Detection of superhumps in dwarf nova NSV 1485 
durings the Sep 2007 superoutburst

 
The poorly studied cataclysmic variable NSV 1485 was reported to be in outburst on Sep 10th, 2007 by Denis V. Denisenko (Space Research Institute IKI), using the 1.5-m Russian-Turkish Telescope (RTT150). The object is located at RA = 04h12m36.89s, Dec. = +6929'06.4" (J2000.0). A CCD image identifying the variable is shown below. NSV 1485 was originally discovered by T. Meshkova on Moscow photographic plates in 1944 (Astron. Tsir. 26, p. 4) as a variable of unknown type with a magnitude range of 12.9-<14.5.

Based on 6 nights of photometric observations between 2007, Aug 26th and 2007, Sep 07th, during quiescence of the variable, D. Denisenko found an orbital period of either 0.0717d and 0.0771d (i.e., 14 and 13 revolutions per day). It was impossible to further distinguish between these two aliases.


11 Sep 2007 at 23h34m UT. (c) Tonny Vanmunster
The marked object is NSV 1485. The brightest star in the image is GSC 4332:777.

 
Follwing the announcement of this rare outburst, I decided to start a CCD photometry session on 2007, Sep 11/12, using a 0.35-m f/6.3 telescope and ST-7XME CCD camera (working unfiltered). I repeated similar unfiltered CCD sessions on the 2 following nights, resulting in the below lightcurve.


The light curve shows a decline by 0.8 mag/day, but no apparent modulations in any of the datasets. An extensive analysis using various period analysis methods in Peranso did not reveal any strong signal. 

 

From precursor outburst to superoutburst

At a moment that everyone was assuming that the variable had returned to quiescence, Patrick Schmeer reported his detection of another outburst of NSV 1485, on 2007, Sep 19th. When I received Patrick's phone call (thanks Patrick !) around 10 PM local time that evening, skies were completely overcast, but the weather satellite images showed a possible clearing later that night. I woke up around 0h UT (Sep 20th) and saw a clear sky.

It remained clear for about 3 hours, during which I started an unfiltered CCD photometry session on NSV 1485, using again a 0.35-m f/6.3 telescope and SBIG ST-7XME CCD camera. The resulting lightcurve, based on a 2.5 hrs session, is shown below and clearly reveals the presence of superhumps, hence classifying NSV 1485 as a new UGSU-type dwarf nova. Using Peranso's ANOVA method, I find a superhump period value of 0.076 +/- 0.001d, and an amplitude of about 0.15 mag. The period window and phase diagram are shown below. My superhump period value seems to favor the orbital period alias of 0.0771d (but see the discussion on the superhump refinement below).

NSV 1485's precursor outburst occured about 10 days before this main superoutburst. A similar combination of outbursts was recorded during the 1998 outburst of QZ Vir (aka T Leo). QZ Vir underwent a supposed precursor outburst on 1998 Apr 2, followed by a superoutburst 10 days later.


CBA Belgium Observatory lightcurve of NSV 1485 - unfiltered CCD observations - 2007, Sep 19/20


ANOVA period window depicting the superhump period at 0.076 +/- 0.001d

 
Phase diagram corresponding with the period at 0.076d

 

Additional CBA observations of NSV 1485

Two long observation sets of NSV 1485 were obtained on Sep 21/22, 2007, by CBA New Mexico (Tom Krajci) and CBA Belgium Observatory (Tonny Vanmunster). The two sets cover a total of 1059 observations, over a time span of 16.7 hours, with only a small gap in between the two sets.

Combined with my Sep 19/20 obs, the CBA dataset for NSV 1485 now comprises 1191 superoutburst observations. Using Peranso's implementation of the ANOVA method (A. Schwarzenberg-Czerny), I find a superhump period of 0.07421 +/- 0.00010d. See the period window below. This is slightly shorter than the value I found on Sep 19/20 (see above), but which was based on a *much* shorter timeline. 

The amplitude derived from all CBA observations is about 0.18 mag. The phase diagram (see below) shows a small dip on the descending branch of the superhump modulation, but I'm not sure how to interpret this. Further observations might tell.


NSV 1485 superoutburst lightcurve combining CBA observations of Tom Krajci (CBA New Mexico, dark obsset) 
and Tonny Vanmunster (CBA Belgium Observatory, purple & blue obsset).


ANOVA period window depicting the superhump period at 0.07
421 +/- 0.0010d


Phase diagram corresponding with the period at 0.07
421d, binned per 10 observations.
Note the small dip on the descending branch of the superhump wave.

 

  
 
 

 

 

Copyright © 2007 - Tonny Vanmunster.