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Multicolor investigation of A new WZ Sge dwarf nova in Draconis PNV J18422792+4837425

N. Katysheva, D. Chochol, S. Shugarov, I. Volkov, M. Andreev, P. Golysheva, T. Irsmambetova (Moscow-Slovak team) E. Pavlenko, K. Antonyuk, N. Pit, V. Malanushenko, A. Baklanov, R. Zvagelsky, O. Antonyuk (Crimean team).

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Multicolor investigation of A new WZ Sge dwarf nova in Draconis PNV J18422792+4837425

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  1. N. Katysheva, D. Chochol, S. Shugarov, I. Volkov, M. Andreev, P. Golysheva, T. Irsmambetova (Moscow-Slovak team) E. Pavlenko, K. Antonyuk, N. Pit, V. Malanushenko, A. Baklanov, R. Zvagelsky, O. Antonyuk (Crimean team) Multicolor investigation of A new WZ Sge dwarf nova in DraconisPNV J18422792+4837425 XI-th Hvar Astrophysical Colloquium The Most Mysterious Binaries: Significance for Astrophysics 2 - 6 July 2012, Hvar, Croatia

  2. PNV J18422792+4837425 - new WZ Sge system in Draconis among the other close binaries K. Petrov-Vodkin, Still life. Mac Dougall’s

  3. Dwarf Novae (DNe) are a subclass of cataclysmic variables - semidetached binaries, consisting of a red dwarf, transferring matter to a white dwarf. Variability of DNe is caused by the orbital motion of the components and quasi periodic outbursts, resulting from instabilities in an accretion disk, surrounding a white dwarf. The WZ Sge-type are the subgroup of SU UMa DNe with a long (several years or even decades) recurrence time of superoutbursts, with a distinguished peculiarity: a hump-shaped modulation appears shortly after maximum, and maintains until the beginning of a quiescence. The humps reveal longer periods in comparison with orbital ones, and evolve during the brightness decline.

  4. Superhumps of WZ Sge-type stars evolve from “early superhumps” with a double-humped profile near the brightness maximum and the period extremely close to the orbital one, through “ordinary superhumps” with a single humped profile and the period of a few percent longer than the orbital one, to “late superhumps”. The duration of superoutburst is about 30-50 day. After the plateau of the superoutburst, the fast decline follows, sometimes with rebrightening(s) – short increase(s) of the brightness.

  5. “Early superhumps” are one of the most remarkable signatures of the WZ Sge-type objects. They appear near a maximum magnitude of superoutburst and have periods almost identical to the orbital one. The profile of “early superhumps” has a character double-humped form. It lasts a few days. Osaki & Meyer (2002, A & Ap, 383, 574) suggested that a double peaked profile of “early superhumps” is manifestation of the tidal 2:1 resonance in accretion disks of binary systems with extremely low mass ratios. “Early superhumps” can be explained by a two-armed spiral pattern of tidal dissipation generated by the 2:1 resonance, first proposed by Lin & Papaloizou (1979, MN, 186, 799).

  6. “Ordinary superhumps”, with a single hump profile, can be explained by the thermal tidal instability model of an accretion disk (Osaki, 1989, PASJ, 41, 1005; Whitehurst, 1988, MN, 232, 35). The presence of the tidal 3:1 resonance in the disk (with the radius smaller than the 2:1 resonance radius) results in the formation of an eccentric outer ring undergoing apsidal precession with a period appreciably longer than the orbital one. The beating of the orbital and precessional periods cause periodic variations, identified as superhumps. “Late superhumps” are proposed to originate in the precessing eccentric disk near the tidal truncation. The eccentric disk slowly expands during the decline of the superoutburst and finally reaches the tidal truncation, where the period is stabilized (Kato et al., 2008, PASJ, 60L, 23).

  7. An example of “early superhumps” in CT Tri = new WZ Sge- type system in Triangulum which bursted in 2008. A double-hump structure is clearly seen (Chochol et al., 2009, Contr. Astron. Obs. Skalnaté Pleso, 39, 43).

  8. An example of “ordinary superhumps” in V466 And = a new WZ Sge-system in Andromedae which bursted in 2009. A saw-tooth structure is general for plateau of superoutburst (Chochol et al., 2010, Contr. Astron. Obs. Skalnate Pleso, 40, 19).

  9. Most of the WZ Sge-binaries have been discovered in a last few years. The sequence: “early superhumps” ~ “ordinary superhumps” ~ “late superhumps” was observed for all of them, except PNV J18422792+4837425 The most of information about SU UMa and WZ Sge DNe are collected in three large papers published by Kato et al. (PASJ, 2009, 61S, 395; 2010, 62, 1525; 2012, 64, 21), devoted to the evolution of superoutburst, superhump periods, etc…

  10. On September 6.55, 2011, A. Arai performed low-resolution optical spectroscopic observations of PNV J1842+4837 at Koyama Astronomical Observatory. The spectrum showed Balmer lines on a blue continuum light. The Hα line clearly showed a strong emission feature (E.W. about -300) in its absorption component. The Hβ and the Hγ lines were dominated by absorption components. These results suggest that the object would be a dwarf nova during its outburst. (www.cc.kyoto-ac.jp/~kao/blog/index.php/view/125). PNV J18422792+4837425 was discovered by H. Nishimura on the 5th of September, 2011 as a new transient with U = 11.8 mag.

  11. The spectrum of the object, taken by Christian Buil on Sept. 6.987, 2011 with the LISA spectrograph (R=800), using the 94-cm telescope of Saint-Caprais observatory (France).

  12. VSNET–“chronicles”: in the early days of the superoutburst the “early superhumps” with a period of 0.0591(4) days were seen. But later on they had either very small amplitude (<0.01 mag), or disappeared. VSNET–“chronicles” reported the very unstable humps with a period of about 0.07 days. Up to September 24, 2011 narrow superhumps appeared and then vanished. During the decline stage of superoutburst there were no visible “ordinary superhumps”. This behaviour is very unusual for WZ Sge-type systems. On October 4, 2011, the first rebrightening was detected. These peculiarities confirmed that J1842+4837 is an unusual WZ Sge-type object.

  13. We observed superoutburst of J1842+4837 from the beginning till its quiescence. Our observations were carried out at: 1. Stará Lesná, Slovakia – 50 cm, Zeiss-600 telescopes 2. Mt. Koshka, Crimea – Zeiss-600, Zeiss-1000 3. Nauchny, Crimea – Zeiss-600, AZT-11 (125 cm), K-38 (38 cm), ZTSh (2.60 m) telescopes 4. Mt. Terskol, Russia – 35 cm, Zeiss-600 telescopes 5. Apache Point Obs., USA – 50 cm telescope ARCSAT 6. Nyzhny Arkhyz, Russia – 35 cm, Zeiss-1000 telescope We got more than 11 000 CCD-frames in UBVRcRjIcIj-bands.

  14. The overall light curves in U-B-V-R-I bands are plotted in the next figure. The first rebrightening wasdetected on October 6, 2011and lasted about 14 days. It was very long rebrightening, which is very unusual, too. The second rebrightening, detected in our observations, was not marked by VSNET. It is possible, that it was taken as a decline of the first rebrightening. But the second rebrigtening is real! We detected the decline of brightness after the first rebrightening. All light curves (LCs) are presentedtogether without any shifts in magnitudes. It is clearly seen thatour star is very bright in UV during the observations. It was brighter in UV atthe first minimum, too.

  15. It is an example of series of rebrighenings ofa remarkable WZ Sge system SDSS J0804+51, which experienced 2 superoutbursts in the last four years (2006–11, 2010 – 6). It is seen that one rebrightening lasted 2-3d (Pavlenko et al., in press).

  16. The results of our observationsofJ1842+4837 are presented below. U B V (Rc+Rj) LCsexhibitthe plateau-like stage of superoutburst with gradual decrease in brightness, then fast decline, and two rebrightenings. Unfortunately, nobody observedanincrease in brightness ofthe second rebrightening.

  17. Overall V- light curve Triangles –VSNET data

  18. The beginning ofthe superoutburst in Rc+Rj, the nightly LCs during theplateau of the superoutburst.

  19. Continuation of thesuperoutbust in Rc and Rj. The nightly LCsduring the superoutburst plateau.

  20. JD55823 JD55826 V-band.The nightly LCsduring the superoutburst plateau. JD55827

  21. Inspite of visual variability, the periodogram analysis during the plateau stagedid not show any strict periodicity. There were no evident superhumps. Periodogram for the plateau stage is shown on the next slide. Reliability of this period is low, but it is close to the period ofthe“ordinary superhumps”, which appeared during thefirst rebrightening (nextly).

  22. Periodogram for theplateau stage. Reliability of this period is low, but it is close to the period of “ordinary superhumps”, which appeared duringthe first rebrightening. One-day aliases to this periodare marked by the arrows.

  23. The phase LC fortheplateau stage. Very small full amplitude of the variability (0.06 mag).

  24. JD55841 JD558542 JD55843 TheV-band, plateau of the first rebrightening, the nightly LCs. The superhumps appeared.

  25. The periodogram for the rebrightening stage. The peak at 0.07275 day is clearly seen. VSNET givesthe period from 0.07 to 0.079 d.

  26. Aggregate LC (B, V, R, I-bands) summed with the periodof 0.07275 day during thefirst rebrightening were used.

  27. The phased LC forthe first rebrightening stage. Black points – mean LC.

  28. The stage after the firstrebrightening. The phased LC for the data before and after the second rebrightening.

  29. Data analysis from the 2.6 m telescope ZTSh (JD 55856, after the second rebrightening) gave the period P = 0.073 d

  30. The systemreturned to quiescence afterthe second rebrightening. Itis the overall LC in R-bands.

  31. The data after the second rebrightening and in quiescence • were used for determination of the period of “late • superhumps”,which is close to the orbital period. There are • not anyapparent displays of “late superhumps” and • theobjectis weak now – of about 20 mag. • By the way, we evaluated the period of 0.0729 d for • quiescencedata from APO .

  32. P = 0.0729 d The phased LC in quiescence for different periods The phased LC in quiescence ~ the most recent data from 2m telescope from Mt.Terskol gives P = 0.0724 d!!!

  33. UBVRI during the 1st rebrightening

  34. The total duration ofthe 1st rebrightening was about 20 days, and the plateau phase ~ 14 days. It is uncommon. The second rebrightening was narrow and lasted ~3-4 days. The shape of the upper part of rebrightening is very similar to the plateau of superoutburst.

  35. The evolution track of J1842+48 is shown by color circles. Red–outburst, lilac–1st min, violet – rebrightening. The days after the outburst are noted. A main sequence, giant branch and black bodysequence are plotted. Open circles correspond to the comparison stars. The diagram U-B, B-V.

  36. The details of diagram U-B, B-V.

  37. 1st min The variations ofthe color indices U-B (below) and B-V (right) during superoutburst. 1st min

  38. The diagram B-V, V-Rc. The position of the star and the number of days after outburst are marked by crosses and numbers. 1 min B-V 2 min V-Rc

  39. Conclusion. At present we know more than 40 WZ Sge stars and the investigation of every object is very important for our understanding of the physical processes in close binaries. A new dwarf nova in Draconis certainly belongs to the WZ Sge type. We have no information for any previous outbursts of our object. We found the arguments for the second rebrightetning. We have detected the mean period of the “ordinary superhumps” P= 0.07275 d. It was very difficult to find the typical change of the superhump period with time because of unsufficiency of clear-cut humps. We also determined a period in queiscence 0.0724 d.

  40. The system had strong UV-excess even at minimum of brightness between rebrightenings. Aknowledgments. We grateful to Dr. V. Goranskij (SAO, SAI) for the observations of J1842+4937 at the Zeiss-1000 telescope of Special Astrophysical Observatory (Russia) and mrs. A. Zharova (SAI). This work was supported by grants: NSh-2374.2012.2, RFBR 11-02-00495a, RFBR 11-02-01213a, VEGA-grant 2/0038/10. N. Katysheva, I. Volkov are thankful for support from SAIA(Slovakia).

  41. Thanks! PNV J18422792+4837425 - new WZ Sge system in Draconis

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