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  • Followup ground-based observations of the dwarf nova KZ Gem

    分类: 天文学 >> 天体物理学 提交时间: 2020-03-09

    摘要: We present spectroscopy of stars in the immediate vicinity of the dwarf nova (DN) KZ Gem to confirm its identification, which had been ambiguous in the literature. Analysis of 73 radial velocities spanning from 2014 to 2019 provides a high-precision orbital period of 0.2224628(2) d (~5.34 hr) and shows KZ Gem to be a double-lined DN. Time series photometry taken from 2016 to 2018 shows a variable double-hump modulation with a full amplitude of ~0.3 mag, along with five Gaussian-like transient events lasting ~30 min or more. Using the light curve code XRBinary and nonlinear fitting code NMfit, we obtain an optimized binary model of the dwarf nova (DN) KZ Gem, from time series photometry, consisting of a Roche-lobe-filling K type dwarf with a mass transfer rate of 2.7 - 7.9 x 10^{-10} solar mass per yr to a large, cool and thick disk surrounding a white dwarf, in an orbit with an inclination of 51.6(+/-1.4) degree. Two hotspots on the disk are demonstrated to cause the observed variations in the ellipsoidal modulations from the secondary star. This physical model is compatible with the Gaia distance of KZ Gem.

  • A Phenomenological Model for the Light Curve of three Quiescent Low-inclination Dwarf Novae and one Pre-Cataclysmic Variable

    分类: 天文学 >> 天体物理学 分类: 天文学 >> 恒星和银河系 提交时间: 2018-09-12

    摘要: We used the light curve code XRBinary to model the quiescent K2 light curves of three low-inclination cataclysmic variables (CVs): 1RXS\,J0632+2536 (J0632+2536), RZ\,Leo, TW\,Vir and the pre-CV WD\,1144+011. Optimized light curve models were obtained using a nonlinear fitting code NMfit and visualized by Phoebe 2.0. The disk model of J0632+2536 shows that one hotspot at the edge of the disk is enough to describe its light curve, while the other two dwarf nova (DN): RZ\,Leo and TW\,Vir require two hotspots. A typical pre-CV model with a weak irradiation effect for WD\,1144+011 can explain its single-hump modulation and the newly observed spectrum confirms its previous classification. The synthetic analyses for the DN clearly indicate that phase zero of the double-hump modulations occurs around the secondary minimum and the primary hump is mainly caused by the hotspot at the edge of the disk. The quiescent disk has a flat temperature distribution with a power index of $\sim0.11$. The disk model of RZ\,Leo implies a truncated disk, supporting its previously speculated classification as an intermediate polar (IP). Except for the IP model of RZ\,Leo, which lacks a component related to the inferred accretion curtain, the models of J0632+2536, TW\,Vir and WD\,1144+011 are consistent with results from the Gaia mission. The derived masses and radii of the secondaries of the three DN are consistent with the semi-empirical relations for CV donor stars, while their effective temperatures are higher than the predictions. Irradiation of the donor stars is investigated to explain this discrepancy.

  • Quiescent photometric modulations of two low-inclination cataclysmic variables KZ Gem and TW Vir

    分类: 天文学 >> 恒星和银河系 提交时间: 2017-08-17

    摘要:Aims. The quiescent periodic photometric modulations of two low-inclination cataclysmic variables observed in Kepler K2 Campaigns 0 and 1, KZ Gem and TW Vir, are investigated. Methods. A phase-correcting method was successfully used to detect the orbital modulations of KZ Gem and TW Vir and improve their orbital periods. The light curve morphologies of both CVs were further analyzed by defining flux ratios and creating colormaps. Results. KZ Gem shows ellipsoidal modulations with an orbital period of 0.22242(1) day, twice the period listed in the updated RK catalogue (Edition 7.24). With this newly determined period, KZ Gem is no longer a CV in the period gap, but a long-period CV. A part of the quiescent light curve of TW Vir that had the highest stability was used to deduce its improved orbital period of 0.182682(3) day. The flat patterns shown in the colormaps of the flux ratios for KZ Gem demonstrate the stability of their orbital modulations, while TW Vir show variable orbital modulations during the K2 datasets. In TW Vir, the single versus double-peaked nature of the quiescent orbital variations before and after superoutburst may be related to the effect of the superoutburst on the accretion disk.