MBCAA Observatory

SDSS J213122.40-003937.0: a new cataclysmic

Observed: 23, 24, 27 Dec 2008

Michel Bonnardeau
25 Dec 2008
Updated 30 Dec 2008, 4 June 2009

Abstract

Photometric measurements and a light curve for this newly discovered variable are presented.

Introduction

This object was recorded as bright on 16 Dec 2008; a 100mn modulation with a 0.1mag amplitude was observed, suggesting a SU UMa type cataclysmic system (Yamaoka et al (2008)).

Observations

The observations were carried out with a 203mm f/6.3 SC telescope, a Clear or a V filter and a SBIG ST7E camera (KAF401E CCD).

Session 23 Dec 2008

Two differential photometry measurements were obtained, one with a Clear filter the other one with a Johnson V filter:

Filter JD Magnitude Comparison

C 2454824.27521 14.767+/-0.067 GSC 5208-00505
assumed unfiltered mag 12.7

V 2454824.27969 14.792+/-0.072 Tycho2 5208-00478
with V=11.156 (converted with
Mamajek et al (2002 & 2006))

Session 24 Dec 2008

To make a light curve, 32 images were obtained, each with an exposure duration of 200s. A Clear filter is used. The comparison star is GSC 5208-00505 with an assumed unfiltered magnitude of 12.7. The check star is GSC 5208-00434, with an observed magnitude of 14.773, an average 1-sigma statistical uncertainty of 0.018mag and a standard deviation of 0.022mag:

Red: VAR/Aqr, blue: the check star, shifted by +1.1mag. The error bars are +/- the 1-sigma statistical uncertainties.

VAR/Aqr is not well placed and the airmass is high. However the sky conditions were good:

The photometry zero point as a function of the airmass.

Session 27 Dec 2008

I try a time-series but the object was no longer visible.
I stack 11 images (total exposure 2200s): there is an object at the position with a magnitude around 19 or 20.
This is a drop of a least 4 mag in 3 days.