New SU UMa star USNO 1425.09823278

(vsnet-alert 1171)

According to IAUC No. 6731, J.-y. Hu (Beijing Astronomical Observatory) et al. reports the discovery of a new apparent bright dwarf nova.

     USNO 1425.09823278

     19h 27m 11s.63 (J2000.0)
     +54o 17' 51".5
R=13.3 on Aug. 31 and 13.5 on Aug. 31. Spectroscopically confirmed to be an outbursting dwarf nova.

Being a large outburst-amplitude object, the variable should be an excellent target for searching for superhumps. Observations are very urgently encouraged. The object is close to galaxy UGC 11443, which may have provided a chance discovery of this dwarf nova during the supernova survey.

Taichi Kato

First successful observations

Visual detection of superhumps

(vsnet-obs 7194, Timo Kinnunen)

USNO 1425.09823278 19970904.793  13.4  Outburst goes on.
USNO 1425.09823278 19970904.810  13.7
USNO 1425.09823278 19970904.822  13.4
USNO 1425.09823278 19970904.847  13.7
USNO 1425.09823278 19970904.863  13.6
USNO 1425.09823278 19970904.886  13.5
USNO 1425.09823278 19970904.910  13.5
USNO 1425.09823278 19970904.933  13.7
                                 Sequence drawn from V1504 Cyg. Now let me 
                                 roughly 0.3 mag superhumps with 1 hour period.

CCD Image (Nick James)

(vsnet-obs 7210)

Dear all,

I obtained a V-Band image of this variable last night (September 5). Identification is by comparison with the DSS.

Regards Nick James.

CCD Detection of Superhumps

(from CVC 149, vsnet-alert 1179)

USNO 1425.09823278 [CV:, 13.3R - 19.9R]
Tonny Vanmunster, Landen, Belgium, obtained unfiltered CCD observations of this newly discovered variable star on September 5/6, 1997, during a 5.9h run, using a ST-7 SBIG CCD camera attached to a 25-cm f/6.3 SCT. 2 * 2 on-chip summation was used, with exposure times of 50 sec and 60 sec, depending on atmospheric conditions.

A visual inspection of the resulting light curve does not show superhumps, although an analysis using the Phase Dispersion Minimi- zation (PDM) method of R.F. Stellingwerf yields a weak signal with a period of 0.057 +/- 0.001 d, which might very well be attributed to the superhump. We applied standard data reduction techniques (dark frame and flat field correction, as well as removal of a linear trend of decline).

The object is declining rapidly from its 'outburst', so we strongly encourage follow-up observations.

(vsnet-alert 1186)

Dear colleagues,

I'v just finished ccd images of new var. star in Cygnus and I detected there superhumps! It seems to be a new SU UMa type dwarf nova. Because of weather, there is only one superhump maximum and possible two minimas (first one is very poor). PDM analyzis shows P=0.07+-0.01 aproximately. I'll prepare light curve to GAMA's page when I'll back at observatory. Right now I'm quite asleep :-) Hacve a nice day Rudolf

* Rudolf Novak                              Private:         Rudolf Novak *
* Nicholas Copernicus Observatory                    Bohuslava Martinu 50 *
* Kravi Hora 2                                                BRNO 602 00 *
* BRNO 616 00                                              Czech Republic *
* Czech Republic                                                          *
*                    e-mail:                      *
*                    h-page:              *
*             " ... no, There's no dark side of the Moon ... "            *

Rapid Decline

(vsnet-alert 1187)

USNO 1425.09823278

Recent reports suggest that the variable has entered a stage of rapid decline. Several observers report by CCD photometry the possible existence of superhumps. Observers should note in some SU UMa stars, superhumps may once decay during the plateau stage and may become prominent again even during the rapid decline, often showing double waves probably consisting of usual superhumps and late superhumps. A good such example was observed during the 1991 December - 1992 January superoutbrust of UV Per. Rudolf Novak's report suggests the superhump signal still persists. Follow-up observations are still highly encouraged until the object finally fades away. Be prepared for rebrightening(s)!

Taichi Kato

Comment by T. Kato

(vsnet-alert 1191)

Dwarf novae which had passed the period minimum (the orbital period get longer then) are expected to show outbursts similar to SU UMa-type dwarf novae (Politano et al.). The main difference of these objects from normal SU UMa stars is the extremely low accretion rates (<10^-2 times lower). The outburst recurrence times of such objects are expected to be very long (may be longer than that of WZ Sge), so the outburst in any given such system may be an "once-in-lifetime" event. In attempts to revealing such objects, early alerts are essential, may be even more crucial than in nova cases (cf. recent vsnet-chat discussion). We should express special thanks to the Beijing team for promptly notifying the outburst of this object, rather than submitting a slow journal paper.

Taichi Kato


(CVC 152, vsnet-alert 1193)

USNO 1425.09823278 [CV:, 13.3R - 19.9R]

Tonny Vanmunster, CBA Belgium Observatory reports a rebrightening of this newly discovered variable. Compared with observations of yesterday evening, the brightness increased by nearly 1.3 mag. The object currently is around (unfiltered) mag 15.2, but visually very likely is about 0.5 mag brighter. Our observations were made with a CCD camera, attached to a 0.25-m f/6.3 SCT (unfiltered). Here are some recent estimates :

1997 Sep 05.977 UT,  14.2  (T. Vanmunster, unfilt. CCD);
     Sep 06.810 UT,  13.9  (J. Pietz);
     Sep 06.831 UT,  14.45 (L. T. Jensen, unfilt. CCD);
     Sep 06.890 UT,  14.0  (J. Pietz);
     Sep 06.964 UT,  14.5  (T. Vanmunster, unfilt. CCD);
     Sep 06.980 UT,  14.0  (J. Pietz);
     Sep 07.810 UT,  15.5  (L. T. Jensen, unfilt. CCD);
     Sep 07.837 UT,  15.3  (T. Kinnunen);
     Sep 07.869 UT,  15.4: (G. Poyner);
     Sep 07.926 UT,  15.5: (G. Poyner);
     Sep 07.938 UT,  15.7  (T. Kinnunen);
     Sep 09.007 UT, [14.7  (G. Poyner);
     Sep 09.772 UT, [14.7  (T. Kinnunen);
     Sep 09.890 UT,  16.5  (T. Vanmunster, unfilt. CCD);
     Sep 09.974 UT, [14.7  (G. Poyner);
     Sep 10.819 UT,  15.2  (T. Vanmunster, unfilt. CCD);

It's a pitty that this object is not followed more intensively by CCD observers worldwide. The present rebrightening clearly proves it should be a priority object for all dwarf novae photometrists !

Early Rebrightening!

(vsnet-alert 1195)

Rebrightening of USNO 1425.09823278

As reported by several groups, the above new dwarf nova is undergoing a post-(super)outburst rebrightening. Summary of observations up to now:

  YYMMDD(UT)   mag  observer
  970904.488   133  (S. Takahashi)
  970904.792   134  (T. Kinnunen)
  970904.810   137  (T. Kinnunen)
  970904.819   135  (J. Pietz)
  970904.822   134  (T. Kinnunen)
  970904.847   137  (T. Kinnunen)
  970904.860   135  (J. Pietz)
  970904.863   136  (T. Kinnunen)
  970904.885   135  (T. Kinnunen)
  970904.891   134  (G. Poyner)
  970904.892   134  (G. Poyner)
  970904.910   135  (T. Kinnunen)
  970904.933   137  (T. Kinnunen)
  970905.021   135  (P. Schmeer)
  970905.110   138  (B. King)
  970905.780   138  (T. Kinnunen)
  970905.806   137  (T. Kinnunen)
  970905.883   136  (G. Poyner)
  970906.017   137  (G. Poyner)
  970906.810   139  (J. Pietz)
  970906.831  14.45  (L. T. Jensen, CCD unfiltered)
  970906.890   140  (J. Pietz)
  970906.980   140  (J. Pietz)
  970907.810   155  (L. T. Jensen, CCD unfiltered)
  970907.837   153  (T. Kinnunen)
  970907.869   154: (G. Poyner)
  970907.926   155: (G. Poyner)
  970907.938   157  (T. Kinnunen)
  970909.007  <147  (G. Poyner)
  970909.772  <147  (T. Kinnunen)
  970909.823  <165  (L. T. Jensen, CCD unfiltered)
  970909.974  <147  (G. Poyner)
  970910.824  14.68  (L. T. Jensen, CCD unfiltered)
  970910.836  14.68  (L. T. Jensen, CCD unfiltered)
  970910.838  14.71  (L. T. Jensen, CCD unfiltered)
  970910.880   142  (J. Pietz)

The interval between the fading from the main outburst (presumably a superoutburst) and the rebrightening is only 3 days, which is one of the shortest ever observed in SU UMa-type dwarf novae. Such "early rebrightening" was only observed on very few occasions such as the 1978 superoutburst of WZ Sge and the 1995 superoutburst of AL Com, both of which are notable examples of so-called "WZ Sge-type dwarf novae". The present pheonomenon observed in USNO 1425.09823278 may be somehow related to these rarely observed specimens. Since the regrowth of superhumps during the rebrightening stage was reported in AL Com, we strongly urge observers to monitor this object closely until the final quiescence is confidently reached.

Taichi Kato

Superhump firmly detected!

(vsnet-alert 1196)

Differential R band CCD photometry of the newly discovered dwarf nova USNO 1425.09823278 were obtained between 0437-0736 UT on 4 September, and between 0359-0623 on UT 5 September 1997, using the Mount Laguna Observatory's 1-m reflector. The 1-min resolution time series of images clearly reveal superhumps with an amplitude of 0.08 mag, recurring with a period of approximately 0.056 days, and thus confirm earlier reports.

Scott Dahm
Allen Shafter

(CVC 153, vsnet-alert 1197)

USNO 1425.09823278 [UGSU, 13.3R - 19.9R]
Unfiltered CCD observations of this object, obtained over a 7.8h run on Sep 10/11, 1997 (during the rebrightening reported in our previous CVC) at CBA Belgium Observatory, show the existence of superhumps with a mean semi-amplitude of 0.05 mag. An analysis using the PDM method shows a distinct signal at 0.0561 +/- 0.0004 d, which clearly is the superhump period. A steady linear trend of decline (approx. 0.3 mag over 8 hours) was removed from the observations.

Given the dominance of this signal, and taking into account the fact that the period is in very good agreement with values obtained during earlier runs [CVC 149 & CVC 151], we feel very confident we finally have revealed the SU UMa-type nature of this newly discovered variable.

Follow-up observations are of course still highly encouraged. A quick inspection of tonight's CCD data shows that the object has become faint again (the linear trend of decline, reported above, presumably has not been interrupted).

Tonny Vanmunster

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