CBA Observations of Var79 Peg (Oct 2004)

Var79 Peg = 1RXS J215434.4+355023 was discovered by S. Antipin (2004, IBVS 5573) on plates of the Moscow collection. The object is located at R.A.=  21h54m33s.66, DEC.=  +3550'17".4 (J2000.0). The light curve, published by Antipin, shows two kinds of outbursts : short-lasting ones and longer ones. The long-lasting outbursts with flat maxima, resemble superoutbursts of SU UMa-type dwarf novae. The amplitude of variability strongly changed during the interval of observations: before 1980, Var79 Peg's photographic magnitudes changed between 14m.0-<18m.1, ander after 1982 this became 14m.35-17m.0. The only exception was 1987, when the star was fainter than 17m.1 on Moscow plates and appeared at b=18m.26, as measured in the GSC 2.2 catalog, on a POSS II blue plate. 

Observations on October 29/30, 2004  

Var79 Peg was announced in outburst on 2004, Oct 29.806 UT (visual detection by Chris Jones, UK) at mag 14.4. Half an hour later, the outburst was confirmed by myself, on an unfiltered CCD image. Immediately following the confirmation, I started an unfiltered time-series photometry session on Var79 Peg (2004, Oct 29/30), at CBA Belgium Observatory, using one of the 0.35-m f/6.3 telescopes, and an SBIG ST-7XME CCD camera. 

The session lasted for 3.4 hours, resulting in 184 observations, under moderate sky conditions (cloud fields, strong moonlight). Ensemble photometry using MIRA AP and Maxim DL revealed small amplitude modulations (around 0.1 - 0.15 mag), and a linear trend of decline (about 0.1 mag over 0.14 d).  

Later that night, Lou Krajci, observing from CBA New Mexico, also started an unfiltered observing session on Var79 Peg. He collected a total of 229 observations, showing a very similar light curve pattern.

 Var79 Peg light curve on Oct 29/30, 2004, composed of CBA Belgium (red dots) and CBA New Mexico (blue dots) 
observations, showing irregular low-amplitude modulations, but no superhump waves.

Observations on October 30/31, 2004

Three CBA observatories participated in this night's session : Tonny Vanmunster (CBA Belgium), Arto Oksanen (CBA Finland) and Lou Krajci (CBA New Mexico). The combined light curve (see below) shows an irregular modulation of about 0.1 mag .

Var79 Peg light curve on Oct 30/31, 2004, composed of CBA Belgium (cyan dots), CBA Finland (green dots) and 
CBA New Mexico (pink dots) observations, showing irregular 0.1 mag modulations.


Light curve analysis

Using Peranso, I performed a detailed period analysis on the collected observations. I first de-activated observations, that were considered erroneous, and then subtracted the average magnitude of each observation set. This resulted in a total of 942 useful observations. Subsequently, I used the ANOVA (see figure below) and PDM period analysis methods to derive the most significant period. This resulted in a period of 0.0651 +/- 0.0006 d. 

The significance of the period (false alarm probability F.A.P.) then was calculated using the Fisher Randomization method of Peranso. This is a Bootstrap approach, and it confirmed the significance of the above period (F.A.P. of 0.005 only), although the signal is quite weak.  The latter is evident when looking at the phase diagram (see below), which depicts an average modulation with an amplitude of 0.04 mag only.

Although the above observations indicate that superhumps have not (yet) developed, it remains interesting to continue monitoring this highly unknown target.

ANOVA period analysis on 942 CBA observations of Var79 Peg

Phase diagram resulting from the ANOVA period analysis





Copyright © 2004 - Tonny Vanmunster.