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)

XI-th Hvar Astrophysical Colloquium The Most Mysterious Binaries: Significance for Astrophysics

2 - 6 July 2012, Hvar, Croatia

K. Petrov-Vodkin, Still life. Mac Dougall’s

PNV J18422792+483

7425 -new WZ Sge

system in Draconis among the other close

binaries

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 iscaused 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.

Superhumps of WZ Sge-type stars evolve from “early superhumps” with a double-humped profile near thebrightness 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.

“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).

“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).

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).

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).

Most of the WZ Sge-binaries have been discoveredin a last few years. The sequence: “early superhumps”~ “ordinary superhumps” ~ “late superhumps” wasobserved for all of them, except PNV J18422792+4837425

The most of information about SU UMa and WZ Sge DNeare collected in three large papers published by Kato etal. (PASJ, 2009, 61S, 395; 2010, 62, 1525; 2012, 64, 21), devotedto the evolution of superoutburst, superhump periods, etc…

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).

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).

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.

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.

The overall light curves in U-B-V-R-I bands are plotted in the next figure. The first rebrightening was detected on October 6, 2011 and 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 presented together without any shifts in magnitudes. It is clearly seen that our star is very bright in UV during the observations. It was brighter in UV at the first minimum, too.

It is an example of series of rebrighenings of a 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).

The results of our observations of J1842+4837 are presented below.

U B V (Rc+Rj) LCs exhibit the plateau-like stage of superoutburst with gradual decrease in brightness, then fast decline, and two rebrightenings.

Unfortunately, nobody observed an increase in brightness of the second rebrightening.

Overall V- light curve

Triangles –VSNET data

The beginning of the superoutburst in Rc+Rj, the nightly LCs during the plateau of the superoutburst.

Continuation of the superoutbustin Rc and Rj. The nightly LCs during the superoutburst plateau.

V-band. The nightly LCs during thesuperoutburst plateau.

JD55823 JD55826

JD55827

In spite of visual variability, the periodogram analysis during the plateau stage did 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 of the “ordinary superhumps”, which appeared during the first rebrightening (nextly).

Periodogram for the plateau stage. Reliability of this periodis low, but it is close to the period of “ordinary superhumps”, which appeared during the first rebrightening. One-day aliases to this period are marked by the arrows.

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

The V-band, plateau of the first rebrightening, the nightly LCs. The superhumps appeared.

JD55841

JD558542

JD55843

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

Aggregate LC (B, V, R, I-bands) summed with the period of 0.07275 day during the first

rebrightening were used.

The phased LC for the first rebrightening stage. Black points – mean LC.

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

The stage after the first rebrightening.

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

The system returned to quiescence after the second rebrightening. It is the overall

LC in R-bands.

The data after the second rebrightening and in quiescence

were used for determination of the period of “latesuperhumps”, which is close to the orbital period.

There are not any apparent displays of “late superhumps”

and the object is weak now – of about 20 mag. By the way, we evaluated the period of 0.0729 d

forquiescence data from APO .

The phased LC in quiescence for

different periods

P = 0.0729 d

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

UBVRI during the 1st rebrightening

The total duration of the 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.

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 body sequence are plotted. Open circles correspond to the comparison stars.

The diagram U-B, B-V.

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

The variations of the color indices U-B (below) and B-V (right) during superoutburst.

1st min

1st min

The diagram B-V, V-Rc.The position of the star and the number of days after outburstare marked by crosses and numbers.

1 min

2 min

B-V

V-Rc

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.

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).

PNV J18422792+4837425 -new WZ Sge system in Draconis

Thanks!