DO Dra Research Articles

The mass of the white dwarf in YY Dra (=DO Dra): Dynamical measurement and comparative study with X-ray estimates

We present a dynamical study of the intermediate polar cataclysmic variable YY Dra based on time-series observations in the K band, where the donor star is known to be the major flux contributor. We covered the 3.97-h orbital cycle with 44 spectra taken between 2020 and 2022 and two epochs of photometry observed in 2021 March and May. One of the light curves was simultaneously obtained with spectroscopy to better account for the effects of irradiation of the donor star and the presence of accretion light. From the spectroscopy, we derived the radial velocity curve of the donor star metallic absorption lines, constrained its spectral type to M0.5–M3.5 with no measurable changes in the effective temperature between the irradiated and non-irradiated hemispheres of the star, and measured its projected rotational velocity vrot sin i = 103 ± 2 km s−1. Through simultaneous modelling of the radial velocity and light curves, we derived values for the radial velocity semi-amplitude of the donor star, K2 = 188−2+1 km s−1, the donor to white dwarf mass ratio, q = M2/M1 = 0.62 ± 0.02, and the orbital inclination, i = 42°−1°+2°. These binary parameters yield dynamical masses of M1 = 0.99−0.09+0.10 M⊙ and M2 = 0.62−0.06+0.07 M⊙ (68 per cent confidence level). As found for the intermediate polars GK Per and XY Ari, the white dwarf dynamical mass in YY Dra significantly differs from several estimates obtained by modelling the X-ray spectral continuum.

Hitting a New Low: The Unique 28 hr Cessation of Accretion in the TESS Light Curve of YY Dra (DO Dra)

We present the Transiting Exoplanet Surveying Satellite light curve of the intermediate polar YY Draconis (YY Dra, also known as DO Dra). The power spectrum indicates that while there is stream-fed accretion for most of the observational period, there is a day-long, flat-bottomed low state at the beginning of 2020 during which the only periodic signal is ellipsoidal variation and there is no appreciable flickering. We interpret this low state to be a complete cessation of accretion, a phenomenon that has been observed only once before in an intermediate polar. Simultaneous ground-based observations of this faint state establish that when accretion is negligible, YY Dra fades to g = 17.37 ± 0.12, which we infer to be the magnitude of the combined photospheric contributions of the white dwarf and its red dwarf companion. Using survey photometry, we identify additional low states in 2018–2019 during which YY Dra repeatedly fades to—but never below—this threshold. This implies relatively frequent cessations in accretion. Spectroscopic observations during future episodes of negligible accretion can be used to directly measure the field strength of the white dwarf by Zeeman splitting. Separately, we search newly available catalogs of variable stars in an attempt to resolve the long-standing dispute over the proper identifier of this system.

Photometric Studies of the Intermediate Polar DO Dra in 2008 and 2019

An analysis is presented of photometric observations of the intermediate polar DO Dra obtained during an epoch of significant reduction in its outburst activity for different average brightnesses of the system: 13m.6-12m.8 (2008) and 14m.7-14m.3 (2019). The observations in 2008 were made in the Johnson BVR system and in 2019, in integrated light. For the first time in quasi-simultaneous observations in the BVR bands, orbital modulation of the brightness was recorded in the form of a two-humped curve in each band, presumably caused by ellipsoidality of the secondary component. For six nights in the BVR bands (2008) and one night in integrated light (2019), stable quasiperiodic oscillations around 0.02 days were observed. On the night of JD 2458575 (2019) an increase in the brightness by 0m.7 was observed over 3 min, followed by exponential decay. The flare lasted about an hour within the first half of which oscillations with a period of about 0.006 days and an amplitude of 0m.1 were observed that may be related either to the rotation period of the white dwarf or to the quasiperiodic oscillations. The nature of the flare is not yet clear and possible reasons for this effect are examined in this article.

Magnetic Dwarf Nova DO Dra: Sub-low-luminosity State and Mini-outbursts

Magnetic Dwarf Nova DO Dra: Sub-low-luminosity State and Mini-outbursts

Magnetic Dwarf Nova DO Dra: Recovering to the Base Luminosity State

Magnetic Dwarf Nova DO Dra: Recovering to the Base Luminosity State

Variability of the Rotation Period of the White Dwarf in the Magnetic Cataclysmic Binary System EX Hya

The observations of the two-periodic magnetic cataclysmic system EX Hya have been carried out, using the telescopes RC16 and TOA-150 of the Tzec Maun observatory. 6 nights of observations were obtained in 2010-2011 (alternatively changing filters VR). Also the databases of WASP, ASAS and AAVSO have been analyzed. Processing time series was carried out using the program MCV. We analyzed changes in the rotation period of the white dwarf, and based on our own and previously published moments of maximum. The ephemeris was determined for the maxima of the radiation flux associated with the rotation of the magnetic white dwarf: Tmax=2437699.89079(59) +0.0465464808(69).E-6.3(2)*10^{-13}E^2, which corresponds to the characteristic timescale of the rotation spin-up of 4.67(14)*10^6 years. This contradicts the estimated value of the mass of the white dwarf of 0.42M_\odot, based on X-ray observations made by Yuasa et al (2010), however, is consistent with estimates of the masses of 0.79 M_\odot (white dwarf) and 0.108 M_\odot (red dwarf) previously published Beuermann and Reinsch (2008), and the assumption that the capture of accreted plasma by magnetic field of the white dwarf is near the border of the Roche lobe. Analyzed moments do not support the assumption of Mauche et al (2009) for a statistically significant cubic term in the ephemeris. Despite the presence of outbursts in EX Hya, there are significant differences from the DO Dra, which supports the introduction to a detailed classification of the intermediate polars the groups of "outbursting intermediate polars" and "magnetic dwarf novae."

Aperiodic optical variability of intermediate polars – cataclysmic variables with truncated accretion disks

We study the power spectra of the variability of seven intermediate polars containing magnetized asynchronous accreting white dwarfs, XSS J00564+4548,IGR J00234+6141, DO Dra, V1223 Sgr, IGR J15094-6649, IGR J16500-3307 and IGR J17195-4100, in the optical band and demonstrate that their variability can be well described by a model based on fluctuations propagating in a truncated accretion disk. The power spectra have breaks at Fourier frequencies, which we associate with the Keplerian frequency of the disk at the boundary of the white dwarfs' magnetospheres. We propose that the properties of the optical power spectra can be used to deduce the geometry of the inner parts of the accretion disk, in particular: 1) truncation radii of the magnetically disrupted accretion disks in intermediate polars, 2) the truncation radii of the accretion disk in quiescent states of dwarf novae

Outburst activity of intermediate polars

Abstract An analysis of the outburst activity of intermediate polars (IPs) is presented, with particular attention to the large-amplitude outbursts of GK Per and DO Dra, which can be explained by the thermal instability of the disk. The decays of the outbursts in DO Dra are faster than in non-magnetic dwarf novae (DN), suggesting that the magnetosphere is not fully compressed during outburst, while the rate of decay in GK Per is comparable to non-magnetic DN. The recurrence times TC of outbursts in both systems display large variations, but are not chaotic. The relation between the optical and X-ray profile of the light curve of outbursts in GK Per is presented. Also the general properties of the outbursts of IPs are discussed.