Dwarf Nova OY Carinae Research Articles

A J-band detection of the donor star in the dwarf nova OY Carinae and an optical detection of its ‘iron curtain’

Purely photometric models can be used to determine the binary parameters of eclipsing cataclysmic variables with a high degree of precision. However, the photometric method relies on a number of assumptions, and to date there have been very few independent checks of this method in the literature. We present time-resolved spectroscopy of the P=90.9 min eclipsing cataclysmic variable OY Carinae obtained with X-shooter on the VLT, in which we detect the donor star from K I lines in the J-band. We measure the radial velocity amplitude of the donor star K2 = 470.0 +/- 2.7 km/s, consistent with predictions based upon the photometric method (470 +/- 7 km/s). Additionally, the spectra obtained in the UVB arm of X-shooter show a series of Fe I and Fe II lines with a phase and velocity consistent with an origin in the accretion disc. This is the first unambiguous detection at optical wavelengths of the `iron curtain' of disc material which has been previously reported to veil the white dwarf in this system. The velocities of these lines do not track the white dwarf, reflecting a distortion of the outer disc that we see also in Doppler images. This is evidence for considerable radial motion in the outer disk, at up to 90 km/s towards and away from the white dwarf.

Decrease in the orbital period of dwarf nova OY Carinae

We have measured the orbital light curve of dwarf nova OY Carinae on 8 separate occasions between 1997 September and 2005 December. The measurements were made in white light using CCD photometers on the Mt Canopus 1 m telescope. The time of eclipse in 2005 December was 168 +- 5 s earlier than that predicted by the Wood et al.(1989) ephemeris. Using the times of eclipse from our measurements and the compilation of published measurements by Pratt et al (1999) we find that the observational data are inconsistent with a constant period and indicate that the orbital period is decreasing by 5+-1 X 10^-12 s/s. This is too fast to be explained by gravitational radiation emission. It is possible that the change is cyclic with a period greater than about 80 years. This is much longer than typical magnetic activity cycles and may be due to the presence of a third object in the system. Preliminary estimates suggest that this is a brown dwarf with mass about 0.016 Msun and orbital radius >= 17 AU.

Extreme Ultraviolet ExplorerObservations of OY Carinae in Superoutburst

The Extreme Ultraviolet Explorer (EUVE) satellite was used for three days beginning on 1997 March 26.96 UT to obtain photometric and spectroscopic observations of the eclipsing SU UMa-type dwarf nova OY Carinae in superoutburst. Because of the longer time on source (143 ks), the larger number of eclipses observed (17), and the higher count rate in the detector (0.5-2.2 counts s -1), we are able to significantly strengthen previous reports that there is little or no eclipse by the secondary of the EUV emission region of OY Car in superoutburst. The mean EUVE spectrum extends from 70 to 190 A and contains broad (FWHM ≈ 1 A) emission lines of N V, O V-O VI, Ne V-Ne VII, Mg IV-Mg VI, Fe VI-Fe VIII, and possibly Fe XXIII. Good fits of the observed spectrum are obtained with a model (similar to that of Seyfert 2 galaxies) wherein radiation from the boundary layer and accretion disk is scattered into the line of sight by the system's photoionized accretion disk wind. It is possible to trade off continuum luminosity for wind optical depth, but reasonable models have a boundary layer temperature Tbl ≈ 90-130 kK and a boundary layer and accretion disk luminosity Lbl = Ldisk 4 × 1034 ergs s-1 ≈ 10 L☉ corresponding to a mass accretion rate a 10-8 M☉ yr-1; an absorbing column density NH ≈ 1.6-3.5 × 1019 cm-2; and a wind mass-loss rate w 10-10 M☉ yr-1 ≈ 0.01a. Because radiation pressure alone falls an order of magnitude short of driving such a wind, magnetic forces must also play a role in driving the wind of OY Car in superoutburst.

An eclipse of the X-ray flux from the dwarf nova OY Carinae in quiescence

We present a phase-resolved ROSAT HRI X-ray light curve of the dwarf nova OY Car in quiescence. The X-ray flux is eclipsed at the same time as the optical eclipse of the primary, and the region of X -ray emission is comparable in size to the white dwarf. We use subsequent optical observations to update the orbital ephemeris of the system.

Optical and ROSAT X-ray observations of the dwarf nova OY Carinae in superoutburst and quiescence

We present ROSAT X-ray and optical light curves of the 1994 February superoutburst of the eclipsing SU UMa dwarf nova OY Carinae. There is no eclipse of the flux in the ROSAT HRI light curve. Contemporaneous `wide B' band optical light curves show extensive superhump activity and dips at superhump maximum. Eclipse mapping of these optical light curves reveals a disc with a considerable physical flare, even three days into the superoutburst decline. We include a later (1994 July) ROSAT PSPC observation of OY Car that allows us to put constraints on the quiescent X-ray spectrum. We find that while there is little to choose between OY Car and its fellow high inclination systems with regard to the temperature of the emitting gas and the emission measure, we have difficulties reconciling the column density found from our X-ray observation with the column found in HST UV observations by Horne et al. (1994). The obvious option is to invoke time variability.

HST eclipse mapping of dwarf nova OY Carinae in quiescence: an 'Fe II curtain' with Mach approx. = 6 velocity dispersion veils the white dwarf

Hubble Space Telescope (HST) observations of the eclipsing dwarf nova OY Car in its quiescent state are used to isolate the ultraviolet spectrum (1150-2500 A at 9.2 A Full Width at Half Maximum (FWHM) resolution) of the white dwarf, the accretion disk, and the bright spot. The white dwarf spectrum has a Stark-broadened photospheric L(alpha) absorption, but is veiled by a forest of blended Fe II features that we attribute to absorption by intervening disk material. A fit gives T(sub w) approx. = 16.5 x 10(exp 3) K for the white dwarf with a solar-abundance, log g = 8 model atmosphere, and T approx. = 10(exp 4) K, n(sub e) approx. = 10(exp 13)/cu cm, N(sub H) approx. = 10(exp 22) sq cm, and velocity dispersion delta V approx. = 60 km/s for the veil of homogeneous solar-abundance local thermodynamic equilibrium (LTE) gas. The veil parameters probably measure characteristic physical conditions in the quiescent accretion disk or its chromosphere. The large velocity dispersion is essential for a good fit; it lowers (chi square)/778 from 22 to 4. Keplerian shear can produce the velocity dispersion if the veiling gas is located at R approx. = 5 R(sub W) with (delta R)/R approx. = 0.3, but this model leaves an unobscured view to the upper hemisphere of the white dwarf, incompatible with absorptions that are up to 80% deep. The veiling gas may be in the upper atmosphere of the disk near its outer rim, but we then require supersonic (Mach approx. = 6) but sub-Keplerian (delta V/V(sub Kep) approx. = 0.07) velocity disturbances in this region to produce both the observed radial velocity dispersion and vertical motions sufficient to elevate the gas to z/R = cos i = 0.12. Such motions might be driven by the gas stream, since it may take several Kepler periods to reestablish the disk's vertical hydrostatic equilibrium. The temperature and column density of the gas we see as Fe II absorption in the ultraviolet are similar to what is required to produce the strong Balmer jump and line emissions seen in optical spectra of OY Car and similar quiescent dwarf novae. The outer accretion disk is detected at mid-eclipse with a spectrum that rises from 0.05 to 0.3 mJy between 2000 and 2500 A, consistent with combinations of cool blackbodies, blended Fe II emission lines, and Balmer continuum emission. The total disk flux density is 0.5 mJy at 2500 A, and this shallow disk eclipse implies a roughly flat surface brightness distribution. The bright spot, somewhat bluer than the disk, has a flux density rising from 0.05 to 0.15 mJy between 1600 and 2500 A. The C IV emission line has a broad shallow eclipse, but the radial velocity variations observed during the eclipse do not clearly distinguish between a disk or wind origin. The only possible indications of boundary layer emission are fast UV flares that appear to arise from near the central object -- not from the bright spot.

Eclipse studies of the dwarf nova OY Carinae in quiescence

view Abstract Citations (183) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Eclipse Studies of the Dwarf Nova OY Carinae in Quiescence Wood, Janet H. ; Horne, Keith ; Berriman, Graham ; Wade, Richard A. Abstract High-speed photometry of OY Car have been obtained which cover 20 eclipses in white light and seven eclipses in UBR. The results show the red dwarf to have a mass of 0.070 + or - 0.002 solar masses and a radius of 0.127 + or - 0.002 solar radii, and the white dwarf to have a temperature of several thousand degrees below 15,000 K. The bright spot is found to have a compact 15,000-K core and a tail that extends along the rim but does not penetrate far into the disk. Publication: The Astrophysical Journal Pub Date: June 1989 DOI: 10.1086/167557 Bibcode: 1989ApJ...341..974W Keywords: Dwarf Novae; Eclipsing Binary Stars; Light Curve; Stellar Spectrophotometry; Red Dwarf Stars; Stellar Models; Stellar Orbits; White Dwarf Stars; Astrophysics; STARS: ACCRETION; STARS: DWARF NOVAE; STARS: ECLIPSING BINARIES; STARS: INDIVIDUAL CONSTELLATION NAME: OY CARINAE; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (5)

The 1985 May superoutburst of the dwarf nova OY Carinae – II. IUE and EXOSAT observations⋆

Ultraviolet (IUE) and X-ray (Exosat) observations of the eclipsing dwarf nova OY Carinae during the superoutburst of May 1985 are presented. From the lack of X-ray eclipse and UV behavior, it is deduced that the X-ray flux originates in an optically thin corona comparable in size to the Roche lobe, and not directly from the white dwarf or boundary layer. The asymmetric UV line emission originates partly in the accretion disk and partly in a wind. There is a strong modulation of the UV continuum flux that is thought to be caused by extended vertical disk structure shadowing the inner regions.

The 1985 May superoutburst of the dwarf nova OY Carinae – I. Optical and infrared photometry⋆

The 1985 May superoutburst of the dwarf nova OY Carinae – I. Optical and infrared photometry⋆

A new analysis of the infrared eclipses of the ultra-short period dwarf nova OY Carinae

Premiere analyse detaillee des formes des eclipses IR de cette nova naine, composee d'une naine blanche au centre d'un disque d'accretion avec une tache lumineuse a sa crete, et d'un compagnon naine rouge

High-speed photometry of the eclipsing dwarf nova OY Carinae

High-speed photometry of the eclipsing dwarf nova OY Car in the quiescent state is presented. OY Car becomes highly reddened during eclipse, with minimum flux colours inconsistent with optically thick emission in the U and B bandpasses. Mass ratios in the range 6.5 to 12 are required to reconcile the eclipse structure with theoretical gas stream trajectories. Primary eclipse timings reveal a significant decrease in the orbital period and the duration of primary eclipse indicates the presence of a luminous ring about the white dwarf. The hotspot eclipse reveals a hotspot which is elongated along the rim of the accretion disc, with optical emission being non-uniformly distributed along the rim. The location of the hotspot in the accretion disc implies a disc radius larger than that of an inviscid disc, with variation in the position of the hotspot being consistent with a fixed stream trajectory.

A visible and infrared study of the eclipsing dwarf nova OY Carinae - I. The visible eclipses of the central object

This paper presents four visible light curves of the highly inclined, short-period cataclysmic binary star OY Carinae in quiescence. These light curves show that the red dwarf eclipses both its white dwarf companion and the accretion disc and hotspot, which originate from material transferred from the red dwarf to the white dwarf. An analysis of the eclipse of the white dwarf, under the assumption that its red dwarf companion fills its Roche lobe, gives the following properties of the system when combined with the observed radial velocity amplitude of the white dwarf: the inclination lies between 73.5° and 81°, the mass of the white dwarf lies between 0.4 M⊙ and 1.4 M⊙ and the red dwarf lies either on or slightly below the lower main-sequence mass–radius relation. This range of properties is somewhat larger than found in previous analyses, where the uncertainties in the poorly known semi-amplitude of the radial velocity of the white dwarf were not taken fully into account. The consequences of our findings are discussed in the light of current ideas about the evolution of cataclysmic variable stars.

Infrared light curves of the dwarf nova OY Carinae

Infrared light curves of the dwarf nova OY Carinae

Spectrophotometry of the eclipsing dwarf nova OY Carinae

Spectrophotometry of the eclipsing dwarf nova OY Carinae