Ultraviolet Observations of Cataclysmic Variables

AbstractThe preliminary results of the analysis of more than 1000 spectra of cataclysmic variables in the archive of the International Ultraviolet Explorer were presented at the meeting. To characterize the slope of the spectra I use F = log(f1460Å/f2880Å). For most spectra F lies between 0.2 and 0.7. No correlation of F with orbital period, inclination, system type or (for dwarf novae) length of the interoutburst interval are found, apart from somewhat lower values of F for DQ Her type systems. Out of 16 dwarf novae for which spectra both at outburst maximum and minimum are available 11 show no large difference in F between maximum and minimum, and in 5 F declines with the flux level. Out of 6 dwarf novae 5 show very red spectra during the rise to maximum, and 1 shows slopes during rise similar to those during decline.In the ultraviolet resonance lines, due to a wind from the disc, no correlation is found between inclination and terminal velocity.

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IUE Observations of WZ Sagittae in Outburst

Symposium - International Astronomical Union ◽

10.1017/s007418090006530x ◽

1980 ◽

Vol 88 ◽

pp. 447-451 ◽

Cited By ~ 1

Author(s):

Albert V. Holm ◽

Chi-Chao Wu ◽

Warren M. Sparks ◽

Francis H. Schiffer ◽

Albert Boggess

Keyword(s):

Accretion Disk ◽

The Sun ◽

Dwarf Novae ◽

Low Resolution ◽

Preliminary Results ◽

International Ultraviolet Explorer ◽

Recurrent Nova

The International Ultraviolet Explorer was used to obtain spectra at both 7 Å and 0.2 Å resolution of the recurrent nova WZ Sagittae during its 1978 outburst. The first spectra were obtained on 1978 Dec 1.8 UT, approximately 0.7 days after discovery. The decay from outburst was followed until 1979 Jan 1, after which it was too near the Sun to be observed. A post-outburst spectrum was obtained on 1979 July 11. In this paper, preliminary results from the analysis of the low resolution spectra are discussed. These observations will be used to support the similarity between WZ Sge and dwarf novae and to test accretion disk models.

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When a Nova Becomes Old

Acta Polytechnica CTU Proceedings ◽

10.14311/app.2015.02.0226 ◽

2015 ◽

Vol 2 (1) ◽

pp. 226-229

Author(s):

A. Ederoclite ◽

C. Tappert ◽

L. Schmidtobreick ◽

N. Vogt

Keyword(s):

Southern Hemisphere ◽

Orbital Period ◽

Cataclysmic Variables ◽

Classical Novae ◽

Preliminary Results

Here we present the preliminary results of a project aimed at unveiling the nature of classical novae decades after their eruption. The ultimate goal of this project is to describe the population of cataclysmic variables which give rise to nova explosions. So far, in four years of observations, we have concentrated on novae in the Southern hemisphere, where we increased by 100% the amount of objects spectroscopically confirmed and increased by 1/5 the amount of objects with known orbital period.

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Spectroscopic properties of the dwarf nova-type cataclysmic variables observed by LAMOST

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa065 ◽

2020 ◽

Vol 72 (5) ◽

Author(s):

Zhongtao Han ◽

Soonthornthum Boonrucksar ◽

Shengbang Qian ◽

Fang Xiaohui ◽

Qishan Wang ◽

...

Keyword(s):

Emission Line ◽

Spectral Type ◽

Orbital Period ◽

White Dwarf ◽

Accretion Rate ◽

Cataclysmic Variables ◽

Spectroscopic Properties ◽

Accretion Disc ◽

Spectral Features ◽

Dwarf Novae

Abstract Spectra of 76 known dwarf novae from the LAMOST survey were presented. Most of the objects were observed in quiescence, and about 16 systems have typical outburst spectra. 36 of these systems were observed by SDSS, and most of their spectra are similar to the SDSS spectra. Two objects, V367 Peg and V537 Peg, are the first spectra of the object. The spectrum of V367 Peg shows a contribution from an M-type donor and its spectral type could be estimated as M3-5 by combining its orbital period. The signature of a white dwarf spectrum can be seen clearly in four low-accretion-rate WZ Sge stars. Other special spectral features worthy of further observations are also noted and discussed. We present a LAMOST spectral atlas of outbursting dwarf novae. Six objects have their first outburst spectra given here, and the others were also compared with the published outburst spectra. We argue that these data will be useful for further investigation of the accretion disc properties. The He ii λ4686 emission line can be found in the outburst spectra of seven dwarf novae. These objects are excellent candidates for probing the spiral asymmetries of accretion disc.

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Testing the disk instability model of cataclysmic variables

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833372 ◽

2018 ◽

Vol 617 ◽

pp. A26 ◽

Cited By ~ 17

Author(s):

Guillaume Dubus ◽

Magdalena Otulakowska-Hypka ◽

Jean-Pierre Lasota

Keyword(s):

Mass Transfer ◽

Orbital Period ◽

Transfer Rate ◽

Mass Transfer Rate ◽

Sampling Rate ◽

Cataclysmic Variables ◽

Irregular Sampling ◽

Light Curves ◽

Stable Region ◽

Dwarf Novae

Context. The disk instability model (DIM) attributes the outbursts of dwarf novae to a thermal-viscous instability of their accretion disk, an instability to which nova-like stars are not subject. Aims. We aim to test the fundamental prediction of the DIM: the separation of cataclysmic variables (CVs) into nova-likes and dwarf novae depending on orbital period and mass transfer rate from the companion. Methods. We analyzed the light curves from a sample of ≈130 CVs with a parallax distance in the Gaia DR2 catalog to derive their average mass transfer rate. We validated the method for converting optical magnitude to mass accretion rate against theoretical light curves of dwarf novae. Results. Dwarf novae (resp. nova-likes) are consistently placed in the unstable (resp. stable) region of the orbital period – mass transfer rate plane predicted by the DIM. None of the analyzed systems present a challenge to the model. These results are robust against the possible sources of error and bias that we investigated. Light curves from Kepler or, in the future, the LSST or Plato surveys, could alleviate a major source of uncertainty, that is, the irregular sampling rate of the light curves, assuming good constraints can be set on the orbital parameters of the CVs that they happen to target. Conclusions. The disk instability model remains the solid basis on which to construct an understanding of accretion processes in CVs.

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The hydrogen Balmer lines and jump in absorption in accretion disc modelling – an ultraviolet–optical spectral analysis of the dwarf novae UZ Serpentis and CY Lyrae

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1093 ◽

2020 ◽

Vol 494 (4) ◽

pp. 5244-5258

Author(s):

Patrick Godon ◽

Edward M Sion ◽

Paula Szkody ◽

William P Blair

Keyword(s):

Spectral Analysis ◽

Accretion Rate ◽

Cataclysmic Variables ◽

Outer Radius ◽

Accretion Disc ◽

Absorption Lines ◽

Dwarf Novae ◽

Balmer Lines ◽

Flux Level ◽

The Continuum

ABSTRACT The spectra of disc-dominated cataclysmic variables (CVs) often deviate from the spectra of accretion disc models; in particular, the Balmer jump and absorption lines are found to be shallower in the observations than in the models. We carried out a combined ultraviolet–optical spectral analysis of two dwarf novae (DNe): UZ Ser in outburst, decline, and quiescence, and CY Lyr on the rise to outburst and in outburst. We fit the Balmer jump and absorption lines, the continuum flux level and slope by adjusting the accretion rate, inclination, and disc outer radius. For both systems, we find an accretion rate $\dot{M} \approx 8 \times 10^{-9}\,\mathrm{ M}_\odot\,\mathrm{ yr}^{-1}$ in outburst, and $\dot{M} \approx 2-3 \times 10^{-9}\,\mathrm{ M}_\odot\,\mathrm{ yr}^{-1}$ for the rise and decline phases. The outer disc radius we derive is smaller than expected (Rdisc ≈ 0.2a, where a is the binary separation), except during late rise (for CY Lyr) where Rdisc = 0.3a. UZ Ser also reveals a 60 000 K white dwarf. These results show that during a DN cycle the radius of the disc is the largest just before the peak of the outburst, in qualitative agreement with the disc instability model for DN outbursts. We suspect that an additional emitting component (e.g. disc wind) is also at work to reduce the slope of the continuum and size of the Balmer jump and absorption lines. We stress that both the outer disc radius and disc wind need to be taken into account for more realistic disc modelling of CVs.

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500 - 3200 Å Observations of the Interacting Binary Stars V356 Sgr and β Lyr

International Astronomical Union Colloquium ◽

10.1017/s0252921100087698 ◽

1989 ◽

Vol 107 ◽

pp. 85-94

Author(s):

R. S. Polidan

Keyword(s):

Binary Stars ◽

Cataclysmic Variables ◽

Circumstellar Matter ◽

Emission Lines ◽

High Dispersion ◽

Total Strength ◽

Uv Emission ◽

Flux Level ◽

Orbital Modulation ◽

Ultraviolet Observations

AbstractIn this paper we present new results from the Voyager ultraviolet spectrometers and the IUE spacecraft on V356 Sgr and β Lyr. The V356 Sgr observations cover, in detail, two eclipses and include one IUE high dispersion SWP image. During both eclipses the total strength of the UV emission lines were found to be invariant. Also, an uneclipsed UV continuum was detected at wavelengths shorter than 1600 Å. The IUE high dispersion SWP spectrum revealed that the emission lines are extremely broad, almost symmetrical lines with weak, slightly blue shifted absorption components. No evidence of carbon is seen in the emission or absorption spectrum of V356 Sgr in eclipse. A model for the origin of the circumstellar matter in this binary system is presented. The Voyager ultraviolet observations of β Lyr show a strong far-UV continuum that is detectable down to 912 Å The far-UV continuum flux level was variable on time scales shorter than the orbital period and displayed no obvious orbital modulation or eclipses. The spectral shape of the far-UV continuum closely resembles that of a UX UMa type cataclysmic variable. On 16 August 1985 an rapid brightening of the far-UV continuum was observed which was also reminiscent of cataclysmic variables. Analysis of the β Lyr data suggest that the central object must be small, with a radius on the order of 1 R⊙ or less.

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Ultraviolet Observations of Some Close Binary Systems by the Astronomical Netherlands Satellite-Ans

Symposium - International Astronomical Union ◽

10.1017/s0074180900011980 ◽

1976 ◽

Vol 73 ◽

pp. 213-223

Author(s):

Chi-Chao Wu

Keyword(s):

Binary Systems ◽

Hot Spot ◽

Close Binary ◽

Spectral Energy ◽

Dwarf Novae ◽

Energy Distributions ◽

Primary Star ◽

Higher Temperature ◽

Far Ultraviolet ◽

Ultraviolet Observations

Observations of δ Pic, a β Lyr type of eclipsing binary and seven dwarf novae are reported. The ultraviolet light curves of δ Pic indicate the accumulation of matter at the triangular Lagrangian points L4 and L5, the presence of a hot spot and a higher temperature for the primary star. The implication is that the cooler secondary fills its Roche lobe and is transfering mass to the primary; mass loss to the circumstellar space and possibly to the system may also be appreciable. The temperatures of dwarf novae are derived by comparing their ultraviolet spectral energy distributions with those for normal stars of luminosity classes IV and V. Piecing together observations for different objects, the SSCyg systems have temperatures of 28 500 K, 10 000 K and 9500 K, respectively, when they are at minimum, immediately before outburst and at the beginning of rise to maximum. At maximum, the temperature is 22 500 K or 17 300 K depending on the interstellar reddening correction for AR And. Immediately before outburst, there is a large excess of flux in the far ultraviolet as indicated by the large value of the ratio of flux at 1550 Å to that at 1800 Å. The observations of Z Cam during standstill gives a temperature of 14 900 K. No excess of flux in the far ultraviolet was observed during the maximum of AR And and the standstill of Z Cam.

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CVs Around the Minimum Orbital Period

Acta Polytechnica CTU Proceedings ◽

10.14311/app.2015.02.0041 ◽

2015 ◽

Vol 2 (1) ◽

pp. 41-45

Author(s):

S. Zharikov ◽

G. Tovmassian

Keyword(s):

Accretion Disk ◽

Accretion Disks ◽

Orbital Period ◽

Cataclysmic Variables ◽

Outer Edge ◽

Light Curves ◽

Mass Ratio ◽

Period Limit ◽

Bounce Back ◽

The Continuum

We discussed features of Cataclysmic Variables at the period minimum. In general, most of them must be WZ Sge-type objects. Main characteristics of the prototype star (WZ Sge) are discussed. A part of WZ Sge-type objects has evolved past the period limit and formed the bounce back systems. We also explore conditions and structure of accretion disks in such systems. We show that the accretion disk in a system with extreme mass ratio grows in size reaching a 2:1 resonance radius and are relatively cool. They also become largely optically thin in the continuum, contributing to the total flux less than the stellar components of the system. In contrast, the viscosity and the temperature in spiral arms formed at the outer edge of the disk are higher and their contribution in continuum plays an increasingly important role. We model such disks and generate light curves which successfully simulate the observed double-humped light curves in the quiescence.

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