MBCAA Observatory

SDSS J015543.40+002807.2 (FL Cet) low state

Observed: 28 Sep, 15, 16, 17, 18 Nov 2011

Michel Bonnardeau
21 Nov 2011

Abstract

This cataclysmic polar with deep, narrow eclipses has dropped by 2 magnitudes since September 2011.

Introduction

SDSS J015543.40+002807.2 (or FL Cet or Cet in the Downes catalog of cataclysmics) is a cataclysmic system, that is a binary with an accreting white dwarf. The white dwarf is strongly magnetized, its spin is synchronized with the orbital motion, and the accretion is funneled by the magnetic field (no accretion disk). This type of cataclysmic is a polar or an AM Her type system. The orbital/spin period of SDSSJ0155 is 87.144 mn.

I observed it in 2010 around magnitude 15, with eclipses at least 4 magnitudes deep.

Observations

The observations were carried out the same way as in 2010: with a 203mm f/6.3 SC telescope, a Clear filter and a SBIG ST7E camera (KAF401E CCD). 253 usable images were obtained in 2011, each with a 200s exposure duration.

For the differential photometry, the same comparison star and check as in 2010 were used: GSC 30-1268 as the comparison star with an Rc magnitude of 13.927, GSC 30-207 as the check star. The check star was measured with the magnitude CR=14.728+/-0.025+/-0.029 where the first +/- is the average 1-sigma statistical uncertainty and the second one is the standard deviation.

The light curve of 28 Sep 2011 is very similar to the light curves of 2010:

Red: the magnitudes of SDSSJ0155, blue: of the check star shifted by +5mag. The error bars are +/- the 1-sigma statistical uncertainties. The vertical green lines are the eclipses according to the ephemeris of O'Donoghue et al (2006).

The eclipse at 833.62 appears to be missing: this is probably due to its narrowness and to my time resolution not good enough.

The light curves of November show a drop of about 2 mag and the eclipses barely discernable with my set up (the circles are upper limits):

The circle is an upper limit.