MBCAA Observatory

MR Ser: a polar cataclysmic

Observed: 16 April, 17, 18 July 2014

Michel Bonnardeau
4 Aug 2014

Abstract

Photometric observations of the polar cataclysmic MR Ser are presented and compared with the ephemeris.

Introduction

MR Ser is a polar cataclysmic system: a magnetic white dwarf orbiting a companion star and accreting matter from it. The spin period of the dwarf is equal to the orbital period and the magnetic field is strong enough to funnel the accretion (no disk). The orbital/spin period is 1.89 hours.

Observations of photometric light curves are presented here.

Observations

The observations were carried out with a 203mm SC telescope, a clear filter, and a SBIG ST7E camera (KAF401E CCD). The exposure durations are 200s. 146 useful images were obtained in 3 observing sessions.

For the differential photometry, the comparison star is GSC 1499-1692 with a Rc magnitude of 12.086, computed from the r' magnitude of the CMC14 catalog and the 2MASS magnitudes, owing to the transformations of Bilir et al (2008) and Smith et al (2002). The unfiltered magnitude is taken as the Rc magnitude, for the mostly red sensitive CCD.

An example of a light curve is:

Red: MR Ser, Blue: the check star (GSC 1499-1899) shifted by +2 mag. The error bars are the 1-sigma statistical uncertainties.

Ephemeris

The following times of minima are obtained:

HJD -
2,456,000 uncertainty

764.5365 0.002

764.610 0.005

856.418 0.008

857.434 0.002

According to Baklanov & Pavlenko (2001) an ephemeris for the minima, from 1999-2001 observations, is:

t(E) = T + P*n
with
T = 2,451,369.9664 HJD
P = 0.078,796,6 day

To fit my 4 times of minima, this ephemeris has to be slightly modified by substracting 4 milliseconds to the period.

A phase plot is then:

Note the strong variation from cycle to cycle.