Detection of the dwarf nova nature of Var Vul 05 (New Var near M27)

Var Vul 05 was discovered as a new variable in the direct vicinity of M27 by Joerg Hanisch (Germany) and Hans-Goeran Lindberg (Sweden), based on CCD images taken on Aug 17/18 and Aug 18, 2005 resp. The object is located at R.A. = 19h59m51.29s and Decl. = +22d42'32.3" (2000.0). More details are available in AAVSO Alert Notice 325.  A good reference image can be found at the Cosmotography website.

Following the discovery announcement of this new variable, I started an unfiltered CCD photometry session on Aug 23/24, 2005. The data were obtained under medium quality sky conditions at CBA Belgium Observatory, using a 0.35-m f/6.3 telescope and ST-7XME CCD camera. The session effectively started at Aug 23.85 UT and lasted for 4.4 hours (more images were obtained before and after, but with insufficient S/N level).

Instead of stacking the images (which did not deliver firm results), I processed the individual images, resulting in a total of 117 useful observations. The resulting light curve (see below) clearly shows a superhump profile. 

Var Vul 05 unfiltered CCD photometry light curve. CBA Belgium Observatory.

I then used a number of different period analysis methods in Peranso (ANOVA, Lomb-Scargle, PDM, CLEANest) and they all show a strong signal at 0.058 +/- 0.003 d. The corresponding phase diagram shows a clear superhump profile. Hence, it is safe to conclude that this object is a new UGSU-type dwarf nova (and maybe even an UGWZ-type dwarf nova). The superhump amplitude is about 0.3 mag.

ANOVA diagram showing the superhump period at 0.058 d.

Phase diagram showing the Var Vul 05 lightcurve folded over a period of 0.058d.


On Aug 25/26, 2005, my colleague Brian Martin from CBA Alberta (Canada) succeeded in confirming above findings. He detected superhumps too with an amplitude of 0.3 mag, and found a superhump period of 0.058 +/- 0.003 d, using Peranso's Anova method. 

On Aug 27/28, 2005, I had another clear night over CBA Belgium Observatory, and using a 0.35-m f/6.3 telescope with unfiltered ST-7XME camera, I started another run on Var Vul 05. This time, the session lasted for 3.1 hours (till clouds made further photometry impossible). The variable had faded to about mag 17.8 (see lightcurve below), but still showed superhumps with an amplitude of about 0.2 mag. Combined with my observations of Aug 23/24, 2005, I found a superhump period of 0.0590 +/- 0.0002d.

Var Vul 05 unfiltered CCD photometry light curve. CBA Belgium Observatory.





Copyright © 2005 - Tonny Vanmunster.