NSV 4838 - a new UGSU-type dwarf nova

Following the announcements by Patrick Schmeer and Jochen Pietz (on CVnet) of an outburst of the dwarf nova NSV 4838, I started an unfiltered photometry session of this target at CBA Belgium Observatory on 2005, Jun 7/8. Sky conditions were moderate only, and I was able to collect about 54 useful images during a time span of 1.6 hours. I furthermore received CBA observations of NSV 4838 from Tom Kracji, USA, obtained on 2005, Jun 8. Tom was able to collect about 100 useful frames during 1.8 hours.

Our data sets clearly revealed the presence of superhumps in NSV 4838, thus classifying the system as a new UGSU-type dwarf nova. Jochen Pietz, Germany independently also detected the superhumps in this dwarf nova.

By June 9th, I received further CCD observations of Tom Kracji and also of David Boyd, UK. Based on a total of nearly 500 observations (fig. 1), obtained between 2005, June 7th and June 9th, I found a superhump period using ANOVA (and several other methods of Peranso) of 0.0697 +/- 0.0003 d (fig. 2). Despite the difficult location of NSV 4838 in the evening sky, the longitudinal spread of the observers worked very well to precisely determine the superhump characteristics of NSV 4838. The average superhump amplitude is 0.3 mag (fig. 3).

Assuming a normal superhump period excess value of 2.6%, the superhump period of 0.0697 d (or 100 min) corresponds to a Porb of 97.8 min, which is in complete agreement with the value of 97.6 min, derived by John Thorstensen through radial velocity spectroscopy. John's spectroscopy yielded a second possible Porb of 91.4 min, which seems to be no longer favoured, given the above Psh value.

Fig. 1. Combined NSV 4838 lightcurve with observations from Vanmunster, Kracji and Boyd (Peranso figure)

Fig. 2. ANOVA period diagram of NSV 4838 (Peranso figure)

Fig. 3. Phase diagram of NSV 4838 (Peranso figure)





Copyright © 2005 - Tonny Vanmunster.