete X-ray light curves were obtained for W UMa, VW Cep and 44t Boo. Nearly simultaneous IUE observations of VW Cep provide important comparisons of the Mg II emission, the UV continuum, and the FES light curve, pointing to extra hot gas at phase 0.75. The observations indicate that contact binaries have highly structured (in temperature and geometry) and highly variable coronae, not preferentially connected with either of the component stars. The observed dips can be interpreted as due to cool absorbing clouds above localized X-ray emitting regions. For VW Cep, 44t Boo, and XY Leo there is evidence that the neck regions are sites for X-ray-emitting hot gas. Publication: The Astrophysical Journal Pub Date: December 1986 DOI: 10.1086/164831 Bibcode: 1986ApJ...311..937V Keywords: Satellite Observation; Spaceborne Astronomy; Stellar Coronas; Stellar Spectrophotometry; X Ray Binaries; Abundance; Emission Spectra; Exosat Satellite; Iue; Light Curve; Ultraviolet Spectra; Astrophysics; STARS: BINARIES; ULTRAVIOLET: SPECTRA; X-RAYS: BINARIES full text sources ADS | data products SIMBAD (7) MAST (1) INES (1)

EXOSAT results on V426 Ophiuchi - Indications of a DQ Herculis system

EXOSAT LE and ME data reveal a sinusoidal l hr modulation during the 6 hr binary orbit of the cataclysmic variable V426 Oph. The amplitude and shape of this modulation, the X-ray fluxes and spectrum, as well as the time scales involved argue for a DQ Her interpretation. In this case, the white dwarf in V426 Oph has the longest rotation period among the known DQ Her systems with orbital periods greater than 3 hr.

Simultaneous infrared and optical photometry of the Eclipsing Dwarf Nova V2051 Ophiuchi

AbstractA complete orbital light-curve of V2051 Oph in the IR H band is presented, together with a second eclipse in the J band. Simultaneous Rc band data were obtained. Eclipse depths in Rc, J and H are 1.8 mag, 1.0 mag and 0.8 mag respectively. No evidence for ellipsoidal variations due to the secondary was seen and constraints on the secondary are discussed.

New photoelectric observations of four W UMa systems: OO aql, V839 Oph, V566 Oph, and SW Lac

The W UMa-type systems (OO Aql, V839 Oph, V566 Oph, and SW Lac) were observed photoelectrically in two wavebands (B andV) during the years 1982–1983. The light curves of these systems are analysed using Kopal's frequency-domain technique and the optimisation method. New geometrical and physical elements have been determined. The absolute elements and the period variations of these systems are discussed.

Radio observations of W Ursae Majoris stars

Radio observations, principally with the VLA at lambda = 6 cm, were made of 12 W UMa stars consisting of eight W-type and four A-type systems. On January 6, 1983, VW Cep was recorded at approximately 0.5 mJy; it subsequently increased to approximately 5 mJy over a two hour period. On January 13, the radio flux level had returned to approximately 0.5 mJy. The flare on VW Cep was at least 100 times less intense than has been observed from RS CVn stars, and injection of material into the chromosphere and corona is proposed as effecting the low-level enhanced background emission. During August, 1982, V502 Oph appeared to consist of two sources, which is suggested as indicating a mass loss from a red giant interacting with its companion, though no companion has been observed.

A MULTIWAVELENGTH STUDY OF THE SHORT-PERIOD CATACLYSMIC VARIABLE V442 OPHIUCHI.

ABSTRACT The results of a program of observations of the cataclysmic variable V442 Oph from UV to IR wavelengths are reported. The observations comprise IUE SWP and LWR-camera spectra from October, 1981; UBVr and R photometry at Manastash Ridge Observatory from August, 1980; UBV photometry and IR measurements at Kitt Peak from July, 1981; and Coudespectroscopy at Mt. Wilson from June, 1980, and at Mt Lemmon from July, 1982. Tables of data, plots of H-alpha and He-II radial velocity, sample spectra, light curves, and a log-log diagram of Flambda vs lambda are given. Flux-ratio analysis of the IR data indicates a disk with very little optically thin material anad an outer-edge temperature of about 7920 K. The calculated period (3.37 h) and mass-accretion rate (1 x 10 to the -8th solar mass/yr) are compared to those of similar objects, and V442 Oph is found to be similar in this respect to systems like H2252-035. Its lack of a rotational period and the weakness of the optical and UV line emissions, however, are more like the old nova V603 Aql.

A POLARIZATION STUDY OF DWARF NOVAE AND NOVA-LIKE OBJECTS.

ABSTRACT Linear polarization measurements for four dwarf novae (SS Cyg, RX And, U Gem, and AH Her) and six nova-like variables (AE Aqr, V426 Oph, UX UMa, CI Cyg, EZ Peg, and TT Ari) are obtained to study variability associated with the outburst cycle. No polarization changes are apparent for SS Cyg or RX And throughout their outburst cycles, but an appreciable difference is noted for AE Aqr. RX And reveals evidence for variability on orbital time scales. All four systems studied at various wavelengths show an unusual wavelength dependence of the polarization.

PERIOD BEHAVIOUR OF V566 OPH : AN UPDATE.

ABSTRACT V566 Oph is a W Ursae Majoris-type eclipsing binary system that undergoes complete eclipses. The present B, V measurements define the primary eclipse curve, and an epoch of minimum light has been determined. All the published photoelectric data have been collected and utilized to reexamine and update the period behavior of the system.

A MINISURVEY OF ?S / UNSTUDIED / SUSPECTED / VARIABLE STARS

ABSTRACT The results of surveying 19 ?s variable stars via wide-wavelength spectral coverage and some photometric measurements are presented. One novalike system (V442 Oph) is identified, while the rest of the stars are classified as either M stars (mostly giants) or A-G stars (possible RR Lyrae or cepheid types).