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تسجيل مستخدم جديدDiscovery of superhumps during a normal outburst of SU Ursae Majoris
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We report on time-resolved photometry during a 2012 January normaloutburst of SU UMa. The light curve shows hump-like modulations with a period of 0.07903(11) d, which coincides with the known superhump period of SU UMa during superoutbursts. We interpret this as superhump, based on the observed periodicity, profiles of the averaged light curve, and the $g-I_{rm c}$ variation during the normal outburst. This is the first case that superhumps are detected during an isolated normal outburst of SU UMa-type dwarf novae. The present result strongly suggests that the radius of the accretion disk already reaches the 3:1 resonance even in the midst of the supercycle.
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We report on a discovery of negative superhumps during the 2011 January superoutburst of ER UMa. During the superoutburst which started on 2011 January 16, we detected negative superhumps having a period of 0.062242(9) d, shorter than the orbital per
iod by 2.2%. No evidence of positive superhumps was detected during this observation. This finding indicates that the disk exhibited retrograde precession during this superoutburst, contrary to all other known cases of superoutbursts. The duration of this superoutburst was shorter than those of ordinary superoutbursts and the intervals of normal outbursts were longer than ordinary ones. We suggest a possibility that such unusual outburst properties are likely a result of the disk tilt, which is supposed to be a cause of negative superhumps: the tilted disk could prevent the disk from being filled with materials in the outmost region which is supposed to be responsible for long-duration superoutbursts in ER UMa-type dwarf novae. The discovery signifies the importance of the classical prograde precession in sustaining long-duration superoutbursts. Furthermore, the presence of pronounced negative superhumps in this system with a high mass-transfer rate favors the hypothesis that hydrodynamical lift is the cause of the disk tilt.
We carried out the photometric observations of the SU UMa-type dwarf nova ER UMa during 2011 and 2012, which showed the existence of persistent negative superhumps even during the superoutburst. We performed two-dimensional period analysis of its lig
ht curves by using a method called least absolute shrinkage and selection operator (Lasso) and phase dispersion minimization (PDM) analysis, and we found that the period of negative superhumps systematically changed between a superoutburst and the next superoutburst. The trend of the period change can beinterpreted as reflecting the change of the disk radius. This change of the disk radius is in good agreement with the predicted change of the disk radius by the thermal-tidal instability (TTI) model. The normal outbursts within a supercycle showed a general trend that the rising rate to maximum becomes slower as the next superoutburst approaches. The change can be interpreted as the consequence of the increased gas-stream flow onto the inner region of the disk as the result of the tilted disk. Some of the superoutbursts were found to be triggered by a precursor normal outburst when the positive superhumps appeared to develop. The positive and negative superhumps co-existed during the superoutburst. The positive superhumps were prominent only during four or five days after the supermaximum, while the signal of the negative superhumps became strong after the middle phase of the superoutburst plateau. A simple combination of the positive and negative superhumps was found to be insufficient in reproducing the complex profile variation. We were able to detect the developing phase of positive superhumps (stage A superhumps) for the first time in ER UMa-type dwarf novae. Using the period of stage A superhumps, we obtained a mass ratio of 0.100(15), which indicates that ER UMa is on the ordinary evolutional track of CVs.
We report on simultaneous $g$, $R_{rm c}$ and $I_{rm c}$ photometry of SU Ursae Majoris during 2011 December - 2012 February using OAO/MITSuME. Our photometry revealed that quiescence is divided into three types based on the magnitude and color. Quie
scent light curves showed complicated profiles with various amplitudes and time scales. Although no superoutbursts were observed during our run, five normal outbursts occurred with intervals of 11 - 21 d. The shapes of the normal outbursts were characteristic of the outside-in type. During the rising phase of a normal outburst, the light curve showed periodic modulations with a period of ${sim}$ 0.048111(354) d, but the origin of this peirod was unclear. We examined daily averaged color-color diagram and found that two cycles exist. This implies that the thermal limit cycle in SU UMa is complicated. We newly discovered that $g-R_{rm c}$ becomes red about 3 days prior to an outburst. Although the working mechanism on this reddening is unclear, we propose two possibilities: one is that the inner portion of the accretion disk is filled by matter and obscures the central white dwarf, and the other is that the stagnation effect works in the outer region of the accretion disk.
We report the results of a long campaign of time-series photometry on the nova-like variable UX Ursae Majoris during 2015. It spanned 150 nights, with ~1800 hours of coverage on 121 separate nights. The star was in its normal `high state near magnitu
de V=13, with slow waves in the light curve and eclipses every 4.72 hours. Remarkably, the star also showed a nearly sinusoidal signal with a full amplitude of 0.44 mag and a period of 3.680 +/- 0.007 d. We interpret this as the signature of a retrograde precession (wobble) of the accretion disc. The same period is manifest as a +/-33 s wobble in the timings of mid-eclipse, indicating that the discs centre of light moves with this period. The star also showed strong `negative superhumps at frequencies w_orb+N and 2w_orb+N, where w_orb and N are respectively the orbital and precession frequencies. It is possible that these powerful signals have been present, unsuspected, throughout the more than 60 years of previous photometric studies.
The Wide-field Infrared Survey Explorer has revealed a T8.5 brown dwarf (WISE J111838.70+312537.9) that exhibits common proper motion with a solar-neighborhood (8 pc) quadruple star system - Xi Ursae Majoris. The angular separation is 8.5 arc-min, an
d the projected physical separation is about 4000 AU. The sub-solar metallicity and low chromospheric activity of Xi UMa A argue that the system has an age of at least 2 Gyr. The infrared luminosity and color of the brown dwarf suggests the mass of this companion ranges between 14 and 38 Jupiter masses for system ages of 2 and 8 Gyr respectively.
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