Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSuperhumps and flickering in V1316 Cygni
187
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present analysis and results of a coordinated CCD photometry campaign to observe the 2006 June superoutburst of the cataclysmic variable V1316 Cyg involving 8 longitudinally-distributed observers. The outburst peaked at magnitude 15.03 on June 10, declined at a rate of 0.14 mag/day, lasted 11 days and had an amplitude above quiescence of 2.4 magnitudes. We detected common superhumps for the first time, thereby confirming that V1316 Cyg is a member of the UGSU class of dwarf novae. We observed a transition to late superhumps two-thirds of the way through the outburst with an associated phase shift of 0.50 +/- 0.06 cycles. The mean common superhump period before this transition was 0.07685 +/- 0.00003 d and the mean late superhump period following the transition was 0.07654 +/- 0.00002 d. The common superhump period decreased at a rate dP/dt = -5.1 +/- 1.7 x10^-5 /cycle. At the onset of late superhumps, there was a transient shift in power from the superhump fundamental frequency to its first harmonic and back again. We detected an orbital period of 0.0740 +/- 0.0002 d giving a fractional superhump period excess of 0.038 +/- 0.003 and a mass ratio of 0.167 +/- 0.010. A scalegram analysis of the flickering behaviour of V1316 Cyg found that the alpha and sigma parameters characterising flickering changed significantly during the superoutburst. We also found flickering to be at a relatively much lower level at the beginning of the superoutburst and during two normal outbursts.
rate research
Read More
We report CCD photometry of the cataclysmic variable V1113 Cygni. During two campaigns, lasting from May to August 2003 and from March to June 2005, we recorded two superoutburst. In the obtained light curves we detected clear superhumps with a mean period 0.07891(3) days (113.63(4) min). That fact confirms that the star is a member of SU UMa class of dwarf novae. During the first observed superoutburst the superhump period was decreasing with an enormous rate of $dot P = -4.5(8)times 10^{-4}$ which is one of the highest values ever observed in SU UMa systems.
We have studied the short-cadence Kepler public light curves of SU UMa stars, V344 Lyr and V1504 Cyg extending over a period of more than two years by using power spectral analysis. We determined the orbital period of V344 Lyr to be Porb=0.087903(1) d. We also reanalyzed the frequency variation of the negative superhump in a complete supercycle of V1504 Cyg with additional data of the O-C diagram, confirming that its characteristic variation is in accordance with the thermal-tidal instability model. We present a new two-dimensional period analysis based on a new method of a least absolute shrinkage and selection operator (Lasso). The new method gives very sharp peaks in the power spectra, and it is very useful for studying of the frequency variation in cataclysmic variable stars. We also analyzed simultaneous frequency variations of the positive and negative superhumps. If they are appropriately converted, it is found that they vary in unison, indicating that they represent a disk-radius variation. We have also studied the frequency (or period) variations of positive superhumps during superoutbursts. These variations can be understood in a qualitative way by combining of the disk radius variation and the variation of pressure effects during a superoutburst. A sudden excitation of oscillation with a frequency range near to the negative superhump (which we call impulsive negative superhump) was observed in the descending branch of several outbursts of V344 Lyr. These events seem to have occurred just prior to the next superoutburst, and to act as a lead of the impending superoutburst.
We made a supplemental study of the superoutbursts and superhumps in SU UMa stars by using the recently released Kepler public data of V1504 Cyg and V344 Lyr. One of the superoutbursts in V1504 Cyg was preceded by a precursor normal outburst which was well separated from the main superoutburst. The superhump first appeared during the descending branch of the precursor normal outburst and it continued into quiescence (the deep dip between the precursor and the main superoutburst), and it began to grow in amplitude with the growth of the main superoutburst after quiescence ended. A similar phenomenon was also observed in V344 Lyr. This observation demonstrates very clearly that the superoutburst was triggered by the superhump (i.e., by the tidal instability), supporting the thermal-tidal instability model. Smak (2013, Acta Astron., 63, 109, arXiv:1301.0187) criticized our previous paper (Osaki and Kato, 2013, PASJ, 65, 50, arXiv:1212.1516) and challenged our main conclusion that various observational lines of evidence of V1504 Cyg support the thermal-tidal instability model for the superoutbursts of SU UMa stars. We present our detailed accounts to all of his criticisms by offering clear explanations. We conclude that the thermal-tidal instability model is after all only the viable model for the superoutbursts and superhumps in SU UMa stars.
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 light 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.
Since the discovery of the largest positive superhump period in TV Col, we have started a program to search for superhumps in CVs with large orbital periods. Here, we summarize preliminary results of TX Col and V4742 Sgr. TX Col is an intermediate polar with a 5.7-h orbital period. V4742 Sgr is a recent nova with no known periods. CCD unfiltered continuous photometry of these 2 objects was carried out during 56 nights in 2002-3. In TX Col, in addition to the orbital period of 5.7 h, we found peaks at 7.1 h and 5.0 h. These are interpreted as positive and negative superhumps correspondingly, although the effects of the quasi-periodic oscillations at about 2 h were not taken into consideration. In the light curve of V4742 Sgr 2 long periods are detected -- 6.1 and 5.4 h as well as a short-term period at 1.6 h. This result suggests that V4742 Sgr is an intermediate polar candidate and a permanent superhump system with a large orbital period (5.4 h) and a superhump period excess of 13 percent. If these results are confirmed, TX Col, V4742 Sgr and TV Col form a group of intermediate polars with extremely large superhump periods. There seems to be now growing evidence that superhumps can occur in intermediate polars with long orbital periods, which is very likely inconsistent with the theoretical prediction that superhumps can only occur in systems with mass ratios below 0.33. Alternatively, if the mass ratio in these systems is nevertheless below the theoretical limit, they should harbour undermassive secondaries and massive white dwarfs, near the Chandrasekhar limit, which would make them excellent candidates for progenitors of supernovae type Ia.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
