MR Ser. Improved ephemeris
Observed: 2014, 2015, 2017, 2018, 2019, 2020, 2026
Michel Bonnardeau
17 July 2026
Abstract
Photometric observations of the polar cataclysmic MR Ser are presented and are used to derived an 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
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. The journal of observations
is:
| Season | Nb of nights | Nb of images |
| 2014 | 3 | 146 |
| 2015 | 3 | 128 |
| 2017 | 2 | 106 |
| 2018 | 2 | 90 |
| 2019 | 1 | 33 |
| 2020 | 4 | 184 |
| 2026 | 1 | 79 |
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:
Red: MR Ser, Blue: the check star (GSC 1499-1899) shifted by +2 mag.
The error bars are the 1-sigma statistical uncertainties.
Observed photometric minima
| Season | Time of minimum HJD-2456000 |
Uncertainty |
| 2014 | 764.5365 | 0.002 |
| 764.610 | 0.005 | |
| 856.418 | 0.008 | |
| 857.434 | 0.002 | |
| 2015 | 1063.731 | 0.001 |
| 1064.599 | 0.001 | |
| 1064.675 | 0.001 | |
| 1120.627 | 0.003 | |
| 2017 | 1810.652 | 0.0015 |
| 1857.535 | 0.005 | |
| 1857.620 | 0.004 | |
| 2018 | 2226.473 | 0.003 |
| 2292.428 | 0.003 | |
| 2019 | 2542.612 | 0.003 |
| 2020 | 2923.517 | 0.002 |
| 2923.597 | 0.002 | |
| 2923.674 | 0.003 | |
| 2943.533 | 0.003 | |
| 3031.390 | 0.005 | |
| 2026 | 5204.394 | 0.002 |
| 5204.475 | 0.004 | |
| 5204.555 | 0.004 |
Improved ephemeris
An ephemeris for the times of minimum, ToM=T+P.E with P the orbital period
and E the "eclipse" number,is derived from the above observed
minima and the one of 1999 reported by Baklanov and Pavlenko, 2001, using
a least squares method. The result, spanning 124808 orbits, is:
T=2451369.9637(12) HJD (1999 July 10)
P=0.078797751(21) day
The resulting O-C plot is:
Phase plots
The resulting phase plots, season by season, are: 
Reference
Baklanov A.V. and E.P. Pavlenko, 2001, Odessa Astronomical Publications, 14, 23.
Bilir S. et al, 2008, MNRAS 384 1178.
Smith J.A. et al, 2002, AJ 123 2121.
Technical notes
Telescope and camera configuration.
Computer and software configuration.
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